Energy Management Optimization For The Plug-in Hybrid Electric Vehicle Equipped With CVT

Pollution of environment and shortage of energy source have become two problems for the development auto industry to face. Because of long driving range and low fuel consumption and emissions, plug-in hybrid electric vehicle(PHEV) is considered to be one of electric vehicles that have most development prospects. The transmission ratio of continuously variable transmission(CVT) is continuously adjustable, which can effectively improve the load of power source. How to achieve the perfect combination between the properties of power source and the properties of CVT, is the key problem of control strategy for PHEV equipped with CVT.This paper, in allusion to the PHEV equipped with CVT, from system design(especially energy management strategy) and system simulation, conducts some thorough researches. The main works are as follows:(1) The basic structure of power system of PHEV was designed, based on a conventional vehicle equipped with CVT. The parameter matching was conducted among ISG motor, engine and power batteries, according to the requirements for driving range and power performance indexes. The models of key components in the power system, vehicle dynamic model and the model of driver were set up on the Matlab/Simulink platform.(2) An analytic method of driver’s demand torque was designed, which was based on external characteristic curve of the power source and the signal from driver’s operation. A method to select drive mode was adopted, which could make full use of electric energy. Then an optimization method for energy management strategy under the given pattern was proposed, which took minimizing the instantaneous energy consumption costs as control objective, with demand torque, state of charge(SOC) of batteries and vehicle speed as state variables, with engine torque, motor torque and speed ratio of CVT as control variables. Offline optimization results were made into MAP tables, which were used for real-time control. In addition, the braking force distribution strategy and energy optimization strategy based on maximizing recyclable electric energy under regenerative braking mode were also designed.(3) The simulations for power performance and economic performance of PHEV were conducted through self-built forward model, which could verify effectiveness of the control strategies. The contrastive analysis between two different controlstrategies for charge depleting stage was carried out. The results show that the design strategy is better in comprehensive economy.(4) The study about the effect of engine start-stop frequency on the performance of PHEV was carried out. Engine start-stop control strategy was introduced on the basis of the original energy management strategy. The results show that the improved control strategy can effectively reduce the frequency of the engine start-stop and fuel consumption.