Active Gate Drive with Gate-Drain Discharge Compensation for Voltage Balancing in Series-Connected SiC MOSFETs

TL;DR

This paper introduces a novel active gate drive with gate-drain discharge compensation to improve voltage sharing in series-connected SiC MOSFETs, using an auxiliary circuit that requires no extra isolation and is compatible with existing drives.

Contribution

It proposes a new active gate drive design that compensates for discharge deviations, enabling effective voltage balancing without additional isolation or device limitations.

Findings

Effective voltage balancing demonstrated in experiments

No extra isolation needed for the auxiliary circuit

Compatible with existing commercial gate drives

Abstract

Imbalanced voltage sharing during the turn-off transient is a challenge for series-connected silicon carbide (SiC) MOSFET application. This article first discusses the influence of the gate-drain discharge deviation on the voltage imbalance ratio, and its primary causes are also presented and verified by LTspice simulation. Accordingly, a novel active gate drive, which aims to compensate the discharge difference between devices connected in series, is proposed and analyzed. By only using the original output of the driving IC, the proposed gate drive is realized by implementing an auxiliary circuit on the existing commercial gate drive. Therefore, unlike other active gate drives for balancing control, no extra isolations for power/signal are needed, and the number of the devices in series is unlimited. The auxiliary circuit includes three sub-circuits as a high-bandwidth current sink for regulating switching performance, a relative low-frequency but reliable sampling and control circuit for closed-loop control, and a trigger combining the former and the latter. The operational principle and the design guideline for each part are presented in detail. Experimental results validate the performance of the proposed gate drive and its voltage balancing control algorithm.