Vector control of a speed sensor-less induction motor at very low speed
DONG Lei, LI Yongdong(Department of Electrical Engineering, Tsinghua University, Beijing 100084, China)
The rotor flux angle of an induction machine at very low speed cannot easily estimated; therefore, an independent highfrequency signal was injected in to the terminal of an induction motor to estimate the flux angle. This paper presents an analysis of an induction motor model with a highfrequency fluctuating signal injection. When the highfrequency fluctuating signal is injected into the terminal of the induction motor, the difference between the impedance of the d and qaxis of the synchronous rotating reference frame can be measured. The rotor flux angle is then tracked by tuning the space vector of the highfrequency signal for vector control of induction motors at very low speed. Experimental results verify that the algorithm is robust against parameter variations and load changes and that the rated torque can be put out at very low speed including zero.