A four-motor drive supplied from a triple three-phase voltage source inverter

Since control of a three-phase machine requires only two currents, it is possible to independently control a number of three-phase machines using reduced-switch-count voltage source inverter (VSI) topologies. One such configuration consists of n three-phase machines, supplied by a (2n+1)-leg inverter, where one inverter leg is common for all machines. This paper deals with a particular case of this topology, namely a four-motor drive supplied from a nine-leg (triple three-phase) VSI. A PWM method, developed recently for two-motor and three-motor drives supplied from a five-leg and a seven-leg VSI, respectively, is extended to the four-motor drive for this purpose. Its main characteristic is that the available dc bus voltage is arbitrarily distributable between the machines within the limits prescribed by the dc bus. The PWM method has been implemented and operation of the four-motor drive, supplied from a custom-designed nine-leg VSI, has been tested. Experimental results are reported for open-loop V/f control and closed-loop current-controlled V/f mode of operation. It is believed that the four-motor drive has a good potential for certain real-world industrial applications, since it may enable a considerable saving in the required number of switches and installed inverter power.