Novel sensorless controller of brushless DC motors

The paper is focused on a sensorless controller design for a brushless DC motor. By utilizing the saturation effect of stator iron core, a low-frequency and low-voltage injection scheme is employed to estimate the initial rotor position. This scheme requires neither any current and position sensors nor faster sampling frequency and shorter time needed to complete processing and estimating such that a low-cost microcontroller would be available. Additionally, without detecting any zero- crossing point (ZCP) of the back EMF, a technique that just determines the leading or lagging commutation is presented to achieve the closed-loop speed control. A clipper is only the addition to this technique. As a result, the proposed controller can eliminate the related circuits which are indispensable to conventional methods, such as the neutral voltage, multi-stage analog filters, ZCP detector, and the complex phase shift circuits. Thereby, it significantly reduces the cost. Finally, the experimental results validate the effectiveness of the proposed controller.