Self-powered maximum power point tracking system for ultralow-frequency piezoelectric energy harvesting

This paper reports on the design, fabrication, and experimental validation of a modular and configurable development platform, named PIEZO-DK, tailored for evaluating and optimizing ultralow-frequency piezoelectric energy harvesting systems. Existing MPPT (maximum power point tracking) techniques often have design weaknesses of high complexity, inevitable periodic disconnection, and low efficiency, especially for sub-Hz range, ultralow-power applications. To address this issue, this study pursues a self-powered MPPT method based on a modified fractional open-circuit voltage approach, which is free from microcontroller units. The PIEZO-DK features tunable resistor–capacitor time constants that allow for dynamic adjustment of the power tracking point, making it adaptable to diverse harvester configurations and outputs, including direct compression-type harvesters such as wearables and those embedded in shoes, and resonant systems such as cantilevers. PIEZO-DK’s configurable architecture enables selective, individual isolation of different circuit stages for debugging, probing, and optimization via pin-header jumpers. This feature provides a user-friendly interface for researchers and developers who do not necessarily have extensive knowledge of circuitry design. The experimental validation using a direct compression-type harvester designed for shoes suggests an MPPT efficiency of 96.2% at 0.9 Hz, the highest known to date at a frequency below 1 Hz among those of self-powered MPPT circuits. The results confirm the effectiveness and feasibility in practice for real-world energy harvesting applications. Such a scalable, simple, and energy-efficient tool is ideal for rapid prototyping and system optimization. It helps to accelerate the development pace of Internet of Things systems powered by wearable, biomechanical energy harvesters.