Power equipment, power equipment control method and photovoltaic power generation system

Abstract

The invention discloses power equipment, a power equipment control method and a photovoltaic power generation system. The input end of the assembly-level power electronic equipment is connected with the photovoltaic assembly, and the output ends of the assembly-level power electronic equipment are connected in series and then connected with the inverter. The component-level power electronic equipment comprises a direct current conversion unit, a signal processing unit and a controller. The direct current conversion unit is used for realizing direct current-direct current power conversion, the signal processing unit is used for receiving periodic communication signals sent by the inverter, and the controller is used for controlling the component-level power electronic equipment to be switched among a shutdown mode, a normal working mode and a safe working mode. And when the component-level power electronic equipment cannot receive the periodic communication signal, maintaining or switching to a shutdown mode, and when the periodic communication signal received by the component-level power electronic equipment comprises a heartbeat frame and does not comprise a voltage regulation instruction, switching to a normal working mode, and when the periodic communication signal received by the component-level power electronic equipment comprises a heartbeat frame and also comprises a voltage regulation instruction, switching to a safe working mode. The three working modes provided by the invention can guarantee the safety of equipment and personnel at the same time, the response speed is high, and the implementation mode is simple.

Description

Technical Field

[0001] This application relates to the field of power electronics, and more particularly to a power device, a power device control method, and a photovoltaic power generation system. Background Technology

[0002] Currently, with the global shortage of non-renewable energy and the increasing severity of environmental pollution, the application of photovoltaic power generation is becoming more and more widespread. Photovoltaic power generation converts the direct current generated by photovoltaic modules into alternating current through an inverter, and then connects it to the AC power grid or supplies it to loads.

[0003] Photovoltaic (PV) power generation is typically applied in three main scenarios: large-scale PV power plants, industrial and commercial applications, and residential applications. In the latter two scenarios, PV modules are usually installed on building rooftops, close to the electricity users. To achieve higher power output, PV modules are often composed of multiple photovoltaic panels connected in series, resulting in a relatively high DC voltage on the PV module side. This creates significant safety hazards: if the inverter or PV modules malfunction, the roof where the PV modules are installed may catch fire. Furthermore, when repairing PV modules and inverters, maintenance personnel face hundreds or even thousands of volts of high-voltage DC current, and excessive DC voltage on the PV module side can also damage the inverter, hindering the long-term stable operation of the PV power generation system.

[0004] Module-level power electronic devices (MLPEs), as an emerging type of distributed photovoltaic (PV) power generation equipment, can control individual PV modules, resulting in further improvements in power generation efficiency compared to traditional string PV power generation. Furthermore, how to utilize MLPEs to reduce the voltage on the PV module side when needed, fully ensuring the personal safety of electricity users or maintenance personnel, protecting the power generation equipment, and improving the safety of power generation and maintenance of distributed PV systems has become a hot research topic in the industry. Summary of the Invention

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

[0006] In a first aspect, embodiments of this application disclose a power conversion device, comprising: a DC-DC converter, a signal processing unit, and a controller. One end of the DC-DC converter is connected to a photovoltaic module, and the other end is connected to the input terminal of a next-stage power conversion device. The signal processing unit is located on the output side of the power conversion device. The signal processing unit is used to receive periodic communication signals sent by the next-stage power conversion device. The controller is used to, in response to the signal processing unit not receiving the periodic communication signals for a period of time, control the power conversion device to switch to a shutdown mode or maintain operation in a shutdown mode. In the shutdown mode, the voltage output by the power conversion device is a shutdown voltage. The shutdown voltage is a preset safe voltage value; in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing a voltage adjustment command, the power conversion device is controlled to switch to a safe operating mode or maintain operation in a safe operating 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 not containing the voltage adjustment command, the power conversion device is controlled to switch to a normal operating mode or maintain operation in a normal operating 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 first aspect of the technical solution, the next-level power conversion equipment and the power conversion equipment have both communication and power connections. Specifically, the communication method between the next-level power conversion equipment and the power conversion equipment is power line communication. Based on this, periodic communication signals are used to control the switching of the operating mode of the power conversion equipment. In this way, using existing power lines for communication transmission reduces the cost required to establish additional communication lines. Using periodic communication signals for communication results in fast response speed and simple implementation. Furthermore, by switching between three operating modes, the power conversion equipment can ensure that the output power of the power conversion equipment is always at its maximum in normal operating mode to meet the user's power needs to the greatest extent. In safe operating mode, faults can be detected in time, and protection mechanisms can be activated to ensure the safety of the equipment on the next-level power conversion equipment side. In shutdown mode, the output voltage of the power conversion equipment can be reduced below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0008] According to the first aspect, in one possible implementation, the periodic communication signal is a PLC signal, which includes a heartbeat frame; the controller is configured to, in response to the signal processing unit not receiving the heartbeat frame for a period of time, control the power conversion device to switch to a shutdown mode or maintain operation in a shutdown mode. By employing 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 operating mode of the power conversion device can be controlled in real time and accurately based on the communication status between the two, utilizing existing power lines.

[0009] According to the first aspect, in one possible implementation, the controller is configured to: control the power conversion device to switch to normal operation mode or maintain operation in normal operation mode in response to the signal processing unit receiving the PLC signal and the PLC signal containing the heartbeat frame but not the voltage regulation command; and control the power conversion device to switch to safe operation mode or maintain operation in safe operation mode in response to the signal processing unit receiving the PLC signal and the PLC signal containing both the heartbeat frame and the voltage regulation command. The PLC signal contains both heartbeat frames and voltage regulation commands. Based on different situations where the power conversion device receives the voltage regulation command, the control of the power conversion device to operate in normal operation mode or safe operation mode can be further refined. Even without interruption of the heartbeat frame, the power conversion device can switch between different operation modes. In different operation modes, the power conversion device can be in a normal power generation state, prioritizing power supply to the next-level power conversion device, or in a safe power generation state, prioritizing the safety of the next-level power conversion device while supplying power to it.

[0010] According to the first aspect, in one possible implementation, when the next-stage power conversion device detects that its input voltage exceeds an overvoltage threshold, and the next-stage power conversion device sends a voltage regulation command 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 detection of overvoltage at the input terminal by the next-stage power conversion device is a trigger condition for the next-stage power conversion device to send a voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, the controller controls the output voltage of the power conversion device to be less than the overvoltage threshold. Thus, when an overvoltage occurs in the next-stage power conversion device, the power converter can quickly reduce its own output voltage, ensuring the safety of the next-stage power conversion device.

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

[0012] According to the first aspect, in one possible implementation, when the next-stage power conversion device detects an islanding effect in the power generation system where the next-stage power conversion device is located, and the next-stage power conversion device sends a voltage regulation command to the power conversion device, the power conversion device receives the voltage regulation command, and the controller controls the output voltage of the power conversion device to decrease. In this implementation, the detection of an islanding effect by the next-stage power conversion device is a trigger condition for the next-stage power conversion device to send a voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, the controller controls the output voltage of the power conversion device to decrease. Thus, when an islanding effect occurs, reducing the output voltage avoids excessive fluctuations in voltage and frequency in the islanded system, which could damage electrical equipment.

[0013] According to the first aspect, in one possible implementation, when the condition that the input voltage of the next-stage power conversion device exceeds an overvoltage threshold is detected for a period of time, the next-stage power conversion device sends a voltage regulation command to control the output voltage of the power conversion device to be less than the overvoltage threshold. In actual power generation systems, 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 before recovering. This implementation eliminates the possibility of overvoltage misjudgment of the next-stage power conversion device caused by grid voltage fluctuations by adding a time-based judgment condition to the voltage regulation command triggering condition.

[0014] According to the first aspect, in one possible implementation, after receiving a voltage regulation command from the next-stage power conversion device, the power conversion device controls its output voltage to be 0.5 or 0.1 times its current output voltage. This implementation reduces the risk of the next-stage power conversion device failing due to prolonged overvoltage 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 one 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 this application does not limit the type of main conversion circuit of the power conversion device and is compatible with various power conversion devices.

[0016] According to the first aspect, in one possible implementation, the controller is configured to, in the normal operating mode, control the DC-DC converter to operate in a maximum power point tracking (MPPT) mode, where the output voltage of the DC-DC converter varies and the output power of the photovoltaic (PV) modules connected to the DC-DC converter is maximized; and in the safe operating mode, control the DC-DC converter to operate in a voltage-limited mode, where the output voltage of the DC-DC converter is constant. In the normal operating mode, the power conversion device can output power at the maximum power output of the current PV modules, and the voltage may vary to ensure maximum power generation capacity. In the safe operating mode, the output voltage of the power conversion device is constant, which effectively ensures the safety of the next-stage power conversion device. These two modes can be changed as needed to fully guarantee the power generation capacity and safety of the power conversion device.

[0017] Secondly, embodiments of this application disclose a power conversion device control method, the method comprising: responding to the power conversion device not receiving 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 safe voltage value; responding to the power conversion device receiving a heartbeat frame but not receiving a voltage regulation command, controlling the power conversion device to be in a normal operating mode, wherein in the normal operating mode, the output voltage of the power conversion device is less than a first voltage; responding to the power conversion device receiving a heartbeat frame and receiving a voltage regulation command, controlling the power conversion device to be in a safe operating mode, wherein in the safe operating mode, 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.

[0018] In the second technical solution, existing power lines are used for communication transmission, reducing the cost required to establish additional communication lines. Communication is achieved using a heartbeat protection mechanism and voltage regulation commands, resulting in fast response and simple implementation. Furthermore, the power conversion equipment switches between three operating modes. In normal operating mode, the output power of the power conversion equipment is always maximized to meet the user's power needs to the greatest extent. In safe operating mode, faults can be detected in time, and the protection mechanism can be activated to ensure the safety of the inverter-side equipment. In shutdown mode, the output voltage of the power conversion equipment can be reduced below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0019] According to the second aspect, in one possible implementation, when the inverter's input voltage is detected to exceed an overvoltage threshold, the inverter sends a voltage regulation command to the power conversion device, controlling the output voltage of the power conversion device to be less than the overvoltage threshold. In this implementation, the inverter detecting an overvoltage at its input is a trigger condition for the inverter to send a voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, it controls its output voltage to be less than the overvoltage threshold. Thus, when an overvoltage occurs in the inverter, the power converter can quickly reduce its own output voltage, ensuring the inverter's safety.

[0020] According to the second aspect, in one possible implementation, when the inverter's input power exceeds an overpower threshold, the inverter sends a voltage regulation command to the power conversion device. Upon receiving the command, the power conversion device controls its output voltage to decrease. In this implementation, the inverter detecting overpower at its input is a trigger condition for sending the voltage regulation command to the power conversion device. When the power conversion device receives the command, the controller controls its output voltage to decrease. Thus, when overpower occurs in the inverter, the power converter can quickly reduce its output voltage, ensuring inverter safety.

[0021] According to the second aspect, in one possible implementation, when an islanding effect is detected in the power generation system where the inverter is located, the inverter sends a voltage regulation command to the power conversion device. Upon receiving the voltage regulation command, the power conversion device controls its output voltage to decrease. In this implementation, the inverter detecting an islanding effect is a trigger condition for sending the voltage regulation command to the power conversion device. After receiving the voltage regulation command, the controller controls the power conversion device to decrease its output voltage. Thus, when an islanding effect occurs, reducing the output voltage prevents excessive voltage and frequency fluctuations in the islanded system from damaging electrical equipment.

[0022] Thirdly, embodiments of this application provide a photovoltaic power generation system. This system includes multiple optimizers, each with an input terminal connected to a photovoltaic module. The output terminals of each optimizer are connected in series. In response to the multiple optimizers not receiving a heartbeat frame, the multiple optimizers operate in a shutdown mode. In shutdown mode, the output voltage of the multiple optimizers is a shutdown voltage, which is a preset safe voltage value. In response to the multiple optimizers receiving a heartbeat frame but not receiving a voltage regulation command, the multiple optimizers operate in a normal operating mode. In normal operating mode, the multiple optimizers... When the output voltage is less than the first voltage, in response to multiple optimizers receiving a heartbeat frame and a voltage regulation command, the optimizers operate in a safe operating mode. In this mode, the output voltage of the multiple optimizers is less than a second voltage, which is less than the first voltage and greater than the shutdown voltage. The inverter's input is connected to the output of multiple optimizers connected in series. The inverter's output is used to connect to the power grid or user load. The inverter sends heartbeat frames and voltage regulation commands to the multiple optimizers. These commands are transmitted through the power line between the inverter's input or the optimizers' outputs.

[0023] In the third aspect of the technical solution, the photovoltaic power generation system consists of multiple optimizers and inverters. These optimizers and inverters utilize existing power lines for communication, reducing the cost of establishing additional communication lines. Communication is achieved through a heartbeat protection mechanism and voltage regulation commands, resulting in fast response and simple implementation. Furthermore, the power conversion equipment switches between three operating modes. In normal operating mode, it ensures the maximum output power of the power conversion equipment to meet the user's electricity needs to the greatest extent. In safe operating mode, it can promptly detect faults and activate protection mechanisms to ensure the safety of the inverter-side equipment. In shutdown mode, it can reduce the output voltage of the power conversion equipment below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0024] According to the third aspect, in one possible implementation, when the inverter's input voltage is detected to exceed an overvoltage threshold, the inverter sends a voltage regulation command to the power conversion device, controlling the output voltage of the power conversion device to be less than the overvoltage threshold. In this implementation, the inverter detecting overvoltage at its input is a trigger condition for the inverter to send a voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, it controls its output voltage to be less than the overvoltage threshold. Thus, when an overvoltage occurs in the inverter, the power converter can quickly reduce its own output voltage, ensuring the inverter's safety.

[0025] According to the third aspect, in one possible implementation, when the inverter's input power exceeds an overpower threshold, the inverter sends a voltage regulation command to the power conversion device. Upon receiving the command, the power conversion device controls its output voltage to decrease. In this implementation, the inverter detecting overpower at its input is a trigger condition for sending the voltage regulation command to the power conversion device. When the power conversion device receives the command, the controller controls the output voltage of the power conversion device to decrease. Thus, when overpower occurs in the inverter, the power converter can quickly reduce its output voltage, ensuring inverter safety.

[0026] According to the third aspect, in one possible implementation, when an islanding effect is detected in the power generation system where the inverter is located, the inverter sends a voltage regulation command to the power conversion device. Upon receiving the voltage regulation command, the power conversion device controls its output voltage to decrease. In this implementation, the inverter detecting an islanding effect is a trigger condition for sending the voltage regulation command to the power conversion device. After receiving the voltage regulation command, the controller controls the power conversion device to decrease its output voltage. Thus, when an islanding effect occurs, reducing the output voltage prevents excessive voltage and frequency fluctuations in the islanded system from damaging electrical equipment.

[0027] According to the third aspect, in one possible implementation, the inverter establishes communication with the optimizer when the start-up conditions are met. The communication content includes heartbeat frames or voltage regulation commands. After detecting 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 start generating electricity. At the same time, after an alarm occurs, the inverter can immediately cut off the communication with the optimizer, prompting the optimizer to enter a safe working mode and ensuring the safety of the inverter equipment.

[0028] Fourthly, this application discloses a power conversion device, comprising: a DC-DC conversion unit, a signal processing unit, and a controller. The DC-DC conversion unit converts the DC power generated by the photovoltaic module and outputs 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 periodic communication signals sent by the next-stage power conversion device. The controller is used to: control the output voltage of the power conversion device to a shutdown voltage, wherein the shutdown voltage is a preset safe voltage value, in response to the signal processing unit receiving the periodic communication signal but the periodic communication signal not containing a voltage regulation command; control the output voltage of the power conversion device to be less than or equal to a first voltage; and control the output voltage of 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, in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing the voltage regulation command.

[0029] In the fourth aspect of the technical solution, the next-stage power conversion equipment and the power conversion equipment have both communication and power connections. Specifically, the communication method between the next-stage power conversion equipment and the power conversion equipment is power line communication. Based on this, periodic communication signals are used to control the magnitude of the output voltage of the power conversion equipment. In this way, using existing power lines for communication transmission reduces the cost required to establish additional communication lines. Using periodic communication signals for communication results in fast response speed and simple implementation. Furthermore, the output voltage of the power conversion equipment is related to three voltage values. When the output voltage is less than or equal to the first voltage, the output power of the power conversion equipment can be guaranteed to be at its maximum, maximizing the satisfaction of the user's power needs. When the output voltage is less than or equal to the second voltage, a protection mechanism can be activated in a timely manner to ensure the safety of the equipment on the next-stage power conversion equipment side. When the output voltage is the shutdown voltage, 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.

[0030] According to the fourth aspect, in one possible implementation, the periodic communication signal is a PLC signal, which includes a heartbeat frame; the controller is configured to, in response to the signal processing unit not receiving the heartbeat frame for a period of time, control the voltage output by the power conversion device to be the shutdown voltage. By employing PLC communication and utilizing a heartbeat protection mechanism to determine the communication status between the power conversion device and the next-stage power conversion device, the voltage output by the power conversion device can be controlled in real-time and accurately based on the communication status between the two, utilizing existing power lines.

[0031] According to the fourth aspect, in one possible implementation, the controller is configured to: control the voltage output of the power conversion device to be less than the first voltage in response to the signal processing unit receiving the PLC signal containing the heartbeat frame but not the voltage regulation command; and control the voltage output of the power conversion device to be less than the second voltage in response to the signal processing unit receiving the PLC signal containing both the heartbeat frame and the voltage regulation command. The PLC signal contains both a heartbeat frame and a voltage regulation command. Depending on the different situations in which the power conversion device receives the voltage regulation command, the voltage output of the power conversion device can be further finely controlled to be less than or equal to the first voltage or the second voltage. Without interruption of the heartbeat frame, the power conversion device can output different voltages. Therefore, the power conversion device can be in a normal power generation state, prioritizing power supply to the next-level power conversion device, or in a safe power generation state, prioritizing the safety of the next-level power conversion device while supplying power to it.

[0032] According to the fourth aspect, in one possible implementation, the controller is configured to, in response to the signal processing unit receiving the PLC signal and the PLC signal simultaneously containing the heartbeat frame and the voltage regulation command, adjust the voltage output of 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, by reducing the output voltage of the power conversion device to half or one-tenth of the original output voltage, minimizes the risk of failure in the next-stage power conversion device due to prolonged overvoltage.

[0033] According to the fourth aspect, in one possible implementation, the controller is configured to: 1) control the DC-DC converter to operate in maximum power point tracking (MPPT) mode in response to the signal processing unit receiving the periodic communication signal but the periodic communication signal not containing the voltage regulation command; 2) control the DC-DC converter to operate in a voltage limiting mode in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing the voltage regulation command; 3) control the DC-DC converter to operate in a voltage limiting mode in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing the voltage regulation command; 4) control the DC-DC converter to operate in a constant voltage limiting mode in response to the signal processing unit receiving the periodic communication signal and the periodic communication signal containing the voltage regulation command. In this voltage limiting mode, the output voltage of the DC-DC converter is constant when the output voltage of the power conversion device is less than or equal to a first voltage. This constant voltage effectively ensures the safety of the next-stage power conversion device. These two modes can be changed as needed to fully guarantee the power conversion capacity and safety of the power conversion device.

[0034] Fifthly, this application discloses a power conversion device control method, the method comprising: responding to the power conversion device not receiving a heartbeat frame, controlling the voltage output by the power conversion device to a shutdown voltage, the shutdown voltage being a preset safe voltage value; responding to the power conversion device receiving the heartbeat frame but not receiving a voltage adjustment command, controlling the voltage output by the power conversion device to be less than or equal to a first voltage; responding to the power conversion device receiving the heartbeat frame and receiving the voltage adjustment command, controlling the voltage output by the power conversion device to be less than or equal to a second voltage, the second voltage being less than the first voltage and greater than the shutdown voltage.

[0035] In the fifth aspect of the technical solution, existing power lines are used for communication transmission, reducing the cost required to establish additional communication lines. Communication is achieved using a heartbeat protection mechanism and voltage regulation commands, resulting in fast response and simple implementation. Furthermore, the output voltage of the power conversion equipment is related to three voltage values. When the output voltage is less than or equal to the first voltage, the output power of the power conversion equipment can be guaranteed to be at its maximum, maximizing the satisfaction of users' power needs. When the output voltage is less than or equal to the second voltage, the protection mechanism can be activated in a timely manner to ensure the safety of the equipment on the next-level power conversion equipment side. When the output voltage is the shutdown voltage, 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.

[0036] According to the fifth aspect, in one possible implementation, when the input voltage of the inverter is detected to exceed an overvoltage threshold, the inverter, which receives the DC power output from the power conversion device and issues a voltage regulation command to the power conversion device, controls the output voltage of the power conversion device to be less than the overvoltage threshold. In this implementation, the inverter detecting overvoltage at its input is a trigger condition for the inverter to issue a voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, it controls the output voltage of the power conversion device to be less than the overvoltage threshold. Thus, when an overvoltage occurs in the inverter, the power converter can quickly reduce its own output voltage, ensuring the inverter's safety.

[0037] According to the fifth aspect, in one possible implementation, when the input power of the inverter is detected to exceed an overpower threshold, the inverter receives the DC power output by the power conversion device and sends the voltage regulation command to the power conversion device, controlling the output voltage of the power conversion device to decrease. In this implementation, the inverter detecting overpower at its input is a trigger condition for the inverter to send the voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, the controller controls the output voltage of the power conversion device to decrease. Thus, when the inverter experiences overpower, the power converter can quickly reduce its own output voltage, ensuring the inverter's safety.

[0038] According to the fifth aspect, in one possible implementation, when an islanding effect is detected in the power generation system where the inverter is located, the inverter receives the DC power output from the power conversion device and sends the voltage regulation command to the power conversion device, controlling the output voltage of the power conversion device to decrease. In this implementation, the detection of an islanding effect by the inverter is a trigger condition for the inverter to send the voltage regulation command to the power conversion device. After the power conversion device receives the voltage regulation command, the controller controls the output voltage of the power conversion device to decrease. Thus, when an islanding effect occurs, reducing the output voltage avoids excessive fluctuations in voltage and frequency in the islanded system that could damage electrical equipment.

[0039] Sixthly, embodiments of this application provide a photovoltaic power generation system, comprising: a plurality of optimizers, the plurality of optimizers being used to convert direct current generated by photovoltaic modules and output it to an inverter; an inverter, the inverter being used to supply power to the grid or user loads, the inverter also being used to send heartbeat frames and voltage regulation commands to the plurality of optimizers, the heartbeat frames and the voltage regulation commands being transmitted through a power line between the inverter and the optimizers; in response to the plurality of optimizers not receiving the heartbeat frame for a period of time, the voltage output by the plurality of optimizers is a shutdown voltage, the shutdown voltage being a preset safe voltage value; in response to the plurality of optimizers receiving the heartbeat frame but not receiving the voltage regulation command, 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 command, the voltage output by the plurality of optimizers is less than or equal to a second voltage, the second voltage being less than the first voltage and greater than the shutdown voltage.

[0040] In the sixth aspect of the technical solution, the photovoltaic power generation system consists of multiple optimizers and inverters. These optimizers and inverters utilize existing power lines for communication transmission, reducing the cost of establishing additional communication lines. Communication is achieved through a heartbeat protection mechanism and voltage regulation commands, resulting in fast response and simple implementation. Furthermore, the output voltage of the power conversion equipment is related to three voltage values. When the output voltage is less than or equal to the first voltage, the output power of the power conversion equipment is always maximized to meet the user's electricity needs to the greatest extent. When the output voltage is less than or equal to the second voltage, a protection mechanism can be activated promptly to ensure the safety of the equipment on the next-stage power conversion equipment side. When the output voltage is the shutdown voltage, the output voltage of the power conversion equipment can be reduced below the safe voltage to ensure the personal safety of maintenance personnel and users.

[0041] According to the sixth aspect, in one possible implementation, when the input voltage of the inverter exceeds an overvoltage threshold, the inverter sends a voltage regulation command to the optimizer, and the optimizer controls its own output voltage to be less than the second voltage. In this implementation, the inverter detecting its input overvoltage is a trigger condition for the inverter to send a voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, it controls its output voltage to be less than the second voltage. Thus, when the inverter experiences overvoltage, the power converter can quickly reduce its own output voltage, ensuring the inverter's safety.

[0042] According to the sixth aspect, in one possible implementation, when the input power of the inverter exceeds an overpower threshold, the inverter sends a voltage regulation command to the optimizer, and the optimizer controls its own output voltage to be less than the second voltage. In this implementation, the inverter detecting overpower at its input is a trigger condition for the inverter to send a voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, the controller controls the output voltage of the power conversion device to be less than the second voltage. Thus, when the inverter experiences overpower, the power converter can quickly reduce its own output voltage, ensuring the inverter's safety.

[0043] According to the sixth aspect, in one possible implementation, in response to some or all of the plurality of optimizers not receiving the heartbeat frame for a period of time, the optimizers that do not receive the heartbeat frame adjust their output voltage to a shutdown voltage, the shutdown voltage being a preset safe voltage value; in response to the plurality of optimizers receiving the heartbeat frame but not receiving the voltage adjustment command, the voltage output by the plurality of optimizers is less than or equal to a second voltage; in response to the plurality of optimizers receiving the heartbeat frame and receiving the voltage adjustment command, the voltage output by the plurality of optimizers is less than or equal to a second voltage, the second voltage being less than the first voltage and greater than the shutdown voltage. The plurality of optimizers benefit from PLC signal transmission, establishing communication with the inverter using heartbeat frames and voltage adjustment commands, and changing their own output voltage according to different situations of the received heartbeat frames and voltage adjustment commands. The communication method is simple and reliable.

[0044] According to the sixth aspect, in one possible implementation, when an islanding effect occurs in the power generation system where the inverter is located, the inverter sends the voltage regulation command to the optimizer, and the optimizer controls its own output voltage to be lower than the second voltage. In this implementation, the detection of an islanding effect by the inverter is a trigger condition for the inverter to send the voltage regulation command to the power conversion device. When the power conversion device receives the voltage regulation command, the controller controls the output voltage of the power conversion device to be lower than the second voltage. Thus, when an islanding effect occurs, reducing the output voltage avoids excessive fluctuations in voltage and frequency in the islanded system that could damage electrical equipment.

[0045] According to the sixth aspect, in one possible implementation, the inverter establishes communication with the optimizer when the start-up conditions are met. The communication content includes heartbeat frames or voltage regulation commands. After detecting 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 operating conditions are met and quickly start generating electricity. At the same time, after an alarm occurs, the inverter can immediately cut off the communication with the optimizer, prompting the optimizer to enter a safe operating mode and ensuring the safety of the inverter equipment.

[0046] According to the sixth aspect, in one possible implementation, multiple optimizer inputs are respectively connected to photovoltaic modules, and the outputs of the multiple optimizers are connected in series to the input of the inverter. The inverter is used to broadcast the heartbeat signal and the voltage regulation command to the multiple optimizers via a PLC. The voltage regulation command adjusts the output voltage of 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 output voltage of the power conversion device to half or one-tenth of the original output voltage, minimizing the risk of failure in the next stage power conversion device due to prolonged overvoltage. Attached Figure Description

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

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

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

[0050] Figure 4 This is another optimizer-inverter connection diagram provided in the embodiments of this application;

[0051] Figure 5 This is a schematic diagram of the optimizer working mode switching process provided in the embodiments of this application;

[0052] Figure 6 This is a schematic diagram of the inverter's working process provided in the embodiments of this application. Detailed Implementation

[0053] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0054] In this application, unless otherwise expressly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. Furthermore, the term "coupled" can refer to a method of electrical connection for signal transmission. "Coupled" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0055] To facilitate understanding, some of the technical terms involved in this application will be explained first.

[0056] Module-level power electronic equipment: Unlike string power electronic equipment, it has module-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 realize module-level rapid shutdown (RSD) function, thereby greatly improving the safety of photovoltaic power generation systems.

[0057] MPPT function: Controls the input voltage at the maximum power point voltage (Vmpp) of the photovoltaic module to achieve the maximum output power of the photovoltaic module.

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

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

[0060] Heartbeat protection mechanism: The heartbeat protection mechanism is a security monitoring mechanism used in communication systems to determine whether communication between devices is normal. In this mechanism, the master device periodically sends a "heartbeat frame" to the slave device. Upon receiving the heartbeat frame, the slave device sends a feedback to the master device to inform it that the communication connection is normal. If the master device does not receive feedback, it will take remedial measures such as attempting to reconnect. In some systems, the slave device does not send a feedback to the master device upon receiving a heartbeat frame; instead, it determines whether the communication is abnormal based on whether it has received a heartbeat frame and takes corresponding actions on the slave device side.

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

[0062] See Figure 1This figure is a schematic diagram of the architecture of a photovoltaic system provided in an embodiment of this application. In this embodiment, the photovoltaic system includes multiple converters 1-n, the positive and negative input terminals of the converters 1-n are connected one-to-one with the positive and negative output terminals of the photovoltaic modules 1-n, and the output terminals of the converters 1-n are coupled to the power grid 105 after being connected in parallel. Under this architecture, multiple photovoltaic modules can be coupled to the power grid 105 through converters, and the output terminals of the multiple converters can be coupled to the power grid 105 in parallel, thereby enabling the power grid to have a large power supply capacity.

[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 to increase the output power of the photovoltaic module. This application does not limit the composition of the photovoltaic module.

[0064] The converter 1-n is used to convert the DC power of the photovoltaic module 1-n into AC power to be transmitted to the power grid, so as to realize the function of photovoltaic power generation. Moreover, the converter 1-n is connected to the output terminal of the photovoltaic module 1-n one by one, and is used to control the output voltage of each photovoltaic module 1-n, so as to realize the maximum power tracking of the photovoltaic module 1-n.

[0065] The converters 1-n include microinverters. A microinverter is a miniaturized, highly integrated power conversion device that can be installed on the roof of a building near the photovoltaic modules. It has inversion, MPPT (Multi-Level Photovoltaic Power Transmission) functions, module-level shutdown or monitoring functions, and when applied to this architecture, it can achieve the following process: Taking photovoltaic module 1 as an example, photovoltaic module 1 converts solar energy into direct current (DC). Converter 1 can then convert this DC into alternating current (AC) with specific frequency, specific voltage, and other electrical parameters required by the power grid 105, which is then supplied to the load.

[0066] It should be understood that in this embodiment, a single photovoltaic module is connected to a single converter. However, 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 a converter. Taking microinverters as an example, a "one-to-one" microinverter solution involves a single photovoltaic module connected to a single microinverter. "One-to-two," "one-to-four," and other similar solutions involve two photovoltaic modules connected to a single microinverter, four photovoltaic modules connected to a single microinverter, and so on.

[0067] See Figure 2 , Figure 2This is a schematic diagram of another photovoltaic system architecture provided in this application embodiment. The photovoltaic system includes converters 1-n and 2-m, and an inverter 104. The input terminals of converters 1-n and 2-m are respectively connected one-to-one to the output terminals of photovoltaic modules 1-n and 2-m. The converters are connected in series to form p photovoltaic strings, where p is greater than or equal to 2. The output terminals of converters 1-1 to 1-n are connected in series to form photovoltaic string 1, and the output terminals of converters 2-1 to 2-m are connected in series to form another photovoltaic string 2.

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

[0069] The output terminal 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 implementation, the converter can be a shutdown device. A shutdown device, which has a module shutdown function, is a module-level power electronic device installed between the photovoltaic modules and the inverter. It enables the rapid shutdown of the connection between each photovoltaic module and the inverter, and is typically installed on the building roof near the photovoltaic modules.

[0071] In another implementation, the converter can be an optimizer, a power conversion device installed between the photovoltaic modules and the inverter. An optimizer eliminates photovoltaic module mismatch and has the MPPT (Multi-Level Photovoltaic Power Transmission) function for a single photovoltaic module, thereby significantly improving the power generation of the entire photovoltaic power generation system. Applying the optimizer to this architecture, the following process can be achieved: Taking photovoltaic string 1 as an example, individual photovoltaic modules 1-1 to 1-n convert solar energy into DC power. After power conversion by the corresponding optimized modules 1-1 to 1-n, the DC power output from multiple converters is connected in series and converged to the input terminal of inverter 104. The inverter is the next-level power conversion device after the optimizer. The input terminal of inverter 104 is called one input path of the inverter. Similarly, photovoltaic string 2 will also connect its output DC power in series and deliver it to the input terminal of inverter 104 in another "path". In this embodiment, the optimizer also has a module-level fast shutdown function, further reducing the safety risks of the photovoltaic power generation system.

[0072] The implementation of the maximum power point tracking (MPPT) and fast shutdown functions of the component-level power electronic equipment provided in this application will be described below with reference to the accompanying drawings. For ease of description, only the optimizer will be used as an example. It should be understood that the methods for implementing fast shutdown described below are not limited to the optimizer; they are equally applicable to devices such as... Figure 1 and Figure 2 More component-level power electronic devices are shown.

[0073] Furthermore, the fast shutdown function of the component-level power electronic equipment provided in this application is not limited to the simple meaning of "shutdown" as reflected in the word "shutdown," which means disconnecting and isolating the component-level power electronic equipment from the photovoltaic power generation system. It also means reducing 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 3This is a schematic diagram of an optimizer-inverter connection provided in an embodiment of this application. In this diagram, photovoltaic modules are connected one-to-one with each optimizer. Specifically, the output terminal of photovoltaic module 1-1 is connected to the input terminal of optimizer 1-1, the output terminal of photovoltaic module 1-(n-1) is connected to the input terminal of optimizer 1-(n-1), and the output terminal of photovoltaic module 1-n is connected to the input terminal of optimizer 1-n. The output terminals of multiple optimizers 1-1 are connected in series and then used as inputs to inverter 104. Specifically, one output terminal of optimizer 1-1 is connected to one input terminal of inverter 104, and the other output terminal of optimizer 1-1 is connected to one output terminal of the connected optimizer 1-2. Similarly, one output terminal of optimizer 1-(n-1) is connected to one output terminal of the connected optimizer 1-(n-2), the other output terminal of optimizer 1-(n-1) is connected to one output terminal of optimizer 1-n, and the other output terminal of optimizer 1-n is connected to another input terminal of inverter 104. More specifically, taking optimizer 1-1 as an example, optimizer 1-1 includes a DC-DC converter unit 101, a signal processing unit 103, and a control unit 102. 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-DC converter 101 described above includes one or more combinations of buck converters, boost converters, buck-boost converters, forward converters, or flyback converters. On one hand, the DC-DC converter 101 operates in MPPT tracking mode. For example, in the photovoltaic system architecture provided in this application, one optimizer is connected to one photovoltaic module. The power output characteristic curve of the photovoltaic module varies due to factors such as temperature, solar radiation, or shading. The DC-DC converter 101 of the optimizer contains multiple switching transistors. The optimizer controls the duty cycle of one or more switching transistors through pulse width modulation, ensuring that the input voltage of the optimizer always tracks the maximum power point operating voltage of the photovoltaic module, thus maximizing the power output of the photovoltaic module. On the other hand, the DC-DC converter 101 operates in voltage-limiting mode. In this mode, the optimizer controls the duty cycle of one or more switching transistors through pulse width modulation, ensuring that the output voltage of the optimizer is a specific voltage threshold. At this specific voltage threshold, the inverter 104 has a lower input voltage than before voltage regulation or maintains the inverter's input voltage within an acceptable range, thereby protecting the inverter. In short, the DC-DC converter 101 can output different voltage values ​​according to different operating strategies to meet the different operating 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 method between the signal processing unit 103 and the inverter 104 shown is one example. The coupling methods between the signal processing unit 103 and the inverter 104 include double-sided coupling (coupled to both sides of the inverter output) and single-sided coupling (coupled to one side of the inverter output). The coupling types include transformer coupling and magnetic ring coupling. This application does not limit the coupling method 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 turning off of the switching transistors in the DC-DC converter 101 of the optimizer based on the information received by the signal processing unit 103 or based on the operating information stored in its internal memory.

[0078] Inverter circuit 109 is used to convert direct current to 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. However, since the output terminals of multiple optimizers are connected in series, the optimizer signal processing unit in each optimizer can process the signals broadcast by inverter 104, so that all optimizers can receive instructions from inverter 104 and execute corresponding actions.

[0080] This application is as follows Figure 1 or Figure 2 In the photovoltaic system shown in the embodiment, the inverter 104 and the optimizer are connected not only by power but also by PLC communication. In addition to PLC communication, the communication methods between the inverter 104 and the optimizer also include RS485, Zigbee, and sub-1G connections. This application primarily uses PLC communication to illustrate the embodiment.

[0081] The following combination Figure 3 The photovoltaic system shown provides a detailed explanation of the PLC communication implementation process.

[0082] refer to Figure 3 In the photovoltaic system, under PLC communication mode, inverter 104 and optimizers 1-1 to 1-n utilize... Figure 3 Data exchange is performed using power lines 106 or 107.

[0083] Taking optimizer 1-1 as an example, since there is data interaction between optimizer 1-1 and inverter 104, and this data interaction is indispensable for maintaining the normal operation of inverter 104 and optimizer 1-1, ensuring the reliability of PLC communication is particularly important. To ensure communication reliability and prevent optimizer 1-1 and inverter 104 from losing or disconnecting from each other, this embodiment of the application uses a heartbeat protection mechanism to detect the communication status between inverter 104 and optimizer 1-1.

[0084] In one embodiment, the master unit in the heartbeat protection mechanism is the inverter 104, and the slave unit is the optimizer 1-1. After the photovoltaic system is turned on, the inverter 104 will send heartbeat frames to the optimizer 1-1 periodically 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 feedback information, it will take remedial measures such as trying to reconnect.

[0085] In one embodiment, the master unit in the heartbeat protection mechanism is the inverter 104, and the slave unit is the optimizer 1-1. After the photovoltaic system is turned on, the inverter 104 will send heartbeat frames to the optimizer 1-1 periodically or periodically. The optimizer 1-1 will not send feedback information to the inverter 104, but will take corresponding actions on the optimizer 1-1 end according to whether it receives the heartbeat frame.

[0086] In this application, in addition to the heartbeat frame, after detecting a fault or receiving a control command from the user, the inverter 104 also sends a voltage regulation command to the optimizer 1-1. This voltage regulation command instructs the optimizer 1-1 to regulate the DC-DC converter 101, thereby causing the optimizer 1-1 to output a specific voltage or current. The frequency of the heartbeat frame and the voltage regulation command can be the same or different.

[0087] Inverter 104 and optimizer interact via signal transceiver unit 108 on the inverter 104 side and signal processing unit 103 on optimizer 1-1. The communication method for this data interaction is PLC communication. The PLC signals used for data interaction include heartbeat frames and voltage regulation commands, both of which are periodic communication signals. The entire communication process is as follows:

[0088] During operation between inverter 104 and optimizer, signal transceiver unit 108 transmits a PLC signal consisting of a heartbeat frame and a voltage regulation command superimposed on the PLC signal via PLC communication to each optimizer via broadcast. After receiving the PLC signal, signal processing unit 103 processes the PLC signal and sends the processed PLC signal to control unit 102 inside the optimizer. Control unit 102 then controls the operation of DC-DC converter 101 based on the processed PLC signal to adjust the output voltage or output current of the optimizer.

[0089] The following explanation uses optimizer 1-1 as an example. It should be understood that optimizers belonging to the same photovoltaic string can all receive PLC signals. The working principle of other optimizers in the same photovoltaic string will not be described in detail below.

[0090] In the photovoltaic system of this application embodiment, the optimizer 1-1 switches between different operating modes based on the received heartbeat frame and voltage regulation command. These operating modes include normal operating mode, safe operating mode, and shutdown mode. The data communication methods and operating principles of the inverter and optimizer devices under these three different operating modes are described below.

[0091] Normal Operating Mode: In normal operating mode, the inverter 104 sends periodic heartbeat frames to the optimizer via 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 absence of a voltage regulation command, the optimizer determines that the communication between the optimizer 1-1 and the inverter 104 is normal and that normal operating mode needs to be executed. In this mode, 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 its input voltage to be at or near the maximum power point voltage of the photovoltaic module, and the DC-DC converter 101 operates in MPPT tracking mode. Common situations that trigger the optimizer 1-1 to execute normal operating mode include when the morning sunlight reaches the initial threshold of sunlight intensity and when a user turns on the photovoltaic power generation system. In the early morning, when the photovoltaic modules receive sunlight exceeding the initial threshold of light intensity, the inverter and optimizer power on and begin operation. The inverter starts sending PLC signals to the optimizer. After receiving periodic heartbeat frames, the optimizer determines that the communication between the inverter and the optimizer is normal and begins to execute the normal operating mode output voltage. When the user powers on the device, the user actively closes the DC switch of inverter 104. The DC switch is installed on the inverter 104 side. After the DC switch is closed, an electrical connection is formed between optimizer 1-1 and inverter 104. Optimizer 1-1 successfully receives the heartbeat frames from inverter 104. After receiving the periodic heartbeat frames, optimizer 1-1 executes the normal operating mode output voltage.

[0092] Safe Operating Mode: In safe operating mode, optimizer 1-1 still receives periodic heartbeat frames from inverter 104 and determines that communication between optimizer 1-1 and inverter 104 is normal based on the successful reception of periodic heartbeat frames. However, in this mode, in addition to heartbeat frames, inverter 104 also sends periodic voltage regulation commands via PLC communication. After successfully receiving the periodic voltage regulation commands, optimizer 1-1 determines that communication between optimizer 1-1 and inverter 104 is normal and that safe operating mode needs to be executed, based on the successful reception of both periodic heartbeat frames and periodic voltage regulation commands. In this mode, according to the voltage regulation command, optimizer 1-1 limits the voltage or current at its output terminal, for example, limiting the output voltage of optimizer 1-1 to a specific voltage, controlling DC unit 101 to be in voltage-limiting mode. In this voltage-limiting mode, the input voltage of the inverter is also limited, thereby protecting the inverter-side equipment in the photovoltaic system. It should be understood that in safe operating mode, the specific value of the voltage can be adjusted. The magnitude of this value is influenced by factors such as local installation standards and the number of optimizers. The specific voltage value is set to ensure that the inverter-side equipment will not be damaged. Furthermore, the triggering of optimizer 1-1 to execute safe operating mode is more complex, and will be discussed below in conjunction with... Figure 4 Explain the various situations that trigger the safe operating mode.

[0093] Shutdown Mode: In shutdown mode, if optimizer 1-1 does not receive a heartbeat frame from inverter 104 for a certain period of time, this period includes M times the period of the heartbeat frame, where M is a constant. This period can also be a preset time, depending on the stability of PLC communication in the optimizer's operating environment. Higher stability results in a longer period, and lower stability results in a shorter period, ensuring normal communication between the optimizer and the inverter. Based on the failure to successfully receive a periodic heartbeat frame, a communication anomaly is determined between optimizer 1-1 and inverter 104. Inverter 104 can no longer effectively control optimizer 1-1, and optimizer 1-1 sets its output voltage to the shutdown voltage, which is the factory preset voltage for optimizer 1-1, ranging from 1 to 48 volts. At this time, even if personnel directly touch the output port of the photovoltaic string, there will be no danger, thus maximizing the safety of users and maintenance personnel. Common situations that trigger optimizer 1-1 to execute shutdown mode include users manually shutting down inverter 104. In this case, the user actively disconnects the DC switch of inverter 104. The DC switch is installed on the inverter 104 side. After the DC switch is disconnected, the electrical connection between optimizer 1-1 and inverter 104 is broken. Optimizer 1-1 can no longer receive heartbeat frames from inverter 104. After optimizer 1-1 has not received a heartbeat frame from inverter 104 for a fixed period of time, optimizer 1-1 executes shutdown mode.

[0094] The optimizer will choose to maintain the current working mode or switch to another working mode depending on the different PLC signals it receives. In some embodiments, if the PLC signal received by optimizer 1-1 before time period t1 contains a heartbeat frame but not a voltage regulation command, then optimizer 1-1 maintains operation in normal working mode. If the PLC signal received by optimizer during time period t1-t2 contains both a heartbeat frame and a voltage regulation command, then optimizer switches to safe working mode at time t2. If the PLC signal received by optimizer during time period t2-t3 contains both a heartbeat frame and a voltage regulation command, then optimizer maintains in safe working mode. If the PLC signal received by optimizer during time period t3-t4 contains a heartbeat frame but no voltage regulation command, then optimizer switches from safe working mode to normal working mode at time t4. If the optimizer does not receive any PLC communication signal during time period t4-t5, i.e., does not receive a heartbeat frame, then at time t5, optimizer will choose to switch from normal working mode to shutdown mode. T1 to T5 occur sequentially, and the time periods between any two times can be equal or unequal.

[0095] The main difference between the three operating modes mentioned above lies in the control of the output voltage state changes of optimizer 1-1. In fact, different operating modes correspond to different output voltage states of optimizer 1-1. In some embodiments, the specific implementation can be described as optimizer 1-1 directly adjusting the output voltage based on whether a heartbeat frame signal is received and the voltage adjustment command, without needing to simultaneously reflect the changes in different operating modes.

[0096] For example: in response to some or all of the plurality of optimizers 1-1 not receiving periodic PLC signals or heartbeat frames from inverter 104 for a period of time, the optimizer 1-1 that does not receive signals adjusts the voltage output at the output terminal of the optimizer 1-1 to the shutdown voltage, which is a preset safe voltage value.

[0097] In response to some or all of the plurality of optimizers 1-1 receiving the heartbeat frame from inverter 104 and not receiving the voltage regulation command, the corresponding optimizer 1-1 controls the output voltage to be less than or equal to the first voltage.

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

[0099] As can be seen, in the aforementioned photovoltaic system, optimizer 1-1 determines the different operating states of inverter 104 or the different power input requirements of the upstream stage based on changes in the PLC signal, thereby adjusting the corresponding operating state of optimizer 1-1 in a timely manner, thus effectively and promptly protecting inverter 104 under various operating conditions. In this embodiment of the invention, by loading voltage regulation commands in the communication between the optimizer and the inverter in the photovoltaic system, such as PLC communication, the optimizer can promptly adjust the output voltage to a safe range after the inverter experiences faults such as overvoltage, overcurrent, or leakage, thereby effectively protecting the downstream inverter equipment and improving the overall operational safety of the photovoltaic system.

[0100] The following combination Figure 4 The various triggering of the security working mode provided in the embodiments of this application will be described. Figure 4 This is another schematic diagram of an optimizer-inverter connection provided in an embodiment of this application. Besides 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-DC conversion circuit 110, a DC bus, an inverter circuit 109, a sampling circuit, and a controller. Figure 4 The inverter 104 shown has three photovoltaic strings connected to its input. Specifically, each photovoltaic string is connected to a corresponding DC-DC converter 110. The DC-DC converter 110 converts the DC power to the DC bus. The inverter then draws power from the DC bus, converts the DC power to AC power, and sends it to the first AC bus. Finally, the DC power is sent to the power grid 105. In some photovoltaic power generation systems with higher power output, the low-voltage AC power on the first AC bus is stepped up by a transformer and sent to the second AC bus before finally being sent to the power grid 105. The sampling circuit in the inverter can collect electrical data such as voltage, current, and power from the input of the DC-DC converter 110 (or the output of the photovoltaic string) and the output of the inverter 109 in real time. The collected data is then transmitted to the controller in the inverter. Based on this real-time collected electrical data, the controller determines the operating state of the inverter and issues different instructions to the internal electrical components of the inverter according to different operating states to execute the optimal operating strategy.

[0101] In some possible embodiments, the inverter 104 may issue a voltage regulation command to the optimizer 1-1 when the following conditions occur: (1) overvoltage at the input terminal of the inverter 104; (2) overpower at the input terminal of the inverter 104; (3) islanding effect occurs in the inverter 104.

[0102] The three situations described above will be briefly explained below.

[0103] (1) Inverter 104 input overvoltage. The controller detects that the input voltage of the DC-DC converter 110 exceeds a preset voltage threshold, and determines that the inverter 104 input is overvoltage. This 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 may cause the inverter to malfunction or be damaged. When an inverter input overvoltage occurs, when the optimizer switches to a safe operating mode, the optimizer's output voltage can be adjusted to K times the current voltage, where K is less than 1. K depends on the specific value of the safe voltage on the inverter input side. 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 only switch itself to a safe operating mode after the input voltage of the DC-DC converter 110 has exceeded a preset voltage threshold for a period of time.

[0104] (2) Overpower at the input terminal of inverter 104. In photovoltaic system design, to ensure full utilization of the inverter, a certain over-sizing ratio is typically allowed. 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. Therefore, the inverter's power over-sizing ratio is the ratio of 12kW to 10kW, which is 1.2. Under normal lighting conditions, the actual output power of the photovoltaic module is less than 10kW, at which point the inverter can operate normally. However, when lighting conditions are good for an extended period, and the actual output power of the photovoltaic module is greater than 10kW for a long time, the inverter will remain in an overloaded operating state. In this case, it is necessary to limit the inverter's input power. In this embodiment, a voltage regulation command is sent to optimizer 1-1 to limit the optimizer's output voltage, thereby limiting the inverter's power and achieving the purpose of protecting the inverter.

[0105] (3) Inverter 104 experiences islanding effect. 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 that could damage electrical equipment, inverter 104 issues a voltage regulation command to optimizer 1-1 based on this situation.

[0106] To meet the input requirements of inverter 104, optimizer 1-1 typically sets its voltage limit point based on the number of optimizers 1-1 in the photovoltaic string and the input voltage limit of inverter 104 during normal operation. After the photovoltaic power generation system starts working normally, optimizer 1-1 will always limit its output voltage to below this voltage limit point. For example, if the input voltage of inverter 104 is limited to 500V, and there are 10 inverters 104 connected to its input terminal, then optimizer 1-1 should set its own voltage limit point to 50V to ensure that optimizer 1-1 always outputs a voltage less than 50V during operation. Taking the voltage limit point of optimizer 1-1 as 50V as an example, this application provides the following two methods to achieve the voltage limit point setting of optimizer 1-1. Method One: After the initial installation and commissioning of optimizer 1-1, optimizer 1-1 sets the voltage limit point to 50V based on the number of optimizers 1-1 and the system voltage limit. This voltage limit point data is then stored internally within optimizer 1-1. Subsequent operations of optimizer 1-1 can directly retrieve this data from its internal storage without requiring resetting the voltage limit point. This method is simple to implement and effective. Method Two: The voltage limit point data required by optimizer 1-1 is sent by inverter 104 and is not stored in optimizer 1-1. In this method, when inverter 104 and optimizer 1-1 are operating normally, inverter 104 periodically sends a 50V voltage limit signal to optimizer 1-1. Optimizer 1-1 receives this signal and always maintains its output voltage below 50V during operation.

[0107] It should be understood that the voltage limiting signal in the second method above may still appear in the safe operating mode of the optimizer 1-1 provided in this application. However, the voltage limiting signal described in the second method is at least one point different from the voltage regulation command in the safe operating mode. That is, the triggering conditions are different. The triggering condition of the voltage limiting signal is that both the inverter 104 and the optimizer 1-1 are working normally, while the triggering condition of the voltage regulation command is that the inverter malfunctions. The specific malfunction types include the above three situations in which the inverter malfunctions: (1) overvoltage at the input terminal of the inverter 104; (2) overpower at the input terminal of the inverter 104; (3) islanding effect in the inverter 104.

[0108] In one embodiment, based on the voltage limit point of the optimizer described above, 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 point tracking (MPPT) on the power output of the connected photovoltaic modules. The shutdown voltage is a preset safe 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 for a period of time, the voltage output of 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 a voltage adjustment instruction, the voltage output of 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 adjustment instruction, the voltage output of 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] Specifically, in the safe operating mode, since the optimizer 1-1 only has its output voltage or current limited, the DC-DC converter 101 is not completely powered down. When the optimizer 1-1 changes from receiving timed heartbeat frames and voltage regulation commands to only receiving heartbeat frames from the inverter 104, the control unit 102 in the optimizer 1-1 can quickly restore the DC-DC converter 101 from the voltage-limited mode to the MPPT tracking mode by changing the duty cycle, etc. The optimizer 1-1 also quickly changes from the safe operating mode to the normal operating mode. Therefore, the photovoltaic string where the optimizer 1-1 is located still has the ability to quickly restore to a higher output voltage, so that the inverter 104 can also restore normal output in a short time.

[0110] Similarly, in normal operating mode, DC-DC converter 101 is in MPPT tracking mode. Inverter 104 periodically sends heartbeat frames to optimizer 1-1, and optimizer 1-1 receives the periodic heartbeat frames. When optimizer 1-1 changes from only receiving periodic heartbeat frames to receiving both heartbeat frames from inverter 104 and voltage regulation commands from inverter 104, control unit 102 in optimizer 1-1 can quickly switch DC-DC converter 101 from MPPT tracking mode to voltage limiting mode by changing the duty cycle, etc. Optimizer 1-1 also quickly switches from normal operating mode to safe operating mode, ensuring the safety of inverter equipment in case of failure.

[0111] In this embodiment, optimizer 1-1 can quickly switch between normal operating mode, safe operating mode, and shutdown mode. This allows for rapid reduction of the photovoltaic string's output voltage in the event of a photovoltaic system failure, ensuring inverter safety. During optimizer 1-1 installation and maintenance, it limits the photovoltaic string's output voltage to a safe level, ensuring personnel safety. Furthermore, it rapidly switches the optimizer's operating mode when the power generation scenario changes. This embodiment not only fully guarantees the safety of the inverter equipment but also ensures the safety of users and maintenance personnel, and significantly reduces the impact of maintenance, installation, and repair work on user electricity consumption.

[0112] The following describes the method for operating the control optimizer provided in the embodiments of this application, with reference to the flowchart.

[0113] Figure 5This is a schematic diagram of the optimizer operating mode switching process provided in this application embodiment. In step 20, the optimizer is powered on. The actual scenario at this time may be when the sun rises in the early morning, and sunlight provides the photovoltaic modules with sunlight for energy conversion. The optimizer has the electrical energy required for power-on. Optionally, the optimizer also receives a power-on command sent from the inverter. Next, the optimizer will execute step 21. In this step, the optimizer will determine whether it has received heartbeat frames at regular intervals. Here, receiving heartbeat frames at regular intervals includes the optimizer receiving heartbeat frame signals sent at a specific frequency within a certain period of time. If this condition is met, step 22 is executed. If not, 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 condition, or no heartbeat frame signal is received at all, step 25 is executed. In step 25, the optimizer performs a power-off action. In the power-off mode, the voltage output of the optimizer is the preset voltage at the factory of the optimizer. This voltage can be greater than or less than the output voltage of the optimizer in the safe mode, but it must be less than the voltage limit point of the optimizer. Under the shutdown voltage, even if multiple optimizers are connected in series in a single photovoltaic string, the voltage on the inverter power line will not exceed the safe voltage. Users or maintenance personnel will not be at risk of electric shock even if they directly touch the power line. In step 22, the optimizer operates in normal working mode. In normal working mode, the optimizer generally executes the MPPT function, adjusting its input voltage to the operating voltage corresponding to the maximum power point on the photovoltaic module's power characteristic curve. Its output voltage fluctuates within a certain range according to the power converter's requirements and the electrical characteristics of the photovoltaic string. Next, the optimizer executes step 23. In this step, the optimizer determines whether it has received a voltage regulation command or whether an alarm has occurred. If so, the optimizer executes step 24; otherwise, it returns to step 22. Here, the voltage regulation command is the PLC signal sent by the inverter to the optimizer when the above three types of faults occur. In step 24, the optimizer operates in a safe operating mode. In this mode, the optimizer limits its output by adjusting the duty cycle of its internal power conversion, for example, by changing the duty cycle relative to the normal operating mode. This keeps the voltage output by the optimizer at a specific voltage, thereby limiting the input voltage of the inverter and ensuring the safety of the inverter equipment.

[0114] In all the above operating modes, the optimizer will report its operating status to the northbound device. In this embodiment, when in shutdown mode, the optimizer reports "shutdown" status; when in normal operating mode and safe operating mode, the optimizer reports "running" status; and when a fault occurs, the optimizer reports "fault" status.

[0115] Figure 6This is a schematic diagram of the inverter's workflow provided in this application embodiment. In step 26, the inverter is in a shutdown state. The actual scenario at this time might be nighttime with no sunlight or weak sunlight, or the user disconnecting the DC switch on the inverter side. At this point, the inverter is not yet powered on, or its voltage is insufficient to power on the various devices used for signal transmission within the inverter. Next is step 27, where the inverter continuously determines whether it meets the power-on conditions. When sunlight is strong or the user turns on the DC switch on the inverter side, causing the inverter voltage to rise above the voltage used for signal transmission, the inverter executes step 28 to begin signal transmission with the optimizer. The signals transmitted between the inverter and the optimizer include the aforementioned heartbeat frame, voltage regulation command, and voltage limit signal. If the inverter determines that it still does not meet the power-on conditions at the current moment, it returns to step 26. After the inverter initiates signal transmission, it executes step 29 to power on. At this point, most of the components in the inverter begin operating. The optimizer continuously inputs DC power to the inverter, and the inverter continuously outputs AC power required by the user load. Next, in step 30, the inverter checks for any alarm conditions. If no alarm occurs, the inverter returns to step 29. If an alarm occurs, it indicates that the inverter is no longer suitable for providing AC power to the user load and should be shut down immediately. Otherwise, the internal electrical components of the inverter may burn out, potentially causing a fire and threatening the safety of users' lives and property. Upon alarm occurrence, the inverter executes step 31, which cuts off signal transmission. After cutting off signal transmission, the inverter returns to step 26 to power off.

[0116] Those skilled 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 beyond the scope of this application.

[0117] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. An optimizer, characterized in that, The optimizer includes a DC-DC converter, a signal processing unit, and a controller. The DC-DC converter is used to connect to the photovoltaic module and to convert DC power and output it to the inverter. The signal processing unit is connected to the output of the optimizer and is used to receive PLC signals sent by the inverter, the PLC signals containing heartbeat frames; The controller is used for, If the signal processing unit does not receive the heartbeat frame within at least two cycles, it controls the voltage output by the optimizer to be the shutdown voltage, where the cycle is the cycle of the PLC signal and the shutdown voltage is a preset safe voltage value. If the signal processing unit receives the PLC signal but the PLC signal does not contain a voltage adjustment command, it controls the voltage output by the optimizer to be less than or equal to the first voltage. If the signal processing unit receives the PLC signal and the PLC signal contains the voltage adjustment command, it controls the voltage output by the optimizer to be less than or equal to the second voltage, the second voltage being less than the first voltage, and the second voltage being greater than the shutdown voltage.

2. The optimizer according to claim 1, characterized in that, The controller is used for, If the signal processing unit receives the PLC signal and the PLC signal contains both the heartbeat frame and the voltage adjustment command, the voltage output by the optimizer is adjusted to K times the current output voltage of the optimizer, where K is less than 1.

3. The optimizer according to claim 2, characterized in that, The controller is used for, If the signal processing unit receives the PLC signal and the PLC signal contains both the heartbeat frame and the voltage adjustment command, the voltage output by the optimizer is adjusted to K times the current output voltage of the optimizer, where K is 0.5 or 0.

1.

4. The optimizer according to claim 1, characterized in that, The controller is used for, If the signal processing unit receives the PLC signal but the PLC signal does not contain the voltage regulation command, it controls the DC-DC converter to operate in maximum power point tracking mode. In maximum power point tracking mode, the output voltage of the DC-DC converter changes, and the output power of the photovoltaic module connected to the DC-DC converter is maximized. If the signal processing unit receives the PLC signal and the PLC signal contains the voltage regulation command, it controls the DC-DC converter to operate in a voltage-limiting mode. In the voltage-limiting mode, the voltage output by the DC-DC converter is constant.

5. The optimizer according to claim 1, characterized in that, The DC-DC converter unit includes a buck circuit or a buck-boost circuit.

6. An optimizer control method, applied to the optimizer, the optimizer being used to receive PLC signals sent by an inverter, the PLC signals including heartbeat frames and voltage regulation instructions, characterized in that, The method comprises: If the optimizer does not receive a heartbeat frame within at least two cycles, the voltage output by the optimizer is controlled to be the shutdown voltage, where the cycle is the cycle of the PLC signal, and the shutdown voltage is a preset safe voltage value. If the optimizer receives the heartbeat frame but does not receive the voltage adjustment command, it controls the voltage output by the optimizer to be less than or equal to the first voltage. If the optimizer receives the heartbeat frame and the voltage adjustment command, it controls the voltage output by the optimizer to be less than or equal to the second voltage, the second voltage being less than the first voltage and greater than the shutdown voltage.

7. The method according to claim 6, characterized in that, If the optimizer receives the PLC signal and the PLC signal contains both the heartbeat frame and the voltage adjustment command, the voltage output by the optimizer is adjusted to K times the current output voltage of the optimizer, where K is less than 1.

8. The method according to claim 7, characterized in that, If the optimizer receives the PLC signal and the PLC signal contains both the heartbeat frame and the voltage adjustment command, the voltage output by the optimizer is adjusted to K times the current output voltage of the optimizer, where K is 0.5 or 0.

1.

9. The method according to claim 6, characterized in that, If the optimizer receives the PLC signal but the PLC signal does not contain the voltage regulation command, it controls the optimizer to work in maximum power point tracking mode. In maximum power point tracking mode, the output voltage of the optimizer changes, and the output power of the photovoltaic module connected to the optimizer is at its maximum. If the optimizer receives the PLC signal and the PLC signal contains the voltage regulation command, it controls the optimizer to operate in a voltage-limited mode, in which the voltage output by the DC-DC converter is constant.

10. A photovoltaic power generation system, characterized in that, include: Multiple optimizers are used to connect to photovoltaic modules and to convert direct current and output it to an inverter. An inverter is used to supply power to the grid or user load. The inverter is also used to send PLC signals to the plurality of optimizers. The PLC signals include heartbeat frames and voltage regulation commands. The PLC signals are transmitted through the power line between the inverter and the optimizer. If the plurality of optimizers fail to receive the heartbeat frame within at least two cycles, the plurality of optimizers output a shutdown voltage, wherein the cycle is the cycle of the PLC signal, and the shutdown voltage is a preset safe voltage value. If the plurality of optimizers receive the heartbeat frame but do not receive the voltage adjustment command, the output voltage of the plurality of optimizers shall be less than or equal to the first voltage. If the plurality of optimizers receive the heartbeat frame and the voltage adjustment command, the output voltage of the plurality of optimizers is less than or equal to the second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

11. The photovoltaic power generation system according to claim 10, characterized in that, If 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 command to the optimizer. When the optimizer receives the voltage regulation command, the output voltage of the optimizer is less than or equal to the second voltage.

12. The photovoltaic power generation system according to claim 10, characterized in that, If some or all of the multiple optimizers fail to receive the heartbeat frame for at least two cycles, the optimizer that fails to receive the heartbeat frame adjusts its output voltage to the shutdown voltage, which is a preset safe voltage value. If the plurality of optimizers receive the heartbeat frame but do not receive the voltage adjustment command, the output voltage of the plurality of optimizers shall be less than or equal to the first voltage. If the plurality of optimizers receive the heartbeat frame and the voltage adjustment command, the voltage output by the plurality of optimizers is less than or equal to the second voltage, the second voltage is less than the first voltage, and the second voltage is greater than the shutdown voltage.

13. The photovoltaic power generation system according to claim 10, characterized in that, When the power generation system in which the inverter is located experiences an islanding effect, the inverter sends the voltage regulation command to the optimizer. Upon receiving the voltage regulation command, the optimizer controls its own output voltage to be less than or equal to the second voltage.

14. The photovoltaic power generation system according to claim 10, characterized in that, When the inverter meets the power-on conditions, the inverter sends the heartbeat frame or the voltage regulation command to the optimizer. When the inverter detects an alarm signal, the inverter stops sending the heartbeat frame or the voltage regulation command to the optimizer and performs a shutdown operation.

15. The photovoltaic power generation system according to claim 10, characterized in that, The multiple optimizer inputs are respectively connected to the photovoltaic modules, and the outputs of the multiple optimizers are connected in series to the input of the inverter. The inverter is used to broadcast the heartbeat signal and the voltage adjustment command to the plurality of optimizers via the PLC. The voltage adjustment command is used to adjust the voltage output by the plurality of optimizers to K times the current output voltage of the plurality of optimizers, where K is less than 1.

16. The photovoltaic power generation system according to claim 15, characterized in that, K is 0.5 or 0.1.

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