Scalar modulation technique applied to a three-level/-phase/-wire back-to-back converter system with reduced dc-link capacitance for AC drives

This work introduces a novel modulation technique applied to a three-level/-phase/-wire back-to-back NPC converter system focusing on reduced dc-link capacitance applications. The technique is implemented within a scalar PWM modulation scheme and is based on the mathematical analysis of the back-to-back NPC system in the αβ0 stationary reference frame. There, the ac-side currents and the modulation signals α and β components from both converters are used to obtain the required 0-axis modulation signal to be employed in the grid-side converter. This ensures that the dc-link center point low frequency current components are canceled out and, thus, that the required dc-link capacitors requirements are lowered. The main consequence of this is the possibility of replacing, for instance, electrolytic capacitors by film capacitors in order to increase reliability, keeping the functionality, performance, volume, weight and cost of the system, while reducing capacitors losses.