A method for suppressing high-frequency resonance in a grid-type SLCC converter valve with CLC limiting.

Abstract

This invention belongs to the field of electrical engineering technology and discloses a high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting. The method includes constructing a topology model of a dual-6-pulse grid-type SLCC converter valve; based on this model, constructing a follow-up SVG sequence impedance model, a grid-type SVG sequence impedance model, and a dual-6-pulse LCC converter station admittance model; using the Nyquist stability criterion and impedance analysis, establishing equivalent impedance circuit models for the follow-up SVG sequence impedance model and the grid-type SVG sequence impedance model respectively, and determining the stability of the corresponding systems; based on the stability determination results, adjusting the VSG parameters and the CLC limiting coefficient to complete high-frequency resonance suppression. This invention achieves autonomous voltage and frequency regulation of the grid-type SLCC and is suitable for weak grid scenarios with a high proportion of new energy access.

Description

Technical Field

[0001] This invention relates to the field of electrical engineering technology, and specifically to a high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting. Background Technology

[0002] The transformation of the energy system towards "high efficiency and high performance" is the core characteristic of the new power system: on the one hand, the penetration rate of renewable energy sources such as wind power and photovoltaics continues to rise, and their intermittency and volatility lead to a decrease in system inertia and a weakening of support capacity; on the other hand, the proportion of power electronic equipment has increased significantly, and traditional grid-connected control equipment relies on grid voltage and frequency signals, which can easily cause stability problems.

[0003] SLCC (Self-commutated Current Source Converter), as a novel converter technology, can enhance system stability through dynamic reactive power compensation. However, existing SLCCs all employ grid-based control, which has three major drawbacks:

[0004] 1. Poor adaptability to weak power grids: The commutation process of grid-connected SLCCs depends on the AC voltage signal provided by the power grid. When the short-circuit ratio of the power grid is <2.0 (weak power grid scenario), the commutation failure rate increases significantly, reaching more than 30%, which seriously threatens the safe operation of the system. For example, in the transmission project of new energy bases, due to the large fluctuations in wind power and photovoltaic output, the equivalent impedance of the power grid increases, and grid-connected SLCCs often cause DC power interruption due to commutation failure.

[0005] 2. High Risk of High-Frequency Resonance: The impedance characteristics of grid-connected SLCCs are prone to mismatch with the grid impedance in the 100~200Hz frequency band, leading to high-frequency resonance. Simulations show that grid-connected SLCCs are prone to resonance around 138Hz, with the total voltage distortion rate at the receiving end reaching 71.9%, severely affecting power quality and even causing sensitive load outages.

[0006] 3. Lack of independent support capability: Grid-connected SLCCs cannot independently establish grid voltage and frequency, and rely entirely on the voltage / frequency signals of the external grid. When new energy sources are connected to the grid on a large scale or when the grid is disturbed, the system has weak anti-disturbance capability and is prone to voltage collapse or frequency instability. For example, in the scenario of isolated microgrids, grid-connected SLCCs cannot independently maintain system voltage and frequency and need to rely on external energy storage devices for support.

[0007] Existing technologies mostly focus on standalone grid-type SVG (Static Var Generator) or grid-type SLCC, without achieving topological integration and control coordination between the two; and lack sequence impedance modeling and resonance mechanism research for grid-type SLCC converter valves, making it difficult to support the stable operation of "high-voltage and high-efficiency" systems. Summary of the Invention

[0008] The technical problem to be solved by this invention is: in order to solve the problems of existing grid-connected SLCC converter valves relying on strong power grids, frequent high-frequency resonance, and high risk of commutation failure, a high-frequency resonance suppression method for grid-connected SLCC converter valves with CLC limiting is provided to achieve the dual objectives of autonomous voltage build-up and frequency regulation and high-frequency resonance suppression.

[0009] To solve the above technical problems, the present invention adopts the following technical solution:

[0010] A method for suppressing high-frequency resonance in a grid-type SLCC converter valve with CLC limiting includes the following steps:

[0011] S1. Construct a dual 6-pulse grid-type SLCC converter valve topology model, which includes dual 6-pulse LCC (Line-Commutated Converter) converter valve units, grid-type SVG units, and DC-side smoothing reactors;

[0012] S2. Based on the topology model of the dual 6-pulse grid-type SLCC converter valve, construct the following SVG sequence impedance model, the grid-type SVG sequence impedance model, and the dual 6-pulse LCC converter station admittance model.

[0013] S3. Using the Nyquist stability criterion, based on impedance analysis, establish equivalent impedance circuit models of dual 6-pulse LCC and mesh-type SVG converter valve, respectively, calculate the theoretical resonant frequency, determine the stability of the corresponding system, and establish a frequency sweep model.

[0014] S4. Based on the stability discrimination results obtained in step S3, adjust the VSG (Virtual Synchronous Generator) parameters and the CLC (Capacitor-Inductor-Capacitor) limiting coefficient to complete high-frequency resonance suppression.

[0015] Furthermore, in step S1, the dual 6-pulse LCC converter valve unit includes two 6-pulse LCC converter valves connected in series, with the midpoint grounded via a low impedance. The two 6-pulse LCC converter valves are connected to the same AC bus via a first YY transformer T1 and a second YY transformer T2, respectively. The grid-type SVG unit has a built-in VSG controller and current limiting control circuit, and the grid-type SVG unit is connected to the AC bus. The DC-side smoothing reactor is connected in series with the DC side of the dual 6-pulse LCC converter valve unit.

[0016] Furthermore, the 6-pulse LCC converter valve uses 12 IGBT modules, grounded at the midpoint, with a minimum impedance of 10Ω;

[0017] Both the first YY type transformer T1 and the second YY type transformer T2 are SFZ11-31500 / 220 type transformers with a rated capacity of 31.5MVA and a short-circuit impedance of 8%.

[0018] The DC-side smoothing reactor is a dry-type hollow reactor with a rated current of 3kA.

[0019] Furthermore, in step S2, a positive and negative sequence disturbance of ±5% of the rated voltage is injected into the PCC (Point of Common Coupling) using the voltage disturbance sequence impedance modeling method. The first positive sequence impedance is obtained based on the phase deviation of the PLL (Phase-Locked Loop) and the dq rotating coordinate system. Then, a sequence impedance model of the SVG network is constructed, and the specific formula is as follows:

[0020] ;

[0021] in, To represent a complex variable, Indicates the SVG filter inductor. This indicates the SVG filter resistor. , Both represent the q-axis PI parameters of the inner current loop. This represents the SPWM (Sinusoidal Pulse Width Modulation) modulation coefficient;

[0022] Assuming that VSG phase angle disturbances have no impact on the high-frequency band, the second positive sequence impedance is obtained by employing VSG control and Kirchhoff's current law, combined with the node current relationship at the grid connection point and the modulation wave after CLC limiting. Then, a grid-type SVG sequence impedance model with CLC limiting is constructed, and the specific formula is as follows:

[0023] ;

[0024] in, This represents the CLC limiting factor. Indicates the VSG control proportional coefficient;

[0025] CLC-limited d-axis voltages The specific formula is:

[0026] ;

[0027] in, This represents the d-axis and q-axis voltages without limiting. This represents the virtual internal potential difference.

[0028] Using harmonic state-space theory and an improved commutation processing method, the AC side current is transformed to a dq rotating coordinate system and averaged. The current disturbance component is extracted by inverse Park transform. Combined with constant DC voltage control and PLL dynamics, the total admittance at the receiving end is obtained. Furthermore, an admittance model for the dual 6-pulse LCC converter station is constructed, with the specific formula as follows:

[0029] ;

[0030] in, This indicates the admittance of the dual 6-pulse LCC converter station. This represents the admittance of the AC filter.

[0031] Furthermore, the VSG control logic includes:

[0032] The voltage and current signals of the AC bus are collected, and the real-time active power is obtained through the instantaneous power calculation module. reactive power ;

[0033] Real-time active power With active power reference value The virtual potential phase angle is obtained through comparison and VSG control. The specific formula is as follows:

[0034] ;

[0035] in, Indicates angular velocity. Indicates the rated angular velocity. Indicates the active damping coefficient. Represents the virtual moment of inertia;

[0036] Real-time reactive power Reactive power reference value The virtual internal potential difference is compared and output through the constant power factor outer loop. , The d-axis and q-axis voltages are obtained by superimposing the bus voltage and then CLC limiting them.

[0037] The d-axis and q-axis voltages after CLC limiting are converted into SPWM modulation waves by Park inverse transformation to control the SVG switching action.

[0038] Further improvements to the commutation process include:

[0039] The AC side current of the dual 6-pulse LCC converter valve unit is converted to the dq rotating coordinate system to obtain the d-axis and q-axis currents. These currents are then averaged to filter out high-frequency components above 200Hz, yielding the processed d-axis and q-axis currents. The processed d-axis and q-axis currents are then converted to the three-phase stationary coordinate system using the inverse Park transform to extract the current disturbance components. The specific formula is as follows:

[0040] ;

[0041] ;

[0042] ;

[0043] in, This represents the current disturbance components of phases a, b, and c. Represents the inverse Park transformation matrix. This indicates a DC current disturbance. This indicates AC voltage disturbance. , , , , , Both represent coupling coefficients. Indicates trigger angle perturbation. This indicates a DC voltage disturbance. and These represent the fluctuations of the converter bus voltage along the d-axis and q-axis in the dq rotating coordinate system, respectively.

[0044] Furthermore, in step S3, the equivalent impedance of the dual 6-pulse LCC and the grid-type SVG converter valve is compared in the equivalent impedance circuit model. The specific formula is:

[0045] ;

[0046] in, This represents the equivalent impedance of the dual 6-pulse LCC converter valve. ;

[0047] Equivalent impedance in the equivalent impedance circuit model of dual 6-pulse LCC and mesh-type SVG converter valve The specific formula is:

[0048] ;

[0049] The AC power grid connected to the converter valve is equivalent to ;

[0050] like and The absence of intersections in the amplitude-frequency characteristics indicates the stability of the dual 6-pulse tracking mesh SLCC system; conversely, the phase difference at the intersection frequency is calculated. The specific formula is as follows:

[0051] ;

[0052] in, express amplitude and frequency phase, express The amplitude-frequency phase;

[0053] like and The absence of intersections in the amplitude-frequency characteristics indicates the stability of the dual-6-pulse mesh SLCC system; conversely, the phase difference at the intersection frequency is calculated. The specific formula is as follows:

[0054] ;

[0055] in, express The amplitude-frequency phase;

[0056] like This indicates that the dual 6-pulse mesh SLCC system is stable; otherwise, there is a risk of resonance.

[0057] like This indicates that the dual-6-pulse mesh SLCC system is stable; otherwise, there is a risk of resonance.

[0058] Furthermore, in step S4, the VSG parameters include the active damping coefficient. and virtual moment of inertia ;

[0059] If a dual 6-pulse follower mesh SLCC system has a resonance risk, after adjusting the VSG parameters and CLC limiting coefficient, when When the error with the measured value is less than 5%, it indicates that the high-frequency resonance suppression of the system has been completed;

[0060] If a dual-6-pulse mesh SLCC system has a resonance risk, after adjusting the VSG parameters and CLC limiting coefficient, when When the error with the measured value is less than 5%, it indicates that the high-frequency resonance suppression of the system has been completed.

[0061] Furthermore, the present invention also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the steps of the high-frequency resonance suppression method for the grid-type SLCC converter valve with CLC limiting.

[0062] Furthermore, the present invention also proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, performs the high-frequency resonance suppression method for the grid-type SLCC converter valve with CLC limiting.

[0063] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0064] This invention has independent grid support capability, high-frequency resonance suppression capability, and weak grid adaptability. It can achieve an integrated solution of commutation stability, resonance suppression, inertia support, and coordinated control, meeting the technical requirements of high-efficiency and high-voltage new power systems. Attached Figure Description

[0065] Figure 1 This is a flowchart illustrating the overall implementation of the present invention.

[0066] Figure 2 This is a topology diagram of the dual 6-pulse LCC converter valve unit of the present invention.

[0067] Figure 3 This is a topological diagram of the 6-pulse LCC converter valve of the present invention.

[0068] Figure 4 This is a topology diagram of the SVG sequence impedance model with CLC limiting in this invention.

[0069] Figure 5 This is the control flowchart for CLC limiting in this invention.

[0070] Figure 6 This is a flowchart of the constant voltage control process of the present invention.

[0071] Figure 7 This is the equivalent circuit diagram of the impedance of the topology model of the dual 6-pulse mesh SLCC converter valve of the present invention.

[0072] Figure 8 This is a comparison chart of the impedance results of the present invention with the mesh-type SVG sequence impedance model and the mesh-type SVG sequence impedance model with CLC limiting.

[0073] Figure 9 This invention relates to the three-phase voltage waveform diagram of the receiving end in the SVG sequence impedance model.

[0074] Figure 10 This is a Fourier decomposition result of the voltage of phase a at the receiving end when resonance occurs in the mesh-type SVG sequence impedance model of this invention.

[0075] Figure 11 This is a waveform diagram of the receiving end three-phase voltage in the grid-type SVG sequence impedance model containing CLC limiting according to the present invention.

[0076] Figure 12 This is a Fourier decomposition result of the phase voltage at the receiving end a when resonance occurs in the SVG sequence impedance model with CLC limiting in this invention. Detailed Implementation

[0077] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0078] To achieve the above objectives, this invention proposes a high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting, such as... Figure 1 As shown, the specific steps are as follows:

[0079] S1. Construct a dual-6-pulse grid-type SLCC converter valve topology model. This model includes dual-6-pulse LCC (Line-Commutated Converter) converter valve units, grid-type SVG units, and DC-side smoothing reactors; specifically:

[0080] like Figure 2 As shown, the dual 6-pulse LCC converter valve unit includes two 6-pulse LCC converter valves connected in series. Figure 2 Within the two green boxes (indicated in the image), the midpoint is grounded via a low impedance. The low-voltage sides of the first YY transformer T1 and the second YY transformer T2 are respectively connected to two 6-pulse LCC converter valves. The high-voltage sides of the first YY transformer T1 and the second YY transformer T2 are connected to the same 220kV AC bus, thus connecting to the grid-side voltage. and impedance connect;

[0081] The grid-type SVG unit incorporates a VSG (Virtual Synchronous Generator) controller and current limiting control circuit. The grid-type SVG unit is connected to the AC bus. The DC-side smoothing reactor is connected in series with the DC side of the dual 6-pulse LCC converter valve unit, and the DC-side smoothing reactor is equivalent to the DC-side equivalent inductance. ;

[0082] like Figure 3 As shown, the 6-pulse LCC converter valve uses 12 IGBT modules, grounded at the midpoint, with a minimum impedance of 10Ω. This is the DC side voltage of the power grid. This is the DC-side current of the power grid. The equivalent inductance on the DC side is... This is the equivalent resistance on the DC side;

[0083] Transformers T1~T1 of the first to twelfth YY type12 All are SFZ11-31500 / 220 type transformers, with a rated capacity of 31.5MVA, a voltage ratio of 220kV / 150.98kV, a short-circuit impedance of 8%, a no-load loss of 12kW, and a load loss of 75kW.

[0084] The DC-side smoothing reactor is a dry-type, air-core reactor with a rated current of 3kA, an inductance of 80mH, insulation class H, and a short-circuit withstand current of 20kA / 2s. The windings of the DC-side smoothing reactor are encapsulated with glass fiber reinforced epoxy resin, providing moisture resistance and aging resistance, making it suitable for outdoor UHV projects. In addition to suppressing DC current pulsation, the DC-side smoothing reactor is also designed with harmonic isolation. By optimizing the inductance value, the reactor exhibits high impedance characteristics in the 100~200Hz high-frequency range, preventing high-frequency harmonics from the DC side from propagating to the AC side, further enhancing the system's anti-resonance capability.

[0085] S2. Based on the topology model of the dual-6-pulse grid-type SLCC converter valve, construct the following models: grid-type SVG sequence impedance model, grid-type SVG sequence impedance model, and dual-6-pulse LCC converter station admittance model; specifically:

[0086] A voltage disturbance sequence impedance modeling method is used to inject positive and negative sequence disturbances of ±5% of the rated voltage into the PCC (Point of Common Coupling). Based on the phase deviation of the PLL (Phase-Locked Loop) and the dq rotating coordinate system, the first positive sequence impedance is obtained. Then, a sequence impedance model of the SVG network is constructed, and the specific formula is as follows:

[0087] ;

[0088] in, To represent a complex variable, Indicates the SVG filter inductor. This indicates the SVG filter resistor. , Both represent the q-axis PI parameters of the inner current loop. This represents the SPWM (Sinusoidal Pulse Width Modulation) modulation coefficient;

[0089] like Figure 4 As shown, assuming that VSG phase angle disturbances have no effect on the high-frequency band, the second positive sequence impedance is obtained by using VSG control and Kirchhoff's current law, combined with the node current relationship at the grid connection point and the modulation wave after CLC (Capacitor-Inductor-Capacitor) limiting. Then, a grid-type SVG sequence impedance model with CLC limiting is constructed, and the specific formula is as follows:

[0090] ;

[0091] in, This represents the CLC limiting factor. Indicates the VSG control proportional coefficient;

[0092] CLC-limited d-axis voltages The specific formula is:

[0093] ;

[0094] in, This represents the d-axis and q-axis voltages without limiting. This represents the virtual internal potential difference.

[0095] The logic of VSG control includes:

[0096] Acquire AC bus voltage signal and current signal Real-time active power is obtained through the instantaneous power calculation module. reactive power ;

[0097] Real-time active power With active power reference value The virtual potential phase angle is obtained through comparison and VSG control. The specific formula is as follows:

[0098] ;

[0099] in, Indicates angular velocity; Indicates the fundamental angular frequency of the power grid; Indicates the active damping coefficient; Represents the virtual moment of inertia;

[0100] Real-time reactive power Reactive power reference value The virtual internal potential difference is compared and output through the constant power factor outer loop. , The d-axis and q-axis voltages are obtained by superimposing the bus voltage and then CLC limiting them.

[0101] The d-axis and q-axis voltages after CLC limiting are converted into SPWM modulation waves by Park inverse transformation to control the SVG switching action;

[0102] Using harmonic state-space theory and an improved commutation processing method, the AC side current is transformed to a dq rotating coordinate system and averaged. The current disturbance component is extracted by inverse Park transform. Combined with constant DC voltage control and PLL dynamics, the total admittance at the receiving end is obtained. Furthermore, an admittance model for the dual 6-pulse LCC converter station is constructed, with the specific formula as follows:

[0103] ;

[0104] in, This indicates the admittance of the dual 6-pulse LCC converter station. Indicates the admittance of the AC filter;

[0105] Figure 4 middle, This represents the transfer function of the reactive power outer-loop PI regulator. This represents the equivalent resistance of the SVG. This represents the filter inductance of the SVG. This represents the DC-side voltage of the SVG. Indicates the rated angular frequency of the power grid. Indicates the phase angle. , These represent the PCC voltages respectively. , Quantity, This represents the phase current of the static var generator. Indicates the AC reference voltage. Indicates the voltage at the point of common coupling. , They represent the coordinate transformations respectively. , shaft voltage, , , These represent the three-phase voltages a, b, and c after coordinate transformation;

[0106] Improved commutation processing methods include:

[0107] The AC side current of the dual 6-pulse LCC converter valve unit is converted to the dq rotating coordinate system to obtain the d-axis and q-axis currents. These currents are then averaged to filter out high-frequency components above 200Hz, yielding the processed d-axis and q-axis currents. The processed d-axis and q-axis currents are then converted to the three-phase stationary coordinate system using the inverse Park transform to extract the current disturbance components. The specific formula is as follows:

[0108] ;

[0109] ;

[0110] ;

[0111] in, This represents the current disturbance components of phases a, b, and c. Represents the inverse Park transformation matrix. This indicates a DC current disturbance. This indicates AC voltage disturbance. , , , , , Both represent coupling coefficients. Indicates trigger angle perturbation. This indicates a DC voltage disturbance. and These represent the fluctuations of the converter bus voltage along the d-axis and q-axis of the dq rotating coordinate system, respectively.

[0112] S3. Using the Nyquist stability criterion, equivalent impedance circuit models of a dual 6-pulsating LCC and a mesh-type SVG converter valve, and equivalent impedance circuit models of a dual 6-pulsating LCC and a mesh-type SVG converter valve are established based on impedance analysis. The theoretical resonant frequency is calculated, and the stability of the corresponding system is determined. Simultaneously, a frequency sweep model is established. Specifically:

[0113] Equivalent impedance in the equivalent impedance circuit model of dual 6-pulse LCC and mesh-type SVG converter valve The specific formula is:

[0114] ;

[0115] in, This represents the equivalent impedance of the dual 6-pulse LCC converter valve. ;

[0116] Equivalent impedance in the equivalent impedance circuit model of dual 6-pulse LCC and mesh-type SVG converter valve The specific formula is:

[0117] ;

[0118] The AC power grid connected to the converter valve is equivalent to ;

[0119] like and The absence of intersections in the amplitude-frequency characteristics indicates the stability of the dual 6-pulse tracking mesh SLCC system; conversely, the phase difference at the intersection frequency is calculated. The specific formula is as follows:

[0120] ;

[0121] in, express amplitude and frequency phase, express The amplitude-frequency phase;

[0122] like and The absence of intersections in the amplitude-frequency characteristics indicates the stability of the dual-6-pulse mesh SLCC system; conversely, the phase difference at the intersection frequency is calculated. The specific formula is as follows:

[0123] ;

[0124] in, express The amplitude-frequency phase;

[0125] like This indicates that the dual 6-pulse mesh SLCC system is stable; otherwise, there is a risk of resonance.

[0126] like This indicates that the dual-6-pulse mesh SLCC system is stable; otherwise, there is a risk of resonance.

[0127] S4. Based on the stability judgment results obtained in step S3, adjust the VSG parameters and CLC limiting coefficient to complete high-frequency resonance suppression; specifically:

[0128] VSG parameters include the active damping coefficient. and virtual moment of inertia ;

[0129] If a dual 6-pulse follower mesh SLCC system has a resonance risk, after adjusting the VSG parameters and CLC limiting coefficient, when When the error with the measured value is less than 5%, it indicates that the high-frequency resonance suppression of the system has been completed;

[0130] If a dual-6-pulse mesh SLCC system has a resonance risk, after adjusting the VSG parameters and CLC limiting coefficient, when When the error with the measured value is less than 5%, it indicates that the high-frequency resonance suppression of the system has been completed.

[0131] Example:

[0132] A topology model of a dual 6-pulse mesh SLCC converter valve was built on the PSCAD platform, and an impedance sweep frequency test of 10~1000Hz was carried out to verify the accuracy of the model.

[0133] Virtual moment of inertia The value ranges from 0.5 to 2.0 kg·m², and the frequency change rate is monitored online. Perform adaptive adjustments: when the frequency drops, It automatically increases to 1.5~2.0 kg·m², providing greater inertia support; when the frequency is stable, Reduce the amount to 0.5~1.0 kg·m² to avoid slow response.

[0134] Active damping coefficient The value range is 5~20pu, and it is adjusted in real time by a proportional-derivative controller to ensure that frequency fluctuations converge quickly.

[0135] CLC limiting process: such as Figure 5 As shown, I max The current threshold is indicated by the output voltage. Calculated by the current limiting circuit control And then After performing amplitude limiting control, the amplitude is limited. ,Right now Substituting into the voltage dynamic equation, we can calculate the result. The specific formula is as follows:

[0136] ;

[0137] ;

[0138] in, This represents bandwidth, taken as 50Hz. Indicates the output filter inductance; This represents the vector of the actual output current in the dq rotating coordinate system; This indicates the feedforward term of the output voltage at the machine terminal after passing through a low-pass filter; The transfer function of the high-pass filter stage is represented by this. Indicates the fundamental angular frequency of the power grid;

[0139] The dynamic equation of alternating current can be obtained by dq transformation:

[0140] ;

[0141] in, This represents the bridge arm output voltage vector in the dq rotating coordinate system. This represents the vector of the grid connection point voltage in the dq rotating coordinate system. This represents the equivalent series resistance of the output filter inductor;

[0142] make = We can obtain:

[0143] ;

[0144] make It tends toward infinity, and We can obtain:

[0145] ;

[0146] Under normal circumstances, much smaller Therefore, the current is infinitely close to the current reference value and does not exceed the current reference value. Thus, by controlling the magnitude of the current reference value, the current output value can be well controlled.

[0147] A maximum current value is preset. When the current reference value is greater than the maximum current value, most of the current is in a fault state and the current is the fault current. The CLC limiting module sends a command to the control system to select the backup phase-locked loop to obtain the phase angle. The PSL power loop is not used for calculation, so the fault switching of PSL / PLL is realized. When the fault current disappears and the current reference value stabilizes, the control loop is switched back to PSL.

[0148] Establish a coordinated control logic between SVG reactive power compensation and LCC commutation voltage. When the LCC commutation voltage is lower than 90% of the rated value, the SVG automatically increases the reactive power output to raise the commutation voltage. When the LCC commutation voltage is higher than 105% of the rated value, the SVG automatically absorbs reactive power to reduce the commutation voltage and ensure the stability of the LCC commutation process.

[0149] The grid-type SVG sequence impedance model is based on DC voltage stability. It generates an active current reference value through a DC voltage control loop to compensate for internal losses. Simultaneously, it generates a reactive current reference value using a constant power factor or reactive power outer loop. Combined with grid phase information obtained from a phase-locked loop, and processed by the inner current loop, the converter switching is controlled via SPWM modulation, enabling the output AC current to track the reference value. This achieves dynamic regulation of the grid's reactive power, stabilizing the grid connection point voltage and power quality. Specifically:

[0150] Step 1: The phase-locked loop (PLL) uses a voltage disturbance sequence impedance modeling method to construct the PLL sequence impedance model. When positive and negative sequence disturbances are injected into the PCC, a phase deviation will occur. Therefore, it is necessary to model the PLL to reflect the adverse effects of this deviation. The specific formula is as follows:

[0151] ;

[0152] in, This represents the transfer function of the phase-locked loop. This represents the proportional gain of the phase-locked loop. This represents the integral coefficient of the phase-locked loop. , Indicates the angular frequency of the disturbance. Indicates the fundamental voltage of the PCC. This indicates the phase error of the phase-locked loop. Indicates the positive sequence disturbance voltage of PCC;

[0153] Phase a voltage of the SVG mesh The expression in the time domain is:

[0154] ;

[0155] in, This represents the phase voltage of PCCa. This represents the a-phase current of the SVG mesh. This represents the equivalent resistance of the SVG. Indicates the filter inductance of the SVG;

[0156] Step 2, PCCa phase voltage and the a-phase current of the grid-type SVG The time-domain representation is:

[0157] ;

[0158] in, This represents the fundamental voltage of phase PCCa. Indicates the fundamental angular velocity of the PCC. This represents the amplitude of the disturbance voltage in phase a. Indicates positive sequence angular velocity. express time, , , These represent the fundamental and positive-sequence component phases of the PCC voltage and SVG output current, respectively. This indicates the fundamental current frequency of the SVG. This represents the positive-sequence perturbation amplitude of the SVG.

[0159] Virtual internal potential amplitude The expression is:

[0160] ;

[0161] in, This represents the transfer function of the reactive power outer-loop PI regulator. , Indicates the PCC voltage;

[0162] Step 3: Based on the power outer loop control architecture, the PCC voltage is first acquired. After comparing the deviation between the power reference value and the actual measured value, the signal is sent to the proportional-integral regulator and other components to generate the command signal for the current inner loop. Through mathematical modeling in the dq rotating coordinate system, the positive-sequence frequency domain expression of the q-axis current reference value in the current inner loop can be derived, as follows:

[0163] ;

[0164] in, This represents the positive-sequence frequency domain reference value of the inner loop of the q-axis current. Represents the rotation factor in the complex frequency domain. This indicates the phase difference between the PCC current and voltage. This represents the PCC disturbance current. This represents the fundamental component of the positive sequence current in the PCC. Indicates the fundamental voltage of the PCC;

[0165] Step 4: The modulation signal of phase a voltage can be obtained through convolution operation, and then... Replace with Based on this, the mathematical expression of the SVG modulated wave in the frequency domain is reconstructed. Then, using the inverse Park transform, the sequence impedance of the SVG can be finally obtained. The expression is as follows:

[0166] ;

[0167] in, The transfer function representing the inner current loop. Indicates the fundamental frequency of the power grid. Indicates the damping coefficient. This represents the fundamental component of the positive-sequence current output by the SVG. This represents the modulation amplitude reference of the SVG. Represents the feedforward coefficient. This represents the equivalent impedance of a dual 6-pulse LCC.

[0168] SVG sequence impedance model with CLC limiting:

[0169] Step 1: Although there are fundamental differences in the core control logic between meshed SVG and follow-mesh SVG, they are completely consistent in the design of the constant power factor outer loop. Therefore, the specific derivation details of the constant power factor outer loop will not be repeated here. Phase angle The expression is:

[0170] ;

[0171] in, Indicates the active power reference value for a network-type SVG; This represents the actual active power of the network-type SVG; Indicates the rated angular frequency of the power grid;

[0172] Step 2: The effect of phase angle disturbance is mainly concentrated in the impedance characteristic region around 50Hz, and it has no substantial impact on the impedance characteristic analysis in the high-frequency range. Based on this characteristic, the influence of phase angle disturbance can be ignored when modeling the network-type SVG. Under this premise, the current reference value can be derived as follows:

[0173] ;

[0174] in, Represents virtual impedance. ; The d-component represents the current reference value. The q-component represents the current reference value. This represents the virtual potential amplitude of the VSG;

[0175] Combining the above formulas, we can obtain and Positive sequence frequency domain expression:

[0176] ;

[0177] in, Indicates the frequency offset. Indicates the frequency of the disturbance voltage;

[0178] Step 3, the real-time power calculation of the outer power loop of the grid-connected SVG, needs to be completed by acquiring the voltage and current signals of the PCC. However, the derivation and calculation of its impedance characteristics require the output current of the grid-connected SVG converter valve itself as the core basic data. Given this difference in calculation basis, in order to accurately derive the current relationship at the grid connection point, it is necessary to... Current components related to grid connection point This is converted to the output current of a mesh-type SVG. The PCC relationship satisfying KCL is:

[0179] ;

[0180] in, This represents the positive sequence current on the outlet side of the converter valve; Indicates the output current of the SVG;

[0181] Step 4: The SVG modulated wave obtained after CLC amplitude limiting control strategy. and The mathematical expression:

[0182] ;

[0183] in, , , ; The differential element coefficient of inductance. Represents the actual current along the d-axis. This represents the equivalent impedance coefficient of the inner current loop. Represents the coefficients of the rotational coupling term. This represents the actual current along the q-axis. This represents the per-unit value of the equivalent resistance on the SVG output side. This represents the per-unit value of the inductor on the SVG output side;

[0184] And thus obtain and The frequency domain expression of the voltage at frequency a can be further derived by performing coordinate transformation using the Park transform, without considering phase angle disturbances. The simplified expression is as follows:

[0185] ;

[0186] in, This represents the amplitude reference of the a-phase output voltage of the SVG in a three-phase stationary coordinate system.

[0187] The obtained sequence impedance of the network-type SVG The expression is:

[0188] .

[0189] Admittance model of dual 6-pulse LCC converter station:

[0190] Step 1: Based on the receiving-end topology of the dual 6-pulse LCC converter valve, and considering the frequency coupling effect of the LCC converter valve, establish the HSS state equations for the sending-end AC system, the DC transmission system, and the receiving-end AC filter system. The specific formula is as follows:

[0191]

[0192] in, Represents the input matrix, This indicates the control input or external excitation signal of the converter station. Indicates the output vector. Indicates the output matrix. Represents the direct transmission matrix. It represents a 12-dimensional state vector (including AC side current, DC voltage, filter voltage, PLL phase, etc.). The 12×12 coefficient matrix is ​​expressed as follows:

[0193] ;

[0194] in, Indicates the equivalent resistance on the AC side. Indicates the equivalent inductance on the AC side. This represents the equivalent resistance of the AC filter. This represents the equivalent capacitance of an AC filter. This represents the equivalent inductance of an AC filter. Indicates the equivalent resistance on the DC side. Indicates the equivalent inductance on the DC side. This represents the proportional coefficient of the current control system in the converter station. This represents the proportional gain of the voltage control system in the converter station. Represents the integral coefficient of the phase-locked loop;

[0195] Step 2, as follows Figure 6 As shown, constant voltage control is adopted at the receiving end. To address the nonlinearity of the LCC commutation process, a method is proposed that combines dq rotating coordinate averaging, inverse Park transform, and coupling coefficient correction. Actual DC-side voltage feedback quantity. Feed into feedforward compensation module This module is typically a first-order inertial or proportional element. It eliminates interference from system cross-coupling terms through feedforward decoupling and outputs a pre-processed voltage signal. This is to improve the dynamic response speed of the control system. DC voltage rated reference value The deviation is calculated at the first comparison node (differential link) to obtain the DC voltage deviation signal. The deviation signal is input to the DC voltage regulator. By proportionally amplifying and integrally eliminating the deviation signal, an intermediate control value for the firing angle is output. This intermediate control value and the phase compensation term are differentially calculated at the second comparison node to finally generate a reference value for the firing angle. This trigger angle command will be sent to the pulse trigger unit, which will adjust the commutation timing of the LCC converter valve to change its DC-side voltage-current characteristics, thereby enabling the actual DC voltage to track the voltage. This enables stable control of the DC-side voltage.

[0196] Step 3: Transform the HSS state equation to the frequency domain, and combine it with the current disturbance equation after the improved commutation treatment to derive the admittance of the dual 6-pulse LCC converter station. Acceptable AC filter The total acceptor is then obtained by calculating the RLC in parallel. , .

[0197] The dual-6-pulse grid-type SLCC converter valve topology model adopts a hybrid connection method of parallel AC side and series DC side to achieve the dual functions of high-capacity DC transmission and dynamic reactive power support. The 220kV AC grid uses the Thevenin equivalent model, with an equivalent electromotive force of 220kV / Short-circuit impedance ;

[0198] To verify the accuracy of the SVG sequence impedance model, the SVG sequence impedance model with CLC limiting, and the admittance model of the dual 6-pulse LCC converter station, an impedance sweep frequency test was conducted on the dual 6-pulse SVG converter valve topology model. The impedance analytical value of the model was then calculated through theoretical derivation. Specifically:

[0199] Step 1: Define a sweep frequency sequence using MATLAB's built-in functions: Use the `linspace` function to generate a linear frequency sequence from 10 to 1000 Hz, with a frequency step size of 25 Hz to ensure uniform frequency distribution within the band; use the `sin` function combined with a loop structure to generate sinusoidal signals one by one according to the preset frequency sequence, and superimpose positive and negative sequence components to form a disturbance signal, with the signal amplitude calibrated to 5% of the rated voltage; after generating the signal, use MATLAB's `plot` function to plot the time-domain waveform, and combine it with the `fft` function for frequency-domain analysis to verify whether the signal frequency range, amplitude, and positive and negative sequence characteristics meet the experimental design requirements, ensuring that the disturbance signal is distortion-free;

[0200] Step 2: In the Simulink model, the generated sweep frequency signal is connected to the SVG and AC bus connection point in the dual 6-pulse mesh SLCC converter valve topology model through the signal injection module. This ensures that the disturbance signal can simultaneously act on the three core sub-modules, collecting multi-dimensional impedance characteristic data. A data acquisition link is built using MATLAB's Scope module and Data Acquisition Toolbox to acquire the three-phase voltage time-domain signal of the PCC, reflecting the voltage response at the disturbance injection point. Simultaneously, the output current time-domain signal of each converter unit is acquired for subsequent impedance calculations.

[0201] Step 3: Design a low-pass filter using MATLAB's `fir1` function to remove high-frequency noise introduced during the acquisition process. For each swept frequency point, extract the time-domain data of the stable segment. Use MATLAB's `fft` function to perform a Discrete Fourier Transform on the preprocessed time-domain signal. Calculate the voltage and current amplitudes at each frequency point using the `abs` function, and obtain the phase information of the voltage and current using the `angle` function combined with the `unwrap` function (to eliminate phase folding). Perform impedance calculations based on the impedance definition.

[0202] Step 4: Compare the calculated measured impedance characteristics with... Figure 7The impedance characteristics calculated from the topology model of the dual 6-pulse mesh-type SLCC converter valve are compared. The amplitude-frequency response curves of the measured and theoretical impedances are plotted using the Bode function, and the relative error at each frequency point is calculated to verify the model's accuracy. Simultaneously, the phase-frequency response curve is plotted to analyze the consistency of the phase difference. The impedance amplitude of the mesh-type SVG sequence impedance model with CLC limiting is significantly improved in the high-frequency band to verify the damping enhancement effect. The voltage-current phase difference at each high-frequency point is calculated, and the system resonance risk is analyzed using the Nyquist stability criterion.

[0203] Figure 7 middle, This represents the equivalent impedance of the static var generator. This represents the equivalent current of the power grid commutator converter. This represents the equivalent impedance of the power grid commutator. Represents the equivalent impedance of the power grid. Indicates the equivalent voltage of the power grid;

[0204] Step 5 Figure 8 This paper presents a comparison between the measured impedance sweep results and the analytical impedance values ​​from the theoretical model. Figure 8 It can be seen that the theoretical calculation curve of impedance is consistent with the results obtained from the frequency sweep test, which shows that the method proposed in this invention can accurately reflect the impedance characteristics of the mesh-type SLCC converter valve.

[0205] The resonance suppression effect was verified, specifically as follows:

[0206] Step 1: In the PSCAD simulation, the converter valve model operates stably for the first 2 seconds. During this stage, the A, B, and C phase voltage waveforms of the receiving-end AC grid exhibit standard sinusoidal characteristics. At 2 seconds, an interference source is introduced. The system resonates instantly upon the interference source's introduction, causing harmonic distortion in the receiving-end three-phase voltage. The simulated waveform of the receiving-end grid voltage is as follows: Figure 9 As shown;

[0207] After performing harmonic characteristic analysis on the phase a voltage of the receiving-end power grid, the results are as follows: Figure 10 As shown, the harmonic components of the current are mainly concentrated in the frequency range of about 138Hz, and the total waveform distortion rate of the voltage of phase a at the receiving end reaches 71.9%.

[0208] Under the premise that the system electrical parameters and operating conditions remain unchanged, the simulation of the grid-type SVG sequence impedance model with CLC limiting is performed. The simulated waveforms of the three-phase voltage at the receiving end are as follows: Figure 11As shown, the amplitude of the three-phase voltage oscillates slightly at the moment the interference source is connected, and the sinusoidality of the voltage waveform is temporarily affected; however, with the rapid response of the current inner loop regulation, the output current of the converter valve is corrected in time, and the three-phase voltage of the AC grid at the receiving end quickly recovers to a stable state close to the rated amplitude after a brief transition process, and the distortion of the voltage waveform is significantly reduced.

[0209] Fourier decomposition was performed on the receiving-end grid voltage after the interference source was connected (2 seconds later). The decomposition results are as follows: Figure 12 As shown; will Figure 12 The results and Figure 10 The results show that the grid-type SVG sequence impedance model with CLC limiting has a significant effect on suppressing high-frequency resonance. At this time, the total waveform distortion rate of the grid-side voltage is only 12.2%, which is significantly reduced compared with the grid-type SLCC converter valve.

[0210] Comparing the resonant responses of the tail-type and mesh-type SLCCs with a 138Hz interference source injected at 2s, theoretical analysis shows that the dual 6-pulse tail-type SLCC system has a high-frequency resonance risk, while the dual 6-pulse mesh-type SLCC system has excellent high-frequency resonance suppression capability. Adjusting the VSG parameters and CLC limiting coefficient allows the dual 6-pulse mesh-type SLCC system to achieve better resonance suppression. The optimal parameter combination is: , , At this point, the error between the equivalent impedance and the measured value is less than 5%, and the total voltage distortion rate under 138Hz interference drops to 12.2%.

[0211] This invention also proposes an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. It should be noted that when the processor executes the computer program, it corresponds to the specific steps of the method provided in this invention, possessing the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in this invention.

[0212] This invention also proposes a computer-readable storage medium storing a computer program. It should be noted that when the computer program is executed by a processor, it corresponds to the specific steps of the method provided in this invention, possessing the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in this invention.

[0213] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method of high frequency resonance suppression for a network-forming SLCC converter valve with CLC limiting, characterized in that, include: S1. Construct a topology model of a dual 6-pulse network-type SLCC converter valve, which includes a dual 6-pulse LCC converter valve unit, a network-type SVG unit, and a DC-side smoothing reactor. S2. Based on the topology model of the dual-6-pulse grid-type SLCC converter valve, construct the following models: grid-type SVG sequence impedance model, grid-type SVG sequence impedance model, and dual-6-pulse LCC converter station admittance model; specifically: The voltage disturbance sequence impedance modeling method is used to inject ±5% rated voltage positive and negative sequence disturbance at the grid-connected point, and the first positive sequence impedance is obtained based on the phase deviation of the phase-locked loop and the dq rotating coordinate system , and the grid-connected SVG sequence impedance model is constructed, and the specific formula is: ； wherein, denotes a complex variable, denotes an SVG filter inductance, denotes an SVG filter resistance, , all denote current inner loop q-axis PI parameters, denotes an SPWM modulation coefficient; The VSG phase angle disturbance has no effect on the high frequency band, the VSG control and the Kirchhoff current law are adopted, the node current relationship of the grid-connected point and the modulated wave limited by the CLC are combined, and the second positive sequence impedance is obtained , and then the grid-connected SVG sequence impedance model containing the CLC limiting is constructed, and the specific formula is: ； in, This represents the CLC limiting factor. Indicates the VSG control proportional coefficient; CLC-limited d-axis voltages The specific formula is: ； in, This represents the d-axis and q-axis voltages without limiting. This represents the virtual internal potential difference. Using harmonic state-space theory and an improved commutation processing method, the AC side current is transformed to a dq rotating coordinate system and averaged. The current disturbance component is extracted by inverse Park transform. Combined with constant DC voltage control and PLL dynamics, the total admittance at the receiving end is obtained. Furthermore, an admittance model for the dual 6-pulse LCC converter station is constructed, with the specific formula as follows: ； in, This indicates the admittance of the dual 6-pulse LCC converter station. Indicates the admittance of the AC filter; S3. Using the Nyquist stability criterion, based on impedance analysis, establish equivalent impedance circuit models of dual 6-pulse LCC and mesh-type SVG converter valve, respectively, calculate the theoretical resonant frequency, determine the stability of the corresponding system, and establish a frequency sweep model. S4. Based on the stability discrimination results obtained in step S3, adjust the VSG parameters and CLC limiting coefficient to complete high-frequency resonance suppression.

2. The high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting according to claim 1, characterized in that, In step S1, the dual 6-pulse LCC converter valve unit includes two 6-pulse LCC converter valves connected in series, with the midpoint grounded via a low impedance. The two 6-pulse LCC converter valves are connected to the same AC bus via a first YY transformer T1 and a second YY transformer T2, respectively. The grid-type SVG unit has a built-in VSG controller and current limiting control circuit, and the grid-type SVG unit is connected to the AC bus. The DC-side smoothing reactor is connected in series with the DC side of the dual 6-pulse LCC converter valve unit.

3. The high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting according to claim 2, characterized in that, The 6-pulse LCC converter valve uses 12 IGBT modules, grounded at the midpoint, with a minimum impedance of 10Ω; Both the first YY type transformer T1 and the second YY type transformer T2 are SFZ11-31500 / 220 type transformers with a rated capacity of 31.5MVA and a short-circuit impedance of 8%. The DC-side smoothing reactor is a dry-type hollow reactor with a rated current of 3kA.

4. The high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting according to claim 1, characterized in that, The logic of VSG control includes: The voltage and current signals of the AC bus are collected, and the real-time active power is obtained through the instantaneous power calculation module. reactive power ; Real-time active power With active power reference value The virtual potential phase angle is obtained through comparison and VSG control. The specific formula is as follows: ； in, Indicates angular velocity. Indicates the rated angular velocity. Indicates the active damping coefficient. Represents the virtual moment of inertia; Real-time reactive power Reactive power reference value The virtual internal potential difference is compared and output through the constant power factor outer loop. , The d-axis and q-axis voltages are obtained by superimposing the bus voltage and then CLC limiting them. The d-axis and q-axis voltages after CLC limiting are converted into SPWM modulation waves by Park inverse transformation to control the SVG switching action.

5. The high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting according to claim 1, characterized in that, Improved commutation processing methods include: The AC side current of the dual 6-pulse LCC converter valve unit is converted to the dq rotating coordinate system to obtain the d-axis and q-axis currents. These currents are then averaged to filter out high-frequency components above 200Hz, yielding the processed d-axis and q-axis currents. The processed d-axis and q-axis currents are then converted to the three-phase stationary coordinate system using the inverse Park transform to extract the current disturbance components. The specific formula is as follows: ； ； ； in, This represents the current disturbance components of phases a, b, and c. Represents the inverse Park transformation matrix. This indicates a DC current disturbance. This indicates AC voltage disturbance. , , , , , Both represent coupling coefficients. Indicates trigger angle perturbation. This indicates a DC voltage disturbance. and These represent the fluctuations of the converter bus voltage along the d-axis and q-axis in the dq rotating coordinate system, respectively.

6. The high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting according to claim 1, characterized in that, In step S3, the equivalent impedance of the dual 6-pulse LCC and the grid-type SVG converter valve is compared in the equivalent impedance circuit model. The specific formula is: ； in, This represents the equivalent impedance of the dual 6-pulse LCC converter valve. , This indicates the admittance of the dual 6-pulse LCC converter station; Indicates the first positive sequence impedance; Equivalent impedance in the equivalent impedance circuit model of dual 6-pulse LCC and mesh-type SVG converter valve The specific formula is: ； in, Indicates the second positive sequence impedance; The AC power grid connected to the converter valve is equivalent to ; like and The absence of intersections in the amplitude-frequency characteristics indicates the stability of the dual 6-pulse tracking mesh SLCC system; conversely, the phase difference at the intersection frequency is calculated. The specific formula is as follows: ； in, express amplitude and frequency phase, express The amplitude-frequency phase; like and The absence of intersections in the amplitude-frequency characteristics indicates the stability of the dual-6-pulse mesh SLCC system; conversely, the phase difference at the intersection frequency is calculated. The specific formula is as follows: ； in, express The amplitude-frequency phase; like This indicates that the dual 6-pulse mesh SLCC system is stable; otherwise, there is a risk of resonance. like This indicates that the dual-6-pulse mesh SLCC system is stable; otherwise, there is a risk of resonance.

7. The high-frequency resonance suppression method for a grid-type SLCC converter valve with CLC limiting according to claim 6, characterized in that, In step S4, the VSG parameters include the active damping coefficient. and virtual moment of inertia ; If a dual 6-pulse follower mesh SLCC system has a resonance risk, after adjusting the VSG parameters and CLC limiting coefficient, when When the error with the measured value is less than 5%, it indicates that the high-frequency resonance suppression of the system has been completed; If a dual-6-pulse mesh SLCC system has a resonance risk, after adjusting the VSG parameters and CLC limiting coefficient, when When the error with the measured value is less than 5%, it indicates that the high-frequency resonance suppression of the system has been completed.

8. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the high-frequency resonance suppression method for the grid-type SLCC converter valve with CLC limiting as described in any one of claims 1 to 7.

9. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is run by the processor, it executes the high-frequency resonance suppression method of the grid-type SLCC converter valve with CLC limiting as described in any one of claims 1 to 7.

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