IGBT-based distribution network pt high-voltage side fast breaking device and method

Abstract

The disclosure provides an IGBT-based distribution network PT high-voltage side fast breaking device and method, the fast breaking device comprising a voltage drop detection module, a resonance detection module, an IGBT driving circuit and an IGBT switching circuit connected in sequence; the IGBT switching circuit is connected between the distribution network voltage transformer and the power grid bus, and the IGBT switching circuit comprises a plurality of series-connected IGBT switches. By using the series connection of IGBTs instead of the traditional fuse, a higher rated working voltage can be obtained, better switching performance can be obtained, the PT failure rate caused by resonance can be reduced, the IGBT switching circuit acts quickly, does not need to be melted by the action of multiple cycles of resonance current, can cut off the PT in the early stage of resonance through control, can greatly reduce the impact of resonance on the PT, thereby protecting the PT and improving the stability and safety of system operation. Improve the efficiency of the power grid system.

Description

Technical Field

[0001] This disclosure relates to the technical field of power system equipment, specifically to a fast-break device and method for the high-voltage side of a distribution network PT based on IGBT. Background Technology

[0002] The statements in this section are merely background information relating to this disclosure and do not necessarily constitute prior art.

[0003] Damage to a voltage transformer and the blowing of its branch fuses can both cause the branch from which the voltage transformer provides voltage information to shut down, potentially threatening the safe operation of the power grid. The operating status is closely related to the power quality and safe operation of the power grid.

[0004] In power grid systems operating with a neutral point that is not directly grounded, a single-phase ground fault does not require immediate tripping and the system can operate with the fault. However, during this period of fault-carrying operation, accidents such as the high-voltage side fuse of the voltage transformer blowing and the voltage transformer (PT) burning out are prone to occur, turning the single-phase ground fault into a multi-phase ground fault, expanding the accident, and causing greater losses. During a fault, the series resonance formed by the equivalent inductance of the voltage transformer and the equivalent capacitance of the line-to-ground capacitance creates an overcurrent. Due to the nonlinearity of the voltage transformer core, a sudden change in the operating state of the distribution network can cause the core of the electromagnetic voltage transformer to saturate, reducing the equivalent reactance value. When its reactance value matches the capacitance parameters of the system, series ferroresonance occurs.

[0005] The inventors discovered that most existing suppression strategies involve designing and adjusting the PT body and its auxiliary circuits, adding auxiliary suppression measures, and changing resonance parameters to reduce PT faults, but the results are not ideal. During the blowing process of the PT high-voltage side fuse, sufficient heat needs to accumulate. When this heat exceeds the fuse's withstand range, the fuse burns out. During this process, the free-oscillating magnetic flux repeatedly impacts the core of the voltage transformer, causing the core to saturate and generating an inrush current with the same frequency as the magnetic flux. The superposition of current and heat causes damage to the voltage transformer. Summary of the Invention

[0006] To address the aforementioned issues, this disclosure proposes a fast-break device and method for the high-voltage side of a distribution network PT based on IGBTs. By employing multiple IGBT switching circuits connected in series, the voltage transformer can be quickly disconnected upon detecting a voltage drop, i.e., the initial stage of harmonic generation, thus preventing damage to the voltage transformer.

[0007] To achieve the above objectives, the present disclosure adopts the following technical solution:

[0008] One or more embodiments provide a fast-break device for the high-voltage side of a distribution network PT based on IGBT, including a voltage drop detection module, a resonance detection module, an IGBT drive circuit, and an IGBT switching circuit connected in sequence; the IGBT switching circuit is connected between the distribution network voltage transformer and the power grid bus, and the IGBT switching circuit includes multiple IGBT switches connected in series.

[0009] One or more embodiments provide a method for fast disconnection of the high-voltage side of a distribution network PT based on IGBT, including the following steps:

[0010] Acquire the voltage signal of the distribution network bus and perform voltage drop detection;

[0011] When a voltage drop occurs, acquire the distribution network bus voltage signal to determine whether resonance has occurred.

[0012] When resonance occurs, the IGBT switching circuit is driven to quickly disconnect the connection between the high-voltage side of the voltage transformer and the distribution bus.

[0013] The IGBT switching circuit is connected between the distribution network voltage transformer and the power grid bus, and the IGBT switching circuit includes multiple IGBT switches connected in series.

[0014] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0015] This disclosure replaces traditional fuses with IGBTs connected in series, achieving higher rated operating voltage and better switching performance. It also reduces the PT failure rate caused by resonance. The IGBT switching circuit operates rapidly, eliminating the need for multiple cycles of resonant current to fuse; it can disconnect the PT at the initial stage of resonance, significantly reducing the impact of resonance on the PT, thus protecting it and improving system stability and safety. This ultimately improves the efficiency of the power grid system.

[0016] The advantages of this disclosure, as well as its additional advantages, will be described in detail in the following specific embodiments. Attached Figure Description

[0017] The accompanying drawings, which form part of this disclosure, are used to provide a further understanding of this disclosure. The illustrative embodiments of this disclosure and their descriptions are used to explain this disclosure and do not constitute a limitation thereof.

[0018] Figure 1 This is a schematic diagram of the PT high-voltage side fast disconnection device according to Embodiment 1 of this disclosure;

[0019] Figure 2 This is a schematic diagram of the voltage drop characteristic calculation principle based on the dq transformation method in Embodiment 1 of this disclosure;

[0020] Figure 3 This is a flowchart of the PT high-voltage side rapid disconnection method according to Embodiment 2 of this disclosure;

[0021] Figure 4 This is a typical voltage spectrum detected after an example fault recovery in Embodiment 1 of this disclosure;

[0022] Figure 5 This is a circuit diagram of the magnetic core synchronization control circuit of Embodiment 1 of this disclosure. Detailed Implementation

[0023] The present disclosure will be further described below with reference to the accompanying drawings and embodiments.

[0024] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of this disclosure. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0025] It should be noted that the terminology used herein is for descriptive purposes only and is not intended to limit the exemplary embodiments according to this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. It should be noted that, without conflict, the various embodiments and features within those embodiments can be combined with each other. The embodiments will now be described in detail with reference to the accompanying drawings.

[0026] Example 1

[0027] Frequent blowouts of PT fuses cause PTs to shut down, preventing the secondary system from providing real-time voltage signals for operation, monitoring, and protection. This also causes inconvenience for maintenance. To ensure stable operation of the distribution network during asymmetrical faults and prevent equipment damage, this embodiment provides a fast-break device for the high-voltage side of the distribution network PT based on IGBTs.

[0028] In one or more of the technical solutions disclosed in the embodiments, such as Figure 1 As shown, the high-voltage side fast disconnection device of the distribution network PT based on IGBT includes a voltage drop detection module, a resonance detection module, an IGBT drive circuit and an IGBT switching circuit connected in sequence; the IGBT switching circuit is connected between the distribution network voltage transformer PT and the power grid bus, and the IGBT switching circuit includes multiple IGBT switches connected in series.

[0029] This embodiment replaces traditional fuses with IGBTs connected in series, achieving higher rated operating voltage and better switching performance. It also reduces the PT failure rate caused by resonance. The IGBT switching circuit operates rapidly, eliminating the need for multiple cycles of resonant current to fuse; it can disconnect the PT at the initial stage of resonance, significantly reducing the impact of resonance on the PT, thus protecting it and improving system stability and safety. This ultimately enhances the efficiency of the power grid system.

[0030] Voltage sag detection module: Configured to acquire the three-phase voltage of the bus, it calculates the voltage sag characteristic quantities based on the instantaneous dq transform method to obtain the amplitude and phase of the voltage sag, which are used to determine whether a voltage sag has occurred. The voltage sag characteristic quantities include voltage amplitude and phase.

[0031] Resonance detection module: configured to perform resonance detection by acquiring the bus voltage and performing Fourier transform spectrum analysis when the voltage drop detection module detects a voltage drop.

[0032] When resonance is detected, the IGBT drive circuit generates an IGBT drive pulse signal.

[0033] The principle of the aforementioned fast-switching device is as follows: By real-time detection of the distribution network bus voltage signal and using the instantaneous dq transform method to detect voltage dips, a system fault is determined. When a voltage dip fault is detected, a Fast Fourier Transform (FFT) analysis is initiated. If the measured signal spectrum contains a sub-frequency resonant component, the IGBT is driven to quickly disconnect the PT high-voltage side from the distribution network bus. After the sub-frequency resonant signal attenuates, the IGBT is driven to conduct again, thereby achieving PT switching and reducing the PT failure rate, thus improving system operational stability. Each part is described in detail below.

[0034] (1) Voltage drop detection module

[0035] When the power grid is operating normally, the three-phase voltages are symmetrical. However, when an asymmetrical fault occurs, a voltage drop will occur. In this embodiment, an asymmetrical voltage detection algorithm is used to determine whether a fault has occurred in the system. This allows for the initiation of spectral analysis of the voltage and current waveforms before and after the fault is recovered to determine whether low-frequency resonance or frequency division resonance will occur. This enables the initiation of the IGBT switching strategy. Therefore, the key to the problem is to quickly and accurately track and detect the voltage signal being detected within a short period of time.

[0036] Optionally, in this embodiment, the instantaneous voltage dq transformation method is used to detect the voltage signal, as detailed below:

[0037] A stationary, three-phase symmetrical abc coordinate system can be transformed to a dq coordinate system using the Park transformation method, with ua u b u c These represent the three-phase voltages, u d u q The components of the d-axis and q-axis are respectively represented, and their relationship can be seen in equation (1):

[0038]

[0039] Where P is the Park transformation matrix:

[0040] The sine and cosine signals sin(ωt) and cos(ωt) are in phase with the voltage of phase a, respectively.

[0041] For an ideal three-phase symmetrical system, the relationship between the phase voltages is as follows:

[0042]

[0043] After dq transformation, we get:

[0044]

[0045] u q =0 (4)

[0046] Equations (3) and (4) above show that the ideal three-phase symmetrical voltage, after dq transformation, is finally represented on the d-axis component as an effective value, and thus the instantaneous amplitude of the voltage drop can be calculated.

[0047] In this embodiment, the instantaneous dq transformation method is used to obtain the instantaneous voltage amplitude and phase, specifically including the following steps:

[0048] Step 1: Using the voltage of one single phase of the three phases as the reference voltage, construct a set of virtual three-phase circuits according to the set phase angle difference; wherein, the phase angle difference of the three-phase circuits is set to 120°.

[0049] Step 2: Using the dq transformation method, the three-phase voltages of the virtual three-phase circuit are transformed to obtain the d-axis and q-axis components, and the amplitude and phase of the voltage are extracted.

[0050] In this embodiment, the instantaneous dq transformation method described above can quickly identify the voltage of lines with asymmetric faults, and can quickly analyze the voltage drop of the power grid, providing time guarantee for starting the harmonic detection algorithm.

[0051] In actual operating systems, voltage often involves distortion and asymmetry. Let the effective value of the fundamental voltage and the initial phase angle be equal to U and zero, respectively. The measured disturbance signal is represented by overlapping high-frequency oscillating components, where the root mean square value of the h-th high-frequency disturbance component and its corresponding initial phase are respectively U... h and θ h And in terms of index attenuation.

[0052] Using the voltage of phase a as the reference voltage, the expression for its phase voltage is as follows:

[0053]

[0054] The above equation can be calculated by applying a 60° delay to obtain -u. c Then with u b =-u a -u c Solving for the solutions, we can obtain the following:

[0055]

[0056]

[0057] By decomposing equations (5) to (7) and performing dq transformation on the fundamental and high-frequency components obtained from the calculation, their transformation expressions can be obtained:

[0058]

[0059] In the formula,

[0060] In formula (8), the effective value of the fundamental voltage wave is obtained by dq transformation to obtain u. d The DC component of the signal, and the h-th high-frequency disturbance signal can be composed of the sum of h±1 components; while in u q The mathematical formula does not include a DC component, while the calculation results for the high-frequency disturbance component are similar to those for the high-frequency disturbance component of ud.

[0061] The above analysis shows that when there are a large number of disturbance components in the system, it is impossible to directly obtain u d To accurately determine the effective value of the fundamental frequency voltage, it is necessary to use an LPF filter to extract its DC component in order to obtain the effective value of the voltage.

[0062] If no phase transition occurs when the drop occurs, then u dThe expression is solved and analyzed. The fundamental phase voltage amplitude is obtained by collecting data from the DC section. The change in amplitude can be used to determine whether a voltage drop has occurred. If a voltage drop is accompanied by a phase jump, the voltage amplitude and phase jump angle can be set as u0. sag The fundamental voltage component of phase α and phase a is then... If the high-frequency disturbances in equations (5) to (7) exist in the system voltage, then the voltages of phases b and c can be constructed by using the 60° delay method for phase a. Figure 2 The detection principle involves extracting the DC portion from the d and q axes, respectively, as u. da and u qa ,Right now:

[0063]

[0064] Correspondingly, based on the measured u da and u qa The magnitude and phase transition of the voltage drop are obtained separately:

[0065]

[0066] The corresponding voltage drop amplitude and phase angle change are calculated using formula (10). When the voltage drop amplitude and phase angle change exceed the set range, a voltage drop has occurred.

[0067] (2) Resonance Detection Module

[0068] In this embodiment, the resonance detection module is configured to perform resonance detection by acquiring the bus voltage and performing Fourier transform spectrum analysis when the voltage drop detection module detects a voltage drop.

[0069] The Fourier transform of a voltage sequence is the frequency response of the sequence. However, the Fourier transform of a sequence is a continuous function of frequency, and the length of the sequence cannot be infinitely long when using a computer for calculation. To facilitate computer processing, it is discretized.

[0070] The sequence x(n) is of finite length. In this embodiment, x(n) refers to the detected voltage signal sequence, where n ranges from 0 to N-1. Frequency ω is then sampled at equal intervals within the range of 0 to 2π, with N sampling points and a sampling interval of 2π / N. The frequency value corresponding to the k-th sampling point is 2πk / N. Therefore, the discrete Fourier transform and its inverse transform are:

[0071]

[0072]

[0073] If we consider a finite-length sequence as a period of a periodic sequence, then the Discrete Fourier Transform is a Fourier series. The Discrete Fourier Transform is also periodic, with a period of N.

[0074] The relationship between digital frequency and analog frequency is as follows:

[0075] ω=2πf / f s ,Right now

[0076] The analog frequency corresponding to the k-th frequency point is:

[0077]

[0078] When performing spectral analysis using the Fast Fourier Transform, two important parameters need to be determined: the sampling rate and the number of sampling points in the frequency domain. The sampling rate can be determined according to the Nyquist sampling theorem, and the number of sampling points can be determined based on the sequence length or the frequency resolution Δf.

[0079] but

[0080] The typical spectrum obtained by the above Fourier transform spectrum analysis method after the power grid asymmetric fault disappears is as follows: Figure 4 As shown in the figure, the horizontal axis represents frequency. The spectrum after the fault disappears includes not only the 50Hz power frequency component but also the 4Hz sub-frequency resonant component. As can be seen from the figure, the sub-frequency resonant signal exists in the system after the fault is recovered, which will also serve as the basis for starting the IGBT switching control signal.

[0081] In this embodiment, the FFT algorithm is used to quickly analyze the spectrum. When a resonant signal is detected, the IGBT is turned off. The response is rapid and can effectively avoid the overheating and burnout of traditional fuses caused by resonance.

[0082] In this embodiment, optionally, a synchronization circuit is also provided between the IGBT drive circuit and the IGBT switching circuit. The synchronization circuit is used to enable multiple IGBT switches to operate simultaneously.

[0083] Optional, such as Figure 5 As shown, the synchronization circuit can be a magnetic core synchronization control circuit. Specifically, the gates of two IGBTs are connected to coupling transformer A. Alternatively, the gates of two adjacent IGBTs can be connected to the same coupling transformer.

[0084] When the drive signals of the IGBT drive circuit are delayed, they can still maintain synchronization due to coupling. This synchronization of the drive signals effectively improves the overshoot phenomenon in the circuit. The control circuit exhibits relatively ideal control performance; when the parameters of the series-connected IGBTs are consistent and the external circuit is strictly synchronized, voltage equalization is good. Because of the presence of the coupling transformer, the requirement for high synchronization of the drive signals is not stringent.

[0085] The system in this embodiment can effectively detect the low-frequency resonant signal generated after the distribution network fault disappears, and effectively prevent the PT from burning out due to resonant overcurrent by turning off the IGBT to destroy the resonant condition. When the resonant condition is detected to disappear, the IGBT can be automatically turned on and the PT can be reconnected to the system, which greatly reduces the PT failure rate, reduces the operation and maintenance time of the distribution network due to PT failure, ensures power supply reliability, and improves power supply quality.

[0086] Example 2

[0087] Based on Example 1, this example provides a fast disconnection method for the high-voltage side of a distribution network PT based on IGBT, such as... Figure 3 As shown, it includes the following steps:

[0088] Step 1: Acquire the detected distribution network bus voltage signal in real time and perform voltage drop detection;

[0089] Step 2: When a voltage drop occurs, acquire the distribution network bus voltage signal to determine whether resonance has occurred;

[0090] Step 3: When resonance occurs, drive the IGBT switching circuit to quickly disconnect the connection between the PT high-voltage side and the distribution network bus; the IGBT switching circuit is connected between the distribution network voltage transformer PT and the power grid bus, and the IGBT switching circuit includes multiple IGBT switches connected in series.

[0091] Furthermore, after disconnecting the voltage transformer in step 3, the process also includes acquiring the distribution network bus voltage signal, monitoring the change of the resonant signal, and driving the IGBT switching circuit to connect the voltage transformer to the power grid after the frequency-division resonant signal attenuates.

[0092] In traditional power grid circuits, after a fault occurs, it takes several cycles of resonance for the fuse to blow the PT (potential transformer). The resonant current generated during this process can damage the voltage transformer. The method in this embodiment, by controlling the disconnection of the PT in the early stage of harmonic generation, can greatly reduce the impact of resonance on the PT, thereby protecting the PT and improving the stability and safety of system operation.

[0093] In step 1, the voltage drop detection uses the instantaneous dq transformation method, such as... Figure 2As shown, specifically: the three-phase voltage of the bus is acquired, and the voltage operation is detected by instantaneous dq transformation. If no voltage drop is detected, the process returns to continue reading the three-phase voltage for instantaneous dq transformation analysis.

[0094] The instantaneous voltage amplitude and phase are obtained using the instantaneous dq transformation method for voltage sag detection. The specific steps include the following:

[0095] Step 11: Using a single-phase voltage from the three phases as a reference voltage, construct a set of virtual three-phase circuits based on the set phase angle difference; wherein, the phase angle difference of the three-phase circuits is set to 120°.

[0096] Step 12: Using the dq transformation method, the three-phase voltages of the virtual three-phase circuit are transformed to obtain the d-axis and q-axis components. The voltage amplitude and phase are extracted. When the voltage exceeds the set range, a voltage drop occurs. The transformation process of the dq transformation method has been described in the embodiments.

[0097] In step 2, the Fourier transform spectrum analysis method is used to determine whether resonance has occurred.

[0098] Once a fault causing a voltage drop is detected, FFT spectrum analysis can be initiated to accurately grasp the voltage spectrum over a period of time from the voltage drop to the disappearance of the fault. Furthermore, if no frequency division or low-frequency resonance is detected, the detection state is maintained. When frequency division or low-frequency resonance is detected, an IGBT turn-off signal is issued to drive the hardware driver circuit to turn off the IGBT. Simultaneously, if the resonance signal disappears due to damping or other reasons, an IGBT turn-on signal is issued to drive the hardware driver circuit to turn on the IGBT. After the IGBT is driven, the drive signal state is recorded. If it is in the turn-on state, the system returns to continue detecting the three-phase voltage. At this time, the resonance may have disappeared or the power grid may have returned to normal. If the IGBT is in the turn-off state, the PT has exited operation, and the resonance state has been destroyed. After a certain delay, an IGBT turn-on state is issued, and the next cycle begins.

[0099] In this embodiment, the instantaneous dq transform method is used to detect voltage dips in real time and determine whether a system fault has occurred. When a voltage dip fault is detected, Fast Fourier Transform (FFT) analysis is initiated. When the measured signal spectrum contains a frequency division resonance component, the IGBT is driven to quickly disconnect the connection between the PT high-voltage side and the distribution network bus. After the frequency division resonance signal decays, the IGBT is driven to conduct again, thereby realizing the switching of the PT, reducing the PT failure rate, and improving the system's operational stability.

[0100] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure.

[0101] While the specific embodiments of this disclosure have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of this disclosure. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of this disclosure are still within the scope of protection of this disclosure.

Claims

1. A fast-break device for the high-voltage side of a distribution network PT based on IGBT, characterized in that: It includes a voltage drop detection module, a resonance detection module, an IGBT drive circuit, and an IGBT switching circuit connected in sequence; the IGBT switching circuit is connected between the distribution network voltage transformer and the power grid bus, and the IGBT switching circuit includes multiple IGBT switches connected in series. Voltage sag detection module: It is configured to acquire the three-phase voltage of the bus and calculate the voltage sag characteristic quantity based on the instantaneous dq transformation method to obtain the amplitude and phase of the voltage sag to determine whether a voltage sag has occurred. The resonance detection module is configured to perform resonance detection by acquiring the bus voltage and using Fourier transform spectrum analysis when the voltage drop detection module detects a voltage drop. When resonance occurs, the IGBT switching circuit is driven to quickly disconnect the connection between the high-voltage side of the voltage transformer and the distribution bus. After disconnecting the connection between the high-voltage side of the voltage transformer and the distribution bus, the following steps are also included: acquiring the distribution bus voltage signal, monitoring the change of the resonance signal, and when the frequency-divided resonance signal decays, driving the IGBT switching circuit to conduct and connect the voltage transformer to the power grid.

2. The fast-break device for high-voltage side of distribution network PT based on IGBT as described in claim 1, characterized in that: Voltage sag characteristics include voltage amplitude and phase; Alternatively, the instantaneous dq transformation method can be used to obtain the instantaneous voltage amplitude and phase, specifically including the following steps: Using the voltage of one single phase of the three phases as a reference voltage, a set of virtual three-phase circuits is constructed based on the set phase angle difference; The dq transformation method is used to transform the three-phase voltage of the virtual three-phase circuit to obtain the d-axis and q-axis components, and then extract the voltage amplitude and phase.

3. The fast-break device for the high-voltage side of the distribution network PT based on IGBT as described in claim 2, characterized in that: The phase angle difference of the virtual three-phase circuit is set to 120°.

4. The fast-break device for high-voltage side of distribution network PT based on IGBT as described in claim 1, characterized in that: A synchronization circuit is also provided between the IGBT drive circuit and the IGBT switching circuit. The synchronization circuit is used to enable multiple IGBT switches to operate simultaneously.

5. The fast-break device for the high-voltage side of the distribution network PT based on IGBT as described in claim 4, characterized in that: The synchronization circuit is a core synchronization control circuit. Specifically, the gates of two adjacent IGBTs are connected to the same coupling transformer.

6. A fast disconnection method for the high-voltage side of a distribution network PT based on IGBT, characterized in that, Includes the following steps: The voltage signal of the distribution network bus is acquired for voltage sag detection. The voltage sag detection adopts the instantaneous dq transformation method, which includes the following steps: taking a single-phase voltage of the three phases as the reference voltage, constructing a set of virtual three-phase circuits according to the set phase angle difference; using the dq transformation method, transforming the three-phase voltages of the virtual three-phase circuits respectively to obtain the d-axis and q-axis components, extracting the voltage amplitude and phase, and when it exceeds the set range, a voltage sag occurs. When a voltage drop occurs, the distribution network bus voltage signal is acquired to determine whether resonance has occurred; the method for determining whether resonance has occurred is Fourier transform spectrum analysis. When resonance occurs, the IGBT switching circuit is driven to quickly disconnect the connection between the high-voltage side of the voltage transformer and the distribution bus. After disconnecting the connection between the high-voltage side of the voltage transformer and the distribution bus, the following steps are also included: acquiring the distribution bus voltage signal, monitoring the change of the resonance signal, and when the frequency-division resonance signal decays, driving the IGBT switching circuit to conduct and connect the voltage transformer to the power grid. The IGBT switching circuit is connected between the distribution network voltage transformer and the power grid bus, and the IGBT switching circuit includes multiple IGBT switches connected in series.

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