Library Categories: Technical Reports

Impact of HVDC Convertor Technology Choice on Reinforcement within the GB Grid

HVDC ‘bootstraps’ are becoming a key option in the reinforcement of the transmission system. As the generation mix moves towards renewables, sources are becoming more dispersed and located further from load centres, requiring extensive transmission network upgrades to get the power to where it is needed. As a result of restrictions in space and consenting issues locating new circuits onshore, there has been a move to locate new circuits offshore. This requires long cable circuits, where HVDC technology must be used. This note explores how the choice of HVDC technology can affect the system integration challenge of the required upgrades to the transmission system. Download file below.

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Stability Assessment and Mitigation of Converter Interactions (Phase 2): Report II-Development and Validation of Type 3 Turbine Impedance

The integration of AC connected wind farms into the existing power network has significantly changed the characteristics of the system and adequate small signal wind turbine models will be required to assess system stability considering the existence of difference converter technologies. While the small signal behaviour of Type 4 turbine has been extensively studied, the small signal impedance of doubly-fed induction generator (DFIG) based Type 3 turbine has not been well understood. The purpose of this study is to develop small signal admittance model of Type 3 turbine under different control modes and operating points. In this report the admittances of Type 3 turbine are then compared to the Type 4 turbine to highlight the main differences between the two. The small-signal admittances of both turbine types from the analytical models are verified against the measurements from time-domain models.

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Stability Assessment and Mitigation of Converter Interactions (Phase 2): Report I-Development and Validation of LCC HVDC System Impedance Models

This report concentrates on the development of small-signal LCC converter and LCC HVDC system models. The development of the analytical impedance model intends to provide further insight into the impact of circuit and control structure/parameters on system impedance, and similarly highlight the factors that need to be considered when an LCC HVDC connection is defining its frequency-dependent impedance accurately ahead of a network scale small-signal interaction study being performed. The developed impedance models can then be used for assessing stability and interactions between different converters (e.g., MMC, LCC, wind farm, etc.).

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Stability Assessment and Mitigation of Converter Interactions (Phase I)

A key research outcome of ‘’Stability Assessment and Mitigation of Converter Interactions (Phase I)’’ project with the University of Strathclyde

The article discuss the details about the innovative analytical methods for small-signal impedance model of modular multilevel converters (MMCs) using harmonic state-space (HSS) method and is studied the stability assessment of single and multiple converters that University of Strathclyde has developed. In this impedance model, the multi-infeed interaction factor (MIIF) measure is adopted to analyse the most significant interactions for multi-infeed converter systems. The effect of different control modes on converter impedance and system stability are considered. The analytical studies and time-domain simulation results are provided to validate the proposed concept and gained further confidence of the obtained impedance models using both methods. This work provides solid foundation for further studies to identify states where risk of instability may exist in a multi-infeed converter system, so as to help and inform operating away from those network or avoid certain converter operating states.

This paper has been accepted in the prestigious IEEE Journal.

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Evolution of Protection Testing in Low-Strength and Converter-rich areas within the GB Grid

Protection schemes form part of the most fundamental components of any power system. They ensure that when faults occur on networks, the effect of the fault is seen only briefly by the wider system and its connections, isolating the faulted infrastructure or generator from the network, hence allowing the healthy elements to continue to operate. By doing so, risks to personnel and risks of damage to the infrastructure of the AC power system are reduced. This article explains how declining system strength presents challenges to confidence over future protection relay operation – and highlights how the HVDC Centre is helping to address these challenges. Click here to read the full briefing note or Download  file below.

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De-risking Integrated Offshore Networks in GB

The Offshore Wind Industry Council (OWIC) transmission group sought guidance from the National HVDC Centre on options for de-risking integrated offshore transmission approaches in GB. The HVDC Centre in consultation with industry led publication of a report, which identifies that:

  • Integrated offshore transmission is technically feasible for projects at design stage;
  • Solutions can be built in stages to meet offshore wind growth and benefit the onshore grid; and
  • Bipole HVDC with return cable option appear to offer greater flexibility and less export cables.

Click here for the full report published on 25 June 2020.


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