Modified multilevel inverter employing half- and full-bridge cells with cascade transformer and its extension to photovoltaic power generation

For the use of stand-alone photovoltaic inverters, it presents a modified multilevel inverter employing a half- and full-bridge cells with a cascade transformer. The circuit configuration is based on a prior (3n−1 + 2) level inverter. Among full-bridge cells employed in the prior inverter, one cell is substituted by a half-bridge cell. Owing to this simple alteration, the proposed inverter has three promising merits. First it can increase the number of output voltage levels resulted in high quality output voltages. Second, it can reduce two power switches by means of employing a half-bridge cell. Third, it can reduce power imposed on a transformer connected with the half-bridge unit. That is to say, most power is transferred to loads via transformers connected with low switching inverters, which are used to synthesize the fundamental output voltage levels whereas the output of a transformer linked to a high switching inverter is used to improve final output voltage waves; thus, it is desirable in the viewpoint of the improvement of the system efficiency. By comparing to the prior inverter, it assesses the performance of the proposed inverter as a stand-alone photovoltaic inverter. The validity of the proposed inverter is verified by computer-aided simulations and experimental results.