Research On Coordinated Control Strategy Of Power Electronic Transformer And Micro-sources

With the increasing severity of energy crisis and environmental issues,it is widely recognized all over the world that traditional fossil generation is supposed to be replaced with renewable energy generation for the sustainable deve lopment of human.In order to reduce the impact of intermittent and volatility of distributed renewable energy on traditional power grid,it is an effective method that renewable energy is consumed locally in the form of microgrid to make full use of renew able energy and enhance the stability of power grid.With the in-depth development of microgrid,the proportion of micro-sources such as wind,photovoltaic,energy storage in the power grid is continuously increasing,and the issue of energy coordination a nd control between the microgrid and the power grid are becoming the focus and hotspot of current research.Power electronic transformer(PET),as the interconnection interface between the microgrid and the power grid,can flexibly integrate AC/DC distributed micro-sources and various loads within the microgrid,and complete the precise control of the flow and direction of energy between the microgrid and the power grid.To further improve the performance of microgrid based on PET interface,this paper takes PET and microsources as the research objects,and proposes the corresponding coordinated control strategies in the microgrid.The specific research work mainly includes:First,the domestic and foreign development situation of microgrid and the interconnection schemes between microgrid and power grid are introduced.The typical topology of a microgrid based on PET interface is illustrated.The structural characteristics of this type of microgrid are analyzed in detail,and the necessity and requirements for the coordinated operation of PET and microsources are clarified for laying the foundation for the following research.In view of the existing operation control strategies of microgrid based on PET interface,the principle of master-slave control and peer-to-peer control is analyzed,and the performance of microgrid and PET under two kinds of control is verified.Aiming at the shortcomings of using traditional peer-to-peer control strategy for microgrid based on PET interface,an improved peer-to-peer control strategy coordinated by PET and distributed generations in microgrid is proposed.Based on the analysis of the microgrid operation mode,the coordinated operation principle of PET and distributed generations under the improved peer-to-peer control is described,and the specific coordination control strategy is given.In the proposed coordinated control strategy,the distributed generations adopt improved droop control to achieve a reasonable load sharing,and effectively enhances the sharing accuracy of reactive power.According to the power demand of the microgrid,PET controls the power grid to absorb or provide energy by the frequency characteristic signal to achieve power balance of the microgrid.The validity and effectiveness of the proposed control strategy is verified by the simulation model based on Matlab/Simulink.For the application of PET frequency regulation in microgrid,a constant-frequency control strategy for the coordination of PET and energy storage in microgrid is proposed.First,a comparative analysis of the existing frequency tuning methods for microgrid based on PET interface is made,and its deficiencies are pointed out.Then,the paper analyzes the feasibility of coordinated control of PET and energy storage,and gives the detailed coordinated control strategy.In this coordinated control strategy,the energy storage adopts constant-voltage constant-frequency control to achieve a constant frequency of the microgrid.PET uses virtual synchronous generator control to adjust energy st orage capacity and ensure smooth operation of the microgrid in the event of energy storage failure.Through PET and energy storage to suppress the power fluctuation in the microgrid,the maximum energy efficiency of the distributed power supply is exerted,and the impact of the volatility power on the main power grid is reduced.Simulation results and experimental results verify the validity and effectiveness of the control strategy.