KR102300064B1 - Apparatus and method for controlling a voltage balance of a capacitor included in a submodule of a modular multilevel converter - Google Patents

Abstract

The present invention relates to a sub-module of a modular multi-level converter that selects a sub-module having the maximum and minimum capacitor voltage among sub-modules of the modular multi-level converter and controls the voltage of the capacitor of the selected sub-module to be similar to a command value. It relates to an apparatus and method for controlling voltage balance of included capacitors.
In the voltage balance control apparatus for controlling the voltage balance of a plurality of sub-modules included in a modular multilevel converter (MMC) according to an embodiment of the present invention, the sub-module is included in the plurality of sub-modules A voltage detection unit for detecting a sub-module having a maximum voltage and a minimum voltage of the capacitor, and a sub-module having a maximum voltage and a minimum voltage on the capacitor based on the maximum and minimum voltage detected by the voltage detection unit. and a control unit for controlling voltage balance of the plurality of submodules by controlling the voltage of the capacitors of the submodules.

Description

Apparatus and method for controlling a voltage balance of a capacitor included in a submodule of a modular multilevel converter

The present invention relates to an apparatus and method for controlling voltage balance of a capacitor included in a sub-module of a modular multi-level converter, and more particularly, selecting a sub-module having the maximum and minimum voltage of the capacitor among the sub-modules of the modular multi-level converter and a voltage balance control apparatus and method of a capacitor included in a sub-module of a modular multi-level converter for controlling a voltage of a capacitor of a selected sub-module to be similar to a command value.

The DC system is a new transmission and distribution system that can efficiently connect DC loads, including digital loads, which are rapidly increasing in recent years, and renewable energy discharge sources. The direct current system can include a high voltage direct current (HVDC) system of several hundred kV, a 1500V class low voltage direct current (LVDC) system, and a medium voltage direct current (MVDC) system. have.

Such a DC system consists of a power conversion device using a power semiconductor device, and recently, a modular multilevel converter (MMC) is widely used among circuits of the power conversion device.

Each sub-module of the modular multi-level converter has an independent DC power source, and the voltage of each DC power source must be controlled equally on average to maintain stable output quality. However, the modular multi-level converter is composed of tens to hundreds of sub-modules, and individual controllers corresponding to the number of sub-modules are required to balance individual DC voltages. However, as the number of controllers increases, the modular multilevel converter has a problem in that it has a greater burden for control.

The present invention is to solve the above-described problem, selecting a sub-module having the maximum and minimum capacitor voltage among sub-modules of a modular multi-level converter, and controlling the voltage of the capacitor of the selected sub-module to be similar to a command value. An object of the present invention is to provide an apparatus and method for controlling voltage balance of a capacitor included in a sub-module of a modular multi-level converter.

In addition to the technical problems of the present invention mentioned above, other features and advantages of the present invention will be described below or will be clearly understood by those skilled in the art from such description and description.

A voltage balance control device for controlling voltage balance of a plurality of sub-modules included in a modular multilevel converter (MMC) according to an embodiment of the present invention for achieving the above-described object is one of the plurality of sub-modules. A voltage detector for detecting a sub-module having a maximum voltage and a minimum voltage of the capacitor included in the sub-module, and the voltage of the sub-module and the capacitor having the maximum voltage based on the maximum voltage and the minimum voltage detected by the voltage detector and a control unit controlling the voltage balance of the plurality of sub-modules by controlling the voltage of the capacitor of the sub-module which is the minimum voltage.

Meanwhile, the voltage balance control method for controlling the voltage balance of a plurality of sub-modules included in a modular multilevel converter (MMC) according to an embodiment of the present invention for achieving the above-described object is a plurality of sub-modules. Detecting a sub-module having a maximum voltage and a minimum voltage of a capacitor included in the sub-module among the modules; and controlling the voltage balance of the plurality of sub-modules by controlling the voltage of the capacitor of the sub-module, which is the voltage.

An apparatus and method for controlling voltage balance of a capacitor included in a sub-module of a modular multi-level converter according to an embodiment of the present invention is selected by selecting a sub-module having the maximum and minimum voltage of the capacitor among the sub-modules of the modular multi-level converter. Since the capacitor voltage of the sub-module is controlled, the capacitor voltage of the sub-module can be controlled with only a small number of controllers.

In addition, it is possible to control the voltage of the capacitor of the sub-module with only a small number of controllers, thereby reducing the burden on the voltage control of the modular multi-level converter.

In addition, other features and advantages of the present invention may be newly recognized through embodiments of the present invention.

1 is a diagram showing the configuration of a modular multi-level converter according to an embodiment of the present invention.
2 is a diagram showing the configuration of a sub-module according to an embodiment of the present invention.
3 is a diagram illustrating a configuration of an apparatus for controlling voltage balance of a capacitor included in a sub-module of a modular multi-level converter according to an embodiment of the present invention.
4 is a diagram illustrating voltage balance control according to an embodiment of the present invention.
5 is a diagram illustrating a capacitor voltage and an output current of a sub-module according to a voltage balance control technique according to an embodiment of the present invention.
6 is a diagram illustrating a voltage balance control method of a capacitor included in a sub-module of a modular multi-level converter according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art can easily implement them. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

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

Referring to FIG. 1 , the modular multi-level converter 100 according to an embodiment of the present invention may include a sub-module 112 , a buffer inductor 114 , and a power supply unit 120 .

The DC system may include several hundred kV of extra-high voltage direct current (HVDC), 1500V-class voltage direct current (LVDC), and medium voltage direct current (MVDC).

Such a DC system may be configured as a power conversion device including a power semiconductor device. The power converter may include a modular multilevel converter (MMC).

The modular multilevel converter 100 may include a plurality of upper arms 110a and lower arms 110b. The plurality of arms 110 represents a circuit for each phase, and may include a plurality of sub-modules 112 and a buffer inductor 114 . The modular multilevel converter 100 may be configured in three phases, and a plurality of submodules 112 and a buffer inductor 114 may be connected in series to each arm 110 for three phases.

For example, in the upper arm 110a, a plurality of sub-modules 112a are serially connected to each of three phases, and an N-th sub-module SMN connected last with respect to the power supply unit 120a among the plurality of sub-modules 112a. ) may be connected to the buffer inductor 114a. Among the plurality of sub-modules 112a, the first sub-module SM01 first connected with respect to the power source unit 120a may be connected to the power source unit 120a. The modular multilevel converter 100 may include three upper arms 110a for each of the upper three phases.

In addition, in the lower arm 110b, a plurality of sub-modules 112b are connected in series to each of the three phases, and an N-th sub-module SMN that is first connected based on the power supply unit 120b among the plurality of sub-modules 112b. ) may be connected to the power supply unit 120b, and the first sub-module SM01 connected last with respect to the power unit 120b among the plurality of sub-modules 112b may be connected to the buffer inductor 114b. The modular multi-level converter 100 may include three lower arms 110b for each of the lower three phases.

Here, although the upper arm (110a) and the lower arm (110b) are separately written for the description of the invention, the upper arm (110a) and the lower arm (110b) can be described as being integrated into the arm (110). In addition, although the submodule 112a of the upper arm 110a and the submodule 112b of the lower arm 110b were separately created, the submodule 112a of the upper arm 110a and the submodule 112a of the lower arm 110b The module 112b may be described as being integrated into the sub-module 112 . In addition, the buffer inductor 114a of the upper arm 110a and the buffer inductor 114b of the lower arm 110b were separately prepared, but the buffer inductor 114a of the upper arm 110a and the buffer of the lower arm 110b The inductor 114b may be described as being integrated as the buffer inductor 114 .

2 is a diagram showing the configuration of a sub-module according to an embodiment of the present invention.

Referring to FIG. 2 , the sub-module 112 of the modular multi-level converter 100 according to an embodiment of the present invention may be configured with various types of circuits. For example, the sub-module 112 may be in the form of a half-bridge converter. That is, the sub-module 112 may include a plurality of switches and a capacitor C. As shown in FIG.

For example, the plurality of switches may include a first switch SW1 and a second switch SW2 , and the first switch SW1 and the second switch SW2 may operate complementarily. That is, when the first switch SW1 is turned on, the second switch SW2 may be turned off, and the first switch SW1 is turned off. In this case, the first switch SW1 may be turned on. The sub-module 112 may be connected to or bypassed by the arm 110 according to the turn-on/turn-off operation of the first switch SW1 and the second switch SW2 .

One end of the capacitor C may be connected to the first switch SW1 , and the other end may be connected to the second switch SW2 . The voltage Vcap of the capacitor C must be maintained at a constant level for a stable output. For example, the constant size may be Vdc/N, and N may be the number of sub-modules 112 .

The arm 110 of the modular multi-level converter 100 may be a voltage source that varies from 0 to the voltage Vcap of the capacitor C according to a switch operation of the plurality of sub-modules 112 . That is, in the case of the modular multi-level converter 100 in which each arm 110 includes N sub-modules 110 , N+1 voltage levels may be output.

Here, in order to achieve a stable output, the voltages of the capacitors C must be controlled by controlling the voltages Vcap of the plurality of sub-modules 112 to maintain the voltage balance. However, in order to control the capacitor C voltage Vcap of the sub-module 112, a controller must be provided for each sub-module 112, and as the number of controllers increases, the sub-module of the modular multi-level converter 100 (112) is burdened. In addition, in order to control the voltage Vcap of the capacitor C of the plurality of sub-modules 112 , the control cycle has to be used slowly.

Accordingly, in the present invention, a voltage balance can be controlled by selecting some sub-modules 112 and controlling only the capacitor C voltage Vcap of the selected sub-module 112 . Due to this, the number of controllers for controlling the capacitor C voltage Vcap of the sub-module 112 may be reduced, and the burden of the modular multi-level converter 100 may also be reduced.

3 is a diagram illustrating a configuration of an apparatus for controlling voltage balance of a capacitor included in a sub-module of a modular multi-level converter according to an embodiment of the present invention.

Referring to FIG. 3 , a voltage balance control device (hereinafter, a voltage balance control device, 200 ) of a capacitor included in a sub-module of a modular multi-level converter according to an embodiment of the present invention includes a voltage detection unit 210 and a controller 220 . ) and a current sign determining unit 230 .

The voltage detector 210 may detect a sub-module having a maximum and a minimum voltage of the capacitor C among the plurality of sub-modules 112 . The voltage detection unit 210 may set the capacitor voltage of one of the plurality of submodules 112 serially connected to each phase as the maximum voltage (Vc.max) and the minimum voltage (Vc.min). Here, the voltage detection unit 210 may set the capacitor voltage of the first sub-module SM01 connected to the first sub-module SM01 to the maximum voltage Vc.max and the minimum voltage Vc.min based on the power supply unit 120a.

The voltage detector 210 compares the voltage of the capacitor C of the second sub-module SM02 connected to the first sub-module SM01 to the maximum voltage Vc.max and the minimum voltage Vc.min in the next cycle. can be compared. When the voltage of the capacitor C of the second sub-module SM02 is greater than the maximum voltage Vc.max, the voltage detection unit 210 resets the maximum voltage to the voltage of the capacitor C of the second sub-module SM02. can do. That is, the voltage detector 210 may set the voltage of the capacitor C of the second sub-module SM02 to the maximum voltage Vc.max. Also, when the voltage of the capacitor C of the second sub-module SM02 is less than the maximum voltage Vc.max, the voltage detection unit 210 may maintain the maximum voltage as it is.

Meanwhile, when the voltage of the capacitor C of the second sub-module SM02 is smaller than the minimum voltage Vc.max, the voltage detection unit 210 sets the minimum voltage to the voltage of the capacitor C of the second sub-module SM02. can be reset to That is, the voltage detection unit 210 may set the voltage of the capacitor C of the second sub-module SM02 to the minimum voltage Vc.min. Also, when the voltage of the capacitor C of the second sub-module SM02 is greater than the minimum voltage Vc.min, the voltage detector 210 may maintain the minimum voltage Vc.min as it is.

The voltage detection unit 210 compares the maximum voltage (Vc.max) and the minimum voltage (Vc.min) with respect to the capacitor voltages of the plurality of sub-modules 112 connected in series with the final maximum voltage (Vc.max) and the minimum voltage. (Vc.min) can be output.

The controller 220 may control the voltage balance of the capacitor C included in the sub-module 112 based on the maximum voltage Vc.max and the minimum voltage Vc.min output from the voltage detection unit 210 . have.

)와 비교할 수 있다. 제어부(220)는 최대전압(Vc.max)과 지령치(

)를 비교하여 오차를 출력할 수 있다. 여기서, 최대전압(Vc.max)은 지령치(

)보다 크기 때문에 두 값의 오차는 양의 값일 수 있다. 또한, 제어부(220)는 최소전압(Vc.min)과 지령치(

)를 비교하여 오차를 출력할 수 있다. 여기서, 최소전압(Vc.min)은 지령치(

)보다 작기 때문에 두 값의 오차는 음의 값일 수 있다.Specifically, the control unit 220 sets the maximum voltage (Vc.max) and the minimum voltage (Vc.min) output from the voltage detection unit 210 as a command value (

) can be compared with The control unit 220 controls the maximum voltage (Vc.max) and the command value (

) can be compared to output the error. Here, the maximum voltage (Vc.max) is the command value (

), so the error between the two values can be positive. In addition, the control unit 220 is the minimum voltage (Vc.min) and the command value (

) can be compared to output the error. Here, the minimum voltage (Vc.min) is the command value (

), so the error between the two values may be negative.

)를 비교한 결과와 최소전압(Vc.min)과 지령치(

)를 비교한 결과를 각각 제어기(222, 224)로 입력할 수 있다. 여기서, 제어부(220)는 최대전압(Vc.max)과 지령치(

)를 비교한 결과가 입력되는 제1제어기(222) 및 최대전압(Vc.max)과 지령치(

)를 비교한 결과가 입력되는 제2제어기(224)를 각각 포함할 수 있다. 제1제어기(222) 및 제2제어기(224)는 비례(proportional, P) 제어기 또는 PI(Proportional integral, PI) 제어기일 수 있다. 제1제어기(222) 및 제2제어기(224)는 제어부(220)의 제어에 의해 동작될 수 있으며, 제어부(220)와 별도의 구성일 수도 있다. The control unit 220 controls the maximum voltage (Vc.max) and the command value (

) and the minimum voltage (Vc.min) and setpoint (

) may be input to the controllers 222 and 224, respectively. Here, the control unit 220 is the maximum voltage (Vc.max) and the command value (

), the first controller 222 and the maximum voltage (Vc.max) and the command value (

) may include a second controller 224 to which the comparison result is input. The first controller 222 and the second controller 224 may be a proportional (P) controller or a PI (Proportional integral, PI) controller. The first controller 222 and the second controller 224 may be operated under the control of the controller 220 , and may be configured separately from the controller 220 .

,

)를 출력할 수 있다. 제어부(220)는 보상치가 양의 값인 경우 서브모듈(112)의 턴온 시간을 증가시킬 수 있고, 제어부(220)는 보상치가 음의 값인 경우 서브모듈(112)의 턴온 시간을 감소시킬 수 있다.When an error value is input to the first controller 222 and the second controller 224, a compensation value (

,

) can be printed. When the compensation value is a positive value, the control unit 220 may increase the turn-on time of the sub-module 112 , and when the compensation value is a negative value, the control unit 220 may decrease the turn-on time of the sub-module 112 .

)보다 크므로, 제1제어기(222)의 출력값은 양의 값일 수 있다. 제어부(220)는 arm(100)에 양의 전류가 흐르는 경우 제1제어기(222)의 출력값에 -1을 곱하여 음의 보상치(

)를 계산할 수 있다. 제어부(220)는 arm(110)에 양의 전류가 흐르는 경우 보상치가 음의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 감소시킬 수 있다.For example, the maximum voltage (Vc.max) is the command value (

), so the output value of the first controller 222 may be a positive value. The control unit 220 multiplies the output value of the first controller 222 by -1 when a positive current flows in the arm 100 to obtain a negative compensation value (

) can be calculated. Since the compensation value becomes a negative value when a positive current flows through the arm 110 , the control unit 220 may reduce the time during which the corresponding sub-module 112 is turned on.

)를 계산할 수 있다. 제어부(220)는 arm(110)에 양의 전류가 흐르는 경우 보상치가 양의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 증가시켜 해당 서브모듈(112)의 커패시터 전압이 증가되도록 할 수 있다. 여기서, 해당 서브모듈(112)은 커패시터(C)의 전압의 최대전압인 서브모듈일 수 있다.On the other hand, when a negative current flows in the arm 110 , the controller 220 multiplies the output value of the first controller 222 by 1 to obtain a positive compensation value (

) can be calculated. Since the compensation value becomes a positive value when a positive current flows through the arm 110 , the control unit 220 increases the turn-on time of the sub-module 112 to increase the capacitor voltage of the sub-module 112 . can Here, the sub-module 112 may be a sub-module that is the maximum voltage of the voltage of the capacitor C.

)보다 작으므로, 제2제어기(224)의 출력값은 음의 값일 수 있다. 제어부(220)는 arm(100)에 양의 전류가 흐르는 경우 제2제어기(224)의 출력값에 -1을 곱하여 양의 보상치(

)를 계산할 수 있다. 제어부(224)는 arm(110)에 양의 전류가 흐르는 경우 보상치의 값이 양의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 증가시켜 해당 서브모듈(112)의 커패시터 전압이 증가되도록 할 수 있다. In addition, the minimum voltage (Vc.min) is

), so the output value of the second controller 224 may be a negative value. The controller 220 multiplies the output value of the second controller 224 by -1 when a positive current flows in the arm 100 to obtain a positive compensation value (

) can be calculated. When a positive current flows through the arm 110 , the compensation value becomes a positive value, so the control unit 224 increases the turn-on time of the sub-module 112 to increase the capacitor voltage of the sub-module 112 . can make it happen

)를 계산할 수 있다. 제어부(224)는 arm(110)에 음의 전류가 흐르는 경우 보상치의 값이 음의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 증가시켜 해당 서브모듈(112)의 커패시터 전압이 증가되도록 할 수 있다. 여기서, 해당 서브모듈(112)은 커패시터(C)의 전압의 최소전압인 서브모듈일 수 있다.On the other hand, when a negative current flows in the arm 110 , the controller 220 multiplies the output value of the second controller 224 by 1 to obtain a negative compensation value (

) can be calculated. When a negative current flows through the arm 110 , the compensation value becomes a negative value, so the control unit 224 increases the turn-on time for the sub-module 112 to increase the capacitor voltage of the sub-module 112 . can make it happen Here, the sub-module 112 may be a sub-module that is the minimum voltage of the capacitor C.

,

)에 정규화된 값을 더해 서브모듈(112)의 변조신호(

,

)를 각각 생성할 수 있다. 여기서, 정규화된 값은

이며, arm(110)의 전압지령에 서브모듈(112)의 개수를 나눈 값일 수 있다. 제어부(220)는 계산된 보상치에 정규화된 값을 각각 더해 생성된 변조신호를 삼각반송파와 비교하여 서브모듈(112)의 스위칭신호를 발생할 수 있다. 여기서, 스위칭신호는 서브모듈(112)에 포함되는 스위치(반도체소자)의 턴온 또는 턴오프를 제어하기 위한 신호일 수 있다. The control unit 220 calculates the compensation value (

,

) by adding the normalized value to the modulated signal (

,

) can be created individually. Here, the normalized value is

, and may be a value obtained by dividing the number of sub-modules 112 by the voltage command of the arm 110 . The control unit 220 may generate a switching signal of the sub-module 112 by comparing the modulated signal generated by adding a normalized value to the calculated compensation value with the triangular carrier. Here, the switching signal may be a signal for controlling the turn-on or turn-off of a switch (semiconductor device) included in the sub-module 112 .

The current sign determining unit 230 may determine the sign of the current according to the direction of the current flowing through the arm 110 . The sign of the current determined by the current sign determining unit 230 may be transmitted to the controller 220 to calculate a compensation value according to the sign of the current.

4 is a diagram illustrating voltage balance control according to an embodiment of the present invention.

Referring to FIG. 4, (a) shows the conventional voltage balance control, (b) shows the voltage balance control according to an embodiment of the present invention, (c) shows the voltage balance control in which the period of (b) is changed indicates FIG. 4 may show voltage balance control when the number of sub-modules 112 per arm 110 is four.

According to (a), in the conventional voltage balance control, the voltage of all sub-modules 112 may follow the command value for every control period. According to (b), it is possible to selectively control only the submodules having the maximum and minimum capacitor (C) voltages. That is, only the sub-module having the maximum and minimum capacitor C voltages in every control period may be controlled. According to (c), it is possible to control with a fast control cycle, thereby reducing the calculation time compared to the conventional method. For example, when the control cycle is doubled, it is possible to control the voltage fluctuation width at the same level as that of the conventional voltage balance control.

5 is a diagram illustrating a capacitor voltage and an output current of a sub-module according to a voltage balance control technique according to an embodiment of the present invention.

Referring to FIG. 5 , the result of performing voltage balance control in the three-phase modular multi-level converter 100 configured with four sub-modules 112 per arm 110 may be shown. For example, an imbalance state is simulated to connect a resistor to the capacitor C included in the first sub-module SMO1, and the voltages of the capacitors C of the plurality of sub-modules 112 are controlled to the same average value. can According to an embodiment of the present invention, voltage balance can be controlled using only the first sub-module SM01, the third sub-module SM03, the fourth sub-module SM04, and the eighth sub-module SM08. Accordingly, it is possible to have the same level of voltage control performance using only a small number of controllers.

6 is a diagram illustrating a voltage balance control method of a capacitor included in a sub-module of a modular multi-level converter according to an embodiment of the present invention.

Referring to FIG. 6 , the voltage detector 210 may detect a sub-module having the maximum and minimum voltages of the capacitor C among the plurality of sub-modules 112 ( S100 ).

The voltage detector 210 may set the capacitor voltage of the first sub-module SM01 to the maximum voltage Vc.max and the minimum voltage Vc.min. The voltage detector 210 calculates the voltage of the capacitor C of the second sub-module SM02 connected to the first sub-module SM01 in the next cycle with the maximum voltage Vc.max and the minimum voltage Vc.min. can be compared. The voltage detector 210 may compare the voltage of the capacitor C of the second sub-module SM02 with the maximum voltage Vc.max to reset the voltage having a larger magnitude to the maximum voltage. Also, the voltage detection unit 210 may compare the voltage of the capacitor C of the second sub-module SM02 with the minimum voltage Vc.min to reset the voltage having a smaller magnitude to the minimum voltage.

)와 각각 비교하여 오차값을 출력할 수 있다(S200).The control unit 220 sets the maximum voltage (Vc.max) and the minimum voltage (Vc.min) detected by the voltage detection unit 110 as a command value (

) and outputting an error value (S200).

)보다 크기 때문에 두 값의 오차는 양의 값일 수 있고, 최소전압(Vc.min)은 지령치(

)보다 작기 때문에 두 값의 오차는 음의 값일 수 있다.The maximum voltage (Vc.max) is the setpoint (

), the error between the two values can be positive, and the minimum voltage (Vc.min) is

), so the error between the two values may be negative.

The controller 220 may input the output error value to the controllers 222 and 224 and calculate a compensation value based on the output value output from the controllers 222 and 224 ( S300 ).

When the compensation value is a positive value, the control unit 220 may increase the turn-on time of the sub-module 112 , and when the compensation value is a negative value, the control unit 220 may decrease the turn-on time of the sub-module 112 .

)보다 크므로, 제1제어기(222)의 출력값은 양의 값일 수 있다. 제어부(220)는 arm(100)에 양의 전류가 흐르는 경우 제1제어기(222)의 출력값에 -1을 곱하여 음의 보상치(

)를 계산할 수 있다. 제어부(220)는 arm(110)에 양의 전류가 흐르는 경우 보상치가 음의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 감소시킬 수 있다.Here, the maximum voltage (Vc.max) is the command value (

), so the output value of the first controller 222 may be a positive value. The control unit 220 multiplies the output value of the first controller 222 by -1 when a positive current flows in the arm 100 to obtain a negative compensation value (

) can be calculated. Since the compensation value becomes a negative value when a positive current flows through the arm 110 , the control unit 220 may reduce the time during which the corresponding sub-module 112 is turned on.

)를 계산할 수 있다. 제어부(220)는 arm(110)에 양의 전류가 흐르는 경우 보상치가 양의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 증가시켜 해당 서브모듈(112)의 커패시터 전압이 증가되도록 할 수 있다. 여기서, 해당 서브모듈(112)은 커패시터(C)의 전압의 최대전압인 서브모듈일 수 있다.On the other hand, when a negative current flows in the arm 110 , the controller 220 multiplies the output value of the first controller 222 by 1 to obtain a positive compensation value (

) can be calculated. Since the compensation value becomes a positive value when a positive current flows through the arm 110 , the control unit 220 increases the turn-on time of the sub-module 112 to increase the capacitor voltage of the sub-module 112 . can Here, the sub-module 112 may be a sub-module that is the maximum voltage of the voltage of the capacitor C.

)보다 작으므로, 제2제어기(224)의 출력값은 음의 값일 수 있다. 제어부(220)는 arm(100)에 양의 전류가 흐르는 경우 제2제어기(224)의 출력값에 -1을 곱하여 양의 보상치(

)를 계산할 수 있다. 제어부(224)는 arm(110)에 양의 전류가 흐르는 경우 보상치의 값이 양의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 증가시켜 해당 서브모듈(112)의 커패시터 전압이 증가되도록 할 수 있다. In addition, the minimum voltage (Vc.min) is

), so the output value of the second controller 224 may be a negative value. The controller 220 multiplies the output value of the second controller 224 by -1 when a positive current flows in the arm 100 to obtain a positive compensation value (

) can be calculated. When a positive current flows through the arm 110 , the compensation value becomes a positive value, so the control unit 224 increases the turn-on time of the sub-module 112 to increase the capacitor voltage of the sub-module 112 . can make it happen

)를 계산할 수 있다. 제어부(224)는 arm(110)에 음의 전류가 흐르는 경우 보상치의 값이 음의 값이 되므로, 해당 서브모듈(112)이 턴온되는 시간을 증가시켜 해당 서브모듈(112)의 커패시터 전압이 증가되도록 할 수 있다. 여기서, 해당 서브모듈(112)은 커패시터(C)의 전압의 최소전압인 서브모듈일 수 있다.On the other hand, when a negative current flows in the arm 110 , the controller 220 multiplies the output value of the second controller 224 by 1 to obtain a negative compensation value (

) can be calculated. When a negative current flows through the arm 110 , the compensation value becomes a negative value, so the control unit 224 increases the turn-on time for the sub-module 112 to increase the capacitor voltage of the sub-module 112 . can make it happen Here, the sub-module 112 may be a sub-module that is the minimum voltage of the capacitor C.

,

)에 정규화된 값을 더해 서브모듈(112)의 변조신호(

,

)를 각각 생성하고, 서브모듈의 스위칭신호를 발생할 수 있다(S400).The control unit 220 calculates the compensation value (

,

) by adding the normalized value to the modulated signal (

,

) may be generated, and a switching signal of the sub-module may be generated (S400).

이며, arm(110)의 전압지령에 서브모듈(112)의 개수를 나눈 값일 수 있다. 제어부(220)는 계산된 보상치에 정규화된 값을 각각 더해 생성된 변조신호를 삼각반송파와 비교하여 서브모듈(112)의 스위칭신호를 발생할 수 있다. 여기서, 스위칭신호는 서브모듈(112)에 포함되는 스위치(반도체소자)의 턴온 또는 턴오프를 제어하기 위한 신호일 수 있다. Here, the normalized value is

, and may be a value obtained by dividing the number of sub-modules 112 by the voltage command of the arm 110 . The control unit 220 may generate a switching signal of the sub-module 112 by comparing the modulated signal generated by adding a normalized value to the calculated compensation value with the triangular carrier. Here, the switching signal may be a signal for controlling the turn-on or turn-off of a switch (semiconductor device) included in the sub-module 112 .

As described above, according to an embodiment of the present invention, a sub-module having the maximum and minimum capacitor voltages is selected from among the sub-modules of the modular multi-level converter, and the voltage of the capacitor of the selected sub-module is controlled to be similar to the command value. It is possible to realize an apparatus and method for controlling voltage balance of a capacitor included in a submodule of a modular multilevel converter.

Those skilled in the art to which the present invention pertains should understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential characteristics thereof, so the embodiments described above are illustrative in all respects and not restrictive. only do The scope of the present invention is indicated by the following claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present invention. .

100: modular multilevel converter
112: submodule
114: buffer inductor
120: power unit
210: voltage detection unit
220: controller
230: current sign determination unit

Claims (22)

In the voltage balance control device for controlling the voltage balance of a plurality of sub-modules included in a modular multilevel converter (Modular Multilevel Converter, MMC),
a voltage detection unit configured to detect a sub-module having a maximum voltage and a minimum voltage of a capacitor included in the sub-module among the plurality of sub-modules;
Control the voltage balance of the plurality of sub-modules by controlling the voltages of the capacitors of the sub-module having the maximum voltage of the capacitor and the sub-module having the minimum voltage of the capacitor based on the maximum and minimum voltages detected by the voltage detection unit including a control unit that
The voltage detection unit sets the capacitor voltage of the first sub-module to a maximum voltage and a minimum voltage,
Comparing the capacitor voltage of the second sub-module connected to the first sub-module with the maximum voltage and the minimum voltage, and resetting the larger voltage among the capacitor voltage and the maximum voltage of the second sub-module to the maximum voltage, the second sub-module A voltage balance control device that resets the smaller of the capacitor voltage and the minimum voltage to the minimum voltage.
According to claim 1,
The control unit includes a controller, and the controller is a proportional (proportional, P) controller or a voltage balance control device comprising a PI (Proportional integral, PI) controller.
delete 3. The method of claim 2,
The control unit outputs an error value by comparing the maximum voltage and the minimum voltage detected by the voltage detection unit with a command value, respectively,
The error value output by comparing the maximum voltage with the command value is a positive value,
An error value output by comparing the minimum voltage with the command value is a negative value.
5. The method of claim 4,
The control unit inputs the output error values to the controller, respectively, and calculates a compensation value based on the output value output from the controller and the direction of the current flowing in the submodule.
6. The method of claim 5,
The control unit increases a turn-on time of the sub-module when the compensation value is a positive value, and decreases a turn-on time of the sub-module when the compensation value is a negative value.
6. The method of claim 5,
When the output value is a positive value and the current flowing through the sub-module is a positive current, the control unit calculates a negative compensation value by multiplying the output value by -1.
6. The method of claim 5,
The control unit calculates a positive compensation value by multiplying the output value by 1 when the output value is a positive value and the current flowing through the sub-module is a negative current.
6. The method of claim 5,
The control unit calculates a positive compensation value by multiplying the output value by -1 when the output value is a negative value and the current flowing through the sub-module is a positive current.
6. The method of claim 5,
The control unit calculates a positive compensation value by multiplying the output value by -1 when the output value is a negative value and the current flowing through the sub-module is a positive current.
6. The method of claim 5,
When the output value is a negative value and the current flowing through the sub-module is a negative current, the controller multiplies the output value by 1 to calculate a negative compensation value.
6. The method of claim 5,
The control unit generates a modulation signal of the sub-module by adding a normalized value to the calculated compensation value, and generates a switching signal of the sub-module through comparison with a triangular carrier,
The normalized value is

is,

is a voltage command value, and N is the number of the sub-modules.
A voltage balance control method for controlling voltage balance of a plurality of sub-modules included in a modular multilevel converter (MMC), the method comprising:
detecting a sub-module having a maximum voltage and a minimum voltage of a capacitor included in the sub-module among the plurality of sub-modules;
Controlling the voltage balance of the plurality of submodules by controlling the voltages of the capacitors of the submodule having the maximum voltage and the submodule having the minimum voltage of the capacitor based on the detected maximum and minimum voltages but,
The step of detecting the submodule comprises:
Set the capacitor voltage of the first sub-module to the maximum voltage and the minimum voltage,
Comparing the capacitor voltage of the second sub-module connected to the first sub-module with the maximum voltage and the minimum voltage, and resetting the larger voltage among the capacitor voltage and the maximum voltage of the second sub-module to the maximum voltage, the second sub-module A voltage balance control method that resets the smaller of the capacitor voltage and the minimum voltage of the voltage to the minimum voltage.
delete 14. The method of claim 13, wherein controlling the voltage balance comprises:
The detected maximum and minimum voltages are compared with the command value, respectively, to output an error value, input the output error value to the controller, respectively, and calculate a compensation value based on the output value output from the controller and the direction of the current flowing through the submodule do,
An error value output by comparing the maximum voltage with the command value is input to the controller, and an output value outputted is a positive value,
An error value output by comparing the minimum voltage with the command value is input to the controller, and an output value outputted by the controller is a negative value.
16. The method of claim 15, wherein controlling the voltage balance comprises:
A voltage balance control method of increasing a turn-on time of the sub-module when the compensation value is a positive value, and decreasing a turn-on time of the sub-module when the compensation value is a negative value.
16. The method of claim 15, wherein controlling the voltage balance comprises:
When the output value is a positive value and the current flowing through the sub-module is a positive current, the voltage balance control method for calculating a negative compensation value by multiplying the output value by -1.
16. The method of claim 15, wherein controlling the voltage balance comprises:
A voltage balance control method of calculating a positive compensation value by multiplying the output value by 1 when the output value is a positive value and the current flowing through the sub-module is a negative current.
16. The method of claim 15, wherein controlling the voltage balance comprises:
When the output value is a negative value and the current flowing through the submodule is a positive current, the voltage balance control method for calculating a positive compensation value by multiplying the output value by -1.
16. The method of claim 15, wherein controlling the voltage balance comprises:
When the output value is a negative value and the current flowing through the submodule is a positive current, the voltage balance control method for calculating a positive compensation value by multiplying the output value by -1.
16. The method of claim 15, wherein controlling the voltage balance comprises:
A voltage balance control method of calculating a negative compensation value by multiplying the output value by 1 when the output value is a negative value and the current flowing through the submodule is a negative current.
16. The method of claim 15, wherein controlling the voltage balance comprises:
By adding a normalized value to the calculated compensation value, each modulated signal of the sub-module is generated, and a switching signal of the sub-module is generated through comparison with a triangular carrier,
The normalized value is

is,

is a voltage command value, and N is the number of the sub-modules.

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