Abstract-This paper compares the many fault tolerant threephase ac motor drive topologies that have been proposed to provide output capacity for the inverter faults of switch short or open-circuits, phase-leg short-circuits, and single-phase open-circuits. Also included is a review of the respective control methods for fault tolerant inverters including two-phase and unipolar control methods. The output voltage and current space in terms of components is identified for each topology and fault. These quantities are then used to normalize the power capacity of each system during a fault to a standard inverter during normal operation. A silicon overrating cost factor is adopted as a metric to compare the relative switching device costs of the topologies compared to a standard three-phase inverter.Index Terms-Inverter faults, phase-leg short-circuits, silicon overrating cost factor (SOCF), single-phase open-circuits, three-phase inverter, three-phase ac motor drive topologies.

Abstract-This paper compares the many fault tolerant threephase ac motor drive topologies that have been proposed to provide output capacity for the inverter faults of switch short or open-circuits, phase-leg short-circuits, and single-phase open-circuits. Also included is a review of the respective control methods for fault tolerant inverters including two-phase and unipolar control methods. The output voltage and current space in terms of components is identified for each topology and fault. These quantities are then used to normalize the power capacity of each system during a fault to a standard inverter during normal operation. A silicon overrating cost factor is adopted as a metric to compare the relative switching device costs of the topologies compared to a standard three-phase inverter.Index Terms-Inverter faults, phase-leg short-circuits, silicon overrating cost factor (SOCF), single-phase open-circuits, three-phase inverter, three-phase ac motor drive topologies.

Abstract-A closed-form solution is presented for the steady-state response of interior permanent magnet (IPM) synchronous machines to symmetrical short circuits including the effects of -axis magnetic saturation. Machine response to single-phase asymmetrical short circuits is also investigated. Experimental data are presented to verify predicted behavior for both types of short circuits. It is shown that single-phase asymmetrical short circuit faults produce more severe fault responses with high pulsating torque and a significant threat of rotor demagnetization. A control strategy that purposely transitions such faults into symmetrical three-phase short circuits can minimize the fault severity and associated demagnetization risks. Implications for the design of IPM machines with improved fault tolerance are discussed.Index Terms-Interior permanent magnet synchronous machine, inverter shutdown, protection, short circuit fault, variable speed drive.

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Abstract-This paper investigates the steady-state and dynamic response of an interior permanent magnet (IPM) synchronous machine drive to a single-phase open-circuit fault. This fault results in rotational electromagnetic asymmetry on both the stator and rotor, making it difficult to analyze using classical -transformation techniques. This paper presents a new synchronous-frame machine model that is capable of handling this highly asymmetrical fault condition, including the effects of axis magnetic saturation. Fault responses with two alternative post-fault control strategies are investigated 1) opening all of the inverter switches so that the machine behaves as an uncontrolled generator (UCG), with the two unfaulted phases connected to the inverter dc link via the antiparallel diodes; 2) shorting the two remaining unfaulted phases together using the inverter switches. Results of this investigation show that the fault response is generally more benign using the UCG control strategy, with significantly lower phase currents and pulsating torque than corresponding values delivered using the phase-shorting strategy.Index Terms-Inverter shutdown, IPM synchronous machine, open circuit fault, protection, variable speed drive.

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Abstract-This paper investigates the steady-state and dynamic response of an interior permanent magnet (IPM) synchronous machine drive to a single-phase open-circuit fault. This fault results in rotational electromagnetic asymmetry on both the stator and rotor, making it difficult to analyze using classical -transformation techniques. This paper presents a new synchronous-frame machine model that is capable of handling this highly asymmetrical fault condition, including the effects of axis magnetic saturation. Fault responses with two alternative post-fault control strategies are investigated 1) opening all of the inverter switches so that the machine behaves as an uncontrolled generator (UCG), with the two unfaulted phases connected to the inverter dc link via the antiparallel diodes; 2) shorting the two remaining unfaulted phases together using the inverter switches. Results of this investigation show that the fault response is generally more benign using the UCG control strategy, with significantly lower phase currents and pulsating torque than corresponding values delivered using the phase-shorting strategy.Index Terms-Inverter shutdown, IPM synchronous machine, open circuit fault, protection, variable speed drive.

Abstract-This paper proposes operating a three-level neutralpoint-clamped (NPC) inverter using a two-level pulsewidth-modulation method. This allows for the clamping diodes to be rated at a fraction of the main switches due to their low average current requirement. The use of a bootstrap charge pump as a low-cost method to obtain the isolated gate drive power supplies is extended for use with the NPC topology. Using this control method and circuits, an inverter based on high-volume, low-cost, low-voltage power MOSFETs is experimentally demonstrated as a possible economic alternative to an insulated-gate-bipolar-transistor-based drive for 120-Vrms-supplied systems.