JPH09271173A - Fault sensing circuit of inverters with parallel connection structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sense surely a fault of unverters with a parallel connection structure, by providing a low-pass filter whereto the output of a computer for the cross current of the inverters is inputted so that it feeds a fault sensing level top a competitor. SOLUTION: The respective output currents of inverters 11, 12, 13 which are sensed respectively by current sensors 31, 32, 33 are inputted to a cross-current sensing circuit 41 to sense three-phase cross currents I41 U-I41 W of the inverter 11. Then, summing the cross currents I41 U-I41 W, the absolute value of the summed current is computed by a computer 51 to give a sensing level FL51' in its output. Further, the sensing level FL51' is inputted to a low-pass filter 71 to output a sensing level FL71 to a comparator 61'. The conspirator 61' comports the sensing level FL71 with a set level FL* to output a fault signal Sf'. Therefore, even in the case of the short-circuit fault of a dummy resistor, the fault can be sensed surely without raising the set level FL* for the fault signal Sf'.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a parallel connection configuration inverter used for a large-capacity power supply device or the like, and more particularly to a parallel connection configuration inverter failure detection circuit for detecting a failure based on cross current detection. It is a thing.

[0002]

2. Description of the Related Art Inverters having a parallel connection configuration in which a plurality of inverters are connected in parallel are used for large-capacity power supply devices such as uninterruptible power supply devices (so-called UPS). Furthermore, such a parallel connection type inverter employs a failure detection circuit that detects a failure based on cross current detection. This is as in FIGS.

FIG. 3 is shown for the purpose of explaining the prior art. Reference numerals 11, 12, and 13 are inverters of a parallel operation example of three units, and 2.
Is a load device commonly connected to the inverters 11, 12 and 13, 31
Is a current detector, 41 is a cross current detection circuit, 51 is a calculator, and 61 is a comparator. Further, FIG. 4 is shown for explaining the cross current detection circuit, and 32 and 33 are the same as the current detector 31 and the inverter 1
Current detectors 4 arranged on the output side of 2 and 13 are cross current detectors. In the cross current detector 4, 411, 421 and 431 are dummy resistors and 412, 422 and 432 are current detectors. However, u, v, and w represent the respective three phases.

That is, the inverter 11 will be explained. The output current of the inverter 11 detected by the current detector 31 and the output currents of the inverters 12 and 13 detected by the current detectors 32 and 33 are detected as cross current detection. Input to circuit 41, inverter 11
The three-phase cross currents I41u, I41v, and I41w are detected. The cross current detection circuit 41 is similar to the cross current detection unit 4 shown in FIG.
Dummy resistors 411u, 411v, 411w are provided on the output sides of the current detectors 31u, 31v, 31w of the inverter 11, respectively, and are connected in common with the same phase as other inverters operating in parallel. . Furthermore, by connecting in this way, the above-mentioned cross currents I41u, I41v, I41w are obtained by the current detectors 412u, 412v, 412w. Then, in the calculator 51, the cross currents I41u, I41v, I
41w is added and the absolute value is calculated, and the detection level FL51
Occurs. Also, with the comparator 61, the detection level FL
51 is compared with the set level FL * of the failure setting signal to make a determination, and the failure signal Sf is output.

Here, the current detectors 412u, 412v, 412
When the current is normally detected by w, the cross current I41u,
The sum of I41v and I41w becomes zero. However, if one of them fails and normal current detection cannot be performed, the sum of the three-phase cross currents does not become zero. Therefore, the three-phase cross currents I41u, I
A detection level FL51 which is the absolute value of the sum of 41v and I41w,
The failure of the current detectors 31, 32, 33 can be detected by comparing with the set level FL * set in consideration of the detection error and the like.

[0006]

In the prior art of this kind, the output currents of the inverters 11, 12, 13 are the same in the steady state, and no cross current flows. Now, let the output current of the u phase be (I sin ωt). If the u-phase dummy resistor 411u of the inverter 11 has a short-circuit fault, the cross current of each of the inverters 11, 12, 13 at the moment of the fault is expressed by the following equation (1),
It becomes like (2) and (3). Therefore, the inverter
The absolute value of the sum of the three-phase cross currents of 11, 12, and 13 may exceed the failure setting signal depending on the phase of the output current.

I41u = (− 2) (I sinωt), I41v = I41w = 0, (1) I42u = (I sinωt), I42v = I42w = 0, (2) I43u = (I sinωt), I43v = I43w = 0 ─── (3)

As described above, when the failure detection of the current detector 412u to the current detector 412w is carried out in this manner, when the dummy resistor has a short-circuit failure, the failed inverter 11 and the normal inverter 12 are activated. , 13 are judged to be faulty at the same time. Further, if the level of the failure setting signal is raised to avoid this, there is a problem that the original purpose of the failure of the current detector 412u to the current detector 412w may not be detected.

An object of the present invention is, therefore, to provide a special parallel-connection-type inverter failure detection circuit capable of detecting a failure of a current detector for detecting cross current and detecting a failure even in the case of a dummy resistance short circuit. There is something to offer.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has the following structure. That is, a current detector that detects the output current of three or more inverters connected in parallel, a cross current detection circuit that detects a cross current from the current detector output, and a three-phase cross current output from the cross current detection circuit are added. An arithmetic unit that calculates absolute values,
In a failure detection circuit of a parallel connection configuration inverter having a detection level based on the output of a computing unit, a comparator that obtains a failure signal and a comparator that obtains a failure signal, the detection level is input to the comparator using the output of the computing unit. Is provided with a low-pass filter for generating.

[0011]

Specifically, a current detector for detecting an output current of an inverter connected in parallel, a cross current detection circuit for detecting a cross current from the current detector output, and a cross current detection circuit output. An arithmetic unit that calculates the absolute value by adding the three-phase cross currents, a low-pass filter that receives the output of this arithmetic unit, and a fault when the detection level of this low-pass filter output exceeds the fault setting level. A comparator that generates a signal
And are provided. Furthermore, based on the example drawings,
Details will be described.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment to which the present invention is applied, similar to FIG. 3, in which 51 'is an arithmetic unit, 61' is a comparator, and 71 is a low-pass filter. In FIG. 1, in particular, an arithmetic unit 51 'which inputs the cross currents I41u, I41v, I41w of the cross current detection circuit 41 to give a detection level FL51' and a logic unit 51 'which inputs the detection level FL51' to give a detection level FL51 '. −
A pass filter 71 'and a comparator 61' for inputting the detection level FL51 'and the set level FL * to generate a failure signal Sf' are provided. Where the calculator
51 'and the comparator 61' are the arithmetic units shown in FIG.
It has the same effect as 51 and the comparator 61.

That is, the cross current detection circuit 41 is a current detector.
The output current of the inverter 11 detected in 31 and the current detector 3
Input the output currents of the inverters 12 and 13 detected by 2 and 33, and the three-phase cross currents I41u, I41v, and I41w of the inverter 11
Is detected. This may be the same as in FIGS. 3 and 4. Then, by the calculator 51 ′, the cross currents I41u, I41
v and I41w are added and the absolute value thereof is calculated to give a detection level FL51 '. Furthermore, this detection level FL5
The detection level FL71 is obtained by the comparator 61 'through the low-pass filter 71 which receives 1'as an input. Further, the comparator 61 'compares the detection level FL71 with the set level FL * and outputs a failure signal Sf'.

Next, the operation of this structure will be described with reference to FIG. It is now assumed that the u-phase output current is (I sin ωt) and the u-phase dummy resistor 411u of the inverter 11 is short-circuited. Here, each inverter at the moment of failure
As described above, the cross currents of the data 11, 12, and 13 are expressed by the equations (1), (2), and (3). Therefore, the absolute value of the sum of the three-phase cross currents of the inverter 11 is (2I sinωt), and the absolute value of the sum of the three-phase cross currents of the inverters 12 and 13 is (I sinωt). This is shown as in FIG. In FIG. 2, FL51 'and FL52' are arithmetic units 5
Detection level of 1 ', 52' output, that is, inverters 11, 12
It is the absolute value waveform of the sum of each three-phase cross current, and F
L71 and FL72 are detection levels of the outputs of the low pass filters 71 and 72. As shown in the figure, in particular, the detection levels FL71, FL
The times T1 and T2 at which 72 reaches the set level FL * are different.

By thus passing the low-pass filter, the time T1 at which the failure of the inverter 11 is detected.
And a time T2 at which the failure of the inverter 12 is detected, the failure signal Sf 'is obtained with a time difference. Therefore, even when the dummy resistor is short-circuited,
It is possible to reliably detect a failed inverter without raising the level of the failure setting signal. Although an example of parallel connection of three inverters has been described, similar effects can be obtained even when three or more inverters are connected in parallel.

[0016]

As described above in detail, according to the fault detecting device of the present invention, the fault of the current detector for detecting the cross current can be detected, and the fault of the dummy resistor is caused even when the fault occurs. It is possible to provide a device having a simple structure that can reliably detect the data.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment to which the present invention is applied.

FIG. 2 is a waveform diagram shown for explaining the operation of FIG.

FIG. 3 is a circuit diagram shown for explaining the prior art.

FIG. 4 is a circuit diagram shown for explaining a cross current detection circuit.

[Explanation of symbols]

 11 Inverter 2 Load device 31 Current detector 41 Cross current detection circuit 4 Cross current detection unit 411 Dummy resistance 412 Current detector 51 Operator 51 'Operator 61 Comparator 61' Comparator 71 Low pass filter I41u Cross current I42u Cross current I43u Cross current FL * Setting level FL51 Detection level FL51 'Detection level FL71 Detection level Sf Failure signal Sf' Failure signal

Claims (1)

[Claims] 1. A current detector for detecting an output current of three or more inverters connected in parallel, a cross current detection circuit for detecting a cross current from the output of the current detector, and a three-phase output of the cross current detection circuit. Fault detection circuit for parallel-connected inverter having a computing unit for computing an absolute value by adding cross currents and a comparator for obtaining a fault signal from a detection level based on the output of the computing unit and a fault setting level 2. A failure detection circuit for a parallel-connection inverter, characterized in that a low-pass filter for generating a detection level is provided to a comparator by using the output of the arithmetic unit as an input.