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Performance Improvement of HVDC Converters Used for the Connection of Remote Offshore Wind Farms : Evaluation of the Potential of New IGCT Components

par Laurence Laffont - publié le , mis à jour le

Davin GUEDON’s thesis defense, intitled "Amélioration des performances des convertisseurs HVDC mis en oeuvre pour le raccordement des parcs éoliens offshore lointains : évaluation du potentiel des nouveaux composants IGCT" (Performance Improvement of HVDC Converters Used for the Connection of Remote Offshore Wind Farms : Evaluation of the Potential of New IGCT Components), will be taking place on Wednesday, February 2nd 2022, at 10:00 am, in the salle des thèses (C002), ENSEEIHT, 2 rue Charles Camichel, 31000 TOULOUSE.

The work for this thesis has been supervized by Philippe LADOUX and Sébastien SANCHEZ.

A link for visioconference will be provided.

Jury :

Cyril BUTTAY (Research director, Laboratory Ampère, Lyon), Rapporteur
Drazen DUJIC (Professor, EPFL STI IEM PEL, Lausanne), Rapporteur
Seddik BACHA (Professor, G2Elab, Grenoble), Reviewer
Mehdi KANOUN (PhD, EDF R&D, Écuelles), Reviewer
Marie-Laure LOCATELLI (Researcher, LAPLACE, Toulouse), Reviewer
Thomas STIASNY (PhD, Hitachi Energy, Lenzburg), Reviewer
Philippe LADOUX (Professor, LAPLACE, Toulouse), thesis supervizor
Sébastien SANCHEZ (Associated researcher, ICAM/LAPLACE, Toulouse), Thesis co-supervizor
Sébastien CORNET (EDF R&D, Écuelles), Industry supervizor
Christian WINTER (Hitachi Energy, Lenzburg), Guest

Abstract :

For more than a decade, high-voltage direct-current (HVDC) grid-connection of offshore wind farms has intensified. It allows transporting to the mainland power levels around 1 GW, over underwater distances exceeding 50 kilometres. A key issue related to the sizing of HVDC converter-stations, based on MMC (Modular Multilevel Converters), is their efficiency. Only 0.1% of power losses represents several GWh lost for each year of operation of the wind farm.
These power losses are related to the characteristics of the semiconductors used. Today, the IGBT (Insulated-Gate Bipolar Transistor) is the only semiconductor device used in this type of application. Historically, the IGBT has been developed for medium-power industrial applications, and does not appear as the best candidate to realize HVDC systems. On the other hand, the IGCT (Integrated Gate-Commutated Thyristor) has performances and features that seem better adapted, however its use in such systems has never been considered.
The aim of this PhD thesis is to optimize the performances of HVDC converters, based on IGCT, as part of the grid-connection of offshore wind farms. This work has been the subject of a collaboration between the LAPLACE Laboratory in Toulouse, Electricité de France Research & Development (EDF R&D), and the semiconductor manufacturer Hitachi ABB Power Grids, Semiconductors.
In a first approach, the static and dynamic characteristics of the IGCTs have been measured experimentally on a double-pulse test bench. Then, an electro-thermal model has been built, in order to determine precisely the power losses in the hundreds of sub-modules present in an MMC arm. This approach has allowed a comparison of different IGCTs, according to their power losses, taking into account the intermittent production of the offshore wind farm.
Following this study based on calculations and simulations, a test bench in steady-state, consisting of two IGCT-based sub-modules connected in a back-to-back configuration, has been designed and implemented to accurately measure on-state and switching losses through dedicated instrumentation. With a working voltage up to 5 kV and currents exceeding 2 kA, 4.5 kV and 10 kV devices have been tested under operating conditions equivalent to those of a 1 GW HVDC station.
The power loss measurements using the calorimetric method have confirmed the validity of the electro-thermal models related to IGCT and its clamp circuit, with an accuracy of about 10%. The waveforms have highlighted larger deviations regarding the switching losses, caused by the stray inductances of connection within the switching cell. The cross-use of electro-thermal models and experimental measurements demonstrates that 4.5 kV IGCTs can allow a significant rise in the power levels of the MMC-based HVDC stations, while 6.5 kV and 10 kV IGCTs are the most suitable devices for prospective applications, guided by the voltage upgrade of HVDC cables. Soft switching circuits are promising to reduce the volume of the sub-modules, and would be particularly relevant for 6.5 kV and 10 kV devices, whose switching losses are the main limiting factor.