Steady State Modeling of Series-Connected Five-Phase and Six-Phase Two-Motor Drives

Two series-connected two-motor drive systems with a single inverter supply have been proposed recently. The first one consists of two five-phase machines supplied from a single five-phase inverter, while the second one comprises one symmetrical six-phase machine, a three-phase machine and a single six-phase inverter. It has been verified experimentally that, by introducing an appropriate phase transposition in the series connection, completely independent dynamic control of the two machines can be realized using principles of vector control. Detailed dynamic models in the stationary common reference frame have also been reported for these two drive systems. These dynamic models are taken here as the starting point and equivalent circuit representation of the series-connected two-motor drive systems 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. This significantly facilitates analysis of the steady state drive behavior and provides analytical tools necessary for the inverter design. DC link voltage required for operation of the two series-connected machines is further investigated. It is shown that the specific winding connection leads to a dc voltage requirement that is smaller than it would have been had the windings of the two machines been connected directly in series. Theoretical considerations are verified by experiments on the series-connected five-phase two-motor drive