Control of asymmetrical cascaded multilevel inverter for a grid-connected photovoltaic system

This article presents a generalised asymmetrical cascaded multilevel inverter (MLI) for a single-phase grid-connected photovoltaic (PV) system and their control strategy. The control strategy, including maximum power tracking along with a suitable interface, is implemented for maximum power transfer from the PV source to the single-phase low-power grid. The balancing of DC-link voltages for an asymmetrical MLI under variable solar parameters as well as grid parameter variation is implemented using the proposed control strategy. The voltage controllers maintain the constant DC-link voltage ratio, whereas the current controller injects the sinusoidal current into the grid at unity power factor and track the grid voltage under variation of grid voltage using grid tracker. Stability analysis of the proposed grid-connected asymmetrical inverter system is also incorporated. The whole grid-tied PV system is simulated in the MATLAB/SIMULINK environment and the exhaustive simulation results of the system under different transient conditions are presented. In addition, a laboratory prototype for a low-power grid-tied PV system has been developed and implemented using DS1103. The performance of the system is also tested at varying irradiance conditions and the corresponding experimental results are also presented.