Control Method and Device of Grid-Connected Inverter for Unbalanced Grid Voltage

Abstract

The present application discloses a control method and device for a grid-connected converter for grid voltage imbalance. The method comprises: obtaining a basic active current action and an additional active current action based on a DC voltage action, a DC voltage detection value, and a converter output current; obtaining a final active current action and a final reactive current action based on the basic active current action, the basic reactive current action, and the additional active current action; adjusting the error between the final active current action and the final reactive current action and the feedback current to obtain a final voltage action; and modulating the final voltage action to obtain a drive signal required for grid-connected converter control. While addressing the current distortion problem associated with generating current commands based on DC bus voltage double frequency fluctuation suppression, the present application can flexibly switch between the two control objectives of constant output power and balanced output current according to the converter's operating needs when the grid voltage is unbalanced.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a control method and device for a grid-connected converter for controlling grid voltage imbalance. Background Art

[0002] Developing renewable energy has become a global consensus in response to the increasingly severe energy crisis. The primary means of utilizing renewable energy is through power generation. As the interface between renewable energy and the power grid, the performance of grid-connected converters is directly related to the quality of the generated power. As the proportion of renewable energy continues to increase, their performance is even more crucial to the stability of the power system.

[0003] However, grid-connected converters often face the problem of unbalanced grid voltage. When faced with unbalanced grid voltage, grid-connected converters using traditional control strategies will experience an oscillatory component at twice the fundamental frequency in their output power, and their output current will also be susceptible to distortion and imbalance. This oscillation in output power is detrimental to the smooth transmission of electrical energy. Furthermore, fluctuations in active power can cause fluctuations in the DC voltage at twice the fundamental frequency, increasing voltage stress and losses on the DC-side capacitors. Unbalanced output current response can lead to unbalanced three-phase current stress in the converter and potentially exacerbate grid voltage imbalance at the node. Furthermore, output current distortion can reduce the quality of transmitted electrical energy.

[0004] To address the numerous issues that arise when grid-connected converters based on traditional control strategies operate under unbalanced grid voltages, the industry has conducted extensive research and proposed numerous improvement strategies. Optimizing the converter's output target current and improving the performance of the converter's current controller are two key areas of focus.

[0005] Under unbalanced grid voltage, the three objectives of output current balance, output current sinusoidal, and output power constant cannot be met simultaneously, and a compromise can only be made [Reference "Guo Xiaoqiang, Zhang Xue, Lu Zhigang, et al. Power / current quality coordinated control strategy for photovoltaic grid-connected inverters under unbalanced grid voltage [J]. Proceedings of the Chinese Society of Electrical Engineering, 2014, 34(3): 346-353."]. Considering the output power quality requirements of the converter, the converter output current is often required to be distortion-free. Under this premise, only one of the two objectives can be chosen: output current balance or output power constant. When the grid voltage imbalance is relatively low and the converter output power is not large, its output current is small and often within the converter current stress range. At this time, in order to reduce the fluctuation of DC voltage, output power constant is often selected as the control target; when the grid voltage imbalance is high and the converter output power is large to a certain extent, continuing to target output power constant will cause the converter's maximum output phase current to exceed its current stress. At this time, in order to avoid converter overcurrent, the control target needs to be switched to output current balance.

[0006] Regardless of whether the control target is set as constant output power or balanced output current, it is ultimately necessary to implement it by optimizing the output current command of the converter [References "Pedro Rodriguez, Adrian V. Timbus, Remus Teodorescu, et al. Flexible active power control of distributed power generation systems during grid faults [J]. IEEE Transactions on Industrial Electronics, 2006, 21 (3): 1530-1540.", References "Bo Yin, Ramesh Oruganti, Sanjib Kumar Panda, et al. An Output-Power-Control Strategy for a Three-Phase PWM Rectifier Under Unbalanced Supply Conditions [J]. IEEE Transactions on Industrial Electronics, 2006, 21 (3): 2140-2150."]. The optimized current command can be calculated according to a specific formula based on the goal of output current balance or constant output power [literature "Bo Yin, Ramesh Oruganti, Sanjib Kumar Panda, et al. An Output-Power-Control Strategy for a Three-Phase PWM Rectifier Under Unbalanced Supply Conditions [J]. IEEE Transactions on Industrial Electronics, 2006, 21 (3): 2140-2150.", literature "Yongsug Suh, Thomas A. Lipo. Control Scheme in Hybrid Synchronous Stationary Frame for PWM AC / DC Converter Under Generalized Unbalanced Operating Conditions [J]. IEEE Transactions on Industrial Applications, 2006, 42 (3): 825-835."].However, this approach, on the one hand, consumes a significant amount of interrupt resources on the controller chip due to the division operation used to calculate the current command. Furthermore, the voltage-sequence component used to calculate the current command often requires filtering and extraction, creating a conflict between the dynamic response and accuracy of the current command. Furthermore, achieving the target current command depends heavily on the performance of the current control strategy. When output current balance is the control objective, the current controller must suppress the negative-sequence current in the converter's feedback current to zero. When constant output power is the control objective, the converter must ensure that the negative-sequence current in the feedback current keeps pace with the negative-sequence component in the target current command. This objective cannot be achieved using traditional current control strategies based on single-rotating coordinate system PI regulation. In other words, to achieve the control objectives of constant output power or balanced output current by calculating the current command according to a specific formula, the converter's current control strategy must also be improved.In this context, the current control strategy based on the positive and negative sequence dual synchronous rotating coordinate system [Literature “Hong-seok Song, Kwanghee Nam. Dual current control for PWM converter under unbalanced input voltage conditions [J]. IEEE Transactions on Industrial Electronics, 1999, 46 (5): 953-959.”, Literature “Xiong Du, Shida Gu, Guoning Wang, et al. Simple current control method for three phase VSC under unbalanced grid condition [J]. IET Power Electron, 2018, 11 (7): 1161-1168.”], and the optimized current control strategy of connecting a double frequency resonant regulator in parallel to the traditional single rotating coordinate system PI regulator [Literature “Etxeberria-Otidui I, Viscarret U, Caballero M, et al. New optimized PWM VSC control structures and strategies under unbalanced voltage transients [J]. IEEE Transactions on Industrial Electronics, 2007, 54(5):2902-2914.”] and a current control strategy that converts current control to a two-phase stationary coordinate system [literature “Zixin Li, Yaohua Li, Haibin Zhu, et al. Control of three-phase boost-type PWM Rectifier in stationary frame under unbalanced input voltage[J]. IEEE Transactions on Power Electronics, 2010, 25(10):2521-2530.”] have been proposed and optimized to varying degrees.

[0007] By connecting a resonant regulator with a center frequency of twice the frequency in parallel to the DC voltage PI regulator, the double-frequency fluctuation of the DC bus voltage caused by the imbalance of the grid voltage can be suppressed, thereby achieving the goal of constant output active power of the converter. Although this can avoid the problems existing in the aforementioned current command calculation, it will cause a mismatch between the active negative-sequence current and the reactive negative-sequence current, resulting in distortion of the converter's output current. Summary of the Invention

[0008] The present application aims to provide a control method and device for a grid-connected converter for grid voltage imbalance, so as to solve the current distortion problem existing in generating current instructions based on suppression of double frequency fluctuation of DC bus voltage.

[0009] In one aspect, the present application provides a control method for a grid-connected converter for grid voltage imbalance, the method comprising:

[0010] According to the DC voltage action, the DC voltage detection value and the converter output current, the basic active current action and the additional active current action are obtained;

[0011] Obtaining a final active current action and a final reactive current action according to the basic active current action, the basic reactive current action, and the additional active current action;

[0012] The final active current action and the final reactive current action are adjusted with the error of the feedback current to obtain the final voltage action;

[0013] The final voltage action is modulated to obtain a driving signal required for controlling the grid-connected converter.

[0014] In another aspect of the present application, a control device for a grid-connected converter for controlling grid voltage imbalance is provided, the device comprising:

[0015] A DC voltage control module is used to obtain a basic active current action and an additional active current action according to a DC voltage action, a DC voltage detection value, and a converter bridge arm inductor current;

[0016] a current instruction generating module, configured to obtain a final active current action and a final reactive current action according to the basic active current action, the basic reactive current action, and the additional active current action;

[0017] The current control module is used to adjust the error between the final active current action and the final reactive current action and the feedback current to obtain the final voltage action;

[0018] The modulation module is used to modulate the final voltage action to obtain a driving signal required for controlling the grid-connected converter.

[0019] The control method and device for a grid-connected converter for grid voltage imbalance provided in the embodiments of the present application solve the current distortion problem existing in generating current instructions based on suppressing the double frequency fluctuation of the DC bus voltage. At the same time, it can flexibly switch between the two control objectives of constant output power and balanced output current according to the operating needs of the converter when the grid voltage is unbalanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A control block diagram of a grid-connected converter for grid voltage imbalance provided in an embodiment of the present application;

[0021] Figure 2 A schematic diagram of the principle of the PLL module provided in an embodiment of the present application;

[0022] Figure 3 A schematic diagram of the principle of the DC voltage control module provided in an embodiment of the present application;

[0023] Figure 4 A schematic diagram of the principle of the current instruction generation module provided in an embodiment of the present application;

[0024] Figure 5 A schematic diagram of the principle of the current control module provided in an embodiment of the present application;

[0025] Figure 6 A schematic diagram of simulation results of two-phase drop in power grid based on the existing method of controlling output power constant based on DC voltage;

[0026] Figure 7 This is a schematic diagram of simulation results of two-phase drop in the power grid when the output power is constant as the control target in the embodiment of the present application;

[0027] Figure 8 This is a schematic diagram of simulation results of a single-phase drop in a power grid when output current balance is the control target in an embodiment of the present application;

[0028] Figure 9 Schematic diagram of a control method for grid voltage imbalance of a grid-connected converter provided in an embodiment of the present application.

[0029] The realization of the objectives, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application clearer and more understandable, this application is 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 this application and are not intended to limit this application.

[0031] In the description of this application, it should be understood that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "front," "back," "left," and "right" are based on the directions or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific direction, be constructed, or operate in a specific direction. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0032] Variables and their definitions involved in the embodiments of this application:

[0033] u oabc : Converter grid connection point voltage

[0034] i oabc : Converter output current

[0035] i Labc : Converter bridge arm inductor current

[0036] L g : Grid equivalent leakage inductance

[0037] θ: Phase-locked loop output phase

[0038] i ref_x 、i ref_y : x-axis and y-axis components of the converter output current

[0039] i x 、i y : x-axis and y-axis components of the converter output current

[0040] G N : Notch filter with center frequency twice the fundamental frequency

[0041] G R : A controller with high gain at twice the fundamental frequency

[0042] G QSG :Quadrature Signal Generator

[0043] e vscref_x 、e vscref_y : The x- and y-axis components of the final voltage action

[0044] e vscref_α 、e vscref_β : α and β axis components of the final voltage action

[0045] Figure 1 This is a control block diagram of the grid-connected converter provided in an embodiment of the present application for grid voltage imbalance.

[0046] like Figure 1 As shown, the grid-connected converter controls the grid voltage imbalance through a PLL (Phase Locked Loop) module, a DC voltage control module, a current command generation module, a current control module, and a PWM modulation module.

[0047] Figure 2 A schematic diagram of the principle of the PLL module provided in an embodiment of the present application.

[0048] like Figure 2 As shown, the input of the PLL (Phase Locked Loop) module is the grid-connected voltage u of the converter. oabc , after coordinate transformation and PI adjustment, the phase θ of the grid voltage is output.

[0049] Figure 3 A schematic diagram of the principle of the DC voltage control module provided in an embodiment of the present application.

[0050] like Figure 3 As shown, the input of the DC voltage control module is the DC voltage action quantity U dc_ref , DC voltage detection value u dc And the converter bridge arm inductor current i Labc , the output is the basic active current action i refMain_d and additional active current action i refAux_d .

[0051] Different from the existing method of maintaining constant output power based on DC voltage control, the DC voltage control of this embodiment is divided into two parts: basic control and double fundamental frequency harmonics.

[0052] Among them, the DC voltage basic control part is used to control the DC voltage action quantity U dc_ref The value after filtering out the double grid fundamental frequency component of the DC voltage The output can be expressed as:

[0053]

[0054] Where K p_VR and K i_VR are the proportional and integral coefficients of the DC voltage PI regulator respectively. N The notch filter with a center frequency of twice the grid fundamental frequency is used to filter out the twice grid fundamental frequency component in the DC voltage. The transfer function of its output to input characteristic can be expressed as:

[0055]

[0056] Among them, ω nis the angular frequency corresponding to the center frequency of the notch filter, and in this embodiment is the angular frequency corresponding to twice the fundamental frequency of the power grid; ω cn The bandwidth coefficient of the notch filter is between 0 and 1.

[0057] The DC voltage double fundamental frequency harmonic control part adjusts the double grid fundamental frequency component in the DC voltage, and its output can be expressed as:

[0058] i refAuxR_d =G R (G N -1)u dc (3)

[0059] Where G R It is a controller with high gain at twice the grid fundamental frequency.

[0060] In this embodiment, G R Assuming that the center frequency of the resonant regulator is twice the fundamental frequency of the power grid, the transfer function of its output to input characteristics can be expressed as:

[0061]

[0062] Among them, ω r is the angular frequency corresponding to the center frequency of the resonant regulator, and in this embodiment is the angular frequency corresponding to twice the fundamental frequency of the power grid; ω cr K is the bandwidth coefficient of the resonant regulator, which ranges from 0 to 1; r is the gain of the resonant regulator.

[0063] Please refer to Figure 3 As shown, the implementation of DC voltage control can be divided into four steps.

[0064] First, use the PI regulator to adjust U dc_ref and The difference between the two values is adjusted to obtain the basic active current action i refMain_d ; Using G R The component of twice the grid fundamental frequency in the DC voltage is adjusted to obtain the initial value of the additional active current action i refAuxR_d .

[0065] Secondly, detect the converter bridge arm inductor current i Labc The maximum value i max , and the additional active current action is determined according to the following rules:

[0066]

[0067] CtrlMode is the output mode switching signal. Its purpose is to set the converter output power constant or converter output current balanced when the grid voltage is unbalanced, provided that the converter output current is undistorted. When CtrlMode = 0, the converter operates in the output power constant mode. When CtrlMode = 1, the converter operates in the output current balanced mode. Its value rules are as follows:

[0068]

[0069] Where, I High and I Low They are the upper and lower limit settings of the current threshold, I High >I Low >0 and I High It can be set to the maximum current that the converter is allowed to operate.

[0070] Figure 4 A schematic diagram of the principle of the current instruction generation module provided in an embodiment of the present application.

[0071] The input of the current command generation module includes the basic active current action quantity i refMain_d , additional active current action i refAux_d And the basic reactive current action i refMain_q ; The output is the final active current action i ref_d And the final reactive current action i ref_q .

[0072] The basic reactive current action quantity includes the positive sequence reactive current setting value set by the converter to control reactive power or participate in grid connection point voltage regulation.

[0073] The execution process is to add the active current action i refAux_d The basic active current action i refMain_d Superposition, get the final active current action i ref_d ; Add active current action i refAux_d Invert the signal and pass it through the orthogonal signal generator G QSG , we can get the additional reactive current action i refAux_q , and then add the additional reactive current action i refAux_q The basic reactive current action i refMain_q By superposition, we can get the final reactive current action i ref_q The transfer function of the output to input characteristic of the orthogonal signal generator is:

[0074]

[0075] Where K qsgis the quadrature signal generator gain, ω qsg is the angular frequency corresponding to the center frequency of the orthogonal signal generator, and in this embodiment is the angular frequency corresponding to twice the grid fundamental frequency.

[0076] Figure 5 A schematic diagram of the principle of the current control module provided in an embodiment of the present application.

[0077] The input of the current control module includes the final active current action i ref_d , the final reactive current action i ref_q , converter bridge arm inductor current i Labc , grid connection point voltage u oabc And the phase θ of the grid voltage output by the phase-locked loop, the output includes the x-axis and y-axis components e of the final voltage action vscref_x 、e vscref_y .

[0078] The execution process is to first use the current command coordinate transformation module to transform the final active current action i ref_d And the final reactive current action i re f _q Convert to the target coordinate system xy coordinate system to get its x and y axis components i ref_x 、i ref_y At the same time, the current control coordinate transformation module is used to convert the converter bridge arm inductor current i Labc and grid connection point voltage u oabc Convert to the target coordinate system xy coordinate system and obtain its x and y axis components i respectively x 、i y and u ox 、u oy .

[0079] When the target coordinate system is the dq coordinate system, the current command coordinate transformation formula is:

[0080]

[0081] Taking the converter bridge arm inductor current as the target controlled current, the current control coordinate transformation formula is:

[0082]

[0083] When the target coordinate system is the αβ coordinate system, the current command coordinate transformation formula is:

[0084]

[0085] Taking the converter bridge arm inductor current as the target controlled current, the current control coordinate transformation formula is:

[0086]

[0087] Secondly, the difference between the current action component of the x-axis and the feedback is sent to the respective current regulator G CR , and then the x and y axis current regulator G CR The output of is respectively superimposed with the x-axis and y-axis components of the grid-connected point voltage to obtain the x-axis and y-axis components of the final voltage action amount e vscref_x 、e vscref_y .

[0088] Finally, the x-axis and y-axis components of the final voltage action amount e are transformed through the wave voltage coordinate transformation module. vscref_x 、e vscref_y Converted to the αβ coordinate system, the α and β axis components e of the final voltage action are obtained vscref_α 、e vscref_β .

[0089] When the target coordinate system is the dq coordinate system, the transformation formula of the wave voltage coordinate transformation module is:

[0090]

[0091] When the target coordinate system is the αβ coordinate system, the transformation formula of the wave voltage coordinate transformation module is:

[0092]

[0093] The PWM modulation module converts the α and β axis components of the final voltage action e vscref_α 、e vscref_β By PWM modulation, for example, a three-phase space vector modulation method is adopted, a driving signal required for controlling the grid-connected converter is obtained.

[0094] Figure 6 This is a schematic diagram of the simulation results of two-phase drop in the power grid based on the existing method of maintaining constant output power based on DC voltage control. Figure 7 Schematic diagram of simulation results of two-phase drop in the power grid when the output power is constant as the control target in an embodiment of the present application. Figure 8 Schematic diagram of simulation results of single-phase drop in the power grid when output current balance is the control target in an embodiment of the present application.

[0095] It can be seen from the above simulation result diagram that the grid-connected converter provided in the embodiment of the present application can control the grid voltage imbalance and solve the current distortion problem existing in the existing method of making the output power constant based on DC voltage control. At the same time, when the grid voltage is unbalanced, it can flexibly switch between the two control goals of constant output power and balanced output current according to the operating needs of the converter when the grid voltage is unbalanced.

[0096] Figure 9 Schematic diagram of a control method for grid voltage imbalance of a grid-connected converter provided in an embodiment of the present application.

[0097] like Figure 9 As shown, the method includes:

[0098] Step S11, obtaining a basic active current action and an additional active current action according to the DC voltage action, the DC voltage detection value, and the converter output current;

[0099] Step S12: Obtaining a final active current action and a final reactive current action according to the basic active current action, the basic reactive current action, and the additional active current action;

[0100] Step S13: adjusting the final active current action and the final reactive current action with the error of the feedback current to obtain a final voltage action;

[0101] Step S14: modulate the final voltage action to obtain a driving signal required for controlling the grid-connected converter.

[0102] In one example, obtaining the basic active current contribution and the additional active current contribution according to the DC voltage contribution, the DC voltage detection value, and the converter output current includes:

[0103] The DC voltage action is adjusted with the value of the DC voltage after filtering out the twice grid fundamental frequency component to obtain the basic active current action; and / or,

[0104] A controller with high gain at twice the grid fundamental frequency is used to adjust the double grid fundamental frequency component in the DC voltage to obtain an initial value of the additional active current action; the maximum value of the converter output current is detected and compared with the current threshold to obtain an output mode switching signal of the converter; and the additional active current action is determined based on the converter output mode switching signal and the initial value of the additional active current action.

[0105] In one example, the value of the DC voltage after filtering out the component of twice the grid fundamental frequency is obtained by using a notch filter or a low-pass filter whose center frequency is twice the grid fundamental frequency.

[0106] In one example, the controller having high gain at twice the grid fundamental frequency includes one of a resonant regulator having a center frequency of twice the grid fundamental frequency, a repetitive controller, a proportional-integral resonant regulator, and a proportional-integral repetitive controller.

[0107] In one example, the converter output current includes one of an effective value of the converter output three-phase current, a modulus value of the three-phase current, and a filtered value of the modulus value of the three-phase current.

[0108] In one example, determining the additional active current contribution according to the output mode switching signal of the converter and the initial value of the additional active current contribution includes:

[0109] Set the output mode of the converter to constant output power or balanced output current.

[0110] In one example, the final active current action and the final reactive current action are obtained according to the basic active current action, the basic reactive current action and the additional active current action, including:

[0111] superimposing the basic active current action and the additional active current action to obtain a final active current action; and / or,

[0112] The additional active current action is inverted and passed through an orthogonal signal generator to obtain an additional reactive current action, and then the additional reactive current action is superimposed on the basic reactive current action to obtain a final reactive current action.

[0113] In one example, the basic reactive current contribution includes a positive sequence reactive current setting value set by the converter to control reactive power or participate in grid voltage regulation.

[0114] In one example, adjusting the final active current action and the final reactive current action with the error of the feedback current to obtain the final voltage action includes:

[0115] The final active current action and the final reactive current action are transformed by current action coordinates to obtain the current components in the target coordinate system;

[0116] The converter output current, the grid connection point voltage and the phase of the grid voltage output by the phase-locked loop are transformed by current control coordinates to obtain the current feedback component and the voltage feedback component in the target coordinate system;

[0117] The difference between the current component in the target coordinate system and the current feedback component in the target coordinate system is current regulated and then superimposed with the voltage feedback component to obtain the final voltage action.

[0118] The preferred embodiments of the present application are described above with reference to the accompanying drawings, but are not intended to limit the scope of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and essence of the present application shall fall within the scope of the present application.

Claims

1. A control method for a grid-connected converter for grid voltage imbalance, characterized in that: The method comprises: According to the DC voltage action, the DC voltage detection value and the converter output current, the basic active current action and the additional active current action are obtained; Obtaining a final active current action and a final reactive current action according to the basic active current action, the basic reactive current action, and the additional active current action; The final active current action and the final reactive current action are adjusted with the error of the feedback current to obtain the final voltage action; Modulating the final voltage action to obtain a driving signal required for controlling the grid-connected converter; The method of obtaining the basic active current action and the additional active current action according to the DC voltage action, the DC voltage detection value and the converter output current includes: The DC voltage action is adjusted with the value of the DC voltage after filtering out the twice grid fundamental frequency component to obtain the basic active current action; and / or, A controller with high gain at twice the grid fundamental frequency is used to adjust the double grid fundamental frequency component in the DC voltage to obtain an initial value of the additional active current action; the maximum value of the converter output current is detected and compared with the current threshold to obtain an output mode switching signal of the converter; and the additional active current action is determined based on the converter output mode switching signal and the initial value of the additional active current action.

2. The method according to claim 1, characterized in that The value of the DC voltage after filtering out the component of twice the grid fundamental frequency is obtained through a notch filter or a low-pass filter whose center frequency is twice the grid fundamental frequency.

3. The method according to claim 1, characterized in that The controller having high gain at twice the grid fundamental frequency comprises one of a resonant regulator and a repetitive controller whose center frequency is twice the grid fundamental frequency.

4. The method according to claim 1, wherein The converter output current includes one of an effective value of the converter output three-phase current, a modulus value of the three-phase current, and a filtered value of the modulus value of the three-phase current.

5. The method according to claim 1, wherein The determining of the additional active current action amount according to the output mode switching signal of the converter and the initial value of the additional active current action amount includes: Set the output mode of the converter to constant output power or balanced output current.

6. The method according to claim 1, characterized in that The final active current action and the final reactive current action are obtained according to the basic active current action, the basic reactive current action and the additional active current action, including: Superimposing the basic active current action and the additional active current action to obtain a final active current action; and / or, The additional active current action is inverted and passed through an orthogonal signal generator to obtain an additional reactive current action, and then the additional reactive current action is superimposed on the basic reactive current action to obtain a final reactive current action.

7. The method according to claim 1, characterized in that The basic reactive current action quantity includes the positive sequence reactive current setting value set by the converter to control reactive power or participate in grid connection point voltage regulation.

8. The method according to claim 1, characterized in that The final active current action, the final reactive current action, and the error between the feedback current and the final voltage action are adjusted to obtain the final voltage action, including: The final active current action and the final reactive current action are transformed by current action coordinates to obtain the current components in the target coordinate system; The converter output current, the grid connection point voltage and the phase of the grid voltage output by the phase-locked loop are transformed by current control coordinates to obtain the current feedback component and the voltage feedback component in the target coordinate system; The difference between the current component in the target coordinate system and the current feedback component in the target coordinate system is current regulated and then superimposed with the voltage feedback component to obtain the final voltage action.

9. A control device for grid-connected converter for grid voltage imbalance, characterized in that: The device comprises: A DC voltage control module is used to obtain a basic active current action and an additional active current action according to a DC voltage action, a DC voltage detection value, and a converter bridge arm inductor current; a current instruction generating module, configured to obtain a final active current action and a final reactive current action according to the basic active current action, the basic reactive current action, and the additional active current action; The current control module is used to adjust the error between the final active current action and the final reactive current action and the feedback current to obtain the final voltage action; A modulation module, configured to modulate the final voltage action to obtain a driving signal required for controlling the grid-connected converter; The method of obtaining the basic active current action and the additional active current action according to the DC voltage action, the DC voltage detection value and the converter output current includes: The DC voltage action is adjusted with the value of the DC voltage after filtering out the twice grid fundamental frequency component to obtain the basic active current action; and / or, A controller with high gain at twice the grid fundamental frequency is used to adjust the double grid fundamental frequency component in the DC voltage to obtain an initial value of the additional active current action; the maximum value of the converter output current is detected and compared with the current threshold to obtain an output mode switching signal of the converter; and the additional active current action is determined based on the converter output mode switching signal and the initial value of the additional active current action.

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