27.1 An 84% Peak Efficiency Bipolar-Input Boost/Flyback Hybrid Converter With MPPT and on-Chip Cold Starter for Thermoelectric Energy Harvesting

Recent advances in energy-harvesting techniques have allowed wearable and IoT devices to operate without batteries. A thermoelectric generator (TEG) is one energy source that can provide a bipolar voltage that is proportional to the temperature difference between its two sides. Most of the prior TEG-harvesting systems could handle the positive input voltage [1–3]; however, the TEG's input voltage polarity may reverse due to environmental changes. Only a few prior publications provide a method to deal with the bipolar input voltage [4–6]. To harvest bipolar input energy, a switch-matrix-based boost converter is proposed in [4], but it cannot self-start and dynamically track the maximum power point. [5] and [6] provide methods for bipolar self-startup with an ultra-low input voltage, but both of them suffer from a low conversion efficiency. Hence, there is no complete system suitable for bipolar-input TEG energy harvesting. A solution must address three challenges: (1) the transfer of energy from a bipolar input voltage via a high-efficiency converter; (2) system self-start-up with a reasonably low bipolar input voltage; (3) a maximum power point tracking (MPPT) method for bipolar input voltage. This paper proposes a bipolar-input boost/flyback hybrid converter (BFHC) with an on-chip cold start-up for TEG energy harvesters.