Research Of Low Voltage Ride-Through Of Directly Driven Wind Turbine System With Permanent Magnet Synchronous Generator

The world’s wind power industry is entering a stage of rapid development, more and more wind turbines are used in the grid, interaction between the wind power system and the grid is more and more complex. It will lead adverse effect to the grid, if the wind power system is off-grid during the fault of grid, so that LVRT capacity of wind power system is very important. And in wind power system, direct-drive permanent magnet synchronous wind turbine have been developing rapidly for simple structure,low maintenance costs, high conversion efficiency, high reliability.This paper research LVRT problem and the related technology to the permanent magnet direct-drive wind power system. Study the main low voltage through technology, and the main theoretical research results are verified by simulation.First of all, to expound the background and significance of wind power researching, and summarize and research the present development of global wind power industry. Comparing all kinds of wind turbine generator system, especially on the adverse effects caused by grid voltage sags fault to the direct-drive permanent magnet wind power system. To discuss the advantage of direct-drive permanent magnet wind power system relative to the doubly-fed wind power generation system in low voltage ride through. To expound the importance of low voltage ride through technology, summarizing low voltage through the standard and the research actuality of low voltage ride through technology.Secondly, the mathematical modelling of the major components of PMSG direct-drive wind power system are set up, including turbine, permanent magnet synchronous generator, machine side converter and grid-side inverter. On the basis, grid-side converter uses voltage-oriented vector control strategy and the controller of motor-side converter uses the rotor flux-oriented vector control strategy, which realize the active power and reactive power decoupling control of the network side.Thirdly, the dynamic response characteristics of permanent magnet direct-drive wind power system operating under low voltage condition are researched. Firstly the dynamic response characteristics of the system are researched from DC-link and grid-side converter. Then, the simulation model with proper control policy are constructed. And verifying the conclusion correct by simulation when grid voltage in normal situation and different duration and extent of the grid fault. Conclude the influence of different duration and extent of the grid fault to grid-side converter and DC bus.Then, we studied low voltage ride through technology which is commonly used by the direct-drive wind power system and compared the advantages and disadvantages of all kinds of low voltage ride through solutions and its suitable occasion. On the basis of previous analysis, we compared many kinds of control methods of crowbar protection circuit in DC-side and summarized the advantages and disadvantages of different control methods.Finally, we simulation validates the low voltage ride through of direct-drive permanent magnet synchronous wind power system.we used the DC-side to increase unloading resistance of low voltage through.In this way, we can better solve the problem of over-voltage and over-current caused by power grid voltage drop. We verified the effectiveness of the low voltage ride through solutions based on DC-side in the way of Matlab/simulink.We compared DC-link crowbar of low voltage ride through with unloading resistance connected by the Buck circuit of low voltage ride through. After we summed up the better solution, we try to consider about deeper falling level and longer falling time of grid voltage, and then we implemented the direct-drive permanent magnet synchronous wind power system of low voltage ride through.