Initial Investigation of Slotless Surface-Mounted Permanent Magnet Machine Equipped with Ferrofluid

A novel slotless surface-mounted permanent magnet machine equipped with ferrofluid is designed and investigated for servo motor applications. The proposed design using ferrofluid is studied with help of finite element analysis (FEA) to achieve sinusoidal back electromagnetic force (back-EMF), high torque density, zero cogging torque and low torque ripple. Due to its relative high permeability comparing to air, there is potential on torque increase by filling ferrofluid into the air gap of the electric motors. In order to highlight this effect, a slotless surface mounted permanent magnet machine with ferrite PM and ferrofluid in the air-gap is proposed and investigated. The electromagnetic performance of the proposed topology is studied by FEA. It is found that both the air-gap flux density and torque are increased with the proposed design. The mechanism behind is analyzed and discussed in detail. Furthermore, the sensitivity effect of ferrofluid relative permeability on torque density is discussed and thus design guidance is proposed.