Study On Control Strategy Of Voltage Stability Of DC Microgrid

With the supply of primary energy supply and the deterioration of the global environment.In recent years,the green renewable energy generation technology,which is typical of solar,hydro and wind energy,has developed rapidly.The most effective way for distributed power supply to access to the power grid is the microgrid,compared with the AC microgrid,because DC microgrid has the advantages of not having to consider the stability of the function angle,phase balance and harmonious wave,so DC microgrid technology is more conducive to the efficient utilization of new energy and the coordinated control of electric energy.As a measureable DC bus voltage of the power quality standard of DC microgrid,the research on its stability control strategy has gradually become the focus of the research,so it is of great significance to study a high-efficiency control strategy with good system stability and flexible operation.Therefore,this paper focuses on the stability control strategy of DC bus voltage,the following content:First,the inertia of DC microgrid is analyzed,the virtual inertia control strategy of DC microgrid is studied,and the effectiveness of virtual inertia control to improve system voltage stability is verified by formula.At the same time,the working principle and control method of DC-DC and DC-AC converter commonly used in microgrid system are analyzed and introduced.Secondly,the control strategy of improving the control of the variable sagging coefficient is put forward.In view of the traditional U-P sagging control coefficient is relatively fixed,the realization is that there is differential adjustment and other shortcomings,through the introduction of virtual capacitance,the traditional U-P sagging control DC voltage sagging coefficient is improved,an improved virtual inertial control strategy is obtained.In addition,due to the characteristics of differential adjustment by the drooping control of the dead zone,the control strategy of improved variant sagging coefficient control is obtained by considering the combination of the constant pressure control based on PI control and the improved virtual inertial control.By building model simulation verification on MATLAB/Simulink platform,thesimulation results confirm the effectiveness of the improved variable sagging coefficient control strategy in suppressing the voltage fluctuation of DC bus.Finally,an improved variable sagging coefficient control strategy with power prediction model is proposed.In view of the long duration of voltage fluctuation caused by disturbance in the improved variable sagging coefficient control system,the equivalent circuit of the four working states of the two-way converter is analyzed and the incremental equation of the converter port voltage and inductive current is written by the equivalent circuit of the discharge mode.Inspired by the model prediction control idea,the voltage and current increment equation is analyzed and processed,and the port voltage and inductive current of the t-time converter are based on the prediction model of the port voltage and inductor current of the t-1-time converter,and then the power prediction model is obtained.The power prediction model and the improved variant sagging control are also considered to be combined,and the improved variant sagging coefficient control with power prediction model is proposed.Through modeling simulation on MATLAB/Simulink platform,it can be seen from the simulation results that the power prediction model shortens the duration of voltage fluctuation caused by power mutation,and further suppresses the fluctuation of DC bus voltage and improves the stability of the system.