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This paper investigates and compares the cooling performance and power conversion efficiency of insulated gate bipolar transistors (IGBT) subjected to various cooling methods in grid connected inverter systems. First, the primary mechanisms responsible for heat generation within IGBT and their associated thermal conduction paths are analyzed. Next, the operating principle, structural configuration, and inherent advantages of dielectric immersion cooling are explained in detail. To evaluate the cooling effectiveness of the immersion method, a dedicated experimental test environment is established, and compatibility assessments are conducted to verify that dielectric immersion does not adversely affect the electrical characteristics or physical integrity of the IGBT modules. Comparative experimental analyses are carried out on a 400kW inverter using three cooling strategies: forced air cooling, liquid cooling, and dielectric immersion cooling. Measurements and analyses are focused on the junction temperature of the IGBTs, ambient temperatures, and overall power conversion efficiency under steady state operating conditions. Finally, based on these experimental outcomes, the feasibility of implementing dielectric immersion cooling in grid connected inverter applications is examined.