Dynamic and Power-Quality Impacts of High Photovoltaic Penetration on Distribution Feeders That Static Load-Flow Studies Overlook

Abstract

Distributed photovoltaic (PV) generation on low- and medium-voltage distribution feeders has grown very quickly, and most studies of its impact use steady-state load-flow analysis. These studies do capture overvoltage and the distortion of the voltage profile under peak generation, but they leave out two effects that matter for how much PV a feeder can really host: the fast voltage changes caused by clouds passing over the panels, and the harmonic distortion that the inverters inject. This article reviews the published work on these two areas. It first sets out the basic equation for voltage rise on a feeder and uses it to explain why the high R/X ratio of distribution lines makes the voltage depend mainly on active power. It then looks at the dynamic side, where passing clouds cause fast power ramps that lead to voltage fluctuation, flicker, and extra switching of tap-changers and capacitor banks, none of which a single snapshot load-flow can show. It then checks inverter harmonic emission against the IEEE 519 limit of 5% total harmonic distortion at the point of common coupling and reviews the main filtering options. Finally it covers inverter-based mitigation under IEEE 1547-2018, in particular the volt-var and volt-watt functions. The main conclusion is that the limit on PV hosting capacity is often a dynamic or power-quality limit rather than a steady-state voltage limit, so assessing a feeder properly needs time-series and harmonic analysis on top of the usual load flow.