Slip-based traction control system with an on-line road condition estimation for electric vehicles

In this paper a slip-based traction control system (TCS) with an on-line road condition estimation is presented. The system is designed for a car with in-wheel electric motors, so that estimation and control are implemented independently for each wheel thus enabling the optimal friction coefficient for every wheel, even if they are on different surfaces or have different tire characteristics. A road condition is approximated using a function which is estimated in the real-time and used as the input to the TCS. The design of the presented TCS is based on the wheel slip ratio, controlled to it´s optimal value by a PI controller and with the addition of a feedforward branch for the transition response speed up. The non-linear model of a small three-wheeled electric car, comprising the hardware in the loop, is used for the system testing.