| This thesis is separated into two areas of research, with a common theme of improving PM synchronous machine drives in general, and specifically, interior PM machine drives.; The first area is cost reduction. A new three-phase motor drive is developed which contains only three active switching devices, compared to the usual six switches. The drive employs unipolar motor phase currents, and is supplied by a split dc bus obtained by a simple voltage doubler diode rectifier. A three-level inverter is developed, based upon low-voltage MOSFETs. The two-level PWM technique is used, which allows for a reduction in the clamp diode rating in the converter. In addition, the bootstrap charge pump technique is extended for use in the neutral point clamped topology. The use of a six-leg inverter is presented as a method to increase the power output and power density of integrated starter alternators for hybrid-electric vehicles.; The second focus area of this thesis is on fault analysis and fault mitigation techniques applied to PM machine drives. A new order-reduced model is developed for an interior PM drive when one phase becomes open-circuited. Post-fault control action of two-phase uncontrolled generator (UCG) mode operation and two-phase short response are presented. Symmetrical and asymmetrical short-circuit faults are analyzed. A closed-form solution is derived for the steady-state response to a symmetrical short-circuit. Design guidelines are presented which relate the short-circuit fault response to system parameters. A comprehensive evaluation of fault-tolerant three-phase motor drive topologies is presented. New contributions identify the operating limits and comparative cost of adding fault tolerance capacity to a standard three-phase inverter for various inverter faults. Fault mitigation to single-switch short-circuit faults using a standard inverter is investigated and shown to be very limited in performance. Fault mitigation techniques employing six-leg inverters are developed. The differences between bus structures of six-leg inverters are developed, and their important relationship to zero sequence voltages and currents is established. A new method to null the permanent magnet flux is developed, which results in a zero torque response to single-switch short-circuit faults or stator winding short-circuits. |
