SVG impedance sweep test method based on secondary side injection signal

Abstract

The SVG impedance sweep test method based on the secondary side injection signal of the application comprises the following steps: connecting the impedance sweep device in series into the secondary circuit of the power grid voltage control of the SVG to be tested, obtaining the phase of the power grid voltage by the impedance sweep device, and outputting the secondary voltage with the same phase; the impedance sweep device outputs the harmonic disturbance voltage and applies it to the secondary voltage circuit of the SVG to be tested; when the impedance sweep device detects that the injection harmonic triggers the oscillation of the SVG to be tested, the injection harmonic is stopped; the positive sequence impedance and the negative sequence impedance are calculated based on the three-phase voltage output by the impedance sweep device and the three-phase current instantaneous value output by the SVG to be tested, and whether the phase frequency characteristic of the SVG to be tested is qualified is evaluated; when the phase frequency characteristic is qualified, the impedance of the power grid system is obtained, and whether the SVG to be tested is stable is judged by using the Nyquist stability criterion; the control defects and the oscillation risk of the SVG can be found in advance, the impedance test of the SVG is accurate, efficient and low in cost, and the safe and stable operation of the new energy station and the power system is ensured.

Description

Technical Field

[0001] This invention relates to the field of SVG testing technology, and in particular to an SVG impedance sweep frequency testing method based on secondary side injected signals. Background Technology

[0002] As a core reactive power compensation device in new energy power plants, SVG (Static Var Generator) is a "stabilizer" for ensuring grid operation and a key device for optimizing power quality. Leveraging its millisecond-level rapid response capability, it can mitigate various grid problems caused by fluctuations and randomness in wind and solar power output, including node voltage deviations, low system power factor, and excessive harmonics. However, with the continuous expansion of new energy installed capacity, numerous broadband oscillation accidents have occurred at power plants both domestically and internationally. These accidents range from minor incidents causing mass disconnection of wind turbines, solar inverters, and SVGs from the grid to severe incidents causing switch tripping and damage to power equipment, directly threatening the safe and stable operation of the regional power grid. The national standard GB38755-2019, "Guidelines for the Safety and Stability of Power Systems," also stipulates that new energy units and their supporting SVGs must not exhibit self-excited oscillations under normal operating conditions. The industry generally relies on impedance characteristics for oscillation risk pre-assessment, and accurate measurement of SVG impedance parameters is the core foundation for completing oscillation risk assessment.

[0003] Currently, there are two main methods in the industry to obtain the impedance characteristics of SVG: hardware-in-the-loop electromagnetic simulation and actual measurement of SVG primary-side disturbance injection. Hardware-in-the-loop simulation has the advantages of convenient implementation and low investment cost, but it cannot fully reproduce the actual working characteristics of physical reactors and IGBT devices in the field. At the same time, it is difficult to reproduce the inherent delay of communication and control loops in real scenarios. The impedance curve obtained by simulation deviates from the actual impedance of the equipment, and the reliability of the evaluation results is limited. Although the actual measurement scheme of direct disturbance injection on the primary side can accurately reproduce the actual impedance characteristics of SVG, the capacity of a single SVG in a new energy power station can reach tens of megavars, and the supporting test equipment is huge and the weight of the whole machine is often tens of tons. The overall cost of on-site transportation, debugging and testing is high, and its practicality is poor. Summary of the Invention

[0004] In view of this, the present invention proposes an SVG impedance sweep frequency test method based on secondary side injected signals, which can detect control defects and oscillation risks in SVG in advance, and ensure the safe and stable operation of new energy power plants and power systems. The technical solution of this invention is implemented as follows: An impedance sweep frequency testing method for SVG based on secondary-side injected signals is implemented using an impedance sweep frequency device with secondary-side injected signals. The testing method includes the following steps: Step S1: Connect the impedance sweep frequency device in series to the secondary circuit of the SVG under test to acquire the grid voltage control. The impedance sweep frequency device obtains the phase of the grid voltage and outputs the secondary voltage with the same phase. Step S2: The impedance sweep frequency device outputs a harmonic disturbance voltage containing positive sequence voltage and negative sequence voltage disturbances according to the set harmonic frequency, harmonic amplitude and harmonic duration. Step S3: Apply the harmonic disturbance voltage to the secondary voltage circuit of the SVG under test. When the impedance sweep frequency device detects that the injected harmonics cause the SVG under test to oscillate, stop injecting the harmonics. Step S4: Calculate the positive sequence impedance and negative sequence impedance based on the three-phase voltage output by the impedance sweep frequency device and the instantaneous value of the three-phase current output by the SVG under test, and evaluate whether the phase frequency characteristics of the SVG under test are qualified. Step S5: When the phase frequency characteristics are qualified, obtain the impedance of the power grid system and use the Nyquist stability criterion to determine whether the SVG under test is stable.

[0005] Preferably, the impedance sweep frequency device includes: The voltage and current sampling module is used to sample the three-phase voltage and current of the power grid, the three-phase voltage output by the impedance sweep frequency device, and the three-phase current output by the SVG under test. The harmonic injection module is used to output harmonic disturbance voltage and apply it to the secondary voltage circuit of the SVG under test. The protection module is used to stop the harmonic injection module from injecting harmonics when the injected harmonics cause oscillations in the SVG under test. The power supply module is used to supply power to the voltage and current sampling module, the harmonic injection module, and the protection module. The harmonic injection module is electrically connected to the protection module, and the power supply module is electrically connected to the voltage and current sampling module, the harmonic injection module, and the protection module, respectively.

[0006] Preferably, the harmonic injection module includes a first power circuit, a second power circuit, and a three-phase output terminal. The first power circuit outputs the rated fundamental voltage at the power frequency to the SVG under test, and the second power circuit outputs the harmonic disturbance voltage to the SVG under test. The first power circuit and the second power circuit are electrically connected to the three-phase output terminal, respectively.

[0007] Preferably, in step S1, after the impedance sweep frequency device is connected in series to the secondary circuit of the SVG under test for acquiring grid voltage control, the impedance sweep frequency device acquires the amplitude and phase of the grid secondary voltage, and the first power circuit outputs a secondary voltage with the same amplitude and phase.

[0008] Preferably, the specific steps of step S2 are as follows: The harmonic sweep frequency is set in three stages: 1~100Hz, 110~1000Hz, and 1000~2500Hz. The frequency interval, harmonic amplitude, and harmonic duration are set separately for different stages; The impedance sweep frequency device outputs harmonic disturbance voltage according to the set frequency interval, harmonic amplitude, and harmonic duration.

[0009] Preferably, the specific steps for stopping the injection of harmonics in step S3 are as follows: The protection module receives the instantaneous values ​​of the three-phase voltage (A, B, and C) from the three-phase output terminal, filters out the 50Hz power frequency, and outputs the harmonic components. When the harmonic components are greater than the set value, the second power circuit stops injecting harmonic disturbance voltage into the SVG under test.

[0010] Preferably, the protection module filters out the center frequency of the power frequency. Its bandwidth is:

[0011] in These are quality parameters, calculated from the inherent parameters of the protection module.

[0012] Preferably, the specific steps of step S4 are as follows: The data logging and analysis instrument records the instantaneous values ​​of three-phase voltage and current on the grid side and at the terminal of the SVG under test, and analyzes the phase frequency and amplitude frequency characteristics based on the instantaneous values ​​of three-phase voltage and current; If the phase frequency and amplitude frequency characteristics are not smooth or have not been calculated, then increase the harmonic disturbance voltage amplitude in step S2. The phase frequency characteristics are used to determine whether there is negative damping. If there is negative damping, the output phase frequency characteristics are unqualified.

[0013] Preferably, the specific steps of step S5 are as follows: When the phase frequency characteristics are qualified, the impedance of the power grid system is obtained based on the monthly operation mode data of the dispatching, and at the same time, a local power grid electromagnetic model is built to obtain the phase frequency and amplitude frequency characteristics of the power grid system. According to the impedance characteristic evaluation technical specifications, the Nyquist stability criterion is used to determine whether the SVG under test is stable.

[0014] Preferably, the construction of the local power grid electromagnetic model includes constructing the other SVGs, equivalent new energy units, equivalent collection lines, main transformers, transmission lines, upstream substations, and connected power stations within the new energy power station where the SVG under test is located.

[0015] Compared with the prior art, the beneficial effects of the present invention are: (1) By injecting harmonics from the secondary side of the SVG under test to analyze the impedance characteristics, the impedance characteristics of the SVG can be obtained accurately and efficiently, and the cost of the existing SVG impedance characteristics field test method can be greatly reduced, shortening the field test of about 1 month and the semi-physical simulation test of about 7 days to 2 days. (2) The impedance sweep frequency device has dual-circuit output rated voltage and harmonic voltage, which improves the control accuracy of output harmonics; the impedance sweep frequency device has the output function of being in phase with the power grid, which avoids the generation of phase difference with the power grid during the test; and it has the oscillation protection function caused by SVG during the test by using hardware to filter out power frequency components and combined with the dual protection of software harmonic current, which avoids unnecessary oscillation of the power grid. (3) Based on the field measured data and combined with the impedance characteristics of the local power grid, the Nyquist judgment was used to analyze the impact of the interaction between SVG and the power grid, which further improved the accuracy of SVG oscillation risk assessment. (4) It helps to discover potential oscillation risks in SVG, helps SVG manufacturers to understand the factors affecting oscillation such as SVG control strategies, parameters, and delays, and promotes the development and progress of SVG manufacturing; and provides accurate and reliable measured data support for the oscillation risk assessment of new energy power plants and power grids; at the same time, it helps new energy to be connected to the grid in a friendly manner and ensures the safe, stable and economical operation of the power grid. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only preferred embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a flowchart illustrating an SVG impedance sweep frequency test method based on secondary side injection signal according to the present invention. Figure 2 This is a schematic diagram of the impedance sweep frequency device used in the SVG impedance sweep frequency test method based on secondary side injection signal according to the present invention. Figure 3 The circuit diagram shows the harmonic injection module and power supply module of the SVG impedance sweep frequency test method based on secondary side injection signal according to the present invention. Figure 4 This is a circuit diagram of the protection module of an SVG impedance sweep frequency test method based on secondary side injection signal according to the present invention. Figure 5 This is a positive sequence impedance characteristic curve of an SVG field test provided in Embodiment 1 of the present invention, which is based on a secondary side injected signal for SVG impedance sweep frequency testing. Figure 6 This is an example of an impedance characteristic curve of an SVG field test interacting with the power grid, provided in Embodiment 2 of the present invention, which is based on a secondary side injected signal for SVG impedance sweep frequency testing. Figure 7This is a Nyquist curve of an SVG field test and its interaction with the power grid, provided as an embodiment 2 of the present invention of an SVG impedance sweep frequency test method based on secondary side injection signal.

[0018] In the diagram, 1. Voltage and current sampling module; 2. Harmonic injection module; 21. First power circuit; 22. Second power circuit; 23. Three-phase output terminal; 3. Protection module; 4. Power supply module. Detailed Implementation

[0019] To better understand the technical content of this invention, a specific embodiment is provided below, and the invention will be further described in conjunction with the accompanying drawings.

[0020] See Figures 1 to 4 This invention provides an SVG impedance sweep frequency test method based on secondary-side injected signals, which is implemented using an impedance sweep frequency device with secondary-side injected signals. The test method includes the following steps: Step S1: Connect the impedance sweep frequency device in series to the secondary circuit of the SVG under test to acquire the grid voltage control. The impedance sweep frequency device obtains the phase of the grid voltage and outputs the secondary voltage with the same phase. Step S2: The impedance sweep frequency device outputs a harmonic disturbance voltage containing positive sequence voltage and negative sequence voltage disturbances according to the set harmonic frequency, harmonic amplitude and harmonic duration. Step S3: Apply the harmonic disturbance voltage to the secondary voltage circuit of the SVG under test. When the impedance sweep frequency device detects that the injected harmonics cause the SVG under test to oscillate, stop injecting the harmonics. Step S4: Calculate the positive sequence impedance and negative sequence impedance based on the three-phase voltage output by the impedance sweep frequency device and the instantaneous value of the three-phase current output by the SVG under test, and evaluate whether the phase frequency characteristics of the SVG under test are qualified. Step S5: When the phase frequency characteristics are qualified, obtain the impedance of the power grid system and use the Nyquist stability criterion to determine whether the SVG under test is stable.

[0021] This invention discloses an SVG impedance sweep frequency testing method based on secondary-side injected signals. The method utilizes an impedance sweep frequency device for secondary-side injected signals. This device is connected in series in the secondary circuit of the SCG under test (SVG) controlling the acquisition of grid voltage. The device not only samples the phase and amplitude of the grid voltage but also acquires data such as the current output by the SVG under test. Simultaneously, the device outputs a secondary voltage in phase, synchronizing the device's fundamental voltage with the grid secondary voltage, thus avoiding phase differences in the test circuit and ensuring accurate superposition of harmonic disturbances onto the SVG voltage sampling circuit. Subsequently, the device outputs harmonic disturbance voltages based on preset harmonic frequencies, amplitudes, and durations, applying them to the secondary voltage circuit of the SVG under test. By analyzing the impedance characteristics through harmonic injection from the secondary side of the SVG under test, the impedance characteristics of the SVG under test can be accurately obtained, significantly reducing the cost and testing cycle of existing SVG impedance characteristic field testing methods.

[0022] During testing, if the SVG under test oscillates due to injected harmonics, the impedance sweep frequency device can be stopped to prevent the harmonic disturbance voltage from being injected, thus preventing the oscillation from amplifying and avoiding overvoltage and overcurrent damage to the SVG under test, the power station equipment, and the power grid. This ensures the safety of the test and the operation of the power grid. During normal testing, the positive-sequence impedance and negative-sequence impedance can be calculated based on the instantaneous values ​​of the three-phase voltage output by the impedance sweep frequency device and the three-phase current output by the SVG under test. Based on this, the phase frequency characteristics of the SVG under test can be evaluated to determine if they are qualified. If the phase frequency characteristics are qualified, it means that there is no negative damping in the system. After obtaining the impedance of the power grid system, the Nyquist stability criterion is used to analyze the interaction between the SVG under test and the power grid, evaluate its stability, and further improve the accuracy of the oscillation risk assessment of the SVG under test. This helps to discover potential oscillation risks of the SVG, helps SVG manufacturers clarify the factors affecting oscillation such as the SVG's control strategy, parameters, and delay, promotes the development and progress of the SVG manufacturing industry, and provides accurate and reliable measured data support for the oscillation risk assessment of new energy power stations and the power grid, facilitating the grid-friendly connection of new energy and ensuring the safe, stable, and economical operation of the power grid.

[0023] Preferably, the impedance sweep frequency device includes: Voltage and current sampling module 1 is used to sample the three-phase voltage and current of the power grid, the three-phase voltage output by the impedance sweep frequency device, and the three-phase current output by the SVG under test; Harmonic injection module 2 is used to output harmonic disturbance voltage and apply it to the secondary voltage circuit of the SVG under test; Protection module 3 is used to stop the harmonic injection module 2 from injecting harmonics when the injected harmonics cause the SVG under test to oscillate. Power supply module 4 is used to supply power to voltage and current sampling module 1, harmonic injection module 2 and protection module 3; The harmonic injection module 2 is electrically connected to the protection module 3, and the power supply module 4 is electrically connected to the voltage and current sampling module 1, the harmonic injection module 2, and the protection module 3, respectively.

[0024] Harmonic injection module 2 includes a multi-winding transformer high-voltage winding N1 and a low-voltage winding N 21 Low-voltage winding N 22 The circuit consists of rectifier M1, rectifier M2, filter capacitor C1, filter capacitor C2, first power circuit 21, second power circuit 22, and three-phase output terminal 23. The input voltage of the high-voltage winding N1 is the external AC power supply (220V) of the impedance sweep frequency device. The low-voltage winding N... 21 Low-voltage winding N 22 Located on the high-voltage winding N1 side, the low-voltage winding N 21 The rectifier M1, filter capacitor C1, and first power circuit 21 are connected in sequence, and the low-voltage winding N... 22 The rectifier M2, filter capacitor C2 and the second power circuit 22 are connected in sequence. The first power circuit 21 outputs the rated fundamental voltage of the power frequency to the SVG under test, and the second power circuit 22 outputs the harmonic disturbance voltage to the SVG under test. The first power circuit 21 and the second power circuit 22 are respectively connected to the three-phase output terminal 23.

[0025] The AC sides of the first power circuit 21 and the second power circuit 22 are both connected to the secondary side voltage of the SVG under test. The first power circuit 21 and the second power circuit 22 can output the rated fundamental voltage and harmonic disturbance voltage to the SCG under test respectively, so that the harmonic disturbance voltage is directly applied to the secondary circuit loop of the SVG under test, thereby improving the control accuracy of the harmonic output.

[0026] Specifically, the first power circuit 21 is driven by a fully controlled voltage-driven device M. A1 M A2 M B1 M B2 M C1 M C2 The second power circuit 22 is composed of a fully controlled voltage-driven device M. A3 M A4 M B3 M B4 M C3 M C4 Composition, low-voltage winding N 21 Connected to the input terminal of rectifier M1, the positive terminal of rectifier M1 is connected to the positive terminal of filter capacitor C1 and the fully controlled voltage driver M. A1 M B1 M C1 The collector is connected, and the fully controlled voltage-driven device MA1 M B1 M C1 The emitters are respectively connected to the fully controlled voltage driver M A2 M B2 M C2 Collector-connected, fully controllable voltage-driven device M A1 M B1 M C2 The emitter is also connected to the three-phase output terminals 23 of ABC respectively. The positive terminal of the rectifier M1 output is connected to the negative terminal of the filter capacitor C1 and the fully controlled voltage driver M. A2 M B2 M C2 The emitter is connected; the low-voltage winding N 22 Connected to the input terminal of rectifier M2, the positive terminal of rectifier M2 output is connected to the positive terminal of filter capacitor C2 and the fully controlled voltage driver M. A3 M B3 M C3 The collector is connected, and the fully controlled voltage-driven device M A3 M B3 M C3 The emitters are respectively connected to the fully controlled voltage driver M A4 M B4 M C4 Collector-connected, fully controllable voltage-driven device M A3 M B3 M C3 The emitter is also connected to the three-phase output terminals 23 of ABC respectively. The positive terminal of the rectifier M2 output is connected to the negative terminal of the filter capacitor C2 and the fully controlled voltage driver M. A4 M B4 M C4 The emitters are connected.

[0027] Power supply module 4 specifically includes hardware protection circuits and software protection. The composition and principle of the hardware protection circuit are as follows: The low-voltage winding N of a multi-winding transformer 23 The transformer consists of rectifier M3, voltage regulator chip LM7812, voltage regulator chip LM7805, capacitors C3, C4, C5, C6, etc., and the low-voltage winding N of the winding transformer. 23The circuit is connected to the AC input terminal of rectifier M3. The positive output terminal of rectifier M3 is connected to the positive terminals of capacitors C3 and C5, and the input terminals of voltage regulator chips LM7812 and LM7805. The output of voltage regulator chip LM7812 is connected to the positive terminal of capacitor C4 and the positive output voltage U3 terminal. The output terminal of voltage regulator chip LM7805 is connected to the positive terminal of capacitor C6 and the positive output voltage U2 terminal. The negative terminals of capacitors C3, C4, C5, and C6, the ground pin of voltage regulator chip LM7812, and the ground pin of the voltage regulator chip are grounded. The voltage U2 is 5V and the voltage U3 is 12V. It is mainly used to power the voltage and current sampling module 1, harmonic injection module 2, protection module 3, etc.

[0028] Protection module 3 specifically includes resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, and R1. 10 It consists of capacitors C7 and C8, operational amplifiers Q1, Q2, Q3, and Q4, etc., and its input terminal V in One end of resistor R1 is connected to the non-inverting input of transport amplifier Q1, and the other end of resistor R1 is connected to one end of resistors R2 and R4. The other end of resistor R2 is grounded. The inverting input of transport amplifier Q1 is connected to one end of resistors R3 and R7, and the output of transport amplifier Q1 is connected to one end of resistors R3, R5, and R6. The inverting input of transport amplifier Q2 is connected to one end of resistor R5 and capacitor C7, and the non-inverting input of transport amplifier Q2 is connected to the non-inverting inputs of transport amplifiers Q3 and Q4 and grounded. The output of transport amplifier Q2 is connected to resistors R4, R8, and capacitor C7. The inverting input of transport amplifier Q3 is connected to one end of resistor R8 and capacitor C8, and the output of transport amplifier Q3 is connected to one end of resistors R7, R9, and capacitor C8. The inverting input of transport amplifier Q4 is connected to resistors R6, R9, and R7. 10 Connected, the output of transport amplifier Q4 is connected to resistor R 10 Output terminal V out Connect them, where appropriate resistors R1, R2, R3, R4, R5, R6, R7, R8, R9, and R are selected. 10 Capacitors C7 and C8 are used to connect the input terminal V. in The AC voltage filters out the 50Hz power frequency, leaving only harmonic components, i.e., the output voltage V. out .

[0029] Preferably, in step S1, after the impedance sweep frequency device is connected in series to the secondary circuit of the SVG under test for acquiring grid voltage control, the impedance sweep frequency device acquires the amplitude and phase of the grid secondary voltage, and the first power circuit 21 outputs a secondary voltage with the same amplitude and phase.

[0030] By outputting a secondary voltage with the same amplitude and phase through the first power circuit 21, phase difference can be avoided in the test circuit, ensuring that harmonic disturbances are accurately superimposed on the SVG voltage sampling circuit.

[0031] Preferably, the specific steps of step S2 are as follows: The harmonic sweep frequency is set in three stages: 1~100Hz, 110~1000Hz, and 1000~2500Hz. The frequency interval, harmonic amplitude, and harmonic duration are set separately for different stages; The impedance sweep frequency device outputs harmonic disturbance voltage according to the set frequency interval, harmonic amplitude, and harmonic duration.

[0032] The specific settings for frequency interval, harmonic amplitude, and harmonic duration are as follows: The frequency intervals from 1 to 100 Hz are 1 Hz, the harmonic amplitude is 0.2% to 0.5%, and the harmonic duration is 2 to 10 s; the frequency intervals from 110 to 1000 Hz are 10 Hz, the harmonic amplitude is 0.5% to 2%, and the harmonic duration is 2 to 10 s; the frequency intervals from 1000 to 2500 Hz are 100 Hz, the harmonic amplitude is 0.5% to 2%, and the harmonic duration is 2 to 10 s.

[0033] Preferably, the specific steps for stopping the injection of harmonics in step S3 are as follows: The protection module 3 receives the instantaneous values ​​of the ABC three-phase voltages output from the three-phase output terminal 23, filters out the 50Hz power frequency, and outputs harmonic components. When the harmonic components exceed a set value, the second power circuit 22 stops injecting harmonic disturbance voltage into the SVG under test. The protection module 3 filters out the center frequency of the power frequency. ,in For feedback resistor, ,capacitance The bandwidth of protection module 3 is:

[0034] in For quality parameters, .

[0035] The input to protection module 3 comes from the instantaneous values ​​of the three-phase voltages (A, B, C) output from harmonic injection module 2. When the harmonics in the three-phase voltages exceed a set value, i.e., the output V... outIf the value exceeds the set value, the second power circuit 22 in the harmonic injection module 2 will stop injecting harmonics to provide protection. The software principle of the protection module 3 is as follows: the voltage and current sampling module 1 samples the three-phase current output by the SVG. If the instantaneous value of the three-phase current exceeds the threshold or the harmonic content of the three-phase current exceeds the set value, the second power circuit 22 in the harmonic injection module 2 will stop injecting harmonics, and the output of the first power circuit 21 will not be affected.

[0036] The software protection collects three-phase current data from the SVG output via voltage and current sampling module 1. The collected real-time data is then sent to the processor for processing and calculation. The processor determines whether the instantaneous value of the three-phase current exceeds a preset threshold and whether the harmonic content of the three-phase current exceeds a set value. If either condition is met, the processor immediately sends a stop command to the harmonic injection module 2, controlling the second power circuit 22 in the harmonic injection module 2 to stop injecting harmonics. The first power circuit 21 remains unaffected, thus completing software-level overcurrent and harmonic over-limit protection, preventing excessive harmonic injection during testing from adversely affecting the SVG or the power grid. Simultaneously, the software records the three-phase current data and harmonic content values ​​at the time of abnormal triggering, storing them in a local cache for easy tracing during subsequent testing. Furthermore, the software includes an emergency stop hardware interrupt. If a sudden abnormality occurs during testing and the operator triggers the emergency stop button, the software will prioritize the interrupt command, immediately cutting off the second power circuit 22 of the harmonic injection module 2 to ensure the safety of the testing equipment and the site.

[0037] Preferably, the specific steps of step S4 are as follows: The data logging and analysis instrument records the instantaneous values ​​of three-phase voltage and current on the grid side and at the terminal of the SVG under test, and analyzes the phase frequency and amplitude frequency characteristics based on the instantaneous values ​​of three-phase voltage and current; If the phase frequency and amplitude frequency characteristics are not smooth or have not been calculated, then increase the harmonic disturbance voltage amplitude in step S2. The phase frequency characteristics are used to determine whether there is negative damping. If there is negative damping, the output phase frequency characteristics are unqualified.

[0038] If the positive and negative sequence phase frequency characteristics of the SVG under test are within the range of -90° to +90° in the frequency bands of 1Hz to 40Hz and 60Hz to 2500Hz respectively, then the phase frequency characteristics of the SVG under test are deemed to be qualified. Otherwise, it is determined to have negative damping. When there is negative damping, the control strategy or parameters of the SVG under test need to be further optimized.

[0039] Preferably, the specific steps of step S5 are as follows: When the phase frequency characteristics are qualified, the impedance of the power grid system is obtained based on the monthly operation mode data of the dispatching. At the same time, a local power grid electromagnetic model is built, including the other SVGs, equivalent new energy units, equivalent collection lines, main transformers, transmission lines, the next-level substation and the connected stations within the new energy power station where the SVG under test is located, to obtain the phase frequency and amplitude frequency characteristics of the power grid system. According to the impedance characteristic evaluation technical specifications such as NB / T 10651-2021 and NB / T 11344-2023, the Nyquist stability criterion is used to determine whether the SVG under test is stable.

[0040] To further verify the method of the present invention, the present invention provides the following example: Example 1: An impedance sweep frequency device for injecting signals into the secondary side is connected in series to the secondary circuit of the SVG for acquiring grid voltage control. The impedance sweep frequency device acquires the phase of the grid voltage and outputs a secondary voltage in phase. The impedance sweep frequency device outputs a positive-sequence voltage disturbance according to the set harmonic frequency, harmonic amplitude, and harmonic duration (1~10Hz, step size 1Hz, harmonic amplitude 0.5%, harmonic duration 10s; 11~100Hz, step size 1Hz, harmonic amplitude 1%, harmonic duration 10s; 110~1250Hz, step size 10Hz, harmonic amplitude 2%, harmonic duration 10s). Based on the three-phase voltage output by the impedance sweep frequency device and the instantaneous three-phase current output by the SVG, the positive-sequence impedance is calculated using FFT decomposition, such as... Figure 5 As shown, the phase of the positive sequence impedance phase frequency characteristic from 1Hz to 40Hz and from 60Hz to 1250Hz is not uniformly within -90° to +90°. Therefore, the positive sequence impedance phase frequency characteristic of the photovoltaic power station reactive power compensation device (SVG) is unqualified.

[0041] Example 2: An impedance sweep frequency device for injecting signals into the secondary side is connected in series to the secondary circuit of the SVG for acquiring grid voltage control. The impedance sweep frequency device acquires the phase of the grid voltage and outputs a secondary voltage in phase. The impedance sweep frequency device outputs a positive-sequence voltage disturbance according to the set harmonic frequency, harmonic amplitude, and harmonic duration (1~10Hz, step size 1Hz, harmonic amplitude 0.5%, harmonic duration 10s; 11~100Hz, step size 1Hz, harmonic amplitude 1%, harmonic duration 10s; 110~1250Hz, step size 10Hz, harmonic amplitude 2%, harmonic duration 10s). Based on the three-phase voltage output by the sweep frequency device and the instantaneous three-phase current output by the SVG, the positive-sequence impedance is calculated using FFT decomposition, such as... Figure 6 As shown, the phase of the positive sequence impedance phase frequency characteristic from 1Hz to 40Hz and from 60Hz to 1250Hz is within -90° to +90°. Therefore, the positive sequence impedance phase frequency characteristic of the photovoltaic power station reactive power compensation device (SVG) is qualified.

[0042] Based on the system impedance of the power grid operation mode, a local power grid electromagnetic model is constructed to obtain the power grid impedance characteristics. The impedance ratio between the power grid and the SVG is calculated, and the Nyquist stability criterion is used to determine whether the SVG is stable. Figure 7 As shown, SVG is stable and there is no risk of wideband oscillation.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for SVG impedance sweep frequency testing based on secondary-side injected signals, characterized in that, The test is achieved using an impedance sweep frequency device with secondary-side injected signals, and the test method includes the following steps: Step S1: Connect the impedance sweep frequency device in series to the secondary circuit of the SVG under test to acquire the grid voltage control. The impedance sweep frequency device obtains the phase of the grid voltage and outputs the secondary voltage with the same phase. Step S2: The impedance sweep frequency device outputs a harmonic disturbance voltage containing positive sequence voltage and negative sequence voltage disturbances according to the set harmonic frequency, harmonic amplitude and harmonic duration. Step S3: Apply the harmonic disturbance voltage to the secondary voltage circuit of the SVG under test. When the impedance sweep frequency device detects that the injected harmonics cause the SVG under test to oscillate, stop injecting the harmonics. Step S4: Calculate the positive sequence impedance and negative sequence impedance based on the three-phase voltage output by the impedance sweep frequency device and the instantaneous value of the three-phase current output by the SVG under test, and evaluate whether the phase frequency characteristics of the SVG under test are qualified. Step S5: When the phase frequency characteristics are qualified, obtain the impedance of the power grid system and use the Nyquist stability criterion to determine whether the SVG under test is stable.

2. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 1, characterized in that, The impedance sweep frequency device includes: The voltage and current sampling module is used to sample the three-phase voltage and current of the power grid, the three-phase voltage output by the impedance sweep frequency device, and the three-phase current output by the SVG under test. The harmonic injection module is used to output harmonic disturbance voltage and apply it to the secondary voltage circuit of the SVG under test. The protection module is used to stop the harmonic injection module from injecting harmonics when the injected harmonics cause oscillations in the SVG under test. The power supply module is used to supply power to the voltage and current sampling module, the harmonic injection module, and the protection module. The harmonic injection module is electrically connected to the protection module, and the power supply module is electrically connected to the voltage and current sampling module, the harmonic injection module, and the protection module, respectively.

3. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 2, characterized in that, The harmonic injection module includes a first power circuit, a second power circuit, and a three-phase output terminal. The first power circuit outputs the rated fundamental voltage at the power frequency to the SVG under test, and the second power circuit outputs the harmonic disturbance voltage to the SVG under test. The first power circuit and the second power circuit are electrically connected to the three-phase output terminal, respectively.

4. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 3, characterized in that, In step S1, after the impedance sweep frequency device is connected in series to the secondary circuit of the SVG under test for collecting grid voltage control, the impedance sweep frequency device collects the amplitude and phase of the grid secondary voltage, and the first power circuit outputs a secondary voltage with the same amplitude and phase.

5. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 1, characterized in that, The specific steps of step S2 are as follows: The harmonic sweep frequency is set in three stages: 1~100Hz, 110~1000Hz, and 1000~2500Hz. The frequency interval, harmonic amplitude, and harmonic duration are set separately for different stages; The impedance sweep frequency device outputs harmonic disturbance voltage according to the set frequency interval, harmonic amplitude, and harmonic duration.

6. The SVG impedance sweep frequency test method based on secondary side injection signal according to claim 3, characterized in that, The specific steps for stopping the injection of harmonics in step S3 are as follows: The protection module receives the instantaneous values ​​of the three-phase voltage (A, B, and C) from the three-phase output terminal, filters out the 50Hz power frequency, and outputs the harmonic components. When the harmonic components are greater than the set value, the second power circuit stops injecting harmonic disturbance voltage into the SVG under test.

7. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 6, characterized in that, The protection module filters out the center frequency of the power frequency. Its bandwidth is: in These are quality parameters, calculated from the inherent parameters of the protection module.

8. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 1, characterized in that, The specific steps of step S4 are as follows: The data logging and analysis instrument records the instantaneous values ​​of three-phase voltage and current on the grid side and at the terminal of the SVG under test, and analyzes the phase frequency and amplitude frequency characteristics based on the instantaneous values ​​of three-phase voltage and current; If the phase frequency and amplitude frequency characteristics are not smooth or have not been calculated, then increase the harmonic disturbance voltage amplitude in step S2. The phase frequency characteristics are used to determine whether there is negative damping. If there is negative damping, the output phase frequency characteristics are unqualified.

9. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 1, characterized in that, The specific steps of step S5 are as follows: When the phase frequency characteristics are qualified, the impedance of the power grid system is obtained based on the monthly operation mode data of the dispatching, and at the same time, a local power grid electromagnetic model is built to obtain the phase frequency and amplitude frequency characteristics of the power grid system. According to the impedance characteristic evaluation technical specifications, the Nyquist stability criterion is used to determine whether the SVG under test is stable.

10. The SVG impedance sweep frequency test method based on secondary side injected signal according to claim 9, characterized in that, The construction of the local power grid electromagnetic model includes constructing the other SVGs, equivalent new energy units, equivalent collection lines, main transformers, transmission lines, upstream substations, and connected power stations within the new energy power station where the SVG under test is located.

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