Vector control of a five-phase series-connected two-motor drive using synchronous current controllers

A novel concept for multi-motor drive applications has been developed recently, which enables dynamically decoupled control of all the machines in the group, although a single voltage source inverter is used as the supply. The concept requires utilization of multi-phase machines, whose stator windings have to be connected in series with an appropriate phase transposition, and it has been developed under the assumption that the inverter currents are controlled in the stationary reference frame. This article addresses the possibility of using synchronous current controllers within such a multi-motor drive system in order to realize fully decoupled dynamic control of all machines. The considerations of the article, although restricted to the series-connected two-motor five-phase drive system, can be extended to any other number of phases. It is shown that, in contrast to the situation that arises when current control is performed in the stationary reference frame, current control in the rotating reference frame requires appropriate modifications of the basic vector control scheme. The need for these modifications is explained and a method of realizing completely independent vector control of the two machines is proposed. The method is developed using rigorous mathematical modeling for the complete two-motor drive system. It is shown that completely decoupled dynamic control of the two machines results only if the calculation of the decoupling voltages during creation of machines' stator d-q axis voltage references is modified. Verification of the novel control scheme is provided by simulation.