Low Voltage Ride-Through Control Method and System for Grid-Connected Inverters under Asymmetric Faults

Abstract

This invention belongs to the field of power system technology and provides a low-voltage ride-through control method and system for grid-connected inverters under asymmetrical faults. The method includes: acquiring real-time grid connection point voltage and determining whether the grid is under asymmetrical fault; determining whether the grid connection point voltage is qualified; if not, the low-voltage ride-through module generates a current command with positive and negative sequence voltage support as the target; determining whether the generated current command exceeds current limits and whether DC-side voltage oscillation limits are exceeded; if no current exceeds current limits and DC-side voltage oscillation limits are met, positive and negative sequence reactive current commands are generated normally; if current exceeds current limits or DC-side voltage oscillation limits are not met, a positive sequence reactive current command is generated, and the negative sequence reactive current command is adjusted; based on the grid-connected inverter's current inner loop, the generated current command or the positive and negative sequence reactive current commands are used to generate a gating signal for the grid-connected inverter, completing the low-voltage ride-through control of the grid-connected inverter under asymmetrical faults.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, specifically relating to a low-voltage ride-through control method and system for grid-connected inverters under asymmetrical faults. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] With the increasing penetration of new energy sources, the number of power electronic converters connected to the power grid is growing. The control systems of power electronic devices are susceptible to voltage dips, which can cause grid disconnection and reduce system safety and reliability. Grid-connected inverters should possess low-voltage ride-through capability, providing some voltage support to the grid during faults. Most voltage dips in power systems are caused by asymmetrical faults; therefore, researching low-voltage ride-through control of grid-connected inverters under asymmetrical fault conditions is of great significance for the safe and reliable operation of power systems.

[0004] According to the inventors, current low-voltage ride-through control methods for grid-connected inverters under asymmetrical faults have the following problems:

[0005] Current research on low-voltage ride-through control methods for grid-connected inverters under asymmetrical faults mostly focuses on boosting the positive-sequence voltage at the grid connection point, neglecting the impact of negative-sequence voltage on the grid. Furthermore, during asymmetrical grid faults, the active power output of the grid-connected inverter exhibits second-harmonic oscillations, causing the DC-side voltage to oscillate at the same frequency, which can easily damage the DC-side capacitors and affect their long-term lifespan. Therefore, an effective control method for grid-connected inverters should consider both supporting the positive and negative-sequence voltages at the grid connection point while suppressing DC-side voltage oscillations, achieving a multi-objective control effect. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a low-voltage ride-through control method and system for grid-connected inverters under asymmetrical faults. Based on the influence of the positive and negative sequence currents of the grid-connected inverter on the grid side during asymmetrical faults, the method limits the overcurrent output by the inverter and suppresses voltage oscillations on the DC side, thereby ensuring precise positive and negative sequence voltage support at the grid connection point.

[0007] According to some embodiments, the first aspect of the present invention provides a low-voltage ride-through control method for grid-connected inverters under asymmetrical faults, employing the following technical solution:

[0008] A low-voltage ride-through control method for grid-connected inverters under asymmetric fault conditions includes:

[0009] Obtain real-time grid connection point voltage to determine whether the power grid is experiencing an asymmetrical fault.

[0010] Determine whether the obtained grid connection point voltage is qualified. If it is not qualified, enter the low voltage ride-through module of the grid-connected inverter and generate a current command with positive and negative sequence voltage support as the target.

[0011] Determine whether the generated current command exceeds the current limit or exceeds the DC side voltage oscillation limit. If the current does not exceed the current limit and the DC side voltage oscillation limit is met, then generate the positive sequence reactive current command and the negative sequence reactive current command normally. If the current exceeds the current limit or the DC side voltage oscillation limit is not met, then generate the positive sequence reactive current command first, and then adjust the negative sequence reactive current command.

[0012] Based on the grid-connected inverter's current inner loop, the generated current command or positive-sequence reactive current command and negative-sequence reactive current command are used to generate the grid-connected inverter's gate signal, thus completing the low-voltage ride-through control of the grid-connected inverter under asymmetrical fault conditions.

[0013] As a further technical limitation, when the generated current command does not exceed the current limit, it is determined whether the current command is within the reasonable range of DC side oscillation. Specifically, when the DC side voltage oscillation amplitude calculated from the current command provided by the grid-connected inverter exceeds the set value, the current command issued by the grid-connected inverter does not meet the DC side voltage oscillation limit.

[0014] As a further technical limitation, in the process of determining whether the generated current command has exceeded the current limit, the inner current loop of the grid-connected inverter is set to the normal operating range. If the current command transmitted to the inner current loop exceeds the range of the normal operating range, it is determined that the current command does not meet the output current limit, that is, the current limit has exceeded the limit.

[0015] As a further technical limitation, when the obtained grid connection point voltage has a negative sequence component, the power grid is determined to be in an asymmetrical fault state.

[0016] As a further technical limitation, when the obtained grid connection point voltage is unqualified, the grid-connected inverter adopts constant power control.

[0017] As a further technical limitation, the grid connection point voltage is considered unqualified if the positive sequence voltage at the grid connection point drops below 0.9 pu.

[0018] According to some embodiments, the second aspect of the present invention provides a low-voltage ride-through control system for a grid-connected inverter under asymmetric faults, employing the following technical solution:

[0019] A low-voltage ride-through control system for a grid-connected inverter under asymmetric fault conditions includes:

[0020] The acquisition module is configured to acquire the real-time grid connection point voltage and determine whether the power grid is in an asymmetrical fault.

[0021] The first judgment module is configured to judge whether the obtained grid connection point voltage is qualified. If it is not qualified, it enters the low voltage ride-through module of the grid-connected inverter to generate a current command with positive and negative sequence voltage support as the target.

[0022] The second judgment module is configured to judge whether the generated current command has exceeded the current limit and whether the DC side voltage oscillation limit has exceeded the limit. If the current does not exceed the limit and the DC side voltage oscillation limit is met, the positive sequence reactive current command and the negative sequence reactive current command are generated normally. If the current exceeds the limit or the DC side voltage oscillation limit is not met, the positive sequence reactive current command is generated first, and then the negative sequence reactive current command is adjusted.

[0023] The control module is configured to generate gating signals for the grid-connected inverter based on the generated current command or positive-sequence reactive current command and negative-sequence reactive current command in the grid-connected inverter current inner loop, thereby completing the low-voltage ride-through control of the grid-connected inverter under asymmetrical fault conditions.

[0024] According to some embodiments, a third aspect of the present invention provides a computer-readable storage medium, employing the following technical solution:

[0025] A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the low-voltage ride-through control method for grid-connected inverters under asymmetric faults as described in the first aspect of the present invention.

[0026] According to some embodiments, the fourth aspect of the present invention provides an electronic device, which adopts the following technical solution:

[0027] An electronic device includes a memory, a processor, and a program stored in the memory and running on the processor, wherein the processor executes the program to implement the steps in the low voltage ride-through control method for a grid-connected inverter under asymmetric faults as described in the first aspect of the present invention.

[0028] According to some embodiments, the fifth aspect of the present invention provides a computer program product, which adopts the following technical solution:

[0029] A computer program product includes software code, wherein the program in the software code performs the steps of the low voltage ride-through control method for grid-connected inverters under asymmetric faults as described in the first aspect of the present invention.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This invention considers the maximum current limit of the inverter output and the DC side voltage oscillation limit during low-voltage breakdown. Based on the influence of the positive and negative sequence current of the grid-connected inverter on the grid side during asymmetrical faults, positive and negative sequence current commands are issued simultaneously to limit the overcurrent of the inverter output, suppress DC side voltage oscillation, and ensure precise positive and negative sequence voltage support at the grid connection point. Attached Figure Description

[0032] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0033] Figure 1 This is a flowchart of a low-voltage ride-through control method for a grid-connected inverter under asymmetric fault, as described in Embodiment 1 of the present invention.

[0034] Figure 2 This is a schematic diagram of the low-voltage ride-through control method for grid-connected inverters under asymmetric faults in Embodiment 1 of the present invention.

[0035] Figure 3 This is a diagram showing the result of achieving positive and negative sequence voltage support in Embodiment 1 of the present invention without exceeding either the current limit or the DC side voltage limit;

[0036] Figure 4 This is a diagram showing the adjustment results in Embodiment 1 of the present invention, where the current limit is exceeded but the DC side voltage does not exceed the limit when positive and negative sequence voltage support is achieved.

[0037] Figure 5 This is a diagram showing the adjustment result in Embodiment 1 of the present invention, where the output current does not exceed the limit even when the positive and negative sequence voltages are supported, even if the DC side voltage limit is exceeded.

[0038] Figure 6 This is a diagram showing the adjustment results in Embodiment 1 of the present invention when achieving positive and negative sequence voltage support, which exceeds both the DC side voltage limit and the current limit.

[0039] Figure 7 This is a structural block diagram of a grid-connected inverter low-voltage ride-through control system under asymmetric fault conditions, as described in Embodiment 2 of the present invention. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0041] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0042] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0043] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0044] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0045] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0046] Example 1

[0047] Embodiment 1 of the present invention introduces a low-voltage ride-through control method for grid-connected inverters under asymmetric fault conditions.

[0048] like Figure 1 The method for low-voltage ride-through control of a grid-connected inverter under asymmetric fault conditions, as shown, includes the following steps:

[0049] Step S01: Monitor the grid connection point voltage in real time and determine whether the grid connection point voltage is qualified; if it is not qualified, proceed to the grid-connected inverter low voltage ride-through module and proceed to step S02.

[0050] Step S02: Determine whether the current command issued by the grid-connected inverter meets the output current limit. If it does not meet the limit, proceed to the positive sequence voltage priority control module. If it does meet the limit, proceed to step S03.

[0051] Step S03: Determine whether the current command issued by the grid-connected inverter meets the DC side voltage oscillation limit. If it does not meet the limit, proceed to the positive sequence voltage priority control module. If it does meet the limit, proceed to step S04.

[0052] Step S04: Based on the current over-limit and DC side voltage over-limit situations determined in steps S02 and S03, divide the scenarios into four types and generate and adjust current commands, then proceed to step S05.

[0053] Step S05: Input the generated current command into the inverter's inner current loop, and generate the inverter's gate signal from the inner current loop, thereby realizing low voltage ride-through control under asymmetrical fault conditions.

[0054] like Figure 2 As shown, in this embodiment, during an asymmetric fault, the controller first uses the sequence component extraction and voltage amplitude calculation functions to decompose the voltage and current output from the grid connection point into positive and negative sequence components and calculate their amplitudes. The current reference value calculation function is the low voltage ride-through method proposed in this invention. The current reference value generated by the current reference value calculation function is input into the current inner loop of the grid-connected inverter to generate a gate signal input to the inverter, thereby realizing low voltage ride-through control during an asymmetric fault.

[0055] As one or more implementation methods, in step S01, a decoupled double synchronous reference frame phase-locked loop (DDSRF-PLL) is used to collect the positive and negative sequence voltages at the grid connection point and monitor in real time whether a drop occurs. Under asymmetrical fault conditions, that is, when the grid connection point voltage has a negative sequence component during the fault period, if the positive sequence voltage at the grid connection point drops below 0.9pu, the grid connection point voltage is determined to be unqualified, and the grid-connected inverter enters the low voltage ride-through control mode.

[0056] As one or more implementation methods, in step S02, when the system determines that the grid connection point voltage is unqualified, the grid-connected inverter automatically enters the low-voltage ride-through control mode. Based on the positive-negative sequence transformation under DDSRF, when an asymmetric fault occurs, the positive sequence relationship between the grid-side voltage, the grid connection point voltage, and the grid-connected inverter output current can be written as:

[0057]

[0058] Among them, v + Indicates the positive sequence component of the grid connection point voltage; i + This represents the positive-sequence component of the inverter output current; For the positive sequence component of the grid-side voltage; L g With R g t represents the inductance and resistance values ​​in the circuit; t represents time.

[0059] Similarly, the negative order relation can be written as:

[0060]

[0061] Among them, v - Indicates the negative sequence component of the grid connection point voltage; i - This represents the negative sequence component of the inverter output current; This represents the negative sequence component of the grid-side voltage.

[0062] Transforming the above formula, we get:

[0063]

[0064] in, V represents the magnitude of the positive sequence component of the grid-side voltage. + ω represents the amplitude of the positive sequence component of the grid connection point voltage; ω represents the angular frequency at the power grid frequency. These are the active and reactive positive sequence current commands output by the inverter.

[0065]

[0066] in, V represents the magnitude of the positive sequence component of the grid-side voltage. - The magnitude of the negative sequence component of the grid connection point voltage;

[0067] These are the active and reactive negative sequence current commands output by the inverter.

[0068] At this point, the three-phase voltage at the grid connection point can be written as:

[0069]

[0070] Among them, V a V b V c The amplitudes of the three-phase voltages a, b, and c at the grid connection point; It represents the phase angle between the positive and negative sequence voltages.

[0071] When an asymmetrical fault occurs, to ensure the system operates within a safe range, maximum and minimum limits should be specified for the phase voltage at the grid connection point. Simultaneously, to achieve the goal of increasing the positive-sequence voltage and decreasing the negative-sequence voltage at the grid connection point, the maximum and minimum phase voltage values ​​should be relatively close. In this case, the maximum and minimum phase voltages can be expressed as:

[0072]

[0073] Among them, V max With V min These represent the maximum and minimum values ​​of the specified grid connection point voltage, respectively; γ max With γ min The maximum and minimum values ​​of the cosine of the phase angle difference between the three-phase positive and negative sequence voltages can be expressed as:

[0074]

[0075] Solving the above equation can improve the positive sequence voltage at the grid connection point and reduce... With the target low grid connection point negative sequence voltage, the reactive current command output by the grid-connected inverter is:

[0076]

[0077]

[0078] in, and These are the positive and negative sequence voltage reference values ​​at the grid connection point, respectively; specifically, they can be expressed as:

[0079]

[0080] in,

[0081] At this point, the reactive current command output by the inverter has been generated.

[0082] As one or more implementation methods, in step S02, the three-phase current output by the inverter can be represented by the positive and negative sequence currents in the DDSRF as follows:

[0083]

[0084] Among them, I a I b I c I represents the amplitude of the three-phase currents (a, b, and c) output by the grid-connected inverter. + with I - The positive and negative sequence current amplitudes output by the grid-connected inverter; The angle between the positive and negative sequence currents output by the grid-connected inverter.

[0085] The three-phase current should satisfy:

[0086] max{I a ,I b ,I c}≤I max ;

[0087] Among them, I max This represents the maximum value of the inverter's output phase current.

[0088] If the requirements are not met, the positive sequence reactive current is output with the maximum positive sequence voltage as the target. The positive sequence reactive current command is the same as in step S02. At the same time, the negative sequence reactive current command is adjusted to meet the inverter output current limit. If the requirements are met, proceed to step S04.

[0089] As one or more implementation methods, in step S03, during an asymmetrical fault, the output power oscillation of the grid-connected inverter will cause DC-side voltage oscillation. The relationship between this voltage oscillation and the active power oscillation can be expressed as follows:

[0090]

[0091] in, This represents the amplitude of the DC-side oscillation term. C represents the amplitude of the oscillation term of the grid-connected inverter's output power. dc This is the DC-side capacitance value; V dc This is the DC side voltage value.

[0092] To stabilize the DC-side voltage and reduce DC-side voltage oscillations, the active power oscillations output by the inverter under asymmetrical fault conditions should be suppressed. In DDSRF, the oscillation amplitude of the inverter's output active power can be expressed as:

[0093]

[0094] If the DC-side voltage oscillation amplitude calculated from the current command in step S02 does not meet the requirements, then first, with the goal of increasing the positive-sequence voltage, a reference value for the positive-sequence reactive current is obtained. Then, the reactive current command is calculated according to the oscillation limit requirements, and the process proceeds to step S04. If the DC-side voltage oscillation amplitude calculated from the current command in step S02 meets the requirements, the process proceeds to step S05.

[0095] Based on current limits and DC-side voltage oscillation limits, the following four scenarios can be summarized: Scenario 1 is where the current command calculated in step S02 ensures that the inverter does not exceed either the current limit or the DC-side voltage limit during the low-voltage ride-through. In this case, the inverter's current command is:

[0096]

[0097] Scenario 2 involves the inverter exceeding the current limit but not the DC-side voltage limit during the low-voltage ride-through period due to the current command calculated in step S02. In this case, the inverter's current command is:

[0098]

[0099] Where, ε max It is the maximum cosine value of the angle between the positive and negative sequence currents.

[0100] Scenario 3 involves a current command calculated in step S02 that causes the inverter to exceed the DC-side voltage limit but not the current limit during the low-voltage ride-through. In this case, the inverter's current command is:

[0101]

[0102] Scenario 4 involves a current command calculated in step S02 that causes the inverter to exceed both the current limit and the DC-side voltage limit during the low-voltage ride-through. In this case, the inverter's current command is:

[0103]

[0104] in, P is the oscillation limit of the DC side voltage; P is the base value of the active power output of the grid-connected inverter; proceed to step S05.

[0105] Based on the current commands in the above four scenarios, the generated current commands are input into the inverter's inner current loop, and the inner current loop generates the inverter's gate signal, thereby realizing low voltage ride-through control under asymmetric fault conditions.

[0106] Figure 3 The simulation results show that the proposed method, under asymmetric fault conditions, neither exceeds the current limit nor the DC-side voltage limit. These results are compared with the traditional positive-sequence voltage control (BPSC) method. Figure 3 Figure (a) shows the phase voltage results, illustrating that the proposed low-voltage ride-through method can control the maximum phase voltage to 0.95 pu and the minimum phase voltage to 0.75 pu. Figure 4 As shown in (c), the positive sequence voltage V + From 0.86 PU to 0.82 PU, negative sequence voltage V - The power consumption was reduced from 0.16 pu to 0.13 pu. Compared with BPSC, the proposed multi-objective low voltage ride-through control sacrifices only 0.46% of the positive sequence voltage support capability, but improves the negative sequence voltage support capability by 25%.

[0107] Figure 4 The simulation results of the proposed method under current over-limit scenarios are shown in the figure. Figure 4 As shown in (b), the overcurrent of the inverter is effectively suppressed, and the inverter capacity is fully utilized. Figure 5 To illustrate the effectiveness of the proposed method in suppressing DC-side voltage oscillations during asymmetric faults, such as... Figure 5 As shown in (c), DC-side voltage oscillations are well suppressed, preventing damage to capacitors in the DC link. Figure 5 (a) and Figure 5 As shown in (b), before and after adjusting the current reference value, the phase current does not exceed the current limit.

[0108] like Figure 6 As shown, to achieve maximum positive and negative sequence voltage support, the phase current exceeds the current limit, while the DC link voltage oscillation exceeds the limit, such as... Figure 6 (a) and Figure 6 As shown in (b) above. By adjusting the current reference value, from Figure 6 (b) It can be seen that the maximum phase current is equal to the current limit. This indicates that the inverter capacity has been fully utilized. For example... Figure 6 As shown in (c), DC-side voltage oscillations can be effectively suppressed after applying the modified current reference value.

[0109] This embodiment considers the maximum current limit of the inverter output and the DC side voltage oscillation limit during low-voltage breakdown. Based on the influence of the positive and negative sequence current of the grid-connected inverter on the grid side during asymmetrical faults, positive and negative sequence current commands are issued to limit the overcurrent of the inverter output, suppress DC side voltage oscillation, and ensure accurate positive and negative sequence voltage support at the grid connection point.

[0110] Example 2

[0111] Embodiment 2 of the present invention introduces a low-voltage ride-through control system for a grid-connected inverter under asymmetric fault conditions.

[0112] like Figure 7 The low-voltage ride-through control system for a grid-connected inverter under asymmetric fault conditions, as shown, includes:

[0113] The acquisition module is configured to acquire the real-time grid connection point voltage and determine whether the power grid is in an asymmetrical fault.

[0114] The first judgment module is configured to judge whether the obtained grid connection point voltage is qualified. If it is not qualified, it enters the low voltage ride-through module of the grid-connected inverter to generate a current command with positive and negative sequence voltage support as the target.

[0115] The second judgment module is configured to judge whether the generated current command has exceeded the current limit and whether the DC side voltage oscillation limit has exceeded the limit. If the current does not exceed the limit and the DC side voltage oscillation limit is met, the positive sequence reactive current command and the negative sequence reactive current command are generated normally. If the current exceeds the limit or the DC side voltage oscillation limit is not met, the positive sequence reactive current command is generated first, and then the negative sequence reactive current command is adjusted.

[0116] The control module is configured to generate gating signals for the grid-connected inverter based on the generated current command or positive-sequence reactive current command and negative-sequence reactive current command in the grid-connected inverter current inner loop, thereby completing the low-voltage ride-through control of the grid-connected inverter under asymmetrical fault conditions.

[0117] The detailed steps are the same as those of the low voltage ride-through control method for grid-connected inverters under asymmetric faults provided in Example 1, and will not be repeated here.

[0118] Example 3

[0119] Embodiment 3 of the present invention provides a computer-readable storage medium.

[0120] A computer-readable storage medium having a program stored thereon, which, when executed by a processor, implements the steps in the low-voltage ride-through control method for grid-connected inverters under asymmetric faults as described in Embodiment 1 of the present invention.

[0121] The detailed steps are the same as those of the low voltage ride-through control method for grid-connected inverters under asymmetric faults provided in Example 1, and will not be repeated here.

[0122] Example 4

[0123] Embodiment 4 of the present invention provides an electronic device.

[0124] An electronic device includes a memory, a processor, and a program stored in the memory and running on the processor. When the processor executes the program, it implements the steps in the low-voltage ride-through control method for a grid-connected inverter under asymmetric faults as described in Embodiment 1 of the present invention.

[0125] The detailed steps are the same as those of the low voltage ride-through control method for grid-connected inverters under asymmetric faults provided in Example 1, and will not be repeated here.

[0126] Example 5

[0127] Embodiment 5 of the present invention provides a computer program product.

[0128] A computer program product includes software code, wherein the program in the software code performs the steps of the low voltage ride-through control method for grid-connected inverters under asymmetric faults as described in Embodiment 1 of the present invention.

[0129] The detailed steps are the same as those of the low voltage ride-through control method for grid-connected inverters under asymmetric faults provided in Example 1, and will not be repeated here.

[0130] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A low-voltage ride-through control method for a grid-connected inverter under asymmetrical fault conditions, characterized in that, include: Obtain real-time grid connection point voltage to determine if the power grid is experiencing an asymmetrical fault. When an asymmetrical fault is detected, [further action is taken]. Determine whether the obtained grid connection point voltage is qualified. If it is not qualified, enter the low voltage ride-through module of the grid-connected inverter and generate a current command with positive and negative sequence voltage support as the target. Determine whether the generated current command exceeds the current limit and whether the DC side voltage oscillation exceeds the limit. If the current does not exceed the limit and the DC side voltage oscillation limit is met, then generate the positive sequence reactive current command and the negative sequence reactive current command normally. If the current exceeds the limit or the DC side voltage oscillation limit is not met, a positive sequence reactive current command will be generated first, and then the negative sequence reactive current command will be adjusted. The generated current command, including positive-sequence reactive current command and negative-sequence reactive current command, is input into the grid-connected inverter's current inner loop. Based on the current inner loop, the grid-connected inverter's gating signal is generated to complete the low-voltage ride-through control of the grid-connected inverter under asymmetrical fault conditions.

2. The low-voltage ride-through control method for a grid-connected inverter under asymmetric faults as described in claim 1, characterized in that, When the generated current command does not exceed the current limit, it is determined whether the current command is within the reasonable range of DC side oscillation. Specifically, if the DC side voltage oscillation amplitude calculated from the current command provided by the grid-connected inverter exceeds the set value, then the current command issued by the grid-connected inverter does not meet the DC side voltage oscillation limit.

3. The low-voltage ride-through control method for a grid-connected inverter under asymmetric faults as described in claim 1, characterized in that, In the process of determining whether the generated current command has exceeded the current limit, the inner current loop of the grid-connected inverter is set to the normal operating range. If the current command transmitted to the inner current loop exceeds the range of the normal operating range, it is determined that the current command does not meet the output current limit, that is, the current limit has exceeded the limit.

4. The low-voltage ride-through control method for a grid-connected inverter under asymmetric faults as described in claim 1, characterized in that, When the obtained grid connection point voltage has a negative sequence component, the power grid is determined to be in an asymmetrical fault state.

5. The low-voltage ride-through control method for a grid-connected inverter under asymmetric faults as described in claim 1, characterized in that, When the obtained grid connection point voltage is unqualified, the grid-connected inverter adopts constant power control.

6. The low-voltage ride-through control method for a grid-connected inverter under asymmetric faults as described in claim 1, characterized in that, When the positive sequence voltage at the grid connection point drops below 0.9 pu, the grid connection point voltage is considered unqualified.

7. A low-voltage ride-through control system for a grid-connected inverter under asymmetric fault conditions, characterized in that, include: The acquisition module is configured to acquire real-time grid connection point voltage, determine whether the power grid is experiencing an asymmetrical fault, and when the power grid is determined to be experiencing an asymmetrical fault... The first judgment module is configured to judge whether the obtained grid connection point voltage is qualified. If it is not qualified, it enters the low voltage ride-through module of the grid-connected inverter to generate a current command with positive and negative sequence voltage support as the target. The second judgment module is configured to judge whether the generated current command has exceeded the current limit and whether the DC side voltage oscillation limit has exceeded the limit. If the current does not exceed the limit and the DC side voltage oscillation limit is met, then the positive sequence reactive current command and the negative sequence reactive current command are generated normally. If the current exceeds the limit or the DC side voltage oscillation limit is not met, a positive sequence reactive current command will be generated first, and then the negative sequence reactive current command will be adjusted. The control module is configured to input the generated current command, including positive-sequence reactive current command and negative-sequence reactive current command, into the grid-connected inverter current inner loop, generate the grid-connected inverter gating signal based on the current inner loop, and complete the low-voltage ride-through control of the grid-connected inverter under asymmetrical fault conditions.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by the processor, the program implements the steps of the low-voltage ride-through control method for grid-connected inverters under asymmetric faults as described in any one of claims 1-6.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the program, it implements the steps of the low-voltage ride-through control method for grid-connected inverters under asymmetric faults as described in any one of claims 1-6.

10. A computer program product, comprising software code, characterized in that, The program in the software code executes the steps of the low-voltage ride-through control method for grid-connected inverters under asymmetric faults as described in any one of claims 1-6.

Images