Design of an eddy-current coupling for slip-synchronous permanent magnet wind generators

In this paper the possibility of using an eddy-current slip coupling to remove cogging torque and torque ripple in a slip-synchronous permanent magnet wind generator is investigated. It is shown that 2D finite element methods are inaccurate compared to 3D finite element methods when solving eddy currents in eddy-current couplings. Two topologies of eddy-current couplings are optimised and compared using 3D finite element transient solutions. An analytical approximation of the solution is proposed and a prototype coupling is manufactured and tested. It is shown that the analytical and 3D finite element solutions compare well with the measured values up to 15% slip speed, where 8% is the rated slip speed. Although the analytical approximation is only valid in the low slip speed region, it is well suited to rapid design optimisation of the eddy-current coupling for slip-synchronous permanent magnet wind generators.