Enhanced Performance of Dual Inverter with a Floating Capacitor for Motor Drive Applications

This article studies a dual inverter supplied by a dc-link and a floating capacitor (FC), emerged as a promising inverter topology for motor drive applications. For this type of inverter, the voltage ratio between the dc-link and the FC can be actively controlled. This ratio design is crucial as it essentially defines both the dc-link voltage utilization and the inverter output quality. Several voltage ratios have previously been discussed to enhance the dual inverter performance, but only one aspect, either the voltage utilization or the output quality, is investigated. As a result, although one performance aspect can be improved, the other aspect has been adversely affected. In this article, a comparative study considering both aspects is carried out for all the possible voltage ratios. Based on this analysis, the optimal ratios for different inverter modulation indices are identified. This is followed by proposing a ratio selection strategy to double the voltage utilization without degrading the output quality. This strategy enables an electric drive to work at a higher maximum speed without flux weakening for a given dc-link voltage. The claimed advantages have been proved by experimental tests on an open-end windings induction motor drive.