**7. Discussion**

It is clearly observable from the provided experimental results, that the seeking algorithm does not operate properly at transients. Furthermore, its behavior depends on the sign of the torque derivative: if it is positive, the estimated angle fluctuates near its previous value, if the derivative is negative, the estimated angle goes to a lower or higher limit, depending on the direction at the previous stage. As a result, the constraints design plays an important role in the dynamic performance by limiting this uncontrollable change.

The experimental results showed that the operation of the seeking algorithm with fixed constraints results in a poorer dynamic and significantly decreases motor efficiency in dynamic modes. Therefore, this method may be recommended only for simple systems, which mainly operate under constant load torque.

The seeking algorithm with constraints designed using a rated MTPA curve with gaps, demonstrates better dynamic and efficiency than the same algorithm with the fixed constraints. It demonstrates acceptable results in the regions, where the true MTPA curve is close to the rated curve. However, its operation is not optimal at the loads, where the true MTPA trajectory significantly deviates from the rated MTPA curve and leaves the area enclosed by the constraints. The experimental motor is a good example of this case, which is illustrated by Figure 17. As a result, this method of constraints design can be suggested for motors, where the MTPA trajectory does not significantly deviate from the rated MTPA trajectory.

It can be observed that the operation of the seeking algorithm with constraints, which is designed according to the proposed method, demonstrated better efficiency and dynamic behavior. Therefore, it is recommended for the motor drives, where the motor was designed for operation with considerable saturation and where the MTPA curve significantly deviates from the curve constructed for the unsaturated parameters.

At the same time, it should be noted that the operation of the seeking algorithm with a different set of constraints at a constant or slowly changing load torque is similar and they differ only in dynamic.
