Method and system for filtering harmonic waves with multiples of 3

Abstract

The invention relates to a method and system for filtering harmonic waves of multiple of 3, and belongs to the technical field of signal processing, and the method comprises the following steps: obtaining a target current signal, and determining the minimum positive period of the target current signal through a frequency domain analysis algorithm; performing time shift operation on the target current signal based on a phase compensation algorithm to obtain a time offset signal; calculating the sum of multiples of harmonics of the target current signal 3 based on the target current signal and the time offset signal; and filtering the harmonic waves of the multiple of 3 in the target current signal based on the sum of the harmonic waves of the multiple of 3 in the target current signal. According to the invention, all harmonic waves with multiples of 3 in the target current signal can be extracted and filtered at one time. According to the method, a filter does not need to be independently designed for each harmonic frequency, so that the filtering efficiency is greatly improved. Through a unified algorithm and flow, synchronous processing of various harmonic waves is realized, the system design is simplified, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to a method and system for filtering 3 - multiple - order harmonics, belonging to the technical field of signal processing. Background Art

[0002] In modern power systems and electronic devices, the harmonic problem has always been a key factor affecting signal quality, device performance, and system stability. Harmonics are caused by nonlinear loads and usually appear as integer multiples of the fundamental frequency. In a three - phase system, 3 - multiple - order harmonics (such as the 3rd, 6th, 9th, etc.) are special because they will be superimposed on the neutral line, resulting in an excessive neutral - line current, and may even cause problems such as equipment overheating and misoperation of protection devices. In addition, 3 - multiple - order harmonics will also have a negative impact on communication systems, power transmission efficiency, and power quality.

[0003] Traditional harmonic - processing methods mainly include passive filtering and active filtering. Passive filtering suppresses harmonics of specific frequencies by designing specific filters (such as LC filters), but this method usually requires separate design of filters for each harmonic frequency, and the filtering effect is easily affected by changes in system parameters. Active filtering, on the other hand, cancels harmonics by detecting harmonics in real - time and generating compensation signals, but this method usually requires complex control algorithms and high - speed processors, with high costs and great implementation difficulties.

[0004] The prior art, such as the Chinese patent application with the publication number "CN109995291A", discloses a compensation method for suppressing motor current harmonics, which includes the following steps: sampling the three-phase current values output by the inverter; performing coordinate transformation on the three-phase current values output by the inverter to obtain the amplitudes and phase angles corresponding to the filtered excitation component and the filtered torque component respectively; obtaining the polarities of the three-phase currents according to the amplitudes and phase angles corresponding to the excitation component and the torque component respectively and a preset mapping table of the current space vector angle and the current polarity; and compensating the conduction times of the three-phase trigger signals through the dead time according to the different polarities of the three-phase currents so that the compensated conduction time is the same as the ideal conduction time. However, the design of the filter in the above patent is crucial for the harmonic suppression effect. If the filter is designed improperly, it may lead to unsatisfactory filtering effect and inability to effectively remove high-frequency harmonics. This means that in practical applications, a large amount of time and effort need to be invested in the adjustment and optimization of the filter parameters, increasing the complexity of system design and implementation. The judgment of the current polarity in the above patent depends on the calculation of the current space vector angle, which requires the coordinate transformation and filtering processes to be accurate. Any error may lead to incorrect judgment of the current polarity, thus affecting the compensation effect. For example, factors such as the accuracy of the current sensor and the stability of the operational amplifier conditioning circuit may introduce errors, thereby affecting the accuracy of the current polarity judgment. And the above patent compensates the conduction times of the three-phase trigger signals through the dead time to suppress the motor current harmonics. However, this compensation method depends on the accurate judgment of the current polarity and can only reduce the current harmonics caused by the dead time to a certain extent and cannot completely eliminate them. This means that when the current polarity is judged incorrectly or the dead time is set improperly, the current harmonics may still exist, affecting the operating performance of the motor. Summary of the Invention

[0005] To solve the problems existing in the above prior art, the present invention proposes a method and system for filtering the 3 - multiple harmonics.

[0006] The technical solution of the present invention is as follows:

[0007] On the one hand, the present invention provides a method for filtering the 3 - multiple harmonics, including the following steps:

[0008] Obtain the target current signal i(t), and determine the minimum positive period T of the target current signal through the frequency domain analysis algorithm;

[0009] Based on the phase compensation algorithm, perform a time displacement operation on the target current signal i(t) to obtain the time - offset signals i(t + T / 3) and i(t + 2T / 3);

[0010] Calculate the sum of the 3 - multiple harmonics of the target current signal based on the target current signal i(t), the time - offset signals i(t + T / 3) and i(t + 2T / 3);

[0011] Filter out the harmonics that are multiples of 3 in the target current signal based on the sum of the harmonics that are multiples of 3 in the target current signal 3.

[0012] As a preferred embodiment, the minimum positive period of the target current signal is determined by the frequency domain analysis algorithm, which is expressed by the formula:

[0013]

[0014] In the formula, T represents the minimum positive period of the target current signal, T ν represents the candidate period, F represents the Fourier transform operator, F -1 represents the inverse Fourier transform operator, W represents the wavelet transform operator, i(t) represents the target current signal at time t, represents the function for determining the minimum candidate period, and t represents the time index.

[0015] As a preferred embodiment, the time displacement operation is performed on the target current signal i(t) based on the phase compensation algorithm to obtain the time offset signals i(t + T / 3) and i(t + 2T / 3), which is expressed by the formula:

[0016]

[0017]

[0018] X(ω) = F(i(t));

[0019] In the formula, F -1 represents the inverse Fourier transform operator, H N (ω) represents the transfer function of the Nth-order all-pass filter, a q represents the qth pole of the all-pass filter, represents the conjugate zero of the qth pole, ω represents the angular frequency, j represents the imaginary unit, q represents the pole index, N represents the order of the all-pass filter, represents the time shift term in the Fourier transform, T represents the minimum positive period of the target current signal, X(ω) represents the target current signal i(t) at time t after Fourier transform, t represents the time index, and F represents the Fourier transform operator.

[0020] As a preferred embodiment, the sum of the harmonics that are multiples of 3 in the target current signal is calculated based on the target current signal i(t), the time offset signals i(t + T / 3) and i(t + 2T / 3), and the specific steps are as follows:

[0021] Express the target current signal i(t), the time offset signals i(t + T / 3) and i(t + 2T / 3) in the form of harmonic synthesis:

[0022] The harmonic synthesis form of the target current signal \(i(t)\) is expressed by the formula:

[0023]

[0024] The harmonic synthesis form of the time-offset signal \(i(t + T / 3)\) is expressed by the formula:

[0025]

[0026] The harmonic synthesis form of the time-offset signal \(i(t + 2T / 3)\) is expressed by the formula:

[0027]

[0028] where \(I\) k represents the \(k\)th harmonic of the target current signal, represents the fundamental angular frequency of the target current signal, represents the initial phase of the \(k\)th harmonic of the target current signal, \(t\) represents the time index, \(T\) represents the minimum positive period of the target current signal, \(k\) represents the harmonic order, and \(\sin\) represents the sine function;

[0029] Adding the target current signal \(i(t)\), the time-offset signals \(i(t + T / 3)\) and \(i(t + 2T / 3)\) is expressed by the formula:

[0030]

[0031] where \(\cos\) represents the cosine function;

[0032] If \(k\) is an odd multiple of 3:

[0033]

[0034] If \(k\) is an even multiple of 3:

[0035]

[0036] That is, when \(k\) is a multiple of 3, the sum of the target current signal \(i(t)\), the time-offset signals \(i(t + T / 3)\) and \(i(t + 2T / 3)\) is expressed by the formula:

[0037]

[0038] If \(k\) is an odd number that is not a multiple of 3:

[0039]

[0040] If \(k\) is an even number that is not a multiple of 3:

[0041]

[0042] That is, when k is not a multiple of 3, the sum of the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3) is expressed by the formula:

[0043]

[0044] The sum of the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3) is the sum of the harmonics of the target current signal at multiples of 3.

[0045] As a preferred embodiment, a time-shifting operation is performed on the target current signal i(t) based on a digital delay line.

[0046] As a preferred embodiment, a time-shifting operation is performed on the target current signal i(t) based on an analog delay circuit.

[0047] On the other hand, the present invention also provides a filtering system for harmonics at multiples of 3, including:

[0048] Data acquisition module: Obtain the target current signal i(t), and determine the minimum positive period T of the target current signal through a frequency-domain analysis algorithm;

[0049] Data shifting module: Perform a time-shifting operation on the target current signal i(t) based on a phase compensation algorithm to obtain time-offset signals i(t + T / 3) and i(t + 2T / 3);

[0050] Harmonic calculation module: Calculate the sum of the harmonics of the target current signal at multiples of 3 based on the target current signal i(t), the time-offset signals i(t + T / 3) and i(t + 2T / 3);

[0051] Harmonic filtering module: Filter the harmonics at multiples of 3 in the target current signal based on the sum of the harmonics of the target current signal at multiples of 3.

[0052] As a preferred embodiment, the minimum positive period of the target current signal is determined by the frequency-domain analysis algorithm, and is expressed by the formula:

[0053]

[0054] In the formula, T represents the minimum positive period of the target current signal, T ν represents the candidate period, F represents the Fourier transform operator, F -1 represents the inverse Fourier transform operator, W represents the wavelet transform operator, i(t) represents the target current signal at time t, represents the function for determining the minimum candidate period, and t represents the time index.

[0055] As a preferred embodiment, the target current signal i(t) is subjected to a time displacement operation based on the phase compensation algorithm to obtain time-offset signals i(t + T / 3) and i(t + 2T / 3), which are expressed by the formula:

[0056]

[0057]

[0058] X(ω) = F(i(t));

[0059] In the formula, F -1 represents the Fourier inverse transform operator, H N (ω) represents the transfer function of an Nth-order all-pass filter, a q represents the qth pole of the all-pass filter, represents the conjugate zero of the qth pole, ω represents the angular frequency, j represents the imaginary unit, q represents the pole index, N represents the order of the all-pass filter, represents the Fourier transform time-shift term, T represents the minimum positive period of the target current signal, X(ω) represents the target current signal i(t) at time t after Fourier transform, t represents the time index, and F represents the Fourier transform operator.

[0060] As a preferred embodiment, the sum of the 3-times harmonics of the target current signal is calculated based on the target current signal i(t), the time-offset signals i(t + T / 3) and i(t + 2T / 3). The specific steps are as follows:

[0061] The target current signal i(t), the time-offset signals i(t + T / 3) and i(t + 2T / 3) are expressed in the form of harmonic synthesis:

[0062] The harmonic synthesis form of the target current signal i(t) is expressed by the formula:

[0063]

[0064] The harmonic synthesis form of the time-offset signal i(t + T / 3) is expressed by the formula:

[0065]

[0066] The harmonic synthesis form of the time-offset signal i(t + 2T / 3) is expressed by the formula:

[0067]

[0068] In the formula, I k represents the kth harmonic of the target current signal, represents the fundamental angular frequency of the target current signal, represents the initial phase of the k-th harmonic of the target current signal, t represents the time index, T represents the minimum positive period of the target current signal, k represents the harmonic order, and sin represents the sine function;

[0069] Add the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3). It is expressed by the formula:

[0070]

[0071] In the formula, cos represents the cosine function;

[0072] If k is an odd multiple of 3:

[0073]

[0074] If k is an even multiple of 3:

[0075]

[0076] That is, when k is a multiple of 3, the sum of the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3) is expressed by the formula:

[0077]

[0078] If k is an odd number that is not a multiple of 3:

[0079]

[0080] If k is an even number that is not a multiple of 3:

[0081]

[0082] That is, when k is not a multiple of 3, the sum of the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3) is expressed by the formula:

[0083]

[0084] The sum of the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3) is the sum of the harmonics of the target current signal that are multiples of 3.

[0085] The present invention has the following beneficial effects:

[0086] 1. The present invention proposes a revolutionary method that can extract and filter all harmonics of multiples of 3 in the target current signal at one time. This method does not require designing filters separately for each harmonic frequency, thus greatly improving the filtering efficiency. Through a unified algorithm and process, synchronous processing of multiple harmonics is achieved, simplifying the system design and reducing costs.

[0087] 2. By filtering the harmonics of multiples of 3, the present invention effectively reduces the current superposition phenomenon on the neutral line. This reduces the risk of excessive neutral line current, thereby improving the overall stability of the power system and electronic devices. This improvement in stability is of great significance for ensuring the reliable operation of the power system and extending the service life of equipment.

[0088] 3. The present invention is based on the phase compensation algorithm and the frequency domain analysis algorithm, and can achieve the extraction and filtering of harmonics through simple mathematical operations. This method does not require complex control algorithms and the support of high-speed processors, thus optimizing the utilization of computing resources. This enables the present invention to reduce the demand for hardware resources while maintaining high filtering performance, improving the cost performance and scalability of the system.

[0089] 4. The present invention can achieve time displacement operations either through a digital delay line or through an analog delay circuit. This diverse implementation method provides users with more options, enabling the present invention to find suitable implementation solutions in different application scenarios, increasing its flexibility and practicality. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] Figure 1 It is a flowchart of the implementation of the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0091] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0092] It should be understood that the step numbers used in the text are only for convenient description and do not limit the execution order of the steps.

[0093] It should be understood that the terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include the plural forms.

[0094] The terms "comprising" and "including" indicate the presence of the described features, wholes, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components and / or their combinations.

[0095] The term "and / or" refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0096] Embodiment 1:

[0097] See Figure 1 , the present invention provides a method for filtering third - multiple - order harmonics, including the following steps:

[0098] Obtain the target current signal i(t), and determine the minimum positive period T of the target current signal through a frequency - domain analysis algorithm;

[0099] Perform a time - displacement operation on the target current signal i(t) based on a phase - compensation algorithm to obtain time - shifted signals i(t + T / 3) and i(t + 2T / 3);

[0100] Calculate the sum of the third - multiple - order harmonics of the target current signal based on the target current signal i(t), the time - shifted signals i(t + T / 3) and i(t + 2T / 3);

[0101] Filter the third - multiple - order harmonics in the target current signal based on the sum of the third - multiple - order harmonics of the target current signal.

[0102] As a preferred embodiment, the determination of the minimum positive period of the target current signal through the frequency - domain analysis algorithm is expressed by the formula:

[0103]

[0104] In the formula, T represents the minimum positive period of the target current signal, T ν represents the candidate period, F represents the Fourier transform operator, F -1 represents the inverse Fourier transform operator, W represents the wavelet transform operator, i(t) represents the target current signal at time t, represents the function for determining the minimum candidate period, and t represents the time index.

[0105] As a preferred embodiment, the time - displacement operation on the target current signal i(t) based on the phase - compensation algorithm to obtain the time - shifted signals i(t + T / 3) and i(t + 2T / 3) is expressed by the formula:

[0106]

[0107] X(ω) = F(i(t));

[0108] In the formula, F -1 represents the inverse Fourier transform operator, and H N (ω) represents the transfer function of an Nth-order all-pass filter, and a q represents the qth pole of the all-pass filter, represents the conjugate zero of the qth pole, ω represents the angular frequency, j represents the imaginary unit, q represents the pole index, and N represents the order of the all-pass filter. represents the time-shift term in the Fourier transform, T represents the minimum positive period of the target current signal, X(ω) represents the target current signal i(t) at time t after the Fourier transform, t represents the time index, and F represents the Fourier transform operator.

[0109] As a preferred embodiment, calculating the sum of the 3rd multiples of the harmonic components of the target current signal based on the target current signal i(t), the time-offset signals i(t + T / 3) and i(t + 2T / 3) specifically includes the following steps:

[0110] Express the target current signal i(t), the time-offset signals i(t + T / 3) and i(t + 2T / 3) in the form of harmonic synthesis:

[0111] The harmonic synthesis form of the target current signal i(t) is expressed by the formula:

[0112]

[0113] The harmonic synthesis form of the time-offset signal i(t + T / 3) is expressed by the formula:

[0114]

[0115] The harmonic synthesis form of the time-offset signal i(t + 2T / 3) is expressed by the formula:

[0116]

[0117] In the formula, I k represents the kth harmonic component of the target current signal, represents the fundamental angular frequency of the target current signal, represents the initial phase of the kth harmonic component of the target current signal, t represents the time index, T represents the minimum positive period of the target current signal, k represents the harmonic order, which is a positive integer, and sin represents the sine function;

[0118] Add the target current signal i(t), the time-offset signals i(t + T / 3) and i(t + 2T / 3), which is expressed by the formula:

[0119]

[0120] Wherein, cos represents the cosine function;

[0121] If k is an odd multiple of 3:

[0122]

[0123] If k is an even multiple of 3:

[0124]

[0125] That is, when k is a multiple of 3, the sum of the target current signal i(t), the time offset signal i(t + T / 3), and i(t + 2T / 3) is expressed by the formula:

[0126]

[0127] If k is an odd number that is not a multiple of 3:

[0128]

[0129] If k is an even number that is not a multiple of 3:

[0130]

[0131] That is, when k is not a multiple of 3, the sum of the target current signal i(t), the time offset signal i(t + T / 3), and i(t + 2T / 3) is expressed by the formula:

[0132]

[0133] The sum of the target current signal i(t), the time offset signal i(t + T / 3), and i(t + 2T / 3) is the sum of the harmonics of the target current signal at multiples of 3.

[0134] As a preferred embodiment, a time displacement operation is performed on the target current signal i(t) based on a digital delay line.

[0135] As a preferred embodiment, a time displacement operation is performed on the target current signal i(t) based on an analog delay circuit.

[0136] Embodiment 2:

[0137] The present invention also provides a filtering system for harmonics at multiples of 3, including:

[0138] Data acquisition module: Obtain the target current signal i(t), and determine the minimum positive period T of the target current signal through a frequency domain analysis algorithm;

[0139] Data displacement module: Perform a time displacement operation on the target current signal i(t) based on a phase compensation algorithm to obtain time offset signals i(t + T / 3) and i(t + 2T / 3);

[0140] Harmonic calculation module: Calculate the sum of the 3 - multiple harmonics of the target current signal based on the target current signal \(i(t)\), the time - shifted signal \(i(t + T / 3)\) and \(i(t + 2T / 3)\);

[0141] Harmonic filtering module: Filter the 3 - multiple harmonics in the target current signal based on the sum of the 3 - multiple harmonics of the target current signal.

[0142] As a preferred implementation, the minimum positive period of the target current signal is determined by the frequency - domain analysis algorithm, which is expressed by the formula:

[0143]

[0144] In the formula, \(T\) represents the minimum positive period of the target current signal, \(T\) ν represents the candidate period, \(F\) represents the Fourier transform operator, \(F\) -1 represents the inverse Fourier transform operator, \(W\) represents the wavelet transform operator, \(i(t)\) represents the target current signal at time \(t\), represents the function to determine the minimum candidate period, and \(t\) represents the time index.

[0145] As a preferred implementation, the time - displacement operation is performed on the target current signal \(i(t)\) based on the phase - compensation algorithm to obtain the time - shifted signals \(i(t + T / 3)\) and \(i(t + 2T / 3)\), which is expressed by the formula:

[0146]

[0147] \(X(\omega)=F(i(t))\);

[0148] In the formula, \(F\) -1 represents the inverse Fourier transform operator, \(H\) N (\(\omega\)) represents the transfer function of the \(N\) - th order all - pass filter, \(a\) q represents the \(q\) - th pole of the all - pass filter, represents the conjugate zero of the \(q\) - th pole, \(\omega\) represents the angular frequency, \(j\) represents the imaginary unit, \(q\) represents the pole index, \(N\) represents the order of the all - pass filter, represents the time - shift term in the Fourier transform, \(T\) represents the minimum positive period of the target current signal, \(X(\omega)\) represents the target current signal \(i(t)\) at time \(t\) after Fourier transform, \(t\) represents the time index, and \(F\) represents the Fourier transform operator.

[0149] As a preferred implementation, the specific steps for calculating the sum of the 3 - multiple harmonics of the target current signal based on the target current signal \(i(t)\), the time - shifted signals \(i(t + T / 3)\) and \(i(t + 2T / 3)\) are as follows:

[0150] Express the target current signal \(i(t)\), the time-offset signal \(i(t + T / 3)\), and \(i(t + 2T / 3)\) in the form of harmonic synthesis:

[0151] The harmonic synthesis form of the target current signal \(i(t)\) is expressed by the formula:

[0152]

[0153] The harmonic synthesis form of the time-offset signal \(i(t + T / 3)\) is expressed by the formula:

[0154]

[0155] The harmonic synthesis form of the time-offset signal \(i(t + 2T / 3)\) is expressed by the formula:

[0156]

[0157] Where \(I\) k represents the \(k\)-th harmonic of the target current signal, represents the fundamental angular frequency of the target current signal, represents the initial phase of the \(k\)-th harmonic of the target current signal, \(t\) represents the time index, \(T\) represents the minimum positive period of the target current signal, \(k\) represents the harmonic order, and \(\sin\) represents the sine function;

[0158] Add the target current signal \(i(t)\), the time-offset signal \(i(t + T / 3)\), and \(i(t + 2T / 3)\), which is expressed by the formula:

[0159]

[0160] Where \(\cos\) represents the cosine function;

[0161] If \(k\) is an odd multiple of 3:

[0162]

[0163] If \(k\) is an even multiple of 3:

[0164]

[0165] That is, when \(k\) is a multiple of 3, the sum of the target current signal \(i(t)\), the time-offset signal \(i(t + T / 3)\), and \(i(t + 2T / 3)\) is expressed by the formula:

[0166]

[0167] If \(k\) is an odd number that is not a multiple of 3:

[0168]

[0169] If k is an even number that is not a multiple of 3:

[0170]

[0171] That is, when k is not a multiple of 3, the sum of the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3) is expressed by the formula:

[0172]

[0173] The sum of the target current signal i(t), the time-offset signal i(t + T / 3), and i(t + 2T / 3) is the sum of the harmonics of the 3rd multiple of the target current signal.

[0174] Embodiment 3:

[0175] This embodiment provides a method for filtering the harmonics of the 3rd multiple of a voltage signal, including the following steps:

[0176] Obtain the target voltage signal i(t), and determine the minimum positive period T of the target voltage signal through a frequency-domain analysis algorithm;

[0177] Based on the phase compensation algorithm, perform a time displacement operation on the target voltage signal i(t) to obtain the time-offset signals i(t + T / 3) and i(t + 2T / 3);

[0178] Calculate the sum of the harmonics of the 3rd multiple of the target voltage signal based on the target voltage signal i(t), the time-offset signals i(t + T / 3) and i(t + 2T / 3);

[0179] Filter the harmonics of the 3rd multiple in the target voltage signal based on the sum of the harmonics of the 3rd multiple of the target voltage signal.

[0180] For the specific implementation method, refer to Embodiment 1, which will not be elaborated here.

[0181] In the embodiments of the present application, "at least one" means one or more, and "a plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent the cases of A existing alone, A and B existing simultaneously, and B existing alone. Where A and B can be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after. "At least one of the following" and its similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, and c can represent: a, b, c, a and b, a and c, b and c, or a and b and c, where a, b, and c can be single or multiple.

[0182] Those of ordinary skill in the art will realize that the various units and algorithm steps described in the embodiments disclosed herein can be implemented by electronic hardware, computer software, or a combination of electronic hardware. Whether these functions are executed in hardware or software depends on the specific application and design constraints of the technical solution. Skilled professionals can use different methods for each specific application to implement the described functions, but such implementation should not be considered to exceed the scope of this application.

[0183] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the systems, devices, and units described above can refer to the corresponding processes in the foregoing method embodiments and will not be elaborated herein.

[0184] In several embodiments provided in this application, if any function is implemented in the form of a software functional unit 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 this application, in essence, or the part that contributes to the prior art or a part of this 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 for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The foregoing storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (hereinafter referred to as ROM), random access memories (hereinafter referred to as RAM), magnetic disks, or optical discs that can store program codes.

[0185] The above are only the embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for filtering harmonics of multiples of 3, characterized in that: The following steps are involved: Obtain the target current signal i(t), and determine the minimum positive period T of the target current signal through a frequency domain analysis algorithm; Based on the phase compensation algorithm, the target current signal i(t) is time-shifted to obtain time-shifted signals i(t+T / 3) and i(t+2T / 3); Calculate the sum of multiple subharmonics of the target current signal 3 based on the target current signal i(t), the time offset signals i(t+T / 3) and i(t+2T / 3); The multiple harmonics of 3 in the target current signal are filtered based on the sum of the multiple harmonics of 3 of the target current signal.

2. The method for filtering out harmonics of multiples of 3 according to claim 1, characterized in that: The minimum positive period of the target current signal is determined by the frequency domain analysis algorithm, which is expressed as follows: Where, T represents the minimum positive period of the target current signal, T ν represents the candidate period, F represents the Fourier transform operator, F -1 represents the inverse Fourier transform operator, W represents the wavelet transform operator, i(t) represents the target current signal at time t, It represents the function for determining the minimum candidate period, and t represents the time index.

3. The method for filtering out harmonics of multiples of 3 according to claim 1, characterized in that: The target current signal i(t) is subjected to a time shift operation based on the phase compensation algorithm to obtain time offset signals i(t+T / 3) and i(t+2T / 3), which are expressed as follows: X(ω)=F(i(t)); In the formula, F -1 represents the inverse Fourier transform operator, H N (ω) represents the transfer function of the Nth-order all-pass filter, a q represents the qth pole of the all-pass filter, represents the conjugate zero of the qth pole, ω represents the angular frequency, j represents the imaginary unit, q represents the pole index, N represents the order of the all-pass filter, represents the Fourier transform time-shift term, T represents the minimum positive period of the target current signal, X(ω) represents the target current signal i(t) at time t after Fourier transform, t represents the time index, and F represents the Fourier transform operator.

4. The method for filtering out harmonics of multiples of 3 according to claim 1, characterized in that: The specific steps of calculating the sum of multiple harmonics of the target current signal 3 based on the target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) are as follows: The target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) are expressed in the form of harmonic synthesis: The harmonic synthesis form of the target current signal i(t) is expressed as follows: The harmonic synthesis form of the time offset signal i(t+T / 3) is expressed as follows: The harmonic synthesis form of the time offset signal i(t+2T / 3) is expressed as follows: In the formula, I k represents the kth harmonic of the target current signal, Indicates the fundamental angular frequency of the target current signal, represents the initial phase of the kth harmonic of the target current signal, t represents the time index, T represents the minimum positive period of the target current signal, k represents the harmonic order, and sin represents the sine function; The target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) are added together and expressed as: In the formula, cos represents the cosine function; If k is an odd multiple of 3: If k is an even multiple of 3: That is, when k is a multiple of 3, the sum of the target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) is expressed as: If k is an odd number that is not a multiple of 3: If k is an even number that is not a multiple of 3: That is, when k is not a multiple of 3, the sum of the target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) is expressed as: The sum of the target current signal i(t), the time-shifted signal i(t+T / 3) and i(t+2T / 3) is the sum of the multiple harmonics of the target current signal 3.

5. The method for filtering out harmonics of multiples of 3 according to claim 1, characterized in that: The target current signal i(t) is time-shifted based on a digital delay line.

6. The method for filtering out harmonics of multiples of 3 according to claim 1, characterized in that: The target current signal i(t) is time-shifted based on an analog delay circuit.

7. A system for filtering harmonics of multiples of 3, characterized in that: include: Data acquisition module: obtain the target current signal i(t), and determine the minimum positive period T of the target current signal through the frequency domain analysis algorithm; Data shift module: performs time shift operation on the target current signal i(t) based on the phase compensation algorithm to obtain time offset signals i(t+T / 3) and i(t+2T / 3); Harmonic calculation module: calculates the sum of multiple harmonics of the target current signal 3 based on the target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3); Harmonic filtering module: Filters the harmonics of multiples of 3 in the target current signal based on the sum of the harmonics of multiples of 3 of the target current signal.

8. The system for filtering out harmonics of multiples of 3 according to claim 7, characterized in that: The minimum positive period of the target current signal is determined by the frequency domain analysis algorithm, which is expressed as follows: Where, T represents the minimum positive period of the target current signal, T ν represents the candidate period, F represents the Fourier transform operator, F -1 represents the inverse Fourier transform operator, W represents the wavelet transform operator, i(t) represents the target current signal at time t, It represents the function for determining the minimum candidate period, and t represents the time index.

9. The system for filtering out harmonics of multiples of 3 according to claim 7, characterized in that: The target current signal i(t) is subjected to a time shift operation based on the phase compensation algorithm to obtain time offset signals i(t+T / 3) and i(t+2T / 3), which are expressed as follows: X(ω)=F(i(t)); In the formula, F -1 represents the inverse Fourier transform operator, H N (ω) represents the transfer function of the Nth-order all-pass filter, a q represents the qth pole of the all-pass filter, represents the conjugate zero of the qth pole, ω represents the angular frequency, j represents the imaginary unit, q represents the pole index, N represents the order of the all-pass filter, represents the Fourier transform time-shift term, T represents the minimum positive period of the target current signal, X(ω) represents the target current signal i(t) at time t after Fourier transform, t represents the time index, and F represents the Fourier transform operator.

10. The 3-fold harmonic filtering system according to claim 1, characterized in that: The specific steps of calculating the sum of multiple harmonics of the target current signal 3 based on the target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) are as follows: The target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) are expressed in the form of harmonic synthesis: The harmonic synthesis form of the target current signal i(t) is expressed as follows: The harmonic synthesis form of the time offset signal i(t+T / 3) is expressed as follows: The harmonic synthesis form of the time offset signal i(t+2T / 3) is expressed as follows: In the formula, I k represents the kth harmonic of the target current signal, Indicates the fundamental angular frequency of the target current signal, represents the initial phase of the kth harmonic of the target current signal, t represents the time index, T represents the minimum positive period of the target current signal, k represents the harmonic order, and sin represents the sine function; The target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) are added together and expressed as: In the formula, cos represents the cosine function; If k is an odd multiple of 3: If k is an even multiple of 3: That is, when k is a multiple of 3, the sum of the target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) is expressed as: If k is an odd number that is not a multiple of 3: If k is an even number that is not a multiple of 3: That is, when k is not a multiple of 3, the sum of the target current signal i(t), the time offset signal i(t+T / 3) and i(t+2T / 3) is expressed as: The sum of the target current signal i(t), the time-shifted signal i(t+T / 3) and i(t+2T / 3) is the sum of the multiple harmonics of the target current signal 3.

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