Comparative study of ferrofluid cooling for permanent magnet machines with different winding structures

This paper investigates the influence of single- and double-layer winding structures on the thermal performances of fractional slot permanent magnet (PM) machines with ferrofluid cooling. Ferrofluid is an oil-based liquid with nano-sized ferromagnetic particles and has been injected into the end space of these machines. Owing to the magnetic body force produced by the end-winding leakage flux, the ferrofluid can circulate without the need for external pumps. This enables the establishment of an effective heat transfer path from the end-windings to the housing with water jacket. As a result, the ferrofluid improves the heat transfer rate and hence machine’s overall thermal performance. Multiphysics models accounting for the coupling between electromagnetic (EM) field, fluid dynamics and heat transfer have been built for the investigations. In addition to the dc field simulation as that carried out in literature, these multi-physics models can also simulate the effect of ac field in the end space. The findings indicate that ferrofluid cooling significantly improves the EM and thermal performances for the fractional slot PM machines. In addition, due to different magnetic fields in the end space produced by the single- and double-layer windings, they exhibit different cooling efficiencies. A motorette has been built to validate the simulations.