It can be seen from Fig. 5(a) that when the resistance
change, the waveform of the circle stator flux linkage produces
central offset with rather big estimation errors by comparison
to Fig. 4(d) and Fig. 6(d). The main reason for the errors is that
we use the formula (1) to estimate the stator flux linkage in the
traditional DTC. The stator resistance Rs is considered as a
constant in the formula (1), but the value of the actual stator
resistance Rs will increase with the temperature change of the
servo motor. When the value is not accord with the formula (1),
it certainly will lead to the estimation error of the stator flux
linkage. Fig. 5(b) shows the electromagnetic torque also
changes a lot when the speed suddenly changes at the
beginning and the time 0.2s. The maximum electromagnetic
torque is about 12.5Nm in the conventional DTC. That value is
larger than that in the EKF-DTC in Fig. 4(e) and Fig. 6(e).