Despite their undoubted advantages, Distributed Generation (DG) systems can negatively impact some aspects of the distribution system operation. In this paper, impacts of inverter-based DGs on fuse-recloser coordination in the fuse-saving protection scheme are thoroughly studied. Various fault conditions with different fault resistances and the effects of different DG locations are investigated. Also, the effects of DG reactive power injection, known as a DG potential ancillary service, on the protection scheme are studied. Furthermore, in order to mitigate the impact of DG on the protection coordination, a simple and effective control strategy is proposed. This strategy limits the DG output current according to the DG terminal voltage. Extensive simulations at different fault conditions and different DG penetration levels showed that the proposed control method is able to eliminate DG's contribution during the fault, and consequently eliminate its impact on the fuse-recloser coordination. In comparison to other methods, this strategy is inexpensive, easy to implement, does not limit DG capacity during normal condition, and does not require any change in the original protection system. The simulation results also demonstrated that the proposed method is robust against non-fault transient disturbances such as load switching, starting of induction motors, etc.
In this paper analysis results of a cooperation of the Unified Power Quality Conditioner (UPQC) with the photovoltaic system are presented. The proposed system consists of a series inverter, a shunt inverter, and some photovoltaic arrays connected in the dc link through the Multi-Input Single-Output (MISO) DC-DC converter. A numerical formulation of the proposed control schemes, which are based on the instantaneous power theory, is presented. The proposed system can improve the power quality at the Point of Common Coupling (PCC) on power distribution systems. The performance of the proposed system was analyzed using simulations with Power System Computer Aided Design/ElectroMagnetic Transients DC (PSCAD/EMTDC) analysis program. Index Terms--Distribution System (DG), Multi-Input Single-Output, photovoltaic array, Power Quality, Unified Power Quality Conditioner (UPQC).
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