Research on a vessel's nonlinear central cooling water temperature control system

In this paper, the differential equation of a cooling system is deduced according to the working principle of a vessel's central cooling water system. Taking the temperatures of low-temper ature fresh water and high-temperature seawater as state variables, a multi-input coupled nonlinear heat transfer model, with the opening of the fresh water regulating solenoid valve and the seawater regulating solenoid valve as control inputs, is studied based on the analysis of the heat transfer model's characteristics. The model is decomposed into two systems: a single-input second-order linear system and a single-input nonlinear system. A sliding model variable structure (SMVS) controller is obtained by transforming the nonlinear model into a linear reductive type. Experiments on the proportional-integral-differential (PID) and SMVS control, using the KING VIKW software platform, are carried out on the temperatures of low-temperature fresh water and high-temperature seawater. The results show that the SMVS control has certain advantages; namely, a small overshoot, fast response speed and strong anti-jamming capability.