Dual-criteria fault identification method based on energy storage programmed stepwise power injection

Abstract

This invention discloses a dual-criteria fault identification method based on programmed stepped power injection of energy storage. First, distribution network parameters are collected. Based on the power balance equation of the downstream islanded system, the basic mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system is derived. Then, the reactive power compensation equation of the downstream islanded system is established. Combining the reactive power compensation start-up conditions and whether inverter current limiting constraints are triggered, the downstream islanded system is divided into four operating intervals. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system in each operating interval is derived, thereby obtaining the downstream islanded system's... U-P Curve; finally, based on downstream islanding systems U-P The curve determines the minimum power regulation amount, and the power regulation amount is determined based on the minimum power regulation amount. The energy storage system injects power according to the power regulation amount, and the fault clearance is detected in real time during the power regulation process. This method enables accurate differentiation between transient and permanent faults.

Description

Technical Field

[0001] This invention belongs to the field of power distribution network fault identification technology, and specifically relates to a dual-criteria fault identification method based on programmed step power injection of energy storage. Background Technology

[0002] With the high penetration of distributed renewable energy, traditional passive distribution networks are rapidly transforming into active distribution networks with multi-source collaboration. When a circuit breaker trips due to a line fault, the downstream area no longer exhibits pure load characteristics but instead forms an islanded system supported by distributed energy resources and energy storage systems. Post-trip fault status identification is a core element in ensuring the safe and stable operation of active distribution networks and achieving rapid power restoration after a fault. Reliable fault status identification can prevent secondary equipment damage and fault propagation caused by reclosing after a permanent fault. It is also an important means to support the optimized operation of islanded systems to ensure power supply to critical loads, improve fault handling efficiency, and reduce operation and maintenance costs. Furthermore, it has significant engineering value for the protection and self-healing control of active distribution networks.

[0003] Current fault state identification methods are mainly divided into two categories: passive detection and active injection. Passive detection often relies on transient fault characteristics or steady-state voltage and current amplitudes to identify faults. Some studies have also used data-driven methods to mine correlations in measurement signals to improve identification results. However, these methods only rely on the system's natural electrical response and cannot actively amplify the characteristic differences between transient and permanent faults. Furthermore, in the early stages of a fault, the electrical characteristics of the two types of faults are highly similar, and feature extraction is easily affected by noise, load fluctuations, and network parameter uncertainties, resulting in insufficient detection stability. Data-driven methods also rely on large-scale labeled datasets, and their generalization ability under different topologies and operating conditions is difficult to guarantee.

[0004] Active signal injection amplifies differences in fault states by injecting controllable disturbances into the system. Existing methods fall into two categories: one relies on additional hardware such as capacitor discharge units and dedicated detection equipment for signal injection, increasing equipment investment and installation space requirements, making large-scale deployment difficult; the other utilizes existing power electronic converters to inject high-frequency or harmonic signals, which suffers from complex control implementation, cumbersome parameter design, and the injected signal can easily interfere with protection devices, cause harmonic pollution, and even affect equipment insulation life, limiting its engineering applications. Energy storage systems are widely deployed in high-penetration distributed energy distribution networks. Through inverter grid connection, they possess flexible power regulation capabilities, enabling power injection without adding extra hardware and without introducing harmonic pollution or severe transient disturbances. They can effectively amplify voltage response differences under different fault states, providing a new approach for fault state identification. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to propose a dual-criteria fault identification method based on programmed step-by-step power injection in energy storage.

[0006] The present invention solves the aforementioned technical problem by adopting the following technical solution: A dual-criteria fault identification method based on programmed stepped power injection in energy storage, characterized by the following steps: Step 1: Collect power distribution network parameters, including rated load power, output power and rated output current of energy storage system, and rated voltage of downstream islanded system; Step 2: Based on the power balance equation of the downstream islanded system, derive the basic mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system. (2) In the formula, This represents the actual voltage of the downstream islanded system. For the output power of the energy storage system, The rated power of the load, The rated voltage for the downstream islanded system. This represents the per-unit value of the output power of the energy storage system. Step 3: Establish the reactive power compensation equation for the downstream islanded system; combining the reactive power compensation start-up conditions and whether the inverter current limiting constraint is triggered, divide the downstream islanded system into 4 operating intervals, derive the mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system in each operating interval, and thus obtain the downstream islanded system's... UP curve; The reactive power compensation equation is: (3) In the formula, For inverter output Shaft reactive current component, This is the reactive power voltage regulation coefficient. This is the rated output current of the energy storage system; First interval: Reactive power compensation needs to be started, but the inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). Second section: No reactive power compensation needs to be started, and the inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). Third section: Reactive power compensation needs to be started, but the inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). The critical voltage that triggers current limiting in the inverter; Fourth section: Reactive power compensation needs to be activated, triggering the inverter's current limiting constraint, and the inverter's output... The axial reactive current component satisfies equation (8). (8) (9) In the formula, Inverter current limiting factor According to equation (8) Calculate the per-unit value of the energy storage system's output power; this can be achieved through the reactive power compensation equation. Calculate the actual voltage of the downstream islanded system, and then obtain the mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system; Step 4: Based on downstream islanding systems UP The curve determines the minimum power adjustment amount, and the power adjustment amount is determined based on the minimum power adjustment amount. The energy storage system starts power adjustment with the rated load power as the initial value. In the first half of the cycle, downward power adjustment is performed based on the power adjustment amount, and the power injection amount of the energy storage system is the difference between the rated load power and the power adjustment amount. In the second half of the cycle, upward power adjustment is performed based on the power adjustment amount, and the power injection amount of the energy storage system is equal to the rated load power. During power regulation, the system continuously monitors whether the fault has been cleared. This involves collecting the three-phase voltage at the downstream outlet of the circuit breaker before and after power regulation, extracting the positive-sequence voltage at the downstream outlet of the circuit breaker before and after power regulation, and obtaining the change in positive-sequence voltage. The positive sequence voltage change criterion is constructed as follows: (10) In the formula, The minimum reliable voltage change threshold; Calculate the instantaneous rate of change of three-phase voltage: (11) In the formula, for The instantaneous rate of change of phase voltage, , They are respectively , Moment Phase voltage, The time interval before and after power adjustment; The voltage waveform distortion criterion is established as follows: (12) In the formula, To take the absolute value, This represents the per-unit value of the maximum voltage of the downstream islanded system during a large-scale load disconnection. This is the highest permissible frequency for the energy storage system to discharge. This refers to the measurement error margin coefficient. When both the positive sequence voltage change criterion and the voltage waveform distortion criterion are met simultaneously, it indicates that the fault has been cleared and is determined to be a transient fault; otherwise, the fault has not been cleared and is determined to be a permanent fault.

[0007] Furthermore, based on the downstream islanding system UP The curve represents the minimum power regulation, which is the power corresponding to the sum of the voltage rise in the downstream islanded system after the load is disconnected from the grid and the reliable voltage change threshold.

[0008] Furthermore, in the fourth step, if the fault is not cleared after three to five consecutive adjustment cycles, it is considered a permanent fault; the power adjustment amounts for each cycle are as follows: , , , , , This is the minimum power adjustment amount.

[0009] Furthermore, the critical voltage for triggering the inverter current limiting satisfies the following equation: (4) In the formula, This is the equivalent resistance of the load.

[0010] Compared with the prior art, the present invention has the following beneficial effects: 1. Divide the operating range of the downstream islanded system into four segments. Based on these operating ranges, perform segmented mapping between the actual voltage of the downstream islanded system and the output power of the energy storage system, thereby obtaining the downstream islanded system... UP Curve. Based on UP The curve determines the minimum power adjustment amount. Based on this, the output power of the energy storage system is adjusted downwards and upwards sequentially, thus obtaining a programmed step-by-step power injection control strategy. After a fault occurs in the distribution network, the energy storage system is controlled to inject power according to the programmed step-by-step power injection control strategy. At the same time, the three-phase voltage at the downstream outlet of the circuit breaker is collected. Based on the dual criteria of positive sequence voltage change and voltage waveform distortion, transient faults and permanent faults are accurately distinguished.

[0011] Programmed operation refers to the fact that the timing of power changes and the magnitude of power regulation in an energy storage system are pre-designed and tuned, and it executes automatically like a program after a fault occurs. Stepped operation refers to the energy storage system sequentially adjusting downward and upward power within each cycle, similar to step-like power regulation.

[0012] 2. This invention constructs a distinguishable dual criterion of positive-sequence voltage change and voltage waveform distortion through active energy storage injection of programmed stepped power. This effectively amplifies the characteristic differences between transient and permanent faults, avoiding misjudgments caused by measurement errors, system disturbances, and partial load disconnection. It is adaptable to complex application scenarios with different fault locations, fault types, and a wide range of fault resistances, significantly improving the reliability and accuracy of fault identification. It has good engineering applicability and promotional value. This method does not require additional dedicated detection equipment, and the use of power frequency injection does not introduce harmonic pollution or severe transient disturbances. It effectively overcomes the problems of weak anti-interference capability of existing passive detection methods, the need for additional hardware or the introduction of harmonic pollution in active injection schemes, poor engineering applicability, difficulty in identifying fault status after tripping of circuit breakers in high-penetration active distribution networks, and the easy occurrence of secondary equipment damage and fault propagation due to reclosing of permanent faults. Attached Figure Description

[0013] Figure 1 This is the overall flowchart; Figure 2 This is a power distribution network topology diagram for an example. Figure 3 The downstream islanding system of the embodiment UP curve; Figure 4 The three-phase voltage waveform diagram at the downstream outlet of the circuit breaker is shown in the example. Figure 5 This is a schematic diagram of the positive sequence voltage at the downstream outlet of the circuit breaker in an embodiment. Figure 6 This is a schematic diagram of the voltage waveform distortion value at the downstream outlet of the circuit breaker in an embodiment. Detailed Implementation

[0014] Specific embodiments are given below with reference to the accompanying drawings. These specific embodiments are only used to describe the technical solution of the present invention in detail and are not intended to limit the scope of protection of this application.

[0015] like Figure 1 As shown, this invention provides a dual-criteria fault identification method based on programmed stepped power injection in energy storage, comprising the following steps: Step 1: Collect power distribution network parameters, including rated load power. Energy storage system output power With rated output current Rated voltage of downstream islanded system ; Step 2: Based on the constant impedance load power conservation characteristics of the downstream islanded system, establish the power balance equation of the downstream islanded system; (1) In the formula, This represents the actual voltage of the downstream islanded system. The load is equivalent to the resistance. Based on the power balance equation, the basic mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system is obtained; (2) In the formula, This represents the per-unit value of the output power of the energy storage system. Step 3: Combine the reactive power compensation rules of the downstream islanded system to establish the reactive power compensation equation of the downstream islanded system; (3) In the formula, For inverter output Shaft reactive current component, This is the reactive power voltage regulation coefficient; Based on the reactive power compensation start-up conditions and whether the inverter current limiting constraint is triggered, the downstream islanded system is divided into four operating intervals. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system in each operating interval is derived, thereby obtaining the downstream islanded system... UP curve; First interval: This indicates that the voltage of the downstream islanded system is too high, and reactive power compensation needs to be started. The actual load power is too low and the equivalent load resistance is too high. The inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). Second section: This indicates that the voltage of the downstream islanded system is within the normal fluctuation range, so there is no need to start reactive power compensation and the inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). Third section: This indicates that the voltage of the downstream islanded system is too low, requiring reactive power compensation to be initiated, but the inverter current limiting constraint is not triggered, and the actual voltage of the downstream islanded system still conforms to the basic mapping relationship of equation (2); where, The critical voltage that triggers inverter current limiting and satisfies the following equation: (4) Fourth section: This indicates that the voltage of the downstream islanded system is too low, requiring the activation of reactive power compensation. Simultaneously, the inverter current limiting constraint is triggered, and the inverter output current reaches the current limiting threshold. After the inverter current limiting constraint is triggered, the inverter output... Shaft reactive current component for: (5) In the formula, This is the inverter current limiting coefficient; Substitute equation (5) into Then Substituting into the reactive power compensation equation of equation (3), we can obtain: (6) Will , Substituting into equation (6), and after simplification, we get: (7) Solving equation (7) yields: (8) (9) From equation (8), it can be seen that, according to The per-unit value of the output power of the energy storage system can be calculated. From the reactive power compensation equation, it can be seen that, according to It can also calculate the actual voltage of the downstream islanded system. This reveals the mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system, thus allowing us to obtain the downstream islanded system's voltage in the fourth interval. UP curve; Step 4: Based on downstream islanding systems UP The curve determines the minimum power adjustment amount, and the power adjustment amount is determined based on the minimum power adjustment amount. During the programmed step power injection process of energy storage, power adjustment is performed according to the power adjustment amount. After each adjustment, the fault status is determined based on the positive sequence voltage change criterion and waveform distortion criterion. Using a conservative design principle based on worst-case conditions, the minimum power regulation is derived. When the load is disconnected from the grid, the energy storage system outputs power. Greater than the rated power of the load According to equation (1), the actual voltage of the downstream islanded system can be obtained. The voltage will rise; the amount of voltage rise will be recorded as... If the output power reduction of the energy storage system coincides with a load disconnection, the voltage rise caused by the load disconnection will offset the voltage change generated by the power adjustment. To ensure that the voltage difference before and after the power adjustment is still greater than the minimum reliable voltage change threshold in this case... Minimum power adjustment amount needs to be set. ;in, Due to the inherent measurement error of voltage transformers, The inherent voltage fluctuation limit for steady-state operation of the distribution network; based on the mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system ( UP (curve), the sum of voltage rise and reliable voltage change threshold The corresponding energy storage system output power is the minimum power regulation amount. This ensures that, in the event of a large-scale load disconnection, the voltage change caused by adjusting the output power of the energy storage system can cover the voltage rise caused by the load disconnection. Energy storage system based on load rated power Power regulation is initiated based on the initial value. Within each cycle, one downward power regulation and one upward power regulation are performed sequentially. The first half of the cycle uses the minimum power regulation amount. As power regulation quantity Downward power regulation is performed, and the power injection amount after downward power regulation (power injection amount refers to the output power of the energy storage system) is: The second half of the cycle uses the minimum power adjustment. As power regulation quantity Upward power regulation is performed to ensure the energy storage system's output power equals its initial value, guaranteeing the downstream islanded system enters a quasi-steady-state operating state and thus obtaining stable and identifiable voltage response characteristics. The power injection amount after upward power regulation is... During power regulation, the fault is checked in real time to see if it has been cleared. If the fault is not cleared after three to five consecutive regulation cycles, it is considered a permanent fault. In this embodiment, the power regulation amount for the second to fifth cycles is... They are respectively , , , ; During power regulation, voltage transformers are used to collect the three-phase voltage at the downstream outlet of the circuit breaker before and after each power regulation, and the positive sequence voltage at the downstream outlet of the circuit breaker before and after power regulation is extracted to obtain the positive sequence voltage change. The criterion for positive sequence voltage change is: (10) Under the condition that the fault has been cleared, the voltage of the downstream islanded system varies monotonically with the output power of the energy storage system, and the calculated positive-sequence voltage change is greater than [missing value]. If the positive sequence voltage change criterion holds, then the positive sequence voltage change criterion holds. Under permanent fault conditions, the fault point continuously clamps the voltage of the downstream islanded system, and the energy storage stepped power injection cannot cause a change in the effective voltage amplitude. The positive sequence voltage change approaches zero, so the positive sequence voltage change criterion does not hold.

[0016] Meanwhile, the discrete difference method is used to calculate the instantaneous rate of change of the three-phase voltage: (11) In the formula, for The instantaneous rate of change of phase voltage, , They are respectively , Moment Phase voltage, The time interval before and after power adjustment; The voltage waveform distortion criterion is established as follows: (12) In the formula, To take the absolute value, The maximum per-unit voltage of the downstream islanded system during large-scale load disconnection is taken as 1.290 pu in this embodiment; This embodiment represents the highest permissible discharge frequency for the energy storage system. , The rated power frequency for the energy storage system; The measurement error margin coefficient is set to 1.05 in this embodiment; Under no-arc fault conditions, the voltage waveform of the downstream islanded system is a quasi-sinusoidal waveform affected by the load, and the fluctuation range of the instantaneous rate of change of voltage is within the range corresponding to the normal power frequency, which satisfies the waveform distortion criterion. Under arc fault conditions, the voltage waveform exhibits severe distortion at the moment of arc combustion and extinction, and the instantaneous rate of change of voltage far exceeds the normal threshold range, so the waveform distortion criterion is not valid.

[0017] Therefore, when both the positive sequence voltage change criterion and the voltage waveform distortion criterion are met simultaneously, it indicates that the fault has been cleared and is determined to be a transient fault; otherwise, it indicates that the fault has not been cleared and is determined to be a permanent fault, thereby improving the reliability of fault identification.

[0018] Example This embodiment takes a distribution network containing a 10kV substation, a 100kW energy storage system, and a 100kW load as an example. Its topology is as follows: Figure 2 As shown, a three-stage current protection system is configured at the substation outlet circuit breaker. The fault identification voltage measurement point is located at the downstream outlet of the circuit breaker, and the voltage signal sampling frequency is 10kHz. After tripping, a 20ms window-shifting FFT is used to calculate the positive sequence voltage at the downstream outlet of the circuit breaker. The reclosing time / blocking command is adjusted based on the positive sequence voltage and the instantaneous rate of change of voltage after tripping. A three-phase transient fault (lasting 200ms) and a permanent fault with a transition resistance of 10Ω are set at feeder F1. After the fault occurs, the circuit breaker trips after 30ms of protection action.

[0019] reactive power regulation coefficient Set to 1, inverter current limiting coefficient Taking 1.2, based on the mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system, the downstream islanded system is obtained. UP Curves Figure 3As shown in the figure. When a simulated fault occurs and the circuit breaker trips, the three-phase voltage at the downstream outlet of the circuit breaker is collected. The positive sequence voltage is calculated using FFT and symmetrical component method, and the instantaneous rate of change of the three-phase voltage is calculated using discrete difference method. The three-phase voltage, positive sequence voltage, and voltage waveform distortion values ​​at the downstream outlet of the circuit breaker are shown in the figure. Figure 4-6 As shown.

[0020] Considering the inherent measurement error of voltage transformers is 3% and the inherent voltage fluctuation limit of distribution network steady-state operation is 5%, the minimum reliable voltage change threshold is derived. Voltage rise after 30% load disconnection It is 0.394 pu. exist UP The curve corresponds to the minimum power adjustment amount The power consumption was 0.577 pu, and the fault was cleared in 200 ms. At the time of clearing, the injected power of the energy storage system was... The positive sequence voltage change at the downstream outlet of the circuit breaker It is 0.348 pu, which is greater than Furthermore, the voltage waveform distortion value did not exceed the threshold, thus satisfying both the positive sequence voltage change criterion and the voltage waveform distortion criterion, and was determined to be a transient fault.

[0021] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A dual-criteria fault identification method based on programmed stepped power injection in energy storage, characterized in that, Includes the following steps: Step 1: Collect power distribution network parameters, including rated load power, output power and rated output current of energy storage system, and rated voltage of downstream islanded system; Step 2: Based on the power balance equation of the downstream islanded system, derive the basic mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system. （2） In the formula, This represents the actual voltage of the downstream islanded system. For the output power of the energy storage system, The rated power of the load, The rated voltage for the downstream islanded system. This represents the per-unit value of the output power of the energy storage system. Step 3: Establish the reactive power compensation equation for the downstream islanded system; combining the reactive power compensation start-up conditions and whether the inverter current limiting constraint is triggered, divide the downstream islanded system into 4 operating intervals, derive the mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system in each operating interval, and thus obtain the downstream islanded system's... UP curve; The reactive power compensation equation is: （3） In the formula, For inverter output Shaft reactive current component, This is the reactive power voltage regulation coefficient. This is the rated output current of the energy storage system; First interval: Reactive power compensation needs to be started, but the inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). Second section: No reactive power compensation needs to be started, and the inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). Third section: Reactive power compensation needs to be started, but the inverter current limiting constraint is not triggered. The mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system satisfies equation (2). The critical voltage that triggers current limiting in the inverter; Fourth section: Reactive power compensation needs to be activated, triggering the inverter's current limiting constraint, and the inverter's output... The axial reactive current component satisfies equation (8). （8） （9） In the formula, Inverter current limiting factor According to equation (8) Calculate the per-unit value of the output power of the energy storage system; The reactive power compensation equation can be used to determine... Calculate the actual voltage of the downstream islanded system, and then obtain the mapping relationship between the actual voltage of the downstream islanded system and the output power of the energy storage system; Step 4: Based on downstream islanding systems UP The curve determines the minimum power adjustment amount, and the power adjustment amount is determined based on the minimum power adjustment amount. The energy storage system starts power adjustment with the rated load power as the initial value. In the first half of the cycle, downward power adjustment is performed based on the power adjustment amount, and the power injection amount of the energy storage system is the difference between the rated load power and the power adjustment amount. In the second half of the cycle, upward power adjustment is performed based on the power adjustment amount, and the power injection amount of the energy storage system is equal to the rated load power. During power regulation, the system continuously monitors whether the fault has been cleared. This involves collecting the three-phase voltage at the downstream outlet of the circuit breaker before and after power regulation, extracting the positive-sequence voltage at the downstream outlet of the circuit breaker before and after power regulation, and obtaining the change in positive-sequence voltage. The positive sequence voltage change criterion is constructed as follows: （10） In the formula, The minimum reliable voltage change threshold; Calculate the instantaneous rate of change of three-phase voltage: （11） In the formula, for The instantaneous rate of change of phase voltage, , They are respectively , Moment Phase voltage, The time interval before and after power adjustment; The voltage waveform distortion criterion is established as follows: （12） In the formula, To take the absolute value, This represents the per-unit value of the maximum voltage of the downstream islanded system during a large-scale load disconnection. This is the highest permissible frequency for the energy storage system to discharge. This refers to the measurement error margin coefficient. When both the positive sequence voltage change criterion and the voltage waveform distortion criterion are met simultaneously, it indicates that the fault has been cleared and is determined to be a transient fault; otherwise, the fault has not been cleared and is determined to be a permanent fault.

2. The dual-criteria fault identification method based on programmed stepped power injection of energy storage according to claim 1, characterized in that, According to the downstream island system UP The curve shows that the minimum power regulation is the power corresponding to the sum of the voltage rise in the downstream islanded system after the load is disconnected from the grid and the reliable voltage change threshold.

3. The dual-criteria fault identification method based on programmed stepped power injection of energy storage according to claim 1 or 2, characterized in that, In the fourth step, if the fault is not cleared after three to five consecutive adjustment cycles, it is a permanent fault; the power adjustment amounts for each cycle are as follows: , , , , , This is the minimum power adjustment amount.

4. The dual-criteria fault identification method based on programmed stepped power injection of energy storage according to claim 1, characterized in that, The critical voltage for triggering the inverter current limiting satisfies the following formula: （4） In the formula, This is the equivalent resistance of the load.

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