JPH11150858A - System interconnection equipment and current limiting method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a system interconnection equipment which allows a passing current to be sufficiently limited, without interrupting between systems if any short circuit occurs in a power system. SOLUTION: An alternating-current reactor ACL and a switch SW connected in a parallel are series-connected on the power system side with a single-phase rectifying bridge circuit comprising diodes D1, D2, D3, D4 and a direct-current reactor DCL to form a system interconnection equipment 1. During the normal operation of the system interconnection equipment 1, the switch SW is closed to efficiently operate the rectifying bridge circuit with the reactance being almost zero. If a trouble occurs in a power system and a current passed through the single-phase rectifying bridge circuit is limited by the direct-current reactor DCL, at some midpoint in the process of the passing current being increased, the switch SW is opened and the alternating-current reactor ACL is inserted. As a result short circuit occurs in a power system, the passing current of the system interconnection equipment 1 is limited to a specified value or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system interconnection device for interconnecting two electric power systems and for preventing an instantaneous voltage drop of an important load of a distributed power supply connection bus or for performing a current limiting cutoff of a general AC system. Things.

[0002]

2. Description of the Related Art A system interconnection device is used to interconnect two electric power systems or to perform a current limiting interruption of a general AC system.

[0003] In particular, a system interconnection device for interconnecting a distributed power connection bus such as a cogeneration connection bus to a commercial power supply system is provided with a distributed power supply connection bus when a short circuit accident or a ground fault accident of the commercial power supply system is detected. Is separated from the commercial power supply system, and plays an important role in preventing a power supply stop and an instantaneous voltage drop in the distributed power supply connection bus.

As one example, a conventional system interconnection device used for instantaneous voltage drop countermeasures proposed by the present applicant in Japanese Patent Application Laid-Open No. 9-285012 is shown in FIG. The configuration is shown. This system interconnection device 101
Are diodes D101, D102, D103, D10
4 and a DC reactor DCL101 and a circuit breaker CB101.

[0005] The system interconnection device 101 interconnects an electric power system to supply electric power in two directions or one direction.
At the time of normal power supply, the current of DC reactor DCL101 is DC, so that DC reactor DCL1
The reactance of 01 is zero. On the other hand, for example, the receiving end R
When a short circuit accident occurs in ec2, DC reactor DCL
Utilizing the effect of suppressing the current change of the receiving end 101, the receiving end Rec1
The current flowing into the fault point from the
The instantaneous voltage drop on the ec1 side is prevented.

[0006]

However, the above-described system interconnection device 101 is configured to prevent a momentary voltage drop until the system is disconnected. When an accident occurs, the circuit breaker CB101 is shut off. You.

[0007] Normally, the recovery from a short-circuit fault requires a few minutes at the longest in order to confirm the fault point of the power distribution system, etc., and during this time, the transportation of power by the interconnection must be cut off. Therefore, if the DC reactor L101 is used to limit the passing current value without opening the circuit breaker CB101, a DC reactor capable of limiting the current for several minutes is required. Not a target.

Accordingly, the above-described system interconnection device 101
Cannot be used for applications in which short-time disconnection of interconnection is not permitted, such as power interchange between trunk lines or power generation to a cogeneration system having no private generator.

An object of the present invention is to provide a system interconnection device capable of sufficiently restricting a passing current without interrupting a power system when a short circuit accident occurs in a power system.

[0010]

According to a first aspect of the present invention, there is provided a system interconnection device for interconnecting two power systems, wherein a DC reactor is provided between two DC terminals of a single-phase rectification bridge circuit having a rectifying element. In a system interconnection device configured to be connected, an AC reactor or a resistor is connected between one of the power systems and the single-phase rectifier bridge circuit, and both ends of the AC reactor or the resistor are connected. It is characterized by having short-circuit means for short-circuiting.

According to the above invention, both ends of the AC reactor or the resistor are short-circuited by the short-circuit means during the normal operation of the system interconnection device, and the system interconnection device is efficiently connected to the power system with almost zero impedance. To interconnect.

Immediately after a short-circuit accident has occurred in one of the power systems, a current limiting operation is performed by a DC reactor.
Prevent the instantaneous voltage drop of the other power system. Further, by releasing the short-circuit means during the current limiting operation, an AC reactor or a resistor is inserted between the power system and the single-phase rectifier bridge circuit, and an increasing passing current is increased by the reactance or the resistor. Restrict.

Therefore, when an accident occurs in the power system,
An overcurrent flowing through the above-described grid connection device due to an accident can be suppressed while the grids are connected.

According to a second aspect of the present invention, in the current limiting method for a grid interconnection device according to the first aspect, a direct current is superimposed on a passing current of the grid interconnection device. When the passing current is equal to or less than a predetermined value, the short-circuit means is opened and the AC reactor is inserted.

According to the above invention, when an AC reactor is inserted between the power system and the single-phase rectifier bridge circuit, the short-circuit means is opened when the current passing through the system interconnection device is equal to or less than a predetermined value. To prevent DC current from being superimposed. For example, the AC reactor is inserted when the current passing through the grid interconnection device does not exceed the current value after the AC reactor is inserted.

As described above, since the DC current is not superimposed,
For example, a transformer installed in a power system does not cause a partial excitation phenomenon or the like.

Therefore, the current of the grid interconnection device can be limited without adversely affecting the connected power system.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1] The following will describe an embodiment of a system interconnection device of the present invention with reference to FIGS.

As shown in FIG. 1, a grid interconnection device 1 according to the present embodiment has diodes arranged in all arms of a single-phase rectification bridge circuit, and a diode is provided between one power system and the single-phase rectification bridge circuit. An AC reactor is connected to this.

More specifically, diodes D1, D2, D3, and D4 as rectifying elements, a DC reactor DCL,
AC reactor ACL, switch S as short-circuit means
W, circuit breaker CB, and switch control circuit SC1.

The DC reactor DCL is connected to a diode D1.
A DC terminal which is a connection point of D3 and diodes D2 and D4
And the DC terminal which is the connection point of Further, the AC reactor ACL and the switch SW are connected in parallel with each other, and these are connected between one power system and an AC terminal which is a connection point of the diodes D3 and D4. A circuit breaker CB is connected between the other power system and an AC terminal that is a connection point between the diodes D1 and D2. Further, the switch control circuit SC1 includes the current transformer 2
And an overcurrent relay 3. The current transformer 2 is disposed at one end of an AC reactor ACL, for example, and the overcurrent relay 3 is connected to a switch SW in order to detect the interconnection current.
It is connected to the.

The operation of the system interconnection device 1 having the above configuration will be described below.

During normal operation of the system interconnection device 1, the switch SW is closed by the control of the switch control circuit SC1, and the passing current of the system interconnection device 1 is controlled by the AC reactor A
It flows on the switch SW side without flowing through CL. Therefore, the grid interconnection device 1 is efficiently operated with the reactance being substantially zero.

When an accident such as a short circuit or ground fault occurs in one power system, the grid interconnection device 1 starts a current limiting operation by the DC reactor DCL, and prevents an instantaneous voltage drop in the other power system. The passing current of the grid interconnection device 1 increases with time. On the way, the current transformer 2 detects the overcurrent and transmits it to the overcurrent relay 3, and is realized by a breaker or a semiconductor switch at the zero point of the passing current. Open the switch SW. Thereby, AC reactor ACL is inserted between the power system and the single-phase rectifier bridge circuit, and the passing current is limited to a predetermined current value or less. When the short-circuit state is released, the switch SW is closed, and the system interconnection device 1 is returned to the normal state.

Therefore, it is possible to limit an overcurrent caused by an accident while keeping the two power systems connected.

Next, FIGS. 2 and 3 show the current limiting characteristics of the system interconnection device 1. FIG. In addition, FIG. 4 shows a current limiting characteristic of the conventional system interconnection device 101 for comparison.

Here, for the sake of simplicity, it is assumed that an accident has occurred when the passing current of the system interconnection device 1 and the conventional system interconnection device 101 is zero and when the voltage of the power system is zero. The temporal change of the passing current waveform is illustrated.

FIG. 2 is a graph showing three AC currents after the occurrence of an accident.
It is a waveform of the passing current when the AC reactor ACL is inserted in the middle of the cycle. Immediately after the occurrence of the short-circuit accident, it is found that the current limiting function of the DC reactor DCL is working, thereby preventing an instantaneous voltage drop. Further, after the AC reactor ACL is inserted, it can be seen that the passing current of the grid interconnection device 1 is limited to within a predetermined value. As described above, the grid interconnection device 1 does not require interconnection interruption when an accident occurs.

FIG. 2 shows a change in the passing current when the AC reactor ACL is inserted at the time when the passing current is relatively small at the beginning of the current limiting operation.

FIG. 3 shows an example in which the AC reactor ACL is inserted after the passing current becomes larger than that in FIG. In this case, immediately after the occurrence of the accident, the DC current limiting function of the DC reactor DCL works, but it can be seen that the DC current is superimposed on the passing current after the AC reactor ACL is inserted.

In general, it is well known that when a reactor is inserted into an AC circuit, a DC current is superimposed on an AC current depending on the phase of voltage and current. In the case of FIG. 2, since the AC reactor ACL is inserted while the passing current is relatively small, the DC reactor DCL in the single-phase rectification bridge circuit is inserted.
The superimposition of the direct current can be prevented by the current change suppressing action by the above. In FIG. 3, the maximum current value before and after the insertion of the AC reactor ACL is the same because the DC reactor D
The CL attempts to maintain the current peak value before the AC reactor ACL is inserted, and as a result, a DC current is superimposed after the AC reactor ACL is inserted.

When the DC current is superimposed on the AC circuit side, a bias excitation phenomenon or the like of the transformer is caused, which may adversely affect the power system. Therefore, it is desirable that the amount of superposition of the DC current is small, and in the grid interconnection device 1, it is preferable to insert the AC reactor ACL when the passing current is within the current value limited by the AC reactor ACL. This adjustment can be performed by changing the reactance of the DC reactor DCL in addition to the high-speed injection of the AC reactor ACL. Which method is to be used is determined from the viewpoint of economical efficiency of both.

On the other hand, the conventional system interconnection device 101
4, as shown in FIG. 4, has a sufficient current limiting action immediately after the occurrence of an accident, and is intended to prevent an instantaneous voltage drop. However, since the interconnection is not interrupted by the circuit breaker CB101 (see FIG. 8), the passing current of the interconnection device 101 increases exponentially with time.

As described above, the grid interconnection device 1 can limit the passing current to within a predetermined value without interrupting the interconnection when a short circuit accident occurs.

A switch control circuit SC2 using a search coil 4 and a detection determination circuit 5 as shown in FIG. 5 can be used as a mechanism for opening and closing the switch SW by detecting an overcurrent in the event of an accident. In this case, the search coil 4
Captures a change in the current of the DC reactor DCL as a change in magnetic flux, and the detection and determination circuit 5 detects this change to open and close the switch SW.

[Embodiment 2] Another embodiment of the system interconnection device of the present invention will be described below with reference to FIGS. For convenience of explanation, components having the same functions as those shown in the drawings of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

In the first embodiment, AC reactor ACL
Has been described, but the same effect can be obtained by inserting a resistor instead of inserting the AC reactor ACL. 6 is an example in which a resistor R is inserted instead of the AC reactor ACL. It goes without saying that any mechanism of the switch control circuit SC1 in FIG. 1 and the switch control circuit SC2 in FIG. 5 may be employed as a mechanism for opening and closing the switch SW by detecting an overcurrent in the event of a short circuit.

FIG. 7 shows the current limiting operation of the system interconnection device 11. As can be seen from the figure, when the resistor R is inserted, there is a feature that the above-described superposition phenomenon of the direct current does not occur. However, since power loss occurs in the resistor R, this method is suitable for application to a system in which short-circuit accident recovery can be performed in a short time.

[0039]

According to the first aspect of the present invention, there is provided a grid interconnection device,
As described above, in a system interconnection device configured by connecting two power systems and connecting a DC reactor between two DC terminals of a single-phase rectification bridge circuit having a rectifier element, An AC reactor or a resistor is connected between a system and the single-phase rectification bridge circuit, and short-circuit means for short-circuiting both ends of the AC reactor or the resistor is provided.

Therefore, by opening the short-circuit means during the current limiting operation after the short-circuit accident has occurred in the power system,
An AC reactor or resistor can be inserted between the power system and the single-phase rectifier bridge circuit, and the increasing passing current can be limited by these reactances or resistances.

As a result, when an accident occurs in the power system, there is an effect that the overcurrent flowing through the system interconnection device due to the accident can be suppressed while the interconnections are maintained.

According to a second aspect of the present invention, there is provided the current limiting method for a grid interconnection device according to the first aspect of the present invention. When the passing current is equal to or less than a predetermined value so that the DC current does not overlap, the short-circuit means is opened and the AC reactor is inserted.

Therefore, when the short-circuit means is opened and the AC reactor is inserted, the DC current does not overlap with the passing current of the grid interconnection device.

As a result, there is an effect that the current of the system interconnection device can be limited without adversely affecting the connected power system.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an example of an electrical configuration of a grid interconnection device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram showing an example of a passing current at the time of current limiting of the system interconnection device of FIG. 1;

FIG. 3 is a waveform diagram showing another example of a passing current at the time of current limiting of the system interconnection device of FIG. 1;

FIG. 4 is a waveform diagram showing a passing current at the time of current limiting in a conventional grid interconnection device.

FIG. 5 is a circuit diagram showing an electrical configuration of another grid interconnection device according to an embodiment of the present invention.

FIG. 6 is a circuit diagram showing an electrical configuration of a system interconnection device according to another embodiment of the present invention.

FIG. 7 is a waveform diagram showing a passing current at the time of current limiting of the system interconnection device of FIG. 6;

FIG. 8 is a circuit diagram showing an electrical configuration of a conventional grid interconnection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Grid connection apparatus 2 Current transformer 3 Overcurrent relay 4 Search coil 5 Detection / judgment circuit 11 Grid connection apparatus D1 Diode (rectifying element) D2 Diode (rectifying element) D3 Diode (rectifying element) D4 Diode (rectifying element) ACL AC reactor DCL DC reactor R resistor SC1 switch control circuit SC2 switch control circuit SW switch (short circuit means)

Claims (2)

[Claims] 1. A system interconnection device comprising two power systems interconnected and a DC reactor connected between two DC terminals of a single-phase rectifier bridge circuit having a rectifier element,
An AC reactor or a resistor is connected between one of the power systems and the single-phase rectifier bridge circuit, and a short-circuit means for short-circuiting both ends of the AC reactor or the resistor is provided. Interconnection equipment. 2. The system according to claim 1, wherein the short-circuit means is opened and the AC reactor is inserted when the passing current is equal to or less than a predetermined value so that the DC current is not superimposed on the passing current of the grid interconnection device. The method for limiting a current of a grid interconnection device according to claim 1.