JPH04151571A - Circuit for detecting abnormality of capacitor - Google Patents

Abstract

PURPOSE:To detect the open fault and the like of a capacitor at an early period, to stop the circuit for protection and to prevent the progress of the accident by detecting the unbalanced current of the ripple currents of the capacitor at the time of abnormality. CONSTITUTION:Up to the time tF when the open fault occurs in a capacitor 51, magnetic flux is changed in a current transformer 70 with polarities for offsetting ripple currents IR1 and IR2, and the secondary output of the current transformer 70 is zero. After the time tF, the current IR1 becomes approximately zero, and the secondary output IRDET corresponding to the current IR2 generates the abnormal voltage. The voltage becomes the abnormal signal VDET through a rectifying circuit 73. The signal is compared 22 with a voltage judging level VLEB through resistors 33 and 34. The signals becomes a wavefor-shaped signal V2 through an inverted logic gate circuit 154. After the abnormality has occurred, the sequence of 0 1 0 1 is repeated until the apparatus is stopped. The signal V2 sets a flip-flop 152 through an AND logic circuit 151 which does not accept interlocking. A fault signal FAULT is changed from 0 to 1, and the apparatus is stopped for protection.

Description

[Detailed description of the invention] [Object of the invention] (Industrial application field) The present invention converts DC power into AC power and configures a DC filter circuit used in an inverter system etc. connected to an AC system. This invention relates to a capacitor abnormality detection circuit.

(Conventional technology) Due to the spread of power semiconductor devices such as thyristors and GT○, in addition to increasing the capacity and pressure of power conversion devices, research and development has recently been conducted in terms of operating costs and reliability, such as energy saving and high efficiency. It is being done. Among these, it is necessary to provide reliability of converter components and protection and detection in the event of failure in conjunction with device development. Fig. 5 is a single line diagram showing the configuration of a typical example of such a power supply. is a self-excited inverter in which the pulse width of the output voltage is controlled according to active reactive power control, and is composed of self-extinguishing elements such as GT○. 5 is a DC filter capacitor, and 6 is an inverter transformer. 7 is a harmonic filter, which includes a contactor 7a, a harmonic suppression reactor 7b,
It is composed of a harmonic filter capacitor 7c. 8 is a reactor for AC grid connection, 9 is a breaker for grid connection/disconnection,
10 indicates an AC system. The load 12 is connected to the AC system via a transformer 11 and a system isolation/connection breaker 13. In the grid-connected system configured in this manner, active reactive power is controlled by performing discharging operation from the DC power supply to the AC system and charging operation from the AC system to the DC power supply in accordance with the power demand of the AC system. Fig. 6 shows an example of the detailed configuration of the DC filter capacitor 5 used in the DC filter circuit of the system configured as described above, 51 to 62 are capacitors 4S3P connected, 51a to 54a are voltage dividing resistors, and 14 is the main circuit. P, Nrllll This is an isolation amplifier that detects DC voltage. Such a configuration is used not only in the example shown in FIG. 5 but also in inverter devices in general.

(Problem to be solved by the invention) Even if an open failure or a short failure occurs in one or two capacitors, since multiple capacitors are connected in series and parallel, it is unlikely that the equipment will immediately stop due to a major failure. A possible problem is that operation continues without any abnormality being detected, and excessive stress is applied to otherwise healthy capacitors, causing deterioration and damage to all capacitors. Further, when the capacitor is damaged, the electrolyte may be scattered outside, reacting with metals in the surrounding parts, and causing further corrosion. SUMMARY OF THE INVENTION An object of the present invention is to provide a capacitor abnormality detection circuit that detects an open failure or short circuit failure of a capacitor at an early stage and stops the protection, thereby preventing the accident from expanding.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention uses a capacitor ripple that conducts current to a group of at least two or more capacitors connected in series and parallel with the same number of even pairs in a normal state. The current direction is configured to be detected through a current transformer with polarity that cancels each other out. In the event of an abnormality, that is, when an unbalanced current occurs due to a short or open failure of the capacitor, the voltage signal obtained from the current difference during the abnormality via the current transformer deviates from a predetermined level, so it is possible to easily detect the abnormality of the capacitor. This is a capacitor abnormality detection circuit characterized in that it is configured so that.

(Function) According to the present invention, as described above, by providing a means for detecting the unbalanced current of the capacitor ripple current at the time of an abnormality, it is possible to detect an abnormality in a group of capacitors in which a plurality of capacitors are connected in series and parallel. Even when the capacitance is increased or the voltage is increased, a detection circuit suitable for the configuration of the capacitor can be provided.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a capacitor abnormality detection method showing an embodiment of the present invention. Components that are the same or equivalent to those in FIG. 6 are given the same reference numerals, and their explanation will be omitted. For purposes of explanation, capacitors 51 to 54 will be referred to as a first capacitor group, and capacitors 55 to 58 will be referred to as a second capacitor group. 51a-6
6a is voltage dividing resistor, 70°71 is current transformer, 72.73
is a rectifier circuit composed of an operational amplifier, and 35 is a variable resistor, in which the voltage signal VDflT generated through the current transformer 70.71 due to an unbalanced current generated when one of the capacitors 51 to 66 fails is set to a predetermined level VLI. ! Voltage level VLI! used to determine whether it exceeds B!
Create B. 31 to 34 are input resistors, 21.22 is an operational amplifier, 44.45 is a Zener diode, 153
, 154 is an inverting logic gate, 150 is an OR logic circuit, 1
Reference numeral 51 indicates an interlock AND logic circuit for preventing abnormality detection from voltages generated other than during operation, and 152 indicates a flip-flop circuit. FIGS. 2 and 3 show time charts for explaining the invention in FIG. 1 in detail. FIG. 2 shows a time chart when the capacitor 51 has an open failure during operation, and FIG. 3 shows a time chart when the capacitor 51 has a short circuit failure. Figure 2 Time t0
Started driving at time 1. At , the capacitor 51 is
Assume that an open failure has occurred. (a) is current transformer 70-2
The following current is shown, and the time t0 to 1. During the period of , magnetic flux is applied to the current transformer 70 with polarity such that the ripple current IRz flowing through the first capacitor group 51 to 54 and the ripple current IRz flowing through the second capacitor group 55 to 58 cancel each other out. Because of the change, the secondary output of the current transformer 70 is zero at time 1.
After that, since the capacitor 51 becomes an open failure, the ripple current IRx of the first capacitor group becomes almost zero (approximately a minute current of the capacitor voltage dividing resistor), so the ripple current IRz of the second capacitor group becomes Corresponding 2 water output I
RDf! As shown in FIG. 2(a), the terminal generates an abnormal voltage. (b) shows a voltage signal VDI! obtained from the abnormal voltage generated by the secondary output IRQET of the current transformer 70 via the rectifier circuit 73! It shows T.

The obtained abnormal signal ■D is the voltage judgment level V Ll! set by the variable resistor 35. B is compared with the operational amplifier 22 through resistors 33 and 34, and the inverting logic gate circuit 154
The waveform shaped signal v2 is obtained through the waveform shaping signal v2. FIG. 2(C) shows how the obtained abnormal voltage signal v2 changes.

After an error occurs, "0" → "1" → r until the device stops.
OJ→“1”→repeat, V□ is OR logic circuit 150
, since I am driving, I do not install the interlock switch A.
The flip-flop 152 is set via the ND logic circuit 151, and the failure signal FAULT is held and changed from "0" to "1". Figure 2(d) shows the FAULT signal “0”
→ Shows the status of change to “1”.

The FAIJLT signal changes from rOJ to "1" and the device stops for protection. FIG. 3 shows that when capacitor 51 has a short-circuit failure at time tF, the first capacitor 5 except for capacitor 51
Capacitors 2 to 54 are charged in a short time with charges from other healthy capacitor groups 55 to 66 including the second capacitor group. As a calculation example, if we assume that the wiring inductance is 1 μH, this time t,1 is C=5600 μH.
If F, tv=z hole C= πJl μH・5600
It is thought that μF=235μs, and this time tlr-t
Secondary output IRDII of current transformer 70 to w! T is shown in Figure 3 (
Abnormal voltage becomes prominent as shown in a). After tw, a voltage is generated corresponding to the ripple current that is the difference between the ripple currents of the first capacitor group and the second capacitor group in which the capacitor 51 is short-circuited. In response to this change, the rectifier circuit 7
The output IDET of No. 3 also shows a similar change, as shown in FIG. 3(b). VD1! τ is the abnormality detection level VLI! At this point, the output V of the inverting gate circuit 154 changes from "0" to "1" as shown in FIG. 3(c). The abnormal signal v2 becomes an input to the OR logic circuit 150, and since it is operating, the AND logic circuit 1 is not interlocked.
51 to set the flip-flop 152. At this point, as shown in FIG. 3(d), the FAULT signal is
Changes from "0" to "1". This causes the device to stop protection.6 or more has been described for the abnormality of the first capacitor group 51-54, but the same applies to the second capacitor group 55-58. Furthermore, capacitor groups 59 to 62.6
3 to 66, abnormality detection can be similarly performed using a separate detection system, current transformer 71, rectifier circuit 72, operational amplifier 21, and inverting gate circuit 153.

Another embodiment of the invention is shown in FIG. Components that are the same or equivalent to those in FIG. 1 are designated by the same reference numerals, and their explanation will be omitted. The converter 70 is used with polarity such that the ripple currents of the capacitor groups 51 to 60 cancel each other out, and magnetic flux changes do not generate secondary induced electromotive force in a normal balanced state. Absolute value amplification circuit 72 and subsequent parts operate in the same manner as shown in Fig. 1.
Although the embodiments of the present invention have been described, the above example is merely an example.6 For example, the case of capacitor 484P has been described. However, the present invention is also applicable to an inverter system in which a large number of inverters are connected in series and parallel. In addition, the detection position of the current transformer is not limited to the N side bus bar side,
It is also applicable to the P side bus bar side.

〔Effect of the invention〕

One embodiment of the present invention has been described above.

In the present invention, since the configuration is such that the current difference can be detected on the main circuit side, differential amplification on the control circuit side can be omitted, and there is no need to provide all current detectors and voltage detectors as a means of detecting capacitor abnormalities. , there is an advantage of reducing the number to the required number. Since a current transformer is provided to detect abnormalities in a large number of capacitors connected in series and parallel, it is possible to detect abnormalities at an early stage even if one or two capacitors fail, and a highly reliable inverter system can be achieved. Also, the current transformer.

Since the capacitor's charging and discharging currents are balanced, they cancel each other out, and changes in magnetic flux do not generate secondary electromotive force. Therefore, changes in capacitance due to capacitor deterioration can be avoided by adjusting the detection level. It is possible to detect
It is also possible to save the time and effort required for periodic inspections.

[Brief explanation of the drawing]

FIG. 2 is a time chart explaining FIG. 1, FIG. 3 is a time chart explaining FIG. 1, and FIG. 4 is a block diagram showing an embodiment of the present invention. FIG. 5 is an inverter system system diagram to which the present invention can be applied, and FIG. 6 is a configuration diagram of a capacitor in the filter circuit of FIG. 5. 1... DC power sources such as solar cells, storage batteries, fuel cells, new batteries, etc., 3... DC reactors, 4... Inverters. 5... DC filter capacitor, 6... Inverter transformer, 7... High frequency filter,
8... Grid connection reactor, 9.13... Breaker, 1
DESCRIPTION OF SYMBOLS 1... Transformer, 12... Load, 10... AC system, 51-66... Capacitor, 51a-66a.
··resistance. 70.71... Transformer, 72.73... Rectifier circuit. 31 to 34...Resistance, 35...Variable resistance. 21.22... Operational amplifier, 44.45... Zener diode-V153.154... Inverting logic circuit, 150... OR logic circuit. 151...AND logic circuit. 152...Flip-flop.

Claims (1)

[Claims] In a circuit that detects an abnormality in a group of capacitors connected to a DC circuit bus bar and configured with at least two or more capacitors connected in parallel,
Under normal conditions, the ripple current in the first capacitor group and the ripple current in the second capacitor group cancel each other out, and the magnetic flux change is 2.
Means for detecting through at least one current transformer in a direction that does not generate secondary induced power, and comparing and detecting that the voltage generated due to the current difference at the time of abnormality exceeds a predetermined level at the secondary output of the current transformer. 1. A capacitor abnormality detection circuit comprising a comparator, and detecting a capacitor abnormality when a secondary output of the current transformer exceeds a predetermined level.