LCL grid-connected inverter and control method thereof for suppressing harmonic current of filter capacitor

Abstract

The invention provides an LCL grid-connected inverter and a control method for suppressing harmonic current of a filter capacitor. The control method comprises the following steps: acquiring capacitor voltage and a power grid phase locking angle of the filter capacitor; based on the capacitor voltage and the power grid phase locking angle, determining a compensation wave generation voltage of a target harmonic order; superposing the compensation wave-emitting voltage and the wave-emitting voltage to obtain a final wave-emitting voltage; and processing the final wave sending voltage by adopting a wave sending algorithm to generate a driving signal for controlling the LCL grid-connected inverter. The method provided by the invention inhibits the harmonic current of the filter capacitor, thereby prolonging the service life of the filter capacitor.

Description

Technical Field

[0001] The present invention relates to the technical field of inverter control, and in particular to an LCL grid-connected inverter and a control method thereof for suppressing harmonic current of a filter capacitor. Background Art

[0002] With the large-scale grid connection of new energy, the background harmonic problem in the power grid is becoming increasingly serious. As the interface device between new energy and the public power grid, the LCL grid-connected inverter plays a key role in the grid connection quality and stable operation of new energy.

[0003] Among them, the filter capacitor is directly added across the grid voltage, playing the role of a high-order filter channel, which can suppress the harmonics caused by high-frequency switching, help output a smoother current waveform, and reduce harmonic pollution to the grid.

[0004] However, since the actual grid voltage cannot be an ideal sinusoidal waveform, there is only the fundamental component but no harmonics of other orders. There may be background harmonics of different orders in the actual grid voltage. For LCL type grid-connected inverters, the background harmonics of the grid voltage will also cause harmonic currents of corresponding orders on the filter capacitor. If no suppression measures are taken, it will bring greater pressure to the filter capacitor and have an adverse effect on the life of the filter capacitor. Summary of the invention

[0005] The invention provides an LCL grid-connected inverter and a control method for suppressing harmonic current of a filter capacitor, which suppresses the harmonic current of the filter capacitor and thus prolongs the working life of the filter capacitor.

[0006] According to a first aspect of an embodiment of the present invention, a control method for suppressing harmonic current of a filter capacitor of an LCL grid-connected inverter is provided, and the control method includes:

[0007] Collect the capacitor voltage of the filter capacitor and the grid phase-locking angle;

[0008] Based on the capacitor voltage and the grid phase-locking angle, the compensation wave voltage of the target harmonic order is determined;

[0009] The compensation wave-generating voltage and the wave-generating voltage are superimposed to obtain the final wave-generating voltage;

[0010] The final wave voltage is processed by a wave algorithm to generate a drive signal for controlling the LCL grid-connected inverter.

[0011] In a possible implementation, based on the capacitor voltage and the grid phase-locking angle, determining the compensation wave voltage of the target harmonic order includes:

[0012] Based on the grid phase-locking angle, the capacitor voltage is transformed into the harmonic rotation coordinate system of the target harmonic order to obtain the target capacitor voltage;

[0013] By filtering the target capacitor voltage, the harmonic voltage is extracted;

[0014] Based on the harmonic voltage, the proportional integral (PI) control link is used for regulation to obtain the regulation amount;

[0015] Transform the adjustment amount into the wave compensation amount in the fundamental wave coordinate system;

[0016] The phase compensation is performed on the wave compensation amount to obtain the compensated wave voltage.

[0017] In a possible implementation, based on the grid phase-locking angle, the capacitor voltage is transformed into a harmonic rotating coordinate system of a target harmonic order to obtain a target capacitor voltage, including:

[0018] Based on the capacitor voltage and the target harmonic order, the target capacitor voltage is determined using the following formula:

[0019]

[0020] Among them, v dcap is the d-axis target capacitor voltage, v qcap is the q-axis target capacitor voltage, n is the target harmonic order, θ g is the grid phase-locking angle, v ab 、v bc 、v ca is the instantaneous value of the three-phase line voltage of the capacitor voltage.

[0021] In a possible implementation, the target capacitor voltage is filtered to extract the harmonic voltage, including:

[0022] The capacitor voltage is filtered using a low-pass filter to obtain the harmonic voltage.

[0023] In a possible implementation, the d-axis set value and the q-axis set value of the PI control link are both 0, the d-axis feedback value is the opposite of the q-axis component of the harmonic voltage, and the q-axis feedback value is the d-axis component of the harmonic voltage; based on the harmonic voltage, the PI control link is used for adjustment to obtain the adjustment amount, including:

[0024] The d-axis given value and the d-axis feedback value are adjusted by using the PI control link to obtain the d-axis adjustment value;

[0025] The q-axis given value and the q-axis feedback value are adjusted using the PI control link to obtain the q-axis adjustment value.

[0026] In a possible implementation, the adjustment amount is transformed into a wave compensation amount in a fundamental wave coordinate system, including:

[0027] Based on the adjustment amount and the target harmonic order, the adjustment amount is transformed into the harmonic compensation amount in the fundamental wave coordinate system using the following formula:

[0028]

[0029] Among them, u dComp is the d-axis wave compensation, u qComp is the q-axis wave compensation, n is the target harmonic order, θ g is the grid phase-locking angle, u dPIout is the d-axis adjustment amount, u qPIout is the q-axis adjustment amount.

[0030] In a possible implementation, performing phase compensation on the wave generation compensation amount to obtain a compensated wave generation voltage includes:

[0031] According to the compensation amount and compensation phase of the wave generator, the compensation wave generator voltage is calculated using the following formula:

[0032]

[0033] Among them, u dh is the d-axis compensation wave voltage, u qh is the q-axis compensation wave voltage, θ comp is the compensation phase, u dComp is the d-axis wave compensation, u qComp It is the q-axis wave compensation amount.

[0034] In a possible implementation, before superimposing the compensation wave-generating voltage and the wave-generating voltage to obtain a final wave-generating voltage, the method further includes:

[0035] Collect the grid-side current, actual bus voltage value, and actual reactive power value of the LCL grid-connected inverter;

[0036] Transform the coordinate system of the grid-side current to obtain the d-axis current feedback value and the q-axis current feedback value;

[0037] The actual bus voltage value and the bus voltage set value are adjusted by the bus voltage control link to obtain the d-axis current set value;

[0038] The reactive power actual value and the reactive power set value are adjusted by the reactive power control link to obtain the q-axis current set value;

[0039] According to the d-axis current feedback value, the q-axis current feedback value, the d-axis current given value and the q-axis current given value, the current control link is adopted to adjust and obtain the wave voltage.

[0040] According to a second aspect of an embodiment of the present invention, a LCL grid-connected inverter is provided, the LCL grid-connected inverter comprising: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, a control method for suppressing the harmonic current of the filter capacitor of the LCL grid-connected inverter is implemented as in the first aspect or any possible implementation method of the first aspect.

[0041] According to a third aspect of an embodiment of the present invention, a computer-readable storage medium is provided, on which computer program instructions are stored. When the computer program instructions are executed by a processor, a control method for suppressing harmonic current of a filter capacitor of an LCL grid-connected inverter in the first aspect of the present invention or any possible implementation of the first aspect is implemented.

[0042] An embodiment of the present invention provides a control method for suppressing the harmonic current of a filter capacitor of an LCL grid-connected inverter. When it is known that the grid voltage contains harmonics of a target harmonic order, a compensation wave voltage of the target harmonic order is calculated according to the sampled capacitor voltage. By superimposing the compensation wave voltage on the output end of the converter, the purpose of suppressing the capacitor current harmonics is achieved, thereby extending the working life of the filter capacitor. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0044] Figure 1 A schematic diagram of a control structure of an LCL grid-connected inverter provided by an embodiment of the present invention;

[0045] Figure 2 A schematic flow chart of a control method for suppressing harmonic current of a filter capacitor of an LCL grid-connected inverter provided by an embodiment of the present invention;

[0046] Figure 3 A schematic diagram of a control structure of a coordinate system transformation link and a low-pass filtering link provided by an embodiment of the present invention;

[0047] Figure 4 A schematic diagram of the control structure of a PI control link and a coordinate system transformation link provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0048] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0049] The embodiment of the present invention provides a control structure of an LCL grid-connected inverter. Figure 1 As shown, including the power grid, power grid and box transformer impedance L g , filter capacitor C, converter internal inductor L, inverter, bus capacitor, DC energy feeding side, and control loop of LCL grid-connected inverter, etc.

[0050] The control loop of the LCL grid-connected inverter includes a phase-locked module, a bus voltage control link, a reactive power control link, a current control link, a capacitor voltage current harmonic suppression link, and a wave generation algorithm processing link.

[0051] Impedance L of power grid, phase-locked module, power grid and box-type transformer g , filter capacitor C, converter internal inductor L, and inverter are connected in sequence, and the wave generation algorithm processing link of the control loop of the LCL grid-connected inverter generates a drive signal to drive the inverter.

[0052] Combine the following Figure 1 A control method for suppressing harmonic current of a filter capacitor of an LCL grid-connected inverter provided by an embodiment of the present invention is described. The control method is applied to the LCL grid-connected inverter, such as Figure 2 As shown, the control method may include the following steps:

[0053] S210, collecting the capacitor voltage of the filter capacitor and the grid phase-locking angle.

[0054] The capacitor voltage of the filter capacitor is sampled to obtain the instantaneous value v of the three-phase line voltage of the capacitor voltage. ab 、v bc 、v ca .

[0055] The phase-locking module locks the phase to obtain the grid phase-locking angle θ g .

[0056] S220, determining a compensation wave voltage of a target harmonic order based on the capacitor voltage and the grid phase-locking angle.

[0057] The capacitor voltage and the grid phase-locking angle are input into the current harmonic suppression link of the capacitor voltage. After the current harmonic suppression link of the capacitor voltage is adjusted, the d-axis compensation wave voltage u of the target harmonic order is output. dh and q-axis compensation wave voltage u qh.

[0058] S230, superimposing the compensation wave-generating voltage and the wave-generating voltage to obtain a final wave-generating voltage.

[0059] Calculate the d-axis compensation wave voltage u dh and d-axis wave voltage u d The final d-axis wave voltage is obtained by Calculate the q-axis compensation wave voltage u qh With q-axis wave voltage u q The final q-axis wave voltage is obtained by

[0060] S240, the final wave-generating voltage is processed by a wave-generating algorithm to generate a driving signal for controlling the LCL grid-connected inverter.

[0061] The d-axis wave voltage And the final q-axis wave voltage The wave generation algorithm is used to process the loop regulation to obtain the A, B, and C phase PWM wave generation amount cmp of the LCL grid-connected inverter a 、cmp b 、cmp c .

[0062] The control method for suppressing the harmonic current of the filter capacitor of the LCL grid-connected inverter provided in an embodiment of the present invention calculates the compensation wave voltage of the target harmonic order according to the sampled capacitor voltage when the grid voltage is known to contain harmonics of the target harmonic order. By superimposing the compensation wave voltage on the output end of the converter, the purpose of suppressing the capacitor current harmonics is achieved, thereby extending the working life of the filter capacitor.

[0063] In one embodiment, in S230, before superimposing the compensation wave voltage and the wave voltage to obtain the final wave voltage, the Figure 1 , the control method further comprises the following steps:

[0064] S1, collects the grid-side current i of the LCL grid-connected inverter a 、i b 、i c , Actual value of bus voltage V dc , Actual value of reactive power Q * .

[0065] S2, transforming the coordinate system of the grid-side current to obtain a d-axis current feedback value and a q-axis current feedback value.

[0066] The grid-side current i a 、i b 、i c After coordinate system transformation, the d-axis current feedback value i is obtained dand q-axis current feedback value i q .

[0067] S3, the actual value of bus voltage V dc and bus voltage setting value The bus voltage control link is used to adjust the d-axis current given value i d * .

[0068] S4, the actual value of reactive power Q * And reactive power given value Q, adopt reactive power control link to adjust, get q axis current given value i q * .

[0069] S5, according to the d-axis current feedback value i d , q-axis current feedback value i q , d-axis current given value i d * and q-axis current given value i q * , the current control link is used to adjust and obtain the wave voltage.

[0070] The control method provided by the embodiment of the present invention adopts a bus voltage control loop, a reactive power control loop and a current control loop to adjust to the wave voltage.

[0071] In one embodiment, S220: determining the compensation wave voltage of the target harmonic order based on the capacitor voltage and the grid phase-locking angle may include the following steps:

[0072] S221, based on the grid phase-locking angle, transform the capacitor voltage into a harmonic rotating coordinate system of the target harmonic order to obtain a target capacitor voltage.

[0073] like Figure 3 As shown, in the coordinate system to harmonic rotation coordinate system transformation link, based on the capacitor voltage and the target harmonic order, the target capacitor voltage is determined by the following formula:

[0074]

[0075] Among them, v dcap is the d-axis target capacitor voltage, v qcap is the q-axis target capacitor voltage, n is the target harmonic order, θ g is the grid phase-locking angle, v ab 、v bc 、v ca is the instantaneous value of the three-phase line voltage of the capacitor voltage.

[0076] S222, extracting harmonic voltage by filtering the target capacitor voltage.

[0077] like Figure 3 As shown, the capacitor voltage is filtered by a low-pass filter in the low-pass filter link to obtain the d-axis harmonic voltage v dcap_filt and q-axis harmonic voltage v qcap_filt .

[0078] In one example, the transfer function of the low-pass filter is Among them, ω c is the corner frequency of the low-pass filter function.

[0079] S223, based on the harmonic voltage, a proportional integral (PI) control link is used to perform regulation to obtain a regulation amount.

[0080] like Figure 4 As shown, the d-axis given value and the q-axis given value of the PI control link are both 0, the d-axis feedback value is the opposite of the q-axis component of the harmonic voltage, and the q-axis feedback value is the d-axis component of the harmonic voltage; based on the harmonic voltage, the PI control link is used for adjustment to obtain the adjustment amount, including:

[0081] The d-axis given value and the d-axis feedback value are adjusted by using the PI control link to obtain the d-axis adjustment value;

[0082] The q-axis given value and the q-axis feedback value are adjusted using the PI control link to obtain the q-axis adjustment value.

[0083] S224, transforming the adjustment amount into a wave compensation amount in a fundamental wave coordinate system.

[0084] like Figure 4 As shown, in the transformation link from harmonic rotation coordinate system to fundamental wave coordinate system, based on the adjustment amount and target harmonic order, the adjustment amount is transformed into the wave compensation amount in the fundamental wave coordinate system by using the following formula:

[0085]

[0086] Among them, u dComp is the d-axis wave compensation, u qComp is the q-axis wave compensation, n is the target harmonic order, θ g is the grid phase-locking angle, u dPIout is the d-axis adjustment amount, u qPIout is the q-axis adjustment amount.

[0087] S225, performing phase compensation on the wave generation compensation amount to obtain a compensated wave generation voltage.

[0088] In one embodiment, the compensation wave voltage is calculated according to the wave compensation amount and the compensation phase using the following formula:

[0089]

[0090] Among them, u dh is the d-axis compensation wave voltage, u qh is the q-axis compensation wave voltage, θ comp is the compensation phase, u dC omp is the compensation value of d-axis wave, u qComp It is the q-axis wave compensation amount.

[0091] Compensation phase θ comp It is configurable based on demand.

[0092] In one example, the grid voltage background harmonic is described as being of order 13. For harmonics of other orders, the method is applicable as long as their frequencies are below half of the controller control frequency (ie, the Nyquist frequency).

[0093] Target harmonic order n = 13:

[0094] First, the capacitor voltage is transformed into the harmonic rotation coordinate system of the target harmonic order using the following formula to obtain the target capacitor voltage:

[0095]

[0096] After the coordinate change, the fundamental wave appears as a 12th sinusoidal component in the corresponding harmonic rotation coordinate, while the 13th harmonic voltage in the relative capacitor voltage appears as a DC component in the 13th rotation coordinate after the coordinate change.

[0097] Therefore, a low-pass filter is used to filter the target capacitor voltage to obtain the harmonic voltage.

[0098] The transfer function is The low-pass filter filters the target capacitor voltage and extracts the d-axis harmonic voltage v dcap_filt and q-axis harmonic voltage v qcap_filt .

[0099] Then, after that, change -v qcap_filt As the feedback value of the PI control link with the d-axis given value of 0 in the 13th harmonic rotating coordinate system; as the feedback of the PI control link with the q-axis given value of 0 in the 13th harmonic rotating coordinate system, the PI control link outputs the d-axis adjustment value u dPIout , and q-axis adjustment u qPIout .

[0100] Secondly, based on the adjustment amount and the target harmonic order, the adjustment amount is transformed into the harmonic compensation amount in the fundamental wave coordinate system using the following formula:

[0101]

[0102] Finally, according to the compensation amount and compensation phase of the wave generator, the compensation wave generator voltage is calculated using the following formula:

[0103]

[0104] will u dh 、u qh The d-axis wave voltage u is superimposed on the current control output d , q-axis wave voltage u q The final wave voltage is obtained

[0105] The control method provided by the embodiment of the present invention transforms the sampled capacitor voltage to a harmonic rotating coordinate system of a corresponding order, extracts the d-axis and q-axis harmonic voltages of the harmonic voltage in the capacitor voltage in the harmonic rotating coordinate system of a corresponding order through a low-pass filtering link, then inverts the q-axis harmonic voltage as feedback of the PI control link with a d-axis given value of 0 in the harmonic rotating coordinate system, and uses the d-axis harmonic voltage as feedback of the PI control link with a q-axis given value of 0 in the harmonic rotating coordinate system, outputs the corresponding adjustment amount, and then transforms the adjustment amount to a fundamental wave synchronous coordinate system through coordinate change, and then superimposes it on the converter wave voltage after a phase compensation link to obtain the final wave voltage. The purpose of suppressing the capacitor current harmonics is achieved by superimposing harmonics with appropriate amplitude and phase of the corresponding order at the output end of the converter.

[0106] An embodiment of the present invention also provides an LCL grid-connected inverter, which includes: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, the control method for suppressing the harmonic current of the filter capacitor of the LCL grid-connected inverter provided in the above embodiment is implemented.

[0107] An embodiment of the present invention also provides a computer-readable storage medium having computer program instructions stored thereon, and the computer program instructions are executed by a processor to execute the steps of the control method of the LCL grid-connected inverter for suppressing the harmonic current of the filter capacitor of the various embodiments of the present invention described above in this specification.

[0108] For the above-mentioned method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the order of the actions described, because according to the present invention, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily required by the present invention.

[0109] It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0110] The steps in the methods of the embodiments of the present invention may be adjusted in order, combined, or deleted according to actual needs, and the technical features recorded in the embodiments may be replaced or combined.

[0111] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control method for suppressing harmonic current of filter capacitor of LCL grid-connected inverter, characterized in that: The control method comprises: Collect the capacitor voltage of the filter capacitor and the grid phase-locking angle; Determining a compensation wave voltage of a target harmonic order based on the capacitor voltage and the grid phase-locking angle; Superimposing the compensation wave-generating voltage and the wave-generating voltage to obtain a final wave-generating voltage; The final wave-generating voltage is processed by a wave-generating algorithm to generate a driving signal for controlling the LCL grid-connected inverter.

2. The control method according to claim 1, characterized in that: The step of determining the compensation wave voltage of the target harmonic order based on the capacitor voltage and the grid phase-locking angle comprises: Based on the grid phase-locked angle, the capacitor voltage is transformed into a harmonic rotating coordinate system of a target harmonic order to obtain a target capacitor voltage; Extracting harmonic voltage by filtering the target capacitor voltage; Based on the harmonic voltage, a proportional-integral (PI) control link is used for regulation to obtain a regulation amount; Transforming the adjustment amount into a wave compensation amount in a fundamental wave coordinate system; Phase compensation is performed on the wave generation compensation amount to obtain a compensated wave generation voltage.

3. The control method according to claim 2, characterized in that: Based on the grid phase-locked angle, the capacitor voltage is transformed into a harmonic rotating coordinate system of a target harmonic order to obtain a target capacitor voltage, including: Based on the capacitor voltage and the target harmonic order, the target capacitor voltage is determined using the following formula: Among them, v dcap is the d-axis target capacitor voltage, v qcap is the q-axis target capacitor voltage, n is the target harmonic order, θ g is the grid phase-locking angle, v ab 、v bc 、v ca is the instantaneous value of the three-phase line voltage of the capacitor voltage.

4. The control method according to claim 2, characterized in that: By filtering the target capacitor voltage, the harmonic voltage is extracted, including: The capacitor voltage is filtered by a low-pass filter to obtain the harmonic voltage.

5. The control method according to claim 2, characterized in that: The d-axis given value and the q-axis given value of the PI control link are both 0, the d-axis feedback value is the opposite of the q-axis component of the harmonic voltage, and the q-axis feedback value is the d-axis component of the harmonic voltage; Based on the harmonic voltage, a PI control link is used for regulation to obtain a regulation amount, including: The d-axis given value and the d-axis feedback value are adjusted by the PI control link to obtain a d-axis adjustment value; The q-axis given value and the q-axis feedback value are adjusted by using the PI control link to obtain the q-axis adjustment value.

6. The control method according to claim 2, characterized in that: The adjustment amount is transformed into a wave compensation amount in a fundamental wave coordinate system, including: Based on the adjustment amount and the target harmonic order, the adjustment amount is transformed into the harmonic compensation amount in the fundamental wave coordinate system using the following formula: Among them, u dComp is the d-axis wave compensation, u qComp is the q-axis wave compensation amount, n is the target harmonic order, θ g is the grid phase-locking angle, u dPIout is the d-axis adjustment amount, u qPIout is the q-axis adjustment amount.

7. The control method according to claim 2, characterized in that: Performing phase compensation on the wave generation compensation amount to obtain a compensated wave generation voltage includes: According to the wave compensation amount and compensation phase, the compensation wave voltage is calculated using the following formula: Among them, u dh is the d-axis compensation wave voltage, u qh is the q-axis compensation wave voltage, θ comp is the compensation phase, u dComp is the d-axis wave compensation, u qComp It is the q-axis wave compensation amount.

8. The control method according to claim 1, characterized in that: Before superimposing the compensation wave-generating voltage and the wave-generating voltage to obtain a final wave-generating voltage, the method further includes: Collecting the grid-side current, actual value of bus voltage, and actual value of reactive power of the LCL grid-connected inverter; Performing coordinate system transformation on the grid-side current to obtain a d-axis current feedback value and a q-axis current feedback value; The actual bus voltage value and the bus voltage set value are adjusted by a bus voltage control link to obtain a d-axis current set value; The reactive power actual value and the reactive power set value are adjusted by a reactive power control link to obtain a q-axis current set value; The wave generating voltage is obtained by adjusting the current control link according to the d-axis current feedback value, the q-axis current feedback value, the d-axis current given value and the q-axis current given value.

9. An LCL grid-connected inverter, characterized in that: The LCL grid-connected inverter comprises: a processor and a memory storing computer program instructions; when the processor executes the computer program instructions, the control method for suppressing harmonic current of the filter capacitor of the LCL grid-connected inverter as described in any one of claims 1-8 is implemented.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer program instructions, and when the computer program instructions are executed by the processor, the control method for suppressing harmonic current of the filter capacitor of the LCL grid-connected inverter as described in any one of claims 1-8 is implemented.

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