An improved PWM for a dual two-level inverter fed open-end winding induction motor drive

Three-level voltage space vector can be synthesized using a dual two-level inverter scheme employing open-end winding induction motor drive. Owing to the advantages this configuration offers over the other popular three-level inverter configurations, many PWM control strategies have been proposed. Towards this end, alternate sub-hexagonal center PWM switching scheme was presented recently that employs each of the two-level inverters as clamping and switching inverters. In this paper, an improved PWM switching scheme is proposed that is aimed at further reducing the number of switching commutations in the dual-inverter. It is attempted to reduce the switching commutations in the dual-inverter especially during the changeover of inverters roles from clamping to switching inverter and vice versa in the entire cycle of the supply. A significant 50% reduction in the number of switching commutations in the dual-inverter is achieved with the use of the proposed PWM scheme. The implementation of the PWM scheme neither requires any look-up tables nor sector identification while it only requires the magnitudes of instantaneous three phase reference voltages. The improved PWM scheme is first simulated and verified experimentally by driving the dual-inverter fed open-end winding induction motor by employing V/f control.