Automatic Impedance Matching With Dual Time-Scale P&O in Fully Self-Powered Electromagnetic Vibration Energy Harvesting
Hongfei Xiao, Han Peng, Hanyi Sun, Yidong Zhao, Xianchao Liu, Cheng Jiang
Abstract
Most of electromagnetic vibration energy harvester (EVEH) systems are only focused on resistance matching at resonant frequency. However, the EVEH will have complex output impedance at nonresonant frequencies. Pure resistance matching cannot fully extract the maximum power at nonresonance. This article is the first to propose an automatic and fully self-powered complex impedance matching EVEH system. The characteristics of the output impedance of the EVEH are analyzed, and it is found that the impedance will be distributed on a circle. An impedance-circle-based perturb-and-observe (P&O) method with dual time-scale is proposed. It perturbs the central angle with a short time-scale for fast response to vibration frequency change, and perturbs both angle and diameter with a long time scale to adapt to the slow aging and wear-out of the EVEH. Such dual time-scale P&O improves the speed and accuracy of complex impedance determination. Besides, a fully self-powered milliwatts impedance control scheme with an inductor-less H-bridge ac–dc converter is designed. Experiments show that the designed system can realize complex impedance matching control stably and quickly. The maximum improvement of the output power of the converter reaches 25% compared to resistance matching scheme at nonresonant frequencies. Under the excitation acceleration amplitude of 3 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at the resonant frequency, the system generates the maximum power of 10.11 mW with the overall system efficiency reaching 82.2%. It is the first time the automatic complex impedance matching is realized in millipower fully self-powered EVEH.