NOVEL TOPOLOGIES OF AC CHOPPERS

Novel topologies of pulse-width modulated (PWM) AC choppers for single -phase and three-phase systems are proposed for buck, boost and buck-b oost types. A PWM AC chopper has important advantages compared with th e phase-controlled AC controller using thyristors. The AC chopper has sinusoidal current waveforms, better power factor, faster dynamics, an d smaller input/output filter. In a recent improved topology for AC ch oppers, an RC bypass snubber is used for minimising high-voltage spike s during the dead time in the gating signals of complementary switches . In the proposed topologies the commutation problem causing high-volt age spikes is resolved by intelligent gate-switching patterns using in formation from the input/output voltage. These switching patterns prov ide a current path for all operation snubbers. power loss are eliminat ed, the efficiency of the chopper is increased. Thus, advantages of th e include increased power harmonic input current, fast dynamics, high efficiency, high reliability, high power capacity, and small size of t he passive filter. The paper describes the operational principle and a nalysis of the proposed topologies. Experimental results show that the proposed topologies give good perfomance for AC choppers.