Influence of winding layout of PMSM on inductance and its impact on suitability for sensorless vector control

Permanent magnet synchronous machines (PMSM) are getting increasingly more used in the area of fractional hp drives. Additionally the specifications often include the demand to control the motor sensorless. Many position sensorless control strategies that still work at low speed or standstill are based on the analysis of the inductance difference in the rotor oriented d- and q-coordinate system. While the influence of the rotor geometry on the inductance has been discussed a lot, the main objective of this paper is to investigate the influence of the winding system on the inductances and the inductance ratio between the d- and q-direction. This serves as a measure for the suitability of the motor for sensorless control. An analytical formula is presented to estimate the flux linkage between the phases as well as the inductance ratio. Both characteristics are verified with FE-analyses and sample measurements.