JPS63163177A - Detection of momentary voltage drop - Google Patents

Abstract

PURPOSE:To enable detection of a momentary voltage drop in real time, by comparing an input with the results obtained by subtracting a instantaneous voltage drop detection level at a peak value point from an input waveform as reference waveform. CONSTITUTION:A PLL circuit 22 receives an input voltage vS and feeds an output thereof as synchronous signal to a reference sine wave generation circuit 23 which generates a reference sine wave vS. The circuit 23 subtracts a momentary voltage drop detection level value vl (e.g. vl=0.1 vSO)at a peak value vP from an official valve VSO of the input voltage VS, giving a waveform. An absolute value conversion circuit 24 output an absolute value ¦v2¦ of the sine wave V2 and an absolute value conversion circuit 25 outputs an absolute value ¦vS¦ of the voltage vS. A circuit 25 derives a difference of the absolute value (¦vS¦-¦2¦=DELTAv20) and an instantaneous voltage drop discriminator circuit 27 judges that a momentary voltage drop occurs if ¦vS¦<¦v2¦ and generates an output U. Thus, the momentary voltage drop is discriminated in real time.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to an instantaneous voltage drop detection method.

<Prior Art> A voltage integration method is used to detect instantaneous voltage drops in instantaneous voltage drop compensators, voltage fluctuation compensators, and the like.

Figure 4 shows the instantaneous voltage drop compensator, where 1 is a commercial power supply;
2 is a power transmission/distribution line, and 6 is a load such as OA equipment or a computer.

4 is a capacitor that is charged with the voltage of the power transmission and distribution line 2; 5 is an inverter that converts the accumulated charge of this capacitor 4 into commercial frequency alternating current; 6 is an injection transformer that injects this voltage into the power transmission and distribution line 2 in series; 7 8 is a voltage transformer, and 8 is a control circuit for controlling the inverter 5, which includes 8 voltage drop detection sections and a control section 8B.

When there is a lightning strike or the like on the power transmission/distribution line 2 and an instantaneous voltage drop or disconnection (hereinafter referred to as an instantaneous voltage drop) occurs, the eight voltage drop detectors detect the voltage drop and control the control unit 8B to control the inverter. 5, a commercial frequency alternating current voltage commensurate with the drop is generated from the accumulated charge in the capacitor 4, and is applied to the power transmission/distribution line 2 via the injection transformer 6 for series compensation.

Therefore, the predetermined commercial voltage continues to be applied to the load 3, and no trouble occurs.

By the way, as the voltage drop detection section 8A described above, one that utilizes the voltage integration method as described above is known.

FIG. 5 is a block diagram for explaining the voltage integration method, and FIG. 6 is a time chart for explaining the operation of the method shown in FIG. In FIG. 5, reference numeral 11 denotes an input terminal, from which the voltage Vs of the power transmission and distribution line 2 is led from the instrument transformer 7.

12 is a PLL circuit whose input is the voltage Vs, and 16 is a PLL circuit.
A reference sine wave generation circuit generates a reference sine wave 1 using the output of the LL circuit 12 as a synchronization signal, 14 is a reference sine wave v1
The absolute value is 1v11 circuit, which is the difference between the two absolute values (1vS1-1v11=Δv10)
The absolute value comparison circuit 17 to be created is a signal from the PLL circuit 12 at fixed time intervals (for example, every 1/4 cycle of the power supply frequency) so as to integrate the difference ΔV1o from the zero point to the peak point and from the peak point to the zero point. i゛Set integral circuit,
Reference numeral 18 denotes an instantaneous voltage drop determination circuit that determines that an instantaneous voltage drop has occurred when the integral value of the integrating circuit 17 reaches the instantaneous voltage drop detection level, and these constitute eight voltage drop detection sections.

In addition, in FIG. 6, Q is the integral value of ΔV10, and L
is the detection level of the instantaneous voltage drop discrimination circuit 18, and U is the circuit 1
The discrimination outputs of 8 are shown respectively.

In the voltage integration method with the above configuration, the difference in absolute value Δv10 is calculated from the voltage Vs of the power transmission and distribution line 2 and the reference sine wave v1, which is synchronized with this voltage Vs and has an amplitude corresponding to its nominal value.
is determined, and when the predetermined time integral value (from the zero point to the peak point, from the peak point to the zero point) Q of this difference Δv10 reaches the detection level L, it is determined that an instantaneous voltage drop has occurred. FIG. 6 shows this state.

<Problems to be Solved by the Invention> When this voltage integration method is used, the time T1 until the integral value Q reaches the detection level L cannot be determined, and for example, a 10% voltage drop in the power transmission and distribution line 2 cannot be detected. When the detection level L is set to
=) on a 0Hz basis, which caused a problem.

<Means for solving the problem> The present invention obtains a waveform obtained by always subtracting the value of the instantaneous voltage drop detection level at the peak value point from the waveform corresponding to the nominal voltage value applied to the input terminal, and uses it as a reference waveform.
This is a method of comparing instantaneous values with the waveform applied to the input terminal to detect an instantaneous voltage drop in real time.

<Operation> According to the method described above, instantaneous voltage drops can be detected in real time.

<Embodiment> FIG. 1 is a block diagram for explaining the present invention, and FIGS. 2(a) and 2(b) are time charts for explaining the operation of the device shown in FIG.

In these figures, 21 represents the voltage v of the power transmission and distribution line 2, for example.
The reference sine wave generating circuit 22 generates a reference sine wave v2 using the output of the voltage Vs as a synchronizing signal and the output of the LIIg22 as a reference voltage. The waveform of the reference sine wave v2 generated by the circuit 26 is, as shown in FIG. Voltage drop detection level value Vl, (for example, 10% drop detection tear lever,
vIt=' 0. It is given as a waveform after subtracting I Vso ). In addition, Vs.

- The value is set to 0 in the interval T2 where the dragon becomes negative.

The detection level value v2 can be arbitrarily changed by changing the setting value of the voltage drop width setting device 26 built in the circuit 23.

24 is an absolute value conversion circuit for obtaining the absolute value 1v21 of the reference sine wave v2, 25 is an absolute value conversion circuit for obtaining the absolute value 1vSl of the voltage Vs introduced into the terminal 21, and the difference in the absolute values (IVSl-IV21= ΔV2Q ) is derived in real time.

27 is an instantaneous voltage drop determination circuit which inputs the difference ΔV20, and if 1v=l is smaller than IV21, the voltage of the power transmission and distribution line 2 is determined to be 10%, which is the specified voltage drop value set above.
It is determined that an instantaneous voltage drop has occurred, and an output U is generated. These constitute a voltage drop detection section.

In the above configuration, when the voltage of the power transmission/distribution line 2 is normal, a negative value is not derived from the comparison circuit 26 in the difference ΔV20, and therefore, there is no voltage drop output from the circuit 27.

However, when an instantaneous voltage drop occurs in the power transmission/distribution line 2 due to a lightning strike or the like, the voltage Vs of the power transmission/distribution line 2 drops as shown in FIG. 2(b). Since the circuit 26 monitors 1v=l-1v21 in real time, it immediately detects the output ΔV20 at time t1 when the voltage drops below 1V=1k=lv21, and the instantaneous voltage drop determination circuit 27 detects the instantaneous voltage drop. It emits an output U.

In this way, a voltage drop in the input voltage Vs is determined in real time.

Further, even if noise N is superimposed on the input voltage Vs near the zero cross as shown in FIG. 2(b), the absolute value IV21 of the reference sine wave will not be exceeded, so malfunction will not occur.

In other words, simply comparing the input voltage Vs with, for example, a 90% waveform thereof, cannot avoid malfunctions due to noise near the zero cross, but in the present invention, the voltage value Vp at the peak point is always subtracted as a reference. Since the sine wave v2 is used, the above-mentioned malfunction will not occur.

Note that the reference sine wave v2 in the reference sine wave generation circuit 25
can be easily obtained using a ROM. Also,
It is also possible to obtain a circuit whose input-output characteristics have a characteristic curve G as shown in FIG.

To change the detection level L, replace these circuits,
This can be easily done by adjusting the variable parts. In the above explanation, the case where the input voltage Vs is the voltage of the power transmission and distribution line 2 has been described, but the present invention is not limited to this, and the gist thereof is as follows. As long as the input voltage Vs
It can be applied at any voltage.

<Effects of the Invention> As described above, according to the present invention, an instantaneous drop in input voltage can be detected without any time delay, and furthermore, there is an effect that malfunctions do not occur due to noise superimposition near the zero cross of the input voltage. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the present invention, Fig. 2 (a) and (b)
1 is a time chart of each part of the one shown in Fig. 1, Fig. 6 is a diagram showing an example of a characteristic curve for obtaining a reference sine wave, Fig. 4 is a block diagram showing an example of an instantaneous voltage drop device, and Fig. 5 is a diagram showing an example of the characteristic curve for obtaining a reference sine wave. Block diagrams showing one embodiment of the invention, FIGS. 6(a) and (
b) is a time chart of each part of the one shown in FIG. vS: Input voltage Vso2 nominal value voltage Vλ: Instantaneous voltage drop detection level value v2: Reference voltage 27: Instantaneous voltage drop discrimination circuit

Claims (1)

[Claims] The waveform obtained by always subtracting the value of the instantaneous voltage drop detection level at the peak value point from the waveform corresponding to the nominal value of the input voltage is defined as the waveform of the reference voltage, and the absolute value of the instantaneous value of this reference voltage and the instantaneous value of the input voltage A method for detecting an instantaneous voltage drop, characterized in that an instantaneous voltage drop in the input voltage is detected by monitoring a difference in absolute values in real time.