Optimal 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 high frequency external disturbance in road reaction torque be attenuated 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, an optimal 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 optimally designed master controller, called "motion controller" in this paper, to address the performance requirement of driver\´s hand feeling, and a slave P-I controller for motor drive to generate sufficient assisting torque, according to the command from the master motion controller