PhD report
Topic : Electrical engineering
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Soutenance : 16 Décembre 2019
ECOLE CENTRALE DE LILLE, France
Ragavendran RAMACHANDRAN
Control and Power Management of an Offshore Wind Power Plant with a Diode Rectifier Based HVDC Transmission
Contributions to Grid Forming and Black Start operations
Gestion des Flux Energétiques d’une Ferme Eolienne en Mer Connectée à un Système
HVDC au travers d’un Redresseur à Diodes
Proclamation des résultats
President :
Pascal MAUSSION, Professeur des Universités, Toulouse INP, ENSEEIHT, LAPLACE
Rapporteurs :
Lieven VANDEVELDE, Professeur, Gent University, EELAB
Salvy BOURGUET, Maître de Conférences HDR, Université de Nantes, IREENA
Examinatrice :
Héloïse DUTRIEUX BARAFFE, Dr. Ingénieur, EDF R&D
Invités:
Abdelkrim BENCHAIB, Dr. HDR, SuperGrid Institute
Serge POULLAIN, Dr. HDR, Supergrid Institute
Co-encadrant :
Seddik BACHA, Professeur des Universités, Grenoble Alpes University, G2ELAB
Directeur de these :
Bruno FRANCOIS, Professeur des Universités, Ecole Centrale de Lille, L2EP
Abstract:
Energy Transition for a more sustainable world is now the priority in societies. Many countries
are adopting the increase of their renewable energy capacity as one of the core strategies
towards reaching this need. Especially in Europe, the offshore wind energy development has
been fast and is playing an important part in the energy transition. Offshore Wind Power Plants
continue to get larger and farther from the shore and, hence, Voltage Source Converter (VSC)
based High Voltage DC (HVDC) Transmission has become the prominent solution for grid integration.
On the Wind Generator (WG) side, the machines are still growing in size and the
Type 4 (Full Scale Converter) with a Permanent Magnet Synchronous Generator (PSMG) is the
norm for capacities greater than 5 MW. The drive towards decreasing the overall cost of Offshore
Wind Power Projects led recently to a breakthrough in the HVDC transmission, with the
use of Diode Rectifier Unit (DRU), replacing the large offshore VSC stations by multiple Diode
Rectifier (DR) stations that are more compact, robust and cheaper but cannot control the power
transfer as done by a VSC station.
This thesis focusses on various technological and scientific problems involved in the control
system of the Offshore Wind Power Plant with a Diode Rectifier based HVDC transmission,
namely: the WG control and grid forming, black start of the offshore AC power system, fault
studies and integration into the Multi Terminal DC (MTDC) grid.
These challenges are first reviewed in detail along with the state of the art. Dynamic analyses
are conducted for the offshore AC system for both islanded and connected (normal) mode of
operation. According to characteristics of the offshore network, it is observed that the active
power and AC voltage of the offshore network are coupled (P-V) and also that the reactive power
and the frequency are coupled (Q-f), provided that an instantaneous means of synchronization
in an arbitrary dq frame is in place. Based on the analysis, a grid forming control scheme is
proposed by using the P-V and Q-f droop relationships. Synchronization is achieved among
the Wind Generators (WGs) by using the Q-f droop scheme and directly deriving the required
phase angle for each Grid Side Converter (GSC).
Following this, some of the selected control solutions for the DR-HVDC offshore wind power
plant topology are reviewed, compared and assessed by using time domain simulations of a
study case. Further, an analysis is conducted on one control solution to understand how to
dispatch reactive power sharing to the WGs, by setting droop coefficients. This part of the
analysis cements the understanding of the various existing grid forming approaches, the operation
of the offshore system and can provide useful insights for future control innovations and
enhancements.
The challenge of black start of the offshore AC power system is then tackled. A Pilot wind
Generator concept is introduced by using an Energy Storage System (ESS) in the existing WG
and locating a suitable number of pilots in each string. A suitable black start sequence is devised
with the aim to use the wind energy as much as possible and exploit the capabilities of the above
said Pilot WGs to enable a black start of the offshore system and transition to the normal mode
of operation. Automating such a sequence to enable a seamless black start of the offshore
AC grid with multiple factors for decision making is shown as an advantage. On this regard,
Discrete Event System (DES) based modeling and Supervisory Control Theory (SCT) enable
the design of a Supervisory Control for the black start sequence, which is then demonstrated by
using a study case.
Following this, the various faults in the offshore system are analyzed, with support from the
literature. Then, the above designed Grid forming control scheme is enhanced with Fault Ride
through (FRT) capability, for offshore AC grid faults. Finally, a brief analysis is done on the
challenges for the integration of this OWPP topology into an MTDC network.
Résumé:
La transition énergétique pour un monde plus durable est désormais la
priorité de nombreux pays. Dans cet objectif, notamment en Europe, le
développement de l’énergie éolienne en mer (offshore) a été rapide. Le
transport de l’électricité en Courant Continu Haute Tension (HVDC) basé
sur un convertisseur électronique à source de tension (VSC) est la
solution de transport, pour les fermes éoliennes en mer éloignées de
plus de 50 km de la côte. La solution d’un redresseur à diodes dans les
stations de conversion en mer est plus compacte, robuste et moins cher.
Cette thèse porte sur les divers problèmes technologiques et
scientifiques liés au contrôle du réseau alternatif isolé en mer
permettant le raccordement des fermes éoliennes. Ces verrous sont
d’abord examinés en détail dans l’état de l’art. Ensuite, une
organisation du contrôle de la tension et de la fréquence de ce réseau
(dit Grid Forming) est proposée en utilisant les caractéristiques
techniques P-V et Q-f avec une solution pour la synchronisation entre
les éoliennes. Certaines des solutions de contrôle en Grid Forming sont
comparées et évaluées à l'aide de simulations dans le domaine temporel,
pour un cas d'étude donné. Puis, une nouvelle solution est proposée pour
le démarrage du réseau offshore (black start) et un contrôle automatisé
de la supervision, basé sur la modélisation sous forme d’un système à
événements discrets. La théorie du contrôle par supervision est
implémentée et testée pour un cas d'étude. Ensuite, les différents types
de défauts du système sont analysés à l’aide de la littérature; et le
schéma de contrôle du Grid Forming conçu dans cette thèse est complétée
pour apporter une capacité de fonctionnement lors d’un défaut du réseau
AC offshore. Enfin, une brève analyse est faite sur les défis pour
l’intégration de ce type de ferme au réseau MTDC.
Contenu :
Chapter 1: General introduction
Chapter 2: Offshore Wind Power Plants: An Overview
Chapter 3: Dynamic Modelling, Analysis and Control
Chapter 4: Grid Forming: Review and Assesment
Chapter 5: On the Black Start of the Offshore AC Grid and System Restoration
Chapter 6: On the Faults and Multi Terminal DC Integration
Conclusion
download
the extended summary (full text available on 2024, 16th december)
Publications:
International conferences
[C1]
RAMACHANDRAN Ragavendran, POULLAIN Serge, BENCHAIB Abdelkrim, BACHA Seddik, FRANCOIS Bruno,
“AC
Grid Forming by Coordinated Control of Offshore Wind Farm connected to
Diode Rectifier based HVDC Link – Review and Assessment of Solutions”,
Proceeding of EPE'18 ECCE Europe, 17-21 Sept. 2018 , Riga, Latvia
[C2]
K. SHINODA, R. RAMACHANDRAN, A. BENCHAIB, J. DAI, B. FRANCOIS, S. BACHA and X. GUILLAUD,
"Energy Control of Modular Multilevel Converter in
MTDC Grids for Wind Power Integration”,
17th International Workshop on Large-Scale Integration of Wind Power
into Power Systems as well as on Transmission Networks for Offshore Wind
Power PlantsAt: Stockholm, Sweden, October 2018
[C3]
R. Ramachandran, S. Poullain, Abdelkrim Benchaib, Bacha Seddik & Bruno Francois,
“On the Black Start of Offshore Wind Power Plants with Diode Rectifier based HVDC Transmission”,
Proceeding of EPE'19 ECCE Europe, 2-6 Sept. 2019 , Genova, Italy
