Patent ID: 7737652

Claim:
A method for safely limiting a torque of a frequency-converter-fed three-phase motor operated under field-oriented control, comprising the steps of: a) measuring phase currents of the three-phase motor, b) forming sum current signals from the measured phase currents and checking on two channels that each of the sum current signals has a sum value of zero, c) determining on two channels a rotor position angle of the three-phase motor, d) computing on the two channels from the measured phase currents corresponding torque-forming current components as a function of the rotor position angle, e) monitoring the computed torque-forming current components and determining if the computed torque-forming current components exceed a predetermined current component limit value, f) crosswise comparing the computed torque-forming current components for equality, and g) generating a pulse cancellation signal when the computed torque-forming current components exceed a limit value or are not equal.