Importance

Loading Importance Indicators...

Abstract

The invention relates to a method of determining rotational speed, size and instantaneous direction of a residual flux of an inverter-supplied squirrel cage induction machine, to be used for starting the squirrel cage induction machine when there is a rotating residual flux (.PSI..sub.s) in the machine (1) and a total leakage inductance (.sigma.L.sub.s) of the machine is known. According to the invention measures are taken, comprising steps of short-circuiting stator windings; measuring a first stator current vector (i.sub.s1) and switching off the stator circuit at the end of a first time period (T.sub.1); short-circuiting the stator windings once more after a second time period (T.sub.2) from the end of the first time period (T.sub.1); measuring a second stator current vector (i.sub.s2) and switching off the stator circuit after a time identical with the first time period (T.sub.1) from the second short-circuiting; determining the frequency (.PSI..sub.s) of the residual flux (.omega..sub.s) on the basis of the directions of the first and the second stator current vector (i.sub.s1, i.sub. s2) and the lengths of the first and the second time period; determining the size of an absolute value ( .PSI..sub.s ) of the residual flux on the basis of the total leakage inductance (.sigma.L.sub.s) of the squirrel cage induction machine and the first or the second stator current vector (i.sub.1, i.sub.s2 and determining the instantaneous direction of the residual flux (.PSI..sub.s) on the basis of the direction of the first or the second stator current vector (i.sub.s1, i.sub.s2).

Loading the Abstract Image...

First Claim