Effect of Zero-Vector Placement in a Dual-Inverter Fed Open-End Winding Induction-Motor Drive With a Decoupled Space-Vector PWM Strategy

An open-end winding induction-motor drive with two two-level inverters achieves three-level inversion. The drawback of this configuration is the presence of a high zero-sequence current, stressing the semiconductor switching devices and the motor. To avoid this, two isolated dc power supplies are needed to feed individual inverters. In this paper, it is shown that it is possible to operate this drive with a single dc power supply, with reasonable engineering compromises. The new decoupled space-vector-based pulsewidth modulation (PWM) strategy proposed in this paper achieves this objective. This PWM strategy exploits the dependence of the zero-sequence voltage on the placement of the zero-vector of individual inverters. It is shown that the zero-sequence voltage of the dual-inverter system is suppressed by forcing the zero-sequence voltage of the individual inverters to a value of zero, in the average sense, in each sampling-time interval. This strategy, therefore, achieves a dynamic balancing of the zero-sequence current. It is also shown that this PWM scheme achieves the center spacing of effective-time period for the dual-inverter drive and its associated advantages. In addition, the effect of the placement of the zero-vector for individual inverters on the dual-inverter drive is investigated, and the experimental results are presented.