Cascaded multilevel inverter topology with high frequency galvanic isolation for grid connected PV system

Abstract

Cascaded H-bridge MLI is an attractive solution for grid connected PV system. DC sources can be replaced by PV module/panel and due to the separated DC link feature and the voltage control becomes possible. Thus, individual maximum power point tracking (MPPT) control in each PV module can be achieved, and the total power extracted from PV panels will be maximized and hence the efficiency improves In this paper, a single phase cascaded H-bridge multilevel inverter topology is proposed for grid connected PV system. The proposed multilevel inverter configuration consists of PV modules, each is connected to one DC-DC flyback converter to achieve best MPPT as well as used for galvanic isolation in order to improve system efficiency. The DC-DC flyback converters are cascaded to amplify the DC voltage in order to be used for medium and high voltage systems and the result output voltage is used as an input to one H-bridge inverter. H-bridge inverters are then cascaded to generate multilevel output voltage. On the other hand, the operation of H-bridge MOSFETS is that the two upper MOSFETS are operating at line frequency while the two lower MOSFETS are operating at switching frequency. This will reduce switching losses and hence extra improving system efficiency can be achieved. Finally, the proposed configuration improves the system efficiency due to the multilevel inverter, obtain the best MPPT, achieve isolation at high frequency, eliminating the leakage current due to parasitic capacitances between PV module and ground, decupling the second harmonic voltage ripple and reducing the switching losses in the inverters.