Abstract: A hybrid powertrain system includes an engine, an electric machine, a power electronics device including a plurality of electric circuit layers, and a cooling system. A method for managing thermal energy in the power electronics device includes monitoring a plurality of temperature sensors in the power electronics device, monitoring electric power into and out of the power electronics device, predicting temperatures for the plurality of electric circuit layers, and controlling the hybrid powertrain system based upon the predicted temperatures for the plurality of electric circuit layers.