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 anti-parallel 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.