A new method for the estimation of the influence of stator saturation on the differential inductances

For sensorless position detection of permanent magnet synchronous machines at very low speed and standstill, signal injection methods are commonly used. As a prerequisite these so called saliency-tracking methods require a differential magnetic anisotropy of the machine, which is both position and load dependent and thus varying during operation. So the performance of sensorless operation strongly depends on the machine design. To investigate the influence of the stator saturation on the differential inductances of a machine with concentrated winding, a model based on a magnetic equivalent circuit is used. The results show that for some angles of the current vector the inductances do not vanish even for high currents. To explain this phenomenon a new method for the qualitative estimation of both the stator tooth and yoke saturation is derived that shows very good agreement with the simulation results.