Power Management
from kinetic energy. But the frequency of the vibrations varies significantly under different operating conditions and working environments, and this complicates the design of systems which use this form of energy. “Because of their greater conversion efficiency and also because developers have many years of experience in using them, solar cells have the greatest market penetration today. Small solar cells are quite widely used in building automation. Depending on the application, however, thermo-electric and vibration transducers are also ready for the market, and with the increasing number of uses to which energy harvesting will be put, further diversification lies ahead,” explains Donaldson.
An agony of choice One of the greatest challenges for the developer in the use of energy harvesting lies in marrying the energy produced with the application’s requirements. With the example of photovoltaic systems, the designer's approach is typically as follows: the lighting conditions at the location where they are planned to be used are evaluated. Using this information, the energy supply is designed (taking into account yield, storage efficiency and the likely power consumption of the system). According to Donaldson “The approach to determining system
efficiency can be extremely complex. Environmental influences, such as varying light or temperature conditions round the clock, are hard to calculate. We wanted to reflect our customers’ concerns in choosing the right components so the Energy Harvesting Platform is both flexible and easy to use. The components of which combine well with each other under realistic operating conditions.” The Energy Harvesting Platform for the development of self-
sufficient energy systems models the whole system from the energy source via storage up to the consumer in the form of an application board. Evaluation in a realistic usage scenario is only possible with the help of tools. Using the Future Energy Solutions platform, the developer can test the specifications of their planned harvesting application in detail at the intended operating location, and see how the components interact. While the values in data sheets for individual components provide some indication of likely performance, the platform captures exact performance under fluctuating ambient conditions.
The system is comprised of a motherboard that measures the energy yield of various harvesting sources by means of interchangeable daughterboards. A graphical user interface displays performance and also makes the process running behind the system transparent. Energy conversion and storage up to usage by the application are represented in the display. The development engineer can use these to test which components are best suited to the conditions of their application. This is why the platform has been kept as generic as possible, allowing the evaluation of different components.
The set-up of the energy harvesting platform reflects the
requirement for high energy efficiency. The platform uses an LPC1114 microcontroller from NXP Semiconductors which performs the task of processing information from the energy source about input power and available current. This MCU meets the requirement for extremely fast data processing, and for fast transition into Sleep mode – much better in this regard than the 8- or 16-bit MCU options available. The LPC1114FBD48 is an ARM Cortex-M0 microcontroller with 32kB of Flash memory, a Fast-Mode Plus I2C bus interface, RS485/EIA485 UART, two SPI interfaces, a 10-bit ADC and 42 I/O pins. In order to precisely capture the voltages of the harvesting source and storage board, a high-precision comparator from Micrel was chosen – the MIC842. The captured energy is stored in two 1F, 5.5V supercapacitors from Illinois Capacitor.
The platform is also equipped at launch with solar panels from Sharp. The ultra-thin polycrystalline cells provide up to 300mW and are optimised for use in energy harvesting. Future Energy Solutions will be expanding its Energy Harvesting Platform with additional daughterboards for the generation of power from heat and vibration during 2012.
The energy harvesting platform provides a development tool that supplies the development engineer with great flexibility. For the developer, it is now easier to choose the right components and adopt this innovative method of powering devices. Energy is available everywhere. It is just waiting to be efficiently harvested and exploited.
Future Energy Solutions is a division of Future Electronics |
www.futureenergysolutions.com
www.cieonline.co.uk
Components in Electronics
September 2012 35
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