VARIABLE SPEED DRIVE SYSTEM, METHOD FOR OPERATING A VARIABLE SPEED DRIVE SYSTEM AND METHOD FOR REFRIGERATING A HYDROCARBON STREAM

摘要

A variable speed drive system employing an electric motor and a frequency converter arranged between an AC power source and the electric motor is operated. The frequency converter functions to convert AC power obtained from the AC power source at a source frequency to converted power at a variable drive frequency. A mechanical assembly can be coupled to the electric motor. Electric modulation circuitry is provided interacting with the frequency converter. It is arranged to impose fluctuations, independently from any torsional excitation in the mechanical assembly and the AC power source, in the inter-harmonic frequencies of inter-harmonic currents generated in the frequency converter.

主权项

1. A method of operating a variable speed drive system comprising an electric motor and a frequency converter arranged between an AC power source and the electric motor, the method comprising the steps of:
converting AC power obtained from the AC power source at a source frequency to converted power at a variable drive frequency that is unequal to the source frequency, wherein the converted power comprises inter-harmonic currents having additional frequency components at inter-harmonic frequencies that are unequal to integer multiples of the source frequency; powering the electric motor with the converted power; driving a mechanical assembly comprising at least a drive shaft and a mechanical load with the electric motor; causing fluctuations in the inter-harmonic frequencies independently from any torsional excitation in the mechanical assembly and the AC power source.