Cycloconverter Control Circuits

Cycloconverter control circuitry is discussed using examples from a practical three-phase to single-phase circulating current free cycloconverter. The voltage biased cosine wave technique is used for phase control. Phase-forward and phase-back limit (PBL) pulses are superimposed on each cosine wave. Spurious gating pulses in the range 180° to 360° are suppressed. A new current zero detector is presented involving continuous monitoring of the voltage across each thyristor. Two types of circulating current elimination logic are used, suitable for 1)resistive and lagging loads, and 2)leading, resistive, and lagging loads. Auxiliary gate pulses are supplied to the incoming converter to prevent large gaps in the load current waveform.