Second Order Sliding Mode Based Direct Power Control Of Doubly Fed Wind Power System

The continuous improvement of wind power generation technology is one of the key factors in promoting the rapid development of wind power industry and responding to China's energy strategy.The Double Fed Induction Generator(DFIG)based wind power generation technology,has been widely researched and applied.However,when the grid voltage imbalance or high harmonic interference and other failures happen,DFIG power generation system will appears power and electromagnetic torque fluctuations and other anomalies.The interaction between the grid and the DFIG power generation system will lead to a vicious circle that seriously damages the stability and safety of the power grid and the wind power system.Therefore,under different faulty grids,this paper develops some targeted control system solutions of the DFIG.At the same time,in the aspect of controllers,In order to solve the problem that the output chattering of the first-order sliding mode,and the structure of the DFIG vector control system under the faulty grid voltage is complicated and the dynamic response speed is reduced,the second order sliding mode(SOMC)based direct power control(DPC)strategy of DFIG power generation system is proposed.Which provides a foundation for the realization of DFIG operational performance optimization strategy.Finally,simulation is carried out on the simulation platform,and some important conclusions and innovative achievements have been obtained.The research ideas and innovative achievements are as follows:Firstly,based on analyze of the basic theory and operational principle of DFIG,the mathematical model of DFIG wind power generation system is established,and the DPC control strategy based on Space Vector Modulation(SVM)is introduced in detail.At the same time,the power simulation model of DFIG is built by toolbox of SimPowerSystems under Simulink environment,which laid the theoretical and practical basis for the follow-up work.Secondly,under the ideal condition of the grid,in order to suppress the output chattering of first-order sliding mode controller,the SOMC control strategy is applied to the DPC of DFIG power generation system,and theoretical analysis is carried out.By comparing the control effects with the first order sliding mode on the DFIG power generation system,the effects of SOMC-DPC control strategy on suppressing the control output chattering,reducing the harmonic content of stator and rotor currents of DFIG are fully verified.Then,in view of the operation problems of current harmonic distortion of DFIG power generation system in harmonic grid,the mathematical model of DFIG system and the changes of its power and current components under harmonic power network are deeply analyzed.The harmonic suppression strategy of stator currents is combined with the SOMC-DPC controller to effectively suppress the stator high-frequency harmonics of the DFIG system under harmonic grid.Finally,an experimental platform of DFIG system under harmonic power grid is built to verify the effectiveness of the proposed scheme.Finally,the SOMC-DPC control scheme of DFIG wind power generation system based on reference power compensation strategy is studied under unbalanced grid voltage.By analyzing the components of DFIG system's powers and currents under unbalanced power grid,a comprehensive reference power compensation strategy is proposed.At the same time,the SOMC-DPC controller of DFIG power generation system is designed to ensure accurate and fast tracking of reference powers.Through the improvement of both compensation strategy and controller,the control effects of the sinusoidal and symmetrical stator current,the active power without harmonic fluctuation and the stator current symmetrical or reactive power without double frequency fluctuations and stator current symmetrical are achieved.The final simulation results verify the effectiveness and feasibility of the proposed controller and reference power compensation strategy.