**8. Conclusions**

An optimization procedure for a fuzzy logic speed controller used in the predictive current control of an induction machine is presented in this paper. The topology of the controller and the choice of optimization decision variables are explained, along with the

chosen limits of the optimization search area. Several different criteria for objective function value calculation are investigated, and the one that produces the best results (small torque overshoot and good speed reference tracking) was the single-objective integral squared error criterion with overshoot limitation using the weighing factor. A drive model with an omitted inverter, modulator, and observer is used for the optimization procedure. This kind of model produces torque and current responses without any ripple or added harmonics. To verify the improvement of the method, optimized parameters are plugged into the full drive model, which produces ripple in the current and torque responses. Torque ripple affects the speed response, which consequently produces a larger speed derivative, which is used as the input of the fuzzy controller. Because of the larger speed derivative during the operation of the drive, high control action can be expected when this derivative becomes even larger, which is why a large amount of torque overshoot still persists when the drive is loaded with nominal torque. By reducing the proportional and integral gains of the controller, this overshoot can be reduced significantly, while still preserving a good speed response. A comparison between the proposed method and several different model predictive control methods is conducted, and proposed method shows a 55% average improvement regarding speed tracking error and 74% average improvement regarding torque overshoot.

**Author Contributions:** Conceptualization, T.V.; methodology, T.V.; software, T.V.; validation, T.B.; formal analysis, T.B. and V.J.Š.; investigation, T.V.; resources, T.V.; data curation, T.B. and V.J.Š.; writing—original draft preparation, T.V.; writing—review and editing, T.B.; visualization, T.V.; supervision, M.B.; project administration, M.B.; funding acquisition, M.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported in part by the Croatian Science Foundation under the project number UIP-05-2017-8572.

**Conflicts of Interest:** The authors declare no conflict of interest. The founders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
