J.W. Kolar, R. Wieser, H. Ertl:
"Analysis of a Wide Speed Range Starter/Alternator System Based on a Novel Converter Topology for Series/Parallel Stator";
Talk: IEEE IAS, Phoenix; 10-03-1999 - 10-07-1999; in: "Proceedings of the 34th IEEE Industry Applications Society Annual Meeting", Proceedings, Vol.4, (1999), 2631 - 2641.

Abstract - The paper presents an inverter concept for the realization of an induction machine drive with an extremely wide constant power range. There, the stator winding of the induction machine is split up into two isolated and quasi-bifilar wound three-phase winding systems. The series operation of the two winding sets permits very high torque at low stator frequencies while keeping the machine terminal current and the converter DC link current relatively low. However, due to the winding arrangement field weakening has to start already at low frequencies (approximately at 50% of rated speed). Nevertheless, with the help of a transition from series to parallel winding arrangement the machine flux can be restored to its nominal value as given for rated machine speed. Consequently, the breakdown torque is increased by a factor of four which gives the basis for high maximum speed with constant machine power.