Double-SVG parallel operation control method based on double-transformer operation

Abstract

The invention discloses a double-SVG parallel operation control method based on double-transformer operation, and relates to the field of electric energy comprehensive governance, each SVG needs to obtain signal data, the closing state of a bus coupler is firstly judged according to the obtained signal data, and when the bus coupler is closed, vectors on the two sides and system current sampling signals are adopted for operation; otherwise, the current sampling signal of the access side system is adopted for operation, and then half compensation of reactive power and harmonic waves under open-loop control is carried out when it is judged that the other SVG is in operation; according to the invention, through parallel operation compensation of the two SVGs, normal compensation under respective operation conditions of the transformer and the buscouple can be considered, organic combination of reactive compensation, harmonic compensation, voltage compensation and parallel operation is realized, the two SVGs can be switched autonomously, a master-slave-free function is realized, and the two SVGs can be switched independently. And the functions can still be freely identified and met under various fault switching conditions when the next bus coupler is connected with two sections, and the robustness is good.

Description

Technical Field

[0001] The present invention relates to the field of comprehensive electric energy management, and in particular to a dual SVG parallel control method based on dual transformer operation. Background Art

[0002] With the continuous development of power electronics technology and computer control technology, various new automatic and fast reactive power compensation and harmonic control devices have emerged one after another. Static VAR generator (SVG) is one of the dynamic reactive power compensation and harmonic control devices widely used in power distribution systems. SVG uses a new power electronic device IGBT, which has controllable breaking and a breaking time of less than 10us. From the perspective of devices, SVG has an essential advantage. Therefore, SVG equipment has an incomparable advantage in response time, and this indicator is of decisive significance for suppressing voltage fluctuations; SVG is adjusted in a stepless manner, and its minimum compensation can be accurate to 0.1kvar, ensuring smooth reactive compensation without fluctuations. SVG is adaptive and automatically adjusts the compensation capacity as external parameters change, ensuring full capacity output. When the system voltage becomes low, SVG can also output reactive current close to the rated working condition. SVG itself can generate both inductive and capacitive reactive power, and its bidirectional compensation capability can be applied to various types of loads; it has perfect compensation capability for both inductive motor loads and cable capacitive charging reactive power to the ground; SVG itself has active filtering capability, and can actively and perfectly output a waveform with the same frequency and opposite phase as the harmonic to offset the harmonic. Its core component IGBT operates at a frequency of 2000Hz, which can meet the filtering requirements of the 5th, 7th, and 11th harmonics. In actual power distribution systems, two transformers are often in operation, and there are many situations such as parallel operation, separate operation, and one-to-two operation. The operation of two SVGs has many problems such as transformer coupling, bidirectional flow of busbar current, and complex and changeable working conditions. The current solutions have the following problems: 1. Using the same controller to control two units has obvious disadvantages, as a single unit cannot operate independently; 2. The current signal of another device is measured and transmitted through a mutual inductor, and then the output is subtracted after comprehensive calculation. This may cause difficulties such as unstable control. 3. Through the controller, the network is used for data parallelization, and there are network delays or data synchronization problems. Summary of the invention

[0003] The object of the present invention is to provide a dual SVG parallel control method based on dual transformer operation, and a sensorless single-line dual SVG control strategy under dual transformer operation conditions to solve the problems raised in the above background technology.

[0004] To achieve the above object, the present invention provides the following technical solution: a dual SVG parallel control method based on dual transformer operation, comprising the following steps: Step 1: Signal data acquisition. The signal data acquired by each SVG includes the access side system current sampling signal, the vector and system current sampling signals on both sides, the access side circuit breaker closing state signal, the busbar state signal and the operating state signal of another SVG; Step 2: Select the calculation method. SVG determines the operation status of the bus coupling and the operation status of another SVG based on the obtained bus coupling status signal and the operation status signal of another SVG: When the busbar is closed, the system uses the vectors on both sides and the system current data obtained by each SVG to perform calculations, and selects the corresponding compensation mode according to the operating status of the other SVG; When the busbar is disconnected, the system uses the access-side system current data obtained by each SVG for calculation, and selects the corresponding compensation mode according to the operating status of the other SVG.

[0005] As a preferred method, in the busbar closed state, the specific method of using the two-side vectors and system current data obtained by each SVG to calculate reactive power and harmonic compensation is as follows: Collect vector and system current data I on both sides of each SVG A φ A ,I B φ B with I C φ C With V A 、V B With V C , each SVG selects the entry point on one side of the transformer as the metering point; Calculate the instantaneous active power Pt and instantaneous reactive power Qt of each SVG at the metering point, and then calculate the average reactive power Qavg based on the instantaneous reactive power Qt. The total reactive power is the sum of the average reactive powers of all SVGs. Use fast Fourier transform to convert the time domain signal into frequency domain signal, separate the fundamental and harmonic components, extract the amplitude and phase of each harmonic, and select the harmonic order h to be compensated. The total harmonic current is the sum of the hth harmonic currents of all SVGs. As a preferred option, the compensation modes under the busbar closing state include half compensation under open-loop control and full compensation under open-loop control. If the SVGs are operating normally and the system requirements allow, the half compensation mode under open-loop control is selected, and each SVG undertakes half of the reactive power and harmonic compensation tasks. If one SVG fails or has a light load and cannot take on half of the task, the other SVG will take on the full compensation task.

[0006] As a preferred method, in the busbar disconnected state, the specific method of using the access-side system current data obtained by each SVG to calculate reactive power and harmonic compensation is as follows: Synchronous sampling is performed to collect the current, voltage and corresponding phase angle data of each phase of the SVG access side system. Each SVG selects the entry point on one side of the transformer as the metering point; The instantaneous active power p(t) and instantaneous reactive power q(t) are obtained by using the collected current, voltage and corresponding phase angle data, and then integrating the instantaneous power within a power frequency cycle and taking the average value to obtain the average active power P 平 and average reactive power Q 平 ; Set a target power factor K as required, and calculate the required reactive power Q based on the target power factor desired : Q desired =P 平 *tan(arccos(K)); According to the current average reactive power Q 平 and the required reactive power Q desired Calculate the reactive power ΔQ that needs to be compensated, ΔQ=Q 平 -Q desired ; The fast Fourier transform method is used to extract the harmonic components from the current signal, and the compensation amount of each harmonic order is calculated based on the extracted harmonic components; As a preferred option, the compensation modes in the busbar disconnection state include full compensation under open-loop control and full compensation under closed-loop control. If all SVGs are operating normally and the system requirements allow, full compensation under closed-loop control is adopted, and each SVG undertakes the corresponding reactive power and harmonic compensation tasks. If one SVG is in standby or faulty state, the other SVG will adopt full compensation under open-loop control and will take on all compensation tasks.

[0007] As a preferred method, when the main coupling is closed and an unoperated SVG is started, a smooth transition strategy is adopted to gradually increase its output to avoid impact on the power grid. At the same time, the output of the running SVG is adjusted to ensure a reasonable distribution of reactive power and harmonic compensation between the two.

[0008] Preferably, the specific method of gradually increasing the output of the smooth transition strategy is as follows: the initial output of the SVG is set to a state close to zero, and according to the response time of the system, the output of the SVG is gradually increased to 95% within a preset three times system response time interval, and the last 5% is controlled within a system response time interval.

[0009] Preferably, the collected current and voltage data are low-pass filtered to remove high-frequency noise, retain useful fundamental and low-order harmonic components, and store the processed data in a buffer.

[0010] Preferably, when both SVGs are operating normally, once one of the SVGs detects any abnormality, it immediately takes measures to protect the system and switches to another compensation mode under the corresponding bus coupling state.

[0011] In summary, the beneficial effects of the present invention are: The present invention uses two SVGs for parallel compensation, which can take into account the normal compensation of the transformer and the bus tie under their respective operating conditions, and does not affect the normal compensation of the system due to changing the operating mode of the transformer and the bus tie, ensuring the target adjustment of the power factor at the metering point, and realizing the minimum loss of the high-voltage line through automatic balancing of the comprehensive target voltage and the target power factor, while ensuring that the high-voltage voltage of each line operates in a safe area, meeting the various operating mode requirements of the on-site transformers and bus tie switching, and smoothly transitioning online, automatically processing without special manual intervention, setting the target power factor and target voltage, and automatically operating according to the settings, and no manual intervention is required for one-time setting; The structure is simple and clear, the cost is low, the product consistency is high, and it is also easy to further expand the number of parallel machines; It realizes the organic combination of reactive power compensation, harmonic compensation, voltage compensation and parallel operation, and has smooth online adaptive adjustment and good control performance. The two units can switch autonomously to achieve a master-slave function. One unit can serve two sections under the mother connection, and can still identify and meet functions freely under various fault switching conditions, with good robustness. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0013] Figure 1 It is a schematic diagram of the process framework structure of a dual SVG parallel control method based on dual transformer operation according to the present invention; Figure 2 A block diagram of a dual SVG application system under dual transformer operation conditions of a dual SVG parallel control method based on dual transformer operation of the present invention; Figure 3 A signal block diagram of an SVG of a dual SVG parallel control method based on dual transformer operation according to the present invention; Figure 4The present invention is a schematic diagram of dual-machine application signals for on-site use of a dual-SVG parallel control method based on dual-transformer operation. DETAILED DESCRIPTION

[0014] The present invention will now be further described in detail in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. These drawings are all simplified schematic diagrams, which only illustrate the basic structure of the present invention in a schematic way, and therefore they only show the composition related to the present invention.

[0015] To facilitate understanding of the present invention, the present invention will be described more comprehensively below with reference to the relevant drawings. Several embodiments of the present invention are shown in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0016] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0017] Any feature disclosed in this specification (including any additional claims, abstract and drawings), unless otherwise stated, may be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0018] In the present invention, unless otherwise clearly defined and specified, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of at least two elements or the interaction relationship between at least two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0019] Combine the following Figure 1 —4 The present invention is described in detail. An embodiment of the present invention is: a dual SVG parallel control method based on dual transformer operation, referring to Figure 2, including the first circuit and the second circuit, the two circuits are connected by the busbar, and each circuit includes a load, SVG and a transformer. According to the 100 circuit breakers, busbars and 200 circuit breakers of the two transformers (1# main transformer and 2# main transformer), there can be multiple situations such as parallel operation, column operation and one-to-two operation. The first load and the second load are dynamically changed in real time. The digital inputs that each SVG needs to obtain are the upper circuit breaker status, the other machine operation status and the busbar status. The digital output is the local operation status. The analog inputs are the access side system voltage, current, vectors on both sides and system current. Figure 3 .

[0020] refer to Figure 1 The single-line control dual SVG control strategy under dual transformer operation conditions is mainly used in the control of dynamic reactive power compensation and harmonic control device SVG. It can be widely used in the fields of comprehensive power management. The specific operation method steps are as follows: Step 1: Signal data acquisition. The signal data acquired by each SVG includes the access-side system current sampling signal, the vector and system current sampling signals on both sides, the access-side circuit breaker closing state signal, the busbar state signal and the operating state signal of the other SVG. In the single-line control dual-SVG control strategy under dual-transformer operation conditions, the information that each SVG needs to obtain is crucial to ensure the stable operation of the system and effective reactive power compensation. The acquired signal data is used to select the reactive power and harmonic compensation amount and compensation mode. Step 2: Select the calculation method According to the information in the first step, the control strategies of each SVG are consistent, but various situations can be taken into account to achieve the purpose of being applicable to various working conditions. The SVG determines the operating status of the bus coupling and the operating status of another SVG based on the obtained bus coupling status signal and the operating status signal of another SVG, thereby obtaining the following four operating states: 1. The busbar is closed and the other SVG operates normally; 2. The busbar is closed and another SVG fails or has a light load; 3. The mother coupling is disconnected and the other SVG operates normally; 4. The busbar is disconnected, another SVG fails or the load is light. Different compensation modes correspond to these four situations, and the calculation of reactive power and harmonic compensation is divided into two cases: the bus tie is closed and the bus tie is disconnected; Specifically, when the busbar is closed, To calculate the reactive power and harmonic compensation, the system uses the two-side vectors and system current data obtained by each SVG to perform operations. The specific method is as follows: Collect vector and system current data I on both sides of each SVG A φ A ,I B φ B ,I C φ C With V A 、V B 、V C , Each SVG selects the entry point on one side of the transformer as the metering point, and ensures that the sampling frequency is high enough, usually several times the fundamental frequency, to accurately capture the harmonic components. For example, for a fundamental frequency of 50Hz, the sampling frequency can be set to 2kHz or higher, and the collected current and voltage data are low-pass filtered to remove high-frequency noise, retain useful fundamental and low-order harmonic components, and store the processed data in a buffer; Calculate the instantaneous reactive power Qt of each SVG at the metering point: Qt=V A (t)I A (t)Sin(φ A )+V B (t)I B (t)Sin(φ B )+V C (t)I C (t)Sin(φ C ); The instantaneous active power and reactive power at time t; Then calculate the average reactive power Qavg based on the instantaneous reactive power Qt;

[0021] The total reactive power is the sum of the average reactive powers of the two SVGs; Use fast Fourier transform to convert the time domain signal into frequency domain signal, separate the fundamental and harmonic components, extract the amplitude and phase of each harmonic, and select the harmonic order h to be compensated. According to system requirements and standards (such as IEEE519), select the harmonic order to be compensated, such as 3rd, 5th, 7th, 11th, 13th, etc., then the total harmonic current is the sum of the hth harmonic currents of all SVGs; The compensation modes under the busbar closed state include half compensation under open-loop control and full compensation under open-loop control; If all SVGs are operating normally and the system requirements allow, select the half compensation mode under open-loop control, and each SVG will take half of the reactive power and harmonic compensation tasks; If one SVG fails or has a light load and cannot take on half of the task, the other SVG will take on the full compensation task.

[0022] It should be noted that, for a more intuitive understanding, this embodiment also provides a specific example as follows: Collect vector and system current data on both sides of each SVG: Voltage: V A 、V B 、V C All are 220V; Current on the first SVG side: I A1 ,I B1 ,I C1 Both are 10A; Current on the second SVG side: I A2 ,I B2 ,I C2 Both are 8A: Phase difference φ A =30°、φ B =30°、φ C =30° Calculate the instantaneous reactive power Qt of each SVG at the metering point Qt=V A (t)I A (t)Sin(φ A )+V B (t)I B (t)Sin(φ B )+V C (t)I C (t)Sin(φ C ); The Qt of the first SVG is 3300VAR, and the Qt of the second SVG is 2640VAR To calculate the average reactive power, the sampling frequency is high enough and the instantaneous value is directly taken as the average value. Then: The Qavg of the first SVG is 3300VAR, and the Qavg of the second SVG is 2640VAR. The total reactive power that needs to be compensated is the sum of the two, which is 5940VAR. Analyze harmonic components: Use FFT to analyze the current signal. Assume that the fifth harmonic current components are I A5 =1A, I B5 =1A, I C5 =1A, the total harmonic current that needs to be supplemented is 3A.

[0023] Determine the compensation model If both SVGs are operating normally and the system requirements allow, select the half-compensation mode under open-loop control, where each SVG takes on half of the reactive power and harmonic compensation tasks. Each SVG is responsible for reactive power compensation of 5940VAR / 2, which is 2970VAR, and harmonic current compensation of 3A / 2, which is 1.5A. At the same time, corresponding compensation instructions are generated and sent to the corresponding SVG.

[0024] If one of the SVGs fails or has a light load and cannot take on half of the task, the full compensation mode under open-loop control is selected and the other SVG will take on the entire compensation task.

[0025] It is worth mentioning that in this embodiment, when the busbar is closed and a non-operating SVG is started, a smooth transition strategy is adopted to gradually increase its output to avoid impact on the power grid. At the same time, the output of the running SVG is adjusted to ensure a reasonable distribution of reactive power and harmonic compensation between the two.

[0026] It should be noted that the specific method of gradually increasing the output of the smooth transition strategy is as follows: the initial output of the SVG is set to a state close to zero, so as to minimize the impact on the power grid at startup. According to the response time of the system, the output of the SVG is gradually increased to 95% within a preset three-time system response time interval, and the last 5% is controlled within a system response time interval. In the process of gradually increasing the output, the voltage, current, frequency and other key parameters of the power grid are monitored in real time to ensure that there are no abnormal fluctuations. If any abnormality is detected, stop the increase immediately and take corresponding measures, so as to maximize the avoidance of shocks and fluctuations to the power grid; Similarly, when the SVG needs to be shut down, the same smooth transition strategy is used to reduce the output, which can effectively avoid the impact on the power grid when starting or stopping the SVG, ensuring the stability and reliability of the system. This strategy not only improves the safety of the system, but also extends the service life of the equipment and improves the power quality.

[0027] When the mother link is disconnected, To calculate the reactive power and harmonic compensation, the system uses the access-side system current data obtained by each SVG for calculation. The specific method is as follows: Synchronous sampling is performed to collect the current, voltage and corresponding phase angle data of each phase of the SVG access side system, I A ,I B ,I C , V A 、V B 、V C With φ A ,φ B ,φ C , perform low-pass filtering on the collected current and voltage data, remove high-frequency noise, retain useful fundamental and low-order harmonic components, store the processed data in the buffer, and each SVG selects the entry point on one side of the transformer as the metering point; The instantaneous active power p(t) and instantaneous reactive power q(t) are calculated using the collected current, voltage and corresponding phase angle data; p(t)=V A (t)I A (t)+V B (t)I B (t)+V C (t)I C (t); q(t)=V A (t)I A (t)Sin(φ A )+V B (t)I B (t)Sin(φ B )+V C (t)I C (t)Sin(φ C ); Then, by integrating the instantaneous power within a power frequency cycle T and taking the average value, the average active power P is obtained. 平 and average reactive power Q 平 ;

[0028]

[0029] Where, T is the power frequency period (for a 50 Hz system, T=20 ms); A target power factor K is set according to the requirements. According to the target power factor, the common target power factor is close to 1, such as 0.95 or higher, and the required reactive power Q is calculated. desired : Q desired =P 平 *tan(arccos(K)); According to the current average reactive power Q 平 and the required reactive power Q desired Calculate the reactive power ΔQ that needs to be compensated: ΔQ=Q 平 -Q desired If ΔQ>0, it means that the system needs to absorb reactive power; if ΔQ<0, it means that the system needs to emit reactive power.

[0030] Use Fast Fourier Transform (FFT) or other harmonic analysis methods to extract harmonic components from the current signal. Focus on the main low-order harmonics (such as 3rd, 5th, 7th, etc.), and calculate the compensation amount of each harmonic order based on the extracted harmonic components. Usually, SVG will generate current with opposite phase to the harmonic current to offset these harmonics; The compensation modes in the busbar disconnected state include full compensation under open-loop control and full compensation under closed-loop control; If all SVGs are operating normally and the system requirements allow, full compensation under closed-loop control is adopted, and each SVG is responsible for the corresponding reactive power and harmonic compensation tasks; If one SVG is in standby or faulty state, the other SVG will adopt full compensation under open-loop control and will take on all compensation tasks.

[0031] It should be noted that, for a more intuitive understanding, this embodiment also provides a specific example as follows: Collect the current, voltage and corresponding phase angle data of each phase of the SVG access side system; Voltage: V A 、V B 、V C All are 220V; Current: I A ,I B ,I C Both 100A Phase angle: φ A =0°、φ B =120°、φ C =-120° Calculate instantaneous active power p(t) and instantaneous reactive power q(t) p(t)=V A (t)I A (t)+V B (t)I B (t)+V C (t)I C (t) = 66000W q(t)=V A (t)I A (t)Sin(φ A )+V B (t)I B (t)Sin(φ B )+V C (t)I C (t)Sin(φ C )=0VAR; Calculate the average power. If the sampling frequency is high enough, take the instantaneous value as the average value directly. Then: the average active power P 平 =66000W and average reactive power Q 平 =0VAR; Set a target power factor K=0.95 Required reactive power Q desired : Q desired =P 平 *tan(arccos(K))≈22000VAR The reactive power that needs to be compensated is ΔQ = 0-22000VAR = -22000VAR, which means that SVG needs to generate 22,000VAR of reactive power to improve the power factor to 0.95.

[0032] Therefore, when the busbar is closed, the vectors on both sides and the system current data obtained by each SVG are used for calculation, which can simultaneously consider the current data on both sides of the SVG (i.e., the power supply areas of the two transformers). It not only pays attention to the reactive power demand at the location of the SVG, but also considers the reactive power distribution of the entire system. By sharing information, the two SVGs can work in a coordinated manner to optimize reactive power distribution, avoid resource waste or overload, and control from a global perspective, which helps maintain system stability and power quality. Especially in the case of large load fluctuations, when one SVG fails or disconnects, the other SVG can adjust the output in time according to the global information to ensure the continuous operation of the system.

[0033] When the main tie is disconnected, the access-side system current data obtained by each SVG is used for calculation, which is more inclined to independent calculation, focusing mainly on the reactive power demand at the location of the SVG. Since it only relies on local data, the calculation and response speed is faster.

[0034] It is worth mentioning that in order to provide certain protection for the operation of the system, a protection module is also provided in the present embodiment. When both SVGs are operating normally, once one of the SVGs detects any abnormality, measures are immediately taken to protect the system and switch to another compensation mode under the corresponding mother coupling state.

[0035] In summary, the parallel compensation of two SVGs in the present invention can take into account the normal compensation of the transformer and the bus tie under their respective operating conditions, and will not affect the normal compensation of the system due to the change of the operating mode of the transformer and the bus tie; ensure the target adjustment of the power factor at the metering point, and achieve the minimum loss of the high-voltage line through the comprehensive target voltage and the automatic balancing of the target power factor, while ensuring that the high-voltage voltage of each line operates in a safe area; meet the various operating mode requirements of each transformer and each bus tie under the switching on site, smoothly transition online, automatically process and do not require special manual intervention, set the target power factor and target voltage, and can automatically operate according to the settings, and no manual intervention is required for one-time setting; The structure is simple and clear, the cost is low, the product consistency is high, and it is also easy to further expand the number of parallel machines; It realizes the organic combination of reactive power compensation, harmonic compensation, voltage compensation and parallel operation, and has smooth online adaptive adjustment and good control performance. The two units can switch autonomously to achieve a master-slave function. One unit can serve two sections under the mother connection, and can still identify and meet functions freely under various fault switching conditions, with good robustness.

[0036] The above is only a specific implementation of the invention, but the protection scope of the invention is not limited to it. Any changes or substitutions that are not conceived through creative work should be included in the protection scope of the invention. Therefore, the protection scope of the invention should be based on the protection scope defined in the claims.

Claims

1. A dual SVG parallel control method based on dual transformer operation, characterized in that: The following steps are involved: Step 1: Signal data acquisition. The signal data acquired by each SVG includes the access side system current sampling signal, the vector and system current sampling signals on both sides, the access side circuit breaker closing state signal, the busbar state signal and the operating state signal of another SVG; Step 2: Select the calculation method. SVG determines the operation status of the bus coupling and the operation status of another SVG based on the obtained bus coupling status signal and the operation status signal of another SVG: When the busbar is closed, the system uses the vectors on both sides and the system current data obtained by each SVG to perform calculations, and selects the corresponding compensation mode according to the operating status of the other SVG; When the busbar is disconnected, the system uses the access-side system current data obtained by each SVG for calculation, and selects the corresponding compensation mode according to the operating status of the other SVG.

2. A dual SVG parallel control method based on dual transformer operation according to claim 1, characterized in that: When the busbar is closed, the specific method of calculating reactive power and harmonic compensation using the vector data on both sides and system current data obtained by each SVG is as follows: Collect vector and system current data I on both sides of each SVG A φ A ,I B φ B with I C φ C With V A 、V B With V C , each SVG selects the entry point on one side of the transformer as the metering point; Calculate the instantaneous active power Pt and instantaneous reactive power Qt of each SVG at the metering point, and then calculate the average reactive power Qavg based on the instantaneous reactive power Qt. The total reactive power is the sum of the average reactive powers of all SVGs. Use fast Fourier transform to convert the time domain signal into frequency domain signal, separate the fundamental and harmonic components, extract the amplitude and phase of each harmonic, and select the harmonic order h to be compensated. The total harmonic current is the sum of the hth harmonic currents of all SVGs.

3. A dual SVG parallel control method based on dual transformer operation according to claim 2, characterized in that: The compensation modes under the busbar closed state include half compensation under open-loop control and full compensation under open-loop control. If the SVGs are operating normally and the system requirements allow, the half compensation mode under open-loop control is selected, and each SVG undertakes half of the reactive power and harmonic compensation tasks. If one SVG fails or has a light load and cannot take on half of the task, the other SVG will take on the full compensation task.

4. The dual SVG parallel control method based on dual transformer operation according to claim 3 is characterized in that: When the busbar is disconnected, the specific method of using the access-side system current data obtained by each SVG to calculate reactive power and harmonic compensation is as follows: Synchronous sampling is performed to collect the current, voltage and corresponding phase angle data of each phase of the SVG access side system. Each SVG selects the entry point on one side of the transformer as the metering point; The instantaneous active power p(t) and instantaneous reactive power q(t) are obtained by using the collected current, voltage and corresponding phase angle data, and then integrating the instantaneous power within a power frequency cycle and taking the average value to obtain the average active power P 平 and average reactive power Q 平 ; Set a target power factor K as required, and calculate the required reactive power Q based on the target power factor desired : Q desired =P 平 *tan(arcs(K)); According to the current average reactive power Q 平 and the required reactive power Q desired Calculate the reactive power ΔQ that needs to be compensated, ΔQ=Q 平 -Q desired ; The fast Fourier transform method is used to extract each harmonic component from the current signal, and the compensation amount of each harmonic order is calculated based on the extracted harmonic components.

5. The dual SVG parallel control method based on dual transformer operation according to claim 4, characterized in that: The compensation modes in the busbar disconnected state include full compensation under open-loop control and full compensation under closed-loop control. If all SVGs are operating normally and the system requirements allow, full compensation under closed-loop control is adopted, and each SVG is responsible for the corresponding reactive power and harmonic compensation tasks. If one SVG is in standby or faulty state, the other SVG will adopt full compensation under open-loop control and will take on all compensation tasks.

6. A dual SVG parallel control method based on dual transformer operation according to claim 5, characterized in that: When the main coupling is closed and a non-operating SVG is started, a smooth transition strategy is adopted to gradually increase its output to avoid impact on the power grid. At the same time, the output of the operating SVG is adjusted to ensure a reasonable distribution of reactive power and harmonic compensation between the two.

7. The dual SVG parallel control method based on dual transformer operation according to claim 6, characterized in that: The specific method of gradually increasing the output of the smooth transition strategy is as follows: The initial output of SVG is set to a state close to zero. According to the response time of the system, the output of SVG is gradually increased to 95% within a preset time interval of three times the system response time. The last 5% is controlled within a system response time interval.

8. The dual SVG parallel control method based on dual transformer operation according to claim 7, characterized in that: The collected current and voltage data are low-pass filtered to remove high-frequency noise, retain useful fundamental and low-order harmonic components, and store the processed data in a buffer.

9. The dual SVG parallel control method based on dual transformer operation according to claim 8, characterized in that: When both SVGs are operating normally, once one of the SVGs detects any abnormality, it immediately takes measures to protect the system and switches to another compensation mode under the corresponding bus coupling state.

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