This paper presents a lumped-parameter thermal model for a multi-barrier interior PM synchronous machine. The model consists of a network of 12 thermal resistances that make it possible to estimate temperatures at 9 critical points inside the machine including the stator end windings, rotor magnets, and
the bearings. The details of the model are presented and two machines are analyzed, including a 6 kW 12-pole automotive starter/alternator and a 0.5 kW 4-pole electric water pump machine. The lumped-parameter model results for both machines demonstrate good agreement with results obtained using detailed thermal finite element analysis.