A three-phase imbalance monitoring method and system for an electric energy metering box

Abstract

The application provides a kind of electric energy metering box three-phase unbalance monitoring method and system, belong to monitoring field.The method includes synchronously collecting three-phase voltage, three-phase current and neutral line current, determining actual power frequency state based on voltage zero-crossing interval, and constructing frequency adaptive correction sequence combined with sampling time stamp, obtaining corrected voltage phasor, corrected current phasor and corrected neutral line current phasor based on the frequency adaptive correction sequence;According to the corrected neutral line current phasor and the neutral line equivalent impedance, the neutral point offset voltage phasor is calculated, and the target zero sequence voltage phasor and the target zero sequence current phasor are obtained;The positive sequence voltage phasor and the positive sequence current phasor are extracted using the symmetrical component method, and the spatial unbalance degree is calculated combined with the equivalent zero sequence impedance, the zero sequence and the positive sequence current module length ratio and the voltage clamping angle phase lock factor;When the spatial unbalance degree continuously exceeds the preset threshold, the alarm signal is triggered.

Description

Technical Field

[0001] This application belongs to the field of monitoring, and in particular relates to a method and system for monitoring three-phase imbalance in an electricity metering box. Background Technology

[0002] Electricity metering boxes are crucial devices in power distribution networks for electricity metering, distribution, and data collection on electricity usage status. Their operational status directly impacts power supply quality and distribution safety. In three-phase AC distribution systems, factors such as differences in single-phase load connections, dynamic changes in user loads, and inconsistent line impedance can easily lead to asymmetry in three-phase voltage and current, i.e., three-phase imbalance. Three-phase imbalance increases line losses, reduces transformer operating efficiency, and in severe cases, can cause equipment overheating, insulation aging, or operational failures. Therefore, continuous monitoring of the three-phase imbalance status within the electricity metering box is of great significance for power distribution network operation and maintenance and electricity safety management.

[0003] Existing three-phase imbalance monitoring schemes typically use transformers or sensor devices to simultaneously acquire three-phase voltage, three-phase current, and neutral current signals within the power metering box. The acquired analog signals are then converted into digital signals to extract phasor information for voltage and current. Common phasor acquisition methods are mostly based on power frequency cycle measurement, zero-crossing detection, or fast Fourier transform algorithms to calculate the amplitude and phase of the base voltage and current signals, thereby constructing three-phase voltage phasors and three-phase current phasors.

[0004] After obtaining phasor data, the symmetrical component method is typically used to analyze the three-phase unbalanced operating state. The symmetrical component method can decompose unbalanced three-phase voltages or currents into positive-sequence, negative-sequence, and zero-sequence components. In a three-phase four-wire distribution system, the neutral current and zero-sequence current components are strongly correlated, and load imbalance can also cause neutral point potential shift. Some monitoring systems combine neutral current and line impedance parameters to estimate the neutral point offset voltage or the equivalent impedance of the zero-sequence loop, to assist in determining the current power grid operating state.

[0005] In terms of unbalance evaluation, existing technologies typically select the magnitude ratio of the negative-sequence component to the positive-sequence component, or the magnitude ratio of the zero-sequence component to the positive-sequence component, as the basic evaluation index. Some schemes further combine voltage, current phase angle, and system reference impedance parameters to construct a comprehensive evaluation index. In actual monitoring, the monitoring device compares the calculated unbalance value with a preset threshold. When the unbalance continuously exceeds the threshold, an alarm signal is output so that the background management system or maintenance personnel can promptly grasp the operating status of the power distribution network.

[0006] However, existing methods are susceptible to power frequency fluctuations, non-integer cycle sampling, and window truncation errors during phasor extraction, leading to deviations in phase calculation results. Furthermore, modeling the relationship between neutral current, neutral point offset, and zero-sequence loop impedance fails to adequately reflect the three-phase imbalance state under actual operating conditions of the power metering box. Therefore, improving the accuracy of three-phase phasor extraction and constructing more stable imbalance monitoring indicators by combining zero-sequence current, zero-sequence impedance, and phase relationships has become a key technical problem to be solved in three-phase imbalance monitoring of power metering boxes. Summary of the Invention

[0007] To address the problems in existing technologies, such as the susceptibility of phasor extraction to power frequency fluctuations, insufficient consideration of the correlation between zero-sequence components and neutral line operating parameters, and the reliance on a single unbalance evaluation index, which leads to insufficient monitoring accuracy, this invention proposes a three-phase unbalance monitoring method and system for power metering boxes.

[0008] According to one aspect of the present invention, a method for monitoring three-phase imbalance in an energy metering box is provided, comprising the following steps: Based on synchronously acquired three-phase voltage, three-phase current and neutral line current, discrete time-domain data sequences corresponding to the three-phase voltage, three-phase current and neutral line current are obtained. A frequency adaptive correction sequence is constructed according to the voltage zero-crossing interval and the deviation of the power frequency cycle. The fundamental phasor is extracted from the discrete time-domain data sequence using the frequency adaptive correction sequence to obtain the corrected voltage phasor, corrected current phasor and corrected neutral line current phasor. The neutral point offset voltage phasor is calculated based on the corrected neutral current phasor and the neutral equivalent impedance. The target zero-sequence voltage phasor and the target zero-sequence current phasor are obtained accordingly. The corrected voltage phasor and the corrected current phasor are decomposed based on the symmetrical component method to obtain the positive sequence voltage phasor and the positive sequence current phasor. The equivalent zero-sequence impedance is calculated based on the modulus ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor. Calculate the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculate the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio, and the phase-locking factor, and trigger an alarm signal when the spatial imbalance continuously exceeds a preset threshold.

[0009] Optionally, the step of acquiring discrete time-domain data sequences corresponding to the three-phase voltage, three-phase current, and neutral line current based on synchronously acquired three-phase voltage, three-phase current, and neutral line current includes: By using three-phase voltage sensors, three-phase current sensors, and neutral line current sensors installed at the input end of the power metering box, the three-phase voltage, three-phase current, and neutral line current are converted from analog to digital at fixed sampling frequencies and other time intervals to obtain discrete time-domain data sequences.

[0010] Optionally, the step of constructing a frequency adaptive correction sequence based on the voltage zero-crossing interval and the power frequency cycle deviation, and using the frequency adaptive correction sequence to extract the fundamental phasor of the discrete time-domain data sequence to obtain the corrected voltage phasor, the corrected current phasor, and the corrected neutral line current phasor includes: Extract two consecutive positive zero-crossing timestamps from the discrete time-domain data sequence, and take the difference between the two timestamps as the current power frequency cycle; The current actual power frequency is calculated based on the current power frequency cycle, and a frequency adaptive correction sequence is constructed based on the current actual power frequency, sampling timestamp, and window function weight. The frequency adaptive correction sequence is used to perform weighted inner product operations on the discrete time domain data sequences corresponding to the three-phase voltage, three-phase current and neutral line current, respectively, to extract the fundamental complex component at the current actual power frequency. The corrected voltage phasor, corrected current phasor, and corrected neutral current phasor are calculated based on the fundamental complex components.

[0011] Optionally, the step of calculating the neutral point offset voltage phasor based on the corrected neutral current phasor and the neutral equivalent impedance, and thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: The equivalent impedance of the neutral line is calculated based on the test values ​​of the neutral line's self-impedance parameters, which include the neutral line resistance and neutral line reactance. Multiplying the neutral line equivalent impedance by the corrected neutral line current phasor yields the neutral point offset voltage phasor; The neutral point offset voltage phasor is used as the target zero-sequence voltage phasor, and the corrected neutral line current phasor is multiplied by one-third to generate the target zero-sequence current phasor.

[0012] Optionally, the step of decomposing the corrected voltage phasor and corrected current phasor based on the symmetrical component method to obtain the positive-sequence voltage phasor and positive-sequence current phasor, and calculating the equivalent zero-sequence impedance based on the modulus ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: Construct the standard symmetric component forward transformation matrix; Using the standard symmetric component forward transformation matrix, matrix multiplication decomposition operations are performed on the three-dimensional column vector containing the correction voltage phasor and the three-dimensional column vector containing the correction current phasor, respectively. The second row of components extracted from the decomposition operation results is determined as the positive sequence voltage phasor and the positive sequence current phasor; When the absolute magnitude of the target zero-sequence current phasor is not less than the preset minimum current threshold, the absolute magnitude of the target zero-sequence voltage phasor is divided by the absolute magnitude of the target zero-sequence current phasor to calculate the equivalent zero-sequence impedance. When the absolute magnitude of the target zero-sequence current phasor is less than the preset minimum current threshold, the calculated value of the equivalent zero-sequence impedance of the previous cycle is maintained.

[0013] Optionally, the step of calculating the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculating the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, and calculating the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio, and the phase-locking factor includes: Calculate the ratio of the target zero-sequence current phasor magnitude to the positive-sequence current phasor magnitude, and use this ratio as the magnitude ratio; Calculate the phase angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the absolute value of the tangent of the phase angle and multiply it by a preset constant to obtain the phase locking factor; The spatial imbalance is obtained by multiplying the square of the modulus ratio by the ratio of the equivalent zero-sequence impedance to the preset reference impedance, multiplying by the phase-locking factor, and then taking the square root.

[0014] Optionally, triggering an alarm signal when the spatial imbalance continuously exceeds a preset threshold includes: Set the upper limit of the count value of the sliding verification window and the preset threshold of spatial imbalance, and initialize the current count value to 0; The calculated spatial imbalance is compared with the preset threshold. If the spatial imbalance is greater than the preset threshold, the current count value is incremented by 1. If the spatial imbalance is less than or equal to the preset threshold, the current count value is reset to 0; Determine whether the current count value is greater than or equal to the upper limit of the count value. If so, generate an alarm control command and trigger the audible and visual alarm device to issue a three-phase imbalance alarm signal through the hardware interface.

[0015] According to another aspect of the present invention, a three-phase imbalance monitoring system for an electricity metering box is provided, comprising the following modules: The module is used to acquire discrete time-domain data sequences corresponding to three-phase voltage, three-phase current and neutral line current based on synchronously acquired three-phase voltage, three-phase current and neutral line current, construct frequency adaptive correction sequences according to voltage zero-crossing interval and power frequency cycle deviation, and use the frequency adaptive correction sequences to extract the fundamental phasor of the discrete time-domain data sequences to obtain the corrected voltage phasor, corrected current phasor and corrected neutral line current phasor. The adjustment module is used to calculate the neutral point offset voltage phasor based on the corrected neutral line current phasor and the neutral line equivalent impedance, thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor. Based on the symmetrical component method, the corrected voltage phasor and the corrected current phasor are decomposed to obtain the positive-sequence voltage phasor and the positive-sequence current phasor. The equivalent zero-sequence impedance is calculated based on the modulus ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor. The calculation module is used to calculate the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculate the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio and the phase-locking factor, and trigger an alarm signal when the spatial imbalance continues to exceed a preset threshold.

[0016] Preferably, the step of acquiring discrete time-domain data sequences corresponding to the three-phase voltage, three-phase current, and neutral line current based on synchronously acquired three-phase voltage, three-phase current, and neutral line current includes: By using three-phase voltage sensors, three-phase current sensors, and neutral line current sensors installed at the input end of the power metering box, the three-phase voltage, three-phase current, and neutral line current are converted from analog to digital at fixed sampling frequencies and other time intervals to obtain discrete time-domain data sequences.

[0017] Preferably, the step of constructing a frequency adaptive correction sequence based on the voltage zero-crossing interval and the deviation of the power frequency cycle, and using the frequency adaptive correction sequence to extract the fundamental phasor of the discrete time-domain data sequence to obtain the corrected voltage phasor, the corrected current phasor, and the corrected neutral line current phasor includes: Extract two consecutive positive zero-crossing timestamps from the discrete time-domain data sequence, and take the difference between the two timestamps as the current power frequency cycle; The current actual power frequency is calculated based on the current power frequency cycle, and a frequency adaptive correction sequence is constructed based on the current actual power frequency, sampling timestamp, and window function weight. The frequency adaptive correction sequence is used to perform weighted inner product operations on the discrete time domain data sequences corresponding to the three-phase voltage, three-phase current and neutral line current, respectively, to extract the fundamental complex component at the current actual power frequency. The corrected voltage phasor, corrected current phasor, and corrected neutral current phasor are calculated based on the fundamental complex components.

[0018] Preferably, the step of calculating the neutral point offset voltage phasor based on the corrected neutral current phasor and the neutral equivalent impedance, and thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: The equivalent impedance of the neutral line is calculated based on the test values ​​of the neutral line's self-impedance parameters, which include the neutral line resistance and neutral line reactance. Multiplying the neutral line equivalent impedance by the corrected neutral line current phasor yields the neutral point offset voltage phasor; The neutral point offset voltage phasor is used as the target zero-sequence voltage phasor, and the corrected neutral line current phasor is multiplied by one-third to generate the target zero-sequence current phasor.

[0019] Preferably, the step of decomposing the corrected voltage phasor and corrected current phasor based on the symmetrical component method to obtain the positive-sequence voltage phasor and positive-sequence current phasor, and calculating the equivalent zero-sequence impedance based on the modulus ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: Construct the standard symmetric component forward transformation matrix; Using the standard symmetric component forward transformation matrix, matrix multiplication decomposition operations are performed on the three-dimensional column vector containing the correction voltage phasor and the three-dimensional column vector containing the correction current phasor, respectively. The second row of components extracted from the decomposition operation results is determined as the positive sequence voltage phasor and the positive sequence current phasor; When the absolute magnitude of the target zero-sequence current phasor is not less than the preset minimum current threshold, the absolute magnitude of the target zero-sequence voltage phasor is divided by the absolute magnitude of the target zero-sequence current phasor to calculate the equivalent zero-sequence impedance. When the absolute magnitude of the target zero-sequence current phasor is less than the preset minimum current threshold, the calculated value of the equivalent zero-sequence impedance of the previous cycle is maintained.

[0020] Preferably, the step of calculating the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculating the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, and calculating the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio, and the phase-locking factor includes: Calculate the ratio of the target zero-sequence current phasor magnitude to the positive-sequence current phasor magnitude, and use this ratio as the magnitude ratio; Calculate the phase angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the absolute value of the tangent of the phase angle and multiply it by a preset constant to obtain the phase locking factor; The spatial imbalance is obtained by multiplying the square of the modulus ratio by the ratio of the equivalent zero-sequence impedance to the preset reference impedance, multiplying by the phase-locking factor, and then taking the square root.

[0021] Preferably, triggering an alarm signal when the spatial imbalance continuously exceeds a preset threshold includes: Set the upper limit of the count value of the sliding verification window and the preset threshold of spatial imbalance, and initialize the current count value to 0; The calculated spatial imbalance is compared with the preset threshold. If the spatial imbalance is greater than the preset threshold, the current count value is incremented by 1. If the spatial imbalance is less than or equal to the preset threshold, the current count value is reset to 0; Determine whether the current count value is greater than or equal to the upper limit of the count value. If so, generate an alarm control command and trigger the audible and visual alarm device to issue a three-phase imbalance alarm signal through the hardware interface.

[0022] The present invention has the following advantages: The actual power frequency state is determined by the voltage zero-crossing interval, and a frequency adaptive correction sequence is constructed based on the sampling timestamp. The fundamental phasor of the three-phase voltage, three-phase current, and neutral current is extracted in a unified manner to reduce the impact of power frequency fluctuations and non-integer period sampling on phasor calculation. At the same time, the neutral point offset voltage is calculated by combining the neutral line equivalent impedance to obtain the target zero-sequence voltage and target zero-sequence current, so that the zero-sequence component evaluation is more in line with the actual operating state of the metering box. Furthermore, the equivalent zero-sequence impedance, the ratio of the zero-sequence to the positive-sequence current magnitude, and the voltage phase lock factor are integrated to generate the spatial imbalance, and the alarm is triggered by continuous over-limit judgment, thereby improving the reliability of three-phase imbalance monitoring and alarm. Attached Figure Description

[0023] Figure 1 A flowchart of the first embodiment; Figure 2 The complex plane diagram of the ordered components. Detailed Implementation

[0024] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] In the first embodiment, the present invention proposes a method for monitoring three-phase imbalance in an energy metering box, such as... Figure 1 As shown, it includes the following steps: S1. Based on the synchronously acquired three-phase voltage, three-phase current and neutral line current, obtain the discrete time domain data sequence corresponding to the three-phase voltage, three-phase current and neutral line current. Construct a frequency adaptive correction sequence according to the voltage zero-crossing interval and the deviation of the power frequency period. Use the frequency adaptive correction sequence to extract the fundamental phasor of the discrete time domain data sequence to obtain the corrected voltage phasor, corrected current phasor and corrected neutral line current phasor.

[0026] Using an energy metering terminal equipped with a high-precision analog-to-digital converter and a global synchronization clock module, the three-phase AC voltage, three-phase AC current and neutral line current at the input of the energy metering box are synchronously and discretely sampled at a fixed sampling frequency to obtain discrete voltage sampling sequences, discrete current sampling sequences and discrete neutral line current sampling sequences containing timestamps.

[0027] Zero-crossing detection hardware circuitry is used to record the zero-crossing moments when the voltage signals of each phase change from negative to positive. The time difference between two adjacent positive zero-crossing moments is calculated as the actual voltage zero-crossing interval. Based on the actual voltage zero-crossing interval, the current actual power frequency is calculated, and the deviation between the current actual power frequency and the standard power frequency is used as a measure of the power frequency cycle deviation. Based on the current actual power frequency, the timestamps of each sampling point, and the window function weights, a frequency adaptive correction sequence is constructed.

[0028] The frequency adaptive correction sequence is used to process the three-phase voltage sampling sequence, the three-phase current sampling sequence, and the neutral line current sampling sequence respectively. The fundamental phasor is re-extracted under the same time reference and the same actual power frequency, and the corrected voltage phasor, corrected current phasor, and corrected neutral line current phasor are output, thereby reducing the impact of power grid frequency fluctuations and non-integer cycle sampling on the phasor extraction results.

[0029] In an optional embodiment, the step of acquiring discrete time-domain data sequences corresponding to the three-phase voltage, three-phase current, and neutral line current based on synchronously acquired three-phase voltage, three-phase current, and neutral line current includes: By using three-phase voltage sensors, three-phase current sensors, and neutral line current sensors installed at the input end of the power metering box, the three-phase voltage, three-phase current, and neutral line current are converted from analog to digital at fixed sampling frequencies and other time intervals to obtain discrete time-domain data sequences.

[0030] During the data acquisition phase, sensors deployed at the input of the electricity metering box are used to synchronously sample analog signals at a fixed sampling frequency, such as 6400Hz. For a 50Hz power frequency system, the number of sampling points per cycle is fixed at 128. The three-phase voltage, three-phase current, and neutral line current are converted into discrete time-domain data sequences by analog-to-digital converters. For example, a data segment x(n) containing 128 discrete points is extracted, where the sequence index n ranges from 0 to 127.

[0031] In an optional embodiment, the step of constructing a frequency adaptive correction sequence based on the voltage zero-crossing interval and the power frequency cycle deviation, and using the frequency adaptive correction sequence to extract the fundamental phasor of the discrete time-domain data sequence to obtain the corrected voltage phasor, the corrected current phasor, and the corrected neutral line current phasor includes: Extract two consecutive positive zero-crossing timestamps from the discrete time-domain data sequence, and take the difference between the two timestamps as the current power frequency cycle; The current actual power frequency is calculated based on the current power frequency cycle, and a frequency adaptive correction sequence is constructed based on the current actual power frequency, sampling timestamp, and window function weight. The frequency adaptive correction sequence is used to perform weighted inner product operations on the discrete time domain data sequences corresponding to the three-phase voltage, three-phase current and neutral line current, respectively, to extract the fundamental complex component at the current actual power frequency. The corrected voltage phasor, corrected current phasor, and corrected neutral current phasor are calculated based on the fundamental complex components.

[0032] By using a linear interpolation algorithm to traverse and analyze the discrete-time data sequence, the timestamp data of two consecutive positive zero-crossings of phase A voltage were located. For example, the timestamp parameter of the first positive zero-crossing point obtained is... =0.0000s, the second adjacent positive zero-crossing timestamp parameter is =0.0202s, the current power frequency cycle is obtained by subtracting the previous timestamp from the subsequent timestamp. =0.0202s.

[0033] Calculate the current actual power frequency based on the current power frequency cycle. The actual power frequency is used as the reference frequency for the fundamental phasor extraction in this round. For any sampling sequence x(n), according to the sampling timestamp... and the current actual power frequency Generate the Hanning window weights w(n) and complex exponential terms corresponding to each sampling point. The frequency adaptive correction sequence is constructed by multiplying each sampling point x(n) with the corresponding sequence term in the frequency adaptive correction sequence and summing the results. The sum is then normalized according to the Hanning window weights to obtain the fundamental complex component at the current actual power frequency. The resulting fundamental phasor extraction result matches the actual power frequency and sampling window. Based on the magnitude and phase angle of the fundamental complex component, the fundamental amplitude and phase of the corresponding signal are obtained.

[0034] The above operations are performed on the three-phase voltage sampling sequences A, B, and C respectively to obtain the corrected voltage phasor; the above operations are performed on the three-phase current sampling sequences A, B, and C respectively to obtain the synchronous corrected current phasor; the operations are performed on the neutral line current sampling sequence under the same reference frequency and the same time base to obtain the corrected neutral line current phasor, so that the subsequent sequence component decomposition, phasor comparison, and phase angle calculation are in the same phase reference system.

[0035] S2. Calculate the neutral point offset voltage phasor based on the corrected neutral current phasor and the neutral equivalent impedance, thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor. Decompose the corrected voltage phasor and the corrected current phasor based on the symmetrical component method to obtain the positive-sequence voltage phasor and the positive-sequence current phasor, and calculate the equivalent zero-sequence impedance based on the magnitude ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor.

[0036] Extract the neutral line resistance and neutral line reactance between the incoming terminal of the power metering box and the neutral point of the distribution transformer, which are pre-measured and stored in non-volatile memory. Use the neutral line resistance as the real part and the neutral line reactance as the imaginary part to construct the neutral line equivalent impedance.

[0037] The neutral point offset voltage phasor is obtained by performing a complex multiplication operation between the corrected neutral line current phasor and the neutral line equivalent impedance; the neutral point offset voltage phasor is used as the target zero-sequence voltage phasor, and the corrected neutral line current phasor is multiplied by one-third to generate the target zero-sequence current phasor.

[0038] A rotation factor with an amplitude of 1 and a phase angle of +120 degrees is introduced using the symmetrical component method. The positive-sequence voltage phasors are calculated by multiplying each of the three-phase corrected voltage phasors by the corresponding rotation factor or the square of the rotation factor, summing the results, and dividing by 3. Similarly, the positive-sequence current phasors are calculated using this forward transformation matrix in conjunction with the three-phase corrected current phasors.

[0039] Calculate the square root of the sum of the squares of the real and imaginary parts of the target zero-sequence voltage phasor and the square root of the sum of the squares of the real and imaginary parts of the target zero-sequence current phasor to obtain their respective magnitudes. When the magnitude of the target zero-sequence current phasor is not less than the preset minimum current threshold, divide the magnitude of the target zero-sequence voltage phasor by the magnitude of the target zero-sequence current phasor to obtain the equivalent zero-sequence impedance value used to represent the current equivalent impedance state of the zero-sequence loop. When the magnitude of the target zero-sequence current phasor is less than the preset minimum current threshold, maintain the equivalent zero-sequence impedance calculated in the previous cycle.

[0040] In an optional embodiment, the step of calculating the neutral point offset voltage phasor based on the corrected neutral current phasor and the neutral equivalent impedance, and thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: The equivalent impedance of the neutral line is calculated based on the test values ​​of the neutral line's self-impedance parameters, which include the neutral line resistance and neutral line reactance. Multiplying the neutral line equivalent impedance by the corrected neutral line current phasor yields the neutral point offset voltage phasor; The neutral point offset voltage phasor is used as the target zero-sequence voltage phasor, and the corrected neutral line current phasor is multiplied by one-third to generate the target zero-sequence current phasor.

[0041] The processor reads pre-measured neutral line impedance parameters from non-volatile memory. These parameters include the neutral line resistance and the signed neutral line reactance between the incoming terminal of the energy metering box and the neutral point of the distribution transformer. The processor uses the neutral line resistance as the real part of the complex impedance and the neutral line reactance as the imaginary part to construct the equivalent neutral line impedance, for example, as follows: =1.0+j0.5Ω.

[0042] The neutral current phasor is calibrated according to a preset reference direction. When the installation direction of the neutral current sensor is opposite to the preset reference direction, the processor first multiplies the calibrated neutral current phasor by -1 to complete the direction reversal. The calibrated neutral current phasor is then multiplied by the neutral equivalent impedance to obtain the neutral voltage drop phasor, which is recorded as the neutral point offset voltage phasor according to a preset voltage reference direction. For example, when the calibrated neutral current phasor is 5.0∠30°A and the neutral equivalent impedance is 1.0+j0.5Ω, multiplying them yields the corresponding neutral point offset voltage phasor. This neutral point offset voltage phasor is used as the target zero-sequence voltage phasor, and the calibrated neutral current phasor is multiplied by one-third to generate the target zero-sequence current phasor.

[0043] In an optional embodiment, the step of decomposing the corrected voltage phasor and corrected current phasor based on the symmetrical component method to obtain the positive-sequence voltage phasor and positive-sequence current phasor, and calculating the equivalent zero-sequence impedance based on the modulus ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: Construct the standard symmetric component forward transformation matrix; Using the standard symmetric component forward transformation matrix, matrix multiplication decomposition operations are performed on the three-dimensional column vector containing the correction voltage phasor and the three-dimensional column vector containing the correction current phasor, respectively. The second row of components extracted from the decomposition operation results is determined as the positive sequence voltage phasor and the positive sequence current phasor; When the absolute magnitude of the target zero-sequence current phasor is not less than the preset minimum current threshold, the absolute magnitude of the target zero-sequence voltage phasor is divided by the absolute magnitude of the target zero-sequence current phasor to calculate the equivalent zero-sequence impedance. When the absolute magnitude of the target zero-sequence current phasor is less than the preset minimum current threshold, the calculated value of the equivalent zero-sequence impedance of the previous cycle is maintained.

[0044] The processor has a pre-defined complex rotation operator a = 1 ∠120° and its square a. 2 =1∠240°, construct the standard symmetric component forward transformation matrix. The forward transformation matrix consists of the coefficient matrix [1, 1, 1; 1, a, a]. 2 ;1,a 2 , a] multiply the whole by 1 / 3 to get.

[0045] Following a fixed phase sequence of phases A, B, and C, the corrected voltage phasors of phases A, B, and C are arranged sequentially into a three-row, one-column voltage phasor column vector. This vector is then left-multiplied by the forward transformation matrix, and the resulting three-dimensional output vector is cached in a register set. The complex component in the second row of the output vector is extracted and designated as the positive-sequence voltage phasor. This operation is then applied to the corresponding three-dimensional current column vector to obtain the positive-sequence current phasor. The representation of the positive-sequence voltage phasor in the complex plane is as follows: Figure 2 As shown.

[0046] Calculate the magnitude of the target zero-sequence voltage phasor, for example, if the absolute voltage magnitude is calculated to be 10.0V; extract the target zero-sequence current phasor using the same modulus method to obtain the absolute current magnitude, such as 5.0A. Divide the obtained absolute magnitude of the target zero-sequence voltage phasor by the corresponding absolute magnitude of the target zero-sequence current. In the example, dividing 10.0 by 5.0 yields a real parameter of magnitude 2.0 ohms. Store this result and mark it as the equivalent zero-sequence impedance.

[0047] S3, calculate the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculate the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio and the phase-locking factor, and trigger an alarm signal when the spatial imbalance continues to exceed the preset threshold.

[0048] Extract the target zero-sequence current phasor magnitude and the positive-sequence current phasor magnitude obtained in the previous steps. Divide the target zero-sequence current phasor magnitude by the positive-sequence current phasor magnitude to obtain the magnitude ratio representing the degree of unbalanced current penetration. Obtain the phase angles of the target zero-sequence voltage phasor and the positive-sequence voltage phasor respectively. Subtract the positive-sequence voltage phase angle from the target zero-sequence voltage phase angle to obtain the phase difference between the two in the complex plane. Calculate the absolute value of the tangent of this phase difference and multiply it by a preset constant to obtain the phase locking factor, which is used to characterize the phase deviation of the zero-sequence voltage phasor relative to the positive-sequence voltage phasor.

[0049] The equivalent zero-sequence impedance is divided by a preset reference impedance that represents the impedance characteristics under rated full-load symmetrical conditions to obtain a dimensionless impedance ratio. The square of the modulus ratio, the impedance ratio, and the phase-locking factor are multiplied together, and the square root of the multiplication result is taken to obtain a comprehensive spatial unbalance value representing the asymmetrical state of the electrical network. Optionally, to avoid abnormal amplification of the tangent value when the phase difference is close to 90 degrees, the phase-locking factor is limited to a preset upper limit.

[0050] A hardware timer and counter variable are configured within the microcontroller of the monitoring motherboard to continuously update the spatial imbalance value in real time with a set calculation cycle of several hundred milliseconds. After each calculation, the value is compared with a preset imbalance threshold stored in the factory flash memory. If the current spatial imbalance value is greater than the preset threshold, the counter variable is incremented by 1; otherwise, it is reset to zero. When the accumulated value of the counter variable multiplied by the calculation cycle reaches a preset duration tolerance limit, the microcontroller outputs a high level to a general-purpose input / output pin to drive a relay to close and illuminate the local audible and visual alarm. The alarm is then triggered by sending a protocol data packet containing the meter box identification code, the time of occurrence, and the current spatial imbalance value to the remote maintenance master station via a wireless communication module.

[0051] In an optional embodiment, the step of calculating the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculating the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, and calculating the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio, and the phase-locking factor includes: Calculate the ratio of the target zero-sequence current phasor magnitude to the positive-sequence current phasor magnitude, and use this ratio as the magnitude ratio; Calculate the phase angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the absolute value of the tangent of the phase angle and multiply it by a preset constant to obtain the phase locking factor; The spatial imbalance is obtained by multiplying the square of the modulus ratio by the ratio of the equivalent zero-sequence impedance to the preset reference impedance, multiplying by the phase-locking factor, and then taking the square root.

[0052] Divide the magnitude of the target zero-sequence current phasor, for example, 1.5A, by the magnitude of the positive-sequence current phasor, for example, 10.0A, to calculate a parameter of the form 0.15. Store this parameter in a global variable as the magnitude ratio.

[0053] Identify the angular attribute parameter of the target zero-sequence voltage phasor, such as a calculated value of 50 degrees, and subtract the positive-sequence voltage phasor phase angle parameter from this parameter, such as 20 degrees. The difference is then used to obtain the phase angle of 30 degrees.

[0054] The absolute value of the tangent corresponding to the 30-degree angle is calculated to be approximately 0.577. This value is then multiplied by a preset constant set in the configuration file, which is set to a constant of 1.5. The phase locking factor coefficient is then calculated to be approximately 0.8655.

[0055] The obtained modulus ratio of 0.15 is squared to obtain a value of 0.0225. The generated equivalent zero-sequence impedance result, such as 4.0 ohms, is divided by the preset reference impedance parameter, such as 8.0 ohms, to obtain an impedance ratio of 0.5. The extracted square term 0.0225, the impedance ratio 0.5, and the phase locking factor 0.8655 are multiplied to generate an intermediate value of 0.009736. The square root of this multiplication result yields a value of approximately 0.0986, which is used as the spatial imbalance value and continuously refreshed and stored.

[0056] In an optional embodiment, triggering an alarm signal when the spatial imbalance continuously exceeds a preset threshold includes: Set the upper limit of the count value of the sliding verification window and the preset threshold of spatial imbalance, and initialize the current count value to 0; The calculated spatial imbalance is compared with the preset threshold. If the spatial imbalance is greater than the preset threshold, the current count value is incremented by 1. If the spatial imbalance is less than or equal to the preset threshold, the current count value is reset to 0; Determine whether the current count value is greater than or equal to the upper limit of the count value. If so, generate an alarm control command and trigger the audible and visual alarm device to issue a three-phase imbalance alarm signal through the hardware interface.

[0057] During the system startup phase, the monitoring module allocates registers to store the judgment mechanism parameters, sets the upper limit variable of the count value of the sliding verification window, for example, limits the upper limit of the integer variable that needs to be confirmed 5 times consecutively to 5; loads the preset threshold of space imbalance, sets the threshold to 0.15; and assigns the initial value of 0 to the current count value parameter used to accumulate the current alarm status.

[0058] When the system refreshes the measured spatial imbalance parameter, it compares this parameter with a preset threshold of 0.15. If the currently acquired spatial imbalance value, for example, 0.18, is found to be greater than the preset threshold, the current count value is incremented by 1. If the spatial imbalance data becomes less than or equal to 0.15 in a certain judgment period, the monitoring terminal resets the current count value parameter to 0. After completing the above adjustment, it checks whether the current count value is greater than or equal to the upper limit parameter, that is, whether the parameter value has been greater than or equal to the threshold value of 5 times. If the determination is true, it indicates that the imbalance event is persistent, and an alarm control command is generated. This command is released to the GPIO pin interface to output a drive level signal, triggering the audible and visual alarm device to issue a three-phase imbalance alarm signal.

[0059] In a second embodiment, the present invention also proposes a three-phase imbalance monitoring system for an energy metering box, comprising the following modules: The module is used to acquire discrete time-domain data sequences corresponding to three-phase voltage, three-phase current and neutral line current based on synchronously acquired three-phase voltage, three-phase current and neutral line current, construct frequency adaptive correction sequences according to voltage zero-crossing interval and power frequency cycle deviation, and use the frequency adaptive correction sequences to extract the fundamental phasor of the discrete time-domain data sequences to obtain the corrected voltage phasor, corrected current phasor and corrected neutral line current phasor. The adjustment module is used to calculate the neutral point offset voltage phasor based on the corrected neutral line current phasor and the neutral line equivalent impedance, thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor. Based on the symmetrical component method, the corrected voltage phasor and the corrected current phasor are decomposed to obtain the positive-sequence voltage phasor and the positive-sequence current phasor. The equivalent zero-sequence impedance is calculated based on the magnitude ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor. The calculation module is used to calculate the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculate the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio and the phase-locking factor, and trigger an alarm signal when the spatial imbalance continues to exceed a preset threshold.

[0060] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for monitoring three-phase imbalance in an electricity metering box, characterized in that, include: Based on synchronously acquired three-phase voltage, three-phase current and neutral line current, discrete time-domain data sequences corresponding to the three-phase voltage, three-phase current and neutral line current are obtained. A frequency adaptive correction sequence is constructed according to the voltage zero-crossing interval and the deviation of the power frequency cycle. The fundamental phasor is extracted from the discrete time-domain data sequence using the frequency adaptive correction sequence to obtain the corrected voltage phasor, corrected current phasor and corrected neutral line current phasor. The neutral point offset voltage phasor is calculated based on the corrected neutral current phasor and the neutral equivalent impedance. The target zero-sequence voltage phasor and the target zero-sequence current phasor are obtained accordingly. The corrected voltage phasor and the corrected current phasor are decomposed based on the symmetrical component method to obtain the positive sequence voltage phasor and the positive sequence current phasor. The equivalent zero-sequence impedance is calculated based on the modulus ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor. Calculate the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculate the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio, and the phase-locking factor, and trigger an alarm signal when the spatial imbalance continuously exceeds a preset threshold.

2. The method according to claim 1, characterized in that, The process of acquiring discrete time-domain data sequences corresponding to the three-phase voltage, three-phase current, and neutral line current based on synchronously acquired data includes: By using three-phase voltage sensors, three-phase current sensors, and neutral line current sensors installed at the input end of the power metering box, the three-phase voltage, three-phase current, and neutral line current are converted from analog to digital at fixed sampling frequencies and other time intervals to obtain discrete time-domain data sequences.

3. The method according to claim 1, characterized in that, The step of constructing a frequency adaptive correction sequence based on the voltage zero-crossing interval and the deviation of the power frequency cycle, and using the frequency adaptive correction sequence to extract the fundamental phasor of the discrete time-domain data sequence to obtain the corrected voltage phasor, the corrected current phasor, and the corrected neutral line current phasor includes: Extract two consecutive positive zero-crossing timestamps from the discrete time-domain data sequence, and take the difference between the two timestamps as the current power frequency cycle; The current actual power frequency is calculated based on the current power frequency cycle, and a frequency adaptive correction sequence is constructed based on the current actual power frequency, sampling timestamp, and window function weight. The frequency adaptive correction sequence is used to perform weighted inner product operations on the discrete time domain data sequences corresponding to the three-phase voltage, three-phase current and neutral line current, respectively, to extract the fundamental complex component at the current actual power frequency. The corrected voltage phasor, corrected current phasor, and corrected neutral current phasor are calculated based on the fundamental complex components.

4. The method according to claim 3, characterized in that, The step of calculating the neutral point offset voltage phasor based on the corrected neutral current phasor and the neutral equivalent impedance, and thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: The equivalent impedance of the neutral line is calculated based on the test values ​​of the neutral line's self-impedance parameters, which include the neutral line resistance and neutral line reactance. Multiplying the neutral line equivalent impedance by the corrected neutral line current phasor yields the neutral point offset voltage phasor; The neutral point offset voltage phasor is used as the target zero-sequence voltage phasor, and the corrected neutral line current phasor is multiplied by one-third to generate the target zero-sequence current phasor.

5. The method according to claim 1, characterized in that, The method of decomposing the corrected voltage phasor and corrected current phasor based on the symmetrical component method to obtain the positive-sequence voltage phasor and positive-sequence current phasor, and calculating the equivalent zero-sequence impedance based on the modulus ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor, includes: Construct the standard symmetric component forward transformation matrix; Using the standard symmetric component forward transformation matrix, matrix multiplication decomposition operations are performed on the three-dimensional column vector containing the correction voltage phasor and the three-dimensional column vector containing the correction current phasor, respectively. The second row of components extracted from the decomposition operation results is determined as the positive sequence voltage phasor and the positive sequence current phasor; When the absolute magnitude of the target zero-sequence current phasor is not less than the preset minimum current threshold, the absolute magnitude of the target zero-sequence voltage phasor is divided by the absolute magnitude of the target zero-sequence current phasor to calculate the equivalent zero-sequence impedance. When the absolute magnitude of the target zero-sequence current phasor is less than the preset minimum current threshold, the calculated value of the equivalent zero-sequence impedance of the previous cycle is maintained.

6. The method according to claim 1, characterized in that, The calculation of the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, the calculation of the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, and the calculation of the spatial imbalance based on the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio, and the phase-locking factor include: Calculate the ratio of the target zero-sequence current phasor magnitude to the positive-sequence current phasor magnitude, and use this ratio as the magnitude ratio; Calculate the phase angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the absolute value of the tangent of the phase angle and multiply it by a preset constant to obtain the phase locking factor; The spatial imbalance is obtained by multiplying the square of the modulus ratio by the ratio of the equivalent zero-sequence impedance to the preset reference impedance, multiplying by the phase-locking factor, and then taking the square root.

7. The method according to claim 1, characterized in that, The step of triggering an alarm signal when the spatial imbalance continuously exceeds a preset threshold includes: Set the upper limit of the count value of the sliding verification window and the preset threshold of spatial imbalance, and initialize the current count value to 0; The calculated spatial imbalance is compared with the preset threshold. If the spatial imbalance is greater than the preset threshold, the current count value is incremented by 1. If the spatial imbalance is less than or equal to the preset threshold, the current count value is reset to 0; Determine whether the current count value is greater than or equal to the upper limit of the count value. If so, generate an alarm control command and trigger the audible and visual alarm device to issue a three-phase imbalance alarm signal through the hardware interface.

8. A three-phase imbalance monitoring system for an electricity metering box, characterized in that, include: The module is used to acquire discrete time-domain data sequences corresponding to three-phase voltage, three-phase current and neutral line current based on synchronously acquired three-phase voltage, three-phase current and neutral line current, construct frequency adaptive correction sequences according to voltage zero-crossing interval and power frequency cycle deviation, and use the frequency adaptive correction sequences to extract the fundamental phasor of the discrete time-domain data sequences to obtain the corrected voltage phasor, corrected current phasor and corrected neutral line current phasor. The adjustment module is used to calculate the neutral point offset voltage phasor based on the corrected neutral line current phasor and the neutral line equivalent impedance, thereby obtaining the target zero-sequence voltage phasor and the target zero-sequence current phasor. Based on the symmetrical component method, the corrected voltage phasor and the corrected current phasor are decomposed to obtain the positive-sequence voltage phasor and the positive-sequence current phasor. The equivalent zero-sequence impedance is calculated based on the magnitude ratio of the target zero-sequence voltage phasor and the target zero-sequence current phasor. The calculation module is used to calculate the magnitude ratio of the target zero-sequence current phasor to the positive-sequence current phasor, calculate the phase-locking factor based on the angle between the target zero-sequence voltage phasor and the positive-sequence voltage phasor, calculate the spatial imbalance by combining the equivalent zero-sequence impedance, the preset reference impedance, the magnitude ratio and the phase-locking factor, and trigger an alarm signal when the spatial imbalance continues to exceed a preset threshold.

9. The system according to claim 8, characterized in that, The process of acquiring discrete time-domain data sequences corresponding to the three-phase voltage, three-phase current, and neutral line current based on synchronously acquired data includes: By using three-phase voltage sensors, three-phase current sensors, and neutral line current sensors installed at the input end of the power metering box, the three-phase voltage, three-phase current, and neutral line current are converted from analog to digital at fixed sampling frequencies and other time intervals to obtain discrete time-domain data sequences.

10. The system according to claim 8, characterized in that, The step of constructing a frequency adaptive correction sequence based on the voltage zero-crossing interval and the deviation of the power frequency cycle, and using the frequency adaptive correction sequence to extract the fundamental phasor of the discrete time-domain data sequence to obtain the corrected voltage phasor, the corrected current phasor, and the corrected neutral line current phasor includes: Extract two consecutive positive zero-crossing timestamps from the discrete time-domain data sequence, and take the difference between the two timestamps as the current power frequency cycle; The current actual power frequency is calculated based on the current power frequency cycle, and a frequency adaptive correction sequence is constructed based on the current actual power frequency, sampling timestamp, and window function weight. The frequency adaptive correction sequence is used to perform weighted inner product operations on the discrete time domain data sequences corresponding to the three-phase voltage, three-phase current and neutral line current, respectively, to extract the fundamental complex component at the current actual power frequency. The corrected voltage phasor, corrected current phasor, and corrected neutral current phasor are calculated based on the fundamental complex components.

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