University of Belgrade
School of Electrical Engineering
http://www.etf.bg.ac.rs
A General PWM Method for a (2n+1) -Leg Inverter
Supplying n Three-Phase Machines
D.Dujic, M. Jones, S.N. Vukosavic, E. Levi
References:
IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, Vol. 56, No. 10, pp. 4107-4118,
Oct, 2009
Abstract:
Control of an ac machine requires only two currents. It is, therefore, possible to achieve
independent control of a number of three-phase machines using various inverter topologies with a
reduced switch count. One such drive system comprises n three-phase induction machines supplied
by a (2n + 1)-leg voltage source inverter (VSI). In such a configuration, one inverter leg is common
for all machines. This paper presents a general pulsewidth modulation (PWM) method that is
applicable for any number of machines n in the group. It is based on utilization of the standard
three-phase modulators in conjunction with additional logic to generate modulation signals for all
(2n + 1) legs of the inverter, and it enables an arbitrary distribution of the available dc bus voltage
between the n machines. A developed PWM method has been implemented and tested in twomachine, three-machine, and four-machine drives, supplied from five-leg, seven-leg, and nine-leg
VSIs, respectively. Experimental results are reported for open-loop V/f control, closed-loop currentcontrolled V/f mode of operation, and full vector control. It is shown that the nonideal nature of the
VSI causes unsatisfactory operation of the drive system in the open-loop V/f mode, and that closedloop current control is, therefore, preferred in this type of a drive system. It is believed that the fourmachine driv
Keywords:
pulsewidth modulation (PWM), reduced switch-count topologies, control, vector control,
Multimachine drive systems