| Recently with the aggravation of global energy shortage and environmental degradation, wind power generation has achieved great development all over the world and our nation which is green with little pollution and is easily exploited. Among the most popular types of wind power generators being used, doubly fed induction generator (DFIG) is being used more and more widely with its fine control and moderate price. The studies of DFIG modeling and operating characteristics are of great significance to large scale DFIG wind farm’s connecting to the grid.Firstly the paper set up mathematical models for each part of DFIG wind energy conversion system, including wind model, wind turbine model, transmission system model and generator model etc. Based on the mathematical models the paper studies and analyses the control and protection parts of DFIG including the maximum wind power tracking mechanism, the control of wind turbine angle, rotor side converter control, grid side converter control as well as the Crowbar protection circuit and etc.Based on the mathematical model and analysis of a simulating model of DFIG wind farms connecting to the grid is built under the MATLAB/Simulink environment.Then, the paper utilizes the experimental simulating model of DFIG wind farms connecting to the grid to simulate DFIG steady state operating characteristics under gradually-changing winds and grid voltage fluctuations. The simulation results are analysed and explained. The results verify that the simulation model has well simulated the practical operating characteristics of DFIG wind farms connecting to the grid.At last, the paper makes an analysis of low voltage riding through characteristics of common DFIGs as well as those with Crowbar protection circuit. Section-based switch control mechanism of Crowbar circuit is put forward. All the theories are tested by simulation. The simulating results verify the accuracy of the theoretical analysis and the effectiveness of the proposed control strategy of Crowbar circuit. |
