JPH04347531A - Abnormality detector for dc capacitor - Google Patents

Abstract

PURPOSE:To obtain an abnormality detector for DC capacitor having simplified circuitry wherein the potential of main circuit can be isolated from the control potential. CONSTITUTION:Photocouplers 811c, 812c detect current produced by the potential difference between the series joint (a) of DC capacitors 11a, 12a and the series joint (b) of other DC capacitors 11b, 12b. When the photocouplers 811c, 812c are turned ON, abnormality in the DC capacitors 11a, 12a, 11b, 12b is detected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormality detector for detecting abnormalities in DC capacitors connected in series. Such a DC capacitor is used, for example, in a DC filter circuit of a power converter that converts DC to AC using a semiconductor element.

0002

[Prior Art] FIG. 4 shows, for example, Japanese Patent Application Laid-Open No. 62-250875
This is a circuit of a DC capacitor abnormality detector shown in the publication, and in the figure, 11a, 12a and 11b, 12b
are DC capacitors 13a and 14a connected in series, respectively.
is a voltage dividing resistor that equalizes the partial voltage of DC capacitors 11a and 12a, and 13b and 14b are also DC capacitors 11b.
, 12b, 15 is a comparison circuit that compares the potential difference between the series connection point a of the DC capacitors 11a and 12a and the series connection point b of the DC capacitors 11b and 12b, and 16 is a comparison circuit. 15 is a differential amplifier as a main element, 17a and 17b are input resistances of the differential amplifier 16,
18 is a feedback resistor of the differential amplifier 16; 19 is a window comparator that detects whether the output of the differential amplifier 16 exceeds a preset reference potential; the comparison circuit 15 and the window comparator 19 form a comparison means 2
0 is configured.

Next, the operation will be explained. In the DC capacitor abnormality detector configured as shown in Fig. 4, when the DC capacitor is normal, the DC capacitor 1
Series connection point a of 1a and 11b and DC capacitor 11b
, 12b and the series connection point b is several volts or less. For example, if the DC capacitor 11a is short-circuited, the difference between the potentials Va and Vb at the connection points a and b, that is, V
a-Vb becomes the voltage VE/2 of the circuit, and the differential amplifier 1
A corresponding voltage is generated at the output of 6, and the window comparator 19 can detect that an abnormality has occurred in the DC capacitor.

[0004] Furthermore, if any of the DC capacitors 11a, 12a and 11b, 12b undergoes a large change in its capacitance due to use over time, or if the leakage current increases, the potential difference between Va and Vb will increase. In order to do this, a potential is generated in the differential amplifier 16 and output, so that it is possible to detect that an abnormality has occurred in any of the DC capacitors.

[0005]

[Problems to be Solved by the Invention] Conventional DC capacitor abnormality detectors are constructed as described above, so the detection circuit is complicated, and when the main circuit potential and control potential are insulated, Since the detection section requires an isolated amplifier, there is a problem in that it is expensive.

The present invention has been made to solve the above-mentioned problems, and provides a DC capacitor abnormality detector that can further simplify the circuit configuration of the detection section and is also insulated from the main circuit potential and the control potential. The purpose is to obtain.

[0007]

[Means for Solving the Problems] A DC capacitor abnormality detector according to the present invention uses a photocoupler that detects a current flowing due to a potential difference between a series connection point of one DC capacitor and a series connection point of another DC capacitor. It was established.

[0008]

[Operation] The DC capacitor abnormality detector according to the present invention detects an abnormality when a photocoupler is turned on.

[0009]

[Example] Example 1. FIG. 1 shows an embodiment of the present invention. Functions corresponding to those in FIG. 4 described above are given the same numbers. Numbers in the 810 series are photocouplers; the subscript c indicates the light emitting side of the photocoupler, and the subscript d indicates the light receiving side of the photocoupler. 801 is the light emitting side of the photocoupler, that is, the first and second light emitting elements 811c, 812
c is the input current limiting resistor, 802 is the pull-up resistor of the photocoupler light receiving side 811d, 812d, 851
is the control power supply, 841 is the photo coupler 811, 812
This is a failure processing circuit that processes failures due to abnormalities in DC capacitors using a wired-OR signal obtained by connecting the outputs of the two in parallel.

Next, the operation of the above embodiment will be explained with reference to FIG. As in the conventional example, when the DC capacitor is abnormal, a potential difference is generated between the series connection points a and b. For example, if the DC capacitor 11b is short-circuited due to some abnormality, the potential at the connection point b will rise, and the current determined by the potential difference between the connection points and the resistor 801 will flow to the light-emitting side 812c (second light-emitting side) of the photocoupler. element). When the potential difference increases and the current flowing through the photocoupler 812c exceeds a certain value, the transistor that is the output of the light receiving side 812d turns on, and the output of the photocoupler 812c (second light emitting element) becomes low level. Next, when the DC capacitor 12b is short-circuited due to some abnormality, the potential at the connection point b decreases, and the potential difference between the above connection points and the resistance 80
The current determined by 1 is the light emitting side 811c of the photocoupler (
(first light emitting element). When the potential difference increases and the current flowing through the photocoupler 811c (first light emitting element) exceeds a certain value, the transistor that is the output of the light receiving side 811d turns on and the output of the photocoupler 811 becomes low level. At this time, the outputs of the photocouplers 811 and 812 are connected in parallel, wired ORed, and applied to the failure processing circuit as a DC capacitor abnormality detection signal.

Example 2. Furthermore, in the above embodiment, two photocouplers are required because the direction of current flow differs depending on the DC capacitor in which the abnormality occurs. Therefore, as shown in FIG. 2, by configuring a full-wave rectifier circuit 820 by connecting the detection section with diodes D821-D824 in a full bridge, a photocoupler consisting of one light emitting element 811c can achieve the same effect regardless of the direction of the current. You can expect it.

Example 3. In the embodiment shown in FIG. 1, when testing the operation of the circuit, the operation cannot be confirmed unless the DC capacitor is shorted. Therefore, as shown in FIG. 3, a series connection point a, a series circuit between the diode D821 and the first light emitting element 811ac of the photocoupler, and a series circuit between the diode D822 and the light receiving side of the photocoupler, that is, the second light emitting element 812c, are connected. Insert terminal 831 between
By connecting 832 to VEP and VEN, operation can be more easily confirmed. For example, terminal 831
By connecting VEP to the positive side of the DC voltage, a current flows to the light emitting side 811c of the photocoupler.
It is possible to simulate the abnormality detection of DC capacitors.

[0013]

[Effects of the Invention] As described above, according to the present invention, the circuit can be simplified by configuring the detection section with a photocoupler, and abnormality detection of a DC capacitor that can isolate the main circuit potential and the control potential is possible. It has the effect of being configurable.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a DC capacitor abnormality detector according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a DC capacitor abnormality detector according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a DC capacitor abnormality detector according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a conventional DC capacitor abnormality detector.

[Explanation of symbols]

11a DC capacitor 11b DC capacitor 12a DC capacitor 12b DC capacitor 811c First light emitting element 812c Second light emitting element 820 Full wave rectifier circuit 821 diode 822 diode a Series connection point b Series connection point

Claims (3)

[Claims] 1. An abnormality detector for detecting an abnormality in a DC capacitor circuit in which a plurality of series circuits each having a plurality of DC capacitors connected in series are connected in parallel, the series connection point of one of the series circuits; A first light emitting element that operates when the potential of one series connection point is higher than the potential of the other series connection point and the potential of the other series connection point of the other series connection point are connected to one of the series connection points of the other series circuit. An abnormality detector for a DC capacitor, characterized in that a second light emitting element is connected which operates when the potential is higher than the potential of a series connection point. 2. An abnormality detector for detecting an abnormality in a DC capacitor circuit in which a plurality of series circuits each having a plurality of DC capacitors connected in series are connected in parallel, the series connection point of one of the series circuits; Abnormality detection in a DC capacitor, characterized in that a full-wave rectifier circuit and a light emitting element that operates when current flows through any arm of the full-wave rectifier circuit are connected between a series connection point of another series circuit. vessel. 3. An abnormality detector for detecting an abnormality in a DC capacitor circuit in which a plurality of series circuits each having a plurality of DC capacitors connected in series are connected in parallel, wherein a series connection point of one of the series circuits; A first series circuit of a light emitting element and a diode, which operates when the potential of one series connection point is higher than the potential of the other series connection point, and the other series connection point are connected to the series connection point of the other series circuit. An abnormality detector for a DC capacitor, characterized in that a second series circuit of a light emitting element and a diode is connected, which operates when the potential is higher than the potential of one series connection point.