Contra-rotating modular wound permanent magnet generator for a wind turbine

This paper presents a new topology for a contra-rotating permanent magnet generator for application in direct drive wind turbines. The external-rotor radial-field design utilises an open-slot armature lamination and a single-layer concentrated ´modular´ winding constructed using preformed coils. Using a parametric finite element model, the magnetic design and pole-slot combination are optimized to meet the application requirements of high specific torque, low starting torque, and high efficiency. A 960 Nm, 50 kW continuous rated prototype generator comprising 36 slots and 30 poles has been manufactured and tested. The attributes of the design are assessed using test results obtained from this purpose built generator, indicating a specific torque equal to 110 kNm/m³, based on the volume of active components.