A power system subsynchronous resonance energy recovery device and method

Abstract

The application discloses a kind of power system subsynchronous resonance energy recovery device and method, belong to power system technical field.The device includes band-pass filter unit, bypass switch unit, three-phase monitoring unit, control unit, three-phase thyristor full-bridge circuit and three-phase inductance energy storage module.Band-pass filter unit is connected in parallel at the unit outlet bus, bypass switch unit is connected in parallel at the filter unit two ends, realizes time-sharing switching;Control unit identifies resonance according to monitoring signal, controls thyristor full-bridge circuit and switches between rectification and inverter mode.The method is: standby bypass filtering, monitor power frequency;Resonance is over threshold, and filter is put in, and energy is stored by rectification;Resonance is eliminated, and energy is fed back to power grid by bypass filtering after inverter.The application realizes accurate detection, fast inhibition and energy lossless recycling and reuse of subsynchronous resonance by pre-filtering and bypass switch cooperation, greatly improves system economy and equipment reliability.

Description

Technical Field

[0001] This invention relates to the field of power system technology, specifically to a subsynchronous resonant energy recovery device and method for power systems. Background Technology

[0002] In projects where large-capacity thermal power units (300MW–1000MW) and large hydropower generator units are transmitted over long distances via series capacitor compensation, subsynchronous resonance (SSR) of 5–45Hz is easily induced between the power grid and the generator units. SSR can cause continuous torsional oscillations in the generator rotor shaft system, leading to metal fatigue and crack propagation. In severe cases, it can cause shaft breakage and unplanned unit shutdowns, directly threatening the safe and stable operation of the power grid and the reliability of power supply.

[0003] Currently, commonly used subsynchronous resonance suppression devices in engineering, such as damping resistors, blocking filters, thyristor-controlled reactors (TCRs), and static var generators (SVG) with additional damping, generally suffer from the following technical defects:

[0004] 1) The resonant energy is completely wasted as heat, resulting in poor system operating economy;

[0005] 2) High-power resistors generate significant heat, have complex heat dissipation structures, and suffer from short equipment lifespan and low reliability;

[0006] 3) It only has a suppression function, but no energy recovery and reuse capabilities, resulting in low overall energy efficiency;

[0007] 4) Some power electronic solutions have insufficient response speed and limited effectiveness in suppressing multimodal subsynchronous oscillations.

[0008] Existing power electronic damping control schemes primarily focus on damping effect and response speed, but they lack dedicated high-power subsynchronous resonance filtering units at the grid level. Instead, they use bandpass filters only for small-signal extraction in the control loop. The 50Hz power frequency signal from the unit's outlet bus and high-frequency electromagnetic noise from the grid directly enter the device's monitoring unit and main circuit, causing severe interference in resonance detection. The FFT algorithm requires additional spectral separation of the power frequency and noise, reducing the speed and accuracy of resonance identification and easily leading to false triggering. Simultaneously, the power frequency signal entering the main circuit causes ineffective operation of the three-phase thyristor full-bridge circuit, increasing device losses and heat generation, further reducing equipment reliability. Furthermore, existing technologies do not systematically combine grid-level high-power pre-filtering with resonant energy recovery, failing to fundamentally solve problems such as energy consumption, heat generation, low efficiency, significant monitoring interference, and poor versatility. Summary of the Invention

[0009] The technical problem solved by this invention is to provide a subsynchronous resonant energy recovery device and method for power systems, so as to realize the lossless recovery and reuse of resonant energy.

[0010] The technical solution adopted by this invention to solve its technical problem is a subsynchronous resonant energy recovery device for power systems, comprising:

[0011] Bandpass filter unit, bypass switch unit, three-phase monitoring unit, control unit, three-phase thyristor full-bridge circuit and three-phase inductor energy storage module;

[0012] The input terminal of the bandpass filter unit is connected to the generator set outlet bus, and the output terminal is connected to the AC side of the three-phase thyristor full-bridge circuit.

[0013] The bypass switch unit is connected in parallel across the bandpass filter unit;

[0014] The input terminal of the three-phase monitoring unit is connected to the generator set outlet bus, and the output terminal is communicatively connected to the input terminal of the control unit.

[0015] The output terminal of the control unit is respectively connected to the gate of the three-phase thyristor full-bridge circuit and the control terminal of the bypass switch unit.

[0016] The DC side of the three-phase thyristor full-bridge circuit is connected in series with a three-phase inductor energy storage module.

[0017] Furthermore, the bandpass filter unit is a power grid-grade high-power passive LC bandpass filter with a passband frequency range of 5–45 Hz, an insertion loss of ≤3 dB within the passband, an attenuation of ≥60 dB for 50 Hz power frequency, and an attenuation of ≥80 dB for high-frequency noise.

[0018] Furthermore, the bypass switch unit is a grid-grade high-voltage vacuum bypass switch, which is disconnected in the rectification absorption suppression mode to enable the bandpass filter unit; and closed in the inverter feedback mode or standby monitoring state to bypass the bandpass filter unit.

[0019] Furthermore, the three-phase monitoring unit includes a voltage transformer, a current transformer, and a signal conditioning circuit, which collects voltage and current signals at the generator set's outlet bus and sends them to the control unit for analysis and calculation of the subsynchronous resonant frequency current component.

[0020] Furthermore, the control unit calculates the subsynchronous resonant frequency, and the formula for calculating the subsynchronous resonant frequency is as follows: ,in This is the subsynchronous resonant frequency. =50 The system's rated frequency, For the series capacitor compensation degree, the current synchronous resonant frequency and the unit shaft torsional vibration frequency. Satisfying complementary relationship + = When the signal is high-risk electrical coupling resonance, it is determined that the subsynchronous resonant frequency current component is calculated by Fourier transform, and the opening and closing of the bypass switch unit is controlled according to the magnitude of the subsynchronous resonant frequency current component.

[0021] Furthermore, the three-phase thyristor full-bridge circuit consists of six anti-parallel thyristors. In rectification mode, it operates at the subsynchronous resonant frequency, rectifies the resonant energy, and stores it in the three-phase inductor energy storage module. In inverter mode, it operates synchronously at the 50Hz system rated frequency, inverting the energy in the three-phase inductor energy storage module into power frequency AC power to be fed back to the grid.

[0022] Furthermore, the three-phase inductive energy storage module adopts a high-permeability iron core inductor or a high-temperature superconducting inductor, with a DC resistance ≤50mΩ, a saturation magnetic flux density ≥1.8T, and a loss ≤0.5%, and is used to temporarily store resonant energy in the form of magnetic field energy.

[0023] A method for recovering subsynchronous resonant energy in a power system, employing a subsynchronous resonant energy recovery device for a power system, includes the following steps:

[0024] Step 1: The system is in standby mode, the bypass switch unit is closed, the filter unit is bypassed, and the three-phase monitoring unit collects the voltage and current signals at the generator set outlet bus in real time.

[0025] Step 2: The control unit performs FFT analysis on the acquired signal to identify the subsynchronous resonant frequency current component;

[0026] Step 3: When the current component at the subsynchronous resonant frequency exceeds 0.3 times the rated current of the unit, the control unit issues a command to disconnect the bypass switch and activate the filter unit;

[0027] Step 4: The three-phase thyristor full-bridge circuit enters the rectification mode, and the pure subsynchronous resonant energy is rectified and stored in the three-phase inductor energy storage module;

[0028] Step 5: When the current component at the subsynchronous resonant frequency drops below 0.05 times the rated current and the system stabilizes, the control unit issues a command to close the bypass switch and bypass the filter unit.

[0029] Step 6: The three-phase thyristor full-bridge circuit enters inverter mode, converting the energy in the three-phase inductor energy storage module into power frequency AC power to be fed back to the grid;

[0030] Step 7: After the energy feedback is completed, the device returns to standby mode and monitors continuously.

[0031] The beneficial effects of this invention are: by using a pre-power grid-level high-power bandpass filter unit, the 5-45Hz subsynchronous resonance components are accurately screened, completely blocking power frequency and noise interference, improving the speed and accuracy of resonance identification, and avoiding false triggering of the device; by using a bypass switch unit to realize the time-division switching of the filter circuit, the bypass filter circuit is used during the inverter / standby stage, completely eliminating power frequency insertion loss, and realizing lossless recovery and reuse of resonance energy. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the structure of the present invention;

[0033] Figure 2 This is a schematic diagram showing the connection between a three-phase thyristor full-bridge circuit and a three-phase inductor energy storage module.

[0034] Figure labels: 1. Bandpass filter unit; 2. Bypass switch unit; 3. Three-phase monitoring unit; 4. Control unit; 5. Three-phase thyristor full-bridge circuit; 6. Three-phase inductor energy storage module. Detailed Implementation

[0035] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0036] like Figure 1 As shown, the present invention provides a subsynchronous resonant energy recovery device for power systems, comprising: a bandpass filter unit 1, a bypass switch unit 2, a three-phase monitoring unit 3, a control unit 4, a three-phase thyristor full-bridge circuit 5, and a three-phase inductor energy storage module 6.

[0037] The input terminal of the bandpass filter unit 1 is connected to the generator set outlet bus (voltage level is 20kV / 24kV / 35kV), and the output terminal is connected to the AC side of the three-phase thyristor full-bridge circuit 5.

[0038] The bypass switch unit 2 is connected in parallel across the two ends of the bandpass filter unit 1 to realize time-division switching of the filter circuit;

[0039] The input terminal of the three-phase monitoring unit 3 is connected to the generator set outlet bus, and the output terminal is communicatively connected to the input terminal of the control unit 4.

[0040] The output terminal of the control unit 4 is respectively connected to the gate of the three-phase thyristor full-bridge circuit 5 and the control terminal of the bypass switch unit 2.

[0041] The three-phase thyristor full-bridge circuit 5 has a three-phase inductor energy storage module 6 connected in series on the DC side.

[0042] The bandpass filter unit 1 is a power grid-grade high-power passive LC bandpass filter, constructed from high-voltage, high-stability capacitors and inductors. The passband frequency range is 5–45Hz: this band covers the most common subsynchronous resonant frequency range in series-compensated power transmission projects, ensuring that the resonant component passes through without attenuation; the passband insertion loss is ≤3dB: ensuring minimal energy loss of the subsynchronous resonant signal when passing through the filter unit, without affecting the detection and suppression effects of subsequent stages; attenuation of 50Hz power frequency signals is ≥60dB: attenuating the power frequency signal to less than one-thousandth, completely blocking the power frequency current from entering the main circuit, avoiding ineffective operating losses in the three-phase thyristor full-bridge circuit; attenuation of high-frequency noise is ≥80dB: attenuating high-frequency electromagnetic interference in the power grid to less than one ten-thousandth, ensuring the purity of the signal entering the monitoring unit and improving the anti-interference capability of resonance identification. This filter unit is compatible with the 20kV / 24kV / 35kV voltage levels of the unit's outlet bus and completes impedance matching with the unit's outlet bus and the AC input terminal of the device. It only operates in rectification suppression mode and is short-circuited by the bypass switch unit in inverter / standby mode to avoid equipment aging and power frequency insertion loss caused by long-term energized operation.

[0043] Furthermore, the bypass switch unit 2 is a grid-grade high-voltage vacuum bypass switch, compatible with unit outlet voltage levels of 20kV / 24kV / 35kV, and features fast switching speed (≤5ms), high current tolerance, low contact loss, and strong anti-interference capability. Its switching state is strictly linked to the device's operating mode.

[0044] Disconnecting in rectification absorption suppression mode allows bandpass filter unit 1 to operate, ensuring that the pure subsynchronous resonant frequency enters subsequent stages.

[0045] When closed in inverter feedback mode or standby monitoring state, the bandpass filter unit 1 is short-circuited to avoid the filter unit from operating under power for a long time.

[0046] The bypass switch unit 2 is equipped with a dedicated switch drive module, which is directly connected to the core of the control unit 4 to achieve fast and uninterrupted transmission of on / off signals; at the same time, a switch status monitoring module is added to provide real-time feedback on the on / off status and improve operational safety.

[0047] Furthermore, the three-phase monitoring unit 3 includes a voltage transformer (PT), a current transformer (CT), and a signal conditioning circuit, which is the core of the device for signal acquisition and preliminary processing.

[0048] The three-phase monitoring unit 3 has the capability to acquire bus voltage and current signals at the generator set outlet; it receives voltage and current signals at the generator set outlet.

[0049] The signal collected by the three-phase monitoring unit 3 is isolated, amplified, and level-converted before being sent to the control unit 4. The subsynchronous resonant frequency electrical signal parameters are accurately extracted using the FFT algorithm, enabling rapid identification of the resonant frequency, amplitude, phase, and grid synchronization phase.

[0050] Furthermore, the control unit 4 adopts a dual-core collaborative architecture of DSP and FPGA, which serves as the overall control core of the device, with a control cycle of ≤100μs, achieving microsecond-level real-time control.

[0051] The DSP is responsible for in-depth processing of voltage and current signals, FFT subsynchronous component analysis, power grid synchronization analysis, resonance state identification, trigger angle calculation, and operating mode decision-making.

[0052] The FPGA is responsible for generating multi-channel thyristor trigger pulses, grid synchronization phase-locking, high-speed sampling, hardware protection, and on / off control of bypass switch unit 2.

[0053] The control unit 4 calculates the subsynchronous resonant frequency current component based on the current signal in the three-phase monitoring unit 3, determines whether the subsynchronous resonant frequency current component exceeds the preset action threshold (0.3 times the rated current of the unit), calculates the trigger angle in real time and outputs the three-phase trigger pulse, and simultaneously outputs the on / off control signal of the bypass switch unit 2 to realize the synchronous and seamless linkage of rectifier / inverter mode switching and filter circuit switching, and eliminates false triggering and false switching caused by noise interference.

[0054] Furthermore, the control unit calculates the subsynchronous resonant frequency, and the formula for calculating the subsynchronous resonant frequency is as follows: ,in This is the subsynchronous resonant frequency. =50 The system's rated frequency, For the series capacitor compensation degree, the current synchronous resonant frequency and the unit shaft torsional vibration frequency. Satisfying complementary relationship + = When the resonance occurs, it is determined to be a high-risk electrical coupling resonance; the torsional vibration frequency of the generator shaft system is the same as that of the generator shaft system; and the current component of the subsynchronous resonance frequency is calculated by Fourier transform, and the opening and closing of the bypass switch unit is controlled according to the magnitude of the current component of the subsynchronous resonance frequency. This achieves accurate identification of the entire process of resonance occurrence, development and disappearance.

[0055] Further, see Figure 2 The three-phase thyristor full-bridge circuit 5 consists of six anti-parallel thyristors forming a three-phase fully controlled bridge circuit, serving as the core of the device's energy conversion. The three-phase thyristor full-bridge circuit 5 possesses bidirectional energy flow capability, eliminates high-power energy-consuming resistors, and significantly reduces the device's foundation losses.

[0056] Operating at the subsynchronous resonant frequency, the resonant energy is rectified and stored in the three-phase inductor energy storage module 6. Since the bandpass filter unit 1 only allows the pure subsynchronous resonant component to pass through, no power frequency signal enters during the rectification process, completely eliminating ineffective operating losses.

[0057] Operating in inverter mode and synchronously at the 50Hz system rated frequency, it inverts the energy in the three-phase inductive energy storage module 6 into power frequency AC power to be fed back to the grid. At this time, the bypass switch unit 2 is closed, the filter unit is bypassed, and there is no power frequency insertion loss.

[0058] The thyristors are high-voltage, high-current anti-parallel thyristors, with voltage ratings matching the generator outlet voltage of 20kV / 24kV / 35kV and current capacity matching the rated current of the unit; a complete di / dt and dv / dt absorption circuit is configured to ensure stable operation in both rectification and inversion modes.

[0059] Furthermore, the three-phase inductor energy storage module 6 is connected in series on the DC side of the three-phase thyristor full-bridge circuit 5, and adopts a high-permeability iron core inductor or a high-temperature superconducting inductor as the core of the device's energy storage.

[0060] The DC resistance of the three-phase inductive energy storage module 6 is ≤50mΩ: reducing resistance loss during energy storage; the saturation magnetic flux density of the three-phase inductive energy storage module 6 is ≥1.8T: ensuring non-saturation under high current conditions and maintaining the stability of inductance; the loss of the three-phase inductive energy storage module 6 is ≤0.5%: further improving energy recovery efficiency.

[0061] The energy storage principle of the three-phase inductive energy storage module 6 follows the law of electromagnetic induction: u = L·di / dt, where u is the induced voltage across the inductor (V), L is the inductance (H), and di / dt is the rate of change of current with respect to time (A / s). Utilizing the characteristic that inductor current cannot change abruptly, it effectively suppresses resonant peak current. The energy storage calculation formula is E = 1 / 2·L·I², where E is the stored magnetic field energy (J), L is the inductance (H), and I is the effective value or peak current (A) of the resonant current flowing through the inductor.

[0062] Inductor parameter design: Based on the unit's resonant energy requirements, using the formula L=μ0·μ r The inductance parameters are determined by the calculation of N²·S / l, where μ₀ is the free permeability and μ₀ is the inductance value. r Where is the relative permeability of the core material, N is the number of turns of the inductor coil, S is the effective cross-sectional area of ​​the magnetic circuit, and l is the average length of the magnetic circuit, thus achieving efficient and lossless temporary storage of resonant energy.

[0063] This invention discloses a method for recovering subsynchronous resonant energy in a power system, the specific steps of which are as follows:

[0064] Step 1: System standby

[0065] When the bypass switch unit 2 is closed, the bandpass filter unit 1 is bypassed, and the three-phase monitoring unit 3 operates at low power, collecting the generator outlet voltage and current signals in real time and sending them to the control unit 4.

[0066] Step 2: FFT Spectrum Analysis

[0067] Control unit 4 continuously performs FFT spectrum analysis to monitor whether subsynchronous resonance occurs. At this time, the other main circuits consume no power and do not affect the normal power generation of the unit.

[0068] Step 3: Resonance Identification and Filtering Input

[0069] When the control unit 4 detects that the subsynchronous resonant frequency current component exceeds the operating threshold of 0.3 times the rated current of the unit, it immediately issues a command to disconnect the bypass switch unit 2 and engage the bandpass filter unit 1. The bandpass filter unit 1 performs grid-level high-power filtering on the generator outlet bus electrical signal, allowing only the pure subsynchronous resonant component of 5-45Hz to pass through, while power frequency and high-frequency noise are deeply attenuated.

[0070] Step 4: Rectification, Suppression, and Energy Storage

[0071] The control unit 4 calculates the trigger angle in real time based on the current component of the subsynchronous resonant frequency, drives the three-phase thyristor full-bridge circuit 5 to enter the rectification mode at the subsynchronous resonant frequency, and stores the pure subsynchronous resonant energy in the form of magnetic field energy in the three-phase inductor energy storage module 6, quickly smoothing the resonant overcurrent and oscillation amplitude, and suppressing the torsional vibration of the unit shaft system.

[0072] Step 5: Resonance cancellation and filtering bypass

[0073] When the three-phase monitoring unit 3 detects that the subsynchronous resonant frequency current component drops below the elimination threshold of 0.05 times the rated current of the unit and the system is stable, the control unit 4 first completes the inverter firing angle calculation and phase lock with the grid, and then issues a command to close the bypass switch unit 2, short-circuit the bandpass filter unit 1 to eliminate the power frequency insertion loss.

[0074] Step 6: Inverter Feedback

[0075] After the bandpass filter unit 1 is bypassed, the three-phase thyristor full-bridge circuit 5 is precisely synchronized with the power grid frequency signal and enters the inverter mode at the 50Hz system rated operating frequency. It converts the magnetic field energy stored in the three-phase inductive energy storage module 6 into AC power with the same frequency and phase as the power grid, and smoothly feeds it back to the generator bus or the plant / station power system, realizing the lossless recovery and reuse of resonant energy.

[0076] Step 7: Cyclic Standby

[0077] After the energy feedback is completed, the control unit 4 drives the three-phase thyristor full-bridge circuit 5 to exit the operation, the device returns to the standby state, the bypass switch unit 2 remains closed, and the three-phase monitoring unit 3 continues to monitor the grid status in real time, waiting for the next resonance trigger to form an automated closed-loop operation.

[0078] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A subsynchronous resonant energy recovery device for a power system, characterized in that, include: Bandpass filter unit, bypass switch unit, three-phase monitoring unit, control unit, three-phase thyristor full-bridge circuit and three-phase inductor energy storage module; The input terminal of the bandpass filter unit is connected to the generator set outlet bus, and the output terminal is connected to the AC side of the three-phase thyristor full-bridge circuit. The bypass switch unit is connected in parallel across the bandpass filter unit; The input terminal of the three-phase monitoring unit is connected to the generator set outlet bus, and the output terminal is communicatively connected to the input terminal of the control unit. The output terminal of the control unit is respectively connected to the gate of the three-phase thyristor full-bridge circuit and the control terminal of the bypass switch unit. The DC side of the three-phase thyristor full-bridge circuit is connected in series with a three-phase inductor energy storage module.

2. The subsynchronous resonant energy recovery device for a power system according to claim 1, characterized in that, The bandpass filter unit is a power grid-grade high-power passive LC bandpass filter with a passband frequency range of 5 to 45 Hz, an insertion loss of ≤3 dB within the passband, an attenuation of ≥60 dB for 50 Hz power frequency, and an attenuation of ≥80 dB for high-frequency noise.

3. The subsynchronous resonant energy recovery device for a power system according to claim 1, characterized in that, The bypass switch unit is a grid-grade high-voltage vacuum bypass switch. It is disconnected in the rectification absorption suppression mode to enable the bandpass filter unit; and closed in the inverter feedback mode or standby monitoring state to bypass the bandpass filter unit.

4. The subsynchronous resonant energy recovery device for a power system according to claim 1, characterized in that, The three-phase monitoring unit includes a voltage transformer, a current transformer, and a signal conditioning circuit. It collects voltage and current signals at the generator set's outlet bus and sends them to the control unit for analysis and calculation of the subsynchronous resonant frequency current component.

5. The subsynchronous resonant energy recovery device for a power system according to claim 4, characterized in that, The control unit calculates the subsynchronous resonant frequency, and the formula for calculating the subsynchronous resonant frequency is as follows: ,in This is the subsynchronous resonant frequency. =50 The system's rated frequency, For the series capacitor compensation degree, the current synchronous resonant frequency and the unit shaft torsional vibration frequency. Satisfying complementary relationship + = At that time, it was determined to be a high-risk electro-coupled resonance; The current component at the subsynchronous resonant frequency is calculated using Fourier transform, and the opening and closing of the bypass switch unit is controlled based on the magnitude of the current component at the subsynchronous resonant frequency.

6. The subsynchronous resonant energy recovery device for a power system according to claim 1, characterized in that, The three-phase thyristor full-bridge circuit consists of six anti-parallel thyristors. In rectification mode, it operates at the subsynchronous resonant frequency, rectifies the resonant energy, and stores it in the three-phase inductor energy storage module. In inverter mode, it operates synchronously at the 50Hz system rated frequency, inverting the energy in the three-phase inductor energy storage module into power frequency AC power to be fed back to the grid.

7. The subsynchronous resonant energy recovery device for a power system according to claim 1, characterized in that, The three-phase inductive energy storage module uses a high-permeability iron core inductor or a high-temperature superconducting inductor with a DC resistance ≤50mΩ, a saturation magnetic flux density ≥1.8T, and a loss ≤0.5%, and is used to temporarily store resonant energy in the form of magnetic field energy.

8. A method for recovering subsynchronous resonant energy in a power system, applied to the subsynchronous resonant energy recovery device for a power system as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Step 1: The system is in standby mode, the bypass switch unit is closed, the filter unit is bypassed, and the three-phase monitoring unit collects the voltage and current signals at the generator set outlet bus in real time. Step 2: The control unit performs FFT analysis on the acquired signal to identify the subsynchronous resonant frequency current component; Step 3: When the current component at the subsynchronous resonant frequency exceeds 0.3 times the rated current of the unit, the control unit issues a command to disconnect the bypass switch and activate the filter unit; Step 4: The three-phase thyristor full-bridge circuit enters the rectification mode, and the pure subsynchronous resonant energy is rectified and stored in the three-phase inductor energy storage module; Step 5: When the current component at the subsynchronous resonant frequency drops below 0.05 times the rated current and the system stabilizes, the control unit issues a command to close the bypass switch and bypass the filter unit. Step 6: The three-phase thyristor full-bridge circuit enters inverter mode, converting the energy in the three-phase inductor energy storage module into power frequency AC power to be fed back to the grid; Step 7: After the energy feedback is completed, the device returns to standby mode and monitors continuously.

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