Renewable energy systems (RESs), such as photovoltaic (PV) systems, are providing increasingly larger shares of power generation. PV systems are the fastest growing generation technology today with almost ~30% increase since 2015 reaching 509.3 GWp worldwide capacity by the end of 2018 and predicted to reach 1000 GWp by 2022. Due to the fluctuating and intermittent nature of PV systems, their large-scale integration into the grid poses momentous challenges. This paper provides a review of the technical challenges, such as frequency disturbances and voltage limit violation, related to the stability issues due to the large-scale and intensive PV system penetration into the power network. Possible solutions that mitigate the effect of large-scale PV system integration on the grid are also reviewed. Finally, power system stability when faults occur are outlined as well as their respective achievable solutions.

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The research presented in this paper explains how the complex-vector-filter (CVF) method can help in minimizing the current harmonic of a grid-tied photovoltaic system. In fact, the harmonic-free positive sequence (HFPS) load current is used to produce referential sinusoidal currents. This control stabilizes the grid’s currents under unbalanced load currents, as well as mitigates undesirable harmonic load currents, while feeding clean active power to the grid. Thanks to the proposed controller, the performance, such as robustness, as well as the stability and dynamics of the CVF are more effective compared to the proportional-integral (PI) with phase-locked-loop (PLL) controller. Moreover, the CVF ensures robustness and stability during the synchronization between the photovoltaic (PV) generator and the utility grid system. The PI&PLL control presents higher active and reactive power fluctuations during synchronization. On the other hand, the CVF ensures the elimination of the reactive power fluctuations during synchronization. The performance of the proposed CVF is validated by simulation through MATLAB software. Under all conditions, the grid current, considering harmonics, is within the limits set by the IEEE-519 power quality standard, where a total harmonic distortion (THD) of 1.56% was achieved in the case of feeding a non-linear load.

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