A Smart Gate Driver with Active Switching Speed Control for Traction Inverters

The IGBTs are dominantly used in traction inverters for automotive applications. Because the Si-based device technology is being pushed to its theoretical performance limit in such applications during recent years, the gate driver design is playing a more prominent role to further improve the traction inverter loss performance. The conventional gate driver design in traction inverter application needs to consider worst case scenarios which adversely limit the semiconductor devices' switching speed in its most frequent operation regions. Specifically, when selecting the gate resistors, the IGBT peak surge voltage induced by fast di/dt and stray inductance must be limited below the device rated voltage rating under any conditions. The worst cases considered include both highest dc bus voltage and maximum load current. However, the traction inverter operates mainly in low current regions and at bus voltage much lower than the worst case voltage. This paper proposes a low-cost and simple gate driver circuit that can actively adjust the turn-off switching speed based on IGBT current levels. The proposed circuit utilizes the current sensing pin which is widely available for IGBTs used in current generation traction inverters. When the current is low, the switching is speeded up to minimize loss. Under worst cases, it can keep the maximum surge voltage same as the value of conventional gate driver. For applications that the system operates mostly in low current regions, the proposed method can significantly improve the system efficiency.