Black Start and Synchronization of Transmission Networks Using Grid-Forming Offshore Wind Farms
Authors
Sommerlund, Daniel Moshage ; Hjermitslev, Søren
Term
4. term
Education
Publication year
2024
Abstract
The transition to a 100% renewable power system increases the need for black start using inverter-based resources. This thesis investigates whether grid-forming (GFM) converters in offshore wind farms can perform black start of transmission islands and subsequently synchronize them safely. Two 9-bus transmission networks with different parameters were modeled, black start procedures were developed, and the energization of passive and active components was analyzed. The islands were then connected via a tie line and circuit breaker, which was closed under varying voltage magnitudes, phase angles, and frequencies to assess synchronization performance. Control structures for both GFM and grid-following (GFL) converters were validated. The results show that the GFM topology can successfully conduct black start on both islands, with component energization causing less than 5% voltage disturbances that are corrected by the GFM within 0.5 s. Synchronization is feasible, but the phase angle difference between systems affects power flow enough to trigger current limitation in one GFM; outer setpoint control and increased generation unit ratings are proposed. It is concluded that the phase angle mismatch at synchronization should be limited to a few degrees. The work is based on modeling and simulations of the specified networks and control strategies.
Overgangen til et 100% vedvarende elsystem øger behovet for black start med inverterbaserede ressourcer. Denne afhandling undersøger, om netdannende (grid-forming, GFM) konvertere i havvindmølleparker kan udføre black start af transmissionsøer og efterfølgende synkronisere dem sikkert. To 9-bus transmissionsnet med forskellige parametre blev modelleret, black start-procedurer blev udviklet, og energisering af passive og aktive komponenter blev analyseret. Øerne blev derefter forbundet med en tie-line og en afbryder, som blev lukket under varierende spændingsniveauer, fasevinkler og frekvenser for at vurdere synkroniseringens robusthed. Kontrolstrukturer for både GFM og grid-following (GFL) konvertere blev valideret. Resultaterne viser, at GFM-topologien kan gennemføre black start på begge øer, hvor komponentenergisering medfører spændingsforstyrrelser under 5%, som korrigeres af GFM inden for 0,5 s. Synkronisering er mulig, men fasevinkelforskellen mellem systemerne påvirker effektflowet tilstrækkeligt til at udløse strømsbegrænsning i en GFM; derfor foreslås ydre setpunktskontrol og øgede enhedsratinger. Det konkluderes, at fasevinkelforskellen ved synkronisering bør begrænses til få grader. Arbejdet er baseret på modeller og simulationer af de beskrevne net og kontrolstrategier.
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