Comparison of Steering Feel Control Strategies in Electric Power Assisted Steering

Paper in proceedings, 2018

This paper presents an objective comparison of two closed-loop steering feel control concepts in an electric power assisted steering (EPAS) system. The closed-loop methods, torque- and position-control, aim to compensate the EPAS motor inertia in an effective manner as compared to the open loop (feed-forward) solution. For a given steering feel reference, the feedback controllers are developed in a sequential manner ensuring coupled stability. Linear system theory is used for the analysis. For a comparable reference tracking and stability margin, higher haptic controller bandwidth is achieved in torque-control. The position controller stability and performance are limited due to feedback control filtering and high system inertia (from EPAS motor and driver arms), which further makes it more sensitive towards muscle co-contraction. Moreover, torque-control offers better road disturbance attenuation for low and high frequency spectrum, whereas position-control is better for mid-frequency range.