## 5 Conclusions
\begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline \multirow{2}{*}{**Ref.**} & \multirow{2}{*}{
\begin{tabular}{c} **Type of** \\ **Converter** \\ \end{tabular} } & \multicolumn{3}{c}{**Components**} & \multicolumn{1}{p{42.7 pt}}{**Operation**} & \multicolumn{1}{p{42.7 pt}}{**Output**} & \multirow{2}{*}{\(V_{in}\)} & \multicolumn{1}{p{42.7 pt}}{**Modulation**} & \multicolumn{1}{p{42.7 pt}}{**Leakage**} \\ \cline{3-3} \cline{5-10}  & S & D & L & C & & & & & & \\ \hline
[28] & HBZVR & 5 & 10 & 2 & 3 & 4 &
\begin{tabular}{c} 2(1.8 mH), \\ 2 uF \\ \end{tabular} & 350 V & PWM & 74.4 mA \\ \hline
[51] & T-type hybrid & 8 & 4 & 5 & 4 & 5 &
\begin{tabular}{c} 2(3 mH) \\ 2(0.6 mH) \\ 2(1 uF) \\ \end{tabular} & 200 V & LSPWM & 16.7 mA \\ \hline
[57] & \
\begin{tabular}{c} Common \\ ground \\ \end{tabular} & 6 & 2 & 1 & 2 &
\begin{tabular}{c} 2 or 3 \\ \end{tabular} & 3 mH & 200 V & PWM & \(\simeq\) 0 mA \\ \hline
[80] & \
\begin{tabular}{c} Common \\ ground \\ \end{tabular} & 2 & 0 & 2 & 1 & 7 &
\begin{tabular}{c} 1 mH, 2.2 uF \\ \end{tabular} & 400 V & PWM & \(\simeq\) 0 mA \\ \hline
[96] & \
\begin{tabular}{c} Step-up \\ non-isolated \\ \end{tabular} & 6 & 1 & 3 & 2 & 6 &
\begin{tabular}{c} 4.4 mH, 0.42 \\ mH, 2.2 uF \\ \end{tabular} & 30–60 V & SPWM & \(\simeq\) 0 mA \\ \hline
[97] & \
\begin{tabular}{c} quasi \\ Z-Source \\ Inverter \\ \end{tabular} & 6 & 1 & 4 & 3 & 5 &
\begin{tabular}{c} 3 mH \\ \end{tabular} & 30–60 V & SPWM & \(\simeq\) 0.4 A \\ \hline
[98] & \
\begin{tabular}{c} Current \\ Source \\ Inverter \\ \end{tabular} & 6 & 6 & 4 & 1 & 3 &
\begin{tabular}{c} 2(2.5 mH), \\ 9.4 uF \\ \end{tabular} & - & SPWM & 140 mA \\ \hline
[99] & CH5 & 5 & 0 & 2 & 1 & 5 & 44 uF & - & SPWM & 24.7 mA \\ \hline
[100] & \
\begin{tabular}{c} Full \\ Bridge \\ \end{tabular} & 6 & 0 & 2 & 1 & 4 &
\begin{tabular}{c} 2(4 mH) \\ 2(4 mH) \\ \end{tabular} & 380 V & bipolar SPWM & 50 mA \\ \hline
[101] & \
\begin{tabular}{c} Common \\ ground \\ \end{tabular} & 7 & 2 & 3 & 1 & 3 &
\begin{tabular}{c} 2.8 mH \\ 6.6 uF \\ \end{tabular} & 400 V & PWM & 10 mA \\ \hline
[102] & NPC & 6 & 0 & 2 & 0 & 3 &
\begin{tabular}{c} 2(4 mH), \\ 6.6 uF \\ \end{tabular} & 400 V & SPWM & 44 mA \\ \hline
[103] & FBNPC & 8 & 4 & 1 & 2 & 6 & 6 mH & 200 V & SPWM & 181.4 mA \\ \hline
[104] & H5 HERIC & 8 & 4 & 1 & 2 & 5 &
\begin{tabular}{c} 1.2 mH \\ 3.3 uF \\ \end{tabular} & 600 V & SLS-PWM & 181 mA \\ \hline
[105] & \
\begin{tabular}{c} Derived \\ HERIC \\ \end{tabular} & 8 & 2 & 1 & 2 & 5 &
\begin{tabular}{c} 3 mH \\ \end{tabular} & 600 V & PWM & 180.3 mA \\ \hline
[106] & CMLI & 8 & 0 & 4 & 3 & 6 &
\begin{tabular}{c} 4(2 mH), \\ 0.1 uF \\ \end{tabular} & 400 V & PWM & 56.5 mA \\ \hline
[107] & \
\begin{tabular}{c} Derived \\ CHB \\ ground \\ \end{tabular} & 10 & 2 & 0 & 2 & 7 &
\begin{tabular}{c} 2(2.5 mH) \\ 2(2.5 mH) \\ \end{tabular} & 72 V & PWM & 17.7 mA \\ \hline
[108] & \
\begin{tabular}{c} Common \\ ground \\ \end{tabular} & 5 & 0 & 2 & 1 & 4 &
\begin{tabular}{c} 3.5 mH, \\ 3.3 uF \\ \end{tabular} & 100 V & - & \(\simeq\) 0 mA \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparision between different structures. and research trends within this topic are highlighted. Hopefully, this review will lead to increased efforts in the research and investigation of leakage current reduction in transformerless inverters. In this paper, it is concluded that grid-connected systems have to comply with specific standards for each region or country. A THD less than 5% and a leakage current less than 300 mA are some of the most important standards to consider. Moreover, the output of the PV requires particular attention, since it presents a voltage ripple that do not damage the PV cell, but it reduces the available power. Furthermore, the unbalance in the inductors of the output filter increases the leakage current. The unbalance in the inductors is due to a dispersion in the capacity, aging rate and temperature behavior of the output inductors.