A dc-link voltage stability analysis technique for hybrid five-phase open-end winding drives

This paper studies the dc-link voltage stability for a hybrid five-phase open-end winding (OeW) drive operating under carrier based (CB) pulse-width modulation (PWM). The drive consists of a five-phase induction machine, supplied using one three-level and one two-level voltage source inverter (VSI). This configuration is analysed for the case of isolated dc-link rails, while dc-link voltage ratio is considered as an additional degree of freedom. It is demonstrated that different dc-link voltage ratios lead to the different overall number of voltage levels across stator windings. Modulation strategies are investigated and their performances are analysed from the dc-link voltages stability point of view. An analytical method for dc-link voltage stability analysis is presented. Results show that the four-level configuration always leads to stable dc-link voltages, regardless of the modulation strategy. On the other hand, if six-level configuration is combined with modulation strategies that lead to an optimal harmonic performance, not all dc-link capacitor voltages will be in balance depending on the operating conditions