Research On The Control Technology Of The Permanent Magnet Direct-Drive Wind Turbine

With the advantages of gearless, high power density and reliability, the permanent-magnet direct-drive wind turbine has become one of the main types in wind generation. Considering such rapidly changeable nonlinear complicated system, researchers have proposed many control methods, which mainly focus on the maximum wind capture, life extension of the wind turbine and the reduction of fatigue load, in order to meet the demand of safety operation. On the one hand, methods above have the one-sidedness that control strategy is proposed to deal with single system, on the other hand, lack of practical application objectives makes those methods and strategy still in the theoretical stage.This essay, on the basis of current national and international research situation of permanent-magnet direct-drive wind turbine, targeting the school-enterprise cooperation project-1.5MW direct-drive wind turbine research and manufacture, deeply study current control technology problems. Main research and achievement are as follows:(1) In this essay, model linear formula of permanent-magnet direct-drive wind turbine mode is derived. And. linear models of generation rotation speed, drive train torque, tower pre-and post displacement and speed mode are included. In view of vibrating mode of variable orders of rotor, drive train and tower as well as the impact between them, this essay proposes an integrated control strategy for permanent-magnet direct-drive wind turbine and a new control strategy for switch between pitch angle controller and torque controller. Simulating results show that the turbine has a good control quality.(2) As to maximum wind capture control under rated wind speed, this essay promotes a torque control method on basis of self-adaptive fuzzy control, in order to accomplish speed control under low wind speed. This method makes the turbine have the ability of steady and rapid electromagnetic torque response. Simulating results show that speed control effect and disturbance resistance ability are better than that of the traditional PI controller. (3) As to constant power control above rated wind speed, this essay provides a creative control method on basis of compound pitch control of fuzziness and SMC, in accordance with nonlinear and disturbance resistance of pitch system and permanent-magnet direct-drive wind turbine pitch control. This method uses pitch position errors switching function and its derivative as input. Through the controller output derived from fuzzy reasoning and defuzzification, pitch regulation can be realized instead of sliding mode switch control, aiming at reducing the impact of wind speed on the turbine. Simulating and experimental results show that this control method is effective.(4) From the aspect of increasing stability of wind turbine, this essay proposes a new torque damping control method, regarding to the drive train torque vibrating problem of permanent-magnet direct-drive wind turbine. Through the method of using direct voltage out of convertor to carry out phase compensation, in order to erase drive train torque turbulence caused by first-order mode frequency in sweeping area. Simulating results show that, without increasing generator power wave, when we add torque damping control, system resonance is eliminated, and the vibration and load impact on drive train is reduced. Therefore, torque damping algorithm is effective.(5) Considering tower vibration control of permanent-magnet direct-drive wind turbine, on basis of rotor-tower coupling vibration analysis, this essay promotes the method of supplying additional pitch by expert PID control. This method controls the tower vibration by adding tower first-order mode frequency damping filter into closed loop control. Simulating results show that comparing with the case without tower damping control algorithm, tower with damping is in a better force situation on both front and back side. This method proves that this algorithm is effective.(6) This essay realizes the combination of simulation research and practical control algorithm. Through existing school-enterprise cooperation and practical wind turbine object, this essay employs the technical route of using respective control strategy simulation to realize multi-system control strategy simulation, which reduces the one-sidedness of single system control strategy, and optimizes themselves and the whole wind turbine control strategy. This essay, of application value, lays a foundation for practical use of wind turbine.