Performance Analysis And Control Method Of Doubly Fed Wind Turbine Under Power Grid Disturbance And Fault Condition

The world energy structure is changing from a system based on fossil energy to a system based on new energy.As a renewable energy,wind power industry develops rapidly,but it also has many problems.Due to the wind power plant which is located in a remote and harsh environment,the sudden change of wind speed and other factors will affect the power quality,making the operation condition monitoring and fault diagnosis of the unit more difficult.Therefore,it is of great significance to study the technology of fan condition monitoring and fault diagnosis under the condition of grid-connected operation,and it is also a key problem to be solved urgently.The main contents of this paper are as follows:(1)Firstly,the types and structures of wind turbines are introduced.Then the basic working principle of wind turbines and the system model of doubly-fed wind turbines are also introduced.Based on the three-phase static coordinates,the mathematical model of doubly-fed wind turbines are established,and the voltage equation and flux linkage equation of the quota doubly-fed machine are also introduced.(2)In view of the unbalanced grid voltage,the operation characteristics of the grid-side converter are analyzed.At the same time,a double closed-loop control strategy is proposed to suppress the positive and negative sequence current of the DC-side voltage second harmonic respectively.The general phase-locked loop(PLL)with oscillation in unbalanced power grid is also improved.The simulation results in PSCAD/EMTDC environment show that the new soft phase-locked loop technology meets the requirements of being and accurate.(3)Under the environment of PSCAD/EMTDC,the models of doubly fed wind power generation system,main circuit of wind farm disturbance generator and its control system are established.The simulation under different working conditions verifies that the functions of doubly fed wind power generation system and wind farm disturbance generator meet the requirements of technical conditions,and the structure of doubly fed wind power generation system and wind farm disturbance generator is explained.The design of parameters and control strategy is reasonable.Finally,the response and control strategy of grid-side converter under unbalanced grid voltage are described in PSCAD simulation software.The simulation results verify the validity ofthe reference current algorithm and the closed-loop control strategy of positive and negative sequence control respectively to suppress DC voltage doubled frequency fluctuation under unbalanced grid voltage.