Pitch Control And Stability Analysis Of Offshore Floating Wind Turbine

Due to China’s offshore wind energy oriented policy and related planning,it will become the “new engine” for the development of China’s wind power industry.Offshore wind turbine are mainly divided into fixed and floating.Among them,the former has the same fixed foundation as the onshore wind turbine,so many of the research results and mature technologies of the onshore wind turbine can be applied to it.Although the latter contains most of the characteristics of onshore wind turbines,including the trend of large-scale developmentof onshore wind turbines and all other structures and related control systems except fixed foundations,it is extremely important to have a non-fixed floating platform.For this reason,it is necessary to make important basic and adaptive research while drawing on the research results and related technologies of onshore wind turbines.Pitch variable speed regulation is the main mode of operation of wind turbines.Onshore wind turbines have mature pitch control systems.On the one hand,when offshore floating wind turbines is subjected to external loads,its floating platform has a multi-degree of freedom dynamic response.On the other hand,the dynamic response of the platform will be transmitted to the rotor through the tower to affect the pitch control effect.Finally,the pitch control of the blades also effects the dynamic response of the platform.This is obviously different from offshore wind turbines and onshore wind turbines,so that it should be studied when referring to the onshore wind turbine pitch control system for the characteristics of offshore floating wind turbines,which is great significance to the development of offshore wind energy.In addition,the large-scale and flexible blade structure of offshore floating wind turbines and the dynamic response of the platform will put forward higher requirements for structural load shedding,which highlights the importance of studying the variable pitch control system for offshore floating wind turbines.To this end,this paper establishes disturbance accommodating control based on modern control theory on the joint simulation platform of open source software FAST developed by NREL and MATLAB/Simulink,which is used to study the collective and independent pitch control of three kind of offshore floating wind turbines.From the comparison of the pitch control performance,the wind turbine blade load and the platform dynamic response with the FAST baseline control.The following conclusions can be drawn from the above work:1.Compared with the FAST baseline control,under disturbance accommodating collective pitch control,the speed fluctuation of the Spar platform offshore floating wind turbine generator is more stable,and the maximum flapwise moment of blade decreases obviously,but the root mean square change is not obvious,and the platform dynamic response increases,but the pitch response of platform decreases.Under disturbance accommodating independent pitch control,the speed fluctuation of the Spar platform offshore floating wind turbine generator is also relatively stable and the reduction of blade load is mainly concentrated in the flapwise,and the dynamic response of surge and yaw increases,however dynamic response of sway decreases obviously,and the dynamic response of pitch and roll,which have important influence on the stability of offshore floating wind turbine,also have certain decreases.In summary,disturbance accommodating collective pitch control in this paper has a good control effect on the Spar platform offshore floating wind turbines.But this good control effect only lies in speed of generator and the maximum flapwise moment of blade.However,disturbance accommodating independent pitch control has a better control effect on the Spar platform offshore floating wind turbine.This better control effect lies not only in the generator speed,but also in significantly reducing the blade flapwise moment(including maximum and root mean square)and in reducing the pitch and roll dynamic responses which affect the stability of the platform to a certain extent.2.Compared with the FAST baseline control,under disturbance accommodating collective pitch control,the speed fluctuation of the Barge platform offshore floating wind turbine generator is slightly better,and the edgewise moment of blade is slightly larger,but the flapwise moment of blade is smaller,and dynamic response of Barge platform is increased.Under disturbance accommodating independent pitch control,the speed fluctuation of Barge platform offshore floating wind turbine generator is slightly better,and the blade load decreases obviously in the flapwise,and dynamic response of the Barge platform increases.In summary,disturbance accommodating control in this paper will increase the dynamic response of Barge platform and have no obvious effect on blade load whether it is used for collective or independent pitch of the Barge platform offshore floating wind turbine,but it will slightly reduce the fluctuation of generator speed.3.Compared with the FAST baseline control,under disturbance accommodating collective pitch control,the TLP platform offshore floating wind turbine has poor speed fluctuation of generator,small blade flapwise and no obvious change in dynamic response of TLP platform.Under disturbance accommodating independent pitch control,the speed fluctuation of TLP platform offshore floating wind turbine generator is worse,and the flapwise moment of blade decreases obviously,and the dynamic response of TLP platform increases in the yaw,while the difference in other directions is small.In summary,disturbance accommodating control in this paper will increase speed fluctuation of generator and have no obvious effect on dynamic response of TLP platform whether it is used for collective or independent pitch of the TLP platform offshore floating wind turbine,but it will slightly reduce the blade flapwise moment.4.Disturbance accommodating control in this paper has different control effects on different platforms offshore floating wind turbines.It has the best control effect on offshore floating wind turbines on Spar platform,the second on Barge platform and TLP platform.In summary,disturbance accommodating control is not suitable for all types platform of offshore floating wind turbines.