Maximum Torque Operation of Open-Winding Induction Motor Dual Drives Using a Floating Capacitor Bridge in the Field Weakening Region

A field weakening controller is presented that extends the speed range of a dual inverter drive using a floating capacitor bridge. The controller utilizes the stator current reference frame to decouple the motor demand into active and reactive components. This is used so that the main bridge supplies the real power and the floating bridge supplies the reactive power until the floating bridge reaches its maximum voltage. The main bridge is then used to supply some of the reactive demand, which in turn adds additional voltage boost that is used to extend the drive’s constant power region, improve the motor speed acceleration performance, output power, and torque. It is found that the presented controller can increase the drive speed extension ratio to 9.2 times the base speed compared to 5 when always operating the main bridge at unity power factor. The motor maximum fundamental voltage is 1.82 p.u when compared to that of a single inverter drive. This controller performance is demonstrated experimentally using both transient and steady-state analysis. The controller is also compared with other two field weakening controllers using the same regulator tunings and experimental setup.