A novel electric differential and synchronization control method for 4WD/4WS electric vehicles based on fictitious master

Abstract

Electric Vehicles (EVs) have been typically proposed to replace conventional vehicles in the near future. The use of an Electric Differential (ED) in EV has many advantages like as high efficiency, low loosing, and lightweight mechanical differentials and transmissions with electric motors directly coupled to the wheels. In this paper, a novel ED mechanism for the four–Wheel–Drive (4WD)/two–Wheel–Steering (2WS) and 4WD/four–Wheel–Steering (4WS) EVs is proposed. The proposed ED is easy-to-implement and solves the problems of previous EDs. The speed synchronization action of all wheels is achieved by using the Fictitious Master technique. Moreover, for independent control of speed and torque, the Ackerman laws are applied to the motors. Also, the currents of EV are controlled with an indirect current vector controller. For a complete assessment of the proposed control method, the EV is analyzed under two different disturbances as positive and negative torque variations. The results showed that ED ensures both reliability and good path tracking. In addition, the robustness and stability of EVs under various disturbances are validated by producing new speed references for all wheels. The considered EV could robust under disturbance conditions, at an acceptable level. Moreover, the overlaps of torque and speed in the 4WD/4WS are about 15% and 23% more than 4WD/2WS, respectively. In essence, the proposed control method shows good results for EVs with various conditions: straight movement, turning, acceleration, and deceleration.