*6.1. Normal Mode*

The first experiment has been carried out under the initial conditions of PV simulator with irradiance of 1000 <sup>W</sup>/m<sup>2</sup> and a temperature of 25 ◦C. In this case, the input power of the first H-bridge unit is approximately 255 W. The reference of the other four H-bridge units' DC-side voltages is 32.02 V, and therefore the output power of the other four H-bridges is about 255 W in theory. As depicted in the Figure 15, both SHMS and HMSWZS enable the CHB inverter to operate at unity power factor with good grid current quality. It can also be seen that SHMS contains four output modes: "+1", "−1", PWM, and "0" mode, which is never adopted in HMSWZS.

**Figure 15.** Experimental results under normal mode: grid voltage (VG), grid current (IS) and the total output voltage of CHB inverter (VHT); the first H-bridge output voltage (VH1) with: (**a**) HMSWZS and (**b**) SHMS.

For the sake of evaluating the characteristic of both two modulation methods in terms of DC-side voltage fluctuation and average output power of the PV module, the following experiments have been performed under the same conditions as the first experiment. As shown in Figure 16, the maximum fluctuation of VPV1 by adopting HMSWZS is 5.3 V, but the value is only 4.1V for SHMS, which is reduced by about 22.64%. In order to compare the output power of the two methods under normal mode, the total output power of the CHB inverter is recorded by the upper computer, respectively. As can be seen from Figure 17, with HMSWZS, the total output power of the CHB inverter ranges from 1218–1244.2 W and the average is about 1233.7 W. When SHMS is utilized, the total output power of the CHB inverter ranges from 1230–1249.3 W and the average is about 1239.8 W. Compared with the HMSWZS, the efficiency of the CHB inverter can be improved about 0.48% by adopting the SHMS. Furthermore, the efficiency of the CHB inverter with both methods is presented in Figure 18. As can be seen from Figure 18, the SHMS is capable of improving the efficiency of the CHB inverter compared with the HMSWZS. Therefore, under normal mode, the SHMS is able to effectively suppress the DC-side voltage fluctuation compared with the HMSWZS, thereby improving the energy acquisition of the PV module.

**Figure 16.** Experimental results under normal mode: the DC-side voltage (VPV1) of the first H-bridge with: (**a**) HMSWZS, and (**b**) SHMS.

**Figure 17.** Experimental results of the total output power of the CHB inverter under normal mode with: (**a**) HMSWZS and (**b**) SHMS.

**Figure 18.** Experimental results of the efficiency of the CHB inverter under normal mode with different methods.
