Hybrid control schemes for wind turbines

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonWind turbines require continuous monitoring and control in order to maintain the power output as the wind speed varies. Traditional control techniques using conventional equipment and devices have been used in small scale generators at a commercial or residential level. A range of techniques have been developed and used to control generation output and to satisfy grid code requirements. Such techniques have demonstrated good performance with constant wind speed and linear system parameters. At the same time classical control techniques, based on the linear Proportional Integral controller and low band-width modulation, present several technical issues during lower switching frequency operation as well as slow response to uncertainty in system parameters. It is important to note that wind turbines are non-linear in nature and therefore require robust controllers that can adjust to the changes in the external environment as well as operational conditions and disturbances. For this reason, advanced control schemes have been proposed to mitigate the effects of potential system disturbances. A variety of advanced control methods have recently been applied in response to wind energy conversion problems, such as fuzzy logic, slide mode, adaptive and predictive that have been applied to solve some of these problems. Such techniques are only valid for a specific operational range and do not cover the whole operational region with regard to rate of change of wind speed. Therefore, when considering large scale power generation from wind energy, high turbulence wind velocities and uncertainty in system parameters require the development of new hybrid controllers in order to address such problems. In order to improve the system performance and deal with uncertainties under different operational conditions, advanced control techniques such as model reference control and model predictive control are combined with fuzzy logic control. This thesis presents detailed analyses, modelling and simulation of novel and hybrid control schemes for variable speed wind turbines as operated in small or large scale such as 2 MW grid-connected Permanent Magnet Synchronous Generators. The proposed controllers show a reduction of steady state errors, reduced overshoot of the rotor speed and an increase in the active power that is generated. The results are compared to conventional controllers such as Proportional Integral controller in order to demonstrate the improved performance and the robustness of system.Ministery of Higher Education and Scientific Research, University of Karbala and Iraqi Cultural Attaché-London for sponsorship and fundin