Inaccurate Switching Loss Measurement of SiC MOSFET Caused by Probes: Modelization, Characterization, and Validation

SiC metal-oxide-semiconductor field-effect transistor (MOSFET) has a fast switching speed and high slew rate. However, its ultrashort switching time approximates the rise time and propagation delay of the measurement instruments, which results in an inaccurate assessment of the switching loss and challenges the thermal design of the power converter. In this article, aiming to reveal the principles of accurate measurement for the switching behavior of SiC MOSFET, insightful models are proposed for baseline probes and transient trajectories to characterize the measurement error of the switching losses. By using the Gaussian function, the mathematical models for the rise time, bandwidth, and propagation delay of the measurement instruments are achieved, which is also confirmed by the surveyed specifications of commercial probes. Concerning the accurate measurement, the turn-on and turn-off losses of the SiC MOSFET influenced by the rise time and propagation delay of probes are comprehensively modeled and characterized. With respect to different current probes, voltage probes, and gate driver resistances, extensive experiments are demonstrated to confirm the validity of the proposed models. The experimental findings are in line with the conducted predictions of the proposed models. It is found that, due to the very fast switching transients of the SiC MOSFET, the limited bandwidth and inevitable propagation delay of measurement instrument may result in a prominent error of the switching loss and impede the widespread implementation of the SiC MOSFET.