Research On Distributed Coordinated Control Strategy Of DC Microgrid With PV And Storage System

With the transformation of the global energy structure to clean and low-carbon,the new installed capacity of distributed power generation mainly based on renewable energy is growing rapidly.In order to avoid the adverse effects of large-scale random distributed renewable energy grid connection,use the microgrid with flexible control and operation mode as the link of energy transmission,give full play to the advantages of renewable energy power generation,improve the consumption level of renewable energy and the reliability of power supply performance and improve the power quality of the power grid.As the proportion of distributed power sources with DC characteristics and DC loads increases,DC microgrids have become a research hotspot,compared with AC microgrids,they do not require phase frequency control and have significant advantages in terms of construction cost,operation control,and energy utilization.In this paper,taking the photovoltaic storage DC microgrid as the research object,the modeling and control methods of photovoltaic power generation units and energy storage units are studied in detail and improved.Refer to relevant national standards,a system-level coordinated control strategy is proposed.For the photovoltaic power generation unit in the DC microgrid,establish an equivalent circuit model and an engineering application model,model the interface converter and analyze the working principle,analyze the MPPT control and droop control method of the photovoltaic power generation unit,and analyze the control structure and characteristic equations in detail,aiming at the situation that the traditional MPPT control method may not be able to track the maximum power under partial shading condition,a photovoltaic MPPT control method based on the tuna swarm optimization algorithm is proposed,for the distributed control strategy of photovoltaic power generation units,the layered control method based on DBS is adopted,and the process of voltage layering and mode switching is explained.For the energy storage unit in the DC microgrid,analyze its function and the advantages of various types of energy storage,establish a second-order RC model for lithium batteries,model and analyze the working principle of the interface converter of the energy storage unit,analyze the droop control principle and limitations of the energy storage unit,and adopt an adaptive droop control method based on SOC considering the relative capacity to solve the above problems,for the distributed control strategy of the energy storage unit,the hierarchical control method based on DBS is adopted,and the voltage stratification and mode switching process are explained.On the basis of the above research,a distributed coordinated control strategy for the DC microgrid is proposed,including island operation mode and grid-connected operation mode,among them,the grid-connected control method adopts virtual synchronous generator control based on voltage amplitude and phase pre-synchronization,and its principle is analyzed in detail,the coordinated control strategy proposed in this paper realizes the stable operation of the DC microgrid under various working conditions.After completing the above-mentioned modeling and control theory analysis of photovoltaic and energy storage units and DC microgrid,use MATLAB/Simulink software for simulation verification,the simulation results show that the MPPT control method based on the tuna swarm optimization algorithm has higher tracking accuracy,smaller oscillation and faster convergence speed than other intelligent algorithms under the same iteration number.The tracking accuracy is 99.9%,and the convergence time is only 0.28 s.The coordinated control strategy proposed in this paper realizes the switching of different working modes,and the simulation results are consistent with the theoretical analysis,which verifies the effectiveness and superiority of the control strategy proposed in this paper,and provides a set of effective coordinated control strategies for the control of DC microgrids.