## 3 Results and Discussion
### DC/DC with MPPT Design  
For the DC/DC design, a multicell configuration with 12 Peltier modules has been considered. First, it is necessary to analyze the equivalent SPICE circuit in order to identify the best connection strategy. Among all the possible configurations, six architectures have been considered, as depicted in Figure 8.  
For each configuration, a load sweep analysis has been performed, in order to obtain the current-voltage (I-V) characteristic trace, as well as the power-voltage (P-V) characteristic curve for a temperature difference of 16 \({}^{\circ}\)C (Figure 9). From the multicell simulation analysis, it can be inferred that the power-voltage curve is a paraboloid, being the equivalent circuital model of a single cell constituted by a simple voltage generator in series with an internal resistor. For 12 cells all connected in series (Figure 9a), the maximum power point is located exactly at \(V_{OC}\)/2, while this point translates to the left, towards a lower voltage value, as the configuration tends to a parallel connection [52]. For 12 cells all connected in parallel, the maximum power point falls out of the lower simulation range for the load sweep. From the obtained results, it can be inferred that the best configurations are the 4 \(\times\) 3 or 3 \(\times\) 4, since it is a compromise between the output voltage and current, and the loss of conversion efficiency due to a possible heat distribution unevenness for the hot side among the cells. On the other hand, from the electrical point of view, the voltage provided by the TEG array should be as high as possible, in order to reduce the DC/DC design critical issues. For this reason, the full series configuration of the 12 cells has been selected in this case for the DC/DC design example, assuming that the temperature difference is uniform for every cell, since the corresponding voltage of the maximum power point is higher, which helps theDC/DC converter to boost the output voltage. In fact, the lower is the input voltage, the more is the complexity of a real DC/DC converter in order to guarantee the voltage translation, since limitations and parasitic elements of single electronic devices that constitute the converter architecture can inhibit its functionality when the input voltage is too low. Figure 8: Configurations for multicell simulation analysis. (**a**) series of 12 cells, (**b**) 6 series of 2 parallel cells, (**c**) 4 parallels of 3 series cells, (**d**) 3 parallels of 4 series cells, (**e**) 2 parallels of 6 series cells and (**f**) 12 parallel cells. Figure 9: _Cont._  
Once the configuration of operation has been selected, it is necessary to analyze the power-voltage curve at different temperature differences, in order to verify that the maximum power point condition is constant for every operative condition. According to previous single-cell characterization for SPICE model identification, the voltage value of the equivalent circuit is linearly dependent on the temperature gradient, thus the P-V curve shape is expected to remain unaltered, as depicted in Figure 10, where a load sweep analysis has been performed for 12 TEG cells connected in series at different \(\Delta\)T values. The simulation shown in Figure 10 demonstrates that the maximum power point condition for series-connected multicell TEG source, at every temperature difference, is equal to  
Figure 10: Power-voltage simulation analysis for 12 cells connected in series with \(\Delta\)T = 16 \({}^{\circ}\)C (yellow), \(\Delta\)T = 10 \({}^{\circ}\)C (grey), \(\Delta\)T = 8 \({}^{\circ}\)C (orange), and \(\Delta\)T = 4 \({}^{\circ}\)C (blue). Figure 9: Multicell current–voltage (blue trace) and power–voltage (orange trace) simulation analysis with \(\Delta\)T = 16 \({}^{\circ}\)C. (**a**) series of 12 cells, (**b**) 6 series of 2 parallel cells, (**c**) 4 parallels of 3 series cells, (**d**) 3 parallels of 4 series cells, (**e**) 2 parallels of 6 series cells, and (**f**) 12 parallel cells.