Research On Control Strategy Of Permanent Magnet Direct Drive Wind Turbine Under Asymmetric Short Circuit Fault

Wind energy is becoming more and more popular as a clean energy,and wind power plays a more and more important role in the power grid.Among them,permanent magnet direct drive wind turbine has become a new wind power generation technology by relying on the advantages of high energy conversion efficiency,more reliable operation and lower maintenance cost.Because asymmetric short-circuit fault accounts for the highest proportion of all kinds of faults,the control strategy of wind turbine under asymmetric short-circuit fault has become a research hotspot.This thesis focuses on the permanent magnet direct drive wind turbine,studies its operation characteristics,and studies the corresponding fault ride through and scheme according to the problems of the unit when the asymmetric short-circuit fault occurs on the power grid side.Firstly,the mathematical model of permanent magnet direct drive wind turbine is established.The maximum power tracking technology and pitch angle control strategy are analyzed,and the maximum power tracking strategy under different operation modes is designed based on the power feedback method.The optimal speed reference value is changed according to the operation state of wind turbine in different wind speed range,and the maximum power tracking strategy is optimized by taking the output power of generator as the switching condition of operation state.Simulation verifies its effectiveness and superiority.Then,the dynamic response of permanent magnet direct drive wind turbine after asymmetric short circuit fault on the grid side is analyzed.The models of generator side and grid side converters are established,and the double closed-loop vector control technology and the control strategy based on adaptive notch filter are adopted respectively.Compared with the traditional control strategy,the improved control strategy effectively solves the three-phase imbalance of grid connected current under asymmetric short-circuit fault.Finally,through the simulation analysis of unit operation under asymmetric shortcircuit fault,it is found that there is a large fluctuation of DC side voltage,and the causes of DC side voltage fluctuation and overvoltage are analyzed.From the direction of increasing hardware equipment,energy consuming crowbar circuit and energy storage crowbar circuit are analyzed.This paper focuses on the energy consuming crowbar circuit based on buck circuit and the energy storage crowbar circuit based on super capacitor,discusses the selection principles of energy dissipation resistance and super capacitor,and verifies the effectiveness of energy consuming crowbar circuit and super capacitor energy storage device on DC side by simulation.