Patent ID: 7141947

Claim:
A braking chopper for dissipating braking power away from the direct-current rails of an AC drive system, said braking chopper being an inverter unit (INU) consisting of upper- and lower-branch controllable semiconductor switches (V 1 –V 6 ), wherein the inverter is connected by its output connectors to the direct-current rails (DC) via a resistor unit, characterized in that the resistor unit comprises two resistors (R 1 , R 2 ), of which the first is connected to the positive direct-current rail (DC+) and the second to the negative direct-current rail (DC−), wherein both lower-branch and upper-branch semiconductor switches are turned on during braking, and wherein one brake resistor is controlled by the lower-branch switch of only one phase and the second brake resistor by the upper-branch switch of another phase.