Research On DC Bus Voltage Stability Control Of Ship Microgrid Based On Hybrid Energy Storage

The shortage of fossil fuels and the growing problem of environmental pollution have led to the increasing use of clean energy.In this context,the application of renewable energy generation to ship microgrids will be a new direction for future research in ships.During the ship's microgrid,there is a load change during the voyage.The load change will cause the power fluctuation of the DC bus terminal,which in turn will affect the voltage stability of the DC bus.Load fluctuations can be divided into high frequency fluctuations and low frequency fluctuations.In order to effectively suppress these fluctuations,it is an effective means to introduce hybrid energy storage systems based on energy storage elements with different discharge characteristics.The purpose of this thesis is to study the DC bus voltage stability control strategy of the ship microgrid and the power allocation of the hybrid energy storage system.The main research contents are as follows:(1)A hybrid energy storage system based on lithium batteries and supercapacitors was studied.Firstly,an equivalent simulation model is built for the lithium battery and the supercapacitor respectively.The charge and discharge characteristics of the lithium battery and the supercapacitor are studied by model simulation.Based on this,the lithium battery and the supercapacitor are respectively constructed based on the DC bus through the bidirectional DC/DC converter.The hybrid energy storage system is followed.The mathematical model of the bidirectional DC/DC converter is established.The PLECS simulation software is used to simulate the constant voltage and constant current modes of the lithium battery and supercapacitor energy storage unit.(2)The related control strategies of ship microgrid with mixed energy storage are studied.Firstly,for the problem that the first-order Butterworth filter generates integral action in response to the hybrid energy storage power command,a power allocation strategy based on second-order filtering for hybrid energy storage system is proposed,which is added when the energy storage unit performs power output.The protection measures for energy storage components are followed.Secondly,for the circulation problem generated by multiple DC power converters in parallel,the parallel current sharing control strategy based on voltage droop is studied.Finally,aiming at the stability problem of DC bus voltage of marine microgrid,the DC bus voltage stability control strategy of hybrid energy storage composed of lithium battery energy storage unit and supercapacitor energy storage unit is simulated.(3)The simulation and experimental verification of the proposed control strategy are carried out by using the corresponding simulation and semi-physical simulation platform.In the Matlab/Simulink and PLECS environments,the hybrid energy storage system power distribution strategy,the parallel current sharing control strategy based on voltage droop and the simulation model of the DC bus voltage control strategy are built.Based on this,the PLECS RT-BOX hardware is in the On the semi-physical simulation platform,the hardware micro-grid system with hybrid energy storage system and its related control strategies were verified by hardware-in-the-loop simulation experiments.The experimental results show that the hybrid energy storage system through the above control strategy can effectively suppress the load fluctuation of different fluctuating frequencies in the ship's microgrid,and provide effective support for DC bus voltage stability.