A compact direct-drive permanent magnet motor for a UAV rotorcraft with improved faulted behaviour through operation as four separate three-phase machines

This paper presents an alternative arrangement of a high specific output direct-drive fault tolerant motor. The target application of this 150 Nm machine is to provide a means of directly powering the main rotor blades of a concept compound rotor wing UAV. The application requirements are high torque per weight, low torque ripple, a compact external- rotor configuration integral to the rotor hub, air-cooling and fault tolerance. Fault tolerance is achieved by configuring the machine radially as four separate three-phase star connected windings. Analytical and finite element analysis, as well as prototype testing and results, are presented for normal working and different fault scenarios showing the benefit of the configuration in minimising torque ripple and additional losses during faulted operation.