KR20180106357A - Reactive power compensation device - Google Patents

Abstract

A reactive power compensating apparatus according to an embodiment of the present invention includes a first STATCOM bank and a second STATCOM bank for receiving a compensation command received from a power system and outputting a reactive power compensation value corresponding to the received compensation command, a first current measuring unit for measuring a first line current at a connection point between the first STATCOM bank and a bus bar of the power system, a second current measuring unit for measuring a second line current at a connection point between the second STATCOM bank and the bus bar, and a controller for performing a protection operation of the reactive power compensating apparatus if the first line current is different from the second line current. Accordingly, the present invention can grasp whether or not a reactive power protecting apparatus normally operates.

Description

REACTIVE POWER COMPENSATION DEVICE [0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reactive power compensation apparatus, and more particularly, to a reactive power compensation apparatus.

The high voltage direct current (HVDC) system converts high voltage AC power generated by a power plant into high voltage direct current power using a power converter and then converts it into AC power using a power converter at the desired power receiving side. .

In this way, when DC power is transmitted, both the DC transmission system and the AC transmission system require compensation of the reactive power.

Reactive power is power that actually does nothing and does not consume heat. Reactive power can not actually be used because it is only generated when the power source and the electric equipment are reciprocated and no energy is generated.

If the reactive power consumption increases, the voltage may be too low during the power transmission, resulting in power failure or power cut-off. Therefore, it is necessary to appropriately compensate the reactive power in order to prevent the above situation from occurring.

To this end, reactive power compensation is used in the transmission system.

A static synchronous compensator (STATCOM) using an insulated gate bipolar transistor (IGBT) element is used as the reactive power compensating device.

The reactive power compensator can utilize a plurality of STATCOM banks to supply or absorb reactive power in the power system.

The conventional reactive power compensator detects the overcurrent or the overvoltage at one of the points and performs the protection operation.

However, when the protection operation is performed by measuring the current or the voltage only at one of the points, there is a problem that the protection operation is not performed even though the STATCOM bank having the delta wiring structure requiring balanced control does not operate normally .

As a result, a ground fault current or a leakage current is generated, and the reactive power compensation device is not properly protected.

The present invention is directed to solving the above-mentioned problems and other problems.

The present invention relates to a reactive power compensating apparatus including a STATCOM bank having a delta connection, which uses a difference current between two points to detect an abnormal state of the reactive power protecting apparatus and protect the reactive power compensating apparatus have.

An object of the present invention is to detect a difference current between two points in a reactive power compensating apparatus including a STATCOM bank having a delta connection so that a ground fault current or a leakage current is not generated.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not intended to limit the invention to the precise form disclosed. It can be understood.

The reactive power compensating apparatus according to an embodiment of the present invention includes a first STATCOM bank and a second STATCOM bank receiving a compensation command received from a power system and outputting a reactive power compensation value corresponding to a received compensation command, A first current meter for measuring a first line current at one STATCOM bank and a bus line connection point of the power system, a second current meter for measuring a second line current at the second STATCOM bank and the bus connection point, And a controller for performing a protection operation of the reactive power compensation device when the first line current and the second line current are different from each other.

Wherein each of the first STATCOM bank and the second STATCOM bank includes three three-phase clusters with delta connections, wherein the first line current corresponds to any one of the three-phase clusters included in the first STATCOM bank and its corresponding And the second line current is the current of any one of the three-phase clusters included in the second STATCOM bank and the corresponding second phase line interconnection point, The one-phase bus line and the second phase bus line may correspond to the same phase.

If the first line current and the second line current are not equal to each other, the controller may output a notification indicating that an abnormal state has occurred in the reactive power compensating device.

The controller may output the notification when the ratio of the first line current and the second line current exceeds a first reference ratio for a predetermined time or longer.

Wherein the controller is further configured to generate a trip signal for shutting off the power provided to the first STATCOM bank and the second STATCOM bank when the ratio of the first line current and the second line current exceeds the second reference ratio for a predetermined time or longer And the second reference rate may be greater than the first reference rate.

In accordance with another embodiment of the present invention, there is provided a reactive power compensator comprising: a plurality of STATCOM banks receiving a compensation command received from a power system and outputting a reactive power compensation value corresponding to a received compensation command; A second current meter for measuring a cluster current flowing in each of the STATCOM banks; a first current meter for measuring a line current of a connecting point between bus lines of the power system, And a controller for performing the protection operation of the reactive power compensating device, if different.

Wherein each STATCOM bank comprises three 3-phase clusters with delta connections, wherein the line current is the current of any one of the three-phase clusters included in each STATCOM bank and the corresponding bus interface connection point, The cluster current may be a current flowing in any one of the phase clusters.

The controller may generate a circulating current command to adjust the difference current to the predetermined current when the difference current is different from the predetermined current.

The controller can control the balance of the current flowing in each phase cluster by adjusting the difference current to the predetermined current.

The controller may output a notification indicating that an abnormal state has occurred in the reactive power compensating device when the difference between the line current and the cluster current is different from a predetermined current.

The controller can output the notification when the ratio of the difference current exceeds a first reference ratio for a predetermined time or longer.

Wherein the controller outputs a trip signal for shutting off the power provided to each STATCOM bank when the ratio of the difference current exceeds the second reference ratio for a predetermined time or longer, Lt; / RTI >

According to the embodiment of the present invention, in the reactive power compensating apparatus including the STATCOM bank having the delta connection, the difference current between the two points can be detected, so that it can be accurately grasped whether the reactive power protecting apparatus is operating normally.

According to the embodiment of the present invention, a ground fault current or a leakage current is not generated through differential current detection between two points, the life of the reactive power compensating device can be extended, and stable operation of the reactive power compensating device is possible.

1 is a block diagram illustrating a configuration of a reactive power compensating apparatus according to an embodiment of the present invention.
Fig. 2 is a single-phase connection diagram for explaining the configuration of the reactive power compensating apparatus according to the embodiment of Fig. 1;
3 is a three-phase wiring diagram illustrating the configuration of the reactive power compensating apparatus according to the embodiment of FIG.
4 is a flowchart illustrating an operation method of a reactive power compensator according to an embodiment of the present invention.
5 is a flowchart illustrating a method of operating a reactive power compensating apparatus according to another embodiment of the present invention.
6 is a view for explaining a method of a protection operation performed by a reactive power compensation device according to an embodiment of the present invention.
FIG. 7 is a power system including a reactive power compensator forming a delta connection according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the technical spirit of the present invention is not limited by the embodiments described below, and other degenerative inventions such as addition, change and deletion of another constituent element and other embodiments included in the technical idea of the present invention Examples can be easily suggested.

The terms used in the present invention are selected as general terms that are widely used in connection with the present technology as much as possible. However, in some cases, there are some terms selected arbitrarily by the applicant. Therefore, it should be understood in advance that the present invention should be grasped as a meaning of a term that is not a name of a simple term. In the following description, the word 'comprising' does not exclude the presence of other elements or steps than those listed.

1 is a block diagram illustrating a configuration of a reactive power compensating apparatus according to an embodiment of the present invention.

Referring to FIG. 1, a reactive power compensating apparatus 100 according to an embodiment of the present invention may include a power system monitoring unit 110, a STATCOM bank set 130, and a controller 150.

The power system monitoring unit 110 may monitor the power system 10. [

The power system monitoring unit 110 may measure at least one of voltage, current, and frequency of the power system 10. [

The power system monitoring unit 110 can measure the voltage of the power system 10 using a voltage meter (not shown) connected to the primary bus line. The voltage meter may be a power transformer (PT) that converts an alternating voltage into a direct voltage proportional thereto.

The power system monitoring unit 110 can measure the current of the power system 10 using the current meter 111 connected to the primary bus. A current transformer (CT) can be used to convert an alternating current into a direct current proportional thereto.

The power system monitoring unit 110 can measure the frequency of the power system 10 using a frequency meter (not shown) connected to the primary bus.

The STATCOM bank set 130 may include a plurality of STATCOM banks 131 and 133.

Each of the plurality of STATCOM banks 131 and 133 may output the reactive power compensation value under the control of the controller 150. [ Each of the plurality of STATCOM banks 131 and 133 may supply reactive power to the power system 10 or absorb reactive power from the power system 10 under the control of the controller 150.

Each of the plurality of STATCOM banks 131 and 133 may include a plurality of sub-modules.

Each sub-module may include a capacitor connected in parallel with four switching elements and four switching elements.

The switching device may include an insulated gate bipolar transistor (IGBT) and a diode.

Each of the sub modules 201 and 211 may have a full bridge type.

In yet another embodiment, each submodule may have a half bridge type using two switching elements.

Each of the plurality of STATCOM banks 131 and 133 may include a plurality of submodules and may supply active power or reactive power to the power system 10 through operation of the plurality of submodules.

The controller 150 can control the overall operation of the reactive power compensation apparatus 100. [

The controller 150 may obtain a compensation command for reactive power compensation from the power system 10. [

The controller 150 may control the operation of the plurality of STATCOM banks 131 and 133 to supply the power system 10 with the reactive power compensation value corresponding to the obtained compensation command.

Details of the operation of the controller 150 will be described later in detail.

The controller 150 may further include a memory (not shown) for storing information for each STATCOM bank.

The information for each STATCOM bank may include one or more of the total operating time of the STATCOM bank, the number of submodules contained in the STATCOM bank, and the number of failed submodules among the total number of submodules contained in the STATCOM bank.

The reactive power compensating apparatus 100 may further include a transformer 170 having a Y-delta (?) Connection, as shown in FIG. 2 to be described later.

Transformer 170 may be located between power system 10 and STATCOM bank set 130.

Transformer 170 may adjust the incoming voltage from power system 10 and deliver the regulated voltage to STATCOM bank set 130.

Hereinafter, the configuration of the reactive power compensating apparatus 100 according to the embodiment of FIG. 1 will be described in detail with reference to a wiring diagram.

Fig. 2 is a single-phase connection diagram for explaining the configuration of the reactive power compensating apparatus according to the embodiment of Fig. 1, and Fig. 3 is a three-phase connection diagram for explaining the configuration of the reactive power compensating apparatus according to the embodiment of Fig.

The single-phase wiring diagram of Fig. 2 includes a plurality of protective relay elements.

Each protective relay element can be identified numerically within a single-phase wiring diagram. Each of the digits may correspond to a relay element to be protected in the reactive power compensating apparatus 100 and the power system 10.

In the embodiment of the present invention, since the main current protection relay element corresponding to No. 87 among the plurality of protective relay elements is the main feature, it will be mainly described.

The secondary current protection relay element may be a relay element that protects the reactive power compensation device 100 by measuring the current difference between the two points.

The first STATCOM bank 131 includes a cluster 201 including a plurality of submodules, a first current meter 202 for measuring the current flowing into the cluster 201, an initial charge resistor 203, a bypass switch 204 and a reactor 205. [

The second current meter 206 may be provided separately from the first STATCOM bank 131.

The second current meter 206 may measure the line current at the connection point between the bus 250 and the first STATCOM bank 131. [

The second STATCOM bank 133 includes a cluster 211 that includes a plurality of submodules, a third current meter 212 that measures the current flowing into the cluster 211, an initial charge resistor 213, a bypass switch 214 and a reactor 215. [

The fourth current meter 216 may be provided separately from the second STATCOM bank 133.

The fourth current meter 216 may measure the line current at the connection point between the bus 250 and the second STATCOM bank 133. [

Next, the three-phase wiring diagram of the reactive power compensating apparatus 100 will be described with reference to Fig.

Referring to FIG. 3, a power system three-phase bus 300 may be connected to the first STATCOM bank 131 and the second STATCOM bank 133 having a delta structure.

The three-phase bus line 300 may be called a three-phase bus.

The three-phase bus line 300 may include a first phase bus line 301 corresponding to the R phase, a second phase bus line 303 corresponding to the S phase, and a third phase bus line 305 corresponding to the T phase.

The first STATCOM bank 131 may comprise first through third phase STATCOM banks 310, 320, 330.

The first to third phase STATCOM banks 310, 320, 330 may be connected to the delta wiring structure.

Each of the first to third phase STATCOM banks 310, 320, and 330 may include first to third phase clusters 311, 321, and 331, respectively.

Each of the first to third phase clusters 311, 321, and 331 may include a plurality of sub-modules connected in series.

The first phase STATCOM bank 310 may be coupled to the first phase line 301 and the second phase STATCOM bank 320 may be coupled to the second phase line 303 and the third phase STATCOM bank 330, May be connected to the third phase bus line (305).

The second STATCOM bank 133 may include fourth through sixth statcombanks 340, 350, 360.

The fourth through sixth STATCOM banks 340, 350, and 360 may be connected to the delta wiring structure.

Each of the fourth through sixth STATCOM banks 340, 350, and 360 may include each of the fourth through sixth phase clusters 341, 351, and 361.

Each of the fourth to sixth phase clusters 341, 351, and 361 may include a plurality of sub-modules connected in series.

The fourth phase STATCOM bank 340 may be coupled to the first phase bus 301 and the fifth phase STATCOM bank 350 may be coupled to the second phase bus 303 and the sixth phase STATCOM bank 360 may be coupled to the second phase bus 303. [ May be connected to the third phase bus line (305).

The controller 150 may perform a protection operation for protecting the reactive power compensation device 100 when an abnormal state occurs in the reactive power compensation device 100. [

For example, when the abnormal state occurs in the reactive power protection apparatus 100, the first line current and the second line current may not be the same.

For example, the first line current may be the current of the phase STATCOM bank included in the first STATCOM bank 131 and the corresponding first phase line interconnection point.

The second line current may be the current of one phase STATCOM bank included in the second STATCOM bank 133 and the corresponding second phase line interconnection point. Here, the first phase bus line and the second phase bus line correspond to the same phase.

As another example, when an abnormal state occurs in the reactive power protection device 100, the difference between the current of one phase STATCOM bank and its corresponding three-phase bus line connection point and the cluster current flowing in the phase STATCOM bank is A case where the current is not set can be shown.

Hereinafter, a process of detecting an abnormal state of the reactive power protection apparatus 100 and performing a protection operation according to the abnormal state will be described in detail.

4 is a flowchart illustrating an operation method of a reactive power compensator according to an embodiment of the present invention.

Hereinafter, an operation method of the reactive power compensating apparatus 100 of FIG. 4 will be described in connection with the embodiments of FIGS. 1 to 3. FIG.

Particularly, FIG. 4 shows an embodiment in which the protection operation of the reactive power compensating apparatus 100 is performed using the line retention measured at the connection point between each STATCOM bank and the bus line.

Referring to FIG. 4, the controller 150 of the reactive power compensating apparatus 100 measures a first line current of the connection point between the first STATCOM bank and the bus via the current meter (S401).

The controller 150 measures the second line current of the second STATCOM bank and the bus connection point through the current meter (S403).

The order of steps S401 and S403 may be reversed.

Steps S401 and S403 will be described with reference to Figs. 2 and 3. Fig.

2, the second current meter 206 may measure the first line current at a point A where the bus 250 and the first STATCOM bank 131 are connected.

Likewise, the fourth current meter 216 may measure the second line current at point B where the bus 250 and the second STATCOM bank 133 are connected.

This will be described in more detail with reference to the three-phase wiring diagram of Fig.

The current meter 323 can measure the first line current for the connection point C between the second phase STATCOM bank 320 and the second phase line 303. [

The current meter 353 can measure the second line current for the connection point D between the fifth phase STATCOM bank 350 and the second phase line 303. [

The measured first line current and the second line current may be transmitted to the controller 150 and monitored.

4 will be described again.

The controller 150 determines whether the measured first line current and the measured second line current are identical (S405).

When each of the first STATCOM bank 131 and the second STATCOM bank 133 outputs the same reactive power, the first line current and the second line current should be the same.

The same first line current and second line current may mean that the magnitude and phase of the current are the same.

The fact that the first line current and the second line current are not equal can be judged as an abnormal state has occurred.

If the first line current and the second line current are not the same, a leakage current and a ground fault current may be generated.

If the first line current and the second line current are not equal to each other, the controller 150 performs the protection operation of the reactive power compensating apparatus 100 (S407).

In one embodiment, the controller 150 may output an alarm indicating that an abnormal state has occurred in the reactive power compensating apparatus 100 when the first line current and the second line current are not equal.

Specifically, when the ratio of the first line current to the second line current is equal to or greater than the first reference ratio for a predetermined time or longer, the controller 150 may output an alarm indicating that an abnormal state has occurred in the reactive power compensating apparatus 100 have.

The first reference rate is 5%, and the predetermined time may be 10 seconds, but this is merely an example, and may vary depending on the setting.

In another embodiment, the controller 150 may output a trip signal when the first line current and the second line current are not the same. The trip signal may be a signal for interrupting the current or power provided to the first STATCOM bank 131 and the second STATCOM bank 133 due to an anomaly occurring in the reactive power compensator 100. [

In another embodiment, the controller 150 may output a trip signal when the ratio of the first line current to the second line current exceeds a second reference ratio for a predetermined time or more. The controller 150 may output a trip signal while outputting a notification.

Here, the second reference rate may be 10%, which is larger than the first reference rate, and the predetermined time may be 10 seconds, but this is merely an example, and may vary depending on the setting.

The reactive power compensating apparatus 100 may further include a circuit breaker (not shown) for interrupting the current or power provided to the first STATCOM bank 131 and the second STATCOM bank 133 according to the trip signal.

Next, Fig. 5 will be described.

5 is a flowchart illustrating a method of operating a reactive power compensating apparatus according to another embodiment of the present invention.

Particularly, FIG. 5 shows an embodiment in which the protection operation of the reactive power compensating apparatus 100 is performed using the cluster current flowing in each STATCOM bank and the line current flowing between each STATCOM bank and the three-phase bus line.

Referring to FIG. 5, the controller 150 of the reactive power compensating apparatus 100 measures the line current of the connection point between the STATCOM bank and the bus via the current measuring device (S501).

The controller 150 measures the cluster current which is the internal current of the STATCOM bank through the current meter (S503).

The order of steps S501 and S503 may be reversed.

Steps S501 and S503 will be described with reference to Figs. 2 and 3. Fig.

Referring to the single-phase wiring diagram of FIG. 2, the third current meter 212 can measure the cluster current, which is the current flowing into the cluster 211.

In addition, the fourth current meter 216 can measure the line current at the point B where the bus bar 250 and the second STATCOM bank 133 are connected.

This will be described in more detail with reference to the three-phase wiring diagram of Fig.

In FIG. 3, a sixth phase STATCOM bank 360 will be described as an example.

The current meter 363 can measure the line current for the connection point E between the sixth phase STATCOM bank 360 and the third phase bus line 305. [

The current measurer 365 can measure the cluster current flowing at one point F in the sixth phase cluster 361. [

5 is described again.

The controller 150 acquires a difference current indicating a difference between the measured line current and the cluster current (S505).

The controller 150 determines whether the difference current is equal to the predetermined current (S507).

In one embodiment, the predetermined current may refer to a current whose magnitude is root 3 and whose phase is 30 degrees.

The controller 150 performs the protection operation of the reactive power compensating apparatus 100 when the difference current is not equal to the predetermined current (S509).

The controller 150 can determine that an unbalance has occurred in the internal current of each phase cluster when the difference current is not a current having a predetermined magnitude and phase.

In one embodiment, the controller 150 can perform a protection operation using a circulating current control scheme when the difference current does not have a predetermined magnitude and phase.

The circulating current control method controls the current flowing in each phase cluster to be balanced.

The controller 150 can generate a circulating current command to adjust the difference current to a predetermined current when the difference current is different from the predetermined current.

A circulating current control method of generating a circulating current command and controlling the current flowing in each phase cluster will be described later.

In another embodiment, the controller 150 can output an alarm signal when the difference current exceeds a preset reference current for a certain period of time or more and deviates from the first reference ratio.

The first reference rate is 5%, and the predetermined time may be 10 seconds, but this is merely an example, and may vary depending on the setting.

In another embodiment, the controller 150 can output a trip signal when the difference current exceeds a preset reference current for a predetermined time or more and deviates from the second reference ratio.

Here, the second reference rate may be 10%, which is larger than the first reference rate, and the predetermined time may be 10 seconds, but this is merely an example, and may vary depending on the setting.

The trip signal may be a signal to interrupt the current or power provided to the first STATCOM bank 131 and the second STATCOM bank 133.

The reactive power compensating apparatus 100 may further include a circuit breaker (not shown) for interrupting the current or power provided to the first STATCOM bank 131 and the second STATCOM bank 133 according to the trip signal.

As described above, according to the embodiment of the present invention, the abnormal state of the reactive power compensator 100 is detected by using the cluster current flowing in each STATCOM bank and the line current flowing between each STATCOM bank and the three- The protection operation can be performed quickly and efficiently.

6 is a view for explaining a method of a protection operation performed by a reactive power compensation device according to an embodiment of the present invention.

Referring to FIG. 6, a method for protecting the reactive power compensating apparatus 100 may include a circulating current control, an alarm output, and a trip signal output.

The alarm output and the trip signal output may be methods applicable to the protection method of the reactive power compensating apparatus 100 described in the embodiment of FIG.

The circulating current control, the alarm output, and the trip signal output may be methods applicable to the protection operation of the reactive power compensating apparatus 100 described in the embodiment of FIG.

Hereinafter, when an unbalance occurs in each STATCOM bank using the cluster current flowing in each STATCOM bank and the line current flowing between each STATCOM bank and the three-phase bus line, the reactive power compensator 100 is controlled through the circulating current control, As shown in Fig.

FIG. 7 is a power system including a reactive power compensator forming a delta connection according to an embodiment of the present invention.

In FIG. 7, the first STATCOM bank 131 of the three-phase wiring diagram of FIG. 3 will be described as an example.

Referring to FIG. 7, the first STATCOM bank 131 can compensate for the reactive power required in the power system.

A first phase STATCOM bank 310, a second phase STATCOM bank 320 and a third phase STATCOM bank 330 can be connected to each of the R phase, S phase and T phase buses 301, 303 and 305 of the power system have.

Specifically, the first phase cluster 311 is connected between the first node n1 and the second node n2, the second phase cluster 321 is connected between the second node n2 and the third node n3, And the third cluster 331 may be connected between the third node n3 and the first node n1.

In the following, it is assumed that the output of the described equation can be calculated by the controller 150. [

When the first to third phase clusters 311, 321 and 331 are constituted by delta wiring, the voltage applied to the first phase cluster 311 is VCab and the voltage applied to the second phase cluster 321 is VCbc , And the voltage applied to the third phase cluster 331 may be VCca. VCab, VCbc, and VCca can be expressed by Equation (1).

[Equation 1]

Here, Vm + is the magnitude of the normal component and Vm- may be the magnitude of the component of the opposite phase component. Further,? V + is the phase of the normal component and? V- can be the phase of the component of the opposite phase component.

VCab, VCbc, and VCca may each have a waveform of an AC voltage including a normal component (Vm +,? V +) and a reverse component (Vm-,? V-).

At this time, the voltages VCab, VCbc, and VCca applied to the respective phase clusters 311, 321, and 331 do not include image components. This is because, in the delta connection structure, the image minute component, that is, the image minute voltage (V0), does not exist.

The current flowing in the first phase cluster 311 is iCab, the current flowing in the second phase cluster 321 is iCbc, and the current flowing in the third phase cluster 331 may be iCca.

Each of iCab, iCbc, and iCca may be expressed by Equation (2).

&Quot; (2) "

Here, Im + is the magnitude of the normal component, Im- is the magnitude of the inverse component, and Imo may be the magnitude of the image component. Also, φi + is the phase of the normal component, φi is the phase of the anti-phase component, and φ0 is the phase of the image component.

Each of iCab, iCbc and iCca may have a waveform of alternating current including a normal component (Im +,? i +), a reverse component (Im-,? -) and an image component (Imo,? 0).

The end terms of Equation (2) represent the image minute current, which may physically refer to the circulating current. The circulating current may be a component injected for leg balance control of the system.

Since the control of the circulating current is required for the balance control, the average effective power of the DC component generated by the leg output voltages VCab, VCbc, and VCca of each phase can be expressed by Equation (3).

&Quot; (3) "

Equation (3) can be expressed by Equation (4) as a power equation for each phase cluster.

&Quot; (4) "

Equation (4) represents the average effective power for each phase cluster.

The three average active powers must have the same value to balance the internal current of the delta wiring. That is, the object of the circulating current control is to control the values of the above three average effective powers to the same value.

In order to simplify the control, the equation (4) is converted into the stationary coordinate system, as shown in Equations (5) and (6).

&Quot; (5) "

&Quot; (6) "

The power of the stationary coordinate system generated by the circulating current is calculated by using the synchronous coordinate system dq of the leg output voltages VCab, VCbc, and VCca and the leg currents iCab, iCbc, and iCca .

,

값은 영상분 성분이므로 그 자체로는 좌표변환을 적용할 수 없다. 하지만, 기준 좌표계의 위상과 일치 시켜, 가상의 2상 변수를 동기좌표축으로 변환하여 등가직류제어의 문제로 치환하는 방식을 적용하였다.On the other hand,

,

Since the value is a fractional component, coordinate transformation can not be applied by itself. However, the method of converting the virtual two - phase variable into the synchronous coordinate axis and replacing it with the problem of the equivalent DC control is applied in accordance with the phase of the reference coordinate system.

Equations (5) and (6) can be expressed in matrix form as shown in Equation (7).

&Quot; (7) "

To obtain the circulating current command, taking the inverse matrix of Equation (7), it can be expressed as Equation (8), and the determinant is as shown in Equation (9).

&Quot; (8) "

&Quot; (9) "

As shown in Equation (9), if the normal voltage and the reverse phase voltage are the same, the determinant is zero, so that the circulating current command becomes infinite, and the controller can diverge.

The output value of the controller 150 for leg balance control using Equation (8) can be converted into the circulating current command io * in the same manner as in Equation (10).

&Quot; (10) "

The controller 150 outputs the circulation current command io * to the first to third phase clusters 311, 321 and 331 to control the first to third phase clusters 311, 321 and 331 equally .

That is, the controller 150 can prevent the imbalance of the current flowing in the first to third phase clusters 311, 321, and 331 using the circulating current command io *.

The present invention described above can be embodied as computer-readable codes on a medium on which a program is recorded. The computer readable medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of the computer readable medium include a hard disk drive (HDD), a solid state disk (SSD), a silicon disk drive (SDD), a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk, .

The foregoing detailed description should not be construed in all aspects as limiting and should be considered illustrative. The scope of the present invention should be determined by rational interpretation of the appended claims, and all changes within the scope of equivalents of the present invention are included in the scope of the present invention.

Claims (12)

A reactive power compensating apparatus comprising:
A first STATCOM bank and a second STATCOM bank receiving the compensation command received from the power system and outputting a reactive power compensation value corresponding to the received compensation command;
A first current meter for measuring a first line current of the first STATCOM bank and a bus line connection point of the power system;
A second current meter for measuring a second line current of the second STATCOM bank and the bus connection point; And
And a controller for performing a protection operation of the reactive power compensation device when the first line current and the second line current are different from each other
Reactive power compensation device. The method according to claim 1,
Wherein each of the first STATCOM bank and the second STATCOM bank includes three three-phase clusters with delta connections,
Wherein the first line current is a current of any one of the three phase clusters included in the first STATCOM bank and a corresponding first phase line interconnection point,
Wherein the second line current is the current of any one of the three phase clusters included in the second STATCOM bank and the corresponding second phase line interconnection point,
Wherein the first phase bus line and the second phase bus line correspond to the same phase
Reactive power compensation device. 3. The method of claim 2,
The controller
When the first line current and the second line current are not equal to each other, a notification indicating that an abnormal state has occurred in the reactive power compensation device is outputted
Reactive power compensation device. The method of claim 3,
The controller
When the ratio of the first line current and the second line current exceeds a first reference ratio for a predetermined time or longer,
Reactive power compensation device. 5. The method of claim 4,
The controller
And outputs a trip signal for shutting off the power provided to the first STATCOM bank and the second STATCOM bank when the ratio of the first line current and the second line current exceeds the second reference ratio for a predetermined time or more,
Wherein the second reference rate is greater than the first reference rate
Reactive power compensation device. A reactive power compensating apparatus comprising:
A plurality of STATCOM banks receiving a compensation command received from the power system and outputting a reactive power compensation value corresponding to the received compensation command;
A first current meter for measuring a line current at a connection point between each STATCOM bank and a bus line of the power system;
A second current meter for measuring a cluster current flowing in each of the STATCOM banks; And
And a controller for performing a protection operation of the reactive power compensation device when the difference current between the line current and the cluster current is different from a predetermined current
Reactive power compensation device. The method according to claim 6,
Each STATCOM bank comprising three 3-phase clusters with delta connections,
Wherein the line current is a current of any one of the three-phase clusters included in each STATCOM bank and a bus-line connection point of a corresponding phase,
Wherein the cluster current is a current flowing in one of the phase clusters
Reactive power compensation device. 8. The method of claim 7,
The controller
Generates a circulating current command when the difference current is different from the predetermined current, and adjusts the difference current to the predetermined current
Reactive power compensation device. 8. The method of claim 7,
The controller
And controls the balance of the current flowing in each phase cluster by adjusting the difference current to the predetermined current
Reactive power compensation device. 8. The method of claim 7,
The controller
When the differential current between the line current and the cluster current is different from the predetermined current, an alarm indicating that an abnormal state has occurred in the reactive power compensating device is outputted
Reactive power compensation device. 11. The method of claim 10,
The controller
When the ratio of the difference current exceeds the first reference ratio for a predetermined time or more,
Reactive power compensation device. 12. The method of claim 11,
The controller
And outputs a trip signal for shutting off power provided to each STATCOM bank when the ratio of the difference current exceeds a second reference ratio for a predetermined time or more,
Wherein the second reference rate is greater than the first reference rate
Reactive power compensation device.

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