Fitness of saturated permanent magnet synchronous machines for sensorless control

Sensorless control schemes that operate well even at low speeds or at standstill are mainly based on the evaluation of the machine saliences. Hence a sufficient inductance ratio independent of the rotor angle is essential for permanent magnet synchronous machine (PMSM) drives. 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.