A method for determining rectifier-stage output current and/or grid-side currents (iu, iv, iw) of a frequency converter (1) having a passive rectifier (3), an inverter (4), a DC-link with a DC-link inductor (Ldc) and a DC-link capacitor (Cdc) between the rectification stage (3) and the inverter stage (4) is described. In a frequency converter the current information for the grid-side currents (iu, iv, iw) should be obtained without a current sensor at the grid-side (2). To this end the method comprises the step of calculating a current in the DC-link (5) by using at least a voltage value (Urec) and characteristics of the rectifier (3) in the DC-link (5) and/or grid side currents to form a corrected current using the calculated current and a measured current or currents or a fraction of a measured current or currents, or a fraction of a measured current or currents.