*5.2. Fault Mode*

The following simulation evaluates the performance of HMSCZS and SHMS under the fault mode where the second PV module fails. The simulation starts with the operation of the system under symmetrical condition (E = 1000 <sup>W</sup>/m<sup>2</sup> and T = 25 ◦C). At t = 1.5 s, the second PV module is removed owing to the fault and, thus, the CHB inverter is operating in the fault condition. Figure 10 depicts the total modulation voltage (Vr) and DC-side capacitor current of the second H-bridge (IC2) with both methods. As shown in Figure 10a IC2 is always negative regardless of the polarity of Vr and, thus, VPV2 gradually diverges from the reference value. As a result, all the DC-side voltages diverge from the references in steady state, which is visible in Figure 11a. For comparison, the SHMS is also subjected to the same test under the identical condition. As presented in Figure 10b, IC2 can be positive and negative whether Vr is positive or negative and, thus, the DC-side capacitor of the second H-bridge could realize the equalization of the charge-discharge. Therefore, the CHB inverter is able to operate properly under fault condition, which is obvious in Figure 11b. Figure 12 shows the output power of the PV module in all H-bridges with both methods. As shown in Figure 12, due to the removal of the second PV module, the output power of the second H-bridge is, therefore, zero. The output power of the PV module in other H-bridges ranges from 243.2–255.1 W by using SHMS and the average is about 253.2 W. However, due to the deviation of the DC-side voltage, the output power of the PV module in other H-bridges ranges from 221.4–255.1 W by utilizing HMSCZS and the average is only about 245.3 W. The total output power (PT) of the CHB inverter with both methods are shown in Figure 13. As could be seen from Figure 13, with HMSCZS, the total output power of the CHB inverter ranges from 935.9–1016 W and the average is about 982.2 W. When SHMS is utilized, the total output power of the CHB inverter ranges from 1000–1020 W and the average is about 1014 W. Compared with the HMSCZS, the e fficiency of the CHB inverter can be improved about 3.12% by adopting the SHMS. Therefore, under the fault mode, the SHMS is still able to make the DC-side voltages reach the references, thus maintaining a higher energy yield.

**Figure 10.** Simulation results under fault mode: the total modulation voltage (Vr), and DC-side capacitor current of the second H-bridge (IC2) with: (**a**) HMSCZS and (**b**) SHMS.

**Figure 11.** Simulation results under fault mode: DC-side voltages of all H-bridges with: (**a**) HMSCZS, and (**b**) SHMS.

**Figure 12.** Simulation results under fault mode: the output power of PV module in all H-bridges with: (**a**) HMSCZS and (**b**) SHMS.

**Figure 13.** Simulation results of the total output power of the CHB inverter under the fault mode with: (**a**) HMSCZS and (**b**) SHMS.
