LLCL grid-connected inverter and power grid voltage full decoupling and resonance feedforward control method thereof

Abstract

The invention relates to an LLCL grid-connected inverter and a power grid voltage full decoupling and resonance feedforward control method thereof, and the method comprises the steps: fitting a function relation between an inductance value and an inductance current according to a current outputted by the inverter and a data manual of a used inductor, and obtaining an inductance parameter instantaneous value; a voltage transformer, a resistance voltage divider and a first-order active low-pass filter are adopted to extract power grid voltage, a power grid voltage full feed-forward algorithm is executed, and disturbance of the power grid voltage is predicted and correspondingly compensated; for different frequencies, proportion and phase parameters of different proportional resonance controllers with phase lead are designed according to phase delay and amplitude deviation of one-beat delay of a first-order active low-pass filter and a digital controller at the frequency, and high-precision feed-forward control is realized by adjusting proportional gain, resonant frequency, resonant bandwidth and resonant gain. According to the method, the feedforward of the power grid voltage can be accurately controlled, the anti-interference capability under the weak power grid condition is enhanced, and the higher electric energy quality standard is met.

Description

Technical Field

[0001] The invention relates to an inverter output current control method in the field of frequency converter control, and in particular discloses an LLCL grid-connected inverter and a grid voltage full decoupling and resonant feedforward control method thereof. Background Art

[0002] With the widespread application of renewable energy, the proportion of grid-connected inverters in power systems has gradually increased, including but not limited to photovoltaic inverters, active filters, etc. These power systems are usually connected to the grid through grid-connected inverters, so the performance of the inverter directly affects the stability and power quality of the grid. In order to meet increasingly stringent power quality standards, grid-connected inverters need to provide high-quality current output under various grid conditions while suppressing current distortion caused by grid voltage harmonics.

[0003] Traditional grid-connected inverters usually use L-type or LCL-type filters to suppress high-frequency harmonics. Compared with L-type filters, LCL filters have stronger high-frequency harmonic suppression capabilities, but they also have resonance problems. Near the resonant frequency, the impedance of the LCL filter is very small, resulting in the amplification of the harmonic current of the corresponding frequency, which may exceed the harmonic standard. In order to solve this problem, researchers have proposed a variety of control strategies, including passive damping and active damping. Among them, the active damping method is limited by the Nyquist frequency of the controller, and the passive damping method of the LCL filter has too large damping loss. The LLCL filter has a relatively small problem, but its current grid voltage feedforward technology mainly uses proportional feedforward technology similar to L-type or LCL filters, so when the grid voltage contains a large number of harmonics or transient mutations, it cannot well suppress its impact on the output current of the grid-connected inverter. Summary of the invention

[0004] The purpose of the present invention is to solve the problems existing in the prior art, design an LLCL grid-connected inverter and a grid voltage full decoupling and resonant feedforward control method thereof, and propose a simple and practical method for real-time calculation of the instantaneous value of the inductor parameter in consideration of the nonlinear characteristics of the inductor. The algorithm is executed according to the derived grid voltage full feedforward transfer function of the LLCL filter, and then a phase-advanced proportional resonant controller is introduced. The amplitude change and phase lag caused by sampling and control delays are eliminated through the proportional resonant feedforward technology, thereby achieving precise control of the inverter output current under various grid conditions.

[0005] The present invention is implemented as follows: an LLCL grid-connected inverter and a grid voltage full decoupling and resonant feedforward control method thereof, characterized in that the grid voltage full decoupling and resonant feedforward control method comprises the following steps: Step 1: First, according to the output current of the inverter and the data sheet of the inductor used, fit the functional relationship between the inductance value and the inductor current, and calculate the inductance value under the current at the current moment, that is, the instantaneous value of the inductance parameter; Step 2, using voltage transformer, resistor divider and first-order active low-pass filter to extract grid voltage and execute grid voltage full feed-forward algorithm; Step 3, for different frequencies, according to the phase delay and amplitude offset of the first-order active low-pass filter and the one-beat delay of the digital controller at the frequency, design different proportional and phase parameters of the proportional resonant controller with phase advance.

[0006] In Step 1, the inductance L is obtained based on the inverter output current and inductance data sheet or actual measurement. 1 The inductance values ​​at 0A and full load are L 0 With L e , we get the following relationship: , Where I is the instantaneous value of the inductor current, I e is the inductor current at full load.

[0007] In the Step 2, the specific method for obtaining the real-time value of the grid voltage is: first, the grid voltage is sampled using a voltage transformer, and then the sampled voltage is divided by a resistor divider to reduce the voltage to a level suitable for measurement, and then the divided voltage signal is filtered using a first-order active low-pass filter to remove noise and interference, and finally, the filtered voltage signal is processed using a grid voltage full feedforward algorithm based on an LLCL filter, and the disturbance of the grid voltage is predicted and compensated by the algorithm to achieve precise control and regulation of the grid voltage.

[0008] The transfer function of the grid voltage full feedforward algorithm is as follows: , , Among them G ff1 is the grid voltage feedforward function at the input of the current control loop, G ff2 is the grid voltage feedforward function at the modulation signal, s is the Laplace operator, L 1 , C 1 , R d and L f are the inductance, capacitance and resistance parameters of LLCL filter respectively, where R d is the passive damping resistor, L 1 is the main inductance of the power circuit, L f is the resonant filter branch inductor.

[0009] In the Step 3, the proportional resonant controller used is a proportional resonant controller with phase shift, and the transfer function of the nth harmonic is in the following two forms: , , Where s is the Laplace operator, k n is the proportional coefficient of the proportional resonant controller, ω cn is the bandwidth of the proportional resonant controller, ω n is the resonant frequency of the proportional resonant controller, θ n is the leading phase of the proportional resonant controller; The transfer function of the first-order active filter is calculated as follows, where ω c is the bandwidth of the first-order active filter: , The leading phase θ of the proportional resonant controller n The grid voltage phase lag caused by the first-order active filter and the one-step digital controller is calculated as follows: , where z -1 is a one-beat delay, which can be expressed as , T s is the sampling frequency of the control system, j is an imaginary number, The proportional coefficient k of the proportional resonant controller n The amplitude attenuation caused by the first-order active low-pass filter is calculated as: .

[0010] The method also includes a real-time sampling circuit for grid voltage, a calculation module and a PWM execution module. The real-time sampling circuit for grid voltage is used to collect the real-time value of grid voltage and filter out high-frequency noise signals for subsequent calculation modules to perform full feedforward and resonant feedforward calculations of grid voltage. The calculation module uses a DSP, MCU or FPGA processor to determine the sampling frequency, perform full feedforward and resonant feedforward calculations of grid voltage, save the inductance value of the inductor under different currents, and perform current outer loop tasks. The PWM execution module is implemented using a PWM output module or CPLD chip provided by the DSP / MCU to control the switch of the grid-connected inverter to be turned on or off.

[0011] The LLCL grid-connected inverter used in the LLCL grid-connected inverter grid voltage full decoupling and resonant feedforward control method is characterized in that: the inverter main circuit of the grid-connected inverter is connected to the grid through an LLCL type filter connected to the circuit, and the grid-connected inverter is also provided with a real-time sampling circuit connected to the LLCL type filter circuit for extracting the grid voltage, a calculation module for performing a grid voltage full feedforward algorithm based on data information obtained through the sampling circuit, and a PWM execution module for accurately controlling and adjusting the grid voltage according to the calculation results, the PWM execution module sends modulation and drive signals to the inverter main circuit through the drive circuit, and the inverter main circuit is provided with a DC side capacitor on the DC side.

[0012] The sampling circuit for extracting the grid voltage includes a voltage transformer for collecting the grid voltage, a resistor divider for dividing the collected voltage, and a first-order active low-pass filter for filtering the divided voltage signal. The calculation module adopts a DSP, MCU or FPGA processor, and the PWM execution module adopts a PWM output module or CPLD chip provided by the DSP / MCU.

[0013] The beneficial effect of the present invention is that the method of the present invention only involves the voltage feedforward inner loop of the grid-connected inverter based on LLCL filter, and its current outer loop can adopt PI, repetitive control, proportional resonance control and various other composite control means to coordinate with the proposed voltage feedforward inner loop to respectively realize accurate current control and suppression of grid voltage harmonics, which can greatly improve the performance of the entire control system.

[0014] The method of the present invention uses advanced control strategies and algorithms to accurately control the feedforward of the grid voltage and the full feedforward output cascade resonant feedforward link, effectively suppressing the influence of the grid voltage harmonics on the inverter output current, improving the output current quality of the LLCL grid-connected inverter under the influence of the grid voltage harmonics, and improving the performance of the grid-connected inverter under various grid conditions, especially the ability to suppress grid voltage harmonics to meet higher power quality standards. Through the method of the present invention, the accuracy of grid voltage sampling and the stability of control can be effectively improved, thereby improving the stability and reliability of the entire power system. The method of the present invention significantly improves the quality of the grid-connected current, reduces the total harmonic distortion, and especially enhances the anti-interference ability under weak grid conditions, which is crucial for the safe and efficient operation of the LLCL grid-connected inverter system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The main circuit structure diagram of the three-phase full-bridge inverter applied in the method of the present invention is shown in FIG.

[0016] Figure 2The main circuit structure diagram of the NPC type three-phase inverter applied by the method of the present invention is shown in FIG.

[0017] Figure 3 The figure is a schematic diagram of the overall architecture of a grid-connected inverter to which the method of the present invention is applied.

[0018] Figure 4 The present invention is a schematic diagram of the structure of the LLCL filter in the grid-connected inverter described in the method of the present invention.

[0019] Figure 5 The figure is a control step block diagram of the method of the present invention.

[0020] Figure 6 The present invention is a schematic diagram of the sampling circuit structure of a first-order active low-pass filter used in the method of the present invention.

[0021] Figure 7 This is a structural diagram of the overall control algorithm of the full feedforward method control strategy based on the instantaneous value of the inductance parameter of the method of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The examples given are only used to explain the present invention and are not used to limit the protection scope of the present invention.

[0023] According to the attached Figures 1 to 7 The present invention is a LLCL grid-connected inverter and a grid voltage full decoupling and resonant feedforward control method thereof, comprising the following control steps: First, the inductance value of the inductive device in the LLCL filter is determined according to the inverter output current to take into account the nonlinear characteristics of the inductor. Then, a voltage transformer, a resistor divider and a first-order active low-pass filter are used to obtain the grid voltage, and a full grid voltage feedforward algorithm is executed to achieve precise control and regulation of the grid voltage by predicting and compensating for grid voltage disturbances.

[0024] According to the phase delay and amplitude offset of one-beat delay of the first-order active low-pass filter and the digital controller at the DSP sampling frequency, different proportional and phase parameters of the proportional resonant controller with phase advance are designed. By adjusting the proportional gain, resonant frequency, resonant bandwidth and resonant gain, high-precision feedforward control of the grid voltage under n-th grid harmonic is achieved.

[0025] The LLCL grid-connected inverter described in the method of the present invention comprises a three-phase full-bridge inverter (such as the one shown in the attached figure) composed of a plurality of fully controlled power electronic switches and capacitors. Figure 1 ) and NPC type three-phase inverter (as shown in the attached Figure 2 as shown) or other structural forms.

[0026] The overall architecture of the LLCL grid-connected inverter using the method of the present invention is shown in the attached figure. Figure 3 As shown, the inverter main circuit of the grid-connected inverter is connected to the grid through an LLCL filter connected to the circuit, and the grid-connected inverter is also provided with a real-time sampling circuit for grid voltage connected to the LLCL filter circuit, a calculation module for performing a full feedforward algorithm for grid voltage via data information obtained from the sampling circuit, and a PWM execution module for accurately controlling and adjusting the grid voltage according to the calculation result, and the PWM execution module sends modulation and drive signals to the inverter main circuit through a drive circuit, and the inverter main circuit is provided with a DC side capacitor on the DC side. The sampling circuit for extracting the grid voltage includes a voltage transformer for collecting the grid voltage, a resistor divider for dividing the collected voltage, and a first-order active low-pass filter for filtering the voltage signal after the voltage division, the calculation module adopts a DSP, MCU or FPGA processor, and the PWM execution module adopts a PWM output module or CPLD chip provided by the DSP / MCU.

[0027] The LLCL filter is shown in the attached Figure 4 As shown, the first inductor L f , the first capacitor C 1 Two inductors connected to each other are additionally provided, namely, the second inductor L 1 and the third inductor L 2 , the first inductor L f One end and the first capacitor C 1 The other end is connected in series with the second inductor L 1 and the third inductor L 2 The first capacitor C 1 A resistor R is also connected d Compared with the traditional LCL filter, the LLCL filter further optimizes the filtering performance by adding an additional inductor.

[0028] The method of the present invention also includes a real-time sampling circuit for grid voltage, a calculation module and a PWM execution module to realize full feedforward and resonant feedforward calculation of grid voltage. The real-time sampling circuit for grid voltage is used to collect the real-time value of grid voltage and filter out high-frequency noise signals for subsequent calculation modules to perform full feedforward and resonant feedforward calculation of grid voltage. The calculation module can use a DSP, MCU or FPGA processor to determine the sampling frequency, perform full feedforward and resonant feedforward calculation of grid voltage, save the inductance value of the inductor under different currents, perform current outer loop and other tasks. The PWM execution module is generally implemented by using a PWM output module or CPLD chip provided by a DSP / MCU to control the switch of the grid-connected inverter to be turned on or off, and realize the control algorithm designed by the method of the present invention.

[0029] The method of the present invention can effectively improve the accuracy of grid voltage sampling and the stability of control, thereby improving the stability and reliability of the entire power system. The method is not only applicable to various grid conditions, but also has important significance for improving the power quality of distributed power generation systems.

[0030] like Figure 5 As shown, the specific steps of the method of the present invention are as follows: Step 1, use the current transformer to collect the current data on the inverter side. According to the inverter output current and inductance data manual, first fit the functional relationship between the inductance value and the inductance current. Through this fitting method, the inductance-current relationship is obtained. This function can help calculate the inductance value of the inductor under the current at the current moment, that is, the instantaneous value of the inductance parameter. During the actual operation of the inverter, the control system will calculate the instantaneous value of the inductance parameter according to the current inverter output current, and adjust the control algorithm in real time to realize the precise grid voltage full feedforward algorithm, ensuring that the grid voltage can be accurately controlled and adjusted under various current conditions. This full feedforward method based on the calculation of the instantaneous value of the inductance parameter enables the control strategy to adapt to the actual working state of the inductor element, and improves the system's response speed and control accuracy to grid voltage changes.

[0031] In Step 1, the inductance L is obtained based on the inverter output current and inductance data sheet or actual measurement. 1 The inductance values ​​at 0A and full load are L 0 With L e , generally speaking, the following relationship can be obtained: , Where I is the instantaneous value of the inverter output current (also the inductor current) collected, I e is the inductor current at full load.

[0032] Step 2, use voltage transformer, resistor divider and first-order active low-pass filter to obtain grid voltage. The grid voltage sampling method includes a series of precise steps to ensure the accurate measurement and processing of grid voltage, including: initially using voltage transformer to accurately collect grid voltage; then using resistor divider to divide the collected voltage to reduce it to a suitable measurement level. This step is crucial to ensure the safety and accuracy of subsequent measurements; next, use a first-order active low-pass filter to filter the divided voltage signal to effectively remove noise and interference and improve the purity of the signal. Finally, the grid voltage full feedforward algorithm based on LLCL filter is implemented to deeply process the filtered voltage signal. The algorithm realizes precise control and regulation of grid voltage by predicting the disturbance of grid voltage and making corresponding compensation, thereby providing a stable and reliable voltage source for the inverter. This process not only improves the accuracy of voltage sampling, but also enhances the stability and reliability of the inverter in the grid.

[0033] The transfer function of the grid voltage full feedforward algorithm is as follows: , , Where s is the Laplace operator, G ff1 is the grid voltage feedforward function at the input of the current control loop, G ff2 is the grid voltage feedforward function at the modulation signal, L 1 , C 1 , R d and L f They are the parameters of the second inductor (i.e. the main inductor of the power circuit), the first capacitor, the resistor and the first inductor (i.e. the inductor of the resonant filter branch) of the LLCL filter, where R d is a passive damping resistor.

[0034] Step 3, after the grid voltage sampling link, the method of the present invention particularly considers the one-beat delay phenomenon existing in the first-order active low-pass filter and the digital controller, which will affect the phase and amplitude of the sampled grid voltage signal. In order to compensate for this, a proportional resonant controller with a phase advance function is adopted. For the nth harmonic, according to the phase delay and amplitude offset of the one-beat delay of the first-order active low-pass filter and the digital controller at this frequency, different proportional and phase parameters of the proportional resonant controller with phase advance are designed. By finely adjusting the proportional gain, resonant frequency, resonant bandwidth and resonant gain, accurate feedforward control of the grid voltage can be achieved at different harmonic frequencies. In this way, the stability of the inverter output current can be maintained even in the case of grid harmonics and voltage mutations. The method of the present invention not only improves the accuracy of grid voltage sampling, but also significantly enhances the stability of the inverter control system, ensuring the high-quality output of the grid-connected current.

[0035] In the Step 3, the proportional resonant controller used is a proportional resonant controller with phase shift, and the transfer function of the nth harmonic can be in the following two forms: , , Where s is the Laplace operator, k n is the proportional coefficient of the proportional resonant controller, ω cn is the bandwidth of the proportional resonant controller, ω n is the resonant frequency of the proportional resonant controller, θ n is the leading phase of the proportional resonant controller; The transfer function of the first-order active filter is calculated as follows, where ω c is the bandwidth of the first-order active filter: , θ n The calculation of needs to consider the grid voltage phase lag caused by the first-order active filter and the one-step digital controller: , where z -1 is a one-beat delay, which can be expressed as , T s is the sampling frequency of the control system, and j is an imaginary number.

[0036] k n The calculation of needs to take into account the amplitude attenuation caused by the first-order active filter: .

[0037] The sampling circuit structure of the first-order active low-pass filter used in the method of the present invention is shown in the attached figure. Figure 6 As shown, the first sampling voltage-dividing resistor R connected in series in the resonant circuit 7 The second sampling voltage divider resistor R 6 A first resistor R is provided between 2 Then connect to the inverting input terminal of the operational amplifier, the fourth resistor R 5 The second resistor R 3 And the third capacitor C 3 After the connection, it is connected to the operational amplifier non-inverting input terminal, and the third resistor R is also connected to the inverting input terminal of the operational amplifier. 4 and the fifth resistor R 8 , and the third resistor R 4 A second capacitor C is also provided in parallel with it. 2 , where the second sampling voltage divider resistor R 6 , the second resistor R 3 , the fourth resistor R 5 and the fifth resistor R 8 These components form a first-order low-pass filter with a bandwidth of ω c is 1 / (R 4 C 2 ).

[0038] The method of the present invention compensates the one-beat delay of the first-order active low-pass filter and digital control through a proportional resonant controller, effectively handles the phase and amplitude deviations in the grid voltage sampling, and ensures the response speed and stability of the system. The design of the proportional resonant controller enables the system to have higher accuracy and stability under n-order grid harmonics, especially when the grid conditions are complex or there is harmonic interference.

[0039] According to the attached Figure 7 , is the overall control algorithm structure diagram of the full feedforward method control strategy based on the instantaneous value of the inductance parameter proposed in the present invention, in which i ref is the current reference value at the input of the current control loop, v pcc is the grid voltage, i 1 is the inverter side current, i 2 is the grid-side current, i h is the LRC series branch current, G c It is a current controller, which can be in various forms such as PI, repetitive control and proportional resonance control. G represents the extraction function of the harmonic voltage of the power grid from 1st to nth order. delay is the delay formed by the first-order low-pass filter and digital control, and its function calculation is as follows: .

[0040] Specifically: first, the inductance value is calculated in real time based on the sampled inductor current, and then the sampled grid voltage v pcc , combined with a proportional resonant controller with phase offset, extract the fundamental and harmonic components of the 1-nth grid voltage and sum them, and finally execute the grid voltage full feedforward algorithm to obtain the grid voltage feedforward function G at the input of the current control loop ff1 And the grid voltage feedforward function G at the modulation signal ff2 , realizing full decoupling of grid voltage and resonant feedforward algorithm.

[0041] By proactively considering the dynamic changes of the grid voltage, the LLCL grid-connected inverter using the method of the present invention can accurately control the output current of the inverter, utilize grid voltage feedforward to eliminate the influence of grid voltage harmonics on the output current of the inverter, make the current output by the inverter independent of the grid, avoid mutual interference, achieve full decoupling, significantly improve the power quality of the grid, have strong adaptability, and be able to dynamically adjust control parameters according to the actual output current changes of the inverter, which is of great significance to the reliability and efficiency of the grid-connected inverter system.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for full grid voltage decoupling and resonant feedforward control of LLCL grid-connected inverter, characterized in that: The following steps are included: Step 1: First, according to the output current of the inverter and the data sheet of the inductor used, fit the functional relationship between the inductance value and the inductor current, and calculate the instantaneous value of the inductance parameter under the current at the current moment; Step 2, using voltage transformer, resistor divider and first-order active low-pass filter to extract grid voltage and execute grid voltage full feed-forward algorithm; Step 3, for different frequencies, according to the phase delay and amplitude offset of the first-order active low-pass filter and the one-beat delay of the digital controller at the frequency, design different proportional and phase parameters of the proportional resonant controller with phase advance.

2. The LLCL grid-connected inverter grid voltage full decoupling and resonant feedforward control method according to claim 1 is characterized by: In Step 1, according to the inverter output current and inductance data sheet or actual measurement, the inductance values ​​of inductor L1 at 0A and full load are L0 and L1 respectively. e , we get the following relationship: ， Where I is the instantaneous value of the inductor current, I e is the inductor current at full load.

3. The LLCL grid-connected inverter grid voltage full decoupling and resonant feedforward control method according to claim 1 is characterized by: In the Step 2, the specific method for obtaining the real-time value of the grid voltage is: first, the grid voltage is sampled using a voltage transformer, and then the sampled voltage is divided by a resistor divider to reduce the voltage to a level suitable for measurement, and then the divided voltage signal is filtered using a first-order active low-pass filter to remove noise and interference, and finally, the filtered voltage signal is processed using a grid voltage full feedforward algorithm based on an LLCL filter, and the disturbance of the grid voltage is predicted and compensated by the algorithm to achieve precise control and regulation of the grid voltage.

4. The LLCL grid-connected inverter grid voltage full decoupling and resonant feedforward control method according to claim 3 is characterized by: The transfer function of the grid voltage full feedforward algorithm is as follows: ， ， Among them G ff1 is the grid voltage feedforward function at the input of the current control loop, G ff2 is the grid voltage feedforward function at the modulation signal, s is the Laplace operator, L1, C1, R d and L f are the inductance, capacitance and resistance parameters of LLCL filter respectively, where R d is a passive damping resistor, L1 is the main inductance of the power circuit, and L f is the inductance of the resonant filter branch.

5. The LLCL grid-connected inverter grid voltage full decoupling and resonant feedforward control method according to claim 1, characterized in that: In the Step 3, the proportional resonant controller used is a proportional resonant controller with phase shift, and the transfer function of the nth harmonic is in the following two forms: ， ， Where s is the Laplace operator, k n is the proportional coefficient of the proportional resonant controller, ω cn is the bandwidth of the proportional resonant controller, ω n is the resonant frequency of the proportional resonant controller, θ n is the leading phase of the proportional resonant controller; The transfer function of the first-order active filter is calculated as follows, where ω c is the bandwidth of the first-order active filter: ， The leading phase θ of the proportional resonant controller n The grid voltage phase lag caused by the first-order active filter and the one-step digital controller is calculated as follows: ， where z -1 is a one-beat delay, which can be expressed as , T s is the sampling frequency of the control system, j is an imaginary number, The proportional coefficient k of the proportional resonant controller n The amplitude attenuation caused by the first-order active low-pass filter is calculated as: 。 6. The LLCL grid-connected inverter grid voltage full decoupling and resonant feedforward control method according to claim 1, characterized in that: The method also includes a real-time sampling circuit for grid voltage, a calculation module and a PWM execution module. The real-time sampling circuit for grid voltage is used to collect the real-time value of grid voltage and filter out high-frequency noise signals for subsequent calculation modules to perform full feedforward and resonant feedforward calculations of grid voltage. The calculation module uses a DSP, MCU or FPGA processor to determine the sampling frequency, perform full feedforward and resonant feedforward calculations of grid voltage, save the inductance value of the inductor under different currents, and perform current outer loop tasks. The PWM execution module is implemented using a PWM output module or CPLD chip provided by the DSP / MCU to control the switch of the grid-connected inverter to be turned on or off.

7. An LLCL grid-connected inverter, used in the LLCL grid-connected inverter grid voltage full decoupling and resonant feedforward control method according to any one of claims 1 to 6, characterized in that: The inverter main circuit of the grid-connected inverter is connected to the power grid through an LLCL filter connected to the circuit. The grid-connected inverter is also provided with a real-time sampling circuit connected to the LLCL filter circuit for extracting the power grid voltage, a calculation module for performing a full feedforward algorithm for the power grid voltage via the data information obtained by the sampling circuit, and a PWM execution module for accurately controlling and adjusting the power grid voltage according to the calculation results. The PWM execution module sends modulation and drive signals to the inverter main circuit through the drive circuit. The inverter main circuit is provided with a DC side capacitor on the DC side.

8. The LLCL grid-connected inverter according to claim 7, characterized in that: The sampling circuit for extracting the grid voltage includes a voltage transformer for collecting the grid voltage, a resistor divider for dividing the collected voltage, and a first-order active low-pass filter for filtering the divided voltage signal. The calculation module adopts a DSP, MCU or FPGA processor, and the PWM execution module adopts a PWM output module or CPLD chip provided by the DSP / MCU.

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