JPH11337596A - Power failure detection method and power failure detection circuit using the method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To enable quick and error-free power failure detection even when a load using a rotating machine such as a motor is connected. SOLUTION: A zero cross detecting circuit 1, a timer means 2 'for measuring a period of the zero cross, and a voltage detecting circuit 7 for detecting a voltage of an AC power supply are provided. When the zero-cross point of the AC input is detected by the zero-cross detection circuit 1, a voltage at a predetermined point from the detected zero-cross point is detected by the voltage detection circuit 7. In the case of noise after a power failure, the detection voltage is attenuated while changing instead of being constant at each detection. Therefore, the power failure is detected by comparing the detected voltage value with a predetermined value. When the zero-cross point of the AC input is no longer detected, the power failure is detected by detecting the interval by the timer means 2 '. By detecting a power failure based on the zero cross in this way, even when a load using a rotating machine such as a motor is connected, the power failure can be promptly detected without error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power failure detection method for an AC power supply and a power failure detection circuit using the method.

[0002]

2. Description of the Related Art As devices become more and more microcomputers and the number of devices that work with programs increases, power failures such as power outages cause the entire device to malfunction or lose valuable data. It may be lost. For this reason, power failure measures are taken according to the system.

The power failure countermeasures are divided into power failure detection and processing after detection and recovery processing. In particular, power failure detection is important.

[0004] Various methods have been considered for this power failure detection method. For example, a power failure detection circuit is provided in a rectifier circuit of a power supply circuit, power failure information (signal) is sent to a control circuit (microcomputer or the like), and the control circuit receiving the power failure information generates an interrupt and performs a countermeasure process. Is generally used.

That is, as shown in FIG. 8, when the zero-cross detection circuit 1 is connected to the microcomputer 2 and the zero-cross detection circuit 1 detects the loss of the power supply waveform as shown in FIG. Suspend and process power failures with the highest priority to deal with power failures that occur as asynchronous events.

In this case, what is important is that the power supply 3 can supply a sufficient voltage during the detection time and the power failure processing time.

[0007]

However, in the power failure detection circuit using the above-mentioned zero cross circuit, as shown in FIG. 8, a circuit using a rotating machine such as a motor in parallel with a rectification circuit is connected as a load. (For example, the compressor 4), after the power failure, the rotating machine functions as a generator, and generates AC noise. Then, the generated noise is circulated through the transformer, and the sneak noise is erroneously recognized as the power supply waveform by the zero cross circuit 1 as shown in FIG. 10, so that the timing of starting the power failure process is delayed. For this reason, when the microcomputer 2 performs the power failure processing, there is a problem that the power supply 3 cannot supply a voltage enough to withstand the power failure processing.

It is an object of the present invention to provide a power failure detection method which does not malfunction even when a load using a rotary machine such as a motor is connected, and a power failure detection circuit using the method.

[0009]

According to a first aspect of the present invention, a zero cross point of an AC power supply voltage is detected, and when a zero cross is detected, a voltage at a predetermined point is detected from the zero cross point. It is compared whether the detected voltage value is within a predetermined value, and when it is detected that the number of times within the predetermined value is continuously repeated n times, it is determined that a power failure has occurred. A detection method is employed in which it is detected whether a predetermined number of zero crossings are detected within a predetermined period, and if not, a power failure is detected.

By adopting such a method, the voltage at the predetermined point from the detected zero crossing point is always the same voltage value in the case of AC. On the other hand, in the case of noise after a power failure, the detected voltage is not constant at every detection, but is attenuated while changing, and finally becomes zero. Therefore, by comparing the detected voltage value with the predetermined value and detecting that the number of times that the detected voltage is within the predetermined value is repeated n times continuously, it is possible to discriminate noise and detect a power failure.

At this time, even if the noise component is not superimposed at the time of the power failure, it is detected whether or not a predetermined number of zero crossings are detected within a predetermined period, so that the power failure can be detected.

According to a second aspect of the present invention, there is provided a zero-cross detecting means for detecting a zero-cross point of the AC power supply voltage, a timer means for measuring a period of the zero-cross based on the zero-cross signal from the zero-cross detecting means, Voltage detecting means for detecting the zero-cross of the AC power supply voltage by the zero-cross detecting means, and when the zero-cross is detected, a voltage at a predetermined point from the zero-cross point is detected by the voltage detecting means, and the detected voltage value Is determined to be within a predetermined value, and when it is detected that the number of times within the predetermined value has been repeated n times continuously, it is determined that a power failure has occurred. Then, a configuration is adopted in which it is detected whether or not a predetermined number is detected, and if not, a power failure is detected.

By employing such a configuration, the zero-cross point of the AC voltage is detected by the zero-cross means, and a voltage at a predetermined point from the zero-cross point is detected by the voltage detection means based on the detected zero-cross signal. If no zero cross is detected, the timer means detects whether or not a predetermined number of zero crosses are detected within a predetermined period.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a control circuit using a power failure detection circuit based on the power failure detection method of the present invention.

This control circuit is a circuit for controlling the compressor of the refrigerator, and the compressor 4 is connected in parallel with an alternating current (AC) power supply.

The control circuit includes a microcomputer 2, a compressor relay 5, a clock IC 6, a zero-cross detection circuit 1, a power supply peak value detection circuit 7, a memory 8 and an I / O interface circuit 8, and a stabilized power supply circuit 3. Are provided on one substrate.

The compressor relay 5, the clock IC 6, the zero-cross detection circuit 1, the power supply peak value detection circuit 7, and other memories and I / O interface circuits 8 in such a board are connected to a microcomputer 2 through a data and address bus 9. Is connected to

The microcomputer 2 is provided with a timer means 2 'by a program so that the period of the zero-cross signal from the zero-cross detection circuit 1 can be measured. The microcomputer 2 includes a power failure processing program including a power failure detection and a process after the power failure is detected, as described later.
In response to a zero-cross signal from the zero-cross detection circuit 1, a power failure detection process by an interrupt process is executed to monitor the AC voltage. Then, when the monitoring voltage decreases, the processing after the power failure detection is executed. Further, the microcomputer 2 has a halt function. When the microcomputer 2 executes a process after detecting a power failure, the microcomputer 2 enters a power consumption mode by a sleep mode and enters a standby state.

The compressor relay 5 has a relay contact 5 'provided between the AC power supply and the compressor 4 as shown in FIG. 1, and is connected to the microcomputer 2 so that the compressor 4 can be turned on and off. I have.

The clock IC 6 outputs date / time data to the microcomputer 2 using a so-called real-time clock.

The zero-cross detecting circuit 1 is a known circuit using a comparator circuit, and is connected to a zero-crossing transformer 10 as shown in FIG. 1, and outputs a detection signal when an AC voltage waveform passes through a zero point.

For example, in this case, the power supply peak value detection circuit 7 includes a sample-and-hold circuit and an A / D converter, and controls the hold timing of the sample-and-hold circuit to obtain the power supply voltage. Can be sampled at an arbitrary timing. The sampled voltage value is A /
The D converter converts the data into digital data so that the microcomputer 2 can read the data.

The stabilized power supply circuit 3 is of an on-board type, is connected to the control board transformer 11, and supplies power to each IC and circuit on the board.

At this time, the clock IC 6 and the microcomputer 2
The switch circuit 12 is connected to the stabilized power supply circuit 3 via the switch circuit 12, and the switch circuit 12 is connected to the microcomputer 2. Therefore, the connection with the stabilized power supply circuit 3 can be turned on / off by the microcomputer 2. Further, the clock IC 6 and the power input terminal Vc of the microcomputer 2 are used.
A battery B is connected to c via a diode D. When the switch circuit 12 is turned off, power can be supplied from the battery B.

This embodiment is configured as described above.
Next, the operation of the control circuit will be described to explain the power failure detection method of the present application.

That is, the microcomputer 2 detects a zero crossing at the same time as the power is turned on, and performs power failure detection processing A and B as shown in FIG. 2 (“processing” 100: hereinafter “processing” is omitted).
Execute

That is, in the power failure detection process (100),
First, i, j = 0 are set (110), and the timer 2 'is operated (120). Then, by the power failure detection processing A,
It is detected whether a zero-cross signal is detected before the timer 2 'times out (130). At this time,
When the timer 2 'times out (140), the timer 2' is reset (150), and the voltage at a predetermined point t3 set for each power supply frequency from the zero crossing point is sampled by the power supply peak value detection circuit 7, and the value is sampled. Is converted into digital data and read (160).

When the predetermined point t3 is 50 Hz,
The peak value is set to 5 ms, and to 4.333 ms at 60 Hz, so that the peak value of the peak voltage for each half cycle at each frequency can be measured.

The value of the predetermined point t3 thus read is compared with a predetermined value set in advance, and it is determined whether the read value is within a predetermined value (170). This predetermined value is
In this embodiment, half the voltage of the peak value (1 / 2V _AC)
Is set as the reference voltage, but is not limited to this value. The value of the reference voltage can be set as appropriate according to the characteristics of the rectifier circuit.

As described above, when the sampled voltage values are read and compared, as shown in FIG. 3, the comparison result is always equal to or higher than the reference voltage in a steady state (state where AC is input). In this case, the process returns to the process (110) and the process is repeated.

Now, when a power failure occurs and the supply power stops, the motor of the rotating compressor 4 becomes a generator and generates a noise voltage.

Therefore, even after the power failure, the zero-cross detector 1
As shown in FIG. 3, a zero-cross signal is output, and a voltage at a predetermined point is sampled by the power supply peak value detection circuit 7. At this time, as shown in the schematic diagram of FIG. 4, the sampled noise voltage V2 gradually attenuates as the motor stops, and becomes smaller than the AC voltage V1.

Therefore, the processes (120) to (190)
Is repeated, the number n of times that the sampled voltage becomes equal to or less than the predetermined value is 3 in this embodiment, as shown in FIG.
It is determined that a power outage has occurred if the power has been turned on consecutive times. Then, as a process (200) after the detection of the power failure, register data and the like are stored and the device enters a sleep state. Further, the switch means 12 is turned off, the clock IC 6 is disconnected from the stabilizing power supply circuit 3, and power is supplied from the backup battery B.

As described above, since the voltage value is detected, even when the zero-cross signal is continuously output due to noise, the noise is discriminated and the power failure is detected promptly, and the timing of starting the power failure processing as in the prior art is determined. Delay can be prevented.

As a result, the system retains the time data, and the system can be reliably restored.

On the other hand, when the zero cross cannot be detected in the process (130). That is, if no noise is generated from the compressor 4 after the power failure, when the timer 2 'times out,
The timer 2 'is reset by the power failure detection process B (21
0), 1 is added to j (220), and the timer is activated while comparing the added j with a predetermined value (230) (12).
0). Then, processing (120) → (130) → (21)
0) → (220) → (230)
As shown in FIG. 6, zero crossing is performed a predetermined number of times (three times in this embodiment, 50 Hz: T = 30 ms, 60 Hz: T = 30 ms).
25 ms) If not detected, it is regarded as a power failure, and the processing after the power failure is detected is executed (200).

As described above, by detecting a period during which there is no zero-cross signal and detecting a power failure, as shown in FIG.
The power failure can be detected regardless of the operation of the compressor.

That is, by detecting whether or not a predetermined number of zero crosses are detected within a predetermined period, a power failure can be detected even when the compressor 4 is stopped and a zero cross signal due to noise is not detected. ing.

In this embodiment, a case where a rotating machine is used as the load has been described. However, it goes without saying that a power failure can be reliably detected even when the load is not a rotating machine.

By detecting the voltage at a predetermined point from the zero-cross point in this way, it is apparent that the same effect can be expected for noises other than those of the rotating machine.

[0042]

According to the present invention, a zero-cross is detected and a power failure is detected based on the detected zero-cross by employing the above-described configuration. For example, a load using a rotating machine such as a motor can be used. A power failure detection method that does not malfunction even when the power supply is connected, and a power failure detection circuit using the method can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment.

FIG. 2 is a flowchart of an embodiment.

FIG. 3 is a diagram illustrating the operation of the embodiment.

FIG. 4 is a schematic diagram illustrating the operation of the embodiment.

FIG. 5 is an operation explanatory view of the embodiment.

FIG. 6 is an operation explanatory view of the embodiment.

FIG. 7 is a diagram illustrating the operation of the embodiment.

FIG. 8 is a block diagram of a conventional example.

FIG. 9 is a diagram illustrating the operation of a conventional example.

FIG. 10 is a diagram illustrating the operation of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Zero cross detection circuit 2 Microcomputer 2 'timer 3 Stabilized power supply circuit 4 Compressor 6 Clock IC 7 Power supply peak value detection circuit

Claims (2)

[Claims] 1. A zero-cross point of an AC power supply voltage is detected,
When a zero cross is detected, a voltage at a predetermined point is detected from the zero cross point, a comparison is made as to whether the detected voltage value is within a predetermined value, and the number of times within the predetermined value is repeated n times continuously. A power failure detection method that detects a power failure when a power failure is detected, and detects whether a predetermined number of zero crosses are not detected within a predetermined time period if no zero cross is detected, and determines that a power failure occurs if no zero cross is detected. 2. A zero-cross detecting means for detecting a zero-cross point of an AC power supply voltage, a timer means for measuring a zero-cross period based on a zero-cross signal from the zero-cross detecting means, and a voltage detecting means for detecting a voltage of the AC power supply voltage. The zero cross detection means detects a zero cross of the AC power supply voltage, and when the zero cross is detected, a voltage at a predetermined point from the zero cross point is detected by the voltage detection means,
By comparing whether the detected voltage value is within a predetermined value,
When it is detected that the number of times within the predetermined value has been repeated n times continuously, it is determined that a power failure has occurred. On the other hand, if a zero cross is not detected, it is detected whether or not a predetermined number of the zero crosses are detected within a predetermined period. A power failure detection circuit using the power failure detection method according to claim 1.