System for operating electric motors

A power supply system for controlling rotating electric machines or motors comprising a propellor, especially heavy machines such as ship motors, the power supply system comprising:

• at least one motor driven by a three phase AC power supply;
• at least two parallel units connected to between the power supply and the motor, comprising a frequency controller configured to provide power within a chosen frequency range to provide a stepless control of the rotation speed of the motor, and a first switch, and also comprising a control unit connected to the frequency controller and the first switch:
• a synchronization unit connected to the AC power supply and being configured to measure chosen parameters therein, comprising voltage, frequency and phase sequence for the AC power supply, the synchronization unit also being connected to frequency controller, the frequency controller being configured to synchronize the power supplied to the motor to the measured parameters to a predetermined RPM before connecting or disconnecting the parallel units;
• and
• wherein the propellor comprises a pitch control adjusting the thrust of the machine and wherein the control unit is connected to the pitch control and configured to adjust the pitch of the propellor, the thrust thus being related both to the RPM and propellor pitch.