A transient response test method for artificial short circuit test of a network-constructed energy storage system

Abstract

This invention discloses a transient response testing method for artificial short-circuit tests on grid-type energy storage systems, comprising: establishing a mathematical model of the transient response of the grid-type energy storage system under artificial short-circuit faults; determining the artificial short-circuit test conditions and constructing a multi-measurement point synchronous acquisition architecture covering multiple voltage levels; constructing an external three-phase short-circuit device for the transformer substation and injecting a three-phase short-circuit fault into the grid-type energy storage system; synchronously acquiring transient data under the short-circuit fault, obtaining transient response data and short-circuit current through sequence component extraction and solving the short-circuit current equation set; and comparing and verifying the measured data with the simulation results. This invention solves the problems of lack of on-site experimental verification of fault equivalent models, unclear transient response characteristics, and difficulty in implementing short-circuit tests on enclosed transformer substations. It can effectively obtain transient response data and short-circuit current levels under three-phase short-circuit faults, providing on-site measured data support for the verification and correction of fault equivalent models and the assessment of low-voltage ride-through capability.

Description

Technical Field

[0001] This invention relates to the field of grid-connected testing technology for grid-type energy storage, and specifically to a transient response testing method for artificial short-circuit tests on grid-type energy storage systems. Background Technology

[0002] Currently, my country's energy structure is accelerating its transformation towards a low-carbon model, with the installed capacity of new energy sources continuing to grow rapidly. Energy storage, as a rigid requirement to ensure the consumption of new energy and power supply, is widely used in new power systems. At present, most energy storage systems adopt a grid-tracking control method to connect to the grid, that is, using a phase-locked loop (PLL) to track the grid voltage phase to achieve grid synchronization. It exhibits current source characteristics to the grid and has a fast power response speed. However, the grid-tracking energy storage's reliance on external grid voltage phase locking makes it difficult to actively provide voltage support and inertial response in weak grid scenarios. Furthermore, its stability heavily depends on the performance of the PLL, and it is prone to oscillation and instability problems as grid strength weakens.

[0003] To overcome the above defects, grid-type energy storage technology has emerged. Grid-type energy storage actively constructs grid voltage and frequency by simulating the rotor motion equation and excitation regulation characteristics of synchronous generators, and has autonomous inertia support, damping regulation and dynamic reactive power compensation capabilities. Reference [1] discloses a low voltage ride-through control method and system for grid-type converters, which maintains the fault ride-through capability of grid-type converters by implementing low voltage ride-through control during faults. However, most of the existing research on grid-type control technology, including Reference [1], is based on theoretical derivation and digital simulation. Its control parameters and fault equivalent characteristics lack verification by field measured data. It is still uncertain whether the simulation model can truly reflect the transient behavior of grid-type energy storage under actual grid faults.

[0004] Furthermore, the large-scale integration of grid-connected energy storage will significantly alter the characteristics of grid faults, reducing the applicability of traditional short-circuit current calculation methods. On one hand, grid-connected energy storage connects to the grid via inverters, requiring low-voltage ride-through control strategies during faults, resulting in a fault equivalent model exhibiting controlled power source characteristics. On the other hand, its fault steady-state response equivalent model is in the form of a voltage source series impedance, and exhibits significant piecewise characteristics due to the influence of virtual impedance current limiting strategies. This leads to non-smooth and nonlinear short-circuit current calculation equations, making short-circuit current calculation difficult and compromising calculation accuracy.

[0005] Existing technologies also have significant shortcomings in testing and verifying the fault characteristics of grid-type energy storage. Reference [2] discloses a voltage withstand test method and system for grid-type energy storage systems based on short-circuit faults. This method connects a grid simulation source and a variable impedance to the grid-type energy storage system. By setting the transient Thevenin equivalent voltage amplitude and the variable impedance, the grid fault is simulated, thereby testing the voltage withstand capability of the grid-type energy storage system. However, this type of method belongs to the simulation test in the laboratory environment. Its fault conditions are generated by the grid simulation source, which differs from the short-circuit capacity, impedance characteristics and fault transient process of the real grid. The test results are difficult to accurately reflect the short-circuit current supply level and transient response characteristics of grid-type energy storage under real field short-circuit faults. Moreover, it cannot solve the engineering problem that field short-circuit tests are difficult to implement when the energy storage unit is connected to the grid through a closed box transformer.

[0006] Reference [3] discloses a method for identifying electromechanical transient models of new energy power plants based on measured faults in the power grid. This method collects fault data that occurs naturally in the power grid, extracts the fundamental positive sequence components of the grid connection point and collection lines, and identifies and corrects the electromechanical transient model parameters of new energy power plants. However, this type of method passively relies on random fault events that occur in the power grid. The fault type, fault location and time are uncontrollable, the experiment cannot be repeated and effective data may not be obtained for a long time. At the same time, it is aimed at conventional new energy power plants that adopt grid-following control and does not involve fault equivalent models of grid-type energy storage. It cannot be used for active testing and verification of the transient response characteristics of grid-type energy storage.

[0007] In summary, there is currently a lack of systematic field experimental research on the transient response characteristics of grid-connected energy storage under artificial short-circuit faults. The effectiveness of its fault equivalent model has not been fully verified by field measurement data, and key indicators such as short-circuit current supply level, transient response time, and reactive power support capability during low-voltage ride-through remain unclear. Furthermore, since energy storage units are typically connected to the grid via enclosed transformer substations, feasible short-circuit injection methods are lacking for field artificial short-circuit tests. Therefore, it is urgent to propose a transient response testing method for artificial short-circuit tests of grid-connected energy storage systems. This method should provide field measurement data support for the verification and correction of the fault equivalent model of grid-connected energy storage through field test scheme design, short-circuit fault injection device construction, transient data acquisition and analysis, and model verification.

[0008] Cited references: Reference [1]: Chinese Patent, Publication No. CN117879039A, Title: A Low Voltage Ride-through Control Method and System for Grid-type Converters; Applicant: Xi'an Jiaotong University, State Grid Hubei Electric Power Research Institute; Application No.: CN202410035961.X; Application Date: January 9, 2024.

[0009] Reference [2]: Chinese Patent, Publication No. CN118795290A, Title: A voltage withstand test method and system for grid-type energy storage system based on short-circuit fault; Applicant: China Electric Power Research Institute Co., Ltd.; Application No.: CN202410862731.0; Application Date: June 28, 2024.

[0010] Reference [3]: Chinese Patent, Publication No. CN117691691A, Title: Method for Identifying Electromechanical Transient Models of New Energy Power Stations Based on Measured Faults in Power Grid; Applicant: Yunnan Electric Power Research Institute (Group) Co., Ltd.; Application No.: CN202311676662.6; Application Date: December 7, 2023. Summary of the Invention

[0011] To address the issues of lack of field verification for fault equivalent models in grid-connected energy storage systems, unclear transient response characteristics, and the difficulty in implementing short-circuit tests on enclosed transformer substations, this invention provides a transient response testing method for artificial short-circuit tests on grid-connected energy storage systems. This method involves establishing a transient response mathematical model, designing a field artificial short-circuit test scheme, constructing an external three-phase short-circuit injection device for the transformer substation, and simultaneously collecting and analyzing transient data to obtain transient response data and short-circuit current levels under three-phase short-circuit faults. This solves the engineering challenge of directly implementing short-circuit tests on enclosed transformer substations, achieving a complete conversion from time-domain transient waveforms to short-circuit current electrical parameters. It effectively verifies the accuracy of the fault equivalent model and provides field measurement data support for simulation model correction and low-voltage ride-through capability assessment, thereby improving the safe and stable operation level of grid-connected energy storage systems.

[0012] The technical solution adopted in this invention is as follows: A transient response testing method for an artificial short-circuit test of a grid-type energy storage system includes the following steps: S1: Establish a mathematical model of the transient response of a grid-type energy storage system under artificial short-circuit fault; S2: Based on the transient response mathematical model, determine the artificial short-circuit test conditions and construct a multi-measurement point synchronous acquisition architecture covering multiple voltage levels; S3: Construct an external three-phase short-circuit device for the transformer substation to inject a three-phase short-circuit fault into the grid-type energy storage system; S4: The transient data under short-circuit fault is synchronously acquired using the multi-point synchronous acquisition architecture. After sequence component extraction and short-circuit current equation solving, the transient response data and short-circuit current of the grid-type energy storage system are obtained. S5: Compare and verify the measured transient response data with the simulation results.

[0013] S1 includes: S1.1: Establish the dynamic equations of the DC / AC converter and LCL filter circuit of the grid-type energy storage system in the dq coordinate system: ; ; in, , These are the d-axis and q-axis components of the converter-side output current; , These are the d-axis and q-axis components of the grid connection point voltage; , These are the d-axis and q-axis components of the converter-side output voltage; , These are the d-axis and q-axis components of the grid-connected current; For filtering inductors; For filtering capacitors; For filtering resistors; The angular frequency of the power grid; S1.2: Based on the dynamic equations described in S1.1, establish the active power-frequency control equations for the outer power loop of the virtual synchronous generator: ; in, This is virtual inertia; For virtual damping; The mechanical power output by the virtual synchronous generator; The electromagnetic power output by the virtual synchronous generator; This is the actual angular frequency; The rated angular frequency; S1.3: Based on the active power-frequency control of S1.2, a reactive power-voltage control equation is established, and the virtual internal potential amplitude is dynamically adjusted by detecting the voltage deviation at the grid connection point. ; in, This represents the amplitude of the virtual internal potential. For regulator gain; The time constant of the excitation winding; Rated voltage; The measured voltage at the grid connection point; Synchronous reactance; Transient reactance; The d-axis component of the grid current injected into the converter; For the Laplace operator.

[0014] S1 further includes: S1.4: Based on the virtual internal potential amplitude determined in S1.3, establish the voltage outer loop equation and generate the d-axis and q-axis reference values ​​for the current inner loop: ; in, , These are the d-axis and q-axis reference values ​​for the inner current loop, respectively. , These are the d-axis and q-axis components of the virtual internal potential, respectively. , These are the d-axis and q-axis components of the measured voltage at the grid connection point, respectively. For filtering resistors; For filter reactance; For virtual resistance; For virtual reactance; S1.5: Using the current inner loop reference value generated in S1.4 as the command value, establish the current inner loop PI control equation: ; in, , These are the internal potential control output signals for the d and q axes, respectively; The q-axis component of the grid current injected into the converter; , These are the d-axis and q-axis current state feedback quantities, respectively. , These are the d-axis and q-axis components of the converter terminal voltage, respectively. , The parameters are PI control parameters; the internal potential control output signal is converted into a PWM modulation signal after Park inverse transformation, realizing full closed-loop control from virtual internal potential to actual output voltage.

[0015] S1 further includes: S1.6: To address the voltage drop caused by a three-phase short-circuit fault at the grid connection point, an adaptive virtual impedance current limiting strategy is established. ; in, This represents the amplitude of the short-circuit current. This is the short-time overcurrent multiple of the inverter. This is the inverter's rated current; This is the virtual resistivity. The impedance ratio of the virtual impedance; when the grid connection point current exceeds the inverter threshold, the virtual impedance is adaptively increased to limit the current, and the power outer loop is blocked to stabilize the amplitude and phase angle of the virtual internal potential, so that the grid-type energy storage system maintains the voltage source characteristics during the fault. S1.7: Based on the adaptive virtual impedance current limiting strategy of S1.6, a positive-sequence equivalent model of the fault steady state of the grid-type energy storage system is established: ; in, This is the commanded value for the outer power loop voltage; This is the positive sequence voltage at the grid connection point; This is the positive sequence current at the grid connection point; This is the equivalent resistance of the filter; The equivalent inductance of the filter; The imaginary unit; And determine the piecewise current limiting critical condition of the positive sequence equivalent model: ; in, This is the current-limiting critical voltage; The current limiting critical current is used; when the grid connection point voltage is higher than the current limiting critical voltage, the virtual impedance is set to zero, and the virtual impedance is activated when an overcurrent occurs.

[0016] S2 includes: S2.1: Set artificial short-circuit test conditions, including the energy storage state of charge (SOC) value, charge and discharge operation status, grid operation mode, and test power; S2.2: Assess the grid strength at the connection point based on the short-circuit ratio of new energy power plants: ; in, Short-circuit ratio; The nominal voltage of the busbar at the grid connection point; Rated power for new energy sources; The equivalent impedance from the grid connection point to the power grid; S2.3: Based on the power grid strength assessment results of S2.2, the fault location is determined according to the relationship between the short-circuit current at the grid connection point and the electrical distance from the fault point to the bus. ; in, This refers to the short-circuit current at the grid connection point. The system's equivalent voltage source voltage; The equivalent impedance of the system; The electrical distance from the fault point to the busbar is used to fully verify the transient response of the grid-type energy storage system under extreme fault conditions. The closer the fault point is to the busbar, the larger the short-circuit current and the deeper the voltage drop.

[0017] S2 further includes: S2.4: After determining the fault location, multiple measuring points are simultaneously deployed on the bus fault recording screens and line fault recording screens at the multiple voltage levels to construct a set of nodal admittance matrix equations for short-circuit current calculation: ; in, , , These are the admittance matrices of the nodes in positive order, negative order, and zero order, respectively. , , These represent the positive-sequence, negative-sequence, and zero-sequence node voltages, respectively. , , These represent the positive-sequence, negative-sequence, and zero-sequence node currents, respectively; the data collected synchronously from the multiple measurement points provide complete measured boundary conditions for the node admittance matrix equations.

[0018] S3 includes: S3.1: A temporary test cable is led out from the high-voltage side of the transformer substation, and after being supported by the post insulator array, it transitions to the copper busbar. The short-circuit point is kept at a safe distance from the energy storage equipment area. The equivalent impedance to ground of the post insulator array is much greater than the system impedance, so that the short-circuit current flows along a predetermined path. S3.2: A three-phase short circuit is achieved at the end of the copper busbar described in S3.1 through a transient fault line, forming a reusable short-circuit injection device. The short-circuit current at the short-circuit point is jointly provided by the system side and the grid-type energy storage side. ; in, The short-circuit current phasor at the short-circuit point; This is the short-circuit current phasor on the system side; This refers to the short-circuit current phasor on the grid-type energy storage side.

[0019] In S3.2, the melting process of the instantaneous failure wire is as follows: At the moment the circuit breaker closes, the short-circuit current flows through the momentarily damaged conductor, generating Joule heat. ; in, The Joule heat generated by the short-circuit current flowing through the momentarily damaged wire; for The short-circuit current at the short-circuit point at any given moment; For instantaneous damage line resistance; The melting time is the time it takes for the circuit to break. When the accumulated Joule heat reaches the melting threshold of the instantaneous failure line, the instantaneous failure line melts, forming a stable metallic three-phase short circuit.

[0020] S4 includes: S4.1: Set the waveform recording trigger threshold value When the sudden change in current at any measuring point exceeds the waveform recording trigger threshold, synchronous waveform recording is triggered at each measuring point to obtain the transient waveforms of the three-phase voltage and three-phase current. S4.2: After Fourier transforming the three-phase voltage and three-phase current collected in S4.1, the sequence components are extracted using the symmetrical component method. ; ; ; ; ; ; in, , , These are three-phase voltage phasors; , , These are three-phase current phasors; The rotation factor; , , These are the positive-sequence, negative-sequence, and zero-sequence voltage components, respectively. , , These are the positive-sequence, negative-sequence, and zero-sequence current components, respectively. S4.3: Substitute the sequence components extracted in S4.2 into the short-circuit current equations and solve: ; in, , , The admittance matrices of the nodes are positive-sequence, negative-sequence, and zero-sequence, respectively. The short-circuit current distribution of each node is obtained by solving the problem, and the transient response data and short-circuit current of the grid-type energy storage system are obtained.

[0021] S5 includes: S5.1: Substitute the measured voltage and injected current at each measuring point into the short-circuit current distribution result obtained from S4.3, and deduce the actual virtual impedance of the grid-type energy storage system during the fault period: ; in, For virtual resistance; For virtual reactance; This is the commanded value for the outer power loop voltage; This is the positive sequence voltage at the grid connection point; This is the positive sequence current at the grid connection point; This is the equivalent resistance of the filter; The equivalent inductance of the filter; This is the actual angular frequency; The imaginary unit; S5.2: Using short-circuit current amplitude, transient response time, and reactive power support capability during low-voltage ride-through as evaluation indicators, calculate the error between the measured value and the simulated value; when all errors are less than the set threshold, the fault equivalent model of the grid-type energy storage system is determined to be accurate; when the error exceeds the set threshold, the simulation model parameters are corrected based on the actual virtual impedance derived from S5.1.

[0022] This invention provides a transient response testing method for artificial short-circuit tests on grid-type energy storage systems, with the following technical advantages: 1) It provides a field measurement and verification method for the fault equivalent model of grid-type energy storage, solving the problems of the lack of field measurement verification of the effectiveness of the fault equivalent model and the unclear transient response characteristics: By establishing a mathematical model of the transient response of a grid-type energy storage system under artificial short-circuit faults, and comparing and verifying the measured data from field artificial short-circuit tests with the simulation results, the accuracy of the fault equivalent model can be effectively verified and the simulation model parameters can be corrected accordingly. Key indicators such as short-circuit current supply level, transient response time, and reactive power support capability during low-voltage ride-through are clarified, providing a theoretical basis and field data support for short-circuit current characteristic analysis and low-voltage ride-through capability assessment.

[0023] 2) It achieves accurate calculation of short-circuit current in grid-type energy storage, improving the poor applicability of traditional short-circuit current calculation methods: By synchronously recording transient waveforms at multiple measurement points, extracting sequence components, and substituting them into the short-circuit current equations for solution, the grid-type energy storage, which exhibits controlled power supply characteristics and piecewise nonlinear characteristics during faults, is incorporated into the short-circuit current calculation system. Furthermore, the actual virtual impedance of the grid-type energy storage during faults can be inferred from measured data, verifying the consistency between the actual operating characteristics of the virtual impedance current limiting strategy and the control logic, thereby improving the accuracy and reliability of short-circuit current calculation.

[0024] 3) It overcomes the shortcomings of laboratory simulation tests and real power grid operating conditions, and the test results can better reflect the characteristics of real-world faults: This invention conducts artificial short-circuit tests in a real-world power grid environment. The short-circuit fault is fed by both the actual power grid and the grid-connected energy storage system. The short-circuit capacity, impedance characteristics, and transient processes of the fault conditions are all under real power grid conditions. The obtained transient response data can accurately reflect the dynamic behavior of the grid-connected energy storage system under actual short-circuit faults, avoiding test deviations caused by the equivalent generation of fault conditions by the power grid simulation source.

[0025] 4) It achieves active injection of short-circuit faults and controllable and repeatable testing, overcoming the limitation of passively relying on random grid faults: By constructing an external three-phase short-circuit device for transformer substations, three-phase short-circuit faults can be actively injected at predetermined fault points and under predetermined test conditions. The fault type, fault location, and test time are all controllable, forming a reusable short-circuit injection platform. This solves the problems of random faults, non-repeatable data, and the potential inability to obtain effective data for a long time when relying on natural faults in the power grid.

[0026] 5) Solved the engineering problem of the difficulty in conducting on-site short-circuit tests under the grid connection mode of enclosed box-type substations: By drawing a temporary test cable from the high-voltage side of the transformer substation, transitioning to the copper busbar through the support of the post insulator array, and achieving a three-phase short circuit with a momentary failure line, a stable metallic three-phase short circuit is formed without affecting the safety of the energy storage equipment area. This provides a safe and feasible on-site short-circuit injection method for energy storage systems connected to enclosed transformer substations, and expands the on-site applicability of artificial short-circuit tests.

[0027] 6) Provided technical support for optimizing the low-voltage ride-through control strategy of grid-connected energy storage and ensuring safe and stable grid-connected operation: The transient response data obtained through field tests can be used to quantitatively analyze the impact of key parameters such as virtual inertia, virtual impedance, and overcurrent multiple on short-circuit current output characteristics, providing a reliable basis for optimizing low-voltage ride-through control strategies, assessing fault ride-through capability, and ensuring the safe and stable operation of grid-connected energy storage systems. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and examples; Figure 1 This is a grid-connected control structure diagram of a grid-type energy storage system in an embodiment of the present invention.

[0029] Figure 2(a) is a block diagram of the active power-frequency control of the virtual synchronous generator power outer loop in an embodiment of the present invention; Figure 2(b) is a block diagram of reactive power-voltage control for the outer power loop of the virtual synchronous generator in an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of the short-circuit point arrangement of the external three-phase short-circuit device for the transformer substation in an embodiment of the present invention.

[0031] Figure 4 This is a comparison chart of transient current between the calculation results of the fault equivalent model and the simulation results in the embodiments of the present invention.

[0032] Figure 5(a) is a comparison diagram of bus voltage changes in an embodiment of the present invention; Figure 5(b) is a comparison diagram of reactive power output after a fault in an embodiment of the present invention.

[0033] Figure 6(a) is a waveform diagram of the voltage support strength improvement of the grid-type energy storage system in an embodiment of the present invention (transient voltage at the grid connection point). Figure 6(b) is a waveform diagram (active power output) of the grid-type energy storage system in the embodiment of the present invention to improve the voltage support strength. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0035] Example 1: like Figures 1-3 As shown, this embodiment provides a transient response test method for artificial short-circuit tests of a grid-type energy storage system, including the following steps S1~S5: Existing energy storage systems mostly adopt grid-connected control, using phase-locked loops to track the grid voltage phase for synchronization, exhibiting current source characteristics to the grid. In contrast, grid-connected energy storage actively constructs grid voltage and frequency by simulating the rotor motion equations and excitation regulation characteristics of synchronous generators, exhibiting voltage source characteristics to the grid. Due to this fundamental difference, the current output characteristics and equivalent model form of grid-connected energy storage under short-circuit faults differ significantly from traditional synchronous and grid-connected power sources. Its fault equivalent model exhibits controlled power source characteristics and piecewise nonlinear features, reducing the applicability of traditional short-circuit current calculation methods based on linear assumptions. Therefore, this embodiment first establishes a transient response mathematical model that accurately characterizes the above characteristics, and then designs an on-site artificial short-circuit test based on this model.

[0036] S1: Establish a mathematical model of the transient response of a grid-type energy storage system under artificial short-circuit faults to provide a theoretical basis for short-circuit current characteristic analysis and low-voltage ride-through capability assessment. S1.1: Establish the dynamic equations for the converter and filter circuit: A grid-connected energy storage system consists of a storage battery, a DC / AC converter, and an LCL filter circuit. The storage battery provides the DC-side energy source, the DC / AC converter performs DC-to-AC power conversion, and the LCL filter circuit filters out high-order harmonics generated by the converter's switching operations, ensuring grid-connected power quality. The dynamic behavior of the converter-side output current and the grid connection point voltage in the dq coordinate system is expressed as follows: (1); (2); in, , These are the d-axis and q-axis components of the converter-side output current; , These are the d-axis and q-axis components of the grid connection point voltage; , These are the d-axis and q-axis components of the converter-side output voltage; , These are the d-axis and q-axis components of the grid-connected current; For filtering inductors; For filtering capacitors; For filtering resistors; This is the angular frequency of the power grid.

[0037] The above dynamic equation describes the electrical coupling relationship between the converter output and the grid connection point during the fault transient process: when a short-circuit fault occurs at the grid connection point, the grid connection point voltage changes abruptly. This change is transmitted to the converter side through the filter circuit and becomes the direct electrical cause of the overcurrent in the converter. Therefore, this equation is the circuit basis for subsequent control loop modeling and current limiting strategy analysis.

[0038] S1.2: Establish the active-frequency control equations for the outer power loop of the virtual synchronous generator: The grid-type control employs virtual synchronous generator (VSG) control. VSG introduces virtual inertia and virtual damping into the power outer loop, simulating the electromechanical transient behavior of a synchronous generator in the converter's external characteristics. As shown in Figure 2(a), the active-frequency control satisfies the following rotor motion equations: (3); in, This is virtual inertia; For virtual damping; The mechanical power output by the virtual synchronous generator; The electromagnetic power output by the virtual synchronous generator; This is the actual angular frequency; This is the rated angular frequency. Its physical significance is that when a disturbance in the power grid causes a sudden change in electromagnetic power, the power imbalance, after being buffered by the virtual inertia, only causes a slow change in the angular frequency, thus enabling grid-type energy storage to autonomously provide inertia support under power grid frequency disturbances; the virtual damping provides damping for system oscillations and suppresses power oscillations.

[0039] S1.3: Establish the reactive power-voltage control equation: As shown in Figure 2(b), the reactive power-voltage control simulates the excitation regulation characteristics of a synchronous generator, dynamically adjusting the virtual internal potential amplitude by detecting the voltage deviation at the grid connection point: (4); in, This represents the amplitude of the virtual internal potential. For regulator gain; The time constant of the excitation winding; Rated voltage; The measured voltage at the grid connection point; Synchronous reactance; Transient reactance; The d-axis component of the grid current injected into the converter; This is a Laplace operator. Through this control loop, when a short-circuit fault causes a drop in the measured voltage at the grid connection point, the voltage deviation increases. The control loop dynamically increases the amplitude of the virtual internal potential, driving the converter to output more reactive power, thereby actively supporting the grid voltage. This is one of the core functional characteristics that distinguishes grid-connected energy storage from grid-connected energy storage.

[0040] S1.4: Establish the outer loop voltage equation: The outer voltage loop generates d- and q-axis reference values ​​for the inner current loop based on the magnitude of the virtual internal potential. (5); in, , These are the d-axis and q-axis reference values ​​for the inner current loop, respectively. , These are the d-axis and q-axis components of the virtual internal potential, respectively. , These are the d-axis and q-axis components of the measured voltage at the grid connection point, respectively. For filtering resistors; For filter reactance; For virtual resistance; This represents the virtual reactance. As can be seen from the equation, the virtual resistance and virtual reactance directly participate in the generation of the current reference value. During a fault, the input of the virtual impedance will change the transmission characteristics of the outer voltage loop, thus demonstrating a current-limiting effect from the control level.

[0041] S1.5: Establish the inner loop PI control equation for the current: like Figure 1 As shown, the inner current loop uses a PI controller to quickly track the output current, and the output of the outer voltage loop serves as the command value for the inner current loop. (6); in, , These are the internal potential control output signals for the d and q axes, respectively; The q-axis component of the grid current injected into the converter; , These are the d-axis and q-axis current state feedback quantities, respectively, used to achieve decoupled control of the d-axis and q-axis. , These are the d-axis and q-axis components of the converter terminal voltage, respectively. , These are the PI control parameters. The output of the inner current loop is converted into a PWM modulation signal after Park inverse transformation, driving the power devices of the converter to operate, thus realizing full closed-loop control from virtual internal potential to actual output voltage. At this point, the signal transmission relationship between the outer power loop, outer voltage loop, and inner current loop is fully established.

[0042] S1.6: Establish an adaptive virtual impedance current limiting strategy: When a three-phase short-circuit fault occurs at the grid connection point, causing a sudden voltage drop, a large voltage difference arises between the converter output and the grid connection point, which can easily trigger overcurrent and damage components. Therefore, this embodiment employs an adaptive virtual impedance current limiting strategy: (7); in, This represents the amplitude of the short-circuit current. This is the short-time overcurrent multiple of the inverter. This is the inverter's rated current; This is the virtual resistivity. The impedance ratio is the virtual impedance. The operational logic of this strategy is as follows: the virtual impedance is connected in series between the power outer loop and the voltage outer loop. When the short-circuit current amplitude does not exceed the current value corresponding to the short-time overcurrent capability of the inverter, the virtual resistance is zero, the virtual impedance is not engaged, and the energy storage maintains normal grid-connected control. When the grid connection point current exceeds the inverter threshold, the virtual impedance adaptively increases according to the current exceeding the limit to limit the fault current. At the same time, the power outer loop is blocked to stabilize the amplitude and phase angle of the virtual internal potential, so that the grid-connected energy storage maintains the voltage source characteristics during the fault and actively supports the grid voltage, thereby taking into account the dual requirements of voltage stabilization and current suppression in low-voltage ride-through control.

[0043] S1.7: Establish a fault steady-state positive sequence equivalent model and determine the segmented current limiting critical conditions: Based on the aforementioned dual-loop decoupled control structure of voltage outer loop and current inner loop, the grid-type energy storage under fault steady state is equivalent to a voltage source series impedance. Its impedance characteristics are jointly determined by the overcurrent multiple and the virtual impedance strategy, and the positive-sequence equivalent model is expressed as: (8); in, This is the commanded value for the outer power loop voltage; This is the positive sequence voltage at the grid connection point; This is the positive sequence current at the grid connection point; This is the equivalent resistance of the filter; The equivalent inductance of the filter; It is the imaginary unit.

[0044] It should be noted that this equivalent model has significant piecewise characteristics: when the grid connection point voltage is higher than the current-limiting critical voltage, the virtual impedance is zero, and the energy storage is equivalent to the voltage source series filter impedance; when overcurrent occurs, the virtual impedance is activated, and the equivalent impedance increases. The piecewise current-limiting critical condition is expressed as: (9); in, This is the current-limiting critical voltage; The current is the critical current for current limiting. Because the virtual impedance is switched between operating conditions, the short-circuit current calculation equations exhibit non-smooth, non-linear characteristics. Traditional short-circuit current calculation methods based on fixed impedance are difficult to apply directly. This is the fundamental reason why this invention needs to obtain measured data through on-site artificial short-circuit tests to verify and correct the equivalent model.

[0045] S2: Based on the transient response mathematical model, determine the artificial short-circuit test conditions and construct a multi-point synchronous acquisition architecture covering multiple voltage levels: S2.1: Set the test conditions: The test conditions in this embodiment are set as follows: the energy storage state of charge (SOC) is 40%, the operating state is charging, the operating mode is grid-connected mode, the test power is 90% of the photovoltaic rated power and the energy storage charging rated power, AVC operates locally, SVG operates in constant reactive power mode, and AGC is controlled locally. The principle for setting the test conditions is to select the charging state and a relatively high power condition so that the energy storage converter is in a heavy load operating state before the fault. At the moment of the fault, the voltage difference and current impact between the converter outlet and the grid connection point are more significant, thereby fully stimulating the transient response process of the grid-connected energy storage, making the transient data obtained from the test more representative and assessable; the energy storage SOC value of 40% can take into account the energy margin of the energy storage before and after the test, and avoid touching the overcharge or over-discharge protection boundary during the test.

[0046] S2.2: Assess the grid strength at the grid connection point: Grid strength directly affects the fault response depth of grid-connected energy storage. The grid strength at the connection point is assessed based on the short-circuit ratio definition of new energy power plants. (10); in, Short-circuit ratio; The nominal voltage of the busbar at the grid connection point; Rated power for new energy sources; This is the equivalent impedance from the grid connection point to the grid. The smaller the short-circuit ratio, the weaker the grid at the connection point, and the deeper the voltage drop caused by the fault. This better tests the voltage support capability and low-voltage ride-through performance of grid-connected energy storage under weak grid conditions.

[0047] S2.3: Determine the location of the fault point: The relationship between the short-circuit current at the grid connection point and the electrical distance from the fault point to the bus is as follows: (11); in, This refers to the short-circuit current at the grid connection point. The system's equivalent voltage source voltage; The equivalent impedance of the system; This represents the electrical distance from the fault point to the busbar. This relationship shows that the closer the fault point is to the busbar, the larger the short-circuit current and the deeper the voltage drop, thus more fully verifying the transient response of grid-type energy storage under extreme fault conditions. Therefore, the fault point should be located as close to the busbar as possible, while ensuring the safety of equipment and personnel, to create the most stringent fault testing conditions for grid-type energy storage.

[0048] S2.4: Deploy a multi-point synchronous data acquisition architecture: This embodiment employs multiple power recording and analysis instruments, with 11 measuring points simultaneously deployed on both the 110kV line fault recording screen and the 35kV bus fault recording screen, covering both 110kV and 35kV voltage levels. Each power recording and analysis instrument achieves strict synchronization of sampling times through a unified clock source, such as using a GPS time signal, ensuring the consistency of transient waveforms at each measuring point on the time axis. This is a prerequisite for subsequent simultaneous solutions based on multi-point data. The short-circuit current calculation uses a set of nodal admittance matrix equations: (12); in, , , These are the admittance matrices of the nodes in positive order, negative order, and zero order, respectively. , , These represent the positive-sequence, negative-sequence, and zero-sequence node voltages, respectively. , , These represent the positive-sequence, negative-sequence, and zero-sequence node currents, respectively. This set of equations decouples all nodes in the entire network into three independent networks of positive-sequence, negative-sequence, and zero-sequence according to their sequential components. The data collected synchronously from 11 measuring points provides complete measured boundary conditions for the above set of equations, transforming the short-circuit current calculation, which originally relied on network parameter assumptions, into a problem that is constrained by measured data.

[0049] S3: Construct an external three-phase short-circuit device for the transformer substation to inject a three-phase short-circuit fault into the grid-type energy storage system. Since energy storage units are usually connected to the power grid through enclosed transformer substations, and the interior of the transformer substations does not have the space and interface to directly conduct short-circuit tests, this embodiment constructs an external three-phase short-circuit device for the transformer substation, as detailed below.

[0050] S3.1: Construct a short-circuit injection loop: like Figure 3 As shown, the 35kV temporary test cable is led out from the high-voltage side of the transformer substation, and transitions to the copper busbar after being supported by an array of post insulators. Post insulators are installed every 1 meter within the first 3 meters and the last 6 meters of the cable lead-out section, and every 1.5 meters along the copper busbar section. A safe distance of more than 15 meters is maintained between the short-circuit point and the energy storage equipment area. The functions of this arrangement are: the equivalent impedance to ground of the post insulator array is much greater than the system impedance, ensuring that the short-circuit current mainly flows along the predetermined path, avoiding leakage to ground; at the same time, the post insulators mechanically fix the cable and copper busbar, suppressing the conductor swaying and deformation caused by the huge electrodynamic force during a short circuit, ensuring the safety of personnel and equipment during the test; the smaller spacing of the insulators within the first 3 meters and the last 6 meters of the cable lead-out section is because these sections are where electrodynamic and mechanical stresses are most concentrated.

[0051] S3.2: Achieve three-phase short circuit via instantaneous failure line: The copper busbar is wrapped with aluminum tape at its end, and a 1mm² instantaneous fault conductor is used to short-circuit the three phases, which is equivalent to short-circuiting the three-phase lines via the instantaneous fault conductor. The short-circuit current at the short-circuit point is provided jointly by the system side and the grid-type energy storage side. (13); in, The short-circuit current phasor at the short-circuit point; This is the short-circuit current phasor on the system side; Let be the phasor of the short-circuit current on the grid-type energy storage side. This superposition relationship indicates that the short-circuit current measured at the short-circuit point contains the true contribution component of the grid-type energy storage, which is the direct physical basis for assessing the short-circuit current contribution level of the grid-type energy storage. Let the instantaneous line resistance be... At the instant the circuit breaker closes, the Joule heat generated by the short-circuit current flowing through the instantaneously damaged conductor is: (14); in, The Joule heat generated by the short-circuit current flowing through the momentarily damaged wire; for The short-circuit current at the short-circuit point at any given moment; For instantaneous damage line resistance; The melting time is the time required for short circuit to break. Its working principle is as follows: Before the circuit breaker closes, the instantaneous fault line pre-short-circuits the three-phase copper busbars; at the instant of closing, the short-circuit current flows through the instantaneous fault line and rapidly accumulates Joule heat; when the accumulated Joule heat reaches the melting threshold of the instantaneous fault line, the fault line melts and vaporizes, and the short-circuit point changes from a conductor connection state to a stable metallic three-phase short circuit state, thus realistically simulating a permanent three-phase metallic short-circuit fault occurring on a transmission line. The above device constitutes a reusable short-circuit injection platform. Each test only requires replacing the instantaneous fault line to perform short-circuit injection again, solving the engineering problem that closed-type transformer substations cannot directly conduct short-circuit tests.

[0052] S4: A multi-point synchronous acquisition architecture is used to synchronously acquire transient data under short-circuit fault conditions. Transient response data and short-circuit current are obtained through sequence component extraction and solving of the short-circuit current equations. S4.1: Trigger synchronous waveform recording: Multiple electrical recording and analysis instruments were used to simultaneously record waveforms at 11 measuring points. Short-circuit faults are short-lived and transient processes are rapid; therefore, a waveform recording trigger threshold was set to accurately capture the transient process at the moment of a short circuit. When the current change at any measuring point exceeds 0.1A, the waveform recording device automatically triggers recording to acquire the transient waveforms of three-phase voltage and three-phase current throughout the entire process of fault occurrence, development, and clearance.

[0053] S4.2: Extracting the order component: Since the calculation of three-phase short-circuit current is based on a sequence component network, the time-domain waveform must first be converted into sequence components. After the fundamental phasors of the three-phase voltage and current collected at each measuring point are extracted using Fourier transform, the sequence components are extracted using the symmetrical component method. (15); (16); (17); (18); (19); (20); in, , , These are three-phase voltage phasors; , , These are three-phase current phasors; Let be the rotation factor, and its value is . ; , , These are the positive-sequence, negative-sequence, and zero-sequence voltage components, respectively. , , These are the positive-sequence, negative-sequence, and zero-sequence current components, respectively. Using the symmetrical component method, the three-phase coupled electromagnetic quantities are decomposed into independent electrical quantities under three sequence networks, laying the foundation for solving the sequence network equations.

[0054] S4.3: Solve the short-circuit current equations: Substitute the extracted sequence components into the short-circuit current equations: (twenty one); in, , , These are the admittance matrices for positive-sequence, negative-sequence, and zero-sequence nodes, respectively. By substituting the measured voltages and injected currents at the 11 measurement points into the above equations, the short-circuit current distribution at each node is obtained. This yields the transient response data and short-circuit current level of the grid-type energy storage system, realizing a complete conversion from time-domain transient waveforms to short-circuit current electrical parameters, and providing experimental basis for the verification of fault equivalent models.

[0055] S5: Compare and verify the measured transient response data with the simulation results: S5.1: Inverse calculation of actual virtual impedance: The actual operating value of the virtual impedance is a key quantity for determining whether the current limiting strategy executes according to the design logic. Substituting the measured voltages and injected currents at each measurement point into the short-circuit current distribution results obtained from S4.3, the actual virtual impedance of the grid-type energy storage system during the fault period can be deduced: (twenty two); in, For virtual resistance; For virtual reactance; This is the commanded value for the outer power loop voltage; This is the positive sequence voltage at the grid connection point; This is the positive sequence current at the grid connection point; This is the equivalent resistance of the filter; The equivalent inductance of the filter; This is the actual angular frequency; The unit is imaginary. The physical meaning of this formula is: after deducting the voltage drop across the filter impedance from the measured electrical quantity at the grid connection point, the remaining portion is the actual voltage drop contribution of the virtual impedance. This allows us to reconstruct the actual virtual impedance value applied by the control strategy during a fault. Comparing the derived virtual impedance value with the theoretical preset value verifies whether the actual operating characteristics of the virtual impedance current limiting strategy are consistent with the control logic.

[0056] S5.2: Comparison and Verification and Parameter Correction: Using short-circuit current amplitude, transient response time, and reactive power support capability during low-voltage ride-through as evaluation indicators, the relative error between measured and simulated values ​​is calculated: (twenty three); in, This is relative error; These are the measured values ​​of the evaluation indicators; These are the simulated values ​​for the evaluation indicators. When all relative errors are less than the set threshold, the fault equivalent model of the grid-type energy storage system is considered accurate and has high computational precision. In this embodiment, the set threshold is 1%. When the error exceeds the set threshold, the simulation model parameters are corrected based on the actual virtual impedance derived from S5.1, and the model is re-simulated and re-compared until the error meets the requirements. This forms a closed-loop process of field measurement, model comparison, parameter correction, and re-verification, providing field measured data support for the fault ride-through capability assessment and simulation model parameter correction of the grid-type energy storage system.

[0057] like Figure 4 As shown, Figure 4 The calculation results and simulation results of the fault equivalent model for the transient current decay process of the virtual synchronous generator during the fault were compared. It can be seen that the changing trends of the two models in the steady-state stage of the fault are basically consistent with the steady-state values, indicating that the positive-sequence equivalent model in the form of voltage source series impedance established in this invention can accurately characterize the current output characteristics of the grid-type energy storage in the steady-state stage of the fault, and verifying that the fault equivalent model has high accuracy in the steady-state stage of the fault.

[0058] As shown in Figures 5(a) and 5(b), the low-voltage problem of new energy power plants is significantly improved after configuring grid-based energy storage: during voltage dips, grid-based energy storage provides more reactive power than grid-connected energy storage, and its support for the voltage at the power plant terminals is superior; after the fault is cleared and the system enters a steady state, the voltage recovery effect of grid-based energy storage is also better. The above comparison verifies the reactive power support capability of grid-based energy storage during low-voltage ride-through from a practical perspective, and also confirms the rationality of using reactive power support capability as a comparative verification and evaluation indicator in this invention.

[0059] As shown in Figures 6(a) and 6(b), a comparison of the transient voltage waveforms at the grid connection point under different reactive power reference values ​​reveals that increasing the reactive power output of the grid-connected energy storage converter can effectively improve the grid connection point voltage level during low voltage ride-through: when the reactive power reference value is 300 Mvar, the grid connection point voltage can be increased from 0.5 pu to 0.95 pu, and the voltage recovery time after the fault shortens with the increase of reactive power injection. This result demonstrates that grid-connected energy storage possesses adjustable voltage support capability under three-phase short-circuit faults, verifies the transient response characteristics of grid-connected energy storage under three-phase short-circuit faults, and also provides experimental basis for the setting of reactive power reference values ​​in low voltage ride-through control strategies.

[0060] In summary, this invention effectively obtains transient response data and short-circuit current levels of grid-connected energy storage under three-phase short-circuit faults by establishing a transient response mathematical model, designing an on-site artificial short-circuit test scheme, constructing an external three-phase short-circuit device for transformer substations, and simultaneously collecting and analyzing transient data and comparing it with simulation results. This verifies the accuracy of the fault equivalent model and provides on-site measured data support for the correction of grid-connected energy storage simulation models and the calculation of short-circuit currents, which helps to improve the safe and stable operation level of grid-connected energy storage systems.

Claims

1. A transient response testing method for artificial short-circuit tests of a grid-type energy storage system, characterized in that... Includes the following steps: S1: Establish a mathematical model of the transient response of a grid-type energy storage system under artificial short-circuit fault; S2: Based on the transient response mathematical model, determine the artificial short-circuit test conditions and construct a multi-measurement point synchronous acquisition architecture covering multiple voltage levels; S3: Construct an external three-phase short-circuit device for the transformer substation to inject a three-phase short-circuit fault into the grid-type energy storage system; S4: The transient data under short-circuit fault is synchronously acquired using the multi-point synchronous acquisition architecture. After sequence component extraction and short-circuit current equation solving, the transient response data and short-circuit current of the grid-type energy storage system are obtained. S5: Compare and verify the measured transient response data with the simulation results.

2. The transient response testing method for artificial short-circuit tests of a grid-type energy storage system according to claim 1, characterized in that: S1 includes: S1.1: Establish the dynamic equations of the DC / AC converter and LCL filter circuit of the grid-type energy storage system in the dq coordinate system: ； ； in, , These are the d-axis and q-axis components of the converter-side output current; , These are the d-axis and q-axis components of the grid connection point voltage; , These are the d-axis and q-axis components of the converter-side output voltage; , These are the d-axis and q-axis components of the grid-connected current; For filtering inductors; For filtering capacitors; For filtering resistors; The angular frequency of the power grid; S1.2: Based on the dynamic equations described in S1.1, establish the active power-frequency control equations for the outer power loop of the virtual synchronous generator: ； in, This is virtual inertia; For virtual damping; The mechanical power output by the virtual synchronous generator; The electromagnetic power output by the virtual synchronous generator; This is the actual angular frequency; The rated angular frequency; S1.3: Based on the active power-frequency control of S1.2, a reactive power-voltage control equation is established, and the virtual internal potential amplitude is dynamically adjusted by detecting the voltage deviation at the grid connection point. ； in, This represents the amplitude of the virtual internal potential. For regulator gain; The time constant of the excitation winding; Rated voltage; The measured voltage at the grid connection point; Synchronous reactance; Transient reactance; The d-axis component of the grid current injected into the converter; For the Laplace operator.

3. The transient response testing method for artificial short-circuit tests of a grid-type energy storage system according to claim 2, characterized in that: S1 further includes: S1.4: Based on the virtual internal potential amplitude determined in S1.3, establish the voltage outer loop equation and generate the d-axis and q-axis reference values ​​for the current inner loop: ； in, , These are the d-axis and q-axis reference values ​​for the inner current loop, respectively. , These are the d-axis and q-axis components of the virtual internal potential, respectively. , These are the d-axis and q-axis components of the measured voltage at the grid connection point, respectively. For filtering resistors; For filter reactance; For virtual resistance; For virtual reactance; S1.5: Using the current inner loop reference value generated in S1.4 as the command value, establish the current inner loop PI control equation: ； in, , These are the internal potential control output signals for the d and q axes, respectively; The q-axis component of the grid current injected into the converter; , These are the d-axis and q-axis current state feedback quantities, respectively. , These are the d-axis and q-axis components of the converter terminal voltage, respectively. , The parameters are PI control parameters; the internal potential control output signal is converted into a PWM modulation signal after Park inverse transformation, realizing full closed-loop control from virtual internal potential to actual output voltage.

4. The transient response testing method for artificial short-circuit tests of a grid-type energy storage system according to claim 3, characterized in that: S1 further includes: S1.6: To address the voltage drop caused by a three-phase short-circuit fault at the grid connection point, an adaptive virtual impedance current limiting strategy is established. ； in, This represents the amplitude of the short-circuit current. This is the short-time overcurrent multiple of the inverter. This is the inverter's rated current; This is the virtual resistivity. The impedance ratio of the virtual impedance; when the grid connection point current exceeds the inverter threshold, the virtual impedance is adaptively increased to limit the current, and the power outer loop is blocked to stabilize the amplitude and phase angle of the virtual internal potential, so that the grid-type energy storage system maintains the voltage source characteristics during the fault. S1.7: Based on the adaptive virtual impedance current limiting strategy of S1.6, a positive-sequence equivalent model of the fault steady state of the grid-type energy storage system is established: ； in, This is the commanded value for the outer power loop voltage; This is the positive sequence voltage at the grid connection point; This is the positive sequence current at the grid connection point; This is the equivalent resistance of the filter; The equivalent inductance of the filter; The imaginary unit; And determine the piecewise current limiting critical condition of the positive sequence equivalent model: ； in, This is the current-limiting critical voltage; The current limiting critical current is used; when the grid connection point voltage is higher than the current limiting critical voltage, the virtual impedance is set to zero, and the virtual impedance is activated when an overcurrent occurs.

5. The transient response testing method for artificial short-circuit testing of a grid-type energy storage system according to claim 4, characterized in that: S2 further includes: S2.1: Set artificial short-circuit test conditions, including the energy storage state of charge (SOC) value, charge and discharge operation status, grid operation mode, and test power; S2.2: Assess the grid strength at the connection point based on the short-circuit ratio of new energy power plants: ； in, Short-circuit ratio; The nominal voltage of the busbar at the grid connection point; Rated power for new energy sources; The equivalent impedance from the grid connection point to the power grid; S2.3: Based on the power grid strength assessment results of S2.2, the fault location is determined according to the relationship between the short-circuit current at the grid connection point and the electrical distance from the fault point to the bus. ； in, This refers to the short-circuit current at the grid connection point. The system's equivalent voltage source voltage; The equivalent impedance of the system; The electrical distance from the fault point to the busbar is used to fully verify the transient response of the grid-type energy storage system under extreme fault conditions. The closer the fault point is to the busbar, the larger the short-circuit current and the deeper the voltage drop.

6. The transient response testing method for an artificial short-circuit test of a grid-type energy storage system according to claim 5, characterized in that: S2 further includes: S2.4: After determining the fault location, multiple measuring points are simultaneously deployed on the bus fault recording screens and line fault recording screens at the multiple voltage levels to construct a set of nodal admittance matrix equations for short-circuit current calculation: ； in, , , These are the admittance matrices of the nodes in positive order, negative order, and zero order, respectively. , , These represent the positive-sequence, negative-sequence, and zero-sequence node voltages, respectively. , , These represent the positive-sequence, negative-sequence, and zero-sequence node currents, respectively; the data collected synchronously from the multiple measurement points provide complete measured boundary conditions for the node admittance matrix equations.

7. The transient response testing method for an artificial short-circuit test of a grid-type energy storage system according to claim 6, characterized in that: S3 includes: S3.1: A temporary test cable is led out from the high-voltage side of the transformer substation, and after being supported by the post insulator array, it transitions to the copper busbar. The short-circuit point is kept at a safe distance from the energy storage equipment area. The equivalent impedance to ground of the post insulator array is much greater than the system impedance, so that the short-circuit current flows along a predetermined path. S3.2: A three-phase short circuit is achieved at the end of the copper busbar described in S3.1 through a transient fault line, forming a reusable short-circuit injection device. The short-circuit current at the short-circuit point is jointly provided by the system side and the grid-type energy storage side. ； in, The short-circuit current phasor at the short-circuit point; This is the short-circuit current phasor on the system side; This refers to the short-circuit current phasor on the grid-type energy storage side.

8. The transient response testing method for an artificial short-circuit test of a grid-type energy storage system according to claim 7, characterized in that: In S3.2, the melting process of the instantaneous failure wire is as follows: At the moment the circuit breaker closes, the short-circuit current flows through the momentarily damaged conductor, generating Joule heat. ； in, The Joule heat generated by the short-circuit current flowing through the momentarily damaged wire; for The short-circuit current at the short-circuit point at any given moment; For instantaneous damage line resistance; The melting time is the time it takes for the circuit to break. When the accumulated Joule heat reaches the melting threshold of the instantaneous failure line, the instantaneous failure line melts, forming a stable metallic three-phase short circuit.

9. The transient response testing method for an artificial short-circuit test of a grid-type energy storage system according to claim 8, characterized in that: S4 includes: S4.1: Set the waveform recording trigger threshold value When the sudden change in current at any measuring point exceeds the waveform recording trigger threshold, synchronous waveform recording is triggered at each measuring point to obtain the transient waveforms of the three-phase voltage and three-phase current. S4.2: After Fourier transforming the three-phase voltage and three-phase current collected in S4.1, the sequence components are extracted using the symmetrical component method. ; ； ； ； ； ； in, , , These are three-phase voltage phasors; , , These are three-phase current phasors; The rotation factor; , , These are the positive-sequence, negative-sequence, and zero-sequence voltage components, respectively. , , These are the positive-sequence, negative-sequence, and zero-sequence current components, respectively. S4.3: Substitute the sequence components extracted in S4.2 into the short-circuit current equations and solve: ； in, , , The admittance matrices of the nodes are positive-sequence, negative-sequence, and zero-sequence, respectively. The short-circuit current distribution of each node is obtained by solving the problem, and the transient response data and short-circuit current of the grid-type energy storage system are obtained.

10. The transient response testing method for an artificial short-circuit test of a grid-type energy storage system according to claim 9, characterized in that: S5 includes: S5.1: Substitute the measured voltage and injected current at each measuring point into the short-circuit current distribution result obtained from S4.3, and deduce the actual virtual impedance of the grid-type energy storage system during the fault period: ； in, For virtual resistance; For virtual reactance; This is the commanded value for the outer power loop voltage; This is the positive sequence voltage at the grid connection point; This is the positive sequence current at the grid connection point; This is the equivalent resistance of the filter; The equivalent inductance of the filter; This is the actual angular frequency; The imaginary unit; S5.2: Using short-circuit current amplitude, transient response time, and reactive power support capability during low-voltage ride-through as evaluation indicators, calculate the error between the measured value and the simulated value; when all errors are less than the set threshold, the fault equivalent model of the grid-type energy storage system is determined to be accurate; when the error exceeds the set threshold, the simulation model parameters are corrected based on the actual virtual impedance derived from S5.1.

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