Sliding mode control in grid-connected wind farms for stability enhancement

Aiming at reducing the rather high percentage of CO2 emissions attributed to the electrical energy production industry, a new generation of power plants has been introduced which produce electricity by using primary energy resources which are said to be renewable, such as wind, solar, geothermal and biomass. This has had not only the benefit of reducing CO2 emissions into the atmosphere to a trickle, by the new power plants but to also encourage a great deal of technological advance in both the manufacturing sector and in research institutions. Wind power is arguably the most advanced form of renewable energy generation today, from the bulk energy production and economic vantages. This doctoral thesis rigorously deals with the analysis, assessment and description of the impact of double-fed variable speed wind turbine on the dynamic behaviour of both, the wind farm itself and its interconnection with the conventional power generation system. Analytical analysis of the results published in the open literature is used as a tool to gain a solid understanding of the dynamic behaviour of power systems with wind generation. The influence of the characteristics of the electrical system and wind turbines or external parameters on stability is assessed using modal analysis. Studies conducted have focused on the analysis of transient stability and small signal stability for the damping of oscillations in power systems and its enhancement. Analysis of small signal stability and transient stability analysis are carried out using modal analysis and dynamic simulations in the time domain. This thesis proposes the implementation of sliding mode control techniques for the DFIG WT converters, both the Machine-Side Converter (MSC) and the Grid-Side Converter (GSC). The proposed control system is assessed on conventional dynamic power systems with wind power generation under different test case scenarios. The newly developed SMC control scheme demonstrates the importance of employing non-linear control algorithms since they yield good operational performances and network support. This is of the utmost important since in power systems with wind power generation is critically important to ensure the robust operation of the whole system with no interaction of controllers. Sliding Mode Control shows to be more robust and exible than the classical controller, opening the door for a more widespread future participation of DFIG-WECS in the damping of power system oscillations. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------