Research On Operation Control And Black Start Strategy Of Microgrid

With the development of the third generation power grid,renewable energy generation accounts for a large share and intellectualization has become the main feature of power grid.The key to using renewable energy is how to efficiently convert renewable energy into electricity.With the drawbacks of traditional large power grids becoming more and more prominent,the use of renewable energy-based distributed generation system has gradually attracted attention.In order to make full use of the advantages of distributed generation system,the microgrid composed of distributed generation system,energy storage system,load and related protection devices has become the focus of research at home and abroad.Good operation control strategy is the basis of realizing various technological and economic advantages of microgrid,and it is also one of the key and hot issues in the field of microgrid research at present.Due to microgrid contains a large number of distributed generations,the operating conditions are relatively complex.It is very important to coordinate various distributed generations in microgrid to make the microgrid operate stably in the process of grid-connected,islanded,two modes switching and realize the black-start recovery after the whole network crash.This paper aims at the above problems,study on microgrid with multiple distributed generations,research the overall operation strategy and black-start of microgrid system deeply.The main jobs of the thesis are as the following.(1)On the basis of elaborating the working principle and control strategy of microgrid system and its generating units.The overall model of typical micro-grid system is given.It lays a foundation for studying the overall operation strategy and black-start strategy of microgrid system.(2)On the basis of elaborating the common control methods of inverters in microgrid.PQ controller,V/f controller and droop controller model are designed and built.Aim at the differential adjustment for traditional droop control,the secondary adjustment of voltage and frequency is added to the traditional droop control.The improved droop controller is analyzed and designed in detail,the simulation test and verify that the frequency can be adjusted without error,and the voltage offset and fluctuation can be reduced at the same time.(3)The master-slave control and peer-to-peer control in the overall operation mode of microgrid are studied in detail.Considering the characteristics of micro-sources,a smooth switching strategy with state compensation is adopted to deal with the transient impact of the microgrid with master-slave control structure when mode switching.The validity of the proposed method is verified on the simulation platform.The improved droop control is applied to peer-to-peer microgrid.The comparison and analysis between the improved droop control and the traditional droop control under three working conditions are carried out,the advantages and disadvantages of the improved droop control are further pointed out.Aim at the impact of peer-to-peer microgrid when micro-grid operates from islanding mode to the grid-connected mode,a pre-synchronization control strategy based on droop control is adopted,the effectiveness of the strategy is verified by simulation.(4)Finally,the black-start function of microgrid is studied.On the basis of elaborating the basic concept of black start and restoration strategy in detail,aim at the characteristics of microgrid in distributed generation and the whole grid structure,a black-start strategy based on serial recovery is proposed.And the corresponding black start recovery process is designed,finally,the effectiveness of the black-start strategy is verified by simulation.