# Comparative Study and Overview of Field-Oriented Control Techniques for Six-Phase PMSMs
## 5 Discussion  
Two approaches of field-oriented control for a six-phase PMSM were segregated according to the number of current controllers for flux- and torque-producing components. An overview of voltage modulation techniques was presented for both cases, where double zero-sequence modulation was realized. To ensure a transparent and meaningful comparison of these two approaches and to highlight their real differences and drawbacks in the examined six-phase PMSM, control structures were demonstrated using a basic shape, without additional algorithms for drive quality improvement. Because two loops of a control algorithm were run in parallel for control in two orthogonal systems (2 d-q), as shown in Figure 2, the execution time of the application might be longer than in one orthogonal system (1 d-q), shown in Figure 4. Such an application requires a more powerful MCU, which would lead to a higher price of the control unit or a longer sample time, thus leading to inaccuracies. This problem becomes more significant in \(n\) d-q control, for 9-, 12-, and 15-phase machines. The 1 d-q control technique requires a shorter computation time and brings the advantage of a standard field-oriented control system, with only one set of torque/flux-producing components. On  
Figure 16: Position loop step response: (**a**) 2 d-q; (**b**) 1 d-q. Figure 17: Position loop frequency analysis: (**a**) 2 d-q; (**b**) 1 d-q. the other hand, the 2 d-q technique allows using a standard, well-known transformation for the control of three-phase machines. Requirements for the execution time of a control algorithm would of course vary when utilizing advanced algorithms, such as VSD or various decoupling methods. The 2 d-q technique is beneficial for natural current sharing between two three-phase windings across all load conditions (Figure 8). Since each three-phase winding is controlled separately, various decoupling methods between them can be managed directly in the d-q control system. Nevertheless, the influence of the phase current higher-harmonic spectra over the whole-load conditions will not be cancelled in 2 d-q, neither 1 d-q control without additional algorithms. To control harmonics and consequently decrease losses, the VSD method can be utilized, with a shorter execution time for 1 d-q control, whereas the current sharing problem can be solved using the VSD method too. Both control approaches are able to achieve the same results in terms of current in the synchronous reference frame, speed, and position, as shown in Figures 11-17. This applies to standard operation in both steady and dynamic states. However, the two approaches do not behave similarly in terms of phase current, as shown in Figure 8.  
In addition, the proposed results show the correctness of the mathematical models and transfer functions for both approaches, previously presented by the author of this paper in [37]. The simulations of dynamic models are displayed in Figures  
On the other hand, the correctness of the control unit function, as another safety requirement, can be verified through a comparison of the algorithms running in parallel paths (Table 2). Signals 3 vs. 3 represent the comparison of three-phase systems. This can be accomplished with speed or torque, but is often done using current, since its high dynamic. Microcontroller or software functionality was the point of comparison shown in Table 2, where the same control algorithms (for the same three-phase star) were run in parallel and compared. Any difference within a system denotes an error in the control unit (physical layer of processor or software). Such a technique should be available even in conditions of one three-phase system fault, which can be more elegantly demonstrated using the 1 d-q control structure, because 2 d-q control would have to run four three-phase control loops to achieve the same asset.