ABSTRACT
The variable-frequency drives (VFDs) for ac motors were initially developed in the 1970s for oil refineries, where numerous motors are used to pump oil all year around. Although costly at the time, the significant energy saving at the end of every month paid back the drive cost within a few years. Since then, for the rest of the 20to 30-year life of the drive, the VFDs added to corporate profits. Most ships now use VFDs with pumps for water, oil, refrigeration, and with fans for air ventilation. Most cruise ships use VFDs for propulsion motors as well.
