Research On Stability Analysis And Coordinated Control Of DC Microgrid

The rapid growth of dc loads along with the inherent dc power generation of most of renewable energy sources have made the dc microgrids an attractive choice for active distribution systems.However,there are still some technical issues associated with the operation of DC microgrids,such as coordination control and stability.DC microgrid is taken as the research object in this thesis.The main contents include:(1)The operation principle and control strategy of the DC/DC converter are researched.The basic topology of the DC/DC converter is introduced,and the working principles of the two basic topology Boost and Buck converters are researched.This paper introduces three control strategies of DC/DC converter: voltage control,peak current control and average current control.The basic principle,operation characteristics,advantages and disadvantages of the three strategies are analyzed.The advantages and disadvantages of peak current control and average current control are compared by simulation.(2)The modeling methods of DC microgrid are researched.The state space average method,energy conservation method and equivalent source method are used to model the DC microgrid respectively.The structure,complexity and accuracy of three models are researched.The applicable scope of the three models is determined through the comparative analysis of simulation.(3)The stability analysis method of DC microgrid and bifurcation theory are introduced.Based on the gyrator model and simplified equivalent circuit model,the eigenvalue analysis method is used to study the small signal stability of small and large DC microgrid systems.For large systems,by analyzing the real part symbols of the eigenvalues of the Jacobian matrix instead of directly obtaining the eigenvalues,combined with the bifurcation theory,the stability range and instability behavior of the system are obtained.At the same time,the influence of system parameters on the stability of large systems is analyzed,and a process for judging the stability of DC microgrid systems is given.Based on RT-LAB,the stability conclusions of small and large systems are verified through hardware-in-the-loop experiments.(4)Aiming at the problems of traditional droop control and considering the influence of line loss,an improved adaptive droop control strategy is proposed,and the key parameters of the control strategy are designed.Compared with the traditional control strategy,the improved control strategy can improve the DC bus voltage quality and reduce line loss.Finally,through example analysis and hardware-in-the-loop experiments,the effectiveness of the improved adaptive droop control strategy considering line loss is verified.This thesis includes 56 figures,9 tables and 90 references.