The temperature of laminated busbars has to be limited to prevent their inner electrical insulators from over-heating. In that purpose, Finite Elements Method (FEM) simulations are usually conducted to evaluate the busbar's temperature. However, the thermal influence of external heat sources such as power modules has to be considered to obtain an accurate temperature repartition estimation. In this paper, the thermal influence of power modules on busbar temperature is first evaluated through simulation and experimental works. Then, a method based on the use of electrical equivalent circuits as boundary conditions is proposed to consider this issue and reduce the computation time.