JP2014007832A - Control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correctly determine the occurrence of tracking between different poles and series tracking even in a product which phase controls an AC load.SOLUTION: A control circuit comprises: a current detection sensor for detecting a current flowing through an AC load to which a current is conducted from a commercial AC power supply by phase control; an operational circuit for retrieving the detection value from the current detection sensor to perform calculation; and a relay for interrupting the conduction from the AC power supply to the load when the occurrence of tracking in the conduction pathway to the AC load is detected by the operational circuit. The operational circuit activates the relay to interrupt the conduction to the load when detecting that a peak value of the current detected by the current detection sensor exceeds a preliminarily stored maximum current, or detecting that a value of integral of the current during a predetermined period after peak detection is smaller than a preliminarily stored integrated current value.

Description

  The present invention relates to a control circuit that accurately detects a tracking phenomenon even in a product that controls the phase of an AC heater driven by a commercial AC power supply. In particular, not only the tracking that occurs between different AC power supply voltages, but also the condition that the resistance of the AC heater is included in the tracking route and the peak current is limited, the tracking phenomenon is accurately detected and ignition occurs. The present invention relates to a control circuit capable of shutting off an AC power supply before reaching an event.

  A printed circuit board has a risk of causing a solder crack due to aging, and the printed circuit board is carbonized from the location where the solder crack has occurred, which develops into a tracking phenomenon and causes intense smoke and ignition. Therefore, product design must be performed assuming smoke generation and ignition from the printed circuit board, which requires space and a large cost increase.

  If the current flowing through the product can be monitored and the tracking phenomenon can be detected before firing or smoking, firing or smoking can be prevented, and many ignition countermeasure parts are not required inside the product. As a result, space can be used effectively and costs can be reduced.

As a conventional technique for detecting tracking, there is Patent Document 1.
The contents confirm that the peak value of the current tends to increase three times or more, and the contents are determined to be tracking. By doing so, it is possible to prevent a waveform such as an inrush current or a load current waveform of an inverter device from being judged as insulation deterioration and malfunctioning.

  However, the above-described apparatus can detect the tracking (hereinafter referred to as “different polarity tracking”) that occurs between different poles of the power supply voltage, but between the switches that turn the heater drive ON / OFF. The generated tracking (hereinafter referred to as “series tracking”) could not be detected because the peak current was limited by the resistance value of the heater.

There exists patent document 2 as another prior art.
The content is that the tracking is determined by the integrated value of the current waveform. The tracking phenomenon develops to tracking when a spark current flows through a minute gap caused by a solder crack, and uses the phenomenon that the spark current does not flow unless a certain level of voltage is applied. . Therefore, by using the technique of Patent Document 2, both the different polar tracking and the series tracking can be detected.

  However, in Patent Document 2, when the AC heater is used in a product that performs phase control, the waveform shape of the phase control is erroneously detected as the tracking waveform shape.

JP2001-41993 JP2004-020296A

  The present invention has been made to solve the above problems, and it is an object of the present invention to accurately determine the occurrence of heteropolar tracking and series tracking even in a product that controls the phase of an AC load. It is.

In order to achieve the above object, according to the first aspect of the present invention, a current detection sensor for detecting a current flowing in an AC load energized by phase control of a commercial AC power supply and a detection value from the current detection sensor are obtained. In the control circuit comprising: an arithmetic circuit that takes in and calculates; and a relay that cuts off the energization from the AC power source to the load when the arithmetic circuit detects the occurrence of tracking in the energization path for the AC load, the arithmetic circuit includes: Detecting that the peak value of the current detected by the current detection sensor exceeds the maximum current stored in advance, or integrating the integrated value of the current for a predetermined period after the peak detection When it is detected that the current value is smaller than the current value, the relay is driven to cut off the power supply to the load.
Therefore, by detecting that the peak value of the current detected by the current detection sensor exceeds the maximum current stored in advance, it is possible to determine the different polarity tracking, and the integrated value of the current for a predetermined period after the peak detection. Can detect series tracking by detecting that the current value is smaller than the accumulated current value stored in advance, and by energizing the load by driving the relay according to any of the determinations, Can be cut off, and problems such as ignition due to the occurrence of tracking can be prevented.

According to a second aspect of the present invention, the control circuit includes a zero-cross detection circuit that informs the arithmetic circuit of a zero-cross point of an AC power supply, and the arithmetic circuit detects a peak of the current detected by the current detection sensor. When it is detected that the integrated value of the current from the detection to the zero cross point is smaller than the accumulated current value stored in advance, the relay is driven to cut off the power supply to the load.
Therefore, the occurrence of series tracking can be accurately determined by notifying the arithmetic circuit of the zero-cross timing of the power supply voltage.

The arithmetic circuit drives the relay to energize the load when detecting that the peak value of the current detected by the current detection sensor exceeds the maximum current stored in advance a plurality of times. It is characterized by blocking.
Therefore, by detecting that the maximum current has been continuously exceeded a plurality of times, occurrence of the different polarity tracking can be accurately determined.

  According to the present invention, it is possible to determine the different polarity tracking by detecting that the peak value of the current detected by the current detection sensor exceeds the maximum current stored in advance, and for a predetermined period after the peak detection. By detecting that the integral value of the current is smaller than the accumulated current value stored in advance, series tracking can be determined, and by any of the determinations, the relay is driven to cut off the power supply to the load, It is possible to cut off the energization of the AC load, and prevent problems such as ignition due to the occurrence of tracking.

The block diagram of the control circuit in this embodiment. Schematic diagram of locations where heteropolar tracking and series tracking occur. The figure which compared the normal current waveform and the different polarity tracking waveform. The figure which compared the normal current waveform and the series tracking waveform. The figure which compared the normal current waveform at the time of phase control, and a series tracking waveform. It is a flowchart of the tracking detection process in this embodiment.

[Block configuration]
FIG. 1 is a block diagram of a control circuit according to an embodiment of the present invention.
The current sensor 1 is attached to a location where all current flows to an AC load in which a commercial AC power source, which is the device 4 to be protected, is energized by phase control. For example, immediately after the power plug or power cord is taken into the product.
The arithmetic circuit 2 is configured to take in the power directly from the power supply voltage, and requires AC-DC conversion.
Further, the relay 3 is a relay that mechanically shorts the contact, and the contact is opened (energization cut-off state) by passing a current through a coil (not shown) according to a command from the arithmetic circuit 2. After it is open, it keeps open even if it doesn't keep current flowing. The relay 3 is a mechanism that allows the user to arbitrarily switch to a short circuit.

  In this configuration, a self switch 6 and a discharge element 7 are provided so that pseudo-tracking can be performed and an operation check can be performed.

Blood FIG. 2 is a schematic diagram of the location where heteropolar tracking and series tracking occur. The heteropolar tracking is tracking that occurs when a track path is formed by carbon between different polarities of the power supply voltage. Series tracking is tracking that occurs when a carbon track path is formed between load driving elements that turn on and off a product load. Series tracking does not occur when the load drive element is short, but tracking occurs when the load drive element is open and a voltage is generated across the element.

  FIG. 3 is a diagram comparing a normal current waveform and a different polarity tracking waveform. The current value depends on the impedance of the carbon path because it is a current that flows when a carbon path is created between different polarities of the power supply voltage. For this reason, the maximum value of the tracking current greatly exceeds the maximum current of the product. Therefore, the different polarity tracking can be detected by monitoring whether the peak of the current does not exceed the maximum current value stored in advance.

  FIG. 4 is a diagram comparing the normal current waveform and the series tracking waveform. A comparison result obtained by integrating from the current peak value to the zero cross point is also shown. Since series tracking is a current that flows due to the formation of a carbon path between drive elements of an AC load, the current value depends on the load impedance. Therefore, the maximum value of the tracking current does not exceed the maximum load current value of the product.

  3 and 4, there is a difference in the peak value of the current, but there is a common point in that the timing at which the current begins to flow and the timing at which the current ends deviates from the zero cross. This is because there is a fine space gap between the carbon part that is the source of the tracking phenomenon and the part that has not been carbonized or the lead part of the part, and spark discharge (spark discharge) is repeated there. . Since there is a fine space gap, the current does not start unless there is a certain level of voltage, and the current stops flowing before the current reaches zero. This phenomenon is a phenomenon that occurs in both the polar tracking and the series tracking.

  With regard to different polarity tracking, tracking can be detected by monitoring the peak value of the current as shown in Fig. 3, but with regard to series tracking, since the current peak is limited to the impedance of the load intervening, Tracking cannot be judged even if the peak value is monitored. Therefore, series tracking is also detected by grasping the characteristics of the tracking waveform in FIG. 4 and detecting it. The detection method integrates from the peak value of the current waveform to a predetermined period, preferably the zero cross point, and detects that the area of the tracking waveform is smaller than the normal waveform. The reason for using the waveform after the peak value of the current waveform is that when the AC load is driven from an arbitrary phase, as in phase control, the waveform is misrecognized as tracking and detected. This is to prevent it.

  FIG. 5 is a diagram comparing the normal current waveform and the series tracking waveform during phase control. In addition, the comparison result which integrated from the peak value of the electric current to the zero cross point is shown. Although the conditions of the phase of 90 degrees and 135 degrees are described, in any condition, the integrated value at the time of tracking is smaller than the integrated value at the normal time. Therefore, when it is detected that the integrated value of the current for a predetermined period after the peak detection is smaller than the accumulated current value stored in advance, it can be determined that the series tracking is performed.

  The flow of the tracking detection process in the present embodiment is illustrated in the flowchart of FIG. 6. Specifically, the current value is constantly monitored at a certain timing, and the detected current value and the current value detected at the previous timing are The difference is calculated, and the peak value is recognized when the difference switches from positive to negative and from negative to positive.

Based on the flowchart of FIG. 6, the tracking detection process in this embodiment is demonstrated in detail.
First, the difference between the measurement data of the current is always taken (S60). The current value when the value switches from positive to negative and from negative to positive is determined as the peak value of the current value (S62). It is determined whether or not the peak value exceeds a threshold value (a pre-stored maximum current value flowing through the AC load at normal time) that is recognized as heteropolar tracking (S64). If it exceeds (S64yes), the current is continuously monitored for a certain period (S66). If the number of times exceeding the threshold exceeds the specified value (S66yes), the relay is activated by accrediting it as a different polarity tracking and AC load. The power supply to is cut off (S70).

  The series tracking determination will be described. When it is determined that the peak value of the current does not exceed the threshold value that is recognized as the heteropolar tracking (S64no), the current value is integrated from the detected peak current to the zero cross point to obtain an area A (S72). Also, the area corresponding to the 1/4 wavelength registered in correspondence with the power when the normal waveform is entered is called from the table to be the area B (S74), the area A actually taken in and the area of the table B is compared (S76), and if the measured result is small, it is recognized that series tracking has occurred (S76yes). At this time, the pass / fail judgment is finely adjusted by multiplying the actually measured result by a correction coefficient α. When the different polarity tracking and the series tracking are recognized, the relay is operated to cut off the energization to the AC load (S70).

1 Current sensor (current detection sensor)
2 Arithmetic circuit 3 Relay 4 Protected equipment (AC load)
5 Zero cross detection circuit 6 Self switch 7 Discharge element 8 Different polarity tracking 9 Series tracking

Claims (3)

A current detection sensor that detects a current flowing in an AC load that is energized by phase control of a commercial AC power supply, an arithmetic circuit that takes in and calculates a detection value from the current detection sensor, and energizes the AC load by the arithmetic circuit In a control circuit comprising a relay that cuts off the energization from the AC power supply to the load when the occurrence of tracking in the path is detected,
The arithmetic circuit detects that the peak value of the current detected by the current detection sensor has exceeded the maximum current stored in advance, or previously stores the integrated value of the current for a predetermined period after the peak detection. And a control circuit for driving the relay to cut off the power supply to the load when it is detected that the current value is smaller than the integrated current value. The control circuit includes a zero-cross detection circuit that notifies the arithmetic circuit of a zero-cross point of the AC power supply, and the arithmetic circuit is an integrated value of the current from the detection of the current peak detected by the current detection sensor to the zero-cross point. 2. The control circuit according to claim 1, wherein when it is detected that is smaller than an accumulated current value stored in advance, the relay is driven to cut off energization to the load. The arithmetic circuit drives the relay to energize the load when detecting that the peak value of the current detected by the current detection sensor exceeds the maximum current stored in advance a plurality of times. The control circuit according to claim 1, wherein the control circuit is cut off.