Stabilization of Bank Selection in No-Circulating Cycloconverter by Means of Reliable Current-Zero and Current-Polarity Detection

A new method is presented of detecting the output current zero-point and polarity in a no-circulating cycloconverter (NCC) of the continuous current type. Reverse polarity characteristics of series thyristor-diode networks are used for this purpose. This method, which assumes an inductive load, is based on the following principles. 1) When a reverse voltage is suddenly applied to the circuit, the voltage drop at the diode terminals becomes almost equal to the impressed voltage at that instant and then decays to zero gradually. (2) When the series circuit is reverse- biased and a positive polarity trigger pulse is applied to the thyristor gate, almost all of the biasing voltage appears across the diode terminals at the triggering instant before decaying to zero.