Abstract
Photovoltaic power plants are obliged to maintain power quality standards when interconnected to the grid based on the grid codes (GCs). Variations in grid frequency can be one of the main sources of harmonic distortions in a generated currents of a grid-connected photovoltaic power plant (GCPPP) as long as it is incorporated with frequency-dependant controllers such as resonant controllers in the current control loops. In fact, either the controller itself or the reference currents can contribute to the harmonic components of the generated currents. Current references in turn may become distorted due to outer voltage controller or inaccurate phase angle detection by phase-locked-loop (PLL) technique. In this paper, a comprehensive analysis of a 3-phase GCPPP under grid frequency variations is performed with the focus on associated frequency-dependant controllers i.e. current controller and filtered-sequence PLL (FSPLL). The resonant controllers are selected in this study which have the capability to attenuate generated odd-order harmonics but their performance under frequency variations need to be investigated for both ideal and non-ideal controller types. FSPLL is an effective PLL, however its performance is highly dependent to the grid frequency which requires more research regarding frequency sensitivity. Afterwards, FSPLL is developed further to detect the instantaneous grid frequency to enhance the GCPPP performance. Finally, the GCPPP is equipped with an active power controller to contribute to the frequency control of the power system. Presented results within MATLAB/Simulink environment verify the enhanced capability of the GCPPP with frequency detector/controller satisfying GCs.
Published Version
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