Filter Position Optimisation in Transmission System using Homotopy Analysis Method
Translated title
Filter Position Optimering i Transmission System ved brug af Homotopi Analyse Metode
Authors
Jakobsen, Troels Østerby ; Vadstrup, Morten
Term
4. term
Education
Publication year
2019
Submitted on
2019-05-31
Abstract
This thesis tackles the growing challenge of harmonic distortion in transmission systems driven by increased use of power electronics, HVDC links, and cable replacement, which lowers resonance frequencies and can amplify harmonic emissions. To support a more global strategy for filter placement, it introduces a new semi-analytical approach that assesses where a filter will have the greatest system-wide impact without specifying actual filter values. The method applies the Homotopy Analysis Method (HAM) to the frequency scan technique by expressing the voltage at a selected node as a power series and using the first-order coefficient as a screening metric to identify the most impactful filter locations for specific resonance points. It requires only the system admittance matrix and a matrix defining the tested filter location. Findings indicate that the magnitude of the first-order coefficient generally reflects the impact at resonance peaks, its real part signals damping or amplification, and its imaginary part provides a relative indication of frequency shifts. Because it does not compute final harmonic voltages after a concrete filter is installed, the method is best used early in planning studies as an efficient screening tool. Applied to a small example system, it correctly identified the most effective locations compared with implementing a C-type filter, and on a larger system structurally resembling the Danish 400 kV western grid, it produced accurate, insight-giving predictions of filter placement effects. The analysis also highlights that the most effective filter location is not always at the emission source, particularly when another location can better damp the underlying resonance. The method is at an early stage of development but shows promise for broader application and efficiency gains.
Denne afhandling adresserer stigende harmoniske udfordringer i transmissionssystemer, drevet af større udbredelse af effektelektronik, HVDC-forbindelser og kabellægning, som sænker resonansfrekvenser og kan forstærke harmonisk emission. For at understøtte en mere global strategi for filterplacering præsenteres en ny semianalytisk metode, der vurderer, hvor et filter vil have størst indvirkning uden at fastsætte konkrete filterværdier. Metoden bygger på Homotopy Analysis Method (HAM) anvendt til frekvensscanningsmetoden, hvor spændingen i et givet netpunkt beskrives som en potensrække. Førsteordenskoefficienten bruges som screeningsmål for at identificere de mest indflydelsesrige filterpositioner ved specifikke resonanspunkter. Metoden kræver kun systemets admittansmatrix og en matrix, der angiver den testede filterplacering. Resultaterne viser, at koefficientens absolutværdi generelt afspejler påvirkningen ved resonansspidser, at realdelen kan indikere dæmpning eller forstærkning, og at imaginærdelen giver en relativ indikation af frekvensforskydning. Metoden beregner ikke de endelige harmoniske spændinger efter implementering af et konkret filter og bør derfor anvendes tidligt i planlægningsstudier som en effektiv screening. Anvendt på et lille eksempelsystem forudsagde metoden korrekt de mest virkningsfulde placeringer sammenlignet med implementering af et C-type filter, og på et større system, der strukturelt ligner det vestdanske 400 kV net, gav den konsistente og indsigtsskabende forudsigelser af filterplaceringers effekt. Analysen peger også på, at den mest effektive filterplacering ikke nødvendigvis er ved selve emissionskilden, især når en anden placering bedre kan dæmpe den underliggende resonans. Metoden er i en tidlig udviklingsfase, men rummer potentiale for videre anvendelse og effektivisering.
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