Transient Analysis Of Reconfigurable Step Utilization Battery Energy Storage System

Under the background of the worsening energy crisis and the strategic decision of"2030carbon peak,2060 carbon neutral",China has actively developed non-fossil energy,and a large number of new energy sources have been incorporated into the power system.Most of the loads in the microgrid are connected to the DC side bus through converters,and such loads have negative impedance characteristics due to the closed-loop control,thus reducing the stability margin of the system.Due to the complex and low inertia characteristics of the microgrid,large disturbance will aggravate the system,and the whole system will have an oscillation collapse in severe cases,threatening the reliable operation of the system.The stability problem of microgrid is one of the most complex and cumbersome problems in microgrid,the small signal analysis method is based on the small signal analysis near the steady-state operating point of the system,and the system deviates from the stable operating point when a large disturbance occurs,at this time,the small signal research method will no longer be applicable,and the large signal analysis method must be used to study the stability of the system under large disturbances.Therefore,it is of great significance to analyze the large signal of the system.In this paper,a multi-port microgrid model including photovoltaic power generation unit,reconfigurable battery energy storage system and constant power load is established,according to the different working modes of energy storage system in the system,the large signal equivalent models of charging and discharging modes of energy storage system in dq coordinate system are established respectively;according to the equivalent system model,the mixed potential function expression is written,and the stability criterion of the large signal of the system is derived by using the third stability theorem.In the operation of the reconfigurable battery,the reconstruction process time is shorter,and the stability of the system is less affected,therefore,in this paper,the influence of a large number of battery switching and constant power load power mutation on the stability of the system is studied,and the power limit value under large signal disturbance is obtained according to the criterion;the energy function of Lyapunov form is constructed,and the influence of constant power load mutation on the asymptotic stability region of the system is given when the energy storage system works in charge and discharge mode.The large signal stability criterion gives the relationship between the DC side voltage stabilizing capacitor C_dc,the AC side filter inductance L_s,the grid-connected converter control parameter k_vp,the photovoltaic power P_PV,the charging and discharging power P_b of the energy storage system and its working mode and the constant power load power P_cpl mutation limit value that the system can withstand.Through the detailed derivation of the voltage outer loop which is regarded as a constant term in the derivation process of the criterion,it is found that the integral link of the voltage outer loop will aggravate the oscillation of the system when a large disturbance occurs in the system,therefore,in order to remove the adverse effects of the voltage outer loop,the first-order linear active disturbance rejection control is considered to replace the voltage outer loop,and its feasibility is analyzed and verified.Finally,the simulation software was used to build the system model,and the C_dc,L_s,k_vp,P_PV and P_b in the criteria were set up a number of different groups to verify the correctness of the criteria.By comparing the power stability boundary of PI voltage outer loop and active disturbance rejection voltage outer loop,it is proved that the active disturbance rejection control can expand the power boundary of the system,and verify the effectiveness of the improved method.