Direct interconnection of offshore electricity generators

Abstract

In distributed energy systems, permanent magnet synchronous generators (PMSG) are often connected to the grid via power converters, such as voltage source converters (VSC). The price of the converter constitutes a large part of the costs of a variablespeed turbine (driven either by wind or ocean energy system) and is often required in order to conform to stringent grid codes imposed by transmission system operators (TSOs). While the addition of these components assure compliance they have an impact on the overall reliability and, in an offshore environment, the reliability factor is paramount. A new approach which can be taken by the industry is to rethink the design of their offshore energy devices. In a "farm" like configuration, a different approach can be taken to make the farm compliant rather than involving each individual device.This approach can also be applied for any offshore renewable energy system using synchronous generators. Furthermore onshore locations could benefit from this configuration especially when remote.The performance of the new approach is analyzed, while general guidelines and recommendations imposed by the industry are applied in the analysis. By analyzing the results produced by the simulation model the guidelines for efficient synchronization and load sharing are presented. The simulation model is used to simulate generator paralleling, electromagnetic torque analysis and load transients. A scaled down prototype Wind Farm (WF) was also constructed and its results analyzed and compared to the simulation model. Practical measurements and observations are highlighted and analyzed. Wind speed is entered in the model to simulate behavior of the new approach in different conditions. Fault ride through and ride through capabilities of the model are also partially studied.Keywords: permanent magnet synchronous generators, power converters, synchronization, load sharing, electromagnetic torque, wind turbine design, reliability, offshore renewable energy systems, ruggedized offshore wind turbine design.ii iii Declaration I hereby declare that this submission is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which has been accepted for the award of any other degree or diploma of the University or other institute of higher learning, except where due acknowledgment has been made in the text. Emmanuel PicanCopyright © 2011 Emmanuel Pican.All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission from the author. Unfortunately, meteorological events act as a major factor in offshore power generation and extreme weather is one of the most destructive factors encountered. Cyclones and hurricanes often challenge the offshore energy industry, exposing manufacturers, owners, and investors to significan...

Blade pitch control malfunction simulation in a wind energy conversion system with MPC five-level converter

“…The technology for wind turbine operation at variable speed based on the use of permanent magnet synchronous generator (PMSG) as an option to conventional synchronous generators has the advantage of higher efficiency, due to null copper losses in the rotor [19] and the exclusion of the gearbox, due to ability to operate at low speed [20]. The exclusion of the gearbox mitigates not only the weight and the dimensions of nacelle equipment, but also the mechanic power losses in the conversion and maintenance requirements [19][20][21], which are of particular relevance for offshore deployment. The wind turbine can be operated at the maximum power operating point for various wind speeds by adjusting the shaft speed trough blade pitch control.…”

“…Wind turbine operation at variable speed is a convenient option, because of the characteristics to achieve better efficiency at all operational range of wind speeds [17], allowing to improve energy capturing and to reduce the total harmonic distortion (THD) [18]. The technology for wind turbine operation at variable speed based on the use of permanent magnet synchronous generator (PMSG) as an option to conventional synchronous generators has the advantage of higher efficiency, due to null copper losses in the rotor [19] and the exclusion of the gearbox, due to ability to operate at low speed [20]. The exclusion of the gearbox mitigates not only the weight and the dimensions of nacelle equipment, but also the mechanic power losses in the conversion and maintenance requirements [19][20][21], which are of particular relevance for offshore deployment.…”

HVDC Power transmission simulation for offshore wind system with three-level converter

“…A small error is acceptable in practice and a convenient achievement of this strategy is accomplished with hysteresis comparators [12]. If the current error, given by the comparators hysteresis output, αβ σ , is quantified in five levels is possible to The control strategy carries out a reduction on the capacitors banks unbalancing voltage by considering three vector tables, which take into account the charging state of each capacitor bank selecting the most appropriate voltage vector according to the voltage level of each converter leg, taking advantage of the redundant output voltage vectors.…”

“…The use of a permanent magnet synchronous generator (PMSG) direct drive allows operating at low speed, omitting the gearbox [11]. Moreover, the employment of conventional PMSG or PMSG with superconductors in wind power energy instead of conventional generators has the advantage of higher efficiency, due to the absence of copper losses in the rotor [12]. The gearbox exclusion and the introduction of the variable speed control reduces dimensions and weight of nacelle equipment, power loss in conversion as well as maintenance requirements and promotes the system efficiency [11,12].…”

Offshore Wind Energy System with DC Transmission Discrete Mass: Modeling and Simulation

“…Variable speed operation technology based on the use of permanent magnet synchronous generator (PMSG) as an alternative to conventional synchronous generators as the advantages generally stated for wind power applications: the higher efficiency, due to null copper losses in the rotor [13]; the exclusion of the gearbox, due to ability to operate at low speed [14]. A variable speed wind turbine equipped with a PMSG needs an electronic full-power converter in order to convert the energy captured from the wind into electric energy at a non-constant frequency into constant one.…”