An Innovate UK joint project to develop magnetic gears for marine propulsion

Three British companies, Rolls-Royce, the magnetic gear developer Magnomatics, and the high-voltage motor manufacturer ATB Laurence Scott, are working in partnership to develop compact, efficient electric drives for marine applications.
Together, they will design, manufacture and test a 2.5MW magnetically geared propulsion motor (MGPM), using Magnomatics’ Pseudo Direct Drive (PDD) technology.
The developers believe that the MGPM will deliver significant benefits for marine propulsion by operating at higher efficiencies than existing electrical machines. In their opinion, the use of magnetic gearing will result in a compact, low-maintenance, robust and flexible propulsion system that could improve efficiencies and cut emissions for various types of vessel
Magnomatics’ patented Pseudo Direct Drive technology combines a magnetic gear with a standard-wound stator, while outer arrays of magnets are fixed to the internal bore of the stator and magnetic fields generated by the windings are used to drive an internal rotor.
The torque produced by this rotor is then geared up by the magnetic gear and transmitted out via steel pole-pieces. This results in a high-torque-density machine with no need of a conventional gearbox. The natural elasticity of the magnetic gear means that the output torque has low levels of ripple – less than 0.3%.
The PDD technology is said to offer a significant benefits over conventional permanent magnet (PM) motor/generator technologies, achieving a continuous torque density up to eight times higher than that of equivalently cooled PM machines, while maintaining high efficiencies.
This allows the motor to drive many loads directly where traditionally a motor and gearbox combination would have been needed. It is ideal for applications requiring a high continuous torque at relatively low speeds. These potential applications range from aerospace actuation, to direct-drive wind turbines and rail traction systems.
The PDD system is also smaller and lighter than a direct-drive equivalent and can be driven by standard power electronic inverters/converters. Its cooling requirements are low and it offers inherent torque overload protection. Built-in torsional compliance reduces drivetrain pulsations, while a large air-gap results in high shock ratings.
The project is co-funded by Innovate UK.

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