SCR self-supplied gate driver for medium-voltage application with capacitor as storage element

The resent increase in the application of medium-voltage variable-frequency drives and solid-state starters to AC motors has revived the idea of the SCR self-supplied gate driver (SSGD). This solution eliminates the need for an isolated power supply board or auxiliary power supply, with substantial savings in cost and space in medium-voltage applications. In this paper, the objective has been to confirm a design method for an SSGD with a capacitor as the storage element. Results of extensive research conducted using a PSpice model to calculate the voltage drop on the storage capacitor due to the thyristor gate current and the SSGD ability to restore charge for a single SCR and a back-to-back SCR in different topologies at medium voltage are presented and discussed. It is shown that, for a single SCR, only voltage across the SCR is used to charge the storage capacitor, while for the back-to-back SCR, the storage capacitor restores charge from energy stored in the snubber capacitor at turn-on and the voltage across the SCR at turn-off. A number of waveforms related to the AC/AC converter in solid-state starters and the thyristor input rectifier in the drive are given for practical assessment of the proposed system. The SSGD has been already successfully applied in medium-voltage solid-state starters, and some experimental results are presented.