VFD Challenges for Shipboard Electrical Power System Design

4Shipboard Power System With LVDC and MVDC for AC and DC Application

The direct current LVDC (up to 1200 VDC) and MVDC (8000 VDC) are being considered for certain applications. The LVDC and MVDC distribution may not be cost effective, as the technology is not matured enough for commercial applications. However, there are major advantages of using the direct current main distribution bus which may be suitable for some applications, including the VFD applications.

Refer to the following Navy standards for recommended use:

Refer to MIL‐STD‐1399 (Navy) for LVDC (Up to 1000 VDC)

Refer to MIL‐STD‐1399 (Navy for MVDC (6000 VDC–18000 VDC)

4.1 The Advantage of Using DC Distribution

The advantages of a direct current (LVDC & MVDC) main distribution system include:

1. The prime mover speed is decoupled from the power quality of the bus. The generator can be optimized for each type of prime mover without having to incorporate reduction gears or speed increasing gears; generators are not restricted to a given number of poles. The speed can even vary across the power operating range of the prime mover.
2. Power conversion equipment can operate at higher frequencies resulting in smaller transformers and other electromagnetic devices.
3. Unlike AC cables, the full cross section of a DC conductor is effective in the transmission of power. Furthermore, power factor does not apply to DC systems and therefore does not influence cable size. Depending on the selected bus voltage, cable weights may decrease ...