# Evolutionary Maximization of Energy Amount Harvested by Means of Panel of Thermoelectric Modules
## 5 Practical Experiment
This is the key feature that makes it possible to operate properly for temperature profile of particular TE devices and it may be promising for systems with TEG converters constructed as a stack of devices (multistage module) to improve the coefficient of performance [36] or for the other ones when thermal flux has a tendency towards variations caused by specific exothermic source or when temperature decomposition is non-uniform. Figure 11 shows oscillograms of collector voltage of transistor T1 from boost converter (Figure 7) and PWM control signal measured for self-oscillating circuit: without control (with recording time base 40 \(\upmu\)s) as well as for PWMs determined for cases \(R_{o}\) = 100 \(\Omega\), \(R_{o}\) = 200 \(\Omega\) and \(R_{o}\) = 500 \(\Omega\) (with time base 200 \(\upmu\)s). As may be interpreted, the local boost converter oscillations frequency is near to 60 kHz and mainly this is defined by the used transformer inductances. The boost converter oscillator wakes up for input voltage near to minimal polarization level 0.7V of semiconductor junction and the non-isolated version of applied topology assures that electric current generated below this threshold is transferred to load, too (i.e., after forward polarization of output Schottky diode). For measurement form Figure 11a, the control signal \(x_{c1}(t)\) is on low state all the time and this means M1 transistor switch-off and permanent oscillations. The next three oscillograms illustrate the properness regulation of PWM waveform. As was expected, for the \(R_{o}\) close to the optimal \(R_{MPPT}\) point this square signal has minimal coefficient of duty cycle and proportionally larger ones for the next two operational points. This regulation tendency is correct and proves the capability of MPP tracking, especially for loads with resistances above the currently optimal one, i.e., when voltage boost operation was successfully applied to MPP correction purpose. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{2}{c}{**With Evolutionary MPPT**} & \multicolumn{2}{c}{**Without**} & \multirow{2}{*}{**Electric Power**} \\ \cline{2-2}
**Load Resistance** & & & & **MPPT** & \\ \cline{2-2}
**\(R_{o}\) [\(\Omega\)]** & **Average Load** & **Average Power** & **Average Load** & **Average Power** & **Enhancement 1** \\  & **Voltage** & **Generated** & **Voltage** & **Generated** & **\(\eta\) [\%]** \\  & **\(\mathbf{U}_{out}\) [V]** & \(\mathbf{P_{o}}\) **[mW]** & \(\mathbf{U}_{out}\) [V]** & \(\mathbf{P_{o}}\) **[mW]** & \\ \hline
50 & 1.87 & 69.94 & 1.26 & 31.75 & 120.28 \\
100 & 2.90 & 84.1 & 1.88 & 35.34 & 137.97 \\
200 & 3.58 & 64.08 & 2.60 & 33.08 & 93.71 \\
500 & 4.11 & 33.78 & 3.66 & 26.79 & 26.10 \\ \hline \hline \end{tabular}  
* Relative increase in electric power obtained.  
\end{table} 
Table 1: The average levels of voltages and load powers comparison. The last Figure 12 allows the evaluation of the general usefulness of used TES1-24106 modules for the energy transformation process. They present unsteady state of temperature decomposition between ceramic sides of the device so that gradient \(\Delta T\) reached about twice that established during the previous experiment. The measurements presented are observed for load \(R_{o}\) = 50 \(\Omega\) and for point reached after 100 s voltage \(U_{out}\) = 3.83 V was measured, which doubled the level of the respective one from Table 1. This result confirms the linear relationship between TE terminals voltage and temperatures plates difference. The output power reached for \(\Delta T\approx\) 24 \({}^{\circ}\)C is equal to \(P_{o}\) = 293.38 mW that may be \(N\)-th time multiplied in sectional panel from Figure 7.  
Figure 11: The DC/DC converter voltage oscillograms measured on collector of switching transistor and on gate of control transistor for PWM signal: (**a**) disabled, (**b**) for \(R_{o}\) = 100 \(\Omega\), (**c**) \(R_{o}\) = 200 \(\Omega\), (**d**) \(R_{o}\) = 500 \(\Omega\).