Study On Optimal Control Of Variable Coefficient Frequency Regulation For Doubly Fed Wind Turbine

With the rapid development of the world economy,it has become an inevitable trend to develop renewable energy power generation technology to reduce and replace the traditional fossil energy power generation.As a clean renewable energy,wind power has huge reserves and great potential for development.Thus,it has become an important source of renewable energy for power generation.In wind power market,Doubly Fed Induction Generator(DFIG)is the mainstream models,but the vector control of power electronic converter(PEC)used in DFIG leads to the decoupling of output active power and system frequency.This strategy makes wind turbines unable to respond to system frequency changes and have an impact on frequency stability of the system.In order to reduce the impact of large-scale wind power Grid-connected on the frequency stability of the system,this paper based on improving the power control method of wind power generation system,in order to enhance the coupling between electromagnetic power and system frequency of wind turbines.The main work of this paper includes:The disadvantage of traditional virtual inertial control is that the robustness of fixed frequency control coefficient is poor under different impact loads and different wind conditions.To solve this problem,this paper studies the virtual inertia characteristics of DFIG-based wind turbines,and analyses the relationship between the speed change and output power of doubly-fed wind turbines controlled by virtual inertia.Thus,a variable coefficient virtual inertia control strategy considering both the frequency regulation efficiency and frequency regulation cost is proposed.In this control strategy,the output active power and speed recovery time of DFIG-based wind turbines are used to measure the efficiency and cost of the frequency regulation.The genetic algorithm is used to calculate the optimal frequency regulation coefficient curve and the rotational speed deviation under different states of the wind turbine,so as to realize the frequency control coefficient changes with the variation of the rotor speed.In order to further enhance the frequency stability of the power system,this paper designs a coordinated strategy of virtual inertia control and pitch angle control under whole wind conditions,considering the characteristics of different frequency control strategies of doubly fed wind turbines.The proposed coordinated control strategy utilizes the rapidity of virtual inertia control response and the sustainability of pitch angle control response of DFIG-based wind turbines,and overcomes the transient of virtual inertial control and the lag of pitch angle control in a complementary way.The frequency control coefficients are adjusted according to the operation status of wind turbine under different wind speeds,in order to guarantee the validity under the whole wind condition.According to the proposed control strategy,the simulation experiment is carried out on the Matlab/Simulink.The results show that the proposed method can make the wind turbine respond to the system frequency changes under different operating conditions,effectively restrain the rapid change of system frequency and reduce the system frequency deviation,and ensure the stable operation of wind turbine itself.