**4. Mid-Point-Clamped SC-MLIs**

High-frequency variable CMV, which results from the varying numbers of HB legs used in the aforementioned single and multiple DC-source SC-MLIs to invert the SC unit/generalized SCC output voltage polarity, is one of the main issues that prevents their widespread use, for example, in grid-tied PV systems. Since their output voltage is monitored at the neutral point of the DC connection, mid-point-clamped MLIs are a common choice in this scenario. While a multilevel output voltage waveform is generated by a single input DC source, the leakage current problem in grid-tied PV applications is significantly reduced. The identical capacitors used in the DC links of single-phase MLIs may be used in three-phase systems. Table 7 provides a comparative study of different mid-point-clamped SC-MLIs [187–197].


**Table 7.** Comparative study of different mid-point-clamped SC-MLIs.

a. Five-Level mid-point-clamped SC-based inverter

The five-level mid-point clamped-based MLI approach, as shown in Figure 21a, involves adding two capacitors, C3 and C4, and a four-quadrant power switch "*p*" to a standard 3L NPC-based inverter to provide five distinct levels of output voltage.

**Figure 21.** Mid-point-clamped SC-based inverters: (**a**) 5-Level inverter, (**b**) 7-Level inverter.

b. Seven-Level mid-point-clamped SC-based inverter

The seven-level mid-point-clamped inverter proposed in [79] and depicted in Figure 21b is another example of this topology, although one that employs nine rather than eight switches. Figure 22 shows the comparison of the efficiency of SC-MLI with multi-source MLIs [198], and Figure 23 shows the measured efficiency of the 19-level SC-MLI at different frequency ranges [144,198–201].

**Figure 22.** Comparison of the efficiency of SC-MLI with multi-source MLIs [61,68,72–74,151,172,198].

**Figure 23.** Measured efficiency of the 19-level SC-MLI at different frequency ranges.
