Speed Sensorless Control of a Surface-mounted Permanent Magnet Drive

Permanent magnet synchronous machines are a popular choice for electric vehicle propulsion, with both interior and surface magnet rotor designs in use. Position feedback is required for commutation, with minimal phase delay. Speed data should be able to track the vehicle speed at maximum acceleration. Elimination of the shaft position sensor reduces cost and improves reliability, but can be challenging for surface magnet machines at low speeds, due to their lack of saliency. However, bread-loaf and inset magnets give sufficient saliency to make signal injection position estimation schemes viable. Experimental results are presented for a commercial 3.27kW machine, using signal injection at low speeds and transitioning to a novel model reference adaptive system back emf estimation scheme at high speeds, which employs an iterative search algorithm to reduce position tracking delays. The rationale for selection of filter frequencies and tuning gains is explained.