Optimal Fault-Tolerant Control of Multiphase Drives Under Open-Phase/Open-Switch Faults Based on DC Current Injection

In recent years, fault-tolerant control of multiphase drives against open-phase faults has been an interesting research topic. However, in contrast, few research efforts have been devoted to fault-tolerant control against open-switch faults in which only one controllable power semiconductor device in a converter leg is open, but its antiparallel diode operates normally. In this article, a fault-tolerant control strategy against open-phase/open-switch faults based on dc current injection is proposed. In open-switch phases, dc currents, whose amplitudes are equal to the amplitudes of the corresponding fundamental phase currents, are injected to eliminate the nonlinearity brought by faults. Therefore, the fundamental currents in open-switch phases can be precisely regulated. To achieve torque-ripple-free postfault operation, minimize the stator winding losses and maximize the postfault torque production, stator winding losses associated with fundamental currents and injected dc currents are optimized over the full torque production range on the premise that no dc current is mapped in the torque-producing subspace. Simulation results on different kinds of multiphase drives and experimental results on a nine-phase induction drive proved the reduced stator winding losses, extended torque operation range, and reduced torque ripple compared with the existing methods.