Determining the Minimal Decoupling Capacitor in a Railway Traction Inverter Using Optimization

This article aims determining the minimum decoupling capacitor Cdec for a railway traction inverter. It is defined when any increase of its value does not decrease the overvoltage at turn off anymore. A simple generic model is deduced from a full understanding of the switching cell behavior, including the effect of all stray inductances and all interactions within the switching cell. This model is used in an optimization process in order to obtain directly the minimal value of Cdec. The methodology is validated in comparison with time simulation, as well as using experimental results. It has been used to analyze the impact of the switching cell parameters on the minimum value of Cdec: switching speed; stray inductances; and additional resistance have been considered.