JPH08331862A - Uninterruptible power supply - Google Patents

Abstract

PURPOSE: To quickly detect a load having an accident without stopping an uninterruptible power supply, in the case where there is an accident wherein an excessive current flows in any of a plurality of the loads. CONSTITUTION: A load current output from an inverter circuit 3 is detected for whether it is increased to an excessive current or not by an excessive current detecting circuit 14. While detecting the excessive current, output voltage of the inverter circuit 3 is decreased by an output voltage decreasing circuit 15. In this way, the load current is controlled so as to be an operating current or more of a load side overcurrent detector and an overload durable amount or less of the inverter circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an uninterruptible power supply provided for a plurality of AC loads equipped with an overcurrent detecting device which operates so as to cut off the input of a current when the load current exceeds a predetermined operating current. It relates to a power supply device.

[0002]

2. Description of the Related Art On the uninterruptible power supply side, an overcurrent detecting device called a breaker is provided which stops the operation of an inverter circuit to stop the output of current when the load current exceeds a predetermined operating current. . However, since the overcurrent detection device attached to the load has a slower response than the overcurrent detection device used for the uninterruptible power supply, a short circuit accident, etc. occurred in one of the multiple loads and an excessive current flowed. At times, the overcurrent detection device on the uninterruptible power supply side operates first. Therefore, it is not possible to immediately detect under which load the accident occurred. In particular, when such a situation occurs in an uninterruptible power supply device used in a place where it is necessary to quickly restore power failure, such as a substation, there is a problem that power failure recovery is delayed.

An object of the present invention is to provide an uninterruptible power supply capable of promptly detecting which AC load among a plurality of AC loads has caused an accident.

Another object of the present invention is to provide an uninterruptible power supply which makes it possible to easily know an AC load in which an overcurrent occurrence accident has occurred without stopping the uninterruptible power supply.

Still another object of the present invention is to provide an uninterruptible power supply device capable of operating an overcurrent detection device on the AC load side when an excessive current flows.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a plurality of AC loads equipped with an overcurrent detection device called a breaker that operates so as to cut off the input of a current when the load current exceeds a predetermined operating current. An uninterruptible power supply device that is provided for the AC power supply and supplies AC power to a plurality of AC loads by operating an inverter circuit using a storage battery as a power supply when a power failure occurs in the AC power supply.

The uninterruptible power supply to be improved by the present invention includes an uninterruptible power supply of a type in which an inverter circuit is constantly operated to supply the output of the inverter circuit to a load, and the inverter circuit is always stopped. The present invention can be applied to any uninterruptible power supply device of a type that operates an inverter circuit to detect an AC power failure and supplies the output of the inverter circuit to a load.

Any control method may be used for the inverter circuit, but in general, there is a constant voltage control method for maintaining the output voltage of the inverter circuit at a predetermined voltage (effective value) using a feedback circuit. Used. When the constant voltage control method is used, control of the inverter circuit is generally performed using a well-known pulse width modulation control circuit (PWM control circuit).

According to the present invention, the overcurrent detection circuit detects whether the load current supplied from the inverter circuit to the AC load is equal to or more than a predetermined overcurrent, and the overcurrent detection circuit detects the overcurrent. And an output voltage lowering circuit that lowers the output voltage of the inverter circuit so that the load current is equal to or higher than the operating current and equal to or lower than the overload withstand amount of the inverter circuit during the operation.

If the overcurrent detection circuit can detect that an excessive current is flowing in the load current,
Any configuration may be used. For example, a rectifier circuit that rectifies the load current, a comparison circuit that compares the output of this rectifier circuit with a reference value that corresponds to the overcurrent, and an overcurrent detection for a predetermined period when a signal is output from the comparison circuit. It is also possible to configure the overcurrent detection circuit from an overcurrent detection signal output circuit that outputs a signal. Here, as the rectifier circuit,
It is preferable to use a half-wave rectifier circuit or a full-wave rectifier circuit in which the presence of excessive current appears as it is. The reference value used in the comparison circuit is determined in consideration of the rated current of the inverter circuit and the overload withstand amount (allowable current that can maintain the operation of the inverter circuit in the overload state). Specifically, a value slightly larger than the rated current can be used as the reference value. The output period of the overcurrent detection signal output from the overcurrent detection signal output circuit, that is, the "predetermined period", is a continuous overcurrent detection signal even when the signal is discontinuously output from the comparison circuit. Is defined to be able to output.

Further, the above-mentioned output voltage lowering circuit is designed so that the load current becomes equal to or higher than the operating current of the overcurrent detection device in the load and equal to or lower than the overload withstanding capacity of the inverter circuit while the excessive current detection circuit detects the excessive current. Any configuration may be used as long as it can reduce the output voltage of the inverter circuit. For example, the output voltage lowering circuit may be configured by a voltage dividing circuit that lowers the voltage of the control signal input to the pulse width modulation control circuit while the excessive current detection signal is being output. When the output voltage of the inverter circuit is lowered by lowering the voltage of the control signal in this manner, the output voltage of the inverter circuit can be reduced to a desired range easily and quickly.

Further, such a voltage dividing circuit includes, for example, a first current limiting means connected in series to a control signal input section of the pulse width modulation control circuit, a control signal input section and a first current limiting means. Of the semiconductor switch circuit and a series circuit including a second current limiting unit electrically connected between the electrical connection point of the above and the negative terminal of the overcurrent detection signal output circuit or the ground. In this case, the semiconductor switch circuit may be configured to be conductive while the overcurrent detection signal is being output. With this configuration, the semiconductor switch circuit is turned on while the excessive current detection signal is being output, and the pulse width modulation control circuit has the control signal divided by the first current limiting unit and the second current limiting unit. Is entered. When the voltage of the control signal decreases, the reference voltage that serves as a reference for pulse width modulation in the pulse width modulation control circuit decreases, and the output voltage of the inverter circuit decreases. In a typical pulse width modulation control circuit, for example, a reference oscillation wave such as a triangular wave generated in a predetermined cycle is compared with a reference voltage of a DC level, a period until the voltage of the reference oscillation wave reaches the reference voltage, The inverter circuit is controlled so that the output is output from the inverter circuit. The control signal controls the reference vibration wave or reference voltage.When the voltage of the control signal increases, the peak voltage or reference voltage of the reference vibration wave increases, and when the voltage of the control signal decreases, the peak voltage of the reference vibration wave. Alternatively, the reference voltage drops. Therefore, if the voltage of the control signal is reduced by dividing the control signal, the peak voltage of the reference vibration wave or the reference voltage is reduced, and the output voltage of the inverter circuit is reduced.

[0013]

When a fault such as a short circuit occurs in one of the plurality of AC loads and an excess current flows, the excess current detection circuit detects the excess current. When the overcurrent detection circuit detects an overcurrent, the output voltage lowering circuit lowers the output voltage of the inverter circuit so that the load current is equal to or higher than the operating current of the overcurrent detection device in the load and is equal to or lower than the overload withstand amount of the inverter circuit. Therefore, even if an overcurrent occurs, the inverter circuit continues to operate in a safe range, and a current equal to or higher than the operating current of the overcurrent detection device continues to flow in the AC load in which the accident has occurred. If this state continues for a while, the overcurrent detection device of the AC load in which the accident has occurred operates to cut off the supply of current to this AC load. When the AC load in which an accident occurs is disconnected from the inverter circuit due to the operation of the overcurrent detection device, the overcurrent detection circuit stops detecting the overcurrent, the output voltage drop circuit stops operating, and the output voltage of the inverter circuit Put back. As described above, according to the present invention, when an accident occurs in an AC load, the overcurrent detection device on the AC load side always operates, so that it is possible to quickly identify the AC load in which the accident has occurred, and take action thereafter. Can be done quickly.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a rectifier circuit that rectifies the output of the commercial AC power source S, 2 is a storage battery that is floatingly charged by the output of this rectifier circuit, and 3 is the DC power of the rectifier circuit 1 that is always AC power. It is an inverter circuit for converting and converting the DC power of the storage battery 2 into AC power when the AC power supply S fails. The output of this inverter circuit 3 is a plurality of AC loads 2
1 to 25, each AC load is provided with an overcurrent detection device (21a to 25a) that shuts off the input of the current when the load current exceeds a predetermined operating current.

Reference numeral 4 is a reference voltage generating circuit, 5 is an inverter output feedback voltage detecting circuit, and 6 is a comparator for comparing the output voltages of these circuits 4 and 5. Reference numeral 7 is an error amplifier that amplifies the output of the comparator 6, and reference numeral 8 is a pulse width that is directly controlled by the output of the error amplifier 7 and outputs a pulse width modulation signal, which is used for switching control of the semiconductor elements forming the inverter circuit 3. It is a modulation control circuit. The blocks 4 to 8 constitute a constant voltage control circuit 9.

Reference numeral 10 is a current transformer for detecting the load current of the inverter 3, 11 is a rectifier circuit for rectifying the output current of the current transformer, and 12 is an output of the rectifier circuit 11 and a reference value corresponding to an excessive load current. Is a comparison circuit for comparing. Reference numeral 13 denotes an overcurrent detection signal output circuit that outputs an overcurrent detection signal for a predetermined period when a detection signal is output from the comparison circuit 12, and is composed of, for example, a triggerable monostable multivibrator or the like. . The blocks 11 to 13 constitute an overcurrent detection circuit 14 that detects whether the load current of the inverter circuit 3 is equal to or more than a predetermined overcurrent. Reference numeral 15 is an output voltage of the inverter circuit 3 for adjusting (specifically dividing) the voltage of the control signal input from the error amplifier 7 to the pulse width modulation circuit 8 while the overcurrent detection signal is being output. Is an output voltage lowering circuit for lowering the voltage. The output voltage reduction circuit 15 allows the output of the error amplifier 7 to pass through the pulse width modulation control circuit 8 as it is when the overcurrent detection signal is not output.

In this embodiment, the constant voltage control circuit 9, the excessive current detection circuit 14, and the output voltage reduction circuit 15 constitute an inverter circuit control device. Reference numerals 21 to 25 are a plurality of loads connected in parallel to the output terminals of the inverter circuit 3, and 21a to 25a are overcurrent detection devices including fuses and the like provided on the respective load sides.

Next, the operation of this embodiment will be described. First,
The operation of the constant voltage control circuit 9 will be described. The reference voltage generation circuit 4 outputs a reference sine wave voltage which serves as a reference for the inverter output. The reference voltage and the inverter output feedback voltage output from the inverter output feedback voltage detection circuit 5 are input to the comparator 6. The comparator 6 outputs an error signal of reverse polarity such that the voltage decreases as the inverter output feedback voltage increases. This error signal is input to the error amplifier 7 and is output from the amplifier 7 to the pulse width modulation control circuit 8
A control signal for controlling is output. The pulse width modulation control circuit 8 controls the peak voltage of the reference vibration wave such as a triangular wave by the input control signal, and according to the magnitude relationship between the reference vibration wave and the constant level reference voltage, the voltage of the reference vibration wave is controlled. The inverter circuit 3 is switching-controlled so that the inverter circuit 3 outputs an output only during a period until the voltage reaches the reference voltage. By the above operation, constant voltage control for holding the output voltage of the inverter circuit 3 at a constant voltage is performed.

The constant voltage control circuit 9 may change the reference voltage in the pulse width modulation control circuit 8 to control the output of the inverter by constant voltage. In that case,
The inverter output feedback voltage detection circuit 5 is configured to include a rectifier circuit inside to convert the inverter output into a DC voltage. Then, the reference voltage generating circuit 4 is configured to generate a constant reference voltage. Further, the comparator 12 compares the output of the inverter output feedback voltage detection circuit 5 with the output of the reference voltage generation circuit 4 and outputs the difference to the error amplifier 7. The error amplifier 7 amplifies the comparison result and outputs it to the pulse width modulation control circuit 8 as a control signal. In this case, the output voltage of the inverter circuit 3 is held at a constant voltage by controlling the reference voltage, which is compared with the reference oscillation wave in the pulse width modulation control circuit 8 by this control signal, according to the change of the control signal. Performs constant voltage control.

Next, the operations of the overcurrent detection circuit 14 and the output voltage lowering circuit 15, which are the main parts of the present invention, will be described with reference to FIG. The output current from the current transformer 10 corresponding to the magnitude of the load current supplied from the inverter circuit 3 is input to the rectifier circuit 11 and full-wave rectified. This rectified output is input to the comparison circuit 12 and compared with the reference value corresponding to the excessive current [see FIG. 2 (A)]. When the rectified output becomes equal to or higher than the reference value Vref, the comparison circuit 12 outputs a pulse signal [see FIG. 2 (B)], and the overcurrent detection signal output circuit 13 outputs a pulse signal in accordance with the pulse signal for a predetermined period. Overcurrent detection signal is continuously output [Fig. 2
(See (C)]. The excess current detection signal output circuit 13 is composed of a monostable multivibrator triggered by the pulse signal output from the comparison circuit 12. Therefore, the overcurrent detection signal output circuit 13 is
While the pulse signal is being output from 2, the monostable multivibrator is continuously triggered to output a continuous overcurrent detection signal. While the overcurrent detection signal is being output, the output voltage reduction circuit 15 keeps the pulse width modulation control circuit 8
The operation of lowering the voltage of the control signal input to is performed.
As a result, the pulse width of the inverter circuit control signal output from the pulse width modulation control circuit 8 is reduced, and the output voltage of the inverter circuit 3 is reduced to the required range. This required range means that the output load current of the inverter circuit 3 is not less than the operating current of the overcurrent detection device in each load,
The output voltage is of a magnitude that is equal to or less than the overload withstand amount of the inverter circuit 3. As described above, when the load current becomes excessive, the output voltage of the inverter circuit 3 is lowered, so that the inverter circuit 3 continues to operate in a safe range even if an excessive current occurs, causing an accident. Continued to flow a current equal to or higher than the operating current of the overcurrent detection device to the load.

FIG. 3 is a waveform diagram showing how the output voltage and the load current of the inverter circuit 3 change according to the above-mentioned control, where e1 is the regular inverter output voltage and i1 is the normal load current. i2 is an overload current. When this overload current i2 is detected, the inverter output voltage is e2.
Is reduced as. Then, the load current flows as the current i3 having the magnitude as described above. As a result, the overcurrent detection device (21a) of the load (21-25) in which the accident has occurred
.About.25a) operates to cut off the power supply to this load. When the load in which the accident has occurred is disconnected from the output of the inverter circuit 3 by the operation of this overcurrent detection device, the overcurrent detection circuit 14 no longer detects the overcurrent, and the output voltage reduction circuit 15 stops its operation. As a result, the output voltage of the inverter circuit 3 returns to the original constant voltage state. As described above, when an accident occurs in a certain load, the overcurrent detection device on the load side operates, so that the load in which the accident has occurred can be quickly identified.

Next, a specific configuration example of the output voltage reduction circuit 15 will be described with reference to FIG. The output voltage reduction circuit 15 uses the pulse width modulation control circuit 8 according to the control signal.
It is used when the output of the inverter is controlled to a low voltage by changing the reference voltage to be compared with the reference oscillation wave inside the. Reference numerals 7, 8 and 13 in FIG. 4 denote an error amplifier, a pulse width modulation control circuit and an overcurrent detection signal output circuit, which are shown by the same reference numerals in FIG. The block 15 constitutes the output voltage lowering circuit of this embodiment, and 15a is a resistor as a first current control means connected in series to the control signal input section of the pulse width modulation control circuit 8. Reference numeral 15b is a switching transistor, and 15c is a resistor as a second current limiting means, which is a series circuit of both 15b and 15c connected between the control signal input section and the ground.

The output voltage lowering circuit 15 of the present embodiment keeps the transistor 15b conductive and keeps the resistors 15a and 15c conductive while the continuous overcurrent detection signal is being input to the base of the transistor 15b from the overcurrent detection signal output circuit. To form a voltage dividing circuit. As a result, the voltage of the control signal input to the pulse width modulation control circuit 8 is lowered. When the voltage of the control signal input to the pulse width modulation control circuit 8 decreases, the reference voltage compared with the reference oscillation wave decreases,
The conduction period of the semiconductor element forming the inverter circuit 3 is shortened, and the output voltage of the inverter circuit 3 is reduced. As a result, the load current increases.

The embodiment described with reference to FIG. 1 is an uninterruptible power supply of the type in which the inverter circuit is always operated and the output of the inverter circuit is supplied to the load, but the present invention is not limited to this. It is needless to say that the present invention can be applied to an uninterruptible power supply device of a type in which the inverter circuit is normally stopped and the inverter circuit is operated to supply the output of the inverter circuit to the load when the AC power supply fails.

[0025]

As described above, according to the uninterruptible power supply device of the present invention, while the overcurrent detection circuit detects that the load current supplied from the inverter circuit to the load has exceeded the overcurrent, , The output voltage drop circuit is operated to reduce the output voltage of the inverter circuit so that the load current is equal to or higher than the operating current of the overcurrent detection device on the load side and is equal to or lower than the overload withstand amount of the inverter circuit. When an accident occurs where an overcurrent flows through a certain load among multiple loads, operate the inverter circuit within a safe range and operate the overcurrent detection device for the accident occurrence load to supply power to the accident occurrence load. Can be shut off. This makes it possible to quickly identify the accident load and deal with it.
The output voltage of the inverter circuit can be quickly restored.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

2A to 2C are waveform charts used for explaining the operation of the excessive current detection circuit in the embodiment of the present invention.

FIG. 3 is a waveform diagram showing how the output voltage and load current of the inverter circuit change according to the control of the present invention.

FIG. 4 is a connection diagram showing an example of an output voltage lowering circuit used in an embodiment of the present invention.

[Explanation of symbols]

 1 Rectifier circuit 2 Storage battery 3 Inverter circuit 4 Reference voltage generation circuit 5 Inverter output feedback voltage detection circuit 6 Comparator 7 Error amplifier 8 Pulse width modulation control circuit 9 Constant voltage control circuit 11 Rectifier circuit 12 Comparison circuit 13 Overcurrent detection signal output circuit 14 Overcurrent detection circuit 15 Output voltage drop circuit

Claims (4)

[Claims] 1. A plurality of alternating current loads provided with an overcurrent detecting device that operates so as to cut off the input of the current when the load current exceeds a predetermined operating current, and a power failure occurs in the alternating current power supply. An uninterruptible power supply device that operates an inverter circuit using a storage battery as a power source to supply AC power to the plurality of AC loads while the load current supplied from the inverter circuit to the AC load is a predetermined excessive value. An overcurrent detection circuit for detecting whether or not the current is more than or equal to the current, and while the overcurrent detection circuit is detecting the overcurrent, the load current is more than the operating current and less than the overload withstand amount of the inverter circuit. And an output voltage reduction circuit that reduces the output voltage of the inverter circuit. 2. The inverter circuit is configured to be controlled by a pulse width modulation control circuit, and the overcurrent detection circuit includes a rectification circuit for rectifying the load current, an output of the rectification circuit and the overcurrent. A comparison circuit that compares a reference value corresponding to the current, and an overcurrent detection signal output circuit that outputs an overcurrent detection signal for a predetermined period when a signal is output from the comparison circuit, The output voltage reduction circuit is configured by a voltage divider circuit that reduces the voltage of a control signal input to the pulse width modulation control circuit during a period in which the overcurrent detection signal is output. The uninterruptible power supply according to 1. 3. The voltage dividing circuit includes a first current limiting unit connected in series to a control signal input unit of the pulse width modulation control circuit, the control signal input unit and the first current limiting unit. Of the semiconductor switch circuit electrically connected between the electrical connection point of the semiconductor device and the ground, and a series circuit including second current limiting means, and the semiconductor switch circuit outputs the overcurrent detection signal. The device according to claim 2, which is configured to conduct for a period of time.
Uninterruptible power supply described in. 4. A rectified output of an AC power supply, which is provided for a plurality of AC loads equipped with an overcurrent detection device that operates so as to cut off the input of the current when the load current exceeds a predetermined operating current. A rectifier circuit, a storage battery charged by the output of the rectifier circuit, an inverter circuit, and normally DC power obtained by rectifying the output of the AC power supply is converted into AC power by the inverter circuit and supplied to the plurality of AC loads. However, when a power failure occurs in the AC power supply, the inverter circuit is operated by using the storage battery as a power source to operate the inverter circuit to supply the AC power to the plurality of AC loads. A power failure power supply device, wherein the inverter circuit control device maintains an output voltage of the inverter circuit at a predetermined voltage. A constant voltage control circuit including a pulse width modulation control circuit for controlling the inverter circuit, and an overcurrent detection for detecting whether or not a load current supplied from the inverter circuit to the AC load is equal to or more than a predetermined overcurrent. Circuit, and an output voltage drop that reduces the output voltage of the inverter circuit so that the load current is equal to or higher than the operating current and equal to or lower than the allowable current of the inverter circuit while the excessive current detection circuit detects the excessive current. A circuit, wherein the output voltage reduction circuit is configured to reduce the output voltage of the inverter circuit by adjusting the voltage of the control signal input to the pulse width modulation control circuit. Uninterruptible power system.