In this paper, a novel cascaded seven-level inverter topology with a single input source integrating switched capacitor techniques is presented. Compared with the traditional cascade multilevel inverter (CMI), the proposed topology replaces all the separate dc sources with capacitors, leaving only one H-bridge cell with a real dc voltage source and only adds two charging switches. The capacitor charging circuit contains only power switches, so that the capacitor charging time is independent of the load. The capacitor voltage can be controlled at a desired level without complex voltage control algorithm and only use the most common carrier phase-shifted sinusoidal pulse width modulation (CPS-SPWM) strategy. The operation principle and the charging-discharging characteristic analysis are discussed in detail. A 1kW experimental prototype is built and tested to verify the feasibility and effectiveness of the proposed topology.
1. Cascaded seven-level inverter
2. Switched capacitor techniques
3. Carrier phase-shifted sinusoidal pulse width modulation
4. Charging and discharging characteristic
Fig. 1. Topologies of the proposed inverter. (a) The novel single dc source cascaded seven-level inverter. (b) Three-input cascaded seven-level inverter for PV systems.
EXPECTED SIMULATION RESULTS:
Fig. 2. Output voltage and current waveforms. (a) At resistive load. (b) At inductive load. (c) THD value of the output voltage
Fig. 3. Voltage waveforms of the charging-switch. (a) SC1. (b) SC3.
Fig. 4. The capacitor voltage and the charging current waveforms of capacitors C1. (a) RESR=5mΩ. (b) RESR=200mΩ.
A novel single DC source cascaded seven-level inverter integrating switched capacitor techniques is developed in this paper. In the proposed topology, the transformerless charging circuit only contains power switches and capacitors, and the charging time is independent of the load. The operation principle and the charging-discharging characteristic analysis are investigated in depth. With the common CPS-SPWM strategy, the sinusoidal output voltage can be well obtained. Moreover, the capacitors are properly charged without complex voltage balancing control algorithm. The peak charging current and the charging loss can be reduced with appropriate circuit parameters. The proposed topology has the features of modularity, low cost and simplicity of control and makes it attractive in DC-AC power applications. A 1Kw experimental prototype verifies the feasibility of the proposed inverter. The proposed inverter is also suitable for photovoltaic-battery multi-input application with high redundancy.
 S. Kouro, M. Malinowski, K. Gopakumar, J. Pou, L. G. Franquelo, B. Wu, J. Rodriguez, M. A. Perez, and J. I. Leon, “Recent advances and industrial applications of multilevel converters,” IEEE Trans. Ind. Electron. , vol. 57, no. 8, pp. 2553–2580, Aug. 2010.
 H. Abu-Rub, J. Holtz, J. Rodriguez, and G. Baoming, “Medium-voltage multilevel converters; state of the art, challenges, and requirements in industrial applications,” IEEE Trans. Ind. Electron. , vol. 57, no. 8, pp. 2581–2596, Aug. 2010.
 J. Dixon, J. Pereda, C. Castillo, and S. Bosch, “Asymmetrical multilevel inverter for traction drives using only one dc supply,” IEEE Trans. Veh. Technol., vol. 59, no. 8, pp. 3736–3743, Oct. 2010.
 S. Lu, K. A. Corzine, and M. Ferdowsi, “A unique ultracapacitor direct integration scheme in multilevel motor drives for large vehicle propulsion,” IEEE Trans. Veh. Technol., vol. 56, no. 4, pp. 1506–1515, Jul. 2007.
 J. Rodriguez, S. Bernet, P. K. Steimer, and I. E. Lizama, “A survey on neutral-point-clamped inverters,” IEEE Trans. Ind. Electron. , vol. 57, no. 7, pp. 2219–2230, Jul. 2010.