Design of Air-Cooled Heat Sink for a 55-kW Power Inverter With Laminar Flow

Abstract

A methodology is developed for the design of an air-cooled 55-kW-rated inverter heat sink. The design constraints are that the power density (PD) must meet or exceed the values associated with liquid-cooled systems of the same power rating, and that the maximum surface temperatures be less than 200 °C. To keep the pressure drop low relative to turbulent flow designs, a laminar flow regime is chosen. A preliminary design that satisfies the PD constraint exactly, and the thermal requirements approximately, is determined. To ensure that the thermal requirements are met by the design configuration, a thermal-fluid analysis based on a three-dimensional conjugate heat transfer model is conducted. Overall, energy balance errors (OEBEs) as high as 15% were encountered in the numerical models. These errors are reduced by taking advantage of the symmetry between fins using a typical unit cell model. A new simplified approach for the simulations was identified which involved modeling fins as highly conductive layers instead of solid domains. This further reduced the OEBEs to less than 0.004%. The design factors considered in this study include effective cooling surface area, fin thickness, fin spacing, and fin height. The results show that the maximum surface temperatures can be kept below 200 °C for safe operation of SiC devices in the inverter module while increasing the PD.