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-boost types. A PWM AC chopper has important advantages compared with the phase-controlled AC controller using thyristors. The AC chopper has sinusoidal current waveforms, better power factor, faster dynamics, and smaller input/output filter. In an improved topology for AC choppers, an RC bypass snubber is used for minimising high-voltage spikes during the dead time in the gating signals of complementary switches. In the proposed topologies the commutation problem causing high-voltage spikes is resolved by intelligent gate-switching patterns using information from the input/output voltage. These switching patterns provide a current path for all operation modes without any RC bypass snubbers. Since RC bypass snubbers causing power loss are eliminated, the efficiency of the chopper is increased. Thus, advantages of the proposed topologies include increased power factor, low harmonic input current, fast dynamics, high efficiency, high reliability, high power capacity, and small size of the passive filter. The paper describes the operational principle and analysis of the proposed topologies. Experimental results show that the proposed topologies give good performance for AC choppers