A method and system for identifying three-phase imbalance type based on waveform skewness

Abstract

The present application belongs to the technical field of three-phase imbalance type identification of power system, and specifically discloses a three-phase imbalance type identification method and system based on waveform skewness, which comprises the following steps: obtaining three-phase voltage data of one cycle with the zero-crossing point of the reference phase as the starting point; constructing a single-cycle combined waveform and a single-cycle symmetric combined waveform respectively; the single-cycle combined waveform takes the positive half-cycle data of the reference phase voltage as the first half-cycle data, and takes the half-cycle data of the deviation phase voltage with the ideal zero-crossing point in the balanced state as the second half-cycle data; the single-cycle symmetric combined waveform is obtained by processing the second half-cycle data of the single-cycle combined waveform; the skewness indexes of the single-cycle combined waveform and the single-cycle symmetric combined waveform are calculated respectively, and the three-phase imbalance disturbance type is identified based on the skewness indexes. The method does not need sequence component decomposition, and can accurately mine the characteristic information of the imbalance disturbance contained in the three-phase voltage waveform itself.

Description

Technical Field

[0001] This invention relates to the field of three-phase imbalance identification technology in power systems, and in particular to a method and system for identifying three-phase imbalance types based on 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] With the high proportion of renewable energy sources such as photovoltaics and wind power being integrated into the power system, the diversification of power load structures, and the rapid growth of diversified power loads such as electric vehicle charging and flexible loads, the power system's source-grid-load structure is undergoing profound changes, and its operating status is becoming increasingly complex. Three-phase imbalance has become one of the most prominent power quality problems. The existence of three-phase imbalance not only leads to increased losses and shortened lifespan of power equipment such as transformers and motors, but may also trigger cascading problems such as voltage fluctuations and harmonic amplification, interfering with the normal operation of precision electrical equipment, and in severe cases, even threatening the safe and stable operation of the power grid and the quality of power supply. Therefore, accurately identifying the specific types of three-phase imbalance provides a reliable basis for the formulation of subsequent targeted governance measures and is of great significance for ensuring the safe, efficient, and high-quality operation of the power system.

[0004] Current technologies for calculating three-phase imbalance require first extracting the fundamental component, then using the symmetrical component method to obtain the positive-sequence, negative-sequence, and zero-sequence components, and finally using the ratio of the amplitude of the negative-sequence component to the positive-sequence component as the degree of imbalance. However, the extraction of the fundamental component and the calculation using the symmetrical component method result in a cumbersome calculation process and high computational complexity; moreover, it can only achieve a quantitative evaluation of the degree of three-phase imbalance and cannot effectively characterize the specific type of imbalance, i.e., it is difficult to distinguish whether it is a simple phase angle imbalance, a simple amplitude imbalance, or a composite imbalance where both phase angle and amplitude exist simultaneously.

[0005] In existing technologies, most three-phase imbalance type identification methods, based on imbalance characterization indicators, incorporate feature extraction methods or utilize intelligent algorithms to refine disturbance type criteria, including mode decomposition and deep learning algorithms. However, the execution of such research methods often relies on high-computing environments, such as concentrators or cloud platforms, which frequently require high-dimensional monitoring data to be transmitted to a centralized processor, exacerbating the pressure on data synchronization and communication. Although they can extract disturbance features with high accuracy, it is difficult to achieve on-site type identification in edge measurement equipment. Summary of the Invention

[0006] To address the aforementioned issues, this invention proposes a three-phase imbalance type identification method and system based on waveform skewness. By constructing single-cycle combined waveform and symmetrical combined waveform models containing a reference phase and a deviation phase, and combining probability distribution histogram features and waveform skewness, specific identification criteria for phase angle imbalance, amplitude imbalance, and imbalance of both are established, enabling accurate identification of the three imbalance types.

[0007] In some implementations, the following technical solutions are adopted: A method for identifying three-phase imbalance types based on waveform skewness includes: Acquire three-phase voltage data for one cycle, starting from the zero-crossing point of the reference phase; Single-cycle combined waveforms and single-cycle symmetrical combined waveforms are constructed respectively. The single-cycle combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data and the deviation phase half-cycle data starting from the ideal zero-crossing point of the deviation phase voltage under equilibrium state as the second half-cycle data. The single-cycle symmetrical combined waveform is obtained by processing the second half-cycle data of the single-cycle combined waveform. The skewness index of the single-cycle combined waveform and the single-cycle symmetrical combined waveform are calculated respectively. Based on the skewness index of the two combined waveforms, the three-phase imbalance type is identified. The three-phase imbalance type is specifically: phase angle imbalance, amplitude imbalance, and imbalance of both phase angle and amplitude.

[0008] As a further embodiment, the single-cycle symmetrical combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data; the second half-cycle data of the single-cycle symmetrical combined waveform is obtained by taking the absolute value of the second half-cycle voltage data of the single-cycle combined waveform and then taking the opposite of the absolute value result.

[0009] As a further solution, the skewness index of the single-cycle combined waveform is obtained by calculating the third-order central moment of the single-cycle combined waveform and then standardizing it.

[0010] As a further solution, the skewness index of the single-cycle symmetrical combined waveform is obtained by calculating the third-order central moment of the single-cycle symmetrical combined waveform and then standardizing it.

[0011] As a further option, the criterion for only phase imbalance is: If the skewness index of the single-cycle symmetrical combined waveform is 0, and the skewness index of the single-cycle combined waveform is not 0, it indicates that the current three-phase imbalance is caused only by phase angle imbalance.

[0012] As a further option, the criterion for determining whether only amplitude imbalance occurs is: If the skewness index of the single-cycle combined waveform is equal to the skewness index of the single-cycle symmetrical combined waveform, and neither is 0, it indicates that the current three-phase imbalance is caused only by amplitude imbalance.

[0013] As a further option, the criterion for imbalance in both phase and amplitude is: If the skewness index of the single-cycle combined waveform and the skewness index of the single-cycle symmetrical combined waveform are both non-zero, and the two skewness indices are not equal, it indicates that the current three-phase imbalance is caused by phase angle imbalance and amplitude imbalance.

[0014] In other embodiments, the following technical solutions are adopted: A three-phase imbalance type identification system based on waveform skewness includes: The data acquisition module is configured to acquire three-phase voltage data for one cycle, starting from the zero-crossing point of the reference phase. The combined waveform construction module is configured to construct single-cycle combined waveforms and single-cycle symmetrical combined waveforms respectively. The single-cycle combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data and the deviation phase half-cycle data starting from the ideal zero-crossing point of the deviation phase voltage under equilibrium state as the second half-cycle data. The single-cycle symmetrical combined waveform is obtained by processing the second half-cycle data of the single-cycle combined waveform. The three-phase imbalance identification module is configured to calculate the skewness index of the single-cycle combined waveform and the single-cycle symmetrical combined waveform respectively, and identify the three-phase imbalance type based on the skewness index of the two combined waveforms. The three-phase imbalance type is specifically: phase angle imbalance, amplitude imbalance, and imbalance of both phase angle and amplitude.

[0015] 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 identify the three-phase imbalance type based on waveform skewness as described above.

[0016] 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 method for identifying three-phase imbalance type based on waveform skewness.

[0017] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention proposes a waveform statistical feature analysis perspective for three-phase unbalance disturbances. Based on the actual three-phase voltage waveforms at the monitoring points, combined waveforms and symmetrical combined waveforms are constructed respectively. The combined waveform is used to construct a single-cycle waveform containing a reference phase and a deviation phase, and for the first time, the three-phase unbalance is transformed from a traditional sequence component problem into an asymmetric problem of the probability distribution of the combined waveform. Compared with the traditional characterization method based on the effective value or peak value of the waveform, this method can more significantly and accurately extract the characteristic information of the unbalance disturbance contained in the three-phase voltage waveform itself. By analyzing the probability distribution characteristics of combined waveforms of different types of disturbances, we can further construct symmetrical combined waveforms with relative deviation symmetry. After symmetry processing, the symmetrical combined waveforms with unbalanced phase angles are consistent with the balanced state, while the symmetrical combined waveforms with unbalanced amplitudes are consistent with the combined waveforms before symmetry. Therefore, based on the comparative analysis results of the probability distributions of symmetrical combined waveforms and combined waveforms, we can construct specific criteria for different disturbance types, thereby making up for the shortcomings of traditional unbalanced disturbance indices in identifying disturbance types.

[0018] (2) This invention leverages the advantages of high-precision synchronous measurement technology and devices to introduce waveform skewness from higher-order statistics into the three-phase imbalance identification scenario. This index can effectively describe the statistical characteristics of data waveforms and does not require complex Fourier decomposition or phase sequence transformation calculation steps, thus ensuring the scientific nature and reliability of the identification method. Compared with traditional three-phase imbalance assessment methods, this invention effectively avoids the shortcomings of its complex calculation process and the fact that it can only evaluate the degree of imbalance but cannot distinguish the type, achieving rapid, accurate, and reliable identification of various typical types of three-phase imbalance.

[0019] (3) This invention conducts identification research from the perspective of the voltage waveform itself. Based on the skewness index of the combined waveform and the symmetrical combined waveform, a three-phase imbalance criterion is constructed. There is no need to perform cumbersome signal processing steps such as fundamental wave extraction and positive and negative sequence component decomposition. This greatly simplifies the identification calculation process and reduces the computational complexity. It is more in line with the lightweight and efficient requirements of three-phase imbalance identification in engineering practice, and provides a brand-new technical idea and implementation path for the accurate diagnosis and treatment of three-phase imbalance.

[0020] 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

[0021] Figure 1 This is a flowchart of the three-phase imbalance type identification method based on waveform skewness in an embodiment of the present invention; Figure 2 This is a schematic diagram of the combined waveform with only phase angle imbalance in an embodiment of the present invention; Figure 3 This is a schematic diagram of a combined waveform with only amplitude imbalance in an embodiment of the present invention; Figure 4 This is a schematic diagram of a combined waveform with unbalanced amplitude and phase angle in an embodiment of the present invention; Figure 5 This is a schematic diagram of the probability distribution histogram of the combined waveform when only the phase angle is unbalanced in an embodiment of the present invention; Figure 6 This is a schematic diagram of the probability distribution histogram of the combined waveform when only the amplitude is unbalanced in an embodiment of the present invention; Figure 7 This is a schematic diagram of the probability distribution histogram of the combined waveform when both amplitude and phase angle are unbalanced in an embodiment of the present invention; Figure 8 This is a schematic diagram of the symmetrical combination waveform when only the phase angle is unbalanced in an embodiment of the present invention; Figure 9 This is a schematic diagram of the probability distribution histogram when only the phase angle is unbalanced in an embodiment of the present invention; Figure 10 This is a schematic diagram of a symmetrical combination waveform in an embodiment of the present invention when only the amplitude is unbalanced; Figure 11 This is a schematic diagram of the probability distribution histogram when only the amplitude is unbalanced in an embodiment of the present invention; Figure 12 This is a symmetrical combination waveform diagram under the condition that both phase angle and amplitude are unbalanced in an embodiment of the present invention; Figure 13 This is a probability distribution histogram of the symmetrical combination waveform in an embodiment of the present invention where both phase angle and amplitude are unbalanced. Figure 14 This is a block diagram of a three-phase imbalance type identification system based on waveform skewness in an embodiment of the present invention. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] Example 1 Higher-order statistics, especially skewness, have significant advantages in describing the probability distribution characteristics of signal waveforms and highlighting asymmetric information. They are sensitive to features such as amplitude distortion and phase shift, and are less susceptible to Gaussian noise. Compared to traditional time-domain and frequency-domain analysis methods, they are more suitable for extracting and identifying the characteristics and types of three-phase imbalance. Therefore, constructing a three-phase imbalance type identification model and criterion based on waveform skewness from higher-order statistics can solve the problem that existing technologies cannot accurately distinguish imbalance types, and has important theoretical significance.

[0025] Based on this, in one or more embodiments, a three-phase imbalance type identification method based on waveform skewness is disclosed, combined with Figure 1 Specifically, it includes the following processes: S101: Obtain three-phase voltage data for one cycle starting from the zero-crossing point of the reference phase; The waveform data of voltage and current in a three-phase system contain the most accurate and comprehensive characteristic information of imbalance disturbances. With the rapid development of synchronous phasor measurement technology, time-stamped synchronous voltage and current waveform data can now be stably acquired. In this embodiment, the phase with the voltage amplitude closest to the rated value and the phase closest to the standard phase is selected as the reference phase. The three-phase voltage data for one cycle, starting from the zero-crossing point of the reference phase, is acquired, providing data support for subsequent three-phase imbalance type identification.

[0026] 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 The system angular frequency is 50Hz.

[0027] Assuming that phase A voltage is unbalanced, but phase C voltage is unbalanced, let phase A voltage be the reference phase voltage and phase C voltage be the deviation phase voltage. Phase C voltage has phase angle offset or amplitude offset, and the degree of offset is expressed by phase angle offset and amplitude coefficient, respectively, as shown in the following formulas: ; 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.

[0028] S102: Construct single-cycle combined waveforms and single-cycle symmetrical combined waveforms respectively; the single-cycle combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data, and the deviation phase half-cycle data starting from the ideal zero-crossing point of the deviation phase voltage under equilibrium state as the second half-cycle data; the single-cycle symmetrical combined waveform is obtained by symmetric processing of the second half-cycle data of the single-cycle combined waveform.

[0029] In this embodiment, the zero-crossing point where the deviation phase voltage changes from the positive half-cycle to the negative half-cycle under balanced operating conditions is defined as the ideal zero-crossing point, and the corresponding zero-crossing point under unbalanced operating conditions is defined as the actual zero-crossing point. Using the positive half-cycle of the reference phase voltage as the first half-cycle data of the combined waveform, and the half-cycle of the deviation phase starting from the ideal zero-crossing point of the deviation phase as the second half-cycle of the combined waveform, a complete single-cycle combined waveform is formed.

[0030] In this embodiment, a combined waveform is constructed using phase A voltage as the reference phase and phase C voltage as the deviation phase. The expression: ; in, Indicates the instantaneous value of the combined waveform; This represents the ideal zero-crossing point of the bias phase voltage. When phase C is the bias phase, .

[0031] Based on this, for three unbalanced operating conditions—phase imbalance, amplitude imbalance, and both imbalance—the corresponding combined waveforms are calculated and plotted, and the characteristics of the combined waveforms are analyzed from the perspective of probability distribution. Figure 2 This is a waveform diagram for a combination of phase angle imbalances only; Figure 3 This is a waveform diagram showing only the amplitude imbalance. Figure 4 The waveform diagram shows a combination of unbalanced amplitude and phase angle. Figure 5 The probability distribution histogram of the combined waveform with only phase angle imbalance; Figure 6 A histogram of the probability distribution of combined waveforms with only amplitude imbalance; Figure 7 The histogram shows the probability distribution of the combined waveform with unbalanced amplitude and phase angle. It can be seen that the three-phase unbalanced combined waveform exhibits the following four main characteristics: (1) The combined waveform of three-phase unbalanced waveform has non-central symmetry characteristics, and the probability distribution diagram of the combined waveform has asymmetry characteristics.

[0032] (2) When there is only phase angle imbalance, since the actual zero crossing point of the deviation phase does not coincide with the ideal zero crossing point, there is a significant special interval in the second half of the combined waveform. The instantaneous value of the waveform in this interval is positive rather than negative in the equilibrium state, resulting in a gap with equal area on both sides of the mean of the probability distribution diagram of the combined waveform.

[0033] (3) When only amplitude imbalance exists, the actual zero-crossing point of the deviation phase coincides with the ideal zero-crossing point, that is, there is no zero-crossing deviation, and the combined waveform does not have a special interval in phase imbalance. However, since the amplitude of the deviation phase has positive or negative deviation, the boundary values ​​on the left and right sides of the mean in the probability distribution diagram of the combined waveform are different.

[0034] (4) When phase imbalance and amplitude imbalance exist simultaneously, the aforementioned special interval and amplitude deviation characteristics exist simultaneously in the negative half-cycle of the combined waveform. Therefore, the above two types of characteristics exist simultaneously in its probability distribution diagram.

[0035] Therefore, the role of the combined waveform is to construct a single-cycle waveform containing a reference phase and a deviation phase, and for the first time transform the three-phase imbalance from a traditional sequence component problem into an asymmetric problem of the probability distribution of the combined waveform. Compared with the traditional characterization method based on the effective value or peak value of the waveform, this method can more significantly and accurately extract the characteristic information of the imbalance disturbance contained in the three-phase voltage waveform itself.

[0036] By further constructing a symmetrical combination waveform with relative deviation, the absolute values ​​of each voltage value are first taken, and then the inverse of the absolute value is taken to form a single-cycle symmetrical combination waveform. Its expression is: ; ; in, This represents the waveform after taking the absolute value of the C-phase voltage and then inverting its sign.

[0037] Based on this, the symmetrical combination waveforms and their probability distribution histograms corresponding to the three types of unbalanced working conditions were calculated and plotted. Figure 8 This is a waveform diagram of a symmetrical combination under the condition of only phase angle imbalance. Figure 9 This is a histogram of the probability distribution of symmetrical combination waveforms under the condition of only phase angle imbalance; Figure 10 This is a symmetrical combination waveform diagram for the case of amplitude imbalance only. Figure 11 This is a histogram of the probability distribution of symmetrical combination waveforms under the condition of only amplitude imbalance. Figure 12 This is a symmetrical combination waveform diagram when both are unbalanced. Figure 13 This is the probability distribution histogram of the symmetrical combination waveform when both are unbalanced.

[0038] Analysis reveals that various imbalance disturbances exhibit different characteristics in the probability distribution diagram of the symmetrical combination waveform, as follows: (1) When only the phase angle is unbalanced, the probability distribution histogram of the symmetrical combination waveform does not coincide with the probability distribution histogram of the combination waveform, and the probability distribution histogram of the symmetrical combination waveform has symmetry. (2) When only the amplitude is unbalanced, the probability distribution histogram of the symmetrical combined waveform coincides with the probability distribution histogram of the combined waveform, and the probability distribution histogram of the symmetrical combined waveform does not have symmetry; (3) When both amplitude and phase angle are unbalanced, the probability distribution histogram of the symmetrical combination waveform does not coincide with the probability distribution histogram of the combination waveform, and the probability distribution histogram of the symmetrical combination waveform does not have symmetry.

[0039] As can be seen from the above analysis, by constructing symmetrical combination waveforms and analyzing their probability distribution characteristics, we can analyze the unique characteristics of various unbalanced disturbances from the perspective of waveforms. This provides an analytical basis for constructing specific criteria for disturbance types from the perspective of waveform statistical characteristics, thereby making up for the deficiency of traditional unbalanced disturbance indicators in being unable to identify disturbance types.

[0040] S103: Calculate the skewness index of single-cycle combined waveform and single-cycle symmetrical combined waveform respectively, construct disturbance type criteria for phase angle imbalance, amplitude imbalance and both imbalance, and identify the three-phase imbalance type.

[0041] Calculate the skewness of the symmetrical combined waveforms respectively. and the skewness of the combined waveform The specific calculation formula is as follows: ; ; ; ; in, E [·] represents the expectation operator; The mean of the combined waveforms; It represents the mean of the symmetrical combination waveform.

[0042] For three types of disturbances—phase imbalance, amplitude imbalance, and imbalance of both—this embodiment constructs specific criteria for phase imbalance, amplitude imbalance, and imbalance of both amplitude and phase, considering the specific characteristics of skewness and its waveform probability distribution. Specifically, the phase imbalance criterion is that the skewness index of the symmetrical combined waveform is 0; the amplitude imbalance criterion is that the skewness index of the combined waveform is equal to that of the symmetrical combined waveform; and the imbalance of both amplitude and phase is that the skewness index of the combined waveform is not 0 and is equal to that of the symmetrical combined waveform. Details are as follows: (1) When only phase imbalance occurs, the portion of the instantaneous voltage value in the symmetrical combined waveform that is less than zero can form a complete negative half-cycle in equilibrium state after translation. In this way, all the instantaneous voltage values ​​in one cycle are symmetrical about the mean. The skewness value calculated for the symmetrical combined waveform is 0, and the skewness value of the combined waveform is not 0, that is... ,and Therefore, the following specific criterion is proposed for the case where only the phase angle is unbalanced: ; in, As a criterion for phase-angle imbalance disturbance only, if the skewness value calculated for the symmetrical combined waveform is 0, and the skewness value of the combined waveform is not 0, then... This indicates that the current three-phase imbalance is caused solely by phase angle imbalance; if the skewness value calculated from the symmetrical combination waveform is not 0, then... This indicates that the current three-phase imbalance is not caused by phase angle imbalance, or that there is no current three-phase imbalance.

[0043] (2) When only amplitude imbalance occurs, the shapes of the symmetrical combined waveform and the combined waveform are completely identical. Therefore, the skewness calculation results of the two are the same and not zero, that is... Therefore, the specific criterion for cases with only amplitude imbalance is proposed as follows: ; in, As a criterion for amplitude imbalance disturbances only, if the skewness values ​​of the symmetrical combined waveform and the combined waveform are equal and neither is zero, then... This indicates that the current three-phase imbalance is caused solely by amplitude imbalance; if the skewness values ​​of the symmetrical combined waveform and the combined waveform are not equal, then... This indicates that the current three-phase imbalance is not caused by amplitude imbalance, or that there is currently no three-phase imbalance.

[0044] (3) When both the phase angle and amplitude are unbalanced, the calculated skewness of the combined waveform is not 0, i.e. The combined waveform and the symmetrical combined waveform cannot be completely identical simply by being symmetrical; therefore, their skewness calculation results are not equal. Furthermore, since all instantaneous voltage values ​​in the symmetrically combined waveform are not symmetrically distributed about the mean, the calculated skewness of the symmetrically combined waveform is not zero. Therefore, the following specific criterion is proposed when both amplitude and phase angle are unbalanced: ; in, The criterion for determining unbalanced disturbances in both phase angle and amplitude is that if the skewness values ​​of both the combined waveform and the symmetrical combined waveform are not zero, and their values ​​are different, then... This indicates that the current three-phase imbalance is caused by both phase angle imbalance and amplitude imbalance; if either the skewness value of the combined waveform or the symmetrical combined waveform is 0, or if their skewness values ​​are equal, then... This indicates that the current three-phase imbalance is not caused by imbalances in both phase angle and amplitude, or that there is currently no three-phase imbalance.

[0045] Based on the calculation results of the imbalance specificity criterion, the three-phase imbalance disturbance results are output. If the calculated results are... When the value is 1, the output displays: the three-phase imbalance type identification result is only phase angle imbalance; if When the value is 1, the output displays: the three-phase imbalance type identification result is only amplitude imbalance; if When the value is 1, the output will show: the three-phase imbalance type identification result is that both the amplitude and phase angle are unbalanced.

[0046] This embodiment analyzes the waveform characteristics of three-phase imbalance, utilizes the asymmetry of combined waveforms to describe the imbalance, and uses the skewness index to quantify the severity of this imbalance. Furthermore, it constructs symmetrical combined waveforms and distinguishes the disturbance type by calculating the skewness of the symmetrical combined waveforms; ultimately, it forms a specific criterion for three-phase imbalance types.

[0047] This embodiment relies on the skewness calculation results of the three-phase voltage combination waveform and the symmetrical combination waveform, as well as the unbalance type specific criteria, to directly output the three-phase unbalance type identification results. It can quickly, accurately and reliably identify the unbalance type in the three-phase system, and at the same time, it can rely on the waveform skewness index to complete the quantitative characterization of the three-phase unbalance characteristics.

[0048] This embodiment addresses the technical shortcomings of traditional national standard unbalance calculation methods, which require multiple cumbersome calculations such as fundamental component extraction and symmetrical component decomposition, and can only quantitatively evaluate the severity of unbalance without identifying specific types. Instead, it directly starts the identification and analysis from the actual waveform of the three-phase voltage at the monitoring point, eliminating the need for various component extraction and decomposition operations. This significantly simplifies the calculation process for three-phase unbalance identification and greatly reduces computational complexity.

[0049] This embodiment addresses the problem that traditional three-phase imbalance assessment methods are insufficient for determining imbalance types in practical engineering applications. Starting from actual power system monitoring applications, it fully explores the imbalance disturbance information contained in the three-phase voltage waveforms. Leveraging the advantages of high-precision synchronous measurement technology, it introduces high-order statistics to support three-phase imbalance type identification in the field of power quality disturbance monitoring. A novel waveform skewness identification system is constructed, effectively overcoming the technical limitations of traditional assessment methods that can only evaluate severity but cannot distinguish types. This system better meets the needs of three-phase imbalance identification in engineering sites, provides direct technical support for determining the type of three-phase imbalance, and offers a new technical approach and implementation path for three-phase imbalance identification research in the field of power quality monitoring.

[0050] Example 2 In one or more embodiments, a three-phase imbalance type identification system based on waveform skewness is disclosed, combined with Figure 14 ,include: The data acquisition module is configured to acquire three-phase voltage data for one cycle, starting from the zero-crossing point of the reference phase. The combined waveform construction module is configured to construct single-cycle combined waveforms and single-cycle symmetrical combined waveforms respectively. The single-cycle combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data and the deviation phase half-cycle data starting from the ideal zero-crossing point of the deviation phase voltage under equilibrium state as the second half-cycle data. The single-cycle symmetrical combined waveform is obtained by processing the second half-cycle data of the single-cycle combined waveform. The three-phase imbalance identification module is configured to calculate the skewness index of the single-cycle combined waveform and the single-cycle symmetrical combined waveform respectively, and identify the three-phase imbalance type based on the skewness index of the two combined waveforms. The three-phase imbalance type is specifically: phase angle imbalance, amplitude imbalance, and imbalance of both phase angle and amplitude.

[0051] 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.

[0052] 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 to identify the three-phase imbalance type based on waveform skewness as described in Embodiment 1.

[0053] 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.

[0054] Memory may include read-only memory and random access memory, and provides instructions and data to the processor. A portion of memory may also include non-volatile random access memory. For example, memory may also store information about the device type.

[0055] In the implementation process, each step of the above method can be completed by the integrated logic circuits in the processor hardware or by instructions in software form.

[0056] 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 type identification method based on waveform skewness described in Embodiment 1.

[0057] 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 method for identifying three-phase imbalance types based on waveform skewness, characterized in that, include: Acquire three-phase voltage data for one cycle, starting from the zero-crossing point of the reference phase; Single-cycle combined waveforms and single-cycle symmetrical combined waveforms are constructed respectively. The single-cycle combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data and the deviation phase half-cycle data starting from the ideal zero-crossing point of the deviation phase voltage under equilibrium state as the second half-cycle data. The single-cycle symmetrical combined waveform is obtained by processing the second half-cycle data of the single-cycle combined waveform. Specifically, the single-cycle symmetrical combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data. The second half-cycle data of the single-cycle symmetrical combined waveform is obtained by taking the absolute value of the second half-cycle voltage data of the single-cycle combined waveform and then taking the opposite of the absolute value. The skewness index of the single-cycle combined waveform and the single-cycle symmetrical combined waveform are calculated respectively. Based on the skewness index of the two combined waveforms, the three-phase imbalance type is identified. The three-phase imbalance type is specifically: phase angle imbalance, amplitude imbalance, and imbalance of both phase angle and amplitude.

2. The three-phase imbalance type identification method based on waveform skewness as described in claim 1, characterized in that, The skewness index of the single-cycle combined waveform is obtained by calculating the third central moment of the single-cycle combined waveform and then standardizing it.

3. The three-phase imbalance type identification method based on waveform skewness as described in claim 1, characterized in that, The skewness index of the single-cycle symmetrical combined waveform is obtained by calculating the third-order central moment of the single-cycle symmetrical combined waveform and then standardizing it.

4. The three-phase imbalance type identification method based on waveform skewness as described in claim 1, characterized in that, The criterion for only phase imbalance is: If the skewness index of the single-cycle symmetrical combined waveform is 0, and the skewness index of the single-cycle combined waveform is not 0, it indicates that the current three-phase imbalance is caused only by phase angle imbalance.

5. The three-phase imbalance type identification method based on waveform skewness as described in claim 1, characterized in that, The criterion for only having amplitude imbalance is: If the skewness index of the single-cycle combined waveform is equal to the skewness index of the single-cycle symmetrical combined waveform, and neither is 0, it indicates that the current three-phase imbalance is caused only by amplitude imbalance.

6. The three-phase imbalance type identification method based on waveform skewness as described in claim 1, characterized in that, The criterion for imbalance in both phase and amplitude is: If the skewness index of the single-cycle combined waveform and the skewness index of the single-cycle symmetrical combined waveform are both non-zero, and the two skewness indices are not equal, it indicates that the current three-phase imbalance is caused by phase angle imbalance and amplitude imbalance.

7. A three-phase imbalance type identification system based on waveform skewness, characterized in that, include: The data acquisition module is configured to acquire three-phase voltage data for one cycle, starting from the zero-crossing point of the reference phase. The combined waveform construction module is configured to construct single-cycle combined waveforms and single-cycle symmetrical combined waveforms respectively. The single-cycle combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data and the deviation phase half-cycle data starting from the ideal zero-crossing point of the deviation phase voltage under equilibrium state as the second half-cycle data. The single-cycle symmetrical combined waveform is obtained by processing the second half-cycle data of the single-cycle combined waveform. Specifically, the single-cycle symmetrical combined waveform uses the positive half-cycle data of the reference phase voltage as the first half-cycle data. The second half-cycle data of the single-cycle symmetrical combined waveform is obtained by taking the absolute value of the second half-cycle voltage data of the single-cycle combined waveform and then taking the opposite of the absolute value. The three-phase imbalance identification module is configured to calculate the skewness index of the single-cycle combined waveform and the single-cycle symmetrical combined waveform respectively, and identify the three-phase imbalance type based on the skewness index of the two combined waveforms. The three-phase imbalance type is specifically: phase angle imbalance, amplitude imbalance, and imbalance of both phase angle and amplitude.

8. 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 by the three-phase imbalance type identification method based on waveform skewness as described in any one of claims 1-6.

9. 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 type identification method based on waveform skewness as described in any one of claims 1-6.

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