MVDC marine electrical distribution: Are we ready?

Abstract

Abstract-Marine high-power on-board electrical systems are predominantly utilizing three-phase medium voltage alternating current (MVAC) distribution. Depending on the size and purpose of the ship, on-board electrical systems provide supply to loads in excess of 60MW. Increasingly, medium voltage direct current (MVDC) distribution systems are being considered as an alternative. An increase in the fuel efficiency of the prime movers, the removal of bulky low frequency transformer and the easier integration of different storage technologies are especially attractive. This paper discusses the opportunities but also the technical difficulties associated with the transition from an MVAC to an MVDC system, using an existing LNG tanker MVAC on-board distribution system, as example.

Dynamic Assessment of Source–Load Interactions in Marine MVDC Distribution

“…The diesel generator sets are usually combination of two discrete parts: 1) prime mover, which is usually a medium-to-high-speed diesel engine providing input mechanical power; and 2) 3φ synchronous generator, which produces the electrical power. These generators are also medium to high speed with two to ten poles, with a frequency of or 60 Hz and voltage levels of or 6.6 kV, with their excitation being controlled by an automatic voltage regulator (AVR) [14], [26]. As no transformers are being used for the voltage coordination in this study and the prospective MVDC system, the voltage of the generators and the distribution system is identical to the voltage class of the propulsion motors.…”

“…These parameters point toward possible system configurations that could be found in the future MVDC systems [14]. For the system to exhibit absolute stability, it must satisfy the Nyquist stability criterion, i.e., it must not encircle (−1, 0).…”

“…It should be noted that commercial cables are designed for MVAC applications [14], [36], so there is a need to develop the MVDC cables. Nonetheless, a single-pole 12-kV XPLE MVAC cable is being considered in the paper [36].…”

“…To utilize the maximum benefit from the MVDC distribution system, improvements are required in the existing medium-voltage drives, high-voltage electrical machines, diesel engines and gas turbines, high-power dc-dc converters, rectifiers, MVDC protection components, MVDC cable technology, active and passive filters, and energy storage systems [14]. Another major challenge is the stability of the MVDC distribution system that arises due to the presence of the high-power motor drives and their constant power load (CPL) behavior [15].…”

Marine MVDC multi-phase multi-pulse supply

“…In the recent years, a possible replacement of the state-ofthe-art on-board medium voltage ac (MVAC) electrical distribution systems for ships with medium voltage dc (MVDC) electrical distribution is being considered [1], [2]. The popularity of the on-board MVDC electrical distribution, as the future ship electrical distribution system, is primarily based on the improvements in the power electronic technologies that provide opportunities to achieve efficient fuel consumption, increased energy density and reduced footprint, and flexibility in the design process of the system [3].…”