Research On Coordinated Control Strategy Of Dc Microgrid With Pv And Storage Ststem

In recent years,the installed capacity of distributed power sources has grown rapidly.To reduce the impact of distributed power sources connected to power systems,microgrid technology has been widely concerned.Microgrid technology has the merits of high power quality,supply reliability and benefits of renewable energy generation,and is considered to apply in energy interaction between distributed power sources and distribution network.Compared with AC microgrid,DC microgrid has obvious advantages in terms of construction cost,control difficulty and power utilization.A coordinated control strategy is proposed to realize the coordination control of DC microgrid with PV and HESS.For the photovoltaics in the DC microgrid,the traditional control methods are reviewed,including MPPT control,droop control,and hierarchical control,based on establishing cell and array models.To achieve smooth switching between MPPT mode and droop mode,the coordinated control methods based on unified controllers are proposed,including Udc-d P/d V droop control and improved I-V droop control.The principle of the control structure,equation of droop characteristic,and process of mode selection of the proposed methods are analyzed in detail.For the energy storage system in the DC microgrid,the traditional control methods of the battery are reviewed,including double closed-loop control and hierarchical control,based on establishing equivalent circuit models.In this dissertation,the power distribution method of HESS is deeply studied.The basic principle of virtual resistance-capacitance droop control and the design process of controller parameters are analyzed in detail.To achieve the terminal voltage recovery of supercapacitors and the SOC balance of the batteries,the virtual capacitance droop control with voltage compensator and the adaptive virtual resistance droop control based on SOC are proposed respectively,and the expandability of the proposed methods are explained.Based on the above achievements,this dissertation proposes the distributed coordinated control strategy for the DC microgrid,including the improved hierarchical control method for the island state and the constant voltage control method for the grid-connected state,which realizes the stable operation of the DC microgrid in various situation.A simulation model was built to verify the theoretical analysis of the coordinated control methods based on unified controllers of PV,the power distribution method of HESS and the coordinated control strategy.Simulation results verify the feasibility and superiority of the proposed methods and strategy.