Research On Operation And Control Of Hybrid Wind Farms With DFIG And PMSG Under Grid Fault

With the rapid development of wind power industry and the further research for various wind turbine generators, the hybrid wind farms will be the tendency to construct large-scale wind farms, which are consist of various eligible wind turbine generators. Especially, the hybrid wind farms consist of permanent magnet synchronous generator(PMSG) and doubly fed induction generator(DFIG) will be attracted more attention. According to the operation characteristic of different wind turbine generators, the hybrid wind farms can be coordinated controlled to further improve the operation stability and safety of the grid-connected wind power generation system. However, the grid faults are frequently occur, due to a large number of wind farms in China are installed in rural or offshore areas where the grid is relatively weak. As a consequent, during the grid voltage fault, the hybrid wind farms can enhance its low voltage ride through(LVRT) capability by the coordinated control strategy between different wind turbine generators. In this dissertation, the operation performance and the control strategy of hybrid wind farms with DFIG and PMSG are investigated under grid fault, for enhancing the LVRT capability of the grid-connected wind farms. The main work is as following:Based on the mathematical models and control models of the DFIG-based wind power generation system and PMSG-based wind power generation system, the simplified model of the hybrid wind farms with DFIG and PMSG are firstly developed. And then the corrections of the established model are verified and its steady state operation performances are researched by simulation results.Then, the reactive current limit expressions of DFIG-basedwind farmand PMSG-based wind farm are deduced respectively under symmetrical grid fault, and the improved LVRT control strategies satisfiedthe grid code LVRT requirements are proposed respectively. And then, based on the proposed control strategies and time-space distribution characteristics of wind farms, the coordinated control strategy of the hybrid wind farms are researched to deliver the maximum reactive currents,for enhancing the transient grid voltage level. In addition, the feasibility of the coordinated control strategy under all operation conditions is verified by simulation.In addition, the operation performances of DFIG-based wind farm and PMSG-based wind farm are investigated respectively under asymmetrical grid fault. And the improved control strategies and corresponding current calculation algorithm of DFIG and PMSG are respectively proposed. Based the above analysis, the coordinated control strategy of the hybrid wind farms under asymmetrical grid fault is proposed, for improving its stability and LVRT capability. The proposed control strategy is still verified by simulation.At last, an experimental platform of the hybrid wind power generation system is developed. On the experimental platform, the validity and efficiency of the coordinated control strategy for hybrid wind power generation system are verified.The work of this dissertation provide the theoretical analysisfor improving the stabilty and the LVRT capability of the hybrid wind farms under the grid fault,which will be helpful to the rapid development of large-scale wind farms.