Emergency power system, and system for automatically detecting whether or not failure of single cell occurs in battery for use in the system

• US 6,577,103 B2
• Filed: 03/23/2001
• Issued: 06/10/2003
• Est. Priority Date: 03/28/2000
• Status: Expired due to Fees

• Current Assignee: Korea Electric Power Corporation (Government of South Korea), NGK Insulators Limited
• Original Assignee: Korea Electric Power Corporation (Government of South Korea), NGK Insulators Limited
• Inventors: Tanaka, Kouji, Mori, Keiichi, Okuno, Akiyasu, Nakahata, Koichi, Bito, Akihiro
• Primary Examiner(s): Sherry, Michael
• Assistant Examiner(s): TIBBITS, PIA FLORENCE
• Application Number:
  US09/815,963
• Publication Number:
  US 20010048286A1
• Time in Patent Office: 809 Days
• Field of Search: 320/116, 320/132, 307/46, 307/66, 429/224, 363/34, 363/35, 363/37
• US Class Current: 320/116
• CPC Class Codes: H02J 9/061 for DC powered loads

Abstract

The present invention provides a space-saving and low-cost emergency power system, which can be installed on a narrow place having limited space and employs a battery that is long in service life and low in frequency of replacement. This emergency power system comprises a circuit having a DC load, a rectifier, and a battery, which are electrically connected to one another. This circuit is adapted so that normally, DC power is supplied from the rectifier to the DC load, and the battery is charged, and that in an emergency, such as a power failure, in which an outage of the rectifier occurs, electric power is automatically supplied from the battery to the DC load. In this system, a sodium sulfur battery is employed as the battery.

Claims

1. An emergency power system, comprising a circuit having a DC load, a rectifier and a sodium sulfur battery electrically connected to one another, and a rectifier output voltage controller provided between said rectifier and said sodium sulfur battery,

wherein DC power is supplied from said rectifier to said DC load under normal operating conditions and said battery is charged by said rectifier, and electric power is automatically supplied from said battery to said DC load during a power failure or an outage of said rectifier,

wherein said output voltage controller lowers an output voltage of said rectifier when a voltage of said sodium sulfur battery reaches a level that is equal to or higher than a predetermined charging voltage, and thus automatically discharges energy from said sodium sulfur battery to said DC load, and said rectifier output voltage controller raises an output voltage of said rectifier when the voltage of said sodium sulfur battery reaches a level that is equal to or lower than a predetermined discharging voltage, and thus charges said sodium sulfur battery.

2. An emergency power system according to claim 1, wherein the predetermined charging voltage and the predetermined discharging voltage of said sodium sulfur battery are within a discharge depth range, and a composition of an active material accommodated in a positive electrode chamber of each single cell within said sodium sulfur battery is compositionally within a two-phase region.

3. An emergency power system according to claim 1, wherein said sodium sulfur battery comprises a plurality of modules each comprising a predetermined number of parallel-connected strings, each string comprising a predetermined number of series-connected single cells, and an output voltage of the rectifier is controlled by monitoring whether a module voltage reaches the predetermined charging and discharging voltages.

4. An emergency power system according to claim 3, wherein an occurrence of a malfunction of a single cell is detected according to whether a difference between a no-load module open circuit voltage and a constant-resistance-load module voltage is larger than an initially determined normal voltage difference, and an alarm is generated at an occurrence of a malfunction of a single cell to continually maintain a function of serving as an emergency power system.

5. The emergency power system of claim 1, wherein said electric power is automatically and only supplied from said sodium sulfur battery to said DC load during a power failure or upon an outage of said rectifier.

6. An emergency power system, comprising a circuit having a DC load, a rectifier and a sodium sulfur battery electrically connected to one another, and a controller,

wherein DC power is supplied from said rectifier to said DC load at a constant voltage under normal operating conditions and said battery is charged, and power is supplied from said battery to said DC load during a power failure or an outage of said rectifier, and

wherein said controller interrupts or connects an output of said rectifier to said battery such that when a voltage of said sodium sulfur battery reaches a level that is equal to or higher than a predetermined charging voltage, an output of said rectifier to said battery is interrupted and energy is automatically discharged from said sodium sulfur battery to said DC load, and when the voltage of said sodium sulfur battery reaches a level that is equal to or lower than a predetermined discharging voltage, the output of said rectifier is connected to said sodium sulfur battery to charge said battery.

7. An emergency power system, comprising a circuit having a DC load, a rectifier and a sodium sulfur battery electrically connected to one another, a controller, and a diode having a forward direction of electrical conduction from said battery to said DC load and a first switch provided between said rectifier and said sodium sulfur battery,

wherein DC power is supplied from said rectifier to said DC load under normal operating conditions, and power is supplied from said sodium sulfur battery to said DC load through said diode during a power failure or an outage of said rectifier,

wherein said controller is provided to connect said first switch to charge said sodium sulfur battery to a predetermined discharge depth using power supplied from said rectifier after the discharge of said battery during said power failure or said outage of said rectifier, and thereafter interrupting said first switch to thereby hold said sodium sulfur battery in a state in which power from said rectifier is prevented from being supplied to said battery by said diode.

8. An emergency power system according to claim 7, further comprising another circuit provided between said circuit comprising said diode and said first switch electrically parallel-connected to one another and said sodium sulfur battery, said another circuit supplying discharging current from said sodium sulfur battery to a heater, and a second switch provided between said heater and said sodium sulfur battery,

wherein a temperature control operation is performed by controlling ON/OFF of said second switch according to a temperature of said sodium sulfur battery under the control of said controller, and

wherein said sodium sulfur battery is maintained at a constant discharge depth and at a constant temperature by repeating at least one cycle comprising the steps of discharging energy from said sodium sulfur battery to said heater, and subsequently charging energy from said rectifier to said sodium sulfur battery at predetermined time intervals under the control of said controller having a timer, and putting said first switch into an interrupted state when a voltage or current of said sodium sulfur battery reaches a level that is equal to or higher than a predetermined voltage level, or that is equal to or lower than a predetermined current level to thereby stop charging of said sodium sulfur battery.

9. A malfunction detection system for automatically detecting an occurrence of a malfunction of a single cell in a battery used in an emergency power system, said malfunction detection system comprising:

a first circuit comprising a DC load, a rectifier, and a sodium sulfur battery electrically connected to one another;

a second circuit comprising a diode and a first switch parallel-connected to one another, said diode having a forward direction of electrical conduction from said battery to said DC load;

a third circuit provided between said second circuit and said sodium sulfur battery for supplying a discharging current from said sodium sulfur battery to a heater;

a second switch provided between said heater and said sodium sulfur battery; and

a controller having a timer,

wherein DC power is supplied from said rectifier to said DC load under normal operating conditions, and power is supplied from said sodium sulfur battery through said diode to said DC load during a power failure, and

wherein a temperature control operation is performed by controlling ON/OFF operations of said second switch according to a temperature of said sodium sulfur battery using said controller, wherein said sodium sulfur battery is maintained at a constant discharge depth and at a constant temperature by repeating at least one cycle comprising the steps of discharging energy from said sodium sulfur battery to said heater, charging energy from said rectifier to said sodium sulfur battery at predetermined time intervals under the control of said controller, and putting said first switch into an interrupted state and stopping charging of said battery when a voltage or current of said sodium sulfur battery reaches a level that is equal to or higher than a predetermined voltage level or that is equal to or lower than a predetermined current level, and wherein an occurrence of a malfunction of a single cell in said sodium sulfur battery is automatically detected by monitoring a discharging current during energy discharge from said sodium sulfur battery to said heater.