From the Measurement of COSS–VDS Characteristic to the Estimation of the Channel Current in Medium Voltage SiC MOSFET Power Modules

This article presents a novel method for the dynamic measurement of
$C_{\mathrm {OSS}}$
–
$V_{\mathbf {DS}}$
characteristic of SiC MOSFET power modules based on the process of charging the output capacitance of the transistors. This technique has been used to determine the
$C_{\mathrm {OSS}}$
–
$V_{\mathrm {DS}}$
characteristics of medium voltage SiC MOSFET modules, which allows for the extraction of the capacitive current while switching off the transistor. Based on this measurement method, the influence of the turn-off gate voltage
$V_{\mathrm {GS-OFF}}$
on the
$C_{\mathrm {OSS}}$
–
$V_{\mathrm {DS}}$
characteristics has been studied, exhibiting an impact on the output capacitance at low drain–source voltages. However, it is shown that the effect of
$V_{\mathrm {GS-OFF}}$
on the capacitive current and power loss is limited in this area. Finally, the channel current and the capacitive current distribution within the drain current were determined based on the determined
$C_{\mathrm {OSS}}$
–
$V_{\mathrm {DS}}$
in the experimental test at various switched currents and switching speeds. According to the capacitive charge calculations for several cases, the method’s accuracy is high enough to perform switching power loss estimations for medium voltage power modules to be employed in the design of the state-of-the-art power converters. Furthermore, the method is very simple, based on basic capacitance equations, and the required experimental setup is very similar to one used in double-pulse tests.