A Power Management System for Electromagnetic Energy Harvesters in Battery/Batteryless Applications

This article presents a miniaturized and cost-effective power management system (PMS) for low-voltage electromagnetic energy harvesters (EMEHs) operating in both battery-powered and batteryless applications. The PMS consists of two converters and their associated controllers. The first converter converts EMEH's ac voltage into a dc one in a single step and provides a maximum efficiency point tracking (MEPT) feature to maximize the harvested energy and can be used alone in battery-powered applications. The second converter provides tight output voltage regulation for batteryless applications. The MEPT converter utilizes a topology that uses a single inductor shared between the positive and negative half cycles of the EMEH voltage, unlike the majority of existing solutions, hence achieving system's cost and size reductions. In addition, its control architecture is based on low-power comparators and does not require zero-crossing detection (ZCD) block, in contrast to many existing solutions, allowing for further reduction in cost, losses, and size. Moreover, the shared inductor is not only used by the power stage but also as a key element of the bias supply scheme allowing for voltage stepping up and hence providing sufficient voltage to supply the control circuits. The voltage regulation converter features a highly integrated dc-dc converter where the power inductor serves as normal inductor and a substrate for the converter. Experimental results show the effectiveness of the PMS with an EMEH that has a damped ac voltage characteristics ranging from 1.0 V to 10 mV for battery and batteryless applications. The presented MEPT converter, switching at 40 kHz, achieves 32.3-mm(3) magnetics volume, which is the biggest contributor to the real estate of the PMS. Also, it can harvest up to 17 mJ out of 20 mJ available energy while achieving a BOM cost less than 0.7(sic). Moreover, the highly integrated buck converter, switching at 4 MHz, provides a tight regulated voltage of 1.2 V at 5 mA for a group of wireless sensors while achieving efficiency of 80% for load currents between 100 mu A and 200 mA.