The Effect of Failure Prognosis and Mitigation on the Reliability of Permanent-Magnet AC Motor Drives

Fault diagnosis and its extensions to failure prognosis aim to develop methods that decrease outages and thus increase reliability. Among these methods are redundancies and changes of topology, power levels, and control algorithms. Since diagnosis methods are imperfect, false positives and negatives, as well as delayed fault diagnosis, may occur. Although the diagnosis of a fault can lead to appropriate maintenance, the estimation of the time to failure through prognosis can lead to the timely mitigation of the fault and, in turn, can extend the lifetime and reliability of the drive. In this paper, we present a new approach to the mitigation of permanent-magnet ac motors that uses a failure prognosis method to predict failures and the remaining useful life and uses the output of the prognosis algorithm to decide when to modify the system and mitigate the fault. A methodology to calculate the mean time between failures with and without mitigation is also presented. The proposed approach is illustrated through a simple example of how the prognosis of failure due to a developing intermittent open circuit in one of the phases increases the drive reliability.