Energy scavenging for autonomous system
Toh, Wang Yun
Date of Issue2017-12-18
Interdisciplinary Graduate School (IGS)
With huge advancements in CMOS technology, portable electronics can now be operated at a lower voltage, hence lowering the stress index on energy storage elements. A relevant application will be the ubiquitous smart sensors deployed for health, structural and environmental monitoring. With regards to the research topic, the most important component in a smart sensor is its power source. The power source should be relatively compact and have a near-infinite energy capacity for an uninterrupted sensing operation throughout its lifetime. For that reason, energy harvesting techniques are being looked upon as a replacement or supplement to improve the reliability of the power source. The processing circuits of the energy harvesting system must be simple and highly efficient in order to be popular with the consumer market. Harvesting energy from ambient sources such as light, heat, motion and radiofrequency is an attractive alternative to the finite capacity primary batteries. Among these available ambient energy, light energy has the highest power density and is readily available under indoor and outdoor conditions. Hence, light energy harvesting techniques are being looked upon as a complement to improve the reliability on the power source of the miniaturised wireless sensor. In order to extract the maximum power from a photovoltaic (PV) panel, maximum-powerpoint-tracking (MPPT) circuitries are required. The MPPT circuitry includes a DC-DC converter and a controller to extract power from the PV panel by operating the PV panel at its maximum power points which varies with irradiance and temperature. This thesis introduces two topologies for light energy harvesting system with MPPT control. The first design is an autonomous wireless sensor node with flexible energy harvesting mechanism that is able to conform to the body's contours, is proposed for biometric monitoring. To fulfill the requirements of sustainability and compact size, the proposed system is equipped with an ultralow power management circuit specially designed on a flexible printed circuit board. The flexible power management circuit is able to transfer near maximum electrical power (88.5 %) from the flexible solar panel to store in the supercapacitor for powering the wireless sensor node. The power consumption of the flexible power management circuit only takes up 32.86 µW. Experimental results show that under indoor conditions with typical average lighting intensity of 320 lux, the wearable sensor node is able to continuously monitor, read and transmit the temperature of the wearer back to the base node without the need of any batteries. In addition, the designed FEH sensor node aligned to the body's contours at an angle of 30° generated 56 µW of electrical power, which was sufficient to sustain its operation for more than fifteen hours. The second design deals with the improvement of the interface circuitry used for maximum power point tracking of a solar panel. A new maximum power tracking technique for the solar panel is introduced. The new MPPT technique is implemented with 0.18 µm CMOS process. The proposed circuitry is equipped with leakage reduction technique and the power consumption of this circuitry is only 12.113 nW while maintaining a tracking efficiency of 98.6 % for an input power of 268 µW.
DRNTU::Engineering::Electrical and electronic engineering::Power electronics