ENMOS: Energy Module for Self-Sustainable Wearable Sensors

ENMOS: Energy Module for Self-Sustainable Wearable Sensors

Parag, Anirudh Kumar (TU Delft Electrical Engineering, Mathematics and Computer Science)

Serdijn, Wouter (mentor)
French, Paddy (graduation committee)
Fan, Qinwen (graduation committee)
Urso, Alessandro (graduation committee)
Rodrigues Mansano, Andre (graduation committee)

Delft University of Technology

Electrical Engineering

2019-08-27

This work focuses on addressing the fundamental limitation on the minimum cold start-up voltage that could be harvested from a thermoelectric element (TEG) for human-body wearable applications. For ultra-low DC voltages, the challenge translates to generating a timed-signal to amplify it up to a value that could be used to drive, say, a boost converter which can then start-up the entire energy module. Contemporary works have, thus, strived to accomplish this using a charge-pump-based or a transformer-based approach, which in turn imposes a limit on the minimum TEG voltage that can be harvested. The solution this work proposes is to decouple the Cold Start-up system from the TEG altogether and instead, use a piezoelectric element (PEH). This element being capable of producing a well-timed (AC) signal for free, based on human body vibrations, can potentially drive a boost converter. To this end, an integrated circuit (IC) is designed that can utilize the voltage from the PEH, amplifying it up to generate a well-controlled signal that could operate the boost converter. At the heart of this IC, is a self-reconfigurable charge pump that arranges its stages in different boosting ratios (without any complex logic or DSP) based on the input voltage, to allow for a maximum harvested power. The proposed self-reconfigurable architecture can potentially lead the charge pump to be load-variation-resistant. It achieves this by providing an almost constant voltage while increasing the power for higher load demands, at the same time maintaining a constant efficiency. Thus, the fully on-chip implementation in TSMC 0.18 um CMOS, can cold start-up the system from 25 mV of thermoelectric voltage to deliver an output voltage of 1 V at 56.5 % converter efficiency, consuming only 240.5 pW of dynamic power (simulation). The minimum Cold Start-up voltage and dynamic power were found to be 18 mV (ΔT = 0.1 K) and 231.6 pW respectively, to supply 1 V at 44 % converter efficiency. Moreover, in order to prove that the fundamental limitation on the Cold Start-up voltage has been addressed successfully, the IC was also simulated to check whether it can further be lowered. In this case, by providing a piezoelectric excitation voltage 73.3 mVRMS higher, the Cold Start-up voltage was found to be reduced to 15 mV to supply a constant 1 V at the load. It was also found that increasing the inductor value in this case, can also allow the energy module to support even lower Cold Start-up voltages.

Energy Harvesting
Cold Start-up
Thermoelectric energy generator (TEG)
Piezoelectric energy harvester (PEH)
Self-Reconfigurable charge pump
Dickson charge pump
Ultra-low power
Ultra-low voltage
Power module
Analog integrated circuit design

http://resolver.tudelft.nl/uuid:b64fdbc9-64cb-44bf-9b17-3c57dcfa9c0a

2020-08-27

Student theses

master thesis

© 2019 Anirudh Kumar Parag