Frequency Adaptive Repetitive Control Of Grid Connected Inverters

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Frequency Adaptive Repetitive Control of Grid-connected Inverters Rabia Nazira,b, Keliang Zhoub, Neville R. Watsonb, Alan Woodb a Electrical Engineering Department, Lahore College for Women University Lahore, Pakistan. bElectrical and Computer Engineering Department University of Canterbury, Christchurch, New Zealand. Abstract—Grid-connected inverters (GCI) are widely used to feed power from renewable energy distributed generators into smarter grids. Repetitive control (RC) enables such inverters to inject high quality fundamental-frequency sinusoidal currents into the grid. However, digital RC which can get approximately no tracking error of any periodic signal in steady-state whose period is known, cannot exactly track or reject periodic signal of frequency variations. Thus digital RC would lead to a significant power quality degradation of GCIs when grid frequency varies and causes periodic signal with non-integer periods. In this research paper a repetitive control scheme capable of frequency adaptation (FARC) at a predefined sampling rate is proposed to deal with all types of periodic signal of variable frequency. A fractional delay filter which is based on Lagrange interpolation is used to estimate the fractional period terms in RC. This proposed FARC controller offers the fast during process modification of fractional delay and fast revise of filter parameters, and then provides GCIs with a simple but very accurate existent time frequency adaptive control

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