## 5 Experimental Validation  
For experimental validation, the system parameters are taken as the same as in the simulation. The components used for the experiment are given in Table 5. The sensor circuits and signal conditioning circuits are designed. The photograph of the experimental setup of the HMLI is shown in Figure 12. In Bridge H1, DC voltage is taken as 100 V and the magnitude of the reference current is set at 6.5 A. To represent the parasitic capacitance of the PV panel, a 100 nF capacitor is inserted into the circuit. Sampling is done at 20 kHz and the setup is tested first for _R-L_ loads of 15 \(\Omega\) and 2 mH.  
Figure 11: Simulation results HMLI: (**a**) common mode voltage in grid connected HMLI, and (**b**) leakage current.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Attributes** \\ \hline Voltage sensor & LEM-LV 55 P \\ Current sensor & LEM-LA 25 P \\ Microprocessor & TI-TMS320F28335 \\ Switches & IRFP540N60K \\ Drivers & FOD-3184 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Components used in experiment.  
The experiment was carried for a 600 W laboratory prototype. The steady-state output voltage and load current waveform are shown in Figure 13. The nine-level voltage waveform has been generated at the output of the HMLI. It consists of 0, \(\pm\)33.33 V, \(\pm\)66.66 V, \(\pm\)100 V, and \(\pm\)133.33 V output voltage levels. The voltage of the capacitor is balanced at 33 V. The output voltage and current magnitude are approximately 84.8 V and 7.05 A (RMS), respectively. The leakage current and CMV waveform are shown in Figure 14. The obtained RMS current is around 20 mA and it can vary within 5% of the given value because of precision errors of the measuring instrument.  
Figure 12: Photograph of the experimental setup.  
Figure 13: HMLI output voltage (CH1), capacitor voltage (CH3), and load current (CH4) waveform.  
The output voltage of the high voltage (HV) bridge and low voltage (LV) bridge are shown in Figure 15. The important observation to make in Figure 15 is that the voltage switchings of the HV bridge happen only in limited time intervals during a period of grid voltage. Leakage current is also minimized as the legs of HV bridge have a DC supply as a PV panel. The HMLI has also been experimentally validated at grid voltage 110 V (RMS). The grid current is precisely regulated to synchronize with the grid voltage. The grid voltage and current are depicted in Figure 16. The control strategy effectively balances the capacitor voltage balancing and tracks the reference current.  
Figures 17 and 18 show the dynamics of the output voltage for increasing and decreasing currents, respectively. For the low-current value, the control algorithm does not choose high voltage levels as the resistance value is fixed. Hence, at 3 A (peak) current, HMLI generates only five levels. In Figure 17, the current reference is decreased from 7 A (peak) to 3 A (peak) and the opposite sequence is implemented for Figure 18. From both of the figures, it can be confirmed that the proposed MPC provides a fast dynamic response.  
Figure 14: Common mode voltage (CH3) and leakage current (CH2) waveform.  
Figure 15: HMLI output voltage (CH1), high-voltage bridge voltage (CH3), and low-voltage bridge voltage (CH4) waveforms.  
The load current dynamics of the proposed controller is also experimentally validated in Figures 19 and 20, respectively, which show that the load current tracks quickly for increased and decreased reference currents, respectively. The system shows excellent dynamic results using the proposed control scheme.  
Figure 16: HMLI output voltage (CH1), capacitor voltage (CH3) and grid voltage (CH4), and grid current (CH2) waveforms.  
Figure 17: Output voltage (CH1) waveform at a decreasing load current (CH4).  
Figure 18: Output voltage (CH1) waveform at an increasing load current (CH4).