Method for operating a drive system comprising a rectifier (1, 21) and at least one inverter (3, 20) having an electric motor, wherein the electric motor is connected to the AC voltage-side terminal of the inverter (3, 20), wherein the DC voltage-side terminal of the inverter (3, 20) is connected to the DC voltage-side terminal of the rectifier (1, 21) by means of at least one inductor provided in addition to the line inductor, wherein a capacitor, in particular a non-polar capacitor, in particular a film capacitor, is connected to the DC voltage-side terminal of the inverter (3, 20) and/or to the DC voltage-side terminal of the rectifier (1, 21), wherein a series circuit formed from a resistor and a controllable semiconductor switch, i.e. a brake chopper, is connected to the DC voltage-side terminal of the inverter (3, 20) and/or to the DC voltage-side terminal of the rectifier (1, 21), wherein the brake chopper is operated at a single frequency f in the same time period in which the brake chopper is operated, wherein the voltage feeding the series circuit, i.e. the DC link voltage, in particular therefore the voltage applied to the DC voltage-side terminal of the inverter (3, 20), is detected, characterised in that the detected value of the voltage, i.e. the DC link voltage, is supplied as a digital serial data stream both to a first digital filter, in particular an FIR filter, and to a second digital filter, in particular an FIR filter, wherein the second digital filter is started up with a time lag relative to the first digital filter, wherein the output signals of both filters are supplied to respective comparison means to be compared with a first and a second threshold value, wherein the output signals of the comparison means are logically gated to a signal generated by a controllable time base, in particular by a controllable clock generator, in order to generate an actuation signal for the brake chopper. wherein the electric motor is connected to the AC voltage-side terminal of the inverter (3, 20), wherein the DC voltage-side terminal of the inverter (3, 20) is connected to the DC voltage-side terminal of the rectifier (1, 21) by means of at least one inductor provided in addition to the line inductor, wherein a capacitor, in particular a non-polar capacitor, in particular a film capacitor, is connected to the DC voltage-side terminal of the inverter (3, 20) and/or to the DC voltage-side terminal of the rectifier (1, 21), wherein a series circuit formed from a resistor and a controllable semiconductor switch, i.e. a brake chopper, is connected to the DC voltage-side terminal of the inverter (3, 20) and/or to the DC voltage-side terminal of the rectifier (1, 21), wherein the brake chopper is operated at a single frequency f in the same time period in which the brake chopper is operated, wherein the voltage feeding the series circuit, i.e. the DC link voltage, in particular therefore the voltage applied to the DC voltage-side terminal of the inverter (3, 20), is detected, characterised in that the detected value of the voltage, i.e. the DC link voltage, is supplied as a digital serial data stream both to a first digital filter, in particular an FIR filter, and to a second digital filter, in particular an FIR filter, wherein the second digital filter is started up with a time lag relative to the first digital filter, wherein the output signals of both filters are supplied to respective comparison means to be compared with a first and a second threshold value, wherein the output signals of the comparison means are logically gated to a signal generated by a controllable time base, in particular by a controllable clock generator, in order to generate an actuation signal for the brake chopper.