Tesis doctoral de Carlos Alvarez Ortega
Wind generation is probably the most important renewable energy technology. Advantages are well known. However, some drawbacks must be considered. Faults in the power system lead to voltage dips around a wide area around the short circuit. Voltage dips affect wind turbines increasing rotor currents and mechanical speed. Safety limits can be then reached and exceeded. When a single event, the fault on the system, can lead to the disconnection of several mw, power system stability is compromised drastically due to the high level of penetration in certain areas of countries such as denmark, germany or spain. Grid codes have been published establishing guidelines and working requirements for wind turbines to comply with. In order to fulfil the grid codes and standards, it is essential to provide an accurate estimation of voltage dip parameters. This information will be used for activating the appropriate control of protecting devices achieving the low voltage ride through (lvrt) capability required. Custom power systems, such as dvr, are needed by fixed speed wind turbines (fswt) as protecting devices for providing the required lvrt. As long as fswt is not able to control its active and reactive power output, custom power systems will provide this capability as well. Simulations for proving dvr helping wind farm are done and shown. Dfig based wind turbines are able to control its active and reactive power but the lvrt capability is not directly achieved. Special devices for dfig called crowbar, can help dfig based wind turbines to comply with grid codes. In order to make a complete study about what presented above, all topics must be analysed. The parts of different grid codes from several countries referred to lvrt requirements are explained. Methods for detecting voltage dips are presented, proposed, compared and tested both in simulations by using matlab and implemented on a dsp with real measurements. Fswts are studied and dvr behaviour is presented through matlab simulations. Results prove that it is able to provide lvrt capabilities to fswts. Dfig is deeply analysed describing its mathematical equations. Reference frames are explained and used for the proper control of the asynchronous machine. Simulations under psim+matlab are carried out. Crowbar action is considered in the model. Results show how lvrt requirements are achieved by selecting the crowbar value properly and with an appropriate control of the rotor side converter (rsc). Finally, the rsc has been studied in order to control the real machine at the laboratory prototype. An advanced non-linear control strategy based on the sliding mode control is developed in order to other the lvrt requirements at dfig wind farms. It is demonstrated how the application of a precise method for detecting voltage dips and power electronic solutions adapted for each kind of wind turbine technology keeps the wind farm voltage magnitudes within the limits required for grid codes achieving the requested lvrt capability. Thus, the power system stability may be enhanced.
Datos académicos de la tesis doctoral «Voltage dip mitigation at wind farms«
- Título de la tesis: Voltage dip mitigation at wind farms
- Autor: Carlos Alvarez Ortega
- Universidad: Carlos III de Madrid
- Fecha de lectura de la tesis: 05/04/2011
Dirección y tribunal
- Director de la tesis
- Olof Samuelsson
- Tribunal
- Presidente del tribunal: julio Usaola García
- inés Romero (vocal)
- mircea Chindris dorin (vocal)
- José Carpio ibañez (vocal)