VFD Challenges for Shipboard Electrical Power System Design

6Shipboard Power Quality and VFD Effect

Shipboard power generation and distribution system design and development must be in accordance with the applicable rules and regulations to ensure that power source characteristics are suitable for the intended ship service applications. The shipboard power systems are classified in many different categories such as type‐I, type‐II, emergency, essential, non‐essential, vital, non‐vital, sensitive, non‐sensitive, etc. The commercial ship power characteristics started with MIL‐STD‐1399 with voltage, frequency tolerances as well as total harmonic distortion limits. The ship power system with variable frequency drive generates electric noise in many different forms deteriorating the power quality in the ship service power distribution system.

The variable frequency drives with various configuration such as six pulse drive, 12 pulse drive, 18 pulse drive, Active front end, Pulse width modulation and many others generate many different levels of harmonics. These harmonics are often much higher than the regulations allow. There are many systems available to deal with harmonic to bring down to acceptable levels. In some cases the total harmonic levels are also manipulated to a higher level giving understanding that higher level of harmonics will have no effect on the overall system.

The harmonic level may be acceptable from the VFD equipment supplier, but detrimental to the shipboard power distribution system as well as other electrical equipment ...