Novel Bipolar Active Miller Clamp for Parallel SiC MOSFET Power Modules

A new Active Miller Clamp (AMC) method to improve the reliability of SiC MOSFETs based converter is presented. The new AMC method is called Bipolar Active Miller Clamp (BAMC). The BAMC consists of 2 clamping mechanisms, which completely bypass the gate resistance and gate loop of the gate driver. In contrast with traditional AMC, the BAMC is capable to bypass not only the Gate incoming path of the gate driver but also the Source returning path to the gate driver power supply. This is a highly valuable feature, especially when power semiconductor devices are connected in parallel for high power applications. When parallel connected IGBTs or SiC MOSFETS are used, the gate resistance (Rg) is split with some portion connected in series with the gate path and the other portion (Rs) in series with the Source path of the semiconductor device, to account for mismatched switching speeds of the parallel devices. The conventional AMC bypasses only the Gate path resistance leaving extra impedance at the Source path where portion of the Miller current, present during high dV/dt conditions, will add a positive voltage to the turn-off voltage and jeopardizing a shoot-thru or undesired gate oscillations. An analysis of the phenomenon is presented and experimental results for a 1.2kV SiC MOSFET confirm our findings.