Discontinuous Decoupled PWMs for Reduced Current Ripple in a Dual Two-Level Inverter Fed Open-End Winding Induction Motor Drive

This paper presents investigations on current ripple in a dual 2-level inverter feeding an open-end winding induction motor drive. Pulsewidth modulations (PWMs) for the independently controlled inverters are implemented using a simple effective time placement affected by offset-time concept, thus, eliminating the use of sector identification and lookup tables. Analytical expressions for ripple content in the motor phase current are developed and a current trajectory is theoretically obtained directly from the switching states of the dual inverter in a stationary reference frame. In addition, this paper also describes a current ripple trajectory in the motor by exploring the freedom of independently operating the individual inverters with different PWMs. Based on the analysis, discontinuous PWMs are employed for the individually inverters that not only offer the advantage of reducing the total switching commutations in the inverters but also reduces the current ripple. Analytical expression for the RMS ripple current and variation in RMS ripple current in one cycle of operation for different PWMs are also presented for the entire speed range of the dual-inverter drive. The performance of the dual-inverter drive with the proposed PWM variants is first studied analytically and then verified by performing suitable experiments on a 1-kW open-end winding induction motor drive.