LPF-BPF Fundamental Current Extractor Based Shunt Active Filtering with Grid Tied PV System

Abstract

Grid tied photovoltaic (PV) systems comprise of a voltage source inverter interfacing PV panels with the grid. These PV systems, which are redundant at night times, can be employed for shunt active power filtering during night times. Thus, harmonic current mitigation and reactive power compensation can be achieved during night times without effecting any change in power structure. For shunt active filtering, fundamental active current estimator is highly essential. This paper proposes a fundamental active current estimator for 3-phase shunt active filter (SAF) operation of grid tied PV system during night times. The estimation algorithm comprises of a low pass filter (LPF) and a band pass filter (BPF). The 3-phase load currents are transformed to stationary reference frame (SRF) and then 2-phase currents are individually processed through the proposed estimation algorithm for extracting the peak value of fundamental active components of load current. Further, with the help of unit vector templates (UVT), the instantaneous fundamental active components of the 2-phase quantities are determined, which can be transformed into 3-phase quantities with inverse Clarke transformation. Drawing of these currents from the grid can result in mitigation of current harmonics in grid. Moreover, as the phase angle of these currents drawn from the grid corresponds to UVT, the reactive power compensation is ensured. Hence, unity power factor operation is observed at the point of common coupling. The use of Clarke transformation results in reduced computational burden as only two quantities, instead of three, are to be processed. From the simulation studies, it is clear that the operation of 3-phase grid tied PV system as SAF, with the reported estimation algorithm, during night time results in reactive power compensation and elimination of harmonics from the grid currents.