Research On Modeling And Operation Control Of Hybrid AC/DC Microgrid

Nowadays,wind energy resources and other clean renewable energy resources have been widely used to access the conventional power system in the form of microgrids.As a form of integration and application of distributed new energy resources,microgrid can play a role in alleviating the energy crisis and environmental problems.The hybrid AC/DC microgrid is a form of microgrid with the advantages of AC microgrid and DC microgrid.It not only facilitates the access of the source and load of AC and DC characteristics,but also reduces the intermediate conversion link and reduces the losses caused by energy conversion.Electric vehicles(EVs),as a green transportation,are the target of future development,and their wide applications will have negative impacts on the power grid,so it is necessary to use the Vehicle to Grid(V2G)technology to control and manage it.The V2 G technology based on hybrid AC/DC microgrid,which combines the advantages of EVs and hybrid AC/DC microgrid,can solve the adverse impact of EVs charging load on the grid and reduce the construction cost of microgrid.This paper mainly studies the modeling and coordinated operation of hybrid AC/DC microgrid and the transient effects on system under the conditions of EVs V2 G mode and so on.Firstly,the structure and working principle of common power generation systems(such as photovoltaic,wind energy,fuel cell)and energy storage system in hybrid AC/DC microgrid are expounded,and the exploration of its mathematical model is emphasized.On this basis,according to function and characteristics of each module in the hybrid AC/DC microgrid,its interface circuit and control strategy are analyzed.At the same time,the factors affecting the charging load of EVs are analyzed,and the charging load curves of different numbers of EVs are simulated with simulation software,and the impact on the power system is given.In order to realize the V2 G interaction between the EVs and the hybrid AC/DC microgrid through electric charger,bidirectional DC charger and three-phase AC charger are selected as the research objects for different topologies and charging methods.The control strategies of chargers are discussed,and the simulation models are established respectively.The results show that the proposed chargers meet the V2 G operation.Secondly,for two-level AC/DC converter itself,it only generates one DC voltage with large harmonic amount and low conversion efficiency.So the three-level AC/DC converter is selected as the interlinking converter(ILC)unfolds the research,analyzes the structure and working mechanism of ILC,and establishes its mathematical model under two coordinate systems.Based on this,the control strategy by adopted it is deeply studied,when operates in grid-connected mode.In view of the fact that today's ILC use a single constant voltage or constant power method,which is not conducive to reducing the cost of the ILC,and promoting the local consumption of the distributed power source,according to the power flowing through the ILC.A method of switching between two control strategies(constant voltage and constant power)is proposed.In the island mode,the constant voltage and constant frequency control strategy is adopted.Finally,based on typical parameter values,the hybrid AC/DC microgrid simulation system is built by MATALB/Simulink.Aiming at the large fluctuation of distributed power supply with environment,the frequent switching of AC and DC non-important load and the instantaneous influence of EVs on the system based on V2 G operation of hybrid AC/DC microgrid,the transient operation simulation is designed and the conclusion is given.For the coordinated operation of the system,it provides analysis and simulation of different operating conditions during grid-connected and island operations.At the same time,the feasibility of the system and the effectiveness of the proposed control strategy are verified.