WO2021003728A1 - 一种应用于光伏发电系统的变换器、方法及系统 - Google Patents

一种应用于光伏发电系统的变换器、方法及系统 Download PDF

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Publication number
WO2021003728A1
WO2021003728A1 PCT/CN2019/095545 CN2019095545W WO2021003728A1 WO 2021003728 A1 WO2021003728 A1 WO 2021003728A1 CN 2019095545 W CN2019095545 W CN 2019095545W WO 2021003728 A1 WO2021003728 A1 WO 2021003728A1
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Prior art keywords
photovoltaic
converter
power
circuit
series
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PCT/CN2019/095545
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English (en)
French (fr)
Inventor
顾桂磊
姚晓锋
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华为技术有限公司
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Publication date
Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to PCT/CN2019/095545 priority Critical patent/WO2021003728A1/zh
Priority to AU2019455851A priority patent/AU2019455851A1/en
Priority to CN201980068255.2A priority patent/CN112868153B/zh
Priority to EP19936621.2A priority patent/EP3905465B1/en
Publication of WO2021003728A1 publication Critical patent/WO2021003728A1/zh
Priority to US17/382,607 priority patent/US20210351592A1/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
    • H02J3/46—Controlling of the sharing of output between the generators, converters, or transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • H02S40/38—Energy storage means, e.g. batteries, structurally associated with PV modules
    • 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
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/10—Power transmission or distribution systems management focussing at grid-level, e.g. load flow analysis, node profile computation, meshed network optimisation, active network management or spinning reserve management
    • 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
    • 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
    • Y02E70/00—Other energy conversion or management systems reducing GHG emissions
    • Y02E70/30—Systems combining energy storage with energy generation of non-fossil origin

Definitions

  • This application relates to the field of photovoltaic power generation technology, and in particular to a converter, method and system applied to a photovoltaic power generation system.
  • Photovoltaic power generation is a technology that uses the photovoltaic effect of the semiconductor interface to convert light energy into electrical energy.
  • Photovoltaic power generation systems usually include photovoltaic square arrays, inverters, AC power distribution and other equipment.
  • the photovoltaic square array usually includes a plurality of photovoltaic modules formed in a certain series and parallel manner.
  • differences in the parameters of different photovoltaic modules and differences in solar radiation conditions will cause energy loss.
  • the photovoltaic modules are installed outdoors, the partial shading, intermittent shading and aging of the photovoltaic modules will also cause energy loss, which will affect the power generation of the photovoltaic power generation system and reduce the power generation efficiency.
  • each photovoltaic module will be connected to a converter with an independent MPPT (Maximum Power Point Tracking) function to maximize the power generation efficiency of the photovoltaic power generation system.
  • MPPT Maximum Power Point Tracking
  • multiple photovoltaic modules are connected in series outside the inverter and then connected to the input end of one inverter, thereby reducing the number of inverters included in the photovoltaic power generation system, thus reducing photovoltaic power generation The cost of the system.
  • the total voltage of multiple photovoltaic modules directly connected in series is relatively high.
  • the inverter of the photovoltaic power generation system shuts down, and the output voltage of the inverter is zero, but multiple photovoltaic modules connected in series It cannot be disconnected, and there is still dangerous high voltage in the photovoltaic array formed by the series-connected photovoltaic modules, which will cause safety risks.
  • this application provides a converter, method and system applied to a photovoltaic power generation system, which can disconnect any two photovoltaic units connected in series when the photovoltaic power generation system is shut down. There is no dangerous high voltage in the photovoltaic array formed by the photovoltaic unit, thereby improving the safety of the photovoltaic power generation system.
  • this application provides a converter for a photovoltaic power generation system.
  • the converter includes: a controller and at least one switch tube; the converter supports the access of at least two photovoltaic units, and the at least two photovoltaic units are converting
  • the inside of the device is connected in series through a switch tube; the photovoltaic unit is formed by at least one photovoltaic module in series and parallel; the controller is used to control the switch tube to turn off when a shutdown command is received or the heartbeat command is lost within a preset time period. Two photovoltaic units connected in series are disconnected.
  • the open circuit voltage of each photovoltaic unit connected to the converter in this application is lower than 80V. Therefore, when the controller controls the switch tube to be turned off, it can prevent dangerous high voltages in the photovoltaic array formed by the photovoltaic units, which improves the photovoltaic power generation system. safety.
  • the controller is further configured to control the switch tube to be closed when the power-on instruction and the heartbeat instruction are received.
  • the controller When the controller receives the power-on command and the heartbeat command, it determines that the converter needs to be switched to the normal working mode at this time, and therefore controls the switch tube to close, so that the photovoltaic unit is connected in series through the switch tube inside the converter.
  • the converter further includes: a power circuit for performing power conversion, and the power circuit may be a DC-DC conversion circuit , DC-AC conversion circuit or on-off control circuit.
  • the controller is also used to determine that the switch is currently needed when a shutdown instruction is received or the heartbeat instruction is lost within a preset time period
  • the power circuit is controlled to stop power conversion, or the output voltage of the power circuit is restricted to be less than the preset voltage value, or the output current of the power circuit is restricted to be less than the preset current value.
  • the preset voltage value is usually low, for example, it may be 10V
  • the preset current value is usually also low, for example, it may be set to 10mA. Therefore, the output terminal of the converter can be free of dangerous high voltage and high current, and the safety of the photovoltaic power generation system is improved.
  • the controller is also used to determine that the converter needs to be switched to normal when it receives a power-on instruction and a heartbeat instruction.
  • the controller controls the power circuit to resume power conversion, or lifts the limitation on the output voltage of the power circuit, or lifts the limitation on the output current of the power circuit, so that the power circuit can work normally.
  • the DC-DC conversion circuit when the power circuit is a DC-DC conversion circuit, the DC-DC conversion circuit may be a boost circuit or a step-down circuit Or buck-boost circuit, the specific type of power circuit can be determined according to actual needs.
  • the converter further includes: a communication unit; the communication unit is used to receive a control signal from an upper level, and to transfer the control signal Forward to the controller.
  • the control signal includes: heartbeat command, power-on command and power-off command.
  • the communication unit can forward the control signal to the controller, so that the controller can timely determine whether the current converter is in the normal working mode or the shutdown mode according to the control signal, so that the controller can control the working state of the switch tube and the power circuit in time.
  • the converter further includes an auxiliary power supply.
  • One of the photovoltaic units is connected to an auxiliary power source to supply power to the auxiliary power source, and the auxiliary power source supplies power to the controller and the communication unit.
  • the auxiliary power supply is powered by a photovoltaic unit connected to the converter and has nothing to do with the conduction state of the switch tube inside the converter. Therefore, the auxiliary power supply can communicate with the controller when at least two photovoltaic units are not connected in series through the switch tube. Unit power supply.
  • the switch tube can be any of the following: relay, transistor, insulated gate bipolar transistor, and metal oxide semiconductor field
  • the specific type of switching tube can be determined according to actual needs.
  • this application also provides a method for controlling a converter.
  • the converter is applied to a photovoltaic power generation system.
  • the converter includes: a controller and at least one switch tube; the converter supports the access of at least two photovoltaic units, and at least Two photovoltaic units are connected in series through a switch tube inside the converter; the photovoltaic unit is formed by at least one photovoltaic module connected in series and parallel; the method includes: controlling the switch tube to turn off when a shutdown command is received or the heartbeat command is lost within a preset time period Open to disconnect any two photovoltaic units connected in series.
  • the switch tube can be controlled to disconnect when the photovoltaic power generation system performs the shutdown function to disconnect any two photovoltaic units connected in series, so that there is no dangerous high voltage on the photovoltaic array formed by the photovoltaic units, thereby ensuring the converter's Safety and safety in a certain range around the photovoltaic array enhance the safety of the entire photovoltaic power generation system.
  • the method further includes: controlling the switch tube to close when the power-on instruction is received and the heartbeat instruction is received.
  • the present application also provides a photovoltaic power generation system, which includes: at least two photovoltaic units and any of the above-mentioned inverters. Wherein, at least two photovoltaic units are connected to the converter, at least two photovoltaic units are connected in series within the converter through a switch tube, and the photovoltaic unit is formed by at least one photovoltaic module connected in series and parallel.
  • the converter includes a controller and at least one switch tube, and the open circuit voltage of each photovoltaic unit connected to the converter is lower than 80V. Therefore, when the controller controls the switch tube to open , Can prevent dangerous high voltage in the photovoltaic array formed by photovoltaic units, and improve the safety of photovoltaic power generation system.
  • the photovoltaic power generation system further includes: a power circuit.
  • the power circuit is a DC-DC conversion circuit, and there are multiple DC-DC conversion circuits, multiple DC-DC conversion circuits
  • the DC conversion circuits are connected in series to form a DC-DC conversion circuit string.
  • the DC-DC conversion circuit string is connected to the input end of the inverter; the inverter is used to convert the DC output of the DC-DC conversion circuit string into Output after alternating current.
  • the number of DC-DC conversion circuits included in the DC-DC conversion circuit string can be determined according to actual conditions. Since each converter of the photovoltaic power generation system provided in this application can still meet the requirements of rapid shutdown when the input end is connected to multiple photovoltaic units simultaneously. Therefore, the number of converters included in the photovoltaic power generation system can be reduced, thereby effectively simplifying field wiring and reducing system costs.
  • the second possible implementation there are multiple DC-DC conversion circuit strings; multiple DC-DC conversion circuit strings are connected in parallel and then connected to the inverter The input terminal of the inverter, or different input ports independently connected to the input terminal of the inverter.
  • the number of DC-DC conversion circuit strings connected to the input end of the inverter can be determined according to the actual situation. Because each converter of the photovoltaic power generation system provided by this application can still meet the requirements of rapid shutdown when the input end is connected to multiple photovoltaic units at the same time. Therefore, the number of converters included in the photovoltaic power generation system can be reduced, thereby effectively simplifying field wiring and reducing system costs.
  • the converter provided in this application supports the access of at least two photovoltaic units.
  • the photovoltaic unit is formed by connecting at least one photovoltaic module in series and parallel.
  • the converter includes a switch tube inside, and the photovoltaic unit is connected in series through a switch tube provided inside the converter.
  • the converter when the input end of the converter is connected to two photovoltaic units, the converter includes a switch tube inside, and the two photovoltaic units are connected in series through the switch tube.
  • a larger number of photovoltaic cells need to be connected in series to achieve a larger number of switching tubes. For example, when N photovoltaic cells are connected in series, N-1 switching tubes are required. The switching state of the switching tube is controlled by the controller of the converter.
  • the controller of the converter When the controller of the converter receives a shutdown command or loses the heartbeat command within a preset time period, the controller controls all switching tubes to be turned off.
  • the switch tubes inside the inverter are connected in series, so any two photovoltaic units connected in series can be disconnected, so that there is no dangerous high voltage in the photovoltaic array formed by the photovoltaic units, thereby meeting the requirements of safety regulations and improving the overall photovoltaic power generation system. safety.
  • Figure 1 is a schematic diagram of a photovoltaic power generation system provided by this application.
  • FIG. 2 is a schematic diagram of a converter used in a photovoltaic power generation system according to Embodiment 1 of the application;
  • FIG. 3 is a schematic diagram of another converter for photovoltaic power generation system provided in the second embodiment of the application.
  • FIG. 4 is a schematic diagram of yet another converter used in a photovoltaic power generation system according to Embodiment 3 of the application;
  • FIG. 5 is a schematic diagram of still another converter used in a photovoltaic power generation system according to Embodiment 3 of the application;
  • Fig. 6a is a schematic diagram of another converter used in a photovoltaic power generation system according to the fourth embodiment of the application.
  • FIG. 6b is a schematic diagram of yet another converter used in a photovoltaic power generation system according to the fourth embodiment of the application.
  • FIG. 7 is a flowchart of a method for controlling a converter according to Embodiment 5 of this application.
  • FIG. 8 is a schematic diagram of a photovoltaic power generation system provided by Embodiment 6 of the application.
  • FIG. 9 is a schematic diagram of another photovoltaic power generation system provided in Embodiment 7 of the application.
  • a plurality of photovoltaic modules are connected in series outside the converter and then connected to the input end of one converter (ie, one tow multiple), which is described in detail below with reference to the drawings.
  • FIG. 1 is a schematic diagram of a photovoltaic power generation system provided by this application.
  • multiple photovoltaic modules 101 are connected to the input end of the converter 102 after being connected in series outside the converter 102, and the multiple photovoltaic modules are connected in series to form a string, and the formed string includes two connecting ends , One of the connection ends is connected to the positive input end of the converter, and the other connection end is connected to the negative input end of the converter.
  • the positive output terminal of the photovoltaic module when connecting, is connected to the negative output terminal of the previous photovoltaic module, and the negative output terminal is connected to the positive output terminal of the next photovoltaic module.
  • the output ends of the converters can also be connected in series to form a converter string.
  • the converter string includes two connection ends, one of which is connected to the positive input of the inverter 105, and the other is connected to the negative input of the inverter 105.
  • the positive output terminal of the converter is connected to the negative output terminal of the previous converter, and the negative output terminal is connected to the positive output terminal of the next converter.
  • multiple converter strings can also be connected in parallel and then connected to the input of the inverter 105 or independently connected to different input ports of the input of the inverter 105.
  • the inverter 105 shown in the figure is connected to two converter strings. , Namely string 103 and string 104.
  • the output end of the inverter 105 is connected to the power grid 106.
  • the inverter 105 can implement a DC-AC conversion function, that is, inverting DC power into AC power and sending it to the power grid.
  • NEC National Electrical Code, National Electrotechnical Standards
  • NEC 2017-690.12(B) requires photovoltaic power generation systems to have a component-level rapid shutdown function.
  • the international authoritative photovoltaic industry standard association (SunSpec Alliance) followed the NEC 2014, NEC 2017, and UL 1741 (Photovoltaic Installation Standards) standards formulated for quick shutdown.
  • NEC is only applicable to distributed power stations on buildings.
  • the 2014 regulations require that the safe area around the photovoltaic system is 3m.
  • the 2017 specification requires that the safe area around the photovoltaic system is 1 foot (approximately equal to 30 cm), which is a module-level shutdown.
  • Specific requirements in 2017NEC Within 30 seconds after the quick-shutdown device is activated, the voltage outside the safe area drops below 30V, and the voltage inside the safe area drops below 80V, which requires component-level shutdown.
  • this application provides a converter, method and system applied to a photovoltaic power generation system.
  • the converter provided in this application is provided with a switch tube inside, and the converter supports the access of at least two photovoltaic units.
  • the units are connected in series through the switch tube inside the converter.
  • the control switch tube is turned off to disconnect any two photovoltaic units connected in series, so that the photovoltaic units form a photovoltaic array
  • There is no dangerous high voltage inside so as to meet the standard requirement of no high voltage in the safe area, which improves the safety of the photovoltaic power generation system.
  • the first embodiment of the present application provides a converter for a photovoltaic power generation system.
  • the input end of the converter can be connected to multiple photovoltaic units, and the multiple photovoltaic units form a photovoltaic array.
  • a single photovoltaic unit in the embodiment of the present application may include
  • a photovoltaic module may also include multiple photovoltaic modules formed in series and parallel. For example, multiple photovoltaic modules are connected in series to form a photovoltaic string, and multiple photovoltaic strings are connected in parallel to form a photovoltaic unit.
  • the embodiments of the present application do not specifically limit the specific number of photovoltaic modules, and those skilled in the art can set it according to actual needs, and the electrical parameters of a single photovoltaic module are not specifically limited in the embodiments of the present application.
  • the converter provided by the embodiment of the present application includes: a power circuit, a controller, and at least one switch tube.
  • the input end of the converter has multiple input ports, each input port includes a positive input terminal and a negative input terminal, and the photovoltaic unit is connected to the converter through the input port of the converter.
  • the converter supports the access of at least two photovoltaic units, and at least two photovoltaic units are connected in series within the converter through a switch tube.
  • Each photovoltaic unit may include only one photovoltaic module, or may be formed by multiple photovoltaic modules in series and parallel.
  • the embodiment of the present application does not limit the number of switch tubes inside the converter.
  • the number of switch tubes inside the converter can be N-1, and the input terminal of the corresponding converter can be connected to N photovoltaic units.
  • N photovoltaic units it is also possible to connect a number of photovoltaic units less than N. In this case, short-circuit the positive input terminal and the negative input terminal corresponding to the input port that is not connected to the photovoltaic unit.
  • the controller When the controller receives a shutdown command or loses a heartbeat command within a preset time period, it controls all the switch tubes to be disconnected to disconnect any two photovoltaic modules connected in series.
  • the preset time period can be set according to actual requirements, which is not specifically limited in this application.
  • the shutdown instruction is issued by the upper level of the controller, and the heartbeat instruction is also issued by the upper level of the controller.
  • the shutdown command refers to directly shut down and stop working.
  • the heartbeat command is to send the heartbeat command during normal work. If the heartbeat command is not received within the preset time, it means a fault has occurred.
  • the preset time can be set according to needs, and is not specifically limited in the embodiment of the present application.
  • the input terminal of the converter includes at least the following two photovoltaic units: the first photovoltaic unit and the second photovoltaic unit, and each photovoltaic unit includes one photovoltaic module as an example for description, that is, the input terminal of the converter It includes at least the following two photovoltaic modules: a first photovoltaic module and a second photovoltaic module, where "first" and “second” are only used to distinguish two photovoltaic units and photovoltaic modules for convenience of description, and do not constitute a limitation on the application . It can be understood that when the input end of the converter includes a larger number of photovoltaic units and each photovoltaic unit includes a plurality of photovoltaic components, the working principle of the converter is similar, and it is not described in full herein.
  • FIG. 2 is a schematic diagram of a converter used in a photovoltaic power generation system according to Embodiment 1 of the application.
  • the converter 200 includes: a power circuit 201, a controller 202, and a switch tube 203.
  • two photovoltaic modules are connected at the input end of the converter: the first photovoltaic module 204 and the second photovoltaic module 205 as an example for description.
  • one switch tube in the converter is used to realize the series connection. It is understandable that when multiple photovoltaic modules are connected to the input end of the converter, multiple switch tubes in the converter are needed to realize the series connection, that is, one switch tube is connected in series between every two adjacent photovoltaic modules.
  • the input end of the converter has two input ports, which are represented by IN1 and IN2 in the figure. Each input port includes a positive input terminal and a negative input terminal.
  • the first photovoltaic component is connected to the input port IN1 of the converter, and the second photovoltaic unit Connected to the input port IN2 of the converter, the first photovoltaic unit and the second photovoltaic unit are connected in series inside the converter through the switch tube 203.
  • the power circuit 201 of the converter 200 is used for power conversion, and the power circuit may be a direct current-direct current (DC-DC) conversion circuit or a direct current-alternating current (DC-AC) conversion circuit, and may also be only an on-off control circuit.
  • DC-DC direct current-direct current
  • DC-AC direct current-alternating current
  • the DC-DC conversion circuit may specifically be a boost (Boost) circuit, a buck (Buck) circuit, or a buck-boost (Buck-Boost) circuit, which is not specifically described in this application limited.
  • Boost boost
  • Buck buck
  • Buck-Boost buck-boost
  • the controller 202 controls the switch tube 203 to close, and the first photovoltaic component 204 and the second photovoltaic component 205 are connected in series inside the converter 200.
  • the controller 202 determines that it is currently necessary to switch to the shutdown mode. At this time, the controller 202 controls the switch tube 203 to turn off so that the first photovoltaic module 204 and When the second photovoltaic module 205 is disconnected, it can also control the power circuit 201 to stop power conversion, or limit the output voltage of the power circuit 201 to be less than a preset voltage value, which is usually low, for example, it can be set to 10V, or limited The output current of the power circuit 201 is less than the preset current value, for example, it can be set to 10 mA. Therefore, there is no dangerous high voltage at the output of the converter.
  • the controller can also control the switch tube to close, and control the power circuit 201 to resume power conversion or release the output voltage to the power circuit 201 or release the output current to the power circuit 201 limits.
  • each photovoltaic unit only includes one photovoltaic module.
  • the corresponding control methods are similar in other cases. For example, when the input of the converter is connected to three photovoltaic units, Corresponding to the use of two switching tubes inside the converter, three photovoltaic units are connected in series through the two switching tubes inside the converter.
  • Table 1 Parameter table of a single photovoltaic module
  • the number of single cells included in a single photovoltaic module is different, and its open circuit voltage is different, but usually the open circuit voltage of a single photovoltaic module is less than 80V, which meets the requirements of the 2017 NEC standard.
  • their open circuit voltage may be greater than 80V.
  • the total open circuit voltage of two photovoltaic modules connected in series It is 91.2V.
  • each photovoltaic unit may include two photovoltaic modules with a cell number of 48.
  • each photovoltaic unit The open circuit voltage of each photovoltaic unit is 62.4V, which is still less than 80V, which meets the requirements of the 2017 NEC standard.
  • the switch tube 203 may be a relay, a BJT tube (Bipolar Junction Transistor, transistor), a MOS tube (metal oxide semiconductor field effect transistor), or an IGBT ( Any of the insulated gate bipolar transistors.
  • BJT tube Bipolar Junction Transistor, transistor
  • MOS tube metal oxide semiconductor field effect transistor
  • IGBT IGBT
  • the converter provided in the embodiment of the present application includes a switch tube for connecting photovoltaic units.
  • the converter supports the access of at least two photovoltaic units.
  • the photovoltaic units are connected in series through the switch tube inside the converter.
  • the working state of the switch tube is determined by Controller control of the converter.
  • the controller of the converter receives a shutdown command or loses a heartbeat command within a preset time period, the controller controls all switch tubes to be disconnected, and can disconnect any two photovoltaic units connected in series.
  • the output voltage of the photovoltaic unit is usually less than the standard required voltage of 80V, so there is no dangerous high voltage in the photovoltaic array formed by the photovoltaic unit, and the safety of the photovoltaic power generation system is improved.
  • the second embodiment of the present application also provides another converter.
  • the power circuit of the converter is a DC-DC conversion circuit and specifically a step-up and step-down circuit as an example. Be explained.
  • the input terminal of the converter includes at least the following two photovoltaic units: a first photovoltaic unit and a second photovoltaic unit, and each photovoltaic unit includes a photovoltaic module as an example for illustration, that is, the input terminal of the converter It includes at least the following two photovoltaic modules: a first photovoltaic module and a second photovoltaic module.
  • FIG. 3 is a schematic diagram of another converter for photovoltaic power generation system provided in the second embodiment of the application.
  • the converter 300 further includes a communication unit 307 and an auxiliary power supply 308.
  • the power circuit 302 may be a DC-DC conversion circuit, a DC-AC conversion circuit, or an on-off control circuit.
  • the power circuit 302 is specifically a DC-DC conversion circuit as an example for introduction.
  • DC -The DC conversion circuit can be a buck-boost circuit.
  • the communication unit 307 is used to communicate with the inverter, that is, the corresponding photovoltaic power generation system includes a DC-DC converter and a DC-AC converter (inverter) .
  • the inverter is used to send control signals to the controller of the DC-DC converter.
  • the communication unit 307 is configured to receive the control signal from the inverter 306 and forward the control signal to the controller 301.
  • the control signal includes: a heartbeat command, a power-on command, and a power-off command.
  • the auxiliary power supply 308 may be connected to one of the photovoltaic units connected to the input end of the converter 300 and powered by the photovoltaic unit.
  • the first photovoltaic component 304 supplies power to the auxiliary power supply 308 as an example.
  • the second photovoltaic component 305 at the input end of the converter can also supply power to the auxiliary power supply 308, which is not specifically limited in this application.
  • the auxiliary power supply 308 is used to supply power to the controller 301 and the communication unit 307.
  • the first photovoltaic module 304 and the second photovoltaic module 305 are connected in series through the switch tube 303 inside the converter 300.
  • the converter 300 is in the off state, and the switch tube 303 is in the off state.
  • the controller 301 receives the power-on instruction and the heartbeat instruction sent by the communication unit 307, the controller 301 controls the switch tube 303 to close, so that the first photovoltaic module 304 and the second photovoltaic module 305 are connected in series.
  • the communication unit 307 receives the control signal from the upper level.
  • the controller 301 drives the controllable switch of the power circuit 302 to perform power conversion.
  • the communication unit 307 When the communication unit 307 receives a shutdown command or loses a heartbeat command within a preset time period, it sends a corresponding control signal to the controller 301, and the controller 301 controls the power circuit 302 to stop working, or limit the output voltage of the power circuit 302 to be less than The preset voltage value, or limit the output current of the power circuit 302 to be less than the preset current value. At this time, there is no dangerous high voltage at the output end of the power circuit 302. At the same time, the controller 301 controls the switch tube 303 to disconnect to disconnect the first photovoltaic module 304 and the second photovoltaic module 305.
  • the output voltage of a single photovoltaic module is usually less than the standard required voltage of 80V, so as to ensure the safety of the converter and the safety in a certain range around it.
  • the controller can also control the switch tube to close, and control the power circuit 302 to resume power conversion or release the output voltage to the power circuit 302 or release the output current to the power circuit. limits.
  • the converter provided by the embodiment of the present application also includes a communication unit and an auxiliary power supply.
  • the auxiliary power supply is powered by a photovoltaic unit connected to the input end of the converter without additional power supply.
  • the auxiliary power supply is used to supply power to the controller and the communication unit.
  • the communication unit can receive the control signal from the upper level and forward the control signal to the controller. When the controller receives a shutdown command or loses a heartbeat command within a preset time period, it controls all switching tubes to be turned off.
  • any two photovoltaic units connected in series can be disconnected to make the converter
  • There are no dangerous high voltages in the output terminal of the PV module and the photovoltaic array formed by the photovoltaic unit so as to ensure the safety of the converter and the safety within a certain range around the photovoltaic array, which improves the safety of the entire photovoltaic power generation system.
  • each input port of the input end of the converter is connected to a photovoltaic unit.
  • the following takes part of the input ports of the converter to be connected to the photovoltaic unit, and some of the input ports of the converter are not connected to the photovoltaic unit as an example for introduction.
  • each photovoltaic unit including one photovoltaic module is an example, and the input end of the converter provided in the embodiment of the present application can also be connected to only one photovoltaic module, which will be described in detail below with reference to the drawings.
  • FIG. 4 is a schematic diagram of another converter used in a photovoltaic power generation system according to the third embodiment of the application.
  • the input end of the converter 300 has two input ports, which are represented by IN1 and IN2 in the figure. Each input port includes a positive input terminal and a negative input terminal.
  • the input end of the converter 300 can be connected to only one photovoltaic module. For example, only the first photovoltaic module 304 is connected. At this time, the input port IN2 is short-circuited.
  • the positive input terminal and the negative input terminal of the input port IN2 can be plugged in pairs to achieve a short circuit.
  • the first photovoltaic component 304 Since only the first photovoltaic component 304 is connected to the converter 300 at this time, the first photovoltaic component 304 is connected to the auxiliary power source 308 to supply power to the controller 301 and the communication unit 307.
  • the auxiliary power supply 308 starts to supply power. Initially, the converter 300 is in the off state and the switch tube 303 is in the off state.
  • the controller 301 receives the power-on instruction and the heartbeat instruction sent by the communication unit 307
  • the control switch tube 303 is closed, the first photovoltaic module 304 is connected to the input terminal of the converter 300 through the switch tube 303, that is, connected to the input terminal of the power circuit 302.
  • the communication unit 307 When the communication unit 307 receives a shutdown command or loses a heartbeat command within a preset time period, it sends a corresponding control signal to the controller 301, and the controller 301 controls the power circuit 302 to stop power conversion, or limit the output voltage of the power circuit 302 It is less than the preset voltage value, or the output current of the limited power circuit 302 is less than the preset current value. There is no dangerous high voltage at the output end of the converter 300. At the same time, the controller 301 controls the switch tube 303 to disconnect. Since the input terminal is only connected to the first photovoltaic module 304, there is no dangerous high voltage on the photovoltaic module at this time.
  • the controller can also control the switch tube to close, and control the power circuit 302 to resume power conversion or release the output voltage of the power circuit 302 or release the restriction on the output current of the power circuit.
  • the converter can also have multiple input ports connected to the photovoltaic unit, and some input ports are not connected to the photovoltaic unit.
  • each photovoltaic unit including a photovoltaic module.
  • FIG. 5 is a schematic diagram of still another converter for photovoltaic power generation system provided in the third embodiment of the application.
  • the difference between the converter shown in this figure and the converter shown in Fig. 4 is that the converter has three input ports, which are represented by IN1, IN2 and IN3 in the figure, where IN1 is connected to the first photovoltaic module 304, and IN2 is connected to In the second photovoltaic component 305, the input port IN3 is short-circuited at this time.
  • the positive input terminal and the negative input terminal of the input port IN2 can be plugged to achieve a short circuit
  • the first photovoltaic component 304 is an auxiliary power supply 308 power supply.
  • the input port of the input end of the converter provided in the embodiment of the application can be partially connected to photovoltaic units and partially not connected to photovoltaic units.
  • the number of switches inside the converter is determined, the number of photovoltaic units connected to the converter can be selected according to the actual situation. For the input port that is not connected to the photovoltaic unit, short-circuit the corresponding two ends of the input port, so it is more convenient and flexible to apply the converter.
  • the input end of the converter is connected to two photovoltaic modules as an example for description, and the input end of the converter provided in this application can also be connected to a larger number of photovoltaic units.
  • the unit includes a photovoltaic module as an example for specific description.
  • the power circuit of the converter is still used as an example of a buck-boost circuit for description.
  • the power circuit of the converter is a circuit of other types, the principle is similar, and will not be repeated in this application.
  • Fig. 6a is a schematic diagram of another converter for photovoltaic power generation system provided in the fourth embodiment of the application.
  • the input end of the converter 400 shown in FIG. 6a includes n photovoltaic modules 404a 1 -404a n , correspondingly including n-1 switch tubes 403a 1 -403a n-1 .
  • the other parts of the converter 400 refer to the second embodiment, which will not be repeated here.
  • any one of the n photovoltaic modules can be connected to the auxiliary power source 408 to supply power to the auxiliary power source 408.
  • the photovoltaic module 404a 1 is connected to the auxiliary power source 408 as an example.
  • the photovoltaic module 404a 1 supplies power to the auxiliary power supply 408, and the auxiliary power supply 408 supplies power to the controller 401 and the communication unit 407.
  • the converter 400 is in the off state, and the switching tubes 403a 1 -403a n- 1 are all in the off state.
  • the controller receives the power-on command and the heartbeat command sent by the communication unit 407, the controller 401 controls the switch tubes 403a 1 -403a n-1 to close.
  • the communication unit 407 receives the control signal from the upper level. After receiving the power-on instruction and periodically receiving the heartbeat instruction, the controller 401 drives the controllable switch of the power circuit 402 to perform power conversion.
  • the communication unit 407 When the communication unit 407 receives a shutdown command or loses a heartbeat command within a preset time period, it sends a corresponding control signal to the controller 401, and the controller 401 controls the power circuit 402 to stop power conversion, or limit the output of the power circuit 402
  • the voltage is less than the preset voltage value, or the output current of the limited power circuit 402 is less than the preset current value. There is no dangerous high voltage at the output end of the converter 400.
  • the controller 401 controls the switching tubes 403a 1 -403a n-1 to be disconnected to disconnect any two photovoltaic modules connected in series.
  • the controller can also control the switch tube to close, and control the power circuit 402 to resume power conversion or release the output voltage to the power circuit 402 or release the output to the power circuit 402 Current limit.
  • the input end of the converter provided in the embodiments of the present application can be connected to multiple photovoltaic units, and multiple photovoltaic units are connected in series inside the converter through switch tubes, and the controller of the converter can control all the switch tubes.
  • the controller receives a shutdown command or loses a heartbeat command within a preset time period, the controller controls all switch tubes to disconnect, disconnecting any two photovoltaic units connected in series, and for each photovoltaic unit,
  • the output voltage is usually less than the standard required voltage of 80V, that is, it meets the voltage standard requirements for fast shutdown.
  • the specific number of photovoltaic units connected at the input end of the converter and the photovoltaic module included in each photovoltaic unit can be determined according to requirements. The quantity is more flexible and convenient when connecting.
  • n photovoltaic modules are connected to the converter through n input ports of the input end of the converter 400, represented by IN1, IN2...INn in the figure, and each input port includes a positive input terminal and a negative input terminal.
  • the input terminal of the corresponding converter can be connected to n photovoltaic modules.
  • the positive input terminal and the negative input terminal that are not connected to the input port of the photovoltaic module can be paired to realize a short circuit. Then, from the photovoltaic components connected to the converter 400, a photovoltaic component that supplies power to the auxiliary power source 408 is determined.
  • the controller when the controller receives a shutdown command or loses a heartbeat command within a preset time period, it can control the switch tube to disconnect to disconnect any two photovoltaic modules, so that the output of the converter and the photovoltaic unit form the photovoltaic There is no dangerous high voltage in the array, so as to ensure the safety of the converter and the safety in a certain range around the photovoltaic array, which improves the safety of the entire photovoltaic power generation system.
  • FIG. 6b is a schematic diagram of yet another converter for photovoltaic power generation system provided in the fourth embodiment of the application.
  • the difference between the converter 400 shown in FIG. 6b and the converter shown in FIG. 3 is that the power circuit of the converter in FIG. 6b is specifically an inverter 402, which can convert direct current into alternating current and output it.
  • the n photovoltaic modules are connected to the converter 400 through n input ports at the input end of the inverter 402.
  • the controller When the controller receives a shutdown command or loses a heartbeat command within a preset time period, it can control the switch tube 403 to disconnect to disconnect any two photovoltaic components, so that the output terminal of the inverter 402 and the photovoltaic unit are formed.
  • There is no dangerous high voltage in the photovoltaic array so as to ensure the safety of the inverter 402 and the safety in a certain range around the photovoltaic array, which improves the safety of the entire photovoltaic power generation system.
  • the fifth embodiment of the present application also provides a method for controlling the inverter, which is described in detail below with reference to the accompanying drawings.
  • FIG. 7 is a flowchart of a method for controlling a converter according to Embodiment 5 of the application.
  • the method provided in this embodiment is used to control a converter, and the converter includes a power circuit, a controller, and at least one switch tube.
  • the input end of the converter has multiple input ports, each input port includes a positive input terminal and a negative input terminal, and the photovoltaic unit is connected to the converter through the input port of the converter.
  • the converter supports the access of at least two photovoltaic units, and at least two photovoltaic units are connected in series within the converter through a switch tube. Each photovoltaic unit is formed by at least one photovoltaic module in series and parallel.
  • the method includes the following steps:
  • the input terminal of the converter includes at least the following two photovoltaic units: a first photovoltaic unit and a second photovoltaic unit, and each photovoltaic unit includes a photovoltaic module as an example for description.
  • the controller when it is not turned on, the power circuit does not work and the switch tube is in the off state.
  • the controller receives the power-on instruction and the heartbeat instruction sent by the communication unit, the controller controls the switch tube to close, so that the first photovoltaic component and the second photovoltaic component are connected in series.
  • the controller drives the controllable switch of the power circuit to perform power conversion.
  • the controller drives the buck-boost circuit to boost or buck the input voltage and then deliver it to the inverter.
  • the communication unit When the communication unit receives a shutdown command or loses a heartbeat command within a preset time period, it sends a corresponding control signal to the controller.
  • the controller controls the power circuit to stop working, or limits the output voltage of the power circuit to be less than the preset voltage Value, or limit the output current of the power circuit to be less than the preset current value. So that there is no dangerous high voltage at the output of the converter.
  • the controller controls the switch tube to disconnect to disconnect the series connection of the first photovoltaic module and the second photovoltaic module. At this time, there is no dangerous high voltage in the photovoltaic array, so as to ensure the safety of the converter and the safety of the surrounding area.
  • the switch tube can be controlled to be disconnected when the photovoltaic power generation system performs the shutdown function to disconnect any two photovoltaic units connected in series, so that the photovoltaic units form a photovoltaic array There is no dangerous high voltage to ensure the safety of the converter and the safety in a certain range around the photovoltaic array, which improves the safety of the entire photovoltaic power generation system.
  • Embodiment 6 is a diagrammatic representation of Embodiment 6
  • the sixth embodiment of the present application also provides a photovoltaic power generation system.
  • the following will continue to take each photovoltaic unit including a photovoltaic module as an example for specific description.
  • FIG. 8 is a schematic diagram of a photovoltaic power generation system according to Embodiment 6 of the application.
  • the photovoltaic power generation system includes: at least two photovoltaic units and a converter 800, and each photovoltaic unit includes a photovoltaic component.
  • the input terminal of the converter has multiple input ports, each input port includes a positive input terminal and a negative input terminal, and the photovoltaic unit is connected to the converter through the input port of the converter.
  • the photovoltaic modules 804a 1 to 804a n shown in the figure are connected in series through switch tubes inside the converter 800, and n is an integer greater than or equal to 2.
  • the converter 800 includes a power circuit 802, a controller 801 and a switch tube 803.
  • the embodiment of the present application does not limit the number of switching tubes 803 inside the converter 800.
  • the number of switching tubes 803 inside the converter 800 can be n-1, and the input terminal of the corresponding converter 800 can be connected to n photovoltaic units.
  • the converter of the photovoltaic power generation system includes a switch tube for connecting the photovoltaic unit, and the working state of the switch tube is controlled by the controller of the converter.
  • the controller of the converter receives a shutdown command or loses a heartbeat command within a preset time period, the controller controls all the switching tubes to be turned off. Since the photovoltaic unit is connected in series through the switching tubes, it can turn off all the switching tubes. Any two photovoltaic units connected in series are disconnected, and for each photovoltaic unit, its output voltage is usually less than the standard required voltage of 80V, so there is no dangerous high voltage in the photovoltaic array formed by the photovoltaic unit, which improves the photovoltaic power generation system Security.
  • the seventh embodiment of the present application also provides another photovoltaic power generation system.
  • the power circuit of the photovoltaic power generation system provided in the embodiment of the present application is a DC-DC conversion circuit, and the DC-DC conversion circuit is more At this time, a plurality of the DC-DC conversion circuits are connected in series to form a DC-DC conversion circuit string, and the DC-DC conversion circuit string is connected to the input end of the inverter.
  • FIG. 9 is a schematic diagram of a photovoltaic power generation system provided in Embodiment 7 of the application.
  • the photovoltaic power generation system includes multiple DC-DC converter circuits, that is, includes multiple DC-DC converters. DC converter.
  • a plurality of photovoltaic units 901 are connected to the input port of the DC-DC converter, and are connected in series through the switch tube inside the DC-DC converter 902, and two adjacent photovoltaic units are connected through the switch tube.
  • the output terminals of multiple DC-DC converters 902 are connected in series with each other to form a DC-DC converter string.
  • the DC converter strings are independently connected to different input ports at the input end of the inverter 905.
  • the inverter 905 is connected to two DC-DC converter strings, namely string 903 and string 904, as an example.
  • the number of strings can be set according to actual conditions, and the number of DC-DC converters included in different strings can be the same or different, which is not specifically limited in this application.
  • the output terminal of the inverter 905 is connected to the power grid 906, and the general inverter 905 can implement a DC-AC conversion function, inverting DC power into AC power and sending it to the power grid 906.
  • the converter of the photovoltaic power generation system includes a switch tube for connecting the photovoltaic unit.
  • the photovoltaic unit is connected in series through the switch tube inside the converter, and the working state of the switch tube is controlled by the controller of the converter.
  • the controller of the converter receives a shutdown command or loses a heartbeat command within a preset time period, the controller controls all the switching tubes to be turned off. Since the photovoltaic unit is connected in series through the switching tubes, it can turn off all the switching tubes.
  • any two photovoltaic units connected in series are disconnected, and for a single photovoltaic unit, its output voltage is usually less than the standard required voltage of 80V, so there is no dangerous high voltage in the photovoltaic array formed by the photovoltaic unit, which improves the photovoltaic power generation system safety.
  • multiple converters can be connected in series to form a string and connected to the input end of the inverter, and multiple converters can be connected in series and parallel to the input end of the inverter.
  • Each converter of the power generation system can still meet the standard requirements for fast shutdown when the input end is connected to multiple photovoltaic units at the same time, so the number of converters of the photovoltaic power generation system can be reduced, thereby effectively simplifying field wiring and reducing system costs.
  • At least one (item) refers to one or more, and “multiple” refers to two or more.
  • “And/or” is used to describe the association relationship of associated objects, indicating that there can be three types of relationships, for example, “A and/or B” can mean: only A, only B, and both A and B , Where A and B can be singular or plural.
  • the character “/” generally indicates that the associated objects are in an “or” relationship.
  • the following at least one item (a)” or similar expressions refers to any combination of these items, including any combination of a single item (a) or plural items (a).
  • At least one 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, and c can be single or multiple.

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Abstract

本申请提供了一种应用于光伏发电系统的变换器、方法及系统。其中，该变换器包括：控制器和至少一个开关管；所述变换器支持至少两个光伏单元接入，所述至少两个光伏单元在变换器内部通过所述开关管串联；所述光伏单元为至少一个光伏组件通过串并联形成；所述控制器，用于在接收到关机指令或者在预设时间段内丢失心跳指令时，控制所述开关管断开以使任意两个串联在一起的所述光伏单元断开连接。利用本申请提供的变换器，能够在光伏发电系统关机时将任意两个串联的光伏单元断开连接，使光伏单元形成的光伏阵列内不存在危险高压，从而提升光伏发电系统的安全性。

Description

一种应用于光伏发电系统的变换器、方法及系统 技术领域
本申请涉及光伏发电技术领域，尤其涉及一种应用于光伏发电系统的变换器、方法及系统。
背景技术
光伏发电是利用半导体界面的光生伏特效应，将光能转变为电能的一种技术。光伏发电系统通常包括光伏方阵、逆变器、交流配电等设备。为了获得较高的输出电压或输出电流，光伏方阵通常包括多个光伏组件通过一定的串并联方式形成。但不同光伏组件的参数存在的差异，以及太阳辐射条件的差异会造成能量损失。另外由于光伏组件安装于室外，光伏组件部分被遮挡、间歇性的遮挡以及老化等现象也会引起能量损失，进而影响光伏发电系统的发电量，降低发电效率。
为了提高光伏发电系统的发电效率，每个光伏组件会连接一个具有独立MPPT(Maximum Power Point Tracking，最大功率点跟踪)功能的变换器，最大限度提高光伏发电系统的发电效率。为了降低光伏发电系统的成本，目前将多个光伏组件在变换器的外部串联连接后再连接在一个变换器的输入端，进而减少了光伏发电系统包含的变换器的数量，因此降低了光伏发电系统的成本。
但该方案多个光伏组件直接串联后的总电压较高，当光伏发电系统执行快速关断功能时，光伏发电系统的变换器关机，变换器的输出电压为零，但串联的多个光伏组件无法断开，串联的光伏组件形成的光伏阵列内仍存在危险高压，这样将存在安全隐患。
发明内容
为了解决现有技术中存在的以上技术问题，本申请提供了一种应用于光伏发电系统的变换器、方法及系统，能够在光伏发电系统关机时将任意两个串联的光伏单元断开连接，使光伏单元形成的光伏阵列内不存在危险高压，从而提升光伏发电系统的安全性。
第一方面，本申请提供了一种用于光伏发电系统的变换器，该变换器包括：控制器和至少一个开关管；变换器支持至少两个光伏单元接入，至少两个光伏单元在变换器内部通过开关管串联；光伏单元为至少一个光伏组件通过串并联形成；控制器，用于在接收到关机指令或者在预设时间段内丢失心跳指令时，控制开关管断开以使任意两个串联在一起的光伏单元断开连接。
本申请接入变换器的每个光伏单元的开路电压均低于80V，因此当控制器控制开关管断开时，可以使光伏单元形成的光伏阵列内不存在危险高压，提升了光伏发电系统的安全性。
结合第一方面，在第一种可能的实现方式中，控制器还用于当收到开机指令且收到心跳指令时，控制开关管闭合。
当控制器接收到开机指令且收到心跳指令时，判断此时变换器需要切换为正常工 作的模式，因此控制开关管闭合，以使光伏单元在变换器内部通过开关管串联连接。
结合第一方面及第一种可能的实现方式，在第二种可能的实现方式中，该变换器还包括：功率电路，功率电路用于进行功率变换，该功率电路可以为直流-直流变换电路、直流-交流变换电路或通断控制电路。
结合第一方面及上述任一种可能的实现方式，在第三种可能的实现方式中，控制器还用于在接收到关机指令或者在预设时间段内丢失心跳指令时，判断当前需要切换为关机模式，控制功率电路停止功率变换，或，限制功率电路的输出电压小于预设电压值，或，限制功率电路的输出电流小于预设电流值。其中，该预设电压值通常较低，例如可以为10V，该预设电流值通常也较低，例如可以设置为10mA。因此能够使变换器的输出端无危险高压与高电流，提升了光伏发电系统的安全性。
结合第一方面及上述任一种可能的实现方式，在第四种可能的实现方式中，控制器还用于当收到开机指令且收到心跳指令时，判断此时变换器需要切换为正常工作的模式，因此控制器控制功率电路恢复功率变换，或，解除对功率电路的输出电压的限制，或，解除对功率电路的输出电流的限制，以使功率电路能够正常工作。
结合第一方面及上述任一种可能的实现方式，在第五种可能的实现方式中，当功率电路为直流-直流变换电路时，该直流-直流变换电路可以为升压电路、降压电路或升降压电路，可以根据实际需求确定功率电路的具体类型。
结合第一方面及上述任一种可能的实现方式，在第六种可能的实现方式中，该变换器还包括：通信单元；通信单元用于接收来自上一级的控制信号，并将控制信号转发给控制器。该控制信号包括：心跳指令、开机指令和关机指令。
通信单元能够转发控制信号给控制器，以使控制器根据该控制信号及时判断出当前变换器处于正常工作模式还是关机模式，进而使控制器能够及时控制开关管和功率电路的工作状态。
结合第一方面及上述任一种可能的实现方式，在第七种可能的实现方式中，该变换器还包括：辅助电源。其中一个光伏单元与辅助电源连接为辅助电源供电，辅助电源为控制器和通信单元供电。
辅助电源由接入变换器的某个光伏单元供电，与变换器内部的开关管的导通状态无关，因此辅助电源能够在至少两个光伏单元未通过开关管串联连接时，向控制器和通信单元供电。
结合第一方面及上述任一种可能的实现方式，在第八种可能的实现方式中，开关管可以为以下任意一种：继电器、晶体三极管、绝缘栅双极型晶体管和金属氧化物半导体场效应晶体管，可以根据实际需求确定开关管的具体类型。
第二方面，本申请还提供了一种变换器的控制方法，变换器应用于光伏发电系统，该变换器包括：控制器和至少一个开关管；变换器支持至少两个光伏单元接入，至少两个光伏单元在变换器内部通过开关管串联；光伏单元为至少一个光伏组件通过串并联形成；该方法包括：在接收到关机指令或者在预设时间段内丢失心跳指令时，控制开关管断开以使任意两个串联在一起的光伏单元断开连接。
利用该方法能够在光伏发电系统执行关断功能时控制开关管断开以使任意两个串联在一起的光伏单元断开连接，使得光伏单元形成的光伏阵列上无危险高压，从而保证变换器的安全以及光伏阵列周围一定范围内的安全，提升了整个光伏发电系统的安全性。
结合第二方面，在第一种可能的实现方式中，该方法还包括：当收到开机指令且收到心跳指令时，控制开关管闭合。
利用该方法能够当接收到开机指令且收到心跳指令时，确定变换器需要切换为正常工作的模式，因此控制开关管闭合，以使光伏单元在变换器内部通过开关管串联连接。
第三方面，本申请还提供了一种光伏发电系统，该光伏发电系统包括：至少两个光伏单元和以上任意一种变换器。其中，至少两个光伏单元接入变换器，至少两个光伏单元在变换器内部通过开关管串联，光伏单元为至少一个光伏组件通过串并联形成。
由于该光伏发电系统包括任意一种变换器，变换器包括控制器和至少一个开关管，接入变换器的每个光伏单元的开路电压均低于80V，因此当控制器控制开关管断开时，可以使光伏单元形成的光伏阵列内不存在危险高压，提升了光伏发电系统的安全性。
结合第三方面，在第一种可能的实现方式中，该光伏发电系统还包括：功率电路，当功率电路为直流-直流变换电路，且直流-直流变换电路为多个时，多个直流-直流变换电路串联在一起形成直流-直流变换电路组串，直流-直流变换电路组串连接在逆变器的输入端；逆变器，用于将直流-直流变换电路组串输出的直流电变换为交流电后进行输出。
可以根据实际情况确定直流-直流变换电路组串包括的直流-直流变换电路的数量，由于本申请提供的光伏发电系统的每个变换器在输入端同时连接多个光伏单元时仍能够满足快速关断的标准要求，因此能够减少光伏发电系统包括的变换器的数量，进而有效简化现场接线和降低系统成本。
结合第三方面及上述任一种可能的实现方式，在第二种可能的实现方式中，直流-直流变换电路组串为多个；多个直流-直流变换电路组串并联后连接在逆变器的输入端，或者独立连接在逆变器输入端的不同输入口。
可以根据实际情况确定逆变器输入端连接的直流-直流变换电路组串的数量，由于本申请提供的光伏发电系统的每个变换器在输入端同时连接多个光伏单元时仍能够满足快速关断的标准要求，因此能够减少光伏发电系统包括的变换器的数量，进而有效简化现场接线和降低系统成本。
本申请至少具有以下优点：
本申请提供的变换器支持至少两个光伏单元接入，光伏单元为至少一个光伏组件的串并联形成，变换器的内部包括开关管，光伏单元通过变换器内部设置的开关管进行串联。例如当变换器的输入端连接两个光伏单元时，变换器的内部包括一个开关管，该两个光伏单元通过该开关管实现串联。更多数目的光伏单元实现串联需要更多数目的开关管，例如N个光伏单元实现串联，对应需要N-1个开关管。开关管的开关状态 由变换器的控制器控制，当变换器的控制器接收到关机指令或者在预设时间段内丢失心跳指令时，控制器控制所有的开关管断开，由于光伏单元通过变换器内部的开关管串联，因此能够将任意两个串联在一起的光伏单元断开连接，使得光伏单元形成的光伏阵列内不存在危险高压，从而满足安全规定的要求，提升了整个光伏发电系统的安全性。
附图说明
图1为本申请提供的一种光伏发电系统的示意图；
图2为本申请实施例一提供的一种用于光伏发电系统的变换器的示意图；
图3为本申请实施例二提供的另一种用于光伏发电系统的变换器的示意图；
图4为本申请实施例三提供的又一种用于光伏发电系统的变换器的示意图；
图5为本申请实施例三提供的再一种用于光伏发电系统的变换器的示意图；
图6a为本申请实施例四提供的另一种用于光伏发电系统的变换器的示意图；
图6b为本申请实施例四提供的又一种用于光伏发电系统的变换器的示意图；
图7为本申请实施例五提供的一种变换器的控制方法的流程图；
图8为本申请实施例六提供的一种光伏发电系统的示意图；
图9为本申请实施例七提供的另一种光伏发电系统的示意图。
具体实施方式
目前为了降低光伏发电系统的成本，将多个光伏组件在变换器的外部串联连接后再连接在一个变换器(即一拖多)的输入端，下面结合附图具体说明。
参见图1，该图为本申请提供的一种光伏发电系统的示意图。
目前采用一拖多的方案时，多个光伏组件101在变换器102的外部串联后接入变换器102的输入端，多个光伏组件串联后形成组串，形成的组串包括两个连接端，其中一个连接端连接变换器的正输入端，另一个连接端连接变换器的负输入端。对于光伏组件，在连接时光伏组件的正输出端连接到上一个光伏组件的负输出端，负输出端连接下一个光伏组件的正输出端。变换器输出端也可以相互串联形成变换器组串，变换器组串包括两个连接端，其中一个连接端连接逆变器105的正输入端，另一个连接端连接逆变器105的负输入端，对于变换器组串，在连接时变换器的正输出端连接到上一个变换器负输出端，负输出端连接到下一个变换器正输出端。同时多个变换器组串也可以并联后再连接逆变器105输入端或者独立连接在逆变器105输入端的不同输入口，图中所示逆变器105接入了两个变换器组串，即组串103和组串104。逆变器105的输出端连接电网106，通常逆变器105能够实现直流-交流变换功能，即将直流电逆变成交流电送入电网。
但NEC(National Electrical Code，美国国家电工标准)在NEC 2017--690.12(B)条款中要求光伏发电系统需要具备组件级别的快速关断功能。国际权威光伏行业标准协会(SunSpec Alliance)跟据NEC 2014，NEC 2017，UL 1741(光伏安装标准)规范制定了的快速关断的标准。NEC仅适用于建筑房屋上的分布式电站，2014年的规范要求光伏系统周边安全区域为3m。2017年的规范要求光伏系统周边安全区域为1英尺(约 等于30cm)，即组件级别的关断。2017NEC中的具体要求：在快速关断装置启动后30秒内，安全区域范围外电压降低到30V以下，安全区域范围内电压降低到80V以下，即要求组件级关断。
多个光伏组件在变换器的外部直接串联连接，串联后的总电压将大于80V，当光伏发电系统关机时，光伏发电系统的变换器关机，变换器102的输出电压为零，但串联的多个光伏组件无法断开，因此串联的光伏组件形成的光伏阵列内仍存在危险高压，致使变换器的输入端仍存在危险高压，不满足2017NEC标准要求，存在安全隐患。
为了解决上述技术问题，本申请提供了一种应用于光伏发电系统的变换器、方法及系统，其中本申请提供的变换器内部设置了开关管，变换器支持至少两个光伏单元接入，光伏单元在变换器内部的通过开关管串联。当变换器的控制器在接收到关机指令或者在预设时间段内丢失心跳指令时，控制开关管断开以使任意两个串联在一起的光伏单元断开连接，使得光伏单元形成的光伏阵列内不存在危险高压，以满足安全区域内无高压的标准要求，提升了光伏发电系统的安全性。
为了使本技术领域的人员更好地理解本发明方案，下面将结合本申请实施例中的附图，对本申请实施例中的技术方案进行清楚、完整地描述。
实施例一：
本申请实施例一提供了一种用于光伏发电系统的变换器，该变换器的输入端可以连接多个光伏单元，多个光伏单元形成光伏阵列，本申请实施例中的单个光伏单元可以包括一个光伏组件，还可以包括多个光伏组件串并联形成，例如多个光伏组件先串联在一起形成光伏组串，多个光伏组串再并联在一起形成光伏单元。本申请实施例中不具体限定光伏组件的具体数量，本领域技术人员可以根据实际需要来设置，而且本申请实施例中对单个光伏组件的电参数不做具体限定。
本申请实施例提供的变换器包括：功率电路、控制器和至少一个开关管。其中，该变换器的输入端有多个输入口，每个输入口包括正输入端子和负输入端子，光伏单元通过变换器的输入口接入变换器。该变换器支持至少两个光伏单元接入，至少两个光伏单元在变换器内部通过开关管串联。每个光伏单元可以只包括一个光伏组件，还可以由多个光伏组件通过串并联形成。本申请实施例不限定变换器内部的开关管的数量，例如变换器内部开关管的数量可以为N-1个，则对应变换器的输入端可以连接N个光伏单元。当然也可以连接比N数量更少的光伏单元，此时将未接入光伏单元的输入口对应的正输入端子和负输入端子短接即可。
控制器在接收到关机指令或者在预设时间段内丢失心跳指令时，控制所有的开关管断开以使任意两个串联在一起的光伏组件断开连接。预设时间段可以根据实际要求设置，本申请对此不作具体限定。
其中，关机指令是控制器的上一级下发的，心跳指令也是控制器的上一级下发的。关机指令是指直接关机，停止工作。而心跳指令是在正常工作时才发送心跳指令，如果预设时间内未收到心跳指令，则说明出现故障。预设时间可以根据需要来设置，本申请实施例中不做具体限定。
为了描述方便，下面以变换器的输入端至少包括以下两个光伏单元：第一光伏单元和第二光伏单元，并且以每个光伏单元包括一个光伏组件为例进行说明，即变换器的输入端至少包括以下两个光伏组件：第一光伏组件和第二光伏组件，其中“第一”和“第二”仅是为区分两个光伏单元和光伏组件以方便说明，并不构成对本申请的限定。可以理解的是，当变换器的输入端包括更多数量的光伏单元以及每个光伏单元包括多个光伏组件时，变换器的工作原理类似，本申请在此不再全部说明。
参见图2，该图为本申请实施例一提供的一种用于光伏发电系统的变换器的示意图。
其中，变换器200包括：功率电路201、控制器202和开关管203。
本实施例中以变换器输入端连接两个光伏组件：第一光伏组件204和第二光伏组件205为例进行说明，对应使用变换器中的一个开关管实现串联。可以理解的是，当变换器的输入端连接多个光伏组件时，需要使用变换器内多个开关管才能实现串联，即每两个相邻的光伏组件间通过一个开关管实现串联。
该变换器的输入端有两个输入口，图中分别用IN1和IN2表示，每个输入口包括正输入端子和负输入端子，第一光伏组件连接变换器的输入口IN1，第二光伏单元连接变换器的输入口IN2，第一光伏单元和第二光伏单元通过开关管203在变换器内部串联连接。
变换器200的功率电路201用于进行功率变换，该功率电路可以为直流-直流(DC-DC)变换电路或直流-交流(DC-AC)变换电路，还可以仅是一个通断控制电路。
当功率电路为直流-直流变换电路时，该直流-直流变换电路具体可以为升压(Boost)电路、降压(Buck)电路或升降压(Buck-Boost)电路，本申请对此不作具体限定。
变换器200处于正常工作模式时，控制器202控制开关管203闭合，第一光伏组件204和第二光伏组件205在变换器200的内部串联连接。
当控制器202接收到关机指令或者在预设时间段内丢失心跳指令时，控制器202判断当前需要切换为关机模式，此时控制器202控制开关管203断开以使第一光伏组件204和第二光伏组件205断开连接，还能够控制功率电路201停止功率变换，或者限制功率电路201的输出电压小于预设电压值，该预设电压值通常较低，例如可以设置为10V，或者限制功率电路201的输出电流小于预设电流值，例如可以设置为10mA。因此变换器的输出端无危险高压。此时，由于第一光伏组件204和第二光伏组件205之间断开连接，第一光伏组件204和第二光伏组件205形成的光伏阵列内无危险高压，同时变换器200的输入端也不存在危险高压。
此外，当再次收到开机指令且收到所述心跳指令时，控制器还能够控制开关管闭合，且控制功率电路201恢复功率变换或解除对功率电路201输出电压或解除对功率电路201输出电流的限制。
以上仅是以变换器接入两个光伏单元且每个光伏单元只包括一个光伏组件为例进行说明，其他情况对应的控制方式类似，例如，当变换器的输入端连接三个光伏单元时，对应使用变换器内部两个开关管，三个光伏单元在变换器内部通过两个开关管实现串联。
下面结合表1所示的单个光伏组件的参数表说明本申请实施例断开串联连接的光 伏组件的原因。
表1：单个光伏组件的参数表
Figure PCTCN2019095545-appb-000001
根据表1可知，单个光伏组件包括的单体电芯Cell的数量不同，其开路电压不同，但通常单个光伏组件的开路电压小于80V，满足2017NEC标准要求。而当多个光伏组件在变换器外部直接串联后连接变换器的输入端时，其开路电压可能会大于80V，例如对于Cell数量为72的光伏组件，两个该光伏组件串联后的总开路电压为91.2V。此时当光伏发电系统执行快速关断功能后，变换器关机，输出电压为零，但外部串联的光伏组件无法断开，变换器的输入电压仍然大于80V，光伏阵列内存在危险高压，不满足2017NEC标准要求。
本申请实施例控制接入变换器的单个光伏单元的开路电压低于80V，例如每个光伏单元可以包括两个Cell数量为48的光伏组件，当光伏单元之间的串联连接断开时，每个光伏单元的开路电压为62.4V，仍小于80V，满足2017NEC标准要求。
本申请中不具体限定开关管的具体类型，例如该开关管203可以为继电器、BJT管(Bipolar Junction Transistor，晶体三极管)、MOS管(metal oxide semiconductor，金属氧化物半导体场效应晶体管)或IGBT(insulated gate bipolar transistor，绝缘栅双极型晶体管)中的任一种。
本申请实施例提供的变换器的内部包括用于连接光伏单元的开关管，该变换器支持至少两个光伏单元接入，光伏单元在变换器的内部通过开关管串联，开关管的工作状态由变换器的控制器控制。当变换器的控制器接收到关机指令或者在预设时间段内丢失心跳指令时，控制器控制所有的开关管断开，能够将任意两个串联在一起的光伏单元断开连接，而对于单个光伏单元，其输出电压通常小于80V的标准要求电压，因此使得光伏单元形成的光伏阵列内不存在危险高压，提升了光伏发电系统的安全性。
基于实施例一提供的用于光伏发电系统的变换器，本申请实施例二还提供另一种变换器，下面以变换器的功率电路为直流-直流变换电路且具体为升降压电路为例进行说明。
实施例二：
本申请实施例中仍以变换器的输入端至少包括以下两个光伏单元：第一光伏单元和第二光伏单元，且每个光伏单元包括一个光伏组件为例进行说明，即变换器的输入端至少包括以下两个光伏组件：第一光伏组件和第二光伏组件。
参见图3，该图为本申请实施例二提供的另一种用于光伏发电系统的变换器的示意图。
图3所示变换器300与图2所示变换器的区别在于：变换器300还包括通信单元307和辅助电源308。并且，功率电路302可以为DC-DC变换电路，也可以为DC-AC变换电路，还可以为通断控制电路，下面以功率电路302具体为DC-DC变换电路为例进行介绍，具体地DC-DC变换电路可以为升降压电路，其余部分的工作原理请参见实施例一中的相关说明，在此不再赘述。
当功率电路302具体为DC-DC变换电路时，通信单元307用于与逆变器进行通信，即对应的光伏发电系统包括DC-DC变换器，也包括DC-AC变换器(逆变器)。逆变器作为DC-DC变换器的控制器的上一级，用于向DC-DC变换器的控制器发送控制信号。
通信单元307，用于接收来自逆变器306的控制信号，并将控制信号转发给控制器301。其中，控制信号包括：心跳指令、开机指令和关机指令。
辅助电源308可以与连接在变换器300的输入端的光伏单元中的一个进行连接，并由该光伏单元供电。本申请实施例中以第一光伏组件304向辅助电源308供电为例，当然变换器输入端的第二光伏组件305也可以为辅助电源308供电，本申请中不做具体限定。辅助电源308，用于为控制器301和通信单元307供电。
如图3所示，第一光伏组件304和第二光伏组件305在变换器300内部通过开关管303串联。初始时，变换器300处于关闭状态，开关管303处于关断状态。当控制器301收到由通信单元307发送的开机指令和心跳指令时，控制器301控制开关管303闭合，以使第一光伏组件304和第二光伏组件305串联连接。
通信单元307接收来上一级的控制信号，当通信单元307接收到开机指令，并且定期接收到心跳指令后，控制器301驱动功率电路302的可控开关管动作以进行功率变换。
当通信单元307接收到关机指令或是在预设时间段内丢失心跳指令时，向控制器301发送相应的控制信号，控制器301控制功率电路302停止工作，或者限制功率电路302的输出电压小于预设电压值，或者限制功率电路302的输出电流小于预设电流值。，此时功率电路302的输出端无危险高压。同时控制器301控制开关管303断开，以使第一光伏组件304和第二光伏组件305的断开连接，此时第一光伏组件304和第二光伏组件305形成的光伏阵列内无危险高压，并且单个光伏组件的输出电压通常也小于80V的标准要求电压，从而保证变换器的安全以及周围一定范围内的安全。
此外，当再次收到开机指令且收到所述心跳指令时，控制器还能够控制开关管闭合，且控制功率电路302恢复功率变换或解除对功率电路302输出电压或解除对功率电路的输出电流的限制。
本申请实施例提供的变换器还包括了通信单元和辅助电源，辅助电源由与变换器输入端连接的一个光伏单元供电，不需要额外的电源，辅助电源用于为控制器和通信单元供电。通信单元能够接收来自上一级的控制信号，并将控制信号转发给控制器。当控制器接收到关机指令或者在预设时间段内丢失心跳指令时控制所有的开关管断开，开关管断开后，可以将任意两个串联在一起的光伏单元断开连接，使得变换器的输出端和光伏单元形成的光伏阵列内均不存在危险高压，从而保证变换器的安全以及光伏 阵列周围一定范围内的安全，提升了整个光伏发电系统的安全性。
上述实施例的变换器的输入端的每个输入口均连接光伏单元，下面以变换器的部分输入口连接光伏单元，部分不连接光伏单元为例进行介绍。
继续以每个光伏单元包括一个光伏组件为例进行说明，而本申请实施例提供的变换器的输入端还可以只接入一个光伏组件，下面结合附图具体说明。
实施例三：
参见图4，该图为本申请实施例三提供的又一种用于光伏发电系统的变换器的示意图。
该变换器300的输入端有两个输入口，图中分别用IN1和IN2表示，每个输入口包括正输入端子和负输入端子，变换器300的输入端可以只连接一个光伏组件，本实施例以只接入第一光伏组件304为例，此时输入口IN2短路，在一种可能的实现方式中，可将输入口IN2的正输入端子和负输入端子对插以实现短路。
由于此时只有第一光伏组件304单独接入变换器300，所以第一光伏组件304与辅助电源308连接，以给控制器301和通信单元307供电。
接入第一光伏组件304后，辅助电源308开始供电，初始时，变换器300处于关闭状态，开关管303处于关断状态，当控制器301收到由通信单元307发送的开机指令和心跳指令时，控制开关管303闭合，第一光伏组件304通过开关管303连接在变换器300的输入端，即连接功率电路302的输入端。
当通信单元307接收到关机指令或是在预设时间段内丢失心跳指令时，向控制器301发送相应的控制信号，控制器301控制功率电路302停止功率变换，或者限制功率电路302的输出电压小于预设电压值，或者限制功率电路302的输出电流小于预设电流值。变换器300的输出端无危险高压。同时控制器301控制开关管303断开，由于输入端只连接第一光伏组件304，此时该光伏组件上无危险高压。
再次收到开机指令且收到所述心跳指令时，控制器还能够控制开关管闭合，且控制功率电路302恢复功率变换或解除对功率电路302输出电压或解除对功率电路的输出电流的限制。
当然，变换器还可以有多个输入口接入光伏单元，并且部分输入口不接入光伏单元，下面仍以每个光伏单元包括一个光伏组件为例进行说明。
参见图5，该图为本申请实施例三提供的再一种用于光伏发电系统的变换器的示意图。
该图所示的变换器与图4所示的变换器的区别在于变换器存在三个输入口，图中分别用IN1、IN2和IN3表示，其中IN1接入第一光伏组件304，IN2接入第二光伏组件305，此时输入口IN3短路，在一种可能的实现方式中，可将输入口IN2的正输入端子和负输入端子对插以实现短路，并且第一光伏组件304为辅助电源308供电。
对于图中其它部分的工作原理可以参见上述实施例，在此不再赘述。
本申请实施例提供的变换器的输入端的输入口可以部分连接光伏单元，部分不连接 光伏单元，当变换器内部的开关数量确定时，可以根据实际情况选择接入变换器的光伏单元的数量，对于不连接光伏单元的输入口，将该输入口对应的两端短接即可，因此应用该变换器时更加便捷灵活。
实施例一和实施例二中以变换器的输入端连接两个光伏组件为例进行说明，而本申请提供的变换器的输入端还可以连接更多数量的光伏单元，下面继续以每个光伏单元包括一个光伏组件为例进行为例具体说明。
实施例四：
本申请实施例中仍以变换器的功率电路为升降压电路为例进行说明，当变换器的功率电路为其它类型电路时的原理类似，本申请在此不再赘述。
参见图6a，该图为本申请实施例四提供的另一种用于光伏发电系统的变换器的示意图。
图6a所示变换器400与图3所示变换器300的区别在于：图6a所示变换器400的输入端包括n个光伏组件404a 1-404a n，相应的包括n-1个开关管403a 1-403a n-1。变换器400的其它部分的说明可参见实施例二，在此不再赘述。
光伏组件404a 1-404a n接入变换器400的输入端时，各个光伏组件在变换器400内部通过开关管串联，每两个相邻的组件之间串联一个开关管。
n个光伏组件中的任意一个光伏组件都可以与辅助电源408连接以向辅助电源408供电，本申请实施例中以光伏组件404a 1连接辅助电源408为例。
接入n个光伏组件后，光伏组件404a 1向辅助电源408供电，辅助电源408向控制器401和通信单元407供电，初始时，变换器400为关断状态，开关管403a 1-403a n-1均处于关断状态，当控制器收到由通信单元407发送的开机指令和心跳指令时，控制器401控制开关管403a 1-403a n-1闭合。
通信单元407接收来上一级的控制信号，当接收到开机指令，并且定期接收到心跳指令后，控制器401驱动功率电路402的可控开关管动作以进行功率变换。
当通信单元407接收到关机指令或是在预设时间段内丢失心跳指令时，则向控制器401发送相应的控制信号，控制器401控制功率电路402停止功率变换，或者限制功率电路402的输出电压小于预设电压值，或者限制功率电路402的输出电流小于预设电流值。变换器400输出端无危险高压。同时控制器401控制开关管403a 1-403a n-1均断开，以使任意两个串联在一起的光伏组件断开连接，此时光伏组件404a 1-404a n形成的光伏阵列内无危险高压，并且单个光伏组件的输出电压通常也小于80V的标准要求电压。因此，变换器的输入端不存在危险高压，从而保证变换器的安全以及周围一定范围内的安全。
此外，当再次收到开机指令且收到所述心跳指令时，控制器还能够控制开关管闭合，且控制功率电路402恢复功率变换或解除对功率电路402输出电压或解除对功率电路402的输出电流的限制。
本申请实施例提供的变换器的输入端可以连接多个光伏单元，多个光伏单元在变换 器的内部通过开关管串联，变换器的控制器能够控制所有的开关管。当控制器接收到关机指令或者在预设时间段内丢失心跳指令时，控制器控制所有的开关管断开，将任意两个串联在一起的光伏单元断开连接，而对于每个光伏单元，其输出电压通常小于80V的标准要求电压，即满足快速关断的电压标准要求，实际应用时可以根据需求确定在变换器输入端连接的光伏单元的具体数量以及每个光伏单元包括的光伏组件的数量，连接时更加灵活便捷。
继续参见图6a，n个光伏组件通过变换器400输入端的n个输入口接入变换器，图中分别用IN1、IN2…INn表示，每个输入口都包括正输入端子和负输入端子。
对于包括n个输入口、n-1个开关管的变换器400，则对应变换器的输入端可以连接n个光伏组件。实际使用时可以只连接m个光伏组件，其它输入口不连接光伏组件，其中m＝1,2，…n-1，本申请实施例对m的具体数值不作限定。在一种可能的实现方式中，可将不连接光伏组件的输入口的正输入端子和负输入端子对插以实现短路。然后从接入变换器400的光伏组件中确定为辅助电源408供电的光伏组件。
此时控制器在接收到关机指令或者在预设时间段内丢失心跳指令时，能够控制开关管断开以使任意两个光伏组件之间断开连接，使得变换器输出端和光伏单元形成的光伏阵列内均不存在危险高压，从而保证变换器的安全以及光伏阵列周围一定范围内的安全，提升了整个光伏发电系统的安全性。
参见图6b，该图为本申请实施例四提供的又一种用于光伏发电系统的变换器的示意图。
图6b所示变换器400与图3所示变换器的区别在于：图6b的变换器的功率电路具体为逆变器402，该逆变器402能够将直流电变换为交流电后进行输出。n个光伏组件通过逆变器402输入端的n个输入口接入变换器400。当控制器在接收到关机指令或者在预设时间段内丢失心跳指令时，能够控制开关管403断开以使任意两个光伏组件之间断开连接，使得逆变器402输出端和光伏单元形成的光伏阵列内均不存在危险高压，从而保证逆变器402的安全以及光伏阵列周围一定范围内的安全，提升了整个光伏发电系统的安全性。
实施例五：
基于上述实施例提供的用于光伏发电系统的变换器，本申请实施例五还提供了一种变换器的控制方法，下面结合附图具体说明。
参见图7，该图为本申请实施例五提供的一种变换器的控制方法的流程图。
本实施例提供的方法用于控制变换器，该变换器包括：功率电路、控制器和至少一个开关管。其中，该变换器的输入端有多个输入口，每个输入口包括正输入端子和负输入端子，光伏单元通过变换器的输入口接入变换器。该变换器支持至少两个光伏单元接入，至少两个光伏单元在变换器内部通过开关管串联。每个光伏单元为至少一个光伏组件通过串并联形成。对于变换器的说明可以参见上述实施例，本实施例在此不再赘述。
该方法包括以下步骤：
S701：当收到开机指令且收到心跳指令时，控制开关管闭合。
下面继续以变换器的输入端至少包括以下两个光伏单元：第一光伏单元和第二光伏单元，且每个光伏单元包括一个光伏组件为例进行说明。
继续参见图3所示的变换器，未开机时，功率电路不工作，开关管处于关断状态。当控制器收到由通信单元发送的开机指令和心跳指令时，控制器控制开关管闭合，以使第一光伏组件和第二光伏组件串联。
控制器驱动功率电路的可控开关管动作以进行功率变换。例如当功率电路为DC-DC变换电路且具体为升降压电路时，控制器驱动该升降压电路将输入电压进行升压或降压后输送到逆变器。
S702：在接收到关机指令或者在预设时间段内丢失心跳指令时，控制开关管断开。
当通信单元接收到关机指令或是在预设时间段内丢失心跳指令时，向控制器发送相应的控制信号，此时控制器控制功率电路停止工作，或者限制功率电路的输出电压小于预设电压值，或者限制功率电路的输出电流小于预设电流值。以使变换器输出端无危险高压。同时控制器控制开关管断开，以使第一光伏组件和第二光伏组件的串联连接断开，此时光伏阵列内也无危险高压，从而保证变换器的安全以及周围一定范围内的安全。
利用本申请实施例提供的变换器的控制方法，能够在光伏发电系统执行关断功能时控制开关管断开以使任意两个串联在一起的光伏单元断开连接，使得光伏单元形成的光伏阵列上无危险高压，从而保证变换器的安全以及光伏阵列周围一定范围内的安全，提升了整个光伏发电系统的安全性。
实施例六：
基于上述实施例提供的用于光伏发电系统的变换器，本申请实施例六还提供了一种光伏发电系统，下面继续以每个光伏单元包括一个光伏组件为例具体说明。
参见图8，该图为本申请实施例六提供的一种光伏发电系统的示意图。
本申请实施例提供的光伏发电系统，包括：至少两个光伏单元和变换器800，每个光伏单元包括一个光伏组件。该变换器的输入端有多个输入口，每个输入口包括正输入端子和负输入端子，光伏单元通过变换器的输入口接入变换器。其中，图中所示的光伏组件804a 1-804a n在变换器800内部通过开关管串联，n为大于或等于2的整数。变换器800包括功率电路802、控制器801和开关管803。
本申请实施例不限定变换器800内部的开关管803的数量，例如变换器800内部开关管803的数量可以为n-1个，则对应变换器800的输入端可以连接n个光伏单元。当然也可以连接比N数量更少的光伏单元，可将不连接光伏单元的输入口的正输入端子和负输入端子对插以实现短路。
关于变换器的具体说明可以参见上述实施例一至实施例四，本实施例在此不再赘述。
本实施例提供的光伏发电系统的变换器的内部包括用于连接光伏单元的开关管，开关管的工作状态由变换器的控制器控制。当变换器的控制器接收到关机指令或者在预设时间段内丢失心跳指令时，控制器控制所有的开关管断开，由于光伏单元通过开关管串联，因此断开所有的开关管后能够将任意两个串联在一起的光伏单元断开连接，而对于每个光伏单元，其输出电压通常小于80V的标准要求电压，因此使得光伏单元形成的光伏阵列内不存在危险高压，提升了光伏发电系统的安全性。
实施例七：
本申请实施例七还提供了另一种光伏发电系统，与实施例六的区别在于，本申请实施例提供的光伏发电系统的功率电路为DC-DC变换电路，且DC-DC变换电路为多个时，多个所述DC-DC变换电路串联在一起形成DC-DC变换电路组串，DC-DC变换电路组串连接在逆变器的输入端。进一步的，DC-DC变换电路组串还可以为多个，多个DC-DC变换电路组串并可以联后连接在逆变器的输入端或分别连接在逆变器输入端的不同输入口，下面结合附图具体说明。
参见图9，该图为本申请实施例七提供的一种光伏发电系统的示意图。
当变换器的功率电路为DC-DC变换电路时，对应的该变换器为DC-DC变换器，图中以902表示，光伏发电系统包括多个DC-DC变换电路即包括了多个DC-DC变换器。
多个光伏单元901连接在DC-DC变换器的输入口，通过DC-DC变换器902内部的开关管串联，相邻两个光伏单元之间均通过开关管连接。
多个DC-DC变换器902输出端相互串联形成DC-DC变换器组串，同时还可以有多个DC-DC变换器组串并联后再接入逆变器905输入端或多个DC-DC变换器组串独立连接在逆变器905输入端的不同输入口，图中以逆变器905接入了两个DC-DC变换器组串，即组串903和组串904为例，组串数量可以根据实际情况设定，不同组串包括的DC-DC变换器的数量可以相同也可以不同，本申请对此均不作具体限定。逆变器905输出端连接到电网906，通常的逆变器905能够实现DC-AC变换功能，将直流电逆变成交流电送入电网906。
本实施例提供的光伏发电系统的变换器的内部包括用于连接光伏单元的开关管，光伏单元在变换器的内部通过开关管串联，开关管的工作状态由变换器的控制器控制。当变换器的控制器接收到关机指令或者在预设时间段内丢失心跳指令时，控制器控制所有的开关管断开，由于光伏单元通过开关管串联，因此断开所有的开关管后能够将任意两个串联在一起的光伏单元断开连接，而对于单个光伏单元，其输出电压通常小于80V的标准要求电压，因此使得光伏单元形成的光伏阵列内不存在危险高压，提升了光伏发电系统的安全性。
具体应用时可以将多个变换器串联形成组串连接在逆变器的输入端，还可以将多个变换器组串并联后连接在逆变器的输入端，由于本申请实施例提供的光伏发电系统的每个变换器在输入端同时连接多个光伏单元时仍能够满足快速关断的标准要求，因 此能够减少该光伏发电系统的变换器的数量，进而有效简化现场接线和降低系统成本。
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，仅是本发明的较佳实施例而已，并非对本发明作任何形式上的限制。虽然本发明已以较佳实施例揭露如上，然而并非用以限定本发明。任何熟悉本领域的技术人员，在不脱离本发明技术方案范围情况下，都可利用上述揭示的方法和技术内容对本发明技术方案做出许多可能的变动和修饰，或修改为等同变化的等效实施例。因此，凡是未脱离本发明技术方案的内容，依据本发明的技术实质对以上实施例所做的任何简单修改、等同变化及修饰，均仍属于本发明技术方案保护的范围内。

Claims (14)

  1. 一种用于光伏发电系统的变换器，其特征在于，包括：控制器和至少一个开关管；
    所述变换器支持至少两个光伏单元接入，所述至少两个光伏单元在变换器内部通过所述开关管串联；所述光伏单元为至少一个光伏组件通过串并联形成；
    所述控制器，用于在接收到关机指令或者在预设时间段内丢失心跳指令时，控制所述开关管断开以使任意两个串联在一起的所述光伏单元断开连接。
  2. 根据权利要求1所述的变换器，其特征在于，所述控制器，还用于当收到开机指令且收到所述心跳指令时，控制所述开关管闭合。
  3. 根据权利要求2所述的变换器，其特征在于，还包括：功率电路，所述功率电路为直流-直流变换电路、直流-交流变换电路或通断控制电路。
  4. 根据权利要求3所述的变换器，其特征在于，所述控制器，还用于在接收到所述关机指令或者在预设时间段内丢失所述心跳指令时，控制所述功率电路停止功率变换，或，限制所述功率电路的输出电压小于预设电压值，或，限制所述功率电路的输出电流小于预设电流值。
  5. 根据权利要求4所述的变换器，其特征在于，所述控制器，还用于当收到所述开机指令且收到所述心跳指令时，控制所述功率电路恢复功率变换，或，解除对所述功率电路的所述输出电压的限制，或，解除对所述功率电路的所述输出电流的限制。
  6. 根据权利要求3所述的变换器，其特征在于，当所述功率电路为直流-直流变换电路时，所述直流-直流变换电路为升压电路、降压电路或升降压电路。
  7. 根据权利要求6所述的变换器，其特征在于，还包括：通信单元；
    所述通信单元，用于接收来自上一级的控制信号，并将所述控制信号转发给所述控制器；所述控制信号包括：所述心跳指令、所述开机指令和所述关机指令。
  8. 根据权利要7所述的变换器，其特征在于，还包括：辅助电源；
    其中一个所述光伏单元与所述辅助电源连接为所述辅助电源供电；
    所述辅助电源为所述控制器和所述通信单元供电。
  9. 根据权利要求1-8任一项所述的变换器，其特征在于，所述开关管为以下任意一种：继电器、晶体三极管、绝缘栅双极型晶体管和金属氧化物半导体场效应晶体管。
  10. 一种变换器的控制方法，其特征在于，所述变换器应用于光伏发电系统，所述变换器包括：控制器和至少一个开关管；所述变换器支持至少两个光伏单元接入，所述至少两个光伏单元在变换器内部通过所述开关管串联；所述光伏单元为至少一个光伏组件通过串并联形成；所述方法包括：
    在接收到关机指令或者在预设时间段内丢失心跳指令时，控制所述开关管断开以使任意两个串联在一起的所述光伏单元断开连接。
  11. 根据权利要求10所述的控制方法，其特征在于，还包括：
    当收到开机指令且收到所述心跳指令时，控制所述开关管闭合。
  12. 一种光伏发电系统，其特征在于，包括：至少两个光伏单元和权利要求1-9 任一项所述的变换器；
    至少两个所述光伏单元接入所述变换器；
    至少两个所述光伏单元在所述变换器内部通过所述开关管串联，所述光伏单元为至少一个光伏组件通过串并联形成。
  13. 根据权利要求12所述的系统，其特征在于，还包括：功率电路，当所述功率电路为直流-直流变换电路，且所述直流-直流变换电路为多个时，多个所述直流-直流变换电路串联在一起形成直流-直流变换电路组串，所述直流-直流变换电路组串连接在逆变器的输入端；
    所述逆变器，用于将所述直流-直流变换电路组串输出的直流电变换为交流电后进行输出。
  14. 根据权利要求13所述的系统，其特征在于，所述直流-直流变换电路组串为多个；
    多个所述直流-直流变换电路组串并联后连接在所述逆变器的输入端，或者独立连接在逆变器输入端的不同输入口。
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