*5.2. Inverter-Side Current Analysis*

Figures 18–20 show the experimental measured inverter-side currents and the corresponding fast Fourier transformation (FFT) waveforms of the three cases in power balance mode, respectively. From Figure 18a, Figure 19a, and Figure 20a, the inverter-side current ripple at the rated load in the three cases are around 14.9%, 14.6%, and 14.1%, respectively, which are roughly in agreemen<sup>t</sup> with the value calculated by Equations (14) and (15). From the FFT waveforms of the inverter-side currents as illustrated in Figure 18b, Figure 19b, and Figure 20b, it can be noticed that the current harmonics around the switching frequency are roughly canceled out in Case-2 and Case-3, but still exist in Case-1. The results demonstrate the analysis in Section 3 that the two individual sets of shunt capacitors of the Type-1 filter break the harmonic cancelation loop, causing the harmonics which should have been canceled still exist in the inverter-side current.

**Figure 18.** Inverter-side current experimental waveforms of Case-1 in power balance mode. (**a**) Inverterside current and current ripples. (**b**) FFT waveforms of the inverter-side current.

**Figure 19.** Inverter-side current experimental waveforms of Case-2 in power balance mode. (**a**) Inverterside current and current ripples. (**b**) FFT waveforms of the inverter-side current.

**Figure 20.** Inverter-side current experimental waveforms of Case-3 in power balance mode. (**a**) Inverterside current and current ripples. (**b**) FFT waveforms of the inverter-side current.

The experimental measured inverter-side currents and the corresponding FFT waveforms of the three cases in power unbalance mode are shown in Figures 21–23, respectively. Observing these figures, when the D3L inverter is working in power unbalance mode, the inverter-side current ripple of the three cases are around 14.6%, 14.4%, and 13.8%, respectively, which are still within the design limit. Besides, as observed from Figures 22b and 23b, the harmonics around the switching frequency also exist in the inverter-side currents in Case-2 and Case-3, which means that the total harmonic cancellation around the switching frequency cannot be realized in power unbalance mode.

**Figure 21.** Inverter-side current experimental waveforms of Case-1 in power unbalance mode. (**a**) Inverter-side current and current ripples. (**b**) FFT waveforms of the inverter-side current.

**Figure 22.** Inverter-side current experimental waveforms of Case-2 in power unbalance mode. (**a**) Inverter-side current and current ripples. (**b**) FFT waveforms of the inverter-side current.

**Figure 23.** Inverter-side current experimental waveforms of Case-3 in power unbalance mode. (**a**) Inverter-side current and current ripples. (**b**) FFT waveforms of the inverter-side current.
