Overmodulation Strategies for an Open-End Winding Induction Motor Drive with a Floating Capacitor Bridge

This paper considers a 3-phase induction motor with open-end windings fed by a primary bridge connected to the main power source and a floating bridge. The floating bridge supplies the motor with the required reactive power, while the primary inverter only exchanges active power with the main power source. This greatly extends the speed range over which the drive can operate at rated power. To further utilize the input power source, the primary inverter can work in the overmodulation region, and the floating bridge, acting as a harmonic compensator, improves the quality of the current flowing through the motor phases. Also, the paper includes some considerations on the sizing of the floating capacitor. Three different overmodulation techniques are evaluated and compared in terms of peak torque/power and efficiency. The highest performance is obtained when the main inverter generates a six-step voltage waveform, which increases motor power by almost 20% and ensures a broader speed range at maximum efficiency.