Renewable energy resources (RES) are being increasingly connected in distribution systems utilizing power electronic converters. This paper presents a novel control strategy for achieving maximum benefits from these grid-interfacing inverters when installed in 3-phase 4-wire distribution systems. The inverter is controlled to perform as a multi-function device by incorporating active power filter functionality. The inverter can thus be utilized as: 1) power converter to inject power generated from RES to the grid, and 2) shunt APF to compensate current unbalance, load current harmonics, load reactive power demand and load neutral current. All of these functions may be accomplished either individually or simultaneously. With such a control, the combination of grid-interfacing inverter and the 3-phase 4-wire linear/non-linear unbalanced load at point of common coupling appears as balanced linear load to the grid. This new control concept is demonstrated with extensive MATLAB/Simulink simulation studies and validated through digital signal processor-based laboratory experimental results.Index Terms-Active power filter (APF), distributed generation (DG), distribution system, grid interconnection, power quality (PQ), renewable energy.

The power electronics plays an important role in the reliable operation of a modern wind energy conversion system (WECS). This study aims at the grid interconnection of a permanent magnet synchronous generator (PMSG)-based wind turbine with harmonics and reactive power compensation capability at the point of common coupling (PCC). The proposed system consists of two back-to-back connected converters with a common dc-link. The generator-side converter is used to achieve maximum power point tracking (MPPT). The grid-side converter is actively controlled to feed generated power as well as to supply the harmonics and reactive power demanded by the non-linear load at PCC, thus enabling the grid to supply only sinusoidal current at unity power factor. A model of directly driven PMSG-based variable speed WECS is developed and simulated in MATLAB/SPS environment. The effectiveness of proposed control approach is validated through extensive simulation and experimental results.

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