A power device, a power device control method and a photovoltaic power generation system

Abstract

A power device, a power device control method and a photovoltaic power generation system. The input end of the component-level power electronic device is connected to the photovoltaic component, and the output end of the component-level power electronic device is connected in series and then connected to the inverter. The component-level power electronic device includes a DC conversion unit, a signal processing unit and a controller. The DC conversion unit is used to realize DC-DC power conversion, the signal processing unit is used to receive the periodic communication signal sent by the inverter, and the controller is used to control the component-level power electronic device to switch between the shutdown mode, the normal working mode and the safe working mode, specifically including: when the component-level power electronic device does not receive the periodic communication signal, maintain or switch to the shutdown mode, when the periodic communication signal received by the component-level power electronic device includes a heartbeat frame and does not include a voltage regulation instruction, switch to the normal working mode, when the periodic communication signal received by the component-level power electronic device includes a heartbeat frame and also includes a voltage regulation instruction, switch to the safe working mode. The three working modes provided in this application can simultaneously ensure the safety of equipment and personnel, with fast response speed and simple implementation.

Description

Technical Field

[0001] The present application relates to the field of power electronics, and in particular to a power device, a power device control method, and a photovoltaic power generation system. Background Art

[0002] At present, with the global shortage of non-renewable energy and the worsening of environmental pollution, the application of photovoltaic power generation is becoming more and more widespread. Photovoltaic power generation is to convert the direct current generated by photovoltaic modules into alternating current through an inverter, and then connect it to the AC grid or provide it to the load.

[0003] Photovoltaic power generation is usually applied in three major scenarios: large-scale photovoltaic power stations, industrial and commercial fields, and household fields. In the latter two scenarios, photovoltaic modules are usually installed on the roof of the building, which is relatively close to the electricity users. In order to obtain a relatively large power generation power, photovoltaic modules are usually composed of multiple photovoltaic panels in series, so the DC voltage on the photovoltaic module side is relatively large. This has caused a safety hazard that cannot be ignored. Once the inverter or photovoltaic module fails, the roof where the photovoltaic module is installed may catch fire. In addition, when the photovoltaic modules and inverters need to be repaired, the maintenance personnel are faced with hundreds or even thousands of high-voltage DC currents, and the excessive DC voltage on the photovoltaic module side will also cause damage to the inverter, which is not conducive to the long-term stable operation of the photovoltaic power generation system.

[0004] As an emerging distributed photovoltaic power generation equipment, module-level power electronic equipment (MLPE) can control individual photovoltaic modules, which further improves the power generation efficiency compared to traditional string photovoltaic power generation. Furthermore, how to use module-level power electronic equipment to reduce the voltage on the photovoltaic module side when necessary, fully ensure the personal safety of power users or maintenance personnel, protect power generation equipment, and improve the safety of distributed photovoltaic equipment power generation and maintenance has become a hot topic in the industry. Summary of the invention

[0005] The present application provides a power conversion device, a working method for controlling the power conversion device, and a photovoltaic power generation system, which can fully ensure the safety of the inverter equipment, fully ensure the safety of users and maintenance personnel, and can also greatly reduce the impact of inspection, installation, and maintenance work on users' electricity consumption.

[0006] In a first aspect, an embodiment of the present application discloses a power conversion device, which includes: a DC conversion unit, a signal processing unit and a controller, wherein one end of the DC conversion unit is used to connect to a photovoltaic component, and the other end of the DC conversion unit is used to connect to an input end of a next-stage power conversion device, and the signal processing unit is located at the output side of the power conversion device; the signal processing unit is used to receive a periodic communication signal sent by the next-stage power conversion device; the controller is used to control the power conversion device to switch to a shutdown mode or maintain operation in the shutdown mode in response to the signal processing unit failing to receive the periodic communication signal within a time period, in which the voltage output by the power conversion device is a shutdown voltage, and the The shutdown voltage is a preset safety voltage value; in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing a voltage regulation instruction, the power conversion device is controlled to switch to a safe working mode or maintain working in a safe working mode, in which the output voltage of the power conversion device is less than a first voltage; in response to the signal processing unit receiving the periodic communication signal but the periodic communication signal does not contain the voltage regulation instruction, the power conversion device is controlled to switch to a normal working mode or maintain working in a normal working mode, in which the output voltage of the power conversion device is less than a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

[0007] In the technical solution of the first aspect, the next-level power conversion device and the power conversion device have a communication connection and a power connection. Specifically, the communication method between the next-level power conversion device and the power conversion device is power line communication. On this basis, a periodic communication signal is used to control the switching of the working mode of the power conversion device. In this way, the existing power line is used for communication transmission, which reduces the cost required to establish an additional communication line. The periodic communication signal is used for communication, which has a fast response speed and a simple implementation method. In addition, the power conversion device switches between three working modes. In the normal working mode, it can ensure that the output power of the power conversion device is always the maximum, and the user's electricity needs are met to the greatest extent. In the safe working mode, faults can be discovered in time, and the protection mechanism can be activated to ensure the safety of the equipment on the side of the next-level power conversion device. In the shutdown mode, the output voltage of the power conversion device can be reduced to below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0008] According to the first aspect, in a possible implementation, the periodic communication signal is a PLC signal, and the PLC signal includes a heartbeat frame; the controller is used to control the power conversion device to switch to a shutdown mode or maintain operation in the shutdown mode in response to the signal processing unit failing to receive the heartbeat frame within a period of time. By using PLC communication and utilizing a heartbeat protection mechanism to determine the communication status between the power conversion device and the next-level power conversion device, the existing power lines can be used to accurately control the working mode of the power conversion device in real time according to the communication status between the two.

[0009] According to the first aspect, in a possible implementation, the controller is used to control the power conversion device to switch to a normal working mode or maintain working in a normal working mode in response to the signal processing unit receiving the PLC signal and the PLC signal including the heartbeat frame but not including the voltage regulation instruction; control the power conversion device to switch to a safe working mode or maintain working in a safe working mode in response to the signal processing unit receiving the PLC signal and the PLC signal including both the heartbeat frame and the voltage regulation instruction. The PLC signal includes two forms, the heartbeat frame and the voltage regulation instruction. According to different situations in which the power conversion device receives the voltage regulation instruction, the power conversion device is further refined to operate in a normal working mode or a safe working mode. In the case of an uninterrupted heartbeat frame, the power conversion device can also switch between different working modes. In different working modes, the power conversion device can be in a normal power generation state, giving priority to powering the next-level power conversion device, or in a safe power generation state. While powering the next-level power conversion device, the safety of the next-level power conversion device is given priority.

[0010] According to the first aspect, in a possible implementation, when the next-level power conversion device detects that the voltage at the input end of the next-level power conversion device exceeds an overvoltage threshold, and the next-level power conversion device sends a voltage adjustment instruction to the power conversion device, the controller controls the output voltage of the power conversion device to be less than the overvoltage threshold. In this implementation, the next-level power conversion device detects that the input end of the next-level power conversion device is overvoltage, which is a trigger condition for the next-level power conversion device to send a voltage adjustment instruction to the power conversion device. After the power conversion device receives the voltage adjustment instruction, the controller controls the output voltage of the power conversion device to be less than the overvoltage threshold. In this way, when the next-level power conversion device is overvoltage, the power converter can quickly reduce its own output voltage to ensure the safety of the next-level power conversion device.

[0011] According to the first aspect, in a possible implementation, when the next-level power conversion device detects that the input power of the next-level power conversion device exceeds an overpower threshold, the next-level power conversion device sends a voltage adjustment instruction to the power conversion device, the power conversion device receives the voltage adjustment instruction, and the controller controls the output voltage of the power conversion device to decrease. In this implementation, the next-level power conversion device detects that the input power of the next-level power conversion device exceeds an overpower threshold, which is a trigger condition for the next-level power conversion device to send a voltage adjustment instruction to the power conversion device. When the power conversion device receives the voltage adjustment instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when the next-level power conversion device has an overpower, the power converter can quickly reduce its own output voltage to ensure the safety of the next-level power conversion device.

[0012] According to the first aspect, in a possible implementation, when the next-level power conversion device detects that the power generation system in which the next-level power conversion device is located has an island effect, and the next-level power conversion device issues a voltage regulation instruction to the power conversion device, the power conversion device receives the voltage regulation instruction, and the controller controls the output voltage of the power conversion device to decrease. In this implementation, the next-level power conversion device detecting that the next-level power conversion device has an island effect is a trigger condition for the next-level power conversion device to issue a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when the island effect occurs, the output voltage is reduced to avoid excessive fluctuations in voltage and frequency in the island system to damage electrical equipment.

[0013] According to the first aspect, in a possible implementation method, when it is detected that the input voltage of the next-stage power conversion device exceeds an overvoltage threshold for a time threshold, the next-stage power conversion device sends a voltage regulation instruction to the power conversion device to control the output voltage of the power conversion device to be less than the overvoltage threshold. In the actual power generation system, the grid voltage often fluctuates within a certain normal range, and the input voltage of the next-stage power conversion device may deviate from the normal voltage threshold for a short time and then recover. This implementation method eliminates the misjudgment of overvoltage of the next-stage power conversion device caused by grid voltage fluctuations by adding a time judgment condition to the voltage regulation instruction trigger condition.

[0014] According to the first aspect, in a possible implementation method, after receiving the voltage regulation instruction sent by the next-stage power conversion device, the power conversion device controls its output voltage to 0.5 or 0.1 times its current output voltage. This implementation method reduces the risk of failure of the next-stage power conversion device due to long-term overvoltage to the greatest extent by reducing the output voltage of the power conversion device to half or one-tenth of the original output voltage.

[0015] According to the first aspect, in a possible implementation, the DC conversion unit of the power conversion device includes a buck circuit, a boost circuit, a buck-boost circuit, a forward circuit and a flyback circuit. The technical solution provided in the present application does not limit the type of the main conversion circuit of the power conversion device and is adaptable to various power conversion devices.

[0016] According to the first aspect, in a possible implementation, the controller is used to, in the normal working mode, control the DC conversion unit to work in the maximum power tracking mode, in which the output voltage of the DC conversion unit changes, and the output power of the photovoltaic component connected to the DC conversion unit is maximum; in the safe working mode, control the DC conversion unit to work in the limiting voltage mode, in which the voltage output by the DC conversion unit is constant. In the normal working mode, the power conversion device can output power at the maximum power generation power of the current photovoltaic component, and the voltage may be variable to ensure the maximization of the power generation capacity. In the safe working mode, the output voltage of the power conversion device is constant, and this voltage can effectively ensure the safety of the power conversion device at the next level. The two modes can be changed according to the situation to fully ensure the power generation capacity and safety of the power conversion device.

[0017] In a second aspect, an embodiment of the present application discloses a method for controlling a power conversion device, the method comprising: in response to the power conversion device failing to receive a heartbeat frame, controlling the power conversion device to be in a shutdown mode, wherein in the shutdown mode, the voltage output by the power conversion device is a shutdown voltage, which is a preset safety voltage value; in response to the power conversion device receiving a heartbeat frame and failing to receive a voltage regulation instruction, controlling the power conversion device to be in a normal working mode, wherein in the normal working mode, the output voltage of the power conversion device is less than a first voltage; in response to the power conversion device receiving a heartbeat frame and receiving a voltage regulation instruction, controlling the power conversion device to be in a safe working mode, wherein in the safe working mode, the output voltage of the power conversion device is less than a second voltage, wherein the second voltage is less than the first voltage, and wherein the second voltage is greater than the shutdown voltage.

[0018] In the technical solution of the second aspect, existing power lines are used for communication transmission, which reduces the cost of establishing additional communication lines. Heartbeat protection mechanism and voltage regulation instructions are used for communication, which has a fast response speed and a simple implementation method. In addition, the power conversion equipment switches between three working modes. In the normal working mode, the output power of the power conversion equipment can be guaranteed to be always maximum to meet the user's electricity needs to the greatest extent. In the safe working mode, faults can be discovered in time and the protection mechanism can be activated to ensure the safety of the inverter side equipment. In the shutdown mode, the output voltage of the power conversion equipment can be reduced to below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0019] According to the second aspect, in a possible implementation, when it is detected that the voltage at the input end of the inverter exceeds an overvoltage threshold, the inverter sends a voltage adjustment instruction to the power conversion device, and the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this implementation, the inverter detects that the input end of the inverter is overvoltage, which is a trigger condition for the inverter to send a voltage adjustment instruction to the power conversion device. When the power conversion device receives the voltage adjustment instruction, the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this way, when the inverter is overvoltage, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0020] According to the second aspect, in a possible implementation, when it is detected that the input power of the inverter exceeds an overpower threshold, the inverter sends a voltage regulation instruction to the power conversion device, and the power conversion device receives the voltage regulation instruction and controls the output voltage of the power conversion device to decrease. In this implementation, the inverter detects that the input power is overpowered, which is a trigger condition for the inverter to send a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when the inverter has overpower, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0021] According to the second aspect, in a possible implementation, when it is detected that an islanding effect occurs in the power generation system where the inverter is located, the inverter sends a voltage regulation instruction to the power conversion device, and the power conversion device receives the voltage regulation instruction and controls the output voltage of the power conversion device to decrease. In this implementation, the inverter detects that an islanding effect occurs in the inverter, which is a trigger condition for the inverter to send a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when an islanding effect occurs, the output voltage is reduced to avoid excessive fluctuations in voltage and frequency in the islanding system to damage electrical equipment.

[0022] In a third aspect, an embodiment of the present application provides a photovoltaic power generation system, which includes multiple optimizers, wherein the input end of each of the multiple optimizers is used to connect to a photovoltaic module, and the output end of each of the multiple optimizers is connected in series in sequence. In response to the multiple optimizers failing to receive a heartbeat frame, the multiple optimizers operate in a shutdown mode. In the shutdown mode, the output end voltage of the multiple optimizers is a shutdown voltage, which is a preset safety voltage value. In response to the multiple optimizers receiving a heartbeat frame and failing to receive a voltage regulation instruction, the multiple optimizers operate in a normal working mode. In the normal working mode, the multiple optimizers The output voltage is less than the first voltage. In response to multiple optimizers receiving a heartbeat frame and receiving a voltage regulation instruction, the optimizer operates in a safe working mode. In the safe working mode, the output voltage of the multiple optimizers is less than the second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage. An inverter, an input end of the inverter is connected to the output ends of multiple optimizers connected in series in sequence, and the output end of the inverter is used to connect to a power grid or a user load. The inverter sends heartbeat frames and voltage regulation instructions to multiple optimizers, and the heartbeat frames and voltage regulation instructions are transmitted through the power lines between the input end of the inverter or the output end of the optimizer.

[0023] In the technical solution provided in the third aspect, the photovoltaic power generation system is composed of multiple optimizers and inverters. Multiple optimizers and inverters use existing power lines for communication transmission, reducing the cost required to establish additional communication lines, and use heartbeat protection mechanism and voltage regulation instructions for communication, with fast response speed and simple implementation. In addition, the power conversion equipment switches between three working modes. In the normal working mode, it can ensure that the output power of the power conversion equipment is always the maximum, and the user's electricity needs are met to the greatest extent. In the safe working mode, faults can be discovered in time, and the protection mechanism can be activated to ensure the safety of the inverter side equipment. In the shutdown mode, the output voltage of the power conversion equipment can be reduced to below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0024] According to the third aspect, in a possible implementation, when it is detected that the voltage at the input end of the inverter exceeds an overvoltage threshold, the inverter sends a voltage adjustment instruction to the power conversion device, and the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this implementation, the inverter detects that the input end of the inverter is overvoltage, which is a trigger condition for the inverter to send a voltage adjustment instruction to the power conversion device. When the power conversion device receives the voltage adjustment instruction, the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this way, when the inverter is overvoltage, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0025] According to the third aspect, in a possible implementation, when it is detected that the input power of the inverter exceeds an overpower threshold, the inverter sends a voltage adjustment instruction to the power conversion device, and the power conversion device receives the voltage adjustment instruction and controls the output voltage of the power conversion device to decrease. In this implementation, the inverter detects that the input power is overpowered, which is a trigger condition for the inverter to send a voltage adjustment instruction to the power conversion device. When the power conversion device receives the voltage adjustment instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when the inverter has overpower, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0026] According to the third aspect, in a possible implementation, when the inverter detects that the power generation system in which the inverter is located has an islanding effect, the inverter sends a voltage regulation instruction to the power conversion device, and the power conversion device receives the voltage regulation instruction and controls the output voltage of the power conversion device to decrease. In this implementation, the inverter detects that the inverter has an islanding effect, which is a trigger condition for the inverter to send a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when the islanding effect occurs, the output voltage is reduced to avoid excessive fluctuations in voltage and frequency in the islanding system to damage the electrical equipment.

[0027] According to the third aspect, in a possible implementation method, the inverter establishes communication with the optimizer when the startup conditions are met, and the communication content includes a heartbeat frame or a voltage regulation instruction. After the inverter detects an alarm signal, the inverter interrupts the communication with the optimizer and performs a shutdown action. In this way, the inverter and the optimizer can establish communication as soon as the working conditions are met and quickly perform power generation. At the same time, the inverter can cut off communication with the optimizer as soon as an alarm occurs, prompting the optimizer to enter a safe working mode and ensure the equipment safety of the inverter.

[0028] In a fourth aspect, an embodiment of the present application discloses a power conversion device, which includes: a DC conversion unit, a signal processing unit and a controller, wherein the DC conversion unit is used to convert the DC power generated by the photovoltaic module and output it to the next-stage power conversion device, and the signal processing unit is connected to the output of the power conversion device and is used to receive a periodic communication signal sent by the next-stage power conversion device; the controller is used to control the voltage output by the power conversion device to be a shutdown voltage in response to the signal processing unit not receiving the periodic communication signal within a time period, and the shutdown voltage is a preset safety voltage value; in response to the signal processing unit receiving the periodic communication signal but the periodic communication signal does not contain a voltage regulation instruction, control the voltage output by the power conversion device to be less than or equal to a first voltage; in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing the voltage regulation instruction, control the voltage output by the power conversion device to be less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

[0029] In the technical solution of the fourth aspect, the next-level power conversion device and the power conversion device have a communication connection and a power connection. Specifically, the communication method between the next-level power conversion device and the power conversion device is power line communication. On this basis, a periodic communication signal is used to control the magnitude of the voltage output by the power conversion device. In this way, the existing power line is used for communication transmission, which reduces the cost required to establish an additional communication line. The periodic communication signal is used for communication, which has a fast response speed and a simple implementation method. In addition, the voltage output by the power conversion device is related to the three voltage values. When the output voltage is less than or equal to the first voltage, the output power of the power conversion device can be guaranteed to be always the maximum, and the user's electricity needs can be met to the greatest extent. When the output voltage is less than or equal to the second voltage, the protection mechanism can be activated in time to ensure the safety of the equipment on the next-level power conversion device side. When the output voltage is the shutdown voltage, the output voltage of the power conversion device can be reduced to below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0030] According to the fourth aspect, in a possible implementation, the periodic communication signal is a PLC signal, and the PLC signal includes a heartbeat frame; the controller is used to control the voltage output by the power conversion device to be the shutdown voltage in response to the signal processing unit failing to receive the heartbeat frame within a period of time. By using PLC communication and utilizing a heartbeat protection mechanism to determine the communication status between the power conversion device and the next-level power conversion device, the existing power lines can be used to accurately control the voltage output by the power conversion device in real time according to the communication status between the two.

[0031] According to the fourth aspect, in a possible implementation, the controller is used to, in response to the signal processing unit receiving the PLC signal and the PLC signal including the heartbeat frame but not including the voltage regulation instruction, control the voltage output by the power conversion device to be less than the first voltage; in response to the signal processing unit receiving the PLC signal and the PLC signal including both the heartbeat frame and the voltage regulation instruction, control the voltage output by the power conversion device to be less than the second voltage. The PLC signal includes two forms, the heartbeat frame and the voltage regulation instruction. According to different situations in which the power conversion device receives the voltage regulation instruction, the voltage output by the power conversion device is further refined to be less than or equal to the first voltage or the second voltage. In the case of the heartbeat frame not being interrupted, the power conversion device can output different voltages. Therefore, the power conversion device can be in a normal power generation state, giving priority to powering the next-level power conversion device, or in a safe power generation state, giving priority to the safety of the next-level power conversion device while powering the next-level power conversion device.

[0032] According to the fourth aspect, in a possible implementation, the controller is used to, in response to the signal processing unit receiving the PLC signal and the PLC signal containing both the heartbeat frame and the voltage regulation instruction, adjust the voltage output by the power conversion device to K times the current output voltage of the power conversion device, wherein K is less than 1 or K is 0.5 or 0.1. This implementation reduces the risk of failure of the next-stage power conversion device due to long-term overvoltage to the greatest extent by reducing the output voltage of the power conversion device to half or one-tenth of the original output voltage.

[0033] According to the fourth aspect, in a possible implementation, the controller is used to, in response to the signal processing unit receiving the periodic communication signal but the periodic communication signal does not contain the voltage regulation instruction, control the DC conversion unit to operate in a maximum power tracking mode, in which the output voltage of the DC conversion unit changes, and the output power of the photovoltaic component connected to the DC conversion unit is maximum; in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing the voltage regulation instruction, control the DC conversion unit to operate in a limiting voltage mode, in which the voltage output by the DC conversion unit is constant. When the voltage output by the power conversion device is less than or equal to the first voltage, the DC conversion unit operates in the maximum power tracking mode, and the power conversion device can output power at the maximum power generation of the current photovoltaic component, and the voltage may be variable to ensure the maximization of the power generation capacity. When the voltage output by the power conversion device is less than or equal to the second voltage, the DC conversion unit operates in the limiting voltage mode, and the output voltage of the power conversion device is constant, which can effectively ensure the safety of the next level of power conversion equipment. The two modes can be changed according to the situation to fully ensure the power generation capacity and safety of the power conversion device.

[0034] In a fifth aspect, an embodiment of the present application discloses a method for controlling a power conversion device, the method comprising: in response to the power conversion device failing to receive a heartbeat frame, controlling the voltage output by the power conversion device to be a shutdown voltage, wherein the shutdown voltage is a preset safety voltage value; in response to the power conversion device receiving the heartbeat frame and failing to receive a voltage adjustment instruction, controlling the voltage output by the power conversion device to be less than or equal to a first voltage; in response to the power conversion device receiving the heartbeat frame and receiving the voltage adjustment instruction, controlling the voltage output by the power conversion device to be less than or equal to a second voltage, wherein the second voltage is less than the first voltage and greater than the shutdown voltage.

[0035] In the technical solution of the fifth aspect, existing power lines are used for communication transmission, which reduces the cost of establishing additional communication lines. Heartbeat protection mechanism and voltage regulation instructions are used for communication, which has a fast response speed and a simple implementation method. In addition, the voltage output by the power conversion device is related to three voltage values. When the output voltage is less than or equal to the first voltage, it can be ensured that the output power of the power conversion device is always the maximum, and the user's electricity needs are met to the greatest extent. When the output voltage is less than or equal to the second voltage, the protection mechanism can be activated in time to ensure the safety of the equipment on the next level of power conversion equipment. When the output voltage is the shutdown voltage, the output voltage of the power conversion device can be reduced to below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0036] According to the fifth aspect, in a possible implementation, when it is detected that the voltage at the input end of the inverter exceeds an overvoltage threshold, the inverter is used to receive the DC power output by the power conversion device and send a voltage adjustment instruction to the power conversion device, and the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this implementation, the inverter detects that the overvoltage at its input end is a trigger condition for the inverter to send a voltage adjustment instruction to the power conversion device. When the power conversion device receives the voltage adjustment instruction, the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this way, when the inverter is overvoltage, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0037] According to the fifth aspect, in a possible implementation, when it is detected that the input power of the inverter exceeds an overpower threshold, the inverter is used to receive the DC power output by the power conversion device and send the voltage regulation instruction to the power conversion device to control the output voltage of the power conversion device to decrease. In this implementation, the inverter detects that the input power is overpowered, which is a trigger condition for the inverter to send the voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when the inverter has overpower, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0038] According to the fifth aspect, in a possible implementation, when it is detected that the power generation system where the inverter is located has an islanding effect, the inverter is used to receive the DC power output by the power conversion device and send the voltage regulation instruction to the power conversion device to control the output voltage of the power conversion device to decrease. In this implementation, the inverter detects that the inverter has an islanding effect, which is a trigger condition for the inverter to send a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to decrease. In this way, when the islanding effect occurs, the output voltage is reduced to avoid excessive fluctuations in voltage and frequency in the islanding system to damage electrical equipment.

[0039] In a sixth aspect, an embodiment of the present application provides a photovoltaic power generation system, which includes: a plurality of optimizers, the plurality of optimizers being used to convert the direct current generated by the photovoltaic components and output it to an inverter; an inverter, the inverter being used to supply power to a power grid or a user load, the inverter being further used to send heartbeat frames and voltage regulation instructions to the plurality of optimizers, the heartbeat frames and the voltage regulation instructions being transmitted through a power line between the inverter and the optimizer; in response to the plurality of optimizers not receiving the heartbeat frame within a time period, the voltage output by the plurality of optimizers is a shutdown voltage, and the shutdown voltage is a preset safety voltage value; in response to the plurality of optimizers receiving the heartbeat frame and not receiving the voltage regulation instruction, the voltage output by the plurality of optimizers is less than or equal to a first voltage; in response to the plurality of optimizers receiving the heartbeat frame and receiving the voltage regulation instruction, the voltage output by the plurality of optimizers is less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

[0040] In the technical solution provided in the sixth aspect, the photovoltaic power generation system is composed of multiple optimizers and inverters. Multiple optimizers and inverters use existing power lines for communication transmission, reducing the cost required to establish additional communication lines, and use heartbeat protection mechanism and voltage regulation instructions for communication, with fast response speed and simple implementation. In addition, the voltage output by the power conversion device is related to three voltage values. When the output voltage is less than or equal to the first voltage, it can ensure that the output power of the power conversion device is always the maximum, and the user's electricity needs are met to the greatest extent. When the output voltage is less than or equal to the second voltage, the protection mechanism can be activated in time to ensure the safety of the equipment on the next level of power conversion equipment side. When the output voltage is the shutdown voltage, the output voltage of the power conversion device can be reduced to below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0041] According to the sixth aspect, in a possible implementation, when the voltage at the input end of the inverter exceeds an overvoltage threshold, the inverter sends the voltage regulation instruction to the optimizer, and the optimizer controls its own output voltage to be less than the second voltage. In this implementation, the inverter detects that its input end is overvoltage, which is a trigger condition for the inverter to send a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, it controls the output voltage of the power conversion device to be less than the second voltage. In this way, when the inverter is overvoltage, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0042] According to the sixth aspect, in a possible implementation, when the input power of the inverter exceeds an overpower threshold, the inverter sends the voltage regulation instruction to the optimizer, and the optimizer controls its own output voltage to be less than the second voltage. In this implementation, the inverter detects that its input end is overpowered, which is a trigger condition for the inverter to send a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to be less than the second voltage. In this way, when the inverter has overpower, the power converter can quickly reduce its own output voltage to ensure the safety of the inverter.

[0043] According to the sixth aspect, in a possible implementation, in response to some or all of the multiple optimizers not receiving the heartbeat frame within a time period, the optimizer that does not receive the heartbeat frame adjusts the output voltage to a shutdown voltage, and the shutdown voltage is a preset safety voltage value; in response to the multiple optimizers receiving the heartbeat frame and not receiving the voltage adjustment instruction, the voltage output by the multiple optimizers is less than or equal to a second voltage; in response to the multiple optimizers receiving the heartbeat frame and receiving the voltage adjustment instruction, the voltage output by the multiple optimizers is less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage. Benefiting from PLC signal transmission, multiple optimizers use heartbeat frames and voltage adjustment instructions to establish communication with the inverter, and change their own output voltage according to different situations of the received heartbeat frames and voltage adjustment instructions. The communication method is simple and reliable.

[0044] According to the sixth aspect, in a possible implementation, when an islanding effect occurs in the power generation system where the inverter is located, the inverter sends the voltage regulation instruction to the optimizer, and the optimizer controls its own output voltage to be less than the second voltage. In this implementation, the inverter detects that the inverter has an islanding effect, which is a trigger condition for the inverter to send a voltage regulation instruction to the power conversion device. When the power conversion device receives the voltage regulation instruction, the controller controls the output voltage of the power conversion device to be less than the second voltage. In this way, when the islanding effect occurs, the output voltage is reduced to avoid excessive fluctuations in voltage and frequency in the islanding system to damage the electrical equipment.

[0045] According to the sixth aspect, in a possible implementation method, the inverter establishes communication with the optimizer when the startup conditions are met, and the communication content includes a heartbeat frame or a voltage regulation instruction. After the inverter detects an alarm signal, the inverter interrupts the communication with the optimizer and performs a shutdown action. In this way, the inverter and the optimizer can establish communication as soon as the working conditions are met and quickly perform power generation. At the same time, the inverter can cut off communication with the optimizer as soon as an alarm occurs, prompting the optimizer to enter a safe working mode and ensure the equipment safety of the inverter.

[0046] According to the sixth aspect, in a possible implementation, multiple optimizer inputs are used to connect photovoltaic modules respectively, and the outputs of the multiple optimizers are connected in series and then connected to the input of the inverter; the inverter is used to broadcast the heartbeat signal and the voltage regulation instruction to the multiple optimizers through PLC, and the voltage regulation instruction adjusts the voltage output by the power conversion device to K times the current output voltage of the power conversion device, where K is less than 1 or K is 0.5 or 0.1. This implementation reduces the risk of failure of the next-level power conversion device due to long-term overvoltage to the greatest extent by reducing the output voltage of the power conversion device to half or one-tenth of the original output voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a schematic diagram of the architecture of a photovoltaic system provided in an embodiment of the present application;

[0048] Figure 2 This is a schematic diagram of the architecture of another photovoltaic system provided in an embodiment of the present application;

[0049] Figure 3 This is a schematic diagram of an optimizer-inverter connection provided in an embodiment of the present application;

[0050] Figure 4 This is another optimizer-inverter connection schematic diagram provided in an embodiment of the present application;

[0051] Figure 5 It is a schematic diagram of the optimizer working mode switching process provided in an embodiment of the present application;

[0052] Figure 6 It is a schematic diagram of the inverter working process provided in an embodiment of the present application. DETAILED DESCRIPTION

[0053] The technical solution in this application will be described below in conjunction with the accompanying drawings.

[0054] In this application, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. In addition, the term "coupling" can be a way of achieving electrical connection for signal transmission. "Coupling" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0055] To facilitate understanding, some of the terms used in this application are first explained.

[0056] Component-level power electronic equipment: Different from string-type power electronic equipment, it has component-level maximum power point tracking (MPPT) and monitoring functions, which can further improve the power generation of photovoltaic power generation systems. With appropriate shutdown strategies, it can also achieve component-level rapid shutdown (RSD) function, thereby greatly improving the safety of photovoltaic power generation systems.

[0057] MPPT function: Control the back-end input voltage to operate at the maximum power point voltage (Vmpp, Maximum Power Point Voltage) of the photovoltaic module to achieve the maximum power output of the photovoltaic module.

[0058] PLC: Power line communication, also called carrier communication, refers to a communication method that uses existing power lines as information transmission media to transmit data or information in the form of digital signals.

[0059] Mismatch: When multiple PV modules are connected in series or in parallel, and the environmental conditions (such as irradiation, temperature, etc.) of some of the multiple PV modules are different from those of other PV modules, the power of the multiple PV modules after being connected in series or in parallel is less than the sum of the maximum power points of each PV module.

[0060] Heartbeat protection mechanism: The heartbeat protection mechanism is a safety monitoring mechanism used in communication systems to determine whether communication between devices is normal. In this mechanism, the host will periodically send a "heartbeat frame" to the slave, and the slave will send feedback to the host after receiving the heartbeat frame to inform the host that the communication connection is normal. If the host does not receive feedback information, it will take remedial measures such as trying to reconnect. In some systems, the slave will not send feedback to the host after receiving the heartbeat frame, but will determine whether the communication is abnormal based on whether it has received the heartbeat frame, and take corresponding actions on the slave side.

[0061] Island effect: In a distributed power generation system, when the power grid trips due to a fault or power outage for maintenance, the distributed grid-connected power generation systems at each user end (such as photovoltaic power generation, wind power generation, fuel cell power generation, etc.) fail to detect the power outage in time and thus disconnect themselves from the municipal power network, ultimately forming a self-sufficient island power generation system consisting of a distributed grid-connected power generation system and its connected loads.

[0062] See also Figure 1, which is a schematic diagram of the architecture of a photovoltaic system provided in an embodiment of the present application. In this embodiment, the photovoltaic system includes a plurality of converters 1-n, the positive and negative input terminals of the converters 1-n are used to be connected to the positive and negative output terminals of the photovoltaic modules 1-n in a one-to-one correspondence, and the output terminals of the converters 1-n are coupled to the power grid 105 after being connected in parallel. Under this architecture, a plurality of photovoltaic modules can be coupled to the power grid 105 through converters, and the output terminals of a plurality of converters are coupled to the power grid 105 in parallel, so that the power grid has a relatively large power supply capability.

[0063] Since the output power of a single photovoltaic cell is relatively small, a photovoltaic module can be composed of multiple photovoltaic cells connected in series or in parallel, thereby increasing the output power of the photovoltaic module. This application does not limit the composition of the photovoltaic module.

[0064] The converters 1-n are used to convert the direct current of the photovoltaic components 1-n into alternating current to be transmitted to the power grid to achieve the function of photovoltaic power generation, and the converters 1-n are respectively connected to the output ends of the photovoltaic components 1-n in a one-to-one correspondence to control the output voltage of each photovoltaic component 1-n to achieve maximum power tracking of the photovoltaic components 1-n.

[0065] The converters 1-n include micro inverters. The micro inverter is a miniaturized, highly integrated power conversion device that can be installed on the roof of a building near a photovoltaic module. It has functions such as inverter, MPPT, module-level shutdown or monitoring, and is applied to this architecture to achieve the following process: Taking photovoltaic module 1 as an example, photovoltaic module 1 converts solar energy into direct current, and converter 1 can convert the direct current into alternating current with electrical parameters such as a specific frequency and a specific voltage required by the power grid 105, and the alternating current is then provided to the load for use.

[0066] It should be understood that in this embodiment, a single photovoltaic module is connected to a single converter, but there are also cases where multiple photovoltaic modules are connected to a single converter. This application does not limit the number of photovoltaic modules connected to the converter. Taking the micro-inverter as an example, the "one-to-one" solution of the micro-inverter is that a single photovoltaic module is connected to a single micro-inverter, and the "one-to-two" and "one-to-four" solutions of the micro-inverter are that two photovoltaic modules are connected to a single micro-inverter, and four photovoltaic modules are connected to a single micro-inverter.

[0067] See also Figure 2 , Figure 21 is a schematic diagram of the architecture of another photovoltaic system provided in an embodiment of the present application. The photovoltaic system includes a converter 1-n, a converter 2-m and an inverter 104. The input ends of the converters 1-n and 2-m are used to connect the output ends of the photovoltaic components 1-n and the photovoltaic components 2-m in a one-to-one correspondence. The converters are connected in series to form p photovoltaic strings, where p is greater than or equal to 2, wherein the output ends of the converters 1-1 to 1-n are connected in series to form a photovoltaic string 1, and the output ends of the converters 2-1 to 2-m are connected in series to form another photovoltaic string 2.

[0068] The input end of the converter 1-1 in the photovoltaic string 1 is connected to the photovoltaic module 1-1, the input end of the converter 1-n is connected to the photovoltaic module 1-n, and the output ends of the converters 1-1 to 1-n are connected in series and connected to the input end of the inverter 104 through the positive DC power line 106 and the negative DC power line 107. Similarly, the input end of the converter 2-1 in the photovoltaic string 2 is connected to the photovoltaic module 2-1, the input end of the converter 2-m is connected to the photovoltaic module 2-m, and the output ends of the converters 2-1 to 2-m are connected in series and connected to the input end of the inverter 104 through the positive DC power line 106 and the negative DC power line 107.

[0069] The output end of the inverter 104 is connected to the power grid 105. The inverter 104 is a three-phase inverter, and the power grid 105 is a three-phase AC power grid. Alternatively, the inverter 104 can also be a single-phase inverter for household use, and the corresponding power grid 105 is a household AC power grid.

[0070] It should be understood that in one embodiment, the converter can be a circuit breaker. The circuit breaker has a component shutdown function and is a component-level power electronic device installed between the photovoltaic component and the inverter. It can quickly shut down the connection between each photovoltaic component and the inverter. It is generally installed on the roof of the building near the photovoltaic component side.

[0071] In another embodiment, the converter can be an optimizer, which is a power conversion device installed between the photovoltaic module and the inverter, which can eliminate the mismatch phenomenon of the photovoltaic module and has the MPPT function of a single photovoltaic module, thereby greatly improving the power generation of the entire photovoltaic power generation system. The optimizer is applied to this architecture to achieve the following process: Taking the photovoltaic string 1 as an example, a single photovoltaic module 1-1 to 1-n converts solar energy into direct current. After the corresponding connected optimizer 1-1 to 1-n performs power conversion, the direct current output of multiple converters is connected in series to the input end of the inverter 104. Relative to the optimizer, the inverter is the next-level power conversion device of the optimizer. The input end of the inverter 104 is called the "one way" input of the inverter. Similarly, the photovoltaic string 2 will also connect the output direct current in series and deliver it to the input end of the inverter 104 in another "one way". In the embodiment of the present application, the optimizer also has a component-level fast shutdown function, which further reduces the safety risk of the photovoltaic power generation system.

[0072] The following is a description of the implementation of the maximum power tracking function and the fast shutdown function of the component-level power electronic equipment provided by the present application in conjunction with the accompanying drawings. For the convenience of description, the following is only described by taking the optimizer as an example. It should be understood that the methods for implementing fast shutdown described below are not limited to the optimizer, and they are also applicable to Figure 1 and Figure 2 More component-level power electronics shown.

[0073] In addition, the meaning of the component-level power electronic equipment rapid shutdown function provided by the present application is not limited to the literal "shutdown" which simply reflects the disconnection and isolation of the component-level power electronic equipment from the photovoltaic power generation system, but also reflects the reduction of the output voltage, output current or output power of the component-level power electronic equipment to below a specific voltage.

[0074] by Figure 2 Based on the connection relationship between the photovoltaic string 1 and the inverter 104, Figure 31-1, and the output end of the optimizer 1-n is connected to the input end of the optimizer 1-n; the output ends of the multiple optimizers 1-1 are connected in series and connected to the inverter 104 as the input of the inverter 104, specifically, one output end of the optimizer 1-1 is connected to one input end of the inverter 104, and the other output end of the optimizer 1-1 is connected to one output end of the connected optimizer 1-2, similarly, one output end of the optimizer 1-(n-1) is connected to one output end of the connected optimizer 1-(n-2), another output end of the optimizer 1-(n-1) is connected to one output end of the optimizer 1-n, and another output end of the optimizer 1-n is connected to another input end of the inverter 104. More specifically, taking optimizer 1-1 as an example, optimizer 1-1 includes a DC conversion unit 101, a signal processing unit 103 and a control unit 102, and inverter 104 includes an inverter 104 signal transceiver unit 108 and an inverter circuit 109. Optimizer 1-1 is connected to inverter 104 via a positive DC power line 106, and optimizer 1-n is connected to inverter 104 via a negative DC power line 107.

[0075] The DC conversion unit 101 includes one or more combinations of buck converters, boost converters, buck-boost converters, forward converters, or flyback converters. On the one hand, the DC conversion unit 101 is used to work in the MPPT tracking mode. For example, under the photovoltaic system architecture provided in the present application, an optimizer is connected to a photovoltaic module, and the power output characteristic curve of the photovoltaic module is affected by factors such as temperature, solar radiation or shadow. The DC conversion unit 101 of the optimizer includes multiple switch tubes. The optimizer controls the duty cycle of the one or more switch tubes through pulse width modulation, so that the input voltage of the optimizer always tracks the maximum power point operating voltage of the photovoltaic module, and the photovoltaic module maintains the maximum power output; on the other hand, the DC conversion unit 101 is used to work in the limited voltage mode. In this mode, the optimizer controls the duty cycle of the one or more switch tubes through pulse width modulation, so that the output voltage of the optimizer is a specific voltage threshold. Under this specific voltage threshold, the inverter 104 has a smaller input voltage than before adjusting the voltage or maintains the input voltage of the inverter within an acceptable range to protect the inverter. In short, the DC conversion unit 101 can output different voltage values ​​according to different operation strategies to meet the different operation requirements of the photovoltaic system.

[0076] The signal processing unit 103 and the signal transceiver unit 108 are used to receive or send PLC signals. It should be understood that Figure 3 The coupling mode between the signal processing unit 103 and the inverter 104 shown in the figure is one of the schematic diagrams. The coupling modes between the signal processing unit 103 and the inverter 104 include double-sided coupling (coupling to both sides of the inverter output) and single-sided coupling (coupling to one side of the inverter output). The coupling types include transformer coupling and magnetic ring coupling. The present application does not limit the coupling mode and coupling type between the signal processing unit 103 and the inverter 104.

[0077] The control unit 102 is used to control the closing or shutting down of the switch tube in the DC conversion unit 101 in the optimizer according to the information received by the signal processing unit 103 or the operation information pre-stored therein.

[0078] The inverter circuit 109 is used to convert direct current into alternating current.

[0079] In the same photovoltaic string, except for optimizer 1-1 and optimizer 1-n, the other optimizers are not directly connected to inverter 104, but because the output ends of multiple optimizers are connected in series, the optimizer signal processing unit in each optimizer can process the signal broadcasted by inverter 104, so that all optimizers can receive instructions from inverter 104 and perform corresponding actions.

[0080] This application Figure 1 or Figure 2 In the photovoltaic system in the embodiment shown, the inverter 104 and the optimizer have not only a power connection mode but also a PLC communication connection mode. The communication mode between the inverter 104 and the optimizer, in addition to the PLC communication connection, also includes RS485, zigbee and sub-1G connection modes. In this application, the embodiment is mainly described in terms of the PLC communication mode.

[0081] The following combination Figure 3 The photovoltaic system shown describes the implementation process of PLC communication in detail.

[0082] refer to Figure 3 In the PLC communication mode, the photovoltaic system uses the inverter 104 and the optimizers 1-1 to 1-n to Figure 3 The power lines 106 or 107 shown are used for data exchange.

[0083] Taking optimizer 1-1 as an example, since there is data interaction between optimizer 1-1 and inverter 104, and these data interactions are indispensable for maintaining the normal operation of inverter 104 and optimizer 1-1, it is particularly important to ensure the reliability of the PLC communication method. In order to ensure the reliability of communication and ensure that the optimizer 1-1 and inverter 104 are not disconnected or disconnected, the embodiment of the present application adopts a heartbeat protection mechanism to detect the communication status between inverter 104 and optimizer 1-1.

[0084] In one embodiment, the host in the heartbeat protection mechanism is the inverter 104, and the slave is the optimizer 1-1. After the photovoltaic system is started, the inverter 104 will send a heartbeat frame to the optimizer 1-1 regularly or periodically. After receiving the heartbeat frame, the optimizer 1-1 will send feedback information to the inverter 104. If the inverter 104 does not receive the feedback information, it will take remedial measures such as attempting to reconnect.

[0085] In one embodiment, the host in the heartbeat protection mechanism is the inverter 104, and the slave is the optimizer 1-1. After the photovoltaic system is started, the inverter 104 will send a heartbeat frame to the optimizer 1-1 regularly or periodically. The optimizer 1-1 will not send feedback information to the inverter 104, but will perform corresponding operations on the optimizer 1-1 end according to different situations of whether the heartbeat frame is received.

[0086] In the present application, in addition to the heartbeat frame, after the inverter detects a fault or receives a control instruction issued by the user, the inverter 104 will also send a voltage regulation instruction to the optimizer 1-1, and the voltage regulation instruction can instruct the optimizer 1-1 to regulate the DC conversion unit 101, so that the optimizer 1-1 outputs a specific voltage or current. The frequency of the heartbeat frame and the voltage regulation instruction can be the same or different.

[0087] The inverter 104 and the optimizer exchange data through the signal transceiver unit 108 on the inverter 104 side and the signal processing unit 103 of the optimizer 1-1. The communication mode of the data exchange is PLC communication. The PLC signals for data exchange include heartbeat frames and voltage regulation instructions. The heartbeat frames and voltage regulation instructions are both periodic communication signals. The entire communication process is as follows:

[0088] During the operation between the inverter 104 and the optimizer, the signal transceiver unit 108 sends the PLC signal superimposed with the heartbeat frame and the voltage regulation instruction to each optimizer by broadcasting through the PLC communication method. After receiving the PLC signal, the signal processing unit 103 processes the PLC signal and sends the processed PLC signal to the control unit 102 inside the optimizer. The control unit 102 controls the operation of the DC conversion unit 101 according to the processed PLC signal to adjust the output voltage or output current of the optimizer.

[0089] The following only takes optimizer 1-1 as an example for explanation. It should be understood that all optimizers belonging to the same PV string can receive the PLC signal, and the working principles of other optimizers in the same PV string will not be described in detail below.

[0090] In the photovoltaic system of the embodiment of the present application, the optimizer 1-1 switches different working modes of the optimizer according to the received heartbeat frame and voltage regulation instruction, and the working modes include normal working mode, safe working mode and shutdown mode. The data communication method and working principle of the inverter and optimizer devices in three different working modes are first introduced below.

[0091] Normal working mode: In normal working mode, the inverter 104 sends periodic heartbeat frames to the optimizer through PLC communication. In this mode, the optimizer 1-1 successfully receives the periodic heartbeat frames from the inverter 104. Based on the successful receipt of the periodic heartbeat frames and the failure to receive the voltage regulation instruction, the optimizer determines that the communication between the optimizer 1-1 and the inverter 104 is normal and needs to execute the normal working mode. In this mode, in order to increase the power input of the inverter 104, the optimizer 1-1 outputs as much power as possible. For example, the optimizer 1-1 controls the voltage at the input end of the optimizer 1-1 to be at the maximum power point voltage of the photovoltaic module or close to the maximum power point near the maximum power point voltage, and the DC conversion unit 101 operates in the MPPT tracking mode. Common situations that trigger the optimizer 1-1 to execute the normal working mode include when the light in the early morning reaches the initial threshold of the light intensity and when the user turns on the photovoltaic power generation system. In the early morning, when the photovoltaic module receives light that exceeds the initial threshold of light intensity, the inverter and optimizer are powered on and start working. The inverter starts to send PLC signals to the optimizer. After the optimizer receives the periodic heartbeat frame, it determines that the communication between the inverter and the optimizer is normal and starts to output voltage in the normal working mode. When the user turns on the power, the user actively closes the DC switch of the inverter 104, which is installed on the side of the inverter 104. After the DC switch is closed, an electrical connection is formed between the optimizer 1-1 and the inverter 104, and the optimizer 1-1 successfully receives the heartbeat frame from the inverter 104. After the optimizer 1-1 receives the periodic heartbeat frame, the optimizer 1-1 executes the normal working mode to output voltage.

[0092] Safe working mode: In the safe working mode, the optimizer 1-1 still receives the periodic heartbeat frame from the inverter 104, and determines that the communication between the optimizer 1-1 and the inverter 104 is normal based on the successful reception of the periodic heartbeat frame. However, in this mode, in addition to the heartbeat frame, the inverter 104 also sends a periodic voltage regulation instruction through the PLC communication method. After the optimizer 1-1 successfully receives the periodic voltage regulation instruction, based on the successful reception of the periodic heartbeat frame and the periodic voltage regulation instruction, the optimizer determines that the communication between the optimizer 1-1 and the inverter 104 is normal and the safe working mode needs to be executed. In this mode, according to the voltage regulation instruction, the optimizer 1-1 limits the output voltage or current of the output end of the optimizer 1-1, for example, limiting the output voltage of the optimizer 1-1 to a certain voltage, and controlling the DC unit 101 to be in the voltage limiting mode. In this voltage limiting mode, the input voltage of the inverter is also limited, thereby realizing the protection of the inverter-side equipment in the photovoltaic system. It should be understood that in the safe working mode, the specific value of the specific voltage can be adjusted. The size of the specific value is affected by factors such as the local standard of the product installation and the number of optimizers. The setting of the specific value of the specific voltage can ensure that the equipment on the inverter side will not be damaged. In addition, the situation of triggering the optimizer 1-1 to execute the safe working mode is more complicated. Figure 4 Various situations that trigger the safe working mode are explained.

[0093] Shutdown mode: In shutdown mode, the optimizer 1-1 does not receive a heartbeat frame from the inverter 104 for more than a period of time, and the period includes M times the period of the heartbeat frame, where M is a constant. The period can also be a preset time, which depends on the stability of the PLC communication in the working environment of the optimizer. The higher the stability, the longer the period, and the lower the stability, the shorter the period, so as to fully ensure the normal communication between the optimizer and the inverter. Then, based on the failure to successfully receive the periodic heartbeat frame, it is determined that the communication between the optimizer 1-1 and the inverter 104 is abnormal, and the inverter 104 can no longer effectively control the optimizer 1-1. The optimizer 1-1 controls the output voltage to the shutdown voltage, which is the voltage preset when the optimizer 1-1 leaves the factory, and the preset low voltage range is 1 to 48 volts. At this time, even if a person directly touches the output port of the photovoltaic string, there will be no danger, thereby maximizing the safety of users and maintenance personnel. Common situations that trigger the optimizer 1-1 to execute the shutdown mode include the user manually shutting down the inverter 104. In this case, the user actively disconnects the DC switch of the inverter 104, which is installed on the side of the inverter 104. After the DC switch is disconnected, the electrical connection between the optimizer 1-1 and the inverter 104 is disconnected, and the optimizer 1-1 can no longer receive the heartbeat frame from the inverter 104. After the optimizer 1-1 does not receive the heartbeat frame from the inverter 104 for more than a fixed time, the optimizer 1-1 executes the shutdown mode.

[0094] For the above three working modes, the optimizer will choose to maintain the current working mode or switch to another working mode according to the different PLC signals it receives. In some embodiments, before the time period t1, the PLC signal received by the optimizer 1-1 contains a heartbeat frame but does not contain a voltage regulation instruction, then the optimizer 1-1 maintains working in the normal working mode; during the time period t1-t2, the PLC signal received by the optimizer contains both a heartbeat frame and a voltage regulation instruction, then the optimizer switches to the safe working mode at time t2; during the time period t2-t3, the PLC signal received by the optimizer contains a heartbeat frame and a voltage regulation instruction, then the optimizer maintains the safe working mode; during the time period t3-t4, the PLC signal received by the optimizer contains a heartbeat frame but does not receive a voltage regulation instruction, then the optimizer switches from the safe working mode to the normal working mode at time t4; during the time period t4-t5, the optimizer does not receive the PLC communication signal, that is, does not receive the heartbeat frame, then at time t5, the optimizer will choose to switch from the normal working mode to the shutdown mode, where t1 to t5 occur in sequence, and the time periods between each two moments may be equal or unequal.

[0095] The main difference between the above three working modes is reflected in the control of the change of the output voltage state of the optimizer 1-1. In fact, different working modes correspond to different output voltage states of the optimizer 1-1. In the description of some embodiments, the specific embodiment can be described as the optimizer 1-1 directly adjusting the output voltage according to whether the heartbeat frame signal and the voltage regulation instruction are received, without the need to simultaneously reflect the changes of different working modes.

[0096] For example: in response to some or all of the multiple optimizers 1-1 not receiving a periodic PLC signal or a heartbeat frame from the inverter 104 within a period of time, the optimizer 1-1 that does not receive the signal adjusts the voltage output by the output end of the optimizer 1-1 to a shutdown voltage, and the shutdown voltage is a preset safety voltage value;

[0097] In response to some or all of the multiple optimizers 1 - 1 receiving the heartbeat frame from the inverter 104 and failing to receive the voltage regulation instruction, the corresponding optimizer 1 - 1 controls the output voltage to be less than or equal to the first voltage;

[0098] In response to the multiple optimizers 1-1 receiving all or part of the heartbeat frame and the voltage adjustment instruction, the corresponding optimizer controls the output voltage to be less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

[0099] It can be seen that in the above photovoltaic system, the optimizer 1-1 determines the different working states of the inverter 104 or the different requirements for the front-stage power input according to the change of the PLC signal, so as to timely adjust the corresponding working state of the optimizer 1-1, so as to effectively and timely protect the inverter 104 under various working conditions. The embodiment of the present invention loads the voltage regulation instruction in the communication between the optimizer and the inverter of the photovoltaic system, such as PLC communication, so that the optimizer can adjust the output voltage regulation to a safe range in time after the inverter has a fault such as overvoltage, overcurrent or leakage, so as to timely and effectively protect the subsequent inverter equipment and improve the operation safety of the entire photovoltaic system.

[0100] The following combination Figure 4 The various triggering safety working modes provided in the embodiments of the present application are described. Figure 4 This is another optimizer-inverter connection diagram provided in the embodiment of the present application. In addition to the photovoltaic module and the optimizer, Figure 4 The photovoltaic power generation system shown also includes an inverter 104, a first AC bus, a second AC bus and a power grid 105. The inverter 104 includes a DC conversion circuit 110, a DC bus, an inverter circuit 109, a sampling circuit and a controller. Figure 4 The input end of the inverter 104 is connected to three photovoltaic strings. Specifically, each photovoltaic string is connected to a corresponding DC conversion circuit 110. The DC conversion circuit 110 converges the converted DC power to the DC bus. The inverter circuit then takes power from the DC bus, converts the DC power into AC power, and then transmits it to the first AC bus, and finally transmits the DC power to the power grid 105. In some photovoltaic power generation systems with large power generation, the low-voltage AC power on the first AC bus will be boosted by a transformer and then transmitted to the second AC bus, and finally the DC power will be transmitted to the power grid 105. The sampling circuit in the inverter can collect electrical data such as voltage, current and power of the input end of the DC conversion circuit 110 (or the output end of the photovoltaic string) and the output end of the inverter circuit 109 in real time, and then transmit the collected data to the controller in the inverter. The controller determines the working state of the inverter based on these real-time collected electrical data, and sends different instructions to each electrical component inside the inverter according to different working states to execute the best operation strategy.

[0101] In some possible embodiments, the inverter 104 may send a voltage adjustment instruction to the optimizer 1-1 when the following situations occur, including: (1) overvoltage at the input end of the inverter 104; (2) overpower at the input end of the inverter 104; (3) islanding effect occurs in the inverter 104.

[0102] The following is a brief description of the above three situations.

[0103] (1) Overvoltage at the input of the inverter 104. The controller detects that the voltage at the input of the DC conversion circuit 110 exceeds a preset voltage threshold, and determines that the input of the inverter 104 is overvoltage. The preset voltage threshold is related to the hardware circuit carrying capacity of the inverter 104. For a single-phase inverter, the preset voltage threshold is 600V, and for a three-phase inverter, the preset voltage threshold is 1100V. Exceeding the above voltage threshold, the inverter may fail or be damaged. When the input of the inverter is overvoltage, when the optimizer switches to the safe working mode, the output voltage of the optimizer can be adjusted to K times the current voltage, where K is less than 1, and the K depends on the specific value of the safe voltage on the input side of the inverter. Preferably, K is 0.5 times or 0.1 times to protect the inverter. In particular, in order to eliminate occasional power fluctuations in the power generation system, the optimizer will switch itself to the safe working mode only when the input voltage of the DC conversion circuit 110 exceeds a preset voltage threshold for more than a period of time.

[0104] (2) Overpower at the input end of inverter 104. When designing a photovoltaic system, in order to make full use of the inverter, the inverter is usually allowed to have a certain over-matching ratio. For example, in a photovoltaic system, the theoretical maximum input power of the photovoltaic module is 12KW, and the maximum allowable input power of the inverter is 10KW. Then the power over-matching ratio of the inverter is 1.2, which is the ratio of 12KW to 10KW. Under normal lighting conditions, the actual output power of the photovoltaic module is less than 10KW. At this time, the inverter can work normally. However, when the lighting conditions are good for a long time and the actual output power of the photovoltaic module is greater than 10KW for a long time, the inverter will remain in an overloaded working state for a long time. At this time, it is necessary to limit the input power of the inverter. The embodiment of the present application sends a voltage regulation instruction to the optimizer 1-1 to limit the output voltage of the optimizer and then limit the power of the inverter, so as to achieve the purpose of protecting the inverter.

[0105] (3) Islanding effect occurs in inverter 104. Due to grid failure and other reasons, the photovoltaic power generation system where inverter 104 is located has become completely independent of the grid. Inverter 104 recognizes that it has experienced islanding effect. In order to avoid excessive fluctuations in voltage and frequency in the islanding system to damage electrical equipment, inverter 104 sends a voltage adjustment instruction to optimizer 1-1 based on this situation.

[0106] In order to meet the input requirements of the inverter 104, the optimizer 1-1 will generally set the voltage limit point of the optimizer 1-1 according to the number of optimizers 1-1 in the photovoltaic string and the input voltage limit of the inverter 104 during normal operation. After the photovoltaic power generation system starts to work normally, the optimizer 1-1 will always limit its output voltage to below the voltage limit point. For example: the input voltage of the inverter 104 is limited to 500V, and there are 10 inverters 104 connected to the input end of the inverter 104, then the optimizer 1-1 should set its own voltage limit point to 50V, so that the optimizer 1-1 always outputs a voltage less than 50V during operation. Taking the voltage limit point of the optimizer 1-1 as 50V as an example, the present application provides the following two methods to achieve the voltage limit point setting of the optimizer 1-1. Method 1: After the optimizer 1-1 is installed for the first time and started up and debugged, the optimizer 1-1 sets the voltage limit point at 50V according to the number of optimizers 1-1 and the system voltage limit. After that, the voltage limit point data is stored inside the optimizer 1-1. When the optimizer 1-1 works subsequently, the data can be directly called from inside the optimizer 1-1 without setting the voltage limit point again. This method has a simple implementation strategy and good effect. Method 2: The voltage limit point data required to be set by the optimizer 1-1 is sent by the inverter 104 and will not be stored in the optimizer 1-1. Under this method, when the inverter 104 and the optimizer 1-1 work normally, the inverter 104 periodically sends a 50V voltage limit point signal to the optimizer 1-1. The optimizer 1-1 receives the voltage limit point signal and always keeps the output voltage of no more than 50V during operation.

[0107] It should be understood that the voltage limit point signal in the second method mentioned above may still appear in the safe working mode of the optimizer 1-1 provided in the present application, but there is at least one obvious difference between the voltage limit point signal described in the second method and the voltage regulation instruction in the safe working mode, that is, the triggering conditions are different. The triggering condition of the voltage limit point signal is that the inverter 104 and the optimizer 1-1 are both operating normally, while the triggering condition of the voltage regulation instruction is when a fault occurs in the inverter. The specific fault types include the above-mentioned three types of inverter failures: (1) overvoltage at the input end of the inverter 104; (2) overpower at the input end of the inverter 104; (3) islanding effect occurs in the inverter 104.

[0108] In combination with the voltage limit point of the above-mentioned optimizer, in one embodiment, the first voltage is the voltage corresponding to the voltage limit point of the optimizer. The optimizer is used to adjust the input voltage of the optimizer within the range of the first voltage or the voltage limit point to perform maximum power tracking MPPT on the power output of the connected photovoltaic assembly. The shutdown voltage is a preset safety voltage value, and the second voltage is between the first voltage and the shutdown voltage. The first voltage can be a preset fixed value, or it can be adjusted and updated according to the needs of the optimizer or the instructions of the inverter. When the signal processing unit of the optimizer does not receive the periodic communication signal within a time period, the voltage output by the power conversion device is controlled to be the shutdown voltage; when the signal processing unit of the optimizer receives the periodic communication signal but the periodic communication signal does not contain the voltage regulation instruction, the voltage output by the power conversion device is controlled to be less than or equal to the first voltage; when the signal processing unit of the optimizer receives the periodic communication signal and the periodic communication signal contains the voltage regulation instruction, the voltage output by the power conversion device is controlled to be less than or equal to the second voltage. In one implementation, the second voltage is P times the first voltage, where P<1, and P includes 0.5 or 0.1.

[0109] In particular, in the safe working mode, since only the output voltage or current of the optimizer 1-1 is limited, the DC conversion unit 101 is not completely powered off. When the optimizer 1-1 changes from receiving timed heartbeat frames and voltage regulation instructions to only receiving heartbeat frames from the inverter 104, the control unit 102 in the optimizer 1-1 can quickly restore the DC conversion unit 101 from the limited voltage mode to the MPPT tracking mode by changing the duty cycle, etc., and the optimizer 1-1 also quickly switches from the safe working mode to the normal working mode. Therefore, the photovoltaic string where the optimizer 1-1 is located still has the ability to quickly recover to output a higher voltage, so that the inverter 104 can also resume normal output in a shorter time.

[0110] Similarly, in normal working mode, the DC conversion unit 101 is in MPPT tracking mode, the inverter 104 periodically sends heartbeat frames to the optimizer 1-1, and the optimizer 1-1 receives the timed heartbeat frames. When the optimizer 1-1 changes from only receiving the timed heartbeat frames to receiving the voltage regulation instructions from the inverter 104 in addition to the heartbeat frames from the inverter 104, the control unit 102 in the optimizer 1-1 can quickly convert the DC conversion unit 101 from the MPPT tracking mode to the voltage limiting mode by changing the duty cycle, etc., and the optimizer 1-1 also quickly converts from the normal working mode to the safe working mode, thereby promptly ensuring the safety of the inverter equipment when a fault occurs.

[0111] In the embodiment of the present application, the optimizer 1-1 can quickly switch between the normal working mode, the safe working mode and the shutdown mode, so that in the event of a failure in the photovoltaic system, the output voltage of the photovoltaic string can be quickly reduced to ensure the safety of the inverter. In the installation and maintenance of the optimizer 1-1, the output voltage of the photovoltaic string is limited to a safe voltage to ensure the personal safety of personnel. When the power generation scenario of the optimizer changes, the working mode of the optimizer is quickly switched. The embodiment of the present application can fully ensure the safety of the inverter equipment, the safety of users and maintenance personnel, and can also greatly reduce the impact of maintenance, installation and maintenance on the user's electricity consumption.

[0112] The following is an explanation of the method for controlling the operation of the optimizer provided in the embodiment of the present application with reference to a flowchart.

[0113] Figure 5It is a schematic diagram of the switching process of the working mode of the optimizer provided in the embodiment of the present application. In step 20, the optimizer is turned on. At this time, the corresponding actual scene may be when the sun rises in the early morning, the sunlight provides the photovoltaic components with sunlight for energy conversion, and the optimizer has the power required for startup. Optionally, the optimizer also receives a startup instruction sent from the inverter. Then the optimizer will execute step 21. Under this step, the optimizer will determine whether the heartbeat frame is received regularly. Here, the situation of receiving the heartbeat frame regularly includes that the optimizer receives a heartbeat frame signal sent at a specific frequency within a period of time. If this condition is met, step 22 is executed. If it is not satisfied, for example, the frequency of the heartbeat frame is not a specific frequency, the time of receiving the heartbeat frame does not meet the above-mentioned period of time, or the heartbeat frame signal is not received at all, etc., then step 25 is executed. In step 25, the optimizer performs a shutdown action. In the shutdown mode, the voltage output at the output end of the optimizer is the preset voltage when the optimizer leaves the factory. The voltage can be greater than the output voltage of the optimizer in the safe mode, or it can be less than the output voltage of the optimizer in the safe mode, but it must be less than the voltage of the voltage limit point of the optimizer. Under the shutdown voltage, even if there are multiple optimizers in series in one photovoltaic string, the voltage on the inverter power line will not exceed the safe voltage, and even if the user or maintenance personnel directly touches the power line, there will be no risk of electric shock. In step 22, the optimizer operates in the normal working mode. In the normal working mode, the optimizer generally performs the MPPT function. The optimizer adjusts its input voltage to the working voltage corresponding to the maximum power point in the power characteristic curve of the photovoltaic module, and its output voltage fluctuates within a certain range according to the needs of the power converter and the electrical characteristics of the photovoltaic string. Then the optimizer will execute step 23. In this step, the optimizer determines whether it has received a voltage regulation instruction or an alarm condition has occurred. If so, the optimizer executes step 24, if not, the optimizer returns to step 22. Here, the voltage regulation instruction is a PLC signal sent by the inverter to the optimizer when the above three faults occur. In step 24, the optimizer operates in a safe working mode. In this mode, the optimizer adjusts the duty cycle of the power conversion inside it. For example, the duty cycle changes relative to the normal working mode, thereby limiting the output of the optimizer and keeping the voltage output by the optimizer at a specific voltage, thereby limiting the input voltage of the inverter and ensuring the equipment safety of the inverter.

[0114] In the above-mentioned various working modes, the optimizer will report its operating status to the northbound device. In the embodiment of the present application, when in shutdown mode, the optimizer reports the "shutdown" status; when in normal working mode and safe working mode, the optimizer reports the "running" status; when a fault occurs, the optimizer reports the "fault" status.

[0115] Figure 6It is a schematic diagram of the inverter workflow provided by the embodiment of the present application. In step 26, the inverter is in the shutdown state. The corresponding actual scene at this time may be that there is no sunlight or the sunlight is weak at night, or the user disconnects the DC switch on the inverter side. At this time, the inverter has not been powered on, or its voltage is not enough to support the power-on of each device used for signal transmission in the inverter. Then comes step 27. The inverter will continue to judge whether it meets the startup conditions. When the sunlight is strong or the user turns on the DC switch on the inverter side, so that the voltage of the inverter is raised to the voltage used by the inverter for signal transmission, the inverter executes step 28 and starts signal transmission with the optimizer. Here, the signal transmitted between the inverter and the optimizer includes the above-mentioned heartbeat frame, voltage regulation instruction and voltage limit point signal; when the inverter judges that it still does not meet the startup conditions at the current moment, it will return to execute step 26. After the inverter starts signal transmission, it will execute step 29 to start up. At this time, all components in the inverter basically start working, the optimizer continues to input DC power to the inverter, and the inverter continues to output AC power required by the user load. Then comes step 30, and the inverter will determine whether it has an alarm condition. If no alarm condition occurs, the inverter returns to execute step 29. If an alarm condition occurs, it means that under the current condition, the inverter is no longer suitable for continuing to provide AC power to the user load, and it should be shut down in time, otherwise the internal electrical components of the inverter will be burned, and in serious cases, a fire will be caused, threatening the safety of the user's life and property. After the alarm condition occurs, the inverter executes step 31, that is, cuts off the signal transmission. After cutting off the signal transmission, the inverter returns to execute step 26 and the inverter is shut down.

[0116] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0117] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A power conversion device, characterized in that: The power conversion device comprises: a DC conversion unit, a signal processing unit and a controller, wherein the DC conversion unit is used to convert the DC power generated by the photovoltaic module and output it to the next-stage power conversion device; The signal processing unit is connected to the output of the power conversion device and is used to receive the periodic communication signal sent by the next-stage power conversion device; The controller is used to: In response to the signal processing unit failing to receive the periodic communication signal within a time period, controlling the voltage output by the power conversion device to be a shutdown voltage, wherein the shutdown voltage is a preset safety voltage value; In response to the signal processing unit receiving the periodic communication signal but the periodic communication signal does not include a voltage regulation instruction, controlling the voltage output by the power conversion device to be less than or equal to a first voltage; In response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing the voltage regulation instruction, the voltage output by the power conversion device is controlled to be less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

2. The power conversion device according to claim 1, characterized in that: The periodic communication signal is a PLC signal, and the PLC signal includes a heartbeat frame; The controller is used to: In response to the signal processing unit failing to receive the heartbeat frame within a period of time, the voltage output by the power conversion device is controlled to be the shutdown voltage.

3. The power conversion device according to claim 2, characterized in that: The controller is used to: In response to the signal processing unit receiving the PLC signal and the PLC signal including the heartbeat frame connection but not including the voltage regulation instruction, controlling the voltage output by the power conversion device to be less than the first voltage; In response to the signal processing unit receiving the PLC signal and the PLC signal including both the heartbeat frame and the voltage regulation instruction, the voltage output by the power conversion device is controlled to be less than the second voltage.

4. The power conversion device according to claim 3, characterized in that: The controller is used to: In response to the signal processing unit receiving the PLC signal and the PLC signal including both the heartbeat frame and the voltage adjustment instruction, the voltage output by the power conversion device is adjusted to K times the current output voltage of the power conversion device, where K is less than 1.

5. The power conversion device according to claim 4, characterized in that: The K is 0.5 or 0.

1.

6. The power conversion device according to claim 1, characterized in that: The controller is used to: In response to the signal processing unit receiving the periodic communication signal but the periodic communication signal does not include the voltage regulation instruction, the DC conversion unit is controlled to operate in a maximum power tracking mode, in which the output voltage of the DC conversion unit changes and the output power of the photovoltaic assembly connected to the DC conversion unit is maximum; In response to the signal processing unit receiving the periodic communication signal and the periodic communication signal including the voltage regulation instruction, the DC conversion unit is controlled to operate in a voltage limiting mode, in which the voltage output by the DC conversion unit is constant.

7. A power conversion device control method, characterized in that: The method comprises: In response to the power conversion device failing to receive a heartbeat frame, controlling the voltage output by the power conversion device to be a shutdown voltage, wherein the shutdown voltage is a preset safety voltage value; In response to the power conversion device receiving the heartbeat frame and failing to receive a voltage regulation instruction, controlling the voltage output by the power conversion device to be less than or equal to a first voltage; In response to the power conversion device receiving the heartbeat frame and the voltage adjustment instruction, the voltage output by the power conversion device is controlled to be less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

8. The method according to claim 7, characterized in that When it is detected that the voltage at the input end of the inverter exceeds an overvoltage threshold, the inverter is used to receive the DC power output by the power conversion device and send the voltage regulation instruction to the power conversion device. The power conversion device receives the voltage regulation instruction and controls the output voltage of the power conversion device to be less than the overvoltage threshold. The power conversion device is connected to the inverter through a power line, and the heartbeat frame and the voltage regulation instruction are transmitted through the power line.

9. The method according to claim 7, characterized in that: When it is detected that the power at the input end of the inverter exceeds an over-power threshold, the inverter is used to receive the DC power output by the power conversion device and send the voltage regulation instruction to the power conversion device. The power conversion device receives the voltage regulation instruction and controls the output voltage of the power conversion device to decrease. The power conversion device is connected to the inverter through a power line, and the heartbeat frame and the voltage regulation instruction are transmitted through the power line.

10. The method according to claim 7, characterized in that When an islanding effect is detected in the power generation system where the inverter is located, the inverter is used to receive the DC power output by the power conversion device and send the voltage regulation instruction to the power conversion device. The power conversion device receives the voltage regulation instruction and controls the output voltage of the power conversion device to decrease. The power conversion device is connected to the inverter through a power line, and the heartbeat frame and the voltage regulation instruction are transmitted through the power line.

11. A photovoltaic power generation system, characterized in that: include: A plurality of optimizers, wherein the plurality of optimizers are used to convert the direct current generated by the photovoltaic assembly and output it to the inverter; An inverter, the inverter being used to supply power to a power grid or a user load, the inverter being further used to send a heartbeat frame and a voltage regulation instruction to the multiple optimizers, the heartbeat frame and the voltage regulation instruction being transmitted through a power line between the inverter and the optimizer; In response to the multiple optimizers failing to receive the heartbeat frame within a time period, the voltage output by the multiple optimizers is a shutdown voltage, and the shutdown voltage is a preset safety voltage value; In response to the multiple optimizers receiving the heartbeat frame and failing to receive the voltage adjustment instruction, the voltages output by the multiple optimizers are less than or equal to the first voltage; In response to the multiple optimizers receiving the heartbeat frame and receiving the voltage adjustment instruction, the voltage output by the multiple optimizers is less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

12. The photovoltaic power generation system according to claim 11, characterized in that: When the input voltage of the inverter exceeds an overvoltage threshold or the input power of the inverter exceeds an overpower threshold, the inverter sends the voltage regulation instruction to the optimizer, and the optimizer receives the voltage regulation instruction, and the optimizer controls its own output voltage to be less than or equal to the second voltage.

13. The photovoltaic power generation system according to claim 11, characterized in that: In response to some or all of the multiple optimizers failing to receive the heartbeat frame within a period of time, the optimizers failing to receive the heartbeat frame adjust the output voltage to a shutdown voltage, where the shutdown voltage is a preset safety voltage value; In response to the multiple optimizers receiving the heartbeat frame and failing to receive the voltage adjustment instruction, the voltages output by the multiple optimizers are less than or equal to the first voltage; In response to the multiple optimizers receiving the heartbeat frame and receiving the voltage adjustment instruction, the voltage output by the multiple optimizers is less than or equal to a second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

14. The photovoltaic power generation system according to claim 11, characterized in that: When an islanding effect occurs in the power generation system where the inverter is located, the inverter sends the voltage regulation instruction to the optimizer. After the optimizer receives the voltage regulation instruction, the optimizer controls its own output voltage to be less than or equal to the second voltage.

15. The photovoltaic power generation system according to claim 11, characterized in that: When the inverter meets the startup condition, the inverter sends the heartbeat frame or the voltage adjustment instruction to the optimizer; When the inverter detects the alarm signal, the inverter stops sending the heartbeat frame or the voltage regulation instruction to the optimizer and performs a shutdown action.

16. The photovoltaic power generation system according to claim 11, characterized in that: The multiple optimizer inputs are used to connect to photovoltaic modules respectively, and the outputs of the multiple optimizers are connected in series and then connected to the input of the inverter; The inverter is used to broadcast the heartbeat frame and the voltage regulation instruction to the multiple optimizers through PLC, and the voltage regulation instruction is used to adjust the voltage output by the multiple optimizers to K times the current output voltage of the multiple optimizers, where K is less than 1.

17. The photovoltaic power generation system according to claim 16, characterized in that: The K is 0.5 or 0.1.

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