Distributed Secondary Control Strategy Of DC Microgrids Based On ADRC

With the increasingly serious problem of energy shortage and environmental pollution,microgrid has emerged as a new structure that is different from the traditional power grid.Microgrid is a new grid form that effectively combines the distributed power sources,energy storage devices and AC/DC loads through power electronics converters.As an independent whole,a microgrid can operate independently or in grid connection,which can reduce the adverse effects caused by various distributed power sources.Compared with the AC micro-grid,DC microgrid does not have the problems of frequency and reactive power as in AC system and can be connected with AC micro-grid by bidirectional DC-AC converter to realize bidirectional power flow.However,at present,the research of DC microgrid is still in the preliminary stage.Therefore,this thesis makes a preliminary explore on the control strategy of DC microgrids that may contribute to the application and development of DC microgrids.Firstly,it introduces the background and significance of this research,analyzes the current research status of microgrid control technology at home and abroad,and models the photovoltaic cells and DC converters based on the the system structure of typical DC microgrids.A disturbance observation method based on variable step sizes is proposed to realize the MPPT control of photovoltaic cells,and is verified by simulation in Matlab/Simulink.Then the theory of traditional droop control strategy and its advantages and disadvantages are analyzed in detail.Aiming at the limitation of the traditional droop control strategy,an advanced distributed secondary control of DC microgrid is proposed by using a distributed secondary control structure for a island DC mricrogrid that is composed of multiple micro-sources and loads,so as to improve the accuracy of current distribution and solve the voltage deviation problem in DC micro-grid.Simulation analysis verifies its validity and reliability.Finally,the concept of ADRC and the principle of the controller are introduced in detail.Aiming at the limitation of traditional PI control,a double-loop droop control strategy based on ADRC is proposed.