Engineering Design Consultants

Pseudo Direct Drive Generator
Concept Design Study

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The Pseudo Direct Drive Generator concept is a coupling of a permanent magnetic gear system with a brushless permanent magnet generator. The PDD concept has significant benefits for wind turbine design both in terms of efficiency and reliability. The PDD generator has a significant weight reduction over a direct drive system whilst not requiring a mechanical gearbox. Mechanical gearboxes have been an Achilles heel of wind turbines for some time with many premature failures occurring due to fatigue. Hence a non mechanical solution could be advantageous.

Atkins carried out a design study for Magnomatics Limited investigating several mechanical aspects of the concept. Combining our working knowledge of wind turbine design with proven design tools such as Catia V5 3-D Modelling and the Ansys Finite Element package a workable concept design was put together.

Several innovative solutions were investigated when design problems arose. Key features investigated included:

• CFRP - Use of structural adhesives and CFRP within the pole piece rotor in order to maximise the rotor efficiency. This included true adhesive bondline testing and subsequent analysis of pole piece stacks.
• Lubrication - Design of a novel Oil Re-circulation system to allow for effective life-time lubrication of multiple rotor bearing assembly.
• Unit Mass – Weight saving study on rotating components in order to achieve a competitive unit mass.
• Modes - Natural Frequencies of rotors analysed for comparison with magnetic/electrical related design frequencies.
• Tolerances – Tolerance build up was critical to the design due to the effect of air gap on the machine performance. A tolerance feasibility study including effects due to production, machining and assembly processes was carried out.
• Assembly – Due to the complexity of the design with several internal rotating components with small clearances the concept was built up around the assembly process to insure a workable design.