An Improved Torque Density Synchronous Reluctance Machine with a Combined Star-Delta Winding Layout

This paper investigates the performance of Synchronous Reluctance Motors (SynRMs) when the stator is equipped with a combined star-delta winding layout. The conventional star winding is used as a benchmark in this study to compare different possible single layer winding layouts. Among these different winding layouts, those which maximize the fundamental MMF component are selected. A simple mathematical formula is then derived to calculate the equivalent winding factor for different shares between star and delta sub windings. It has been proved that for the same copper volume and line current magnitude, the star-delta connection can offer an enhancement in the torque density of approximately 5.2% over the conventional star case under rated conditions. However, this gain is affected by the employed number of poles and stator slots. On the other hand, the effect of the winding layout on either power factor or core loss can be merely neglected over a wide range of speeds and currents. Nevertheless, the machine efficiency under a combined star-delta connection is relatively improved under light loading as a result to the machine torque/current ratio enhancement. The theoretical findings are experimentally validated using two identical 5.5 kW prototype machines, having star and combined star-delta winding connections.