JPS59188335A - Ground-fault detecting circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting a ground fault condition on the load side of a forward conversion circuit that converts AC power into DC power.

In Figure 5 (100) shown in Figure 1 is a typical configuration example of a forward conversion circuit that converts AC power into DC and its load circuit.
A forward conversion circuit in which rectifying elements such as U diodes and thyristors are connected in a bridge configuration, a smoothing capacitor (110), and a load circuit (200) connected in antiparallel to a controllable element (210) such as a transistor From the diode or the motor (220) connected to the circuit. (300) is the first current detector provided on the positive side of the DC section. First, Figure 5 will explain the operation of this type of circuit configuration in a ground fault state on the load circuit side using Figure 2. (700) fd forward converter (100
), one phase of which is normally grounded is called the S phase. (100) is a forward conversion circuit consisting of a diode, (110) is a smoothing capacitor, (
200) is a load circuit, (210) id) is an inverse conversion circuit consisting of a transistor and a diode, and (220) is an electric motor.The load circuit (200) is an inverse conversion circuit (210).
) and a motor (220), the input power supply has the R phase at the highest potential and the T phase at the lowest potential.
It is assumed that TN is in a conductive state. In addition, the inverse conversion circuit (2
10) is the frequency command, voltage command (based on the specified switch
The transistor is controlled by the −I switching pattern, and the motor' (220) is supplied with DC power FjlQ = Vd(!
It is assumed that X Idc (the average value of one song) is supplied. Here, Vclc is the DC section voltage, Idc
is the load current. In this state, the inverter output W
When the phase is grounded L'f, as shown in the figure, the positive side transistor TRWp of the W phase is in a conductive state, and the negative side transistor TRWN is in a conductive state.
is in the cut-off state, the R phase of the input power supply Dp, p,
The earth terminal power GI flows through TRWp and the earth to the input power supply S phase. Also, when TRwp becomes non-conductive and the W-phase negative side transistor TRWN becomes conductive, the input power supply S
The earth terminal power G2 flows from the phase to the input power supply T phase through the earth +' TRWN and DTN.

The same can be said when other phases have a ground fault. Therefore, when a ground fault occurs on the load circuit side, the load voltage
In the configuration shown in Figure 1, current is detected only on the positive DC side. Therefore, if the ground fault current is excessive, it may damage the rectifying element of the inverter circuit, or it may cause damage to the rectifying element of the inverter circuit even if it is not excessive. This invention was made in order to eliminate the above-mentioned drawbacks, such as the undesirable situation where the operation continues in the condition of 7. Provide each current detection signal? An embodiment of the present invention, which aims to provide a ground fault detection circuit that detects a ground fault state by comparison, will be described below with reference to the drawings.

In Figure 3, (100) is the forward conversion circuit, (110) is the smoothing capacitor, (200) is the load of the forward conversion circuit, (
210) is an inverse conversion circuit, (220) is an electric motor, (300
) is the first current detector provided on the positive electrode side of the DC section, (4
00) is a second current detector provided on the DC section load side,
(500) is the output S30 of the first current detector (800)
This is a discriminator that receives as input the output S40 of the second current detector (400), and compares them to determine whether there is a ground fault state. , the load (200) is composed of an inverse conversion circuit (210) and an electric motor (220).The operation shown in FIG. 3 will now be explained using the above-mentioned FIG. 2. As shown in the figure, there is a ground fault, and now DC power is being sent from the forward conversion circuit +210) to the load side, llMc-■C
- When the hill E is supplied, the first current detector (80
0) detection signal 83G and second current detector (400)
The detection signal S4+B is clearly a load voltage peak dc, and the discriminator (500) determines that it is normal.

Next, consider a situation where the W phase is grounded in this state.

For example, when TRwp is in a conductive state, the output 830 of the first current detector (800) is the load current D and the ground fault G.
l and the output 84 of the second current detector (400)
G is the load current voltage dc, and the discriminator (500) determines that the difference between the two is the ground termination voltage Gl, thereby detecting a ground fault state. The state of 330 and S40 at this time is
Shown in Figure (a). Also, considering when TRWN is in a conductive state, the output S3[1 of the first current detector (800)
is the load current Idc, which is the sum of the output 54i1H load current Idc of the second current detector (400) and the ground fault current IG2.Since the difference between the two is the ground fault current IO2, the discriminator (
'500), a ground fault condition can be detected. The states of 8311 and 84G at this time are shown in FIG. 4(b).

5 to 7 show discriminators according to embodiments of the present invention.

(500) is a diagram showing a specific example.

FIG. 5 shows a discriminator for detecting ground faults, which is designed to detect the difference between S3o and S40, and (570) is the first current detector (
800) output 5311 and the second current detector (400)
a difference calculator (550) that calculates the difference between the outputs 840 of
This is a discriminator that determines that a ground fault condition exists when the output Ssy of the difference calculator (570) is higher than a predetermined level.

Fig. 6 is a discriminator that compares the levels of S30 and S34 (1) and detects a ground fault depending on whether they are within a predetermined deviation. 1))-
(520) is a second current detector (4001) which converts the level of the output S40 at a predetermined ratio;
The second level converter circuit (530) that outputs S52 compares the output 53 (1) of the first current detector (300) and the output S52 of the second level converter (520), and S52 and 330 are A comparison circuit that compares whether the deviation is within a predetermined deviation.
(540) is the output S4 of @2'-current detector 400)
[+] is compared with the output Ssr of the first level converter (510), and Ss+ and S4[+ are within a predetermined level. 540), and when at least one of the outputs 353 and 354 is a signal determined to be not within a predetermined deviation, it is determined that there is a ground fault state.

FIG. 7 is a diagram showing an improvement of the apparatus shown in FIG. 6. S
This circuit performs the determination shown in FIG. 5 only when the levels of signals 30 and 840 are equal to or higher than a predetermined level. ,(
560) is a comparison circuit added for that purpose, and (5
50) receives the output SS6 of the comparator circuit (560), and
When 4o and 330 are above a predetermined level, a ground fault is determined.

According to this, the first and second current detectors (300) (4
It is possible to avoid the problem of erroneously detecting a ground fault due to the adjustment error or noise that exists in 00).

Furthermore, a nine-plane current detector usually has an insulated configuration to insulate between the main circuit and the control circuit. It may have a configuration consisting of a resistor and an isolated amplifier, a configuration consisting of a cut core that converges magnetic flux, a magnetically sensitive element inserted in the gap thereof, and an amplifier, or any other configuration.

Further, in this invention, a case has been described in which a ground fault occurs on the load side of the forward conversion circuit, but an unbalanced state may occur between the DC section positive electrode 1111 current and the DC section member pole side current not only due to a ground fault but also for other reasons. It goes without saying that this invention can also be applied to other cases.As described above, according to the present invention, current detectors are provided at both poles on the DC side of the forward converter, so if there is a ground fault on the load side, what will happen? It is now possible to easily detect ground faults even in remote mode.

Therefore, by issuing a device abnormality alarm or shutting down the operation using the detection signal, it is possible to prevent the abnormal situation from expanding. In addition, with this circuit configuration, the normal load current is also measured, so it is possible to detect overload conditions during normal operation or excessive current due to a short circuit between the load side δ electric circuits, and to protect elements within the load. It helps to be there.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the general configuration of a forward conversion circuit and a load circuit, Fig. 2 is a diagram explaining a ground fault mode, Fig. 3 is a diagram showing an embodiment of the present invention, and Fig. 4 1 is a diagram showing a ground fault mode. 1 is a diagram showing a specific example of a discriminator. In the figure, (100) is a forward conversion circuit, (110) is a smoothing capacitor, (200) is a load circuit, (210) is an inverse converter (220) is a motor, (300) is a first current detector, ( 400) is the second current detector, (500) is the discriminator, (510) is the first level conversion circuit, (520) is the second level conversion circuit, (530) (540) (560)
(550) is a discrimination circuit, and (570) is a differential source 'JL unit. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Oiwa Figure 3 zo. Figure 4 (α) (b) Figure 5 Figure 6 500 W-7 Figure 2---111111---------
1. Procedural Amendment (Voluntary) July'9, 1980 Director General of the Japan Patent Office 1. Indication of the case: Japanese Patent Application No. 511-061810 2. Title of the invention: Earth fault detection circuit 3. Person making the amendment. To Representative Hitoshi Katayama Part i Subject of amendment (1) Claims column of the specification (2) Detailed explanation of the invention column 6 of the specification, Contents of amendment (1) Scope of claims of the specification amend the attached circular. (2) In the specification, ``Load current Ia J'' in the 5th and 6th lines of page 4 is corrected to ``Load current Idc.'' (3) In the same book, on page 5, line 6, the phrase "DC section load side" is corrected to "DC section member pole side." (4) In the same book, on page 6, line 18, the phrase "discriminator," is corrected to "by discriminator." (5) In the same book, on page 6, line 20, r (550) J is corrected to read "(550) wa." 7. A document stating the scope of claims after the list of attached documents has been corrected. One or more copies of the scope of claims. +11 A forward conversion circuit that converts AC power into DC. and a load circuit supplied with DC power from the forward converter, and a first current detector provided on the positive electrode side of the DC section of the forward converter. A discriminator that compares the outputs of the first current detector and the second current detector with a second current detector provided on the negative seal l, and determines whether the deviation is at a predetermined level. A ground fault detection circuit characterized by comprising: (2) A comparison circuit that compares the outputs of the first current detector and the second current detector with a predetermined level. 2. The ground fault detection circuit according to claim 1, wherein ground fault detection is performed when the output of the first current detector or the second current detector is above a predetermined level.

Claims (2)

[Claims] (1) In a device consisting of a forward conversion circuit that converts AC power into DC power and a load circuit that supplies DC power from this forward conversion circuit, the 1 current detector, a second current detector provided on the negative polarity side, and the outputs of the first current detector and the second current detector are compared, and the deviation is at a predetermined level. What is claimed is: 1. A ground fault detection circuit characterized by comprising a discriminator for discriminating whether (2) A comparison circuit is provided to compare the output of the first current detector and the second current detector with a predetermined level, and the output of the first current detector or the second current detector is set to a predetermined level. The ground fault detection circuit according to claim 1, which performs ground fault detection when the voltage is higher than the ground fault level.