Nonlinear speed observer for high-performance induction motor control

In this paper, we consider tbe problem of estimah ing the angular velocity of an induction motor using encoder measurements. -0 methods are compared, In tbe first method, tbe speed is found by calculating the backward differes~ce of tbe position measurem ent and low-pass filtering the result. In the second method, the velocity is estimated using a nonlinear observer constructed using the known dynamic model of the induction motor. Tbe performance of the two methods is evaluated in the context of their use for velocity feedback in a high-performance fieldoriented control law. Experimental results demonstrate that the sped observer leads to a smoother operation of the motor in closed-loop. With the estimator based on differentiation, either tbe delay imposed by the low-pass filter is too large to maintain high bandwidth feedback, or the fluctuations in tbe estimated speed are so large that much more energy ends up being dissipated to achieve the same control task.