Observer using low-frequency injection for sensorless induction motor control-parameter sensitivity analysis

The zero-frequency vector control of an induction motor without a speed sensor has proven to be a very difficult task. Uncertainty and variation in the electrical parameters of the motor deteriorate the performance of fundamental-wave flux observers as the frequency approaches zero, and observers based on high-frequency signal injection rely on motor-specific phenomena. A new method has been proposed, where a low-frequency current signal is injected in the estimated rotor flux direction. If there is an error in the orientation, the signal gives rise to a torque oscillation and affects the back-EMF through the mechanical system. The phenomenon makes it possible to reach sensorless zero frequency operation. This paper shows that the method is insensitive to the variation of the motor parameters. Experiments confirm the result.