| In DC microgrid,there is no need to consider issues such as reactive power,frequency,phase,etc.,and its structure is simple and easy to control,meanwhile,it has higher power supply reliability.However,the DC microgrid composed of a large number of power electronic devices has a fast response speed,which causes the DC microgrid to become a low-inertia system,and the DC microgrid is extremely vulnerable to the influence of the output power fluctuation of the distributed generation supply and the frequent switching of loads.In addition,as a large number of energy storage units are connected to the DC microgrid in a distributed manner,the unreasonable power distribution among the energy storage units will reduce the stability and economy of the microgrid operation.Therefore,it is of great practical significance to research on converter control and realize reasonable power distribution among energy storage units.The control of the bidirectional DC/DC converter of the multi-energy storage DC microgrid is studied in this paper,the aim is to improve the ability of the DC microgrid to deal with power disturbances and reduce the problems of overcharge and overdischarge of the energy storage unit,thereby improving the stability and economy of the DC microgrid operation.The main work of this paper is as follows:(1)The mathematical model and working principle of the photovoltaic unit,energy storage unit and the converter connected to the DC bus were analyzed,and its small signal model was established,PSCAD/EMTDC was used to construct an optical storage DC microgrid model including photovoltaic power supply,storage battery and load,which laid the foundation for the follow-up work.(2)The mathematical model and working principle of the virtual DC generator were analyzed,considering the influence of moment of inertia and damping coefficient on the inertia of the system,the characteristics of bus voltage fluctuation under power disturbances and the demand for inertia of the system in different fluctuation stages,an adaptive virtual DC generator control method with inertia damping is proposed.In this method,the variety of the exponential function is used and according to the change of the bus voltage,the inertia of the system is adjusted in stages,so as to meet the inertia requirements of the system in different fluctuation stages and improve the anti-disturbance ability of the DC microgrid.(3)Aiming at the limitation of the application scope of the traditional state-of-charge balanced power distributed method,considering the influence of the battery state of charge,a power distributed method suitable for multiple virtual DC generators parallel operation was proposed.This method is not affected by the change of battery working voltage,and it can adjust the power of each battery in real time according to the capacity and state of charge of each battery in operation to achieve the balance of the state of charge between the batteries,which can avoid the problems that overcharge and overdischarge of the battery and early withdrawal of power supply are appeared.Therefore,it has the characteristics of wide application range,simple operation and strong expandability.(4)A DC microgrid simulation model was built in PSCAD/EMTDC to simulate and verify the inertia damping adaptive control method and the state-of-charge balance power distribution method,the traditional control method of the virtual DC generator and the existing power distribution method were compared and analyzed.The effectiveness and superiority of the method proposed in this paper was proved by simulation results.The research shows that the inertial damping adaptive control method proposed in this paper can better provide inertial support for the DC microgrid and improve its anti-disturbance ability;The method of the power distribution can adjust the equilibrium speed of the state of charge according to the demand,and realize the equilibrium of the state of charge among multiple virtual DC generators parallel operation. |
PDF Full Text Request