Position Sensorless Control of Synchronous Reluctance Motors at Low-Speeds

Synchronous reluctance motors (SynRMs) have attracted much attention because they do not require magnets. Position sensorless control of SynRMs at low speeds is necessary, and several methods have been proposed in this regard. A new position sensorless control method for SynRMs operating in the very low-speed region is proposed. This approach superimposes a high-frequency current with a small and constant amplitude and a constant frequency to the torque current for driving the SynRMs, by using a high-frequency current control system. It has been shown that robust position sensorless control against inductance variations can be realized using this proposed method. In the position sensorless control method based on a superimposing signal, the current should be small. Therefore, in this paper, the capability of the presented approach to achieve a minimum constant amplitude of the high-frequency current is investigated. The experimental results indicate that the proposed method is a feasible one as position sensorless control of SynRMs in very-low speed region even if the superimposed current has a minimum constant amplitude.