Study On Optimization Control Of Diesel Electric Hybrid Dynamic Positioning Propulsion System

Energy crisis is a serious problem all over the world. Therefore, many countries have set a strategic goal to develop deep-sea and put energy-saving and emission reduction as an important research direction. Marine offshore ship has advantages of high automation, accurate positioning, which are significant guarantees for deep-sea oil exploitation. Because operating conditions are fickle and certain dynamic positioning accuracy is required, marine offshore ship uses diesel electric hybrid dynamic positioning propulsion system, which applies diesel electric hybrid propulsion and has dynamic positioning function. The propulsion system of marine offshore ship is complex, equipped with multi propellers, powered by two kinds of power sources including the auxiliary engines and main engines and power forms include electrical and mechanical power.Due to the multiple power sources, various propulsion modes, limited propulsion power and the in-depth concept of energy saving and environmental protection, the research on optimization control of diesel electric hybrid dynamic positioning propulsion system is very necessary. This paper introduces the structure and characteristics of the propulsion system of the offshore engineering ship, and transforms the optimization of the propulsion system into a specific mathematical model. The concept of degree of hybridization is introduced, and the optimal control of power allocation under different working conditions is studied. Based on fuel consumption rate curves of prime movers (main engines and auxiliary engines), using the ship’s power demand as input, the equivalent fuel consumption minimum of prime movers as the optimization objective, the control strategy allocates the ship driving devices power timely. Control strategy can achieve optimal power distribution between auxiliary engines and main engines to achieve the minimum equivalent fuel consumption under different power range. The carrying power of auxiliary engines is used to supply power to grid. The carrying power of the main diesel engine is used for three feasible modes of operation including propulsion, power generation, and propulsion and power generation and analysis is necessary to choose suitable working mode under different working conditions.The demand power calculation method and power allocation analysis of four kinds of typical working conditions are descripted including the dynamic positioning, maximum speed, pull and cruise. Because ship needs to maintain a certain position or heading under dynamic positioning mode, multi thrusters are used to offset the force produced by wind, wave and current. Using some control algorithms to restrain the output of each propeller can achieve minimal power consumption. So thrust allocation optimization should be done first. The thrust allocation model is established, and the thrust allocation is optimized by genetic algorithm to ensure the positioning accuracy and the minimum power consumption. In addition, it involved the construction of the dynamic positioning system simulation platform, including the mathematical model of the ship motion and the propulsion model etc. Optimal control of diesel electric hybrid propulsion system provides a theoretical guidance for the choice of the propulsion modes under different working conditions, which is of great significance to reduce the fuel consumption and reduce the environmental cost.