A METHOD FOR DETERMINING THE ROTATIONAL SPEED, MAGNITUDE AND INSTANTANEOUS DIRECTION OF A FLUX

摘要

The present invention relates to a method for determining the rotational speed, magnitude and instantaneous direction of a flux, said method intended to be used for synchronizing a mains inverter (VVS) arranged to transfer electric power in both directions between an n-phase AC main system (U) and a DC intermediate circuit (1) with the AC main system (U). When there is no current flowing via the mains inverter, the method comprises the steps of short-circuiting the phases of the AC main system for a determined period, and measuring the first short-circuit current vector during the short circuit; short-circuiting the phases of the AC main system again for a determined period after a certain period from the first short circuit, and measuring the second short-circuit current vector during the short circuit; determining the phase sequence, i.e. the direction of rotation, and frequency of the AC main system on the basis of the short-circuit current vectors and the difference of their measuring moments; determining the direction of the flux by rotating the second short-circuit current vector 90 DEG in a determined direction of rotation; and measuring the DC intermediate circuit voltage and determining the magnitude of the flux on the basis of this measured direct voltage.