Photovoltaic inverter and control method thereof

Abstract

This application discloses a photovoltaic inverter and its control method, relating to the field of power electronics technology. It solves the problem of how to prevent photovoltaic power generation system instability and achieve stable operation when the system is subjected to large disturbances. The controller outputs a first pulse width modulation (PWM) signal to drive the inverter circuit when the voltage at the input terminal of the inverter circuit is less than a first voltage threshold and greater than or equal to a second voltage threshold. The second voltage threshold is greater than the voltage corresponding to the maximum power point of the photovoltaic array. The controller is further configured to, after outputting the first PWM signal, output a second PWM signal to drive the inverter circuit if a first frequency deviation is greater than or equal to a frequency deviation threshold, a second frequency deviation is less than or equal to zero, and a voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold.

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] A photovoltaic (PV) power generation system includes a PV inverter, which converts the direct current (DC) output from the PV array into alternating current (AC) and transmits it to the power grid. PV inverters can be controlled in two ways: grid-connected and grid-connected. A grid-connected PV inverter uses a grid-connected control method, while a grid-connected PV inverter uses a grid-connected control method. Grid-connected PV inverters output AC power following the voltage and frequency of the AC power in the grid, while grid-connected PV inverters actively control the voltage and frequency of their output AC power, rather than simply following the grid's AC power. Grid-connected PV inverters operate in AC voltage source mode and can provide auxiliary services such as inertia and damping to the grid, contributing to improved grid stability. The application of grid-connected PV inverters is becoming increasingly widespread.

[0003] Grid-type photovoltaic (PV) inverters require reserved power to achieve grid-connection functionality, meaning their output power is less than their maximum usable power. When the grid-type PV inverter operates to the right of the maximum power point (MPP) on the PV array's power-voltage (PV) curve, and the PV system is subjected to disturbances, it exhibits the advantage of power self-balancing. Specifically, when the PV system is disturbed and the output power of the grid-type PV inverter exceeds the output power of the PV array, the capacitors connected in parallel with the PV array in the grid-type PV inverter discharge to provide additional power. The capacitor voltage drops, the PV array's operating point shifts towards the MPP, the PV array's output power increases, the capacitors charge, and their voltage rises, thus achieving automatic balancing of the PV system and ensuring stable operation.

[0004] However, under conditions of significant disturbance, the operating point of the photovoltaic (PV) array may cross the maximum potential power output (MPP) and reach the left side of the MPP. The output power of the PV array will continuously decrease as the capacitor discharges, and the capacitor voltage will also continuously decrease, leading to instability in the PV system. Therefore, how to prevent instability and achieve stable operation of the PV system under significant disturbances has become an urgent problem to solve. Summary of the Invention

[0005] This application provides a photovoltaic inverter and its control method, which solves the problem of how to avoid instability of the photovoltaic power generation system and achieve stable operation of the photovoltaic power generation system when it is subjected to large disturbances.

[0006] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0007] A first aspect of this application provides a photovoltaic inverter, which includes a controller and an inverter circuit. The input terminal of the inverter circuit is connected to a photovoltaic array, and the output terminal of the inverter circuit is connected to a power grid or a load. The controller is configured to output a first pulse width modulation (PWM) signal to drive the inverter circuit when the voltage at the input terminal of the inverter circuit is less than a first voltage threshold and greater than or equal to a second voltage threshold. The second voltage threshold is greater than the voltage corresponding to the maximum power point of the photovoltaic array. The duty cycle of the first PWM signal is determined based on the voltage at the input terminal of the inverter circuit, the voltage at the output terminal of the inverter circuit, and the current. The controller is further configured to, after outputting the first PWM signal, output a second PWM signal to drive the inverter circuit if a first frequency deviation is greater than or equal to a frequency deviation threshold, a second frequency deviation is less than or equal to zero, and a voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold. The first frequency deviation is determined based on the voltage at the input terminal of the inverter circuit, the second frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit, the initial value of the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the voltage amplitude deviation threshold is less than or equal to zero, and the duty cycle of the second pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit.

[0008] Based on this scheme, when the voltage at the input terminal of the inverter circuit is less than the first voltage threshold and greater than or equal to the second voltage threshold, the controller adopts a DC voltage control mode to control the inverter circuit. This ensures that when the photovoltaic power generation system is subjected to large disturbances, the output power of the photovoltaic array is equal to or nearly equal to the output power of the photovoltaic inverter (which can also be considered as the actual operating power of the grid or load). This prevents the operating point of the photovoltaic array from exceeding the MPP and reaching the left side of the MPP, thus preventing instability in the photovoltaic power generation system and achieving stable operation. Simultaneously, after the controller adopts the DC voltage control mode to control the inverter circuit, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the second frequency deviation is less than or equal to zero, and the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, indicating that the large disturbance has ended and the photovoltaic power generation system is stable, the controller switches from the DC voltage control mode to the power control mode. This achieves stable operation of the photovoltaic power generation system, smooth switching of control modes, and improves the reliability of the photovoltaic power generation system.

[0009] In conjunction with the first aspect, in one possible implementation, the controller is further configured to adjust the voltage amplitude deviation and output a third pulse width modulation signal to drive the inverter circuit when the voltage at the input terminal of the inverter circuit is less than a second voltage threshold. The duty cycle of the third pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation. The controller is also configured to, after outputting the third pulse width modulation signal, if the first frequency deviation is greater than or equal to a frequency deviation threshold, the third frequency deviation is less than or equal to zero, and the adjusted voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold, output a second pulse width modulation signal to drive the inverter circuit. The third frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation.

[0010] Based on this scheme, when the voltage at the input terminal of the inverter circuit is less than the second voltage threshold, the controller adjusts the voltage amplitude deviation to reduce the amplitude of the AC output voltage of the photovoltaic inverter, thereby reducing the output power of the photovoltaic inverter and narrowing the gap between the output power of the photovoltaic inverter and the output power of the photovoltaic array. This ensures that when the photovoltaic power generation system is subjected to large disturbances, the output power of the photovoltaic array is equal to or nearly equal to the output power of the photovoltaic inverter, preventing the operating point of the photovoltaic array from exceeding the MPP and reaching the left side of the MPP, thus preventing instability of the photovoltaic power generation system and achieving stable operation. After outputting the third pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold and the third frequency deviation is less than or equal to zero, indicating the large disturbance has ended and the photovoltaic power generation system is stable, the controller stops adjusting the voltage amplitude deviation and switches to power control mode to control the inverter circuit. This achieves stable operation of the photovoltaic power generation system, smooth switching of control modes, and improves the reliability of the photovoltaic power generation system.

[0011] In conjunction with the first aspect, in one possible implementation, the controller is further configured to, before adjusting the voltage amplitude deviation, if the voltage at the input terminal of the inverter circuit is less than a third voltage threshold, subtract a preset voltage adjustment amount from the voltage amplitude deviation before adjustment to determine the voltage amplitude deviation adjusted in the current cycle. The controller is further configured to, after adjusting the voltage amplitude deviation in the previous cycle, if the voltage at the input terminal of the inverter circuit is less than the third voltage threshold, subtract the preset voltage adjustment amount from the adjusted voltage amplitude deviation to determine the voltage amplitude deviation adjusted in the current cycle. The controller is further configured to, after adjusting the voltage amplitude deviation in the previous cycle, if the voltage at the input terminal of the inverter circuit is greater than a fourth voltage threshold, add the preset voltage adjustment amount to the adjusted voltage amplitude deviation to determine the voltage amplitude deviation adjusted in the current cycle. The controller is further configured to, after adjusting the voltage amplitude deviation in the previous cycle, if the voltage at the input terminal of the inverter circuit is greater than or equal to the third voltage threshold and less than or equal to the fourth voltage threshold, use the voltage amplitude deviation adjusted in the previous cycle as the voltage amplitude deviation adjusted in the current cycle. The third voltage threshold is less than or equal to the second voltage threshold, and the fourth voltage threshold is greater than or equal to the first voltage threshold.

[0012] Based on this scheme, when the voltage at the input terminal of the inverter circuit is less than the second voltage threshold, the controller adjusts the voltage amplitude deviation to reduce the amplitude of the AC output voltage of the photovoltaic inverter, thereby reducing the output power of the photovoltaic inverter and narrowing the gap between the output power of the photovoltaic inverter and the output power of the photovoltaic array. This ensures that when the photovoltaic power generation system is subjected to large disturbances, the output power of the photovoltaic array is equal to or nearly equal to the output power of the photovoltaic inverter. This prevents the operating point of the photovoltaic array from crossing the MPP and reaching the left side of the MPP, thus preventing instability of the photovoltaic power generation system and achieving stable operation of the photovoltaic power generation system.

[0013] In conjunction with the first aspect, in one possible implementation, the controller is further configured to, within a preset time threshold, after outputting a first pulse width modulation signal, output a second pulse width modulation signal if a first frequency deviation is greater than or equal to a frequency deviation threshold, a second frequency deviation is less than or equal to zero, and a voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold. The controller is further configured to, within a preset time threshold, after outputting a third pulse width modulation signal, if a first frequency deviation is greater than or equal to a frequency deviation threshold, a third frequency deviation is less than or equal to zero, and an adjusted voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold, output a second pulse width modulation signal.

[0014] Based on this scheme, when the controller determines that the conditions are met within a preset time threshold, it outputs a second pulse width modulation signal, which can avoid controller malfunctions when large disturbances have not ended, improve the reliability of the photovoltaic power generation system, and achieve smooth switching of control modes.

[0015] A second aspect of this application provides a control method for a photovoltaic inverter, applied to a photovoltaic inverter including an inverter circuit. The input terminal of the inverter circuit is connected to a photovoltaic array, and the output terminal of the inverter circuit is connected to a power grid or a load. The method includes: when the voltage at the input terminal of the inverter circuit is less than a first voltage threshold and greater than or equal to a second voltage threshold, outputting a first pulse width modulation signal to drive the inverter circuit to operate. The second voltage threshold is greater than the voltage corresponding to the maximum power point of the photovoltaic array. The duty cycle of the first pulse width modulation signal is determined based on the voltage at the input terminal of the inverter circuit, the voltage at the output terminal of the inverter circuit, and the current. After outputting the first pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the second frequency deviation is less than or equal to zero, and the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the second pulse width modulation signal is output to drive the inverter circuit to work. The first frequency deviation is determined based on the voltage at the input terminal of the inverter circuit, the second frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit, the initial value of the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the voltage amplitude deviation threshold is less than or equal to zero, and the duty cycle of the second pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit.

[0016] In conjunction with the second aspect, in one possible implementation, the method further includes: when the voltage at the input terminal of the inverter circuit is less than a second voltage threshold, adjusting the voltage amplitude deviation and outputting a third pulse width modulation signal to drive the inverter circuit, wherein the duty cycle of the third pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation. After outputting the third pulse width modulation signal, if the first frequency deviation is greater than or equal to a frequency deviation threshold, the third frequency deviation is less than or equal to zero, and the adjusted voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold, outputting a second pulse width modulation signal to drive the inverter circuit, wherein the third frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation.

[0017] In conjunction with the second aspect, in one possible implementation, the aforementioned adjustment of voltage amplitude deviation includes: If, before adjusting the voltage amplitude deviation, the voltage at the input terminal of the inverter circuit is less than a third voltage threshold, subtract a preset voltage adjustment amount from the voltage amplitude deviation before adjustment to determine the voltage amplitude deviation after adjustment in the current cycle. If, after adjusting the voltage amplitude deviation in the previous cycle, the voltage at the input terminal of the inverter circuit is less than the third voltage threshold, subtract the preset voltage adjustment amount from the adjusted voltage amplitude deviation to determine the voltage amplitude deviation after adjustment in the current cycle. If, after adjusting the voltage amplitude deviation in the previous cycle, the voltage at the input terminal of the inverter circuit is greater than a fourth voltage threshold, add the preset voltage adjustment amount to the adjusted voltage amplitude deviation to determine the voltage amplitude deviation after adjustment in the current cycle. If, after adjusting the voltage amplitude deviation in the previous cycle, the voltage at the input terminal of the inverter circuit is greater than or equal to the third voltage threshold and less than or equal to the fourth voltage threshold, use the voltage amplitude deviation after adjustment in the previous cycle as the voltage amplitude deviation after adjustment in the current cycle. The third voltage threshold is less than or equal to the second voltage threshold, and the fourth voltage threshold is greater than or equal to the first voltage threshold.

[0018] In conjunction with the second aspect, in one possible implementation, the method further includes: within a preset time threshold, after outputting a first pulse width modulation signal, if a first frequency deviation is greater than or equal to a frequency deviation threshold, a second frequency deviation is less than or equal to zero, and a voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold, then outputting a second pulse width modulation signal. Within a preset time threshold, after outputting a third pulse width modulation signal, if the first frequency deviation is greater than or equal to a frequency deviation threshold, the third frequency deviation is less than or equal to zero, and the adjusted voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold, then outputting a second pulse width modulation signal.

[0019] A third aspect of this application provides a photovoltaic power generation system, which includes a photovoltaic inverter. The input terminal of the photovoltaic inverter is used to connect to a photovoltaic array, and the output terminal of the photovoltaic inverter is used to connect to a power grid or a load. The photovoltaic inverter is the photovoltaic inverter described in the first aspect or any possible implementation thereof.

[0020] The descriptions of the second and third aspects in this application can be referenced to the detailed description of the first aspect; and the beneficial effects of the second and third aspects can be referenced to the analysis of the beneficial effects of the first aspect, which will not be repeated here. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating an application scenario of a photovoltaic inverter provided in an embodiment of this application;

[0022] Figure 2A schematic diagram of the power-voltage curve of a photovoltaic array provided in an embodiment of this application;

[0023] Figure 3 A schematic diagram of a process for generating a pulse width modulation signal is provided for an embodiment of this application;

[0024] Figure 4 A schematic diagram illustrating another process for generating a pulse width modulation signal, provided in an embodiment of this application;

[0025] Figure 5 A schematic diagram illustrating another process for generating a pulse width modulation signal, provided in an embodiment of this application;

[0026] Figure 6 A schematic diagram of a process for adjusting voltage amplitude deviation provided in an embodiment of this application;

[0027] Figure 7 A waveform diagram of the voltage at the input terminal of an inverter circuit provided in an embodiment of this application;

[0028] Figure 8 A schematic diagram of the power-voltage curve of another photovoltaic array provided in an embodiment of this application;

[0029] Figure 9 A waveform diagram of the voltage at the input terminal of another inverter circuit provided in an embodiment of this application;

[0030] Figure 10 A waveform diagram of a second frequency deviation provided in an embodiment of this application;

[0031] Figure 11 A waveform diagram of a first frequency deviation provided in an embodiment of this application;

[0032] Figure 12 A waveform diagram of the active power output of an inverter circuit provided in an embodiment of this application;

[0033] Figure 13 A schematic diagram of the power-voltage curve of another photovoltaic array provided in the embodiments of this application;

[0034] Figure 14 A waveform diagram of the voltage at the input terminal of another inverter circuit provided in an embodiment of this application;

[0035] Figure 15 A waveform diagram of another second frequency deviation provided in an embodiment of this application;

[0036] Figure 16 A waveform diagram of another first frequency deviation provided in an embodiment of this application;

[0037] Figure 17 A waveform diagram of the active power output of another inverter circuit provided in an embodiment of this application;

[0038] Figure 18 A waveform diagram of the voltage at the input terminal of another inverter circuit provided in an embodiment of this application;

[0039] Figure 19 A waveform diagram of a third frequency deviation provided in an embodiment of this application;

[0040] Figure 20 A waveform diagram illustrating yet another first frequency deviation provided in an embodiment of this application;

[0041] Figure 21 A waveform diagram of voltage amplitude deviation is provided for an embodiment of this application;

[0042] Figure 22 A waveform diagram of the active power output of another inverter circuit provided in an embodiment of this application;

[0043] Figure 23 This is a flowchart illustrating a control method for a photovoltaic inverter provided in an embodiment of this application. Detailed Implementation

[0044] The following sections will discuss the fabrication and use of various embodiments in detail. However, it should be understood that many applicable inventive concepts provided in this application can be implemented in a variety of specific environments. The specific embodiments discussed are merely illustrative of specific ways of implementing and using this description and technology, and do not limit the scope of this application.

[0045] Unless otherwise defined, all technical terms used herein have the same meaning as commonly known to one of ordinary skill in the art.

[0046] Each circuit or other component may be described or referred to as "for" performing one or more tasks. In this context, "for" is used to imply a structure by indicating that the circuit / component includes a structure (e.g., a circuit system) that performs one or more tasks during operation. Therefore, even when the specified circuit / component is currently inoperable (e.g., not turned on), it can still be referred to as "for performing that task." Circuits / components used with the term "for" include hardware, such as circuits that perform operations.

[0047] In the embodiments of this application, the terms "first," "second," etc., do not limit the quantity or order. In this application, words such as "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design described as "exemplary" or "for example" in this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0048] Before introducing the embodiments of this application, the background technology involved in this application will be introduced first.

[0049] like Figure 1 The diagram illustrates an application scenario of a photovoltaic inverter 100. This photovoltaic inverter 100 can be applied to a photovoltaic power generation system 200. The input terminal of the photovoltaic inverter 100 is connected to a photovoltaic array 300, and the output terminal is connected to the power grid or a load 400. The photovoltaic array 300 converts solar energy into direct current (DC), and the photovoltaic inverter 100 converts this DC into alternating current (AC) and transmits it to the power grid or the load 400.

[0050] Reference Figure 1 The photovoltaic inverter 100 has a positive input terminal and a negative input terminal. The inverter 100 includes an inverter circuit 110, which includes a first capacitor C1, a first switching bridge arm, and a second switching bridge arm disposed between the positive and negative input terminals. The midpoint of the first and second switching bridge arms is used for connection to the grid or the two ends of the load 400. The first switching bridge arm includes a first switching transistor Q1 and a second switching transistor Q2 connected in series. The second switching bridge arm includes a third switching transistor Q3 and a fourth switching transistor Q4 connected in series. This inverter circuit 110 can be referred to as an H4 bridge inverter circuit. Each switching transistor can include a metal-oxide-semiconductor field-effect transistor (MOSFET), which can also be simply referred to as a MOS transistor. Each MOS transistor includes a reverse-biased body diode. Alternatively, refer to... Figure 1 Taking the first switching transistor Q1 as an example, each switching transistor may include an insulated-gate bipolar transistor (IGBT) and a diode D. The collector of the IGBT is connected to the negative terminal of the diode D, and the emitter of the IGBT is connected to the positive terminal of the diode D. In this embodiment of the application, each switching transistor includes an IGBT and a diode D as an example for illustrative purposes.

[0051] Continue to refer to Figure 1The photovoltaic inverter 100 may also include a first inductor L1, a second capacitor C2, and a second inductor L2. The first inductor L1 and the second inductor L2 are connected in series and are positioned between the midpoint of the first switching bridge arm and one end of the power grid or load 400. The midpoint of the second switching bridge arm is connected to the other end of the power grid or load 400. The second capacitor C2 is positioned between the connection point of the first inductor L1 and the second inductor L2 and the midpoint of the second switching bridge arm. The circuit composed of the first inductor L1, the second capacitor C2, and the second inductor L2 can be called an LCL filter.

[0052] When the photovoltaic inverter 100 is controlled using a grid-based control method, it can be called a grid-based photovoltaic inverter. It should be understood that a grid-based photovoltaic inverter is a current-source inverter, primarily controlling the output current, while a grid-based photovoltaic inverter is a voltage-source inverter, primarily controlling the output voltage. The output voltage and phase of the grid-based inverter can be controlled autonomously. To achieve grid-based functionality, the photovoltaic inverter 100 needs to reserve power; at this time, the output power of the photovoltaic inverter 100 is less than its maximum usable power. When the photovoltaic inverter 100 operates to the right of the MPP (Maximum Power Point) of the photovoltaic array 300, and the photovoltaic power generation system 200 is subjected to disturbances, the photovoltaic power generation system 200 has the advantage of power self-balancing.

[0053] Specifically, such as Figure 2 The image shows a schematic diagram of the power-voltage curve of a photovoltaic array 300. This schematic diagram of the power-voltage curve of the photovoltaic array 300 can also be called a schematic diagram of the operating point of the photovoltaic array 300, where "1 kilowatt / square meter (KW / m)" is used. 2 ")" represents the power density of photovoltaic array 300, which can be used to indicate the light intensity of photovoltaic array 300. "V" mpp "This refers to the voltage corresponding to the MPP of the photovoltaic array 300. When the photovoltaic inverter 100 is operating to the right of the MPP of the photovoltaic array 300, for example, at operating point a, and the photovoltaic power generation system 200 is disturbed, and the output power of the photovoltaic inverter 100 is greater than the output power of the photovoltaic array 300, the first capacitor C1 in the photovoltaic inverter 100 discharges to provide additional power. The voltage of the first capacitor C1 drops, which will cause the operating point of the photovoltaic array 300 to shift towards the MPP, for example, from operating point a to operating point b. At this time, operating point b is still located to the right of the MPP. Refer to..." Figure 2Understandably, compared to when the photovoltaic array 300 operates at operating point a, when the photovoltaic array 300 operates at operating point b, the output power of the photovoltaic array 300 increases, the first capacitor C1 will charge, and the voltage of the first capacitor C1 will increase. If the output power of the photovoltaic array 300 is equal to or substantially equal to the output power of the photovoltaic inverter 100 (which can also be considered as the actual operating power of the grid or load 400) when the photovoltaic array 300 operates at operating point b, the operating point of the photovoltaic array 300 will no longer move, thereby achieving automatic balancing of the photovoltaic power generation system 200 and ensuring stable operation of the photovoltaic power generation system 200.

[0054] However, when the photovoltaic power generation system 200 is subjected to a large disturbance, such as a sudden decrease in the light intensity of the photovoltaic array 300 due to shading; or a significant drop in the grid frequency due to load switching, grid phase transitions, or grid faults (where "switching" refers to the load being connected to the grid and "disconnection" refers to the load being disconnected from the grid); or a sudden increase in load power due to the addition of new loads, the operating point of the photovoltaic array 300 will cross the MPP and reach the left side of the MPP, for example... Figure 2 Operating point c. The output power of photovoltaic array 300 will continuously decrease as the first capacitor C1 discharges, and the voltage of the first capacitor C1 will also continuously decrease, leading to instability of photovoltaic power generation system 200. Therefore, how to avoid instability of photovoltaic power generation system 200 and achieve stable operation of photovoltaic power generation system 200 under large disturbances has become an urgent problem to be solved.

[0055] Based on this, this application provides a photovoltaic inverter, the circuit topology of which can be as described above. Figure 1 The circuit topology of the photovoltaic inverter 100 shown is as follows. In the following embodiments of this application, the circuit topology of the photovoltaic inverter is as follows: Figure 1 Taking the circuit of the photovoltaic inverter 100 shown as an example, the solution of this application will be illustrated by way of example. The photovoltaic inverter 100 provided in this application embodiment, when controlled by a grid-type control method, and applied to the aforementioned photovoltaic power generation system 200, can ensure that the output power of the photovoltaic array 300 is equal to or substantially equal to the output power of the photovoltaic inverter 100 when the photovoltaic power generation system 200 is subjected to a large disturbance. This prevents the operating point of the photovoltaic array 300 from crossing the MPP and reaching the left side of the MPP, thereby preventing instability of the photovoltaic power generation system 200 and achieving stable operation of the photovoltaic power generation system 200. Furthermore, it is not limited by the circuit topology of the inverter circuit 110 and can be applied to photovoltaic inverters with various topologies, thus having a wide range of applications.

[0056] like Figure 1As shown, the photovoltaic inverter 100 provided in this application embodiment includes an inverter circuit 110 and a controller 120. The input terminal of the inverter circuit 110 is used to connect to the photovoltaic array 300, and the output terminal of the inverter circuit 110 is used to connect to the power grid or the load 400.

[0057] Controller 120 is used to obtain the voltage V at the input terminal of inverter circuit 110. dc The voltage V at the input terminal of inverter circuit 110 dc Less than the first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 In this case, obtain the voltage V at the output terminal of the inverter circuit 110. g and current I g It outputs a first pulse width modulation (PWM) signal to drive the inverter circuit 110 to operate, for example, referring to... Figure 1 The first pulse width modulation signal is used to drive the first switch Q1 to the fourth switch Q4 in the inverter circuit 110. The second voltage threshold V... dc_min2 The voltage greater than the maximum power point (MPP) voltage of the photovoltaic array 300, in this embodiment of the application, is for the first voltage threshold V. dc_min1 Second voltage threshold V dc_min2 The specific value is not limited; the duty cycle of the first pulse width modulation signal is determined based on the voltage V at the input terminal of the inverter circuit 110. dc The voltage V at the output terminal of inverter circuit 110 g and current I g It is confirmed that the photovoltaic inverter 100 is now operating in DC voltage control mode.

[0058] In one possible embodiment, refer to Figure 1 The controller 120 can obtain the voltage across the first capacitor C1 as the input voltage V of the inverter circuit 110. dc The controller 120 can obtain the voltage across the second capacitor C2 as the output voltage V of the inverter circuit 110. g This reduces the voltage V at the output of the inverter circuit 110. g The difficulty lies in the fact that the controller 120 can obtain the current flowing through the second inductor L2 as the output current I of the inverter circuit 110. g .

[0059] In one possible embodiment, such as Figure 3 The diagram shows a flowchart for generating a pulse width modulation signal. The controller 120 adjusts the voltage V at the input terminal of the inverter circuit 110. dc The voltage V at the output terminal of inverter circuit 110g and current I g The process of outputting the first pulse width modulation signal includes: First, the controller 120 converts the voltage V at the input terminal of the inverter circuit 110 into a signal. dc With DC voltage reference value V dc_ref The difference is calculated, and the result is processed using a proportional-integral (PI) controller to determine the first frequency deviation Δf. cv_pu The controller 120 will determine the first frequency deviation Δf cv_pu The sum is calculated with 1, and the result is used to calculate the rated angular frequency (ω0). The result of the rated angular frequency calculation is then integrated (1 / s), and the result of the integration is used to calculate a sine function (sin). Simultaneously, the controller 120 calculates the voltage V at the output terminal of the inverter circuit 110. g and current I g Calculate reactive power q c_pu The reactive power reference value q c_ref_pu With reactive power q c_pu The difference is calculated, and the result is processed using a PI controller. The processed result is then compared with 1 and the voltage amplitude deviation ΔV. m_pu Summing yields the voltage amplitude reference value V. m_ref Then, the controller 120 compares the result of the above sine function calculation (sin) with the voltage amplitude reference value V. m_ref Multiply to obtain the AC voltage reference value V g_ref The AC voltage reference value V g_ref The voltage V at the output terminal of inverter circuit 110 g The difference is calculated, and the result is processed using a proportional resonant (PR) controller to determine the current reference value I. g_ref , the current reference value I g_ref The difference between the current Ig at the output terminal of inverter circuit 110 and the current Ig is calculated. The result of the difference is processed by a PI controller. The result processed by the PI controller is then compared with the AC voltage reference value V. g_ref Summation. Finally, controller 120 divides the sum by the voltage V at the input of inverter circuit 110. dc The calculated result is then modulated to generate the aforementioned first pulse width modulation signal. In this embodiment, the aforementioned DC voltage reference value V... dc_ref and reactive power reference value q c_ref_pu The specific value is not limited.

[0060] The aforementioned first frequency deviation Δf cv_pu reactive power q c_pu Reactive power reference value q c_ref_puand voltage amplitude deviation ΔV m_pu All values ​​are per unit (PU). A per-unit (PU) value is a commonly used numerical representation method in power system analysis and calculation. A PU value is the ratio of the actual value of a physical quantity to its corresponding reference value. The unit of this ratio is PU, and it can also be considered a dimensionless relative value. The formula for calculating a PU value is: PU = Measured Value / Reference Value, where the measured value refers to the measured value, such as the voltage V at the input terminal of the inverter circuit 110 mentioned above. dc A reference value is a physical quantity that has the same unit as a named value and is used as a standard for comparison. In this application, the specific value of the reference value used in calculating each per-unit value is not limited.

[0061] In one possible embodiment, the controller 120 is further configured to, after outputting the first pulse width modulation signal, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu Second frequency deviation Δf cp_pu Voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Obtain the voltage V at the output terminal of inverter circuit 110. g and current I g It outputs a second pulse width modulation signal to drive the inverter circuit 110 to operate. The duty cycle of the second pulse width modulation signal is based on the voltage V at the output terminal of the inverter circuit 110. g and current I g It is confirmed that the photovoltaic inverter 100 is now operating in power control mode.

[0062] Among them, the aforementioned first frequency deviation Δf cv_pu According to the voltage V at the input terminal of inverter circuit 110 dc It is confirmed that, in this application embodiment, the frequency deviation threshold Δf cv_min_pu The specific value is not limited. The controller 120 determines the value based on the voltage V at the input terminal of the inverter circuit 110. dc Determine the first frequency deviation Δf cv_pu The process can be referred to above. Figure 3 The controller 120 determines the first frequency deviation Δf cv_pu The process is not described in detail in the embodiments of this application.

[0063] The aforementioned second frequency deviation Δf cp_pu According to the voltage V at the output terminal of inverter circuit 110 g and current I g Sure.

[0064] In one possible embodiment, such as Figure 4The figure shows a method for determining the second frequency deviation Δf. cp_pu The flowchart is shown. Controller 120 adjusts the voltage V at the output terminal of inverter circuit 110. g and current I g Determine the second frequency deviation Δf cp_pu The process includes: First, the controller 120 determines the voltage V at the output terminal of the inverter circuit 110. g and current I g Calculate active power P c_pu Then, controller 120 will input the active power reference value P. c_ref_pu With active power P c_pu Subtract the values ​​and then compare the result with the damping coefficient D. g Summation. Finally, the controller 120 integrates the summed result to determine the second frequency deviation Δf. cp_pu In integral operations, "H" g " is the inertia constant. In the embodiments of this application, the active power reference value P..." c_ref_pu Damping coefficient D g and inertia constant "H" g The specific value of " is not limited.

[0065] The above voltage amplitude deviation ΔV m_pu The initial value is greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Voltage amplitude deviation threshold ΔV m_min_pu Less than or equal to zero, in this application embodiment, the voltage amplitude deviation ΔV m_pu and voltage amplitude deviation threshold ΔV m_min_pu The specific value is not limited.

[0066] In one possible embodiment, such as Figure 4 The diagram shows another process for generating pulse width modulation signals. The controller 120 adjusts the voltage V at the output of the inverter circuit 110. g and current I g The process of outputting the second pulse width modulation signal includes: First, the controller 120 outputs the signal based on the voltage V at the output terminal of the inverter circuit 110. g and current I g Determine the second frequency deviation Δf cp_pu The specific process can be referred to above. The controller 120 determines the voltage V at the output terminal of the inverter circuit 110. g and current I g Determine the second frequency deviation Δf cp_pu The description of the present application embodiments will not be repeated here. Then, the controller 120 will adjust the second frequency deviation Δf cp_puThe sum is calculated by adding 1, and the result is used to calculate the rated angular frequency (ω0). The result of the rated angular frequency calculation is then integrated (1 / s), and the result of the integration is used to calculate a sine function (sin). The remaining steps of the controller 120 in generating the second pulse width modulation signal are the same as described above. Figure 3 The steps for the controller 120 to generate the first pulse width modulation signal are the same; the specific process can be referred to the above. Figure 3 The description of the first pulse width modulation signal generated by the controller 120 is not repeated here in the embodiments of this application.

[0067] In one possible embodiment, when the photovoltaic inverter 100 is connected to the grid and operates in grid-connected mode, the photovoltaic power generation system 200 is subjected to a large disturbance, and the voltage V at the input terminal of the inverter circuit 110... dc Less than the first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 In this case, the controller 120 uses the aforementioned DC voltage control mode to control the inverter circuit 110. Since it directly controls the voltage V at the input terminal of the inverter circuit 110... dc The photovoltaic power generation system 200 has better stability and is less prone to instability.

[0068] In one possible embodiment, the controller 120 is further configured to, after outputting the first pulse width modulation signal within a preset time threshold, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu Second frequency deviation Δf cp_pu Voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu The second pulse width modulation signal is output. In this embodiment, the specific value of the preset time threshold is not limited; for example, the preset time threshold can be equal to the duration of multiple consecutive cycles. Therefore, the controller 120 can switch from controlling the inverter circuit 110 using DC voltage control mode to controlling the inverter circuit 110 using power control mode when it accurately determines that a large disturbance has ended and the photovoltaic power generation system 200 is stable. This avoids malfunctions, improves the reliability of the photovoltaic power generation system 200, and enables smooth switching of control modes.

[0069] In one possible embodiment, when the photovoltaic power generation system 200 is not subjected to significant disturbances, the controller 120 in the photovoltaic inverter 100 can also be used. Figure 4 The second pulse width modulation signal is generated in the manner shown, and the inverter circuit 110 is driven by the second pulse width modulation signal.

[0070] In one possible embodiment, the circuit topology of the inverter circuit 110 can be as described above. Figure 1 The circuit topology of the inverter circuit 110 can be any other type of inverter circuit topology, and this application embodiment does not limit this.

[0071] In one possible embodiment, the controller 120 may be a microcontroller unit (MCU) or a digital signal processor (DSP), and this application embodiment does not limit this.

[0072] In the photovoltaic inverter 100 provided in this application embodiment, the voltage V at the input terminal of the controller 120 of the inverter circuit 110 is... dc Less than the first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 In the case of a large disturbance, the inverter circuit 110 is controlled using DC voltage control mode. This ensures that the output power of the photovoltaic array 300 is equal to or nearly equal to the output power of the photovoltaic inverter 100 when the photovoltaic power generation system 200 is subjected to a large disturbance. This prevents the operating point of the photovoltaic array 300 from crossing the MPP and reaching the left side of the MPP, thus preventing instability of the photovoltaic power generation system 200 and achieving stable operation. Simultaneously, after the controller 120 controls the inverter circuit 110 using DC voltage control mode, if the first frequency deviation Δf... cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu Second frequency deviation Δf cp_pu Voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Once the large disturbance has subsided and the photovoltaic power generation system 200 is stable, switching from DC voltage control mode to power control mode for the inverter circuit 110 ensures stable operation of the photovoltaic power generation system 200, achieves smooth switching of control modes, and improves the reliability of the photovoltaic power generation system 200. Furthermore, it is not limited by the circuit topology of the inverter circuit 110 and can be applied to photovoltaic inverters with various topologies, thus having a wide range of applications.

[0073] In one possible embodiment, if the controller 120 controls the inverter circuit 110 using a DC voltage control mode, the voltage V at the input terminal of the inverter circuit 110 will... dc Continue to decrease until it falls below the second voltage threshold V dc_min2 In the event of a large disturbance, or when the voltage V at the input terminal of the inverter circuit 110... dc Less than the second voltage threshold Vdc_min2 In this case, the solution also provides a control mode for controlling the photovoltaic inverter 100 to avoid instability of the photovoltaic power generation system 200.

[0074] Specifically, the controller 120 is also used to control the voltage V at the input terminal of the inverter circuit 110. dc Less than the second voltage threshold V dc_min2 In this case, adjust the voltage amplitude deviation ΔV m_pu Obtain the voltage V at the output terminal of inverter circuit 110. g and current I g It outputs a third pulse width modulation signal to drive the inverter circuit 110. The duty cycle of the third pulse width modulation signal is based on the voltage V at the output terminal of the inverter circuit 110. g and current I g Deviation ΔV from the adjusted voltage amplitude m_pu It is confirmed that the photovoltaic inverter 100 is now operating in voltage amplitude deviation control mode.

[0075] In one possible embodiment, such as Figure 5 The diagram shows another process for generating pulse width modulation (PWM) signals. The controller 120 adjusts the voltage V at the output of the inverter circuit 110. g and current I g Deviation ΔV from the adjusted voltage amplitude m_pu The process of outputting the third pulse width modulation signal includes: First, the controller 120 adjusts the voltage amplitude deviation ΔV m_pu Summing with 1 and then squaring the result, then comparing the result with the active power reference value P. c_ref_pu The result of the multiplication is used as the updated active power reference value P*. c_ref_pu Then, the controller 120 determines the voltage V at the output of the inverter circuit 110. g and current I g Calculate active power P c_pu and reactive power q c_pu The active power P c_pu Compared with the updated active power reference value P* c_ref_pu Subtract the values ​​and then compare the result with the damping coefficient D. g Summing, and then integrating the summation results to determine the third frequency deviation Δf*. cp_pu The remaining steps of the controller 120 in generating the third pulse width modulation signal are the same as described above. Figure 4 The description of the second pulse width modulation signal generated by the controller 120 is similar, the difference being the third frequency deviation Δf*. cp_pu Instead of the aforementioned second frequency deviation Δf cp_pu Voltage amplitude deviation ΔV m_puThe adjusted voltage amplitude deviation ΔV m_pu For details, please refer to the above. Figure 3 The description of the controller 120 generating the first pulse width modulation signal, and the above Figure 4 The description of the second pulse width modulation signal generated by the controller 120 is not repeated here in the embodiments of this application.

[0076] In one possible embodiment, such as Figure 6 As shown, the controller 120 adjusts the voltage amplitude deviation ΔV. m_pu A flowchart is provided. (Refer to the flowchart.) Figure 6 The voltage V at the input terminal of the controller 120 to the inverter circuit 110 dc Less than the second voltage threshold V dc_min2 In this case, adjust the voltage amplitude deviation ΔV m_pu The process includes:

[0077] Controller 120 is used to adjust the voltage amplitude deviation ΔV m_pu Previously, the voltage V at the input terminal of inverter circuit 110 was... dc Less than the third voltage threshold V dc_d In this case, the voltage amplitude deviation ΔV before adjustment will be adjusted. m_pu (K-1) minus the preset voltage adjustment amount ΔV step To determine the voltage amplitude deviation ΔV after the current cycle adjustment. m_pu (K), thereby reducing the voltage V at the output terminal of the inverter circuit 110. g Among them, the third voltage threshold V dc_d Less than or equal to the second voltage threshold V dc_min2 In this application embodiment, for the third voltage threshold V dc_d The specific value is not limited, (K-1) represents the adjustment voltage amplitude deviation ΔV m_pu The previous cycle, (K) represents the current cycle.

[0078] For example, the controller 120 first detects the voltage V at the input of the inverter circuit 110. dc Less than the second voltage threshold V dc_min2 This step can be performed under certain circumstances. After the controller 120 performs this step, the voltage V at the input terminal of the inverter circuit 110 can be used as a reference. dc Regarding the relationship with the voltage threshold, perform any of the following steps:

[0079] Controller 120 is also used to adjust the voltage amplitude deviation ΔV in the previous cycle. m_pu Then, the voltage V at the input terminal of the inverter circuit 110 dc Less than the third voltage threshold V dc_dIn this case, the adjusted voltage amplitude deviation ΔV m_pu (K-1) minus the preset voltage adjustment amount ΔV step To determine the voltage amplitude deviation ΔV after the current cycle adjustment. m_pu (K), thereby reducing the voltage V at the output terminal of the inverter circuit 110. g Where (K-1) represents the previous period and (K) represents the current period.

[0080] Controller 120 is also used to adjust the voltage amplitude deviation ΔV in the previous cycle. m_pu Then, the voltage V at the input terminal of the inverter circuit 110 dc Greater than the fourth voltage threshold V dc_u In this case, the adjusted voltage amplitude deviation ΔV m_pu (K-1) plus the preset voltage adjustment amount ΔV step To determine the voltage amplitude deviation ΔV after the current cycle adjustment. m_pu (K), thereby increasing the voltage V at the output terminal of the inverter circuit 110. g This helps increase the voltage V at the output terminal of the inverter circuit 110. g The voltage is restored to its state before the large disturbance. The fourth voltage threshold V is also considered. dc_u Greater than or equal to the first voltage threshold V dc_min1 In this application embodiment, for the fourth voltage threshold V dc_u The specific value of (K-1) is not limited, where (K-1) represents the previous period and (K) represents the current period.

[0081] Controller 120 is also used to adjust the voltage amplitude deviation ΔV in the previous cycle. m_pu Then, the voltage V at the input terminal of the inverter circuit 110 dc Greater than or equal to the third voltage threshold V dc_d And less than or equal to the fourth voltage threshold V dc_u In this case, the voltage amplitude deviation ΔV adjusted in the previous cycle will be... m_pu (K-1) represents the voltage amplitude deviation ΔV after the current cycle adjustment. m_pu (K), where (K-1) represents the previous period, and (K) represents the current period. (Refer to...) Figure 6 The voltage V at the input terminal of inverter circuit 110 dc Greater than or equal to the third voltage threshold V dc_d And less than or equal to the fourth voltage threshold V dc_u It can also be referred to as the input voltage V of inverter circuit 110. dc Located in a dead zone.

[0082] In one possible embodiment, the controller 120 adjusts the voltage amplitude deviation ΔV m_puWhen the following formula is satisfied:

[0083]

[0084] Where, ΔV m_pu (K) represents the voltage amplitude deviation of the current cycle (K), ΔV m_pu (K-1) represents the voltage amplitude deviation of the previous cycle (K-1), ΔV step This indicates the preset voltage adjustment amount.

[0085] In one possible embodiment, the controller 120 is further configured to, after outputting the third pulse width modulation signal, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu The third frequency deviation Δf* cp_pu The adjusted voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Obtain the voltage V at the output terminal of inverter circuit 110. g and current I g It outputs the second pulse width modulation signal to drive the inverter circuit 110 to work.

[0086] Among them, the third frequency deviation Δf* cp_pu According to the voltage V at the output terminal of inverter circuit 110 g and current I g Deviation ΔV from the adjusted voltage amplitude m_pu Sure.

[0087] In one possible embodiment, the controller 120 adjusts the voltage V at the output of the inverter circuit 110. g and current I g Deviation ΔV from the adjusted voltage amplitude m_pu Determine the third frequency deviation Δf* cp_pu The process can be referred to above. Figure 5 The controller 120 adjusts the voltage V at the output terminal of the inverter circuit 110. g and current I g Deviation ΔV from the adjusted voltage amplitude m_pu The description of the output third pulse width modulation signal is not repeated here in the embodiments of this application.

[0088] In one possible embodiment, the controller 120 is further configured to, after outputting the third pulse width modulation signal within a preset time threshold, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu The third frequency deviation Δf* cp_puThe adjusted voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu The second pulse width modulation signal is output. In this embodiment, the specific value of the preset time threshold is not limited; for example, the preset time threshold can be equal to the duration of multiple consecutive cycles. Therefore, the controller 120 can stop adjusting the voltage amplitude deviation ΔV when it accurately determines that the large disturbance has ended and the photovoltaic power generation system 200 is stable. m_pu Switching to power control mode for inverter circuit 110 can prevent malfunctions, improve the reliability of photovoltaic power generation system 200, and achieve smooth switching of control modes.

[0089] In one possible embodiment, the controller 120 is further configured to, after outputting the third pulse width modulation signal, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu The third frequency deviation Δf* cp_pu The adjusted voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Adjust the voltage amplitude deviation ΔV m_pu The initial value is restored so that when the photovoltaic power generation system 200 is subjected to a large disturbance again, the solution provided in the embodiments of this application can be used again to avoid the photovoltaic power generation system 200 from becoming unstable and to achieve stable operation of the photovoltaic power generation system 200.

[0090] In one possible embodiment, the control scheme provided in this application can be applied to a virtual synchronous machine (VSM) control strategy, or it can be applied to a control strategy such as droop control. This application does not limit the scope of the application.

[0091] In the photovoltaic inverter 100 provided in this application embodiment, the voltage V at the input terminal of the controller 120 of the inverter circuit 110 is... dc Less than the second voltage threshold V dc_min2 In this case, adjust the voltage amplitude deviation ΔV m_puThis reduces the amplitude of the AC output voltage of the photovoltaic inverter 100, thereby reducing the output power of the photovoltaic inverter 100 and narrowing the gap between the output power of the photovoltaic inverter 100 and the output power of the photovoltaic array 300. This ensures that when the photovoltaic power generation system 200 is subjected to large disturbances, the output power of the photovoltaic array 300 is equal to or nearly equal to the output power of the photovoltaic inverter 100. This prevents the operating point of the photovoltaic array 300 from crossing the MPP and reaching the left side of the MPP, thus preventing instability in the photovoltaic power generation system 200 and ensuring stable operation. cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu The third frequency deviation Δf* cp_pu The adjusted voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Once the large disturbance has ended and the photovoltaic power generation system is stable at 200V, stop adjusting the voltage amplitude deviation ΔV. m_pu Switching to power control mode to control inverter circuit 110 can ensure stable operation of photovoltaic power generation system 200, achieve smooth switching of control mode, and improve the reliability of photovoltaic power generation system 200.

[0092] In one possible embodiment, when the photovoltaic power generation system 200 is subjected to a large disturbance, such as a sudden drop in the light intensity of the photovoltaic array 300 or a significant drop in the grid frequency, without employing the solution provided in the embodiments of this application, the voltage V at the input terminal of the inverter circuit 110 will... dc The waveform is as follows Figure 7 As shown, the sudden drop in light intensity corresponds to a sudden decrease in the light intensity of the photovoltaic array 300, and the sudden drop in frequency corresponds to a large decrease in the grid frequency. At this time, the operating point of the photovoltaic array 300 may cross the MPP and reach the left side of the MPP, which will cause the photovoltaic power generation system 200 to become unstable.

[0093] In one possible embodiment, after adopting the solution provided in the embodiments of this application, the photovoltaic power generation system 200 is connected to the grid. When the photovoltaic power generation system 200 experiences a large disturbance, such as a significant drop in grid frequency, ... Figure 8 The diagram shows a power-voltage curve for a photovoltaic array 300, where "1KW / m 2"This indicates the power density of the photovoltaic array 300, which can be used to indicate the light intensity of the photovoltaic array 300. At time 'a', when the photovoltaic power generation system 200 is in a stable state, the photovoltaic array 300 operates at operating point 'a', at which time some power is reserved to support the photovoltaic inverter 100 in realizing a grid-connected photovoltaic inverter. When the grid frequency drops significantly, the voltage of the first capacitor C1 drops rapidly to generate more power, and the operating point of the photovoltaic array 300 moves from operating point 'a' to operating point 'b' at time 'b'. At this time, the voltage V at the input terminal of the inverter circuit 110..." dc The first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 The controller 120 uses a DC voltage control mode to control the inverter circuit 110. The voltage V at the input terminal of the inverter circuit 110 is... dc Stabilize at the preset DC voltage reference value V dc_ref The operating point of the photovoltaic array 300 moves from operating point b to operating point c at time c and remains at operating point c until time d. This operating point c can also be called operating point d. At the end of the large disturbance, the grid frequency rises, the power output of the photovoltaic array 300 decreases, and the voltage V at the input of the inverter circuit 110... dc As the photovoltaic array 300 rises, its operating point moves from operating point d to operating point e at time e. Under the condition of satisfying the power control mode, the controller 120 switches from controlling the inverter circuit 110 using DC voltage control mode to controlling the inverter circuit 110 using power control mode. The operating point of the photovoltaic array 300 moves from operating point e to operating point f at time f, which coincides with operating point a. It can be understood that by adopting the solution provided in this application embodiment, when the photovoltaic power generation system 200 is subjected to a large disturbance, the operating point of the photovoltaic array 300 can be prevented from crossing the MPP and reaching the left side of the MPP, thereby preventing instability of the photovoltaic power generation system 200 and achieving stable operation of the photovoltaic power generation system 200.

[0094] Combination Figure 8 When the photovoltaic power generation system 200 is connected to the grid after adopting the solution provided in the embodiments of this application, and the large disturbance experienced by the photovoltaic power generation system 200 is a large drop in grid frequency:

[0095] like Figure 9 The figure shows the voltage V at the input terminal of inverter circuit 110. dc A waveform diagram. (Refer to...) Figure 9 When the operating point of the photovoltaic array 300 moves from operating point a to operating point b, the voltage V at the input terminal of the inverter circuit 110... dc The first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 .

[0096] like Figure 10 The figure shows the second frequency deviation Δf cp_pu A waveform diagram. (Refer to...) Figure 10 At the operating point e of the photovoltaic array 300, the second frequency deviation Δf cp_pu Less than zero.

[0097] like Figure 11 The first frequency deviation Δf is shown. cv_pu A waveform diagram. (Refer to...) Figure 11 With frequency deviation threshold Δf cv_min_pu Taking -0.05 as an example, at the operating point e of the photovoltaic array 300, the first frequency deviation Δf cv_pu Greater than the frequency deviation threshold Δf cv_min_pu .

[0098] like Figure 12 The diagram shows the active power P output by inverter circuit 110. c_pu The waveform diagram, based on Figure 12 It is understandable that by adopting the solution provided in the embodiments of this application, the photovoltaic power generation system 200 can be prevented from becoming unstable when subjected to large disturbances, and the active power P output by the inverter circuit 110 can be increased. c_pu It supports the grid frequency and can recover to the initial rated value of 0.8 when the large disturbance ends, which helps to improve grid stability.

[0099] In one possible embodiment, after adopting the solution provided in the embodiments of this application, when the photovoltaic power generation system 200 is connected to the grid, and the large disturbance experienced by the photovoltaic power generation system 200 is a sudden drop in the light intensity of the photovoltaic array 300, such as... Figure 13 The diagram shows a power-voltage curve for a photovoltaic array 300, where "1KW / m 2 "and 0.6KW / m" 2 "These represent the power density of photovoltaic array 300, which can be used to indicate the irradiance of photovoltaic array 300. Each of these two irradiance values ​​corresponds to a power-voltage curve. At time 'a', when photovoltaic power generation system 200 is in a stable state, photovoltaic array 300 operates at operating point 'a', at which point some power is reserved to support photovoltaic inverter 100 in achieving a grid-connected photovoltaic inverter configuration. When the irradiance of photovoltaic array 300 increases from '1KW / m'..." 2 Reduced to 0.6KW / m 2 At time b, the voltage of the first capacitor C1 drops rapidly to generate more power, and the operating point of the photovoltaic array 300 shifts from operating point a to operating point b at time b. At this time, the voltage V at the input of the inverter circuit 110... dc The first voltage threshold V dc_min1And greater than or equal to the second voltage threshold V dc_min2 The controller 120 uses a DC voltage control mode to control the inverter circuit 110. The voltage V at the input terminal of the inverter circuit 110 is... dc Stabilize at the preset DC voltage reference value V dc_ref The operating point of photovoltaic array 300 moves from operating point b to operating point c at time c and remains at operating point c. At the end of the large disturbance, the irradiance of photovoltaic array 300 decreases from 0.6 kW / m². 2 "Rising to 1KW / m" 2 The operating point of the photovoltaic array 300 moves from operating point c to operating point d and remains there until time e. This operating point d can also be called operating point e. When the conditions of the power control mode are met, the controller 120 switches from controlling the inverter circuit 110 using DC voltage control mode to controlling the inverter circuit 110 using power control mode. The operating point of the photovoltaic array 300 moves from operating point e to operating point f at time f, which coincides with operating point a. It can be understood that by adopting the solution provided in this application embodiment, when the photovoltaic power generation system 200 is subjected to a large disturbance, the operating point of the photovoltaic array 300 can be prevented from crossing the MPP and reaching the left side of the MPP, thereby preventing instability of the photovoltaic power generation system 200 and achieving stable operation of the photovoltaic power generation system 200.

[0100] Combination Figure 13 When the photovoltaic power generation system 200 is connected to the grid after adopting the solution provided in the embodiments of this application, and the large disturbance to the photovoltaic power generation system 200 is a sudden drop in the light intensity of the photovoltaic array 300:

[0101] like Figure 14 The figure shows the voltage V at the input terminal of inverter circuit 110. dc A waveform diagram. (Refer to...) Figure 14 When the operating point of the photovoltaic array 300 moves from operating point a to operating point b, the voltage V at the input terminal of the inverter circuit 110... dc The first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 .

[0102] like Figure 15 The figure shows the second frequency deviation Δf cp_pu A waveform diagram. (Refer to...) Figure 15 At the operating point e of the photovoltaic array 300, the second frequency deviation Δf cp_pu Less than zero.

[0103] like Figure 16 The first frequency deviation Δf is shown. cv_pu A waveform diagram. (Refer to...) Figure 16 With frequency deviation threshold Δfcv_min_pu Taking -0.05 as an example, at the operating point e of the photovoltaic array 300, the first frequency deviation Δf cv_pu Greater than the frequency deviation threshold Δf cv_min_pu .

[0104] like Figure 17 The diagram shows the active power P output by inverter circuit 110. c_pu The waveform diagram, based on Figure 17 It is understandable that by adopting the solution provided in the embodiments of this application, the photovoltaic power generation system 200 can be prevented from becoming unstable when subjected to large disturbances.

[0105] In one possible embodiment, after adopting the solution provided in the embodiments of this application, the photovoltaic power generation system 200 is disconnected from the grid. When the large disturbance experienced by the photovoltaic power generation system 200 is a sudden increase in load power, such as... Figure 18 The figure shows the voltage V at the input terminal of inverter circuit 110. dc The waveform diagram is shown below. At time a, the photovoltaic power generation system 200 is in a stable state. Around 2 seconds (s), the load power suddenly increases, and the photovoltaic power generation system 200 is disturbed. Specifically, at time b, the voltage V at the input terminal of the inverter circuit 110... dc The first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 The controller 120 uses a DC voltage control mode to control the inverter circuit 110. If the controller 120 uses a DC voltage control mode to control the inverter circuit 110, the voltage V at the input terminal of the inverter circuit 110 will... dc The voltage continues to decrease; at time c, the voltage V at the input terminal of inverter circuit 110... dc Less than the second voltage threshold V dc_min2 In this case, controller 120 adjusts the voltage amplitude deviation ΔV m_pu This is to reduce the output power of the photovoltaic inverter 100 and narrow the gap between the output power of the photovoltaic inverter 100 and the output power of the photovoltaic array 300, so as to achieve stable operation of the photovoltaic power generation system 200. Between time c and time d, the voltage V at the input terminal of the inverter circuit 110... dc After rising, the voltage amplitude deviation ΔV remains stable. At time e, if the conditions are met, and the large disturbance has ended and the photovoltaic power generation system is stable (200), then adjustments to the voltage amplitude deviation ΔV are stopped. m_pu The inverter circuit 110 is switched to power control mode. At time f, the voltage V at the input terminal of the inverter circuit 110 is... dc Restore the initial value and maintain it.

[0106] Combination Figure 18When the photovoltaic power generation system 200 is disconnected from the grid after adopting the solution provided in the embodiments of this application, and the large disturbance experienced by the photovoltaic power generation system 200 is a sudden increase in load power:

[0107] like Figure 19 The figure shows the third frequency deviation Δf* cp_pu A waveform diagram. (Refer to...) Figure 19 At time e, the third frequency deviation Δf* cp_pu Less than zero.

[0108] like Figure 20 The first frequency deviation Δf is shown. cv_pu A waveform diagram. (Refer to...) Figure 20 With frequency deviation threshold Δf cv_min_pu Taking -0.05 as an example, at time e, the first frequency deviation Δf cv_pu Greater than the frequency deviation threshold Δf cv_min_pu .

[0109] like Figure 21 The figure shows the voltage amplitude deviation ΔV. m_pu A waveform diagram. (Refer to...) Figure 21 The voltage amplitude deviation ΔV after adjustment at time e m_pu Greater than the voltage amplitude deviation threshold ΔV m_min_pu .

[0110] like Figure 22 The diagram shows the active power P output by inverter circuit 110. c_pu The waveform diagram, based on Figure 22 It is understandable that by adopting the solution provided in the embodiments of this application, the photovoltaic power generation system 200 can be prevented from becoming unstable when subjected to large disturbances, and the active power P output by the inverter circuit 110 can be increased. c_pu It supports the grid frequency and can recover to the initial rated value of 0.8 when the large disturbance ends, which helps to improve grid stability.

[0111] like Figure 23 As shown, this application example provides a control method for a photovoltaic inverter, applied to the photovoltaic inverter 100 described above. The method includes steps S2301-S2302.

[0112] S2301, controller 120 obtains the voltage V at the input terminal of inverter circuit 110. dc The voltage V at the input terminal of inverter circuit 110 dc Less than the first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 In this case, obtain the voltage V at the output terminal of the inverter circuit 110. g and current I gIt outputs a first pulse width modulation signal to drive the inverter circuit 110 to work.

[0113] Wherein, the second voltage threshold V dc_min2 The voltage corresponding to an MPP greater than 300 for the photovoltaic array, in this embodiment of the application, is for a first voltage threshold V. dc_min1 Second voltage threshold V dc_min2 The specific value is not limited; the duty cycle of the first pulse width modulation signal is determined based on the voltage V at the input terminal of the inverter circuit 110. dc The voltage V at the output terminal of inverter circuit 110 g and current I g Sure.

[0114] S2302, after the controller 120 outputs the first pulse width modulation signal, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu Second frequency deviation Δf cp_pu Voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Obtain the voltage V at the output terminal of inverter circuit 110. g and current I g It outputs a second pulse width modulation signal to drive the inverter circuit 110 to operate. The duty cycle of the second pulse width modulation signal is based on the voltage V at the output terminal of the inverter circuit 110. g and current I g Sure.

[0115] In one possible embodiment, the controller 120 is further configured to, after outputting the first pulse width modulation signal within a preset time threshold, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu Second frequency deviation Δf cp_pu Voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu The second pulse width modulation signal is output. In this embodiment, the specific value of the preset time threshold is not limited; for example, the preset time threshold can be equal to the duration of multiple consecutive cycles. Therefore, the controller 120 can switch from controlling the inverter circuit 110 using DC voltage control mode to controlling the inverter circuit 110 using power control mode when it accurately determines that a large disturbance has ended and the photovoltaic power generation system 200 is stable. This avoids malfunctions, improves the reliability of the photovoltaic power generation system 200, and enables smooth switching of control modes.

[0116] The photovoltaic inverter control method provided in this application embodiment, the voltage V at the input terminal of the controller 120 of the inverter circuit 110. dc Less than the first voltage threshold V dc_min1 And greater than or equal to the second voltage threshold V dc_min2 In the case of a large disturbance, the inverter circuit 110 is controlled using DC voltage control mode. This ensures that the output power of the photovoltaic array 300 is equal to or nearly equal to the output power of the photovoltaic inverter 100 when the photovoltaic power generation system 200 is subjected to a large disturbance. This prevents the operating point of the photovoltaic array 300 from crossing the MPP and reaching the left side of the MPP, thus preventing instability of the photovoltaic power generation system 200 and achieving stable operation. Simultaneously, after the controller 120 controls the inverter circuit 110 using DC voltage control mode, if the first frequency deviation Δf... cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu Second frequency deviation Δf cp_pu Voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Once the large disturbance has ended and the photovoltaic power generation system 200 is stable, switching from the DC voltage control mode to the power control mode of the inverter circuit 110 can achieve stable operation of the photovoltaic power generation system 200, achieve smooth switching of control modes, and improve the reliability of the photovoltaic power generation system 200.

[0117] In one possible embodiment, such as Figure 23 As shown, the control method for the photovoltaic inverter provided in this application embodiment further includes steps S2303-S2304. When the controller 120 executes steps S2303-S2304 and the aforementioned steps S2301-S2302, it can adjust the voltage V at the input terminal of the inverter circuit 110 according to the voltage V. dc The relationship with the voltage threshold is selected for execution.

[0118] S2303, the voltage V at the input terminal of the controller 120 in the inverter circuit 110 dc Less than the second voltage threshold V dc_min2 In this case, adjust the voltage amplitude deviation ΔV m_pu Obtain the voltage V at the output terminal of inverter circuit 110. g and current I g It outputs a third pulse width modulation signal to drive the inverter circuit 110. The duty cycle of the third pulse width modulation signal is based on the voltage V at the output terminal of the inverter circuit 110. g and current I g Deviation ΔV from the adjusted voltage amplitude m_pu Sure.

[0119] In one possible embodiment, the voltage V at the input terminal of the inverter circuit 110 of the controller 120 is... dc Less than the second voltage threshold V dc_min2 In this case, adjust the voltage amplitude deviation ΔV m_pu The process can be referred to above. Figure 6 The relevant descriptions and embodiments of this application will not be repeated here.

[0120] S2304, after the controller 120 outputs the third pulse width modulation signal, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu The third frequency deviation Δf* cp_pu The adjusted voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Obtain the voltage V at the output terminal of inverter circuit 110. g and current I g It outputs the second pulse width modulation signal to drive the inverter circuit 110 to work.

[0121] In one possible embodiment, the controller 120 is further configured to, after outputting the third pulse width modulation signal within a preset time threshold, if the first frequency deviation Δf cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu The third frequency deviation Δf* cp_pu The adjusted voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu The second pulse width modulation signal is output. In this embodiment, the specific value of the preset time threshold is not limited; for example, the preset time threshold can be equal to the duration of multiple consecutive cycles. Therefore, the controller 120 can stop adjusting the voltage amplitude deviation ΔV when it accurately determines that the large disturbance has ended and the photovoltaic power generation system 200 is stable. m_pu Switching to power control mode for inverter circuit 110 can prevent malfunctions, improve the reliability of photovoltaic power generation system 200, and achieve smooth switching of control modes.

[0122] The photovoltaic inverter control method provided in this application embodiment, the voltage V at the input terminal of the controller 120 of the inverter circuit 110. dc Less than the second voltage threshold V dc_min2 In this case, adjust the voltage amplitude deviation ΔV m_puThis reduces the amplitude of the AC output voltage of the photovoltaic inverter 100, thereby reducing the output power of the photovoltaic inverter 100 and narrowing the gap between the output power of the photovoltaic inverter 100 and the output power of the photovoltaic array 300. This ensures that when the photovoltaic power generation system 200 is subjected to large disturbances, the output power of the photovoltaic array 300 is equal to or nearly equal to the output power of the photovoltaic inverter 100. This prevents the operating point of the photovoltaic array 300 from crossing the MPP and reaching the left side of the MPP, thus preventing instability in the photovoltaic power generation system 200 and ensuring stable operation. cv_pu Greater than or equal to the frequency deviation threshold Δf cv_min_pu The third frequency deviation Δf* cp_pu The adjusted voltage amplitude deviation ΔV is less than or equal to zero. m_pu Greater than or equal to the voltage amplitude deviation threshold ΔV m_min_pu Once the large disturbance has ended and the photovoltaic power generation system is stable at 200V, stop adjusting the voltage amplitude deviation ΔV. m_pu Switching to power control mode to control inverter circuit 110 can ensure stable operation of photovoltaic power generation system 200, achieve smooth switching of control mode, and improve the reliability of photovoltaic power generation system 200.

[0123] Based on this, such as Figure 1 As shown in the figure, this application embodiment also provides a photovoltaic power generation system 200, which includes a photovoltaic inverter 100. The input terminal of the photovoltaic inverter 100 is used to connect to a photovoltaic array 300, and the output terminal of the photovoltaic inverter 100 is used to connect to the power grid or a load 400. The circuit topology of the photovoltaic inverter 100 is as described above. Figure 1 The circuit topology of the photovoltaic inverter 100 is shown.

[0124] The above detailed description of the photovoltaic inverter 100 and the analysis of its beneficial effects can be applied to the control method of the photovoltaic inverter and the photovoltaic power generation system 200, and will not be repeated here in the embodiments of this application.

[0125] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A photovoltaic inverter, characterized in that, The photovoltaic inverter includes a controller and an inverter circuit. The input terminal of the inverter circuit is used to connect to the photovoltaic array, and the output terminal of the inverter circuit is used to connect to the power grid or a load. The controller is configured to output a first pulse width modulation signal to drive the inverter circuit to operate when the voltage at the input terminal of the inverter circuit is less than a first voltage threshold and greater than or equal to a second voltage threshold. The second voltage threshold is greater than the voltage corresponding to the maximum power point of the photovoltaic array. The duty cycle of the first pulse width modulation signal is determined based on the voltage at the input terminal of the inverter circuit, the voltage at the output terminal of the inverter circuit, and the current. The controller is further configured to, after outputting the first pulse width modulation signal, output a second pulse width modulation signal to drive the inverter circuit to operate if the first frequency deviation is greater than or equal to a frequency deviation threshold, the second frequency deviation is less than or equal to zero, and the voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold, wherein the first frequency deviation is determined based on the voltage at the input terminal of the inverter circuit, the second frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit, the initial value of the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the voltage amplitude deviation threshold is less than or equal to zero, and the duty cycle of the second pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit.

2. The photovoltaic inverter according to claim 1, characterized in that, The controller is further configured to adjust the voltage amplitude deviation and output a third pulse width modulation signal to drive the inverter circuit when the voltage at the input terminal of the inverter circuit is less than the second voltage threshold. The duty cycle of the third pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation. The controller is further configured to, after outputting the third pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the third frequency deviation is less than or equal to zero, and the adjusted voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, output the second pulse width modulation signal to drive the inverter circuit to operate, wherein the third frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation.

3. The photovoltaic inverter according to claim 2, characterized in that, The controller is further configured to, before adjusting the voltage amplitude deviation, if the voltage at the input terminal of the inverter circuit is less than a third voltage threshold, subtract a preset voltage adjustment amount from the voltage amplitude deviation before adjustment, so as to determine the voltage amplitude deviation after adjustment in the current cycle. The controller is further configured to, after adjusting the voltage amplitude deviation in the previous cycle, if the voltage at the input terminal of the inverter circuit is less than a third voltage threshold, subtract the preset voltage adjustment amount from the adjusted voltage amplitude deviation to determine the adjusted voltage amplitude deviation in the current cycle. The controller is further configured to, after adjusting the voltage amplitude deviation in the previous cycle, add the preset voltage adjustment amount to the adjusted voltage amplitude deviation when the voltage at the input terminal of the inverter circuit is greater than the fourth voltage threshold, so as to determine the adjusted voltage amplitude deviation in the current cycle. The controller is further configured to, after adjusting the voltage amplitude deviation in the previous cycle, if the voltage at the input terminal of the inverter circuit is greater than or equal to the third voltage threshold and less than or equal to the fourth voltage threshold, use the voltage amplitude deviation adjusted in the previous cycle as the voltage amplitude deviation adjusted in the current cycle. The third voltage threshold is less than or equal to the second voltage threshold, and the fourth voltage threshold is greater than or equal to the first voltage threshold.

4. The photovoltaic inverter according to any one of claims 2-3, characterized in that, The controller is further configured to, within a preset time threshold, after outputting the first pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the second frequency deviation is less than or equal to zero, and the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, output the second pulse width modulation signal. The controller is further configured to, within the preset time threshold, after outputting the third pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the third frequency deviation is less than or equal to zero, and the adjusted voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, output the second pulse width modulation signal.

5. A control method for a photovoltaic inverter, characterized in that, The method is applied to a photovoltaic inverter, which includes an inverter circuit, wherein the input terminal of the inverter circuit is used to connect to a photovoltaic array, and the output terminal of the inverter circuit is used to connect to the power grid or a load; the method includes: When the voltage at the input terminal of the inverter circuit is less than a first voltage threshold and greater than or equal to a second voltage threshold, a first pulse width modulation signal is output to drive the inverter circuit to work. The second voltage threshold is greater than the voltage corresponding to the maximum power point of the photovoltaic array. The duty cycle of the first pulse width modulation signal is determined based on the voltage at the input terminal of the inverter circuit, the voltage at the output terminal of the inverter circuit, and the current. After outputting the first pulse width modulation signal, if the first frequency deviation is greater than or equal to a frequency deviation threshold, the second frequency deviation is less than or equal to zero, and the voltage amplitude deviation is greater than or equal to a voltage amplitude deviation threshold, a second pulse width modulation signal is output to drive the inverter circuit. The first frequency deviation is determined based on the voltage at the input terminal of the inverter circuit, the second frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit, the initial value of the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the voltage amplitude deviation threshold is less than or equal to zero, and the duty cycle of the second pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit.

6. The method according to claim 5, characterized in that, The method further includes: When the voltage at the input terminal of the inverter circuit is less than the second voltage threshold, the voltage amplitude deviation is adjusted, and a third pulse width modulation signal is output to drive the inverter circuit to work. The duty cycle of the third pulse width modulation signal is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation. After outputting the third pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the third frequency deviation is less than or equal to zero, and the adjusted voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the second pulse width modulation signal is output to drive the inverter circuit to work. The third frequency deviation is determined based on the voltage and current at the output terminal of the inverter circuit and the adjusted voltage amplitude deviation.

7. The method according to claim 6, characterized in that, The adjustment of the voltage amplitude deviation includes: If the voltage at the input terminal of the inverter circuit is less than the third voltage threshold before adjusting the voltage amplitude deviation, the voltage amplitude deviation before adjustment is subtracted by the preset voltage adjustment amount to determine the voltage amplitude deviation after adjustment in the current cycle. If the voltage at the input terminal of the inverter circuit is less than the third voltage threshold after the voltage amplitude deviation was adjusted in the previous cycle, the preset voltage adjustment amount is subtracted from the adjusted voltage amplitude deviation to determine the voltage amplitude deviation after the current cycle. If the voltage at the input terminal of the inverter circuit is greater than the fourth voltage threshold after the voltage amplitude deviation was adjusted in the previous cycle, the adjusted voltage amplitude deviation is added to the preset voltage adjustment amount to determine the voltage amplitude deviation adjusted in the current cycle. If, after adjusting the voltage amplitude deviation in the previous cycle, the voltage at the input terminal of the inverter circuit is greater than or equal to the third voltage threshold and less than or equal to the fourth voltage threshold, the voltage amplitude deviation adjusted in the previous cycle shall be used as the voltage amplitude deviation adjusted in the current cycle. The third voltage threshold is less than or equal to the second voltage threshold, and the fourth voltage threshold is greater than or equal to the first voltage threshold.

8. The method according to any one of claims 6-7, characterized in that, The method further includes: Within a preset time threshold, after outputting the first pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the second frequency deviation is less than or equal to zero, and the voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the second pulse width modulation signal is output. Within the preset time threshold, after outputting the third pulse width modulation signal, if the first frequency deviation is greater than or equal to the frequency deviation threshold, the third frequency deviation is less than or equal to zero, and the adjusted voltage amplitude deviation is greater than or equal to the voltage amplitude deviation threshold, the second pulse width modulation signal is output.

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