Note: Descriptions are shown in the official language in which they were submitted.
CA 02227641 1998-01-21
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
CA 02227641 1998-01-21
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
CA 02227641 1998-01-21
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
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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
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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
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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.
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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
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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.
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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.
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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
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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,
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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
CA 02227641 1998-01-21
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.
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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.
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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.
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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.
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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
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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
CA 02227641 1998-01-21
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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
-20-
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.
