U.S. patent application number 14/580170 was filed with the patent office on 2015-07-30 for inverter and control method thereof.
The applicant listed for this patent is Delta Electronics (Shanghai) Co., Ltd.. Invention is credited to Ke-Rou WANG, Bing-Wen WENG, Xuan-Cai ZHU.
Application Number | 20150214831 14/580170 |
Document ID | / |
Family ID | 53638545 |
Filed Date | 2015-07-30 |
United States Patent
Application |
20150214831 |
Kind Code |
A1 |
WENG; Bing-Wen ; et
al. |
July 30, 2015 |
INVERTER AND CONTROL METHOD THEREOF
Abstract
The present invention discloses an inverter and a control method
thereof. The inverter includes a first bridge leg having a series
of first switch, second switch, third switch, fourth switch and
fifth switch, and a second first bridge leg having a series of
sixth switch, seventh switch, eighth switch, ninth switch, tenth
switch. The control method includes steps of synchronously turning
on or off the first switch, second switch, ninth switch and tenth
switch, controlling that an on/off state of the third switch or
eighth switch is complementary to an on/off state of the first
switch, second switch, ninth switch and tenth switch, and
synchronously turning on or off the fourth switch, fifth switch,
sixth switch and seventh switch.
Inventors: |
WENG; Bing-Wen; (Shanghai,
CN) ; ZHU; Xuan-Cai; (Shanghai, CN) ; WANG;
Ke-Rou; (Shanghai, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Delta Electronics (Shanghai) Co., Ltd. |
Shanghai |
|
CN |
|
|
Family ID: |
53638545 |
Appl. No.: |
14/580170 |
Filed: |
December 22, 2014 |
Current U.S.
Class: |
363/132 |
Current CPC
Class: |
H02M 2001/0003 20130101;
H02M 7/5387 20130101; H02M 1/088 20130101 |
International
Class: |
H02M 1/088 20060101
H02M001/088; H02M 7/5387 20060101 H02M007/5387 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 2014 |
CN |
201410042042.1 |
Claims
1. An inverter, comprising: a first bridge leg electrically
connected to a direct-current (DC) source, the first bridge leg
comprising a first switch, a second switch, a third switch and a
fourth switch and a fifth switch which are sequentially connected
in series; a second bridge leg connected to the first bridge leg in
parallel, the second bridge leg comprising a sixth switch, a
seventh switch, an eighth switch, a ninth switch and a tenth switch
which are sequentially connected in series; a first diode connected
in anti-parallel with the first switch and the second switch which
are connected in series; a second diode connected in anti-parallel
with the fourth switch and the fifth switch which are connected in
series; a third diode connected in anti-parallel with the sixth
switch and the seventh switch which are connected in series; a
fourth diode connected in anti-parallel with the ninth switch and
the tenth switch which are connected in series; a cathode of a
fifth diode connected to a connection point between the second
switch and the third switch and an anode of the fifth diode
connected to a connection point between the eighth switch and the
ninth switch; and a cathode of a sixth diode connected to a
connection point between the seventh switch and the eighth switch
and an anode of the sixth diode connected to a connection point
between the third switch and the fourth switch.
2. The inverter of claim 1, wherein the first switch and the second
switch are connected in anti-series, the fourth switch and the
fifth switch are connected in anti-series, the sixth switch and the
seventh switch are connected in anti-series, and the ninth switch
and the tenth switch are connected in anti-series.
3. The inverter of claim 1, wherein each of the first switch, the
second switch, the third switch, the fourth switch, the fifth
switch, the sixth switch, seventh switch, the eighth switch, the
ninth switch and the tenth switch is a metal-oxide-semiconductor
field effect transistor.
4. The inverter of claim 1, wherein each of the first diode, the
second diode, the third diode and the fourth diode is a fast
recovery diode or a silicon carbide diode.
5. The inverter of claim 1, wherein the DC source is a photovoltaic
array.
6. The inverter of claim 1, wherein the connection point between
the third switch and the fourth switch serves as a first common
coupling point; the connection point between the eighth switch and
the ninth switch serves as a second common coupling point.
7. The inverter of claim 1, wherein the connection point between
the second switch and the third switch serves as a first common
coupling point; the connection point between the seventh switch and
the eighth switch serves as a second common coupling point.
8. The inverter of claim 7, wherein the first common coupling point
is connected to a first inductor; the second common coupling point
is connected to a second inductor.
9. The inverter of claim 8, wherein the first inductor and the
second inductor are connected to an filter.
10. A control method of controlling the inverter of claim 1, the
control method comprising: synchronously turning on or off the
first switch, the second switch, the ninth switch and the tenth
switch, and controlling that the eighth switch is turning on or off
in complementary with the first switch, the second switch, the
ninth switch and the tenth switch; synchronously turning on or off
the fourth switch, the fifth switch, the sixth switch and the
seventh switch; controlling that the third switch is turning on or
off in complementary with the fourth switch, the fifth switch, the
sixth switch and the seventh switch.
11. The control method of claim 10, wherein the connection point
between the third switch and the fourth switch serves as a first
common coupling point, and the connection point between the eighth
switch and the ninth switch serves as a second common coupling
point.
12. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the third switch, and
synchronously turning on or off the first switch, the second
switch, the ninth switch and the tenth switch, wherein the first
switch, the second switch, the ninth switch and the tenth switch is
turning on or off in complementary with the eighth switch, and
after the first switch, the second switch, the ninth switch and the
tenth switch are turned on, the DC source charges first inductor
and the second inductor, so that an inductor current of the first
inductor and a voltage of an output terminal of the inverter are
positive values.
13. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the third switch, and
synchronously turning on or off the first switch, the second
switch, the ninth switch and the tenth switch, wherein the first
switch, the second switch, the ninth switch and the tenth switch is
turning on or off in complementary with the eighth switch, wherein
after the first switch, the second switch, the ninth switch and the
tenth switch are turned off, when the eighth switch is not turned
on, a freewheeling current path for the first inductor and the
second inductor passes through the third switch and the fifth
diode, wherein after the eighth switch is turned on, no current go
through the eighth switch, so that an inductor current of the first
inductor and a voltage of an output terminal of the inverter are
positive values.
14. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the third switch, and
synchronously turning on or off the first switch, the second
switch, the ninth switch and the tenth switch, wherein the first
switch, the second switch, the ninth switch and the tenth switch is
turning on or off in complementary with the eighth switch, wherein
after the eighth switch is turned on, a voltage of an output
terminal of the inverter charges the first inductor and the second
inductor through the sixth diode and the eighth switch, and no
current go through the third switch that is turned on, so that the
voltage of the output terminal of the inverter is a positive value,
and an inductor current of the first inductor is a negative
value.
15. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the third switch, and
synchronously turning on or off the first switch, the second
switch, the ninth switch and the tenth switch, wherein the first
switch, the second switch, the ninth switch and the tenth switch is
turning on or off in complementary with the eighth switch, wherein
after the eighth switch is turned off, when the first switch, the
second switch, the ninth switch and the tenth switch are not turned
on, a freewheeling current of the first inductor and the second
inductor go through the first diode, the third switch and the
fourth diode, wherein when the first switch, the second switch, the
ninth switch and the tenth switch are turned on synchronously, the
freewheeling current of the first inductor and the second inductor
go through the first switch, the second switch, the ninth switch
and the tenth switch, so that a voltage of an output terminal of
the inverter is a positive value, and an inductor current of the
first inductor is a negative value.
16. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the eighth switch, and
synchronously turning on or off the fourth switch, the fifth
switch, the sixth switch and the seventh switch, wherein the fourth
switch, the fifth switch, the sixth switch and the seventh switch
is turning on or off in complementary with the third switch,
wherein after the fourth switch, the fifth switch, the sixth switch
and the seventh switch are turned on, the DC source charges the
first inductor and the second inductor, so that an inductor current
of the first inductor and a voltage of an output terminal of the
inverter are negative values.
17. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the eighth switch, and
synchronously turning on or off the fourth switch, the fifth
switch, the sixth switch and the seventh switch, wherein the fourth
switch, the fifth switch, the sixth switch and the seventh switch
is turning on or off in complementary with the third switch,
wherein after the fourth switch, the fifth switch, the sixth switch
and the seventh switch are turned off, when the third switch is not
turned on, a freewheeling current path for the first inductor and
the second inductor passes through the eighth switch and the sixth
diode, wherein after the third switch is turned on, no current go
through the third switch, so that an inductor current of the first
inductor and a voltage of an output terminal of the inverter are
negative values.
18. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the eighth switch, and
synchronously turning on or off the fourth switch, the fifth
switch, the sixth switch and the seventh switch, wherein the fourth
switch, the fifth switch, the sixth switch and the seventh switch
is turning on or off in complementary with the third switch,
wherein after the third switch is turned on, a voltage of an output
terminal of the inverter charges the first inductor and the second
inductor through the fifth diode and the third switch, and on
current go through the eighth switch that is turned on, so that the
voltage of the output terminal of the inverter is a negative value,
and an inductor current of the first inductor is a positive
value.
19. The control method of claim 11, the first common coupling point
connected to a first inductor, the second common coupling point
connected to a second inductor, and the control method further
comprising: uninterruptedly turning on the eighth switch, and
synchronously turning on or off the fourth switch, the fifth
switch, the sixth switch and the seventh switch, wherein the fourth
switch, the fifth switch, the sixth switch and the seventh switch
is turning on or off in complementary with the third switch,
wherein after the third switch is turned off, when the fourth
switch, the fifth switch, the sixth switch and the seventh switch
are not turned on, a freewheeling current of the first inductor and
the second inductor go through the second diode, the eighth switch
and the third diode, wherein after the fourth switch, the fifth
switch, the sixth switch and the seventh switch are turned on
synchronously, the freewheeling current of the first inductor and
the second inductor go through the fourth switch, the fifth switch,
the sixth switch and the seventh switch, so that a voltage of an
output terminal of the inverter is a negative value, and an
inductor current of the first inductor is a positive value.
20. A control method of controlling the inverter of claim 1, the
control method comprising: synchronously turning on or off the
first switch, the second switch, the ninth switch and the tenth
switch, and controlling that the third switch is turning on or off
in complementary with the first switch, the second switch, the
ninth switch and the tenth switch; synchronously turning on or off
the fourth switch, the fifth switch, the sixth switch and the
seventh switch; controlling that the eighth switch is turning on or
off in complementary with the fourth switch, the fifth switch, the
sixth switch and the seventh switch.
21. The control method of claim 20, wherein the connection point
between the second switch and the third switch serves as a first
common coupling point, and the connection point between the seventh
switch and the eighth switch serves as a second common coupling
point.
Description
RELATED APPLICATIONS
[0001] This application claims priority to Chinese Application
Serial Number 201410042042.1, filed Jan. 28, 2014, which is herein
incorporated by reference.
BACKGROUND
[0002] 1. Field of Invention
[0003] The present invention relates to power converter circuit.
More particularly, the present invention relates to an inverter and
control methods thereof.
[0004] 2. Description of Related Art
[0005] An Inverter is a power converter circuit which converts
direct current (DC) power to alternating current (AC). In the
photovoltaic application, the solar inverter is widely used for
converting the DC power from solar arrays into AC and delivering to
the grid.
[0006] The transformer-less inverter which has no isolation
transformer is widely used in photovoltaic applications because of
its high efficiency, low cost and light weight. With the
transformer-less solar inverter, the common mode voltage, which is
generated by the inverter, will cause leakage current through to
the parasitic capacitance of the photovoltaic arrays. And it will
affect the life of the array and user safety.
SUMMARY
[0007] The following presents a simplified summary of the
disclosure in order to provide a basic understanding to the reader.
This summary is not an extensive overview of the disclosure and it
does not identify key/critical components of the present invention
or delineate the scope of the present invention. The only purpose
is to present some concepts disclosed herein in a simplified form
as a prelude to the more detailed description that is presented
later.
[0008] In one aspect, the present disclosure provides an inverter
with transformer-less structure and control method thereof to
improve the efficiency.
[0009] In one embodiment, an inverter includes a first bridge leg,
a second bridge leg, a first diode, a second diode, a third diode,
a fourth diode, a fifth diode and a sixth diode. The first bridge
leg is electrically connected to a direct-current (DC) source, and
the first bridge leg includes a first switch, a second switch, a
third switch and a fourth switch and a fifth switch which are
sequentially connected in series. The second bridge leg is
connected to the first bridge leg in parallel, and the second
bridge leg includes a sixth switch, a seventh switch, an eighth
switch, a ninth switch and a tenth switch which are sequentially
connected in series. The first diode is connected in anti-parallel
with the first switch and the second switch which are connected in
series. The second diode is connected in anti-parallel with the
fourth switch and the fifth switch which are connected in series.
The third diode is connected in anti-parallel with the sixth switch
and the seventh switch which are connected in series. The fourth
diode is connected in anti-parallel with the ninth switch and the
tenth switch which are connected in series. The cathode of a fifth
diode is connected to a connection point between the second switch
and the third switch, and an anode of the fifth diode is connected
to a connection point between the eighth switch and the ninth
switch. The cathode of a sixth diode is connected to a connection
point between the seventh switch and the eighth switch, and an
anode of the sixth diode is connected to a connection point between
the third switch and the fourth switch.
[0010] In one embodiment, the widely used unipolar modulation can
be used for the presented inverter. A control method of controlling
aforesaid inverter includes following steps: synchronously turning
on or off the first switch, the second switch, the ninth switch and
the tenth switch, and controlling that the eighth switch is turning
on or off in complementary with the first switch, the second
switch, the ninth switch and the tenth switch; synchronously
turning on or off the fourth switch, the fifth switch, the sixth
switch and the seventh switch; controlling that the third switch is
turning on or off in complementary with the fourth switch, the
fifth switch, the sixth switch and the seventh switch.
Alternatively, the control method includes following steps:
synchronously turning on or off the first switch, the second
switch, the ninth switch and the tenth switch, and controlling that
the third switch is turning on or off in complementary with the
first switch, the second switch, the ninth switch and the tenth
switch; synchronously turning on or off the fourth switch, the
fifth switch, the sixth switch and the seventh switch; controlling
that the eighth switch is turning on or off in complementary with
the fourth switch, the fifth switch, the sixth switch and the
seventh switch.
[0011] Compared to existing techniques, the technical solutions of
the present disclosure can provide significant advantages and
beneficial effects. For the photovoltaic application, the present
invention provides the inverter which has low common mode noise and
high efficiency and also reactive power output capability. The
inverter is suit for grid-connected photovoltaic systems that have
no isolation transformer or other applications.
[0012] To provide better understanding, the detailed description
together with drawings is presented as following.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The detailed description and accompanying drawing are given
as below to provide better understanding, wherein:
[0014] FIG. 1 is a schematic diagram of an inverter according to
one embodiment of the present disclosure;
[0015] FIG. 2 is a waveform of voltage, current and control signals
of the inverter of FIG. 1 according to one exemplary embodiment of
the present disclosure;
[0016] FIG. 3 is a schematic diagram illustrating an inverter in a
first operating mode;
[0017] FIG. 4 is a schematic diagram illustrating the inverter of
FIG. 1 in a second operating mode;
[0018] FIG. 5 is a schematic diagram illustrating the inverter of
FIG. 1 in a third operating mode;
[0019] FIG. 6 is a schematic diagram illustrating the inverter of
FIG. 1 in a fourth operating mode;
[0020] FIG. 7 is a schematic diagram illustrating the inverter of
FIG. 1 in a fifth operating mode;
[0021] FIG. 8 is a schematic diagram illustrating the inverter of
FIG. 1 in a sixth operating mode;
[0022] FIG. 9 is a schematic diagram illustrating the inverter of
FIG. 1 in a seventh operating mode;
[0023] FIG. 10 is a schematic diagram illustrating the inverter of
FIG. 1 in a eighth operating mode;
[0024] FIG. 11 is a schematic diagram of an inverter according to
another embodiment of the present disclosure; and
[0025] FIG. 12 is a waveform of voltage, current and control
signals of the inverter of FIG. 11 according to one exemplary
embodiment of the present disclosure.
DETAILED DESCRIPTION
[0026] The embodiments can be fulfilled as the detailed description
and figures as below. In these figures the various described
features/elements are not drawn to scale but instead of best
illustrate specific features/elements relevant to the present
invention. Moreover, well-known structures and devices are
schematically shown in order to simplify the drawing and avoid
unnecessary limitation to the claimed invention.
[0027] It will be understood that when an element is referred to as
being "connected" or "coupled" to another element, it can be
directly connected or coupled to the other element or intervening
elements may be present. In contrast, when an element is referred
to as being "directly connected" or "directly coupled" to another
element, there are no intervening elements present.
[0028] As used in the description herein and throughout the claims
that follow, the meaning of "a", "an", and "the" includes reference
to the plural unless the context clearly dictates otherwise.
[0029] FIG. 1 is a circuit diagram of an inverter 100 according to
one embodiment of the present disclosure. As illustrated in FIG. 1,
the inverter 100 includes a first bridge leg 110, a second bridge
leg 120, a first diode (D1), a second diode (D2), a third diode
(D3), a fourth diode (D4), a fifth diode (D5) and a sixth diode
(D6). For example, the DC source 130 may be a photovoltaic array, a
storage battery, etc.
[0030] In FIG. 1, the first bridge leg 110 is electrically
connected to a direct-current (DC) source, the first bridge leg 110
includes a first switch (S1), a second switch (S2), a third switch
(S3) and a fourth switch (S4) and a fifth switch (S5) which are
sequentially connected in series, wherein the connection point
between the third switch (S3) and the fourth switch (S4) serves as
a first common coupling point (a). The second bridge leg 120 is
connected to the first bridge leg 110 in parallel, the second
bridge leg 120 includes a sixth switch (S6), a seventh switch (S7),
an eighth switch (S8), a ninth switch (S9) and a tenth switch (S10)
which are sequentially connected in series, wherein the connection
point between the eighth switch (S8) and the ninth switch (S9)
serves as a second common coupling point (b). The first diode (D1)
is connected in anti-parallel with the first switch (S1) and second
switch (S2) which are connected in series; the second diode (D2) is
connected in anti-parallel with the fourth switch (S4) and the
fifth switch (S5) which are connected in series; the third diode
(D3) is connected in anti-parallel with the sixth switch (S6) and
the seventh switch (S7) which are connected in series; the fourth
diode (D4) is connected in anti-parallel with the ninth switch (S9)
and tenth switch (S10) which are connected in series. The cathode
of the fifth diode (D5) is connected to a connection point between
the second switch (S2) and third switch (S3) and the anode of the
fifth diode (D5) is connected to a second common coupling point (b)
of the second bridge leg 120. The cathode of the sixth diode (D6)
is connected to a connection point between the seventh switch (S7)
and eighth switch (S8) and the anode of the sixth diode (D6) is
connected to a first common coupling point (a) of the first bridge
leg 110.
[0031] The DC source 130 provides DC voltage V.sub.dc, the control
circuit of the inverter 100 uses an unipolar modulation, and the a
control method of controlling aforesaid inverter includes steps of:
synchronously turning on or off the first switch (S1), second
switch (S2), ninth switch (S9) and tenth switch (S10); controlling
that the eighth switch (S8) is turning on or off in complementary
with the first switch (S1), second switch (S2), ninth switch (S9)
and tenth switch (S10); synchronously turning on or off the fourth
switch (S4), fifth switch (S5), sixth switch (S6) and seventh
switch (S7), and controlling that the third switch (S3) is turning
on or off in complementary with the fourth switch (S4), fifth
switch (S5), sixth switch (S6) and seventh switch (S7). Thus, these
switches are symmetrically selected so that the sum of voltage
potentials of the first common coupling point (a) and second common
coupling point (b) is with low common mode voltage. Therefore, the
inverter 100 of FIG. 1 can be adapted in grid-connected
photovoltaic systems that have no isolation transformer, or other
similar applications.
[0032] In one embodiment, the first to tenth switches (S1)-(S10)
are transistors, such as N channel metal-oxide-semiconductor field
effect transistors; the first to fourth diodes (D1)-(D4) may be
fast recovery diodes having good reverse recovery characteristics
and/or silicon carbide diodes. Structurally, the first switch (S1)
and the second switch (S2) are connected in anti-series, and the
first diode (D1) is connected in anti-parallel with the first
switch (S1) and second switch (S2). The fourth switch (S4) and the
fifth switch (S5) are connected in anti-series, and the second
diode (D2) is connected in anti-parallel with the fourth switch
(S4) and fifth switch (S5). The sixth switch (S6) and the seventh
switch (S7) are connected in anti-series, and the third diode (D3)
is connected in anti-parallel with the sixth switch (S6) and
seventh switch (S7). The ninth switch (S9) and the tenth switch
(S10) are connected in anti-series, and the fourth diode (D4) is
connected in anti-parallel with the ninth switch (S9) and tenth
switch (S10).
[0033] Specifically, as shown in FIG. 1, the source electrode of
the first switch (S1) is connected to the source electrode of the
second switch (S2), the cathode of the first diode (D1) is
connected to the drain electrode of the first switch (S1), and the
anode of the first diode (D1) is connected to the drain electrode
of the second switch (S2). The source electrode of the fourth
switch (S4) is connected to the source electrode of the fifth
switch (S5), the cathode of the second diode (D2) is connected to
the drain electrode of the fourth switch (S4), and the anode of the
second diode (D2) is connected to the drain electrode of the fifth
switch (S5). The source electrode of the sixth switch (S6) is
connected to the source electrode of the seventh switch (S7), the
cathode of the third diode (D3) is connected to the drain electrode
of the sixth switch (S6), and the anode of the third diode (D3) is
connected to the drain electrode of the seventh switch (S7). The
source electrode of the ninth switch (S9) is connected to the
source electrode of the tenth switch (S10), the cathode of the
fourth diode (D4) is connected to the drain electrode of the ninth
switch (S9), and the anode of the fourth diode (D4) is connected to
the drain electrode of the tenth switch (S10).
[0034] The first switch (S1) and the second switch (S2) can be
swapped over; thus, the drain electrode of the first switch (S1) is
connected to the drain electrode of the second switch (S2), the
cathode of the first diode (D1) is connected to the source
electrode of the first switch (S1), and the anode of the first
diode (D1) is connected to the drain electrode of the second switch
(S2). Similarly, the fourth switch (S4) and the fifth switch (S5)
can be swapped over, the sixth switch (S6) and the seventh switch
(S7) can be swapped over, the ninth switch (S9) and the tenth
switch (S10) can be swapped over, and their swapping manner is
substantially the same as the way of swapping the first switch (S1)
and the second switch (S2), and thus, are not repeated herein.
[0035] Moreover, in FIG. 1, the first common coupling point (a) is
connected to a first inductor (La), the second common coupling
point (b) is connected to a second inductor (Lb), and the first
inductor (La) and the second inductor (Lb) are connected to an
filter 140. The output of the filter 140 serves as an output
terminal of the inverter 100 and is connected to the power grid.
The filter 140 can reduce an electromagnetic interference noise
generated by the inverter 100, so as to avoid adversely affect to
other devices from the noise through the power grid.
[0036] FIG. 2 is a diagram illustrating the grid voltage v.sub.grid
(i.e., the voltage of output terminal of the inverter), the
inductor current i.sub.L and control signals. As shown in FIG. 2,
control signals (G1), (G2), (G9) and (G10) respectively for the
first switch (S1), the second switch (S2), the ninth switch (S9)
and the tenth switch, (S10) are complementary to a control signal
(G8) for the eighth switch (S8); control signals (G4), (G5), (G6)
and (G7) respectively for the fourth switch (S4), the fifth switch
(S5), the sixth switch (S6) and the seventh switch (S7) are
complementary to a control signal (G3) for the third switch
(S3).
[0037] The control circuit may control the inverter according to
the control method as shown in FIG. 2. The control method executed
by the control circuit for controlling the inverter includes eight
operating modes. For a more complete understanding of the eight
operating modes, and the advantages thereof, please refer to FIGS.
3-10 below.
[0038] Referring to FIG. 3, in the first operating mode, the
control method further includes a step of: uninterruptedly turning
on the third switch (S3), uninterruptedly turning off the fourth
switch (S4), the fifth switch (S5), the sixth switch (S6) and the
seventh switch (S7), and synchronously turning on or off the first
switch (S1), the second switch (S2), the ninth switch (S9) and the
tenth switch (S10), wherein the first switch (S1), the second
switch (S2), the ninth switch (S9) and the tenth switch (S10) is
turning on or off in complementary with the eighth switch (S8);
after the first switch (S1), the second switch (S2), the ninth
switch (S9) and the tenth switch (S10) are turned on, the DC source
130 charges the first inductor (La) and the second inductor (Lb),
so that the inductor current i.sub.L of the first inductor (La) and
a voltage of the output terminal of the inverter 100 (e.g., grid
voltage v.sub.grid of the output terminal of filter 140) are
positive values.
[0039] Referring to FIG. 4, in the second operation mode, the
control method further includes a step of: uninterruptedly turning
on the third switch (S3), uninterruptedly turning off the fourth
switch (S4), the fifth switch (S5), the sixth switch (S6) and the
seventh switch (S7), and synchronously turning on or off the first
switch (S1), the second switch (S2), the ninth switch (S9) and the
tenth switch (S10), wherein the first switch (S1), the second
switch (S2), the ninth switch (S9) and the tenth switch (S10) is
turning on or off in complementary with the eighth switch (S8);
after the first switch (S1), the second switch (S2), the ninth
switch (S9) and the tenth switch (S10) are turned off, when the
eighth switch (S8) is not turned on, a freewheeling current path
for the first inductor (La) and the second inductor (Lb) passes
through the third switch (S3) and the fifth diode (D5); in the
freewheeling state, after dead time is over, i.e., after the eighth
switch (S8) is turned on, no current go through the eighth switch
(S8) as shown in FIG. 4, so that the inductor current i.sub.L of
the first inductor (La) and a voltage of the output terminal of the
inverter 100 (e.g., grid voltage v.sub.grid of the output terminal
of filter 140) are positive values.
[0040] It should be noted that the control circuit of the
switch-mode power supply performs switching function with the "dead
time" feature so as to avoid that multiple switches are
synchronously turned on to generate current surge. For example, in
the second operation mode, after the first switch (S1), the second
switch (S2), the ninth switch (S9) and the tenth switch (S10) are
turned off, the eighth switch (S8) is still not turned on during a
time period, and this time period is the "dead time" in the second
operation mode.
[0041] Referring to FIG. 5, in the third operating mode, the
control method further includes a step of: uninterruptedly turning
on the third switch (S3), uninterruptedly turning off the fourth
switch (S4), the fifth switch (S5), the sixth switch (S6) and the
seventh switch (S7), and synchronously turning on or off the first
switch (S1), the second switch (S2), the ninth switch (S9) and the
tenth switch (S10), wherein the first switch (S1), the second
switch (S2), the ninth switch (S9) and the tenth switch (S10) is
turning on or off in complementary with the eighth switch (S8);
after the eighth switch (S8) is turned on, a voltage of the output
terminal of the inverter 100 (e.g., grid voltage v.sub.grid of the
output terminal of filter 140) charges the first inductor (La) and
second inductor (Lb) through the sixth diode (D6) and the eighth
switch (S8), and no current go through the third switch (S3) that
is turned on, so that the voltage of the output terminal of the
inverter 100 (e.g., grid voltage v.sub.grid of the output terminal
of filter 140) is a positive value, and the inductor current
i.sub.L of the first inductor (La) is a negative value.
[0042] Referring to FIG. 6, in the fourth operating mode, the
control method further includes a step of: uninterruptedly turning
on the third switch (S3), turning off the fourth switch (S4), the
fifth switch (S5), the sixth switch (S6) and the seventh switch
(S7), and synchronously turning on or off the first switch (S1),
the second switch (S2), the ninth switch (S9) and the tenth switch
(S10), wherein the first switch (S1), the second switch (S2), the
ninth switch (S9) and the tenth switch (S10) is turning on or off
in complementary with the eighth switch (S8); after the eighth
switch (S8) is turned off, when the first switch (S1), the second
switch (S2), the ninth switch (S9) and the tenth switch (S10) are
still not turned on, the freewheeling current of the first inductor
(La) and second inductor (Lb) go through the first diode (D1), the
third switch (S3) and the fourth diode (D4) because of the blocking
effect of the second switch (S2) and the tenth switch (S10); after
the dead time, when the first switch (S1), the second switch (S2),
the ninth switch (S9) and the tenth switch (S10) are turned on
synchronously, the freewheeling current of the first inductor (La)
and second inductor (Lb) go through the first switch (S1), second
switch (S2), ninth switch (S9) and tenth switch (S10), so that the
voltage of the output terminal of the inverter 100 (e.g., grid
voltage v.sub.grid of the output terminal of filter 140) is a
positive value, and the inductor current i.sub.L of the first
inductor (La) is a negative value.
[0043] It should be noted that the dead time in the fourth
operation mode is a time period during which the first switch (S1),
the second switch (S2), the ninth switch (S9) and the tenth switch
(S10) are still not turned on after the eighth switch (S8) is
turned off. During the dead time, a body diode of the second switch
(S2) and a body diode of the first switch (S1) are connected in
anti-series, and a body diode of the ninth switch (S9) and a body
diode of the tenth switch (S10) are connected in anti-series;
therefore, the freewheeling current cannot flow through the body
diodes of the first switch (S1) and ninth switch (S9) and go
through the first diode (D1) and the fourth diode (D4). Because the
body diode of MOSFET has poor reverse recovery characteristics,
when the current go through the body diode of the MOSFET, it may
cause the failure of the MOSFET during the reverse recovery
process. However, freewheeling current of aforesaid inverter 100
cannot go through the body diodes of the MOSFETs but go through the
external anti-paralleled diodes, here as the first diode (D1), the
second diode (D2), the third diode (D3) and the fourth diode (D4),
connected in parallel with the MOSFETs. Furthermore, the diodes may
be fast recovery diodes having good reverse recovery
characteristics and/or silicon carbide diodes so as to avoid
aforesaid serious influence. Therefore, the efficiency of the
inverter can be improved, and the presented inverter can also have
ability to provide reactive power.
[0044] Referring to FIG. 7, in the fifth operating mode, the
control method further includes a step of: uninterruptedly turning
on the eighth switch (S8), uninterruptedly turning off the first
switch (S1), the second switch (S2), the ninth switch (S9) and the
tenth switch (S10), and synchronously turning on or off the fourth
switch (S4), the fifth switch (S5), the sixth switch (S6) and the
seventh switch (S7), wherein the fourth switch (S4), the fifth
switch (S5), the sixth switch (S6) and the seventh switch (S7) is
turning on or off in complementary with the third switch (S3);
after the fourth switch (S4), the fifth switch (S5), the sixth
switch (S6) and the seventh switch (S7) are turned on, the DC
source 130 reversely charges the first inductor (La) and second
inductor (Lb), so that the inductor current i.sub.L of the first
inductor (La) and a voltage of the output terminal of the inverter
100 (e.g., grid voltage v.sub.grid of the output terminal of filter
140) are negative values.
[0045] Referring to FIG. 8, in the sixth operating mode, the
control method further includes a step of: uninterruptedly turning
on the eighth switch (S8), uninterruptedly turning off the first
switch (S1), the second switch (S2), the ninth switch (S9) and the
tenth switch (S10), and synchronously turning on or off the fourth
switch (S4), the fifth switch (S5), the sixth switch (S6) and the
seventh switch (S7), wherein the fourth switch (S4), the fifth
switch (S5), the sixth switch (S6) and the seventh switch (S7) is
turning on or off in complementary with the third switch (S3);
after the fourth switch (S4), the fifth switch (S5), the sixth
switch (S6) and the seventh switch (S7) are turned off, the when
the third switch (S3) is not turned on, a freewheeling current path
for the first inductor (La) and the second inductor (Lb) passes
through the eighth switch (S8) and the sixth diode (D6); in the
freewheeling state, after the dead time is over, i.e., after the
third switch (S3) is turned on, no current go through the third
switch (S3), so that the inductor current i.sub.L of the first
inductor (La) and a voltage of the output terminal of the inverter
100 (e.g., grid voltage v.sub.grid of the output terminal of filter
140) are negative values. In the sixth working mode, the dead time
is a time period during which the third switch (S3) is not turned
on after the fourth switch (S4), the fifth switch (S5), the sixth
switch (S6) and the seventh switch (S7) are turned off.
[0046] Referring to FIG. 9, in the seventh operating mode, the
control method further includes a step of: uninterruptedly turning
on the eighth switch (S8), uninterruptedly turning off the first
switch (S1), the second switch (S2), the ninth switch (S9) and the
tenth switch (S10), and synchronously turning on or off the fourth
switch (S4), the fifth switch (S5), the sixth switch (S6) and the
seventh switch (S7), wherein the fourth switch (S4), the fifth
switch (S5), the sixth switch (S6) and the seventh switch (S7) is
turning on or off in complementary with the third switch (S3);
after the third switch (S3) is turned on, a voltage of an output
terminal of the inverter 100 (e.g., grid voltage v.sub.grid of the
output terminal of filter 140) charges the first inductor (La) and
the second inductor (Lb) through the fifth diode (D5) and the third
switch (S3), and no current go through the eighth switch (S8) that
is turned on, so that the voltage of the output terminal of the
inverter 100 (e.g., grid voltage v.sub.grid of the output terminal
of filter 140) is a negative value, and the inductor current
i.sub.L of the first inductor (La) is a positive value.
[0047] Referring to FIG. 10, in the eighth operating mode, the
control method further includes a step of: uninterruptedly turning
on the eighth switch (S8), uninterruptedly turning off the first
switch (S1), the second switch (S2), the ninth switch (S9) and the
tenth switch (S10), and synchronously turning on or off the fourth
switch (S4), the fifth switch (S5), the sixth switch (S6) and the
seventh switch (S7), wherein the fourth switch (S4), the fifth
switch (S5), the sixth switch (S6) and the seventh switch (S7) is
turning on or off in complementary with the third switch (S3);
after the third switch (S3) is turned off, when the fourth switch
(S4), the fifth switch (S5), the sixth switch (S6) and the seventh
switch (S7) are not turned on, a freewheeling current of the first
inductor (La) and the second inductor (Lb) go through the second
diode (D2), the eighth switch (S8) and the third diode (D3) because
of the blocking effect of the seventh switch (S7) and the fifth
switch (S5); after the dead time, when the fourth switch (S4), the
fifth switch (S5), the sixth switch (S6) and the seventh switch
(S7) are turned on synchronously, the freewheeling current of the
first and second inductors go through the fourth switch (S4), the
fifth switch (S5), the sixth switch (S6) and the seventh switch
(S7), so that the voltage of the output terminal of the inverter
100 (e.g., grid voltage v.sub.grid of the output terminal of filter
140) is a negative value, and the inductor current i.sub.L of the
first inductor (La) is a positive value.
[0048] It should be noted that the dead time in the eighth
operation mode is a time period during which the fourth switch
(S4), the fifth switch (S5), the sixth switch (S6) and the seventh
switch (S7) are still not turned on after the third switch (S3) is
turned off. During the dead time, a body diode of the fifth switch
(S5) and a body diode of the fourth switch (S4) are connected in
anti-series, and a body diode of the seventh switch (S7) and a body
diode of the sixth switch (S6) are connected in anti-series; the
freewheeling current cannot flow through the body diodes of the
fourth switch (S4) and the sixth switch (S6) and go through the
second diode (D2) and the third diode (D3), so as to avoid the
serious influence that results from the poor reverse recovery
characteristics of the body diode of MOSFET. Therefore, the
non-isolated inverter may also have ability to provide reactive
power.
[0049] In the first, fourth, fifth and eighth operating modes, sum
of voltage potentials of the first and second common coupling
points (a) and (b) is V.sub.dc, in the second, third, sixth and
seventh operating modes, the first common coupling point (a) and
second common coupling point (b) are electrically in a "floating"
state, and their voltage potentials are clamped by the capacitor
and other switches. Each of the voltage potentials of the first
common coupling point (a) and the second common coupling point (b)
can be V.sub.dc/2 by properly selecting switches and maintaining
the symmetry. In other words, the sum of voltage potentials of the
first common coupling point and the second common coupling point
may be remain as Vdc by symmetrically selecting switches, so that
the inverter of FIG. 1 can be adapted in non-isolated photovoltaic
systems. In addition, when the non-isolated inverter of the present
invention operating in freewheeling states, the freewheeling
current does not pass through the body diodes of the transistors
and passes through the external diodes that are connected in
parallel with the transistors, so as to avoid the serious influence
that results from the poor reverse recovery characteristics of the
body diodes of MOSFET. Therefore, aforesaid non-isolated inverter
can provide active power (e.g., first, second, fifth and sixth
operating modes), and can also provide reactive power (e.g., third,
fourth, seventh, eighth operating modes).
[0050] In another aspect, FIG. 11 is a circuit diagram of an
inverter 200 according to another embodiment of the present
disclosure. The differences between the inverter 100 of FIG. 1 and
the inverter 200 of FIG. 11 are the changes of the position of the
common coupling points. As illustrated in FIG. 11, the connection
point between the second switch (S2) and third switch (S3) serves
as a first common coupling point (a'); the connection point between
the seventh switch (S7) and the eighth switch (S8) serves as a
second common coupling point (b').
[0051] The DC source 130 provides DC voltage V.sub.dc, the control
circuit of the inverter 200 uses an unipolar modulation, and the a
control method of controlling aforesaid inverter includes steps of:
synchronously turning on or off the first switch (S1), the second
switch (S2), the ninth switch (S9) and the tenth switch (S10),
controlling that the third switch (S3) is turning on or off in
complementary with the first switch (S1), the second switch (S2),
the ninth switch (S9) and the tenth switch (S10), synchronously
turning on or off the fourth switch (S4), the fifth switch (S5),
the sixth switch (S6) and the seventh switch (S7), and controlling
that the eighth switch (S8) is turning on or off in complementary
with the fourth switch (S4), the fifth switch (S5), the sixth
switch (S6) and the seventh switch (S7). Thus, these switches are
symmetrically selected so that the sum of voltage potentials of the
first point (a) and second common coupling point (b) is with low
common mode voltage.
[0052] Specifically, FIG. 12 is a waveform illustrating the grid
voltage v.sub.grid of the inverter 200 of FIG. 11 (i.e., the
voltage of output terminal of the inverter), the inductor current
i.sub.L and control signals (G1).about.(G10). As shown in FIG. 12,
control signals (G1), (G2), (G9) and (G10) respectively for the
first switch (S1), the second switch (S2), the ninth switch (S9)
and the tenth switch (S10) is complementary to a control signal
(G3) for the third switch (S3); control signals (G4), (G5), (G6)
and (G7) respectively for the fourth switch (S4), the fifth switch
(S5), the sixth switch (S6) and the seventh switch (S7) is
complementary to a control signal (G8) for the eighth switch (S8).
Thus, the inverter 200 outputs alternating current. In this way,
the control method not only provides active power output but also
controls reactive power output.
[0053] The control circuit may control the inverter 200 according
to the control method as shown in FIG. 12. The control method
executed by the control circuit for controlling the inverter
includes eight operating modes. The eight operating modes of the
inverter 200 is similar to the eight operating modes of the
inverter 100, in which the difference is that an on/off operation
of the third switch (S3) and an on/off operation of the eighth
switch (S8) are swapped over, and thus, are not repeated
herein.
[0054] In summary, a control method of controlling aforesaid
inverter includes steps of: synchronously turning on or off the
first switch (S1), the second switch (S2), the ninth switch (S9)
and the tenth switch (S10), and controlling that the eighth switch
(S8) is turning on or off in complementary with the first switch
(S1), the second switch (S2), the ninth switch (S9) and the tenth
switch (S10); synchronously turning on or off the fourth switch
(S4), the fifth switch (S5), the sixth switch (S6) and the seventh
switch (S7); controlling that the third switch (S3) is turning on
or off in complementary with the fourth switch (S4), the fifth
switch (S5), the sixth switch (S6) and the seventh switch (S7).
Alternatively, the control method includes following steps:
synchronously turning on or off the first switch (S1), the second
switch (S2), the ninth switch (S9) and the tenth switch (S10), and
controlling that the third switch (S3) is turning on or off in
complementary with the first switch (S1), the second switch (S2),
the ninth switch (S9) and the tenth switch (S10); synchronously
turning on or off the fourth switch (S4), the fifth switch (S5),
the sixth switch (S6) and the seventh switch (S7); controlling that
the eighth switch (S8) is turning on or off in complementary with
the fourth switch (S4), the fifth switch (S5), the sixth switch
(S6) and the seventh switch (S7).
[0055] Although various embodiments of the invention have been
described above with a certain degree of particularity, or with
reference to one or more individual embodiments, they are not
limiting to the scope of the present disclosure. Those with
ordinary skill in the art could make numerous alterations to the
disclosed embodiments without departing from the spirit or scope of
this invention. Accordingly, the protection scope of the present
disclosure shall be defined by the accompany claims.
* * * * *