A method, system, storage medium, and processor for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform.

Abstract

This invention relates to the field of power system technology, and particularly to a method, system, storage medium, and processor for decomposing positive, negative, and zero-sequence components of three-phase voltage and current signals based on the Hilbert-Huang transform. Starting from the raw data of the three-phase voltage / current signals, this invention first obtains the complex signal information of the three-phase voltage / current signals through the Hilbert-Huang transform, which preserves all frequency information of the original signals to the greatest extent. Then, based on the original definition of positive and negative sequence signals, the positive, negative, and zero-sequence signal components are obtained by multiplying the complex signal vector by the positive, negative, and zero-sequence decomposition transform matrix T, ensuring the accuracy of the positive, negative, and zero-sequence decomposition. By performing the Hilbert-Huang transform on the three-phase voltage and current signals, effective decomposition of positive, negative, and zero-sequence components can be achieved. This invention not only improves the ability to identify fault signals but also provides accurate data support for the stable control of power electronic equipment.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method, system, storage medium, and processor for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform. Background Technology

[0002] Against the backdrop of increasingly prominent global "dual-carbon" goals, promoting energy structure transformation and the widespread application of renewable energy has become an important strategy for all countries. As the core of energy conversion and transmission, the safe, stable, and efficient operation of the power system directly affects the integration and utilization of renewable energy. With the rapid development of power electronics technology, more and more power electronic devices are being introduced into power systems, such as frequency converters, flexible DC transmission equipment, and power quality control devices. These devices not only improve the flexibility and controllability of the power system but also enable dynamic management of power quality, thus providing strong support for promoting a high proportion of renewable energy grid connection. However, the control requirements of power electronic devices in the power system are also constantly increasing. To achieve efficient and stable control, it is necessary to monitor and analyze various operating states of the power system in real time. Especially in the event of a power system fault, the control strategy needs to be able to respond quickly to ensure the stability and safety of the system. Therefore, the accurate analysis and processing of voltage and current signals in the power system is particularly important.

[0003] In power systems, asymmetrical faults such as single-phase short circuits are common. These faults not only affect the normal operation of the power system but also pose a potential threat to equipment safety. During the fault occurrence and recovery process, asymmetrical voltage and current appear in the system. This asymmetry challenges traditional signal processing methods because they typically cannot accurately distinguish and extract the positive-sequence and negative-sequence components of the signal. To achieve stable control of power electronic equipment, it is essential to accurately extract the positive-sequence and negative-sequence signals from the three-phase voltage and current signals. The positive-sequence signal reflects the characteristics of the power system under normal operating conditions, while the negative-sequence signal characterizes the impact of asymmetrical faults on the system.

[0004] In existing technologies, positive and negative zero-sequence decomposition is mostly based on phase-locked loops and filters, using low-pass filters to obtain the positive and negative dq-axis component signals. However, in actual three-phase signals, the positive and negative sequence components are coupled together, and low-pass filters often cannot accurately obtain the positive and negative sequence components. Moreover, the phase delay of low-pass filters further increases the measurement error. Summary of the Invention

[0005] To address the problems in existing technologies, this invention provides a method, system, storage medium, and processor for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on the Hilbert-Huang transform. The Hilbert-Huang transform is a powerful signal processing tool capable of effectively separating different frequency components in a signal and providing information about the instantaneous frequency and envelope of the signal. The specific technical solution is as follows:

[0006] A method for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform includes the following steps: Step S1, acquiring the three-phase voltage / current measurement signals v at the grid connection point of power electronic equipment. a v b v c , where v a For phase A voltage / current measurement signal, v b For phase B voltage / current measurement signal, v c This is the voltage / current measurement signal for phase C;

[0007] Step S2, measure the three-phase voltage / current signal v a v b v c Perform Hilbert-Huang transforms on each phase to obtain the complex three-phase voltage / current signals V. a V b V c ;where V a The complex signal of phase A voltage / current, V b For phase B voltage / current complex signal, V c This is a complex signal representing the voltage / current of phase C.

[0008] Step S3, convert the three-phase voltage / current complex signal V a V b V c The vector is multiplied by the positive and negative zero-sequence decomposition transformation matrix T to obtain the positive-sequence voltage / current complex signal V. p Negative sequence voltage / current complex signal V n and zero-sequence voltage / current complex signal V o Step S4, for the positive sequence voltage / current complex signal V p Multiply Obtain positive sequence voltage / current complex processed signal For negative sequence voltage / current complex signals V n Multiply Obtain the complex processed signal of negative sequence voltage / current Where θ pll The synchronization phase output by the synchronization control loop in power electronic equipment;

[0009] Step S5: Process the positive sequence voltage / current complex signal. Taking the real part yields the positive-sequence d-axis voltage / current v. dp Taking the imaginary part yields the positive-sequence q-axis voltage / current v. qp Complex processing signals for negative sequence voltage / current Taking the real part yields the negative-sequence d-axis voltage / current v. dn Taking the imaginary part yields the negative-sequence q-axis voltage / current v. qn .

[0010] Preferably, the Hilbert-Huang transform performed in step S2 is as follows:

[0011] Step S21, calculate v using the Fast Fourier Transform algorithm. i frequency domain of the signal Specifically, it is expressed as follows:

[0012]

[0013] Among them, v i This represents the voltage / current measurement signal of the i-th phase, FFT(*) represents Fast Fourier Transform calculation, and v i [n] represents a set of values ​​within the fast Fourier transform time window. i The signal, where n represents the number of data points in the set, and n is an even number;

[0014] Step S22, create a... Frequency domain array of the same size make express The kth data point, express For the k-th data point:

[0015]

[0016] Step S23: Calculate the inverse Fourier transform to obtain the Hilbert transform signal.

[0017]

[0018] Where IFFT(*) represents the calculation of the inverse fast Fourier transform;

[0019] Step S24, construct the complex voltage signal V of the i-th phase. i for:

[0020]

[0021] Preferably, the calculation formula in step S3 is:

[0022]

[0023] Preferably, the positive and negative zero order decomposition transformation matrix T is as follows:

[0024]

[0025] Preferably, the calculation formula in step S4 is:

[0026]

[0027] Preferably, the synchronization control loop in step S4 is a phase-locked loop or a virtual synchronization control loop.

[0028] Preferably, the calculation formula in step S5 is:

[0029]

[0030] Where Real[*] represents the real part and Imag[*] represents the imaginary part.

[0031] A decomposition system for the positive, negative, and zero sequences of three-phase voltage and current signals based on the Hilbert-Huang transform, applied to the method described, includes:

[0032] The acquisition module is used to acquire the three-phase voltage / current measurement signals at the grid connection point of power electronic equipment. a v b v c , where v a For phase A voltage / current measurement signal, v b For phase B voltage / current measurement signal, v c This is the voltage / current measurement signal for phase C;

[0033] Hilbert-Huang transform module, used for three-phase voltage / current measurement signal v a v b v c Perform Hilbert-Huang transforms on each phase to obtain the complex three-phase voltage / current signals V. a V b V c ;where V a The complex signal of phase A voltage / current, V b For phase B voltage / current complex signal, V c This is a complex signal representing the voltage / current of phase C.

[0034] The decomposition module is used to decompose the three-phase voltage / current complex signals V a V b V c The vector is multiplied by the positive and negative zero-sequence decomposition transformation matrix T to obtain the positive-sequence voltage / current complex signal V. p Negative sequence voltage / current complex signal Vn and zero-sequence voltage / current complex signal V o ;

[0035] The first processing module is used to process the positive-sequence voltage / current complex signal V. p Multiply Obtain positive sequence voltage / current complex processed signal For negative sequence voltage / current complex signals V n Multiply Obtain the complex processed signal of negative sequence voltage / current Where θ pll The synchronization phase output by the synchronization control loop in power electronic equipment;

[0036] The second processing module is used to process positive-sequence voltage / current complex signals. Taking the real part yields the positive-sequence d-axis voltage / current v. dp Taking the imaginary part yields the positive-sequence q-axis voltage / current v. qp Complex processing signals for negative sequence voltage / current Taking the real part yields the negative-sequence d-axis voltage / current v. dn Taking the imaginary part yields the negative-sequence q-axis voltage / current v. qn .

[0037] A computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device where the computer-readable storage medium is located to perform the method for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform.

[0038] A processor for running a program, wherein the program executes the aforementioned method for decomposing the positive and negative zero sequences of three-phase voltage and current signals based on the Hilbert-Huang transform.

[0039] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0040] This invention starts with the raw data of three-phase voltage / current signals. First, it uses the Hilbert-Huang transform to obtain the complex signal information of the three-phase voltage / current signals, preserving all frequency information of the original signals to the greatest extent possible. Then, based on the original definitions of positive and negative sequence signals, the positive, negative, and zero sequence signal components are obtained by multiplying the complex signal vector by the positive, negative, and zero sequence decomposition transformation matrix T, ensuring the accuracy of the positive, negative, and zero sequence decomposition. By performing the Hilbert-Huang transform on the three-phase voltage and current signals, effective decomposition of the positive, negative, and zero sequence components can be achieved. This invention not only improves the ability to identify fault signals but also provides precise data support for the stable control of power electronic equipment. Attached Figure Description

[0041] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0042] Figure 1 This is a schematic diagram illustrating the principle of the method of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0045] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0046] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0047] Example 1:

[0048] like Figure 1 As shown, this embodiment provides a method for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on the Hilbert-Huang transform, including the following steps:

[0049] Step S1: Acquire the three-phase voltage / current measurement signal v at the grid connection point of the power electronic equipment. a v b v c , where v a For phase A voltage / current measurement signal, v b For phase B voltage / current measurement signal, vc This is the voltage / current measurement signal for phase C.

[0050] Step S2, measure the three-phase voltage / current signal v a v b v c Perform Hilbert-Huang transforms on each phase to obtain the complex three-phase voltage / current signals V. a V b V c ;where V a The complex signal of phase A voltage / current, V b For phase B voltage / current complex signal, V c This is a complex signal of C-phase voltage / current.

[0051] The Hilbert-Huang transform is performed as follows:

[0052] Step S21, calculate v using the Fast Fourier Transform algorithm. i frequency domain of the signal Specifically, it is expressed as follows:

[0053]

[0054] Among them, v i This represents the voltage / current measurement signal of the i-th phase, FFT(*) represents Fast Fourier Transform calculation, and v i [n] represents a set of values ​​within the fast Fourier transform time window. i The signal, where n represents the number of data points in the set, and n is an even number;

[0055] Step S22, create a... Frequency domain array of the same size make express The kth data point, express For the k-th data point:

[0056]

[0057] Step S23: Calculate the inverse Fourier transform to obtain the Hilbert transform signal.

[0058]

[0059] Where IFFT(*) represents the calculation of the inverse fast Fourier transform;

[0060] Step S24, construct the complex voltage signal V of the i-th phase. i for:

[0061]

[0062] Step S3, convert the three-phase voltage / current complex signal V a V b V c The vector is multiplied by the positive and negative zero-sequence decomposition transformation matrix T to obtain the positive-sequence voltage / current complex signal V. p Negative sequence voltage / current complex signal V n and zero-sequence voltage / current complex signal V o The calculation formula is:

[0063]

[0064] The positive and negative zero order decomposition transformation matrix T is shown below:

[0065]

[0066] Step S4, for the positive sequence voltage / current complex signal V p Multiply Obtain positive sequence voltage / current complex processed signal For negative sequence voltage / current complex signals V n Multiply Obtain the complex processed signal of negative sequence voltage / current Where θ pll This refers to the synchronization phase output by the synchronization control loop in power electronic equipment, where the synchronization control loop is either a phase-locked loop (PLL) or a virtual synchronization control loop. The calculation formula is:

[0067]

[0068] Step S5: Process the positive sequence voltage / current complex signal. Taking the real part yields the positive-sequence d-axis voltage / current v. dp Taking the imaginary part yields the positive-sequence q-axis voltage / current v. qp Complex processing signals for negative sequence voltage / current Taking the real part yields the negative-sequence d-axis voltage / current v. dn Taking the imaginary part yields the negative-sequence q-axis voltage / current v. qn The calculation formula is:

[0069]

[0070] Where Real[*] represents the real part and Imag[*] represents the imaginary part.

[0071] This invention starts with the raw data of three-phase voltage / current signals. First, it obtains the complex signal information of the three-phase voltage / current signals through the Hilbert-Huang transform, which preserves all the frequency information of the original signals to the greatest extent. Then, based on the original definition of positive and negative sequence signals, the positive and negative zero sequence signal components are obtained by multiplying the complex signal vector by the positive and negative zero sequence decomposition transformation matrix T, which ensures the accuracy of the positive and negative zero sequence decomposition.

[0072] Example 2:

[0073] Based on the same inventive concept as Embodiment 1, this embodiment provides a decomposition system for the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform, applied to the method described, including:

[0074] The acquisition module is used to acquire the three-phase voltage / current measurement signals at the grid connection point of power electronic equipment. a v b v c , where v a For phase A voltage / current measurement signal, v b For phase B voltage / current measurement signal, v c This is the voltage / current measurement signal for phase C;

[0075] Hilbert-Huang transform module, used for three-phase voltage / current measurement signal v a v b v c Perform Hilbert-Huang transforms on each phase to obtain the complex three-phase voltage / current signals V. a V b V c ;where V a The complex signal of phase A voltage / current, V b For phase B voltage / current complex signal, V c This is a complex signal representing the voltage / current of phase C.

[0076] The decomposition module is used to decompose the three-phase voltage / current complex signals V a V b V c The vector is multiplied by the positive and negative zero-sequence decomposition transformation matrix T to obtain the positive-sequence voltage / current complex signal V. p Negative sequence voltage / current complex signal V n and zero-sequence voltage / current complex signal V o ;

[0077] The first processing module is used to process the positive-sequence voltage / current complex signal V. p Multiply Obtain positive sequence voltage / current complex processed signal For negative sequence voltage / current complex signals Vn Multiply Obtain the complex processed signal of negative sequence voltage / current Where θ pll The synchronization phase output by the synchronization control loop in power electronic equipment;

[0078] The second processing module is used to process positive-sequence voltage / current complex signals. Taking the real part yields the positive-sequence d-axis voltage / current v. dp Taking the imaginary part yields the positive-sequence q-axis voltage / current v. qp Complex processing signals for negative sequence voltage / current Taking the real part yields the negative-sequence d-axis voltage / current v. dn Taking the imaginary part yields the negative-sequence q-axis voltage / current v. qn .

[0079] Example 3:

[0080] Based on the same inventive concept as Embodiment 1, this embodiment provides a computer-readable storage medium including a stored program, wherein, when the program is executed, it controls the device where the computer-readable storage medium is located to execute the decomposition method of positive, negative and zero sequence of three-phase voltage and current signals based on Hilbert-Huang transform.

[0081] Example 4:

[0082] Based on the same inventive concept as Embodiment 1, this embodiment provides a processor for running a program, wherein the program executes the decomposition method for positive and negative zero sequence of three-phase voltage and current signals based on Hilbert-Huang transform.

[0083] Those skilled in the art will recognize that the modules of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0084] In the embodiments provided by this invention, it should be understood that the division of modules is only a logical functional division. In actual implementation, there may be other division methods, such as multiple modules can be combined into one module, one module can be split into multiple modules, or some features can be ignored.

[0085] Furthermore, the functional modules in the various embodiments of the present invention can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module. The integrated modules described above can be implemented in hardware or as software functional modules.

[0086] If the integrated module is implemented as a software functional module and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform, characterized in that, Includes the following steps: Step S1: Acquire the three-phase voltage / current measurement signal v at the grid connection point of the power electronic equipment. a v b v c , where v a For phase A voltage / current measurement signal, v b For phase B voltage / current measurement signal, v c This is the voltage / current measurement signal for phase C; Step S2, measure the three-phase voltage / current signal v a v b v c Perform Hilbert-Huang transforms on each phase to obtain the complex three-phase voltage / current signals V. a V b V c ;where V a The complex signal of phase A voltage / current, V b For phase B voltage / current complex signal, V c This is a complex signal representing the voltage / current of phase C. Step S3, convert the three-phase voltage / current complex signal V a V b V c The vector is formed and multiplied by the positive and negative zero-sequence decomposition transformation matrix T to obtain the positive-sequence voltage / current complex signal V. p Negative sequence voltage / current complex signal V n and zero-sequence voltage / current complex signal V o ; Step S4, for the positive sequence voltage / current complex signal V p Multiply Obtain positive sequence voltage / current complex processed signal For negative sequence voltage / current complex signals V n Multiply Obtain the complex processed signal of negative sequence voltage / current Where θ pll The synchronization phase output by the synchronization control loop in power electronic equipment; Step S5: Process the positive sequence voltage / current complex signal. Taking the real part yields the positive-sequence d-axis voltage / current v. dp Taking the imaginary part yields the positive-sequence q-axis voltage / current v. qp Complex processing signals for negative sequence voltage / current Taking the real part yields the negative-sequence d-axis voltage / current v. dn Taking the imaginary part yields the negative-sequence q-axis voltage / current v. qn .

2. The method for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform according to claim 1, characterized in that, The Hilbert-Huang transform performed in step S2 is as follows: Step S21, calculate v using the Fast Fourier Transform algorithm. i frequency domain of the signal Specifically, it is expressed as follows: Among them, v i This represents the voltage / current measurement signal of the i-th phase, FFT(*) represents Fast Fourier Transform calculation, and v i [n] represents a set of values ​​within the fast Fourier transform time window. i The signal, where n represents the number of data points in the set, and n is an even number; Step S22, create a... Frequency domain array of the same size make express The kth data point, express For the k-th data point: Step S23: Calculate the inverse Fourier transform to obtain the Hilbert transform signal. Where IFFT(*) represents the calculation of the inverse fast Fourier transform; Step S24, construct the complex voltage signal V of the i-th phase. i for:

3. The method for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform according to claim 1, characterized in that, The calculation formula in step S3 is:

4. A method for decomposing the positive and negative zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform according to claim 1 or 3, characterized in that, The positive and negative zero order decomposition transformation matrix T is shown below:

5. The method for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform according to claim 1, characterized in that, The calculation formula in step S4 is:

6. The method for decomposing the positive and negative zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform according to claim 1, characterized in that, The synchronization control loop in step S4 is a phase-locked loop or a virtual synchronization control loop.

7. The method for decomposing the positive and negative zero sequences of three-phase voltage and current signals based on Hilbert-Huang transform according to claim 1, characterized in that, The calculation formula in step S5 is: Where Real[*] represents the real part and Imag[*] represents the imaginary part.

8. A system for decomposing the positive, negative, and zero sequences of three-phase voltage and current signals based on the Hilbert-Huang transform, characterized in that, The method applied to any one of claims 1 to 7 includes: The acquisition module is used to acquire the three-phase voltage / current measurement signals at the grid connection point of power electronic equipment. a v b v c , where v a For phase A voltage / current measurement signal, v b For phase B voltage / current measurement signal, v c This is the voltage / current measurement signal for phase C; Hilbert-Huang transform module, used for three-phase voltage / current measurement signals v a v b v c Perform Hilbert-Huang transforms on each phase to obtain the complex three-phase voltage / current signals V. a V b V c ;where V a The complex signal of phase A voltage / current, V b For phase B voltage / current complex signal, V c This is a complex signal representing the voltage / current of phase C. The decomposition module is used to decompose the complex three-phase voltage / current signals V a V b V c The vector is formed and multiplied by the positive and negative zero-sequence decomposition transformation matrix T to obtain the positive-sequence voltage / current complex signal V. p Negative sequence voltage / current complex signal V n and zero-sequence voltage / current complex signal V o ; The first processing module is used to process the positive-sequence voltage / current complex signal V. p Multiply Obtain positive sequence voltage / current complex processed signal For negative sequence voltage / current complex signals V n Multiply Obtain the complex processed signal of negative sequence voltage / current Where θ pll The synchronization phase output by the synchronization control loop in power electronic equipment; The second processing module is used to process positive-sequence voltage / current complex signals. Taking the real part yields the positive-sequence d-axis voltage / current v. dp Taking the imaginary part yields the positive-sequence q-axis voltage / current v. qp Complex processing signals for negative sequence voltage / current Taking the real part yields the negative-sequence d-axis voltage / current v. dn Taking the imaginary part yields the negative-sequence q-axis voltage / current v. qn .

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium includes a stored program, wherein, when the program is executed, it controls the device containing the computer-readable storage medium to perform the decomposition method for the positive, negative, and zero sequences of three-phase voltage and current signals based on the Hilbert-Huang transform as described in any one of claims 1 to 7.

10. A processor, characterized in that, The processor is used to run a program, wherein the program executes the method for decomposing the positive and negative zero sequence of three-phase voltage and current signals based on the Hilbert-Huang transform as described in any one of claims 1 to 7.

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