Research On Cooperative Control Strategy For Distributed DC Micro Grid

DC micro grid has flexible structure,and low transmission power loss,and is easy for distributed generation integration,which is the reason why DC micro grid has become a hotspot in academia and industry.Due to the micro grid structure based on DC bus,photovoltaic or wind power generation can be integrated into DC bus through only one stage converter,which can increase the transmission efficiency.And there are few controlled parameters in control strategy of DC micro grid,including DC bus voltage rather than frequency and phase.In this thesis,topology operating principle,control strategy and operating modes of DC micro grid networking units are researched in details.In order to deal with the problem of the large number of submodules and low simulation efficiency in MMC,this thesis proposed a novel equivalent model based on controlled voltage source,which can increase the simulation efficiency of MMC with the acceptable accuracy.Aiming at the problems of the DC bus voltage fluctuation with the local load disturbance,this thesis proposed a novel DC bus voltage control strategy based on active disturbance rejection control algorithm,which considers both the transient state fluctuation inhibition and steady state accuracy increase.According to the research on characteristic of PV generation module,energy storage module and AC grid-connected module,this thesis proposed a novel DC micro grid cooperative control strategy based on DC bus voltage hierarchy.And with the strategy,the system can operate in various conditions including some extreme conditions and power grid fault,and all the networking units can operate cooperatively in a decentralization-and-self-regulation-based mode.In this thesis,a DC micro gird simulation test platform is built based on Matlab/Simulink software,which verifies the validity of local control strategy of all the networking units,the micro grid system operating modes and the mode switching strategy.In this thesis,a DC micro grid prototype is built,which verifies auxiliarily the validity of the proposed cooperative control strategy.