Field Weakening Operation of Open-Winding Induction Motor Dual Drives Using a Floating Capacitor Bridge Inverter

A field weakening control scheme of open-ended winding induction motors with a floating capacitor bridge is presented. The main bridge is operated at unity power factor to maximize the output mechanical power until the floating bridge hits its maximum voltage. After which, the main bridge is operated to supply some reactive demand to extend the drive speed extension ratio to 9.2 times the base speed compared to 5 for only unity power factor operation. The maximum voltage this scheme can supply is 0.83 p.u, 0.52 p.u, and 0.17 p.u higher compared to the single inverter drive, unity power factor, and single DC-link dual inverter drives, respectively, and only 0.17 p.u lower than that of two separate DC-links dual inverter drive. The presented scheme is also compared with four field weakening control schemes, three of which are dual inverter drive schemes, in terms of maximum stator voltage, speed extension ratio, and available output power. The feasibility of the control scheme is experimentally demonstrated by performing transient and steady state analysis.