Thermal Modeling of a Claw-Pole Electrical Generator: Steady-State Computation and Identification of Free and Forced Convection Coefficients

The production of heat is a key characteristic of a machine's behavior. Heat sources come mainly from energy losses (electrical in copper, magnetic in iron, aerolic in fans, and mechanical in bearings). Temperature changes can be described owing to thermal conduction, convection, and radiation equations. To understand and design a machine, it is important to construct a dedicated model and to know every physical loss. The aim is therefore to build a static thermal model adapted to the simulation and sizing of claw-pole car alternators. Currently, in cars with internal combustion engines, generators rotors are wire wound, doubly excited with a dc concentrated winding and small permanent magnets, and self-air-cooled with fans. This paper proposes a nodal model with 16 nodes, taking all the heat transfers and space directions into account. The thermal characterization of the machine is permitted by only four physical parameters, varying with the temperature T and the rotating velocity Ω, shown to be sufficient to deduce the model conductances. These properties are as follows: the thermal exchange coefficients due to free and forced convection into the air gap and the cavity, the thermal exchange coefficient due to free superficial convection at the external surface, and the thermal equivalent conductivity within the bearings. The consistency and usefulness of both the model and identifications are checked against numerical studies and measurements.