Design and analysis of secure offshore wind farms

  • James Gordon Tait

Student thesis: Doctoral Thesis

Abstract

This thesis investigates methods and system architectures which improve system security of offshore wind farms. This is demonstrated through enhancing dc collector network fault resiliency which also remain reliable throughout ac network disturbances.Initially key techniques applied to alleviate the effects of power imbalance during ac network faults for permanent magnet synchronous generator (PMSG) based wind energy conversion systems (WECSs), are comparatively analysed based on performance, economic and practical metrics. Based on a qualitative review of technically viable designs, this study presents quantitative substantiation with time-domain simulations. At wind turbine level, the assessment findings suggest potential financial and practical barriers that may exist regarding the implementation of the LVFRT solutions especially with energy storage-based techniques. However, the flexibility, benefits and increasing feasibility regarding energy storage systems may make them a preferred option for LVFRT of critical WECSs, particularly used in a coordinated manner with other lower cost techniques.Expanding to system level this research proposes an enhanced system for series-connected offshore wind farm (SC-OWF) with enhanced fault resilience to internal collector faults, where comprehensive circuit configuration and protection strategies are articulated. A grouping scheme and substation are adopted to realise prompt fault bypass/isolation and protection functions in the event of offshore collector faults. Additionally, an onshore fault tolerant modular multilevel converter with a modified dc-system-oriented control is employed to enable smooth and secure operation under steady-state and fault conditions. The SC-OWF presented system is quantitatively substantiated by time-domain simulations. The results consolidate the feasibility of the proposed configuration by demonstrating enhanced resiliency to dc collector faults and remaining post ac network disturbances via adoption of the proposed coordinated control system and bypass station configuration. However, due to current technical and practical limitations regarding component and cable ratings.To address challenges with windfarm sizing limitations a modular-series-parallel topology with reduced weight and volume requirements is proposed. A comprehensive circuit configuration and protection strategies are presented, which aim to minimise the detrimental effects caused by dc cable faults to ensure system security in a cost-effective manner. The system architecture employs a grouping scheme, where each group consists of a string of series connected wind energy converter systems (WECS) interfaced to a uni directional high gain dc/dc converter with parallel connection at the high voltage dc (HVDC) transmission point. The system configuration allows the containment off collector faults with in each of the groups, allowing secure system operation via control and balancing systems, with power quality achieved through an adaptive phase-shift control function on the dc output of the offshore converter station. The proposed wind farm system is quantitatively substantiated by time-domain simulations where two dc fault cases are considered. The results consolidate the feasibility of the proposed configuration and control, indicating fault resilience of the MSPC-OWF system without requirement for dc circuit breakers (DCCBs). Furthermore, a weight/size assessment demonstrates weight and volume reductions in comparison to HVDC converter stations interfaced to ac collector networks.
Date of Award2 Jun 2023
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorKhaled Ahmed (Supervisor) & Graeme Burt (Supervisor)

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