Research On Power Distribution And Stability Of Hybrid Energy Storage System In DC Microgrid

With the increase of global energy crisis and aggravating of environmental pollution,the disadvantages of traditional power generation technologies are becoming increasingly prominent,and people are gradually turning their attention to renewable energy power generation technologies such as photovoltaic and wind power.The DC microgrid integrates distributed generation,energy storage devices,and load,which is of great significance in improving the power quality and energy efficiency of newable energy generation.Among them,energy storage devices,as an important link in the microgrid system,take effects on shifting peak load and suppressing power fluctuations.How to overcome the key problems of energy storage technology has become a research hotspot in microgrids.In practical applications,a single energy storage converter is difficult to meet the requirements of the microgrid,a system with multiple converters in parallel is conventional.In this paper,the power distribution between multiple converters in a hybrid energy storage parallel system is studied in depth.Firstly,in this paper,the bidirectional Buck/Boost converter is selected as the energy storage converter topology,and the working principle of the converter is briefly explained.The characteristic of energy storage components is analyzed,and parameters of inductance and capacitance are designed.Besides,related circuits are designed according to control chip and switch tube.A small-signal mathematical model of the converter is established,the PI controller parameters is designed.Simulation results show that the dynamic response characteristics of the converter satisfy requirements.Secondly,the parallel system of multiple battery energy storage converters is taken as the research object,the working principle and defects of the traditional droop control and droop curve translation method are analyzed.An improved method of adaptive droop coefficient based on inductor current is proposed.The current adjustment loop improves the accuracy of steady power distribution and the voltage adjustment loop compensates the bus voltage drop.The output impedance of converter under droop control is analyzed,and it is theoretically showed that a small communication delay will not affect the stability of the system.The simulation results verify the effectiveness of the proposed control method.Thirdly,the parallel storage battery and supercapacitor hybrid energy storage system is taken as the research object,and the working principle of the virtual resistance-capacitance droop control and the transient power distribution characteristics of the converter are analyzed.The output impedance charac teristics of the converter under the two control methods are compared and analyzed,and the influence of parameter selection on the transient power distribution of the converter is studied accordingly.By analyzing the scalability of the control method,th e steady power distribution between different storage batterys and the transient power distribution between storage battery and super capacitor can be achieved at the same time.A bus voltage compensation strategy is proposed,which can eliminate the bus voltage deviation caused by line impedance and virtual resistance.The theoretical analysis results and control methods are verified by simulation.Finally,a small-signal mathematical model of the hybrid energy storage system is established,and the Lyapunov indirect method is applied to analyze the stability of the hybrid energy storage system cascaded constant power load.To overcome the defect that the port voltage changes greatly during the charging and discharging of the supercapacitor,a supercapacitor voltage recovery method is proposed.On this basis,the energy management strategy of the hybrid energy storage system based on the SOC of energy storage element is designed and verified in the simulation software.The results show that the energy management strategy can autonomously determine and control the working mode of the energy storage converter according to the change of SOC,and the effectiveness of the energy management strategy is proved.