Demagnetization fault diagnosis method for PMSM of electric vehicle

Permanent magnet synchronous motor (PMSM) is attractive candidate for traction motor of electric vehicle (EV). But several kinds of faults can occur in PMSM system: bearing faults, electrically short/open faults and demagnetization fault, etc. Demagnetization fault means that strengths of permanent magnets (PM) in PMSM significantly decrease. The magnet flux linkage, which is proportional to the strengths of the PMs, can be estimated by means of conventional parameter identification methods and the estimation results can be used for detection of the fault. However, variations of q-d axis inductances and stator resistance can cause inaccurate estimation and failure of demagnetization fault detection . In this paper, demagnetization fault diagnosis method for PMSM subject to the parameter variations has been proposed. This method consists of the following serial processes: estimation of parameters variations, data extraction, the least square method, calculation of upper bounds of estimation error rate and magnet flux linkage, fault decision. This method is robust against estimation errors becuase of the upper bounds. It will be demonstrated in chapter IV.