29. ADVANCED ENERGY STORAGE AND POWER ELECTRONIC SYSTEMS

As energy storage systems continue to advance, two areas have surfaced in which technology advances are needed:

• In battery or electrochemical capacitor strings, slight differences in individual cells can grow over time, leading to premature failure of the system. External circuitry sometimes is applied in an attempt to minimize this problem. Solutions for intrinsic cell balancing, without the use of external circuitry at the cell level, are sought.

• As silicon carbide devices become more available for system level power electronic applications, wire bonding of these devices into circuits is expected to become a reliability issue. Solutions are sought for novel “wireless” bonding techniques to alleviate this potential problem.

Grant applications are sought only in the following subtopics.

a. Intrinsic Cell Balancing for Advanced Energy Storage Systems—In most energy storage applications, individual electrochemical cells and/or capacitors are connected together in a variety of series/parallel configurations to form modules, strings, and ultimately systems. During repeated charge and discharge of the system, differences in the behavior of individual cells can lead to cell imbalances, which can lead to system failure. In many cases, the systems are externally monitored at the cell level in order to minimize abuse of the cells themselves – abuse that can lead to shortened lifetime or, in the worst case, a potentially life-threatening situation (e.g., overcharge leading to thermal runaway and deflagration). As larger and larger systems are built to meet large-scale utility applications, the potential for these imbalances increases significantly, and the complexity of the required monitoring circuits and control software leads to increased costs and decreased reliability. In order to obviate the need for this additional circuitry and electronic monitoring/control of individual cells, grant applications are sought to develop new approaches to cell balancing for batteries and electrochemical capacitors. Possible examples include the use of either intrinsic or external techniques such as overcharge redox shuttles in each cell or module-level circuitry and algorithms to replace individual cell-level systems. Designs and approaches that are applicable to multiple battery and capacitor chemistries are preferred.

Questions – Imre Gyuk (imre.gyuk@hq.doe.gov)

b. Advanced Bonding Techniques for Silicon Carbide (SiC) Switches—Wide band-gap devices such as silicon carbide (SiC) are becoming more attractive to various applications – such as high power motor drives, Flexible AC Transmission Systems (FACTS) controllers, and power conversion systems – because of their increase in performance compared to silicon-based systems. Advantages include lower losses, high operating frequencies, higher operating voltages, and higher operating temperatures. Most SiC devices to date utilize one or more wire bonds to provide the electrical path needed for conduction.  These wire bonds are typically made of aluminum or gold wires that are ultrasonically or thermosonically bonded to bond pads on the SiC chip. However, such wire bonds are known to have catastrophic failure mechanisms that occur during high current or high temperature cycling. The wire bonds also add to the overall electrical inductance of the switch and can be especially problematic in high frequency power applications. Consequently, these wire bonds often are considered the weakest link in the overall packaging. Grant applications are sought to develop an advanced wire-bondless approach to high power (greater than 100A and 10kV) SiC packaging. The Phase I project should examine the feasibility of a wire-bondless approach along with the current state of research and development. The potential Phase II project would include the testing and improvement of these devices and the inclusion of these devices into power conversion system for high power applications.

Questions – Imre Gyuk (imre.gyuk@hq.doe.gov)

References:

1 Kiessling, R., and J. Mills, “A Battery Model for the Monitoring of, and Corrective Action

on, Lead/Acid Electric-Vehicle Batteries”, Journal of Power Sources, Volume 53, Number 2, February 1995 , pp. 339-340(2). (URL: Elsevier, http://www.ingentaconnect.com/content/els/03787753;jsessionid=awhhevxtagej.henrietta Publisher link: http://www.ingentaconnect.com/content/els;jsessionid=awhhevxtagej.henrietta )

2 Lee, Yuang-Shung, Ming-Wang Cheng, Shun-Ching Yang, and Co-Lin Hsu, “Individual Cell Equalization for Series Connected Lithium-Ion Batteries”, IEICE-Transactions on Communications, Volume E89-B, Number 9, Pp. 2596-2607 (URL: http://ietcom.oxfordjournals.org/ Another link: http://ietcom.oxfordjournals.org/content/volE89-B/issue9/index.dtl )

3 Baughman, A.; Ferdowsi, M., “Double-Tiered Capacitive Shuttling Method for Balancing Series-Connected Batteries”, Vehicle Power and Propulsion, 2005 IEEE Conference , no. pp. 109- 113, 7-9 Sept. 2005. (URL: http://scholarsmine.umr.edu/post_prints/01554531_09007dcc8030d80c.html )

4 Bentley, W.F., “Cell Balancing Considerations for Lithium-Ion Battery Systems”, Battery Conference on Applications and Advances, 1997., Twelfth Annual, 14-17 January 1997, pp 223-226. (URL: http://ieeexplore.ieee.org/xpl/RecentCon.jsp?punumber=4373 (another link: http://ieeexplore.ieee.org/Xplore/login.jsp?url=/search/searchresult.jsp?disp=cit&queryText=(bentley%20%20w.%20f.%3cIN%3eau)&valnm=Bentley%2C+W.F.&reqloc%20=others&history=yes )

5 Skarstad, Paul M., “Battery And Capacitor Technology for Uniform Charge Time in Implantable Cardioverter-Defibrillators”, Journal of Power Sources, Volume 136, Issue 2, 1 October 2004, Pages 263-2. (URL: http://www.sciencedirect.com/science/journal/03787753 another link: http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235269%232004%23998639997%23520265%23FLA%23&_cdi=5269&_pubType=J&view=c&_auth=y&_acct=C000059129&_version=1&_urlVersion=0&_userid=2914253&md5=b23c1ef1a48a5055452f647290097fcf )