Winding Layout Considerations for Variable-Pole Induction Motors in Electric Vehicles

Winding layout plays a crucial role in enabling variable-pole operation in an induction machine (IM). Several winding design alternatives, which consist of toroidal and distributed single- and double-layer windings, have been shown to increase speed range and improve partial load efficiency in traction applications. These windings have different pole-changing capability, end-winding length, leakage, harmonic content, and inv erter requirements. This article compares these winding alternatives with a generalized variable-pole machine design framework that captures the impact of winding selection on key performance metrics such as losses, volume, and torque–speed envelop. This framework shows that the core aspect ratio, defined as ratio of stack length to rotor diameter, selected to minimize losses depends on whether a distributed or toroidal winding is used. When a toroidally wound IM is designed with a low aspect ratio, it can provide the largest torque–speed envelop with highest efficiency over a wide speed range. An experimental toroidally wound IM driven by an 18-leg converter is used to validate the design framework. The experimental setup is configured externally to emulate a single-layer winding and to show benefits gained from the extra pole-changing flexibility of a toroidal winding.