Power Fluctuation Control Strategy Of Ship Power System Based On Hybrid Energy Storage System

With the rapid development of marine development and coastal defense construction in many countries,the types and sizes of ships are increasing,and the operating conditions of ships vary greatly.In order to meet the requirements of operating conditions,ships are usually equipped with corresponding large,medium and small power equipments,at the same time,their power demand will change greatly with the drastic changes of the external environmental disturbance in the ship operation,the load power fluctuation of the ship is aggravated,which leads to the frequent fluctuations of the voltage of the ship generating unit and bus,and affects the power supply quality of the power grid.First,after analyzing the load characteristic curve of the ship,a model that can effectively simulate the characteristics of load fluctuation is established.Hybrid energy storage system is composed of lead-acid batteries and supercapacitors,and then the principle of each energy storage medium is analyzed,and the third-order equivalent model of lead-acid battery and the classical equivalent model of supercapacitor are established.At the same time,the model of grid-connected units,bidirectional DC/DC converter,that can connect hybrid energy storage system to ship power system is established and its control method is analyzed,last,the effectiveness of the established models and control method are verified in the simulation system.Then,the hybrid energy storage control strategy is divided into two parts including upper and lower control strategies.The upper control strategy is based on the load fluctuation characteristics and the difference in the characteristics of the energy storage units.It aims to reduce battery charging and discharging times and increase the participation of energy-based energy storage in undertaking load power.The lower control strategy is based on the state difference between energy storage units,and optimally allocates the power to be compensated among different energy storage units.The lower control strategy is an improved and optimized droop control based on the SOC of storage units,meanwhile,in order to further improve the battery pack’s ability to adjust to load fluctuations and the lower control strategy,as the energy storage unit SOC converges to the average uniformity,a consensus algorithm based on the equivalent SOC is proposed to re-adjust the allocated power by the lower control strategy.Finally,simulation experiments verify the effectiveness of the proposed hybrid energy storage control strategy.The charge and discharge times of the battery pack are reduced by 30%,and the bus voltage fluctuation is maintained within 3%.At the same time,the lower optimization strategy reduces the SOC difference of the battery energy storage units from 18.4% to 17.45% after the simulation.