Overload protection for a DC to AC conversion apparatus including an N-phase inverter

摘要

A thyristor inverter having N parallel branches is controlled by an impulse supply source which normally excites the individual thyristors in each branch in cyclic succession. In the presence of an overload in a branch, the impulse source is switched to an override mode which simultaneously excites all of the inverter thyristors. A coil disposed in each of the inverter branches defines, with a reactive circuit including a storage capacitor connected across the branches, an oscillatory circuit. The inductance of the branch coils is chosen such that during the override mode, the oscillatory current is larger in magnitude than the overload current. The inverter thyristors are thus extinguished during the half-cycle of oscillation in which the polarity of the oscillation opposes that of the overload current. After such quench, the impulse source may either be disabled to prevent re-ignition of the thyristors, or switched back to its normal mode.