Hybrid Electrical Energy Storage Systems
Apr 20, 2012
from 02:00 PM to 03:30 PM
|Where||ENGR. IV Bldg., Tesla Rm. 53-125|
|Contact Name||Puneet Gupta|
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Seoul National University, Korea
Storage of excessive electrical energy and compensation of the energy shortage can significantly mitigate the over-investment in the generation facilities as well as enhance quality of renewable energy. Development of a better battery technology has been focused as a key to success of high-performance energy storage systems. However, despite active research on the new battery technologies, it is not likely for us to have an ultimate high-efficiency, high-power/energy capacity, low-cost, light-weight, and long-cycle life batteries in the near future. In other words, there is no single type of electrical energy storage element that can fulfill all the desirable requirements.
In computer systems, system architects have been facing with the same problem over decades: there is no single type of memory device in the world that provides high-speed, low-cost, large-density, low-power, nonvolatile, long-endurance, etc. Therefore, computer systems use memory hierarchy such that L1 cache, L2 cache, L3 cache, main memory DDR SDRAM, flash memory, disk drive, and so forth. Memory hierarchy gives programmers illusion (transparency) such that there is a big, unified memory that meets all the desired requirement.
The proposed hybrid electrical energy storage system idea is analogous to the computer memory hierarchy. We use two or more heterogeneous electrical energy storage elements (various types of batteries and supercapacitors), thereby realizing the advantages of each electrical storage element while hiding its weaknesses. Hybrid electrical energy storage systems consist of multiple heterogeneous battery and super capacitor banks (each bank is a homogeneous electrical storage element array), which are connected by the charge transfer interconnect.
To realize this idea, hybrid electrical energy storage systems mandate elaborated architectural design and charge management policies. We formulate the management problems and project them into computer memory system design, interconnect architecture and management problems. This enables us to utilize profound systematic optimization tools that have been used in computer systems design over decades.
We set up the hybrid electrical storage system management problems into charge allocation that determines a part of storage banks to be charged, charge replacement (discharge) that determines a part of storage banks to be discharged. The charge allocation and replacement are performed to achieve the best efficiency considering the power loss in the battery (or supercapacitor) banks (IR loss, rate capacity effect, leakage, etc.) and the power loss in the charger and converters which significantly varies by the input/output voltage and current. As the best set of banks for individual charge allocation and replacement process can be different in general, we provide charge migration that moves charge among the storage banks. All these operations are performed by elaborated online optimization process.
This talk also covers architectural consideration of the hybrid electrical storage systems. To accommodate many number of banks for a large-scale storage systems, there should be highly flexible interconnects among the storage banks. The interconnect architectures include a shared bus, multiple buses, mesh interconnects, etc. We introduce a mesh interconnect architecture and associated routing problems. Furthermore, sharing the interconnect by multiple charge management operations require scheduling issues. We will also introduce HEES prototype implementation.
Naehyuck Chang is a Full Professor in Dept. of Electrical Engineering and Computer Science, Seoul National University, Korea. He was a Visiting Associate Professor at Arizona State University in 2005, and a Visiting Professor at University of Southern California in 2009-2010. He is a Senior Member of ACM and a Fellow of IEEE.