UDT 2020 Latest Developments in Energy Systems Dipl.-Ing. Peter - PDF document

UDT 2020 Latest Developments in Energy Systems UDT 2020 – Latest Developments in Energy Systems Dipl.-Ing. Peter Hauschildt Head of Technology and Innovation thyssenkrupp Marine Systems GmbH, Werftstrasse 112-114, 24143 Kiel, Germany peter.hauschildt@thyssenkrupp.com Abstract — For SSKs energy storage is crucial; since the time being completely submerged – thus not having the need to snorkel – is essential to keep the operational advance of being stealthy. Air independent propulsion (AIP) systems today are state of the art while most submarine builders do not have mature systems operational; almost all are working on fuel cell systems. thyssenkrupp Marine Systems having supplied most AIP submarines that are operational based on fuel cells (FC) has developed a fourth generation of fuel cells. Compared to previous systems the new system features latest FC technology, thus improving operational availability, cost and independence of suppliers. T In addition, batteries are the traditional energy storage for SSKs. Having used lead-acid batteries for over 100 years, a technology change is under way. Lithium Ion batteries offer higher capacity, more power, faster charging and a longer lifetime. The paper will show the special requirements of the submarine application and the technical solutions, which are now ready for use on board of submarines. 1 Introduction 2 Submarine Batteries Submarines are the ultimate stealth ships mainly due to one Lead acid batteries have been standard for submarines major feature – they can dive. In contrast to nuclear since the early days. They are relatively cheap and can be submarines, whose diving times are almost unlimited, non- manufactured in different sizes to ideally fit to the nuclear submarines are always limited by the energy sup- respective submarine design. However, lead acid batteries ply. have some major drawbacks: Because of available technology, diesel electric • In comparison to other battery types their energy submarines with lead acid batteries are limited to a few density is low days of continuous dive, even if they just move slowly. When the batteries are exhausted, the submarine needs to recharge the batteries using the diesel generator sets while • They need maintenance: While not in use they snorkelling. should be completely charged. They need to be Snorkelling significantly increases the vulnerability of the “gas charged” on a regular basis: A procedure submarine, because it loses a major part of its stealth during which the battery produces dangerous feature: hydrogen that enters the boats atmosphere. For this an external charging unit is required. The snorkel and other hoistable masts have radar and infrared signatures, the diesel and the exhaust generate • The battery degrades during the mission until it noise and the hull itself can be spotted either visually or by is maintained by “gas charging” which is laser. normally done n port with no crew on board for safety reasons. Therefore, it is always a major goal for submarine yards to improve the energy system. This paper gives a status about • On a regular basis water has to be refilled the latest development in batteries and in air independent manually to each of the cells propulsion (AIP). • At higher charging stages the charging current has to be limited • To avoid damaging by deep discharge, a lead acid battery should not be used with the full specified capacity

UDT 2020 Latest Developments in Energy Systems • When almost discharged the battery cannot give Modules are put in series until the desired voltage of the it’s nominal current, limiti ng the flank speed of boats network is reached. This is called a string. Many the submarine strings are put parallel to have the desired capacity. Modern batteries can overcome all these disadvantages. So why are almost all submarines still relying on lead acid batteries? Lead acid batteries have some advantages: • They are relatively cheap • They can be produced in adaptable sizes to be an ideal fit to the respective submarine design. In the last years large format Lithium-Ion-Battery (LIB) cells have become commercially available. The e- mobility demand is a major driving factor for their development. But for a submarine LIB integration is not an easy task: • Depending on the chemistry LIB are a significant fire hazard. Fig 1 : LIB module, inside view • Fires could be cause by misuse (overcharge, Each string is connected to the network by a DC-DC overheat), internal failures or mechanical converter that can limit the current in case of a short circuit damage. in the network and can galvanically separate each string from the network, if necessary. In addition these CD-DC • LIB can drive very high currents which are hard converters called string switch device are used to equalize to handle. and optimise use or charging of the strings. thyssenkrupp Marine Systems has developed a LIB for During development, many submarine requirements have submarines based on a safe chemistry with low to no fire to be considered: hazard – the Iron Phosphate chemistry. Also the energy density of other Nickel or Cobalt based chemistries is • Shock higher, safety analysis has shown, that their integration into the closed manned atmosphere of a submarine would • impose unacceptable hazards. Magnetic (German Submarines are non magnetic) Since available cells are significantly smaller than today’s Lead Acid batteries, many of the commercial cells are • Electromagnetic compatibility mounted in a common frame and form so called modules. • Temperatures Since deep discharge and overcharge as well as overcurrent or over temperature have to be securely • Charging and discharging rates avoided, a monitoring electronic has to be part of the system, which fulfils highest standards in terms of reliability and safety. Each module has it’s own battery • Reliability monitoring system. • Maintainability In addition, the battery monitoring system takes care, that all cells are equally charged.

UDT 2020 Latest Developments in Energy Systems with 30-40 kWel for each Module. This system is operated successfully by the German and the Italian navy on board of their submarines since then. A third generation of fuel cells was developed together with SIEMENS for the HDW Class 214 submarines now having a power output of 120kW per FC module and 240kW in total. Fig3 : FC testing on “U1” in 1988 Fig 1 : EMC testing of battery string Based on our vast experience with prior generations of fuel thyssenkrupp Marine Systems with it’s partners SAFT and cell systems, we have decided to develop a fourth ABB has developed under a contract of the German generation of fuel cells based on latest technology. Procurement agency BAAINBw and tested the new This so-called Advanced Submarine Fuel Cell (ASFC) system on prototype level and is in discussion with initial unites advances in the development of the fuel cell industry customers about submarine integration. over the last 20 years. The configuration of ASFC is based on four independent systems with 80 kW each, namely the ASFC line, resulting in 320 kW total FC power output. 3 Air Independent Propulsion The ASFC system is operated on pure hydrogen and oxygen. As single fuel cells always require gas in excess Even with LIB submarines are limited to some days to dispose of the reaction water, the system design includes without snorkelling. To dive even longer air independent gas recirculation for hydrogen and oxygen. Recirculation propulsion (AIP) Systems are needed which use a fuel and ensures that the fuel cells are always operated in optimal liquidly stored oxygen (LOx) to generate power. conditions, under full load as well as partial load. These AIP systems enable submarines to stay submerged for weeks at slow speed, while for fast transits the diesel gensets are still needed and only batteries give the power for flank speed. thyssenkrupp Marine Systems is working in the field of Fuel Cell based air independent propulsion (AIP) Systems for more than 30 years. We have chosen fuel cells over combustion systems since fuel cells have some outstanding advantages: • Very high efficiency • As a consequence low consumption of LOx • As a consequence low heat transfer to the sea water • Absolute silence of the energy generating process • No exhaust gas to be dumped over board As a consequence all relevant submarine builders claim today to have or develop fuel cell AIP, but so far only the systems of thyssenkrupp Marine Systems are operational in submarines. The first test fuel cell AIP system was realized on board of the submarine U1, which was in operation at the German navy, in 1988. The first series of fuel cell AIP is integrated in the HDW Class 212A, based on nine SIEMENS FC-Modules, Fig 4 : ASFC module