Converter current control method and device for improving power grid fault ride-through performance

Abstract

The application discloses a converter current control method and device for improving power grid fault ride-through performance, and the device comprises: a current instruction coordinate transformation module for obtaining a current instruction component; a grid-side current coordinate transformation module for obtaining a grid-side current component; a power grid voltage coordinate transformation module for obtaining a power grid voltage component; a current error adjustment module for adjusting a difference between the current instruction component and the grid-side current component and outputting an adjustment amount; a voltage feedforward control module for processing the power grid voltage component to obtain a power grid voltage feedforward amount; a wave generation voltage coordinate transformation module for calculating a final wave generation voltage instruction; and a modulation module for obtaining a driving signal required by converter control. The application is simple, does not increase the hardware cost of the converter, can solve the contradiction between transient impact overcurrent and grid connection stability of the grid-connected converter when responding to power grid voltage drop, enhances the adaptability of the converter to strong / weak power grids, and guarantees that the output power quality meets the requirements under different power grid intensities.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of grid-connected technology, and particularly relates to a converter current control method and device for improving grid fault ride-through performance. 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 grid, the operation performance of the grid-connected converter is related to the power quality of the power generated by the new energy. 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] In recent years, with the increase of power electronic equipment connected to the grid, the impedance of the grid-connected point connected to the grid-connected converter increases, and the "weak grid" characteristics of voltage distortion caused by load are more obvious. Weak grid easily causes the output current of the converter using traditional current control method near the access point to be distorted, and the distorted current in turn will worsen the grid-connected point voltage, and further affect the grid-connected stability of the converter.

[0004] Filtering the grid voltage feedforward term of the current control loop of the converter can solve the current distortion problem of the converter under weak grid

Document 1 "Jinming Xu, Qiang Qian, Shaojun Xie, et al. Grid-Voltage Feedforward Based Control for Grid-Connected LCL-Filtered Inverter with High Robustness and Low Grid Current Distortion in Weak Grid [C] IEEE Applied Power Electronics Conference & Exposition, 2016, 1919-1925."

[0005] With the increasing number of grid-connected converters operating under weak grid conditions due to the large-scale access of power electronic devices to the grid, related problem research and countermeasures are constantly updated. Early research often treats the dynamic performance problem and the grid-connected stability problem of grid-connected converters separately, that is, when studying the dynamic performance problem, the grid-connected stability problem is not considered, or the dynamic performance is sacrificed to improve the grid-connected stability. In addition, in the traditional research method, the grid-connected converter is often approximated as a linear time-invariant system, that is, it is believed that the grid-connected stability is not much related to the input and is mainly determined by the mathematical model describing the system, such as the transfer function. The control parameters designed have little influence on the grid voltage or the output current of the converter, and have strong robustness. However, more and more research has proved that this is not the case

Document 2“Jiabing Hu, Qi Hu, Bo Wang, et al. Small Signal Instability of PLL-Synchronized Type-4 Wind Turbines Connected to High-Impedance AC Grid During LVRT [J] IEEE Trans. Energy Conversion, 2016, 31(4): 1676–1687.”

Document 3“Leming Zhou, Siyi Liu, Yandong Chen, et al. Harmonic Current and Inrush Fault Current Coordinated Suppression Method for VSG Under Non-ideal Grid Condition [J] IEEE Trans. Power Electron, 2021, 36(1): 1030–1041.”, Document 4“Heng Wu, Xiongfei Wang. Design-Oriented Transient Stability Analysis of PLL-Synchronized Voltage-Source Converters [J] IEEE Trans. Power Electron, 2020, 35(4): 3573–3589.”

[0006] To solve this problem, document 2

"Jiabing Hu, Qi Hu, Bo Wang, et al. Small Signal Instability of PLL-Synchronized Type-4 Wind Turbines Connected to High-Impedance AC Grid During LVRT [J] IEEE Trans. Energy Conversion, 2016, 31(4): 1676-1687."

"Gao Jiaoyuan, Xiao Fan, Jiang Fei, et al. Impedance phase remolding control of grid-connected inverter with new PLL structure under weak grid [J]. Proceedings of the Chinese Society of Electrical Engineering, 2020, 40(20): 6682-6693."

[0007] The present application aims to provide a converter current control method and device for improving grid fault ride-through performance to solve the problem that the dynamic response capability improvement and grid stability improvement of the grid-connected converter in the prior art cannot be considered.

[0008] In one aspect of the present application, a converter current control device for improving grid fault ride-through performance is provided, which includes a phase-locked loop configured to obtain a phase-locked loop output angle according to a grid voltage, and further includes:

[0009] A current command coordinate transformation module configured to obtain a current command component according to a current command of the grid-connected converter and the phase-locked loop output angle;

[0010] A grid-side current coordinate transformation module configured to obtain a grid-side current component according to a grid-side current and the phase-locked loop output angle;

[0011] A grid voltage coordinate transformation module configured to obtain a grid voltage component according to the grid voltage and the phase-locked loop output angle;

[0012] A current error regulation module configured to regulate the difference between the current command component and the grid-side current component and output a regulation amount;

[0013] A voltage feedforward control module configured to process the grid voltage component to obtain a grid voltage feedforward amount;

[0014] The generating wave voltage coordinate transformation module is configured to calculate a final generating wave voltage instruction according to a generating wave voltage instruction obtained by superimposing the grid voltage feedforward quantity and the adjustment quantity;

[0015] The modulation module modulates the final generating wave voltage instruction to obtain a driving signal required for converter control.

[0016] In another aspect of the present application, a converter current control method for improving grid fault ride-through performance is provided, and the method comprises:

[0017] A current instruction component is obtained according to a current instruction of a grid-connected converter and an output angle of a phase-locked loop; a grid-side current component is obtained according to a grid-side current and the output angle of the phase-locked loop; and an adjustment quantity is obtained by adjusting a difference between the current instruction component and the grid-side current component.

[0018] A grid voltage component is obtained according to a grid voltage and the output angle of the phase-locked loop; and a grid voltage feedforward quantity is obtained by processing the grid voltage component.

[0019] A final generating wave voltage instruction is calculated according to a generating wave voltage instruction obtained by superimposing the grid voltage feedforward quantity and the adjustment quantity.

[0020] The final generating wave voltage instruction is modulated to obtain a driving signal required for converter control.

[0021] The converter current control method for improving grid fault ride-through performance provided by the embodiments of the present application can inhibit transient output impact current of the converter while ensuring grid-connected stability when the grid voltage drops, by improving voltage feedforward control of the current control loop. The method is simple to implement and does not increase hardware cost of the converter, and can solve the contradiction between transient impact overcurrent and grid-connected stability of the grid-connected converter when the grid voltage drops, improve grid fault ride-through performance, enhance adaptability of the converter to strong / weak grid, and ensure that the output of the converter meets the requirements of power quality under different grid strengths. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The current control block diagram of the grid-connected converter provided by the embodiments of the present application is shown in FIG. 1;

[0023] Figure 2 The principle schematic diagram of the voltage feedforward control module provided by the embodiments of the present application is shown in FIG. 2;

[0024] Figure 3 The principle schematic diagram of the grid fault judgment module provided by the embodiments of the present application is shown in FIG. 3;

[0025] Figures 4-5 The simulation result of the current control method of the present example when the three-phase grid voltage drops to 20% under a weak grid is shown in FIG. 4.

[0026] Figures 6-7 Simulation results of the traditional unit ratio voltage feedforward when the three-phase voltage of the weak power grid drops to 20%;

[0027] Figures 8-9 Simulation results of filtering the traditional unit ratio voltage feedforward only when the three-phase voltage of the weak power grid drops to 20%;

[0028] Figure 10 A schematic diagram of the current control method of the grid-connected converter provided by the embodiment of the application.

[0029] The implementation, functional features and advantages of the application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0030] In order to make the technical problems, technical solutions and beneficial effects of the application more clear, explicit and apparent, the 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 application and not to limit the application.

[0031] In the description of the 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 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 on the application. In addition, the terms "first" and "second" are only for the purpose of description and cannot be understood as indicating or implying relative importance.

[0032] The variables involved in the embodiments of the application and their definitions are as follows:

[0033] u gabc : grid voltage

[0034] i gabc : grid-side current

[0035] i oabc : grid-connected current

[0036] L g : equivalent leakage inductance of the grid

[0037] L gf : grid-side filter inductance

[0038] C f : grid-side filter capacitance

[0039] θ g : phase-locked loop output angle

[0040] i gref_d 、i gref_q : d, q axis components of grid-side current command

[0041] i gref_x 、i gref_y : x, y axis components of grid-side current command

[0042] i g_x 、i g_y : x, y axis components of grid-side current

[0043] u g_x 、u g_y : x, y axis components of grid voltage

[0044] u CR_x 、u CR_y : x, y axis current error regulation module output

[0045] u gFw_x 、u gFw_y : x, y axis components of grid voltage feedforward

[0046] u gf_x 、u gf_y : x, y axis components of grid voltage fundamental

[0047] u gh_x 、u gh_y : x, y axis components of grid voltage harmonic

[0048] u ghFw_x 、u ghFw_y : x, y axis components of grid voltage harmonic feedforward voltage

[0049] u gm : grid voltage component modulus

[0050] u gm_nom : grid voltage rated modulus

[0051] u gmpu : grid voltage component modulus per unit

[0052] m J : grid voltage amplitude jump index

[0053] Vdist_flag: grid voltage disturbed flag

[0054] VJmp_flag: grid voltage amplitude jump flag

[0055] h flag : timing control module output flag

[0056] mJL The exit threshold for grid voltage disturbances

[0057] m JH Trigger threshold for grid voltage disturbance

[0058] K fwh Percentage of grid voltage harmonic feedforward

[0059] e vscref_x e vscref_y : x and y axis components of the transmitted voltage command

[0060] e vscref_α e vscref_β : α and β axis components of the transmitted voltage command

[0061] Figure 1 A block diagram of the current control of a grid-connected converter provided in an embodiment of this application.

[0062] like Figure 1 As shown, the current control of the grid-connected converter is achieved through a phase-locked loop (PLL) module, a current command coordinate transformation module, a grid-side current coordinate transformation module, a grid voltage coordinate transformation module, a current error adjustment module, a voltage feedforward control module, a ripple voltage coordinate transformation module, and a PWM modulation module.

[0063] The input to the PLL is the grid voltage u of the converter. gabc The output is the angle θ of the positive sequence voltage of the power grid. g .

[0064] The current command coordinate transformation module is configured to transform the grid-connected converter according to the current command i. gref_d i gref_q and the phase-locked loop output angle θ g The current command component i in the current control coordinate system is obtained. gref_x i gref_y .

[0065] The grid-side current coordinate transformation module is configured to transform the grid-side current i into coordinates. gabc and the phase-locked loop output angle θ g The grid-side current component i in the current-controlled coordinate system is obtained. g_x i g_y Grid-side current i gabc It can be the grid-connected current of the converter or the current in its AC inductor.

[0066] The grid voltage coordinate transformation module is configured to transform the grid voltage u. gabc And the phase-locked loop output angle, to obtain θ g Grid voltage component u in current-controlled coordinate systemg_x g_y .

[0067] When the current control coordinate system is the synchronous rotating (dq) coordinate system, the transformation formulas of the current instruction coordinate transformation module, the grid-side current coordinate transformation module, and the grid voltage coordinate transformation module are respectively:

[0068]

[0069]

[0070]

[0071] When the current control coordinate system is the two-phase static (αβ) coordinate system, the transformation formulas of the current instruction coordinate transformation module, the grid-side current coordinate transformation module, and the grid voltage coordinate transformation module are respectively:

[0072]

[0073]

[0074]

[0075] The current error regulation module is configured to regulate the difference i gref_k (k=x, y) between the current instruction component i g_k (k=x, y) and the feedback grid-side current component i err_k (k=x, y), and output the regulation amount u CR_k (k=x, y).

[0076] The voltage feedforward control module is configured to process the grid voltage components u g_x , u g_y to obtain the grid voltage feedforward amount u gFw_k (k=x, y).

[0077] Specifically, as shown in Figure 2 , the voltage feedforward control module processes the grid voltage components u g_x , u g_y as follows:

[0078] a) calculating the grid voltage components u g_x , u g_y to obtain the grid voltage component modulus u gm and the grid voltage component modulus unit value u gmpu . The calculation formula is as follows:

[0079]

[0080] ​wherein u gm_nom is the rated value of the grid voltage.

[0081] At the same time, the grid voltage components u g_x , u g_y are input to the filter, and the grid voltage fundamental components u gf_x , u gf_y are obtained after filtering. When the current control coordinate system is the synchronous rotating (dq) coordinate system, the filter is a low-pass filter; when the current control coordinate system is the two-phase static (αβ) coordinate system, the filter is a band-pass filter with the center frequency being the grid fundamental frequency.

[0082] b) the grid voltage components u g_x , u g_y are subtracted by the grid voltage fundamental components u gf_x , u gf_y , and the grid voltage harmonic components u gh_x , u gh_y are obtained.

[0083] c) the grid voltage harmonic components u gh_x , u gh_y are divided by the rated value of the grid voltage u gm_nom , and the per-unit values of the grid voltage harmonic components u ghpu_x , u ghpu_y are obtained, and u ghpu_x , u ghpu_y are input to the grid fault judgment module.

[0084] As shown in FIG. 1, the grid fault judgment module is implemented as follows: Figure 3

[0085] 1) the per-unit values of the grid voltage harmonic components u ghpu_x , u ghpu_y are input to the transient component coordinate transformation module, and the corresponding d, q axis components u ghpu_d , u ghpu_q are obtained.

[0086] When the current control coordinate system is the dq coordinate system, the transient component coordinate transformation formula is:

[0087]

[0088] When the current control coordinate system is the αβ coordinate system, the transient component coordinate transformation formula is:

[0089]

[0090] 2) the maximum value in the absolute values of the d, q axis components u ghpu_d , u ghpu_q is taken, and the grid voltage amplitude jump index m is obtained.​J i.e.

[0091] m J = max(|u ghpu_d |, |u ghpu_q |) (6)

[0092] It should be noted that in other examples, the square root of the sum of squares of the d-axis and q-axis components u ghpu_d , u ghpu_q may also be calculated to obtain the grid voltage amplitude jump index m J .

[0093] 3) According to m J , it is determined whether the grid voltage amplitude jumps or the harmonic content is high, and the hysteresis rule is used to update the grid voltage disturbance flag Vdis_flag. The hysteresis rule and its threshold are:

[0094]

[0095] In the formula, m JH and m JL (m JH > m JL > 0) are the trigger threshold and exit threshold of the grid voltage disturbance, respectively.

[0096] 4) According to the value of the grid voltage disturbance flag Vdis_flag, it is determined whether to start the timing control module count, and the value of the output flag hflag is updated according to the count value hcnt. In this example, the timing control module count is counted in the following way:

[0097]

[0098] The update rule of the value of the output flag is:

[0099]

[0100] In the formula, hcnt_set is the set value of the time corresponding to the grid voltage amplitude jump.

[0101] According to the value of the grid voltage disturbance flag Vdis_flag and the value of the timing control module output flag hflag, the value of the grid voltage amplitude jump flag VJmp_flag is updated, and the update rule is as follows:

[0102]

[0103] 5) According to the value of the grid voltage amplitude jump flag VJmp_flag, the percentage K fwh of the grid voltage harmonic feedforward amount of the current control loop is updated. The update rule is:

[0104]

[0105] d) The voltage feed-forward amount generation module (not shown) multiplies the percentage K of the grid voltage harmonic feed-forward amount fwh with the harmonic component u gh_x of the grid voltage, to obtain the grid voltage harmonic feed-forward amount u gh_y . ghFw_x ghFw_y ;

[0106] e) The grid voltage harmonic feed-forward amount u ghFw_x is superimposed on the grid voltage fundamental component u ghFw_y , to obtain the grid voltage feed-forward amount u gf_x . gf_y gFw_x gFw_y .

[0107] The obtained grid voltage feed-forward amount u gFw_k (k = x, y) is superimposed on the regulation amount u CR_k (k = x, y) output by the current error regulation module, to obtain the x-axis and y-axis components e vscref_x and e vscref_y of the generated-wave voltage instruction.

[0108] The generated-wave voltage coordinate transformation module is configured to convert the x-axis and y-axis components e vscref_x and e vscref_y of the generated-wave voltage instruction into the α-axis and β-axis components e vscref_α and e vscref_β in the αβ coordinate system. Of course, it can also be converted into the dq coordinate system.

[0109] When the current control coordinate system is the dq coordinate system, the conversion formula of the generated-wave voltage coordinate transformation link is:

[0110]

[0111] When the current control coordinate system is the αβ coordinate system, the conversion formula of the generated-wave voltage coordinate transformation link is:

[0112]

[0113] Finally, the α-axis and β-axis components e vscref_α and e vscref_β of the generated-wave voltage instruction are modulated by the PWM modulation module, for example, by using the three-phase space vector modulation method, to obtain the driving signal required for the grid-connected converter control, so as to achieve the basic power target and realize the suppression target of the converter output current harmonics. ​​​

[0114] Figures 4-5 Simulation results of the current control of the example when the three-phase voltage of the power grid drops to 20% under a weak power grid;

[0115] Figures 6-7 Simulation results of the traditional unit proportion voltage feedforward when the three-phase voltage of the power grid drops to 20% under a weak power grid;

[0116] Figures 8-9 Simulation results of filtering only the traditional unit proportion voltage feedforward when the three-phase voltage of the power grid drops to 20% under a weak power grid.

[0117] As can be seen from the simulation result diagrams, the current control of the grid-connected converter provided in the embodiments of the present application can inhibit transient output impact current of the converter while ensuring grid connection stability when the grid voltage drops, by improving voltage feedforward control of the current control loop. The implementation is simple, does not increase hardware cost of the converter, and can solve the contradiction between transient impact overcurrent and grid connection stability of the grid-connected converter when the grid voltage drops, enhance adaptability of the converter to strong / weak power grids, and ensure that the output of the converter meets the requirements of power quality under different power grid strengths.

[0118] Figure 10 A schematic diagram of the current control method of the grid-connected converter provided in the embodiments of the present application.

[0119] As shown in Figure 10 , the method comprises the steps of:

[0120] S11, obtaining a current command component according to a current command of the grid-connected converter and an output angle of a phase-locked loop, and obtaining a grid-side current component according to a grid-side current and the output angle of the phase-locked loop; adjusting a difference between the current command component and the grid-side current component and outputting an adjustment amount;

[0121] S12, obtaining a grid voltage component according to a grid voltage and the output angle of the phase-locked loop; processing the grid voltage component to obtain a grid voltage feedforward amount;

[0122] S13, calculating a final wave launch voltage command according to a wave launch voltage command obtained by superimposing the grid voltage feedforward amount and the adjustment amount;

[0123] S14, modulating the final wave launch voltage command to obtain a driving signal required by the converter control.

[0124] The steps S11 and S12 do not have a sequence.

[0125] In an example, the method further comprises:

[0126] filtering the grid voltage component to obtain a grid voltage fundamental component;

[0127] obtaining a grid voltage harmonic feed-forward percentage according to a grid voltage harmonic component norm value and a grid voltage component norm value;

[0128] obtaining the grid voltage feed-forward according to the grid voltage fundamental component, the grid voltage harmonic feed-forward percentage and the grid voltage harmonic component.

[0129] In an example, the grid voltage harmonic component norm value is obtained by dividing the grid voltage harmonic component by a grid voltage rated norm value, the grid voltage harmonic component being obtained by subtracting the grid voltage fundamental component from the grid voltage component;

[0130] The grid voltage component norm value is calculated according to the grid voltage component and the grid voltage rated norm value.

[0131] In an example, the method further comprises:

[0132] obtaining a component corresponding to the grid voltage harmonic component norm value by a transient component coordinate transformation module according to the grid voltage harmonic component norm value;

[0133] obtaining a grid voltage amplitude jump index according to the component corresponding to the grid voltage harmonic component norm value;

[0134] updating a grid voltage disturbed flag according to the grid voltage amplitude jump index;

[0135] updating a grid voltage amplitude jump flag according to the grid voltage disturbed flag and an output flag of a timing control module;

[0136] updating the grid voltage harmonic feed-forward percentage according to the grid voltage amplitude jump flag and the grid voltage component norm value.

[0137] In an example, the grid voltage amplitude jump index is calculated according to a maximum value in absolute values of the component corresponding to the grid voltage harmonic component norm value, or a square root of a sum of squares of the component corresponding to the grid voltage harmonic component norm value.

[0138] In an example, the grid voltage disturbed flag is updated according to the grid voltage amplitude jump index, a trigger threshold and an exit threshold of the grid voltage being disturbed.

[0139] In an example, whether to start counting of the timing control module is determined according to the grid voltage disturbed flag.

[0140] In one example, the grid voltage harmonic feedforward quantity is obtained by multiplying a percentage of the grid voltage harmonic feedforward quantity with a harmonic component of the grid voltage; and the grid voltage feedforward quantity is obtained by superimposing the grid voltage harmonic feedforward quantity to a fundamental component of the grid voltage.

[0141] The preferred embodiments of the present application are described above with reference to the accompanying drawings, and are not intended to limit the scope of the present application. Any modification, equivalent replacement and improvement made by those skilled in the art without departing from the scope and spirit of the present application shall fall within the scope of the present application.

Claims

1. A converter current control device for improving grid fault ride-through performance, comprising a phase-locked loop (PLL) configured to obtain the PLL output angle based on the grid voltage, characterized in that, The device further includes: The current command coordinate transformation module is configured to obtain the current command component based on the current command of the grid-connected converter and the output angle of the phase-locked loop when the current control coordinate system is a two-phase stationary coordinate system, or, when the current control coordinate system is a synchronous rotating coordinate system, the current command component is the current command of the grid-connected converter. The grid-side current coordinate transformation module is configured to obtain the grid-side current component based on the grid-side current and the output angle of the phase-locked loop; The grid voltage coordinate transformation module is configured to obtain the grid voltage components based on the grid voltage and the output angle of the phase-locked loop; The current error adjustment module is configured to adjust the difference between the current command component and the grid-side current component and output the adjustment amount; The voltage feedforward control module is configured to process the grid voltage component to obtain the grid voltage feedforward quantity; The voltage coordinate transformation module is configured to calculate the final voltage command based on the voltage command obtained by superimposing the grid voltage feedforward and the regulation amount. The modulation module modulates the final transmitted voltage command to obtain the drive signal required for converter control.

2. The apparatus according to claim 1, characterized in that, The voltage feedforward control module includes: The filter is configured to filter the grid voltage component to obtain the grid voltage fundamental component; The power grid fault judgment module is configured to obtain the percentage of power grid voltage harmonic feedforward based on the per-unit value of the power grid voltage harmonic component and the per-unit value of the power grid voltage component magnitude. The voltage feedforward generation module is configured to obtain the grid voltage feedforward based on the grid voltage fundamental component, the percentage of the grid voltage harmonic feedforward, and the grid voltage harmonic components.

3. The apparatus according to claim 2, characterized in that, The filter includes a low-pass filter or a band-pass filter with a center frequency of the fundamental frequency of the power grid.

4. The apparatus according to claim 2, characterized in that, The per-unit value of the grid voltage harmonic component is obtained by dividing the grid voltage harmonic component by the grid voltage rated modulus, and the grid voltage harmonic component is obtained by subtracting the grid voltage fundamental component from the grid voltage component. The per-unit value of the grid voltage component magnitude is calculated based on the grid voltage component and the grid voltage rated magnitude.

5. The apparatus according to claim 2, characterized in that, The power grid fault detection module is configured as follows: Based on the per-unit value of the grid voltage harmonic components, the component corresponding to the per-unit value is calculated through the transient component coordinate transformation module; The grid voltage amplitude jump index is calculated based on the components corresponding to the per-unit value. Update the grid voltage disturbance flag based on the grid voltage amplitude jump index; Update the grid voltage amplitude jump flag based on the grid voltage disturbance flag and the output flag of the timing control module; The percentage of the grid voltage harmonic feedforward is updated based on the grid voltage amplitude jump flag and the per-unit value of the grid voltage component magnitude.

6. The apparatus according to claim 5, characterized in that, The power grid fault judgment module is configured to calculate the power grid voltage amplitude jump index based on the maximum absolute value of the components corresponding to the per-unit value, or the square root of the sum of squares of the components corresponding to the per-unit value.

7. The apparatus according to claim 5, characterized in that, The power grid fault judgment module is configured to update the power grid voltage disturbance flag based on the power grid voltage amplitude jump index, the trigger threshold and exit threshold for power grid voltage disturbance.

8. The apparatus according to claim 5, characterized in that, The power grid fault judgment module is configured to determine whether to start the timing control module to count based on the power grid voltage disturbance flag.

9. The apparatus according to claim 2, characterized in that, The voltage feedforward generation module is configured to multiply the percentage of the grid voltage harmonic feedforward by the harmonic component of the grid voltage to obtain the grid voltage harmonic feedforward; and to superimpose the grid voltage harmonic feedforward onto the grid voltage fundamental component to obtain the grid voltage feedforward.

10. A converter current control method for improving grid fault ride-through performance, characterized in that, The method includes: When the current control coordinate system is a two-phase stationary coordinate system, the current command component is obtained based on the current command of the grid-connected converter and the output angle of the phase-locked loop; or, when the current control coordinate system is a synchronous rotating coordinate system, the current command component is the current command of the grid-connected converter; the grid-side current component is obtained based on the grid-side current and the output angle of the phase-locked loop; the difference between the current command component and the grid-side current component is adjusted and the adjustment amount is output; The grid voltage component is obtained based on the grid voltage and the output angle of the phase-locked loop; the grid voltage component is processed to obtain the grid voltage feedforward. The final transmission voltage command is calculated based on the transmission voltage command obtained by superimposing the grid voltage feedforward and the regulation amount. The final transmitted voltage command is modulated to obtain the drive signal required for converter control.

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