Estimating SOC Of Li-ion Battery And Constructing Circuits

The Li-ion battery management system is a very important part of electrical vehicles.The state of charge(SOC)of Li-ion battery is a key parameter in monitoring the remaining mileage of electrical vehicles.SOC can only be estimated indirectly for it could not be measured directly.There are many algorithms to predict Li-ion battery SOC,but each way has drawback.The extend kalman filter can resist noise and has self-correction function.This paper uses Thevenin model optimized by genetic algorithm to predict Li-ion battery SOC by extend kalman filter.At the same time,an electrical panels and a PCB circuit has been designed,realized in a variety of platforms.The main work of this paper includes the following aspects:Li-ion battery has been measured,modeled and optimized.Firstly,the standard internal resistance,polarization internal resistance and polarization capacitance of lithium-ion battery are measured by impedance spectroscopy.Then the Thevenin equivalent circuit model is selected as the SOC estimation model.Then genetic algorithm is used to optimize the parameters of the Thevenin model of lithium-ion battery,so that it can adapt to the extended Kalman filter algorithm to get the optimal solution.The SOC of Li-ion battery has been estimated by extended Kalman filter algorithm and Kalman filter has been designed.The extended Kalman state equation and observation equation corresponding to the davining model of Li-ion battery are established.Starting from Kalman filter,it is extended to extended Kalman filter by expansion of Taylor series.Then,the SOC of Li-ion battery estimated by algorithm of the extended Kalman filter which run successfully in MATLAB has been implemented on the platform of DSP,STM32 and Lab VIEW.A low SOC single battery replacement control circuit for lithium-ion batteries has been designed and built.The low SOC battery in the battery pack was replaced by the spare lithium-ion battery.In the experiment,the battery inspection instrument was used to acquired data of lithium-ion battery,PLC uses as control unit,PC personal computer was used to process data,Lab VIEW software was used as user operation platform,RS485 interface and MODBUS serial port communication protocol was adopted as communication interface and protocol.In the experiment of charge discharge estimation,the SOC value of extended Kalman filter estimation is stable.Extended Kalman filter(EKF)can eliminate theaccumulated error caused by ampere hour integration by self-tuning.The longer of lithium-ion battery runs continuously,the higher of the estimation accuracy is.