Abstract
Wind energy has recently become one of the most prominent technologies among electrical energy generation systems. As a result, wind-based renewable energy generation systems are incessantly growing, and wind turbines of different characteristics are being installed in many locations around the world. One drawback associated with different characteristics of the wind turbines is that controllers have to be designed individually for each of them. Additionally, stable performance of the wind turbines needs to be ensured in the whole range of their operating conditions. Nowadays, there are many causes for uncertainties in the actual performance of a horizontal axis wind turbine, such as variations in the characteristics of the wind turbine, fabrication tolerances of its elements or non-linearities related to different operating-points. Hence, in order to respond to these uncertainties and ensure the stability of the wind turbine, robust control and stability theories have been gaining importance during recent years. Nevertheless, the use of robust stability analyses with complex wind turbine models still needs to be faced and remarkably improved. In this paper, a stability analysis of the pitch system control of a horizontal axis wind turbine based on the Kharitonov robust stability method is proposed. The objective was to assess the robust stability of a pitch controller in response to uncertainties arising from varying operating conditions of the National Renewable Energies Laboratory (NREL) 5 MW class IIA wind turbine. According to the results, the proposed method could satisfactorily respond to limited variations in the characteristics of the model, but could lack accuracy in cases of bigger variations or employment of high order complex mathematical models.
Highlights
Wind energy based electrical generation has undergone important growth during the last decade.According to a report by the association WindEurope [1], the cumulative capacity of the wind energy raised from nearly 60 GW in the year 2008 to around 180 GW in the year 2018, which depicts an increment of 200% in 10 years
In comparison to other Kharitonov theorem based robust stability analyses found in the literature, such as the one presented by Ahmed et al [29], the analysis presented in this paper presents a method to ensure the closed loop stability of the pitch control system in the whole range of operating conditions in which the pitch control loop is active in a real wind turbine
In the analysis presented in this paper, the Kharitonov robust stability criterion is applied to the pitch control system of the National Renewable Energies Laboratory (NREL) 5 MW wind turbine
Summary
Wind energy based electrical generation has undergone important growth during the last decade. The objective of the analysis proposed in this paper is to evaluate the viability of the Kharitonov theorem when assessing the stability of a pitch controller of a wind turbine subjected to uncertainties due to variations in its operating conditions. It is to be evaluated if the complexity and degree of detail of the wind turbine model used in the analysis, as well as the deviation in the operating conditions, may compromise the correct performance of the Kharitonov theorem.
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