*5.3. Grid Current Analysis*

The experimental tests for the grid current are conducted at 30% load to verify whether the current quality satisfies the grid standard [34]. Figures 24 and 25 show the grid current waveforms and the corresponding harmonic spectrums of the three cases in power balance mode, respectively. Figures 26 and 27 show the grid current waveforms and the corresponding harmonic spectrums of the three cases in power unbalance mode, respectively. The test cases along with the grid current THD and the dominating current harmonic amplitude percentage (higher than 35th) are summarized in Table 3. As observed from the table, even though the inverter is working at 30% load, the current THD are all still below the 5% [34] limit, and the dominant harmonics (higher than 35th) are all within the 0.3% limit as well.

**Figure 24.** Grid current experimental waveforms of the three cases in power balance mode. (**a**) Case-1. (**b**) Case-2. (**c**) Case-3.

**Figure 25.** Grid current FFT waveforms of the three cases in power balance mode. (**a**) Case-1, (**b**) Case-2, (**c**) Case-3.

**Figure 26.** Grid current experimental waveforms of the three cases in power unbalance mode. (**a**) Case-1, (**b**) Case-2, (**c**) Case-3.

**Figure 27.** Grid current FFT waveforms of the three cases in power unbalance mode. (**a**) Case-1, (**b**) Case-2, (**c**) Case-3.


**Table 3.** THD and dominant harmonic percentage of grid current in different cases and modes.

In summary, the analysis of the experimental inverter-side currents and the grid currents of all cases confirms the effectiveness of the filters' parameters designed using the proposed method. Consequently, the discussions in Section 4.3 can be confirmed as well.
