CA2227641A1 - Energy management and distribution control system - Google Patents
Energy management and distribution control system Download PDFInfo
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- CA2227641A1 CA2227641A1 CA 2227641 CA2227641A CA2227641A1 CA 2227641 A1 CA2227641 A1 CA 2227641A1 CA 2227641 CA2227641 CA 2227641 CA 2227641 A CA2227641 A CA 2227641A CA 2227641 A1 CA2227641 A1 CA 2227641A1
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- 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
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E70/00—Other energy conversion or management systems reducing GHG emissions
- Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin
Abstract
A system for energy management and distribution.
The system comprises a power distribution bus having an input, module for receiving electrical energy from a primary energy source, one or more energy converters coupled to the power distribution bus, and a controller. The energy converters provide alternative energy sources to augment and/or replace the primary energy source. The controller determines the present energy demand for the consumer and controls the input module and/or energy converters to provide the power needed by the consumer. The system may also include energy storage devices coupled to the power distribution bus. The energy storage devices store electrical energy obtained at off-peak times for injection into the bus at peak times when the supply of energy from the primary energy source is more expensive.
The system comprises a power distribution bus having an input, module for receiving electrical energy from a primary energy source, one or more energy converters coupled to the power distribution bus, and a controller. The energy converters provide alternative energy sources to augment and/or replace the primary energy source. The controller determines the present energy demand for the consumer and controls the input module and/or energy converters to provide the power needed by the consumer. The system may also include energy storage devices coupled to the power distribution bus. The energy storage devices store electrical energy obtained at off-peak times for injection into the bus at peak times when the supply of energy from the primary energy source is more expensive.
Description
ENERGY MANA~.RM~NT AND DISTRIBUTION CONTROL SYSTEM
FIELD OF THE lNV~r~llON
The present invention relates to electrical power systems, and more particularly to an energy management and distr:ibution system.
RACR~ROUWD OF THE lNV~-llON
Electrical energy remains the primary source of energy for fuelling the modern industrial world.
Historically, public and private power utilities have provicled for the energy needs of society. Electrical energy is used on a demand basis by the consumer and the power utility is paid based on the power consumed.
With rising energy costs, consumers have turned to alternative energy sources, such as solar-powered, wind-powered and fossil fuel powered generators. Suchgenerators are operated independently to power electrical equipment and thereby reduce the power needs from the utility. Alternative power generators can be effective in generating power, but can be limited as to operating periods, e.g. solar-powered generators are non-operational at night, and wind-powered generators need a steady wind to generate electricity.
The deregulation of power utilities is also changing the way electric power is being sold to the consumer. Deregulation means that to be economically viable a power utility must be able to deliver power in a cost-effective manner. In practical terms, electrical energy will remain available on a continuous basis, however, the cost of energy at peak ~e~an~ times will be consid~erably higher than at off-peak times. This trend has already been seen in the deregulated sectors of the power industry in the United States. In less developed countries, deregulation of the power industry will mean that electric power will be available on a less frequent basis with limited or no power available at any cost during certain times of the day.
While alternative energy sources provide a means to augment the electricity supply for a user, there remains a need for a system which can minimize the cost of electric energy and maximize the availability of power by effectively integrating the alternative energy sources with the primary source from the power utilities and providing electricity to the consumer in a cost effective manner.
Such a system preferably would have the capability to store energy purchased from a power utility at off-peak (i.e. low cost) periods, or energy generated during low demand periods for use at a later time. Such a system would also have the capability to continue to provide power in the event the electricity supply from the power utility is interrupted.
SUMMARY OF THE lNv~ lON
The present invention provides a system for energy management and distribution of one or more sources to one or more loads. The energy may be supplied through conventional AC power mains, fossil fuel powered generators, wind-powered generators, solar-powered generators, electrochemical fuel cells, etc. The energy management system includes means for storing and retrieving energy for load levelling, loss of alternative energy sources, or AC mains drop out using battery, flywheel, super-capacitor, super-conducting magnetic devices, etc.
The system also includes a low-harmonic/high power factor PWM utility interface to supply a "clean" load to the AC mains supply from the power utility. It is a feature of the invention that energy from all the sources is co:nverted to a medium voltage DC (or low frequency AC) power distribution level on a bus. The voltage on the bus is regulated by any of the energy sources connected to the bus which are capable of both sourcing and sinking energy from the bus. The energy management system controller determines which energy source has regulation control of the bus. Control of the bus is based on a number of decision factors including availability of energy, load recluirements, and time of day. Preferably only one energy source will have regulation control of the DC bus under impressed voltage control. All the other sources will run under impressed current or power control.
It is a feature that all loads will draw energy from the bus as recluired unless limited or interrupted by the energy management system controller. All control systems are powered from the DC bus in order to guarantee system control is not lost due to a local power loss. In the event all energy sources go off-line and the DC bus is powered down the system is restarted in manual mode by any of th,e dual energy sources. The energy management system controller comes on-line and takes over control of the system once the DC bus has been pre-charged to a minimum voltage level.
In a first aspect, the present invention provides an energy management system for managing the supply of electrical energy to a consumer, said energy management system comprising: (a) an input -module for receiving electrical energy from a primary energy source, said input module having a converter for converting said electrical energy for local distribution; ~b) a power distribution bus for distributing said converted electrical energy; (c) a plurality of energy converters coupled to said power distribution bus and having means for generating electrical energy and means for injecting said electrical energy into said power distribution bus; (d) a controller having means for determining a present energy demand for the consumer and means for controlling said input module and means for controlling said energy converters; (e) said input module having means responsive to control signals from said controller for receiving electrical energy from the primary enerqy source and injecting said energy into said distr-ibution bus; and (f) said means for injecting for said enerqy converter being responsive to control signals from said controller for injecting electrical energy into said power distribution bus.
In a second aspect, the present invention a methc,d for managing the energy supply from a power utility to a consumer, said method comprising the steps of: (a) determining a present power demand for the consumer; (b) providing additional energy for the consumer if there is an increase in the present power ~em~n~i (c) said step of providing additional energy comprises: (i) rec~uesting additional energy from the power utility, or (ii) connecting additional local energy sources to supply energy to the consumer.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will now be made to the accompanying drawings which show, by way of example, a preferred embodiment of the present invention, and in which:
Fig. 1 is a block diagram of an energy management system according to the present invention; and Figs. 2(a) to 2(c~ are flow charts showing process control steps performed by the energy management system of Fig. 1 according to the present invention.
DETATr-Fn DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference is first made to Fig. 1 which shows in block diagram form an energy management system 1 according to the present invention. The energy management system 1 receives electrical energy from a power utility 2 and supp:Lies electrical power to a plant. In another aspect, the energy electrical management system 1 supplies energy to the power utility 2. The power utility 2 may comprise a public electrical utility or a power feed from an interconnected power network. The plant is indicated generally by reference 3 and represents the consumer of the elect:rical energy. In commercial applications, the plant 3 comprises a factory, an office building or the like. In a residential application, the plant 3 comprises a resiclential dwelling. Typically, a large manufacturing plant: will consume about 1 MW of power, while an individual resiclence consumes power in the 5 to 25 KW range.
The energy management system 1 receives elect.rical energy from the power utility 2 through a utility interface 12 and a power converter 14, such as a pulse width modulator (PWM) converter (i.e.
rectifier/inverter). The utility interface 12 is coupled to the power utility 2 through an AC line 13, i.e. the AC
mains supply. The AC line 13 comprises a conventional high voltage AC transmission line, for example, 480 VAC, 3-Phase at 60 Hz. The utility interface 12 and PWM converter 14 taken together form an AC line interface denoted generally by 15. The principal function of the AC line interface 15 is to control the reactive power and thereby the power factor. The power factor interface 12 may optionally comprise a device of known design which offers the capability to operate as a controlled reactive power source with a variable power factor. This capability allows the AC line interface 15 to compensate for lagging reactive power "sinks" such as inductive motors connected to the AC
line 13, thereby improving the overall system power factor and provide local voltage stabilization for the AC line 13.
As shown in Fig. 1, the energy management system 1 also includes a PWM VAR/Harmonic compensator 17. The PWM
compensator 17 comprises a three-phase voltage-fed PWM
converter of known design and comprises a power semiconductor and a DC capacitor (not shown). The PWM
compensator 17 is coupled to the AC line 13 through an AC
line filter 19 and is fed three-phase voltage from the line 13. The PWM VAR/Harmonic compensator 17 performs a function similar to that of the PWM utility interface 15, that is, the PWM compensator 17 functions as a controlled reactive power (i.e. VAR) source (or sink) for improving the utility-reflected power factor of an otherwise lower power factor 60 Hz load. Advantageously, the PWM
VAR/]~armonic compensator 17 provides higher reactive power compensation for a given current rating for the power semiconductor and ripple current capability for the DC
capa~itor than the main DC-bus active power balancing interface, i.e. the PWM utility interface 15. In another aspect, the PWM VAR/Harmonic compensator 17 is used to impress AC line current harmonics of an instantaneous waveshape. This closely compensates for harmonic components of currents demanded by existing, grid-connected, non-linear loads, such as non-PWM type power converters. Thus, the energy management system 1 has the capability to effectively reduce pre-existing utility service harmonic distortion.
The energy management system 1 comprises an energy management system controller 10 and a series of energy devices which are coupled to a power bus 16. In the following description, the power bus 16 is described as DC
(Direct Current) bus, however, it may be advantageous for a particular application to implement the power bus 16 as an AC' bus, operating at a low frecluency.
The energy devices comprise electrical power generators 18, energy converter/storage devices 20, and energy output converters 22. The energy output converters 22 include an electric vehicle (E.V.) charger 22a and an AC
energy output converter 22b (e.g. an "On-line" U.P.S.
converter). The energy converter devices 18 comprise alternative energy generators including a solar-powered generator 18a, a wind-powered generator 18b, or a fossil fuel powered generator, e.g. a diesel generator, or an elect:rochemical fuel cell (not shown). The energy converter/storage devices denoted generally by reference 20 include a storage battery converter 20a, a super-capacitor converter 20b, a super-conducting magnet (e.g. cryogenic coil) converter 20c, and a high speed flywheel converter 20d.
The energy management system controller 10 provides supervisory control for the system 1, with the principal function of maintaining an energy supply for the plant 3 in the most cost effective manner. The energy management system controller 10 preferably comprises a digital computer or microprocessor suitably programmed to perform the process control steps according to the present invention. The process steps are described below in conjunction with Figs. 2(a) to 2(c). The energy management system controller 10 controls the energy devices through an energy converter communication and control bus 11.
As shown in Fig. 1, the energy management system controller 10 includes a utility comml~n;cation interface 24 and a user interface module 26. The utility communication interface 24 provides a two-way commlln-cation link between the energy management system 1 and a supervisory computer (not shown) located at the power utility 2. Information and data are transferred between the energy management controller 10 and the electrical power utility 2. The utility communication interface 24 is preferably implemented as a serial link through a modem and telecommunication line. The user interface 26 accepts input comm~n~.s from a user, e.g. the plant superintendent, and displays information to user. The user interface 26 i8 implemented using a display terminal 27 and an input device, e.g. a keyboard. The user interface 26 may also include a communication link to a plant control computer 28 for the plant 3 to allow for the exchange of command and status information under programmed control.
Referring to Fig. 1, the utility communication interface 24 provides a two-way communication path between the energy management system 1 and the power utility 2.
From the utility, two principal types of information are provided, namely, ENERGY AVAILABLE information and ENERGY
RATES data. The ENERGY AVAILABLE information is provided by the power utility 2 to notify the energy management system 1 of any planned interruptions in the supply of electrical energy on the AC line 13, and may also include the m~;ml~m energy which may be taken from the AC line 13.
The ENERGY RATES data comprises a rate schedule giving cost for energy delivered from the AC line 13 (i.e. power utility 2) and payment for energy delivered to the AC line 13 (i.e. power utility 2).
In the upstream direction, the energy management controller 10 sends information to the power utility 2 relating to load ~em~n~ at the plant 3, i.e. LOAD DEMAND
information, and energy available from the energy devices, i.e. LOCAL ENERGY AVAILABLE information. The LOAD DEMAND
information provides the power utility 2 with current projected energy requirements for the plant 3. The LOCAL
ENERGY AVAILABLE information provides the utility 2 with information on the amount of energy stored in the system 1 and the price at which that energy would be available to the utility 2. The energy management controller 10 uses the information obtained over the utility communication interface 24 to determine when to extract energy from the AC line 13, i.e. buy or take power from the utility 2, and when to supply or sell energy to the utility 2 in order to maintain plant operation at the minimum cost.
As described, the user interface 26 provides a comm~lnication link to the control computer 28 in the plant 3, ar.Ld/or a human interface comprising the keyboard and display 27 for the primary purpose of exchanging information and comm~n~ between the user and the system 1.
In the context of an industrial plant application, the user woulcl be the plant superintendent. The user provides the controller 10 with control information to establish the operating parameters for the energy management system 1 including information related to the energy requirements (i.e. PLANT LOAD REQUIREMENT data) and load priorities (i.e. PLANT LOAD PRIORITIES data) needed for the operation of the plant 3. The energy requirement information comprises projected energy usage for the plant 3, and typically is in the form of a schedule of daily needs which is e,stablished when the energy management system 1 is installed in the plant 3. As the need arises, the user or plant computer 28 updates the energy requirements which then are communicated to the energy management system controller 10 through the user interface 26.
As described, the user or plant superintendent uses the user interface 26 to supply PLANT LOAD PRIORITIES
to the energy management system controller 10. The PLANT
LOAD PRIORITIES data comprises priority data used by the energy management controller 10 to determine which loads to shed~during a energy shortage or cutback in the system 1 as will be described in more detail below. For example, during a system energy shortage, the energy controller 10 may decide to shed the energy storage devices 20 comprising the storage battery 20a, the super capacitor 20b and the super-conducting magnet 20c. The control information supplied by the plant superintendent also includes a desired RESERVE ENERGY LEVEL which is to be maintained by the energy management system 1. The desired RESERVE ENERGY
LEVEL may further include a maximum cost for maintaining the energy level.
As an output device, the energy management system controller 10 uses the user interface 26 to provide the user, e.g. plant superintendent, with PLANT SYSTEM STATUS
data and PLANT HISTORY information. The PLANT SYSTEM
STATIJS data includes energy available from the various energy inputs. The energy inputs include the electrical power feed over the AC line 13 from the power utility 2.
The PLANT SYSTEM STATUS data on the energy available from the power utility 2 preferably includes any scheduled interruptions. The energy devices 18, 20, 22 shown in Fig.
1 provide the other inputs for the PLANT SYSTEM STATUS, and include for example, the solar-powered generator 18a, the wind-powered generator 18b (and fossil fuel powered generators), and the energy currently stored in the energy storage devices 20, e.g. the storage battery 20a, the super-conducting magnetic converter 20b, the super-capacitor converter 20c, and the flywheel converter 20d.
The PLANT HISTORY INFORMATION includes summary reports on the flow of energy to and from each energy device 18, 20, 22 in the system 1. This information is used to determine energy cost and to schedule periodic maintenance of the components in the system 1.
The energy management system controller 10 also provides the user with information on faults in the system 1, and other information which would assist in fault diagnosis, or periodic maintenance scheduling.
The energy converter communication and control bus 11 comprises a communications channel which connects the system controller 10 to the devices in the energy management system, i.e. the PWM rectifier/inverter 14 and the energy devices 18, 20, 22. Preferably the communication and control bus 11 is implemented as a multi-drop serial communication bus to facilitate the connection of ad,~itional energy devices in order to expand the system 1. Each of the energy devices 18, 20, and 22 in the system 1 includes an interface for coupling to the communication and c:ontrol bus 11. The interface preferably comprises a module programmed for receiving, processing and tran~mitting command and status information with the energy management controller 10 and controlling the energy device in response thereto.
The information transmitted from an energy device 18, 20, 22 to the energy management system controller 10 includes DEVICE ENERGY AVAILABLE data and DEVICE LOAD
DEMAND data. The DEVICE ENERGY AVAILABLE data indicates energy which can be supplied to the power bus 16 from a particular energy converter in the system 1. The form of DEVICE ENERGY AVAILABLE data can range from a simple AVAILABLE/NOT AVAILABLE indication from sources such as the AC line interface 15 to a more detailed quantitative value from sources such as the storage battery 20a. The DEVICE
LOAD DEMAND information, on the other hand, is concerned with energy devices which take energy from the power bus 16, i.e. supply energy loads to the system 1. The DEVICE
LOAD DEMAND information provides the energy management system controller 10 with the desired power level of the energy device, for example, the energy required by the super capacitor 42.
The energy management system controller 10 also uses the communication bus 11 to send control cc~mm~n~s to the energy devices, i.e. generators 18, storage/converter devices 20 and converters 22. The system controller 10 uses the communication bus 11 to inform each energy converter 20, 22 requesting energy the maximum amount of energy which it can extract from the power bus 16.
It is a feature of the present invention that the energy management controller 10 maintains the power bus 16 at a constant voltage level. According to the invention, the energy management controller 10 determines which energy device, i.e. AC line interface 15, power generator 18, enerqy storage device 20, is responsible for maintaining or regulating the voltage level and informs the device accordingly. For example, in a typical system, the energy management controller 10 would command the AC line interface 15 to maintain the voltage level on the power 16 when AC power is available from the power utility 2. If the AC supply, i.e. AC line 13, is interrupted, the energy management controller 10 instructs one of the power generators 18, or storage devices 20 to take over and maintain the constant voltage level on the power bus 16.
The operation of the energy management system 1 is described in greater detail below with reference to Figs.
FIELD OF THE lNV~r~llON
The present invention relates to electrical power systems, and more particularly to an energy management and distr:ibution system.
RACR~ROUWD OF THE lNV~-llON
Electrical energy remains the primary source of energy for fuelling the modern industrial world.
Historically, public and private power utilities have provicled for the energy needs of society. Electrical energy is used on a demand basis by the consumer and the power utility is paid based on the power consumed.
With rising energy costs, consumers have turned to alternative energy sources, such as solar-powered, wind-powered and fossil fuel powered generators. Suchgenerators are operated independently to power electrical equipment and thereby reduce the power needs from the utility. Alternative power generators can be effective in generating power, but can be limited as to operating periods, e.g. solar-powered generators are non-operational at night, and wind-powered generators need a steady wind to generate electricity.
The deregulation of power utilities is also changing the way electric power is being sold to the consumer. Deregulation means that to be economically viable a power utility must be able to deliver power in a cost-effective manner. In practical terms, electrical energy will remain available on a continuous basis, however, the cost of energy at peak ~e~an~ times will be consid~erably higher than at off-peak times. This trend has already been seen in the deregulated sectors of the power industry in the United States. In less developed countries, deregulation of the power industry will mean that electric power will be available on a less frequent basis with limited or no power available at any cost during certain times of the day.
While alternative energy sources provide a means to augment the electricity supply for a user, there remains a need for a system which can minimize the cost of electric energy and maximize the availability of power by effectively integrating the alternative energy sources with the primary source from the power utilities and providing electricity to the consumer in a cost effective manner.
Such a system preferably would have the capability to store energy purchased from a power utility at off-peak (i.e. low cost) periods, or energy generated during low demand periods for use at a later time. Such a system would also have the capability to continue to provide power in the event the electricity supply from the power utility is interrupted.
SUMMARY OF THE lNv~ lON
The present invention provides a system for energy management and distribution of one or more sources to one or more loads. The energy may be supplied through conventional AC power mains, fossil fuel powered generators, wind-powered generators, solar-powered generators, electrochemical fuel cells, etc. The energy management system includes means for storing and retrieving energy for load levelling, loss of alternative energy sources, or AC mains drop out using battery, flywheel, super-capacitor, super-conducting magnetic devices, etc.
The system also includes a low-harmonic/high power factor PWM utility interface to supply a "clean" load to the AC mains supply from the power utility. It is a feature of the invention that energy from all the sources is co:nverted to a medium voltage DC (or low frequency AC) power distribution level on a bus. The voltage on the bus is regulated by any of the energy sources connected to the bus which are capable of both sourcing and sinking energy from the bus. The energy management system controller determines which energy source has regulation control of the bus. Control of the bus is based on a number of decision factors including availability of energy, load recluirements, and time of day. Preferably only one energy source will have regulation control of the DC bus under impressed voltage control. All the other sources will run under impressed current or power control.
It is a feature that all loads will draw energy from the bus as recluired unless limited or interrupted by the energy management system controller. All control systems are powered from the DC bus in order to guarantee system control is not lost due to a local power loss. In the event all energy sources go off-line and the DC bus is powered down the system is restarted in manual mode by any of th,e dual energy sources. The energy management system controller comes on-line and takes over control of the system once the DC bus has been pre-charged to a minimum voltage level.
In a first aspect, the present invention provides an energy management system for managing the supply of electrical energy to a consumer, said energy management system comprising: (a) an input -module for receiving electrical energy from a primary energy source, said input module having a converter for converting said electrical energy for local distribution; ~b) a power distribution bus for distributing said converted electrical energy; (c) a plurality of energy converters coupled to said power distribution bus and having means for generating electrical energy and means for injecting said electrical energy into said power distribution bus; (d) a controller having means for determining a present energy demand for the consumer and means for controlling said input module and means for controlling said energy converters; (e) said input module having means responsive to control signals from said controller for receiving electrical energy from the primary enerqy source and injecting said energy into said distr-ibution bus; and (f) said means for injecting for said enerqy converter being responsive to control signals from said controller for injecting electrical energy into said power distribution bus.
In a second aspect, the present invention a methc,d for managing the energy supply from a power utility to a consumer, said method comprising the steps of: (a) determining a present power demand for the consumer; (b) providing additional energy for the consumer if there is an increase in the present power ~em~n~i (c) said step of providing additional energy comprises: (i) rec~uesting additional energy from the power utility, or (ii) connecting additional local energy sources to supply energy to the consumer.
BRIEF DESCRIPTION OF THE DRAWINGS
Reference will now be made to the accompanying drawings which show, by way of example, a preferred embodiment of the present invention, and in which:
Fig. 1 is a block diagram of an energy management system according to the present invention; and Figs. 2(a) to 2(c~ are flow charts showing process control steps performed by the energy management system of Fig. 1 according to the present invention.
DETATr-Fn DESCRIPTION OF THE PREFERRED EMBODIMENTS
Reference is first made to Fig. 1 which shows in block diagram form an energy management system 1 according to the present invention. The energy management system 1 receives electrical energy from a power utility 2 and supp:Lies electrical power to a plant. In another aspect, the energy electrical management system 1 supplies energy to the power utility 2. The power utility 2 may comprise a public electrical utility or a power feed from an interconnected power network. The plant is indicated generally by reference 3 and represents the consumer of the elect:rical energy. In commercial applications, the plant 3 comprises a factory, an office building or the like. In a residential application, the plant 3 comprises a resiclential dwelling. Typically, a large manufacturing plant: will consume about 1 MW of power, while an individual resiclence consumes power in the 5 to 25 KW range.
The energy management system 1 receives elect.rical energy from the power utility 2 through a utility interface 12 and a power converter 14, such as a pulse width modulator (PWM) converter (i.e.
rectifier/inverter). The utility interface 12 is coupled to the power utility 2 through an AC line 13, i.e. the AC
mains supply. The AC line 13 comprises a conventional high voltage AC transmission line, for example, 480 VAC, 3-Phase at 60 Hz. The utility interface 12 and PWM converter 14 taken together form an AC line interface denoted generally by 15. The principal function of the AC line interface 15 is to control the reactive power and thereby the power factor. The power factor interface 12 may optionally comprise a device of known design which offers the capability to operate as a controlled reactive power source with a variable power factor. This capability allows the AC line interface 15 to compensate for lagging reactive power "sinks" such as inductive motors connected to the AC
line 13, thereby improving the overall system power factor and provide local voltage stabilization for the AC line 13.
As shown in Fig. 1, the energy management system 1 also includes a PWM VAR/Harmonic compensator 17. The PWM
compensator 17 comprises a three-phase voltage-fed PWM
converter of known design and comprises a power semiconductor and a DC capacitor (not shown). The PWM
compensator 17 is coupled to the AC line 13 through an AC
line filter 19 and is fed three-phase voltage from the line 13. The PWM VAR/Harmonic compensator 17 performs a function similar to that of the PWM utility interface 15, that is, the PWM compensator 17 functions as a controlled reactive power (i.e. VAR) source (or sink) for improving the utility-reflected power factor of an otherwise lower power factor 60 Hz load. Advantageously, the PWM
VAR/]~armonic compensator 17 provides higher reactive power compensation for a given current rating for the power semiconductor and ripple current capability for the DC
capa~itor than the main DC-bus active power balancing interface, i.e. the PWM utility interface 15. In another aspect, the PWM VAR/Harmonic compensator 17 is used to impress AC line current harmonics of an instantaneous waveshape. This closely compensates for harmonic components of currents demanded by existing, grid-connected, non-linear loads, such as non-PWM type power converters. Thus, the energy management system 1 has the capability to effectively reduce pre-existing utility service harmonic distortion.
The energy management system 1 comprises an energy management system controller 10 and a series of energy devices which are coupled to a power bus 16. In the following description, the power bus 16 is described as DC
(Direct Current) bus, however, it may be advantageous for a particular application to implement the power bus 16 as an AC' bus, operating at a low frecluency.
The energy devices comprise electrical power generators 18, energy converter/storage devices 20, and energy output converters 22. The energy output converters 22 include an electric vehicle (E.V.) charger 22a and an AC
energy output converter 22b (e.g. an "On-line" U.P.S.
converter). The energy converter devices 18 comprise alternative energy generators including a solar-powered generator 18a, a wind-powered generator 18b, or a fossil fuel powered generator, e.g. a diesel generator, or an elect:rochemical fuel cell (not shown). The energy converter/storage devices denoted generally by reference 20 include a storage battery converter 20a, a super-capacitor converter 20b, a super-conducting magnet (e.g. cryogenic coil) converter 20c, and a high speed flywheel converter 20d.
The energy management system controller 10 provides supervisory control for the system 1, with the principal function of maintaining an energy supply for the plant 3 in the most cost effective manner. The energy management system controller 10 preferably comprises a digital computer or microprocessor suitably programmed to perform the process control steps according to the present invention. The process steps are described below in conjunction with Figs. 2(a) to 2(c). The energy management system controller 10 controls the energy devices through an energy converter communication and control bus 11.
As shown in Fig. 1, the energy management system controller 10 includes a utility comml~n;cation interface 24 and a user interface module 26. The utility communication interface 24 provides a two-way commlln-cation link between the energy management system 1 and a supervisory computer (not shown) located at the power utility 2. Information and data are transferred between the energy management controller 10 and the electrical power utility 2. The utility communication interface 24 is preferably implemented as a serial link through a modem and telecommunication line. The user interface 26 accepts input comm~n~.s from a user, e.g. the plant superintendent, and displays information to user. The user interface 26 i8 implemented using a display terminal 27 and an input device, e.g. a keyboard. The user interface 26 may also include a communication link to a plant control computer 28 for the plant 3 to allow for the exchange of command and status information under programmed control.
Referring to Fig. 1, the utility communication interface 24 provides a two-way communication path between the energy management system 1 and the power utility 2.
From the utility, two principal types of information are provided, namely, ENERGY AVAILABLE information and ENERGY
RATES data. The ENERGY AVAILABLE information is provided by the power utility 2 to notify the energy management system 1 of any planned interruptions in the supply of electrical energy on the AC line 13, and may also include the m~;ml~m energy which may be taken from the AC line 13.
The ENERGY RATES data comprises a rate schedule giving cost for energy delivered from the AC line 13 (i.e. power utility 2) and payment for energy delivered to the AC line 13 (i.e. power utility 2).
In the upstream direction, the energy management controller 10 sends information to the power utility 2 relating to load ~em~n~ at the plant 3, i.e. LOAD DEMAND
information, and energy available from the energy devices, i.e. LOCAL ENERGY AVAILABLE information. The LOAD DEMAND
information provides the power utility 2 with current projected energy requirements for the plant 3. The LOCAL
ENERGY AVAILABLE information provides the utility 2 with information on the amount of energy stored in the system 1 and the price at which that energy would be available to the utility 2. The energy management controller 10 uses the information obtained over the utility communication interface 24 to determine when to extract energy from the AC line 13, i.e. buy or take power from the utility 2, and when to supply or sell energy to the utility 2 in order to maintain plant operation at the minimum cost.
As described, the user interface 26 provides a comm~lnication link to the control computer 28 in the plant 3, ar.Ld/or a human interface comprising the keyboard and display 27 for the primary purpose of exchanging information and comm~n~ between the user and the system 1.
In the context of an industrial plant application, the user woulcl be the plant superintendent. The user provides the controller 10 with control information to establish the operating parameters for the energy management system 1 including information related to the energy requirements (i.e. PLANT LOAD REQUIREMENT data) and load priorities (i.e. PLANT LOAD PRIORITIES data) needed for the operation of the plant 3. The energy requirement information comprises projected energy usage for the plant 3, and typically is in the form of a schedule of daily needs which is e,stablished when the energy management system 1 is installed in the plant 3. As the need arises, the user or plant computer 28 updates the energy requirements which then are communicated to the energy management system controller 10 through the user interface 26.
As described, the user or plant superintendent uses the user interface 26 to supply PLANT LOAD PRIORITIES
to the energy management system controller 10. The PLANT
LOAD PRIORITIES data comprises priority data used by the energy management controller 10 to determine which loads to shed~during a energy shortage or cutback in the system 1 as will be described in more detail below. For example, during a system energy shortage, the energy controller 10 may decide to shed the energy storage devices 20 comprising the storage battery 20a, the super capacitor 20b and the super-conducting magnet 20c. The control information supplied by the plant superintendent also includes a desired RESERVE ENERGY LEVEL which is to be maintained by the energy management system 1. The desired RESERVE ENERGY
LEVEL may further include a maximum cost for maintaining the energy level.
As an output device, the energy management system controller 10 uses the user interface 26 to provide the user, e.g. plant superintendent, with PLANT SYSTEM STATUS
data and PLANT HISTORY information. The PLANT SYSTEM
STATIJS data includes energy available from the various energy inputs. The energy inputs include the electrical power feed over the AC line 13 from the power utility 2.
The PLANT SYSTEM STATUS data on the energy available from the power utility 2 preferably includes any scheduled interruptions. The energy devices 18, 20, 22 shown in Fig.
1 provide the other inputs for the PLANT SYSTEM STATUS, and include for example, the solar-powered generator 18a, the wind-powered generator 18b (and fossil fuel powered generators), and the energy currently stored in the energy storage devices 20, e.g. the storage battery 20a, the super-conducting magnetic converter 20b, the super-capacitor converter 20c, and the flywheel converter 20d.
The PLANT HISTORY INFORMATION includes summary reports on the flow of energy to and from each energy device 18, 20, 22 in the system 1. This information is used to determine energy cost and to schedule periodic maintenance of the components in the system 1.
The energy management system controller 10 also provides the user with information on faults in the system 1, and other information which would assist in fault diagnosis, or periodic maintenance scheduling.
The energy converter communication and control bus 11 comprises a communications channel which connects the system controller 10 to the devices in the energy management system, i.e. the PWM rectifier/inverter 14 and the energy devices 18, 20, 22. Preferably the communication and control bus 11 is implemented as a multi-drop serial communication bus to facilitate the connection of ad,~itional energy devices in order to expand the system 1. Each of the energy devices 18, 20, and 22 in the system 1 includes an interface for coupling to the communication and c:ontrol bus 11. The interface preferably comprises a module programmed for receiving, processing and tran~mitting command and status information with the energy management controller 10 and controlling the energy device in response thereto.
The information transmitted from an energy device 18, 20, 22 to the energy management system controller 10 includes DEVICE ENERGY AVAILABLE data and DEVICE LOAD
DEMAND data. The DEVICE ENERGY AVAILABLE data indicates energy which can be supplied to the power bus 16 from a particular energy converter in the system 1. The form of DEVICE ENERGY AVAILABLE data can range from a simple AVAILABLE/NOT AVAILABLE indication from sources such as the AC line interface 15 to a more detailed quantitative value from sources such as the storage battery 20a. The DEVICE
LOAD DEMAND information, on the other hand, is concerned with energy devices which take energy from the power bus 16, i.e. supply energy loads to the system 1. The DEVICE
LOAD DEMAND information provides the energy management system controller 10 with the desired power level of the energy device, for example, the energy required by the super capacitor 42.
The energy management system controller 10 also uses the communication bus 11 to send control cc~mm~n~s to the energy devices, i.e. generators 18, storage/converter devices 20 and converters 22. The system controller 10 uses the communication bus 11 to inform each energy converter 20, 22 requesting energy the maximum amount of energy which it can extract from the power bus 16.
It is a feature of the present invention that the energy management controller 10 maintains the power bus 16 at a constant voltage level. According to the invention, the energy management controller 10 determines which energy device, i.e. AC line interface 15, power generator 18, enerqy storage device 20, is responsible for maintaining or regulating the voltage level and informs the device accordingly. For example, in a typical system, the energy management controller 10 would command the AC line interface 15 to maintain the voltage level on the power 16 when AC power is available from the power utility 2. If the AC supply, i.e. AC line 13, is interrupted, the energy management controller 10 instructs one of the power generators 18, or storage devices 20 to take over and maintain the constant voltage level on the power bus 16.
The operation of the energy management system 1 is described in greater detail below with reference to Figs.
2(a) to 2(c).
Referring to Figure 1, the utility power source interface 15 couples the energy management system 1 to the power utility 2 which is the primary energy supplier. The energy management system 1 also obtains energy from the power generators 18 including the solar-powered generator 18a, the wind-powered generator 18b or fossil fuel powered generator, e.g. diesel. As shown in Fig. 1, the system 1 further includes the energy converter/storage devices 20 comprising the storage battery converter 20a, the super-capacitor converter 20b, the super-conducting magnet converter 20c, and the high-speed flywheel converter 20d.
The principal function of the energy converter/storage devices 20 is to extract energy from power bus 16 for use at a :Later time for the purposes of load levelling, loss of alternative energy sources, e.g. the solar-powered generator 18a, or drop-out of the AC mains supply, i.e.
power feed from the power utility 2.
The AC line interface 15 couples the energy management system 1 to the power feed from the public utility 2. The public utility 2 supplies the system 1 with a fixed voltage/frequency sinusoidal AC power feed, e.g. 3-phase 480 VAC at 60 Hz. The PWM rectifier/inverter 14 converts, i.e. rectifies, the AC power feed into a fixed voltage DC power output at variable current for the power bus 16. The PWM 14 also has the capability to convert the DC output from the bus 16 into a fixed voltage AC signal for the power utility 2 which enables the energy management system 1 to sell surplus power back to the power utility 2.
As shown in Fig. 1, the AC line interface 15 includes the power-factor correction module 12 which preferably operates at a high power factor (i.e. approaching one) and with low 5~ maximum total harmonic distortion of the input current on the AC line 13 from the power utility 2. As described above, the energy management system may also include the PWM V.~R/Harmonic compensator 17.
The solar-powered generator 18a, and the wind-powered generator 18b (or fossil fuel powered generators) provide alternative energy sources for energizing the power bus 16. As shown in Fig. 1, the solar-powered generator 18a comprises a solar array 30 and a boost converter 32.
The solar-powered generator 18a is a conventional apparatus and t~he implementation as such is within the knowledge of one skilled in the art. The solar array 30 generates a variable DC voltage/current which is converted by the boost conve:rter 32 to a variable current output at the DC voltage level fixed (e.g. 900 VDC) for the power bus 16. The mode of control for the solar-powered generator 18a, i.e.
voltage, current, or power, will depend upon the opera~ional limits of the solar-array 30 and the net DC
current supply requirements of the power bus 16 at a particular time. The wind-powered generator 18b comprises a wind-turbine 34 and an energy converter 36. The wind-turbine 34 and energy converter 36 comprise conventional technology within the understanding of one skilled in the art and the same factors for control apply as discussed for the solar-powered generator 18a.
CA 0222764l l998-0l-2l The energy flow between the energy converter/storage devices 20 and the power bus 16 is reversible. Energy may be extracted from the bus 16 or injected back into the bus 16. The energy extracted from the power bus 16 is stored for use at a later time.
Situations where the energy converter/storage device 20 inject power into the bus 16 include load levelling to maintain the voltage level of the bus 16 when being loaded, make-up power due to loss of an alternative power generator 18 or drop-out of the AC mains supply 13 from the power utility 2.
Referring to Fig. 1, the storage battery converter 20a comprises a battery 38 which is coupled to the power bus 16 through a buck/boost energy converter 40.
The <,torage battery converter 20a provides a variable voltage DC power source/sink, i.e. battery 38, which interfaces to the fixed voltage DC power source/sink, i.e.
the power bus 16. The storage battery 20a is controlled to provide current, voltage or power regulation for the power bus 16. The battery 38 and buck/boost converter 40 are implemented using conventional devices as will be within the knowledge of one skilled in the art.
The super-capacitor converter 20b comprises a super-capacitor 42 and a buck/boost energy converter 44 which couples the capacitor 42 to the power bus 16. The capacitor 42 provides a variable voltage DC power source/sink which is coupled to the fixed voltage power bus 16. The energy flow from the capacitor 42 is reversible, i.e. the voltage on the capacitor 42 can be increased or decreased thereby varying the energy stored in the electric field. Under the supervision of the energy management controller 10, the super-capacitor converter 20b can be used t:o provide current, voltage or power regulation on the power bus 16.
The super-conducting magnetic converter 20c also provides a reversible energy flow to the power bus 16. The magnetic converter 20c comprises a super-conducting magnetic (cryogenic) coil 46 and a buck/boost converter 48 for connecting to the bus 16. The coil 46 and buck/boost converter 48 are implemented in known manner. The coil 46 provides a variable DC power source/sink which is coupled to thie fixed voltage DC power bus 16. Energy is stored in the magnetic field of the coil and is increased or decreased by varying the current to the coil 46. Under the supervision of the controller 10, the converter 20c provides current, voltage or power regulation for the power bus 16. A suitable coil 46 is commercially available and within the understanding of one skilled in the art.
The other energy storage/converter device 20 shown in Fig. 1 is the high speed flywheel converter 20d.
The flywheel converter 20d comprises a high speed flywheel driving a reversible machine 52 coupled to a PWM
inverter/rectifier 54. The flywheel 50 comprises a high speed/high-inertia rotating mass, and the energy stored in the flywheel 50 is converted into AC by the machine 52 and into DC by the PWM rectifier 54 for the fixed voltage DC
bus 16. The flywheel converter 20d provides a reversible energy flow, where the speed of the machine 52 is increased or decreased to vary the energy stored in the rotating flywheel 50. Optionally, the flywheel converter 20d may include a gear drive 56 between the flywheel 50 and the AC
machine 54. The flywheel converter 20d is suitable for providing current, voltage, power or torclue regulation.
Suitable high-density/inertia/speed composite flywheels are available. Preferably the flywheel 50 is of the type which operates in a near vacuum and utilizes pneumatic or magnetic bearing suspension. Suitable AC machine 52 and gear drive 56 are commercially available and within the understanding of those skilled in the art.
The energy output devices 22 shown in Fig. 1 comprise the E.V. charger 22a and the AC output converter 22b. The E.V. charger 22a provides a means for charging an electrical vehicle battery denoted by B. The charger 22a comprises a PWM inverter 58 coupled to the power bus 16.
The E~WM inverter 58 converts fixed voltage DC power from the bus 16 to variable voltage AC power at a variable current for the purpose of exciting the primary winding of an isolation transformer 60. The secondary of the transformer 60 powers a rectifier 62 which produces a DC
output to charge the vehicle battery B. Under the supervision of the energy management controller 10 the charger 22a may be operated in a regulated current, voltage or power mode, or a combination thereof. Suitable equipment for the PWM inverter 58, transformer 60 and rectifier 62 is commercially available and within the understanding of those skilled in the art.
The AC output converter 22b comprises an "On-line" U.P.S. converter which provides an AC output at selected voltage and frequency, for example 3-phase 480 VAC. As shown in Fig. 1, the converter 22b includes a PWM
inverter 64, an isolation transformer 66, and a low-pass AC
output filter 68. The PWM inverter 64 converts fixed voltage DC power from the bus 16 into a fixed voltage/frequency AC power at variable current for the purposes of exciting the primary winding of the isolation transEormer 66. The secondary of the transformer 66 is connected to the low-pass AC filter 68. The AC filter 68 attemlates the voltage switching harmonics to very low levels, preferably less than 1~ of rated value. The output from lhe filter 68 is connected to load (e.g. in the plant or residence) which is to be protected from AC line voltage surges/sags and outages. Generally, the on-line converter 22b operates in output voltage and frequency regulated mode.
Reference is next made to Figs. 2(a) to 2(c), which show in flow-chart form processing steps performed by the energy management controller 10 according to the present invention.
- The processing commences at step 100, and at step 102, the controller 10 "gets" the next available energy source or if the system 1 is being started, the available energy source from the list. Preferably, the availability of energy sources is stored in memory as a prioritized list. The prioritized list is preferably updated periol~ically by the controller 10 in response to polling the potential energy sources and logging the responses, i.e. DEVICE AVAILAELE/NOT AVAILAELE, or according to a schedule .
If there are no further energy sources available to supply the load at step 104, the controller 10 issues a LOAD SHED command to the energy converters at step 106.
The controller 10 then initiates an ALARM at step 108. The ALARM is initiated because the energy management system 1 has reached capacity.
If there are energy sources available as deterrnined at step 104, the controller 10 next determines at st:ep 110 if the selected energy source from the prioritized list is "on-line", i.e. coupled to the power bus 16, and available to provide power. If the selected energy source is not "on-line", then the controller 10 select:s the next energy source from the prioritized list in step 102. An energy source is "off-line", i.e. not on-line, when it is not available to supply power to the power bus 16, for example, the solar-powered generator 18a is off-line at night, and the wind-powered generator 18b is off-line when there is no wind to turn the wind-turbine 34.
If the selected energy source is on-line, then the controller 10 sends a REGULATE BUS COMMAND to the device at step 112. Next at step 114 as shown in Fig.
2(b), the controller 10 determines if the energy source which is regulating the bus 16 is still on-line. If the regu.Lating energy has gone off-line, then the controller 10 returns to step 100 and proceeds to get the next energy source from the prioritized list (step 102). If the regu]ating energy source is still on-line, i.e. regulating the bus 16, the controller 10 determines the PRESENT ENERGY
DEMA~D at step 116.
Next at step 118, the controller 10 determines if the energy capacity exceeds the energy demand, i.e. PRESENT
ENERGY DEMAND determined in previous step 116. If the capacity exceeds the demand, then the controller 10 cycles through the loop starting at step 114. If the capacity is exceeded by the PRESENT ENERGY DEMAND, i.e. the energy demand cannot be met by the energy sources currently on-line, the controller 10 determines the next available energy source in step 120.
20If there are no further energy sources available as determined at step 122, then the PRESENT ENERGY DEMAND
cannc,t be met and the controller 10 determines a load to be shed, i.e. disconnected from the power bus 16, for example the super-capacitor converter 20b. Referring to Fig. 2(c), 25at step 124 the controller 10 selects the load to be shed, i.e. next lowest priority load, from a LOAD PRIORITY LIST
which may be stored in memory accessible by the controller 10. If there are no further loads to be shed as determined at step 126, the energy d~m~n~ cannot to be met and the controller 10 sends load shed comm~n~s to all the energy converters as indicated at step 128, followed by an ALARM
at step 130. The ALARM indicates that the capacity of the energy management system 1 has been reached.
Referring still to Fig. 2(c), if there are still loads available to be shed (i.e. headroom) as determined at step 126, the controller 10 sends a load shed command to a selected energy converter, e.g. the E.V. charger 22a, at step 132. Next at step 134, the controller 10 determines a new value for the ENERGY DEMAND. If the ENERGY DEMAND is greater than the sum of energy available from the active energy sources (step 136), then the controller 10 returns to step 124 in order to attempt to shed additional loads at step 132. If the DEMAND is less than the sum of energy available as determined in step 136, then the controller 10 returns to loop at 114.
Referring back to Fig. 2(b), if there are energy sources available as determined at step 122, the controller 10 calculates if the capacity of the new source exceeds the demand less the sum of currently active energy sources at step 138. If the capacity does not exceed the demand as determined at step 138, the controller 10 sends a SUPPLY
MAXIMUM ENERGY command to the new source at step 140. The controller 10 then updates the energy available from the sum of active sources in step 142 as shown in Fig. 2(b).
Referring again to Fig. 2(b), if there are available energy sources and the capacity exceeds the demand as determined at step 138, then the controller 10 sends a SUPPLY COMMAND to the new source at step 144 in order to obtain additional energy. The additional energy is determined as the difference between the LOAD DEMAND and the sum of the AVAILABLE ENERGY available from the currently active energy sources.
In another aspect of the invention, the controller 10 performs a cost evaluation in the determination of which energy sources or loads to connect/disconnect from the bus 16.
From the foregoing, it will be appreciated that CA 0222764l l998-0l-2l as shown in Fig. l(a) steps 100 to 112, the controller 10 connects energy sources (from the prioritized list), and if necessary sheds loads, when the energy management system 1 is first started (i.e. step 100) or if the energy source regulating the bus 16 goes off-line (step 114). The rest of the time, the controller 100 cycles through the loop comprising steps 114 to 118 shown in Fig. 2(b). This arrangement allows the energy demand to increase without triggering a re-evaluation of the energy source which is regulating the bus.
In a typical consumer application, the energy management system as described above monitors energy costs, deten~Lines the least costly energy sources, and stores the energy for anticipated requirements in the storage devices.
In day to day operation, peak power d~m~n~s from the power utility usually occur when the work force is arriving at home and manufacturing plants are still operating. The peak power load increases as the consumers demand energy for various appliances. By utilizing cheaper alternate energy sources, e.g. wind turbine 18b, or stored energy, e.g. super capacitor storage device 20b, the energy management system 1 reduces the reliance on expensive elect:rical energy from the power utility 2 at peak time.
The present invention may be embodied in other speci:Eic fonms without departing from the spirit or essenl_ial characteristics thereof. Therefore, the presently discussed em-bodiments are considered to be illuslrative and not restrictive, the scope of the invenlion being indicated by the appended claims rather than lhe foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Referring to Figure 1, the utility power source interface 15 couples the energy management system 1 to the power utility 2 which is the primary energy supplier. The energy management system 1 also obtains energy from the power generators 18 including the solar-powered generator 18a, the wind-powered generator 18b or fossil fuel powered generator, e.g. diesel. As shown in Fig. 1, the system 1 further includes the energy converter/storage devices 20 comprising the storage battery converter 20a, the super-capacitor converter 20b, the super-conducting magnet converter 20c, and the high-speed flywheel converter 20d.
The principal function of the energy converter/storage devices 20 is to extract energy from power bus 16 for use at a :Later time for the purposes of load levelling, loss of alternative energy sources, e.g. the solar-powered generator 18a, or drop-out of the AC mains supply, i.e.
power feed from the power utility 2.
The AC line interface 15 couples the energy management system 1 to the power feed from the public utility 2. The public utility 2 supplies the system 1 with a fixed voltage/frequency sinusoidal AC power feed, e.g. 3-phase 480 VAC at 60 Hz. The PWM rectifier/inverter 14 converts, i.e. rectifies, the AC power feed into a fixed voltage DC power output at variable current for the power bus 16. The PWM 14 also has the capability to convert the DC output from the bus 16 into a fixed voltage AC signal for the power utility 2 which enables the energy management system 1 to sell surplus power back to the power utility 2.
As shown in Fig. 1, the AC line interface 15 includes the power-factor correction module 12 which preferably operates at a high power factor (i.e. approaching one) and with low 5~ maximum total harmonic distortion of the input current on the AC line 13 from the power utility 2. As described above, the energy management system may also include the PWM V.~R/Harmonic compensator 17.
The solar-powered generator 18a, and the wind-powered generator 18b (or fossil fuel powered generators) provide alternative energy sources for energizing the power bus 16. As shown in Fig. 1, the solar-powered generator 18a comprises a solar array 30 and a boost converter 32.
The solar-powered generator 18a is a conventional apparatus and t~he implementation as such is within the knowledge of one skilled in the art. The solar array 30 generates a variable DC voltage/current which is converted by the boost conve:rter 32 to a variable current output at the DC voltage level fixed (e.g. 900 VDC) for the power bus 16. The mode of control for the solar-powered generator 18a, i.e.
voltage, current, or power, will depend upon the opera~ional limits of the solar-array 30 and the net DC
current supply requirements of the power bus 16 at a particular time. The wind-powered generator 18b comprises a wind-turbine 34 and an energy converter 36. The wind-turbine 34 and energy converter 36 comprise conventional technology within the understanding of one skilled in the art and the same factors for control apply as discussed for the solar-powered generator 18a.
CA 0222764l l998-0l-2l The energy flow between the energy converter/storage devices 20 and the power bus 16 is reversible. Energy may be extracted from the bus 16 or injected back into the bus 16. The energy extracted from the power bus 16 is stored for use at a later time.
Situations where the energy converter/storage device 20 inject power into the bus 16 include load levelling to maintain the voltage level of the bus 16 when being loaded, make-up power due to loss of an alternative power generator 18 or drop-out of the AC mains supply 13 from the power utility 2.
Referring to Fig. 1, the storage battery converter 20a comprises a battery 38 which is coupled to the power bus 16 through a buck/boost energy converter 40.
The <,torage battery converter 20a provides a variable voltage DC power source/sink, i.e. battery 38, which interfaces to the fixed voltage DC power source/sink, i.e.
the power bus 16. The storage battery 20a is controlled to provide current, voltage or power regulation for the power bus 16. The battery 38 and buck/boost converter 40 are implemented using conventional devices as will be within the knowledge of one skilled in the art.
The super-capacitor converter 20b comprises a super-capacitor 42 and a buck/boost energy converter 44 which couples the capacitor 42 to the power bus 16. The capacitor 42 provides a variable voltage DC power source/sink which is coupled to the fixed voltage power bus 16. The energy flow from the capacitor 42 is reversible, i.e. the voltage on the capacitor 42 can be increased or decreased thereby varying the energy stored in the electric field. Under the supervision of the energy management controller 10, the super-capacitor converter 20b can be used t:o provide current, voltage or power regulation on the power bus 16.
The super-conducting magnetic converter 20c also provides a reversible energy flow to the power bus 16. The magnetic converter 20c comprises a super-conducting magnetic (cryogenic) coil 46 and a buck/boost converter 48 for connecting to the bus 16. The coil 46 and buck/boost converter 48 are implemented in known manner. The coil 46 provides a variable DC power source/sink which is coupled to thie fixed voltage DC power bus 16. Energy is stored in the magnetic field of the coil and is increased or decreased by varying the current to the coil 46. Under the supervision of the controller 10, the converter 20c provides current, voltage or power regulation for the power bus 16. A suitable coil 46 is commercially available and within the understanding of one skilled in the art.
The other energy storage/converter device 20 shown in Fig. 1 is the high speed flywheel converter 20d.
The flywheel converter 20d comprises a high speed flywheel driving a reversible machine 52 coupled to a PWM
inverter/rectifier 54. The flywheel 50 comprises a high speed/high-inertia rotating mass, and the energy stored in the flywheel 50 is converted into AC by the machine 52 and into DC by the PWM rectifier 54 for the fixed voltage DC
bus 16. The flywheel converter 20d provides a reversible energy flow, where the speed of the machine 52 is increased or decreased to vary the energy stored in the rotating flywheel 50. Optionally, the flywheel converter 20d may include a gear drive 56 between the flywheel 50 and the AC
machine 54. The flywheel converter 20d is suitable for providing current, voltage, power or torclue regulation.
Suitable high-density/inertia/speed composite flywheels are available. Preferably the flywheel 50 is of the type which operates in a near vacuum and utilizes pneumatic or magnetic bearing suspension. Suitable AC machine 52 and gear drive 56 are commercially available and within the understanding of those skilled in the art.
The energy output devices 22 shown in Fig. 1 comprise the E.V. charger 22a and the AC output converter 22b. The E.V. charger 22a provides a means for charging an electrical vehicle battery denoted by B. The charger 22a comprises a PWM inverter 58 coupled to the power bus 16.
The E~WM inverter 58 converts fixed voltage DC power from the bus 16 to variable voltage AC power at a variable current for the purpose of exciting the primary winding of an isolation transformer 60. The secondary of the transformer 60 powers a rectifier 62 which produces a DC
output to charge the vehicle battery B. Under the supervision of the energy management controller 10 the charger 22a may be operated in a regulated current, voltage or power mode, or a combination thereof. Suitable equipment for the PWM inverter 58, transformer 60 and rectifier 62 is commercially available and within the understanding of those skilled in the art.
The AC output converter 22b comprises an "On-line" U.P.S. converter which provides an AC output at selected voltage and frequency, for example 3-phase 480 VAC. As shown in Fig. 1, the converter 22b includes a PWM
inverter 64, an isolation transformer 66, and a low-pass AC
output filter 68. The PWM inverter 64 converts fixed voltage DC power from the bus 16 into a fixed voltage/frequency AC power at variable current for the purposes of exciting the primary winding of the isolation transEormer 66. The secondary of the transformer 66 is connected to the low-pass AC filter 68. The AC filter 68 attemlates the voltage switching harmonics to very low levels, preferably less than 1~ of rated value. The output from lhe filter 68 is connected to load (e.g. in the plant or residence) which is to be protected from AC line voltage surges/sags and outages. Generally, the on-line converter 22b operates in output voltage and frequency regulated mode.
Reference is next made to Figs. 2(a) to 2(c), which show in flow-chart form processing steps performed by the energy management controller 10 according to the present invention.
- The processing commences at step 100, and at step 102, the controller 10 "gets" the next available energy source or if the system 1 is being started, the available energy source from the list. Preferably, the availability of energy sources is stored in memory as a prioritized list. The prioritized list is preferably updated periol~ically by the controller 10 in response to polling the potential energy sources and logging the responses, i.e. DEVICE AVAILAELE/NOT AVAILAELE, or according to a schedule .
If there are no further energy sources available to supply the load at step 104, the controller 10 issues a LOAD SHED command to the energy converters at step 106.
The controller 10 then initiates an ALARM at step 108. The ALARM is initiated because the energy management system 1 has reached capacity.
If there are energy sources available as deterrnined at step 104, the controller 10 next determines at st:ep 110 if the selected energy source from the prioritized list is "on-line", i.e. coupled to the power bus 16, and available to provide power. If the selected energy source is not "on-line", then the controller 10 select:s the next energy source from the prioritized list in step 102. An energy source is "off-line", i.e. not on-line, when it is not available to supply power to the power bus 16, for example, the solar-powered generator 18a is off-line at night, and the wind-powered generator 18b is off-line when there is no wind to turn the wind-turbine 34.
If the selected energy source is on-line, then the controller 10 sends a REGULATE BUS COMMAND to the device at step 112. Next at step 114 as shown in Fig.
2(b), the controller 10 determines if the energy source which is regulating the bus 16 is still on-line. If the regu.Lating energy has gone off-line, then the controller 10 returns to step 100 and proceeds to get the next energy source from the prioritized list (step 102). If the regu]ating energy source is still on-line, i.e. regulating the bus 16, the controller 10 determines the PRESENT ENERGY
DEMA~D at step 116.
Next at step 118, the controller 10 determines if the energy capacity exceeds the energy demand, i.e. PRESENT
ENERGY DEMAND determined in previous step 116. If the capacity exceeds the demand, then the controller 10 cycles through the loop starting at step 114. If the capacity is exceeded by the PRESENT ENERGY DEMAND, i.e. the energy demand cannot be met by the energy sources currently on-line, the controller 10 determines the next available energy source in step 120.
20If there are no further energy sources available as determined at step 122, then the PRESENT ENERGY DEMAND
cannc,t be met and the controller 10 determines a load to be shed, i.e. disconnected from the power bus 16, for example the super-capacitor converter 20b. Referring to Fig. 2(c), 25at step 124 the controller 10 selects the load to be shed, i.e. next lowest priority load, from a LOAD PRIORITY LIST
which may be stored in memory accessible by the controller 10. If there are no further loads to be shed as determined at step 126, the energy d~m~n~ cannot to be met and the controller 10 sends load shed comm~n~s to all the energy converters as indicated at step 128, followed by an ALARM
at step 130. The ALARM indicates that the capacity of the energy management system 1 has been reached.
Referring still to Fig. 2(c), if there are still loads available to be shed (i.e. headroom) as determined at step 126, the controller 10 sends a load shed command to a selected energy converter, e.g. the E.V. charger 22a, at step 132. Next at step 134, the controller 10 determines a new value for the ENERGY DEMAND. If the ENERGY DEMAND is greater than the sum of energy available from the active energy sources (step 136), then the controller 10 returns to step 124 in order to attempt to shed additional loads at step 132. If the DEMAND is less than the sum of energy available as determined in step 136, then the controller 10 returns to loop at 114.
Referring back to Fig. 2(b), if there are energy sources available as determined at step 122, the controller 10 calculates if the capacity of the new source exceeds the demand less the sum of currently active energy sources at step 138. If the capacity does not exceed the demand as determined at step 138, the controller 10 sends a SUPPLY
MAXIMUM ENERGY command to the new source at step 140. The controller 10 then updates the energy available from the sum of active sources in step 142 as shown in Fig. 2(b).
Referring again to Fig. 2(b), if there are available energy sources and the capacity exceeds the demand as determined at step 138, then the controller 10 sends a SUPPLY COMMAND to the new source at step 144 in order to obtain additional energy. The additional energy is determined as the difference between the LOAD DEMAND and the sum of the AVAILABLE ENERGY available from the currently active energy sources.
In another aspect of the invention, the controller 10 performs a cost evaluation in the determination of which energy sources or loads to connect/disconnect from the bus 16.
From the foregoing, it will be appreciated that CA 0222764l l998-0l-2l as shown in Fig. l(a) steps 100 to 112, the controller 10 connects energy sources (from the prioritized list), and if necessary sheds loads, when the energy management system 1 is first started (i.e. step 100) or if the energy source regulating the bus 16 goes off-line (step 114). The rest of the time, the controller 100 cycles through the loop comprising steps 114 to 118 shown in Fig. 2(b). This arrangement allows the energy demand to increase without triggering a re-evaluation of the energy source which is regulating the bus.
In a typical consumer application, the energy management system as described above monitors energy costs, deten~Lines the least costly energy sources, and stores the energy for anticipated requirements in the storage devices.
In day to day operation, peak power d~m~n~s from the power utility usually occur when the work force is arriving at home and manufacturing plants are still operating. The peak power load increases as the consumers demand energy for various appliances. By utilizing cheaper alternate energy sources, e.g. wind turbine 18b, or stored energy, e.g. super capacitor storage device 20b, the energy management system 1 reduces the reliance on expensive elect:rical energy from the power utility 2 at peak time.
The present invention may be embodied in other speci:Eic fonms without departing from the spirit or essenl_ial characteristics thereof. Therefore, the presently discussed em-bodiments are considered to be illuslrative and not restrictive, the scope of the invenlion being indicated by the appended claims rather than lhe foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Claims (13)
1. An energy management system for managing the supply of electrical energy to a consumer, said energy management system comprising:
(a) an input module for receiving electrical energy from a primary energy source, said input module having a converter for converting said electrical energy for local distribution;
(b) a power distribution bus for distributing said converted electrical energy;
(c) a plurality of energy converters coupled to said power distribution bus and having means for generating electrical energy and means for injecting said electrical energy into said power distribution bus;
(d) a controller having means for determining a present energy demand for the consumer and means for controlling said input module and means for controlling said energy converters;
(e) said input module having means responsive to control signals from said controller for receiving electrical energy from the power utility and injecting said energy into said distribution bus; and (f) said means for injecting for said energy converter being responsive to control signals from said controller for injecting electrical energy into said power distribution bus.
(a) an input module for receiving electrical energy from a primary energy source, said input module having a converter for converting said electrical energy for local distribution;
(b) a power distribution bus for distributing said converted electrical energy;
(c) a plurality of energy converters coupled to said power distribution bus and having means for generating electrical energy and means for injecting said electrical energy into said power distribution bus;
(d) a controller having means for determining a present energy demand for the consumer and means for controlling said input module and means for controlling said energy converters;
(e) said input module having means responsive to control signals from said controller for receiving electrical energy from the power utility and injecting said energy into said distribution bus; and (f) said means for injecting for said energy converter being responsive to control signals from said controller for injecting electrical energy into said power distribution bus.
2. The energy management system as claimed in claim 1, further including at least one energy storage device coupled to said power distribution bus, said energy storage device having means for storing energy supplied from said power distribution bus and means for returning said stored energy to said power distribution bus in response to control signals from said controller.
3. The energy management system as claimed in claim 2, further including a communication interface for communicating with the primary energy source and said controller issuing said control signals to said input module based on the energy demand for the consumer and the energy available from the primary energy source.
4. The energy management system as claimed in claim 2, wherein said controller includes communication means for communicating with the primary energy source and determining energy availability and energy rate, and said controller issuing control signals to said energy storage device to store energy from said primary energy source when the energy rate is low.
5. The energy management system as claimed in claim 2, wherein said controller includes means for determining if the present energy demand for the consumer is being met and means for issuing control signals to store energy from said energy converter.
6. The energy management system as claimed in claim 1, wherein said energy converters include a battery charger coupled to said power distribution bus and having means for receiving electrical energy from said power distribution bus and charging an electrical vehicle battery.
7. The energy management system as claimed in claim 1, wherein the converter for said input module comprises a pulse-width modulator rectifier and inverter adapted for electrical energy supplied by the power utility as a three-phase high voltage fuel.
8. The energy management system as claimed in claim 1, wherein said electrical energy is converted into a direct current for distribution on said power distribution bus.
9. The energy management system as claimed in claim 2, wherein said energy storage devices include devices selected from the group comprising battery storage devices, capacitive storage devices, and magnetic coil storage devices.
10. A method for managing the energy supply from a power utility to a consumer, said method comprising the steps of:
(a) determining a present power demand for the consumer;
(b) providing additional energy for the consumer if there is an increase in the present power demand;
(c) said step of providing additional energy comprises:
(i) requesting additional energy from the power utility, or (ii) connecting additional local energy sources to supply energy to the consumer.
(a) determining a present power demand for the consumer;
(b) providing additional energy for the consumer if there is an increase in the present power demand;
(c) said step of providing additional energy comprises:
(i) requesting additional energy from the power utility, or (ii) connecting additional local energy sources to supply energy to the consumer.
11. The method as claimed in claim 10, further including the step of taking energy from the power utility at non-peak times and storing said energy locally in an energy storage device.
12. The method as claimed in claim 11, further including the step of transferring energy stored in said energy storage device back to the power utility.
13. The method as claimed in claim 11, further including the step of shedding said energy device when the present power demand is not being met.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US78529497A | 1997-01-21 | 1997-01-21 | |
| US08/785,294 | 1997-01-21 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2227641A1 true CA2227641A1 (en) | 1998-07-21 |
Family
ID=25135023
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2227641 Abandoned CA2227641A1 (en) | 1997-01-21 | 1998-01-21 | Energy management and distribution control system |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2227641A1 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2015123650A1 (en) * | 2014-02-14 | 2015-08-20 | The Powerwise Group, Inc. | Meter/voltage regulator with volt-ampere reactive control positioned at customer site |
| EP2911262A3 (en) * | 2009-11-06 | 2015-12-16 | Panasonic Intellectual Property Management Co., Ltd. | Power distribution system |
| CN113452067A (en) * | 2021-06-22 | 2021-09-28 | 湖北工业大学 | Electric energy quality adjusting device and control method |
-
1998
- 1998-01-21 CA CA 2227641 patent/CA2227641A1/en not_active Abandoned
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2911262A3 (en) * | 2009-11-06 | 2015-12-16 | Panasonic Intellectual Property Management Co., Ltd. | Power distribution system |
| WO2015123650A1 (en) * | 2014-02-14 | 2015-08-20 | The Powerwise Group, Inc. | Meter/voltage regulator with volt-ampere reactive control positioned at customer site |
| CN113452067A (en) * | 2021-06-22 | 2021-09-28 | 湖北工业大学 | Electric energy quality adjusting device and control method |
| CN113452067B (en) * | 2021-06-22 | 2022-07-05 | 湖北工业大学 | Electric energy quality adjusting device and control method |
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