There are two types of flux estimators, current model estimator and voltage model estimator. Compared
with the voltage model, the current model estimator is more suitable for low speed application, in spite of
sensitivity to parameter variations [23]. As a result, the flux estimator used in this project is the current
model estimator implemented in Indirect Field Orientation(IFO), which indicates that the quantities used
for the flux estimation are currents taken from the d − q system. With ~is from the d − q system and the
electrical rotor angular speed ωr as inputs, the flux determination equations for the estimator can be derived
from Eq. 5.15b. Splitting Eq. 5.15b into real and imaginary part and assuming that ~
R = Rd + j0; since
this is the wanted orientation of the d − q system, the rotor flux equation can be expressed as