Thermal Modeling and Optimization of an AC/DC Bidirectional Converter

Air cooling is widely used in power electronics converters due to its various advantages. It is simpler, cheaper, and lighter than liquid cooling. However, air-cooled solutions’ lower thermal efficiency and sensitivity to ambient conditions make their design and optimization a challenge, therefore nowadays numerical simulations are often used to improve and speed up this process. The thermal performance of power converters is always taken into consideration during its design stage and is often limited by the overheating of the semiconductor modules. To decrease temperatures of these critical components, one can try to lower the thermal resistance between the module and heat sink or create a numerical/mathematical model that allows for a broad parameter study and at the end optimization of the module performance. This paper presents a complete thermal model of an air-cooled AC/DC bidirectional converter to get the best out of the cooling system. The aim is to improve its thermal performance by focusing on heat sink optimization. Several heat sinks are considered and the impact on semiconductors junction temperatures as well as passive components is studied. A three-phase semiconductor module is analyzed and thermally modeled to find hot spots under worse operating conditions. Losses are calculated for each chip based on the electrical operating point and thermal simulations are run to ensure junction temperatures are kept within safe operating range. Impacts of heatsink choice on air velocity and pressure drop inside the converter are also presented. Maximum temperature reduction of 15% is obtained and confirmed by experimental results.