Thesis

Black-start provision from grid-forming converters : a new network restoration paradigm

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Awarding institution
  • University of Strathclyde
Date of award
  • 2023
Thesis identifier
  • T16510
Person Identifier (Local)
  • 201952134
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Abstract
  • Black-start service has been long associated with conventional power plants such as large synchronous generators. Given the rising penetration of converter-based resources such as solar, wind and battery storage, this thesis addresses black-start provision from the power electronic-based grid-forming converters (GFCs). Key challenges for converters black-start utilization can be attributed to their input resources intermittency, limited overcurrent capabilities against high network energization inrush currents, in addition to identifying suitable controllers for reliable GFC operation and black-start compatibility. To tackle these points, the investigations in this thesis begin by proposing an innovative energy management system (EMS) that aims to maintain the converter input DC side reliable operation for prolonged periods, especially when a GFC is interfaced to a DC network consisting of multiple resources. The EMS is validated through simulations and a scaled lab setup. Then, the high transformer energization inrush currents are addressed through analyzing techniques that require direct GFC control manipulation such as soft energization (SE), against classical methods such as controlled switching (CS). Detailed theoretical transformer models are derived to quantify inrush current influencing factors. A new SE voltage ramp-rate estimation framework is then introduced, given the arbitrary ramp-rates definition in the literature. These techniques are tested in a detailed case study, where a GFC is used to energize a large network consisting of multiple transformers, and under various sensitivity scenarios.Four GFC controllers are benchmarked to assess their SE and black-start compatibility, namely: droop, power synchronizing control (PSC), virtual synchronous machine (VSM), and matching control. VSM grid-forming control is selected based on the comparison, and modifications to its classical form are proposed to improve its black-start compatibility such as voltage support and grid-synchronization. The modified controller is validated in complete black-start scenarios, through simulation and novel power hardware in the loop (PHiL) experiments that enable testing hardware converters to energize and synchronize to simulated networks in digital real-time simulation (DRTS) platforms. Overall, the presented in-depth analysis and investigations aim to provide thorough insights to researchers and industrial engineers on black-start feasibility from GFCs.
Advisor / supervisor
  • Ahmed, Khaled
  • Egea-Àlvarez, Agusti
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