Research on a novel three-level AC chopper and voltage controlling method of the flying-capacitor

A novel three-level AC chopper is proposed, which is a new multi-level converter applied to high voltage conversion, and utilizes more electric levels to form output voltage and decrease the harmonic content of output waveform. A stable flying capacitor voltage must be maintained to facilitate the operation of the chopper. When the circuit is working, there are two switching modes corresponding to the same voltage level, but the current direction in flying-capacitor is opposite, so the voltage of flying capacitor can be controlled by the ratio of the two different modes with the same voltage level. The detail control method of flying-capacitor voltage is discussed. Experiments were carried out to confirm its working principle.