Active Optical Modulation for Series-Connected Emitter Turn-OFF Thyristors

Series connection of high-power thyristors is proposed in the literature for high-voltage applications. Due to the high dv/dt across series-connected thyristors during turn-OFF, charge equalization techniques have been pursued that increase the fall time to avoid overshoot voltage and device breakdown. Longer fall time for thyristors yields reduced switching frequency and increased losses. As such, a new method to control turn-OFF transition for the series connection of recently developed optical emitter turn-OFF (o-ETO) thyristor is outlined in this letter. The turn-OFF speed of series-connected o-ETOs and their voltage balance are controlled by modulating the optical intensity of the triggering (instead of the high-power) device of the o-ETO.