Operation And Control For Hybrid Wind Farms With FSIG-based And PMSG-based Wind Farm Under Grid Faults

Due to the increasingly strict requirements of the grid code and the uncontrollable nature of the traditional fixed-speed induction generator(FSIG), it is urgently needed to study the renovation of FSIG based wind farm to achieve low voltage ride through(LVRT) and the improvement of FSIG's transient stability. Currently, the solutions of adding parallel reactive power compensation equipments to improve the LVRT performance of FSIG-based wind farm have been approved both in the domestic and overseas. With rapid development of wind power industry in China, it has been a trend to construct large capacity of hybrid wind farms by combining different wind power generation systems. Therefore, the permanent magnet synchronous generators could be used to replace the parallel reactive power compensation equipments for providing transient reactive adjacent to nearby fixed-speed induction generators during grid fault conditions. In order to improve the LVRT performance and the power quality of FSIG-based wind farm, the hybrid wind farm combining both FSIG-based wind power generation system and PMSG-based wind power generation system is researched in this paper. In addition, the operation performance and the control strategy of the hybrid wind farm is investigated under grid fault conditions.(1) Based on the simplified equivalent model of the grid connected FSIG-based wind farm containing line parameters and the detailed analysis of the transient characteristic as well as power characteristic, the relationship between the critical clearing slip and the reactive power compensation capacity of the FSIG-based wind farm is presented quantitatively. These works lay the foundation for the capacity configuration of hybrid wind farm under grid fault conditions.(2) The influence of fault type, fault location and the reactive power control strategy of the PMSG-based wind farm to capacity configuration of hybrid wind farm is analyzed. With the power-slip characteristic of FSIG-based wind farm, the capacity cofiguration method of hybrid wind farm under grid fault conditons is proposed. And the method is verified by simulation results. Moreover, the relationship between the reactive capacity of the PMSG and the electrical distance between wind farm and the connected power grid are analyzed, and the influence of the reactive power capacity to FSIG's transient operating characteristic is assessed.(3) The coupling relationship between positive- and negative-sequence of grid voltage during unbalanced grid fault conditons is also deduced. Meanwhile, the influence of the reactive power supporting and the negative-sequence voltage suppressing to the positive- and negative-sequence of grid voltage is investigated. Based above analyses, the coordinated positive- and negative-sequence control strategy is designed for the hybrid wind farm. The control effect is verified by simulation results.(4) An experimental hybrid wind power generation system is establised. The capacity configuration is verified by the experimental results. What is more, the LVRT operations of the FSIG with and without PMSG reactive power support have been studied by experiment.