Design of a Fault-tolerant IPM Motor for Electric Power Steering

This paper deals with the design of an interior permanent magnet (IPM) motor for power-steering. Such an application requires an imperative fault-tolerant capability, so that a redundant solution with two motors on the same shaft is presented. A ball-screw system converts the rotating movement into the linear movement of the steering rack. In addition the IPM motor has to exhibit very low brake torque after a short-circuit fault. To this purpose, the maximum brake torque is computed. A useful relationship between the maximum brake torque and the motor parameters is found. Such a relationship is used in the design of the motor