## 5 Maximum Power Point Tracking  
### MPPT Algorithm  
If a thermoelectric module is to provide maximum power output in different temperature ranges and temperature differences, maximum power tracking is required to operate the thermoelectric module at the maximum power point. In addition, the PV characteristic curve of a thermoelectric module is similar to that of a solar cell. However, the difference between them is that the PV characteristic curve of a thermoelectric module is more symmetrical. Consequently, according to this feature, a maximum power tracking method based on three-point-weighting MPPT is relatively suitable for thermoelectric modules in practice.  
Figure 22 shows the MPPT flow chart used in this paper. The principle of this control method is to calculate the power value by continuously detecting the output power value at three points and comparing their power magnitudes. First of all, set a duty cycle of \(D_{b}\) at the reference point \(b\), and detect the output voltage and current of the thermoelectric module to calculate the power value \(P_{b}\); sequentially, increase the duty cycle by one unit of disturbance, i.e., \(D_{b}+\Delta D\), to obtain the second duty cycle of \(D_{c}\) at the point \(c\), and detect and calculate the power value of \(P_{c}\); then reduce the duty cycle by one unit of disturbance, i.e., \(D_{b}-\Delta D\), to obtain the third duty cycle of \(D_{a}\) at the point \(a\), and detect and calculate the power value of \(P_{a}\). By doing so, the power sampling procedure is completed. Afterwards, if the power \(P_{a}\) is greater than or equal to the power \(P_{b}\), the weight value of \(W_{1}\) will be increased by one; if the power \(P_{b}\) is greater than or equal to the power \(P_{a}\), the weight value of \(W_{2}\) will be increased by one, and if not, the weight value of \(W_{2}\) will be decreased by one. Eventually, calculate the weight value to determine the direction of movement of the reference point. If the sum of \(W_{1}\) and \(W_{2}\) is \(+2\), then the point \(c\) is used as the new reference point with the duty cycle of \(D_{c}\); if the sum of \(W_{1}\) and \(W_{2}\) is \(-2\), the point \(a\) is used as the new reference point with the duty cycle of \(D_{a}\); if the sum of \(W_{1}\) and \(W_{2}\) is \(0\), then the reference point \(b\) remains unchanged with the duty cycle of \(D_{b}\). After completing the above actions, the weight value is returned to zero and the above actions are repeated to achieve maximum power point tracking.  
\begin{table}
\begin{tabular}{c c} \hline
**Component** & **Specification** \\ \hline MOSFET switches \(S_{1a}\), \(S_{1b}\), \(S_{2a}\), \(S_{2b}\) & IRF3205Z \\ \hline Diodes \(D_{1}\), \(D_{2}\), \(D_{3}\) & SFF1008G \\ \hline Diodes \(D_{4}\) & STPS20H100 CT \\ \hline Energy-transferring capacitors \(C_{1}\), \(C_{3}\) & 100 μF Electrolytic Capacitor \\ \hline Energy-transferring capacitor \(C_{2}\) & 68 μF Electrolytic Capacitor \\ \hline Clamping capacitors \(C_{4}\), \(C_{5}\) & 10 μF Electrolytic Capacitor \\ \hline Output capacitor \(C_{o}\) & 22 μF Electrolytic Capacitor \\ \hline Coupling inductor \(1/\)Coupling inductor \(2\) & \(L_{m1}=365.6\) μH, \(n=3/L_{m2}=87.3\) μH, \(n=3\) \\ \hline Isolated gate driver & FOD3182 \\ \hline \end{tabular}
\end{table}
Table 5: Component specifications.