Integral assessment criterion of commutation margin in line commutated thyristor inverter at states of asymmetry in the power system

Line commutated thyristor inverters used for energy transmission to the power system from DC constant voltage sources (e.g. MHD generator, regenerative load testing of large internal combustion engines, etc.) need special control procedures against AC fault conditions. The authors propose a new original system for determination of the minimum angle of thyristor triggering advance at short circuits. The system reported predicts the required commutation margin. It analyses current load and time integral of the waveform of commutation voltage. The authors present a schematic block diagram and performance of the inverter control system at different states of operation. Theoretical considerations are illustrated by exemplary waveforms of inverter current and thyristor voltages at faults in the power system. The waveforms were obtained by digital simulation. The reported inverter system is immune to the states of voltage asymmetry in AC mains. It can co-operate with either a synchronous or an asynchronous controller