U.S. patent application number 16/461245 was filed with the patent office on 2019-10-17 for interleaved parallel inverters with integrated filter inductor and interphase transformer.
The applicant listed for this patent is SCHNEIDER ELECTRIC SOLAR INVERTERS USA, INC.. Invention is credited to Jason Elliott, Robert Pasterczyk, Benjamin Wun Wang Tam, Zbigniew Wolanski.
Application Number | 20190319549 16/461245 |
Document ID | / |
Family ID | 60570240 |
Filed Date | 2019-10-17 |
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United States Patent
Application |
20190319549 |
Kind Code |
A1 |
Pasterczyk; Robert ; et
al. |
October 17, 2019 |
INTERLEAVED PARALLEL INVERTERS WITH INTEGRATED FILTER INDUCTOR AND
INTERPHASE TRANSFORMER
Abstract
A power electronics system, comprising a first inverter
configured to receive DC power from a power source and a second
inverter configured to receive DC power from the power source is
provided. The system includes a first output inductor connected in
series to an output of the first inverter, a second output inductor
connected in series to an output of the second inverter, a coupling
inductor configured to receive current from the first output
inductor and the second output inductor, and an AC power
output.
Inventors: |
Pasterczyk; Robert; (Froges,
FR) ; Elliott; Jason; (Delta, CA) ; Wolanski;
Zbigniew; (Burnaby, CA) ; Tam; Benjamin Wun Wang;
(Vancouver, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SCHNEIDER ELECTRIC SOLAR INVERTERS USA, INC. |
Livermore |
CA |
US |
|
|
Family ID: |
60570240 |
Appl. No.: |
16/461245 |
Filed: |
November 15, 2017 |
PCT Filed: |
November 15, 2017 |
PCT NO: |
PCT/US2017/061727 |
371 Date: |
May 15, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62422838 |
Nov 16, 2016 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 7/49 20130101; H02M
2001/0074 20130101; H01F 27/385 20130101; H02M 1/0061 20130101;
H02M 2007/4822 20130101; H02M 2001/0064 20130101; H02M 7/493
20130101; H02M 1/126 20130101 |
International
Class: |
H02M 7/493 20060101
H02M007/493; H02M 1/12 20060101 H02M001/12; H02M 1/00 20060101
H02M001/00 |
Claims
1. A power electronics system, comprising: a first inverter
configured to receive direct current (DC) power from a power
source; a second inverter configured to receive DC power from the
power source; a first output inductor connected in series to an
alternating current (AC) output of the first inverter; a second
output inductor connected in series to an AC output of the second
inverter; a coupling inductor configured to receive current from
the first output inductor and the second output inductor; and an AC
power output to provide current from the coupling inductor.
2. The power electronics system of claim 1 further comprising a
control system configured to provide a control signal associated
with a disturbance frequency, determine an amplitude of oscillation
in an output power of the AC power output, wherein the oscillation
is caused by the disturbance frequency, detect an islanding
condition, if the amplitude of oscillation is below a threshold,
and disconnect the grid from the AC power output if the islanding
condition is detected.
3. The power electronics system of claim 1 wherein the coupling
inductor includes a coil winding around a coupled core and a
self-inductance core.
4. The power electronic system of claim 3 wherein the coil winding
includes a series of elongated turns.
5. A power electronics system, comprising: a first multi-phase
inverter configured to receive direct current (DC) power from a
power source; a second multi-phase inverter configured to receive
DC power from the power source; a first plurality of output
inductors, each of the first plurality of output inductors
connected in series to an output phase of the first multi-phase
inverter; a second plurality of output inductors, each of the
second plurality of output inductors connected in series to an
output phase of the second multi-phase inverter; a plurality of
coupling inductors, each of the plurality of coupling inductors
configured to receive current from a respective output inductor of
the first plurality of output inductors and a respective output
inductor of the second plurality of output inductors; and a
multi-phase alternating current (AC) power output to provide
current from the plurality of coupling inductors.
6. The power electronics system of claim 5 further comprising a
control system configured to provide a control signal associated
with a disturbance frequency, determine an amplitude of oscillation
in an output power of the AC power output, wherein the oscillation
is caused by the disturbance frequency, detect an islanding
condition, if the amplitude of oscillation is below a threshold,
and disconnect the grid from the AC power output if the islanding
condition is detected.
7. The power electronics system of claim 5 wherein each of the
plurality of coupling inductors includes a coil winding around a
coupled core and a self-inductance core.
8. The power electronic system of claim 7 wherein the coil winding
includes a series of elongated turns.
9. An inductor coil winding comprising: a first terminal; a series
of concentric turns in a first plane, the series of concentric
turns leading in from the first terminal and having a diameter
allowing for an opening within the series of concentric turns; a
series of elongated turns in a second plane, the series of
elongated turns leading in from the series of concentric turns and
having a length greater than the diameter of the series of
concentric turns, and allowing for an opening within the series of
elongated turns; and a second terminal, the second terminal leading
out form the series of elongated turns.
10. The inductor coil winding of claim 9 wherein the series of
concentric turns provides main inductance.
11. The inductor coil winding of claim 10 wherein the series of
elongated turns provides coupled inductance.
12. The inductor coil winding of claim 11 wherein the first
terminal is an input terminal electrically connected to an output
of an inverter to receive current from the inverter.
13. The inductor coil winding of claim 9 further comprising a
self-inductance core in the opening within the series of concentric
turns and a coupled core in the opening within the series of
elongated turns, the coupled core configured to provide a magnetic
coupling to another inductor coil winding.
14. A filter assembly comprising: a first self-inductance core; a
second self-inductance core; a coupler core; a first plurality of
inductor coil windings, each of the first plurality of inductor
coil windings having a series of first turns around the first
self-inductance core, and a series of second turns around the first
self-inductance core and the coupler core; and a second plurality
of inductor coil windings, each of the second plurality of inductor
coil windings having a series of first turns around the second
self-inductance core, and a series of second turns around the
second self-inductance core and the coupler core.
15. The filter assembly of claim 14 wherein the first
self-inductance core, the second self-inductance core, and the
coupler core each include three limbs, one limb for each of three
phases.
16. The filter assembly of claim 14 wherein the first turns of each
of the first plurality of inductor coil windings are concentric
turns and the first turns of each of the second plurality of
inductor coil windings are concentric turns.
17. The filter assembly of claim 16 wherein the second turns of
each of the first plurality of inductor coil windings are elongated
turns and the second turns of each of the second plurality of
inductor coil windings are elongated turns.
18. The filter assembly of claim 14 wherein the first plurality of
inductor coil windings is configured to electrically connect to a
first inverter at a first terminal to receive an alternating
current output from the first inverter and the second plurality of
inductor coil windings is configured to electrically connect to a
second inverter at a second terminal to receive an alternating
current output from the second inverter.
19. The filter assembly of claim 18 wherein the first plurality of
inductor coil windings is electrically connected to the second
plurality of inductor coil windings at a third terminal configured
to provide a combined alternating current from the first and second
inverter.
20. The filter assembly of claim 14 further comprising a plurality
of thermal plates interspersed among the first and second plurality
of inductor coil windings and configured to remove thermal energy
from the first and second plurality of inductor coil windings.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C. .sctn.
119(e) and claims the benefit of priority under PCT Article 8, as
applicable, of co-pending U.S. Provisional Patent Application No.
62/422,838 titled COMPACT AC FILTER MODULE FOR INTERLEAVED POWER
CONVERTER filed on Nov. 16, 2016, which is herein incorporated by
reference in its entirety for all purposes.
BACKGROUND
Field of Invention
[0002] Embodiments of the present invention relate generally to
utility scale power inverters.
Discussion of Related Art
[0003] A power inverter, or inverter, is an electronic device or
circuitry that converts direct current (DC) to alternating current
(AC). Inverters may be used in a number of different contexts, with
different DC power sources (such as lead acid batteries,
photovoltaic solar panels, wind turbines, etc), and may be designed
to satisfy different power demands of a system.
[0004] Utility scale solar inverters, in particular, convert
variable DC output of a photovoltaic (PV) solar panel into a
utility frequency AC to provide power to either a commercial
electrical grid or a local, off-grid electrical network. Solar
inverters are connected to a plurality of photovoltaic cells that
provide DC input to the inverter. The inverter comprises at least
one DC-to-AC power conversion bridge, associated filter electronics
and an AC (output) module. The DC-to-AC power conversion bridge
uses a plurality of electronic switches, typically insulated gate
bipolar transistors (IGBTs), and diodes to convert the DC input
into AC output. For grid-connected inverters providing power to an
electricity grid, the AC output is filtered to provide an AC output
waveform that is suitable for the grid. Furthermore, solar power
inverters have special functions adapted for use with photovoltaic
arrays, including maximum power point tracking and anti-islanding
protection.
[0005] A sine wave inverter produces a multiple-step sinusoidal AC
waveform, although in most cases the output is a choppy or rough
approximation of a sine wave, rather than a smooth sine wave. As a
substitute for standard AC line power, power inverter devices
approximate a sine wave output because many electrical products are
engineered to work best with a sine wave AC power source. Further,
grid-connected inverters are designed to feed power into the
electric power distribution system. They transfer synchronously
with the line, and should have as little harmonic content as
possible.
[0006] The output from an inverter can be single phase or
three-phase. Three-phase inverters are generally used in higher
power applications. A basic three-phase inverter consists of three
single-phase legs each connected to one of the three load
terminals. The operation of the three phase legs is coordinated so
that one operates at each 120 degree point of the fundamental
output waveform. Certain harmonics are eliminated and other
harmonics can be removed by further processing.
[0007] As shown in FIG. 1, an LC filter comprising one or more
inductor and capacitor can be used to smooth the AC waveform from a
single phase inverter (as shown in FIG. 1). Such low-pass filters
allow the fundamental component of the waveform to pass to the
output while limiting the passage of harmonic components. LC
filters may similarly be used in connection with a three phase
inverter, with an LC filter applied to each output phase of the
inverter.
[0008] When two or more inverters are connected in parallel, their
switching times (single phase or 3-phase) can be synchronized or
can be offset relative to one another in an "interleaved"
configuration. Interleaving is implemented by phase-shifting the
switching times of each inverter by a unique multiple of
360.degree./n, where n is the number of inverters. The switching of
the multiple inverters is thereby staggered, and the overall
switching frequency may thereby be increased.
[0009] Interleaving can result in the cancellation of higher order
harmonics and a reduction in distortion. Also, the higher frequency
noise reduces the size of the inverter AC output filters that are
needed. Parallel interleaved three-phase inverters can provide
significant cost reductions while improving system reliability and
efficiency. FIG. 2 shows two 3-phase DC-AC inverters connected in
parallel, with output LC filters.
[0010] Interleaved converters are sometimes magnetically coupled
with a coupling inductor, and then share the same output filter.
The coupling combines high frequency components (which may be
interleaved) and may thereby reduce ripple. FIG. 3 shows a pair of
inverters (bridges) magnetically coupled via a coupling inductor
which is connected to a shared LC filter. With this arrangement the
combined current from bridge 1 and bridge 2 passes through the
output filter inductor.
SUMMARY
[0011] Particularly for large scale inverter systems, AC filters
required to smooth out the unacceptably rough AC power waveform of
the inverters would conventionally be large and costly in order to
handle the level of power and power quality required. In accordance
with principles of the present invention, some embodiments provide
for two or more inverters to be connected in parallel, in an
extremely compact configuration, with efficient use of magnetic
inductor material (thereby reducing cost). These embodiments may
drastically reduce the overall AC filter size and cost, and can
provide a filtered AC output quality suitable for the grid.
[0012] According to one aspect, a power electronics system is
provided that includes a first inverter configured to receive
direct current (DC) power from a power source, a second inverter
configured to receive DC power from the power source, a first
output inductor connected in series to an alternating current (AC)
output of the first inverter, a second output inductor connected in
series to an AC output of the second inverter, a coupling inductor
configured to receive current from the first output inductor and
the second output inductor, and an AC power output to provide
current from the coupling inductor.
[0013] Some embodiments also include a control system configured to
provide a control signal associated with a disturbance frequency,
determine an amplitude of oscillation in an output power of the AC
power output, wherein the oscillation is caused by the disturbance
frequency, detect an islanding condition, if the amplitude of
oscillation is below a threshold, and disconnect the grid from the
AC power output if the islanding condition is detected.
[0014] In some embodiments, the coupling inductor includes a coil
winding around a coupled core and a self-inductance core. In
further embodiments, the coil winding includes a series of
elongated turns.
[0015] According to another aspect, power electronics system is
provided that includes a first multi-phase inverter configured to
receive direct current (DC) power from a power source, a second
multi-phase inverter configured to receive DC power from the power
source, a first plurality of output inductors, each of the first
plurality of output inductors connected in series to an output
phase of the first multi-phase inverter, a second plurality of
output inductors, each of the second plurality of output inductors
connected in series to an output phase of the second multi-phase
inverter, a plurality of coupling inductors, each of the plurality
of coupling inductors configured to receive current from a
respective output inductor of the first plurality of output
inductors and a respective output inductor of the second plurality
of output inductors, and a multi-phase alternating current (AC)
power output to provide current from the plurality of coupling
inductors.
[0016] Some embodiments also include a control system configured to
provide a control signal associated with a disturbance frequency,
determine an amplitude of oscillation in an output power of the AC
power output, wherein the oscillation is caused by the disturbance
frequency, detect an islanding condition, if the amplitude of
oscillation is below a threshold, and disconnect the grid from the
AC power output if the islanding condition is detected.
[0017] In some embodiments, the coupling inductor includes a coil
winding around a coupled core and a self-inductance core. In
further embodiments, the coil winding includes a series of
elongated turns.
[0018] According another aspect, an inductor coil winding is
provided that includes a first terminal, a series of concentric
turns in a first plane, the series of concentric turns leading in
from the first terminal and having a diameter allowing for an
opening within the series of concentric turns, a series of
elongated turns in a second plane, the series of elongated turns
leading in from the series of concentric turns and having a length
greater than the diameter of the series of concentric turns, and
allowing for an opening within the series of elongated turns, and a
second terminal, the second terminal leading out form the series of
elongated turns.
[0019] According to some embodiments, the series of concentric
turns provides main inductance.
[0020] According to some embodiments, the series of elongated turns
provides coupled inductance.
[0021] According to some embodiments, the first terminal is an
input terminal electrically connected to an output of an inverter
to receive current from the inverter.
[0022] Some embodiments also include a self-inductance core in the
opening within the series of concentric turns and a coupled core in
the opening within the series of elongated turns, the coupled core
configured to provide a magnetic coupling to another inductor coil
winding.
[0023] According to another aspect, a filter assembly is provided
that includes a first self-inductance core, a second
self-inductance core, a coupler core, a first plurality of inductor
coil windings, each of the first plurality of inductor coil
windings having a series of first turns around the first
self-inductance core, and a series of second turns around the first
self-inductance core and the coupler core, and a second plurality
of inductor coil windings, each of the second plurality of inductor
coil windings having a series of first turns around the second
self-inductance core, and a series of second turns around the
second self-inductance core and the coupler core.
[0024] In certain embodiments, the first self-inductance core, the
second self-inductance core, and the coupler core each include
three limbs, one limb for each of three phases.
[0025] In some embodiments, the first turns of each of the first
plurality of inductor coil windings are concentric turns and the
first turns of each of the second plurality of inductor coil
windings are concentric turns.
[0026] In some embodiments, the second turns of each of the first
plurality of inductor coil windings are elongated turns and the
second turns of each of the second plurality of inductor coil
windings are elongated turns.
[0027] According to certain embodiments, the first plurality of
inductor coil windings is configured to electrically connect to a
first inverter at a first terminal to receive an alternating
current output from the first inverter and the second plurality of
inductor coil windings is configured to electrically connect to a
second inverter at a second terminal to receive an alternating
current output from the second inverter.
[0028] In some further embodiments, the first plurality of inductor
coil windings is electrically connected to the second plurality of
inductor coil windings at a third terminal configured to provide a
combined alternating current from the first and second
inverter.
[0029] Certain embodiments also include a plurality of thermal
plates interspersed among the first and second plurality of
inductor coil windings and configured to remove thermal energy from
the first and second plurality of inductor coil windings.
[0030] In various embodiments in accordance with principles of the
present invention, a power electronics system comprises a first
inverter configured to receive DC power from a power source, a
second inverter configured to receive DC power from the power
source, a first output inductor connected in series to an output of
the first inverter, a second output inductor connected in series to
an output of the second inverter, a coupling inductor configured to
receive current from the first output inductor and the second
output inductor; and an AC power output.
[0031] In other embodiments consistent with principles of the
invention, a power electronics system comprises a first multi-phase
inverter configured to receive DC power from a power source, a
second multi-phase inverter configured to receive DC power from the
power source, a first plurality of output inductors, each output
inductor connected in series to an output phase of the first
multi-phase inverter, a second plurality of output inductors, each
output inductor connected in series to an output phase of the
second multi-phase inverter, a plurality of coupling inductors
configured to receive current from an output inductor of the first
plurality of output inductors and a output inductor of the second
plurality of output inductors having a corresponding phase, and a
multi-phase AC power output.
[0032] Other embodiments of the power electronic systems further
comprise a control system configured to provide a control signal
associated with a disturbance frequency, determine an amplitude of
oscillation in an output power of the AC power output, wherein the
oscillation is caused by the disturbance frequency, detect an
islanding condition, if the amplitude of oscillation is below a
threshold, and disconnect the grid from the AC power output if the
islanding condition is detected.
[0033] In accordance with principles of the invention, an inductor
coil winding comprises an input with a series of concentric turns
in a first plane, the concentric turns having a diameter allowing
for an opening within the series of concentric turns that provide
main inductance to a filter system. The concentric turns lead into
a series of elongated turns in a second plane, the series of
elongated turns leading in from the series of concentric turns and
having a length greater than the diameter of the concentric turns
of the series of concentric turns, and allowing for an opening
within the series of elongated turns. The opening within the series
of elongated turns being larger than the opening of the within the
series of concentric turns to accommodate for a shared inductance.
The series of elongated turns leads to an output of the inductor
coil.
[0034] Other embodiments of the present invention provide a filter
assembly comprising a first self-inductance core, a second
self-inductance core, and a coupler core. The embodiments further
comprise a first plurality of inductor coil windings, each inductor
coil winding having an input leading to a series of concentric
turns in a first plane, the concentric turns having a diameter
allowing for an opening within the series of concentric turns. The
concentric turns lead to a series of elongated turns in a second
plane, the series of elongated turns leading in from the series of
concentric turns and having a length greater than the diameter of
the concentric turns of the series of concentric turns, and
allowing for an opening within the series of elongated turns an
output. The first plurality of inductor coil windings are arranged
such that the opening within the series of concentric turns of the
inductor coil windings accommodate the first self-inductance core,
and the opening within the series of elongated turns of the
inductor coil windings accommodate the first self-inductance core
and the coupler core. A second group of similar inductor coils are
arranged such that the opening within the series of concentric
turns of the inductor coil windings accommodate the second
self-inductance core, and the opening within the series of
elongated turns of the inductor coil windings accommodate the
second self-inductance core and the coupler core. In embodiments
consistent with principles of the present invention,
self-inductance cores and a coupled core of a filter assembly may
be provided for three phases in a fully integrated
implementation.
[0035] Still other aspects, examples, and advantages are discussed
in detail below. Embodiments disclosed herein may be combined with
other embodiments in any manner consistent with at least one of the
principles disclosed herein, and references to "an embodiment,"
"some embodiments," "an alternate embodiment," "various
embodiments," "one embodiment" or the like are not necessarily
mutually exclusive and are intended to indicate that a particular
feature, structure, or characteristic described may be included in
at least one embodiment. The appearances of such terms herein are
not necessarily all referring to the same embodiment. Various
aspects and embodiments described herein may include means for
performing any of the described methods or functions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Various aspects of at least one example are discussed below
with reference to the accompanying figures, which are not intended
to be drawn to scale. The figures are included to provide
illustration and a further understanding of the various aspects and
examples, and are incorporated in and constitute a part of this
specification, but are not intended as a definition of the limits
of the invention. In the figures, identical or nearly identical
components illustrated in various figures may be represented by
like numerals. For purposes of clarity, not every component may be
labeled in every figure. In the figures:
[0037] FIG. 1 is a schematic diagram of single phase power
conversion bridge with an AC filter;
[0038] FIG. 2 is a schematic diagram of two three-phase power
bridges connected in parallel employing output AC filters;
[0039] FIG. 3 is a schematic diagram of two single phase power
conversion bridges coupled via a coupling inductor with a shared
output AC filter;
[0040] FIG. 4 is a schematic diagram of two single phase power
conversion bridges, with each bridge having an output AC filter,
connected in parallel and coupled via a coupling inductor in
accordance with principles of the invention;
[0041] FIG. 5 is a schematic diagram of two three phase power
conversion bridges, with each phase of each bridge having an output
AC filter, connected in parallel with each phase coupled via
coupling inductors in accordance with principles of the
invention;
[0042] FIG. 6 is a perspective view of an example inductor coil in
accordance with principles of the invention;
[0043] FIG. 7 is a perspective view of an example filter assembly
for a single phase output of an inverter pair with connections to
each inverter bridge in accordance with principles of the
invention;
[0044] FIG. 8 is a perspective view of an example 3-phase inductor
assembly in accordance with principles of the invention;
[0045] FIG. 9 is a top view of the example 3-phase inductor
assembly of FIG. 8;
[0046] FIG. 10 is a perspective view of the example 3-phase
inductor assembly of FIG. 8 including example integrated cooling
components; and
[0047] FIG. 11 is a perspective view of the example cooling
components of FIG. 10, apart from the example 3-phase inductor
assembly.
DETAILED DESCRIPTION
[0048] Aspects and embodiments provide inductor arrangements to
couple two or more inverters in parallel, in an extremely compact
configuration, with efficient use of magnetic inductor material
(thereby reducing cost). Embodiments in accordance with principles
of the invention can drastically reduce the overall AC filter size
and cost, and can provide a filtered AC output quality suitable for
the grid. A cooling system may be mechanically integrated into the
compact AC filter module for thermal management in some
embodiments.
[0049] It is to be appreciated that examples of the methods,
systems, and apparatuses discussed herein are not limited in
application to the details of construction and the arrangement of
components set forth in the following description or illustrated in
the accompanying drawings. The methods, systems, and apparatuses
are capable of implementation in other examples and of being
practiced or of being carried out in various ways. Examples of
specific implementations are provided herein for illustrative
purposes only and are not intended to be limiting. Examples
disclosed herein may be combined with other examples in any manner
consistent with at least one of the principles disclosed herein,
and references to "an example," "some examples," "an alternate
example," "various examples," "one example" or the like are not
necessarily mutually exclusive and are intended to indicate that a
particular feature, structure, or characteristic described may be
included in at least one example. The appearances of such terms
herein are not necessarily all referring to the same example. Also,
the phraseology and terminology used herein is for the purpose of
description and should not be regarded as limiting. The use herein
of "including," "comprising," "having," "containing," "involving,"
and variations thereof is meant to encompass the items listed
thereafter and equivalents thereof as well as additional items.
References to "or" may be construed as inclusive so that any terms
described using "or" may indicate any of a single, more than one,
and all of the described terms. Any references to front and back,
left and right, top and bottom, upper and lower, and vertical and
horizontal are intended for convenience of description, not to
limit the present systems and methods or their components to any
one positional or spatial orientation.
[0050] In an embodiment according to principles of the present
invention, FIG. 4 illustrates an example of two single-phase
inverters 410, 420 (bridge 1 and bridge 2) connected in parallel,
each inverter 410, 420 having a corresponding output inductor 412,
422 (L1 and L2), respectively providing self-inductance. The
outputs are then magnetically coupled via a coupled inductor 430
(L.sub.coupled). With this arrangement, there is half as much
current passing through each of inductors L1 and L2, as there would
be passing through L.sub.filter in the conventional filter
arrangement of FIG. 3. Thus in the arrangement of FIG. 4 losses may
be approximately halved relative to FIG. 3, for the same overall
output current, reducing the amount of heat generated and providing
more efficient power conversion.
[0051] In other embodiments according to principles of the present
invention, FIG. 5 shows a solar inverter system 500 of similar
arrangement to FIG. 4, but for two 3-phase inverters 510, 520
(bridges) connected in parallel. Corresponding phases (A, B, C)
from each of the inverters 510, 520 are coupled via a coupled
inductor 530. In some embodiments, the inverters 510, 520 of solar
inverter system 500 may be DC-to-AC inverters (or "power conversion
bridges"), each rated for up to 1 MW (as 2 MW of power cannot be
handled by a single inverter). Each inverter produces a 3-phase
output. The two bridges are connected in parallel and the 3-phase
outputs of the 2 bridges are interleaved (180.degree. out of phase
relative to each other). The inverters 510, 520 on their own may
produce an unacceptably rough AC power waveform. Therefore, an AC
filter module 540, consisting of inductor and capacitor components,
is used to smooth the waveform.
[0052] To handle the level of power and power quality requirements,
an AC filter would conventionally be large and costly. For example,
a classical approach to this problem, even after much optimization,
requires inductors that cost approximately 9% of the system cost
and capacitors that are approximately 2% of the system cost. The
inductor used in the classical approach also produces significant
energy losses (around 4 kW), which inflates the required cooling
system and adds additional cost and volume to the system.
[0053] As mentioned above, switching of the two 3-phase inverters
510, 520 in the example system 500 may be interleaved, thereby
doubling the switching frequency. This essentially doubles the
frequency seen by the inductors and therefore the amount of
filtering required is reduced. In various embodiments, for each of
the two inverters 510, 520, there is a core for each AC phase that
provides self-inductance 550. For each AC phase, there is also a
third core that provides a coupled inductance 530 between the
inverters 510, 520 (for each phase). Each of the self-inductors 550
is positioned between each inverter 510, 520 and the respective
coupled inductor 530, per phase.
[0054] The AC filter module 540 thereby includes coupling between
inverters and in some implementations also includes coupling
between phases.
[0055] As discussed above, a solar inverter system may comprise two
3-phase inverters connected in parallel, but a similar approach
consistent with principles of the invention can be taken with more
than two 3-phase inverters and/or with two or more single phase or
other multi-phase inverters.
[0056] The above-described electrical configurations can be
implemented in many different embodiments, not limited to those
described in further detail below.
[0057] In embodiments according to principles of the invention, the
mechanical design of an AC filter module has multiple novel aspects
that allow the technology to be practically and commercially
realized. Overall the coupled inductor is 1/3 the total mass and
1/2 the volume of the classical inductors when designed for
equivalent losses. This results in a cost reduction of the inductor
components. Additional reductions in system cost can be obtained
through mechanical integration of cooling, structural features, and
size reduction.
[0058] In conventional inductor systems, the coils or windings are
wrapped around a central core (often a straight cylindrical rod or
a continuous loop or ring, doughnut). Embodiments of the present
invention involve a unique winding geometry that is particularly
suited for use in embodiments of an AC filter module. An example of
such a winding is shown in FIG. 6.
[0059] The conductive material of an example winding 600 (e.g.
copper or aluminum) may have a rectangular cross-section as shown.
In various embodiments, the conductive material may be one or more
strands, and may be multi-strand transpose wire in certain
embodiments, e.g., to achieve additional reduction in losses. The
winding 600 is shaped to form a series of concentric turns 610 in a
first plane for the main inductance, then transitions to a second
plane (parallel to the first) and is formed in to a series of
concentric elongated turns 620. The circular opening 612
accommodates a self-inductor core and the elongated opening 622
accommodates a coupled inductor core. The coupled inductor turns
620 also contribute to the self-inductance. In certain embodiments,
the winding 600 may be generally coated in an electrically
insulating material, such as a plastic, except for the terminals
630.
[0060] Various embodiments of winding geometry, with respect to the
example illustrated in FIG. 6, offer particular advantages. They
are designed to integrate the self and coupled inductor cores, and
are designed to stack in a space-efficient manner, with the main
inductance turns of one winding in the same plane as the coupled
inductance turns of an adjacent winding. The stacks of windings can
also be packed together tightly side-by-side because of their
quasi-rectangular shape. The flat/planar structure of the windings
also allows good thermal contact with thermal plates, such as
liquid-cooled thermal plates, which can be interposed between
stacked windings, for cooling the assembly (as described in more
detail below). Input and output terminals can be conveniently
located at almost any desired location around the perimeter of the
winding. In conventional windings, one terminal is often located
inside the winding where it is less accessible.
[0061] Variations on the above winding geometry or quite different
winding geometries can be used in various implementations of the
present invention. For example, in some variations on the above
winding geometry, the cross-section of the winding may be
non-rectangular. The number of turns for the main inductance and
the coupled inductance can be varied. The shape of the windings
need not be as shown. The various winding turns need not be in two
planes as shown, e.g., they may be in a single plane or in multiple
planes. In other winding geometries, the winding turns may not have
a planar-like configuration like the winding of FIG. 6. They may,
for example, have a helical structure or a more conventional
geometry etc.
[0062] FIG. 7 shows an example AC filter assembly 700 for
single-phase output of an inverter pair with connections to each
inverter bridge. The assembly comprises 16 windings similar to
those shown in FIG. 6 (with circular openings to accommodate the
cores), stacked in two side-by-side stacks of 8. Self-inductance
turns of the 8 windings connected to bridge 1 are wound around
self-inductance core 710. Similarly, self-inductance turns of the 8
windings connected to bridge 2 are wound around self-inductance
core 720. The coupled inductor turns of all 16 windings are wound
around the coupler core 730.
[0063] The physically interleaved windings stacked on each core are
positioned to cancel what could otherwise be massive losses in the
coupler core. There are multiple windings in parallel surrounding
the various cores, which tends to reduce or minimize current
crowding that can occur due to proximity of the windings to the
magnetic material (cores) and other conductors (windings).
[0064] For a pair of inverters with 3-phase (interleaved) output,
three separate mechanical assemblies like that shown in FIG. 7 may
be used. In certain embodiments, however, the windings and
inductors for all three phases of two or more inverters may be
integrated into a single, compact assembly. An example of such an
assembly is illustrated in perspective view in FIG. 8. A top view
of the same example assembly is illustrated in FIG. 9.
[0065] In the example of FIG. 8, the 1st and 5th limbs of each core
are optional, depending on application, and/or the yoke of one or
more of the cores may be removed, e.g., in an air core design. For
example, a yokeless design for the self-inductor cores is enabled
due to the core material magnetic properties and the arrangement of
the cores. Such can reduce the core material mass and cost
significantly.
[0066] The self-inductor cores and coupler cores can be made of any
suitable magnetic material. In some embodiments the self-inductor
cores are powdered iron or powdered iron alloys, and the coupler
cores are pillars or rods made of an amorphous material, with the
perimeter constructed from Cold Rolled Grain Oriented laminated
steel. Such a composition and construction can improve power losses
and dissipation in the magnetic material.
[0067] FIG. 10 shows an example AC filter module for a pair of
interleaved 3-phase inverters comprising the assembly of FIG. 8
integrated with a liquid cooling system rack (shown individually in
FIG. 11 below). For example, aluminum thermal plates with internal
flow channels may be interposed between the phase A/phase B
windings and between the phase B/phase C windings, and above the
phase A windings and below the phase C windings. Liquid coolant
supplied via a main coolant inlet manifold and coolant lines, may
be circulated through the plates, in parallel, to cool the
electrical and magnetic components, and then directed via
corresponding outlet lines and an outlet manifold to an air-cooled
heat exchanger. A pair of solid aluminum heat spreader plates may
be included to help dissipate heat generated deep inside the
module, near the coupler core, for example.
[0068] As mentioned above, in the assemblies shown in FIGS. 8-10,
windings are tightly packed close together, reducing the size of
the cores and the amount of magnetic material that is needed, and
thereby reducing losses. Magnetic material in the pairs of phases
may be shared in some embodiments. Embodiments of an inductor
assembly, such as the example assembly shown in FIGS. 8-10,
including a compact arrangement of inductor windings for three
phases (e.g., as compared to three separate assemblies like that
assembly shown in FIG. 7), may provide improved compensation and
cancellation of noise between coils of the assembly.
[0069] In some embodiments, an assembly or module as shown in FIGS.
8-10 may be potted, e.g., in high temperature, thermally
conductive, electrically insulating material.
[0070] FIG. 11 illustrates the example cooling system components of
the module shown in FIG. 10. The example cooling system includes
liquid coolant that is distributed through coolant lines to various
thermal plates to remove heat generated from the inductor coils and
electrical components.
[0071] Embodiments of the present invention provide a number of
advantages, including the reduction of an AC filter size and cost,
through use of a compact configuration, with efficient use of
magnetic inductor and conductor materials. Examples and embodiments
of AC filter/inductor assemblies described herein have the effect
of providing an increased power density. In addition, they may
provide reduced losses due to lower current from the self-inductors
being "upstream" of the coupled inductor, and reduced losses due to
the interleaved physical arrangement of the windings on the coupler
cores. The reduced losses result in less heat generation, and
reduced requirement for cooling. The design of the cores and
windings provide for simple assembly, supporting manufacturing
feasibility. Further, the design allows for the use of liquid
cooling of a filter/inductor, which is generally more
cost-efficient than air-cooling, and allows for greater control or
optimization of the degree of thermal transfer.
[0072] In various embodiments, windings, arrangements, assemblies,
and modules in accord with aspects of those illustrated in FIGS.
4-10 may be beneficially applied to provide electrical filtering to
any of numerous power converter applications, including those of
solar inverters as described herein, but also of DC-to-DC
converters, AC-to-DC converters, and other DC-to-AC converters for
applications other than solar. Such arrangements may provide
compact and efficient filtering to remove high frequency components
from an electrical waveform at inputs and/or outputs of various
power converters. Such arrangements may also be beneficially
adapted to differing scale of power conversion equipment than those
discussed herein. For example, power factor correction (PFC)
equipment, uninterruptible power supply (UPS) equipment, and the
like.
[0073] Having described above several aspects of at least one
embodiment, it is to be appreciated various alterations,
modifications, and improvements will readily occur to those skilled
in the art. Such alterations, modifications, and improvements are
intended to be part of this disclosure, and are intended to be
within the spirit and scope of the invention. Accordingly, the
foregoing description and drawings are by way of example only, and
the scope of the invention should be determined from proper
construction of the appended claims, and their equivalents.
* * * * *