Study and Active Enhancement by Converter Reconfiguration of the Performance in Terms of Stator Copper Loss, Derating Factor and Converter Rating of Multiphase Drives Under Two Open Legs With Different Stator Winding Connections

Multiphase machines offer inherent tolerance to faults such as open converter legs (OCLs), which are especially frequent. Because of this reason, they are particularly attractive for applications where fault tolerance is important, such as offshore wind energy or aerospace, naval and military vehicles. It has been previously shown that, under an OCL, certain stator winding configurations (SWCs) different from star yield smaller stator copper loss (SCL) and larger maximum achievable torque (MAT) than star SWC for the same torque command and machine. This advantage comes just at the expense of a moderate increase in converter rating. However, only the case of single OCL was studied in general. The SCL, MAT and required converter rating for two OCLs are currently unknown for different combinations of phase number, faulted legs and SWCs. Actually, under two OCLs (unlike for one OCL) it may be possible to actively modify the order of the faulted/healthy legs to enhance the performance in these terms, but this possibility has not been studied so far in spite of its potential. This paper addresses the postfault performance of multiphase drives with two OCLs, for various SWCs. The MAT (derating factor), SCL and necessary converter rating are assessed in numerous possible scenarios. The most convenient alternatives are established. Most importantly, in view of the conclusions of this analysis, a novel method is proposed to improve substantially the MAT and SCL by actively altering the connections between the converter and machine terminals. Experimental results with six-phase and twelve-phase setups are provided.