# Evolutionary Maximization of Energy Amount Harvested by Means of Panel of Thermoelectric Modules
## 5 Practical Experiment  
The correctness of MPPT regulation by means of the described evolutionary method was tested practically and the results from one string of 16 relatively low-cost TES1-24106  
Figure 5: Convergence speed of the compared methods. Figure 6: Average fitness into population progress curves. modules (dimensioned as 40 \(\times\) 40 \(\times\) 2.8 mm) connected in series are presented in this section. The electric diagram of boost converter used during this experiment is presented in Figure 7. A simple joule thief, a supercharged version of self-powered and self-oscillating boost converter topology is chosen for local MPPT low power processing. This self-oscillating circuit is cheap for realization, assures start for a low supply voltage [33; 34; 35] and after a small modification may be useful for the sectional optimal power point tracking by NMOS M1 PWM switching signal respective adjusting. An evolutionary system was implemented to STM32L476 firmware and the complete laboratory test station assembled is shown in Figure 8.  
Figure 8: The laboratory test station of TE panel with passive cooling. Figure 7: Electric diagram with simple boost converter dedicated to each TE string. The 16 TES1-24106 modules are placed in four rows between a heating plate and aluminum radiator that assures passive cooling of the TE panel low temperature side by means of surrounding air convection. This cooling method is not quite effective, but any power supply and additional mechanical, moving components are not needed there. Silicon thermo paste is applied on both ceramic sides of each TE devices and together with heating surface they are pressed mechanically to the radiator by means of a few springs and bottom rigid plate screwed on. Additionally, on the hot side there is thermo-isolation rock wool layer reducing undesired energy dissipation to the air. The matching power curve obtained for the constructed TE panel is presented in Figure 9.  
The above curve presents the relationship between output power \(P_{o}\) delivered and load resistance \(R_{o}\) for temperature difference \(T_{H}\)-\(T_{C}\approx 5\)\({}^{\circ}\)C and 40 \({}^{\circ}\)C on the hot side. As it may be noticed, for the assumed temperature point, the match resistance is about \(R_{MPPT}=120\)\(\Omega\) and the microcontroller should operate with PWM signal assuring the operation of energies converting possibly close to this optimal load level. Low power boost converter and TE modules string output current-voltage measurement block are presented in Figure 8 on the right side of the panel and they are connected to the evaluation board equipped with ultra-low power ARM microcontroller family STM32L4 that accepts a wide range of 1.71-3.6 V of voltage supply and consumes just 100 uA/MHz during run mode. The STM32L476 chip has the three embedded 12 bits A/D converters and offers up to the seven internal counters that allows it to generate PWM signals on output terminals (more than 20 independent channels available for the \(N=20\) TE strings individual controlling). The tested evolutionary method was implemented to microcontroller and run with system clock \(f_{CLK}=48\) MHz, ADC sampling frequency \(f_{S}\approx 50\) kHz and \(D_{MX}=16{,}000\) discrete levels available for duty cycle settings. The optimized square signal generated by counter TIM1 had a frequency of \(f_{PWM}=3\)kHz with impulses durations evolutionarily determined in the way described in Section 3. Evolutionary computations were started for initial parameters: population size \(K=20\); one controlled channel \(N=1\); maximal steps of one iteration \(C_{MX}=1000\); and genetic operations probabilities \(P_{mm}=0.2\), \(P_{\sigma}=0.9\), \(P_{mu}=0.2\), respectively.