Analysis And Control Of Passive Speed Variation Operation Mode For Long-term Frequency Regulation Wind Turbines

With higher wind power penetration,wind power fluctuations under maximum power point tracking(MPPT)mode will influence the grid stability.Besides,integrated through power electronic equipment,a large scale of wind power will weaken the inertial support for the grid.To support active power balance in the power system and maintain the frequency stability,it is necessary for wind turbines(WT)to generate the power commanded by the frequency regulation requirement.MPPT utilizes the aerodynamic characteristic that the wind energy captured efficiency is maximum at the point with the zero-degree pitch angle and the optimal tip speed ratio(TSR).Thus,it is the operation mode that zero-degree rotor tracks the optimal rotor speed with respect to the optimal TSR.Accordingly,the two typical MPPT methods actively regulate rotor speed to track the optimal speed.By modifying MPPT mothods,the existing frequency regulation methods are obtained.However,with operation target transferred from maximizing the captured wind energy to generating the commanded output power,it is urgent to discuss the adaptability between the traditional active speed variation operation mode and the new operation target.This paper summaries and purifies the two speed variation operation mode from the existing frequency regulation methods,and draw the conclusion that the passive speed variation operation mode is more suitable for the long-term frequency regulation operation target by comparsion and analysis.Based on the above,the proposed frequency regulation method is proposed.The main contributions of this thesis are as follows:A.The two speed variation operation modes are summaried and purified,and the passive speed variation mode is more suitable for the long-term frequency regulation.For the wind turbine participating the long-term frequency regulation,its target is to generate the commanded power other than to maximize the captured wind energy.Facing the new operation target,the active speed variation mode under MPPT is not suitable any more,but also the main factor to affect the frequency regulation performance,such as the power command response performance and the amount of pitch regulation.Therefore,the paper explores WT's physical characteristics which are conducive to realizing the operation target,that a large inertia rotor can buffer the power difference and the aerodynamic power curve of approximate parabola type makes WT operate stably.The conclusion is drawn that the passive speed variation operation mode is more suitable for the long-term frequency regulation target.Moreover,to solve the problem of frequent pitch regulation due to limiting the speed variation mode under zero-degree pitch angle,the speed variation mode is improved to non-zero-degree pitch angle.B.The frequency regulation control is proposed that realizes the passive speed variation operation mode under arbitrary pitch angle,fully utilizing the passive mode to alleviate the fatigue of the pitch servo system efficiently.The existing frequency regulation methods limit the speed variation mode under the zerodegree pitch angle,resulting in frequent pitch action.The paper proposes the improved frequency regulation control that realizes the passive speed variation operation mode under arbitrary pitch angle,and designs the method to the pitch control that limits the passive speed variation mode under any degree pitch angle among the speed zone,so the kinetic buffer is fully utilized.The improved AGC control and smoothing control are proposed for the specified power requirement.On the basis of guaranteeing the performance of frequency control,the amount of pitch action is significantly reduced protecting the pitch servo from wear-and-tear,and the blade loads are alleviated.C.The fuzzy variable-parameter pitch control considering complex working conditions is proposed,improving the rotor speed regulation performance.When the WT operates in the speed variation mode under arbitrary pitch angle,the rotor speed changes freely among the speed zone,only triggering the pitch action at the boundaries.So the speed regulation performance is affected by the pitch control.The paper discovers that wind speed and power command both affect the performance to a large extent,and the existing pitch control cannot attain the satisfactory performance when wind speed and power command both vary.On the basis of analyzing the law of the both factors affecting the performance,the paper proposes the fuzzy variable-parameter pitch control considering varying wind speed and power command,and the rotor speed regulation performance at the boundaries is greatly improved.