KR20230149415A - System for controlling sub-modules of modular multilevel converter - Google Patents

Abstract

This disclosure provides a system for controlling submodules of a modular multi-level converter. The system includes a controller configured to perform modulation and voltage balancing control; And it may include one or more sub-module groups consisting of a plurality of sub-modules (SMs). Each sub-module may include a control unit for firing control and status measurement of the corresponding sub-module. One of the submodules of the submodule group may be a master submodule, and the remaining submodules of the submodule group may be slave submodules. For the sub-module group, the controller is directly connected to the master sub-module through a cable and not directly connected to the slave sub-modules, and the master sub-module may be directly connected to each of the slave sub-modules. According to the present disclosure, there is an effect of reducing cable connection complexity of a modular multi-level converter and increasing utilization of a control unit built in a sub-module.

Description

System for controlling submodules of a modular multilevel converter {SYSTEM FOR CONTROLLING SUB-MODULES OF MODULAR MULTILEVEL CONVERTER}

The present disclosure relates to a modular multilevel converter, and more particularly to a system for controlling submodules of a modular multilevel converter.

Demand for new and renewable energy is increasing day by day, and demand and research on modular multi-level converters (MMC) are increasing significantly to improve power quality problems for new and renewable energy sources. there is. In addition, in order to handle the increasing demand for power, the number of installation cases of high voltage transmission lines (HVDC: High Voltage Direct Current) is increasing not only domestically but also internationally, and MMC can be used when installing HVDC.

As mentioned above, MMC can be a good solution in the development of new renewable energy sources and HVDC, but in general, MMC can have hundreds of sub-modules (SM: Sub-Modules), so the system configuration is excessively complex. And the construction cost is also very high.

When building an MMC system, the complexity of the connection between the controller and submodules can be a major factor that increases system complexity and cost, and it is necessary to present an MMC submodule control structure that can solve these problems.

The purpose of the present disclosure to solve these problems is to provide a system for controlling submodules of a modular multi-level converter.

According to one embodiment of the present disclosure, a system for controlling submodules of a modular multi-level converter is provided. The system includes a controller configured to perform modulation and voltage balancing control; And it may include one or more sub-module groups consisting of a plurality of sub-modules (SMs). Each sub-module may include a control unit for controlling firing and measuring the status of the corresponding sub-module. One of the submodules of the submodule group may be a master submodule, and the remaining submodules of the submodule group may be slave submodules. For the submodule group, the controller is directly connected to the master submodule through a firing signal line and a status signal line and is not directly connected to the slave submodules, and the master submodule is connected to each slave in the submodule group. It can be directly connected to the submodule through the second firing signal line and the second status signal line.

In addition, the controller generates gate signals (G 1 to G _n ) for firing control for all sub-modules (SM1 to SMn) of the sub-module group and transmits the gate signals (G ₁ to G n ) to the master sub-module through the firing signal line. It can be passed on. The control unit of the master sub-module will be configured to distribute the remaining gate signals (G ₂ to G _n ) excluding the gate signal ( G ₁ ) for itself to the corresponding slave sub-modules through each second firing signal line. You can.

In addition, the control unit of the master sub-module receives the voltage values (v ₂ to v _n ) of the slave sub-modules of the sub-module group through each second state signal line and receives its own voltage value (v ₁ ). It may be configured to transmit voltage values (v ₁ to v _n ) of all sub-modules of the sub-module group including the sub-module group to the controller through the status signal line.

In addition, the control unit of the master sub-module is configured to control the sub-module including voltage values (v ₁ to v _n ) of all sub-modules of the sub-module group and current values (i _up or i _lw ) of the sub-module group. It may be configured to transmit group status measurement data to the controller through the status signal line.

Additionally, the sub-module may be a half-bridge type sub-module (HB-SM).

In addition, the modular multi-level converter is connected to a three-phase power system, and each sub-module group of the one or more sub-module groups constitutes an upper arm or lower arm for each phase. You can.

In addition, the system may further include a higher level controller connected to the controller and configured to perform reactive power control and voltage control of the modular multi-level converter.

According to the present disclosure, there is an effect of reducing cable connection complexity of a modular multi-level converter and increasing utilization of a control unit built in a sub-module.

In addition, according to the present disclosure, instead of the central controller being cable-connected to each of hundreds of sub-modules, the central controller is cable-connected only to the master sub-module, and is able to control the slave sub-modules through the master sub-module, thereby reducing the cable connection. The complexity and resulting costs can be dramatically reduced, and it has the advantage of utilizing the control unit built into the existing submodule without the need to install separate additional devices for the master/slave submodule control structure.

1 is an exemplary diagram showing the basic configuration of a modular multilevel converter.
Figure 2 is a diagram showing an example of a half-bridge type submodule (HB-SM).
3 is a diagram showing an exemplary control structure of a modular multilevel converter.
FIG. 4 is a diagram illustrating a control structure based on master/slave submodules of a modular multilevel converter according to an embodiment of the present disclosure.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. First, when adding reference numerals to components in each drawing, it should be noted that identical components are given the same reference numerals as much as possible even if they are shown in different drawings. Additionally, in describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description will be omitted.

Various aspects of the invention are described below. It is to be understood that the inventions presented herein may be implemented in a wide variety of forms and that any particular structure, function, or both, presented herein is illustrative only. Based on the inventions presented herein, those skilled in the art will understand that one aspect presented herein can be implemented independently of any other aspects and that two or more of these aspects can be implemented in various ways. You will understand that it can be combined with . For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. Additionally, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more aspects described herein.

The modular multi-level converter (MMC) presented in this specification may be a voltage-type converter type device that can be applied to flexible transmission systems (FACTS) and high-voltage transmission lines (HVDC). Additionally, the power system referred to herein may be a three-phase power system.

1 is an exemplary diagram showing the basic configuration of a modular multilevel converter (MMC).

MMC is a type of voltage source converter and is a device that can generate alternating current (AC) voltage by converting direct current (DC) power into a step wave. The main functions of MMC can be reactive power compensation, harmonic removal, and phase imbalance resolution.

Referring to Figure 1, the MMC may be composed of three phases in accordance with the three phases 130 of the power system, and each phase may include an upper arm 120 and a lower arm 121. there is. Each arm may include a plurality of submodules (SM: Sub Modules) 110, and these submodules may be configured in series. Additionally, a reactor (L) to prevent overcurrent may be connected to each arm. Depending on the implementation, the submodule (SM) 100 is a half bridge SM (HB-SM), a full bridge SM (FB-SM), and a 3-level flying-capacitor SM (3L-FCSM). ), etc. Below, for convenience of explanation, the description will be based on the HB-SM type submodule 100.

Figure 2 is a diagram showing an example of a half bridge type submodule (HB-SM).

As shown in FIG. 2, the half-bridge type submodule (HB-SM) 110 includes two IGBT (Insulated-Gate Bipolar Transistor) switches 111 and 113 and two diodes 115 and 117. and an energy storage element 119 such as a capacitor. Each sub-module 110 may be connected in series to another sub-module 110 using two terminals 121 and 123. In addition, each sub-module 110 may have a built-in control unit that can be implemented with a central processing unit (CPU), a field programmable gate array (FPGA), etc., and the firing (firing) of the corresponding sub-module through the control unit. firing) control (e.g., on/off control of IGBT) and status measurement (e.g., measurement of voltage value and current value of sub-module) can be performed.

The HB-SM type submodule 110 as shown in FIG. 2 can have a two-level voltage of 0V and +Vdc_cell according to the control signal input to the IGBT switches 111 and 113, and the FB-SM type submodule 110 ) can have three voltage levels: -Vdc_cell, 0V, and +Vdc_cell. The MMC may operate by controlling the IGBT switches 111 and 113 of all submodules 110 within the MMC on/off so that AC power in the form of a sine wave can be generated at the AC terminal of each phase.

3 is a diagram showing an exemplary control structure of a modular multilevel converter.

As shown in FIG. 3, the MMC control system may include an upper controller 210, a lower controller 220, and a plurality of sub-modules 110. The upper controller 210 may be configured to perform reactive power control and voltage control of the MMC. The lower controller 220 is connected to the upper controller 220 and may be configured to perform modulation and voltage balancing control. The modulation method applied to MMC may be a PWM (Pulse Width Modulation) method or a staircase method depending on the implementation. For example, the PWM method may be CPS-PWM, LSC-PWM, etc., and the staircase method may be NLM, Selective Harmonic Elimination (SHE), Equivalent Area Method (EAM), etc. The lower controller 220 may be connected to each of the plurality of sub-modules 110 through cables (e.g., electric cables, optical cables, etc.), and determines which sub-modules 110 to use according to the voltage level to be formed. And by controlling them on/off, voltage balancing control can be performed. Each sub-module 110 may include a control unit (not shown) that can be implemented with a CPU, FPGA, etc., and the control unit transfers the voltage/current information of the corresponding sub-module to the lower controller 220 and the lower controller ( 220), it can receive a firing control signal and operate to control the IGBT of the corresponding sub-module.

In the control structure of FIG. 3, the lower controller 220 is directly connected to each sub-module 110, and for this purpose, a plurality of sub-controllers 220 and a plurality of sub-modules 110 are connected to each other for 1:n communication. Cables are needed. In actual implementation, there is a considerable physical distance between the lower controller 220 and the sub-modules 110, and typically more than 200 sub-modules can be applied to the MMC. Therefore, when designing an MMC control system like the control structure of FIG. 3, the sub-controller 220 must be connected with a cable to each of 200 or more sub-modules, so the system structure may become excessively complex, and such implementation requires Costs can also increase significantly. In addition, when applying an expensive optical cable, not only does the cost of the cable itself increase significantly due to the considerable physical distance, but also a photoelectric conversion module must be additionally applied, which can further increase system complexity and cost. Therefore, the present disclosure seeks to propose an MMC control structure based on the master/slave submodules below.

FIG. 4 is a diagram illustrating a control structure based on master/slave submodules of a modular multilevel converter according to an embodiment of the present disclosure.

In this implementation, the submodules 110 of the MMC may be configured as one or more submodule groups consisting of a plurality (eg, N (N is a positive integer)) of submodules. For example, the upper arm 120 or the lower arm 121 composed of multiple (N) sub-modules may be set as one sub-module group. If the upper arm 120 and lower arm 121 of each phase connected to the three-phase power system are defined as each submodule group, the MMC control system has 6 submodule groups (3 upper arms and 3 lower arms) cancers). However, the present disclosure is not limited thereto, and a specific number of sub-modules 110, not arm units, may be defined as one sub-module group.

In the submodule group, one of the submodules may be set as the master submodule 310, and the remaining submodules of the submodule group may be set as slave submodules 311-2, 311-i, and 311-n. can be set. As shown in Figure 4, for a sub-module group, the sub-controller 220 may be directly connected to the master sub-module 310 through a cable including a firing signal line and a status signal line, and the slave sub-module within the group It is not directly connected to fields 311-2, 311-i, and 311-n. Instead, the master submodule 310 is a separate submodule including each slave submodule (311-2, 311-i, 311-n) within the corresponding submodule group, a second firing signal line, and a second status signal line. can be connected directly via a cable. Since the submodules 310, 311-2, 311-i, and 311-n constituting one submodule group are arranged adjacent to each other in series, the length of the cable between submodules in the group is determined by the subcontroller 220 ) and may be much shorter than the cable length between the master submodule 310. Through this configuration, the sub-controller 220 is not connected with a cable to each of all sub-modules 110 constituting the MMC, but is connected only to the master sub-modules 310 and 320 of each sub-module group to control the MMC control system. Complexity can be greatly reduced.

In the control structure shown in FIG. 4, the controller 220 provides a gate signal for firing control for all sub-modules (SM1 to SMn) (310, 311-2, 311-i, 311-n) of the sub-module group. G ₁ to G _n can be generated and transmitted to the master sub-module 310 through a firing signal line. The control unit of the master sub-module 310 distributes the remaining gate signals (G ₂ to G _n ), excluding the gate signal (G ₁ ) for itself, to the corresponding slave sub-modules through each second firing signal line. It can be configured. The control unit of the master sub-module 310 can control on/off according to its gate signal (G ₁ ), and controls each of the slave sub-modules 311-2, 311-i, and 311-n. The unit can control on/off according to its own gate signal (G) received from the master sub-module 310.

The control unit of the master sub-module 310 connects the voltage values (v ₂ to v _n ) of the slave sub-modules (311-2, 311-i, 311-n) of the corresponding sub-module group to each second state. It can be received through the signal line. Through this, the control unit of the master sub-module 310 controls the voltage values of all sub-modules (310, 311-2, 311-i, 311-n) of the corresponding sub-module group, including its own voltage value (v ₁ ). (v ₁ to v _n ) can be obtained and configured to transmit them to the controller 220 through a status signal line. In addition, the control unit of the master sub-module 310 can acquire the current value (i _up or i _lw ) of the corresponding sub-module group, and all sub-modules 310, 311-2, 311- of the corresponding sub-module group The status measurement data of the corresponding submodule group, including the voltage values (v ₁ to v _n ) of (i, 311-n) and the current values (i _up or i _lw ) of the corresponding submodule group, are sent to the controller through the status signal line. It can be delivered to (220).

Again, the controller 220 updates gate signals for firing control through modulation and voltage balancing control based on the voltage values (v ₁ to v _n ) of the corresponding sub-module group received from the master sub-module 310. (G ₁ ~ G _n ) can be generated and transmitted to the master sub-module 310 through the firing signal line, and the master sub-module 310 can generate the corresponding slave sub-module 310 through each second state signal line as described above. By transmitting the gate signal (G) corresponding to the module, each submodule (310, 311-2, 311-i, 311-n) within the corresponding submodule group turns on again according to the updated gate signal (G) for itself. You can control /off.

The above-described operations performed by the master sub-module 310 on the slave sub-modules 311-2, 311-i, and 311-n within the corresponding sub-module group are performed by mounting separate additional devices on the master sub-module 310. It can be performed using the control unit built in the master sub-module 310 without any need, and through this, the utilization of the control unit built in the sub-module can be increased.

The description of the presented embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the scope of the invention. Thus, the present invention is not limited to the embodiments presented herein, but is to be construed in the broadest scope consistent with the principles and novel features presented herein.

110: submodule
120: Top Cancer
121: Sub arm
130: 3-phase power system
210: upper controller
220: Sub-controller
310, 320: Master submodule
311-2, 311-i, 311-n: Slave submodule

Claims (7)

A system for controlling submodules of a modular multi-level converter, comprising:
A controller configured to perform modulation and voltage balancing control; and
Includes one or more submodule groups consisting of a plurality of submodules (SMs),
Each submodule includes a control unit for controlling the firing and measuring the status of the submodule,
One of the submodules in the submodule group is a master submodule, and the remaining submodules in the submodule group are slave submodules,
For the submodule group, the controller is directly connected to the master submodule through a firing signal line and a status signal line and is not directly connected to the slave submodules, and the master submodule is connected to each slave in the submodule group. Directly connected to the submodule through a second firing signal line and a second status signal line,
System for controlling submodules of modular multi-level converters. According to claim 1,
The controller generates gate signals (G ₁ to G _n ) for firing control for all sub-modules (SM1 to SMn) of the sub-module group and transmits them to the master sub-module through the firing signal line. And, the control unit of the master sub-module distributes the remaining gate signals (G ₂ to G _n ) excluding the gate signal ( G ₁ ) for itself to the corresponding slave sub-modules through each second firing signal line. composed,
System for controlling submodules of modular multi-level converters. According to claim 1,
The control unit of the master sub-module receives the voltage values (v ₂ to v _n ) of the slave sub-modules of the sub-module group through each second state signal line and includes the voltage value (v ₁ ) of the master sub-module. Configured to transmit voltage values (v ₁ to v _n ) of all sub-modules of a sub-module group to the controller through the status signal line,
System for controlling submodules of modular multi-level converters. According to claim 3,
The control unit of the master sub-module is a control unit of the sub-module group including voltage values (v ₁ to v _n ) of all sub-modules of the sub-module group and current values (i _up or i _lw ) of the sub-module group. configured to transmit status measurement data to the controller via the status signal line,
System for controlling submodules of modular multi-level converters. According to claim 1,
The submodule is a half bridge type submodule (HB-SM),
System for controlling submodules of modular multi-level converters. According to claim 1,
The modular multi-level converter is connected to a three-phase power system, and each sub-module group of the one or more sub-module groups constitutes an upper arm or lower arm for each phase,
System for controlling submodules of modular multi-level converters. According to claim 1,
Further comprising an upper controller connected to the controller and configured to perform reactive power control and voltage control of the modular multi-level converter,
System for controlling submodules of modular multi-level converters.