KR102369644B1 - Reactive power compensation device - Google Patents

Abstract

Reactive power compensation apparatus according to an embodiment of the present invention receives a compensation command received from a power system, and outputs a reactive power compensation value corresponding to the received compensation command, the first STATCOM bank and the second STATCOM bank and the second 1 STATCOM bank and a first current measuring instrument for measuring a first line current of the connection point between the bus bar of the power system, and a second current measuring instrument for measuring a second line current at the connecting point between the second STATCOM bank and the bus bar, and the When the first line current and the second line current are different, it may include a controller for performing a protection operation of the reactive power compensator.

Description

Reactive power compensation device {REACTIVE POWER COMPENSATION DEVICE}

The present invention relates to a reactive power compensating device, and more particularly, to a reactive power compensating device.

The High Voltage Direct Current (HVDC) system converts high-voltage AC power produced at the power plant into high-voltage DC power using a power converter and transmits it, then converts it back to AC power using a power converter at the desired power receiving side It is a system that provides

As such, when transmitting DC power, both the DC transmission system and the AC transmission system require compensation of reactive power.

Reactive power is power that does not actually do anything and consumes no heat. Reactive power only goes back and forth between the power source and the electrical equipment, and cannot be used in practice because no energy is generated.

If reactive power consumption increases, the voltage may become too low during the transmission process, resulting in a power outage or power cut-off. Therefore, it is necessary to properly compensate reactive power to prevent the above situation from occurring.

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

As the reactive power compensator, a static synchronous compensator (STATCOM) using an insulated gate bipolar transistor (IGBT) device is used.

The reactive power compensation device may supply or absorb reactive power to the power system by using a plurality of STATCOM banks.

A conventional reactive power compensation device detects an overcurrent or an overvoltage for any one point, and performs a protection operation.

However, when the protection operation is performed by measuring the current or voltage only at one point, there is a problem that the protection operation is not performed even though the STATCOM bank having a delta connection structure that requires balance control does not operate normally. .

Accordingly, there is a problem in that a ground fault current or a leakage current is generated, and the reactive power compensating device is not properly protected.

SUMMARY OF THE INVENTION The present invention aims to solve the above and other problems.

The present invention uses the difference current between two points in a reactive power compensation device including a STATCOM bank having a delta connection, to detect an abnormal state of the reactive power protection device, and to protect the reactive power compensation device there is.

An object of the present invention is to prevent a ground fault or leakage current from occurring by detecting a difference current between two points in a reactive power compensation device including a STATCOM bank having a delta connection.

The technical problems to be achieved in the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned are clear to those of ordinary skill in the art to which the embodiments proposed by the description below belong. can be understood clearly.

Reactive power compensation apparatus according to an embodiment of the present invention receives a compensation command received from a power system, and outputs a reactive power compensation value corresponding to the received compensation command, the first STATCOM bank and the second STATCOM bank and the second 1 STATCOM bank and a first current measuring instrument for measuring a first line current of the connection point between the bus bar of the power system, and a second current measuring instrument for measuring a second line current at the connecting point between the second STATCOM bank and the bus bar, and the When the first line current and the second line current are different, it may include a controller for performing a protection operation of the reactive power compensator.

Each of the first STATCOM bank and the second STATCOM bank includes three three-phase clusters having a delta connection, and the first line current corresponds to any one of the three-phase clusters included in the first STATCOM bank and corresponding thereto. is a current of a connection point between the first phase busbars, and the second line current is a current of a connection point between any one of the three-phase clusters included in the second STATCOM bank and a corresponding second phase bus connection point, The first phase bus bar and the second phase bus bar may correspond to the same phase.

When the first line current and the second line current are not the same, the controller may output a notification indicating that an abnormal state has occurred in the reactive power compensation device.

The controller may output the notification when the ratio of the first line current to the second line current is out of the first reference ratio for more than a predetermined time.

When the ratio of the first line current to the second line current deviates from a second reference ratio for more than a predetermined time, the controller generates a trip signal for cutting off the power provided to the first STATCOM bank and the second STATCOM bank. output, and the second reference ratio may be greater than the first reference ratio.

Reactive power compensation apparatus according to another embodiment of the present invention receives a compensation command received from a power system, and outputs a reactive power compensation value corresponding to the received compensation command a plurality of STATCOM banks and each STATCOM bank and the A first current meter for measuring the line current at the connection point between the busbars of the power system, a second current meter for measuring the cluster current flowing inside each STATCOM bank, and a current in which the difference current between the line current and the cluster current is preset If different from, it may include a controller for performing a protective operation of the reactive power compensation device.

Each STATCOM bank includes three three-phase clusters having a delta connection, and the line current is a current of a connection point between any one of the three-phase clusters included in each STATCOM bank and a bus bar of the corresponding phase, The cluster current may be a current flowing inside the one of the phase clusters.

When the difference current is different from the preset current, the controller may generate a circulating current command to adjust the difference current to the preset current.

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

When the difference current between the line current and the cluster current is different from a preset current, 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 difference current is out of the first reference ratio for more than a predetermined time.

The controller outputs a trip signal for cutting off the power provided to each STATCOM bank when the ratio of the difference current is out of a second reference ratio for more than a predetermined time, and the second reference ratio is the first reference ratio can be larger than

According to an embodiment of the present invention, in a reactive power compensation device including a STATCOM bank having a delta connection, by detecting a difference current between two points, it can be accurately identified whether the reactive power protection device operates normally.

According to an embodiment of the present invention, no ground fault current or leakage current is generated through the detection of a difference current between two points, so that the lifespan 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 for explaining the configuration of a reactive power compensation apparatus according to an embodiment of the present invention.
FIG. 2 is a single-phase connection diagram illustrating the configuration of the reactive power compensation device according to the embodiment of FIG. 1 .
3 is a three-phase connection diagram illustrating the configuration of the reactive power compensation device according to the embodiment of FIG. 1 .
4 is a flowchart for explaining a method of operating a reactive power compensation apparatus according to an embodiment of the present invention.
5 is a flowchart for explaining a method of operating a reactive power compensation apparatus according to another embodiment of the present invention.
6 is a view for explaining a method of a protection operation performed by the reactive power compensation apparatus according to an embodiment of the present invention.
7 is a power system having a reactive power compensation device forming a delta connection according to an embodiment of the present invention.

Hereinafter, specific 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 inventions that are degenerate by addition, change, and deletion of other components or other implementations included within the scope of the technical spirit of the present invention Examples can easily be suggested.

As for the terms used in the present invention, general terms that are currently widely used in relation to the current technology are selected as possible, but in special cases, there are also terms arbitrarily selected by the applicant, and in this case, the meaning is described in detail in the description of the corresponding invention. Therefore, it is clarified in advance that the present invention should be understood as the meaning of the term rather than the simple name of the term. In the description set forth below, the word 'comprising' does not exclude the presence of elements or steps other than those listed.

1 is a block diagram for explaining the configuration of a reactive power compensation apparatus according to an embodiment of the present invention.

Referring to FIG. 1 , the reactive power compensation 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 one or more of a voltage, a current, and a frequency of the power system 10 .

The power system monitoring unit 110 may measure the voltage of the power system 10 by using a voltage measuring device (not shown) connected to the primary side bus. As the voltage measuring device, a power transformer (PT) that converts an AC voltage into a DC voltage proportional thereto may be used.

The power system monitoring unit 110 may measure the current of the power system 10 by using the current measuring device 111 connected to the primary side bus. As the current measuring device, a current transformer (CT) that converts an alternating current into a direct current proportional thereto may be used.

The power system monitoring unit 110 may measure the frequency of the power system 10 by using a frequency measuring device (not shown) connected to the primary side bus.

STATCOM bank set 130 may include a plurality of STATCOM banks (131, 133).

Each of the plurality of STATCOM banks 131 and 133 may output a 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 four switching elements and a capacitor connected in parallel with the four switching elements.

The switching element 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 another embodiment, each sub-module 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 sub-modules, and may supply active power or reactive power to the power system 10 through the operation of the plurality of sub-modules.

The controller 150 may 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 reactive power compensation value corresponding to the acquired compensation command to the power system 10 .

A detailed operation of the controller 150 will be described later.

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

Information on each STATCOM bank may include one or more of the total operating time of the STATCOM bank, the number of sub-modules included in the STATCOM bank, and the number of faulty sub-modules among the total number of sub-modules included in the STATCOM bank.

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

The transformer 170 may be located between the power grid 10 and the STATCOM bank set 130 .

The transformer 170 may adjust the voltage introduced from the power system 10 , and transmit the adjusted voltage to the STATCOM bank set 130 .

Hereinafter, the configuration of the reactive power compensation apparatus 100 according to the embodiment of FIG. 1 will be described in detail using a connection diagram.

FIG. 2 is a single-phase connection diagram illustrating the configuration of the reactive power compensation device according to the embodiment of FIG. 1 , and FIG. 3 is a three-phase connection diagram illustrating the configuration of the reactive power compensation device according to the embodiment of FIG. 1 .

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

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

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

The differential current protection relay element may be a relay element that measures a current difference between two points to protect the reactive power compensation apparatus 100 .

The first STATCOM bank 131 includes a cluster 201 including a plurality of sub-modules, a first current meter 202 for measuring the current flowing into the cluster 201, an initial charging resistor 203, and 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 measuring device 206 may measure a line current of a connection point between the bus bar 250 and the first STATCOM bank 131 .

The second STATCOM bank 133 includes a cluster 211 including a plurality of sub-modules, a third current meter 212 for measuring the current flowing into the cluster 211, an initial charging resistor 213, and 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 measuring device 216 may measure a line current of a connection point between the bus bar 250 and the second STATCOM bank 133 .

Next, a three-phase connection diagram of the reactive power compensation apparatus 100 will be described with reference to FIG. 3 .

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

The three-phase bus 300 may be referred to as a three-phase bus.

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

The first STATCOM bank 131 may include first to three-phase STATCOM banks 310 , 320 , and 330 .

The first to three-phase STATCOM banks 310 , 320 , and 330 may be connected in a delta connection structure.

Each of the first to three-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 connected to the first phase busbar 301 , the second phase STATCOM bank 320 may be connected to the second phase busbar 303 , and the third phase STATCOM bank 330 may be connected to the second phase busbar 303 . may be connected to the third phase bus bar 305 .

The second STATCOM bank 133 may include fourth to sixth phase STATCOM banks 340 , 350 , and 360 .

The fourth to sixth phase STATCOM banks 340 , 350 , and 360 may be connected in a delta connection structure.

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

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 connected to the first phase bus line 301 , the fifth phase STATCOM bank 350 may be connected to the second phase bus line 303 , and the sixth phase STATCOM bank 360 . may be connected to the third phase bus bar 305 .

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

As an example, the case in which an abnormal state occurs in the reactive power protection device 100 may indicate a case in which the first line current and the second line current are not the same.

For example, the first line current may be a current of a connection point between a phase STATCOM bank included in the first STATCOM bank 131 and a first phase bus corresponding thereto.

The second line current may be a current of a connection point between the one-phase STATCOM bank included in the second STATCOM bank 133 and a second phase bus corresponding thereto. Here, the first phase bus bar and the second phase bus bar correspond to the same phase.

As another example, when an abnormal state occurs in the reactive power protection device 100, the difference current between the current at the connection point between one phase STATCOM bank and the corresponding three-phase bus bar and the cluster current flowing inside the phase STATCOM bank is It may indicate a case where the current is not set.

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

4 is a flowchart for explaining a method of operating a reactive power compensation apparatus according to an embodiment of the present invention.

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

In particular, FIG. 4 is an embodiment of performing the protection operation of the reactive power compensation device 100 by using the line storage measured at the connection point between each STATCOM bank and the bus.

Referring to FIG. 4 , the controller 150 of the reactive power compensation device 100 measures the first line current of the connection point between the first STATCOM bank and the bus bar through a current measuring device (S401).

The controller 150 measures the second line current of the connection point between the second STATCOM bank and the bus through the current measuring device (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 .

First, referring to the single-phase wiring diagram of 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.

Similarly, the fourth current measuring device 216 may measure the second line current at the point (B) where the bus bar 250 and the second STATCOM bank 133 are connected.

This time, with reference to the three-phase connection diagram of FIG. 3, it will be described in more detail.

The current measuring device 323 may measure the first line current for the connection point C between the second phase STATCOM bank 320 and the second phase bus 303 .

The current measuring device 353 may measure a second line current for the connection point D between the fifth phase STATCOM bank 350 and the second phase bus 303 .

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

Fig. 4 will be described again.

The controller 150 determines whether the measured first line current and the second line current are the same (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 must be the same.

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

If the first line current and the second line current are not the same, it may be determined that an abnormal state has occurred.

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

When the first line current and the second line current are not the same, the controller 150 performs the protection operation of the reactive power compensation device 100 (S407).

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

Specifically, the controller 150 may output an alarm indicating that an abnormal state has occurred in the reactive power compensation device 100 when the ratio of the first line current and the second line current is equal to or greater than the first reference ratio for a certain period of time or more. there is.

The first reference ratio is 5%, and the predetermined time may be 10 seconds, but this is only an example and may vary according to settings.

In another embodiment, when the first line current and the second line current are not the same, the controller 150 may output a trip signal. The trip signal may be a signal for blocking current or power provided to the first STATCOM bank 131 and the second STATCOM bank 133 when an abnormal state occurs in the reactive power compensation device 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 deviates from the 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 ratio may be 10% greater than the first reference ratio, and the predetermined time may be 10 seconds, but this is only an example and may vary according to settings.

The reactive power compensation apparatus 100 may further include a circuit breaker (not shown) to block 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 for explaining a method of operating a reactive power compensation apparatus according to another embodiment of the present invention.

In particular, FIG. 5 shows an embodiment in which a protection operation of the reactive power compensation device 100 is performed using a cluster current flowing inside each STATCOM bank and a line current flowing between each STATCOM bank and a three-phase bus.

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

The controller 150 measures the cluster current that 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 .

Referring to the single-phase connection diagram of FIG. 2 , the third current measuring device 212 may measure a cluster current that is a current flowing into the cluster 211 .

In addition, the fourth current measuring device 216 may measure the line current at the point (B) where the bus bar 250 and the second STATCOM bank 133 are connected.

This time, with reference to the three-phase connection diagram of FIG. 3, it will be described in more detail.

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

The current measuring device 363 may measure a line current for the connection point E between the sixth phase STATCOM bank 360 and the third phase bus 305 .

The current meter 365 may measure a cluster current flowing at a point F inside the sixth phase cluster 361 .

Fig. 5 will be described again.

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

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

In an embodiment, the preset current may mean a current having a magnitude of root 3 and a phase of 30 degrees.

When the difference current is not the same as the preset current, the controller 150 performs a protective operation of the reactive power compensation apparatus 100 (S509).

When the difference current is not a current having a preset magnitude and phase, the controller 150 may determine that an imbalance has occurred in the internal current of each phase cluster.

In an embodiment, when the difference current does not have a preset magnitude and phase, the controller 150 may perform a protection operation using a circulating current control method.

The circulating current control method is a method of controlling the current flowing inside each phase cluster to be balanced.

When the difference current is different from the preset current, the controller 150 may generate a circulating current command to adjust the differential current to the preset current.

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

In another embodiment, the controller 150 may output an alarm signal when the difference current is out of the first reference ratio compared to the preset current for a predetermined time or more.

The first reference ratio is 5%, and the predetermined time may be 10 seconds, but this is only an example and may vary according to settings.

In another embodiment, the controller 150 may output a trip signal when the difference current is out of the second reference ratio compared to the preset current for a predetermined time or more.

Here, the second reference ratio may be 10% greater than the first reference ratio, and the predetermined time may be 10 seconds, but this is only an example and may vary according to settings.

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

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

As such, according to an embodiment of the present invention, by using the cluster current flowing inside each STATCOM bank and the line current flowing between each STATCOM bank and the three-phase bus bar, the abnormal state of the reactive power compensation device 100 is detected, In this regard, the protection operation can be performed quickly and efficiently.

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

Referring to FIG. 6 , a method for protecting the reactive power compensation 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 compensation apparatus 100 described in the embodiment of FIG. 4 .

The circulating current control, alarm output, and trip signal output may be methods applicable to the protection operation of the reactive power compensation apparatus 100 described in the embodiment of FIG. 5 .

Hereinafter, by using the cluster current flowing inside each STATCOM bank and the line current flowing between each STATCOM bank and the three-phase bus, when an imbalance occurs inside each STATCOM bank, the reactive power compensation device 100 through circulating current control An example of protecting

7 is a power system having a reactive power compensation device forming a delta connection according to an embodiment of the present invention.

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

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

A first phase STATCOM bank 310, a second phase STATCOM bank 320, and a third phase STATCOM bank 330 may be connected to each of the R-phase, S-phase, and T-phase busbars 301, 303, 305 of the power system. there is.

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

Hereinafter, 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 configured in a delta connection, the voltage applied to the first phase cluster 311 is VCab, and the voltage applied to the second phase cluster 321 is VCbc, , the voltage applied to the third phase cluster 331 may be VCca. VCab, VCbc, and VCca may be expressed as in Equation (1).

[Equation 1]

Here, Vm+ may be the magnitude of the normal component, and Vm− may be the magnitude of the inverse component. Also, φv+ may be a phase of a normal component, and φv− may be a phase of an inverse component.

Each of VCab, VCbc, and VCca may have a waveform of an AC voltage including a positive component (Vm+, φv+) and an inverse component component (Vm−, φv−).

At this time, the voltages VCab, VCbc, and VCca applied to each of the phase clusters 311 , 321 , and 331 do not include an image component. This is because, in the delta connection structure, a zero component component, that is, a zero component voltage V0 does not exist.

A current flowing through the first phase cluster 311 may be iCab, a current flowing through the second phase cluster 321 may be iCbc, and a current flowing through the third phase cluster 331 may be iCca.

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

[Equation 2]

Here, Im+ may be the size of the normal component, Im− may be the size of the inverse component, and Imo may be the size of the zero component. Also, φi+ may be the phase of the normal component, φi− may be the phase of the inverse component, and φ0 may be the phase of the zero component.

Each of iCab, iCbc, and iCca may have a waveform of an alternating current including a positive component (Im+, φi+), an inverse component component (Im-, φi-), and a zero component component (Imo, φ0).

The last terms of Equation 2 represent zero current, and may physically mean circulating current. The circulating current may be a component injected for leg balance control of the system.

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

[Equation 3]

If Equation 3 is expressed as a power expression for each phase cluster, Equation 4 is obtained.

[Equation 4]

Equation 4 represents the average active power for each phase cluster.

If the three average active powers have the same value, the internal current of the delta connection can be balanced. That is, the purpose of circulating current control is to control the above three average active power values to the same value.

When Equation 4 is converted to a stationary coordinate system for the sake of simplification of control, Equations 5 and 6 are obtained.

[Equation 5]

[Equation 6]

As shown in Equations 5 and 6, the power of the stationary coordinate system created by the circulating current is generated using the synchronous coordinate system dq value of the leg output voltages (VCab, VCbc, and VCca) and the leg currents (iCab, iCbc, and iCca). can be arranged in this way.

,

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, the circulating current

,

Since the value is an image component, coordinate transformation cannot be applied by itself. However, by matching the phase of the reference coordinate system, a method of replacing the virtual two-phase variable with the synchronous coordinate axis to the problem of equivalent DC control was applied.

When Equations 5 and 6 are expressed in a matrix form, it can be expressed as Equation 7 below.

[Equation 7]

In order to obtain the circulating current command, if the inverse matrix of Equation 7 is taken, it can be expressed as Equation 8, and the determinant is equal to Equation 9.

[Equation 8]

[Equation 9]

As shown in Equation 9, if the positive-sequence voltage and the negative-sequence voltage are the same, the determinant is 0, so 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) may be converted into a circulating current command (io*) in the same manner as in Equation (10).

[Equation 10]

The controller 150 may output the circulating current command io* to the first to three-phase clusters 311 , 321 , and 331 to uniformly control the first to three-phase clusters 311 , 321 , and 331 . .

That is, the controller 150 may prevent an imbalance of current flowing inside each of the first to third phase clusters 311 , 321 , and 331 by using the circulating current command io*.

The present invention described above can be implemented as computer-readable codes on a medium in which a program is recorded. The computer-readable medium includes all types of recording devices in which data readable by a computer system is stored. Examples of computer-readable media include Hard Disk Drive (HDD), Solid State Disk (SSD), Silicon Disk Drive (SDD), ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage device, etc. There is this.

The above detailed description should not be construed as restrictive in all respects and should be considered as exemplary. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the equivalent scope of the present invention are included in the scope of the present invention.

Claims (12)

In the reactive power compensation device,
a first STATCOM bank and a second STATCOM bank for 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 first line current of a connection point between the first STATCOM bank and a bus bar of the power system;
a second current meter for measuring a second line current of a connection point between the second STATCOM bank and the bus bar; and
When the first line current and the second line current are different, comprising a controller for performing a protection operation of the reactive power compensator,
the controller
Outputting a notification indicating that an abnormal state has occurred in the reactive power compensation device when the ratio of the first line current and the second line current is out of the first reference ratio for more than a predetermined time
Reactive power compensation device. According to claim 1,
Each of the first STATCOM bank and the second STATCOM bank comprises three three-phase clusters having a delta connection,
The first line current is a current of a connection point between any one of the three-phase clusters included in the first STATCOM bank and the corresponding first phase bus,
The second line current is a current of a connection point between any one of the three-phase clusters included in the second STATCOM bank and a corresponding second-phase bus bar,
The first phase bus bar and the second phase bus bar correspond to the same phase
Reactive power compensation device. delete delete 3. The method of claim 2,
the controller
When the ratio of the first line current to the second line current deviates from a second reference ratio for more than a predetermined time, a trip signal for cutting off the power provided to the first STATCOM bank and the second STATCOM bank is output;
the second reference ratio is greater than the first reference ratio
Reactive power compensation device. In the reactive power compensation device,
a plurality of STATCOM banks for 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 bar of the power system;
a second current meter for measuring the cluster current flowing inside each of the STATCOM banks; and
When the difference current between the line current and the cluster current is different from a preset current, a controller configured to protect the reactive power compensator,
the controller
Outputting a notification indicating that an abnormal state has occurred in the reactive power compensation device when the ratio of the difference current between the line current and the cluster current is out of the first reference ratio for more than a certain time
Reactive power compensation device. 7. The method of claim 6,
Each STATCOM bank contains three three-phase clusters with delta connection,
The line current is the current of the connection point between any one of the three-phase clusters included in each STATCOM bank and the bus bar of the corresponding phase,
The cluster current is a current flowing inside the one of the phase clusters.
Reactive power compensation device. 8. The method of claim 7,
the controller
When the differential current is different from the preset current, generating a circulating current command to adjust the differential current to the preset current
Reactive power compensation device. 8. The method of claim 7,
the controller
Controlling the balance of current flowing inside each phase cluster by adjusting the difference current to the preset current
Reactive power compensation device. delete delete 8. The method of claim 7,
the controller
When the ratio of the difference current is out of the second reference ratio for more than a predetermined time, a trip signal for cutting off the power provided to each STATCOM bank is output,
the second reference ratio is greater than the first reference ratio
Reactive power compensation device.

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