Control of Current in a Six-phase Traction Motor with Open-end Windings in Case of a Phase Open-circuit Fault

The electric propulsion system of an aircraft or unmanned aerial vehicle must meet high safety standards and provide fault tolerant operation in case of partial failures. This requirement is met by means of both hardware and a control system. An open circuit fault in one phase is the most common fault, during which it is still possible to continue producing the same torque by changing the current settings in the other phases. The article considers a six-phase permanent magnet traction motor with open-end windings and proposes a method for forming a reference current vector using the phases remained in operation. It is shown that a 23.6% increase in current amplitude is required, while a mere 20% increase in currents produces the same average torque per revolution, but with 20% torque ripple. Since torque ripple can cause mechanical resonance and propeller failure, the proposed method is feasible even at somewhat higher ohmic losses. The presented method is suitable for use as part of an aircraft propulsion control system.