A comparison of two high performance, wide speed range drive techniques for interior magnet motors

The interior magnet synchronous motor is perhaps the highest energy-density motor available. However its adoption has so far been hindered by its highly nonlinear torque characteristic. This is mainly due to the exploitation of the torque production from both variable reluctance and electromagnetic field coupling principles involved. In conventional control strategies, current regulated schemes are used, usually in the rotor reference frame. In another scheme, the so called direct torque control scheme, developed by the authors of this paper, torque is controlled by controlling applied voltage vector to the stator. The latter method do not use any current regulators. This paper critically examines these two schemes, highlighting the merits and problems of each technique.