# Hybrid Modulation Strategy to Eliminate Current Distortion for PV Grid-Tied H6 Inverter
## 6 Experimental Validation  
In order to further verify the preceding analysis and test the validity of the proposed design, a 4.67 kW prototype has been designed and built. The DC voltage \(E\) is provided and regulated at 400 V by a pre-boost converter [1]. A picture of the laboratory prototype is depicted in Figure 18, the main parameters and devices of the inverter prototype are provided in Table 3.  
Figure 19 shows the terminal voltage of switches and inductor current of the H6 inverter for MMI when the power factor angle \(\theta\) = 0\({}^{\circ}\). It can be seen that current distortion does indeed exist in the area of zero crossing. Figure 20 shows the grid voltage and inductor current of the H6 inverter utilizing the new HMM strategy for a power factor angle = 0\({}^{\circ}\). As shown in Figure 20a, the current distortion is eliminated. Figure 20b shows that we adopt the MMI in a region of 10.8\({}^{\circ}\) around the zero crossing which is indicated by the drive pulses to S6 in this region. Figure 21 shows the voltage and current for non-unity power factor, \(\theta\) = -30\({}^{\circ}\), for the H6 inverter with HMM. It clearly shows that there is no uncontrollable area therefore the issue of the current's distortion is effectively removed. Figure 22, verifies that the common-mode voltage is constant with very small fluctuations with leakage current of  
Figure 17: Inductor current and tracking error. (**a**) Non-adaptive PIR control. (**b**) FSAPIR control. \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline Rated power & 4.67 kW & Capacitor & 1000 μF \\ DC bus voltage & 400 V & Inductors & 2 mH \\ Switching frequency & 19.2 kHz & S1 to S4 & CoolMosIPW60R045 CP \\ Grid voltage & 220 V/50 Hz & S5 to S6 & IKW75N60T(ICBT) \\ D1 to D2 & 60 EPU06 PBF & DSP chip & TMS320F2802 \\ \hline \end{tabular}
\end{table} 
Table 3: Parameters of the experimental prototype. Figure 18: The prototype of H6 grid-tied inverter. 21 mA. This is below the lowest level of leakage current of 30 mA where disconnection was necessary, as stated in the German DIN VDE 0126 standard [21]. Figure 19: Terminal voltage of switches and inductor current MMI. Figure 20: Voltage and inductor current under the HMM. (**a**) HMM: Voltage and inductor current, \(\theta=0^{\circ}\). (**b**) HMM: Zoom in during the zero-crossing area, \(\theta=0^{\circ}\). Figure 21: Voltage and inductor current under the HMM for 30\({}^{\circ}\) phase shift between voltage and current. HMM: Grid voltage and current, \(\theta=-30^{\circ}\). In order to validate the performance of the proposed FSAPIR controller, the grid voltage with frequency variation has been simulated with a Chroma grid simulator. Figure 23 shows the experimental waveforms of the system under FSAPIR control when the frequency of current reference signal is 55.11 Hz with amplitude of 30 A. It can be seen from Figure 23 that the real current can track the reference signal with low error and the total harmonic distortion (THD) is 2.53%, which is substantially less than 5% requirement of the IEEE929-2000 standard [22]. In the H6 implementation with HMM a separate diode is used to replace the body-diode of the switches with a positive impact on efficiency. Figure 24 shows the power efficiency curve; it can be seen that the efficiency of the system can achieve a maximum 98.2% when the system is operating at 50% of the power rating. According to further calculation, we can calculate the European efficiency as defined in [22] as 97.9%. For comparison Figure 24 also shows the efficiencies for the H4, H5, and HERIC topologies. These converter efficiencies are obtained from measurements. The H6, H5, and HERIC configuration efficiencies are higher than H4 [11; 23; 24]. Therefore, the HMM H6 inverter can be an inverter with a high efficiency and the capability of reactive power outputting. Figure 23: Voltage and current under the FSAPIR controller. Figure 22: Common mode voltage. HMM: 2 times the common-mode voltage, \(\theta=-30^{\circ}\).