Three-phase unbalanced current detection method for refined control of power quality

Abstract

The present application relates to the field of current measurement technology, and specifically to a three-phase unbalanced current detection method for refined power quality control, the method comprising: constructing a waveform interval distortion rate based on the characteristic of the destroyed symmetry of the three-phase current signal, and at the same time constructing the instantaneousness corresponding to the waveform interval based on the characteristic of transient unbalance phenomena that may occur during the three-phase unbalanced current detection process, completing the initial weight construction of the LMS algorithm through the waveform interval distortion rate, instantaneousness and signal deviation, and adaptively completing the update of the step size in the LMS algorithm, so that there will be no large fluctuations when the weight is updated, and the convergence effect can be better achieved, so that the fundamental component of the obtained three-phase current signal is more accurate, and then completing the three-phase imbalance detection based on the fundamental component, thereby improving the accuracy and efficiency of the three-phase imbalance detection.

Description

Technical Field

[0001] The present application relates to the field of current measurement technology, and specifically to a three-phase unbalanced current detection method for refined power quality control. Background Art

[0002] The three-phase power system is the cornerstone of power supply. It provides efficient and stable energy to various electrical devices through the balanced distribution of three-phase current. Three-phase imbalance occurs when the amplitude, phase, or frequency of the three-phase current or voltage are inconsistent. Three-phase imbalance is a critical issue in the refined management and control of power quality. It can lead to a series of problems, including increased equipment losses, reduced operational reliability, increased power supply safety risks, and even shortened service life.

[0003] When calculating three-phase current imbalance, the three-phase fundamental component must first be extracted from the original waveform of the three-phase current signal. Accurately extracting the fundamental component is key to assessing power quality and calculating imbalance. Traditional algorithms typically use the least mean square error (LMS) algorithm to extract the fundamental component. However, the LMS algorithm requires setting initial weights and step sizes. In traditional algorithms, the initial weights are typically randomly initialized, resulting in large fluctuations during weight updates, making convergence difficult. Consequently, it is difficult to obtain an accurate fundamental component, reducing the accuracy of three-phase current imbalance detection. Summary of the Invention

[0004] In order to solve the above technical problems, the present application provides a three-phase unbalanced current detection method for refined power quality control to solve the existing problems.

[0005] The three-phase unbalanced current detection method for refined power quality control in this application adopts the following technical solutions:

[0006] An embodiment of the present application provides a three-phase unbalanced current detection method for refined power quality control, the method comprising the following steps:

[0007] Collect three-phase current signals in real time and obtain the original waveform signals of three-phase current;

[0008] Obtaining a sinusoidal signal synchronized with the fundamental wave of the three-phase current signal as a reference signal;

[0009] Divide the waveform interval by the zero point in the original waveform signal; obtain the midpoint of the waveform interval and the maximum value of the current signal intensity in the waveform interval; and take each pair of current signal points in the waveform interval that are equidistant from the midpoint as each corresponding point pair;

[0010] Determining the distortion rate of the waveform interval based on the difference between the current signal intensity at the midpoint and the maximum value, and the difference in current signal point intensities between the corresponding point pairs;

[0011] Calculate the sum of the change rates of the signal strength values of all current signals in each waveform interval, calculate the difference in distortion rate between each waveform interval and its previous waveform interval, and use the product of the sum of the change rates and the distortion rate difference as the instantaneousness of each waveform interval; calculate the signal strength difference between the first current signal point in each waveform interval and the current signal point at the same moment in the reference signal, use the product of the distortion and signal strength differences of each waveform interval and the sum of a preset minimum positive number as the denominator, and the instantaneousness of each waveform interval as the numerator, and use the obtained ratio as the initial weight of each waveform interval; obtain the filter weight corresponding to each current signal point in each waveform interval through the initial weight; and obtain the adjustment step size of the current waveform interval through the filter weight of the previous waveform interval;

[0012] The filter weight and the adjustment step are combined with the LMS algorithm to filter each phase current to obtain the fundamental component of each phase current; the three-phase imbalance of the three-phase current is detected by the fundamental component of the three-phase current.

[0013] In one embodiment, the waveform interval is: an interval between any two zero points in the original waveform signal of each phase current.

[0014] In one embodiment, the distortion rate of the waveform interval is expressed as: , where is the distortion rate of the Qth waveform interval, is the signal strength value of the midpoint q in the Qth waveform interval, is the maximum signal intensity of the current signal point in the Qth waveform interval, is the number of corresponding point pairs of the current signal in the Qth waveform interval, is the absolute value of the difference between the signal strength values of the two current signal points in the zth corresponding point pair in the Qth waveform interval. In one embodiment, the instantaneous expression of each waveform interval is:

[0015] , where is the instantaneousness of the Qth waveform interval, is the absolute value of the difference between the distortion rate of the Qth waveform interval and the previous waveform interval, is the number of current signal points in the Qth waveform interval, is the rate of change of the signal strength value of the yth current signal point in the Qth waveform interval. In one embodiment, the expression of the initial weight of each waveform interval is:

[0016] , where is the initial weight of the Qth waveform interval; 、 are the instantaneous and distortion properties of the Qth waveform interval respectively; is the absolute value of the difference between the signal strength of the first current signal point in the Qth waveform interval and the current signal point at the same moment in the reference signal; In one embodiment, the process of obtaining the filter weight corresponding to each current signal point in each waveform interval is as follows:

[0017] The difference between the reference signal and the filtered signal obtained by the LMS algorithm of the three-phase current is used as the error signal; the expression of the filter weight is:

[0018] , where 、 They are the first and The filter weight corresponding to each current signal point; Indicates the adjustment step of the current waveform interval; The first The signal strength of the current signal point corresponding to each current signal point in the error signal; The first In one embodiment, the process of obtaining the adjustment step size of the current waveform interval is as follows:

[0019] Based on the filter weight corresponding to each current signal point in the previous waveform interval and the difference between each current signal point and the corresponding signal point in the reference signal, the weighted mean value of the previous waveform interval is obtained, which is recorded as ;Record the adjustment step of the current waveform interval as , The expression is:

[0020] , where is the step size used when performing LMS filtering on the previous waveform interval; t represents the preset first adjustment factor; f is the preset direction adjustment factor; wherein, the direction adjustment factor is set as follows:

[0021] like is greater than 1, then f is 1; if is less than 1, then f is -1; if If is equal to 1, then f is 0. In one embodiment, the expression of the weighted mean value of the previous waveform interval is:

[0022] , where P represents the number of current signal points in the previous waveform interval, is the normalized value of the filter weight corresponding to the pth current signal point in the previous waveform interval, is the normalized value of the absolute value of the difference in signal strength between the pth current signal point in the previous waveform interval and the signal point at the same moment in the reference signal. In one embodiment, the filtering of each phase current by the filter weight and the adjustment step size is combined with the LMS algorithm, specifically:

[0023] When the current signal of each waveform interval is filtered by the LMS algorithm, the filter weight corresponding to the current signal point in the waveform interval and the adjustment step size of the waveform interval are used as the filter weight and step size in the LMS algorithm respectively, and the fundamental component of each phase current is output to obtain the fundamental component of each phase current signal.

[0024] This application has at least the following beneficial effects:

[0025] In this application, the three-phase current signal is divided into different waveform intervals. According to the characteristic that the current signal will produce waveform distortion when it is interfered with, the distortion rate of the waveform interval is constructed according to the characteristic that the symmetry of the signal in the waveform interval is destroyed. At the same time, the instantaneousness corresponding to the waveform interval is constructed according to the characteristics of the transient unbalance phenomenon that may occur during the three-phase unbalanced current detection process, thereby reducing the distortion effect caused by the transient unbalance phenomenon, thereby improving the detection accuracy and efficiency of the real transient unbalance phenomenon. The initial weight construction of the LMS algorithm is completed through the distortion rate, instantaneousness and signal deviation of the waveform interval, so that there will be no large fluctuations when the weight is updated, and the convergence effect can be better achieved. At the same time, the step size update in the LMS algorithm is adaptively completed, which improves the acquisition accuracy and efficiency of the fundamental component of the current signal, and then completes the three-phase imbalance detection based on the fundamental component, thereby improving the three-phase imbalance detection accuracy and efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] 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.

[0027] Figure 1 Flowchart of the three-phase unbalanced current detection method for refined power quality control provided in this application;

[0028] Figure 2 Schematic diagram of the process of obtaining the distortion rate of the waveform interval. DETAILED DESCRIPTION

[0029] In order to further illustrate the technical means and effects adopted by this application to achieve the predetermined invention purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, describes in detail the specific implementation method, structure, features and effects of the three-phase unbalanced current detection method for refined power quality control proposed in this application. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics of one or more embodiments may be combined in any suitable form.

[0030] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0031] The specific scheme of the three-phase unbalanced current detection method for refined power quality control provided by this application is described in detail below with reference to the accompanying drawings.

[0032] An embodiment of the present application provides a three-phase unbalanced current detection method for refined power quality control.

[0033] Specifically, the following three-phase unbalanced current detection method for refined power quality control is provided. Figure 1 , the method comprises the following steps:

[0034] Step S1: collect three-phase current signals in real time to obtain original waveform signals of the three-phase currents.

[0035] Data preparation: In this application, a high-precision current transformer is used to collect the three-phase current signal of the power system in real time, wherein the three-phase current signal is converted into a digital signal through a signal conditioning circuit and ADC conversion (analog-to-digital converter), wherein the fixed sampling rate in the ADC conversion is set to 3.2kHz. As other embodiments of this application, the implementer can set the fixed sampling rate according to the actual situation. The three-phase signals are synchronously sampled by ADC to ensure time alignment and avoid errors in phase calculation, and then a three-phase current digital signal can be obtained as the original waveform signal of the three-phase current signal. Signal conditioning circuits and ADC conversion are both well-known technologies, and the specific process will not be repeated here.

[0036] Step S2, obtaining a sinusoidal signal synchronized with the fundamental wave of the three-phase current signal as a reference signal; dividing the waveform interval by the zero point in the original waveform signal; and constructing the distortion rate of the waveform interval based on the distribution symmetry of the current signal intensity in the waveform interval.

[0037] The original waveform signals of the three-phase current signals are obtained according to the above steps. Ideally, the three-phase current signals should be sinusoidal waves with equal amplitudes and a phase difference of 120°. However, in actual systems, amplitude imbalance, phase offset, harmonic distortion, and noise interference may exist, which can cause the three-phase current signals to be unbalanced. The three phases are respectively designated as phase A, phase B, and phase C.

[0038] Traditional three-phase current imbalance detection directly calculates the three-phase current imbalance based on the difference between the three-phase currents. However, during this process, noise, harmonics, and transients in the current signal can interfere with the current signal, leading to algorithm misjudgment and incorrect detection of three-phase current imbalance.

[0039] Therefore, when calculating three-phase current imbalance, it is necessary to first extract the three-phase fundamental components from the original waveform of the three-phase current signal. The three-phase fundamental component refers to the sinusoidal component in each phase current in a three-phase AC system, whose frequency is consistent with the system's nominal power frequency. It is the dominant component during normal operation of the power system and is used to characterize the core parameters of power transmission. However, the superposition of harmonic components (such as third and fifth harmonics) on the fundamental wave can cause waveform distortion. Accurately extracting the fundamental component is key to assessing power quality and calculating imbalance. The system's nominal power frequency refers to the standard operating frequency specified during power system design.

[0040] The traditional LMS algorithm is an adaptive filtering algorithm based on gradient descent. It iteratively adjusts filter weights to minimize the mean squared error between the output signal and the desired signal. The LMS algorithm requires setting initial weights and a step size. In traditional algorithms, initial weights are often randomly initialized, resulting in large fluctuations during weight updates and difficulty achieving convergence. While a large step size can accelerate convergence, it may cause oscillations or divergence near the optimal solution, resulting in only a local optimal solution. A small step size requires more iterations for the model to converge, resulting in poor results.

[0041] The input signal in the LMS algorithm is a three-phase current signal with interference, including fundamental, harmonics, and noise. The reference signal in the LMS algorithm is set to a sinusoidal signal synchronized with the fundamental to extract the target fundamental component. The sinusoidal signal synchronized with the fundamental can be generated by tracking the grid frequency through a phase-locked loop (PLL). The original waveform signal of the three-phase current is filtered through the traditional LMS algorithm to obtain the filtered signal. The error signal can then be expressed as , where is the nth current signal point in the error signal, is the nth current signal point in the reference signal, is the nth current signal point in the filtered signal. Among them, the LMS algorithm and the acquisition of the error signal therein, as well as the phase-locked loop are all well-known technologies, and the specific process will not be repeated here. Here, the A-phase current signal is taken as an example, the original waveform signal in the A-phase current signal is analyzed, the zero point of the original waveform signal is obtained, and the interval between any two adjacent zero points is recorded as the waveform interval. According to the characteristics of the sine wave, the waveform interval is symmetrical. However, when there are harmonics or noise in the three-phase current signal, the symmetry of the waveform signal will be destroyed. The distortion rate of the waveform interval is constructed according to the degree of destruction of the symmetry of the waveform interval, specifically:

[0042] Taking the Qth waveform interval as an example, first, obtain the midpoint between the two zero points of the waveform interval. The current signal points on both sides of the midpoint can be formed into corresponding point pairs with equal distances according to the distance between the current signal point and the midpoint. That is, the two current signal points in the corresponding point pair are respectively located on both sides of the midpoint q of the waveform interval, and the timing distances between these two current signal points and the midpoint q are equal.

[0043] Furthermore, for each waveform interval of the phase A current signal, the distortion rate of the waveform interval is constructed by the difference in the current signal point intensity of the corresponding point pair and the distribution characteristics of the signal intensity of the midpoint in the waveform interval. The expression is: , where is the distortion rate of the Qth waveform interval, is the signal strength value of the midpoint q in the Qth waveform interval, is the maximum signal intensity of the current signal point in the Qth waveform interval, is the number of corresponding point pairs of the current signal in the Qth waveform interval, is the absolute value of the difference in signal strength between the two current signal points in the zth corresponding point pair within the Qth waveform interval. The signal strength of a current signal point is the absolute value of its amplitude. The greater the difference between the midpoint signal strength and the maximum signal strength, the less likely the midpoint in the Qth waveform interval is a symmetrical midpoint, and the greater the distortion rate. The larger the value is, the less symmetric the waveform interval is and the greater the distortion rate is.

[0044] The greater the distortion rate, the greater the interference experienced by the waveform interval, that is, the greater the degree of symmetry destruction, and the smaller the corresponding weight, which is the smaller the contribution to the current filter output. The smaller the distortion rate, the less interference experienced by the waveform interval, and the greater the corresponding weight.

[0045] Step S3 : constructing the instantaneousness of each waveform interval based on the difference in distortion rate between each waveform interval and the previous waveform interval, and the current signal intensity variation characteristics of each waveform interval.

[0046] According to the above steps, the distortion rate of the waveform interval can be obtained. In the detection of three-phase current imbalance, transient imbalance is usually involved. Transient imbalance refers to the short-term imbalance of three-phase current or voltage in the power system or equipment due to instantaneous load changes, faults, or other rapidly changing factors. It usually occurs instantaneously and returns to a balanced state in a short time. When this transient imbalance occurs, it usually causes the generation of harmonic components, resulting in instantaneous distortion or distortion of the current waveform, that is, the current waveform no longer conforms to the ideal sinusoidal waveform. The distortion rate of the waveform interval is large. Therefore, when the distortion rate is directly used to obtain the weight of the current signal at this time, the current signal corresponding to the transient imbalance will be filtered, resulting in the inability to detect the transient imbalance phenomenon or low detection accuracy. Therefore, in this application, the instantaneous nature of the waveform interval is constructed by analyzing the transient characteristics of the waveform interval, and the distortion rate is constrained and optimized by the instantaneous nature, so that the current signal corresponding to the transient imbalance phenomenon still has a higher weight, thereby improving the detection accuracy and efficiency of the transient imbalance phenomenon. The specific process is as follows:

[0047] Taking each waveform interval in the A-phase current signal as an example, the waveform interval before the Q-th waveform interval is obtained and recorded as waveform interval W. When waveform interval Q is affected by transient unbalance and the distortion rate is large, the current signal intensity within waveform interval Q changes sharply, that is, the current signal intensity changes at a fast rate. Due to the rapid change, the distortion rate between different waveform intervals also varies greatly. However, the distortion rate between waveform intervals affected by noise and other factors varies less. Therefore, the instantaneous nature of each waveform interval is adaptively constructed by the change in current signal intensity and distortion between waveform intervals. The expression is:

[0048] , where is the instantaneousness of the Qth waveform interval, is the absolute value of the difference between the distortion rate of the Qth waveform interval and the previous waveform interval W, is the number of current signal points in the Qth waveform interval, is the rate of change of the signal strength value of the yth current signal point in the Qth waveform interval. The rate of change may be obtained by calculating the absolute value of the difference between the signal strengths of each current signal point and the next current signal point, and using the ratio of the absolute value of the difference to the time between the two current signal points as the rate of change of each current signal point.

[0049] The greater the degree to which the current waveform does not conform to the ideal sine waveform, the greater the distortion rate of the waveform interval. Therefore, when the difference between the distortion rate of the Qth waveform interval and the previous waveform interval W is greater, the greater the difference in the degree of the ideal sine waveform between the two adjacent waveform intervals, that is, The larger the value, the more likely it is that the waveform interval’s distortion rate difference is caused by transient imbalance. Therefore, a larger initial weight should be assigned to the waveform interval to avoid the initial weight being too small, which will cause the model to require too many iterations to converge. In this case, the greater the instantaneity.

[0050] When transient unbalance occurs, it usually causes the generation of harmonic components, resulting in instantaneous distortion or distortion of the current waveform, which increases the rate of change of the signal strength values of certain current signal points in the waveform interval. Therefore, when the rate of change of the signal strength values of each current signal point in the waveform interval is greater, the possibility of transient unbalance in the waveform interval is greater, and the waveform interval should be given a larger initial weight to avoid the initial weight value being too small, which will require too many iterations for the model to converge. In this case, the instantaneousness is greater;

[0051] On the contrary, the smaller the difference between the distortion rates of the waveform interval W and the smaller the rate of change of the signal strength value of each current signal point, the smaller the possibility of transient imbalance in the waveform interval, and the smaller the initial weight should be assigned to the waveform interval. At this time, the instantaneousness S is smaller.

[0052] Step S4, based on the distortion rate and instantaneousness of each waveform interval, and the difference between the current signal at each moment and the current signal at the corresponding moment in the reference signal, determine the initial weight of each waveform interval; obtain the filter weight corresponding to each current signal point in each waveform interval through the initial weight; obtain the adjustment step of the current waveform interval through the filter weight of the previous waveform interval.

[0053] According to the above steps, the instantaneous and distortion properties corresponding to the waveform interval are obtained. Taking the Qth waveform interval in the A-phase current signal as an example, based on the instantaneous and distortion properties, the initial weight of the current signal in the waveform interval for the LMS algorithm is adaptively obtained, and the expression is:

[0054] , where is the initial weight of the first current signal point in the Qth waveform interval; is the instantaneousness of the Qth waveform interval; is the distortion of the Qth waveform interval; is the absolute value of the difference between the signal strength of the first current signal point in the Qth waveform interval and the current signal point at the same moment in the reference signal; To preset a minimum positive number to prevent the denominator from being 0, preferably, in the embodiment of the present application, The value of is set to 0.01. As other embodiments of this application, the implementer can set it according to the actual situation. value. The larger the value, the greater the possibility of signal distortion, and the smaller the corresponding filter weight. The current signal in each waveform interval is used as the input of the LMS algorithm, and the initial weight value of each waveform interval is used as the initial value of the weight in the algorithm to complete the weight initialization of the LMS algorithm. Furthermore, the update of the filter weight in the LMS algorithm can be adaptively completed. The LMS algorithm updates the filter weight through iteration, and its process is well known, and the expression can be:

[0055] , where 、 They are the first and The filter weight corresponding to each current signal point; Indicates the adjustment step of the current waveform interval; The first The signal strength of the current signal point corresponding to each current signal point in the error signal; The first The signal strength of each current signal point.

[0056] Furthermore, the step size in the LMS algorithm corresponding to the current waveform interval is adjusted based on the filter weight corresponding to the current signal point in the previous waveform interval and the signal strength difference between the current signal and the reference signal in the previous waveform interval to obtain the adjustment step size of the current waveform interval. The expression is:

[0057] , where is the adjustment step of the current waveform interval; is the step size used when performing LMS filtering on the previous waveform interval; t represents a preset first adjustment factor, the value range of t is 0-1, and is used to limit the adjustment amplitude to avoid an excessively large step adjustment range. Preferably, in the embodiment of the present application, t is set to 0.1; f is a preset direction adjustment factor, used to adjust the direction; is the weighted mean of the previous waveform interval. As other embodiments of the present application, the implementer can set the value of t according to the actual situation. , where P represents the number of current signal points in the previous waveform interval, is the normalized value of the filter weight corresponding to the pth current signal point in the previous waveform interval, is the normalized value of the absolute value of the difference between the signal strength of the pth current signal point in the previous waveform interval and the signal point at the same moment in the reference signal. In this embodiment of the present application, the initial step size in the LMS algorithm is set to 0.05. As other embodiments of the present application, the implementer can set the initial step size according to the actual situation. If is greater than 1, then f is 1; if If it is less than 1, f is -1, and the maximum value of the step size change after each adjustment is limited to ;like If it is equal to 1, then f is 0, that is, the step size does not change. A value equal to 1 indicates that at this step size, the signal quality and signal difference are balanced, the filter processing effect is good, and no adjustment is required. The step size is adaptively updated after each waveform interval signal is processed. This allows adaptive weight initialization and step size adjustment of the LMS algorithm. Step S5: Using the filter weights and the adjusted step size, the LMS algorithm is combined to filter each phase current to obtain the fundamental component of each phase current; the three-phase current imbalance is detected using the fundamental components of the three-phase current.

[0058] When filtering the current signal in each waveform interval using the LMS algorithm, the filter weights corresponding to the current signal points in the waveform interval and the adjustment step size of the waveform interval obtained above are used as the filter weights and step size in the LMS algorithm, respectively, where the filter order is set to 20. The fundamental component of each waveform interval is output, and the fundamental component of each phase current signal is obtained. It should be noted that the filter order can be set by the implementer according to actual conditions and is not specifically limited in this application.

[0059] The three-phase current signal can be processed through the above steps to complete the extraction of the three-phase current fundamental component, and the three-phase current imbalance degree can be calculated based on the extracted three-phase current fundamental component. The three-phase current imbalance degree refers to the degree of deviation of the three-phase current and reflects the balance state between the phases in the three-phase system. The calculation of the three-phase current imbalance degree is a well-known technology and the calculation formula is:

[0060] ,in is the current imbalance, Indicates the maximum value among the three-phase currents. Indicates the minimum value among the three-phase currents. Indicates the average value of three-phase current.

[0061] The schematic diagram of the process of obtaining the distortion rate of the waveform interval is as follows: Figure 2 shown.

[0062] In summary, the embodiment of the present application divides the three-phase current signal into different waveform intervals, and constructs the waveform distortion rate of the waveform interval according to the characteristic that the current signal will produce waveform distortion due to interference and the characteristic that the symmetry of the signal in the waveform interval is destroyed. At the same time, the instantaneousness corresponding to the waveform interval is constructed according to the characteristics of the transient unbalance phenomenon that may occur during the three-phase unbalanced current detection process, thereby reducing the distortion effect caused by the transient unbalance phenomenon, thereby improving the detection accuracy and efficiency of the real transient unbalance phenomenon. The initial weight construction of the LMS algorithm is completed through the distortion rate, instantaneousness and signal deviation of the waveform interval, so that there will be no large fluctuations when the weight is updated, and the convergence effect can be better achieved. At the same time, the step size update in the LMS algorithm is adaptively completed, thereby improving the acquisition accuracy and efficiency of the fundamental component of the current signal, and then completing the three-phase imbalance detection based on the fundamental component, thereby improving the three-phase imbalance detection accuracy and efficiency.

[0063] It should be noted 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 above descriptions are of specific embodiments of the present application. 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.

[0064] The various embodiments in this application 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.

[0065] The above-described embodiments are only used to illustrate the technical solutions of the present application, and not to limit them. Modifications to the technical solutions described in the aforementioned embodiments, or equivalent replacements of some of the technical features therein, 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 application, and should all be included in the scope of protection of the present application.

Claims

1. A three-phase unbalanced current detection method for refined power quality control, characterized in that: The method comprises the following steps: Collect three-phase current signals in real time and obtain the original waveform signals of three-phase current; Obtaining a sinusoidal signal synchronized with the fundamental wave of the three-phase current signal as a reference signal; Divide the waveform interval by the zero point in the original waveform signal; obtain the midpoint of the waveform interval and the maximum value of the current signal intensity in the waveform interval; and take each pair of current signal points in the waveform interval that are equidistant from the midpoint as each corresponding point pair; Determining the distortion rate of the waveform interval based on the difference between the current signal intensity at the midpoint and the maximum value, and the difference in current signal point intensities between the corresponding point pairs; Calculating the sum of the change rates of the signal strength values of all current signals in each waveform interval, calculating the difference in distortion rate between each waveform interval and its previous waveform interval, and taking the product of the sum of the change rates and the difference in distortion rate as the instantaneousness of each waveform interval; Calculating the signal strength difference between the first current signal point in each waveform interval and the current signal point at the same moment in the reference signal, using the product of the distortion and signal strength difference of each waveform interval and the sum of a preset minimum positive number as the denominator, and the instantaneousness of each waveform interval as the numerator, and the resulting ratio as the initial weight of each waveform interval; obtaining the filter weight corresponding to each current signal point in each waveform interval based on the initial weight; and obtaining the adjustment step size of the current waveform interval based on the filter weight of the previous waveform interval; By using the filter weight and the adjustment step size, combined with the LMS algorithm, each phase current is filtered to obtain the fundamental component of each phase current; the three-phase imbalance of the three-phase current is detected by the fundamental component of the three-phase current; The expression of the distortion rate of the waveform interval is: , where is the distortion rate of the Qth waveform interval, is the signal strength value of the midpoint q in the Qth waveform interval, is the maximum signal intensity of the current signal point in the Qth waveform interval, is the number of corresponding point pairs of the current signal in the Qth waveform interval, It is the absolute value of the difference between the signal strength values of the two current signal points in the zth corresponding point pair in the Qth waveform interval.

2. The three-phase unbalanced current detection method for refined power quality control according to claim 1, characterized in that: The waveform interval is: the interval between any two zero points in the original waveform signal of each phase current.

3. The three-phase unbalanced current detection method for refined power quality control according to claim 1, characterized in that: The instantaneous expression of each waveform interval is: , where is the instantaneousness of the Qth waveform interval, is the absolute value of the difference between the distortion rate of the Qth waveform interval and the previous waveform interval, is the number of current signal points in the Qth waveform interval, is the rate of change of the signal intensity value of the yth current signal point in the Qth waveform interval.

4. The three-phase unbalanced current detection method for refined power quality control according to claim 1, characterized in that: The expression of the initial weight of each waveform interval is: , where is the initial weight of the Qth waveform interval; 、 are the instantaneous and distortion properties of the Qth waveform interval respectively; is the absolute value of the difference between the signal strength of the first current signal point in the Qth waveform interval and the current signal point at the same moment in the reference signal; A preset minimum positive number.

5. The three-phase unbalanced current detection method for refined power quality control according to claim 1, characterized in that: The process of obtaining the filter weight corresponding to each current signal point in each waveform interval is as follows: The difference between the reference signal and the filtered signal obtained by the LMS algorithm of the three-phase current is used as the error signal; the expression of the filter weight is: , where 、 They are the first and The filter weight corresponding to each current signal point; Indicates the adjustment step of the current waveform interval; The first The signal strength of the current signal point corresponding to each current signal point in the error signal; The first The signal strength of each current signal point.

6. The three-phase unbalanced current detection method for refined power quality control according to claim 1, characterized in that: The process of obtaining the adjustment step size of the current waveform interval is as follows: Based on the filter weight corresponding to each current signal point in the previous waveform interval and the difference between each current signal point and the corresponding signal point in the reference signal, the weight mean of the previous waveform interval is obtained, which is recorded as ;Record the adjustment step of the current waveform interval as , The expression is: , where is the step size used when performing LMS filtering on the previous waveform interval; t represents the preset first adjustment factor; f is the preset direction adjustment factor; wherein, the direction adjustment factor is set as follows: like is greater than 1, then f is 1; if is less than 1, then f is -1; if is equal to 1, then f is 0.

7. The three-phase unbalanced current detection method for refined power quality control according to claim 6, characterized in that: The expression of the weighted mean value of the previous waveform interval is: , where P represents the number of current signal points in the previous waveform interval, is the normalized value of the filter weight corresponding to the pth current signal point in the previous waveform interval, It is the normalized value of the absolute value of the difference in signal strength between the pth current signal point in the previous waveform interval and the signal point at the same moment in the reference signal.

8. The three-phase unbalanced current detection method for refined power quality control according to claim 1, characterized in that: The filtering of each phase current is performed by using the filter weight and the adjustment step size in combination with the LMS algorithm, specifically: When the current signal of each waveform interval is filtered by the LMS algorithm, the filter weight corresponding to the current signal point in the waveform interval and the adjustment step size of the waveform interval are used as the filter weight and step size in the LMS algorithm respectively, and the fundamental component of each phase current is output to obtain the fundamental component of each phase current signal.

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