Power Oscillation Damping Using Expandable VSC-HVDC Transmission System
Authors
Heo, Hun ; Mexis, Ioannis
Term
4. term
Education
Publication year
2018
Submitted on
2018-06-01
Pages
66
Abstract
Dette speciale undersøger udvidelsen af COBRAcable ved at tilføje en offshore vindmøllepark-konverter til den eksisterende punkt-til-punkt HVDC-forbindelse (højspændings jævnstrøm), så der dannes et tre-terminalt system, som envisaget af Cigre. Formålet er at forstå, hvordan den ekstra terminal påvirker den eksisterende POD-styring (power oscillation damping), der stabiliserer langsomme effektoscillationer, og hvordan POD kan retunes til det udvidede system. Et simpelt AC-system med to områder opstilles i DIgSILENT PowerFactory for at fremkalde inter-område-oscillationer. HVDC-forbindelsen modelleres som en spændingsstyret konverter (VSC) baseret på en modulær multilevel-konverter (MMC) med halv-bro. En POD-funktion lægges oven på konverternes hovedstyring, HVDC-linket kobles til AC-modellen, og systemet udsættes for en forstyrrelse for at vurdere POD-ydelsen. Herefter tilføjes den ekstra offshore-terminal til punkt-til-punkt-konfigurationen. Onshore-konverterne køres i to styretilstande: master-slave (én enhed sætter reference, den anden følger) og DC-spændings droop (delt styring via droop-karakteristik). Indvirkningen på POD vurderes ved at variere vindparkens effektprofiler. Til sidst kompenseres POD-controllerens udgang for at forbedre dæmpningen, når konverterne kører i DC-spændings droop-tilstand.
This thesis explores expanding the COBRAcable by adding an offshore wind farm converter to the existing point-to-point HVDC (high-voltage direct current) link, creating a three-terminal system as envisioned by Cigre. It examines how the extra terminal affects the existing power oscillation damping (POD) control—which stabilizes slow swings in power flow—and how to retune POD for the expanded system. A simple two-area AC system is set up in DIgSILENT PowerFactory to excite inter-area oscillations. The HVDC link is modeled as a voltage-sourced converter (VSC) based on a half-bridge modular multilevel converter (MMC). A POD function is added on top of the converters’ main controls, the HVDC link is connected to the AC model, and the system is disturbed to assess POD performance. The additional offshore terminal is then added to the point-to-point configuration. The onshore converters operate under two modes: master-slave (one unit sets the reference, the other follows) and DC voltage droop (sharing control through droop characteristics). The impact on POD is evaluated by varying the wind farm’s power output profiles. Finally, the POD controller output is compensated to improve damping when the converters operate in DC voltage droop mode.
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