| With the rapid technological development,electric vehicles have gradually been paid close attention.Alternating current charging predominates the charging stations and charging piles,which is mainly studied.And then output low-power DC charging through the car charger,which charging speed is slow.However,a little research has been done on the direct current charging measurement with faster charging speed and more suitable for future development.At present,there is an electric energy meter for DC electric energy measurement on the market,but the problems such as large measurement error,small application range,and low safety are appeared when it is applied to a high-power electric vehicle DC charging measurement system.Therefore,an in-depth study on the DC measurement error analysis and improved algorithm of electric vehicle is lucubrated in this thesis.The principle of electric energy measurement is started with in this thesis,and the instantaneous power integration method of time domain method and the principle of three existing DC algorithms are analyzed.According to the characteristics of charging ripple,the influences of the average method and the RMS method are analyzed.The MATLAB simulation is carried out to obtain the influence of ripple on the error.Furthermore,two methods to reduce the influence of ripple are proposed—adaptive filtering algorithm and improved metrology algorithm.In order to reduce the ripple content,the adaptive filtering algorithm is studied in this thesis.The principle,advantages and limitations of the three basic adaptive algorithms are analyzed in detail.The variable step size LMS algorithm based on sigmoid function is derived and the algorithm is lucubrated.Under the condition of not affecting the steady-state error,the objective function is optimized and the convergence speed is improved,so that an improved SVSLMS adaptive filtering algorithm is obtained.In order to reduce the influence of ripple on the algorithm,the influence of the actual single-chip system on the algorithm is studied in this thesis.According to the hardware characteristics of the DC measurement system,an improved algorithm which is more suitable for the single-chip system is proposed.The performance of the improved algorithm proposed is verified by analog signal simulation.The simulation model of the DC charging pile rectification system of electric vehicle is established and the actual output signal is simulated.The results show that the improved SVSLMS adaptive filtering algorithm proposed in this paper is combined with the improved DC algorithm with small error and fast convergence speed.It is suitable for electric vehicle DC metering system. |
