Design, fabrication and testing of a stacked variable-reluctance motor

Abstract

A new type of variable-reluctance motor with axially stacked stator and rotor plates is explored in this thesis. This stacked variable-reluctance motor (SVRM) has mechanically parallel air gaps, carrying magnetic flux in series. Magnetic models are developed to predict the maximum and minimum flux linkage of the motor, as well as the average torque over an electrical cycle. A geometric optimization is carried out using a combination of the Monte Carlo method and the simulated annealing method on a prototype, designed as a hip motor for a cheetah like robot. A one-phase 56 polepair prototype is designed and constructed to confirm the theory. The prototype can maintain its two 100 pm axial air gaps over a 5 inch diameter. The prototype, given all its practical constraints, produces 2 Nm of torque at 30 A phase current. After material property adjustments, the model predictions match well with the experimental performance of the prototype. Another round of optimization is done using the modified material properties, the best torque-to-mass ratio found for a ferrite motor with no more than 100 pole pairs is 8.4 Nm/kg. It is concluded that ferrite's flux carrying capacity is insufficient for high toque-to-mass ratio motors, given the requirements of the hip motor. A steel SVRM can have torque-to-mass ratio as high as 35.7 Nm/kg, but is restricted to low speed operation due to the slow magnetic diffusion.