We are all aware about self-driving cars, and all exciting projects the automotive industry is engaged in, but very few have heard about unmanned ship and projects to operate large fleets of vessels navigating from dock to dock without operational crews (see Figure 1). In early stages, projects such as Maritime Unmanned Navigation Through Intelligence In Networks (MUNIN) investigated feasibility and test-bed development for future developments. Considering unmanned ships will require extreme reliability from the main generator to single point-of-load, challenges placed on power designers will be far beyond anything we have known.
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Figure 01 – Rolls-Royce unmanned ship project (source: Rolls-Royce)
State of the art in marine power
Future generations of power supplies for unmanned ship are still under definition though it is important to understand the specificity of the Marine segment, which is quite unique in terms of environmental and regulations. Due to the nature of the business, the requirements imposed on products and systems deployed in shipping and offshore installations are heavier than what is currently requested for land industrial and office environment.
In addition, International regulations and standards applying to the Marine Industry are very complex, requiring in depth knowledge of the application and where it will be operated. Power designers must know a lot about marine specific voltage distribution, combining DC and AC networks, safety regulation and many others such as “Operational Zones” which, from ship to ship and nature of merchandized transported could be totally different.
The Zones
Generally two zones are distinguished on a ship; the “bridge and the open deck zone”, and the "general power zone", which basically extends to all other spaces in the ship.
One example of specific requirement per zone is the electromagnetic emission and immunity (EMC). The areas open deck and bridge have extra demands on the electromagnetic emission and immunity (EMC), as a lot of sensitive equipment is positioned here, such as communication, radar and navigation devices. These EMC requirements regarding emissions are well below the known EN55022 Level B and measurement starts already at 10 kHz, instead of the usual 150 kHz.
The limits regarding mechanical and climatic requirements are also higher than for the average industrial application. Vibration levels up to 4g are common, as well as large temperature fluctuations from -25°C and +70°C and high relative humidity where condensation cannot be excluded.
The rules
It is common to say that; every country with a maritime sector has its own certification-authority with specific demand for local certification, which forces power designers to keep track of the final application where the power supplies will be installed.
In general, there is a common group of standards and qualification processes that have similar roots for all countries-certification though, from country to country and maritime sub segments, there are as well, a number of very specific requirements increasing complexity. The difficulty is there is no de-facto percentage of “common standards” versus specific, requiring power designers to start any new project by reviewing a large number of documents prior designing anything.
In order to develop a sustainable way-of-working, to ensure that the power solutions can be utilized all over the world, Marine power supplies designers used to combine the requirements from all countries active in marine construction and operation, to establish a cross reference table with equivalence and specific action in case of major deviations (i.e. higher demand on shock and vibration).
Once such equivalence table is established, the toughest requirements of each category is selected and used as reference for designing, verifying and qualifying the final power supply. This is done in close cooperation with the final customer, reducing risk to under-specified the power supply and to miss final qualification.
From this design methodology, combined with in depth knowledge of local standards and regulations results a test protocol that meet international and local requirements. This test protocol is then applied to all products, simplifying the final approval but as well that the power supply can be used in case of replacement or system-upgrade in any country.
Usually Marine Customers expect the power supplies to comply, certified and be stamped with the type approval logo of Germanischer Lloyd (GL) though, because of the extensive testing to meet EN60945 for extended approvals by Bureau Veritas (BV), Lloyds Register (LRS), America Bureau of Shipping (ABS), Det Norske Veritas (DNV), Korean Register of Shipping (KR) and many other notified bodies in the maritime world.
More power in smaller footprint
With the increase number of embedded electronics, the marine industry has a need for more functionality in a smaller space. Nowadays, ship owners want to equip their vessels with broadband internet connections for both passengers and crew with as much as possible the same features than when ashore.
For instance, position tracking systems are built-in to monitor requiring very compact power supplies, operated in confined environment without fan. Such power supplies have to be designed for conduction cooling, with high attention on dissipative components placement and optimized conduction cooling (see Figure 2).
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Figure 02 – Powerbox PT571 - Marine grade power supply designed optimized for conduction cooling in confined environment
For most of the power distribution systems, power units are preferably in cassette format, which is simpler to install, maintain and upgrade. The Marine Cassettes are usually fixed on DIN-Rail though electrical designers within the ship-industry are requiring the power supply to be as well compliant with standalone conduction cooling installation anywhere on the ship, meaning, as for the embedded power supply, the design has to be highly optimized for conduction cooling (see Figure 3).
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Figure 03 – Powerbox PT577 - Marine grade power supply in cassette format with built-in ORing diodes
Packaging more power in smaller box, with optimized conduction cooling requires a high degree of integration of the power circuits. The efficiency should be as high as possible, because a small housing also means that the cooling surface is smaller. By using the of the most recent resonant circuits and switching control methods, efficiency up to 95% can be achieved.
Power designers are exploring new technologies such as digital control and the latest generation of Gallium Nitride (GaN) power FETs, targeting higher efficiency and flatter curves, keeping the efficiency high from very low loads to high loads. All new technologies are explored though the nature of the business (often ships are in the middle of oceans and weeks from any lands) requirement for extremely high reliability applies and new technologies have to be verified for extreme conditions. This an ongoing process, which is also mandatory for future unmanned ship were maintenance during operation almost impossible.
Reliability and zero downtime are the rule. For that, power supplies should be able to be connected in parallel for redundancy operation. It is very common to add an external ORing block (usually in similar dimensions as the power supplies) which the electricians interconnect to the power supplies. This conventional way tends to disappear and electronics paralleling circuitry built-in the power supply itself. Adding that function into the power unit saved space in the shelf for more vital equipment but add requirement on power designer to integrate more into smaller packaging.
What’s next in marine?
Existing power solutions for the Marine Industry have proven their robustness and international compliances. Power designers are exploring new technology to permanently improve efficiency, decrease power consumption and dissipation. Unmanned ships will require a level of reliability that will be close to the mythic “Fault Zero” and ability for power supplies to be controlled and monitor from a central office (see Figure 4), which could be on the other side of the planet.
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Figure 04 - Rolls-Royce oX Land-based control center (source: Rolls-Royce)
For the power designer, it will be an amazing challenge to combine state-of-the arts technology in switching, thermal management, control and intelligence. We are close to a new era where power supplies will become self-controlled and able to diagnose early sign of failures to apply corrective action. Is that a dream or reality? In my opinion it’s knocking at the door and will soon be there!
References:
Maritime Unmanned Navigation Through Intelligence In Networks (MUNIN)
http://www.unmanned-ship.org/munin/
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