Novel High-Efficiency Frequency-Variable Buck–Boost AC–AC Converter With Safe-Commutation and Continuous Current

In this article, a novel high-efficiency single-phase frequency-variable buck-boost ac-ac converter is proposed. AC input voltage can be bucked and boosted with step-changed frequency operation. In the topology, only six switches and total ten semiconductors are utilized, which is at the lowest level among existing works. Only two of the switches are operating at high frequency and only one switch is switched on and off in each switching period, Therefore, the proposed converter has less power loss and features high efficiency. With simple and flexible control strategy, the converter is immune of commutation problem and thus no additional safe-commutation strategy or snubber circuit is needed. Power density of proposed converter is high considering the volume metric of the energy storage components. Moreover, the input current of proposed ac-ac converter is continuous. Therefore bulky input filter required by other existing works is totally removed, which further improve the power density. Operation principles and circuit analysis is provided. To verify the performance, a 200-W laboratory prototype is constructed and experiments are conducted in operation of buck and boost mode at step-changed output frequency of 30, 60, and 120 Hz.