The Optimal Current Ratio Control of Redundant Electric Drive Systems and Diagnostic Strategies for Disagreement

As research into technology for autonomous vehicles becomes ever more intensive, the need for redundant system designs, as a solution for fail-operational functionality, has also increased. Redundant systems are those involved in maintaining normal operation even when one or more components fails. In particular, in electric power steering (EPS) systems, redundancy is achieved by applying dual-winding (DW), permanent magnet synchronous motors (PMSMs) and dual electronic control units (ECUs). In this study, the torque and efficiency of DW-PMSMs is analysed based on the manner in which the currents in each winding mechanism are combined. It was found that the PMSMs have maximum torque and efficiency when the current ratio was the same between DWs. A diagnostic strategy is proposed whereby the phase current ratio of dual lanes is not matched. The proposed diagnostic process includes the selection of the optimal fault threshold of the current difference between two ECUs and a method for distinguishing which of these was a failure for disagreement. In addition, depending on whether or not failure detection has occurred, a current compensation control method is proposed for reverting to normal operation or for failure operations. The dual-lane system was fabricated and the proposed solutions were experimentally verified.