Full-Duty-Cycle Regulated Three-Level AC/AC Converter With Self-Following Flying Capacitor

The three-level (TL) AC/AC converter needs to control the output voltage as well as the voltage of flying capacitor, which makes the control circuit relatively complicated. At the same time, the ranges of the output voltage and load are limited because of the influence of the flying capacitor voltage correction on the duty cycle of the output voltage. For the applications of high-voltage and high-power conversion, a full-duty-cycle-regulated TL AC/AC converter with a self-following flying capacitor was proposed and studied, which adopts a small volume auxiliary transformer. The flying capacitor is directly supplied from the auxiliary transformer, can self-follow half of the input voltage, and does not need to be controlled by other control circuit. The proposed converter only needs to control its output voltage, which makes control strategy simple and easy to be realized. The output voltage can be regulated within the range of full-duty cycle. The capacity of an auxiliary transformer is very small, under ideal condition which only needs to supply the reactive load of the flying capacitor. The circuit operational principle was analyzed in detail, and a prototype was designed. With a simple control circuit, the experimental results were given and the full-duty-cycle regulation of the TL AC/AC converter was realized.