| Title | (Invited Paper) Room-Temperature Fuel Cells and Their Integration into Portable and Embedded Systems |
| Author | *Naehyuck Chang, Jueun Seo, Donghwa Shin, Younghyun Kim (Seoul National University, Republic of Korea) |
| Page | pp. 69 - 74 |
| Keyword | Fuel cell, DMFC, hybrid, BOP control |
| Abstract | Direct methanol fuel cells (DMFCs) are a promising next-generation energy source for portable applications, due to their high energy density and the ease of handling of the liquid fuel. However, the limited range of output power obtainable from a fuel cell requires hybridization the introduction of a battery to form a stand-alone portable power source. Furthermore, the stringent operating conditions to be met by active DMFC systems mandate complicated balance of plant (BOP) control. We present a complete hybrid active DMFC system design and implementation in which a DMFC stack and a li-ion battery are linked by a hybridization circuit to share the applied load to exploit high energy density of the fuel cell and high power density of the battery. We describe systems for fuel delivery, air supply, temperature management, current and voltage measurement, DC--DC conversion and power distribution, motor driving, battery charge management, DMFC and circuit protection, and control of the DMFC and battery as a hybrid. We have designed and implemented an embedded system controller that consists of a 32-bit microcontroller, running under a real-time operating system, that incorporating multiple cascaded feedback control loops which manage the dynamics of BOP control. We demonstrate reliable and efficient maintenance of a constant fuel cell output current in spite of severe fluctuation of the load current. |
| Title | (Invited Paper) Maximizing the Harvested Energy for Micro-power Applications through Efficient MPPT and PMU Design |
| Author | Hui Shao, *Chi-Ying Tsui, Wing-Hung Ki (Hong Kong University of Science and Technology, Hong Kong) |
| Page | pp. 75 - 80 |
| Keyword | Energy harvessting, micro-power systems, MPPT, power management |
| Abstract | Energy harvesting is becoming more and more popular for micro-power applications where the environmental energy is used to power up the systems. In order to prolong the device lifetime and guarantee the system operation, the harvested power from the energy transducer to supply the system load should be maximized. This paper reviews different techniques and solutions to maximize the harvested power. Different environmental energy sources and the characteristics of the corresponding energy transducers are discussed. Algorithms to detect and track the maximum power point (MPP) of the energy transducer are summarized. Different power management unit (PMU) designs to execute MPP tracking (MPPT) algorithms are presented. |
| Title | (Invited Paper) Dynamic Power Management in Environmentally Powered Systems |
| Author | Clemens Moser, *Jian-Jia Chen, Lothar Thiele (ETH Zurich, Switzerland) |
| Page | pp. 81 - 88 |
| Keyword | power management, embedded systems, energy harvesting, model predictive control, optimization |
| Abstract | In this paper a framework for energy management in energy harvesting embedded systems is presented. As a possible example scenario, we focus on wireless sensor nodes which are powered by solar cells. We demonstrate that classical power management solutions have to be reconceived and/or new problems arise if perpetual operation of the system is required. In particular, we provide a set of algorithms and methods for different application scenarios, including real-time scheduling, application rate control as well as reward maximization. The goal is to optimize the performance of the application subject to given energy constraints. Our methods optimize the system performance which allows the usage of, e.g., smaller solar cells and smaller batteries. Our theoretical results are supported by simulations using long-term measurements of solar energy in an outdoor environment. Furthermore, to demonstrate the practical relevance of our approaches, we measured the implementation overhead of our algorithms on real sensor nodes. |
| Title | (Invited Paper) Micro-scale Energy Harvesting: A System Design Perspective |
| Author | Chao Lu, *Vijay Raghunathan, Kaushik Roy (Purdue University, U.S.A.) |
| Page | pp. 89 - 94 |
| Keyword | Energy Harvesting, Low Power Design, Power Management |
| Abstract | Harvesting electrical power from environmental energy sources is an attractive and increasingly feasible option for several micro-scale electronic systems such as biomedical implants and wireless sensor nodes that need to operate autonomously for long periods of time (months to years). However, designing highly efficient micro-scale energy harvesting systems requires an in-depth understanding of various design considerations and tradeoffs. This paper provides an overview of the area of micro-scale energy harvesting and discusses the various challenges and considerations involved from a system-design perspective. |