Fault tolerant control of electric power steering using H-infinity filter-simulation study

In a physical system, faults could occur time to time and, for safety purpose, measures have to be implemented to keep the physical system continuously operating if a fault does not result in global shut-down. In this paper, a Fault tolerant Control (FTC) design is proposed for the electric power steering (EPS) system in an automobile to address the case of electric connection fault incurred in the torsion bar torque sensor. In particular, the total torque that acts on the assisting motor shaft is the sum of the torsion bar torque and road reaction torque. An H_¿ filter is designed to estimate the total torque on the motor shaft and the road reaction torque can be calculated out using the available signals from the vehicle stability system. The torque sensor signal can then be deduced and used to replace the torsion bar sensor signal when the electric connection is broken. It is claimed that the proposed robust filter design yields huge advantage over a Luenberger type estimator.