A constant extinction angle control for a magnetohydrodynamic generator inverter system

There is a need to provide efficient, economical, and reliable power conversion from the direct current output of magnetohydrodynamic generators to the alternating current of an AC power grid. A study was made on inverter systems and the current-fed line-commutated inverter (CFLCI) was found to be the most likely long range candidate for achieving this purpose. A significant factor affecting the choice was the method of inverter control and simplicity of design. The method of control found to work best with the CFLCI was the constant extinction angle (CEA) control. CEA control can provide the CFLCI with near unity power factor under DC and AC voltage variations consequently reducing the KVA rating of the transformers needed, minimizing the stress in thyristor valves, and increasing the efficiency of the inverter, among other advantages. Even though the power factor is kept as near unity as possible, this method of control eliminates, almost entirely, the threat of commutation failures.

The concept of CEA control is presented in considerable detail. In the laboratory, a CEA control circuit was design, built, and calibrated to handle the variations in direct current encountered in a lOOA experimental model CFLCI.