Fault positioning method using opposite-end grid-connected converter negative sequence suppression strategy

Abstract

The invention discloses a fault positioning method using a negative sequence suppression strategy of an opposite-end grid-connected converter, and the method specifically comprises the steps: 1, enabling a new energy system to be connected to a transmission line of an AC system, carrying out the starting judgment when the transmission line has a single-phase grounding fault, and enabling a starting element to act when a starting criterion is met; step 2, adopting a power frequency fault sequence component phase difference on a fault line to realize fault phase selection, extracting three-phase voltage and current phasors, and decomposing the three-phase voltage and current phasors into symmetrical sequence components; step 3, the new energy system switches a control strategy to obtain positive and negative sequence components, and a negative sequence current strategy is adopted to construct an open circuit condition as a control constraint; and 4, constructing a composite network diagram, and calculating a fault distance. According to the invention, the problem of inaccurate line fault positioning in the existing fault positioning method is solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power transmission line fault location, and particularly relates to a fault location method using a negative sequence suppression strategy of a grid-connected converter at the opposite end. BACKGROUND

[0002] New energy power generation technology is developing rapidly, and the installed capacity of new energy power sources represented by photovoltaic and wind power is rapidly increasing, which has become the main development direction of global energy transformation. New energy units represented by direct-drive wind turbines and photovoltaic devices are increasingly applied in power grids, and their impact on power grid protection is becoming more and more significant.

[0003] New energy units are connected to the grid through power electronic devices, and the power electronic devices have flexible regulation and control capabilities. The inherent characteristics of power electronic devices result in the short-circuit current during power system faults, which is significantly different from the characteristics of synchronous generators, such as limited amplitude, non-power frequency, and controlled phase. The characteristics of line faults change, and the traditional relay protection principle based on power frequency steady-state quantities faces severe challenges. The traditional fault location method is based on the assumption that the phase of the fault point current is consistent with that of the measuring point current, and is only applicable when the phase of the power source and the line impedance is similar. When one end of the line is connected to a power electronic device, due to the high controllability of the power electronic device, the fault current phase at the new energy side is controlled, and the amplitude is controlled. At this time, the assumption that the phase of the fault point current is consistent with that of the measuring point current no longer holds, and accurate fault location of the line cannot be achieved. Moreover, the traditional fault location method focuses on solving the problem of the opposite side system being a traditional synchronous generator system. When the opposite side system is a power electronic system, the parameters to be identified in the opposite side system are affected by the control strategy of the power electronic device before and after the fault, and have time-varying characteristics, which cannot be accurately identified. For the scenario where the opposite end of the line is connected to a new energy source through a power electronic device, when a single-phase ground fault occurs, the existing fault location method has poor transition resistance resistance, inaccurate identification of the opposite side system parameters, and inaccurate fault location. SUMMARY

[0004] The purpose of the application is to provide a line fault location method using a negative sequence suppression strategy of a grid-connected converter at the opposite end, which solves the problem of inaccurate line fault location caused by the inability to identify the parameters of the opposite side system and poor transition resistance resistance in the existing fault location method.

[0005] The technical solution adopted by the application is a fault location method using a negative sequence suppression strategy of a grid-connected converter at the opposite end, which is implemented according to the following steps: Step 1, when a new energy system is connected to an AC system through an AC transmission line, and a single-phase ground fault occurs in the transmission line, a start-up judgment is performed on the fault line. When the start-up criterion is met, the start-up element operates. Step 2, the phase selection of fault is realized by using the phase difference of power frequency fault sequence component on the fault line, and the three-phase voltage and current phasors under power frequency are extracted and decomposed into symmetrical sequence components; Step 3, the new energy system switching control strategy is obtained, the open circuit condition is constructed by using the negative sequence current strategy as a control constraint; Step 4, the composite network graph is constructed by using the control constraint and the sequence component, and the fault distance is calculated.

[0006] The application also has the characteristics of, Step 1, the new energy system is used as a counter element, specifically for the centralized photovoltaic sending line scene, including the photovoltaic grid-connected topological structure, the photovoltaic grid-connected topological structure includes a photovoltaic panel, the photovoltaic panel is connected through a direct current boost circuit Boost module, the direct current side voltage level is improved, then a converter is connected, the converter is connected to a controller, the converter is inverted to an alternating current system, the alternating current system includes a transformer T1 and a transformer T2, the voltage level of the alternating current side is improved through the transformer T1 and the transformer T2, the transformer T2 is finally connected to a 110kV alternating current sending line, the fault line to be measured in the 110kV alternating current sending line is L1, the measuring point on one side of the fault line L1 is denoted as K 1m , the measuring point on the other side of the fault line L1 is denoted as K 1n , the fault point between the measuring points K 1m and K 1n is denoted as f 1, the back side of the measuring point K 1m is a large grid Grid of the alternating current system, and the counter element of the line on which the measuring point K 1n is located is the photovoltaic grid-connected topological structure.

[0007] When a single-phase ground fault occurs in the alternating current sending line of the alternating current system, starting judgment is performed on the measuring point K 1m of the fault line L1, and when the following starting criterion is met, the starting element acts; (1) , wherein, the voltage amplitude in the time domain collected by the measuring point K1m, is the rated voltage of the normal operation of the alternating current system, t is the time after the fault occurs.

[0008] Step 2, on the measuring point K 1m of the fault line L1, the phase selection element realizes fault selection by using the phase difference of the power frequency fault sequence component, and then extracts the three-phase voltage and current phasors under power frequency; the three-phase voltage phasors are respectively , and the three-phase current phasors are respectively ; The extracted phase voltage and phase current are respectively decomposed into three groups of symmetrical sequence components with the fault phase as the reference by using the symmetrical component method, and are respectively positive sequence voltage, negative sequence voltage, zero sequence voltage, positive sequence current, negative sequence current and zero sequence current, so as to realize decoupling of mutual inductance elements in the line parameter; (2) Wherein, The formula represents the electrical quantity under three-phase components, The formula represents the electrical quantity under positive sequence, negative sequence and zero sequence components, and α is the complex representation of 120° phase angle difference.

[0009] Step 3 is specifically, Step 3.1, after starting step 1, the converter on the AC side of the photovoltaic grid-connected access is used as the grid-side converter, and the voltage drop of the grid-connected point is detected at the measuring point K of the fault line L1 1n , the controller of the grid-side converter is switched from the normal operation mode to the low voltage ride through mode, and the controller of the grid-side converter collects the voltage and current of the grid-connected point respectively; Step 3.2, the voltage and current collected in step 3.1 are respectively separated into positive sequence components and negative sequence components; Step 3.3, the negative sequence current suppression strategy is adopted for the negative sequence components separated in step 3.2, the negative sequence current at the outlet of the grid-side converter is approximately equal to zero, and an open circuit condition is constructed in the negative sequence network, and the photovoltaic side is approximately equivalent to an open circuit.

[0010] When the negative sequence current suppression strategy is adopted, PI control is designed in the negative sequence coordinate system, the output voltage of the converter is adjusted to offset the negative sequence component in the voltage of the fault line L1; In the rotating coordinate system, the d-axis negative sequence current and the q-axis negative sequence current are suppressed respectively, the reference value is set to 0, and the negative feedback control is carried out through the PI control link to realize the difference-free adjustment, and the output result is the negative sequence voltage, which is then used as the modulation wave to enter the modulation link.

[0011] The negative sequence voltage is calculated as: (3) Wherein, , The negative sequence inner loop current on the d-axis and the q-axis respectively, ω is the angular velocity under power frequency, L is the equivalent inductance of the converter, , The negative sequence voltage output on the d-axis and the q-axis respectively, is a complex frequency domain variable, Kp is the proportional parameter of PI control, Ki is the integral parameter of PI control, , negative sequence components of the d-axis and q-axis grid-side voltages, respectively; The control result under PI control, after the fault occurs, K 1n The negative sequence current of the measuring point, which is attenuated to 0 on the d-axis and q-axis respectively through the negative sequence current suppression strategy, achieves the control effect.

[0012] Step 4 is specifically, Step 4.1, according to the boundary condition of single-phase grounding fault, on the fault line L1, a composite sequence network graph of series connection of positive sequence, negative sequence and zero sequence network is constructed, the positive sequence, negative sequence and zero sequence network are connected in series as a series branch, each series branch is a fault branch, and three transition resistors are connected in series between the three fault branches, 、 and represent the positive sequence, negative sequence and zero sequence components of the voltage at the fault branch, respectively, is the transition resistance of the fault branch; 、 and represent the positive sequence, negative sequence and zero sequence components of the voltage at the measuring point K 1m , respectively, 、 and represent the positive sequence, negative sequence and zero sequence components of the voltage at the measuring point K 1m , respectively, 、 and represent the positive sequence, negative sequence and zero sequence components of the current at the measuring point K 1n , respectively, The unit line impedance of the positive sequence, negative sequence and zero sequence of the fault line L1 is 、 and , the equivalent positive sequence, negative sequence and zero sequence impedance of the grid side in the alternating current system is 、 and , the equivalent source potential of the grid side is ; the equivalent positive sequence and zero sequence impedance of the photovoltaic grid-connected topology is and , and the equivalent source potential of the photovoltaic grid-connected topology is ; L is the full length of the fault line L1, d is the fault distance, 、 and represent the positive sequence, negative sequence and zero sequence total impedance from the measuring point K 1m to the fault point, respectively, 、 and They represent measuring point K respectively. 1n The total impedance of positive sequence, negative sequence, and zero sequence to the fault point.

[0013] Step 4.2: Based on the circuit relationship of the composite sequence network diagram in Step 4.1, obtain the measurement point K. 1m The measured negative sequence current is equal to the negative sequence current at the faulty branch, that is: (4); Total current at the faulty branch for: (5); Taking a single-phase ground fault as an example (phase A grounding), from measuring point K... 1m At the measuring point, calculate the equivalent impedance of the faulty line L1 to be measured. ; (6); (7) in, The zero-order compensation coefficient is... , These are the zero-sequence and positive-sequence unit line impedances of the faulty line L1, respectively. K 1m Positive, negative, and zero-sequence fault currents measured at the measuring points; The negative sequence current of the faulty branch; These are the voltage and current of the phase A ground fault, respectively; After transition resistance During a short circuit, the equivalent impedance of the faulty line L1 to be measured is... for; (8) in, For K 1m The measured current obtained at the measuring point, For from K 1m The line impedance from the measuring point to the fault point is used to obtain information about the fault distance. d Transition resistance The complex equation is: (9) Decompose the complex equation into real and imaginary part equations, and the distance to the fault. d for; (10) Where Re represents the real part and Im represents the imaginary part of the equation.

[0014] The converter adopts a two-level voltage source type converter.

[0015] The beneficial effects of this invention are as follows: This invention utilizes the fault location method based on the negative sequence suppression strategy of the grid-connected converter at the opposite end. Taking advantage of the high controllability of new energy power electronic equipment, when a single-phase ground fault occurs on the new energy transmission line, the control strategy constraints for power electronic equipment faults are introduced, thereby constructing a composite sequence network diagram during the fault period. The negative sequence network on the new energy side is open, achieving the purpose of fault location using only single-end electrical quantities without communication, which greatly improves the accuracy. Attached Figure Description

[0016] Figure 1 This is a flowchart of the fault location method of the present invention that utilizes the negative sequence suppression strategy of the grid-connected converter at the opposite end; Figure 2 This is a connection model diagram of the 110kV centralized photovoltaic transmission line in Embodiment 2 of the present invention; Figure 3 This is a diagram of the negative sequence current suppression module of the grid-connected inverter controller of the present invention; Figure 4 This is a dynamic response curve of the d-axis negative sequence current under the negative sequence current suppression strategy of this invention; Figure 5 This is a dynamic response curve of the q-axis negative sequence current under the negative sequence current suppression strategy of this invention; Figure 6 This is the composite sequence network diagram constructed in Embodiment 2 of the present invention; Figure 7 This is a comparison chart of actual error and standard error in the simulation test of this invention. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0018] Example 1 This invention utilizes a fault location method based on the negative sequence suppression strategy of the peer-end grid-connected converter. The process is as follows: Figure 1 As shown, the specific implementation steps are as follows: Step 1: The new energy system is connected to the AC transmission line of the AC system. When a single-phase ground fault occurs on the transmission line, the faulty line is judged for starting. When the starting criteria are met, the starting element is activated. Step 2: On the faulty line, the phase difference of the power frequency fault sequence component is used to select the fault phase, extract the three-phase voltage and current phasors under the power frequency, and decompose them into symmetrical sequence components. Step 3: The new energy system switching control strategy is used to obtain positive and negative sequence components. The negative sequence current strategy is used to construct open circuit conditions as control constraints. Step 4: Construct a composite network graph using control constraints and order components, and calculate the fault distance.

[0019] Example 2 This invention utilizes a fault location method based on the negative sequence suppression strategy of the peer-end grid-connected converter, and is implemented according to the following steps: Step 1: When a single-phase ground fault occurs on the new energy transmission line, the new energy system is connected to the line as the counterpart element and connected to the AC system. The AC system performs a start-up judgment on the AC transmission line with the AC fault. When the start-up criteria are met, the start-up element is activated. The new energy system serves as the counterparty component, specifically in the scenario of centralized photovoltaic transmission lines, such as... Figure 2 As shown, the topology includes a photovoltaic (PV) grid-connected system. The PV panels are connected to a DC-DC boost module to increase the DC voltage level, which is then connected to an inverter. The inverter connects to a controller and inverts the voltage to an AC system. The AC system includes transformers T1 and T2, which further increase the AC voltage level. Transformer T2 is finally connected to a 110kV AC transmission line. The fault line to be measured in the 110kV AC transmission line is L1. The location of the measuring point on one side of fault line L1 is denoted as K. 1m The location of the measuring point is on the other side of the faulty line L1, denoted as K. 1n Measurement point K 1m and K 1n The fault point between them is denoted as f 1. Measuring point K 1m The location is on the back side of a large AC power grid, measuring point K. 1n The opposite end of the line is a photovoltaic grid-connected topology.

[0020] Step 2: On the faulty line, the phase difference of the power frequency fault sequence component is used to select the fault phase, extract the three-phase voltage and current phasors under the power frequency, and decompose them into symmetrical sequence components. Step 3: The new energy system switching control strategy is used to obtain positive and negative sequence components. The negative sequence current strategy is used to construct open circuit conditions as control constraints. Step 4: Construct a composite network graph using control constraints and order components, and calculate the fault distance.

[0021] Example 3 This invention utilizes a fault location method based on the negative sequence suppression strategy of the peer-end grid-connected converter, and is implemented according to the following steps: Step 1: When a single-phase ground fault occurs on the new energy transmission line, the new energy system is connected to the line as the counterpart element and connected to the AC system. The AC system performs a start-up judgment on the AC transmission line with the AC fault. When the start-up criteria are met, the start-up element is activated. The new energy system, as the counterpart component, specifically refers to a centralized photovoltaic (PV) transmission line scenario. This includes a grid-connected PV topology, which consists of PV panels. These panels are connected to a DC boost circuit (Boost module) to increase the DC voltage level, which is then connected to an inverter. The inverter connects to a controller and inverts the voltage to an AC system. The AC system includes transformers T1 and T2, which boost the AC voltage level. Transformer T2 finally connects to a 110kV AC transmission line. The fault line to be measured in this 110kV AC transmission line is L1. The location of the measuring point on one side of fault line L1 is denoted as K. 1m The location of the measuring point is on the other side of the faulty line L1, denoted as K. 1n Measurement point K 1m and K 1n The fault point between them is denoted as f 1. Measuring point K 1m The location is on the back side of a large AC power grid, measuring point K. 1n The opposite end of the line is a photovoltaic grid-connected topology.

[0022] Step 2: On the faulty line, the phase difference of the power frequency fault sequence component is used to select the faulty phase, extract the three-phase voltage and current phasors under power frequency, and decompose them into symmetrical sequence components; at measurement point K of the faulty line L1... 1m The fault phase selection element uses the phase difference of the power frequency fault sequence component to achieve fault phase selection, and then extracts the three-phase voltage and current phasors under the power frequency; the three-phase voltage phasors are respectively The three-phase current phasors are respectively Using the symmetrical component method, the extracted phase voltage and phase current are decomposed into three sets of symmetrical sequence components based on the fault phase: positive sequence voltage, negative sequence voltage, zero sequence voltage, positive sequence current, negative sequence current, and zero sequence current, thereby achieving decoupling of mutual inductance elements in the line parameters.

[0023] Step 3: The new energy system switching control strategy is used to obtain positive and negative sequence components. The negative sequence current strategy is used to construct open circuit conditions as control constraints. Step 4: Construct a composite network graph using control constraints and order components, and calculate the fault distance.

[0024] Example 4 This invention utilizes a fault location method based on the negative sequence suppression strategy of the peer-end grid-connected converter, and is implemented according to the following steps: Step 1: When a single-phase ground fault occurs on the new energy transmission line, the new energy system is connected to the line as the counterpart element and connected to the AC system. The AC system performs a start-up judgment on the AC transmission line with the AC fault. When the start-up criteria are met, the start-up element is activated. The new energy system, as the counterpart component, specifically refers to a centralized photovoltaic (PV) transmission line scenario. This includes a grid-connected PV topology, which consists of PV panels. These panels are connected to a DC boost circuit (Boost module) to increase the DC voltage level, which is then connected to an inverter. The inverter connects to a controller and inverts the voltage to an AC system. The AC system includes transformers T1 and T2, which boost the AC voltage level. Transformer T2 finally connects to a 110kV AC transmission line. The fault line to be measured in this 110kV AC transmission line is L1. The location of the measuring point on one side of fault line L1 is denoted as K. 1m The location of the measuring point is on the other side of the faulty line L1, denoted as K. 1n Measurement point K 1m and K 1n The fault point between them is denoted as f 1. Measuring point K 1m The location is on the back side of a large AC power grid, measuring point K. 1n The opposite end of the line is a photovoltaic grid-connected topology.

[0025] Step 2: On the faulty line, the phase difference of the power frequency fault sequence component is used to select the faulty phase, extract the three-phase voltage and current phasors under power frequency, and decompose them into symmetrical sequence components; at measurement point K of the faulty line L1... 1m The fault phase selection element uses the phase difference of the power frequency fault sequence component to achieve fault phase selection, and then extracts the three-phase voltage and current phasors under the power frequency; the three-phase voltage phasors are respectively The three-phase current phasors are respectively Using the symmetrical component method, the extracted phase voltage and phase current are decomposed into three sets of symmetrical sequence components based on the fault phase: positive sequence voltage, negative sequence voltage, zero sequence voltage, positive sequence current, negative sequence current, and zero sequence current, thereby achieving decoupling of mutual inductance elements in the line parameters.

[0026] Step 3: The new energy system switching control strategy is used to obtain positive and negative sequence components. The negative sequence current strategy is used to construct open circuit conditions as control constraints. Step 3.1: After starting in Step 1, the photovoltaic grid-connected AC converter acts as the grid-side converter, at measurement point K on the faulty line L1. 1n Upon detecting a voltage drop at the grid connection point, the controller of the grid-side converter switches from normal operation mode to low voltage ride-through mode. The controller of the grid-side converter collects the voltage and current at the grid connection point. Step 3.2: Separate the positive-sequence and negative-sequence components of the voltage and current acquired in Step 3.1. Step 3.3: The negative sequence component separated in step 3.2 is subjected to a negative sequence current suppression strategy. The negative sequence current at the grid-side converter outlet is approximately zero. An open-circuit condition is constructed in the negative sequence network, and the photovoltaic side is approximately equivalent to an open circuit.

[0027] like Figure 3 As shown, when adopting the negative sequence current suppression strategy, PI control is designed in the negative sequence coordinate system to cancel the negative sequence component in the voltage of the fault line L1 by adjusting the output voltage of the converter. In the rotating coordinate system, the negative sequence currents of the d-axis and q-axis are suppressed respectively. The reference value is set to 0, and negative feedback control is performed through the PI control loop to achieve error-free regulation. The output result is a negative sequence voltage, which is then used as a modulation wave to enter the modulation loop.

[0028] The negative sequence voltage is calculated as follows: (3) in, , These are the negative sequence inner loop currents on the d-axis and q-axis, respectively. Angular velocity at power frequency For the equivalent inductance of the converter, , These are the negative sequence voltages output on the d-axis and q-axis, respectively. For complex frequency domain variables, For PI control, the proportional parameter For PI control integral parameters, , These are the negative sequence components of the grid-side voltages on the d-axis and q-axis, respectively. The control results under PI control, such as Figure 4 and Figure 5 As shown, after the fault occurred, K 1n The negative sequence current at the measuring point is attenuated to 0 on both the d-axis and q-axis through a negative sequence current suppression strategy, thereby achieving the control effect.

[0029] Step 4: Construct a composite network graph using control constraints and order components, and calculate the fault distance.

[0030] Example 5 This invention utilizes a fault location method based on the negative sequence suppression strategy of the peer-end grid-connected converter, and is implemented according to the following steps: Step 1: When a single-phase ground fault occurs on the renewable energy transmission line, the renewable energy system is connected to the line as the counterpart component. Specifically, the renewable energy system is a centralized photovoltaic transmission line scenario, including a grid-connected photovoltaic topology. This topology includes photovoltaic panels (PV1), which are connected to a DC boost circuit (Boost module) to increase the DC voltage level. The photovoltaic panels are then connected to a converter (VSC), which is connected to a controller. The converter is a two-level voltage source converter, which inverts the voltage to the AC system. The AC system includes transformers T1 and T2, which boost the AC voltage level. Transformer T2 is finally connected to the 110kV AC transmission line. The faulty line to be measured in the 110kV AC transmission line is L1. The location of the measuring point on one side of the faulty line L1 is denoted as K. 1m The location of the measuring point is on the other side of the faulty line L1, denoted as K. 1n Measurement point K 1m and K 1n The fault point between them is denoted as f 1. Measuring point K 1m The location is on the back side of a large AC power grid, measuring point K. 1n The opposite end of the line is a photovoltaic grid-connected topology.

[0031] When a single-phase ground fault occurs on the AC transmission line of the AC system, at measuring point K on the faulty line L1... 1m The starting judgment is performed, and the starting element is activated when the following starting criteria are met; (1) in, The voltage amplitude in the time domain collected at measuring point K1m. The rated voltage for normal operation of the AC system. t This refers to the time after the fault occurred.

[0032] Step 2: After starting in Step 1, the phase difference of the power frequency fault sequence component is used on the faulty line to select the faulty phase, extract the three-phase voltage and current phasors under the power frequency, and decompose them into symmetrical sequence components. At measurement point K of faulty line L1 1m The fault phase selection element uses the phase difference of the power frequency fault sequence component to achieve fault phase selection, and then extracts the three-phase voltage and current phasors under the power frequency; the three-phase voltage phasors are respectively The three-phase current phasors are respectively Using the symmetrical component method, the extracted phase voltage and phase current are decomposed into three sets of symmetrical sequence components based on the fault phase, namely positive sequence voltage, negative sequence voltage, zero sequence voltage, positive sequence current, negative sequence current, and zero sequence current, thereby achieving decoupling of mutual inductance elements in the line parameters. (2) in, The formula represents the electrical quantities in three-phase components. Represents electrical quantities in positive sequence, negative sequence, and zero sequence components, where α is a complex representation of a 120° phase angle difference.

[0033] Step 3: The new energy system switching control strategy is used to obtain positive and negative sequence components. The negative sequence current strategy is used to construct open circuit conditions as control constraints. Step 3.1: After starting in Step 1, the photovoltaic grid-connected AC converter acts as the grid-side converter, at measurement point K on the faulty line L1. 1n Upon detecting a voltage drop at the grid connection point, the controller of the grid-side converter switches from normal operation mode to low voltage ride-through mode. The controller of the grid-side converter collects the voltage and current at the grid connection point. Step 3.2: Separate the positive-sequence and negative-sequence components of the voltage and current acquired in Step 3.1. Step 3.3: The negative sequence component separated in step 3.2 is subjected to a negative sequence current suppression strategy. The negative sequence current at the grid-side converter outlet is approximately zero. An open-circuit condition is constructed in the negative sequence network, and the photovoltaic side is approximately equivalent to an open circuit.

[0034] When adopting the negative sequence current suppression strategy, PI control is designed in the negative sequence coordinate system to cancel the negative sequence component in the voltage of the faulty line L1 by adjusting the output voltage of the converter. In the rotating coordinate system, the negative sequence currents of the d-axis and q-axis are suppressed respectively. The reference value is set to 0, and negative feedback control is performed through the PI control loop to achieve error-free regulation. The output result is a negative sequence voltage, which is then used as a modulation wave to enter the modulation loop.

[0035] The negative sequence voltage is calculated as follows: (3) in, , These are the negative sequence inner loop currents on the d-axis and q-axis, respectively. Angular velocity at power frequency For the equivalent inductance of the converter, , These are the negative sequence voltages output on the d-axis and q-axis, respectively. For complex frequency domain variables, For PI control, the proportional parameter For PI control integral parameters, , These are the negative sequence components of the grid-side voltages on the d-axis and q-axis, respectively. The control result under PI control, after a fault occurs, K 1nThe negative sequence current at the measuring point is attenuated to 0 on both the d-axis and q-axis through a negative sequence current suppression strategy, thereby achieving the control effect.

[0036] Step 4: Construct a composite network graph using the control constraints obtained in Step 3 and the order components obtained in Step 2; Step 4.1: Based on the boundary conditions of a single-phase ground fault, construct a composite sequence network diagram on the faulty line L1, consisting of positive-sequence, negative-sequence, and zero-sequence networks connected in series, as shown below. Figure 6 As shown, the positive-sequence, negative-sequence, and zero-sequence networks are connected in series as series branches. Each series branch is a fault branch, and three transition resistors are connected in series between the three fault branches. , and These represent the positive-sequence, negative-sequence, and zero-sequence components of the voltage at the faulty branch, respectively. This is the transition resistance of the faulty branch.

[0037] The boundary conditions for an equivalent single-phase ground fault, where K 1m The measurement point is located on one side of the positive-sequence, negative-sequence, and zero-sequence networks, and the measurement point K is... 1m The back side of the building is a large power grid for AC systems; , and K 1m Positive-sequence, negative-sequence, and zero-sequence components of the voltage at the measuring point. , and K 1m Positive sequence, negative sequence, and zero sequence components of the current at the measuring point; K 1n The measurement point is located on the other side of the positive-sequence, negative-sequence, and zero-sequence network, and the measurement point K is located on the other side of the network. 1n The opposite end of the line is a photovoltaic grid-connected topology. , and K 1n The positive sequence, negative sequence, and zero sequence components of the current at the measuring point; The unit line impedances of the faulty line L1 for positive sequence, negative sequence, and zero sequence are respectively , and The equivalent positive-sequence, negative-sequence, and zero-sequence impedances on the grid side of the AC system are respectively , and The equivalent power source potential on the grid side is The equivalent positive-sequence and zero-sequence impedances of the grid-connected photovoltaic topology are respectively and The equivalent power source potential of the photovoltaic grid-connected topology is .

[0038] L For the faulty line L1, d The distance to the fault. , and They represent measuring point K respectively. 1m The total impedance of positive sequence, negative sequence, and zero sequence to the fault point. , and They represent measuring point K respectively. 1n The total impedance of positive sequence, negative sequence, and zero sequence to the fault point.

[0039] Step 4.2: Based on the circuit relationship of the composite sequence network diagram in Step 4.1, obtain the measurement point K. 1m The measured negative sequence current is equal to the negative sequence current at the faulty branch, that is: (4); Total current at the fault point for: (5); Taking a single-phase ground fault as an example (phase A grounding), from measuring point K... 1m At the measuring point, calculate the equivalent impedance of the faulty line L1 to be measured. ; (6); (7) in, The zero-order compensation coefficient is... , These are the zero-sequence and positive-sequence unit line impedances of the faulty line L1, respectively. K 1m Positive, negative, and zero-sequence fault currents measured at the measuring points; The negative sequence current of the faulty branch; These are the voltage and current of the phase A ground fault, respectively; After transition resistance During a short circuit, the equivalent impedance of the faulty line L1 to be measured is... for; (8) in, For K 1m The measured current obtained at the measuring point, For from K 1m The line impedance from the measuring point to the fault point is used to obtain information about the fault distance. d Transition resistance The complex equation is: (9) Decompose the complex equation into real and imaginary part equations, and the distance to the fault. d for; (10) Where Re represents the real part and Im represents the imaginary part of the equation.

[0040] This invention utilizes a fault location method based on the negative sequence suppression strategy of the grid-connected converter at the opposite end. After a fault occurs, the grid-connected converter of the photovoltaic system on the sending line is controlled. Three sets of symmetrical sequence components decouple the mutual inductance elements in the line parameters, providing a network topology that facilitates the analysis of fault distance. For asymmetrical faults such as single-phase grounding faults, the controller of the grid-side converter separates the positive and negative sequence components of the voltage and current collected at the grid connection point. This provides reliable mathematical constraints for time-varying power electronic equipment, assisting in the solution of fault distance. The voltage and current measured at the measurement point, along with the fault distance, enables single-end location of single-phase grounding faults.

[0041] Example 6 To verify the accuracy of the fault location method using the negative sequence suppression strategy of the grid-connected converter at the opposite end of the present invention, this embodiment takes the 110kV transmission line as an example and uses the Berylon model of the electromagnetic transient simulation software PSCAD to establish a simulated photovoltaic grid-connected system model. The parameters of the model are shown in Table 1. Table 1 shows the main parameters of the photovoltaic grid-connected system model.

[0042] Among them, the faulty line section L1 is a transmission line for fault location measurement. Single-end electrical quantities are collected through the measuring point at this end, and the length of the faulty line section L1 is determined. L For example, L1 = 100km; different fault distances and transition resistances were set in the middle section of line L1 to verify the accuracy of single-end fault location in this invention.

[0043] While the controller switches control, ranging is calculated under different fault distances and transition resistances, and the results are shown in Table 2. Table 2 shows the ranging results under different fault distances and transition resistances.

[0044] In the simulation test, the actual fault distances were set to 10, 30, 50, 70, and 90 km, and the actual transition resistances were set to 0, 10, 50, 100, and 300 Ω, respectively. The fault distance results are shown in the table. The data in the same row are the distance measurement results for different transition resistances at the same fault distance. As the transition resistance changes, the distance measurement result is always approximately equal to the actual simulated fault distance. Therefore, the fault location method of the present invention has good resistance to transition resistance.

[0045] The ranging errors are shown in Table 3; Table 3 shows the ranging error.

[0046] The ranging errors are shown in Table 3. Combined with the error curves, as shown... Figure 7 As shown, x The axis coordinates represent the distance to the fault. y The x-axis coordinates represent the transition resistance. z The axis coordinate variable represents the ranging error. The black plane represents the maximum allowable ranging error under different transition resistances and fault distances, while the gray-white gradient curved surface represents the actual ranging error under different transition resistances and fault distances. By observing and comparing the two curved surfaces, it can be seen that as the fault distance and transition resistance increase, the actual ranging error also increases. However, the ranging errors are all within the allowable error range. The ranging results of the fault location method of this invention are feasible, solving the problems of existing fault location methods, such as the inability to identify the parameters of the opposite system, poor resistance to transition resistance, and inaccurate line fault location.

Claims

1. A fault location method utilizing the negative sequence suppression strategy of the peer-end grid-connected converter, characterized in that, The specific steps are as follows: Step 1: The new energy system is connected to the AC transmission line of the AC system. When a single-phase ground fault occurs on the transmission line, the faulty line is judged for starting. When the starting criteria are met, the starting element is activated. Step 2: On the faulty line, the phase difference of the power frequency fault sequence component is used to select the fault phase, extract the three-phase voltage and current phasors under the power frequency, and decompose them into symmetrical sequence components. Step 3: The new energy system switching control strategy is used to obtain positive and negative sequence components. The negative sequence current strategy is used to construct open circuit conditions as control constraints. Step 4: Construct a composite network graph using control constraints and order components, and calculate the fault distance.

2. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 1, characterized in that, Step 1: The new energy system serves as the counterpart component, specifically a centralized photovoltaic (PV) transmission line scenario. This includes a PV grid-connected topology, which comprises PV panels. The PV panels are connected to a DC boost circuit (Boost module) to increase the DC-side voltage level, and then connected to an inverter. The inverter connects to a controller and inverts the voltage to the AC system. The AC system includes transformers T1 and T2, which boost the AC-side voltage level. Transformer T2 is finally connected to a 110kV AC transmission line. In this 110kV AC transmission line, the faulty line to be measured is L1. The location of the measuring point on one side of the faulty line L1 is denoted as K. 1m The location of the measuring point is on the other side of the faulty line L1, denoted as K. 1n Measurement point K 1m and K 1n The fault point between them is denoted as f 1. Measuring point K 1m The location is on the back side of a large AC power grid, measuring point K. 1n The opposite end of the line is a photovoltaic grid-connected topology.

3. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 2, characterized in that, When a single-phase ground fault occurs on the AC transmission line of the AC system, at measuring point K on the faulty line L1... 1m The starting judgment is performed, and the starting element is activated when the following starting criteria are met; （1） in, The voltage amplitude in the time domain collected at measuring point K1m. The rated voltage for normal operation of the AC system. t This refers to the time after the fault occurred.

4. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 3, characterized in that, Step 2: At measurement point K of the faulty line L1 1m The fault phase selection element uses the phase difference of the power frequency fault sequence component to achieve fault phase selection, and then extracts the three-phase voltage and current phasors under the power frequency. The three-phase voltage phasors are respectively The three-phase current phasors are respectively ; Using the symmetrical component method, the extracted phase voltage and phase current are decomposed into three sets of symmetrical sequence components based on the fault phase, namely positive sequence voltage, negative sequence voltage, zero sequence voltage, positive sequence current, negative sequence current, and zero sequence current, thereby achieving decoupling of mutual inductance elements in the line parameters. （2） in, The formula represents the electrical quantities in three-phase components. Represents electrical quantities in positive sequence, negative sequence, and zero sequence components, where α is a complex representation of a 120° phase angle difference.

5. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 4, characterized in that, Step 3 specifically involves: Step 3.1: After starting in Step 1, the photovoltaic grid-connected AC converter acts as the grid-side converter, at measurement point K on the faulty line L1. 1n Upon detecting a voltage drop at the grid connection point, the controller of the grid-side converter switches from normal operation mode to low voltage ride-through mode. The controller of the grid-side converter collects the voltage and current at the grid connection point. Step 3.2: Separate the positive-sequence and negative-sequence components of the voltage and current acquired in Step 3.

1. Step 3.3: The negative sequence component separated in step 3.2 is subjected to a negative sequence current suppression strategy. The negative sequence current at the grid-side converter outlet is approximately zero. An open-circuit condition is constructed in the negative sequence network, and the photovoltaic side is approximately equivalent to an open circuit.

6. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 5, characterized in that, When adopting the negative sequence current suppression strategy, PI control is designed in the negative sequence coordinate system. By adjusting the output voltage of the converter, the negative sequence component in the voltage of the fault line L1 is canceled. In the rotating coordinate system, the negative sequence current of the d-axis and the negative sequence current of the q-axis are suppressed respectively. The reference value is set to 0, and negative feedback control is performed through the PI control loop to achieve error-free regulation. The output result is the negative sequence voltage, which is then used as the modulation wave to enter the modulation loop.

7. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 6, characterized in that, The negative sequence voltage is calculated as follows: （3） in, , These are the negative sequence inner loop currents on the d-axis and q-axis, respectively. Angular velocity at power frequency The equivalent inductance of the converter, , These are the negative sequence voltages output on the d-axis and q-axis, respectively. For complex frequency domain variables, For PI control, the proportional parameter For PI control integral parameters, , These are the negative sequence components of the grid-side voltages on the d-axis and q-axis, respectively. The control result under PI control, after a fault occurs, K 1n The negative sequence current at the measuring point is attenuated to 0 on both the d-axis and q-axis through a negative sequence current suppression strategy, thereby achieving the control effect.

8. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 6, characterized in that, Step 4 specifically involves: Step 4.1: Based on the boundary conditions of a single-phase ground fault, construct a composite sequence network diagram on the faulty line L1, connecting the positive-sequence, negative-sequence, and zero-sequence networks in series. Connect the positive-sequence, negative-sequence, and zero-sequence networks as series branches, with each series branch being the fault branch. Connect the three fault branches in series with three transition resistors. , and These represent the positive-sequence, negative-sequence, and zero-sequence components of the voltage at the faulty branch, respectively. The transition resistance of the faulty branch; , and K 1m Positive-sequence, negative-sequence, and zero-sequence components of the voltage at the measuring point. , and K 1m Positive sequence, negative sequence, and zero sequence components of the current at the measuring point; , and K 1n The positive sequence, negative sequence, and zero sequence components of the current at the measuring point; The unit line impedances of the faulty line L1 for positive sequence, negative sequence, and zero sequence are respectively , and The equivalent positive-sequence, negative-sequence, and zero-sequence impedances on the grid side of the AC system are respectively , and The equivalent power source potential on the grid side is The equivalent positive-sequence and zero-sequence impedances of the grid-connected photovoltaic topology are respectively and The equivalent power source potential of the photovoltaic grid-connected topology is ; L For the faulty line L1, d The distance to the fault. , and They represent measuring point K respectively. 1m The total impedance of positive sequence, negative sequence, and zero sequence to the fault point. , and They represent measuring point K respectively. 1n The total positive-sequence, negative-sequence, and zero-sequence impedances to the fault point; Step 4.2: Based on the circuit relationship of the composite sequence network diagram in Step 4.1, obtain the measurement point K. 1m The measured negative sequence current is equal to the negative sequence current at the faulty branch, that is: （4）； Total current at the faulty branch for: （5）； Taking a single-phase ground fault as an example (phase A grounding), from measuring point K... 1m At the measuring point, calculate the equivalent impedance of the faulty line L1 to be measured. ; （6）； （7） in, For zero-order compensation coefficient, , These are the zero-sequence and positive-sequence unit line impedances of the faulty line L1, respectively. K 1m Positive, negative, and zero-sequence fault currents measured at the measuring points; The negative sequence current of the faulty branch; These are the voltage and current of the phase A ground fault, respectively; After transition resistance During a short circuit, the equivalent impedance of the faulty line L1 to be measured is... for; （8） in, For K 1m The measured current obtained at the measuring point, For from K 1m The line impedance from the measuring point to the fault point is used to obtain information about the fault distance. d Transition resistance The complex equation is: （9） Decompose the complex equation into real and imaginary part equations, and the distance to the fault. d for; （10） Where Re represents the real part and Im represents the imaginary part of the equation.

9. The fault location method using the negative sequence suppression strategy of the peer-end grid-connected converter according to claim 2, characterized in that, The converter adopts a two-level voltage source type converter.

Images