Social, economic and environmental concerns request higher efficiency and more sustainable electrical power systems. Wind power is considered as the most promising renewable source and is increasingly widespread worldwide. This has implied two facts: the incredible growth in turbine size and the high wind power integration. The concept of the wind turbine has evolved from being a passive and minority element to become an important part of the grid. Modern wind turbines must contribute to power system stability and are required to take over control tasks that were traditionally focused on conventional power plants. New turbine topologies face the need of operating at very high power rates overcoming the current electrical and structural limits. In addition, the fulfillment of new grid codes requires topologies integrating more power electronics and advanced controls.

In this thesis, the direct-drive permanent magnet synchronous generator with full power converter has been found to be the most promising configuration in order to fulfill the above mentioned requirements. An outer rotor generator has been envisaged with the aim of obtaining a lighter mechanical structure. On the other hand, taking into account the current limitations of the power semiconductors, multilevel converters have been considered, since they offer, among others, the great advantage of working at high voltage, and thus, at high power.

From the standpoint of power control, it is important to ensure that the system is as immune as possible to external disturbances, such as wind speed variations. For that purpose, feedforward controls have been implemented in order to counteract these disturbances before they affect the system.

Finally, a very important issue for the proper operation of any grid-connected power electronic system is the detection of the grid voltage positive sequence. This information is essential for the active and reactive power injection, and critical under unbalanced and distorted grid conditions, especially under the new regulations. The main objective of this thesis and, where most of the work has been concentrated, has been to design robust methods to detect the positive sequence of the grid voltage. Lately, there have been many contributions on this subject. Nevertheless, new grid codes imply the operation of the wind turbines under large disturbances and the positive sequence detectors have to be fast and accurate in the presence of harmonics, voltage dips, phase jumps and frequency variations simultaneously.