Critical Inductance and Controlled Rectifiers

The design of an inductive input filter for a rectifier requires a certain minimum value of inductance in order to have a continuous current in the inductor and, therefore, maintain good regulation. This value is known as the critical inductance. Overbeck determined the critical inductance as a function of firing angle in a controlled rectifier. In this paper we add a diode to the filter which provides a path for the inductor current in the prefiring interval of the controlled rectifiers. We show that for any fixed firing angle the critical value of inductance is reduced and, therefore, for a given inductor that the usable range of dc output is extended.