Dual-Tap Chopping Stabilizer With Subcyclic AC Soft Switching

AC voltage and phase regulators based on tap changers implemented with silicon-controlled rectifiers and triacs are widely used due to their robustness. Tap changing is achieved under natural commutation of semiconductors during the zero crossing of current, so that the response time exceeds the half cycle of the mains. High-power transistors and gate turn-off thyristor switches make new and faster tap commutation techniques possible to achieve several tap changes in one half cycle. This paper analyzes and synthesizes a dual-tap chopping stabilizer with a compensating transformer, with a pulsewidth-modulation frequency of about 5 kHz and a new soft-switching technique achieved by two auxiliary small-power branches. Unlike other supercyclic ac soft-switching solutions, the new commutating method allows zero current turn-off, several times in a half cycle, for any sign combination of voltage and current, thus reducing the electrical stress in the switches and the electromagnetic emission. Zero-crossing current detection is not needed. A technical study and an evaluation of the power of the required components are done on the commutation techniques that extend the application field of tap changers to the reduction of the fast perturbations of the mains as flicker, voltage harmonics, voltage oscillations, etc. Experimental results with insulated-gate bipolar transistor switches are obtained in a 1 kVA prototype.