Power Management for Electric Tugboats Through Operating Load Estimation

Abstract

This brief presents an optimal power management scheme for an electromechanical marine vessel's powertrain. An optimization problem is formulated to optimally split the power supply from engines and battery in response to a load demand, while minimizing the engine fuel consumption and maintaining the battery life, wherein the cost function associates penalties corresponding to the engine fuel consumption, the change in battery's state of charge (SOC), and the excess power that cannot be regenerated. Utilizing the nonlinear optimization approach, an optimal scheduling for the power output of the engines and optimal charging/discharging rate of the battery is determined while accounting for the constraints due to the rated power limits of engine/battery and battery's SOC limits. The proposed optimization algorithm can schedule the operation, i.e., starting time and stopping time for a multiengine configuration optimally, which is a key difference from the previously developed optimal power management algorithms for land-based hybrid electric vehicles. Afterward, a novel load prediction scheme that requires only the information regarding the general operational characteristics of the marine vessel that anticipates the load demand at a given time instant from the historical load demand data during that operation is introduced. This prediction scheme schedules the engine and battery operation by solving prediction-based optimizations over consecutive horizons. Numerical illustration is presented on an industry-consulted harbor tugboat model, along with a comparison of the performance of the proposed algorithm with a baseline conventional rule-based controller to demonstrate its feasibility and effectiveness. The simulation results demonstrate that the optimal cost for electric tugboat operation is 9.31% lower than the baseline rule-based controller. In the case of load uncertainty, the prediction-based algorithm yields a cost 8.90% lower than the baseline rule-based controller.Index Terms-Hybrid electric vehicle (HEV), load estimation, marine powertrain, marine vessel, optimization, power management.

Design of Minimum Fuel Consumption Energy Management Strategy for Hybrid Marine Vessels with Multiple Diesel Engine Generators and Energy Storage

“…The problem of optimum fuel consumption has been studied in detail for vessels without energy storage [6] [7] and to some extent also for vessels with energy storage. In [8] a simple load leveling strategy is used, [9][10] [11] and [12] utilizes different online optimization techniques, [13] uses load prediction for the optimization while [14] and [15] utilizes offline optimization.…”

Optimising design and power management in energy-efficient marine vessel power systems: a literature review

“…In practical designs, these interactions lead to fairly low dynamics between the machinery operating point and the actual vessel motion. Therefore, the static propeller loads are sufficient in system modelling in most cases as stated in Vu et al (2015). Due to the hydrodynamics of the propeller, the ability to recuperate energy efficiently using regenerative braking is a feature that is typically missing in marine vessels.…”

“…The integrating element of a rechargeable energy storage with capacity limits brings a time aspect to the problem. Vu et al (2014aVu et al ( ,2014bVu et al ( ,2015 presented variations of a power management optimisation method using a series hybrid tugboat. The penalty function included elements for fuel consumption, load demand tracking and changes in battery energy.…”

The Study of the Influence of Port Scale on Tugboat Configuration Based on System Simulation

“…Su [6] use simulation software ARENA to look into the harbor tugboat operation, and also use performance indicator to evaluate the harbor tugboat utilization, effectiveness of man power scheduling and the waiting status of the ships. Vu [7] presents an optimal power management scheme for an electromechanical marine vessel's powertrain, and also proposed an optimization algorithm which can schedule the operation, i.e., starting time and stopping time for a multiengine configuration optimally, which is a key difference from the previously developed optimal power management algorithms for landbased hybrid electric vehicles. Jung C H et al [8] make a comparison of tugboat requirements among Korea major ports, proposed a criteria of tugboat requirement and method for calculation.…”