Marine propulsion PM motor control under inverter partial fault

Fault tolerance is an essential feature in marine and naval electric propulsion drives. Therefore, there is a growing research interest in developing fault tolerant technologies for marine applications. This paper investigates the control and operation of an inverter fed PM propulsion motor under a specific power electronic failure case. Compared to the technologies reported in literature, this paper formulates a special control strategy for the motor operation during the situation where only one high side switch and one low side switch in two different phases are operational in a standard three-phase six-switch inverter. The proposed control strategy assumes that the remaining switches are failed in open circuit while the corresponding antiparallel diodes are functional. The mathematical background of the two quadrant control strategy is formulated. The operation is analyzed in the context of marine propulsion power/speed requirements. Simulations for a 50 kW three-phase fault tolerant motor is presented for the operation with the proposed dual switch control strategy. Controllability of motor torque for speeds up to 45% rated speed corresponding to approximately 9% rated propulsion power output is achieved without overrating the device current ratings.