Study On Hybrid Energy Storage System Of Extended Range Electric Vehicle Based On Internal Combustion Constrained Linear Generator

With the concern of air pollution and fossil fuel consumption,the development of new energy vehicles has become a necessary trend.The promotion of pure electric vehicles is limited by many problems in driving range and battery,and extended range electric vehicles which can extend driving range will become an effective transition from fuel vehicles to pure electric vehicles.The traditional range extender directly transplanted has the problems of long transmission chain and low transmission efficiency,and the single power supply can not meet the requirements of high specific energy and high specific power of the energy storage system in the process of driving.In view of this,this paper focuses on the dynamic characteristics of the internal combustion constrained linear power generation system and the parameter optimization and energy management strategy of the composite energy storage system.（1）For the internal combustion constrained linear power generation system,the general layout scheme was determined,and its four stroke working cycle was designed;The dynamic and thermodynamic models of the piston were established,and the dynamic motion law of the piston and the variation characteristics of the pressure in the cylinder are mainly analyzed;The design scheme and related technical indexes of linear generator are determined,and a cylindrical moving magnet permanent magnet linear generator was designed.Based on Maxwell,a two-dimensional simulation model was established to simulate its air and load characteristics.The system efficiency can reach 30%.（2）The topology of hybrid energy storage system for extended range electric vehicle based on internal combustion constrained linear generation system was analyzed;Based on the analysis of the characteristics of driving conditions,the parameters of the main power transmission system were optimized and matched according to the requirements of vehicle dynamic performance index;Based on the analysis of the characteristics of the power supply,the equivalent circuit models of battery and super capacitor were established,focusing on the performance attenuation model of Li Fe PO₄ battery.Based on the analysis of the working principle of bidirectional DC/DC converter,the efficiency model was established.（3）Aiming at the parameter optimization problem of composite energy storage system,a joint optimization method considering the coupling of system parameters and energy management algorithm control parameters was proposed.Firstly,the range of system parameters and control parameters was limited,and a multi-objective evaluation equation based on battery performance degradation and system cost was constructed;Based on NSGA-II algorithm,the integrated optimization process of system simulation model in the loop was designed;Different solutions of Pareto frontier solution were compared and analyzed.Based on the prediction model of driving range in battery life cycle,the optimal solution to reach a compromise between battery performance degradation and system cost was determined.Compared with single battery,its effectiveness was verified.（4）In view of the energy management strategy of composite energy storage system,a multi-level wavelet transform strategy based on the division of super capacitor working area was proposed.The corresponding relationship between the different charging and discharging intensity levels and wavelet decomposition levels of supercapacitor was derived from adjusting the wavelet decomposition level,realizing the frequency conversion distribution of load power,and effectively extending the battery life.Compared with fuzzy control strategy,the cut-off frequency of battery power was controlled below 0.05Hz,which greatly reduces the impact of high frequency and transient peak power on the battery,and the battery performance loss was reduced by 12.6%;Compared with traditional wavelet transform strategy,the supercapacitor SOC was effectively maintained near the target value of 0.7,and the"peak cutting and valley filling"function was fully exerted,and the battery performance loss was reduced by 7.6%.