A Novel Five-Level Inverter and Its Optimal Modulation and Control Method

This paper proposes a novel five-level grid connected inverter oriented to 1500V PV-string power generation. Compared with other five-level inverters, in this inverter current can flow through only two switches during high voltage levels, so that the conduction losses of switches can be fundamentally reduced. Meanwhile, a novel modulation strategy and control method suitable for this inverter is also proposed. This modulation strategy can realize reliable switch between adjacent states without dead-time. What's more, with the control method the voltage of flying capacitor can be well balanced within several periods of carrier wave. Hence, the size of flying capacitor can be significantly reduced and correspondingly power density increases. In addition, the factors that have influence on the voltage of flying capacitor are analyzed. Finally, by experiment the feasibility of the novel five level inverter and its modulation strategy as well as control method is verified.