Influence of geometric parameters and cutting edge deterioration on the differential inductances

A prerequisite for self-sensing field oriented control of PMSM for standstill operation is a sufficient saliency ratio (magnetic anisotropy) of the differential inductances over the desired operating area. High frequency injection methods are very common in order to perform saliency tracking based self-sensing operation. Vanishing saliency for certain operating points or a change of the sign of the inductance difference, which needs to be known for the self-sensing algorithm, causes loss of stability of the self-sensing control method. This paper uses a simple, parameterized Finite-Element model in order to simulate the influence of geometric parameters and cutting edge deterioration. The simulations have shown that the cutting edge deterioration has only a slight influence on the saliency ratio of the differential inductances, although worst case conditions are assumed for the deterioration. This result is verified on a FE-model of a real PMSM. The most significant influence on the saliency ratio derives from the size of the tooth tip. For low ratios between stator yoke height and tooth width the area with vanishing magnetic anisotropy is increased. The area of magnetic anisotropy is increased with the width of the magnets, however the value of the anisotropy is decreased for large magnet widths.