Research On Control And Fault Ride Through Of Direct-drive Permanent Magnet Wind Power Generation System

As countries around the world pay more attention to clean,renewable energy,wind power has the advantages of clean,non-polluting,short construction period and low operating costs,which causes installed capacity of wind turbines is growing rapidly.When the grid connected wind power generation accounts for higher and higher proportion of the total electricity in the grid,the power system stability will be influenced deeply.In order to ensure that the power system can operate safely and reliably,all countries have made developed their own wind farm gird specifications,requiring the wind farm must have a certain fault ride through capability,including low voltage and high voltage ride through.The direct-drive permanent magnet wind power generation system has the high utilization of wind energy and no gearbox,so it has been widely used.The thesis takes the permanent magnet wind power generation system as the research object and studies methods of improving the fault ride through capability in detail.The main research contents and the results of this thesis are as follows:1.The wind speed,wind turbine,permanent magnet synchronous generator and grid-side converter mathematical model are studied and it analyzes the basic principle of maximum power point tracking,which provide a theoretical basis for the direct-drive permanent magnet wind power system control and fault ride through.2.For the steady state of gird,it analyzes the speed outer loop and current inner loop based on ZDAC of vector control for the machine side converter and the DC voltage outer loop and reactive current of vector control for the grid side converterFor the machine side converter speed PI controller of vector control,it proposes an improved anti-windup PI with tracking back calculation which can significantly improve response of generator rotor speed based on antiwindup PI with tracking back calculation and be proved through simulation.3.For the three phase symmetrical voltage sag,it analyzes the strategies of reducing the generator output power,crowbar circuit,providing reactive power compensation to accomplish the low voltage ride through in detail and proposes a coordinated control strategy based on the improvement of reducing the generator output power.The coordinated control strategy can protect the pitch angle system,prevent the generator from exceeding the speed limit,ensure the operation safety of the converter and reduce the working time of the crowbar resistance to the maximum extent,and finally realizes the low voltage ride through.The simulation results can verify the effectiveness of the coordinated control strategy.4.For the three-phase symmetrical voltage swells,it analyzes the system characteristics when the gird is in voltage swells and based on the low voltage ride through control strategy,proposes a control strategy which uses the crowbar circuit on the DC side and provides the maximum reactive power compensation on the gird side to achieve to high voltage ride through and is verified by simulation.