Research On Fault Ride Through And Power Smooth Control Of Direct-drive Wind Power Generator With Supercapacitor

Wind energy has the characteristics of wide distribution, renewable and pollution-free as a kind of green energy. In the field of wind power generation, Direct-drive permanent magnet synchronous generator wind turbine generation system(D-PMSG WTGS) has aroused more and more attention and gained its market share for its operation reliability and control flexibility. In order to further improve its performance, the control strategies of fault ride through and power smooth for D-PMSG WTGS with supercapacitor(SC) energy storage device is investigated in this dissertation.Firstly, the purpose of research is elaborated, the world’s energy consumption structure and the present development situation of the wind power generation and the SC are introduced, and the present research situations of the fault ride through and the grid-connected power smooth in D-PMSG WTGS are summarized.Secondly, According to the structure and working principle of D-PMSG WTGS with SC, the mathematical models of grid side converter(GSC) and bi-directional Buck-Boost converter(BDBBC) are derived, which included their switch function models and the state function and transfer function models of BDBBC.Thirdly, with regard to the normal and failure operations of the grid, the coordinated control strategy which is composed of the control for GSC and BDBBC is developed. In the proposed control scheme, the second-order generalized integral phase-locked loop(SOGI-PLL) is used to detect the grid voltage, under normal grid operation, the improved voltage orientation control(VOC) for GSC based on feed-forward control of negative sequence voltage is applied, i.e., the DC-link voltage is controlled by the outer voltage loop and the current response is controlled by the inner current loop, meanwhile current single closed-loop control for BDBBC is developed to release the energy in SC to the preset level;under grid fault, power control for GSC based on feed-forward control of negative sequence voltage and the voltage control for BDBBC based on voltage outside loop and current inside loop are adopted to remain D-PMSG WTGS connected to grid. Simulation of control performance is carried out in Matlab/Simulink, and the simulation results verify that the coordinated control strategy could improve the fault ride through ability of D-PMSG WTGS.Fourthly, the grid-connected power smooth control of D-PMSG WTGS is studied.The “wind power model” is designed to simulate the power fluctuation of generator in D-PMSG WTGS caused by wind fluctuation. In order to make the grid-connected power relatively smooth, the grid voltage oriented vector control for GSC and the control of current single closed-loop for BDBBC are adopted, where the set value of active power for BDBBC is obtained by the generator output power and its averaging power, and the effect of two power averaging way, included of the numerical average method and the low passfilter method, is contrasted and analyzed. Simulation results show that the active power fluctuation of PMSG can be compensated by SC, and the grid-connected active power can be controlled smoothly and stable.At last, the main contents of the dissertation are summarized, and the further research directions are also prospected.