Effective turn fault mitigation by creating zero sequence current path for a triple redundant 3x3-phase PMA SynRM

Effective mitigation of excessive stator turn fault current is crucial for fault tolerant machine drives. In this paper, a simple and effective method is proposed for a triple redundant 3x3-phase permanent magnet assisted synchronous reluctance machine (PMA SynRM) by using 3-phase 4-leg inverters. The fourth leg creates a zero sequence current path when a terminal short circuit (TSC) is applied in an event of a turn fault in a 3-phase winding set. Consequently, the zero sequence flux linkages are reduced by the resultant zero sequence current. This leads to lower residual flux linkage and decreased fault current. The machine drive can therefore have larger safety margin or can be designed for improved torque density and efficiency. The proposed approach is verified by both FE simulations and experimental tests in a wide operation range. It shows the fault current is reduced by ~40% and the output torque is not affected.