Design and test results for dual-lane fault-tolerant PM motor for safety critical aircraft actuator

This paper presents the design and test results for a dual-lane fault-tolerant PM motor for a safety critical aircraft actuator. Motor topology has been chosen to meet the system availability and reliability criterion considering principal faults that can occur within the motor including winding open circuit, line to line and phase to ground short circuits. The motor has two 3-phase windings which are powered from two independent inverters connected to different power supplies. The motor control strategy employs a healthy winding channel to have the capability to drive the load with the other winding channel short circuited in a faulted condition. The windings are designed to have a high impedance to limit the short circuit current to 1 p.u. A rectangular winding conductor is chosen to achieve a higher slot fill factor and for better manufacturability, which would also minimise the probability of turn to turn faults due to its thicker insulation. The effect of lateral magnetic pull has been considered to determine the locations of the dual-lane windings. Performance has been predicted by finite element analysis in healthy and faulted conditions. A prototype machine has been built and tested. Test results agree with the analysis in healthy and most of faulted conditions. However, measured drag torque with shorted windings is greater than the prediction at higher speeds, which is thought to be the effect of eddy currents in the conductors and magnets. It has confirmed that the induced current in a shorted turn is greatly affected by its location and the induced current may not be limited to 1 p.u. by short circuiting the machine phase terminals.