Improved Stepwise Inertial Control Considering The Output Characteristics Of Synchronous Machines When Wind Turbines Quitting Frequency Modulation

In recent years,as the penetration rate of wind power continues to increase,the inertia of the power system has decreased and the frequency response has become more sensitive.It is not enough to only rely on the synchronous machines for frequency adjustment to cope with the impact of load disturbance.So it is necessary for wind turbines(WTs)to have the ability to participate in the primary frequency modulation.Among them,stepwise inertial control(SIC),which based on rotor kinetic energy of WTs,can increase output in steps at the moment of disturbance and improve the frequency deviation of the power grid.However,because this control strategy quickly reduces its output when the WTs quit the frequency adjustment,the active power of the grid is unbalanced again,which in turn leads to a secondary frequency drop(SFD).To this end,this article first compares the electromechanical dynamic characteristics(including structural characteristics,speed operation characteristics and active power output characteristics)of two different power sources of synchronous machines and WTs,and analyzes the influence of power regulation rate and wind power penetration rate on frequency deviation.On this basis,making full use of the advantage of the sensitive output characteristics of WTs and the strong frequency adjustment ability of the synchronous machine,this paper proposed the improved SIC strategy considering the output characteristics of the synchronous machine.When a load event occurs on the power grid,the output of the wind turbine is immediately increased and the constant power is maintained for a certain period of time.When the frequency reaches the lowest point,the output of WTs decreases,and the output of the synchronous machine rises to make up for the grid power shortage in time.Since the WTs exit the frequency modulation process,the system power balance is always maintained,so as to avoid the occurrence of SFD.At the same time,by optimizing and setting the parameters in the improvement strategy,the initial power support of WTs is further improved,and more rotor kinetic energy is used in the initial stage of frequency modulation,thereby reducing the maximum frequency deviation of the power grid.Finally,based on the simulation model built by Matlab/Simulink,the verification is carried out under different proportions of WTs.Furthermore,making use of the dynamic simulation experiment platform containing WTs carries out the experimental verification.It can be seen from the verification results that compared with other methods,the method proposed in this paper effectively suppresses the SFD,reduces the maximum frequency deviation of the power grid,and improves the frequency stability.