Method and device for loop flow suppression and power balance control in dual SVG parallel operation

Abstract

The embodiment provides a circulating current suppression and power balance control method for parallel operation of double SVGs, establishes a dynamic model of two static var generators connected in parallel to a public parallel bus, decomposes output currents into common mode currents and differential mode currents, collects electrical quantities to identify equivalent impedance parameters of each connecting reactor online, determines target impedance according to the equivalent impedance parameters, superimposes virtual impedance compensation voltage to make the equivalent output impedances of the two static var generators consistent, sends the common mode currents and the differential mode currents into orthogonal common mode control channels and differential mode control channels respectively, performs zero sequence transformation on three-phase output currents to extract zero sequence circulating currents, suppresses the circulating currents through resonance, synthesizes each compensation voltage into a modulation instruction and sends the modulation instruction to power devices, calculates a comprehensive health index according to device temperature, DC capacitor state, output margin and fault history to distribute reactive currents, collects parallel operation monitoring results, feeds back the monitoring results to update control rules and returns the control rules to the common mode control channels.

Description

Technical Field

[0001] This application relates to the field of power electronic parallel operation and reactive power compensation control technology, specifically to a circulating current suppression and power balance control method and device for dual SVG parallel operation. Background Technology

[0002] When existing dual static var generators are operated in parallel, manufacturing deviations in the parameters of the connecting reactors of the two devices, inconsistencies in the characteristics of power devices, and clock synchronization errors in the control system lead to amplitude and phase differences in the output voltages of the two devices, generating circulating currents on the parallel bus. These circulating currents do not participate in external reactive power compensation but consume equipment capacity and increase device losses. In severe cases, the amplitude of the circulating current can reach a significant proportion of the rated current, reducing the effective capacity and operating efficiency of the system. Existing circulating current suppression methods typically superimpose a circulating current suppression component onto the inner current loop and generate a compensation voltage using a proportional-integral controller (PIC). This passive suppression method has a lag response, and the circulating current suppression is coupled with reactive power control. During dynamic processes, it is difficult to balance the circulating current suppression effect with the reactive power response speed, resulting in oscillations during the adjustment process and a long settling time.

[0003] Existing parallel control methods mostly employ a master-slave control mode, where the master determines the output voltage reference, and the slave follows the master. However, differences in response speed between the master and slave lead to uneven dynamic power distribution and large instantaneous power deviations during rapid load fluctuations, exacerbating circulating current fluctuations and affecting compensation effectiveness. When the DC-side voltages of the two devices differ due to capacitor parameter deviations or active power losses, a zero-sequence circulating current component is generated in the parallel system. This component has a frequency three times the fundamental frequency and its odd multiples (3rd, 9th, etc.). Existing methods have limited effectiveness in suppressing zero-sequence circulating currents, which cause neutral point potential shifts, affecting equipment insulation safety and compensation accuracy.

[0004] Existing methods lack the ability to online assess and adaptively adjust the operating status of two static var generators (SVMs). When the performance of one device deteriorates due to component aging or increased temperature, power is still allocated according to a fixed ratio, leading to prolonged overload operation of the less efficient device, accelerating equipment degradation and increasing the risk of failure. Existing parallel operation schemes mostly only address steady-state circulating current suppression and task-level execution sequence, neglecting circulating current source elimination based on impedance matching, power balance feedforward for dynamic processes, specific suppression of zero-sequence circulating current, and adaptive power allocation based on device status. Therefore, a circulating current suppression and power balance control method for parallel operation of two SVMs is needed, combining parallel modeling and impedance identification, virtual impedance matching, modal decoupling and zero-sequence suppression, and adaptive allocation based on comprehensive health index. Summary of the Invention

[0005] To address the problems of circulating current caused by parameter deviations, uneven dynamic power distribution in master-slave control, coupled oscillations between circulating current suppression and reactive power control, insufficient zero-sequence circulating current suppression, and lack of state adaptation in fixed-ratio distribution in existing dual static var generator (SVG) parallel operation, this application provides a circulating current suppression and power balance control method and device for dual SVG parallel operation. This method can eliminate impedance difference circulating current at its source by online identification of the equivalent impedance parameters of the connected reactors and virtual impedance matching; separate reactive power control and circulating current control through orthogonal decoupling of common mode and differential mode; eliminate zero-sequence circulating current through zero-sequence transformation and resonance suppression; and dynamically distribute power through a comprehensive health index and update control rules based on feedback from parallel operation monitoring results. This improves the circulating current suppression effect, dynamic power distribution balance, and equipment state adaptability.

[0006] To solve at least one of the above problems, this application provides the following technical solution: In a first aspect, this application provides a circulating current suppression and power balancing control method for dual SVG parallel operation, comprising: establishing a dynamic model of two static var generators connected in parallel to a common parallel bus and decomposing the output current into common mode current and differential mode current; acquiring the output voltage, current, and parallel bus voltage; superimposing differential mode excitation on the operating command and identifying the equivalent impedance parameters of each connected reactor according to the recursive least squares rule; determining the target impedance and calculating the virtual impedance according to the equivalent impedance parameters; superimposing virtual impedance compensation voltage in the voltage control loop to make the equivalent impedances of the two reactors consistent; sending the common mode current into the common mode control channel to adjust the reactive power; and controlling the differential mode current. The differential mode compensation voltage is obtained by adjusting the mode current to zero in the proportional resonant control channel. The zero-sequence circulating current is extracted by zero-sequence transformation of the three-phase current and generated into a zero-sequence compensation voltage through a resonant stage at three times the fundamental frequency. The virtual impedance compensation voltage, differential mode compensation voltage and zero-sequence compensation voltage are superimposed on the common mode voltage reference and synthesized into a modulation command, which is then sent to the power device. The comprehensive health index is calculated based on the device temperature, capacitor status, output margin and fault history, and reactive current is allocated. The effective value of circulating current, power deviation and carrier synchronization status are collected to generate parallel operation monitoring results. The virtual impedance matching rules and comprehensive health index weights are updated based on the monitoring results and fed back to the common mode control channel.

[0007] Furthermore, it also includes: establishing a dynamic equation in a synchronous rotating coordinate system to show the changes in the output current of each static var generator as a function of the impedance of the connected reactor, its own output voltage, and the voltage of the parallel bus; defining half of the difference between the output currents of two static var generators as the differential mode current; defining the average value of the output currents of two static var generators as the common mode current; decomposing the parallel control into a common mode subproblem that determines the external reactive power output and a differential mode subproblem that determines the differential mode current according to the dynamic equation; and sending the common mode subproblem and the differential mode subproblem into two mutually orthogonal control channels for adjustment respectively.

[0008] Furthermore, it also includes: acquiring the three-phase output voltage, three-phase output current, and parallel bus three-phase voltage of the two static var generators at a preset sampling rate, and obtaining synchronous rotating coordinate system components through coordinate transformation; superimposing pseudo-random differential mode excitations with opposite polarities on the two static var generators on the operation command; identifying the equivalent resistance and equivalent inductance of each connected reactor based on the recursive least squares rule and introducing a forgetting factor and regularization term; comparing the identification results with the nameplate values ​​and historical identification values; registering an identification anomaly flag when the deviation exceeds a preset threshold condition and continuing to use the previous equivalent resistance and equivalent inductance.

[0009] Furthermore, it also includes: taking the larger of the actual equivalent impedances of the two static var generators and amplifying it according to a preset margin factor to determine the target impedance; using the difference between the target impedance and the actual equivalent impedance of each static var generator as the virtual resistance and virtual inductance of the static var generator; constructing a virtual impedance compensation voltage containing resistive voltage division and inductive coupling voltage division according to the virtual resistance and the virtual inductance in a synchronous rotating coordinate system; and superimposing the virtual impedance compensation voltage onto the voltage control command of the static var generator so that its equivalent output impedance approaches the target impedance.

[0010] Furthermore, it also includes: sending the common mode current into a common mode control channel containing an outer voltage loop and an inner current loop, and generating a reactive current reference based on the voltage deviation at the common connection point; sending the differential mode current into a proportional resonance control channel configured with a fundamental resonant element and adjusting it to zero to obtain a differential mode compensation voltage; performing zero-sequence transformation on the three-phase output current of the two static var generators to extract the zero-sequence circulating current component; generating a zero-sequence compensation voltage by passing the zero-sequence circulating current component through a resonant element at three times the fundamental frequency; performing DC voltage equalization fine-tuning on the active power output of the two static var generators based on the DC side voltage difference; and distributing the differential mode compensation voltage and the zero-sequence compensation voltage to the modulation commands of the two static var generators with opposite polarities.

[0011] Furthermore, it also includes: superimposing the common mode voltage reference and differential mode voltage reference obtained from mode decoupling, the virtual impedance compensation voltage and the zero-sequence compensation voltage according to their corresponding polarities, and transmitting them synchronously to the power devices of the two static var generators through Park inverse transformation and space vector pulse width modulation with the aid of optical fiber carrier; normalizing each index according to the device junction temperature, DC capacitor equivalent series resistance, output margin and fault history, and then weighting and synthesizing them into a comprehensive health index for each static var generator; and slowly distributing the common mode reactive current reference according to a preset time constant based on the ratio of the comprehensive health index between the two static var generators.

[0012] Furthermore, it also includes: continuously calculating the effective value and peak value of the circulating current and comparing them with alarm threshold conditions and protection threshold conditions; monitoring the deviation between the actual output power and the target allocated power of the two static var generators and the communication and carrier synchronization status to generate parallel operation monitoring results; adjusting and supplementing the virtual impedance matching rules, proportional resonance rules and comprehensive health index weights according to the parallel operation monitoring results and cooperation effect feedback; after comparing and verifying the indicators before and after the update, the updated power allocation ratio is fed back to the common mode control channel; and switching to single-unit independent operation when synchronization is lost.

[0013] Secondly, this application provides a circulating current suppression and power balancing control device for dual SVG parallel operation, comprising: a parameter identification module, used to establish a dynamic model of two static var generators connected in parallel to a common parallel bus and decompose the output current into a common mode current and a differential mode current, and superimpose differential mode excitation on the operation command to identify the equivalent impedance parameters of each connected reactor according to the recursive least squares rule; an impedance matching module, used to determine the target impedance according to the equivalent impedance parameters and calculate the virtual impedance for each static var generator, and superimpose virtual impedance compensation voltage in the voltage control stage to make the equivalent output impedance of the two static var generators consistent; and a decoupling control module, used to send the common mode current and the differential mode current into orthogonal common mode control channels and differential mode control channels respectively, wherein the former adjusts the common mode current according to the reactive power demand and the latter controls the differential mode current according to the proportional resonance rule. The differential mode compensation voltage is obtained by adjusting to zero. The zero-sequence circulating current component is extracted by zero-sequence transformation of the three-phase output current and generated into a zero-sequence compensation voltage through a resonant circuit at three times the fundamental frequency. The DC voltage is then finely adjusted to balance the active power output of the two static var generators based on the DC side voltage difference. The integrated allocation module is used to superimpose the virtual impedance compensation voltage, differential mode compensation voltage, zero-sequence compensation voltage, and common mode voltage reference to form a modulation command, which is then sent to the power devices. The integrated health index is calculated based on the device temperature, DC capacitor status, output margin, and fault history, and the common mode reactive current is allocated according to the integrated health index. The monitoring and protection module is used to continuously collect the effective value of the circulating current, power deviation, and carrier synchronization status to generate parallel operation monitoring results. The virtual impedance matching rules, proportional resonance rules, and integrated health index weights are updated based on the parallel operation monitoring results and effect feedback and fed back to the common mode control channel.

[0014] Thirdly, this application provides 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 program to implement the steps of the circulating current suppression and power equalization control method for parallel operation of dual SVG.

[0015] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the described method for circulating current suppression and power equalization control of dual SVG parallel operation.

[0016] Fifthly, this application provides a computer program product, including a computer program / instruction, which, when executed by a processor, implements the steps of the circulating current suppression and power equalization control method for parallel operation of dual SVG.

[0017] As can be seen from the above technical solution, this application provides a circulating current suppression and power balancing control method and device for parallel operation of dual SVG. By online identification of the equivalent impedance parameters of the connected reactors and virtual impedance compensation, the equivalent output impedances of the two static var generators are made consistent, thereby eliminating circulating current at the source. By orthogonal decoupling of the common mode control channel and the differential mode control channel, reactive power regulation and circulating current suppression do not interfere with each other. By zero-sequence transformation and three times the fundamental frequency resonance, the zero-sequence circulating current caused by DC voltage difference is eliminated. By dynamically allocating the common mode reactive current through the comprehensive health index, the virtual impedance matching rules, proportional resonance rules and comprehensive health index weights are updated according to the parallel operation monitoring results and effect feedback, and the current flows back to the common mode control channel to form a closed loop. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below.

[0019] Figure 1 This is a flowchart illustrating the circulating current suppression and power equalization control method for dual SVG parallel operation in this application embodiment; Figure 2 This is a schematic diagram of the main circuit topology and control device structure of the dual static var generator parallel system in the embodiments of this application; Figure 3 This is a schematic diagram illustrating the circulating current generation mechanism and virtual impedance matching principle in the embodiments of this application; Figure 4 This is a schematic diagram of online identification of the connection reactor impedance and common mode differential mode decoupling control in an embodiment of this application; Figure 5 This is a schematic diagram of the process for comprehensively issuing zero-sequence circulating current detection suppression and modulation commands in the embodiments of this application; Figure 6 This is a schematic diagram of the closed-loop calculation of the comprehensive health index, adaptive power allocation, and parallel operation monitoring in the embodiments of this application. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0021] Considering the problems of circulating current caused by parameter deviations of connected reactors and differences in device characteristics when existing dual static var generators are operated in parallel, uneven dynamic power distribution under load fluctuations in master-slave control, oscillation caused by the mutual coupling of circulating current suppression and reactive power control, insufficient zero-sequence circulating current suppression, and lack of equipment state adaptation in fixed ratio distribution, this application provides a circulating current suppression and power balance control method for dual SVG parallel operation. Through parallel modeling and impedance identification, virtual impedance matching, mode decoupling and zero-sequence suppression, adaptive allocation based on comprehensive health index, and monitoring of backflow during parallel operation, the circulating current and power distribution of dual static var generators are coordinated and controlled.

[0022] This application provides an embodiment of a circulating current suppression and power equalization control method for dual SVG parallel operation, see [link to embodiment]. Figure 1 The method specifically includes the following: Step S101: Establish a dynamic model of two static var generators connected in parallel to a common parallel bus and decompose the output current into common mode current and differential mode current; collect the output voltage, current and parallel bus voltage, superimpose differential mode excitation on the operation command and identify the equivalent impedance parameters of each connected reactor according to the recursive least squares rule.

[0023] In this embodiment, the method operates in a dual static var generator parallel control system, such as... Figure 1 As shown, two chain-type static var generators are each connected to a common parallel bus via a connecting reactor. The common parallel bus is then connected to the grid's point of common coupling via a common impedance. The control system adopts a digital signal processor and field-programmable gate array architecture. The two devices exchange control signals and carrier synchronization signals via a fiber optic link.

[0024] In one feasible implementation, a parallel dynamic model of two static var generators is established, such as... Figure 3 As shown. Let the resistance and inductance of the reactor connected to the first static var generator and the resistance and inductance of the reactor connected to the second static var generator be the quantities to be described. Write the dynamic equations of the output current of each static var generator as a function of the impedance of the connected reactor, its own output voltage and the voltage of the parallel bus in a synchronous rotating coordinate system.

[0025] Accordingly, the output current is decomposed into common-mode current and differential-mode current. The common-mode current is the average of the output currents of the two static var generators, reflecting the total current output by the parallel system. The differential-mode current is half the difference between the output currents of the two static var generators, representing the circulating current component flowing between the two devices but not output to the outside. The driving force of the differential-mode current comes from the difference in the output voltages of the two generators, and the path impedance is the parallel value of the impedances of the two connected reactors.

[0026] In one specific implementation, the three-phase output voltage and three-phase output current of two static var generators and the three-phase voltage of the parallel bus are simultaneously acquired at a preset sampling rate, such as... Figure 4 As shown, each electrical quantity is transformed by Parker to obtain the direct-axis and quadrature-axis components in the synchronous rotating coordinate system. The sampled data is written to the identification data cache with the device identifier and timestamp as the primary key. Data with sampling abnormalities is registered with a sampling abnormality flag and compensated by interpolation between adjacent periods.

[0027] Optionally, to improve identification accuracy, a differential-mode excitation signal is superimposed on the control commands during normal operation. The excitation signal uses pseudo-random sequence modulation, with the amplitude controlled within 1% to 2% of the rated value to avoid affecting normal operation, and the spectrum covers 10Hz to 500Hz. The excitation signal is injected synchronously into the two static var generators but with opposite polarities, so that their effects on the parallel bus voltage cancel each other out, and only the differential-mode channel is excited for impedance identification.

[0028] The dynamic equations are rewritten in a parametrically linearized form, with the four parameters to be identified being the equivalent resistance and equivalent inductance of the two connected reactors. Each parameter is identified using the recursive least squares rule. A regularization term is introduced to constrain the parameters to vary within a reasonable range. A forgetting factor is introduced to track the slow change in resistance caused by temperature. The forgetting factor is calibrated based on the rate of parameter change, and its value ranges from 0.95 to 0.99.

[0029] The identification results are compared with the equipment nameplate parameters and historical identification values. If the deviation exceeds the preset threshold, it is judged as an identification anomaly and an identification anomaly flag is registered. The previous equivalent resistance and equivalent inductance are used, and re-identification is triggered. The preset threshold is calibrated based on the equipment manufacturing tolerance. The equivalent impedance parameter is written to the parameter cache with the equipment identifier as the primary key, so that step S102 can read it by the equipment identifier at the impedance matching entry. The parameter change trend is also available for step S602 to call at the equipment status evaluation entry.

[0030] Step S102: Determine the target impedance and calculate the virtual impedance based on the equivalent impedance parameters. Superimpose the virtual impedance compensation voltage in the voltage control loop to make the equivalent impedances of the two units consistent. Send the common mode current into the common mode control channel to adjust the reactive power. Send the differential mode current into the proportional resonance control channel to adjust it to zero to obtain the differential mode compensation voltage. Perform zero-sequence transformation on the three-phase current to extract the zero-sequence circulating current and generate the zero-sequence compensation voltage through the three-fold fundamental frequency resonance loop.

[0031] The equivalent impedance parameter output in step S101 is read into the impedance matching circuit, such as... Figure 3 As shown. The equivalent resistance and equivalent inductance of two static var generators are associated with the equipment identifier. When parameters are missing, a parameter not ready identifier is registered and the nameplate value is used temporarily. Impedance matching is performed in sequence according to the target impedance determination, virtual impedance calculation and compensation voltage construction.

[0032] In one feasible implementation, the target impedance is determined by amplifying the larger of the actual equivalent impedances of the two static var generators using a preset margin factor. The margin factor is chosen such that the target impedance is slightly larger than the larger one to ensure that the virtual impedance is positive. The value ranges from 1.05 to 1.15, and is specifically calibrated according to the system stability margin requirements. A positive virtual impedance is beneficial to the stability of the parallel system.

[0033] Based on this, the virtual impedance of each static var generator is calculated. The virtual resistance is the difference between the target resistance and the actual resistance of the device, and the virtual inductance is the difference between the target inductance and the actual inductance of the device. If the virtual impedance calculated for a device is negative, a negative virtual impedance flag is registered, the target impedance is increased, and the calculation is repeated to avoid the stability risk introduced by negative virtual impedance.

[0034] Construct a virtual impedance compensation voltage in a synchronously rotating coordinate system, such as Figure 3 As shown. The compensation voltage consists of two parts: resistive voltage division and inductive coupling voltage division. The resistive voltage division is obtained by multiplying the virtual resistance by the corresponding axis current. The inductive coupling voltage division is obtained by multiplying the virtual inductance, the grid angular frequency, and the orthogonal axis current. The direct axis and quadrature axis components are cross-combined according to the coordinate system coupling relationship. The virtual impedance compensation voltage is read by step S103 using the device identifier as the primary key.

[0035] The common-mode current and differential-mode current output in step S101 are read into the decoupling control loop, such as... Figure 4 As shown, the common mode current is fed into the common mode control channel, which contains an outer voltage loop and an inner current loop. The outer voltage loop generates a reactive current reference based on the voltage deviation at the common coupling point, and the inner current loop adjusts the common mode current to track the reference value. The common mode channel uses a high control bandwidth to quickly respond to reactive power demand.

[0036] The differential-mode current is fed into the proportional resonant control channel and adjusted to zero. The proportional element provides a fast response, while the resonant element provides high gain at the fundamental frequency to eliminate steady-state circulating current. The resonant frequency is set to the grid fundamental frequency and extended to the 5th and 7th harmonic frequencies to suppress harmonic circulating current. The differential-mode control channel outputs a differential-mode compensation voltage. The two channels operate in orthogonal mode space, ensuring that reactive power response and circulating current suppression do not interfere with each other.

[0037] Zero-sequence transformation is performed on the three-phase output currents of two static var generators to extract the zero-sequence circulating current component, such as... Figure 5 As shown. The difference in zero-sequence current between the two devices reflects the magnitude of the zero-sequence circulating current. The frequency of the zero-sequence circulating current is three times the fundamental frequency and its odd multiples (3rd, 9th, etc.). Based on this, the zero-sequence circulating current component is used to generate a zero-sequence compensation voltage through a resonant circuit at three times the fundamental frequency. The DC voltage output of the two devices is then finely adjusted for DC voltage balancing based on the DC side voltage difference. The differential-mode compensation voltage and the zero-sequence compensation voltage are read by step S103 according to their corresponding polarities, using the device identifier as the primary key. When the zero-sequence component exceeds the limit, a zero-sequence over-limit flag is registered and DC balancing is triggered.

[0038] Step S103: The virtual impedance compensation voltage, differential mode compensation voltage, and zero-sequence compensation voltage are superimposed on the common mode voltage reference and synthesized into a modulation command, which is then sent to the power device. The comprehensive health index is calculated based on the device temperature, capacitor status, output margin, and fault history, and reactive current is allocated. The circulating current RMS value, power deviation, and carrier synchronization status are collected to generate parallel operation monitoring results. The virtual impedance matching rules and comprehensive health index weights are updated based on the monitoring results and fed back to the common mode control channel.

[0039] The virtual impedance compensation voltage, differential mode compensation voltage, and zero-sequence compensation voltage output in step S102 are read into the integrated modulation stage, such as... Figure 5 As shown. For the first static var generator, the final voltage reference is obtained by superimposing the common mode voltage reference obtained from mode decoupling, the differential mode voltage reference, the virtual impedance compensation voltage, and the zero-sequence compensation voltage. The differential mode component and the zero-sequence component of the second static var generator have opposite polarities.

[0040] In one specific implementation, a feedforward component based on load prediction is added to the voltage reference. The reactive power change rate of the load is collected, and when the change rate exceeds a preset threshold condition, it is determined to be an impact load. The expected reactive power change is calculated and distributed to two static var generators according to the power distribution ratio as the current reference feedforward quantity. The feedforward threshold condition is calibrated based on the statistical quantile of historical load fluctuations, so that the system can respond in advance when an impact load arrives.

[0041] Accordingly, the voltage reference in the synchronous rotating coordinate system is converted into a three-phase stationary coordinate system modulation wave via Park inverse transform, and then the switching signals for each bridge arm are generated via space vector pulse width modulation, such as... Figure 5As shown. Two static var generators use a synchronous carrier, with one as the carrier master and the other as a phase-locked tracking unit. The carrier synchronization is achieved by exchanging synchronization signals via an optical fiber link, and the synchronization accuracy is controlled within a preset range to suppress high-frequency circulating currents caused by differences in switching timing.

[0042] Device temperature, DC capacitor status, output margin, and fault history are read into the equipment status assessment process, such as... Figure 6 As shown. Device temperature is estimated by obtaining junction temperature from the temperature sensor of the insulated gate bipolar transistor module. DC capacitor status is estimated by voltage ripple analysis to obtain equivalent series resistance. Output margin is the ratio of current output power to rated capacity. Fault history is the number and type of recent protection actions. All indicators are written to the status cache with the device identifier as the primary key.

[0043] After normalizing the above indicators, a weighted sum is obtained to obtain the comprehensive health index of each static var generator, such as... Figure 6 As shown. The comprehensive health index ranges from 0 to 1, and the weights are determined based on the degree of influence of each indicator on the safe operation of the equipment, with device temperature having the highest weight and parameter deviation having the lowest weight. Based on this, the common mode reactive current reference is allocated according to the ratio of the comprehensive health indices of the two static var generators, and the allocation adjustment is carried out slowly according to the preset time constant to avoid sudden power changes.

[0044] When the overall health index falls below the derating threshold, derating operation is triggered, and the static var generator only handles the minimum power. When it falls below the exit threshold, parallel operation is exited and an insufficient capacity alarm is generated. The derating and exit thresholds are calibrated according to the equipment's safety margin classification. The system continuously collects the RMS and peak values ​​of the circulating current, power deviation, and carrier synchronization status to generate parallel operation monitoring results. When the circulating current exceeds the protection threshold, protection coordination is triggered.

[0045] Based on this, the virtual impedance matching rules, proportional resonance rules, and comprehensive health index weights are updated according to the parallel operation monitoring results and feedback on the collaborative effect. The effect feedback collects the circulating current false alarm rate and the equipment utilization balance. When the false alarm rate exceeds the threshold condition or the balance is lower than the threshold condition, an update is triggered. The update methods include parameter adjustment, rule supplementation, and rule abandonment. After the update, the indicators before and after the update are compared and verified. After the verification is passed, the updated power distribution ratio is fed back to the common mode control channel in step S102, forming a closed loop of detection, distribution, feedback, and update.

[0046] As can be seen from the above description, the circulating current suppression and power equalization control method for dual SVG parallel operation provided in this application embodiment can eliminate impedance difference circulating current from the source by online identification of the equivalent impedance parameters of the connected reactor and virtual impedance matching, separate reactive power control and circulating current control by orthogonal decoupling of common mode and differential mode, eliminate zero-sequence circulating current by zero-sequence transformation and resonance suppression, and dynamically allocate power by comprehensive health index and update the control rules for backflow through feedback of parallel operation monitoring results.

[0047] In one embodiment of the circulating current suppression and power equalization control method for dual SVG parallel operation of this application, see [link to relevant documentation]. Figure 4 It can also specifically include the following: Step S201: Establish a dynamic equation for the output current of each static var generator as a function of the impedance of the connected reactor, its own output voltage and the voltage of the parallel bus in the synchronous rotating coordinate system. Define half of the difference between the output currents of two static var generators as the differential mode current and define the average value of the output currents of two static var generators as the common mode current. Step S202: Based on the dynamic equation, the parallel control is decomposed into a common mode subproblem that determines the reactive power output and a differential mode subproblem that determines the differential mode current, and the common mode subproblem and the differential mode subproblem are sent to two mutually orthogonal control channels for adjustment respectively.

[0048] The parallel modeling described in step S101 is unfolded in a synchronous rotating coordinate system, as follows: Figure 4 As shown. Let the resistance and inductance of the reactor connected to the first static var generator and the resistance and inductance of the reactor connected to the second static var generator be the coefficients of the dynamic equation. Write the dynamic equations for the direct-axis current and quadrature-axis current of each static var generator as a function of the voltage drop across the connected reactor, its own output voltage, and the voltage of the parallel bus. The dynamic equations for the two devices have the same structure but different impedance coefficients. Half the difference in output current between the two static var generators is defined as the differential-mode current, and the average value of the output currents of the two static var generators is defined as the common-mode current. The two modes can be analyzed and controlled independently.

[0049] The dynamic equations decompose parallel control into common mode subproblems and difference mode subproblems, such as Figure 4 As shown. The common mode subproblem determines the reactive power output of the parallel system, and the differential mode subproblem determines the differential mode current, i.e., the circulating current characteristic. The two subproblems are fed into the mutually orthogonal common mode control channel and differential mode control channel for adjustment respectively. The common mode channel focuses on reactive power compensation performance, while the differential mode channel focuses on circulating current suppression. The parameters of the two can be independently tuned. The mode decomposition results are read at the channel inlet in step S501 in timestamp order, and the mode mapping relationship is written into the mode configuration table.

[0050] In one embodiment of the circulating current suppression and power equalization control method for dual SVG parallel operation of this application, see [link to relevant documentation]. Figure 4 It can also specifically include the following: Step S301: Acquire the three-phase output voltage, three-phase output current and parallel bus voltage of the two static var generators at a preset sampling rate and obtain synchronous rotating coordinate system components through coordinate transformation. Superimpose pseudo-random differential mode excitation with opposite polarities on the running command. Step S302: Based on the recursive least squares rule and by introducing a forgetting factor and a regularization term, identify the equivalent resistance and equivalent inductance of each connected reactor in the synchronous rotating coordinate system components. Compare the identification results with the nameplate values ​​and historical identification values. If the deviation exceeds the preset threshold, register an identification anomaly and continue using the previous equivalent resistance and equivalent inductance.

[0051] The electrical quantity acquisition described in step S101 is performed synchronously at a preset sampling rate, such as... Figure 4 As shown. The three-phase output voltage and current of the two static var generators, and the three-phase voltage of the parallel bus are collected. Each electrical quantity is transformed by Parker transformation to obtain the direct-axis and quadrature-axis components in a synchronous rotating coordinate system, which are then written into the identification data buffer. A pseudo-random differential-mode excitation with opposite polarities is superimposed on the operating command for the two static var generators. The excitation amplitude is controlled to a small proportion of the rated value to avoid affecting normal operation. The opposite polarities of the excitations ensure that their effects on the parallel bus voltage cancel each other out, and only the differential-mode channel used for impedance identification is excited.

[0052] The components of the synchronous rotating coordinate system are identified according to the recursive least squares rule after parameter linearization, such as... Figure 4As shown, a forgetting factor is introduced to track the slow changes in parameters caused by temperature, and a regularization term is introduced to constrain the parameters to change within a reasonable range, thereby identifying the equivalent resistance and equivalent inductance of each connected reactor. Specifically, in the parameter identification based on the recursive least squares rule, this embodiment introduces a forgetting factor and a regularization term. The forgetting factor is a commonly used adaptive adjustment parameter in the recursive least squares algorithm. Its function is to assign exponentially decaying weights to historical sampling data, so that older data has less influence on the current identification result, thereby enhancing the contribution of recent data. This allows the algorithm to track the slow time-varying characteristics of the equivalent impedance of the connected reactors caused by factors such as temperature changes and current thermal effects. The specific value of the forgetting factor can be determined empirically or through simple adjustments based on the rate of change of system parameters and the required identification accuracy. Regularization terms are also a common method for solving ill-conditioned problems in parameter estimation. By constructing additional constraint terms, they constrain the parameters to be identified within a reasonable physical range, avoiding divergence in identification results or the appearance of non-physical values ​​such as negative resistance and negative inductance due to insufficient input signal excitation or measurement noise interference, thereby ensuring the numerical stability of the identification process and the reliability of the results. This application specifically applies the well-known algorithms in the prior art to the online identification of the equivalent impedance of the connecting reactors in a dual static var generator parallel system. Combined with the differential mode excitation injection and electrical quantity acquisition described above, the equivalent resistance and equivalent inductance parameters of each connecting reactor can be obtained in real time and stably for use in the subsequent impedance matching stage.

[0053] The identification result is compared with the nameplate value and historical identification value. If the deviation exceeds the preset threshold condition, an identification anomaly mark is registered and the previous equivalent resistance and equivalent inductance are used. The preset threshold condition is calibrated according to the equipment manufacturing tolerance. The equivalent impedance parameter obtained by identification is used as the primary key for step S401 to read at the impedance matching entry.

[0054] In one embodiment of the circulating current suppression and power equalization control method for dual SVG parallel operation of this application, see [link to relevant documentation]. Figure 3 It can also specifically include the following: Step S401: Take the larger of the actual equivalent impedances of the two static var generators and amplify it according to the preset margin factor to determine the target impedance. Use the difference between the target impedance and the actual equivalent impedance of each static var generator as the virtual resistance and virtual inductance of the static var generator. Step S402: In the synchronous rotating coordinate system, construct a virtual impedance compensation voltage containing resistive voltage division and inductive coupling voltage division based on the virtual resistor and the virtual inductor, and superimpose the virtual impedance compensation voltage onto the voltage control command of the static var generator so that its equivalent output impedance approaches the target impedance.

[0055] After the equivalent impedance parameters in step S201 are ready, the target impedance determination is performed, such as... Figure 3 As shown. The larger of the actual equivalent impedances of the two static var generators is taken and amplified by a preset margin factor to determine the target impedance. The margin factor is chosen so that the target impedance is slightly larger than the larger one to ensure that the virtual impedance is positive. The value is calibrated based on the system stability margin requirements. The difference between the target impedance and the actual equivalent impedance of each static var generator is used as the virtual resistance and virtual inductance of that static var generator. When the virtual impedance is negative, a negative virtual impedance flag is registered, and the target impedance is increased before recalculation.

[0056] The virtual resistor and the virtual inductor construct a virtual impedance compensation voltage in a synchronously rotating coordinate system, such as Figure 3 As shown. The compensation voltage includes resistive voltage division and inductively coupled voltage division. The resistive voltage division is obtained by multiplying the virtual resistance by the corresponding axis current, and the inductively coupled voltage division is obtained by multiplying the virtual inductance, the grid angular frequency, and the orthogonal axis current. The direct axis component and the quadrature axis component are cross-combined according to the coordinate system coupling relationship. The virtual impedance compensation voltage is superimposed on the voltage control command of the static var generator, so that the equivalent output impedance of the two static var generators seen from the parallel bus is close to the target impedance. The virtual impedance compensation voltage is read at the integrated modulation input in step S601 using the device identifier as the primary key.

[0057] In one embodiment of the circulating current suppression and power equalization control method for dual SVG parallel operation of this application, see [link to relevant documentation]. Figure 5 It can also specifically include the following: Step S501: Send the common mode current into the common mode control channel containing the voltage outer loop and the current inner loop, and generate a reactive current reference according to the voltage deviation of the common connection point. Send the differential mode current into the proportional resonance control channel configured with the fundamental resonant link and adjust it to zero to obtain the differential mode compensation voltage. Step S502: Perform zero-sequence transformation on the three-phase output current of the two static var generators to extract the zero-sequence circulating current component. Generate a zero-sequence compensation voltage by passing the zero-sequence circulating current component through a resonant circuit at three times the fundamental frequency. Perform DC voltage equalization fine-tuning on the active output of the two static var generators based on the DC side voltage difference. Distribute the differential mode compensation voltage and the zero-sequence compensation voltage to the modulation command of the two static var generators with opposite polarities.

[0058] After the common mode current and differential mode current are ready in step S201, mode decoupling control is executed, such as... Figure 5 As shown. The common-mode current is fed into a common-mode control channel containing an outer voltage loop and an inner current loop. The outer voltage loop generates a reactive current reference based on the voltage deviation at the common coupling point, and the inner current loop adjusts the common-mode current to track the reference value. The differential-mode current is fed into a proportional-resonant control channel configured with a fundamental resonant element and adjusted to zero. The proportional element provides a fast response, and the resonant element provides high gain at the fundamental frequency to eliminate steady-state circulating current and obtain differential-mode compensation voltage.

[0059] Zero-sequence transformation is performed on the three-phase output currents of two static var generators to extract the zero-sequence circulating current component, such as... Figure 5 As shown. The difference in zero-sequence current between the two devices reflects the magnitude of the zero-sequence circulating current. The frequency of the zero-sequence circulating current is three times the fundamental frequency and its odd multiples (3rd, 9th, etc.). The zero-sequence circulating current component is used to generate a zero-sequence compensation voltage through a resonant circuit at three times the fundamental frequency. Based on the DC-side voltage difference, the active power output is finely adjusted for DC voltage balancing. The device with the higher DC-side voltage slightly increases its active power output, and the device with the lower DC-side voltage slightly decreases its active power output to make the DC voltages more uniform. The differential-mode compensation voltage and the zero-sequence compensation voltage are distributed to the modulation commands of the two static var generators with opposite polarities. The compensation voltage uses the device identifier as the primary key for step S601 to read at the integrated modulation input.

[0060] In one embodiment of the circulating current suppression and power equalization control method for dual SVG parallel operation of this application, see [link to relevant documentation]. Figure 5 It can also specifically include the following: Step S601: The common mode voltage reference and differential mode voltage reference obtained by mode decoupling, the virtual impedance compensation voltage and the zero sequence compensation voltage are superimposed according to their corresponding polarities, and then transmitted to the power devices of the two static var generators through Park inverse transformation and space vector pulse width modulation with the help of optical fiber carrier synchronous transmission. Step S602: Based on the device junction temperature, DC capacitor equivalent series resistance, output margin and fault history, the indicators are normalized and weighted to form a comprehensive health index for each static var generator. The common mode reactive current reference is slowly distributed according to a preset time constant based on the ratio of the comprehensive health index between two static var generators.

[0061] After the compensation voltage is ready in step S501, the modulation command synthesis is executed, such as... Figure 5 As shown. The common mode voltage reference obtained from mode decoupling is superimposed with the differential mode voltage reference, the virtual impedance compensation voltage, and the zero-sequence compensation voltage according to their corresponding polarities. The first static var generator takes the positive polarity of the differential mode component and the zero-sequence component, while the second static var generator takes the opposite polarity. The superposition result is converted into a three-phase stationary coordinate system modulated wave by inverse Park transform, and then transmitted synchronously to the power devices of the two static var generators via space vector pulse width modulation and fiber optic carrier. When carrier synchronization is lost, a synchronization anomaly flag is registered.

[0062] The device junction temperature, DC capacitance equivalent series resistance, output margin, and fault history are normalized and weighted together to form a comprehensive health index, such as... Figure 6As shown. The device junction temperature is obtained by a temperature sensor, the equivalent series resistance is estimated by capacitor voltage ripple analysis, the output margin is the ratio of the current output power to the rated capacity, the fault history is the most recent protection action record, and the comprehensive health index ranges from 0 to 1. The common mode reactive current reference is slowly distributed according to a preset time constant based on the ratio of the comprehensive health index between the two static var generators. When the health indices are equal, they are evenly distributed; when one decreases, its power share is automatically reduced. The distribution ratio is read by the common mode control channel in step S501 using the device identifier as the primary key.

[0063] In one embodiment of the circulating current suppression and power equalization control method for dual SVG parallel operation of this application, see [link to relevant documentation]. Figure 6 It can also specifically include the following: Step S701: Continuously calculate the effective value and peak value of the circulating current and compare them with the alarm threshold conditions and protection threshold conditions. Monitor the deviation between the actual output power of the two static var generators and the target allocated power, as well as the communication and carrier synchronization status to generate parallel operation monitoring results. Step S702: Based on the parallel operation monitoring results and cooperation effect feedback, adjust the execution parameters and supplement the rules for virtual impedance matching, proportional resonance, and comprehensive health index weights. After comparing and verifying the indicators before and after the update, return the updated power distribution ratio to the common mode control channel. If synchronization is lost, switch to single-machine independent operation.

[0064] After the allocation results of step S601 are ready, perform parallel operation monitoring, such as... Figure 6 As shown. The system continuously calculates the effective value and peak value of the circulating current and compares them with alarm and protection threshold conditions. When the alarm threshold condition is exceeded, the system records and analyzes the results to identify anomalies and synchronization loss. When the protection threshold condition is exceeded, the system triggers protection logic. The system monitors the deviation between the actual output power and the target allocated power of the two static var generators, as well as the communication and carrier synchronization status, generating parallel operation monitoring results. When communication is interrupted, the system switches to single-unit independent operation mode. Monitoring data is written to the operation record storage in timestamp order.

[0065] When the false alarm rate of the circulating flow or the equipment utilization balance exceeds the threshold, the rules are updated based on the parallel operation monitoring results and the feedback of the cooperation effect, such as... Figure 6 As shown. The update objects cover virtual impedance matching rules, proportional resonance rules, and comprehensive health index weights. The update methods include parameter adjustment, rule addition, and rule abandonment. After the update, the circulating current effective value and balance index before and after the update are compared and verified. If the verification is successful, the updated power distribution ratio is fed back to the common mode control channel and virtual impedance matching rule library in step S501. When the protection of a device is discharged, the healthy device will adjust the power distribution ratio to the full value and determine whether the single-unit capacity meets the compensation requirements, forming a closed loop of detection, distribution, feedback, and update.

[0066] To implement all or part of the method described above, this application provides an embodiment of an apparatus for implementing the circulating current suppression and power equalization control method for parallel operation of dual SVG systems. See [link to embodiment]. Figure 2 The device specifically includes the following components: The parameter identification module is used to establish a dynamic model of two static var generators connected in parallel to a common parallel bus and decompose the output current into common mode current and differential mode current. The differential mode excitation is superimposed on the operation command and the equivalent impedance parameters of each connected reactor are identified according to the recursive least squares rule. The impedance matching module is used to determine the target impedance based on the equivalent impedance parameters and calculate the virtual impedance for each static var generator. The virtual impedance compensation voltage is superimposed in the voltage control stage to make the equivalent output impedance of the two static var generators consistent. The decoupling control module is used to send the common mode current and the differential mode current into the orthogonal common mode control channel and differential mode control channel, respectively. The former adjusts the common mode current according to the reactive power demand, and the latter adjusts the differential mode current to zero according to the proportional resonance rule to obtain the differential mode compensation voltage. The zero-sequence transformation is performed on the three-phase output current to extract the zero-sequence circulating current component, which is then used to generate the zero-sequence compensation voltage through a resonant circuit at three times the fundamental frequency. The active power output of the two static var generators is then finely adjusted for DC voltage balancing based on the DC side voltage difference. The integrated allocation module is used to combine the virtual impedance compensation voltage, differential mode compensation voltage, zero-sequence compensation voltage and common mode voltage reference into a modulation command and send it to the power device. It calculates the comprehensive health index based on the device temperature, DC capacitor status, output margin and fault history and allocates the common mode reactive current according to the comprehensive health index. The monitoring and protection module is used to continuously collect the effective value of circulating current, power deviation and carrier synchronization status to generate parallel operation monitoring results. Based on the parallel operation monitoring results and effect feedback, it updates the virtual impedance matching rules, proportional resonance rules and comprehensive health index weights and feeds them back to the common mode control channel.

[0067] The parameter identification module establishes a dynamic model of two static var generators connected in parallel to a common parallel bus, such as... Figure 2As shown, the output current of the two static var generators is decomposed into a common mode current reflecting the external reactive power output and a differential mode current reflecting the inter-generator circulating current. The output voltage, output current, and parallel bus voltage of the two static var generators are collected at a preset sampling rate and transformed to obtain synchronous rotating coordinate system components. A pseudo-random differential mode excitation of opposite polarity is superimposed on the operating command, and the equivalent impedance parameters of each connected reactor are identified according to the recursive least squares rule. The impedance matching module determines the target impedance by amplifying the larger of the two actual impedances according to the equivalent impedance parameters and amplifying it with a preset margin factor. It calculates the virtual resistance and virtual inductance of each static var generator and superimposes a virtual impedance compensation voltage on the voltage control command to make the equivalent output impedance of the two devices consistent.

[0068] The decoupling control module sends the common mode current to a common mode control channel containing an outer voltage loop and an inner current loop to adjust the reactive power output. It sends the differential mode current to a proportional resonance control channel configured with a fundamental resonant element and adjusts it to zero. It performs zero-sequence transformation on the three-phase output currents of the two static var generators to extract the zero-sequence circulating current component and generates a zero-sequence compensation voltage based on the DC-side voltage difference via a resonant element at three times the fundamental frequency. The integrated allocation module superimposes the common mode voltage reference, differential mode voltage reference, virtual impedance compensation voltage, and zero-sequence compensation voltage according to their corresponding polarities to form a modulation command. This command is then transmitted synchronously to the power devices via Parker inverse transformation and space vector pulse width modulation using fiber optic carrier. Based on device temperature, DC capacitor status, output margin, and fault history, it calculates a comprehensive health index and allocates the common mode reactive current according to this index.

[0069] The monitoring and protection module continuously calculates the effective and peak values ​​of the circulating current and compares them with alarm and protection threshold conditions. It monitors the deviation between the actual output power and the target allocated power of the two static var generators, as well as the communication and carrier synchronization status, generating parallel operation monitoring results. When communication is interrupted or synchronization is lost, it switches to independent operation of a single unit. When the circulating current exceeds the protection threshold condition, protection coordination is triggered. Based on the parallel operation monitoring results and effect feedback, the monitoring and protection module adjusts and supplements the virtual impedance matching rules, proportional resonance rules, and comprehensive health index weights. After comparing and verifying the indicators before and after the update, the updated power allocation ratio is fed back to the common mode control channel. When the protection of one device is deactivated, the healthy device takes over its load and determines whether the single unit capacity meets the compensation requirements.

[0070] As can be seen from the above description, the circulating current suppression and power balancing control device for dual SVG parallel operation provided in this application embodiment can coordinate and control the circulating current suppression and power balancing of dual static var generators in parallel operation and provide status feedback through the coordinated operation of five modules: parameter identification, impedance matching, decoupling control, comprehensive allocation and monitoring and protection.

[0071] This invention also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the above-described method.

[0072] This invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the above-described method.

[0073] This invention also provides a computer program product, which includes a computer program that, when executed by a processor, implements the above-described method.

[0074] In this embodiment, online identification of the equivalent impedance parameters of the connected reactors and virtual impedance compensation make the equivalent output impedances of the two static var generators consistent, thus eliminating circulating current at the source. Orthogonal decoupling of the common mode control channel and the differential mode control channel ensures that reactive power regulation and circulating current suppression do not interfere with each other. Zero-sequence transformation and third-fold fundamental frequency resonance suppression eliminate zero-sequence circulating current caused by DC voltage difference. The common mode reactive current is dynamically allocated by a comprehensive health index composed of device temperature, DC capacitor state, output margin, and fault history. The virtual impedance matching rules, proportional resonance rules, and comprehensive health index weights are updated based on the parallel operation monitoring results and effect feedback, and the current flows back to the common mode control channel to form a closed loop.

[0075] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for circulating current suppression and power equalization control of dual SVG parallel operation, characterized in that, The method includes: A dynamic model of two static var generators connected in parallel to a common parallel bus is established, and the output current is decomposed into common mode current and differential mode current. The output voltage, current and parallel bus voltage are collected, differential mode excitation is superimposed on the operation command, and the equivalent impedance parameters of each connected reactor are identified according to the recursive least squares rule. The target impedance is determined based on the equivalent impedance parameters and the virtual impedance is calculated. The virtual impedance compensation voltage is superimposed in the voltage control loop to make the equivalent impedances of the two units consistent. The common mode current is sent into the common mode control channel to adjust the reactive power. The differential mode current is sent into the proportional resonance control channel to adjust to zero to obtain the differential mode compensation voltage. The three-phase current is subjected to zero-sequence transformation to extract the zero-sequence circulating current and generates the zero-sequence compensation voltage through the three-fold fundamental frequency resonance loop. The virtual impedance compensation voltage, differential mode compensation voltage, and zero-sequence compensation voltage are superimposed on the common mode voltage reference to form a modulation command, which is then sent to the power device. The comprehensive health index is calculated based on the device temperature, capacitor status, output margin, and fault history, and reactive current is allocated. The circulating current RMS value, power deviation, and carrier synchronization status are collected to generate parallel operation monitoring results. The virtual impedance matching rules and comprehensive health index weights are updated based on the monitoring results and fed back to the common mode control channel.

2. The circulating current suppression and power equalization control method for dual SVG parallel operation according to claim 1, characterized in that, The process of establishing a dynamic model of two static var generators connected in parallel to a common parallel bus and decomposing the output current into common mode current and differential mode current includes: In a synchronous rotating coordinate system, a dynamic equation is established for the output current of each static var generator as a function of the impedance of the connected reactor, its own output voltage and the voltage of the parallel bus. Half of the difference between the output currents of two static var generators is defined as the differential mode current, and the average value of the output currents of two static var generators is defined as the common mode current. Based on the dynamic equation, the parallel control is decomposed into a common mode subproblem that determines the reactive power output and a differential mode subproblem that determines the differential mode current. The common mode subproblem and the differential mode subproblem are then fed into two mutually orthogonal control channels for adjustment.

3. The circulating current suppression and power equalization control method for dual SVG parallel operation according to claim 1, characterized in that, The acquisition of output voltage, current, and parallel bus voltage, superimposed differential-mode excitation on the operating command, and identification of the equivalent impedance parameters of each connected reactor according to the recursive least squares rule, includes: The three-phase output voltage, three-phase output current and parallel bus voltage of the two static var generators are collected at a preset sampling rate and obtained by coordinate transformation to obtain synchronous rotating coordinate system components. Pseudo-random differential mode excitation with opposite polarities of the two static var generators is superimposed on the operation command. Based on the recursive least squares rule and by introducing a forgetting factor and a regularization term, the equivalent resistance and equivalent inductance of each connected reactor are identified for the components of the synchronous rotating coordinate system. The identification results are compared with the nameplate values ​​and historical identification values. If the deviation exceeds the preset threshold, an identification anomaly is registered and the previous equivalent resistance and equivalent inductance are used.

4. The circulating current suppression and power equalization control method for dual SVG parallel operation according to claim 1, characterized in that, The process of determining the target impedance based on the equivalent impedance parameters and calculating the virtual impedance, and then superimposing a virtual impedance compensation voltage in the voltage control stage to make the two equivalent impedances consistent, includes: The target impedance is determined by amplifying the larger of the actual equivalent impedances of the two static var generators according to a preset margin factor. The difference between the target impedance and the actual equivalent impedance of each static var generator is used as the virtual resistance and virtual inductance of the static var generator. In a synchronous rotating coordinate system, a virtual impedance compensation voltage containing resistive voltage division and inductive coupling voltage division is constructed based on the virtual resistance and the virtual inductance. The virtual impedance compensation voltage is superimposed on the voltage control command of the static var generator so that its equivalent output impedance approaches the target impedance.

5. The circulating current suppression and power equalization control method for dual SVG parallel operation according to claim 1, characterized in that, The process of sending the common mode current into the common mode control channel to regulate reactive power, sending the differential mode current into the proportional resonance control channel to adjust it to zero to obtain the differential mode compensation voltage, and performing zero-sequence transformation on the three-phase current to extract the zero-sequence circulating current to generate the zero-sequence compensation voltage through a resonant element at three times the fundamental frequency includes: The common mode current is sent into the common mode control channel containing the voltage outer loop and the current inner loop, and a reactive current reference is generated according to the voltage deviation of the common connection point. The differential mode current is sent into the proportional resonance control channel configured with the fundamental resonant link and adjusted to zero to obtain the differential mode compensation voltage. Zero-sequence circulating current components are extracted by zero-sequence transformation of the three-phase output current of the two static var generators. The zero-sequence circulating current components are then used to generate zero-sequence compensation voltage through a resonant circuit at three times the fundamental frequency. Based on the DC voltage difference, the active output of the two static var generators is finely adjusted to achieve DC voltage balancing. The differential mode compensation voltage and the zero-sequence compensation voltage are then distributed to the modulation commands of the two static var generators with opposite polarities.

6. The circulating current suppression and power equalization control method for dual SVG parallel operation according to claim 1, characterized in that, The process of superimposing the virtual impedance compensation voltage, differential mode compensation voltage, and zero-sequence compensation voltage onto a common mode voltage reference to synthesize a modulation command is then sent to the power device. Based on device temperature, capacitor status, output margin, and fault history, a comprehensive health index is calculated and reactive current is allocated. This includes: The common mode voltage reference and differential mode voltage reference obtained by mode decoupling, the virtual impedance compensation voltage and the zero sequence compensation voltage are superimposed according to their corresponding polarities, and then transmitted synchronously to the power devices of the two static var generators through Park inverse transformation and space vector pulse width modulation with the help of optical fiber carrier. Based on the device junction temperature, DC capacitor equivalent series resistance, output margin, and fault history, each index is normalized and weighted to form a comprehensive health index for each static var generator. The common modal reactive current reference is then slowly distributed according to a preset time constant based on the ratio of the comprehensive health index between two static var generators.

7. The circulating current suppression and power equalization control method for dual SVG parallel operation according to claim 1, characterized in that, The acquisition of circulating current RMS value, power deviation, and carrier synchronization status generates parallel operation monitoring results. Based on these monitoring results, the virtual impedance matching rules and comprehensive health index weights are updated and fed back to the common mode control channel, including: The effective value and peak value of the circulating current are continuously calculated and compared with the alarm threshold conditions and protection threshold conditions. The deviation between the actual output power and the target allocated power of the two static var generators and the communication and carrier synchronization status are monitored to generate parallel operation monitoring results. Based on the parallel operation monitoring results and feedback on the collaborative effect, the virtual impedance matching rule, proportional resonance rule and comprehensive health index weight execution parameters are adjusted and the rules are supplemented. After the index before and after the update is compared and verified, the updated power distribution ratio is fed back to the common mode control channel. When synchronization is lost, it switches to single-machine independent operation.

8. A circulating current suppression and power balancing control device for dual SVG parallel operation, characterized in that, The device includes: The parameter identification module is used to establish a dynamic model of two static var generators connected in parallel to a common parallel bus and decompose the output current into common mode current and differential mode current. The differential mode excitation is superimposed on the operation command and the equivalent impedance parameters of each connected reactor are identified according to the recursive least squares rule. The impedance matching module is used to determine the target impedance based on the equivalent impedance parameters and calculate the virtual impedance for each static var generator. The virtual impedance compensation voltage is superimposed in the voltage control stage to make the equivalent output impedance of the two static var generators consistent. The decoupling control module is used to send the common mode current and the differential mode current into the orthogonal common mode control channel and differential mode control channel, respectively. The former adjusts the common mode current according to the reactive power demand, and the latter adjusts the differential mode current to zero according to the proportional resonance rule to obtain the differential mode compensation voltage. The zero-sequence transformation is performed on the three-phase output current to extract the zero-sequence circulating current component, which is then used to generate the zero-sequence compensation voltage through a resonant circuit at three times the fundamental frequency. The active power output of the two static var generators is finely adjusted for DC voltage balancing based on the DC side voltage difference. The integrated allocation module is used to combine the virtual impedance compensation voltage, differential mode compensation voltage, zero-sequence compensation voltage and common mode voltage reference into a modulation command and send it to the power device. It calculates the comprehensive health index based on the device temperature, DC capacitor status, output margin and fault history and allocates the common mode reactive current according to the comprehensive health index. The monitoring and protection module is used to continuously collect the effective value of circulating current, power deviation and carrier synchronization status to generate parallel operation monitoring results. Based on the parallel operation monitoring results and effect feedback, it updates the virtual impedance matching rules, proportional resonance rules and comprehensive health index weights and feeds them back to the common mode control channel.

9. 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 program, it implements the steps of the circulating current suppression and power equalization control method for dual SVG parallel operation as described in any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the circulating current suppression and power equalization control method for parallel operation of dual SVG as described in any one of claims 1 to 7.

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