One-Dimensional Maximum Power Point Tracking Design of Switched-Capacitor Charge Pumps for Thermoelectric Energy Harvesting

Abstract

This paper proposes a one-dimensional (1D) maximum power point tracking (MPPT) design which only requires measurement of one parameter (the input voltage of a switched-capacitor charge pump) for calibrating a power converter including the charge pump and thermoelectric generator. The frequency of the clock to drive the charge pump is designed to minimize the circuit area of the entire charge pump circuit for generating a target output current at a specific output voltage. The ratio of the capacitance value of each boosting capacitor (C) to the size of the switching MOSFET can be determined to maximize the transferring current at the same time. When a thermoelectric generator (TEG) is given, its output impedance is determined. Its open-circuit voltage varies with the temperature difference between two plates of the TEG. MPPT maximizes the output power of the charge pump even when the temperature difference varies. It was indicated that the number of stages of charge pump (N) needs to increase when the temperature difference lowers, whereas C needs to decrease inversely proportional to N, meaning that the C–N product should be kept unchanged for MPPT. Demonstration of the circuit design was conducted in 65 nm CMOS, and the measured results validated the concept of the 1D MPPT.