## 4 AC/DC Converter
### Architectures: Evaluation and Selection
#### 4.4.4 Summary of Results and Circuit Selection  
The results of the converter simulations achieved are summarized in Tables 23 and 24 and Figure 35 that shows the most significant results for the tested maximum and minimum wind velocities. The efficiency of the harvester is set to 100% for all the test cases.  
The best system efficiencies (generator + converter) are obtained with Split NP architecture. With 3 m/s wind flow the efficiencies are: 17.61% for the generator, 81.52% for the converter; thus the whole system has an efficiency of 14.36%. With 10 m/s wind flow the efficiencies are: 14.81% of the generator, 74.33% of the converter and 11% of the complete system. In this second case Split NP does not have the best conversion efficiency but it does in the complete system.  
Although the D-Bridge was discarded from the beginning, the later statement was verified. The results show that the D-Bridge architecture does not reach the minimum requirement of 3 V at the output point with 3 m/s wind flow; consequently, it would not be valid.  
The efficiencies are directly related with the wind flow velocity/pressure condition or input voltage/power level. Furthermore, the same effect occurs with the converters with the selection of MOSFETs. This is because the operating principles of the MOSFET are the maximum responsible for the efficiency of the AC/DC converter.  
Based on the results obtained, the Split NP architecture was identified as the AC/DC converter architecture with the best performance, i.e., the highest system efficiency in the considered wind  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Architect.** & \(V_{in}\) (\(V_{pp}\)) & \(f_{in}\) (kHz) & \(R_{load}\) (f) & \(D\) & \(f_{sw}\) (kHz) & \(V_{out}\) (V) (mA) & \(P_{out}\) (mW) & \(I_{generator}\) (\%) & \(I_{counterter}\) (\%) & \(I_{system}\) (\%) \\ \hline Harvester & 0.54 & 1.89 & 27 & - & - & 0.54 & 28.24 & 15.25 & 24.37 & 100 & 24.37 \\ D-bridge & 1.05 & 1.79 & 100 & - & - & 0.57 & 5.71 & 3.26 & 12.35 & 35.02 & 4.32 \\ Side diode & 0.4 & 2.4 & 1500 & 0.5 & 200 & 3.08 & 2.05 & 6.32 & 13.6 & 74.32 & 10.11 \\ Split N & 0.85 & 1.57 & 1300 & 0.5 & 333 & 3.20 & 2.46 & 7.88 & 15.37 & 75 & 11.53 \\ Split NP & 0.68 & 2.12 & 1500 & 0.5 & 200 & 3.41 & 2.62 & 8.95 & 17.61 & 81.52 & 14.36 \\ \hline \hline \end{tabular}
\end{table}
Table 23: Converters’ best results with the minimum input value: 3 m/s.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Architect.** & \(V_{in}\) (\(V_{pp}\)) & \(f_{in}\) (kHz) & \(R_{load}\) (f) & \(D\) & \(f_{sw}\) (kHz) & \(V_{out}\) (V) (mA) & \(P_{out}\) (mW) & \(I_{generator}\) (\%) & \(I_{counterter}\) (\%) & \(I_{system}\) (\%) \\ \hline Harvester & 0.54 & 1.89 & 27 & - & - & 0.54 & 28.24 & 15.25 & 24.37 & 100 & 24.37 \\ D-bridge & 1.05 & 1.79 & 100 & - & - & 0.57 & 5.71 & 3.26 & 12.35 & 35.02 & 4.32 \\ Side diode & 0.4 & 2.4 & 1500 & 0.5 & 200 & 3.08 & 2.05 & 6.32 & 13.6 & 74.32 & 10.11 \\ Split N & 0.85 & 1.57 & 1300 & 0.5 & 333 & 3.20 & 2.46 & 7.88 & 15.37 & 75 & 11.53 \\ Split NP & 0.68 & 2.12 & 1500 & 0.5 & 200 & 3.41 & 2.62 & 8.95 & 17.61 & 81.52 & 14.36 \\ \hline \hline \end{tabular}
\end{table}
Table 24: Converters’ best results with the maximum input value: 10 m/s.  
Figure 35: System efficiencies with different topologies.  
conditions. Moreover, there are techniques to improve further the efficiency: adaptively set the converter to its maximum efficiency point based on the energy harvester and the load conditions, i.e., an Maximum Power Point Track (MPPT) control and reduce the quiescent consumption.  
Finally, the efficiency of the present research is compared with other topologies to verify the improvement achieved. The Table 25 shows this comparison, and the better performance of proposed design.