Robust control of electric power-assisted steering system

EPS (electric power-assisted steering) system has been used to replace traditional hydronic power steering system in vehicles. In an EPS system, the assisting torque is from an electric motor for steering effort. The performance of an EPS system requires that the system can take care the road reaction torque so that the driver could feel comfortable-light and less vibration-during the steering process, while the low frequency dynamics in the road reaction torque, which is regarded as "road surface information", be transferred sufficiently to the steering shaft so that the motor assisting torque could be determined appropriately. In this paper, a robust control design is presented for the EPS system with a brushed motor. In particular, a two-controllers structure is proposed to achieved the specified essential performance, which consists of a robust master controller, called "motion controller" in this paper, to address the driver's feeling and also regulate the motion response, and a slave P-I controller for motor drive to generate sufficient assisting torque, according to the command from the master motion controller.