Comparison of Postfault Control Strategies in Terms of Converter Losses for Dual Three-Phase Machines

Dual three-phase machines are attractive due to advantages such as inherent fault tolerance. During postfault situation, the same magneto-motive force as in healthy operation should be maintained. Furthermore, it is also important to minimize the copper losses. Several strategies have been proposed to improve the postfault performance under open-phase fault. The maximum-torque (MT) strategy obtains the widest torque operation range (TOR) in faulty situation, but without optimizing the stator winding losses. The minimum-losses (ML) strategy minimizes the stator winding losses, at the cost of reducing the TOR. The full-range ML (FRML) strategy ensures minimum stator winding losses, for each torque value, in the whole TOR (that of the MT strategy). For the development and analysis of these strategies, only the stator winding losses were taken into account. Since the losses in a converter represent an important part of the overall system losses, they should also be considered. This paper compares the main postfault control strategies in terms of converter losses with carrier-based pulsewidth modulation (PWM) with sinusoidal references for dual three-phase machines with sinusoidally distributed windings under single open-phase fault. Furthermore, a strategy aiming to optimize both the converter and the stator copper losses is obtained, which results nearly identical to the FRML one. It is concluded that the FRML strategy is optimum in the whole TOR not only in terms of stator winding losses, but also of converter losses. Experimental results are provided.