Advanced modelling capabilities in the Opera electromagnetic simulator are helping Magnomatics to bring ground-breaking magnetic power transmission innovations to market.
A recent spin-out from the University of Sheffield, Magnomatics is currently working with numerous organisations on magnetic gearing and power transmission applications. Among the advantages of its magnetic linkage technology are long maintenance-free lifecycles, very high efficiency, an intrinsic tolerance of overloads, no noise, and an ability to tolerate misalignments.
During the current equipment design and prototyping phases, and to satisfy interest of many organisations working in a very wide range of application areas, Magnomatics needs to produce design ideas and refinements rapidly, and it has invested in the Opera electromagnetic simulation tool from Vector Fields for this purpose.
Magnetic gearboxes are one of the company’s key technologies. This innovation uses an arrangement of three concentric cylindrical shapes: two rotors with differing numbers of permanent magnet poles, and an intermediate ring with stationary magnetic pole-pieces that modulate the magnetic fields to link the rotors’ movement.
Other product technologies the team are involved with include magnetic couplings, eddy-current dampers and brakes, and a very novel, patent-pending ‘pseudo’ direct drive. This latter development integrates a permanent magnet motor/generator with magnetic gearing in a single machine that offers torque densities that are typically eight times greater than a standard naturally cooled permanent magnet machine, and approximately double a transverse flux machine – without the usual penalty of a low power factor.
Magnomatics developers chose the Opera computer aided engineering (CAE) tool because of a number of special facilities, and for the package’s reputation. Among the qualities the development team rely on greatly is the speed of simulation, as Magnomatics’ designs can feature very large numbers of magnetic poles, with no magnetic symmetry that would allow the scale of the simulation to be reduced. The tool’s flexible ability to dynamically model any number of ‘moving’ air gaps in three dimensions – some electromagnetic tools will only support one – is important here, as it provides the technical platform to simulate the products while additionally accurately accounting for the differing speeds of the rotors.
Opera’s fine mesh controls and adaptive finite element meshing are very helpful to optimise both the accuracy and simulation speed of the two- and three-dimensional models used, which can vary in size from a few centimetres to more than three metres in diameter. The modelling language’s parameterisation and scripting capabilities have also become critical to the design team, as they allow previously developed macros for the special geometric shapes to be quickly reused to create proof-of-principle simulations or designs for new applications.
These simulations include accurate reports on the torque coupling, which are calculated by Opera’s built-in post-processor. “At this stage in our company development, short turnaround times on design concepts and ideas are very important to us,” says Richard Clark of Magnomatics. “Opera allows us to create our own scripts, which greatly shortens the time required to prove the benefits of our magnetic power transmission technology to potential clients. Because our larger designs can have many poles, and because we don’t have the symmetry that would allow us to model a segment, simulation speed really matters. Opera’s algorithms execute very quickly, enabling us to respond quickly.”
Background information on Magnomatics’ technologies.
Mechanical gearboxes are used extensively to match the operational speed of prime movers to the requirement of their loads, and to increase output torque. However, although high system torque densities can be achieved, mechanical gearboxes usually require lubrication and cooling, and noise, vibration and reliability are often significant issues. Magnetic gear systems can eliminate mechanical gears in many applications and dramatically improve both reliability and efficiency.
A magnetic gear uses permanent magnets to transmit torque between an input and output shaft. The gear ratio of the transmission is dependent on the design of the magnetic circuit. Typically, a magnetic gear has an efficiency of 99%, with torque densities of up to 150 kN/m3 (comparable with two- and three-stage helical gearboxes). Since there is no mechanical contact between moving parts, wear is negligible. Further, magnetic gears inherently protect against overloading, i.e. the gear simply slips if an overload torque is applied, and only re-engages when input torque falls below the limiting threshold. Magnetic gears can be realised in radial, axial or linear topologies – and optimal designs have been developed to realise both low (2 to 30:1) and very high (30 to 1000:1) ratios in a single stage. Suitable applications include hybrid vehicles, wind turbine powertrains, marine propulsion, electric traction systems, high speed pumps and compressors, robotic control, etc.
Pseudo direct drives
With conventional electrical machines, it is only possible to achieve a relatively low torque for a given volume, due to limits on the magnetic and electric loadings, so that mechanical gearing is often required to match the machine to its load. Magnomatics’ ‘pseudo’ direct drive (PDD) technology combines torque production and magnetic gearing within a single integrated machine. This results in a very high torque density. PDDs offer several advantages over conventional machine topologies, including reduced size, reduced maintenance, improved reliability and higher efficiency, and the low electrical loading can remove the requirement for forced or liquid cooling. The drive technology also has inherent torque overload protection, a high power factor (typically, 0.9) removing the need for significantly high VA rating overheads associated with transverse flux machines , and the possibility of having two output shafts with different rotational speeds. PDDs can be realised in both radial- and axial-field topologies. Applications include hybrid vehicles, wind turbines, electrical generators, white goods, power tools, etc.