Evolution of External Thermal Bottlenecks in Liquid-Cooled IGBT Modules and Mechanisms for Regulating Thermal Shortcut

To address the challenge of achieving a balanced match between internal thermal resistance bottlenecks and enhanced external heat dissipation in high-power-density liquid-cooled IGBT modules, this paper establishes a three-dimensional conjugate heat transfer model comprising the IGBT/FRD chip, the packaging layer, the substrate, the elliptical pin-fin heat sink, and the fluid domain, and identifies the thermal resistance bottlenecks along the main heat transfer paths through interlayer temperature-drop decomposition. Furthermore, the thermal shortcut number (SN), defined based on the ratio of overall equivalent thermal resistances, is introduced as a supplementary metric to evaluate the relative changes in overall thermal resistance among different heat dissipation structures. In conjunction with the maximum chip temperature and pressure drop, the effects of cooling conditions, pin-fin structural parameters, and zonal regulation strategies on the thermal performance and flow resistance of the module are investigated. The results indicate that when the coolant flow rate is increased from 4 L/min to 12 L/min, the maximum chip temperature decreases by 16.27 K. However, the pressure drop increases from 1.93 kPa to 13.59 kPa, demonstrating a clear diminishing marginal return. While global thinning of the pin fins, reduction in their cross-sectional dimensions and lowering of their height can reduce the pressure drop, these measures weaken the solid–liquid heat transfer area and the capacity of external thermal shortcut; by contrast, zone-based control and flow-direction gradient structures can effectively improve the thermal–flow matching; amongst these, the local high-temperature suppression structure reduces the maximum chip temperature by 0.84 K, lowers the pressure drop by 3.89%, and increases the SN to 1.003; while the height-gradient structure along the flow direction reduces the pressure drop by 17.91% with a temperature rise of only 0.63 K. The study indicates that the optimisation of thermal management for liquid-cooled IGBT modules should balance the reduction of internal thermal resistance with the enhancement of external heat dissipation, in order to establish an external thermal shortcut characterized by low thermal resistance and low pressure drop that are well-matched to the distribution of heat sources, thereby achieving the synergistic optimisation of thermal and flow performance.