b. SC Voltage Doubler Unit

A voltage doubler SC unit, as shown in Figure 20c, is a two-port converter that utilizes a single DC source, two capacitors, two complementary power switches, and two power diodes. Each capacitor has its own charging channel, which includes a diode and a power switch. Being a two-port SC-based basic unit, it can provide five different DC-link voltages, including 0 VDC, ±VDC, and ±2VDC. This fundamental SC unit's adaptability to operation comes at the expense of a lack of bidirectional power flow capacity [172–176].

c. SC Half-Mode Units

When using an SC half-mode device, the DC-link capacitors can be charged to a voltage that is only a small multiple of the DC-input source's voltage. Several other SC half-mode units have been introduced recently, as illustrated in Figure 20d. This is connected to the charging activities of the capacitors in the SC half-mode Unit-I; two fixed values of discrete DC-link voltages are required at its output, and this requires four DC-link capacitors, two complementary switches, and two diodes. Using a capacitive charging channel consisting of two diodes and a single power switch, the capacitors in this setup are charged to half the main DC-link voltage, earning this configuration the designation SC half-mode Unit-II, as shown in Figure 20e.

d. SC Bipolar Unit

The SC bipolar unit, shown in Figure 20f, has the ability to generate bipolar output voltage levels, such as 0VDC, ±VDC. In this device, just one DC-link capacitor is required to be charged in parallel to the input DC-source voltage, whereas five power switches are required for the entire operation.

e. SC Voltage Tripler Units

Basic units based on SC technology give SC-MLI topologies with voltage increases that are three times the normal value. Figure 20g shows the functioning concept of the most common type of SC voltage tripler unit. It is comprised of two DC-link capacitors, two power diodes, and four power switches [177–181]. As can be observed, both capacitors in this device are charged by the DC input. Table 4 provides a comparative study of different single DC source SC-MLIs [151], Table 5 describes the comparative study of different SC-MLIs with two asymmetric DC sources, and Table 6 provides a comparative study of cross-connected asymmetrical 15-level SC-MLIs [182–186].


**Table 4.** Comparative study of different single DC source SC-MLIs.

**Table 5.** Comparative study of different SC-MLIs with two asymmetric DC sources.



**Table 6.** Parametric comparisons of cross-connected 15-level SC-MLIs.
