Frequency Modulation Control Strategy Of Doubly Fed Wind Turbine With Redundant Energy Storage

The goal of conventional wind turbine is to pursue the maximum output power,which leads to the decoupling of unit power and system frequency,resulting in the imbalance of power system inertia and the increase of frequency modulation pressure.Doubly fed wind turbine generator based on virtual synchronous generator control（DFIG-VSG）can increase the inertia and damping of the system,and then improve the frequency stability of the system.However,due to the constant virtual inertia and damping provided by the traditional DFIG-VSG,the effect of frequency support and regulation is not ideal.This paper takes doubly fed wind turbine with redundant energy storage as the object,and deeply studies the wind power virtual inertia and frequency modulation control strategy.The main contents of this paper are as follows:The model of dual source wind turbine is radicated,including dual source turbine,dual source converter and standby power supply.The model of DFIG consists of stator voltage,motor current and rotor motion equation.On this foundation,the frequency of dual source generator,the output of dual source generator and the affect of control mode on power grid frequency are analyzed.In order to solve the problem that the virtual inertia synchronous control of traditional doubly fed wind turbine does not change with the working condition,resulting in poor frequency regulation adaptability,an arctangent flexible virtual synchronous doubly fed generator frequency modulation control strategy（DFIG-FVSG）with dynamic adjustment of virtual inertia is proposed,according to the changes of virtual rotor angular velocity and unit output power,the imitating inertia is adjusted in real time to improve the frequency stability of ventilation system and power grid.The simulation results show that FVSG control can effectively reduce the vibration amplitude of the system,shorten the control time of the system,and quickly restore the frequency and response performance of the system.In order to further improve the ability of double energy storage wind turbine to regulate the frequency of power grid and introduce standby power,a frequency modulation control strategy of double energy storage wind turbine considering load state is proposed.The strategy adjusts the frequency modulation depth coefficient according to the dynamic state of the load in the energy storage system,and allows the process to exit the frequency modulation range in time to avoid excessive adjustment.Simulation and comparative experiments show that the doubly fed generator with adaptive redundant standby state control has obvious frequency response and power advantages in the process of primary frequency regulation.In order to verify the feasibility and effectiveness of the control strategy proposed in this paper,a fire wind storage system model based on 1.5MW DFIG with redundant energy storage is established and simulated under step load disturbance.The results show that compared with four different frequency modulation control strategies,when using wind energy storage frequency modulation,the system output power deviation is reduced to 1.4（pu）,and the system frequency deviation is reduced to 0.28 Hz.The expected goal of improving the frequency modulation capability of doubly fed wind turbine is achieved.