Optimization of a fuzzy self-tuning PID control system for a marine low-flashpoint fuel supply system

초록

This study proposes and evaluates a fuzzy-logic-based self-tuning proportional–integral–derivative (PID) control system to stabilize the supply pressure of a marine low-flashpoint fuel supply system (LFSS) for liquefied petroleum gas (LPG). In low-flashpoint fuel systems, it is crucial to maintain the pump discharge pressure above the cargo's saturation pressure at all times; otherwise, vapor pockets can form in the supply line, potentially causing engine trips. Since the fuel valve train opening—and consequently the system's head loss—varies continuously with engine load, a fixed-gain PID controller is insufficient for maintaining stable pressure regulation across the entire operating range. To address this, we developed a hybrid fuzzy–PID architecture in which the proportional, integral, and derivative gains are adjusted in real time based on the pressure error and its rate of change, utilizing Mamdani fuzzy inference. A real-time closed-loop test platform was established by integrating an Aspen HYSYS dynamic process model, a Microsoft Excel database, and a Visual Basic for Applications fuzzy inference module. Parametric simulations demonstrated that the resolution of the fuzzy control surface has minimal impact on steady-state control error, whereas the gain search range is the key factor influencing stability and transient response. A range that is too wide can lead to sustained pressure overshoot and undershoot, whereas a well-bounded range can reduce the settling time by over ten seconds and mitigate oscillations. Under a variable-load profile (100%→50%→10%→100%), the proposed controller maintained the supply pressure within ±0.15 bar of the set point, well within the ±1 bar acceptance band. This confirms that fuzzy self-tuning PID control significantly enhances stability and responsiveness in nonlinear marine fuel supply systems.

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