JPH08126214A - Method and circuit for measuring capacity of storage battery - Google Patents

Abstract

PURPOSE: To provide a method and a circuit for measuring the capacity of a storage battery wherein a measurement requires a relatively short time, wherein feeding can be continued even if service interruption occurs during measurement, and wherein the degradation of specific cells will not be accelerated. CONSTITUTION: The present invention relates to an uninterruptible power supply system comprising a power converter 2 that is fed with power from an a.c or d.c. power supply 1 and outputs a required d.c. voltage to a load device 4; and a storage battery 3 that is connected to the output terminals of the power converter 2 in parallel, and that is floating-charged when the power converter 2 is in operation and supplies the load device 4 with power when the power converter 2 is out of operation. Thus the preset output voltage of the power converter 2 is reduced to a level at which the load device 4 is capable of properly operating. The storage battery 3 is thereby discharged, and its terminal voltage is measured. The time taken for the voltage to reach the discharge and voltage, is estimated based on the rate of the terminal voltage drop.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacity measuring method for measuring the capacity of a storage battery in use in an uninterruptible power supply system composed of an AC or DC power converter and a backup storage battery. The present invention relates to a circuit configuration for realizing it.

[0002]

2. Description of the Related Art A conventional capacity test method is shown in FIG. Figure 9
In the figure, 1 is an AC or DC power supply, 2 is a power conversion device, 3 is a storage battery, 4 is a load device, 5 is a changeover switch, and 6
Is a constant current load for discharge. In this method, the storage battery 3 that is normally connected in parallel to the output terminal of the power conversion device 2 is disconnected and connected to the constant current load 6 for discharging to discharge at a predetermined current, and the terminal voltage of the storage battery 3 ends discharge. The time to reach the voltage is measured, and the product It (Ah) of the discharge current value I and the discharge time t is obtained. For simplicity, the discharging constant-current load 6 may use a simple resistor. This method can accurately grasp the capacity of the storage battery 3, but it takes a long time to measure, and the storage battery 3 is disconnected from the power supply system during the measurement. Therefore, if a power failure occurs at this time, power supply to the load device 4 cannot be continued. is there. When the load device 4 is a communication device such as an exchange or a transmission device, the effect of this power failure is very large.

In order to solve the drawback that the storage battery is disconnected from the power supply system during measurement, a method as shown in FIG. 10 has been conventionally performed. 10, 1 to 4 are the same as those in FIG. 9, 7 is a battery cell having the lowest voltage, 8 is a changeover switch, and 9
Is a constant current load for discharging, 10 is a charger for recharging discharged battery cells, and 11 is an AC or DC power supply. Figure 10
In this method, all the cell voltages of the storage battery 3 are measured in advance, and the discharge test as described above is performed on the cell with the lowest voltage among them, and the product It (Ah) of the discharge current value I and the discharge time t. Was seeking. According to this method, since only one cell of the storage battery 3 composed of a plurality of cells is discharged, even if a power failure occurs during the test, the maximum voltage of the storage battery 3 is one cell lower. Just do
Power supply to the load device 4 can be continued.

[0004]

However, even with this method, the measurement time cannot be shortened and there is the inconvenience that all cell voltages must be measured in advance. Further, when the method is repeatedly performed, the cells on which the capacity test is performed tend to be the same all the time, and a new defect occurs in that the deterioration of cells whose capacity is low and is beginning to deteriorate is further accelerated.

The present invention has been made in view of the above circumstances, and enables measurement in a relatively short time, power supply to be continued even if a power failure occurs during measurement, and further deterioration of a specific battery cell can be accelerated. An object of the present invention is to provide a storage battery capacity measuring method and circuit.

[0006]

In order to achieve the above object, a storage battery capacity measuring method of the present invention comprises a power converter for inputting an AC power supply or a DC power supply and outputting a DC voltage required for a load device, and a power conversion. In an uninterruptible power supply system that is connected in parallel to the device output terminals and is floatingly charged when the power conversion device is operating and that supplies power to the load when the power conversion device is stopped, the output set voltage of the power conversion device is set to the load device. The battery voltage is reduced to a level at which the battery can maintain normal operation, the storage battery is discharged, the terminal voltage is measured, and the time to reach the discharge end voltage is estimated from the rate of decrease of the terminal voltage.

The storage battery capacity measuring method of the present invention is the storage battery capacity measuring method, wherein the terminal voltage in the storage battery discharging state is changed from the battery temperature at the time of measurement to the voltage at the reference temperature, and from the battery discharge current at the time of measurement to the reference discharge. After correcting each of the voltages in the current, the time to reach the discharge end voltage is estimated from the rate of decrease of the terminal voltage after the correction.

Further, the storage battery capacity measuring circuit of the present invention is a power conversion device which is connected in parallel to a power conversion device which outputs a DC voltage required for a load device by inputting an AC power supply or a DC power supply, and a power conversion device which is connected in parallel. In an uninterruptible power supply system configured by a storage battery that is floatingly charged during operation and that supplies power to a load when the power conversion device is stopped, means for lowering the output voltage of the power conversion device, and means for measuring the storage battery terminal voltage, A signal that lowers the output voltage of the power conversion device using an external signal as a trigger and a timing signal generation circuit that generates a timing signal at two different times during the output voltage reduction signal generation period, and a storage battery terminal voltage signal passes by the timing signal. Gate circuit, memory circuit that stores the gate circuit output signal, and residual discharge based on the data in the memory circuit It is characterized in that it comprises an arithmetic circuit for finding between.

Further, the storage battery capacity measuring circuit of the present invention includes a power converter that inputs an AC power supply or a DC power supply and outputs a DC voltage required for a load device, and a power converter connected in parallel to a power converter output terminal. In an uninterruptible power supply system configured by a storage battery that is floatingly charged during operation and that supplies power to a load when the power conversion device is stopped, a means for lowering the output voltage of the power conversion device, a storage battery terminal voltage,
Means for measuring the storage battery discharge current and the storage battery temperature respectively, a signal for lowering the output voltage of the power conversion device by using an external signal as a trigger, and a timing signal generation for generating timing signals at two different times during the output voltage reduction signal generation period A circuit, a gate circuit that passes a storage battery terminal voltage, a storage battery discharge current, and a storage battery temperature signal according to the timing signal, a memory circuit that stores a gate circuit output signal, and an arithmetic circuit that determines the remaining discharge time based on the data of the memory circuit And is provided.

[0010]

With the above-mentioned means, the present invention reduces the output voltage of the power converter within the range permitted by the load device without disconnecting the storage battery incorporated in the uninterruptible power supply system, and uses the actual load device to store the storage battery. The main feature is that the storage battery capacity is obtained from the rate of decrease by discharging for a short time. The conventional technique is different in that the discharge test is performed up to the discharge end voltage by using another discharge load.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. [Embodiment 1] FIGS. 1 and 2 show an embodiment corresponding to claim 1. FIG. 1 is a structural explanatory view, and FIG. 2 is a characteristic diagram for explaining the operation. In FIG. 1, 1 is an AC or DC power supply,
2 is a power converter, 3 is a storage battery, 4 is a load device,
In FIG. 2, V _F is a floating charging voltage (power converter constant output setting voltage), V _E is discharge end voltage (load device allowable minimum input voltage), t ₁ and t ₂ are actual discharge times, and V ₁ and V ₂
Is the storage battery terminal voltage at the actual discharge time, and V _A is the set voltage when the power converter output decreases.

The operation of this embodiment will be described. First, at the time of steady operation, as shown in FIG. 1A, the power converter 2 receives an output voltage V _F (see FIG.
The floating charging voltage in 1) is output to supply the electric power to the load device 4 while floating charging the storage battery 3. The output voltage of the power conversion device 2 has a stabilizing function such that a constant voltage V _F can always be output even when the voltage of the input AC or DC power supply 1 changes or the output current changes. In such a configuration, when the power supply from the AC or DC power supply 1 continues for a certain time or more (normally 24 hours or more), the storage battery 3 is in a fully charged state, and thus the charging current (floating charging current) of the storage battery 3 Is small, and most of the current output from the power conversion device 2 is supplied to the load device 4 as a load current.

Next, as shown in FIG. 1B, the power converter 2
Reducing the output setting voltage V _A (when the output reduction of 2 set voltage). However, V _A is set to a value higher than the discharge end voltage of the storage battery 3, that is, the load device allowable minimum input voltage V _E. Since the power conversion device 2 outputs a constant voltage V _A , the terminal voltage of the storage battery 3 becomes higher, and the storage battery 3 supplies power to the load device 4. When the terminal voltage of the storage battery 3 is measured in this state, power is not supplied from the power conversion device 2, and therefore the discharge characteristic (FIG. 2) of the storage battery 3 appears as it is. Here, at time t ₁ and time t ₂ , the storage battery voltages V ₁ and V ₂
When measuring the time t _E to reach the discharge end voltage V _E is obtained by the following equation as the discharge voltage characteristics decreases almost linearly.

T _E = t ₁ + {(V _E −V ₁ ) / (V ₂ −
V ₁ )} (t ₂ −t ₁ ) Time t ₁ is about 30 seconds to 5 minutes after the start of discharge, and t ₂ is a discharge time of about 30% or less of the total discharge amount of the storage battery (for example, at a discharge rate of 10 hours). Use within 3 hours if available).

The storage battery capacity Q is the average value I of the load current.
Is calculated by the following equation: Q = I · t _E. Note here measurement time has been illustrated in two points, as measured over 3 points is divided between t ₁ ~t _2, it is also possible to estimate the discharge voltage characteristics curves more precisely.

By operating as described above, the capacity of the storage battery 3 can be estimated in a relatively short time. Since the storage battery 3 is not disconnected from the power feeding system during measurement,
Even if a power failure occurs during the measurement, the power supply to the load device 4 can be continued. In addition, even if the capacity of the storage battery 3 is significantly reduced due to deterioration or the like, the power conversion device 2 outputs a voltage equal to or higher than the allowable minimum input voltage of the load device 4 and the power is supplied to the load device 4 unless a power failure occurs. Since it continues, power supply is not stopped. Therefore, according to this embodiment, the capacity of the storage battery can be measured while maintaining the high reliability of the power feeding system, as compared with the conventional example. Further, unlike the case of another conventional example, the complexity of previously measuring the voltage of each battery cell and the deterioration of a specific battery cell are not accelerated. [Embodiment 2] FIGS. 3 and 4 are diagrams for explaining the operation of the present invention. The operation of this embodiment is similar to that of the first embodiment.
First, during steady operation, as shown in FIG. 1A, the power converter 2 outputs a constant output voltage V _F (floating charging voltage in FIG. 2) with the AC or DC power supply 1 as an input, and the storage battery 3 floats. While charging, the load device 4 is supplied with power. Next, as shown in FIG. 1B, the output setting voltage of the power conversion device 2 is reduced to V _A (setting voltage when the output is reduced in FIG. 2). Since the power conversion device 2 outputs a constant voltage V _A , the terminal voltage of the storage battery 3 becomes higher, and the storage battery 3 supplies power to the load device 4. When the terminal voltage of the storage battery 3 is measured in this state, power is not supplied from the power conversion device 2, and therefore the discharge characteristic (FIG. 2) of the storage battery 3 appears as it is. Here, at time t ₁ and time t ₂ , the storage battery voltage V ₁
And V ₂ , discharge currents I ₁ and I ₂ , and battery temperatures T ₁ and T ₂ are measured. Since the storage battery voltage changes as shown in FIGS. 3 and 4 depending on the temperature and the discharge current, respectively, the detected storage battery voltages V ₁ and V ₂ are corrected to the values V ₁₀ and V ₂₀ at the reference temperature and the reference discharge current by the following formulas. To do. The following formula assumes that the storage battery voltage changes linearly with temperature and discharge current.

V ₁₀ = V ₁ / {1 + α (T ₁ -T ₀ ) -β
(I ₁ −I ₀ )} V ₂₀ = V ₂ / {1 + α (T ₂ −T ₀ ) −β (I ₂ −I
₀ )} where α and β are proportional constants of voltage change with respect to temperature and discharge current, for example, in a sealed lead acid battery of 1000 Ah, under a discharge condition of 10 hours to 5 hours, α =
It is about 0.5 mV / deg and β = 1 mV / A.

Next, the time t _E to reach the discharge end voltage V _E is calculated by the following equation. t _E = t ₁ + {(V _E −V ₁₀ ) / (V ₂₀ −V ₁₀ )} (t
The values of _2- t ₁ ) t ₁ and t ₂ are the same as in the first embodiment.

The storage battery capacity Q is the average value I of the load current.
Is calculated as follows: Q = I · t _E It is also possible to increase the number of measurement points (time) to express the discharge curve more accurately, or to use another method for correcting the voltage with respect to the temperature and the discharge current.

By operating as described above, the capacity of the storage battery can be estimated in a relatively short time even when the temperature or the load current changes. Further, according to the present embodiment, similarly to the first embodiment, the capacity of the storage battery can be measured while maintaining the high reliability of the power feeding system, and the voltage of each battery cell is measured in advance as compared with the conventional example. It is not complicated and does not accelerate deterioration of a specific battery cell. [Embodiment 3] FIG. 5 is an explanatory view of the construction of an embodiment corresponding to claim 3, and FIG. 7 is an operation waveform chart of each portion of FIG. In FIG. 5, 1 is an AC or DC power supply, 2 is a power converter, 3 is a storage battery, 4 is a load device, 12 is a power converter input terminal, 13 is a rectifying / smoothing unit, 14 is an inverter unit, 1
5 is a transformer, 16 is a rectifying / smoothing unit, 17 is a power converter output terminal, 18 is a comparator, 19 is an error amplifier, 20 is an oscillator, 21 is a reference voltage, 22 and 23 are resistors, 24 is a capacitance test circuit, 25 is a measurement start trigger signal input terminal, 26
Is a discharge time output terminal, 27 is a timing signal generating circuit for outputting a signal b for changing the reference voltage with the measurement trigger as an input and a signal c for specifying the timing of data acquisition to the memory, and 28 is a timing signal generating circuit output signal c. A gate circuit for fetching the storage battery voltage data at a designated time, 29 is a memory circuit for storing the time designated by the timing signal generating circuit output signal c and the storage battery voltage data, and 30 is a time stored in the memory circuit and This is an arithmetic circuit that calculates the remaining discharge time based on the voltage data.

The operation of FIG. 5 will be described. Inside the power conversion device 2, after the input of the AC or DC power supply 1 is converted into a DC voltage by the rectification / smoothing unit 13, it is converted into a high frequency AC voltage by the inverter unit 14 and stepped up / down by the transformer 15, and the rectification / smoothing unit 16 is used. Is converted into a DC voltage and output. The output voltage is divided by the resistors 22 and 23, and then compared with the reference voltage 21 by the error amplifier 19. The output of the error amplifier 19 is the oscillator 20.
Is compared with a saw-tooth wave and the like in the comparator 18 and becomes a pulse signal to drive the internal switch element of the inverter unit 14.
Even when the input voltage or the output current is varied, the power converter output voltage VOU _T is determined by the reference voltage V _r resistors _{R 1, R 2 V OUT =} (R 1 + R 2) with a value of V _r / R ₂ Is kept constant. When floating charging, this V
_OUT is V _F (floating charging voltage shown in FIG. 2).

On the other hand, in the capacitance test circuit, as shown in FIG. 7, the timing signal generating circuit 27 generates the signal b for lowering the reference voltage 21 by the input trigger signal a from the outside, and the reference voltage is output to the output voltage V _OUT. Is changed to V _A shown in FIG. The means for lowering the output voltage V _OUT can be realized not only by changing the reference voltage but also by changing the resistors R ₁ and R ₂ on the output voltage detecting side. As a result, the voltage of the storage battery 3 becomes higher than the output voltage of the power conversion device 2, power is supplied from the storage battery 3 to the load device 4, and the storage battery 3 starts discharging. The timing signal generation circuit 27 operates the gate circuit 28 after t ₁ and t _{2 have} elapsed from the input of the external trigger signal to the terminal 25,
In the memory circuit 29, the storage battery voltages V ₁ and V ₂ and the times t ₁ and t
₂ is captured. The arithmetic circuit 30 has V ₁ , V ₂ , t ₁ ,
From the value of t ₂ , the time t _E to reach the discharge end voltage V _E is obtained by the method shown in the first embodiment. It should be noted that the measurement time is shown by two points, but it can be realized by this configuration even if more measurement times are set.

By operating as described above, the capacity of the storage battery can be estimated in a relatively short time. Further, according to the present embodiment, as compared with the conventional example, the capacity of the storage battery can be measured while maintaining the high reliability of the power supply system, and the complexity of previously measuring the voltage of each battery cell and the specific battery cell The feature is that it does not accelerate the deterioration of. [Embodiment 4] FIG. 6 is an explanatory view of the structure of an embodiment corresponding to claim 4, and FIG. 8 is an operation waveform diagram of each portion of FIG. 6, 1 to 25 and 27 are the same as those in FIG.
1 is a discharge time and a storage battery capacity output terminal, 32 is a storage battery current detection circuit, 33 is a storage battery temperature detection circuit, 34 is a storage battery voltage, a storage battery discharge current, and a storage battery temperature data at the time designated by the timing signal generation circuit output signal c. A gate circuit for taking in, 35 is a memory circuit for storing the time designated by the timing signal generating circuit output signal c and its storage battery voltage, storage battery discharge current, storage battery temperature data, and 36 is the time, voltage stored in the memory circuit, This is an arithmetic circuit that calculates the remaining discharge time and the capacity based on the current and temperature data.
Although the storage battery current detection circuit 32 is described as directly measuring the storage battery current here, it is measured by measuring the load current and the output current of the power conversion circuit and obtaining the difference between them, or by measuring the output current of the power conversion circuit as almost zero. It goes without saying that it can be realized by using the load current as it is.

Among the operations shown in FIG. 6, the internal operation of the power conversion device 2 is the same as that shown in FIG.
2, the timing signal generating circuit 27 generates the signal b for lowering the reference voltage 21 by the input trigger signal a from the outside, and the reference voltage is changed so that the output voltage V _OUT becomes V _A shown in FIG. Let The means for lowering the output voltage V _OUT is not only to change the reference voltage, as described in the third embodiment, but also to the resistance R ₁ on the output voltage detecting side,
It can also be realized by changing R ₂ . As a result, the storage battery voltage becomes higher than the power converter output voltage, the storage battery 3 supplies power to the load device 4, and the storage battery 3 starts discharging. The timing signal generation circuit 27
The gate circuit 34 is operated after the lapse of t ₁ and t ₂ from the input of the external trigger signal to the terminal 25, and the storage battery voltages V ₁ and V ₂ , the storage battery discharge currents I ₁ and I ₂ , the storage battery temperatures T ₁ and T ₂ are stored in the memory circuit 35. And the times t ₁ and t ₂ are captured. The arithmetic circuit 36 includes V ₁ , V ₂ , I ₁ , I ₂ , T ₁ , T ₂ , and t.
_From the values of ₁ and t ₂ , the time t _E to reach the discharge end voltage V _E is obtained by the method shown in the second embodiment. It should be noted that the measurement time is shown by two points, but it can be realized by this configuration even if more measurement times are set.

By operating as described above, the capacity of the storage battery can be estimated in a relatively short time even when the temperature or the load current changes. Further, according to the present embodiment, as in the case of the third embodiment, the capacity of the storage battery can be measured while maintaining the high reliability of the power feeding system, and the voltage of each battery cell is measured in advance as compared with the conventional example. It is not complicated and does not accelerate deterioration of a specific battery cell.

[0026]

As described above, according to the present invention, the capacity of the storage battery can be estimated in a relatively short time, and the storage battery is not disconnected from the power supply system even during the measurement, so that a power failure occurs during the measurement. Even if this occurs, there is a feature that power supply to the load device can be continued. In addition, even if the capacity of the storage battery is significantly reduced due to deterioration, etc., the power converter outputs a voltage higher than the allowable input voltage of the load and continues to supply power to the load unless power failure occurs. There is no stopping. Furthermore, the present invention does not accelerate the deterioration of a specific battery cell and the complexity of previously measuring the voltage of each battery cell as shown in another conventional example. Therefore, according to the present invention, a highly reliable power supply system can be economically configured without spending a lot of maintenance work.

[Brief description of drawings]

FIG. 1 is a configuration explanatory view showing a first embodiment of the present invention.

FIG. 2 is a characteristic diagram illustrating the operation of the first embodiment of the present invention.

FIG. 3 is a characteristic diagram illustrating the operation of the second embodiment of the present invention.

FIG. 4 is a characteristic diagram illustrating the operation of the second embodiment of the present invention.

FIG. 5 is a configuration explanatory view showing a third embodiment of the present invention.

FIG. 6 is a structural explanatory view showing a fourth embodiment of the present invention.

FIG. 7 is a waveform diagram showing operation waveforms according to the third embodiment of the present invention.

FIG. 8 is a waveform diagram showing operation waveforms according to the fourth embodiment of the present invention.

FIG. 9 is a configuration explanatory view showing an example of a conventional capacity test method.

FIG. 10 is a configuration explanatory view showing another example of the conventional capacity test method.

[Explanation of symbols]

1 ... AC or DC power supply, 2 ... Power conversion device, 3 ... Storage battery, 4 ... Load device, 5 ... Changeover switch, 6 ... Discharge constant current load, 7 ... Lowest voltage battery cell, 8 ... Changeover switch,
9 ... Constant current load for discharging, 10 ... Charger for recharging discharged battery cells, 11 ... AC or DC power supply, 12 ... Power converter input terminal, 13 ... Rectifying / smoothing section, 14 ... Inverter section, 15 ... Transformer, 16 ... Rectifying / smoothing section, 17 ...
Power converter output terminal, 18 ... Comparator, 19 ... Error amplifier, 20 ... Oscillator, 21 ... Reference voltage, 22-23 ... Resistance, 24 ... Capacitance test circuit, 25 ... Measurement start trigger signal input terminal, 26 ... Discharge time Output terminal, 27 ... A timing signal generation circuit that outputs a signal that changes the reference voltage using the measurement trigger as an input and a signal that specifies the timing of data acquisition to the memory, 28 ... the storage battery voltage at the time specified by the timing signal generation circuit output A gate circuit for taking in data, 29 ... A memory circuit for storing the time designated by the output of the timing signal generating circuit and its storage battery voltage data, 30 ... A discharge time based on the time and the voltage data stored in the memory circuit. Calculation circuit for calculation, 31 ... Discharge time and storage battery capacity output terminal, 32 ... Storage battery current detection circuit, 33 ... Storage battery temperature Output circuit, 34 ... Gate circuit for taking in storage battery voltage, storage battery discharge current, storage battery temperature data at the time specified by the timing signal generation circuit output, 35 ... Time specified by the timing signal generation circuit output and its storage battery voltage, Memory circuit for storing storage battery discharge current, storage battery temperature data, 36 ... Arithmetic circuit for calculating discharge time and capacity based on time, voltage, current and temperature data stored in the memory circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takashi Nakayama 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation (72) Inoue Tsunehiro Sato 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nihonhon Telegraph and Telephone Corporation (72) Inventor Kazuo Takano 1-34 Roppongi, Minato-ku, Tokyo Inside NTT FACILITIES CORPORATION

Claims (4)

[Claims] 1. A power converter that inputs an AC power supply or a DC power supply and outputs a DC voltage required for a load device, and a power converter that is connected in parallel to a power converter output terminal and is floatingly charged when the power converter is operating. In an uninterruptible power supply system that consists of a storage battery that supplies power to the load when it is stopped, the output voltage of the power converter is lowered to a voltage at which the load device can maintain normal operation, the storage battery is discharged, and its terminal voltage is reduced. A storage battery capacity measuring method in which the time until the discharge end voltage is reached is estimated by measuring the terminal voltage. 2. The storage battery capacity measuring method according to claim 1, wherein the terminal voltage in the storage battery discharging state is changed from the battery temperature at the time of measurement to the reference temperature, and from the battery discharge current at the time of measurement to the voltage at the reference discharge current, respectively. After correcting
A storage battery capacity measuring method for estimating the time to reach the discharge end voltage based on the corrected terminal voltage decrease rate. 3. A power converter that inputs an AC power supply or a DC power supply and outputs a DC voltage necessary for a load device, and a power converter that is connected in parallel to a power converter output terminal and is floatingly charged when the power converter is operating. In an uninterruptible power supply system that is configured by a storage battery that supplies power to the load when stopped, a means for lowering the output voltage of the power converter, a means for measuring the storage battery terminal voltage, and an external signal as a trigger for the power converter. A signal for lowering the output voltage and a timing signal generating circuit for generating a timing signal at two different times during the output voltage lowering signal generation period, a gate circuit for passing a storage battery terminal voltage signal according to the timing signal, and a gate circuit output signal And a calculation circuit for calculating the remaining discharge time based on the data of the memory circuit. Battery capacity measurement circuit, wherein the door. 4. A power converter that inputs an AC power supply or a DC power supply and outputs a DC voltage necessary for a load device, and a power converter that is connected in parallel to a power converter output terminal and is floating-charged when the power converter is operating. In an uninterruptible power supply system that consists of a storage battery that supplies power to a load when it is stopped, a means to reduce the output voltage of the power converter, a means to measure the storage battery terminal voltage, a storage battery discharge current, and a storage battery temperature, and an external device. A signal that triggers a signal to lower the output voltage of the power converter and a timing signal generation circuit that generates a timing signal at two different times during the output voltage drop signal generation period, and a storage battery terminal voltage and a storage battery discharge current according to the timing signal. , A gate circuit for passing the battery temperature signal, and a memory circuit for storing the gate circuit output signal Battery capacity measurement circuit characterized by comprising an arithmetic circuit for finding the remaining discharge time on the basis of the data of the memory circuit.