JPH01176948A - Detector for power failure in no power failure system - Google Patents

Abstract

PURPOSE:To detect a voltage drop within a half cycle and to detect further quickly the time of power failure by outputting a power failure detecting signal when signals exceeding the time limits settled respectively in 1st and 2nd level detectors are detected. CONSTITUTION:When a commercial power source 1 which is full-wave rectified by a rectifier 7 is supplied to the 1st level detector 12, a normal level is bypassed by a 1st timer 14 having about 2-3msec time limit, as the detector 12 is always capable of detecting the power at a low level around zero voltage, while the power failure state is detected in a short time. On the other hand, a high level voltage is detected by a 2nd level detector 13, and the normal level is bypassed by a 2nd timer 15 as the detection is made once a half cycle, while the voltage drop is detected in a half cycle. When either detection is made, an inverter is started by an OR circuit 16 in such a manner as controlling a switching circuit 10, and at the same time, a switch 5 can be changed over to the inverter side from the commercial electric power side.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to a power outage detection device for detecting a power outage voltage of an AC power source in an uninterruptible power supply system (hereinafter referred to as UPS). Prior Art) A block diagram of a conventional always-on commercial UPS is shown in FIG.

Power is normally supplied from the commercial power source 1 to the load 6 via the switch 5, but when the voltage of the commercial power source 1 drops or there is a power outage, the voltage detector 9 detects this and the switching circuit 10 starts the inverter 4. At the same time, the switch 5 is switched from A to B and the power source is switched to the inverter power supply within one cycle. This method is a UPS method often used for office automation equipment and computer class computer power supplies.

The charger 2 is configured to charge the battery 3 when the commercial power supply is normal, and to supply power to the inverter 4 to supply AC power during a power outage.

In this case, in order to detect a voltage drop or instantaneous power outage in the power supply 1, conventionally, the commercial power supply is rectified by a rectifier 7, smoothed by a capacitor 8, and then a voltage detector 9 detects the value of the commercial power supply when it falls below a certain level. It is configured so that the switching circuit 1o is activated when this happens.

(Problem to be Solved by the Invention) However, in the conventional configuration described above, since an electrolytic capacitor is generally used as the capacitor 8 in the power supply voltage detection circuit, a variation of about ±50% in capacitance occurs, and when discharging The constants vary, and the time it takes to detect a voltage drop varies depending on the product. Furthermore, since the capacitance of an electrolytic capacitor changes significantly over time, it is difficult to select a capacitor for detection in the shortest possible time.

In addition, it is sufficient that the allowable instantaneous interruption time of the UPS load matches the time constant of the voltage detection circuit or that the detection time of the voltage detection circuit is short, but generally the allowable instantaneous interruption time of the UPS load is about half a cycle. Therefore, it is necessary to detect a drop or momentary power outage in the power supply voltage during this period. However, in the conventional circuit, the detection is delayed due to the above-mentioned time constant, which is disadvantageous.

In addition, if the time constant is shortened in an attempt to shorten the detection time, the constant voltage detector is likely to malfunction, so the time constant should be set to 50~
It is difficult to reduce the voltage to 60 m5 or less, and there is a drawback that a sudden voltage drop causes a delay in switching time.

As explained above, in a continuous commercial UPS system, it is important to detect instantaneous power outages as quickly as possible and switch to the inverter side as quickly as possible.In the present invention, even voltage drops can be detected in half a cycle, resulting in complete power outages. It is an object of the present invention to provide a power failure detection device for an uninterruptible system that can detect power failures in about 2 to 3 ms.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the power failure detection device of the present invention includes first and second level detectors that detect first and second voltage levels of an AC power supply; First and second timers are provided for outputting a power outage detection signal when the signals detected by the first and second level detectors exceed first and second set time limits. .

(Function) The first level detector detects a low voltage level and always detects it near the zero voltage of the AC power supply, so it takes 2 to 3 ms.
This can be avoided by using a first timer with a certain time limit, and a power outage can be detected in a short time.

Since the second level detector detects a high voltage level and can detect it once every half cycle, the second timer detects the voltage drop of the AC power supply every half cycle.

When either of these two detection circuits is detected, the alternating current (
Switch from commercial) power supply to inverter power supply.

(Embodiment) An embodiment of the present invention is shown in FIG. 1. The same parts as those of the conventional system (FIG. 4) are omitted in FIG. 1, and only the instantaneous power failure detection circuit is shown.

A commercial power supply 1 is full-wave rectified by a rectifier 7, a low level of voltage is detected by a first level detector 12, and is inputted to an OR circuit 16 via a first timer 14.

On the other hand, the second level detector 13 detects the high level of the voltage, and the OR circuit 16 detects the high level of the voltage via the second timer 15.
is input, and the output of the OR circuit 16 controls the switching circuit IO to start the inverter, and at the same time switches the switch 5 from the commercial power supply side to the inverter side.

A specific circuit example of the main part of the present invention is shown in FIG.

The commercial power supply 1 is rectified by the rectifier 7, and the transistor 22 is turned on with the divided voltage of the resistors 20 and 21 to detect the first low voltage level.

The voltage charged in the capacitor 35 by the diode 25 is connected to the collector of the transistor 22 via the resistor 24 and the photodiode 23 of the photocoupler, and when the transistor 22 is turned on, the phototransistor 26 of the photocoupler is turned on and V is It becomes zero.

On the other hand, Zener diode 29, resistor 30. The level of the second high voltage is detected by the resistor 31 and the transistor 32, and when the transistor 32 is turned on, a current flows from the resistor 34 to the photodiode 33 of the photocoupler, and the phototransistor 37 is turned on, and the output V3? becomes zero.

The operation will be explained below using the operating waveforms shown in FIG.

The output voltage VZS of the phototransistor 26 detects the first level E of the output voltage (full-wave rectified waveform) v7 of the rectifier 7, and therefore outputs a signal of "1" for a short time only near the zero cross of the sine wave voltage. do. This signal V is ignored by passing through the timer 14, and the signal V14 is not output.

On the other hand, the output V3 of phototransistor 37? detects the second level E2 or lower of the full-wave rectified waveform v7. Therefore, during the period when the signal Vat is "1", if the power supply is normal (in the figure, the first two wave pieces are shorter than the half cycle T of the power supply, as shown by T□. However, when the power supply voltage is 2 (the last wave in the diagram), V3? remains “even if the time T2 set by the timer 15 has passed”.
Since it does not become 0'', the signal Vig becomes "1", and a voltage drop is detected at time t□.

Furthermore, when a power outage occurs and the voltage v7 becomes lower than the first level E1 at time t2, the signal V2& remains at "1",
At time t after time delay T1, signal L4 becomes “
1”.

The signals VL4 and vl are sent to the switching circuit 1 via the OR circuit 16.
0 and switches from AC (commercial) power supply to inverter power supply.

If the power supply voltage suddenly drops, the signal V14 can be output even before time t□ and can be detected after time delay T1.

According to this embodiment, the AC power supply side and the control circuit side can be easily insulated by the photocoupler.

In addition, when the power supply frequency is 507 and 607, the period T1 of "1" of the signal v3□ which detects the second level E2 or lower
It is desirable to change the set time T2 of the timer 15 depending on the frequency. For this reason, a circuit is provided to detect the frequency of the power supply voltage, and the time of the timer 15 is switched using this output.

Frequency detection, timer switching, etc. can be easily performed by using a microcomputer.

〔Effect of the invention〕

As explained above, according to the present invention, a power outage is detected within 2 to ams by the first level detector, and the time during which the undervoltage is below the second detection level is measured. Therefore, by providing two detection circuits that detect within one cycle ÷ , we provide a power failure detection device for an uninterruptible system that can detect a power drop within a cycle and detect a power failure even earlier. can do.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a detailed circuit diagram of Fig. 1, Fig. 3 is a waveform diagram explaining the action of Fig. 2, and Fig. 4 is a conventional uninterruptible power supply. It is a block diagram of a device. 1... AC (commercial) power supply, 2... Charger 3...
Battery, 4... Inverter 5... Switch, 6... Load 7... Rectifier,
8... Capacitor 9... Voltage detector,
DESCRIPTION OF SYMBOLS 10... Switching circuit 12... First level detector, 13... Second level detector 14... First timer, 15... Second timer 16... OR circuit , 23.26...Photocoupler 22,
32... Transistor, 29... Zener diode 33, 37... Photocoupler agent Patent attorney Nori Chika Ken Shu Ken Daikomaru Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] a first detecting first and second voltage levels of the alternating current power supply;
and a second level detector, and a first level detector that outputs a power outage detection signal when the signals detected by the first and second level detectors exceed the first and second set time limits.
and a second timer, and is characterized in that it detects a power outage earlier than half a cycle and detects an undervoltage in about a half cycle.