Symmetric/Asymmetric Hybrid Multilevel Inverters Integrating Switched-Capacitor Techniques

In conventional hybrid multilevel inverters (MLIs), the voltage balance controls of floating capacitors are usually realized by redundant switching states using high-frequency modulation. The switching frequency, as well as the switching loss, is hence increased, and the topologies are limited to low-frequency output occasions as a result. In switched-capacitor MLIs (SCMLIs), the capacitors are self-balanced, since they are charged to fixed voltage levels by the input source directly or indirectly. By integrating switched-capacitor techniques into conventional hybrid MLIs, a pair of symmetric/asymmetric hybrid MLIs is proposed in this paper with boost ability. Complicated balance controls are avoided for capacitor voltages, and thus the modulation gets simplified. Compared with SCMLIs, the backend H-bridges that withstand the accumulated voltage stress are removed. The peak inverse voltages of devices are decreased, and thus only low-voltage components are needed. Meanwhile, the component numbers are reduced greatly. All these advantages contribute to high efficiency and reduced costs. Consequently, the proposed hybrid MLIs are especially appropriate for synthesizing a staircase output directly from an input source of low voltage. Analyses and their operational principles are firstly presented for the proposed topologies. Comparisons are then carried out to illustrate their superiority. To evaluate the performance, simulation and experimental prototypes are implemented, whose results confirm the feasibility of the proposed hybrid MLIs.