JPH031893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter device having a function of converting the frequency of an alternating current power source and supplying the frequency to a load device, as well as detecting a ground fault or overload condition on the load side.

FIG. 1 shows a typical configuration example of an inverter device that converts the frequency of alternating current supplied from an alternating current power source into alternating current of a predetermined frequency and supplies the converted alternating current to a load device. In the figure, 100 is a forward conversion circuit in which rectifying elements such as diodes and thyristors are connected in a bridge shape;
10 is a smoothing capacitor as a smoothing circuit that smoothes the output current of the forward conversion circuit 100, and 210 is an inverse conversion circuit consisting of a controllable element such as a transistor and a diode connected in antiparallel to the controllable element. An electric motor 220 as a load device is connected to the output side of. 300 is a first current detector provided on the positive electrode side of the DC section.

FIG. 2 is a diagram showing a detailed circuit configuration of the inverter device, load device, and AC power supply shown in FIG. 1, and the operation in a ground fault state on the load device side will be explained with reference to this diagram.

In the figure, 700 is an input power supply connected to the forward conversion circuit 100, and normally one phase is grounded, but that phase is assumed to be the S phase.

Now, in the input power supply, the R phase is at the highest potential and the T phase is at the lowest potential, and the forward conversion circuit 100 is connected to the diode D _RP .
Assume that D _TN is conducting. Further, in the inverse conversion circuit 210, the transistors are controlled according to a predetermined switching pattern based on the frequency command and the voltage command, and the DC power P _dp =V _dc × _dc is supplied to the motor 220 from the forward conversion circuit 100 through the inverse conversion circuit 210.
( _dc is the average value of I _dc ) is supplied. Here, V _dc is the DC section voltage and I _dc is the load current. In this state, it is assumed that the output W phase of the inverter has a ground fault. As shown in the figure, the positive side transistor TR _WP of the W phase is in a conductive state, and the negative side transistor TR _WN
is in the cut-off state, from the input power R phase
A ground fault current I _GI flows through D _RP , TR _WP , and the ground to the S phase of the input power supply. Further, when TR _WP becomes non-conductive and the W-phase negative side transistor TR _WN becomes conductive, a ground fault current I _G2 flows from the input power supply S phase to the input power supply T phase through the ground, TR _WN and D _TN .

The same can be considered when other phases are grounded.

Therefore, when a ground fault occurs on the load circuit side, the load utility pole I _dc and the ground fault current I _G1 flow to the positive pole side of the DC section, and the load current I _dc flows to the negative pole side, creating an unbalanced state by the ground fault current I _G1 . Then, the load current I _dc flows on the positive electrode side, and the load current I _dc and the ground fault current I _G2 flow on the load side, resulting in a repeated state of being unbalanced by the ground fault current I _G2 .

In the configuration shown in FIG. 1, since the current detector is closely attached only to the DC positive electrode side, a ground fault condition cannot be detected. Therefore, if the ground fault current is excessive, it may damage the rectifying element of the inverse conversion circuit, or
This has the disadvantage that even if the amount is not excessive, the operation continues in the same state, which is an undesirable situation.

This invention was made to eliminate the above-mentioned drawbacks, and includes a pair of current detection means at both poles between the output side of the smooth circuit and the input side of the inversion circuit.
Provided is an inverter device equipped with abnormality detection means for detecting a ground fault state and an overload state on the load side by comparing each current detection signal and comparing the current detection signal with a predetermined reference value. It is intended to.

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

In FIG. 3, 100 is a forward conversion circuit, 110 is a smoothing capacitor as a smoothing circuit, 210 is an inverse conversion circuit, 220 is an electric motor as a load device, 3
00 is a first current detector provided on the positive electrode side of the DC section, and 400 is a second current detector provided on the negative electrode side of the DC section. This constitutes a pair of current detection means. 500 is the output of the first current detector 300
This is an abnormality detection means that receives S ₃₀ and the output S ₄₀ of the second current detector 400 and compares them to detect a ground fault state on the output side of the inverse conversion circuit 210.

Next, the operation shown in FIG. 3 will be explained using FIG. 2 described above.

As shown in Figure 2, when there is no ground fault,
Now, direct current power P _dc is transferred from the forward conversion circuit 210 to the negative pole side.
= V _dc · I _dc is supplied, the detection signal S ₃₀ of the first current detector 300 and the detection signal S ₄₀ of the second current detector 400 are both the load current I _dc ,
The abnormality detection means 500 determines that it is normal.

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

For example, when TR _WP is conducting, the output S ₃₀ of the first current detector 300 is the load current I _dc and the ground fault current
I _G1 and the output of the second current detector 400
_S40 is the load current _Idc , and the abnormality detection means 500 determines that the difference between the two is the ground fault current _IG1 ,
Detects ground fault conditions. The states of S ₃₀ and S ₄₀ at this time are shown in FIG. 4a. Also, considering when TR _WN is in a conductive state, the output of the first current detector 300
S ₃₀ is the load current I _dc , and the output S ₄₀ of the second current detector 400 is the sum of the load current I _dc and the ground fault current I _G2 ,
Since the difference between the two is the ground fault current I _G2 , the abnormality detection means 500 can detect the ground fault state. The states of S ₃₀ and S ₄₀ at this time are shown in FIG. 4b.

5 to 7 are diagrams showing specific examples of the abnormality detection means 500 according to the embodiment of the present invention.

FIG. 5 shows an abnormality detection means 500 that detects a ground fault by detecting the difference between S ₃₀ and S ₄₀ , and 570 indicates the output S ₃₀ of the first current detector 300 and the output S of the second current detector 400. A difference calculator 550 serves as a first comparison means for calculating the difference between ₄₀ and 550, and 550 is a discrimination circuit serving as a discrimination means that determines that there is a ground fault state when the output _S57 of the difference calculator 570 is above a predetermined level. be.

FIG. 6 shows an abnormality detection means 500 that compares the levels of S ₃₀ and S ₄₀ and detects a ground fault depending on whether the levels are within a predetermined deviation. 510 is a first level conversion circuit that converts the level of the output S ₃₀ of the first current detector 300 at a predetermined ratio and outputs S ₅₁ ;
20 is a second level conversion circuit that converts the level of the output S ₄₀ of the second current detector 400 at _a predetermined ratio and outputs S ₅₂ ; 540 is a comparison circuit that compares the output S ₅₂ of the level converter 520 and compares whether S ₅₂ and S ₃₀ are within a predetermined deviation, 540 is the second current detector 40
0 output S ₄₀ and the output of the first level converter 510
_{This is a comparison circuit that compares S 51 and S 40} to see if they are within a predetermined level. ₅₄ , and when at least one of the signals is determined to be not within a predetermined deviation, it is determined that there is a ground fault condition.

FIG. 7 is a diagram showing an improvement of the apparatus shown in FIG. 6. This circuit performs the above-mentioned determination shown in FIG. 5 only when the levels of S ₃₀ and S ₄₀ are above a predetermined level. 560 is a comparison circuit added as a second comparison means for this purpose, and 550 receives the output S ₅₆ of the comparison circuit 560 and performs ground fault determination when S ₄₀ and S ₃₀ are above a predetermined level. .

According to this, the first and second current detectors 30
It is possible to avoid the problem of erroneously detecting a ground fault due to the adjustment error or noise that exists at 0.400.

Note that an insulated configuration is used to insulate between the main circuit, such as the current detector, 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 magnetic sensing element inserted in the gap thereof, and an amplifier, or any other configuration.

Further, in this invention, the case where a ground fault occurs on the load side of the forward conversion circuit has been described, but it is not limited to a ground fault, but when an unbalanced state occurs between the DC section positive electrode side current and the DC section negative electrode side current for other reasons. Needless to say, it can also be applied to

As described above, according to the present invention, since the current detectors are provided at both poles on the DC side of the forward conversion circuit, if a ground fault occurs on the negative pole side, the ground fault can be easily detected in any mode. became possible.

Therefore, by issuing a device abnormality alarm or shutting down the device using the detection signal, it is possible to prevent the abnormal situation from expanding. In addition, with this circuit configuration, since the normal load current is also measured, in FIG. It can also be used to detect excessive current caused by short circuits between side lines and protect elements within the load.

[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 is a diagram showing a ground fault mode. FIGS. 5 to 7 are diagrams showing specific examples of the discriminator. In the figure, 100 is a forward conversion circuit, 110 is a smoothing capacitor as a smoothing circuit, 210 is an inverse conversion circuit, 220 is an electric motor as a load device, 300,
400 is a first current detector and a second current detector as a pair of current detection means, 500 is an abnormality detection means, 510 is a first level conversion circuit, 520 is a second level conversion circuit, 530, 540 560 is a comparison circuit as a second comparison circuit, 550 is a discrimination circuit as discrimination means, and 570 is a difference calculator. In addition,
The same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1 Equipped with a forward conversion circuit that rectifies alternating current, a smoothing circuit that smoothes the output current of this forward conversion circuit, and an inverse conversion circuit that converts the output current of this smoothing circuit into alternating current of a predetermined frequency and supplies it to a load device. In the inverter device, a pair of current detection means detects the positive and negative currents between the output side of the smoothing circuit and the input side of the inversion circuit, and outputs a signal according to the magnitude of the current; a first comparison means that outputs a signal if the difference between the absolute values of the input signals from the pair of current detection means is equal to or higher than a predetermined value; an inverter device comprising: a second comparing means for outputting the second comparing means; and a determining means for determining the occurrence of an abnormality on the output side of the inverse conversion circuit based on the signal input from the first and second comparing means. .