Power Quality Assessment of Electric Distribution Grids Integrated with Distributed Energy Resources
Authors
Maruszak, Mariusz ; Foyer, Jens William
Term
4. term
Education
Publication year
2020
Abstract
This thesis examines how the integration of distributed energy resources affects power quality in a low-voltage distribution feeder, with a focus on harmonic distortion introduced by non-linear interfaces. The core research question is how photovoltaic (PV) inverters and electric vehicle (EV) chargers influence feeder harmonic levels at different penetration rates and which mitigation strategies most effectively keep distortion within applicable standards. Methodologically, a CIGRE benchmark low-voltage grid is modeled in PowerFactory, including background harmonics from the medium-voltage grid. Two converter types (three-phase Graetz bridge and two-level voltage source converter) are represented, and their harmonic injections are addressed both through assumptions based on characteristic harmonics and standard limits and through equivalent modeling of PV inverters to analyze grid-absorbed harmonic currents. Scenario studies vary PV capacity and EV charger numbers/configurations (unfiltered and filtered), compare outcomes to relevant IEC/IEEE limits, and identify possible network resonances. As mitigation, passive single-tuned and damped filters are designed to reduce EV charger harmonics and attenuate grid distortions from other sources; their impact on resonant frequencies is assessed. The study provides an estimate of maximum PV penetration under power quality criteria and shows that appropriately designed passive filters can lower harmonic levels and influence resonance behavior in the distribution network.
Denne afhandling undersøger, hvordan integrationen af distribuerede energikilder påvirker spændingskvaliteten i et lavspændingsfordelingsnet med særligt fokus på harmoniske forvrængninger fra ikke-lineære grænseflader. Forskningsspørgsmålet er, hvordan fotovoltaiske (PV) invertere og elbilopladere påvirker nettes harmoniske niveauer ved forskellige indtrængningsgrader, samt hvilke afhjælpende tiltag der mest effektivt kan begrænse forvrængningen i overensstemmelse med gældende standarder. Metodisk opbygges et CIGRE-benchmarkeret lavspændingsnet i PowerFactory, hvor baggrundsharmoniske fra mellemspændingsnettet indgår. To konvertertyper modelleres (tre-faset Graetz-bro og 2-niveaus spændingskildeomformer), og deres harmoniske indsprøjtninger behandles både via antagelser baseret på karakteristiske harmoniske og standardgrænser samt via ækvivalentmodellering af PV-invertere for at analysere optagne harmoniske strømme. Der gennemføres scenariestudier med varierende PV-kapacitet og antal/udførelse af elbilopladere (u/med filter), resultaterne holdes op mod relevante IEC/IEEE-grænser, og mulige resonanser i nettet identificeres. Som afhjælpning udformes passive enkeltindstillede og dæmpede filtre til at reducere forvrængning fra elbilopladere og dæmpe netpåvirkninger fra andre kilder; filtrets indvirkning på nettes resonansfrekvenser vurderes. Studiet giver et estimat af maksimal PV-indtrængning under kvalitetskriterierne og viser, at passende udformede passive filtre kan sænke de harmoniske niveauer og påvirke resonansforholdene i fordelingsnettet.
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Keywords