Half and Full-Bridge Cell based Stand-Alone Photovoltaic Multi-Level Inverter

A new multilevel PWM inverter using a half-bridge and full-bridge cells is proposed for the use of stand-alone photovoltaic inverters. The configuration of the proposed multilevel PWM inverter is based on a prior 11-level shaped PWM inverter. Among three 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 increases the number of output voltage levels resulted in high quality output voltages. Second, it reduces two power switching devices by means of employing a half-bridge cell. Third, it reduces power imposed on a transformer connected with the half-bridge unit. That is to say, most power is transferred to loads via cascaded 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 the final output voltage waves; thus, it is desirable in the point of the improvement of the system efficiency. By comparing to the prior 11-level PWM 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.