Sensorless Control for Induction Machines Based on Square-Wave Voltage Injection
In this study, a sensorless control method for induction machines, using a square-wave voltage injection into the q-axis. This study considered two nonideal phenomena that severely degrade the performance of sensorless controls for induction machines. Multiple saliency problems can be overcome by injecting a square-wave signal into the estimated synchronous reference frame. By injecting the square-wave signal into the q-axis, the robustness of rotor flux position estimation with respect to load conditions and operating speed can be enhanced. Variation of saliency characteristics can easily be compensated by a linear function of the torque command. The experimental results showed reasonable performances, even when the reference speed changed slowly near zero speed and when load torque disturbances occurred at low frequencies, including zero stator frequency.