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

The increase in the application of medium voltage variable frequency drives and solid state starters to AC motors has revived the idea about 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 SSGD with capacitor as storage element. Results of extensive research conducted using 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 single SCR and back to back SCR in different topology at medium voltage are presented and discussed. It is shown that for single SCR, only voltage across the SCR is used to charge the storage capacitor, while for back to back SCR 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 AC/AC converter in solid state starters and thyristor input rectifier in a drive are given for practical assessment of the proposed system. The SSGD has already been successfully applied in medium voltage solid state starters, and some experimental results are presented.