JPH0528788B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low voltage detection circuit that outputs an instantaneous signal and a timed signal during a power outage or phase failure.

[Conventional technology]

Circuits that use thyristors to control converters, such as Thyristor Leonard, are used in many devices. The firing angle control circuit generally compares a lamp signal synchronized with the power supply voltage phase with a firing angle command using a comparator, and outputs a firing pulse when the signals cross.

However, recently, in order to eliminate the need for circuit adjustments and improve reliability, digitalization has been attempted using CPUs and other devices. As a result, the signal generation circuit can now output firing angle signals for three phases by calculation or reading from a ROM table using a one-phase synchronization signal.

On the other hand, if a phase loss or instantaneous power failure occurs in the reference phase that becomes the synchronization signal, this will affect the firing angle signals of all three phases, which may cause thyristor destruction or fuse blowout failure. There is sex.

In contrast, the conventional low voltage detection method, as shown in Fig. 4, rectifies the secondary voltage of the control power transformer 1 with a diode bridge 2, and compares the voltage value with a reference value with a comparator 3. It was used as a low voltage signal. The filter 4 is for setting the operating time.

In addition, Utility Model Application Publication No. 55-1706 discloses a detection circuit that detects when the voltage of a power supply falls below a predetermined value, a pulse generation circuit that operates only during the detection period based on the detection signal of this detection circuit, and A voltage fluctuation detection circuit for a power supply is described that includes a counter that counts pulses output from a pulse generation circuit and outputs a signal when the count reaches a predetermined value.

[Problem that the invention seeks to solve]

However, with the conventional method shown in FIG. 4, instantaneous power outages, total power outages, and low voltages can be detected, but the filter 4 determines the operating time, so even in an open phase state, the output of the filter 4 is adjusted accordingly. phase loss cannot be detected sufficiently.

In addition, in the circuit described in Utility Model Application Publication No. 55-1706, if an open phase occurs while counting pulses, the count value may be reset before the count up, and the open phase cannot be detected sufficiently. The problem was that I couldn't do it.

Therefore, when using a digital firing angle control circuit, these conventional low voltage detection methods cannot provide sufficient protection against phase loss.

SUMMARY OF THE INVENTION The present invention aims to solve the problem of the conventional method which does not have a measure against phase loss protection, and to provide a low voltage detection method that improves the time accuracy of a detection signal through digitization.

[Means for solving problems]

The low voltage detection circuit of the present invention includes a rectifier circuit that performs full-wave rectification of a three-phase AC power supply voltage, a comparator that compares the full-wave rectified voltage in this rectifier circuit with a DC reference voltage, and an output of this comparator. A separator that separates low voltage signals from noise based on the pulse width of the signal, a counter that starts counting clock pulses of a predetermined period after the output of this separator is generated, and a timer in which this counter is preset. a logic circuit that outputs a signal if the output signal of the separator continues after counting up a count number corresponding to time T ₂ ; a logic circuit that outputs an on signal until a count number corresponding to a preset timer time _T1 , which is longer than time _T2 , is counted up;
The present invention is characterized by comprising a logic circuit that does not output the signal of the separator as a counter clear signal while counting the timer time _T1 .

[Effect]

The low voltage circuit of the present invention outputs a low voltage signal as follows.

The three-phase full-wave rectified signal obtained by the rectifier circuit is input to a comparator to instantly detect voltage outages due to power outages, voltage drops, open phases, etc.

The counter outputs a signal with a pulse width T of ₁ second (for example, 30 ms) in order to eliminate the thyristor firing signal.

After low voltage is detected by the counter and logic circuit,
T If the low voltage state continues after ₂ seconds (for example, 15 ms), a low voltage signal and an open phase signal are output.

After detecting low voltage, if the voltage returns to normal value after T ₂ seconds, the thyristor firing signal returns to normal after T ₁ second.

〔Example〕

Hereinafter, the present invention will be specifically described based on embodiments shown in the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, 3 is a comparator that detects low voltage without delay, 5 is a low voltage detection level setter, 6 is a pulse width separator for distinguishing commutation overlap angle and low voltage, 7 to 9 are AND circuits, and 10 is a NOT circuit,
11 is an OR circuit, and 12 is a counter that serves as a timer.

Signal A is a three-phase full-wave rectified signal from a power source whose voltage has been stepped down by a transformer. When the signal A becomes lower than the low voltage detection level of the signal B due to low voltage or open phase, the comparator 3 immediately detects this and outputs the signal C as shown in FIG. Since the signal C is also output depending on the commutation overlap angle when the power source impedance of the main power source is high, the pulse width separator 6 distinguishes these and outputs only the low voltage detection signal as the signal C'.

FIG. 3 is a time chart showing the operation of each part when a low voltage is generated. Under normal conditions, the counter 12 is counting up, so the AND circuit 7 outputs the signal E without delay to the signal C'. This becomes a clear signal for the counter 12.

Here, T ₁ = 30ms, T ₂ = 15ms, T ₂ = 256
Assuming the pulse count time, the frequency of clock D is 1.71KHz.

Signal E is high level (hereinafter abbreviated as "H")
At the same time, the output signal of the counter 12 becomes low level, and returns to "H" after counting 512 pulses of the clock D. Therefore, if this signal H is used, the OR circuit 11 outputs the signal J for T ₁ second,
This becomes the firing signal removal signal for the thyristor. Also, signal G counts 256 pulses of clock D,
After T ₂ seconds, the pulse becomes T ₂ seconds wide. If signal C' is output again while signal G is "H",
AND circuit 9 outputs low voltage signal I.

Furthermore, if an open phase occurs while the signal G is "H", the logic circuit 9 detects this as a low voltage signal, and after T ₂ seconds have elapsed, an open phase signal ( (see FIG. 2) is output as signal I.

As mentioned above, in this example, T ₁ =30ms,
Although T ₂ =15 ms and clock D = 17.1 KHz, these values can be changed depending on the specifications.

〔Effect of the invention〕

As described above, the present invention provides the following effects.

There are no parts that require adjustment or settings, and the reliability of the circuit can be improved.

Since a clock signal is used, detection time accuracy is dramatically improved.

Open phase detection can now be performed reliably, and as a result, protection against power supply abnormalities during operation can be ensured.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a time chart showing the waveforms of each part during open phase detection, Fig. 3 is a time chart showing the waveforms of each part during normal operation, and Fig. 4 is a time chart showing the waveforms of each part during normal operation. FIG. 2 is a block diagram showing a conventional example. 1: Control power transformer, 2: Diode bridge, 3: Comparator, 5: Low voltage detection level setter, 6: Pulse width separator, 7 to 9: AND circuit,
10: NOT circuit, 11: OR circuit, 12: counter.

Claims (1)

[Claims] 1. A rectifier circuit 2 that performs full-wave rectification of a three-phase AC power supply voltage, a comparator 3 that compares the full-wave rectified voltage in this rectifier circuit 2 with a DC reference voltage, and a pulse width of the output signal of this comparator 3. a separator 6 that separates low voltage signals and noise based on;
A counter 12 starts counting clock pulses of a predetermined period after the output of the separator 6 is generated.
and a logic circuit 9 that outputs the output signal of the separator 6 if it continues after the counter 12 has counted up a count corresponding to a preset timer time _T2 , and the counter 12. a logic circuit 11 that outputs an on signal from the time when the output of the separator 6 is generated until the timer counts up a count corresponding to a preset timer time _T1 , which is longer than the timer time _T2 ; and a logic circuit 7 that does not output the signal from the separator 6 as a counter clear signal while counting the timer time _T1 .