Operation of interior permanent magnet synchronous machines with fractional slot concentrated windings under both healthy and faulty conditions

Design for fault tolerance and early detection of insulation failure are critical for automotive and aerospace applications to ensure passenger safety. Permanent magnet machines can be designed to better withstand stator insulation failures. In this work, the performance of three fault tolerant fractional slot concentrated winding machine designs experiencing stator winding insulation failure are evaluated. Two of the machines are designed with double-layer windings and one with single-layer. The single-layer fractional slot concentrated winding design is shown most reliable; however this design has the worst torque performance. A ripple reduction control technique is developed based on an analytical description of torque. This technique is shown to improve the torque performance of the single-layer fractional slot design. Fault tolerant design alone does not provide high reliability since thermal stress from aging, overloading, cycling or fast switching of the inverter causes most stator insulation failures. Early detection of incipient stator winding faults could avoid catastrophic machine failure, allow implementation of mitigation techniques to continue operation, reduce the occurrence of secondary faults and allow adequate time to plan maintenance. In this work, two of the machines designed were manufactured with windings that allow the introduction of faults with three severity levels and varying degrees of incipient faults. Through a parametric identification method, the characteristic flux linkages of the machines are extracted under both healthy and faulty conditions. It is shown that incipient stator windings faults are reflected in the machine's characteristic parameters. These parametric changes are reflected in the phase voltage for current-controlled applications. Incipient stator winding faults can be detected online, if accurate knowledge of the healthy machine parameters is available.