A novel nine-phase four-motor drive system with completely decoupled dynamic control

The paper proposes a novel configuration of a nine-phase drive system, in which four ac machines have stator windings connected in series. By applying an appropriate phase transposition in the series connection of the stator windings, it becomes possible to realize completely independent vector control of the four machines although a single current-controlled nine-phase voltage source inverter is utilized as the supply for the whole drive system. Theoretical background of the concept, which is independent of the ac machine type, is at first presented. The feasibility of the proposed four-motor drive is then verified by simulation. Finally, main advantages and shortcomings of this drive configuration are addressed, in comparison to an equivalent four-motor three-phase drive.