This paper proposes sensorless direct torque control for interior permanent-magnet synchronous motors using square-wave-type stator flux injection
at low-speed regions. The conventional sensorless method injecting sinusoidal type stator flux injection has complex signal processing and time delay
owing to the use of digital filters such as a band-pass filter and low-pass filter. In the proposed method injecting square-wave-type is advantageous in that the signal processing of estimating the rotor position is simplified and the time delay decreases because the low-pass filter is eliminated. The
validity of our proposed method is demonstrated via simulation and experimental results.