Abstract
This paper introduces a novel control strategy into the insulation space for liquid natural gas carriers. The control strategy proposed can improve the effects of control for differential pressure and reduce the energy consumption of nitrogen. The method combines a nonlinear feedback technique with a closed-loop gain shaping algorithm (CGSA). It is designed for the pressure control system which is vital for liquid natural gas carriers (LNGCs) in marine transportation. The control error is modulated using nonlinear function. The deviation signal is replaced with a nonlinear feedback signal. Comparison experiments are conducted under different conditions to prove the effectiveness of this strategy. This paper compares three control strategies: a control strategy with nonlinear feedback based on CGSA, a control strategy without nonlinear feedback based on CGSA, and a two-degree-of-freedom (DOF) control strategy. The simulation results show that this control strategy with nonlinear feedback performs better than the other two. The average reduction of control input is about 38.8%. The effect of pressure control is satisfactory.
Highlights
A liquefied natural gas carrier (LNGC) is a special ship used to transport liquid natural gas (LNG) cargo at low temperature (−163 ◦C) [1]
This paper discusses pressure control and energy saving for the insulation space of LNG carriers
A novel optimized controller is designed with a nonlinear feedback technique based on a closed-loop gain shaping algorithm (CGSA)
Summary
A liquefied natural gas carrier (LNGC) is a special ship used to transport liquid natural gas (LNG) cargo at low temperature (−163 ◦C) [1]. The insulation layer can effectively isolate the liquid natural gas inside the tank from the external environment and prevent heat transfer between the interior of the tank and the external environment [6]. Another important role is to ensure that the tank shape is complete by maintaining the pressure difference between the primary and secondary insulating layers. Pressure control technology of the insulation layer is one of the important technologies of membrane LNGCs. nitrogen is very expensive. How to control the pressure difference of the insulating space by adjusting the rate of nitrogen effectively and how to save the resource of nitrogen are important issues to be considered. The work of this paper is mainly divided into the following sections: research work on feedback control recently, nonlinear feedback principle, insulation layer description and pressure control, controller design, simulation results and analysis, and conclusion and discussion
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