Low Voltage Ride-Through Improvement of a Two-Stage Grid-Connected Photovoltaic System by Using an Optimized SPWM Technique

Due to the increasing use of solar power plants as clean sources, their protection is vital to having desirable interaction with the main grids. This paper proposes a zero-sequence injection sinusoidal pulse-width modulation (ZSI-SPWM) technique for a three-level neutral point clamped (NPC) inverter for a photovoltaic (PV) system connected to the unbalanced three-phase grid. The proposed modulation technique injects the zero-sequence components to the grid as one of the SPWM reference signals, thereby significantly reducing the DC-link voltage oscillations and improve the low voltage ride-through (LVRT) condition. Also, this paper suggests optimal Sugeno fuzzy logic controllers (FLCs) to improve the LVRT capability of a PV connected to an unbalanced main grid, in which FLC rules are designed using the meta-heuristic krill Herding algorithm (KHA). The Gaussian memberships of Sugeno FLCs and proportional-integral (PI) parameters are optimally derived and used for reactive power and ZSI-SPWM simultaneously. The three-phase grid-connected PV system’s power quality is improved by minimizing the multi-objective fitness function with multi-dimensionality. The proposed strategy reduces the DC side voltage oscillation, decreases the total harmonic distortion (THD), and stabilizes the output current, voltage, and flowing power. In this article, a dual second-order generalized integrator frequency locked loop (DSOGI-FLL) is used for better synchronizing the inverter with the grid during asymmetric faults due to its noise attenuation and frequency adaptability characteristics. The performance of the proposed approach is confirmed using simulations in different scenarios in the MATLAB/Simulink environment.

کلیدواژه ها:

Fuzzy-Krill herding algorithm ، low voltage ride-through ، proportional-integral-Krill herding algorithm ، zero sequence current control