KR20220082406A - Moudlar multi-level converter and operating method for the same - Google Patents

Abstract

In the modular multi-level converter according to an embodiment of the present disclosure, when reactive power output from a plurality of phase clusters including a plurality of sub-modules and the modular multi-level converter is less than or equal to a reference power, a circulating current flows in the phase clusters It may include a processor that controls the

Description

Modular multilevel converter and method of operation thereof

The present disclosure relates to a modular multilevel converter and a method of operating the same.

As the industry develops and the population increases, the demand for electricity surges, but there is a limit to electricity production.

Accordingly, the power system for stably supplying power generated in the production area to the demand area without loss is becoming increasingly important.

The need for FACTS (Flexible AC Transmission System) facilities to improve power flow, grid voltage and stability is emerging. Among the FACTS facilities, the STATCOM (STATic synchronous compensator) facility, a type of power compensation device called the third generation, is fed in parallel to the power system to compensate for the reactive power required by the power system.

1 shows a general power system system.

As shown in FIG. 1 , the general power system 10 may include a power generation source 20 , a power system 30 , a load 40 , and a plurality of reactive power compensation devices 50 .

The power generation source 20 refers to a place or facility that generates power, and may be understood as a producer that generates power.

The power system 30 may mean any facility including a power line, a pylon, a lightning arrester, an insulator, and the like that transmits the power generated by the power generation source 20 to the load 40 .

The load 40 means a place or facility that consumes power generated by the power generation source 20 , and may be understood as a consumer who consumes power.

The reactive power compensation device 50 is a STATCOM, and may be a device for compensating for a shortage of reactive power among the power flowing to the power system 30 in connection with the power system 30 .

The reactive power compensation device 50 includes a modular multi-level converter capable of converting AC power of the power system into DC power or converting DC power into AC power.

The modular multilevel converter includes a cluster consisting of a plurality of sub-modules connected in series to each other for each of the three phases.

FIG. 2A is a circuit diagram of a modular multilevel converter having a star connection topology, and FIG. 2B is a circuit diagram of a modular multilevel converter having a delta connection topology.

As shown in FIGS. 2A and 2B , each of the three-phase clusters 52 has a structure in which a plurality of sub-modules 54 are connected in series with each other.

In the modular multi-level converter, an algorithm for reducing the switching loss of the sub-module is used, which is an algorithm for reducing the energy loss that occurs when the switching of the sub-module occurs more than necessary.

However, when the output of the modular multi-level converter is in the low output section, the capacitor charging and discharging period of each sub-module is shortened, and the difference in voltage fluctuations occurring during charging and discharging of each sub-module is an algorithm for reducing the switching loss. It fluctuates less than the allowable difference in

For this reason, when the modular multi-level converter is in the low output section, there is a problem that only the switched sub-modules are continuously switched, and the non-switched sub-modules are not continuously switched.

The present disclosure intends to present an apparatus for alleviating a switching frequency imbalance of a sub-module in a modular multi-level converter and an operating method thereof.

The modular multi-level converter of the present disclosure includes a plurality of phase clusters including a plurality of sub-modules and a processor for controlling a circulating current to flow in the phase cluster when reactive power output from the modular multi-level converter is less than or equal to a reference power may include

The reference power may be 0 Mvar.

The processor may include a reference generator and a comparator, and the comparator may compare the reference voltage generated by the reference generator with input voltages other than the reference voltage.

The reference generator may generate an average voltage value of the plurality of phase cluster voltages as the reference voltage.

The processor further includes a low-power detection unit and a voltage generator, wherein the low-output detection unit is configured to input the voltage generated by the voltage generator to the comparator when the reactive power output from the modular multi-level converter is less than or equal to a reference power can

The comparator may compare a value obtained by adding a actually measured average voltage of each sub-module of each phase cluster to the voltage generated by the voltage generator with the reference voltage.

The comparator may compare a value obtained by subtracting the voltage input from the voltage generator from the reference voltage with the actually measured average voltage of the sub-modules of each phase cluster.

The comparator may transmit a control signal to each of the phase clusters when a value obtained by subtracting the voltage input from the voltage generator from the reference voltage is different from the actually measured average voltage of the sub-modules of each phase cluster.

The operating method of the modular multi-level converter of the present disclosure includes the steps of determining whether reactive power output from the output of the modular multi-level converter is equal to or less than a reference power, and when the reactive power is equal to or less than the reference power, a circulating current in a plurality of phase clusters It may include the step of controlling the flow.

The step of controlling the circulating current to flow through the plurality of phase clusters includes comparing the value obtained by subtracting the voltage input from the voltage generator from the reference voltage generated by the reference generator with the actually measured average voltage of the sub-modules of each phase cluster. may include steps.

In the step of controlling the circulating current to flow through the plurality of phase clusters, the difference between the actual measured sub-module average voltage of each phase cluster and the value obtained by subtracting the voltage input from the voltage generator from the reference voltage generated by the reference generator If there is, the method may further include transmitting a control signal to each of the phase clusters.

According to the present disclosure, since the switching frequency of each sub-module is uniformly controlled even in the low-output section, it is possible to overcome the shortening of the lifespan of the product because only a specific sub-module is used.

1 shows a general power system system.
Figure 2a is a circuit diagram of a modular multilevel converter with star connections.
Figure 2b is a circuit diagram of a modular multilevel converter with a delta connection.
3 shows a power system having a modular multi-level converter of star connection according to the present invention.
4 shows a power system system having a modular multi-level converter of delta connection according to the present invention.
5 is a block diagram illustrating a modular multi-level converter according to an embodiment of the present invention.
6 is a detailed block diagram illustrating a processor of a modular multi-level converter according to an embodiment of the present disclosure.
7 is an exemplary diagram illustrating a waveform of a voltage generated by a voltage generator of a processor according to an embodiment of the present disclosure.

Hereinafter, the embodiments disclosed in the present specification will be described in detail with reference to the accompanying drawings, but the same or similar components are assigned the same reference numbers regardless of reference numerals, and redundant description thereof will be omitted. The suffixes "module" and "part" for components used in the following description are given or mixed in consideration of only the ease of writing the specification, and do not have distinct meanings or roles by themselves. In addition, in describing the embodiments disclosed in the present specification, if it is determined that detailed descriptions of related known technologies may obscure the gist of the embodiments disclosed in this specification, the detailed description thereof will be omitted. In addition, the accompanying drawings are only for easy understanding of the embodiments disclosed in the present specification, and the technical idea disclosed herein is not limited by the accompanying drawings, and all changes included in the spirit and scope of the present invention , should be understood to include equivalents or substitutes.

3 shows a power system system having a modular multi-level converter of star connection according to the present invention.

As shown in FIG. 3 , the modular multi-level converter 100 of the star connection is fed in parallel to the power system 140 to compensate for the reactive power required by the power system 140 .

In the modular multi-level converter 100 of the star connection, the first to third phase clusters 130 , 132 , 134 may be individually connected to the three-phase lines 142 , 144 , 146 of the power system 140 . .

Specifically, the first phase cluster 130 is connected between the first phase line 142 and the node n of the power system 140 , and the second phase cluster 132 is the second phase of the power system 140 . It is connected between the phase line 144 and the node n, and the third phase cluster 134 may be connected between the third phase line 146 and the node n of the power system 140 .

Each phase cluster 130 , 132 , 134 may include a plurality of sub-modules 136 connected in series with each other. Each sub-module 136 may include a plurality of switching elements, a plurality of diodes and capacitors connected in parallel to the switching elements.

When the power system 140 is operated, the capacitor of each sub-module 136 may be charged or discharged at any time.

AC reactive power is generated by the sum of the voltages of capacitors in each sub-module 136 according to the number of sub-modules 136 selected or unselected in each phase cluster 130 , 132 , 134 , and the power system 140 ) can be compensated for

Selection of the sub-module 136 may mean that the sub-module 136 is activated, and non-selection of the sub-module 136 may mean that the sub-module 136 is deactivated.

When the sub-module 136 is selected, a specific switching element among a plurality of switching elements in the sub-module 136 may be turned on to output the voltage of the capacitor.

When the sub-module 136 is not selected, a current flow path is not formed with the capacitor in the corresponding sub-module 136 and the corresponding sub-module 136 is bypassed and the corresponding sub-module 136 is bypassed. ) of the capacitor is not output.

4 shows a power system having a modular multi-level converter of delta connection according to the present invention.

The modular multilevel converter of the delta connection of FIG. 4 differs from the modular multilevel converter of the star connection of FIG. 3 only in a connection structure, but the configuration is the same. Accordingly, in the description of the modular multilevel converter of the delta connection, the same reference numerals are given to the same components as the modular multilevel converter of the star connection.

As shown in FIG. 4 , the modular multi-level converter 101 of the delta connection is fed in parallel to the power system 140 to compensate for the reactive power required by the power system 140 .

In the modular multi-level converter 101 of the delta connection, the first to third phase clusters 130 , 132 , and 134 may be connected to the three-phase lines 142 , 144 , 146 of the power system 140 .

Specifically, the three-phase lines 142 , 144 , and 146 of the power system 140 may be connected to the first to third nodes n1 , n2 , and n3 .

The first phase cluster 130 is connected between the first node n1 and the second node n2 , and the second phase cluster 132 is connected between the second node n2 and the third node n3 . The third cluster 134 may be connected between the third node n3 and the first node n1 .

The detailed configuration of the first to third phase clusters 130, 132, 134 constituting the delta connection may have the same detailed configuration as the first to third phase clusters 130, 132, 134 constituting the star connection. .

Accordingly, a desired AC voltage waveform and AC current waveform may be generated according to the selected number of sub-modules 136 in each phase cluster 130 , 132 , 134 .

As such, when the first to third phase clusters 130 , 132 , and 134 are configured with a delta connection, the voltage applied to the first phase cluster 130 is Vab, and the voltage applied to the second phase cluster 132 is Vbc, and the voltage applied to the third phase cluster 134 may be Vca.

5 is a block diagram illustrating a modular multilevel converter according to an embodiment of the present invention.

Referring to FIG. 5 , the modular multilevel converter 100 according to an embodiment of the present invention includes a processor 110 , first to third phase cluster controllers 120 , 122 , and 124 , and first to third phases. It may include three-phase clusters 130 , 132 , 134 .

The first to third phase cluster controllers 120, 122, and 124 may be referred to as a-th to c-th phase cluster controllers 120, 122, and 124, and the first to third phase clusters 130, 132 and 134 may be referred to as a-th to c-th phase clusters 130 , 132 , and 134 .

As shown in FIG. 3 , each of the first to third phase clusters 130 , 132 , and 134 includes a plurality of sub-modules 136 connected in series with each other, and each sub-module 136 includes a plurality of sub-modules 136 . It may include a switching element, a plurality of diodes and a capacitor connected in parallel with the switching element.

Each of the first to third phase cluster controllers 120 , 122 , and 124 may control the first to third phase clusters 130 , 132 , and 134 . Alternatively, one cluster controller may control the first to third phase clusters 130 , 132 , and 134 , but the present invention is not limited thereto.

In addition, wired communication or wireless communication is possible between the processor 110 and the first to third phase cluster controllers 120 , 122 , and 124 . Wired or wireless communication is possible between the first to third phase cluster controllers 120 , 122 , and 124 and the first to third phase clusters 130 , 132 and 134 , but the present invention is not limited thereto.

Each of the first to third phase cluster controllers 120 , 122 , and 124 may generate first to third switching control signals for controlling the first to third phase clusters 130 , 132 , and 134 , respectively. .

Specifically, the first phase cluster controller 120 may generate a first switching control signal for controlling each sub-module 136 in the first phase cluster 130 . The second phase cluster controller 122 may generate a second switching control signal for controlling each sub-module 136 in the second phase cluster 132 . The third phase cluster controller 124 may generate a third switching control signal for controlling each sub-module 136 in the third phase cluster 134 .

The first to third phase cluster controllers 120 , 122 , and 124 may generate first to third switching control signals based on a command value and/or a control signal provided from the processor 110 .

The processor 110 may control the first to third phase cluster controllers 120 , 122 , and 124 . That is, the processor 110 may generate a command value for controlling the first to third phase cluster controllers 120 , 122 , and 124 .

Specifically, the processor 110 includes the power status information obtained from the power system 140 and/or the first to third phase clusters 130, 132, 134, and the respective state information and the respective phase clusters 130, 132, 134), it is possible to generate a command value based on the status information of each sub-module 136 in the. The command value generated in this way may be transmitted to the first to third phase cluster controllers 120 , 122 , and 124 .

State information of each sub-module 136 in each phase cluster 130 , 132 , 134 may include whether each sub-module 136 is dropped, voltage information of each sub-module 136 , and the like.

State information of each of the first to third phase clusters 130 , 132 , and 134 may be voltage and/or current information. For example, the state information of each of the first to third phase clusters 130 , 132 , and 134 may include, for example, voltage values Vcan, Vcbn, and Vccn detected in each of the first to third phase clusters 130 , 132 and 134 . ) (Vab, Vbc, Vca) and current values (ica, icb, icc)(iab, ibc, ica).

The processor 110 may generate a signal for each phase cluster 130 , 132 , 134 based on, for example, the voltage value and the current value detected in each of the first to third phase clusters 130 , 132 , and 134 . can

Each of the sub-modules 136 in the first to third phase clusters 130 , 132 , and 134 may be switched according to the command signal generated by the processor 110 .

In the conventional case, the processor 110 controls the energy between the first to third phase clusters 130, 132, and 134 through energy balancing control such that the energy of each of the phase clusters 130, 132, and 134 is equally distributed. can be kept equal. Since this is a known technique, a detailed description thereof will be omitted.

On the other hand, in the modular multi-level converter 100, in addition to the energy balancing control, an algorithm for reducing the switching loss of the sub-module 136 is used together, which occurs when the switching of the sub-module 136 occurs more than necessary. It is an algorithm to reduce the energy loss (switching loss).

However, when the output of the modular multi-level converter 100 is in the low output section, the capacitor charging/discharging period of each sub-module 136 is shortened, and voltage fluctuations occurring during charging/discharging of each sub-module 136 . The difference of ? is fluctuated smaller than the difference allowed by the algorithm for reducing the switching loss.

For this reason, when the modular multi-level converter 100 is in the low output section, there is a problem in that the switched sub-module is continuously switched, and the non-switched sub-module is not continuously switched. That is, when the modular multi-level converter 100 is in the low output section, there is a problem in that the switching frequencies of the plurality of sub-modules 136 are not uniformly controlled.

6 is a detailed block diagram illustrating a processor of a modular multi-level converter according to an embodiment of the present disclosure.

5 and 6 , the processor 110 may include a reference generator 112 , a voltage generator 114 , a low-power detector 116 , and a comparator 118 .

In FIG. 6 , for convenience of description, the processor 110a for controlling the first phase cluster (or a phase cluster), the processor 110b for controlling the second phase cluster (or the phase b cluster), and the third phase cluster Although the processor 110c for controlling the cluster (or the c-phase cluster) has been separately illustrated, the present invention is not limited thereto, and overlapping descriptions of the first to third phases or the a-phase to c are omitted.

The processor 110a for controlling the first phase cluster (or the a-phase cluster) includes a first reference generator 112a , a first voltage generator 114a , a first low-power detector 116a , and a first comparator (118a) may be included.

The processor 110b for controlling the second phase cluster (or b-phase cluster) includes a second reference generator 112b , a second voltage generator 114b , a second low-power detector 116b , and a second comparator (118b).

The processor 110c for controlling the third phase cluster (or c-phase cluster) includes a third reference generator 112c , a third voltage generator 114c , a third low-power detector 116c , and a third comparator. (118c).

The first to third reference generators 112a , 112b , and 112c may generate an average energy reference voltage value of each of the phase clusters 130 , 132 , and 134 . For example, the reference generator 112 senses the capacitor voltage value of the sub-module 136 in each phase cluster 130 , 132 , and 134 to calculate the average voltage value of each phase cluster 130 , 132 , 134 . , and an average voltage value of the calculated voltages of each of the phase clusters 130 , 132 , and 134 may be generated as a reference voltage value. That is, the reference voltage values output from the first reference generation unit 112a, the second reference generation unit 112b, and the third reference generation unit 112c may be the same, and the reference voltage value is the same for all sub-modules 136 . may be the average capacitor voltage value of

The first to third voltage generators 114a , 114b , and 114c may generate a pulse waveform voltage. For example, the first to third voltage generators 114a , 114b , and 114c may generate a third harmonic of the system frequency. If the system frequency of the modular multi-level converter 100 is 60hz, the first to third voltage generators 114a, 114b, and 114c may generate a pulse wave voltage having a frequency of 180hz. At this time, the waveform of the voltage generated by the first voltage generator 114a may have the same shape as in FIG. 7A , and the waveform of the voltage generated by the second voltage generator 114b is shown in FIG. 7B ), and the waveform of the voltage generated by the third voltage generator 114c may have the same shape as (c) of FIG. 7 .

The first to third low-power detection units 116a, 116b, and 116c may generate a low-output detection signal when the reactive power output from the modular multi-level converter 100 is less than or equal to the reference power. For example, when the reference power is 0 [Mvar], the first to third low-power detection units 116a, 116b, and 116c when the reactive power output from the modular multi-level converter 100 is 0 [Mvar] , it is possible to generate a low-power detection signal. The low-power detection signal generated by the first to third low-power detection units 116a, 116b, and 116c may be 0 or 1. The first to third low-power detection units 116a, 116b, and 116c output 1 when the reactive power output from the modular multi-level converter 100 is less than or equal to the reference power, and output from the modular multi-level converter 100 When the reactive power to be used exceeds the reference power, 0 may be output. This is only an example, and the reference power may be changed according to an embodiment.

The first to third low-power detection units 116a, 116b, and 116c detect the low output of the modular multi-level converter 100 and generate a low-output detection signal, thereby generating the above-described first to third voltage generators 114a, 114b. , 114c) may be adjusted to be input to the first to third comparators 117a, 117b, and 117c, respectively. For example, when the signal output from the first to third low-power detection units 116a, 116b, and 116c is 1, the voltage values output from the first to third voltage generators 114a, 114b, and 114c are Each of the first to third comparators 117a, 117b, and 117c may be transmitted, but when the signals output from the first to third low-power detection units 116a, 116b, and 116c are 0, the first to third voltages The voltage values output from the generators 114a, 114b, and 114c may be multiplied by 0, which is the low-output detection signal, and may not be transmitted to the first to third comparators 117a, 117b, and 117c.

The first to third comparators 117a, 117b, and 117c may compare the reference voltage values generated by the first to third reference generators 112a, 112b, and 112c with input voltages other than the reference voltage value. . For example, the first to third comparators 117a, 117b, and 117c may compare the reference voltage value with the actually measured average voltage value of the first to third phase clusters 130, 132, and 134 sub-modules 136 and It may be compared with the sum of voltage values input from the first to third voltage generators 114a, 114b, and 114c. The first to third comparators 117a, 117b, and 117c include the average voltage value of each of the phase clusters 130, 132, and 134 submodule 136 for which the reference voltage value is actually measured, and the first to third voltage generators. When there is a difference from the sum of the voltage values input at 114a , 114b , and 114c , control signals for the first to third phase cluster controllers 120 , 122 , and 124 may be generated, respectively. For example, the control signals for the first to third phase cluster controllers 120, 122, and 124 turn on the switching elements in each sub-module included in the first to third phase clusters 130, 132, and 134. It may be a signal to turn off /off.

Next, an operating method of a processor according to an embodiment of the present disclosure will be described with a focus on the first phase cluster control method.

First, when the output of the modular multi-level converter 100 is not the low output, the first low output detection unit 116a outputs a value of 0. The first voltage generator 114a generates the voltage of FIG. 7A , but is multiplied by the output value of the low-power detector 116a and is not input to the first comparator 117a. The first comparator 117a compares the reference voltage value generated by the first reference generator 112a with the actually measured average voltage value of the first phase cluster 130 sub-module 136 and the first voltage generator 114a ) and compare the sum of the input voltage values. Alternatively, the first comparator 117a subtracts the voltage value input from the first voltage generator 114a from the reference voltage value generated by the first reference generator 112a and the actual measured first phase cluster ( 130) The average voltage value of the sub-module 136 may be compared.

As described above, when the output is not low, the voltage value input from the first voltage generator 114a becomes 0, so the first comparator 117a compares the reference voltage value generated by the first reference generator 112a. Only the actually measured average voltage value of the first phase cluster 130 sub-module 136 is compared. In this case, if there is no difference between the reference voltage value generated by the first reference generator 112a and the actual measured average voltage value of the first phase cluster 130 sub-module 136, the first phase cluster controller 120 is No control signal is input.

Conversely, when the output of the modular multi-level converter 100 is a low output, the first low output detection unit 116a outputs a value of 1. The first voltage generator 114a generates the voltage of FIG. 7A , which is input to the first comparator 117a. The first comparator 117a compares the reference voltage value generated by the first reference generator 112a with the actually measured average voltage value of the first phase cluster 130 sub-module 136 and the first voltage generator 114a ) and compare the input voltage value with the added value. When the voltage generated by the first voltage generator 114a is the same as that of FIG. 7A , in the block section a, the reference voltage value generated by the first reference generator 112a is the actually measured first phase cluster (130) A difference occurs from the sum of the average voltage value of the sub-module 136 and the voltage value input from the first voltage generator 114a. Alternatively, the first comparator 117a subtracts the voltage value input from the first voltage generator 114a from the reference voltage value generated by the first reference generator 112a and the actual measured first phase cluster ( 130) The average voltage value of the sub-module 136 may be compared. Similarly, when the voltage generated by the first voltage generator 114a is the same as that of FIG. A value obtained by subtracting the input voltage value from 114a is different from the actually measured average voltage value of the sub-module 136 of the first phase cluster 130 . That is, in section a in which the voltage value generated by the first voltage generator 114a is input to the first comparator 117a, a control signal is input to the first phase cluster controller 120 .

In this way, the second voltage generator 114b generates a voltage as shown in (b) of FIG. 7 , and the second comparator 117b sends a control signal to the second phase cluster controller 122 only in the section b of FIG. 7 . will convey The third voltage generator 114c generates a voltage as shown in (c) of FIG. 7 , and the third comparator 117c transmits a control signal to the third phase cluster controller 124 only in the section c of FIG. 7 . do.

Through this, the modular multi-level converter 100 of the present disclosure can artificially input a control signal to the first to third phase clusters 130, 132, and 134 in the low output section to forcibly generate a circulating current, , it is possible to control so that the switching frequency of the sub-modules constituting each phase cluster is equal.

Therefore, according to the present disclosure, since the switching frequency of each sub-module is uniformly controlled even in the low-output section, it is possible to overcome the shortening of the lifespan of the product because only a specific sub-module is used.

The above description is merely illustrative of the technical spirit of the present disclosure, and various modifications and variations will be possible without departing from the essential characteristics of the present disclosure by those of ordinary skill in the art to which the present disclosure pertains.

Accordingly, the embodiments disclosed in the present disclosure are for explanation rather than limiting the technical spirit of the present disclosure, and the scope of the technical spirit of the present disclosure is not limited by these embodiments.

The protection scope of the present disclosure should be interpreted by the following claims, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present disclosure.

100: modular multilevel converter
110: processor
112: reference generating unit
114: voltage generator
116: low power detection unit
117: comparison unit

Claims (11)

In the modular multilevel converter,
a plurality of phase clusters including a plurality of sub-modules; and
When the reactive power output from the modular multi-level converter is less than or equal to the reference power, comprising a processor for controlling the circulating current to flow in the phase cluster,
Modular multilevel converter. The method according to claim 1,
The reference power is
0 Mvar,
Modular multilevel converter. The method according to claim 1,
the processor is
Includes a reference generating unit and a comparison unit,
The comparison unit
comparing the reference voltage generated by the reference generator with the remaining input voltages except for the reference voltage,
Modular multilevel converter. 4. The method according to claim 3,
The reference generator,
generating an average voltage value of the plurality of phase cluster voltages as the reference voltage,
Modular multilevel converter. 4. The method according to claim 3,
the processor is
Further comprising a low-power detection unit and a voltage generator,
The low-power detection unit
When the reactive power output from the modular multi-level converter is less than or equal to the reference power, the voltage generated by the voltage generator is input to the comparator,
Modular multilevel converter. 6. The method of claim 5,
The comparison unit
Comparing a value obtained by adding the actually measured average voltage of each sub-module of each phase cluster to the voltage generated by the voltage generator with the reference voltage,
Modular multilevel converter. 6. The method of claim 5,
The comparison unit
Comparing the value obtained by subtracting the voltage input from the voltage generator from the reference voltage with the average voltage of each sub-module of each phase cluster actually measured,
Modular multilevel converter. 8. The method of claim 7,
The comparison unit
When a value obtained by subtracting the voltage input from the voltage generator from the reference voltage is different from the actually measured average voltage of each sub-module of each phase cluster,
Transmitting a control signal to each phase cluster,
Modular multilevel converter. In the operating method of the modular multi-level converter,
determining whether reactive power output from the modular multi-level converter is less than or equal to a reference power; and
When the reactive power is less than or equal to the reference power, comprising the step of controlling a circulating current to flow in a plurality of phase clusters
How a modular multilevel converter works. 10. The method of claim 9,
The step of controlling the circulating current to flow in the plurality of phase clusters,
Comprising the step of comparing the value obtained by subtracting the voltage generated by the voltage generator from the reference voltage generated by the reference generator with the average voltage of the sub-modules of each phase cluster actually measured,
How a modular multilevel converter works. 11. The method of claim 10,
The step of controlling the circulating current to flow in the plurality of phase clusters,
If the value obtained by subtracting the voltage input from the voltage generator from the reference voltage generated by the reference generator is different from the actual measured average voltage of the sub-modules of each phase cluster,
Further comprising the step of transmitting a control signal to the respective phase cluster
How a modular multilevel converter works.

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