The direct torque method performs very well even without speed sensors. However, the flux estimation is usually based on the integration of the motor phase voltages. Due to the inevitable errors in the voltage measurement and stator resistance estimate the integrals tend to become erroneous at low speed.
The direct torque method's ability to function well without speed sensors is a benefit, but it relies on accurate voltage measurements and stator resistance estimates for flux estimation. At low speeds, these estimations are prone to error, leading to inaccurate flux calculations.