Modeling And Stability Analysis Of Hybrid AC/DC Microgrid

Microgrid is effective to solve the problem of the large-scale access of DGs(Distributed Generations)to power grid,it not only takes full advantage of DGs,but also supports power distributed network and enhances the reliability of power supply and the stability of the electric system.Among the structures of microgrid,hybrid AC/DC microgrid has the benefits of both DC and AC microgrid,is the inevitable trend of future development of microgrid.But most of the modelling of microgrid is focused on DC microgrid or AC microgrid,and single method can not apply in the modelling of hybrid AC/DC microgrid well.To understand the dynamic characteristics of hybrid AC/DC microgrid,it is necessary to find a simple and effective method to build its whole model.In addition,stability analysis is also one of the main technologies of microgrid,but it is usually focused on the small-signal stability analysis and the research of transient stability analysis of microgrid is not mature yet.Analyzing the stability of hybrid AC/DC microgrid roundly is also vital to guarantee its safe and stable operation.In this paper,hybrid AC/DC microgrid is systematically studied from build its mathematic model and completing its stability analysis respectively.The main work is as follows:Firstly,the current research status of microgrid and modelling and stability analysis of microgrid is summarized.Combined with the fact that there are DC and AC variables in hybrid AC/DC microgrid,state-space averaging method and dynamic phasor method are introduced in detail and their advantages that they can apply well in the modelling of DC and AC microgrid respectively are stressed.Secondly,the topology of hybrid AC/DC microgrid is simplified and it is divided into three parts:DC MSs(Microsources)and DC Loads,AC MSs and AC Loads and ILC(Interlinking Converter).Considering the different characteristics of the three parts,state-space averaging method and dynamic phasor method are applied in the modelling of DC and AC part while ILC is equivalent to a mathematic model,and the whole model of hybrid AC/DC microgrid is built based on the hybrid model.This hybrid model considers the different characteristics of the three parts,simplifies the modelling process greatly and reduce the calculation under the promise of guaranteeing accuracy.Thirdly,the concept of static stability of hybrid AC/DC microgrid is built and the whole model is linearized to infer the small-signal model.And the static stability analysis of hybrid AC/DC microgrid is conduct with the basic theory of eigenvalue analysis method and its conclusions are verified by simulation.It shows that the control parameters are the main factors that affect the static stability of the hybrid system.Then,the meaning of transient stability analysis is highlighted and the transient characteristics of hybrid AC/DC microgrid are analyzed.To overcome the limitations and deficiencies of Lyapunov direct method,three numerical analysis methods are proposed based on the whole model of hybrid AC/DC microgrid.The results of simulation verify the validity of numerical analysis methods.In actual systems,it is flexible and efficient to choose a suitable numerical analysis method according to the specific requirements of calculation precision and speed.Finally,hardware-in-loop simulation and the operating principle of RT-LAB real-time simulation system are introduced in brief.Three states of hybrid AC/DC microgrid,including steady-state operation,static stability and transient stability,are respectively simulated based on HEL simulation.The comparsion among conclusions of stability analysis,MATLAB/Simulink simulation and HIL simulation proved the validity of the proposed hybrid model and stability analysis of hybrid AC/DC microgrid.