Research On Control Approaches For Wind Power Generation Systems With A Doubly-Fed Induction Generator

In the current wind power grid-connected system,the mainstream models in the market include direct-drive permanent magnet synchronous generators and doubly-fed induction generators.Among them,the permanent magnet synchronous generators is characterized by large initial hardware investment,and easy grid-connected control method;while the doubly-fed induction motor is characterized by small initial hardware investment and complicated control method.The main purpose of this paper is to apply complex control methods,support the grid-connected operation of doubly-fed generator,and use improved control methods to solve the problem of high wind power hardware investment.At the same time,advanced control theory will be used to solve the problem of grid-connected operation rate and power quality improvement of doubly-fed wind turbines.The main work and innovations of this paper are as follows:Firstly,this paper proposes a soft crowbar control approach with an integrated design of the flux damping method and virtual resistance method,for the fault ride-through(FRT)improvement in wind power generation systems with a doubly-fed induction generator(DFIG).First,the paper describes the damage to DFIG system caused by voltage fault and the system characteristics are analyzed theoretically.Then,the theory basis and the implementation method of the soft crowbar control approach are provided.Finally,compared with 3 different method,the simulation on a 1.5MW DFIG system with soft crowbar control approach are given.It shows that the proposed control approach is effective,and the DFIG system has strong adaptability and robustness.Secondly,this paper proposes a second-order active disturbance rejection control(ADRC)-based control strategy with an integrated design of the flux damping method,for the control effect improvement under complicated working conditions in wind power generation systems with a doubly-fed induction generator(DFIG).The stability of the second-order ADRC is theoretically analyzed,and the advantages and disadvantages of PI control,first-order ADRC,and second-order ADRC control are simulated and analyzed.It is verified that the second-order ADRC controller designed in this paper can effectively improve the robustness of the DFIG system in the case of system interference and parameter drift,so that the DFIG system can always maintains good control effects and fault ride-through capability.Finally,this paper proposes a DFIG power adjustment control scheme based on generalized predictive control,enhances the adj ust power quality ability of DFIG,and improves the reactive output capability of the DFIG system.The control method of DFIG system and unified power quality regulator is compared and analyzed,and the limit of DFIG reactive power compensation ability is discussed.In order to solve the dynamic multi-variable process of DFIG power allocation,a generalized predictive control scheme with three inputs and three outputs is designed to effectively improve the reactive power compensation capability of DFIG through model prediction,rolling optimization and feedback correction.The simulation compares the reactive power output of DFIG under MPPT control and generalized predictive control.It proves that the generalized predictive control can effectively improve the total reactive power compensation of DFIG and enhance the adjust power quality ability of DFIG.