Research on Variable Structure Control Strategy Based on Direct BUCK AC-AC Converter

The researches on direct AC-AC convertors have been an important field. The DC-modulated method, which was used in DC-DC convertors before, is used in AC-AC convertors to realize a direct AC-AC converting now. The method as regulating the duty of switch periods can control the circuit to output an acceptable sinusoid voltage wave. But this method can always bring forth a small phase shift between input and output. In this paper, variable structure control (VSC) is used in BUCK circuit. Simulations for these different control strategies based on the Simulink platform are used to analyze and compare. The result shows that the VSC can reduce the phase shift hardly to zero. In the same time, the switch period of VSC is not unchanged. It's changing following the error. Compared to PWM control method, the VSC can gain a smaller response time and a balance between reducing switching loss and improving quality of output.