Sensorless Control of Low Inductance Coreless AFPM Machines for Fault-tolerant Operation of Propulsion Systems

In motor-drive systems utilized in safety-critical applications and demanding conditions like electric aircraft propulsion systems, the reliability of the system is greatly affected by position sensors, given their susceptibility within the motor-drive system. Consequently, there is a need to eliminate sensors in vector-controlled motor drives to decrease overall hardware complexity and expenses, bolster the mechanical durability and dependability of the drive system. In this paper, a fault-tolerant sensorless control system for low inductance coreless axial flux PM (AFPM) machines, integrated into electric aircraft propulsion systems, is introduced. The proposed control system spans a wide operating range, from zero to ultra-high speed, all without the need for a position sensor, enhancing fault tolerance. The system is capable of accelerating the motor from standstill to a certain speed where fundamental signals become available for a flux observer. This observer estimates the rotor position and speed, which are then fed into a field-oriented control scheme. The effectiveness of the introduced control scheme was experimentally verified using a prototype coreless AFPM machine with a PCB stator as a case study.