Research On Operational Control Strategy Of Ship’s DC Microgrid With Hybrid Energy Storage System

The ship’s power system provides electricity for the entire ship,covering the entire process of electricity generation,transmission,distribution and use,and is an important part of the ship’s power system.With the increasingly large-scale ships and the complexity of the application of marine engineering equipment,the capacity of the ship’s power system is also increasing.At the same time,there are often large-load equipment in the system.These equipment have a very large demand for instantaneous power.It is required that the ship’s power system can provide instantaneous pulse power,otherwise,it will cause a large drop in the grid voltage,and in severe cases,it will cause the grid to collapse.Conventional power systems are generally difficult to face such complex working conditions,and there is an urgent need to upgrade the existing power systems.The currently widely adopted solution is to introduce an energy storage system as a buffer for impulsive loads to make up for the lack of power supply from generators,thereby improving the safety and stability of the ship’s power system.The energy storage system and the generator set are connected to the public DC bus through the power converter.Considering that the design of a controller with superior performance for the power converter is also an important means to maintain the stability of the DC bus voltage.Therefore,this article focuses on the research on the control strategy of the power converter.The main contents of the full text are as follows:1.First,establish mathematical models of generators,voltage source rectifiers,hybrid energy storage systems,and marine electric propulsion systems in the ship’s DC microgrid to prepare for the next control strategy design and simulation experiment.Then,comprehensively consider the generator’s climbing power,bus load change rate,battery and super capacitor characteristics and other factors to design the ship energy management system,so that the generator can output according to the maximum climbing power,and the remaining power is distributed to the battery and super capacitor through frequency decoupling.2.In view of the complicated working conditions that may occur in the ship system such as the sudden acceleration and deceleration of the propulsion system and the impulsive load being used irregularly,a terminal sliding mode controller based on preset performance is designed to stabilize the ship’s DC bus voltage.Firstly,a preset performance control is introduced into the DC bus voltage control loop,and the preset performance function is used to constrain the tracking error of the DC bus voltage so that it can converge at a predetermined speed and finally stabilize within the preset boundary.In the current control loop,a terminal sliding mode controller is designed to ensure the rapidity and accuracy of current tracking.Then the asymptotic stability of the control system is proved based on the Lyapunov stability theory.Finally,the effectiveness of the proposed control strategy is verified by simulation,and compared with the traditional reverse thrust and terminal sliding mode control strategy,the superiority of the proposed controller is further highlighted.3.Aiming at the chattering caused by terminal sliding mode control and the uncertainty of the parameters in the model,an adaptive fractional sliding mode control strategy based on preset performance is designed.Firstly,in order to take into account the dynamic and steady-state performance of DC bus voltage tracking at the same time,a preset performance control is introduced into the DC bus voltage control loop to make the error converge at a predetermined speed while meeting the steady-state error requirement.Secondly,in order to solve the voltage chattering caused by the terminal sliding mode,a novel fractional-order sliding mode controller is designed in the current control loop.In addition,considering that the parameters in the mathematical model are often affected by system power changes and external uncontrollable factors,the uncertainty of the parameters is also a factor that cannot be ignored in the control accuracy,so this paper uses the adaptive rate to identify unknown parameters online,at the same time,in order to ensure the boundedness of the estimated parameters,a projection operator is introduced to correct the adaptive rate in real time.Finally,the comparison and simulation verify the effectiveness and superiority of the set control strategy in improving the ship’s DC bus voltage stability.