Waxholmsbolaget Yxlan Ice-class hybrid passenger ferry provides year-round travel in the Stockholm Archipelago.


Safety has other considerations as well; there is disaster safety at the cell level, and then there is safe use of batteries. We designed a BMS that is inherently focussed on protecting the ship, the battery system and the cells. This is done at its core by monitoring the voltage and temperature of every individual cell in the system, and then balancing the performance of the vessel within the safe operating principals of the ship.


There are two different ways to design a BMS; one that is ideal for a fully electric ship and one that suits hybrid applications. While both in principal will give the operators choices in the event of a battery failure, in a fully electric ship, the safe operation of the vessel becomes the guiding principal of the decision making of the BMS and Power Management System (PMS). In a hybrid application, the batteries can become the focus of the performance of the PMS as the vessel has alternative propulsion systems and is not totally reliant on the battery for operation. Once we define the type of application as either hybrid or electric, we can optimize the operational logic of the BMS as it pertains to the PMS/ operator decision making criteria.


Another critical element of safety in design has been the inclusion of contactors in our building block modules. Basically, as we are building DC voltage systems that range from 300-1500VDC, the risk of personal injury in transportation and service are very high. For example, a 1500 VDC arc flash can permanently disable a technician. By adding contactors in the individual battery modules, we eliminate voltage at the terminals until the system is fully engaged and the BMS can approve that all cables are correctly sequenced and protected. There is no voltage or


power on the terminals as long as they are open. We also reduce the risk by isolating the building blocks as single units no matter how large the overall size. The element of crew safety of our technicians and the operators of the vessels cannot be overstated in terms of benefit to our customers. We can now train ships engineers and crew to do maintenance on the batteries, we don’t need to bring in specially qualified electricians to do basic maintenance. This design decision was not free, but it is the right way to go to improve overall safety for our customers ships.


SPBES patented eVent system showing path of gas extraction in a single cell thermal event.


The Report • March 2020 • Issue 91 | 61


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