Case-specificity and Its Implications in Distribution Network Analysis with Increasing Penetration of Photovoltaic Generation

Distribution system analysis(DSA)currently faces several challenges due to inclusion of distributed energy resources(DERs),which have many characteristics,such as inherent variability,uncertainty,possibility of flexible four quadrant converter operations with distributed generation(DG),and the need for efficient operations to improve reliability of the supply system.This article argues for a high degree of case-specificity and discusses its implications in distribution networks with increasing DG penetration.The research is based on the exhaustive yearly simulation analyses of 132 candidate scenarios and investigates the effects of feeder-specific factors,such as geo-electric size and feeder spread,load density,and phase unbalancing.Nineteen(19)feeder variants—with phase-domain detailed modeling of all feeder components,including DGs,are subjected to increasing penetration of photovoltaic generation without altering the type and location of DGs.The objective is to analyze the role of feederspecific factors on feeder response characteristics in terms of annualized operational parameters,such as energy losses,feeder voltage profile,average power factor,and peak demand at a substation node,as well as tap-changer operations of voltage regulating equipment and their interaction with shunt compensation.Recorded annual load profiles—industrial,commercial,and residential—as well as location specific weather data are used to simulate the candidate scenarios based on three IEEE test feeders and one actual spot network in India.Results signify the consideration of feeder-specific factors in the planning exercise of grouping“similar”feeders for formulating the strategies that can improve daily operations of distribution feeders.The demonstrated case-specificity also implies that optimization algorithms for improved operations with DGs will need to be based on an integrated approach that accounts for feeder-specific factors as well as cyclic variability of DERs.

Multi-conductor Line Models for Harmonic Load-flow Calculations in LV Networks with High Penetration of PV Generation

Low-voltage(LV) distribution networks are unbalanced and present loads with nonlinear behavior, which introduce harmonics in the networks. The predictable increase in photovoltaic microgeneration(PV μG) accentuates this unbalanced characteristic, as well as poses new technical problems,namely voltage rise and reverse power flow. To accurately account for the distributed PV and loads in the LV network, unbalanced three-phase power flow algorithms should be utilized,where different approaches may be used to represent lines with various degrees of accuracy. The more accurate algorithm considers the electromagnetic coupling between the line conductors,whereas the simpler algorithm represents each conductor of the line as a single-phase line with pure resistive behavior. This paper aims to analyze the influence of the line model on the load flow in a highly unbalanced LV network with a high penetration of PV production, and considers the impact of the harmonics produced by nonlinear loads. Based on the results obtained,it is possible to identify the most suitable model to be used, depending on the study to be performed. Different scenarios of PV generation and loads are addressed in this paper.