Research On Reactive Power Compensation Of Wind Power Grid Connected System Based On STATCOM

Because of the increasing demand for energy,the research on wind power related technology has also made great progress,so the installed capacity of wind power equipment in each country is becoming more and more large.As the mainstream fan,doubly fed asynchronous wind turbine will absorb a certain amount of reactive power,and with the fluctuation of wind speed,the fan absorbs reactive power and will fluctuate.If all the reactive power is provided by the power grid,it will reduce the voltage level of the regional power grid,even cause voltage instability and even voltage failure.In order to ensure the reliable and stable operation of the wind farm,it is very necessary to study the reactive power compensation of wind power system.This chapter first analyzes the historical process related to the wind farm and the shortcomings existing in the present,and interprets the benefits of the reactive power compensation to the wind power,and analyses the characteristics of the reactive power compensation equipment of different design schemes,and then draws the conclusion that the adoption of the STATCOM scheme is correct.Secondly,the constitution of STATCOM and the detailed working principle of the compensator are studied,and the classical main circuit model of the device is determined.The characteristics of current reactive current detection methods are analyzed,and the theory of instantaneous reactive current,which is widely used,is selected,and the i_p-i _qdetection method and the dq coordinate transformation method are introduced.Through theoretical analysis,a direct current control method based on dq coordinates and double loop feedback is selected as the control strategy of STATCOM.Then,taking STATCOM voltage main circuit as an example,the mathematical models of three-phase stationary coordinate system and two-phase rotating coordinate system are established respectively.The influence of the STATCOM on the asymmetrical fault of the power grid is analyzed theoretically,that is,the voltage fluctuation of the capacitor voltage of the DC side appears two frequency doubling,and the three harmonics will appear on the AC side.In this paper,the traditional direct control strategy based on coordinate current is improved,and a control strategy based on positive negative sequence network decoupling and space vector pulse width modulation is proposed.This method can compensate the negative sequence current during the asymmetrical fault of the power grid,eliminate the fluctuation of the inverter DC side energy transmission,and ensure the normal operation between the STATCOM in the asymmetric fault period,and the decoupling can be calculated accurately and quickly.The reactive power that needs compensation is calculated.Meanwhile,the application of space vector PWM reduces the switching frequency and improves the utilization of DC side voltage.Finally,the practical application of STATCOM in wind farms proves that STATCOM has good dynamic compensation from the data point of view.Secondly,the detailed simulation models of STATCOM's main circuit,control circuit and wind farm are established,and a wind farm simulation model with STATCOM configuration is built.The simulation results verify the superiority of STATCOM compared with other reactive power compensation devices,and verify the correctness of the improved control strategy proposed in this paper.During the unsymmetrical fault of the power grid,the improved control strategy proposed in this paper can effectively reduce the fluctuation of the capacitance voltage of the STATCOM DC side,avoid the device off the net,carry out the reactive power compensation for the power grid accurately and quickly,and achieve the stability of the voltage of the grid connected to the wind farm.