Integrated System Design and Control Optimization of Hybrid Electric Propulsion System Using a Bi-Level, Nested Approach

Abstract

Hybrid electric powertrain systems present as effective alternatives to traditional vehicle and marine propulsion means with improved fuel efficiency, as well as reduced greenhouse gas (GHG) emissions and air pollutants. In this study, a new integrated, model-based design and optimization method for hybrid electric propulsion system of a marine vessel (harbor tugboat) has been introduced. The sizes of key hybrid powertrain components, especially the Li-ion battery energy storage system (ESS), which can greatly affect the ship’s life-cycle cost (LCC), have been optimized using the fuel efficiency, emission and lifecycle cost model of the hybrid powertrain system. Moreover, the control strategies for the hybrid system, which is essential for achieving the minimum fuel consumption and extending battery life, are optimized. For a given powertrain architecture, the optimal design of a hybrid marine propulsion system involves two critical aspects: the optimal sizing of key powertrain components, and the optimal power control and energy management. In this work, a bi-level, nested optimization framework was proposed to address these two intricate problems jointly. The upper level optimization aims at component size optimization, while the lower level optimization carries out optimal operation control through dynamic programming (DP) to achieve the globally minimum fuel consumption and battery degradation for a given vessel load profile. The optimized Latin hypercube sampling (OLHS), Kriging and the widely used Expected Improvement (EI) online sampling criterion are used to carry out “small data” driven global optimization to solve this nested optimization problem. The obtained results showed significant reduction of the vessel LCC with the optimized hybrid electric powertrain system design and controls. Reduced engine size and operation time, as well as improved operation efficiency of the hybrid system also greatly decreased the GHG emissions compared to traditional mechanical propulsion.

Mission-oriented Modular Control of Retrofittable Marine Power Plants

“…With electric propulsion, the shaft is driven by an electric motor instead of a diesel 1. INTRODUCTION (a) Typical power profile of a cargo ship [6] (b) Typical power profile of a tugboat [8] Figure 1.1: Power profiles of a cargo ship and tugboat engine. This removes the need of a gearbox, so the propeller is directly connected to the shaft.…”

Li-Ion Battery Performance Degradation Modeling for the Optimal Design and Energy Management of Electrified Propulsion Systems

“…The fuel cost is mainly determined by the operating efficiency of the engine that can be affected by the system design, component sizing, and power control. In this work, it is assumed that engine maintenance cost is closely related to its working time and the engine size [35].…”

“…More detailed information of LCC model, such as the price of marine fuels, the evaluation of fuel consumption cost and engine maintenance cost, etc. can be found in [35].…”

Simultaneous and Global Optimizations of LNG-Fueled Hybrid Electric Ship for Substantial Fuel Cost, CO2, and Methane Emission Reduction

“…To improve the design and EMS optimization integration, Zhu et al [22] introduced a multi-objective, bi-level search scheme for powertrain component sizing and EMS optimization method for optimizing the HEPS, considering fuel consumption, average GHG emissions and net cost. Chen et al [23] introduced a nested approach for designing and controlling the HEPS. Besides the bi-level and nested optimization approach, the simultaneous optimization of the HEPS was also reported.…”

“…Using an asynchronous power unit, Kumar et al [26] minimized the total fuel consumption of tugboats through advanced control and energy management [26]. At present, research on the design and control optimizations of vessel HEPS primarily focus on fuel/energy efficiency [23] [25] [26], total cost [27] [28], and diesel engine GHG emissions [29], using gradient-free optimizers. Chen et al [27] established a battery performance degradation model supporting the cost minimization of a hybrid electric ship.…”