METHOD AND APPARATUS FOR CONTROLLING A MOTOR

摘要

The invention concerns a method and an apparatus for controlling a three-or-more-phase motor driven by a frequency converter. In the method, a change-over switch of the frequency converter is controlled to a continuously conducting state and at the same time the phase voltages or phase currents of the other phases are controlled by switching the change-over switches in those motor phases at a switching frequency substantially higher than the frequency of the fundamental wave of the phase voltage or phase current. The apparatus comprises in conjunction with the frequency converter a number of change-over switches, at least one change-over switch for each motor phase. The change-over switches comprise controllable change-over contacts. The apparatus further comprises in conjunction with the frequency converter means for determining the motor phase currents and means for controlling the change-over contacts.