WO2018171767A1 - 五电平低共模漏电流单相光伏并网逆变器及光伏并网系统 - Google Patents

五电平低共模漏电流单相光伏并网逆变器及光伏并网系统 Download PDF

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WO2018171767A1
WO2018171767A1 PCT/CN2018/080350 CN2018080350W WO2018171767A1 WO 2018171767 A1 WO2018171767 A1 WO 2018171767A1 CN 2018080350 W CN2018080350 W CN 2018080350W WO 2018171767 A1 WO2018171767 A1 WO 2018171767A1
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Prior art keywords
power switch
grid
switch tube
inverter
photovoltaic grid
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PCT/CN2018/080350
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English (en)
French (fr)
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黄敏
杨勇
方刚
卢进军
谢胜仁
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江苏固德威电源科技股份有限公司
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Publication of WO2018171767A1 publication Critical patent/WO2018171767A1/zh

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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
    • H02J3/383—
    • 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
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac 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
    • H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac 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 with automatic control of output voltage or current, e.g. switching regulators
    • 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
    • H02M5/02—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 without intermediate conversion into dc
    • H02M5/04—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 without intermediate conversion into dc by static converters
    • H02M5/22—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 without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M5/275—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 without intermediate conversion into dc 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
    • H02M5/293—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 without intermediate conversion into dc 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
    • 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
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade
    • 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
    • H02M1/12—Arrangements for reducing harmonics from ac input or output
    • H02M1/123—Suppression of common mode voltage or current
    • 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 field of photovoltaic power generation, and particularly relates to a novel five-level photovoltaic grid-connected inverter.
  • Photovoltaic power generation is a kind of clean and renewable energy. Due to its abundant and widely distributed solar energy resources, it has received extensive attention and application in recent years.
  • a photovoltaic grid-connected inverter is an interface between a photovoltaic array and a grid or load. Its main function is to convert direct current into alternating current.
  • the photovoltaic inverter is the core equipment of the photovoltaic power generation system, and its performance will affect the performance of the entire photovoltaic power generation system. For photovoltaic grid-connected inverters, they can be divided into isolated and non-isolated types.
  • non-isolated photovoltaic grid-connected inverters have the advantages of high efficiency, small size, light weight and low cost, most commercial photovoltaic inverters currently adopt this structure.
  • non-isolated photovoltaic grid-connected inverters have no transformer isolation.
  • Photovoltaic cells, photovoltaic inverters and power grids form a common-mode loop through the parasitic capacitance of the photovoltaic cells to the ground.
  • the common mode voltage changes continuously in the common-mode loop.
  • Common mode current This high frequency common mode current can cause conduction and radiation interference and increase system losses, even jeopardizing the safety of equipment and maintenance personnel. Therefore, in non-isolated grid-connected inverters, common mode current must be suppressed.
  • the five-level inverter which has the advantages of smaller filter inductance of the inverter, smaller pulsation of the output current of the inverter, and smaller voltage change rate than the three-level inverter. Improve inverter efficiency and reduce inverter output current ripple. Therefore, the five-level photovoltaic grid-connected inverter is beneficial to the performance and efficiency of the grid-connected inverter. However, the existing five-level inverter can not solve the problem of the mold current.
  • the common-mode leakage current of the photovoltaic grid-connected inverter can be effectively suppressed or eliminated, but with the single-phase five-level photovoltaic inverter.
  • the topology of the five-level inverter does not take into account the common mode leakage current suppression and elimination of the photovoltaic inverter.
  • a five-level low common mode leakage current single-phase photovoltaic grid-connected inverter is connected between a DC bus connected to a photovoltaic array and a grid/load, and includes H for converting electric current into alternating current for performing electric energy conversion a bridge circuit, an AC bypass switch circuit for bypass control of an alternating current, and a DC clamp switch circuit for limiting a voltage of the direct current;
  • An input end of the H-bridge circuit is connected to both ends of the DC bus, an output end of the H-bridge circuit is connected to the power grid/load; and the AC bypass switch circuit is connected to the H-bridge Between the two outputs; the DC clamp switch circuit is connected between a capacitor midpoint of the DC bus and an output of the H-bridge circuit.
  • the H-bridge circuit includes a power switch tube S1, a power switch tube S2, a power switch tube S3, and a power switch tube S4.
  • the power switch tube S1 and the power switch tube S2 are connected to form a connection to the DC line.
  • a bridge arm between the two ends of the bus bar, the power switch tube S3 and the power switch tube S4 are connected to form another bridge arm connected between the two ends of the DC bus, and the two ends of the two bridge arms are formed At the input of the H-bridge circuit, the midpoints of the two bridge arms form the output of the H-bridge circuit.
  • the AC bypass switch circuit includes a power switch tube S5 and a power switch tube S6.
  • the power switch tube S5 and the power switch tube S6 are connected in series and connected between the two output ends of the H bridge.
  • the DC clamp switch circuit comprises a diode D1, a diode D2, a power switch tube S8, a power switch tube S7, which are sequentially connected in series to form a loop, a midpoint of the diode D1 and the diode D2 and the DC bus The midpoints of the capacitors are connected, and the midpoints of the power switch S8 and the power switch S7 are connected to an output of the H-bridge circuit.
  • the H-bridge circuit is connected to the grid/load via an LC filter.
  • a photovoltaic grid-connected system includes a photovoltaic array, a DC bus connected to the photovoltaic array, a photovoltaic grid-connected inverter connected to the DC bus, and an LC connected to the photovoltaic grid-connected inverter
  • the filter, the grid is connected to the LC filter, and the photovoltaic grid-connected inverter adopts the above-mentioned five-level low common mode leakage current single-phase photovoltaic grid-connected inverter.
  • the present invention has the following advantages over the prior art: the photovoltaic grid-connected inverter topology of the present invention fully utilizes the advantages of five levels (overcoming the output power of the single-phase three-level inverter) Insufficient level), improve the performance of photovoltaic grid-connected inverter (current ripple, efficiency, voltage change rate, etc.), and at the same time effectively suppress the common mode leakage current of single-phase photovoltaic grid-connected inverter.
  • FIG. 1 is a schematic diagram of a photovoltaic grid-connected system of the present invention.
  • FIG. 2 is a schematic diagram of current flow when a grid voltage is positive half cycle and an output voltage is V dc in a five-level low common mode leakage current single-phase photovoltaic grid-connected inverter of the present invention.
  • FIG. 3 is a schematic diagram of current flow when the grid voltage is positive half cycle and the output voltage is V dc /2 in the five-level low common mode leakage current single-phase photovoltaic grid-connected inverter of the present invention.
  • FIG. 4 is a schematic diagram of current flow when the grid voltage is positive half cycle and the output voltage is 0 in the five-level low common mode leakage current single-phase photovoltaic grid-connected inverter of the present invention.
  • FIG. 5 is a schematic diagram of current flow when the grid voltage is in a negative half cycle and the output voltage is -V dc in the five-level low common mode leakage current single-phase photovoltaic grid-connected inverter of the present invention.
  • FIG. 6 is a schematic diagram of current flow when the grid voltage is in a negative half cycle and the output voltage is -V dc /2 in the five-level low common mode leakage current single-phase photovoltaic grid-connected inverter of the present invention.
  • FIG. 7 is a schematic diagram of current flow when the grid voltage is in a negative half cycle and the output voltage is 0 in the five-level low common mode leakage current single-phase photovoltaic grid-connected inverter of the present invention.
  • the photovoltaic grid-connected system includes a photovoltaic array, a DC bus PN connected to both ends of the photovoltaic array 1, a photovoltaic grid-connected inverter connected to the DC bus PN, and a photovoltaic grid-connected inverter.
  • the LC filter connected to the transformer, the grid 5 or the load connected to the LC filter, so that the electric energy generated by the photovoltaic array 1 is inverted by the photovoltaic grid-connected inverter and supplied to the grid 5 or the load.
  • the photovoltaic grid-connected inverter adopts a new five-level low-common-mode leakage current single-phase photovoltaic grid-connected inverter (hereinafter referred to as a five-level single-phase photovoltaic grid-connected inverter), which is connected to the photovoltaic array 1
  • a new five-level low-common-mode leakage current single-phase photovoltaic grid-connected inverter (hereinafter referred to as a five-level single-phase photovoltaic grid-connected inverter)
  • the access grid 5 is taken as an example in FIG.
  • the five-level single-phase photovoltaic grid-connected inverter includes an H-bridge circuit 2, an AC bypass switch circuit 3, and a DC clamp switch circuit 4.
  • the H-bridge circuit 2 is used for electrical energy conversion to convert direct current into alternating current, its input terminal is connected to both ends of the DC bus, and the output terminal is connected to the grid 5/load.
  • the H-bridge circuit 2 includes a power switch tube S1, a power switch tube S2, a power switch tube S3, and a power switch tube S4.
  • the power switch tube S1 and the power switch tube S2 are connected to form a bridge arm connected between the two ends of the DC bus PN, and the power switch tube S3 and the power switch tube S4 are connected to form another bridge connected between the two ends of the DC bus PN.
  • the two ends of the two bridge arms form the input end of the H-bridge circuit 2, and the midpoint O of the two bridge arms constitutes two output ends (positive output end, negative output end) of the H-bridge circuit 2.
  • the output of the H-bridge circuit 2 is connected to the grid 5/load via an LC filter, which includes a filter capacitor C and filter inductors L1, L2.
  • the AC bypass switch circuit 3 is used for bypass control of the AC power, which is connected between the two outputs of the H-bridge.
  • the AC bypass switch circuit 3 includes a power switch tube S5 and a power switch tube S6.
  • the power switch tube S5 and the power switch tube S6 are connected in series and connected between the two output ends of the H bridge.
  • the DC clamp switch circuit 4 is used to limit the voltage of the direct current, which is connected between the midpoint of the capacitance of the DC bus and the negative output of the H-bridge circuit 2.
  • the DC clamp switch circuit 4 includes a diode D1, a diode D2, a power switch tube S8, and a power switch tube S7 which are sequentially connected in series to form a loop.
  • the midpoint of the diode D1 and the diode D2 are connected to the capacitor midpoint O of the DC bus PN, and the power switch
  • the midpoint of the tube S8 and the power switch tube S7 is connected to the negative output terminal of the H-bridge circuit 2.
  • the output voltage u out of the five-level single-phase photovoltaic grid-connected inverter is:
  • R is the total resistance between the output of the five-level single-phase photovoltaic grid-connected inverter and the grid 5.
  • the common mode voltage u cm of the output of a five-level single-phase photovoltaic grid-connected inverter is:
  • the low frequency power switch S6 In the positive half cycle of the grid voltage (e g >0), the low frequency power switch S6 is always on, and the low frequency power switch S5 is always off; in the negative half cycle of the grid voltage (e g ⁇ 0), the low frequency power switch S5 is always Turned on, and the low frequency power switch S6 is always turned off.
  • the following is a detailed analysis of the current flow of a five-level photovoltaic grid-connected inverter in a switching cycle:
  • the five-level single-phase photovoltaic grid-connected inverter topology of the invention fully utilizes the advantages of five levels (overcoming the shortcomings of the single-phase three-level inverter), and can effectively suppress the single-phase photovoltaic grid-connected inverter Common mode leakage current.

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  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

一种五电平低共模漏电流单相光伏并网逆变器以及采用该逆变器的光伏并网系统。该逆变器包括H桥电路（2）、交流旁路开关电路（3）和直流钳位开关电路（4）。H桥电路连接于直流母线和电网/负载之间；交流旁路开关电路连接于H桥的两个输出端之间；直流钳位开关电路连接于直流母线的电容中点与H桥电路的输出端之间。H桥电路包括功率开关管S1、功率开关管S2、功率开关管S3、功率开关管S4；交流旁路开关电路包括功率开关管S5、功率开关管S6；直流钳位开关电路包括二极管D1、二极管D2、功率开关管S8、功率开关管S7。该逆变器和光伏并网系统能够充分发挥五电平的优势，提高逆变器性能，还可以有效抑制共模漏电流。

Description

五电平低共模漏电流单相光伏并网逆变器及光伏并网系统 技术领域
本发明属于光伏发电领域，具体涉及一种新型的五电平光伏并网逆变器。
背景技术
光伏发电是一种清洁可再生能源，由于太阳能资源丰富、分布广泛，近年来得到广泛的关注和应用。光伏并网逆变器是光伏阵列与电网或负载的接口，它主要功能将直流电转化为交流电。光伏逆变器是光伏发电系统核心设备，其性能将影响整个光伏发电系统性能。对于光伏并网逆变器，可分为隔离型和非隔离型两种。由于非隔离型光伏并网逆变器具有效率高、体积小、质量轻以及成本低等优点，目前大部分商用光伏逆变器采用这种结构。但非隔离型光伏并网逆变器没有变压器隔离，光伏电池、光伏逆变器和电网通过光伏电池对地寄生电容形成了共模回路，共模电压不断变化在共模回路中产生较大的共模电流。该高频共模电流会导致传导和辐射干扰以及增加系统的损耗，甚至危及设备和检修人员的安全，因此，在非隔离型并网逆变器中，必须抑制共模电流。目前，为了抑制非隔离型并网逆变器共模电流，多种新型拓扑结构被提出，如H5拓扑结构、H6拓扑结构、HERIC拓扑结构等。但这些逆变器拓扑结构逆变器输出电压为三个电平，称为三电平逆变器。
目前还现有一种五电平逆变器，它相对于三电平逆变器，具有逆变器的滤波电感更小、逆变器输出电流脉动更小、电压变化率更小等优点，可以提高逆变器效率和降低逆变器输出电流纹波。因此，五电平光伏并网逆变器有利于并网逆变器性能和效率的提高。但现有的五电平逆变器却不能解决工模电流的问题，例如专利号为ZL201310090983.8的发明中提出的一种新型五电平逆变器拓扑结构，它和三电平逆变器相比，能够提高逆变器效率，但该发明专利没有考虑光伏并网逆变器共模漏电流抑制问题。
因此，对于常规单相三电平光伏并网逆变器(如H5、H6等)可以有效抑制甚至消除光伏并网逆变器共模漏电流，但和单相五电平光伏逆变器相比，在效率、电流纹波、电压变化率等方面存在不足。而五电平逆变器的拓扑结构却没有考虑到光伏逆变器共模漏电流抑制和消除问题。
发明内容
本发明的目的是提供一种能够充分发挥五电平的优势，又能够有效抑制单相光伏并网逆变器的共模漏电流的单相光伏并网逆变器。
为达到上述目的，本发明采用的技术方案是：
一种五电平低共模漏电流单相光伏并网逆变器，连接于光伏阵列所连接的直流母线和电网/负载之间，其包括用于进行电能转换而将直流电转化为交流电的H桥电路、用于对交流电进行旁路控制的交流旁路开关电路、用于限制直流电的电压的直流钳位开关电路；
所述H桥电路的输入端与所述直流母线的两端相连接，所述H桥电路的输出端与所述电网/负载相连接；所述交流旁路开关电路连接于所述H桥的两个输出端之间；所述直流钳位开关电路连接于所述直流母线的电容中点与所述H桥电路的一个输出端之间。
优选的，所述H桥电路包括功率开关管S1、功率开关管S2、功率开关管S3、功率开关管S4，所述功率开关管S1和所述功率开关管S2连接构成一条连接于所述直流母线两端之间的桥臂，所述功率开关管S3和所述功率开关管S4连接构成另一条连接于所述直流母线两端之间的桥臂，两条所述桥臂的两端构成所述H桥电路的输入端，两条所述桥臂的中点构成所述H桥电路的输出端。
优选的，所述交流旁路开关电路包括功率开关管S5、功率开关管S6，所述功率开关管S5和所述功率开关管S6串联后连接于所述H桥的两个输出端之间。
优选的，所述直流钳位开关电路包括依次串联构成回路的二极管D1、二极管D2、功率开关管S8、功率开关管S7，所述二极管D1和所述二极管D2的中点与所述直流母线的电容中点相连接，所述功率开关管S8和所述功率开关管S7的中点与所述H桥电路的一个输出端相连接。
优选的，所述H桥电路经LC滤波器而连接至所述电网/负载。
一种光伏并网系统，包括光伏阵列、与所述光伏阵列相连接的直流母线、与所述直流母线相连接的光伏并网逆变器、与所述光伏并网逆变器相连接的LC滤波器，电网与所述LC滤波器相连接，所述光伏并网逆变器采用上述五电平低共模漏电流单相光伏并网逆变器。
由于上述技术方案运用，本发明与现有技术相比具有下列优点：本发明的光伏并网逆变器拓扑结构充分发挥五电平的优势(克服了单相三电平逆变器 的输出电平不足)，提高光伏并网逆变器性能(电流纹波、效率、电压变化率等)，同时可以有效抑制单相光伏并网逆变器的共模漏电流。
附图说明
附图1为本发明的光伏并网系统的原理图。
附图2为本发明的五电平低共模漏电流单相光伏并网逆变器中电网电压正半周期、输出电压为V dc时的电流流向示意图。
附图3为本发明的五电平低共模漏电流单相光伏并网逆变器中电网电压正半周期、输出电压为V dc/2时的电流流向示意图。
附图4为本发明的五电平低共模漏电流单相光伏并网逆变器中电网电压正半周期、输出电压为0时的电流流向示意图。
附图5为本发明的五电平低共模漏电流单相光伏并网逆变器中电网电压负半周期、输出电压为-V dc时的电流流向示意图。
附图6为本发明的五电平低共模漏电流单相光伏并网逆变器中电网电压负半周期、输出电压为-V dc/2时的电流流向示意图。
附图7为本发明的五电平低共模漏电流单相光伏并网逆变器中电网电压负半周期、输出电压为0时的电流流向示意图。
以上附图中：1、光伏阵列；2、H桥电路；3、交流旁路开关电路；4、直流钳位开关电路；5、电网。
具体实施方式
下面结合附图所示的实施例对本发明作进一步描述。
实施例一：参见附图1所示，光伏并网系统包括光伏阵列1、连接于光伏阵列1两端的直流母线PN、与直流母线PN相连接的光伏并网逆变器、与光伏并网逆变器相连接的LC滤波器、与LC滤波器相连接的电网5或负载，从而光伏阵列1所发的电能经过光伏并网逆变器进行逆变后提供给电网5或负载使用。其中，光伏并网逆变器采用新型的五电平低共模漏电流单相光伏并网逆变器(以下简称五电平单相光伏并网逆变器)，它连接于光伏阵列1所连接的直流母线和电网5/负载之间，附图1中以接入电网5为例。
该五电平单相光伏并网逆变器包括H桥电路2、交流旁路开关电路3和直流钳位开关电路4。
H桥电路2用于进行电能转换而将直流电转化为交流电，它的输入端与直流母线的两端相连接，而输出端则与电网5/负载相连接。H桥电路2包括功率开关管S1、功率开关管S2、功率开关管S3和功率开关管S4。功率开关管S1和功率开关管S2连接构成一条连接于直流母线PN两端之间的桥臂，功率开关管S3和功率开关管S4连接构成另一条连接于直流母线PN两端之间的桥臂，两条桥臂的两端构成H桥电路2的输入端，两条桥臂的中点O构成H桥电路2的两个输出端(正输出端、负输出端)。H桥电路2的输出端经LC滤波器而连接至电网5/负载，LC滤波器包括滤波电容C和滤波电感L1、L2。
交流旁路开关电路3用于对交流电进行旁路控制，它连接于H桥的两个输出端之间。交流旁路开关电路3包括功率开关管S5、功率开关管S6，功率开关管S5和功率开关管S6串联后连接于H桥的两个输出端之间。
直流钳位开关电路4用于限制直流电的电压，它连接于直流母线的电容中点O与H桥电路2的负输出端之间。直流钳位开关电路4包括依次串联构成回路的二极管D1、二极管D2、功率开关管S8、功率开关管S7，二极管D1和二极管D2的中点与直流母线PN的电容中点O相连接，功率开关管S8和功率开关管S7的中点与H桥电路2的负输出端相连接。
根据附图1，该五电平单相光伏并网逆变器输出电压u out为：
Figure PCTCN2018080350-appb-000001
其中R为五电平单相光伏并网逆变器输出与电网5之间总电阻。
五电平单相光伏并网逆变器的输出的共模电压u cm为：
Figure PCTCN2018080350-appb-000002
为实现五电平单相光伏逆变器低共模电流，共模电压u cm需变化比较小或需维持恒定值。下表1为该五电平单相光伏并网逆变器的输出电压、共模电压与逆变器开关状态的关系：
表1 五电平单相光伏逆变器输出电压、共模电压与开关状态的关系
e g S1 S2 S3 S4 S5 S6 S7 S8 u out u cm
正半周 1 0 0 1 0 1 0 0 V dc V dc/2
正半周 1 0 0 0 0 1 0 1 V dc/2 3V dc/4
正半周 0 0 0 0 0 1 0 0 0 V dc/2
负半周 0 1 1 0 1 0 0 0 -V dc V dc/2
负半周 0 1 0 0 1 0 1 0 -V dc/2 3V dc/4
负半周 0 0 0 0 1 0 0 0 0 V dc/2
从表1的关系可以看出：(1)五电平单相光伏逆变器输出电压u out为V dc、V dc/2、0、-V dc/2、-V dc，为5个电平；(2)逆变器输出的共模电压u cm为V dc/2和3V dc/4，变化比较小(大部分状态维持在V dc/2)。和三电平逆变器相比，提高逆变器性能并可以有效抑制光伏并网逆变器的共模电流。
在电网电压正半周期(e g＞0)，低频功率开关管S6一直开通，而低频功率开关管S5一直关断；在电网电压负半周期(e g＜0)，低频功率开关管S5一直开通，而低频功率开关管S6一直关断。下面具体分析在一个开关周期五电平光伏并网逆变器的电流流向：
(1)在电网电压正半周期(e g＞0)，输出电压为V dc时电流流向如图2所示。
(2)在电网电压正半周期(e g＞0)，输出电压为V dc/2时电流流向如图3所示。
(3)在电网电压正半周期(e g＞0)，输出电压为0时的电流流向如图4所示。
(4)在电网电压负半周期(e g＜0)，输出电压为-V dc时电流流向如图5所示。
(5)在电网电压负半周期(e g＜0)，输出电压为-V dc/2时电流流向如图6所示。
(6)在电网电压负半周期(e g＜0)，输出电压为0时电流流向如图7所示。
本发明的五电平单相光伏并网逆变器拓扑结构充分发挥五电平的优势(克服了单相三电平逆变器的不足)，又可以有效抑制单相光伏并网逆变器的共模漏电流。
上述实施例只为说明本发明的技术构思及特点，其目的在于让熟悉此项技术的人士能够了解本发明的内容并据以实施，并不能以此限制本发明的保护范围。凡根据本发明精神实质所作的等效变化或修饰，都应涵盖在本发明的保护范围之内。

Claims (6)

  1. 一种五电平低共模漏电流单相光伏并网逆变器，连接于光伏阵列所连接的直流母线和电网/负载之间，其特征在于：其包括用于进行电能转换而将直流电转化为交流电的H桥电路、用于对交流电进行旁路控制的交流旁路开关电路、用于限制直流电的电压的直流钳位开关电路；
    所述H桥电路的输入端与所述直流母线的两端相连接，所述H桥电路的输出端与所述电网/负载相连接；所述交流旁路开关电路连接于所述H桥的两个输出端之间；所述直流钳位开关电路连接于所述直流母线的电容中点与所述H桥电路的一个输出端之间。
  2. 根据权利要求1所述的五电平低共模漏电流单相光伏并网逆变器，其特征在于：所述H桥电路包括功率开关管S1、功率开关管S2、功率开关管S3、功率开关管S4，所述功率开关管S1和所述功率开关管S2连接构成一条连接于所述直流母线两端之间的桥臂，所述功率开关管S3和所述功率开关管S4连接构成另一条连接于所述直流母线两端之间的桥臂，两条所述桥臂的两端构成所述H桥电路的输入端，两条所述桥臂的中点构成所述H桥电路的输出端。
  3. 根据权利要求1所述的五电平低共模漏电流单相光伏并网逆变器，其特征在于：所述交流旁路开关电路包括功率开关管S5、功率开关管S6，所述功率开关管S5和所述功率开关管S6串联后连接于所述H桥的两个输出端之间。
  4. 根据权利要求1或3所述的五电平低共模漏电流单相光伏并网逆变器，其特征在于：所述直流钳位开关电路包括依次串联构成回路的二极管D1、二极管D2、功率开关管S8、功率开关管S7，所述二极管D1和所述二极管D2的中点与所述直流母线的电容中点相连接，所述功率开关管S8和所述功率开关管S7的中点与所述H桥电路的一个输出端相连接。
  5. 根据权利要求1所述的五电平低共模漏电流单相光伏并网逆变器，其特征在于：所述H桥电路经LC滤波器而连接至所述电网/负载。
  6. 一种光伏并网系统，包括光伏阵列、与所述光伏阵列相连接的直流母线、与所述直流母线相连接的光伏并网逆变器、与所述光伏并网逆变器相连接的LC滤波器，电网与所述LC滤波器相连接，其特征在于：所述光伏并网逆变器采用如权力摇旗1至5中任一项所述的五电平低共模漏电流单相光伏并网逆变器。
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