A PWM method for seven-leg inverters supplying three three-phase motors

Industrial robotic systems often require high performance control of a number of converter-fed motors. Although the advantages of using industrial robots during the manufacturing process are numerous the initial capital cost of the robotic system can be prohibitively expensive. One possibility to reduce these costs is to construct the multi-motor drive system using component minimized converters. This article develops a three-motor drive system supplied using a seven-leg voltage source inverter (VSI). The three-motor drive offers a saving of two inverter legs when compared to the standard equivalent triple three-phase VSI topology. It is believed that this supply system is particularly well suited to three-axis robots often found in pick and place applications. The performance of the seven-leg VSI-fed three-motor drive is verified by simulation and experiments using a custom built rig.