Thermal Analysis of the Laminated Busbar System of a Multilevel Converter

Laminated busbar systems are commonly used in power electronic converters because of their low stray inductance. While the electromagnetic analysis of a busbar system is widely presented in the literature, there is a lack of accurate thermal modeling. In this paper, the thermal analysis of the busbar system is presented. An analytical lumped parameter thermal model (LPTM) of the busbar system is developed. The LPTM is applied to the fast estimation of the mean temperature and temperature-dependent power losses of the busbars by the proposed algorithm. Joule losses produced by nonsinusoidal currents flowing through the busbars in the converter are estimated. The skin and proximity effects, which have a strong influence on the ac resistance of the busbars, are considered in the loss estimation. Thus, a comprehensive electrothermal model of the busbar system is developed, which is of practical use in the converter design. It allows optimizing the stray inductance, material consumption, and cost of the busbar system as long as the specified temperature limits are not exceeded. The finite-element method thermal modeling validates the developed LPTM. Laboratory measurements in two operating points of the converter have been performed, and they show good correlation with the simulation results.