Network And Energy Management For Distributed DC Microgrid

In the background of rising of social power demand, diminishing of non-renewableenergy and environmental degradation, renewable energy application becomes aproblem which various countries pay close attention to. Microgrid can not only improvethe level of renewable energy using, but also to avoid a lot of problems that thetraditional centralized power supply brings to. This paper studies DC microgrid systemsbased on distributed photovoltaic, in order to achieve efficient use of energy and protectuninterruptible power supply for the loads, and designs DC microgrid with5kW loadpower system, mainly used as civilian power.This paper presents an improved automatic energy management strategy based onthe DC bus voltage. It is designed to achieve effective utilization of new energy sourcesand system stability. This system contains two photovoltaic arrays and PV interfaces, aset of batteries and an energy storage interface, network interface and load. System runsat grid-connected mode under normal circumstances, and can also lead to runningwithout grid when special cases or artificial selection happen. System status and cutoverdepend on the DC bus voltage, without centralized controller and communication,improving system reliability and reducing costs. At the same time, system configurationis flexible and maintenance is convenient, because some components can be removed atany time.The paper designs power based on energy flow of each module, presents thetopology of the system, analyses the energy flow process of the modules particularlyand calculates the main parameters of the topology. Control method of photovoltaic,network interface and energy storage interface is given. Control method of photovoltaicincludes MPPT and constant voltage control. Network interface and energy storageinterface are used control method with voltage loop outside and current loop inside.Mathematical models of PV interfaces, storage interfaces and network interfaces aregiven to get their transfer function, combined with the control transfer function, andBode diagram and Nyquist curve are drawn to analyse stability. Hereafter, impedancestability analysis of system is done. By stability analysis, the system run with theoreticalbasis. Contradiction between speed and stability is effectively reconciled even thesystem is running under extreme conditions.A physical simulation model of DC microgrid system is established in theMATLAB/Simulink environment, striving to accurately simulate the PV arraymaximum power point tracking, battery charge and discharge and network interfacescontrol. State switchings between various operating modes of DC microgrid are simulated. Simulation results verify the correctness and effectiveness of the control andenergy management strategy.