Conceptualization and Evaluation of DC link Cooling for a 6-phase 500-kW Inverter with Respect to Life Time

This paper presents an experimental and modelling-based evaluation of DC-link cooling strategies for a six-phase, 500 kW SiC-based traction inverter for heavy-duty electric vehicles. Two configurations - top and bottom bus-bar cooled - are characterized under passive and active cooling using high ripple current excitation. The results show that DC-link capacitors exhibit large thermal time constants of 0.5-1 h, leading to slow temperature dynamics and thermal accumulation over the drive cycle. As a result, external cooling primarily reduces the bus-bar temperature, while the capacitor hotspot temperature is limited by internal thermal resistance.A physics-based electro-thermal model, parameterized from experimental data and combined with an HHDDT mission-profile simulation, is used to estimate capacitor lifetime. The top bus-bar cooled configuration achieves a lifetime increase from 7.0 to 8.65 years (23%), while the bottom bus-bar cooled configuration increases from 7.88 to 9.83 years (24%) and maintains a higher baseline lifetime. The results demonstrate that capacitor lifetime is primarily governed by the thermal design of the DC-link, with the bottom bus-bar cooled topology providing superior performance.