A Voltage-Feedback-Based Maximum Power Point Tracking Technique for Piezoelectric Energy Harvesting Interface Circuits

This article presents and demonstrates a voltage feedback-based technique to implement a power management integrated circuit (PMIC) for piezoelectric energy harvesting. It is analytically shown that the conducting time interval of a rectifying diode at the maximum power point is a fixed ratio of the vibration period. Thus, it can be used as a feedback to track the maximum power without measuring the output current/power. The technique can be tailored to various interface circuits, including full-bridge (FB), voltage doubler, and synchronized switch harvesting on an inductor. The micro-fabricated PMIC includes a FB rectifier, a digital maximum power point tracking (MPPT) controller, and a zero-current-switching (ZCS) integrated buck converter that uses two off-chip inductor and rectifying capacitor. The proposed technique enables the implementation of robust and power-efficient PMICs for MPPT of piezoelectric energy harvesters. To evaluate the performance of the technique, a PMIC using 130-nm CMOS technology is implemented and tested with a low power $( < 0.5$ mW) piezoelectric energy harvester. The results show that the PMIC effectively tracks the maximum power point at different vibration frequencies and amplitudes while the power consumption of its control circuitry is less than 0.001 mW.