The Research On DFIG Control Strategy Under Crid Harmonic Environment

With the development of China’s wind power industry, its development model has changed gradually from a single "building large bases, incorporated into the large grid" to the coordinate of "centralized incorporate " and "decentralized incorporate " development model. Decentralized incorporate has a huge challenge that is distribution grid is relatively weak so that the problem of harmonics, asymmetry, voltage drop, voltage flicker and other issues are outstanding. Given that the research of DFIG’s operation under non-ideal conditions is challenging and realistic.This paper takes DFIG’s control under full wind speed and harmonic conditions as the main line, makes deep and detailed research from theoretical analysis, modeling and simulation, experimental validation three aspects.(1) This paper studies the control strategy of DFIG aiming to tracking maximum wind power when under rated wind speed and restricting unit speed and power when above rated wind speed. From pitch angle and converter coordinated control perspective, it emphasizes that different converter control modes should have different pitch angle control modes, which lay the foundation for the efficient utilization of wind resources.(2) This paper establishes the accurate mathematical model of DFIG and grid side converter under three-phase static coordinate and two-phase rotating coordinate system, assesses the impact of harmonic on DFIG’s running performance.(3) This paper focuses on the improvement of control strategies of DFIG under harmonic environment. Which includes:1) summarizes the existing control strategies to improve operating performance of DFIG under harmonic environment and discusses their own characteristics and advantages and disadvantages.2) proposes improved control strategy.3) studies the design method of PI and PI-R current controller.4) simulates based on PSCAD/EMTDC simulation platform, and compares traditional control method and harmonic control method with improved harmonic control method. Verifies the effectiveness of the improved control method.