WO2024067317A1 - 光伏系统和光伏系统的电路保护方法 - Google Patents

光伏系统和光伏系统的电路保护方法 Download PDF

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Publication number
WO2024067317A1
WO2024067317A1 PCT/CN2023/120195 CN2023120195W WO2024067317A1 WO 2024067317 A1 WO2024067317 A1 WO 2024067317A1 CN 2023120195 W CN2023120195 W CN 2023120195W WO 2024067317 A1 WO2024067317 A1 WO 2024067317A1
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WIPO (PCT)
Prior art keywords
conversion circuit
protection switch
voltage
input voltage
active protection
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Application number
PCT/CN2023/120195
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English (en)
French (fr)
Inventor
戚鑫
徐志武
张秀锋
Original Assignee
华为数字能源技术有限公司
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Publication of WO2024067317A1 publication Critical patent/WO2024067317A1/zh

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/20—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for electronic equipment
    • 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
    • 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 field of photovoltaic power generation technology, and in particular to a photovoltaic system and a circuit protection method for the photovoltaic system.
  • photovoltaic systems are evolving towards higher power.
  • the increase in photovoltaic system power will also lead to a continuous increase in safety risks. If timely and effective protection is not provided, it may not only cause the photovoltaic components or inverters in the photovoltaic system to burn out, but also easily cause single point failures to spread and cause more serious accidents.
  • a protective device can be installed in the photovoltaic system, which can cut off the energy input of the photovoltaic module when a fault occurs.
  • the protective device may fail to cut off the circuit due to mechanical failure, which will bring safety hazards to the photovoltaic system.
  • the present application provides a photovoltaic system and a circuit protection method for the photovoltaic system, which can eliminate the reverse current in the photovoltaic system through further protection measures when it is detected that the protection device is not effectively disconnected, avoid burning and fault spread in the photovoltaic system, thereby improving the safety and reliability of the photovoltaic system.
  • the present application provides a photovoltaic system, including an active protection switch, a DC-DC conversion circuit and a controller; one end of the active protection switch is used to connect to a photovoltaic component, and the other end is connected to an input end of the DC-DC conversion circuit, and an output end of the DC-DC conversion circuit is used to connect to a load; the controller is used to send a disconnection instruction to the active protection switch to trigger the disconnection of the active protection switch according to the input voltage of the DC-DC conversion circuit when the reverse current of the photovoltaic component is greater than or equal to a current threshold, and to adjust the input voltage of the DC-DC conversion circuit to less than or equal to a first voltage threshold when the active protection switch is not effectively disconnected within a preset time after the disconnection instruction is sent to the active protection switch.
  • the photovoltaic system of this solution can further determine the fault scenario through the input voltage of the DC-DC conversion circuit when reverse current is detected. After determining the fault scenario, the circuit can be protected by disconnecting the active protection. When the active protection switch fails to disconnect, further protection measures can be taken - reducing the input voltage of the DC-DC conversion circuit to eliminate the reverse current in the photovoltaic system, avoid burning and fault spread in the photovoltaic system, and thus improve the safety and reliability of the photovoltaic system.
  • the controller is used to detect that the active protection switch is not effectively disconnected when it is detected that the current of the DC-DC conversion circuit is greater than or equal to the critical value.
  • This solution can determine whether the active protection switch is effectively disconnected by detecting the current of the DC-DC conversion circuit, and has a simple design, easy mass production, and high reliability.
  • the controller is used to adjust the input voltage of the DC-DC conversion circuit to be greater than 0 and less than or equal to a first voltage threshold, and when it is detected that the current of the DC-DC conversion circuit is greater than or equal to a critical value, it is detected that the active protection switch is not effectively disconnected.
  • the DC-DC conversion circuit is in a state close to short circuit but not short circuit. It can not only detect whether the active protection switch is effectively disconnected, but also maintain the output voltage of the DC-DC conversion circuit at a certain value, so as to supply power to the load in the photovoltaic inverter (the load may include a heat sink, which can work under the drive of electric energy to maintain the heat dissipation performance of the photovoltaic inverter), so that the photovoltaic inverter does not need additional power supply, thereby simplifying the design and reducing costs.
  • the controller is used to control the switch device of the DC-DC conversion circuit to remain normally on, and when it is detected that the current of the DC-DC conversion circuit is greater than or equal to the critical value, it is detected that the active protection switch is not effectively disconnected.
  • the judgment logic of this solution is simple, easy to mass produce, and has high reliability.
  • the active protection switch is used to generate a contact position feedback signal; the controller is used to detect that the active protection switch is not effectively disconnected when the contact position feedback signal is detected to be a target signal.
  • the circuit design and judgment logic of this solution are relatively simple, easy to mass produce, and highly reliable.
  • the controller is used to detect that the active protection switch is not effectively disconnected when the input voltage of the DC-DC circuit is greater than or equal to the second voltage threshold.
  • This solution can determine whether the active protection switch is effectively disconnected by detecting the input voltage of the DC-DC conversion circuit, and has a simple design, easy mass production, and high reliability.
  • the controller is used to adjust the input voltage of the DC-DC conversion circuit to a level greater than 0 and less than or equal to a first voltage threshold when it is detected that the active protection switch is not effectively disconnected.
  • the DC-DC conversion circuit is in a state close to short circuit but not short circuit, which can not only reduce the reverse current flowing through the photovoltaic module, but also maintain the output voltage of the DC-DC conversion circuit at a certain value, so as to supply power to the load in the photovoltaic inverter (the load may include a heat sink, which can work under the drive of electric energy to maintain the heat dissipation performance of the photovoltaic inverter), so that the photovoltaic inverter does not need additional power supply, thereby simplifying the design and reducing costs.
  • the controller is used to control the DC-DC conversion circuit to generate a target output voltage so that the input voltage of the DC-DC conversion circuit is greater than 0 and less than or equal to a first voltage threshold.
  • This solution adjusts the input voltage of the DC-DC conversion circuit by controlling the output voltage of the DC-DC conversion circuit, and has a relatively simple design and good mass production performance.
  • the controller is used to control the switch device of the DC-DC conversion circuit to remain normally on when it is detected that the active protection switch is not effectively disconnected.
  • the DC-DC conversion circuit can be in a short-circuit state, and the input voltage of the DC-DC conversion circuit can be reduced to 0.
  • This solution puts the DC-DC conversion circuit in a short-circuit state, which can reduce the reverse current flowing through the photovoltaic unit.
  • the controller is also used to send a disconnection instruction to the active protection switch when the reverse current of the photovoltaic component is greater than or equal to the current threshold and the input voltage of the DC-DC conversion circuit is less than a fourth voltage threshold; or, the controller is used to send a disconnection instruction to the active protection switch when the reverse current of the photovoltaic component is greater than or equal to the current threshold, the input voltage of the DC-DC conversion circuit is greater than or equal to the fourth voltage threshold, and when it is detected that the reverse current is greater than the current threshold after a set time period.
  • the controller can determine the fault scenario based on the reverse current and the input voltage.
  • the controller determines that a reverse polarity fault has occurred.
  • the controller sends a disconnection instruction to the active protection switch to perform a disconnection protection action to reduce the reverse current.
  • the controller determines that an open circuit voltage inconsistency fault has occurred.
  • the controller can determine the waiting time and continue to detect the reverse current during the waiting time. If the controller detects that the reverse current has not disappeared after the waiting time, the disconnection protection action is performed.
  • This solution can identify different fault scenarios based on reverse current and input voltage, and take different protection actions for different fault scenarios.
  • the controller is used to adjust the input voltage of the DC-DC conversion circuit to less than or equal to the first voltage threshold when the reverse current of the photovoltaic component is greater than or equal to the current threshold and the input voltage of the DC-DC conversion circuit is greater than or equal to the third voltage threshold, and send a disconnection instruction to the active protection switch, wherein the third voltage threshold is greater than the first voltage threshold.
  • the controller determines that the input voltage is greater than or equal to the third voltage threshold, the voltage difference across the contacts of the active protection switch will be large, which may cause arcing when the active protection switch is disconnected, causing the contacts of the active protection switch to stick together, making it impossible for the active protection switch to be successfully disconnected. Therefore, when it is determined that the input voltage is greater than or equal to the third voltage threshold, the input voltage is reduced to less than or equal to the first voltage threshold, and after the input voltage is reduced, a disconnection instruction is issued to control the active protection switch to disconnect. After the input voltage is reduced to the first voltage threshold, the voltage difference across the contacts of the active protection switch can be reduced, reducing the arcing energy, which is conducive to the smooth disconnection of the active protection switch.
  • the photovoltaic system includes a current sensor, which is used to detect the reverse current of the photovoltaic unit and send the magnitude of the reverse current to the controller; and/or the photovoltaic system includes a voltage sensor, which is used to detect the input voltage of the DC-DC conversion circuit and send the detection result to the controller.
  • the use of sensors can simplify the circuit design.
  • the load includes a DC-AC conversion circuit, and the DC-AC conversion circuit connects the output end of the DC-DC conversion circuit to the power grid.
  • the photovoltaic system of this solution can be connected to the power grid, and because the photovoltaic system can more reliably eliminate reverse current, it can prevent faults in the photovoltaic system from spreading to the power grid.
  • the present application provides a circuit protection method for a photovoltaic system, wherein the photovoltaic system includes an active protection switch, a DC-DC conversion circuit and a controller; one end of the active protection switch is used to connect the photovoltaic component, and the other end is connected to the input end of the DC-DC conversion circuit, and the output end of the DC-DC conversion circuit is used to connect the load;
  • the circuit protection method includes: when the reverse current of the photovoltaic component is greater than or equal to the current threshold, according to the input voltage of the DC-DC conversion circuit, a disconnection instruction is sent to the active protection switch, and the disconnection instruction is used to trigger the active protection switch to disconnect; when the active protection switch is not effectively disconnected within a preset time after the disconnection instruction is sent to the active protection switch, the input voltage of the DC-DC conversion circuit is adjusted to be less than or equal to the first voltage threshold.
  • the circuit protection method of this solution can further determine the fault scenario through the input voltage of the DC-DC conversion circuit when reverse current is detected. After determining the fault scenario, circuit protection can be performed by disconnecting active protection. When the active protection switch fails to disconnect, further protection measures can be taken - reducing the input voltage of the DC-DC conversion circuit to eliminate the reverse current in the photovoltaic system, avoid burning and fault spread in the photovoltaic system, and thus improve the safety and reliability of the photovoltaic system.
  • detecting that the active protection switch is not effectively disconnected includes: detecting that the current of the DC-DC conversion circuit is greater than or equal to the critical value. This solution can determine whether the active protection switch is effectively disconnected by detecting the current of the DC-DC conversion circuit. It has simple design, easy mass production and high reliability.
  • detecting that the active protection switch is not effectively disconnected includes: adjusting the input voltage of the DC-DC conversion circuit to be greater than 0 and less than or equal to a first voltage threshold; detecting that the current of the DC-DC conversion circuit is greater than or equal to a critical value.
  • the DC-DC conversion circuit is in a state close to short circuit but not short circuit. It can not only detect whether the active protection switch is effectively disconnected, but also maintain the output voltage of the DC-DC conversion circuit at a certain value, so as to supply power to the load in the photovoltaic inverter (the load may include a heat sink, which can work under the drive of electric energy to maintain the heat dissipation performance of the photovoltaic inverter), so that the photovoltaic inverter does not need additional power supply, thereby simplifying the design and reducing costs.
  • detecting that the active protection switch is not effectively disconnected includes: controlling the switch device of the DC-DC conversion circuit to remain normally on; detecting that the current of the DC-DC conversion circuit is greater than or equal to a critical value.
  • detecting that the active protection switch is not effectively disconnected includes: detecting that the contact position feedback signal generated by the active protection switch is a target signal.
  • “detecting that the active protection switch is not effectively disconnected” includes: detecting that the input voltage of the DC-DC circuit is greater than or equal to the second voltage threshold. This solution can determine whether the active protection switch is effectively disconnected by detecting the input voltage of the DC-DC conversion circuit, has a simple design, is easy to mass produce, and has high reliability.
  • adjusting the input voltage of the DC-DC conversion circuit to be less than or equal to the first voltage threshold includes: adjusting the input voltage of the DC-DC conversion circuit to be greater than 0 and less than or equal to the first voltage threshold.
  • the DC-DC conversion circuit is in a state close to short circuit but not short circuit, which can not only reduce the reverse current flowing through the photovoltaic module, but also maintain the output voltage of the DC-DC conversion circuit at a certain value, so as to supply power to the load in the photovoltaic inverter (the load may include a heat sink, which can work under the drive of electric energy to maintain the heat dissipation performance of the photovoltaic inverter), so that the photovoltaic inverter does not need additional power supply, thereby simplifying the design and reducing costs.
  • “adjusting the input voltage of the DC-DC conversion circuit to be greater than 0 and less than or equal to the first voltage threshold” includes: controlling the DC-DC conversion circuit to generate a target output voltage so that the input voltage of the DC-DC conversion circuit is greater than 0 and less than or equal to the first voltage threshold.
  • This solution adjusts the input voltage of the DC-DC conversion circuit by controlling the output voltage of the DC-DC conversion circuit, and has a relatively simple design and good mass production performance.
  • "adjusting the input voltage of the DC-DC conversion circuit to be less than or equal to the first voltage threshold” includes: controlling the switch device of the DC-DC conversion circuit to remain normally on.
  • the DC-DC conversion circuit can be in a short-circuit state, and the input voltage of the DC-DC conversion circuit can be reduced to 0.
  • This solution puts the DC-DC conversion circuit in a short-circuit state, which can reduce the reverse current flowing through the photovoltaic unit.
  • "issuing a disconnection instruction to the active protection switch based on the input voltage of the DC-DC conversion circuit” includes: detecting whether the input voltage of the DC-DC conversion circuit is greater than or equal to a fourth voltage threshold; when the input voltage is less than the fourth voltage threshold, issuing a disconnection instruction to the active protection switch; when the input voltage is greater than or equal to the fourth voltage threshold, and when it is detected that the reverse current is greater than the current threshold after a set time period, issuing a disconnection instruction to the active protection switch.
  • the fault scenario can be determined based on the reverse current and the input voltage.
  • the input voltage is less than the fourth voltage threshold, it can be determined that a reverse polarity fault has occurred.
  • a disconnection instruction is sent to the active protection switch to execute a disconnection protection action to reduce the reverse current.
  • the input voltage is greater than or equal to the fourth voltage threshold, it can be determined that an open circuit voltage inconsistency fault has occurred.
  • the waiting time can be determined, and the reverse current can be continuously detected during the waiting time. If it is detected that the reverse current has not disappeared after the waiting time, the disconnection protection action is performed.
  • This solution can identify different fault scenarios based on the reverse current and the input voltage, and take different protection actions for different fault scenarios.
  • "issuing a disconnection instruction to the active protection switch” includes: detecting whether the input voltage of the DC-DC conversion circuit is greater than or equal to a third voltage threshold, wherein the third voltage threshold is greater than the first voltage threshold; when the input voltage is greater than or equal to the third voltage threshold, adjusting the input voltage of the DC-DC conversion circuit to less than or equal to the first voltage threshold, and issuing a disconnection instruction to the active protection switch; when the input voltage is less than the third voltage threshold, issuing a disconnection instruction to the active protection switch.
  • the controller determines that the input voltage is greater than or equal to the third voltage threshold, the voltage difference across the contacts of the active protection switch will be large, which may cause arcing when the active protection switch is disconnected, causing the contacts of the active protection switch to stick together, making it impossible for the active protection switch to disconnect successfully. Therefore, when it is determined that the input voltage is greater than or equal to the third voltage threshold, the input voltage is reduced to less than or equal to the first voltage threshold, and after the input voltage is reduced, a disconnection instruction is issued to control the active protection switch to disconnect. After the input voltage is reduced to the first voltage threshold, The voltage difference between the two ends of the contact of the active protection switch can be reduced, the arc energy can be reduced, and it is beneficial to make the active protection switch disconnect smoothly.
  • FIG1 is a schematic diagram of a circuit framework structure of a photovoltaic system according to an embodiment of the present application
  • FIG. 2 is a schematic diagram showing a circuit framework structure of a reverse polarity fault
  • FIG3 is a schematic diagram of a circuit framework structure showing an open circuit voltage inconsistency fault
  • FIG4 is a flow chart of the overall circuit protection method according to an embodiment of the present application.
  • FIG5 is a flowchart of the fault detection scenario portion of the circuit protection method in FIG4 ;
  • FIG6 is a flowchart of the circuit protection method of FIG4 for performing a disconnection protection portion
  • FIG. 7 is a flowchart of the redundant protection part of the circuit protection method in FIG. 4;
  • FIG8 shows the current situation after the circuit protection method of the embodiment of the present application is applied to a photovoltaic system with a reverse polarity fault
  • FIG. 9 shows the current situation after the circuit protection method of the embodiment of the present application is applied to a photovoltaic system that has an open circuit voltage inconsistency fault.
  • a and/or B can represent: A exists alone, A and B exist at the same time, and B exists alone.
  • Photovoltaic system is a power generation system that uses photovoltaic modules to directly convert solar energy into electrical energy. It can include photovoltaic strings, batteries, controllers and photovoltaic inverters. Among them, photovoltaic modules refer to the smallest indivisible photovoltaic cell combination device that can provide direct current output independently. Photovoltaic strings include multiple photovoltaic modules combined in series or/and parallel.
  • FIG1 illustrates a framework structure of a photovoltaic system 10 of an embodiment of the present application.
  • the photovoltaic system 10 may include a plurality of photovoltaic units 101 and a photovoltaic inverter 11, and the plurality of photovoltaic units 101 are connected in parallel to the photovoltaic inverter 11.
  • the photovoltaic inverter 11 may include a plurality of branch current sensors 102, an active protection switch 103, a combined current sensor 104, an input voltage sensor 105, a direct current-to-direct current (DC-DC) conversion circuit 106, an output voltage sensor 107, a direct current-to-alternating current (DC-AC) conversion circuit 108, and a controller 109.
  • DC-DC direct current-to-direct current
  • DC-AC direct current-to-alternating current
  • the photovoltaic inverter 11 may also be considered as a photovoltaic system, the photovoltaic unit 101 may not be a device in the photovoltaic system 10, and the photovoltaic unit 101 is connected to the photovoltaic system (referring to the photovoltaic inverter 11).
  • the photovoltaic unit 101 may be formed by connecting a component in series or in parallel.
  • the photovoltaic units 101 appear in parallel in this figure and can also be connected in series in some embodiments.
  • the specific connection method of the photovoltaic units 101 is not a specific implementation method of the present application. Those skilled in the art can combine multiple photovoltaic components in series and parallel according to the input requirements of the photovoltaic inverter 11 to obtain the required input voltage.
  • the photovoltaic unit 101 may be labeled as PV.
  • the photovoltaic unit 101 may be the photovoltaic string mentioned above, or may be a photovoltaic array formed by connecting a plurality of photovoltaic strings in parallel, or may be a single photovoltaic module in some embodiments.
  • the number of photovoltaic units 101 may be configured as required, and may be at least one.
  • FIG. 1 schematically illustrates a plurality of photovoltaic units 101, and the plurality of photovoltaic units 101 are connected in parallel to form a plurality of branches.
  • each photovoltaic unit 101 is connected in series with an active protection switch 103, and the other end of the active protection switch 103 is connected in parallel to the input end of the DC-DC conversion circuit 106, so that multiple photovoltaic units 101 are connected to the input end of the DC-DC conversion circuit 106 through the active protection switch 103.
  • the active protection switch 103 there may be only one active protection switch 103, which has a built-in motion mechanism and multiple contacts.
  • One photovoltaic unit 101 is connected to a group of contacts in the active protection switch 103.
  • the motion mechanism can control the multiple contacts to act simultaneously to achieve simultaneous connection or disconnection of all photovoltaic units 101 and the active protection switch 103.
  • the active protection switch 103 has an active disconnection performance and can actively disconnect the circuit based on current, voltage and other information.
  • the active protection switch 103 can be, for example, a DC trip switch or a DC circuit breaker.
  • the number of branch current sensors 102 is consistent with the number of photovoltaic units 101, and one photovoltaic unit 101 can correspond to one branch current sensor 102.
  • the branch current sensor 102 can be connected in series with the photovoltaic unit 101 and arranged in a branch where the photovoltaic unit 101 is located.
  • the branch current sensor 102 can be arranged between the parallel point of the active protection switch 103 (i.e., the parallel position of multiple contacts of the active protection switch 103, which is connected to the input end of the DC-DC conversion circuit 106) and the photovoltaic unit 101.
  • the branch current sensor 102 is used to detect the current (which can be called the branch current) of the photovoltaic unit 101 connected in series with it, and each branch current detected by each branch current sensor 102 can be marked as Idc1, Idc2...Idcn in sequence.
  • the combined current sensor 104 can be connected in series with the parallel point of the active protection switch 103 and can be located between the parallel point and the DC-DC conversion circuit 106.
  • the combined current sensor 104 is used to detect the total current (which can be called the total current) of all photovoltaic units 101 connected in parallel.
  • the combined current detected by the combined current sensor 104 may be denoted as Idc.
  • the input voltage sensor 105 may be located at the input end of the DC-DC conversion circuit 106, for example, between the parallel point of the active protection switch 103 and the DC-DC conversion circuit 106.
  • the input voltage sensor 105 is used to detect the input voltage of the DC-DC conversion circuit 106.
  • the input voltage detected by the input voltage sensor 105 may be denoted as Vin.
  • the input voltage is also equal to the voltage across the photovoltaic unit 101 of each branch.
  • the output voltage sensor 107 may be located at the output end of the DC-DC conversion circuit 106, and is used to detect the output voltage of the DC-DC conversion circuit 106.
  • the output end of the DC-DC conversion circuit 106 may be connected to the DC-AC conversion circuit 108 via a DC bus (labeled as BUS), so the output voltage detected by the output voltage sensor 107 may be labeled as Vbus.
  • BUS DC bus
  • the DC-DC conversion circuit 106 may be an independent device, such as a DC-DC converter, or a circuit module in a system.
  • the DC-AC conversion circuit 108 can connect the output end of the DC-DC conversion circuit 106 to the AC grid Grid.
  • the photovoltaic system 10 can input the converted electric energy into the AC grid.
  • the DC-AC conversion circuit 108 and the AC power grid can both be referred to as AC loads, that is, the output end of the DC-DC conversion circuit 106 is connected to the AC load.
  • the load in addition to the AC load described above, the load can also be other DC-DC conversion devices, energy storage devices (such as batteries) and other DC loads. Therefore, in summary, the output end of the DC-DC conversion circuit 106 is connected to a load, and the load includes but is not limited to AC loads such as the DC-AC conversion circuit 108 and the AC power grid, and DC loads such as other DC-DC conversion devices and energy storage devices.
  • the DC-AC conversion circuit 108 may be an independent device, such as a DC-AC converter, or a circuit module in the system.
  • the DC-DC conversion circuit 106 and the DC-AC conversion circuit 108 can be used as components of a photovoltaic inverter, and the photovoltaic inverter is a two-stage architecture, the DC-DC conversion circuit 106 is the front stage, and the DC-AC conversion circuit 108 is the back stage.
  • the photovoltaic system may not contain the DC-AC conversion circuit 108.
  • the photovoltaic system may not have the DC-AC conversion circuit 108. In such a photovoltaic system without the DC-AC conversion circuit 108, there is no photovoltaic inverter.
  • the controller 109 can be electrically connected to each branch current sensor 102, active protection switch 103, combined current sensor 104, input voltage sensor 105, DC-DC conversion circuit 106, and output voltage sensor 107 to obtain the signals detected by them, determine their working status, control them to work, etc.
  • the controller 109 can coordinate the work of each component according to the functional requirements of the instruction, and is the nerve center and command center of the photovoltaic system 10 (to be described below).
  • the controller 109 may be composed of components such as an instruction register (IR), a program counter (PC), and an operation controller (OC).
  • the controller 109 may refer to one or more devices, circuits, and/or processing cores for processing data (e.g., computer program instructions).
  • the controller 109 may be a processor or a general term for multiple processing elements.
  • the processor may be a general central processing unit (CPU) or an application-specific integrated circuit (ASIC).
  • the processor may be one or more integrated circuits for controlling the execution of the program of the present application, such as one or more microprocessors (digital signal processors, DSPs); or one or more field programmable gate arrays (field programmable gate arrays, FPGAs).
  • sensors such as branch current sensor 102, combined current sensor 104, input voltage sensor 105, and output voltage sensor 107 are used to flexibly select sensors with corresponding sampling current range or sampling voltage range according to the specifications of PV, so that the photovoltaic system 10 can be flexibly deployed and constructed.
  • the sampling circuit built into the controller can also be used to realize the sampling function of sensors such as branch current sensor 102, combined current sensor 104, input voltage sensor 105, and output voltage sensor 107. In this case, there is no need to additionally arrange sensors such as branch current sensor 102, combined current sensor 104, input voltage sensor 105, and output voltage sensor 107. This solution can simplify the circuit.
  • the photovoltaic inverter 11 includes a branch current sensor 102, an active protection switch 103, a combined current sensor 104, an input voltage sensor 105, a DC-DC conversion circuit 106, an output voltage sensor 107, a DC-AC conversion circuit 108 and a controller 109, which is only an example.
  • the photovoltaic inverter may include a DC-DC conversion circuit and a DC-AC conversion circuit, but does not have at least one of the branch current sensor 102, the active protection switch 103, the combined current sensor 104, the input voltage sensor 105, the output voltage sensor 107 and the controller 109 built in, that is, at least one of the branch current sensor 102, the active protection switch 103, the combined current sensor 104, the input voltage sensor 105, the output voltage sensor 107 and the controller 109 can be independent of the photovoltaic inverter.
  • the branch current sensor 102 can detect the current of the photovoltaic unit 101 and send the detection result to the controller 109.
  • the controller 109 judges the detection result and can determine whether the reverse current is greater than or equal to the current threshold.
  • FIG2 shows a fault scenario in which a large reverse current is caused by the reverse polarity connection of the photovoltaic unit 101, in which the circuit connection between the five photovoltaic units 101 and the photovoltaic inverter 11 is schematically drawn.
  • the five photovoltaic units 101 are connected in parallel to the photovoltaic inverter 11, and the polarity of the first four photovoltaic units 101 is correctly connected to the polarity of the photovoltaic inverter 11 (positive pole connected to positive pole, negative pole connected to negative pole), and the polarity of the fifth photovoltaic unit 101 is reversed to the polarity of the photovoltaic inverter 11 (negative pole connected to positive pole, positive pole connected to negative pole).
  • the current of each photovoltaic unit 101 in the first four photovoltaic units 101 is marked as Idc. Since the polarity of the fifth photovoltaic unit 101 is reversed, the fifth photovoltaic unit 101 is short-circuited, so the current of the first four photovoltaic units 101 will flow into the fifth photovoltaic unit 101 (this current is called reverse current, and the reverse current can be 4*Idc), and will not flow into the photovoltaic inverter 11 (this phenomenon is called current backflow). Therefore, the current direction of the fifth photovoltaic unit 101 is opposite to the current direction of the first four photovoltaic units 101, and the current of the fifth photovoltaic unit 101 is larger. This is a reverse current fault caused by reverse polarity connection.
  • the input voltage detected by the input voltage sensor 105 is relatively small.
  • FIG3 shows a fault scenario in which a large reverse current is caused by inconsistent open-circuit voltages of the photovoltaic units 101, wherein the circuit connection between five photovoltaic units 101 and the photovoltaic inverter 11 is schematically drawn. As shown in FIG3 , the five photovoltaic units 101 are connected in parallel to the photovoltaic inverter 11, and the polarity of each photovoltaic unit 101 is correctly connected to the polarity of the photovoltaic inverter 11.
  • the number of photovoltaic cells connected in series in the first four photovoltaic cells 101 is the same, so that the open circuit voltages of the first four photovoltaic cells 101 are consistent (the open circuit voltage is the voltage when the branch is open and no current is output); the number of photovoltaic cells connected in series in the fifth photovoltaic cell 101 is less than the number of photovoltaic cells connected in series in other photovoltaic cells 101, that is, the number of photovoltaic cells connected in series in the fifth photovoltaic cell 101 is the least, which causes the current of the photovoltaic cells 101 of the first four branches to flow into the fifth photovoltaic cell 101 (this current is called reverse current, and the reverse current may depend on the difference in open circuit voltage between the photovoltaic cells 101 of the first four branches and the fifth photovoltaic cell 101), and will not flow into the photovoltaic inverter 11 (current backflow occurs). Therefore, the current direction of the fifth photovoltaic cell 101 is opposite to that of the first four photovoltaic cells 101
  • the input voltage detected by the input voltage sensor 105 is larger. Therefore, for the reverse current fault of reverse polarity connection and the reverse current fault of inconsistent open circuit voltage, the input voltage corresponding to the former fault is smaller than the input voltage corresponding to the latter fault.
  • the photovoltaic system 10 of this embodiment can detect reverse current, determine the fault scenario corresponding to the reverse current, and perform corresponding actions for different fault scenarios, thereby reducing or eliminating the reverse current, avoiding the burning of the faulty photovoltaic unit 101, preventing the spread of the fault, and ultimately improving the safety and reliability of the photovoltaic system. This will be described in detail below.
  • this embodiment provides a photovoltaic system circuit protection method 20, which can be applied to the photovoltaic system 10.
  • the circuit protection method 20 may include the following functional parts: detecting fault scenarios, performing disconnection protection, and performing redundant protection. Each of these will be described in detail below.
  • FIG5 may illustrate a flowchart of a fault detection scenario. As shown in FIG5 , the fault detection scenario may include the following steps:
  • step 201 When the reverse current is less than the current threshold, the process returns to step 201; when the reverse current is greater than or equal to the current threshold, the process proceeds to step 202;
  • step 203 When the input voltage is less than the fourth voltage threshold, step 203 is executed; when the input voltage is greater than or equal to the fourth voltage threshold, step 204 is executed;
  • step 201 When it is detected that the reverse current is less than the current threshold after the waiting time has passed, step 201 is executed; when it is detected that the reverse current is greater than or equal to the current threshold after the waiting time has passed, step 203 is executed.
  • step 201 the controller 109 can control each branch current sensor 102 to detect the current of each branch, and determine whether each branch has a reverse current greater than or equal to a current threshold value according to the detection results of each branch current sensor 102.
  • the current threshold value can be determined according to the current tolerance of the photovoltaic unit 101. For example, the current threshold value can be less than or equal to the current tolerance value of the photovoltaic unit 101.
  • FIG5 when the judgment result of step 201 is YES, it indicates that a fault that requires a protection action to be executed has occurred in a branch.
  • the judgment result is NO, indicating that there is no reverse current or the reverse current does not exceed the current tolerance value, and there is no need to perform protection action immediately.
  • the controller 109 when the controller 109 detects a reverse current greater than or equal to the current threshold, the controller 109 can control the input voltage sensor 105 to detect the input voltage of the DC-DC conversion circuit 106, and determine whether the input voltage is greater than or equal to the fourth voltage threshold according to the detection result of the input voltage sensor 105.
  • the fourth voltage threshold can be determined according to the configuration of the photovoltaic unit 101, which can be equal to the upper limit of the voltage displayed to the outside when the photovoltaic unit 101 generates a reverse current. As described above, the input voltage corresponding to the inconsistent open circuit voltage is larger, and the input voltage corresponding to the reverse polarity is smaller. Therefore, when the judgment result of step 202 is YES, indicating that the fault is the inconsistent open circuit voltage, step 204 is executed; if the judgment result of step 202 is NO, indicating that the fault is the reverse polarity, step 203 is executed.
  • step 203 when the controller 109 determines that the fault scenario is reverse polarity connection, the controller 109 may perform a disconnection protection action.
  • the execution of the disconnection protection action will be further described below.
  • step 204 when the controller 109 determines that the fault scenario is that the open circuit voltage is inconsistent, the controller 109 can determine the waiting time and continuously detect the reverse current during the waiting time.
  • the controller 109 can calculate the waiting time according to the built-in strategy. Based on the strategy, a larger reverse current can correspond to a shorter waiting time, and a smaller reverse current can correspond to a longer waiting time. If the controller 109 detects that the reverse current has not disappeared after the waiting time, the controller 109 performs a disconnection protection action; if the controller 109 detects that the reverse current has disappeared after the waiting time, the controller returns to step 201.
  • the voltage of the photovoltaic system 10 during grid-connected operation is reduced to the maximum power point tracking (MPPT) window (in the P-V curve, the voltage interval corresponding to the maximum power point is determined, and the voltage interval can be referred to as the MPPT window), or after the shadow blocking the photovoltaic unit 101 disappears, the reverse current may disappear.
  • MPPT maximum power point tracking
  • the fault scenario detection part in the circuit protection method 20 can identify different fault scenarios according to the reverse current and the input voltage, and take different protection actions for different fault scenarios.
  • FIG6 is a flowchart of a disconnection protection part. As shown in FIG6, the disconnection protection part may include the following steps:
  • 301 Detect whether an input voltage of a DC-DC conversion circuit is greater than or equal to a third voltage threshold, where the third voltage threshold is greater than the first voltage threshold;
  • step 302 When the input voltage is greater than or equal to the third voltage threshold, execute step 302 and then execute step 303; when the input voltage is less than the third voltage threshold, execute step 303;
  • step 302 reducing the input voltage to a level less than or equal to a first voltage threshold
  • step 303 issuing a disconnection instruction.
  • the scheme of this embodiment detects the input voltage and performs corresponding protection actions based on the detection results. This will be explained below.
  • the controller 109 may control the input voltage sensor 105 to detect the input voltage of the DC-DC conversion circuit 106, and determine whether the input voltage is greater than or equal to a third voltage threshold according to the detection result of the input voltage sensor 105.
  • the third voltage threshold is related to the specification of the active protection switch 103 and may be determined according to the breaking capacity of the active protection switch 103.
  • the third voltage threshold may be equal to the upper limit of the working voltage of the active protection switch 103.
  • the third voltage threshold is independent of the fourth voltage threshold described above, and the third voltage threshold may be greater than the first voltage threshold to be described below.
  • the controller 109 determines that the input voltage is greater than or equal to the third voltage threshold, the controller 109 reduces the input voltage to less than or equal to the first voltage threshold, and after the input voltage is reduced, issues a disconnection instruction to control the active protection switch 103 to disconnect.
  • the first voltage threshold can be determined according to the configuration of the photovoltaic unit 101.
  • the first voltage threshold can be less than, equal to, or greater than the lower limit of the voltage displayed to the outside when the photovoltaic unit 101 generates a reverse current.
  • the first voltage threshold and the lower limit can be slightly different.
  • the first voltage threshold is less than the third voltage threshold.
  • the voltage difference across the contacts of the active protection switch 103 can be reduced, and the arcing energy can be reduced, which is conducive to the smooth disconnection of the active protection switch 103.
  • the controller 109 may directly issue a disconnection instruction to control the active protection switch 103 to disconnect.
  • the disconnection protection part in the circuit protection method 20 can control the active protection switch 103 to disconnect after determining the fault scenario, thereby cutting off the DC energy input, eliminating reverse current, preventing the fault from spreading, and ultimately improving the safety and reliability of the photovoltaic system.
  • the circuit protection method 20 can continue to perform redundant protection to ensure that the fault is eliminated.
  • FIG7 may be a flowchart of performing a redundancy protection part. As shown in FIG7 , performing a redundancy protection part may include the following steps:
  • the active protection switch 103 needs a certain amount of time to perform the disconnection action, so in step 304 and step 305, as shown in FIG1 , the controller 109 can determine whether the active protection switch 103 is effectively disconnected after a preset time period according to the state of the active protection switch 103.
  • the state judgment of the active protection switch 103 can be implemented in the following implementation manner in this embodiment.
  • the controller 109 may send a current control signal to the DC-DC conversion circuit 106, so that the DC-DC conversion circuit 106 generates current.
  • the current may be continuous for a certain period of time (i.e., the current value is not zero at all times), or intermittent for a certain period of time (i.e., the current is sometimes present and sometimes absent, similar to a pulse).
  • the current value of the current may be fixed or variable.
  • the controller 109 may also detect the current of the DC-DC conversion circuit 106 through the combined current sensor 104. When the controller 109 detects that the current is greater than or equal to the critical value, the controller 109 determines that the active protection switch 103 is not effectively disconnected.
  • the critical value may be determined according to actual conditions, for example, the critical value may be a smaller non-zero value determined by taking into account the drift of the current detection accuracy.
  • the detection principle of the first embodiment is: if the active protection switch 103 is effectively disconnected, the circuit is broken, the closing current sensor 104 cannot respond to the current control signal of the controller 109, and the current detected by the closing current sensor 104 is 0. On the contrary, if the active protection switch 103 is not effectively disconnected, the circuit is closed, the closing current sensor 104 can respond to the current control signal of the controller 109, and the current detected by the closing current sensor 104 is positive. Therefore, when the controller 109 detects that the current is greater than or equal to the critical value, it indicates that the active protection switch 103 is not effectively disconnected.
  • the controller 109 may reduce the input voltage of the DC-DC conversion circuit 106 to a level greater than 0 and less than or equal to the first voltage threshold, at which time the input voltage may be small, so that the DC-DC conversion circuit 106 is close to a short circuit (but not a real short circuit).
  • the controller 109 may generate a target output voltage by controlling the DC-DC conversion circuit 106 so that the input voltage is greater than 0 and less than or equal to the first voltage threshold.
  • the target output voltage may have any suitable constant voltage value.
  • the controller 109 may also detect the current of the DC-DC conversion circuit 106 through the combined current sensor 104.
  • the controller 109 determines that the active protection switch 103 is not effectively disconnected.
  • the critical value may be determined according to actual conditions, for example, the critical value may be a smaller non-zero value determined by considering the drift of the current detection accuracy.
  • the critical value in implementation mode two may be the same as the critical value in implementation mode one.
  • the detection principle of the second embodiment is: if the active protection switch 103 is effectively disconnected, the circuit is broken, the closing current sensor 104 cannot respond to the control signal of the controller 109, and the current detected by the closing current sensor 104 is 0. On the contrary, if the active protection switch 103 is not effectively disconnected, the circuit is closed, the closing current sensor 104 can respond to the control signal of the controller 109, and the current detected by the closing current sensor 104 is positive. Therefore, when the controller 109 detects that the current is greater than or equal to the critical value, it indicates that the active protection switch 103 is not effectively disconnected.
  • Embodiment 2 can be considered as an alternative to the above-mentioned embodiment 1, and the difference is that: Embodiment 1 realizes detection by controlling the current of the DC-DC conversion circuit 106, and Embodiment 2 realizes detection by controlling the input voltage of the DC-DC conversion circuit 106.
  • Embodiment 2 controls the input voltage to a level greater than 0 and less than or equal to the first voltage threshold, so that the DC-DC conversion circuit 106 is in a state close to short circuit but not short circuit, which can not only detect whether the active protection switch 103 is effectively disconnected, but also maintain the output voltage of the DC-DC conversion circuit 106 at a certain value, so as to supply power to the load in the photovoltaic inverter 11 (the load may include a heat dissipation device, and the heat dissipation device can work under the drive of electric energy to maintain the heat dissipation performance of the photovoltaic inverter 11), so that the photovoltaic inverter 11 does not need additional power supply, thereby simplifying the design and reducing costs.
  • the controller 109 can control the switch device in the DC-DC conversion circuit 106 to remain normally on, and the DC-DC conversion circuit 106 can be in a short-circuit state. Then, the controller 109 can detect the current of the DC-DC conversion circuit 106 through the closing current sensor 104. When the controller 109 detects that the current of the DC-DC conversion circuit 106 is greater than or equal to the critical value, the controller 109 determines that the active protection switch 103 is not effectively disconnected.
  • the critical value can be determined according to actual conditions. For example, the critical value can be a smaller positive value determined by considering the drift of the current detection accuracy.
  • the critical value in implementation mode three can be the same as the critical value in implementation mode one.
  • the detection principle of the third embodiment is: if the active protection switch 103 is effectively disconnected, the circuit is broken, and the current detected by the closing current sensor 104 is 0. On the contrary, if the active protection switch 103 is not effectively disconnected, the circuit is closed, and the closing current sensor 104 can detect the reverse current. Therefore, when the controller 109 detects that the current of the DC-DC conversion circuit 106 is greater than or equal to the critical value, it indicates that the active protection switch 103 is not effectively disconnected.
  • the active protection switch 103 may have a contact position feedback function, and the active protection switch 103 may be able to output a contact position feedback signal.
  • the contact position feedback signal may be a level signal, which may indicate the position of the contact in the active protection switch 103, so as to determine whether the active protection switch 103 is disconnected.
  • the controller 109 may detect the contact position feedback signal sent by the active protection switch 103, and determine whether the active protection switch 103 is effectively disconnected based on the contact position feedback signal.
  • the controller 109 may determine that the active protection switch 103 is in a closed state; when the contact position feedback signal is at a high level (or a low level), the controller 109 may determine that the active protection switch 103 is in a closed state; When the position feedback signal is at a low level (or a high level), the controller 109 can determine that the active protection switch 103 is in an open state.
  • the controller 109 when the voltage of the contact position feedback signal is in the first interval, the controller 109 can determine that the active protection switch 103 is in a closed state; when the voltage of the contact position feedback signal is in the second interval, the controller 109 can determine that the active protection switch 103 is in an open state.
  • Implementation method 4 can directly read the working state of the active protection switch 103, and the detection is relatively simple.
  • the controller 109 may detect the input voltage of the DC-DC conversion circuit 106, and when the input voltage is greater than or equal to the second voltage threshold, determine that the active protection switch 103 is not effectively disconnected.
  • the second voltage threshold may be determined according to the configuration of the photovoltaic unit 101, for example, it may be the minimum voltage for starting the DC-DC conversion circuit 106.
  • the second voltage threshold is related to the DC-DC conversion circuit 106 and has nothing to do with the above-mentioned voltage thresholds.
  • the detection principle of the fifth embodiment is: when the input voltage of the DC-DC conversion circuit 106 reaches the minimum voltage, the DC-DC conversion circuit 106 can work normally. In other words, when the DC-DC conversion circuit 106 is working, it indicates that it has reached the minimum voltage. If it is detected that the input voltage of the DC-DC conversion circuit 106 is greater than or equal to the second voltage threshold, it indicates that the DC-DC conversion circuit 106 is started normally, and further indicates that the photovoltaic unit 101 is connected to the input side of the DC-DC conversion circuit 106, so the active protection switch 103 is not effectively disconnected.
  • step 306 when the controller 109 determines that the active protection switch 103 is not effectively disconnected, the controller 109 can reduce the input voltage of the DC-DC conversion circuit 106 to no more than the first voltage threshold. At this time, the input voltage can be relatively small, and the reverse current will flow into the DC-DC conversion circuit 106, thereby shunting the reverse current, reducing or eliminating the reverse current flowing through the photovoltaic unit 101, and preventing the photovoltaic unit 101 from being burned.
  • step 306 can be implemented by the following implementation.
  • the controller 109 when the controller 109 determines that the active protection switch 103 is not effectively disconnected, the controller 109 can control the input voltage of the DC-DC conversion circuit 106 to be greater than 0 and less than or equal to the first voltage threshold. For example, the controller 109 can generate a target output voltage by controlling the DC-DC conversion circuit 106 so that the input voltage of the DC-DC conversion circuit 106 is greater than 0 and less than or equal to the first voltage threshold.
  • the target output voltage can have any suitable constant voltage value.
  • the DC-DC conversion circuit 106 by controlling the input voltage to a level greater than 0 and less than or equal to the first voltage threshold, the DC-DC conversion circuit 106 is in a state close to short circuit but not short circuit, which can not only reduce the reverse current flowing through the photovoltaic unit 101, but also maintain the output voltage of the DC-DC conversion circuit 106 at a certain value, so as to supply power to the load in the photovoltaic inverter 11 (the load may include a heat sink, which can work under the drive of electric energy to maintain the heat dissipation performance of the photovoltaic inverter 11), so that the photovoltaic inverter 11 does not need additional power supply, thereby simplifying the design and reducing costs.
  • the controller 109 when the controller 109 determines that the active protection switch 103 is not effectively disconnected, the controller 109 can control the switch device in the DC-DC conversion circuit 106 to remain normally on, at which time the DC-DC conversion circuit 106 can be in a short-circuit state, and the input voltage of the DC-DC conversion circuit 106 can be reduced to 0.
  • This embodiment puts the DC-DC conversion circuit 106 in a short-circuit state, which can reduce the reverse current flowing through the photovoltaic unit 101.
  • FIG8 shows the current situation of the photovoltaic system 10 after executing the circuit protection method 20 for a reverse polarity fault.
  • FIG8 shows the current situation of the photovoltaic system 10 after executing the circuit protection method 20 for a reverse polarity fault.
  • FIG8 shows the current situation of the photovoltaic system 10 after executing the circuit protection method 20 for a reverse polarity fault.
  • FIG8 shows the current situation of the photovoltaic system 10 after executing the circuit protection method 20 for a reverse polarity fault.
  • FIG8 shows that after executing the redundant protection part in the circuit protection method 20
  • most of the reverse current flows into the photovoltaic inverter 11
  • only a small reverse current flows through the fifth photovoltaic unit 101 with reverse polarity. Comparing FIG8 with FIG2, it can be seen that the reverse current in the fifth photovoltaic unit 101 is greatly reduced, and the risk of burning it is greatly reduced.
  • FIG9 shows the current situation of the photovoltaic system 10 after executing the circuit protection method 20 for an open circuit voltage inconsistency fault.
  • the reverse current flows into the photovoltaic inverter 11, and there may be no reverse current in the fifth photovoltaic unit 101. This can prevent the fifth photovoltaic unit 101 from being burned.

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Abstract

一种光伏系统（10）和光伏系统（10）的电路保护方法。光伏系统（10）包括主动保护开关（103）、直流-直流变换电路（106）和控制器（109）；主动保护开关（103）的一端用于连接光伏组件，另一端与直流-直流变换电路（106）的输入端连接，直流-直流变换电路（106）的输出端用于连接负载；控制器（109）用于在光伏单元（101）的反向电流大于或等于电流阈值时，根据直流-直流变换电路（106）的输入电压，向主动保护开关（103）下发用于触发主动保护开关（103）断开的分断指令，并在向主动保护开关（103）下发分断指令后的预设时长内主动保护开关（103）未有效断开的情况下，调节直流-直流变换电路（106）的输入电压至小于或等于第一电压阈值。能够提高光伏系统（10）的安全性与可靠性。

Description

光伏系统和光伏系统的电路保护方法
本申请要求于2022年09月28日提交中国专利局、申请号为202211191849.2、申请名称为“光伏系统和光伏系统的电路保护方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及光伏发电技术领域，尤其涉及一种光伏系统和光伏系统的电路保护方法。
背景技术
随着光伏产业的发展，光伏系统朝着功率更大的方向不断演进。然而，光伏系统功率的提升也会导致安全风险的持续提升。若无法提供及时且有效的保护，不仅可能导致光伏系统中的光伏组件或逆变器等烧毁，也极易使单点故障扩散，酿成更严重的事故。
为了改善该问题，光伏系统中可以设置保护装置，当出现故障时，该保护装置可以切断光伏组件的能量输入。但是，该保护装置存在因机械失效而无法切断电路的可能，会给光伏系统带来安全隐患。
发明内容
本申请提供了一种光伏系统和光伏系统的电路保护方法，能够在检测到保护装置未有效断开时，通过进一步的保护措施来消除光伏系统中的反向电流，避免光伏系统中的烧毁和故障扩散，从而提高了光伏系统的安全性与可靠性。
第一方面，本申请提供了一种光伏系统，包括主动保护开关、直流-直流变换电路和控制器；主动保护开关的一端用于连接光伏组件，另一端与直流-直流变换电路的输入端连接，直流-直流变换电路的输出端用于连接负载；控制器用于在光伏组件的反向电流大于或等于电流阈值时，根据直流-直流变换电路的输入电压，向主动保护开关下发用于触发主动保护开关断开的分断指令，并在向主动保护开关下发分断指令后的预设时长内主动保护开关未有效断开的情况下，调节直流-直流变换电路的输入电压至小于或等于第一电压阈值。
本方案的光伏系统，能够在检测到反向电流时，进一步通过直流-直流变换电路的输入电压，判断故障场景。在确定故障场景后，能够通过断开主动保护进行电路保护。当检测到主动保护开关分断失败时，能够通过进一步的保护措施——降低直流-直流变换电路的输入电压，来消除光伏系统中的反向电流，避免光伏系统中的烧毁和故障扩散，从而提高了光伏系统的安全性与可靠性。
在第一方面的一种实现方式中，控制器用于在检测到直流-直流变换电路的电流大于或等于临界值时，检测到主动保护开关未有效断开。本方案可以通过检测直流-直流变换电路的电流判断主动保护开关是否有效断开，设计简单，容易量产，可靠性较高。
在第一方面的一种实现方式中，控制器用于调节直流-直流变换电路的输入电压至大于0且小于或等于第一电压阈值，并在检测到直流-直流变换电路的电流大于或等于临界值时，检测到主动保护开关未有效断开。
本方案中，通过将输入电压控制在大于0且小于或等于该第一电压阈值的水平，使得直流-直流变换电路处于接近于短路但并未短路的状态，不仅能够检测主动保护开关是否有效断开，还能使得直流-直流变换电路的输出电压维持在一定值，以便于向光伏逆变器内的负载供电(该负载可以包括散热装置，散热装置能够在电能驱动下工作以维持光伏逆变器的散热性能)，使得光伏逆变器无需额外供电，从而能简化设计、降低成本。
在第一方面的一种实现方式中，控制器用于控制直流-直流变换电路的开关器件保持常通，并在检测到直流-直流变换电路的电流大于或等于临界值时，检测到主动保护开关未有效断开。本方案的判断逻辑简单，容易量产，可靠性较高。
在第一方面的一种实现方式中，主动保护开关用于产生触点位置反馈信号；控制器用于在检测到触点位置反馈信号为目标信号时，检测到主动保护开关未有效断开。本方案的电路设计及判断逻辑较为简单，容易量产，可靠性较高。
在第一方面的一种实现方式中，控制器用于检测到直流-直流电路的输入电压大于或等于第二电压阈值时，检测到主动保护开关未有效断开。本方案可以通过检测直流-直流变换电路的输入电压判断主动保护开关是否有效断开，设计简单，容易量产，可靠性较高。
在第一方面的一种实现方式中，控制器用于在检测到主动保护开关未有效断开时，调节直流-直流变换电路的输入电压至大于0且小于或等于第一电压阈值。本方案中，通过将输入电压控制在大于0且小于或等于该第一电压阈值的水平，使得直流-直流变换电路处于接近于短路但并未短路的状态，不仅能够减小流经光伏组件的反向电流，还能使得直流-直流变换电路的输出电压维持在一定值，以便于向光伏逆变器内的负载供电(该负载可以包括散热装置，散热装置能够在电能驱动下工作以维持光伏逆变器的散热性能)，使得光伏逆变器无需额外供电，从而能简化设计、降低成本。
在第一方面的一种实现方式中，控制器用于控制直流-直流变换电路产生目标输出电压，以使直流-直流变换电路的输入电压大于0且小于或等于第一电压阈值。本方案通过控制直流-直流变换电路的输出电压，进而调节直流-直流变换电路的输入电压，设计较为简单，量产性较好。
在第一方面的一种实现方式中，控制器用于在检测到主动保护开关未有效断开时，控制直流-直流变换电路的开关器件保持常通。本方案中，直流-直流变换电路可以处于短路状态，直流-直流变换电路输入电压可以降为0。本方案使得直流-直流变换电路处于短路状态，能够减小流经光伏单元的反向电流。
在第一方面的一种实现方式中，控制器还用于在光伏组件的反向电流大于或等于电流阈值，且直流-直流变换电路的输入电压小于第四电压阈值时，向主动保护开关下发分断指令；或者，控制器用于在光伏组件的反向电流大于或等于电流阈值、直流-直流变换电路的输入电压大于或等于第四电压阈值时，且检测到在经过设定时长后反向电流大于电流阈值时，向主动保护开关下发分断指令。
本方案中，当控制器可以根据反向电流与输入电压确定故障场景。当输入电压小于第四电压阈值，控制器判断发生了极性接反故障。此时，控制器向主动保护开关下发分断指令，以执行分断保护动作，以减小反向电流。当输入电压大于或等于第四电压阈值时，控制器判断发生了开路电压不一致故障。此时，控制器可以确定等待时长，并在等待时长内持续检测反向电流。若控制器检测到在经过等待时长后反向电流消失仍未消失，则进行分断保护动作。
本方案能够根据反向电流与输入电压，识别不同的故障场景，并针对不同的故障场景采取不同的保护动作。
控制器用于在光伏组件的反向电流大于或等于电流阈值，且直流-直流变换电路的输入电压大于或等于第三电压阈值时，调节直流-直流变换电路的输入电压至小于或等于第一电压阈值，并向主动保护开关下发分断指令，其中，第三电压阈值大于第一电压阈值。
本方案中，控制器判断输入电压大于或等于第三电压阈值时，主动保护开关的触点两端的压差会较大，可能导致主动保护开关分断时可能产生拉弧，导致主动保护开关的触点粘连，使得主动保护开关无法成功分断。因此，当判断输入电压大于或等于第三电压阈值时，将输入电压降低至小于或等于第一电压阈值，并在输入电压降低之后，下发分断指令，以控制主动保护开关分断。将输入电压降至该第一电压阈值后，可以降低主动保护开关的触点两端的压差，减小拉弧能量，有利于使得主动保护开关顺利分断。
在第一方面的一种实现方式中，光伏系统包括电流传感器，电流传感器用于检测光伏单元的反向电流，并向控制器发送反向电流的大小；和/或，光伏系统包括电压传感器，电压传感器用于检测直流-直流变换电路的输入电压，并向控制器发送检测结果。本方案中，使用传感器能够使得电路设计简单。
在第一方面的一种实现方式中，负载包括直流-交流变换电路，直流-交流变换电路连接直流-直流变换电路的输出端与电网。本方案的光伏系统可以连接电网，由于光伏系统能较为可靠地消除反向电流，从而能够避免光伏系统中的故障扩散至电网。
第二方面，本申请提供了一种光伏系统的电路保护方法，光伏系统包括主动保护开关、直流-直流变换电路和控制器；主动保护开关的一端用于连接光伏组件，另一端与直流-直流变换电路的输入端连接，直流-直流变换电路的输出端用于连接负载；电路保护方法包括：当光伏组件的反向电流大于或等于电流阈值时，根据直流-直流变换电路的输入电压，向主动保护开关下发分断指令，分断指令用于触发主动保护开关断开；当向主动保护开关下发分断指令后的预设时长内主动保护开关未有效断开时，调节直流-直流变换电路的输入电压至小于或等于第一电压阈值。
本方案的电路保护方法，能够在检测到反向电流时，进一步通过直流-直流变换电路的输入电压，判断故障场景。在确定故障场景后，能够通过断开主动保护进行电路保护。当检测到主动保护开关分断失败时，能够通过进一步的保护措施——降低直流-直流变换电路的输入电压，来消除光伏系统中的反向电流，避免光伏系统中的烧毁和故障扩散，从而提高了光伏系统的安全性与可靠性。
在第二方面的一种实现方式中，“检测到主动保护开关未有效断开”包括：检测到直流-直流变换电路的电流大于或等于临界值。本方案可以通过检测直流-直流变换电路的电流判断主动保护开关是否有效断 开，设计简单，容易量产，可靠性较高。
在第二方面的一种实现方式中，“检测到主动保护开关未有效断开”包括：调节直流-直流变换电路的输入电压大于0且小于或等于第一电压阈值；检测到直流-直流变换电路的电流大于或等于临界值。
本方案中，通过将输入电压控制在大于0且小于或等于该第一电压阈值的水平，使得直流-直流变换电路处于接近于短路但并未短路的状态，不仅能够检测主动保护开关是否有效断开，还能使得直流-直流变换电路的输出电压维持在一定值，以便于向光伏逆变器内的负载供电(该负载可以包括散热装置，散热装置能够在电能驱动下工作以维持光伏逆变器的散热性能)，使得光伏逆变器无需额外供电，从而能简化设计、降低成本。
在第二方面的一种实现方式中，“检测到主动保护开关未有效断开”包括：控制直流-直流变换电路的开关器件保持常通；检测到直流-直流变换电路的电流大于或等于临界值。本方案的判断逻辑简单，容易量产，可靠性较高。
在第二方面的一种实现方式中，“检测到主动保护开关未有效断开”包括：检测到主动保护开关生成的触点位置反馈信号为目标信号。本方案的电路设计及判断逻辑较为简单，容易量产，可靠性较高。
在第二方面的一种实现方式中，“检测到主动保护开关未有效断开”包括：检测到直流-直流电路的输入电压大于或等于第二电压阈值。本方案可以通过检测直流-直流变换电路的输入电压判断主动保护开关是否有效断开，设计简单，容易量产，可靠性较高。
在第二方面的一种实现方式中，“将直流-直流变换电路的输入电压调节至小于或等于第一电压阈值”包括：调节直流-直流变换电路的输入电压至大于0且小于或等于第一电压阈值。
本方案中，通过将输入电压控制在大于0且小于或等于该第一电压阈值的水平，使得直流-直流变换电路处于接近于短路但并未短路的状态，不仅能够减小流经光伏组件的反向电流，还能使得直流-直流变换电路的输出电压维持在一定值，以便于向光伏逆变器内的负载供电(该负载可以包括散热装置，散热装置能够在电能驱动下工作以维持光伏逆变器的散热性能)，使得光伏逆变器无需额外供电，从而能简化设计、降低成本。
在第二方面的一种实现方式中，“调节直流-直流变换电路的输入电压至大于0且小于或等于第一电压阈值”包括：控制直流-直流变换电路产生目标输出电压，以使直流-直流变换电路的输入电压大于0且小于或等于第一电压阈值。本方案通过控制直流-直流变换电路的输出电压，进而调节直流-直流变换电路的输入电压，设计较为简单，量产性较好。
在第二方面的一种实现方式中，“将直流-直流变换电路的输入电压调节至小于或等于第一电压阈值”包括：控制直流-直流变换电路的开关器件保持常通。本方案中，直流-直流变换电路可以处于短路状态，直流-直流变换电路输入电压可以降为0。本方案使得直流-直流变换电路处于短路状态，能够减小流经光伏单元的反向电流。
在第二方面的一种实现方式中，“根据直流-直流变换电路的输入电压，向主动保护开关下发分断指令”包括：检测直流-直流变换电路的输入电压是否大于或等于第四电压阈值；当输入电压小于第四电压阈值时，向主动保护开关下发分断指令；当输入电压大于或等于第四电压阈值时，且检测到在经过设定时长后反向电流大于电流阈值时，向主动保护开关下发分断指令。
本方案中，可以根据反向电流与输入电压确定故障场景。当输入电压小于第四电压阈值，可以判断发生了极性接反故障。此时，向主动保护开关下发分断指令，以执行分断保护动作，以减小反向电流。当输入电压大于或等于第四电压阈值时，可以判断发生了开路电压不一致故障。此时，可以确定等待时长，并在等待时长内持续检测反向电流。若检测到在经过等待时长后反向电流消失仍未消失，则进行分断保护动作。本方案能够根据反向电流与输入电压，识别不同的故障场景，并针对不同的故障场景采取不同的保护动作。
在第二方面的一种实现方式中，“向主动保护开关下发分断指令”包括：检测直流-直流变换电路的输入电压是否大于或等于第三电压阈值，其中，第三电压阈值大于第一电压阈值；当输入电压大于或等于第三电压阈值时，调节直流-直流变换电路的输入电压至小于或等于第一电压阈值，并向主动保护开关下发分断指令；当输入电压小于第三电压阈值时，向主动保护开关下发分断指令。
本方案中，控制器判断输入电压大于或等于第三电压阈值时，主动保护开关的触点两端的压差会较大，可能导致主动保护开关分断时可能产生拉弧，导致主动保护开关的触点粘连，使得主动保护开关无法成功分断。因此，当判断输入电压大于或等于第三电压阈值时，将输入电压降低至小于或等于第一电压阈值，并在输入电压降低之后，下发分断指令，以控制主动保护开关分断。将输入电压降至该第一电压阈值后， 可以降低主动保护开关的触点两端的压差，减小拉弧能量，有利于使得主动保护开关顺利分断。
附图说明
图1是本申请实施例的光伏系统的电路框架结构示意图；
图2是表示极性接反故障的电路框架结构示意图；
图3是表示开路电压不一致故障的电路框架结构示意图；
图4是本申请实施例的电路保护方法的整体流程框图；
图5是图4中的电路保护方法的检测故障场景部分的流程框图；
图6是图4中的电路保护方法的进行分断保护部分的流程框图；
图7是图4中的电路保护方法的进行冗余保护部分的流程框图；
图8表示针对产生极性接反故障的光伏系统，应用本申请实施例的电路保护方法后的电流情况；
图9表示针对产生开路电压不一致故障的光伏系统，应用本申请实施例的电路保护方法后的电流情况。
具体实施方式
本申请实施例中涉及的第一、第二等以及各种数字编号仅为描述方便进行的区分，并不用来限制本申请的保护范围。本文中的术语“和/或”，仅仅是一种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：单独存在A，同时存在A和B，单独存在B这三种情况。
光伏系统是利用光伏组件(photovoltaic module)直接将太阳能转换成电能的发电系统，其可以包括光伏组串、蓄电池、控制器和光伏逆变器等。其中，光伏组件是指能够单独提供直流电输出、不可分割的最小光伏电池组合装置。光伏组串包括多个以串联或/和并联的方式组合在一起的光伏组件。
图1示意了本申请实施例的一种光伏系统10的框架结构。如图1所示，所述光伏系统10可以包括若干个光伏单元101和光伏逆变器11，若干个光伏单元101并联接入光伏逆变器11。光伏逆变器11可以包括若干个支路电流传感器102、主动保护开关103、合路电流传感器104、输入电压传感器105、直流-直流(DC-DC)变换电路106、输出电压传感器107、直流-交流(DC-AC)变换电路108和控制器109。在其他实施例中，光伏逆变器11也可以认为是一种光伏系统，光伏单元101可以不是光伏系统10中的设备，光伏单元101与该光伏系统(指光伏逆变器11)连接。所述光伏单元101可以是一个获得组件进行串联或并联形成。所述光伏单元101在本图中是以并联形式出现，在一些实施例中也可以串联在一起，具体光伏单元101的连接方式并不是本申请的具体实现方式，本领域技术人员可以根据光伏逆变器11的输入需求进行多个光伏组件的串并联结合，以获得需要的输入电压。
如图1所示，光伏单元101可以标示为PV。光伏单元101可以是上述的光伏组串，也可以是由若干个光伏组串并联形成的光伏阵列，在一些实施方式中还可以是单个光伏组件。光伏单元101的数量可以根据需要配置，可以为至少一个。图1示意性地画出了多个光伏单元101，多个光伏单元101并联以形成多个支路。
如图1所示，每个光伏单元101均与主动保护开关103串联，主动保护开关103的另一端并联接入直流-直流变换电路106的输入端，由此使得多个光伏单元101均通过主动保护开关103与直流-直流变换电路106的输入端连接。
示意性的，可以仅有一个主动保护开关103，主动保护开关103内置有运动机构和多个触点，一个光伏单元101与主动保护开关103内的一组触点对应连接，该运动机构可控制多个触点同时动作，以实现所有光伏单元101与主动保护开关103的同时连接或者同时断开。主动保护开关103具备主动分断性能，能够基于电流、电压等信息主动断开电路。主动保护开关103例如可以为直流脱扣开关或者直流断路器等。
如图1所示，支路电流传感器102的数量与光伏单元101的一致，一个光伏单元101可以对应一个支路电流传感器102。支路电流传感器102可以与光伏单元101串联，并设在一个光伏单元101所在的支路中，例如支路电流传感器102可以设在主动保护开关103的并联点(即主动保护开关103的多个触点的并联位置，该并联点与直流-直流变换电路106的输入端连接)与光伏单元101与之间。支路电流传感器102用于检测与其串联的光伏单元101的电流(可以称为支路电流)，各个支路电流传感器102所检测的各支路电流可以依次标示为Idc1、Idc2…Idcn。
如图1所示，合路电流传感器104可以与主动保护开关103的并联点串联，并可以位于该并联点与直流-直流变换电路106之间。合路电流传感器104用于检测所有光伏单元101并联后的总电流(可以称为 合路电流)。合路电流传感器104所检测的合路电流可以标示为Idc。
如图1所示，输入电压传感器105可以位于直流-直流变换电路106的输入端，例如位于主动保护开关103的并联点与直流-直流变换电路106之间。输入电压传感器105用于检测直流-直流变换电路106的输入电压。输入电压传感器105所检测的输入电压可以标示为Vin。该输入电压也等于每个支路的光伏单元101两端的电压。
如图1所示，输出电压传感器107可以位于直流-直流变换电路106的输出端，用于检测直流-直流变换电路106的输出电压。直流-直流变换电路106的输出端可以通过直流母线(标示为BUS)与直流-交流变换电路108连接，因此输出电压传感器107所检测的输出电压可以标示为Vbus。
本实施例中，直流-直流变换电路106可以是独立的设备，如直流-直流变换电路106可以是DC-DC变换器。或者，直流-直流变换电路106可以是系统中的电路模块。
如图1所示，直流-交流变换电路108可以连接直流-直流变换电路106的输出端与交流电网Grid。由此，光伏系统10可以将转换的电能输入交流电网。
对于直流-直流变换电路106而言，直流-交流变换电路108与交流电网均可以称为交流负载，即直流-直流变换电路106的输出端连接交流负载。本申请实施例中，负载除了上文所述的交流负载，还可以是其他DC-DC转换设备、储能设备(如电池)等直流负载。因此概括来说，直流-直流变换电路106的输出端连接负载，负载包括但不限于直流-交流变换电路108与交流电网等交流负载，以及其他DC-DC转换设备、储能设备等直流负载。
本实施例中，直流-交流变换电路108可以是独立的设备，如直流-交流变换电路108可以是DC-AC变换器。或者，直流-交流变换电路108可以是系统中的电路模块。
本实施例中，直流-直流变换电路106与直流-交流变换电路108可以作为光伏逆变器的组成部分，该光伏逆变器为双级架构，直流-直流变换电路106为前级，直流-交流变换电路108为后级。在其他实施例中，光伏系统可以不含直流-交流变换电路108，例如当直流-直流变换电路106连接直流负载时，光伏系统可以没有直流-交流变换电路108。此种不含直流-交流变换电路108的光伏系统中不存在光伏逆变器。
如图1所示，控制器109可以与各个支路电流传感器102、主动保护开关103、合路电流传感器104、输入电压传感器105、直流-直流(DC-DC)变换电路106以及输出电压传感器107电连接，以获取其检测的信号、判断其工作状态、控制其进行工作等。控制器109能够将各个部件按照指令的功能要求协调工作，是光伏系统10的神经中枢和指挥中心(下文将继续说明)。
一种实施例中，控制器109可以由指令寄存器(instruction register，IR)、程序计数器(program counter，PC)和操作控制器(operation controller，OC)等部件组成。控制器109可以指一个或多个设备、电路、和/或用于处理数据(例如计算机程序指令)的处理核。
其他实施例中，控制器109可以是一个处理器，也可以是多个处理元件的统称。其中，处理器可以是一个通用中央处理器(central processing unit，CPU)，也可以是特定应用集成电(application-specific integrated circuit，ASIC)。或者，处理器可以是一个或多个用于控制本申请方案程序执行的集成电路，例如：一个或多个微处理器(digital signal processor，DSP)；或一个或者多个现场可编程门阵列(field programmable gate array，FPGA)。
在上述实施例中，采用支路电流传感器102、合路电流传感器104、输入电压传感器105、输出电压传感器107等传感器，便于根据PV的规格，灵活选择具有对应的采样电流范围或者采样电压范围的传感器，使得光伏系统10能够灵活地部署构建。在其他实施例中，也可以内置于控制器的采样电路，来实现支路电流传感器102、合路电流传感器104、输入电压传感器105、输出电压传感器107等传感器的采样功能，此时无需额外布置支路电流传感器102、合路电流传感器104、输入电压传感器105、输出电压传感器107等传感器，此种方案能够简化电路。
上述实施例中，光伏逆变器11包括支路电流传感器102、主动保护开关103、合路电流传感器104、输入电压传感器105、直流-直流变换电路106、输出电压传感器107、直流-交流变换电路108和控制器109，这仅仅是一种举例。在其他实施例中，光伏逆变器可以包括直流-直流变换电路与直流-交流变换电路，但是未内置支路电流传感器102、主动保护开关103、合路电流传感器104、输入电压传感器105、输出电压传感器107和控制器109中的至少一个，也即支路电流传感器102、主动保护开关103、合路电流传感器104、输入电压传感器105、输出电压传感器107和控制器109中的至少一个可以独立于光伏逆变器之外。
上文描述了光伏系统10的电路框架结构，下文将详细说明光伏系统10的工作原理。
光伏系统10中的各路光伏单元101在工作时，由于某支路的光伏单元101出现故障，其它各正常支路的光伏单元101的电流将会流向故障支路的光伏单元101，导致该故障支路出现反向电流。若反向电流不超过电流阈值，由于光伏单元101具有一定电流耐受能力，因此可以无需采取保护动作。若反向电流大于或等于电流阈值，则需要采取保护动作，以避免光伏单元101被烧毁。
参考图1所示，支路电流传感器102可以检测光伏单元101的电流，并将检测结果发送至控制器109。控制器109对该检测结果进行判断，可以确定反向电流是否大于或等于电流阈值。
通常，有两种故障可以导致较大的反向电流：一种是光伏单元101的极性接反，另一种是光伏单元101的开路电压不一致。下面将分别进行说明。
图2表示由于光伏单元101的极性接反导致较大的反向电流的故障场景，其中示意性地绘出了五个光伏单元101与光伏逆变器11的电路连接。如图2所示，五个光伏单元101并联接入光伏逆变器11，前四个光伏单元101的极性与光伏逆变器11的极性连接正确(正极连正极，负极连负极)，第五个光伏单元101的极性与光伏逆变器11的极性接反(负极连正极，正极连负极)。将前四个光伏单元101中的每个光伏单元101的电流标示为Idc，由于第五个光伏单元101的极性接反，导致第五个光伏单元101被短路，因此前四个光伏单元101的电流都会流入第五个光伏单元101(该电流称为反向电流，反向电流可以为4*Idc)，而不会流入光伏逆变器11(此种现象称为电流倒灌)。因此，第五个光伏单元101的电流方向与前四个光伏单元101的电流方向相反，且第五个光伏单元101的电流较大，这就是极性接反导致的反向电流故障。
对于极性接反导致的反向电流故障，结合图1所示，输入电压传感器105检测到的输入电压较小。
图3表示由于光伏单元101的开路电压不一致导致较大的反向电流的故障场景，其中示意性地绘出了五个光伏单元101与光伏逆变器11的电路连接。如图3所示，五个光伏单元101并联接入光伏逆变器11，且每个光伏单元101的极性与光伏逆变器11的极性连接正确。但是，前四个光伏单元101中串联的光伏单元的数量相同，使得前四个光伏单元101的开路电压一致(开路电压即支路开路、不输出电流时的电压)；第五个光伏单元101中串联的光伏单元的数量少于其他光伏单元101中串联的光伏单元的数量，也即第五个光伏单元101中串联的光伏单元最少，这导致前四个支路的光伏单元101的电流将流入第五个光伏单元101(该电流称为反向电流，反向电流可取决于前四个支路的光伏单元101与第五个光伏单元101的开路电压的差异)，而不会流入光伏逆变器11(出现电流倒灌现象)。因此，第五个光伏单元101的电流方向与前四个光伏单元101的电流方向相反，且第五个光伏单元101的电流较大，这就是开路电压不一致导致的反向电流故障。
对于开路电压不一致导致的反向电流故障，结合图1所示，输入电压传感器105检测到的输入电压较大。因此，对于极性接反的反向电流故障与开路电压不一致的反向电流故障，前一故障对应的输入电压小于后一故障对应的输入电压。
本实施例的光伏系统10能够检测反向电流，判断反向电流对应的故障场景，并分别针对不同故障场景进行相应的动作，从而减小或者消除反向电流，避免发生故障的光伏单元101被烧毁，防止故障扩散，最终提高了光伏系统的安全性与可靠性。下面将进行详细说明。
如图4所示，本实施例提供了一种光伏系统的电路保护方法20，可应用于光伏系统10。电路保护方法20可以包括如下功能部分：检测故障场景，进行分断保护，进行冗余保护。下面将分别进行详细说明。
图5可以示意检测故障场景部分的流程框图。如图5所示，检测故障场景部分可以包括如下步骤：
201：检测反向电流是否大于或等于电流阈值；
当反向电流小于电流阈值时，返回执行步骤201；当反向电流大于或等于电流阈值时，执行步骤202；
202：检测直流-直流变换电路的输入电压是否大于或等于第四电压阈值；
当输入电压小于第四电压阈值时，执行步骤203；当输入电压大于或等于第四电压阈值时，执行步骤204；
203：进行分断保护；
204：确定等待时长，并检测经过等待时长后反向电流是否大于或等于电流阈值；
当检测到经过等待时长后反向电流小于电流阈值时，执行步骤201；当检测到经过等待时长后反向电流大于或等于电流阈值时，执行步骤203。
在步骤201中，结合图1所示，控制器109可以控制各个支路电流传感器102检测各个支路的电流，并根据各个支路电流传感器102的检测结果判断各个支路是否出现大于或等于电流阈值的反向电流。电流阈值可以根据光伏单元101的电流耐受能力确定，例如电流阈值可以小于或等于光伏单元101的电流耐受值。如图5所示，当步骤201的判断结果为YES，表明某支路出现了需要执行保护动作的故障。当步骤201 的判断结果为NO，表明没有反向电流或者反向电流未超过电流耐受值，无需立即执行保护动作。
结合图1所示，当控制器109检测到了大于或等于电流阈值的反向电流时，控制器109可以控制输入电压传感器105检测直流-直流变换电路106的输入电压，并根据输入电压传感器105的检测结果判断该输入电压是否大于或等于第四电压阈值。第四电压阈值可以根据光伏单元101的配置情况确定，其可以等于光伏单元101产生反向电流时对外表现的电压的上限。上文已经说明，开路电压不一致对应的输入电压较大，极性接反对应的输入电压较小。因此，当步骤202的判断结果为YES，表明故障是开路电压不一致，则执行步骤204；若步骤202的判断结果是NO，表明故障是极性接反，则执行步骤203。
在步骤203中，结合图1所示，当控制器109判断故障场景为极性接反后，控制器109可以进行分断保护动作。执行分断保护动作将在下文继续说明。
在步骤204中，结合图1所示，当控制器109判断故障场景为开路电压不一致后，控制器109可以确定等待时长，并在等待时长内持续检测反向电流。其中，控制器109可以根据内置的策略计算出该等待时长。基于该策略，较大的反向电流可以对应较短的等待时长，较小的反向电流可以对应较长的等待时长。若控制器109检测到在经过等待时长后反向电流消失仍未消失，则进行分断保护动作；若控制器109检测到在经过等待时长后反向电流消失，则返回至步骤201。其中，当光伏系统10并网工作时的电压降低至最大功率点追踪(maximum power point tracking，MPPT)窗口(在P-V曲线中，确定最大功率点对应的电压区间，可将该电压区间称为MPPT窗口)内时，或者遮挡光伏单元101的阴影消失后，反向电流可能消失。
根据上文所述可知，电路保护方法20中的检测故障场景部分，能够根据反向电流与输入电压，识别不同的故障场景，并针对不同的故障场景采取不同的保护动作。
图6可以示意进行分断保护部分的流程框图。如图6所示，进行分断保护部分可以包括如下步骤：
301：检测直流-直流变换电路的输入电压是否大于或等于第三电压阈值，第三电压阈值大于第一电压阈值；
当该输入电压大于或等于该第三电压阈值时，执行步骤302，并执行步骤303；当该输入电压小于该第三电压阈值时，执行步骤303；
其中，302：将该输入电压降低至小于或等于第一电压阈值，步骤303：下发分断指令。
若直流-直流变换电路106的输入电压过大，主动保护开关103的触点两端的压差将会较大，导致主动保护开关103分断时可能产生拉弧，拉弧能量可能导致主动保护开关103的触点粘连，使得主动保护开关103无法成功分断。因此，本实施例的方案会检测输入电压，并根据检测结果进行相应的保护动作。下面将进行说明。
在步骤301中，结合图1所示，控制器109可以控制输入电压传感器105检测直流-直流变换电路106的输入电压，并根据输入电压传感器105的检测结果判断该输入电压是否大于或等于第三电压阈值。第三电压阈值与主动保护开关103的规格有关，可以根据主动保护开关103的分断能力确定。例如，第三电压阈值可以等于主动保护开关103的工作电压上限。第三电压阈值与上述的第四电压阈值无关，第三电压阈值可以大于下文将要描述的第一电压阈值。
结合图1所示，当控制器109判断输入电压大于或等于第三电压阈值时，控制器109将输入电压降低至小于或等于第一电压阈值，并在输入电压降低之后，下发分断指令，以控制主动保护开关103分断。第一电压阈值可以根据光伏单元101的配置情况确定。例如，第一电压阈值可以小于、等于或者大于光伏单元101产生反向电流时对外表现的电压的下限，示意性的，第一电压阈值与该下限可以相差较小。第一电压阈值小于该第三电压阈值。本实施例中，将输入电压降至该第一电压阈值后，可以降低主动保护开关103的触点两端的压差，减小拉弧能量，有利于使得主动保护开关103顺利分断。
结合图1所示，当控制器109判断输入电压小于第三电压阈值时，控制器109可直接下发分断指令，以控制主动保护开关103分断。
根据上文所述可知，电路保护方法20中的进行分断保护部分，能够在确定故障场景之后，控制主动保护开关103分断，从而切断直流能量输入，消除反向电流，防止故障扩散，最终提高光伏系统的安全性与可靠性。
本实施例中，若主动保护开关103因机械失效等原因无法切断电路，电路保护方法20可继续进行冗余保护，以确保消除故障。
图7可以示意进行冗余保护部分的流程框图。如图7所示，进行冗余保护部分可以包括如下步骤：
304：在下发分断指令后经过预设时长后，检测主动保护开关的状态；
305：判断主动保护开关是否有效断开；
306：当主动保护开关未有效断开时，将直流-直流变换电路的输入电压降低至小于或等于第一电压阈值。
主动保护开关103执行分断动作需要一定时间，因此在步骤304与步骤305中，结合图1所示，控制器109可以在经过预设时长后，根据主动保护开关103的状态，判断主动保护开关103是否有效断开。示意性的，本实施例可以通过以下实施方式实现主动保护开关103的状态判断。
在实施方式一中，控制器109可以向直流-直流变换电路106发送电流控制信号，使得直流-直流变换电路106产生电流。该电流可以是连续地持续一定时长(即电流值时时刻刻不为零)，或者间断性的持续一定时长(即电流时有时无，类似脉冲)。该电流的电流值可以固定或者变化。控制器109还可以通过合路电流传感器104检测直流-直流变换电路106的该电流。当控制器109检测到该电流大于或等于临界值时，控制器109判断主动保护开关103未有效断开。该临界值可以根据实际情况确定，例如该临界值可以是考虑了电流检测精度的漂移情况而确定的一个较小非零值。
实施方式一的检测原理是：若主动保护开关103有效断开，则电路断路，合路电流传感器104无法响应控制器109的电流控制信号，合路电流传感器104检测的电流为0。反之，若主动保护开关103未有效断开，则电路闭合，合路电流传感器104可以响应控制器109的电流控制信号，合路电流传感器104检测的电流为正。因此，当控制器109检测到该电流大于或等于临界值时，表明主动保护开关103未有效断开。
或者，在实施方式二中，控制器109可以将直流-直流变换电路106的输入电压降低至大于0且小于或等于该第一电压阈值的水平，此时该输入电压可以较小，使得直流-直流变换电路106接近于短路(但并不是真正的短路)。示意性的，控制器109可以通过控制直流-直流变换电路106产生目标输出电压，以使该输入电压大于0且小于或等于该第一电压阈值。其中，目标输出电压可以具有任意合适的恒定电压值。然后，控制器109还可以通过合路电流传感器104检测直流-直流变换电路106的电流。当控制器109检测到直流-直流变换电路106的电流大于或等于临界值时，控制器109判断主动保护开关103未有效断开。该临界值可以根据实际情况确定，例如该临界值可以是考虑了电流检测精度的漂移情况而确定的一个较小非零值。实施方式二中的临界值可以同实施方式一种的临界值。
实施方式二的检测原理是：若主动保护开关103有效断开，则电路断路，合路电流传感器104无法响应控制器109的控制信号，合路电流传感器104检测的电流为0。反之，若主动保护开关103未有效断开，则电路闭合，合路电流传感器104可以响应控制器109的控制信号，合路电流传感器104检测的电流为正。因此，当控制器109检测到该电流大于或等于临界值时，表明主动保护开关103未有效断开。
实施方式二可以认为是上述实施方式一的替代方案，区别在于：实施方式一是通过控制直流-直流变换电路106的电流实现检测，实施方式二是通过控制直流-直流变换电路106的输入电压实现检测。实施方式二通过将输入电压控制在大于0且小于或等于该第一电压阈值的水平，使得直流-直流变换电路106处于接近于短路但并未短路的状态，不仅能够检测主动保护开关103是否有效断开，还能使得直流-直流变换电路106的输出电压维持在一定值，以便于向光伏逆变器11内的负载供电(该负载可以包括散热装置，散热装置能够在电能驱动下工作以维持光伏逆变器11的散热性能)，使得光伏逆变器11无需额外供电，从而能简化设计、降低成本。
或者，在实施方式三中，控制器109可以控制直流-直流变换电路106中的开关器件保持常通，此时直流-直流变换电路106可以处于短路状态。然后，控制器109可以通过合路电流传感器104检测直流-直流变换电路106的电流。当控制器109检测到直流-直流变换电路106的电流大于或等于临界值时，控制器109判断主动保护开关103未有效断开。该临界值可以根据实际情况确定，例如该临界值可以是考虑了电流检测精度的漂移情况而确定的一个较小正值。实施方式三中的临界值可以同实施方式一种的临界值。
实施方式三的检测原理是：若主动保护开关103有效断开，则电路断路，合路电流传感器104检测的电流为0。反之，若主动保护开关103未有效断开，则电路闭合，合路电流传感器104能够检测到反向电流。因此，当控制器109检测到直流-直流变换电路106的电流大于或等于临界值时，表明主动保护开关103未有效断开。
或者，在实施方式四中，主动保护开关103可以具有触点位置反馈功能，主动保护开关103能够输出触点位置反馈信号。示意性的，触点位置反馈信号可以是电平信号，可以指示主动保护开关103中的触点所处的位置，以便判断主动保护开关103是否断开。控制器109可以检测主动保护开关103发送的触点位置反馈信号，并根据该触点位置反馈信号判断主动保护开关103是否有效断开。示意性的，当该触点位置反馈信号为高电平时(或者低电平时)，控制器109可以判断主动保护开关103处于闭合状态；当该触点 位置反馈信号为低电平时(或者高电平时)，控制器109可以判断主动保护开关103处于断开状态。或者，当该触点位置反馈信号的电压在第一区间时，控制器109可以判断主动保护开关103处于闭合状态；当当该触点位置反馈信号的电压在第二区间时，控制器109可以判断主动保护开关103处于断开状态。实施方式四能够直接读取主动保护开关103的工作状态，检测较为简单。
或者，在实施方式五中，控制器109可以检测直流-直流变换电路106的输入电压，并在该输入电压大于或等于第二电压阈值时，判断主动保护开关103未有效断开。第二电压阈值可以根据光伏单元101的配置情况确定，例如可以是使直流-直流变换电路106启动的最低电压，第二电压阈值与直流-直流变换电路106有关，与上述各个电压阈值无关。
实施例方式五的检测原理是：当直流-直流变换电路106的输入电压达到最低电压时，直流-直流变换电路106才能正常工作。换言之，当直流-直流变换电路106工作时，表明其已达到最低电压。若检测到直流-直流变换电路106的输入电压大于或等于该第二电压阈值时，表明直流-直流变换电路106正常启动，进而说明直流-直流变换电路106的输入侧有光伏单元101接入，因此主动保护开关103未有效断开。
在步骤306中，当控制器109判断主动保护开关103未有效断开时，控制器109可以将直流-直流变换电路106的输入电压降低至不高于第一电压阈值。此时，该输入电压可以较小，反向电流将会流入直流-直流变换电路106，从而起到对反向电流的分流作用，减小或者消除流经光伏单元101的反向电流，避免光伏单元101被烧毁。
示意性的，可以通过以下实施方式实现步骤306。下面将进行说明。
在一种实施方式中，当控制器109判断主动保护开关103未有效断开时，控制器109可以控制直流-直流变换电路106的输入电压大于0且小于或等于该第一电压阈值。例如，控制器109可以通过控制直流-直流变换电路106产生目标输出电压，以使直流-直流变换电路106的输入电压大于0且小于或等于该第一电压阈值。其中，目标输出电压可以具有任意合适的恒定电压值。本实施方式中，通过将输入电压控制在大于0且小于或等于该第一电压阈值的水平，使得直流-直流变换电路106处于接近于短路但并未短路的状态，不仅能够减小流经光伏单元101的反向电流，还能使得直流-直流变换电路106的输出电压维持在一定值，以便于向光伏逆变器11内的负载供电(该负载可以包括散热装置，散热装置能够在电能驱动下工作以维持光伏逆变器11的散热性能)，使得光伏逆变器11无需额外供电，从而能简化设计、降低成本。
在另一种实施方式中，当控制器109判断主动保护开关103未有效断开时，控制器109可以控制直流-直流变换电路106中的开关器件保持常通，此时直流-直流变换电路106可以处于短路状态，直流-直流变换电路106输入电压可以降为0。本实施方式使得直流-直流变换电路106处于短路状态，能够减小流经光伏单元101的反向电流。
图8表示针对极性接反故障，光伏系统10在执行电路保护方法20之后的电流情况。如图8所示，执行了电路保护方法20中的冗余保护部分之后，大部分反向电流流入光伏逆变器11，极性接反的第五个光伏单元101中仅有较小的反向电流流过。对比图8与图2可知，第五个光伏单元101中的反向电流大大减少，其被烧毁的风险大大降低。
图9表示针对开路电压不一致故障，光伏系统10在执行电路保护方法20之后的电流情况。如图9所示，执行了电路保护方法20中的冗余保护部分之后，反向电流流入光伏逆变器11，第五个光伏单元101中可以没有反向电流。这能避免第五个光伏单元101被烧毁。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到变化或替换，都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以所述权利要求的保护范围为准。

Claims (13)

  1. 一种光伏系统，其特征在于，
    包括主动保护开关、直流-直流变换电路和控制器；
    所述主动保护开关的一端用于连接光伏组件，另一端与所述直流-直流变换电路的输入端连接，所述直流-直流变换电路的输出端用于连接负载；
    所述控制器用于在所述光伏组件的反向电流大于或等于电流阈值时，根据所述直流-直流变换电路的输入电压，向所述主动保护开关下发用于触发所述主动保护开关断开的分断指令，并在向所述主动保护开关下发分断指令后的预设时长内所述主动保护开关未有效断开的情况下，调节所述直流-直流变换电路的输入电压至小于或等于第一电压阈值。
  2. 根据权利要求1所述的光伏系统，其特征在于，
    所述控制器用于在检测到所述主动保护开关未有效断开时，调节所述直流-直流变换电路的输入电压至大于0且小于或等于所述第一电压阈值。
  3. 根据权利要求2所述的光伏系统，其特征在于，
    所述控制器用于控制所述直流-直流变换电路产生目标输出电压，以使所述直流-直流变换电路的输入电压大于0且小于或等于所述第一电压阈值。
  4. 根据权利要求1-3任一项所述的光伏系统，其特征在于，
    所述控制器用于在检测到所述主动保护开关未有效断开时，控制所述直流-直流变换电路的开关器件保持常通。
  5. 根据权利要求1-4任一项所述的光伏系统，其特征在于，
    所述控制器还用于在所述光伏组件的反向电流大于或等于电流阈值，且所述直流-直流变换电路的输入电压小于第四电压阈值时，向所述主动保护开关下发分断指令；
    或者，所述控制器用于在所述光伏组件的反向电流大于或等于电流阈值、所述直流-直流变换电路的输入电压大于或等于第四电压阈值时，且检测到在经过设定时长后所述反向电流大于所述电流阈值时，向所述主动保护开关下发分断指令。
  6. 根据权利要求1-5任一项所述的光伏系统，其特征在于，
    所述控制器用于在所述光伏组件的反向电流大于或等于所述电流阈值，且所述直流-直流变换电路的输入电压大于或等于第三电压阈值时，调节所述直流-直流变换电路的输入电压至小于或等于所述第一电压阈值，并向所述主动保护开关下发分断指令，其中，所述第三电压阈值大于所述第一电压阈值。
  7. 根据权利要求1-6任一项所述的光伏系统，其特征在于，
    所述负载包括直流-交流变换电路，所述直流-交流变换电路连接所述直流-直流变换电路的输出端与电网。
  8. 一种光伏系统的电路保护方法，其特征在于，
    所述光伏系统包括主动保护开关、直流-直流变换电路和控制器；所述主动保护开关的一端用于连接光伏组件，另一端与所述直流-直流变换电路的输入端连接，所述直流-直流变换电路的输出端用于连接负载；所述电路保护方法包括：
    当所述光伏组件的反向电流大于或等于电流阈值时，根据所述直流-直流变换电路的输入电压，向所述主动保护开关下发分断指令，所述分断指令用于触发所述主动保护开关断开；
    当向所述主动保护开关下发分断指令后的预设时长内所述主动保护开关未有效断开时，调节所述直流-直流变换电路的输入电压至小于或等于第一电压阈值。
  9. 根据权利要求8所述的电路保护方法，其特征在于，
    所述“将所述直流-直流变换电路的输入电压调节至小于或等于第一电压阈值”包括：
    调节所述直流-直流变换电路的输入电压至大于0且小于或等于所述第一电压阈值。
  10. 根据权利要求9所述的电路保护方法，其特征在于，
    所述“调节所述直流-直流变换电路的输入电压至大于0且小于或等于所述第一电压阈值”包括：
    控制所述直流-直流变换电路产生目标输出电压，以使所述直流-直流变换电路的输入电压大于0且小于或等于所述第一电压阈值。
  11. 根据权利要求8-10任一项所述的电路保护方法，其特征在于，
    所述“将所述直流-直流变换电路的输入电压调节至小于或等于第一电压阈值”包括：
    控制所述直流-直流变换电路的开关器件保持常通。
  12. 根据权利要求8-11任一项所述的电路保护方法，其特征在于，
    所述“根据所述直流-直流变换电路的输入电压，向所述主动保护开关下发分断指令”包括：
    检测所述直流-直流变换电路的输入电压是否大于或等于第四电压阈值；
    当所述输入电压小于所述第四电压阈值时，向所述主动保护开关下发分断指令；
    当所述输入电压大于或等于所述第四电压阈值时，且检测到在经过设定时长后所述反向电流大于所述电流阈值时，向所述主动保护开关下发分断指令。
  13. 根据权利要求8-12任一项所述的电路保护方法，其特征在于，
    所述“向所述主动保护开关下发分断指令”包括：
    检测所述直流-直流变换电路的输入电压是否大于或等于第三电压阈值，其中，所述第三电压阈值大于所述第一电压阈值；
    当所述输入电压大于或等于所述第三电压阈值时，调节所述直流-直流变换电路的输入电压至小于或等于所述第一电压阈值，并向所述主动保护开关下发分断指令；
    当所述输入电压小于所述第三电压阈值时，向所述主动保护开关下发分断指令。
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CN115528649A (zh) * 2022-09-28 2022-12-27 华为数字能源技术有限公司 光伏系统和光伏系统的电路保护方法

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