Data Accuracy for Power Management

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Data Accuracy for Power Management [Copy link]

Generally, the phase-to-phase voltage range of the closed line and the through line is between 0V-300V, and the current range is between 0A-100A. Considering the instantaneous overvoltage and overcurrent, the measurement range can be appropriately increased by changing the transformation ratio of the external voltage transformer and the current transformer. The measurement can generally meet the requirements by using AD574. AD574 is a 12bi analog-to-digital converter. Taking voltage measurement as an example, its accuracy is: 300212=0.07V, which can meet the accuracy requirements of most measurements. Data acquisition can be divided into two types: AC signal and DC signal. The acquisition of AC signal can be completed using high-speed DSP, and the purpose of accurate measurement can be achieved by collecting several data points in one cycle. Practice has proved that it is more appropriate to collect 16 data in one cycle, that is, an average of 3.125ms. To collect one round of data, the normal conversion rate of AD574 is 25us. Considering the action rate of the multi-channel analog conversion switch and related factors, each round of data acquisition can be completed within 1.6ms. Using the 16-point data collected in each cycle, the corresponding AC voltage and current values can be calculated by Fourier algorithm for comparison and judgment. Fourier algorithm can effectively filter out the interference caused by high-order harmonics. If conditions permit, the hardware circuit can be slightly modified to achieve simultaneous acquisition of 16-channel data, and the cost performance is correspondingly improved.
DC signal acquisition is mainly used in occasions where the accuracy requirements are not very high. The AC signal is converted into a DC signal through a sensor (such as the three-phase voltage and current sensor of Mianyang No. 58 Institute), and the DC signal is measured and converted into the corresponding monitoring value. This measurement method can eliminate the external instantaneous peak interference through the characteristics of the sensor itself, and can also ensure the safety of the device during instantaneous overvoltage. The measurement of DC signals can be processed by average filtering or peak filtering according to the characteristics of environmental noise. The measurement interval period can be appropriately adjusted according to different sensitivity requirements.