Dual-tap chopping stabilizer with mixed seminatural switching. Analysis and synthesis

Onload tap changers based on silicon-controlled rectifiers or triacs are widely used to regulate ac voltage. Response time is bigger than half-cycle due to the natural commutation used during the zero-current crossing. N. Burany proposed a commutation method for direct ac/ac matrix converters based on power transistors, or other switches with active turn-off, by permitting a freewheeling current path during commutation. This can be applicable to tap changers and release commutation from the zero-current crossing, thus allowing a faster voltage regulation. This paper presents a new two-tap chopped ac/ac voltage stabilizer with compensating transformer and PWM frequency in the order of 5 kHz based on this kind of commutation. The circuit proposed, resulted from a topology search guided by an iterative analysis+synthesis cost comparative method, fits well to low voltage stabilizers and regulators in the range of 0.1 to 1000 kVA and 1 ms response time. The switching behavior and the input and output filtering is fully analyzed. An exhaustive synthesis study follows, giving the component rates as a function of the equipment specification. This allows an easy equipment cost evaluation. Experimental results with IGBT switches are obtained in a 1 kVA prototype.