SiC MOSFET switching voltage sensing probe based on electric field coupling principle

Abstract

Power devices are the core of electrical power conversion. Accurate measurement of device switching voltage can optimize switching behavior, evaluate switching loss, and provide important guidance for the design of power conversion systems. Wide bandgap semiconductor devices represented by SiC MOSFETs exhibit high-speed switching characteristics, and traditional commercial voltage probes are difficult to meet the measurement requirements of low interference, strong anti-interference, high bandwidth, and small volume simultaneously. Therefore, a coaxial cylindrical voltage probe was proposed based on the principle of electric field coupling. The probe reduces the intrusion capacitance by surrounding the lead end with sensing electrode, and achieves the suppression of ambient noise by applying the strong immunity structure of shielded copper cladding, via array and shielded copper tube. In addition, finite element simulation was used to guide the scheme of probe parameter selection and verify the noise suppression ability of the shielding structure. Moreover, the mechanism by which coaxial probes effectively reduce invasiveness was analyzed in detail from a theoretical perspective. The designed coaxial probe has a bandwidth of 280 MHz, a range of - 750 V ~ + 750 V, and an intrusion capacitance of approximately 0. 92 pF. Finally, the double-pulse test demonstrates that the coaxial probe can accurately measure the switching time at the ns level, meeting the measurement requirements of SiC MOSFET switching voltage.