Generalized Topology of a Hybrid Switched-Capacitor Multilevel Inverter for High-Frequency AC Power Distribution

The generalized topology of a hybrid switched-capacitor multilevel inverter (SCMLI) for high-frequency ac (HFAC) power distribution system is presented. By employing the series-parallel conversion technique, the proposed SCMLI can achieve self-balancing of capacitor voltages and voltage step-up with arbitrary numbers of SC cells. The output power quality is improved by the intermediate voltage levels provided by the bidirectional switched converter connected to the dc source string. Besides, several active switches can be replaced with diodes if the large phase difference between output current and voltage is not required. Since the voltage ripple magnitude of the SC units is inversely proportional to the fundamental output frequency, the proposed SCMLI is more preferable for HFac applications. This paper elucidates the working principle of the proposed inverter with the detailed circuit and switching states' description under staircase modulation. The mathematical analyses associated with the capacitor voltage ripples, sizing, and power loss are also provided. A 19-level MLI with a voltage gain of three was realized by cooperating two SC units with a voltage source string consisting of three symmetric dc sources. The operation and performance of the proposed inverter have been validated by the simulation and experiment on the inverter. The results showed that the inverter performed better at HFac condition and the power quality was satisfactory with the 19-level staircase output modulated at the fundamental frequency.