A three-phase unbalance characterization method and system based on combined waveform skewness

Abstract

The present application belongs to the technical field of three-phase imbalance of power system, and specifically discloses a three-phase imbalance characterization method and system based on combined waveform skewness; the method comprises the following steps: obtaining three-phase voltage data of one half cycle with the rising zero point of the reference phase voltage as the starting point; constructing a single-cycle combined voltage waveform containing the reference phase and the deviation phase; calculating the third-order central moment of the combined waveform and normalizing to obtain the combined waveform skewness index; combining the skewness index and the combined waveform probability distribution histogram to realize qualitative identification and quantitative characterization of three-phase imbalance disturbance. The present application greatly reduces the calculation complexity, reduces the precision requirement of the monitoring equipment, can quickly adapt to the real-time processing requirements of edge and end lightweight monitoring scenes, and effectively avoids the problems of data processing delay and high equipment cost in the prior art.

Description

Technical Field

[0001] This invention relates to the field of three-phase imbalance technology in power systems, and in particular to a method and system for characterizing three-phase imbalance based on combined waveform skewness. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] As the core link connecting power sources and users in the power system, the operation of the distribution network directly affects the reliability and quality of power supply. With the high proportion of distributed renewable energy integration and the rapid growth of nonlinear and asymmetrical loads such as electric vehicle charging facilities and precision electronic equipment, three-phase imbalance is becoming increasingly prominent. This problem not only leads to increased transformer and line losses and shortened equipment lifespan, but may also trigger cascading power quality issues such as voltage sags and harmonic amplification, seriously affecting the continuity of industrial production and the safety of residential electricity use. Therefore, there is an urgent need to construct an efficient and accurate three-phase imbalance monitoring and characterization scheme.

[0004] Existing methods for calculating three-phase unbalance require extracting the fundamental component from sampled voltage data using Fourier decomposition, then decomposing it into positive-sequence, negative-sequence, and zero-sequence components using the symmetrical component method. Finally, the ratio of negative-sequence voltage to positive-sequence voltage is used as the unbalance evaluation index. However, this calculation method relies on precise fundamental voltage amplitude and phase angle information, placing extremely high demands on the accuracy of monitoring equipment. Furthermore, the calculation process is complex and computationally intensive, and delays are prone to occur in real-time processing of massive amounts of data. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a three-phase imbalance characterization method and system based on combined waveform skewness. The method constructs a single-cycle combined voltage waveform containing a reference phase and a deviation phase, determines the skewness index by calculating the third-order central moment of the combined waveform, and uses the skewness index to characterize the three-phase imbalance.

[0006] In some implementations, the following technical solutions are adopted: A three-phase imbalance characterization method based on combined waveform skewness includes: Acquire three-phase voltage data for one half-cycle, starting from the zero-crossing point of the reference phase voltage rise; A single-cycle combined voltage waveform containing a reference phase and a deviation phase is constructed. The positive half-cycle of the combined voltage waveform is composed of the positive half-cycle of the reference phase voltage, and the negative half-cycle is composed of the half-cycle waveform of the deviation phase voltage starting from the ideal zero crossing point. Calculate the mean of the first-order origin moments of the combined waveform, and calculate the third-order central moments of the combined waveform based on the mean; standardize the third-order central moments to obtain the skewness index of the combined waveform. The three-phase imbalance disturbance is characterized based on the combined waveform skewness index.

[0007] As a further embodiment, the single-cycle combined voltage waveform is specifically as follows: ; in, The instantaneous value of the combined waveform is represented by T; T represents the period of the voltage waveform. Represents the instantaneous value of the reference phase voltage. This represents the instantaneous value of the deviation phase voltage. It represents the angle difference between the ideal waveform of the deviation phase and the reference phase.

[0008] As a further solution, the third-order central moment of the combined waveform is calculated based on the mean, specifically as follows: ; in, The third central moment of the combined waveform is represented by... Represents the instantaneous value of the combined waveform. This represents the mean of the first-order raw moments of the combined waveform. E [·] represents the expectation operator.

[0009] As a further solution, the third-order central moment is standardized to obtain a combined waveform skewness index, specifically: ; in, To combine waveform skewness indices, Represents the instantaneous value of the combined waveform. This represents the mean of the first-order raw moments of the combined waveform. E [·] represents the expectation operator.

[0010] As a further approach, the three-phase unbalance disturbance is characterized based on the combined waveform skewness index, specifically as follows: If the combined waveform skewness index is zero, it indicates a three-phase balanced operating condition. If the combined waveform skewness index is not zero, it indicates the presence of a three-phase imbalance disturbance; and the magnitude of the combined waveform skewness index is used to characterize the severity of the three-phase imbalance.

[0011] As a further solution, it also includes: when it is determined that there is a three-phase unbalanced disturbance, drawing a probability distribution histogram of the single-cycle combined voltage waveform, and determining the three-phase unbalanced operating condition based on the probability distribution histogram; the three-phase unbalanced operating condition includes phase angle unbalance, amplitude unbalance, and both phase angle and amplitude unbalance.

[0012] As a further approach, the three-phase imbalance condition is determined based on the probability distribution histogram, specifically as follows: If the probability distribution histogram has a characteristic distribution of missing blocks and multiple blocks on both sides of the axis of symmetry, it is determined that there is a phase angle imbalance, and the direction of phase angle offset is determined according to the characteristic distribution. If the probability distribution histogram has a characteristic distribution where the extreme points are far from the zero symmetry axis, it is determined that there is an imbalance in amplitude, and the sign of the amplitude deviation is determined based on the characteristic distribution. If the probability distribution histogram simultaneously exhibits the composite characteristic distribution of phase imbalance and amplitude imbalance mentioned above, it is determined that both phase imbalance and amplitude imbalance exist simultaneously.

[0013] In other embodiments, the following technical solutions are adopted: A three-phase imbalance characterization system based on combined waveform skewness includes: The data acquisition module is configured to acquire three-phase voltage data for one half-cycle, starting from the zero-crossing point of the reference phase voltage. The combined waveform construction module is configured to construct a single-cycle combined voltage waveform containing a reference phase and a deviation phase. The positive half-cycle of the combined voltage waveform is composed of the positive half-cycle of the reference phase voltage, and the negative half-cycle is composed of the half-cycle waveform of the deviation phase voltage starting from the ideal zero crossing point. The skewness index calculation module is configured to calculate the mean of the first-order origin moments of the combined waveform, calculate the third-order central moments of the combined waveform based on the mean, and standardize the third-order central moments to obtain the skewness index of the combined waveform. The three-phase imbalance characterization module is configured to characterize the three-phase imbalance disturbance based on the combined waveform skewness index.

[0014] In other embodiments, the following technical solutions are adopted: A terminal device includes a processor and a memory, the processor being used to implement instructions; the memory being used to store multiple instructions adapted to be loaded and executed by the processor to represent the three-phase imbalance based on combined waveform skewness as described above.

[0015] In other embodiments, the following technical solutions are adopted: A computer-readable storage medium storing a plurality of instructions adapted for loading and execution by a processor of a terminal device of the above-described three-phase imbalance characterization method based on combined waveform skewness.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) Existing three-phase imbalance characterization methods rely on accurate voltage amplitude and phase information, and require Fourier decomposition to extract the fundamental component and then the symmetric component method to decompose the sequence component. The calculation process is complex and computationally intensive, making it difficult to adapt to the lightweight monitoring scenario at the edge of the distribution network and the real-time processing requirements of massive data. This invention starts from the actual needs of efficient monitoring and accurate characterization of the distribution network, and innovatively constructs a combined waveform model containing the reference phase and the deviation phase. It transforms the traditional imbalance characterization problem based on the sequence component into an asymmetric analysis problem of the probability distribution of the combined waveform. It does not rely on Fourier decomposition and the symmetric component method, which greatly reduces the computational complexity and the accuracy requirements of the monitoring equipment. It can quickly adapt to the real-time processing requirements of the lightweight monitoring scenario at the edge and effectively avoid the problems of data processing delay and high equipment cost in the existing technology.

[0017] (2) Traditional three-phase imbalance evaluation indexes can only achieve a single quantification of the degree of imbalance and cannot accurately identify the specific working condition type of imbalance. This invention can intuitively capture the waveform feature differences under different imbalance working conditions by drawing a histogram of probability distribution of combined waveforms, and realize the qualitative identification of specific working condition types such as only phase angle imbalance, only amplitude imbalance, and both, which solves the pain point that traditional technology cannot distinguish the cause of imbalance. At the same time, the skewness index is introduced, and quantitative characterization parameters are constructed based on the standardization of the third-order central moment. The odd power characteristic of skewness is used to accurately reflect the probability distribution deviation state. When the three phases are balanced, the skewness is 0. When unbalanced, the index value deviates regularly with the severity. It can quickly judge the existence of imbalance disturbance and quantitatively characterize the severity of imbalance, forming a dual technical capability of "qualitative identification + quantitative characterization".

[0018] Compared to the traditional single characterization mode that only uses the ratio of negative-sequence voltage to positive-sequence voltage as an evaluation index, the characterization method of this invention is more comprehensive and targeted. It not only simplifies the monitoring and calculation process, but also improves the accuracy and reliability of three-phase imbalance characterization. It can provide stronger technical support for real-time monitoring, fault diagnosis and precise management of three-phase imbalance in distribution networks, and has significant engineering application value and innovation.

[0019] Other features and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] Figure 1 This is a flowchart of the three-phase imbalance characterization method based on combined waveform skewness in an embodiment of the present invention; Figure 2 This is a schematic diagram of the voltage waveform under the condition of phase angle imbalance only in an embodiment of the present invention; Figure 3This is a schematic diagram of the voltage waveform under the condition of amplitude imbalance only in an embodiment of the present invention; Figure 4 This is a schematic diagram of the voltage waveform under the condition of unbalanced amplitude and phase angle in an embodiment of the present invention; Figure 5 This is a schematic diagram of the combined waveform with only phase angle imbalance in an embodiment of the present invention; Figure 6 This is a schematic diagram of a combined waveform with only amplitude imbalance in an embodiment of the present invention; Figure 7 This is a schematic diagram of a combined waveform with unbalanced amplitude and phase angle in an embodiment of the present invention; Figure 8 This is a histogram of the probability distribution of the combined waveform when only the phase angle is unbalanced in an embodiment of the present invention; Figure 9 This is a histogram of the probability distribution of the combined waveform when only the amplitude is unbalanced in an embodiment of the present invention; Figure 10 This is a histogram of the probability distribution of the combined waveform when both amplitude and phase angle are unbalanced in an embodiment of the present invention. Figure 11 This is a block diagram of a three-phase imbalance characterization system based on combined waveform skewness in an embodiment of the present invention. Detailed Implementation

[0021] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] Example 1 In one or more embodiments, a three-phase imbalance characterization method based on combined waveform skewness is disclosed, combining... Figure 1 Specifically, it includes the following process: S101: Acquire three-phase voltage data for one half-cycle, starting from the zero-crossing point of the reference phase voltage.

[0024] In this embodiment, three-phase voltage data for one half-cycle is acquired, starting from the zero-crossing point of the reference phase voltage. The waveform data for one half-cycle includes the rising zero-crossing point and the falling zero-crossing point. The falling zero-crossing point refers to the zero-crossing point where the voltage waveform changes from the positive half-cycle to the negative half-cycle; the rising zero-crossing point refers to the zero-crossing point where the voltage waveform changes from the negative half-cycle to the positive half-cycle. One half-cycle starting from the rising zero-crossing point of the reference phase voltage can ensure that the negative half-cycle data of the deviation phase voltage is obtained.

[0025] Assume the voltage expression in the measured three-phase AC power system is as follows: ; in, , , These are the instantaneous voltages of phases A, B, and C, respectively. 、 、 These are the root mean square values ​​of the three-phase voltages; , , These are the initial phases of the three-phase voltages; ω This is the system angular frequency.

[0026] The uneven distribution of three-phase loads in a distribution network can cause changes in the voltage amplitude or phase of a particular phase. When the load connected to a certain phase differs significantly from the loads of the other two phases, it can lead to phase angle imbalance, amplitude imbalance, or imbalance in both amplitude and phase angle of the voltage in that phase. For ease of analysis, we assume that the voltage of phase A is the reference phase, and that its amplitude and phase angle remain constant during the disturbance. We also set... Let phase C voltage be the deviation phase. Phase C voltage has phase angle offset or amplitude offset. The degree of offset is expressed by phase angle offset and amplitude coefficient, respectively, as shown in the following formula: ; in, This represents the phase angle offset of the C-phase voltage, when When, the phase angle of phase C voltage shifts positively; when When, the phase angle shifts in the opposite direction; when At that time, there is no phase angle shift. This represents the amplitude coefficient of the C-phase voltage. When, the voltage amplitude of phase C has a positive deviation; when When, the amplitude has a negative deviation; when At that time, there was no amplitude deviation.

[0027] Figure 2 The waveform of the three-phase voltage with phase angle lags behind that of the C-phase voltage under equilibrium conditions is shown. Figure 3The three-phase voltage waveforms are shown when the amplitude of phase C voltage is higher than the standard value. Figure 4 The three-phase unbalanced waveform is shown, where the phase angle of the C-phase voltage lags and the amplitude is higher than the standard value.

[0028] S102: Construct a single-cycle combined voltage waveform containing a reference phase and a deviation phase. The positive half-cycle of the combined voltage waveform is composed of the positive half-cycle of the reference phase voltage, and the negative half-cycle is composed of the half-cycle waveform of the deviation phase voltage starting from the ideal zero crossing point.

[0029] In this embodiment, with phase A voltage as the reference phase and phase C voltage as the deviation phase, the mathematical expression for the combined waveform is as follows: ; in, The instantaneous value of the combined waveform is represented by T; T represents the period of the voltage waveform. This represents the instantaneous value of the deviation phase voltage. This represents the angle difference between the ideal waveform of the deviation phase and the reference phase. For example, when the deviation phase is phase B, for , for When the deviation phase is phase C, for , for .

[0030] draw Figures 2-4 The combined waveforms corresponding to the three types of unbalanced operating conditions are as follows: Figures 5-7 As shown, the positive half-cycle of the combined waveform is composed of the positive half-cycle of the reference phase voltage; the negative half-cycle is composed of the half-cycle waveform of the deviation phase voltage starting from the ideal zero crossing point.

[0031] Figure 5 The combined waveform is only unbalanced in phase angle. Since the actual zero-crossing point of the deviation phase does not coincide with the ideal zero-crossing point, there is a special interval in the second half of the combined waveform. The instantaneous value of the waveform in this interval is positive rather than negative. When the phase angle shifts positively, the special interval appears near π, and vice versa. Furthermore, since there is no amplitude imbalance, the amplitude of the second half of the combined waveform remains consistent with the balanced condition, only the phase or time corresponding to the amplitude is different.

[0032] Figure 6 The combined waveform is for the case of amplitude imbalance only. The actual zero-crossing point of the bias phase coincides with the ideal zero-crossing point, meaning there is no zero-crossing deviation. The combined waveform does not have the special range in phase imbalance. However, due to the positive or negative deviation of the amplitude of the bias phase, the combined waveform still has non-central symmetry, but the phase or time corresponding to the amplitude remains consistent with the balanced condition.

[0033] Figure 7 This is a combined waveform where both amplitude and phase are unbalanced. The unique range and amplitude deviation characteristics coexist in the negative half-cycle of the combined waveform. In this case, the non-central symmetry of the combined waveform is more pronounced.

[0034] S103: Calculate the mean of the first-order origin moments of the combined waveform, and calculate the third-order central moments of the combined waveform based on the mean; standardize the third-order central moments to obtain the skewness index of the combined waveform.

[0035] In this embodiment, the imbalance is quantitatively characterized based on the skewness of the combined waveform. By constructing a combined waveform containing a reference phase and a deviation phase, the corresponding characteristics of the three-phase imbalance combined waveform are revealed, including the non-central symmetry of the time-domain waveform and the asymmetry of its probability distribution histogram.

[0036] Specifically, the severity of three-phase imbalance disturbance is characterized using the skewness meter results of the combined waveform. First, the combined waveform is calculated. First-order raw moment mean With the variance of the second central moments : ; in, E [·] represents the expectation operator.

[0037] However, when using the first-order origin moment mean and the second-order central moment variance to describe the characteristics of three-phase imbalance, the former can reflect the reference center of the combined waveform, but cannot distinguish whether the distribution pattern is symmetrical about the reference center; the latter can measure the fluctuation of the waveform sampling points around the mean, but still cannot determine whether its distribution pattern is tilted left or right. It can be seen that the mean and variance of the combined waveform cannot effectively identify the symmetry and tilt of the distribution.

[0038] Based on this, this embodiment introduces the third-order central moment to describe the asymmetry of the probability density distribution and standardizes it to obtain the skewness index. Specifically, the third-order central moment is an effective way to describe the asymmetry of the probability density distribution of a single-cycle combined waveform, and its expression is: ; in, The third central moment of the combined waveform.

[0039] Finally, the third-order central moments are standardized, and the standardized third-order central moments are defined as the combined waveform skewness index. Its expression is as follows: ; in, The key to its significant advantage in representing asymmetry lies in the odd power function in its expression. Its sign depends on the deviation. The symbol.

[0040] S104: Characterize three-phase unbalanced disturbances based on the skewness index of combined waveforms.

[0041] When the probability distribution of the combined waveform is about its mean μ RT When perfectly symmetrical, i.e., in three-phase equilibrium condition, the deviations in the distribution of the mean on the left and right sides, as well as the results of the power function calculation, cancel each other out, resulting in... .

[0042] When the probability distribution of the combined waveform is asymmetrical, i.e., there is a three-phase imbalance disturbance, if the probability distribution is denser on the right side, the positive deviation is greater than the negative deviation, leading to... Conversely, a denser distribution on the left side will lead to... Furthermore, the stronger the asymmetry, The more the calculation result deviates from the ideal value of zero.

[0043] Therefore, the odd-power characteristic in skewness calculation allows it to accurately reflect distribution shifts; the skewness is 0 when the three phases are in equilibrium. In imbalance, a denser distribution on the right side results in a positive skewness, while a denser distribution on the left side results in a negative skewness, and the degree to which the value deviates from 0 is positively correlated with the severity of the imbalance. The skewness index can be used to determine whether an imbalance disturbance exists and to quantitatively characterize its severity.

[0044] As a further implementation method, when a three-phase unbalanced disturbance is determined to exist, the combined waveform characteristics under the unbalanced operating condition are further analyzed from the perspective of probability distribution. The voltage amplitude of the combined waveform is plotted on the horizontal axis, and the probability density of the voltage amplitude of the combined waveform is plotted on the vertical axis to draw a probability distribution histogram of the combined waveform. This histogram can intuitively show the non-central symmetry characteristics of the combined waveform under the unbalanced operating condition, clearly reflect the difference in the distribution on both sides of the mean caused by the difference between the negative half-cycle and the balanced operating condition waveform, and better characterize the specific changes in the combined waveform brought about by different types of three-phase unbalanced operating conditions. Among them, the three-phase unbalanced operating conditions include three types: phase angle unbalance, amplitude unbalance, and both phase angle and amplitude unbalance.

[0045] This embodiment determines the three-phase unbalanced operating condition based on the probability distribution histogram, specifically as follows: (1) If the probability distribution histogram has a characteristic distribution of missing blocks and multiple blocks on both sides of the axis of symmetry, it is judged that there is a phase angle imbalance, and the direction of phase angle offset can be determined based on the characteristic distribution.

[0046] Figure 8An example of a probability distribution histogram for phase angle imbalance only is given. The voltage instantaneous values ​​in the specific interval caused by phase angle imbalance result in an asymmetry of the probability distribution histogram. The phase angle of the C-phase voltage shifts positively, and the specific interval appears near π. The probability distribution histogram will have an extra piece in the part greater than zero to the right of the axis of symmetry, and a missing piece in the part less than zero to the left of the axis of symmetry. The direction of the phase angle shift can be inferred from this characteristic distribution as a positive shift. If the phase angle shift is less than zero, the change in the probability distribution histogram is the opposite.

[0047] (2) If the probability distribution histogram has a characteristic distribution of extreme points far from the zero axis of symmetry, it is judged that there is an imbalance in amplitude, and the sign of the amplitude deviation can be determined based on the characteristic distribution.

[0048] Figure 9 An example of a probability distribution histogram with only amplitude imbalance is given. The voltage amplitude of phase C has a negative deviation, and the minimum instantaneous voltage value is further away from the axis of symmetry located at zero. The probability distribution histogram shows asymmetry. The amplitude deviation can be judged to be negative by the distribution characteristics of this extreme point. If the voltage amplitude is positive, the change of the probability distribution histogram will be the opposite.

[0049] (3) If the probability distribution histogram simultaneously exhibits the composite characteristic distribution of phase angle imbalance and amplitude imbalance, it is judged that phase angle imbalance and amplitude imbalance exist simultaneously.

[0050] Figure 10 An example of a probability distribution histogram for an unbalanced amplitude and phase angle is given. The phase angle of the C-phase voltage is positively offset and the amplitude has a negative deviation. Its probability distribution histogram exhibits asymmetry. Compared with the probability distribution histogram for the balanced operating condition, the minimum instantaneous voltage value is further away from the axis of symmetry located at zero. At the same time, there is an extra piece of the part greater than zero on the right side of the axis of symmetry, and a missing piece of the part less than zero on the left side of the axis of symmetry. This histogram simultaneously shows the asymmetric characteristics caused by the phase angle offset and amplitude deviation, and can accurately present the waveform change pattern under the condition of unbalanced amplitude and phase angle.

[0051] Therefore, by observing the asymmetric shape of the probability distribution histogram, the specific type of three-phase imbalance can be directly determined. This histogram also serves as an intuitive and effective carrier for identifying the type of three-phase imbalance from the perspective of probability distribution and characterizing the waveform change pattern.

[0052] This embodiment quantitatively characterizes the imbalance based on the skewness of the combined waveform, calculates the skewness index of the combined waveform containing the reference phase and the deviation phase, and reveals the non-central symmetry of the three-phase unbalanced combined waveform and the asymmetry of its probability distribution histogram.

[0053] This embodiment proposes a comprehensive analysis approach for three-phase imbalance from a waveform perspective, constructs a combined waveform containing a reference phase and a deviation phase, transforms the essence of three-phase imbalance into a problem of the asymmetry of the combined waveform and its probability distribution, analyzes the characteristics of the combined waveform corresponding to various imbalance disturbances, and defines a combined waveform skewness index, which can accurately quantify the degree of asymmetry in the waveform probability distribution.

[0054] The method in this embodiment only needs to obtain the waveform data of the three-phase voltage, construct a combined waveform based on the waveform data, and then calculate the skewness index of the combined waveform to characterize the three-phase imbalance. It does not require obtaining the amplitude and phase angle of the three-phase voltage through Fourier decomposition, nor does it require obtaining the positive sequence voltage and negative sequence voltage through the symmetrical component method. The calculation process is simple and can achieve efficient and accurate assessment of the severity of three-phase imbalance disturbance.

[0055] Example 2 In one or more embodiments, a three-phase imbalance characterization system based on combined waveform skewness is disclosed, combined with Figure 11 Specifically, it includes: The data acquisition module is configured to acquire three-phase voltage data for one half-cycle, starting from the zero-crossing point of the reference phase voltage. The combined waveform construction module is configured to construct a single-cycle combined voltage waveform containing a reference phase and a deviation phase. The positive half-cycle of the combined voltage waveform is composed of the positive half-cycle of the reference phase voltage, and the negative half-cycle is composed of the half-cycle waveform of the deviation phase voltage starting from the ideal zero crossing point. The skewness index calculation module is configured to calculate the mean of the first-order origin moments of the combined waveform, calculate the third-order central moments of the combined waveform based on the mean, and standardize the third-order central moments to obtain the skewness index of the combined waveform. The three-phase imbalance characterization module is configured to characterize the three-phase imbalance disturbance based on the combined waveform skewness index.

[0056] It should be noted that the specific implementation methods of the above modules are exactly the same as those in Example 1, and will not be described in detail again.

[0057] Example 3 In one or more embodiments, a terminal device is disclosed, comprising a processor and a memory, wherein the processor is used to implement instructions; and the memory is used to store multiple instructions adapted to be loaded by the processor and executed by the processor for the three-phase imbalance characterization method based on combined waveform skewness in Embodiment 1.

[0058] It should be understood that in this embodiment, the processor can be a central processing unit (CPU), or it can be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0059] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of the memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0060] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by software instructions.

[0061] Example 4 In one or more embodiments, a computer-readable storage medium is disclosed, wherein a plurality of instructions are stored, the instructions being adapted to be loaded by a processor of a terminal device and executed by the three-phase imbalance characterization method based on combined waveform skewness in Embodiment 1.

[0062] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A three-phase imbalance characterization method based on combined waveform skewness, characterized in that, include: Acquire three-phase voltage data for one half-cycle, starting from the zero-crossing point of the reference phase voltage rise; A single-cycle combined voltage waveform containing a reference phase and a deviation phase is constructed. The positive half-cycle of the combined voltage waveform is composed of the positive half-cycle of the reference phase voltage, and the negative half-cycle is composed of the half-cycle waveform of the deviation phase voltage starting from the ideal zero crossing point. Calculate the mean of the first-order origin moments of the combined waveform, and calculate the third-order central moments of the combined waveform based on the mean; standardize the third-order central moments to obtain the skewness index of the combined waveform. The three-phase imbalance disturbance is characterized based on the combined waveform skewness index.

2. The three-phase imbalance characterization method based on combined waveform skewness as described in claim 1, characterized in that, The single-cycle combined voltage waveform is specifically as follows: ； in, The instantaneous value of the combined waveform is represented by T; T represents the period of the voltage waveform. Represents the instantaneous value of the reference phase voltage. This represents the instantaneous value of the deviation phase voltage. It represents the angle difference between the ideal waveform of the deviation phase and the reference phase.

3. The three-phase unbalance characterization method based on combined waveform skewness as described in claim 1, characterized in that, The third central moment of the combined waveform is calculated based on the mean, specifically as follows: ； in, The third central moment of the combined waveform is represented by... Represents the instantaneous value of the combined waveform. This represents the mean of the first-order raw moments of the combined waveform. E [·] represents the expectation operator.

4. The three-phase imbalance characterization method based on combined waveform skewness as described in claim 1, characterized in that, The third-order central moments are standardized to obtain the combined waveform skewness index, specifically: ； in, To combine waveform skewness indices, Represents the instantaneous value of the combined waveform. This represents the mean of the first-order raw moments of the combined waveform. E [·] represents the expectation operator.

5. The three-phase imbalance characterization method based on combined waveform skewness as described in claim 1, characterized in that, The three-phase imbalance disturbance is characterized based on the combined waveform skewness index, specifically as follows: If the combined waveform skewness index is zero, it indicates a three-phase balanced operating condition. If the combined waveform skewness index is not zero, it indicates the presence of a three-phase imbalance disturbance; and the magnitude of the combined waveform skewness index is used to characterize the severity of the three-phase imbalance.

6. The three-phase imbalance characterization method based on combined waveform skewness as described in claim 1, characterized in that, It also includes: when it is determined that there is a three-phase unbalanced disturbance, drawing a probability distribution histogram of the single-cycle combined voltage waveform, and determining the three-phase unbalanced operating condition based on the probability distribution histogram; the three-phase unbalanced operating condition includes phase angle unbalance, amplitude unbalance, and both phase angle and amplitude unbalance.

7. The three-phase imbalance characterization method based on combined waveform skewness as described in claim 6, characterized in that, The three-phase unbalanced operating condition is determined based on the probability distribution histogram, specifically as follows: If the probability distribution histogram has a characteristic distribution of missing blocks and multiple blocks on both sides of the axis of symmetry, it is determined that there is a phase angle imbalance, and the direction of phase angle offset is determined according to the characteristic distribution. If the probability distribution histogram has a characteristic distribution where the extreme points are far from the zero symmetry axis, it is determined that there is an imbalance in amplitude, and the sign of the amplitude deviation is determined based on the characteristic distribution. If the probability distribution histogram simultaneously exhibits the composite characteristic distribution of phase imbalance and amplitude imbalance mentioned above, it is determined that both phase imbalance and amplitude imbalance exist simultaneously.

8. A three-phase unbalance characterization system based on combined waveform skewness, characterized in that, include: The data acquisition module is configured to acquire three-phase voltage data for one half-cycle, starting from the zero-crossing point of the reference phase voltage. The combined waveform construction module is configured to construct a single-cycle combined voltage waveform containing a reference phase and a deviation phase. The positive half-cycle of the combined voltage waveform is composed of the positive half-cycle of the reference phase voltage, and the negative half-cycle is composed of the half-cycle waveform of the deviation phase voltage starting from the ideal zero crossing point. The skewness index calculation module is configured to calculate the mean of the first-order origin moments of the combined waveform, calculate the third-order central moments of the combined waveform based on the mean, and standardize the third-order central moments to obtain the skewness index of the combined waveform. The three-phase imbalance characterization module is configured to characterize the three-phase imbalance disturbance based on the combined waveform skewness index.

9. A terminal device comprising a processor and a memory, the processor for implementing instructions; the memory for storing multiple instructions, characterized in that, The instructions are adapted to be loaded by a processor and executed as described in any one of claims 1-7, the three-phase imbalance characterization method based on combined waveform skewness.

10. A computer-readable storage medium storing a plurality of instructions, characterized in that, The instructions are adapted to be loaded by the processor of the terminal device and executed by the three-phase imbalance characterization method based on combined waveform skewness as described in any one of claims 1-7.

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