Modeling of Supercapacitors as an Energy Buffer for Cyber-Physical Systems

Supercapacitors have superior power density, 10x higher than that of the rechargeable batteries, while their energy density (i.e., charge storage capacity) is only one tenth that of comparable size rechargeable batteries. Despite this low energy density, supercapacitors have been the indispensable components of high-powered industrial applications, such as elevators, car starters, and brake energy regeneration systems in hybrid cars. One noticeable commonality in all of these applications is the irrelevance of the energy loss during the storage and consumption of energy. Since the energy is being stored and consumed at rates unmanageable by any other energy storage device, the loss of energy is tolerated. In this paper, we concentrate on a set of embedded systems that utilize supercapacitors for completely different reasons: In addition to their peak power output capability, supercapacitors also possess superior features such as environmental-friendliness, long operational lifetime (e.g., a million charge/discharge cycles, as opposed to a maximum of 5,000 as in the best commercially available rechargeable batteries), and energypredictability. Our target embedded systems consume only 1–10 Watts of power, as opposed to the nearMW levels for the aforementioned industrial applications, and are nearly agnostic to the peak power capability. While these systems can significantly benefit from these superior features of the supercapacitors, one feature becomes the most important one: the energy storage and consumption efficiency. Through MATLAB-based simulations utilizing the existing supercapacitor models, we show that, at certain power consumption levels, supercapacitors are nearly 100% efficient, while their efficiency suffers dramatically when they are pushed outside their comfortable operating region. We demonstrate this using simulations on four different size (and type) supercapacitors and determine these efficient operation regions for each size supercapacitor.