Method and system for suppressing third harmonic of grid-forming converter

Abstract

The invention provides a control method for suppressing third harmonic current of a grid-constructing type converter, which is applied to a three-phase four-wire grid-constructing type converter, and the converter is connected in parallel with a generator containing a third harmonic voltage component. The method comprises the following steps: sampling an output voltage and an output current of the network-forming converter; performing coordinate transformation on the sampled output voltage to extract a zero-axis voltage component; third harmonic compensation voltage is generated through a quasi-resonance controller based on the zero-axis voltage component, and the resonant frequency of the quasi-resonance controller is set to be three times of the rated angular frequency of the system; and introducing the third harmonic compensation voltage into a zero-axis voltage and current double-closed-loop control loop of the network-forming converter to offset a third harmonic voltage component in the voltage feedback signal. Quasi-resonance control is added to the zero-axis voltage loop to obtain the third harmonic compensation voltage to offset third harmonic voltage feedback, and generation of third harmonic current is suppressed, so that the quality of output electric energy of the converter is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of grid-forming energy storage converter control, and more particularly, to a method and system for suppressing third harmonic of grid-forming converter. BACKGROUND

[0002] With the development and popularization of new energy power generation technology, and the inevitable trend of high proportion of power electronic power supply such as new energy to energy transformation, grid-forming converter is a key device connecting new energy generation and power grid. However, due to the structural characteristics and magnetic circuit non-uniformity of the generator rotor winding, there is more or less third harmonic voltage in the generator. When the grid-forming converter is connected to the power grid or diesel generator system, since the grid-forming converter is a voltage source control, the feedback voltage of the voltage loop will generate distorted current in response to the distorted voltage, reducing the output power quality. When the grid-forming energy storage converter is combined with the diesel generator to access industrial, residential and other unbalanced loads, the three-phase four-wire connection method provides a loop for unbalanced current and also provides a loop for third harmonic current, reducing the output power quality of the converter. Therefore, in order to improve the output power quality of the grid-forming converter, it is necessary to suppress the third harmonic current of the converter.

[0003] Therefore, there is a need for a new solution. SUMMARY

[0004] The present application aims to suppress the output third harmonic current of the grid-forming converter caused by the third harmonic voltage of the diesel engine, and provides a method for suppressing the third harmonic of the grid-forming converter, and improves the output power quality of the converter.

[0005] According to one aspect of the present application, a control method for suppressing third harmonic current of a grid-forming converter is provided, which is applied to a three-phase four-wire grid-forming converter, the converter is connected in parallel with a generator containing a third harmonic voltage component, and the method comprises: sampling the output voltage and output current of the grid-forming converter; performing coordinate transformation on the sampled output voltage to extract a zero-axis voltage component; generating a third harmonic compensation voltage based on the zero-axis voltage component through a quasi-resonant controller, the resonant frequency of the quasi-resonant controller is set to three times the rated angular frequency of the system; introducing the third harmonic compensation voltage into the zero-axis voltage and current double closed-loop control loop of the grid-forming converter, which is used to offset the third harmonic voltage component in the voltage feedback signal, so as to suppress the third harmonic current output by the grid-forming converter.

[0006] In the control method for suppressing third harmonic current of the grid-forming converter provided by the present application, the transfer function of the quasi-resonant controller is:

[0007] wherein, is a resonance gain; is a bandwidth coefficient of the resonance peak; is a resonance frequency.

[0008] In the control method for suppressing the third harmonic current of the grid-connected converter provided by the present application, the step of introducing the third harmonic compensation voltage into the zero-axis voltage and current double closed loop control loop of the grid-connected converter for canceling the third harmonic voltage component in the voltage feedback signal to suppress the third harmonic current output by the grid-connected converter comprises: superimposing the difference between the zero-axis voltage component and the zero-axis voltage component reference value and the third harmonic compensation voltage to input a voltage compensation network to generate a zero-axis current reference instruction; According to the zero-axis current reference instruction and the sampled output current, a modulation wave signal is generated through current inner loop control to drive the converter to generate a compensation voltage opposite in phase to the third harmonic voltage of the generator, thereby suppressing the third harmonic current flowing through the converter.

[0009] According to another aspect of the present application, a control system for suppressing the third harmonic current of a grid-connected converter is also provided, which is applied to a three-phase four-wire grid-connected converter connected in parallel with a generator containing a third harmonic voltage component, comprising: a sampling module for sampling the output voltage and output current of the grid-connected converter; a voltage extraction module for performing coordinate transformation on the sampled output voltage to extract a zero-axis voltage component; a compensation voltage generation module for generating a third harmonic compensation voltage based on the zero-axis voltage component through a quasi-resonant controller, the resonance frequency of the quasi-resonant controller being set to three times the rated angular frequency of the system; a suppression module for introducing the third harmonic compensation voltage into the zero-axis voltage and current double closed loop control loop of the grid-connected converter for canceling the third harmonic voltage component in the voltage feedback signal to suppress the third harmonic current output by the grid-connected converter.

[0010] In the control system for suppressing the third harmonic current of the grid-connected converter provided by the present application, the transfer function of the quasi-resonant controller is:

[0011] wherein, is a resonance gain; is a bandwidth coefficient of the resonance peak; is a resonance frequency.

[0012] In the control system for inhibiting the third harmonic current of the grid-connected converter provided by the application, the inhibition module comprises: a zero-axis current reference instruction generation unit, configured to input the difference between the zero-axis voltage component and a zero-axis voltage component reference value and the third harmonic compensation voltage into a voltage compensation network after superposition, and generate a zero-axis current reference instruction; a driving unit, configured to generate a modulation wave signal through current inner loop control according to the zero-axis current reference instruction and the sampled output current, so as to drive the converter to generate a compensation voltage opposite to the phase of the third harmonic voltage of the generator, thereby inhibiting the third harmonic current flowing through the converter.

[0013] According to still another aspect of the application, there is also provided a control device for inhibiting the third harmonic current of the grid-connected converter, comprising a processor and a memory, wherein the memory stores a computer program, and the computer program is executed by the processor to implement the steps of the control method for inhibiting the third harmonic current of the grid-connected converter.

[0014] According to still another aspect of the application, there is also provided a grid-connected converter comprising the control system for inhibiting the third harmonic current of the grid-connected converter.

[0015] The control method and system for inhibiting the third harmonic current of the grid-connected converter provided by the application have the following beneficial effects: the control method for inhibiting the third harmonic current of the grid-connected converter provided by the application compensates for the third harmonic voltage disturbance introduced by the diesel generator in the zero-axis control channel, thereby inhibiting the generation of the third harmonic current from the source; the quasi-resonant controller can provide extremely high gain at three times the fundamental frequency, thereby realizing approximate zero-error tracking and active cancellation of the third harmonic component, and the harmonic suppression effect is remarkable; the method is an improvement based on the existing control structure of the grid-connected converter, only one quasi-resonant compensation link needs to be added in the zero-axis voltage loop, without increasing the hardware cost of the main circuit, and it is easy to implement on the existing control platform. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only constitute the embodiments of the application, and for those skilled in the art, other drawings can also be obtained without creative labor based on the provided drawings: Figure 1 A grid-connected converter provided by the application is combined with a diesel engine.

[0017] Figure 2 A control system block diagram of a grid-connected converter provided by the application.

[0018] Figure 3 A VSG control block diagram of a grid-forming converter provided by the present application.

[0019] Figure 4 A voltage-current double closed-loop transfer function block diagram of a grid-forming converter provided by the present application.

[0020] Figure 5 A voltage-current double closed-loop transfer function block diagram of a grid-forming converter provided by the present application with compensation voltage control.

[0021] Figure 6 A Bode diagram of a third harmonic resonance controller of a grid-forming converter provided by the present application.

[0022] Figure 7 An experimental result diagram of a grid-forming converter provided by the present application without compensation voltage control under no-load.

[0023] Figure 8 An experimental result diagram of a grid-forming converter provided by the present application with compensation voltage control under no-load.

[0024] Figure 9 An experimental result diagram of a grid-forming converter provided by the present application without compensation voltage control under 50kW load.

[0025] Figure 10 An experimental result diagram of a grid-forming converter provided by the present application with compensation voltage control under 50kW load. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the present application, a more comprehensive description of the present application will be given below with reference to the relevant drawings. The drawings show typical embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application herein are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0028] Figure 1 A grid-forming converter combined with a simplified model of a diesel generator, wherein, and are the output voltage and output current of the grid-forming converter, respectively; and are the output voltage and current of the diesel generator, respectively; are the voltage and current of the load, respectively; are the voltage and current of the load, respectively; are the voltage and current of the load, respectively; is the line impedance. If the influence of the line impedance is ignored, the voltage across the load is equal to the output voltage of the diesel engine . .

[0029] Specifically, in the present application, the grid-forming converter adopts Virtual Synchronous Generator (VSG) control and droop control, and the control system is as shown in Figure 2 , wherein and are the converter-side inductance and grid-side inductance, respectively; is the filter capacitance; is the converter-side inductance current; is the three-phase pulse width modulation (PWM) modulation voltage reference value; is the DC-side voltage of the converter; , , , , , , are the three-phase alternating components of , , , , , , , respectively; , , , are the components of , , , in the synchronous rotating coordinate system. The control system mainly includes power calculation, VSG power control link and voltage and current double closed-loop control link.

[0030] Specifically, in the present application, the VSG power control link is mainly divided into active power control link and reactive power control link, and the control link is as shown in Figure 3 . The VSG active power control link simulates the inertia and damping characteristics of the synchronous generator by introducing the rotor motion equation, thereby providing frequency support for the system. The specific expression is as follows.

[0031]

[0032] wherein, and are active power instruction value and actual output active power of the converter, respectively; and are virtual moment of inertia and damping coefficient of the VSG, respectively; and are rated and actual output angular frequency of the VSG, respectively; is active power-frequency primary frequency modulation coefficient.

[0033] The reactive power control link adopts reactive power-voltage droop control, and generates voltage amplitude by simulating the droop characteristics of the generator, and the expression is as follows.

[0034]

[0035] wherein, and are virtual inertia coefficient and droop coefficient of the VSG, respectively; is effective value of rated output voltage of the VSG; is effective value of output voltage.

[0036] Since the grid-forming converter and the diesel generator adopt three-phase four-wire connection mode, in the voltage and current double closed-loop control link, the d-axis, q-axis and z-axis components need to be controlled respectively. The voltage and current double closed-loop transfer function block diagram is shown in Figure 4 , wherein, is reference voltage of the VSG control to the voltage and current double closed-loop control link; and are transfer functions of the voltage loop and the current loop controller, both are proportional integral control; is PWM coefficient.

[0037] It can be obtained by Figure 4 analysis that since the load voltage is equal to the output voltage of the diesel engine, there is a relationship

[0038] When the grid-forming converter is no-load, i.e. is 0, only can satisfy , i.e. the voltage drop on is 0, at this time is clamped by , and the feedback voltage of the voltage loop is . When is not 0, sinceThe sensitivity is very small, typically on the order of microhenries. The pressure drop is very small, so it can be obtained At this time, it is believed that... quilt Clamped, the feedback voltage of the voltage loop is .

[0039] Due to the structural characteristics and magnetic circuit non-uniformity of the generator rotor windings, third harmonic voltages exist in generators to varying degrees. Assuming the amplitudes of the three-phase third harmonic voltages are all... Furthermore, the third harmonic voltages are in phase, as expressed below.

[0040]

[0041] The third harmonic voltage of the three-phase system exists on the zero axis, and its expression is as follows:

[0042] because quilt Clamped, resulting in The feedback third harmonic voltage is in the z-axis voltage-current loop, but the integral controller cannot track the third harmonic component without error, resulting in the converter outputting a third harmonic current.

[0043] Therefore, in order to suppress the third harmonic current caused by the third harmonic voltage, the present invention provides a control method for suppressing the third harmonic current in a grid-type converter, the method comprising the following steps: Step S1: Sample the output voltage and output current of the grid-type converter; Step S2: Perform coordinate transformation on the sampled output voltage and extract the zero-axis voltage component; Step S3: Based on the zero-axis voltage component, a third harmonic compensation voltage is generated by a quasi-resonant controller, wherein the resonant frequency of the quasi-resonant controller is set to three times the rated angular frequency of the system. Specifically, in one embodiment of the present invention, a quasi-resonant controller at the third harmonic is used. Compensation voltage can be obtained The transfer function of the quasi-resonant controller is:

[0044] in, This is the resonant gain; The bandwidth coefficient of the resonance peak; The resonant frequency, .

[0045] Furthermore, in the third harmonic suppression method for the grid-type converter, the resonant gain of the quasi-resonant controller... bandwidth coefficient Determination is made through the following steps: First, according to the system parameters of the grid-forming converter and the diesel generator, an open-loop model of a control system containing a zero-axis voltage and current double closed loop is established. The resonance frequency of a quasi-resonant controller is set as three times the fundamental angular frequency. The resonance gain is set as a conservative initial value based on engineering experience. bandwidth coefficient A set of conservative initial values are set.

[0046] Then, the set initial parameters are substituted into the open-loop model of the control system, and the open-loop Bode diagram of the system is drawn. The phase margin and amplitude margin of the system are analyzed: if the phase margin is lower than a preset safety threshold, the resonance gain is first reduced until the system stability meets the requirements; on the premise of ensuring that the system has sufficient stability margin, if the suppression ability of the control method on the target frequency harmonic needs to be enhanced, the resonance gain can be gradually increased; if the frequency of the power grid or the speed of the generator may fluctuate, the bandwidth coefficient can be appropriately increased to enhance the robustness of the control method to frequency deviation; conversely, if the selectivity on the third harmonic frequency needs to be improved, the bandwidth coefficient can be appropriately reduced.

[0047] Finally, the above adjusted parameters are verified on a laboratory experimental platform. First, the third harmonic content of the output current of the converter is measured under no-load conditions; then, the current waveform distortion rate is observed under load (such as a 50kW load). According to the measured harmonic suppression effect and the dynamic response of the system, the final fine-tuning and setting of the and are made to ensure stable operation of the system and achieve the optimal harmonic suppression effect.

[0048] Finally, the Bode diagram of the quasi-resonant control of the third harmonic is as shown in the figure, and the phase delay at three times the frequency is 0, which can be used to offset the third harmonic component . Among them, Figure 6 Therefore, the compensation voltage is .

[0049] Step S4, introducing the third harmonic compensation voltage into the zero-axis voltage and current double closed loop control loop of the grid-forming converter, to offset the third harmonic voltage component in the voltage feedback signal, so as to suppress the third harmonic current output by the grid-forming converter.

[0050] Specifically, in an embodiment of the present application, by introducing a compensation voltage control on the z-axis voltage and current double closed loop, the compensation voltage is used to offset the third harmonic component . As​​Figure 5 The difference between the zero-axis voltage component and the zero-axis voltage component reference value is superimposed with the third harmonic compensation voltage to input a voltage compensation network, and a zero-axis current reference instruction is generated; and according to the zero-axis current reference instruction and the sampled output current, a modulation wave signal is generated through current inner loop control to drive the converter to generate a compensation voltage opposite to the third harmonic voltage of the generator in phase, so as to suppress the third harmonic current flowing through the converter.

[0051] In order to verify the feasibility of the method, an experimental platform of the grid-connected converter combined with the diesel generator is built in the laboratory, L1=150μH, L2=15μH, C=40μF, the effective value of the phase voltage of the diesel generator is 230V, and the power frequency period is 50Hz. In the case that the grid-connected converter is in no-load state, without adding compensation voltage control, due to the existence of large third harmonic voltage of the diesel generator, the converter outputs large harmonic current, as shown in Figure 7 The amplitude of the third harmonic current is about 18A. After adding the compensation voltage control, the amplitude of the third harmonic current is reduced to within 9A, and the harmonic suppression effect is obvious, as shown in Figure 8 Figure 9 In the case that the grid-connected converter is in 50kW charging state, without adding compensation voltage control, the three-phase current distortion is obvious, as shown in Figure 10

[0052] The present application directly aims at the third harmonic voltage disturbance introduced by the diesel generator, and compensates in the zero-axis control channel, thereby suppressing the generation of the third harmonic current from the source. The quasi-resonant controller can provide extremely high gain at three times the fundamental frequency, realize approximate zero-error tracking and active cancellation of the third harmonic component, and the harmonic suppression effect is obvious. The method is based on the improvement of the existing grid-connected converter control structure, only a quasi-resonant compensation link is added in the zero-axis voltage loop, without increasing the hardware cost of the main circuit, and it is easy to realize on the existing control platform.

[0053] ​​The application also provides a control system for inhibiting third harmonic current of a grid-connected converter, which is applied to a three-phase four-wire grid-connected converter, and the converter is connected in parallel with a generator containing a third harmonic voltage component, and the control system comprises: a sampling module for sampling output voltage and output current of the grid-connected converter; a voltage extraction module for performing coordinate transformation on the sampled output voltage to extract a zero-axis voltage component; a compensation voltage generation module for generating a third harmonic compensation voltage based on the zero-axis voltage component through a quasi-resonant controller, and a resonant frequency of the quasi-resonant controller is set to three times of a rated angular frequency of the system; and an inhibition module for introducing the third harmonic compensation voltage into a zero-axis voltage and current double closed loop control loop of the grid-connected converter to offset a third harmonic voltage component in a voltage feedback signal, so as to inhibit third harmonic current output by the grid-connected converter.

[0054] The application also provides a device for inhibiting third harmonic of a grid-connected converter, which can comprise: a memory for storing a computer program; a processor for implementing the following steps when executing the computer program stored in the memory: sampling output voltage and output current of the grid-connected converter; performing coordinate transformation on the sampled output voltage to extract a zero-axis voltage component; generating a third harmonic compensation voltage based on the zero-axis voltage component through a quasi-resonant controller, and a resonant frequency of the quasi-resonant controller is set to three times of a rated angular frequency of the system; and introducing the third harmonic compensation voltage into a zero-axis voltage and current double closed loop control loop of the grid-connected converter to offset a third harmonic voltage component in a voltage feedback signal, so as to inhibit third harmonic current output by the grid-connected converter.

[0055] In the specification provided herein, a large number of specific details are described. However, it can be understood that the embodiments of the application can be practiced without these specific details. In some examples, well-known methods, structures and techniques are not shown in detail in order not to obscure the understanding of the present specification.

[0056] Similarly, it is to be understood that the embodiments of the present application can be positioned and described in ways not specifically stated in the above description and drawings. Thus, it is contemplated that the application can admit to other configurations and / or modifications in addition to those shown and described herein.

[0057] Those skilled in the art will appreciate that the modules in the apparatuses in the embodiments can be adapted and placed in one or more apparatuses other than the embodiments. The modules or units or components in the embodiments can be combined into one module or unit or component, and further can be divided into more sub-modules or sub-units or sub-components. Any combination of all the features disclosed in the specification (including the accompanying claims, abstract and drawings), and any method or apparatus so disclosed, can be taken in any combination, unless the context explicitly states otherwise. Unless explicitly stated otherwise, each feature disclosed in the specification (including the accompanying claims, abstract and drawings) can be replaced by alternative features that serve the same, equivalent or similar purpose.

[0058] Further, those skilled in the art will appreciate that a combination of features of different embodiments can mean within the scope of the application and form a different embodiment. For example, in the following claims, any one of the claimed embodiments can be used in any combination.

[0059] The various component embodiments of the present application can be implemented in hardware, or as software modules running in one or more processors, or in combinations thereof. Those skilled in the art will appreciate that a microprocessor or a digital signal processor (DSP) can be used in practice to implement some or all of the functions of some or all of the components in accordance with the embodiments of the present application. The present application can also be implemented as a program for executing part or all of the methods described herein on a computer or a processor (for example, a computer program and a computer program product). Such a program implementing the present application can be stored on a computer-readable medium or can have the form of one or more signals. Such a signal can be downloaded from an Internet website, or provided on a carrier signal, or provided in any other form.

[0060] It should be noted that the above-mentioned embodiments illustrate rather than limit the application, and that one skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word 'comprising' does not exclude the presence of elements or steps other than those listed in a claim. The word 'a' or 'an' preceding an element does not exclude the presence of a plurality of such elements. The application can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In a unitary claim, several devices, apparatuses or means can be listed, comprising means for carrying out a certain function. The functions of the separate means can be carried out by one specific means. The use of the terms first, second and third, etc. does not imply any ordering but rather are used for naming the elements and should be interpreted as 'first','second' and 'third' etc.

Claims

1. A control method for suppressing third harmonic current in a grid-connected converter, applied to a three-phase four-wire grid-connected converter, wherein the converter is connected in parallel with a generator containing a third harmonic voltage component, characterized in that... The method includes: Sample the output voltage and output current of the grid-type converter; The sampled output voltage is subjected to coordinate transformation to extract the zero-axis voltage component; Based on the zero-axis voltage component, a third harmonic compensation voltage is generated by a quasi-resonant controller, the resonant frequency of which is set to three times the system's rated angular frequency. The third harmonic compensation voltage is introduced into the zero-axis voltage-current dual closed-loop control loop of the grid converter to cancel the third harmonic voltage component in the voltage feedback signal, thereby suppressing the third harmonic current output by the grid converter.

2. The control method for suppressing third harmonic current in a grid-type converter according to claim 1, characterized in that, The transfer function of the quasi-resonant controller is: in, This is the resonant gain; The bandwidth coefficient of the resonance peak; It is the resonant frequency.

3. The control method for suppressing third harmonic current in a grid-type converter according to claim 1, characterized in that, The step of introducing the third harmonic compensation voltage into the zero-axis voltage-current dual closed-loop control loop of the grid converter to cancel the third harmonic voltage component in the voltage feedback signal and suppress the third harmonic current output by the grid converter includes: The difference between the zero-axis voltage component and the zero-axis voltage component reference value is superimposed with the third harmonic compensation voltage and then input into the voltage compensation network to generate a zero-axis current reference command. Based on the zero-axis current reference command and the sampled output current, a modulation wave signal is generated through the current inner loop control to drive the converter to generate a compensation voltage that is opposite in phase to the third harmonic voltage of the generator, thereby suppressing the third harmonic current flowing through the converter.

4. A control system for suppressing third harmonic current in a grid-connected converter, applied to a three-phase four-wire grid-connected converter, wherein the converter is connected in parallel with a generator containing a third harmonic voltage component, characterized in that... include: The sampling module is used to sample the output voltage and output current of the grid-type converter; The voltage extraction module is used to perform coordinate transformation on the sampled output voltage and extract the zero-axis voltage component; The compensation voltage generation module is used to generate a third harmonic compensation voltage based on the zero-axis voltage component through a quasi-resonant controller, wherein the resonant frequency of the quasi-resonant controller is set to three times the rated angular frequency of the system. The suppression module is used to introduce the third harmonic compensation voltage into the zero-axis voltage-current dual closed-loop control loop of the grid converter to cancel the third harmonic voltage component in the voltage feedback signal, thereby suppressing the third harmonic current output by the grid converter.

5. The control system for suppressing third harmonic current in a grid-type converter according to claim 4, characterized in that, The transfer function of the quasi-resonant controller is: in, This is the resonant gain; The bandwidth coefficient of the resonance peak; It is the resonant frequency.

6. The control system for suppressing third harmonic current in a grid-type converter according to claim 4, characterized in that, The suppression module: The zero-axis current reference command generation unit is used to superimpose the difference between the zero-axis voltage component and the zero-axis voltage component reference value with the third harmonic compensation voltage and input the superposition to the voltage compensation network to generate a zero-axis current reference command. The drive unit is used to generate a modulation wave signal through the current inner loop control according to the zero-axis current reference command and the sampled output current, so as to drive the converter to generate a compensation voltage that is opposite in phase to the third harmonic voltage of the generator, thereby suppressing the third harmonic current flowing through the converter.

7. A control device for suppressing third harmonic current in a grid-connected converter, comprising a processor and a memory, the memory storing a computer program, wherein the computer program, when executed by the processor, implements the steps of the control method for suppressing third harmonic current in a grid-connected converter as described in any one of claims 1-3.

8. A grid-type converter, characterized in that, Includes a control system for suppressing third harmonic current in a grid-type converter as described in any one of claims 4-6.

Images