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Improved voltage harmonic control for sensorless shunt active power filters

A new control method for active filters based only on voltage detection at the Point of Common Coupling (PCC) is proposed. This technique allows using the active filter as a plug-and-play sensorless device, as it is possible to compensate the harmonics produced by the distorting loads just by measuring the PCC voltage, without needing to measure the distorting load current, and just with an approximate knowledge of the grid characteristics. A harmonic extraction structure is designed to calculate the active filter compensating current in the reference frames rotating at different harmonic frequencies. All the harmonic frames are decoupled so to avoid interactions between the control loops. A real-time implementation of Discrete Fourier Transform is utilized for accurate estimation of the fundamental phase and the harmonics amplitudes and phases. No low-pass or band-pass filters are needed for the harmonic identification.