Structurally Integrated Slotless PM Brushless Motor with Spiral Wound Laminations for Marine Thrusters

Rim driven thrusters with structurally integrated brushless PM motors are now an established technology with an increasing range of applications. In these thrusters, the stator of the motor is housed within the thruster duct, and the rotor forms a ring around the tips of the propeller. Such high pole number motors tend to be very thin radialy, have very small length to diameter ratios, and have relatively large airgaps to accommodate corrosion protection layers on the surfaces of the rotor and stator. The relatively large diameter stator laminations of such machines tend therefore to have very thin back of core and narrow teeth, which make them expensive and difficult to manufacture. This paper proposes an alternative potentially lower cost motor topology featuring a slotless stator whose laminations are manufactured from a single strip of steel that is edge wound into a spiral (like a "slinky" and then fitted over the windings that are preformed on the outside surface of a non-conducting former. The former is also part of the sealed housing that protects the stator from corrosion in seawater. The paper discusses the design optimisation of such a motor using analytical and finite element analysis (FEA), describes a demonstrator motor and reports experimental and FEA results.