High-precision ac power metering method

Abstract

This invention discloses a high-precision AC power metering method. At a high sampling frequency, it acquires raw data of voltage and current signals through fixed-frequency sampling. In a harmonic environment, it obtains the phase difference between the voltage and current signals through digital filtering and software zero-crossing point determination. During a specific test period, it calculates the instantaneous power of a single sampling process using a dot product summation method, and accumulates this power periodically to obtain the active power value. The introduction of a filtering stage improves the accuracy of zero-crossing point determination, thereby enhancing the metering accuracy of active power.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, and more specifically, relates to a high-precision AC power metering method. Background Technology

[0002] Accurate metering of electrical energy is crucial for the power system and a necessary technology for promoting the new energy market. For AC power applications, a typical metering method is the instantaneous power integration method: first, the product of the instantaneous current and voltage values ​​is calculated; then, the phase difference between the two values ​​is corrected; finally, the energy value is calculated by summing the results. The accuracy of current and voltage signal measurement depends on the precision of the acquisition channel; accurate phase difference measurement depends on the precision of the system timer. When using zero-crossing detection, signal noise fluctuations can also affect phase judgment. Electronic energy metering devices designed based on these principles have poor immunity to dynamic distortion, and their metering accuracy needs further improvement. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-precision AC power metering method. During a specified test period, the instantaneous power of a single sampling process is calculated by the dot product sum method, and the power is accumulated periodically as the active power value.

[0004] To achieve the above-mentioned objectives, the present invention provides a high-precision AC power metering method, characterized by comprising the following steps:

[0005] (1) The sampling clock and sampling channel range are provided by the control unit, and the sampling channel range is set to 1.5 to 3 times the current signal amplitude through real-time feedback to ensure higher resolution. Then, voltage and current data are collected at a high sampling rate.

[0006] (2) The collected voltage and current data are filtered by cascading a low-pass filter and a high-pass filter.

[0007] (3) The phase difference and frequency value of the filtered voltage and current data are calculated by the zero-crossing comparator;

[0008] (4) The phase difference calculated by the zero-crossing comparator is used to correct the instantaneous power, and the frequency value is used to dynamically set the system sampling frequency;

[0009] (5) Calculate the active energy value of a single sampling process using the dot product and summation formulas.

[0010] The objective of this invention is achieved as follows:

[0011] This invention discloses a high-precision AC power metering method. At a high sampling frequency, it acquires raw data of voltage and current signals through fixed-frequency sampling. In a harmonic environment, it obtains the phase difference between the voltage and current signals through digital filtering and software zero-crossing detection. During a specific test period, it calculates the instantaneous power of a single sampling process using a dot product sum method, and accumulates this power periodically to obtain the active power value. The introduction of a filtering stage improves the accuracy of zero-crossing detection, thereby enhancing the metering accuracy of active power. Attached Figure Description

[0012] Figure 1 This is a flowchart of a high-precision AC power metering method according to the present invention;

[0013] Figure 2 This is a schematic diagram of the system structure of the present invention used in a specific embodiment;

[0014] Figure 3 It shows the waveform effects before and after the digital filter bank operation. Detailed Implementation

[0015] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0016] Example

[0017] Figure 1 This is a flowchart of a high-precision AC power metering method according to the present invention.

[0018] In this embodiment, please refer to Figure 2 This paper presents a high-precision AC power metering method for a metering test case of a three-phase four-wire high-power circuit. The sampling process is realized by a voltage conditioning channel, an ADC sampling circuit, and a current conditioning channel. The digital filtering stage and zero-crossing point judgment and power value accumulation are realized by a DSP unit. The sampling rate and channel range are set in real time by a control unit. The power data is output by the system program and the power metering test process is controlled.

[0019] like Figure 1 As shown, the present invention provides a high-precision AC power metering method, comprising the following steps:

[0020] (1) For the sampling process, the main sources of error are: spectral leakage caused by signal frequency fluctuations and system errors introduced by the inconsistency in phase response between the voltage sensor and the current sensor. To solve the signal frequency fluctuation problem, the sampling clock is provided by the control unit and set to 250 times the measured frequency; the system errors caused by sensor phase delays are synchronously corrected through the DSP processing stage. To improve the quantization accuracy of the signal, the range of the sampling channel is provided by the control unit, and the channel range is set to 1.5 to 3 times the current signal amplitude through real-time feedback to ensure higher resolution.

[0021] In this embodiment, the sampling frequency is set to more than 200 times the fundamental signal and is an integer multiple of the fundamental signal. The quantization amplitude of the voltage and current data is maintained in the range of 1 / 3 to 2 / 3 of the analog-to-digital converter.

[0022] (2) The collected voltage and current data are filtered by cascading a low-pass filter and a high-pass filter.

[0023] In this embodiment, the cutoff frequency of the low-pass filter should be lower than 49.75Hz, and the cutoff frequency of the high-pass filter should be higher than 50.25Hz.

[0024] (3) The phase difference and frequency value of the filtered voltage and current data are calculated by the zero-crossing comparator;

[0025] In this embodiment, the zero-crossing comparator is implemented in software and calculated by averaging multiple test points. For the DSP processing stage, the main sources of error are: waveform distortion caused by the DC and harmonic components of the measured signal, and zero-crossing quantization error caused by the discontinuity of the waveform data. To solve the waveform distortion problem, signal conditioning is performed by cascading a low-pass filter and a high-pass filter to obtain the fundamental component before determining the zero-crossing point. To reduce the quantization error in zero-crossing point determination of discrete waveform data, a proportional conversion method is used to obtain the zero-crossing point position and improve the measurement accuracy of the zero-crossing point. The specific calculation method is as follows: record the amplitude at the positive and negative ends of the signal, and let their coordinate positions be (x0, y0) and (x1, y1). Treat the signal waveform between the two points as a straight line, then the zero-crossing coordinates can be expressed as: t = x0 - (x0 - x1) / (y0 - y1) × y0.

[0026] The actual effect of the above AC measurement model can be analyzed through simulation experiments on the Simulink platform. The measured signal model is set as: u(t) = 220·sin(ωt) + 4·sin(3ωt) + 4·sin(5ωt) + 3·sin(7ωt). The waveform effects of this signal before and after processing by the digital filter bank are shown in [the figure]. Figure 3As shown in the figure, the white signal is the original input signal, which undergoes some waveform distortion due to the presence of harmonics and DC bias; the gray signal is the waveform after filtering, which appears as a standard fundamental sine wave after removing harmonic interference. The signal phase shift caused by the filtering stage is approximately 0.1 rad, which does not affect the real-time performance of the subsequent zero-crossing phase determination. Assuming the AC load circuit under test is purely resistive, the current signal model corresponding to u(t) is set as follows:

[0027] i(t)=30·sin(ωt)+0.5·sin(3ωt)+0.5·sin(5ωt)+0.4·sin(7ωt)

[0028] The phase error introduced by the voltage conditioning channel and the current conditioning channel is set to π / 12. The phase difference obtained directly by the above zero-crossing judgment stage is 0.234947. After the filtering stage, the phase difference obtained by zero-crossing judgment is 0.261721. The relative error of the phase difference is reduced from 10.3% to 0.03%. It can be seen that the filtering stage has a significant improvement effect on phase difference and signal frequency accuracy.

[0029] Different test durations were selected to conduct power consumption simulation experiments. For each experiment, a different phase difference between the voltage and current signals was set. The standard power value was calculated from the initial signal's current and voltage signals. The measured power value was corrected by measuring the phase difference of the signal's fundamental component to obtain the corrected power value. The obtained data are recorded in Table 1. It can be seen that as the test duration increases, the relative error of the corrected power value gradually decreases. Due to signal distortion and system phase deviation, the power measurement error after correction by the DSP stage eventually stabilizes at around 0.002%, exhibiting high accuracy.

[0030] Test duration (min) 1 2 4 6 8 Standard energy value (kWh) 0.055 0.11 0.22 0.33 0.44 Energy correction value (kWh) 0.05498 0.10998 0.21999 0.33001 0.44002 Relative error (%) -0.0545 -0.0364 -0.0182 -0.0045 -0.0020

[0031] Table 1

[0032] (4) The phase difference calculated by the zero-crossing comparator is used to correct the instantaneous power, and the frequency value is used to dynamically set the system sampling frequency;

[0033] (5) Calculate the active energy value of a single sampling process using the dot product and summation formulas.

[0034] The method for measuring active energy is as follows: Where N is the total number of points recorded in a single sampling process, Δt is the sampling time interval, and u(t) i ), i(t) i ) represent the original voltage data points and the original current data points, respectively, and K is the error correction coefficient.

[0035] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A high-precision AC power metering method, characterized in that, Includes the following steps: (1) The sampling clock and sampling channel range are provided by the control unit, and the sampling channel range is set to 1.5 to 3 times the current signal amplitude through real-time feedback to ensure higher resolution. Then, voltage and current data are collected at a high sampling rate. (2) The collected voltage and current data are filtered by cascading a low-pass filter and a high-pass filter. (3) The phase difference and frequency value of the filtered voltage and current data are calculated by the zero-crossing comparator; (4) The phase difference calculated by the zero-crossing comparator is used to correct the instantaneous power, and the frequency value is used to dynamically set the system sampling frequency; (5) Calculate the active energy value of a single sampling process using the dot product and summation formulas.

2. The high-precision AC power metering method according to claim 1, characterized in that, The sampling frequency of the high sampling rate is set to be more than 200 times that of the fundamental signal and is an integer multiple of the fundamental signal.

3. The high-precision AC power metering method according to claim 1, characterized in that, The cutoff frequency of the low-pass filter should be lower than 49.75Hz, and the cutoff frequency of the high-pass filter should be higher than 50.25Hz.

4. The high-precision AC power metering method according to claim 1, characterized in that, The zero-crossing comparator is implemented in software and is calculated by averaging multiple test points.

5. The high-precision AC power metering method according to claim 1, characterized in that, The method for measuring the active energy value is as follows: Where N is the total number of points recorded in a single sampling process, Δt is the sampling time interval, and u(t) i ), i(t) i ) represent the original voltage data points and the original current data points, respectively, and K is the error correction coefficient.

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