Thermal and Electro-Thermal Analysis of DC-DC convertor for 3 wheeler electric vehicle

Abstract

The power electronics involved in 3-wheeler electric vehicles are exposed to rough and challenging thermal environments which can have a damaging effect on the thermal reliability of the electric components on the electric vehicles. One such critical power electronic section of electric vehicles is DC-DC convertor which converts a source of direct current from one voltage level to another voltage level. DC-DC convertor is used to interface the elements in the electric powertrain by boosting or chopping the voltage levels. Due to automotive constraints, the power convertor structure has to be reliable, lightweight, small volume, with high efficiency, low electromagnetic interference and low current/voltage ripple. The difference between DC-DC convertor for a 4-wheeler and 3- wheeler is that the previous one is isolated and has a bigger size and higher thermal loads whereas the latter is non isolated with lower thermal loads. The challenge for 3-wheeler DC-DC is that the heat load has to be contained by natural convection and conduction mode only. Moreover, for the DC-DC to be thermally reliable the internal air temperature has to be maintained below 100 °C. The product consists of a top and bottom enclosure with heat sink and fins, PCB, surface mount electronic components on PCB, potting material, thermal interface material between PCB and bottom heat sink. The PCB is a multilayer CU-FR4 board, no forced air flow is allowed at the mounting location. First the placement of components was optimized with electro thermal analysis of the PCB board to see areas in the copper traces with high current density and high joule heating. By doing an electro thermal analysis with the help of FloThermXT we arrived at the required trace width and design and then the optimized placement of components was done in order to take care of joule heating aspect. Further after the complete placement of components were done the entire steady state thermal analysis of DC-DC was done first without potting material and then with potting material so as to the see the effect of potting material on the internal air temperature inside the product. The difference between simulation results and measurement is a cumulative average of 10.5 %. The usage of potting material helps in approximate of 5% reduction of temperature. A well-established correlation between experimental and numerical method for thermal analysis of DC-DC for 3 -wheeler electric vehicle has been achieved.