A Sensorless Control Strategy for IPMSM based Electric Power Steering Systems

Electric power steering systems are a quite common equipment of modern vehicles. They are based on torque controlled electromechanical actuators assisting the driver in moving the steering wheel. These systems must generate low torque fluctuations and mechanical vibrations, while featuring a low cost and a simple and rugged control system. In order to comply with these requirements an electromechanical actuator based on a sensorless controlled synchronous motor is proposed in this paper. It exploits a sensorless torque control technique based on the injection of high frequency voltage signals and the manipulation of induced high frequency stator current components. A key feature of this technique is a very simple implementation using a low cost mixed (analog/digital) circuitry, requiring a minimal computational power. Implementation issues and experimental results obtained on a laboratory prototype, based on a standard electric power steering system, are presented to confirm the consistence of the proposed approach.