H-infinity Based Observer For State Of Charge Estimation Of Lithium-ion Battery

While the automobile brings convenience to people's lives,automobile exhaust has also become one of the major sources of urban haze.In recent years,the hybridization and electrification of automobile propulsion systems have become the main trend of the automotive industry.Power lithium batteries are the main source of energy for pure electric vehicles.The battery's state-of-charge(SOC)plays a crucial role in power distribution and battery protection.However,the lithium battery is a typical nonlinear system,and the SOC cannot be directly measured by the on-board sensors,so the research on the SOC estimation is very necessary.The main research work of the thesis is as follows:(1)The principle of electrochemical reaction of the lithium battery is introduced,and the theoretical basis of the polarization characteristics of the lithium battery is provided.Then,an experimental platform for studying the characteristics of lithium batteries was established in this thesis.A series of experiments on lithium batteries were conducted on the experimental platform.Through the experimental results,experimental performance of the lithium battery has been fully understood.Then the modeling and parameter identification with implementation of the main functions of the BMS have been paved.(2)According to the characteristics of the lithium battery in charge and discharge experiments,a second-order Resistor-Capacitor(RC)equivalent circuit model of a lithium battery is established.The current and voltage responses of the battery pack are used to identify the model parameters and the open circuit voltage nonlinear function of the remaining battery capacity.Furthermore,considering that the equivalent circuit model contains capacitor elements,and the fractional-order capacitors can simulate the characteristics of the capacitors better,a fractional order second-order RC equivalent circuit model is established.And the minimum terminal voltage error as an indicator is proposed to identify the order of the fractional order.The discharge experiments verify the validity of the second-order RC model.And the modeling accuracy of the fractional-order model relative to the integer-order model is higher.As a result,it lays a foundation for the model-based SOC estimation method.(3)The deficiencies of the classical SOC estimation method based on Kalman filter are analyzed.Considering the good suppression effect of nonlinear observer on the dynamic error and the advantage of the H infinity design criterion to solve the observer gain,the nonlinear H-infinity observer method based on a second-order RC model is proposed to estimate the SOC.The Lyapunov stability principle is used to ensure the convergence of the estimation error of the residual power.By further ensuring the infinite performance of the error system,a linear matrix inequality group is established and solved.So the design of the nonlinear H-infinity observer is completed and the design process is completed.It is simple and effective.Furthermore,based on the fractional model and the equivalent theorem of the continuous frequency distribution model,a nonlinear H-infinity observer is proposed for the established fractional model.Lastly,considering the applications of the observer method on low-cost microcontrollers,bounded gain disturbances are introduced and a non-fragile H-infinity observer is proposed.Finally,the effectiveness of the proposed algorithm is verified by static dynamic discharge experiments and vehicle cycle conditions experiments.(4)In order to realistically demonstrate the practical application of the SOC algorithm on a low-cost microcontroller,an embedded BMS template with the Freescale MC9S12P64 microcontroller as the control core was used for exploration.First,the system hardwares of the BMS model are introduced.For the design of system software,?C/OS-II real-time operating system was transplanted on the MC9S12P64 main control chip in order to improve the stability,reliability and real-time performance of BMS.And the flow chart of the main program and subroutine of the system software was given.As a result,the SOC estimation platform for ?C-OS real-time operating system was established.