Research On Anti-jamming Control Of DC Grid-connected System Of Doubly-fed Wind Turbines

Doubly-fed induction generator(DFIG)is one of the two main types of wind farms.With the increase of the scale of wind farms in recent years,the demand for long-distance power transmission is increasing.The research of wind turbine generator system which can directly realize DC-grid connection has become a new research field.The DFIG wind energy conver-sion system which is most suitable for large-scale wind power become the main research object,and the double-VSI DFIG based on DC-grid is proposed.For double-VSI DFIG wind power system,it is a highly nonlinear system due to the influence of aerodynamics and internal struc-ture.At the same time,the system is often in a transient state due to random wind speed,and there are parameter uncertainties,unmodeled disturbances,low voltage ride through and so on.These inevitable disturbances cause difficulties for controller design.Based on this,the anti-interference of double-VSI DFIG system in maximum power point tracking(MPPT)is studied.The main research contents are as follows,1.This thesis presents a single-loop input-output feedback linearization control strategy(FLC)for stator and rotor cooperative work of double-VSI DFIG.The strategy directly takes the required stator and rotor state as the system input to form a single-loop control.Compared with the traditional double-loop control,it reduces the complexity of the control structure,the number of control parameters and control steps,shortens the operation time of the control s-trategy,and improves the running speed of the system.The simulation results show that the proposed FLC has better control accuracy and tracking speed in slope variable wind speed and random wind speed environment.2.This thesis proposes a simple stator flux sliding-mode observer for double-VSI DFIG system.The traditional voltage model or current model stator flux estimation algorithm depends on the system parameters.When the system parameters drift away from their rated values due to the changes of the external environment,the calculation results of the traditional method will appear large estimation errors.For double-VSI DFIG system,the stator flux is an essential state variable,the incorrect stator flux estimation will weaken the robustness of the system.There-fore,in double-VSI DFIG system,the correct estimation of stator flux is very necessary.This paper improves the stator flux sliding-mode observer of AC-based DFIG system.The structure of the stator current sliding mode observer is redesigned,increases the resistance online identi-fication,and the stator flux is estimated by the control signal of current sliding-mode observer.The structure of the whole observer is simple and easy to realize,and only two parameters need to be set and determined.The simulation results show that the robustness of the proposed observer is better than that of the traditional voltage model.3.An adaptive feedback linearization controller(FLC-A)based on a flux observer for double-VSI DFIG to track the maximum power point(MPP)is introduced in this thesis.Based on the single-loop input-output feedback linearization algorithm,an adaptive controller is used to overcome the parameter uncertainty and improve the MPPT tracking performance of the system.FLC-A takes the variation of DFIG resistance as the perturbation term of the system,and designs an adaptive law to estimate the perturbation term.Even if the system is disturbed by the variation of DFIG inductance,the system can still accurately track the MPP.At the same time,in order to accurately estimate the stator flux,an adaptive stator flux observer based on online resistance identification is designed.When the continuous excitation condition is not satisfied,the resistance cannot be estimated online,but the observer can still accurately estimate the stator flux.The simulation results show that the FLC-A can achieve stable and efficient MPPT tracking under the disturbance of the stator resistance uncertainty and the wind speed rapid change.At the same time,the proposed adaptive stator flux observer has high accuracy in flux estimation.4.Two kinds of PID feedback controllers based on extended perturbation observer for double-VSI DFIG system are proposed to improve the performance of MPPT:one is based on high-gain perturbation observer PID feedback controller;the other is based on sliding-mode perturbation observer PID feedback controller.In addition to the parameter uncertainties,double-VSI DFIG wind power generation system also has many perturbations such as aero-dynamic disturbances,unmodeled dynamics,highly nonlinear coupling,etc.,which are called lumped perturbations.Based on the single-loop input-output feedback linearization algorithm,two kinds of extended perturbation observers are designed to realize the observation of lumped perturbations,and two kinds of PID controllers are designed to realize the MPPT of the system.The performance of the two controllers is analyzed and compared in detail through simulation and experiment,which can improve the transient performance and achieve the design purpose.