(ii) Classification

In any physical design, switches and DC-link voltages can be connected in any topology. Often, there is no required architecture, but other times there are ladders, staircases, columns, U-shaped structures, and cascade structures. As can be seen in Figure 6, the resulting RSC-MLIs can be categorized in accordance with their topological and functional properties, as discussed in [114–116].

**Figure 6.** Classification of RSC-MLI topologies.

(iii) The Evaluation Criteria for an MLI

In contrast, this review study takes into consideration broad criteria for rating the proposed topologies:

Several MLI evaluation parameters are context dependent, as shown in Figures 7 and 8, and some of the key features of an MLI that contribute to the different capabilities of the power system are discussed [117–121].

**Figure 7.** MLI evaluation criteria [103].

**Figure 8.** Characteristics of MLIs.

An interconnected multilevel converter system can use renewable energy sources, including solar PV, wind energy, and fuel cells. Their operation, effectiveness, improved power quality, and applications are mostly determined by the control scheme used in the MLI-PWM. Multiple MLI topologies have been suggested in recent years [122–125]. Based on the number of DC sources in their topology, MLIs have been classified as shown in Figure 9, and based on a categorization of the reduced switch in their topology, MLIs have been classified as shown in Figure 10. The NPC-MLI or DC-MLI, FC-MLI, and CHB-MLI are the most prevalent industrial topologies [126–130].

**Figure 9.** Simplified classification of multilevel inverters.

**Figure 10.** Categorization of reduced switch count MLI topologies.


• Flying capacitor multilevel inverter (FC-MLI): Meynard and Foch [25,39] suggested the FC-MLI topology in 1992 to address the issue of static and dynamic sharing of the voltage between semiconductor switches as implemented in the NPC-MLI architecture.
