Research On Order Reduction Method And Stability For Low Voltage Dc Distribution System

With the further expansion of the capacity and scale of DC distribution network,users’ requirements for the stability of distribution network system are increasing day by day.For the DC distribution system containing a variety of distributed power sources and loads,the electrical distance between different micro sources,loads and lines is short,and the degree of coupling is high.After power electronic equipment is connected,it is easy to resonate with other components of the system.The mechanism of multi-scale interaction is complex,and it is easy to be destabilized by external interference.And because the structure and operation characteristics of DC distribution network are quite different from that of AC system,the traditional modeling and stability analysis methods can not fully describe the dynamic characteristics of DC distribution system.At the same time,in the process of stability analysis of the system,due to the high order of the model and the inclusion of a variety of time scales,the calculation time is long,and the stability analysis is difficult.Therefore,it is necessary to analyze the model order reduction and stability of DC distribution system.This paper is based on order reduction and stability analysis of low-voltage DC distribution system model with multiple power electronic converters,which lays a theoretical foundation for the safe and stable operation of DC distribution network.The main research summary of this paper is as follows:Firstly,the topology of the low-voltage DC distribution system and the control mode and operation principle of each converter are briefly introduced,and the fullorder mathematical model of the low-voltage DC distribution system with three-port photovoltaic DC converter,DAB converter,VSC converter and constant power load is established.Matlab/Simulink software was used to build the full-order mathematical model of the system,and the transient response curves of the system were compared with the electromagnetic transient simulation model under the condition of small disturbance to verify the correctness of the full-order model.Secondly,based on the principle of singular perturbation,a method is proposed to reduce the order of the full-order mathematical model of the LVDC distribution system from the time scale.The order reduction model of the LVDC distribution system is derived from the time scale.The full-order and down-order models of the system are built by MATLAB /Simulink software,and the correctness and effectiveness of the proposed singularity perturbation theory applied to the down-order model of the lowvoltage DC distribution system are verified from three aspects of eigenvalue analysis of the system,comparison of transient response under small perturbation,and numerical calculation speed.Thirdly,based on eigenvalue analysis and participation factor analysis,the dominant mode of the system was obtained,and the eigenvalue to be optimized and the corresponding control parameters were determined.The influence of different parameters on the dominant eigenvalues of the system was determined by root locus analysis,and the stability boundary of the system was obtained.Based on Matlab/Simulink simulation and RT-Lab hardware-in-the-loop simulation experimental platform,the correctness of small signal stability analysis is verified.On this basis,the optimization parameters were adjusted to verify the optimization effect from two aspects: dominant eigenvalue distribution and comparison of transient response under small disturbance conditions.