Offshore VSC-HVDC networks stability impacts
The power system is currently undergoing the challenging transition from a fossil-fuel dominated energy mix to a platform that will, eventually, run on renewable energy sources. Offshore wind power is abundantly available in Northwestern Europe and is considered indispensable to meet the goals set by policy makers. large wind power plants will be located far offshore, which necessitates the utilisation of high voltage direct current transmission based on voltage sourced converter technology (VSC-HVDC).
The technical properties of VSC-HVDC allow its behaviour at the connection points to be fully dictated by its control scheme. This in contrast to the onshore transmission system, the rotating machinery of which exhibit mainly physical behaviour. These need to be made compatible for various performance indicators such as voltage and transient stability, usually studied by simulation experiments comprising both transmission types.
Modelling and simulation methods for HVDC and AC transmission, however, inherently differ. HVDC transmission is commonly studied by detailed electromagnetic transients (EMT) type simulations whereas large scale AC transmission is associated with stability-type simulations. These simplify the system and device models such that only the response relevant to transient stability is included into the calculations, and are not well suited for HVDC. Studying the grid integration of VSC-HVDC therefore requires rethinking about the simulation approach to adopt.
The work conducted for this project considered two main options to cope with the simulation challenge. The first encompassed the development of a dynamic model for VSC-HVDC, which was on its turn included into a stability-type simulation. The second covered the application of a hybrid EMT/stability type simulator.
The inclusion of a VSC-HVDC model into the stability-type simulation needed either HVDC model reduction or numerical improvements in the integration algorithm in order to obtain workable simulation speeds. Using the multi-rate approach execution speeds increased sevenfold compared to the reference implementation. The hybrid simulation required a redesign of the associated interfacing techniques to incorporate VSC-HVDC accordingly. Similar speed and accuracy performance was obtained as compared to the first option considered. The multi-rate approach was then used to study the impact (fault ride through, active power recovery, reactive current injection, topological changes) of a multi-terminal offshore network based on VSC-HVDC on the transient stability of the Dutch transmission system.
As the mainland power system is strong the transient stability impacts turned out to be low for scenarios in which the relative amount of renewables in the generation mix is small. For high-wind scenarios, however, few conventional power plants were committed and stability effects were more prominent, especially in case the active power recovery of VSCs was slow. The actual network topology did not show significant effect on the onshore network stability. The main recommendations of this work entail the introduction of a stochastic approach on input parameters such as wind and solar infeed, the extension of the set of performance parameters for transient stability, and improved dynamic modelling of the transmission system surrounding The Netherlands.
A. van der Meer
Dr.ir. Arjen van der Meer was born on July 4th, 1982 in Dokkum, the Netherlands. He started his study Electrical Engineering at the Leeuwarden University of Applied Sciences (NHL) in 2002. During his B.Sc., he ran an internship at the Physics Shop of the University of Groningen where he investigated the noise generation of onshore wind turbines. He conducted his graduation project at Essent Netwerk Noord, Zwolle, where he was responsible for the development of a substation switching simulator for training purposes. After obtaining his B.Sc. degree in 2006 he joined Delft University of Technology for a M.Sc. in Electrical Engineering. In 2007, he conducted an internship at Enexis, Zwolle, where he assessed directional relay protection schemes for ungrounded medium voltage networks. In 2008, he obtained his M.Sc. degree (cum laude) with a thesis on power hardware-in-the-loop based directional relay co-ordination. In October 2008, he started his Ph.D. at the power systems group (now IEPG) of the Electrical Engineering, Mathematics, and Computer Science faculty of TU Delft. His main research topic comprised the modelling and stability impacts of VSC-HVDC connected offshore wind power. During his research, he temporarily stayed at TenneT TSO B.V., Arnhem for developing a dynamic VSC-HVDC model for \PSSE\ . In 2015 he continued at Delft university of Technology as a researcher: on the COBRAcable research project in 2015 and on the ERIGrid smart grid project from 2016 onwards. From of January 2018, he is also affiliated with the AMS institute as a postdoctoral research fellow. His research interests are power system modelling, simulation, and control, renewable energy resources, power electronics, power system protection, and the roll-out of smart grids.