We have split Vangaurd’s electrical system into three parts. Power, Hotel, and Instrumentation. A bit complicated due to the redundancy requirements but I think it’s worth the work up-front. Our approach to redundancy has a hierarchy:
Redundant (duplicated in parallel)
Very high mean time between failures (such as the hull or a good anchor so can exist without duplication)
Existent alternatives (such as shore power where we can also generate on board, inherently low risk)
None critical (e.g. TV surround sound, who cares really?)
Main E-Motor and Generator
We had to start somewhere, so we started small and worked from that. First on the drawing board was the power system. It had such a significant influence on everything else that we needed to confirm how this would configure before moving on. In reality, we were obliged to imagine how it would affect other systems, but we can confine the major decisions to how the boat will be powered.
So let’s start with the overall philosophy. Similar to Hull No 1, Mobius, Vanguard will carry a large battery bank. It’s kind of “battery-centric”. Generation, shore power, and solar will feed the bank, hotel loads, instrumentation, and propulsion will draw from it. We went for Lithium technologies for their advanced charge and discharge rates and will make allowances for their down sides. We have two 60kWh banks giving 50% redundancy. These feed either directly to the hybrid drive via Variable Frequency Inverters or into Active-Front-End Inverters that produce a pure sine wave AC feed into a 3 phase 230VAC transformer that powers the hotel load Bus Bar. An additional line filter removes potential harmonics (we can speak about that in another Blog). The transformer is 3-phase (delta output windings); we will balance the phases for the hotel side later. We have two such systems for redundancy, each capable of about 20-25KVA (kilovolt amps; kW at null power factor). One of them has an additional winding that will accept 230VAC shore supply. The output is a clean 230VAC 3-phase again, electrically and galvanically isolated from the shore supply, so no hull or “people” damage from floating neutral or earth lines.
The 60kWh battery bank is high-voltage DC floating between about 550 and 770VDC depending on the state of charge. This feeds into a DC bus bar that supplies all high voltage DC needs. A bus bar is more reliable and simpler than individual wiring connections, which we also see as an advantage. Each one of two 30kW hybrid drive motors draws power via a Variable Frequency Drive inverter to normalize the voltage and provide a control function. These inverters will also act as chargers when the diesel engines drive the hybrids, decoupled from the props. Each engine can be completely electrically isolated if needs be.
The 230VAC bus bars feed frequency inverters for 24VDC and 48VDC systems, 230VAC hotel loads, and the bow thruster (230VAC 3-phase, long run, and proportional control). 8kW of Solar Cells also feed into the hotel load system via MPPT controllers and their inverter to step-up and clean their output.
House batteries also feed to 24/48VDC systems that give us a dead ship cold start capability if the power batteries die. (Note – Lead Acid, Firefly batteries have better verylow temperature performance in comparison to Lithium alternatives.) These house batteries will be preferentially charged by the Solar Cells or shore supply. Once fully charged, any excess will be fed back through the power inverters to charge the power batteries in a cascade type of array. Waste not, want not, perhaps?
Power Management system
A power management system will control shore charging and switching off power/charge sources. An energy management system will control what power flows to where and how. This system is duplicated and will report on battery charge state, system run hours, remaining life and control the thruster and hybrid drives …. etc including the diesel engines in generator mode or direct drive. It will also register through the MFD displays on the bridge and flybridge, and local displays in the engine room.
Cooling of all power inverters and the two-hybrid drives will use a fully redundant water/glycol cooling loop and hull skin tank. 50/50 mix <35deg.C inlet.
We can upgrade hybrid power or battery capacity without a major redesign of the overall system if we wish to. We have duplicate and, in some cases, an alternative workaround of all major systems. I think we are good to go and will schedule a Factory Acceptance Test before shipping to keep problems where they are best worked on.
I hope it works as per plan!