A strategy for power management of electric hybrid marine power systems
Chua, Liza Wan Yuan
Date of Issue2019-04-26
School of Mechanical and Aerospace Engineering
ABB Pte. Ltd.
With the increasing concern in environmental impacts contributed by shipping industries, the International Maritime Organization set stringent requirements to monitor ship energy efficiency and ship emissions during operation. Some ships with highly dynamic loads, often face difficulty to maintain energy efficient operations with conventional mechanical propulsion design. Through technology advancements over the years, the all-electric hybrid power and propulsion system with DC distribution is the current state-of-the-art design, which can improve fuel efficiency and simplify the integration of DC power sources. However, the increased flexibility of the system and additional control requirements pose new challenges for power management control. The conventional rule-based (RB) power management strategies currently employed in the industry could not guarantee optimal control. An intelligent power management approach is necessary to address these challenges. Hence, the main objective in this thesis is to propose a power management strategy for the optimal power allocation problem of an all-electric hybrid power and propulsion system with DC distribution, to improve fuel efficiency and to reduce emission. Firstly, dynamic models of the all-electric hybrid power system are developed in MATLAB\Simulink to simulate power system response. A laboratory-scale hybrid power system test bed is built in NTU to validate and calibrate the hybrid power system models. An instantaneous optimization-based power management strategy is then proposed, using the Equivalent Consumption Minimization Strategy (ECMS) concept, to determine the power allocation among the power sources that will result in minimal fuel consumption. A multi-level power management framework is then proposed for real-time execution of the strategy. Preliminary experimental testing and investigations on the laboratory-scale test bed shows satisfactory real-time performances. Subsequently, feasibility and performance of the proposed framework is validated on a full-scale system designed based on an actual all-electric hybrid vessel with DC distribution, in a laboratory facility in MARINTEK, Trondheim. Experimental results show the advantages of the proposed strategy with improvements in fuel saving over an improved RB strategy of up to 24.4%. The proposed strategy is then enhanced in two areas. Firstly, the control objective is extended to include emission reduction. Among the major composition of ship emissions (CO2, NOx, SO2, HC, CO, PM), a tradeoff between NOx emission and fuel consumption has been observed. Hence, a method is proposed to manage the compromise between fuel consumption and NOx emissions, which allows the control on the influence of NOx emission on the power split solution. Secondly, the flexibility of the proposed strategy to adapt to offshore applications is investigated. The control objective is refined for jack-up applications to include charge-sustaining due to the limited access to shore charging. A case study on tripping operations shows the effectiveness of the approach to maintain SOC within the target range, demonstrating the flexibility of the proposed strategy for more applications in the future.
DRNTU::Engineering::Electrical and electronic engineering::Electric power