A new approach to minimize the cogging torque of axial flux pmg for under water applications

The rotor of a typical water current turbine rotates below 100 rpm. In conventional hydro installation the generator is coupled to the turbine via a gear box, so that it can typically rotate at a speed of 1500 or 1800 rpm. The water current turbine can be simplified by eliminating the gear box and by using a low-speed generator, the rotor of which rotates at the same speed as the rotor of the turbine. The main design challenge for a direct driven Permanent Magnet Generator (PMG) is to minimize the cogging torque. Cogging torque is an inherent characteristic of PMGs and is caused by the geometry of the generator. In this paper a new approach to minimize the PMG cogging torque is proposed. Basic design of a low cogging torque generator is also provided.