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Effect of DC-DC voltage step-up converter impedance on thermoelectric energy harvester system design strategy

Watson, Thomas C., Vincent, Joshua N., Lee, Hohyun
Applied energy 2019 v.239 pp. 898-907
electric potential difference, geometry, harvesting, heat, systems engineering
Conventional thermoelectric energy harvester design strategies often focus on improving the material property thermoelectric figure of merit (ZT); however, enhanced performance through improved materials cannot be achieved without optimized integration of subcomponents. The low voltage output from a thermoelectric module makes it challenging to design a practically usable wearable energy harvester. In addition to consideration of effective heat dissipation along with matching module geometry, a voltage needs to be boosted at a usable voltage value to utilize produced power. Using a DC to DC voltage step-up converter adds additional design complexity as the power cannot be harnessed at maximum power point of thermoelectric module due to input impedance requirement of the power conditioning circuit. Moreover, additional power loss occurs due to inherent voltage conversion inefficiency, which also depends on the harvesting voltage value. A recent design framework on wearable thermoelectric energy harvester assumed that a Maximum Power Point Tracking (MPPT) boost converter can be utilized for thermoelectric energy harvester systems, however it is unable to accurately determine the maximum power point during operation because of the transient nature of thermoelectric systems. Additionally, an MPPT circuit consumes power and adds complexity to the system design, which may not economically justify the use of such a circuit. This work proposes an encompassing thermoelectric system design framework for small scale energy harvesting using only state-of-the-art commercial products. Particularly, thermoelectric module geometry design is examined with the incorporation of a DC to DC voltage step-up converter without the use of MPPT. The framework can provide guidance for further development of subcomponents and materials, as well as system integration. An operational wearable energy harvester system was built using off-the-shelf components and demonstrated a usable power output which provides experimental evidence for the proposed design strategy.