Gate Control Optimization of Si/SiC Hybrid Switch for Junction Temperature Balance and Power Loss Reduction

The hybrid switch concept of paralleling a higher-current main Si IGBT and a lower-current auxiliary SiC mosfet offers an improved cost/performance tradeoff in power converters. Currently, the gate control strategy of these two internal devices emphasizes on minimizing the total power loss, and is referred to as the efficiency control mode in this paper. However, there is a serious risk of overheating and reliability degradation of the SiC mosfet if solely relying on this control strategy. In this paper, we propose a new method of gate control optimization, referred to as the thermal balance control mode, to keep the junction temperature of both devices within the specified temperature range, and to minimize the total power loss simultaneously. We first investigate the dependency of the hybrid switch switching losses on the gate control pattern both theoretically and experimentally. We then extensively study control optimization in these two distinct control modes in a dc-dc boost converter. It is found that the thermal balance control mode can achieve almost the same total power loss as the efficiency control mode, but much lower and more balanced junction temperatures of the two internal devices. Experimental results demonstrate that the Si/SiC hybrid switch in an optimal thermal balance control mode can achieve a 163% higher power handling capability in the 20-kHz boost converter or four times higher switching frequency in the 4-kW boost converter than a single IGBT solution with hard switching condition, and yet a considerably lower component cost than a single SiC mosfet solution in the boost converter.