Study of Voltage Balancing Techniques for Series-Connected Insulated Gate Power Devices

An efficient and cost-effective medium-voltage (MV) power semiconductor switch capable of high switching speed is highly desirable for many existing and emerging high-power MV power conversion applications. The emerging MV silicon carbide (SiC) 10-kV/15-kV MOSFETs and IGBTs can be the potential candidate for these applications. However, high cost, lack of reliability data, and limited availability are the major hurdles for the successful adoption of these devices. Efficient and cost-effective MV switches can also be realized by a series-connected reliable, cost-effective, and commercially available low-voltage (LV) devices. This article reviews various methods to achieve MV switch by series-connected LV power devices. Achieving equal voltage balance among series-connected devices is a challenge that can be addressed by passive snubber, voltage-clamped, gate pulse control, and active gate control techniques. A comprehensive comparison is discussed between these techniques. It concludes that the active gate control is the most effective and efficient solution in ensuring proper voltage balancing at the expense of increased control complexity. A closed-loop active gate driver circuit was developed, and its effectiveness in voltage balancing was verified experimentally.