Novel low-loss active voltage clamp circuit for series connection of RCGCT thyristors

Abstract

This paper describes novel low-loss active voltage clamp circuits for the series connection of RCGCT thyristors. For high-voltage converters the series connection of power semiconductor devices is an essential technique for direct switching of high voltages. Several protection circuits have been applied to the series connection of RCGCT thyristors such as CRD snubber circuits which suppress overvoltages across RCGCT thyristors, and voltage balancing resistors to equalize voltage sharing in steady states. However, significant losses in these protection circuits were the converter's efficiency. We propose novel low-loss protection circuits, which have active voltage clamp snubber circuits and static voltage balancing circuits. The clamp capacitor voltage of the active voltage clamp snubber circuits is designed to be higher than the equally divided DC-link voltage. This method can reduce the loss of the clamp circuit to no more than 1/10 of that of the conventional CRD snubber. Also, the static voltage balancing circuits compensate for the voltage imbalance generated by the difference in the leakage current between the series connection RCGCT thyristors. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 153(1): 42–53, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20193