Active Reduction of Pressure Ripple for Electric Power Steering Systems via Fuzzy Control Approach

Pressure ripple in electric power steering (EPS) system can be caused by the phase lag between driver's steering torque and steer angle, the nonlinear frictions, and the disturbances from road and sensor noise especially during high frequency maneuvers. This paper novelly applied the robust fuzzy control method of active reduction of pressure ripple for EPS system, which achieves remarkable progress on steering maneuverability. First, an EPS dynamics are described by an eight-order nonlinear state-space model and approximated by a Takagi-Sugeno (T-S) fuzzy model with time-varying delays and external disturbances. Then, a fuzzy controller is applied based on the fuzzy model of the EPS system. The closed loop stability conditions of EPS system with the fuzzy controller are parameterized in terms of Linear Matrix Inequality (LMI) problem, which can be solved efficiently by using the convex optimization techniques. The numerical simulation of the EPS system with and without the use of the developed controller has been carried out. The simulation result shows that the proposed fuzzy control method can reduce the torque ripple to achieve a better steering feel and more stable driving.