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Details of Grant 

EPSRC Reference: EP/L021455/1
Title: Mitigating the effect of low inertia and low short-circuit level in HVDC-rich AC grids
Principal Investigator: Liang, Professor J
Other Investigators:
Ugalde-Loo, Professor CE Jenkins, Professor N
Researcher Co-Investigators:
Project Partners:
Alstom Group Parsons Brinckerhoff
Department: Sch of Engineering
Organisation: Cardiff University
Scheme: Standard Research
Starts: 15 December 2014 Ends: 30 April 2018 Value (£): 295,632
EPSRC Research Topic Classifications:
Sustainable Energy Networks
EPSRC Industrial Sector Classifications:
Energy
Related Grants:
Panel History:
Panel DatePanel NameOutcome
28 Feb 2014 HVDC Challenge Announced
Summary on Grant Application Form
Renewable power, particularly offshore wind power, will be a major element of the UK's transition to meet its energy demands while reducing carbon emissions. HVDC will be the key technology for integrating offshore wind power into the UK AC grid and for interconnecting other AC grids in Europe. Line commutated converter (LCC) HVDC is particularly suitable for bulk power transfer while voltage source converter (VSC) HVDC is particularly suitable for connecting offshore power into AC grids with low inertia and low short-circuit level. Multi-terminal HVDC networks and DC grids based on VSC technology will be developed across the North Sea to form a future SuperGrid to increase the flexibility, redundancy and economic viability of offshore wind power transmission.

Conventional synchronous generators will be replaced increasingly by renewable generation with power electronic converters and HVDC transmission. This causes significant reduction of system inertia and short-circuit level. Particularly in the UK, large scale offshore wind power and interconnection with grids in other European countries will lead to an HVDC-rich AC grid. This will result in AC grids with low fault-circuit and low inertia which will present a series of challenges for AC system operation such as the potential impact on existing relaying protection; frequency instability and commutation failure of LCC HVDC.

This proposed project will look at the behaviour of low-inertia and low short-circuit level in HVDC-rich AC grids supplied through power electronic converters. The challenges will be that the capability of HVDC links to provide the system support could be (at the same time) adversely affected by these effects on the grids. LCC HVDC can provide artificial inertia but requires high short-circuit ratio of the grid to work properly. During AC fault and post-fault restoration, the inertia support capability of the LCC would be limited at the very time it is most needed. VSC HVDC control is less dependent to AC grids. However a DC fault can be easily propagated across whole HVDC grid due to the very low resistance of DC lines, which in turn affects the AC sides of all terminals. During the DC fault, the real power injected into AC grids as well as the inertia support from VSC HVDC grids would be lost at the very moment it is much needed to maintain the system frequency. At the same time, reactive power support to AC grids from VSC HVDC grids would also be lost completely or partially depending on converter topologies.

Investigations will be undertaken of the inertia support from HVDC converters, on the capabilities of the different types of converters to mitigate low-inertia effects and on their coordination through the AC side (for point-to-point HVDC links) or through the DC side (for converters within the same DC grid).

The hardware-in-loop (HIL) platform at Cardiff University, which consists of a HVDC grid test rig, a real time digital simulator (RTDS) and a power amplifier, will play a key role in the modelling and testing of HVDC-rich grids and HVDC converter control for mitigating low-inertia and low short-circuit level effects.

Through this project, in-depth understanding of operation characteristics of AC grids which are rich in HVDC links will be achieved. Solutions will be founded to enhance the system inertia and short-circuit level. More renewable power through HVDC can be integrated into AC grids without deteriorate the system performance. The research outputs of this project will be disseminated through industrial partners, international academic associations, conferences and journal publications.
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Organisation Website: http://www.cf.ac.uk