Independent Control of Two Five-Phase Induction Machines Connected in Parallel to a Single Inverter Supply

Multi-phase machines possess additional degrees of freedom, which can be utilised to control other machines within a multi-motor drive system. The stator windings of the multi-phase machines can be connected in series in such a manner as to enable independent control of each machine using vector control principles, although the complete multi-motor drive system is supplied from a single multi-phase voltage source inverter (VSI). One shortcoming of the series arrangement is the need to bring out to the terminal box of an n-phase machine both beginnings and endings of each phase. Parallel connection of machines would circumvent this shortcoming, since the machines can have the neutral point connected within the machine. This paper therefore discusses such a parallel connection of two five-phase machines. The drive configuration and a suitable control scheme are detailed and verification of the concept is provided by simulation. Dynamic model in the stationary reference frame is given and equivalent circuit representation of the parallel-connected five-phase two-motor drive system is developed. It is shown that, due to orthogonal relationship of the two planes that are used for independent control of the two machines, phasor approach can be applied at each of the two fundamental frequencies used to control the two machines. The paper finally explains that, although parallel multi-phase multi-motor drives are feasible and in principle offer the same quality of dynamic performance as series-connected multi-phase multi-motor drive systems, they do not hold a real prospect for industrial applications