Study Of Low Voltage Ride Through For Direct-driven Permanent Magnet Wind Power System

Wind power，which is supposed to be an emerging representative of the renewable energy，has aroused widespread concern in recent years. On the other hand，with the rising penetration ofwind power in the entire grid, the impact of wind power on the power system is more and moreobvious. In order to reduce the negative factor of wind power to the grid, a higher demand to windpower has been proposed, which calls for the wind power system to keep connected to grid and tobe able to provide effective support to grid voltage during grid faults, so-called low voltage ridethrough capability.In this paper, the study focuses on the low voltage ride through capability of direct-drivepermanent magnet wind power system and places emphasis on the control strategy of thepermanent magnet wind power system converter and additional protection circuit two side toanalyze. A permanent magnet wind power system simulation model is built based on Simulink,and the simulation case shows the correctness of the low voltage ride through strategy. Thespecific contents of this paper are as follows:1. Wind power development status domestic and overseas is overviewed, and the relevantprovisions of Low voltage ride through at home and abroad are introduced, the specificquantitative requirements are summed up.2. The major components of the mathematical model and the principles of direct-drivepermanent magnet wind power generation system are presented, including the wind turbine, PWMconverter and synchronization permanent magnet generator etc. A simulation model as the basicplatform for the study of the direct-drive permanent magnet generator system is built based onmathematical model in Simulink environment.3. A detailed description of the general principles and procedures of the space vectormodulation method are given. Combining with the electrical vector relationship of permanentmagnet generator, four types of PWM converter control strategy are introduced. The variousprinciples of control strategies as well as their advantages and disadvantages are explained. Aftermaking an analysis of the characteristics of different control strategies, a control strategy thatmachine side converter control DC-link voltage and generator stator voltage, grid-side convertercontrol the power factor,is adopted in this study. During the converter controller designing, an improved instantaneous symmetrical components method is applied, and the vector controllingmodulate method is based on it. The grid-side converter to maintain a certain power factor duringvarious grid fault conditions can be made based on this control method.4. The specific simulation cases to simulate the response characteristics of the permanentmagnet wind power generation system during symmetric and asymmetric grid fault are studied. Ananalysis of the impact on the electrical part of the wind power generation system during the gridfault is carried out, and the control strategy to solve low voltage ride through of permanent magnetwind power system is concluded.5. The specific simulation cases according with the new national codes in wind turbine lowvoltage ride through are employed to research on DC-link discharging and DC-link energy storagetwo types of important low voltage ride through technology based on DC-link protection. Thecharacteristics of each technology from the working principle, control method and control effectsare compared and analyzed. Proposition and verification of the integrated low voltage ride throughmethods are worked out, which has some theoretical and practical significance.