JPH03850Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention relates to an AC undervoltage detection circuit used, for example, in a detection stage of an AC undervoltage relay or an AC undercurrent relay.

<Prior Art> Conventionally, an AC undervoltage detection circuit in a relay as described above has been configured as shown in FIG. Receives AC input via an isolation transformer 10, full-wave rectifies it in a rectifier circuit 12, and further rectifies it in a smoothing circuit 14.
smooth it and convert it to DC voltage. The first comparison circuit 18 compares this DC voltage with a reference voltage set by the reference voltage generation circuit 16 .

When the AC input voltage level falls below a predetermined value,
The DC voltage obtained by rectifying and smoothing this voltage becomes equal to or lower than the reference voltage, and the comparison circuit 18 outputs a detection signal.

<Problems to be solved by the invention> In the conventional circuit shown in Fig. 1, the smoothing circuit 14 has a large reactance due to the smoothing capacitor, etc., so a change in the AC input voltage causes a change in the rectified and smoothed DC voltage. It takes a considerable amount of time for it to appear. Therefore, there is a considerable delay time from when the AC input voltage drops until the detection signal of the comparator circuit 18 is output. This poor responsiveness is directly linked to the responsiveness of AC undervoltage relays using this.

An object of this invention is to provide an AC undervoltage detection circuit that can quickly detect a drop in AC input voltage.

<Means and operations for solving the problems> The AC undervoltage detection circuit of the present invention that achieves the above object receives a sine wave AC input and detects a sine wave of a predetermined peak voltage at the same frequency and the same phase. A waveform shaping circuit that generates a wave signal, a differential amplifier circuit that performs calculations after directly connecting or rectifying the output of this waveform shaping circuit and the above AC input, and comparing the output of this differential amplifier circuit with a predetermined reference voltage. It consists of a comparison circuit.

<Embodiment> FIG. 2 shows an AC undervoltage detection circuit according to an embodiment of the present invention, and FIG. 3 shows operating waveforms of each part thereof. In this embodiment, an isolation transformer 10, a rectifier circuit 12, a smoothing circuit 14, a reference voltage generation circuit 1
6. The circuit of the present invention is added to the same conventional circuit as shown in FIG. 1, consisting of the first comparator circuit 18.

The circuit of the present invention is constructed as follows. The sine wave AC input A on the secondary side of the isolation transformer 10 passes through a bandpass filter 20 (passes the frequency of the AC input), removes noise, etc., and becomes a waveform B.
and is input to the comparison circuit 22. Comparison circuit 2
2 is a cross comparator which shapes the signal B into a square wave signal C using the zero volt line as a threshold value. This square wave signal C has the same frequency and the same phase as the sine wave signal B, but the voltage of the square wave signal C is a constant value determined by the power supply voltage of the comparison circuit 22, and the voltage of the sine wave signal B I don't want to be affected by fluctuations.

The square wave signal C is input to the bandpass filter 24. This bandpass filter 24 also passes only the frequency of the AC input signal A (for example, 50 Hz). Therefore, only the fundamental frequency component of the square wave signal C passes through the bandpass filter 24, and a sine wave signal D having the same frequency and phase as the AC input signal A is obtained. The peak voltage of this sine wave signal D is determined by the voltage of the square wave signal C and is constant, and is not affected by voltage fluctuations of the AC input signal A.

The above is the waveform shaping circuit for obtaining the reference sine wave signal D from the AC input signal A. This reference sine wave signal D is full-wave rectified by the rectifier circuit 26 to form a signal E, and this signal E and the AC input signal D are sent to the rectifier circuit 26.
The full-wave rectified signal F in step 2 is input to the differential amplifier circuit 28 to obtain a voltage deviation signal G corresponding to the instantaneous voltage difference between the two signals E and F. The deviation signal G is compared with a predetermined reference voltage in the second comparison circuit 30, and when the voltage of the deviation signal G exceeds the reference voltage, the comparison circuit 3
Detection signal H is output from 0. The detection signals of the two comparison circuits 18 and 30 are outputted to the outside via an OR gate 32.

In the above configuration, when the voltage of the AC input signal A is at the rated value, the comparison circuit 22
The characteristics of the band pass filter 24 and the like are set. Therefore, when the AC input signal A is at the rated voltage, the deviation signal G is approximately zero. When the voltage of the AC input signal A falls below the rated value, the voltage of the deviation signal G corresponding to the undervoltage increases, and when the undervoltage exceeds a certain value, the detection signal H is output.

In the circuit of the present invention, since the voltage of the AC input signal A is compared as it is in the AC waveform, the AC input signal A
Compared to conventional circuits that rectify and smooth the signal, its operational response is much faster.

The reason why the conventional circuit is also installed in parallel is that when the control power is turned on to this detection circuit, if the AC input signal A has already become zero, the detection signal H of this detection circuit will be zero. is the first due to the charge accumulated in the smoothing capacitor of the conventional smoothing circuit 14.
This is because the output of the comparison circuit is output, and the detection signal is output from the OR circuit 32.

FIG. 4 shows another embodiment of the invention. In this embodiment, the reference sine wave signal D and the AC input signal A are
is directly input to the differential amplifier 28, and the differential amplifier 2
8 deviation signal is sent to the comparison circuit 3 via the rectifier circuit 34.
The configuration is such that 0 is input. Even with this configuration, the same effects as in the previous embodiment can be obtained.

<Effects of the invention> As explained in detail above, in the AC undervoltage detection circuit according to this invention, since the AC input voltage is monitored as it is in the AC waveform without rectifying or smoothing it, voltage drop may occur. And it can be detected immediately. Therefore, it is possible to realize a high-speed AC undervoltage relay with extremely little delay in operation.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a conventional circuit, Fig. 2 is a block diagram of a first embodiment circuit of the present invention, Fig. 3 is a waveform diagram showing the operation of each part in the circuit of Fig. 2, and Fig. 4 is a block diagram of the circuit of the present invention. FIG. 2 is a configuration diagram of a second embodiment circuit. 10...Isolation transformer, 18...First comparison circuit, 20, 24...Band pass filter, 22...
... Comparison circuit, 28 ... Differential amplifier circuit, 30 ... Second comparison circuit, 32 ... OR gate.

Claims (1)

[Scope of utility model registration request] A first comparator circuit that compares a DC voltage obtained by rectifying and smoothing a sine wave AC input with a reference voltage; , a waveform shaping circuit that outputs a sine wave alternating current as an alternating current reference voltage with the same frequency and the same phase as the sine wave alternating current input, and calculation of the output of this waveform shaping circuit and the sine wave alternating current input, either directly or after rectification, respectively. a differential amplifier circuit that rectifies or directly compares the output of the differential amplifier circuit with the reference voltage; and a second comparator circuit that rectifies or directly compares the output of the differential amplifier circuit with the reference voltage; An AC undervoltage detection circuit comprising an OR circuit that outputs an AC undervoltage signal as an input.