Page 163 - Power Quality in Electrical Systems

Uninterruptible Power Supplies 145

are coming on line [9.22]. Usage of ultracapacitors to supply peak
power loads over average power is described by Maher [9.26].
■ Problems: Because of the low voltage rating of ultracapacitor cells—
for example, 2.5 V DC—the cells must be connected in series for a typ-
ical 48 V DC application, with the usual problems of cell current and
voltage division during charging [9.26]. Cost of $9500/kWh is five
times that of lead-acid batteries [9.26].

Summary
The uninterruptible power system is necessary to provide reliable power
to critical loads that cannot tolerate interruption. The most widely used
equipment is the battery inverter UPS module that is available in power
ratings from 100 W to 1000 kW (and higher) at all commercial input
and output voltage and phase configurations. Energy storage is usually
provided by flooded or VLRA-type batteries for full-load operating times
in the range of minutes. Recently developed energy-storage alterna-
tives include flywheels and fuel cells.

References

[9.1] A. Kusko, Emergency Standby Power Systems, McGraw-Hill, New York 1989.
[9.2] B. D. Bedford and R. G. Hoft, Principles of Inverter Circuits, John Wiley,New York 1964.
[9.3] J. L. Fink, J. F. Johnston, and F. C. Krings, “The Application of Static Inverters for
Essential Loads,” IEEE Transactions on Power Apparatus and Systems, December
1963, pp. 1068–1072.
[9.4] A. Kusko and F. C. Gilmore, “Concept of a Modular Static Uninterruptible Power
System,” Conf. Record, Second IEEE IGA Annual Meeting, Pittsburgh, October
1967, pp. 147–153.
[9.5] EC&M, February 2006, p. 58.
[9.6] APC, “Solutions,” Winter/Spring 2005, p. 25.
[9.7] Pentadyne Power Corp., Chatsworth, CA, Brochure.
[9.8] A. Kusko and J. DeDad, “Short-Term, Long-Term, Energy Storage Methods for
Standby. Electric Power Systems,” Conference Record of the 2005 IEEE Ind. Appl.
Conf 40th Annual Meeting, Hong Kong, October 2–6, 2005, pp. 2672–2678.
[9.9] C. Robillard, A. Vallee, and H. Wilkinson, “The Impact of Lithium-Metal-Polymer
Battery Characteristics of Telecom Power System Design,” INTELEC 2004, pp. 25–31.
[9.10] I. Kiyokawa, K. Niida, T. Tsujikawa, and T. Motozu, “Integrated VRLA-Battery.
Management System,” INTELEC 2000, pp. 703–706.
[9.11] S. S. Misra, “VRLA Battery Development and Reliability Considerations,”
INTELEC 2004, pp. 296–300.
[9.12] M. R. Cosley and M. P. Garcia, “Battery Thermal Management System,” INTELEC
2004, pp. 38–45.
[9.13] R. S. Weissbach, G. G. Karady, and R. G. Farmer, “A Combined Uninterruptible
Power Supply and Dynamic Voltage Compensator Using a Flywheel Energy Storage
System,” IEEE Trans. on Power Delivery, vol. 16, no. 2, April 2001, pp. 265–270.
[9.14] G. Reiner and N. Wehlau, “Concept of a 50 MW/650 MJ Power Source Based on
Industry-Established MDS Flywheel Units,” Pulsed Power Plasma Science, 2001,
vol. 1, pp. 17–22, June 2001.
[9.15] R. G. Lawrence, K. L. Craven, and G. D. Nichols, “Flywheel UPS,” IEEE IAS
Magazine, May/June 2003, pp. 44–50.