Power conversion device, power conversion device control method, and photovoltaic power generation system

Abstract

To provide a power conversion device, a power conversion device control method, and a photovoltaic power generation system.SOLUTION: In a photovoltaic power generation system, an input end of a module-level power electronic device is connected to a photovoltaic power generation module, and an output end is connected in series and then connected to an inverter. A component-level power electronic device includes a DC conversion unit, a signal processing unit, and a controller. The DC conversion unit performs DC-DC power conversion. The signal processing unit receives a periodic communication signal sent by the inverter. The controller controls the component-level power electronic device to switch among a shutdown mode, a normal operation mode, and a safety operation mode. These three operation modes can ensure the safety of both devices and people, have a fast response speed, and are easy to implement.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] This application relates to the field of power electronics, and more particularly, to power conversion devices, power conversion device control methods, and photovoltaic power generation systems.

Background Art

[0002] Currently, with the shortage of non-renewable energy and deteriorating environmental pollution, photovoltaic power generation is being increasingly widely used. Photovoltaic power generation converts the direct current generated by photovoltaic modules into alternating current using an inverter, and then the alternating current is connected to an alternating current power grid or supplied to a load.

[0003] Photovoltaic power generation is usually used in large-scale photovoltaic power stations, industrial and commercial fields, and household fields. In the latter two scenarios, photovoltaic modules are usually installed on the roofs of buildings near power-consuming users. To obtain a large power generation, a photovoltaic module is usually further formed by a plurality of photovoltaic panels connected in series. Therefore, the DC voltage on the photovoltaic module side is large. Therefore, non-negligible safety problems occur. Specifically, when the inverter or the photovoltaic module fails, the roof on which the photovoltaic module is installed may catch fire. Also, when it is necessary to repair the photovoltaic module and the inverter, maintenance personnel will face hundreds or thousands of high-voltage direct currents. The excessively high DC voltage on the photovoltaic module side can also cause damage to the inverter. This is not conducive to the long-term stable operation of the photovoltaic power generation system.

[0004] As a new distributed solar power generation device, a single solar power generation module can be controlled by a module-level power electronics (MLPE) device. Compared with traditional string solar power generation, the power generation efficiency of the MLPE device is improved. Also, how to use the module-level power electronics device to reduce the voltage on the solar power generation module side when necessary, fully ensure the personal safety of power consumers or maintenance personnel, protect the power generation device, and improve the power generation and maintenance safety of the distributed solar power generation device has become a research hot spot in the industry.

Summary of the Invention

[0005] This application provides a power conversion device, an operating method for controlling the power conversion device, and a solar power generation system to fully ensure both the safety of the inverter device and the safety of users and maintenance personnel, and to greatly reduce the impact of operations such as overhaul, installation, and maintenance on user power consumption.

[0006] According to a first aspect, one embodiment of this application discloses a power conversion device. The power conversion device includes a DC conversion unit, a signal processing unit, and a controller. One end of the DC conversion unit is configured to be connected to a photovoltaic module, and the other end of the DC conversion unit is configured to be connected to an input end of a next-level power conversion device. The signal processing unit is placed on the output side of the power conversion device, and the signal processing unit is configured to receive a periodic communication signal transmitted by the next-level power conversion device. The controller is configured to control the power conversion device to switch to a shutdown mode or continue operating in the shutdown mode in response to the signal processing unit not receiving the periodic communication signal for a period of time. In the shutdown mode, the output voltage of the power conversion device is a shutdown voltage, and 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 including a voltage adjustment command, the controller is configured to control the power conversion device to switch to a safe operation mode or continue operating in the safe operation mode. In the safe operation mode, the output voltage of the power conversion device is lower than a first voltage. In response to the signal processing unit receiving the periodic communication signal but the periodic communication signal not including a voltage adjustment command, the controller is configured to control the power conversion device to switch to a normal operation mode or continue operating in the normal operation mode. In the normal operation mode, the output voltage of the power conversion device is lower than a second voltage, the second voltage is lower than the first voltage, and the second voltage is higher than the shutdown voltage.

[0007] In the technical solution of the first aspect, the next-level power conversion device and the power conversion device have a communication connection and an electrical connection. Specifically, the communication method between the next-level power conversion device and the power conversion device is power line communication. Based on this, the switching of the operation mode of the power conversion device is controlled by using a periodic communication signal. In this way, communication transmission is carried out using the existing power line, thereby reducing the cost required to build an additional communication line, and by using the periodic communication signal to execute communication, the response speed is fast and the implementation is simple. In addition, the power conversion device switches between three operation modes. The output power of the power conversion device is always maximum in the normal operation mode, and it can be ensured that the power consumption requirements of users are fully met. In the safe operation mode, a failure can be detected in a timely manner, and a protection mechanism is started to ensure the safety of the devices on the next-level power conversion device side. In the shutdown mode, the output voltage of the power conversion device can be reduced to a value lower than 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, and the PLC signal includes a heartbeat frame. The controller is configured to control the power conversion device to switch to the shutdown mode or continue to operate in the shutdown mode in response to the signal processing unit not receiving the heartbeat frame within a certain period. By using PLC and determining the communication status between the power conversion device and the next-level power conversion device by using the heartbeat protection mechanism, based on the communication status between the power conversion device and the next-level power conversion device using the existing power line, the operation mode of the power conversion device can be accurately controlled in real time.

[0009] According to the first aspect, in one possible implementation, the controller is configured to control the power conversion device to switch to the normal operation mode or continue to operate in the normal operation mode in response to the signal processing unit receiving a PLC signal and the PLC signal including a heartbeat frame but not including a voltage adjustment command, and to control the power conversion device to switch to the safe operation mode or continue to operate in the safe operation mode in response to the signal processing unit receiving a PLC signal and the PLC signal including both a heartbeat frame and a voltage adjustment command. The PLC signal includes two forms: a heartbeat frame and a voltage adjustment command. According to different cases where the power conversion device receives a voltage adjustment command, the power conversion device is further finely controlled to operate in the normal operation mode or the safe operation mode. When the heartbeat frame is not interrupted, the power conversion device can also switch between different operation modes. In different operation modes, the power conversion device can be in a normal power generation state and preferentially supply power to the next-level power conversion device, or the power conversion device can be in a safe power generation state and preferentially ensure the safety of the next-level power conversion device when supplying power to the next-level power conversion device.

[0010] According to the first aspect, in one possible implementation, when the next-level power conversion device detects that the input terminal voltage of the next-level power conversion device exceeds the overvoltage threshold, and the next-level power conversion device distributes a voltage adjustment 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 next-level power conversion device detecting the input terminal overvoltage of the next-level power conversion device is a trigger condition for the next-level power conversion device to distribute a voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment 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-level power conversion device, the power conversion device can quickly reduce the output voltage thereof, thereby ensuring the safety of the next-level power conversion device.

[0011] According to the first aspect, in one possible implementation, when the next-level power conversion device detects that the input terminal power of the next-level power conversion device exceeds the over-power threshold, and the next-level power conversion device distributes a voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command, and the controller controls the output voltage of the power conversion device to decrease. In this implementation, the next-level power conversion device detecting the input terminal over-power of the next-level power conversion device is a trigger condition for the next-level power conversion device to distribute a voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls the output voltage of the power conversion device to decrease. Thus, when an over-power occurs in the next-level power conversion device, the power conversion device can quickly reduce the output voltage thereof, thereby ensuring the safety of the next-level power conversion device.

[0012] According to the first aspect, in one possible implementation, when the next-level power conversion device detects that an isolation effect has occurred in a power generation system where the next-level power conversion device is placed, and when the next-level power conversion device distributes a voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command, and the controller controls to lower the output voltage of the power conversion device. In this implementation, the detection by the next-level power conversion device that an isolation effect has occurred in the next-level power conversion device is a trigger condition for the next-level power conversion device to distribute a voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls to lower the output voltage of the power conversion device. Thus, after the isolation effect occurs, by lowering the output voltage, damage to electrical devices caused by excessive fluctuations in voltage and frequency in the isolated system is avoided.

[0013] According to the first aspect, in one possible implementation, after it is detected that the input terminal voltage of the next-level power conversion device continues to exceed the overvoltage threshold for a time threshold, the next-level power conversion device distributes a voltage adjustment command to the power conversion device to control the output voltage of the power conversion device to be less than the overvoltage threshold. In an actual power generation system, the power grid voltage often fluctuates within the normal range, and the input terminal voltage of the next-level power conversion device can recover after a short deviation from the normal voltage threshold. In this implementation, a time determination condition is added to the voltage adjustment command trigger condition to eliminate the overvoltage misjudgment of the next-level power conversion device that may occur due to the voltage fluctuation of the power grid.

[0014] According to the first aspect, in one possible implementation, after receiving a voltage adjustment command transmitted by the next-level power conversion device, the power conversion device controls the output voltage of the power conversion device to be 0.5 times or 0.1 times the current output voltage of the power conversion device. In this implementation, the output voltage of the power conversion device is reduced to half or one-tenth of the original output voltage, thereby minimizing the risk of the next-level power conversion device failing due to long-term overvoltage.

[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 the primary conversion circuit of the power conversion device and is applicable to various power conversion devices.

[0016] According to the first aspect, in one possible implementation, the controller is configured to control the DC conversion unit to operate in the maximum power tracking mode in the normal operation mode, and the output voltage of the DC conversion unit changes in the maximum power tracking mode, and the output power of the solar power generation module connected to the DC conversion unit is the maximum. Also, in the safe operation mode, the controller is configured to control the DC conversion unit to operate in the voltage limiting mode, and the voltage output by the DC conversion unit in the voltage limiting mode is constant. In the normal operation mode, the power conversion device can output power at the current maximum power generation of the solar power generation module, the voltage can be variable, and the maximization of the power generation capacity is ensured. In the safe operation mode, the output voltage of the power conversion device is constant, and this voltage can effectively ensure the safety of the next-level power conversion device. These two modes can be changed based on the actual situation to ensure the power generation capacity and safety of the power conversion device.

[0017] According to a second aspect, an embodiment of this application discloses a method for controlling a power conversion device. The method controls the output voltage of the power conversion device to a shutdown voltage in response to the power conversion device not receiving a heartbeat frame, where the shutdown voltage is a pre-set safe voltage value. In response to the power conversion device receiving a heartbeat frame and not receiving a voltage adjustment command, the method controls the power conversion device to enter a shutdown mode, and in the shutdown mode, the output voltage of the power conversion device is the shutdown voltage, where the shutdown voltage is a pre-set safe voltage value. In response to the power conversion device receiving a heartbeat frame and not receiving a voltage adjustment command, the method controls the power conversion device to enter a normal operation mode, and in the normal operation mode, the output voltage of the power conversion device is lower than a first voltage. In response to the power conversion device receiving a heartbeat frame and receiving a voltage adjustment command, the method controls the power conversion device to enter a safe operation mode, and in the safe operation mode, the output voltage of the power conversion device is lower than a second voltage, where the second voltage is lower than the first voltage and the second voltage is higher than the shutdown voltage.

[0018] In the technical solution of the second aspect, existing power lines are used for communication transmission, thereby reducing the cost required to build additional communication lines. By using the heartbeat protection mechanism and voltage adjustment commands for communication, the response speed is fast and the implementation is simple. Also, the power conversion device switches between three operation modes. The output power of the power conversion device is always maximum in the normal operation mode, and it can be ensured that the power consumption requirements of users are fully met. In the safe operation mode, faults can be detected in a timely manner, and a protection mechanism is activated to ensure the safety of the devices on the inverter side. In the shutdown mode, the output voltage of the power conversion device can be reduced to a value lower than the safe voltage to ensure the safety of maintenance personnel and users.

[0019] According to a second aspect, in one possible implementation, when it is detected that the input terminal voltage of the inverter exceeds an overvoltage threshold, and when the inverter distributes a voltage adjustment command to the power conversion device, the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this implementation, the inverter detecting the input terminal overvoltage of the inverter is a trigger condition for the inverter to distribute a voltage adjustment command to the power conversion device. After receiving the voltage adjustment command, the power conversion device 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 conversion device can quickly reduce the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0020] According to a second aspect, in one possible implementation, when it is detected that the input terminal power of the inverter exceeds an over-power threshold, and when the inverter distributes a voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command and controls the output voltage of the power conversion device to decrease. In this implementation, the inverter detecting the input terminal over-power of the inverter is a trigger condition for the inverter to distribute a voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls the output voltage of the power conversion device to decrease. Thus, when an over-power occurs in the inverter, the power conversion device can quickly reduce the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0021] According to a second aspect, in one possible implementation, it is detected that an isolation effect has occurred in a power generation system where an inverter is placed. When the inverter distributes a voltage adjustment command to a power conversion device, the power conversion device receives the voltage adjustment command and controls to reduce the output voltage of the power conversion device. In this implementation, the inverter detecting that an isolation effect has occurred in the inverter is a trigger condition for the inverter to distribute a voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls to reduce the output voltage of the power conversion device. Thus, after the isolation effect occurs, by reducing the output voltage, damage to electrical devices caused by excessive fluctuations in voltage and frequency in the isolated system is avoided.

[0022] According to a third aspect, an embodiment of this application provides a photovoltaic power generation system. The system includes a plurality of optimizers, each input terminal of the plurality of optimizers is configured to be connected to a photovoltaic power generation module, and each output terminal of the plurality of optimizers is connected in series in sequence. In response to the plurality of optimizers not receiving a heartbeat frame, the plurality of optimizers operate in a shutdown mode, and in the shutdown mode, the output voltage of the plurality of optimizers is a shutdown voltage, and the shutdown voltage is a preset safety voltage. In response to the plurality of optimizers receiving a heartbeat frame and not receiving a voltage adjustment command, the plurality of optimizers operate in a normal operation mode, and in the normal operation mode, the output voltage of the plurality of optimizers is lower than a first voltage. In response to the plurality of optimizers receiving a heartbeat frame and receiving a voltage adjustment command, the plurality of optimizers operate in a safe operation mode, and in the safe operation mode, the output voltage of the plurality of optimizers is lower than a second voltage, the second voltage is lower than the first voltage, and the second voltage is higher than the shutdown voltage. The system includes an inverter, the input terminal of the inverter is connected to the output terminals of the plurality of optimizers connected in series in sequence, and the output terminal of the inverter is configured to be connected to a power grid or a user load. The inverter distributes a heartbeat frame and a voltage adjustment command to the plurality of optimizers, and the heartbeat frame and the voltage adjustment command are transmitted via a power line between the input terminal of the inverter or the output terminal of the optimizer.

[0023] In the technical solution provided in the third aspect, the photovoltaic power generation system includes a plurality of optimizers and an inverter. The plurality of optimizers and the inverter use the existing power line for communication transmission, thereby reducing the cost required to build additional communication lines. Communication is performed by using the heartbeat protection mechanism and voltage adjustment commands, resulting in a fast response speed and simple implementation. Further, the power conversion device switches between three operating modes. The output power of the power conversion device is always maximum in the normal operating mode, and it can be ensured that the power consumption requirements of the user are maximally satisfied. In the safe operating mode, a fault can be detected in a timely manner, and a protection mechanism is activated to ensure the safety of the devices on the inverter side. In the shutdown mode, the output voltage of the power conversion device can be reduced to a value lower than the safe voltage to ensure the safety of maintenance personnel and users.

[0024] According to the third aspect, in one possible implementation, when it is detected that the input terminal voltage of the inverter exceeds the overvoltage threshold and the inverter distributes a voltage adjustment command to the power conversion device, the output voltage of the power conversion device is controlled to be less than the overvoltage threshold. In this implementation, the inverter detecting the input terminal overvoltage of the inverter is the trigger condition for the inverter to distribute a voltage adjustment command to the power conversion device. After receiving the voltage adjustment command, the power conversion device 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 conversion device can quickly reduce the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0025] According to the third aspect, in one possible implementation, when it is detected that the input terminal power of the inverter exceeds the over-power threshold and the inverter distributes a voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command and controls to reduce the output voltage of the power conversion device. In this implementation, the inverter detecting the over-power at the input terminal of the inverter is the trigger condition for the inverter to distribute the voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls to reduce the output voltage of the power conversion device. Thus, when over-power occurs in the inverter, the power conversion device can quickly reduce the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0026] According to the third aspect, in one possible implementation, when it is detected that an islanding effect has occurred in the power generation system where the inverter is placed and the inverter distributes a voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command and controls to reduce the output voltage of the power conversion device. In this implementation, the inverter detecting the occurrence of the islanding effect in the inverter is the trigger condition for the inverter to distribute the voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls to reduce the output voltage of the power conversion device. Thus, after the islanding effect occurs, by reducing the output voltage, damage to electrical devices caused by excessive fluctuations in voltage and frequency in the isolated system is avoided.

[0027] According to a third aspect, in one possible implementation, the inverter establishes communication with the optimizer when the startup conditions are met. The communication content includes a heartbeat frame or a voltage adjustment command. After detecting an alarm signal, the inverter interrupts communication with the optimizer and performs a shutdown operation. Thus, when the operating conditions are met, the inverter and the optimizer can establish communication for the first time and quickly execute the power generation operation. Also, after an alarm occurs, the inverter can cut off communication with the optimizer for the first time, and the optimizer can enter a safe operating mode to ensure the safety of the inverter.

[0028] According to a fourth aspect, one embodiment of this application discloses a power conversion device. The power conversion device includes a DC conversion unit, a signal processing unit, and a controller. The DC conversion unit is configured to convert the DC generated by the photovoltaic module and output the converted DC to the next-level power conversion device. The signal processing unit is connected to the output of the power conversion device and is configured to receive a periodic communication signal transmitted by the next-level power conversion device. The controller is configured to control the output voltage of the power conversion device to a shutdown voltage in response to the signal processing unit not receiving a periodic communication signal within a certain period, where the shutdown voltage is a pre-set safe voltage value, and to control the output voltage of the power conversion device to be below a first voltage in response to the signal processing unit receiving a periodic communication signal but the periodic communication signal not including a voltage adjustment command, and to control the output voltage of the power conversion device to be below a second voltage in response to the signal processing unit receiving a periodic communication signal and the periodic communication signal including a voltage adjustment command, where the second voltage is lower than the first voltage and the second voltage is higher than the shutdown voltage.

[0029] In the technical solution of the fourth aspect, the next-level power conversion device and the power conversion device have a communication connection and an electrical connection. Specifically, the communication method between the next-level power conversion device and the power conversion device is power line communication. Based on this, the output voltage of the power conversion device is controlled using a periodic communication signal. In this way, communication transmission is performed using the existing power lines, thereby reducing the cost required to construct additional communication lines. By performing communication using the periodic communication signal, the response speed is fast and the implementation is simple. Also, the output voltage of the power conversion device is related to three voltage values. When the output voltage is below the first voltage, the output power of the power conversion device is always maximum, and it can be ensured that the power consumption requirements of the user are maximally satisfied. When the output voltage is below the second voltage, the protection mechanism is timely activated to ensure the safety of the devices on the next-level power conversion device side. When the output voltage is the shutdown voltage, the output voltage of the power conversion device is reduced to a value lower than the safety voltage, and the personal safety of maintenance personnel and users can be ensured.

[0030] According to the fourth aspect, in one possible implementation, the periodic communication signal is a PLC signal, and the PLC signal includes a heartbeat frame. The controller is configured to control the output voltage of the power conversion device to the shutdown voltage in response to the signal processing unit not receiving the heartbeat frame within a certain period. By using PLC and determining the communication status between the power conversion device and the next-level power conversion device using the heartbeat protection mechanism, the output voltage of the power conversion device can be accurately controlled in real time based on the communication status between the power conversion device and the next-level power conversion device using the existing power lines.

[0031] According to a fourth aspect, in one possible implementation, the controller is configured to control the output voltage of the power conversion device to be less than a first voltage in response to the signal processing unit receiving a PLC signal and the PLC signal including a heartbeat frame but not including a voltage adjustment command, and to control the output voltage of the power conversion device to be less than a second voltage in response to the signal processing unit receiving a PLC signal and the PLC signal including both a heartbeat frame and a voltage adjustment command. The PLC signal includes two forms: a heartbeat frame and a voltage adjustment command. According to different cases where the power conversion device receives a voltage adjustment command, the output voltage of the power conversion device is further finely controlled to be less than or equal to the first voltage or the second voltage. When the heartbeat frame is not interrupted, the power conversion device can output different voltages. Therefore, the power conversion device can preferentially supply power to the next-level power conversion device in a normal power generation state, or the power conversion device can preferentially ensure the safety of the next-level power conversion device when supplying power to the next-level power conversion device in a safe power generation state.

[0032] According to a fourth aspect, in one possible implementation, the controller is configured to adjust the output voltage of the power conversion device to K times the current output voltage of the power conversion device in response to the signal processing unit receiving a PLC signal and the PLC signal including both a heartbeat frame and a voltage adjustment command, where K is less than 1, or K is 0.5 or 0.1. In this implementation, the output voltage of the power conversion device is reduced to half or one-tenth of the original output voltage, thereby minimizing the risk of the next-level power conversion device failing due to long-term overvoltage.

[0033] According to a fourth aspect, in one possible implementation, the controller is configured to control the DC conversion unit to operate in a maximum power tracking mode in response to the signal processing unit receiving a periodic communication signal that does not include a voltage adjustment command. In the maximum power tracking mode, the output voltage of the DC conversion unit changes, and the output power of the photovoltaic module connected to the DC conversion unit is maximized. In response to the signal processing unit receiving a periodic communication signal and the periodic communication signal including a voltage adjustment command, the controller is configured to control the DC conversion unit to operate in a voltage limit mode. In the voltage limit mode, the output voltage of the DC conversion unit is constant. When the output voltage of the power conversion device is less than or equal to a first voltage, the DC conversion unit operates in the maximum power tracking mode, and the power conversion device can output power at the current maximum power generation of the photovoltaic module, the voltage can be variable, and maximization of the power generation capacity is ensured. When the output voltage of the power conversion device is less than or equal to a second voltage, the DC conversion unit operates in the voltage limit mode, and the output voltage of the power conversion device is constant, and this voltage can effectively ensure the safety of the next-level power conversion device. These two modes can be changed based on the actual situation to ensure the power generation capacity and safety of the power conversion device.

[0034] According to a fifth aspect, an embodiment of this application discloses a method for controlling a power conversion device. The method includes controlling the output voltage of the power conversion device to a shutdown voltage in response to the power conversion device not receiving a heartbeat frame, where the shutdown voltage is a preset safe voltage value; controlling the output voltage of the power conversion device to be less than or equal to a first voltage in response to the power conversion device receiving a heartbeat frame and not receiving a voltage adjustment command; and controlling the output voltage of the power conversion device to be less than or equal to a second voltage in response to the power conversion device receiving a heartbeat frame and receiving a voltage adjustment command, where the second voltage is lower than the first voltage and the second voltage is higher than the shutdown voltage.

[0035] In the technical solution of the fifth aspect, an existing power line is used for communication transmission, thereby reducing the cost required to construct an additional communication line. By using a heartbeat protection mechanism and a voltage regulation command for communication, the response speed is fast and the implementation is simple. Further, the output voltage of the power conversion device is related to three voltage values. When the output voltage is below the first voltage, the output power of the power conversion device is always maximum, and it can be ensured that the power consumption requirements of the user are fully met. When the output voltage is below the second voltage, the protection mechanism can be started in a timely manner to ensure the safety of the device on the next-level power conversion device side. When the output voltage is the shutdown voltage, the output voltage of the power conversion device is reduced to a value lower than the safety voltage, and the safety of maintenance personnel and users can be ensured.

[0036] According to the fifth aspect, in one possible implementation, when it is detected that the input terminal voltage of the inverter exceeds the overvoltage threshold, the inverter receives the DC power output by the power conversion device and is configured to control the output voltage of the power conversion device to be less than the overvoltage threshold when distributing the voltage regulation command to the power conversion device. In this implementation, the inverter detecting the input terminal overvoltage of the inverter is the trigger condition for the inverter to distribute the voltage regulation command to the power conversion device. After receiving the voltage regulation command, the power conversion device 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 conversion device can quickly reduce the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0037] According to a fifth aspect, in one possible implementation, when it is detected that the input terminal power of the inverter exceeds the over-power threshold, the inverter receives the DC power output by the power conversion device, distributes a voltage adjustment command to the power conversion device, and is configured to control the output voltage of the power conversion device to decrease. In this implementation, the inverter detecting the over-power at the input terminal of the inverter is the trigger condition for the inverter to distribute the voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls the output voltage of the power conversion device to decrease. Thus, when over-power occurs in the inverter, the power conversion device can quickly decrease the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0038] According to a fifth aspect, in one possible implementation, when it is detected that an islanding effect has occurred in the power generation system where the inverter is located, the inverter receives the DC power output by the power conversion device, distributes a voltage adjustment command to the power conversion device, and is configured to control the output voltage of the power conversion device to decrease. In this implementation, the inverter detecting the occurrence of the islanding effect in the inverter is the trigger condition for the inverter to distribute the voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls the output voltage of the power conversion device to decrease. Thus, after the islanding effect occurs, by decreasing the output voltage, damage to electrical devices caused by excessive fluctuations in voltage and frequency in the isolated system is avoided.

[0039] According to a sixth aspect, an embodiment of this application provides a solar power generation system. The solar power generation system includes a plurality of optimizers configured to convert direct current generated by solar power generation modules and output the converted direct current to an inverter, and an inverter configured to supply power to a power grid or a user load. The inverter is further configured to transmit a heartbeat frame and a voltage adjustment command to the plurality of optimizers, and the heartbeat frame and the voltage adjustment command are transmitted via a power line between the inverter and the optimizers. In response to the plurality of optimizers not receiving a heartbeat frame during a certain period, the output voltage of the plurality of optimizers is set to a shutdown voltage, and the shutdown voltage is a preset safe voltage value. In response to the plurality of optimizers receiving a heartbeat frame but not receiving a voltage adjustment command, the output voltage of the plurality of optimizers is set to be equal to or lower than a first voltage. Alternatively, in response to the plurality of optimizers receiving a heartbeat frame and receiving a voltage adjustment command, the output voltage of the plurality of optimizers is set to be equal to or lower than a second voltage, the second voltage is lower than the first voltage, and the second voltage is higher than the shutdown voltage.

[0040] In the technical solution provided in the sixth aspect, the photovoltaic power generation system includes a plurality of optimizers and an inverter. The plurality of optimizers and the inverter use the existing power lines for communication transmission, thereby reducing the cost required to build additional communication lines. Communication is performed by using the heartbeat protection mechanism and voltage adjustment commands, resulting in a fast response speed and simple implementation. Also, the output voltage of the power conversion device is related to three voltage values. When the output voltage is below the first voltage, the output power of the power conversion device is always maximum, and it can be ensured that the power consumption requirements of the user are maximally satisfied. When the output voltage is below the second voltage, the protection mechanism is timely activated to ensure the safety of the devices on the next-level power conversion device side. When the output voltage is the shutdown voltage, the output voltage of the power conversion device is reduced to a value lower than the safety voltage, ensuring the safety of maintenance personnel and users.

[0041] According to the sixth aspect, in one possible implementation, when the input terminal voltage of the inverter exceeds the overvoltage threshold, the inverter distributes a voltage adjustment command to the optimizer, and the optimizer controls the output voltage of the optimizer to be less than the second voltage. In this implementation, the inverter detecting the input terminal overvoltage of the inverter is the trigger condition for the inverter to distribute the voltage adjustment command to the power conversion device. After receiving the voltage adjustment command, the power conversion device controls the output voltage of the power conversion device to be less than the second voltage. Thus, when an overvoltage occurs in the inverter, the power conversion device can quickly reduce the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0042] According to the sixth aspect, in one possible implementation, when the input terminal power of the inverter exceeds the over-power threshold, the inverter distributes a voltage adjustment command to the optimizer, and the optimizer controls to make the output voltage of the optimizer less than a second voltage. In this implementation, the inverter detecting the input terminal power of the inverter is a trigger condition for the inverter to distribute a voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls to make the output voltage of the power conversion device less than the second voltage. Thus, when over-power occurs in the inverter, the power conversion device can quickly reduce the output voltage of the power conversion device, thereby ensuring the safety of the inverter.

[0043] According to the sixth aspect, in one possible implementation, in response to some or all of the plurality of optimizers not receiving a heartbeat frame within a certain period, the optimizer that does not receive the heartbeat frame adjusts the output voltage to a shutdown voltage, and the shutdown voltage is a preset safe voltage value. In response to the plurality of optimizers receiving the heartbeat frame and not receiving a voltage adjustment command, the output voltage of the plurality of optimizers is made less than a first voltage. In response to the plurality of optimizers receiving the heartbeat frame and receiving a voltage adjustment command, the output voltage of the plurality of optimizers is made less than a second voltage, the second voltage is lower than the first voltage, and the second voltage is higher than the shutdown voltage. Thanks to the PLC signal transmission, the plurality of optimizers establish communication with the inverter by using the heartbeat frame and the voltage adjustment command, and change the output voltage of the plurality of optimizers based on different situations of the received heartbeat frame and voltage adjustment command. This communication method is simple and reliable.

[0044] According to a sixth aspect, in one possible implementation, when an isolation effect occurs in a power generation system in which an inverter is placed, the inverter distributes a voltage adjustment command to the optimizer, and the optimizer controls to make the output voltage of the optimizer less than a second voltage. In this implementation, the inverter detecting the occurrence of the isolation effect in the inverter is a trigger condition for the inverter to distribute a voltage adjustment command to the power conversion device. After the power conversion device receives the voltage adjustment command, the controller controls to make the output voltage of the power conversion device less than the second voltage. Thus, after the isolation effect occurs, by reducing the output voltage, damage to electrical devices caused by excessive fluctuations in voltage and frequency in the isolated system is avoided.

[0045] According to a sixth aspect, in one possible implementation, the inverter establishes communication with the optimizer when the startup conditions are met. The communication content includes a heartbeat frame or a voltage adjustment command. After detecting an alarm signal, the inverter interrupts communication with the optimizer and performs a shutdown operation. Thus, when the operating conditions are met, the inverter and the optimizer can establish communication for the first time and quickly execute the power generation operation. Also, after an alarm occurs, the inverter can cut off communication with the optimizer for the first time, and the optimizer can enter the safe operating mode to ensure the safety of the inverter.

[0046] According to a sixth aspect, in one possible implementation, the inputs of the plurality of optimizers are each configured to be connected to a photovoltaic module, and the outputs of the plurality of optimizers are connected in series and then connected to the input of an inverter. The inverter is configured to transmit a heartbeat frame and a voltage adjustment command to the plurality of optimizers in a broadcast manner via a PLC, and the voltage adjustment 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. In this implementation, the output voltage of the power conversion device is reduced to half or one-tenth of the original output voltage, thereby minimizing the risk of failure of the next-level power conversion device due to long-term overvoltage.

Brief Description of the Drawings

[0047]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0048] The technical solution in this application will be described below with reference to the accompanying drawings.

[0049] In this application, unless otherwise explicitly specified or limited, the term "connected" should be understood in a broad sense. For example, "connected" may be a fixed connection, a detachable connection, or an integrated one, which may be directly connected or indirectly connected using an intermediate medium. Also, the term "coupling" can be a way to implement an electrical connection for signal transmission. "Coupling" may be a direct electrical connection or an indirect electrical connection using an intermediate medium.

[0050] For ease of understanding, first, some proper nouns in this application will be explained.

[0051] Module-level power electronics device: Different from string-type power electronics devices, module-level power electronics devices provide a maximum power point tracking (MPPT) function and a monitoring function to further improve the power generation of a photovoltaic power generation system. Module-level power electronics devices can also implement a module-level rapid shutdown (RSD) function with an appropriate shutdown policy. This greatly improves the safety of the photovoltaic power generation system.

[0052] MPPT function: To achieve the maximum output power of a photovoltaic module, the backend input voltage is controlled to operate at the maximum power point voltage (Vmpp) of the photovoltaic module.

[0053] PLC: Power line communication, also called carrier communication, is a communication method in which existing power lines are used as an information transmission medium to transmit data or information in the form of digital signals.

[0054] Mismatch: For a plurality of photovoltaic modules connected in series or parallel, when the environmental conditions (such as radiation and temperature) of some of the plurality of photovoltaic modules are different from those of other photovoltaic modules, the power of the plurality of photovoltaic modules connected in series or parallel will be smaller than the sum of the maximum power points of each photovoltaic module.

[0055] Heartbeat protection mechanism: The heartbeat protection mechanism is a safety monitoring mechanism used to determine whether the communication between devices in a communication system is normal. In this mechanism, the master machine periodically sends a heartbeat frame to the slave machine. After receiving the heartbeat frame, the slave machine sends feedback to the master machine to notify the master machine that the communication connection is normal. If the master machine does not receive the feedback information, the master machine takes corrective measures such as attempting to reconnect. In some systems, after receiving the heartbeat frame, the slave machine does not send feedback to the master machine, but instead determines whether the communication is abnormal based on whether the heartbeat frame is received, and executes corresponding operations on the slave machine.

[0056] Islanding effect: In a distributed power generation system, when the power grid trips due to a fault or power outage, each user-side distributed grid-connected power generation system (such as photovoltaic power generation, wind power generation, and fuel cell power generation) cannot timely detect the power outage state and disconnect itself from the main network. As a result, an isolated power generation system that supplies power by itself and consists of the distributed grid-connected power generation system and the load connected to it is formed.

[0057] FIG. 1 is a schematic diagram of the architecture of a photovoltaic power generation system according to an embodiment of this application. In this embodiment, the photovoltaic power generation system includes a plurality of converters 1 to n, and the positive and negative input terminals of converters 1 to n are respectively connected to the positive and negative output terminals of photovoltaic power generation modules 1 to n in a one-to-one correspondence. The output terminals of converters 1 to n are connected in parallel and then coupled to the power grid 105. In this architecture, a plurality of photovoltaic power generation modules can be coupled to the power grid 105 by using converters, and the output terminals of the plurality of converters are used so that the plurality of photovoltaic power generation modules are coupled to the power grid 105 in parallel, such that the power grid has a relatively large power supply capacity.

[0058] Since the output power of a single photovoltaic cell is low, a photovoltaic power generation module can be formed by combining a plurality of photovoltaic cells in series or in parallel. As a result, the output power of the photovoltaic power generation module increases. The configuration of the photovoltaic power generation module is not limited in this application.

[0059] Photovoltaic power generation is implemented by configuring converters 1 to n to convert the direct current of photovoltaic power generation modules 1 to n into alternating current transmitted to the power grid. Also, converters 1 to n are connected to the output terminals of photovoltaic power generation modules 1 to n in a one-to-one correspondence, and are configured to control the output voltage of each of photovoltaic power generation modules 1 to n so as to achieve maximum power tracking of photovoltaic power generation modules 1 to n.

[0060] Converters 1 to n include micro-inverters. A micro-inverter is a miniaturized and highly integrated power conversion device that can be installed near a solar power generation module on the rooftop of a building and has functions such as, for example, an inverter function, an MPPT function, and a module-level shutdown or monitoring function. The micro-inverter can be applied to this architecture to implement the following process. Taking the solar power generation module 1 as an example, the solar power generation module 1 converts solar energy into direct current, and the converter 1 can convert the direct current into alternating current required by the power grid 105 with specific electrical parameters such as a specific frequency and a specific voltage. Then, the alternating current is provided for use by the load.

[0061] It should be understood that in this embodiment, one solar power generation module is connected corresponding to one converter, but there may also be a case where multiple solar power generation modules are connected corresponding to one converter. The number of solar power generation modules connected corresponding to the converter is not limited in this application. Taking the micro-inverter as an example. The "one-to-one" solution of the micro-inverter is one in which one solar power generation module is connected corresponding to one micro-inverter, and the "one-to-two" and "one-to-four" solutions of the micro-inverter are those in which two solar power generation modules are connected corresponding to one micro-inverter, and four solar power generation modules are connected corresponding to one micro-inverter.

[0062] FIG. 2 is a schematic diagram of the configuration of another photovoltaic power generation system according to an embodiment of this application. The photovoltaic power generation system includes converters 1-n, converters 2-m, and inverter 104. The input ends of converters 1-n and 2-m are configured to be connected to the output ends of photovoltaic power generation modules 1-n and 2-m in a one-to-one correspondence, respectively. The converters are connected in series to form p photovoltaic power generation strings, where p is 2 or more. The output ends of converters 1-1 to 1-n are connected in series to form photovoltaic power generation string 1, and the output ends of converters 2-1 to 2-m are connected in series to form another photovoltaic power generation string 2.

[0063] The input end of converter 1-1 in photovoltaic power generation string 1 is connected to photovoltaic power generation module 1-1, the input end of converter 1-n is connected to photovoltaic power generation module 1-n, and the output ends of converters 1-1 to 1-n are all connected in series and connected to the input end of inverter 104 via positive DC power line 106 and negative DC power line 107. Similarly, the input end of converter 2-1 in photovoltaic power generation string 2 is connected to photovoltaic power generation module 2-1, the input end of converter 2-m is connected to photovoltaic power generation module 2-m, and the output ends of converters 2-1 to 2-m are all connected in series and connected to the input end of inverter 104 via positive DC power line 106 and negative DC power line 107.

[0064] The output end of inverter 104 is connected to power grid 105. Inverter 104 is a three-phase inverter, and power grid 105 is a three-phase AC power grid. Alternatively, inverter 104 may be a household single-phase inverter, and the corresponding power grid 105 is a household AC power grid.

[0065] It should be understood that in one implementation solution, the converter can be a shutdown device. The shutdown device has a module shutdown function and is a module-level power electronics device installed between the photovoltaic module and the inverter. The shutdown device can quickly shut down the connection between each photovoltaic module and the inverter, and is generally installed on the roof of a building near the photovoltaic module side.

[0066] In another implementation solution, the converter can be an optimizer. The optimizer is a power conversion device installed between the photovoltaic module and the inverter, which can eliminate the mismatch phenomenon of the photovoltaic module, has the MPPT function of a single photovoltaic module, and thereby can greatly improve the power generation of the entire photovoltaic system. The optimizer can be used in this architecture to implement the following process. Taking the photovoltaic string 1 as an example. After each of the photovoltaic modules 1-1 to 1-n converts solar energy into direct current and power conversion is performed by the corresponding connected optimizers 1-1 to 1-n, the direct current output by a plurality of converters is connected in series to the input end of the inverter 104. Compared with the optimizer, the inverter is the next-level power conversion device of the optimizer. The input end of the inverter 104 is referred to as the "1-channel" input of the inverter. Similarly, the photovoltaic string 2 also combines the output direct current in series and transmits the output direct current to the input end of the inverter 104 in another "1-channel" manner. In this embodiment of this application, the optimizer further has a module-level high-speed shutdown function, thereby further reducing the safety risk of the photovoltaic system.

[0067] With reference to the accompanying drawings, the implementation of the maximum power tracking function and the fast shutdown function of the component-level power electronics device provided in this application will be described below. To facilitate the description, an optimizer will be used as an example for illustration hereinafter. It should be understood that the method of implementing the fast shutdown described below is not limited to the optimizer and is also applicable to many more component-level power electronics devices shown in FIGS. 1 and 2.

[0068] Also, the meaning of the fast shutdown function of the module-level power electronics device function provided in this application is not limited to isolating the module-level power electronics device from the photovoltaic power generation system, but is simply reflected by the term "shutdown". This also reflects that the output voltage, output current, or output power of the component-level power electronics device is reduced below a specific voltage.

[0069] Based on the connection relationship between the photovoltaic string 1 and the inverter 104 in FIG. 2, FIG. 3 is a schematic diagram of the optimizer-inverter connection according to this embodiment of this application. The photovoltaic modules are each connected to an optimizer in a one-to-one correspondence. Specifically, the output end of the photovoltaic module 1-1 is connected to the input end of the optimizer 1-1, the output end of the photovoltaic module 1-(n-1) is connected to the input end of the optimizer 1-(n-1), and the output end of the photovoltaic module 1-n is connected to the input end of the optimizer 1-n. The output ends of the plurality of optimizers 1-1 to 1-n are connected in series and then connected to the inverter 104 as the input of the inverter 104. Specifically, one output end of the optimizer 1-1 is connected to one input end of the inverter 104, and the other output end of the optimizer 1-1 is connected to one output end of the connected optimizer 1-2. Similarly, one output end of the optimizer 1-(n-1) is connected to one output end of the connected optimizer 1-(n-2), the other output end of the optimizer 1-(n-1) is connected to the output end of the optimizer 1-n, and the other output end of the optimizer 1-n is connected to the other input end of the inverter 104. More specifically, taking the optimizer 1-1 as an example, the optimizer 1-1 includes a DC conversion unit 101, a signal processing unit 103, and a controller 102, and the inverter 104 includes an inverter signal transceiver unit 108 and an inverter circuit 109. The optimizer 1-1 is connected to the inverter 104 via the positive DC power line 106, and the optimizer 1-n is connected to the inverter 104 via the negative DC power line 107.

[0070] The DC conversion unit 101 includes one or a combination of Buck Converters, Boost Converters, Buck-Boost Converters, Forward Converters, or Flyback Converters. On the other hand, the DC conversion unit 101 is configured to operate in the MPPT tracking mode. For example, in the photovoltaic power generation system architecture provided in this application, one optimizer is connected corresponding to one photovoltaic power generation module, and the power output characteristic curve of the photovoltaic power generation module is affected by factors such as temperature, solar radiation, or shadow. The DC conversion unit 101 of the optimizer includes a plurality of switching transistors, and the optimizer controls the duty ratio of one or more switching transistors through pulse width modulation so that the input voltage of the optimizer always follows the maximum power point operating voltage of the photovoltaic power generation module and the photovoltaic power generation module maintains the maximum power output. On the other hand, the DC conversion unit 101 is configured to operate in the voltage limit mode. In this mode, the optimizer controls the duty ratio of one or more switching transistors through pulse width modulation so that the output voltage of the optimizer is a specific voltage threshold. Below this specific voltage threshold, the inverter 104 has a lower input voltage than before the voltage is adjusted or maintains the input voltage of the inverter within a tolerable range to protect the inverter. In short, the DC conversion unit 101 can output different voltage values according to different operating strategies to meet different operating requirements of the photovoltaic power generation system.

[0071] The signal processing unit 103 and the signal transceiver unit 108 are configured to receive or transmit PLC signals. It should be understood that the coupling method between the signal processing unit 103 shown in FIG. 3 and the inverter 104 is an example. The coupling methods between the signal processing unit 103 and the inverter 104 include bilateral coupling (coupled to both sides output by the inverter) and unilateral coupling (coupled to one side output by the inverter), and 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.

[0072] The control unit 102 is configured to control to close or cut off the switching transistor in the DC conversion unit 101 of the optimizer based on the information received by the signal processing unit 103 or based on the operation information pre-stored in the signal processing unit 103.

[0073] The inverter circuit 109 is configured to convert direct current into alternating current.

[0074] In the same solar power generation string, other optimizers other than the optimizer 1-1 and the optimizer 1-n are not directly connected to the inverter 104. However, since the output terminals of these multiple optimizers are connected in series, the optimizer signal processing units in each optimizer can process the signals transmitted by the inverter 104 in a broadcast manner, and therefore, each optimizer can receive commands from the inverter 104 and execute corresponding actions.

[0075] In the photovoltaic power generation system according to the embodiment shown in FIG. 1 or FIG. 2 of this application, the inverter 104 and the optimizer not only have an electrical connection method, but also have a PLC connection method. In addition to the PLC connection, the communication method between the inverter 104 and the optimizer further includes connection methods such as, for example, RS485, Zigbee, and sub-1G. In this application, this embodiment will be mainly described using the PLC method.

[0076] Hereinafter, with reference to the photovoltaic power generation system shown in FIG. 3, the implementation process of the PLC will be described in detail.

[0077] Referring to FIG. 3. In the photovoltaic power generation system using the PLC method, the inverter 104 and the optimizers 1-1 to 1-n exchange data via the power lines 106 or 107 shown in FIG. 3.

[0078] Taking the optimizer 1-1 as an example. There is data exchange between the optimizer 1-1 and the inverter 104, and this data exchange is essential to maintain the normal operation of the inverter 104 and the optimizer 1-1. Therefore, it is particularly important to ensure the reliability of the PLC method. In order to ensure the reliability of communication and ensure that the optimizer 1-1 and the inverter 104 do not lose communication or become disconnected, in this embodiment of this application, a heartbeat protection mechanism is used to detect the communication status between the inverter 104 and the optimizer 1-1.

[0079] In one implementation, in the heartbeat protection mechanism, the master machine is the inverter 104 and the slave machine is the optimizer 1-1. After the photovoltaic power generation system is started and operates, the inverter 104 periodically or cyclically sends a heartbeat frame to the optimizer 1-1. After receiving the heartbeat frame, the optimizer 1-1 sends feedback information to the inverter 104. If the inverter 104 does not receive the feedback information, the inverter 104 takes corrective measures such as attempting to reconnect.

[0080] In one implementation, in the heartbeat protection mechanism, the master machine is the inverter 104, and the slave machine is the optimizer 1-1. After the photovoltaic power generation system is started and operates, the inverter 104 periodically or cyclically sends a heartbeat frame to the optimizer 1-1, and the optimizer 1-1 executes corresponding operations on its own side according to different situations of whether the heartbeat frame is received without sending feedback information to the inverter 104.

[0081] In this application, in addition to the heartbeat frame, after the inverter detects a fault or receives an adjustment command distributed by the user, the inverter 104 further sends a voltage adjustment command to the optimizer 1-1. The voltage adjustment command can instruct the optimizer 1-1 to adjust the DC conversion unit 101 so that the optimizer 1-1 outputs a specific voltage or current. The frequency of the heartbeat frame may be the same as or different from the frequency of the voltage adjustment command.

[0082] The inverter 104 and the optimizer perform data exchange by using the signal transceiver unit 108 on the inverter 104 side and the signal processing unit 103 of the optimizer 1-1. The communication method of data exchange is PLC. The PLC signal used for data exchange includes the heartbeat frame and the voltage adjustment command, and both the heartbeat frame and the voltage adjustment command belong to periodic communication signals. The entire communication process is as follows.

[0083] During the operation of the inverter 104 and the optimizer, the signal transceiver unit 108 transmits, in a PLC manner, a PLC signal with a heartbeat frame and a voltage adjustment command superimposed thereon to each optimizer in a broadcast manner. After receiving the PLC signal, the signal processing unit 103 processes the PLC signal and transmits the processed PLC signal to the control unit 102 inside the optimizer. The control unit 102 controls the operation of the DC conversion unit 101 based on the processed PLC signal to adjust the output voltage or output current of the optimizer.

[0084] Hereinafter, only Optimizer 1-1 is used as an example for explanation. It should be understood that all optimizers belonging to the same photovoltaic string can receive the PLC signal, and hereinafter, the operating principles of other optimizers within the same photovoltaic string will not be described in detail.

[0085] In the photovoltaic power generation system according to this embodiment of this application, Optimizer 1-1 switches different operating modes of the optimizer based on the received heartbeat frame and the received voltage adjustment command. The operating modes include a normal operating mode, a safe operating mode, and a shutdown mode. Hereinafter, first, the data communication method and operating principle of the inverter and the optimizer device in these three different operating modes will be described.

[0086] Normal operation mode: In the normal operation mode, the inverter 104 transmits a periodic heartbeat frame to the optimizer in the PLC mode. In this mode, the optimizer 1-1 successfully receives the periodic heartbeat frame from the inverter 104. Based on the fact that the periodic heartbeat frame is received normally and no voltage adjustment command is received, the optimizer determines that the communication between the optimizer 1-1 and the inverter 104 is normal and it is necessary to execute the normal operation mode. In this mode, in order to increase the power input of the inverter 104, the optimizer 1-1 outputs the maximum possible power. For example, the optimizer 1-1 controls the input terminal voltage of the optimizer 1-1 to be the maximum power point voltage of the photovoltaic module, or to approach the maximum power point near the maximum power point voltage, and the DC conversion unit 101 operates in the MPPT tracking mode. General cases where the optimizer 1-1 is triggered to execute the normal operation mode include in the morning when the light reaches the initial threshold of light intensity and when the user's photovoltaic power generation system is started. In the morning, when the photovoltaic module receives light exceeding the initial light intensity threshold, the inverter and the optimizer are powered on and start operating, and the inverter starts to transmit a PLC signal to the optimizer. After receiving the periodic heartbeat frame, the optimizer determines that the communication between the inverter and the optimizer is normal and starts to execute the normal operation mode to output voltage. When the user starts, the user actively closes the DC switch of the inverter 104. The DC switch is installed on the inverter 104 side. After the DC switch is closed, an electrical connection is formed between the optimizer 1-1 and the inverter 104. The optimizer 1-1 successfully receives the heartbeat frame from the inverter 104. After the optimizer 1-1 receives the periodic heartbeat frame, the optimizer 1-1 executes the normal operation mode to output voltage.

[0087] Safe operation mode: In the safe operation mode, Optimizer 1-1 still receives the periodic heartbeat frames from the inverter 104, and based on the successfully received periodic heartbeat frames, determines that the communication between Optimizer 1-1 and the inverter 104 is normal. However, in this mode, in addition to the heartbeat frames, the inverter 104 further sends periodic voltage adjustment commands in the PLC mode. After successfully receiving the periodic voltage adjustment commands, Optimizer 1-1 determines that the communication between Optimizer 1-1 and the inverter 104 is normal and that it is necessary to execute the safe operation mode based on the successfully received periodic heartbeat frames and the successfully received periodic voltage adjustment commands. In this mode, Optimizer 1-1 limits the output terminal voltage or current of Optimizer 1-1 based on the voltage adjustment commands. For example, the output voltage of Optimizer 1-1 is limited to a specific voltage, and the DC conversion unit 101 is controlled to be in the voltage limit mode. In the voltage limit mode, the input voltage of the inverter is also limited so that protection is implemented for the inverter-side devices in the photovoltaic power generation system. It should be understood that in the safe operation mode, the specific value of a specific voltage can be adjusted, and the specific value of a specific voltage is affected by factors such as, for example, the local specifications of the product installation and the number of optimizers. The setting of the specific value of a specific voltage can satisfy that the inverter-side devices are not damaged. Also, the cases where Optimizer 1-1 is triggered to execute the safe operation mode are complex. Hereinafter, with reference to FIG. 4, a plurality of cases where the safe operation mode is triggered will be described.

[0088] Shutdown Mode: In the shutdown mode, the optimizer 1-1 cannot receive the heartbeat frame from the inverter 104 within a certain period. This period includes a period that is M times the period of the heartbeat frame, where M is a constant. This period can also be a preset period and depends on the stability of the PLC in the operating environment where the optimizer is placed. To ensure sufficient normal communication between the optimizer and the inverter, the higher the stability, the longer the period, and the lower the stability, the shorter the period. Based on the fact that the periodic heartbeat frame is not successfully received, it is determined that the communication between the optimizer 1-1 and the inverter 104 is abnormal, and the inverter 104 cannot effectively control the optimizer 1-1. The optimizer 1-1 is controlled to set the output voltage to the shutdown voltage, which is the voltage preset by the optimizer 1-1 before shipment, and the preset low voltage range is from 1 volt to 48 volts. In this case, even if a person directly touches the output port of the solar power generation string, there is no danger, thereby maximizing the safety of users and maintenance personnel. A common case where the optimizer 1-1 is triggered to execute the shutdown mode includes the user manually shutting down the inverter 104. In this case, the user actively turns off the DC switch of the inverter 104, and the DC switch is installed on the inverter 104 side. After the DC switch is turned off, the electrical connection between the optimizer 1-1 and the inverter 104 is disconnected, and the optimizer 1-1 can no longer receive the heartbeat frame from the inverter 104. After the optimizer 1-1 fails to receive the heartbeat frame from the inverter 104 for a period longer than a certain time, the optimizer 1-1 executes the shutdown mode.

[0089] In the above three operation modes, the optimizer selects whether to maintain the current operation mode or switch to another operation mode based on the different statuses of the received PLC signals. In some embodiments, if the PLC signal received by optimizer 1-1 before period t1 contains a heartbeat frame but does not contain a voltage adjustment command, optimizer 1-1 continues to operate in the normal operation mode. If the PLC signal received by the optimizer during the period from t1 to t2 contains both a heartbeat frame and a voltage adjustment command, the optimizer switches to the safe operation mode at time t2. If the PLC signal received by the optimizer during the period from t2 to t3 contains both a heartbeat frame and a voltage adjustment command, the optimizer maintains the safe operation mode. If the PLC signal received by the optimizer during the period from t3 to t4 contains a heartbeat frame but does not receive a voltage adjustment command, the optimizer switches from the safe operation mode to the normal operation mode at time t4. If the optimizer does not receive a PLC signal during the period from t4 to t5, that is, does not receive a heartbeat frame, the optimizer selects to switch from the normal operation mode to the shutdown mode at time t5, where t1 to t5 occur in sequence, and the periods between every two time points may or may not be equal.

[0090] The main difference among the above three operation modes lies in the control of the output voltage state change of optimizer 1-1. In fact, different operation modes respectively correspond to different output voltage states of optimizer 1-1. In the description of some embodiments, a specific embodiment can be described as follows: Optimizer 1-1 directly adjusts the output voltage without simultaneously reflecting the change of different operation modes based on whether a heartbeat frame signal and a voltage adjustment command are received.

[0091] For example, in response to some or all of the plurality of optimizers 1-1 not receiving a periodic PLC signal or a heartbeat frame from the inverter 104 within a certain period, the optimizer 1-1 that did not receive the signal adjusts the output voltage at the output end of the optimizer 1-1 to a shutdown voltage, and the shutdown voltage is a preset safe voltage value.

[0092] In response to some or all of the plurality of optimizers 1-1 receiving a heartbeat frame from the inverter 104 and not receiving a voltage adjustment command, the corresponding optimizer 1-1 controls the output voltage to be below a first voltage.

[0093] In response to all or some of the plurality of optimizers 1-1 receiving a heartbeat frame and receiving a voltage adjustment command, the corresponding optimizer controls the output voltage to be below a second voltage, the second voltage is lower than the first voltage, and the second voltage is higher than the shutdown voltage.

[0094] It can be understood that in the above photovoltaic power generation system, the optimizer 1-1 determines different operating states of the inverter 104 or different requirements for upstream power input based on changes in the PLC signal, and timely adjusts the corresponding operating state of the optimizer 1-1, thereby effectively and timely protecting the inverter 104 under various different operating conditions. In this embodiment of the present invention, after a fault such as overvoltage, overcurrent, or leakage occurs in the inverter, the optimizer can timely adjust the output voltage to a safe range, thereby effectively protecting the downstream inverter device in a timely manner, and improving the operation safety of the entire photovoltaic power generation system, a voltage adjustment command is loaded into the communication between the optimizer and the inverter of the photovoltaic power generation system, such as PLC.

[0095] Hereinafter, with reference to FIG. 4, a plurality of cases for triggering the safe operation mode according to an embodiment of this application will be described. FIG. 4 is a schematic diagram of yet another optimizer-inverter connection according to this embodiment of this application. The photovoltaic power generation system shown in FIG. 4 further includes an inverter 104, a first AC bus, a second AC bus, and a power grid 105 in addition to the photovoltaic power generation module and the optimizer. The inverter 104 includes a DC conversion circuit 110, a DC bus, an inverter circuit 109, a sampling circuit, and a controller. As shown in FIG. 4, the input end of the inverter 104 is connected to three solar cell strings. Specifically, each solar cell string is connected to a corresponding DC conversion circuit 110. The DC conversion circuit 110 couples the converted DC to the DC bus, and the inverter circuit obtains power from the DC bus, converts the DC to AC, and transfers the AC to the first AC bus, and finally transfers the AC to the power grid 105. In some photovoltaic power generation systems with high power generation, the low-voltage AC on the first AC bus is further boosted by a transformer and then transferred to the second AC bus, and finally the DC is transferred to the power grid 105. The sampling circuit in the inverter collects electrical data such as voltage, current, and power in real time at the input end of the DC conversion circuit 110 (or the output end of the photovoltaic power generation string) and the output end of the inverter circuit 109, and can transmit the collected data to the controller in the inverter. The controller determines the operating state of the inverter based on the electrical data collected in real time, and distributes different commands to the electrical elements in the inverter based on different operating states to execute an optimal operating strategy.

[0096] In some possible embodiments, the inverter 104 may distribute a voltage adjustment command to the optimizer 1-1 in the following cases: (1) an input end overvoltage occurs in the inverter 104; (2) an input end over-power occurs in the inverter 104; (3) an isolation effect occurs in the inverter 104.

[0097] Hereinafter, the above three cases will be briefly described.

[0098] (1) An input terminal overvoltage occurs in the inverter 104. The controller detects that the input terminal voltage of the DC conversion circuit 110 exceeds a preset voltage threshold value, and determines that an input terminal overvoltage has occurred in the inverter 104. The preset voltage threshold value is related to the tolerance of the hardware circuit of the inverter 104. In a single-phase inverter, the preset voltage threshold value is 600V, and in a three-phase inverter, the preset voltage threshold value is 1100V. When exceeding the above-mentioned voltage threshold value, the inverter may malfunction or be damaged. When an input terminal overvoltage occurs in the inverter, if the optimizer is switched to the safe operation mode, the output voltage of the optimizer can be adjusted to K times the current voltage, where K is less than 1, and K depends on a specific value of the safe voltage on the input side of the inverter. Preferably, in order to protect the inverter, K is 0.5 times or 0.1 times. In particular, in order to eliminate accidental power fluctuations in the power generation system, the optimizer switches the optimizer to the safe operation mode only after the input terminal voltage of the DC conversion circuit 110 exceeds the preset voltage threshold value for a certain period of time.

[0099] (2) Overpower occurs at the input terminal of the inverter 104. In the design of a solar power generation system, in order to fully utilize the inverter, the inverter is generally allowed to have a specific power excess ratio. For example, in a solar power generation system, the theoretical maximum input power of the solar power generation module is 12 kW, and the maximum allowable input power of the inverter is 10 kW. Therefore, the power excess ratio of the inverter is the ratio of 12 kW to 10 kW, that is, 1.2. Under general light conditions, the actual output power of the solar power generation module is less than 10 kW. In this case, the inverter can operate normally. However, if the light conditions remain good for a long time and the actual output power of the solar power generation module is greater than 10 kW for a long time, the inverter will remain in an overload operating state for a long time. In this case, it is necessary to limit the input power of the inverter. In this embodiment of this application, in order to protect the inverter, an output voltage adjustment command is distributed to the optimizer 1-1 to limit the output voltage of the optimizer so as to limit the power of the inverter.

[0100] (3) An isolation effect occurs in the inverter 104. Due to a power grid failure or the like, the solar power generation system in which the inverter 104 is placed becomes completely independent from the power grid. The inverter 104 identifies that an isolation effect has occurred in the inverter 104. In order to avoid excessive fluctuations in voltage and frequency in the isolated system from damaging electrical devices, the inverter 104 distributes a voltage adjustment command to the optimizer 1-1 based on this case.

[0101] To meet the input requirements of the inverter 104, the optimizer 1-1 generally sets the voltage limit point of the optimizer 1-1 based on the number of optimizers 1-1 in the photovoltaic string and the input voltage limit of the inverter 104 when the optimizer 1-1 operates normally. After the photovoltaic power generation system starts to operate normally, the optimizer 1-1 always limits the output voltage of the optimizer 1-1 to be less than the voltage limit point. For example, if the input voltage of the inverter 104 is limited to 500V and 10 optimizers are connected to the input terminal of the inverter 104, the optimizer 1-1 should set the voltage limit point of the optimizer 1-1 to 50V so that the optimizer 1-1 always outputs a voltage less than 50V during the operation process. For example, the voltage limit point of the optimizer 1-1 is 50V. This application provides the following two methods for setting the voltage limit point of the optimizer 1-1. Method 1: After the optimizer 1-1 is first installed, started, and debugged, the voltage limit point of the optimizer 1-1 is set to 50V based on the number of optimizers 1-1 and the system voltage limit. Then, the voltage limit point data is stored in the optimizer 1-1. When the optimizer 1-1 operates later, the data can be directly called from the optimizer 1-1, and there is no need to set the voltage limit point again. This method is simple and has good effects. Method 2: The voltage limit point data that needs to be set by the optimizer 1-1 is distributed by the inverter 104 and is not stored in the optimizer 1-1. In this method, when the inverter 104 and the optimizer 1-1 are operating normally, the inverter 104 periodically distributes a voltage limit point signal of 50V to the optimizer 1-1, and the optimizer 1-1 receives the voltage limit point signal and maintains that the output voltage does not exceed 50V during operation.

[0102] It should be understood that the voltage limit point signal in the above-mentioned method 2 may still occur in the safe operating mode of the optimizer 1-1 provided in this application. However, the voltage limit point signal in method 2 has at least one obvious difference from the voltage adjustment command in the safe operating mode, that is, the trigger conditions are different. The trigger condition of the voltage limit point signal is that both the inverter 104 and the optimizer 1-1 operate normally. The trigger condition of the voltage adjustment command is that there is a fault in the inverter, and the specific fault types include: (1) overvoltage at the input terminal occurs in the inverter 104; (2) over-power at the input terminal occurs in the inverter 104; (3) the isolation effect occurs in the inverter 104, including three types of inverter faults.

[0103] Referring to the voltage limit point of the optimizer, in one implementation, the first voltage is the voltage that matches the voltage limit point of the optimizer. The optimizer is configured to adjust the input voltage of the optimizer within the first voltage or the voltage limit point range in order to perform maximum power point tracking MPPT on the power output of the connected photovoltaic module. 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 may be a preset fixed value, or may be adjusted and updated based on the requirements of the optimizer or the command of the inverter. When the signal processing unit of the optimizer does not receive a periodic communication signal within a certain period, the output voltage of the power conversion device is controlled to be the shutdown voltage. When the signal processing unit of the optimizer receives a periodic communication signal, but the periodic communication signal does not include a voltage adjustment command, the output voltage of the power conversion device is controlled to be below the first voltage. When the signal processing unit of the optimizer receives a periodic communication signal and the periodic communication signal includes a voltage adjustment command, the output voltage of the power conversion device is controlled to be below the second voltage. In one implementation, the second voltage is P times the first voltage, P < 1, and P includes 0.5 or 0.1.

[0104] In particular, in the safe operation mode, since only the output voltage or current of the optimizer 1-1 is limited, the DC conversion unit 101 is not completely powered off. Since the optimizer 1-1 receives the periodically transmitted heartbeat frame and voltage adjustment command, when it changes to receiving only the heartbeat frame from the inverter 104, the control unit 102 in the optimizer 1-1 can quickly return the DC conversion unit 101 from the voltage limit mode to the MPPT tracking mode by changing the duty ratio, etc., and the optimizer 1-1 can also quickly switch from the safe operation mode to the normal operation mode. Therefore, the photovoltaic string where the optimizer 1-1 is placed still has the ability to quickly return and output a high voltage, and thus the inverter 104 can also recover normal output in a short time.

[0105] Similarly, in the normal operation mode, the DC conversion unit 101 is in the MPPT tracking mode, the inverter 104 periodically transmits a heartbeat frame to the optimizer 1-1, and the optimizer 1-1 receives the periodic heartbeat frame. Since the optimizer 1-1 receives only the periodic heartbeat frame, when it changes to receiving not only the heartbeat frame from the inverter 104 but also the voltage adjustment command from the inverter 104, the control unit 102 in the optimizer 1-1 can quickly switch the DC conversion unit 101 from the MPPT tracking mode to the voltage limit mode by changing the duty ratio, and the optimizer 1-1 can also quickly switch from the normal operation mode to the safe operation mode, thereby ensuring the safety of the inverter device in a timely manner when a failure occurs.

[0106] In this embodiment of this application, the optimizer 1-1 can quickly switch between the normal operation mode, the safety operation mode, and the shutdown mode. Therefore, when there is a fault in the solar power generation system, the output voltage of the solar power generation string is quickly reduced, and the safety of the inverter is ensured. For example, in scenarios such as the installation and maintenance of the optimizer 1-1, the output voltage of the solar power generation string is limited to a safe voltage, and personal safety is ensured. When the power generation scenario of the optimizer changes, the operation mode of the optimizer is quickly switched. This embodiment of this application can fully ensure the safety of the inverter device, fully ensure the safety of users and maintenance personnel, and further greatly reduce the impact of operations such as overhaul, installation, and maintenance on user power consumption.

[0107] Hereinafter, with reference to the flowchart, a method for controlling the operation of the optimizer provided in the embodiment of this application will be described.

[0108] FIG. 5 is a schematic flowchart for switching the operating mode of an optimizer according to an embodiment of this application. At step 20, the optimizer is activated. In this case, the corresponding actual scenario could be that in the morning when the sun rises, sunlight provides sunlight to the solar power generation module for energy conversion, and the optimizer has the electrical energy required for activation. Optionally, the optimizer further receives an activation command transmitted by the inverter. Next, the optimizer executes step 21. In this step, the optimizer determines whether a heartbeat frame is received periodically. Here, the case where a heartbeat frame is received periodically includes the optimizer receiving a heartbeat frame signal transmitted at a specific frequency within a certain period. If the condition is satisfied, step 22 is executed. If the condition is not satisfied, for example, if the frequency of the heartbeat frame is not a specific frequency, the time for receiving the heartbeat frame does not meet the conditions of the aforementioned period, or the heartbeat frame signal is not received, step 25 is executed. At step 25, the optimizer executes a shutdown operation. In the shutdown mode, the voltage output by the output terminal of the optimizer is the preset voltage of the optimizer before shipment. This voltage may be higher or lower than the output voltage of the optimizer in the safety mode, but it needs to be lower than the voltage at the voltage limit point of the optimizer. Under the shutdown voltage, even if multiple optimizers are connected in series in the solar power generation string, the voltage on the power line of the inverter does not exceed the safety voltage. Even if a user or maintenance personnel touches the power line directly, electric shock will not occur. At step 22, the optimizer operates in the normal operating mode. In the normal operating mode, the optimizer generally executes the MPPT function. The optimizer adjusts the input voltage of the optimizer to the operating voltage corresponding to the maximum power point in the power characteristic curve of the solar power generation module, and the output voltage of the optimizer varies within a specific range based on the requirements of the power conversion device and the electrical characteristics of the solar power generation string.Next, the optimizer executes step 23. In this step, the optimizer determines whether a voltage adjustment command has been received or an alarm state has occurred. If YES, the optimizer executes step 24. If NO, the optimizer returns to step 22. Here, the voltage adjustment command is a PLC signal transmitted from the inverter to the optimizer when the above three faults occur. In step 24, the optimizer operates in the safe operation mode. In this mode, the optimizer adjusts and controls the duty ratio of the power conversion executed inside the optimizer. For example, the output of the optimizer is limited, the output voltage of the optimizer is maintained at a specific voltage, the input voltage of the inverter is limited, and thereby the duty ratio changes with respect to the normal operation mode so as to ensure the device safety of the inverter.

[0109] In the various operation modes described above, the optimizer reports the operating state of the optimizer to the northbound device. In this embodiment of this application, when the optimizer is in the shutdown mode, the optimizer reports the "shutdown" state. When the optimizer is in the normal operation mode and the safe operation mode, the optimizer reports the "operating" state. When a fault occurs, the optimizer reports the "fault" state.

[0110] FIG. 6 is a schematic diagram of the operation procedure of an inverter according to an embodiment of this application. At step 26, the inverter is in a shutdown state. In this case, the corresponding actual scenario may be that there is no sunlight, or it is nighttime and the sunlight is weak, or the user cuts off the DC switch on the inverter side, the inverter is not powered on, or the voltage of the inverter is not sufficient to support the power-on and operation of the components used for signal transmission in the inverter. Then, step 27 is executed. The inverter continuously determines whether the inverter meets the startup conditions. When the sunlight is strong or the user turns on the DC switch on the inverter side, the voltage of the inverter rises to the voltage used by the inverter for signal transmission, and the inverter executes step 28 to start signal transmission with the optimizer. The signals transmitted between the inverter and the optimizer include heartbeat frames, voltage adjustment commands, and voltage limit point signals. If the inverter determines that it still does not meet the startup conditions at this time, the inverter returns to execute step 26. After the inverter starts signal transmission, step 29 is executed to start the inverter. In this case, basically all components in the inverter start to operate. The optimizer continuously inputs DC current to the inverter, and the inverter continuously outputs the AC required by the user load. Then, step 30 is executed. The inverter determines whether an alarm state has occurred in the inverter. If no alarm state occurs, the inverter returns to execute step 29. If an alarm state occurs, it indicates that the inverter is no longer suitable for continuously providing AC to the user load under the current state, and shutdown should be executed in a timely manner. Otherwise, the internal electrical components of the inverter will be burnt out, and in serious cases, a fire will occur, threatening the safety of the user's life and property. After the alarm state occurs, the inverter executes step 31, that is, cuts off the signal transmission. After cutting off the signal transmission, the inverter returns to execute step 26, and the inverter is shut down.

[0111] As will be appreciated by those skilled in the art, in combination with the examples described in the embodiments disclosed in this specification, the units and algorithm steps may be implemented by electronic hardware or a combination of computer software and electronic hardware. Whether a function is executed by hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art may use different methods to implement the functions described for each specific application, but such implementation should not be regarded as exceeding the scope of this application.

[0112] The above description is only a specific implementation of this application, and the protection scope of this application is not limited thereto. Any modification or replacement that can be easily conceived by those skilled in the art within the technical scope disclosed in this application falls within the protection scope of this application. Therefore, the protection scope of this application shall follow the protection scope of the claims.

Claims

1. A power conversion device, the power conversion device including a DC conversion unit, a signal processing unit, and a controller, the DC conversion unit being configured to convert a DC generated by a photovoltaic power generation module and output the converted DC to a next-level power conversion device; the signal processing unit is connected to an output of the power conversion device and configured to receive a periodic communication signal transmitted by the next-level power conversion device; The controller: The signal processing unit is configured to control an output voltage of the power conversion device to a shutdown voltage in response to not receiving the periodic communication signal within a certain period of time, the shutdown voltage being a preset safe voltage value; configured to control the output voltage of the power conversion device to be equal to or lower than a first voltage in response to the signal processing unit receiving the periodic communication signal but the periodic communication signal not including a voltage adjustment command; the signal processing unit is configured to, in response to receiving the periodic communication signal and the periodic communication signal including the voltage adjustment command, control the output voltage of the power conversion device to be equal to or lower than a second voltage, the second voltage being lower than the first voltage and the second voltage being higher than the shutdown voltage; Power conversion devices.

2. the periodic communication signal is a power line communication (PLC) signal, the PLC signal including a heartbeat frame; The controller: and configured to control the output voltage of the power conversion device to the shutdown voltage in response to the signal processing unit not receiving the heartbeat frame within a certain period of time. The power conversion device of claim 1 .

3. The controller: the signal processing unit is configured to receive the PLC signal, and in response to the PLC signal including the heartbeat frame but not including the voltage adjustment command, control the output voltage of the power conversion device to be less than the first voltage; the signal processing unit is configured to receive the PLC signal, and in response to the PLC signal including both the heartbeat frame and the voltage regulation command, control the output voltage of the power conversion device to be less than the second voltage. The power conversion device of claim 2 .

4. The controller: the signal processing unit is configured to receive the PLC signal, and in response to the PLC signal including both the heartbeat frame and the voltage adjustment command, adjust the output voltage of the power conversion device to K times a current output voltage of the power conversion device, where K is less than 1, or K is 0.5 or 0.1; The power conversion device of claim 3 .

5. The controller: The signal processing unit is configured to control the DC conversion unit to operate in a maximum power tracking mode in response to receiving the periodic communication signal but the periodic communication signal does not include the voltage adjustment command, and in the maximum power tracking mode, an output voltage of the DC conversion unit changes and an output power of the solar power generation module connected to the DC conversion unit is maximum; the signal processing unit is configured to receive the periodic communication signal, and in response to the periodic communication signal including the voltage adjustment command, control the DC conversion unit to operate in a voltage limiting mode, where in the voltage limiting mode the output voltage of the DC conversion unit is constant; A power conversion device according to any one of claims 1 to 4.

6. 1. A method for controlling a power conversion device, comprising: In response to the power conversion device not receiving the heartbeat frame, control an output voltage of the power conversion device to a shutdown voltage, the shutdown voltage being a preset safe voltage value; in response to the power conversion device receiving the heartbeat frame and not receiving a voltage adjustment command, controlling the output voltage of the power conversion device to be equal to or less than a first voltage; in response to the power conversion device receiving the heartbeat frame and receiving the voltage adjustment command, controlling the output voltage of the power conversion device to be equal to or lower than a second voltage, the second voltage being lower than the first voltage and the second voltage being higher than the shutdown voltage; How to have that.

7. When it is detected that an input end voltage of an inverter exceeds an overvoltage threshold, the inverter is configured to receive DC power output by the power conversion device and deliver the voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command and controls the output voltage of the power conversion device to be less than the overvoltage threshold, the power conversion device is connected to the inverter via a power line, and the heartbeat frame and the voltage adjustment command are transmitted via the power line. The method according to claim 6.

8. When it is detected that an input end power of an inverter exceeds an overpower threshold, the inverter is configured to receive DC power output by the power conversion device and deliver the voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command and controls the output voltage of the power conversion device to decrease, the power conversion device is connected to the inverter via a power line, and the heartbeat frame and the voltage adjustment command are transmitted via the power line. The method according to claim 6.

9. When an occurrence of an islanding effect is detected in a power generation system in which an inverter is placed, the inverter is configured to receive DC power output by the power conversion device and deliver the voltage adjustment command to the power conversion device, the power conversion device receives the voltage adjustment command and controls the power conversion device to reduce the output voltage, the power conversion device is connected to the inverter via a power line, and the heartbeat frame and the voltage adjustment command are transmitted via the power line. The method according to claim 6.

10. a plurality of optimizers configured to convert direct current generated by the photovoltaic power generation modules and output the converted direct current to an inverter; an inverter, the inverter configured to supply power to a power grid or a user load, the inverter further configured to send heartbeat frames and voltage adjustment commands to the plurality of optimizers, the heartbeat frames and the voltage adjustment commands being transmitted via power lines between the inverter and the optimizers; having in response to the plurality of optimizers not receiving the heartbeat frame within a period of time, an output voltage of the plurality of optimizers is forced 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 output voltages of the plurality of optimizers are caused to be equal to or less than a first voltage; in response to the plurality of optimizers receiving the heartbeat frame and receiving the voltage adjustment command, the output voltages of the plurality of optimizers are caused to be equal to or less than a second voltage, the second voltage being less than the first voltage and the second voltage being greater than the shutdown voltage; Photovoltaic power generation system.

11. When an input end voltage of the inverter exceeds an overvoltage threshold or an input end power of the inverter exceeds an overpower threshold, the inverter delivers the voltage adjustment command to the optimizer, the optimizer receives the voltage adjustment command, and the optimizer controls the output voltage of the optimizer to be equal to or lower than the second voltage. The solar power generation system according to claim 10.

12. in response to some or all of the plurality of optimizers not receiving the heartbeat frame within a period of time, the optimizers that did not receive the heartbeat frame adjust the output voltage to the shutdown voltage, the shutdown voltage being the preset safe voltage value; in response to the plurality of optimizers receiving the heartbeat frame but not receiving the voltage adjustment command, the output voltages of the plurality of optimizers are caused to be equal to or less than the first voltage; in response to the plurality of optimizers receiving the heartbeat frame and receiving the voltage adjustment command, the output voltages of the plurality of optimizers are made equal to or less than the second voltage, the second voltage being less than the first voltage and the second voltage being greater than the shutdown voltage; The solar power generation system according to claim 10.

13. When an islanding effect occurs in a power generation system in which the inverter is installed, the inverter delivers the voltage adjustment command to the optimizer, the optimizer receives the voltage adjustment command, and the optimizer controls the output voltage of the optimizer to be equal to or lower than the second voltage. The solar power generation system according to claim 10.

14. When the inverter satisfies a start-up condition, the inverter sends the heartbeat frame or the voltage adjustment 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. The solar power generation system according to claim 10.

15. The inputs of the plurality of optimizers are each configured to be connected to a photovoltaic power generation module, and the outputs of the plurality of optimizers are connected in series and then connected to the input of the inverter; The inverter is configured to send the heartbeat frame and the voltage adjustment command to the plurality of optimizers in a broadcast manner via a PLC, and the voltage adjustment command is used to adjust the output voltage of the plurality of optimizers to K times the current output voltage of the plurality of optimizers, where K is less than 1, or K is 0.5 or 0.1; The solar power generation system according to claim 10.

Images