Research On Individual Pitch Control For Large-scale Wind Turbine

The presupposition of the wind turbine design with collective pitchcontrol (CPC) is that wind distribution of the whole swept surface is uniform.However, the wind speeds at the blade different position are differentbecause of wind shear, tower shadow, turbulence and so on, and the lifts aredifferent from the position of the whole swept surface. These different liftsmake the wind turbine torque fluctuation which affects the output power ofthe wind turbine and the power quality, and cause imbalance loads on thewind turbine and the blade imbalance. The imbalance loads lead to the bladeedgewise vibration and blade torque fluctuation. Furthermore, the bladetorque s fluctuations also cause the torque fluctuation of the wind rotor shaft,the drive train, the hub and the tower. Moreover, the unbalanced loads willbring many problems to the wind turbine mechanical strength, the vibration,the fatigue life and the power grid quality. The collective pitch angle givenaffected by wind shear, tower shadow, turbulence, wind speed modeling,wind turbine aerodynamic modeling, wind turbine torque emulation,individual pitch control (IPC) strategy, individual pitch system design andother aspects are studied in this paper.First of all, the CPC strategy of the collective pitch angle given whichfeed-forward Fuzzy and Fuzzy-PID are combined on the basis of Fuzzyswitching is proposed according to the problem of the stability of the outputpower of the wind turbine generator system (WTGS) affected by the randomwind speed, and the CPC system of the DDPMSG is simulated. The resultsshow the collective pitch controller using the proposed control strategy hasbetter capacity of resisting disturbance, good static and dynamicperformances improved and strong applicability than the conventional PID controller or Fuzzy-PID controller. Meanwhile, the collective pitch anglegiven based on the combination of feed-forward Fuzzy and Fuzzy-PIDprovides a reference for the superiority comparison of the IPC system.Because the collective pitch angle of the conventional wind turbinemodel and the aerodynamic loads are coupled mutually, the fluctuationinfluences of the aerodynamic loads on the single blade, the wind turbinetorque, the output power of WTGS and the voltage of the Point of CommonCoupling (PCC) can not be separated out of the influence of wind shear,tower shadow and turbulence. A new large-scale wind turbine aerodynamicmodeling considered the lossless of the hub and the blade tip, the assumptionof infinite number of the blades, and the huge torque difference between theblade tip and the blade root is proposed. Therefore the wind turbineaerodynamic loads affected by wind shear, tower shadow, turbulence andother aerodynamic imbalance factors are calculated, and the influence rulesof the load fluctuations are deduced at length. These rules provide the basisto the wind turbine mathematical model based on IPC, provide thetheoretical guidance to the IPC strategies, and solve the collective pitchangles coupled problems. Moreover, the experiment platform of the virtualwind farm and the wind turbine torque is established. It not only verifies theaccuracy and the correctness of the wind turbine torque model but also laysthe foundation for the further IPC study.In order to smooth the wind turbine torque fluctuation, a new IPCstrategy based on edgewise moment is proposed. That is the present controlstrategy can directly smooth the edgewise moment and the wind turbinetorque fluctuation. The multi-stage dynamic weight coefficient distributionIPC strategy and the single neuron adaptive PID IPC strategy are comparedon the basis of the WTGS mathematical model. Then the control effects ofthe edgewise moment fluctuation and the wind turbine torque fluctuationused by the single neuron adaptive PID IPC strategy are better than thecontrol effects by the multi-stage dynamic weight coefficient distributionIPC strategy according to the results. In addition, in order to reduce the wind turbine torque and the unbalanced aerodynamic loads on the wind turbinesimultaneously, a new IPC strategy based on the feedback of the edgewisemoment and the flapwise moment is proposed. And the research on this IPCstrategy is on the basis on the IPC base on the flapwise moment. That is thesum of the edgewise pith angle deviation optimized and the flapwise pithangle deviation optimized by the weight coefficient is the pitch angle givenof each blade. And the verification of this IPC strategy is simulated in theIPC system of the Direct-driven Permanent Magnet Synchronous Generator(DDPMSG). The performance of this individual pitch controller is illustratedits capability of not only reducing the wind turbine fluctuation, but alsosmoothing the unbalanced loads on the wind turbine.For the problem of the wind turbine torque and the drive shaft torqueare difficult to detect directly, a method of torque indirect observation basedon the electric power is proposed. First, the generator electromagnetic torqueis calculated by the measurement of the wind turbine speed, the generatorspeed, the stator current and the stator voltage. Then the inverse model of thedrive chain is built, and the wind turbine torque and the drive shaft torqueare calculated by this model. Finally the correctness of the observation of thewind turbine torque and the drive shaft torque is verified by the DDPMSGsimulation.The IPC system is designed and implemented in this paper. Thedetailed design of the IPC system structure, the blade pitch load is calculatedspecifically, the electric servo controller which the Fuzzy adaptive PIDcontrol strategy is used in the position controller is designed, and thehardware and the software of electric servo pitch are established.Simulation results verify the correctness and the feasibility of the Fuzzyadaptive PID position controller. And the performance of the controller isillustrated its capability of meeting the accurate positioning, the fast dynamicresponses and others performance requirements of high-performance servosystems. In addition, the experimental results show the electric servo pitch system can pith control independently, and establish the technical base forthe application of the IPC system.