WO2019206289A1 - 逆变器、发电系统以及抑制交流系统谐波失真的方法 - Google Patents

逆变器、发电系统以及抑制交流系统谐波失真的方法 Download PDF

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Publication number
WO2019206289A1
WO2019206289A1 PCT/CN2019/084623 CN2019084623W WO2019206289A1 WO 2019206289 A1 WO2019206289 A1 WO 2019206289A1 CN 2019084623 W CN2019084623 W CN 2019084623W WO 2019206289 A1 WO2019206289 A1 WO 2019206289A1
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Prior art keywords
filter
switch
inverter
alternating current
capacitor
Prior art date
Application number
PCT/CN2019/084623
Other languages
English (en)
French (fr)
Inventor
石荣亮
邵章平
辛凯
Original Assignee
华为技术有限公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
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 EP19792515.9A priority Critical patent/EP3780308A4/en
Publication of WO2019206289A1 publication Critical patent/WO2019206289A1/zh
Priority to US17/081,076 priority patent/US11336094B2/en

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02M1/126—Arrangements for reducing harmonics from ac input or output using passive filters
    • 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
    • H02M7/539—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 with automatic control of output wave form or frequency
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • 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
    • H02M1/44—Circuits or arrangements for compensating for electromagnetic interference in converters or inverters
    • 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
    • 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
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

Definitions

  • the present application relates to the field of power technology, and more particularly to an inverter, a power generation system, and a method of suppressing harmonic distortion of an AC system.
  • the inverter is generally connected between the DC system and the grid, and is a device that converts DC power into AC power.
  • the inverter is mainly composed of an inverter circuit, an AC filter, an AC switch, and an AC magnetic interference (EMI) filter.
  • the inverter circuit is used for converting direct current into alternating current, and the alternating current filter and the alternating current EMI filter are used for filtering the alternating current generated by the inverter current, and outputting the filtered alternating current to the power grid.
  • Differential mode and common mode filter capacitors are commonly present in AC EMI filters of typical construction, making AC EMI filters exhibit capacitive impedance characteristics. Therefore, when the inverter is off-grid (the AC switch is turned off), the AC EMI filter is directly connected to the grid, and a parallel capacitor is introduced for the grid. These parallel capacitors form a resonant loop with the inductance of the grid to generate resonance. When the resonant circuit and the harmonic voltage band in the power grid overlap each other, the harmonic voltage will be seriously amplified, and the voltage distortion caused by the resonance will further deteriorate the control stability of the inverter and affect the performance of the inverter.
  • the application provides an inverter, a power generation system, and a method for suppressing harmonic distortion of an AC system to suppress harmonic distortion of an input AC system.
  • an inverter configured to: an inverter circuit, an alternating current filter, an alternating current EMI filter, and a first alternating current switch.
  • the output port of the inverter circuit is connected to the input port of the AC filter, and the first AC switch is connected between the output port of the AC filter and the input port of the AC EMI filter;
  • the inverter further includes a first split capacitor, and the first split capacitor is disposed between the first AC switch and the input port of the AC EMI filter, and when the first AC switch is in an off state, the first split capacitor and the AC filter The output port of the device is disconnected, and the first split capacitor is connected to the loop of the AC system connected to the output port of the AC EMI filter to suppress harmonic distortion of the input AC system.
  • the above inverter can convert the direct current into alternating current by using the inverter circuit, and filter the alternating current obtained by the inverter conversion by using the alternating current filter and the alternating current EMI filter, and transmit the filtered alternating current to the alternating current system.
  • the AC system can be used for power supply after obtaining AC power.
  • the first split capacitor when the first AC switch is in a closed state, the first split capacitor is connected to an output port of the AC filter, and the first split capacitor constitutes a filter capacitor of the AC filter.
  • the first split capacitor is the capacitor of the AC filter, but the capacitor is disposed outside the AC filter. When the first AC switch is closed, the first split capacitor constitutes the filter capacitor of the AC filter.
  • the first split capacitor is a full capacitor or a partial capacitor of the AC filter.
  • the AC filter may include other capacitors in addition to the first split capacitor, and other capacitors may be located between the input port and the output port of the AC filter.
  • the first split capacitor may be a single-phase capacitor or a three-phase capacitor.
  • the first AC switch When the first split capacitor is a single-phase capacitor, the first AC switch is a single-phase AC switch; when the first split capacitor is a three-phase capacitor, the first AC switch is a three-phase AC switch, and the first split capacitor is three-phase
  • the sub-capacitor is configured.
  • the first split capacitor when the first split capacitor is a three-phase capacitor, the first split capacitor may be composed of a first split capacitor, a second split capacitor, and a third split capacitor.
  • the first split capacitor when the first AC switch is disconnected, the first split capacitor is connected to the loop where the AC system is located, and can be changed, such as increasing the capacitance value of the loop in which the AC system is located, thereby suppressing harmonic distortion of the AC system.
  • the original capacitance of the AC filter and the setting of the switch can be used to suppress the harmonic distortion of the AC system without adding additional components, so that no additional hardware cost and power consumption are generated.
  • the resonant frequency of the resonant branch of the AC system can be changed, thereby avoiding the frequency band in which the harmonic voltage of the AC system is located, and suppressing harmonic distortion of the AC system.
  • the resonant frequency of the resonant branch of the AC system is related to the capacitance and inductance contained in the resonant branch.
  • the output port of the AC filter is connected to the input port of the AC EMI filter through the first AC switch, and the first split capacitor is connected in parallel to the input of the AC EMI filter. a port, and the first split capacitor is connected in parallel to the output port of the alternating current filter through the first alternating current switch.
  • the AC filter includes an input port and an output connected in series to the AC filter An inductance L between the ports and a second split capacitor, wherein the second split capacitor is connected in parallel between the input port and the output port of the alternating current filter and disposed between the inductor L and the output port of the alternating current filter; when the first alternating current switch When in the off state, the second split capacitor constitutes a filter capacitor of the AC filter to change the capacitance value of the loop in which the input AC system is located; when the first AC switch is in the closed state, both the first split capacitor and the second split capacitor are After being connected in parallel with each other, the inductor L is connected in series to form a filter capacitor of the AC filter.
  • the filter capacitor of the AC filter is used to filter the AC power obtained by inverter circuit inverter.
  • the AC filter By closing and opening the first AC switch, it is possible to flexibly control whether part of the filter capacitor of the AC filter is incorporated into the AC system or the filter capacitor that constitutes the AC filter, and the AC filter can be used when the required harmonic distortion is suppressed. Part of the capacitance is incorporated into the AC system.
  • the first split capacitor is connected to the loop where the AC system is located, and the capacitance value of the resonant branch of the AC system can be changed, thereby changing the resonance of the AC system.
  • the resonant frequency of the branch can thus suppress the harmonic distortion of the AC system.
  • the foregoing inverter further includes a second AC switch, where the second AC switch is disposed in the first AC switch and the AC EMI filter Between the input ports, the first split capacitor is disposed between the first AC switch and the second AC switch; when the first AC switch is in the off state and the second AC switch is in the closed state, the first split capacitor and the AC filter The output port of the device is disconnected, and the first split capacitor is connected to the loop of the AC system connected to the output port of the inverter to suppress harmonic distortion of the AC system; when the first AC switch is in the closed state When the second AC switch is in the off state, the first split capacitor and the second split capacitor are connected in parallel with each other and then connected in series with the inductor L of the filter to form a filter capacitor of the AC filter.
  • the configuration of the filter capacitor of the AC filter can be more conveniently adjusted by means of two AC switches.
  • the output port of the AC filter is connected to the input port of the AC EMI filter through the first AC switch and the second AC switch.
  • the first split capacitor is connected in parallel to the output port of the AC filter through the first AC switch, and the first split capacitor is connected in parallel to the input port of the AC EMI filter through the second AC switch.
  • first split capacitor and the second split capacitor may be a single capacitor or a plurality of capacitors connected in parallel.
  • the capacitance value of the first split capacitor is an AC filter K times the capacitance value of the filter capacitor, where K is a value that causes the harmonic distortion of the AC system to be less than the preset harmonic distortion.
  • the filter capacitor of the above AC filter may refer to the total capacitance of the AC filter, and the capacitance value of the filter capacitor may refer to the total capacitance value of the AC filter.
  • the value of K is determined based on the equivalent capacitance of the AC EMI filter, the equivalent inductance of the AC system, and the harmonics of the AC system of the AC system.
  • the value of K can be determined according to at least one of an equivalent capacitance of the AC EMI filter, an equivalent inductance of the AC system, and an AC system harmonic of the AC system, so that the value of K can satisfy the harmonic distortion of the AC system. Less than the preset harmonic distortion.
  • the value of K is obtained based on a simulation test or an actual test.
  • the harmonic distortion of the AC system can be obtained by analog test or actual test, and the K value obtained in this case is obtained by adjusting the value of K so that the harmonic distortion of the AC system is smaller than the preset harmonic distortion. Is the value that meets the requirements.
  • a photovoltaic power generation system comprising a photovoltaic module, an alternating current system, and an inverter in any one of the foregoing first aspects, wherein an output port of the photovoltaic component and an input port of the inverter Connected, the output port of the inverter is connected to the input end of the AC system, the PV module is used to generate DC power, the inverter is used to invert the DC power, and the AC power obtained by the inverter processing is input to the AC system, and the AC is exchanged.
  • the system is used to provide AC power.
  • the first split capacitor can be incorporated into the loop where the AC system is located by controlling the AC switch in the inverter, thereby changing The capacitance value of the loop in which the AC system is located to suppress harmonic distortion of the AC system.
  • photovoltaic modules may also be referred to as photovoltaic arrays, solar panels.
  • a photovoltaic component is a device that converts solar energy directly into electrical energy using a photovoltaic effect that occurs under the illumination of a semiconductor material.
  • the photovoltaic power generation system further includes a rectifier connected between the output port of the photovoltaic component and the input port of the inverter, the rectifier is used for rectifying the direct current generated by the photovoltaic component, and is obtained by rectifying DC input to the inverter.
  • a grid-connected power generation system comprising: an AC system, N inverters in a third implementation manner of the first aspect, and N DC systems, wherein N DC systems
  • the output port is connected one-to-one with the input ports of the N inverters, N is an integer greater than or equal to 1, and the output ports of the N inverters are connected to the input ports of the AC system.
  • the first split capacitor can be incorporated into the loop where the AC system is located by controlling the AC switch in the inverter, thereby changing the capacitance value of the loop in which the AC system is located to suppress the harmonic distortion of the AC system.
  • a method for suppressing harmonic distortion of an AC system is provided, the method being applied to the grid-connected power generation system in the third aspect, wherein the first AC in any one of the N inverters When the switch and the second AC switch are both in an off state, the method includes: Step 1: acquiring a current total harmonic distortion THD of an AC system voltage of the AC system; and Step 2, in a case where the current THD is greater than a preset threshold, controlling The second AC switch of at least one of the N inverters is closed such that the current THD is less than a preset threshold.
  • the first split capacitor of some inverters can be connected to the AC system by controlling the closing of the AC switch of the inverter therein. It can suppress harmonic distortion of the AC system voltage of the AC system.
  • the first split capacitor can be connected in parallel to the AC system, and the system resonance branch can be dynamically changed.
  • the resonant frequency avoids the frequency band in which the system harmonic voltage of the AC system is located, to avoid serious amplification of the system harmonic voltage.
  • the second AC switch that controls at least one of the N inverters is closed, so that the current THD is less than a preset threshold, including: reversing one of the N inverters After the second AC switch of the transformer is closed, steps 1 and 2 are repeatedly performed until the current THD is less than or equal to the preset threshold.
  • the current THD is determined in time, and the current THD is continuously reduced by turning off the second AC switch of the inverter when the current THD cannot meet the requirements, so that the current THD Can be less than or equal to a preset threshold.
  • harmonic distortion can be flexibly suppressed by controlling the opening and closing of the AC switch.
  • the method further includes: determining whether the output voltage of the inverter meets the grid-connected power generation condition if the current THD is less than or equal to the preset threshold; and the output voltage of the inverter meets the grid-connected power generation. In the condition, all the first unconnected AC switch and the second AC switch in the N inverters are closed.
  • the above DC system may be a power generation system, for example, a wind power generation system, a photovoltaic power generation system, or the like.
  • the above DC system satisfies the power generation condition, which may mean that the power generation system can generate power normally.
  • the DC system is a wind power generation system
  • the DC system satisfies the power generation condition, which may mean that the wind level reaches a preset requirement, and the fan can generate power normally.
  • FIG. 1 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 2 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 3 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 4 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 5 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 6 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 7 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 8 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 9 is a schematic block diagram of an inverter according to an embodiment of the present application.
  • FIG. 10 is a schematic block diagram of a grid-connected power generation system according to an embodiment of the present application.
  • FIG. 11 is a schematic block diagram of a grid-connected power generation system according to an embodiment of the present application.
  • FIG. 12 is a schematic block diagram of a grid-connected power generation system according to an embodiment of the present application.
  • FIG. 13 is a schematic block diagram of a grid-connected power generation system according to an embodiment of the present application.
  • FIG. 14 is a schematic block diagram of a photovoltaic power generation system according to an embodiment of the present application.
  • 15 is a schematic block diagram of a wind turbine grid-connected power generation system according to an embodiment of the present application.
  • 16 is a schematic block diagram of an energy storage grid-connected power generation system according to an embodiment of the present application.
  • 17 is a schematic flow chart of a method for suppressing harmonic distortion according to an embodiment of the present application.
  • FIG. 19 is a schematic flow chart of a method for suppressing harmonic distortion according to an embodiment of the present application.
  • FIG. 1 is a schematic block diagram of an inverter of an embodiment of the present application.
  • the inverter 100 shown in FIG. 1 specifically includes an inverter circuit 101, an alternating current filter 102, an alternating current switch 103, and an alternating current EMI filter 104.
  • the output port of the inverter circuit 101 is connected to the input port of the AC filter 102, and the AC switch 103 is connected between the output port of the AC filter 102 and the input port of the AC EMI filter 104.
  • the AC switch 103 is specifically It may be the first AC switch S1.
  • the inverter 100 further includes a first split capacitor C1, which is disposed between S1 and an input port of the AC EMI filter 104.
  • a first split capacitor C1 which is disposed between S1 and an input port of the AC EMI filter 104.
  • S1 When S1 is in the off state, the connection of C1 to the output port of the AC filter 102 is broken, and C1 is connected to the circuit of the AC system connected to the output port of the AC EMI filter 104 to suppress the AC system. Harmonic distortion; when S1 is in the closed state, the first split capacitor is connected to the output port of the AC filter, and the first split capacitor constitutes the filter capacitor of the AC filter.
  • the output port of the inverter 100 (specifically, the output port of the AC EMI filter) can also be connected to an AC system.
  • the inverter 100 can convert the direct current into alternating current by using the inverter circuit 101, and filter the alternating current obtained by the inverter conversion by using the alternating current filter 102 and the alternating current EMI filter 104, and transmit the filtered alternating current to the alternating current.
  • the system which can be used for power supply after obtaining AC power.
  • C1 is the capacitance of the AC filter, except that C1 is disposed outside the output port of the AC filter 102. When S1 is closed, C1 truly constitutes the filter capacitor of the AC filter.
  • C1 is all or part of the capacitance of the AC filter.
  • the AC filter 102 may include other capacitors in addition to C1, which may be located between the input port and the output port of the AC filter 102.
  • the first split capacitor may be a single-phase capacitor or a three-phase capacitor.
  • the first AC switch When the first split capacitor is a single-phase capacitor, the first AC switch is a single-phase AC switch; when the first split capacitor is a three-phase capacitor, the first AC switch is a three-phase AC switch, and the first split capacitor is three-phase
  • the sub-capacitor is configured.
  • the first split capacitor when the first split capacitor is a three-phase capacitor, the first split capacitor may be composed of a first split capacitor, a second split capacitor, and a third split capacitor.
  • the first split capacitor when the first AC switch is turned off, the first split capacitor is incorporated into the loop where the AC system is located, and the capacitance value of the loop in which the AC system is located can be changed, thereby suppressing harmonic distortion of the AC system.
  • the original capacitance of the AC filter and the setting of the switch can be used to suppress the harmonic distortion of the AC system without adding additional components, so that no additional hardware cost and power consumption are generated.
  • the resonant frequency of the resonant branch of the AC system can be changed, thereby avoiding the frequency band in which the harmonic voltage of the AC system is located, and suppressing harmonic distortion of the AC system.
  • the resonant frequency of the resonant branch of the AC system is related to the capacitance and inductance contained in the resonant branch.
  • the output port of the AC filter 102 is connected to the input port of the AC EMI filter 104 through S1, C1 is connected in parallel to the input port of the AC EMI filter 104, and C1 is connected in parallel to the AC filter through S1.
  • the output port of 102 is connected to the input port of the AC EMI filter 104 through S1
  • C1 is connected in parallel to the input port of the AC EMI filter 104
  • C1 is connected in parallel to the AC filter through S1.
  • the alternating current filter 102 includes an inductance L and a second split capacitor C2 connected in series between the input port and the output port of the alternating current filter 102, wherein C2 is connected in parallel to the input port of the alternating current filter 102.
  • C2 is connected in parallel to the input port of the alternating current filter 102.
  • the inductor L is connected in series with the inductor L to form a filter capacitor of the AC filter 102.
  • the filter capacitor of the AC filter 102 is used to filter the AC power obtained by the inverter circuit 101.
  • the S1 can flexibly control whether part of the filter capacitor of the AC filter is incorporated into the AC system or the filter capacitor that constitutes the AC filter, and can be used when suppressing harmonic distortion as needed. Part of the capacitance of the AC filter is incorporated into the AC system.
  • the AC switch 103 may further include a second AC switch S2 in addition to the first AC switch S1.
  • the AC switch 103 in the inverter 100 includes a second AC switch S2 in addition to S1, and S2 is disposed between S1 and an input port of the AC EMI filter 104, and C1 is set. Between S1 and S2; when S1 is in the off state and S2 is in the closed state, the connection of C1 to the output port of the AC filter 102 is broken, and C1 is connected to the output port of the inverter 100.
  • the circuit in which the AC system is located changes the capacitance value of the loop in which the AC system is located; when S1 is in the closed state and S2 is in the off state, C1 and C2 are connected in parallel with each other and in series with the inductance L of the filter to form the AC filter 102. Filter capacitor.
  • the configuration of the filter capacitor of the AC filter can be more conveniently adjusted by the two AC switches.
  • the output port of the AC filter 102 passes through the inputs of S1 and S2 and the AC EMI filter 104.
  • the ports are connected, C1 is connected in parallel to the output port of the AC filter 102 via S1, and C1 is connected in parallel to the input port of the AC EMI filter 104 via S2.
  • C1 and C2 may be either a single capacitor or a plurality of capacitors connected in parallel.
  • the AC switch 103 may include only S1, and may include both S1 and S2.
  • the specific structure of the AC switch 103 is different. The specific structure of the AC switch 103 and the connection relationship between the AC switch 103 and the AC filter 102 and the AC EMI filter will be described in detail below with reference to FIGS. 4 to 6.
  • the AC switch 103 includes a single-phase AC switch S1, the fixed ends of S1 include A1, A2, B1, and B2, and the active ends of S1 include D1 and D2.
  • C1 is a single-phase capacitor, and both ends of C1 are E1 and E2, respectively.
  • D1 and D2 are respectively connected to the fixed ends A1 and A2, and when the movable ends D1 and D2 of S1 are respectively connected with the fixed ends B1 and B2 of S1, S1 is in a closed state, and the fixed ends A1 and A2 are respectively fixed and fixed ends.
  • B1 and B2 are connected to achieve conduction of S1 such that the output port of the AC filter 102 is connected to the input port of the AC EMI filter 104.
  • E1 and E2 are connected to the fixed terminals B1 and B2 of S1, respectively, and E1 and E2 are also directly connected to the input port of the AC EMI filter.
  • the filter capacitor of the AC filter 102 includes a second split capacitor C2.
  • the connection relationship between each fixed end and the active end of S1 is the same as that of FIG. 4.
  • Both C1 and C2 are single-phase capacitors.
  • Both ends of C1 are E1 and E2, and the two ends of C2 are E3 and E4, respectively.
  • E1 and E2 are respectively connected to the fixed ends B1 and B2 of S1
  • E1 and E2 are also directly connected to the input ports of the AC EMI filter
  • E3 and E4 are respectively connected to the fixed ends A1 and A2 of S1.
  • the AC switch 103 includes single-phase AC switches S1 and S2, wherein S1 and S2 are disposed between the output port of the AC filter 102 and the input port of the AC EMI filter 104, and C1 and C2 are single-phase. Capacitor, C1 is located between S1 and S2, and C2 is disposed between the input port and the output port of the AC filter 102.
  • the fixed end of S1 includes A1, A2, B1 and B2, the active end of S1 includes D1 and D2, the fixed end of S2 includes A3, A4, B3 and B4, and the active end of S2 includes D3 and D4, C1 Both ends are E1 and E2, and the two ends of C2 are E3 and E4, respectively.
  • S1 and D2 are connected to A1 and A2, respectively.
  • D1 and D2 are respectively connected to B1 and B2, respectively, S1 is in a closed state;
  • D3 and D4 are connected to A3 and A4, respectively, when D3 When D4 and B4 are connected to B3 and B4, respectively, S2 is in a closed state.
  • E1 and E2 are connected to B1 and B2, respectively, and E1 and E2 are also connected to A3 and A4, respectively, and E3 and E4 are connected to fixed ends A1 and A2 of S1, respectively.
  • C1 may also be disposed between S2 and an input port of the AC EMI filter 104.
  • the AC switch 103 includes S1 and S2, wherein the connection between each fixed end and the active end of S1 and S2 is The same as Figure 6.
  • both ends E1 and E2 of C1 are connected to the active ends B3 and B4 of S2, respectively, and E1 and E2 are also connected to the input ports of the AC EMI filter 104, respectively.
  • the inverter shown in FIG. 7 may further include C2, wherein the port included in C2, and the connection relationship between C2 and other ports may be as shown in FIG. 6.
  • the AC switch 103 shown in Fig. 7 is the same as the AC switch 103 shown in Fig. 6, except that in Fig. 6, C1 is located between S1 and S2, and in Fig. 7, C1 is located at S2 and AC EMI filtering. Between the devices 104.
  • the filter capacitor in the AC filter 102 is a single-phase capacitor and the AC switch included in the AC switch 103 is a single-phase AC switch has been described above with reference to FIGS. 1 to 7.
  • the filter capacitor in the AC filter 102 may also be a three-phase capacitor
  • the AC switch in the AC switch 103 may also be a three-phase AC switch.
  • the case where the filter capacitor is a three-phase capacitor and the AC switch is a three-phase AC switch will be described in detail below with reference to FIGS. 8 and 9.
  • the AC switch 103 includes a first AC switch S1, the fixed ends of S1 include A1, A2, A3, B1, B2, and B3, and the active ends of S1 include D1, D2, and D3, when the active end D1 of S1 When D2 and D3 are respectively connected to the fixed ends B1, B2 and B3 of S1, S1 is in a closed state, and at this time, the fixed ends A1, A2 and A3 are respectively connected to the fixed ends B1, B2 and B3, thereby realizing the conduction of S1.
  • the output port of the AC filter 102 is connected to the input port of the AC EMI filter 104.
  • C1 is a three-phase capacitor
  • C1 is composed of a first partial capacitor, a second partial capacitor, and a third partial capacitor
  • the first partial capacitor includes a first end E1 and a second end E2
  • the second sub-portion The capacitor includes a third end E3 and a fourth end E4, and the third partial capacitor includes a fifth end E5 and a sixth end E6.
  • E1, E3, and E5 are connected to the fixed ends B1, B2, and B3, respectively, and E2, E4, and E6 are connected to each other.
  • the AC switch 103 includes a first AC switch S1 and a second AC switch S2.
  • the fixed end of S1 includes A1, A2, A3, B1, B2 and B3, the active end of S1 includes D1, D2 and D3, and the fixed end of S1 includes A1, A2, A3, B1, B2 and B3, and the active end of S1 includes D1, D2 and D3, the fixed ends of S2 include A4, A5, A6 and B4, B5 and B6, and the active ends of S2 include D4, D5 and D6.
  • C1 is a three-phase capacitor
  • C1 is composed of a first partial capacitor, a second partial capacitor, and a third partial capacitor.
  • the first end to the sixth end of C1 are E1, E2, E3, E4, and E5, respectively.
  • E1, E3, and E5 are connected to the fixed ends B1, B2, and B3, respectively, and E1, E3, and E5 are also connected to the fixed ends B4, B5, and B6, respectively, and E2, E4, and E6 are connected to each other.
  • the capacitance of the first split capacitor is K times the capacitance of the filter capacitor, where K is a value that causes the harmonic distortion of the AC system to be less than the preset harmonic distortion.
  • the K value is an integer greater than 0 and less than or equal to 1, and the K value can be obtained according to the actual test. Specifically, in actual testing, the value of K may be set, and the ratio of the first split capacitor to the filter capacitor when the harmonic distortion of the AC system meets the preset requirement is determined as the value of K.
  • the value of K can be estimated based on the equivalent capacitance of the AC EMI filter, the equivalent inductance of the AC system, and the harmonics of the AC system.
  • the capacitance value of the first split capacitor is C1
  • the capacitance value of the filter capacitor is C
  • the grid-connected power generation system composed of inverters has different ways of suppressing harmonic distortion of the AC system. The following is a method for suppressing harmonic distortion of the AC system by the grid-connected power generation system composed of the inverters shown in FIG. 1 to FIG. Detailed introduction.
  • the S1 can be kept in the off state (initial state)
  • the lower S1 is in the off state, and no operation is required on S1 at this time.
  • C1 is disconnected from the alternating current filter 102 and is connected to the alternating current system in which the alternating current EMI filter 104 is located. Suppress harmonic distortion of the AC system.
  • the S2 can be kept in the off state (in the initial state, both S1 and S2 are disconnected). State, in this case only need to keep S2 in the off state, for S1, it can be kept off or closed), at this time, C1 disconnects from the AC filter 102, and Being connected to the AC system in which the AC EMI filter 104 is located can suppress harmonic distortion of the AC system.
  • the grid-connected power generation system includes a DC system, an AC system, and an inverter.
  • the output port of the DC system is connected to the input port of the inverter.
  • the output port of the inverter is connected to the input port of the AC system, the DC system is used to output DC power, the inverter is used to convert the DC power outputted by the DC system into AC power, and the AC system is used to provide AC power.
  • the communication system in FIG. 10 may specifically be an AC communication system for providing AC power.
  • the inverter shown in FIG. 10 may be any one of the inverters of FIG. 1 to FIG. 9.
  • the definition and explanation of the inverter in the embodiment of the present application are also applicable to the grid connection shown in FIG. Inverter in the power generation system.
  • the connection between the first split capacitor and the AC filter can be disconnected, and the first split capacitor can be connected to the input port of the inverter.
  • the loop in which the connected AC system is located can suppress the distortion of the AC system.
  • the inverter in the grid-connected power generation system in the embodiment of the present application may be a single-phase inverter or a three-phase inverter.
  • the filter capacitor of the AC filter is composed of two single-phase first split capacitors C1 and second split capacitors C2, and the AC switch is composed of two single-phase first AC switches S1 and second AC switches S2. Composition.
  • the second single-phase split capacitor C2 is connected in parallel with the single-phase filter inductor L.
  • the parallel branch can be regarded as a whole.
  • the front end of the parallel branch is connected to the AC side of the inverter circuit, and the rear end end is connected with the AC switch.
  • the first single-phase AC switch S1 is sequentially connected in series; the first single-phase split capacitor C1 is connected in parallel with the first single-phase AC switch S1, and the parallel branch can be regarded as a whole, and the parallel branch and the second of the AC switch
  • the single-phase AC switches S2 are sequentially connected in series.
  • the first single-phase split capacitor C1 can be incorporated into the AC system by controlling the second single-phase AC switch S2 in the AC switch to dynamically change the resonant branch of the AC system.
  • the resonant frequency avoids the frequency band in which the system harmonic voltage is located, avoids serious amplification of the system harmonic voltage, and ensures that the single-phase inverter starts automatically.
  • first single-phase split capacitor C1 shown in FIG. 11 above may be equivalent to the first split capacitor in the above, and the first single-phase split capacitor C1 may be a partial capacitor of the filter capacitor of the alternating current filter.
  • the filter capacitor is composed of two three-phase first split capacitors C1 and a second split capacitor C2, and the AC switch is composed of two three-phase first alternating current switches S1 and second alternating current switches S2.
  • the second three-phase split capacitor C2 is connected in parallel with the three-phase filter inductor L.
  • the parallel branch can be regarded as a whole.
  • the front end of the parallel branch is connected to the AC side of the inverter circuit, and the rear end point and the AC switch are
  • the first three-phase AC switch S1 is sequentially connected in series;
  • the first three-phase split capacitor C1 is connected in parallel with the first three-phase AC switch S1
  • the parallel branch can be regarded as a whole, and the parallel branch and the second of the AC switch
  • the three-phase AC switches S2 are sequentially connected in series.
  • the first three-phase split capacitor C1 can be incorporated into the AC system by dynamically controlling the second three-phase AC switch S2 in the AC switch to dynamically change the resonant branch of the AC system.
  • the resonant frequency avoids the frequency band where the system harmonic voltage is located, avoids serious amplification of the system harmonic voltage, and ensures that the three-phase inverter starts automatically.
  • first three-phase split capacitor C1 shown in FIG. 12 above may be equivalent to the first split capacitor in the above, and the first three-phase split capacitor C1 may be a partial capacitor of the filter capacitor of the alternating current filter.
  • the grid-connected power generation system described above may include one inverter or multiple inverters. It should be understood that in the grid-connected power generation system, one DC system corresponds to one inverter, and each inverter is used to convert the direct current output of the corresponding DC system into alternating current, and the alternating current system may have only one, and finally multiple inverters The converted AC power can be input to the AC system.
  • the present application also proposes a grid-connected power generation system, which includes an AC system, N inverters of the embodiment of the present application, and N DC systems, wherein an output port of N DC systems and N inverters
  • N is an integer greater than or equal to 1
  • the output ports of the N inverters are connected to the input ports of the AC system.
  • the grid-connected power generation system includes a total of N DC systems (DC system 1 to DC system N, where N is an integer greater than or equal to 1), wherein DC system 1 to DC system N respectively Corresponding to the inverter 1 to the inverter N, the inverter 1 to the inverter N respectively convert the direct current input from the direct current system 1 to the direct current system N into alternating current, and finally, the inverter 1 to the inverter N are converted.
  • the AC power is output to the AC system, and the AC system in the embodiment of the present invention is a power grid, such as a national power grid.
  • the grid-connected power generation system generates a direct current system, such as a photovoltaic solar panel, a wind power generator, or the like, which generates direct current into a grid by converting an inverter into a specific voltage and an alternating current of a working frequency.
  • a direct current system such as a photovoltaic solar panel, a wind power generator, or the like
  • the grid-connected power generation system shown in Fig. 13 is a grid-connected power generation system composed of N single-phase inverters and a DC system and a power grid.
  • the grid-connected power generation system of the embodiment of the present application may also be composed of N three-phase inverters, and a DC system and a power grid.
  • the present application proposes a method for suppressing harmonic distortion of the power grid.
  • the inverter is operated by operating the AC switch.
  • Part of the capacitance of the filter capacitor is incorporated into the grid, reducing harmonic distortion in the grid.
  • the embodiment of the present application also provides a photovoltaic power generation system.
  • the photovoltaic power generation system includes: a photovoltaic module, an AC power grid, and an inverter of the embodiment of the present application.
  • the output port of the photovoltaic module is connected to the input port of the inverter, the output port of the inverter is connected to the input end of the power grid, the photovoltaic component is used to generate direct current, and the inverter is used for inverting the direct current power, and
  • the AC power obtained by the inverter processing is input to the power grid, and the power grid is used to provide AC power.
  • the photovoltaic power generation system of the embodiment of the present application can integrate the first split capacitor into the power grid by controlling the AC switch in the inverter.
  • the loop which changes the capacitance of the loop in which the grid is located, to suppress harmonic distortion in the grid.
  • a photovoltaic component is a device that converts solar energy directly into electrical energy using a photovoltaic effect that occurs under the illumination of a semiconductor material.
  • the above photovoltaic modules may also be referred to as photovoltaic arrays, solar panels.
  • a rectifier may also be provided in the photovoltaic power generation system, the rectifier being connected between the output port of the photovoltaic module and the input port of the inverter for performing the direct current generated by the photovoltaic module. Rectify and input the rectified DC power to the inverter.
  • the photovoltaic power generation system in FIG. 14 is equivalent to a specific case of the grid-connected power generation system shown in FIG. 10 to FIG. 13
  • the photovoltaic module in the photovoltaic power generation system in FIG. 14 is equivalent to the one shown in FIG. 10 to FIG. 13 .
  • the above-mentioned grid-connected power generation system may be a wind turbine grid-connected power generation system and an energy storage grid-connected power generation system.
  • the above-mentioned grid-connected power generation system may specifically be a wind turbine grid-connected power generation system.
  • the inverter of the embodiment of the present application can be applied to the wind turbine grid-connected power generation system.
  • the alternating current output from the wind turbine power generation system can be rectified by the rectifier to obtain direct current power, and then DC stabilized by the direct current capacitor. Pressure, and finally use the inverter to convert the DC power obtained by the DC voltage regulation into AC power, and finally transmit the AC power to the AC power grid.
  • the fan in FIG. 15 is equivalent to the DC system in the grid-connected power generation system shown in FIGS. 10 to 13 for generating direct current.
  • the above-mentioned grid-connected power generation system may specifically be an energy storage grid-connected power generation system.
  • the inverter of the embodiment of the present application can be applied to the energy storage grid-connected power generation system, and the energy storage grid-connected power generation system is composed of a storage system, an inverter, and an AC power grid.
  • the inverter converts the direct current output from the energy storage system into alternating current, and transmits the converted alternating current to the alternating current grid.
  • the energy storage system in FIG. 16 is equivalent to the DC system in the grid-connected power generation system shown in FIGS. 10 to 13 for generating direct current.
  • FIG. 17 is a schematic flowchart of a method for suppressing harmonic distortion according to an embodiment of the present application.
  • the method shown in FIG. 17 can be applied to a grid-connected power generation system including N inverters and a DC system and a power grid, wherein an input port of the N inverters is connected to an output port of the DC system.
  • the output ports of the N inverters are connected to the input ports of the grid.
  • the specific structure of the inverter in the grid-connected power generation system can be as shown in FIGS. 6, 9, and 12. That is, the AC switch of the inverter in the grid-connected power generation system applied by the method shown in FIG.
  • the 17 includes a first alternating current switch and a second alternating current switch, and the first split capacitor is disposed in the first alternating current switch and the first Between the two AC switches, the first split capacitor can be connected to the loop where the grid is located by turning off the second AC switch and keeping the first AC switch in the off state.
  • the grid-connected power generation system to which the method shown in FIG. 17 is applied may be as shown in FIG. 16.
  • the method shown in FIG. 17 specifically includes step 1001 and step 1002. Steps 1001 and 1002 are respectively described in detail below.
  • controlling the second AC switch closure of at least one of the N inverters can connect the first split capacitor of the at least one inverter to the grid connected to the output port of the inverter.
  • the second AC switch of the device is closed to reduce the current THD.
  • the first split capacitor of some inverters can be connected to the power grid by controlling the closing of the AC switch of the inverter therein, and the power grid can be suppressed. Harmonic distortion of the grid voltage.
  • the first split capacitor can be connected in parallel to the power grid, and the resonant frequency of the system resonant branch can be dynamically changed. In turn, avoid the frequency band where the system harmonic voltage of the power grid is located, and avoid serious amplification of the system harmonic voltage.
  • the second AC switch that controls at least one of the N inverters is closed, so that the current THD is less than a preset threshold, and specifically includes: an inverter of the N inverters.
  • steps 1001 and 1002 are repeatedly performed until the current THD is less than or equal to the preset threshold.
  • the current THD is determined in time, and the current THD is continuously reduced by turning off the second AC switch of the inverter when the current THD cannot meet the requirements, so that the current THD Can be less than or equal to a preset threshold.
  • harmonic distortion can be flexibly suppressed by controlling the opening and closing of the AC switch.
  • the current THD is less than or equal to the preset threshold, determining whether the output voltage of the inverter meets the grid-connected power generation condition; when the output voltage of the inverter meets the grid-connected power generation condition, The first unconnected first alternating current switch and the second alternating current switch among the N inverters are all closed.
  • the above DC system may be a power generation system, for example, a wind power generation system, a photovoltaic power generation system, or the like.
  • the above DC system satisfies the power generation condition, which may mean that the power generation system can generate power normally.
  • the DC system is a wind power generation system
  • the DC system satisfies the power generation condition, which may mean that the wind level reaches a preset requirement, and the fan can generate power normally.
  • the method for suppressing harmonic distortion in the embodiment of the present application can be applied to various application scenarios.
  • the method for suppressing harmonic distortion in the embodiment of the present application can be applied to two scenarios: a grid-connected operation scenario and a off-network shutdown scenario.
  • the methods for suppressing harmonic distortion in the embodiments of the present application are described in detail in the following two scenarios.
  • FIG. 18 is a specific flowchart of a method for suppressing harmonic distortion according to an embodiment of the present application in a grid-connected operation scenario.
  • the method shown in FIG. 18 can be applied to the grid-connected power generation system shown in FIG. 16.
  • the method shown in FIG. 18 can perform harmonic suppression on the grid-connected power generation system shown in FIG. 16, and the method shown in FIG. 18 specifically includes the following. step:
  • the grid voltage of the grids of the inverters is collected and the voltage THD analysis is performed to obtain the current THD of the grid voltage.
  • THDm is the set THD threshold that satisfies the normal startup of the inverter. If the current THD is greater than THDm, then step 2004 is performed; if the current THD is less than THDm, then step 2005 is performed.
  • step 2002 is performed again to perform THD analysis to obtain the current THD, and then step 2003 is performed again. If the current THD is greater than THDm, step 2004 is performed again; If the current THD is less than THDm, then step 2005 is performed.
  • the inverter is started normally and connected to the grid.
  • the current THD is less than THDm, and the inverter can be started normally, thereby completing the safe and stable grid connection of the inverter in the system.
  • FIG. 19 is a specific flowchart of a method for suppressing harmonic distortion according to an embodiment of the present application in a grid-connected operation scenario.
  • the method shown in FIG. 19 can be applied to the grid-connected power generation system shown in FIG. 16.
  • the method shown in FIG. 19 can perform harmonic suppression on the grid-connected power generation system shown in FIG. 16, and the specific flow of the method shown in FIG. Includes the following steps:
  • K ranges from (0, 1).
  • the grid voltage of the grids of the inverters is collected and the voltage THD analysis is performed.
  • THDm is the set THD threshold that satisfies the normal startup of the inverter. If the current THD is greater than THDm, then step 3004 is performed; if the current THD is less than THDm, then step 3005 is performed.
  • step 402 is performed again to perform THD analysis to obtain the current THD, and then step 3003 is performed again. If the current THD is greater than THDm, step 404 is performed again; If the current THD is less than THDm, then step 3005 is performed.
  • the inverter starts normally and realizes grid-connected operation.
  • the current THD is less than THDm, which realizes the suppression of grid voltage harmonics under the state of off-grid shutdown of the inverter.
  • the method shown in FIG. 18 above finally realizes the normal startup of the inverter to realize the normal operation of the grid-connected power generation system, and suppresses the harmonic distortion of the power grid before the startup process or startup.
  • the purpose of the method shown in FIG. 19 is only to achieve how to suppress the harmonic distortion of the power grid when the inverter is in the off-network stop state.

Abstract

本申请提供了逆变器、发电系统以及抑制交流系统谐波失真的方法。该逆变器包括逆变电路；交流滤波器，交流滤波器的输入端口与逆变电路的输出端口相连；交流电磁干扰EMI滤波器；第一交流开关，连接在交流滤波器的输出端口与交流EMI滤波器的输入端口之间；其中，交流滤波器包括第一分裂电容，第一分裂电容设置在第一交流开关与交流EMI滤波器的输入端口之间，当第一交流开关处于断开状态时，第一分裂电容与交流滤波器的输出端口的连接断开，且第一分裂电容被接入到与交流滤波器的输出端口相连的交流系统所在的回路，以抑制交流系统的谐波失真。本申请实施例能够抑制交流系统的谐波失真。

Description

逆变器、发电系统以及抑制交流系统谐波失真的方法
本申请要求于2018年04月28日提交中国专利局、申请号为201810401979.1、申请名称为“逆变器、发电系统以及抑制交流系统谐波失真的方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及电力技术领域，并且更具体地，涉及一种逆变器、发电系统以及抑制交流系统谐波失真的方法。
背景技术
逆变器一般连接在直流系统和电网之间，是一种将直流电转变成交流电的装置。逆变器主要由逆变电路、交流滤波器、交流开关和交流电磁干扰(electro magnetic interference，EMI)滤波器组成。其中，逆变电路用于将直流电转换为交流电，交流滤波器和交流EMI滤波器用于对逆变电流产生的交流电进行滤波处理，并将滤波处理后的交流电输出到电网。
典型结构的交流EMI滤波器中一般会存在差模和共模滤波电容，使得交流EMI滤波器呈现容性阻抗特性。因此，当逆变器脱网(交流开关断开)时，交流EMI滤波器会直接与电网连接，为电网引入并联电容，这些并联电容会与电网的电感构成谐振回路进而产生谐振。当该谐振回路与电网内的谐波电压频带相互重叠时，将会导致谐波电压严重放大，谐振引起的电压畸变又会进一步恶化逆变器的控制稳定性，影响逆变器的性能。
为了削弱或者抑制系统谐振，传统方案常采用增加电学元器件的方式来对逆变器导致的谐振(或者称为谐波失真)进行抑制，但是增加元器件的方式不仅会增加硬件成本，同时也会影响整个系统的可靠性，实际应用效果不佳。
发明内容
本申请提供一种逆变器、发电系统以及抑制交流系统谐波失真的方法，以抑制输入交流系统的谐波失真。
第一方面，提供了一种逆变器，该逆变器具体包括：逆变电路、交流滤波器、交流EMI滤波器和第一交流开关。
其中，逆变电路的输出端口与交流滤波器的输入端口相连，第一交流开关连接在交流滤波器的输出端口与交流EMI滤波器的输入端口之间；
上述逆变器还包括第一分裂电容，第一分裂电容设置在第一交流开关与交流EMI滤波器的输入端口之间，当第一交流开关处于断开状态时，第一分裂电容与交流滤波器的输出端口的连接断开，且第一分裂电容被接入到与交流EMI滤波器的输出端口相连的交流系统所在的回路，以抑制输入交流系统的谐波失真。
应理解，上述逆变器可以利用逆变电路将直流电转化为交流电，并采用交流滤波器和交流EMI滤波器对逆变转化得到的交流电进行滤波处理，并将滤波处理后的交流电传输给交流系统，交流系统在获取交流电之后可以用于供电。
可选地，当第一交流开关处于闭合状态时，第一分裂电容与交流滤波器的输出端口的相连，第一分裂电容构成交流滤波器的滤波电容。
应理解，上述第一分裂电容是交流滤波器的电容，只是该电容被设置在交流滤波器的外部，当第一交流开关闭合时，第一分裂电容就构成了交流滤波器的滤波电容。
可选地，上述第一分裂电容为交流滤波器的全部电容或者部分电容。
当上述第一分裂电容为交流滤波器的部分电容时，除了第一分裂电容之外，交流滤波器还可以包含其它电容，其它电容可以位于交流滤波器的输入端口和输出端口之间。
可选地，上述第一分裂电容既可以是单相电容也可以是三相电容。
当第一分裂电容为单相电容时，第一交流开关为单相交流开关；当第一分裂电容为三相电容时，第一交流开关为三相交流开关，并且第一分裂电容由三相分电容构成，具体地，当第一分裂电容为三相电容时，第一分裂电容可以由第一分电容，第二分电容和第三分电容构成。
本申请中，当第一交流开关断开时，第一分裂电容接入到交流系统所在的回路，能够改变，如增加交流系统所在回路的电容值，进而可以抑制交流系统的谐波失真。
进一步地，本申请中通过交流滤波器的原有的电容以及开关的设置就可以实现对交流系统谐波失真的抑制，不会增加额外的元器件，因此不会产生额外的硬件成本和功率消耗。
应理解，当第一分裂电容接入交流系统所在的回路时能够改变交流系统的谐振支路的谐振频率，从而避开交流系统谐波电压所在的频带，抑制交流系统的谐波失真。具体地，交流系统的谐振支路的谐振频率与谐振支路中包含的电容和电感有关，当第一分裂电容接入交流系统后，接入交流系统的谐振支路的电容值会发生改变，使得电网的谐振支路的谐振频率也发生改变。
结合第一方面，在第一方面的第一种实现方式中，交流滤波器的输出端口通过第一交流开关与交流EMI滤波器的输入端口相连，第一分裂电容并联在交流EMI滤波器的输入端口，且第一分裂电容通过第一交流开关并联到交流滤波器的输出端口。
应理解，由于交流滤波器和交流EMI滤波器之间设置有第一交流开关，因此，当第一交流开关断开时，交流滤波器的输出端口与交流EMI滤波器的输入端口之间的连接断开；而当第一交流开关闭合时，交流滤波器的输出端口与交流EMI滤波器的输入端口之间处于连接状态。
结合第一方面或者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，在一种可能的实现方式中，交流滤波器包括串联在交流滤波器的输入端口和输出端口之间的电感L以及第二分裂电容，其中第二分裂电容并联在交流滤波器的输入端口和输出端口之间并设置于电感L与交流滤波器的输出端口之间；当第一交流开关处于断开状态时，第二分裂电容构成交流滤波器的滤波电容，以改变输入交流系统所在的回路的电容值；当第一交流开关处于闭合状态时，第一分裂电容和第二分裂电容均相互并联后与电感L串联，共同构成交流滤波器的滤波电容，其中，交流滤波器的滤波电容用于对逆变电路逆变得到的交流电进行滤波。
通过第一交流开关的闭合和断开，能够灵活控制交流滤波器的部分滤波电容并入到交流系统还是构成交流滤波器的滤波电容，并在需要的抑制谐波失真的时候可以将交流滤波器的部分电容并入到交流系统。
具体地，当第一交流开关断开且第二交流开关闭合时，第一分裂电容接入到交流系统所在的回路，能够改变交流系统的谐振支路的电容值，进而可以改变交流系统的谐振支路的谐振频率，从而可以起到抑制交流系统谐波失真的作用。
结合第一方面的第二种实现方式，在第一方面的第三种实现方式中，上述逆变器还包括第二交流开关，该第二交流开关设置在第一交流开关与交流EMI滤波器的输入端口之间，第一分裂电容设置在第一交流开关和第二交流开关之间；当第一交流开关处于断开状态且第二交流开关处于闭合状态时，第一分裂电容与交流滤波器的输出端口的连接断开，且第一分裂电容被接入到与逆变器的输出端口相连的交流系统所在的回路，以抑制交流系统的谐波失真；当第一交流开关处于闭合状态且第二交流开关处于断开状态时，第一分裂电容和第二分裂电容相互并联后与滤波器的电感L串联，共同构成交流滤波器的滤波电容。
通过两个交流开关能够更方便地调整交流滤波器的滤波电容的构成。
结合第一方面的第三种实现方式，在第一方面的第四种实现方式中，上述交流滤波器的输出端口通过第一交流开关和第二交流开关与交流EMI滤波器的输入端口相连，第一分裂电容通过第一交流开关并联到交流滤波器的输出端口，第一分裂电容通过第二交流开关并联到交流EMI滤波器的输入端口。
应理解，上述第一分裂电容和第二分裂电容既可以是单个电容，也可以是由多个电容并联而成。
结合第一方面以及第一方面的第一种实现方式至第三种实现方式中的任意一种，在第一方面的第五种实现方式中，第一分裂电容的电容值为交流滤波器的滤波电容的电容值的K倍，其中，K是使得交流系统的谐波失真小于预设谐波失真的数值。
应理解，上述交流滤波器的滤波电容可以是指交流滤波器的总电容，该滤波电容的电容值可以是指交流滤波器的总电容值。
可选地，K的数值是根据交流EMI滤波器的等效电容、交流系统的等效电感和交流系统的交流系统谐波确定的。
具体地，可以根据交流EMI滤波器的等效电容、交流系统的等效电感和交流系统的交流系统谐波中的至少一个来确定K的数值，使得K的数值能够满足交流系统的谐波失真小于预设谐波失真。
可选地，K的数值是根据模拟测试或者实际测试获取的。
具体地，可以通过模拟测试或者实际测试的方式来获取交流系统的谐波失真，并通过调整K的数值使得交流系统的谐波失真小于预设的谐波失真，这种情况下得到的K值就是满足要求的数值。
第二方面，提供了一种光伏发电系统，该系统包括光伏组件、交流系统以及上述第一方面任意一种实现方式中的逆变器，其中，光伏组件的输出端口与逆变器的输入端口相连，逆变器的输出端口用于与交流系统的输入端相连，光伏组件用于产生直流电，逆变器用于对直流电进行逆变处理，并将逆变处理得到的交流电输入到交流系统，交流系统用于提供 交流电。
通过采用上述第一方面中任意一种实现方式中的逆变器构成光伏发电系统，能够通过对逆变器中交流开关的控制，将第一分裂电容并入到交流系统所在的回路，从而改变交流系统所在回路的电容值，以抑制交流系统的谐波失真。
上述光伏组件还可以称为光伏阵列、太阳能面板。光伏组件是指利用半导体材料在光照条件下发生的光生伏特效应(photovoltaic)将太阳能直接转换为电能的器件。
可选地，上述光伏发电系统还包括整流器，该整流器连接在光伏组件的输出端口和逆变器的输入端口之间，该整流器用于对光伏组件产生的直流电进行整流，并将整流后得到的直流电输入到逆变器。
第三方面，提供了一种并网发电系统，该系统包括：交流系统、N台如第一方面的第三种实现方式中的逆变器以及N台直流系统，其中，N台直流系统的输出端口与N台逆变器的输入端口一对一相连，N为大于或者等于1的整数，N台逆变器的输出端口与交流系统的输入端口相连。
本申请中，能够通过对逆变器中交流开关的控制，将第一分裂电容并入到交流系统所在的回路，从而改变交流系统所在回路的电容值，以抑制交流系统的谐波失真。
第四方面，提供了一种抑制交流系统谐波失真的方法，该方法应用于第三方面中的并网发电系统，当N台逆变器中的任意一台逆变器中的第一交流开关和第二交流开关均处于断开状态时，该方法包括：步骤1，获取交流系统的交流系统电压的当前总谐波失真THD；步骤2，在当前THD大于预设阈值的情况下，控制N台逆变器中的至少一台逆变器的第二交流开关闭合，以使得当前THD小于预设阈值。
交流系统本申请中，在由N台逆变器组成的并网发电系统中，可以通过控制其中的逆变器的交流开关的关闭使得一些逆变器的第一分裂电容连接到交流系统中，能够抑制交流系统的交流系统电压的谐波失真。
具体而言，当并网发电系统中的交流系统含有电压谐波时，通过控制交流开关的开启和关闭，能够将第一分裂电容并联接入到交流系统中，可以动态改变系统谐振支路的谐振频率，进而避开交流系统的系统谐波电压所在的频带，避免系统谐波电压严重放大。
在一种实现方式中，控制N台逆变器中的至少一台逆变器的第二交流开关闭合，以使得当前THD小于预设阈值，包括：将N台逆变器中的一台逆变器的第二交流开关闭合后，重复执行步骤1和步骤2，直到当前THD小于或者等于预设阈值。
在每次将逆变器的第二交流开关闭合后，及时确定当前THD，在当前THD不能满足要求的下继续通过关闭逆变器的第二交流开关的方式来减小当前THD，使得当前THD能够小于或者等于预设阈值。
本申请中，通过控制交流开关的开启和关闭，能够灵活抑制谐波失真。
在一种实现方式中，上述方法还包括：在当前THD小于或者等于预设阈值的情况下，确定逆变器的输出电压是否满足并网发电条件；在逆变器的输出电压满足并网发电条件时，将N台逆变器中剩余未闭合的第一交流开关和第二交流开关全部闭合。
当直流系统满足发电条件时，可以将逆变器中未闭合的交流开关全部闭合，从而构成一个完整的回路，使得逆变器能够将直流系统产生的直流电转化为交流电，并将该交流电传输给交流系统。
上述直流系统可以为发电系统，例如，风力发电系统、光伏发电系统等等。
上述直流系统满足发电条件可以指发电系统可以正常发电，例如，当上述直流系统为风力发电系统时，直流系统满足发电条件可以是指风力级别达到预设要求，风机可以正常发电。
附图说明
图1是本申请实施例的逆变器的示意性框图；
图2是本申请实施例的逆变器的示意性框图；
图3是本申请实施例的逆变器的示意性框图；
图4是本申请实施例的逆变器的示意性框图；
图5是本申请实施例的逆变器的示意性框图；
图6是本申请实施例的逆变器的示意性框图；
图7是本申请实施例的逆变器的示意性框图；
图8是本申请实施例的逆变器的示意性框图；
图9是本申请实施例的逆变器的示意性框图；
图10是本申请实施例的并网发电系统的示意性框图；
图11是本申请实施例的并网发电系统的示意性框图；
图12是本申请实施例的并网发电系统的示意性框图；
图13是本申请实施例的并网发电系统的示意性框图；
图14是本申请实施例的光伏发电系统的示意性框图；
图15是本申请实施例的风机并网发电系统的示意性框图；
图16是本申请实施例的储能并网发电系统的示意性框图；
图17是本申请实施例的抑制谐波失真的方法的示意性流程框图；
图18是本申请实施例的抑制谐波失真的方法的示意性流程框图；
图19是本申请实施例的抑制谐波失真的方法的示意性流程框图。
具体实施方式
下面将结合附图，对本申请中的技术方案进行描述。
光伏发电系统光伏发电系统下面结合图1至图5对本申请实施例的逆变器进行详细的介绍。
图1是本申请实施例的逆变器的示意性框图。图1所示的逆变器100具体包括：逆变电路101、交流滤波器102、交流开关103和交流EMI滤波器104。
其中，逆变电路101的输出端口与交流滤波器102的输入端口相连，交流开关103连接在交流滤波器102的输出端口与交流EMI滤波器104的输入端口之间，具体地，交流开关103具体可以是第一交流开关S1。
此外，逆变器100还包括第一分裂电容C1，C1设置在S1与交流EMI滤波器104的输入端口之间。当S1处于断开状态时，C1与交流滤波器102的输出端口的连接断开，且C1被接入到与交流EMI滤波器104的输出端口相连的交流系统所在的回路，以抑制交流系统的谐波失真；当S1处于闭合状态时，第一分裂电容与交流滤波器的输出端口的相连， 此时第一分裂电容构成交流滤波器的滤波电容。
如图1所示，逆变器100的输出端口(具体是交流EMI滤波器的输出端口)还可以连接有交流系统。上述逆变器100可以利用逆变电路101将直流电转化为交流电，并采用交流滤波器102和交流EMI滤波器104对逆变转化得到的交流电进行滤波处理，并将滤波处理后的交流电传输给交流系统，该交流系统在获取交流电之后可以用于供电。
应理解，C1是交流滤波器的电容，只是C1被设置在交流滤波器102的输出端口的外部，当S1闭合时，C1就真正构成了交流滤波器的滤波电容。
可选地，C1为交流滤波器的全部电容或者部分电容。
当C1为交流滤波器的部分电容时，除了C1之外，交流滤波器102还可以包含其它电容，该其它电容可以位于交流滤波器102的输入端口和输出端口之间。
可选地，上述第一分裂电容既可以是单相电容也可以是三相电容。
当第一分裂电容为单相电容时，第一交流开关为单相交流开关；当第一分裂电容为三相电容时，第一交流开关为三相交流开关，并且第一分裂电容由三相分电容构成，具体地，当第一分裂电容为三相电容时，第一分裂电容可以由第一分电容，第二分电容和第三分电容构成。
本申请中，当第一交流开关断开时，第一分裂电容并入到交流系统所在的回路，能够改变交流系统所在回路的电容值，进而可以抑制交流系统的谐波失真。
进一步地，本申请中通过交流滤波器的原有的电容以及开关的设置就可以实现对交流系统谐波失真的抑制，不会增加额外的元器件，因此不会产生额外的硬件成本和功率消耗。
应理解，当第一分裂电容接入交流系统所在的回路时能够改变交流系统的谐振支路的谐振频率，从而避开交流系统谐波电压所在的频带，抑制交流系统的谐波失真。具体地，交流系统的谐振支路的谐振频率与谐振支路中包含的电容和电感有关，当第一分裂电容并入交流系统后，交流系统的谐振支路的电容值会发生改变，使得交流系统的谐振支路的谐振频率也发生改变。
进一步地，如图1所示，交流滤波器102的输出端口通过S1与交流EMI滤波器104的输入端口相连，C1并联在交流EMI滤波器104的输入端口，且C1通过S1并联到交流滤波器102的输出端口。
如图1所示，由于交流滤波器102和交流EMI滤波器104之间设置有S1，因此，当S1断开时，交流滤波器102的输出端口与交流EMI滤波器104的输入端口之间的连接断开；而当S1闭合时，交流滤波器102的输出端口与交流EMI滤波器104的输入端口之间处于连接状态。
可选地，如图2所示，交流滤波器102包括串联在交流滤波器102的输入端口和输出端口之间的电感L以及第二分裂电容C2，其中C2并联在交流滤波器102的输入端口和输出端之间并设置于电感L与交流滤波器的输出端口之间；当S1处于断开状态时，C2构成交流滤波器的滤波电容；当S1处于闭合状态时，C1和C2均相互并联后与电感L串联，共同构成交流滤波器102的滤波电容，其中，交流滤波器102的滤波电容用于对逆变电路101逆变得到的交流电进行滤波。
在如图2所示的逆变器中，通过S1能够灵活控制交流滤波器的部分滤波电容并入到交流系统还是构成交流滤波器的滤波电容，并在需要的抑制谐波失真的时候可以将交流滤 波器的部分电容并入到交流系统。
可选地，交流开关103除了包含第一交流开关S1之外，还可以包含第二交流开关S2。
具体地，如图3所示，逆变器100中的交流开关103除了包含S1之外，还包含第二交流开关S2，S2设置在S1与交流EMI滤波器104的输入端口之间，C1设置在S1和S2之间；当S1处于断开状态且S2处于闭合状态时，C1与交流滤波器102的输出端口的连接断开，且C1被接入到与逆变器100的输出端口相连的交流系统所在的回路，以改变交流系统所在的回路的电容值；当S1处于闭合状态且S2处于断开状态时，C1和C2相互并联后与滤波器的电感L串联，共同构成交流滤波器102的滤波电容。
具体地，当S1断开且S2闭合时，C1接入到交流系统所在的回路，能够改变交流系统的谐振支路的电容值，进而可以改变交流系统的谐振支路的谐振频率，从而可以起到抑制交流系统谐波失真的作用。
在如图3所示的逆变器中，通过两个交流开关能够更方便地调整交流滤波器的滤波电容的构成。
进一步地，如图3所示，当交流开关103包含S1和S2，交流滤波器102的滤波电容包含C1和C2时，交流滤波器102的输出端口通过S1和S2与交流EMI滤波器104的输入端口相连，C1通过S1并联到交流滤波器102的输出端口，C1通过S2并联到交流EMI滤波器104的输入端口。
在本申请中，C1和C2既可以是单个电容，也可以是由多个电容并联而成。
在本申请中，交流开关103既可以只包含S1，也可以既包含S1又包含S2，当交流开关103包含的开关数目不同时交流开关103的具体结构有所不同。下面结合图4至图6对交流开关103的具体结构以及交流开关103与交流滤波器102以及交流EMI滤波器的连接关系进行详细介绍。
如图4所示，交流开关103包含单相交流开关S1，S1的固定端包括A1、A2、B1和B2，S1的活动端包括D1和D2。C1为单相电容，C1的两端分别是E1和E2。其中，D1和D2分别与固定端A1和A2相连，当S1的活动端D1和D2分别与S1的固定端B1和B2连接时，S1处于闭合状态，此时固定端A1和A2分别与固定端B1和B2相连，实现了S1的导通，使得交流滤波器102的输出端口与交流EMI滤波器104的输入端口相连。另外，E1和E2分别与S1的固定端B1和B2相连，并且，E1和E2还直接与交流EMI滤波器的输入端口相连。
如图5所示，交流滤波器102的滤波电容包含第二分裂电容C2。其中，S1的各个固定端和活动端的连接关系与图4相同。C1和C2均为单相电容，C1的两端分别是E1和E2，C2的两端分别是E3和E4。其中，E1和E2分别与S1的固定端B1、B2相连，E1和E2还直接与交流EMI滤波器的输入端口相连，E3和E4分别与S1的固定端A1和A2连接。
如图6所示，交流开关103包含单相交流开关S1和S2，其中，S1和S2设置在交流滤波器102的输出端口和交流EMI滤波器104的输入端口之间，C1和C2为单相电容，C1位于S1和S2之间，C2设置在交流滤波器102的输入端口和输出端口之间。
在图6中，S1的固定端包括A1、A2、B1和B2，S1的活动端包括D1和D2，S2的固定端包括A3、A4、B3和B4，S2的活动端包括D3和D4，C1两端分别是E1和E2， C2的两端分别是E3和E4。对于S1来说，D1和D2分别与A1和A2相连，当D1和D2分别与B1和B2分别连接时，S1处于闭合状态；对于S2来说，D3和D4分别与A3和A4相连，当D3和D4分别与B3和B4连接时，S2处于闭合状态。对于C1来说，E1和E2分别与B1和B2相连，E1和E2还分别与A3和A4相连，E3和E4分别与S1的固定端A1和A2相连。
可选地，C1还可以设置在S2与交流EMI滤波器104的输入端口之间，如图7所示，交流开关103包括S1和S2，其中，S1和S2的各个固定端和活动端的连接关系与图6相同。在图7中，C1的两端E1和E2分别与S2的活动端B3和B4连接，E1和E2还分别与交流EMI滤波器104的输入端口相连。应理解，图7所示的逆变器还可以包含C2，其中，C2包含的端口，以及C2与其它端口的连接关系可以如图6所示。
图7所示的交流开关103与图6所示的交流开关103相同，所不同的是，在图6中，C1位于S1和S2之间，而在图7中，C1位于S2和交流EMI滤波器104之间。
上文结合图1至图7对交流滤波器102中的滤波电容为单相电容，交流开关103包含的交流开关为单相交流开关的情况进行了说明。可选地，上述交流滤波器102中的滤波电容还可以是三相电容，交流开关103中的交流开关还可以是三相交流开关。下面结合图8和图9对滤波电容为三相电容，交流开关为三相交流开关的情况进行详细说明。
如图8所示，交流开关103包括第一交流开关S1，S1的固定端包括A1、A2、A3、B1、B2和B3，S1的活动端包括D1、D2和D3，当S1的活动端D1、D2和D3分别与S1的固定端B1、B2和B3连接时，S1处于闭合状态，此时固定端A1、A2和A3分别与固定端B1、B2和B3相连，实现了S1的导通，使得交流滤波器102的输出端口与交流EMI滤波器104的输入端口相连。
在图8中，C1为三相电容，并且C1由第一分电容、第二分电容以及第三分电容组成，其中，第一分电容包括第一端E1和第二端E2，第二分电容包括第三端E3和第四端E4，第三分电容包括第五端E5和第六端E6。E1、E3和E5分别与固定端B1、B2和B3连接，E2、E4和E6彼此连接在一起。
如图9所示，交流开关103包括第一交流开关S1和第二交流开关S2。S1的固定端包括A1、A2、A3、B1、B2和B3，S1的活动端包括D1、D2和D3，S1的固定端包括A1、A2、A3、B1、B2和B3，S1的活动端包括D1、D2和D3，S2的固定端包括A4、A5、A6和B4、B5和B6，S2的活动端包括D4、D5和D6。
在图9中，C1为三相电容，并且C1由第一分电容、第二分电容以及第三分电容组成，C1的第一端至第六端分别是E1、E2、E3、E4、E5和E6。E1、E3和E5分别与固定端B1、B2和B3连接，且E1、E3和E5还分别与固定端B4、B5和B6连接，E2、E4和E6彼此连接在一起。
可选地，作为一个实施例，上述第一分裂电容的电容值为滤波电容的电容值的K倍，其中，K是使得交流系统的谐波失真小于预设谐波失真的数值。
应理解，K值为大于0并且小于或者等于1的整数，K值可以根据实际测试时获取。具体地，在实际测试时，可以设置K的数值，将交流系统的谐波失真满足预设要求时的第一分裂电容与滤波电容的比值确定为K的数值。
除了通过实际测试得到K值之外，还可以根据交流EMI滤波器的等效电容、交流系 统的等效电感和交流系统谐波来估计上述K的数值。
例如，第一分裂电容的电容值为C1，滤波电容的电容值为C，C1＝K*C，假设交流系统的系统谐波的频率为2KHz，当K＝0.2时交流系统最小阻抗所在的频带也为2KHz，那么，当K大于或者等于0.2时，交流系统最小阻抗所在的频带将逐渐远离系统谐波所在的频带，从而能够避免系统谐波出现严重放大，因此，在设置K的数值时，可以根据情况将K的数值设置为一个较大的数值(例如，将K值设置为一个比较接近1的数值)。
当图1至图9所示的逆变器与直流系统和交流系统共同组成并网发电系统时，如果逆变器中的交流开关均处于断开状态，那么由图1至图9所示的逆变器组成的并网发电系统抑制交流系统谐波失真的方式有所不同，下面对图1至图9所示的逆变器组成的并网发电系统抑制交流系统谐波失真的方式进行详细介绍。
当图1、5、7、8和11所示的逆变器与直流系统和交流系统共同组成并网发电系统时，为了抑制交流系统的谐波失真，可以保持S1处于断开状态(初始状态下S1处于断开状态，此时不需要对S1进行任何操作)，此时，C1断开与交流滤波器102的连接，并被接入到与交流EMI滤波器104所在的交流系统中，可以抑制交流系统的谐波失真。
当图3、9和12所示的逆变器与直流系统和交流系统共同组成并网发电系统时，为了抑制交流系统的谐波失真，可以保持S1处于断开状态并闭合S2(初始状态下S1和S2均处于断开状态，此时只需要闭合S2即可)，此时，C1断开与交流滤波器102的连接，并被接入到与交流EMI滤波器104所在的交流系统中，可以抑制交流系统的谐波失真。
当图7所示的逆变器与直流系统和交流系统共同组成并网发电系统时，为了抑制交流系统的谐波失真，可以保持S2处于断开状态(初始状态下S1和S2均处于断开状态，此时只需要保持S2处于断开状态即可，对于S1来说，既可以将其保持断开状态也可以将其闭合)，此时，C1断开与交流滤波器102的连接，并被接入到与交流EMI滤波器104所在的交流系统中，可以抑制交流系统的谐波失真。
本申请还提出了一种并网发电系统，如图10所示，该并网发电系统包括直流系统、交流系统以及逆变器组成，其中，直流系统的输出端口与逆变器的输入端口相连，逆变器的输出端口与交流系统的输入端口相连，直流系统用于输出直流电，逆变器用于将直流系统输出的直流电转化为交流电，交流系统用于提供交流电。
其中，图10中的交流系统具体可以为交流交流系统，用于提供交流电。
应理解，图10所示的逆变器可以是如图1至图9中的任意一个逆变器，本申请实施例中对逆变器的限定和解释同样适用于图10所示的并网发电系统中的逆变器。
本申请中，通过将并网发电系统中的交流开关设置到断路状态，可以将第一分裂电容与交流滤波器的连接断开，并且将第一分裂电容接入到与逆变器的输入端口相连的交流系统所在的回路，能够抑制交流系统的失真。
本申请实施例中的并网发电系统中的逆变器既可以是单相逆变器，也可以是三相逆变器。
如图11所示，交流滤波器的滤波电容由两个单相的第一分裂电容C1和第二分裂电容C2构成，交流开关由两个单相的第一交流开关S1和第二交流开关S2构成。
其中，第二单相分裂电容C2与单相滤波电感L并联，该并联支路可以看成一个整体，该并联支路的前端端点连接到逆变电路的交流侧，后端端点与交流开关中的第一单相交流 开关S1顺序串联连接；第一单相分裂电容C1与第一单相交流开关S1并联，该并联支路可以看成一个整体，该并联支路与交流开关中的第二单相交流开关S2顺序串联连接。
当单相逆变器处于脱网状态时，可以通过控制交流开关中的第二单相交流开关S2闭合，将第一单相分裂电容C1并入交流系统，从而动态地改变交流系统谐振支路的谐振频率，避开系统谐波电压所在的频带，避免系统谐波电压严重放大，保证单相逆变器自动启动。
应理解，上述图11中所示的第一单相分裂电容C1可以相当于上文中的第一分裂电容，该第一单相分裂电容C1可以是交流滤波器的滤波电容的部分电容。
如图12所示，滤波电容由两个三相的第一分裂电容C1和第二分裂电容C2构成，交流开关由两个三相的第一交流开关S1和第二交流开关S2构成。
其中，第二三相分裂电容C2与三相滤波电感L并联，该并联支路可以看成一个整体，该并联支路的前端端点连接到逆变电路的交流侧，后端端点与交流开关中的第一三相交流开关S1顺序串联连接；第一三相分裂电容C1与第一三相交流开关S1并联，该并联支路可以看成一个整体，该并联支路与交流开关中的第二三相交流开关S2顺序串联连接。
当三相逆变器处于脱网状态时，可以通过控制交流开关中的第二三相交流开关S2闭合动作，将第一三相分裂电容C1并入交流系统，动态改变交流系统谐振支路的谐振频率，避开系统谐波电压所在的频带，避免系统谐波电压严重放大，保证三相逆变器自动启动。
应理解，上述图12中所示的第一三相分裂电容C1可以相当于上文中的第一分裂电容，该第一三相分裂电容C1可以是交流滤波器的滤波电容的部分电容。
上述并网发电系统既可以包括一个逆变器，也可以包含多个逆变器。应理解，在并网发电系统中，一个直流系统对应一个逆变器，每个逆变器用于将对应的直流系统输出的直流电转化成交流电，而交流系统可以只有一个，最终多个逆变器转化得到的交流电均可以输入到该交流系统中。
本申请还提出了一种并网发电系统，该并网发电系统包括交流系统、N台本申请实施例的逆变器以及N台直流系统，其中，N台直流系统的输出端口与N台逆变器的输入端口一对一相连，N为大于或者等于1的整数，N台逆变器的输出端口与交流系统的输入端口相连。
具体地，如图13所示，并网发电系统共包含N个直流系统(直流系统1至直流系统N，其中，N为大于或者等于1的整数)，其中，直流系统1至直流系统N分别对应逆变器1至逆变器N，逆变器1至逆变器N分别将直流系统1至直流系统N输入的直流电转化成交流电，最后，逆变器1至逆变器N将转化得到的交流电输出到交流系统中，本本发明实施例中所述交流系统是电网，如国家电网。所述并网发电系统将产生的直流系统，如光伏太阳能板、风力发电机等等产生直流电通过逆变器转换成特定电压以及工作频率的交流电，来并入电网。
图13所示的并网发电系统是由N个单相逆变器以及直流系统和电网组成的并网发电系统。
可选地，本申请实施例的并网发电系统还可以由N个三相逆变器以及直流系统和电网组成。
为了解决逆变器在脱网状态下引起的电网的谐波失真，本申请提出了一种抑制电网谐 波失真的方法，在电网谐波失真的情况下，通过操作交流开关，使得逆变器的滤波电容中的部分电容并入到电网中，从而减小电网的谐波失真。
本申请实施例还提供一种光伏发电系统。如图14所示，该光伏发电系统包括：光伏组件、交流电网以及本申请实施例的逆变器。
其中，光伏组件的输出端口与逆变器的输入端口相连，逆变器的输出端口用于与电网的输入端相连，光伏组件用于产生直流电，逆变器用于对直流电进行逆变处理，并将逆变处理得到的交流电输入到电网，电网用于提供交流电。
由于上述光伏发电系统采用的是本申请实施例的逆变器，因此，本申请实施例的光伏发电系统能够通过对逆变器中交流开关的控制，将第一分裂电容并入到电网所在的回路，从而改变电网所在回路的电容值，以抑制电网的谐波失真。
光伏组件是指利用半导体材料在光照条件下发生的光生伏特效应(photovoltaic)将太阳能直接转换为电能的器件。上述光伏组件还可以称为光伏阵列、太阳能面板。
为了对光伏组件产生的直流电进行整流，还可以在光伏发电系统中设置整流器，该整流器连接在光伏组件的输出端口和逆变器的输入端口之间，该整流器用于对光伏组件产生的直流电进行整流，并将整流后得到的直流电输入到逆变器。
应理解，图14中的光伏发电系统相当图10至图13所示的并网发电系统的一种具体情况，图14中的光伏发电系统中的光伏组件相当于图10至图13所示的并网发电系统中的直流系统。
除了光伏发电系统之外，上述并网发电系统除了可以是风机并网发电系统和储能并网发电系统。
如图15所示，上述并网发电系统具体可以是风机并网发电系统。本申请实施例的逆变器可以应用在该风机并网发电系统中，在风机并网发电系统中，通过整流器可以对风机发电系统输出的交流电进行整流，得到直流电，然后通过直流电容进行直流稳压，最后再利用逆变器将直流稳压得到的直流电转化为交流电，最后再将交流电传输到交流电网。其中，图15中的风机相当于图10至图13所示的并网发电系统中的直流系统，用于产生直流电。
如图16所示，上述并网发电系统具体可以是储能并网发电系统。本申请实施例的逆变器可以应用在该储能并网发电系统中，该储能并网发电系统由存储系统、逆变器和交流电网组成。在该储能并网发电系统中，逆变器将储能系统输出的直流电转化为交流电，并将转化得到的交流电传输到交流电网。其中，图16中的储能系统相当于图10至图13所示的并网发电系统中的直流系统，用于产生直流电。
图17是本申请实施例的抑制谐波失真的方法示意性流程图。图17所示的方法可以适用于并网发电系统，该并网发电系统包括N台逆变器以及直流系统和电网，其中，该N台逆变器的输入端口与直流系统的输出端口相连，该N台逆变器的输出端口与电网的输入端口相连。该并网发电系统中的逆变器的具体结构可以如图6、9以及12所示。也就是说，图17所示的方法所应用的并网发电系统中的逆变器的交流开关均包含第一交流开关和第二交流开关，且第一分裂电容设置在第一交流开关和第二交流开关之间，通过关闭第二交流开关并保持第一交流开关处于断开状态，能够将第一分裂电容连接到电网所在的回路。
具体地，图17所示的方法所应用的并网发电系统可以如图16所示。
图17所示的方法具体包括步骤1001和步骤1002，下面对步骤1001和步骤1002分别进行详细的介绍。
1001、获取电网的电网电压的当前总谐波失真THD。
1002、在当前THD大于预设阈值的情况下，控制N台逆变器中的至少一台逆变器的第二交流开关闭合，以使得当前THD小于所述预设阈值。
应理解，控制N台逆变器中的至少一台逆变器的第二交流开关闭合能够将该至少一台逆变器的第一分裂电容接入到与逆变器的输出端口相连的电网所在的回路，并且断开该第一分裂电容与交流滤波器的输出端口之间的连接，可以抑制所述电网的谐波失真，因此，通过将N台逆变器中的至少一台逆变器的第二交流开关闭合，能够降低当前THD。
本申请中，在由N台逆变器组成的并网发电系统中，可以通过控制其中的逆变器的交流开关的关闭使得一些逆变器的第一分裂电容连接到电网中，能够抑制电网的电网电压的谐波失真。
具体而言，当并网发电系统中的电网含有电压谐波时，通过控制交流开关的开启和关闭，能够将第一分裂电容并联接入到电网中，可以动态改变系统谐振支路的谐振频率，进而避开电网的系统谐波电压所在的频带，避免系统谐波电压严重放大。
具体地，上述控制N台逆变器中的至少一台逆变器的第二交流开关闭合，以使得当前THD小于预设阈值，具体包括：将N台逆变器中的一台逆变器的第二交流开关闭合后，重复执行步骤1001和步骤1002，直到当前THD小于或者等于所述预设阈值。
在每次将逆变器的第二交流开关闭合后，及时确定当前THD，在当前THD不能满足要求的下继续通过关闭逆变器的第二交流开关的方式来减小当前THD，使得当前THD能够小于或者等于预设阈值。
应理解，在本申请实施例的抑制谐波失真的方法中，通过逐个闭合逆变器的第二交流开关，能够逐渐改变当前THD，使得当前THD能够最终小于或者等于预设阈值，从而达到抑制谐波失真的目的。
具体地，随着闭合第二交流开关数目的增多，越来越多的第一分裂电容会连接到电网所在的回路，进而可以逐渐降低当前THD，并且在当前THD小于或者等于预设阈值的情况下停止闭合逆变器的第二交流开关，从而实现抑制谐波失真的目的。
本申请中，通过控制交流开关的开启和关闭，能够灵活抑制谐波失真。
可选地，作为一个实施例，在当前THD小于或者等于预设阈值的情况下，确定逆变器的输出电压是否满足并网发电条件；在逆变器的输出电压满足并网发电条件时，将N台逆变器中剩余未闭合的第一交流开关和第二交流开关全部闭合。
当直流系统满足发电条件时，可以将逆变器中未闭合的交流开关全部闭合，从而构成一个完整的回路，使得逆变器能够将直流系统产生的直流电转化为交流电，并将该交流电传输给电网。
上述直流系统可以为发电系统，例如，风力发电系统、光伏发电系统等等。
上述直流系统满足发电条件可以指发电系统可以正常发电，例如，当上述直流系统为风力发电系统时，直流系统满足发电条件可以是指风力级别达到预设要求，风机可以正常发电。
本申请实施例的抑制谐波失真的方法可以应用到多种应用场景中，例如，本申请实施 例的抑制谐波失真的方法可以应用到并网运行场景和脱网停机场景这两种场景，下面对这两种场景下本申请实施例的抑制谐波失真的方法进行详细的介绍。
下面先结合图18对并网运行场景下本申请实施例的抑制谐波失真的方法的具体过程进行详细的介绍。
图18为并网运行场景下利用本申请实施例的抑制谐波失真的方法的具体流程图。图18所示的方法可以应用到图16所示并网发电系统中，图18所示的方法能够对图16所示的并网发电系统进行谐波抑制，图18所示的方法具体包括以下步骤：
2001、将逆变器的滤波电容C分裂成C1和C2。
具体地，可以将N台逆变器中每台逆变器的滤波电容C按特定比例分裂成并联的第一分裂电容C1和第二分裂电容C2两部分，其中，C1＝KC，C2＝(1-K)C，分裂电容系数K的取值范围为(0,1]。
2002、采集电网电压并进行THD分析，得到当前THD。
具体地，当N台逆变器处于脱网状态时，采集逆变器并网点的电网电压并进行电压THD分析，得到电网电压的当前THD。
2003、确定当前THD是否小于或者等于THDm。
THDm为设定的满足逆变器正常启动的THD阀值，如果当前THD大于THDm，那么就执行步骤2004；如果当前THD小于THDm，那么就执行步骤2005。
2004、闭合S2将一台逆变器的C1接入电网。
当第1台逆变器的C1接入到电网统后，再次执行步骤2002，进行THD分析，得到当前THD，接下来再次执行步骤2003，如果当前THD大于THDm，那么就再次执行步骤2004；如果当前THD小于THDm，那么就执行步骤2005。
2005、逆变器正常启动实现并网运行。
当前THD小于THDm，逆变器可以正常启动，进而完成系统内逆变器安全、稳定并网。
下面先结合图19对脱网停机场景下本申请实施例的抑制谐波失真的方法的具体过程进行详细的介绍。
图19为并网运行场景下利用本申请实施例的抑制谐波失真的方法的具体流程图。图19所示的方法可以应用到图16所示并网发电系统中，图19所示的方法能够对图16所示的并网发电系统进行谐波抑制，图19所示的方法的具体流程包括以下步骤：
3001、将逆变器的滤波电容C分裂成C1和C2。
具体地，可以将逆变器的滤波电容C按特定比例分裂成并联的第一分裂电容C1和第二分裂电容C2两部分，且C1＝KC，C2＝(1-K)C，分裂电容系数K的取值范围为(0,1]。
3002、采集电网电压并进行THD分析，以得到当前THD。
具体地，当N台逆变器处于脱网状态时，采集逆变器并网点的电网电压并进行电压THD分析。
3003、确定当前THD是否小于或者等于THDm。
THDm为设定的满足逆变器正常启动的THD阀值，如果当前THD大于THDm，那么就执行步骤3004；如果当前THD小于THDm，那么就执行步骤3005。
3004、闭合S2将一台逆变器的C1接入电网。
当第1台逆变器的C1接入到电网统后，再次执行步骤402，进行THD分析，得到当前THD，接下来再次执行步骤3003，如果当前THD大于THDm，那么就再次执行步骤404；如果当前THD小于THDm，那么就执行步骤3005。
3005、逆变器正常启动实现并网运行。
当前THD小于THDm，实现了逆变器脱网停机状态下的对电网电压谐波抑制。
应理解，上述图18所示的方法最终要实现逆变器的正常启动进而实现并网发电系统的正常运行，并且在启动过程或者启动之前要抑制电网的谐波失真。而图19所示的方法的目的仅仅在于在逆变器处于脱网停机状态下如何实现对电网的谐波失真的抑制。
以上所述，仅为本申请的具体实施方式，但本申请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申请揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以所述权利要求的保护范围为准。

Claims (10)

  1. 一种逆变器，其特征在于，包括：
    逆变电路；
    交流滤波器，所述交流滤波器的输入端口与所述逆变电路的输出端口相连；
    交流电磁干扰EMI滤波器；
    第一交流开关，连接在所述交流滤波器的输出端口与所述交流EMI滤波器的输入端口之间；
    其中，所述逆变器还包括第一分裂电容，所述第一分裂电容设置在所述第一交流开关与所述交流EMI滤波器的输入端口之间；
    当所述第一交流开关闭合时，所述第一分裂电容构成所述交流逆变器的滤波电容；
    当所述第一交流开关处于断开状态时，所述第一分裂电容与所述交流滤波器的输出端口的连接断开，所述第一分裂电容被接入到与所述交流EMI滤波器的输出端口相连的交流系统所在的回路，以抑制向所述交流系统输入的谐波失真。
  2. 如权利要求1所述的逆变器，其特征在于，所述交流滤波器的输出端口通过所述第一交流开关与所述交流EMI滤波器的输入端口相连，所述第一分裂电容并联在所述交流EMI滤波器的输入端口，且所述第一分裂电容通过所述第一交流开关并联到所述交流滤波器的输出端口。
  3. 如权利要求1或2所述的逆变器，其特征在于，所述交流滤波器包括串联在所述交流滤波器的输入端口和输出端口之间的电感L以及第二分裂电容，其中所述第二分裂电容并联在所述交流滤波器的输入端口和输出端之间并设置于所述电感L与所述交流滤波器的输出端口之间；
    当所述第一交流开关处于断开状态时，所述第二分裂电容构成所述交流滤波器的滤波电容；
    当所述第一交流开关处于闭合状态时，所述第一分裂电容和所述第二分裂电容均相互并联后与所述电感L串联，共同构成所述交流滤波器的滤波电容，
    其中，所述交流滤波器的滤波电容用于对所述逆变电路逆变得到的交流电进行滤波。
  4. 如权利要求3所述的逆变器，其特征在于，所述逆变器还包括：
    第二交流开关，设置在所述第一交流开关与所述交流EMI滤波器的输入端口之间，所述第一分裂电容设置在所述第一交流开关和所述第二交流开关之间；
    当所述第一交流开关处于断开状态且所述第二交流开关处于闭合状态时，所述第一分裂电容与所述交流滤波器的输出端口的连接断开，且所述第一分裂电容被接入到与所述逆变器的输出端口相连的交流系统所在的回路，使得所述交流系统所在的回路的电容值被增加以抑制输入所述交流系统的谐波失真；
    当所述第一交流开关处于闭合状态且所述第二交流开关处于断开状态时，所述第一分裂电容和所述第二分裂电容相互并联后与所述滤波器的电感L串联，共同构成所述交流滤波器的滤波电容。
  5. 如权利要求4所述的逆变器，其特征在于，所述交流滤波器的输出端口通过所述 第一交流开关和所述第二交流开关与所述交流EMI滤波器的输入端口相连，所述第一分裂电容通过所述第一交流开关并联到所述交流滤波器的输出端口，所述第一分裂电容通过所述第二交流开关并联到所述交流EMI滤波器的输入端口。
  6. 一种光伏发电系统，其特征在于，所述系统包括光伏组件、以及如权利要求1-5中任一项所述的逆变器，其中，所述光伏组件的输出端口与所述逆变器的输入端口相连，所述逆变器的输出端口用于与交流系统的输入端相连，所述光伏组件用于产生直流电，所述逆变器用于对所述直流电进行逆变处理，并将逆变处理得到的交流电输入到所述交流系统。
  7. 一种并网发电系统，其特征在于，所述系统包括：N台如权利要求4所述的逆变器以及N台直流系统，其中，所述N台直流系统的输出端口与所述N台逆变器的输入端口一对一相连，N为大于或者等于1的整数，所述N台逆变器的输出端口与交流系统的输入端口相连。
  8. 一种抑制交流系统谐波失真的方法，所述方法应用于如权利要求7所述的并网发电系统，其特征在于，当所述N台逆变器中的任意一台逆变器中的第一交流开关和第二交流开关均处于断开状态时，所述方法包括：
    步骤1，获取所述交流系统的电压的当前总谐波失真THD；
    步骤2，在所述当前THD大于预设阈值的情况下，控制所述N台逆变器中的至少一台逆变器的第二交流开关闭合，以使得所述当前THD小于所述预设阈值。
  9. 如权利要求8所述的方法，其特征在于，所述控制所述N台逆变器中的至少一台逆变器的第二交流开关闭合，以使得所述当前THD小于所述预设阈值，包括：
    将所述N台逆变器中的一台逆变器的第二交流开关闭合后，重复执行步骤1和步骤2，直到所述当前THD小于或者等于所述预设阈值。
  10. 如权利要求9所述的方法，其特征在于，所述方法还包括：
    在所述当前THD小于或者等于所述预设阈值的情况下，确定所述逆变器的输出电压是否满足并网发电条件；
    在所述逆变器的输出电压满足并网发电条件时，将所述N台逆变器中剩余未闭合的第一交流开关和第二交流开关全部闭合。
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