Reduced Flux based Direct Torque Control of Synchronous Reluctance Machine for Electric Vehicle applications

Synchronous reluctance motors (SyRMs) generate electromagnetic torque that depend on the saliency of the rotor structure. SyRMs are seen as attractive alternative to permanent magnet machines in applications that require high dynamic performance, high power density etc. A new direct torque control (DTC) scheme is proposed in this paper for the SyRM aimed at improving overall performance of the motor especially under light load conditions. This is accomplished by dynamically adjusting the motor stator flux based on the load conditions. Analytical expressions for the required stator flux is presented in detail. Furthermore, the proposed idea is extended to an electric vehicle (EV) application and benefits of the envisaged DTC scheme is thoroughly investigated considering constant speed-constant load torque, constant speed-variable load torque conditions and is also tested using Inspection and Maintenance drive cycle (IM240) for testing the variable speed-constant load torque condition. Superior performance of the proposed reduced flux based DTC scheme for SyRM over the conventional DTC scheme is presented. The SyRM draws less current for a given torque, results in reduced ripple content in the electromagnetic torque developed and more importantly achieves improved motor efficiency thus facilitating improved energy savings which is a useful feature desired in EV applications.