UNINTERRUPTIBLE POWER SUPPLY SYSTEM

• US 20080084185A1
• Filed: 10/05/2006
• Published: 04/10/2008
• Est. Priority Date: 10/05/2006
• Status: Active Grant

• Current Assignee: Fuji Electric Company Limited (Fuji Electric Systems Company Limited)
• Original Assignee: Denki Kagaku Kogyo Kabushiki Kaisha (TDK Corporation)
• Inventors: Nakazawa, Hiroshi
• Granted Patent: US 7,535,201 B2
• Time in Patent Office: Days
• US Class Current: 320/128
• CPC Class Codes: H02J 7/0071 with a programmable schedule
• CPC Class Codes: H02J 9/061 for DC powered loads

Abstract

There is provided an uninterruptible power supply system capable of preventing life shortening of a lithium-ion secondary battery attributable to its overcharge over the whole period of its use. At the start of use of the lithium-ion secondary battery 22, a charging voltage is set comparatively low. On the other hand, as the lithium-ion secondary battery 22 comes closer to an end of its life, its charging voltage becomes higher. A charging control means 37 variably sets the charging voltage applied to the lithium-ion secondary battery 22 so as to realize a discharge duration thereof may become slightly longer than a backup time required for the system and hence life shortening of the lithium-ion secondary battery 22 attributable to overcharge can be prevented.

Claims

1. An uninterruptible power supply system which charges a lithium-ion secondary battery when an input voltage is normal, and discharges the same at the time of voltage reduction or power interruption to thereby supply an electric power to a load, comprising:

a timing means for counting an elapsed time from the start of use of said lithium-ion secondary battery; and

a charging control means for increasing a charging voltage applied to said lithium-ion secondary battery as said elapsed time increases.

2. The uninterruptible power supply system according to claim 1, wherein said charging control means sets the charging voltage to the lithium-ion secondary battery variably over the whole duration of service of said lithium-ion secondary battery so that a discharge duration thereof may become slightly longer than a backup time required for said uninterruptible power supply system.

3. The uninterruptible power supply system according to claim 1, wherein said charging control means increases the charging voltage to the lithium-ion secondary battery in stages as said elapsed time increases.

4. The uninterruptible power supply system according to claim 1, wherein said charging control means increases the charging voltage applied to the lithium-ion secondary battery continuously as said elapsed time increases.

5. The uninterruptible power supply system according to claim 1, further comprising a voltage transforming unit including a voltage increasing or decreasing unit for increasing or decreasing a supply voltage applied from a power supply circuit to the lithium-ion secondary battery to an optimal charging voltage applied to said lithium-ion secondary battery, said voltage transforming unit being provided between said power supply circuit and the lithium-ion secondary battery with said timing means and charging control means being incorporated in said voltage transforming unit.

6. The uninterruptible power supply system according to claim 5, wherein said voltage transforming unit comprises a full charge detector which stops power supply to the lithium-ion secondary battery and then allows the lithium-ion secondary battery to perform self-discharge upon detecting the lithium-ion secondary battery has been charged fully.

7. The uninterruptible power supply system according to claim 5, wherein said voltage transforming unit comprises a low-voltage detector which starts power supply to the lithium-ion secondary battery upon detecting a terminal voltage of the lithium-ion secondary battery has dropped to a preset value.

8. An uninterruptible power supply system which charges a lithium-ion secondary battery when an input voltage is normal, and discharges the same at the time of voltage reduction and power interruption to thereby supply an electric power to a load, comprising:

a discharge duration obtaining means for discharging the lithium-ion secondary battery and then counting the discharge duration taken for a terminal voltage of the lithium-ion secondary battery to drop to a preset voltage; and

a charging control means for controlling a charging voltage applied to the lithium-ion secondary battery variably so that the discharge duration comes closer to a preset time.

9. The uninterruptible power supply system according to claim 8, wherein said charging control means sets the charging voltage applied to the lithium-ion secondary battery variably over the whole duration of service of said lithium-ion secondary battery so that the discharge duration thereof may come closer to said preset time that is slightly longer than a backup time required for said uninterruptible power supply system.

10. The uninterruptible power supply system according to claim 8, wherein said charging control means increases the charging voltage applied to said lithium-ion secondary battery when said discharge duration is shorter than said preset time as preliminarily stored, but decreases the charging voltage when said discharge duration is longer than said preset time, while said charging control means keeps the charging voltage unchanged when said discharge duration is equal to said preset time.

11. The uninterruptible power supply system according to claim 8, further comprising a voltage transforming unit including a voltage increasing and decreasing unit for increasing and decreasing a supply voltage applied from a power supply circuit to said lithium-ion secondary battery to an optimal charging voltage to said lithium-ion secondary battery, said voltage transforming unit being provided between said power supply circuit and said lithium-ion secondary battery with said discharge duration obtaining means and charging control means being incorporated in said voltage transforming unit.

12. The uninterruptible power supply system according to claim 11, wherein said voltage transforming unit comprises a full charge detection element which stops power supply to said lithium-ion secondary battery and then allows the lithium-ion secondary battery to perform self-discharge upon detecting the lithium-ion secondary battery has been charged fully.

13. The uninterruptible power supply system according to claim 11, wherein said voltage transforming unit comprises a low-voltage detector which starts power supply to said lithium-ion secondary battery upon detecting a terminal voltage of the lithium-ion secondary battery has dropped to a preset value.