Abstract—In the sensorless speed control of induction motors with direct field orientation, the rotor flux and speed information are dependent on the observers. However, the exact values of the parameters that construct the observers are difficult to measure and changeable with respect to the operating conditions. When the motor parameters are changed and thus different from the preset values, the estimated flux will deviate from the real values. To make flux estimation robust to parameter variations, a flux observer is proposed in the paper. The stability of the method is proven by Lyapunov theory.