Research On The Energy Management Strategy For Plug-in Hybrid Electric Bus At Low Temperatures

The electrification is now an inevitable trend of the vehicle powertrain.As a kind of new energy vehicle,the Plug-in hybrid vehicle(PHEV)adds a pure electric drive structure to the original traditional vehicle,which not only ensures the driving range of the vehicle,but also maximizes the use of electric drive,thereby exerting energy saving and emission reduction.The performance of lithium-ion battery in electric drive is easily affected by the ambient temperature.In subzero temperature environment,the power batteries will be an exhibition of performance cutback and life degradation,which has caused great obstacles to the development and promotion of Plug-in hybrid vehicles in the cold northern regions at high latitudes.Aiming at the characteristics of two phases with charge depleting and charge sustaining in PHEV operation process,an energy management strategy for two-stage embedded battery heating management is proposed in this dissertation.The simulation study and feasibility analysis are also carried out.In this dissertation,the working principle of series plug hybrid power system is analyzed.The working mode and the corresponding power flow generated by the cooperation between the power battery and the auxiliary power unit(APU)are analyzed.At the same time,through adding convection heating channel to the traditional series structure,the power flow of the PHEV power system with convection heating function is proposed.Secondly,the key components model of plug-in hybrid power system is established.Including Rint equivalent circuit model,degradation model for Arrhenius formula and battery thermal model.And also the optimal power curve model of APU,the efficiency map model of drive motor,vehicle dynamics model and the driving cycle.Thirdly,the PHEV energy management strategy with preheating system in cold environment is proposed.The strategy is based on charge depleting-charge sustaining(CD-CS)strategy and embedded in battery thermal management.The implementation of the overall strategy is divided into three parts: state and state switching,SOC and temperature estimation,and logic judgment unit.The three units are described separately.Finally,the simulation results are analyzed.This dissertation discusses three kinds of scenarios: non-recharging opportunity,once recharging opportunity and twice recharging opportunity,and the battery SOC,temperature and degradation in three scenarios.At the same time,the economy produced by using power grid or auxiliary power unit to preheating compared with non-heating is analyzed,and the quantitative analysis of cost is given to provide guidance for the layout of charging station.