Research On The Control Strategy Of Primary Frequency Modulation For Wind Power Grid Connection

Nowadays,resources are becoming more and more scarce,and the development and application of wind energy has become one of the keys to solving energy shortages.The doublyfed asynchronous generator is currently the mainstream model used in wind farms in the world,but it is decoupled from the grid and cannot directly participate in the primary frequency regulation process of the grid.Under high wind power penetration,the inertia and frequency regulation effect of the generators in the grid will be reduced.With the rapid development of wind power technology,the capacity of wind turbines at home and abroad is also increasing.Traditional units alone can no longer meet the requirements for power quality.Therefore,it is necessary to improve the conventional grid-connected control strategy of wind turbines.This article mainly analyzes the strategy of connecting wind farms to the grid to participate in a frequency modulation.The main research contents are as follows:First,carry out the modeling of the doubly-fed wind power grid connection.Analyze the composition structure,working mechanism and mathematical model of the wind power system,including natural wind,wind turbines,transmission systems,dual PWM converters,etc.,build a simulation model that meets the dynamic control requirements of the wind power system on the Matlab/Simulink platform.The principle and equivalent circuit of the doubly-fed wind generator are analyzed,and the mathematical model under the synchronous rotating coordinate system is deduced in detail.Secondly,through the vector control method of stator field orientation and grid voltage orientation,a steady-state control strategy for the rotor-side converter and the grid-side converter is constructed to realize the decoupling control of the stator active and reactive power and the constant DC bus voltage.On this basis,the rotor speed is adjusted by controlling the components of the rotor current on the d-axis and the q-axis,so that the wind turbine can obtain the maximum wind energy capture and realize the conventional maximum power tracking control of the wind turbine.Finally,establish a low-order frequency response model of thermal power,analyze the way that traditional synchronous generators participate in primary frequency modulation,and derive three frequency modulation strategies for variable-speed wind turbines.(1)Using the rapidity of power electronic converter adjustment,the rotational kinetic energy in the wind turbine rotor is used as virtual inertia to simulate the inertia characteristics of synchronous generators.(2)Use the variable pitch system to give up the maximum wind energy capture for load shedding,so as to obtain the reserve capacity to participate in the droop control of the system.(3)By analyzing and researching the simulation results of two doubly-fed wind turbines connected to the grid and participating in a frequency modulation,a wind power grid-connected control strategy with integrated virtual inertia and droop control is derived.The frequency modulation effect before and after the control strategy is changed is compared,and the static frequency modulation characteristic of the primary frequency modulation is verified.