Static var generator based on improved dq method and control method thereof

Abstract

The application discloses a static var generator based on an improved dq method and a control method thereof, and relates to the technical field of power electronic device control. The method comprises the following steps: acquiring three-phase voltage signals and three-phase load current signals of a power distribution network; extracting real-time phases according to the three-phase voltage signals, performing dq coordinate transformation and filtering on the three-phase load current signals, extracting fundamental positive-sequence reactive current components, and generating reactive compensation instruction currents; generating active current regulation amounts according to voltage deviations of a direct-current side, superimposing the active current regulation amounts on the reactive compensation instruction currents to obtain comprehensive instruction currents; and performing decoupling control on deviations between the comprehensive instruction currents and feedback currents to generate drive signals to control a converter to output compensation currents. The application improves reactive compensation precision and system stability by compensating phase delays through the improved dq method, maintaining direct-current side voltage stability through voltage outer-loop PI regulation, and performing current inner-loop decoupling control.

Description

Technical Field

[0001] This invention relates to the field of power electronic equipment control technology, and in particular to a static var generator based on the improved dq method and its control method. Background Technology

[0002] With the continuous development of my country's economy and society, the demand for electricity from various industries is increasing, and higher requirements are being placed on power quality. However, the operation of a large number of inductive devices in the distribution network consumes capacitive reactive power in the system, leading to a serious shortage of reactive power, which in turn causes problems such as voltage drops, reduced power factor, and increased line losses. In recent years, with the upgrading and transformation of industries in various regions, the electricity load for production and daily life has grown rapidly. The extensive use of inductive devices has resulted in significant voltage drops at the end of lines and persistently high system losses, seriously affecting the normal supply and utilization efficiency of electricity.

[0003] Low voltage issues directly impact industrial production and residential electricity consumption. In industrial settings, voltage fluctuations reduce product yield and, in severe cases, even lead to equipment failure. On the consumer side, low voltage can cause lighting equipment to malfunction, and some household appliances can generate harmonics, affecting the power quality of the grid. Currently, low voltage has become a critical issue that urgently needs to be addressed in the operation of power distribution networks.

[0004] Currently, common technical means for managing low voltage in distribution networks mainly include adjusting transformer taps and installing reactive power compensation devices. Adjusting transformer taps has a limited adjustment range and is difficult to adapt to dynamic changes in reactive power. For reactive power compensation, parallel capacitor banks are commonly used. Capacitor compensation is simple in structure and low in cost, but its limitations are also significant: it is difficult to dynamically adjust according to the actual reactive power demand of the grid, and harmonics in the grid may cause resonant breakdown of capacitors, leading to power accidents. In some cases, thyristor-controlled reactors are used for reactive power compensation, but their compensation capacity varies in steps, their response speed is slow, and they themselves generate harmonic pollution to the grid.

[0005] With the development of power electronics technology, Static Var Generators (SVGs) have become an important research direction in the field of reactive power compensation due to their superior dynamic compensation performance. SVGs, based on voltage source inverters, can achieve continuous and rapid adjustment of reactive power by regulating the amplitude and phase of the output voltage. In reactive power detection, the dq method, based on instantaneous reactive power theory, is widely used for command current extraction in SVGs because it is unaffected by voltage distortion and has high detection accuracy. However, existing dq methods suffer from detection delays in the phase-locked loop (PLL) stage, leading to reduced reactive power compensation accuracy. Simultaneously, the strong coupling between the d-axis and q-axis components in the SVG's inner current loop control complicates control strategy design. Furthermore, the DC-side voltage in the outer voltage loop control is susceptible to fluctuations due to system losses, affecting the stable operation of the device. Regarding converter modulation, traditional PWM modulation strategies suffer from significant switching losses, especially reducing system reliability under frequent switching conditions.

[0006] To address the issues of detection delay, control coupling, and switching losses in reactive power compensation SVG, it is necessary to conduct in-depth research on its control strategy and device structure, and develop an SVG device with high compensation accuracy, fast dynamic response, and reliable operation to meet the actual engineering needs of reactive power compensation in power distribution networks. Summary of the Invention

[0007] To address these issues, this invention provides a static var generator and its control method based on an improved dq method. This method solves the problems of low reactive power detection accuracy due to phase-locked loop delay, complex control strategies due to coupling of d-axis and q-axis components in the current inner loop, and the impact of DC-side voltage fluctuations on stable device operation.

[0008] To address the aforementioned technical problems, embodiments of the present invention provide a control method for a static var generator based on an improved dq method, comprising: Acquire the three-phase voltage signal and three-phase load current signal of the power distribution network; The real-time phase is extracted from the three-phase voltage signal, and the real-time phase is used to perform dq coordinate transformation on the three-phase load current signal. The transformed current component is then low-pass filtered to extract the fundamental positive sequence reactive current component. A reactive power compensation command current is generated based on the fundamental positive sequence reactive current component. Based on the deviation between the actual DC-side voltage value and the given reference value, an active current regulation amount is generated, and the active current regulation amount is superimposed on the reactive power compensation command current to obtain the comprehensive command current. The deviation between the integrated command current and the real-time feedback current is decoupled and controlled to generate a drive signal to control the converter output compensation current.

[0009] Preferably, the step of extracting the real-time phase based on the three-phase voltage signal includes: Obtain the instantaneous value of phase A voltage, perform derivative calculation on the instantaneous value of phase A voltage, and calculate the real-time phase that is synchronized with phase A voltage based on the instantaneous value of phase A voltage and the derivative of phase A voltage: , in, This represents the instantaneous value of phase A voltage. The derivative of phase A voltage; The real-time phase It replaces the output phase of the phase-locked loop to compensate for detection phase errors.

[0010] Preferably, the step of performing dq coordinate transformation on the three-phase load current signal using the real-time phase includes: According to the real-time phase Calculate the corresponding sine and cosine values; The three-phase load current signal is transformed from the abc coordinate system to the dq rotating coordinate system based on the transformation matrix: , in, , , This represents the instantaneous value of the three-phase load current. The current component is the d-axis component. For the q-axis current component, Let be the transformation matrix.

[0011] Preferably, the step of low-pass filtering the transformed current component to extract the fundamental positive-sequence reactive current component includes: The d-axis current component and the q-axis current component The high-frequency AC components are filtered out by low-pass filters to obtain the DC components. and ; The DC component of the q-axis current component This is the fundamental positive sequence reactive current component.

[0012] Preferably, the step of generating reactive power compensation command current based on the fundamental positive sequence reactive current component includes: For the fundamental positive sequence reactive current component Perform an inverse coordinate transformation, changing it from the dq coordinate system to the abc coordinate system, to obtain the three-phase reactive power compensation command current: , in, , , This is the command current for three-phase reactive power compensation.

[0013] Preferably, generating the active current regulation amount based on the deviation between the actual DC-side voltage value and a given reference value includes: The actual value of the DC side voltage Compared with a given reference value The difference is adjusted by proportional-integral control to obtain the active current regulation. : , in, This is the proportionality coefficient. is the integral coefficient.

[0014] Preferably, the decoupling control of the deviation between the integrated command current and the real-time feedback current includes: Based on the SVG mathematical model in a rotating coordinate system, the d-axis voltage command is... and q-axis voltage command Set them to: , , in, , Let d-axis and q-axis components of the grid voltage in the dq coordinate system be the components of the grid voltage. The angular frequency of the power grid. This is the value of the filter inductance. , These are the d-axis and q-axis current command values. , These are the d-axis and q-axis current feedback values. , , , This is a PI control parameter used to eliminate the current coupling effect between the d-axis and q-axis.

[0015] This invention also provides a static var generator based on the improved dq method, comprising: The acquisition module is used to acquire the three-phase voltage signal and three-phase load current signal of the power distribution network; The controller, connected to the acquisition module, is configured to perform the following steps: extracting the real-time phase from the three-phase voltage signal; performing dq coordinate transformation on the three-phase load current signal using the real-time phase; low-pass filtering the transformed current component to extract the fundamental positive-sequence reactive current component; generating a reactive power compensation command current based on the fundamental positive-sequence reactive current component; generating an active current adjustment amount based on the deviation between the actual DC-side voltage value and a given reference value; superimposing the active current adjustment amount onto the reactive power compensation command current to obtain a comprehensive command current; and decoupling the deviation between the comprehensive command current and the real-time feedback current to generate a drive signal. The power module, connected to the controller, is used to control the switching of the switching transistors in the converter according to the drive signal, and output compensation current to the distribution network.

[0016] Preferably, the power module includes a converter, a filter inductor, and a DC-side energy storage capacitor. The AC side of the converter is connected to the power distribution network via the filter inductor, and the DC-side energy storage capacitor is connected in parallel across the DC side of the converter. The converter includes three-phase bridge arms, and each phase bridge arm is composed of an upper bridge arm switch and a lower bridge arm switch connected in series.

[0017] Preferably, the acquisition module includes a signal acquisition unit and a signal processing unit. The signal acquisition unit is used to acquire the three-phase voltage signal and the three-phase load current signal. The signal processing unit is used to filter, amplify and level-convert the acquired signal, and input the processed signal to the controller.

[0018] As can be seen from the above technical solutions, this invention application has the following beneficial effects: First, this invention employs an improved dq method. By differentiating the instantaneous value of phase A voltage, it calculates a real-time phase θ1 synchronized with the grid voltage to replace the traditional phase-locked loop (PLL) output phase. This effectively compensates for the phase error introduced by the inherent delay of the PLL, making phase extraction unaffected by voltage distortion or imbalance, improving the accuracy of reactive current detection, and thus enhancing the reactive power compensation effect of the SVG. Simulation and experimental results show that the system power factor increases from 0.8 to over 0.94 after adopting the control strategy of this invention.

[0019] Secondly, this invention implements decoupled control of the inner current loop. By setting feedforward compensation terms in the d-axis and q-axis voltage commands respectively, the current coupling effect between the d-axis and q-axis is eliminated, enabling independent control of the two axes. This reduces the design complexity of the control strategy while improving current tracking accuracy and the dynamic response speed of the system. Experimental results show that the device of this invention can quickly reach a steady state under transient conditions of sudden load changes.

[0020] Third, this invention introduces DC-side voltage closed-loop PI regulation in the voltage outer loop control. The deviation between the actual DC-side voltage value and the given reference value is used to generate an active current regulation quantity through proportional-integral control, which is superimposed on the reactive power compensation command current. This allows the SVG to absorb a small amount of active power from the grid to compensate for the device's own losses while compensating for reactive power, effectively maintaining the constant DC-side voltage, avoiding compensation errors or even system collapse caused by voltage fluctuations, and improving the reliability and stability of the device operation. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly described below. Referring to the drawings will make the features and advantages of the present invention clearer. The drawings are illustrative and should not be construed as limiting the present invention in any way. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 This is a flowchart of a control method for a static var generator based on the improved dq method provided by the present invention; Figure 2 This is a schematic diagram of a system containing a reactive power compensation device in this invention; Figure 3 This is a block diagram illustrating the principle of real-time phase extraction based on the improved dq method in this invention. Figure 4 This is a block diagram illustrating the principle of PI control for regulating DC-side voltage in the outer voltage loop of this invention. Figure 5 This is a block diagram illustrating the principle of current inner loop decoupling control in this invention; Figure 6 This is a block diagram illustrating the principle of generating a PWM drive signal to control the output compensation current of the converter in this invention. Figure 7 This is a schematic diagram of the overall structure of a static var generator based on the improved dq method provided by the present invention; Figure 8 This is a voltage curve of the 10kV busbar of the substation before the SVG is put into operation in this invention; Figure 9 This is a voltage curve of the 10kV busbar of the substation after the SVG is put into operation in this invention; Figure 10 This is a comparison chart of the power factor changes before and after the commissioning of the SVG in this invention. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1: To address the problems of low reactive power detection accuracy due to phase-locked loop delay, complex control strategies caused by coupling of d-axis and q-axis components in the current inner loop, and the impact of DC-side voltage fluctuations on stable operation of the device in existing dq-methods, this invention proposes a static var generator (SGA) based on an improved dq-method and its control method. Figure 1 This is an overall flowchart of the control method provided in an embodiment of the present invention. Figure 1 As shown, the method includes the following steps: S1: Acquire the three-phase voltage signal and three-phase load current signal of the distribution network; S2: Extract the real-time phase from the three-phase voltage signal, use the real-time phase to perform dq coordinate transformation on the three-phase load current signal, and perform low-pass filtering on the transformed current component to extract the fundamental positive sequence reactive current component. S3: Generate reactive compensation command current based on the fundamental positive sequence reactive current component; S4: Based on the deviation between the actual DC side voltage value and the given reference value, generate the active current regulation amount, and superimpose the active current regulation amount onto the reactive power compensation command current to obtain the comprehensive command current. S5: Decouples the deviation between the integrated command current and the real-time feedback current to generate a drive signal to control the converter output compensation current.

[0024] As can be seen from the above technical solution, this invention proposes a static var generator and its control method based on the improved dq method. First, step S1 acquires the three-phase voltage signal and three-phase load current signal of the distribution network, providing a real-time and accurate raw data foundation for subsequent reactive power detection and compensation control of the system. Based on this, step S2 extracts the real-time phase from the three-phase voltage signal, uses the real-time phase to perform dq coordinate transformation on the three-phase load current signal, and performs low-pass filtering on the transformed current component to extract the fundamental positive-sequence reactive current component. The real-time phase, which is synchronized with the grid voltage, is calculated based on the instantaneous value of phase A voltage and its derivative, replacing the output phase of the traditional phase-locked loop (PLL). This effectively solves the phase error problem caused by the delay of the PLL in the existing dq method, improving the accuracy of reactive current detection. Furthermore, step S3 generates a reactive power compensation command current based on the fundamental positive-sequence reactive current component, providing accurate compensation for the converter. The target value is determined. Based on this, step S4 generates an active current regulation based on the deviation between the actual DC-side voltage value and the given reference value. This active current regulation is then superimposed on the reactive power compensation command current to obtain a comprehensive command current. This allows the SVG to absorb a small amount of active power from the grid to compensate for its own losses while compensating for reactive power, effectively solving the problem of DC-side voltage fluctuations caused by system losses and ensuring the long-term stability of the device. Finally, step S5 decouples the deviation between the comprehensive command current and the real-time feedback current. By setting feedforward compensation terms in the d-axis and q-axis voltage commands respectively, the current coupling effect between the d-axis and q-axis is eliminated, enabling independent control of the d-axis and q-axis currents. This solves the problem of complex control strategies caused by the coupling of d-axis and q-axis components in the existing current inner-loop control, improves the dynamic response performance and anti-disturbance capability of the system, and generates a drive signal to control the converter output compensation current. Through the coordinated operation of the above five control strategies, a complete and efficient reactive power compensation closed-loop control system is formed, which improves the reactive power compensation accuracy, dynamic response speed and operational stability of SVG. It can be effectively applied to reactive power compensation and low voltage management in distribution networks, improve power quality, reduce line losses, and has good economic benefits and prospects for promotion and application.

[0025] Further, in step S1, the three-phase voltage signal and the three-phase load current signal of the distribution network are acquired.

[0026] Specifically, such as Figure 2 As shown, Figure 2 This is a schematic diagram of a system containing a reactive power compensation device according to the present invention. In this system structure, the power supply side of the distribution network supplies power to the load via transmission lines. The load is an inductive load, which consumes capacitive reactive power in the system, causing a voltage drop. The reactive power compensation device (i.e., the static var generator of the present invention) is connected in parallel to the transmission lines through a coupling transformer.

[0027] The instantaneous three-phase voltage values ​​of phases A, B, and C on the distribution network side are collected using voltage transformers and recorded as follows: , , The instantaneous values ​​of the three-phase load current are collected by current transformers and recorded as follows: , , Voltage transformers can be installed on the 10kV bus side of the substation, and current transformers can be installed at the load-side feeders to accurately obtain grid-side voltage information and load-side current information.

[0028] The acquired voltage and current signals are filtered, amplified, and level-converted by the signal conditioning circuit, and then converted into digital signals by the analog-to-digital converter before being input to the controller for subsequent calculations. This step provides the raw data foundation for the entire control method.

[0029] Further, in step S2, the real-time phase is extracted based on the three-phase voltage signal, the real-time phase is used to perform dq coordinate transformation on the three-phase load current signal, and the transformed current component is low-pass filtered to extract the fundamental positive sequence reactive current component.

[0030] In a preferred embodiment of the present invention, step S2 specifically includes the following sub-steps: Step S21: Extract the real-time phase synchronized with the grid voltage based on the improved dq method.

[0031] In the traditional dq method, the phase-locked loop (PLL) experiences a detection delay when there is voltage distortion or frequency fluctuation, leading to an error between the extracted phase and the actual grid phase, which in turn affects the accuracy of subsequent reactive power detection. To solve this problem, this invention employs an improved dq method to extract the real-time phase.

[0032] like Figure 3 As shown, obtain the instantaneous value of phase A voltage. The derivative of phase A voltage is obtained by taking the derivative of the instantaneous value of phase A voltage. When the grid frequency is stable, the instantaneous value of phase A voltage can be expressed as: , Taking its derivative, we get: ; At this time, the real-time phase It can be calculated using the following formula: , in, This represents the instantaneous value of phase A voltage. This is the derivative of the phase A voltage. This is the real-time phase. It remains synchronized with the A-phase voltage, independent of the voltage amplitude. The calculated real-time phase... Replacing the phase output of a traditional phase-locked loop (PLL) can effectively compensate for the detection phase error introduced by the inherent delay of the PLL, making phase extraction unaffected by voltage distortion or imbalance, thereby improving the accuracy of subsequent reactive power detection.

[0033] Step S22: Perform dq coordinate transformation on the three-phase load current signal according to the real-time phase.

[0034] Real-time phase is extracted Then, firstly based on the real-time phase Calculate the corresponding sine and cosine values. Specifically, using... Calculate separately , , as well as , , .

[0035] Then, as Figure 3 As shown, the three-phase load current signal is transformed from the abc coordinate system to the dq rotating coordinate system based on the transformation matrix: , in, , , This represents the instantaneous value of the three-phase load current. The current component is the d-axis component. This represents the q-axis current component. Transformation matrix. The specific expression is: .

[0036] After the above dq coordinate transformation, the fundamental positive-sequence component of the three-phase load current with the same frequency as the rotating coordinate system is converted into a DC quantity, while the harmonic and negative-sequence components are converted into AC quantities, laying the foundation for the subsequent extraction of the fundamental component through low-pass filtering.

[0037] Step S23: Perform low-pass filtering on the transformed current components to extract the fundamental positive-sequence reactive current component.

[0038] After dq coordinate transformation, the d-axis current component and q-axis current component Both include DC and AC components: , in, , This is the DC component (corresponding to the fundamental positive sequence current). , This refers to the alternating current component (corresponding to harmonics and negative sequence current).

[0039] like Figure 3 As shown, the d-axis current components and q-axis current component Input low-pass filters separately to filter out high-frequency AC components. and The DC component is obtained. and Among them, the DC component of the q-axis current component. This is the required fundamental positive-sequence reactive current component, which represents the missing reactive current value in the distribution network; the DC component of the d-axis current component. This corresponds to the fundamental positive sequence active current component.

[0040] Furthermore, in step S3, a reactive power compensation command current is generated based on the fundamental positive sequence reactive current component.

[0041] The fundamental positive sequence reactive current component was extracted. Afterwards, as Figure 3 As shown, an inverse coordinate transformation is performed on it, transforming it from the dq coordinate system to the abc coordinate system, to obtain the three-phase reactive power compensation command current: , in, , , This is the command current for three-phase reactive power compensation. Inverse transformation matrix. The specific expression is: .

[0042] In the above inverse transformation process, due to the active component of the d-axis This corresponds to the fundamental positive-sequence active current. Since this invention only needs to compensate for reactive power, the d-axis component is set to 0, and only the q-axis reactive component is compensated. The inverse transformation yields the three-phase current values, which serve as the command signal to drive the converter to generate reactive power compensation current.

[0043] Furthermore, in step S4, based on the deviation between the actual value of the DC side voltage and the given reference value, an active current regulation amount is generated, and the active current regulation amount is superimposed on the reactive power compensation command current to obtain the comprehensive command current.

[0044] During the operation of a voltage-type SVG, the DC-side energy storage capacitor will continuously discharge due to factors such as converter switching losses and line losses, causing a drop in the DC-side voltage. If the DC-side voltage cannot be kept stable, it will directly affect the amplitude of the converter output voltage, resulting in a large compensation error in the system, and in severe cases, even causing system collapse.

[0045] like Figure 4 As shown, the actual value of the DC side voltage is obtained. Compare it with a given reference value By comparison, the deviation value is obtained. The deviation value is input into a proportional-integral (PI) controller for adjustment to obtain the active current regulation. : , in, This is the proportionality coefficient. For the integral coefficient, the proportional element is used to respond quickly to the current error, while the integral element is used to eliminate the steady-state error.

[0046] Active current regulation The three-phase reactive power compensation command current generated in step S3 is superimposed on it. , , In the middle, that is, superimposed in the direction of the active component along the d-axis. This yields the comprehensive command current. This comprehensive command current, while compensating for reactive power, also allows the SVG to absorb a small amount of active power from the grid to compensate for its own losses, thereby maintaining a constant DC-side voltage.

[0047] Furthermore, in step S5, the deviation between the comprehensive command current and the real-time feedback current is decoupled and controlled to generate a drive signal to control the converter output compensation current.

[0048] The mathematical model of SVG in the dq rotating coordinate system is as follows: , , in, , Let be the component of the converter terminal voltage in the dq coordinate system. , This is the current feedback value. , Let the grid voltage be the component in the dq coordinate system. The angular frequency of the power grid. This is the value of the filter inductance. This is the system's equivalent resistance.

[0049] As can be seen from the above mathematical model, there are coupling terms in the d-axis equation related to the q-axis current. The q-axis equation contains coupling terms related to the d-axis current. The two are coupled together, which increases the difficulty of current loop control.

[0050] To solve this problem, this invention implements decoupling control of the inner current loop. For example... Figure 5 As shown, the composite command current is used as the current command value. , Using real-time feedback current as , The current deviations of the d-axis and q-axis are calculated separately, and a feedforward compensation term is added after passing through a PI regulator to eliminate the coupling effect.

[0051] Specifically, based on the SVG mathematical model in a rotating coordinate system, the d-axis voltage command is... and q-axis voltage command Set them to: , , in, , Let d-axis and q-axis components of the grid voltage in the dq coordinate system be the components of the grid voltage. The angular frequency of the power grid. This is the value of the filter inductance. , These are the d-axis and q-axis current command values ​​(i.e., the d-axis and q-axis components of the combined command current). , These are the d-axis and q-axis current feedback values. , This is the d-axis PI adjustment parameter. , This is the q-axis PI adjustment parameter.

[0052] In the above settings, The term is used to cancel out coupling terms in the d-axis equation. , The term is used to cancel out coupling terms in the q-axis equation. This eliminates the current coupling effect between the d-axis and q-axis, allowing the d-axis and q-axis currents to be controlled independently.

[0053] Generating d-axis voltage command and q-axis voltage command Then, an inverse coordinate transformation is performed to obtain the three-phase voltage command. This three-phase voltage command is compared with the carrier signal to generate a pulse width modulation (PWM) drive signal. Figure 6 As shown, the drive signal is used to control the on and off of each switch in the converter, thereby enabling the static var generator to output compensation current to the distribution network and realize dynamic compensation of reactive power.

[0054] Example 2: This invention also provides a static var generator based on the improved dq method, used to execute the control method described in Embodiment 1 above. Figure 7 As shown, the device includes a data acquisition module 100, a controller 200, and a power module 300.

[0055] The acquisition module 100 is used to acquire three-phase voltage signals and three-phase load current signals from the distribution network. Specifically, the acquisition module 100 includes a signal acquisition unit and a signal processing unit. The signal acquisition unit includes a voltage transformer and a current transformer. The voltage transformer is used to acquire the three-phase voltage signals of phases A, B, and C on the distribution network side, and the current transformer is used to acquire the three-phase load current signals. The signal processing unit includes a signal conditioning circuit and an analog-to-digital conversion circuit. The signal conditioning circuit is used to filter, amplify, and level-convert the acquired voltage and current signals, converting the processed signals into a standard signal range suitable for the controller input. The analog-to-digital conversion circuit is used to convert the conditioned analog signals into digital signals and input them to the controller 200.

[0056] The controller 200, connected to the acquisition module 100, uses a TMS320F2812 digital signal processor (DSP) chip as its core processing unit. The controller 200 is configured to perform the following steps: extract the real-time phase from the three-phase voltage signal; perform dq coordinate transformation on the three-phase load current signal using the real-time phase; perform low-pass filtering on the transformed current component to extract the fundamental positive-sequence reactive current component; generate a reactive power compensation command current based on the fundamental positive-sequence reactive current component; generate an active current adjustment amount based on the deviation between the actual DC-side voltage value and a given reference value; superimpose the active current adjustment amount onto the reactive power compensation command current to obtain a comprehensive command current; and decouple the deviation between the comprehensive command current and the real-time feedback current to generate a drive signal. The specific operation process of the controller 200 has been described in detail in Embodiment 1 and will not be repeated here.

[0057] The power module 300, connected to the controller 200, controls the switching of the transistors in the converter according to the drive signal, and outputs compensation current to the distribution network. Specifically, the power module 300 includes a converter, a filter inductor, and a DC-side energy storage capacitor. The converter adopts a three-phase full-bridge voltage-source inverter topology, including three-phase bridge arms. Each bridge arm consists of an upper bridge arm switch and a lower bridge arm switch connected in series, and the switches are IGBT power devices. The AC side of the converter is connected to the distribution network through the filter inductor, which is used to filter out high-order harmonics near the switching frequency. The DC-side energy storage capacitor is connected in parallel across the DC side of the converter to maintain DC-side voltage stability and provide energy buffer for the converter. The power module 300 is also equipped with a relay protection circuit. When a fault such as short circuit, overvoltage, or overtemperature occurs in the system, the relay protection circuit quickly generates a fault signal. After receiving the fault signal, the controller 200 stops the PWM modulation module and blocks the pulse signal in the main circuit, causing the device to quickly shut down and isolate itself from the grid, ensuring equipment and personnel safety.

[0058] Preferably, the controller 200 further includes a phase-locked loop (PLL) subsystem. The PLL subsystem first converts the high-frequency voltage signal into a square wave signal, and then converts the square wave signal into a phase signal value to achieve real-time tracking of the grid voltage phase and provide a phase reference for the implementation of the improved dq method.

[0059] Example 3: To further verify the effectiveness of the static var generator and its control method based on the improved dq method provided in the above embodiments of the present invention, simulation experimental data are given in this embodiment.

[0060] The simulation software used is MATLAB / SIMULINK, with a simulation voltage level of 380V, a load active power of 1000W, and inductive reactive power of 3000Var. The SVG simulation parameters are shown in Table 1. Table 1 SVG Simulation Parameters

[0061] Before the SVG was implemented, the voltage and current in the system were out of phase by approximately 90 degrees, resulting in a high load current distortion rate and a low power factor. After implementing the SVG using the control method described in this embodiment of the invention, the system's d-axis and q-axis current curves could track the commanded values ​​in a very short time, compensating for the reactive power in the system, ensuring that the voltage and current phases remained consistent, and significantly improving the power factor. Simultaneously, the current distortion rate after SVG compensation was significantly reduced, indicating that the control method proposed in this invention can effectively compensate for reactive power and harmonic currents in the system.

[0062] Furthermore, in automatic operation mode, both steady-state and transient compensation experimental results demonstrate that the SVG designed in this invention exhibits excellent performance in both capacitive and inductive compensation, achieving complete system compensation. Under transient conditions of sudden load changes, the SVG designed in this invention can reach a stable state within a short time, demonstrating good dynamic response performance. In manual fixed compensation mode, steady-state and transient experimental results also verify the reactive power compensation capability of the device of this invention.

[0063] Example 4: To further verify the operational performance of the SVG device provided by this invention in a real power distribution network, this embodiment presents data from the trial operation of the device on the low-voltage side of a 110kV substation.

[0064] Located in the eastern part of a certain area, this substation currently has two incoming lines and 16 outgoing lines. It houses two transformers operating in parallel, with a total capacity of 31,500 kVA. The transformers step down the voltage to supply power to the 10 kV outgoing lines on the low-voltage side, which uses a double busbar connection. This substation primarily supplies power to a surrounding industrial park with numerous downstream manufacturing enterprises. During the day, the park frequently operates at full load, causing sudden drops in the 10 kV busbar voltage and a power factor that often falls to around 0.8. Currently, the substation only has one 600 kVar capacitor as a reactive power compensation device, which is insufficient to meet the current reactive power deficit requirements.

[0065] Before the SVG was put into operation, the power quality of the station was recorded through the SCADA system, as shown in Table 2.

[0066] Table 2 Reactive power operation status of the substation before SVG commissioning

[0067] As shown in Table 2, the power quality of the substation had the following problems before the SVG was put into operation: Voltage deviation exceeds standard: Phase A voltage deviation reaches a maximum of 6.83%, Phase B reaches 7.10%, and Phase C reaches 6.65%, all exceeding the ±7.7% range allowed by the power company (in actual operation, it is close to exceeding the limit, and the standard in some areas is even stricter), seriously affecting the normal power supply of surrounding users.

[0068] Excessive flicker: The short-term flicker value of phase A reached 2.17, which seriously exceeded the standard limit of 1.0, indicating severe voltage fluctuation.

[0069] High harmonic content: The content of the 4th and 5th harmonics exceeded the standard, with the 5th harmonic A phase reaching as high as 6.73%, indicating that there is serious harmonic pollution in the system.

[0070] The 10kV bus voltage curve of the substation before commissioning is as follows: Figure 8As shown in the figure, the bus voltage fluctuates significantly, especially during peak daytime electricity consumption periods, when the voltage amplitude drops noticeably, the maximum voltage deviation exceeds the allowable range, and the voltage qualification rate is low.

[0071] To address the voltage fluctuation issue on the low-voltage side bus of the substation, the SVG device provided in this embodiment of the invention was put into operation on the 10kV low-voltage side of the substation to compensate for reactive power loss and thus mitigate the voltage drop. The power quality after the device was put into operation is shown in Table 3.

[0072] Table 3. Reactive power operation status of the substation after SVG commissioning

[0073] As shown in Table 3, after the SVG is put into operation: The voltage deviation has been effectively controlled, with the voltage deviation of phase A reduced to -3.79%, phase B to -2.13%, and phase C to -3.87%, all within the allowable range; The total voltage distortion rate was significantly reduced, with the three-phase distortion rates dropping to 0.97%, 0.73%, and 0.82%, respectively, far below the limit requirement of 4.00%. The short-time flicker value decreased from 2.17 (phase A) before commissioning to 0.12~0.13, meeting the standard requirements; The voltage content of each harmonic decreased significantly, and the content of the 4th and 5th harmonics both dropped to within the allowable range.

[0074] The voltage curve of the 10kV busbar of the substation after the SVG is put into operation is as follows: Figure 9 As shown in the figure, after the SVG equipment was put into operation, the voltage was relatively stable, the fluctuation was significantly reduced, and the minimum voltage error was only 0.5kV, which met the power company's standards and also met the power requirements of surrounding enterprises.

[0075] After the SVG was put into operation, the reference voltage was set to 10.5kV, and the 10kV bus voltage qualification rate was statistically analyzed for 7 consecutive days, as shown in Table 4. The data in the table shows that the voltage qualification rate reached 100% after commissioning, indicating good regulation performance.

[0076] Table 4. 10kV bus voltage qualification rate after SVG commissioning

[0077] The power factor changes of the 10kV bus before and after the commissioning of the SVG equipment are as follows: Figure 10 As shown in the figure, the power factor was as low as 0.80 before commissioning, and the average power factor was also low; after commissioning, the minimum power factor reached over 0.94, effectively improving the power transmission efficiency of the system.

[0078] Table 5 shows the comparison of electricity consumption data before and after the SVG was put into operation on the low-voltage side of the substation. In the week before commissioning (day 1 to day 7), the average daily electricity consumption of the substation was 96,056 kWh, and in the week after commissioning (day 8 to day 14), the average daily electricity consumption of the substation increased to 104,010 kWh, and the power loss was significantly reduced.

[0079] Table 5 Comparison of daily power generation of substations before and after SVG commissioning (unit: kWh)

[0080] After the power loss of the substation is reduced, the corresponding electricity sales volume increases, and the increased revenue is calculated as follows: , in, This indicates an increase in annual revenue. This indicates the annual increase in electricity consumption. This represents the profit from electricity prices. Based on an average daily increase in electricity consumption of approximately 7,954 kWh, the annual increase in electricity consumption is approximately 2.9 million kWh, which can generate an additional revenue of approximately 305,300 yuan per year.

[0081] Simultaneously, the average power factor improved from 0.80 to 0.98 after commissioning. For every 1 kVar of reactive power input, approximately 0.65 kW of active power loss can be reduced. With a rated capacity of 10 MVar and an operating efficiency of 0.8, the annual active power savings are approximately: .

[0082] The inherent losses generated by the device during operation are calculated as 0.8% of the maximum losses: .

[0083] Based on a price of 0.5 yuan / kWh for electricity, the annual savings would be approximately: .

[0084] The above trial operation data fully verifies the effectiveness of the static var generator and its control method based on the improved dq method provided by this invention in the actual low voltage management of distribution networks. It can effectively improve voltage qualification rate and power quality, reduce system losses, and has good economic benefits and prospects for promotion and application.

[0085] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A control method for a static var generator based on the improved dq method, characterized in that, include: Acquire the three-phase voltage signal and three-phase load current signal of the power distribution network; The real-time phase is extracted from the three-phase voltage signal, and the real-time phase is used to perform dq coordinate transformation on the three-phase load current signal. The transformed current component is then low-pass filtered to extract the fundamental positive sequence reactive current component. A reactive power compensation command current is generated based on the fundamental positive sequence reactive current component. Based on the deviation between the actual DC-side voltage value and the given reference value, an active current regulation amount is generated, and the active current regulation amount is superimposed on the reactive power compensation command current to obtain the comprehensive command current. The deviation between the integrated command current and the real-time feedback current is decoupled and controlled to generate a drive signal to control the converter output compensation current.

2. The control method for a static var generator based on the improved dq method according to claim 1, characterized in that, The step of extracting the real-time phase based on the three-phase voltage signal includes: Obtain the instantaneous value of phase A voltage, perform derivative calculation on the instantaneous value of phase A voltage, and calculate the real-time phase that is synchronized with phase A voltage based on the instantaneous value of phase A voltage and the derivative of phase A voltage: ， in, This represents the instantaneous value of phase A voltage. The derivative of phase A voltage; The real-time phase It replaces the output phase of the phase-locked loop to compensate for detection phase errors.

3. The control method for a static var generator based on the improved dq method according to claim 2, characterized in that, The step of performing dq coordinate transformation on the three-phase load current signal using the real-time phase includes: According to the real-time phase Calculate the corresponding sine and cosine values; The three-phase load current signal is transformed from the abc coordinate system to the dq rotating coordinate system based on the transformation matrix: ， in, , , This represents the instantaneous value of the three-phase load current. The current component is the d-axis component. For the q-axis current component, Let be the transformation matrix.

4. The control method for a static var generator based on the improved dq method according to claim 3, characterized in that, The step of performing low-pass filtering on the transformed current components to extract the fundamental positive-sequence reactive current component includes: The d-axis current component and the q-axis current component The high-frequency AC components are filtered out by low-pass filters to obtain the DC components. and ; The DC component of the q-axis current component This is the fundamental positive sequence reactive current component.

5. The control method for a static var generator based on the improved dq method according to claim 4, characterized in that, The step of generating reactive power compensation command current based on the fundamental positive sequence reactive current component includes: For the fundamental positive sequence reactive current component Perform an inverse coordinate transformation, changing it from the dq coordinate system to the abc coordinate system, to obtain the three-phase reactive power compensation command current: ， in, , , This is the command current for three-phase reactive power compensation.

6. The control method for a static var generator based on the improved dq method according to claim 1, characterized in that, The process of generating active current regulation based on the deviation between the actual DC-side voltage value and a given reference value includes: The actual value of the DC side voltage Compared with a given reference value The difference is adjusted by proportional-integral control to obtain the active current regulation. : ， in, This is the proportionality coefficient. is the integral coefficient.

7. The control method for a static var generator based on the improved dq method according to claim 1, characterized in that, The decoupling control of the deviation between the integrated command current and the real-time feedback current includes: Based on the SVG mathematical model in a rotating coordinate system, the d-axis voltage command is... and q-axis voltage command Set them to: ， ， in, , Let d-axis and q-axis components of the grid voltage in the dq coordinate system be the components of the grid voltage. The angular frequency of the power grid. This is the value of the filter inductance. , These are the d-axis and q-axis current command values. , These are the d-axis and q-axis current feedback values. , , , This is a PI control parameter used to eliminate the current coupling effect between the d-axis and q-axis.

8. A static var generator based on the improved dq method, characterized in that, include: The acquisition module is used to acquire the three-phase voltage signal and three-phase load current signal of the power distribution network; The controller, connected to the acquisition module, is configured to perform the following steps: extract the real-time phase based on the three-phase voltage signal, perform dq coordinate transformation on the three-phase load current signal using the real-time phase, and perform low-pass filtering on the transformed current component to extract the fundamental positive sequence reactive current component. A reactive power compensation command current is generated based on the fundamental positive sequence reactive current component; an active current regulation is generated based on the deviation between the actual DC side voltage value and the given reference value; the active current regulation is superimposed on the reactive power compensation command current to obtain a comprehensive command current; the deviation between the comprehensive command current and the real-time feedback current is decoupled and controlled to generate a drive signal. The power module, connected to the controller, is used to control the switching of the switching transistors in the converter according to the drive signal, and output compensation current to the distribution network.

9. The static var generator based on the improved dq method according to claim 8, characterized in that, The power module includes a converter, a filter inductor, and a DC-side energy storage capacitor. The AC side of the converter is connected to the power distribution network via the filter inductor, and the DC-side energy storage capacitor is connected in parallel across the DC side of the converter. The converter includes three-phase bridge arms, and each phase bridge arm is composed of an upper bridge arm switch and a lower bridge arm switch connected in series.

10. The static var generator based on the improved dq method according to claim 8, characterized in that, The acquisition module includes a signal acquisition unit and a signal processing unit. The signal acquisition unit is used to acquire the three-phase voltage signal and the three-phase load current signal. The signal processing unit is used to filter, amplify and level-convert the acquired signal, and input the processed signal to the controller.

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