Research On Voltage Control Of DC Microgrid Composed Of Photovoltaic And Storage

The emphasis on environmental and climate issues accompanied by technological breakthroughs in related fields have made renewable energy gradually occupy an important position in the power system.In recent years,the installed capacity of photovoltaic has grown rapidly,and with the innovation and iteration of various links and supporting equipment,photovoltaic energy will become an important force in the energy transition.Due to the limitations of power electronics,systems containing a high proportion of renewable energy lack sufficient inertia support to cope with the instability of the output power of renewable energy itself.Similar to the idea of virtual synchronous generator control applied to grid-connected converters to provide inertia for AC microgrids,virtual DC motor control strategies are proposed to solve the problem of low inertia in DC microgrids.In this paper,taking the DC microgrid composed of photovoltaic and storage as the basic research framework and the energy storage converter as the research object,on the basis of the inertial support provided by the virtual DC motor control,the dynamic characteristics after voltage disturbance are further improved,and the State of Charge balance of parallel multi-energy storage is realized.This paper first introduces the mathematical model,working principle and basic control mode of the components of the DC microgrid and each converter,and then,the virtual DC motor control applied in energy storage converters is improved,which is elaborated in the following two parts.The first part proposes adaptive control of inertia coefficient and damping coefficient in view of the fixed inertia coefficient and damping coefficient in virtual DC motor control that cannot meet the different needs of voltage fluctuation after power disturbance.Through the small signal analysis of the converter and virtual DC motor control,based on the influence of inertia coefficient and damping coefficient on voltage fluctuation and system stability,the piecewise adaptive function of the inertia coefficient and damping coefficient is designed.Simulation is carried out in matlab to compare the parameters of the voltage fluctuation process to verify the feasibility of the proposed control and its superiority over other adaptive functions.In the second part,the same parameter control strategy for multiple parallel energy storage units may cause unbalanced charge and discharge,and further affect the energy storage life,drawing on the droop control SOC equilibrium control and combining the DC motor armature equation to propose the substation armature resistance control.Based on the conclusion that the change rate of SOC is inversely proportional to the armature resistance,this paper takes the state of charge as an example,introduces the SOC dispersion into the armature resistance,equalization coefficient is set to adjust the equilibrium speed and accuracy,and realizes the equilibrium of the discharge process by exchanging the SOC value;The influence of armature resistance value on system stability was analyzed by small signal;Secondly,considering the voltage drop problem caused by droop control,the real-time compensation of the speed deviation is increased;Finally,the simulation in matlab verifies the SOC equalization effect and voltage control effect during charging and discharging.