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

Abstract

Wide-band-gap technologies enable ultra-high efficiencies in high-frequency power conversion. However, inadequate accuracies in electrical measurements could lead to spurious efficiency measurements, even above 100%. Furthermore, bandwidth limitations, particularly for 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 with high-frequency excitations. Calorimetric methods overcome this issue by a direct loss measurement through the generated heat. Nevertheless, limited ranges and accuracies of 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 adjustable cooling and can measure losses down to 500 mW, enabling the evaluation of highperformance power converters and their components with no dependencies on the geometries of the evaluated devices or systems.

Calibration-Free Calorimeter for Sensitive Loss Measurements: Case of High-Frequency Inductors

“…The proposed calorimeter [21] enables geometry-independent loss measurements by transferring the heat to the water through heat-exchangers (convection) and cold plates (conduction). Two identical heat-insulated chambers are placed inside an outer chamber that isolates the calorimeter from the ambient (See Fig.…”

“…DC calibrations were performed to verify that both chambers are identical and to ensure that the measurement method has no dependency on the geometry of the DUT [21]. As illustrated in Fig.…”

“…The calorimeter is suitable for evaluating losses up to 100 W; nonetheless, evaluating lower losses requires a much higher sensitivity. Our proposed double-chamber closed-type calorimeter [21], shown in Fig. 1, overcomes the limitations of the aforementioned methods by: 1) Reducing flow rate drastically for achieving higher sensitivity.…”

Active-Device Losses in Resonant Power Converters: A Case Study with Class-E Inverters

“…Thus, a direct and accurate method to measure hysteresis losses during actual circuit operation is required. On the other hand, existing calorimetric methods involve relatively slow systems that are also limited in accuracy, especially in mW-range power levels [13]. Furthermore, they often determine system-level losses, and therefore, lack the ability to perform a complete loss break-down of a real converter in operation.…”

Small-Signal Approach for Precise Evaluation of Gate Losses in Soft-Switched Wide-Band-Gap Transistors

“…Due to several limitations, direct electrical measurements (especially for the gate current) are not feasible [18], [19]; however, one can alternatively measure dc power fed to the gate driver to extract overall PG.…”