Variable Flux Permanent Magnet Synchronous Machines: Building and Testing Simple Designs with High-Coercivity Magnets
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- Institutt for elkraftteknikk 
Variable flux permanent magnet synchronous machines (VF-PMSMs) use a novel operation concept based on changing the magnetization level of the permanent magnets in accordance with variations in speed and torque. This may improve the efficiency of wide-speed operation, reducing or removing the need for flux weakening current to counter-act excessive back-emf at high speeds. Magnetization change in these machines is achieved through short d-axis current pulses into the stator windings. The technology has gain increased attention the last few years, having numerous publications attempting to solve the various challenges related to design and operation. This paper will first give a conceptual introduction to VF-PMSMs and briefly summarize some of the literature published on various designs. Then, partly based on the findings of others, two simple VF-PMSM rotors are designed and built to fit a pre-existing stator. A rotor built with only strong samarium-cobalt magnets had its viability as a VF-PMSM experimentally tested. Results show that the magnet material used is stronger than ideal and that laminating the rotor may be crucial for functional VF-PMSM designs.