Design and Control of an Axial Flux Machine for a Wide Flux-Weakening Operation Region

This paper describes the strategy to design and control of an axial flux SPM machine for achieving a wide flux-weakening operating region. By using a slotted stator with fractional slot windings and additional cores enclosing end windings, the axial flux machine satisfies the specification of a wide constant power speed range. The design procedure is presented for increasing flux-weakening capability while obtaining low harmonic back-electromotive-force and low cogging torque. This technique is applied to design an 8 Nm axial flux prototype machine that exhibits about 3:1 flux-weakening range. To the aim of exploiting full capability of the machine, a flux-weakening controller is designed and implemented. This controller utilizes the voltage difference between the current regulator and the output voltage, limited by a voltage source inverter. With this method, the output torque in the flux- weakening region can be increased up to that of the six-step operation while maintaining the current control capability. The goodness of both design and control algorithm is proved by experimental tests on a prototype.