Abstract
Increase in the capacity of GTOs has made remarcable progress in recent years. At present, 4.5kV-4.0kA GTOs are commercially available. Now, 6kV-6kA GTOs which are made from 6-inch silicon wafer are developing. The 6-inch GTOs are going to be applied to our 3-level GTO inverter system. In order to apply GTOs to voltage-source-inverters snubber circuits are necessary for limiting on turn-on di/dt and turn-off dv/dt. To realize the system of high efficiency, regenerative snubber circuit is applied. A conventional circuit, which could be applied to 3-level GTO inverter, had a problem that long paths are created for snubber circuits of inner GTOs. In order to solve the problem, a circuit using a transformer which is provided for recovering the trapped energy of snubber circuits for inner GTOs was presented. In this paper, newly regenerative snubber circuit is proposed, which is more suitable for 3-level GTO inverter system with many phase-legs. By applying this snubber circuit, snubber energy generated by the switching of all GTOs' in the main circuit can be regenerated to DC-link capacitors. High turn-off capability of both inner GTO and outer GTOs are verified by several successful experimental results using 6-inch (6kV, 6kA) GTO.
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