Self-Sensing and Power Conversion Comparison for Flux Weakening Surface Mounted Permanent Magnet Servo Motors Designed using Symmetric and Asymmetric Rotors

Servo motors are widely used in automation and industrial robots. These motors achieve high dynamic performance with high peak torque and acceleration rates. Flux Weakening Surface mounted Permanent Magnet Synchronous Motors (FW-SPMSMs) which are known as SPMSMs can be used in servo application. They are designed to achieve very low ripple and cogging torque to enable precise speed and position control. This can be done by shaping the magnet to achieve low airgap flux harmonics or through using shifted ring magnets with asymmetric rotor structures to cancel the airgap flux harmonics. Standard SPMSMs are not suitable for injection-based self-sensing control due to low saliencies. Many techniques have been reported in the literature to design slightly salient SPMSMs. In this paper, two SPMSMs for servo applications are designed, one using bread-loaf magnets and another with shifted ring magnets. The power conversion performance and the injection-based self-sensing properties will be fairly compared for both designs, pros and cons for each design will be highlighted.