A method for extracting inter-harmonic clusters based on double synchronous rotating coordinate system

Abstract

A kind of interharmonic cluster extraction method based on double synchronous rotating coordinate system, comprising: (1) sampling the measured data of arc furnace three-phase voltage and current signal;(2) the three-phase voltage signal is handled by phase-locked loop, and three-phase voltage frequency, phase ω t ; (3) the three-phase current signal is transformed with phase ω t , positive and negative sequence dq of fundamental wave, and the direct current component and low-frequency component and high-frequency component of dq axis are obtained;(4) the direct current component and low-frequency component of dq axis are obtained by low-pass filter;(5) interharmonic component cluster is reproduced by dq inverse transformation and superimposing positive and negative sequence components.The method is simple, accurate, fast, and the cut-off frequency of low-pass filter is higher, and the delay is small.

Description

Technical Field

[0001] This invention relates to an interharmonic extraction method, specifically to an interharmonic cluster extraction method based on a dual synchronous rotating coordinate system. Background Technology

[0002] AC arc furnaces are rapidly fluctuating, nonlinear, high-power loads that inject time-varying harmonics and interharmonics into the power grid, generating harmonic and interharmonic voltage components, thus causing flickering at the point of common coupling (PCC). Due to the nonlinear and stochastic nature of arc furnace operation, it is necessary to quickly and accurately determine the spectral content of the arc furnace current in order to develop reactive power compensation and harmonic and interharmonic mitigation techniques using new power converter technologies, such as Static Synchronous Compensators (STATCOMs) and Active Power Filters (APFs). Analyzing the harmonics and interharmonics of such intermittent loads is a hot research topic in the field of power systems.

[0003] While not as popular as harmonic analysis, various methods have been proposed since the early 1990s for interharmonic analysis. Because no recommended interharmonic limits were available in any standard prior to the announcement of new limits for interharmonic voltages in July 2014, interharmonic analysis received far less attention in regulations compared to harmonic analysis. However, given the known intertwining relationship between interharmonics and flicker, power quality (PQ) analysis for electric arc furnace (EAF) power plants should consider interharmonics, which are typically present in the low-frequency currents of EAFs.

[0004] Currently, the main methods for analyzing interharmonics are as follows:

[0005] (1) Fourier transform is often used instead of Fourier series for interharmonic analysis in power systems. However, as is well known, Fourier transform requires special attention to reduce spectral leakage in the actual case of frequency oscillation in power systems, and in most cases, it is not easy to reduce the interharmonic calculation error to a negligible rate.

[0006] (2) The use of time-domain averaging and differential filters can be used for harmonic and interharmonic detection within the framework of IEC standards to improve the accuracy of interharmonic calculation. However, the purpose of this work is not to calculate the amplitude and phase of each interharmonic.

[0007] (3) Adaptive notch filters are used to selectively decompose harmonics and interharmonics. However, in waveforms with fast-fluctuating harmonic and interharmonic content and comparable positive and negative sequence amplitudes, such as AC arc furnaces, such filters cannot provide a fast enough response.

[0008] (4) In recent years, the method based on multiple synchronous reference frames (MSRF) has become popular because MSRF provides time-domain waveforms for each harmonic and interharmonic frequency. However, in this analysis method, the low-pass filter limits the processing time. Using the multi-synchronous rotation method to extract each interharmonic component separately, and accurately extracting N interharmonic components, requires 2N dq transformations and inverse transformations. The cutoff frequency of the low-pass filter will be very low, resulting in a heavy computational burden and large delay in the system.

[0009] Therefore, there is an urgent need to find a simple, accurate, fast, low-pass filter cutoff frequency with small delay method based on a dual synchronous rotating coordinate system for interharmonic cluster extraction. Summary of the Invention

[0010] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a simple, accurate and fast method for interharmonic cluster extraction based on a dual synchronous rotating coordinate system, which can accurately and quickly track the original signal, has no large phase deviation, a high low-pass filter cutoff frequency, and small delay.

[0011] The technical solution adopted by this invention to solve its technical problem is as follows: A method for interharmonic cluster extraction based on a dual synchronous rotating coordinate system, comprising the following steps:

[0012] (1) Sample the measured data of the three-phase voltage and current signals of the electric arc furnace;

[0013] (2) Process the three-phase voltage signal obtained in step (1) using a phase-locked loop to obtain the corresponding three-phase voltage frequency and phase ωt;

[0014] (3) The three-phase current signal obtained in step (1) is transformed into the fundamental positive and negative sequence dq transformations with the phase ωt obtained in step (2) to obtain the dq axis DC component, dq axis low frequency component and dq axis high frequency component of the fundamental positive and negative sequence dq transformations.

[0015] (4) Pass the results of the fundamental positive and negative sequence dq transformations obtained in step (3) through a low-pass filter to obtain the fundamental positive and negative sequence dq transformations of the DC component and the low-frequency component of the dq axis.

[0016] (5) The DC component of the dq axis and the low-frequency component of the dq axis obtained by the positive and negative sequence dq transformation of the fundamental wave obtained in step (4) are transformed by dq inverse transformation, and the positive and negative sequence components are superimposed to obtain the clustered reproduction of the interharmonic components.

[0017] The inventive idea of ​​this invention is to propose an interharmonic cluster extraction scheme based on the positive and negative sequence transformation of the fundamental frequency, taking into account the characteristic that the interharmonic frequencies of the system are concentrated near the fundamental frequency (preferably 50Hz).

[0018] Preferably, in step (2), the process of the phase-locked loop is as follows: the three-phase voltage signal is input into the phase-locked loop control loop, and the frequency and phase of the oscillation signal inside the loop are controlled by the three-phase voltage signal to realize the automatic tracking of the frequency of the output signal to the frequency of the input signal. When the frequency of the output signal is equal to the frequency of the input signal, the output voltage and the input voltage maintain a fixed phase difference, that is, the phase of the output voltage and the input voltage are locked. The phase of the output voltage is the phase of the three-phase voltage signal. In Simulink, the three-phase voltage signal can be output through the three-phase PLL module to output its phase ωt.

[0019] In step (3), since the interharmonic components concentrated around 50Hz include both positive-sequence and negative-sequence components, and the results of dq transformation of positive and negative-sequence components are different, dq transformation is performed separately.

[0020] Preferably, in step (3), after the fundamental positive sequence dq transformation, the DC component of the dq axis corresponds to the fundamental positive sequence component, and the low-frequency component of the dq axis corresponds to the positive and negative sequence components of the interharmonic.

[0021] Preferably, the positive sequence component of the interharmonic is the positive sequence component of the interharmonic at a frequency near the fundamental frequency.

[0022] Preferably, the positive sequence component of the interharmonic is f0~(f0+f)Hz.

[0023] Preferably, the negative sequence component of the interharmonic is the negative sequence component of the interharmonic at a frequency near the fundamental frequency.

[0024] Preferably, the negative sequence component of the interharmonic is (f0-f)~f0Hz.

[0025] Preferably, f0 is the fundamental frequency value, and f = 20~30Hz.

[0026] Preferably, in step (3), after the fundamental negative sequence dq transformation, the DC component of the dq axis corresponds to the fundamental negative sequence component, and the low-frequency component of the dq axis corresponds to the negative sequence component and positive sequence component of the interharmonic.

[0027] Preferably, the negative sequence component of the interharmonic is the negative sequence component of the interharmonic at a frequency near the fundamental frequency.

[0028] Preferably, the negative sequence component of the interharmonic is f0~(f0+f)Hz.

[0029] Preferably, the positive sequence component of the interharmonic is the positive sequence component of the interharmonic at a frequency near the fundamental frequency.

[0030] Preferably, the positive sequence component of the interharmonic is (f0-f)~f0Hz.

[0031] Preferably, f0 is the fundamental frequency value, and f = 20~30Hz.

[0032] In step (3), since the interharmonic components are concentrated in the frequency range near the fundamental frequency (preferably 50Hz), the components corresponding to the (f0±f)Hz frequency range (f0-f) to (f0+f)Hz on the dq axis are selected for focus. The interharmonic components in the (f0-f) to (f0+f)Hz range are extracted in a cluster. Compared with the existing method of extracting each interharmonic component individually by performing a dq transformation on the frequency corresponding to each interharmonic component, so that the target component corresponds to the DC component on the dq axis, and the low-pass filter added to the dq axis only passes through the DC component, resulting in a very low cutoff frequency, the low-pass filter in the cluster extraction method of the present invention has a relatively high cutoff frequency, thus the delay is also smaller.

[0033] Preferably, in step (3), the angular frequency is ω k The transformation process of the three-phase positive sequence components in a synchronous rotating coordinate system with the corresponding angular frequency ω is as follows:

[0034]

[0035] angular frequency is ω k The transformation process of the three-phase negative sequence components in the synchronous rotating coordinate system with the corresponding angular frequency ω is as follows:

[0036]

[0037]

[0038] Among them, i a+ i b+ i c+ The angular frequency of the three-phase current signal is ω k The positive-order component of the component, I m For the peak value of the three-phase current, ω k Corresponding to the angular frequencies of each component in the three-phase current signal in step (3), t is time, θ is the initial phase, and T abc / dq This is the transformation matrix for converting a three-phase signal to the dq axis, where ω is the fundamental angular frequency, and i d i q The current signals on the d and q axes are the three-phase current signals after dq transformation, i a- i b- i c- The angular frequency of the three-phase current signal is ω k The negative-order component of the component;

[0039] Similarly, the angular frequency is ω kThe transformation process of the three-phase positive and negative sequence components in a synchronous rotating coordinate system rotating in the direction of corresponding angular frequency -ω differs from the above process in that ω is replaced with -ω.

[0040] Preferably, in step (4), the cutoff frequency f of the low-pass filter is set to 20-30Hz, and its frequency domain transfer function is: H(s)=(2π×f) / (s+2π×f), where H(s) represents the frequency domain transfer function in the s-domain. The result after dq transformation can be passed through a low-pass filter with a cutoff frequency of fHz to extract the target components of (f0-f)~(f0+f)Hz. Since the interharmonic components are concentrated in the frequency range near the fundamental frequency, the components in the frequency range of (f0±f)Hz, that is, (f0-f)~(f0+f)Hz, are selected for focus, which corresponds to the low-frequency components within fHz on the dq axis. If a wider range of interharmonics is to be extracted, the cutoff frequency of the low-pass filter can be designed as needed.

[0041] Preferably, in step (5), the method of the dq inverse transform is: to transform the i after passing through the low-pass filter d i q Multiply by T abc / dq The inverse matrix is ​​obtained, which yields the corresponding three-phase current signal. This enables the inverse transformation from the dq axis to the three-phase coordinate system. Then, in Simulink, the signals output by the d and q axis low-pass filters after the positive and negative sequence dq transformations can be transformed inversely using the dq to abc module.

[0042] Preferably, in step (5), the superposition method is to superimpose the positive and negative dq inverse transformation results through the Add module in Simulink simulation.

[0043] Preferably, when reactive power compensation is required, the DC component of the dq axis of the fundamental positive and negative sequence dq transformation obtained in step (4) and the q axis component of the low frequency component of the dq axis are superimposed to obtain the interharmonic reactive power compensation command corresponding to the component.

[0044] Preferably, the superposition method is to superimpose the signals output by the q-axis low-pass filters after positive and negative dq transformations using the Add module in Simulink simulation.

[0045] Preferably, the low-frequency component is ≤ f.

[0046] Preferably, the final result is the interharmonic reactive power compensation command corresponding to the (f0-f) to (f0+f) Hz components.

[0047] Preferably, f0 is the fundamental frequency value, and f = 20~30Hz.

[0048] Preferably, in steps (3) to (5), the low-frequency component is ≤ f.

[0049] Preferably, in steps (3) and (4), the high-frequency component is greater than f.

[0050] Preferably, in step (5), the positive and negative sequence components of (f0-f) to (f0+f)Hz are superimposed.

[0051] Preferably, in step (5), the final result is a clustered reproduction of harmonic components between (f0-f) and (f0+f) Hz.

[0052] Preferably, f0 is the fundamental frequency value, and f = 20~30Hz.

[0053] The beneficial effects of the method of the present invention are: the method of the present invention is simple to implement, can accurately and quickly track the original signal, has no large phase deviation, and has a high low-pass filter cutoff frequency and small delay. Attached Figure Description

[0054] Figure 1 This is a Simulink simulation block diagram of sampling the measured data in steps (1) and (2) of the present invention.

[0055] Figure 2 This is a Simulink simulation block diagram of steps (3) to (5) of the present invention for clustered extraction of the fundamental frequency (50Hz) and the frequencies near the fundamental frequency (25-50Hz and 50-75Hz);

[0056] Figure 3 This is a simulation result diagram of the original signal and the clustered extraction of the fundamental frequency (50Hz) and the frequencies near the fundamental frequency (25-50Hz and 50-75Hz) of the signal in steps (3) to (5) of the embodiment of the present invention;

[0057] Figure 4 This is a comparison diagram of the spectrum of the original signal and the frequency spectrum of the signal after cluster extraction in steps (3) to (5) of the present invention, which extracts the fundamental frequency (50Hz) and the frequencies near the fundamental frequency (25-50Hz and 50-75Hz).

[0058] Figure 5 This is a Simulink simulation block diagram of the embodiment of the present invention for obtaining the harmonic reactive power compensation command between the fundamental frequency (50Hz) and the frequencies near the fundamental frequency (25-50Hz and 50-75Hz).

[0059] Figure 6 This is a simulation result diagram of obtaining the harmonic reactive power compensation command between the fundamental frequency and the frequencies near the fundamental frequency (25-50Hz and 50-75Hz) in an embodiment of the present invention. Detailed Implementation

[0060] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0061] An embodiment of an interharmonic cluster extraction method based on a dual synchronous rotating coordinate system:

[0062] The Simulink simulation block diagram in Matlab software for steps (1) and (2) is as follows: Figure 1 As shown:

[0063] (1) Sample the measured data of the three-phase voltage Vabc and current signal Iabc of the electric arc furnace, i.e., the var module in the Simulink model;

[0064] (2) The three-phase voltage signal Vabc obtained in step (1) is processed by a phase-locked loop to obtain its corresponding three-phase voltage frequency f1 and phase ωt;

[0065] The process of the phase-locked loop (PLL) is as follows: the three-phase voltage signal is input into the PLL control loop, and the frequency and phase of the internal oscillation signal are controlled by the three-phase voltage signal to achieve automatic tracking of the output signal frequency to the input signal frequency. When the frequency of the output signal is equal to the frequency of the input signal, the output voltage and the input voltage maintain a fixed phase difference, that is, the phase of the output voltage and the input voltage are locked. The phase of the output voltage is the phase of the three-phase voltage signal. In Simulink, the three-phase voltage signal can be output through the three-phase PLL module to output its phase ωt.

[0066] The Simulink simulation block diagrams in Matlab software for steps (3) to (5) are as follows: Figure 2 As shown:

[0067] (3) The three-phase current signal Iabc obtained in step (1) is transformed into the positive and negative sequence dq of the fundamental wave with the phase ωt obtained in step (2) respectively, to obtain the DC component of the dq axis of the positive and negative sequence dq transformation of the fundamental wave, the low frequency component within 25Hz of the dq axis, and the high frequency component above 25Hz.

[0068] angular frequency is ω k The transformation process of the three-phase positive sequence components in a synchronous rotating coordinate system with the corresponding angular frequency ω is as follows:

[0069] After the 50Hz fundamental positive sequence dq transformation, the DC component of the dq axis corresponds to the 50Hz fundamental positive sequence component, and the low frequency component within 25Hz of the dq axis corresponds to the positive sequence component of the interharmonic within 50-75Hz and the negative sequence component of the interharmonic within 25-50Hz.

[0070] angular frequency is ω kThe transformation process of the three-phase negative sequence components in the synchronous rotating coordinate system with the corresponding angular frequency ω is as follows:

[0071]

[0072]

[0073] After the 50Hz fundamental negative sequence dq transformation, the DC component of the dq axis corresponds to the 50Hz fundamental negative sequence component, and the low frequency components within 25Hz of the dq axis correspond to the negative sequence components of the interharmonics within 50-75Hz and the positive sequence components of the interharmonics within 25-50Hz.

[0074] Among them, i a+ i b+ i c+ The angular frequency of the three-phase current signal is ω k The positive-order component of the component, I m For the peak value of the three-phase current, ω k Corresponding to the angular frequencies of each component in the three-phase current signal in step (3), t is time, θ is the initial phase, and T abc / dq This is the transformation matrix for converting a three-phase signal to the dq axis, where ω is the fundamental angular frequency, and i d i q The current signals on the d and q axes are the three-phase current signals after dq transformation, i a- i b- i c- The angular frequency of the three-phase current signal is ω k The negative-order component of the component;

[0075] Similarly, the angular frequency is ω k The transformation process of the three-phase positive and negative sequence components in a synchronous rotating coordinate system rotating in the direction of corresponding angular frequency -ω differs from the above process in that ω is replaced with -ω.

[0076] (4) The DC component of the dq axis and the low-frequency component within 25Hz of the dq axis and the high-frequency component above 25Hz of the dq axis obtained in step (3) are respectively passed through a low-pass filter to obtain the DC component of the dq axis and the low-frequency component within 25Hz of the dq axis of the fundamental positive and negative sequence dq transformation.

[0077] The cutoff frequency of the low-pass filter is set to 25Hz, and its frequency domain transfer function is: H(s)=(2π×25) / (s+2π×25), where H(s) represents the frequency domain transfer function in the s domain;

[0078] (5) The DC component of the dq axis and the low frequency component within 25Hz of the dq axis obtained by the fundamental positive and negative sequence dq transformation in step (4) are transformed by dq inverse, and the positive and negative sequence components of 25 to 75Hz are superimposed to obtain Ii, that is, the harmonic components between 25 and 75Hz are clustered and reproduced.

[0079] The method of the inverse dq transform is: to transform the i after passing through a low-pass filter d i q Multiply by T abc / dq The inverse matrix is ​​obtained, which yields the corresponding three-phase current signal. This enables the inverse transformation from the dq axis to the three-phase coordinate system. Then, in Simulink, the signals output by the d and q axis low-pass filters after the positive and negative sequence dq transformations can be transformed inversely using the dq to abc module.

[0080] The superposition method is to superimpose the positive and negative dq inverse transformation results using the Add module in Simulink simulation.

[0081] like Figure 1 The figure shown is a Simulink simulation diagram of sampling measured data in Matlab software. The measured data is loaded through the var module to obtain the three-phase voltage Vabc and current signal Iabc. The three-phase voltage signals are processed by phase-locked loop to obtain their corresponding three-phase voltage frequency f1 and phase ωt.

[0082] like Figure 3 As shown, the results of cluster extraction from the fundamental frequency and nearby frequencies of the signal indicate that the method of the present invention can track the original signal well with no large phase deviation, indicating good tracking speed.

[0083] like Figure 4 As shown, a comparison of the spectrum of the original signal and the spectrum of the signal after cluster extraction of the fundamental frequency and the frequencies near the fundamental frequency reveals that there are interharmonics near the fundamental frequency, and the tracking effect of interharmonics near the fundamental frequency is good.

[0084] In summary, the interharmonic cluster extraction method of the present invention is simple to implement; by Figure 4 Spectral comparison shows that the method of this invention can accurately track the interharmonic content contained in the original signal; Figure 3 Waveform comparison shows that there is no large phase deviation between the extracted signal and the original signal, indicating that the method of the present invention can quickly track the original signal; Figure 2The low-pass filter after the dq transform has a cutoff frequency of 25Hz. However, for the low-pass filter in the multi-synchronous rotating coordinate transformation method that only passes the DC component, its cutoff frequency needs to be slightly higher than 0Hz. The low-pass filter in the method of this invention has a significantly higher cutoff frequency. Since a lower cutoff frequency of the low-pass filter increases the delay, the method of this invention achieves a smaller delay for the low-pass filter at a higher cutoff frequency. Figure 3 Waveform comparison shows that there is no significant phase deviation between the extracted signal and the original signal. The method of this invention can quickly track the original signal with minimal delay, improving upon the shortcomings of using multi-synchronous rotating coordinate transformation to extract each interharmonic component separately, which results in heavy computational burden and large delay.

[0085] When reactive power compensation is required, the DC components of the dq axis of the fundamental positive and negative sequence dq transformations obtained in step (4) and the q-axis components of the low-frequency components within 25Hz of the dq axis are superimposed to obtain the interharmonic reactive power compensation command corresponding to the Iq component, i.e., the 25-75Hz component. The superposition method is as follows: the signals output by the q-axis low-pass filters after the positive and negative sequence dq transformations are superimposed through the Add module in the Simulink simulation. Its Simulink simulation block diagram in Matlab software is as follows. Figure 5 As shown, the low-pass filter and its preceding part and Figure 2 The process is the same.

[0086] like Figure 6 As shown, this represents the reactive component of the extracted interharmonics, derived from... Figure 3 , 4 As can be seen, the method of the present invention can extract interharmonics relatively accurately. Therefore, based on the known accuracy, the reactive component of the interharmonics can be extracted separately. If reactive power compensation is required, it can be used as a reactive power compensation command for compensation.

Claims

1. A method for interharmonic cluster extraction based on a dual synchronous rotating coordinate system, characterized in that, Includes the following steps: (1) Sample the measured data of the three-phase voltage and current signals of the electric arc furnace; (2) Process the three-phase voltage signals obtained in step (1) using a phase-locked loop to obtain the corresponding three-phase voltage frequencies and phases ω. t ; (3) The three-phase current signal obtained in step (1) is converted into the phase ω obtained in step (2). t Perform positive and negative sequence dq transformations on the fundamental wave respectively to obtain the DC component, low-frequency component, and high-frequency component of the dq axis of the positive and negative sequence dq transformations on the fundamental wave. (4) Pass the dq-axis DC component, dq-axis low-frequency component, and dq-axis high-frequency component of the fundamental positive and negative sequence dq transforms obtained in step (3) through a low-pass filter to obtain the dq-axis DC component and dq-axis low-frequency component of the fundamental positive and negative sequence dq transforms; the cutoff frequency f of the low-pass filter is set to 20-30Hz, and its frequency domain transfer function is: H(s)=(2π×f) / ( s +2π×f), where H(s) represents the frequency domain transfer function in the s domain; (5) The DC component of the dq axis and the low-frequency component of the dq axis obtained by the positive and negative sequence dq transformation of the fundamental wave obtained in step (4) are transformed by dq inverse, and the positive and negative sequence components are superimposed to obtain the clustered reproduction of the interharmonic components. In steps (3) to (5), the low-frequency component is ≤f; in steps (3) and (4), the high-frequency component is >f; in step (5), the positive and negative sequence components of (f0-f) to (f0+f) Hz are superimposed; the final result is the clustered reproduction of harmonic components between (f0-f) and (f0+f) Hz; where f0 is the fundamental frequency value and f = 20 to 30 Hz.

2. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 1, characterized in that: In step (2), the phase-locked loop (PLL) processing is as follows: the three-phase voltage signal is input into the PLL control loop, and the frequency and phase of the internal oscillation signal are controlled by the three-phase voltage signal to achieve automatic tracking of the output signal frequency to the input signal frequency. When the frequency of the output signal is equal to the frequency of the input signal, the output voltage and the input voltage maintain a fixed phase difference, that is, the phase of the output voltage and the input voltage are locked. The phase of the output voltage is the phase of the three-phase voltage signal. In Simulink, the three-phase voltage signal is output through the three-phase PLL module, and its phase ω is output. t That's all.

3. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 1 or 2, characterized in that: In step (3), after the fundamental positive-sequence dq transformation, the DC component of the dq axis corresponds to the fundamental positive-sequence component, and the low-frequency component of the dq axis corresponds to the positive-sequence and negative-sequence components of the interharmonics; the positive-sequence component of the interharmonics is the interharmonic positive-sequence component of the frequency near the fundamental wave; the positive-sequence component of the interharmonics is f0~(f0+f)Hz; the negative-sequence component of the interharmonics is the interharmonic negative-sequence component of the frequency near the fundamental wave; the negative-sequence component of the interharmonics is (f0-f)~f0Hz; where f0 is the fundamental frequency value, f=20~3 0Hz; After fundamental negative sequence dq transformation, the DC component of the dq axis corresponds to the fundamental negative sequence component, and the low-frequency component of the dq axis corresponds to the negative and positive sequence components of the interharmonics; the negative sequence component of the interharmonics is the interharmonic negative sequence component of the frequency near the fundamental wave; the negative sequence component of the interharmonics is f0~(f0+f)Hz; the positive sequence component of the interharmonics is the interharmonic positive sequence component of the frequency near the fundamental wave; the positive sequence component of the interharmonics is (f0-f)~f0Hz; where f0 is the fundamental frequency value, and f=20~30Hz.

4. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 1 or 2, characterized in that: In step (3), the angular frequency is ω k The transformation process of the three-phase positive sequence components in a synchronous rotating coordinate system with the corresponding angular frequency ω is as follows: , , ; angular frequency is ω k The transformation process of the three-phase negative sequence components in the synchronous rotating coordinate system with the corresponding angular frequency ω is as follows: , , ; in, i a+ 、i b+ 、i c+ The angular frequency of the three-phase current signal is ω k The positive-order components of the component. I m For the peak value of the three-phase current, ω k Corresponding to the angular frequencies of each component contained in the three-phase current signal in step (3), t For time, θ This is the initial phase. T abc / dq Let ω be the transformation matrix for converting a three-phase signal to the dq axis, where ω is the fundamental angular frequency. i d 、i q This refers to the d-axis and q-axis current signals obtained after dq transformation of the three-phase current signal. i a- 、i b- 、i c- The angular frequency of the three-phase current signal is ω k The negative-order component of the component; Similarly, the angular frequency is ω k The transformation process of the three-phase positive and negative sequence components in a synchronous rotating coordinate system rotating in the direction of corresponding angular frequency -ω differs from the above process in that ω is replaced with -ω.

5. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 3, characterized in that: In step (3), the angular frequency is ω k The transformation process of the three-phase positive sequence components in a synchronous rotating coordinate system with the corresponding angular frequency ω is as follows: , , ; angular frequency is ω k The transformation process of the three-phase negative sequence components in the synchronous rotating coordinate system with the corresponding angular frequency ω is as follows: , , ; in, i a+ 、i b+ 、i c+ The angular frequency of the three-phase current signal is ω k The positive-order components of the component. I m For the peak value of the three-phase current, ω k Corresponding to the angular frequencies of each component contained in the three-phase current signal in step (3), t For time, θ This is the initial phase. T abc / dq Let ω be the transformation matrix for converting a three-phase signal to the dq axis, where ω is the fundamental angular frequency. i d 、i q This refers to the d-axis and q-axis current signals obtained after dq transformation of the three-phase current signal. i a- 、i b- 、i c- The angular frequency of the three-phase current signal is ω k The negative-order component of the component; Similarly, the angular frequency is ω k The transformation process of the three-phase positive and negative sequence components in a synchronous rotating coordinate system rotating in the direction of corresponding angular frequency -ω differs from the above process in that ω is replaced with -ω.

6. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 1 or 2, characterized in that: In step (5), the method of the inverse dq transform is: to transform the dq transform after passing through a low-pass filter... i d 、i q Multiply T abc / dq The inverse matrix is ​​obtained, which yields the corresponding three-phase current signal. This enables the inverse transformation from the dq axis to the three-phase coordinate system. Then, in Simulink, the signals output by the d and q axis low-pass filters after the positive and negative sequence dq transformations are transformed by the dq to abc module to achieve the inverse dq transformation. The superposition method is to superimpose the positive and negative dq inverse transformation results using the Add module in the Simulink simulation.

7. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 3, characterized in that: In step (5), the method of the inverse dq transform is: to transform the dq transform after passing through a low-pass filter... i d 、i q Multiply T abc / dq The inverse matrix is ​​obtained, which yields the corresponding three-phase current signal. This enables the inverse transformation from the dq axis to the three-phase coordinate system. Then, in Simulink, the signals output by the d and q axis low-pass filters after the positive and negative sequence dq transformations are transformed by the dq to abc module to achieve the inverse dq transformation. The superposition method is to superimpose the positive and negative dq inverse transformation results using the Add module in the Simulink simulation.

8. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 4, characterized in that: In step (5), the method of the inverse dq transform is: to transform the dq transform after passing through a low-pass filter... i d 、i q Multiply T abc / dq The inverse matrix is ​​obtained, which yields the corresponding three-phase current signal. This enables the inverse transformation from the dq axis to the three-phase coordinate system. Then, in Simulink, the signals output by the d and q axis low-pass filters after the positive and negative sequence dq transformations are transformed by the dq to abc module to achieve the inverse dq transformation. The superposition method is to superimpose the positive and negative dq inverse transformation results using the Add module in the Simulink simulation.

9. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 1 or 2, characterized in that: When reactive power compensation is required, the DC component of the dq axis of the fundamental positive and negative sequence dq transformation and the q-axis component of the low-frequency component of the dq axis obtained in step (4) are superimposed to obtain the interharmonic reactive power compensation command corresponding to the component. The superposition method is to superimpose the signals output by the q-axis low-pass filters after the positive and negative sequence dq transformation through the Add module in Simulink simulation. The low-frequency component is ≤ f. The final result is the interharmonic reactive power compensation command corresponding to the (f0-f)~(f0+f)Hz component. Where f0 is the fundamental frequency value and f=20~30Hz.

10. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 3, characterized in that: When reactive power compensation is required, the DC component of the dq axis of the fundamental positive and negative sequence dq transformation and the q-axis component of the low-frequency component of the dq axis obtained in step (4) are superimposed to obtain the interharmonic reactive power compensation command corresponding to the component. The superposition method is to superimpose the signals output by the q-axis low-pass filters after the positive and negative sequence dq transformation through the Add module in Simulink simulation. The low-frequency component is ≤ f. The final result is the interharmonic reactive power compensation command corresponding to the (f0-f)~(f0+f)Hz component. Where f0 is the fundamental frequency value and f=20~30Hz.

11. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 4, characterized in that: When reactive power compensation is required, the DC component of the dq axis of the fundamental positive and negative sequence dq transformation and the q-axis component of the low-frequency component of the dq axis obtained in step (4) are superimposed to obtain the interharmonic reactive power compensation command corresponding to the component. The superposition method is to superimpose the signals output by the q-axis low-pass filters after the positive and negative sequence dq transformation through the Add module in Simulink simulation. The low-frequency component is ≤ f. The final result is the interharmonic reactive power compensation command corresponding to the (f0-f)~(f0+f)Hz component. Where f0 is the fundamental frequency value and f=20~30Hz.

12. The interharmonic cluster extraction method based on a dual synchronous rotating coordinate system according to claim 6, characterized in that: When reactive power compensation is required, the DC component of the dq axis of the fundamental positive and negative sequence dq transformation and the q-axis component of the low-frequency component of the dq axis obtained in step (4) are superimposed to obtain the interharmonic reactive power compensation command corresponding to the component. The superposition method is to superimpose the signals output by the q-axis low-pass filters after the positive and negative sequence dq transformation through the Add module in Simulink simulation. The low-frequency component is ≤ f. The final result is the interharmonic reactive power compensation command corresponding to the (f0-f)~(f0+f)Hz component. Where f0 is the fundamental frequency value and f=20~30Hz.

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