This paper proposes an online dynamic electro-thermal model to compute the junction temperature of an IGBT under real time operating conditions. The proposed computational model is based on transient thermal capacitance and power loss calculations. Insulated Gate Bipolar Junction Transistor is popularly used in mission safety critical applications such as aerospace. Usually mission critical application requires well-designed thermal management to ensure the safety of power devices from thermal runaway. Hence, real time estimation of the junction temperature has become more important to develop health monitoring model as well to predict the lifetime of power converter system. In order to analyze the accuracies of the junction temperature estimation method, the results from the proposed dynamic electro thermal model is compared with the experimental results (measured junction temperature) obtained from the laboratory test rig.