Design of a Stability Compensator to Optimize Steering Feel in Electric Power Steering Systems

The speed-dependent steering assistance is a fundamental function in electric power steering (EPS) systems. However, excessive levels of steering assistance can result in system instability, causing steering oscillations that compromise steering safety. Consequently, ensuring steering stability has become a primary focus in EPS development. Currently, the design of stability compensators for speed-dependent steering assistance has primarily focused on achieving system stability, often neglecting the attenuation of the designed assist gain by the compensator. In this paper, a novel method for the design of stability compensators within speed-dependent steering assistance is presented, aimed at ensuring system stability while reducing the attenuation of the designed assist gain by the compensator. First, a dynamic model of the EPS system is established, incorporating system inertia and viscous damping. The frequency response characteristics of the EPS system are obtained through vehicle frequency sweep tests, and the model parameters are identified using genetic algorithms. The stability conditions of the EPS system under constant assistance are derived from the established model. The phase lag and amplitude attenuation introduced by the compensator are analyzed in terms of their effects on steering feel. Based on these analyses, design criteria for the compensator are then proposed. The compensator parameters are optimized using Particle Swarm Optimization (PSO) algorithms, and system stability is evaluated across the primary vehicle speed range. The effectiveness of the optimized compensator is demonstrated through simulation. Subsequently, vehicle steering tests are conducted under various operating conditions. The experimental results confirm that the proposed compensator ensures EPS system stability while preserving a satisfactory steering feel for the driver.