Power Management and Storage
This theme focuses on the design, modelling, characterisation and prototyping of power management and storage circuit for different types of energy harvesting transducers and a wide range of industrial applications. The sub-areas we are researching include:
- Maximum power point tracking and power extraction
- Energy flow management
- Adaptive/reconfigurable circuit and energy storage
- Multi-source power management
Adaptive maximum power point tracking
- High energy transfer & low power consumption
- Adaptive to
- time-varying ambient input
- variable energy sources
- variable end-user demand
- Energy-aware wireless sensing
- Without start-up issue
- MPPT capability: 98.3%
- MPPT power-consumption: 5-7 µW
- System efficiency: ~80%
- Quiescent current in the energy-aware interface : 950 nA
- Minimum start-up power: ~10 µW
The developed control circuit is implemented using micropower consumption analogue differentiator and comparator without power hungry sensing circuitry and microcontroller. Maximum power transfer of most energy harvesters occurs at half of the open-circuit voltage (VOC/2) of the energy harvesters. The control circuit uses an innovative method, which is the RC response of a charging capacitor to determine VOC/2 of the energy harvesters. The performance of this control scheme is verified by using the prototyped circuit to track the maximum power point of a macro-fiber composite (MFC) piezoelectric energy harvester. Experimental results demonstrate that the implemented full analogue control circuit (ACC) has a tracking capability of up to 98.28% and consumes as little as 5.16 µW of power during operation. Combined with the maximum power point tracking circuit, more power can be extracted from some non-resistive energy harvesters such as piezoelectric transducers.
- Adaptive Maximum Power Point Finding Using DirectVOC/2 Tracking Method With Microwatt Power Consumption for Energy Harvesting
- Microwatt power consumption maximum power point tracking circuit using an analogue differentiator for piezoelectric energy harvesting
- Combined power extraction with adaptive power management module for increased piezoelectric energy harvesting to power wireless sensor nodes
Energy harvesting powered wireless monitoring system design has been driven by the need to reduce power consumption of the wireless sensor nodes (WSNs). The mismatch between the energy harvested from ambient vibration and the energy demanded by WSNs to achieve the functions required by end users is always a bottleneck issue as the ambient environmental energy is time-varying and limited. We have developed an energy-aware interface (EAI) to deal with the mismatch between energy harvested and energy demanded by the end of users for energy flow management. The EAI reduces the sleep current of wireless sensor nodes from the commercial 200-300µA to 1μA. This ensures most of the harvested energy can be accumulated in the energy storage. The developed EAI has led to that Exeter have developed a high performance “proof-of-concept” energy harvesting powered wireless sensor node demonstrator harvesting aircraft wing strain energy for structural health monitoring and harvesting knee-joint motion energy for body sensor networks.
Sometimes it is difficult to rely on a single circuit topology to operate effectively and efficiently across a wide range of operating conditions that occur in the environment. Therefore, circuits that are adaptive and reconfigurable would be able to meet the requirements in real-world applications where the environmental conditions may vary a lot and unpredictably. An adaptive self-reconfigurable rectifier has been developed to extend the operating range of piezoelectric energy harvesting.
Similarly, a single fixed size energy storage in the power management circuit may not be able to meet the demand of all the industrial applications. For example, a large capacitor may take a long time to be charged up if the harvested energy is low whereas a small capacitor may not be able to provide the energy required by a wireless sensor node for its operation. Therefore, an adaptive and reconfigurable energy storage would make a system more versatile, capable of operating under different conditions based on the harvested energy level or energy demand from the wireless sensor nodes.
Often, many different energy sources are available to be harvested in a location. This research aims to harvest multiple sources using a single power management circuit with a shared DC–DC converter and a common energy storage. Using only one DC–DC converter that is shared among the energy harvesters would reduce the overall power consumption of the circuit. Since the availability of different energy sources might vary with time and location, a common energy storage that stores the energy from all the different energy harvesters would potentially allow the end devices connected to the power management circuit to operate continuously with energy from the different sources. Low power consumption and high efficiency remain the key features to be achieved in this circuit.