## 4 Hardware and Implementation Results  
The experimental validation of the grid-connected mode was performed using Imperix modular power converters from Imperix, Sion, Switzerland, with two independent 3-leg modules configured for grid-side and load-side operations, as shown in Figure 14. An Imperix pre-charge unit was used to safely energize the DC-link capacitors during startup. Real-time voltage and current measurements were acquired through Imperix measurement units and a DEWE PA7 analyzer from Dewetron, Grambach, Austria, to monitor the system's operation. A programmable residential inverter emulated the customer-side load, ensuring complete isolation from the grid-side harmonics. Figure 15 presents the laboratory measurements for the system operating under fundamental frequency (50 Hz) conditions. The top left graph shows the three-phase grid voltages \(U_{g,a}U_{g,b}\), and \(U_{g,c}\), highlighting a typical balanced three-phase waveform. The middle-left graph illustrates the HLI side voltages \(U_{L,a^{\prime}}U_{L,b}\), and \(U_{L,c^{\prime}}\) where clean 50 Hz voltage signals are maintained through the DC-link isolation. The bottom left graph compares the phase-a currents, showing the grid current \(I_{g,a}\) (red) and the HLI current \(I_{L,a}\) (blue), demonstrating effective current transfer between the two sides. Figure 13: Grid voltage and current waveforms under 5 th and 7 th harmonic injection during battery charge–discharge transition. (red: phase a, yellow: phase b, blue: phase c). On the top right, the frequency spectrum analysis shows a sharp dominant peak at 50 Hz for all measured quantities, with negligible harmonic content at 250 Hz (5 th harmonic) and 350 Hz (7 th harmonic), confirming the absence of multi-frequency injection in this mode. The table below the spectrum quantifies the RMS values of voltages and currents for both the grid and HLI sides. The middle right section reports the active power measurements, where the total and fundamental active powers at the grid side (\(P_{t,g}P_{\text{fund},g}\)) and load side (\(P_{t,L},P_{\text{fund},L}\)) are nearly identical, confirming minimal losses and efficient power transfer. Finally, the bottom right plot depicts the DC-link voltage \(U_{dc}\), regulated around 376 V, ensuring stable energy exchange across the system. The results presented in Figure 16 reveal the system response to a 5 th harmonic voltage component (negative sequence, 250 Hz) applied to the grid. The grid voltages  
Figure 14: Experimental setup. Figure 15: System operating under fundamental frequency. show clear signs of distortion because the injected harmonic exists, while the House Load-Inverter (HLI) voltages stay purely sinusoidal at 50 Hz, which proves the low-voltage DC-link provides effective isolation. The grid current waveforms show visible distortion because of the harmonic injection, yet the HLI load currents remain clean, sinusoidal shapes. The spectral analysis shows that the grid voltages and currents contain a substantial 5 th harmonic component, yet the HLI side shows no harmonic presence. The total active power on the grid side reaches 735 W, but the fundamental active power decreases to 687 W because of the injected distortion. The HLI side demonstrates no power difference between total and fundamental measurements because the customer receives power without distortion. The DC-link voltage operates at a stable 375 V level, which provides reliable operation and complete electrical isolation between the distorted grid and customer load. The experimental results presented in Figure 17 show the effects of injecting both the 5 th harmonic (negative sequence, 250 Hz) and 7 th harmonic (positive sequence, 350 Hz) voltage components into the grid. The grid voltages become more severely distorted compared to the case of only 5 th harmonic injection, confirming the simultaneous presence of two harmonic orders.