An FPGA-Based Advanced Control Strategy of a Grid­Tied PV CHB Inverter

In this paper, an advanced control strategy for grid-tied photovoltaic (PV) cascaded H-bridge (CHB) inverter is proposed. The circuit topology consists of a proper number of power cells (H-bridge configuration) connected in series and supplied by individual PV modules. The adopted control method is a mixed staircase-PWM technique performed by means of a sorting algorithm to determine cells' switching state. The cells' state is related to the need of charging or discharging a particular cell much more than the others by calculating the voltage error at each dc-link (e.g., by considering the difference between the maximum power point tracking (MPPT) reference and the measured quantity). A dedicated P&O MPPT permits to control independently the voltage of each dc-link; thus, increasing the power extraction even in mismatched conditions. In order to prove the effectiveness and feasibility of the proposed approach, a set of experiments are performed on a laboratory prototype of a single-phase five-level PV CHB. The control section is implemented on FPGA by using a dSPACE real-time hardware platform; thus, obtaining fully dedicated digital circuits. Experimental results show good performance in terms of MPPT efficiency, total harmonic distortion, and power factor in both normal operation and mismatch conditions.