Novel wide range speed control of permanent magnet brushless motor drives

This paper presents a novel approach for the wide range speed control of a permanent magnet (PM) brushless motor drive, including both sinewave and squarewave versions. As compared with conventional flux-weakening control, the approach has definite advantages in that it can be applied to the squarewave PM brushless motor drive directly, and even to the motor drive with negligible mutual inductances between phase windings. Moreover, it is easier to implement than flux-weakening control because no coordinate transformation is needed. The key of this approach is to make use of the transformer EMF in such a way that it weakens the rotational EMF when the motor operates above the base speed, leading to the achievement of constant-power operation. Computer simulation and experimental results show that the proposed approach works well