Current harmonized improvement method: A concept of the optimal electrical array configuration of thermoelectric modules for minimizing the mismatch loss of a thermoelectric generator

In a thermoelectric generator (TEG), a considerable amount of unexpected mismatch loss occurs because of the deviation in the temperature difference that individual thermoelectric modules (TEMs) experience when the TEMs are electrically connected in a conventional manner such as in series and/or parallel connections. This study proposes a current harmonized improvement method (CHIME), a novel and practical concept of an electrical array configuration using which the mismatch power loss can be minimized by adjusting the electric current flowing through each TEM close to its optimal value. Considering that the optimal current for each TEM varies according to the temperature difference induced across each TEM, the CHIME-based optimal configuration comprises at least two separate electrical layers with different numbers of electric circuit branches. By allocating a group of TEMs experiencing a lower-temperature difference to a layer with a larger number of branches and the other group of TEMs experiencing a higher-temperature difference to a layer with a smaller number of branches, different magnitudes of electric current can be induced for electric branches of the two layers. By theoretically optimizing the major design parameter of CHIME, the electric branch ratio of the two layers, a near-optimal electric current is induced to each TEM. An additional major parameter of the CHIME-based optimal configuration is the TEM module ratio between the two electric layers, which is determined by applying Kirchhoff's voltage and current laws to a generalized electric array configuration. A series of numerical studies conducted using an experimentally validated numerical model showed that the CHIME configuration shows 15.6 % and 16.2 % improvements in the output power and conversion efficiency, respectively, compared to the case in which all TEMs are electrically connected in parallel when the engine is rotating at a speed of 1000 rpm. Furthermore, the mismatch loss of a TEG whose TEMs are connected based on the CHIME decreases to 1.9 % which is ∼6.6 times lower than the case in which all the TEMs are connected in parallel with the mismatch loss of 12.5 %.