SCR inverter commutated by an auxiliary impulse

THE KEY to efficient inverter circuits, using silicon controlled rectifiers (SCR's), is the method of commutation — the process of transferring current from one controlled rectifier to another. When feedback rectifiers are used to provide an alternative path for reactive load current, the size of the commutating components can be greatly reduced,1 and the commutation transient takes the form of an impulse. This impulse must be large enough to extinguish the current in the conducting controlled rectifier and long enough to provide inverse voltage for the required turn-off time. In many inverters,1 commutation is initiated by turning on the controlled rectifier that is complementary to the one being turned off. This paper describes a new circuit in which the commutating impulse is initiated by gating auxiliary controlled rectifiers. The inductance-capacitance (LC) pulse circuit is separate from the main power circuit except during commutation.