Harmonic current control method and device for grid-connected converter

Abstract

The application discloses a harmonic current control method and device of a grid-connected converter. The device comprises a harmonic power instruction calculation module, which obtains harmonic active power instructions and harmonic reactive power instructions according to grid-side currents and grid voltages; a power control module, which obtains active current instructions and reactive current instructions according to the harmonic active power instructions, the harmonic reactive power instructions, the grid-side currents, the grid voltages, basic active power instructions and basic reactive power instructions; a current controller, which obtains a wave-emitting voltage instruction according to the active current instructions, the reactive current instructions, the grid-side currents, the grid voltages and a phase-locked loop output angle; and a modulator, which modulates the wave-emitting voltage instruction to obtain a driving signal required by converter control. The application extracts fundamental wave components and harmonic components in the grid-side currents of the converter, generates harmonic power instructions required for suppressing harmonic of the output currents of the converter, and further achieves the purpose of suppressing the harmonic of the output currents.

Description

TECHNICAL FIELD

[0001] The application relates to the field of grid-connected technology, and in particular to a harmonic current control method and device of a grid-connected converter. BACKGROUND

[0002] Developing new energy has become a global consensus to cope with the increasingly severe energy crisis, and the use of new energy is mainly realized through power generation. As the energy transmission interface between new energy and the power grid, the operation performance of the grid-connected converter is related to the power quality of the new energy generated. Under the background of the increasing scale of new energy grid connection, the operation performance of the grid-connected inverter is related to the stability of the power system.

[0003] However, with the increase in the scale of power electronic equipment connected to the power grid, problems such as unbalanced grid voltage, grid background harmonic voltage, and deviation of grid voltage frequency from the rated value often occur, resulting in a complex and changeable grid environment and bringing many challenges to the operation of the grid-connected converter.

[0004] As a common problem in the current power grid, the occurrence of grid background harmonic voltage is easy to cause the output current of the grid-connected converter connected thereto to have harmonic current of the same frequency. The occurrence of harmonic current in turn easily aggravates the content of grid background harmonic voltage, threatens the reliable operation of other equipment in the power grid, and in severe cases, even causes a large number of power electronic equipment to shut down due to failure, endangering the stability of the power system. In order to ensure the stable operation of the power system and reduce the risk of harmonics as much as possible, the output harmonic current of the new energy grid-connected specification is specifically limited and required

Document 1 "GB20320-2006 Same as IEC61400-21 Wind Turbine Generator Unit Power Quality Detection and Evaluation Method", Document 2 "GBT37408-2019 Photovoltaic Power Generation Grid-connected Inverter Technical Requirements."

[0005] To deal with the influence of grid background harmonic voltage on the output current of grid-connected converter, a large number of researches have been done and many harmonic current suppression methods have been proposed. Among them, adding a harmonic regulator in the current control loop of grid-connected converter is the most direct and commonly used method to suppress harmonic current at present

Document 3 "Yaoqin Jia, Jiqian Zhao, and Xiaowei Fu. Direct Grid Current Control of LCL-Filtered Grid-Connected Inverter Mitigating Grid Voltage Disturbance [J]. IEEE Transactions on Power Electronics, 2014, 29(3): 1532-1541."

Document 4 "Bin Zhang, Danwei Wang, Keliang Zhou, et al. Linear Phase Lead Compensation Repetitive Control of a CVCF PWM Inverter [J]. IEEE Transactions on Industrial Electronics, 2008, 55(4): 1595-2002.", Document 5 "Zhu Mingzhe, Ye Yongqiang, Zhao Qiangsong, et al. Anti-grid frequency fluctuation repetitive control parameter design method [J]. Proceedings of the Chinese Society for Electrical Engineering, 2016, 36(14): 3857-3867."

Document 6 "Marco Liserre, Remus Teodorescu, and Frede Blaabjerg. Stability of Photovoltaic and Wind Turbine Grid-Connected Inverters for a Large Set of Grid Impedance Values [J]. IEEE Transactions on Power Electronics, 2006, 21(1): 263-272.", Document 7 "Jinming Xu, Shaojun Xie, Ting Tang. Evaluations of current control in weak grid case for grid-connected LCL-filtered inverter [J].. IET Power Electron, 2013, 6(2): 227-234."

Document 8 "Xu Jinming, Xie Shaojun, Tang Ting. Adaptive current control of LCL-filtered grid-connected inverter under weak grid [J]. Proceedings of the Chinese Electrical Engineering Society, 2014, 34(24): 4031-4039.", Document 9 "Xuehua Wang, Xinbo Ruan, Shangwei Liu, et al. Full Feedforward of Grid Voltage for Grid-Connected Inverter With LCL Filter to Suppress Current Distortion Due to Grid Voltage Harmonics [J]. IEEE Transactions on Power Electronics, 2010, 25(12): 3119-3127."

[0006] Whether it is to increase the harmonic current regulator or to improve the voltage feedforward control of the current loop, its essence is to enhance the output harmonic impedance of the converter. At present, most of the researches and methods to enhance the output harmonic impedance of the converter are done at the current control loop level, and there are few based on the current outer loop control level. In order to ensure the stable operation of the grid-connected converter under the wide range of changing grid impedance, the methods based on the current control loop level will be more or less limited when used in engineering practice, which will reduce the application effect. SUMMARY

[0007] The present application aims to provide a harmonic current control method and device of a grid-connected converter to solve the problem of output harmonic current of the grid-connected converter under the grid background harmonic voltage and enhance the harmonic output impedance of the grid-connected converter.

[0008] In one aspect of the present application, a harmonic current control device of a grid-connected converter is provided, which comprises:

[0009] a harmonic power instruction calculation module configured to obtain harmonic active power instructions and harmonic reactive power instructions according to a grid-side current and a grid voltage;

[0010] a power control module configured to obtain active current instructions and reactive current instructions according to the harmonic active power instructions, the harmonic reactive power instructions, the grid-side current, the grid voltage, basic active power instructions and basic reactive power instructions;

[0011] a current controller configured to obtain a wave emission voltage instruction according to the active current instructions, the reactive current instructions, the grid-side current, the grid voltage and a phase-locked loop output angle;

[0012] a modulator configured to modulate the wave emission voltage instruction to obtain a driving signal required by the converter control.

[0013] In another aspect of the present application, a harmonic current control method of a grid-connected converter is provided, which comprises:

[0014] obtaining harmonic active power instructions and harmonic reactive power instructions according to a grid-side current and a grid voltage;

[0015] obtaining active current instructions and reactive current instructions according to the harmonic active power instructions, the harmonic reactive power instructions, the grid-side current, the grid voltage, basic active power instructions and basic reactive power instructions;

[0016] obtaining a wave emission voltage instruction according to the active current instructions, the reactive current instructions, the grid-side current, the grid voltage and a phase-locked loop output angle;

[0017] The wave launch voltage instruction is modulated to obtain a driving signal required by the converter control.

[0018] The harmonic current control method and device of the grid-connected converter provided by the embodiments of the present application extract the fundamental component and the harmonic component in the grid-side current of the converter to generate the harmonic power instruction required for suppressing the harmonic of the output current of the converter. The method is simple to implement and does not increase the hardware cost of the converter. On the one hand, the harmonic suppression capability thereof depends on the outer loop of the converter to be realized, and no special requirement is imposed on the performance of the current control loop, which can relieve the contradiction between the harmonic suppression and the stability of the converter. On the other hand, the harmonic suppression effect thereof can be superimposed with the effect of the harmonic suppression strategy based on the current control loop, thereby improving the harmonic suppression capability of the converter for the output current without affecting the stable operation of the converter in grid connection. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The harmonic current control block diagram of the grid-connected converter provided by the embodiments of the present application;

[0020] Figure 2 The principle schematic diagram of the harmonic power instruction calculation module provided by the embodiments of the present application;

[0021] Figure 3 The principle schematic diagram of the power control module provided by the embodiments of the present application;

[0022] Figure 4 The principle schematic diagram of the current controller provided by the embodiments of the present application;

[0023] Figure 5 The simulation result schematic diagram when the grid voltage contains 5 / 7 background harmonics without using the harmonic suppression strategy;

[0024] Figure 6 The simulation result schematic diagram when the grid voltage contains 5 / 7 background harmonics with using the harmonic suppression strategy;

[0025] Figure 7 The harmonic current control method schematic diagram of the grid-connected converter provided by the embodiments of the present application.

[0026] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0027] In order to make the technical problems, technical solutions and beneficial effects of the present application more clear, explicit and understandable, the present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0028] In the description of the present application, it should be understood that the terms "center", "upper", "lower", "front", "back", "left", "right" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0029] The variables involved in the embodiments of the present application and their definitions are as follows:

[0030] u gabc : grid-connected point voltage

[0031] i gabc : grid-side current

[0032] L g : equivalent leakage inductance of power grid

[0033] L gf : grid-side filter inductance

[0034] C f : grid-side filter capacitance

[0035] θ g : phase-locked loop output angle

[0036] i gref_d , i gref_q : d, q-axis components of current command

[0037] i gref_x , i gref_y : x, y-axis components of current command

[0038] i gx , i gy : x, y-axis components of current

[0039] G N : notch filter with center frequency being power grid fundamental frequency

[0040] G BPF : band-pass filter with center frequency being power grid fundamental frequency

[0041] e vscref_x , e vscref_y : x, y-axis components of wave-emitting voltage command

[0042] e vscref_α , e vscref_β : α, β-axis components of wave-emitting voltage command

[0043] P ref0 , Qref0 : basic active power command and basic reactive power command

[0044] P refh , Q refh : harmonic active power command and harmonic reactive power command

[0045] i gfund : grid-side current fundamental component

[0046] u gh : grid voltage harmonic component

[0047] Figure 1 A harmonic current control block diagram of a grid-connected converter provided by an embodiment of the present application.

[0048] As shown in Figure 1 , the harmonic current control of the grid-connected converter is implemented through a phase-locked loop module (PLL), a harmonic power command calculation module, a power control module, a current controller, and a PWM modulator.

[0049] The input of the PLL is the grid voltage of the converter u gabc , and the output is the angle θ g of the grid positive sequence voltage.

[0050] Figure 2 A principle schematic diagram of the harmonic power command calculation module provided by an embodiment of the present application.

[0051] As shown in Figure 2 , the input of the harmonic power command calculation module is the grid-side current i gabc and the grid voltage u gabc (i.e., the grid point voltage), and the output is the harmonic power command. The grid-side current i gabc may be the grid-connected current of the converter or the current on the AC inductance thereof. The implementation principle is as follows.

[0052] First, the grid-side current i gabc and the grid voltage u gabc are input one by one into a band-pass filter and a notch filter, respectively, to obtain the grid-side current fundamental component i gfund and the grid voltage harmonic component u gh . The transfer function from the output to the input of the band-pass filter and the notch filter can be represented as:

[0053]

[0054]

[0055] where ω nω is the angular frequency corresponding to the center frequency of the bandpass filter / notch filter; in this example, it is the angular frequency corresponding to the fundamental frequency of the power grid. c This is the bandwidth coefficient of the bandpass filter / notch filter, which takes a value between 0 and 1.

[0056] Secondly, based on the fundamental component i of the grid-side current gfund and grid voltage harmonic components u gh The harmonic power command is calculated. In this example, the power calculation is performed in two steps:

[0057] The first step is to use Clark transform to obtain the α and β components of the fundamental component of the grid-side current and the harmonic components of the grid voltage. The specific calculations are as follows:

[0058]

[0059]

[0060] The second step involves calculating the harmonic power command using the αβ components of the fundamental component of the grid-side current and the αβ components of the harmonic components of the grid voltage. The calculation method is as follows:

[0061]

[0062] Figure 3 This is a schematic diagram of the power control module provided in an embodiment of this application.

[0063] like Figure 3 As shown, the input to the power control module is the basic active power command P of the grid-connected converter. ref0 Basic reactive power command Q ref0 Harmonic active power command P refh Harmonic reactive power command Q refh The output is the active current command i. gref_d and reactive current command i gref_q Among them, the basic active power command and the basic reactive power command are the command values ​​set for the active and reactive power that the inverter is expected to generate.

[0064] In this example, the implementation principle of this module is as follows:

[0065] First, the basic active power command P ref0 Harmonic active power command P refh Adding them together yields the active power command P of the grid-connected converter. ref ; the basic reactive power command Q ref0 Harmonic reactive power command Q refh Adding them together yields the reactive power command Q of the grid-connected converter. ref Simultaneously utilizing the grid-side current i of the grid-connected convertergabc and grid voltage u gabc active power P of the grid-connected converter is calculated vsc and reactive power Q vsc The calculation of the active power of the converter is similar to the aforementioned harmonic power calculation and is carried out in two steps as shown in the following equations:

[0066]

[0067]

[0068]

[0069] Secondly, the active power instruction P ref of the grid-connected converter is subtracted from the active power P vsc , to obtain the active power error P err ; the reactive power instruction Q ref of the grid-connected converter is subtracted from the reactive power Q vsc , to obtain the reactive power error Q err ;

[0070] Then, the active power error P err is sent to an active power regulator composed of a PI regulator and a HC (Harmonic Control) regulator with high gain at harmonic frequencies, to obtain the active current basic instruction i gref_d0 and the harmonic active current instruction i gref_dh respectively; the reactive power error Q err is sent to a reactive power regulator composed of a PI and a HC with high gain at harmonic frequencies, to obtain the reactive current basic instruction i gref_q0 and the harmonic reactive current instruction i gref_qh ; wherein the transfer function from the output to the input of the HC regulator with high gain at harmonic frequencies can be expressed as:

[0071]

[0072] In the formula, ω h is the angular frequency corresponding to the harmonic frequency of the main harmonic component in the harmonic active power and the harmonic reactive power, ω ch is the bandwidth coefficient of the HC regulator, and K rh is the gain of the HC regulator.

[0073] Finally, the active current basic instruction i gref_d0 and the harmonic active current instruction i gref_dh are added to obtain the active current instruction i gref_d ; the reactive current basic instruction i gref_q0Harmonic reactive current command i gref_qh Add up to get reactive current command i gref_q .

[0074] Figure 4 The principle diagram of the current controller provided by the embodiment of the application.

[0075] As Figure 4 shown, the input of the current controller includes active current command i gref_d , reactive current command i gref_q , grid-side current i gabc , grid voltage u gabc , phase-locked loop output angle θ g , and the output is the α, β axis components e gref_α , e gref_β of the wave generation voltage command. The implementation of the function of the current controller is divided into two steps:

[0076] First, according to the phase-locked loop output angle, the current command i gref_d , i gref_q is converted to the target coordinate system xy by using the current command coordinate conversion, to obtain the x, y axis current command components i gref_x , i gref_y ; at the same time, the grid-side current i gabc and the grid voltage u gabc are converted to the target coordinate system xy coordinate system by using the current control coordinate conversion, to obtain the x, y axis grid-side current components i gx , i gy and the grid voltage components u gx , u gy .

[0077] When the target coordinate system is a synchronous rotating (dq) coordinate system, the current command coordinate conversion formula is:

[0078]

[0079] The current control coordinate conversion formula is:

[0080]

[0081] When the target coordinate system is a two-phase static (αβ) coordinate system, the current command coordinate conversion formula is:

[0082]

[0083] The current control coordinate conversion formula is:

[0084]

[0085] Secondly, the x, y axis current command components and the grid-side current components are subtracted respectively and sent to the current regulator G CR The output of the current regulator G CR is superimposed with the x, y axis grid voltage components respectively to obtain the x, y axis wave emission voltage command components e gref_x , e gref_y .

[0086] Then, through the wave emission voltage coordinate transformation module, the x, y axis wave emission voltage command components e gref_x , e gref_y are converted to the αβ coordinate system to obtain the α, β axis components e gref_α , e gref_β of the wave emission voltage command. Of course, it can also be converted to the dq coordinate system.

[0087] When the target coordinate system of current control is the dq coordinate system, the transformation formula of the wave emission voltage coordinate transformation module is:

[0088]

[0089] When the target coordinate system of current control is the αβ coordinate system, the transformation formula of the wave emission voltage coordinate transformation module is:

[0090]

[0091] Finally, the α, β axis components e gref_α , e gref_β of the wave emission voltage command are modulated by the PWM modulator, for example, the three-phase space vector modulation method is adopted, to obtain the driving signal required by the grid-connected converter control, so as to achieve the basic power target and realize the suppression target of the converter output current harmonics.

[0092] Figure 5 It is a simulation result schematic diagram when the grid voltage contains 5 / 7 background harmonics without adopting the harmonic suppression strategy.

[0093] Figure 6 It is a simulation result schematic diagram when the grid voltage contains 5 / 7 background harmonics with the harmonic suppression strategy. The harmonic suppression strategy can refer to the foregoing content.

[0094] As can be seen from the simulation result diagram, the harmonic current control of the grid-connected converter provided in the embodiment of the application extracts the fundamental component and the harmonic component in the grid-side current of the converter, generates the harmonic power instruction required for suppressing the harmonic of the output current of the converter, is simple to implement and does not increase the hardware cost of the converter, and on one hand, the harmonic suppression capability thereof depends on the outer loop of the converter to be realized, and the performance of the current control loop has no special requirement, and the contradiction between the harmonic suppression and the stability of the converter can be relieved; on the other hand, the harmonic suppression effect thereof can be superimposed with the effect of the harmonic suppression strategy based on the current control loop, so that the harmonic suppression capability of the output current of the converter is improved without affecting the stable operation of the grid-connected converter.

[0095] Figure 7 A schematic diagram of the harmonic current control method of the grid-connected converter provided in the embodiment of the application is shown.

[0096] As Figure 7 shown, the method comprises:

[0097] S11, obtaining a harmonic active power instruction and a harmonic reactive power instruction according to a grid-side current and a grid voltage;

[0098] S12, obtaining an active current instruction and a reactive current instruction according to the harmonic active power instruction, the harmonic reactive power instruction, the grid-side current, the grid voltage, a basic active power instruction and a basic reactive power instruction;

[0099] S13, obtaining a wave generation voltage instruction according to the active current instruction, the reactive current instruction, the grid-side current, the grid voltage and a phase-locked loop output angle;

[0100] S14, modulating the wave generation voltage instruction to obtain a driving signal required for the control of the converter.

[0101] In an example, a grid-side current fundamental component and a grid voltage harmonic component are obtained according to the grid-side current and the grid voltage; the harmonic active power instruction and the harmonic reactive power instruction are calculated according to the grid-side current fundamental component and the grid voltage harmonic component.

[0102] In an example, a band-pass filter with a center frequency of a grid fundamental frequency is used to extract the grid-side current fundamental component from the grid-side current; a high-pass filter or a notch filter with a center frequency of the grid fundamental frequency is used to extract the grid voltage harmonic component from the grid voltage.

[0103] In an example, the harmonic active power instruction is superimposed to the basic active power instruction to obtain an active power instruction; the harmonic reactive power instruction is superimposed to the basic reactive power instruction to obtain a reactive power instruction; the grid-side current and the grid voltage are used to calculate active power and reactive power of the grid-connected converter; the active power instruction is subtracted from the active power of the grid-connected converter to obtain an active power error, and the reactive power instruction is subtracted from the reactive power of the grid-connected converter to obtain a reactive power error; the active power error is adjusted by an active power regulator to obtain an active current instruction, and the reactive power error is adjusted by a reactive power regulator to obtain a reactive current instruction.

[0104] In an example, the active power regulator or the reactive power regulator is composed of a PI regulator and an HC regulator with high gain at the harmonic frequency.

[0105] In an example, the HC regulator with high gain at the harmonic frequency includes any one of a resonance regulator with a center frequency equal to the harmonic frequency, a repetitive controller, and a vector controller.

[0106] In an example, according to an output angle of a phase-locked loop, the active current instruction and the reactive current instruction are converted into a target coordinate system by current instruction coordinate transformation to obtain corresponding current instruction components; meanwhile, the grid-side current and the grid voltage are converted into the target coordinate system by current control coordinate transformation to obtain corresponding grid-side current components and grid voltage components;

[0107] The current instruction components are subtracted from the grid-side current components and sent into a current regulator, and the output of the current regulator is superimposed to the grid voltage components respectively to obtain wave emission voltage instruction components in the target coordinate system;

[0108] The wave emission voltage instruction components in the target coordinate system are converted by a wave emission voltage coordinate transformation module to obtain the wave emission voltage instruction.

[0109] In an example, the target coordinate system includes a synchronous rotating coordinate system or a two-phase stationary coordinate system.

[0110] In an example, the grid-side current includes a converter grid-connected current or a current on an AC inductor.

[0111] The preferred embodiments of the present application are described above with reference to the accompanying drawings, and the scope of the right of the present application is not limited thereby. Any modification, equivalent replacement and improvement made by those skilled in the art without departing from the scope and essence of the present application shall be within the scope of the right of the present application.

Claims

1. A harmonic current control device for a grid-connected converter, characterized in that, The device includes: The harmonic power command calculation module is configured to obtain harmonic active power command and harmonic reactive power command based on grid-side current and grid voltage. The power control module is configured to obtain active current command and reactive current command based on the harmonic active power command, the harmonic reactive power command, the grid-side current, the grid voltage, the basic active power command and the basic reactive power command. The current controller is configured to obtain the ripple voltage command based on the active current command, the reactive current command, the grid-side current, the grid voltage, and the phase-locked loop output angle. The modulator modulates the transmitted voltage command to obtain the drive signal required for converter control. The power control module is configured to superimpose the harmonic active power command onto the basic active power command to obtain an active power command; superimpose the harmonic reactive power command onto the basic reactive power command to obtain a reactive power command; calculate the active power and reactive power of the grid-connected converter using the grid-side current and the grid voltage; obtain the active power error by subtracting the active power command from the active power of the grid-connected converter, and obtain the reactive power error by subtracting the reactive power command from the reactive power of the grid-connected converter; obtain the active current command by adjusting the active power error through an active power regulator, and obtain the reactive current command by adjusting the reactive power error through a reactive power regulator.

2. The apparatus according to claim 1, characterized in that, The harmonic power command calculation module is configured to obtain the fundamental component of the grid-side current and the harmonic component of the grid voltage based on the grid-side current and the grid voltage; and to calculate the harmonic active power command and the harmonic reactive power command based on the fundamental component of the grid-side current and the harmonic component of the grid voltage.

3. The apparatus according to claim 2, characterized in that, The harmonic power command calculation module is configured to extract the fundamental component of the grid-side current from the grid-side current using a bandpass filter with a center frequency of the grid fundamental frequency; and to extract the harmonic component of the grid voltage from the grid voltage using a high-pass filter or a notch filter with a center frequency of the grid fundamental frequency.

4. The apparatus according to claim 1, characterized in that, The active power regulator or the reactive power regulator consists of a PI regulator and an HC regulator with high gain at harmonic frequencies.

5. The apparatus according to claim 4, characterized in that, The HC regulator with high gain at harmonic frequencies includes any one of the following: a resonant regulator with a center frequency equal to the harmonic frequency, a repetitive controller, and a vector controller.

6. The apparatus according to claim 1, characterized in that, The current controller is configured as follows: Based on the output angle of the phase-locked loop, the active current command and the reactive current command are transformed into the target coordinate system using current command coordinate transformation to obtain the corresponding current command components. Simultaneously, by utilizing current-controlled coordinate transformation, the grid-side current and the grid voltage are converted to the target coordinate system to obtain the corresponding grid-side current components and grid voltage components. The difference between the current command component and the grid-side current component is sent to the current regulator. The output of the current regulator is then superimposed with the grid voltage component to obtain the transmission voltage command component in the target coordinate system. The voltage transmission command components in the target coordinate system are transformed using the voltage transmission coordinate transformation module to obtain the voltage transmission command.

7. The apparatus according to claim 6, characterized in that, The target coordinate system includes a synchronous rotating coordinate system or a two-phase stationary coordinate system.

8. The apparatus according to claim 1, characterized in that, The grid-side current includes the converter grid-connected current or the current on the AC inductor.

9. A harmonic current control method for a grid-connected converter, characterized in that, The method includes: Based on the grid-side current and grid voltage, the harmonic active power command and harmonic reactive power command are obtained. Based on the harmonic active power command, the harmonic reactive power command, the grid-side current, the grid voltage, the basic active power command, and the basic reactive power command, the active current command and the reactive current command are obtained. The ionization voltage command is obtained based on the active current command, the reactive current command, the grid-side current, the grid voltage, and the phase-locked loop output angle. The transmitted voltage command is modulated to obtain the drive signal required for converter control; The process of obtaining active current command and reactive current command based on the harmonic active power command, the harmonic reactive power command, the grid-side current, the grid voltage, the basic active power command, and the basic reactive power command includes: The harmonic active power command is superimposed on the basic active power command to obtain the active power command; the harmonic reactive power command is superimposed on the basic reactive power command to obtain the reactive power command; the active power and reactive power of the grid-connected converter are calculated using the grid-side current and the grid voltage; the active power error is obtained by subtracting the active power command from the active power of the grid-connected converter, and the reactive power error is obtained by subtracting the reactive power command from the reactive power of the grid-connected converter; the active power error is adjusted by the active power regulator to obtain the active current command, and the reactive power error is adjusted by the reactive power regulator to obtain the reactive current command.

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