Static var generator control method suitable for suppressing load power oscillation

Abstract

The invention relates to the cross technical field of new energy power generation and power system stability control, in particular to a static var generator control method suitable for suppressing load power oscillation, which comprises the following steps: synchronously acquiring instantaneous voltage and current at a load end, calculating load instantaneous impedance, an impedance effective value and a change rate thereof, and calculating the load power oscillation. Constructing a virtual impedance and negative feedback damping mechanism based on the impedance change rate, finally generating a reactive current instruction with a dynamic damping characteristic, and controlling the SVG to inject reactive power when the load impedance is increased and absorb reactive power when the impedance is decreased; according to the invention, the impedance disturbance suppression module is additionally arranged in the SVG control system, so that source suppression of load power oscillation is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy power generation and power system stability control, and particularly relates to a static var generator control method suitable for inhibiting load power oscillation. BACKGROUND

[0002] In modern power distribution systems, with the increasing penetration of new energy generation and the widespread application of various types of electrical equipment in industrial production, a large number of nonlinear impact loads, power electronic equipment, high-power frequency conversion equipment, and periodic mechanical loads are connected to the power grid. The characteristics of such loads result in frequent fluctuations and even oscillations in load power. When load power oscillation occurs, it will cause periodic changes in grid voltage, current, and reactive power exchange.

[0003] The harm caused by such changes has obvious hierarchical nature: on the one hand, it may cause voltage flicker, abnormal vibration of equipment, and affect the normal operation accuracy and service life of electrical equipment; on the other hand, it may cause system stability deterioration, misoperation of relay protection devices, and even collapse of bus voltage in extreme cases, posing a serious threat to the safe and reliable operation of the entire power distribution system.

[0004] To solve the above problems, various methods for inhibiting power oscillation have been developed in the prior art, mainly including: (1) Increasing the compensation capacity on the load side, by increasing the capacity of the reactive power compensation device to offset the impact of power fluctuations; (2) Adjusting the SVG / STATCOM reactive current response strategy to increase system damping to alleviate oscillation; (3) Additional configuration of dedicated devices such as dynamic voltage regulators (DVRs) and active filters in the power grid to specifically suppress oscillation and harmonics; (4) Using a voltage disturbance detection method based on PLL (phase-locked loop) to adjust the reactive output according to the detected voltage fluctuations.

[0005] However, the above existing methods still have significant deficiencies in practical application, which are as follows: (1) The conventional SVG control strategy is based only on voltage or reactive power deviation for adjustment, and cannot directly reflect the dynamic change law of load impedance. In essence, load power oscillation is caused by periodic changes in impedance, but the voltage outer loop and current inner loop in the traditional control scheme cannot directly sense the dynamic fluctuations of impedance, resulting in a lack of targeted adjustment; (2) Traditional control methods such as PLL and dq decoupling are sensitive to non-sinusoidal voltage conditions. When the load produces harmonics or the grid has unbalanced voltage, the traditional dq control is prone to false reactive power adjustment, which not only fails to effectively suppress oscillation, but may even exacerbate system fluctuations; (3) The existing compensation mode has limited response speed, and the response performance of the traditional SVG depends on the loop bandwidth, so it is difficult to achieve accurate and rapid suppression for high-frequency and small-amplitude power oscillation caused by rapid impedance change; (4) There is a lack of quantitative analysis means for dynamic impedance of the load, and a mature reactive power control strategy based on impedance change rate has not been formed in the industry, so the strength and trend of load disturbance cannot be quantified from the source, which limits the adaptability and suppression effect of the control strategy.

[0006] Therefore, there is an urgent need for an SVG control strategy that can directly target the essential law of load impedance change, obtain real-time adjustable reactive current instructions through accurate impedance analysis, and suppress power oscillation from the source. The present application proposes a damping control method based on the dynamic characteristics of load impedance, which can achieve rapid and accurate suppression of power oscillation without changing the existing SVG main circuit structure. SUMMARY

[0007] The present application provides a static var generator control method suitable for suppressing load power oscillation, which calculates the effective value and change rate of load impedance in real time, constructs a "virtual damping" damping reactive power control mechanism with clear physical meaning, so that the SVG can quickly generate reactive current response with damping characteristics when the load power oscillates, thereby suppressing the load power oscillation from the source and significantly improving the stability and power supply reliability of the distribution system.

[0008] In order to achieve the above purpose, the present application adopts the following technical scheme: A static var generator control method suitable for suppressing load power oscillation, comprising the following steps: S1, constructing an SVG system main wiring topology: the SVG is connected in parallel between the power grid and the load, and the AC side is directly connected to the load node, so as to realize the injection and absorption of reactive power or active power at the load port; S2, constructing an SVG control topology: the control topology includes a voltage outer loop, a current inner loop, a phase-to-phase DC voltage balance control, and an impedance disturbance control, wherein the voltage outer loop output is the d-axis given value of the current inner loop, and the impedance disturbance suppression module output is the q-axis given value of the current inner loop; S3, constructing an impedance disturbance control and generating a reactive current instruction, the specific implementation steps are as follows: S3.1, using synchronous sampling technology to collect the instantaneous three-phase voltage at the load end And the instantaneous three-phase current ; S3.2, calculating the load instantaneous impedance according to the circuit law , and decomposing it into impedance amplitude |Z| and phase angle The calculation formula of the load instantaneous impedance is as follows: ; S3.3, the load impedance effective value is calculated by using the sliding average method , and the calculation formula is as follows: ; Wherein, T is the time window of effective value calculation, and the value range is 0.01s-0.1s;t is the current time; is the time Corresponding to the load instantaneous impedance; is the integral variable, which represents any time in the time window ([t-T,t]); S3.4, the impedance effective value is obtained by differentiation, and the impedance effective value change rate is obtained, and the calculation formula is as follows: ; S3.5, the negative feedback term of impedance change rate is introduced to construct virtual impedance , and the calculation formula is as follows: ; Wherein, It is an adjustable gain coefficient; S3.6, based on the virtual impedance The reactive current instruction is generated , and the calculation formula is as follows: ; Wherein, It is the effective value of load terminal voltage, It is the system reference impedance, and the value is the ratio of system rated voltage and rated current.

[0009] Further, in the step S3.1, the sampling frequency of synchronous sampling is not less than 20kHz, and the time synchronization error of voltage and current signals is less than 10us.

[0010] Further, in the step S3.4, the differential of the impedance effective value Is obtained by using first-order difference method or Kalman filter differential method.

[0011] Further, the SVG control topology adopts modular multilevel topology.

[0012] Compared with the prior art, the beneficial effects of the present application are: 1) Realize the source of load power oscillation suppression: Unlike the traditional method of only responding to voltage or current oscillation, the method directly targets the essence of power oscillation, i.e., the dynamic change of load impedance, realizes accurate regulation through impedance analysis, and has better damping effect. 2) Build a dynamic damping mechanism with clear physical meaning: Through the introduction of virtual impedance, the SVG not only has the traditional reactive power compensation function, but also has the characteristics of "damping device", and the physical logic of damping adjustment is clear, which is convenient for engineering debugging and parameter optimization. 3) Strong engineering practicability: Without changing the hardware structure of the existing SVG main circuit, the calculation logic of the impedance disturbance suppression module is added in the control software, which has low transformation cost, strong compatibility and is easy to popularize and apply in the existing system. 4) Outstanding anti-interference ability: Smooth the instantaneous noise through impedance effective value calculation, and do not depend on the precise synchronization of PLL and dq decoupling, which has strong adaptability to non-sinusoidal conditions such as harmonics and unbalanced voltage, and avoids the generation of false regulation amount. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is the connection diagram of the SVG system main wiring topology and the SVG control topology described in the application.

[0014] Figure 2 It is the structure diagram of the impedance disturbance suppression module described in the application. DETAILED DESCRIPTION

[0015] The specific embodiment of the application will be further described below in combination with the drawings: See Figure 1 The application is a kind of static var generator control method suitable for suppressing load power oscillation, comprising the following steps: S1, construct the SVG system main wiring topology; The main circuit is composed of SVG, power grid and load, and the connection relationship is that SVG is connected in parallel between power grid and load, and the AC side is directly connected with the load node, which can realize the injection and absorption of reactive power or active power at the load port according to the load characteristics and system demand, and ensure the rapid response to load disturbance.

[0016] S2, construct the SVG control topology; The SVG control topology adopts modular multilevel topology, and the control topology includes voltage outer ring, current inner ring, phase-to-phase DC voltage balance control and impedance disturbance control, wherein the voltage outer ring output is the d-axis given value of the current inner ring, and the impedance disturbance suppression module output is the q-axis given value of the current inner ring; The current inner ring can adopt dq coordinate system PI controller.

[0017] S3. Construct an impedance disturbance suppression module and generate reactive current commands, see Figure 2 The specific implementation steps are as follows: S3.1, Collect load-side voltage With current ; Synchronous sampling technology is used to acquire instantaneous three-phase voltage and three-phase current signals at the load end. The sampling frequency of synchronous sampling is not less than 20kHz, and the time synchronization error of voltage and current signals is less than 10μs, ensuring the time synchronization of voltage and current signals and providing data support for the accuracy of subsequent impedance calculation. The acquired signals serve as the core input quantity for impedance analysis.

[0018] S3.2 Calculate the instantaneous impedance of the load. ; According to the fundamental laws of circuits, the instantaneous impedance of the load can be calculated using the following formula (1). It is decomposed into impedance magnitude |Z| and phase angle. This allows for the initial quantification of impedance characteristics. (1) in, This refers to the instantaneous three-phase voltage at the load end. This refers to the instantaneous three-phase current at the load end; S3.3 Calculation of Effective Impedance Value To avoid the impact of instantaneous data jitter on control accuracy, the effective value of the load impedance is calculated using the following formula (2). This value can smooth out instantaneous fluctuation noise, retaining only the physical trend of impedance change, and improving the stability of the control strategy. (2) Where T is the time window for calculating the effective value, and its value ranges from 0.01s to 0.1s. The value of the time window T is adaptively adjusted according to the load oscillation frequency. The higher the oscillation frequency, the smaller the value of T. t is the current time. For a moment The corresponding instantaneous load impedance; Let be the integral variable, representing any moment within the time window ([tT, t]); S3.4 Calculation of the effective value change rate of impedance; The effective value of impedance is obtained by the following formula (3). The rate of change of the effective impedance is obtained by using the first-order difference method or the Kalman filter differentiation method to calculate the differential. This parameter can intuitively reveal the rate of change of load impedance and is a core characteristic quantity for quantifying the intensity of load dynamic disturbances. (3) S3.5, Virtual impedance construction; To introduce negative feedback damping, a virtual impedance is constructed according to the following equation (4). ,in, This is an adjustable gain coefficient used to flexibly adjust the vibration suppression force. It can adaptively adjust within the range of 0.1 to 10 according to the degree of system oscillation. The larger the oscillation amplitude, the larger the value of Kr. (4) S6, Generate reactive current command; Based on virtual impedance Z virt (t), the reactive current command is generated by the following formula (5). Its physical essence is to construct "dynamic damping": when the impedance increases (the load absorbs less power), the SVG injects reactive power into the system; when the impedance decreases (the load surge increases), the SVG absorbs reactive power from the system. Through reactive power regulation that is opposite to the impedance change, it effectively suppresses power oscillations. (5) in, This is the effective value of the load-side voltage. The system reference impedance is the ratio of the system's rated voltage to its rated current.

[0019] This invention is applicable to new energy grid-connected scenarios containing nonlinear impulsive loads, power electronic equipment, high-power frequency converters, and periodic mechanical loads. Addressing the shortcomings of existing technologies, such as the inability to directly sense dynamic changes in load impedance, sensitivity to harmonics, and insufficient response speed, this invention adds an impedance disturbance suppression module to the SVG control system to suppress load power oscillations at their source. This can be achieved without altering the SVG main circuit structure, solely through software algorithm optimization. It features excellent vibration suppression, strong anti-interference capabilities, and high engineering practicality, effectively improving the voltage stability of the power distribution system and avoiding problems such as voltage flicker and protection malfunctions. It is suitable for new energy grid-connected scenarios containing nonlinear impulsive loads and power electronic equipment.

[0020] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0021] Example 1 This embodiment is designed for low-voltage industrial power distribution scenarios (typical 380V / 50Hz system) and aims to verify the overall adaptability of the "SVG + impedance disturbance suppression module". The system structure is as follows: Figure 1 As shown, the core configuration is as follows: Grid side: Set as a three-phase balanced grid, with an effective line voltage of 380V, a frequency of 50Hz, and a system equivalent impedance of 0.1Ω (simulating the weak grid characteristics of a low-voltage distribution network). The base capacity is designed as 100kVA (to match the load requirements of small and medium-sized industrial applications). SVG device: adopts modular multilevel topology MMC, rated capacity 100kvar, switching frequency 10kHz (balancing regulation speed and switching loss), AC side is connected in parallel to load node through circuit breaker, supports reactive power ±100kvar continuous output, active power ±5kvar auxiliary regulation (to offset a small amount of active power loss). Load side: Simulates a typical industrial load combination—including one 100kW variable frequency motor (periodic load, speed changes cause periodic impedance fluctuations, fluctuation frequency 5-15Hz) and one 50kVA medium frequency furnace (impact load, impedance at startup from...). Sudden drop (It rebounded after 0.5 seconds). The basic parameters of the control system are designed based on conventional industrial experience: the proportional coefficient Kp=0.6 and integral coefficient Ki=40 of the current inner loop PI controller (tuned by the step response method to ensure current tracking error <2%); the proportional coefficient Kp=0.15 and integral coefficient Ki=8 of the voltage outer loop PI controller (balancing voltage stability accuracy and dynamic response speed, with steady-state voltage deviation <1%); the output of the impedance disturbance suppression module is directly used as the q-axis setpoint of the current inner loop, which, together with the d-axis setpoint of the voltage outer loop output, controls the power output of the SVG.

[0022] Impedance disturbance suppression module construction The impedance disturbance suppression module generates reactive current commands through the following six steps, the specific process of which is as follows: S3.1, Collect load-side voltage With current ; Synchronous sampling technology is used to acquire instantaneous three-phase voltage and three-phase current signals at the load end, ensuring the time synchronization of voltage and current signals, providing data support for the accuracy of subsequent impedance calculations, and the acquired signals serve as the core input for impedance analysis.

[0023] S3.2 Calculate the instantaneous impedance of the load. ; According to the fundamental laws of circuits, the instantaneous impedance of the load can be calculated using the following formula (1). It is decomposed into impedance magnitude |Z| and phase angle. This allows for the initial quantification of impedance characteristics. (1) in, This refers to the instantaneous three-phase voltage at the load end. This refers to the instantaneous three-phase current at the load end; S3.3 Calculation of Effective Impedance Value To avoid the impact of instantaneous data jitter on control accuracy, the effective value of the load impedance is calculated using the following formula (2). This value can smooth out instantaneous fluctuation noise, retaining only the physical trend of impedance change, and improving the stability of the control strategy. (2) Where T is the time window for calculating the effective value, with a value range of 0.01s to 0.1s, and t is the current time, which can be adjusted according to the actual system operation. For a moment The corresponding instantaneous load impedance; Let be the integral variable, representing any moment within the time window ([tT,t]); S3.4 Calculation of the effective value change rate of impedance; The effective value of impedance is obtained by the following formula (3). The rate of change of the effective impedance is obtained by using the first-order difference method or the Kalman filter differentiation method to calculate the differential. This parameter can intuitively reveal the rate of change of load impedance and is a core characteristic quantity for quantifying the intensity of load dynamic disturbances. (3) S3.5, Virtual impedance construction; To introduce negative feedback damping, a virtual impedance is constructed according to the following equation (4). ,in, This is an adjustable gain coefficient, used to flexibly adjust the vibration suppression force. It can be adaptively adjusted within the range of 0.1 to 10 according to the degree of system oscillation. (4) S6, Generate reactive current command; Based on virtual impedance Z virt (t), the reactive current command is generated by the following formula (5). Its physical essence is to construct "dynamic damping": when the impedance increases (the load absorbs less power), the SVG injects reactive power into the system; when the impedance decreases (the load surge increases), the SVG absorbs reactive power from the system. Through reactive power regulation that is opposite to the impedance change, it effectively suppresses power oscillations. (5) in, () represents the effective value of the load-side voltage. The system reference impedance is the ratio of the system's rated voltage to its rated current.

Claims

1. A control method of a static var generator suitable for damping power oscillations under load, characterized in that, The method comprises the following steps: S1, constructing an SVG system main wiring topology: the SVG is connected in parallel between the power grid and the load, the AC side is directly connected with the load node, and the SVG can realize injection and absorption of reactive power or active power at the load port; S2, constructing an SVG control topology: the control topology comprises a voltage outer loop, a current inner loop, phase-to-phase DC voltage balance control, and impedance disturbance control, wherein the voltage outer loop output is a d-axis given value of the current inner loop, and the impedance disturbance suppression module output is a q-axis given value of the current inner loop; S3, constructing impedance disturbance control and generating a reactive current instruction, and the specific implementation steps are as follows: S3.1, collecting the instantaneous three-phase voltage at the load end by using the synchronous sampling technique and the instantaneous three-phase current ; S3.2, calculating the load instantaneous impedance according to the circuit law , and decomposed into impedance amplitude |Z| and phase angle , the load instantaneous impedance The calculation formula is: ； S3.3, the load impedance effective value is calculated by using the sliding average method The calculation formula is: ； Wherein, T is the time window of effective value calculation, the value range is 0.01s~0.1s;t is the current time; For time Corresponding load instantaneous impedance; Is the integral variable, represents the arbitrary time in the time window ([t-T, t]); S3.4, Impedance effective value The differential is obtained, and the impedance effective value change rate is obtained The calculation formula is: ； S3.5, Constructing virtual impedance by introducing negative feedback term of impedance change rate The calculation formula is: ； wherein is an adjustable gain coefficient; S3.6, based on virtual impedance Generating a reactive current command The calculation formula is: ； wherein, is the load end voltage effective value, is the system reference impedance, which is the ratio of the system rated voltage to the rated current.

2. The control method of a static var generator for damping power oscillations according to claim 1, wherein In the step S3.1, the sampling frequency of synchronous sampling is not less than 20 kHz, and the time synchronization error of the voltage and current signals is less than 10 μs.

3. The control method of a static var generator for damping power oscillations according to claim 1, wherein The step S3.4, the impedance effective value The differential is calculated using a first-order difference method or a Kalman filter differential method.

4. The control method of a static var generator for damping power oscillation according to claim 1, wherein The SVG control topology adopts a modular multilevel topology.

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