Control strategy for a multilevel inverter in grid-connected photovoltaic applications

A novel conversion structure for photovoltaic (PV) grid connection is proposed in this paper. The conversion system is aimed to be relatively simple and effective in medium and high power range. The topology utilizes a dual two-level voltage source inverter (VSI), fed by two insulated PV fields, supplying a grid transformer with open-end connection. Use of proposed scheme doubles the output power range of the conversion system with respect to the rated power of a single inverter, without the need of series/parallel connections of power switches. Furthermore, the dual inverter structure allows multilevel voltage waveforms, reducing grid current harmonics and mitigating output voltage derivatives. An original control method has been introduced to regulate the dc-link voltages for each VSI. The proposed algorithm has been verified by numerical tests with reference to different operating conditions.