Optimal Design of a Fault-Tolerant IPM Motor with High Torque Density for Electric Power Steering System

Electric Power Steering system provides the assist steer torque in vehicle through an electric motor. Since the electric motor is directly connected to the mechanical steering rack, must have the following features: Torque production with minimum Ripple for Precise steer control, High efficiency, easy Manufacturing technology and minimum size and weight. Motor structure optimization is done in order to increasing force to motor volume ratio, increasing fault tolerance, decreasing Permanent Magnet volume and force ripple. In this paper, Analytical relations Necessary and relevant for optimization have been obtained and finally desired objective function is defined in terms of machine design parameters such as air gap length, inner and outer machine diameter, slots dimensions, PM dimensions and location and machine electric and magnetic characteristics. Motor behavior study and confirmation in force production with determined power supply is done with finite element method simulation. At the end, entire electric power steering system including electric motor, power supply and controller have been simulated and the performance evaluation of system is done. Key-Words: Electric Power Steering-Optimization-Finite Element Method-Fault Tolerance-Torque Ripple