Extended Field Weakening Range in Slotless/Coreless Permanent Magnet Machines

This paper presents a comprehensive design methodology to achieve wide field weakening operation in low inductance slotless or coreless Permanent Magnet Synchronous Machines (PMSMs). Design constraints and steps are presented to achieve wide constant power speed range (CPSR) and desired torque-speed characteristics. Extended Field weakening Range is achieved through a stator-embedded inductor integrated with the torque producing machine windings. System efficiency and power factor maps over the speed range are summarized with and without the embedded inductor. The concept helps to achieve the desirable extended torque speed range beyond the base speed. In addition to desired CPSR, this method also helps to reduce PWM induced current ripple, and core losses while improving high-speed efficiency for a slotless machine.