A multilevel voltage space phasor generation for an open-end winding induction motor drive using a dual-inverter scheme with asymmetrical D.C.-link voltages

摘要

An open-end winding induction motor drive fed from two inverters with different d.c.-link voltages is proposed in this paper. This scheme is capable of producing 64 voltage space phasor combinations, distributed over 37 space phasor locations. In the proposed scheme, the neutral connection of the induction motor is removed (open-end winding) and is fed from both the ends. Two 2-level inverters with isolated d.c.-link voltages of(2/3)V{sub}dc and (1/3)V{sub}dc are used for driving the motor where V{sub}dc denotes the d.c. -link voltage of an equivalent conventional (single-inverter) scheme. The voltage space phasor locations can be associated with three regions according to the speed range. In the lowest speed range, the phase voltage exhibits a six-step envelope (or a 2-level inverter waveform similar to the conventional scheme) and in the middle range the motor phase voltage, shows a 12-step envelope (or a 3-level inverter waveform). In the higher speed range, including over modulation, the motor phase voltage has an 18- step envelope (or a 4-level inverter waveform).