Increasing the saliency ratio of fractional slot concentrated winding interior permanent magnet synchronous motors

In permanent magnet synchronous motor (PMSM) servo systems, the saliency ratio is an important factor in sensorless control and flux-weakening control. Compared with the interior PMSM (IPMSM) with distributed windings, the IPMSM with concentrated windings gains more popularity in servo system applications. However, the saliency ratio of current fractional slot concentrated windings (FSCWs) IPMSM is low and hard to increase, without much literature investigating how to improve the ratio. In this paper, the components of d- and q-axes inductances of FSCW IPMSM are determined, a novel concept named mechanical phase region is introduced and the key parameters influencing the saliency ratio of FSCW PMSMs have been investigated through thorough theoretical analysis and simulation. The design principles on increasing the saliency ratio of FSCW IPMSMs are proposed and the maximum saliency ratio of a 10 poles 12 slots motor is obtained. On the basis of the theory, a novel rotor structure with higher saliency ratio is designed. A new experimental method of measuring d- and q-axes inductances closes this paper with three experimental prototypes built to verify the theory and simulation results.