Design of an advanced traction controller for an electric vehicle equipped with four direct driven in-wheel motors

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Design of an advanced traction controller for an electric vehicle equipped with four direct driven in-wheel motors

Jalali, Kiumars / Bode, Kai / Lambert, Steve / McPhee, John

A traction control strategy has been proposed for an electric vehicle with four independently driven in-wheel motors. At first, a simplified mathematical description of a PMDC in-wheel motor has been developed and the transfer functions were implemented. A complete dynamic model of the vehicle is developed in ADAMS/View using Pacejka 2002 tire models. The vehicle's slip response to a torque step input at all wheels served as a basis for an approximation of the transfer function from motor torque to the tire's slip ratio. Together with the motor model, the control path for a slip ratio controller is formulated and a PID controller is designed. The controller parameters have been determined with the method proposed by Ziegler and Nichols. Since the slip value at peak friction is a function of the road friction coefficient, a road condition estimator has been developed and implemented, which determines the road condition under each wheel, allowing the selection of the ideal controller and target slip ratio for each wheel. The performance of the system is examined on a micro-split road and a wet road. The controller was able to estimate the correct friction coefficient immediately. In the future, the PMDC motors will be replaced by appropriate PMSMs, which are more appropriate to be used as in-wheel motors. Moreover, the incorporation of an active steering system is appealing, in particular to compensate the yaw moment on micro-split surfaces. The integration of an advanced traction controller and an active steering system will avoid any unwanted side pushing effect of the vehicle, while driving on a micro-split surface.