The invention relates to a method for the open-loop or closed-loop control of an asynchronous machine with or without speed feedback, the asynchronous motor being controlled by a control device (converter or servo converter). First of all, a voltage vector rotating at a rotary field frequency is specified and impressed, both the rotary field frequency and the voltage vector being determined by an open-loop or closed-loop control based on a voltage-frequency characteristic curve configured in any manner and the voltage vector being adapted by a cos φ closed-loop control. Desired values of cos φ are calculated using rating plate data and equivalent circuit diagram data for an optimum-loss or loss-optimized operation of the asynchronous machine for the calculation of cos φdesired value, which results in optimized-loss operation. A value for cos φactual is then determined using the impressed voltage vector and a current vector or using the real power and apparent power. Thereafter, the difference is calculated between cos φdesired value and cos φactual and a cos φ closed-loop control is fed with this input difference. A control value of the controller for cos φ is calculated and restricted and the voltage vector is adapted by the control value of the cos φ closed-loop control.