Frequency-adaptive complex-coefficient filter-based control for grid-integrated PV system

This work deals with a frequency-adaptive complex-coefficient filter-based control for three-phase grid supportive double-stage photovoltaic (PV) system. This control eliminates harmonic components, DC offset at unbalanced loads and robust against phase frequency shift and on utility grid voltage disturbances. It uses harmonic-free positive sequence current components to generate sinusoidal reference currents without amplitude scaling. Moreover, tuning of parameters is not required due to the absence of gain parameters. This system responds quickly to balance the grid currents under unbalanced load currents, mitigates load current harmonics while feeding active power to the distribution network. The presented topology has enhanced the voltage source converter (VSC) utility, particularly in the absence of PV array generation, thus, VSC payback period is reduced. The PV dynamic term is utilized to enhance VSC input voltage profile, to avoid overshoots and undershoots in grid currents, and to mitigate transients in PV array current under varying irradiance. The behaviors under dynamic state and steady state of the presented system are validated under varying irradiance, load currents unbalance and grid voltage disturbances through simulated and test results. The power quality concerns are addressed, by achieving harmonic contents in grid currents below to 5% in accordance to the IEEE-519 standard.