Hardware-in-the-loop simulation of fault tolerant control for an electric power steering system

Electric power steering (EPS) systems are rapidly replacing existing traditional hydraulic power steering systems due to fuel and cost savings. The reliability of a column mounted EPS is improved by adding an alternate control scheme that is tolerant to a torque sensor failure (FTC). To accomplish this, a motor model based observer is used to estimate the total torque on the motor shaft. An independent estimate of the road reaction torque is generated from vehicle navigation signals and subtracted from the total to estimate the torque sensor output. A Hardware-in-the-loop (HIL) simulation is described where the EPS model, road vehicle dynamics and developed control scheme are simulated on an Opal RTtrade real-time platform. As the steering assist motor is the integral component to the control and estimation schemes, a physical DC motor is placed in-the-loop in lieu of the motor model. This simulation validates the developed method under more realistic operating conditions than using software simulation alone; such a HIL simulation can be useful as a development tool since it is more repeatable and cost effective than a full in-vehicle test.