Online Junction Temperature Estimation for IGBT Devices Through Knee Voltage

On-state saturation voltage of insulated gate bipolar transistor (IGBT) devices at low current levels has been widely employed for offline junction temperature evaluation but rarely implemented online. This article investigates the IGBT on-state voltage at conduction currents ranging from tens to over one hundred milliamps, identified as knee voltage. A practical implementation for online junction temperature estimation using knee voltage in an operating power converter is presented, encompassing data acquisition and processing as well as a converter-level calibration scheme. The knee voltage is acquired from the zero-crossing transient of the converter current, and the relationship between junction temperature and knee voltage is calibrated with converter start-up events, which can be accomplished in a short term with an accuracy comparable to offline calibration. The uncertainty imposed by converter operating conditions on the estimation accuracy is comprehensively analyzed and corresponding solutions are given. The component-level characterization tests and converter-level proof-of-concept experiments validate the feasibility and effectiveness of the proposed method.