Research On SOC Estimation Method In Lithium Supercapacitor

Due to zero emission and no pollution,pure electric vehicles have been recognized by more and more countries and become the main direction of the development of energy conservation and environmental protection in the world.But batteries as the energy source of electric vehicles,have not yet reached the same level with traditional cars.At present,the specific energy density of batteries is so low,and they can not meet the mileage of traditional cars.Therefore,the research of batteries for electric vehicles is very significant.The battery management system(BMS)is one of the key technologies to study the development of electric vehicles.The core is that the estimation of the battery's residual quantity is also called the SOC estimation of the battery.Through the research of battery SOC,not only can we know the remaining capacity of the battery,but also improve the battery life and battery performance,so the estimation of SOC is very important.This paper firstly introduces the development of electric vehicles,then introduces the types of batteries what be used in electric vehicles,finally selects lithium supercapacitor as the research object of this paper.By comparing various kinds of batteries for electric vehicles,in order to understand the performance of lithium supercapacitor and prepare for the subsequent establishment of equivalent models,the characteristics of internal resistance,capacity,charge-discharge characteristics and self-discharge characteristics of lithium supercapacitor.Secondly,several commonly used battery models are introduced,such as RC model,trapezoid model,three branch model,neural network model and so on.By analyzing the advantages and disadvantages of various models,a model based on lithium supercapacitor was selected.Through the experiment and make sure the relation of open circuit voltage and SOC and meanwhile verify the parameter of equivalent circuit model,and then make sure the equivalent circuit model of this paper can accurately reflect the actual state of the lithium supercapacitor.Finally,research and introduce some common methods for calculating SOC,such as time integral method,internal resistance method,open circuit voltage method,neural network method,fuzzy logic algorithm,particle method,kalman filter method,through the research and analysis of kalman filter,finally this paper selects the unscented kalman filter(UKF)algorithm as the SOC estimation algorithm.Through setting up unscented kalman filter model in simulink and put the experiment data into the model and then compare the simulation and experiment results make sure that based on unscented kalman filter of equivalent circuit voltage has high computing precision and accuracy.