Power and life extension of battery-ultracapacitor hybrids

The performance of a battery-ultracapacitor hybrid power source under pulsed load conditions is analytically described using simplified models. We show that peak power can be greatly enhanced, internal losses can be considerably reduced, and that discharge life of the battery is extended. Greatest benefits are seen when the load pulse rate is higher than the system eigenfrequency and when the pulse duty is small. Actual benefits are substantial; adding a 23 F ultracapacitor bank (3 /spl times/ 7 PC10 ultracapacitors) in parallel with a typical Li-ion battery of 7.2 V and 1.35 A hr capacity can boost the peak power capacity by 5 times and reduce the power loss by 74%, while minimally impacting system volume and weight, for pulsed loads of 5 A, 1 Hz repetition rate, and 10% duty.

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