High-Accuracy Calibration-Free Calorimeter for the Measurement of Low Power Losses

Abstract

Wide-band-gap technologies enable ultra-high efficiencies in the high-frequency power conversion. However, inadequate accuracies in electrical measurements could lead to spurious efficiency measurements, even above 100%. Furthermore, bandwidth limitations, particularly of current probing, delay mismatches between current and voltage probes, loading effects, and electromagnetic interferences, make electrical techniques inappropriate for measuring extremely-low losses in switches with high dv/dt and di/dt values and magnetic components under high-frequency excitations. Calorimetric methods overcome this issue by a direct loss measurement through the generated heat. Nevertheless, limited ranges and accuracies of the existing systems hinder their application in sensitive measurements. Moreover, time-consuming calibrations with extensive data processing impede rapid design assessments. In this work, we propose a closed-type double-chamber calorimeter based on a real-time calibration between two identical chambers to eliminate extra compensation for ambient variations or changes within the system itself. By streaming the same coolant in both chambers, our system removes the need for flow measurements, enabling extremely low flow rates, which improves sensitivity and reduces complexity and system cost. The system provides an adjustable cooling and can measure losses down to 500 mW, enabling the evaluation of high-performance power converters and their components with no dependence on the geometry of the evaluated devices or systems.