Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J9/00—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting
  • H02J9/04—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source
  • H02J9/06—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems
  • H02J9/062—Circuit arrangements for emergency or stand-by power supply, e.g. for emergency lighting in which the distribution system is disconnected from the normal source and connected to a standby source with automatic change-over, e.g. UPS systems for AC powered loads
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
  • Y02B70/30—Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
  • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
  • Y04S20/00—Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
  • Y04S20/20—End-user application control systems

Definitions

• any of the foregoing departures of the power line from a constant, fixed-frequency, substantially noise-free sinewave can cause loss of stored information and/or improper handling b ⁇ information by the load apparatus, either of which can have very serious adverse results.
• UPS uninterruptible power supply
• a battery charger a battery and an inverter in tandera with each other, the charger being supplied from the AC power line and the inverter supplying AC to the computer or other critical load.
• the power line keeps the battery adequately charged despite small over-voltages, under-voltages or interfering noise on the utility line, and the inverter utilizes the stored energy of the battery to produce substantially pure single-frequency sinewaves of constant amplitude for supply to the critical load.
• the battery and inverter will maintain the desired AC current and voltage at the load for a substantial period of time, after which discharge of the battery can be detected and the equipment appropriately shut down, its use discontinued, or other protective measures taken, such as shifting to other standby power.
• phase of the sinewave generated by the inverter can be varied as desired with respect to the phase of the utility line voltage, thereby varying the magnitude and phase of the contribution of the inverter current to the load current.
• this phase angle may be set, and preferably automatically maintained, at a value sufficient to supply the power demanded by the load, plus any losses in the system, plus any amount of power which it is desired to supply to the battery to maintain it charged or to recharge it.
• the magnitude of the alternating voltage supplied to the load from the utility line, and hence also supplied to the output terminals of the inverter is substantially equal to the utility line voltage itself.
• the ratio of the turns of the winding connected to the utility line is equal to the number of turns coupled to the load terminals; that is, the ratio of the turns is 1:1 based on the concept that the load equipment is to be supplied with the same alternating voltage as is present on the power lines.
• an object of the present invention to provide an uninterruptible power supply and line conditioner of the type which employs an inductance through which the utility line voltage is fed to the inverter output and the load terminals, and in which the inverter is of the four-quadrant PWM sinewave type, but in which the inverter current required for normal operation near the "break even" operating point is minimized and the through-put efficiency of the system maximized.
• FIG. 1 is a schematic representation of a UPS system of the prior art
• Figure 2 is a schematic representation of a class of system to which the present invention is applicable;
• Figure 3 is an equivalent-circuit diagram for the system of Fig. 2;
• Figures 4 and 5 are phasor diagrams to which reference is made in explaining the operation of the system of Fig. 3;
• Figures 6 and 8 are graphical representations of the relationship between certain parameters in the system of Fig. 2;
• Figure 7 is an equivalent-circuit diagram of a system according to the present invention.
• Figure 9 is a graphical representation showing the variations of certain parameters in a system according to the present invention.
• Figure 10 is a circuit diagram of apparatus in accordance with a preferred embodiment of the invention.
• Figure 11 is a schematic view of a form of transformer used in the system of Fig. 10;
• Figure 12(a) is a phasor diagram for a system not using a principal feature of the present invention
• Figure 12(b) is a similar type of diagram for a system using the present invention
• Figure 13 is a block diagram illustrating one type of complete microprocessor-controlled system in which the apparatus of the present invention may be used.
• Figures 14A and 14B are graphical plots of voltages and currents, respectively, in a preferred system according to the invention, illustrating respectively the substantial immunity of load voltage to electrical noise on the power lines and the absence of line-current distortion in the power-line current when the load current is substantially distorted.
• Figure 1 illustrates in broad form a system previously known in the prior art in which the utility line 10 is connected to a rectifier/charger 12, which converts the alternating utility voltage to direct voltage so as to charge a battery 16. The voltage across the latter battery is then utilized to operate an inverter 18, which converts the DC voltage of the battery to alternating current and supplies it over output line 22 to the critical load.
• the utility line can be disconnected for substantial periods while the inverter continues to supply the desired alternating voltage, while at the same time substantial protection is provided against interfering noise, current surges, momentary voltage drops and irregularities in the waveform of the utility line voltage.
• FIG 2 is a diagram similar to Figure 1 but illustrating a class of equipment to which the invention is particularly applicable.
• the utility line 24 supplies alternating voltage to the four-quadrant PWM sinewave inverter 26 by way of a series inductance, and the output of the inverter is connected over line 28 to the critical load;
• the battery 30 is connected to the inverter, and the inverter determines how much of the critical load current is supplied from the utility line and how much from the battery, and how much of the utility line current is supplied to charge the battery.
• Figure 3 is a simplified equivalent circuit for the general arrangement of Fig . 2 , depicting the utility line voltage E u , the series inductance L s through which the current I L flows, the inverter with a voltage E. across it and a current I- through it, and the critical load Z O to which the load current I O is supplied.
• the inverter and critical load are effectively in parallel with each other, and supplied with voltage from the utility line by way of the series inductor L s .
• the generalized phaser diagram for such a circuit is shown in Fig. 4 for the case in which the angle between the utility line voltage E u and the inverter output voltage E i is ⁇ , with the inverter voltage lagging.
• the voltage E L across the inductance is the vector difference between the vectors E u and E i , and hence is a vector joining the heads of the vectors of the latter two quantites, as shown.
• I L for a substantially lossless inductance, is at right angles to E L and the load current I O is assumed to lag the inverter voltage by a load power factor angle ⁇ .
• the inverter current I i is equal to the vector difference between the load current I O and the inductance current I L , as shown in the drawing. Also shown is the angle by which I L lags E u .
• Figure 5 illustrates the effect of changing the angle ⁇ between the utility line voltage E u and the inverter output voltage E i ; the magnitudes of E u and E i are equal, and for simplicity the case is shown wherein the load power factor is unity.
• the input or inductor current I LI is also small; the inverter current I il is nearly in phase with the inverter voltage E i and therefore the inverter is delivering real power to meet the power requirements of the load not supplied by the utility line; thus, in this case the inverter battery is discharging.
• I O the utility supplies all of the load power. Since I i2 is at 90° to the inverter voltage E i , no real power flows into or out of the inverter and therefore the battery current is zero (ignoring losses). However, there is a substantial reactive current in the inverter, as depicted by the vector I i2 . This condition in which sub stantially no real power flows in or out of the inverter we designate as the "break even" case.
• I L3 is substantially larger, as is the inverter current I i3 ; however, the direction of the vector I i3 indicates that real power is flowing into the inverter, while the inverter battery is being charged during such operation at the angle ⁇ 3 .
• the input voltage displacement angle ⁇ for any given load, input voltage, and charge current condition increases with increasing value of the inductance L S .
• inverter current is minimal when L S equals 0.4 P.U.
• the inverter still must be sized to handle 130% full load current (at "break even") when the load power factor is 0.8 lagging.
• to charge the battery at 0.2 P.U. requires an inverter rated at 150%.
• Figure 6 illustrates the variation of inverter current as a function of input voltage (normalized), at the break-even operation condition. It is noted that for unity power factor, inverter current is minimum when the input or utility voltage E is equal to 1.1 P.U.
• the system performance is improved by scaling or transforming the input utility voltage upward by a factor of 1.1, as shown in Figure 7.
• Figure 7 shows a system according to the invention in equivalent circuit form, with a step-up of
• load current I O is plotted as abscissae and two variables are plotted as ordinates, namely input voltage displacement angle ⁇ and input currents (I u , I L ).
• the graphs contained therein illustrate the effects on load current I O of varying I u , I L and ⁇ for a 1.1 transformation ratio.
• FIG 10 there is shown a preferred embodiment of the invention for the typical case of a utility voltage of 120 volts AC, a load voltage of 120 volts AC, a load power requirement of three KVA at 60hz, and a load power factor of unity.
• a battery 40 in this example providing 120 volts DC, is connected through an appropriate fuse 42 to a shunt capacitor 44, typically having a value of about 15,000 microfarad.
• the four-quadrant PWM sinewave inverter 46 made up of the PWM filter 48 and the four transistor-diode sections A, B, C and D arranged in a bridge configuration, where the battery is connected between the top and bottom junctions 50, 52 of the bridge and the opposed side junctions 54 and 56 of the bridge are connected to the respective input lines 58 and 60 of the PWM filter.
• Each of the bridge sections A, B, C and D is made up of a high current NPN switching transistor having a high-current semiconductor diode in parallel therewith.
• the collectors of the two transistors are connected to the positive side of the battery and their emitters are connected to bridge output lines 58 and 60 respectively; the two diodes in the upper sections A and C are poled so that their cathodes are connected to the positive end of the battery.
• the transistors and diodes in the lower bridge sections B and D are poled oppositely from those in sections A and C.
• Such circuits and their operation are well known in the art for use as PWM inverters.
• the bases of the four switching transistors are turned ON and OFF in pairs in a predetermined sequence at predetermined times and for predetermined intervals, in this example 26 times per sinewave cycle, so that the output leads 58 and 60 of the bridge circuit are provided with a pulse-width modulated pulse signal having energies representing a sinewave, which signal after passage through the low-pass PWM filter 48 therefore produces a sinewave in response to energy from the battery.
• each of the capacitors C T and C F of the filter may have a value of about 200 microfarad
• the inductance of each of the two coils L F may be about 400 microhenries and the inductance of the coil L T may be about 13 microhenries, producing a low-pass filter having an upper band limit at about 400 Hz and a rejection trap at the carrier frequency of the PWM pulses.
• the output termimls 70,72 of the inverter are connected across the inverter winding 76 of a transformer 78.
• the transformer winding 76 may have a number of turns equal to about 1/2 the number of turns of the load winding 80 thereon which supplies power to the load, that is, if the numbar of turns of winding 80 is N 2 then the number of turns of inverter output winding 76 may equal 1/2 N 2 .
• Transformer windings 76 and 80 are tightly coupled to each other, e.g. may be wound one on top of the other on a common iron core 84 so that the inverter output voltage is the load voltage.
• Transformer winding 80 is connected directly to the load input terminals 88 and 90, in this example by way of a normally-closed manual switch 92.
• a bypass switch-contact 94 is provided so that switch 92 may be placed in an alternate position wherein the high side of the transformer winding 80 is replaced by the high side 96 of the AC utility line, the neutral side 98 of the utility line being permanently connected to the lower end of transformer winding 80, thus enabling an operator to mechanically bypass the entire UPS system and connect the critical load directly to the utility line vhen conditions warrant r.uch action.
• a static bypass circuit 102 may be employed, made up of a pair of parallel, oppositely-pol ed silicon-controllod-rectifiers each of which can be triggered on by signals applied to its gate electrode, the pair thus serving as a bidi rectional electronic switch, actuatable in response to electrical signals indicative of any selected malfunction, such as a large change in load voltage due to a load disturbance.
• the AC utility line made up of the high line
• transformer winding 112 which is located on the same core as the windings 76 and 80 but is loosely coupled thereto by virtue of the intervening magnetic shunts 114 and 116, which typically comprise bodies of ferro-magnetic material positioned to shunt or bypass a portion of the magnetic flux which otherwise would extend between coil 112 and the coils 76 and 80; each magnetic shunt is designed to provide at least, a small air gap on each side of the shunt so that complete shunting does not occur.
• Such constructions an d procedures are well known in the art and need not be described herein in detail, and a physical arrangement of such a transformer is illustrated schematically in Fig.
• transformer windings are designated by the same numerals as previously and the magnetic shunts are designated as 140 and 142.
• This decoupling by the inductance permits the vectors representing the voltages at winding 112 and at winding 76 to be independently adjusted.
• connection between the high utility line 96 and winding 112 may include a series fuse 150 and an AC disconnect switch 152, similar in form to the static bypass switch 102 and similarly operable, when desired, by electrical signals applied to the gate electrodes of the SCR's; for example, when the utility line fails, switch 152, is automatically opened and the load is supplied with AC power entirely from the battery and inverter.
• the simplified equivalent circuit illustrated in Fig. 7 is applicable to the system of Fig. 10, the the ratio N 2 /N 1 of the turns of windings 80 and 112 being represented by the tap position on an autotransformer which, in effect, increases the line voltage applied to the input end of inductance L s from E u to a 10% higher value Eu'.
• the series inductance L s is effectively provided, in the example of Fig. 10, by the transformer and the magnetic shunts built into it.
• this step-up ratio of 1.1 minimizes the break-even inverter current required by the system during normal operation and maximizes the through-put efficiency.
• the transformer 78 in this example is of El constrti tion, with the magnetic shunts described previously serving to attenuate the magnetic path between winding 112 and windings 76 and 80, in this example giving an effective value for L s of about 5 millihenries.
• Figures 12A and 12B illustrate from a different viewpoint the operation and effect of the line voltage step-up employed according to the present invention.
• the difference vector E L again represents the voltage across the series inductance L S , and the current through that inductance is represented by the vector I L at right angles thereto.
• the output current in this example is assumed to be in phase with the inverter output voltage, i.e. the load is unity power factor, so that the I O vector lies along the same direction as the E i vector as shown.
• the difference vector I i then represents the substantial circulating current in the inverter, which always exists under these conditions even though no real power is then being delivered to or from the inverter.
• Figure 12B shows conditions existing in a comparable system modified according to the present invention so that the line voltage E u is in effect, transformed upwardly by a factor 1.1 to a new value E u ', this increased value of E u ' being sufficient so that the E L vector is vertical and the I L vector, being at right angles to E L , lies directly along the direction of the inverter current I O and is equal thereto. It therefore supplies all of the load current, leaving no current, reactive or real, in or out of the inverter, as is desired to produce the previously-described improvements with regard to minimizing inverter current and improved through-put efficiency.
• FIG. 13 illustrates by way of example one type of system in which the UPS of the invention may be included.
• a microprocessor 300 such as a Z80 microprocessor chip, controls the frequency and phase ⁇ of the inver ter output sinewave and is supplied with appropriate program memory information from memory 302; with system personality information indicative of the particular application parameters from system personality 304; with digital information with respect to line voltage, load voltage, line current, load current, battery current and battery voltage from A/D device 308; with a variety of monitoring information with respect to conditions of the line switch, the bypass switch, overtemperature, over-voltage or any other parameters which it is desired to monitor, by way of I/O port 310; and with a mutual interchange of information with an appropriate display device 312.
• the microprocessor also preferably receives information from an interrupt control 360 with respect to such parameters as line voltage, inverter voltage, time and any other parameters found desirable.
• the microprocessor controls a counter timer chip (CTC) carrier generator 400 and a CTC 60Hz generator 402, which operate to produce on line 404 a carrier frequency equal to the repetition rate of the pulse-width modulated pulses (typically at 26 times the 60 Hertz line frequency) and to produce from sine generator 410 a substantially pure sinewave function at utility-line frequency and of the desired 120-volt magnitude.
• the PWM control 420 controls the inverter 422, which in this case is assumed to be the entire circuit of Figure 10, so as to determine the phase and the widths of the pulses which turn on the transistors in the PWM bridge circuit.
• An inverter feedback connection extends from the load 450 to a comparison or error amplifier circuit 452 which detects and amplifies any differences between the voltage fed beck from the inverter and the idealized sinewave from sine generator 410, this difference: then being fed to PWM control 420 in a polarity and amount to correct any deficiencies in the sinewave appearing at the load.
• the sinewave is locked to the utility line sinewave.
• the microprocessor includes a stable crystal-controlled reference oscillator, powered by the battery, from which the desired ideal sinewave at the desired line frequency is derived.
• the microprocessor maintains frequency lock between the sine-wave reference and the utility as well as manipulating the displacement phase angle between them. It also examines all system parameters and compares then against preset software limits. The user can access these system parameters through a front graphics display panel.
• Figures 14A and 14B illustrate the bidirectional line conditioning obtained with applicants' isolated system. As shown in Fig. 14A, if the line voltage E u consists of a sinewave with the noise spikes shown thereon, the inverter voltage E i supplied to the load has the substantially pure sinewave appearance shown in the latter figure; Figure 14B shows that even if the load current
• the preferred embodiment of the invention has been shown as utilizing a transformer in which magnetic shunts provide the effective series inductance L S , and the voltage step-up R is provided by the ratio N 2 /N 1 in the number of turns of entirely separate and isolated transformer windings.
• the series inductance L S is in fact a real lumped-circuit series inductor connected between the high side of the line and the inverter output, much as represented schematically in the simplified equivalent circuit of Fig. 7, and it is in fact possible to utilize an autotransformer as suggested by the equivalent circuit of Fig. 7 rather than the completely isolated transformer winding arrangement of the preferred embodiment.
• the minimum inverter current may in some instances occur at a different value than 1.1, in which case R may be differently chosen to minimize inverter current during breakeven operation. That is, in some cases the load power factor may not be centered about unity, but may have a known average fixed value departing substantially from unity, in which case the value of R may be chosen to be substantially different from 1.1, so as to minimize the required inverter current during normal operation.

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• Business, Economics & Management (AREA)
• Emergency Management (AREA)
• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Inverter Devices (AREA)

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Cited By (14)

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Citations (5)

• 1984
  • 1984-09-27 IN IN760/DEL/84A patent/IN162259B/en unknown
  • 1984-09-27 CA CA000464184A patent/CA1236524A/en not_active Expired
  • 1984-09-28 AU AU34368/84A patent/AU3436884A/en not_active Abandoned
  • 1984-09-28 WO PCT/US1984/001553 patent/WO1985001842A1/en unknown
  • 1984-09-28 EP EP84903703A patent/EP0157855A1/en not_active Withdrawn

Patent Citations (5)

Non-Patent Citations (1)

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