Harmonic control method, system and device for frequency converter

Abstract

The present application relates to the technical field of harmonic control of frequency converters, and specifically to a harmonic control method, system, and device applied to frequency converters. The method includes: obtaining current data on the rectifier input side and the inverter output side of the frequency converter; obtaining the difference coefficient of the overall pulsation amplitude change of each cycle and the irregularity coefficient of the corresponding pulsation time change, thereby obtaining the harmonic influence coefficient of the rectifier input side current of each cycle with pulsation amplitude difference and irregular characteristics; calculating the deviation coefficient and jitter anomaly coefficient of the inverter output side current of each cycle to obtain the harmonic influence coefficient of the inverter output side current of each cycle with waveform deviation and rapid jitter; thereby obtaining the harmonic delay superposition interference coefficient, and correcting the inverter output current in combination with the current data of the inverter output side. The present application can improve the harmonic control accuracy of the frequency converter.

Description

Technical Field

[0001] The present application relates to the technical field of frequency converter harmonic control, and in particular to a harmonic control method, system, and device applied to a frequency converter. Background Art

[0002] Harmonics exist to varying degrees on both the rectifier input and inverter output sides of the inverter, affecting the normal operation of the power grid, motor, and inverter. Harmonics in different locations can overlap and interfere with each other. For example, harmonics generated by the rectifier and inverter output circuits can overlap in the power grid, further distorting the grid voltage and current waveforms. High-frequency harmonics on the rectifier input side can be modulated by low-frequency harmonics in the rectifier circuit, generating new harmonic components on the output side.

[0003] Existing methods typically detect and suppress the harmonic components of the inverter's output current, but fail to fully consider the superposition and interference characteristics of harmonic circuits, resulting in insufficient harmonic control capabilities. Publication No. CN117118245A discloses an inverter harmonic control system and control method for an inverter harmonic control system. This method uses a main control board to dynamically select reactor coils of varying inductances based on the inverter's input power. However, this method fails to fully consider the specific characteristics of harmonics and superposition interference, resulting in high system complexity and insufficient harmonic control capabilities. Summary of the Invention

[0004] In order to solve the above technical problems, the purpose of this application is to provide a harmonic control method, system and device for inverters. The technical solutions adopted are as follows:

[0005] In a first aspect, an embodiment of the present application provides a harmonic control method applied to a frequency converter, comprising the following steps:

[0006] Obtain current data on the rectifier input side and inverter output side of the inverter;

[0007] The period of the preset current data is used to obtain the difference coefficient of the overall pulsation amplitude change in each period through the difference and fluctuation degree of the rectifier input side current in each period. The irregularity coefficient of the pulsation time change corresponding to each period is obtained based on the chaotic change of the current corresponding to the time in each period. Combined with the difference coefficient of the overall pulsation amplitude change, the harmonic influence coefficient of the rectifier input side current with pulsation amplitude difference and irregular characteristics in each period is obtained;

[0008] Obtaining a deviation coefficient of the inverter output side current in each period based on the deviation of the inverter output side current data in each period; obtaining a jitter anomaly coefficient of the inverter output side current in each period based on the degree of change of the inverter output side current in each period and the frequency of change of the frequency amplitude in the frequency domain; and obtaining a harmonic influence coefficient of the inverter output side current having waveform deviation and rapid jitter in each period in combination with the deviation coefficient of the inverter output side current;

[0009] The harmonic influence coefficients corresponding to the rectifier input side current and the inverter output side current in each cycle are used to obtain the harmonic delay superposition interference coefficient to correct the inverter output current.

[0010] Preferably, the method for obtaining the difference coefficient of the overall pulsation amplitude change of each cycle is:

[0011] The rectifier input side current is fitted, and all extreme points of the rectifier input side current curve after fitting are extracted. The mean of the difference between all two adjacent extreme values ​​in each cycle is calculated as the pulsation amplitude difference coefficient of the input side current of each cycle. The standard deviation of each cycle and all extreme values ​​in the two cycles before and after it is calculated. The mean of the two standard deviations is used as the pulsation amplitude fluctuation coefficient of each cycle. The mean of the pulse amplitude difference coefficient and the pulse amplitude fluctuation coefficient is used as the difference coefficient of the overall pulse amplitude change of each cycle.

[0012] Preferably, the method for obtaining the irregular coefficient of the pulsation time change corresponding to each period is:

[0013] A time window of each cycle is constructed with each cycle as the center, and the first-order difference sequence of the sequence corresponding to the time of the extreme point of the same sequence number of all cycles in the time window is statistically analyzed. The fractal dimension of each first-order difference sequence is extracted, and the average value of all fractal dimensions obtained with each cycle as the center and the average value of the distance between all arbitrary two first-order difference sequences is used as the irregularity coefficient of the pulsation time change corresponding to each cycle.

[0014] Preferably, the harmonic influence coefficient of the pulsation amplitude difference and irregular characteristics of the rectified input-side current in each cycle is the product of the difference coefficient and the irregularity coefficient.

[0015] Preferably, the method for obtaining the deviation coefficient and jitter anomaly coefficient of the inverter output side current in each cycle is:

[0016] The inverter output side current in each cycle is fitted to obtain a waveform fitting curve of each cycle, and the average of the shortest distances between all inverter output side currents and the waveform fitting curve in each cycle is calculated as the deviation coefficient of the inverter output side current in each cycle;

[0017] A local window of each peak and trough is constructed with each peak and trough in the waveform fitting curve of each cycle as the center. The cumulative sum of the ranges in all local windows of each cycle is used as the jitter amplitude abnormal value of the inverter output side current of each cycle;

[0018] Perform frequency domain conversion on the current data in each local window, define the frequency with the largest amplitude as the fundamental frequency of the current data in each local window, and define other frequencies as non-fundamental frequencies. Calculate the ratio of the cumulative sum of the amplitudes corresponding to all non-fundamental frequencies in each cycle to the cumulative sum of the amplitudes corresponding to all frequencies as the jitter frequency anomaly value of the inverter output side current in each cycle.

[0019] The product of the jitter amplitude abnormal value and the jitter frequency abnormal value is used as the jitter abnormality coefficient of the inverter output side current in each cycle.

[0020] Preferably, the calculation method of the harmonic influence coefficient of the inverter output side current having waveform deviation and rapid jitter in each cycle is:

[0021] Where, is the harmonic influence coefficient of the inverter output current with waveform deviation and rapid jitter in the i-th cycle, are the jitter anomaly coefficient and deviation coefficient of the inverter output side current in the i-th cycle respectively.

[0022] Preferably, the method for obtaining the harmonic delay superposition interference coefficient is: taking the distance between the harmonic influence coefficient with pulsation amplitude difference and irregular characteristics in each cycle and the previous preset number of cycles and the harmonic influence coefficient with waveform deviation and rapid jitter as the harmonic delay superposition interference coefficient of each cycle.

[0023] Preferably, the correction formula for the inverter output current is: , where T is the correction current of the inverter output current in the current cycle, is the current data of the inverter output side, To preset the current adjustment range parameters, It is the normalized result of the harmonic delay superposition interference coefficient of the current cycle.

[0024] In a second aspect, an embodiment of the present application also provides a harmonic control system applied to a frequency converter, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, wherein when the processor executes the computer program, the steps of the harmonic control method applied to the frequency converter as described above are implemented.

[0025] In a third aspect, an embodiment of the present application further provides a harmonic control device applied to a frequency converter, wherein a computer program is stored in the device, and when the computer program is executed by a processor, any one of the above-mentioned harmonic control methods applied to a frequency converter is implemented.

[0026] As can be seen from the above, the harmonic control method, system, and device for a frequency converter provided by this application have at least the following beneficial effects:

[0027] This application deeply analyzes the abnormal waveform characteristics of the rectifier input side current and the inverter output side current in the inverter due to harmonic component interference, further considers the delayed superposition interference of the rectifier input side harmonics on the inverter output side current, calculates the harmonic delay superposition interference coefficient, and corrects the current output by the inverter based on this, thereby reducing the delayed superposition interference of the harmonics inside the inverter, improving the accuracy of the filter's harmonic suppression, and helping to make up for the defect of insufficient harmonic control capability of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0029] Figure 1 A flowchart of the steps of the harmonic control method applied to the frequency converter provided in this application;

[0030] Figure 2 A schematic diagram of the original current effect provided in an embodiment of the present application;

[0031] Figure 3 Schematic diagram of the waveform of the difference coefficient and irregular coefficient provided in the embodiment of the present application;

[0032] Figure 4 Schematic diagram of fluctuations in deviation coefficient and jitter anomaly coefficient provided in the embodiment of the present application;

[0033] Figure 5 A schematic diagram comparing harmonic influence coefficients provided in the embodiments of the present application;

[0034] Figure 6 A schematic diagram of comparative analysis of harmonic delay superposition interference coefficients provided in an embodiment of the present application;

[0035] Figure 7 A schematic diagram comparing the current spectrum correction effects provided in the embodiments of the present application;

[0036] Figure 8A schematic diagram comparing the inverter output current correction effects provided in an embodiment of the present application. DETAILED DESCRIPTION

[0037] To further illustrate the technical means and effectiveness of this application to achieve the intended invention objectives, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the harmonic control method, system, and device for a frequency converter proposed in this application, including its specific implementation, structure, features, and effectiveness. In the following description, different references to "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics of one or more embodiments may be combined in any suitable manner.

[0038] Unless otherwise specified and limited, terms such as "comprises", "includes" or any other variants thereof are intended to cover non-exclusive inclusion, so that a circuit structure, article or device comprising a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such article or device. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the article or device comprising the element. In addition, the term "and\or" used herein includes any and all combinations of one or more related listed items. All technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs.

[0039] The specific scheme of the harmonic control method, system and device for the inverter provided by the present application is described in detail below with reference to the accompanying drawings.

[0040] See also Figure 1 , which shows a flowchart of a harmonic control method applied to a frequency converter provided by an embodiment of the present application, including the following steps:

[0041] Step 1: Obtain current data on the rectifier input side and inverter output side of the inverter.

[0042] The core of a frequency converter (VFD) is to convert industrial AC power into AC power with adjustable frequency and voltage through the switching action of power electronic components, thereby achieving motor speed control. However, the rapid switching characteristics of these power electronic components cause distortion in the current waveform, generating harmonics. Taking a common AC-DC-AC VFD as an example, during the rectification process, the input current is non-sinusoidal. In addition to the fundamental wave (50 Hz), it also contains a series of higher-order harmonics. The frequencies of these harmonics are typically integer multiples of the fundamental frequency, such as the 5th, 7th, and 11th harmonics. This distortion causes the current data to no longer resemble a standard sine wave, but rather an irregular shape with spikes, dips, and multiple pulsations within a half-cycle. Even after processing by the VFD, the output current still contains various harmonic components. While the waveform is relatively regular and generally resembles a sine wave, harmonic suppression is still required to minimize interference with the motor. However, the harmonic characteristics of the rectifier input interfere with the inverter output current after a short delay. Therefore, in this embodiment, harmonic control is performed by analyzing the specific characteristics of the current on the rectifier input side and the inverter output side and the delay interference characteristics.

[0043] In this embodiment, the frequency converter mainly consists of three parts: a rectifier unit, a DC bus link, and an inverter unit. The rectifier unit converts AC power into DC power. In this embodiment, an IGBT rectifier bridge is used; the DC bus filters out pulsations and stabilizes the current through capacitors and inductors; the inverter unit uses PWM technology to invert DC power into variable-frequency AC power to drive the motor speed regulation. In addition, a filter is integrated at the output end to suppress harmonic interference. The impact of input-side harmonics on the rectifier unit is more significant, and the harmonic components of the rectifier unit will be transmitted to the inverter unit, further causing an increase in the harmonic components of the output-side current. In this embodiment, an oscilloscope is used to collect current waveform data on the input and output sides of the frequency converter. The data acquisition frequency is set to 1000HZ, and the collected currents are all AC.

[0044] So far, according to the above process of this embodiment, the current data of the rectifier input side and the inverter output side of the inverter can be obtained.

[0045] Specifically, in this embodiment, the original current effect diagram is as follows Figure 2 As shown in the original current effect diagram, the blue waveform is the current waveform diagram of the rectifier input side, and the red waveform is the current waveform diagram of the inverter output side. The specific original current waveform is as follows Figure 2 shown.

[0046] Step 2: Preset the cycle of current data, and obtain the difference coefficient of the overall pulsation amplitude change of each cycle through the difference degree of current data corresponding to the extreme points in the rectifier input side current in each cycle, and the fluctuation degree of the current data corresponding to the extreme points. According to the chaotic situation of the change of the extreme points in each cycle, the irregularity coefficient of the pulsation time change corresponding to each cycle is obtained. Combined with the difference coefficient of the overall pulsation amplitude change, the harmonic influence coefficient of the rectifier input side current in each cycle with pulsation amplitude difference and irregular characteristics is obtained.

[0047] The harmonics in the current data on the inverter's rectifier input side originate from grid fluctuations, the operation of the rectifier circuit, and other control circuits, resulting in significant distortion of the current waveform on the rectifier input side. Because the inverter circuit exhibits nonlinearity with respect to the grid, the grid current is no longer a standard sine wave but contains a significant amount of harmonic components. Furthermore, the current pulsates twice per half cycle. Therefore, the abnormal characteristics of this pulsation can better reflect the degree of distortion. Specifically, the greater the amplitude variation of the current pulsation and the more pronounced the irregularity of the pulsation position, the greater the impact of the harmonic components on the rectifier input side.

[0048] In view of this, in this embodiment, a quadratic polynomial fitting technique is used to fit the rectifier input side current to obtain the rectifier input side current curve. Then all the extreme points of the input side current curve are obtained, and the location of the extreme points is the location of the pulsation generated by the current. Furthermore, a standard current is preset, and the period corresponding to the fundamental frequency of the standard current is used as each period of the current, and the corresponding extreme point data under each period can be obtained, wherein the setting of the standard current is selected by the implementer in the actual application scenario. Taking the i-th cycle as an example, the amplitude change of the current pulsation is reflected in the degree of difference within the cycle and between cycles. Therefore, the difference between the two adjacent extreme values ​​in the i-th cycle is calculated respectively, and the average of the difference is used as the pulsation amplitude difference coefficient of the input side current of the i-th cycle, which is recorded as , income It reflects the difference characteristics of the current pulsation amplitude within the cycle.

[0049] Furthermore, the standard deviation of all extreme values ​​in the ith cycle and the two cycles before and after it is calculated respectively, and the mean of the two standard deviations is taken as the pulsation amplitude fluctuation coefficient of the ith cycle, which is recorded as . Income It reflects the fluctuation characteristics of the pulsation amplitude under different cycles.

[0050] Therefore, according to the pulsation amplitude difference coefficient and pulsation amplitude fluctuation coefficient of the input side current in each cycle, the difference coefficient of the overall pulsation amplitude change in each cycle is calculated. Preferably, in this embodiment, for the i-th cycle, and The mean of is taken as the difference coefficient of the overall pulsation amplitude change in the i-th cycle, recorded as , which reflects the difference in the change characteristics of the pulsation amplitude within a cycle and between cycles.

[0051] Furthermore, to obtain the irregular variation characteristics of the pulsation position, this embodiment sets a time window centered at the i-th cycle and with N cycles, where N is an odd number in the range [7, 11], and in this embodiment, is 9. Furthermore, the first-order difference sequence of the sequence corresponding to the time components of the extreme points of all cycles in the time window is calculated. For example, the first-order difference sequence of the sequence corresponding to the time components of the first extreme point of all cycles in the time window is calculated. The same calculation steps are used for each extreme point in the cycle to obtain the corresponding first-order difference sequence. Furthermore, the fractal dimension of each first-order difference sequence is obtained using the Higuchi algorithm. The method for calculating the fractal dimension is conventional and will not be described in detail in this embodiment.

[0052] In this embodiment, the average value of all fractal dimensions obtained with the i-th period as the center is recorded as , then calculate the average value of the distance between any two first-order difference sequences in all first-order difference sequences centered on each period. Preferably, the average value of the Manhattan distance between any two first-order difference sequences centered on the i-th period is recorded as , income 、 Respectively reflects the chaotic characteristics between the same subpulsation time and between different subpulsation times. and The mean of is taken as the irregular coefficient of the pulsation time change corresponding to the i-th cycle, recorded as , which reflects the irregularity of the pulsation time variation in the i-th cycle.

[0053] Therefore, in this embodiment, based on the irregular variation coefficient and the difference coefficient of each cycle, the harmonic influence coefficient of the rectifier input side current having the pulsation amplitude difference and irregular characteristics of each cycle is calculated. Preferably, the product of the difference coefficient and the irregular coefficient is used as the harmonic influence coefficient of the rectifier input side current having the pulsation amplitude difference and irregular characteristics of each cycle. For the convenience of understanding in this embodiment, the specific formula is:

[0054] Where, is the harmonic influence coefficient of the rectifier input side current with pulsation amplitude difference and irregular characteristics in the i-th cycle, is the difference coefficient of the overall pulsation amplitude change in the i-th cycle, is the irregular coefficient of the pulsation time change corresponding to the i-th cycle.

[0055] Among them, the income It reflects the abnormal characteristics of the current waveform on the rectifier input side, which has the irregular characteristics of pulsation amplitude difference and position.

[0056] Specifically, in this embodiment, the waveform diagram of the difference coefficient and the irregular coefficient is as follows: Figure 3 As shown, Figure 3 A-in is a fluctuation diagram of the difference coefficient of the overall pulsation amplitude change, which is used to characterize the difference in the amplitude change of the overall pulsation. Figure 3 R-in is a schematic diagram of the irregular coefficient fluctuation of the pulsation time change, which is used to characterize the irregularity of the pulsation time change. The specific situation is as follows Figure 3 shown.

[0057] Step 3: Obtain the deviation coefficient of the inverter output side current in each cycle based on the deviation of the inverter output side current data in each cycle, obtain the jitter abnormality coefficient of the inverter output side current in each cycle through the degree of current change in the local neighborhood of the inverter output side current peak and trough in each cycle, and the frequency of change of the frequency amplitude in the frequency domain, and combine the deviation coefficient of the inverter output side current to obtain the harmonic influence coefficient of the inverter output side current in each cycle with waveform deviation and rapid jitter.

[0058] Furthermore, the harmonics in the inverter output current data originate from pulse-width modulation, load variations, and the rectifier circuit. While the output current waveform is close to a sine wave and contains relatively few harmonics, there is still some deviation from the standard sine waveform, and the waveform exhibits high-frequency, rapid jitter, which is particularly noticeable at peaks and troughs. The more pronounced these characteristics are, the greater the impact of harmonics on the output current.

[0059] In view of this, this embodiment uses the sine wave fitting technology to fit the inverter output side current in each cycle to obtain the waveform fitting curve of the inverter output side current. Since the collected current data contains a certain amount of harmonic components, there is a certain deviation between it and the waveform fitting curve. Taking the i-th cycle as an example, the shortest distance between all the inverter output side current data and the waveform fitting curve in the i-th cycle is calculated respectively, and the average of all the shortest distances is used as the deviation coefficient of the inverter output side current. The deviation coefficient of the inverter output side current in the i-th cycle is recorded as Among them, the deviation coefficient of the inverter output side current reflects the degree of deviation between the inverter output side current and the standard current waveform.

[0060] Since the rapid jitter at the peaks and troughs is more severe than at other locations, the peaks and troughs of the waveform fitting curve are extracted. In this embodiment, a range of 0.002 seconds with each peak and trough as the center is set as the local window of each peak and trough. The range of all local windows in the i-th cycle is calculated, and the cumulative sum of all ranges is used as the jitter amplitude abnormal value of the inverter output side current in this cycle. The jitter amplitude abnormal value of the inverter output side current in the i-th cycle is recorded as . Income It reflects the abnormal characteristics of the jitter amplitude at the local positions of the peaks and troughs.

[0061] In order to further reflect the frequency characteristics of its jitter, the current data in each local window is converted into the frequency domain. In this embodiment, the discrete Fourier transform technology is used to obtain the frequency amplitude spectrum of the output side current data corresponding to each local window, where the frequency with the largest amplitude is the fundamental frequency of the current data in each local window, and the other frequencies are all harmonic frequency components of the non-fundamental frequency. All other frequencies are recorded as non-fundamental frequencies. The ratio of the cumulative sum of the amplitudes corresponding to all non-fundamental frequencies in the spectrum diagram to the cumulative sum of the amplitudes corresponding to all frequencies is calculated as the jitter frequency anomaly value of the inverter output side current in this cycle. The jitter frequency anomaly value of the inverter output side current in the i-th cycle is recorded as , income It reflects the abnormal characteristics of the jitter frequency of the output side current in the local window.

[0062] Furthermore, according to the jitter amplitude abnormal value and the jitter frequency abnormal value, the jitter abnormality coefficient of the inverter output side current of each cycle is calculated. Preferably, the product of the jitter amplitude abnormal value and the jitter frequency abnormal value is used as the jitter abnormality coefficient of the inverter output side current of each cycle. In this embodiment, for ease of understanding, the specific calculation formula is:

[0063] Where, is the jitter abnormality coefficient of the inverter output side current in the i-th cycle, is the abnormal value of the jitter amplitude of the inverter output side current in the i-th cycle, is the abnormal value of the jitter frequency of the inverter output side current in the i-th cycle.

[0064] Among them, the income It reflects the abnormal jitter amplitude and frequency characteristics at the peaks and troughs of the output current affected by harmonics.

[0065] Furthermore, in this embodiment, based on the jitter abnormality coefficient of the inverter output side current in each cycle and the deviation coefficient of the inverter output side current, the harmonic influence coefficient of the inverter output side current having waveform deviation and rapid jitter is calculated. Preferably, in this embodiment, the calculation formula is:

[0066] Where, is the harmonic influence coefficient of the inverter output current with waveform deviation and rapid jitter in the i-th cycle, is the jitter abnormality coefficient of the inverter output side current in the i-th cycle, is the deviation coefficient of the inverter output current in the i-th cycle.

[0067] Specifically, in this embodiment, the deviation coefficient and the jitter abnormality coefficient fluctuation diagram are as follows: Figure 4 As shown, Figure 4 In the diagram, B-out corresponds to the waveform of the deviation coefficient of the inverter output side current, and J-out is a schematic diagram of the fluctuation of the jitter abnormality coefficient of the inverter output side current. The specific changes are as follows: Figure 4 shown.

[0068] Among them, the income This reflects the abnormal characteristics of the inverter output side current waveform deviation and high-frequency rapid jitter. The larger it is, the more obvious the corresponding abnormal characteristics are.

[0069] Specifically, the schematic diagram of the comparison of harmonic influence coefficients in this embodiment is as follows: Figure 5 As shown, Figure 5 The specific waveforms of the harmonic influence coefficient H-in of the rectifier input side current with pulsation amplitude difference and irregular characteristics and the harmonic influence coefficient H-out of the inverter output side current with waveform deviation and rapid jitter are as follows: Figure 5 The blue and red waveforms in the middle, the specific changes are as follows Figure 5 shown.

[0070] Step 4: Utilize the harmonic influence coefficient of the pulsation amplitude difference and irregular characteristics of the rectifier input side current in each cycle and the harmonic influence coefficient of the waveform deviation and rapid jitter of the inverter output side current to obtain the harmonic delay superposition interference coefficient, and combine it with the current data of the inverter output side to correct the inverter output current.

[0071] In a frequency converter, AC power is first converted to DC by a rectifier. After filtering and stabilizing the power supply, it is then inverted back to variable-frequency AC power by an inverter. Therefore, the harmonic components on the rectifier input side have a certain degree of superimposed interference with the harmonic components on the inverter output side. This superimposed interference has a slight time delay. However, the more significant the indirect interference, the more likely the inverter's output current contains harmonic components.

[0072] Therefore, the distance between the harmonic influence coefficient with pulsation amplitude difference and irregular characteristics and the harmonic influence coefficient with waveform deviation and rapid jitter in each cycle and the previous preset number of cycles is used as the harmonic delay superposition interference coefficient of each cycle. Preferably, in this embodiment, the SBD (ShapeBasedDistance) distance between the harmonic influence coefficient with pulsation amplitude difference and irregular characteristics and the harmonic influence coefficient with waveform deviation and rapid jitter in the i-th cycle and the first five cycles is set as the harmonic delay superposition interference coefficient of the i-th cycle. The larger the harmonic delay superposition interference coefficient is, the more significant the delay superposition interference characteristics of the harmonics on the rectifier input side of the inverter on the inverter output side current in the cycle are. The calculation process of SBD is a well-known technology for those skilled in the art and will not be repeated in this embodiment.

[0073] This embodiment analyzes the waveform anomalies of the inverter's rectifier input and inverter output currents due to harmonic interference. Furthermore, the delayed and superimposed interference of the rectifier input harmonics on the inverter output current is considered. The harmonic delay and superimposed interference coefficient is calculated. A larger value indicates that the inverter's output current is more likely to contain harmonic components, resulting in a larger true inverter output current than the sampled current. Therefore, this embodiment uses this characteristic to correct the inverter output current.

[0074] Specifically, for the current cycle, the sigmoid function is used to normalize the obtained harmonic delay superposition interference coefficient, and the result is recorded as , the correction formula of the inverter output current is: , where T is the correction current of the inverter output current in the current cycle, is the current data of the inverter output side, is the normalized result of the harmonic delay superposition interference coefficient of the current cycle, is a current adjustment range parameter used to control the current adjustment range. Its value range is 2 to 8. The implementer can set it according to the actual application. In this embodiment, the value is 5.

[0075] Specifically, in this embodiment, the comparative analysis diagram of the harmonic delay superposition interference coefficient is as follows: Figure 6 As shown, Figure 6 In the equation, SBD is the SBD distance between the harmonic influence coefficient with pulsation amplitude difference and irregular characteristics and the harmonic influence coefficient with waveform deviation and rapid jitter. Figure 6 SBD is a waveform diagram of the harmonic delay superposition interference coefficient before normalization, and N (normalization) is a waveform diagram after the obtained harmonic delay superposition interference coefficient is normalized using a sigmoid function.

[0076] In this embodiment, the current spectrum correction effect comparison diagram is as follows: Figure 7 As shown, Figure 7 The figure shows the spectrum comparison diagram of the inverter output current in the frequency domain before and after the correction. At the same time, the harmonic components in the frequency domain before and after the correction are compared and analyzed. Figure 7 As shown; Among them, the comparison diagram of the inverter output current correction effect is shown in Figure 8 As shown, Figure 8 In the current correction effect comparison, the red and blue lines are schematic diagrams of the inverter output current waveforms before and after correction, respectively. The green line in the current correction difference is used to represent the deviation of the inverter output current before and after correction. The specific correction comparison and deviation are shown in Figure 2. Figure 8 shown.

[0077] Therefore, according to the above process of this embodiment, the inverter output current data can be corrected, and PID control technology is used in the filter to suppress harmonics. The PID input is the corrected current of the inverter output current and the standard desired current, thereby achieving real-time harmonic control. This helps to compensate for the defect of insufficient harmonic control capability of the inverter.

[0078] Based on the same inventive concept as the above method, an embodiment of the present application also provides a harmonic control system applied to a frequency converter, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of any one of the above-mentioned harmonic control methods applied to the frequency converter are implemented.

[0079] At the same time, an embodiment of the present application also provides a harmonic control device applied to a frequency converter, wherein a computer program is stored in the device, and when the computer program is executed by a processor, any one of the above-mentioned harmonic control methods applied to a frequency converter is implemented.

[0080] It should be understood that the order in which the embodiments of the present application are presented is for illustrative purposes only and does not necessarily represent the superiority or inferiority of the embodiments. Furthermore, the foregoing descriptions of specific embodiments of this specification are provided. Furthermore, the processes depicted in the accompanying drawings do not necessarily require the specific order or sequential sequence shown to achieve the desired results. In certain embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0081] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0082] The above content is only an implementation method of the present application and is not intended to limit the scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the scope of protection of the present application.

Claims

1. A harmonic control method applied to a frequency converter, characterized in that: The following steps are involved: Obtain current data on the rectifier input side and inverter output side of the inverter; The period of the preset current data is used to obtain the difference coefficient of the overall pulsation amplitude change in each period through the difference and fluctuation degree of the rectifier input side current in each period. The irregularity coefficient of the pulsation time change corresponding to each period is obtained based on the chaotic change of the current corresponding to the time in each period. Combined with the difference coefficient of the overall pulsation amplitude change, the harmonic influence coefficient of the rectifier input side current with pulsation amplitude difference and irregular characteristics in each period is obtained; Obtaining a deviation coefficient of the inverter output side current in each period based on the deviation of the inverter output side current data in each period; obtaining a jitter anomaly coefficient of the inverter output side current in each period based on the degree of change of the inverter output side current in each period and the frequency of change of the frequency amplitude in the frequency domain; and obtaining a harmonic influence coefficient of the inverter output side current having waveform deviation and rapid jitter in each period in combination with the deviation coefficient of the inverter output side current; The harmonic influence coefficient corresponding to the rectifier input side current and the inverter output side current in each cycle is used to obtain the harmonic delay superposition interference coefficient to correct the inverter output current; The method for obtaining the difference coefficient of the overall pulsation amplitude change of each cycle is: Fit the rectifier input side current, extract all extreme points of the fitted rectifier input side current curve, calculate the average of the differences between all two adjacent extreme values ​​in each cycle as the pulsation amplitude difference coefficient of the input side current in each cycle, calculate the standard deviation of each cycle and all extreme values ​​in the two cycles before and after it, take the average of the two standard deviations as the pulsation amplitude fluctuation coefficient of each cycle, and take the average of the pulse amplitude difference coefficient and the pulse amplitude fluctuation coefficient as the difference coefficient of the overall pulse amplitude change of each cycle; The method for obtaining the deviation coefficient and jitter abnormality coefficient of the inverter output side current in each cycle is as follows: The inverter output side current in each cycle is fitted to obtain a waveform fitting curve of each cycle, and the average of the shortest distances between all inverter output side currents and the waveform fitting curve in each cycle is calculated as the deviation coefficient of the inverter output side current in each cycle; A local window of each peak and trough is constructed with each peak and trough in the waveform fitting curve of each cycle as the center. The cumulative sum of the ranges in all local windows of each cycle is used as the jitter amplitude abnormal value of the inverter output side current of each cycle; Perform frequency domain conversion on the current data in each local window, define the frequency with the largest amplitude as the fundamental frequency of the current data in each local window, and define other frequencies as non-fundamental frequencies. Calculate the ratio of the cumulative sum of the amplitudes corresponding to all non-fundamental frequencies in each cycle to the cumulative sum of the amplitudes corresponding to all frequencies as the jitter frequency anomaly value of the inverter output side current in each cycle. The product of the jitter amplitude abnormal value and the jitter frequency abnormal value is used as the jitter abnormality coefficient of the inverter output side current in each cycle.

2. The harmonic control method applied to a frequency converter according to claim 1, characterized in that: The method for obtaining the irregular coefficient of the pulsation time change corresponding to each cycle is: A time window of each cycle is constructed with each cycle as the center, and the first-order difference sequence of the sequence corresponding to the time of the extreme point of the same sequence number of all cycles in the time window is statistically analyzed. The fractal dimension of each first-order difference sequence is extracted, and the average value of all fractal dimensions obtained with each cycle as the center and the average value of the distance between all arbitrary two first-order difference sequences is used as the irregularity coefficient of the pulsation time change corresponding to each cycle.

3. The harmonic control method applied to a frequency converter according to claim 1, wherein: The harmonic influence coefficient of the pulsation amplitude difference and irregular characteristics of the rectified input-side current in each cycle is the product of the difference coefficient and the irregular coefficient.

4. The harmonic control method for a frequency converter according to claim 1, wherein: The calculation method of the harmonic influence coefficient of the inverter output side current having waveform deviation and rapid jitter in each cycle is as follows: R i =L i ×Q i Where R i is the harmonic influence coefficient of the inverter output current with waveform deviation and rapid jitter in the i-th cycle, Q i 、L i are the jitter anomaly coefficient and deviation coefficient of the inverter output side current in the i-th cycle respectively.

5. The harmonic control method for a frequency converter according to claim 1, wherein: The method for obtaining the harmonic delay superposition interference coefficient is: the distance between the harmonic influence coefficient with pulsation amplitude difference and irregular characteristics in each cycle and the previous preset number of cycles and the harmonic influence coefficient with waveform deviation and rapid jitter is used as the harmonic delay superposition interference coefficient of each cycle.

6. The harmonic control method for a frequency converter according to claim 1, wherein: The correction formula for the inverter output current is: Y = W + Y × γ, where T is the correction current of the inverter output current in the current cycle, W is the current data on the inverter output side, Y is the preset current adjustment range parameter, and γ is the normalized result of the harmonic delay superposition interference coefficient in the current cycle.

7. A harmonic control system for a frequency converter, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that: When the processor executes the computer program, the steps of the harmonic control method applied to the frequency converter as claimed in any one of claims 1 to 6 are implemented.

8. A harmonic control device for a frequency converter, wherein a computer program is stored in the device, characterized in that: When the computer program is executed by a processor, the harmonic control method applied to a frequency converter as claimed in any one of claims 1 to 6 is implemented.

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