U.S. patent application number 10/734293 was filed with the patent office on 2008-12-18 for photovoltaic power converter system with a controller configured to actively compensate load harmonics.
This patent application is currently assigned to General Electric Company. Invention is credited to Michael Andrew de Rooij, Eladio Clemente Delgado, Robert Louis Steigerwald.
Application Number | 20080308141 10/734293 |
Document ID | / |
Family ID | 34710441 |
Filed Date | 2008-12-18 |
United States Patent
Application |
20080308141 |
Kind Code |
A1 |
de Rooij; Michael Andrew ;
et al. |
December 18, 2008 |
PHOTOVOLTAIC POWER CONVERTER SYSTEM WITH A CONTROLLER CONFIGURED TO
ACTIVELY COMPENSATE LOAD HARMONICS
Abstract
Photovoltaic power converter system including a controller
configured to reduce load harmonics is provided. The system
comprises a photovoltaic array and an inverter electrically coupled
to the array to generate an output current for energizing a load
connected to the inverter and to a mains grid supply voltage. The
system further comprises a controller including a first circuit
coupled to receive a load current to measure a harmonic current in
the load current. The controller includes a second circuit to
generate a fundamental reference drawn by the load. The controller
further includes a third circuit for combining the measured
harmonic current and the fundamental reference to generate a
command output signal for generating the output current for
energizing the load connected to the inverter. The photovoltaic
system may be configured to compensate harmonic currents that may
be drawn by the load.
Inventors: |
de Rooij; Michael Andrew;
(Clifton Park, NY) ; Steigerwald; Robert Louis;
(Burnt Hills, NY) ; Delgado; Eladio Clemente;
(Burnt Hills, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Assignee: |
General Electric Company
|
Family ID: |
34710441 |
Appl. No.: |
10/734293 |
Filed: |
December 15, 2003 |
Current U.S.
Class: |
136/243 |
Current CPC
Class: |
H02J 3/381 20130101;
H02J 3/383 20130101; H02J 2300/24 20200101; Y02B 10/10 20130101;
H02J 3/01 20130101; Y02E 40/40 20130101; Y02E 10/563 20130101; Y02B
10/14 20130101; Y02E 10/56 20130101 |
Class at
Publication: |
136/243 |
International
Class: |
H01L 25/00 20060101
H01L025/00 |
Goverment Interests
[0001] This invention was made with U.S. Government support through
Government Contract Number Sandia 55792 awarded by the Department
of Energy, and, in accordance with the terms set forth in said
contract, the U.S. Government may have certain rights in the
invention.
Claims
1. A photovoltaic power converter system comprising: a photovoltaic
array; an inverter electrically coupled to said photovoltaic array
to inject an output current to a mains grid supply voltage; and a
controller including a first circuit coupled to receive a load
current and separate out a harmonic component from the load current
to measure a load harmonic current; a second circuit for
determining an amplitude of an injectable current available from
the photovoltaic array to generate a fundamental sinusoidal current
reference that is phased locked with the mains grid supply voltage;
and a third circuit for combining the load harmonic current and the
fundamental sinusoidal current reference to generate a command
output signal, wherein the controller is configured to generate an
error signal based on a difference between the command output
signal and the output current, and wherein the controller is
configured to process the error signal and to generate a switching
signal for actuating a switching gate of said inverter to
compensate for the load harmonic current when said inverter injects
the output current to the mains grid supply voltage.
2. The photovoltaic power converter system of claim 1, wherein said
first circuit comprises a notch filter configured to pass harmonics
present in said load current.
3. The photovoltaic power converter system of claim 1, wherein said
second circuit comprises a phase lock loop coupled to receive said
supply voltage and generate a sinusoid corresponding to the
frequency of said supply voltage.
4. The photovoltaic power converter system of claim 3, wherein said
second circuit further comprises a mixer configured to receive said
sinusoid and a signal indicative of the magnitude of current
available from the photovoltaic array for generating said
fundamental reference.
5. The photovoltaic power converter system of claim 1, wherein said
controller is selected from the group consisting of a
micro-controller, a Field Programmable Gate Array device and an
Application Specific Integrated Circuit device.
6. A controller for a photovoltaic power converter system including
a photovoltaic array coupled to an inverter to generate an output
current for energizing a load connected to said inverter, said
controller comprising: a first circuit coupled to receive a load
current and separate out a harmonic component from the load current
and to measure a harmonic current; a second circuit for determining
an amplitude of an injectable current available from the
photovoltaic array to generate a fundamental sinusoidal current
reference that is phased locked with a mains grid supply voltage;
and a third circuit for combining the load harmonic current and the
fundamental sinusoidal current reference to generate a command
output signal, wherein the controller is configured to generate an
error signal based on a difference between the command output
signal and the output current, and wherein the controller is
configured to process the error signal and to generate a switching
signal for actuating a switching gate of said inverter to
compensate for the load harmonic current when said inverter injects
the output current to the mains grid supply voltage.
7. The controller of claim 6, wherein said first circuit comprises
a notch filter configured to pass harmonics present in said load
current.
8. The controller of claim 6, wherein said second circuit comprises
a phase lock loop coupled to receive a supply voltage and generate
a sinusoid corresponding to a frequency of said supply voltage.
9. The controller of claim 8, wherein said second circuit further
comprises a mixer configured to receive said sinusoid and a signal
indicative of the magnitude of current available from the
photovoltaic array for generating the fundamental reference drawn
by said load.
10. The controller of claim 6, selected from the group consisting
of a micro-controller, a Field Programmable Gate Array device, and
an Application Specific Integrated Circuit device.
11. A method for controlling a photovoltaic power converter system
including a photovoltaic array coupled to an inverter to generate
an output current for energizing a load connected to said inverter,
said method comprising: receiving a load current to separate out a
harmonic component from the load current and to measure a load
harmonic current; determining an amplitude of an injectable current
available from the photovoltaic array and generating a fundamental
sinusoidal current reference that is phase locked with the mains
grid supply voltage; and combining the load harmonic current and
the fundamental sinusoidal current reference to generate a command
output signal, whereby the controller is configured to generate an
error signal based on a difference between the command output
signal and the output current, and whereby the controller is
configured to process the error signal and to generate a switching
signal for actuating a switching gate of said inverter to
compensate for the load harmonic current when said inverter injects
the output current to the mains grid supply voltage.
12. The method of claim 11, wherein the receiving of the load
current comprises processing said load current to pass harmonics
present in said load current.
13. The method of claim 11, wherein said generating of a
fundamental reference comprises receiving a supply voltage to
generate a sinusoid corresponding to a frequency of said supply
voltage.
14. The method of claim 13, wherein said generating of a
fundamental reference further comprises mixing said sinusoid and a
signal indicative of the magnitude of current available from the
photovoltaic array for generating the fundamental reference drawn
by said load.
Description
BACKGROUND OF THE INVENTION
[0002] The invention relates to a power conversion system, and,
more particularly, to a photovoltaic power converter system with a
controller configured to actively compensate harmonics that may be
drawn by a load coupled to the photovoltaic system.
[0003] Environmental concerns and the search for alternative
sources to generate electrical energy suitable for supplying
households or small commercial sites have driven the need for power
converter systems, such as photovoltaic array converters that can
process sunlight into a standard and usable electrical form, e.g.,
supplying energy to the mains grid during daylight hours.
[0004] It is known that many of these photovoltaic array converters
simply inject a unity power factor sinusoidal current onto the
mains grid supply thereby reducing the total energy drawn by the
local load from the mains grid supply. Loads on the local grid can
draw currents, which may contain harmonics. These harmonic currents
can potentially disturb the mains grid supply and other loads on
the system. For example, these harmonic currents may lead to poor
utilization of the grid supply and can cause voltage distortions
and, in severe cases, cause other loads on the same supply to
malfunction.
[0005] Some power electronic systems may be designed not to draw
harmonic currents and are referred to as low Total Harmonic
Distortion (THD) unity power factor converters. However, not all
loads draw unity power factor with a low THD and it is for these
loads that compensation is needed. The number of the loads that can
generate harmonic currents may further aggravate the problem. Large
active power compensators installed by power utilities are
sometimes used on the mains grid supply to reduce the harmonic
currents that are present on the system and various main nodes.
These large and bulky systems unfortunately are limited in the
number of the harmonics that can be compensated for, are expensive
and generally do not reduce the harmonic currents at all points on
the mains grid.
BRIEF DESCRIPTION OF THE INVENTION
[0006] One aspect of the invention provides a photovoltaic power
converter system, such as may comprise a photovoltaic array, and an
inverter electrically coupled to the array to generate an output
current for energizing a load connected to the inverter and to a
mains grid supply voltage. The photovoltaic power converter system
may further comprise a controller including a first circuit coupled
to receive a load current to measure a harmonic current in the load
current. The controller includes a second circuit to generate a
fundamental reference drawn by the load. The controller further
includes a third circuit for combining the measured harmonic
current and the fundamental reference to generate a command output
signal for generating the output current for energizing the load
connected to the inverter.
[0007] The features and advantages of the present invention will
become apparent from the following detailed description of the
invention when read with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a block diagram of a photovoltaic power converter
system constructed in accordance with an exemplary embodiment of
the invention.
[0009] FIG. 2 is a block diagram of a controller providing active
compensation to the photovoltaic power converter system of FIG.
1.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The inventors of the present invention have innovatively
recognized a power conversion system, such as a photovoltaic array
in combination with an inverter, that not only supplies electrical
energy to a load, such as a standard household, but also may be
configured to compensate for local load harmonic currents that may
be drawn. Local load systems may comprise every load on a local
mains grid, such that a single breaker can disconnect the local
grid from a mains supply grid, such as the main circuit breaker in
a household. The photovoltaic system may be suitable for
households, office, warehouse or commercial site and may operate in
a grid tied mode.
[0011] FIG. 1 is a block diagram of an exemplary embodiment of an
active compensator photovoltaic converter system 10. The converter
system 10 may include an inverter 12 coupled to a load 14 and a
photovoltaic array 16 operating as a power source. The details of
the inverter are not particularly relevant for purposes of the
present invention. For readers desirous of such details in
connection with one exemplary inverter architecture reference is
made to U.S. patent application Ser. No. 10/329,906, filed Dec. 26,
2002, assigned in common to the same assignee of the present
invention and herein incorporated by reference in its entirety.
[0012] The operation of a standard photovoltaic converter system
can be mathematically described by equations 1 through 3 below. The
mains grid voltage may be a standard sinusoidal time varying
voltage at a fundamental frequency, usually 50 Hz or 60 Hz with an
amplitude of V volts.
V.sub.net(t)=Vsin(.omega.t) (1)
where:
[0013] V.sub.net(t)=Mains grid supply voltage [V]
[0014] V=Amplitude of the mains grid supply voltage [V]
[0015] .omega.=Mains grid supply frequency [s.sup.-1]
[0016] t=Time [s]
[0017] The available photovoltaic array power may be used to
determine the amplitude of the current that will be injected into
the mains grid supply--load system. The amplitude of this current
is given in equation 2 and the time varying form is given in
equation 3.
I .alpha. = P array V ##EQU00001##
where:
[0018] P.sub.array=The available power from the photovoltaic array
[W]
[0019] I.sub.a=Amplitude of the injected current [A]
I.sub.out(t)=I.sub.asin(.omega.t) (3)
where:
[0020] I.sub.out(t)=Injected current [A]
[0021] In one exemplary embodiment, the active compensator
photovoltaic converter system is configured so that the harmonic
current content of the load is measured and is subtractively
injected together with the active power current into the mains grid
supply--load system. The result is that if the photovoltaic array
is able to supply sufficient power, the current in the mains grid
will have just a fundamental component.
[0022] Equations 4 and 5 may be used to illustrate the mathematical
basis for the harmonic compensation.
I.sub.h(t)=I.sub.load-1(t)-I.sub.load(t) (4)
where:
[0023] I.sub.h(t)=Harmonic current of the load [A]
[0024] I.sub.load-1(t)=Fundamental current drawn by the load
[A]
[0025] I.sub.load(t)=Load current [A]
I.sub.out(t)=I.sub.asin(.omega.t)+I.sub.h(t) (5)
[0026] FIG. 2 is a block diagram of one exemplary controller 20 for
the active compensator photovoltaic converter system of FIG. 1. The
diagram shows one example of how the above-identified mathematical
relationships can be implemented. It will be appreciated that if
the load current (I.sub.load(t)) measurement is omitted, then the
system would revert to that of a standard photovoltaic converter
controller.
[0027] At a multiplier 22, the controller 20 receives a maximum
power point reference (e.g., available array power, P.sub.array),
such as may be obtained from a standard maximum power tracker.
Multiplier 22 allows multiplying P.sub.array with the inverse
(e.g., 1N) of the mains grid voltage amplitude (V) to determine the
amplitude of the injectable current (I.sub.a). This current
reference is mixed at a mixer 24 with a sinusoidal waveform that is
phase locked with the mains grid voltage by a phase lock loop 26 to
generate the actual fundamental sinusoidal current reference
(I.sub.1(t)). The load harmonic current (I.sub.h(t)) may be
determined by measuring the load current (I.sub.load(t)) and
filtering out with a notch filter 28 the fundamental component. The
fundamental current reference I.sub.1(t) and the inverse (e.g.,
opposite polarity achieved by sign inversion) of the harmonic
current reference I.sub.h(t) are then summed together at a summer
30 to produce a current reference (I.sub.out-ref(t)) for the
system. This current reference is then processed using standard
feedback techniques to control the actual output current of the
system (I.sub.out(t)). For example, an error signal (I.sub.err(t)
that comprises the difference between (I.sub.out-ref(t)) and
(I.sub.out(t)) as may be obtained in a summer 32 may be processed
by a proportional plus integral (PI) controller 34 in turn coupled
to a pulse width modulator (not shown) using standard pulse width
modulation techniques to generate the switching signals for
actuating the switching gates of the inverter. It will be
appreciated from the mathematical relationships and the controller
diagram that measurement of the mains grid current into the system
is not a requirement. For example, processing just the local load
current to extract the harmonic content would allow performing the
desired compensation. That is, this harmonic compensation may be
conveniently and effectively achieved through a relatively minor
modification to a standard power converter system.
[0028] In operation, a photovoltaic power converter system may
include a photovoltaic array 16 (FIG. 1). The converter system may
further include an inverter 12 electrically coupled to the array 16
to generate an output current I.sub.out(t) for energizing a load 14
connected to the inverter 14 and to a mains grid supply voltage
V.sub.net(t). In one exemplary embodiment, a controller 20 (FIG. 2)
includes a first circuit, such as a notch filter 28, coupled to
receive a load current I.sub.load(t) to measure a harmonic current
I.sub.h(t) in the load current. The controller includes a second
circuit to generate a fundamental reference I.sub.1(t) drawn by the
load. The second circuit may comprise the mixer 24 that receives a
sinusoid from the phase lock loop 26 and the signal indicative of
the magnitude of injectable current (I.sub.a) available from the
photovoltaic array for generating the fundamental reference. The
controller may further include a third circuit, such as a summer
30, for combining the measured harmonic current and the fundamental
reference to generate a command or reference output signal
(I.sub.out-ref(t) for generating the output current I.sub.out(t)
for energizing the load connected to the inverter.
[0029] Aspects of the invention can be embodied in the form of
computer-implemented processes and apparatus for practicing those
processes. Aspects of the invention can also be embodied in the
form of computer program code containing computer-readable
instructions embodied in tangible media, such as floppy diskettes,
CD-ROMs, hard drives, or any other computer-readable storage
medium, wherein, when the computer program code is loaded into and
executed by a computer, the computer becomes an apparatus for
practicing the invention. Aspects of the invention can also be
embodied in the form of computer program code, for example, whether
stored in a storage medium, loaded into and/or executed by a
computer, or transmitted over some transmission medium, such as
over electrical wiring or cabling, through fiber optics, or via
electromagnetic radiation, wherein, when the computer program code
is loaded into and executed by a computer, the computer becomes an
apparatus for practicing the invention. When implemented on a
general-purpose computer, the computer program code segments
configure the computer to create specific logic circuits or
processing modules. Other embodiments may be a micro-controller,
such as a dedicated micro-controller, a Field Programmable Gate
Array (FPGA) device, or Application Specific Integrated Circuit
(ASIC) device.
[0030] While the preferred embodiments of the invention have been
shown and described herein, it will be obvious that such
embodiments are provided by way of example only. Numerous
variations, changes and substitutions will occur to those of skill
in the art without departing from the invention herein.
Accordingly, it is intended that the invention be limited only by
the spirit and scope of the appended claims.
* * * * *