An inverter grid connection method and system with a wide grid impedance adaptation range

Abstract

The present invention belongs to the field of converter control, and discloses an inverter grid connection method and system with a wide grid impedance adaptation range. The method includes: setting a current loop control and adding a capacitor voltage feedforward thereto; sampling the capacitor voltage and calculating the phase θ of the capacitor voltage c ; performing phase-locked tracking on the phase based on obtaining the capacitor voltage phase; estimating the obtained angle θ est and taking the difference from the capacitor voltage angle θ c . The error passes through a PI regulator and a new adjustment frequency is obtained; integrating the sum of the base frequency and the adjustment frequency to obtain an estimated angle θ est , which is used as the wave generation angle of the PWM. The present invention enables the inverter to adapt to grid conditions with a wide range of impedance variations, so as to ensure the stable operation of the inverter in both strong and weak grids without switching the control strategy

Description

Technical Field

[0001] The present invention belongs to the technical field of converter control, and particularly relates to an inverter grid-connected method and system with a wide grid impedance adaptation range. Background Art

[0002] In the weak grid state, the grid impedance is large, and the traditional grid-following inverter oscillates due to the negative impedance effect of the phase-locked loop. In recent years, some scholars have proposed the grid-forming inverter to improve the weak grid oscillation problem and made great progress. The grid-forming inverter simulates the working principle of a synchronous generator and has the characteristics of a voltage source. When it works in the strong grid grid-connected state, it is similar to the parallel connection of voltage sources, and the weak impedance between the inverter and the grid is not conducive to the stability of the system. Some scholars have also proposed control strategies such as virtual impedance and virtual inertia, but it is difficult to adapt to the grid conditions with a large change in impedance range. At the same time, since the grid-forming inverter is equivalent to a voltage source and regulates the output power by controlling the power angle and internal potential, this results in a slow regulation speed and it is difficult to effectively ride through the low voltage fault of the grid, causing a larger off-grid accident.

[0003] In view of the above analysis, the technical problems that need to be urgently solved in the existing technology are:

[0004] (1) The ordinary grid-following inverter directly tracks and uses the grid phase, resulting in system instability when the grid phase information is disordered or lost;

[0005] (2) The grid-forming inverter has the characteristics of a voltage source by simulating the working principle of a synchronous generator and has a good grid support effect in the weak grid state, but in the strong grid state, it is equivalent to the parallel connection of voltage sources, resulting in stability problems. Summary of the Invention

[0006] Aiming at the problems existing in the existing technology, the present invention provides an inverter grid-connected method and system with a wide grid impedance adaptation range.

[0007] The present invention is implemented as follows. An inverter grid-connected method with a wide grid impedance adaptation range is characterized in that the inverter grid-connected method with a wide grid impedance adaptation range specifically includes:

[0008] S1: Set the current loop control and add the capacitor voltage feedforward on this basis;

[0009] S2: Sample the capacitor voltage and calculate the phase θ of the capacitor voltage c ;

[0010] S3: Perform phase-locked tracking on the phase on the basis of obtaining the capacitor voltage phase;

[0011] S4: Estimate the obtained angle θ est and the capacitor voltage angle θ cTake the difference, and this error passes through a PI regulator and a new adjustment frequency is obtained;

[0012] S5: Integrate the sum of the base frequency and the adjustment frequency to obtain the estimated angle θ est , which is used as the wave - sending angle of PWM.

[0013] Furthermore, in S1, a capacitor voltage feed - forward is added on the basis of the current loop. This voltage feed - forward can directly sample the capacitor voltage or sample the capacitor voltage as a given value and use closed - loop control.

[0014] Furthermore, in S3, the PLL algorithm sets the base frequency and the adjustment frequency. The base frequency can be the same as the standard grid frequency, and the adjustment frequency is given by the PI regulator.

[0015] Furthermore, the inverter grid - connection method with a wide grid impedance adaptation range can be adapted to both single - phase and three - phase grid - connected inverters simultaneously.

[0016] Another object of the present invention is to provide an inverter grid - connection system with a wide grid impedance adaptation range, which specifically includes:

[0017] A current - loop control module, configured to add a capacitor voltage feed - forward on the basis of current - loop control;

[0018] A sampling and calculation module, configured to sample the capacitor voltage and calculate the phase of the capacitor voltage;

[0019] A phase - locked loop tracking module, configured to perform phase - locked loop tracking on this phase on the basis of obtaining the capacitor voltage phase;

[0020] A frequency adjustment module, configured to take the difference between the estimated obtained angle and the capacitor voltage angle. This error passes through a PI regulator and a new adjustment frequency is obtained;

[0021] An integration and wave - sending module, configured to integrate the sum of the base frequency and the adjustment frequency to obtain an estimated angle, which is used as the wave - sending angle of PWM.

[0022] Furthermore, the current - loop control module is further configured as:

[0023] This voltage feed - forward can directly sample the capacitor voltage or sample the capacitor voltage as a given value and use closed - loop control.

[0024] Furthermore, the phase - locked loop tracking module is further configured as:

[0025] Set the base frequency and the adjustment frequency, where the base frequency can be the same as the standard grid frequency, and the adjustment frequency is given by the PI regulator.

[0026] Furthermore, the inverter grid - connection system with a wide grid impedance adaptation range is further configured as:

[0027] It can be adapted to single-phase or three-phase grid-connected inverters simultaneously.

[0028] Combined with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0029] First, the present invention designs a phase-locked loop strategy. This phase-locking method tracks the grid phase twice, and then uses the obtained angle for grid connection control, greatly enhancing the stability of the system.

[0030] Through the control strategy designed by the present invention, the inverter can adapt to grid conditions with wide-range impedance changes, so as to ensure the stable operation of the inverter in both strong and weak grids without switching the control strategy.

[0031] Second, the present invention proposes a grid connection method for an inverter with a wide grid impedance adaptation range, aiming to solve the problems of insufficient stability and adaptability of existing inverters when the grid impedance changes greatly. This method realizes the stable grid connection operation of the inverter under wide-range grid impedance conditions through a series of fine steps. First, a capacitor voltage feedforward is added on the basis of the current loop control. This innovative design significantly enhances the response speed and adaptability of the inverter to grid impedance changes.

[0032] In step S2, the present invention details the process of sampling the capacitor voltage and calculating its phase. By accurately capturing the phase information of the capacitor voltage, it provides key data support for subsequent phase-locking tracking. This step ensures that the inverter can quickly and accurately adjust its output when the grid impedance changes to maintain synchronous operation with the grid.

[0033] Steps S3 and S4 further demonstrate the core control strategy of the present invention. A phase-locking algorithm is used to accurately track the capacitor voltage phase, and a base frequency and an adjustment frequency are set. The base frequency is consistent with the standard grid frequency to ensure that the inverter is synchronized with the grid under normal conditions; while the adjustment frequency is given by the PI regulator in real time according to the phase error, realizing the dynamic compensation of the inverter to grid impedance changes. The difference between the estimated angle and the capacitor voltage angle is calculated and processed by the PI regulator to obtain a new adjustment frequency, thereby ensuring the precise control of the inverter output frequency.

[0034] Finally, the grid connection method of the inverter with a wide grid impedance adaptation range of the present invention is not only applicable to single-phase inverters, but also to three-phase grid-connected inverters, demonstrating its broad application prospects. This method significantly improves the stability and adaptability of the inverter in complex grid environments through fine current loop control, capacitor voltage feedforward, phase-locked loop tracking, and dynamic frequency adjustment. Compared with the prior art, the present invention has made remarkable technological progress in solving the problem of inverter grid connection stability, providing a strong guarantee for the stable operation of renewable energy power generation systems. Description of the Drawings

[0035] Figure 1 is the flowchart of the grid connection method of the inverter with a wide grid impedance adaptation range provided by the embodiment of the present invention;

[0036] Figure 2 is the control block diagram of the grid connection system of the inverter with a wide grid impedance adaptation range provided by the embodiment of the present invention;

[0037] Figure 3 is the simulation model provided by the embodiment of the present invention;

[0038] Figure 4 is the control effect provided by the embodiment of the present invention. Detailed Embodiments

[0039] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the following further describes the present invention in detail with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not used to limit the present invention.

[0040] The following are two specific embodiments, showing the situation of the grid connection method of the inverter with a wide grid impedance adaptation range in practical applications:

[0041] Embodiment 1: Wide-range grid-connected inverter based on capacitor voltage feedforward

[0042] In a certain distributed photovoltaic power generation system, due to the large range of impedance changes in the grid connection, traditional inverters are prone to grid connection instability problems when the grid impedance fluctuates.

[0043] 1) Set up current loop control: First, establish a basic current loop control strategy for the inverter to ensure the stability and accuracy of the inverter output current.

[0044] 2) Add capacitor voltage feedforward: On the basis of current loop control, introduce a capacitor voltage feedforward link. By directly sampling the capacitor voltage at the output end of the inverter and adding it as a feedforward signal to the current loop control, the change of the grid impedance can be quickly responded to.

[0045] 3) Phase-locked loop tracking: Sample the capacitor voltage and calculate its phase, and use phase-locked loop (PLL) technology to accurately track the phase. The PLL technology can adjust the output phase of the inverter in real time to keep it synchronized with the grid phase.

[0046] 4) Dynamic frequency adjustment: Compare the estimated obtained angle with the actual angle of the capacitor voltage, and input the error signal into the PI regulator. The PI regulator adjusts the frequency according to the error signal. After adding the adjusted frequency to the base frequency, the estimated angle for PWM modulation is obtained through integral operation.

[0047] 5) Grid connection test: Connect the inverter to the actual grid for grid connection test. The results show that under the condition of large fluctuations in the grid impedance, the inverter can still maintain stable grid connection operation, with good output voltage and current waveforms, meeting the grid connection requirements.

[0048] Example 2: Application of a high-bandwidth grid-connected inverter in a weak grid

[0049] The grid connected to a certain wind farm is weak, with large fluctuations in the grid impedance, posing high requirements for the robustness of the grid-connected inverter.

[0050] 1) High-bandwidth inverter design: Design a high-bandwidth grid-connected inverter using a new type of wide bandgap device (such as GaN). By increasing the switching frequency, the high-bandwidth characteristics of the inverter are achieved to quickly respond to changes in the grid impedance.

[0051] 2) Control strategy optimization: Optimize the control strategy of the inverter and introduce an appropriate phase lead compensation link. This compensation link can expand the positive damping interval, widen the resonant frequency design range, and improve the robustness of the inverter under weak grid conditions.

[0052] 3) Grid connection parameter debugging: According to the actual situation of the wind farm, debug the grid connection parameters of the inverter. This includes setting appropriate current loop control parameters, capacitor voltage feedforward coefficients, PI regulator parameters, etc., to ensure stable grid connection operation of the inverter under weak grid conditions.

[0053] 4) Grid connection experimental verification: Connect the high-bandwidth grid-connected inverter to the actual grid of the wind farm for grid connection experiments. The experimental results show that the inverter can still maintain stable grid connection operation under weak grid conditions, with good output voltage and current waveforms, and has strong adaptability to fluctuations in the grid impedance.

[0054] The above two examples respectively show the application of a wide-range grid-connected inverter based on capacitor voltage feedforward and a high-bandwidth grid-connected inverter in a weak grid. These examples show that by adopting appropriate control strategies and technical means, the grid connection stability and robustness of the inverter within a wide grid impedance adaptation range can be significantly improved.

[0055] As Figure 1 shown, an embodiment of the present invention provides a grid - connection method for an inverter with a wide grid impedance adaptation range, and the method specifically includes:

[0056] S1: Set the current - loop control and add the capacitor - voltage feed - forward on this basis;

[0057] S2: Sample the capacitor voltage and calculate the phase θ of the capacitor voltage c ;

[0058] S3: Based on the obtained capacitor - voltage phase, perform phase - locked tracking on this phase;

[0059] S4: Estimate the obtained angle θ est and make a difference with the capacitor - voltage angle θ c , and this error passes through a PI regulator to obtain a new adjusted frequency;

[0060] S5: Integrate the sum of the base frequency and the adjusted frequency to obtain an estimated angle θ est , as the wave - generation angle of PWM.

[0061] In the above S1, the current - loop control enables the system to have the properties of a current source, thus having a fast dynamic response; adding the capacitor - voltage feed - forward on the basis of the current loop, this voltage feed - forward can directly sample the capacitor voltage, or sample the capacitor voltage as a given value and use closed - loop control.

[0062] In the above S3, the phase - locked algorithm sets the base frequency and the adjusted frequency. The base frequency can be the same as the standard grid frequency, and the adjusted frequency is given by the PI regulator.

[0063] The grid - connection method for an inverter with a wide grid impedance adaptation range provided by the embodiment of the present invention can be adapted to single - phase or three - phase grid - connected inverters simultaneously.

[0064] The characteristics of the embodiment of the present invention are that it does not directly use the voltage angle obtained by calculating at the grid - connection point for control, but sets a phase - locked loop to track this phase. It avoids the situation in a weak grid where due to the interaction between the inverter and the grid, the phase at the grid - connection point is disordered and the phase information is completely lost. At the same time, in a strong grid, the phase at the grid - connection point is stable, and the inverter has the characteristics of current - source grid - connection and strong stability.

[0065] The present invention provides a grid - connection method for an inverter with a wide grid impedance adaptation range. This method realizes the stable grid - connection operation of the inverter under different grid impedance conditions through multiple steps, and the specific working principle is as follows:

[0066] Step S1: Set the current - loop control and add the capacitor - voltage feed - forward on this basis

[0067] The current loop control is the core of the inverter control system. Its main function is to regulate the output current of the inverter to ensure synchronization with the power grid. To further improve the dynamic response and stability of the system, the present invention adds capacitor voltage feedforward on the basis of the current loop. The capacitor voltage feedforward can directly sample the capacitor voltage signal and introduce it into the control loop to compensate for the deficiencies of the current loop control. This feedforward mechanism can quickly respond to changes in the capacitor voltage and enhance the anti-interference ability of the system.

[0068] Step S2: Sample the capacitor voltage and calculate the phase of the capacitor voltage

[0069] Sample the voltage across the capacitor through a voltage sensor to obtain the real-time capacitor voltage signal. Then, use a phase calculation algorithm (such as Fourier transform, etc.) to calculate the phase of the capacitor voltage. The purpose of this step is to obtain the phase information of the capacitor voltage relative to the reference signal for subsequent phase locking and frequency adjustment.

[0070] Step S3: Perform phase-locked tracking on the obtained capacitor voltage phase

[0071] Perform phase-locked tracking on the phase of the capacitor voltage through a phase-locked loop (PLL). The phase-locked loop is a closed-loop control system. Its input is the phase signal of the capacitor voltage, and its output is the tracked phase signal. The phase-locked loop adjusts its internal oscillation frequency to make the phase of the output signal consistent with the phase of the input signal, thereby achieving phase locking. During this process, the phase-locked loop sets the base frequency and the adjustment frequency. The base frequency is usually consistent with the standard power grid frequency (such as 50Hz or 60Hz), and the adjustment frequency is given by the error calculated in the subsequent steps through a PI regulator.

[0072] Step S4: Subtract the estimated angle from the capacitor voltage angle, and this error passes through a PI regulator to obtain a new adjustment frequency

[0073] Calculate the error between the phase angle output by the phase-locked loop and the actual phase angle of the capacitor voltage, and input this error signal into the PI regulator. The PI regulator performs proportional (P) and integral (I) regulation according to the error signal and outputs a new frequency adjustment signal. The role of the PI regulator is to continuously adjust the output frequency to make the error tend to zero, thereby ensuring the phase synchronization between the inverter output current and the power grid voltage.

[0074] Step S5: Integrate the sum of the base frequency and the adjustment frequency to obtain an estimated angle, which is used as the wave generation angle of the PWM

[0075] Add the base frequency signal to the frequency adjustment signal obtained through the PI regulator, and perform an integration operation on it to obtain a continuously changing phase angle. This phase angle is used to generate the firing angle of the PWM (pulse width modulation) signal. By adjusting the firing angle of the PWM signal, the phase of the inverter output voltage can be precisely controlled, thereby achieving synchronous grid connection with the grid voltage.

[0076] The method of the present invention can adapt to different grid impedance conditions, including high-impedance and low-impedance scenarios. The reason is that the combination of current loop control and capacitor voltage feedforward can quickly respond to changes in grid impedance, adjust the output parameters of the inverter, and maintain the stability of grid connection. Moreover, this method is applicable to single-phase and three-phase grid-connected inverters, and through the comprehensive application of the above steps, it ensures the reliable operation of the inverter under various grid conditions.

[0077] In summary, the present invention provides an inverter grid connection method with a wide grid impedance adaptation range through precise phase tracking, frequency adjustment, and capacitor voltage feedforward mechanisms, significantly improving the stability and reliability of inverter grid connection.

[0078] As Figure 2 shown, an inverter grid connection system with a wide grid impedance adaptation range provided by an embodiment of the present invention specifically includes:

[0079] A current loop control module, used to make the system have the properties of a current source to achieve fast dynamic response;

[0080] A phase-locked loop module, used to track the grid phase and use the obtained angle for grid connection control.

[0081] The present invention relates to an inverter grid connection method with a wide grid impedance adaptation range, and the specific steps are as follows:

[0082] Step S1: Set up current loop control and add capacitor voltage feedforward

[0083] Current loop control: Set up current loop control in the control system of the inverter to adjust the inverter output current to ensure that the inverter can output a current that meets the requirements.

[0084] Capacitor voltage feedforward: Add capacitor voltage feedforward on the basis of current loop control. The feedforward can directly sample the capacitor voltage or use the capacitor voltage as a given value for closed-loop control. The introduction of feedforward helps to improve the dynamic response performance and steady-state accuracy of the system.

[0085] Step S2: Sample the capacitor voltage and calculate the phase of the capacitor voltage

[0086] Obtain the real-time capacitor voltage value by sampling the capacitor voltage.

[0087] Calculate the phase of the capacitor voltage using the corresponding algorithm. Methods such as Fourier transform and phase detector can be used for phase calculation to ensure accurate voltage phase information.

[0088] Step S3: Phase-locked tracking of the capacitor voltage phase

[0089] Phase-locked loop (PLL): Based on the obtained capacitor voltage phase, perform phase-locked tracking on this phase. The phase-locked loop is a commonly used phase tracking technology that adjusts the system frequency to make the output phase consistent with the input phase.

[0090] Base frequency and adjustment frequency: The phase-locked algorithm sets the base frequency and adjustment frequency. The base frequency is usually consistent with the standard grid frequency, and the adjustment frequency is given by the PI regulator to compensate for the phase error.

[0091] Step S4: Calculate the angle error and perform PI regulation

[0092] Angle error calculation: Compare the estimated obtained angle with the capacitor voltage angle to calculate the phase error.

[0093] PI regulator: Input the phase error into the PI regulator for proportional-integral regulation and output a new adjustment frequency. The parameters (proportional gain and integral time constant) of the PI regulator need to be adjusted according to the system characteristics to ensure the fast response and stability of the system.

[0094] Step S5: Calculate the wave-issuing angle

[0095] Angle integration: Integrate the sum of the base frequency and the adjustment frequency to obtain the estimated angle.

[0096] PWM wave-issuing: Use the estimated angle as the wave-issuing angle of the PWM (pulse width modulation) signal to control the switching devices of the inverter and achieve synchronization between the inverter output current and the grid current.

[0097] This method can be adapted to both single-phase and three-phase grid-connected inverters, with a wide adaptation range. Whether it is a single-phase inverter or a three-phase inverter, stable grid connection within a wide range of grid impedances can be achieved through the above steps.

[0098] Detailed explanation of the working principle:

[0099] 1. Current loop control and capacitor voltage feedforward

[0100] Current loop control is the basis of inverter grid connection control. By adjusting the inverter output current to make it consistent with the reference current. On this basis, capacitor voltage feedforward is introduced to further improve the dynamic response speed and steady-state accuracy of the system. Feedforward control can reduce the phase lag of the system and improve the control accuracy.

[0101] 2. Capacitor Voltage Sampling and Phase Calculation

[0102] After sampling the capacitor voltage, the phase of the voltage is calculated through a phase detection algorithm. The accuracy of this step is crucial for phase-locked tracking. Common methods include Fourier transform, phase-locked loop, etc.

[0103] 3. Phase-Locked Tracking and Frequency Adjustment

[0104] The phase-locked loop (PLL) adjusts the output frequency to make the output phase consistent with the phase of the input capacitor voltage. The frequency adjustment during the phase-locked process is completed by a PI regulator. The PI regulator adjusts the phase error and outputs a compensated frequency to ensure phase synchronization.

[0105] 4. Error Calculation and PI Regulation

[0106] After calculating the phase error, it is input into the PI regulator for proportional-integral regulation. The PI regulator outputs an adjusted frequency, and the sum of this adjusted frequency and the base frequency forms the total frequency, which is used for subsequent angle integration.

[0107] 5. Angle Integration and PWM Wave Generation

[0108] The total frequency is integrated to obtain the wave generation angle. This angle is used to generate the PWM control signal, which controls the on / off of the inverter switching devices to achieve the synchronization of the current output and the grid current.

[0109] Applicable to Single-Phase and Three-Phase Grid-Connected Inverters

[0110] This method is applicable to single-phase and three-phase grid-connected inverters. By adjusting the control parameters and algorithms, it can ensure the stable grid connection of the inverter under different grid impedance conditions, improving the adaptability and reliability of the system.

[0111] Technological Progress:

[0112] 1) Improve dynamic response and steady-state accuracy: Through capacitor voltage feedforward, the dynamic response speed and steady-state accuracy of the system are improved.

[0113] 2) Wide adaptation range: This method is applicable to the grid connection of inverters within a wide grid impedance range, with strong adaptability.

[0114] 3) High-precision phase-locked tracking: A PI regulator is used to adjust the phase error to achieve high-precision phase-locked tracking.

[0115] 4) Stable grid connection control: Through precise control of the wave generation angle, the stable grid connection of the inverter and the grid is achieved, ensuring the reliable operation of the system.

[0116] The case simulation model is as Figure 3As shown, the three-phase inverter is connected to the grid using a current source control strategy. A parameter-setting component is used as the line impedance for grid connection. Initially, a small line impedance is set, and the grid is in a strong grid state and the inverter is started; around 0.3 s, the grid line impedance is increased, and at this time the grid is in a weak grid state; at 0.57 s, it switches back to the strong grid state again. The simulation results are as Figure 4 shown, and it can be seen that the system can operate stably in both strong and weak grid states.

[0117] As described above, the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be covered within the protection scope of the present invention.

Claims

1. A grid-connected method for an inverter with a wide grid impedance adaptation range, characterized in that The method specifically includes: S1: Set current loop control and add capacitor voltage feedforward on this basis; S2: Sample the capacitor voltage and calculate the phase of the capacitor voltage; S3: Perform phase-locked tracking on the phase based on obtaining the capacitor voltage phase; S4: Calculate the error by subtracting the estimated obtained angle from the capacitor voltage angle. This error passes through a PI regulator and a new adjustment frequency is obtained; S5: Integrate the sum of the base frequency and the adjustment frequency to obtain the estimated angle, which is used as the PWM wave generation angle; In S1, capacitor voltage feedforward is added on the basis of the current loop. This voltage feedforward directly samples the capacitor voltage, or samples the capacitor voltage as a given value and uses closed-loop control; In S3, the phase-locked algorithm sets the base frequency and the adjustment frequency. The base frequency can be the same as the standard grid frequency, and the adjustment frequency is given by the PI regulator; Based on the inverter grid-connected system with the wide grid impedance adaptation range, this system specifically includes: A current loop control module configured to add capacitor voltage feedforward on the basis of current loop control; A sampling and calculation module configured to sample the capacitor voltage and calculate the phase of the capacitor voltage; A phase-locked tracking module configured to perform phase-locked tracking on the phase based on obtaining the capacitor voltage phase; A frequency adjustment module configured to calculate the difference between the estimated obtained angle and the capacitor voltage angle. This error passes through a PI regulator and a new adjustment frequency is obtained; An integration and wave generation module configured to integrate the sum of the base frequency and the adjustment frequency to obtain the estimated angle, which is used as the PWM wave generation angle; The current loop control module is further configured to: This voltage feedforward directly samples the capacitor voltage, or samples the capacitor voltage as a given value and uses closed-loop control; The phase-locked tracking module is further configured to: Set the base frequency and the adjustment frequency, where the base frequency can be the same as the standard grid frequency, and the adjustment frequency is given by the PI regulator; The inverter grid-connected system with the wide grid impedance adaptation range is further configured to: Be adaptable to single-phase or three-phase grid-connected inverters simultaneously.

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