Study On Simulation And Intelligent Control Of Marine Central Cooling System

Central cooling system is an important part of the marine power plant. Cooling water circulars in this system in order to cool each component and equipment, reduce heat load and ensure that each device operates properly and reliably. The performance of cooling system can affect the marine power plant directly, thereby has an impact on the reliability and economy of the ship. On the other hand, as Energy Efficiency Design Index has taken effect, higher requirements are put forward on cooling system. Therefore, the simulation study of central cooling system and using frequency conversion control method can be of great significance to improve the performance of the system and realize the energy saving and emission reduction of the ship.This thesis first introduced common form and composition structure of central cooling system. The system was divided into high-temperature fresh water system, low-temperature fresh water system and sea water system according to the different cooling media. A dynamic mathematical model of central cooling system has been established through the analysis of the operation process based on the heat transfer and fluid mechanics theory.Second,on the basis of the dynamic mathematical model, this thesis adopted a bottom-up design process to finish simulation modeling of the main equipment of the central cooling system by using computer simulation technology. The simulation module of the whole system was obtained to realize the dynamic simulation of the different conditions.Then, a research prototype of a 57000 dwt bulk carrier central cooling system was used as the object to verify the correctness of the simulation model by comparative analysis of the experimental data and simulation results. A scheme of frequency conversion control was proposed according to the control target. On this basis, the simulation study on the marine central cooling system was finished to obtain control strategies under the typical conditions of the ship. Through the analysis of the energy consumption, the result showed that using frequency conversion control technology can change cooling sea water flow continuously, realize full utilization of sea water cooling capacity and reduce the energy consumption and the navigation costs of the ship.Finally, considering nonlinear and delay characteristics of central cooling system and defects of traditional PID controller in the tracking set value and disturbance rejection, this thesis used neural network to control central cooling system intelligently, established the neural network controller model and applied it to the dynamic study of the variable condition. The results showed that neural network control can not only achieve the frequency conversion control target but also have strong adaptability and anti-jamming, and improve the control performance of the system.