Economic and Environmental Generation and Voyage Scheduling of All-Electric Ships

Abstract

An all-electric ship (AES) uses integrated power generators and an energy storage system (ESS) to match its propulsion and service loads, thus forming an isolated microgrid. Existing work has hitherto set the minimisation of the AES operational cost as the single optimisation objective, with the reduction of the greenhouse gas (GHG) emission merely treated as a constraint of the optimisation. Moreover, the potential of the ESS as part of the scheduling has not been fully exploited. The work presented in this paper emphasises the environmental concerns and makes GHG mitigation a separate objective, thus expanding the optimisation into multi-objective. In achieving both objectives, the ESS-integrated joint generation – voyage scheduling of the AES is proposed: the generation scheduling is combined with the load management (propulsion load – cruising speed) and the ESS dispatch to optimally operate the diesel generators. The optimisation is formulated using optimal control, and is solved using non-dominated sorting genetic algorithm II (NSGA-II). Extensive simulations demonstrate that optimising the cruising speed (voyage) jointly with the generation scheduling results in the reduction of both operational cost and GHG emission, compared to the fixed-voyage generation scheduling. Integrating the ESS dispatch into the generation scheduling further enhances the benefits.