Modeling Of Microgrid With Power Electronic Transformer & Its Effects On AC Main Grid

With the development of distributed power generation technology and microgrids,the distribution network has transformed from a power receiving network into an active distribution network.The increase of grid-connected microgrids in the distribution network affects the operation of the original AC distribution network,i.e.active power,reactive power,harmonics and even stability etc.The composition of different microgrids and different access devices have variety effects on the operation of the distribution network due to their performance differences.As a new type of equipment with multiple functions and flexible interfaces,power electronic transformer(PET)have the ability to control its output when connected to the main grid,which is more worthy of attention and research.First of all,the theoretical knowledge required for the analysis of the effect of PET based on the distribution network is reviewed,including three parts: microgrid,PET and distribution network operation analysis.First,on the basis of introducing the composition of the microgrid,this thesis analyzes the characteristics of the main electrical equipment and the operation mode of the microgrid;Second,according to the structure and working principle of PET,the main functions of PET and its role under different scenarios in distribution network are analyzed.Third,methods for steady-state operation of microgrids and distribution networks,as well as harmonic power flow analysis methods are given.Secondly,based on ETAP power system analysis software,the modeling of PET,microgrid and distribution network was carried out.After comparing various analysis software’s of the power system,ETAP was selected as the modeling analysis tool;then,the IEEE13-node distribution network steady-state analysis model is constructed including PET model,energy storage,photovoltaic,DC Microgrid and AC loads.In addition,an equivalent model of harmonic source for harmonic power flow analysis is proposed.Finally,a simulation of the effect of the PET-connected microgrid to the AC main network is carried out.First,the main indicators of the distribution network operation analysis are given,including network power loss,voltage deviation,harmonic distribution indicators,etc.;then,the isolated and connected microgrid are simulated,comparing the distribution network operation situation with and without harmonic;lastly,the influences of the microgrid to the main grid,which are network loss,voltage,and harmonics,are simulated,and corresponding control schemes and suggestions are given.