History and State of the Art in Commercial Electric Ship Propulsion, Integrated Power Systems, and Future Trends

Abstract

| Electric propulsion has emerged as one of the most efficient propulsion arrangements for several vessel types over the last decades. Even though examples can be found in the history at the end of 19th century, and further into the 20th century, the modern use of electric propulsion started in the 1980s along with the development of semiconductor switching devices to be used in high power drives (dc drives and later acto-ac drives). This development opened up for full rpm control of propellers and thrusters, and thereby enabling a simplification of the mechanical structure. However, the main reason for using electric propulsion in commercial ship applications is the potential for fuel savings compared to equivalent mechanical alternatives, except for icebreakers where the performance of an electric powered propeller is superior to a combustion engine powered propeller. The fuel saving potential lies within the fact that the applicable vessels have a highly varying operation profile and are seldom run at full power. This favors the power plant principle in which electric power can be produced at any time with optimum running of prime movers, e.g., diesel engines, by turning on and off units depending on the power demand for propulsion and other vessel loads. Icebreakers were among the first vessels to take advantage of this technology later followed by cruise vessel, and the offshore drilling vessels operating with dynamic positioning (DP). The converter technology was rapidly developing and soon the dc drives were replaced with ac drives. In the same period electric propulsion emerged as basic standard for large cruise liners, and DP operated drilling vessels, but also found its way into other segments as shuttle tankers, ferries, and other special vessels. At the same time podded propulsion were introduced, where the electric motor was mounted directly on the propeller shaft in a submerged 360 steerable pod, adding better efficiency, improved maneuvering, and reduced installation space/cost to the benefits of electric propulsion. The future trends are now focusing on further optimization of efficiency by allowing multiple energy sources, independent operation of individual power producers, and energy storage for various applications, such as power back up, peak shaving, or emission free operation (short voyages).

Hierarchical Control Design for a Shipboard Power System With DC Distribution and Energy Storage Aboard Future More-Electric Ships

“…In this case, VCM source will automatically provide supporting functions to the system, including spinning reserve, peak-shaving, and load conditioning. It is important to notice that these supporting functions are exactly the same with the expected functions of using ESSs in SPSs as listed in [2]. In another word, the new proposal provides an effective method to integrate ESSs in DC-SPS and to exploit the benefit.…”

“…Correspondingly, the total power demand of the system can be hundreds of kilowatts to tens of megawatts depending on the different types/classes and the different usage of the vessel. Normally, the propulsion systems will consume most of the onboard power with some load fluctuations due to the inherent uncertainty of the water surface [2]. In addition, the unique dynamic positioning (DP) operation of drilling and supporting vessels will introduce fast and dramatic load changing to the system.…”

“…The final version of record is available at http://dx.doi.org/10.1109/TII.2017.2772343 rated power, and degrades considerably in both light and heavy load conditions [2]. Moreover, the load fluctuations will also increase the fuel consumption and introduce mechanical issues.…”

“…INTRODUCTION RIVEN by the increased onboard electrical power demand and the progressively stricter environmental requirements, marine industry is dedicating to develop new solutions for the future vessels [1]- [4]. In 1990s, power electronic converters (PECs) have made breakthrough in the field of marine vessels for enabling electrification of the propulsion systems through variable voltage variable frequency drive technology [2]- [4]. The advantages obtained from PECs, including efficiency improvement, space saving and maneuverability enhancement, have resulted in the current tendency to further electrify the vessel, namely more-electric ship (MES).…”

“…PV array) [17]. Among them, DC distribution and ESS can contribute to both the efficiency and reliability of the SPS, thus becoming the trend of future MES [1], [2], [12]. Moreover, it is noteworthy that ESSs inherently operate in DC, therefore, DC distribution based SPS (DC-SPS) is more efficient to integrate ESSs, as well as to support electric propulsion systems.…”