Research On The Distributed Control Strategy For Reliable Operation Of Interconnected DC Micro-grids

Driven by the force of the internet of energy,the fast developing technologies and growing number of Micro-grids(MGs)lead to the new trend of the research on the interconnection of Micro-grids.In this field of research,control strategy is one of the key techniques to achieve the interconnection of Micro-grids.In MG,with dc type distributed sources such as photovoltaic battery,fuel cell and energy storage unit(ESU),and user side dc load demand highly increasing,DC Micro-grid has a great potential for development.So the research on the control strategy of interconnected DC Micro-grids has important significance.This paper mainly presents a distributed hierarchical control framework to ensure reliable operation of interconnected DC MGs.In this hierarchy,primary control is used to regulate bus voltage inside each MG locally.An SOC adaptive droop method is proposed for this level,which prevents excessive charge and discharge of battery cells.A small-signal model is developed to investigate effects of constant power loads and SOC changes on stability of the system.Based on the primary control,a discrete consensus-based distributed control strategy for interconnected DC MGs is proposed,including a voltage secondary control designed to eliminate voltage deviation produced by droop control and a power flow control employed to provide power sharing among MGs which enables full utilization of resources and suppresses stress and aging of the components.In order to further optimize the energy management,a tertiary distributed control strategy based on second-order consensus algorithm for energy storage system in interconnected DC MGs is proposed,which makes ESU in each MG distribute load power or absorb charging energy according to its own SOC and rated capacity.So the greater the SOC of ESU,the greater the load power providing or the smaller energy absorbing.Gradually,the SOC and charge/discharge current of the whole ESUs in the cluster converge,which improves the reliability of MGs clusters.These distributed controllers on each MG only communicate with neighbor MGs to get global accordance and achieve stable operation of DC MGs clusters.Communication pressure is reduced.Beside,A discrete control system model is developed to analysis the stability of system and a simulation model is established in MTALAB to demonstrate the feasibility of the proposed control strategy.Finally,an experimental platform of three interconnected DC MGs is built and experimental results and analysis are given.