Abstract: The present invention relates to a method for controlling the power to be transferred via a mains inverter, the mains inverter (VVS) being arranged to transfer electric power in both directions between the n-phase AC main system (U) and the DC intermediate circuit (1).

Abstract: A method and an apparatus for direct torque control are specified for a three-phase machine fed via a harmonic filter, which method manages as far as possible without any major adaptation to already known DTC methods and DTC apparatuses. In addition, the oscillations caused by the filter are intended to be damped effectively. This is achieved in that a current flowing through the filter and/or a filter output voltage are/is measured, and the reference flux value and the reference torque value are corrected on the basis of the measured voltage and/or of the measured current. The correction comprises a transformation of the filter output voltage into a first component at right angles to a stator flux and into a second component parallel to the stator flux, as well as a reduction in the reference torque and flux values in proportion to the oscillating part of the filter output voltage.

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.

Abstract: The present invention relates to a method for controlling an ac motor supplied by an inverter having several switches. In order that the torque can be adjusted to be as desired as rapidly as possible both with maximum voltage and in the vicinity thereof, one proceeds in accordance with the invention in such a way that a value (.DELTA..gamma.) representing the difference between the reference value and actual value of the angle between the stator flux and rotor flux of the motor is determined on the basis of a value representing the requirement for torque change of the motor, e.g. by means of the difference (.DELTA.T) between the reference valve (T*) and actual valve (T) of the torque, and a quantity representing the magnetic state of the motor, the next switching moment of the switches of the inverter, i.e. the so called limit between flux sectors (.DELTA..phi.), is shifted with a first quantity (k.sub.1 .DELTA..gamma.) proportional to the determined differential value to change the angle (.gamma.