U.S. patent application number 16/622282 was filed with the patent office on 2021-04-29 for single-stage three-phase high-gain boost type three-port integrated inverter.
This patent application is currently assigned to Qingdao University. The applicant listed for this patent is Qingdao University. Invention is credited to Daolian CHEN.
Application Number | 20210126553 16/622282 |
Document ID | / |
Family ID | 1000005520335 |
Filed Date | 2021-04-29 |
![](/patent/app/20210126553/US20210126553A1-20210429\US20210126553A1-2021042)
United States Patent
Application |
20210126553 |
Kind Code |
A1 |
CHEN; Daolian |
April 29, 2021 |
SINGLE-STAGE THREE-PHASE HIGH-GAIN BOOST TYPE THREE-PORT INTEGRATED
INVERTER
Abstract
A single-stage three-phase high-gain boost-type three-port
integrated inverter includes a center-tapped energy storage
inductor, a three-phase inverter bridge and a three-phase filter,
which are successively connected in cascade. A drain terminal and a
source terminal of the energy storage switch are respectively
connected to the center tap of the energy storage inductor and the
negative electrode of an input DC power source. A battery
charge/discharge switch unit is connected between a positive
electrode of the input DC power source, a positive electrode of a
battery and two ends of the center-tapped energy storage inductor.
The inverter has three ports, an input port, an output port, and an
energy storage port. The inverter has three modes which are the
input power supply supplies power to the output load and the
battery, the input power supply and battery supply power to the
output load, and the battery supplies power to the load.
Inventors: |
CHEN; Daolian; (Qingdao,
CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Qingdao University |
Qingdao |
|
CN |
|
|
Assignee: |
Qingdao University
Qingdao
CN
|
Family ID: |
1000005520335 |
Appl. No.: |
16/622282 |
Filed: |
December 6, 2018 |
PCT Filed: |
December 6, 2018 |
PCT NO: |
PCT/CN2018/000413 |
371 Date: |
December 12, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H02J 7/0068 20130101;
H02J 7/35 20130101; H02M 7/5387 20130101 |
International
Class: |
H02M 7/5387 20060101
H02M007/5387; H02J 7/00 20060101 H02J007/00; H02J 7/35 20060101
H02J007/35 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 10, 2018 |
CN |
201811176804.1 |
Claims
1. A single-stage three-phase high-gain boost-type three-port
integrated inverter, comprising: a center-tapped energy storage
inductor, a three-phase inverter bridge, and a three-phase filter;
wherein the center-tapped energy storage inductor, the three-phase
inverter bridge, and the three-phase filter are successively
connected in cascade; a drain terminal and a source terminal of the
energy storage switch are respectively connected to a center tap of
the energy storage inductor and a negative electrode of an input DC
power source; a battery charging/discharging switch unit is
connected between a positive electrode of the input DC power
source, a positive electrode of a battery and two ends of the
center-tapped energy storage inductor; the battery
charging/discharging switch unit comprises a charging subcircuit
switch, a discharging subcircuit switch, and a blocking diode; an
anode and a cathode of a charging subcircuit diode are respectively
connected to a right end of the center-tapped energy storage
inductor and a drain terminal of the charging subcircuit switch; a
source terminal of the charging subcircuit switch is connected to a
drain terminal of the discharging subcircuit switch and a positive
electrode of the battery; a source terminal of the discharging
subcircuit switch is connected to a cathode of the blocking diode
and a left end of the center-tapped energy storage inductor; an
anode of the blocking diode is connected to the positive electrode
of the input DC power source; a negative electrode of the battery
is connected to the negative electrode of the input DC power
source; the blocking diode is configured to avoid a short circuit
between the battery and the input DC power source circuit when the
discharging subcircuit switch is turned on, and a terminal voltage
U.sub.b of the battery is greater than a voltage U.sub.i of the
input DC power source; the voltage U.sub.i of the input DC power
source or the terminal voltage U.sub.b of the battery, a left part
inductor L.sub.1 of the center-tapped energy storage inductor L,
and the energy storage switch form a magnetizing loop; the voltage
U.sub.i of the input DC power source or the terminal voltage
U.sub.b of the battery, the center-tapped energy storage inductor
L, one of the line-to-line voltage loops of the three-phase
inverter bridge having an instantaneous value of a line-to-line
voltage not less than ( {square root over (6)}/2)U.sub.p or the
charging subcircuit switch, and the battery form a demagnetizing
loop; wherein U.sub.p is an RMS line-to-neutral voltage of a
three-phase output; the three-phase inverter bridge comprises
two-quadrant power switches configured to withstand bidirectional
voltage stress and unidirectional current stress; a maximum voltage
gain of the inverter is (1+dN.sub.2/N.sub.1)/(1-d), wherein, d is a
duty ratio of the inverter varying according to a sine law, and
N.sub.1 and N.sub.2 respectively are number of turns of a left part
and a right part windings of the center-tapped energy storage
inductor L; the inverter has an input port, an output port, and an
intermediate port for energy storage composed of the
charging/discharging switch unit of the battery; the inverter has
three power supply modes including a first mode, a second mode and
a third mode; in the first mode, the input DC power source supplies
power to the output load and the battery; in the second mode, the
input DC power source and the battery supply power to the output
load; and in the third mode, and the battery supplies power to the
load; the first mode, the second mode and the three mode are
respectively equivalent to a single-input double-output converter,
a double-input single-output inverter with parallel connection and
time-phased supplying power and a single-input single-output
inverter; the inverter employs an energy management and control
strategy including a master-slave load sharing for photovoltaic
cells and the battery, a double-loop improved separate zone SPWM
with an outer RMS output voltage loop of the inverter with a
maximum power point tracking of the photovoltaic cells and an inner
current loop of the energy storage inductor, and the inverter is
configured to be switched smoothly and seamlessly among the three
power supply modes.
Description
CROSS REFERENCE TO THE RELATED APPLICATIONS
[0001] This application is the national phase entry of
International Application No. PCT/CN2018/000413, filed on Dec. 6,
2018, which is based upon and claims priority to Chinese Patent
Application No. 201811176804.1, filed on Oct. 10, 2018, the entire
contents of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The present disclosure relates to a single-stage three-phase
high-gain boost-type three-port integrated inverter and belongs to
the technical field of power electronic conversion.
BACKGROUND
[0003] The inverter is a static converter that converts
direct-current (DC) electricity into alternating-current (AC)
electricity by using a power semiconductor device to supply power
for an AC load or to be grid connected with a public grid for power
supply.
[0004] With the growing scarcity of fossil energy such as
petroleum, coal and natural gas, serious environmental pollution,
global warming, and nuclear waste and environmental pollution
caused by nuclear energy production energy and the environmental
challenges have become critical issues facing humanity in the 21st
century. Renewable energy sources such as solar, wind, tide and
geotherm benefit from the advantages of being clean,
pollution-free, low-cost, reliable and having abundant reserves.
These benefits have drawn increasing attention in the exploitation
and utilization as well as played an important role in the
sustainable development of the global economy. The DC electricity
converted from the renewable energy sources such as solar, wind,
hydrogen, tide and geotherm is usually unstable, so the DC
electricity needs to be converted into AC electricity by an
inverter for the load to use or to be grid connected with the
public grid for power supply. In occasions where the DC generators,
batteries, solar cells, fuel cells and wind power generators are
used as the main DC power supply in the inversion, the inverters
have broad prospective applications.
[0005] At present, the circuit structure of a single-stage
three-phase buck inverter is usually adopted in the occasions of
medium and large capacity inversion and has no energy storage
function. Such types of inverters require the voltage of the DC
side to be greater than the peak value of the line-to-line voltage
of the AC side to work normally, so there is an obvious defect.
When the voltage of the DC side (e.g. the output capability of a
photovoltaic cell) decreases, for example, in rainy days or nights,
the output power of the entire power generation system will be
reduced or the system would even stop operating, and the
utilization rate of the system will be reduced, which is unable to
meet the demand of the load for electricity and is difficult to
form an independent power supply system. To solve this problem, the
following three solutions are usually used: (1) add a boost DC
converter to the first stage of the circuit of the inverter to form
a two-stage circuit structure. However, when the duty ratio D is
close to the limit value, 1-D is rather small and the adjustment
range of D is limited. This solution has some disadvantages, such
as poor system dynamic characteristics and decrease in the step-up
voltage gain due to the influence of circuit parasitic parameters,
making it unsuitable to be applied in the conversion occasions
requiring high voltage gain. (2) Add a power frequency transformer
to the output circuit. By doing so, the size, weight and cost of
the system will be greatly increased, which is not applicable to
the current situation where the prices of copper and iron raw
materials continue to increase sharply. (3) Adopt a high-frequency
transformer to realize electrical isolation and voltage matching,
which belongs to two-stage power conversion structure, and the
output capacity and application range are limited.
[0006] Therefore, it is extremely urgent to find a single-stage
three-phase high-gain boost-type three-port integrated inverter
having an input port, an output port and an intermediate port for
energy storage which is composed of a charging/discharging switch
unit of the battery, and a photovoltaic power generation system
thereof. This purpose is of great significance to overcome the
defects that the single-stage three-phase buck-type inverter cannot
be directly applied in the three-phrase boost-type inversion and
cannot meet the demand of the load for electricity when the output
capability of the input DC power source of the inverter is reduced.
This purpose also plays an important role in improving the overload
capability, short circuit capability, and service life of the
inverter, reducing the electromagnetic interference at the input DC
side, improving the theory of inversion technology in the field of
power electronics, promoting the development of renewable energy
power generation industry, and developing an energy-saving and
economical society.
SUMMARY
[0007] The objective of the present disclosure is to provide a
single-stage three-phase high-gain boost-type three-port integrated
inverter with the advantages of high voltage gain, single-stage
power conversion, high conversion efficiency, low cost, high
reliability in the event of overload and short circuit, large or
middle level output capacity, and having an input port, an output
port and an intermediate port for energy storage which is composed
of a charging/discharging switch unit of the battery.
[0008] The technical solution of the present disclosure is as
follows. A single-stage three-phase high-gain boost-type three-port
integrated inverter includes a center-tapped energy storage
inductor, a three-phase inverter bridge, and a three-phase filter.
The center-tapped energy storage inductor, the three-phase inverter
bridge, and the three-phase filter are successively connected in
cascade. A drain terminal and a source terminal of the energy
storage switch are respectively connected to a center tap of the
energy storage inductor and the negative electrode of an input DC
power source. A battery charging/discharging switch unit is
connected between a positive electrode of the input DC power
source, a positive electrode of a battery and two ends of the
center-tapped energy storage inductor. The battery
charging/discharging switch unit includes a charging subcircuit
switch, a discharging subcircuit switch, and a blocking diode. An
anode and a cathode of a charging subcircuit diode are respectively
connected to a right end of the center-tapped energy storage
inductor and a drain terminal of the charging subcircuit switch. A
source terminal of the charging subcircuit switch is connected to a
drain terminal of the discharging subcircuit switch and a positive
electrode of the battery. A source terminal of the discharging
subcircuit switch is connected to a cathode of the blocking diode
and a left end of the center-tapped energy storage inductor. An
anode of the blocking diode is connected to the positive electrode
of the input DC power source. A negative electrode of the battery
is connected to the negative electrode of the input DC power
source. The blocking diode is configured to avoid a short circuit
between the battery and the input DC power source circuit when the
discharging subcircuit switch is turned on, and a terminal voltage
U.sub.b of the battery is greater than a voltage U.sub.i of the
input DC power source. The voltage U.sub.i of the input DC power
source or the terminal voltage U.sub.b of the battery, a left part
inductor L.sub.1 of the center-tapped energy storage inductor L and
the energy storage switch form a magnetizing loop. The voltage
U.sub.i of the input DC power source or the terminal voltage
U.sub.b of the battery, the center-tapped energy storage inductor
L, anyone of the line-to-line voltage loops of the three-phase
inverter bridge having an instantaneous value of a line-to-line
voltage not less than ( {square root over (6)}/2)U.sub.p or the
charging subcircuit switch, and the battery form a demagnetizing
loop. U.sub.p is an RMS line-to-neutral voltage of a three-phase
output. The three-phase inverter bridge includes two-quadrant power
switches configured to withstand bidirectional voltage stress and
unidirectional current stress. A maximum voltage gain of the
inverter is (1+dN.sub.2/N.sub.1)/(1-d), wherein, d is a duty ratio
of the inverter varying according to the sine law, and N.sub.1 and
N.sub.2 respectively are the number of turns of the left part and
the right part windings of the center-tapped energy storage
inductor L. The inverter has an input port, an output port, and an
intermediate port for energy storage composed of the
charging/discharging switch unit of the battery. The inverter has
three power supply modes. Mode 1 is the input DC power source
supplies power to the output load and the battery. Mode 2 is the
input DC power source and the battery supply power to the output
load. Mode 3 is the battery supplies power to the load. The first
mode, the second mode and the three mode are respectively
equivalent to a single-input double-output converter, a
double-input single-output inverter with parallel connection and
time-phased supplying power and a single-input single-output
inverter. The inverter employs an energy management control
strategy including a master-slave load sharing for the photovoltaic
cell and battery, a double-loop improved separate zone SPWM with an
outer RMS output voltage loop of the inverter with a maximum power
point tracking of photovoltaic cells and an inner current loop of
the energy storage inductor, and the system can be switched
smoothly and seamlessly among the three power supply modes.
[0009] The present disclosure constructs "the circuit structure of
a single-stage three-phase high-gain boost-type three-port
integrated inverter which is constituted by successively cascading
the center-tapped energy storage inductor, the three-phase inverter
bridge, and the three-phase filter, wherein, the drain terminal and
the source terminal of the energy storage switch are respectively
connected to the center tap of the energy storage inductor and the
negative electrode of the input DC power source, and the battery
charging/discharging switch unit is connected between the positive
electrodes of the input DC power source and battery and two ends of
the center-tapped energy storage inductor" based on "the circuit
structure of a conventional single-stage three-phase buck-type
two-port inverter which is constituted by successively cascading a
three-phase inverter bridge and a three-phase LC filter". Namely,
by configuring an inductor L.sub.1 for the energy storage loop with
an inductance smaller than the inductance of the inductor L
(corresponding to the windings N.sub.1+N.sub.2) for the energy
releasing circuit, the voltage boosting with a high voltage gain of
the inverter can be achieved. By integrating the
charging/discharging switch unit of the battery and adding an
intermediate port for energy storage, the three power supply modes
can be achieved. Namely, in mode 1, the input DC power source
supplies power to the output load and the battery. In mode 2, the
input DC power source and the battery supply power to the output
load and in mode 3, the battery supplies power to the load.
[0010] The present disclosure can convert unstable and low-quality
DC electricity with low amplitude into stable and high-quality
three-phase output sinusoidal AC electricity with high amplitude,
and has the advantages of having three ports, single-stage power
conversion, high power density, high conversion efficiency, high
voltage gain, low distortion of output waveform, high reliability
in the event of overload and short circuit, long service life, and
low cost. Thus it is suitable for the occasions of medium and large
capacity three-phase boost inversion, especially for an independent
photovoltaic power supply system. With the presence of the novel
devices such as the IGBT capable of bidirectional blocking, such
type of inverter no longer needs to be serially connected with a
diode and solves the problem of diode loss.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 shows a circuit structure of the single-stage
three-phase high-gain boost-type three-port integrated inverter in
which the energy storage inductor is at the positive end of the
input DC bus;
[0012] FIG. 2 shows a circuit structure of the single-stage
three-phase high-gain boost-type three-port integrated inverter in
which the energy storage inductor is at the negative end of the
input DC bus;
[0013] FIG. 3 shows the waveforms according to the principle of the
single-stage three-phase high-gain boost-type three-port integrated
inverter;
[0014] FIG. 4 shows six 60-degree intervals of the three-phase
output voltage in a low-frequency output period;
[0015] FIG. 5 shows a magnetizing equivalent circuit of the energy
storage inductor of the single-stage three-phase high-gain
boost-type three-port integrated inverter during the period of
dT.sub.S/2 in interval I;
[0016] FIG. 6 shows a demagnetizing equivalent circuit of the
energy storage inductor of the single-stage three-phase high-gain
boost-type three-port integrated inverter during the period of
(1-d)T.sub.S/2 in interval I passing through the a and b
phases;
[0017] FIG. 7 shows a demagnetizing equivalent circuit of the
energy storage inductor of the single-stage three-phase high-gain
boost-type three-port integrated inverter during the period of
(1-d)T.sub.S/2 in interval I passing through the c and b
phases;
[0018] FIG. 8 shows the first embodiment of the topology of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in a the schematic diagram of a three-phase filter circuit
with capacitor;
[0019] FIG. 9 shows the second embodiment of the topology of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in a the schematic diagram of a three-phase filter circuit
with capacitor and inductor;
[0020] FIG. 10 shows an equivalent circuit of the single-stage
three-phase high-gain boost-type three-port integrated inverter in
power supply mode 1 in which the power flows from the input port to
the output port and the intermediate port;
[0021] FIG. 11 shows an equivalent circuit of the single-stage
three-phase high-gain boost-type three-port integrated inverter in
power supply mode 2 in which the power flows from the input port
and the intermediate port to the output port;
[0022] FIG. 12 shows an equivalent circuit of the single-stage
three-phase high-gain boost-type three-port integrated inverter in
power supply mode 3 in which the power flows from the intermediate
port to the output port;
[0023] FIG. 13 is a block diagram of the energy management and
control including a master-slave load sharing for the photovoltaic
cell and battery, a double-loop improved separate zone SPWM with an
outer RMS output voltage loop of the inverter with a maximum power
point tracking of photovoltaic cells and an inner current loop of
the energy storage inductor, and the system can be switched
smoothly and seamlessly among the three power supply modes;
[0024] FIG. 14 shows the waveforms according to the principle of
the energy management and control having a master-slave load
sharing for the photovoltaic cell and battery and a double-loop
improved separate zone SPWM with an outer RMS output voltage loop
of the inverter with a maximum power point tracking of photovoltaic
cells and an inner current loop of the energy storage inductor
within the first half of the low-frequency period in the power
supply mode 1 and the latter half of the low-frequency period in
the power supply mode 2;
[0025] FIG. 15 shows the waveforms according to the principle of
the generation of the control signal of the power switch of the
single-stage three-phase high-gain boost-type three-port integrated
inverter within a low-frequency output period in interval I (0-60
degrees);
[0026] FIG. 16 shows the control signal of the power switch of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in interval I in power supply mode 1;
[0027] FIG. 17 shows the control signal of the power switch of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in interval I in power supply mode 2;
[0028] FIG. 18 shows the control signal of the power switch of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in interval I in power supply mode 3;
[0029] FIG. 19 shows an equivalent circuit of the mode I-1 and mode
I-3 of the single-stage three-phase high-gain boost-type three-port
integrated inverter in power supply mode 1 where D.sub.5, S,
S.sub.b2 are turned on and S.sub.a2, S.sub.b1, S.sub.c2, S.sub.a1,
S.sub.c1 are turned off;
[0030] FIG. 20 shows an equivalent circuit of the mode I-2 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.a1, S.sub.b2 are turned on and S.sub.a2, S.sub.b1, S.sub.c2,
S, S.sub.c1 are turned off;
[0031] FIG. 21 shows an equivalent circuit of the mode I-4 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.c1, S.sub.b2 are turned on and S.sub.a2, S.sub.b1, S.sub.c2,
S, S.sub.a1 are turned off;
[0032] FIG. 22 shows an equivalent circuit of the mode II-1 and
mode II-3 of the single-stage three-phase high-gain boost-type
three-port integrated inverter in power supply mode 1 where
D.sub.5, S, S.sub.a1 are turned on and S.sub.a2, S.sub.b1,
S.sub.c1, S.sub.b2, S.sub.c2 are turned off;
[0033] FIG. 23 shows an equivalent circuit of the mode II-2 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.b2, S.sub.a1 are turned on and S.sub.a2, S.sub.b1, S.sub.c1,
S, S.sub.c2 are turned off;
[0034] FIG. 24 shows an equivalent circuit of the mode II-4 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.c2, S.sub.a1 are turned on and S.sub.a2, S.sub.b1, S.sub.c1,
S, S.sub.b2 are turned off;
[0035] FIG. 25 shows an equivalent circuit of the mode III-1 and
mode III-3 of the single-stage three-phase high-gain boost-type
three-port integrated inverter in power supply mode 1 where
D.sub.5, S, S.sub.c2 are turned on and S.sub.a2, S.sub.b2,
S.sub.c1, S.sub.a1, S.sub.b1 are turned off;
[0036] FIG. 26 shows an equivalent circuit of the mode III-2 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.a1, S.sub.c2 are turned on and S.sub.a2, S.sub.b2, S.sub.c1,
S, S.sub.b1 are turned off;
[0037] FIG. 27 shows an equivalent circuit of the mode III-4 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.b1, S.sub.c2 are turned on and S.sub.a2, S.sub.b2, S.sub.c1,
S, S.sub.a1 are turned off;
[0038] FIG. 28 shows an equivalent circuit of the mode IV-1 and
mode IV-3 of the single-stage three-phase high-gain boost-type
three-port integrated inverter in power supply mode 1 where
D.sub.5, S, S.sub.b1 are turned on and S.sub.a1, S.sub.b2,
S.sub.c1, S.sub.a2, S.sub.c2 are turned off;
[0039] FIG. 29 shows an equivalent circuit of the mode IV-2 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.a2, S.sub.b1 are turned on and S.sub.a1, S.sub.b2, S.sub.c1,
S, S.sub.c2 are turned off;
[0040] FIG. 30 shows an equivalent circuit of the mode IV-4 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.c2, S.sub.b1 are turned on and S.sub.a1, S.sub.b2, S.sub.c1,
S, S.sub.a2 are turned off;
[0041] FIG. 31 shows an equivalent circuit of the mode V-1 and mode
V-3 of the single-stage three-phase high-gain boost-type three-port
integrated inverter in power supply mode 1 where D.sub.5, S,
S.sub.a2 are turned on and S.sub.a1, S.sub.b2, S.sub.c2, S.sub.b1,
S.sub.c1 are turned off;
[0042] FIG. 32 shows an equivalent circuit of the mode V-2 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.b1, S.sub.a2 are turned on and S.sub.a1, S.sub.b2, S.sub.c2,
S, S.sub.c1 are turned off;
[0043] FIG. 33 shows an equivalent circuit of the mode V-4 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.c1, S.sub.a2 are turned on and S.sub.a1, S.sub.b2, S.sub.c2,
S, S.sub.b1 are turned off;
[0044] FIG. 34 shows an equivalent circuit of the mode VI-1 and
mode VI-3 of the single-stage three-phase high-gain boost-type
three-port integrated inverter in power supply mode 1 where
D.sub.5, S, S.sub.c1 are turned on and S.sub.a1, S.sub.b1,
S.sub.c2, S.sub.a2, S.sub.b2 are turned off;
[0045] FIG. 35 shows an equivalent circuit of the mode VI-2 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.a2, S.sub.c1 are turned on and S.sub.a1, S.sub.b1, S.sub.c2,
S, S.sub.b2 are turned off; and
[0046] FIG. 36 shows an equivalent circuit of the mode VI-4 of the
single-stage three-phase high-gain boost-type three-port integrated
inverter in power supply mode 1 where D.sub.5, D.sub.6, S.sub.6,
S.sub.b2, S.sub.c1 are turned on and S.sub.a1, S.sub.b1, S.sub.c2,
S, S.sub.a2 are turned off.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0047] The technical solution of the present disclosure is further
described below with reference to the drawings and embodiments.
[0048] A single-stage three-phase high-gain boost-type three-port
integrated inverter includes a center-tapped energy storage
inductor, a three-phase inverter bridge, and a three-phase filter.
The center-tapped energy storage inductor, the three-phase inverter
bridge, and the three-phase filter are successively connected in
cascade. A drain terminal and a source terminal of the energy
storage switch are respectively connected to a center tap of the
energy storage inductor and the negative electrode of an input DC
power source. A battery charging/discharging switch unit is
connected between the positive electrodes of the input DC power
source and the battery and two ends of the center-tapped energy
storage inductor. The battery charging/discharging switch unit
includes a charging subcircuit switch, a discharging subcircuit
switch, and a blocking diode. An anode and a cathode of a charging
subcircuit diode are respectively connected to a right end of the
center-tapped energy storage inductor and a drain terminal of the
charging subcircuit switch. A source terminal of the charging
subcircuit switch is connected to a drain terminal of the
discharging subcircuit switch and a positive electrode of the
battery. A source terminal of the discharging subcircuit switch is
connected to a cathode of the blocking diode and a left end of the
center-tapped energy storage inductor. An anode of the blocking
diode is connected to the positive electrode of the input DC power
source. A negative electrode of the battery is connected to the
negative electrode of the input DC power source. The blocking diode
is configured to avoid a short circuit between the battery and the
input DC power source circuit when the discharging subcircuit
switch is turned on, and a terminal voltage U.sub.b of the battery
is greater than a voltage U.sub.i of the input DC power source. The
voltage U.sub.i of the input DC power source or the terminal
voltage U.sub.b of the battery, a left part inductor L.sub.1 of the
center-tapped energy storage inductor L, and the energy storage
switch form a magnetizing loop. The voltage U.sub.i of the input DC
power source or the terminal voltage U.sub.b of the battery, the
center-tapped energy storage inductor L, anyone of the line-to-line
voltage loops of the three-phase inverter bridge having an
instantaneous value of a line-to-line voltage not less than (
{square root over (6)}/2)U.sub.p or the charging subcircuit switch,
and the battery form a demagnetizing loop. U.sub.p is an RMS
line-to-neutral voltage of a three-phase output. The three-phase
inverter bridge includes two-quadrant power switches configured to
withstand bidirectional voltage stress and unidirectional current
stress. A maximum voltage gain of the inverter is
(1+dN.sub.2/N.sub.1)/(1-d), wherein, d denotes a duty ratio of the
inverter varying according to the sine law, and N.sub.1 and N.sub.2
respectively denote the number of turns of the left part and the
right part windings of the center-tapped energy storage inductor L.
The inverter has an input port, an output port, and an intermediate
port for energy storage composed of the charging/discharging switch
unit of the battery. The inverter has three power supply modes.
Mode 1 is the input DC power source supplies power to the output
load and the battery. Mode 2 is the input DC power source and the
battery supply power to the output load, and mode 3 is the battery
supplies power to the load. The inverter employs an energy
management control strategy including a master-slave load sharing
for the photovoltaic cell and a battery, a double-loop improved
separate zone SPWM with an outer RMS output voltage loop of the
inverter with a maximum power point tracking of photovoltaic cells
and an inner current loop of the energy storage inductor, and the
system can be switched smoothly and seamlessly among the three
power supply modes.
[0049] The circuit structure and principle waveforms of the
single-stage three-phase high-gain boost-type three-port integrated
inverter are shown in FIGS. 1, 2 and 3. In FIGS. 1, 2 and 3,
U.sub.i is the voltage of the input DC power source. U.sub.b is the
voltage of the battery. N(N=N.sub.1+N.sub.2) is the number of turns
of the winding of the entire energy storage inductor. N.sub.1 is
the number of turns of the winding on the left part of the center
tap of the energy storage inductor and N.sub.2 is the number of
turns of the winding on the right part of the center tap of the
energy storage inductor. L, L.sub.1, and L.sub.2 are the inductance
values corresponding to N, N.sub.1, and N.sub.2, respectively. M=r
{square root over (L.sub.1L.sub.2)} is the mutual inductance
between L.sub.1 and L.sub.2 (r is the coupling coefficient between
windings N.sub.1 and N.sub.2). Z.sub.La, Z.sub.Lb, Z.sub.Lc
respectively denote the three-phase output impedance of passive
load and u.sub.a, u.sub.b, u.sub.c respectively denote the
line-to-neutral voltages of the three-phase output impedance of
passive load or the voltages of the three-phase AC grid. The
working principle and performance of the two circuit structures
shown in FIGS. 1 and 2 are identical, except some fine differences
on the circuit connections. When the center-tapped energy storage
inductor is at the positive end of the input DC bus, an energy
storage switch is connected between the center tap of the energy
storage inductor and the negative end of the input DC power source.
The blocking diode is connected to the positive DC bus in series,
and the battery and the input DC power source have the same
negative end. When the center-tapped energy storage inductor is at
the negative end of the input DC bus, an energy storage switch is
connected between the center tap of the energy storage inductor and
the positive end of the input DC power source, the blocking diode
is connected to the negative DC bus in series, and the battery and
the input DC power source have the same positive end.
[0050] The energy storage switch in the two circuit structures is
composed of MOSFET or IGBT, GTR and other power devices. The
three-phase inverter bridge includes a plurality of two-quadrant
power switches configured to withstand bidirectional voltage stress
and unidirectional current stress. The three-phase filter is a
three-phase filter with a capacitor or a three-phase filter with a
capacitor and an inductor. The three-phase output end can be
connected to the three-phase AC passive load Z.sub.La, Z.sub.Lb,
Z.sub.Lc, or can be connected to the three-phase AC grid u.sub.a,
u.sub.b, u.sub.c. An input filter may be or may not be set between
the input DC power source U.sub.i and the blocking diode. The
ripple of the input DC current can be suppressed by setting the
input filter. Taking the power supply mode 1 in which the input DC
power source U.sub.i supplies power to the output AC load and the
battery as an example, when the energy storage switch is turned on,
the input DC power source U.sub.i magnetizes the energy storage
inductor L1, and the three-phase AC load Z.sub.La, Z.sub.Lb,
Z.sub.Lc or the three-phase AC grid u.sub.a, u.sub.b, u.sub.c rely
on the three-phase filter to maintain the power supply. When the
energy storage switch is turned off, the energy storage inductor L1
is demagnetized and works with the input DC power source U.sub.i to
supply power to the corresponding two-phase AC load (or AC grid)
and the battery during different time periods. The energy storage
switch modulates the input DC power source U.sub.i into rippled
high-frequency pulsed DC currents i.sub.L1, i.sub.L2 which are then
inverted into the tri-state modulated currents i.sub.ma, i.sub.mb,
i.sub.mc by the three-phase inverter bridge. After the three-phase
filtering, the high-quality three-phase sinusoidal voltages
u.sub.a, u.sub.b, u.sub.c can be obtained at the three-phase AC
load (or the high-quality three-phase sinusoidal currents waves
i.sub.a, i.sub.b, i.sub.c can be obtained at the three-phase AC
grid), or the i.sub.L2 charges the battery U.sub.b through the
charging subcircuit switch. It should be added that, at the moment
when the energy storage switch is turned on or turned off, the
magnetic potential of the windings N of the entire energy storage
inductor is equal to the magnetic potential of the left part
windings N1 of the energy storage inductor.
[0051] In order to ensure the quality of the output waveform, the
inverter must satisfy the working mechanism of the Boost-type
converter. Namely, the energy storage inductor must have both of
the opposite processes of magnetization and demagnetization in a
high-frequency switching period. Taking the zero value points of
the three-phase output instantaneous voltage waveform as the
dividing points, a low-frequency output cycle is divided into six
60-degree intervals, as shown in FIG. 4. In FIG. 4, U.sub.p is the
effective value of the three-phase output voltage. For any one of
the 60-degree intervals, there are always two instantaneous
line-to-line voltages not less than ( {square root over
(6)}/2)U.sub.P. For example, in the interval I (0 degree-60
degrees), the line-to-line voltages u.sub.ab and u.sub.cb are not
less than ( {square root over (6)}/2)U.sub.p, so the input voltage
U.sub.i is merely required to be less than ( {square root over
(6)}/2)U.sub.p. The magnetizing and demagnetizing equivalent
circuits of the single-stage three-phase high-gain boost-type
three-port integrated inverter within a high-frequency switching
period shown in FIGS. 5, 6 and 7 are the result of the interval I
(0 degree-60 degrees) shown in FIG. 4, the circuit structure shown
in FIG. 1, the power supply mode 1 in which the input DC power
source U.sub.i supplies power to the output AC load and the
battery. Let the high-frequency switching period of the three-phase
inverter bridge be T.sub.S, then the switching period of the energy
storage switch is T.sub.S/2, and the duty ratio d of the on-time
T.sub.on of the energy storage switch in T.sub.S/2 is
d=T.sub.on/(T.sub.S/2). The energy storage inductor is magnetized
twice within a high-frequency switching period T.sub.S, and is
respectively demagnetized once through the loop of the a and b
phases and the battery charging subcircuit and once through the
loop of the c and b phases and the battery charging subcircuit, so
as to ensure that the input DC power source evenly supplies power
to the three-phase output load and to realize the magnetic reset of
the energy storage inductor. Obviously, the duty ratios of the
energy storage inductor corresponding to the two magnetization
processes in one T.sub.S must differ from each other. The following
equations can be obtained according to the magnetizing equivalent
circuit during the dT.sub.S/2 shown in FIG. 5,
U i = N 1 .times. .DELTA..phi. + d .times. T s / 2 . ( 1 )
##EQU00001##
[0052] According to the demagnetizing equivalent circuit during the
period of (1-d)T.sub.S/2 shown in FIG. 6, if the demagnetization is
performed only through the loop of the a and b phases during this
period, then,
u ab - U i = ( N 1 + N 2 ) .times. .DELTA..phi. - ( 1 - d ) .times.
T s / 2 . ( 2 ) ##EQU00002##
[0053] In fact, the demagnetization is performed through the loop
of the a and b phases and the charging subcircuit circuit of the
battery during different time periods. Therefore, in the steady
state, .DELTA..phi..sub.-.ltoreq..DELTA..phi..sub.+, and the
maximum voltage gain can be obtained according to equations (1) and
(2) as below,
u.sub.ab/U.sub.i.ltoreq.(1+dN.sub.2/N.sub.1)/(1-d) (3).
[0054] Similarly, the maximum voltage gain can be deduced as
u.sub.cb/U.sub.i=u.sub.ac/U.sub.i.ltoreq.(1+dN.sub.2/N.sub.1)/(1-d)
(4).
[0055] In equations (1), (2), (3) and (4), U.sub.i is the voltage
of the input DC power source, and N.sub.1 and N.sub.2 respectively
are the number of turns of the left part windings and right part
windings of the center-tapped energy storage inductor L. The
maximum voltage gain (1+dN.sub.2/N.sub.1)/(1-d) of the inverter is
always greater than 1, and greater than the voltage gain 1/(1-d) of
the traditional boost-type inverter. The voltage gain of the
inverter is improved by configuring the energy storage loop with
the inductance L.sub.1 (corresponding to the windings N.sub.1) less
than the inductance L (corresponding to the windings
N.sub.1+N.sub.2) of the energy releasing loop. By integrating the
charging/discharging switch unit of the battery with an
intermediate port for energy storage, three power supply modes can
be achieved. Therefore, the inverter is called a single-stage
three-phase high-gain boost-type three-port integrated inverter.
The voltage gain can be adjusted by adjusting the position of the
center tap of the energy storage inductor (i.e. adjusting the
number of turns N.sub.1 and N.sub.2 of the windings) and the duty
ratio of the inverter.
[0056] The inverter of the present disclosure has the circuit
structure of the single-stage three-phase high-gain boost-type
three-port integrated inverter, in which the voltage gain of the
inverter is improved by configuring the energy storage loop with
the inductance L.sub.1 (corresponding to the windings N.sub.1) less
than the inductance L (corresponding to the windings
N.sub.1+N.sub.2) of the energy releasing loop and by integrating
the charging/discharging switch unit of the battery with an
intermediate port for energy storage. The inverter of the present
disclosure is essentially different from the circuit structure of
the single-stage three-phase buck-type inverter. Therefore, the
inverter of the present disclosure is novel and creative, and has
the advantages of having three ports, high conversion efficiency
(standing for low energy loss), high power density (standing for
small volume and light weight), high voltage gain (which means that
lower DC voltage can be converted into higher AC voltage), low
cost, and wide applications. The inverter of the present disclosure
is an ideal energy-saving and consumption-reducing three-phase
inverter, which is of great value in today's vigorous promotion of
building an energy-saving and economical society.
[0057] Taking the circuit structure shown in FIG. 1 as an example,
embodiments of the circuit topology of the single-stage three-phase
high-gain boost-type three-port integrated inverter are shown in
FIGS. 8 and 9. FIG. 8 shows the filter circuit with a capacitor,
which is suitable for the occasions of inversion where the quality
requirement for the output waveform is not very strict. FIG. 9
shows the filter circuit with a capacitor and an inductor, which is
suitable for the occasions of inversion where the quality
requirement for output waveform is strict. In the circuits shown in
FIGS. 8 and 9, the input DC power source U.sub.i is the input port,
the three-phase output AC load Z.sub.La, Z.sub.Lb, Z.sub.Lc or the
three-phase AC grid u.sub.a, u.sub.b, u.sub.c are the output ports.
The battery U.sub.b is the intermediate port for energy storage.
The terminal voltage of the battery U.sub.b is greater than
U.sub.i. S.sub.6, D.sub.6 are the charging subcircuit switches of
the battery. S5 is the discharging subcircuit switch of the
battery. D5 is the blocking diode. The energy storage switch S may
be a MOSFET device, or an IGBT, GTR or other devices. The
three-phase inverter bridge may be an IGBT device, or a MOSFET, GTR
or other devices. The six switches S.sub.a1, S.sub.b1, S.sub.c1,
S.sub.a2, S.sub.b2, S.sub.c2 of the three-phase inverter bridge are
respectively serially connected with one blocking diode in the
forward direction to form six two-quadrant power switches
configured to withstand bidirectional voltage stress and
unidirectional current stress, thereby avoiding short circuit of
the capacitor of the three-phase AC filter when the inverter bridge
is in operation. With the presence of new devices such as IGBT
capable of bidirectional blocking, the inverter no longer needs to
be connected with a diode in series, which solves the problem of
diode loss. The inverter of the present disclosure can convert the
unstable low-voltage DC electricity (e.g. the electricity from the
sources such as batteries, photovoltaic cells, and fuel cells) into
a desired, stable, high-quality, high-voltage three-phase
sinusoidal AC electricity. Thus, the inverter of the present
disclosure can be widely used in the inverter power sources for
civil use (e.g. communication inverter and photovoltaic
grid-connected inverter 24 VDC/380V50HzAC, 48 VDC/380V50HzAC, 96
VDC/380V50HzAC) and the inverter power sources for national defense
use (e.g. aviation static inverter 27 VDC/200V400HzAC) in medium
and large capacity, voltage step-up occasions.
[0058] Taking the capacitor filter circuit shown in FIG. 8 as an
example, the single-stage three-phase high-gain boost-type
three-port integrated inverter has three power supply modes, as
shown in FIGS. 10, 11 and 12. In power supply mode 1 shown in FIG.
10, the power flows from the input port to the output port and the
intermediate port, which is equivalent to a single-input
double-output converter. In power supply mode 2 shown in FIG. 11,
the power flows from the input port and the intermediate port to
the output port, which is equivalent to a double-input
single-output inverter with parallel connection and time-phased
supplying power. In power supply mode 3 shown in FIG. 12, the power
flows from the intermediate port to the output port, which is
equivalent to a single-input single-output inverter.
[0059] The energy management and control strategy for the
independent power supply system of the single-stage three-phase
high-gain boost-type three-port photovoltaic integrated inverter
needs to meet the requirements of the characteristics of the ports
of the photovoltaic cell, the battery, and the electrical load.
Namely, the functions including master-slave load sharing of the
photovoltaic cell and battery, the photovoltaic power generation
MPPT of the input port, and stabilization of output voltage need to
be achieved. As shown in FIGS. 13 and 14, the energy management and
control strategy includes a master-slave load sharing for the
photovoltaic cell and battery, a double-loop improved separate zone
SPWM with an outer RMS output voltage loop of the inverter with a
maximum power point tracking of photovoltaic cells and an inner
current loop of the energy storage inductor, and the system can be
switched smoothly and seamlessly among the three power supply modes
is employed. The waveform of the first half low-frequency period in
FIG. 14 is the waveform of power supply mode 1, and the waveform of
the second half low-frequency period in FIG. 14 is the waveform of
power supply mode 2. The control signals of the intervals within
one low-frequency output cycle of the inverter are shown in Table
1. Taking the reference voltages e.sub.a, e.sub.b and e.sub.c as
separate zone signals, after the judgement of the six intervals of
the output low-frequency voltage, the voltage selection, and the
absolute value circuit, the interval reference sinusoidal signals
m.sub.1,m.sub.2 are obtained. Detecting and feeding back the energy
storage inductor current signals i.sub.L and i.sub.L2, and
converting i.sub.L2 into i.sub.L1, the energy storage inductor
current signal i.sub.L=(i.sub.L1+N.sub.2/N.sub.1i.sub.L2) (let the
sampling coefficient of the inductor current be 1), so the
continuity of the sampling current within a switching period is
ensured. The double-loop control includes an outer loop of feedback
of effective value of output voltage and an inner loop of energy
storage inductor current. The double-loop control is realized by
the output RMS voltage feedback outer loop and the energy storage
inductor inner current loop. Namely, the effective value
U.sub.abrms of the output line-to-line voltage is compared with the
effective reference value U*.sub.abrms of the line-to-line voltage,
and the energy storage inductor average current reference signal
I*L.sub.avg is obtained after PI regulator. The energy storage
inductor average current signal I.sub.Lavg is compared with
I*L.sub.avg and amplified to obtain the modulation degree k, and
the modulation wave signals u.sub.c1=km.sub.1, u.sub.c2=km.sub.2.
Let |Z.sub.La|=|Z.sub.Lb|=|Z.sub.Lc|=|Z.sub.L|, then the
three-phase output phase-to-neutral voltage satisfies the following
condition u.sub.a=kI.sub.Lavg|Z.sub.L|e.sub.a,
u.sub.b=kI.sub.Lavg|Z.sub.L|e.sub.b,
u.sub.c=kI.sub.Lavg|Z.sub.L|e.sub.c. Specially, the stability of
the energy storage inductor current I.sub.Lavg is realized by
adjusting the load sharing of the photovoltaic cell and the
battery. When the photovoltaic power is greater than the load
power, the photovoltaic cells store the remaining energy into the
battery to suppress the increase of the energy storage inductor
current. When the photovoltaic power is less than the load power,
the battery complements the load with the rest of the part of the
power to prevent the drop of the energy storage inductor current.
It can be seen from FIGS. 13 and 14 that the energy storage switch
S operates at a switching frequency equal to the frequency of the
carrier waves u.sub.c1 and u.sub.c2. However, the six energy
releasing switches S.sub.a1, S.sub.a2, S.sub.b1, S.sub.b2,
S.sub.c1, S.sub.c2 of the inverter bridge work according to the
following switch rules within a low-frequency output cycle. The
high-frequency switch works 2/6 low-frequency output cycle, is
always turned on 1/6 low-frequency output cycle, and is turned off
3/6 low-frequency output cycle. Obviously, the frequency of the
high-frequency switch of the six energy releasing switches is 1/2
that of the energy storage switch S.
TABLE-US-00001 TABLE 1 the separate zone control signals of the
inverter within a low-frequency output cycle inter- signal val
m.sub.1 m.sub.2 S.sub.a1 S.sub.a2 S.sub.b1 S.sub.b2 S.sub.c1
S.sub.c2 S.sub.1 S.sub.2 S.sub.0 I e.sub.a e.sub.c n.sub.1 0 0 1
n.sub.2 0 n.sub.3 n.sub.4 n.sub.1 + n.sub.2 & n.sub.4 II
-e.sub.b -e.sub.c 1 0 0 n.sub.1 0 n.sub.2 III e.sub.b e.sub.a
n.sub.1 0 n.sub.2 0 0 1 IV -e.sub.c -e.sub.a 0 n.sub.2 1 0 0
n.sub.1 V e.sub.c e.sub.b 0 1 n.sub.1 0 n.sub.2 0 VI -e.sub.a
-e.sub.b 0 n.sub.1 0 n.sub.2 1 0
[0060] The energy management and control strategy realizes the
three power supply modes of the integrated inverter. It is known
that the power required by the load is mainly supplied by the
master power supply device which is the photovoltaic cells, and the
rest part of power required by the load is supplied by the slave
power supply device which is the battery. Mode 1 is as follows:
when the photovoltaic power is greater than the load power,
u.sub.e3.gtoreq.1, u.sub.e4.gtoreq.0, the discharging switch
S.sub.5 is turned off, and the charging switch S.sub.6 PWM is
turned on; the photovoltaic cell stores the remaining energy to the
battery, and the photovoltaic cell supplies power to the load and
the battery in different time periods within a switching cycle.
Mode 2 is as follows: when the photovoltaic power is less than the
load power, u.sub.e3<1, u.sub.e4<0, the discharging switch
S.sub.5 PWM is turned on, the charging switch S.sub.6 is turned
off, and the photovoltaic cell and the battery supply power to the
load in different time periods within a switching cycle. Mode 3 is
as follows: when the photovoltaic cell does not output power,
u.sub.e3=0, the discharging switch S.sub.5 is turned on, the
battery supplies power to the load independently.
[0061] FIG. 15 shows the generation of the control signals of the
power switch and the waveform of the energy storage inductor
current of the single-stage three-phase high-gain boost-type
three-port integrated inverter in interval I (0.degree.-60.degree.)
of a low-frequency output cycle. The energy storage inductor is
magnetized twice within a high-frequency switching period T.sub.S,
and is respectively demagnetized once through the loop of the a and
b phases and once through the loop of the c and b phases. The duty
ratios of the energy storage inductor corresponding to the two
times of magnetization in one T.sub.S are d.sub.1 and d.sub.2,
respectively, and the duty ratio varies with the reference
voltage.
[0062] Taking the interval I as an example, the control signals of
the power switch under three working modes of the inverter are
shown in FIGS. 16, 17 and 18. When the inverter is working in mode
1, u.sub.e3 has no intersection with carrier wave u.sub.c1, the
discharging switch S.sub.5 is turned off, u.sub.e4 intersects with
carrier wave u.sub.c2, and the charging switch S.sub.6 PWM is
turned on. As the photovoltaic power decreases gradually, u.sub.e3
and u.sub.e4 decrease gradually, and the on-time of the charging
switch S.sub.6 decreases gradually. When u.sub.e3=1, u.sub.e4=0, at
this time, the photovoltaic power is equal to the load power, the
charging switch and the discharging switch are both turned off, and
the photovoltaic cell supplies power to the load independently. As
the photovoltaic power decreases again, u.sub.e3 will intersect
with carrier wave u.sub.c1 to obtain the control signal of the
discharging switch S.sub.5 PWM, and the photovoltaic cell and the
battery supplies power to the load in different time periods, where
mode 2 is one such example. When the photovoltaic power decreases
to zero, u.sub.e3=0 and u.sub.e4=-1, at this time, the discharging
switch S.sub.5 is always turned on, the charging switch S.sub.6 is
turned off, and the battery supplies power to the load
independently, where mode 3 is one such example. When the inverter
is working in mode 1, u.sub.e3 has no intersection with the carrier
wave u.sub.c1, the discharging switch S.sub.5 is turned off,
u.sub.e4 intersects with the carrier wave u.sub.c2, the charging
switch S.sub.6 PWM is turned on. As the load power increases,
u.sub.e4 decreases gradually, the duty ratio of the charging switch
S.sub.6 decreases gradually, and the energy storage time of the
inductor increases gradually. When u.sub.e4=0, the photovoltaic
power is equal to the load power. As the load power increases
further, the charging switch S.sub.6 is turned off, the discharging
switch S.sub.5 PWM is turned on, and the photovoltaic cell and the
battery supply power to the load in different time periods, where
mode 2 is one such example. It can be seen that the single-stage
three-phase high-gain boost-type three-port integrated inverter can
realize a smooth and seamless switch from mode 1 to mode 2 to mode
3. Similarly, the inverter also can realize a smooth and seamless
switch from mode 3 to mode 2 to mode 1.
[0063] Taking the topology of the inverter with three-phase
capacitor filter and power supply mode 1 (the power flows from the
input port to the output port and the intermediate port) shown in
FIG. 8 as an example, the operating modes of the six intervals
obtained by dividing a low-frequency output cycle of the inverter
are discussed. Each interval contains multiple high-frequency
switching periods T.sub.S. Each high-frequency switching period has
three different equivalent circuits, including the two times of
magnetization on the identical loop and the two times of
demagnetization on two different loops of the energy storage
inductor.
[0064] Interval I: the energy releasing switches S.sub.a2, S.sub.b1
and S.sub.c2 are turned off, S.sub.b2 is turned on, and the state
of the switches are in the order of mode I-1, 1-2, I-3 and I-4 in
each high-frequency switch cycle T.sub.S in this interval.
[0065] The mode I-1 is shown in FIG. 19: D.sub.5, S, S.sub.b2 are
turned on, S.sub.a2, S.sub.b1, S.sub.c2, S.sub.a1, S.sub.c1 are
turned off. The voltage source U.sub.i, the inductor L.sub.1, and
the energy storage switch S form a loop. The inductor L.sub.1
stores energy. The inductor current i.sub.L1 rises linearly at the
rate U.sub.i/L.sub.1. The filter capacitors C.sub.fa, C.sub.fb,
C.sub.fc maintain the load currents i.sub.a, i.sub.b, i.sub.c.
[0066] The mode I-2 is shown in FIG. 20: D.sub.5, D.sub.6, S.sub.6,
S.sub.a1, S.sub.b2 are turned on, S.sub.a2, S.sub.b1, S.sub.c2, S,
S.sub.c1 are turned off. The voltage source U.sub.i, the energy
storage inductor L, and the energy releasing switches S.sub.a1 and
S.sub.b2 or the charging subcircuit switch of the battery form a
loop, and the inverter transmits energy to the load or charges the
battery. If u.sub.ab>U.sub.i, the inductor current i.sub.L2
decreases linearly at the rate (u.sub.ab-U.sub.i)/L or
(U.sub.b-U.sub.i)/L, and the inductor releases energy. If
u.sub.ab<U.sub.i, the inductor current i.sub.L2 increases
linearly at the rate (U.sub.i-u.sub.ab)/L, the inductor continues
to store energy, and the filter capacitor C.sub.fc maintains the
load current i.sub.c.
[0067] Mode I-3 is the same as model-1, as shown in FIG. 19.
[0068] The mode I-4 is shown in FIG. 21: D.sub.5, D.sub.6, S.sub.6,
S.sub.c1, S.sub.b2 are turned on, S.sub.a2, S.sub.b1, S.sub.c2, S,
S.sub.a1 are turned off. The voltage source U.sub.i, the energy
storage inductor L, and the energy releasing switches S.sub.c1 and
S.sub.b2 or the charging subcircuit switch of the battery form a
loop, and the inverter transmits energy to the load or charges the
battery. If u.sub.cb>U.sub.i, the inductor current i.sub.L2
decreases linearly at the rate (u.sub.cb-U.sub.i)/L or
(U.sub.b-U.sub.i)/L, and the inductor releases energy. If
u.sub.cb<U.sub.i, the inductor current i.sub.L2 increases
linearly at the rate (U.sub.i-u.sub.cb)/L, the inductor continues
to store energy, and the filter capacitor C.sub.fa maintains the
load current i.sub.a.
[0069] Interval II: the energy releasing switches S.sub.a2,
S.sub.b1 and S.sub.c1 are turned off, S.sub.a1 is turned on, and
the state of the switches are in the order of mode II-1, II-2, II-3
and II-4 in each high-frequency switch cycle T.sub.S in this
interval.
[0070] The mode II-1 is shown in FIG. 22: D.sub.5, S, S.sub.a1 are
turned on, and S.sub.a2, S.sub.b1, S.sub.c1, S.sub.b2, S.sub.c2 are
turned off. The voltage source U.sub.i, the inductor L.sub.1 and
the energy storage switch S form a loop. The inductor stores
energy. The inductor current i.sub.L1 rises linearly at the rate
U.sub.i/L.sub.1. The filter capacitors C.sub.fa, C.sub.fb, C.sub.fc
maintain the load currents i.sub.a, i.sub.b, i.sub.c.
[0071] The mode II-2 is shown in FIG. 23: D.sub.5, D.sub.6,
S.sub.6, S.sub.b2, S.sub.a1 are turned on, and S.sub.a2, S.sub.b1,
S.sub.c1, S, S.sub.c2 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
Sal and S.sub.b2 or the charging subcircuit switch of the battery
form a loop, and the inverter transmits energy to the load or
charges the battery. If u.sub.ab>U.sub.i, the inductor current
i.sub.L2 decreases linearly at the rate (u.sub.ab-U.sub.i)/L or
(U.sub.b-U.sub.i)/L, and the inductor releases energy. If
u.sub.ab<U.sub.i, the inductor current i.sub.L2 increases
linearly at the rate (U.sub.i-u.sub.ab)/L, the inductor continues
to store energy, and the filter capacitor C.sub.fc maintains the
load current i.sub.c.
[0072] Mode II-3 is the same as mode II-1, as shown in FIG. 22.
[0073] The mode II-4 is shown in FIG. 24: D.sub.5, D.sub.6,
S.sub.6, S.sub.c2, S.sub.a1 are turned on, and S.sub.a2, S.sub.b1,
S.sub.c1, S, S.sub.b2 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
S.sub.a1 and S.sub.c2 or the charging subcircuit switch of the
battery form a loop, and the inverter transmits energy to the load
or charges the battery. If u.sub.ac>U.sub.i, the inductor
current i.sub.L2 decreases linearly at the rate
(u.sub.ac-U.sub.i)/L or (U.sub.b-U.sub.i)/L, and the inductor
releases energy. If u.sub.ac<U.sub.i, the inductor current
i.sub.L2 increases linearly at the rate (U.sub.i-u.sub.ac)/L, the
inductor continues to store energy, and the filter capacitor
C.sub.fb maintains the load current i.sub.b.
[0074] Interval III: the energy releasing switches S.sub.a2,
S.sub.b2 and S.sub.c1 are turned off, S.sub.c2 is turned on, and
the state of the switches are in the order of mode III-2, III-3 and
III-4 in each high-frequency switch cycle T.sub.S in this
interval.
[0075] The mode III-1 is shown in FIG. 25: D.sub.5, S, S.sub.c2 are
turned on, S.sub.a2, S.sub.b2, S.sub.c1, S.sub.a1, S.sub.b1 are
turned off. The voltage source U.sub.i, the inductor L.sub.1, and
the energy storage switch S form a loop. The inductor L.sub.1
stores energy. The inductor current in rises linearly at the rate
U.sub.i/L.sub.1. The filter capacitors C.sub.fa, C.sub.fb, C.sub.fc
maintain the load currents i.sub.a, i.sub.b, i.sub.c.
[0076] The mode III-2 is shown in FIG. 26: D.sub.5, D.sub.6,
S.sub.6, S.sub.a1, S.sub.c2 are turned on, S.sub.a2, S.sub.b2,
S.sub.c1, S, S.sub.b1 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
S.sub.a1 and S.sub.c2 or the charging subcircuit switch of the
battery form a loop, and the inverter transmits energy to the load
or charges the battery. If u.sub.ac>U.sub.i, the inductor
current i.sub.L2 decreases linearly at the rate
(u.sub.ac-U.sub.i)/L or (U.sub.b-U.sub.i)/L, and the inductor
releases energy. If u.sub.ac<U.sub.i, the inductor current
i.sub.L2 increases linearly at the rate (U.sub.i-u.sub.ac)/L, the
inductor continues to store energy, and the filter capacitor
C.sub.fb maintains the load current i.sub.b.
[0077] Mode III-3 is the same as mode as shown in FIG. 25.
[0078] The mode III-4 is shown in FIG. 27: D.sub.5, D.sub.6,
S.sub.6, S.sub.b1, S.sub.c2 are turned on, S.sub.a2, S.sub.b2,
S.sub.c1, S, S.sub.a1 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
S.sub.b1 and S.sub.c2 or the charging subcircuit switch of the
battery form a loop, and the inverter transmits energy to the load
or charges the battery. If u.sub.bc>U.sub.i, the inductor
current i.sub.L2 decreases linearly at the rate
(u.sub.bc-U.sub.i)/L or (U.sub.b-U.sub.i)/L, and the inductor
releases energy. If u.sub.bc<U.sub.i, the inductor current
i.sub.L2 increases linearly at the rate (U.sub.i-u.sub.bc)/L, the
inductor continues to store energy, and the filter capacitor
C.sub.fa maintains the load current i.sub.a.
[0079] Interval IV: the energy releasing switches S.sub.a1,
S.sub.b2 and S.sub.c1 are turned off, S.sub.b1 is turned on, and
the state of the switches are in the order of mode IV-1, IV-2, IV-3
and IV-4 in each high-frequency switch cycle T.sub.S in this
interval.
[0080] The mode IV-1 is shown in FIG. 28: D.sub.5, S, S.sub.b1 are
turned on, and S.sub.a1, S.sub.b2, S.sub.c1, S.sub.a2, S.sub.c2 are
turned off. The voltage source U.sub.i, the inductor L.sub.1 and
the energy storage switch S form a loop. The inductor L.sub.1
stores energy. The inductor current i.sub.L1 rises linearly at the
rate U.sub.i/L.sub.1. The filter capacitors C.sub.fa, C.sub.fb,
C.sub.fc maintain the load currents i.sub.a, i.sub.b, i.sub.c.
[0081] The mode IV-2 is shown in FIG. 29: D.sub.5, D.sub.6,
S.sub.6, S.sub.a2, S.sub.b1 are turned on, S.sub.a1, S.sub.b2,
S.sub.c1, S, S.sub.c2 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
S.sub.b1 and S.sub.a2 or the charging subcircuit switch of the
battery form a loop, and the inverter transmits energy to the load
or charges the battery. If u.sub.ba>U.sub.i, the inductor
current i.sub.L2 decreases linearly at the rate
(u.sub.ba-U.sub.i)/L or (U.sub.b-U.sub.i)/L, and the inductor
releases energy. If u.sub.ba<U.sub.i, the inductor current
i.sub.L2 increases linearly at the rate (U.sub.i-u.sub.ba)/L, the
inductor continues to store energy, and the filter capacitor
C.sub.fc maintains the load current i.sub.c.
[0082] Mode IV-3 is the same as mode IV-1, as shown in FIG. 28.
[0083] The mode IV-4 is shown in FIG. 30: D.sub.5, D.sub.6,
S.sub.6, S.sub.c2, S.sub.b1 are turned on, and S.sub.a1, S.sub.b2,
S.sub.c1, S, S.sub.a2 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
S.sub.b1 and S.sub.c2 or the charging subcircuit switch of the
battery form a loop, and the inverter transmits energy to the load
or charges the battery. If u.sub.bc>U.sub.i, the inductor
current i.sub.L2 decreases linearly at the rate
(u.sub.bc-U.sub.i)/L or (U.sub.b-U.sub.i)/L, and the inductor
releases energy. If u.sub.bc<U.sub.i, the inductor current
i.sub.L2 increases linearly at the rate (U.sub.i-u.sub.bc)/L, the
inductor continues to store energy, and the filter capacitor
C.sub.fa maintains the load current i.sub.a.
[0084] Interval V: the energy releasing switches S.sub.a1, S.sub.b2
and S.sub.c2 are turned off, S.sub.a2 is turned on, and the state
of the switches are in the order of mode V-1, V-2, V-3 and V-4 in
each high-frequency switch cycle T.sub.S in this interval.
[0085] The mode V-1 is shown in FIG. 31: D.sub.5, S, S.sub.a2 are
turned on, and S.sub.a1, S.sub.b2, S.sub.c2, S.sub.b1, S.sub.c1 are
turned off. The voltage source U.sub.i, the inductor L.sub.1 and
the energy storage switch S form a loop. The inductor L.sub.1
stores energy. The inductor current i.sub.L1 rises linearly at the
rate U.sub.i/L.sub.1. The filter capacitors C.sub.fa, C.sub.fb,
C.sub.fc maintain the load currents i.sub.a, i.sub.b, i.sub.c.
[0086] The mode V-2 is shown in FIG. 32: D.sub.5, D.sub.6, S.sub.6,
S.sub.b1, S.sub.a2 are turned on, and S.sub.a1, S.sub.b2, S.sub.c2,
S, S.sub.c1 are turned off. The voltage source U.sub.i, the energy
storage inductor L, and the energy releasing switches S.sub.b1 and
S.sub.a2 or the charging subcircuit switch of the battery form a
loop, and the inverter transmits energy to the load or charges the
battery. If u.sub.ba>U.sub.i, the inductor current i.sub.L2
decreases linearly at the rate (u.sub.ba-U.sub.i)/L or
(U.sub.b-U.sub.i)/L, and the inductor releases energy. If
u.sub.ba<U.sub.i, the inductor current i.sub.L2 increases
linearly at the rate (U.sub.i-u.sub.ba)/L, the inductor continues
to store energy, and the filter capacitor C.sub.fc maintains the
load current i.sub.c.
[0087] Mode V-3 is the same as mode V-1, as shown in FIG. 31.
[0088] The mode V-4 is shown in FIG. 33: D.sub.5, D.sub.6, S.sub.6,
S.sub.c1, S.sub.a2 are turned on, S.sub.a1, S.sub.b2, S.sub.c2, S,
S.sub.b1 are turned off. The voltage source U.sub.i, the energy
storage inductor L, the energy releasing switches S.sub.c1 and
S.sub.a2 or the charging subcircuit switch of the battery form a
loop, and the inverter transmits energy to the load or charges the
battery. If u.sub.ca>U.sub.i, the inductor current i.sub.L2
decreases linearly at the rate (u.sub.ca-U.sub.i)/L or
(U.sub.b-U.sub.i)/L, and the inductor releases energy. If
u.sub.ca<U.sub.i, the inductor current i.sub.L2 increases
linearly at the rate (U.sub.i-u.sub.ca)/L, the inductor continues
to store energy, and the filter capacitor C.sub.fb maintains the
load current i.sub.b.
[0089] Interval VI: the energy releasing switches S.sub.a1,
S.sub.b1 and S.sub.c2 are turned off, S.sub.c1 is turned on, and
the state of the switches are in the order of mode VI-1, VI-2, VI-3
and VI-4 in each high-frequency switch cycle T.sub.S in this
interval.
[0090] The mode VI-1 is shown in FIG. 34: D.sub.5, S, S.sub.c1 are
turned on, and S.sub.a1, S.sub.b1, S.sub.c2, S.sub.a2, S.sub.b2 are
turned off. The voltage source U.sub.i, the inductor L.sub.1 and
the energy storage switch S form a loop. The inductor L.sub.1
stores energy. The inductor current i.sub.L1 rises linearly at the
rate U.sub.i/L.sub.1. The filter capacitors C.sub.fa, C.sub.fb,
C.sub.fc maintain the load currents i.sub.a, i.sub.b, i.sub.c.
[0091] The mode VI-2 is shown in FIG. 35: D.sub.5, D.sub.6,
S.sub.6, S.sub.a2, S.sub.c1 are turned on, and S.sub.a1, S.sub.b1,
S.sub.c2, S, S.sub.b2 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
S.sub.c1 and S.sub.a2 or the charging subcircuit switch of the
battery form a loop, and the inverter transmits energy to the load
or charges the battery. If u.sub.ca>U.sub.i, the inductor
current i.sub.L2 decreases linearly at the rate
(u.sub.ca-U.sub.i)/L or (U.sub.b-U.sub.i)/L, and the inductor
releases energy. If u.sub.ca<U.sub.i, the inductor current
i.sub.L2 increases linearly at the rate (U.sub.i-u.sub.ca)/L, the
inductor continues to store energy, and the filter capacitor
C.sub.fb maintains the load current i.sub.b.
[0092] Mode VI-3 is the same as mode VI-1, as shown in FIG. 34.
[0093] The mode VI-4 is shown in FIG. 36: D.sub.5, D.sub.6,
S.sub.6, S.sub.b2, S.sub.c1 are turned on, S.sub.a1, S.sub.b1,
S.sub.c2, S, S.sub.a2 are turned off. The voltage source U.sub.i,
the energy storage inductor L, and the energy releasing switches
S.sub.c1 and S.sub.b2 or the charging subcircuit switch of the
battery form a loop, and the inverter transmits energy to the load
or charges the battery. If u.sub.cb>U.sub.i, the inductor
current i.sub.L2 decreases linearly at the rate
(u.sub.cb-U.sub.i)/L or (U.sub.b-U.sub.i)/L, and the inductor
releases energy. If u.sub.cb<U.sub.i, the inductor current
i.sub.L2 increases linearly at the rate (U.sub.i-u.sub.cb)/L, the
inductor continues to store energy, and the filter capacitor
C.sub.fa maintains the load current i.sub.a.
* * * * *