How is the speed of the propeller shaft directly coupled to an AC synchronous drive motor changed when powered by either a dedicated or integrated constant frequency alternator in an AC diesel-electric drive system?

Correct Answer: Option C — Varying the output frequency of the power converter

When using a constant frequency alternator, the generator speed cannot be varied to control the motor. Instead, a power converter (VFD) is placed between the generator and the motor. This converter rectifies the fixed frequency input and inverts it to a variable frequency output to control the motor's synchronous speed.