Adaptive Droop Control Strategy For Isolated Island Operation Of Direct Current Microgrid

With the rapid depletion of global fossil energy resources,new energy power generation has increasingly become a research hotspot.Distributed generation is simple in structure,flexible in application,capable of consuming the generated electric energy locally,high in energy utilization rate and capable of supplying power to remote areas.Therefore,it is gradually replacing traditional fossil energy and becoming the main way to realize efficient new energy power generation.However,distributed generation system has its own defects.Because the micro-sources of distributed generation are easily affected by external natural environment,distributed generation has the defect of poor stability compared with traditional generation methods.Therefore,distributed generation system needs to be controlled to run safely and stably.This paper mainly studies the bus voltage stability of optical storage DC microgrid in isolated island operation,and applies control from two aspects: equipment level and system level.In this paper,firstly,the device-level control method in optical storage DC microgrid is studied,and the photovoltaic power generation unit,battery pack and super capacitor in optical storage DC microgrid are modeled.MPPT control and constant voltage droop control are adopted for the unidirectional DC-DC interface converter of photovoltaic power generation unit under two different working conditions,and simulation verification is carried out.After analyzing the limitations of droop control commonly used in bi-directional DC-DC interface converter of battery pack,an improved droop control based on battery state of charge is proposed,and fuzzy PI control is added to enhance the control effect.Aiming at the inherent defect that droop control will lead to bus voltage drop,a control method of adding secondary voltage compensation is proposed to compensate bus voltage drop.Supercapacitors mainly absorb or release fluctuating power in the system,and jointly maintain the stability of bus voltage.The simulation experiment is carried out in Matlab/Simulink environment.The simulation results show that the improved droop control with fuzzy PI control can make the battery pack with large SOC value charge more and charge less,and finally make the SOC value of the battery pack tend to be consistent,so as to achieve the purpose of balancing load current and stabilizing bus voltage.After adding secondary voltage compensation,the bus voltage is more stable,and the supercapacitor can well bear the fluctuating power when the working condition changes.Then,the system-level control is studied.After the system-level controller collects the parameters of each energy storage unit,photovoltaic power generation unit and load,the system operation is divided into six modes through analysis and judgment,which improves the stability of the system,maximizes the utilization of energy and improves the economy.Simulation results show the effectiveness of the above multi-mode operation mode.