Research On Staging Variable Inertia Control Technology Of Optical Storage DC Microgrid

With the development of new energy sources,such as,photovoltaics,wind power and energy storage,as well as the sharp increase in the proportion of DC load power,DC microgrid technology is booming and the research process is advancing rapidly.For the access of distributed power and DC loads,the DC microgrid has no problems of the reactive circulating current,frequency fluctuation and power angle stability,which greatly simplifies the control system.However,the incorporation of a large number of distributed power sources increases the density of power electronic converters in DC microgrids;each converter is a stationary component,with no rotational kinetic energy and mechanical inertia,resulting in less inertial support of the DC microgrid system.Unstable output power and sudden load fluctuations of distributed power generation can also cause severe fluctuations in DC voltage,affect the power quality of DC microgrids,and endanger the safe and stable operation of DC microgrids.Aiming at the problem of small inertia of DC microgrid,the inertial control strategy of DC microgrid with PV and battery is deeply studied.The main research contents are as follows:(1)This paper introduces the typical topology of DC microgrid,analyzes the basic working principles of photovoltaic,wind power and energy storage,and establishes their mathematical model.A DC microgrid system model consisting of photovoltaic cells,wind power generation systems,energy storage batteries,AC and DC loads,related power electronic converters and corresponding control systems is built to provide a platform for inertial control research of DC microgrids with PV and battery.(2)A segmented variable inertia control strategy for DC microgrid is proposed.In order to solve the DC voltage oscillation problem caused by the power shortage in the system due to the low inertia of the PV DC microgrid,an inertial control strategy based on the U-I droop control for linear function and exponential function change is proposed;when the DC voltage is disturbed,The control strategy changes the battery charge and discharge rate and slows the voltage shock by swinging the droop characteristic curve.Considering the difference of the inertial requirements under different voltage change rates,the characteristics of the two strategies of comprehensive linear and exponential mode are proposed.Variable inertia control strategy,which combines the above two modes to provide inertial power,delays voltage oscillation;(3)A segmented voltage regulation control strategy is proposed.In order to suppress the DC voltage oscillation caused by power shortage,a segmented voltage regulation control strategy is proposed based on U-P droop control.The DC voltage is regulated bychanging the battery delivered power,and the DC voltage oscillation signal is used as a control variable.The stable voltage is predicted,and the DC voltage change trend is judged as the basis for increasing or decreasing the inertia,and the DC voltage oscillation is suppressed.(4)The DC microgrid model is built in MATLAB/Simulink software,and the proposed control strategy is simulated and verified.The simulation results show that,when the system suddenly has power shortage,the proposed segmented inertial control strategy can increase the inertia of the DC system and slow down the voltage change,the proposed segmented voltage regulation control strategy can suppress the DC voltage oscillation;improving the voltage transient response and system operation stability.