Symmetrical six-phase PWM methods using similar and dissimilar zero-sequence signals injection

Multiphase machine is used where safety and better fault tolerance are desired. Among the various types of multiphase machine, six-phase machine is more attractive to the researchers as it can be easily obtained by rewinding conventional three-phase machine. For six-phase machine with two isolated neutrals, three-phase carrier based PWM (CBPWM) methods can be directly applied onto each of the three-phase windings. Furthermore, zero-sequence signals can be injected to provide additional benefits such as better dc-bus utilisation, better THD, lower switching losses etc., similar to three-phase scenario. However, there is another possibility of operation for six-phase machine, where different combination of zero-sequence signals injection can be applied onto the two three-phase windings. In this paper, the performances of such CBPWM using similar and dissimilar zero-sequence signals injection are investigated. It is found that though different combinations of zero-sequence injection are possible, the best current THD is still obtained when SVPWM (Min-Max) zero-sequence signals are used for both three-phase windings.