## 5 Discussion  
In this paper, it was shown that the current and torque ripple of a nominally delta-connected machine can be decreased by utilizing a simple delta-star changeover technique that is commonly used to extend the base-speed region, efficiency, and power factor of IM drives. Since almost all papers dealing with the control of three-phase AC machines silently assumed that the machine winding is star connected, this paper also analyzes necessary modifications in the transformation of the measured currents of a delta-connected machine along with the differences in the inverter voltage vectors and their reconstruction. Another  
Figure 16: Comparison of the motor phase voltage in a star configuration with the inverter line-to-line voltage (i.e., the phase voltage for a delta configuration); DC-link voltage 560 V.  
Figure 15: XY chart of the estimated stator flux linkage vector in the stationary \(\alpha\beta\) coordinate system; reference speed 750 RPM, reference stator flux 1.7 Wb, load torque 0 Nm: (**a**) star-connected winding; (**b**) delta-connected winding.  
theoretical analysis presented in the paper was focused on the constraints that are imposed on the flux, speed, and torque control after the winding changeover from delta to star.  
To realize the proposed approach, it is essential to respect the actual machine winding connection in the control algorithm. It was shown in simulations that not respecting the winding topology leads to inaccurate flux and torque estimation. If the algorithm supposes a delta winding connection and the machine is star-connected, then the motor operates in an under-excited state, with the actual stator flux being approximately \(\sqrt{3}\) times smaller than the reference one. On the other hand, if the algorithm supposes a star-connected winding and the machine is delta-connected, then the motor operates in an over-excited state, with the actual stator flux being approximately \(\sqrt{3}\) times higher than the reference one.  
The experiments were predominantly focused on validating the proposed method by the analysis of the current THD and consumed electric power in multiple drive operating points. It was confirmed that if the operating point is achievable in both winding configurations, then the switchover to star leads to reduced current THD and less consumed power. The THD reduction was particularly significant at light mechanical loads.  
The authors' future research will focus on defining suitable conditions for the online winding changeover to maximize the power savings. Another important task will be to develop an approach that will ensure that the actual transition, either with a mechanical contactor semiconductor switch, is as smooth as possible.  
Conceptualization, O.L.; methodology, O.L.; software, P.K. ([PERSON]); validation, O.L. and P.K. ([PERSON]); formal analysis, O.L.; investigation, O.L.; resources, O.L. and P.K. ([PERSON]); data curation, P.K. ([PERSON]); writing--original draft preparation, O.L. and P.K. ([PERSON]); writing--review and editing, J.B. and P.K. ([PERSON]); visualization, O.L.; supervision, J.B.; project administration, O.L.; funding acquisition, P.K. ([PERSON]). All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Student Grant Agency of the Czech Technical University in Prague under grant No. SGS21/116/OHK3/2T/13.  
Not applicable.  
Data Availability Statement: Data is contained within the article.  
The authors declare no conflict of interest.