Photovoltaic inverter and method of controlling the same

Abstract

This application provides a photovoltaic inverter and its control method. The photovoltaic inverter is suitable for power supply systems and includes a conversion circuit, a data acquisition circuit, and a controller. The data acquisition circuit acquires the positive and negative DC bus voltages of the conversion circuit. The controller generates an even-order harmonic voltage regulation signal based on the phase of the positive and negative DC bus voltages of the conversion circuit and the output voltage of the photovoltaic inverter. Based on the even-order harmonic voltage regulation signal, it generates a drive control signal to control the switching transistors in the conversion circuit to turn on or off, thereby controlling the output target voltage of the conversion circuit and reducing the difference between the positive and negative DC bus voltages. Using this application, the on / off state of the switching transistors in the conversion circuit can be adjusted, improving the voltage stability at the midpoint of the conversion circuit. The structure is simple, the method is convenient, and it has strong applicability.

Description

Technical Field

[0001] This application relates to the field of power electronics technology, and in particular to a photovoltaic inverter and its control method. Background Technology

[0002] In the field of power electronics, the conversion circuit in an inverter converts direct current (DC) energy into alternating current (AC) energy to supply the load. Among these, conversion circuits (e.g., neutral point clamped (NPC) inverter circuits) are widely used due to their advantages such as high safety, high efficiency, low losses, and low harmonics. Please see [link to relevant documentation]. Figure 1 , Figure 1 These are schematic diagrams of the two NPC inverter circuits provided in this application. Figure 1 Part (a) and Figure 1 As shown in section (b), the NPC inverter circuit (i.e., the converter circuit) includes two capacitors connected in series and three switching arms. The series connection point of the two capacitors is the midpoint of the converter circuit. Each switching arm includes four switching transistors and two clamping diodes. Ideally, during one power supply cycle of the converter circuit, the amount of charge flowing into and out of the midpoint of the converter circuit is the same; that is, the voltage across the two capacitors connected in series in the converter circuit is equal. However, in practical applications, the operating states of the switching transistors in the switching bridge arm of the converter circuit are usually asymmetrical (for example, different switching transistor models, different losses, asymmetrical loads, or affected by factors such as switching dead zones). This results in the amount of charge flowing into and out of the midpoint of the converter circuit not being the same within a power supply cycle. In other words, the charging (or discharging) of the two series-connected capacitors in the converter circuit is not equal, leading to unequal voltages on the two series-connected capacitors (i.e., the positive DC bus voltage and the negative DC bus voltage of the converter circuit are not equal, or the midpoint voltage of the converter circuit is unbalanced). This will cause distortion in the output voltage (or output current) of the converter circuit, and may even damage the power components in the system.

[0003] During their research and practice, the inventors of this application discovered that the method of adjusting the redundant small vector based on the DC bus voltage difference to adjust the midpoint voltage is complex, cumbersome, costly, and complicated to control. The method of injecting zero-sequence voltage into the modulation wave to balance the midpoint voltage has many limitations on the modulation wave algorithm and load type of the converter circuit. For example, in the case of discontinuous pulse width modulation (DPWM) waves, the space for injecting zero sequence voltage into the modulation wave is limited, resulting in poor adaptability, poor regulation capability, and poor control effect of this method of modulating the midpoint voltage. Summary of the Invention

[0004] This application provides a photovoltaic inverter and its control method, which can improve the voltage stability of the midpoint of the conversion circuit by adjusting the on or off time of the switching transistor in the conversion circuit. It has a simple structure, convenient control method, and strong applicability.

[0005] Firstly, this application provides a photovoltaic inverter suitable for power supply systems. The photovoltaic inverter includes a conversion circuit, a data acquisition circuit, and a controller. Here, the input terminal of the conversion circuit can be connected to a power source via a positive DC bus and a negative DC bus, and the output terminal of the conversion circuit can be used to connect a load. The data acquisition circuit can acquire the positive DC bus voltage and the negative DC bus voltage of the conversion circuit. The controller can generate an even-order harmonic voltage regulation signal based on the phase of the positive DC bus voltage, the negative DC bus voltage, and the output voltage of the photovoltaic inverter, and generate a drive control signal based on the even-order harmonic voltage regulation signal to control the switching transistors in the conversion circuit to turn on or off, thereby controlling the output target voltage of the conversion circuit and reducing the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit.

[0006] In this application, the power supply can be connected to a conversion circuit via a positive DC bus and a negative DC bus. The conversion circuit can convert the DC power provided by the power supply into AC power to supply the load. During the power supply process, the conversion circuit can charge and discharge the capacitors in the conversion circuit by turning on and off different switching transistors, converting the DC power provided by the power supply into AC power to be transmitted to the load. It is understood that when the output voltage (or output current) of the photovoltaic inverter is asymmetrical (e.g., due to different switching transistor models, different losses, asymmetrical load, or the influence of factors such as switching dead time), the positive DC bus voltage and the negative DC bus voltage of the conversion circuit will not be equal within a power supply cycle, or in other words, there will be a difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit. This will cause distortion of the output voltage (or output current) of the conversion circuit, and may even damage the power components in the system.

[0007] In this application, the acquisition circuit can acquire the positive DC bus voltage and negative DC bus voltage of the conversion circuit. The controller can generate an even-order harmonic voltage regulation signal based on the phase of the positive DC bus voltage, negative DC bus voltage, and output voltage of the photovoltaic inverter. Furthermore, it can generate a drive control signal (e.g., a Pulse Width Modulation (PWM) wave drive control signal) based on the even-order harmonic voltage regulation signal to control the switching transistors in the conversion circuit to turn on or off. Here, the drive control signal generated based on the even-order harmonic voltage regulation signal can control the conversion circuit to output an output voltage containing even-order harmonics. The even-order harmonics in the output voltage generate an output current containing even-order harmonic components through the load. The even-order harmonic components in the output current can interact with the fundamental component in the drive control signal, and / or the even-order harmonic components in the drive control signal can interact with the fundamental component in the output current, thereby reducing the difference between the positive DC bus voltage and the negative DC bus voltage. It is understood that the photovoltaic inverter provided in this application can be applied to conversion circuits that use discontinuous pulse width modulation (DPWM) waves as drive control signals, as well as conversion circuits that use other PWM waves (e.g., sinusoidal pulse width modulation (SPWM) waves, third harmonic injection pulse width modulation (THIPWM) waves, carrier-based space vector pulse width modulation (CBPWM) waves, etc.) as drive control signals. It has a wide range of applications and good control performance.

[0008] By adopting this application, the photovoltaic inverter can reduce the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit while controlling the output target voltage of the conversion circuit, thereby improving the voltage stability at the midpoint of the conversion circuit. It has a simple structure, convenient control method, and strong applicability.

[0009] In conjunction with the first aspect, in a first possible implementation, the conversion circuit may include two sets of capacitors and at least one switching bridge arm. Each switching bridge arm includes multiple switching transistors. The two sets of capacitors are connected in series and then connected in parallel with the at least one switching bridge arm between the positive DC bus and the negative DC bus of the conversion circuit. The series connection point of the two sets of capacitors is the midpoint of the conversion circuit. The input terminal of the acquisition circuit is connected to the positive DC bus, the negative DC bus, and the midpoint of the conversion circuit. This acquisition circuit can also obtain the positive DC bus voltage and negative DC bus voltage of the conversion circuit based on the potentials of the positive DC bus, the negative DC bus, and the midpoint. The connection method is simple, the detection method is convenient, and the detection efficiency is high.

[0010] In conjunction with the first aspect or the first possible implementation of the first aspect, in the second possible implementation, the controller can also be used to generate an even harmonic amplitude signal based on the positive DC bus voltage and the negative DC bus voltage, generate an even harmonic phase signal based on the phase of the output voltage, and generate an even harmonic voltage regulation signal based on the even harmonic amplitude signal and the even harmonic phase signal.

[0011] Using this application, the controller can obtain the midpoint voltage difference of the conversion circuit based on the positive DC bus voltage and the negative DC bus voltage, and generate an even-order harmonic amplitude signal based on the midpoint voltage difference. The controller can also generate a corresponding even-order harmonic phase signal by multiplying the phase of the photovoltaic inverter's output voltage. It can be understood that the controller can generate an even-order harmonic voltage regulation signal based on the even-order harmonic amplitude signal and the even-order harmonic phase signal, and then generate a drive control signal based on the even-order harmonic voltage regulation signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. Further, it can be understood that the even-order harmonic voltage regulation signal here can be an even-order harmonic voltage regulation signal generated based on one even-order harmonic (e.g., the second harmonic, etc.), or it can be an even-order harmonic voltage regulation signal generated by superimposing multiple even-order harmonics (e.g., the second harmonic, the fourth harmonic, etc.).

[0012] Using this application, a photovoltaic inverter can determine the amplitude of the even-order harmonic voltage regulation signal based on the positive and negative DC bus voltages of the conversion circuit, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the photovoltaic inverter's output voltage. Furthermore, a drive control signal is generated based on the even-order harmonic voltage regulation signal. While controlling the target output voltage of the conversion circuit, the difference between the positive and negative DC bus voltages of the conversion circuit is reduced, improving the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is precise and convenient, and it has strong applicability.

[0013] In conjunction with the second possible implementation of the first aspect, in the third possible implementation, the acquisition circuit can also be used to acquire the phase of the output voltage and the phase of the output current of the photovoltaic inverter. The acquisition circuit can also determine the load type based on the phase of the output voltage and the phase of the output current of the photovoltaic inverter, and generate even-order harmonic phase signals based on the phase of the output voltage and the load type. Here, the load type is one or more of inductive, capacitive, and / or resistive loads. It can be understood that the photovoltaic inverter can acquire the phase of its output voltage and the phase of its output current through the acquisition circuit, and then determine the load type based on the phase of the output voltage and the phase of the output current. Here, different phases have different adjustment effects for different types of loads. In other words, for different types of loads, the photovoltaic inverter can generate a first phase for resistive loads, a second phase for capacitive loads, a third phase for inductive loads, or a fourth phase for mixed load types. Alternatively, it can superimpose the first, second, or third phases according to weights to generate a new phase (e.g., a fifth phase) for mixed load types. This new phase is then multiplied by the phase of the photovoltaic inverter's output voltage and superimposed with the first, second, third, fourth, or fifth phases to generate an even-order harmonic phase signal. Furthermore, the photovoltaic inverter can also determine its output power (including active and reactive power) based on its output voltage and current, and determine the load type based on the signs of the active and reactive power. Alternatively, the inverter can determine the power factor of the conversion circuit based on its output voltage and current, and determine the load type based on the power factor, depending on the application scenario. Here, the photovoltaic inverter can generate an even-order harmonic voltage regulation signal based on the even-order harmonic amplitude signal and the even-order harmonic phase signal. This even-order harmonic voltage regulation signal can be generated based on one even-order harmonic (e.g., the second harmonic), or it can be generated by superimposing multiple even-order harmonics (e.g., the second harmonic, the fourth harmonic, etc.). Furthermore, the photovoltaic inverter can generate multiple even-order harmonic phase signals of different phases for various types of mixed loads, and generate multiple even-order harmonic voltage regulation signals based on these signals and their amplitude signals. These multiple even-order harmonic voltage regulation signals are then superimposed according to weights to obtain the final even-order harmonic voltage regulation signal.

[0014] Using this application, a photovoltaic inverter can determine the load type based on the phase of its output voltage and the phase of its output current, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the output voltage and the load type. Then, a drive control signal is generated based on the even-order harmonic voltage regulation signal. In other words, the photovoltaic inverter can generate targeted drive control signals based on different load types, thereby reducing the difference between the positive and negative DC bus voltages of the conversion circuit while controlling the target output voltage of the conversion circuit. This improves the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is convenient, the applicability is strong, and the control efficiency is high.

[0015] In conjunction with the third possible implementation of the first aspect, in the fourth possible implementation, the controller may include a signal generation unit, a voltage control unit, and a drive control unit. The signal generation unit may be connected to the acquisition circuit and the voltage control unit, and the voltage control unit may be connected to the conversion circuit through the drive control unit. Here, the signal generation unit may generate even-order harmonic amplitude signals based on the positive and negative DC bus voltages, generate even-order harmonic phase signals based on the phase of the photovoltaic inverter's output voltage, and generate even-order harmonic voltage regulation signals based on the even-order harmonic amplitude and phase signals. Here, the voltage control unit may generate voltage command signals for the conversion circuit based on the even-order harmonic voltage regulation signals. Here, the drive control unit may generate drive control signals based on the voltage command signals of the conversion circuit, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signals. It is understandable that the photovoltaic inverter here can generate a voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal. Then, the photovoltaic inverter can generate a drive control signal based on the voltage command signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. This allows the conversion circuit to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient.

[0016] In conjunction with the fourth possible implementation of the first aspect, in the fifth possible implementation, the voltage control unit can also be used to acquire the fundamental frequency command from the external central control system. Here, the voltage control unit can also be used to superimpose the fundamental frequency command and the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit. It can be understood that the photovoltaic inverter here can acquire the fundamental frequency command sent by the external central control system, directly obtain the fundamental frequency signal based on the fundamental frequency command, or obtain the fundamental frequency signal through calculation, and superimpose and modulate the fundamental frequency signal with the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit. Furthermore, the drive control unit can generate a drive control signal based on the voltage command signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. This method is simple in structure, convenient in control method, and highly efficient in control.

[0017] In conjunction with the fifth possible implementation of the first aspect, in the sixth possible implementation, the controller may further include a voltage feedback unit, which may be connected to the acquisition circuit and the voltage control unit. Here, the voltage feedback unit can be used to acquire the output voltage of the photovoltaic inverter through the acquisition circuit and use the output voltage of the photovoltaic inverter as a voltage feedback signal. Here, the voltage control unit can also generate a first-level voltage command signal based on the voltage feedback signal and the voltage command signal of the conversion circuit. Here, the drive control unit can also generate a drive control signal based on the first-level voltage command signal. It can be understood that the voltage control unit here can be a voltage control loop. Here, the voltage feedback unit can acquire the output voltage of the photovoltaic inverter and input the output voltage of the photovoltaic inverter as a voltage feedback signal to the voltage control unit. Then, the voltage control unit can compare and adjust based on the voltage feedback signal and the voltage command signal to generate a first-level voltage command signal (i.e., the voltage command signal adjusted based on the voltage feedback signal). Furthermore, the drive control unit can also generate a drive control signal based on the first-level voltage command signal and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal.

[0018] By adopting this application, the conversion circuit can maintain the stability of the midpoint voltage of the conversion circuit while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output voltage of the photovoltaic inverter as the voltage feedback signal, resulting in high control efficiency.

[0019] In conjunction with the sixth possible implementation of the first aspect, in the seventh possible implementation, the controller may further include a current control unit and a current feedback unit. The current control unit may be connected to the voltage control unit and the drive control unit, and the current feedback unit may be connected to the acquisition circuit and the current control unit. Here, the current feedback unit can be used to acquire the output current of the photovoltaic inverter through the acquisition circuit and use the output current of the photovoltaic inverter as a current feedback signal. Here, the current control unit can generate a second-level voltage command signal based on the first-level voltage command signal output by the voltage control unit and the current feedback signal. Here, the drive control unit can also generate a drive control signal based on the second-level voltage command signal. It can be understood that the current control unit here can be a current control loop, and the current feedback unit can acquire the output current of the photovoltaic inverter and input the output current of the photovoltaic inverter as a current feedback signal to the current control unit. Then, the current control unit can compare and adjust the current feedback signal with the first-level voltage command signal output by the voltage control unit to generate a second-level voltage command signal (i.e., a voltage command signal adjusted based on the voltage feedback signal and the current feedback signal). Here, the drive control unit can also generate a drive control signal based on the second-level voltage command signal and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal.

[0020] By adopting this application, the conversion circuit can maintain the stability of the midpoint voltage of the conversion circuit while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output current of the photovoltaic inverter as the feedback signal, resulting in high control efficiency.

[0021] In conjunction with the seventh possible implementation of the first aspect, in the eighth possible implementation, the drive control unit can also be connected to the signal generation unit. Here, the drive control unit can also be used to acquire the even-order harmonic voltage regulation signal from the signal generation unit, and generate a drive control signal based on the even-order harmonic voltage regulation signal and the secondary voltage command signal. Alternatively, the drive control unit can acquire the even-order harmonic voltage regulation signal from the signal generation unit and the fundamental signal generated based on the fundamental command from an external central control system (or directly acquire the signal resulting from the superposition of the even-order harmonic voltage regulation signal and the fundamental signal), and generate the drive control signal based on the even-order harmonic voltage regulation signal, the fundamental signal, and the secondary voltage command signal. It can be understood that the drive control unit here can be a PWM wave generation circuit or a modulation signal generation circuit of other types, or a combination circuit of a PWM wave generation circuit or a modulation signal generation circuit of other types and a switching transistor drive circuit. Here, the drive control unit can acquire the even-order harmonic voltage regulation signal output by the signal generation unit, and then the drive control unit can generate the drive control signal based on the even-order harmonic voltage regulation signal and the secondary voltage command signal. Here, when the photovoltaic inverter does not include a current control unit and a current feedback unit, the drive control unit can also generate drive control signals based on even-order harmonic voltage regulation signals and first-order voltage command signals.

[0022] By using this application, the conversion circuit can maintain the stability of the midpoint voltage of the conversion circuit while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the drive control unit can further generate a drive control signal based on the even harmonic voltage adjustment signal and the secondary voltage command signal. This is equivalent to adding an even harmonic component to the drive control signal, further maintaining the midpoint balance of the conversion circuit and achieving high control efficiency.

[0023] Secondly, this application provides a power supply system that may include a power source and a photovoltaic inverter as described in the first aspect or any possible implementation of the first aspect.

[0024] By adopting this application, the power supply system can reduce the difference between the positive DC bus voltage and the negative DC bus voltage in the conversion circuit of the photovoltaic inverter while outputting the target voltage, thereby improving the voltage stability at the midpoint of the conversion circuit. The system has a simple structure, convenient control method, and strong applicability.

[0025] Thirdly, this application provides a photovoltaic inverter control method applicable to photovoltaic inverters. The photovoltaic inverter includes a conversion circuit and positive and negative DC buses. One end of the positive and negative DC buses is connected to the conversion circuit, and the other end is used to connect to a power source. The method includes: detecting the positive DC bus voltage and the negative DC bus voltage of the conversion circuit; generating an even-order harmonic voltage regulation signal based on the phase of the positive DC bus voltage, the negative DC bus voltage, and the output voltage of the photovoltaic inverter; and generating a drive control signal based on the even-order harmonic voltage regulation signal to control the switching transistors in the conversion circuit to turn on or off, thereby controlling the output target voltage of the conversion circuit and reducing the difference between the positive and negative DC bus voltages of the conversion circuit.

[0026] In this application, the photovoltaic inverter can generate an even-order harmonic voltage regulation signal based on the phase of the positive DC bus voltage, negative DC bus voltage, and output voltage of the conversion circuit. Furthermore, the photovoltaic inverter can generate a drive control signal based on the even-order harmonic voltage regulation signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. Here, the drive control signal generated based on the even-order harmonic voltage regulation signal can control the conversion circuit to output an output voltage containing even-order harmonics. The even-order harmonics in the output voltage generate an output current containing even-order harmonic components through the load. The even-order harmonic components in the output current can interact with the fundamental component in the drive control signal, and / or the even-order harmonic components in the drive control signal can interact with the fundamental component in the output current, reducing the difference between the positive and negative DC bus voltages of the conversion circuit.

[0027] By adopting this application, the photovoltaic inverter can reduce the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit while controlling the output target voltage of the conversion circuit, thereby improving the voltage stability at the midpoint of the conversion circuit. It has a simple structure, convenient control method, and strong applicability.

[0028] In conjunction with the third aspect, in the first possible implementation, the conversion circuit may include two sets of capacitors and at least one switching bridge arm, and detect the positive DC bus voltage and the negative DC bus voltage of the conversion circuit, including: detecting the positive DC bus voltage and the negative DC bus voltage of the conversion circuit based on the potential of the positive DC bus, the potential of the negative DC bus and the potential of the midpoint of the conversion circuit. The connection method is simple, the detection method is convenient and the detection efficiency is high.

[0029] In conjunction with the third aspect or the first possible implementation of the third aspect, in the second possible implementation, generating an even-order harmonic voltage regulation signal based on the positive DC bus voltage of the conversion circuit, the negative DC bus voltage of the conversion circuit, and the output voltage of the photovoltaic inverter may include: generating an even-order harmonic amplitude signal based on the positive DC bus voltage and the negative DC bus voltage of the conversion circuit, generating an even-order harmonic phase signal based on the phase of the output voltage of the photovoltaic inverter, and generating an even-order harmonic voltage regulation signal based on the even-order harmonic amplitude signal and the even-order harmonic phase signal.

[0030] Using this application, the photovoltaic inverter can detect the positive DC bus voltage and negative DC bus voltage of the conversion circuit, thereby obtaining the voltage difference at the midpoint of the conversion circuit, and generating an even-order harmonic amplitude signal based on the voltage difference at the midpoint of the conversion circuit. It can also detect the phase of the output voltage of the photovoltaic inverter, and generate a corresponding even-order harmonic phase signal by frequency multiplication of the output voltage phase. It can be understood that the photovoltaic inverter can generate an even-order harmonic voltage regulation signal based on the even-order harmonic amplitude signal and the even-order harmonic phase signal, and then generate a drive control signal (e.g., a PWM wave drive control signal) based on the even-order harmonic voltage regulation signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. Furthermore, it can be understood that the even-order harmonic voltage regulation signal here can be an even-order harmonic voltage regulation signal generated based on one even-order harmonic (e.g., the second harmonic, etc.), or it can be an even-order harmonic voltage regulation signal generated by superimposing multiple even-order harmonics (e.g., the second harmonic, the fourth harmonic, etc.).

[0031] Using this application, a photovoltaic inverter can determine the amplitude of the even-order harmonic voltage regulation signal based on the positive and negative DC bus voltages of the conversion circuit, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the photovoltaic inverter's output voltage. Furthermore, a drive control signal is generated based on the even-order harmonic voltage regulation signal. While controlling the target output voltage of the conversion circuit, the difference between the positive and negative DC bus voltages of the conversion circuit is reduced, improving the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is precise and convenient, and it has strong applicability.

[0032] In conjunction with the second possible implementation of the third aspect, in the third possible implementation, generating an even-order harmonic phase signal based on the phase of the photovoltaic inverter's output voltage may include: detecting the phase of the photovoltaic inverter's output voltage and the phase of the photovoltaic inverter's output current. The load type is determined based on the phase of the photovoltaic inverter's output voltage and the phase of the photovoltaic inverter's output current, and an even-order harmonic phase signal is generated based on the phase of the photovoltaic inverter's output voltage and the load type, where the load type is one or more of inductive, capacitive, and / or resistive loads. It can be understood that the photovoltaic inverter can detect the phase of the photovoltaic inverter's output voltage and the phase of the photovoltaic inverter's output current through a data acquisition circuit, and then determine the load type based on the phase of the photovoltaic inverter's output voltage and the phase of the output current. Here, the adjustment effect of different phases varies for different types of loads. In other words, for different types of loads, the photovoltaic inverter can generate a first phase for resistive loads, a second phase for capacitive loads, a third phase for inductive loads, or a fourth phase for mixed load types. Alternatively, it can superimpose the first, second, or third phases according to weights to generate a new phase (e.g., a fifth phase) for mixed load types. This new phase is then multiplied by the phase of the photovoltaic inverter's output voltage and superimposed with the first, second, third, fourth, or fifth phases to generate an even-order harmonic phase signal. Furthermore, the photovoltaic inverter can also determine its output power (including active and reactive power) based on its output voltage and current, and determine the load type based on the signs of the active and reactive power in the conversion circuit. Alternatively, the photovoltaic inverter can determine the power factor of the conversion circuit based on its output voltage and current, and determine the load type based on the power factor, depending on the application scenario. Here, the photovoltaic inverter can generate an even harmonic voltage regulation signal based on the even harmonic amplitude signal and the even harmonic phase signal. The even harmonic voltage regulation signal can be generated based on one even harmonic (e.g., the second harmonic, etc.) or it can be generated based on the superposition of multiple even harmonics (e.g., the second harmonic, the fourth harmonic, etc.).

[0033] Using this application, a photovoltaic inverter can determine the load type based on the phase of its output voltage and the phase of its output current, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the output voltage and the load type. Then, a drive control signal is generated based on the even-order harmonic voltage regulation signal. In other words, the photovoltaic inverter can generate targeted drive control signals based on different load types, thereby reducing the difference between the positive and negative DC bus voltages of the conversion circuit while controlling the target output voltage of the conversion circuit. This improves the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is convenient, the applicability is strong, and the control efficiency is high.

[0034] In conjunction with the third possible implementation of the third aspect, in the fourth possible implementation, generating the drive control signal based on the even-order harmonic voltage regulation signal may include: generating a voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal. The drive control signal is then generated based on the voltage command signal of the conversion circuit. It can be understood that the photovoltaic inverter here can generate a voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal, and further, the photovoltaic inverter can generate a drive control signal based on the voltage command signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. This ensures that the conversion circuit maintains a stable midpoint voltage while outputting the target voltage, resulting in a simple structure and convenient control method.

[0035] In conjunction with the fourth possible implementation of the third aspect, in the fifth possible implementation, the voltage command signal for the conversion circuit is generated based on the even-order harmonic voltage regulation signal. This may include: detecting the fundamental frequency command from an external central control system; and superimposing the fundamental frequency command and the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit. It can be understood that the photovoltaic inverter here can detect the fundamental frequency command sent by the external central control system, directly obtain the fundamental frequency signal based on the fundamental frequency command, or obtain the fundamental frequency signal through calculation, and then superimpose and modulate the fundamental frequency signal with the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit. Furthermore, the photovoltaic inverter can generate a drive control signal based on the voltage command signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. This method is simple in structure, convenient in control method, and highly efficient in control.

[0036] In conjunction with the fifth possible implementation of the third aspect, in the sixth possible implementation, after generating the voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal, the method may further include: detecting the output voltage of the photovoltaic inverter and using the output voltage of the photovoltaic inverter as a voltage feedback signal; generating a first-level voltage command signal based on the voltage feedback signal and the voltage command signal of the conversion circuit; and generating a drive control signal based on the first-level voltage command signal. It can be understood that the photovoltaic inverter here can detect its output voltage and use it as a voltage feedback signal. The photovoltaic inverter can then adjust itself based on the voltage feedback signal and the voltage command signal to generate the first-level voltage command signal (i.e., the voltage command signal adjusted based on the voltage feedback signal). Furthermore, the photovoltaic inverter can also generate a drive control signal based on the first-level voltage command signal and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal.

[0037] By adopting this application, the conversion circuit can maintain the stability of the midpoint voltage of the conversion circuit while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output voltage of the photovoltaic inverter as the voltage feedback signal, resulting in high control efficiency.

[0038] In conjunction with the sixth possible implementation of the third aspect, in the seventh possible implementation, after generating the first-level voltage command signal based on the voltage feedback signal and the voltage command signal of the conversion circuit, the method may further include: detecting the output current of the photovoltaic inverter and using the output current of the photovoltaic inverter as a current feedback signal; generating a second-level voltage command signal based on the first-level voltage command signal and the current feedback signal; and generating a drive control signal based on the second-level voltage command signal. It can be understood that the photovoltaic inverter here can detect its output current and use it as a current feedback signal. The photovoltaic inverter can then adjust itself based on the current feedback signal and the first-level voltage command signal to generate the second-level voltage command signal (i.e., the voltage command signal adjusted based on the voltage feedback signal and the current feedback signal). Here, the photovoltaic inverter may also generate a drive control signal based on the second-level voltage command signal and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal.

[0039] By adopting this application, the conversion circuit can maintain the stability of the midpoint voltage of the conversion circuit while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output current of the photovoltaic inverter as the current feedback signal, resulting in high control efficiency.

[0040] In conjunction with the seventh possible implementation of the third aspect, in the eighth possible implementation, after generating the second-level voltage command signal based on the first-level voltage command signal and the current feedback signal, the method may further include: detecting the even-order harmonic voltage regulation signal, and generating a drive control signal based on the even-order harmonic voltage regulation signal and the second-level voltage command signal. Here, the photovoltaic inverter can also detect the even-order harmonic voltage regulation signal and the fundamental signal generated based on the fundamental command from an external central control system (or it can directly detect the signal resulting from the superposition of the even-order harmonic voltage regulation signal and the fundamental signal), and generate the drive control signal based on the even-order harmonic voltage regulation signal, the fundamental signal, and the second-level voltage command signal. It can be understood that the photovoltaic inverter can generate the drive control signal based on the even-order harmonic voltage regulation signal and the second-level voltage command signal. Here, when there is no current control unit in the photovoltaic inverter, the photovoltaic inverter can also generate the drive control signal based on the even-order harmonic voltage regulation signal and the first-level voltage command signal.

[0041] By adopting this application, the conversion circuit can maintain the stability of the midpoint voltage of the conversion circuit while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can further generate a drive control signal based on the even harmonic voltage regulation signal and the secondary voltage command signal. This is equivalent to adding an even harmonic component to the drive control signal, further maintaining the midpoint balance of the conversion circuit and achieving high control efficiency. Attached Figure Description

[0042] Figure 1 These are schematic diagrams of the two NPC inverter circuits provided in this application;

[0043] Figure 2 This is a schematic diagram illustrating the application scenario of the photovoltaic inverter provided in the embodiments of this application;

[0044] Figure 3 This is a schematic diagram of the structure of a photovoltaic inverter provided in an embodiment of this application;

[0045] Figure 4 This is another structural schematic diagram of the photovoltaic inverter provided in the embodiments of this application;

[0046] Figure 5 This is another structural schematic diagram of the photovoltaic inverter provided in the embodiments of this application;

[0047] Figure 6 This is another structural schematic diagram of the photovoltaic inverter provided in the embodiments of this application;

[0048] Figure 7 This is a schematic diagram of the power supply system provided in an embodiment of this application;

[0049] Figure 8 This is a flowchart illustrating the control method provided in an embodiment of this application;

[0050] Figure 9 This is another schematic diagram of the control method provided in the embodiments of this application. Detailed Implementation

[0051] The photovoltaic inverter provided in this application can be applied to various fields, including new energy power generation, traditional power generation peak shaving and frequency regulation, power supply for important equipment, and new energy vehicles. The specific application scenario can be determined accordingly, and no limitations are imposed here. The photovoltaic inverter provided in this application can also be applied to different power supply systems, such as energy storage systems, uninterruptible power supply systems, and motor drive systems. The specific application scenario can be determined accordingly, and no limitations are imposed here. The photovoltaic inverter provided in this application is adaptable to different application scenarios, such as applications controlling conversion circuits in solar power environments, wind power environments, pure energy storage environments, or other application scenarios. The following explanation will use the application scenario of controlling conversion circuits in a pure energy storage environment as an example; further details will not be elaborated upon here.

[0052] Please see Figure 2 , Figure 2 This is a schematic diagram illustrating an application scenario of the photovoltaic inverter provided in this application embodiment. In a pure energy storage power supply system, such as... Figure 2 As shown, the power supply system includes a photovoltaic inverter 1, a power supply 2, and a load 3. The photovoltaic inverter 1 includes a conversion circuit 13. The power supply 2 can be connected to the load 3 through the conversion circuit 13. The input terminal of the photovoltaic inverter 1 can be connected to both the input and output terminals of the conversion circuit 13. In some feasible embodiments, the power supply 2 can supply power to the load 3 through the conversion circuit 13. It is understood that the power supply 2 provided in this application is suitable for powering base station equipment in remote areas with no or poor mains power, or for powering household appliances (such as refrigerators, air conditioners, etc.), and other application scenarios involving powering various types of electrical equipment. The specific application scenario can be determined accordingly, and no limitations are imposed here. Furthermore, it can be understood that... Figure 2 The load 3 in the diagram can include the power grid, which may include transmission lines, power transfer stations, communication base stations, or household appliances and other electrical equipment or power transmission equipment. The load 3 can also include motors, rectifiers, and other loads (electrical devices or power transmission devices) whose voltage and current relationships are non-linear during operation (power supply or power consumption). In some feasible implementations, the conversion circuit 13 can be an NPC inverter circuit; please refer to this description. Figure 1 ,like Figure 1As shown, the conversion circuit 13 may include two sets of capacitors (e.g., C11 and C12) and at least one switching bridge arm (e.g., a switching bridge arm composed of switching transistors Ta1, Ta2, Ta3, and Ta4; a switching bridge arm composed of switching transistors Tb1, Tb2, Tb3, and Tb4; and a switching bridge arm composed of switching transistors Tc1, Tc2, Tc3, and Tc4). Here, a set of capacitors can be a single capacitor or a capacitor composed of multiple integrated capacitors. During power supply, the conversion circuit 13 can charge and discharge the two sets of capacitors respectively by turning on and off different switching transistors in the switching bridge arm, converting the DC power supplied by the power source into AC power for transmission to the load. It can be understood that when the output voltage (or output current) of the photovoltaic inverter 1 is asymmetrical (e.g., due to different switching transistor models, different losses, asymmetrical load, or the influence of factors such as switching dead zone), the amount of charge flowing into and out of the conversion circuit 13 within one power supply cycle is not the same. In other words, the charging (or discharging) amounts of the two sets of capacitors in the conversion circuit 13 are not equal, resulting in unequal voltages on the two sets of capacitors in the conversion circuit 13 (i.e., the positive DC bus voltage and the negative DC bus voltage of the conversion circuit 13 are unequal, or the midpoint voltage of the conversion circuit 13 is unbalanced). This will cause distortion in the output voltage (or output current) of the photovoltaic inverter 1, and may even damage the power components in the system. Here, the photovoltaic inverter 1 may also include a data acquisition circuit 11 and a controller 12. Here, the data acquisition circuit 11 can acquire the positive DC bus voltage and the negative DC bus voltage of the conversion circuit 13. Then, the controller 12 can generate an even-order harmonic voltage regulation signal based on the phase of the positive DC bus voltage, the negative DC bus voltage and the output voltage of the photovoltaic inverter 13, and generate a drive control signal (e.g., a PWM wave drive control signal) based on the even-order harmonic voltage regulation signal to control the switching transistors in the conversion circuit to turn on or off. Here, the photovoltaic inverter 1 can reduce the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit 13 while controlling the output target voltage of the conversion circuit 13, thereby improving the voltage stability at the midpoint of the conversion circuit 13. It has a simple structure, a convenient control method, and strong applicability.

[0053] The following will combine Figures 3 to 9 This application provides an example illustrating the photovoltaic inverter and its working principle.

[0054] Please see Figure 3 , Figure 3 This is a structural schematic diagram of a photovoltaic inverter provided in an embodiment of this application. Figure 3As shown, the power supply system includes a power source, a photovoltaic inverter, a conversion circuit 103, and a load. The photovoltaic inverter includes a data acquisition circuit 101 and a controller 102. Here, the power source can be connected to the load via the conversion circuit 103. The first sampling terminal of the data acquisition circuit 101 can be connected to the DC bus of the conversion circuit 103, the second sampling terminal of the data acquisition circuit 101 can be connected to the output terminal of the conversion circuit 103, the output terminal of the data acquisition circuit 101 can be connected to one end of the controller 102, and the other end of the controller 102 can be connected to the control terminal of the conversion circuit 103. Here, the conversion circuit 103 may include two sets of capacitors (e.g., C1 and C2) and at least one switching bridge arm (…). Figure 3 The conversion circuit 103 shown includes a switch bridge arm composed of three sets of switching transistors Ta1, Ta2, Ta3 and Ta4, a switch bridge arm composed of switching transistors Tb1, Tb2, Tb3 and Tb4, and a switch bridge arm composed of switching transistors Tc1, Tc2, Tc3 and Tc4. Each switch bridge arm includes multiple switching transistors. Two sets of capacitors are connected in series and then connected in parallel with at least one switch bridge arm between the positive DC bus and the negative DC bus of the conversion circuit 103. The series connection point of the two sets of capacitors is the midpoint of the conversion circuit 103. The three terminals of the first sampling terminal of the acquisition circuit are respectively connected to the positive DC bus, the negative DC bus and the midpoint of the conversion circuit 103.

[0055] Here, the controller 102 can generate an even-order harmonic voltage regulation signal based on the phase of the positive DC bus voltage, negative DC bus voltage, and output voltage of the photovoltaic inverter of the conversion circuit 103. In some feasible embodiments, the acquisition circuit 101 can also acquire the positive DC bus voltage and negative DC bus voltage of the conversion circuit 103 based on the potential of the positive DC bus, the potential of the negative DC bus, and the potential of the midpoint of the conversion circuit 103. This method is simple to connect, easy to detect, and has high detection efficiency. The controller 102 can generate a drive control signal (e.g., a PWM wave drive control signal) based on the even-order harmonic voltage regulation signal, and control the switching transistors in the conversion circuit 103 to turn on or off based on the drive control signal. Here, the drive control signal generated by the controller 102 based on the even-order harmonic voltage regulation signal can control the conversion circuit 103 to output an output voltage containing even-order harmonics. The even-order harmonics in the output voltage generate an output current containing even-order harmonic components through the load. The even harmonic components in the output current can interact with the fundamental component in the drive control signal, and / or the even harmonic components in the drive control signal can interact with the fundamental component in the output current, thereby adjusting the midpoint potential of the conversion circuit 103 so that the midpoint potential of the conversion circuit 103 remains balanced.

[0056] It is understood that the photovoltaic inverter provided in this application can be applied to conversion circuits that use DPWM waves as drive control signals, as well as conversion circuits that use other PWM waves (e.g., SPWM waves, THIPWM waves, CBSVPWM waves, etc.) as drive control signals. It has a wide range of applications and good control effect.

[0057] Using the implementation method provided in this application, the photovoltaic inverter can reduce the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit while controlling the output target voltage of the conversion circuit, thereby improving the voltage stability at the midpoint of the conversion circuit. It has a simple structure, convenient control method, and strong applicability.

[0058] In some feasible implementations, controller 102 can generate even-order harmonic amplitude signals based on the positive and negative DC bus voltages. Controller 102 can also generate even-order harmonic phase signals based on the phase of the output voltage. Controller 102 can also generate even-order harmonic voltage regulation signals based on the even-order harmonic amplitude and phase signals. It can be understood that controller 102 can obtain the midpoint voltage difference of converter circuit 103 based on the positive and negative DC bus voltages of the converter circuit, and generate even-order harmonic amplitude signals based on the midpoint voltage difference of converter circuit 103. Controller 102 can also generate corresponding even-order harmonic phase signals by multiplying the phase of the output voltage of the photovoltaic inverter. It can also be understood that controller 102 can generate even-order harmonic voltage regulation signals based on the even-order harmonic amplitude and phase signals, and then generate drive control signals based on the even-order harmonic voltage regulation signals, and control the switching transistors in converter circuit 103 to turn on or off based on the drive control signals. Furthermore, it can be understood that the even harmonic voltage regulation signal here can be an even harmonic voltage regulation signal generated based on an even harmonic (e.g., the second harmonic, etc.), or it can be an even harmonic voltage regulation signal generated by superimposing multiple even harmonics (e.g., the second harmonic, the fourth harmonic, etc.).

[0059] Using the embodiments provided in this application, the photovoltaic inverter can determine the amplitude of the even-order harmonic voltage regulation signal based on the positive and negative DC bus voltages of the conversion circuit, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the output voltage of the photovoltaic inverter, thereby generating a drive control signal based on the even-order harmonic voltage regulation signal. While controlling the target output voltage of the conversion circuit, the difference between the positive and negative DC bus voltages of the conversion circuit is reduced, improving the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is precise and convenient, and it has strong applicability.

[0060] In some feasible implementations, the acquisition circuit 101 can also be used to acquire the phase of the output voltage and the phase of the output current of the photovoltaic inverter. The controller 102 can also determine the load type based on the phase of the output voltage and the phase of the output current of the photovoltaic inverter, and generate even-order harmonic phase signals based on the phase of the output voltage and the load type. Here, the load type is one or more of inductive, capacitive, and / or resistive loads. It can be understood that the photovoltaic inverter can acquire the phase of its output voltage and the phase of its output current through the acquisition circuit 101, and then determine the load type based on the phase of the output voltage and the phase of the output current. Here, the adjustment effect of different phases varies for different types of loads. In other words, for different types of loads, a photovoltaic inverter can generate a first phase for resistive loads, a second phase for capacitive loads, a third phase for inductive loads, or a fourth phase for mixed load types. Alternatively, it can weightedly superimpose the first, second, or third phases to generate a new phase (e.g., a fifth phase) for mixed load types. This new phase is then multiplied by the phase of the inverter's output voltage and superimposed with the first, second, third, fourth, or fifth phases to generate an even-order harmonic phase signal. Furthermore, the inverter can also determine its output power (including active and reactive power) based on its output voltage and current, and determine the load type based on the signs of the active and reactive power. Alternatively, the inverter can determine its power factor based on its output voltage and current, and determine the load type based on the power factor, depending on the application scenario. Here, the photovoltaic inverter can generate an even-order harmonic voltage regulation signal based on the even-order harmonic amplitude signal and the even-order harmonic phase signal. This even-order harmonic voltage regulation signal can be generated based on one even-order harmonic (e.g., the second harmonic), or it can be generated by superimposing multiple even-order harmonics (e.g., the second harmonic, the fourth harmonic, etc.). Furthermore, the photovoltaic inverter can generate multiple even-order harmonic phase signals of different phases for various types of mixed loads, and generate multiple even-order harmonic voltage regulation signals based on these signals and their amplitude signals. These multiple even-order harmonic voltage regulation signals are then superimposed according to weights to obtain the final even-order harmonic voltage regulation signal.

[0061] Using this application, a photovoltaic inverter can determine the load type based on the phase of its output voltage and the phase of its output current, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the output voltage and the load type. Then, a drive control signal is generated based on the even-order harmonic voltage regulation signal. In other words, the photovoltaic inverter can generate targeted drive control signals based on different load types, thereby reducing the difference between the positive and negative DC bus voltages of the conversion circuit while controlling the target output voltage of the conversion circuit. This improves the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is convenient, the applicability is strong, and the control efficiency is high.

[0062] In some feasible implementations, the controller may include a signal generation unit, a voltage control unit, and a drive control unit. See also... Figure 4 , Figure 4 This is another structural schematic diagram of the photovoltaic inverter provided in the embodiments of this application. For example... Figure 4 As shown, the controller 302 may include a signal generation unit 3020, a voltage control unit 3021, and a drive control unit 3022. The signal generation unit 3020 can be connected to the voltage control unit 3021 and the acquisition circuit 301. The voltage control unit 3021 can be connected to the conversion circuit 303 through the drive control unit 3022. The signal generation unit 3020 can generate even-order harmonic amplitude signals based on the positive and negative DC bus voltages, generate even-order harmonic phase signals based on the phase of the photovoltaic inverter's output voltage, and generate even-order harmonic voltage regulation signals based on the even-order harmonic amplitude and phase signals. The voltage control unit 3021 can generate voltage command signals for the conversion circuit 303 based on the even-order harmonic voltage regulation signals. The drive control unit 3022 can generate drive control signals based on the voltage command signals of the conversion circuit 303, and control the switching transistors in the conversion circuit 303 to turn on or off based on the drive control signals. It is understandable that the photovoltaic inverter here can generate a voltage command signal for the conversion circuit 303 based on the even harmonic voltage regulation signal. Then, the photovoltaic inverter can generate a drive control signal based on the voltage command signal, and control the switching transistors in the conversion circuit 303 to turn on or off based on the drive control signal. This allows the conversion circuit 303 to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient.

[0063] In some feasible implementations, the voltage control unit 3021 can also be used to acquire the fundamental frequency command from an external central control system. Here, the voltage control unit 3021 can also be used to superimpose the fundamental frequency command and the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit 303. It can be understood that the photovoltaic inverter here can acquire the fundamental frequency command sent by the external central control system, directly obtain the fundamental frequency signal based on the fundamental frequency command, or obtain the fundamental frequency signal through calculation, and then superimpose and modulate the fundamental frequency signal with the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit 303. Subsequently, the drive control unit 3022 can generate a drive control signal based on the voltage command signal, and control the switching transistors in the conversion circuit 303 to turn on or off based on the drive control signal. The structure is simple, the control method is convenient, and the control efficiency is high.

[0064] In some feasible implementations, the controller may also include a voltage feedback unit, as detailed in the following documents. Figure 5 , Figure 5 This is another structural schematic diagram of the photovoltaic inverter provided in the embodiments of this application. For example... Figure 5 As shown, the controller 402 may further include a voltage feedback unit 4023. This voltage feedback unit 4023 can be connected to the acquisition circuit 401 and the voltage control unit 4021. Wherein, Figure 5 The acquisition circuit 401 and signal generation unit 4020 are the same as those mentioned above. Figure 4 The connection method and working principle of the acquisition circuit 301 and the signal generation unit 3020 are the same, and will not be described again here. The voltage feedback unit 4023 can be used to acquire the output voltage of the photovoltaic inverter through the acquisition circuit 401 and use the output voltage of the photovoltaic inverter as a voltage feedback signal. The voltage control unit 4021 can also generate a first-level voltage command signal based on the voltage feedback signal and the voltage command signal of the conversion circuit 403. The drive control unit 4022 can also generate a drive control signal based on the first-level voltage command signal. It can be understood that the voltage control unit 4021 can be a voltage control loop, and the voltage feedback unit 4023 can acquire the output voltage of the photovoltaic inverter and input the output voltage of the photovoltaic inverter as a voltage feedback signal to the voltage control unit. The voltage control unit can then compare and adjust the voltage feedback signal with the voltage command signal to generate a first-level voltage command signal (i.e., the voltage command signal adjusted based on the voltage feedback signal). Furthermore, the drive control unit 4022 can also generate a drive control signal based on the first-level voltage command signal and control the switching transistors in the conversion circuit 403 to turn on or off based on the drive control signal.

[0065] The implementation method provided in this application enables the conversion circuit to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output voltage of the photovoltaic inverter as a voltage feedback signal, resulting in high control efficiency.

[0066] In some feasible implementations, the controller may also include a current control unit and a current feedback unit. See details below. Figure 6 , Figure 6 This is another structural schematic diagram of the photovoltaic inverter provided in the embodiments of this application. For example... Figure 6 As shown, the controller 502 may further include a current control unit 5024 and a current feedback unit 5025. Here, the current control unit 5024 can be connected to the voltage control unit 5021 and the drive control unit 5022, and the current feedback unit 5025 can be connected to the acquisition circuit 501 and the current control unit 5024. Figure 6 The acquisition circuit 501 and the aforementioned Figure 5 The connection method and working principle of the acquisition circuit 401 are the same, and will not be described again here. The current feedback unit 5025 here can obtain the output current of the photovoltaic inverter through the acquisition circuit 501 and use the output current of the photovoltaic inverter as a current feedback signal. The current control unit 5024 here can generate a secondary voltage command signal based on the primary voltage command signal output by the voltage control unit 5021 and the current feedback signal. The drive control unit 5022 here can also generate a drive control signal based on the secondary voltage command signal. It can be understood that the current control unit 5024 here can be a current control loop. The current feedback unit 5025 can obtain the output current of the photovoltaic inverter and input the output current of the photovoltaic inverter as a current feedback signal to the current control unit 5024. Then, the current control unit 5024 can compare and adjust the current feedback signal with the primary voltage command signal output by the voltage control unit 5021 to generate a secondary voltage command signal (that is, the voltage command signal adjusted based on the voltage feedback signal and the current feedback signal). Here, the drive control unit 5022 can also generate a drive control signal based on the secondary voltage command signal, and control the switching transistor in the conversion circuit 503 to turn on or off based on the drive control signal.

[0067] The implementation method provided in this application enables the conversion circuit to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output current of the photovoltaic inverter as the current feedback signal, resulting in high control efficiency.

[0068] In some feasible implementations, the drive control unit 5022 may also be connected to the signal generation unit 5020. Here, the drive control unit 5022 can also be used to acquire the even-order harmonic voltage regulation signal from the signal generation unit 5020, and generate a drive control signal based on the even-order harmonic voltage regulation signal and the secondary voltage command signal. Alternatively, the drive control unit 5022 can acquire the even-order harmonic voltage regulation signal from the signal generation unit 5020 and the fundamental signal generated based on the fundamental command from an external central control system (or it can directly acquire the signal resulting from the superposition of the even-order harmonic voltage regulation signal and the fundamental signal), and generate a drive control signal based on the even-order harmonic voltage regulation signal, the fundamental signal, and the secondary voltage command signal. It can be understood that the drive control unit 5022 here can be a PWM wave generation circuit or a circuit for generating other types of modulated signals, or it can be a combination circuit of a PWM wave generation circuit or a circuit for generating other types of modulated signals and a switching transistor drive circuit. The drive control unit 5022 here can acquire the even-order harmonic voltage regulation signal output by the signal generation unit 5020, and then the drive control unit 5022 can generate a drive control signal based on the even-order harmonic voltage regulation signal and the secondary voltage command signal. In some feasible embodiments, when the photovoltaic inverter does not include the current control unit 5024 and the current feedback unit 5025, the drive control unit 5022 can also generate a drive control signal based on the even-order harmonic voltage regulation signal and the primary voltage command signal (that is, the voltage command signal adjusted by the voltage control unit 5021 based on the voltage feedback signal transmitted by the voltage feedback unit 5023).

[0069] The implementation method provided in this application enables the conversion circuit to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the drive control unit can further generate a drive control signal based on the even-order harmonic voltage adjustment signal and the secondary voltage command signal. This is equivalent to adding an even-order harmonic component to the drive control signal, further maintaining the midpoint balance of the conversion circuit and achieving high control efficiency.

[0070] In some feasible implementation methods, please refer to [the document / reference]. Figure 7 , Figure 7 This is a schematic diagram of the power supply system provided in an embodiment of this application. For example... Figure 7 As shown, the power supply system is applicable to the power supply system, which also includes a power source and a photovoltaic inverter. The photovoltaic inverter described here is applicable to the aforementioned... Figures 1 to 6 Any of the power supply systems shown, or the photovoltaic inverters within those systems, Figure 7 China only Figure 6 The photovoltaic inverter shown is used as an example for illustration. It can be understood that... Figure 7The signal generation unit 6020, voltage control unit 6021, drive control unit 6022, voltage feedback unit 6023, current control unit 6024, and current feedback unit 6025 in the acquisition circuit 601 and controller 602 are the same as those mentioned above. Figure 6 The connection method and working principle of the signal generation unit 5020, voltage control unit 5021, drive control unit 5022, voltage feedback unit 5023, current control unit 5024, and current feedback unit 5025 in the acquisition circuit 501 and controller 502 are the same, and will not be repeated here. Figure 7 The power supply system shown may also include a transformer 604, which can connect the conversion circuit 603 and the load. Please refer to further details. Figure 7 The power supply system may also include a grid connection device 605, through which the conversion circuit 603 can supply power to electrical equipment or power transmission equipment such as transmission lines, power transfer stations, batteries, communication base stations or household appliances in the load.

[0071] In this application, the photovoltaic inverter, power supply system, and functional modules within the power supply system are arranged in diverse and flexible ways to adapt to different power supply environments, thereby increasing the diversity of application scenarios and enhancing the adaptability of the power supply system. Meanwhile, the aforementioned... Figures 1 to 7 Any of the power supply systems or photovoltaic inverters shown can control the on or off time of the switching transistors in the conversion circuit. While controlling the target output voltage of the conversion circuit, it reduces the difference between the positive and negative DC bus voltages, improving the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is convenient, and it has strong applicability. For ease of description, the following will use... Figure 2 The structure of the power supply system shown is used as an example to illustrate the grid connection control method provided in the embodiments of this application.

[0072] Please see Figure 8 , Figure 8 This is a flowchart illustrating the control method provided in this application. The control method provided in this application is applicable to photovoltaic inverters, which include a conversion circuit and positive and negative DC buses. One end of the positive and negative DC buses is connected to the conversion circuit, and the other end is used to connect to a power source. This control method is also applicable to the aforementioned... Figures 1 to 7 Any power supply system or photovoltaic inverter within a power supply system shown. For example... Figure 8 As shown, the control method provided in this application includes the following steps:

[0073] S701: Detects the positive DC bus voltage and negative DC bus voltage of the conversion circuit.

[0074] S702: Based on the phase of the positive DC bus voltage of the conversion circuit, the negative DC bus voltage of the conversion circuit, and the output voltage of the photovoltaic inverter, an even-order harmonic voltage regulation signal is generated, and a drive control signal is generated based on the even-order harmonic voltage regulation signal to control the switching transistors in the conversion circuit to turn on or off.

[0075] In the embodiments provided in this application, the photovoltaic inverter can generate an even-order harmonic voltage regulation signal based on the phase of the positive DC bus voltage, negative DC bus voltage, and output voltage of the conversion circuit. Furthermore, the photovoltaic inverter can generate a drive control signal based on the even-order harmonic voltage regulation signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. Here, the drive control signal generated based on the even-order harmonic voltage regulation signal can control the conversion circuit to output an output voltage containing even-order harmonics. The even-order harmonics in the output voltage generate an output current containing even-order harmonic components through the load. The even-order harmonic components in the output current can interact with the fundamental component in the drive control signal, and / or the even-order harmonic components in the drive control signal can interact with the fundamental component in the output current, thereby adjusting the midpoint potential of the conversion circuit to maintain a balanced midpoint potential.

[0076] By adopting this application, the photovoltaic inverter can reduce the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit while controlling the output target voltage of the conversion circuit, thereby improving the voltage stability at the midpoint of the conversion circuit. It has a simple structure, convenient control method, and strong applicability.

[0077] In some feasible implementations, the conversion circuit may include two sets of capacitors and at least one switching bridge arm. The method for detecting the positive DC bus voltage and negative DC bus voltage of the conversion circuit in step S701 may include: detecting the positive DC bus voltage and negative DC bus voltage based on the potential of the positive DC bus, the potential of the negative DC bus, and the potential of the midpoint of the conversion circuit. This method features simple connection, convenient detection, and high detection efficiency.

[0078] In some feasible implementation methods, please refer to [the document / reference]. Figure 9 , Figure 9 This is another flowchart illustrating the control method provided in this application. For example... Figure 9 As shown, the generation of even-order harmonic voltage regulation signals based on the phase of the positive DC bus voltage of the conversion circuit, the negative DC bus voltage of the conversion circuit, and the output voltage of the photovoltaic inverter in step S701 can include the following steps:

[0079] S801: Generates even-order harmonic amplitude signals based on the positive DC bus voltage and negative DC bus voltage of the conversion circuit.

[0080] S802: Generates even-order harmonic phase signals based on the phase of the output voltage of the photovoltaic inverter.

[0081] S803: Generates even-harmonic voltage regulation signals based on even-harmonic amplitude signals and even-harmonic phase signals.

[0082] It can be understood that a photovoltaic (PV) inverter can detect the positive and negative DC bus voltages of the conversion circuit, thereby obtaining the voltage difference at the midpoint of the conversion circuit, and generating an even-order harmonic amplitude signal based on this voltage difference. The PV inverter can also detect the phase of its output voltage, and generate a corresponding even-order harmonic phase signal by multiplying the phase of the output voltage. Furthermore, the PV inverter can generate an even-order harmonic voltage regulation signal based on the even-order harmonic amplitude and phase signals, and then generate a drive control signal (e.g., a PWM wave drive control signal) based on this signal, controlling the switching transistors in the conversion circuit to turn on or off. Further, it can be understood that the even-order harmonic voltage regulation signal can be generated based on a single even-order harmonic (e.g., the second harmonic), or it can be generated by superimposing multiple even-order harmonics (e.g., the second harmonic, the fourth harmonic, etc.).

[0083] Using this application, a photovoltaic inverter can determine the amplitude of the even-order harmonic voltage regulation signal based on the positive and negative DC bus voltages of the conversion circuit, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the photovoltaic inverter's output voltage. Furthermore, a drive control signal is generated based on the even-order harmonic voltage regulation signal. While controlling the target output voltage of the conversion circuit, the difference between the positive and negative DC bus voltages of the conversion circuit is reduced, improving the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is precise and convenient, and it has strong applicability.

[0084] In some feasible implementations, the generation of even-order harmonic phase signals based on the phase of the photovoltaic inverter's output voltage in step S802 may include: detecting the phase of the photovoltaic inverter's output voltage and the phase of the photovoltaic inverter's output current. The load type is determined based on the phase of the photovoltaic inverter's output voltage and the phase of the photovoltaic inverter's output current, and an even-order harmonic phase signal is generated based on the phase of the photovoltaic inverter's output voltage and the load type. The load type can be one or more of inductive, capacitive, and / or resistive loads. It can be understood that the photovoltaic inverter can detect the phase of its output voltage and the phase of its output current through a data acquisition circuit, and then determine the load type based on the phase of the photovoltaic inverter's output voltage and the phase of its output current. Here, the adjustment effect of different phases varies for different types of loads. In other words, for different types of loads, the photovoltaic inverter can generate a first phase for resistive loads, a second phase for capacitive loads, a third phase for inductive loads, or a fourth phase for mixed load types. Alternatively, it can superimpose the first, second, or third phases according to weights to generate a new phase (e.g., a fifth phase) for mixed load types. This new phase is then multiplied by the phase of the photovoltaic inverter's output voltage and superimposed with the first, second, third, fourth, or fifth phases to generate an even-order harmonic phase signal. Furthermore, the photovoltaic inverter can also determine its output power (including active and reactive power) based on its output voltage and current, and determine the load type based on the signs of the active and reactive power in the conversion circuit. Alternatively, the photovoltaic inverter can determine the power factor of the conversion circuit based on its output voltage and current, and determine the load type based on the power factor, depending on the application scenario. Here, the photovoltaic inverter can generate an even harmonic voltage regulation signal based on the even harmonic amplitude signal and the even harmonic phase signal. The even harmonic voltage regulation signal can be generated based on one even harmonic (e.g., the second harmonic, etc.) or it can be generated based on the superposition of multiple even harmonics (e.g., the second harmonic, the fourth harmonic, etc.).

[0085] Using this application, a photovoltaic inverter can determine the load type based on the phase of its output voltage and the phase of its output current, and determine the phase of the even-order harmonic voltage regulation signal based on the phase of the output voltage and the load type. Then, a drive control signal is generated based on the even-order harmonic voltage regulation signal. In other words, the photovoltaic inverter can generate targeted drive control signals based on different load types, thereby reducing the difference between the positive and negative DC bus voltages of the conversion circuit while controlling the target output voltage of the conversion circuit. This improves the voltage stability at the midpoint of the conversion circuit. The structure is simple, the control method is convenient, the applicability is strong, and the control efficiency is high.

[0086] In some feasible implementations, the step S702 above, which generates a drive control signal based on the even-order harmonic voltage regulation signal, may include: generating a voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal. The drive control signal is then generated based on the voltage command signal of the conversion circuit. It can be understood that the photovoltaic inverter here can generate a voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal, and further, the photovoltaic inverter can generate a drive control signal based on the voltage command signal. The drive control signal is then used to control the switching transistors in the conversion circuit to turn on or off, ensuring that the conversion circuit maintains a stable midpoint voltage while outputting the target voltage. This method is simple in structure and convenient in control.

[0087] In some feasible implementations, the step S702 above, which generates the voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal, may include: detecting the fundamental frequency command from an external central control system; and superimposing the fundamental frequency command and the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit. It can be understood that the photovoltaic inverter here can detect the fundamental frequency command sent by the external central control system, directly obtain the fundamental frequency signal based on the fundamental frequency command, or obtain the fundamental frequency signal through calculation, and then superimpose and modulate the fundamental frequency signal with the even-order harmonic voltage regulation signal to obtain the voltage command signal for the conversion circuit. Furthermore, the photovoltaic inverter can generate a drive control signal based on the voltage command signal, and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal. This method is simple in structure, convenient in control method, and highly efficient in control.

[0088] In some feasible implementations, after generating the voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal in step S702, the method may further include: detecting the output voltage of the photovoltaic inverter and using the output voltage of the photovoltaic inverter as a voltage feedback signal; generating a first-level voltage command signal based on the voltage feedback signal and the voltage command signal of the conversion circuit; and generating a drive control signal based on the first-level voltage command signal. It can be understood that the photovoltaic inverter can detect its output voltage and use it as a voltage feedback signal. The photovoltaic inverter can then adjust the voltage command signal based on a comparison between the voltage feedback signal and the voltage command signal to generate the first-level voltage command signal (i.e., the voltage command signal adjusted based on the voltage feedback signal). Furthermore, the photovoltaic inverter can also generate a drive control signal based on the first-level voltage command signal and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal.

[0089] The implementation method provided in this application enables the conversion circuit to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output voltage of the photovoltaic inverter as a voltage feedback signal, resulting in high control efficiency.

[0090] In some feasible implementations, after generating a first-level voltage command signal based on the voltage feedback signal and the voltage command signal from the conversion circuit, the method may further include: detecting the output current of the photovoltaic inverter and using the output current of the photovoltaic inverter as a current feedback signal; generating a second-level voltage command signal based on the first-level voltage command signal and the current feedback signal; and generating a drive control signal based on the second-level voltage command signal. It can be understood that the photovoltaic inverter can detect its output current and use it as a current feedback signal. The photovoltaic inverter can then adjust itself based on the current feedback signal and the first-level voltage command signal to generate the second-level voltage command signal (i.e., the voltage command signal adjusted based on the voltage feedback signal and the current feedback signal). Here, the photovoltaic inverter can also generate a drive control signal based on the second-level voltage command signal and control the switching transistors in the conversion circuit to turn on or off based on the drive control signal.

[0091] The implementation method provided in this application enables the conversion circuit to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the photovoltaic inverter can adjust the drive control signal in real time based on the output current of the photovoltaic inverter as the current feedback signal, resulting in high control efficiency.

[0092] In some feasible implementations, after generating the secondary voltage command signal based on the primary voltage command signal and the current feedback signal, the method may further include: detecting the even-order harmonic voltage regulation signal of the signal generation unit, and generating a drive control signal based on the even-order harmonic voltage regulation signal and the secondary voltage command signal. Here, the photovoltaic inverter can also detect the even-order harmonic voltage regulation signal and the fundamental signal generated based on the fundamental command from an external central control system (or it can directly detect the signal resulting from the superposition of the even-order harmonic voltage regulation signal and the fundamental signal), and generate the drive control signal based on the even-order harmonic voltage regulation signal, the fundamental signal, and the secondary voltage command signal. It can be understood that the photovoltaic inverter can generate the drive control signal based on the even-order harmonic voltage regulation signal and the secondary voltage command signal. Here, when there is no current control unit in the photovoltaic inverter, the drive control unit can also generate the drive control signal based on the even-order harmonic voltage regulation signal and the primary voltage command signal.

[0093] The implementation method provided in this application enables the conversion circuit to maintain a stable midpoint voltage while outputting the target voltage. The structure is simple and the control method is convenient. At the same time, the drive control unit can further generate a drive control signal based on the even-order harmonic voltage adjustment signal and the secondary voltage command signal. This is equivalent to adding an even-order harmonic component to the drive control signal, further maintaining the midpoint balance of the conversion circuit and achieving high control efficiency.

[0094] In this application, the photovoltaic inverter can reduce the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit while controlling the output target voltage of the conversion circuit, thereby improving the voltage stability at the midpoint of the conversion circuit. It has a simple structure, a convenient control method, and strong applicability.

[0095] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A photovoltaic inverter for use in a power supply system, characterized in that, The photovoltaic inverter includes a conversion circuit, a data acquisition circuit, and a controller; The input terminal of the conversion circuit is used to connect to the power supply through the positive DC bus and the negative DC bus, and the output terminal of the conversion circuit is used to connect to the load. The acquisition circuit is used to acquire the positive DC bus voltage and the negative DC bus voltage of the conversion circuit. The controller is used to generate even-order harmonic amplitude signals based on the positive DC bus voltage and the negative DC bus voltage, generate multiple even-order harmonic phase signals with different phases based on the phases corresponding to the inductive load, capacitive load, and / or resistive load of the photovoltaic inverter, generate multiple even-order harmonic voltage adjustment signals based on the even-order harmonic amplitude signals and the multiple even-order harmonic phase signals with different phases, and superimpose the multiple even-order harmonic voltage adjustment signals according to weights to obtain an even-order harmonic voltage adjustment signal, and generate a drive control signal based on the even-order harmonic voltage adjustment signal to control the switching transistors in the conversion circuit to turn on or off, so as to control the output target voltage of the conversion circuit and reduce the difference between the positive DC bus voltage and the negative DC bus voltage.

2. The photovoltaic inverter according to claim 1, characterized in that, The conversion circuit includes two sets of capacitors and at least one switching bridge arm. Each switching bridge arm includes multiple switching transistors. The two sets of capacitors are connected in series and then connected in parallel with the at least one switching bridge arm between the positive DC bus and the negative DC bus of the conversion circuit. The series connection point of the two sets of capacitors is the midpoint of the conversion circuit. The input terminal of the acquisition circuit is connected to the positive DC bus, the negative DC bus, and the midpoint of the conversion circuit. The acquisition circuit is used to acquire the positive DC bus voltage and the negative DC bus voltage of the conversion circuit based on the potential of the positive DC bus, the potential of the negative DC bus, and the potential of the midpoint of the conversion circuit.

3. The photovoltaic inverter according to claim 1 or 2, characterized in that, The controller includes a signal generation unit, a voltage control unit, and a drive control unit. The signal generation unit is connected to the acquisition circuit and the voltage control unit, and the voltage control unit is connected to the conversion circuit through the drive control unit. The signal generation unit is used to generate even-order harmonic amplitude signals based on the positive DC bus voltage and the negative DC bus voltage, generate multiple even-order harmonic phase signals of different phases based on the phases corresponding to the inductive load, capacitive load and / or resistive load of the photovoltaic inverter, and generate multiple even-order harmonic voltage regulation signals based on the even-order harmonic amplitude signals and the multiple even-order harmonic phase signals of different phases, and superimpose the multiple even-order harmonic voltage regulation signals according to weights to obtain an even-order harmonic voltage regulation signal. The voltage control unit is used to generate a voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal; The drive control unit is used to generate the drive control signal based on the voltage command signal of the conversion circuit, and to control the switching transistors in the conversion circuit to be turned on or off based on the drive control signal.

4. The photovoltaic inverter according to claim 3, characterized in that, The voltage control unit is also used to acquire the fundamental frequency command from the external central control system; The voltage control unit is also used to superimpose the fundamental wave command and the even harmonic voltage adjustment signal to obtain the voltage command signal of the conversion circuit.

5. The photovoltaic inverter according to claim 4, characterized in that, The controller further includes a voltage feedback unit, which is connected to the acquisition circuit and the voltage control unit; The voltage feedback unit is used to obtain the output voltage of the photovoltaic inverter through the acquisition circuit, and use the output voltage of the photovoltaic inverter as a voltage feedback signal; The voltage control unit is also used to generate a first-level voltage command signal based on the voltage feedback signal and the voltage command signal of the conversion circuit; The drive control unit is also used to generate the drive control signal based on the first-level voltage command signal.

6. The photovoltaic inverter according to claim 5, characterized in that, The controller further includes a current control unit and a current feedback unit. The current control unit is connected to the voltage control unit and the drive control unit, and the current feedback unit is connected to the acquisition circuit and the current control unit. The current feedback unit is used to obtain the output current of the photovoltaic inverter through the acquisition circuit, and use the output current of the photovoltaic inverter as a current feedback signal; The current control unit is used to generate a second-level voltage command signal based on the first-level voltage command signal output by the voltage control unit and the current feedback signal; The drive control unit is also used to generate the drive control signal based on the secondary voltage command signal.

7. The photovoltaic inverter according to claim 6, characterized in that, The drive control unit is also connected to the signal generation unit; The drive control unit is further configured to acquire the even-order harmonic voltage adjustment signal of the signal generation unit, and generate the drive control signal based on the even-order harmonic voltage adjustment signal and the secondary voltage command signal.

8. A photovoltaic inverter control method for a photovoltaic inverter, the photovoltaic inverter including a conversion circuit and positive and negative DC buses, one end of the positive and negative DC buses being connected to the conversion circuit, and the other end of the positive and negative DC buses being used to connect to a power source, characterized in that... The method includes: The positive DC bus voltage and the negative DC bus voltage of the conversion circuit are detected. Even-order harmonic amplitude signals are generated based on the positive DC bus voltage and the negative DC bus voltage. Multiple even-order harmonic phase signals with different phases are generated based on the phases corresponding to the inductive load, capacitive load, and / or resistive load of the photovoltaic inverter. Multiple even-order harmonic voltage adjustment signals are generated based on the even-order harmonic amplitude signals and the multiple even-order harmonic phase signals with different phases. The multiple even-order harmonic voltage adjustment signals are superimposed according to weights to obtain an even-order harmonic voltage adjustment signal. A drive control signal is generated based on the even-order harmonic voltage adjustment signal to control the switching transistors in the conversion circuit to turn on or off, so as to control the output target voltage of the conversion circuit and reduce the difference between the positive DC bus voltage and the negative DC bus voltage of the conversion circuit.

9. The control method according to claim 8, characterized in that, The conversion circuit includes two sets of capacitors and at least one switching bridge arm. Each switching bridge arm includes multiple switching transistors. The two sets of capacitors are connected in series and then connected in parallel with the at least one switching bridge arm between the positive DC bus and the negative DC bus of the conversion circuit. The series connection point of the two sets of capacitors is the midpoint of the conversion circuit. Detecting the positive DC bus voltage and the negative DC bus voltage of the conversion circuit includes: The positive DC bus voltage and the negative DC bus voltage of the conversion circuit are detected based on the potential of the positive DC bus, the potential of the negative DC bus, and the potential of the midpoint of the conversion circuit.

10. The control method according to claim 8 or 9, characterized in that, The generation of the drive control signal based on the even-order harmonic voltage regulation signal includes: The voltage command signal for the conversion circuit is generated based on the even-order harmonic voltage regulation signal. The drive control signal is generated based on the voltage command signal of the conversion circuit.

11. The control method according to claim 10, characterized in that, The step of generating the voltage command signal for the conversion circuit based on the even-order harmonic voltage regulation signal includes: Detect the fundamental frequency command of the external central control system; The voltage command signal of the conversion circuit is obtained by superimposing the fundamental wave command and the even harmonic voltage adjustment signal.

Images