Solar power generation system and method for controlling optimizer

Abstract

To provide a photovoltaic power generation system and a method for controlling an optimizer.SOLUTION: After an alternating current output end of the inverter is disconnected from a power grid and an input voltage of the optimizer increases to a preset value, the optimizer outputs a first voltage, and when receiving no communication signal from the inverter within a preset time period, the optimizer switches from outputting the first voltage to outputting a second voltage, where the second voltage is greater than the first voltage, so that an input voltage of the inverter is greater than a startup voltage of the inverter, and the input voltage of the inverter is equal to a sum of output voltages of all optimizers. When the input voltage of the inverter is greater than the startup voltage of the inverter, the inverter sends a communication signal to the optimizer, so that the optimizer switches from outputting the second voltage to a normal working mode.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] This application relates to the field of power electronics, and in particular to a photovoltaic power generation system and a method for controlling an optimizer. [Background technology]

[0002] In photovoltaic (PV) systems, the system must support disaster recovery in some special geographical environments. To meet this requirement, the system must support the startup capability of devices within the system, such as inverters, when the power grid does not supply power. When PV modules are connected in series and then directly to an inverter, the PV string can continuously supply power to the inverter after the AC side is powered off to support the inverter's startup. When PV modules are connected to an optimizer, which is then connected in series and then to the inverter, considering the safety of the PV system, the optimizer continues to output a very low voltage before receiving an inverter startup command. This prevents the inverter's minimum startup voltage from being met. In this case, i.e., when the power grid does not supply power after the AC side is powered off, neither the AC side nor the DC side can supply power to the inverter, and as a result, the inverter cannot be started. Currently, a supercapacitor is added to the inverter in an inverter startup solution for the above scenario. After the power supply to the PV modules is restored, a start button is manually pressed, and the supercapacitor discharges for a short time to provide power to the inverter's communication module. The communication module sends a start-up command to the optimizer, which converts the voltage and outputs a voltage that meets the start-up requirements of the inverter. However, adding a supercapacitor to the inverter increases costs and requires manual operation. Furthermore, multiple start-ups in the absence of light will cause the energy stored in the capacitor to be depleted, and the capacitor will not be able to discharge normally after the energy is depleted. Summary of the Invention

[0003] The embodiments of the present application provide a photovoltaic power generation system and a method for controlling an optimizer, which can actively increase the output voltage after the inverter is powered off and shut down to meet the inverter startup requirements with simple operation and high startup reliability, and no additional components are required in the inverter startup process.

[0004] According to a first aspect, this application provides a solar power generation system. The solar power generation system includes a plurality of optimizers and an inverter. One end of each of the plurality of optimizers is configured to connect to a solar power generation module, and the other end of all of the plurality of optimizers is connected in series and then configured to connect to a DC input terminal of the inverter. After the AC output terminal of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, the optimizer outputs a first voltage. When no communication signal is received from the inverter within a preset period, the optimizer switches from outputting the first voltage to outputting a second voltage, where the second voltage is greater than the first voltage such that the input voltage of the inverter is greater than a start-up voltage of the inverter, and the input voltage of the inverter is equal to the sum of the output voltages of all the optimizers. When the input voltage of the inverter is greater than the start-up voltage of the inverter, the inverter sends a communication signal to the optimizer to switch from outputting the second voltage to a normal operation mode.

[0005] This application describes an optimizer for a solar power generation system in which the inverter's AC output terminal is disconnected from the power grid and the solar power generation module continues to supply power normally. To ensure the safety of the solar power generation system, the optimizer outputs a first voltage. The optimizer determines the inverter's operating status based on whether a communication signal is received from the inverter within a preset period. After determining that the inverter is powered off and shut down, the optimizer actively increases the output voltage to a second voltage to meet the inverter startup conditions, thereby supporting the startup of the inverter in the system when the power grid does not supply power. Furthermore, no additional components are required during the inverter startup process, reducing device costs, simplifying operation, and increasing startup reliability.

[0006] In one possible implementation, the optimizer includes a first communication port, the inverter includes a second communication port, and the first communication ports of the optimizers are configured to connect to the second communication port of the inverter via a communication cable. The optimizers are configured to receive a communication signal from the inverter via the communication cable connected to the first communication port. When the optimizers output a first voltage and do not receive a communication signal from the inverter via the communication cable connected to the first communication port of each optimizer within a preset period of time, the optimizers switch from outputting the first voltage to output the second voltage to the inverter, and the inverter is started.

[0007] In one possible implementation, the preset period is one minute or more. After the AC output of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, each optimizer outputs a first voltage to the inverter. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within one minute or for more than one minute, the optimizer adjusts its output DC voltage to increase. In this case, the sum of the DC voltages output by the multiple optimizers is greater than the inverter's startup voltage, satisfying the inverter's startup requirements and supporting the startup of inverters in a system when the power grid does not provide power.

[0008] In one possible implementation, the first voltage is 10 volts or less. When the photovoltaic modules are normally supplying power and the AC output terminal of the inverter is disconnected from the power grid, each optimizer outputs DC to the inverter at or below 10 volts. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within a preset period, the optimizer adjusts the output DC voltage to increase. In this case, the sum of the DC voltages output by the multiple optimizers is greater than the inverter's startup voltage, satisfying the inverter's startup requirements and supporting the startup of inverters in a system when the power grid does not provide power.

[0009] In one possible implementation, the second voltage is greater than the first voltage and less than 15 volts. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within a preset period, the optimizer adjusts the output DC voltage to increase, where the voltage value is greater than the first voltage and less than 15 volts. In this case, the sum of the DC voltages output by the multiple optimizers is greater than the starting voltage of the inverter, satisfying the startup requirement of the inverter and supporting the startup of the inverter in the system when the power grid does not provide power.

[0010] In one possible implementation, after the AC output of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, the optimizer outputs a first voltage and continues to output the first voltage upon receiving a command to keep the inverter shut down.

[0011] In one possible implementation, the optimizer includes a DC conversion circuit configured to perform voltage conversion on DC from the photovoltaic power generation module, the DC conversion circuit including a capacitor, an inductor, a switching transistor, and a diode, wherein a first end of the capacitor is configured to connect to a positive terminal of the photovoltaic power generation module, a first end of the capacitor is connected to a cathode of the diode via the switching transistor, a cathode of the diode is connected to a first DC input terminal of an inverter or other DC conversion circuit via the inductor, a second end of the capacitor is configured to connect to a negative terminal of the photovoltaic power generation module, a second end of the capacitor is connected to an anode of the diode, and a connection end of the capacitor and the diode is connected to a second DC input terminal of the inverter or other DC conversion circuit.

[0012] According to a second aspect, the application provides a method for controlling an optimizer, the method including: controlling the optimizer to output a first voltage after an AC output terminal of the inverter is disconnected from a power grid and an input voltage of the optimizer increases to a preset value, the optimizer having one end configured to connect to a photovoltaic power generation module and the other end configured to connect to a DC input terminal of the inverter, and the AC output terminal of the inverter configured to connect to the power grid; and controlling the optimizer to switch from outputting the first voltage to outputting a second voltage when no communication signal is received from the inverter within a preset period, the second voltage being greater than the first voltage such that the input voltage of the inverter is greater than a start-up voltage of the inverter.

[0013] In this application, when the power grid is powered off and the solar power generation module normally supplies power, the optimizer in the solar power generation system determines the operating state of the inverter based on whether a communication signal is received from the inverter within a preset period, and after determining that the inverter is powered off and shut down, actively increases the output voltage to meet the inverter startup conditions. No additional components are required in the inverter startup process, reducing device costs, simplifying operation, and increasing startup reliability.

[0014] In one possible implementation, the preset period is one minute or more. After the AC output of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to the preset value, the optimizer is controlled to output a first voltage to the inverter. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within one minute or more, the DC voltage output by the optimizer is controlled to increase. In this case, the DC voltage of the optimizer meets the startup requirements of the inverter, supporting startup of the inverter in the system when the power grid does not provide power.

[0015] In one possible implementation, the first voltage is 10 volts or less. When the photovoltaic module normally supplies power and the AC output terminal of the inverter is disconnected from the power grid, the corresponding optimizer is controlled to output DC to the inverter at or below 10 volts. When the input voltage of the optimizer reaches a certain threshold and no communication signal is received from the inverter within a preset period, the DC voltage output by the optimizer is controlled to increase. In this case, the DC voltage of the optimizer meets the startup requirements of the inverter, supporting startup of the inverter in the system when the power grid does not supply power.

[0016] In one possible implementation, the second voltage is greater than the first voltage and less than 15 volts. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within a preset period, the optimizer adjusts the output DC voltage to increase, where the voltage value is greater than the first voltage and less than 15 volts. In this case, the sum of the DC voltages output by the multiple optimizers is greater than the starting voltage of the inverter, satisfying the startup requirement of the inverter and supporting the startup of the inverter in the system when the power grid does not provide power. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram of an application scenario of a photovoltaic power generation system according to the present application. [Figure 2] 1 is a diagram of another application scenario of a photovoltaic power generation system according to the present application. [Figure 3] 1 is a diagram of a configuration of a solar power generation system according to the present application. [Figure 4] FIG. 2 is a diagram of another configuration of a solar power generation system according to the present application. [Figure 5] FIG. 2 is a diagram of another configuration of a solar power generation system according to the present application. [Figure 6] 1 is a diagram of a DC converter circuit according to this application. [Figure 7] 1 is a schematic flow chart of a method for controlling an optimizer according to the present application. DETAILED DESCRIPTION OF THE INVENTION

[0018] FIG. 1 is a diagram of an application scenario of a solar power generation system according to this application. The solar power generation system provided in this application may include multiple optimizers and an inverter. One end of each optimizer is configured to connect to one solar power generation module, and the other ends of the multiple optimizers are connected in series and then configured to connect to a DC input terminal of the inverter, and the AC output terminal of the inverter is configured to connect to a power grid. Each optimizer is configured to perform voltage conversion on the DC from the corresponding solar power generation module and output the DC to the inverter. The inverter can perform inversion conversion on the DC provided by the multiple optimizers and output the AC obtained after the inversion conversion to the power grid for power supply.

[0019] In some possible implementations, the solar power generation system may further include an energy storage unit and a load. Figure 2 is a diagram of another application scenario of the solar power generation system according to this application. The energy storage unit in the solar power generation system may be an energy storage battery, and one end of some of the multiple optimizers is configured to connect to one energy storage battery. The AC output end of the inverter is configured to connect to a power grid and a load. The optimizer can perform voltage conversion on the DC provided by the energy storage battery and output the DC to the inverter. The inverter can perform inversion conversion on the DC provided by the multiple optimizers and output the AC obtained after the inversion conversion to the power grid or the load for power supply.

[0020] In the application scenarios shown in Figures 1 and 2, photovoltaic power generation systems need to support disaster recovery in some special geographical environments. Therefore, photovoltaic power generation systems must support the startup capability of devices within the system, such as inverters, when the power grid does not provide power. When photovoltaic modules are connected to optimizers, and the optimizers are connected in series and then connected to the inverter, the optimizers output a very low voltage before receiving the inverter startup command, considering the safety of the photovoltaic power generation system. This prevents the inverter's minimum startup voltage from being met. For example, if a photovoltaic power generation system includes 20 optimizers, each of which outputs 1 volt of DC voltage before receiving the inverter startup command, the 20 optimizers connected in series will only output 20 volts. In this case, when the power grid does not provide power, neither the AC power grid nor the photovoltaic modules on the DC side can supply power to the inverter, and the inverter cannot start up. Currently, in the above-mentioned inverter startup solution when the power grid does not provide power, a supercapacitor is added to the inverter. After the power supply of the photovoltaic module is restored, the start button is manually pressed, causing the supercapacitor to discharge for a short time and supply power to the inverter's communication module. The communication module then sends a start-up command to the optimizer, which then converts the voltage and outputs a voltage that meets the inverter's start-up requirements. However, adding a supercapacitor to the inverter increases device costs and requires manual operation. Furthermore, multiple start-ups in the absence of light will deplete the energy stored in the capacitor, and after the energy is depleted, the capacitor will no longer be able to discharge normally. As a result, the inverter's start-up reliability is poor.

[0021] The solar power generation system provided in this application may include a plurality of optimizers and an inverter. One end of each of the optimizers is configured to connect to a solar power generation module, and the other end of the optimizers is connected in series to a DC input terminal of an inverter, and the AC output terminal of the inverter is configured to connect to a power grid. When the solar power generation modules connected to each optimizer normally supply power and the AC output terminal of the inverter is disconnected from the power grid, i.e., when the input voltage of the optimizer increases to a preset value and the power grid is turned off, the optimizer outputs a first voltage to ensure the safety of the solar power generation system. In this case, the sum of the DC voltages output by the optimizers is smaller than the inverter's startup voltage, i.e., the inverter's startup requirements cannot be met. When each optimizer does not receive a communication signal from the inverter within a preset period, i.e., when the optimizer determines that the inverter is normally powered on and shut down, the optimizer switches from outputting a first voltage to outputting a second voltage, where the second voltage is greater than the first voltage. In this case, the sum of the DC voltages output by the multiple optimizers, i.e., the inverter's input voltage, is greater than the inverter's startup voltage, satisfying the inverter's startup requirements and supporting the startup of the inverter in the system when the power grid does not supply power. The inverter is started and sends a communication signal to each optimizer, causing each optimizer to switch from outputting the second voltage to a normal operating mode. Here, when the corresponding photovoltaic module normally supplies power, the optimizer in the photovoltaic system determines the inverter's operating state based on whether a communication signal is received from the inverter within a preset period. After determining that the inverter is powered off and shut down, the optimizer actively increases the output voltage to satisfy the inverter's startup requirements and supporting the startup of the inverter in the system when the power grid does not supply power.No additional components are required in the start-up process of the inverter, which reduces the device cost, makes the operation simple, and has high start-up reliability.

[0022] In some possible implementations, after the AC output terminal of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, each optimizer outputs a first voltage to the inverter. Optionally, the first voltage may be 10 volts or less. In this case, the sum of the DC voltages output by the multiple optimizers is less than the inverter's start-up voltage, i.e., the inverter's start-up requirements cannot be met. The sum of the DC voltages output by the multiple optimizers may be further used to determine whether an optimizer is abnormally connected. For example, when the first voltage is 1 volt, the photovoltaic power generation module is normally supplying power, and the AC output terminal of the inverter is disconnected from the power grid, each optimizer outputs a DC voltage of 1 volt to the inverter. When the sum of the DC voltages output by the multiple optimizers is equal to the number of the multiple optimizers, it indicates that all optimizers in the photovoltaic power generation system are normally connected. When the optimizer outputs a first voltage and does not receive a communication signal from the inverter within a preset period of time, the optimizer switches from outputting the first voltage to outputting a second voltage to the inverter, where the second voltage is greater than the first voltage so that the input voltage of the inverter is greater than the inverter's startup voltage. Optionally, the preset period of time can be 1 minute or more, and the second voltage can be greater than the first voltage but less than 15 volts. For example, the preset period of time can be 5 minutes, the first voltage is 1 volt, and the second voltage is 10 volts. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within 5 minutes, the optimizer adjusts the output DC voltage to increase from 1 volt to 10 volts. Here, an internal circuit of the optimizer can be controlled to increase the output DC voltage from 1 volt to 10 volts. In this case, the sum of the DC voltages output by the multiple optimizers is greater than the inverter's startup voltage, meeting the inverter's startup requirements and supporting the startup of the inverter in a system when the power grid does not provide power.In this case, when the corresponding photovoltaic module normally supplies power, the optimizer in the photovoltaic power generation system determines the working state of the inverter based on whether a communication signal is received from the inverter within a preset period, and after determining that the inverter is powered off and shut down, actively increases the output voltage to meet the inverter startup conditions, thereby supporting the startup of the inverter in the system when the power grid does not supply power. No additional components are required in the inverter startup process, reducing device costs, simplifying operation, and increasing startup reliability.

[0023] In a solar power generation system, information may be transmitted between the optimizer and the inverter via wired communication or wireless communication. For example, information is transmitted between the optimizer and the inverter via wired communication. Specifically, the communication mode may be a power line carrier (PLC) communication mode. Specifically, the optimizer includes a first communication port, the inverter includes a second communication port, and the first communication ports of the optimizers are configured to connect to the second communication port of the inverter via a communication cable. FIG. 3 is a diagram of a configuration of a solar power generation system according to this application. The solar power generation system shown in FIG. 3 includes multiple optimizers. For example, the solar power generation system includes a total of n optimizers, including optimizer a1, optimizer a2, ..., and optimizer an. One end of optimizer a1, optimizer a2, ..., and optimizer an are configured to be connected to photovoltaic power generation module 11, photovoltaic power generation module 12, ..., and photovoltaic power generation module 1n, respectively, and the other ends of optimizer a1, optimizer a2, ..., and optimizer an are connected in series and then connected to a DC input terminal of an inverter. The AC output terminal of the inverter is configured to be connected to a power grid. A first communication port of each optimizer is configured to be connected to a second communication port of the inverter via a communication cable. After the AC output terminal of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, each optimizer outputs a first voltage to the inverter. When the optimizers output a first voltage and do not receive a communication signal from the inverter within a preset period of time via a communication cable connected to the first communication port of each optimizer, the optimizer switches from outputting the first voltage to output a second voltage to the inverter, where the second voltage is greater than the first voltage such that the input voltage of the inverter is greater than the start-up voltage of the inverter. It may be appreciated that information may alternatively be transmitted between the optimizers and the inverter via wireless communication.For example, the optimizer communicates with the inverter via Bluetooth® or Wi-Fi®. Here, when the corresponding photovoltaic module normally supplies power, the optimizer in the photovoltaic power system determines the operating state of the inverter based on whether a communication signal is received from the inverter within a preset period. After determining that the inverter is powered off and shut down, the optimizer actively increases the output voltage to meet the inverter startup conditions, thereby supporting the startup of the inverter in the system when the power grid does not supply power. No additional components are required in the inverter startup process, reducing device costs, simplifying operation, and increasing startup reliability.

[0024] Optionally, in a scenario where the power grid does not supply power and the inverter does not need to start up automatically in the solar power generation system, for a plurality of optimizers, after the AC output terminal of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, the optimizer outputs a first voltage, and upon receiving a command to keep the inverter shut down, the optimizer continues to output the first voltage and the inverter remains in a shut down state.

[0025] A solar power generation system may include multiple solar power generation arrays, each including multiple optimizers. For example, the solar power generation system may include two solar power generation arrays. FIG. 4 is a diagram of another configuration of a solar power generation system according to the present application. The solar power generation system shown in FIG. 4 includes two solar power generation arrays. The first solar power generation array includes n optimizers, including optimizer a1, optimizer a2, ..., and optimizer an, where one end of optimizer a1, optimizer a2, ..., and optimizer an are configured to be connected to solar power generation module 11, solar power generation module 12, ..., and solar power generation module in, respectively, and the other ends of optimizer a1, optimizer a2, ..., and optimizer an are connected in series and then configured to be connected to the DC input of an inverter. Similarly, the second photovoltaic power array includes a total of n optimizers, namely optimizer b1, optimizer b2, ..., and optimizer bn, where one end of optimizer b1, optimizer b2, ..., and optimizer bn is configured to be connected to photovoltaic power generation module 21, photovoltaic power generation module 22, ..., and photovoltaic power generation module 2n, respectively, and the other end of optimizer b1, optimizer b2, ..., and optimizer bn is configured to be connected in series and then connected to the DC input end of the inverter. A first communication port of each optimizer is configured to be connected to a second communication port of the inverter via a communication cable. After the AC output end of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, each optimizer outputs a first voltage to the inverter. When the optimizers output a first voltage and do not receive a communication signal from the inverter within a preset period via a communication cable connected to the first communication port of each optimizer, the optimizer switches from outputting the first voltage to the inverter to output a second voltage, where the second voltage is greater than the first voltage such that the input voltage of the inverter is greater than the start-up voltage of the inverter.For example, for each optimizer in the first photovoltaic power array, after the AC output of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, each optimizer outputs a first voltage to the inverter. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within a preset period via a communication cable connected to the first communication port of each optimizer, the optimizer switches from outputting the first voltage to outputting a second voltage to the inverter. The sum of the DC voltages output by the multiple optimizers in the first photovoltaic power array is greater than the start-up voltage of the inverter, meeting the start-up requirement of the inverter and supporting the start-up of the inverter in the system when the power grid does not provide power.

[0026] Optionally, the inverter in the solar power generation system includes a boost circuit and an inverter circuit. The boost circuit is configured to boost the DC voltage output by the multiple optimizers. The inverter circuit is configured to perform inversion on the boosted DC voltage output by the boost circuit and output the AC voltage obtained after the inversion to a power grid or a load. The solar power generation system shown in Figure 4 is used as an example. Two solar power generation arrays in the solar power generation system can be separately connected to one boost circuit in the inverter. Figure 5 is a diagram of another configuration of a solar power generation system according to this application. The solar power generation system shown in Figure 5 includes two solar power generation arrays. The first solar power array includes a total of n optimizers, namely optimizer a1, optimizer a2, ..., and optimizer an, and one ends of optimizer a1, optimizer a2, ..., and optimizer an are configured to be connected to solar power generation module 11, solar power generation module 12, ..., and solar power generation module 1n, respectively, and the other ends of optimizer a1, optimizer a2, ..., and optimizer an are connected in series and then configured to be connected to one end of boost circuit 1 in the inverter. Similarly, the second photovoltaic power array includes a total of n optimizers, namely optimizer b1, optimizer b2, ..., and optimizer bn, in which one ends of optimizer b1, optimizer b2, ..., and optimizer bn are configured to be connected to photovoltaic power generation module 21, photovoltaic power generation module 22, ..., and photovoltaic power generation module 2n, respectively, and the other ends of optimizer b1, optimizer b2, ..., and optimizer bn are connected in series and then configured to be connected to one end of boost circuit 2. The other ends of boost circuit 1 and boost circuit 2 are connected to the inverter circuit.

[0027] In some possible implementations, the optimizer includes a DC converter circuit and a controller. The DC converter circuit is configured to perform voltage conversion on the DC from the photovoltaic power generation module, for example, to perform voltage reduction on the DC from the photovoltaic power generation module. The DC converter circuit in the optimizer includes a capacitor, an inductor, a switching transistor, and a diode, where a first end of the capacitor is configured to connect to a positive terminal of the photovoltaic power generation module, a first end of the capacitor is connected to a cathode of the diode via the switching transistor, a cathode of the diode is connected to a first DC input terminal of an inverter or other DC conversion circuit via the inductor, a second end of the capacitor is configured to connect to a negative terminal of the photovoltaic power generation module, a second end of the capacitor is connected to an anode of the diode, and the connection end of the capacitor and the diode is connected to a second DC input terminal of the inverter or other DC conversion circuit. Figure 6 is a diagram of a configuration of a DC converter circuit according to this application. 6, the DC converter circuit includes a capacitor C1, an inductor L1, a switching transistor S1, and a diode D1, where a first end of the capacitor C1 is connected to a positive electrode PV+ of a photovoltaic module, a first end of the capacitor C1 is connected to a cathode of the diode D1 via the switching transistor S1, a cathode of the diode D1 is connected to a first DC input terminal of an inverter or other DC converter circuit via the inductor L1, a second end of the capacitor C1 is connected to a negative electrode PV- of the photovoltaic module, and a second end of the capacitor C1 is connected to an anode of the diode D1, and a connection terminal of the capacitor C1 and the diode D1 is connected to a second DC input terminal of the inverter or other DC converter circuit. It may be understood that each switching transistor in the above-mentioned optimizer may be a metal-oxide-semiconductor field-effect transistor (MOSFET), abbreviated as MOS transistor, or alternatively, an insulated gate bipolar transistor (IGBT) or the like.This is not intended to be limiting. In a solar power generation system, the sum of the DC voltages output by the multiple optimizers, i.e., the input voltage of the inverter, is greater than the inverter's start-up voltage, meeting the inverter's start-up requirements and supporting the start-up of the inverter in the system when the power grid does not supply power. The inverter is started and sends a communication signal to each optimizer, causing each optimizer to switch from outputting a second voltage to a normal operation mode. In the normal operation mode, each optimizer can control the operation of a switching transistor in a DC conversion circuit via a controller to perform maximum power tracking and the like.

[0028] 7 is a schematic flowchart of a method for controlling an optimizer according to the present application. The method for controlling an optimizer provided in the present application is applicable to the optimizer in the solar power generation system shown in FIGS. 1 to 5. As shown in FIG. 7, the method for controlling an optimizer provided in the present application includes the following steps:

[0029] S701: After the AC output terminal of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value, control the optimizer to output a first voltage.

[0030] S702: The optimizer outputs a first voltage and determines whether a communication signal is received from the inverter within a preset period. If the determination result is No, step S703 is executed; if the determination result is Yes, step S704 is executed.

[0031] S703: Control the optimizer to switch from outputting the first voltage to outputting the second voltage.

[0032] S704: Control the optimizer to switch to the normal operation mode from outputting the second voltage.

[0033] In some possible implementations, one end of the optimizer is configured to connect to a photovoltaic power generation module, the other end of the optimizer is configured to connect to a DC input terminal of an inverter, and the AC output terminal of the inverter is configured to connect to a power grid. When the photovoltaic power generation module connected to the optimizer normally supplies power and the AC output terminal of the inverter is disconnected from the power grid, i.e., when the input voltage of the optimizer increases to a preset value and the power grid is powered off, the optimizer is controlled to output a first voltage to the inverter. In this case, the DC voltage output by the optimizer cannot meet the inverter's startup requirements. Then, when the optimizer outputs the first voltage and does not receive a communication signal from the inverter within a preset period, i.e., when the optimizer determines that the inverter is normally powered on and shuts down, the optimizer is controlled to output a second voltage to the inverter, where the second voltage is greater than the first voltage so that the input voltage of the inverter is greater than the inverter's startup voltage. In this case, the DC voltage output by the optimizer meets the inverter's startup requirements, and the inverter is started up normally. In this case, when the corresponding photovoltaic module normally supplies power, the optimizer in the photovoltaic power generation system determines the working state of the inverter based on whether a communication signal is received from the inverter within a preset period, and after determining that the inverter is powered off and shut down, actively increases the output voltage to meet the inverter startup conditions, thereby supporting the startup of the inverter in the system when the power grid does not supply power. No additional components are required in the inverter startup process, reducing device costs, simplifying operation, and increasing startup reliability.

[0034] Optionally, when the input voltage of the optimizer increases to a preset value and the power grid is powered off, the optimizer is controlled to output a first voltage to the inverter. The first voltage may be 10 volts or less. In this case, the DC voltage output by the optimizer cannot meet the inverter's startup requirements. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within a preset period, the optimizer switches from outputting the first voltage to outputting a second voltage to the inverter, where the second voltage is greater than the first voltage so that the inverter's input voltage is greater than the inverter's startup voltage. The preset period may be 1 minute or more, and the second voltage may be greater than the first voltage but less than 15 volts. For example, the preset period may be 5 minutes, the first voltage may be 1 volt, and the second voltage may be 10 volts. When the optimizer outputs the first voltage and does not receive a communication signal from the inverter within 5 minutes, the optimizer adjusts the output DC voltage to increase from 1 volt to 10 volts. In this case, the DC voltage output by the optimizer meets the inverter's startup requirements, allowing the inverter to start up normally. When the corresponding photovoltaic module normally supplies power, the optimizer determines the inverter's operating state based on whether a communication signal is received from the inverter within a preset period. After determining that the inverter is powered off and shut down, the optimizer actively increases the output voltage to meet the inverter's startup requirements, supporting the startup of the inverter in the system when the power grid does not supply power. No additional components are required in the inverter startup process, reducing device costs, simplifying operation, and increasing startup reliability.

Claims

1. A photovoltaic power generation system having a plurality of optimizers and an inverter, wherein one end of each of the plurality of optimizers is configured to connect to a photovoltaic power generation module, and the other ends of all of the plurality of optimizers are connected in series and then configured to connect to a DC input end of the inverter; outputting a first voltage by the optimizer after the AC output terminal of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to a preset value; and switching from outputting the first voltage to outputting a second voltage by the optimizer when no communication signal is received from the inverter within a preset period of time, the second voltage being greater than the first voltage such that the input voltage of the inverter is greater than a start-up voltage of the inverter, and the input voltage of the inverter is equal to the sum of the output voltages of all the optimizers; sending a communication signal to the optimizer by the inverter to switch the optimizer from outputting the second voltage to a normal operating mode when the input voltage of the inverter is greater than the start-up voltage of the inverter; Solar power generation system.

2. the optimizer has a first communication port, the inverter has a second communication port, and the first communication ports of the optimizers are configured to connect to the second communication ports of the inverter via communication cables; the optimizer is configured to receive the communication signal from the inverter via the communication cable connected to the first communication port. The solar power generation system according to claim 1 .

3. The solar power generation system according to claim 1 , wherein the preset period is equal to or greater than one minute.

4. The solar power generation system of claim 1 , wherein the first voltage is less than or equal to 10 volts.

5. 2. The solar power generation system of claim 1, wherein the second voltage is greater than the first voltage and less than 15 volts.

6. 6. The solar power generation system of claim 5, wherein the optimizer outputs the first voltage after the AC output of the inverter is disconnected from the power grid and the input voltage of the optimizer increases to the preset value, and continues to output the first voltage upon receiving a command to keep the inverter shut down.

7. the optimizer includes a DC converter circuit configured to perform voltage conversion on the DC from the solar power generation module; the DC conversion circuit has a capacitor, an inductor, a switching transistor, and a diode, a first end of the capacitor configured to be connected to a positive electrode of the solar power generation module, the first end of the capacitor connected to a cathode of the diode via the switching transistor, the cathode of the diode connected to a first DC input terminal of the inverter or another DC conversion circuit via the inductor, a second end of the capacitor configured to be connected to a negative electrode of the solar power generation module, the second end of the capacitor connected to an anode of the diode, and a connection terminal of the capacitor and the diode connected to a second DC input terminal of the inverter or another DC conversion circuit; The solar power generation system according to claim 6.

8. 1. A method for controlling an optimizer, comprising: controlling the optimizer to output a first voltage after an AC output terminal of the inverter is disconnected from the power grid and an input voltage of the optimizer increases to a preset value, wherein one terminal of the optimizer is configured to connect to a photovoltaic power generation module, the other terminal of the optimizer is configured to connect to a DC input terminal of the inverter, and the AC output terminal of the inverter is configured to connect to the power grid; controlling the optimizer to switch from outputting the first voltage to outputting a second voltage when no communication signal is received from the inverter within a preset time period, the second voltage being greater than the first voltage such that an input voltage of the inverter is greater than a start-up voltage of the inverter; A method having the following.

9. The method of claim 8 , wherein the preset period is equal to or greater than one minute.

10. 9. The method of claim 8, wherein the first voltage is less than or equal to 10 volts.

11. 9. The method of claim 8, wherein the second voltage is greater than the first voltage and less than 15 volts.

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