Controller design method for electric power steering system with variable gear transmission system using decoupling control

In this paper a new controller design method for Electric Power Steering (EPS) system with Variable Gear Transfer System (VGTS) is proposed. The control purpose is to achieve the desired steering gear ratio, the desired power assist with good steering feel and the desired feedback of reaction force from road surfaces to the driver. The basic idea of controller design is to apply decoupling control to this system and to separately design controllers for two decoupled systems. The angle control system and the torque control system are designed for the decoupled systems. In the angle control system the PID control is used for the desired gear ratio. In the torque control system the PID control is used for the desired assist torque designed so as to achieve good steering feel. In order to evaluate steering feel the Lissajous curve between the steering torque and steering angle is used. The effectiveness of the proposed controller is verified by using a test bench.