Research On DC Charging Measurement Of Electric Vehicle And Measurement Module Design

With the rapid development of the Electric Vehicle(EV)industry,the charging stations have been on a large-scale construction.The charger is a new high-power and highly nonlinear load as well as a harmonic power source.Therefore,the influence of the DC signal characteristics on the measurement needs to be studied intensively.In this paper,the reasonability of traditional AC measurement method towards ripple DC signal and the intermittent charging is studied.Besides,high-power DC charging data of an actual EV is analyzed.In addition,a DC measurement module with DSP is designed which is based on the characteristics of the DC measurement.The main work and conclusions of this paper are as follows.(1)Firstly,the paper introduces two energy measurement methods,time domain integral method and effective value method.In view of the situation that the DC high-power charging of EV will cause harmonic,using time domain integral method to calculate the charging power demonstrates that it contains the DC power as well as the active power of harmonics.While adopting the effective value method,the Emanuel power decomposition theory shows that the current distortion power,the voltage distortion power and harmonic apparent power are existed except for the DC power.Finally,the cause of the error in the calculation of the electric energy with the ripple is analysed.(2)In the case that the voltage and current signals contain ripple when charging,this paper analyses the error model of effective value method.Due to the influence of amplitude and phase of each harmonic signal,the model of the relationship between the ripple coefficient and the energy metering error is difficult to obtain.Therefore,the influence of the amplitude and phase of each harmonic wave on the measurement is studied,and it is used to reflect the influence of the ripple coefficient on the electric energy measurement error.Through the simplification of the error model,it can be seen that the measurement error is related to the magnitude and phase of each harmonic.Ignoring the influence of ripple on the electric energy measurement,this paper uses time domain integral method and effective value method to measure the impulse charging,ReflexTM charging and variable voltage intermittent charging,derive the error models of three charging methods and get its influencing factors.As a consequence,the effective value method is not applicable to measure the energy of intermittent charging.(3)The simulation analysis of the measurement error models are done for the ripple DC signal and the pulse charging,the ReflexTM charging and the variable voltage intermittent charge method and obtain the influence of variable quantity on error.It can be seen that the effective value method is not suitable for the measurement of high ripple signal and intermittent charging of electric vehicles.Finally,the pulsating DC signal is sampled by different sampling rates,and the sampling rate has little influence on the measurement of the pulsating DC signal.It can provide reference for setting the sampling rate of electric energy metering module.(4)In order to study the characteristics of voltage and current signal and its influence on energy metering.The voltage and current data of charging piles in the laboratory and the charging of EV in charging station are measured by waveform recorder.Firstly,the frequency spectrum of voltage and current in AC and DC side is analysed when the constant resistance is charged by constant voltage and current.Then the energy consumption of the charger and the ripple coefficient of the voltage and the current signal are obtained.It also discusses the effect of the ripple on the energy measurement in the case of constant voltage and constant current charging.Finally,Due to the large fluctuation of DC signal,the influence of different sampling rates on DC measurement is studied.The same method is used to analyse the voltage and current data of EV charging.(5)The paper introduces the component of DC power measurement module based on DSP.The conditioning circuit module converts the external high voltage and large current signal into a suitable small signal and send into sampling module.The sampling module transforms analogy signals into digital signals and send into the DSP module.DSP not only need to process voltage and current data,but also need to control the LCD module.Power module supply different specifications voltage for the measurement module.Firstly,the current generator and DC voltage stabilized power supply are used as the signal source of the measurement module and the precision of measurement module is obtained.Then the time domain integral method and effective value method are used to measure the DC signal with ripple and pulse signal in the measurement module,and the measurement error was basically the same as theoretical value.