A fault control method and system for a power distribution network

Abstract

This invention discloses a fault control method and system for distribution networks, belonging to the field of fault control technology. The method comprises: acquiring the voltage and current signals of the converter grid connection point based on the distribution network to be controlled, and determining the operating state of the distribution network to be controlled; if it is an asymmetrical fault operating state, then blocking the active and reactive power loops of the distribution network to obtain the positive-sequence voltage component, the negative-sequence voltage component, and the positive and negative-sequence virtual internal potentials of the converter; calculating the positive and negative-sequence virtual impedance coefficients based on the above data; calculating the positive and negative-sequence virtual impedances based on the above data; and inputting the positive and negative-sequence virtual impedances into the distribution network to be controlled and reacquiring the voltage and current signals of the converter grid connection point to redetermine the operating state of the distribution network to be controlled until it is in a normal operating state. The fault control method for distribution networks provided by this invention can achieve stable control of new distribution networks under fault scenarios, ensuring the safe and efficient operation of new distribution networks.

Description

Technical Field

[0001] This invention relates to the field of fault control technology, and in particular to a fault control method and system for power distribution networks. Background Technology

[0002] As the global energy transition accelerates, the penetration rate of new energy sources such as wind and solar power in distribution networks continues to rise, and traditional distribution networks are gradually evolving into new distribution networks dominated by new energy sources. Traditional new energy power generation systems mostly use grid-connected converters. The operation of these converters depends on the grid voltage and frequency support, and they are prone to grid disconnection when grid faults occur, leading to an expansion of the fault range and a longer grid recovery time, making it difficult to meet the high requirements of new distribution networks for fault ride-through capability and power supply reliability. In contrast, grid-connected converters, with their core advantages of actively supporting grid voltage and frequency and having autonomous grid connection, have become the key to solving the shortcomings of grid-connected converters. They can improve the operating characteristics of synchronous generators and exhibit strong transient stability and fault support capabilities under grid fault scenarios.

[0003] Under the current technological background, although grid-type converters have significant technical advantages over grid-type converters, the transient characteristics of distribution networks containing grid-type renewable energy sources are affected by a combination of factors during faults, such as the control strategy of grid-type converters, fault types (symmetrical and asymmetrical faults), and renewable energy penetration rates, making the fault mechanism more complex. At the same time, traditional fault control strategies are designed based on the characteristics of synchronous generators, which are no longer suitable for the operating characteristics of grid-type renewable energy distribution networks, making it difficult to achieve effective fault control. Summary of the Invention

[0004] The present invention aims to provide a fault control method and system for distribution networks to solve the above-mentioned technical problems, avoid the problems of converter disconnection and fault range expansion in new distribution networks during faults, achieve stable control of new distribution networks under fault scenarios, and ensure the safe and efficient operation of new distribution networks.

[0005] To address the aforementioned technical problems, this invention provides a fault control method for a power distribution network, comprising: Based on the distribution network to be controlled, acquire the voltage signal and current signal of the converter grid connection point; The operating status of the distribution network to be controlled is determined based on the voltage signal and current signal at the grid connection point of the converter. If the operating state of the distribution network to be controlled is an asymmetrical fault operating state, then the active power loop and the reactive power loop of the distribution network are locked to obtain the positive sequence d-axis voltage component, the positive sequence q-axis voltage component, the negative sequence d-axis voltage component, the negative sequence q-axis voltage component, the positive sequence virtual internal potential, and the negative sequence virtual internal potential of the converter. Calculate the positive-sequence virtual internal potential, the negative-sequence virtual internal potential, and the converter grid connection point voltage signal based on the positive-sequence virtual internal potential, the negative-sequence virtual internal potential, and the converter grid connection point voltage signal. Calculate the positive-sequence virtual impedance and negative-sequence virtual impedance based on the positive-sequence d-axis voltage component, the positive-sequence q-axis voltage component, the negative-sequence d-axis voltage component, the negative-sequence q-axis voltage component, the positive-sequence virtual impedance coefficient, and the negative-sequence virtual impedance coefficient of the converter; The positive-sequence virtual impedance and negative-sequence virtual impedance are introduced into the distribution network to be controlled, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the distribution network to be controlled is re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the distribution network to be controlled is normal operation.

[0006] In the above scheme, fault identification and status classification of the distribution network are achieved by using the voltage and current signals at the converter grid connection point, thus determining the operating status of the distribution network and providing a basis for subsequent targeted fault control. Next, by blocking the active and reactive power loops and extracting several core characteristic parameters under asymmetrical fault operating conditions, it is possible to avoid exacerbating the distribution network imbalance and causing converter disconnection during dynamic adjustment of the power loop. Then, the positive-sequence virtual internal potential, negative-sequence virtual internal potential, and converter grid connection point voltage signal are used to calculate the positive-sequence and negative-sequence virtual impedance coefficients. These coefficients, along with several core characteristic parameters under asymmetrical fault operating conditions, provide control parameters to prevent the fault range from expanding and to stabilize the grid voltage. Finally, by inputting positive-sequence virtual impedance and negative-sequence virtual impedance and re-acquiring the voltage signal and current signal at the converter grid connection point, the distribution network under control is continuously adjusted and its operating state is redefined until it returns to normal operation. This ultimately achieves stable control of the new distribution network under fault scenarios, ensuring its safe and efficient operation.

[0007] Furthermore, the operating state of the distribution network to be controlled includes asymmetrical fault operating state, symmetrical fault operating state, and normal operating state; the determination of the operating state of the distribution network to be controlled based on the converter grid connection point voltage signal and the converter grid connection point current signal includes: If the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is less than the preset transient current trigger threshold, then the distribution network to be controlled is in normal operation. If the converter grid connection point voltage signal is less than or equal to a preset transient voltage trigger threshold or the converter grid connection point current signal is greater than or equal to a preset transient current trigger threshold, then the converter grid connection point A phase voltage, converter grid connection point B phase voltage and converter grid connection point C phase voltage are obtained based on the converter grid connection point voltage signal. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, or the voltage of phase C at the converter grid connection point are not equal, then the distribution network to be controlled is in an asymmetrical fault operation state. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, and the voltage of phase C at the converter grid connection point are all equal, then the distribution network to be controlled is in a symmetrical fault operation state.

[0008] In the above scheme, by using both the converter grid connection point voltage signal and a preset transient voltage trigger threshold, and the converter grid connection point current signal and a preset trigger threshold for dual determination, the normal operation and fault operation states of the distribution network can be distinguished. This avoids ineffective control when the distribution network is fault-free and ensures the stable operation of the distribution network under normal operating conditions. Next, if the converter grid connection point voltage signal is less than or equal to the preset transient voltage trigger threshold, or the converter grid connection point current signal is greater than or equal to the preset transient current trigger threshold, the voltages of phase A, phase B, and phase C at the converter grid connection point are extracted from the converter grid connection point voltage signal, providing data support for detailed differentiation of subsequent fault operation states. Then, by determining whether the three-phase voltages at the converter grid connection point are equal, the distribution network can be accurately identified as being in an asymmetrical or symmetrical fault operation state, providing a judgment condition for subsequently initiating the corresponding fault control strategy.

[0009] Furthermore, it also includes: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the grid connection point of the converter is less than or equal to the preset transient voltage trigger threshold and the current signal at the grid connection point of the converter is less than the preset transient current trigger threshold, then the converter output voltage, grid-side voltage and real-time operating power angle are obtained. Calculate the unbalanced power of the distribution network based on the converter output voltage, grid-side voltage, and real-time operating power angle; Fault power adjustment commands are obtained based on the preset active power and unbalanced power of the distribution network. The power adjustment command is used to adjust the distribution network under control, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the distribution network under control is then re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the distribution network under control is normal operation.

[0010] In the above scheme, under symmetrical fault operation, when the converter grid-connected voltage signal is less than or equal to the preset transient voltage trigger threshold and the converter grid-connected current signal is less than the preset transient current trigger threshold, the core calculation parameters for subsequent transient power angle control can be collected by acquiring the converter output voltage, grid-side voltage, and real-time operating power angle, providing basic data support for subsequent unbalanced power calculation. Then, by calculating the distribution network unbalanced power using the converter output voltage, grid-side voltage, and real-time operating power angle, the power angle instability of the distribution network can be quantitatively analyzed, providing a quantitative basis for power angle stability control. Subsequently, by obtaining fault power adjustment commands through preset distribution network active power and distribution network unbalanced power, the converter can be corrected to achieve the control objectives of reducing unbalanced power and stabilizing the power angle. Finally, the distribution network is adjusted through fault power adjustment commands, and the converter grid-connected voltage signal and converter grid-connected current signal are re-acquired to re-determine the distribution network operating state until the distribution network returns to normal operation, avoiding converter disconnection and fault range expansion caused by power angle instability.

[0011] Furthermore, it also includes: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is greater than or equal to the preset transient current trigger threshold, then the voltage drop degree and the grid-side voltage are obtained. Fault voltage regulation commands are obtained based on the degree of voltage drop and grid-side voltage. The controllable distribution network is adjusted based on the fault voltage regulation command, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the controllable distribution network is then re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the controllable distribution network is normal.

[0012] In the above scheme, under symmetrical fault operation, when the converter grid-connected point voltage signal is greater than the preset transient voltage trigger threshold and the converter grid-connected point current signal is greater than or equal to the preset transient current trigger threshold, the voltage drop degree and grid-side voltage are acquired, providing data support for the accurate calculation of fault voltage regulation commands. Next, by acquiring the fault voltage regulation command through the voltage drop degree and grid-side voltage, the fault voltage command of the distribution network can be adaptively tuned, achieving the control objectives of suppressing fault overcurrent and compensating for grid voltage drops. Then, the distribution network is adjusted through the fault voltage regulation command, and the converter grid-connected point voltage signal and converter grid-connected point current signal are re-acquired to re-determine the distribution network operating state until the distribution network returns to normal operation, avoiding converter disconnection and fault range expansion caused by overcurrent, and ensuring stable operation of the distribution network under fault scenarios.

[0013] Furthermore, the acquisition of the converter grid connection point voltage signal and the converter grid connection point current signal based on the distribution network to be controlled includes: Based on the distribution network to be controlled, acquire the initial voltage signal and the initial current signal of the converter grid connection point; The converter grid connection point initial voltage signal and the converter grid connection point initial current signal are low-pass filtered to obtain the converter grid connection point filtered voltage signal and the converter grid connection point filtered current signal. The converter grid connection point filter voltage signal and the converter grid connection point filter current signal are converted from analog to digital to obtain the converter grid connection point discrete voltage signal and the converter grid connection point discrete current signal. Both the discrete voltage signal and the discrete current signal at the grid connection point of the converter are subjected to sliding filtering and low-pass filtering to obtain the voltage signal and current signal at the grid connection point of the converter.

[0014] In the above scheme, acquiring the initial voltage and current signals at the converter grid connection point provides a data foundation for subsequent signal processing and fault diagnosis. Next, low-pass filtering of these signals suppresses high-frequency electromagnetic interference and switching ripple, retains the fundamental effective component, and improves the original signal quality, thus acquiring the filtered voltage and current signals at the converter grid connection point. Then, analog-to-digital conversion (ADC) transforms these signals into discrete digital signals to meet subsequent digital computation and processing requirements. Finally, by performing sliding filtering and low-pass filtering on both the discrete voltage signal and discrete current signal at the converter grid connection point, random measurement noise and residual high-frequency harmonics in the digital signals can be filtered out twice, resulting in the converter grid connection point voltage signal and converter grid connection point current signal. This provides accurate and reliable data support for subsequent determination of distribution network fault status and calculation of control parameters, avoiding control errors and fault misjudgments caused by signal distortion.

[0015] This invention provides a fault control system for a power distribution network, comprising a signal acquisition module, a fault state determination module, a virtual internal potential extraction module, a virtual impedance coefficient calculation module, a virtual impedance solution module, and a power distribution network recovery module, specifically: The signal acquisition module is used to acquire the voltage signal and current signal of the converter grid connection point based on the distribution network to be controlled. The fault status determination module is used to determine the operating status of the distribution network to be controlled based on the voltage signal and current signal of the converter grid connection point. If the operating state of the distribution network to be controlled is an asymmetrical fault operating state, the virtual internal potential extraction module is used to lock the active power loop and the reactive power loop of the distribution network to obtain the positive sequence d-axis voltage component, positive sequence q-axis voltage component, negative sequence d-axis voltage component, negative sequence q-axis voltage component, positive sequence virtual internal potential, and negative sequence virtual internal potential of the converter. The virtual impedance coefficient calculation module is used to calculate the positive-sequence virtual impedance coefficient and the negative-sequence virtual impedance coefficient based on the positive-sequence virtual internal potential, the negative-sequence virtual internal potential and the voltage signal at the converter grid connection point. The virtual impedance calculation module is used to calculate the positive-sequence virtual impedance and the negative-sequence virtual impedance based on the positive-sequence d-axis voltage component of the converter, the positive-sequence q-axis voltage component of the converter, the negative-sequence d-axis voltage component of the converter, the negative-sequence q-axis voltage component of the converter, the positive-sequence virtual impedance coefficient, and the negative-sequence virtual impedance coefficient. The distribution network recovery module is used to input the positive-sequence virtual impedance and negative-sequence virtual impedance into the distribution network to be controlled and reacquire the voltage signal and current signal of the converter grid connection point, so as to redetermine the operating state of the distribution network to be controlled based on the reacquired voltage signal and current signal of the converter grid connection point, until the operating state of the distribution network to be controlled is the normal operating state.

[0016] This invention provides a fault control system for a distribution network. In practical applications, only a fault state determination module is needed. This module identifies and classifies distribution network faults using converter grid-connected voltage and current signals, determining the network's operating status and providing a basis for subsequent targeted fault control. Next, a virtual internal potential extraction module is used. By blocking the active and reactive power loops and extracting several core characteristic parameters during asymmetrical fault operation, this avoids exacerbating network imbalance and causing converter disconnection during dynamic power loop adjustments. Then, a virtual impedance coefficient calculation module is used to calculate the positive and negative sequence virtual impedance coefficients using positive-sequence virtual internal potential, negative-sequence virtual internal potential, and converter grid-connected voltage signals. Finally, a virtual impedance solving module uses these coefficients and core characteristic parameters during asymmetrical fault operation to obtain the positive and negative sequence virtual impedances, providing control parameters to prevent fault expansion and stabilize grid voltage. Finally, a distribution network recovery module is used. By inputting positive-sequence virtual impedance and negative-sequence virtual impedance and re-acquiring the voltage signal and current signal of the converter grid connection point, the distribution network under control is continuously adjusted and its operating state is redefined until it is restored to normal operation. This ultimately achieves stable control of the new distribution network under fault scenarios and ensures its safe and efficient operation.

[0017] Furthermore, the operating state of the distribution network to be controlled includes an asymmetrical fault operating state, a symmetrical fault operating state, and a normal operating state; the fault state determination module is used to determine the operating state of the distribution network to be controlled based on the converter grid connection point voltage signal and the converter grid connection point current signal, including: If the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is less than the preset transient current trigger threshold, then the distribution network to be controlled is in normal operation. If the converter grid connection point voltage signal is less than or equal to a preset transient voltage trigger threshold or the converter grid connection point current signal is greater than or equal to a preset transient current trigger threshold, then the converter grid connection point A phase voltage, converter grid connection point B phase voltage and converter grid connection point C phase voltage are obtained based on the converter grid connection point voltage signal. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, or the voltage of phase C at the converter grid connection point are not equal, then the distribution network to be controlled is in an asymmetrical fault operation state. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, and the voltage of phase C at the converter grid connection point are all equal, then the distribution network to be controlled is in a symmetrical fault operation state.

[0018] In the above scheme, by using both the converter grid connection point voltage signal and a preset transient voltage trigger threshold, and the converter grid connection point current signal and a preset trigger threshold for dual determination, the normal operation and fault operation states of the distribution network can be distinguished. This avoids ineffective control when the distribution network is fault-free and ensures the stable operation of the distribution network under normal operating conditions. Next, if the converter grid connection point voltage signal is less than or equal to the preset transient voltage trigger threshold, or the converter grid connection point current signal is greater than or equal to the preset transient current trigger threshold, the voltages of phase A, phase B, and phase C at the converter grid connection point are extracted from the converter grid connection point voltage signal, providing data support for detailed differentiation of subsequent fault operation states. Then, by determining whether the three-phase voltages at the converter grid connection point are equal, the distribution network can be accurately identified as being in an asymmetrical or symmetrical fault operation state, providing a judgment condition for subsequently initiating the corresponding fault control strategy.

[0019] Furthermore, it also includes a power regulation module: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the grid connection point of the converter is less than or equal to the preset transient voltage trigger threshold and the current signal at the grid connection point of the converter is less than the preset transient current trigger threshold, then the power regulation module is used to obtain the converter output voltage, grid side voltage and real-time operating power angle. The power regulation module is used to calculate the unbalanced power of the distribution network based on the converter output voltage, grid-side voltage and real-time operating power angle. The power regulation module is used to obtain fault power regulation instructions based on the preset active power of the distribution network and the unbalanced power of the distribution network. The distribution network recovery module is used to adjust the distribution network to be controlled based on the fault power adjustment command, and to reacquire the voltage signal and current signal of the converter grid connection point, so as to redetermine the operating state of the distribution network to be controlled based on the reacquired voltage signal and current signal of the converter grid connection point, until the operating state of the distribution network to be controlled is the normal operating state.

[0020] In the above scheme, under symmetrical fault operation, when the converter grid-connected voltage signal is less than or equal to the preset transient voltage trigger threshold and the converter grid-connected current signal is less than the preset transient current trigger threshold, the power regulation module acquires the core calculation parameters for subsequent transient power angle control by obtaining the converter output voltage, grid-side voltage, and real-time operating power angle, providing basic data support for subsequent unbalanced power calculation. Then, by calculating the distribution network unbalanced power using the converter output voltage, grid-side voltage, and real-time operating power angle, the power angle instability of the distribution network can be quantitatively analyzed, providing a quantitative basis for power angle stability control. Subsequently, by obtaining fault power regulation commands through preset distribution network active power and distribution network unbalanced power, the converter can be corrected to achieve the control objectives of reducing unbalanced power and stabilizing the power angle. Finally, the distribution network is adjusted through fault power regulation commands, and the converter grid-connected voltage signal and converter grid-connected current signal are re-acquired to re-determine the distribution network operating status until the distribution network returns to normal operation, avoiding converter disconnection and fault range expansion caused by power angle instability.

[0021] Furthermore, it also includes a voltage regulation module: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is greater than or equal to the preset transient current trigger threshold, then the voltage regulation module is used to obtain the voltage drop degree and the grid-side voltage. The voltage regulation module is used to obtain fault voltage regulation commands based on the degree of voltage drop and the grid-side voltage; The distribution network recovery module is used to adjust the distribution network to be controlled based on the fault voltage adjustment command, and to reacquire the converter grid connection point voltage signal and converter grid connection point current signal, so as to re-determine the operating state of the distribution network to be controlled based on the reacquired converter grid connection point voltage signal and converter grid connection point current signal, until the operating state of the distribution network to be controlled is a normal operating state.

[0022] In the above scheme, under symmetrical fault operation, when the converter grid-connected voltage signal is greater than the preset transient voltage trigger threshold and the converter grid-connected current signal is greater than or equal to the preset transient current trigger threshold, the voltage regulation module acquires the voltage drop level and grid-side voltage, providing data support for the accurate calculation of fault voltage regulation commands. Then, by acquiring the fault voltage regulation command through the voltage drop level and grid-side voltage, the fault voltage command for the distribution network can be adaptively tuned, achieving the control objectives of suppressing fault overcurrent and compensating for grid voltage drops. Next, the distribution network is adjusted through the fault voltage regulation command, and the converter grid-connected voltage signal and converter grid-connected current signal are re-acquired to re-determine the distribution network operating state until the distribution network returns to normal operation, avoiding converter disconnection and fault range expansion caused by overcurrent, and ensuring stable operation of the distribution network under fault scenarios.

[0023] Furthermore, the signal acquisition module is used to acquire the converter grid connection point voltage signal and the converter grid connection point current signal based on the distribution network to be controlled, including: Based on the distribution network to be controlled, acquire the initial voltage signal and the initial current signal of the converter grid connection point; The converter grid connection point initial voltage signal and the converter grid connection point initial current signal are low-pass filtered to obtain the converter grid connection point filtered voltage signal and the converter grid connection point filtered current signal. The converter grid connection point filter voltage signal and the converter grid connection point filter current signal are converted from analog to digital to obtain the converter grid connection point discrete voltage signal and the converter grid connection point discrete current signal. Both the discrete voltage signal and the discrete current signal at the grid connection point of the converter are subjected to sliding filtering and low-pass filtering to obtain the voltage signal and current signal at the grid connection point of the converter.

[0024] In the above scheme, acquiring the initial voltage and current signals at the converter grid connection point provides a data foundation for subsequent signal processing and fault diagnosis. Next, low-pass filtering of these signals suppresses high-frequency electromagnetic interference and switching ripple, retains the fundamental effective component, and improves the original signal quality, thus acquiring the filtered voltage and current signals at the converter grid connection point. Then, analog-to-digital conversion (ADC) transforms these signals into discrete digital signals to meet subsequent digital computation and processing requirements. Finally, by performing sliding filtering and low-pass filtering on both the discrete voltage signal and discrete current signal at the converter grid connection point, random measurement noise and residual high-frequency harmonics in the digital signals can be filtered out twice, resulting in the converter grid connection point voltage signal and converter grid connection point current signal. This provides accurate and reliable data support for subsequent determination of distribution network fault status and calculation of control parameters, avoiding control errors and fault misjudgments caused by signal distortion. Attached Figure Description

[0025] To more clearly illustrate the technical solution of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 A flowchart illustrating a fault control method for a power distribution network according to an embodiment of the present invention; Figure 2 This is an architecture diagram of a fault control system for a power distribution network provided in one embodiment of the present invention; Figure 3 This invention provides a fault current waveform for a three-phase symmetrical fault, as shown in one embodiment of the invention. Figure 4 This is a fault current waveform diagram for an asymmetrical fault, provided as an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] Unless otherwise defined, 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; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0029] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0032] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0033] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0034] See Figure 1To avoid converter disconnection and fault range expansion in new distribution networks during faults, and to achieve stable control of the new distribution network under fault scenarios, ensuring its safe and efficient operation, this embodiment provides a fault control method for distribution networks. The flowchart of this method can be found in [link to flowchart]. Figure 1 ,include: Step S1: Based on the distribution network to be controlled, acquire the voltage signal and current signal at the grid connection point of the converter; Step S2: Determine the operating status of the distribution network to be controlled based on the voltage signal and current signal at the grid connection point of the converter; Step S3: If the operating state of the distribution network to be controlled is an asymmetrical fault operating state, then the active power loop and the reactive power loop of the distribution network are locked to obtain the positive sequence d-axis voltage component, the positive sequence q-axis voltage component, the negative sequence d-axis voltage component, the negative sequence q-axis voltage component, the positive sequence virtual internal potential, and the negative sequence virtual internal potential of the converter. Step S4: Calculate the positive-sequence virtual internal potential, negative-sequence virtual internal potential, and converter grid connection point voltage signal based on the positive-sequence virtual internal potential, negative-sequence virtual internal potential, and converter grid connection point voltage signal; Step S5: Calculate the positive-sequence virtual impedance and negative-sequence virtual impedance based on the positive-sequence d-axis voltage component, the positive-sequence q-axis voltage component, the negative-sequence d-axis voltage component, the negative-sequence q-axis voltage component, the positive-sequence virtual impedance coefficient, and the negative-sequence virtual impedance coefficient. Step S6: Input the positive-sequence virtual impedance and negative-sequence virtual impedance into the distribution network to be controlled and reacquire the converter grid connection point voltage signal and converter grid connection point current signal, so as to redetermine the operating state of the distribution network to be controlled based on the reacquired converter grid connection point voltage signal and converter grid connection point current signal, until the operating state of the distribution network to be controlled is the normal operating state.

[0035] In this embodiment, fault identification and status classification of the distribution network are performed using the converter grid connection point voltage signal and converter grid connection point current signal, which can determine the operating status of the distribution network and provide a basis for subsequent targeted fault control. Next, by blocking the active power loop and reactive power loop and extracting several core characteristic parameters under asymmetrical fault operating conditions, it is possible to avoid exacerbating the distribution network imbalance and causing converter disconnection during dynamic adjustment of the power loop. Then, the positive-sequence virtual internal potential, negative-sequence virtual internal potential, and converter grid connection point voltage signal are used to calculate the positive-sequence virtual impedance coefficient and the negative-sequence virtual impedance coefficient, specifically: in, This represents the voltage difference between the positive-sequence virtual internal potential and the voltage signal at the converter's grid connection point. This represents the voltage difference between the negative-sequence virtual internal potential and the voltage signal at the converter's grid connection point. This represents the preset positive-sequence virtual resistance, and n represents the preset virtual impedance ratio. This indicates the preset maximum output current of the converter, typically taken as 1.2 times the rated output current of the converter. This is the positive-sequence virtual impedance coefficient. The negative-order virtual impedance coefficient, To pre-configure the grid current threshold, The rated output current of the converter is preset. Then, the positive-sequence virtual impedance and negative-sequence virtual impedance are obtained through the positive-sequence virtual impedance coefficient, the negative-sequence virtual impedance coefficient, and several core characteristic parameters under asymmetrical fault operation conditions. Specifically: in, For positive sequence virtual resistance, For positive sequence virtual inductance, For negative sequence virtual resistance, For negative sequence virtual inductance, To preset the rated virtual internal potential, This represents the positive-sequence d-axis voltage component of the converter. This represents the negative sequence d-axis voltage component of the converter. This represents the positive-sequence q-axis voltage component of the converter. The negative-sequence q-axis voltage component of the converter is used. The positive-sequence virtual resistance, positive-sequence virtual inductance, negative-sequence virtual resistance, and negative-sequence virtual inductance are calculated using the above formula. These are then used to obtain the positive-sequence and negative-sequence virtual impedances, which are applied to the control loop for current limiting. This provides control parameters to prevent the fault range from expanding and to stabilize the grid voltage. Finally, by applying the positive-sequence and negative-sequence virtual impedances and re-acquiring the converter grid connection point voltage and current signals, the controllable distribution network is continuously adjusted and its operating state is redefined until it returns to normal operation. This ultimately achieves stable control of the new distribution network under fault scenarios, ensuring its safe and efficient operation.

[0036] Furthermore, the operating state of the distribution network to be controlled includes asymmetrical fault operating state, symmetrical fault operating state, and normal operating state; the determination of the operating state of the distribution network to be controlled based on the converter grid connection point voltage signal and the converter grid connection point current signal includes: If the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is less than the preset transient current trigger threshold, then the distribution network to be controlled is in normal operation. If the converter grid connection point voltage signal is less than or equal to a preset transient voltage trigger threshold or the converter grid connection point current signal is greater than or equal to a preset transient current trigger threshold, then the converter grid connection point A phase voltage, converter grid connection point B phase voltage and converter grid connection point C phase voltage are obtained based on the converter grid connection point voltage signal. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, or the voltage of phase C at the converter grid connection point are not equal, then the distribution network to be controlled is in an asymmetrical fault operation state. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, and the voltage of phase C at the converter grid connection point are all equal, then the distribution network to be controlled is in a symmetrical fault operation state.

[0037] In this embodiment, the dual determination is made using the converter grid connection point voltage signal and a preset transient voltage trigger threshold, and the converter grid connection point current signal and a preset trigger threshold. Specifically: ,in, It is a transient voltage trigger signal, when its When the value is 1, transient power angle control is initiated. The voltage signal at the grid connection point of the converter is set to a preset transient voltage trigger threshold of 0.9pu (0.9 times the preset rated voltage). ,in, For transient current trigger signal, when When the value is 1, transient current control is initiated. The current signal at the converter's grid connection point is preset to a transient current trigger threshold of 1.2. Or 1.5 , Preset the rated current for the converter. Pre-set steady-state operating current for the distribution network; ,in, This is a transient operating signal, determined by both transient voltage and transient current signals. When either signal is activated, The value changes to 1, transitioning from normal operation to fault operation. By comparing the converter grid connection point voltage signal with a preset transient voltage trigger threshold, and the converter grid connection point current signal with a preset trigger threshold, the normal operation and fault operation states of the distribution network can be distinguished. This avoids ineffective control when the distribution network is fault-free, ensuring stable operation of the distribution network under normal conditions. Next, if the converter grid connection point voltage signal is less than or equal to the preset transient voltage trigger threshold, or the converter grid connection point current signal is greater than or equal to the preset transient current trigger threshold, then the voltages of phase A, phase B, and phase C at the converter grid connection point are extracted using the converter grid connection point voltage signal. Specifically: ,in, The voltage of phase A at the converter's grid connection point. The voltage of phase B at the converter's grid connection point. The voltage of phase C at the converter's grid connection point is used. The voltages of phase A, phase B, and phase C at the converter's grid connection point provide data support for detailed differentiation of subsequent fault operation states. Then, by determining whether the three-phase voltages at the converter's grid connection point are equal, it is possible to accurately identify whether the distribution network is in an asymmetrical or symmetrical fault operation state, providing a judgment condition for subsequently initiating corresponding fault control strategies.

[0038] Furthermore, it also includes: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the grid connection point of the converter is less than or equal to the preset transient voltage trigger threshold and the current signal at the grid connection point of the converter is less than the preset transient current trigger threshold, then the converter output voltage, grid-side voltage and real-time operating power angle are obtained. Calculate the unbalanced power of the distribution network based on the converter output voltage, grid-side voltage, and real-time operating power angle; Fault power adjustment commands are obtained based on the preset active power and unbalanced power of the distribution network. The power adjustment command is used to adjust the distribution network under control, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the distribution network under control is then re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the distribution network under control is normal operation.

[0039] In this embodiment, under symmetrical fault operation, when the converter grid connection point voltage signal is less than or equal to a preset transient voltage trigger threshold and the converter grid connection point current signal is less than a preset transient current trigger threshold, the core calculation parameters for subsequent transient power angle control can be collected by acquiring the converter output voltage, grid-side voltage, and real-time operating power angle, providing basic data support for subsequent unbalanced power calculation. Then, the unbalanced power of the distribution network is calculated using the converter output voltage, grid-side voltage, and real-time operating power angle, specifically: ,in, Indicates the unbalanced power in the distribution network. This is the output voltage of the converter. Indicates the grid-side voltage. To obtain the impedance of the distribution network lines, Indicates the preset rated power angle. The change in power angle can be calculated using the real-time operating power angle and the preset rated power angle. By calculating the unbalanced power of the distribution network, the power angle instability of the distribution network can be quantitatively analyzed, providing a quantitative basis for power angle stability control. Subsequently, fault power adjustment commands are obtained by preset active power and unbalanced power of the distribution network, specifically: ,in, This is a fault power adjustment command. The system presets the active power of the distribution network. By receiving fault power adjustment commands, the converters can be corrected to reduce unbalanced power and stabilize the power angle. Finally, the distribution network is adjusted using fault power adjustment commands, and the voltage and current signals at the converter grid connection points are re-acquired to reassess the distribution network's operating status until the distribution network returns to normal operation, thus preventing converter disconnection and the expansion of the fault range caused by power angle instability.

[0040] Furthermore, it also includes: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is greater than or equal to the preset transient current trigger threshold, then the voltage drop degree and the grid-side voltage are obtained. Fault voltage regulation commands are obtained based on the degree of voltage drop and grid-side voltage. The controllable distribution network is adjusted based on the fault voltage regulation command, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the controllable distribution network is then re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the controllable distribution network is normal.

[0041] In this embodiment, under symmetrical fault operation, when the converter grid-connected point voltage signal is greater than a preset transient voltage trigger threshold and the converter grid-connected point current signal is greater than or equal to a preset transient current trigger threshold, transient current control is initiated to obtain the voltage drop level and grid-side voltage, providing data support for the accurate calculation of fault voltage regulation commands. Since the current cannot be directly and independently regulated under the control framework of a grid-connected converter, it must be indirectly implemented through voltage commands. Initiating transient current control essentially transforms the constraint that the current does not exceed the threshold into a control command to adjust the grid-connected point voltage. Then, utilizing the relationship that the power angle is equal before and after the fault occurs under power angle control, the fault voltage regulation command is obtained through the voltage drop level and grid-side voltage, specifically: ,in, This is a fault voltage adjustment command. The equivalent voltage coupling coefficient is... , This indicates the preset rated voltage of the distribution network, and k represents the voltage drop level. Indicates the grid-side voltage. A preset steady-state operating current is established for the distribution network. Fault voltage regulation commands enable adaptive tuning of the distribution network fault voltage, achieving the control objectives of suppressing fault overcurrent and compensating for grid voltage dips. Then, the fault voltage regulation commands adjust the distribution network and re-acquire the voltage and current signals at the converter grid connection points to reassess the distribution network's operating status until it returns to normal operation. This prevents converter disconnection and fault range expansion caused by overcurrent, ensuring stable operation of the distribution network under fault scenarios.

[0042] Furthermore, the acquisition of the converter grid connection point voltage signal and the converter grid connection point current signal based on the distribution network to be controlled includes: Based on the distribution network to be controlled, acquire the initial voltage signal and the initial current signal of the converter grid connection point; The converter grid connection point initial voltage signal and the converter grid connection point initial current signal are low-pass filtered to obtain the converter grid connection point filtered voltage signal and the converter grid connection point filtered current signal. The converter grid connection point filter voltage signal and the converter grid connection point filter current signal are converted from analog to digital to obtain the converter grid connection point discrete voltage signal and the converter grid connection point discrete current signal. Both the discrete voltage signal and the discrete current signal at the grid connection point of the converter are subjected to sliding filtering and low-pass filtering to obtain the voltage signal and current signal at the grid connection point of the converter.

[0043] In this embodiment, acquiring the initial voltage and current signals at the converter grid connection point provides a data foundation for subsequent signal processing and fault diagnosis. Next, low-pass filtering of these signals suppresses high-frequency electromagnetic interference and switching ripple, preserves the fundamental effective component, and improves the original signal quality, thus acquiring the filtered voltage and current signals at the converter grid connection point. Then, analog-to-digital conversion (ADC) transforms these signals into discrete digital signals to meet subsequent digital computation and processing requirements. Finally, by performing sliding filtering and low-pass filtering on both the discrete voltage signal and discrete current signal at the converter grid connection point, random measurement noise and residual high-frequency harmonics in the digital signals can be filtered out twice, resulting in the converter grid connection point voltage signal and converter grid connection point current signal. This provides accurate and reliable data support for subsequent determination of distribution network fault status and calculation of control parameters, avoiding control errors and fault misjudgments caused by signal distortion.

[0044] This embodiment provides a fault control system for a power distribution network. Please refer to [link / reference]. Figure 2It includes a signal acquisition module, a fault status determination module, a virtual internal potential extraction module, a virtual impedance coefficient calculation module, a virtual impedance solution module, and a distribution network restoration module, specifically: The signal acquisition module is used to acquire the voltage signal and current signal of the converter grid connection point based on the distribution network to be controlled. The fault status determination module is used to determine the operating status of the distribution network to be controlled based on the voltage signal and current signal of the converter grid connection point. If the operating state of the distribution network to be controlled is an asymmetrical fault operating state, the virtual internal potential extraction module is used to lock the active power loop and the reactive power loop of the distribution network to obtain the positive sequence d-axis voltage component, positive sequence q-axis voltage component, negative sequence d-axis voltage component, negative sequence q-axis voltage component, positive sequence virtual internal potential, and negative sequence virtual internal potential of the converter. The virtual impedance coefficient calculation module is used to calculate the positive-sequence virtual impedance coefficient and the negative-sequence virtual impedance coefficient based on the positive-sequence virtual internal potential, the negative-sequence virtual internal potential and the voltage signal at the converter grid connection point. The virtual impedance calculation module is used to calculate the positive-sequence virtual impedance and the negative-sequence virtual impedance based on the positive-sequence d-axis voltage component of the converter, the positive-sequence q-axis voltage component of the converter, the negative-sequence d-axis voltage component of the converter, the negative-sequence q-axis voltage component of the converter, the positive-sequence virtual impedance coefficient, and the negative-sequence virtual impedance coefficient. The distribution network recovery module is used to input the positive-sequence virtual impedance and negative-sequence virtual impedance into the distribution network to be controlled and reacquire the voltage signal and current signal of the converter grid connection point, so as to redetermine the operating state of the distribution network to be controlled based on the reacquired voltage signal and current signal of the converter grid connection point, until the operating state of the distribution network to be controlled is the normal operating state.

[0045] This embodiment provides a fault control system for a distribution network. In practical applications, only a fault state determination module is needed. This module identifies and classifies distribution network faults using the voltage and current signals at the converter grid connection point, determining the network's operating status and providing a basis for subsequent targeted fault control. Next, a virtual internal potential extraction module is used. By blocking the active and reactive power loops and extracting several core characteristic parameters during asymmetrical fault operation, this avoids exacerbating network imbalance and causing converter disconnection during dynamic adjustment of the power loop. Then, a virtual impedance coefficient calculation module is used to calculate the positive and negative sequence virtual impedance coefficients using the positive-sequence virtual internal potential, negative-sequence virtual internal potential, and converter grid connection point voltage signal. Finally, a virtual impedance solving module is used to obtain the positive-sequence and negative-sequence virtual impedances using these coefficients and several core characteristic parameters during asymmetrical fault operation. This provides control parameters to prevent the fault range from expanding and to stabilize the grid voltage. Finally, a distribution network recovery module is used. By inputting positive-sequence virtual impedance and negative-sequence virtual impedance and re-acquiring the voltage signal and current signal of the converter grid connection point, the distribution network under control is continuously adjusted and its operating state is redefined until it is restored to normal operation. This ultimately achieves stable control of the new distribution network under fault scenarios and ensures its safe and efficient operation.

[0046] Furthermore, the operating state of the distribution network to be controlled includes an asymmetrical fault operating state, a symmetrical fault operating state, and a normal operating state; the fault state determination module is used to determine the operating state of the distribution network to be controlled based on the converter grid connection point voltage signal and the converter grid connection point current signal, including: If the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is less than the preset transient current trigger threshold, then the distribution network to be controlled is in normal operation. If the converter grid connection point voltage signal is less than or equal to a preset transient voltage trigger threshold or the converter grid connection point current signal is greater than or equal to a preset transient current trigger threshold, then the converter grid connection point A phase voltage, converter grid connection point B phase voltage and converter grid connection point C phase voltage are obtained based on the converter grid connection point voltage signal. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, or the voltage of phase C at the converter grid connection point are not equal, then the distribution network to be controlled is in an asymmetrical fault operation state. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, and the voltage of phase C at the converter grid connection point are all equal, then the distribution network to be controlled is in a symmetrical fault operation state.

[0047] In this embodiment, by using both the converter grid-connected point voltage signal and a preset transient voltage trigger threshold, and the converter grid-connected point current signal and a preset trigger threshold, the normal operation and fault operation states of the distribution network can be distinguished. This avoids ineffective control when the distribution network is fault-free, ensuring the stable operation of the distribution network under normal operating conditions. Next, if the converter grid-connected point voltage signal is less than or equal to the preset transient voltage trigger threshold, or the converter grid-connected point current signal is greater than or equal to the preset transient current trigger threshold, the voltages of phase A, phase B, and phase C at the converter grid-connected point are extracted from the converter grid-connected point voltage signal, providing data support for detailed differentiation of subsequent fault operation states. Then, by determining whether the three-phase voltages at the converter grid-connected point are equal, the distribution network can be accurately identified as being in an asymmetrical or symmetrical fault operation state, providing a judgment condition for subsequently initiating the corresponding fault control strategy.

[0048] Furthermore, it also includes a power regulation module: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the grid connection point of the converter is less than or equal to the preset transient voltage trigger threshold and the current signal at the grid connection point of the converter is less than the preset transient current trigger threshold, then the power regulation module is used to obtain the converter output voltage, grid side voltage and real-time operating power angle. The power regulation module is used to calculate the unbalanced power of the distribution network based on the converter output voltage, grid-side voltage and real-time operating power angle. The power regulation module is used to obtain fault power regulation instructions based on the preset active power of the distribution network and the unbalanced power of the distribution network. The distribution network recovery module is used to adjust the distribution network to be controlled based on the fault power adjustment command, and to reacquire the voltage signal and current signal of the converter grid connection point, so as to redetermine the operating state of the distribution network to be controlled based on the reacquired voltage signal and current signal of the converter grid connection point, until the operating state of the distribution network to be controlled is the normal operating state.

[0049] In this embodiment, under symmetrical fault operation, when the converter grid-connected voltage signal is less than or equal to a preset transient voltage trigger threshold and the converter grid-connected current signal is less than a preset transient current trigger threshold, the power regulation module acquires the converter output voltage, grid-side voltage, and real-time operating power angle. This allows for the collection of core calculation parameters for subsequent transient power angle control, providing fundamental data support for subsequent unbalanced power calculation. Then, by calculating the distribution network unbalanced power using the converter output voltage, grid-side voltage, and real-time operating power angle, quantitative analysis of distribution network power angle instability can be performed, providing a quantitative basis for power angle stability control. Subsequently, by acquiring fault power regulation commands based on preset distribution network active power and distribution network unbalanced power, the converter can be corrected to reduce unbalanced power and stabilize the power angle. Finally, the distribution network is adjusted using fault power regulation commands, and the converter grid-connected voltage and current signals are re-acquired to re-determine the distribution network operating state until the distribution network returns to normal operation, preventing converter disconnection and fault range expansion caused by power angle instability.

[0050] Furthermore, it also includes a voltage regulation module: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is greater than or equal to the preset transient current trigger threshold, then the voltage regulation module is used to obtain the voltage drop degree and the grid-side voltage. The voltage regulation module is used to obtain fault voltage regulation commands based on the degree of voltage drop and the grid-side voltage; The distribution network recovery module is used to adjust the distribution network to be controlled based on the fault voltage adjustment command, and to reacquire the converter grid connection point voltage signal and converter grid connection point current signal, so as to re-determine the operating state of the distribution network to be controlled based on the reacquired converter grid connection point voltage signal and converter grid connection point current signal, until the operating state of the distribution network to be controlled is a normal operating state.

[0051] In this embodiment, under symmetrical fault operation, when the converter grid-connected point voltage signal is greater than a preset transient voltage trigger threshold and the converter grid-connected point current signal is greater than or equal to a preset transient current trigger threshold, the voltage regulation module acquires the voltage drop level and grid-side voltage, providing data support for the accurate calculation of the fault voltage regulation command. Then, by acquiring the fault voltage regulation command through the voltage drop level and grid-side voltage, the fault voltage command for the distribution network can be adaptively tuned, achieving the control objectives of suppressing fault overcurrent and compensating for grid voltage drops. Next, the distribution network is adjusted using the fault voltage regulation command, and the converter grid-connected point voltage signal and converter grid-connected point current signal are re-acquired to re-determine the distribution network operating state until the distribution network returns to normal operation, preventing converter disconnection and fault range expansion caused by overcurrent, and ensuring stable operation of the distribution network under fault scenarios.

[0052] Furthermore, the signal acquisition module is used to acquire the converter grid connection point voltage signal and the converter grid connection point current signal based on the distribution network to be controlled, including: Based on the distribution network to be controlled, acquire the initial voltage signal and the initial current signal of the converter grid connection point; The converter grid connection point initial voltage signal and the converter grid connection point initial current signal are low-pass filtered to obtain the converter grid connection point filtered voltage signal and the converter grid connection point filtered current signal. The converter grid connection point filter voltage signal and the converter grid connection point filter current signal are converted from analog to digital to obtain the converter grid connection point discrete voltage signal and the converter grid connection point discrete current signal. Both the discrete voltage signal and the discrete current signal at the grid connection point of the converter are subjected to sliding filtering and low-pass filtering to obtain the voltage signal and current signal at the grid connection point of the converter.

[0053] In this embodiment, acquiring the initial voltage and current signals at the converter grid connection point provides a data foundation for subsequent signal processing and fault diagnosis. Next, low-pass filtering of these signals suppresses high-frequency electromagnetic interference and switching ripple, preserves the fundamental effective component, and improves the original signal quality, thus acquiring the filtered voltage and current signals at the converter grid connection point. Then, analog-to-digital conversion (ADC) transforms these signals into discrete digital signals to meet subsequent digital computation and processing requirements. Finally, by performing sliding filtering and low-pass filtering on both the discrete voltage signal and discrete current signal at the converter grid connection point, random measurement noise and residual high-frequency harmonics in the digital signals can be filtered out twice, resulting in the converter grid connection point voltage signal and converter grid connection point current signal. This provides accurate and reliable data support for subsequent determination of distribution network fault status and calculation of control parameters, avoiding control errors and fault misjudgments caused by signal distortion.

[0054] To more intuitively and fully illustrate how the fault control method for distribution networks provided in this embodiment can avoid the problems of converter disconnection and fault range expansion in new distribution networks during faults, achieve stable control of new distribution networks under fault scenarios, and ensure the safe and efficient operation of new distribution networks, the following embodiments are provided for specific explanation: A simulation model of a single-unit grid-connected converter system using virtual synchronous machine control was built in Matlab / Simulink. The preset simulation parameters are shown in Tables 1 and 2 below. =21.42A, =1.099Ω, = =311, n=5, positive sequence current setting value It is 1 pu. The converter has a rated active power of 10kW, a rated output voltage of 220V, and a preset frequency of 50Hz.

[0055] Table 1 Parameters of the main circuit of the new distribution network Table 2 Line Parameters To verify that transient current control is initiated when the transient current trigger signal is 1 during symmetrical fault operation, the three-phase voltage drop at the converter grid connection point is set to 0.6 pu at 0.5 s. The fault current waveform during a three-phase symmetrical fault is as follows: Figure 3As shown, the fault is cleared in 1.3s; therefore, the fault voltage regulation command can be calculated. =212V.

[0056] To verify the asymmetrical fault control, the voltage drop of phase A at the converter grid connection point was set to 0.6 pu at 0.5 s. The fault current waveform when an asymmetrical fault occurs is as follows: Figure 4 As shown, the fault is cleared in 1.3s; therefore, the calculation yields... =0.8, =0.145, and then the positive sequence virtual impedance and negative sequence virtual impedance are calculated using the positive sequence virtual impedance coefficient and negative sequence virtual impedance coefficient, and then put into the control loop for current limiting to prevent the fault range from expanding and to provide control parameters for stabilizing the grid voltage.

[0057] This embodiment also provides a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the functions of the system as described above.

[0058] It is understood that the above system item embodiments correspond to the method item embodiments of the present invention, and can implement the fault control method for power distribution network provided by any of the above method item embodiments of the present invention.

[0059] It should be noted that the system embodiments described above are merely illustrative, and some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0060] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A fault control method for a power distribution network, characterized in that, include: Based on the distribution network to be controlled, acquire the voltage signal and current signal of the converter grid connection point; The operating status of the distribution network to be controlled is determined based on the voltage signal and current signal at the grid connection point of the converter. If the operating state of the distribution network to be controlled is an asymmetrical fault operating state, then the active power loop and the reactive power loop of the distribution network are locked to obtain the positive sequence d-axis voltage component, the positive sequence q-axis voltage component, the negative sequence d-axis voltage component, the negative sequence q-axis voltage component, the positive sequence virtual internal potential, and the negative sequence virtual internal potential of the converter. Calculate the positive-sequence virtual internal potential, the negative-sequence virtual internal potential, and the converter grid connection point voltage signal based on the positive-sequence virtual internal potential, the negative-sequence virtual internal potential, and the converter grid connection point voltage signal. Calculate the positive-sequence virtual impedance and negative-sequence virtual impedance based on the positive-sequence d-axis voltage component, the positive-sequence q-axis voltage component, the negative-sequence d-axis voltage component, the negative-sequence q-axis voltage component, the positive-sequence virtual impedance coefficient, and the negative-sequence virtual impedance coefficient of the converter; The positive-sequence virtual impedance and negative-sequence virtual impedance are introduced into the distribution network to be controlled, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the distribution network to be controlled is re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the distribution network to be controlled is normal operation.

2. The fault control method for a power distribution network according to claim 1, characterized in that, The operating state of the distribution network to be controlled includes asymmetrical fault operating state, symmetrical fault operating state, and normal operating state; determining the operating state of the distribution network to be controlled based on the converter grid connection point voltage signal and the converter grid connection point current signal includes: If the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is less than the preset transient current trigger threshold, then the distribution network to be controlled is in normal operation. If the converter grid connection point voltage signal is less than or equal to a preset transient voltage trigger threshold or the converter grid connection point current signal is greater than or equal to a preset transient current trigger threshold, then the converter grid connection point A phase voltage, converter grid connection point B phase voltage and converter grid connection point C phase voltage are obtained based on the converter grid connection point voltage signal. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, or the voltage of phase C at the converter grid connection point are not equal, then the distribution network to be controlled is in an asymmetrical fault operation state. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, and the voltage of phase C at the converter grid connection point are all equal, then the distribution network to be controlled is in a symmetrical fault operation state.

3. The fault control method for a power distribution network according to claim 2, characterized in that, Also includes: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the grid connection point of the converter is less than or equal to the preset transient voltage trigger threshold and the current signal at the grid connection point of the converter is less than the preset transient current trigger threshold, then the converter output voltage, grid-side voltage and real-time operating power angle are obtained. Calculate the unbalanced power of the distribution network based on the converter output voltage, grid-side voltage, and real-time operating power angle; Fault power adjustment commands are obtained based on the preset active power and unbalanced power of the distribution network. The power adjustment command is used to adjust the distribution network under control, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the distribution network under control is then re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the distribution network under control is normal operation.

4. The fault control method for a power distribution network according to claim 2, characterized in that, Also includes: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is greater than or equal to the preset transient current trigger threshold, then the voltage drop degree and the grid-side voltage are obtained. Fault voltage regulation commands are obtained based on the degree of voltage drop and grid-side voltage. The controllable distribution network is adjusted based on the fault voltage regulation command, and the voltage signal and current signal of the converter grid connection point are reacquired. The operating state of the controllable distribution network is then re-determined based on the reacquired voltage signal and current signal of the converter grid connection point until the operating state of the controllable distribution network is normal.

5. The fault control method for a power distribution network according to claim 1, characterized in that, The acquisition of the converter grid connection point voltage signal and converter grid connection point current signal based on the distribution network to be controlled includes: Based on the distribution network to be controlled, acquire the initial voltage signal and the initial current signal of the converter grid connection point; The converter grid connection point initial voltage signal and the converter grid connection point initial current signal are low-pass filtered to obtain the converter grid connection point filtered voltage signal and the converter grid connection point filtered current signal. The converter grid connection point filter voltage signal and the converter grid connection point filter current signal are converted from analog to digital to obtain the converter grid connection point discrete voltage signal and the converter grid connection point discrete current signal. Both the discrete voltage signal and the discrete current signal at the grid connection point of the converter are subjected to sliding filtering and low-pass filtering to obtain the voltage signal and current signal at the grid connection point of the converter.

6. A fault control system for a power distribution network, characterized in that, It includes a signal acquisition module, a fault status determination module, a virtual internal potential extraction module, a virtual impedance coefficient calculation module, a virtual impedance solution module, and a distribution network restoration module, specifically: The signal acquisition module is used to acquire the voltage signal and current signal of the converter grid connection point based on the distribution network to be controlled. The fault status determination module is used to determine the operating status of the distribution network to be controlled based on the voltage signal and current signal of the converter grid connection point. If the operating state of the distribution network to be controlled is an asymmetrical fault operating state, the virtual internal potential extraction module is used to lock the active power loop and the reactive power loop of the distribution network to obtain the positive sequence d-axis voltage component, positive sequence q-axis voltage component, negative sequence d-axis voltage component, negative sequence q-axis voltage component, positive sequence virtual internal potential, and negative sequence virtual internal potential of the converter. The virtual impedance coefficient calculation module is used to calculate the positive-sequence virtual impedance coefficient and the negative-sequence virtual impedance coefficient based on the positive-sequence virtual internal potential, the negative-sequence virtual internal potential and the voltage signal at the converter grid connection point. The virtual impedance calculation module is used to calculate the positive-sequence virtual impedance and the negative-sequence virtual impedance based on the positive-sequence d-axis voltage component of the converter, the positive-sequence q-axis voltage component of the converter, the negative-sequence d-axis voltage component of the converter, the negative-sequence q-axis voltage component of the converter, the positive-sequence virtual impedance coefficient, and the negative-sequence virtual impedance coefficient. The distribution network recovery module is used to input the positive-sequence virtual impedance and negative-sequence virtual impedance into the distribution network to be controlled and reacquire the voltage signal and current signal of the converter grid connection point, so as to redetermine the operating state of the distribution network to be controlled based on the reacquired voltage signal and current signal of the converter grid connection point, until the operating state of the distribution network to be controlled is the normal operating state.

7. A fault control system for a power distribution network according to claim 6, characterized in that, The operating states of the distribution network to be controlled include asymmetrical fault operating state, symmetrical fault operating state, and normal operating state; The fault status determination module is used to determine the operating status of the distribution network to be controlled based on the voltage signal and current signal at the converter grid connection point, including: If the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is less than the preset transient current trigger threshold, then the distribution network to be controlled is in normal operation. If the converter grid connection point voltage signal is less than or equal to a preset transient voltage trigger threshold or the converter grid connection point current signal is greater than or equal to a preset transient current trigger threshold, then the converter grid connection point A phase voltage, converter grid connection point B phase voltage and converter grid connection point C phase voltage are obtained based on the converter grid connection point voltage signal. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, or the voltage of phase C at the converter grid connection point are not equal, then the distribution network to be controlled is in an asymmetrical fault operation state. If the voltage of phase A at the converter grid connection point, the voltage of phase B at the converter grid connection point, and the voltage of phase C at the converter grid connection point are all equal, then the distribution network to be controlled is in a symmetrical fault operation state.

8. A fault control system for a power distribution network according to claim 7, characterized in that, It also includes a power regulation module: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the grid connection point of the converter is less than or equal to the preset transient voltage trigger threshold and the current signal at the grid connection point of the converter is less than the preset transient current trigger threshold, then the power regulation module is used to obtain the converter output voltage, grid side voltage and real-time operating power angle. The power regulation module is used to calculate the unbalanced power of the distribution network based on the converter output voltage, grid-side voltage and real-time operating power angle. The power regulation module is used to obtain fault power regulation instructions based on the preset active power of the distribution network and the unbalanced power of the distribution network. The distribution network recovery module is used to adjust the distribution network to be controlled based on the fault power adjustment command, and to reacquire the voltage signal and current signal of the converter grid connection point, so as to redetermine the operating state of the distribution network to be controlled based on the reacquired voltage signal and current signal of the converter grid connection point, until the operating state of the distribution network to be controlled is the normal operating state.

9. A fault control system for a power distribution network according to claim 7, characterized in that, It also includes a voltage regulation module: If the operating state of the distribution network to be controlled is a symmetrical fault operating state, and the voltage signal at the converter grid connection point is greater than the preset transient voltage trigger threshold and the current signal at the converter grid connection point is greater than or equal to the preset transient current trigger threshold, then the voltage regulation module is used to obtain the voltage drop degree and the grid-side voltage. The voltage regulation module is used to obtain fault voltage regulation commands based on the degree of voltage drop and the grid-side voltage; The distribution network recovery module is used to adjust the distribution network to be controlled based on the fault voltage adjustment command, and to reacquire the converter grid connection point voltage signal and converter grid connection point current signal, so as to re-determine the operating state of the distribution network to be controlled based on the reacquired converter grid connection point voltage signal and converter grid connection point current signal, until the operating state of the distribution network to be controlled is a normal operating state.

10. A fault control system for a power distribution network according to claim 6, characterized in that, The signal acquisition module is used to acquire the voltage signal and current signal at the grid connection point of the converter based on the distribution network to be controlled, including: Based on the distribution network to be controlled, acquire the initial voltage signal and the initial current signal of the converter grid connection point; The converter grid connection point initial voltage signal and the converter grid connection point initial current signal are low-pass filtered to obtain the converter grid connection point filtered voltage signal and the converter grid connection point filtered current signal. The converter grid connection point filter voltage signal and the converter grid connection point filter current signal are converted from analog to digital to obtain the converter grid connection point discrete voltage signal and the converter grid connection point discrete current signal. Both the discrete voltage signal and the discrete current signal at the grid connection point of the converter are subjected to sliding filtering and low-pass filtering to obtain the voltage signal and current signal at the grid connection point of the converter.

Images