Research On The Method Of The Co-estimation Of State For Lithium Ion Batteries

With the development of China's electric vehicle market,the requirements for electric vehicle performance and safety have become higher and higher in these years.As the main energy source of electric vehicles,power batteries are important factors affecting the power characteristics and safety of battery vehicles.In order to maximize the performance and safety of the battery,it is necessary to accurately obtain the state of charge,state of health,and state of power.But these states cannot be measured and affect each other.This article takes lithium ion battery as the research object to develop a method of co-estimation algorithm that can accurately obtain its state of charge,state of health,and state of power.The test experiments are designed according to the existing research results and the laboratory conditions in thesis.The characteristics of the battery's open circuit voltage,ohmic internal resistance,polarization internal resistance,and polarization capacitor under different states of charge and health are analyzed.The effects of different current on ohmic internal resistance,polarization internal resistance,and polarization capacitance are analyzed.The first-order Thevenin model is used to model the battery,the model parameters are identified by the least square method,and the model is verified using experimental data under different operating conditions.The estimation algorithms for the state of charge,health and power of the battery are studied.Among them,the state of charge estimation uses the unscented Kalman filter algorithm,and by analyzing the influence of battery model parameters on the estimation accuracy,a simplified estimation scheme is proposed.State of health estimation is based on an aging model of the relationship between the capacity loss rate and the cumulative battery discharge capacity.Fit the relational expressions of ohmic internal resistance and current magnitude,the relational expressions of polarization internal resistance and current,and the relational expressions of time constant and current,and bring these relations into the battery model to estimate the state of power.The influence of battery model parameters on estimating state of charge under different state of health is also analyzed in this thesis.Then combining the relationship between battery model parameters and capacity loss rate,a state of charge estimation algorithm for updating model parameters according to battery capacity loss rate is proposed.Finally,method of the co-estimation of state for lithium ion batteries was designed and its feasibility is successfully verified.