Sensorless very low-speed and zero-speed estimations with online rotor resistance estimation of induction motor without signal injection

In the speed-sensorless control of the induction motor, the machine parameters (especially rotor resistance R-2) have a strong influence on the speed estimation. It is known that the simultaneous estimation of speed and R-2 is impossible in the slip-frequency-type vector control, because the rotor flux is constant. In addition, the output voltage error due to the deadtime and the voltage drop of the inverter influences the rotor flux estimation, but the simultaneous compensation of the output voltage and stator resistance R-1 is very difficult. In this paper, the R-2 estimation without adding any additional signal to the stator current is proposed. In the high-frequency range, R-2 is estimated in the transient state and, in the very low-frequency range, R-2 is estimated in proportion to the estimated R-1 when the ideal voltage source by the power op-amp is used instead of the voltage-source inverter to avoid the output voltage error. Using these algorithms, the low-speed estimation was possible and the zero-speed control was achieved under the 10%-40% load condition. This paper clarifies that the zero-speed estimation is possible with the stator and rotor resistance estimations when the output voltage is ideal.