Control Strategy to Attenuate Voltage Oscillations under Unbalanced Power Distribution in Large Scale Photovoltaic Cascaded Multilevel Converters

In this paper, a control system is developed to address the power imbalance in a large-scale grid-tied photovoltaic (PV) cascaded multilevel inverter. The proposed approach helps handling the unequal irradiance distribution among independent PV arrays located as input sources at each one of the stages of the multilevel converter, balancing all dc link voltages and improving the transient response of the buses. Depending on the power transferred to the grid, the individual control signals for each H-bridge cell are adjusted through a direct relation between the output of the individual dc link voltage controllers and the corresponding general voltage controller. Simulation tests are developed to evaluate the performance and transient response of the balancing method under sudden unbalanced irradiance variations.