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Basic Operation Principles and Electrical Conversion Systems of Wind Turbines. H. Polinder, S.W.H. de Haan, J.G. Slootweg, M.R. Dubois. Norpie, 14-16 June 2004. 1 Introduction. Environmental concern. 1 Structure. Introduction Basic relations Often used generator systems
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Basic Operation Principles and Electrical Conversion Systems of Wind Turbines H. Polinder, S.W.H. de Haan, J.G. Slootweg, M.R. Dubois Norpie, 14-16 June 2004
1 Introduction Environmental concern
1 Structure • Introduction • Basic relations • Often used generator systems • Alternatives and trends • Conclusions
2 Stall principle Increasing wind speed > increasing angle of attack Blade design so that at rated power the airflow becomes loose from the blade > eddy’s
2 Rated speed Rated speed limited because of noise production by blade tip speed:
2 Generator dimensions For direct drive:
3 Generator systems Constant speed • Squirrel cage induction generator • Stall principle Variable speed with gear • Doubly-fed induction generator • Pitch Variable speed direct drive • Synchronous generator • Pitch
4 Alternatives • Squirrel cage induction generator with converter • + Brushless generator • + Cheaper (IG) generator • + Grid fault ride through capabilities • - More expensive converter • - More converter losses • Brushless synchronous generator with converter • + More efficient generator
4 Trends in geared generator systems • Towards variable speed • Hardly development in doubly-fed induction generators • Development in converter performance during grid faults • Brushless synchronous generator?
4 Trends in direct drive systems Unique machines: • low speed • high torque • limited efficiency • Induced voltage • Resistive voltage drop > Interesting research field!
4 Trends in direct drive systems • From electrical to permanent-magnet excitation • lower losses • significant reduction in active mass • reduction of magnet cost • Not from radial to axial flux • axial flux may be smaller • but axial flux is heavier and more expensive
4 Trends in trends in voltage levels • The current voltage level is mostly 400 - 700 - 1000 V • Windformer ABB • Zephyros: 3 - 4 kV • NEG-Micon (VTDI) stator: 6 kV • Expected: trend to several kV to limit losses
5 Conclusions • Trend towards variable speed • Geared and direct-drive turbines will remain both • Radial flux permanent-magnet machine most suitable for direct-drive • Rise of voltage level up to several kV for large turbines