WO2017054680A1 - 多电平逆变器 - Google Patents

多电平逆变器 Download PDF

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Publication number
WO2017054680A1
WO2017054680A1 PCT/CN2016/099893 CN2016099893W WO2017054680A1 WO 2017054680 A1 WO2017054680 A1 WO 2017054680A1 CN 2016099893 W CN2016099893 W CN 2016099893W WO 2017054680 A1 WO2017054680 A1 WO 2017054680A1
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Prior art keywords
switch
switch tube
capacitor
connection point
bidirectional
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PCT/CN2016/099893
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English (en)
French (fr)
Inventor
石磊
傅电波
曹震
Original Assignee
华为技术有限公司
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Publication date
Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to JP2018535220A priority Critical patent/JP6454056B2/ja
Priority to EP16850304.3A priority patent/EP3343749A4/en
Priority to BR112018006287-1A priority patent/BR112018006287B1/pt
Publication of WO2017054680A1 publication Critical patent/WO2017054680A1/zh
Priority to US15/938,193 priority patent/US10177683B2/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/36—Means for starting or stopping converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
    • H02M5/443—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means
    • H02M5/45—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/4837—Flying capacitor converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H02M7/487—Neutral point clamped inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0095—Hybrid converter topologies, e.g. NPC mixed with flying capacitor, thyristor converter mixed with MMC or charge pump mixed with buck
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

  • the invention belongs to the technical field of power sources, and in particular relates to a multi-level inverter.
  • a typical photovoltaic power generation system comprising one or more photovoltaic panels, converts solar energy into a direct current of a certain voltage and current through series and parallel, and then converts the direct current into alternating current through a photovoltaic inverter, and delivers it to the grid.
  • Solar energy to grid energy conversion In the range where the insulation is acceptable, the voltage of the DC output of the panel is generally increased by the series connection of the panels, so that in the case of the same current (cable diameter), more power can be output, thereby saving system cost, which is currently large.
  • the panel output voltage of the panel is up to 1000V, and the panel with the 1500V withstand capability has been introduced, and the system cost is expected to be further reduced.
  • higher requirements are placed on the performance of the switching semiconductor device in the power conversion part of the inverter.
  • the mainstream power semiconductor device has better switching and loss when the withstand voltage is below 1200V. Characteristics, at a higher switching frequency, can obtain better conversion efficiency, higher switching frequency can reduce the size and weight of the filter circuit, which is conducive to system miniaturization.
  • multi-level converters used in the field of high voltage and high power have attracted great attention in the power electronics industry. Due to the limitation of the voltage capacity of power electronic devices, the traditional two-level inverter usually adopts "high-low-high” mode to step down and boost the transformer to obtain high voltage and high power, or adopt multiple small-capacity inverter units. Implemented by multiplexing multiple winding transformers, which makes the system System efficiency and reliability are declining.
  • the present application provides a multi-level inverter capable of achieving more level outputs to ensure system efficiency and reliability of the circuit.
  • a multilevel inverter including a DC input unit and an inverter unit, the multilevel inverter further including a first bidirectional switch, a second bidirectional switch, and a first a three capacitor C3, wherein: the DC input unit comprises a first capacitor C1 and a second capacitor C2, the first capacitor C1 and the second capacitor C2 being connected in series between the positive and negative ends of the input DC power source;
  • the inverter unit includes four switch tubes connected in series in the same direction between the positive and negative ends of the input DC power supply, and the four switch tubes include a first switch tube Q1, a second switch tube Q2, and a third switch tube Q3.
  • a fourth switch tube Q4 wherein the four switch tubes are connected in series in the same direction in the order of Q1, Q2, Q3, and Q4 between the positive and negative poles of the input DC power source; one end of the first bidirectional switch is connected a connection point between the third switching transistor Q3 and the fourth switching transistor Q4, and the other end is connected to a connection point between the first capacitor C1 and the second capacitor C2 for the first bidirectional switch The current between the two ends is double-conducted and closed Disconnecting control; one end of the second bidirectional switch is connected to a connection point between the first switch tube Q1 and the second switch tube Q2, and the other end is connected between the first capacitor C1 and the second capacitor C2 a connection point for performing bidirectional conduction and turn-off control on current between the two ends of the second bidirectional switch; a positive terminal of the third capacitor C3 is connected to the first switch tube Q1 and the second switch tube A connection point between Q2, the negative end is connected to a connection point between the third switch tube Q3 and the fourth switch tube Q4; each
  • the first bidirectional switch includes a fifth switch tube Q5 and a sixth switch tube Q6 connected in reverse, the fifth switch tube Q5 is connected at one end to a connection point between the first capacitor C1 and the second capacitor C2, and the other end is connected to the sixth switch tube One end of the Q6 is connected, and the other end of the sixth switch tube Q6 is connected to a connection point between the third switch tube Q3 and the fourth switch tube Q4.
  • the second bidirectional switch includes a seventh switch tube Q7 and an eighth switch tube that are connected in series in reverse Q8, one end of the seventh switch tube Q7 is connected to a connection point between the first capacitor C1 and the second capacitor C2, and the other end is connected to one end of the eighth switch tube Q8, and the eighth switch tube Q8 is The other end is connected to a connection point between the first switching transistor Q1 and the second switching transistor Q2.
  • each of the first or second bidirectional switches is connected in parallel with a diode.
  • the multi-level inverter further includes a first switch S1 The second switch S2 and a resistor Rc, the first switch S1 is connected in parallel across the first switch tube Q1, and the second open tube S2 is connected in series with the resistor Rc and then connected in parallel across the fourth switch tube Q4.
  • the multi-level inverter further includes a DC/DC converter, The two input ends of the DC/DC converter are respectively connected to two ends of the DC input unit, and the two output ends of the DC/DC converter are respectively connected to both ends of the third capacitor C3.
  • the multi-level inverter further includes a filtering unit, where the filtering unit is The input terminal is connected to a connection point between the second switching transistor Q2 and the third switching transistor Q3.
  • an embodiment of the present invention provides a power supply system including a DC power supply and a DC/DC converter. And a multi-level inverter according to the above first aspect, wherein the output of the PV solar panel is connected to an input of a DC/DC converter, the DC/DC converter output and the multi-level The input end of the inverter is connected, and the output end of the multi-level inverter is connected to the power grid to deliver the alternating current obtained after the multi-level inverter is inverted to the power grid.
  • the above multi-level inverter realizes more levels of output by connecting two sets of bidirectional switches across the circuit between the DC input unit and the inverter unit, and the harmonics of the output waveform are increased by the increase of the output voltage level The content is reduced, thereby increasing system efficiency and stability.
  • FIG. 1 is a circuit diagram of a multilevel inverter according to a first embodiment of the present invention.
  • FIGS. 2a and 2b are circuit control diagrams of a state of a multilevel inverter according to a first embodiment of the present invention.
  • 3a and 3b are circuit control diagrams of a state 2 of a multilevel inverter according to a first embodiment of the present invention.
  • 4a and 4b are circuit control diagrams of a multi-level inverter in a state three according to a first embodiment of the present invention.
  • 5a and 5b are circuit control diagrams of a state of a multilevel inverter in accordance with a first embodiment of the present invention.
  • FIG. 6a and FIG. 6b are circuit diagrams of a multi-level inverter in a state five according to a first embodiment of the present invention.
  • 7a and 7b are circuit control diagrams of a multi-level inverter in a state six according to a first embodiment of the present invention.
  • 8a and 8b are circuit control diagrams of a multilevel inverter in state seven according to the first embodiment of the present invention.
  • 9a and 9b are circuit control diagrams of a multi-level inverter in a state eight according to a first embodiment of the present invention.
  • FIG. 10 is a circuit control state diagram of a multilevel inverter according to Embodiment 1 of the present invention.
  • FIG. 11 is a circuit diagram of a first implementation of a multilevel inverter in Embodiment 2 of the present invention.
  • FIG. 12 is a circuit diagram of a second implementation of a multilevel inverter according to Embodiment 2 of the present invention.
  • FIG. 13 is a schematic diagram of a power supply system according to Embodiment 3 of the present invention.
  • a multi-level inverter 100 provided by an embodiment of the present invention may be disposed between an input DC power source E and a load RL, wherein the input DC power source E has a voltage of E, which may be a solar cell.
  • E which may be a solar cell.
  • the multi-level inverter 100 described above includes a DC input unit 102, a first bidirectional switch 104, a second bidirectional switch 106, a third capacitor C3, and an inverter unit 108, and optionally includes a filtering unit 110.
  • Filter Wave unit 110 has an input for connection to node Va and an output for connection to node Vo. Node V0 is used to connect the load.
  • the DC input unit 102 described above includes two input capacitors in series, the two input capacitors including a first capacitor C1 and a second capacitor C2.
  • the first capacitor C1 and the second capacitor C2 are connected in series between the two output terminals of the input DC power source E.
  • the first capacitor C1 and the second capacitor C2 generally have the same capacitance capacity, such that the DC voltage applied to the DC input unit 102 is evenly divided to the ends of each of the capacitors C1, C2, that is, the first capacitor.
  • the voltage across C1 is E/2
  • the voltage across the second capacitor C2 is E/2.
  • the intermediate connection point of the first capacitor C1 and the second capacitor C2 is generally referred to as the neutral point of the multilevel inverter 100, wherein the neutral point refers to a point at which the voltage is zero, in a specific application, where Sex points can be used for grounding.
  • the above-described inverter unit 108 includes four power switching tubes connected in series between the two output terminals of the input DC power source E.
  • the four power switch tubes include a first switch tube Q1, a second switch tube Q2, a third switch tube Q3, and a fourth switch tube Q4.
  • the four power switch tubes are connected in series in the same direction in the order of Q1, Q2, Q3, and Q4 between the positive and negative poles of the input DC power source E, and there is a connection between each two adjacent switch tubes of the adjacent connection. The connection point of the two switch tubes.
  • the input end of the filtering unit 110 is connected to the connection point between the second switching tube Q2 and the third switching tube Q3, that is, the input end of the filtering unit 110 is connected to the intermediate point of the bridge arm formed by the inverter unit 108.
  • the filtering unit 110 includes an inductor and a filter capacitor. Both ends of the inductor are used to connect the Va point and the Vo point, respectively. One end of the filter capacitor is connected to the Vo point, and the other end is grounded.
  • the filtering unit 110 may be an LC filter circuit, or another filter circuit that can filter unnecessary harmonics in the voltage waveform outputted by the node Va point, and may be integrated in the multi-level inverter 100, or may be used as The discrete components are externally coupled to filter the multilevel output of the inverter unit 108 to form a sinusoidal output waveform.
  • the above-mentioned inverter unit 108 further includes four diodes, and the four diodes are respectively opened with the four
  • the switches Q1 to Q4 are one-to-one corresponding to the anti-parallel, and include a first diode D1, a second diode D2, a third diode D3, and a fourth diode D4.
  • the one-to-one corresponding reverse parallel connection means that the first diode D1 is connected in reverse parallel to the two ends of the first switching tube Q1; the second diode D2 is connected in reverse parallel to the two ends of the second switching tube Q2;
  • the third diode D3 is connected in reverse parallel to the third switch tube Q3; the fourth diode D4 is connected in reverse parallel with the fourth switch tube Q4.
  • the first bidirectional switch 104 includes a fifth switching transistor Q5 and a sixth switching transistor Q6 connected in reverse. One end of the first bidirectional switch 104 is connected to a connection point between the third switch tube Q3 and the fourth switch tube Q4, and the other end is connected to a connection point between the first capacitor C1 and the second capacitor C2 .
  • the second bidirectional switch 106 described above includes a seventh switching transistor Q7 and an eighth switching transistor Q8 that are connected in reverse series. One end of the second bidirectional switch 106 is connected to a connection point between the first switch tube Q1 and the second switch tube Q2, and the other end is connected to a connection between the first capacitor C1 and the second capacitor C2. point.
  • the switching tubes connected in series in each bidirectional switch are respectively connected in parallel with one diode in a one-to-one correspondence, for example, the fifth switching tube Q5 corresponds to the anti-parallel fifth diode D5, and the sixth switching tube Q6 corresponds to the anti-parallel sixth pole
  • the first or second bidirectional switch tube 104/106 is formed by connecting two unidirectional switch tubes in series.
  • the arrow in any one of the switch tubes Q1-Q8 in FIG. 1 indicates that the switch tube can control the current direction of conduction and turn-off.
  • the switch tube is turned off in a direction opposite to the direction of the arrow, and in order to prevent reverse overvoltage breakdown of the switch tube, a diode is connected in reverse parallel across each switch tube.
  • the reverse parallel connection means that the direction of the arrow indicating the conduction of the switch tube is opposite to the conduction direction of the diode. It can be seen that the two-way switch tubes connected in two reverse series and the two diodes respectively connected in parallel on the two switch tubes can form a bidirectional switch capable of double-conducting and turn-off control and avoid reverse over-voltage breakdown.
  • the positive terminal of the third capacitor C3 is connected to the first switching transistor Q1 and the second switching transistor Q2
  • the connection point is connected to the connection point of the third switch tube Q3 and the fourth switch tube Q4.
  • the voltage difference across C3 is generally equal to E/4.
  • the control signals of the second switching transistor Q2 and the third switching transistor Q3 are complementary, and the control signals of the first switching transistor Q1 and the sixth switching transistor Q6 are complementary.
  • the fourth switch tube Q4 and the eighth switch tube Q8 control signals are complementary, and the fifth switch tube Q5 and the seventh switch tube Q7 control signals are complementary.
  • the signal complementation means that the control signal is opposite.
  • the second switch tube Q2 and the third switch tube Q3 are complementary to each other when the control signal of the second switch tube Q2 is turned on.
  • the control signal is off.
  • the above control signal can be applied to the gate (base) of each switching transistor.
  • the control and output principle of the multilevel inverter 100 is described below, wherein the logic 1 represents the switch tube is turned on, the logic 0 represents the switch tube is turned off, and the control signals of the two switch tubes are complementary to the output.
  • the two control signals of one switch tube have logic [0, 1] or [1, 0], and the output voltages of different switch states corresponding to point Va are as shown in Table 1 below:
  • the state 0 (Mode0) in the table indicates a mode in which the third capacitor C3 is not in the charge and discharge state
  • the state 1 (Mode1) indicates a mode in which the third capacitor C3 is in the discharge state
  • the state 2 (Mode2) indicates the third capacitor C3.
  • the current switch state can be selected according to a previous switch state, that is, the previous switch state corresponds to the state of charge of the third capacitor C3, and the current switch state can be selected to discharge corresponding to the third capacitor C3.
  • a previous switch state that is, the previous switch state corresponds to the state of charge of the third capacitor C3
  • the current switch state can be selected to discharge corresponding to the third capacitor C3. The state of the switch, and so on.
  • the column corresponding to a switch tube in Table 1.1 or 1.2 below indicates the control of the switch and conduction of the switch tube during a power frequency cycle of the power grid.
  • the multilevel inverter 100 maintains a positive power output when the load is a general resistance or power consuming device, and the output current and voltage are both greater than zero.
  • the load is the power grid
  • the power grid since the power grid itself is also a way of transmitting sinusoidal voltage or current, different voltages at different times require that each voltage output state of the multi-level inverter 100 further includes an active output and a reactive output. In the state, the output current i is greater than zero at the active output, and the output current i is less than zero at the reactive output.
  • the diagonal lines on the switch tube indicate the turn-off, that is, the switch tubes Q1, Q2, Q5, and Q8 are turned on, and the switch tubes Q3, Q4, Q6, and Q7 are turned off.
  • both of the bidirectional switches 104 and 106 are turned off, and the third and fourth switching tubes Q3 and Q4 are both turned off, so that the third capacitor C3 and the second capacitor C2 are both in an open state and no voltage can be generated at the point Va. Therefore, the output voltage at the point Va is E/2.
  • the voltage output at other levels below is also the same principle.
  • the output of the voltage is regulated by the conduction and deactivation of the switching tube. The specific control principle will not be repeated later.
  • Va point voltage is E/4, and in the Mode2 state, see Table 4 and Figures 4a to 4b:
  • the third capacitor C3 when io>0 or io ⁇ 0, in the two switching modes of Mode1 and Mode2, the third capacitor C3 is in a discharging state and a charging state, that is, It is said that regardless of the state of the current io, the charge and discharge state of the third capacitor C3 can be controlled by adjusting the state of the switch tube while maintaining the voltage of the output Va at E/4, thereby controlling the voltage across C3 to be maintained at E.
  • Mode1 and Mode2 both Mode1 and Mode2 switch modes respectively correspond to the third capacitor C3 in a discharging and charging state, and the third capacitor C3 voltage is maintained at E/4, the latter is no longer cumbersome.
  • the four switching tubes Q2, Q3, Q6 and Q8 select 600V withstand voltage semiconductor switching devices, while the other four switching tubes Q1, Q4, Q5 and Q7 can select 1200V voltage-resistant semiconductor switching device, so that the multi-level inverter 100 can bridge the DC input unit 102 and the inverter unit 108 through two sets of bidirectional switches, and can use 600V and The 1200V excellent switching tube combination can realize the inverter conversion of the 1500V DC system and output 5 levels at the same time.
  • Embodiment 2 of the present invention provides two solutions to the problem of precharging processing of the third capacitor C3 on the basis of the first embodiment.
  • the first solution is as shown in FIG. 11.
  • the first switch S1, the second switch S2 and the resistor Rc are added to realize the third capacitor C3.
  • Pre-charge function The first switch S1 is connected in parallel between the first switch tube Q1 and the first diode D1; the second open tube S2 is connected in series with the resistor Rc and then connected in parallel to the fourth switch tube Q4 and the fourth diode D4. end.
  • the first switch S1 and the second switch S2 are closed, and the DC input voltage E passes through the first switch S1.
  • First The second switch S2 and the resistor Rc charge the third capacitor C3, and the resistor Rc is used to limit the current of the charging.
  • the first switch S1 and the second switch S2 are turned off. Then, the circuit works normally, and the first switch S1 and the second switch S2 can make a power semiconductor device, or a relay or an optical coupling device having an on-off function.
  • the second scheme is shown in FIG. 12, and a DC/DC converter is added to the first embodiment.
  • the input ends of the DC/DC converters are respectively connected to two ends of the DC power source E, and the output ends are respectively connected to both ends of the third capacitor C3.
  • the third capacitor C3 is charged from the DC input through the DC/DC converter, so that the third The voltage Vc across the capacitor C3 rises to the threshold voltage Vcth, and the DC/DC converter is turned off after soft, and the multilevel inverter can operate normally.
  • the DC/DC converter may be in the form of a circuit such as forward, flyback or push-pull.
  • a power supply system is provided in Embodiment 3 of the present invention, including an input DC power source E, a DC/DC converter, and a multi-level inverter.
  • the multi-level inverter in this embodiment is identical to the multi-level inverter in the first or second embodiment in circuit structure and control principle, and the multi-level inverter will not be repeatedly described herein. Circuit structure and control principle.
  • the input DC power source E may be a solar panel array or an energy storage device such as a rechargeable battery pack, a fuel cell stack, or the like.
  • the output of the DC power supply is connected to the input of the DC/DC converter to deliver DC power to the DC/DC converter.
  • An output of the DC/DC converter is coupled to an input of the multilevel inverter to transfer the converted power to the multilevel inverter.
  • the multi-level inverter converts the DC power transmitted from the DC power source into an AC point and outputs it to the load or the power grid to implement AC power supply.
  • the DC power source is a solar panel
  • the PV solar panel converts the light energy into electrical energy, and the output end thereof is connected to the input end of the DC/DC converter.
  • the DC/DC converter output is coupled to the input of the multilevel inverter to deliver the current and voltage converted by the rectification to the multilevel inverter.
  • the output end of the multi-level inverter is connected to the power grid to supply the AC power obtained after the inverter processing by the multi-level inverter to the power grid to realize power supply and grid connection.

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Abstract

一种多电平逆变器包括直流输入单元（102）、第一双向开关（104）、第二双向开关（106）、第三电容器（C3）和逆变单元（108）。直流输入单元包括串联连接在输入直流电源（E）的正负两端之间的第一电容器（C1）和第二电容器（C2）；逆变单元包括顺序同向串联连接在输入直流电源的正负两端之间的第一开关管（Q1）、第二开关管（Q2）、第三开关管（Q3）以及第四开关管（Q4）；第一双向开关的一端连接到第三开关管和第四开关管之间的连接点，第二双向开关的一端连接到第一开关管和第二开关管之间的连接点，两个双向开关的另外一端都连接到第一电容器和第二电容器之间的连接点；第三电容器的正端连接在第一开关管和第二开关管之间的连接点，负端连接在第三开关管和第四开关管之间的连接点。通过两组双向开关跨接直流输入单元和逆变单元之间的电路设计，实现更多电平的输出，通过输出电压电平数的增加，使得输出波形的谐波含量减小，从而提高系统效率以及稳定性。

Description

多电平逆变器 技术领域
本发明属于电源技术领域，具体涉及一种多电平逆变器。
背景技术
近年来，可再生能源特别是光伏太阳能越来越多的受到重视，并在欧洲、北美和亚洲等区域得到大规模应用。典型的光伏发电系统，包含一个或多个光伏电池板通过串联和并联的形式将太阳能转换为一定电压和电流的直流电，然后通过光伏逆变器，将此直流电转换为交流，输送到电网，实现太阳能到电网能量的转换。在绝缘可接受的范围内，一般会通过电池板串联方式提升电池板输出直流电的电压，这样在相同电流(电缆线径)的情况下，可以输出更大的功率，从而节省系统成本，目前大规模使用的三相并网的太阳能发电系统中，电池板串联输出电压最大达到1000V，且已有更改1500V耐受能力的电池板推出，系统成本有望得到进一步降低。但是随着电池板输出电压的提升，对逆变器功率变换部分的开关半导体器件性能提出了更高的要求，目前主流的功率半导体器件，耐压在1200V以下时，有较好的开关和损耗特性，在较高的开关频率下，可以得到较为理想的转换效率，较高的开关频率可以降低滤波电路的体积和重量，有利于系统小型化。
为了降低逆变器滤波部分体积和重量，应用于高压大功率领域的多电平变换器引起了电力电子行业的极大关注。由于受电力电子器件电压容量的限制，传统的两电平变频器通常采用“高-低-高”方式经变压器降压和升压来获得高压大功率，或采用多个小容量逆变单元,经多绕组变压器多重化来实现，这使得系 统效率和可靠性下降。
发明内容
本申请提供了一种多电平逆变器，能够实现更多电平输出，从而保证电路的系统效率和可靠性。
为达到上述目的，本发明的实施例采用如下技术方案：
第一方面，提供了一种多电平逆变器，包括一直流输入单元以及一逆变单元，所述多电平逆变器还包括一第一双向开关、一第二双向开关以及一第三电容器C3，其中：所述直流输入单元包括包括第一电容器C1和第二电容器C2，所述第一电容器C1和第二电容器C2串联连接在输入的直流电源正负两端之间；所述逆变单元包括同向串联连接在输入的直流电源的正负两端之间的四个开关管，所述四个开关管包括第一开关管Q1、第二开关管Q2、第三开关管Q3以及第四开关管Q4，其中所述四个开关管按照Q1，Q2，Q3，Q4的顺序同向串联连接在所述输入直流电源的正负极之间；所述第一双向开关的一端连接到所述第三开关管Q3和第四开关管Q4之间的连接点，另一端连接到所述第一电容器C1和第二电容器C2之间的连接点，用于对所述第一双向开关两端间的电流实现双向导通和关断控制；所述第二双向开关的一端连接到所述第一开关管Q1和第二开关管Q2之间的的连接点，另外一端连接到所述第一电容器C1和第二电容器C2之间的连接点，用于对所述第二双向开关两端间的电流实现双向导通和关断控制；所述第三电容器C3的正端连接在所述第一开关管Q1和第二开关管Q2之间的连接点，负端连接在所述第三开关管Q3和第四开关管Q4之间的连接点；所述开关管Q1-4中每一开关管均反向并联一二极管。
结合第一方面，在第一方面的第一种实现方式中，所述第一双向开关包括 反向串联的第五开关管Q5和第六开关管Q6，所述第五开关管Q5一端连接到所述第一电容器C1和第二电容器C2之间的连接点，另一端与第六开关管Q6的一端连接，所述第六开关管Q6的另一端与所述第三开关管Q3和第四开关管Q4之间的连接点连接。
结合第一方面或第一方面的第一种实现方式，在第一方面的第二种实现方式中，所述第二双向开关包括反向串联在一起的第七开关管Q7和第八开关管Q8，所述第七开关管Q7的一端与所述第一电容器C1和第二电容器C2之间的连接点连接，另一端与第八开关管Q8的一端连接，所述第八开关管Q8的另一端与所述第一开关管Q1和第二开关管Q2之间的的连接点连接。
结合第一方面或第一方面的第一种实现方式或第一方面的第二种实现方式，所述第一或第二双向开关中的每一开关管均反向并联一二极管。
结合第一方面或第一方面的上述三种实现方式中任一种实现方式，在第一方面的第四种实现方式中，所述多电平逆变器还包括一第一开关S1、一第二开关S2和一电阻Rc，所述第一开关S1并联在第一开关管Q1两端，所述第二开管S2与电阻Rc串联之后并联在第四开关管Q4两端。
结合第一方面或第一方面的上述四种实现方式中任一种实现方式，在第一方面的第五种实现方式中，所述多电平逆变器还包含一DC/DC变换器，所述DC/DC变换器两输入端分别连接在所述直流输入单元的两端，所述DC/DC变换器的两输出端分别连接在第三电容器C3的两端。
结合第一方面或第一方面的上述五种实现方式中任一种实现方式，在第一方面的第六种实现方式中，所述多电平逆变器还包含滤波单元，所述滤波单元的输入端与第二开关管Q2以及第三开关管Q3之间的连接点连接。
第二方面，本发明实施例提供了一种供电系统，包括直流电源、DC/DC变 换器以及如上述第一方面所述的多电平逆变器，所述PV太阳能板的输出端与DC/DC变换器的输入端连接，所述DC/DC变换器输出端与多电平逆变器的输入端连接，所述多电平逆变器的输出端接入电网，以将经过多电平逆变器逆变处理后获得的交流电输送给电网。
上述多电平逆变器通过两组双向开关跨接直流输入单元和逆变单元之间的电路设计，实现更多电平的输出，通过输出电压电平数的增加，使得输出波形的谐波含量减小，从而提高系统效率以及稳定性。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1为本发明实施例一中一种多电平逆变器的电路图。
图2a和图2b为本发明实施例一中一种多电平逆变器状态一下的电路控制图。
图3a和图3b为本发明实施例一中一种多电平逆变器状态二下的电路控制图。
图4a和图4b为本发明实施例一中一种多电平逆变器状态三下的电路控制图。
图5a和图5b为本发明实施例一中一种多电平逆变器状态四下的电路控制图。
图6a和图6b为本发明实施例一中一种多电平逆变器状态五下的电路控制 图。
图7a和图7b为本发明实施例一中一种多电平逆变器状态六下的电路控制图。
图8a和图8b为本发明实施例一中一种多电平逆变器状态七下的电路控制图。
图9a和图9b为本发明实施例一中一种多电平逆变器状态八下的电路控制图。
图10为本发明实施例一中一种多电平逆变器的电路控制状态图。
图11为本发明实施例二中一种多电平逆变器的第一种实现的电路图。
图12为本发明实施例二中一种多电平逆变器的第二种实现的电路图。
图13为本发明实施例三中一种供电系统的示意图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有付出创造性劳动的前提下所获得的所有其他实施例，都属于本发明保护的范围。
实施例1：
如图1所示，本发明实施例所提供的一种多电平逆变器100可以配置于输入直流电源E和负载RL之间，其中输入直流电源E的电压为E，可能是一个太阳能电池板阵列，或者一个能量存储设备，比如可充电电池、燃料电池等。
上述多电平逆变器100包括直流输入单元102、第一双向开关104、第二双向开关106、第三电容器C3和逆变单元108，以及可选的包括滤波单元110。滤 波单元110有一个输入端用于连接到节点Va和一个输出端用于连接到节点Vo。节点V0用于连接负载。
上述直流输入单元102包括两个串联的输入电容器，所述两输入电容器包括第一电容器C1和第二电容器C2。所述第一电容器C1和第二电容器C2串联连接在输入直流电源E的两个输出端之间。具体应用中，第一电容器C1和第二电容器C2一般具有相同的电容容量，这样施加到直流输入单元102的直流电压被均匀的分割到每个电容器C1、C2的两端，也就是第一电容器C1两端电压为E/2，第二个电容器C2两端电压为E/2。一般将第一电容器C1和第二电容器C2的中间连接点称为多电平逆变器100的中性点，其中所述中性点是指电压为零的点，在具体应用中，该中性点可以用于接地。
上述逆变单元108包括串联连接在输入直流电源E的两个输出端之间的四个功率开关管。所述四个功率开关管包括第一开关管Q1、第二开关管Q2、第三开关管Q3以及第四开关管Q4。所述四个功率开关管按照Q1，Q2，Q3，Q4的顺序同向串联连接在所述输入直流电源E的正负极之间，在相邻连接的每两个开关管之间有连接所述两开关管的连接点。
上述滤波单元110的输入端与第二开关管Q2以及第三开关管Q3之间的连接点连接，也就是滤波单元110的输入端与逆变单元108形成的桥臂的中间点连接。所述滤波单元110包括电感以及滤波电容。所述电感两端用于分别连接Va点和Vo点。所述滤波电容一端连接Vo点，另一端接地。所述滤波单元110可以为LC滤波电路，或其它可滤除节点Va点输出的电压波形中不必要的谐波的滤波电路，可以集成在所述多电平逆变器100内，也可以作为分立部件外接，用于对逆变单元108输出的多电平进行滤波以形成正弦输出波形。
上述逆变单元108还包括四个二极管，所述四个二极管分别与所述四个开 关管Q1至Q4一一对应反向并联，包括第一二极管D1、第二二极管D2、第三二极管D3以及第四二极管D4。所述一一对应反向并联是指第一二极管D1反向并联连接在第一开关管Q1两端；所述第二二极管D2反向并联连接在第二开关管Q2两端；所述第三二极管D3反向并联连接在第三开关管Q3两端；所述第四二极管D4反向并联连接在第四开关管Q4两端。
上述第一双向开关104包括反向串联的第五开关管Q5和第六开关管Q6。所述第一双向开关104的一端连接到所述第三开关管Q3和第四开关管Q4之间的连接点，另一端连接到所述第一电容器C1和第二电容器C2之间的连接点。
上述第二双向开关106包括反向串联在一起的第七开关管Q7和第八开关管Q8。所述第二双向开关106的一端连接到开关所述第一开关管Q1和第二开关管Q2之间的连接点，另外一端连接到所述第一电容器C1和第二电容器C2之间的连接点。每个双向开关中串联的开关管分别一一对应地反向并联一个二极管，如第五开关管Q5对应反向并联第五二极管D5，第六开关管Q6对应反向并联第六二极管D6，第七开关管Q7对应反向并联第七二极管D7，第八开关管Q8对应反向并联第八二极管D8。
上述第一或第二双向开关管104/106均由两单向开关管串联而成，如图1中开关管Q1-Q8任一个中的箭头表示开关管可控制导通与关断的电流方向，所述开关管在与箭头方向相反的方向上是关断的，而且为了防止开关管反向过压击穿，在每个开关管两端反向并联一二极管。所述反向并联是指开关管指示导通的箭头方向与二极管导通方向相反。可见，由二反向串联的单向开关管以及分别反向并联在二开关管上的两二极管可组成能实现双向导通以及关断控制的双向开关而且避免反向过压击穿。
上述第三电容器C3的正级端连接在所述第一开关管Q1和第二开关管Q2 的连接点，负端连接在所述第三开关管Q3和第四开关管Q4的连接点。在具体应用中，一般C3两端电压差等于E/4。
对于上述多电平逆变器100，在具体应用中，所述第二开关管Q2和第三开关管Q3控制信号互补，而所述第一开关管Q1和第六开关管Q6控制信号互补，所述第四开关管Q4和第八开关管Q8控制信号互补，所述第五开关管Q5和第七开关管Q7控制信号互补，通过控制所述开关管Q1～Q8的开关状态，节点Va电压可输出包括E/2，E/4，0，-E/4，-E/2共五个电平。所述信号互补是指控制信号相反，例如，所述第二开关管Q2和第三开关管Q3控制信号互补是指所述第二开关管Q2的控制信号为导通时第三开关管Q3的控制信号为关断。上述控制信号可以施加在各开关管的栅极(基极)。
以下介绍所述多电平逆变器100的控制与输出原理，其中用逻辑1代表开关管开通，逻辑0代表开关管关断，某两个开关管的控制信号互补是指输出到所述两个开关管的两路控制信号逻辑为[0,1]或[1,0]，不同开关状态对应Va点的输出电压如下表1所示：
Figure PCTCN2016099893-appb-000001
表1
如上表1所示，通过控制开关管Q1-Q8的开通与关断来实现Va点不同电压的输出，表中五个电平下电压输出时各个开关管所处的一种或两种状态，其中0为关断，1为开通。表中状态0(Mode0)表示第三电容器C3不处于充放电状态的一种模式，状态1(Mode1)表示第三电容器C3处于放电状态的一种模式，状态2(Mode2)表示第三电容器C3处于充电状态的一种模式，其中当前的开关状态可以根据前一开关状态来进行选择，也就是前一开关状态对应第三电容器C3的充电状态，当前的开关状态可选择对应第三电容器C3放电状态的开关状态，如此类推。
如下表1.1或1.2中某一开关管对应的纵栏表示该开关管在一个电网工频周期内的开关与导通的控制情况。
Figure PCTCN2016099893-appb-000002
表1.1
Figure PCTCN2016099893-appb-000003
表1.2
此外，在负载是一般电阻或者耗电设备时多电平逆变器100保持正功输出，输出电流和电压都是大于零的。当负载为电网时，由于电网自身也是正弦电压或电流的传输的方式，不同时刻由于相位的不同就要求多电平逆变器100的每个电压输出状态下还包括有功输出与无功输出两种状态，在有功输出时输出电流i大于零，无功输出时输出电流i小于零。
各个电压输出的具体控制逻辑分别说明如下：
1)Va点电压为E/2时，参见表1以及图2a至2b：
Figure PCTCN2016099893-appb-000004
表2
同时参见表1和图2a和2b，图中开关管上的斜线表示关断，也就是开关管Q1、Q2、Q5、Q8导通，开关管Q3、Q4、Q6、Q7关断。此时，两个双向开关104、106均断开，而且第三、四开关管Q3、Q4均断开，使第三电容器C3以及第二电容器C2均处于断路状态而无法对Va点产生电压。因此，Va点此时的输出电压为E/2。后面其它电平下的电压输出也是同样的原理，通过开关管的导通与关断来调节电压的输出，后面对具体控制原理就不再重复说明。
2)Va点电压为E/4，Model 1状态时，参见表3和图3a至3b：
Figure PCTCN2016099893-appb-000005
表3
3)Va点电压为E/4，Mode2状态时，参见表4和图4a至4b：
Figure PCTCN2016099893-appb-000006
Figure PCTCN2016099893-appb-000007
表4
需要补充说明的是，从图4a和图4b可以看到，当io>0或io<0时，Mode1和Mode2两种开关模式下，所述第三电容器C3分别处于放电和充电状态，也就是说，不管电流io处于何种状态，可以在保持输出Va点电压为E/4的情况下，通过调整开关管状态来控制第三电容器C3的充放电状态，进而控制C3两端电压维持在E/4，从而使第二、三开关管Q2、Q3最高只承受E/4的电压，也就是所述五电平逆变器100实现1500V最高输出时，第二、三开关管Q2、Q3承受的电压小于600V，可以使用性能最好而且可选择型号最多的600伏耐压的开关管，如此既可以降低成本也保证性能。对于后面描述的具有Mode1和Mode2两种模式的电压输出情况下，Mode1和Mode2两种开关模式均分别对应所述第三电容器C3分别处于放电和充电状态，而且所述第三电容器C3电压维持在E/4，后面就不再累赘说明。
4)Va点电压为0，Mode 1状态时，参见表5以及图5a至5b：
Figure PCTCN2016099893-appb-000008
表5
5)Va点电压为0，Mode 2状态时，参见表6和图6a至6b：
Figure PCTCN2016099893-appb-000009
表6
6)Va点电压为-E/4，Mode 1状态时，参见表7以及图7a至7b：
Figure PCTCN2016099893-appb-000010
Figure PCTCN2016099893-appb-000011
表7
7)Va点电压为-E/4，Mode 2状态时，参见表8以及图8a至8b：
Figure PCTCN2016099893-appb-000012
表格8
8)Va点电压为-E/2时，参见表9以及图9a至9b：
Figure PCTCN2016099893-appb-000013
表9
综合上面各种电平输出情况，上述多电平逆变器100的开关状态及各开关管承受应力情况汇总如下：
Figure PCTCN2016099893-appb-000014
表10
从上述各种情况以及表10汇总情况可以看出，上述多电平变换器100中四个开关管Q2，Q3，Q6和Q8所承受的电压为E/4，而另外四个开关Q1，Q4，Q5和Q7管所承受的电压最大为3E/4。对于1500V系统来讲，所述四个开关管Q2，Q3，Q6和Q8选择600V耐压半导体开关器件，而另外四个开关管Q1， Q4，Q5和Q7可选择1200V耐压半导体开关器件，这样所述多电平逆变器100通过两组双向开关跨接直流输入单元102和逆变单元108之间的电路设计，可以使用600V和1200V性能较为优异的开关管组合，即可实现1500V直流系统的逆变变换，同时输出5电平。
实施例2：
由于存在上述第三电容器C3，系统在启动工作时，为了避免第三开关管Q3，第四开关管Q4承受过高电压，需要对第三电容器C3两端做预充电处理。如图10所示，当系统所有开关管都闭环时，由于没有通路，第三电容器C3上没有电荷存在，可以认为第三电容器C3两端电压Vc非常低，接近为0，此时如果Va要建立输出E/2的状态，则第一开关管Q1和第二开关管Q2导通，第三开关管Q3，第四开关管Q4关闭，而电容电压不能突变，也就是Vc接近为0，则输入电压通过第一开关管Q1和第三电容器C3(Vc＝0)直接加到了第四开关管Q4两端，这样第四开关管Q4将承受整个直流输入电压E，超过了前面所述的3E/4，将会导致第四开关管Q4过压损坏。为了避免此问题，需要在开关动作前，对第三电容器C3进行充电，并将第三电容器C3两端电压充至E/4。
本发明实施例二在实施例一的基础上对第三电容器C3预充电处理问题提供了两个解决方案。
第一个解决方案如图11所示，在本发明实施例一的多电平逆变器100的基础上增加第一开关S1、第二开关S2和电阻Rc，以实现对第三电容器C3的预充电功能。所述第一开关S1并联在第一开关管Q1与第一二极管D1两端；所述第二开管S2与电阻Rc串联之后并联在第四开关管Q4与第四二极管D4两端。
在所述多电平逆变器100工作前，所有开关管Q1～Q8都处于断开状态，此时闭合所述第一开关S1和第二开关S2，直流输入电压E通过第一开关S1，第 二开关S2和电阻Rc对第三电容器C3进行充电，电阻Rc用于限制充电的电流，当Vc两端电压逐步升高到阈值电压Vcth时，断开所述第一开关S1和第二开关S2，然后电路正常工作，所述第一开关S1和第二开关S2可以使功率半导体器件，也可以是具有通断功能的继电器或光耦定器件。
第二个方案如图12所示，在实施例一的基础上增加一个DC/DC变换器。所述DC/DC变换器输入端分别连接在直流电源E的两端，输出端分别连接在第三电容器C3的两端。在所述多电平逆变器100工作以前，所有开关管Q1～Q8保持断开状态，此时通过DC/DC变换器从直流输入取电对第三电容器C3进行充电，使所述第三电容器C3两端电压Vc升高到阈值电压Vcth，软后关闭DC/DC变换器，所述多电平逆变器即可正常工作。所述DC/DC变换器可以是正激、反激或推挽等电路形式。
实施例3：
如图13所示，本发明实施例三中提供一种供电系统，包括输入直流电源E、DC/DC变换器以及多电平逆变器。
本实施例中的多电平逆变器与实施例一或二中的多电平逆变器在电路结构以及控制原理上是一致的，在此不再重复说明所述多电平逆变器的电路结构以及控制原理。
上述输入直流电源E可能是一个太阳能电池板阵列，或者一个能量存储设备，比如可充电电池组、燃料电池组等。
上述直流电源的输出端与DC\DC变换器的输入端连接，以将直流电输送给DC\DC变换器。所述DC\DC变换器的输出端与多电平逆变器的输入端连接，以将经过变换后的电能传输给多电平逆变器。所述多电平逆变器将从直流电源传输过来的直流电转换为交流点后输出给负载或者电网，以实现交流供电。
在所述直流电源为太阳能电池板时，上述PV太阳能板将光能转换成电能之后，其输出端与DC/DC变换器的输入端连接。所述DC/DC变换器输出端与多电平逆变器的输入端连接，以将通过整流变换的电流和电压输送给多电平逆变器。所述多电平逆变器的输出端接入电网，以将经过多电平逆变器逆变处理后获得的交流电输送给电网实现供电并网。
以上所述，仅为本发明的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应以权利要求的保护范围为准。

Claims (12)

  1. 一种多电平逆变器用于连接输入直流电源，其特征在于，包括：直流输入单元逆变单元、第一双向开关、第二双向开关以及第三电容器C3，其中：
    所述直流输入单元包括第一电容器C1和第二电容器C2，所述第一电容器C1和第二电容器C2用于串联连接在所述输入直流电源的正负极之间；
    所述逆变单元包括第一开关管Q1、第二开关管Q2、第三开关管Q3以及第四开关管Q4，所述四个开关管按照Q1，Q2，Q3，Q4的顺序同向串联连接在所述输入直流电源的正负极之间；
    所述第一双向开关的一端连接所述第三开关管Q3和第四开关管Q4之间的连接点，另一端连接所述第一电容器C1和第二电容器C2之间的连接点，用于对所述第一双向开关两端间的电流实现双向导通和关断控制；
    所述第二双向开关的一端连接所述第一开关管Q1和第二开关管Q2之间的连接点，另外一端连接所述第一电容器C1和第二电容器C2之间的连接点，用于对所述第二双向开关两端间的电流实现双向导通和关断控制；
    所述第三电容器C3的正级连接所述第一开关管Q1和第二开关管Q2之间的连接点，所述第三电容器C3的负级连接所述第三开关管Q3和第四开关管Q4之间的连接点；
    所述开关管Q1至Q4中每一开关管均反向并联一二极管。
  2. 根据权利要求1所述的多电平逆变器，其特征在于，所述第一双向开关包括反向串联的第五开关管Q5和第六开关管Q6，所述第五开关管Q5一端连接所述第一电容器C1和第二电容器C2之间的连接点，另一端与第六开关管Q6的一端连接，所述第六开关管Q6的另一端与所述第三开关管Q3和第四开关管Q4之间的连接点连接。
  3. 根据权利要求1或2所述的多电平逆变器，其特征在于，所述第二双向开关包括反向串联在一起的第七开关管Q7和第八开关管Q8，所述第七开关管Q7的一端与所述第一电容器C1和第二电容器C2之间的连接点连接，另一端与第八开关管Q8的一端连接，所述第八开关管Q8的另一端与所述第一开关管Q1和第二开关管Q2之间的连接点连接。
  4. 根据权利要求3所述的多电平逆变器，其特征在于，所述第一或第二双向开关中的每一开关管均反向并联一二极管。
  5. 根据权利要求1至4任一项述的多电平逆变器，其特征在于，所述多电平逆变器还包括第一开关S1、第二开关S2和电阻Rc，所述第一开关S1并联在第一开关管Q1两端，所述第二开管S2与电阻Rc串联之后并联在第四开关管Q4两端。
  6. 根据权利要求1至5任一项所述的多电平逆变器，其特征在于，所述多电平逆变器还包含一DC/DC变换器，所述DC/DC变换器的两输入端分别连接在所述直流输入单元的两端，所述DC/DC变换器的两输出端分别连接在第三电容器C3的两端。
  7. 根据权利要求1至6任一项所述的多电平逆变器，其特征在于，还包括滤波单元，所述滤波单元的输入端与第二开关管Q2以及第三开关管Q3之间的连接点连接。
  8. 一种供电系统，其特征在于，包括输入直流电源、DC/DC变换器以及多电平逆变器，所述输入直流电源的输出端与DC/DC变换器的输入端连接，所述DC/DC变换器输出端与多电平逆变器的输入端连接，所述多电平逆变器的输出端用于接入电网，以将经过多电平逆变器逆变处理后获得的交流电输送给电网；
    所述多电平逆变器包括直流输入单元、逆变单元、第一双向开关、第二双 向开关、第三电容器C3，其中：
    所述直流输入单元包括包括第一电容器C1和第二电容器C2，所述第一电容器C1和第二电容器C2串联连接在所述输入直流电源正负两端之间；
    所述逆变单元包括包括第一开关管Q1、第二开关管Q2、第三开关管Q3以及第四开关管Q4，其中所述四个开关管按照Q1，Q2，Q3，Q4的顺序同向串联连接在所述输入直流电源的正负极之间；
    所述滤波单元的输入端连接第二开关管Q2以及第三开关管Q3之间的连接点，所述滤波单元的输出端用于连接电网；
    所述第一双向开关的一端连接所述第三开关管Q3和第四开关管Q4之间的连接点，所述第一双向开关的另一端连接所述第一电容器C1和第二电容器C2之间的连接点，用于对所述第一双向开关两端间的电流实现双向导通和关断控制；
    所述第二双向开关的一端连接开关所述第一开关管Q1和第二开关管Q2之间的的连接点，所述第二双向开关的另外一端连接所述第一电容器C1和第二电容器C2之间的连接点，用于对所述第二双向开关两端间的电流实现双向导通和关断控制；
    所述第三电容器C3的正端连接所述第一开关管Q1和第二开关管Q2之间的连接点，负端连接所述第三开关管Q3和第四开关管Q4之间的连接点；
    所述开关管Q1至Q4中每一开关管均反向并联一二极管。
  9. 根据权利要求8所述的供电系统，其特征在于，所述第一双向开关包括反向串联的第五开关管Q5和第六开关管Q6，所述第五开关管Q5一端连接所述第一电容器C1和第二电容器C2之间的连接点，另一端与第六开关管Q6的一端连接，所述第六开关管Q6的另一端与所述第三开关管Q3和第四开关管Q4 之间的连接点连接。
  10. 根据权利要求8或9所述的供电系统，其特征在于，所述第二双向开关包括反向串联在一起的第七开关管Q7和第八开关管Q8，所述第七开关管Q7的一端与所述第一电容器C1和第二电容器C2之间的连接点连接，另一端与第八开关管Q8的一端连接，所述第八开关管Q8的另一端与所述第一开关管Q1和第二开关管Q2之间的连接点连接。
  11. 根据权利要求10所述的供电系统，其特征在于，所述第一或第二双向开关中的每一开关管均反向并联一二极管。
  12. 根据权利要求8至11任一项所述的供电系统，其特征在于，所述直流电源包括太阳能电池板或电池组。
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