WO2022126351A1 - 一种光伏系统、保护方法及逆变系统 - Google Patents

一种光伏系统、保护方法及逆变系统 Download PDF

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Publication number
WO2022126351A1
WO2022126351A1 PCT/CN2020/136339 CN2020136339W WO2022126351A1 WO 2022126351 A1 WO2022126351 A1 WO 2022126351A1 CN 2020136339 W CN2020136339 W CN 2020136339W WO 2022126351 A1 WO2022126351 A1 WO 2022126351A1
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WIPO (PCT)
Prior art keywords
inverter
inverters
parallel
current
grid
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PCT/CN2020/136339
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English (en)
French (fr)
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WO2022126351A9 (zh
Inventor
于心宇
辛凯
张彦忠
高拥兵
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华为数字能源技术有限公司
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Priority to PCT/CN2020/136339 priority Critical patent/WO2022126351A1/zh
Priority to CN202080105556.0A priority patent/CN116783816A/zh
Priority to EP20965369.0A priority patent/EP4250513A4/en
Publication of WO2022126351A1 publication Critical patent/WO2022126351A1/zh
Publication of WO2022126351A9 publication Critical patent/WO2022126351A9/zh
Priority to US18/334,653 priority patent/US20230327453A1/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
    • H02J3/38—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
    • 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
    • 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
    • H02M1/0074—Plural converter units whose inputs are connected in series
    • 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
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • 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
    • H02M7/493—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 the static converters being arranged for operation in parallel
    • 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
    • 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
    • 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 present application relates to the technical field of photovoltaic power generation, and in particular, to a photovoltaic system, a protection method and an inverter system.
  • Typical photovoltaic power generation is the direct current output from the photovoltaic array, which is converted into alternating current by the inverter and then connected to the grid or provided to the load.
  • a common implementation method is to connect the AC output terminals of multiple inverters in parallel to obtain greater power.
  • the DC bus voltage of the non-faulty inverter will increase. The components of the inverter are damaged, resulting in the expansion of the fault.
  • the present application provides a photovoltaic system, a protection method and an inverter system, which can protect the parallel inverters and the parallel inverters in time when a short-circuit fault occurs, so as to prevent the expansion of the fault range.
  • An embodiment of the present application provides a photovoltaic system including: a controller and two groups of inverters; the two groups of inverters include: a pole inverter group and a negative pole inverter group; the positive inverter group includes the following at least two inverters Inverters: a first inverter and a third inverter, the negative inverter group includes at least two inverters: the second inverter and the fourth inverter; the first inverter and the third inverter The AC output terminals of the inverters are connected in parallel, the DC input terminals of the first inverter and the second inverter are connected in series; the AC output terminals of the second inverter and the fourth inverter are connected in parallel; the third inverter The DC input terminal of the inverter and the fourth inverter are connected in series; the controller obtains the circulating current between at least two inverters whose AC output terminals are connected in parallel, and the circulating current is greater than the preset current threshold or the rising rate of the circulating
  • the inverter is protected in time, and the further influence caused by the short-circuit fault is minimized. That is, when at least one of the inverters has a short-circuit fault, the circulating current will flow back from the AC output end of the parallel inverters through the path formed by the filter capacitor to the DC input end, thereby affecting the inverters connected in series. In order to ensure the safety of each inverter in the photovoltaic system, as long as the circulating current of the parallel inverters is greater than the preset current threshold, the inverter will be blocked to protect the inverter and other inverters that may be affected. , so as to avoid short-circuit faults causing greater safety hazards.
  • the system and method provided by the embodiments of the present application can realize comprehensive short-circuit fault protection without adding any new hardware.
  • the controller after the wave is blocked, is further configured to disconnect the grid-connected switch corresponding to the faulty inverter whose DC bus voltage is less than the preset voltage threshold, and the grid-connected switch is connected in series with the corresponding inverter between the AC output of the device and the grid.
  • the faulty inverter is judged based on the fact that the DC bus voltage is less than the preset voltage threshold.
  • the DC bus voltage drop rate is greater than the preset drop rate, it can also be judged
  • the inverter has a short-circuit fault, that is, the faulty inverter. For the safety of the system, the faulty inverter needs to be isolated from the system. Therefore, the grid-connected switch corresponding to the faulty inverter needs to be disconnected.
  • the controller is also used to disconnect the grid-connected switch corresponding to the inverter connected in series with the faulty inverter after the wave is blocked . That is, when there are inverters connected in series to the faulty inverters, the inverters connected in series with the faulty inverters also need to be isolated, that is, they are removed from the system, do not participate in the failure of the system, and also disconnect their grid-connected switches.
  • the controller controls the power devices of the non-faulty inverter to resume the switching action, that is, unsealing
  • the non-faulty inverter starts to switch according to the driving signal, and converts the direct current into alternating current.
  • each inverter may correspond to one controller, that is, there may be multiple controllers, the inverters and the controllers are in one-to-one correspondence, and the controller completes its own controller corresponding to the inverter.
  • the controller can be integrated with the inverter, eg in the cabinet of the inverter.
  • the embodiment of the present application does not limit the number of controllers, and all inverters may share one controller, and each inverter may communicate with the controller.
  • each controller when each inverter corresponds to a controller, each controller is further configured to obtain a common-mode output current according to the three-phase output current of the corresponding inverter, and the common-mode output current is greater than a preset value
  • the inverter is controlled to block the wave, and the inverter connected in parallel with the parallel output terminal of the inverter is controlled to block the wave.
  • the common mode output current is used to represent the circulating current between the inverters.
  • the bipolar photovoltaic system includes: a controller and two sets of inverters; the two sets of inverters include: a positive pole inverter An inverter group and a negative inverter group; the positive inverter group includes the following at least two inverters: a first inverter and a third inverter, and the negative inverter group includes the following at least two inverters: The second inverter and the fourth inverter; the AC output terminals of the first inverter and the third inverter are connected in parallel, and the DC input terminals of the first inverter and the second inverter are connected in series; the second inverter The AC output terminals of the inverter and the fourth inverter are connected in parallel; the DC input terminals of the third inverter and the fourth inverter are connected in series;
  • the method includes: obtaining a circulating current between at least two inverters whose AC output ends are connected in parallel; the circulating current is greater than a preset current threshold or the rising rate of the circulating current is greater than a preset rate, and controlling all the corresponding AC output ends connected in parallel
  • the inverters are all blocked, and the blocked wave means that all the power devices of the inverter stop switching.
  • the method further includes: disconnecting the parallel connection corresponding to the faulty inverter whose DC bus voltage is less than the preset voltage threshold.
  • the grid switch is connected in series between the AC output end of the corresponding inverter and the grid.
  • the controller after controlling all the inverters connected in parallel with the corresponding AC output terminals to block the wave, further includes: disconnecting the parallel connection corresponding to the inverter connected in series with the faulty inverter. network switch.
  • the method further includes: controlling the power device of the non-faulty inverter to resume the switching action.
  • obtaining a circulating current between at least two inverters whose AC output ends are connected in parallel specifically includes: obtaining a three-phase output current of each inverter whose AC output ends are connected in parallel; The common mode output current of the corresponding inverter is obtained according to the three-phase output current, and the common mode output current is used as the circulating current of the inverter.
  • the above is based on the photovoltaic system including multiple inverters with AC output terminals connected in parallel.
  • the following introduces a universal inverter system, without limiting the specific application scenario, as long as it includes multiple inverters with AC output terminals connected in parallel. device can be used.
  • An inverter system provided by an embodiment of the present application includes: a controller and at least two inverters; the input ends of the at least two inverters are respectively used to connect their corresponding DC power supplies; The AC output ends are connected in parallel; the controller is specifically used to obtain the circulating current between at least two inverters whose AC output ends are connected in parallel. All inverters whose AC output terminals are connected in parallel are blocked, where blocking means that all power devices of the inverter stop switching.
  • the controller after the wave is blocked, is further configured to disconnect the grid-connected switch corresponding to the faulty inverter whose DC bus voltage is less than the preset voltage threshold, and the grid-connected switch is connected in series with the corresponding inverter between the AC output of the device and the grid.
  • the controller is further configured to control the power device of the non-faulty inverter to resume the switching action.
  • the controller is further configured to obtain the common-mode output current according to the three-phase output current of the corresponding inverter, where the common-mode output current is greater than a preset current threshold or the common-mode output current rising rate is greater than a preset
  • the inverter is controlled to block the wave
  • the inverter connected in parallel with the parallel output terminal of the inverter is controlled to block the wave.
  • the embodiments of the present application have the following advantages:
  • the DC bus short-circuit fault includes the entire DC bus short-circuit fault, that is, the two capacitors connected in series at the inverter input end are both short-circuited; it also includes the half-DC bus-to-ground fault, that is, a capacitor at the inverter input end is short-circuited. Since the inverters connected in parallel at the AC output terminals will affect each other, for example, when the DC bus of one of the inverters is short-circuited, a circulating current will occur between the paralleled inverters.
  • the inverter is protected in time, and the further influence caused by the short-circuit fault is minimized. That is, when at least one of the inverters has a short-circuit fault, the circulating current will flow back from the AC output end of the parallel inverters through the path formed by the filter capacitor to the DC input end, thereby affecting the inverters connected in series.
  • the inverter In order to ensure the safety of each inverter in the photovoltaic system, as long as the circulating current of the parallel inverters is greater than the preset current threshold, the inverter will be blocked to protect the inverter and other inverters that may be affected. , so as to avoid short-circuit faults causing greater safety hazards.
  • the system and method provided by the embodiments of the present application can realize comprehensive short-circuit fault protection without adding any new hardware.
  • FIG. 1 is a schematic diagram of a photovoltaic system provided by an embodiment of the present application
  • FIG. 2 is a schematic diagram of a unipolar photovoltaic system
  • FIG. 3 is a schematic diagram of another photovoltaic system provided by an embodiment of the present application.
  • FIG. 4 is a schematic diagram of another photovoltaic system provided by an embodiment of the present application.
  • FIG. 5 is a schematic diagram of still another photovoltaic system provided by an embodiment of the present application.
  • FIG. 6 is a schematic diagram of another photovoltaic system provided by an embodiment of the present application.
  • FIG. 7 is a schematic diagram of another photovoltaic system provided by an embodiment of the present application.
  • FIG. 8 is a flowchart of a method for protecting a photovoltaic system provided by an embodiment of the present application.
  • FIG. 9 is a flowchart of another method for protecting a photovoltaic system provided by an embodiment of the present application.
  • FIG. 10 is a flowchart of another method for protecting a photovoltaic system provided by an embodiment of the present application.
  • FIG. 11 is a flowchart of still another method for protecting a photovoltaic system provided by an embodiment of the present application.
  • FIG. 12 is a schematic diagram of an inverter system provided by an embodiment of the present application.
  • directional terms such as “upper” and “lower” may include, but are not limited to, definitions relative to the schematic placement of components in the drawings. It should be understood that these directional terms may be relative concepts, They are used for relative description and clarification, which may vary accordingly depending on the orientation in which the components are placed in the drawings.
  • connection should be understood in a broad sense.
  • connection may be a fixed connection, a detachable connection, or an integrated body; it may be directly connected, or Can be indirectly connected through an intermediary.
  • coupled may be a manner of electrical connection that enables signal transmission.
  • Coupling can be a direct electrical connection or an indirect electrical connection through an intermediate medium.
  • FIG. 1 this figure is a schematic diagram of a photovoltaic system provided by an embodiment of the present application.
  • the bipolar photovoltaic system is only used as an example for introduction, and the specific implementation form of the photovoltaic system is not limited.
  • bipolar photovoltaic system includes three bus bars, namely: DC positive bus BUS+, neutral bus M and DC negative bus BUS -.
  • the bipolar photovoltaic system provided in the embodiment of the present application can be applicable to the safety regulation of 1500V, thereby reducing the withstand voltage requirements for the power converter and the power tube in the inverter.
  • the input end of the power converter 200 is used to connect to the photovoltaic array 100 , the first output end of the power converter 200 is connected to the first end of the DC positive bus BUS+, and the second output end of the power converter 200 is connected to the first end of the neutral bus M. terminal, the third output terminal of the power converter 200 is connected to the first terminal of the DC negative bus BUS-.
  • the bipolar photovoltaic system includes at least two inverters: a first inverter 300 and a second inverter 400 .
  • the first input end of the first inverter 300 is connected to the second end of the DC positive busbar BUS+, and the second input end of the first inverter 300 is connected to the second end of the neutral busbar M;
  • the first input end of the second inverter 400 is connected to the second end of the neutral bus M, and the second input end of the second inverter 400 is connected to the second end of the DC negative bus BUS-.
  • the neutral bus M may also not exist, that is, there is no open wire, as long as the potentials of the neutral point of the power converter 200 and the neutral point of the inverter side are within the preset voltage range, for example, for the above introduction
  • the 3000V photovoltaic system the preset voltage range can be 100V.
  • M is only used as an example for the existence of an open line for description.
  • a load or an energy storage battery can be connected between BUS+ and M, or between BUS- and M, as shown in Figure 1, an energy storage battery BAT1 is connected between BUS+ and M, and between BUS- and M An energy storage battery BAT2 is connected between them, a load 1 is connected between BUS+ and M, and a load 2 is connected between BUS- and M.
  • FIG. 2 is a schematic diagram of a conventional monopolar photovoltaic system.
  • the power converter 200 includes two output ends. The first output end of the power converter 200 is connected to the DC positive bus BUS+, and the second output end of the power converter 200 is connected to the DC negative bus BUS-.
  • the inverter 1000 includes two There are two input terminals, wherein the first input terminal of the inverter 1000 is connected to BUS+, and the second input terminal of the inverter 1000 is connected to BUS-. The input end of the power converter 200 is connected to the photovoltaic array 100 .
  • the monopolar photovoltaic system shown in Fig. 2 includes two DC bus bars, namely BUS+ and BUS-. If the total DC bus voltage continues to be 3000V, and the voltage level connected to the input terminal of the inverter 1000 is 3000V, the withstand voltage of the power tube inside the inverter 1000 is higher than that of the single inverter shown in FIG. 1 . The pressure resistance of the tube is twice as high. Therefore, the bipolar photovoltaic system shown in FIG. 1 can reduce the voltage drop borne by the power devices, which is beneficial for device selection.
  • the total voltage of the DC bus corresponding to Figure 1 is 3000V. The higher the voltage, the smaller the corresponding current, which can reduce the loss on the DC bus.
  • a bipolar photovoltaic system can include multiple groups of bipolar inverters, such as M groups of bipolar inverters, where M is an integer greater than or equal to 2, each group includes 2 inverters, and one One positive inverter, one negative inverter, M groups of bipolar inverters include M*2 inverters, such as 4, 6, 8, etc.
  • M groups of bipolar inverters include M*2 inverters, such as 4, 6, 8, etc.
  • M is an integer greater than or equal to 2
  • M groups of bipolar inverters include M*2 inverters, such as 4, 6, 8, etc.
  • the embodiments of the present application do not specifically limit the specific value of M, and the value of M may be set according to actual power requirements.
  • the following takes M as 2, that is, 2 sets of bipolar inverters as an example, which corresponds to 4 inverters, including 2 positive inverters and 2 negative inverters.
  • the bipolar photovoltaic system includes a positive inverter group and a negative inverter group.
  • the inverters connected in parallel at the AC output terminals will affect each other, for example, when one of the inverters has a short-circuit fault, a circulating current will appear between the paralleled inverters. If the circulating current is too large, the power components of the inverter will be damaged, and it will cause excessive power consumption. In severe cases, the protection shutdown will be triggered.
  • the inverter is protected in time, and the further influence caused by the short-circuit fault is minimized.
  • FIG. 1 and FIG. 2 are only schematic illustrations.
  • FIG. 3 this figure is a schematic diagram of another photovoltaic system provided by the embodiment of the present application.
  • the bipolar photovoltaic system provided by the embodiments of the present application includes: a controller and two sets of inverters;
  • the two groups of inverters include: positive inverter group and negative inverter group;
  • the positive inverter group includes the following at least two inverters: the first inverter 300a and the third inverter 300b
  • the negative inverter group includes the following at least two inverters: the second inverter 400a and the third inverter 300b.
  • Four inverters 400b; the AC output terminals of the first inverter 300a and the third inverter 300b are connected in parallel, and the DC input terminals of the first inverter 300a and the second inverter 400a are connected in series, as shown in FIG.
  • the DC negative input terminal of the first inverter 300a is connected to the DC positive input terminal of the second inverter 400a; the AC output terminals of the second inverter and the fourth inverter are connected in parallel ; The DC input terminals of the third inverter and the fourth inverter are connected in series;
  • Each of the first inverter 300a, the second inverter 400a, the third inverter 300b, and the fourth inverter 400b is connected to its corresponding DC power source DC.
  • the direct current power source DC may correspond to the photovoltaic array respectively.
  • a photovoltaic array may include a plurality of photovoltaic strings connected together in parallel.
  • a controller (not shown in the figure), which is specifically configured to obtain a circulating current between at least two inverters whose AC output ends are connected in parallel, where the circulating current is greater than a preset current threshold or the rising rate of the circulating current is greater than a preset rate, All inverters connected in parallel with the corresponding AC output terminals are controlled to block the wave, wherein the blocking means that all the power devices of the inverter stop switching.
  • the preset rate here is the preset ascent rate.
  • the criteria for the inverter wave blocking may include two types. The first is that the circulating current is larger, that is, the circulating current is greater than the preset current threshold. The second is that the circulation rises faster, that is, the rising rate of the circulation is greater than the preset rate, and any one of the above two can be used.
  • the technical solutions provided in the embodiments of the present application are suitable for the short-circuit fault of the DC bus capacitor connected to the input end of the inverter.
  • the first inverter 300a is taken as an example for introduction. As shown in FIG. 3 , the first inverter 300a has a The input terminal is connected with two capacitors in series, a first capacitor C and a second capacitor C2, the first terminal of the first capacitor C1 is connected to the DC positive input terminal of the first inverter 300a, and the second terminal of the first capacitor C1 is connected to The first end of the second capacitor C2 and the second end of the second capacitor C2 are connected to the DC negative input end of the first inverter 300a.
  • the DC bus capacitor short-circuit fault may include both C1 and C2 short-circuit faults, and also include one of the capacitor short-circuit faults, that is, C1 short-circuit fault or C2 short-circuit fault. Since the DC bus voltage of the first inverter 300a is the voltage on C1 and C2, when C1 and/or C2 is short-circuited, the DC bus of the first inverter 300a will be short-circuited. Other inverters are similar and will not be introduced one by one here.
  • Another manifestation that the circulating current is greater than the preset current threshold value can also be detecting the rising rate of the circulating current. When the rising rate of the circulating current is greater than the preset rate, it is considered that the inverter has a short-circuit fault.
  • the photovoltaic system may include multiple sub-arrays. For each inverter of the sub-array, the local common-mode output current is collected as the circulating current. When the circulating current is greater than the preset current threshold, the wave blocking operation is performed.
  • the inverters whose output terminals are connected in parallel its circulating current needs to be monitored. As long as the circulating current of one inverter is greater than the preset current threshold, it is necessary to control all the inverters connected in parallel with the inverter to block the wave. As shown in FIG. 3 , when the circulating current between the first inverter 300a and the parallel third inverter 300b is greater than the preset current threshold, both the first inverter 300a and the third inverter 300b need to be sealed wave, regardless of whether the circulating current flows from the first inverter 300a to the third inverter 300b, or from the third inverter 300b to the first inverter 300a.
  • the controller here is a general term. In practical applications, there may be multiple controllers, that is, the inverter and the controller correspond one-to-one.
  • the implementation form of the controller is also not specifically limited in the embodiments of the present application, and may be, for example, a single-chip microcomputer, a microprocessor, a digital signal processor, or a logic control circuit.
  • multiple inverters may also share one controller, which is not limited in this embodiment of the present application.
  • each controller is also used to obtain the common-mode output current according to the three-phase output current of the corresponding inverter, and when the common-mode output current is greater than the preset current threshold, control the inverter
  • the inverter blocks the wave, and the inverter connected in parallel with the parallel output terminal of the inverter also blocks the wave.
  • the common-mode output current of each inverter can be used to characterize the circulating current between the inverter and the parallel-connected inverters.
  • the following describes a specific implementation of using the three-phase output current to obtain the common-mode output current. Way.
  • the three-phase output current of the inverter can be obtained through a current detection circuit, such as a current sensor.
  • the current sensor obtains the three-phase output current and sends it to the controller corresponding to the inverter.
  • the current detection circuit corresponding to each inverter detects its own three-phase output currents i a , ib and ic in real time, and the controller calculates the common mode output current i cir according to the following formula.
  • the controller compares the common-mode output current with the preset current threshold.
  • the common-mode output current is greater than the preset current threshold, it means that there is a large circulating current between the inverter and the paralleled inverter, and protection needs to be taken. measure. Therefore, the controller needs to block the wave of the inverter.
  • the controller of the inverter connected in parallel with the inverter will also judge that there is a large circulating current, and also block the wave of the corresponding inverter.
  • L1 in FIG. 3 is a filter inductor connected in series between the AC output terminal of each inverter and the transformer T1. Specifically, the first terminal of L1 is connected to the AC output terminal of the inverter, and the second terminal of L1 is connected to the AC output terminal of T1. primary winding.
  • Cflt is the filter capacitor connected to the AC output end of each inverter. Specifically, the first end of Cflt is connected to the second end of L1, and the second end of Cflt is connected to the DC input end of the inverter. One way is to connect the DC positive input end and the DC negative input end of the inverter. For two bus capacitors connected in series, the second end of Cflt is connected to the common point of the two bus capacitors.
  • the DC bus of the first inverter 300a is short-circuited, the current at the AC output end of the third inverter 300b will flow to the DC input end of the first inverter 300a, and the current at the DC input end of the first inverter 300a will flow to the DC input terminal of the second inverter 400a, the AC output terminal of the second inverter 400a will flow to the AC output terminal of the fourth inverter 400b, and flow from the AC output terminal of the fourth inverter 400b to the fourth inverter 400b.
  • the DC input terminal of the inverter 400b flows from the DC input terminal of the fourth inverter 400b to the DC input terminal of the third inverter 300b.
  • a power converter may also be included between the inverter and the corresponding photovoltaic array, for example, the power converter may include a boost circuit, etc.
  • the embodiment of the present application does not specifically limit the implementation type of the power converter.
  • the inverter when a short-circuit fault occurs in one of the inverters, a circulating current occurs between the faulty inverter and the parallel inverters.
  • the inverters are connected in series at the DC input terminals. Therefore, the circulating current will flow back to the DC input terminal from the AC output terminals of the parallel inverters through the path formed by the filter capacitor Cflt, thereby affecting the series inverters.
  • the inverter will be blocked to protect the inverter and the other inverters that may be affected. Inverter, so as to avoid short-circuit faults causing greater safety hazards.
  • Fig. 3 is only an introduction of the bipolar photovoltaic system including 2 groups of bipolar inverters as an example, that is, M is 2, and when M is 3, it includes 3 groups of bipolar inverters, see Fig. 4.
  • This figure is a schematic diagram of another photovoltaic system provided by the embodiment of the present application.
  • the positive inverter group in FIG. 4 includes the following three inverters with AC output terminals connected in parallel: a first inverter 300a, a third inverter 300b and a fifth inverter 300c;
  • the inverter group includes the following three inverters with AC output terminals connected in parallel: a second inverter 400a, a fourth inverter 400b and a sixth inverter 400c.
  • the DC input terminal of the first inverter 300a is connected in series with the DC input terminal of the second inverter 400a
  • the DC input terminal of the third inverter 300b is connected in series with the DC input terminal of the fourth inverter 400b
  • the fifth inverter The DC input terminal of the inverter 300c is connected in series with the DC input terminal of the sixth inverter 400c.
  • the DC bus of the first inverter 300a when the DC bus of the first inverter 300a has a short-circuit fault, it will affect the third inverter 300b and the fifth inverter 300c connected in parallel with it. At the same time, due to the series connection of the DC input terminals, it will also affect The second inverter 400a, the fourth inverter 400b, and the sixth inverter 400c.
  • the positive inverter group and the negative inverter group share one transformer T1 as an example.
  • the positive inverter group and the negative inverter group may respectively correspond to one transformer.
  • this figure is a schematic diagram of still another photovoltaic system provided by an embodiment of the present application.
  • FIG. 5 two groups of bipolar inverters are taken as an example, in which the AC output terminal of the positive inverter group is connected to the primary winding of the first inverter T1A, and the AC output terminal of the negative inverter group is connected to the second inverter. Primary winding of inverter T1B.
  • the embodiment of the present application does not limit the application scenarios of the bipolar photovoltaic system, for example, it can be applied to a large photovoltaic power station, and the corresponding inverters are all three-phase inverters.
  • this figure is a schematic diagram of yet another photovoltaic system provided by an embodiment of the present application.
  • the photovoltaic system corresponding to Figure 6 can be applied to a larger photovoltaic power station, the power of the inverter can be relatively large, the input end of each inverter can be connected to a corresponding combiner box, and the combiner box can include a power converter.
  • each combiner box may include multiple parallel power converters.
  • the input end of each power converter is connected to the corresponding photovoltaic array PV.
  • FIG. 6 is only a schematic diagram of the photovoltaic array PV.
  • the implementation form of the photovoltaic array is not specifically limited in each embodiment of the present application, for example, it may include multiple photovoltaic strings , each PV group is connected in series and parallel. Each PV string can include PV panels connected in series or in parallel.
  • the first inverter 300a is connected as a positive inverter to the corresponding positive MPPT combiner box 200a.
  • the third inverter 300b as a positive inverter is connected to the corresponding positive maximum power point tracking (MPPT, Maximum Power Point Tracking). ) combiner box 200c.
  • MPPT Maximum Power Point Tracking
  • the second inverter 400a as a negative inverter is connected to the corresponding negative MPPT combiner box 200b, and similarly, the fourth inverter 400b as a negative inverter is connected to the corresponding negative MPPT combiner box 200d.
  • the combiner box may not be included, the input end of the inverter is directly connected to the power converter, and the input end of the power converter is connected to the corresponding photovoltaic array.
  • the technical solutions provided by the embodiments of the present application do not limit the power size and specific topology of the photovoltaic system. As long as there are parallel inverters, the circulating current between the parallel inverters is used to monitor whether a short-circuit fault occurs, and when a short-circuit fault occurs, it will be timely to protect.
  • the above embodiment describes the timely closure of the wave when the short-circuit fault causes a large circulating current, but the photovoltaic system needs to continue to operate normally. Therefore, the fault needs to be isolated. After isolation, the normal inverter will work, that is, the faulty inverter will be isolated. Restore the non-faulty inverter to work, remove the wave blocking of the non-faulty inverter, that is, the power device of the non-faulty inverter resumes the switching action.
  • FIG. 7 is a schematic diagram of another photovoltaic system provided by the embodiment of the present application.
  • the controller is also used to disconnect the grid-connected switch corresponding to the faulty inverter whose DC bus voltage is less than the preset voltage threshold, and the grid-connected switch is connected in series with the corresponding inverter. between the AC output and the grid.
  • the faulty inverter is determined by the DC bus voltage undervoltage.
  • the controller of the faulty inverter can notify the controller of the inverter connected in series with it that a short-circuit fault has occurred.
  • the first inverter 300a corresponds to the grid-connected switch KM1
  • the second inverter 400a corresponds to the grid-connected switch KM2
  • the third inverter 300b corresponds to the grid-connected switch KM3
  • the fourth inverter 400b corresponds to the parallel connection Net switch KM4.
  • the DC bus voltage of the first inverter 300a will definitely drop.
  • the DC bus voltage drops it indicates that the inverter has a short-circuit fault.
  • the DC bus voltage drops rapidly it can also be determined that the inverter has a short-circuit fault by the fact that the drop rate of the DC bus voltage is greater than the preset drop rate.
  • the DC bus voltage is less than the preset voltage threshold, it indicates that the corresponding inverter is a faulty inverter, and the inverter needs to be isolated, that is, disconnect the grid-connected switch of the faulty inverter.
  • the grid-connected switch is integrated in the Inside the inverter, so as to avoid the faulty inverter affecting other inverters and equipment on the AC grid side, such as the transformer T1.
  • the grid connection switches corresponding to the second inverter 400a, the third inverter 300b and the fourth inverter 400b may be turned off or not.
  • a feasible implementation manner is that, after blocking the wave, the controller is also used to disconnect the grid-connected switch corresponding to the inverter connected in series with the faulty inverter. That is, when a short-circuit fault occurs in the first inverter 300a, in addition to turning off KM1, the grid connection switch KM2 of the second inverter 400a connected in series with the first inverter 300a is also turned off.
  • the implementation form of the grid-connected switch is not limited in the embodiments of the present application, for example, it may be a relay.
  • the relay can be integrated inside the cabinet of the inverter.
  • the non-faulty inverter can be controlled to operate and work normally.
  • the photovoltaic system starts generating electricity and is connected to the grid. That is, the controller is also used to control the power devices of the non-faulty inverters to perform switching operations after the grid-connected switch corresponding to the faulty inverter is turned off.
  • the power devices of the non-faulty second inverter 400a, the third inverter 300b and the fourth inverter 400b are controlled to perform switching operations, that is, the non-faulty second inverter
  • the inverter 400a, the third inverter 300b and the fourth inverter 400b all release the wave blocking.
  • the embodiments of the present application further provide a protection method for the bipolar photovoltaic system.
  • FIG. 8 is a flowchart of a method for protecting a photovoltaic system according to an embodiment of the present application.
  • the protection method for a bipolar photovoltaic system is applied to a bipolar photovoltaic system.
  • the bipolar photovoltaic system includes: a controller and two sets of inverters; the two sets of inverters include: a positive pole inverter An inverter group and a negative inverter group; the positive inverter group includes the following at least two inverters: a first inverter and a third inverter, and the negative inverter group includes the following at least two inverters Inverters: a second inverter and a fourth inverter; the AC output ends of the first inverter and the third inverter are connected in parallel, and the first inverter and the third inverter are connected in parallel.
  • the DC input terminals of the two inverters are connected in series; the AC output terminals of the second inverter and the fourth inverter are connected in parallel; the DC input terminals of the third inverter and the fourth inverter are connected in parallel.
  • the inputs are connected in series.
  • the method includes:
  • S801 Obtain a circulating current between at least two inverters whose AC output ends are connected in parallel.
  • the method is to obtain the common mode output current of the inverter, and use the common mode output current to characterize the circulating current of the inverter.
  • the common mode output current of each inverter is obtained in the same manner, that is, the three-phase output current of each inverter is obtained, and the average value of the obtained three-phase output current becomes the common mode output current of the inverter.
  • the common mode output current of the corresponding inverter is obtained according to the three-phase output current, and the common mode output current is used as the circulating current of the inverter.
  • the circulating current is greater than the preset current threshold or the rising rate of the circulating current is greater than the preset rate, control all inverters connected in parallel with the corresponding AC output terminals to block the wave, where the blocking means that all the power devices of the inverter stop switching action.
  • the circulating current is greater than the preset current threshold, it means that the inverter has a short-circuit fault, and the driving pulse signal of its power device needs to be blocked, that is, wave blocking.
  • An implementation manner is that the driving pulse signals output by the controller are all low level, that is, the corresponding power device is turned off.
  • the specific type of the power device is not limited in the embodiments of the present application, for example, it may be any of the following: Insulated Gate Bipolar Transistor (IGBT, Insulated Gate Bipolar Transistor), silicon carbide SiC tube and gallium nitride GaN tube may be IGBT .
  • the drive pulse signal output by the general controller is sent to the control terminal of the power device.
  • the driving pulse signal can be generated by a complex programmable logic device (CPLD, Complex Programmable Logic Device).
  • the above embodiment describes the timely closure of the wave when the short-circuit fault causes a large circulating current, but the photovoltaic system needs to continue to operate normally. Therefore, it is necessary to isolate the fault, and then allow the normal inverter to work after isolation. Restore the non-faulty inverter to work, remove the wave blocking of the non-faulty inverter, that is, the power devices in the non-faulty inverter resume the switching action.
  • this figure is a flow chart of yet another method for protecting a photovoltaic system according to an embodiment of the present application.
  • S901 Obtain a circulating current between at least two inverters whose AC output ends are connected in parallel.
  • the circulating current is greater than the preset current threshold or the rising rate of the circulating current is greater than the preset rate, control all inverters connected in parallel with the corresponding AC output terminals to block the wave, where the blocking means that all the power devices of the inverter stop switching action.
  • S901 and S902 are respectively the same as S801 and S802 in FIG. 8 , and will not be repeated here.
  • S903 Disconnect the grid-connected switch corresponding to the faulty inverter whose DC bus voltage is less than the preset voltage threshold, where the grid-connected switch is connected in series between the AC output end of the corresponding inverter and the grid.
  • the grid-connected switch is integrated inside the casing of the corresponding inverter.
  • a grid-connected switch is set at the output end of each phase of the inverter.
  • the grid-connected switch corresponding to a three-phase inverter includes three switches. , respectively, in series with the output terminals of each phase.
  • S903 has a sequential relationship with S902, and S903 needs to be executed after S902.
  • a feasible implementation manner is that, after blocking the wave, the controller is also used to disconnect the grid-connected switch corresponding to the inverter connected in series with the faulty inverter.
  • FIG. 10 is a flowchart of another method for protecting a bipolar photovoltaic system provided by an embodiment of the present application.
  • S1002 The circulating current is greater than the preset current threshold, and all the inverters connected in parallel with the corresponding AC output terminals are controlled to block the wave, wherein the blocking means that all the power devices of the inverter stop switching.
  • S1001 and S1002 are respectively the same as S801 and S802 in FIG. 8 , and will not be repeated here.
  • the method further includes:
  • S1003 Disconnect the grid-connected switch corresponding to the faulty inverter whose DC bus voltage is less than a preset voltage threshold, and disconnect the grid-connected switch corresponding to the inverter connected in series with the faulty inverter.
  • the grid-connected switch is connected in series between the AC output end of the corresponding inverter and the grid.
  • S1003 has a sequential relationship with S1002, and S1003 needs to be executed after S1002.
  • the non-faulty inverter can be controlled to operate and work normally.
  • the photovoltaic system starts generating electricity and is connected to the grid. That is, the controller is also used to control the power devices of the non-faulty inverters to perform switching operations after the grid-connected switch corresponding to the faulty inverter is turned off.
  • FIG. 11 is a flowchart of still another method for protecting a photovoltaic system provided by an embodiment of the present application.
  • the circulating current is greater than the preset current threshold, and all the inverters connected in parallel with the corresponding AC output terminals are controlled to block the wave, wherein the blocking of the wave means that all the power devices of the inverter stop switching;
  • S1103 Disconnect the grid-connected switch corresponding to the faulty inverter whose DC bus voltage is less than the preset voltage threshold, and disconnect the grid-connected switch corresponding to the inverter connected in series with the faulty inverter.
  • S1101-S1103 are respectively the same as S1001-S1003, and are not repeated here.
  • the method further includes: controlling the power device of the non-faulty inverter to resume the switching action, that is, to release the wave blocking of the non-faulty inverter.
  • S1104 and S1103 have a sequence, and S1104 needs to be executed after S1103.
  • the protection method for a bipolar photovoltaic system when a short-circuit fault occurs on the DC bus of the inverter, the short-circuit fault can be judged in time, and wave-blocking measures can be taken to avoid further expansion of the fault. components are damaged.
  • the faulty inverter can also be accurately isolated, that is, the DC bus voltage of the inverter with a short-circuit fault is low, and the inverter whose DC bus voltage is less than the preset voltage threshold can be isolated to make it separate from the bipolar photovoltaics.
  • the system is disconnected, and then the non-faulty inverter is contacted to block the wave, and starts to run for photovoltaic power generation.
  • the protection method provided by the embodiment of the present application according to the strict action sequence, can ensure that the faulty equipment is accurately isolated in the event of a short-circuit fault, and the normal operation of the non-faulty equipment is ensured.
  • the photovoltaic system provided in the above embodiment is introduced by taking a bipolar photovoltaic system as an example.
  • the following describes a common inverter system, without limiting the specific application scenario of the inverter system. It can be a photovoltaic system or other power sources. Fields where DC needs to be converted to AC.
  • FIG. 12 this figure is a schematic diagram of an inverter system provided by an embodiment of the present application.
  • the inverter system provided in this embodiment includes: a controller 1203 and at least two inverters.
  • the input ends of the at least two inverters are respectively used to connect to the corresponding photovoltaic arrays.
  • the AC output terminals of at least two inverters are connected in parallel.
  • this embodiment is described by taking the following at least two inverters as an example: a first inverter 1201 and a second inverter 1202 . As shown in FIG. 12 , the AC output terminal of the first inverter 1201 and the AC output terminal of the second inverter 1202 are connected in parallel.
  • the controller 1203 is specifically used to obtain the circulating current between at least two inverters with AC output terminals connected in parallel, and the circulating current is greater than the preset current threshold or the rising rate of the circulating current is greater than the preset rate, and controls the corresponding AC output terminals to be connected in parallel. All inverters together are blocked, where blocking means that all power devices of the inverter stop switching.
  • the controller 1202 will block both the first inverter 1201 and the second inverter 1202, because the first inverter 1201 and the second inverter 1202 are blocked.
  • the AC output terminals of an inverter 1201 and a second inverter 1203 are connected in parallel.
  • the controller 1203 after the wave is blocked, is also used to disconnect the grid-connected switch corresponding to the faulty inverter whose DC bus voltage is less than the preset voltage threshold, and the grid-connected switch is connected in series between the AC output end of the corresponding inverter and the power grid. between.
  • the controller 1203 is further configured to disconnect the grid-connected switch corresponding to the inverter connected in series with the faulty inverter.
  • the controller 1203 is further configured to control the power devices of the non-faulty inverter to resume the switching action after the grid-connected switch corresponding to the faulty inverter is turned off. For example, if the second inverter 1202 is not faulty, it is sufficient to control the second inverter 1202 to resume operation.
  • the controller 1203 is further configured to obtain the common-mode output current according to the three-phase output current of the corresponding inverter, and control the inverter when the common-mode output current is greater than a preset current threshold or the common-mode output current rising rate is greater than a preset rate The wave is blocked, and the inverter connected in parallel with the parallel output end of the inverter is controlled to block the wave.
  • the common-mode output current is used to represent the circulating current between the inverters, and the controller can judge whether a short-circuit fault has occurred through the common-mode output current, so as to block the inverters.
  • the inverters connected in parallel at the AC output terminals will affect each other, for example, when one of the inverters has a short-circuit fault, a circulating current will appear between the paralleled inverters. If the circulating current is too large, the power components of the inverter will be damaged, and it will cause excessive power consumption. In severe cases, the protection shutdown will be triggered.
  • the inverter is protected in time, and the further influence caused by the short-circuit fault is minimized.
  • At least one (item) refers to one or more, and "a plurality” refers to two or more.
  • “And/or” is used to describe the relationship between related objects, indicating that there can be three kinds of relationships, for example, “A and/or B” can mean: only A, only B, and both A and B exist , where A and B can be singular or plural.
  • the character “/” generally indicates that the associated objects are an “or” relationship.
  • At least one item(s) below” or similar expressions thereof refer to any combination of these items, including any combination of single item(s) or plural items(s).
  • At least one (a) of a, b or c can mean: a, b, c, "a and b", “a and c", “b and c", or "a and b and c" ", where a, b, c can be single or multiple.

Abstract

本申请提供一种光伏系统、保护方法及逆变系统，系统包括：控制器和两组逆变器；两组逆变器包括正极逆变器组和负极逆变器组；正极逆变器组包括至少两个逆变器：第一逆变器和第三逆变器，负极逆变器组包括至少两个逆变器：第二逆变器和第四逆变器；第一逆变器和第三逆变器的交流输出端并联，第一逆变器和第二逆变器的直流输入端串联；第二逆变器和第四逆变器的交流输出端并联；第三逆变器和第四逆变器的直流输入端串联；控制器获得交流输出端并联的至少两个逆变器之间的环流，环流大于预设电流阈值或环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波。该方案可以准确判断直流母线短路故障，并封波避免故障扩大。

Description

一种光伏系统、保护方法及逆变系统 技术领域
本申请涉及光伏发电技术领域，尤其涉及一种光伏系统、保护方法及逆变系统。
背景技术
目前，光伏发电越来越受重视，而且电压等级越来越高。典型的光伏发电是光伏阵列输出的直流电，经过逆变器转换为交流电后进行并网，或者提供给负载。
为了提高逆变器的功率容量，常用的实现方式是将多个逆变器的交流输出端并联在一起，进而获得更大的功率。但是，在多个逆变器并联后，如果一台逆变器发生直流母线电容短路故障，则会导致非故障逆变器的直流母线电压升高，严重时会因为直流母线过压而导致逆变器的元器件损坏，导致故障扩大。
发明内容
本申请提供了一种光伏系统、保护方法及逆变系统，能够在并联的逆变器发生短路故障时，及时对其以及并联的逆变器进行保护，防止故障范围扩大。
本申请实施例提供一种光伏系统包括：控制器和两组逆变器；两组逆变器包括：极逆变器组和负极逆变器组；正极逆变器组包括以下至少两个逆变器：第一逆变器和第三逆变器，负极逆变器组包括以下至少两个逆变器：第二逆变器和第四逆变器；第一逆变器和第三逆变器的交流输出端并联在一起，第一逆变器和第二逆变器的直流输入端串联；第二逆变器和第四逆变器的交流输出端并联在一起；第三逆变器和第四逆变器的直流输入端串联；控制器获得交流输出端并联在一起的至少两个逆变器之间的环流，环流大于预设电流阈值或环流的上升速率大于预设速率，如果交流侧并联在一起的逆变器之间出现较大的环流，则说明有逆变器发生短路故障，此时为了保护逆变器以及光伏系统的运行安全，需要控制对应的交流输出端并联在一起的所有逆变器均封波，即控制与故障逆变器并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作，一般情况下封波可以控制全部功率器件均关断。本申请实施例提供方式尤其适用于出现故障的逆变器还存在直流侧串联在一起的逆变器，更容易形成环流，这样短路故障影响范围大，不进行及时的控制，将导致整个系统出现故障。
本申请实施例为了解决短路故障时，对逆变器进行及时保护，尽量减少短路故障带来的进一步影响。即在其中至少一台逆变器发生短路故障时，环流会从并联的逆变器的交流输出端经过滤波电容形成的通路回流到直流输入端，进而影响到串联的逆变器。为了保证光伏系统中每台逆变器的安全，只要并联的逆变器的环流大于预设电流阈值，则对该逆变器封波，从而保护该逆变器以及可能波及的其他逆变器，从而避免短路故障引起更大的安全隐患。本申请实施例提供的系统和方法不需要新增加任何硬件，便可以实现全面的短路故障的保护。
在一种可能的实现方式中，控制器，在封波之后，还用于断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，并网开关串联在对应的逆变器的交流输出端与电网之间。以上是以直流母线电压小于预设电压阈值来判断故障逆变器，另一方面，也可以在直流母线电压跌落迅速时，即通过直流母线电压的下降速率大于预设下降速率，也可以 判断出该逆变器发生短路故障，即为故障逆变器。为了系统的安全性，需要将故障逆变器从系统中隔离，因此，需要断开故障逆变器对应的并网开关。
在一种可能的实现方式中，为了进一步保障系统的安全性，避免故障范围波及更大，控制器还用于在封波之后断开与故障逆变器串联的逆变器对应的并网开关。即对于故障逆变器存在串联的逆变器时，则需要将故障逆变器串联的逆变器也进行隔离，即从系统中剔除，不参与系统的故障，也断开其并网开关。
在一种可能的实现方式中，在故障逆变器隔离之后，即在故障逆变器对应的并网开关断开之后，控制器控制非故障逆变器的功率器件恢复开关动作，即解除封波，非故障逆变器开始按照驱动信号进行开关动作，将直流电变换为交流电。
在一种可能的实现方式中，可以每个逆变器对应一个控制器，即控制器可以为多个，逆变器和控制器一一对应，控制器完成自身对应逆变器的控制器。控制器可以与逆变器集成在一起，例如集成在逆变器的机柜中。本申请实施例不限定控制器的数量，也可以所有逆变器共用一个控制器，各个逆变器可以和控制器通信即可。
在一种可能的实现方式中，当每个逆变对应一个控制器时，每个控制器还用于根据对应逆变器的三相输出电流获得共模输出电流，共模输出电流大于预设电流阈值或共模输出电流上升速率大于预设速率时，控制该逆变器封波，且控制与该逆变器的并联输出端并联在一起的逆变器封波。本实施例中以共模输出电流来表征逆变器之间的环流。
基于以上实施例提供的一种光伏系统，本申请实施例还提供一种光伏系统的保护方法，双极性光伏系统包括：控制器和两组逆变器；两组逆变器包括：正极逆变器组和负极逆变器组；正极逆变器组包括以下至少两个逆变器：第一逆变器和第三逆变器，负极逆变器组包括以下至少两个逆变器：第二逆变器和第四逆变器；第一逆变器和第三逆变器的交流输出端并联在一起，第一逆变器和第二逆变器的直流输入端串联；第二逆变器和第四逆变器的交流输出端并联在一起；第三逆变器和第四逆变器的直流输入端串联；
该方法包括：获得交流输出端并联在一起的至少两个逆变器之间的环流；环流大于预设电流阈值或环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
在一种可能的实现方式中，在控制对应的交流输出端并联在一起的所有逆变器均封波之后，还包括：断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，并网开关串联在对应的逆变器的交流输出端与电网之间。
在一种可能的实现方式中，控制器，在控制对应的交流输出端并联在一起的所有逆变器均封波之后，还包括：断开与故障逆变器串联的逆变器对应的并网开关。
在一种可能的实现方式中，在故障逆变器对应的并网开关断开之后，还包括：控制非故障逆变器的功率器件恢复开关动作。
在一种可能的实现方式中，获得交流输出端并联在一起的至少两个逆变器之间的环流，具体包括：获得交流输出端并联在一起的每个逆变器的三相输出电流；根据三相输出电流获得对应逆变器的共模输出电流，将共模输出电流作为该逆变器的环流。
以上光伏系统各个优点同样适用于本实施例提供的方法，在此不再赘述。
以上是以光伏系统包括多台交流输出端并联在一起的逆变器，下面介绍一种普适性逆变系统，不限定具体的应用场景，只要包括多台交流输出端并联在一起的逆变器即可。
本申请实施例提供的一种逆变系统，包括：控制器和至少两个逆变器；至少两个逆变器的输入端分别用于连接各自对应的直流电源；至少两个逆变器的交流输出端并联在一起；控制器，具体用于获得交流输出端并联在一起的至少两个逆变器之间的环流，环流大于预设电流阈值或环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
在一种可能的实现方式中，控制器，在封波之后，还用于断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，并网开关串联在对应的逆变器的交流输出端与电网之间。
在一种可能的实现方式中，在封波之后，还用于断开与故障逆变器串联的逆变器对应的并网开关。
在一种可能的实现方式中，控制器，在故障逆变器对应的并网开关断开之后，还用于控制非故障逆变器的功率器件恢复开关动作。
在一种可能的实现方式中，控制器，还用于根据对应逆变器的三相输出电流获得共模输出电流，共模输出电流大于预设电流阈值或共模输出电流上升速率大于预设速率时，控制该逆变器封波，且控制与该逆变器的并联输出端并联在一起的逆变器封波。
以上光伏系统各个实施例对应的优点，同样适用于逆变系统，在此不再赘述。
从以上技术方案可以看出，本申请实施例具有以下优点：
本申请实施例提供的技术方案，判断逆变器的直流母线发生短路故障及时采取保护。直流母线短路故障包括整个直流母线短路故障，即逆变器输入端的两个串联的电容均短路故障；也包括半直流母线对地故障，即逆变器输入端的一个电容发生短路故障。由于交流输出端并联在一起的逆变器会互相影响，例如其中一台逆变器的直流母线发生短路故障时，并联的逆变器之间会出现环流。环流太大会对逆变器的功率器件产生损坏，而且引起过大的功耗，严重时会触发保护关机。本申请实施例为了解决短路故障时，对逆变器进行及时保护，尽量减少短路故障带来的进一步影响。即在其中至少一台逆变器发生短路故障时，环流会从并联的逆变器的交流输出端经过滤波电容形成的通路回流到直流输入端，进而影响到串联的逆变器。为了保证光伏系统中每台逆变器的安全，只要并联的逆变器的环流大于预设电流阈值，则对该逆变器封波，从而保护该逆变器以及可能波及的其他逆变器，从而避免短路故障引起更大的安全隐患。本申请实施例提供的系统和方法不需要新增加任何硬件，便可以实现全面的短路故障的保护。
附图说明
图1为本申请实施例提供的一种光伏系统的示意图；
图2为一种单极性光伏系统的示意图；
图3为本申请实施例提供的又一种光伏系统的示意图；
图4为本申请实施例提供的另一种光伏系统的示意图；
图5为本申请实施例提供的再一种光伏系统的示意图；
图6为本申请实施例提供的又一种光伏系统的示意图；
图7为本申请实施例提供的另一种光伏系统的示意图；
图8为本申请实施例提供的一种光伏系统的保护方法的流程图；
图9为本申请实施例提供的又一种光伏系统的保护方法的流程图；
图10为本申请实施例提供的另一种光伏系统的保护方法的流程图；
图11为本申请实施例提供的再一种光伏系统的保护方法的流程图；
图12为本申请实施例提供的一种逆变系统的示意图。
具体实施方式
以下说明中的“第一”、“第二”等用词仅用于描述目的，而不能理解为指示或暗示相对重要性或者隐含指明所指示的技术特征的数量。由此，限定有“第一”、“第二”等的特征可以明示或者隐含地包括一个或者更多该特征。在本申请的描述中，除非另有说明，“多个”的含义是两个或两个以上。
此外，本申请中，“上”、“下”等方位术语可以包括但不限于相对附图中的部件示意置放的方位来定义的，应当理解到，这些方向性术语可以是相对的概念，它们用于相对于的描述和澄清，其可以根据附图中部件附图所放置的方位的变化而相应地发生变化。
在本申请中，除非另有明确的规定和限定，术语“连接”应做广义理解，例如，“连接”可以是固定连接，也可以是可拆卸连接，或成一体；可以是直接相连，也可以通过中间媒介间接相连。此外，术语“耦接”可以是实现信号传输的电性连接的方式。“耦接”可以是直接的电性连接，也可以通过中间媒介间接电性连接。
系统实施例
为了使本领域技术人员更好地理解本申请实施例提供的技术方案，下面介绍本申请实施例提供的一种光伏系统。
参见图1，该图为本申请实施例提供的一种光伏系统的示意图。
本实施例中仅是示意以双极性光伏系统为例进行介绍，不限定光伏系统的具体实现形式。
本申请实施例提供的双极性光伏系统，与传统的单极性光伏系统的区别是，双极性光伏系统包括三条母线，分别为：直流正母线BUS+、中性母线M和直流负母线BUS-。
例如，BUS+的电压为+1500V，BUS-的电压为-1500V，则该双极性光伏系统的电压等级为正负1500V。但是BUS+和BUS-串联后的电压为3000V。因此，本申请实施例提供的双极性光伏系统可以适用1500V的安规即可，从而降低对于功率变换器以及逆变器中功率管的耐压要求。
功率变换器200的输入端用于连接光伏阵列100，功率变换器200的第一输出端连接直流正母线BUS+的第一端，功率变换器200的第二输出端连接中性母线M的第一端，功率变换器200的第三输出端连接直流负母线BUS-的第一端。
而且该双极性光伏系统至少包括两个逆变器：第一逆变器300和第二逆变器400。
第一逆变器300的第一输入端连接直流正母线BUS+的第二端，第一逆变器300的第二输入端连接所述中性母线M的第二端；
第二逆变器400的第一输入端连接中性母线M的第二端，第二逆变器400的第二输入端连接直流负母线BUS-的第二端。
其中，中性母线M也可以不存在，即不是明线存在，只要保证功率变换器200的中性点和逆变器侧的中性点的电位在预设电压范围内即可，例如对于以上介绍的3000V的光伏系统，预设电压范围可以为100V。本申请实施例中仅是以M为明线存在为例进行介绍。
在BUS+与M之间，或者在BUS-与M之间可以挂接负载或者储能电池，如图1所示，在BUS+和M之间挂接有储能电池BAT1，在BUS-和M之间挂接有储能电池BAT2，在BUS+和M之间挂接有负载1，在BUS-和M之间挂接有负载2。
为了使本领域技术人员更好地理解本申请实施例提供的双极性光伏系统的优点，参见图2，该图为传统的单极光伏系统的示意图。
功率变换器200包括两个输出端，功率变换器200的第一输出端连接直流正母线BUS+，功率变换器200的第二输出端连接直流负母线BUS-，同理，逆变器1000包括两个输入端，其中逆变器1000的第一输入端连接BUS+，逆变器1000的第二输入端连接BUS-。功率变换器200的输入端连接光伏阵列100。
对比图1和图2可以发现，图2所示的单极光伏系统中，包括两条直流母线，分别为BUS+和BUS-。如果直流母线总电压继续为3000V，则逆变器1000的输入端连接的电压等级为3000V，则逆变器1000内部的功率管的耐压要比图1所示的单个逆变器中的功率管的耐压要高一倍。因此，图1所示的双极性光伏系统可以降低功率器件所承受的压降，利于器件选型。
因为实际工作时，功率变换器与后级逆变器的距离可能较远，因此，在直流母线对应的电力线缆上的损耗比较大，因此，为了提高发电效率，需要尽量降低该损耗。图1对应的直流母线总电压为3000V，电压越高，则对应的电流越小，进而可以降低在直流母线上的损耗。
实际工作中，对于双极性光伏系统，可以包括多组双极性逆变器，例如M组双极性逆变器，M为大于等于2的整数，每组包括2台逆变器，一台正极逆变器，一台负极逆变器，M组双极性逆变器包括M*2台逆变器，例如4台、6台、8台等。本申请实施例不具体限定M的具体取值，可以根据实际的功率需要，来设置M的数值。下面以M为2，即2组双极性逆变器为例进行介绍，即对应4台逆变器，包括2台正极逆变器，2台负极逆变器。双极性光伏系统包括正极逆变器组和负极逆变器组，正极逆变器组中的所有逆变器的交流输出端并联在一起，负极逆变器组中的所有逆变器的交流输出端并联在一起。
由于交流输出端并联在一起的逆变器会互相影响，例如其中一台逆变器发生短路故障时，并联的逆变器之间会出现环流。环流太大会对逆变器的功率器件产生损坏，而且引起过大的功耗，严重时会触发保护关机。本申请实施例为了解决短路故障时，对逆变器进行及时保护，尽量减少短路故障带来的进一步影响。
以上的图1和图2均是以光伏系统包括功率变换器为例进行的介绍，另外，还有一种实现情况为光伏系统不包括功率变换器，即光伏阵列可以直接连接逆变器，也在本申请实施例介绍的范围内，本申请实施例中的图1和图2仅是示意性说明。
下面以两组双极性逆变器为例进行介绍。
参见图3，该图为本申请实施例提供的又一种光伏系统的示意图。
本申请实施例提供的双极性光伏系统包括：控制器和两组逆变器；
两组逆变器包括：正极逆变器组和负极逆变器组；
正极逆变器组包括以下至少两个逆变器：第一逆变器300a和第三逆变器300b，负极逆变器组包括以下至少两个逆变器：第二逆变器400a和第四逆变器400b；第一逆变器300a和第三逆变器300b的交流输出端并联在一起，第一逆变器300a和第二逆变器400a的直流输入端串联，如图3所示，具体为第一逆变器300a的直流负输入端连接第二逆变器400a的直流正输入端；所述第二逆变器和所述第四逆变器的交流输出端并联在一起；所述第三逆变器和所述第四逆变器的直流输入端串联；
第一逆变器300a、第二逆变器400a、第三逆变器300b和第四逆变器400b各自连接自身对应的直流电源DC。直流电源DC可以分别对应光伏阵列。光伏阵列可以包括多个并联在一起的光伏组串。
控制器(图中未示出)，具体用于获得交流输出端并联在一起的至少两个逆变器之间的环流，环流大于预设电流阈值或所述环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。一种可能的实现方式是，将全部功率器件均关断。此处的预设速率为预设上升速率。
应该理解，具体实施时，对于逆变器封波的判据可以包括两种，第一种为环流较大，即环流大于预设电流阈值。第二种是环流上升较快，即环流的上升速率大于预设速率，采取以上两种中的任意一种均可。
本申请实施例提供的技术方案适用于，逆变器的输入端连接的直流母线电容短路故障，以第一逆变器300a为例进行介绍，如图3所示，第一逆变器300a的输入端连接有串联的两个电容，第一电容C和第二电容C2，第一电容C1的第一端连接第一逆变器300a的直流正输入端，第一电容C1的第二端连接第二电容C2的第一端，第二电容C2的第二端连接第一逆变器300a的直流负输入端。直流母线电容短路故障可以包括C1和C2均短路故障，也包括其中一个电容短路故障，即C1短路故障或C2短路故障。由于第一逆变器300a的直流母线电压为C1和C2上的电压，因此，C1和/或C2短路故障时，将导致第一逆变器300a的直流母线短路故障。其他逆变器与此类似，在此不一一介绍。
环流大于预设电流阈值的另一种表现形式，也可以为检测环流的上升速率，当环流的上升速率大于预设速率时，认为逆变器出现短路故障。
本实施例中，光伏系统可以包括多个子阵，对于子阵的每个逆变器，都采集本地自身的共模输出电流作为环流，当环流大于预设电流阈值时，就进行封波操作。
对于输出端并联在一起的逆变器，均需要监测其环流，只要有一台逆变器的环流大于预设电流阈值，则需要控制与该逆变器并联的所有逆变器均封波。如图3所示，当第一逆变器300a与并联的第三逆变器300b之间的环流大于预设电流阈值时，需要对第一逆变器300a和第三逆变器300b均封波，无论该环流是从第一逆变器300a流向第三逆变器300b，还是从第三逆变器300b流向第一逆变器300a。
此处的控制器为一个统称，实际应用中，控制器可以为多个，即逆变器和控制器一一对应。控制器的实现形式本申请实施例也不做具体限定，例如可以为单片机、微处理器、数字信号处理器或逻辑控制电路等。另外，也可以多个逆变器共用一个控制器，本申请实施例中不做限定。
当一台逆变器对应一个控制器时，每个控制器，还用于根据对应逆变器的三相输出电流获得共模输出电流，共模输出电流大于预设电流阈值时，控制该逆变器封波，且控制与该逆变器的并联输出端并联在一起的逆变器也封波。
实际应用中，可以利用每个逆变器的共模输出电流来表征该逆变器与并联的逆变器之间的环流，下面介绍一种利用三相输出电流获得共模输出电流的具体实现方式。
需要说明的是，逆变器的三相输出电流可以通过电流检测电路来获得，例如电流传感器。电流传感器获得三相输出电流后发送给逆变器对应的控制器。每台逆变器对应的电流检测电路实时检测自身的三相输出电流i a、i b和i c，控制器按照下式计算共模输出电流i cir。
Figure PCTCN2020136339-appb-000001
控制器将该共模输出电流与预设电流阈值进行比较，当共模输出电流大于预设电流阈值时，说明该逆变器与并联的逆变器之间出现较大的环流，需要采取保护措施。因此，控制器需要对该逆变器进行封波，同理，与该逆变器并联的逆变器的控制器也会判断出现较大的环流，对对应的逆变器也进行封波。
下面结合附图介绍一种可能的故障引起的环流路径。图3中的L1为每台逆变器的交流输出端与变压器T1之间串联的滤波电感，具体地，L1的第一端连接逆变器的交流输出端，L1的第二端连接T1的原边绕组。Cflt为每台逆变器的交流输出端连接的滤波电容。具体地，Cflt的第一端连接L1的第二端，Cflt的第二端连接逆变器的直流输入端，一种方式是，逆变器的直流正输入端和直流负输入端之间连接串联的两个母线电容，Cflt的第二端连接两个母线电容的公共点。
例如，第一逆变器300a的直流母线发生短路故障，第三逆变器300b的交流输出端的电流会流向第一逆变器300a的直流输入端，第一逆变器300a的直流输入端的电流会流向第二逆变器400a的直流输入端，第二逆变器400a的交流输出端会流向第四逆变器400b的交流输出端，从第四逆变器400b的交流输出端流向第四逆变器400b的直流输入端，从第四逆变器400b的直流输入端流向第三逆变器300b的直流输入端。
因此，从以上分析可知，虽然双极性光伏系统中第一逆变器300a的直流母线发生了短路故障，但是，因为短路故障引起的环流会流经四台逆变器，即流经了所有的逆变器，因此，结果是每台逆变器的控制器均会检测对应的逆变器的共模输出电流大于预设电流阈值，从而对所有逆变器均进行封波，即关断逆变器中全部功率器件，例如可以给全部功率器件发送低电平的驱动脉冲信号，所有功率器件不进行开关动作。
需要说明的是，在逆变器和对应的光伏阵列之间还可以包括功率变换器，例如功率变换器可以包括升压电路等，本申请实施例对于功率变换器的实现类型不做具体限定。
本申请实施例提供的双极性光伏系统，在其中一台逆变器发生短路故障时，会导致故障逆变器与并联的逆变器之间出现环流，又由于每台逆变器存在与其直流输入端串联的逆 变器，因此，环流会从并联的逆变器的交流输出端经过滤波电容Cflt形成的通路回流到直流输入端，进而影响到串联的逆变器。为了保证双极性光伏系统中每台逆变器的安全，只要并联的逆变器的环流大于预设电流阈值，则对该逆变器封波，从而保护该逆变器以及可能波及的其他逆变器，从而避免短路故障引起更大的安全隐患。
图3中仅是是双极性光伏系统包括2组双极性逆变器为例进行的介绍，即M为2，当M为3时，即包括3组双极性逆变器，参见图4，该图为本申请实施例提供的另一种光伏系统的示意图。
图4中的正极逆变器组包括交流输出端并联在一起的以下3台逆变器：第一逆变器300a、第三逆变器300b和第五逆变器300c；同理，负极逆变器组包括交流输出端并联在一起的以下3台逆变器：第二逆变器400a、第四逆变器400b和第六逆变器400c。
其中，第一逆变器300a的直流输入端与第二逆变器400a的直流输入端串联，第三逆变器300b的直流输入端和第四逆变器400b的直流输入端串联，第五逆变器300c的直流输入端和第六逆变器400c的直流输入端串联。
同理，当第一逆变器300a的直流母线发生短路故障时，会影响与其并联的第三逆变器300b和第五逆变器300c，同时，由于直流输入端串联的原因，也会影响第二逆变器400a、第四逆变器400b和第六逆变器400c。
图3和图4中以正极逆变器组和负极逆变器组共用一个变压器T1为例进行的介绍，另外，正极逆变器组和负极逆变器组可以分别对应一个变压器。
参见图5，该图为本申请实施例提供的再一种光伏系统的示意图。
图5中以2组双极性逆变器为例，其中，正极逆变器组的交流输出端连接第一逆变器T1A的原边绕组，负极逆变器组的交流输出端连接第二逆变器T1B的原边绕组。
下面结合图5说明一台逆变器发生短路故障时可能危害其他逆变器的过程。
每个逆变器的直流正输入端和直流负输入端之间连接串联的两个电容，假设每个电容的电压是U，则逆变器的直流输入电压为2U，第一逆变器300a和第二逆变器400a的直流输入端串联，因此两个逆变器串联后对应的直流电压为4U，当其中一个电容对应的母线发生电路，即半母线短路时，第二逆变器400a的直流母线电压将被充电到与第三逆变器300b和第四逆变器400b的直流电压之和即4U一致，即最终导致第二逆变器400a的直流输入电压为4U，导致第二逆变器400a的直流输入端的电容损坏，有可能会爆炸。
本申请实施例不限定双极性光伏系统的应用场景，例如可以应用于大型光伏电站，对应的逆变器均为三相逆变器。
下面介绍双极性光伏系统应用于大型光伏电站的情景。
参见图6，该图为本申请实施例提供的又一种光伏系统的示意图。
图6对应的光伏系统可以应用于较大型的光伏电站，逆变器的功率可以比较大，每台逆变器的输入端可以连接对应的汇流箱，汇流箱中可以包括功率变换器，为了增加功率容量，每个汇流箱可以包括多个并联的功率变换器。每个功率变换器的输入端连接对应的光伏阵列PV，图6中仅是示意性了光伏阵列PV，本申请各个实施例中不具体限定光伏阵列的实现形式，例如可以包括多个光伏组串，各个光伏组串并联在一起。每个光伏组串可以 包括串联或串并联的光伏电池板。
第一逆变器300a作为正极逆变器连接对应的正极MPPT汇流箱200a，同理，作为正极逆变器的第三逆变器300b连接对应的正极最大功率点追踪(MPPT，Maximum Power Point Tracking)汇流箱200c。
第二逆变器400a作为负极逆变器连接对应的负极MPPT汇流箱200b，同理，作为负极逆变器的第四逆变器400b连接对应的负极MPPT汇流箱200d。
对于功率等级比较小的光伏系统，可以不包括汇流箱，逆变器的输入端直接连接功率变换器，功率变换器的输入端连接对应的光伏阵列。本申请实施例提供的技术方案不限定光伏系统的功率大小以及具体的拓扑结构，只要存在并联逆变器，通过并联逆变器之间的环流来监测是否发生短路故障，当发生短路故障时及时进行保护。
为了及时抑制环流，需要对所有逆变器均进行封波。
以上实施例介绍了在短路故障引起环流较大时及时封波，但是光伏系统需要继续正常运行，因此，需要将故障进行隔离，隔离之后让正常的逆变器工作，即将故障逆变器隔离，将非故障逆变器恢复工作，解除非故障逆变器的封波，即非故障逆变器的功率器件恢复开关动作。
参见图7，该图为本申请实施例提供的另一种光伏系统的示意图。
故障隔离的措施具体为：控制器在以上的封波之后，还用于断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，并网开关串联在对应的逆变器的交流输出端与电网之间。
本实施例中通过直流母线电压欠压判断出故障逆变器，一种可能的实现情况是，故障逆变器的控制器可以通知与其串联的逆变器的控制器发生了短路故障。
如图7所示，第一逆变器300a对应并网开关KM1，第二逆变器400a对应并网开关KM2，第三逆变器300b对应并网开关KM3，第四逆变器400b对应并网开关KM4。
例如，第一逆变器300a的直流母线发生短路故障，则第一逆变器300a的直流母线电压肯定会跌落，即可以通过直流母线电压与预设电压阈值进行比较来判断是否发生跌落，当直流母线电压发生跌落时，则表明该逆变器发生短路故障。另一方面，直流母线电压跌落迅速时，也可以通过直流母线电压的下降速率大于预设下降速率，则也可以判断出该逆变器发生短路故障。
只要直流母线电压小于预设电压阈值则表明对应的逆变器为故障逆变器，需要隔离该逆变器，即断开故障逆变器的并网开关，一般情况下该并网开关集成在逆变器的内部，从而避免故障逆变器影响其他逆变器以及交流电网侧的设备，例如变压器T1。
当第一逆变器300a发生短路故障时，则需要断开对应的并网开关KM1。
对于以下3台非故障逆变器第二逆变器400a、第三逆变器300b和第四逆变器400b对应的并网开关可以断开，也可以不断开。
为了更全面地对短路故障进行隔离，一种可行的实现方式是，控制器在封波之后，还用于断开与故障逆变器串联的逆变器对应的并网开关。即，第一逆变器300a发生短路故障时，除了断开KM1以外，还将与第一逆变器300a串联的第二逆变器400a的并网开关KM2 也断开。
本申请实施例中不限定并网开关的实现形式，例如可以为继电器。继电器可以集成在逆变器的机柜内部。
以上介绍的是故障时进行隔离的过程，待故障隔离之后，可以控制非故障逆变器运行，进行正常工作，例如光伏系统开始发电，并网运行。即控制器，在故障逆变器对应的并网开关断开之后，还用于控制非故障逆变器的功率器件进行开关动作。例如，第一逆变器300a故障，则控制非故障的第二逆变器400a、第三逆变器300b和第四逆变器400b的功率器件进行开关动作，即非故障的第二逆变器400a、第三逆变器300b和第四逆变器400b均解除封波。
方法实施例
基于以上实施例提供的一种双极性光伏系统，本申请实施例还提供一种双极性光伏系统的保护方法。
为了更清楚描述逆变器出现短路故障时的保护逻辑，下面结合流程图来介绍控制器执行的保护方法。
参见图8，该图为本申请实施例提供的一种光伏系统的保护方法的流程图。
本申请实施例提供的双极性光伏系统的保护方法，应用于双极性光伏系统，双极性光伏系统包括：控制器和两组逆变器；所述两组逆变器包括：正极逆变器组和负极逆变器组；所述正极逆变器组包括以下至少两个逆变器：第一逆变器和第三逆变器，所述负极逆变器组包括以下至少两个逆变器：第二逆变器和第四逆变器；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第一逆变器和所述第二逆变器的直流输入端串联；所述第二逆变器和所述第四逆变器的交流输出端并联在一起；所述第三逆变器和所述第四逆变器的直流输入端串联。
对于双极性光伏系统的结构可以参见以上系统实施例的具体描述以及附图，在此不再赘述。下面仅介绍保护逻辑。
该方法包括：
S801：获得交流输出端并联在一起的至少两个逆变器之间的环流。
并联的多个逆变器，只要有一个逆变器出现短路故障，将会影响与其并联的其他逆变器，判别的方式可以通过并联的逆变器之间的环流来判断，获得环流的一个方式是获得逆变器的共模输出电流，利用共模输出电流来表征逆变器的环流。
每个逆变器的共模输出电流的获取方式相同，即获得每个逆变器的三相输出电流，获得三相输出电流的平均值变为该逆变器的共模输出电流。
获得交流输出端并联在一起的至少两个逆变器之间的环流，具体包括：
获得交流输出端并联在一起的每个逆变器的三相输出电流；
根据所述三相输出电流获得对应逆变器的共模输出电流，将所述共模输出电流作为该逆变器的所述环流。
S802：环流大于预设电流阈值或环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
由于并联的一台逆变器出现短路故障时，会导致与其并联的其他逆变器的出现较大的环流，因此，为了保护与其并联的逆变器，需要对其并联的逆变器也封波。
环流大于预设电流阈值，说明该逆变器出现了短路故障，需要封锁其功率器件的驱动脉冲信号，即封波。一种实现方式是，控制器输出的驱动脉冲信号全部为低电平，即对应功率器件关断。本申请实施例中不限定功率器件的具体类型，例如可以为以下任意一种：绝缘栅双极型晶体管(IGBT，Insulated Gate Bipolar Transistor)，、碳化硅SiC管和氮化镓GaN管可以为IGBT。也可以为金属-氧化物半导体场效应晶体管(MOSFET，Metal-Oxide-Semiconductor Field-Effect Transistor)。一般控制器输出的驱动脉冲信号发送给功率器件的控制端。例如驱动脉冲信号可以由复杂可编程逻辑器件(CPLD，Complex Programmable Logic Device)来生成。
以上实施例介绍了在短路故障引起环流较大时及时封波，但是光伏系统需要继续正常运行，因此，需要将故障进行隔离，隔离之后让正常的逆变器工作，即将故障逆变器隔离，将非故障逆变器恢复工作，解除非故障逆变器的封波，即非故障逆变器中的功率器件恢复开关动作。
参见图9，该图为本申请实施例提供又一种光伏系统的保护方法的流程图。
S901：获得交流输出端并联在一起的至少两个逆变器之间的环流。
S902：环流大于预设电流阈值或环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
S901和S902分别与图8中的S801和S802相同，在此不再赘述。
在所述控制对应的交流输出端并联在一起的所有逆变器均封波之后，需要隔离故障逆变器，即还包括：
S903：断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，所述并网开关串联在对应的逆变器的交流输出端与电网之间。
一般情况下，并网开关集成在对应的逆变器的壳体内部，另外，逆变器的每相输出端均设置并网开关，例如三相逆变器对应的并网开关包括三个开关，分别串联在每相输出端。
S903与S902具有先后关系，S903需要在S902之后执行。
为了更全面地对短路故障进行隔离，一种可行的实现方式是，控制器在封波之后，还用于断开与故障逆变器串联的逆变器对应的并网开关。
参见图10，该图为本申请实施例提供的另一种双极性光伏系统的保护方法的流程图。
S1001：获得交流输出端并联在一起的至少两个逆变器之间的环流；
S1002：环流大于预设电流阈值，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
S1001和S1002分别与图8中的S801和S802相同，在此不再赘述。
在所述控制对应的交流输出端并联在一起的所有逆变器均封波之后，还包括：
S1003：断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，断开与所述故障逆变器串联的逆变器对应的并网开关。
并网开关串联在对应的逆变器的交流输出端与电网之间。
S1003与S1002具有先后关系，S1003需要在S1002之后执行。
以上介绍的是故障时进行隔离的过程，待故障隔离之后，可以控制非故障逆变器运行，进行正常工作，例如光伏系统开始发电，并网运行。即控制器，在故障逆变器对应的并网开关断开之后，还用于控制非故障逆变器的功率器件进行开关动作。
参见图11，该图为本申请实施例提供的再一种光伏系统的保护方法的流程图。
S1101：获得交流输出端并联在一起的至少两个逆变器之间的环流；
S1102：环流大于预设电流阈值，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作；
S1103：断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，断开与所述故障逆变器串联的逆变器对应的并网开关。
S1101-S1103分别与S1001-S1003相同，在此不再赘述。
S1104：在所述故障逆变器对应的并网开关断开之后，还包括：控制所述非故障逆变器的功率器件恢复开关动作，即解除对非故障逆变器的封波。
S1104与S1103具有先后顺序，S1104需要在S1103之后执行。
本申请实施例提供的双极性光伏系统的保护方法，在逆变器的直流母线发生短路故障时，可以及时判断出短路故障，并采取封波措施，避免故障进一步扩大，对逆变器的元器件造成损坏。另外，还可以准确隔离出故障逆变器，即发生短路故障的逆变器的直流母线电压较低，将直流母线电压小于预设电压阈值的逆变器进行隔离，使其与双极性光伏系统断开，然后将非故障逆变器接触封波，开始运行，进行光伏发电。本申请实施例提供的保护方法，按照严格的动作时序，可以保证在短路故障时，准确隔离故障设备，保证非故障设备的正常运行。
逆变系统实施例
以上实施例提供的光伏系统是以双极性光伏系统为例进行的介绍，下面介绍普通的一种逆变系统，不限定逆变系统的具体应用场景，可以为光伏系统，也可以为其他电源领域的直流需要转换为交流的场合。
参见图12，该图为本申请实施例提供的一种逆变系统的示意图。
本实施例提供的逆变系统，包括：控制器1203和至少两个逆变器。
至少两个逆变器的输入端分别用于连接各自对应的光伏阵列。
至少两个逆变器的交流输出端并联在一起。
为了方便描述，本实施例中以包括以下至少两个逆变器为例进行介绍：第一逆变器1201和第二逆变器1202。如图12所示，第一逆变器1201的交流输出端和第二逆变器1202的交流输出端并联在一起。
控制器1203，具体用于获得交流输出端并联在一起的至少两个逆变器之间的环流，环流大于预设电流阈值或环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
例如，第一逆变器1201的环流大于预设电流阈值或环流的上升速率大于预设速率，则控制器1202会将第一逆变器1201和第二逆变器1202均封波，因为第一逆变器1201和第 二逆变器1203的交流输出端并联在一起。
控制器1203，在封波之后，还用于断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，并网开关串联在对应的逆变器的交流输出端与电网之间。
在封波之后，控制器1203，还用于断开与故障逆变器串联的逆变器对应的并网开关。
控制器1203，在故障逆变器对应的并网开关断开之后，还用于控制非故障逆变器的功率器件恢复开关动作。例如，第二逆变器1202没有故障，则控制第二逆变器1202恢复工作即可。
控制器1203，还用于根据对应逆变器的三相输出电流获得共模输出电流，共模输出电流大于预设电流阈值或共模输出电流上升速率大于预设速率时，控制该逆变器封波，且控制与该逆变器的并联输出端并联在一起的逆变器封波。
本实施例中以共模输出电流来表征逆变器之间的环流，控制器可以通过共模输出电流来判断是否发生了短路故障，从而对逆变器进行封波。
由于交流输出端并联在一起的逆变器会互相影响，例如其中一台逆变器发生短路故障时，并联的逆变器之间会出现环流。环流太大会对逆变器的功率器件产生损坏，而且引起过大的功耗，严重时会触发保护关机。本申请实施例为了解决短路故障时，对逆变器进行及时保护，尽量减少短路故障带来的进一步影响。
应当理解，在本申请中，“至少一个(项)”是指一个或者多个，“多个”是指两个或两个以上。“和/或”，用于描述关联对象的关联关系，表示可以存在三种关系，例如，“A和/或B”可以表示：只存在A，只存在B以及同时存在A和B三种情况，其中A，B可以是单数或者复数。字符“/”一般表示前后关联对象是一种“或”的关系。“以下至少一项(个)”或其类似表达，是指这些项中的任意组合，包括单项(个)或复数项(个)的任意组合。例如，a，b或c中的至少一项(个)，可以表示：a，b，c，“a和b”，“a和c”，“b和c”，或“a和b和c”，其中a，b，c可以是单个，也可以是多个。
以上所述，以上实施例仅用以说明本申请的技术方案，而非对其限制；尽管参照前述实施例对本申请进行了详细的说明，本领域的普通技术人员应当理解：其依然可以对前述各实施例所记载的技术方案进行修改，或者对其中部分技术特征进行等同替换；而这些修改或者替换，并不使相应技术方案的本质脱离本申请各实施例技术方案的精神和范围。

Claims (16)

  1. 一种光伏系统，其特征在于，包括：控制器和两组逆变器；
    所述两组逆变器包括：正极逆变器组和负极逆变器组；
    所述正极逆变器组包括以下至少两个逆变器：第一逆变器和第三逆变器，所述负极逆变器组包括以下至少两个逆变器：第二逆变器和第四逆变器；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第一逆变器和所述第二逆变器的直流输入端串联；所述第二逆变器和所述第四逆变器的交流输出端并联在一起；所述第三逆变器和所述第四逆变器的直流输入端串联；
    所述控制器，具体用于获得交流输出端并联在一起的至少两个逆变器之间的环流，所述环流大于预设电流阈值或所述环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
  2. 根据权利要求1所述的系统，其特征在于，所述控制器，在封波之后，还用于断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，所述并网开关串联在对应的逆变器的交流输出端与电网之间。
  3. 根据权利要求2所述的系统，其特征在于，所述控制器，在封波之后，还用于断开与所述故障逆变器串联的逆变器对应的并网开关。
  4. 根据权利要求2或3所述的系统，其特征在于，所述控制器，在所述故障逆变器对应的并网开关断开之后，还用于控制所述非故障逆变器的功率器件恢复开关动作。
  5. 根据权利要求1-5任一项所述的系统，其特征在于，所述控制器为多个，所述逆变器和所述控制器一一对应。
  6. 根据权利要求1-4任一项所述的系统，其特征在于，每个所述控制器，还用于根据对应逆变器的三相输出电流获得共模输出电流，所述共模输出电流大于所述预设电流阈值或所述共模输出电流上升速率大于所述预设速率时，控制该逆变器封波，且控制与该逆变器的并联输出端并联在一起的逆变器封波。
  7. 一种光伏系统的保护方法，其特征在于，所述双极性光伏系统包括：控制器和两组逆变器；所述两组逆变器包括：正极逆变器组和负极逆变器组；所述正极逆变器组包括以下至少两个逆变器：第一逆变器和第三逆变器，所述负极逆变器组包括以下至少两个逆变器：第二逆变器和第四逆变器；所述第一逆变器和所述第三逆变器的交流输出端并联在一起，所述第一逆变器和所述第二逆变器的直流输入端串联；所述第二逆变器和所述第四逆变器的交流输出端并联在一起；所述第三逆变器和所述第四逆变器的直流输入端串联；
    该方法包括：
    获得交流输出端并联在一起的至少两个逆变器之间的环流；
    所述环流大于预设电流阈值或所述环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
  8. 根据权利要求7所述的方法，其特征在于，在所述控制对应的交流输出端并联在一起的所有逆变器均封波之后，还包括：
    断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，所述并网开关串 联在对应的逆变器的交流输出端与电网之间。
  9. 根据权利要求8所述的方法，其特征在于，所述控制器，在所述控制对应的交流输出端并联在一起的所有逆变器均封波之后，还包括：
    断开与所述故障逆变器串联的逆变器对应的并网开关。
  10. 根据权利要求8或9所述的方法，其特征在于，在所述故障逆变器对应的并网开关断开之后，还包括：
    控制所述非故障逆变器的功率器件恢复开关动作。
  11. 根据权利要求7-10任一项所述的方法，其特征在于，所述获得交流输出端并联在一起的至少两个逆变器之间的环流，具体包括：
    获得交流输出端并联在一起的每个逆变器的三相输出电流；
    根据所述三相输出电流获得对应逆变器的共模输出电流，将所述共模输出电流作为该逆变器的所述环流。
  12. 一种逆变系统，其特征在于，包括：控制器和至少两个逆变器；
    所述至少两个逆变器的输入端分别用于连接各自对应的直流电源；
    所述至少两个逆变器的交流输出端并联在一起；
    所述控制器，具体用于获得交流输出端并联在一起的至少两个逆变器之间的环流，所述环流大于预设电流阈值或所述环流的上升速率大于预设速率，控制对应的交流输出端并联在一起的所有逆变器均封波，其中封波是指逆变器的全部功率器件停止开关动作。
  13. 根据权利要求12所述的系统，其特征在于，所述控制器，在封波之后，还用于断开直流母线电压小于预设电压阈值的故障逆变器对应的并网开关，所述并网开关串联在对应的逆变器的交流输出端与电网之间。
  14. 根据权利要求13所述的系统，其特征在于，在封波之后，还用于断开与所述故障逆变器串联的逆变器对应的并网开关。
  15. 根据权利要求13或14所述的系统，其特征在于，所述控制器，在所述故障逆变器对应的并网开关断开之后，还用于控制所述非故障逆变器的功率器件恢复开关动作。
  16. 根据权利要求12-15任一项所述的系统，其特征在于，所述控制器，还用于根据对应逆变器的三相输出电流获得共模输出电流，所述共模输出电流大于所述预设电流阈值或所述共模输出电流上升速率大于所述预设速率时，控制该逆变器封波，且控制与该逆变器的并联输出端并联在一起的逆变器封波。
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