U.S. patent application number 15/948380 was filed with the patent office on 2018-08-09 for converter topologies and control.
This patent application is currently assigned to SunPower Corporation. The applicant listed for this patent is SunPower Corporation. Invention is credited to Patrick L. Chapman, Jonathan List Ehlmann, Fernando Rodriguez.
Application Number | 20180226899 15/948380 |
Document ID | / |
Family ID | 60785361 |
Filed Date | 2018-08-09 |
United States Patent
Application |
20180226899 |
Kind Code |
A1 |
Chapman; Patrick L. ; et
al. |
August 9, 2018 |
CONVERTER TOPOLOGIES AND CONTROL
Abstract
Systems, methods, and articles of manufacture are provided
wherein inverter topologies and inverter control employ primary and
secondary windings with a half-bridge circuit and an unfolding
bridge circuit positioned between the second winding and an AC
grid. Certain topologies may employ control circuits for
controlling the bridges suitable for a phase angle of the AC
grid.
Inventors: |
Chapman; Patrick L.;
(Austin, TX) ; Ehlmann; Jonathan List; (Austin,
TX) ; Rodriguez; Fernando; (Austin, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SunPower Corporation |
San Jose |
CA |
US |
|
|
Assignee: |
SunPower Corporation
San Jose
CA
|
Family ID: |
60785361 |
Appl. No.: |
15/948380 |
Filed: |
April 9, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15199239 |
Jun 30, 2016 |
9954462 |
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15948380 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02M 2001/007 20130101;
H02M 7/5387 20130101; Y02E 10/50 20130101; H02M 1/15 20130101; H02M
7/4807 20130101; Y02B 70/10 20130101; H02M 5/458 20130101 |
International
Class: |
H02M 7/48 20060101
H02M007/48; H02M 5/458 20060101 H02M005/458; H02M 7/5387 20060101
H02M007/5387; H02M 1/15 20060101 H02M001/15 |
Claims
1. A multi-port inverter for converting an input direct current
(DC) waveform from a DC source to an output alternating current
(AC) waveform for delivery to an AC grid, the inverter comprising:
a transformer; a DC-AC inverter electrically coupled to a first
winding of the transformer, wherein the DC-AC inverter is adapted
to convert the input DC waveform to an AC waveform delivered to the
transformer at the first winding; an AC-AC converter electrically
coupled to a second winding of the transformer, wherein the AC-AC
converter is adapted to convert an AC waveform received at the
second winding of the transformer to the output AC waveform having
a grid frequency of the AC grid, the AC-AC converter comprising: a
first set of electrical switches electrically coupled to a first
terminal of the second winding of the transformer; a capacitor
divider electrically coupled with the first set of electrical
switches and to a second terminal of the second winding of the
transformer; a second set of electrical switches electrically
coupled to the AC grid; a first capacitor electrically coupled
across the first set of electrical switches; and a sensor
electrically coupled between the first capacitor and the second set
of electrical switches, the sensor sensing the AC grid current; and
an active filter coupled to a winding of the transformer, wherein
the active filter is adapted to sink and source power with one or
more energy storage devices based on a mismatch in power between
the DC source and the AC grid.
2. The inverter of claim 1, wherein: the first set of electrical
switches comprises a half-bridge circuit; and the second set of
electrical switches comprises an unfolding bridge circuit.
3. The inverter of claim 2, wherein: the capacitor divider
comprises second and third capacitors having first terminals
electrically coupled at a first node to a first terminal of the
second winding of the transformer; the half-bridge circuit
comprises: a first electrical switch having a first terminal
electrically coupled at a second node to a second terminal of the
second capacitor and a second terminal electrically coupled at a
third node to a first terminal of a first inductor, the second
terminal of the inductor electrically coupled to the second
terminal of the second winding of the transformer; and a second
electrical switch having a first terminal electrically coupled at a
fourth node to a second terminal of the third capacitor and a
second terminal electrically coupled at the third node to the first
terminal of the inductor; the first capacitor is electrically
coupled between the second and fourth nodes; and the unfolding
bridge circuit comprises: a first pair of series-coupled electrical
switches electrically coupled to each other at a fifth node; and a
second pair of series-coupled electrical switches electrically
coupled to each other at a sixth node, the first pair and second
pair electrically coupled in parallel at the seventh node and at an
eighth node, and the eighth node electrically coupled to the second
node; a resistor is electrically coupled between the fourth node
and seventh nodes, and the fifth and sixth nodes are electrically
coupled to first and second terminals, respectively, of the AC
grid.
4. The inverter of claim 1, further comprising an EMI filter having
components electrically coupled between the unfolding bridge
circuit and the AC grid.
5. The inverter of claim 1, further comprising an EMI filter having
components electrically coupled between the half-bridge circuit and
the unfolding bridge circuit.
6. The inverter of claim 1, wherein the one or more energy storage
devices consists of a capacitor and wherein the sensor is a sensing
resistor.
7. The inverter of claim 1, wherein the DC source comprises a
photovoltaic module.
8. The inverter of claim 1, further comprising a controller having
a processor and a memory comprising a plurality of instructions
stored thereon and executable by the processor, wherein: the second
set of switches comprises an unfolding bridge circuit comprising
first, second, third, and fourth electrical switches; and in
response to execution by the processor, the plurality of
instructions cause the inverter to control the switching cycles of
the second set of switches, whereby: when a voltage across the AC
grid is substantially positive during a first period, the first and
fourth electrical switches are on and the second and third
electrical switches are off; when the voltage across the AC grid is
substantially negative during a second period, the first and fourth
electrical switches are off and the second and third electrical
switches are on; and during a third period comprising a blanking
time period between the first and second periods when the voltage
across the AC grid is approximately zero, the first, second, third,
and fourth electrical switches are off.
9. A multi-port inverter for converting an input direct current
(DC) waveform from a DC source to an output alternating current
(AC) waveform for delivery to an AC grid, the inverter comprising:
an AC-AC converter electrically coupled through a transformer to a
DC-AC inverter electrically coupled to the DC source, the AC-AC
converter comprising: a half-bridge circuit electrically coupled to
a winding of the transformer; and an unfolding bridge circuit
electrically coupled between the half-bridge circuit and the AC
grid; wherein the AC-AC converter is adapted to convert an AC
waveform received from the transformer to output the AC waveform
having a grid frequency of the AC grid; and a controller having a
processor and a memory wherein the controller is adapted to control
the switching cycles of electrical switches of the unfolding bridge
circuit, whereby: when a voltage across the AC grid is
substantially positive during a first period, a first set of
electrical switches is on and a second set of electrical switches
is off; when the voltage across the AC grid is substantially
negative during a second period, the first set of electrical
switches is off and the second set of electrical switches is on;
and during a third period comprising a blanking time period between
the first and second periods when the voltage across the AC grid is
approximately zero, the first and second, sets of electrical
switches are off.
10. The inverter of claim 9, further comprising an EMI filter
having components electrically coupled between the unfolding bridge
circuit and the AC grid.
11. The inverter of claim 9, further comprising an EMI filter
having components electrically coupled between the half-bridge
circuit and the unfolding bridge circuit.
12. A multi-port inverter for converting an input direct current
(DC) waveform from a DC source to an output alternating current
(AC) waveform for delivery to an AC grid, the inverter comprising:
a transformer; a DC-AC inverter electrically coupled to a first
winding of the transformer, wherein the DC-AC inverter is adapted
to convert the input DC waveform to an AC waveform delivered to the
transformer at the first winding; an AC-AC converter electrically
coupled to a second winding of the transformer and adapted to
convert the AC waveform received at the second winding of the
transformer to the output AC waveform having a grid frequency of
the AC grid, the AC-AC converter comprising: a half-bridge circuit
electrically coupled to the first winding of the transformer; and
an unfolding bridge circuit electrically coupled between the
half-bridge circuit and the AC grid; an active filter electrically
coupled to a winding of the transformer wherein the active filter
is adapted to sink and source power with one or more energy storage
devices based on a mismatch in power between the DC source and the
AC grid; and a controller electrically coupled to receive an AC
voltage from the AC grid and having an output signal comprising an
estimate of the phase angle of the AC voltage, wherein the
controller, in response to the estimated phase angle of the AC
voltage, controls the switching cycles of a plurality of electrical
switches of the AC-AC converter.
13. The inverter of claim 12, wherein: the unfolding bridge circuit
comprises first, second, third, and fourth electrical switches; and
in response to the estimated phase angle of the AC voltage, the
controller controls the switching cycles of the first, second,
third, and fourth electrical switches, whereby: when a voltage
across the AC grid is substantially positive during a first period,
the first and fourth electrical switches are on and the second and
third electrical switches are off; when the voltage across the AC
grid is substantially negative during a second period, the first
and fourth electrical switches are off and the second and third
electrical switches are on; and during a third period comprising a
blanking time period between the first and second periods when the
voltage across the AC grid is approximately zero, the first,
second, third, and fourth electrical switches are off.
14. The inverter of claim 12, further comprising an electromagnetic
interference (EMI) filter electrically coupled between the
unfolding bridge circuit and the AC grid circuit.
15. The inverter of claim 12, further comprising an electromagnetic
interference (EMI) filter electrically coupled between the
half-bridge circuit and the unfolding bridge circuit.
16. The inverter of claim 12, wherein the DC source comprises a
photovoltaic module.
17. A method for controlling operation of electrical switches of an
unfolding bridge in an inverter configured to convert an input
direct current (DC) waveform from a DC source to an output
alternating current (AC) waveform for delivery to an AC grid,
wherein the inverter comprises a transformer and a DC-AC inverter
electrically coupled to the transformer, an active filter
electrically coupled to the transformer, and an AC-AC converter,
wherein the AC-AC converter comprises a half-bridge circuit
electrically coupled to the transformer and an unfolding bridge
circuit electrically coupled between the half-bridge circuit and
the AC grid, the method comprising the steps of: determining a
phase of the AC grid voltage; and generating a set of signals for
actuation of the electrical switches of the unfolding bridge
circuit based on the determined phase, whereby: when a voltage
across the AC grid is positive during a first period, first and
fourth electrical switches are on and second and third electrical
switches are off; when the voltage across the AC grid is negative
during a second period, the first and fourth electrical switches
are off and the second and third electrical switches are on; and
during a third period comprising a blanking time period between the
first and second periods when the voltage across the AC grid is
approximately zero, the first, second, third, and fourth electrical
switches are off.
18. The method of claim 17, wherein the determining and generating
steps are performed in a controller electrically coupled to the
AC-AC converter by one or more processors executing instructions
stored in memory.
19. The method of claim 17 further comprising: providing an active
filter electrically coupled to a winding of the transformer wherein
the active filter is adapted to sink and source power with one or
more energy storage devices based on a mismatch in power between
the DC source and the AC grid.
20. The method of claim 18 wherein the one or more processors
generates the set signals for actuation of the electrical switches
based on multiple determined phase shifts of the AC grid voltage.
Description
CROSS-REFERENCE TO COMMONLY-OWNED CO-PENDING U.S. PATENT
APPLICATIONS
[0001] The present application is related to commonly-owned
co-pending U.S. patent application Ser. No. 15/080,110 entitled
"DC-TO-AC INVERTER TOPOLOGIES" by Fernando Rodriguez, Hengsi Qin
and Patrick Chapman, which was filed on Mar. ______, 2016 and
claims priority under 35 U.S.C. .sctn. 119(e) to U.S. Provisional
Patent Application Ser. No. 62/138,184, entitled "DC-TO-AC INVERTER
TOPOLOGIES" by Patrick Chapman, which was filed on Mar. 25, 2015.
The entirety of both applications are hereby fully incorporated,
into this application, by reference.
TECHNICAL FIELD
[0002] The present disclosure relates, generally, to power
converters for converting direct current (DC) power to alternating
current (AC) power and, more particularly, to converter topologies
and control techniques.
BACKGROUND
[0003] Power inverters convert a DC power to an AC power. For
example, some power inverters are configured to convert a DC power
to an AC power suitable for supplying energy to an AC grid and, in
some cases, an AC load that may or may not be coupled to the AC
grid. One particular application for such power inverters is the
conversion of DC power generated by an alternative energy source,
such as photovoltaic cells ("PV cells" or "solar cells"); fuel
cells; DC wind turbines; DC water turbines; and other DC power
sources, to a single-phase AC power for delivery to the AC grid at
the grid frequency. The amount of power that can be delivered by
certain alternative energy sources, such as PV cells, may vary in
magnitude over time due to temporal variations in operating
conditions. For example, the output of a typical PV cell will vary
as a function of variations in sunlight intensity, angle of
incidence of sunlight, ambient temperature and other factors.
[0004] In a typical photovoltaic power system, an inverter may be
associated with one or more solar cell panels. For example, some
systems include strings of solar cell panels that deliver a
relatively high, combined voltage (e.g., nominal 450 V) to a
single, large inverter. Alternatively, in other systems such as a
distributed photovoltaic power system, an inverter may be
associated with each solar cell panel. In such systems, the solar
cell panels are typically small with relatively low voltage (e.g.,
25 V). The inverter may be placed in close proximity to the
associated solar cell panel to increase the conversion efficiency
of the overall system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a simplified block diagram as may be employed in
embodiments of a system for converting DC power to AC power;
[0006] FIG. 2 is a simplified block diagram of an AC photovoltaic
module of the system of FIG. 1;
[0007] FIG. 3 is a simplified block diagram of an inverter of the
system of FIG. 1 or as may otherwise be employed in
embodiments;
[0008] FIG. 4 is a simplified electrical schematic of an embodiment
of the inverter of FIG. 3 or as may otherwise be employed in
embodiments;
[0009] FIG. 5 is a simplified electrical schematic of the AC-AC
converter of FIG. 3 or as may otherwise be employed in
embodiments;
[0010] FIG. 6 is a simplified electrical schematic of available
topologies of the AC-AC converter of FIG. 3 or as may otherwise be
employed in embodiments;
[0011] FIG. 7 illustrates a module configured for estimating the
grid phase angle from grid voltage as may be employed in
embodiments;
[0012] FIG. 8A is a simplified electrical schematic identifying the
four switches in an unfolding bridge that may be used in the
inverter of the system of FIG. 1 as well as other embodiments;
[0013] FIG. 8B is a representative plot of the grid voltage
relative to the grid phase angle illustrating the timing of pairs
of switches as they are turned on and off as may be employed in
embodiments; and
[0014] FIG. 9 is a simplified flow diagram of an embodiment of a
method for controlling the inverter of FIG. 1 or may otherwise be
employed in embodiments.
DETAILED DESCRIPTION
[0015] While the concepts of the present disclosure are susceptible
to various modifications and alternative forms, specific exemplary
embodiments thereof have been shown by way of example in the
drawings and will herein be described in detail. It should be
understood, however, that there is no intent to limit the concepts
of the present disclosure to the particular forms disclosed, but on
the contrary, the intention is to cover all modifications,
equivalents, and alternatives falling within the spirit and scope
of the invention as defined by the appended claims.
[0016] References in the specification to "one embodiment", "an
embodiment", "an example embodiment", etc., indicate that the
embodiment described may include a particular feature, structure,
or characteristic, but every embodiment may not necessarily include
the particular feature, structure, or characteristic. Moreover,
such phrases are not necessarily referring to the same embodiment.
Further, when a particular feature, structure, or characteristic is
described in connection with an embodiment, it is submitted that it
is within the knowledge of one skilled in the art to effect such
feature, structure, or characteristic in connection with other
embodiments whether or not explicitly described.
[0017] Some embodiments of the disclosure, or portions thereof, may
be implemented in hardware, firmware, software, or any combination
thereof. Embodiments of the disclosure may also be implemented as
instructions stored on a tangible, machine-readable storage medium,
which may be read and executed by one or more processors. A
machine-readable medium may include any mechanism for storing or
transmitting information in a form readable by a machine (e.g., a
computing device). For example, a machine-readable medium may
include read only memory (ROM); random access memory (RAM);
magnetic disk storage media; optical storage media; flash memory
devices; and others.
[0018] This specification includes references to "one embodiment"
or "an embodiment." The appearances of the phrases "in one
embodiment" or "in an embodiment" do not necessarily refer to the
same embodiment. Particular features, structures, or
characteristics may be combined in any suitable manner consistent
with this disclosure.
[0019] Terminology. The following paragraphs provide definitions
and/or context for terms found in this disclosure (including the
appended claims):
[0020] "Comprising." This term is open-ended. As used in the
appended claims, this term does not foreclose additional structure
or steps.
[0021] "Configured To." Various units or components may be
described or claimed as "configured to" perform a task or tasks. In
such contexts, "configured to" is used to connote structure by
indicating that the units/components include structure that
performs those task or tasks during operation. As such, the
unit/component can be said to be configured to perform the task
even when the specified unit/component is not currently operational
(e.g., is not on/active). Reciting that a unit/circuit/component is
"configured to" perform one or more tasks is expressly intended not
to invoke 35 U.S.C. .sctn. 112, sixth paragraph, for that
unit/component.
[0022] "First," "Second," etc. As used herein, these terms are used
as labels for nouns that they precede, and do not imply any type of
ordering (e.g., spatial, temporal, logical, etc.).
[0023] "Based On." As used herein, this term is used to describe
one or more factors that affect a determination. This term does not
foreclose additional factors that may affect a determination. That
is, a determination may be solely based on those factors or based,
at least in part, on those factors. Consider the phrase "determine
A based on B." While B may be a factor that affects the
determination of A, such a phrase does not foreclose the
determination of A from also being based on C. In other instances,
A may be determined based solely on B.
[0024] "Coupled"--The following description refers to elements or
nodes or features being "coupled" together. As used herein, unless
expressly stated otherwise, "coupled" means that one
element/node/feature is directly or indirectly joined to (or
directly or indirectly communicates with) another
element/node/feature, and not necessarily mechanically.
[0025] "Inhibit"--As used herein, inhibit is used to describe a
reducing or minimizing effect. When a component or feature is
described as inhibiting an action, motion, or condition it may
completely prevent the result or outcome or future state
completely. Additionally, "inhibit" can also refer to a reduction
or lessening of the outcome, performance, and/or effect which might
otherwise occur. Accordingly, when a component, element, or feature
is referred to as inhibiting a result or state, it need not
completely prevent or eliminate the result or state.
[0026] In addition, certain terminology may also be used in the
following description for the purpose of reference only, and thus
are not intended to be limiting. For example, terms such as
"upper", "lower", "above", and "below" refer to directions in the
drawings to which reference is made. Terms such as "front", "back",
"rear", "side", "outboard", and "inboard" describe the orientation
and/or location of portions of the component within a consistent
but arbitrary frame of reference which is made clear by reference
to the text and the associated drawings describing the component
under discussion. Such terminology may include the words
specifically mentioned above, derivatives thereof, and words of
similar import.
[0027] In this description, numerous specific details are set
forth, such as specific operations, in order to provide a thorough
understanding of embodiments of the present disclosure. It will be
apparent to one skilled in the art that embodiments of the present
disclosure may be practiced without these specific details. In
other instances, well-known techniques are not described in detail
in order to not unnecessarily obscure embodiments of the present
disclosure.
[0028] Embodiments may comprise a multi-port inverter for
converting an input direct current (DC) waveform from a DC source
to an output alternating current (AC) waveform for delivery to an
AC grid may include a transformer that includes a first winding and
at least a second winding. The inverter may further include a DC-AC
inverter electrically coupled to the first winding of the
transformer, an AC-AC converter electrically coupled to the second
winding of the transformer, and an active filter electrically
coupled to a second winding of the transformer. The DC-AC inverter
may be adapted to convert the input DC waveform to an AC waveform
delivered to the transformer at the first winding. The AC-AC
converter may be adapted to convert an AC waveform received at the
second winding of the transformer to the output AC waveform having
a grid frequency of the AC grid. The active filter may be adapted
to sink and source power with one or more energy storage devices
based on a mismatch in power between the DC source and the AC
grid.
[0029] The AC-AC converter may include a first set of electrical
switches electrically coupled to a first terminal of the second
winding of the transformer, a capacitor divider electrically
coupled with the first set of electrical switches and to a second
terminal of the second winding of the transformer, a second set of
electrical switches electrically coupled to the AC grid, a first
capacitor electrically coupled across the first set of electrical
switches, and a resistor electrically coupled between the first
capacitor and the second set of electrical switches.
[0030] Embodiments may also comprise a multi-port inverter for
converting an input direct current (DC) waveform from a DC source
to an output alternating current (AC) waveform for delivery to an
AC grid. This topology may include an AC-AC converter electrically
coupled through a transformer to a DC-AC inverter electrically
coupled to the DC source adapted to convert an AC waveform received
from the transformer to output the AC waveform having a grid
frequency of the AC grid. The AC-AC converter may include a
half-bridge circuit electrically coupled to the transformer and an
unfolding bridge circuit electrically coupled between the
half-bridge circuit and the AC grid. The inverter may also include
a controller having a processor and a memory wherein the controller
is adapted to control the switching cycles of electrical switches
of the unfolding bridge circuit. These cycles may trigger the
switches such that when a voltage across the AC grid is
substantially positive during a first period, a first set of
electrical switches is on and a second set of electrical switches
is off. The cycle may also trigger the switches such that when the
voltage across the AC grid is substantially negative during a
second period, the first set of electrical switches is off and the
second set of electrical switches is on. Still further, the cycle
may also include a third period comprising a blanking time period
between the first and second periods such that when the voltage
across the AC grid is approximately zero, the first and second sets
of electrical switches are off.
[0031] Embodiments may also further comprise a multi-port inverter
topology for converting an input direct current (DC) waveform from
a DC source to an output alternating current (AC) waveform for
delivery to an AC grid. This topology may include a transformer
that includes a first winding and at least a second winding, a
DC-AC inverter electrically coupled to the first winding of the
transformer adapted to convert the input DC waveform to an AC
waveform delivered to the transformer at the first winding, an
AC-AC converter electrically coupled to the second winding of the
transformer and adapted to convert the AC waveform received at the
second winding of the transformer to the output AC waveform having
a grid frequency of the AC grid, an active filter electrically
coupled to the at least second winding of the transformer wherein
the active filter is adapted to sink and source power with one or
more energy storage devices based on a mismatch in power between
the DC source and the AC grid, and a controller, comprising a phase
locked loop (PLL) electrically coupled to receive an AC voltage
from the AC grid and having an output signal comprising an estimate
of the phase angle of the AC voltage, wherein the controller, in
response to the estimated phase angle of the AC voltage, controls
the switching cycles of a plurality of electrical switches of the
AC-AC converter. The AC-AC converter may include a half-bridge
circuit electrically coupled to the first winding of the
transformer and an unfolding bridge circuit electrically coupled
between the half-bridge circuit and the AC grid.
[0032] In the aforementioned commonly-owned application, U.S. Ser.
No. 15/080,110, a number of DC-AC inverter topologies are
disclosed. General topologies therein comprise a multi-winding
transformer, a DC-AC inverter electrically coupled between a DC
source and winding of the transformer, an active filter
electrically coupled to a winding of the transformer, an AC-AC
cycloconverter, electrically coupled between a winding of the
transformer and an AC grid, and an inverter controller electrically
coupled to the DC-AC inverter, the active filter, and the
cycloconverter. In embodiments described and illustrated, the
cycloconverter comprises a resonant tank circuit and a circuit that
resembles a half-bridge circuit. The half-bridge circuit uses two
full-blocking switches that allow the voltage source, the AC grid,
to be bi-polar. The full-blocking circuit of the cycloconverter
comprises two common source MOSFETS, which doubles the conduction
losses compared with a half-bridge circuit.
[0033] In embodiments of the present invention, the cycloconverter
is replaced by an AC-AC converter comprising a half-bridge circuit
and an unfolding bridge circuit. Simulations have indicated that
such a topology performs as expected and generates power at a unity
power factor as well as leading and lagging reactive power.
Performance of the electromagnetic interference (EMI) filter in the
topologies of the present inventions may be comparable to that of
the EMI filter in the cycloconverter.
[0034] Compared to the cycloconverter, conduction losses may be
reduced in embodiments of the AC-AC converter of the present
invention. For example, for a given operating condition, both the
half bridge of the present invention and the cycloconverter switch
at high frequency can process current with a high RMS magnitude.
However, given that the cycloconverter has four switches while the
half-bridge has two switches, conduction losses may be reduced in
half or by another amount.
[0035] Additionally, the gate driver power supply for the AC-AC
converter of the present invention may be less complex than in
topologies employing a cycloconverter. For example, cycloconverter
topologies comprise two pairs of full blocking switches that
require two isolated gate driver power supplies. Comparatively, in
embodiments of the present invention, a half-bridge plus unfolding
bridge circuitry may be provided and may require only a single
non-isolated gate driver power supply.
[0036] Circuits employing the half-bridge and unfolding bridge
topology of embodiments may also have reduced losses. These losses
may be derived from synchronous rectification of the AC grid
voltage performed by the unfolding bridge. This synchronous
rectification may employ switching at 60 Hz near zero-voltage
transitions. Therefore, switching loses are very low. Conduction
losses may also be reduced in embodiments as current through the
unfolding bridge is the average output current of the high
frequency resonant half-bridge, which results in reduced conduction
losses.
[0037] In embodiments, replacing the cycloconverter with the
topology of the embodiments of the present invention may be
substantially cost neutral. The cycloconverter requires four high
performing switches, two isolated gate drivers, and two isolated
gate driver power supplies. Comparatively, the AC-AC converter of
the present invention comprises six switches, the half-bridge
comprises two high performing switches and the unfolding bridge
comprises four low to average performing switches. This AC-AC
converter can require three gate drivers; however, none need to
have isolation and can, therefor, all share one gate driver power
supply.
[0038] Referring to FIG. 1, a system 100 for supplying alternating
current (hereinafter "AC") power to an AC grid 102 at a grid
frequency includes a direct current (hereinafter "DC") source 104
and an inverter 106. The DC source 104 may be embodied as any type
of DC source configured to generate or produce a DC power, which is
supplied to the inverter 106. For example, the DC power may be
embodied as a photovoltaic solar cell or array, a fuel cell, a wind
turbine configured to generate a DC power (e.g., via a rectifying
circuit), a water turbine configured to generate a DC power, or
other unipolar power source.
[0039] The inverter 106 is electrically connected to the DC source
104 and configured to convert a DC waveform generated by the DC
source 104 to an AC waveform suitable for delivery to the AC grid
102 and, in some embodiments, loads coupled to the AC grid 102. The
AC grid 102 may be embodied as, for example, a utility power grid
that supplies utility AC power to residential and commercial users.
Such utility power grids may be characterized as having an
essentially sinusoidal bipolar voltage at a fixed grid frequency
(e.g., f=.omega.)/2.pi.=50 Hz or 60 Hz).
[0040] As discussed above, in some embodiments, the DC source 104
may be embodied as one or more photovoltaic cells. In such
embodiments, the DC source 104 and the inverter 106 may be
associated with each other to embody an AC photovoltaic module
(ACPV) 200, as illustrated in FIG. 2. The ACPV 200 includes a DC
photovoltaic module (DCPV) 202, which operates as the DC source
104, electrically coupled to the inverter 106. The DCPV 202
includes one or more photovoltaic cells and is configured to
deliver a DC waveform to the inverter 106 in response to receiving
an amount of sunlight. The DC power delivered by the ACPV 200 is a
function of environmental variables, such as, e.g., sunlight
intensity, sunlight angle of incidence and temperature. In some
embodiments, the inverter 106 is positioned in a housing of the
ACPV 200. Alternatively, the inverter 106 may include its own
housing secured to the housing of the ACPV 200. Additionally, in
some embodiments, the inverter 106 is separate from the housing,
but located near the DCPV 202. As discussed above, the inverter 106
is configured to convert the DC power received from the DCPV 202 to
an AC power suitable for delivery to the AC grid 102 at the grid
frequency. It should be appreciated that multiple ACPVs 200 may be
used to form a solar array with each ACPV 200 having a dedicated
inverter 106.
[0041] Referring now to FIG. 3, in some embodiments, the inverter
106 includes a DC-AC inverter 300, a transformer 302, a AC-AC
converter 304, and an active filter 306. Depending on the
particular embodiment, the transformer 302 may be embodied as a
three-winding transformer that includes a first winding, a second
winding, and a third winding or a two-winding transformer that
includes a first winding and a second winding (see, for example,
FIGS. 4-5). Although the transformer 302 may be described herein as
a two-winding transformer or a three-winding transformer, it should
be appreciated that such transformers may include more than two or
three windings, respectively, in some embodiments. For example, in
various embodiments, a three-winding transformer may include three
windings, four windings, five windings, or a greater number of
windings.
[0042] The DC-AC inverter 300 is electrically coupled to the first
winding (not shown) of the transformer 302 and is electrically
couplable to the DC source 104. As shown in FIG. 3, the DC-AC
inverter 300 includes a DC-AC inverter circuit 310 and, in some
embodiments, may include a resonant tank circuit 312 or a portion
thereof. The DC-AC inverter circuit 310 is adapted to convert an
input DC waveform from the DC source 14 to an AC waveform delivered
to the transformer 302 at the first winding. In some embodiments,
the resonant tank circuit 312 includes a capacitor and an inductor.
It should be appreciated that, in some embodiments, the resonant
tank circuit 312 may be formed by one or more discrete capacitors
(e.g., a capacitor divider) and a leakage inductance of the
transformer 302 (e.g., in half-bridge inverter embodiments).
[0043] The AC-AC converter 304 is electrically coupled to the
second winding (not shown) of the transformer 302 and electrically
couplable to the AC grid 102. As shown in FIG. 3, the AC-AC
converter 304 includes a half-bridge circuit 314 and an unfolding
bridge circuit 316. The AC-AC converter circuit 304 is adapted to
convert an AC waveform received at the second winding of the
transformer 302 to the output AC waveform delivered to the AC grid
102 and having the same frequency as a waveform of the AC grid 102
(i.e., the grid frequency). That is, the AC-AC converter 304 is
configured to convert an input AC waveform to an output AC waveform
having a frequency that is different from the input AC
waveform.
[0044] Depending on the particular embodiment, the active filter
306 may be coupled to the first winding, the second winding, or the
third winding (not shown) of the transformer 302. For example, in
embodiments in which the transformer 302 is embodied as a
three-winding transformer, the active filter 306 may be
electrically coupled to the third winding of the transformer 302,
whereas in embodiments in which the transformer 302 is embodied as
a two-winding transformer, the active filter 306 may be
electrically coupled to the first winding or, as illustrated in
FIG. 4, the second winding of the transformer 302. The active
filter 306 is adapted to sink and source power with one or more
energy storage devices 320 of the active filter 306 and using a
DC-AC inverter circuit 318 based on a mismatch in power (e.g., an
instantaneous mismatch in power) between the DC source 104 and the
AC grid 102. That is, the active filter 306 supplies power from or
absorbs power with the one or more energy storage devices 320 based
on the mismatch in power.
[0045] For example, it should be appreciated that the DC source 104
delivers a relatively constant power to the DC-AC inverter 300.
However, the AC grid 102 has a relatively sinusoidal power that
fluctuates (e.g., between zero and peak power). When the power of
the AC grid 102 is zero, the power delivered to the AC grid 102
should also be zero; accordingly, the constant power delivered by
the DC source 104 is supplied to the one or more energy storage
devices 320 of the active filter 306. However, when the AC grid 102
is at peak power, the power of the AC grid 102 is generally twice
that of the input power from the DC source 104; as such, all of the
power from the DC source 104 is delivered to the AC grid 102 and
the other half of the power is supplied from the one or more energy
storage devices 320 of the active filter 306. In some embodiments,
the one or more energy storage devices 320 are embodied as one or
more capacitors; however, the energy storage devices 320 may be
embodied as other devices in other embodiments.
[0046] The inverter 106 also includes an inverter controller 308,
which controls the operation of the DC-AC inverter 300, the AC-AC
converter 304, and the active filter 306. Although the inverter
controller 308 is illustratively embodied as a single controller in
the embodiment of FIG. 3, the inverter controller 308 may be
embodied as multiple separate controllers in other embodiments. For
example, in some embodiments, the inverter 106 may include an input
controller to control the operation of the DC-AC inverter 300, an
output controller to control the operation of the AC-AC converter
304, and/or a filter controller to control the operation of the
active filter 306. In such embodiments, each of the controllers may
be galvanically isolated from one another.
[0047] As discussed above, the inverter controller 308 is
electrically coupled to and adapted to control operation of the
DC-AC inverter 300, the AC-AC converter 304, and the active filter
306. To do so, the inverter controller 308 may provide a plurality
of switching and/or control signals to various circuits of the
DC-AC inverter 300, the AC-AC converter 304, and the active filter
306. For example, in some embodiments, the inverter controller 308
controls the operation of the DC-AC inverter 300 based on a global
maximum power point tracking ("MPPT") method. As shown in FIG. 3,
the illustrative inverter controller 308 utilizes an algorithm to
control various switches of the inverter 106. To do so, the
inverter controller 308 may provide a plurality of switching and/or
control signals to various circuits of the inverter 106. In
embodiments, such signals may be repeated duty cycle signals, e.g.
50% duty cycle signals, for each of the three ports of the inverter
106, with a small blanking time and appropriate phases shifts
between duty cycles at each port. It should be appreciated that, in
some embodiments, the inverter controller 308 is adapted to control
switching cycles of the various electrical switches of the DC-AC
inverter 300, the AC-AC converter 304, and/or the active filter 306
using zero-voltage switching techniques.
[0048] The inverter controller 308 may include a processor 324 and
a memory 326, both of which may be integrated into a single
integrated circuit or as separate integrated circuits connected via
wires on a printed circuit board. The processor 324 may execute
instructions stored on the memory 326 and cause the inverter
controller 308 to perform various actions to control the DC-AC
inverter 300, the AC-AC converter 304, and/or the active filter
306. The memory 326 may be any of a number of known tangible
storage mediums (e.g., RAM, DRAM, SRAM, ROM, EEPROM, Flash memory,
etc.).
[0049] Additionally, in some embodiments, the inverter 106 may
include circuits not shown herein for clarity of the description.
For example, the inverter 106 may include communication circuitry,
which may be communicatively coupled to the inverter controller 308
or may be incorporated therein. In such embodiments, the inverter
controller 308 may utilize the communication circuitry to
communicate with remote devices, such as remote controllers or
servers. For example, depending on the particular embodiment, the
communication circuitry may be configured to communicate with
remote devices over an AC power line, such as the AC power line
interconnects coupled to the output of the AC-AC converter 304, or
using other communication technologies and/or protocols. For
example, in some embodiments, the communication circuitry may be
embodied as a wireless or wired communication circuit configured to
communicate with remote devices utilizing one or more wireless or
wired communication technologies and/or protocols such as
Wi-Fi.TM., Zigbee.RTM., ModBus.RTM., WiMAX, Wireless USB,
Bluetooth.RTM., TCP/IP, USB, CAN-bus, HomePNA.TM., and/or other
wired or wireless communication technology and/or protocol.
Further, in some embodiments, the inverter 106 may include an input
filter electrically coupled (e.g., in series) with the DC source
104 and/or an output filter electrically coupled (e.g., in series)
with the AC grid 102.
[0050] Referring now to FIG. 4, a multi-port resonant converter
topology in which the inverter 106 is embodied as a three-port
inverter 500, and includes a two-winding transformer 302, is shown.
The illustrative inverter 500 of FIG. 4 includes a set of full
and/or half bridge converter circuits 502, 506, a set of impedances
508, 510, 512, the half-bridge circuit 314, and the unfolding
bridge circuit 316. As shown, in the illustrative embodiment, the
converter circuit 502 and the impedance 508 form the DC-AC inverter
300, the half-bridge circuit 314, the impedance 510, and the
unfolding bridge 316 form the AC-AC converter 304, and the
converter circuit 506, the impedance 512, and the energy storage
device 320 form the active filter 306. As shown and described
above, the DC-AC inverter 300 is electrically coupled to the first
winding 414 of the transformer 302 and the AC-AC converter 304 and
the active filter 306 are electrically coupled to the second
winding 416 of the transformer 302. It should be appreciated that
two-winding transformer 302 topologies may reduce the complexity
and, therefore, cost associated with manufacturing the transformer
302 compared to three-winding transformer topologies. In other
embodiments, the DC-AC inverter 300 and the active filter 306 may
be electrically coupled to the first winding 414 and the AC-AC
converter 304 may be electrically coupled to the second winding
416. In embodiments, the transformer may have three windings with
the DC-AC inverter 300 electrically coupled to the first winding,
the AC-AC converter 304 electrically coupled to the second winding,
the active filter 306 electrically coupled to the third
winding.
[0051] The converter circuit 502 may be embodied as the DC-AC
inverter circuit 310 and, depending on the particular embodiment,
may be embodied as a half-bridge inverter circuit or a full-bridge
inverter circuit. Similarly, the converter circuit 506 is embodied
as the DC-AC inverter circuit 318, which depending on the
particular embodiment, may be embodied as a half-bridge inverter
circuit or a full-bridge inverter circuit. The illustrative AC-AC
converter circuit 304 is embodied as the half-bridge circuit 314
and unfolding bridge circuit 316. The impedance 508 may be
representative of leakage inductances from the two-winding
transformer 302. The impedance 512 may be representative of the
impedance of a trace on the printed circuit board on which the
inverter 106 is assembled. The impedance 510 may comprise a
discrete component of the AC-AC converter 304.
[0052] As shown in FIG. 4, the half-bridge 314 of the AC-AC
converter 304 includes electrical switches 520, 522, a capacitor
divider comprising capacitors 524, 526, and an inductor 510. The
unfolding bridge 316 of the AC-AC converter 304 includes electrical
switches 530, 532, 534, 536. The AC-AC converter 304 also includes
a capacitor 540 and a resistor 542. The resistor 542 senses the
current of the AC grid to permit the current to be regulated.
[0053] More specifically, first terminals of the electrical
switches 520, 522 are electrically coupled to one another and to a
first terminal of the inductor 510. The second terminal of the
inductor 510 is electrically coupled to the second winding 416 of
the transformer 302. A first terminal of the capacitor 524 is
electrically coupled to a first terminal of the capacitor 526 and
to the second terminal of the second winding 416 of the transformer
302. The second terminal of the capacitor 524 is electrically
coupled to the second terminal of the electrical switch 520 and the
second terminal of the capacitor 526 is electrically coupled to the
second terminal of the electrical switch 522.
[0054] The unfolding bridge 316 of the AC-AC converter 304 is
electrically coupled to the AC grid 102. More specifically, first
terminals of each of a first pair of the electrical switches 530,
532 are electrically coupled to each other, to the second terminal
of the switch 520 and to the second terminal of the capacitor 524.
Similarly, first terminals of each of a second pair of the
electrical switches 534, 536 are electrically coupled to each
other, to the second terminal of the switch 522 and to a first
terminal of the resistor 542. Second terminals of the switches 530,
534 are electrically coupled to each other and to one side of the
AC grid 102. Second terminals of the electrical switches 532, 536
are electrically coupled to each other and to the other side of the
AC grid 102.
[0055] A first terminal of the capacitor 540 is electrically
coupled to the second terminal of the switch 520. The second
terminal of the capacitor 540 is electrically coupled to a second
terminal of the resistor 542 and to the second terminal of the
switch 522.
[0056] In embodiments, the AC-AC converter 304 may also include an
EMI filter. The EMI filter may include the two inductors and the
common mode inductor, collectively identified in FIGS. 5 and 6 by
the dashed box 552 and electrically coupled between the unfolding
bridge 316 and the AC grid 102, and the capacitor 540, electrically
coupled between the half-bridge 314 and the unfolding bridge 316.
In one embodiment, illustrated in FIG. 5, the EMI filter 550A is
comprises additional components electrically coupled between the
unfolding bridge 316 and the AC grid 102 including an inductor 554,
electrically coupled between the second terminals of the switches
530, 534 and one side of the AC grid 102 and a capacitor 556
electrically coupled across the components 552.
[0057] FIG. 6 shows that embodiments may have the EMI filter 550
comprising additional components electrically coupled between the
half-bridge 314 and the unfolding bridge 316. In such topologies,
the inductor 554 may be electrically coupled between the second
terminal of the switch 520 and the first terminal of the switch 530
and the capacitor 556 may be electrically coupled between the first
terminals of the switches 530, 534.
[0058] Each of the electrical switches described herein is a MOSFET
in the illustrative embodiments; however, other types of
transistors or electrical switches may be used in other
embodiments. In some MOSFETs, the source metallization may connect
N and P doped regions on the top of the FET structure, forming a
diode between the drain and the source of the MOSFET, which is
represented as body diodes for each of the corresponding electrical
switches. It should be appreciated that, in some embodiments, the
inverter 106 may utilize one or more other types of transistors
(e.g., bipolar junction transistors (BJT), insulated-gate bipolar
transistors (IGBT), GaN (gallium nitride), etc.) or thyristors.
[0059] Turning to FIG. 7, the gate signals used to control the
electrical switches 530, 532, 534, 536 unfolding bridge 316 of the
AC-AC converter 304 are based on the grid phase angle of the AC
grid 102. The controller 308 receives the AC voltage V.sub.grid and
the processor 324 executes an algorithm 700 stored in the memory
326 to estimate the grid phase angle .THETA..sub.grid. FIG. 8A is a
simplified electrical schematic diagram of the four electrical
switches 530, 534, 532, 536 (now labeled Q1-Q4, respectively) in
the unfolding bridge 316. As illustrated in the plot of FIG. 8B,
representing the grid phase angle .THETA..sub.grid relative to the
grid voltage V.sub.grid as estimated by the algorithm 700, the
diagonally opposite electrical switches Q1, Q4 are turned on and
diagonally opposite electrical switches Q2, Q3 are turned off when
the grid voltage V.sub.grid has risen above approximately the
zero-crossing and is positive (period `A`). Conversely, the
electrical switches Q1, Q4 are turned off and the electrical
switches Q2, Q3 are turned on when the grid voltage V.sub.grid has
fallen below approximately the zero-crossing and is negative
(period `B`). Because the derivation of the grid phase angle
.THETA..sub.grid may be approximate, the control signal may impose
a brief blanking time period between the first and second periods
during which all four electrical switches Q1-Q4 are off (period
`C`). In this way, a negative voltage across the half-bridge 314
may be prevented.
[0060] Referring now to FIG. 9, in some embodiments, the inverter
controller 308 may execute a method 1500 for closed-loop control of
the inverter 106. The method begins with block 1502 in which the
inverter controller 308 determines the grid voltage V.sub.grid of
the AC grid 102 and estimates the angle (.theta..sub.e) of the grid
voltage. As described above, the controller 308 may utilize a PLL
or other suitable angle estimator to do so. In block 1504, the
controller 108 determines the switching frequency of the electrical
switches of the inverter 106 based on the grid voltage (e.g., the
instantaneous grid voltage) and/or other circuit parameters. For
example, the switching frequency may be determined based on the
input power of the DC source 104, component values of various
components of the inverter 106 (e.g., component inductances and/or
capacitances), and/or operating values of the inverter 106 (e.g.,
voltages and/or currents at various points in the inverter 106).
For example, in block 1506, the controller 108 may determine the
switching frequency based on the parameters of one or more of the
resonant tank circuits of the inverter 106 (e.g., inductance and
capacitance values).
[0061] In block 1508, the controller 108 determines a phase shift
of the actuation signal (.theta..sub.1) for the electrical switches
of the DC-AC inverter 300 relative to the actuation signal (e.g.,
.theta..sub.3=0) for the electrical switches of the active filter
306. To do so, in block 1510, the controller 108 may determine the
DC source current for regulation of the DC source voltage of the DC
source 104 (e.g., PV panel) based on a suitable MPPT technique.
Further, in block 1512, the controller 108 may eliminate
double-frequency ripple from the AC grid 102. In block 1514, the
controller 108 may scale the switching frequency for system
linearized operation as described above. In particular, in block
1516, the controller 108 may scale the actuation signal of the
DC-AC inverter 300 based on a gain scheduling function of switching
frequency. In block 1518, the controller 108 may determine a linear
operating range for zero-voltage switching based on the DC source
voltage and the active filter voltage.
[0062] In block 1520, the controller 108 determines a phase shift
of the actuation signal (.theta..sub.2) for the electrical switches
of the AC-AC converter 304 relative to the actuation signal for the
electrical switches of the active filter 306. To do so, in block
1522, the controller 108 may determine the grid current of the AC
grid 102 for regulation of the active filter capacitor voltage
(e.g., across the energy storage device 320) of the active filter
306. Further, in block 1524, the controller 108 may eliminate
double-frequency ripple from the AC grid 102. In block 1526, the
controller 108 may scale the switching frequency for system
linearized operation as described above. In particular, in block
1528, the controller 108 may scale the actuation signal of the
AC-AC converter 304 based on a gain scheduling function of
switching frequency. In block 1530, the controller 108 may
determine a linear operating range for zero-voltage switching based
on the grid voltage and the active filter voltage. It should be
appreciated that, in some embodiments, the blocks 1508 and 1520 may
be performed in parallel.
[0063] In block 1532, the controller 108 generates a set of signals
for actuation of the electrical switches of the inverter 106 based
on the determined phase shifts .theta..sub.1 and .theta..sub.2. In
particular, the controller 108 may generate a signal for actuation
of the electrical switches of the DC-AC inverter 300, a signal for
actuation of the electrical switches of the AC-AC converter 304,
and a signal for actuation of the electrical switches of the active
filter 306. The signals may preferably provide 50% duty cycles and
vary the phase shifts among the ports of the inverter 106 and the
switching frequency, thereby controlling the power flow. These duty
cycles may also be set for other percentages, vary within a margin
of error from 50% or other target percentage, and have duty cycle
ranges or targets for both certain instantaneous conditions and
over short or long periods of time for actuating the switches of
the DC-AC inverter 300, the switches of the AC-AC converter 304,
and the switches of the active filter 306.
[0064] In embodiments the inverter controller 108 or other modules
or components may utilize various other techniques to control
operations of inverter 106. For example, in some embodiments, the
controller 108 may utilize an alternative mode of operation for
controlling the electrical switches of the inverter 106. That is,
in normal operation, all three ports of the inverter 106 (i.e., the
DC-AC inverter 300, the AC-AC converter 304, and the active filter
306) receive signals to actuate the corresponding electrical
switches of those components. However, during the alternative mode
of operation, the inverter controller 108 may disable the signal
transmission to one of the ports (i.e., the DC-AC inverter 300, the
AC-AC converter 304, or the active filter 306), which results in
lower switching losses. In particular, in some embodiments, the
signal transmission to the port may be disabled every other
switching period, which may reduce the number of switching
instances of that port by fifty percent. For example, in some
embodiments, the signals supplied to the active filter 306 may be
disabled every other switching period.
[0065] There is a plurality of advantages of the present disclosure
arising from the various features of the apparatuses, circuits, and
methods described herein. It will be noted that alternative
embodiments of the apparatuses, circuits, and methods of the
present disclosure may not include all of the features described
yet still benefit from at least some of the advantages of such
features. Those of ordinary skill in the art may readily devise
their own implementations of the apparatuses, circuits, and methods
that incorporate one or more of the features of the present
disclosure and fall within the spirit and scope of the present
invention as defined by the appended claims.
* * * * *