Modulation Technique for Grid-Tied PV Multilevel Inverter

In this paper the control of a grid-tied PV (Photovoltaic) Cascaded H-bridge inverter is discussed. The operation principle of the considered circuit is analyzed and a particular attention is paid to the different modulation techniques well-suited for this configuration. Moreover, some critical implementation issues are addressed, while a fair comparison between the proposed modulation scheme and the Phase Shifted PWM (Pulse Width Modulation) is carried out. The adopted control strategy is based upon a sorting algorithm in order to modulate only one power cell (i.e. H-bridge) per sorting cycle while the others are in fixed state. This technique allows to reduce power switching losses, thus increasing overall system efficiency. The numerical results reported in the paper permit to confirm the feasibility of the proposed modulation strategy and the better performance with respect to PS-PWM in terms of power efficiency.