含跟网型储能的新能源多馈入系统小扰动电压支撑强度分析OA北大核心CSTPCD

With the integration of large-scale renewable energy resources and energy storage into the power grid through power electronic converters,power electronic multi-infeed system is becoming a typical form of modern power system.In particular,the growing penetration of grid-following converters through phase-lock loop under weak grid strength has resulted in frequent oscillation instability risks.Therefore,it is increasingly important to accurately quantify the system voltage support strength(referred to as system strength)and evaluate the stability margin of the system.The relative difference between the short-circuit ratio and device critical short-circuit ratio is commonly used to quantify the system strength and the small-disturbance synchronous stability margin.However,there are two operating modes of charging and discharging when the energy storage system works normally,which leads to the change of the steady-state operating point of the power electronic multi-infeed system composed of multiple energy storage converter and multiple renewable energy converter,and further aggravates the difficulty of small-disturbance synchronous stability analysis.In order to solve the above problems,this paper proposes the generalized short-circuit ratio(gSCR)as the grid strength index of multi-infeed system with energy storage and then presents a fast evaluation method of system strength source-network collaboration based on this index. Firstly,the frequency-domain model and the closed-loop characteristic equation of multi-infeed system with energy storage are established based on linearization analysis.Secondly,it is theoretically proved that the multi-infeed system with energy storage can be equivalently decoupled into a set of single-infeed subsystems based on the modal decoupling theory.On this foundation,the definition of the gSCR is extended from conventional renewable energy multi-infeed system to multi-infeed system with energy storage considering the charging/discharging operation mode.The system voltage support strength analysis method based on gSCR and the device critical short-circuit ratio(CSCR)is proposed,and then the fast evaluation of the small-disturbance synchronous stability margin is realized.Furthermore,the influence of the charging/discharging operation mode of the grid-following energy storage converter on the small-disturbance synchronization stability margin of the system is explored through the matrix interlocking eigenvalue theorem.Finally,the effectiveness of the proposed small-disturbance synchronization stability analysis method is verified by simulation example of the 5-infeed power system. The following conclusions can be drawn:(1)The gSCR(which is related to the grid strength)and CSCR(which is related to the apparatuses'tolerance towards AC grid)can reflect the system strength and the small-disturbance synchronization stability margin of the multi-infeed system with energy storage,which thus significantly reduces the complexity of small-disturbance synchronization stability analysis of the original multi-infeed system.This proposed method can be applied to different scenarios where multiple energy storage converters work in charging or discharging modes.(2)The two operating modes of grid-following energy storage correspond to different steady-state operating points of the multi-infeed power system,and the steady-state operating points further affect the small-disturbance stability of the system through the phase-locked loop.According to the matrix interlocking eigenvalue theorem,it is demonstrated that the small-disturbance synchronization stability margin of the multi-infeed system when the grid-following energy storage converter works in the charging mode is higher than that of the discharging mode.