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 capacitors voltage, 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, 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 a 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.

A novel single-phase nine-level switched-capacitor inverter (9LSCI) is presented with quadruple boost ability and reduced components. The proposed topology with single dc source employs only eight switches to realize nine-level output, self-voltage balance of capacitors, quadruple boost and inductive-load ability, thus, the effective cost is cut down compared to other switched-capacitor multilevel inverters (SCMLIs). Different from other SCMLIs, the proposed 9LSCI has no need for back-end H-bridge, of which four switches need to withstand the peak voltage of output. Hence, total standing voltage can be reduced. The operation principles containing the self-voltage balance of capacitors are described in detail. The quantitative comparisons, modified cost function, as well as the loss evaluations are examined in depth. Finally, multicarrier phase disposition pulsewidth modulation method is adopted and a laboratory prototype is implemented with the rated output of 220 V–500 W. The experimental results also verify the feasibility of the proposed topology.

In this paper, a quasi-resonant switched-capacitor (QRSC) multilevel inverter (MLI) is proposed with self-voltage balancing for single-phase high-frequency ac (HFAC) microgrids. It is composed of a QRSC circuit (QRSCC) in the frontend and an H-bridge circuit in the backend. The input voltage is divided averagely by the series-connected capacitors in QRSCC, and any voltage level can be obtained by increasing the capacitor number. The different operational mechanism and the resulting different application make up for the deficiency of the existing switched-capacitor topologies. The capacitors are connected in parallel partially or wholly when discharging to the load, thus the self-voltage balancing is realized without any high-frequency balancing algorithm. In other words, the proposed QRSC MLI is especially adapted for HFAC fields, where fundamental frequency modulation is preferred when considering the switching frequency and the resulting loss. The quasi-resonance technique is utilized to suppress the current spikes that emerge from the instantaneous parallel connection of the series-connected capacitors and the input source, decreasing the capacitance, increasing their lifetimes, and reducing the electromagnetic interference, simultaneously. The circuit analysis, power loss analysis, and comparisons with typical switched-capacitor topologies are presented. To evaluate the superior performances, a nine-level prototype is designed and implemented in both simulation and experiment, whose results confirm the feasibility of the proposed QRSC MLI.

This paper proposed a single-source multilevel inverter (MLI) based on the novel K-type unit (KTU). The 13-level topology with two KTUs and 1.5 voltage gain is firstly introduced and its operation modes at different output levels are described in the paper. The two capacitors in series connection of each KTU can get self-voltage balance due to their symmetric operation in a cycle, reducing the complexity of control compared with conventional MLIs. The analysis of self-balance and capacitance calculation are given in detail. Afterward, the single-source generalized structure equipped with more KTUs is presented for increasing output levels. The output levels are significantly increased with additional KTUs, and the voltage gain rises as well. Moreover, through the comparative study against other MLI topologies proposed in recent years, the advantages of the proposed KTU topology are indicated in the aspects for reduced components, self-balance, voltage stress, and overall cost. Finally, the 13-level simulation and 1kVA experimental prototype with fundamental frequency modulation are implemented to verify the feasibility and transient performance of the proposed topology.

This paper proposes a new active-neutral-point clamped (ANPC) seven-level inverter based on switched-capacitor technique. The proposed seven-level inverter employs only nine switches and one floating capacitor. With the input amplitude of VDC, the peak output of the proposed topology can reach 1.5VDC. Its boost ability indicates a wider range of output compared with other APNC converters. Needless for auxiliary control methods, the voltages of capacitors in dc link can naturally maintain at 0.5VDC, and the floating capacitor can get self-balance at VDC. The mechanism of natural balance for capacitors and operation principle of the proposed topology are described in detail. The merits of the proposed topology on reduced components, lower overall voltage stress, natural balance, and boost ability are also demonstrated through the comparison against the latest similar topologies, showing its suitability for distributed generation, electric vehicle, and other applications. Definitively, the simulation and experimental prototype are implemented to verify the feasibility and performance of the proposed topology. The voltage balance of capacitors has been fully demonstrated through multiple transient experiments.