Abstract: IGBT has been used in many power electronic applications,especially in the voltage source converters,and the power loss analysis of IGBT is one of the main works in power electronics.This paper presented an improved waveform fitting model to analyze power losses of IGBT and diodes in voltage source converters.It took into account variety of diode’s reverse recovery parameters with varied currents in different switching periods of the converters.This model also included dependency of collector-emitter voltages,currents,junctional temperature,and stray inductance,especially the tail current of IGBT.The validity of this model was further demonstrated by a 2.5 kV-rated boost converter.The experimental results were in accord with analytic results of the presented model.This power loss model can be applied in power loss analysis of high voltage and high power applications,such as voltage source converters,high voltage direct current transmission（VSC-HVDC）,static synchronous compensators（STATCOM） and unified power flow controllers（UPFC）.