IES: Equalising airgap radial forces in direct drive generators

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Permanent magnet generators for direct-drive wind turbines normally have massive weight to hold the stiffness and small airgap for higher flux density. However, the airgap would deflect during operation due to the effects like electromagnetic attraction force, gravitational pull, rotational velocity, nacelle motion and unbalanced magnetic pull etc. One of the downsides of small airgap clearance is the tremendous attraction force between stator and rotor. Such large magnitude attraction force combined with varying airgap clearance has always been a major challenge to the generator stiffness.The project intends to develop an equalization strategy of the radial attraction forces within the airgap during real-time operation, enabling smaller airgap clearances and reducing the material cost of these large generators. The intention is to equalize the radial forces in different parts of the machine by controlling discrete three-phase stator "modules" with variable flux-weakening and flux-strengthening capability. The sub-objectives of the project are to improve the magneto-static control strategy and extend it to the rotating machine. With validation using Finite Element Analysis and testing on real prototype, the project would then develop an attached multi-converter system to realize the equalization.