Electric Vehicle Stability with Rear Electronic Differential Traction K. Hartani, Y. Miloud, A. Miloudi Département d’Electrotechnique, Université de Saida BP 138 En-Nasr, Saida 20000, ALGERIE kada_hartani@yahoo.fr Abstract – In this paper, we model an electronic differential that will offer the best stability of vehicle in the curved road. The use of electronic differential constitutes a technological advance of vehicle design along the concept of more electric vehicles. Electronic differential have the advantages of replacing loosely, heavy and inefficient mechanical transmission and mechanical differential with a more efficient, light and small electric motors directly coupled to the wheels via a single gear or an in-wheel motor. To date, electronic differentials have been proposed for two and four wheeled vehicles. The proposed traction system consists of two permanent magnet synchronous (PMS) machines that ensure the drive of two back-driving wheels. The proposed control structure is based on the direct torque control for each wheel- motor. Different simulations have been carried out: vehicle driven on straight road, vehicle driven on straight road with slope, and vehicle driven over a road curved left and right. The simulation results show good vehicle stability on a curved road. Keywords : Eelectric vehicle, electronic differential, vehicle stability, direct torque control, multimachine drive. I. INTRODUCTION Electric vehicle is a road vehicle, based on electric propulsion. The electric propulsion system is the heart of new generation of EV [1]. It consists of the motor drive, transmission device, and wheels. The motor drive consists of the electric motor, power converter, and electronic controller, which are the core of the EV propulsion system. Traditionally, DC motors have been prominent in electric propulsion because their torque-speed characteristic have suited to traction requirement well and their speed control is simple. Recently, technological developments have replaced commutatorless motors to a new era, leading with the advantages of high efficiency, high power density, low operating cost, enhanced reliability, and low maintenance over DC motors. Permanent magnet synchronous motors (PMSM) are a widely accepted commutatorless motor for EV propulsion because they are robust and highly reliable. For improving the dynamic performance of PSM motor drives for electric vehicle propulsion, generally vector control technique is preferred. However vector control needs quite complicated coordinate transformations on line to decoupled the interaction between flux control and torque control to provide fast torque control of a permanent magnet synchronous motor. Hence the computation is time consuming and its implementation usually requires a high performance DSP chip. In recent years (DTC) an innovative control method called direct torque control has gained the attraction for electric propulsion system [2-4]; because it can also produce fast torque control of the induction motor and does not need heavy computation on-line, in contrast to vector control. In order to characterise the electronic differential system for an electric vehicle driven by two permanent synchronous motors attached to the rear wheel using direct torque control (Fig. 1), different simulations have been carried out: simulating the vehicle driven vehicle on a straight road, a straight road with slope and driven over a road curved right and left. Fig. 1 : Vehicle structure with two independent rear wheels. II. TRACTION SCHEME In traditional traction systems, the internal combustion engine transmits the propulsion force to the wheels through the mechanical differential. This mechanism consists of a set of gearings that basically applies the same torque on both traction wheels allowing different speed values. This traction system presents losses due to friction and cannot independently control torque in each wheel. An electronic differential, on the contrary, prevents such losses, while optimizing the device profitability. It also allows a stronger control of the vehicle traction. Fig. 2 shows the adopted scheme, which allows replacing the mechanical differential and satisfies the EV requirements. The traction motors, controlled by DTC[5]-[6] through two independent inverters, coupled to one of the rear wheels each, can be observer in this scheme. The motors used are three-phase PMS motors. The specific parameters of these motors are shown in Table A1. Thus, the electronic differential must take account of the speed difference between the two wheels when cornering. The system uses the vehicle speed and steering angle as input parameters and calculates the required inner and outer wheel speeds where the two wheels are controlled independently by two PMS motors. M1 Battery M2 Rear wheels (Driving part) SC1 SC2 Front wheels (Sreering part) EFEEA’10 International Symposium on Environment Friendly Energies in Electrical Applications 2-4 November 2010, Ghardaïa, Algeria 1