Research On Weak Damping Low Frequency Oscillation Suppression And Additional Damping Controller Of Wind Power System

The reason for the low frequency oscillation of the power system is generally due to the weak damping or even the negative damping effect of the power system.It is especially common in the power system with weak inter-regional connection and longdistance transmission.The low-frequency oscillation of the power system will seriously affect the safe and stable operation of the power equipment in the power grid.The gridconnected Doubly-fed Induction Generator(DFIG)will have a new impact on the original low-frequency oscillation mode of the power system,and it will pose new challenges to the study of the low-frequency oscillation of the power system.Installing a power system stabilizer(PSS)in DFIG helps to enhance the ability of the power system to dampen oscillations and improve the safety and stability of the power system.Therefore,it is of great significance to study the mechanism of DFIG on the low-frequency oscillation of the power system and design the corresponding power system stabilizer to improve the low-frequency oscillation mode of the power system.The main work is as follows:(1)This paper introduces the research background of low-frequency oscillation of DFIG wind power system and the current research status at home and abroad,analyzes the main directions of existing research and their shortcomings,including DFIG additional damping control technology.(2)Carry out detailed dynamic modeling of DFIG,and consider the dynamic relationship between DFIG and synchronous generators.Take DFIG grid-connected point voltage as input,DFIG output active power and reactive power as output,and DFIG as In the feedback link,the transfer function of the wind power system with DFIG is established,and the block diagram of the transfer function of the wind power system with DFIG is drawn.(3)Derive the analytical expression of the DFIG additional damping torque and calculate the DFIG additional torque,and analyze the size and nature of the damping torque provided by DFIG to the interval mode.The influence of wind power penetration rate and DFIG operation mode on the low-frequency oscillation mode of the power system is analyzed by changing the number of connected DFIG units and wind speed.(4)The structure of DFIG-PSS is designed,and the parameters of PSS are adjusted by phase compensation method,and the mechanism of PSS suppressing low-frequency oscillation is analyzed.(5)Install the DFIG-PSS in the Rotor side converter(RSC)and the grid side converter(Grid side converter,GSC)respectively,and analyze the DFIG-PSS in different installation positions by calculating the additional torque of the DFIG The impact on the oscillation damping ability of the power system under the following conditions,and the calculation results are verified by time-domain simulation.