Experimental verification of rotor demagnetization in a fractional-slot concentrated-winding PM synchronous machine under drive fault conditions

This paper presents the results of experimental tests designed to verify analytical predictions of the rotor demagnetization characteristics of a 0.6 kW (cont.) 9-slot/6-pole fractional-slot concentrated winding (FSCW) interior PM (IPM) synchronous machine. The demagnetization characteristics of the rotor magnets in this commercially-produced FSCW-IPM machine are measured using a test configuration that is designed to conduct multiple demagnetization tests on the same test machine under controlled temperature conditions. In this paper, finite element predictions of the rotor demagnetization characteristics of the experimental machine during 3-phase symmetrical short-circuit (SSC) and single-phase asymmetrical short-circuit (ASC) faults are presented. These results are compared to experimental test measurements of the post-fault currents and the magnet flux density distribution following demagnetization, demonstrating very good agreement of many key features. These comparisons also confirm that 3D effects and magnet material properties such as the magnet thermal coefficients have a significant impact on some details of the FE predictions of the machine's fault-mode response characteristics.