AU2012242967A1 - Electrical apparatus and control system - Google Patents

Abstract

A system receives power from a power grid, has a variable frequency AC drive has an output connected to an AC motor, and an input connected to the grid. The motor is connected with a load, and the drive includes an active converter having a maximum apparent power capacity. The converter is coupled to a controller programmed to regulate reactive power generation and consumption of the drive so that the drive produces reactive power which is fed to the grid when the converter is utilizing less than maximum apparent power capacity. A device calculates power factor, which is fedback to a controller that generates a reference signal to control the system's power factor. The controller is programmed to respond to the signal, so that the apparent power does not exceed the maximum capacity of the converter and avoids generating reactive power thats result in a leading power factor.

Description

WO 2012/142082 PCT/US2012/033009 1 ELECTRICAL APPARATUS AND CONTROL SYSTEM 2 (Docket No. 9948a) 3 4 Inventors: 5 Craig Lamascus 6 Citizenship USA 7 City of Residence La Habra, CA 8 9 and 10 11 Lloyd Wentworth 12 Citizenship USA 13 City of Residence Silverado, CA 14 15 16 This international application is being filed with the United States Patent and 17 Trademark Office as the receiving office. 18 19 C/O John J. Connors . 20 Patent Attorney 21 CUSTOMER NUMBER 021905 22 Connors & Associates, pc 23 13421 Danbury Lane, Unit 134i 24 Seal Beach, California, 90740, USA 25 949-833-3622 (Phone) 26 562-431-5881 (Fax) 27 email: john@connorspatentlaw.com 28 29 30 RELATED PATENT APPLICATIONS & INCORPORATION BY REFERENCE 31 32 This application is a PCT application filed pursuant to 35 USC 363 and claims 33 priority based on U. S. Provisional Patent Application No. 61/475,336, entitled "Electrical 34 Apparatus and Control System," filed April 14, 2011. This related provisional patent 35 application is incorporated herein by reference and made a part of this application. If any 36 conflict arises between the disclosure of the invention in this PCT application and that in the 37 related provisional patent application, the disclosure in this PCT application shall govern. 38 Moreover, any and all U. S. patents, U. S. patent applications, and other documents, hard 39 copy or electronic, cited or referred to in this application are incorporated herein by reference 40 and made a part of this application. 1 WO 2012/142082 PCT/US2012/033009 DEFINITIONS 2 3 The words "comprising," "having," "containing," and "including," and other forms 4 thereof, are intended to be equivalent in meaning and be open ended in that an item or items 5 following any one of these words is not meant to be an exhaustive listing of such item or 6 items, or meant to be limited to only the listed item or items. 7 The words "substantially" and "essentially" have equivalent meanings. 8 The words "oil well" include natural gas wells, and oil and gas wells including water 9 or other fluids. 10 The word "power" means the rate of flow of energy past a given point in an electrical 11 circuit. 12 The words "apparent power capacity" mean the limit of a given circuit or device to 13 electrically transfer apparent power. Usually, apparent power capacity is expressed in units 14 of volt-amperes or kilovolt-amperes (KVA) and is meant to convey the KVA limit for an 15 extended period of time, or on a continuous basis. 16 The words "apparent power" mean the vector sum of the real power and the reactive 17 power. Units are usually expressed as kilovolt-amperes (KVA). 18 The words "real power" mean the portion of power, averaged over one complete 19 cycle of an alternating current period of the AC wave form, resulting in the net transfer of 20 energy in one direction. Units are usually expressed as kilowatts (KW). 21 The words "reactive power" mean the portion of power due to stored energy returned 22 to the source (power grid, for example) in each AC cycle. Units are usually expressed as 23 kilovolt-amperes reactive (KVAR). 24 The words "power factor" mean the ratio of real power to apparent power. 25 The words "leading power factor" mean a power factor in which current leads the 26 voltage in phase. 27 The words "lagging power factor" mean a power factor in which the current lags the 28 voltage in phase. 29 The following abbreviations mean 30 AC - Alternating Current 31 C- Celsius 32 CB - Circuit Breaker 33 DC - Direct Current 34 F - Fahrenheit 2 WO 2012/142082 PCT/US2012/033009 1 HZ-Hertz 2 IGBT - Insulated Gate Bipolar Transistor 3 K- Kelvin 4 K - kilo or 1,000 of any unit 5 M - million or 1,000,000 of any unit 6 PF - Power Factor 7 RMS - Root Mean Square 8 VAC - Volts Alternating Current 9 - Vector in an xy plane 10 |xj - Absolute Value of x 11 PG - Electrical Power Grid 12 13 BACKGROUND 14 15 Some electrical systems use AC electric motors that are from time to time operated at 16 horsepower levels below that for which they are rated. These motors may be connected to an 17 electric power grid through a variable frequency AC drive, which includes an active 18 converter having a predetermined maximum apparent power capacity. These systems may 19 include one or more motors and one or more variable frequency AC drives. Other electric 20 equipment such as transformers may also be included in the system. For example, in oil 21 fields hundreds of motors driving pumps are connected to the power grid. Some are 22 connected directly to the power grid and others are connected to the grid through individual 23 drives. The system has a power factor that is less than unity (1), but it varies with the 24 changing loads over time as power is demanded from the grid upon operation of the electrical 25 equipment. A leading power factor indicates a circuit that produces reactive power. A 26 lagging power factor indicates a circuit that consumes reactive power. In general, operation 27 of an entire electrical power grid in a leading power factor condition is undesirable and can 28 lead to instability. It is desirable to operate with a slightly lagging power factor, which is 29 close to unity, for example, substantially from 0.93 to 0.97. If the power factor is much 30 below 0.93, current is high and energy may be wasted. 31 Many variable frequency AC drives use an active converter typically employing 32 insulated gate bipolar transistors (IGBT's) to control and conduct electrical current. In many 33 applications the lifetime of an IGBT is determined by the effects of power cycling. Modern, 34 high power IGBT's are complex devices using silicon dies and substrates. Common failure 3 WO 2012/142082 PCT/US2012/033009 1 modes are bond wire fatigue or cracks in a solder layer between the dies and the substrate. 2 This bond wire fatigue can be accelerated under power cycling conditions. While there exists 3 no industry accepted standard to describe "power cycling," in general, power cycling is any 4 method or mode of operation which causes the level of current conducted through the IGBT 5 to change substantially from a high level to a low level in a relatively short time frame, for 6 example, substantially from 3 seconds to 5 minutes. 7 Power cycling detrimentally affects IGBT lifetime because it results in thermal 8 cycling of the IGBT. Although power cycling results in thermal cycling, thermal cycling can 9 be caused by other factors. For example, thermal cycling can also be the result of inadequate 10 or inconsistent cooling of IGBT's. Thermal cycling can also be the result of ambient 11 temperature conditions that change cyclically. Therefore, thermal cycling and power cycling 12 are related, but not identical. Power cycling, and the resulting thermal cycling, produces 13 shortened lifetimes of IGBT's. There are many manufacturing techniques and materials that 14 are used to reduce the detrimental effects of power cycling on expected lifetime of IGBT's. 15 The term "power cycling" is somewhat misleading. A high level of current flow 16 through the IGBT is what causes the IGBT to become hotter. A low level of current flow 17 through the IGBT is what causes the IGBT to become cooler. Therefore, it is a pattern of a 18 high level of current flow followed by a low level of current flow that cause the thermal 19 cycling that can lead to shortened lifetimes of IGBT's. Therefore, power cycling would be 20 more accurately described as "current cycling." However, the term "power cycling" has 21 become the industry accepted term to describe the phenomenon described herein. AC current 22 measured in a power distribution system (power grid) is composed of both real power 23 components, comprised of current that has a phase difference of O'with respect to voltage, 24 and reactive power components, comprised of current that has a phase difference of 90' with 25 respect to voltage. Power cycling describes current flow and includes both real power and 26 reactive power, which are discussed in greater detail in "APPENDIX A- TUTORIAL" 27 attached. 28 The specific location where the temperature is relevant in regard to shortened IGBT 29 lifetime is the bond wire junction between the die and the substrate. However, in most 30 circumstances using IGBT's in industrial applications the bond wire junction is not equipped 31 with a sensor that measures temperature. In most IBGT applications what is measured is 32 something called "case temperature." Most IGBT's are equipped with a sensor embedded or 33 mounted on the case that encloses all of the semiconductor and other electrical components 4 WO 2012/142082 PCT/US2012/033009 1 that comprise the IBGT. Therefore, the relationship of case temperature and bond wire 2 junction temperature must be known or approximated. 3 The diagram of Fig. 1 shows an example of the transient temperature response during 4 thermal cycling that occurs as the result of power cycling. In this diagram Tj is the junction 5 temperature. Te is the measured case temperature measured under the hottest die. Tcomer is the 6 measured case temperature at the corner of the substrate solder layer. As can be seen in the 7 above diagram Tj changes much more rapidly than Torner or T, during power cycling. During 8 power cycling Tj can be as much as 2 times greater than Te and 3 times greater than Tcomer. 9 However, during cooling of the IGBT the difference in temperature measured amongst Tj, Te 10 and Tcomer is very small. In the above graph, the temperature axis is scaled at 10' per 11 division. Therefore, the change from its minimum temperature to maximum temperature of 12 Tj is 720 C. The change from minimum temperature to maximum temperature is called AT 13 (pronounced delta tee). In the above graph: ATj =72'C; ATc =33'C; ATcomer =22'C. 14 It is AT under power cycling operating conditions that causes shortened lifetime of 15 IGBT's. Much research has been done on the effects of power cycling on the lifetime of 16 IGBT's. It is not the overall absolute value of temperature that is at issue in this explanation 17 of power cycling and associated shortened lifetime of IGBT's. The maximum absolute safe 18 operating temperature need not be exceeded. It is thermal cycling, however, even thermal 19 cycling that does not result in temperatures above the maximum safe temperature for the 20 IGBT that shortens lifetimes of IGBT's during power cycling. Let's consider an example: 21 Say for example an IGBT has a maximum safe operating temperature of 130 'C measured at 22 Tc. If the IGBT is operated in a power cycling circumstance in which Te varies between 65 23 'C and 125 *C. Then the ATc = 125'C - 65*C = 60'C. An IGBT operated in this manner 24 may be subject shortened lifetime and premature unexpected failure. The IGBT may have a 25 shortened lifetime even though the maximum safe operating temperature is never exceeded. 26 The graph of Fig. 2 shows how ATc reduces the number of power cycling events that 27 can be accommodated in the lifetime of an IGBT. As can be seen in this graph, for a ATc = 28 60'C the IGBT will be capable of a given number of thermal cycles as a result of power 29 cycling. However, as both axes are on a logarithmic scale, if ATc = 30'C, reduction of 50%, 30 the number of power cycles increases by 2000% or 20 times. In general, any significant 31 reduction in AT results in relatively large increase in the number of power cycles the IGBT is 32 capable of. Ultimately, this can be summarized as follows: Any significant decrease in AT 0 33 of an IGBT under power cycling operating conditions results in a relatively large increase in 34 the useful lifetime of the IGBT. 5 WO 2012/142082 PCT/US2012/033009 1 This background discussion is not intended to be an admission of prior art. 2 3 SUMMARY 4 5 When an active converter of a variable frequency AC drive is operated at less than its 6 maximum power capacity, reactive power is generated. In our apparatus, a variable frequency 7 AC drive produces reactive power when the active converter is utilizing less than its 8 predetermined maximum apparent power capacity, and the reactive power is generated 9 without substantially compromising the ability of the drive to provide real power as 10 demanded by a load driven by the AC motor. In a system in which our apparatus is 11 connected, this reactive power is fed to a power grid, provided it does not result in a leading 12 power factor for the system. A device monitors current and voltage from the power grid and 13 generates a reference signal corresponding to a power factor for a system in which our 14 apparatus is connected, and the controller is programmed to respond to this reference signal. 15 Our control system includes a variable frequency AC drive, adapted to be electrically 16 coupled to a power grid, that drives at least one motor receiving power from this power grid. 17 The drive comprises an input to be connected to the power grid, and an output to be 18 connected to one or more motors driven by the AC Drive. The power grid may be 19 simultaneously connected to a plurality of electric motors or other loads receiving power 20 from the grid. Between the input and output is the active converter coupled to a controller. 21 The controller is programmed to regulate reactive power generation and reactive power 22 consumption of the variable frequency AC drive so that the drive produces or consumes 23 reactive power (the drive does not simultaneously produce and consume power). This 24 reactive power is transferred to the power grid, and thus can be consumed by other motors or 25 loads receiving electric power from the same power grid. The real power is determined by the 26 mechanical load on the one motor connected to the output of the drive. Our system may 27 include a single variable frequency AC drive or a plurality of variable frequency AC drives, 28 all of which may have an active converter, or only some of which may have an active 29 converter. The variable frequency AC drive may be adapted to be connected in parallel with a 30 plurality of loads that receive power from the power grid, and the active converter may be 31 connected to at least one inverter through a DC bus, and the converter may have an output 32 connected to more than one inverter. 33 The reference signal to the variable frequency AC drives equipped with an active 34 converter may be a fixed constant or generated by an external mechanism or by software 6 WO 2012/142082 PCT/US2012/033009 1 programmed to regulate overall power factor of the system. Variable frequency AC drives 2 that use a regenerative converter are often called regenerative variable frequency AC drives. 3 In the most general case, however, the control modes and operation of the active converter in 4 our system can be applied to regenerative or non-regenerative converters used in variable 5 frequency AC drives. A plurality of variable frequency drives may be used, and none, some 6 or all may be regenerative drives. Using each variable frequency drive connected to the same 7 electrical grid as a source of reactive current creates a distributed reactive current source. 8 Using distributed reactive current sources can have the effect of lowering overall current in 9 an electrical power distribution system. This can result in a more economical, efficient and 10 flexible operation of the electric power distribution system. See Example #3 and Example #4 11 "APPENDIX A- TUTORIAL" for a detailed discussion. 12 Our apparatus may be programmed for different modes controls that establish which 13 one, or more then one, of a plurality of control strategies is employed. These strategies 14 govern the combination of reactive power and real power to avoid the apparent power 15 exceeding the maximum apparent power capacity of the active converter, and they include, 16 but are not limited to, (1) a first control strategy where the load on the motor changes slowly, 17 (2) a second control strategy where the load changes rapidly, and (3) a third control strategy 18 where the load is cyclic. According to the first control strategy, the reactive power is a 19 function of the maximum apparent power capacity of the converter and the real power 20 demanded. In this first strategy, the real power requirements change at a frequency of less 21 than 4 Hertz. According to the second control strategy, a real power limit implemented in 22 the inverter is employed. This real power limit of the inverter is a function of the maximum 23 apparent power capacity of the active converter and the instantaneous reactive power of the 24 active converter. For example, the instantaneous reactive power may be multiplied by a 25 scaling factor that may range substantially from 1.01 to 1.10. Using the second strategy, as 26 the real power demanded by a load approaches levels resulting in an overload of the active 27 converter, a predetermined real power limit is lowered, and, as said predetermined real power 28 limit is lowered, a predetermined instantaneous reactive power limit is reduced, and as the 29 instantaneous reactive power is reduced, the predetermined real power limit is increased. 30 According to the third control strategy, the reactive power is controlled so that variations in 31 apparent power are kept at a minimum, ideally essentially constant. 32 One embodiment of our system is an oil well including a pump operatively connected 33 to an AC motor controlled by a programmable, variable frequency AC drive that has an 34 active converter having a maximum apparent power capacity and that transfers electrical 7 WO 2012/142082 PCT/US2012/033009 1 energy from a power grid to the AC motor. The AC drive is programmed to produce 2 reactive power that is fed to the power grid when the converter is utilizing less than the 3 converter's maximum apparent power capacity, and the reactive power is generated without 4 compromising the ability of the drive to provide real power as demanded by the pump being 5 driven by the AC motor. 6 Our apparatus has improved expected IGBT lifetime regardless of the manufacturing 7 technique or materials used, allowing the IGBT to enjoy a significantly extended useful 8 lifetime in the same service. Or considered another way, regardless of the method or 9 materials used in the manufacture of the IGBT, our system and method allows the IGBT 10 module to be operated at higher real power levels when used in a variable frequency AC 11 drive equipped with an active converter without detrimentally effecting the expected lifetime 12 of the IGBT. In our system this reactive power is used advantageously to beneficially affect 13 the power factor, thereby avoiding high current and wasted energy. 14 Our apparatus and system have one or more of the features depicted in the 15 embodiments discussed in the section entitled "DETAILED DESCRIPTION OF SOME 16 ILLUSTRATIVE EMBODIMENTS," and the claims that follow define our apparatus and 17 system, distinguishing them from the prior art; however, without limiting the scope of our 18 apparatus and method as expressed by these claims, in general terms, some, but not 19 necessarily all, of their features are: 20 One, our electrical apparatus includes a variable frequency AC drive having an input 21 adapted to be electrically coupled to an electric power grid and an output adapted to be 22 electrically connected to an AC electric motor. The variable frequency AC drive includes an 23 active converter having a predetermined maximum apparent power capacity. The variable 24 frequency AC drive may be adapted to be connected in parallel with a plurality of loads that 25 receive power from said power grid. 26 Two, the converter is coupled to a controller programmed to regulate reactive power 27 generation and consumption of the variable frequency AC drive so that the drive produces 28 reactive power when said converter is utilizing less than the converter's maximum apparent 29 power capacity. The reactive power is being generated without substantially compromising 30 the ability of the drive to provide real power as demanded by a load driven by the AC motor. 31 The reactive power is fed to the power grid. The active converter may have an output 32 connected to one or more inverters. 33 Three, our apparatus may include a device that monitors current and voltage from the 34 power grid and generates a reference signal corresponding to a power factor for a system in 8 WO 2012/142082 PCT/US2012/033009 1 which our apparatus is connected. The controller is programmed to respond to this reference 2 signal. 3 Four, the controller may have a selectable mode control that establishes which one or 4 more then one of a plurality of control strategies is employed. These strategies govern the 5 combination of reactive power and real power to avoid the apparent power exceeding the 6 maximum apparent power capacity of the active converter. The control strategies may 7 include (1) a first control strategy where the load on the motor changes slowly, (2) a second 8 control strategy where the load changes rapidly, and (3) a third control strategy where the 9 load is cyclic. According to the first control strategy the reactive power is a function of the 10 maximum apparent power capacity of the converter and the real power demanded. The real 11 power requirements may, for example, change at a frequency of less than 4 Hertz. According 12 to the second control strategy the real power limit of an inverter connected to the converter 13 through a DC bus may be a function of the maximum apparent power capacity of the active 14 converter and the instantaneous reactive power of the active converter. The instantaneous 15 reactive power is multiplied by a scaling factor. As the real power demanded by a load 16 approaches levels resulting in an overload of the active converter, a predetermined real power 17 limit of the inverter may be lowered, and, as the predetermined real power limit is lowered, a 18 predetermined instantaneous reactive power limit is reduced, and as the instantaneous 19 reactive power is reduced, the predetermined real power limit of the inverter is increased. 20 According to the third control strategy the reactive power may be controlled so that apparent 21 power is kept essentially constant. 22 In one embodiment, our system receives power from an electric power grid and 23 includes a load connected to the power grid, an AC electric motor connected to the power 24 grid through a variable frequency AC drive in parallel connection with the load, and a device 25 that monitors current and voltage from the power grid and generates a reference signal 26 corresponding to a power factor for the system. The variable frequency AC drive has an 27 input electrically connected to the power grid and an output electrically connected to the AC 28 electric motor and includes an active converter having a predetermined maximum apparent 29 power capacity. The converter is coupled to a controller programmed to regulate reactive 30 power generation and consumption of the variable frequency AC drive so that the drive 31 produces reactive power when the converter is utilizing less than its maximum power 32 capacity. The reactive power is to be fed to the power grid. The controller is programmed to 33 respond to the reference signal, controlling power generation and consumption so that the 34 combination of reactive power and real power does not result in apparent power exceeding 9 WO 2012/142082 PCT/US2012/033009 1 the maximum capacity of the active converter and avoids generating reactive power that 2 would result in a leading power factor for the system. There may be a plurality of loads in 3 parallel connection with the drive, and there may be a plurality of variable frequency AC 4 drives in parallel connection with the loads. The system may include a plurality of inverters, 5 each inverter having an input connected to the output of the active converter and an output 6 connected to an AC motor. As discussed above, the controller may have a selectable mode 7 control. 8 In another embodiment, our system comprises an AC motor having its output 9 connected to cyclic load and a variable frequency AC drive including an active converter 10 subjected to damage due to rapid thermal cycling. The converter is coupled to a controller 11 programmed to regulate reactive power generation and consumption of the variable 12 frequency AC drive so that said drive avoids rapid thermal cycling that may damage the 13 active converter. The active converter may comprise a plurality of insulated gate bipolar 14 transistors. 15 Our apparatus has been utilized in an oil well. This oil well includes a pump 16 operatively an AC motor and a programmable, variable frequency AC drive that transfers 17 electrical energy from a power grid to the AC motor. The AC drive includes an active 18 converter having a maximum apparent power capacity and programmed to produce reactive 19 power that is fed to the power grid when the converter is utilizing less than the converter's 20 maximum apparent power capacity. The reactive power is being generated without 21 compromising the ability of the drive to provide real power as demanded by the pump being 22 driven by the AC motor. The oil well may include a device that monitors current and voltage 23 from the power grid and generates a reference signal corresponding to a power factor for a 24 system including the pump. The controller is programmed to respond to said signal to avoid 25 generating reactive power that would result in a leading power factor for the system. 26 27 DESCRIPTION OF THE DRAWING 28 29 Some embodiments of our system and method are discussed in detail in connection 30 with the accompanying drawing, which is for illustrative purposes only. This drawing 31 includes the following figures (Figs.), with like numerals indicating like parts: 32 33 Fig. 1 is a graph illustrating transient temperature changes in an active converter over 34 time. 10 WO 2012/142082 PCT/US2012/033009 1 Fig. 2 is a graph illustrating how the number of cyclic temperature changes reduces 2 the number of power cycling events. 3 Fig. 3 is a schematic diagram of our system employing at least one variable frequency 4 AC drive connected to a power grid providing electrical power to a plurality of loads. 5 Fig. 3A is a schematic diagram of an active converter having its output connected to 6 a plurality of inverters. 7 Fig. 3B is a circuit diagram showing the active converter and inverter of the variable 8 frequency drive. 9 Fig. 3C is a schematic diagram of a walking beam oil well pump having its motor 10 energized by power from a power grid through our apparatus. 11 Fig. 4 is a graph illustrating a slow change in the power requirements of a mechanical 12 load. 13 Fig. 5 is a graph illustrating the real power requirements of the mechanical load 14 depicted in Fig. 4 and the reactive power that is generated using Control Mode I. 15 Fig. 6 is a graph illustrating the real power requirements of the mechanical load 16 depicted in Fig. 4 and the reactive power that is generated using Control Mode I and the 17 resulting apparent power. 18 Fig. 7 is a graph illustrating the problem of delay of the reactive power in response to 19 a changing reactive power reference. . 20 Fig. 8 is a graph illustrating an operational state employing a Mode I control. 21 Fig. 9 is graph illustrating an operational state employing a Mode II. 22 Fig. 10 is a graph illustrating a single cycle of a repetitive power profile 23 Figs. 11 through 13 are graphs illustrating the repetitive profile depicted in Fig. 10 24 over greater and greater periods of time. 25 Fig. 14 is a graph illustrating an operational state employing Mode III. 26 Fig. 15 is a graph illustrating the real power requirements of those in Fig. 10 and the 27 resulting converter current and converter temperature where reactive power is controlled to 28 be nil. 29 Fig. 16 is a graph illustrating the real power requirements of those in Fig. 10 and the 30 resulting converter current and converter temperature using Mode II to control reactive 31 power. 32 Fig. 17 is a graph illustrating the real power requirements of those in Fig. 10 and the 33 resulting converter current and converter temperature using a combination of Mode II and 34 Mode III to control reactive power 11 WO 2012/142082 PCT/US2012/033009 1 Fig. 18 is a schematic diagram of a power circuit and instrumentation that may be 2 used to monitor that power circuit. 3 Fig. 19 is a schematic diagram of a power circuit that is a sub-circuit of the power 4 circuit shown in Fig. 18 and instrumentation that may be used to monitor that power circuit. 5 Fig. 20 is a schematic diagram of a power circuit that is a sub-circuit of the power 6 circuit shown in Fig. 18 and the instrumentation that may be used to monitor that power 7 circuit. 8 Fig. 21 is a schematic diagram of a power circuit that is a sub-circuit of that power 9 circuit shown in Fig. 18 and the instrumentation that may be used to monitor that power 10 circuit. 11 Fig. 22 is a schematic diagram of a power circuit that is a sub-circuit of that power 12 circuit shown in Fig. 18 and the instrumentation that may be used to monitor that power 13 circuit. 14 Fig. 23A is an illustration of how power is transferred through an electric motor when 15 power is being transferred from the power grid PG to the mechanical load. 16 Fig. 23B is an illustration of how power is transferred through an electric motor when 17 power is being transferred from the mechanical load to the power grid PG. 18 Fig 23C is an illustration of how power is transferred through a transformer. 19 Fig. 24 is a vector diagram illustrating an electrical power circuit with a lagging 20 power factor of 0.8. 21 Fig. 25 is a vector diagram illustrating an electrical power circuit with a lagging 22 power factor of 0.9. 23 Fig 26A is a vector diagram illustrating an electrical power circuit with a lagging 24 power factor of 0.9. 25 Fig 27A is a vector diagram illustrating the current components resulting from the 26 operation condition shown in Fig 26A. 27 - Fig 28 is a vector diagram illustrating the electrical power circuit described in 28 Example #0. 29 Fig 29 is a vector diagram illustrating the electrical power circuit described in 30 Example #1. 31 Fig 30 is a vector diagram illustrating the electrical power circuit described in 32 Example #2. 33 Fig 31 is a vector diagram illustrating the electrical power circuit described in 34 Example #3. 12 WO 2012/142082 PCT/US2012/033009 1 Fig 32 is a vector diagram illustrating the electrical power circuit described in 2 Example #4. 3 4 DETAILED DESCRIPTION OF SOME ILLUSTRATIVE EMBODIMENTS 5 6 As depicted in Fig. 3, one embodiment of our system is generally designated by the 7 numeral 10 and includes at least one programmable variable frequency AC drive VFD 8 designed, manufactured and installed in such a way as to control the speed of an AC motor 9 M4 that is operably connected to mechanical equipment ME4. A suitable variable frequency 10 AC drive VFD may be obtained from ABB, Oy of Helsinki, Finland. A plurality of variable 11 frequency drives (a second AC drive is shown in dotted lines connected to motor M3) may be 12 used, and none, some or all may be regenerative drives. The motor M4 and motors Ml, M2, 13 and M3 are all connected at their inputs to a common power grid PG through a transformer, 14 and respectively at their outputs to mechanical equipment designated by MEl, ME2, ME3, 15 and ME4. The mechanical equipment may be, for example, a pump, fan, conveyor, extruder, 16 drive train of a vehicle, or any other mechanical device that requires power in the form of 17 torque and speed transferred through a rotating shaft. In the embodiment illustrated in Fig. 18 3C, the mechanical equipment is a walking beam pump that pumps fluid from an oil well. 19 The pump may be above or below ground or a beam or long-stroke pump, or other type of 20 pump. 21 As depicted in Fig. 3B, the variable frequency AC drive VFD comprises an input 12a 22 adapted to be connected to the power grid PG, a circuit breaker CB, an active converter 23 connected to an inverter through a DC bus, and an output 12b adapted to be connected to the 24 motor M4. All the motors Ml, M2, M3, and M4 receive power from the power grid PC, but 25 only the motor M4 is driven directly by the variable frequency AC drive VFD. The power 26 grid PG receives reactive power transferred thereto from the variable frequency AC drive 27 VFD. As shown in Fig. 3, between the input 12a and output 12b, is the active converter 28 coupled to a controller 14. The controller 14 includes a microprocessor 14a programmed to 29 regulate reactive power generation and reactive power consumption of the variable frequency 30 AC drive VFD so that the drive produces reactive power that is fed to the power grid. 31 Reactive power is produced only in a manner that does not significantly impair the ability of 32 the AC inverter to provide real power to the motor M4 as the load varies under different 33 operating circumstances. This requires different control strategies be employed under 34 different operating circumstances. 13 WO 2012/142082 PCT/US2012/033009 1 The real power is determined by the mechanical load on the one motor M4 connected 2 to the output 12b of the variable frequency AC drive VFD. As discussed subsequently, 3 production and consumption of reactive power is according to one or more different control 4 strategies. The user selects a control strategy depending on the operational characteristics of 5 the active converter, inverter, motor, mechanical load, and the PG requirements. A selection 6 is made by setting a Control Mode parameter by switching on one of the Control Mode 7 Buttons I, II, or III. The controller signals to each of the variable frequency AC drives 8 equipped with an active converter may be a fixed constant or generated by an external 9 mechanism or software programmed to regulate overall electrical power factor. In the 10 embodiment depicted, the signal from the monitoring device S is directed to one input of an 11 adder lla and the other input of the adder lla has a set point that may be manually or 12 automatically adjusted as called for by the particular system using our apparatus. The device 13 S monitors on the line from the transformer the current and voltage that is being applied to 14 the motors Ml, M2, M3, and M4. This measurement and subsequent calculation yields the 15 actual power factor of the system. The set point signal is a desired power factor that is less 16 than unity, for example, 0.94. The difference between the set point signal and the actual 17 power factor signal is the error signal 1l c of the output of the adder 11 a. The error signal 1 c 18 is used in an external controller shown as a Proportional and Integral controller lId. The 19 external controller lId either increases or decreases reactive power to maintain the desired 20 power factor of the system. 21 The variable frequency AC drive VFD is typically constructed as shown in Fig. 3B, 22 and includes a power supply panel 262, an active converter panel 260a, and an inverter panel 23 270. The converter panel 260a includes a transistorized converter IGBT that converts 24 electrical energy in the form of alternating current (AC) into electrical energy in form of 25 direct current (DC) in an electrolytic capacitor EC in the inverter panel 270 that functions as 26 a DC bus. All transistorized converters are controlled in such a way that power can flow 27 from the incoming AC lines to the DC Bus. However, only some transistorized converters 28 are controlled in such a way that power can flow from the incoming AC lines to the DC Bus 29 or from the DC Bus to the AC lines. In those cases where the power can flow in only one 30 direction the transistorized converter is called a non-regenerative converter. In those cases 31 where the power can flow in either direction the transistorized converter is called a 32 regenerative converter. 33 Many modern variable frequency AC drives equipped with such active converters 34 have the ability to control the amount of reactive power consumed or produced in the power 14 WO 2012/142082 PCT/US2012/033009 1 distribution system by the active converter. This reactive power control can be described by 2 Equation 1 as follows: 3 Q = Q, kvar 4 5 Where: 6 Q = Reactive Power produced or consumed by the active converter 7 Q,. = Reactive Power reference 8 However, operating an active converter in such a manner as to produce or consume a 9 given amount of reactive power is not a useful control mode in many applications for variable 10 frequency AC drives equipped with active converters. The primary deficiency of this 11 "reactive power reference" mode of control is that most variable frequency AC drives 12 equipped with an active converter are used to control motors that are connected to 13 mechanical loads that have changing real power requirements. A given level of reactive 14 power that is suitable with one level of real power may be entirely unsuitable at another level 15 of real power. For example, an active converter rated at 100 KVA can accommodate 70.7 16 KW of real power and 70.7 KVAR of reactive power. This example can be described as 17 follows by Equation 2: 18 Is1|= 1|R 1 2 + |Q 1

|

2 19 Where in the above example: 20

|R

1 | = 70.7 kw 21 IQ, 1 70.7 kvar 22 IS11 = 100 kva 23 24 However, if the real power requirements change to 90 KW and the reactive power level were 25 maintained at the same level, 70.7 KVAR, then the converter would be overloaded at 114 26 KVA. This second example can be described as follows: 27 ISI = |1R1 2 + IQ,1 2 28 Where in the above example: 29

|R

2 1 = 90 kw 30 1Q 1 1 = 70.7 kvar 31 1521 = 114.4 kva 32 33 34 This overload of the active converter could cause the converter to trip off line due to 35 excessive converter current. The reactive current level in the above example must be altered 36 by some control method to insure that the converter is not overloaded. 15 WO 2012/142082 PCT/US2012/033009 1 Consider a similar example using the same active converter rated at 100 KVA. 2 Again, let's consider the active converter operating at its rated 100 KVA of apparent power 3 and 70.7 KW of real power and 70.7 KVAR of reactive power. This is the same 4 circumstance as described in the example above and can be described as follows: 5 1sIl = f|R 1 7z +1Q 2 6 7 Where in the above example: 8 |RIl = 70.7 kw 9 I1Q, = 70.7 kvar 10 Isl = 100 kva 11 12 Now consider a changing real power requirement that results in a new real power 13 requirement of 40 KW. If the reactive power level were maintained at 70.7 KVAR, then the 14 converter would be loaded at an apparent power level of 81.2 KVA. This circumstance can 15 be described as follows: 16 |s| = 1R |1 2 + 1|Q 17 18 Where in the above example: 19

|R

3 1 = 40 kw 20 1Q 1 1 =70.7 kvar 21 IS31 81.2 kva 22 23 At an active converter loading level of 81.2 KVA, the active converter has capacity that is not 24 being used. If one had a goal of maximizing reactive power production, then one would want 25 to use the excess capacity present in the active converter to produce reactive power when the 26 real power requirements allowed such operation. 27 Real power requirements of typical real-world mechanical loads are seldom constant. 28 Real power requirements may change slowly or quickly, in small or large amounts, 29 predictably or randomly. The real power requirements of the active converter are a function 30 of and determined ultimately by the mechanical load. The example given previously is a 31 simple example, however, it does outline some of the deficiencies encountered with most 32 reactive power control modes available in most modem variable frequency AC drives 33 equipped with active converter. 34 There is at least one manufacturer that does attempt to eliminate the "overloaded 35 converter" problem associated discussed above. Siemens manufactures a variable frequency 36 AC drive equipped with an active converter that has a "current limiting" feature. However, 16 WO 2012/142082 PCT/US2012/033009 1 this control mode is deficient in several regards. To understand how a current limit control 2 mode on the active converter is deficient one must fully understand all the functions that the 3 active converter must perform. In our system we use the active converter to produce or 4 consume reactive power in the power grid. However, the active converter performs another 5 important and fundamental task as well: DC bus voltage control. 6 In our system as illustrated in Fig. 3, the active converter is controlled in such a way 7 as to maintain a constant DC voltage level in the electrolytic capacitors. The DC voltage 8 level controller, implemented in the active converter, is extremely responsive, stable and 9 dynamic. The inverter will control the AC motor M4 in such a way as to produce the 10 required level of real power in the motor M4. As the mechanical load requires more real 11 power, the DC voltage level measured on the electrolytic capacitors will tend to drop. 12 Simultaneously, the DC voltage level controller functioning in the converter will 13 automatically control the active converter to consume more real power from the electrical 14 power grid and supply that real power to the DC circuit, thereby maintaining the DC voltage 15 level measured in the electrolytic capacitors at the DC voltage set-point. Conversely, as the 16 mechanical load requires less real power the DC voltage level measured on the electrolytic 17 capacitors will tend to increase. Simultaneously, the DC voltage controller functioning in the 18 converter will automatically control the active converter to consume less real power from the 19 electrical power and grid and supply that lower level of real power to the DC circuit, thereby 20 maintaining the DC voltage level measured in the electrolytic capacitors at the DC voltage 21 set-point. It is because of the DC voltage level controller in the active converter that the 22 variable frequency AC drive equipped with an active converter is capable of operating at all 23 levels of real power within its rating in a reliable, seamless, stable and dynamic manner. 24 The primary function of the variable frequency AC drive equipped with an active 25 converter is to safely, reliably, effectively, efficiently and economically control a motor that 26 is connected to a mechanical load. The mechanical load and its control is the most important 27 aspect of any variable frequency AC drive, including a variable frequency AC drive equipped 28 with an active converter. To the extent that controlling reactive power beneficially affects the 29 safety, reliability, effectiveness, efficiency or economics of the control of the mechanical 30 load, then reactive power control is included in the primary and most important aspects of 31 operating a variable frequency AC drive equipped with an active converter. In our system 32 and method: 33 1. Reactive current control can be used to decrease AT of IGBT's used in an 34 active converter. Decreasing AT results in increased useful lifetime of IGBT's used in 17 WO 2012/142082 PCT/US2012/033009 1 operational circumstances involving heavy power cycling as described previously. In this 2 regard, reactive current control is included in the most important fundamental aspects of 3 operating a variable frequency Drive equipped with active converter. To the extent that 4 reactive current control can be used to increase the useful lifetime of IGBT's used in the 5 active converter, reactive current control is desirable, necessary and valuable in virtually all 6 operational circumstances involving heavy power cycling as described previously. 7 2. Reactive power control can be used to improve the operation of the electric 8 power distribution system to which the variable frequency AC drive equipped with an active 9 converter is connected. In this regard, reactive power control is desirable in some 10 circumstances and could be considered valuable in some circumstances. However, there may 11 be other circumstances in which reactive power control used to improve the operation of the 12 electric power distribution system is not desirable, valuable or necessary. Furthermore, 13 reactive power control strictly and only for the purposes of improving the operation of the 14 electric power distribution system is not among the most important or fundamental aspects of 15 operating a variable frequency Drive equipped with an active converter. Avoiding any 16 compromise that sacrifices performance of the AC Drive in its fundamental aspects is 17 worthwhile. 18 When a "current limiting" control mode is used in the active converter, the active 19 converter can no longer effectively control DC Bus voltage level in a stable manner. There 20 are times this may cause the variable frequency AC drive equipped with an active converter 21 to trip off-line as well. Many mechanical loads are characterized by large and rapid changes 22 in real power requirements. It is for this reason, that other methods of control of the reactive 23 power in the active converter are used in our apparatus and system. In addition, in our 24 control system control modes may be used that coordinate real power loading in the motor 25 M4 and reactive power levels in the active converter. 26 Mode II uses the real power limit implemented in the inverter. The real power limit is 27 not intended to be implemented in the active converter. The reason the real power limit is not 28 a suitable mode of control for the active converter is the same as that explained above for the 29 "current limiting" mode of control for the active converter. In general, any limit on the 30 current or power in the active converter will compromise the performance of the active 31 converter in its primary function. Namely, that of controlling and maintaining the DC 32 voltage level of the DC bus capacitors at the desired level. The real power limit in the 33 inverter may implemented using many different control strategies which are unique to 34 different AC variable frequency drive manufacturers. In general, however, these control 18 WO 2012/142082 PCT/US2012/033009 1 strategies can be typically described as follows. The actual level of instantaneous real power 2 in the inverter is measured or calculated. This actual level of real power is compared to a 3 threshold, called the real power limit. If the actual level of real power exceeds the threshold 4 value of real power limit, then a control implemented in the inverter control will intervene. 5 This intervention could be in the form of reducing inverter current or motor torque to limit 6 the actual level of instantaneous real power in the inverter. The intervention must be 7 controlled to insure that the instantaneous real power does not exceed the threshold value of 8 real power limit. 9 10 Modes Of Control 11 12 If generation of reactive power can be used to improve the operation of the electric 13 power distribution system (the power grid) and not adversely affect the fundamental and 14 important aspects of AC drive operation to any substantial degree in any substantial way, 15 then the controlled generation of reactive power may, in such circumstances, be highly 16 desirable. In our system one or more different control strategies may be employed depending 17 on the changing load demands under different operational circumstances. These control 18 strategies take into consideration safety, reliability, effectiveness and efficiency of the control 19 of the mechanical load. The following are examples control strategies under different 20 operational modes: (Mode I) Reactive Power Control Using Apparent Power Limit, (Mode 21 II) Converter Apparent Power Limiting Using Inverter Real Power Limit, (Mode III) Cyclical 22 Apparent Power Control. 23 24 Reactive Power Control Using Apparent Power Limit (Mode I) 25 26 The ideal active converter control method would allow for reactive power to be 27 produced or consumed according to a reactive power reference without compromising the 28 ability of the converter to produce or consume power (kilowatts) according to the real power 29 requirements of the mechanical load. In order to accomplish this operational goal, the ideal 30 active converter control method would limit reactive power in circumstances in which the 31 combination of reactive power and real power would result in apparent power that would 32 exceed the capacity of the active converter if not controlled. In addition, the ideal active 33 converter control method would result in reactive power production or consumption that 34 followed the reactive power reference in those circumstances in which the combination of 19 WO 2012/142082 PCT/US2012/033009 1 reactive power and real power result in apparent power that does not exceed the capacity of 2 the active converter. This reactive power control using apparent power limit would appear 3 as follows: 4 Q = Q,. kvar ,where Q Qucm 5 |1um| = Isum|2 _ IR,,\2 6 7 Where in the above example: 8 Q = Reactive Power (RealTime Actual) 9 Q,. = Reactive Power Reference 10 Qum = Reactive Power Limit 11 Sum = Apparent Power Limt 12 An example will be used to demonstrate the above described ideal active converter control 13 method. Consider the following sample power profile shown in Fig. 4. Given the power 14 profile above, if the following references and limits are assumed: 15 Q, =100 kvar 16 Sum = 100 kva 17 18 Given the formulas: 19 Q = Q,- kvar ,where Q Qujm 20 |iumi = \sm2 - IR 2 21 22 Reactive Power and Real Power results are shown in Fig. 5: 23 24 Given the formula: 25 Isac5 = r|Ract12 + 1Q 2 26 27 Results in real power, reactive power and apparent power are illustrated in Fig. 6. 28 The above example shows many of the desirable characteristics of reactive power 29 control using apparent power limit to control an active converter. Here is a list of desirable 30 characteristics of this method of control: 31 - Real power requirement of the mechanical load are provided for in a reliable and 32 dynamic manner. Real power required by the mechanical load is unimpeded and not 33 compromised. 34 - Apparent power limit is never exceeded. If incoming voltage Vu is assumed to be 35 fixed and constant, then the maximum current rating of the active converter is never 36 exceeded. 20 WO 2012/142082 PCT/US2012/033009 1 * Reactive power is maintained at the reactive power reference level whenever possible. 2 - Reactive power is maximized according to the control method and the reactive power 3 reference. 4 The above-described control strategy of Mode I works well for applications in which 5 real power requirements change slowly over time. The term "slowly over time" must be put 6 into a proper context. The following description of exactly how the real time reactive power 7 responds to the reactive power reference will offer some context for what might be 8 considered "slowly over time". However, as a general rule of thumb, one could assert that 9 the above described control method will function extremely well if real power requirements 10 do not change from one level to any other level in less than about 500 milliseconds. This can 11 also be described using the concept of bandwidth. The maximum real power bandwidth of 12 this control mode used to control the reactive power in an active converter associated with a 13 variable frequency AC drive is 2 Hz. As long as the power requirements are changing at a 14 frequency less than 2 HZ, then this control mode is adequate for control. If the real power 15 requirement is changing at a frequency of greater than 2 HZ, but less than 4 HZ, then this 16 control mode is marginal. If the real power requirement is changing at a frequency of greater 17 than 4 HZ, then this control mode becomes unstable and unreliable for controlling reactive 18 power in an active converter associated with a variable frequency AC drive. Many of the 19 mechanical loads that are controlled by variable frequency AC drives are centrifugal pumps 20 and fans. Most centrifugal pumps and fans have mechanical loads that can be characterized 21 by slowly changing real power requirements. Most centrifugal pumps and fans have real 22 power requirements that change at a frequency lower than 2 HZ. 23 The example above is theoretical. If the real time reactive power followed the 24 reactive power reference in a dynamic, accurate, reliable and rapid manner, then the above 25 example would be the ideal reactive power control for an active converter. However, the real 26 time reactive power does not follow the reactive power reference in a dynamic, accurate, 27 reliable and rapid manner. The reasons that the real time reactive power does not follow the 28 reactive power reference in a dynamic, accurate, reliable and rapid manner are complex. 29 However, the primary reasons can be described as follows: 30 - Active Converter Control Stability - the design and manufacture of the active 31 converter and its components is extremely complex. The design of the converter 32 involves many decisions that can be characterized as compromises between dynamic 33 response versus stability, expensive versus low cost, large versus small, emitting large 21 WO 2012/142082 PCT/US2012/033009 1 amounts of EMI versus emitting small amounts of EMI, high switching frequency 2 versus lower switching frequency, etc. For a more complete description of these 3 design decision please see "Stability Improvements of an LCL-filter Based Three 4 phase Active Rectifier" by Marco Liserre, Antonio Dell' Aquila and Frede Blaabjerg. 5 The design compromises associated with the stability of the active converter control 6 are the primary reason that there exists a significant delay between the real time active 7 converter reactive power and the reactive power reference. 8 - Large Inductor - Inductors store magnetic energy as flux. The nature of inductors is 9 to maintain a constant current flow and resist changes to the current flow. Therefore 10 inductors inherently degrade dynamic current response. The large inductor that is 11 generally associated with an active converter has a small effect on the dynamic 12 response of the active converter. However, this effect is not negligible. 13 For a more thorough and complete description of the magnitude of the reactive power delay, 14 consider the graph depicted in Fig. 7, which shows that the actual reactive power follows the 15 reactive power reference with a delay that can be characterized by an exponential time 16 constant t. For the graph of Fig. 7, t = 86 milliseconds. The delay demonstrated is the cause 17 of significant complications in using an active converter to produce or consume reactive 18 power in many real-world applications of a variable frequency AC drive equipped with a 19 active converter in which the real power requirements may change rapidly. The term 20 "rapidly" in any real power requirement is one that changes at a frequency of greater than 5 21 HZ. 22 When the above described Reactive Power Control Using Apparent Power Limit 23 strategy of Mode I is used to control the active converter associated with a variable frequency 24 AC drive in circumstances in which the real power requirements change rapidly, there are 25 many undesirable results, and the control strategy of Mode II is then employed. 26 Converter Apparent Power Limiting Using Inverter Real Power Limit (Mode II) 27 Consider the graph shown in Fig. 8 depicting real power varying rapidly. The rapidly 28 varying real power combined with a reactive power control that is relatively slow to react, 29 results in several instances of overloading the active converter. This can lead to undesirable 30 behavior in the active converter. This type of behavior can cause tripping of the active 31 converter or, depending on how the active converter is controlled, this type of behavior can 22 WO 2012/142082 PCT/US2012/033009 1 cause tripping of the inverter. This situation is potentially very troublesome and, without the 2 proper control, can render the active converters ability to produce or consume reactive power 3 not beneficial in circumstances in which the real power requirements change rapidly. 4 However, there is a control strategy that overcomes some of the problems associated with the 5 relatively slow control methods of reactive power associated with the active converter. 6 Consider the following Equation 10: 7 ~ ~ ~ ~ Q, IR~m = IS iiI -1 8 |GumII , 2sh - (|R..r|* 1.02)2 9 10 Where in the above Equation 10: 11 Q = Reactive Power (Instantaneous, RealTime Actual) 12 Qum = Reactive Power Limit 13 Slim = Apparent Power Limt 14 Ract = Real Power (RealTime Actual), measured in inverter 15 Rlim = Real Power Limit of the inverter 16 17 In the Control Mode II, the real power limit of the inverter is a function of the 18 maximum apparent power capacity of the active converter and the instantaneous reactive 19 power measured in the active converter. However, simultaneously, the Control Mode II 20 limits the maximum reactive power based on the maximum apparent power capacity of the 21 active converter and the instantaneous power multiplied by a scaling factor. As the 22 mechanical load demands more power, the maximum power that the mechanical load is 23 permitted to consume or generate as the case may be is limited by the controller. However, 24 as the real power demanded by the load approaches levels that could result in an overloaded 25 converter the reactive power limit is lowered. At any time that the real power generated or 26 consumed is being limited in the inverter by Control Mode II the "Active Intervention" status 27 of Control Mode II is said to be ON. At any time that the real power generated or consumed 28 is not being limited in the inverter by Control Mode II the "Active Intervention" status of 29 Control Mode II is said to be OFF. Any operational circumstance to results in the "Active 30 Intervention" status of Control Mode II being ON results in an automatic reduction of the 31 reactive power limit. As the reactive power limit is lowered, the instantaneous reactive 32 power will be reduced. As the instantaneous reactive power is reduced the real power limit is 33 increased as a function of Equation 10 above. These are two simultaneous controls that 34 affect each other when the real power, reactive power or apparent power are at their limits. 23 WO 2012/142082 PCT/US2012/033009 1 Using the Control Mode II allows the reactive power reference, to be set to any level, 2 including very high levels, without adversely affecting the operation of the active converter, 3 inverter or the mechanical load. The reactive power reference may be set to very high levels 4 even when the variable frequency AC drive equipped with an active converter is used to 5 power loads with rapidly changing real power requirements. When using the above 6 described control method the resulting performance results are illustrated in the graph of Fig. 7 9, which demonstrates the following regarding the control mode called real power limit as a 8 function of reactive power: 9 - There is minimal negative impact on the ability of the variable frequency drive 10 equipped with an active converter to deliver real power to the mechanical load as 11 power is required. 12 - Very high levels of reactive power can be generated by the active converter without 13 any significant overloading of the active converter, even when considered on an 14 instantaneous basis. 15 - Current limiting of the active converter is usually eliminated as an operation 16 requirement. Thereby eliminating all of the detrimental effects of employing current 17 limiting in the active converter. Although, the capability and control mode that 18 allows current limiting of the active converter may still be employed, the necessity of 19 using the current limiting control mode will seldom be encountered. 20 - While this control method does greatly reduce any overload condition of the active 21 converter, it does not fully maximize the ability of the active converter to generate 22 reactive power. There are instances in which the utilized capacity of the active 23 converter, measured in KVA, is not maintained at its maximum allowable level. This 24 situation, while not ideal, is not a significant problem in most installations. 25 Cyclical Apparent Power Control Mode (Control Mode III) 26 27 There is a unique type of mechanical load for which the real power requirement is 28 repetitive and cyclic with respect to time. Generally, any type of mechanical motion that is 29 reciprocating, whether linearly or rotationally, is cyclic and repetitive. Examples of these 30 types of mechanical load include the following: 31 - Pumping units used to produce oil and natural gas 24 WO 2012/142082 PCT/US2012/033009 1 - Packaging equipment 2 - Rotary Die 3 * Labeling equipment 4 - Indexing conveyor 5 - Carriage drives 6 - Flywheels 7 - Punch Presses 8 In some cases, the real power requirement of a load may be consistently repetitive 9 according to a known cycle. If the real power requirement of a driven mechanical load has a 10 natural, cyclic, consistent and repetitive pattern, then the real power requirement can be 11 predicted. In other words, if the real power requirement of a load is consistently repetitive, 12 one can predict the cyclical pattern of real power based on the previous cycle, or many 13 previous, cycle. Consider the graph of Fig. 10, which graphically shows how the real power 14 varies with respect to time. This particular profile shows a single cycle that is about 12 15 seconds in duration. We will use the start of this cycle as our time reference for this example. 16 Now, consider the next two cycles in the graph shown in Fig. 11, which shows two cycles. 17 As can be seen in the graph of Fig. 11, each cycle of about 12 seconds, looks very similar to 18 the previous cycle illustrated in Fig. 10, but its profile is compressed. In addition, the next 19 cycle can be assumed to be very much like the previous cycle. In this way, real power 20 requirements can be considered to be predictable. A predictable real power requirement may 21 be useful. Further illustrating the repetitive and oscillatory nature of this particular example, 22 consider the graph of Fig. 12, which shows the next 4 cycles. And then the next 10 cycles 23 illustrated in Fig. 13. One could imagine many hours of operation represented by thousands 24 of these virtually identical cycles. 25 In the examples shown above, the real power requirements of the mechanical load are 26 shown as a function of time. However, the real power requirements need not necessarily be a 27 function of time. The real power requirement may be a function of position of the load, for 28 example. If the position of the load is known over the course of a cycle, and the real power 29 requirements repeat at each given position throughout a cycle, then the real power 30 requirement can be considered similarly predictable. It is necessary that the real power 31 requirement be a function of some known (either by calculation, estimation or direct 32 measurement) variable, or variables, for the real power requirement to be considered cyclical 25 WO 2012/142082 PCT/US2012/033009 1 and predictable. There may be a single variable, or a mix of multiple variables, that can be 2 used to predict real power requirements. 3 In all cases in which real power requirements are cyclical and predictable, the real 4 power requirements repeat in a way that allows reactive power to be controlled in such a way 5 that apparent power can be kept constant. Constant apparent power has many advantages. 6 Consider the control mode illustrated in Fig. 14 where the mechanical load has real power 7 requirements that repeat according the graph of Fig. 10. In this mode, each point in time has 8 associated with it a real power requirement. If we dissect the above graph and identify real 9 power requirements associated with each interval of 100 milliseconds. This cycle is 12 10 seconds in duration. There are 120 intervals of 100 milliseconds in a 12 second interval. 11 Therefore the above cyclical real power requirement will be represented by 120 unique 12 variables. Thus, the real power requirement of the above graph is described by the following 13 parameters we shall call the Real Power Array: 14 RO = 1.47 kw 15 1= -76.8 kw 16

R

2 = -123.3 kw 17

R

3 = -110.7 kw 18 19 20 21

R

119 = 77.5 kw 22 R12 = 23.8 kw 23 24 We can now calculate the reactive power needed to maintain constant apparent power. The 25 calculation of reactive power to maintain a constant apparent power will be done according to 26 the following Equation: 27 IQn I = rISrz - IR.I 2 28 29 Where: 30 Q. = Reactive Power Reference for n'h 31 S,. = Apparent Power Reference (desired apparent power) 32 R, = Real Power (as described above)Q 33 34 The above equation is solved for each value of n. Since the equation has two knowns and 35 one unknown, the unknown is solved for each value of n. Assuming Sr=120kva results in the 36 following Reactive Power Reference Array: 37 Qo = 120 kvar 38 Q1 = 92.2 kvar 26 WO 2012/142082 PCT/US2012/033009 1Q2 = 0 kvar 2 3= 46.3 kvar 3 4 5 Q = 91.6 kva.r 6

Q

120 = 117.6 kvar 7 8 This control strategy, which may be referred to as Cyclical Apparent Power Control (CAP), 9 results in the real power, reactive power and apparent power profiles for the cyclical load in 10 the graph of Fig. 15. 11 In practice, due to the delay in the actual reactive power to follow the reactive power 12 reference, the Reactive Power Reference Array is necessarily time shifted by a constant that 13 is approximately the time constant of the delay of the reactive power with respect to the 14 reactive power reference. 15 Using CAP yields several very desirable results: 16 - Nearly constant apparent power in the active converter. 17 - No overloaded operation of the active converter. This is true on an average and 18 instantaneous basis. 19 - Reactive power production is essentially optimal at all times. If it is desired under 20 certain circumstances to produce a maximum amount of reactive power, the CAP 21 control method results in full utilization of the active converter to produce reactive 22 power without any type of overload of the active converter. 23 - No interference with the ability of the variable frequency AC drive equipped with 24 Active converter to supply real power to the mechanical load. This is the primary 25 objective of all variable frequency AC drives as described above. 26 Using CAP also eliminates some of the undesirable effects of other control methods, such as: 27 - Eliminates the undesirable effects of using current limit to prevent overloads of the 28 active converter. 29 - Eliminates interference with the ability of the variable frequency AC drive equipped 30 with active converter to supply real power to the mechanical load. 31 - Eliminates the under-utilization of the active converter to supply reactive power in 32 maximum quantities when desired. 27 WO 2012/142082 PCT/US2012/033009 1 CAP can only be applied to mechanical loads that are characterized by cyclical and 2 predictable real power profiles. However, when CAP can be used the result is the optimum 3 performance of the active converter to perform all desired operations. 4 There are circumstances in which a mechanical load may have a real power 5 requirement that is cyclical and predictable most of the time, or even only occasionally. CAP 6 can be used to beneficially affect performance of the variable frequency AC drive equipped 7 with an active converter in these circumstances as well. There are several ways CAP might 8 be used in these types of circumstances. CAP could be combined with other control methods 9 described herein. CAP might be combined with Reactive Power Control using Apparent 10 Power Limit. CAP may be combined with Reactive Power Control using Real Power Limit, 11 especially for loads that are characterized by rapid, large, abrupt or very dynamic changes in 12 real power requirements. In these circumstances the beneficial effects of CAP may be 13 realized in wide variety of loads that have real power requirements that are only occasionally 14 cyclical. 15 Apparent Power Used To Reduce 16 Temperature Change In Transistors 17 18 As discussed above, heavy power cycling leads to thermal cycling which in turn leads 19 to premature transistor failure. Power cycling is characterized by large changes in current 20 through a transistor. To the extent that current can be stabilized in a transistor the 21 temperature of the transistor can be stabilized. As was explained previously, relatively small 22 decreases in AT 0 can lead to extremely large increases in the useful lifetime of an IGBT 23 transistor. A decrease in ATe and a more stable transistor temperature are synonymous. The 24 graph shown in Fig. 15 doesn't employ any of the control strategies. Reactive power in the 25 converter is controlled to be nil.Therefore, the current in the converter is a function of the 26 mechanical real power requirements. Controlled in this way, the converter current varies in 27 magnitude significantly over the course of a single cycle. The measured converter 28 temperature changes significantly over the course of a single cycle. ATc = 46'C for the graph 29 shown in Fig. 15. 30 Now consider operation of the active converter using the Mode II. In this example 31 the converter has a constant reactive power reference 32 Qef = 100 kvar 33 The graph shown in Fig. 16 illustrates employing Mode II, where the reactive power in the 34 converter and real power in the inverter and converter are controlled as described previously. 28 WO 2012/142082 PCT/US2012/033009 1 The current in the converter is a function of the mechanical real power requirements and the 2 reactive power Control Mode I. Controlled in this way, the converter current varies in 3 magnitude over the course of a single cycle, but far less than the operational circumstance 4 described previously. The measured converter temperature changes over the course of a 5 single cycle. ATc = 23*C for the graph of Fig. 16. This is roughly a 50 % reduction from the 6 previously described ATc = 46'C. As was explained previously, this reduction in ATc will 7 result in significantly increased useful life of the converter IGBT transistors. The increase in 8 useful lifetime will be approximately 2000% or 20 times in this case. 9 Now consider the graph of Fig. 17 were the operation of the active converter is 10 controlled using the Mode III where the converter has a constant reactive power reference 11 Q4 = 120 kvar 12 The graph of Fig. 17 shows reactive power in the active converter controlled as described 13 previously. The current in the converter is a function of the mechanical real power 14 requirements and the reactive power Control Mode III. Controlled in this way, the converter 15 current is essentially constant over the course of a single cycle. The measured converter 16 temperature changes over the course of a single cycle. ATc = 2*C for the graph above. Thus 17 Mode III virtually eliminates thermal stress due to power cycling on the converter IGBT's. 18 As was explained previously, this reduction in ATc will result in elimination of thermal stress 19 due to power cycling and elimination of the degradation in expected lifetime due to power 20 cycling. 21 22 As discussed in greater detail in the attached APPENDIX A-TUTORIAL, reactive 23 power is a function of voltage and reactive current. Reactive current and reactive power are 24 proportional to each other only if voltage is considered constant. However, many power 25 distribution systems have voltages that vary over the course of time. There are IEEE and 26 ANSI Standards that regulate the amount of voltage variation that are considered generally 27 acceptable in most power distribution systems. 28 Each of the control strategies described above could be controlled and implemented 29 using reactive current rather than reactive power. However, with limited exceptions as 30 discussed above, using reactive current as a limiting factor does not noticeably change the 31 effectiveness of each control strategy. In addition, using reactive current is not manifestly 32 different in any significant way, as far as the control strategies themselves are concerned. All 33 quantities discussed in the section entitled "Modes Of Control," can be defined in terms of 29 WO 2012/142082 PCT/US2012/033009 1 current and voltage. Reactive power and real power can be defined in terms of apparent 2 power, and apparent power can be defined in terms of voltage and current. 3 4 SCOPE OF THE INVENTION 5 6 The above presents a description of the best mode we contemplate of carrying out our 7 control system and method, and of the manner and process of making and using them, in such 8 full, clear, concise, and exact terms as to enable a person skilled in the art to make and use. 9 Our system and method is, however, susceptible to modifications and alternate constructions 10 from the illustrative embodiments discussed above which are fully equivalent. Consequently, 11 it is not the intention to limit our system and method to the particular embodiments disclosed. 12 On the contrary, our intention is to cover all modifications and alternate constructions coming 13 within the spirit and scope of our system and method as generally expressed by the following 14 claims, which particularly point out and distinctly claim the subject matter of our invention: 15 30 WO 2012/142082 PCT/US2012/033009 APPENDIX A- TUTORIAL 2 3 The following tutorial is presented to assist in better understanding of the above 4 disclosure and is not intended to be an admission of prior art. 5 Power in an electrical circuit is the rate of flow of energy past a given point in a 6 circuit. In AC circuits, energy storage elements such as inductance and capacitance may 7 result in periodic reversals of the direction of energy flow. The portion of power, averaged 8 over one complete cycle of the AC period of the AC waveform, results in net transfer of 9 energy in one direction is known as real power. The portion of power due to stored energy, 10 which returns to the source in each cycle is known as reactive power. 11 In a simple AC circuit consisting of a source and a linear load, both the current and 12 the voltage are sinusoidal. If the load is purely resistive, the two quantities reverse their 13 polarity at the same time. At every instant the product of the voltage and current is positive, 14 indicating that the direction of energy flow does not reverse. In this case, only real power is 15 transferred. If the load is purely reactive, then the voltage and current are 900 out of phase. 16 For half of each cycle, the product of voltage and current is positive, but on the other half of 17 the cycle, the product is negative, indicating that on average, exactly as much energy flows 18 toward the load as flows back. There is no net energy flow over one cycle. In this case, only 19 reactive energy flows-there is no net transfer of energy to the load. All real-world loads have 20 resistance, inductance and capacitance, so both real and reactive power will flow to real 21 world loads. Power engineers measure apparent power as the vector sum of real and reactive 22 power. Apparent power is the product of the root-mean-square (RMS) voltage and current. 23 Power Engineers care about apparent power because even though the current associated with 24 reactive power does no work in the load, it heats wires, wasting energy. Conductors, 25 transformers and generators must be sized to carry the total current, not just the current that 26 does useful work. 27 If a capacitor and an inductor are placed in parallel, then the currents flowing through 28 the inductor and the capacitor tend to cancel out rather. than adding. Conventionally, 29 capacitors are considered to generate reactive power and inductors are considered to consume 30 reactive power. Reactive power generation and reactive power consumption is the 31 fundamental mechanism for controlling the power factor in electric power transmission and 32 distribution; typically capacitors are inserted in a circuit to partially cancel reactive power 33 'consumed' by the load. 34 37 WO 2012/142082 PCT/US2012/033009 1 The Power Triangle of Fig. 24 shows the relationship of vectors in a plane. 2 3 P = Real Power (watt [W]) 4 Q Reactive Power (volt-amperes reactive [VAR]) 5 S = Complex Power (volt-ampere [VA]) 6 SI = Apparent Power (volt-ampere [VA]) 7 = Phase of Current (degree [0]) 8 For the above shown power triangle: 9 |P= 4 10 IQI=3 11 |S= 5 12 0 = 36.87' 13 There are several important mathematical relationships between Real Power, Reactive Power, 14 Apparent Power and Phase. The following is a partial list of Equations setting forth these 15 mathematical relationships: 16 17 Equation 18 \s|= 1Pz 2 +1QF 19 IPI =ISI cos() 20 IQi = ISI sin($) $= tan-I Q 21 IPI 22 S P + Q 23 24 Understanding the relationship between the quantities listed above is at the heart of 25 understanding electrical power engineering. Without further elaboration the concepts defined 26 in the definition of the Power Triangle will be assumed to be accepted, established, well 27 defined and understood by skilled power engineers. 28 For most electrical quantities "K" can be added for multiples of 1,000. "M" can be 29 added for multiples of 1,000,000. For example, 100 KW is 100,000 Watts. 10 MVAR is 30 10,000,000 VAR. 31 38 WO 2012/142082 PCT/US2012/033009 POWER DISTRIBUTION SYSTEMS 2 3 Introduction 4 A sample power distribution system is shown on Fig. 18 through Fig. 23. These types 5 of drawings are called "single line" or "one line" diagrams. Virtually all commercial and 6 industrial power distribution systems are 3 phase AC (Alternating Current) systems. Single 7 line diagrams are used to describe relevant aspects of electrical power distribution systems 8 succinctly using a single line to represent all 3 phases of voltage and all 3 phases of current. 9 3 phase systems can be of a 3-wire or a 4-wire type. 3 phase systems can be referenced to 10 ground or not referenced to ground. Transformers described in single line diagrams are 11 virtually always devices that are comprised of 3 separate magnetic circuits that use changing 12 magnetic flux to induce voltage and current in electrical circuits which are connected to the 13 transformer. These magnetic circuits may be enclosed in single enclosure or 3 separate 14 enclosures. Regardless of the type of electrical power distribution system and the 15 components that comprise that electrical power distribution system, single line diagrams are 16 useful for designing, analyzing, describing and specifying electrical power distribution 17 systems. Without further elaboration this application will use single line diagrams to 18 describe electrical power distributions systems and to describe the components that comprise 19 said electrical power distribution system. Single line diagrams are accepted, well-defined 20 and understood by skilled power engineers as a method to represent electrical power 21 distribution systems and associated components. 22 Ratings used in single line diagrams can be of many different types. For example, 23 voltage ratings used in single line diagrams may be considered as voltage measured between 24 phases or voltage ratings used in single line diagram may be considered as voltage measured 25 between any of the three phases and ground. However, most ratings used in single line 26 diagrams, and the ratings used in this application, are considered to be defined as follows: 27 VOLTAGE - / RMS AC voltage between any two of the three phases'. So-called 28 line to line voltage 29 CURRENT - / RMS AC current measured in any single conductor'. So-called line 30 current. 3 1 VA - / Product of volts and amps of all 3 phases 2 . 32 - Voltage and current in single line diagrams is considered to be balanced. An electrical 33 power distribution system characterized by balanced voltage has equal RMS AC voltage 34 levels between any one reference phase and either of the remaining two phases. The 39 WO 2012/142082 PCT/US2012/033009 1 balanced voltage is present regardless of which three phases is used as the reference phase 2 described above. An electrical power distribution system characterized by balanced current 3 has equal RMS AC current levels in all 3 phase conductors. KV is a unit of measure that 4 equal 1,000 RMS AC Volts. 5 2 - VA rating is the scaled product of the line to line voltage and the line current. KVA is a 6 unit of measure that is equal to 1,000 volt-amperes. MVA is a unit of measure that equals 7 1,000,000 volt-amperes. 8 9 Fundamental Frequency 10 11 The fundamental frequency, often referred to simply as the fundamental and abbreviated f 0 or 12 F , is defined as the lowest frequency of a periodic waveform. In electrical power systems 13 analysis, unless stated otherwise, the vectors used to described voltage, current, real power, 14 apparent power and reactive power are intended to describe power systems at their 15 fundamental frequency. If frequencies other than the fundamental are to be considered, this 16 is usually explicitly stated and referred to as harmonic frequencies. 17 18 Distribution Transformers 19 20 A transformer is a device that converts AC voltage and AC current at one level to a 21 different AC current and voltage level. There are many different types of transformers used 22 in various electrical applications. In its most basic description a transformer will have an 23 electrical connection for high voltage (high-side), an electrical connection for low voltage 24 (low-side) and a volt-ampere rating (VA, KVA or MVA). In the case of a distribution 25 transformer the high-side is called the primary and the low-side is called the secondary. The 26 principal function of the distribution transformer is to transmit electrical power from the 27 primary to the secondary. Power flow is considered to be from the primary to the secondary. 28 The primary is fed from an electrical circuit that ultimately is supplied with electrical power 29 from an electrical power generation facility. The secondary is connected to an electrical 30 circuit that consumes power that is used in electrical loads in the local distribution circuit. 31 The secondary of the transformer must provide all of the voltage and current to the various 32 electrical loads powered by the local electrical power distribution circuit. 33 40 WO 2012/142082 PCT/US2012/033009 1 Real Power Consumption 2 3 Real power is measured in watts (W or KW or MW). Consumption of real power is 4 the result of a given amount of energy being consumed in a given amount of time. Motors 5 consume large amounts of real power. Real power in a motor is proportional to the product 6 of speed and torque measured at the motor's output shaft plus losses due to inefficiency. 7 Please see Fig. 23A for a graphical representation of electrical power, mechanical power and 8 losses characterized by a motor. The electrical power consumed is equal to the mechanical 9 power plus the losses. Or considered another way, the mechanical power is equal to the 10 electrical power minus the losses. Motors consume relatively small amounts of real power 11 that is lost to inefficiency. The real power that is lost in a motor is defined as inefficiency of 12 the motor. Transformers are electrical devices that are typically considered to consume 13 power in the primary connection and produce power in the secondary connection. Therefore, 14 there is little net change in real power as real power is conducted through the transformers. 15 What change there is in net real power when considering a transformer is the losses due to 16 inefficiency in the transformer. All devices, components and conductors in an industrial 17 electrical power distribution system lose some real power due to inefficiency. The losses in 18 most electrical devices increase as the load is increased. However, some losses of real power 19 will exist at very light or zero load due to circulating reactive power required to magnetize 20 components. 21 22 Real Power Generation 23 24 Real power is measured in watts (W or KW or MW). Generation of real power is the 25 result of a given amount of energy being generated in a given amount of time. Generators 26 generate large amounts of real power. Real power in a generator is proportional to the 27 product of speed and torque measured at the generator's input shaft plus losses due to 28 inefficiency. Please see Fig. 23B for a graphical representation of electrical power, 29 mechanical power and losses characterized by a generator. The electrical power generated is 30 equal to the mechanical power minus the losses. Or considered another way, the mechanical 31 power is equal to the electrical power plus the losses. Generators generate relatively small 32 amounts of real power that is lost to heating of the generator. The real power that is lost to 33 heating in a generator is virtually all the result of inefficiency of the generator. Please note, 34 there are no generators shown in the sample power system in Fig. 18 through Fig. 23. 41 WO 2012/142082 PCT/US2012/033009 2 Reactive Power Consumption 3 4 Reactive power, as described above, does not necessarily require real power to be 5 generated or consumed. Generally, any device that requires magnetic flux to operate will 6 require reactive power. Transformers, as described previously, use magnetic flux to 7 transform electrical power. Transformers will consume reactive power regardless of the 8 amount of real power being transferred through the transformer. A good estimate of the 9 reactive power required by a transformer is equal to about 10% of the transformer's rating. 10 Using this estimate - a 225 KVA rating transformer for example would require 22.5 KVAR 11 of reactive power. Transformers are energized on the primary side. Therefore, the reactive 12 power in a transformer is usually considered to be supplied by the circuit connected to the 13 primary side of the transformer. Induction motors require magnetic flux as well to generate 14 torque. A good estimate of the reactive power required by a motor is equal to about 40% of 15 the motor's rating. Using this estimate - a 150 HP motor @ 480 VAC would require about 16 57 KVAR of reactive power. It is important to note that the reactive power requirements of 17 both transformers and motors is approximately constant regardless of load. Another way to 18 say this is that both transformers and motors require reactive power regardless of the amount 19 of real power being transferred or consumed. 20 21 Reactive Power Generation 22 23 In most electrical power distribution systems capacitors are used to generate reactive 24 power. There are, however, other means of generating reactive power. Namely static VAR 25 compensators, synchronous condensers and synchronous generators can be used to generate 26 reactive power. For the purposes of this tutorial, capacitors will be used as a source of 27 reactive power. Capacitors that are used in applications for the purpose of generating 28 reactive power are typically called "power factor correction capacitors" or PF Cap. Altering 29 the power factor is a result of the PF Cap generating reactive power, as will be discussed 30 later. PF Caps generally have a VAR or KVAR rating and a voltage rating. PF Caps can be 31 of a single rating: for example, 200 KVAR. PF Caps with a single rating simply produce the 32 rated amount of reactive power when energized with voltage. PF Caps can be adjustable: for 33 example 20 - 200 KVAR. This type of capacitor typically consists of many small PF Caps 34 that can be switched on or off to produce the desired amount of reactive power. 42 WO 2012/142082 PCT/US2012/033009 1 2 Reactive Power and Variable Frequency Drives with an Active Line Side Converter 3 4 Variable frequency drives with active line side converters can also be used to generate 5 or consume reactive power. Variable Frequency Drives with Active Line Side Converters 6 typically consists of many large capacitors connected together internally. A transistorized 7 converter can be used to inject reactive power into the electrical power distribution system at 8 a level that corresponds to a reactive power reference that is connected to the drive. The 9 same transistorized converter can be used to consume reactive power from the electrical grid 10 at a level that corresponds to a reactive power reference that is connected to the drive. A 11 transistorized converter uses transistors, switched at very high frequency to control the 12 amount of reactive power that is either consumed or generated by the converter. 13 14 Apparent Power 15 16 Apparent Power is used to combine concisely real power and reactive power into a 17 single mathematical quantity. Fig. 26A and Fig. 27B are used to represent relationship 18 amongst apparent power, real current, reactive current, real power, reactive power, voltage 19 and total current. Apparent power is a phasor representation of the scaled product of voltage 20 and current in a power. circuit. However, the convention is that apparent power is the 21 complex conjugate of the product of voltage and current. A complex conjugate is a 22 mathematical concept that is well understood by skilled power engineers. In Fig. 26A the 23 apparent power is shown to lead the real power in phase by the angle 25.84'. However, in 24 Fig. 27B the total current is shown to lag the real current by the angle 25.84*. Real power is 25 the scaled product of voltage and current with zero phase difference. As can be shown in Fig. 26 26A and Fig. 27B real current and real power are in phase with each other. Real current and 27 real power are also in phase with voltage. "In phase" is used to mean there exists zero phase 28 difference between these vectors. Reactive power is the scaled product of voltage and current 29 with a phase difference of 900. If one assumes the voltage, real current and real power axis to 30 be 0', then it is evident that the reactive current lags the voltage by 90". As will be explained 31 later, this is said to be a lagging power factor circuit. Inductors, transformers and motors are 32 considered by this convention to be devices that are characterized by a lagging power factor. 33 The total current shown in Fig. 27B is the vector sum of the real current and reactive current. 34 The total current is what is measured in any of the 3 phase conductors in an electrical power 43 WO 2012/142082 PCT/US2012/033009 1 distribution network. Therefore, apparent power and total current are proportional to each 2 other if voltage is considered to be constant. In addition, real power and real current are 3 proportional to each if the voltage is considered to be constant. In addition, reactive power 4 and reactive current are proportional to each other if the voltage is considered to be constant. 5 In most electrical power distribution systems voltage is very stable and can be considered to 6 be a constant. There are exceptions to the constant voltage assumption that will be discussed 7 later. However, for most analysis voltage can be considered to be constant. Apparent Power 8 and total current is conserved, which is to say that the sum of the apparent power and current 9 flows out of sources equals the sum of the apparent power flows and current into the other 10 elements of the circuit. 11 12 Voltage Drop 13 14 Voltage drop is the result of current being conducted through an impedance. 15 Virtually all conductors and transformers have impedance. Therefore, as either the level of 16 impedance or the level of current increases, the voltage drop will tend to increase. This is 17 true of both conductors and transformers. 18 19 Power Factor 20 21 Power factor is the ratio between real power and apparent power. Power factor is a 22 dimensionless quantity between 0 and 1. Formula for power factor magnitude: 23 Equation pf = 24 |SI 25 26 Rearranging this formula results in: 27 Equation 28 IPI =IS*pf 29 30 31 However, examining the power triangle in Fig. 24 reveals this relationship as well: 32 33 Equation 44 WO 2012/142082 PCT/US2012/033009 1 |P = ISI * cos(*) 2 3 Therefore: 4 5 Equation 6 pf = cos(4) 7 8 9 The power factor is the cosine of the phase angle between real power and complex power. 10 This also is the phase difference between voltage and total current in an AC circuit. 11 The magnitude of power factor, however, is not all that is necessary to describe power 12 factor in its entirety. One must also specify whether the power factor is "leading" or 13 "lagging". A lagging power factor is one in which the current lags the voltage in its phase. A 14 lagging power factor is one in which the voltage leads the current in its phase. A leading 15 power factor is one in which the current leads the voltage in phase. A leading power factor is 16 one in which the voltage lags the current in phase. Fig. 26A and Fig 27B show a power 17 triangle which represents a lagging power factor. Fig. 26A shows the classic power triangle 18 with the apparent power leading the real power. However, the conventions between apparent 19 power and current is that these two quantities are calculated using a complex conjugate. Fig. 20 27B shows the total current lagging the real current. Since real power results in current flow 21 that is exactly in phase with voltage, the voltage phase is the same as the phase of the real 22 current. Therefore, the total current lags the voltage in phase by the angle 25.84'. 23 The power triangle shown in Fig. 24 characterizes a lagging power factor and has 24 dimensions as follows: 1P 7 1 = 4, 1Q 7 1 = 3 and IS71= 5 25 26 Equation 27 4,=36.87* 28 29 ,and 30 31 Equation 32 pf =cos(36.78

*

) = 0.8 33 34 Analyzing this power triangle would yield the following results: 35 45 WO 2012/142082 PCT/US2012/033009 1 Equation 2 3 4 5 Let us now consider the power triangle of Fig. 25 which characterizes a lagging power factor 6 and has dimensions as follows: 7 8 IP 8 I = 4, |Q 8 I = 1.937 and 1S l = 4.444 9 and 10 11 Analyzing this power triangle would yield the following results: 12 4 = 25.842* 13 14 Equation 15 pf=cos25.842=0.9 16 17 If we analyze the differences between the two power triangles shown in Fig. 24 and 18 Fig. 25 the following observations can be made. First, real power is 4 in both Fig. 24 and 19 Fig. 25. There is no change in net power flow between these two figures. Second, the 20 reactive power level in Fig. 25 is lower than the reactive power level in Fig. 24. The reactive 21 power level in Fig. 25 is 64.6% of the reactive power in Fig. 24. Third, lowering the net 22 reactive power level lowers the apparent power level, even maintaining the real power level 23 constant. Since, as was explained earlier, apparent power and total current are proportional to 24 each other, the total current in Fig. 25 is 88.9% of the total current in Fig. 24. Therefore, 25 lowering the net reactive power level will result in a lower level of current measured in each 26 conductor. Fourth, it is shown that in these typical power triangles, changing the level 27 reactive power results in a significantly smaller relative change in apparent power. It is for 28 this reason, that near unity power factor, relatively large changes in reactive power result in 29 relatively small changes in apparent power, relatively small changes in total current and 30 relatively small changes in power factor. And finally, fifth, changing the net level of reactive 31 power changes the power factor if the real power is maintained constant. 32 33 Reactive Power vs. Reactive Current 34 46 WO 2012/142082 PCT/US2012/033009 1 Reactive power and reactive current are closely related, but not identical. Reactive 2 current is measured in Amps. Reactive Power is measured in VAR, or volt-amperes-reactive. 3 Reactive power is the scaled product of voltage and reactive current with a phase difference 4 of 90'. Therefore, reactive current and reactive power are proportional to each other only 5 when voltage is constant. 6 7 Power Distribution Example 8 9 Figs. 18 through Fig. 23 show how real power, reactive power and apparent power are 10 analyzed to describe the operation of an electrical power distribution system. Figs. 18 11 through 23 depict a power distribution network with different operating modes for each of the 12 described pieces of electrical equipment. 13 The secondary of the transformer T-PAD5AA, Fig. 18, is rated at 12.4 KV @ 116 14 Amps. Therefore, if the transformer T-PAD5AA is not to be overloaded, the amperes 15 measured at its secondary must not exceed 116 A. There are 4 sub-circuits, sometimes called 16 feeders, that are powered by the secondary of transformer T-PAD5AA. These feeders are 17 CKT-A, CKT-E, CKT-Y and CKT-W. 18 There are 5 different Bus Monitoring devices installed in this power distribution 19 system. The 5 different bus monitoring devices will be called 20 1. BUS - CKT-PRIMARY 21 2. BUS - CKT-A 22 3. BUS - CKT-E 23 4. BUS - CKT-Y 24 5. BUS - CKT-W 25 Each of the bus monitors measures current and voltage in all 3 phases of the electrical power 26 distribution system. Each of the bus monitors measures current and voltage at one location 27 only. The one location that the bus monitor measures current and voltage is shown in the one 28 line diagram. The bus monitor is a sophisticated device. It has the capability to calculate real 29 power, reactive power, real current, reactive current, total current, power factor, apparent 30 power and many other quantities associated with an electrical power distribution system. 31 Additionally, the bus monitor is equipped with communication capabilities. The bus monitor 47 WO 2012/142082 PCT/US2012/033009 1 has the capacity to transmit all of its measured and calculated quantities via a communication 2 network (not shown) to a central computer (not shown). The central computer will typically 3 be equipped with software that can analyze the entire electrical power distribution network 4 using information measured and calculated at each of the bus monitors. 5 Power engineers can use this information to make decisions regarding the operation 6 of the electrical power distribution system. Decisions such as which circuits to energize or 7 de-energize, which devices to operate or not operate and how to control devices that are in 8 operation can all be made manually or automatically by analyzing information from the bus 9 monitors and other information. Bus monitors and associated software are useful for safe, 10 reliable, efficient and economical operation of a power distribution system. Bus monitors 11 and associated software are the result of technology and knowledge developed by power 12 engineers over the course of many decades that is mature, well developed, extremely 13 powerful and refined. Bus monitors and associated software are typically relatively 14 expensive to purchase and require skilled power engineers to operate. 15 For the purposes of the following examples, it will be assumed that the current and 16 voltage is measured and known at all points in the electrical power distribution system. In 17 order to keep the examples simple and relevant, certain assumptions will be made. 18 Conductors shall be considered to be ideal with zero resistance, zero inductance, zero 19 capacitance phase to ground and zero capacitance phase to phase. Assuming ideal 20 conductors is not something that could be done in real-world analysis of a power distribution 21 system. However, this does greatly reduce the complexity of the analysis without detracting 22 from the conveying the relevant aspects of our system and method. Another assumption shall 23 be that all quantities and analysis shall be done on an average basis. This assumption is 24 extremely important and requires further elaboration. Many mechanical loads change rapidly 25 and unpredictably. An example could be a conveyor belt. The conveyor belt may be 26 powered by a one of the motors shown in our sample power distribution system. The 27 conveyor belt may be operated in such a way that it is moving heavy boxes. Considering this 28 conveyor belt further, the heavy boxes may be placed onto the conveyor belt and taken off 29 the conveyer belt at different locations and at random intervals of time. As the heavy boxes 30 are placed on the conveyor belt the load may spike upwards. As the boxes are taken off of 31 the conveyor belt the load may rapidly drop. Therefore, the load may be characterized by 32 rapid changes. However, if the load is averaged over a given period of time the average load 33 will be much more stable. It is the average load that will be considered in the analysis of our 48 WO 2012/142082 PCT/US2012/033009 1 examples. This particular average loading assumption is typical when analyzing electrical 2 power distribution systems. This is because of a concept called "load diversity". 3 Load diversity is a well understood and complex concept that involves analysis of 4 probabilities. For example, if a factory has dozens of the conveyors as described previously 5 the probability of the loads of all conveyors spiking simultaneously is virtually zero. 6 Therefore, the power distribution system need not be specified, designed or installed to 7 accommodate this worst case scenario. Additional assumptions for all analysis of sample 8 power distribution system examples: Transformer efficiency is 98%, motor efficiency is 9 90%, transformer magnetizing current is 10% of rating and motor magnetizing current is 40% 10 of rating. Electrical representation of motors and transformers for the purposes of this 11 application shall be assumed to be the simplest most basic models for transformers and 12 motors. For example, the transformer magnetizing branch used in the transformer model 13 shall include inductance only. Magnetic branch losses shall be ignored and electrical 14 resistance of the magnetizing branch shall be assumed to be infinite. These assumptions will 15 greatly reduce the complexity of the information and calculations without negatively 16 impacting the description of our system and method. 17 Finally, one point of clarification should be made. Transformers are unique devices 18 in that they have a primary voltage and secondary voltage and a single KVA rating. So one 19 might ask, does the KVA rating apply to the primary side of the transformer or the secondary 20 side of the transformer. In fact, the KVA rating applies to both the primary and secondary 21 side of the transformer. This is because the transformer reduces the voltage by the exact 22 same ratio that it increases the current. Said another way, if an example transformer reduces 23 voltage by a factor of 10, and if the primary has a current rating of 10 amps and voltage 24 rating of 100, then the secondary will have the a current rating of 100 amps and voltage 25 rating of 10. The product of voltage and amperage is the same on both the primary and 26 secondary. It is for this reason that, some of the analysis shows unloaded transformers 27 drawing apparent power at 480 VAC even though there is actually zero load on the secondary 28 (480 VAC) side of the transformer. For the purposes of our analysis, it does not matter if the 29 KVA, KVAR or KW is referred to the primary or the secondary side of the transformer. 30 Furthermore, it clarifies the information and calculation to choose one side of the transformer 31 to refer all calculations. Therefore, we shall choose the secondary side for the purposes of 32 this application. Therefore, a typical summary report for this electrical power distribution 33 system will appear as follows: 34 49 WO 2012/142082 PCT/US2012/033009 1 Example #0 - No equipment operating. Transformers energized. Reactive current required 2 to magnetize distribution transformers only. Zero reactive power injection. 3 SUMMARY REPORT Example #0 Description: No equipment operating. CKT-PRIMARY Voltage 12362VAC Current 17AMPS Real Power OKW Reactive Power 378KVAR Apparent Power 378KVA Power Factor 0.00 4 5 See Fig 28 for schematic illustrating power triangle for Example #0. 50 WO 2012/142082 PCT/US2012/033009 CKT-A Voltage 12362VAC Current 3AMPS Real Power OKW Reactive Power 73KVAR Apparent Power 73KVA Power Factor 0.00 CKT-E Voltage 12362VAC Current 4AMPS Real Power OKW Reactive Power 95KVAR Apparent Power 95KVA Power Factor 0.00 CKT-Y Voltage 12362VAC Current 4AMPS Real Power OKW Reactive Power 80KVAR Apparent Power 80KVA Power Factor 0.00 CKT-W Voltage 12362VAC Current 6AMPS Real Power OKW Reactive Power 130KVAR Apparent Power 130KVA Power Factor 0.00 Summary Components CKT-A (Components) PF CAP Voltage 12362VAC Current QAMPS Real Power OKW Reactive Power OKVAR Apparent Power OKVA Power Factor 0 426A Voltage 475VAC Current 27AMPS Real Power OKW 51 WO 2012/142082 PCT/US2012/033009 Reactive Power 22.5KVAR Apparent Power 22.5KVA Power Factor 0.00 526A Voltage 475VAC Current 60AMPS Real Power OKW Reactive Power 50KVAR Apparent Power 50KVA Power Factor 0.00 CKT-E (Components) 427E Voltage 475VAC Current 27AMPS Real Power OKW Reactive Power 22.5KVAR Apparent Power 23KVA Power Factor 0.00 622E Voltage 475VAC Current 27AMPS Real Power OKW Reactive Power 22.5KVAR Apparent Power 23KVA Power Factor 0.00 627E Voltage 475VAC Current 60AMPS Real Power OKW Reactive Power 50KVAR Apparent Power 50KVA Power Factor 0.00 CKT-Y (Components) 811Y Voltage 475VAC Current 18AMPS Real Power OKW Reactive Power 15KVAR Apparent Power 15KVA Power Factor 0.00 305Y Voltage 475VAC Current 18AMPS Real Power OKW Reactive Power 15KVAR Apparent Power 15KVA Power Factor 0.00 314Y 52 WO 2012/142082 PCT/US2012/033009 Voltage 475VAC Current 60AMPS Real Power OKW Reactive Power 50KVAR Apparent Power 50KVA Power Factor 0.00 CKT-W (Components) 333W Voltage 475VAC Current 48AMPS Real Power OKW Reactive Power 40KVAR Apparent Power 40KVA Power Factor 0.00 334W Voltage 475VAC Current 48AMPS Real Power OKW Reactive Power 40KVAR Apparent Power 40KVA Power Factor 0.00 335W Voltage 475VAC Current 60AMPS Real Power OKW Reactive Power 50KVAR Apparent Power 50KVA Power Factor 0.00 2 Analysis of Example #0 3 Voltage at CKT-PRIMARY is 12,362VAC. This voltage level is 108 VAC lower 4 than the nominal voltage at this circuit location, which is 12,470. 108 VAC represents a 5 0.9% voltage drop vs. nominal voltage. This small voltage drop is due to the impedance of 6 the T-PAD5A transformer. Transformers, in general, will have a slight voltage drop as which 7 increases as the current through the transformer increases. At maximum current, 116 Amps 8 for T-PAD5A, the voltage drop at CKT-PRIMARY would be 5.75% of nominal voltage. The 9 number 5.75% is the rated impedance of the transformer shown on the drawing in Fig. 1. 10 Current at CKT-PRIMARY is 17 Amps. This current is due, in its entirety, to the 11 magnetizing of the smaller distribution transformers in the electrical power distribution 12 system. 53 WO 2012/142082 PCT/US2012/033009 1 KW at CKT-PRIMARY is 0. This example is considered at no load with ideal 2 conductors and ideal transformers. Therefore, there is no real power transferred in this 3 example. 4 KVAR at CKT-PRIMARY is 378 KVAR. This value is the sum of all the reactive 5 power required to magnetize all of the distribution transformers in this electrical power 6 distribution network. 7 KVA at CKT-PRIMARY is 378 KVA. The apparent power will equal the reactive 8 power when there is no real power transferred. 9 Power Factor at CKT-PRIMARY is 0. Power factor is KW/KVA. Since KW is zero, 10 the pf is zero. 11 12 Example #1 - All equipment operating at 80% load. Transformers energized. Reactive 13 current required to magnetize distribution transformers and induction motors. The motor 14 located at 627-E has a power factor correction capacitor that is integrated into its electrical 15 circuit. Therefore, 627-E cannot be energized without energizing the power factor correction 16 capacitor associated with this piece of electrical equipment. The circuit associated with 627 17 E has a net reactive power consumption of 115 KVAR. There is zero reactive power 18 injection from other sources. 19 SUMMARY REPORT Example #1 Description: All equipment operating 80% load Reactive Power from PF Cap on 627-E only Tuned PF Cap on CKT-A de-energized CKT-PRIMARY Voltage 11876VAC Current 96AMPS Real Power 1860KW Reactive Power 919KVAR Apparent Power 2074KVA Power Factor 0.90 20 21 See Fig 29 for schematic illustrating power triangle for Example #1. 54 WO 2012/142082 PCT/US2012/033009 1 CKT-A Voltage 11876VAC Current 21AMPS Real Power 365KW Reactive Power 269KVAR Apparent Power 453KVA Power Factor 0.81 CKT-E Voltage 11 876VAC Current 23AMPS Real Power 465KW Reactive Power 160KVAR Apparent Power 492KVA Power Factor 0.95 CKT-Y Voltage 11876VAC Current 20AMPS Real Power 365KW Reactive Power 220KVAR Apparent Power 426KVA Power Factor 0.86 CKT-W Voltage 11876VAC Current 33AMPS Real Power 665KW Reactive Power 270KVAR Apparent Power 718KVA Power Factor 0.93 Summary Components CKT-A (Components) PF CAP Voltage 11876VAC Current GAMPS Real Power OKW Reactive Power OKVAR Apparent Power OKVA Power Factor 0 426A Voltage 457VAC Current 153AMPS Real Power 100KW 55 WO 2012/142082 PCT/US2012/033009 Reactive Power 78.5KVAR Apparent Power 127KVA Power Factor 0.79 526A Voltage 457VAC Current 392AMPS Real Power 265KW Reactive Power 190KVAR Apparent Power 326KVA Power Factor 0.81 CKT-E (Components) 427E Voltage 457VAC Current 123AMPS Real Power 100KW Reactive Power 22.5KVAR Apparent Power 103KVA Power Factor 0.98 622E Voltage 457VAC Current 123AMPS Real Power 100KW Reactive Power 22.5KVAR Apparent Power 103KVA Power Factor 0.98 627E Voltage 457VAC Current 347AMPS Real Power 265KW Reactive Power 115KVAR Apparent Power 289KVA Power Factor 0.92 CKT-Y (Components) 811Y Voltage 457VAC Current 63AMPS Real Power 50KW Reactive Power 15KVAR Apparent Power 52KVA Power Factor 0.96 305Y Voltage 457VAC Current 63AMPS Real Power 50KW Reactive Power 15KVAR Apparent Power 52KVA Power Factor 0.96 314Y 56 WO 2012/142082 PCT/US2012/033009 Voltage 457VAC Current 392AMPS Real Power 265KW Reactive Power 190KVAR Apparent Power 326KVA Power Factor 0.81 CKT-W (Components) 333W Voltage 457VAC Current 245AMPS Real Power 200KW Reactive Power 40KVAR Apparent Power 204KVA Power Factor 0.98 334W Voltage 457VAC Current 245AMPS Real Power 200KW Reactive Power 40KVAR Apparent Power 204KVA Power Factor 0.98 335W Voltage 457VAC Current 392AMPS Real Power 265KW Reactive Power 190KVAR Apparent Power 326KVA Power Factor 0.81 2 Analysis of Example #1 3 Focusing on CKT-W component 334W is useful. Consider the reactive power shown 4 component 334W in Example #1 vs. CKT-W component 334W in Example #0. In both 5 examples, the required reactive power is 40 KVAR. As we established in Example #0, the 40 6 KVAR for this component is the required reactive current to magnetize the distribution 7 transformer associated with this particular component. The reason no additional reactive 8 power is indicated in Example #1 is that this component is equipped with an Variable 9 frequency AC drive with Active Converter. The Variable frequency AC drive with Active 10 Converter requires zero magnetizing current to operate the motor in all circumstances. As 11 will be discussed in subsequent examples, the Variable frequency AC drive with Active 12 Converter has the capability to inject or consume reactive power according to a reference and 13 a control mode to be described later. The power factor shown for CKT-W component 334W 14 is shown to be 0.98. This is, in fact, one of the characteristics of all Variable frequency AC 15 drives equipped with Active Converter when said drive is operated in a control mode to 57 WO 2012/142082 PCT/US2012/033009 1 neither inject nor consume reactive power. If we consider this component in even more 2 details, one might ask "what is the source of the magnetizing current for the 300 Hp motor 3 associated 334W?" The answer is, the Variable frequency AC drive with Active Converter is 4 the source of the magnetizing current. The 40 KVAR shown for 334W is the amount of 5 KVAR the electrical power distribution system must provide to this component. However, 6 there is much more KVAR that is not "seen" by the electrical power distribution network. 7 The induction motor on 334W must have magnetizing current. There is approximately 110 8 KVAR of reactive power required by the 300 Hp to magnetize its rotor. The 110 KVAR is 9 present and can be measured between the wires connecting the output of Variable frequency 10 AC drive equipped with Active Converter and the motor. However, this current does not 11 exist on the wires connecting the input of the Variable frequency AC drive equipped with 12 Active Converter and the electrical distribution system. One might say the Variable 13 frequency AC drive equipped with Active Converter is manufacturing magnetizing current 14 within itself. This is a true statement. The Variable frequency AC drive equipped with 15 Active Converter has a large internal capacitor. Reactive Power is simply controlled and 16 "circulated" between the output of the Variable frequency AC drive equipped with Active 17 Converter and the induction motor. The input of the Variable frequency AC drive equipped 18 with Active Converter never "sees" this current and this current cannot be measured in the 19 electrical power distribution system. 20 Analyzing CKT-Y component 314Y shows a component operating at a relatively low 21 power factor. This component is a large induction motor installed without a Variable 22 frequency AC drive with Active Converter. Because there is no drive, the reactive power 23 required to magnetize the induction motor must be provided by the electrical power 24 distribution system. This is indicated by the large amount of reactive power, 190 KVAR, as 25 compared to the real power, 267 KW. In this example, there is no KVAR injection, 26 therefore, the reactive power for 314Y must be supplied the T-PAD5A transformer. The 27 current associated with the reactive power must flow through the electrical power distribution 28 system connecting the T-PAD5A transformer and 314Y. 29 Analyzing 627E in comparison to 314Y is informative as well. Both components 30 627E and 314Y are similar large induction motors. Both motors are consuming real power at 31 the same level: 267 KW. However, 314Y is consuming 190 KVAR of reactive power and 32 operating at a 0.81 pf. 627E is consuming 115 KVAR of reactive power and operating at a 33 0.92 pf. The reason 627E is consuming less KVAR of reactive power is that this motor is 34 equipped with a reactive current source, namely the 75KVAR "Tuned PF Cap" shown in the 58 WO 2012/142082 PCT/US2012/033009 1 drawing. Both motors are in fact consuming the same amount of reactive power: 140KVAR. 2 However, 627E has a source of reactive power that is always active when the motor is 3 energized. The Tune PF Cap produces 75KVAR. Therefore, the net reactive power that 4 must be supplied by the electrical power distribution system is the difference between the 5 reactive power consumed by the motor and the reactive power produced by the Tuned PF 6 Cap: 140KVAR - 75KVAR = 65 KVAR. When the 65 KVAR required by the combination 7 of the motor and Tuned PF Cap is added to the 60 KVAR required to magnetize the 8 transformer associated with 627E, the result is 1 I5KVAR of reactive power. 314Y is similar 9 in every regard to 627E with the exception of the Tuned PF Cap. Therefore, 314Y requires 10 75KVAR more than 627E, or 190 KVAR. Furthermore, consider the amperage required for 11 314Y vs. 627E. 314Y draw 392 Amps vs. 627E draw 347 Amps. Increasing the power 12 factor and lowering reactive power demand results in significant reductions in overall amp 13 draw. In this particular example 314Y requires 13% more amps than 627E. 14 The item to analyze in Example #2 is the overall totals measured at CKT-PRIMARY. 15 The transformer T-PAD5A is supplying 2074 KVA, or about 83% of its rated capacity of 16 2500 KVA. This level of loading is within the transformer's capacity. However, one must 17 bear in mind the fact that this example is calculated at 80% motor loading. Most power 18 engineers would consider this electrical power distribution network fully loaded, if not 19 slightly overloaded. Most power engineers would not consider adding any additional load to 20 this electrical power distribution network as it presently configured and operating. 21 22 Example #2 - All equipment operating at 50% load. Transformers energized. Reactive 23 current required to magnetize distribution transformers and induction motors. Zero net 24 reactive power injection from any sources. 25 26 SUMMARY REPORT Example #2 Description: All equipment operating 50% load Zero net reactive power injection from sources. CKT-PRIMARY Voltage 12047VAC Current 68AMPS Real Power 1160KW Reactive Power 919KVAR Apparent Power 1479KVA Power Factor 0.78 59 WO 2012/142082 PCT/US2012/033009 1 2 See Fig 30 for schematic illustrating power triangle for Example #2. .3 60 WO 2012/142082 PCT/US2012/033009 1 CKT-A Voltage 12047VAC Current 16AMPS Real Power 228KW Reactive Power 269KVAR Apparent Power 352KVA Power Factor 0.65 CKT-E Voltage 12047VAC Current 15AMPS Real Power 290KW Reactive Power 160KVAR Apparent Power 331KVA Power Factor 0.88 CKT-Y Voltage 12047VAC Current 15AMPS Real Power 227KW Reactive Power 220KVAR Apparent Power 316KVA Power Factor 0.72 CKT-W Voltage 12047VAC Current 23AMPS Real Power 415KW Reactive Power 270KVAR Apparent Power 495KVA Power Factor 0.84 Summary Components CKT-A (Components) PF CAP Voltage 12047VAC Current OAMPS Real Power OKW Reactive Power OKVAR Apparent Power OKVA Power Factor 0 426A Voltage 463VAC Current 121AMPS Real Power 62.5KW 61 WO 2012/142082 PCT/US2012/033009 Reactive Power 78.5KVAR Apparent Power 1OOKVA Power Factor 0.62 526A Voltage 463VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 CKT-E (Components) 427E Voltage 463VAC Current 80AMPS Real Power 62.5KW Reactive Power 22.5KVAR Apparent Power 66KVA Power Factor 0.94 622E Voltage 463VAC Current 80AMPS Real Power 62.5KW Reactive Power 22.5KVAR Apparent Power 66KVA Power Factor 0.94 627E Voltage 463VAC Current 242AMPS Real Power 165KW Reactive Power 115KVAR Apparent Power 201KVA Power Factor 0.82 CKT-Y (Components) 811Y Voltage 463VAC Current 41AMPS Real Power 31KW Reactive Power 15KVAR Apparent Power 34KVA Power Factor 0.90 305Y Voltage 463VAC Current 41AMPS Real Power 31KW Reactive Power 15KVAR Apparent Power 34KVA Power Factor 0.90 314Y 62 WO 2012/142082 PCT/US2012/033009 Voltage 463VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 CKT-W (Components) 333W Voltage 463VAC Current 158AMPS Real Power 125KW Reactive Power 40KVAR Apparent Power 131KVA Power Factor 0.95 334W Voltage 463VAC Current 158AMPS Real Power 125KW Reactive Power 40KVAR Apparent Power 131KVA Power Factor 0.95 335W Voltage 463VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 1 2 63 WO 2012/142082 PCT/US2012/033009 1 2 Analysis of Example #2 3 There is little change between Example # 2 and Example #1. However, Example #2 4 represents a much more realistic operating configuration for most electrical power 5 distribution networks. It is very common, in practice, to measure loading levels of between 6 40% and 70% on most electrical power distribution networks. In fact, most power 7 distribution networks operate at this level of load 99% of to the time. Looking into specifics 8 characteristics of Example #2, the overall power factor measured at CKT-PRIMARY is 0.78. 9 The transformer loading is 1479 KVAR or 59% of rated load. Both the power factor and 10 loading level of Example #2 are significantly lower than that in Example #1. Again, 11 Example #2 is a more realistic representative configuration of most real-world electrical 12 power distribution networks. 13 14 Example #3 - All equipment operating at 50% load. Transformers energized. Reactive 15 current required to magnetize distribution transformers and induction motors. Maximum 16 Reactive Power produced CKT-A component PF CAP. Zero net reactive power injected 17 from other sources. 18 SUMMARY REPORT Example #3 Description: All equipment operating 50% load Maximum Reactive Power Injection from Tuned PF Cap on CKT-A Zero Net Reactive Power Injection from other sources CKT-PRIMARY Voltage 12135VAC Current 54AMPS Real Power 1160KW Reactive Power 169KVAR Apparent Power 1172KVA Power Factor 0.99 19 20 See Fig 31 for schematic illustrating power triangle for Example #3. 21 64 WO 2012/142082 PCT/US2012/033009 1 CKT-A Voltage 12135VAC Current 25AMPS Real Power 228KW Reactive Power -482KVAR Apparent Power 533KVA Power Factor 0.43 CKT-E Voltage 12135VAC Current 15AMPS Real Power 290KW Reactive Power 160KVAR Apparent Power 331KVA Power Factor 0.88 CKT-Y Voltage 12135VAC Current 15AMPS Real Power 227KW Reactive Power 220KVAR Apparent Power 316KVA Power Factor 0.72 CKT-W Voltage 12135VAC Current 23AMPS Real Power 415KW Reactive Power 270KVAR Apparent Power 495KVA Power Factor 0.84 Summary Components CKT-A (Components) PF CAP Voltage 12135VAC Current 35AMPS Real Power OKW Reactive Power -750KVAR Apparent Power 750KVA Power Factor 0 426A Voltage 467VAC Current 121AMPS Real Power 62.5KW 65 WO 2012/142082 PCT/US2012/033009 Reactive Power 78.5KVAR Apparent Power 100KVA Power Factor 0.62 526A Voltage 467VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 CKT-E (Components) 427E Voltage 467VAC Current 80AMPS Real Power 62.5KW Reactive Power 22.5KVAR Apparent Power 66KVA Power Factor 0.94 622E Voltage 467VAC Current 80AMPS Real Power 62.5KW Reactive Power 22.5KVAR Apparent Power 66KVA Power Factor 0.94 627E Voltage 467VAC Current 242AMPS Real Power 165KW Reactive Power 115KVAR Apparent Power 201KVA Power Factor 0.82 CKT-Y (Components) 811Y Voltage 467VAC Current 41AMPS Real Power 31KW Reactive Power 15KVAR Apparent Power 34KVA Power Factor 0.90 305Y Voltage 467VAC Current 41AMPS Real Power 31KW Reactive Power 15KVAR Apparent Power 34KVA Power Factor 0.90 314Y 66 WO 2012/142082 PCT/US2012/033009 Voltage 467VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 CKT-W (Components) 333W Voltage 467VAC Current 158AMPS Real Power 125KW Reactive Power 40KVAR Apparent Power 131KVA Power Factor 0.95 334W Voltage 467VAC Current 158AMPS Real Power 125KW Reactive Power 40KVAR Apparent Power 131 KVA Power Factor 0.95 335W Voltage 467VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 2 Analysis of Example #3 3 There are few differences between the summary report of Example #2 and that of 4 Example #3. However, the differences that do exist are significant and informative. All 5 equipment in Example #2 and Example #3 is operating identically except for CKT-A Tuned 6 PF CAP. In Example #3 the Tuned PF Cap is energized and producing its maximum rated 7 amount of reactive power: 750 KVAR. In Example #3, CKT-A no shows a net reactive 8 power consumption of -482 KVAR. -482 KVAR of reactive power consumption is identical 9 to 482 KVAR of reactive power production according to the standard. Therefore, CKT-A is 10 now a net producer of reactive power. Notice the power factor or CKT-A is shown as 0.43 in 11 Example #3. This is a leading power factor, as opposed to a lagging power factor. As 12 explained in the Apparent Power section above, a leading power factor is a circumstance in 13 which the current leads the voltage in phase. 14 Finally, we must examine the CKT-PRIMARY results between the two examples. 15 Here are the results: 67 WO 2012/142082 PCT/US2012/033009 1 Example #2 CKT-PRIMARY Voltage 12047VAC Current 68AMPS Real Power 1160KW Reactive Power 919KVAR Apparent Power 1479KVA Power Factor 0.78 2 3 Example #3 CKT-PRIMARY Voltage 12135VAC Current 54AMPS Real Power 1160KW Reactive Power 169KVAR Apparent Power 1172KVA Power Factor 0.99 4 5 6 The total reactive power of Example #3 is 169 KVAR. The total reactive power of 7 Example #2 is 919 KVAR. As one would expect, there exists a net 750 KVAR difference 8 between the two totals. This is due to the fact that Example #3 has the Tuned PF CAP 9 injecting its maximum rated 750 KVAR of reactive power. However, as can be seen, there 10 are many other effects of lowering the net reactive power demand in Example #3 vs. 11 Example #2. The apparent power of Example #3 is 1172 KVA, while the apparent power of 12 Example #2 is 1479 KVA. Reducing reactive power level also reduces apparent power 13 levels. The current of Example #3 is 54 Amps, while the current of Example #2 is 68 Amps. 14 As was explained earlier, lowering the current draw also reduces the voltage drop. Therefore, 15 the voltage in Example #3 is 12,135 VAC, while the voltage in Example #2 is 12,047. In 16 general, reducing reactive power requirements reduces the load on the T-PAD5A transformer 17 and reduces the current in the conductors connected to the T-PAD5A transformer. Reducing 18 the reactive power also increases the voltage, and makes the voltage more stable. The power 19 factor in Example #3 is 0.99, while the power factor of Example #2 is 0.78. In most 20 circumstances a slightly lagging power factor at the T-PAD5A transformer is desirable. A 21 leading power factor at the T-PAD5A transformer would be highly undesirable. Most power 22 systems are not designed or controlled to operate with a leading power factor for many 23 reasons that are primarily related to voltage stability. The specific reasons that power 24 systems are not designed to operate with a leading power are well understood by skilled 25 power system engineers and will not be elaborated on further. However, it is not the case that 68 WO 2012/142082 PCT/US2012/033009 1 no portions of the power system are to be operated with a leading power factor. For example, 2 the feeder CKT-A in Example #3 is operated with a leading power factor. Operating portions 3 of the system, so long as the system is designed to accommodate such operation, at a leading 4 power factor is accepted practice and may, in some cases, be desirable. In any event, 5 operation at a power factor of 0.99 at the CKT-PRIMARY location is the absolute maximum 6 power factor that would be considered acceptable. 7 Please bear in mind, Example #3 and Example #2 are considered at identical real 8 power levels: 1160 KW. The mechanical loading of the motors in both examples are 9 identical. It is by changing the operation of the electrical system that one can change the 10 electrical system's reliability, stability and versatility. 11 12 Example #4 - All equipment operating at 40% load. Transformers energized. Reactive 13 current required to magnetize distribution transformers and induction motors. CKT-A 14 component PF CAP is de-energized. Reactive power injected from active converters at 40% 15 of rating. 16 SUMMARY REPORT Example #4 Description: All equipment operating 50% load 40% of Rated Reactive Power Injection from Tuned PF Cap on CKT-A 40% of Rated Reactive Power Injection from Active Converters CKT-PRIMARY Voltage 12132VAC Current 55AMPS Real Power 1160KW Reactive Power 227KVAR Apparent Power 1181KVA Power Factor 0.98 17 18 See Fig 32 for schematic illustrating power triangle for Example #4. 19 69 WO 2012/142082 PCT/US2012/033009 1 CKT-A Voltage 12132VAC Current 1 lAMPS Real Power 228KW Reactive Power -32KVAR Apparent Power 230KVA Power Factor 0.99 CKT-E Voltage 12132VAC Current 14AMPS Real Power 290KW Reactive Power 48KVAR Apparent Power 294KVA Power Factor 0.99 CKT-Y Voltage 12132VAC Current 13AMPS Real Power 227KW Reactive Power 164KVAR Apparent Power 280KVA Power Factor 0.81 CKT-W Voltage 12132VAC Current 19AMPS Real Power 415KW Reactive Power 46KVAR Apparent Power 418KVA Power Factor 0.99 Summary Components CKT-A (Components) PF CAP Voltage 12132VAC Current 14AMPS Real Power OKW Reactive Power -300KVAR Apparent Power 300KVA Power Factor 0 426A Voltage 467VAC Current 121AMPS Real Power 62.5KW 70 WO 2012/142082 PCT/US2012/033009 Reactive Power 78.5KVAR Apparent Power 1OOKVA Power Factor 0.62 526A Voltage 467VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 CKT-E (Components) 427E Voltage 467VAC Current 85AMPS Real Power 62.5KW Reactive Power -33.5KVAR Apparent Power 71KVA Power Factor 0.88 622E Voltage 467VAC Current 85AMPS Real Power 62.5KW Reactive Power -33.5KVAR Apparent Power 71KVA Power Factor 0.88 627E Voltage 467VAC Current 242AMPS Real Power 165KW Reactive Power 115KVAR Apparent Power 201KVA Power Factor 0.82 CKT-Y (Components) 811Y Voltage 467VAC Current 40AMPS Real Power 31KW Reactive Power -13KVAR Apparent Power 34KVA Power Factor 0.92 305Y Voltage 467VAC Current 40AMPS Real Power 31KW Reactive Power -13KVAR Apparent Power 34KVA Power Factor 0.92 314Y 71 WO 2012/142082 PCT/US2012/033009 Voltage 467VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 CKT-W (Components) 333W Voltage 467VAC Current 174AMPS Real Power 125KW Reactive Power -72KVAR Apparent Power 144KVA Power Factor 0.87 334W Voltage 467VAC Current 174AMPS Real Power 125KW Reactive Power -72KVAR Apparent Power 144KVA Power Factor 0.87 335W Voltage 467VAC Current 303AMPS Real Power 165KW Reactive Power 190KVAR Apparent Power 252KVA Power Factor 0.66 1 2 Analysis of Example #4 3 Analysis of the power system operated in this configuration is complex, however, it is 4 extremely helpful and information to consider this type of operation to appreciate the benefits 5 of distributed reactive power production. Example #4 is best analyzed in comparison to 6 Example #3: Example #4 Example #3 CKT-PRIMARY Voltage 12132VAC 12135VAC Current 55AMPS 54AMPS Real Power 1160KW 1160KW Reactive Power 227KVAR 169KVAR Apparent Power 1181KVA 1172KVA Power Factor 0.98 0.99 7 72 WO 2012/142082 PCT/US2012/033009 1 As can be seen in the two examples above, the conditions at the large transformer T 2 PAD5A are virtually identical between the two examples. Again, real power in both 3 examples is identical. The voltage, current, real power, apparent power and power factor 4 show no significant differences between the two examples. The reactive power is slightly 5 different, with Example #4 being 34% higher than that of Example #3. However, as can be 6 seen in the numbers above, the overall level of reactive power in both examples is not 7 sufficiently large enough to significantly change the overall operation of the T-PAD5A 8 transformer. 9 Next, let's look at the feeder circuits: 10 Example #4 Example #3 CKT-A Current IlAMPS 25AMPS Reactive Power -32KVAR -482KVAR CKT-E Current 14AMPS 15AMPS Reactive Power 48KVAR 160KVAR CKT-Y Current 13AMPS 15AMPS Reactive Power 164KVAR 220KVAR CKT-W Current 19AMPS 23AMPS Reactive Power 46KVAR 270KVAR 11 12 13 To understand the changes in the feeder circuits shown above, one must recall that in 14 Example #3 there was a single large source of reactive power located in CKT-A. This single 15 large source of reactive power in Example #3 was a single Tuned PF Capacitor that had a 16 rating of 750 KVAR. This capacitor was the source of reactive power used by all the loads 17 on all the other feeders that consumed reactive power. However, in Example #4 there are 18 many distributed sources of reactive power. It is the distributed nature of the reactive power 19 that causes the feeder amperages to drop significantly. For example, feeder CKT-W in 20 Example #4 draws 19 amps vs. an amp draw in Example #3 of 23 amps. The reduction in 21 amps in Example #4 is due to the fact that in this example, there are reactive current sources 22 on feeder CKT-W, not just reactive loads. The reactive sources on feeder CKT-W can feed 23 reactive power to the reactive loads on CKT-W, therefore, the total current measured flowing 24 from T-PAD5A to the feeder CKT-W is reduced. Using distributed reactive power sources 25 has the effect reducing current loads in feeders as shown in these examples. In very large and 73 WO 2012/142082 PCT/US2012/033009 1 complex electrical power distribution networks the effect of having many diverse and 2 distributed sources of reactive power and many diverse and distributed loads that consume 3 reactive power would be to effectively lower the current in virtually all feeder circuits. 4 Depending on the specific circumstances present in the electrical power distribution system, 5 this effect could be significant. In fact, lowering current on feeder circuits could allow more 6 loads to be fed from existing feeders or allow existing loads to operate at higher loading 7 levels. 74

Claims (31)

1. CLAIMS 1. An electrical apparatus including

   a variable frequency AC drive having an input adapted to be electrically coupled to an electric power grid and an output adapted to be electrically connected to an AC electric motor,

   said variable frequency AC drive including an active converter having a predetermined maximum apparent power capacity,

   said converter coupled to a controller programmed to regulate reactive power generation and consumption of the variable frequency AC drive so that said drive produces reactive power when said converter is utilizing less than said converter's maximum apparent power capacity, said reactive power being generated without substantially compromising the ability of the drive to provide real power as demanded by a load driven by the AC motor, said reactive power to be fed to the power grid.
2. 2. The apparatus of claim 1 where said variable frequency AC drive is adapted to be connected in parallel with a plurality of loads that receive power from said power grid.
3. 3. The apparatus of claim 1 where said active converter has an output connected to one or more inverters.
4. 4. The apparatus of claim 1 where the controller has a selectable mode control that establishes which one or more then one of a plurality of control strategies is employed, said strategies governing the combination of reactive power and real power to avoid the apparent power exceeding the maximum apparent power capacity of the active converter.
5. 5. The apparatus of claim 4 where the control strategies include (1) a first control strategy where the load on the motor changes slowly, (2) a second control strategy where the load changes rapidly, and (3) a third control strategy where the load is cyclic.
6. 6. The apparatus of claim 5 where according to the first control strategy the reactive power is a function of the maximum apparent power capacity of the converter and the real power demanded.

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7. 7. The apparatus of claim 6 where the real power requirements change at a frequency of less than 4 Hertz.
8. 8. The apparatus of claim 5 where according to the second control strategy the real power limit of an inverter connected to the converter through a DC bus is a function of the maximum apparent power capacity of the active converter and the instantaneous reactive power of the active converter.
9. 9. The apparatus of claim 8 where the instantaneous reactive power is multiplied by a scaling factor.
10. 10. The apparatus of claim 8 where, as the real power demanded by a load approaches levels resulting in an overload of the active converter, a predetermined real power limit of the inverter is lowered, and, as said predetermined real power limit is lowered, a predetermined instantaneous reactive power limit is reduced, and as said instantaneous reactive power is reduced, the predetermined real power limit of said inverter is increased.
11. 11. The apparatus of claim 5 where according to the third control strategy the reactive power is controlled so that apparent power is kept essentially constant.
12. 12. The apparatus of claim 1 including a device that monitors current and voltage from the power grid and generates a reference signal corresponding to a power factor for a system in which the apparatus is connected, and the controller is programmed to respond to said signal.
13. 13. An electrical apparatus including

    a variable frequency AC drive having an input adapted to be electrically coupled to an electric power grid,

    said variable frequency AC drive including an active converter connected through a DC bus to an inverter having an output adapted to be electrically connected to an AC electric motor, said converter having a predetermined maximum apparent power capacity, and

    a controller programmed to regulate reactive power generation and consumption of the variable frequency AC drive so that (a) said drive produces a combination of reactive power and real power that avoids producing apparent power exceeding the maximum

    32 capacity of the active converter, and (b) said reactive power is generated without substantially compromising the ability of the AC drive to provide real power as demanded by a load driven by the AC motor.
14. 14. The apparatus of claim 13 including a device that monitors current and voltage from the power grid and generates a reference signal corresponding to a power factor for a system in which the apparatus is connected, and the controller is programmed to respond to said signal.
15. 15. A system that receives power from an electric power grid, said system including

    a load connected to the power grid,

    an AC electric motor connected to the power grid through a variable frequency AC drive in parallel connection with the load,

    said variable frequency AC drive having an input electrically connected to the power grid and an output electrically connected to the AC electric motor and including an active converter having a predetermined maximum apparent power capacity,

    said converter coupled to a controller programmed to regulate reactive power generation and consumption of the variable frequency AC drive so that said drive produces reactive power when said converter is utilizing less than its maximum power capacity, said reactive power to be fed to the power grid, and

    a device that monitors current and voltage from the power grid and generates a reference signal corresponding to a power factor for the system,

    said controller being programmed to respond to said signal, controlling power generation and consumption so that the combination of reactive power and real power does not result in apparent power exceeding the maximum capacity of the active converter and avoids generating reactive power that would result in a leading power factor for the system.
16. 16. The system of claim 15 where there are a plurality of loads in parallel connection with the drive.
17. 17. The system of claim 16 where there are a plurality of variable frequency AC drives in parallel connection with the loads.

    33
18. 18. The system of claim 15 including a plurality of inverters, each inverter having an input connected to the output of the active converter and an output connected to an AC motor.
19. 19. The system of claim 15 where the controller has a selectable mode control that establishes which one or more then one of a plurality of control strategies is employed, said strategies governing the combination of reactive power and real power to avoid the apparent power exceeding the maximum capacity of the active converter.
20. 20. The system of claim 19 where the control strategies include (1) a first control strategy where the load on the motor changes slowly, (2) a second control strategy where the load changes rapidly, and (3) a third control strategy where the load is cyclic.
21. 21. The system of claim 20 where according to the first control strategy the reactive power is a function of the maximum apparent power capacity of the converter and the real power demanded.
22. 22. The system of claim 21 where the real power requirements change at a frequency of less than 4 Hertz.
23. 23. The system of claim 20 where according to the second control strategy the real power limit is implemented in an inverter connected by a DC bus to the active converter, said real power limit being a function of the maximum apparent power capacity of the active converter and the instantaneous reactive power of the active converter.
24. 24. The system of claim 23 where the instantaneous reactive power is multiplied by a scaling factor.
25. 25. The system of claim 23 where, as the real power demanded by a load approaches levels resulting in an overload of the active converter, a predetermined real power limit of the inverter is lowered, and, as said predetermined real power limit is lowered, a predetermined instantaneous reactive power limit is reduced, and as said instantaneous reactive power is reduced, the predetermined real power limit of the inverter is increased.

    34
26. 26. The system of claim 25 where according to second strategy a controlled intervention in the inverter is used to insure that the instantaneous real power does not exceed a predetermined threshold value of a real power limit of the inverter.
27. 27. The system of claim 20 where according to the third control strategy the reactive power is controlled so that apparent power is kept essentially constant.
28. 28. A system comprising

    an AC motor having its output connected to cyclic load,

    a variable frequency AC drive including an active converter subjected to damage due to rapid thermal cycling,

    said converter coupled to a controller programmed to regulate reactive power generation and consumption of the variable frequency AC drive so that said drive avoids rapid thermal cycling that may damage the active converter.
29. 29. The system of claim 28 where the active converter comprises a plurality of insulated gate bipolar transistors.
30. 30. An oil well including

    a pump operatively an AC motor,

    a programmable, variable frequency AC drive that transfers electrical energy from a power grid to the AC motor,

    said AC drive including an active converter having a maximum apparent power capacity and programmed to produce reactive power that is fed to the power grid when said converter is utilizing less than said converter's maximum apparent power capacity, said reactive power being generated without compromising the ability of the drive to provide real power as demanded by the pump being driven by the AC motor.
31. 31. The oil well of claim 30 including a device that monitors current and voltage from the power grid and generates a reference signal corresponding to a power factor for a system including the pump, and the controller is programmed to respond to said signal to avoid generating reactive power that would result in a leading power factor for the system.

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