Electricity: battery or capacitor charging or discharging – Serially connected batteries or cells
Reexamination Certificate
2001-03-23
2003-06-10
Sherry, Michael (Department: 2838)
Electricity: battery or capacitor charging or discharging
Serially connected batteries or cells
C307S066000, C429S224000
Reexamination Certificate
active
06577103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an emergency power system, and to a system for automatically detecting whether not a failure of a single cell occurs in a battery for use in the system.
2. Description of the Related Art
FIG. 10
illustrates a float charging system employing a lead acid battery
30
in an emergency power system. Ordinarily, DC power is supplied from a rectifier
31
to a DC load
32
. A constant voltage is applied to the lead acid battery
30
. Thus, a self-discharged quantity of energy is charged into the lead acid battery
30
. Consequently, the lead acid battery
30
is continually kept in a fully charged condition. In the case of an emergency, for example, in the event of an outage of the rectifier
31
, electric power is supplied from the DC load
32
to the lead acid storage battery
30
. Thus, in the case of an emergency, for instance, in the event of a power failure, the conventional emergency power system can supply electric power to the DC load without an outage of power to the DC load.
However, the conventional emergency power system has drawbacks in that the system requires a large space for placing a lead storage battery therein, due to a low energy density thereof, and thus, the conventional system cannot be installed in a narrow place having limited space. Moreover, the conventional emergency power system has additional drawbacks in that the service life of the lead acid storage battery is short, which causes the frequency of replacement of the battery to be relatively high. Furthermore, the cost of the lead acid battery is relatively high.
The invention is accomplished in view of the aforementioned drawbacks. Accordingly, an object of the invention is to provide a space-saving emergency power system that can be placed in a narrow place having limited space. Further, another object of the invention is to provide a low-cost emergency power system employing a battery that is long in service life and low in frequency of replacement. Moreover, another object of the invention is to provide a system for detecting whether or not a single cell failure occurs in a battery used in an emergency power system.
SUMMARY OF THE INVENTION
To achieve the foregoing objects, according to an aspect of the invention, there is provided an emergency power system that includes a circuit having a DC load, a rectifier, and a battery, which are electrically connected to one another. The circuit is adapted so that normally, DC power is supplied from the rectifier to the DC load, and the battery is charged. 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, the battery is a sodium sulfur battery.
Further, in an embodiment of the invention, preferably, a rectifier output voltage controller is provided between the rectifier and the sodium sulfur battery for lowering, when the voltage of the sodium sulfur battery reaches a level that is equal to or higher than the predetermined charging voltage, an output voltage of the rectifier thereby to automatically discharge energy from the sodium sulfur battery to the DC load. The rectifier output voltage controller also operates to raise, when the voltage of the sodium sulfur battery reaches a level that is equal to or lower than the predetermined discharging voltage, an output voltage of the rectifier to thereby charge the sodium sulfur battery.
Further, in an embodiment of the emergency power system of the invention, preferably, the predetermined charging voltage and the predetermined discharging voltage of the sodium sulfur battery are within a discharge depth range in the case that the composition of an active material accommodated in a positive electrode chamber of each of sodium sulfur single cells is in a two-phase region.
Further, in an embodiment of the invention, it is preferable that the sodium sulfur battery is an assembled battery obtained by constituting strings, each consisting of a predetermined number of series-connected single cells, and then parallel-connecting a predetermined number of the strings. An output voltage of the rectifier is controlled by monitoring whether or not a module voltage reaches the predetermined charging voltage and whether or not the module voltage reaches the predetermined discharging voltage.
Furthermore, preferably, an embodiment of the invention detects an occurrence of a malfunction of a single cell according to whether or not the difference &Dgr;V (=Vocv−Vm) between the no-load module open circuit voltage Vocv and the constant-resistance-load module voltage Vm is larger than an initially determined normal voltage difference &Dgr;Vn (&Dgr;V>&Dgr;Vn). An alarm is generated when a malfunction of a single cell occurs, thus maintaining the function of continually serving as an emergency power system.
The above-discussed detection of malfunctions is governed by the following principles. The voltage difference in the case of no occurrence of a malfunction is: &Dgr;V=I.R, where I is the module current, and R is the module resistance. When a malfunction of a single cell occurs, the resistance R rises, which, in turn, causes a corresponding increase in the voltage difference &Dgr;V.
According to the invention, there is provided another emergency power system, which includes a circuit consisting of a DC load, a rectifier and a battery electrically connected to one another and adapted so that under normal operating conditions, DC power is supplied from the rectifier to the DC load at a constant voltage, and the battery is charged. In an emergency situation, including a power failure, in which an outage of the rectifier occurs, power is supplied from the battery to the DC load. In this system, the battery is a sodium sulfur battery.
A controller having a timer is provided between the rectifier and the sodium sulfur battery and interrupts or connects an output of the rectifier. When the current from the sodium sulfur battery reaches a level that is equal to or lower than a predetermined charging current, an output of the rectifier is interrupted, and energy is automatically discharged from the sodium sulfur battery to the DC load for a predetermined period. After energy is discharged from the battery for the predetermined period, the output of the rectifier is connected to the sodium sulfur battery so as to charge the battery.
According to the invention, there is provided yet another emergency power system, which includes a circuit including a DC load, a rectifier and a battery electrically connected to one another and adapted so that under normal operating conditions, DC power is supplied from the rectifier to the DC load at a constant voltage, and the battery is charged. In an emergency situation, including a power failure, in which an outage of the rectifier occurs, power is supplied from the battery to the DC load. In this system, the battery is a sodium sulfur battery. The power system further comprises a controller which interrupts or connects an output of the rectifier. 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 the rectifier is interrupted, and energy is automatically discharged from the sodium sulfur battery to the DC load. When the voltage of the sodium sulfur battery reaches a level that is equal to or lower than a predetermined discharging voltage, the output of the rectifier is connected to the sodium sulfur battery so as to charge the battery.
According to the invention, there is provided still another emergency power system, which includes a circuit consisting of a DC load, a rectifier and a battery electrically connected to one another. A diode, the forward direction of electrical conduction of which is a direction from the battery to said DC load, and a first switch are provided between the rectifier and the sodium sulfur battery. This emergency power is adapted so that under normal
Bito Akihiro
Mori Keiichi
Nakahata Koichi
Okuno Akiyasu
Tanaka Kouji
Burr & Brown
Sherry Michael
The Tokyo Electric Power Company Inc.
Tibbits Pia
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