JPS5812556Y2 - Unbalanced current detection device for inverter parallel operation system - Google Patents

Description

[Detailed description of the invention] The present invention relates to an inverter parallel operation system that operates multiple inverters in parallel, and particularly relates to an unbalanced current detection device that detects unbalanced current between inverters. The object of the present invention is to provide a special device that improves reliability in an inverter parallel operation system.

The purpose of an inverter parallel operation system is, of course, to increase output capacity, but it is also characterized by ensuring reliability as a system by disconnecting a failed inverter and continuing operation of the remaining healthy inverters. In particular, increasing the scale of load systems such as computers,
The latter purpose has become more important as technology becomes more sophisticated and widespread.

In order to improve the reliability of such an inverter parallel operation system, firstly, it is necessary to improve the reliability of each inverter itself, and secondly, it is necessary to improve the reliability of each inverter itself. It is important to reduce the number of mechanical failures.

Thirdly, to reduce common failures that force the system to be stopped for repairs, even if they are not directly linked to system shutdowns.Fourthly, to reduce the number of common failures that force the system to be stopped for repairs, even if they are not directly linked to system shutdowns.Fourthly, to reduce the number of common failures that require the system to be stopped for repairs, even if they are not directly linked to system shutdowns. The aim is to improve maintainability or safety by not causing anxiety to other healthy inverters.

Furthermore, fifthly, system safety becomes an extremely important factor when inverters are frequently added as load systems become larger.

On the other hand, it is necessary to control the number of inverters operated in parallel to prevent unbalanced currents that occur between them by operating the inverters with the same mode and voltage, and to maintain the specified sharing amount determined by the total load and the number of parallel operated inverters. There is.

For this purpose, it is known to control the output phase and output voltage of each inverter based on the correlation with the active current and reactive current shared by each inverter or the correlation with the active current and reactive current of the entire load. There is.

A device for detecting such a correlation, that is, an unbalanced current detection device, is conventionally not only complicated, but it is particularly important that this complicated unbalanced current detection device is a device that is common to the entire inverter parallel operation system. This means that the reliability, maintainability, safety, etc. of the system based on each of the factors mentioned above are reduced.

In view of the above-mentioned points, the present invention realizes an unbalanced current detection device for an inverter parallel operation system with improved reliability.

The present invention will be explained below based on the drawings.

FIG. 1 shows an embodiment of the single-phase unbalanced current detection method according to the present invention.・・・・・・I
N.V.

are n inverters operated in parallel, CB1. CB2゜...CBn is the output breaker of each inverter, C
D1゜CD2. ...... CDo is the output current detector of each inverter, W is the inverter INV, , INV2 . ．．
．． , , is a common load powered by INVo.

In FIG. 1, an output current detector CD1. CD2. ......CDo each has a current transformer CT□1. CT2□, ...... Resistors R1, R2, ... connected to CTnl and its secondary winding
・Unbalanced current detector CT1゜, CT consisting of Rn, each of whose output ends are illustrated as a current transformer.
2゜...CTn2 and each inverter's output shutoff CB□, CB2. . . . synchronized with each CBn, the coil is excited and operated to close the circuit when the circuit breaker is closed, that is, when the inverter is running in parallel.
-Contact SW1. SW2. ...SW.

A common connection section S including common connection buses 01 and 02 via
Commonly connected with W.

Here, all inverters INV1 in such a configuration
．． INV2. Let's consider a case where INV, 1 is running in parallel.

Now, if the output current of each inverter is 11 to fn and the load current is to, then L+L...+1n=I.

It is.

Also, the current that each inverter should normally share is (Io/.

), and the current transformers CT1□, CT2□, , , , , ,
Letting the current transformation ratio of CT,1 be equal to k, it is shown as follows.

x, -It/k x2=L/k +++++++ t
.

-L/tt+s 2””+1n=fo/ On the other hand, the voltage between the common connection buses 01 and 02 is ■.

, resistance R□. R2, . . . R9n resistance values are equalized R1 unbalanced current detector CT engineering 2. CT2□,...
...The current of CTn2 is 11□, i2□, ......l
If nl, the unbalanced current detectors CT1□, CT2□, ・
...Current flowing through CTn2 111, 12□, ...
. . . lnl is the vector current 11-in output by each inverter and the vector current 1-in which each inverter should originally share (fo/.

), that is, the unbalanced vector current.

The active and reactive components of this unbalanced vector current for each inverter output voltage are the differences between the active and reactive currents output by each inverter and the active and reactive currents that each inverter should share, respectively. It is clear that this signal is necessary and sufficient for controlling the parallel operation of inverters.

Furthermore, as shown in FIG. 1, a component detector CU1. CU2゜・・・
... By providing CUn, inverters INV□, IN■2. . . . INV, each can be controlled so that the unbalanced current can be controlled to almost zero.

In addition, unbalanced current detectors CT1° and CT2□ are used here.

....Equivalent resistance such as CTn2 and wiring resistance are ignored.

If such resistance exists, detailed explanation will be omitted, but
Unbalanced current [eg (io/.

)−L], the only difference being the gain of the detection current (for example, I There are no problems with control.

Also, unbalanced current detector CT□2. CT22.・・・・・・
- CTn2 may be replaced with a current transformer as shown, and may be configured with a resistor and a detection transformer that detects the voltage across the resistor.

Furthermore, it is clear that the difference in resistance value between each inverter, as described above, is not an essential problem because of the nature of the control, which ultimately brings the unbalanced current to almost zero.

FIG. 2 is a main circuit diagram showing an embodiment of another three-phase unbalanced current detection method according to the present invention, and only one inverter INVl' is shown.

In Fig. 2, an inverter INV for a three-phase circuit
1', output breaker CB1', output current detector CD1'
, unbalanced current detector C-12', relay contact sw1',
The circuit configuration consisting of the common connection part BW' and the component detector CU1' is similar to that for the single-phase circuit shown in FIG. 1, and for example, the output current detector CD1' for the three-phase circuit.
has the same function as the output current detector CD shown for the single-phase circuit.

Although a detailed explanation of such an embodiment will be omitted, this embodiment can also be detected and controlled in the same manner as the embodiment shown in FIG.

As is clear from the above configuration and description, the present invention has the following features.

First, common to the entire system is the current transformer CT in the output current detectors CD1 to CDo and CD1'.
The secondary side portion consisting of the secondary of 1, and its resistance R0, the unbalanced current detector CT engineering 2 to CTn2. It has an extremely simple configuration, consisting only of the primary side portion of the CT machine 2', relay contacts SW□ to SWn, SW1', common connecting portions BW, BW', and connection lines between these.

Moreover, all of them can be easily designed to be highly reliable, including the relay contact portion described later, and common device failures are substantially prevented.

Therefore, not only is it possible to prevent the parallel operation system from stopping due to a common device failure, but there is also no need to stop the system or cause instability in the system because there is no need to repair the failure. System reliability can be greatly improved.

Second, it is possible to obtain a signal necessary and sufficient for parallel operation at the AC stage.

This allows signal isolation and shielding if necessary, and considering that the secondary current rating of a typical current transformer is 5A, the common parts mentioned above are constructed with extremely low impedance. It is something that will be done.

Therefore, noise resistance, which is one of the most important performance characteristics of an inverter, can be improved, and the reliability of each inverter as well as the system can be improved.

Thirdly, the stopped inverter and other inverters are completely electrically isolated by the relay contacts SW~sw, , sw1'.

As a result, when preventive maintenance of each inverter or investigation and repair of a failure limited to each inverter is performed, the other inverters operating in parallel are not affected at all.

Fourth, the output current detectors CD1 to CDo of each inverter
, CD1' is unbalanced current detector CT1□~CTo2°C
The unbalance detection current is constantly reduced to zero by the detection method in which the output is output to the common connection portions BW, BW' via T1□' and relay contacts SW1 to SWn, SW□'.

Note that the main point in this is the relay contact part, but unless a complete disconnection occurs, changes in impedance, including the contact state of the circuit, will only slightly change the detection gain, and this is not an essential problem in control. Therefore, safe control is possible.

In addition, the three-phase configuration of commonly used parallel-operated inverters with a three-phase configuration itself provides redundancy.

Therefore, even if one phase or two phases are completely disconnected, high reliability and stability can be achieved without affecting the system.

Fifth, it is very easy to protect the system in the event of failure and maintenance of the relay contact section, which is the only component that can fail or requires maintenance in the embodiment.

In other words, there are three types of failures in polarized contact type relays: contact welding, contact failure, and coil breakage, and there is also artificial removal of the relay as a maintenance factor, but in the application shown in the example, contact welding is essential. cannot occur.

Furthermore, this relay contact part is connected to output shutoff circuits CB1 to CB.
o, it is possible to use a make contact that closes the coil by energizing the coil when the CB' is closed and operating in parallel, so that relay failure and maintenance factors are concentrated in the disconnected state described in the fourth feature above. be able to.

It is extremely easy to protect against this disconnected state, and for example, a three-phase configuration may be sufficient, and furthermore, a plurality of relay contacts or a plurality of relays may be used in parallel.

Also, if maintenance factors and contact failures in the relay excitation circuit are taken into consideration, a so-called fail-safe interlock that detects that the relay contact is not closed and stops the inverter when the circuit breaker is turned on can be installed. good.

Sixthly, the structural consistency with other inverters is achieved only by wiring between the common connection portions BW and BW'.

Therefore, when expanding the installation, all verification tests can be easily performed at the production factory, and the common connections BW and B
Since there is no need to modify other existing parts by just making the connection to W', it can be done in a short time and without causing any anxiety to the system.

It is also clear that it will be extremely easy to divide the system, and there is also a greater degree of freedom, such as performing parallel operation between systems by interconnecting the common connections of multiple parallel operation systems as necessary. and can configure a secure system.

As explained above, according to the present invention, extremely high reliability and
It is possible to provide an exceptional device with high maintainability and a high degree of freedom, and it realizes an ideal inverter parallel operation system, which has great effects.

In addition, in this explanation, the output current detector part has been described using a configuration example using a current source using a current transformer and its secondary side resistance, but since this is equivalent to a voltage source with internal impedance, it is not necessarily the case that the above configuration example is used. The present invention is not limited to this, as long as it generates an AC voltage whose instantaneous value corresponds to the output current of each inverter, and if necessary, a resistor corresponding to impedance may be provided externally.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the single-phase unbalanced current detection method according to the present invention, and FIG. 2 is a circuit diagram of main parts showing an embodiment of another three-phase unbalanced current detection method according to the present invention. . INV1 to INVn, INV1'-----Inverter, CD1 to CDo, CD1'... Output current detector, CT. ~CTo1...Current transformer, R1-Rn...
・Resistance, CT□2~CTo2. CT1゜'・・・・・・
Unbalanced current detector, sw1~swn, sw1'-,,,
-・Relay contact, BW. BW'...Common connection part.

Claims (3)

[Scope of utility model registration request] (1) It has an output current detector that provides an AC voltage corresponding to the instantaneous value of the output current of each inverter in the inverter parallel operation system, and the output terminals of the output current detectors are commonly connected, and the output current is detected. An unbalanced current detection device for an inverter parallel operation system, characterized in that an unbalanced current detector is provided to detect the current of each output of the inverter. (2) An unbalanced current detection device for an inverter parallel operation system according to claim (1), wherein the output current detector is constituted by a current transformer and its secondary resistance. (3) Utility model registration claim No. 1 in which the output terminals of each of the output current detectors are connected in common through a contact whose coils are excited and closed during inverter parallel operation.
An unbalanced current detection device for an inverter parallel operation system as described in .