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By using a single dc voltage source to feed a 4-level switched-capacitor (SC) unit and a 3level NPP/NPC unit simultaneously, a new 9-level inverter is developed in this work. The 4-level unit is implemented by cascading an inverting half-bridge with a double-or half-mode SC circuit. It involves four transistors, two diodes and two capacitors with self-balanced voltage. Inrush charging current variation di/dt of capacitors at switching instants is successfully suppressed by inserting a small inductor into the SC unit. Compared with the existing solutions for 9-level inverters, the proposed circuit has the advantages of simpler structure and lower cost per level. These make the proposed inverter very suitable for low voltage applications such as PV and fuel cells. Circuit configuration, operation, system characteristics under POD-PWM modulation are analyzed in detail. Feasibility and dynamic performance are also demonstrated experimentally.

To use fewer components to construct a multilevel inverter (MLI) with more levels and high quality of the output voltage, a hybrid MLI is developed by combining a double-mode switched-capacitor (SC) unit with a T-type unit fed by flying capacitors (FCs). The SC unit is used to boost the amplitude of the output voltage to twice the dc input voltage, while the T-type unit is responsible for increasing the number of output levels. A total of ten transistors, four capacitors, and two diodes are used to generate 17 different levels. As two of the four capacitors are charged by a single dc source directly and the other two operate as FCs, there is no capacitor voltage ripple accumulation (CVRA) problem, resulting in high-quality output voltage. In addition to topology, a voltage balance controller of the FCs is developed to cooperate with the APOD-PWM strategy. Compared with other single-phase SC-based MLIs, the proposed inverter has a lower cost per level. Finally, to verify the feasibility of the proposed inverter, both the simulation model and experimental prototype are established. The results show that the proposed inverter has high-quality output voltage waveform and good dynamic response. The measured efficiency is above 96.5 for a wide range of loads, and the maximum value is up to 98.36. INDEX TERMSMultilevel inverter, switched-capacitor, flying capacitor. XIAOLIN WANG received the B.Sc. degree in electrical engineering and automation from Three Gorges University, Yichang, China, in 2012, and the M.Sc. and Ph.D. degrees from The