Analysis Of De-loading Capacity And Research On Coordinated Control Of Primary Frequency Of Doubly-fed Wind Turbine

With the large-scale wind power grid, the grid frequency stability is becoming increasingly serious. For the currently widely used doubly-fed asynchronous wind turbine, the variable speed constant frequency is realized by the rotor-side converter, so that when the system frequency changes, the rotor speed cannot respond to the change of the grid frequency, and the unit usually runs in the maximum power tracking mode , making it impossible to provide additional active power to participate in frequency adjustment. At present, the research on the frequency modulation of wind turbine is mainly focused on the realization of function. This paper mainly studies the frequency of double frequency of wind turbine.Firstly, the working principle of the doubly fed wind turbine is analyzed and its mathematical model is established, including wind speed model, wind turbine model, shaft system model, generator model and control system model. On this basis, the stator flux linkage control strategy of the rotor side converter, the voltage vector directional control strategy and the pitch angle control strategy of the grid side converter are studied.Secondly, the basic principle of the frequency regulation of the power system and the basic requirements of the primary frequency modulation are introduced. The principle of the first frequency modulation of the doubly fed wind turbine is introduced, and the frequency control methods of the rotor kinetic energy control and the power reserve control are analyzed and comparison.Then, according to the different wind speed conditions, the control method of speed control and pitch angle control combined with load shedding control is developed. Low wind speed, the use of speed control for load shedding; stroke speed, the use of speed control and pitch angle control combined with the load shedding control strategy; high wind speed, the use of pitch angle control for load shedding. And the simulation model of the primary frequency control system of the doubly fed wind turbine was established and simulated. It is concluded that the load shedding control can provide sufficient spare capacity for the system FM in different control modes.Finally, based on the three kinds of load shedding control strategies, combined with the rotor kinetic energy control of the generator, the frequency control coordination strategy of the doubly-fed wind turbine is realized and compared with the traditional combination control strategy. The simulation results show that the coordinated control strategy not only allows the wind turbine to have enough spare capacity, but also has good frequency response characteristics.