Power grid strength identification and parameter adaptive control method

Abstract

The invention relates to the technical field of power system automation and control, in particular to a power grid strength identification and parameter adaptive control method, which comprises the following steps of: acquiring a power grid strength signal through a power grid strength identification module according to an injected small disturbance component and a reactive power feedback signal; the power grid strength signal is input to a reactive power control parameter self-adaptive adjustment module, and the reactive power control parameter self-adaptive adjustment module outputs a PI control parameter adjustment signal according to an expected value of reactive power control bandwidth; and inputting the PI control parameter adjusting signal to a reactive power control module, performing closed-loop control on reactive power, and outputting an excitation voltage adjusting signal. The method has the advantages that the change of strength indexes such as the short-circuit capacity ratio of the system is sensed in real time, the parameters of the reactive power PI controller are dynamically adjusted according to the change, the inherent defect that the performance is degraded when the power grid strength fluctuates in a traditional fixed parameter control strategy is overcome, and the control system is made to be always matched with the dynamic characteristics required by the current power grid working condition.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power system automation and control technology, and particularly relates to a power grid strength identification and parameter adaptive control method. BACKGROUND

[0002] With the increasing penetration of new energy generation equipment such as wind power and solar power and power electronic conversion devices in power systems, the equivalent short-circuit capacity of the power grid is continuously decreasing, and the system strength is gradually weakening. Under this background of "double high" (high proportion of new energy, high proportion of power electronic equipment), the demand for dynamic reactive power compensation and voltage support capacity of the power grid is increasingly urgent.

[0003] As an advanced reactive power compensation device, grid-forming SVG constructs terminal voltage by simulating the excitation characteristics of synchronous generators. This characteristic enables grid-forming SVG to maintain stable operation even when connected to a weak grid with a low short-circuit capacity ratio, and provides necessary reactive power buffer and voltage support for the system, so it is considered as a key device to enhance the stability of weak power grids.

[0004] However, factors such as the volatility of new energy generation, the complexity of load, and the extension of the power grid to remote areas have led to a continuous decrease in the system's equivalent short-circuit ratio and dynamic changes in the impedance characteristics of the power grid. This poses a serious challenge to the reactive power control of grid-forming SVG: 1. Poor adaptability of fixed parameter control strategy: Traditional grid-forming SVG control strategies usually design fixed controller parameters based on ideal strong grid assumptions or simplified impedance models. When the actual grid strength fluctuates dynamically, this fixed parameter control system is difficult to achieve optimal regulation, and may easily cause problems such as reactive power response lag, voltage overshoot increase, and even oscillation or resonance between SVG and the grid, threatening system safety.

[0005] 2. Decline in dynamic response performance and stability: When the power grid is disturbed, such as sudden changes in new energy output or load switching, fixed controller parameters cannot adapt to changes in the system operating point, leading to deterioration of the reactive power-voltage dynamic response characteristics of grid-forming SVG, a significant reduction in system stability margin, and possible voltage instability at the grid connection point, directly affecting the safe grid-connected operation of new energy generation systems.

[0006] Existing SVG reactive power control methods, such as conventional droop control, can achieve preliminary allocation of reactive power, but the droop coefficient is usually fixed. In the scenario of dynamic changes in grid strength, the fixed droop coefficient lacks real-time awareness and adaptive ability to changes in grid strength. SUMMARY

[0007] The purpose of the present application is to provide a power grid strength identification and parameter adaptive control method, which aims at the reactive power control performance bottleneck of the network structure SVG under weak power grid, identifies the power grid strength in real time and accurately, and dynamically optimizes the parameters of the reactive power controller based on this, so as to improve the dynamic response performance and stability of the SVG under wide range of power grid strength fluctuations.

[0008] In order to achieve the above purpose, the present application realizes the following technical scheme: A power grid strength identification and parameter adaptive control method, comprising: Through the power grid strength identification module, the injected small disturbance component ΔQ and the reactive power feedback signal are used to obtain the power grid strength signal ; The power grid strength signal is input to the reactive power control parameter adaptive adjustment module, and the reactive power control parameter adaptive adjustment module outputs the PI control parameter adjustment signal according to the expected value of the reactive power control bandwidth. The PI control parameter adjustment signal ΔK is input to the reactive power control module, the reactive power is closed-loop controlled, and the excitation voltage adjustment signal ΔE is output.

[0009] The input quantity of the reactive power control module includes the reactive power given signal and the reactive power feedback signal , and the difference between the reactive power given signal and the reactive power feedback signal is input to the PI controller after being filtered by a first-order low-pass filter, and the PI controller outputs the excitation voltage amplitude adjustment signal .

[0010] The transfer function of the reactive power control module is expressed as: ①; In expression ①: represents the rated voltage of the SVG, and the unit is volt; represents the rated capacity of the SVG, and the unit is volt-ampere; represents the proportional control coefficient; represents the integral control coefficient, and the unit is second-1; represents the Laplace operator, and the unit is second -1 ; represents the transfer function of the first-order low-pass filter; T s is a time constant, T s is in the range of 0.01s.

[0011] The grid strength recognition module acquires the grid strength signal , including: Injecting a small signal disturbance component with a frequency of f in the reactive power given signal ; Measuring and extracting the component with a frequency of f in the reactive power feedback signal ; Calculating and the amplitude ratio q, expressed as: ②; If the amplitude ratio q is less than 0.7, gradually increase f and repeat the above steps until q≥0.7; At this time, the frequency f of the grid strength signal is assigned, and is input into the reactive power control parameter adaptive adjustment module.

[0012] The component with a frequency of f in the reactive power feedback signal is extracted by Fourier decomposition, expressed as: ③; In expression ③: is the complex Fourier vector of order f of ; N represents the number of samples; represents the input signal at sample point k.

[0013] The expression of the PI control parameter adjustment signal is: ④; In expression ④: represents the proportional constant; represents the expected value of the preset reactive power control bandwidth.

[0014] The expression of the reactive power given signal is: ⑤; In expression ⑤, the reactive power given signal is usually a fixed constant.

[0015] The grid strength identification and parameter adaptive control system comprises a reactive power control module, a grid strength identification module and a reactive control parameter adaptive adjustment module. The reactive power control module is used for realizing closed-loop control of reactive power. The grid strength identification module is used for identifying grid strength in real time and outputting a grid strength signal g i . The reactive control parameter adaptive adjustment module is used for outputting a PI control parameter adjustment signal according to the grid strength signal and a preset expected value of a reactive power control bandwidth. .

[0016] Compared with the prior art, the grid strength identification and parameter adaptive control system has the following beneficial effects: 1. The grid strength identification module is used for sensing the change of the strength index such as the short-circuit capacity ratio in real time, and the parameters of the reactive power PI controller are dynamically adjusted according to the change, so that the inherent defect of performance degradation of the traditional fixed parameter control strategy in the grid strength fluctuation is overcome, and the control system always matches the dynamic characteristics required by the current grid working condition. 2. The identified grid strength is associated with the expected control bandwidth, and the control parameters are adaptively adjusted, so that the tracking speed of the reactive power is effectively accelerated, and the response time (such as the rise time is shortened from 200 ms to within 50 ms) is reduced, which greatly improves the transient stability and operation robustness of the grid-forming SVG in the weak grid and high impedance change environment. 3. Small signal injection and frequency domain analysis are combined, the grid strength is quantified by detecting the cut-off frequency of the open-loop frequency response of the system, the anti-interference ability is strong, the dynamic change of the grid strength can be accurately captured, and reliable and real-time input basis is provided for adaptive adjustment of the parameters. 4. Due to the closed-loop adaptive mechanism of "perception-decision-adjustment", the grid-forming SVG can automatically adapt to the large-scale change of the grid strength caused by new energy fluctuation, load switching and the like, without manual intervention for parameter resetting, so that the intelligent level and wide applicability of the equipment are improved. 5. By optimizing the dynamic response of the reactive power, the grid-connected point voltage can be supported more quickly and more smoothly, voltage instability is effectively prevented, and the power quality and safe operation margin of the power system containing a high proportion of new energy are comprehensively improved. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 The parameter adaptive adjustment device structure diagram.

[0018] Figure 2 The reactive power control module principle diagram.

[0019] Figure 3Grid strength recognition and reactive power control parameter adaptive adjustment flow chart.

[0020] Figure 4 Closed-loop frequency characteristics under different reactive power controller parameters.

[0021] Figure 5 Dynamic characteristics before adaptive adjustment of reactive power control parameters.

[0022] Figure 6 Dynamic characteristics after adaptive adjustment of reactive power control parameters. DETAILED DESCRIPTION

[0023] The application will be described in detail below with reference to the accompanying drawings of the specification, but it should be pointed out that the implementation of the application is not limited to the following embodiments.

[0024] A grid strength recognition and parameter adaptive control system includes a reactive power control module, a grid strength recognition module, and a reactive power control parameter adaptive adjustment module, and the specific content is as follows: S1, a reactive power control module; 1) Purpose: The reactive power control module is used to realize closed-loop control of reactive power, and outputs an excitation voltage adjustment signal to the SVG converter valve.

[0025] 2) Input signal: Reactive power given signal ; Measured reactive power feedback signal .

[0026] 3) Control logic: Calculate the error signal, the formula is as follows: ①; In formula ①, e represents the error signal of the reactive power given signal and the measured reactive power feedback signal ; The error signal e passes through a first-order low-pass filter, and the transfer function is: ; The time constant Ts is 0.01S, which is used to filter out high-frequency noise.

[0027] The filtered signal is sent to a PI controller (proportional-integral controller), and an excitation voltage amplitude adjustment signal is output.

[0028] 4) Normalization model; To facilitate analysis and controller design, the closed-loop transfer function of the reactive power control module is normalized, and the expression is as follows: ①; In formula ①: This indicates the rated voltage of the SVG, in units of: V; Indicates the rated capacity of the SVG, in VA; By standardizing the data, the system parameters are decoupled from the physical dimensions, which facilitates unified design and analysis in SVG systems with different capacities and voltage levels, and improves the versatility and portability of the controller.

[0029] S2, Power Grid Strength Identification Module; 1) Purpose: The power grid strength identification module is used to identify the current power grid strength in real time and quantify it into a power grid strength signal. .

[0030] 2) Execution steps, see Figure 3 : S21, Signal Input: In reactive power given signal A small-signal disturbance component with frequency f and constant amplitude is superimposed on it. The initial frequency is f0 = 0 Hz.

[0031] S22. Response Measurement: Reactive power feedback signal of the measurement system .

[0032] S23. Harmonic Extraction: right Perform Fourier decomposition to extract the response component with frequency f. The calculation formula is: ②; in, yes The complex Fourier vector at frequency f; N represents the number of samples; This represents the signal value at the k-th sampling point.

[0033] S24. Amplitude Ratio Calculation: The formula for calculating the amplitude ratio at the current frequency is: ③.

[0034] S25, Threshold Judgment and Frequency Scanning: If the amplitude ratio q is less than 0.7, then the frequency f is increased in increments of 1Hz, i.e., f = f + 1, and steps S22 to S25 are repeated. If q≥0.7, then proceed to step S26.

[0035] S26. Intensity signal generation: Record the current frequency f and assign it to the power grid strength signal. ,Right now ,Should The value represents the bandwidth of the current system's reactive power control, directly reflecting the grid strength.

[0036] S3, reactive power control parameter adaptive adjustment module; 1) Purpose: The reactive power control parameter adaptive adjustment module adjusts the parameters based on the identified grid strength signal. Dynamically calculate and output the adjustment amount of the PI parameter. .

[0037] 2) Adjustment logic: Receive power grid strength signal And the expected value of the preset reactive power control bandwidth By comparing the two, an adjustment signal is output, and the calculation formula is as follows: ④; in, This indicates a settable proportional constant; It is sent to the reactive power control module for real-time adjustment of PI controller parameters, for example: ; ; in, and This represents the allocation coefficient, thereby determining the actual control bandwidth. To the expected value near.

[0038] 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.

[0039] Example 1 See Figure 1 This paper presents an adaptive optimization method for reactive power control parameters of grid-connected SVG under scenarios of varying grid strength.

[0040] Considering the dynamics of the power grid impedance, the small-signal relationship between reactive power and voltage difference is as follows: ; in: This indicates the rated voltage of the SVG, in volts. Indicates frequency as Electrical grid impedance, in ohms; Indicates frequency as Electrical grid impedance, in ohms; Represents the imaginary unit; This represents the Laplace operator, with units of seconds - 1.

[0041] based on Figure 2 The reactive power control flowchart shows that the difference between the reactive power setpoint signal and the reactive power feedback signal is input to a first-order low-pass filter module with a time constant of 10ms, and then the excitation voltage control component is output by the PI regulator. The per-unit transfer function is as follows: ; The transfer function between the reactive power command signal and the reactive power feedback signal is obtained as follows: ; See Figure 4 This demonstrates that K... p =0.02, K i The amplitude-frequency and phase-frequency characteristic curves of the transfer function when the values ​​are 30, 60, and 90.

[0042] Example 2 The frequency response of the closed-loop transfer function is tested, specifically at Q. in A small disturbance signal ΔQ(f) is injected, and the reactive power feedback signal ΔQ of the disturbance is measured. out (f).

[0043] For reactive power feedback signal Q out Harmonic analysis is performed, and the component with frequency f is extracted through Fourier decomposition. The expression is as follows: ; Disturbance signal frequency from Beginning, with Gradually increase: ; Measure the amplitude-frequency response of the transfer function, when the amplitude When the frequency decays to around 0.7, the current frequency f is recorded and assigned to the power grid strength signal. The data is then input into the reactive power control parameter adaptive adjustment module.

[0044] when When the bandwidth g is different from the set bandwidth, the output parameter adjustment signal is: ; Where, k q It is a proportionality constant.

[0045] When the grid strength decreases (SCR=2), see Figure 5 The dynamic response performance of reactive power control deteriorates, with a rise time of 200ms.

[0046] After using the method of the present invention, the real-time calculation is obtained This is less than the set bandwidth g=16Hz. (Take...) ,pass Adjust the PI parameters to shorten the rise time to <50ms, see [link / reference]. Figure 6 .

[0047] Example 3 In this embodiment, a power grid strength identification and parameter adaptive control method is the same as in Embodiment 1, but with the addition of adaptive control process verification, including: S1, Adaptive process initiation: System Input Disturbance amplitude Initiate the frequency scanning process.

[0048] S2, Intensity Identification Results: Real-time calculated power grid strength signal The range of 3 Hz to 4 Hz indicates a narrow control bandwidth under the current weak power grid (SCR=2).

[0049] S3, Parameter adaptive adjustment: Set g=16Hz, calculate: ; Will Output to the reactive power control module to adjust the PI parameters.

[0050] S4. Control effect verification: See after adjustment Figure 6 The rise time of the system step response is shortened to <50ms, the control bandwidth is significantly improved, and the dynamic response performance is improved.

[0051] By identifying grid strength in real time and adaptively adjusting controller parameters, the adaptability problem of fixed parameter controllers when grid strength fluctuates is effectively solved, and the operating performance of SVG under weak grid conditions is significantly improved.

[0052] The application perceives the change of the strength index such as system short-circuit capacity ratio in real time through the grid strength identification module, and dynamically adjusts the parameters of the reactive power PI controller accordingly, overcomes the inherent defects of the performance degradation of the traditional fixed parameter control strategy when the grid strength fluctuates, and makes the control system always match the dynamic characteristics required by the current grid operating condition; by associating the identified grid strength with the expected control bandwidth and adaptively adjusting the control parameters, the tracking speed of the reactive power is effectively accelerated, and the response time (such as the rise time is shortened from 200 ms to within 50 ms), which greatly improves the transient stability and operating robustness of the grid-forming SVG in the weak grid and high impedance change environment; small signal injection and frequency domain analysis are combined, the cutoff frequency of the open-loop frequency response of the system is detected to quantify the grid strength, which has strong anti-interference ability and can accurately capture the dynamic change of the grid strength, providing reliable and real-time input basis for adaptive adjustment of parameters; due to the closed-loop adaptive mechanism of "perception-decision-adjustment", the grid-forming SVG can automatically adapt to the large-scale change of the grid strength caused by new energy fluctuation, load switching and the like, without the need for manual intervention to reset the parameters, improving the intelligent level and wide applicability of the equipment; by optimizing the dynamic response of the reactive power, the grid-connected point voltage can be supported more quickly and smoothly, effectively preventing voltage instability, and thus comprehensively improving the power quality and safe operation margin of the power system with high proportion of new energy.

Claims

1. A power grid strength identification and parameter adaptive control method, characterized in that, Comprise: Through the grid strength identification module, the grid strength signal is acquired according to the injected small disturbance component ΔQ and the reactive power feedback signal . ​ The grid strength signal is input to a reactive power control parameter adaptive adjustment module The reactive power control parameter adaptive adjustment module outputs a PI control parameter adjustment signal according to an expected value of a reactive power control bandwidth ; The PI control parameter adjustment signal ΔK is input to the reactive power control module, the reactive power is closed loop controlled, and the excitation voltage adjustment signal ΔE is output.

2. The grid strength identification and parameter adaptive control method of claim 1, wherein, The input quantity of the reactive power control module includes a reactive power given signal and a reactive power feedback signal The difference between the reactive power given signal and the reactive power feedback signal is input to a PI controller after being filtered by a first-order low-pass filter, and the PI controller outputs an excitation voltage amplitude adjustment signal .

3. The grid strength identification and parameter adaptive control method of claim 2, wherein, The transfer function of the reactive power control module is expressed as: ①； In expression ①: SVG represents the rated voltage in volts; represents the rated capacity of the SVG in volt-amperes; represents a proportional control coefficient; represents the integral control coefficient, in seconds-1; denotes the Laplacian operator in seconds -1 ; represents the transfer function of a first order low pass filter; T s T is a time constant, T s has a value in the range of 0.01 s.

4. The grid strength identification and parameter adaptive control method of claim 1, wherein, The power grid strength recognition module acquires a power grid strength signal , comprising: injecting a small signal perturbation component of frequency f in the reactive power given signal ; Measuring and extracting a component of a reactive power feedback signal at a frequency f ; Computing with the amplitude ratio q of the complex number z, expressed by the formula: ②； If the amplitude ratio q is less than 0.7, gradually increase f and repeat the above steps until q is greater than or equal to 0.7; assigning the frequency f at this time to the grid strength signal and inputting the reactive power control parameter adaptive adjustment module.

5. The grid strength identification and parameter adaptive control method according to claim 4, characterized in that, The component of the reactive power feedback signal with the frequency f By Fourier decomposition extraction, the expression is: ③； In expression ③: is a complex Fourier vector of frequency order f of ; N denotes the number of samples, denotes the input signal at sample point k.

6. The grid strength identification and parameter adaptive control method of claim 1, wherein, The PI control parameter adjustment signal The expression is: ④； In expression (IV): represents a proportionality constant; represents a desired value of the preset reactive power control bandwidth.

7. The grid strength identification and parameter adaptive control method of claim 1, wherein, The reactive power given signal The expression is: ⑤； In the expression (5), the reactive power given signal Generally, it is a fixed constant.

Images