Simulation and comparison of three phase CHB MLI and three phase cascaded voltage source MLI topologies for grid connected PV applications

Cascaded multilevel inverter (MLI) topologies have received an attractive solution for grid connected PV system. In this paper, two-cascaded MLI topologies are presented for grid connected PV system. These are seven level cascaded H-bridge multilevel inverter and three phase cascaded voltage source multilevel inverter. In both presented MLI configurations, each PV module is connected to one DC-DC isolated Cuk converter to achieve best MPPT as well as used for galvanic isolation in order to improve system efficiency. The DC-DC isolated Cuk converters are cascaded to amplify the DC voltage in order to be used for medium and high voltage systems. On the other hand, the operation of H-bridge switches is that the two upper switches are operating at line frequency while the two lower switches are operating at switching frequency in order to reduce the switching losses. Simulation results show that both system are well functioning in improving the grid power quality. The three phase grid currents in both systems are at unity power factor and THD of the grid currents are within the acceptable range. Finally, both configurations are compared to each other. The comparison results show that both of them has advantages and disadvantages of the other.