Analysis and Comparison of a Fast Turn on Series IGBT Stack and High Voltage Rated Commercial IGBTS

High voltage rated solid-state switches such as insulated-gate bipolar transistors (IGBTs) are commercially available up to 6.5 kV. Such voltage ratings are attractive for pulsed power and switch-mode converter applications. However, as the IGBT voltage ratings increase, the rate of current rise and fall are generally reduced. This trade-off is difficult to avoid as IGBTs must maintain a low resistance in the n" epitaxial or drift region layer. For high voltage rated IGBTs with thick drift regions, the high carrier concentrations are injected at turn-on and removed at turn-off, which slows the switching speed. An option for faster switching is to series multiple, lower voltage rated IGBTs. A customized IGBT stack with six, 1200 V rated IGBTs in series has been experimentally tested. The six-seriesed IGBT stack consists of individual, optically isolated, gate drivers and aluminum cooling plates for forced air cooling which results in a compact package. Each IGBT is overvoltage protected by transient voltage suppressors. The turn-on current rise time of the six-series IGBT stack and a single 6.5 kV rated IGBT has been experimentally measured in a pulsed resistive-load capacitor discharge circuit. The IGBT stack has also been compared to a two seriesed IGBT stack, each rated at 3.3 kV, in a boost circuit application switching at 9 kHz and an output of 5 kV. The six-series IGBT stack results in significantly improved power conditioning efficiency due to a reduced current tail during turn-off. The experimental test parameters and the results of the comparison tests are discussed in the following paper.