Speed control using direct torque control of induction motor
Without shaft speed feedback, the steady state speed error of an induction motor controlled by a VFD is likely to be 0.1% to 0.8% of rated speed. The error would include any speed change due to change in load plus changes due to variations in power-line voltage and temperature from a cold start. The error would be about the same for an excellent implementation of direct torque control and some other control strategies. The superiority of direct torque control is realized mostly in dynamic performance and performance at very low operating speeds.