Modeling and Optimal 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. Two different topologies are proposed. It is shown that two-dimensional (2-D) finite-element methods are inaccurate compared to three-dimensional (3-D) finite-element methods when solving eddy currents in eddy current couplings. The 3-D finite-element transient simulations are validated using a manufactured prototype 15-kW eddy current coupling. An analytical approximation is developed and used for the design optimization of two eddy current coupling topologies. Using the optimally designed eddy current coupling, it is shown that the analytical and 3-D finite-element solutions compare very well and that the proposed eddy current coupling topology has no torque ripple. The analytical approximation is well suited to the rapid design optimization of eddy current couplings that use a conductive material in the air gap.