A nonlinear modified robust control of differential pressure in liquid tank insulation of LNG ship based on positive feedback

In order to verify the effectiveness of positive feedback control in liquid tank pressure control of ships, this paper adopted the mirror mapping method to map the unstable system of liquid tank insulation differential pressure of Liquefied Natural Gas（LNG） ships into a stable system. Then a robust controller was designed with a closed-loop gain shaping algorithm to reduce the effects of model perturbation due to the pure lag link, followed by a nonlinear modification technique of the S-function to reduce the amplitude of the controller output. Finally, positive feedback was used to realize the control of the whole control system. The theoretical analysis and experimental simulation results show that the positive feedback control can achieve the same control effect as the negative feedback control. The control effect of the algorithm proposed in this paper is superior to that of the published negative feedback algorithms. The feasibility and effectiveness of applying positive feedback control in ship control systems are initially demonstrated, which has a specific guiding significance for further theoretical analysis and practical engineering application of positive feedback control.