A Comparison of Induction Machine Rotor Flux Observers in Stationary Reference Frame for Rotor Flux Position Estimation

For induction machine field-oriented controls, it is important to have a good estimation of the rotor flux position to achieve torque accuracy. In this paper, the impact of motor parameter estimation error such as L
m
(magnetizing inductance), R
s
(stator resistance), R
r
(rotor resistance), L
lr
(rotor leakage inductance) and L
ls
(stator leakage inductance) on position estimation error and torque achieved error is derived. Next, two stationary reference frame flux observers are compared: the Gopinath style observer and the Kubota Style observer. The closed loop transfer function of the Kubota style flux observer is derived. Using the transfer function, the rotor flux magnitude and angle are compared in presence of motor parameter estimation inaccuracies. It is shown that the Kubota style observer has better parameter insensitivity specially at low speeds. A discretization technique of predictor corrector method was also demonstrated for the Kubota style observer that produced stable performance under varying speed range.