Infrared thermal imaging analysis of a 1-kW variable capacity compressor frequency inverter

The present paper deals with the experimental characterization via infrared thermography of the temperature distribution in the electronic components of a frequency inverter of a 1-kW cooling capacity variable-speed refrigeration compressor. The transient thermal behavior was measured at the maximum compressor cooling capacity, and the tests were kept as closely as possible to real operating conditions by having the compressor connected to a hot-gas cycle calorimeter during the experiment. The printed circuit board was kept inside the hard plastic enclosure designed to protect the electronic components from airborne dust particles and moisture. Therefore, the experimental analysis involved the application of infrared-transparent material (plastic tape) on specific regions of the plastic enclosure to allow visual access to the electronic components. The infrared transmissivity of the plastic tape was experimentally determined as part of the analysis. The results reveal details about the thermal interaction between the components and confirm the applicability of infrared thermography in the analysis of heat transfer effects inside closed cavities. The insulated-gate bipolar transistors exhibited the largest and fastest variation among all components, while the capacitors presented the smallest temperature change. Agreement between infrared thermography and calibrated type-T thermocouples was within +/- 3 degrees C at steady state for some components.