Power management and applications
As presented in Figure 3
, the final step (which is essential) to develop an EH module is the electrical-electrical converter inserted between VEh and storage because VEh output power is characterized by high AC voltage and low current that cannot be used as is to power electronic components.
This step can be achieved by different DC/DC converters: buck, buck-boost or flyback. These converters allow a DC/DC conversion that can reach more than 80 percent of efficiency and need quite simple control circuits that generally consume less than 5µW. An example of a flyback converter and its application to VEH is presented in Figure 8
Figure 8: VEH, DC/DC converter and storage/application
Table 2: VEH today, tomorrow and after tomorrow
These converters have another great interest: by transferring VEh energy to storage at the right moment (e.g. when VEh output voltage is maximum or minimum), it is possible to add non-linear behaviors (synchronized switch harvesting) to improve power extraction from VEh and therefore to increase VEh output power.
Roadmap – Perspectives
As VEh considered as complete systems rely on technologies derived from many research fields (electronic, wireless communications, materials, power management etc.), predicting future developments is quite difficult. As a consequence, we will only present in Table 2 our vision of VEH Today, Tomorrow and After Tomorrow with expected sizes and output powers and their applications to WSN.
Thanks to consumption reduction of basic functions, it is today possible to replace batteries by VEH for WSN. Measurement frequencies are still small but the concept has been validated.
The future of VEH and more generally of EH seems pretty bright as it is consistent with present topics, such as power budget reduction, green power and durable supply sources. Nevertheless, technologies are still emerging and they have not yet been adopted by industry.
Our main objectives today are focused on three points: (i) increase frequency bandwidth, which is probably the most important point to improve in VEh; (ii) increase VEh output power and (iii) decrease electronic circuit power consumption. Improving these different points should help a more widespread use of VEh to power WSN.
Sebastien Boisseau and Ghislain Despesse are researchers at CEA-Leti, a French institute focused on micro- and nanotechnologies and their applications. CEA-Leti is part of CEA, French Atomic Energy and Alternative Energies Commission.
The authors would like to thank their VEH coworkers, B. Ahmed Seddik, J.J. Chaillout, A.B. Duret, P. Gasnier, P.D. Berger, S. Riché and S. Dauvé for their contributions to this article.
. Energy harvesting, wireless sensor networks & opportunities for industrial applications
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