A Four-Level Inversion Scheme for a 6n-Pole Open-End Winding Induction Motor Drive for an Improved DC-Link Utilization

In this paper, a new power-circuit configuration for four-level inversion with an open-end winding induction motor is proposed. This configuration is suitable for an induction motor with 6n (n = 1, 2, ...) number of poles. Two isolated dc power supplies, each rated for one third of the total dc-link voltage, are sufficient to realize this four-level inverter scheme. It is shown that it is possible to produce a voltage vector of 1-p.u. magnitude with a total dc-link voltage of 0.66 p.u., indicating that the dc-link utilization is enhanced by a factor of 33% with this power-circuit configuration. In the proposed power circuit, the zero-sequence current is arrested as the motor phase windings of the open-end winding induction motor are segmented into two separate groups in the ratio of 2 : 1, with one end of each group forming an isolated neutral point. Each phase group is then powered by two individual two-level inverters with two separate dc-power supplies with a common negative rail. The existence of this common negative rail is the principal cause of an increased dc-bus utilization. A simple decoupled space-vector pulsewidth modulation is adequate to control both of these inverters, which further demonstrates the simplicity of the drive control.