There is no mention of catapults in the document? This seems mostly about naval IEPS/IPES.
I would like to understand more why AC is bad? Tesla cars use induction AC motors even though their energy source is DC. From my limited understanding brushless DC motors require powerful permanent magnets, which are not cheap to manufacture, think rare earths (except maybe for China?). They are also quite heavy in comparison.
Update: I saw you gave one example of energy recovery during aircraft arrest.
However, how does that connect to MVDC?
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Mid-term: Capitalize on the rotational inertia of generators, essentially spinning energy storage currently not exploited.
It does not say A
To clarify, AC is bad to be the grid, nothing else. But because the grid is connecting everything of different voltage and frequency, it is critical. Therefor, as a whole system, DC grid is better than AC grid.
Tesla cars use induction AC motor, even in a MVDC network including Professor Ma' envisioned (realized in the sub) DC based the motor is AC motor. AC motor is still better than DC (for the moment) because they can be made power denser.
The problem of AC grid (DC's advantage) is that:
- AC grid MUST maintain a highly accurate and stable frequency, 60Hz in US or 50Hz in China and Europe. All consuming devices and the generator must be syncing to that frequency. Primary movers such as GT must use gearbox to adjust to a fixed RPM (RPM=N*Frequency, N is the number of poles). If the primary movers RPM changes due to load (temperature as in Type45's break down), the control system must immediately adjust the gear. If this is not done in time, the generator and consuming devices will be out of sync. This will generate fluctuating voltage and current which can be strong enough to burn the system. Even circuit breaker won't be able to save, think about the blackout in US recently.
- Flywheels are both motor and generator, when it acts as generator, its RPM will drastically drop, that means frequency drop. The launcher is linear motor which also relies on stable frequency. So you can imagine the challenge of regulating the frequency through an AC grid.
Catapult are the biggest consumer in a IEPS CV. Talking about IEPS have to have catapult in the centre of everything.
@taxiya
I don't quite follow your example for the AAG. From what I could find, energy recovery was not a requirement for the system. Whether it is networked to AC or DC for that purpose is irrelevant.
If they have need of that, they could hook it up to a battery/capacitor.
The induction motor is used to accelerate the arrestor shaft in the initial phase and decelerate it in the closing phase, according to the filed patent:
"To complement the energy-dissipating fluid turbine, an electric motor is coupled to the shaft for creating a decelerating torque on the shaft when the line is pulled by the moving object. For aircraft landing applications, an electric motor control system is provided that is configured to cause the electric motor to produce an accelerating torque on the shaft upon initial engagement of the pendant with the arresting hook to allow for a smooth engagement between the pendant and the arresting hook. After a smooth engagement has been obtained, the electric motor control system causes the electric motor to generate a decelerating torque on the shaft to slow the landing aircraft. "
AAG and Catapult are only used by CV, so in other ships, they are irrelevant. On a CV however, considering the motor providing 30% of break in my post, AAG is the second important element in an IEPS.
AAG energy recovery must be fed to DC grid:
It was not a requirement not because they don't want to, but because they can't do it without DC grid. One can not just connect the electricity from AAG to anything without regulating its current. AAG generate AC, the voltage and current alternate directions. Battery and Capacitor charging must be DC, either constant current or constant voltage, or some specially designed DC form varying current or voltage, but never alternating direction.
I must clarify that, I am not saying that PLAN's current arresting gear is recovering the energy as I suggested. What I am trying to say is that it can only be done in a DC grid, and doing so is advantageous.
