Thermal analysis of fault-tolerant electrical machines for aerospace actuators

For safety-critical applications, electrical machines need to satisfy several constraints, in order to be considered fault tolerant. In fact, if specific design choices and appropriate control strategies are embraced, fault-tolerant machines can operate safely even in faulty conditions. However, particular care should be taken for avoiding uncontrolled thermal overload, which can either cause severe failures or simply shorten the machine lifetime. This study describes the thermal modelling of two permanent magnet synchronous machines for aerospace applications. In terms of the winding's layout, both machines employ concentrated windings at alternated teeth, with the purpose of accomplishing fault-tolerance features. The first machine (i.e. Machine A) adopts a three-phase winding configuration, while a double three-phase configuration is used by the second one (i.e. Machine B). For both machines, the winding temperatures are evaluated via simplified thermal models, which were experimentally validated. Copper and iron losses, necessary for the thermal simulations, are calculated analytically and through electromagnetic finite-element analysis, respectively. Finally, two aerospace study cases are presented, and the machines' thermal behaviour is analysed during both healthy and faulty conditions. Single-phase open-circuit and three-phase short-circuit are accounted for Machines A and B, respectively.