Electrical drives for direct drive renewable energy systems © Woodhead Publishing Limited, 2013 Related titles: Wind energy systems (ISBN 978-1-84569-580-4) Stand-alone and hybrid wind energy systems (ISBN 978-1-84569-527-9) Concentrating solar power technology (ISBN 978-1-84569-769-3) Details of these books and a complete list of titles from Woodhead Publishing can be obtained by: • • • visiting our web site at www.woodheadpublishing.com contacting Customer Services (e-mail: sales@woodheadpublishing.com; fax: +44 (0) 1223 832819; tel.: +44 (0) 1223 499140 ext 130; address: Woodhead Publishing Limited, 80 High Street, Sawston, Cambridge CB22 3HJ, UK) contacting our US office (e-mail: usmarketing@woodheadpublishing.com; tel.: (215) 928 9112; address: Woodhead Publishing, 1518 Walnut Street, Suite 1100, Philadelphia, PA 19102–3406, USA) If you would like e-versions of our content, please visit our online platform: www woodheadpublishingonline.com Please recommend it to your librarian so that everyone in your institution can benefit from the wealth of content on the site We are always happy to receive suggestions for new books from potential editors To enquire about contributing to our Materials series, please send your name, contact address and details of the topic/s you are interested in to sarah.hughes@ woodheadpublishing.com We look forward to hearing from you The Woodhead team responsible for publishing this book: Commissioning Editor: Sarah Hughes Publications Coordinator: Lucy Beg Project Editor: Sarah Lynch Editorial and Production Manager: Mary Campbell Production Editor: Adam Hooper Freelance Project Manager: Bhavani Ganesh Kumar, Newgen Knowledge Works Pvt Ltd Freelance Copyeditor: Nancy Richardson Proofreader: Suma George, Newgen Knowledge Works Pvt Ltd Cover Designer: Terry Callanan © Woodhead Publishing Limited, 2013 Woodhead Publishing Series in Energy: Number 24 Electrical drives for direct drive renewable energy systems Edited by Markus Mueller and Henk Polinder Oxford Cambridge Philadelphia New Delhi © Woodhead Publishing Limited, 2013 Published by Woodhead Publishing Limited, 80 High Street, Sawston, Cambridge CB22 3HJ, UK www.woodheadpublishing.com www.woodheadpublishingonline.com Woodhead Publishing, 1518 Walnut Street, Suite 1100, Philadelphia, PA 19102–3406, USA Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India www.woodheadpublishingindia.com First published 2013, Woodhead Publishing Limited © Woodhead Publishing Limited, 2013 The publisher has made every effort to ensure that permission for copyright material has been obtained by authors wishing to use such material The authors and the publisher will be glad to hear from any copyright holder it has not been possible to contact The authors have asserted their moral rights This book contains information obtained from authentic and highly regarded sources Reprinted material is quoted with permission, and sources are indicated Reasonable efforts have been made to publish reliable data and information, but the authors and the publishers cannot assume responsibility for the validity of all materials Neither the authors nor the publishers, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing Limited The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying Trademark notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Control Number: 2013930286 ISBN 978-1-84569-783-9 (print) ISBN 978-0-85709-749-1 (online) ISSN 2044-9364 Woodhead Publishing Series in Energy (print) ISSN 2044-9372 Woodhead Publishing Series in Energy (online) The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp which is processed using acid-free and elemental chlorine-free practices Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards Typeset by Newgen Knowledge Works Pvt Ltd Printed by MPG Printgroup, UK © Woodhead Publishing Limited, 2013 Contents Contributor contact details Woodhead Publishing Series in Energy ix xi Part I Electrical drive technology 1 Electrical generators for direct drive systems: a technology overview M MUELLER and A ZAVVOS, University of Edinburgh, UK 1.1 1.2 1.3 1.4 1.5 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Introduction Excitation methods Permanent magnet direct drive (PMDD) generator topologies Conclusion References Principles of electrical design of permanent magnet generators for direct drive renewable energy systems H POLINDER, Delft University of Technology, The Netherlands Introduction Design requirements and evaluation criteria Scaling laws for dimensioning machines Design choices Design example Future trends References 21 23 30 30 30 32 33 39 47 48 v © Woodhead Publishing Limited, 2013 vi Contents Electrical, thermal and structural generator design and systems integration for direct drive renewable energy systems A McDONALD, University of Strathclyde, UK and M MUELLER and A ZAVVOS, University of Edinburgh, UK 3.1 3.2 3.3 3.4 3.5 3.6 3.7 Introduction Integrated systems design of machine topologies Structural considerations and mechanical design Thermal considerations Designs of machine topologies for 5–20 MW direct drive wind turbines Application to direct drive marine energy systems References An overview of power electronic converter technology for renewable energy systems Z CHEN, Aalborg University, Denmark 51 51 55 58 70 74 75 76 80 4.1 4.2 4.3 4.4 4.5 4.6 4.7 Introduction Power electronic components Topologies of power electronic converters Modulation techniques in voltage source converters (VSCs) Power control of voltage source converters Conclusion References 80 81 84 88 94 104 104 Power electronic converter systems for direct drive renewable energy applications Z CHEN, Aalborg University, Denmark 106 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 Introduction Characteristics of wind and marine energy generation systems Back-to-back voltage source converter (BTB-VSC) Diode rectifier plus DC/DC converter as the generator side converter Application of current source converters (CSCs) Power electronic system design considerations Power electronic system challenges and reliability Conclusion and future trends References © Woodhead Publishing Limited, 2013 106 107 111 116 121 123 127 132 133 Contents vii Part II Applications: wind and marine 137 Wind turbine drive systems: a commercial overview E DE VRIES, Rotation Consultancy, The Netherlands 139 6.1 6.2 6.3 6.4 6.5 6.6 Introduction Early geared wind turbine drive systems Direct drive generators Doubly fed induction generators (DFIGs) Low- and medium-speed (MS) geared hybrid concept Permanent magnet generators (PMGs) in direct drive wind turbines Alternative technologies and power conversion Reliability, availability and total systems efficiency References 139 140 143 145 147 6.7 6.8 6.9 150 152 154 156 Case study of the permanent magnet direct drive generator in the Zephyros wind turbine 158 A JASSAL, Delft University of Technology, The Netherlands, K VERSTEEGH, XEMC-Darwind, The Netherlands and H POLINDER, Delft University of Technology, The Netherlands 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 Introduction Design process and the resulting design Other design considerations Generator assembly Generator testing Operational experience and problems faced Reliability Future trends Conclusion References Direct drive wave energy conversion systems: an introduction M PRADO and H POLINDER, Delft University of Technology, The Netherlands 8.1 8.2 8.3 8.4 Introduction Wave energy Direct drive in wave energy Conclusion © Woodhead Publishing Limited, 2013 158 158 164 165 167 170 171 172 173 174 175 175 176 184 192 viii Contents 8.5 8.6 Acknowledgement References Case study of the Archimedes Wave Swing (AWS) direct drive wave energy pilot plant M PRADO and H POLINDER, Delft University of Technology, The Netherlands 9.1 9.2 9.3 9.4 9.5 9.6 9.7 10 10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8 10.9 10.10 Introduction AWS wave energy converter AWS pilot plant power take-off (PTO): design and construction AWS pilot plant power take-off (PTO): test results Conclusion Acknowledgement References 192 192 195 195 195 201 208 217 217 217 Application of high-temperature superconducting machines to direct drive renewable energy systems O KEYSAN, University of Edinburgh, UK 219 Introduction Common superconducting wire materials Advantages of superconducting machines Challenges Superconducting machine topologies Direct drive applications Application to wind turbines Application to wave energy Conclusion References 219 223 227 229 231 235 237 246 247 248 Index 253 © Woodhead Publishing Limited, 2013 Contributor contact details (* = main contact) EH9 3JL UK Editors E-mail: markus.mueller@ed.ac.uk Professor Markus Mueller Institute for Energy Systems School of Engineering Mayfield Road University of Edinburgh Edinburgh EH9 3JL UK E-mail: markus.mueller@ed.ac.uk Dr Henk Polinder Electrical Power Processing Electrical Engineering, Mathematics and Computer Science Delft University of Technology Mekelweg 2628 CD Delft The Netherlands E-mail: H.Polinder@tudelft.nl Chapter Professor Markus Mueller* and Aristides Zavvos Institute for Energy Systems School of Engineering Mayfield Road University of Edinburgh Edinburgh Chapter Dr Henk Polinder Electrical Power Processing Electrical Engineering, Mathematics and Computer Science Delft University of Technology Mekelweg 2628 CD Delft The Netherlands E-mail: H.Polinder@tudelft.nl Chapter Dr Alasdair McDonald* Wind Energy Systems Doctoral Training Centre Department for Electronic and Electrical Engineering Room 3-36, Royal College Building University of Strathclyde 204 George Street Glasgow G1 1XW UK E-mail: alasdair.mcdonald@strath ac.uk ix © Woodhead Publishing Limited, 2013 250 Electrical drives for direct drive renewable energy systems Kakani, S (2009) Superconductivity Anshan Ltd Kalsi, S., Gamble, B., Snitchler, G and Ige, S (2006) The status of HTS ship propulsion motor developments IEEE Power Engineering Society General Meeting, 5pp Kalsi, S., Weeber, K., Takesue, H., Lewis, C., Neumueller, H and Blaugher, R (2004) Development status of rotating machines employing superconducting field windings Proceedings of the IEEE, 92(10):1688–704 Kalsi, S S (2011) Applications of High Temperature Superconductors to Electric Power Equipment John Wiley & Sons, Inc., Hoboken, NJ, USA Kautz, R (2012) 100 years of superconductivity Physics Today, 65(7):54 Keysan, O and Mueller, M A (2011) A homopolar HTSG topology for large direct-drive wind turbines IEEE Transactions on Applied Superconductivity, 21(5):3523–31 Keysan, O and Mueller, M A (2012) A linear superconducting generator for wave energy converters In Power Electronics, Machines and Drives, PEMD, IET Conference on, p B134, Bristol Klaus, G., Nick, W., Neumueller, H., Nerowski, G and McCown, W (2006) Development of high-temperature superconducting electrical machines at Siemens AG In International Conference on Electrical Machines, ICEM, pp 1–6 Klaus, G., Wilke, M., Frauenhofer, J., Nick, W and Neumueller, H (2007) Design challenges and benefits of HTS synchronous machines IEEE Power Engineering Society General Meeting, pp 1–8 Lee, S.-H., Hong, J., Kwon, Y., Jo, Y.-S and Baik, S K (2008) Study on homopolar superconductivity synchronous motors for ship propulsion applications IEEE Transactions on Applied Superconductivity, 18(2):717–20 Leijon, M., Danielsson, O., Eriksson, M., Thorburn, K., Bernhoff, H., Isberg, J., Sundberg, J., Ivanova, I., Sjostedt, E., Agren, O and others (2006) An electrical approach to wave energy conversion Renewable Energy, 31(9):1309–19 Lesser, M and Müller, J (2009) Superconductor Technology Generating the Future of Offshore Wind Power Renewable Energy World Conference, Cologne, Germany, pp 1–10 Lewis, C and Muller, J (2007) A Direct Drive Wind Turbine HTS Generator 2007 IEEE Power Engineering Society General Meeting, pp 1–8 Maki, N (2008) Design study of high-temperature superconducting generators for wind power systems Journal of Physics: Conference Series, (97)012155 Maples, B., Hand, M and Musial, W (2010) Comparative Assessment of Direct Drive High Temperature Superconducting Generators in Multi-Megawatt Class Wind Turbines Technical Report October, National Renewable Energy Laboratory (NREL), Golden, CO Masson, P J., Breschi, M., Tixador, P and Luongo, C A (2007a) Design of HTS Axial Flux Motor for Aircraft Propulsion IEEE Transactions on Applied Superconductivity, 17(2):1533–6 Masson, P J., Pienkos, J E and Luongo, C A (2007b) Scaling up of HTS motor based on trapped flux and flux concentration for large aircraft propulsion IEEE Transactions on Applied Superconductivity, 17(2):1579–82 Matsuzaki, H., Kimura, Y., Ohtani, L., Marita, E., Ogata, H., Izumi, M., Ida, T., Sugimoto, H., Miki, M., Kitano, M and Fujimoto, H (2006) Mechanical and © Woodhead Publishing Limited, 2013 Application of high-temperature superconducting machines 251 cryogenic design of a synchronous rotating machines with HTS pole-field magnets IEEE Power Engineering Society General Meeting, p Mueller, M., Polinder, H and Baker, N (2007) Current and novel electrical generator technology for wave energy converters 2007 IEEE International Electric Machines & Drives Conference, (1):1401–6 Ohsaki, H., Sekino, M., Suzuki, T and Terao, Y (2009) Design study of wind turbine generators using superconducting coils and bulks 2009 International Conference on Clean Electrical Power, pp 479–84 Okazaki, T., Sugimoto, H and Takeda, T (2006) Liquid nitrogen cooled HTS motor for ship propulsion In IEEE Power Engineering Society General Meeting, p Putti, M and Grasso, G (2011) MgB2, a two-gap superconductor for practical applications MRS Bulletin, 36(08):608–13 Quddes, M R., Sekino, M., Ohsaki, H., Kashima, N and Nagaya, S (2011) Electromagnetic design study of transverse flux enhanced type superconducting wind turbine generators IEEE Transactions on Applied Superconductivity, 21(3):1101–4 Razeti, M., Angius, S., Bertora, L., Damiani, D., Marabotto, R., Modica, M., Nardelli, D., Perrella, M and Tassisto, M (2008) Construction and operation of cryogen free MgB2 magnets for open MRI systems IEEE Transactions on Applied Superconductivity, 18(2):882–6 Sawada, K (2009) Outlook of the superconducting Maglev Proceedings of the IEEE, 97(11):1881–5 Schiferl, R., Flory, A., Umans, S and Livoti, W (2006) High temperature superconducting synchronous motors: Economic issues for industrial applications IEEE Industry Applications Society 53rd Annual Petroleum and Chemical Industry Conference, pp 1–9 Snitchler, G (2010) Progress on high temperature superconductor propulsion motors and direct drive wind generators Power Electronics Conference (IPEC), 2010, (c):5–10 Stumberger, G., Aydemir, M., Zarko, D and Lipo, T (2004) Design of a linear bulk superconductor magnet synchronous motor for electromagnetic aircraft launch systems IEEE Transactions on Appiled Superconductivity, 14(1):54–62 Sugimoto, H., Tsuda, T., Morishita, T., Hondou, Y., Takeda, T., Togawa, H., Oota, T., Ohmatsu, K and Yoshida, S (2007) Development of an axial flux type PM synchronous motor with the liquid nitrogen cooled HTS armature windings IEEE Transactions on Applied Superconductivity, 17(2):1637–40 SuperOx Web Page Available at: http://www.superox.ru/ [Accessed 13 August 2012] Terao, Y., Sekino, M and Ohsaki, H (2010) Design study of linear synchronous motors using superconducting coils and bulks In Power Electronics Conference (IPEC), 2010 International, pp 1760–5 IEEE Terao, Y., Sekino, M and Ohsaki, H (2012) Electromagnetic design of 10 MW class fully superconducting wind turbine generators IEEE Transactions on Applied Superconductivity, 22(3):5201904 Tong, W (2010) Wind Power Generation and Wind Turbine Design WIT Press UpWind (2011) UpWind – Design Limits and Solutions for Very Large Wind Turbines – EU 6th Frame Project Technical report © Woodhead Publishing Limited, 2013 252 Electrical drives for direct drive renewable energy systems Wen, H., Bailey, W., Goddard, K., Al-Mosawi, M K., Beduz, C and Yang, Y (2009) Performance test of a 100 kW HTS generator operating at 67 K-77 K IEEE Transactions on Applied Superconductivity, 19(3):1652–5 Yen, F., Li, J., Zheng, S J., Liu, L., Ma, G T., Wang, J S and Wang, S Y (2010) A single-sided linear synchronous motor with a high temperature superconducting coil as the excitation system Superconductor Science and Technology, 23(10):105015 Zhang, T., Haran, K., Laskaris, E and Bray, J (2011) Design and test of a simplified and reliable cryogenic system for high speed superconducting generator applications Cryogenics, 51(7):380–3 © Woodhead Publishing Limited, 2013 Index AC/AC converter, 177, 178, 185, 196, 198 AC voltage-oriented vector control, 95–8 VOC on d-q reference frame vector diagram, 97 voltage source converter connected to an AC source, 96 active stall control, 141 AF PMDD machines, 13–19 air cored PMDD generator topology, 18 double-sided AF PMDDTORUS machine, 16 double-sided slotted AF PMDD machine with double stator, 16 single-sided slotted AF PMDD machine, 14 single-sided slotted AF PMDD machine with stator balance, 15 single-sided surface-mounted TFPM machine, 19 three-stage TORUS machine, 18 air cored rotor, 232 American Superconductor, 48 ANSYS, 66 Archimedes Wave Swing (AWS) direct drive wave energy pilot plant, 195–217 power take-off (PTO), 201–8, 208–16 wave energy converter, 195–201 axial-flux generators, 35 axial-flux machines, 234–5 magnetised bulk HTS, 235 cascaded H-bridge, with medium-frequency transformer, 116, 117 combination of multilevel topology and a multi-H bridge topology, 115–16 control schemes of BTB-VSC PWM converters, 113 P, Q control of a vector-controlled PWM VSC, 112 3P HP-BTB, 115 schemes of deriving reference signals for power electronic control systems, 114 three-level neutral-point clamped back-to-back converter (3LNPC-BTB), 115 three-level neutral-point diode-clamped back-to-back topology (3L NPC-BTB), 114–15 three-phase H-bridge back-to-back topology (3P HB-BTB), 115 udc,Q control of vector-controlled PWM VSC, 113 bearing configuration, 159–60 single-bearing design used in the Z72/2000 wind turbine, 160 Bi-2212, 224 Bi-2223, 224 bismuth strontium calcium copper oxide (BSCCO), 223–4 tape vs rated copper wire, 224 brushless induction generator, 152 back-to-back voltage source converter (BTB-VSC), 111–16, 117 back-to-back two-level PWM voltage source converter system, 111 Carter factor, 40 Cascade H-Bridge (CHB) converter, 85, 86 centripetal forces, 54 253 © Woodhead Publishing Limited, 2013 254 Index cogging torque, 165 continuous load test, 169 control system response, 169 conventional stator, 231–3 different stator topologies of HTS machines, 233 copper, 33–4 cryocoolers, 248 current source converter (CSC), 83 Danish Concept, 140–1 demagnetisation, 35 diode rectifier plus DC/DC converter, 116–21 24-pulse inverter with multi-winding transformer, 120 control schemes of diode rectifier + DC/DC converter and PWM converter, 118 diode rectifier configurations for modular PM generators, 119 interleaved DC/DC converter topologies, 119 multi-interleaved converter power electronic grid interface, 120 multi-modular diode rectifier systems, 118–19 multi-voltage source converter topologies, 119–21 power electronic conversion system with diode rectifier, 118 power electronic system with an interleaved DC/DC converter, 119 direct drive generators application to direct drive marine, 75–6 direct drive tidal power, 75 direct drive wave power, 75–6 OpenHydro integrated turbine/ generator rotor with blades and magnets, 76 challenges – forces, 62–4 generator weight, 63 thermal strain, 63–4 cylinder model of torque produced by a generator, 52 direct drive permanent magnet generator, 53 electrical, thermal and structural design and systems integration, 51–76 electromagnetic, thermal and structural design, 54–5 forces at play in the generator, 54 forces in electrical machines, 52–4 integrated systems design of machine topologies, 55–8, 59, 60 design perspectives, 55–7 early design stages – integrated approach, 60 early design stages – traditional approach, 59 electrical design perspective, 56 flowchart of design process, 57–8 manufacturing design perspective, 59 mechanical design perspective, 57 thermal design perspective, 58 interactions between electrical, thermal and mechanical design aspects, 55 machine topologies designs for 5–20 MW direct drive wind turbines, 74–5 modelling approaches, 64–9 analytical approaches: axial-flux machines, 66 analytical approaches: radial-flux machine, 66 analytical approaches to strain modelling, 65–6 axial-flux model, 67 cost modelling through scaling, 64–5 deflection modes for radial-flux machine, 66 Grauers’ structure cost modelling through scaling, 64 numerical approaches, 66–7 optimisation, 67–9 radial-flux models, 67 variable dimensions used for optimisation of generator structures, 68 size, 51–2 structural consideration and mechanical design, 58, 60–70 © Woodhead Publishing Limited, 2013 Index design approaches and alternative solutions, 69–70 direct drive wind turbine layout, 58, 60–2 generator downwind of the tower, Scanwind/GE, 60 generator over the tower, MTorres, 61 generator upwind of the tower with single bearing, STX93, 61 inner and outer rotor generator variants, 62 thermal considerations, 70–4 cooling approaches in direct drive wind turbines, 72–3 ironless radial-flux generator, 72 shortening of the load path using various airgap bearing technologies, 71 thermal modelling of electrical machines, 74 Vensys 2.5MW, 73 VENSYS 1.5MW wind turbine, 73 direct drive machine wave energy, 184–92 direct drive option for the SEAREV WEC, 188 ‘Duck’ WEC concept, 186 experimental linear generator, 187 historical review, 185–9 limitations and solutions, 189–92 patent of a linear generator application, 185 total cost of a linear generator for the AWS WEC, 192 WECs equipped with direct drive PTO, 188 direct drive renewable energy systems electrical, thermal and structural generator design and systems integration, 51–76 application to direct drive marine, 75–6 integrated systems design of machine topologies, 55–8 machine topologies designs for 5–20 MW direct drive wind turbines, 74–5 255 structural consideration and mechanical design, 58–70 thermal considerations, 70–4 high temperature superconducting machines, 219–48 advantages, 227–9 application to wave energy, 246–7 application to wind turbines, 237–46 challenges, 229–31 direct drive applications, 235–7 overview, 219–23 superconducting wire materials, 223–7 topologies, 231–5 permanent magnet generators electrical design principals, 30–48 design choices, 33–9 design example, 39–46 design requirements and evaluation criteria, 30–1 future trends, 47–8 scaling laws for dimensioning machines, 32–3 power electronic converter systems for applications, 106–32 back-to-back voltage source converter (BTB-VSC), 111–16 challenges and reliability, 127–31 design considerations, 123–7 diode rectifier plus DC/DC converter, 116–21 direct drive wind turbine system with full rate power electronic interface, 107 future trends, 132 thyristor converter with active compensator, 121–3 wind and marine energy generation systems characteristics, 107–11 direct drive systems electrical generators, 3–23 excitation methods, 5–9 permanent magnet direct drive generator topologies (PMDD), 9–21 schematic diagram, © Woodhead Publishing Limited, 2013 256 Index direct drive wave energy conversion systems, 175–92 direct drive machine in wave energy, 184–92 wave energy, 176–84 direct drive wave energy pilot plant Archimedes Wave Swing (AWS), 195–217 power take-off (PTO), 201–8, 208–16 wave energy converter, 195–201 direct drive wind turbines, 150–2 direct power control (DPC) block diagram of direct torque (power) control, 103 direct torque control (DTC), 102–3 block diagram of direct torque (power) control, 103 doubly fed induction generators (DFIG), 145–7 alternatives, 152–3 developments, 146–7 grid requirements, 146 dynamic tidal power (DTP), 109 E-17 wind turbine, 142–3 E-18 wind turbine, 142–3 E-32 wind turbine, 142–3 E-40 wind turbine, 143 E-66 wind turbine, 144 E-70 wind turbine, 144 E-82 wind turbine, 144 E-92 wind turbine, 144 E-101 wind turbine, 144 E-112 wind turbine, 144 E-115 wind turbine, 144 E-126 wind turbine, 144 earthing, 169 electrical excitation, 35–7 electrical generators, 3–23 dimensions of rotating machine and acting shear stress, direct drive system, excitation methods, 5–9 electrically excited direct drive (EEDD) generators, 5–6 Enercon E-126 MW WEC, interior parts of MW GE wind turbine, permanent magnet direct drive (PMDD) generators, 7–8 SRG operating principle, switched reluctance direct drive generators, 8–9 permanent magnet direct drive generator topologies (PMDD), 9–21 AF PMDD machines, 13–19 air cored PMDD generator topology, 18 double-sided AF PMDDTORUS machine, 16 double-sided slotted AF PMDD machine with double stator, 16 ironless RF PMDD machine, 12 magnetic bearing set-up for an iron cored RF PMDD generator, 14 NewGen generator concept, 13 outer rotor RF PMDD machine, 11 permanent magnet synchronous machine with cheap fractional pitch winding, 12 RF PMDD machine, 10 RF PMDD machine with flux concentrators housing the PM material, 11 RF PMDD machines, 9–13, 14 single-sided slotted AF PMDD machine, 14 single-sided slotted AF PMDD machine with stator balance, 15 single-sided surface-mounted TFPM machine, 19 suggested TF PMDD topologies found in literature, 21, 22 TF PMDD machine with toothed rotor and flux concentrators, 23 TF PMDD machines, 19–21 three-stage TORUS machine, 18 electrically excited direct drive (EEDD) generators, 5–6 Enercon E-126 MW WEC, EU-FP6 UPWIND project, 121 exciter permanent magnet generator, 146 external field excitation, 143–5 competing designs, 144–5 Enercon technology developments, 144 © Woodhead Publishing Limited, 2013 Index fault tree analysis, 129–30 firing through, 169 first-order reliability method (FORM), 129 fixed-speed generator, 140–1, 153 fixed-speed turbine, 141–2 Flexi-Slip, 142 flux pinning, 222 Flying Capacitor (FLC) converter, 85 force density, 32 forced air cooling, 72 Forced Commutation Controlled Series Capacitor (FCSC), 116 force–speed relation, 203, 204 full-pitch double-layer winding, 164 Gate Turn-Off Thyristors (GTO), 82 generator force, 202–6 force–speed characteristic of the linear generator, 205 generator housing assembly, 166 generator rotor assembly finite element (FE) estimation of deflection of rotor structure, 166 generator shaft assembly, 166 generator stator assembly, 166 gravity, 54, 63 high temperature superconductors, 191, 223 advantages, 227–9 high power density, 227–8 size and mass of direct drive permanent magnet vs.superconducting generator, 228 slow thermal ageing, 229 superior rigid performance, 228–9 application to wave energy, 246–7 application to wind turbines, 237–46 challenges, 229–31 comparison of cooling power required with different coolant gases, 229 cooling, 229–31 rotor mechanical structure, 231 typical liquid nitrogen cryocooler layout, 230 direct drive applications, 235–7 257 direct drive renewable energy systems, 219–48 overview, 219–23 electrical resistivity variation with temperature, 220 superconducting elements and compounds, 220 superconductivity region boundaries, 221 superconductor properties, 221 superconducting wire materials, 223–7 topologies, 231–5 High Voltage Direct Current (HVDC) system, 84 homopolar superconducting machine, 233–4 layout, 234 horizontal-axis wind turbines, 140 hysteresis controllers, 93 IC40 cooling, 160 importance sampling, 129 Ingecon Clean Power Series System, 146 Injected Enhanced Gate Transistors (IEGT), 82, 83 Insulated Gate Bipolar Transistors (IGBT), 82, 83 Insulated Gate Commutated Thyristors (IGCT), 82, 83 Intelligent Power Module (IPM), 83 IQgear, 154 laminated electrical steel, 33 Life Cycle Costs (LCC), 149 light load test, 169 liquid cooling, 73 longitudinal flux machine (LFM), 187 LW30 wind turbine, 142 LW80 wind turbine, 142 33M-VS wind turbine, 143 magnesium diboride (MgB2 ), 226 magnetic rotor arrangement, 232 magnets, 34–5 matrix converter, 88 © Woodhead Publishing Limited, 2013 258 Index mechanical impedance, 202–6 bode diagram of the total electrical impedance, 205 medium-speed wind turbines, 149 medium-voltage converter, 161 Megger, 168 Meissner-Ochsenfeld Effect, 222 modulation, 88 Monte Carlo analysis, 129 mooring, 198 multibrid technology, 148–9 Multilevel Converters (M2LC or M2C or MMC), 85, 86 1.5 MW/2 MW PMG wind turbine, 151 10 MW Clipper Britannia, 151 2.5 MW GE wind turbine, 151 MW Multibrid M5000 wind turbine, 148 MW Multibrid wind turbine, 148 MW V164–7.0 MW wind turbine, 149 MW V164–8.0 MW wind turbine, 150 natural sinusoidal PWM, 88–9 neodymium iron boron (NdFeB) magnet, 34 neutral-point clamped converters, 85, 104 NewGen, 70 normal component of Maxwell stress, 63 normal stress, 53 NTK1500/60 wind turbine, 144 optimal power conversion, 180–2 fraction of optimal input active power absorbed by the PTO, 182 OptiSlip, 142 ovalising, 65 over-speed test, 169 passive cooling, 72 perfect diamagnetism, 222 superconductor levitating above permanent magnets, 223 permanent magnet direct drive generator, 7–8 assembly, 165–7 design considerations, 164–5 design process and result, 158–64 generator efficiency curve, 164 geometry and dimensions, 162–3 radial-flux PM generator, 162 single line diagram of the whole turbine, 162 site conditions and general layout, 159–60 sizing and topology, 160–1 voltage level and converter selection, 161–2 winding, 163–4 Z72 design features, 163 future trends, 172–3 cost breakdown of Zephyros turbine, 173 interior parts of MW GE wind turbine, operation, 170–1 calculated and measured power curve, 171 erection of Zephyros wind turbine, 170 reliability, 171–2 testing, 167–70 back-to-back test set-up, 167 back-to-back testing, 168 converter and control tests, 168–70 insulation resistance, 168 topologies, 9–21, 22, 23 AF PMDD machines, 13–19 air cored PMDD generator topology, 18 double-sided AF PMDDTORUS machine, 16 double-sided slotted AF PMDD machine with double stator, 16 ironless RF PMDD machine, 12 magnetic bearing set-up for an iron cored RF PMDD generator, 14 NewGen generator concept, 13 outer rotor RF PMDD machine, 11 permanent magnet synchronous machine with cheap fractional pitch winding, 12 RF PMDD machine, 10 RF PMDD machine with flux concentrators housing the PM material, 11 RF PMDD machines, 9–13, 14 © Woodhead Publishing Limited, 2013 Index single-sided slotted AF PMDD machine, 14 single-sided slotted AF PMDD machine with stator balance, 15 single-sided surface-mounted TFPM machine, 19 suggested TF PMDD topologies found in literature, 21, 22 TF PMDD machine with toothed rotor and flux concentrators, 23 TF PMDD machines, 19–21 three-stage TORUS machine, 18 Zephyros wind turbine, 158–74 permanent magnet generators, 145 alternatives, 152–3 design choices, 33–9 design example, 39–46 design optimisation, 43 efficiency, 45–6 generator system characteristics, 45 loss calculations, 41–2 material characteristics, main dimensions, parameters and weights, 44 parameter calculations, 40–1 resulting design, 43–4 rough numbers characterising active materials of direct drive generators, 45 scaling laws, 44–5 design requirements and evaluation criteria, 30–1 direct drive wind turbines, 150–2 electrical design principals, 30–48 future trends, 47–8 machine topology choices, 35–9 buried magnets with flux concentration or surface-mounted magnets, 38 distributed windings or concentrated fractional pitch windings, 37–8 electrical or PM excitation, 35–7 equivalent circuit of a PM synchronous machine and phasor diagram, 39 four pole pitches of a permanent magnet excited generator, 36 259 machine with concentrated fractional pitch winding, 38 open slots, semi-closed slots or slots with magnetic wedges, 37 power factor, 38–9 radial-flux or axial-flux generators, 35 skew or not, 38 stators with slots, air-gap winding or air cored machines, 37 two pole pitches of an electrically excited generator, 36 voltage level selection, 38 material choices, 33–5 copper for windings, 33–4 indications for characteristics of permanent magnets, 34 laminated electrical steel, 33 magnets, 34–5 scaling laws for dimensioning machines, 32–3 rotor surface with a surface area that produces a force, 32 permanent magnet (PM), 158, 167, 201, 235 excitation, 35–7 piston chamber sealing, 197 pitch-controlled fixed speed, 141–2 plastic-pack IGBT, 83 pole-switchable generators, 141 power conversion systems, 153–4 Power Electronic Building Block (PEBB), 88 power electronic converter systems back-to-back voltage source converter (BTB-VSC), 111–16, 117 back-to-back two-level PWM voltage source converter system, 111 cascaded H-bridge back-to-back converter medium-frequency transformers (CHB-MFT), 116, 117 combination of multilevel topology and a multi-H bridge topology, 115–16 control schemes of BTB-VSC PWM converters, 113 © Woodhead Publishing Limited, 2013 260 Index power electronic converter systems (cont.) P, Q control of a vector-controlled PWM VSC, 112 3P HP-BTB, 115 schemes of deriving reference signals for power electronic control systems, 114 three-level neutral-point clamped back-to-back converter (3LNPC-BTB), 115 three-level neutral-point diode-clamped back-to-back topology (3L NPC-BTB), 114–15 three-phase H-bridge back-to-back topology (3P HB-BTB), 115 udc,Q control of vector-controlled PWM VSC, 113 challenges and reliability, 127–31 condition monitoring and reliability improvements, 131 factors affecting reliability, 127–9 fault tree for reliability analysis, 129–30 fault tree for solid-state shunt substation sag suppressor, 130 reliability evaluation, 129 design considerations, 123–7 comparative study, 125–7 power loss simulation results of the converters, 126 diode rectifier plus DC/DC converter, 116–21 24-pulse inverter with multi-winding transformer, 120 control schemes of Diode rectifier + DC/DC converter and PWM converter, 118 diode rectifier configurations for modular PM generators, 119 interleaved DC/DC converter topologies, 119 multi-interleaved converter power electronic grid interface, 120 multi-modular diode rectifier systems, 118–19 multi-voltage source converter topologies, 119–21 power electronic conversion system with diode rectifier, 118 power electronic system with an interleaved DC/DC converter, 119 direct drive renewable energy systems applications, 106–32 direct drive wind turbine systems with a full rate power electronic interface, 107 future trends, 132 thyristor converter with active compensator, 121–3 12-pulse SCR-CSC, 122 diode rectifier plus SCR-CSC at grid side, 121–2 power electronic conversion system with BTB PWM-CSC configuration, 123 PWM current-source converters, 122–3 wind and marine energy generation systems characteristics, 107–11 tidal power conversion, 109–10 wave power conversion, 110–11 wind power converter characteristics, 108 wind turbine power conversion, 107–9 power electronic converter technology, 80–104 modulation techniques in voltage source converters (VSC), 88–94 controllers of current controlled VSC, 93 current-control PWM techniques, 93–4 modulation methods for voltage source converter (VSC), 89 natural sinusoidal PWM waveforms, 90 space voltage vector PWM scheme, 91 voltage-control PWM techniques, 88–92 power control of voltage source converters, 94–103 AC voltage-oriented vector control, 95–8 © Woodhead Publishing Limited, 2013 Index block diagram of direct torque (power) control, 103 block diagram of VFOC on the d-q reference frame, 100 block diagram of VOC on d-q reference frame, 98 diagram of rotor flux-oriented vectors, 100 direct torque control (DTC) and direct power control (DPC) methods, 102–3 flux-oriented control (FOC) vector diagram, 99 reference frames, 94 reference frames for vector control, 94–5 rotor flux-oriented vector control for synchronous machines, 100–2 virtual flux-oriented reference frame, 98–100 VOC on d-q reference frame vector diagram, 97 voltage source converter connected to an AC source, 96 power electronic components, 81–3 characteristics of main switchable semiconductor devices, 82 medium- and high-power semiconductors classification, 81 topologies, 84–8 AC↔DC power electronic converters classification, 84 matrix converter circuit configuration, 87 one-leg/single-phase multilevel VSC, 86 six-pulse power electronic converters, 85 three-phase multilevel voltage source converter, 87 Z-source converter circuit converter, 87 power factor, 38–9 power output smoothing, 182–3 Pelamis, 183 Wave Dragon, 183 Wave Star, 183 power overshoot, 141 261 power systems efficiency, 155–6 power take-off (PTO), 177–82, 184–5, 201–8, 208–16 assembly, 208–10 Alstom AC/AC converter, resistor banks, capacitors and power transformers, 210 calculated flux linkage from measured no-load generator output voltage, 211 measured no-load voltage, 210 construction and installation, 207–8 converter with resistor banks, power factor correction capacitors and transformers, 209 linear generator stator and translator segments, 209 stator segment with coils, 208 translator segment with magnets, 208 converter, 206–7 AC/AC converter equivalent models, 207 AC/AC converter used to grid connect the linear generator, 206 generator design, 201–6 overlapping of translator and stator and four pole pitches of the linear PM generator, 203 single-phase circuit model of the linear generator, cable and land station, 204 grid connected, 213–16 generator position estimates based on air pressure measurements, 214 measured currents at the input of converter, 215 test results with generator connected to the grid via the converter, 216 resistive load, 210–13 measured voltage and measured/ computed current, 212 test result with generator connected to the resistor bank, 212, 214 press-pack IGBT, 83 © Woodhead Publishing Limited, 2013 262 Index proportional integral (PI)-controllers, 97 pulse width modulation (PWM) voltage source converter system, 111 quench, 222 radial-flux generators, 35 rare earth elements (REE), 150, 152–3 materials use, 155–6 rare earth magnet, 34 reliability, availability and maintainability (RAM), 172 renewable energy systems power electronic converter technology, 80–104 modulation techniques in voltage source converters (VSC), 88–94 power control of voltage source converters, 94–103 power electronic components, 81–3 topologies, 84–8 RF PMDD machines, 9–13, 14 ironless RF PMDD machine, 12 magnetic bearing set-up for an iron cored RF PMDD generator, 14 NewGen generator concept, 13 outer rotor, 11 permanent magnet synchronous machine with cheap fractional pitch winding, 12 RF PMDD machine with flux concentrators housing the PM material, 11 schematic diagram, 10 rotor current control (RCC), 142 rotor eccentricity, 165 rotor flux-oriented vector control, 100–2 rotor speed, 153, 161–2 SEAREV, 187 second-order reliability method (SORM), 129 semiconductors, 81 shear stress, 53, 62–3 ship propulsion systems, 236–7 AMSC36.5 MW, superconducting vs conventional machine, 236 converteam MW HTS ship propulsion motor, 236 short-circuit analysis, 165 slotless stator, 233 slotted stator, 233 space vector pulse width modulation (SVPWM), 90, 125 squirrel-cage induction generator, 152 stall point, 141 superconducting rotor, 231–3 superconducting wind turbine generator requirements, 240–2 availability, 241 cost, 242 reliability, 240–1 superGEAR hydrostatic system, 154 Sustainable Energy Technologies (SET), 154 switched reluctance generator (SRG), 5, 8–9 operating principle, Symmetrical Gate Commutated Thyristors (SGCT), 82, 83 thermal strains, 54 thermo-mechanical fatigue, 128 three-level neutral-point clamped back-to-back converter (3LNPC-BTB), 115 three-level neutral-point diode-clamped back-to-back topology (3L NPC-BTB), 114–15 three-phase H-bridge back-to-back topology (3P HB-BTB), 115 thyristor converter with active compensator, 121–3 12-pulse SCR-CSC, 122 diode rectifier plus SCR-CSC at grid side, 121–2 power electronic conversion system with BTB PWM-CSC configuration, 123 PWM current-source converters, 122–3 tidal barrages, 109 tidal power conversion, 109–10 tidal stream generators (TSG), 109 tilt angle, 63 torque transmission, 53 TORUS, 16–17 © Woodhead Publishing Limited, 2013 Index total harmonic distortion (THD), 125 total magnetic reluctance, 165 translator–stator attractive forces, 189 translator–stator overlap, 190 transverse flux machine (TFM), 190 Transverse Flux Permanent Magnet Direct Drive, 69 turbine availability, 155 TW1.5 wind turbine, 144 type II superconductors, 222 variable reluctance machines, 47 variable-speed wind turbine, 142–3 Vernier hybrid machine, 47 vertical-axis wind turbines, 140 virtual flux-oriented control (VFOC), 99 virtual flux-oriented reference frame, 98–100 block diagram of VFOC on the d-q reference frame, 100 block diagram of VOC on d-q reference frame, 98 diagram of rotor flux-oriented vectors, 100 flux-oriented control (FOC) vector diagram, 99 V63–1.5MW wind turbine, 144 voltage-oriented control (VOC), 98 voltage source converter (VSC), 104 AC voltage-oriented vector control, 95–8 VOC on d-q reference frame vector diagram, 97 voltage source converter connected to an AC source, 96 direct torque control (DTC) and direct power control (DPC) methods, 102–3 block diagram of direct torque (power) control, 103 modulation techniques, 88–94 controllers of current controlled VSC, 93 current-control PWM techniques, 93–4 natural sinusoidal PWM waveforms, 90 schematic diagram, 89 263 space voltage vector PWM scheme, 91 voltage-control PWM techniques, 88–92 power control, 94–103 reference frames for vector control, 94–5 reference frames, 94 rotor flux-oriented vector control for synchronous machines, 100–2 virtual flux-oriented reference frame, 98–100 block diagram of VFOC on the d-q reference frame, 100 block diagram of VOC on d-q reference frame, 98 diagram of rotor flux-oriented vectors, 100 flux-oriented control (FOC) vector diagram, 99 wave energy, 176–84, 246–7 direct drive machine, 184–92 direct drive option for the SEAREV WEC, 188 ‘Duck’ WEC concept, 186 experimental linear generator, 187 historical review, 185–9 limitations and solutions, 189–92 patent of a linear generator application, 185 total cost of a linear generator for the AWS WEC, 192 WECs equipped with direct drive PTO, 188 linear superconducting generator for direct drive WEC, 247 World resources, 176–7 World distribution of offshore wave power, 176 wave energy converter (WEC), 177–8, 182, 183–4, 184–5, 186–7, 195–201 concept, 195–6 AWS operating principle, 196 design challenges, 183–4 developments, 201 fundamentals, 177–83 AC/AC converter and its basic functional unit, 177 © Woodhead Publishing Limited, 2013 264 Index wave energy converter (WEC) (cont.) equivalent electrical circuit of the captors dynamics, 179 one degree of freedom oscillating captor, 178 PTO velocity and input mechanical power signals, 180 pilot plant, 197–201 AWS at the beginning of the submersion operation, 200 AWS connected to land station, 199 AWS during final assembly, 199 moving piston with guiding structure and pontoon, 198 underwater image of AWS’s piston first motion, 200 wave power conversion, 110–11 wind turbine drive systems alternative technologies and power conversion, 152–4 commercial overview, 139–56 types, 139–40 direct drive generators, 143–5 doubly fed induction generators (DFIG), 145–7 early geared, 140–3 low and medium-speed geared hybrid concept, 147–50 product development, 149–50 permanent magnet generators in direct drive wind turbines, 150–2 reliability, availability and total systems efficiency, 154–6 wind turbines, 237–46 commercial projects, 242–6 AML 10 MW 10 rpm fully superconducting generator, 244 AMSC 10 MW SeaTitan generator, 243 converteam 1.7 MW 214 rpm HTS hydro generator and MW 12 and rpm direct drive HTS wind turbine generator, 245 emerging market projection for offshore wind energy converters, 237 loading, 53 mass comparison of direct drive systems, 238–40 mass of different large direct drive machines, 240 torque density comparison of conventional and superconducting generators, 239 power conversion, 107–9 superconducting wind turbine generator requirements, 240–2 xDFM, 146–7 yttrium barium copper oxide (YBCO), 224–7 coated conductor layers, 225 performance and price comparison for some common superconductors, 227 performance comparison of some common superconductors, 226 price projection, 226 Z72 wind turbine, 165, 168, 171–2 Zephyros permanent magnet direct drive generator, 158–74 design considerations, 164–5 design process and result, 158–64 future trends, 172–3 generator assembly, 165–7 generator testing, 167–70 operation, 170–1 reliability, 171–2 Z72/2000 wind turbine, 159 zero resistivity, 221 electrical representation of a superconductor, 222 © Woodhead Publishing Limited, 2013