A high-voltage direct-current interference active treatment device

Abstract

The application discloses a kind of high voltage direct current interference active treatment device, including high frequency chain AC / DC converter unit, H bridge converter unit and main control unit, main control unit is used to determine the expected output voltage of the H bridge converter unit according to the pipe ground potential signal of section pipeline monitoring point, determines direct current bus voltage instruction value according to the expected output voltage of the H bridge converter unit, controls high frequency chain AC / DC converter unit to realize direct current bus voltage self-adapting regulation and alternating current side high power factor operation.The application can consider input and output electrical isolation and alternating current side high power factor operation, without additional setting independent power factor correction circuit, improve the energy conversion efficiency of treatment equipment.

Description

Technical Field

[0001] This invention relates to the field of DC interference control, and in particular to an active device for controlling high-voltage DC interference. Background Technology

[0002] When ultra-high voltage direct current (UHVDC) transmission projects operate using a single grounding electrode, the grounding electrode releases thousands of amperes of current into the soil, creating a non-uniform soil electric field over a large area. Oil and gas pipelines, as long-distance metallic conductors, are situated within this non-uniform electric field, significantly altering the original ground current distribution and generating a current-collecting effect. This causes stray currents to concentrate at points of corrosion damage, leading to corrosion interference. For long metallic pipelines located close to the grounding electrode, the interference caused by grounding electrode discharge is even more pronounced. There have been reports of grounding electrode discharge causing abnormal potential shifts in pipelines over hundreds of kilometers and failures of cathodic protection systems at some stations.

[0003] To avoid corrosion of buried pipelines caused by DC interference and maintain the normal operation of cathodic protection equipment, active drainage equipment is needed to forcibly correct the pipe-to-ground potential of long-distance pipelines. Unlike conventional DC interference, the discharge behavior of UHVDC grounding electrodes is characterized by uncertain occurrence and duration, variable polarity of the ground current, and short-duration strong impact. Active drainage equipment should possess high-power, wide-range bipolar output, electrical isolation, and strong interference resistance capabilities. To address these requirements, invention patent application CN105337512A proposes a high-power bidirectional active drainage device. This device uses two sets of anti-parallel thyristor rectifier circuits to rectify the AC power stepped down by the power frequency transformer into pulsating DC, achieving bipolar output. However, due to the inherent characteristics of thyristor rectifier circuits, this equipment injects a large amount of harmonics into the power grid during operation, requiring additional power factor correction circuits, resulting in high costs; furthermore, the power frequency transformer is large, making equipment installation easily restricted. Invention patent application CN114884367A proposes an active stray current absorption device that combines active drainage and buffer absorption capabilities. It uses a flyback converter to achieve electrical isolation between the input and output terminals, effectively reducing the equipment size. However, this equipment relies on low-voltage batteries instead of grid power, and its output power is limited by the maximum discharge capacity of the batteries. It is only suitable for drainage at local interference points and cannot effectively correct the potential of pipeline sections when faced with strong DC interference caused by grounding electrode discharge. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an active high-voltage DC interference control device that addresses the shortcomings of the existing technology, taking into account both input and output electrical isolation and high power factor operation on the AC side, without the need for an additional independent power factor correction circuit, thereby improving the energy conversion efficiency of the control equipment.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an active high-voltage DC interference mitigation device, comprising:

[0006] High-frequency AC / DC converter unit, with the input side connected to the AC power grid;

[0007] The H-bridge converter unit has its DC side connected to the output DC bus of the high-frequency chain AC / DC converter unit, and its positive output is connected to the deep well anode, while its negative output is connected to the buried pipeline.

[0008] The main control unit is used to determine the desired output voltage of the H-bridge converter unit based on the pipeline ground potential signal at the monitoring point of the pipeline section, determine the DC bus voltage command value based on the desired output voltage of the H-bridge converter unit, and control the high-frequency link AC / DC converter unit to achieve adaptive adjustment of the DC bus voltage and high power factor operation on the AC side; the specific implementation process includes:

[0009] The desired output voltage of the H-bridge converter unit The DC bus voltage command value was calculated. ;

[0010] DC bus voltage command value Subtract the actual value of the sampled DC bus voltage The difference is input into the PI controller, and the output of the PI controller is the command value for the grid-side current amplitude. ;

[0011] The command value of the grid-side current amplitude Multiply by a unit cosine that is in phase with the grid voltage. The instantaneous command value of the grid-side current is obtained. ; The phase of the grid voltage;

[0012] grid-side current command value Compared with the actual value of grid-side current The difference is input to the quasi-proportional resonant controller to obtain the instantaneous power command value on the grid side. Calculate the voltage conversion ratio using the expected value of the DC bus voltage. ;

[0013] according to and Calculate control variables , and After modulation, corresponding switching control signals are generated. These signals are used to control the switching devices of the high-frequency AC / DC converter unit, converting the grid-side power frequency energy into high-frequency AC energy. This is then converted into high-frequency magnetic energy through a high-frequency transformer for electrical isolation, and finally rectified into DC energy for output to the DC bus. Since the grid-side current command value of the high-frequency AC / DC converter is a cosine quantity in phase with the grid voltage, rather than a multi-harmonic component determined by the load type, no additional power factor correction circuit is needed. This reduces the number of energy conversion steps and improves the overall efficiency of the power management equipment.

[0014] control variables , and The specific expression is:

[0015]

[0016] In the formula, The initial switching frequency, The calculated switching frequency. Inverter voltage The normalized internal phase shift angle, Inverter voltage and The normalized external phase shift angle. The phase of the grid voltage. The determination process includes:

[0017] Acquire grid voltage signal Two orthogonal sine signals are generated by a second-order generalized integrator. and ; ;in, For filter gain coefficients, The angular frequency of the input AC signal. It is a complex frequency;

[0018] Will , Input the phase-locked loop to obtain the phase of the power grid at this time. .

[0019] DC bus voltage command value The calculation formula is:

[0020] ;

[0021] in, This is the initial DC bus voltage. , , The output values ​​of the DC bus voltage at different stages. , , The switching thresholds for the three rising phases, , , The threshold for switching between the three descent phases.

[0022] The main control unit is also used to adjust the amplitude and polarity of the output voltage of the H-bridge converter unit. The specific implementation process includes:

[0023] 1) Collection Monitor the pipe-to-ground potential at points 1 to N at all times ;

[0024] 2) Construct the objective function using the sum of the squares of the deviations of the pipeline-to-ground potential from the cathodic protection potential at the oil and gas pipeline monitoring points. The objective function expression is: ,in Indicates the first The pipe-to-ground potential at each monitoring point Indicates the cathodic protection potential. For the sign function of the pipe-to-ground potential offset, when the first When the pipe-to-ground potential at a monitoring point deviates from the cathodic protection range ,on the contrary ;

[0025] 3) Monitoring point ground potential at any time Substitute into the objective function In the middle, calculate Time objective function The value;

[0026] 4) Calculation Time's up Output voltage change value at time ,as well as Time's up The change in the objective function due to the change in output voltage at any given time ;

[0027] 5) Calculate using the change in the objective function The expected change in output voltage at time t , ,in, To fix the voltage step size, It is an adaptive compensation factor;

[0028] 6) According to Time's up The change in the objective function at time t and Calculate the expected output voltage change at time t. Desired output voltage at time ;

[0029] 7) Desired output voltage at time The difference between the sampled output voltage of the H-bridge converter unit and the output voltage is input to a PI controller, which then uses closed-loop control to obtain the duty cycle. After being limited, a corresponding switching control signal is generated, which is used to control the on / off state of the switching devices in the H-bridge converter unit.

[0030] 8) When the output voltage of the H-bridge converter unit satisfies Repeat steps 1) to 7) until the minimum value of the objective function M is found.

[0031] This invention continuously adjusts the output voltage value by observing the changing trend of the objective function under small perturbations, ultimately achieving the desired result for the objective function. Finding the minimum output voltage of the device. Considering that using a fixed step size might prevent the algorithm from quickly finding the minimum point or cause oscillations, an adaptive compensation factor is introduced. This factor is applied when the system deviates from the objective function. When the minimum point is far away, the adaptive compensation factor is larger, which speeds up the system's dynamic response; when the system approaches the objective function... At the minimum point, the adaptive compensation factor is relatively small, preventing the system from deviating from the objective function. It oscillates frequently near the minimum point. Desired output voltage at time The calculation formula is:

[0032] like , ,but ;

[0033] like , ,but ;

[0034] like , ,but ;

[0035] like , ,but ;

[0036] like ,but .

[0037] Duty cycle The calculation formula is: ;in, This is the DC bus voltage signal.

[0038] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention adopts a single-stage high-frequency chain AC / DC energy conversion structure, which can simultaneously achieve input-output electrical isolation and high power factor operation on the AC side in a single stage, eliminating the need for an additional independent power factor correction circuit. This improves the energy conversion efficiency of the treatment equipment and offers advantages such as high-frequency isolation, small size, compact structure, and low cost. This invention can adjust the output voltage of the equipment in real time according to the pipeline-to-ground potential deviation of the oil and gas pipeline section, achieving bidirectional forced correction of the pipeline-to-ground potential, effectively suppressing pipeline-to-ground potential deviation and corrosion interference caused by the ground current from ultra-high voltage direct current projects. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall structure of the active high-voltage DC interference mitigation system according to an embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the structural unit of the active high-voltage DC interference control equipment according to an embodiment of the present invention;

[0041] Figure 3 This is a closed-loop control block diagram of the high-voltage direct current interference active control equipment according to an embodiment of the present invention;

[0042] Figure 4(a) and Figure 4(b) are simulation diagrams of the optimal cathodic protection method for pipeline sections according to the embodiments of the present invention; Figure 4(a) is a simulation diagram of the location of each damaged point in the oil and gas pipeline section, and Figure 4(b) is a simulation diagram of the objective function of the location offset of the pipeline section.

[0043] Figure 5 This is a simulation diagram of the DC bus voltage adaptive high power factor operation method according to an embodiment of the present invention. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] Figure 1 This is a schematic diagram of the overall structure of the high-voltage strong DC interference active control system according to an embodiment of the present invention. The system includes stray current active control equipment, a deep well anode, and a long-lasting reference electrode, and its features are as follows:

[0046] The active power supply equipment is installed inside the pipeline valve chamber. The positive output terminal is connected to the deep well anode via a wire, and the negative output terminal is connected to the pipeline via a wire. The deep well anode is a vertical anode with a burial depth of ≥15m to reduce grounding resistance and make the compensation current distribution more uniform. Long-term reference electrodes 1 to N are used to collect the pipe-to-ground potential along the pipeline. The obtained data is then uploaded to the active protection equipment inside the valve chamber. The active protection equipment dynamically adjusts the polarity and amplitude of the compensation current based on the real-time feedback of the pipeline's ground potential distribution, thereby achieving optimal cathodic protection for the entire pipeline section.

[0047] Figure 2 This is a schematic diagram of the structural units of the active high-voltage DC interference mitigation equipment according to an embodiment of the present invention, including a high-frequency AC / DC converter unit, an H-bridge converter unit, a sampling circuit unit, a main control unit, a drive circuit unit, and an auxiliary power supply unit. A detailed description follows:

[0048] The high-frequency chain AC / DC converter unit is the input stage of the active power control equipment in this embodiment of the invention. One end is connected to the AC power grid, and the other end is connected to the DC bus capacitor. It is used to achieve AC-DC energy conversion and electrical isolation, providing a stable and adjustable DC bus voltage for the subsequent H-bridge converter. Specifically, the high-frequency chain AC / DC converter unit includes a filter inductor... and filter capacitor The grid-side LC filter is composed of and The first four-quadrant switch is formed by and The second four-quadrant switch is formed by and The third and fourth quadrant switches are constructed from... and The fourth quadrant switch and high-frequency transformer constitute AC side auxiliary inductor First DC side switch Second DC side switch Third DC side switch Fourth DC side switch and bus capacitor The LC filter is used to remove harmonic components from the grid-connected current, while the filter capacitor... This also endows the grid-side circuit with voltage source characteristics, which is beneficial for the introduction of optimized control strategies; AC-side auxiliary inductor and high frequency transformer Used for power transmission and electrical isolation; four-quadrant switch ( , ) and DC side switch ( The mains voltage / DC bus voltage is cyclically switched on and off according to the switching commands of the drive circuit, converting it into a high-frequency square wave source. and ,adjust and The phase shift angle between the phases enables bidirectional energy flow; the DC bus capacitor reduces bus voltage ripple, providing a stable DC voltage for the subsequent H-bridge converter. Compared to similar solutions, the high-frequency chain AC / DC converter helps reduce the number of power conversion stages and improves the energy conversion efficiency of active power generation equipment.

[0049] The H-bridge converter unit is the output stage of the active power control equipment in this embodiment of the invention, and its output voltage and output current are respectively... and By controlling the timing of the switching transistors in the H-bridge converter unit, the operation can be changed. , The polarity and amplitude of the H-bridge converter are used to achieve bidirectional and rapid compensation of the pipeline-to-ground potential in the pipeline section. Specifically, the H-bridge converter unit includes a first output-side switch. Second output side switch Third output side switch Fourth output switch and by inductance ,capacitance The output-side LC filter is constructed. The LC filter is used to filter out ripple near the switching frequency and stabilize the equipment's output voltage; the output-side switch ( )of and The drive signals are the same. and The drive signals are the same. and When the circuit is turned on, the equipment outputs a positive voltage. At this time, the compensation current flows into the pipeline through the deep well anode, while... and When the circuit is turned on, the equipment outputs a negative voltage, and the compensation current flows out through the pipeline. By dynamically changing the drive signal of the output switch of the H-bridge converter unit, bidirectional and rapid compensation of the pipeline-to-ground potential in a section can be achieved.

[0050] The sampling circuit unit is used to acquire the required analog signals and convert them into digital signals that the main control unit can recognize, for use in subsequent core algorithms. In this embodiment of the invention, it is necessary to acquire the grid voltage signal. Grid-connected current signal Voltage signal of filter capacitor DC bus voltage signal and output voltage signal .

[0051] Based on the sampled signal and the cathodic protection status of the pipeline section, the main control unit executes the optimal cathodic protection method for the pipeline section and the DC bus voltage adaptive high power factor operation method, generates corresponding switching control signals, and sends the switching control signals to the drive circuit unit.

[0052] The drive circuit unit amplifies the switching control signal and converts it into a gate signal to drive the switching transistor, thereby driving the four-quadrant switch. , DC side switch ( ) and output side switch ( Correct action.

[0053] The auxiliary power supply unit provides DC power to the main control unit, drive circuit unit and sampling circuit unit.

[0054] Figure 3 The block diagram of the closed-loop control equipment for active stray current control described in this embodiment of the invention mainly includes an optimal cathodic protection method for pipeline sections and a DC bus voltage adaptive high power factor operation method. The implementation process of the proposed optimal cathodic protection method for pipeline sections includes:

[0055] 1. Collection Monitor the pipe-to-ground potential at points 1 to N at all times .

[0056] 2. The sum of the squares of the deviations of the pipeline-to-ground potential from the cathodic protection potential at the monitoring points of the oil and gas pipeline is used as the objective function. The objective function expression is: ,in Indicates the first Pipe-to-ground potential at each monitoring point; Indicates the cathodic protection potential; For the sign function of the pipe-to-ground potential offset, when the first When the pipe-to-ground potential at the monitoring point deviates from the cathodic protection range, ,on the contrary .

[0057] 3. Monitoring point ground potential at any time Substitute into the objective function In the middle, calculate The value of .

[0058] 4. Collection The output voltage of the H-bridge converter unit at any time ,calculate Time's up Output voltage change value at time ,calculate Time's up The change in the objective function due to the change in output voltage at any given time .

[0059] 5. Calculation The expected change in output voltage at time t The formula is In the formula To fix the voltage step size, This is an adaptive compensation factor.

[0060] 6. According to Time's up Calculate the change in the objective function and the change in the output voltage at time t. Desired output voltage at time The calculation process is as follows:

[0061] like , ,but ;

[0062] like , ,but ;

[0063] like , ,but ;

[0064] like , ,but ;

[0065] like ,but .

[0066] 7. Expected output voltage The value is subtracted from the sampled output voltage of the H-bridge converter, and the result is input into the PI controller. The duty cycle is obtained through closed-loop control. After being limited, a corresponding switching control signal is generated. This enables the output voltage to dynamically follow the command value. Output voltage and duty cycle The calculation formula is: .

[0067] 8. When the output voltage of the H-bridge converter satisfies Then, repeat steps 1 to 7 until the minimum value of the objective function M is found, and the pipeline section is considered to have reached the target cathodic protection state.

[0068] During the optimization process, the extremely large ground current during the switching between single-pole operation and fault in UHVDC transmission lines causes strong interference to the pipeline, and a fixed DC bus voltage may limit the output of the H-bridge converter. Therefore, a DC bus voltage adaptive high power factor operation method is proposed. This method controls the high-frequency AC / DC converter to flexibly operate in rectification and inversion modes based on changes in the bus voltage command value and power flow direction, achieving adaptive bus voltage regulation and unity power factor operation. The implementation process of the proposed DC bus voltage adaptive high power factor operation method includes:

[0069] 1. Acquire power grid voltage signals Two orthogonal sine signals are generated by a second-order generalized integrator (SOGI). and The formula is:

[0070]

[0071] In the formula, For filter gain coefficients, The angular frequency of the input AC signal.

[0072] 2. , Input a phase-locked loop (PLL) to obtain the current phase of the power grid. and through The function generates a unit cosine quantity that is in phase with the grid voltage. .

[0073] 3. Based on the desired output voltage Substituting the values ​​into the piecewise function of the DC bus voltage, we obtain the command value of the DC bus voltage. .

[0074] The DC bus voltage and rise / fall switching threshold at different stages are shown in the following formula:

[0075] ;

[0076] in: This is the initial DC bus voltage. , , The output values ​​of the DC bus voltage at different stages. , , The switching thresholds for the three rising phases, , , The threshold for switching between the three descent phases. "Time" indicates the upward phase; The time indicates the falling phase. The difference between the rising and falling thresholds within the same phase is the ring width. Appropriately increasing the ring width can prevent the DC bus voltage from repeatedly switching at the critical point; the reference value of the DC bus voltage within each phase. It should be greater than the rising switching threshold. This ensures that the H-bridge converter output has sufficient voltage margin. When selecting the switching threshold, both of these requirements must be considered simultaneously to achieve a wide voltage range output for the H-bridge converter and relative stability of the DC bus voltage.

[0077] 4. DC bus voltage command value Subtract the actual value of the sampled DC bus voltage The difference is input into the PI controller, and the output of the PI controller is the command value for the grid-side current amplitude. .

[0078] 5. The command value of the obtained grid-side current amplitude Multiply by a unit cosine that is in phase with the grid voltage. The instantaneous command value of the grid-side current is obtained. .

[0079] 6. Actual value of sampling grid-side current and the grid-side current command value Compared with actual value The differential input current inner loop controller is used. A quasi-proportional resonant controller is employed here as the grid-side current controller, which can adapt to small fluctuations in grid frequency, ensuring that the converter's grid-side current is in phase with the grid voltage, and achieving high power factor operation. The transfer function of the quasi-proportional resonant controller is shown below. The expression is:

[0080]

[0081] In the formula, This is the proportionality coefficient. The resonance coefficient, The angular frequency of the input AC signal. This represents the bandwidth coefficient.

[0082] 7. In steady state, the output of the quasi-proportional resonant controller is the instantaneous power command value on the grid side. , The amplitude represents the power level. The positive and negative signs represent the power transmission direction. For the active power control equipment, its output power changes in real time with the pipe-to-ground potential adjustment requirements and ground current disturbances. The power command received by the high-frequency link AC / DC converter... The constant variation over a wide range can lead to significant high-frequency link peak currents and reactive circulating currents. In one implementation, a peak current optimization modulation strategy can be used to determine the modulation control quantity to improve converter operating efficiency. This optimization method requires calculating the voltage conversion ratio. The calculation formula is: In this invention, the voltage conversion ratio is calculated using the expected value of the DC bus voltage instead of the sampled value. This helps reduce the impact of DC bus voltage switching on control parameter calculations. The calculation formula is as follows: .

[0083] 8. The results and Substituting these values ​​into the optimization method, we can obtain the optimal control variables D1, D2, and f. s After modulation, corresponding switching control signals are generated. , and .

[0084]

[0085] In the formula, The initial switching frequency, The calculated switching frequency. Inverter voltage The normalized internal phase shift angle, Inverter voltage and The normalized external phase shift angle.

[0086] Figures 4(a) and 4(b) are simulation diagrams of the optimal cathodic protection method for pipeline sections according to an embodiment of the present invention. The pipe-to-ground potential at each damaged point of the oil and gas pipeline section was determined. As shown in Figures 4(a) and 4(b), at 0.1s, the power electronic active compensation device was activated. Through continuous optimization of the optimal cathodic protection method for the pipeline section, the device output current gradually increased from 0A to 0.98A, causing the pipe-to-ground potential at each damaged point of the oil and gas pipeline section to gradually decrease from -0.65V to within the optimal protection range (-0.85V to -1.2V), and the objective function M value decreased from 0.612 to 0.031. Ultimately, the oil and gas pipeline section reached its optimal protection state.

[0087] Figure 5 This is a simulation diagram of the DC bus voltage adaptive high power factor operation method according to an embodiment of the present invention. Figure 5 It can be seen that under the proposed DC bus voltage adaptive high power factor operation method, a single stage of the high-frequency chain AC / DC converter can simultaneously achieve input-output electrical isolation and AC side high power factor operation, and the grid current sinusoidal degree is relatively high, meeting the grid connection standard.

[0088] Although preferred embodiments of this application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this application.

[0089] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A high-voltage direct current interference active mitigation device, characterized in that, include: High-frequency AC / DC converter unit, with the input side connected to the AC power grid; The H-bridge converter unit has its DC side connected to the output DC bus of the high-frequency chain AC / DC converter unit, and its positive output is connected to the deep well anode, while its negative output is connected to the buried pipeline. The main control unit is used to determine the desired output voltage of the H-bridge converter unit based on the pipeline ground potential signal at the monitoring point of the pipeline section, determine the DC bus voltage command value based on the desired output voltage of the H-bridge converter unit, and control the high-frequency link AC / DC converter unit to achieve adaptive adjustment of the DC bus voltage and high power factor operation on the AC side; the specific implementation process includes: The desired output voltage of the H-bridge converter unit The DC bus voltage command value was calculated. ; DC bus voltage command value Subtract the actual value of the sampled DC bus voltage The difference is input into the PI controller, and the output of the PI controller is the command value for the grid-side current amplitude. ; The command value of the grid-side current amplitude Multiply by a unit cosine that is in phase with the grid voltage. The instantaneous command value of the grid-side current is obtained. ; The phase of the grid voltage; Instantaneous command value of grid-side current Compared with the actual value of grid-side current The difference is input to the quasi-proportional resonant controller to obtain the instantaneous power command value on the grid side. ; Calculate the voltage conversion ratio using the DC bus voltage command value ; according to and Calculate control variables , and After modulation, a corresponding switching control signal is generated, which is used to control the on / off state of the switching devices in the high-frequency AC / DC converter unit; wherein, The calculated switching frequency. The voltage after DC bus voltage inversion The normalized internal phase shift angle, The voltage after grid voltage inversion The voltage after DC bus voltage inversion The normalized external phase shift angle.

2. The active high-voltage DC interference mitigation device according to claim 1, characterized in that, The phase of the grid voltage The determination process includes: Acquire grid voltage signal Two orthogonal sine signals are generated by a second-order generalized integrator. and ; ;in, For filter gain coefficients, The angular frequency of the input AC signal, where s is a complex frequency; Will , Input the phase-locked loop to obtain the phase of the power grid at this time. .

3. The active high-voltage DC interference mitigation device according to claim 1, characterized in that, DC bus voltage command value The calculation formula is: ； in, This is the initial DC bus voltage. , , The output values ​​of the DC bus voltage at different stages. , , The switching thresholds for the three rising phases, , , The threshold for switching between the three descent phases.

4. The active high-voltage DC interference mitigation device according to claim 1, characterized in that, ;in, This refers to the voltage signal of the filter capacitor in the LC filter on the grid side of the high-frequency AC / DC converter unit. This represents the output stage of the DC bus voltage, where n = 1, 2, 3.

5. The active high-voltage DC interference mitigation device according to claim 1, characterized in that, The main control unit is also used to adjust the amplitude and polarity of the output voltage of the H-bridge converter unit, and the specific implementation process includes: 1) Collection Monitor the pipe-to-ground potential at points 1 to N at all times ; 2) Construct the objective function using the sum of the squares of the pipe-to-ground potential signals from the monitoring points of the pipeline section relative to the cathodic protection potential. The objective function expression is: ,in Indicates the first The pipe-to-ground potential at each monitoring point Indicates the cathodic protection potential. The sign function for the pipe-to-ground potential offset; 3) Monitoring point ground potential at any time Substitute into the objective function In the middle, calculate Time objective function The value; 4) Calculation Time's up Output voltage change value at time ,as well as Time's up The change in the objective function due to the change in output voltage at any given time ; 5) Calculate using the change in the objective function The expected change in output voltage at time t , ,in, To fix the voltage step size, It is an adaptive compensation factor; 6) According to Time's up The change in the objective function at time t and Calculate the expected output voltage change at time t. Desired output voltage at time ; 7) Desired output voltage at time The difference between the sampled output voltage of the H-bridge converter unit and the output voltage is input to a PI controller, which then uses closed-loop control to obtain the duty cycle. After being limited, a corresponding switching control signal is generated, which is used to control the on / off state of the switching devices in the H-bridge converter unit.

6. The active high-voltage DC interference mitigation device according to claim 5, characterized in that, Also includes: 8) When the output voltage of the H-bridge converter unit satisfies Repeat steps 1) to 7) until the minimum value of the objective function M is found.

7. The active high-voltage DC interference mitigation device according to claim 5, characterized in that, Desired output voltage at time The calculation formula is: like , ,but ; like , ,but ; like , ,but ; like , ,but ; like ,but .

8. The active high-voltage DC interference mitigation device according to claim 5, characterized in that, Duty cycle The calculation formula is: ;in, This is the DC bus voltage signal.

9. The active high-voltage DC interference mitigation device according to claim 1, characterized in that, control variables , and The calculation formula is: ； in, The initial switching frequency, This represents the output stage of the DC bus voltage, where n=1,2,3. This is the DC bus voltage signal. This refers to the voltage signal of the filter capacitor in the LC filter on the grid side of the high-frequency AC / DC converter unit. This is the value of the auxiliary inductance on the AC side of the high-frequency AC / DC converter unit.

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