Multi-objective Optimization For Power Allocation In Diesel-electric Hybrid Propulsion System

The situation of environmental pollution resulting from ship is becoming increasingly serious.In the past,shipowners are only required to consider economic benefits,but now they need to take both economy and emission factors into account due to the regulations.Diesel-electric hybrid propulsion is a novel form,which combines economic factor of main engine propulsion and maneuverability of electric propulsion,and it could reduce emission.While,how to balance economic benefits and pollution emissions has become one of the research hotspots in the field of ship hybrid propulsion.Therefore,the Offshore Oil 681,a diesel-electric hybrid propulsion ship,is taken as research object,and in-depth research on the power allocation problem of the hybrid propulsion system is conducted,including the following aspects.According to the structure of the diesel-electric hybrid propulsion system,a mathematical model for hybrid propulsion system is established,including the ship's resistance model which uses the Froude classification method and considers towing resistance,the propeller's characteristics model using the Dutch B4-55 propeller map,the wake and thrust reduction model using the empirical formula,the fuel consumption rate and the NOx emission rate model based on the bench test data,and the propulsion system efficiency model.Based on the theory of multi-objective optimization and integer programming,an optimization model of power allocation problem of hybrid propulsion system is constructed.Hybrid propulsion system power allocation problem is a multi-objective optimization problem with nonlinear constraints and mixed integer constraints.The decision variables,the objective function of economic index and emission index and the equality and inequality constraints of the optimization problem are given.The innovation of this model is to subdivide the power flow of the hybrid propulsion system,a more complete optimization solution result can be obtained.A ship power allocation algorithm for solving the power distribution problem is designed.The problem is solved by the proposed algorithm as well as NSGA-? algorithm considering seven typical ship working conditions.The method of dealing with mixed integer constraints is to narrow down the search branch by calculating the effective scheme under a certain working condition.For each effective scheme,the solution of the relaxation problem after removing the integer constraints is calculated,all the Pareto optimal solutions are merged,and the dominated solutions are judged and deleted to obtain a merged Pareto front.A multi-attribute decision making method with preference is adopted for the merged Pareto front,an optimal solution is selected for each working condition as the final solution,and the influence of different weight vectors on the decision result is analyzed.The designed ship power allocation algorithm is compared with the single-objective optimization algorithm for optimizing fuel consumption under full-speed conditions.Its emission index is reduced by 1.34%,and the economic index is slightly increased by 0.65%.The ship's environmental protection operation is realized while considering the economy factors,and ship pollution emission is effectively reduced,providing a theoretical basis for real ship applications.