Synchronized Method And Control Strategies For Grid Side Converter In Direct Drive Wind Power System

With the power electronics application in power system is growing, as a common problem that phase-locked synchronous technology of converter is also a fundamental question of converted control system. Phase-locked synchronization performance will be directly related to technical performance and operational stability of the converter. High power direct drive wind power system is the most practical prospect of wind power systems in the world. However, the voltage synchronization signal of grid side converter was easily distorted under unbalanced voltage and interference in the system, DC voltage of grid side converter will fluctuate, while harmonics will be pulled in AC input current.This main research content is synchronized method and control strategies for grid side converter in direct drive wind power. Decoupled double synchronous reference frame software phase-locked method and positive sequence and negative sequence rotated reference frame double current loop control strategy under unbalanced voltage condition is deeply analysed, and the correctness of the theoretical results is verified by the simulation.The components of direct drive wind power converter control system, grid side and machine side converter control strategy is given in this paper. The principle and advantages and disadvantages by themselves of the traditional single synchronous reference frame software phase-locked method and single synchronous reference frame software phase-locked method based on symmetry is focused in this article. The phase-locked synchronization performance is verified under unbalanced voltage condition, mutated frequency and mutated phase. As methods for these two phase-locked under unbalanced voltage condition exists phase-locked error, decoupled double synchronous reference frame software phase-locked method is proposed in this paper and phase-locked principle of this method is detailed analysed under unbalanced voltage condition. Then phase-locked synchronization performance of this method under unbalanced voltage condition is verified by simulation.Finally, the mathematical model of grid side converter uner unbalanced voltage condition is discussed. The causes of DC side voltage fluctuations and input current with harmonic components in grid converter under unbalanced voltage condition is detailed discussed, positive sequence and negative sequence rotated reference frame double current loop control strategy is proposed in grid side converter. The simulation results show the feasibility of the control strategy.