A study on applicable control methods of electric power steering system in dynamic redundancy environments

The reliability is defined as a probability that a system will perform properly for a specified period of time without any failures, and it is considered as one of the important design attributes. In automotive industry, safety-critical systems such as the electrical power steering (EPS) are considering dynamic redundant systems, which are configured two identical controllers, to ensure the higher functionality, reliability and distributed intelligence which can recover from failures. Two identically configured controllers (one active, one backup) should swap roles within the deadline in the redundancy scheme when a system failure is detected in active controller. A challenge of dynamic redundant systems is to determine a precise role as the active controller to operate a system, error detection of the active controller and how to take over to a backup controller in the defined time. Moreover, a role of each controller has to be independently protected to ensure mutual exclusion under safety requirements. This paper studies dynamic redundant architectures and arbitration control methods that can provide full fault-tolerance without any deviation of functionality even in the presence of faults. The system performance of the dynamic redundant architecture is evaluated experimentally by actual test scenarios to show the practical implication of our architecture.