Experimentally Extracting Multiple Spatial Thermal Models that Accurately Capture Slow and Fast Properties of Assembled Power Semiconductor Converter Systems

Models describing transient heat transfer within power electronics are commonly formed using step response curves and numerical models. Unfortunately, data sheet transient thermal impedance curves only characterize the junction-to-case spatial domain segment. Also, computationally intense transient numerical models require a detailed specification procedure. This paper presents an experimental methodology to capture thermal response properties of assembled power semiconductor converter systems, including fast (die-level) and slow (sink-level) modes. The method utilizes semiconductor devices as modulators of dynamic loss (heat) injections, and discrete temperature measurements, to form multiple thermal impedance models using the frequency response function (FRF) metric. Complementary investigation of numerical and analytical models yields a general, compact thermal model topology including a physics-based, spatiotemporal delay term, critical for correctly interpreting FRFs. The evaluation utilizes a power converter having integrated temperature sensing. Ambient-referred and relative FRF results are obtained across wide frequency ranges and are parameterized using the compact thermal model.