Fitness of saturated PMSM for use with sensorless control

Sensorless control schemes that operate well even at low speeds or at standstill are mainly based on evaluating the machine saliencies. Hence a sufficient inductance ratio is essential for PMSM drives independent of the rotor angle. This paper analyzes the origin of the angle dependence of the inductance ratio and shows that saturation has an important influence. In many cases saturation deteriorates the inductance ratio, but it can be shown that saturation can also be used to improve it. This is especially important for non-salient machines to make them suitable for sensorless control. The paper concludes with design guidelines to improve the inductance ratio for non-salient machines.