Open-End Winding Induction Motor Drive with a Floating Capacitor Bridge and Overmodulation of the Primary Inverter

A dual inverter bridge is used to feed a 3-phase induction motor with open-end stator windings. The dual inverter is composed of a primary bridge connected to the power source and a secondary bridge with a floating capacitor. While the primary bridge operates at unity power factor, the secondary inverter produces the reactive power and boosts the voltage applied to the stator phases of the machine. As a result, the constant-power speed range of the induction machine increases in proportion to the secondary DC-link voltage. Another feature is that the primary inverter can operate in the overmodulation range without reducing the quality of the stator currents due to the compensating action of the secondary inverter. Experimental results show that the output power rises by about 10% in the field weakening speed region.