Loss and Thermal Analyses of a Power Converter Designed for Free-Piston Engine Generators

The insulated-gate bipolar transistor (IGBT) is the most important part of a power converter. The heat generated during operation will cause the junction temperature of the IGBT to rise above ambient temperature. The junction temperature must stay within its predefined limit to ensure reliable operation. A properly designed cooling system is crucial for the overall operation, and an accurate prediction of power loss is critical in the design of a good thermal system. In this paper, a pulse-width modulation (PWM) full-bridge converter is designed for free-piston engine generators (FPEGs), and a low-cost forced-air cooling system is used for heat dissipation. For the converter to choose the IGBT module or discrete IGBT as the switching device, loss and thermal analyses are carried out. The loss analysis model of the converter is established, which considers the influence of the IGBT parasitic capacitance and gate driver voltage on the switching losses. The accuracy of the loss analysis model is verified by comparison with experiments. The converter thermal analysis, in which a three-dimensional (3-D) thermal model is built and is carried out based on the loss analysis data. The results of loss analysis and thermal analysis show that, compared with discrete IGBT, the use of an IGBT module can improve the efficiency of the converter and is more conducive for heat dissipation.