Contents I. Introduction
Due to its inherent modularity, cascaded H-bridge (CasHB) multilevel inverters (MLI) are commonly used in high-voltage applications. As an alternative, there have been recent efforts to displace the H-bridge by developing module topologies that can produce more voltage levels with fewer switches. One of the many module topologies [1], [2] uses a T-type inverter along with a few extra switches to control four uneven dc sources in an envelope type module. On the other hand, a square T-type module that has been successfully shown consists of two back-to-back coupled T-type inverters that can generate 17 levels using just 12 switches and four uneven dc sources. However, unlike CASHB where all switches are required to limit their peak inverse voltage (PIV) to one level (one dc source), these recently established module topologies require some of their switches to block voltage greater than one level (the sum of all the dc sources) [5] during OFF state, making them less suitable for high-voltage applications [6]. Although several series-connected switches can be used to support PIV at levels higher than one, they will effectively lose their advantage over h-bridge in terms of switch count reduction. Another promising compact module that has gained favour recently is the switched-capacitor based topology [7–8]. This is mostly due to its capacity to boost voltage, which allowed for a reduction in the number of dc sources. With a single dc source, a novel switched-capacitor module (SCM) topology has recently been disclosed in [9], [10] and can provide up to 9 different voltage levels. The achievement of a maximum voltage level double that of the input dc source serves as evidence that voltage boosting is effective [11]. Since two capacitors are integrated so that their average voltage is equal when operating, capacitor voltage balancing is not a problem [12].
