Research On Modeling And Pitch Control Of Wind Turbines

Wind turbines develop toward the trend of large-scale,variable speed and pitch adjustable nowadays.Control is crucial to the efficiency and reliability of wind turbines. As a part of the National Science Foundation of China Project 'Research on optimizing control strategy overall operating condition for variable speed wind turbine hybrid system(50677021)' and Ministry of Education Important Project 'Research on advanced control technique for large-scale wind turbines(105049)',this thesis studies modeling and control of variable speed pitch-adjustable wind turbine generator(WTG).Thus the main contents in this dissertation are divided into two parts according to the two projects. One part researches hybrid system application in modeling and control of WTG based on the first project,the other part devotes modeling of aerodynamic device and pitch control into the second project.Primary original contributions of the thesis can be summarized as follows:Firstly,in order to solve the problem of traditional modeling method,wind speed model is identified and emulated based on theory of higher-order statistics time series according to the actual wind speed series.Not only the problem of difficult realization of statistic wind speed model and not presenting the model of all kinds of wind is solved, but also eliminates the error caused by recognizing natural wind as Gaussian processes and the effect of measure noise.Simulations in contrast with traditional modeling method illustrate superiority of the model making use of theory of higher-order statistics.Secondly,two basic methods of modeling wind wheel are analyzed:one is based on blade element theory;the other is based on blade aerodynamicist theory.For the problem in these two methods,the blade element is divided by using weight number in first method and the influence by trailing vortex is considered correspondingly.As a result, the wind wheel model is more reasonable and accurate.Thirdly,through analyzing characteristics of WTG and requisitions of pitch control, a compound approach was investigated by combining dynamical feed forward and fuzzy-PI to control pitch angle.Fuzzy control can solve the problem of modeling WTG system,and PI control is introduced to promote the precision of compound control system.Wind speed,the main interference,was used as forward feed signal.So it erases the influence on control quality as a result of variable wind speed.On the other hand,it also enhances rapidity and anti-interference capability of pitch system.Utilizing the model considering trailing vortex as example,the simulation shows the effectiveness and practicability of the proposed method. Fourthly,a fact was discovered that wind turbine system showed the typical feature of hybrid system by analyzing its characteristics.Therefore,the hybrid dynamic model of WTG was built based on theory of hybrid automata,at same time hybrid global control system was designed according to control strategy of WTG.Emulation results present the hybrid automata model can accomplish the global simulation of WTG,and the designed hybrid control system fulfills the demand of WTG global control.Moreover, hybrid system theory is demonstrated as an effective theoretical method applied in the field of the WTG's modeling and control.Fifthly,MLD model of WTG is realized by making use of HYSDEL based on analyzing the structure of MLD model.The model predictive control based on MLD is applied to optimize power output of WTG.It not only overcomes the fluctuation at time of transition of states,but also makes system pay the minimum cost.