Direct Power Control Of DFIG Wind Generation System Under Unbalanced And Distortedgrid Voltage

With the increasingly serious energy and environmental problems, Renewable energy sources such as wind turbine generation has developed rapidly. System based on doubly-fed induction generator(DFIG) has been widely applied because of its lighter weight, smaller size and no full range converter required. Due to most of areas which abundant of wind resource are far away from load centers in China, DFIG have to face unideal situation such as unbalanced and distorted grid voltage. Thus, the paper focused on DFIG’s control strategy considered unbalanced and distorted grid voltage.Firstly, this paper introduced the direct power control strategy of DFIG system. Compared with the traditional lookup table direct power control(LUT-DPC), space vector modulation direct power control(SVM-DPC) has advantages such as constant frequency and less current harmonic. So SVM-DPC strategy has been adopted in this paper to control both gird side converter and rotor side converter.Secondly, grid synchronization signal is the foundation of converter’s control. Synchronous rotating frame PLL(SRF-PLL) cannot afford this work in unideal grid anymore. Multiple complex coefficient filter(MCCF) is acquired to separate the fundamental positive sequence from negative and harmonic sequences, and frequency locked loop(FLL) is used to catch grid’s fundamental frequency in this paper. This method can simplify the structure of the system and achieve faster frequency response than PLL.Then, the DFIG control strategy under unbalanced and distorted grid voltage has been analyzed and proposed. Active and reactive power fluctuation components are calculated and some flexible control targets have been raised. PIDR regulator has been used to track both dc and ac components in reference accurately and effectively.Finally, the experimental platform based on d SPACE and the hardware design of this platform also been introduced in this paper. Simulation and experimental waveforms have been given to verify the correctness of those methods mentioned above.