A Generic Model-Based Advanced Control of Electric Power-Assisted Steering Systems

Electric power-assisted steering (EPS) systems have been used to replace traditional hydraulic power steering systems in vehicles. In an EPS system, the assisting steering torque is from an electric motor. In principle, the control of an EPS system involves two aspects: 1) motor torque control to satisfy the torque requirement and 2) steering motion control to yield a satisfied feeling of the driver during the steering process in a disturbed environment. In this paper, a column-mounted steering system is taken as a generic target system to illustrate a model-based approach for advanced steering control design. In particular, we present a two-controller structure proposal for the generic EPS system, addressing motor torque and steering motion, by applying H-2 and H-infinity design methods, respectively. Controller model reduction is also discussed and compared to show that, actually, a reduced-order controller could be applied. This is important for industrial applications because a reduced-order control law costs less in computing resources. Finally, simulation for the EPS control system is discussed and a software-in-loop approach is presented using off-the-shelf software. It is interesting to see that, based on the simulation results, the advanced two-controller design yields superior performance to the one-controller structure for the steering control.