Measurement Error Analysis Of DC Meter Of DC Charging Pile And Method Of Improving Measurement Accuracy

With the widespread use of electric vehicles,DC charging piles and other supporting charging facilities have been rapidly constructed in China.Charging pile output power generally measured by the built-in dc watt-hour meter,dc watt-hour meter measuring accuracy is influenced by factors such as temperature,ripple,the billing error to the user and power supply company unnecessary damage to property.Therefore,it is necessary to analyze the influence of temperature and ripple on the measurement accuracy of DC electric energy,and take measures to reduce the measurement error.Firstly,Three methods of DC energy metering are recommended,namely,the average value method,the effective value method and the time domain integration method.The definition of ripple is introduced,the characteristics of constant voltage,constant current charging mode and pulse charging mode of electric vehicles are analyzed.This paper introduces the basic theory of thermal analysis of temperature field and determines the heat transfer process of DC watt-hour meter.Secondly,the effect of temperature on the metering accuracy of the DC electric energy meter of the DC charging pile is studied.The three-dimensional model of the temperature field of the DC electric energy meter is built.Perform thermal simulation analysis on the DC electric energy meter.The effect of the outside temperature and the shunt calorific value on the metering accuracy of the DC meter is studied.United with the thermal simulation analysis results of the DC electric energy meter,the metering errors produced by the DC electric energy meter in different ambient temperature ranges are studied.Thirdly,considering the effect of ripple on the metering accuracy,united with three DC power metering methods,the components of the effective value method and the instantaneous integral method for measuring power are respectively given.The metering error model under the effect of ripple is built.Then the metering error model of pulse charging and intermittent charging is built.And determine the main parameters that affect the metering accuracy.The three-dimensional distribution diagram of the error is obtained by simulation,and the effect of ripple content and pulse duty cycle on the metering error of DC electric energy is deeply analyzed.Finally,according to the measured DC output signal of the DC charging pile for electric vehicles,the sliding filter way and the wavelet noise reduction way are used for filtering.A new threshold method is proposed to improve the soft and hard threshold wavelet denoising,and the filtered waveforms are obtained by simulation.And compare and analyze the denoising effects of different filtering methods.The wavelet method with improved threshold can effectively filter the ripple in the DC output signal and improve the accuracy of DC power metering.