Direct-drive permanent magnet generators for multi-MW wind turbines are low speed high torque electrical machines requiring large, heavy and robust structures to maintain the airgap clearance open and stable. The structural mass of radial-flux generators can be estimated at an early phase of the design process. Using distinct approaches, the integrity of a 3MW electrical machine structure has been addressed from a dynamic perspective by carrying out modal analyses with a view to minimize its mass. A versatile tool has also been developed to help the engineers with the dynamic design of generator disc structures. Conical structures have been analysed and compared with the baseline disc model obtaining very promising results. Potential improvements have been proposed for more ambitious structural designs.
Wind turbine direct-drive generator structures are analysed in order to optimise and reduce mass. A method for modelling key stiffness parameters including a magnetic air-gap stiffness is outlined. Different approaches are used to parametrically calculate structural stiffness and mass. Finite element and analytical techniques are used to model mode 0 and mode 1 deflections and these can be used along with parametric models of electromagnetically active material.
Direct-drive generators for wind turbines are high torque, low speed machines which require a heavy robust structure to maintain the air-gap clearance open and stable. The mass of the structural material can be assessed at the early stages of the design process for radial-flux generators. By using low density materials, such as composites, the entire mass of the machine can be significantly reduced. A comparison between steel structures and structures made with composite materials working under the same loading conditions is made using small scale (100 kW) and large scale (3 MW) generator models. Potential improvements to the lightweight proposed structures are also suggested.
Heavy, large and robust supporting structures are needed to keep the airgap clearance of direct-drive multi-MW wind turbine electrical generators open and stable. As rotating pieces of machinery, generators vibrate when their natural frequencies are excited introducing potentially large amplitude oscillations due to the forces acting on them that could cause structural fatigue, noise and, in the worst-case scenario, their sudden collapse. A novel procedure for cost-effective and dynamically efficient structural design of a generator has been developed through a series of different finite element studies for a proposed 3MW machine with a conical rotor structure working under extreme conditions. Following a parametric approach coupled with the use of a topology optimisation tool it was demonstrated that the structural mass and dynamic response of the machine can be minimised, while complying with the deflection requirements.
One way to achieve increased wind capacity is by installing larger and more efficient wind turbines, which results in larger/heavier generators. Direct-drive, permanent magnet generators are favoured due to their increased efficiency, but the added weight is an issue, as this drives up the cost of the nacelle and turbine support structure, along with increasing the manufacturing and installation costs. Therefore, minimizing the mass, particularly the structural mass, of these low speed generators is becoming much more important. A vast amount of research has been done on trying to reduce the electromagnetically ‘active’ materials, but it is the supporting structure or ‘inactive’ materials, that makes up the biggest percentage of the generator’s mass. Therefore, this paper studies the statics and dynamics of a large offshore direct-drive generator’s supporting structure and the opportunities for light-weighting, as well as improvements to the generator’s rotor structure through structural optimisation. The indicator for optimised design is system weight under each predefined scenario. These scenarios will cover different design considerations of the generator’s rotor structure.
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