Independent vector control of a seven-phase three-motor drive system supplied from a single voltage source inverter

Vector control principles enable independent flux and torque control of an AC machine by means of only two stator d-q currents. This means that in AC machines with a phase number greater than three there exist additional degrees of freedom, which are nowadays most frequently looked at as a mean of enhancing the overall torque production of a multiphase machine through injection of higher harmonics. However, these additional degrees of freedom can be used to control independently other machines within a multimotor drive system. In order to do so, it is necessary to connect in series stator windings of all the multiphase machines, with an appropriate phase transposition, and supply the stator windings of the multimachine set from a single current controlled voltage source inverter (VSI). The concept is introduced in this paper using the general theory of electrical machines. Verification of the proposed seven-phase three-motor system is provided by simulation. The main advantage of the proposed drive configuration over the standard three-phase solution is the reduction of the number of inverter legs from nine to seven.