Research On Torque Ripple Suppression And Variable Current Control Strategy Of Permanent Magnet Wind Turbine

As Permanent Magnet Synchronous Generators(PMSG)continue to develop in the direction of high capacity,some of the problems that arise during their operation are becoming more and more apparent.For example,torque ripple may reduce the quality of wind turbine power generation,generate noise,increase the mechanical stress on the structure of the power generation system,and affect the working life of the system.Based on this,the following research work is carried out in this paper in terms of pneumatic torque ripple reduction and electromagnetic torque ripple reduction.Firstly,this paper analyzes the sources of PMSG torque ripple and their respective generation mechanisms so as to identify the idea of reducing both pneumatic torque ripple and electromagnetic torque ripple.Secondly,for the reduction of pneumatic torque ripple,a mathematical model of the wind turbine as well as the pneumatic torque is established,based on which the idea of using the adjustment of the pitch angle to reduce pneumatic torque ripple is determined.Under the relationship between speed fluctuation and pneumatic torque ripple,this paper proposes the pneumatic torque ripple extraction module based on rotational speed measurement and the independent pitch control strategy based on azimuth angle weight number assignment.Then,starting from the reduction of electromagnetic torque ripple and based on its relationship with harmonics,this paper determines the scheme of indirect influence of electromagnetic torque ripple by harmonics,proposes a harmonic current detection method based on synchronous rotating reference frame by deriving the mathematical model and harmonic model of PMSG under ideal conditions.Recursive least squares(RLS)adaptive filter & mean filter is selected as the filtering device to improve the detection effect.On this basis,an electromagnetic torque ripple reduction module based on harmonic voltage compensation is designed to offset the detected corresponding harmonic components by calculating the compensation voltage of selective harmonics.In addition,to further reduce the harmonic distortion rate and reduce the electromagnetic torque ripple of PMSG,two converter modulation methods,namely,Space Vector Pulse Width Modulation(SVPWM)and Selective Harmonic Elimination Pulse Width Modulation(SHEPWM),which can achieve the neutral-point potential balance,are studied and compared.Finally,in order to verify the effectiveness of the theory proposed in this paper,after simulating the proposed harmonic current detection system and the pneumatic torque ripple extraction module based on the rotational speed measurement and proving the feasibility,the two converter modulation techniques are compared and the SHEPWM modulation technique,which can achieve the neutral-point potential balance,is found to be more beneficial to the reduction of torque ripple.Then,the pneumatic torque ripple reduction strategy and the electromagnetic torque ripple reduction strategy are added to the model in turn,and the results show that the torque ripple amplitude becomes smaller after the pneumatic torque ripple reduction strategy is added.When the electromagnetic torque ripple reduction strategy is added,the torque ripple is further reduced and the waveform becomes smoother.