Patent ID: 8054019
Filing Date: 2011-11-08
Classification: B66B,H02P

Abstract:
1. A method for controlling a three-or-more-phase motor driven by a frequency converter, the frequency converter comprising a number of change-over switches, of which at least one change-over switch for each motor phase, the change-over switches being fitted in the motor phases and comprising controllable change-over contacts, the method comprising: determining magnitudes of phase currents of the motor; controlling the change-over switch to a continuously conducting state in one motor phase at a time; switching the change-over switches in the other motor phases at a switching frequency substantially higher than a frequency of a fundamental wave of a phase voltage or the phase current; and controlling the change-over switch of the motor phase with a highest absolute value of the phase current or a phase current reference to a continuously conducting state for a period of time during which the absolute values of the phase current or the phase current reference in the phases with the highest and a next highest absolute values of the phase current or the phase current reference differ from each other by at least a predetermined limit value.