Surface NdFeB versus Ferrite IPM motor drive for low power (100W to 2000W) applications: FEM embedded optimal design with full step torque response validation in sensorless vector control

Low power high efficiency permanent magnet synchronous motor drives are needed for better home appliances. As the price of sintered (high energy NdFeB magnets) used for the scope so far has risen spectacularly in the last two-three years, the economics of their use to such high efficiency applications is in question. The present paper is investigating in comparison NdFeB surface rotor versus Ferrite interior PM rotor motor drives in the 100W to 2000W range to see if Ferrite motors can compete in terms of initial active material cost at above 94% efficiency. FEM embedded optimal design methodologies are introduced with case studies at 120W, 500W, 1000W, 2000W, 4500rpm, 290 (380) VDC. The torque pulsations with sinusoidal current control are reduced by shaping the airgap and by two segmental skewing. Also the optimal designs have been checked for full step torque response validation in sensorless vector control for 4500rpm. The results show Ferrite motors superior in initial cost at 120W and 2000W, but about the same for 500W and 1000W, for about the same efficiency, around 94%.