A global power quality index for assessment in distributed energy systems connected to a harmonically polluted network

Abstract

ABSTRACT Renewable-based generation technologies are gradually making their way into modern delivery grids due to their various advantages, but power quality (PQ) remains a deciding factor for their satisfactory operation. The assessment of overall power quality performance of grid-connected renewable-based distributed energy systems (DESs) is undeniably a complicated process due to their susceptibility to load side and background PQ disturbances, as well as quite a few PQ disturbances produced by the distributed generator (DG) itself. The aim of this article to make the PQ evaluation of the identical rather streamlined by integrating the apprehensive PQ indices at separate bus groups along with the total PQ performances of separate bus groups in one composite index by making use of the analytic hierarchy process (AHP). The technique suggested for formulation yields a centralized global power quality index (GPQI) intended for three categories of bus, namely utility, load, and DG, as well as the overall system. The proposed GPQI is supposed to be exclusively ample to benchmark the global PQ performance of grid-connected DGs with respect to the customized threshold level, in addition to the PQ performance levels grading between the diverse DG systems differentiated by either resource forms or sittings in a large distribution power system. This kind of global index would significantly facilitate the PQ evaluation of grid-integrated DESs. In addition, it may also be extremely useful for distribution network operators (DNOs) to track and penalize DG operators for working inadequately on PQ perspective, and to inspire them to follow the best alternative across numerous power quality improvement (PQI) technologies. The proposed methodology’s applicability is developed and authenticated by applying it in MATLAB on a grid-integrated solar energy conversion system (SECS). The obtained values of GPQIs, by applying the proposed approach in the test system, for the utility, DG, load bus and overall system respectively are 1.530, 1.727, 1.719, and 1.659, respectively, indicating the poor PQ performance of the DG unit under study. The effects of background voltage distortion (BVD) on the utility side and nonlinearity level (NLL) on the load side on the proposed index are also thoroughly investigated. The simulation findings obtained at different NLL and BVD levels affirm the proposed approach’s efficacy in correctly indicating the status of overall PQ in the concerned DG system.