Converter, power grid power supply system, and converter control method

Abstract

The present application provides a converter, a power grid power supply system, and a control method for the converter, wherein the input end of the converter is coupled to a power supply in the power grid power supply system, the output end of the converter is coupled to an AC power grid, and the converter includes a converter module and a fault ride-through control module. The fault ride-through control module is used to obtain the fault ride-through duration of the most recent historical asymmetric fault ride-through of the AC power grid when an asymmetric fault is detected in the AC power grid, and control the converter module to inject negative-sequence reactive current into the AC power grid based on the obtained fault ride-through duration. By adopting the present application, the converter can inject a stable negative-sequence reactive current into the AC power grid during an asymmetric fault, thereby enhancing the stability and safety of the power supply in a weak power grid and improving the reliability of power grid fault recovery.

Description

Technical Field

[0001] The present application relates to the field of electronic power technology, and in particular to a converter, a power grid power supply system, and a control method for the converter. Background Art

[0002] As the penetration of distributed energy sources such as photovoltaics, wind power, and energy storage devices increases, the interaction between electronic power grid-connected inverters (or converters), as key components of energy exchange, and the power grid is becoming increasingly significant. When supplying power to the AC grid, factors such as short circuits in transmission lines between devices or equipment failures can cause low or high voltage faults in the AC grid. Currently, grid-connection standards in many countries require converters to have fault ride-through capability. This means that when a low or high voltage fault occurs on the grid, the power supply-side equipment must continue to operate without disconnecting from the grid and inject reactive current to help the grid return to normal voltage.

[0003] During research and experimentation, the inventors of this application discovered that, when the grid-connected environment of a converter is a weak power grid, if a low-voltage fault or a high-voltage fault occurs in the AC power grid, the reactive current output by the converter will significantly change the imbalance of the converter port voltage. The changing port voltage will interfere with the converter's fault detection and reactive current control of the power grid, and even affect the converter's operating state, causing the converter to repeatedly enter and exit the fault ride-through state in the weak power grid environment, and the reactive current output by the converter to repeatedly oscillate, ultimately leading to the converter's fault ride-through failure. Therefore, how to solve the problem of repeated oscillation of the reactive current output by the converter in a weak power grid environment and avoid the converter's fault ride-through failure is one of the technical problems that urgently need to be solved. Summary of the Invention

[0004] The present application provides a converter, a grid power supply system, and a control method for the converter, which can inject stable negative-sequence reactive current into the AC grid during an asymmetric fault, thereby enhancing the stability and safety of the grid power supply in a weak grid condition and increasing the reliability of grid fault recovery.

[0005] In a first aspect, the present application provides a converter suitable for a power grid power supply system. The converter's input end is coupled to a power supply in the power grid power supply system, and the converter's output end is coupled to an AC power grid. The converter includes a converter module and a fault ride-through control module. The fault ride-through control module is configured to, when an asymmetric fault parameter of the AC power grid is greater than a fault determination threshold, control the converter module to inject negative-sequence reactive current into the AC power grid based on the fault ride-through duration of the most recent historical asymmetric fault ride-through in the AC power grid. The asymmetric fault parameter includes a first negative-sequence voltage, including the difference between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase line voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude, or one of the differences between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase phase voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude.

[0006] In the present application, the fault ride-through control module in the converter obtains the duration of the last fault ride-through when an asymmetric fault occurs in the AC power grid, that is, the fault ride-through duration of the most recent historical asymmetric fault ride-through. The fault ride-through control module can control the converter module to inject negative-sequence reactive current into the AC power grid based on the fault ride-through duration, and adjust the current value of the negative-sequence reactive current injected into the AC power grid based on different fault ride-through durations. This can avoid the problem that in a weak power grid environment, the negative-sequence reactive current with an excessively high current value changes the imbalance of the converter port voltage (such as reducing the negative-sequence voltage of the converter port) to interfere with the detection of asymmetric faults. During an asymmetric fault, the converter can inject a stable negative-sequence reactive current into the AC power grid, thereby enhancing the stability and safety of the power supply to the power grid in a weak power grid, and the reliability of power grid fault recovery is strong.

[0007] In conjunction with the first aspect, in a first possible implementation, the fault ride-through control module is further configured to, when the fault ride-through duration is null or the fault ride-through duration is greater than or equal to a preset time threshold, determine a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the occurrence of the current asymmetric fault in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and control the converter module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid. The fault ride-through control module obtains the fault ride-through duration of the most recent asymmetric fault ride-through and injects a negative-sequence reactive current of a corresponding magnitude into the AC power grid based on the fault ride-through duration, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault, thereby enhancing the stability and security of power supply in weak power grid conditions.

[0008] In conjunction with the first aspect, in a second possible implementation, the fault ride-through control module is further configured to, when the fault ride-through duration is null or the fault ride-through duration is greater than or equal to a preset time threshold, determine a second negative-sequence reactive current value based on the first negative-sequence reactive current before the occurrence of the current asymmetric fault in the AC power grid, the fault determination threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and control the converter module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid. The fault ride-through control module obtains the fault ride-through duration of the most recent asymmetric fault ride-through and injects a negative-sequence reactive current of a corresponding magnitude into the AC power grid based on the fault ride-through duration, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault, thereby enhancing the stability and security of power supply in weak power grid conditions.

[0009] In conjunction with the first aspect, in a third possible implementation, the fault ride-through control module is further configured to, when the fault ride-through duration is less than a preset time threshold, determine a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the current asymmetric fault occurred in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage; determine a third negative-sequence reactive current value based on the second negative-sequence reactive current value; and control the converter module to inject a third negative-sequence reactive current into the AC power grid equal to the third negative-sequence reactive current value, wherein the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current. The fault ride-through control module reduces the amount of negative-sequence reactive current injected into the AC power grid when the fault ride-through duration is less than the preset time threshold, thereby preventing the negative-sequence reactive current output by the converter from reducing the negative-sequence voltage at the converter port in a weak power grid environment and interfering with asymmetric fault detection, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault.

[0010] In conjunction with the first aspect, in a fourth possible implementation, the fault ride-through control module is further configured to, when the fault ride-through duration is less than a preset time threshold, determine a second negative-sequence reactive current value based on the first negative-sequence reactive current before the current asymmetric fault occurred in the AC power grid, the fault determination threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage; determine a third negative-sequence reactive current value based on the second negative-sequence reactive current value; and control the converter module to inject a third negative-sequence reactive current into the AC power grid equal to the third negative-sequence reactive current value, wherein the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current. The fault ride-through control module reduces the amount of negative-sequence reactive current injected into the AC power grid when the fault ride-through duration is less than the preset time threshold, thereby preventing the negative-sequence reactive current output by the converter from reducing the negative-sequence voltage at the converter port in a weak power grid environment and interfering with asymmetric fault detection, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault.

[0011] In combination with the first possible implementation manner of the first aspect or the third possible implementation manner of the first aspect, in a fifth possible implementation manner, the second negative-sequence reactive current satisfies:

[0012]

[0013] Wherein, U2 is the second negative-sequence voltage, Iqn1 is the first negative-sequence reactive current, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the first negative-sequence voltage, K is a positive number, and Iqn2 is the second negative-sequence reactive current. The fault ride-through control module can obtain a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid based on the above expression, and control the conversion module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid.

[0014] In combination with the second possible implementation manner of the first aspect or the fourth possible implementation manner of the first aspect, in a sixth possible implementation manner, the second negative-sequence reactive current satisfies:

[0015]

[0016] Wherein, Iqn1 is the first negative-sequence reactive current, Unv is the fault determination threshold, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the first negative-sequence voltage, K is a positive number, and Iqn2 is the second negative-sequence reactive current. The fault ride-through control module can obtain a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid based on the above expression, and control the conversion module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid.

[0017] In a second aspect, the present application provides a power grid power supply system, which includes a power supply, a transformer, and a converter provided by the first aspect and any possible implementation method of the first aspect. The power supply is used to provide energy input or power input to the converter, the converter is used to convert the energy input or power input provided by the power supply to obtain a first alternating current and output the transformer, the transformer is used to perform power conversion based on the first alternating current and output a second alternating current to the AC grid, and the converter is also used to obtain the fault ride-through duration of the most recent historical asymmetric fault that occurred in the AC grid when an asymmetric fault is detected in the AC grid, and inject negative-sequence reactive current into the AC grid based on the fault ride-through duration.

[0018] In combination with the second aspect, in a first possible implementation, the power supply includes at least one of a solar panel, a wind turbine, or an energy storage battery.

[0019] In the present application, the converter provided based on the above-mentioned first aspect can inject stable negative-sequence reactive current into the AC power grid in the power grid power supply system during an asymmetric fault, thereby enhancing the stability and safety of the power grid power supply in a weak power grid condition and having strong reliability in power grid fault recovery.

[0020] In a third aspect, the present application provides a converter control method for a power grid power supply system, which is applicable to the converter in the power grid power supply system. The power grid power supply system includes a power supply, a transformer and the converter. The input end of the converter is coupled to the power supply, and the output end of the converter is coupled to the AC power grid through the transformer. The converter includes a converter module and a fault ride-through control module. In this method, when the asymmetric fault parameter of the AC power grid is greater than the fault judgment threshold, the fault ride-through control module controls the converter module to inject negative-sequence reactive current into the AC power grid based on the fault ride-through duration of the most recent historical asymmetric fault ride-through in the AC power grid. The asymmetric fault parameters include the first negative-sequence voltage, and the differences between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase line voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude, as well as one of the differences between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase phase voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude.

[0021] In the present application, the fault ride-through control module in the converter obtains the duration of the last fault ride-through when an asymmetric fault occurs in the AC power grid, that is, the fault ride-through duration of the most recent historical asymmetric fault ride-through. The fault ride-through control module can be used to control the converter module to inject negative-sequence reactive current into the AC power grid based on the fault ride-through duration, and the current value of the negative-sequence reactive current injected into the AC power grid is adjusted based on different fault ride-through durations. This can avoid the problem that in a weak power grid environment, the negative-sequence reactive current with an excessively high current value changes the imbalance of the converter port voltage (such as reducing the negative-sequence voltage at the converter port) to interfere with the detection of asymmetric faults. During an asymmetric fault, the converter can inject a stable negative-sequence reactive current into the AC power grid, thereby enhancing the stability and safety of the power supply to the power grid in a weak power grid, and increasing the reliability of power grid fault recovery.

[0022] In conjunction with the third aspect, in a first possible implementation, when the fault ride-through duration is null or the fault ride-through duration is greater than or equal to a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and controls the converter module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid. The fault ride-through control module obtains the fault ride-through duration of the most recent asymmetric fault ride-through, and based on the fault ride-through duration, injects a negative-sequence reactive current of a corresponding magnitude into the AC power grid, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault, thereby enhancing the stability and security of the power supply in weak power grid conditions.

[0023] In conjunction with the third aspect, in a second possible implementation, when the fault ride-through duration is null or the fault ride-through duration is greater than or equal to a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the fault determination threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and controls the converter module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid. The fault ride-through control module obtains the fault ride-through duration of the most recent asymmetric fault ride-through, and based on the fault ride-through duration, injects a negative-sequence reactive current of a corresponding magnitude into the AC power grid, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault, thereby enhancing the stability and security of the power supply in weak power grid conditions.

[0024] In conjunction with the third aspect, in a third possible implementation, when the fault ride-through duration is less than a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage; obtains a third negative-sequence reactive current value based on the second negative-sequence reactive current value; and controls the converter module to inject a third negative-sequence reactive current into the AC power grid equal to the third negative-sequence reactive current value, wherein the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current. The fault ride-through control module reduces the amount of negative-sequence reactive current injected into the AC power grid when the fault ride-through duration is less than the preset time threshold, thereby preventing the negative-sequence reactive current output by the converter from reducing the negative-sequence voltage at the converter port in a weak power grid environment and interfering with asymmetric fault detection, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault.

[0025] In conjunction with the third aspect, in a fourth possible implementation, when the fault ride-through duration is less than a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the fault determination threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage; obtains a third negative-sequence reactive current value based on the second negative-sequence reactive current value; and controls the converter module to inject a third negative-sequence reactive current into the AC power grid equal to the third negative-sequence reactive current value, wherein the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current. The fault ride-through control module reduces the amount of negative-sequence reactive current injected into the AC power grid when the fault ride-through duration is less than the preset time threshold, thereby preventing the negative-sequence reactive current output by the converter from reducing the negative-sequence voltage at the converter port in a weak power grid environment and interfering with asymmetric fault detection, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 This is a schematic diagram of an application scenario of the power grid power supply system provided by this application;

[0028] Figure 2a This is a schematic diagram of repeated entry and exit of the asymmetric fault ride-through state provided by this application;

[0029] Figure 2b This is a schematic diagram of negative-sequence reactive current instruction and feedback for fault ride-through failure provided by this application;

[0030] Figure 3 This is a schematic diagram of the voltage and current at the converter port when a fault ride-through failure occurs, as provided by this application;

[0031] Figure 4 It is a structural diagram of the power grid power supply system provided by this application;

[0032] Figure 5a This is a schematic diagram of the stability of the asymmetric fault ride-through state provided by this application;

[0033] Figure 5b This is a schematic diagram of negative-sequence reactive current instruction and feedback for successful asymmetric fault ride-through provided by the present application;

[0034] Figure 6 This is a schematic diagram of the voltage and current at the converter port after a successful fault ride-through provided by this application;

[0035] Figure 7 It is a flow chart of the converter control method of the power grid power supply system provided by this application. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0037] See also Figure 1 , Figure 1 This is a schematic diagram of an application scenario of the grid power supply system provided by this application. The grid power supply system provided by this application may include a power supply, a transformer and a converter, wherein the power supply may be composed of a photovoltaic array, the output end of the photovoltaic array may be connected to the first end of the converter, and the second end of the converter may be connected to the AC grid through the transformer. Figure 1 In the grid power supply system shown, a photovoltaic array can be composed of one or more photovoltaic strings connected in parallel. A photovoltaic string can be formed by connecting one or more photovoltaic modules in series. The converter can invert the DC power output by the photovoltaic array and output the resulting AC power to the transformer. The transformer then converts the AC power to power devices such as batteries, communication base stations, and household appliances in the AC grid.

[0038] In some possible implementations, please refer again to Figure 1 The power supply may also include an energy storage battery. The output end of the energy storage battery may be connected to the first end of the converter, and the second end of the converter may be connected to the AC power grid via a transformer. The converter may invert the DC power provided by the energy storage battery and output the resulting AC power to the transformer. The transformer then converts the AC power to power batteries, communication base stations, household appliances, and other electrical devices in the AC power grid.

[0039] In some possible implementations, please refer again to Figure 1 The power supply may also include a wind turbine generator. The output end of the wind turbine generator may be connected to a first end of the converter, and the second end of the converter may be connected to an AC power grid via a transformer. The converter may convert the voltage of the AC power provided by the wind turbine generator (this may be by rectifying the AC power provided by the wind turbine generator to obtain DC power, and then inverting the rectified DC power to obtain voltage-converted AC power), and output the converted AC power to the transformer. The transformer then further converts the AC power to power electrical devices such as batteries, communication base stations, or household appliances in the AC power grid.

[0040] exist Figure 1In the application scenario shown, during the power grid power supply system's operation of an AC grid, factors such as a short circuit in a transmission line between devices or equipment failure can cause low or high voltage faults in the AC grid. Typically, an AC grid consists of three-phase AC power (also referred to as a three-phase grid), consisting of phases A, B, and C. Three-phase AC power (or three-phase grid voltage) can be divided into positive-sequence, negative-sequence, and zero-sequence components based on the order of the three phases. The positive-sequence component is: phase A leads phase B by 120 degrees, phase B leads phase C by 120 degrees, and phase C leads phase A by 120 degrees. The negative-sequence component is: phase A lags phase B by 120 degrees, phase B lags phase C by 120 degrees, and phase C lags phase A by 120 degrees. The zero-sequence component is: phases A, B, and C are in phase. Furthermore, in AC power, there is a phase difference between current and voltage. Using vector analysis, current can be decomposed into two components: active current, which is in phase with the voltage, and reactive current, which leads or lags the voltage by 90 degrees. In other words, current can be decomposed into active and reactive components. Combining the positive sequence, negative sequence and zero sequence components in the above three-phase AC power, the positive sequence active current, negative sequence active current, positive sequence reactive current or negative sequence reactive current can be divided from the AC power. For example, the negative sequence reactive current can be the negative sequence component in the AC power, and the reactive current is obtained based on the decomposition of the negative sequence component. According to whether the voltage of the three-phase power grid is balanced when the fault occurs, the fault is divided into symmetrical faults and asymmetrical faults. Asymmetrical faults can include three types: single-phase grounding fault, two-phase short circuit grounding fault and two-phase interphase short circuit fault. In order to ensure that when the AC power grid fails (that is, the voltage or frequency at the grid connection point exceeds the normal operating range allowed by the standard), the power supply (such as photovoltaic array, wind turbine) does not disconnect from the grid and continues to operate, and can smoothly transition to the normal operating state, the converter is required to have fault ride-through capability. Taking an asymmetric fault as an example, when the converter detects an asymmetric fault (for example, by detecting the negative-sequence voltage value at the converter port, that is, the voltage value corresponding to the negative-sequence component of the converter port voltage, and determining whether an asymmetric fault has occurred based on the negative-sequence voltage value), the converter can inject a negative-sequence reactive current into the AC grid to restore the unbalanced voltage in the asymmetric fault. The above-mentioned negative-sequence reactive current is the negative-sequence component in the AC power, and the negative-sequence component contains a reactive component. However, when the converter's grid-connected environment is a weak grid, and an asymmetric fault occurs in the AC grid, the negative-sequence reactive current output by the converter will significantly change the imbalance of the converter port voltage (for example, change the negative-sequence voltage). The changing port voltage will interfere with the converter's asymmetric fault detection and negative-sequence reactive current control, and even affect the converter's operating state, causing the converter to repeatedly enter and exit the asymmetric fault ride-through state in a weak grid environment, and the converter output current to repeatedly oscillate. The converter fails to output a stable negative-sequence reactive current within the time required by the standard, which ultimately leads to the failure of the converter to ride through the fault. See Figure 2a , Figure 2aThis is a schematic diagram of the asymmetric fault ride-through state repeatedly entering and exiting. Figure 2a As shown, when the asymmetric fault ride-through flag is 1, it indicates that the converter triggers the asymmetric fault ride-through state (the converter may inject negative sequence reactive current into the AC grid), and when the asymmetric fault ride-through flag is 0, it indicates that the converter exits the asymmetric fault ride-through state. Figure 2a During an asymmetric fault in the , the asymmetric fault ride-through flag switches multiple times (switching between 0 and 1). In other words, in a weak grid environment, the negative sequence reactive current output by the converter changes the unbalance of the converter port voltage, thereby interfering with the converter's asymmetric fault detection and causing the converter to repeatedly enter and exit the asymmetric fault ride-through state in a short period of time. Please also refer to Figure 2b , Figure 2b This is a schematic diagram of negative sequence reactive current instruction and feedback for fault ride-through failure provided by this application, such as Figure 2b As shown in Figure 2, during an asymmetric fault, the negative-sequence reactive current injected by the converter into the AC grid is unstable due to repeated entry and exit of the asymmetric fault ride-through state. That is, the converter's associated negative-sequence reactive current instruction (which can be the ratio of the current output negative-sequence reactive current to the rated negative-sequence reactive current) and the corresponding feedback value are unstable (returning to zero multiple times). Please also refer to Figure 3 , Figure 3 This is a schematic diagram of the voltage and current at the converter port when the fault ride-through fails. Figure 3 As shown, Figure 3 During the asymmetric fault period (between 5s and 5.45s), the converter port voltage (which can be the three-phase line voltage) and the converter port current oscillate repeatedly during the asymmetric fault ride-through state caused by interference with the converter's asymmetric fault detection. This indicates that in a weak grid environment, the negative-sequence reactive current output by the converter will simultaneously interfere with the converter's asymmetric fault ride-through.

[0041] In the power grid power supply system provided by the present application, the converter includes a converter module and a fault ride-through control module, wherein the fault ride-through control module is used to detect an asymmetric fault (which may be a single-phase ground fault, a two-phase short-circuit ground fault, or a two-phase short-circuit fault) occurring in the AC power grid, and obtain the duration of the last fault ride-through when an asymmetric fault is detected in the AC power grid, that is, the fault ride-through duration of the most recent historical asymmetric fault ride-through. The fault ride-through control module can control the converter module to inject negative-sequence reactive current into the AC power grid based on the fault ride-through duration, and adjust the current value of the negative-sequence reactive current injected into the AC power grid based on different fault ride-through durations, thereby avoiding the problem that the negative-sequence reactive current with excessively high current value changes the voltage imbalance of the converter port (such as reducing the negative-sequence voltage of the converter port) in a weak power grid environment to interfere with the detection of asymmetric faults. During the asymmetric fault, the converter can inject a stable negative-sequence reactive current into the AC power grid, thereby enhancing the stability and safety of the power supply in the weak power grid, and the reliability and success rate of the power grid fault recovery are high.

[0042] See also Figure 4 , Figure 4 This is a schematic diagram of the structure of the power grid power supply system provided by this application. Figure 4 The grid power supply system shown includes a power supply, a converter and a transformer, wherein the power supply can be a solar panel, a wind turbine or an energy storage battery, etc. The input end of the converter is coupled to the power supply in the grid power supply system, and the output end of the converter is coupled to the AC grid through the transformer. Figure 4 In the grid power supply system shown, the power supply is used to provide energy input or power input for the converter. The converter performs current conversion based on the energy input or power input provided by the power supply, and outputs the AC power obtained after the current conversion to the transformer. The transformer performs power conversion based on the input AC power and outputs the AC power after power conversion to the AC grid to supply power to the AC grid.

[0043] In some possible implementations, Figure 4In the illustrated power grid power supply system, the converter includes a converter module and a fault ride-through control module. The converter can detect an asymmetric fault (which may be a single-phase ground fault, a two-phase short-circuit ground fault, or a two-phase short-circuit fault) in the AC grid through the ride-through control module. When an asymmetric fault is detected in the AC grid, the converter obtains the fault ride-through duration of the most recent historical asymmetric fault ride-through in the AC grid (for ease of description, referred to as the fault ride-through duration). The fault ride-through control module can control the converter module to inject negative-sequence reactive current into the AC grid based on the fault ride-through duration. This can prevent the negative-sequence reactive current with excessive current values ​​from changing the voltage imbalance of the converter port (e.g., reducing the negative-sequence voltage at the converter port) in a weak grid environment, thereby interfering with the detection of asymmetric faults. This ensures that the converter can inject stable negative-sequence reactive current into the AC grid during an asymmetric fault, thereby enhancing the stability and security of the grid power supply in weak grid conditions and improving the reliability of grid fault recovery.

[0044] The following will be combined Figures 5a to 6The converter provided in the embodiment of the present application is described by way of example. In some feasible implementations, when the converter detects an asymmetric fault occurring in an AC power grid through a fault ride-through control module, the fault ride-through control module may detect a negative-sequence voltage (i.e., a first negative-sequence voltage) at the output of the converter module. The first negative-sequence voltage may be a negative-sequence component of the voltage at the output of the current converter module, and the first negative-sequence voltage may be used as an asymmetric fault parameter. If the first negative-sequence voltage exceeds a set threshold, the ride-through control module determines that an asymmetric fault has occurred in the current AC power grid. In other words, the fault ride-through control module may detect the first negative-sequence voltage as an asymmetric fault parameter, and determine that an asymmetric fault has occurred in the current AC power grid when the asymmetric fault parameter is greater than a set threshold (which may be referred to as a fault determination threshold) corresponding to the first negative-sequence voltage. Optionally, the fault ride-through control module can also detect the three-phase line voltage at the output end of the converter module, and use the difference between the maximum effective value and the minimum effective value of the three-phase line voltage (which can be the voltage between any two phases, such as the voltage between phase A and phase B, the voltage between phase A and phase C, and the voltage between phase B and phase C) as an asymmetric fault parameter. If the difference between the maximum effective value and the minimum effective value of the above three-phase line voltage exceeds the corresponding set threshold (which can be called the fault judgment threshold), it is determined that an asymmetric fault has occurred in the current AC power grid. In addition, the difference between the maximum peak-to-peak value and the minimum peak-to-peak value of the above three-phase line voltage, or the difference between the maximum amplitude and the minimum amplitude of the three-phase line voltage can also be used as an asymmetric fault parameter. The specific difference can be determined according to the actual application scenario and is not limited here. Optionally, the fault ride-through control module can also detect the three-phase voltage at the output end of the converter module (which can be the A phase voltage, the B phase voltage, and the C phase voltage), and use the difference between the maximum effective value and the minimum effective value of the three-phase voltage as an asymmetric fault parameter. If the difference between the maximum effective value and the minimum effective value of the three-phase voltage exceeds the corresponding set threshold (which can be called the fault judgment threshold), it is determined that an asymmetric fault has occurred in the current AC power grid. In addition, the difference between the maximum peak-to-peak value and the minimum peak-to-peak value of the three-phase voltage, or the difference between the maximum amplitude and the minimum amplitude of the three-phase voltage can be used as an asymmetric fault parameter. The specific parameters can be determined according to the actual application scenario and are not limited here. The fault ride-through control module can obtain the asymmetric fault parameter by detecting the first negative sequence voltage, the three-phase line voltage, or the three-phase voltage at the output end of the converter module. The specific parameters can be determined according to the actual application scenario and are not limited here. The fault ride-through control module performs asymmetric fault detection on the AC power grid based on the fault judgment threshold corresponding to the asymmetric fault parameter. When an asymmetric fault occurs in the AC power grid, the fault can be detected immediately and an asymmetric fault ride-through can be performed to ensure the stability and safety of the power supply process of the power grid.

[0045] In some feasible implementations, the fault ride-through control module can obtain the duration of the previous fault ride-through when an asymmetric fault is detected in the AC power grid, that is, obtain the fault ride-through duration of the most recent historical asymmetric fault ride-through from the current time (for the convenience of description, referred to as the fault ride-through duration). Here, when the fault ride-through control module detects that an asymmetric fault has occurred in the AC power grid for the first time, that is, no asymmetric fault has occurred in the AC power grid before the current time, the fault ride-through duration obtained by the fault ride-through control module is null. The fault ride-through control module determines a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid based on the negative-sequence voltage (which may be a second negative-sequence voltage, that is, the negative-sequence component of the voltage at the output end of the converter module before the current asymmetric fault) and the negative-sequence reactive current (which may be a first negative-sequence reactive current, that is, the reactive current corresponding to the negative-sequence component of the current at the output end of the converter module before the current asymmetric fault), the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and controls the converter module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid. Optionally, when the fault ride-through duration obtained by the fault ride-through control module is not null and the fault ride-through duration is greater than or equal to a preset time threshold, a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid is determined based on the second negative-sequence voltage and the first negative-sequence reactive current, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and the converter module is controlled to inject a second negative-sequence reactive current having a current magnitude equal to the second negative-sequence reactive current value into the AC power grid. Here, the fault ride-through control module obtains the fault ride-through duration of the most recent asymmetric fault ride-through and injects a negative-sequence reactive current of a corresponding current magnitude into the AC power grid based on the fault ride-through duration, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault, thereby enhancing the stability and security of the power supply to the power grid in weak power grid conditions.

[0046] In some feasible implementations, the second negative-sequence reactive current determined by the fault ride-through control module can be expressed as:

[0047]

[0048] Where, U2 is the second negative - sequence voltage mentioned above, Iqn1 is the first negative - sequence reactive current mentioned above, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the first negative - sequence voltage, K is an adjustment coefficient (which can take a positive number, for example, 0 < K < 10), and Iqn2 is the second negative - sequence reactive current mentioned above. The above - mentioned fault - ride - through control module can obtain the value of the second negative - sequence reactive current corresponding to the second negative - sequence reactive current injected into the above - mentioned AC power grid based on the above - mentioned expression, and control the converter module to inject into the AC power grid a second negative - sequence reactive current whose magnitude is equal to the value of the second negative - sequence reactive current.

[0049] In some feasible embodiments, when the fault - ride - through control module detects an asymmetrical fault in the AC power grid, it can obtain the fault - ride - through duration of the most recent historical asymmetrical fault - ride - through closest to the current time. And when the fault - ride - through duration is empty, or the fault - ride - through duration is greater than or equal to a preset time threshold, it can obtain the value of the second negative - sequence reactive current corresponding to the second negative - sequence reactive current injected into the above - mentioned AC power grid based on the first negative - sequence reactive current at the output end of the converter module detected before the current asymmetrical fault, the above - mentioned fault - determination threshold, the rated voltage of the converter, the rated current of the converter, and the above - mentioned first negative - sequence voltage, and control the converter module to inject into the AC power grid a second negative - sequence reactive current whose magnitude is equal to the value of the second negative - sequence reactive current. It can be understood that when the first negative - sequence voltage is used as the asymmetrical - fault parameter, the above - mentioned fault - determination threshold is the fault - determination threshold corresponding to the first negative - sequence voltage. Similarly, when the difference between the maximum effective value and the minimum effective value of the three - phase line voltage (or three - phase phase voltage) (or, the difference between the maximum peak - to - peak value and the minimum peak - to - peak value, the difference between the maximum amplitude and the minimum amplitude) is used as the asymmetrical - fault parameter, the above - mentioned fault - determination threshold is the fault - determination threshold corresponding to the above - mentioned difference. The fault - ride - through control module ensures that the converter can inject a stable negative - sequence reactive current into the AC power grid during an asymmetrical fault by obtaining the fault - ride - through duration of the most recent asymmetrical fault - ride - through and injecting a negative - sequence reactive current with a corresponding current magnitude into the above - mentioned AC power grid based on this fault - ride - through duration, enhancing the stability and security of the power supply of the power grid in the case of a weak power grid.

[0050] In some feasible embodiments, the second negative - sequence reactive current determined by the above - mentioned fault - ride - through control module can be expressed as:

[0051]

[0052] Among them, Iqn1 is the above-mentioned first negative-sequence reactive current, Unv is the above-mentioned fault determination threshold, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the above-mentioned first negative-sequence voltage, K is an adjustment coefficient (a positive number can be taken, for example, 0 < K < 10), and Iqn2 is the above-mentioned second negative-sequence reactive current. The above-mentioned fault ride-through control module can obtain the value of the second negative-sequence reactive current corresponding to the second negative-sequence reactive current injected into the above-mentioned AC power grid based on the above expression, and control the converter module to inject a second negative-sequence reactive current with a current magnitude equal to the value of the second negative-sequence reactive current into the AC power grid.

[0053] In some feasible implementation manners, when the fault ride-through control module detects an asymmetric fault in the AC power grid, it can obtain the fault ride-through duration of the nearest historical asymmetric fault ride-through to the current time, and when the fault ride-through duration is less than a preset time threshold, based on the second negative-sequence voltage and the first negative-sequence reactive current at the output end of the converter module detected before the current asymmetric fault, the rated voltage of the converter, the rated current of the converter, and the above-mentioned first negative-sequence voltage, determine the value of the second negative-sequence reactive current corresponding to the second negative-sequence reactive current, obtain the value of the third negative-sequence reactive current based on the value of the second negative-sequence reactive current, and control the converter module to inject a third negative-sequence reactive current with a current magnitude equal to the value of the third negative-sequence reactive current into the AC power grid. Here, the absolute value of the current of the above-mentioned third negative-sequence reactive current is less than the absolute value of the current of the second negative-sequence reactive current, that is, the third negative-sequence reactive current can be expressed as

[0054] Iqn3 = Iqn2 - ΔIqn

[0055] Among them, Iqn2 is the above-mentioned second negative-sequence reactive current, Iqn3 is the third negative-sequence reactive current, and 0 < |ΔIqn| < |Iqn2|. When the fault ride-through duration is less than the preset time threshold, the fault ride-through control module reduces the magnitude of the negative-sequence reactive current injected into the AC power grid, avoiding that the negative-sequence reactive current output by the converter in a weak power grid environment reduces the negative-sequence voltage at the converter port to interfere with the asymmetric fault detection, and ensuring that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault.

[0056] In some feasible embodiments, the fault ride-through control module can obtain the fault ride-through duration of the most recent historical asymmetric fault ride-through when an asymmetric fault is detected in the AC power grid, and when the fault ride-through duration is less than a preset time threshold, determine the second negative-sequence reactive current value corresponding to the second negative-sequence reactive current based on the first negative-sequence reactive current at the output end of the converter module detected before the current asymmetric fault, the above-mentioned fault judgment threshold, the rated voltage of the converter, the rated current of the converter and the above-mentioned first negative-sequence voltage, obtain a third negative-sequence reactive current value based on the second negative-sequence reactive current value, and control the converter module to inject a third negative-sequence reactive current with a current equal to the third negative-sequence reactive current value into the AC power grid, where the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current. The fault ride-through control module reduces the magnitude of the negative-sequence reactive current injected into the AC grid when the fault ride-through duration is less than a preset time threshold, thereby preventing the negative-sequence reactive current output by the converter from reducing the negative-sequence voltage at the converter port in a weak grid environment and interfering with asymmetric fault detection, thereby ensuring that the converter can inject a stable negative-sequence reactive current into the AC grid during an asymmetric fault.

[0057] See also Figure 5a , Figure 5a This is a schematic diagram of the asymmetric fault ride-through state stability provided by this application. Figure 5a As shown, when the asymmetric fault ride-through flag is 1, it indicates that the converter triggers the asymmetric fault ride-through state (the converter may inject negative sequence reactive current into the AC grid), and when the asymmetric fault ride-through flag is 0, it indicates that the converter exits the asymmetric fault ride-through state. Figure 5a The system includes two asymmetric fault ride-throughs. During the second asymmetric fault ride-through, the fault ride-through control module obtains the fault ride-through duration corresponding to the first asymmetric fault ride-through (which can be 5.02s to 5.06s, with the fault ride-through duration represented by T0). If T0 is less than the preset time threshold, a third negative-sequence reactive current value with a smaller current value is obtained based on the second negative-sequence reactive current value, and the converter module is controlled to inject the third negative-sequence reactive current into the AC power grid. During the second asymmetric fault ride-through (which can be between 5.08s and 5.44s), the asymmetric fault ride-through state is stable (the asymmetric fault ride-through flag remains 1). Please also refer to Figure 5b , Figure 5b This is a schematic diagram of negative sequence reactive current instruction and feedback for successful asymmetric fault ride-through provided by this application. Figure 5b As shown, Figure 5bIt also includes two asymmetric fault ride-throughs. The fault ride-through duration T0 corresponding to the first asymmetric fault ride-through is less than the preset time threshold. Then, the fault ride-through control module injects a third negative-sequence reactive current with a smaller current value into the AC grid during the second asymmetric fault ride-through (which can be between 5.08s and 5.44s), so that the asymmetric fault ride-through state is stable (the negative-sequence reactive current instruction and the corresponding feedback value remain unchanged). The fault ride-through duration T0 corresponding to the first asymmetric fault ride-through is less than the preset time threshold, indicating that the negative-sequence reactive current injected into the AC grid during the first asymmetric fault ride-through is too large, causing the negative-sequence voltage at the converter port to decrease, thereby interfering with the asymmetric fault detection of the fault ride-through control module and exiting the asymmetric fault ride-through state too quickly. The fault ride-through control module adjusts the negative-sequence reactive current injected into the AC grid based on the fault ride-through duration T0 (from the second negative-sequence reactive current to the smaller third negative-sequence reactive current) to ensure that the converter can inject a stable negative-sequence reactive current into the AC grid during the asymmetric fault. Please also refer to Figure 6 , Figure 6 This is a schematic diagram of the converter port voltage and current after a fault ride-through is successful provided by this application. Figure 6 As shown, Figure 6 During the asymmetric fault period (between 5s and 5.45s), the fault ride-through control module detects that the negative-sequence reactive current injected into the AC grid during the first asymmetric fault ride-through is too large (the fault ride-through duration is less than a preset time threshold), and adjusts the negative-sequence reactive current injected into the AC grid so that a stable negative-sequence reactive current can be injected into the AC grid. The converter port voltage (which can be a three-phase line voltage) and the converter port current remain stable after oscillation, and the asymmetric fault ride-through reliability is strong.

[0058] In the present application, the converter in the power grid power supply system includes a converter module and a fault ride-through control module. The fault ride-through control module can detect an asymmetric fault occurring in the AC power grid (the first negative-sequence voltage, three-phase line voltage, or three-phase phase voltage at the output end of the converter module can be detected to detect whether an asymmetric fault occurs). When an asymmetric fault occurs in the AC power grid, the fault ride-through control module can obtain the duration of the last fault ride-through, that is, obtain the fault ride-through duration of the most recent historical asymmetric fault ride-through from the current time, and when the fault ride-through duration is empty or the fault ride-through duration is greater than or equal to a preset time threshold, determine a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the above-mentioned AC power grid, and control the converter module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid. When the fault ride-through duration is less than a preset time threshold, a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current is determined, a third negative-sequence reactive current value is obtained based on the second negative-sequence reactive current value, and the converter module is controlled to inject a third negative-sequence reactive current having a current magnitude equal to the third negative-sequence reactive current value into the AC power grid. Here, the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current. The fault ride-through control module adjusts the current magnitude of the negative-sequence reactive current injected into the AC power grid based on different fault ride-through durations, thereby avoiding the problem of excessively high current values ​​of negative-sequence reactive currents reducing the negative-sequence voltage at the converter port to interfere with the detection of asymmetric faults in a weak power grid environment. During an asymmetric fault, the converter can inject a stable negative-sequence reactive current into the AC power grid, thereby enhancing the stability and security of the power supply to the power grid in a weak power grid and improving the reliability of power grid fault recovery.

[0059] See also Figure 7 , Figure 7 The flow chart of the converter control method of the power grid power supply system provided by this application is applicable to the above-mentioned Figures 1 to 6 The converter in any power grid power supply system shown in the figure includes a converter module and a fault ride-through control module. The input end of the converter is coupled to the power supply in the power grid power supply system, and the output end of the converter is coupled to the AC grid. Figure 7 As shown, the converter control method of the power grid power supply system provided by the present application includes the following steps:

[0060] S701 , when an asymmetric fault is detected in the AC power grid, obtaining a fault ride-through duration of a most recent historical asymmetric fault ride-through in the AC power grid.

[0061] In some feasible embodiments, the converter detects the negative sequence voltage (i.e., the first negative sequence voltage) at the output end of the converter module through a fault ride-through control module, and uses the first negative sequence voltage as an asymmetric fault parameter. If the first negative sequence voltage exceeds a fault determination threshold, the ride-through control module determines that an asymmetric fault has occurred in the current AC power grid. Optionally, the fault ride-through control module can also detect the three-phase line voltage at the output end of the converter module, and use the difference between the maximum effective value and the minimum effective value of the three-phase line voltage (which can be the voltage between any two phases) as the asymmetric fault parameter. If the difference between the maximum effective value and the minimum effective value of the three-phase line voltage exceeds the corresponding fault determination threshold, it is determined that an asymmetric fault has occurred in the current AC power grid. In addition, the difference between the maximum peak-to-peak value and the minimum peak-to-peak value of the three-phase line voltage, or the difference between the maximum amplitude and the minimum amplitude of the three-phase line voltage, can also be used as the asymmetric fault parameter. The specific parameters can be determined according to the actual application scenario and are not limited here. Optionally, the three-phase voltage at the output end of the converter module can also be detected by the fault ride-through control module, and the difference between the maximum effective value and the minimum effective value of the three-phase voltage can be used as an asymmetric fault parameter. If the difference between the maximum effective value and the minimum effective value of the three-phase voltage exceeds the corresponding fault judgment threshold, it is determined that an asymmetric fault has occurred in the current AC power grid. In addition, the difference between the maximum peak-to-peak value and the minimum peak-to-peak value of the three-phase voltage, or the difference between the maximum amplitude and the minimum amplitude of the three-phase voltage can be used as an asymmetric fault parameter. The specific value can be determined according to the actual application scenario and is not limited here. Asymmetric fault detection of the AC power grid is performed based on the fault judgment threshold corresponding to the asymmetric fault parameter. When an asymmetric fault occurs in the AC power grid, the fault can be detected immediately and an asymmetric fault ride-through can be performed to ensure the stability and safety of the power supply process of the power grid.

[0062] In some feasible implementations, when an asymmetric fault is detected in the AC power grid, the converter obtains the duration of the last fault ride-through through the fault ride-through control module, that is, obtains the fault ride-through duration of the most recent historical asymmetric fault ride-through from the current time (for the convenience of description, referred to as the fault ride-through duration). Please refer again to Figure 5a , Figure 5a The asymmetric fault ride-through process includes two asymmetric fault ride-throughs. Taking the second asymmetric fault ride-through as an example, during the second asymmetric fault ride-through process, the fault ride-through control module obtains the fault ride-through duration T0 (which can be 5.02s to 5.06s) corresponding to the first asymmetric fault ride-through. The fault ride-through control module obtains the fault ride-through duration of the most recent asymmetric fault ride-through and, based on the fault ride-through duration, injects a negative-sequence reactive current of a corresponding magnitude into the AC power grid. This prevents the current value corresponding to the negative-sequence reactive current injected into the AC power grid from being too high, preventing the negative-sequence reactive current from reducing the negative-sequence voltage at the converter port and interfering with asymmetric fault detection.

[0063] S702, determine whether the fault ride-through duration is empty. If the determination result is yes, execute step S704. If the determination result is no, execute step S703.

[0064] S703, determine whether the fault ride-through duration is less than a preset time threshold. If the determination result is yes, execute step S705. If the determination result is no, execute step S704.

[0065] S704, determine the second negative-sequence reactive current value and inject a second negative-sequence reactive current into the AC power grid, where the magnitude of the injected current is equal to the second negative-sequence reactive current value.

[0066] In some feasible embodiments, when the fault ride-through control module detects that an asymmetrical fault first occurs in the AC power grid, that is, no asymmetrical fault has occurred in the AC power grid before the current time, the fault ride-through duration obtained by the fault ride-through control module is empty (null). The fault ride-through control module determines the second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid based on the negative-sequence voltage (which can be the second negative-sequence voltage) and negative-sequence reactive current (which can be the first negative-sequence reactive current) at the output end of the converter module detected before the current asymmetrical fault, the rated voltage of the converter, the rated current of the converter, and the above-mentioned first negative-sequence voltage, and controls the converter module to inject a second negative-sequence reactive current into the AC power grid, where the magnitude of the injected current is equal to the second negative-sequence reactive current value. Alternatively, when the fault ride-through duration obtained by the fault ride-through control module is not empty and the fault ride-through duration is greater than or equal to the preset time threshold, the second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid is determined based on the above-mentioned second negative-sequence voltage, the above-mentioned first negative-sequence reactive current, the rated voltage of the converter, the rated current of the converter, and the above-mentioned first negative-sequence voltage, and the converter module is controlled to inject a second negative-sequence reactive current into the AC power grid, where the magnitude of the injected current is equal to the second negative-sequence reactive current value. Specifically, the second negative-sequence reactive current determined by the above-mentioned fault ride-through control module can be expressed as:

[0067]

[0068] where U2 is the above-mentioned second negative-sequence voltage, Iqn1 is the above-mentioned first negative-sequence reactive current, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the above-mentioned first negative-sequence voltage, K is an adjustment coefficient (a positive number can be taken, for example, 0 < K < 10), and Iqn2 is the above-mentioned second negative-sequence reactive current. Through the above-mentioned fault ride-through control module, the second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid is obtained based on the above-mentioned expression, and the converter module is controlled to inject a second negative-sequence reactive current into the AC power grid, where the magnitude of the injected current is equal to the second negative-sequence reactive current value.

[0069] In some feasible embodiments, when the above-mentioned fault ride-through duration is empty, or the fault ride-through duration is greater than or equal to the preset time threshold, the second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid can also be determined based on the first negative-sequence reactive current at the output end of the converter module detected before the current asymmetric fault, the above-mentioned fault determination threshold, the rated voltage of the converter, the rated current of the converter, and the above-mentioned first negative-sequence voltage. Then, the fault ride-through control module controls the converter module to inject a second negative-sequence reactive current into the AC power grid, and the magnitude of the current injected is equal to the second negative-sequence reactive current value. Here, when the first negative-sequence voltage is used as the asymmetric fault parameter, the above-mentioned fault determination threshold is the fault determination threshold corresponding to the first negative-sequence voltage. Similarly, when the difference between the maximum effective value and the minimum effective value of the three-phase line voltage (or three-phase phase voltage) (or, the difference between the maximum peak-to-peak value and the minimum peak-to-peak value, the difference between the maximum amplitude and the minimum amplitude) is used as the asymmetric fault parameter, the above-mentioned fault determination threshold is the fault determination threshold corresponding to the above-mentioned difference. Specifically, the second negative-sequence reactive current determined by the above-mentioned fault ride-through control module can be expressed as:

[0070]

[0071] where, Iqn1 is the above-mentioned first negative-sequence reactive current, Unv is the above-mentioned fault determination threshold, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the above-mentioned first negative-sequence voltage, K is an adjustment coefficient (which can be a positive number, for example, 0 < K < 10), and Iqn2 is the above-mentioned second negative-sequence reactive current. The fault ride-through control module can obtain the second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid based on the above expression, and control the converter module to inject a second negative-sequence reactive current into the AC power grid, and the magnitude of the current injected is equal to the second negative-sequence reactive current value. By adjusting the magnitude of the negative-sequence reactive current injected into the AC power grid by the fault ride-through control module based on different fault ride-through durations, it is ensured that the converter can inject a stable negative-sequence reactive current into the AC power grid during the asymmetric fault, enhancing the stability and security of the power grid power supply in the case of a weak power grid.

[0072] S705, determine the second negative-sequence reactive current value, obtain the third negative-sequence reactive current value based on the second negative-sequence reactive current value, and inject a third negative-sequence reactive current into the AC power grid, and the magnitude of the current injected is equal to the third negative-sequence reactive current value.

[0073] In some feasible embodiments, when the fault ride-through duration is less than a preset time threshold, a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current is determined based on the second negative-sequence voltage and first negative-sequence reactive current detected at the output terminal of the converter module before the current asymmetric fault, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage. A third negative-sequence reactive current value is obtained based on the second negative-sequence reactive current value, and the converter module is controlled to inject a third negative-sequence reactive current having a current magnitude equal to the third negative-sequence reactive current value into the AC power grid. Specifically, the third negative-sequence reactive current can be expressed as:

[0074] Iqn3=Iqn2-ΔIqn

[0075] Wherein, Iqn2 is the second negative-sequence reactive current, Iqn3 is the third negative-sequence reactive current, and 0<|ΔIqn|<|Iqn2|. Here, the second negative-sequence reactive current Iqn2 can be determined based on the second negative-sequence voltage, the first negative-sequence reactive current, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, or can be determined based on the first negative-sequence reactive current, the fault determination threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage. The fault ride-through control module reduces the negative-sequence reactive current injected into the AC power grid when the fault ride-through duration is less than a preset time threshold. This prevents the negative-sequence reactive current output by the converter from reducing the negative-sequence voltage at the converter port in a weak power grid environment, thereby interfering with asymmetric fault detection. This ensures that a stable negative-sequence reactive current can be injected into the AC power grid during an asymmetric fault.

[0076] In the present application, the converter can detect an asymmetric fault occurring in the AC power grid through a fault ride-through control module (the occurrence of an asymmetric fault can be detected by detecting the first negative-sequence voltage, three-phase line voltage, or three-phase phase voltage at the output end of the converter module). When an asymmetric fault occurs in the AC power grid, the fault ride-through control module can obtain the fault ride-through duration of the most recent historical asymmetric fault ride-through from the current time, and when the fault ride-through duration is null or the fault ride-through duration is greater than or equal to a preset time threshold, determine a second negative-sequence reactive current value corresponding to the second negative-sequence reactive current injected into the AC power grid, and control the converter module to inject a second negative-sequence reactive current equal to the second negative-sequence reactive current value into the AC power grid. When the fault ride-through duration is less than the preset time threshold, determine the second negative-sequence reactive current value corresponding to the second negative-sequence reactive current, obtain a third negative-sequence reactive current value based on the second negative-sequence reactive current value, and control the converter module to inject a third negative-sequence reactive current equal to the third negative-sequence reactive current value into the AC power grid, where the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current. The converter uses a fault ride-through control module to adjust the magnitude of the negative-sequence reactive current injected into the AC grid based on varying fault ride-through durations. This prevents excessively high negative-sequence reactive current from reducing the negative-sequence voltage at the converter's ports and interfering with asymmetric fault detection in weak grid environments. During asymmetric faults, the converter can inject a stable negative-sequence reactive current into the AC grid, enhancing the stability and security of power supply in weak grid conditions and ensuring reliable grid fault recovery.

Claims

1. A converter, the converter being applicable to a power grid power supply system, characterized in that: The input end of the converter is coupled to the power supply in the power grid power supply system, and the output end of the converter is coupled to the AC power grid; the converter includes a conversion module and a fault ride-through control module; The fault ride-through control module is used to control the conversion module to inject negative-sequence reactive current into the AC power grid when the asymmetric fault parameter of the AC power grid is greater than the fault judgment threshold, based on the fault ride-through duration of the most recent historical asymmetric fault ride-through of the AC power grid. The asymmetric fault parameters include a first negative-sequence voltage, and the difference between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase line voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude, and one of the differences between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase phase voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude.

2. The converter according to claim 1, characterized in that The fault ride-through control module is further configured to, when the fault ride-through duration is empty or the fault ride-through duration is greater than or equal to a preset time threshold, obtain a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and control the conversion module to inject a second negative-sequence reactive current having a current magnitude equal to the second negative-sequence reactive current value into the AC power grid.

3. The converter according to claim 1, characterized in that The fault ride-through control module is further used to obtain a second negative-sequence reactive current value based on the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the fault judgment threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage when the fault ride-through duration is empty or the fault ride-through duration is greater than or equal to a preset time threshold, and control the conversion module to inject a second negative-sequence reactive current with a current equal to the second negative-sequence reactive current value into the AC power grid.

4. The converter according to claim 1, characterized in that The fault ride-through control module is also used to, when the fault ride-through duration is less than a preset time threshold, obtain a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage; obtain a third negative-sequence reactive current value based on the second negative-sequence reactive current value; and control the conversion module to inject a third negative-sequence reactive current having a current magnitude equal to the third negative-sequence reactive current value into the AC power grid, where the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current.

5. The converter according to claim 1, characterized in that The fault ride-through control module is also used to obtain a second negative-sequence reactive current value based on the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the fault judgment threshold, the rated voltage of the converter, the rated current of the converter and the first negative-sequence voltage when the fault ride-through duration is less than a preset time threshold; obtain a third negative-sequence reactive current value based on the second negative-sequence reactive current value; and control the conversion module to inject a third negative-sequence reactive current with a current equal to the third negative-sequence reactive current value into the AC power grid, where the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current.

6. The converter according to claim 2 or 4, characterized in that: The second negative sequence reactive current satisfies: Among them, U2 is the second negative-sequence voltage, Iqn1 is the first negative-sequence reactive current, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the first negative-sequence voltage, K is a positive number, and Iqn2 is the second negative-sequence reactive current.

7. The converter according to claim 3 or 5, characterized in that: The second negative sequence reactive current satisfies: Among them, Iqn1 is the first negative-sequence reactive current, Unv is the fault judgment threshold, Un is the rated voltage of the converter, In is the rated current of the converter, U1 is the first negative-sequence voltage, K is a positive number, and Iqn2 is the second negative-sequence reactive current.

8. A power grid power supply system, characterized in that: The grid power supply system comprises a power supply, a transformer and a converter according to any one of claims 1 to 7; The power supply is used to provide energy input or power input for the converter; The converter is used to convert the energy input or power input provided by the power supply into a first alternating current and output the first alternating current to the transformer; The transformer is used to perform power conversion based on the first alternating current and output a second alternating current to the alternating current grid; The converter is further configured to, when an asymmetric fault occurs in the AC power grid, inject a negative-sequence reactive current into the AC power grid according to the fault ride-through duration of a most recent historical asymmetric fault that occurred in the AC power grid.

9. The grid power supply system according to claim 8, characterized in that: The power supply includes at least one of a solar panel, a wind turbine or an energy storage battery.

10. A converter control method for a power grid power supply system, characterized in that: The method is applicable to a converter in the power grid power supply system, wherein the power grid power supply system includes a power supply, a transformer, and the converter. The input end of the converter is coupled to the power supply, and the output end of the converter is coupled to the AC power grid via the transformer. The converter includes a conversion module and a fault ride-through control module. The method includes: When the asymmetric fault parameter of the AC power grid is greater than the fault judgment threshold, the fault ride-through control module controls the conversion module to inject negative-sequence reactive current into the AC power grid based on the fault ride-through duration of the most recent historical asymmetric fault ride-through of the AC power grid. The asymmetric fault parameters include a first negative-sequence voltage, and the difference between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase line voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude, and one of the differences between the maximum effective value, maximum peak-to-peak value, and maximum amplitude of the three-phase phase voltage and the corresponding minimum effective value, minimum peak-to-peak value, and minimum amplitude.

11. The method according to claim 10, characterized in that The controlling, by the fault ride-through control module, of injecting a negative-sequence reactive current into the AC power grid according to a fault ride-through duration of a most recent historical asymmetric fault ride-through occurring in the AC power grid includes: When the fault ride-through duration is empty or the fault ride-through duration is greater than or equal to a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and controls the conversion module to inject a second negative-sequence reactive current with a current magnitude equal to the second negative-sequence reactive current value into the AC power grid.

12. The method according to claim 10, characterized in that The controlling, by the fault ride-through control module, of injecting a negative-sequence reactive current into the AC power grid according to a fault ride-through duration of a most recent historical asymmetric fault ride-through occurring in the AC power grid includes: When the fault ride-through duration is empty or the fault ride-through duration is greater than or equal to a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the fault judgment threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and controls the conversion module to inject a second negative-sequence reactive current with a current magnitude equal to the second negative-sequence reactive current value into the AC power grid.

13. The method according to claim 10, characterized in that The controlling, by the fault ride-through control module, of injecting a negative-sequence reactive current into the AC power grid according to a fault ride-through duration of a most recent historical asymmetric fault ride-through occurring in the AC power grid includes: When the fault ride-through duration is less than a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the second negative-sequence voltage and the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage, and obtains a third negative-sequence reactive current value based on the second negative-sequence reactive current value. The conversion module is controlled to inject a third negative-sequence reactive current having a current magnitude equal to the third negative-sequence reactive current value into the AC power grid, where the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current.

14. The method according to claim 10, characterized in that The controlling, by the fault ride-through control module, of injecting a negative-sequence reactive current into the AC power grid according to a fault ride-through duration of a most recent historical asymmetric fault ride-through occurring in the AC power grid includes: When the fault ride-through duration is less than a preset time threshold, the fault ride-through control module obtains a second negative-sequence reactive current value based on the first negative-sequence reactive current before the current asymmetric fault occurs in the AC power grid, the fault judgment threshold, the rated voltage of the converter, the rated current of the converter, and the first negative-sequence voltage; obtains a third negative-sequence reactive current value based on the second negative-sequence reactive current value; and controls the conversion module to inject a third negative-sequence reactive current having a current magnitude equal to the third negative-sequence reactive current value into the AC power grid, where the absolute value of the third negative-sequence reactive current is less than the absolute value of the second negative-sequence reactive current.

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