Fault Tolerant Electric Machine Concept for Aircraft Propulsion with PM Rotor and DC Current Stator Dual-Stage Excitation

The development of electrically propelled aircraft requires electric machines that are fault-tolerant, compact, and efficient at multiple operating points. This paper proposes a novel machine topology combining a coreless Halbach PM array axial flux unit and a PM-less synchronous hybrid excited radial flux unit. Both units are coupled on the same shaft to take advantage of the opportunities available in the unique usage profile for aviation. The machines can be used simultaneously for the take off and altitude climbing stage or used individually during the cruising stage. The coreless axial flux PM (CAFPM) motor unit consists of two Halbach array PM rotors, two stators, and an integrated cooling plate to enable high efficiency at maximal current density. The stator DC-excited synchronous (SDCES) motor unit operates using AC 3-phase and DC stator windings employing concentrated non-overlapping toroidal coils with a reluctance consequent-pole rotor. Both units have two stator modules which are independently excited and controlled, allowing for continued propulsion under partial system deterioration. Combining both units takes advantage of the high specific power and efficiency of the CAFPM due to the Halbach array and cooling potential and the fault tolerance of the SDCES, with no potential for demagnetization and separate excitation.