Research On Switched System Large Signal Stability Of DC Microgrids

DC microgrid is a micro-power network that can realize self-control,protection and management.It is usually composed of multiple heterogeneous units,such as photovoltaics,wind turbines,energy storage systems and various loads.According to local sampling signals,each power generation unit has different operating states,such as maximum power tracking and droop control of photovoltaic,and charging and discharging control of energy storage.In order to realize the efficient,reliable and stable operation of the DC microgrid,energy management will control it to operate in different operating modes,and the stability of switching between modes is urgently needed for further study.Therefore,this thesis proposes a large-signal stability analysis method for the switched system,which aims to analyze the system-level large-signal stability of the DC microgrid from the perspective of the switched system.The main tasks completed are:First,a large-signal reduced model of the DC microgrid is established.According to different control modes,the port equivalent model of the source side interface converter is derived,and then combined with the switching strategy of energy management,a large signal model of the overall switched system of the DC microgrid is established.Secondly,the stability of the subsystem and switching system is analyzed.The nonlinear state space model of the subsystem corresponding to the operating mode is established,and the eigenvalues of the system matrix are identified,and sufficient conditions for the stable operation of the subsystem are obtained;based on the Lyapunov function method,different Region of Attraction(ROA)of the state variables are drawn;the large-signal stability of the switched system of the DC microgrid from the perspective of system energy changes is evaluated by derived multiple Lyapunov function(Multiple Lyapunov Function,MLF)criterion.Finally,the analysis is verified by simulation and experiment.With the aid of the PSIM simulation platform,a DC microgrid simulation model was built;at the same time,a48 V photovoltaics-storage DC microgrid experimental platform was built,with photovoltaic analog power and lead-acid battery packs as input power sources,and the load was of constant power characteristics.Through simulation and experimental results,the energy changes of the subsystem and the switched system conform to the dynamic response of the system after being disturbed,which verifies the validity of the large signal stability analysis of the switched dynamic system of the DC microgrid.