FPGA implementation of an adaptive modulation method for a three-phase grid-tied PV CHB inverter

This work deals with an optimal control strategy for a three-phase grid-tied photovoltaic (PV) cascade H-bridge inverter. The main challenge for the control of this system topology derives from the inherent power imbalance among the phases as well as from the different power levels of the H-bridge cells in each phase leg. The power imbalance among the phases is compensated by the injection of a proper zero-sequence voltage. The power distribution among the cells of each phase could be affected by uneven irradiance and temperature conditions of PVGs (PV Generators). This latter issue is addressed by means of an adaptive modulation method especially suited to manage unequal dc sources, while assuring stable circuit operation and maximizing the power extraction through a dedicated MPPT (Maximum Power Point Tracking) algorithm. The digital controller is developed and tested in Matlab/Simulink environment integrated with XSG (Xilinx System Generator), thus allowing an easy transfer on FPGA embedded in dSPACE real-time platform. Simulations and experimental results prove the validity of the proposed design and control approach.