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Magnetically Geared Induction Machines

Final Report Summary - MAGIM (Magnetically Geared Induction Machines)

The project is called the "MaGIM" project for Magnetically Geared Induction Machines. MaGIM combines an induction machine and a magnetic gear in the same device which results in a high torque density electromechanical energy conversion. The aim of the research is to investigate new MaGIM topologies for which modelling and design tools will be developed. The new MaGIM concept consists of a magnetically, electrically and mechanically coupled wound rotor induction machine - magnetic gear. The high speed rotor of this MaGIM is common for the gear and the machine sides. The gear side has a hybrid excitation composed of permanent magnets and dc windings which are directly supplied, through a rotating 3-phase diode rectifier, from the induced currents in the induction machine ac windings rotor side. This new topology has 2 important advantages compared to a conventional solution which combines a PM machine and a magnetic gear:
- The torque transmitted to the low speed rotor (the load) is not limited by the magnets since the high-speed dc windings act as a “boost” for providing extra power
- The magnet volume is reduced which results in a more economical drive solution.

This topology is also interesting for power energy generation, especially for wind turbine systems which uses a doubly fed induction generator and a mechanical planetary gear. Indeed, it offers a better reliability (suppression of the mechanical gear) and an enhanced operating flexibility. Another potential application of the system concerns hybrid/electrical vehicles. Indeed, MaGIM could easily be used as induction machine/magnetic gear based power split device as to constitute a continuously variable transmission. Furthermore, the demonstrated torque boost capabilities of MaGIM are of great interest to overcome the problems due to mechanical overloads (severe torque transients) in hybrid/electric vehicles.

As an application example, a MaGIM rated at 100 kW, #=115-120 rpm, 8000Nm is considered for the simulation studies. A continuous torque density transmission in excess of 80 Nm/L is obtained. To show the impact of the boost winding on the performances of MaGIM, if you compare the transmitted pull-out torque for different values of the number of turns/slot of the boost winding, Ndc: compared to the situation where the boost is disconnected (Ndc=0), a torque increase of about 15% is obtained when Ndc=10.