KR102524800B1 - 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 a plurality of phase clusters including a plurality of sub-modules and reactive power output from the modular multi-level converter is less than or equal to reference power, a circulating current flows through the phase clusters. It may include a processor that controls to

Description

Modular multi-level converter and its operating method {MOUDLAR MULTI-LEVEL CONVERTER AND OPERATING METHOD FOR THE SAME}

The present disclosure relates to a modular multilevel converter and an operating method thereof.

As the industry develops and the population increases, electricity demand soars, but electricity production is limited.

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

The need for FACTS (Flexible AC Transmission System) facilities to improve power flow, system voltage, and stability is emerging. STATCOM (STATic synchronous COMpensator), a type of power compensator called the 3rd generation among FACTS facilities, is fed in parallel to the power system and compensates for the reactive power required by the power system.

1 shows a general power system.

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

The power generation source 20 means 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 steel tower, a lightning arrester, an insulator, and the like that transmits power generated by the power generation source 20 to the load 40 .

The load 40 refers to a place or facility consuming the power generated by the power generation source 20, and may be understood as a consumer consuming power.

The reactive power compensator 50 is a STATCOM, and may be a device that is linked to the power system 30 and compensates for a lack of reactive power among power flowing through the power system 30 .

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

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

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 serially connected to each other.

In the modular multilevel converter, an algorithm for reducing switching loss of submodules is used, which is an algorithm for reducing energy loss that occurs when switching of submodules occurs more than necessary.

However, when the output of the modular multi-level converter is in the low-output range, the capacitor charging and discharging period of each sub-module is shortened, and the difference in voltage fluctuation generated during charging and discharging of each sub-module is an algorithm for reducing switching loss. fluctuates less than the difference allowed by

For this reason, when the modular multilevel converter is in a low-output period, there is a problem in that only switched submodules are continuously switched and unswitched submodules are not continuously switched.

The present disclosure intends to propose a device and method for mitigating switching frequency imbalance of submodules in a modular multilevel converter and its operation method.

The modular multi-level converter of the present disclosure includes a plurality of phase clusters including a plurality of sub-modules and a processor that controls circulating current to flow through the phase clusters when reactive power output from the modular multi-level converter is less than or equal to reference power. can include

The reference power may be 0Mvar.

The processor may include a reference generator and a comparator, and the comparator may compare the reference voltage generated by the reference generator with other input voltages excluding 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 detector and a voltage generator, and the low power detector allows the voltage generated by the voltage generator to be input to the comparator when reactive power output from the modular multi-level converter is less than or equal to reference power. can

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

A method of operating a modular multi-level converter of the present disclosure includes determining whether reactive power output from an 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 a reference power, a circulating current in a plurality of phase clusters It may include a step of controlling to flow.

The step of controlling the circulating current to flow through the plurality of phase clusters includes comparing a 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 submodules of each phase cluster. steps may be included.

In the step of controlling the circulating current to flow through the plurality of phase clusters, a value obtained by subtracting the voltage input from the voltage generator from the reference voltage generated by the reference generator is different from the actually measured average voltage of the submodules of each phase cluster. If there is, the step of transmitting a control signal to each phase cluster may be further included.

According to the present disclosure, since the switching frequency of each sub-module is uniformly controlled even in a low-output period, it is possible to overcome shortening of a product's lifespan due to the use of only a specific sub-module.

1 shows a general power system.
Figure 2a is a circuit diagram of a modular multilevel converter with a star connection.
Figure 2b is a circuit diagram of a modular multilevel converter with a delta connection.
Figure 3 shows a power system system having a modular multi-level converter of star connection according to the present invention.
Figure 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 block diagram showing in detail 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 this specification will be described in detail with reference to the accompanying drawings, but the same or similar elements are given the same reference numerals regardless of reference numerals, and redundant description thereof will be omitted. The suffixes "module" and "unit" for components used in the following description are given or used together in consideration of ease of writing the specification, and do not have meanings or roles that are distinct from each other by themselves. In addition, in describing the embodiments disclosed in this specification, if it is determined that a detailed description of a related known technology may obscure the gist of the embodiment 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 this specification, the technical idea disclosed in this specification is not limited by the accompanying drawings, and all changes included in the spirit and technical scope of the present invention , it should be understood to include equivalents or substitutes.

Figure 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 star connection modular multilevel converter 100 is fed into the power system 140 in parallel to compensate for reactive power required by the power system 140 .

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

Specifically, the first phase cluster 130 is connected between the first phase line 142 of the power system 140 and the node n, and the second phase cluster 132 is the second phase cluster 132 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 of the power system 140 and the node n.

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, and a plurality of diodes and capacitors connected in parallel with the switching elements.

When the power system 140 is operated, capacitors 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 the capacitors in each sub-module 136 according to the number of sub-modules 136 selected or unselected in each phase cluster 130, 132, 134, so that the power system 140 ) can be compensated for

Selecting the sub-module 136 may mean that the sub-module 136 is activated, and non-selecting the sub-module 136 may mean that the sub-module 136 is inactivated.

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

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

Figure 4 shows a power system 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 is the same as the modular multilevel converter of the star connection of FIG. 3 except for the connection structure. Therefore, in the description of the delta connection modular multilevel converter, the same reference numerals will be assigned to the same components as those of the star connection modular multilevel converter.

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

In the delta connection modular multilevel converter 101 , the first to third phase clusters 130 , 132 , and 134 may be connected to the three-phase lines 142 , 144 , and 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. And, 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, and 134 constituting the delta connection may have the same detailed configuration as the first to third phase clusters 130, 132, and 134 constituting the star connection. .

Accordingly, desired AC voltage and AC current waveforms may be generated according to the selected number of submodules 136 in each phase cluster 130 , 132 , and 134 .

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

5 is a block diagram showing a modular multi-level converter according to an embodiment of the present invention.

Referring to FIG. 5, a 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 a three-phase cluster (130, 132, 134).

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

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 command values and/or control signals 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 command values for controlling the first to third phase cluster controllers 120 , 122 , and 124 .

Specifically, the processor 110 transmits power condition information obtained from the power system 140 and/or state information of each of the first to third phase clusters 130, 132, and 134 and each phase cluster 130, 132, 134), command values may be generated based on state information of each sub-module 136. The command values generated in this way may be transmitted to the first to third phase cluster controllers 120 , 122 , and 124 .

Status information of each sub-module 136 in each phase cluster 130 , 132 , and 134 may include whether each sub-module 136 is dropped or not, 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 is the voltage value (Vcan, Vcbn, and Vccn) detected in each of the first to third phase clusters 130, 132, and 134, for example. ) (Vab, Vbc, Vca) and current values (ica, icb, icc) (iab, ibc, ica), but are not limited thereto.

The processor 110 generates signals for each phase cluster 130, 132, and 134 based on voltage values and current values detected in each of the first to third phase clusters 130, 132, and 134, for example. can

Each sub-module 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 balancing so that the energy of each phase cluster 130, 132, 134 is equally distributed, and the energy between the first to third phase clusters 130, 132, and 134 can be maintained evenly. Since this is a well-known technique, a detailed description thereof will be omitted.

Meanwhile, in the modular multilevel converter 100, in addition to energy balancing control, an algorithm for reducing the switching loss of the submodule 136 is used together, which occurs when the switching of the submodule 136 occurs more than necessary It is an algorithm to reduce the energy loss (switching loss) of

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

For this reason, when the modular multilevel converter 100 is in a low-output period, there is a problem in that sub-modules that are switched are continuously switched and sub-modules that are not switched are not continuously switched. That is, when the modular multilevel converter 100 is in a low output period, there is a problem in that the switching frequencies of the plurality of submodules 136 are not equally controlled.

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

Referring to FIGS. 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, a processor 110a for controlling a first-phase cluster (or a-phase cluster), a processor 110b for controlling a second-phase cluster (or b-phase cluster), and a third-phase cluster Although the processor 110c for cluster (or c-phase cluster) control is separately illustrated, it is not limited thereto, and overlapping descriptions of the first to third phases or a to c phases 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).

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 3-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 phase cluster 130, 132, and 134. For example, the reference generator 112 calculates an average voltage value of each phase cluster 130 , 132 , 134 by sensing the capacitor voltage value of the sub module 136 in each phase cluster 130 , 132 , 134 . And, the average voltage value of the calculated voltages of each phase cluster 130, 132, and 134 may be generated as a reference voltage value. That is, the reference voltage values output from the first reference generator 112a, the second reference generator 112b, and the third reference generator 112c may be the same, and the reference voltage values are the same as those of the entire submodule 136. may be the average capacitor voltage value of

The first to third voltage generators 114a, 114b, and 114c may generate pulse waveform voltages. For example, the first to third voltage generators 114a, 114b, and 114c may generate third harmonics of the system frequency. If the system frequency of the modular multilevel 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 be in the form of (a) in FIG. 7, and the waveform of the voltage generated by the second voltage generator 114b is shown in (b) of FIG. ), and the waveform of the voltage generated by the third voltage generator 114c may be in the form of FIG. 7(c).

The first to third low power detection units 116a, 116b, and 116c may generate a low power detection signal when the reactive power output from the modular multilevel converter 100 is equal to or less than 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]. , can generate a low-power detection signal. The low power detection signal generated by the first to third low power detectors 116a, 116b, and 116c may be 0 or 1. The first to third low power detecting units 116a, 116b, and 116c output 1 when the reactive power output from the modular multilevel converter 100 is less than or equal to the reference power, and output from the modular multilevel converter 100. When the reactive power to be used exceeds the reference power, 0 may be output. This is just an example, and the reference power may be changed according to embodiments.

The first to third low power detection units 116a, 116b, and 116c sense the low power of the modular multilevel converter 100 and generate a low power detection signal, thereby generating the above-described first to third voltage generators 114a and 114b. , 114c) may be input to the first to third comparison units 117a, 117b, and 117c, respectively. For example, when signals output from the first to third low power detectors 116a, 116b, and 116c are 1, the voltage values output from the first to third voltage generators 114a, 114b, and 114c are Although it may be transmitted to the first to third comparison units 117a, 117b, and 117c, respectively, 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 the low output detection signal 0, and may not be transmitted to the first to third comparators 117a, 117b, and 117c.

The first to third comparison units 117a, 117b, and 117c may compare the reference voltage values generated by the first to third reference generators 112a, 112b, and 112c with other input voltages excluding the reference voltage values. . For example, the first to third comparators 117a, 117b, and 117c may set the reference voltage value to the actually measured average voltage value of the submodule 136 of the first to third phase clusters 130, 132, and 134. 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 combine the average voltage values of the sub-modules 136 of each phase cluster 130, 132, and 134 from which the reference voltage values are 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, a control signal for the first to third phase cluster controllers 120, 122, and 124 turns on a switching element in each sub-module included in the first to third phase clusters 130, 132, and 134. / It can be a signal to turn off.

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

First, when the output of the modular multilevel converter 100 is not low power, the first low power detection unit 116a outputs a value of 0. The first voltage generator 114a generates the voltage shown in FIG. 7 (a), but it is multiplied with the output value of the low output detector 116a and is not input to the first comparator 117a. The first comparator 117a converts the reference voltage value generated by the first reference generator 112a to the actually measured average voltage value of the sub-module 136 of the first phase cluster 130 and the first voltage generator 114a. ), 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 actually measured first phase cluster ( 130) Average voltage values of the submodules 136 may be compared.

As described above, when the output is not low, since the voltage value input from the first voltage generator 114a becomes 0, the first comparator 117a uses the reference voltage value generated by the first reference generator 112a. Only the actually measured average voltage values of the submodules 136 of the first phase cluster 130 are compared. In this case, if there is no difference between the reference voltage value generated by the first reference generator 112a and the average voltage value of the submodule 136 of the first phase cluster 130 that is actually measured, the first phase cluster controller 120 Control signal is not input.

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

As such, 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 period b of FIG. will deliver 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. do.

Through this, the modular multi-level converter 100 of the present disclosure can forcibly generate a circulating current by artificially inputting a control signal to the first to third phase clusters 130, 132, and 134 in a low power section, , the switching frequencies of the submodules constituting each phase cluster can be controlled to be equal.

Therefore, according to the present disclosure, since the switching frequency of each sub-module is uniformly controlled even in a low power period, it is possible to overcome the shortening of a product's lifespan due to the use of only a specific sub-module.

The above description is merely an example of the technical idea of the present disclosure, and various modifications and variations can be made to those skilled in the art without departing from the essential characteristics of the present disclosure.

Therefore, the embodiments disclosed in this disclosure are not intended to limit the technical idea of the present disclosure but to explain, and the scope of the technical idea of the present disclosure is not limited by these embodiments.

The protection scope of the present disclosure should be construed by the claims below, 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 comprising a plurality of submodules; and
And a processor for controlling the circulating current to flow in the phase cluster when the absolute value of the reactive power output from the modular multilevel converter is less than or equal to the reference power.
Modular multilevel converter. The method of claim 1,
The reference power is,
0 Mvar,
Modular multilevel converter. The method of claim 1,
The processor
Including a reference generator, a voltage generator and a comparison unit,
the comparison unit
comparing the reference voltage generated by the reference generator with the sum of the average voltage of each of the plurality of phase clusters and the pulse wave voltage output from the voltage generator;
Modular multilevel converter. The method of claim 3,
The reference generator,
Generating an average voltage value of the plurality of phase cluster voltages as the reference voltage,
Modular multilevel converter. The method of claim 3,
The processor
Further comprising a low power detection unit,
The low power sensor
When the absolute value of the reactive power output from the modular multilevel converter is less than or equal to the reference power, the voltage of the pulse wave output by the voltage generator is input to the comparator,
Modular multilevel converter. The method of claim 5,
the comparison unit
Comparing a value obtained by adding the actually measured submodule average voltage of each phase cluster and the voltage of the pulse wave output by the voltage generator to the reference voltage,
Modular multilevel converter. The method of claim 5,
the comparison unit
comparing 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-module of each phase cluster;
Modular multilevel converter. 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 the sub-module of each phase cluster,
Transmitting a control signal to each phase cluster,
Modular multilevel converter. In the operating method of the modular multilevel converter,
determining whether an absolute value of reactive power output from the modular multilevel converter is less than or equal to reference power; and
Controlling a circulating current to flow in a plurality of phase clusters when the absolute value of the reactive power is less than or equal to the reference power
Operation method of modular multi-level converter. The method of claim 9,
The step of controlling the circulating current to flow through the plurality of phase clusters,
Comprising the step of comparing a value obtained by subtracting the voltage of the pulse wave output from the voltage generator from the reference voltage generated by the reference generator with the actually measured average voltage of the submodules of each phase cluster,
Operation method of modular multi-level converter. The method of claim 10,
The step of controlling the circulating current to flow through 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 differs from the actually measured average voltage of each phase cluster sub-module,
Transmitting a control signal to each phase cluster
Operation method of modular multi-level converter.

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