Session: 05-04 Phase change cooling technologies

Paper Number: 97412

97412 - Performance Validation of Voltage Blocking Technologies for Direct Cooling of High-Density Power Electronics 

This effort seeks to advance the feasibility of a direct cooling approach to enable high voltage power conversion with improved power density. While wide band gap devices offer improved efficiency, performance, and potentially higher power density, traditional packaging and cooling approaches are struggling to keep up. High voltage systems in particular face the challenge of concurrent voltage isolation and thermal resistance, which are typically at odds. In such packages, voltage isolation requirements further increase junction-case thermal resistance (θ_jc) through increased thickness of the ceramic dielectric layers that typically come between the power devices and heat sink.

Direct cooling using dielectric fluids and surface coatings can unlock the opportunity to meet the cooling demands in these >1kV power electronics; however, their voltage blocking characteristics under direct forced convective cooling as well as long-term reliability remain to be fully understood. In this study, we propose to explore the mechanisms driving flow-dependent breakdown using different electrode configurations. Focus is placed on fluorinated coolants including hydrofluoroethers such as HFE7500, which are more favorable for electronics cooling due to their low viscosity. Point-point electrodes but also large area plane-plane electrodes are used to allow for improved flow analysis between discharge locations and to help crystallize the role played by factors such as the formation of a boundary layer on the electrodes, the sweeping action of flow on impurities and charge carriers. Chemical degradation of the dielectric fluid following repeated discharge events as well as particulate participation represent other areas of interest to supplement the learnings on the long-term voltage blocking characteristics of the DF’s. Tools such as Fourier-transform infrared spectroscopy (FTIR) are used for the verification of these properties. Finally, while dielectric fluids (DF’s) offer some advantage in concurrent voltage blocking and heat rejection, their breakdown voltage is still generally lower than solid dielectrics. Consequently, the combined voltage shielding capacity of DF’s and dielectric coatings is also explored.

Presenting Author: Ange Christian Iradukunda University of Arkansas