Abstract: The constructions of hybrid electric vehicle (HEV) are classified according to the change of charge state of battery pack, and a study on current situation and trend of control strategies for HEV are analysed. The power train system in HEV is basically divided into three types: serial, parallel and combined type. The combined hybrid system integrates the functions of the series and parallel system. It provides more possibility and flexibility to control the power flow and to minimize the energy consumption. Several combined hybrid power train configurations are provided. The research indicates that the current control strategies for HEV are not perfect and need further optimization. The control strategies should realize the optimum match among engine, motor, battery and transmis-sion to the characteristics of each component and vehicle’s driving conditions. Many aspects including the fuel economy, emission, the life of battery pack, drivability, the reliability of each component and HEV’s manufacture cost should be con-sidered in the control strategies. The PHEV equipped with small motor, small engine and continuously variable transmission is pointed out and is an ideal system construction for getting op-timal fuel economy, lower emissions, steady drivability, lower manufacture cost and HEV’s mass. A study on the control strategies and its optimization that take account of the aspects mentioned above is a work emphasis in the future.

Key words: Control strategy, Hybrid electric vehicle, Optimization