SINGLE-STAGE THREE-PHASE HIGH-GAIN BOOST TYPE THREE-PORT INTEGRATED INVERTER
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.
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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 FIELDThe 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.
BACKGROUNDThe 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.
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.
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.
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.
SUMMARYThe 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.
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 Ub of the battery is greater than a voltage Ui of the input DC power source. The voltage Ui of the input DC power source or the terminal voltage Ub of the battery, a left part inductor L1 of the center-tapped energy storage inductor L and the energy storage switch form a magnetizing loop. The voltage Ui of the input DC power source or the terminal voltage Ub 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)Up or the charging subcircuit switch, and the battery form a demagnetizing loop. Up 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+dN2/N1)/(1−d), wherein, d is a duty ratio of the inverter varying according to the sine law, and N1 and N2 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.
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 L1 for the energy storage loop with an inductance smaller than the inductance of the inductor L (corresponding to the windings N1+N2) 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.
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.
The technical solution of the present disclosure is further described below with reference to the drawings and embodiments.
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 Ub of the battery is greater than a voltage Ui of the input DC power source. The voltage Ui of the input DC power source or the terminal voltage Ub of the battery, a left part inductor L1 of the center-tapped energy storage inductor L, and the energy storage switch form a magnetizing loop. The voltage Ui of the input DC power source or the terminal voltage Ub 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)Up or the charging subcircuit switch, and the battery form a demagnetizing loop. Up 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+dN2/N1)/(1−d), wherein, d denotes a duty ratio of the inverter varying according to the sine law, and N1 and N2 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.
The circuit structure and principle waveforms of the single-stage three-phase high-gain boost-type three-port integrated inverter are shown in
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 ZLa, ZLb, ZLc, or can be connected to the three-phase AC grid ua, ub, uc. An input filter may be or may not be set between the input DC power source Ui 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 Ui 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 Ui magnetizes the energy storage inductor L1, and the three-phase AC load ZLa, ZLb, ZLc or the three-phase AC grid ua, ub, uc 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 Ui 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 Ui into rippled high-frequency pulsed DC currents iL1, iL2 which are then inverted into the tri-state modulated currents ima, imb, imc by the three-phase inverter bridge. After the three-phase filtering, the high-quality three-phase sinusoidal voltages ua, ub, uc can be obtained at the three-phase AC load (or the high-quality three-phase sinusoidal currents waves ia, ib, ic can be obtained at the three-phase AC grid), or the iL2 charges the battery Ub 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.
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
According to the demagnetizing equivalent circuit during the period of (1−d)TS/2 shown in
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, Δφ−≤Δφ+, and the maximum voltage gain can be obtained according to equations (1) and (2) as below,
uab/Ui≤(1+dN2/N1)/(1−d) (3).
Similarly, the maximum voltage gain can be deduced as
ucb/Ui=uac/Ui≤(1+dN2/N1)/(1−d) (4).
In equations (1), (2), (3) and (4), Ui is the voltage of the input DC power source, and N1 and N2 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+dN2/N1)/(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 L1 (corresponding to the windings N1) less than the inductance L (corresponding to the windings N1+N2) 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 N1 and N2 of the windings) and the duty ratio of the inverter.
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 L1 (corresponding to the windings N1) less than the inductance L (corresponding to the windings N1+N2) 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.
Taking the circuit structure shown in
Taking the capacitor filter circuit shown in
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
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, ue3≥1, ue4≥0, the discharging switch S5 is turned off, and the charging switch S6 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, ue3<1, ue4<0, the discharging switch S5 PWM is turned on, the charging switch S6 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, ue3=0, the discharging switch S5 is turned on, the battery supplies power to the load independently.
Taking the interval I as an example, the control signals of the power switch under three working modes of the inverter are shown in
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
Interval I: the energy releasing switches Sa2, Sb1 and Sc2 are turned off, Sb2 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 TS in this interval.
The mode I-1 is shown in
The mode I-2 is shown in
Mode I-3 is the same as model-1, as shown in
The mode I-4 is shown in
Interval II: the energy releasing switches Sa2, Sb1 and Sc1 are turned off, Sa1 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 TS in this interval.
The mode II-1 is shown in
The mode II-2 is shown in
Mode II-3 is the same as mode II-1, as shown in
The mode II-4 is shown in
Interval III: the energy releasing switches Sa2, Sb2 and Sc1 are turned off, Sc2 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 TS in this interval.
The mode III-1 is shown in
The mode III-2 is shown in
Mode III-3 is the same as mode as shown in
The mode III-4 is shown in
Interval IV: the energy releasing switches Sa1, Sb2 and Sc1 are turned off, Sb1 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 TS in this interval.
The mode IV-1 is shown in
The mode IV-2 is shown in
Mode IV-3 is the same as mode IV-1, as shown in
The mode IV-4 is shown in
Interval V: the energy releasing switches Sa1, Sb2 and Sc2 are turned off, Sa2 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 TS in this interval.
The mode V-1 is shown in
The mode V-2 is shown in
Mode V-3 is the same as mode V-1, as shown in
The mode V-4 is shown in
Interval VI: the energy releasing switches Sa1, Sb1 and Sc2 are turned off, Sc1 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 TS in this interval.
The mode VI-1 is shown in
The mode VI-2 is shown in
Mode VI-3 is the same as mode VI-1, as shown in
The mode VI-4 is shown in
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 Ub of the battery is greater than a voltage Ui of the input DC power source; the voltage Ui of the input DC power source or the terminal voltage Ub of the battery, a left part inductor L1 of the center-tapped energy storage inductor L, and the energy storage switch form a magnetizing loop; the voltage Ui of the input DC power source or the terminal voltage Ub 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)Up or the charging subcircuit switch, and the battery form a demagnetizing loop; wherein Up 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+dN2/N1)/(1−d), wherein, d is a duty ratio of the inverter varying according to a sine law, and N1 and N2 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.
Type: Application
Filed: Dec 6, 2018
Publication Date: Apr 29, 2021
Applicant: Qingdao University (Qingdao)
Inventor: Daolian CHEN (Qingdao)
Application Number: 16/622,282