Comparison of stator winding connections in multiphase drives under healthy operation and with one open converter leg

Abstract

Multiphase machines with symmetrical windings offer various stator winding configurations (SWCs). It is known that, for a given five-phase machine, the pentagon SWC implies, compared with star, smaller voltage rating and greater current rating of the converter. For healthy conditions, the stator copper loss (SCL) and maximum achievable torque (MAT) are almost identical for both SWCs, provided such converter-rating adjustments and negligible circulating currents. Regarding the operation of five-phase machines under open converter leg (especially common fault), the pentagon SWC attains lower SCL (for given torque) and larger MAT than star. However, it is unknown if these characteristics hold (and to which extent) for other phase numbers and SWCs. This study compares for multiple phase numbers the SWCs in terms of converter rating, MAT and SCL, under healthy operation and with an open converter leg. Most importantly, it is shown that, for phase numbers higher than five (the case previously studied), the improvement in performance (especially postfault MAT) by resorting to SWCs other than star can be much larger than for five phases, and it is thus of considerable interest. The most convenient alternatives (often different from the five-phase case) are established. Experimental results with two multiphase drives are included.