Module dead zone compensation control method and system of modular multilevel converter

Abstract

The invention belongs to the technical field of modular multilevel converters, and provides a module dead-zone compensation control method and system for a modular multilevel converter, and the method comprises the steps: obtaining a switching control instruction of each sub-module according to a bridge arm modulation voltage instruction, a sub-module voltage sorting result and a bridge arm current direction; then, according to the switching control instruction, the charging and discharging conditions of bridge arm current are determined; if the current of the bridge arm is in the charging direction, delay input control is carried out on the sub-module which is switched from cutting to input; if the current of the bridge arm is in the discharge direction, carrying out delay input control on the sub-module which is converted from input to cut off; according to the method, instruction change sub-modules in different current directions are counted, and then sub-module instructions of which the states are changed oppositely are delayed, so that loss or redundancy of bridge arm voltage caused by dead time is compensated, alternating-current and direct-current harmonic waves in an MMC operation process can be reduced, internal circulating current of a converter is reduced, and the service life of the converter is prolonged. And the operation characteristics of the flexible direct-current power transmission system are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of modular multi-level converters, and in particular relates to a module dead zone compensation control method and system of a modular multi-level converter. Background Art

[0002] With the exhaustion of offshore resources, offshore wind power will further develop in the deep and offshore areas in the future. The flexible DC transmission system with black start capability and independent AC voltage control capability is the main system solution for the transmission of deep and offshore wind power. However, the expensive offshore flexible DC converter station has restricted the development of offshore wind power to a certain extent. In order to achieve the lightweight of the flexible DC transmission system, the use of sub-modules with higher voltage specifications and the reduction of the number of sub-modules is the most effective technical means to reduce the volume and weight of the converter valve. At present, power semiconductors with higher voltage specifications have gradually met the conditions for engineering application. The use of power semiconductors with higher specifications can increase the operating voltage of sub-modules and reduce the number of sub-modules, thereby realizing the compactness and lightness of the entire converter; however, the integrated gate-commutated thyristor (IGCT) device or the insulated gate bipolar transistor (IGBT) device needs a certain amount of time to reach a stable state during the switching process. The switching characteristics of the device itself determine that the sub-module needs to be set with a longer dead time.

[0003] When the dead time of a sub-module is large, when the bridge arm current is in the charging direction, the output voltage of the sub-module that changes from being put into operation to being removed will not change in time, and when the bridge arm current is in the discharging direction, the output voltage of the sub-module that changes from being removed into operation will not change in time. For sub-modules with long dead time, during the operation of the converter, the long dead time of the sub-module affects the accuracy of the bridge arm output voltage, further leading to problems such as increased AC and DC harmonics and increased internal circulating current of the converter. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a module dead zone compensation control method and system for a modular multilevel converter. When the bridge arm current is in the charging direction, the present invention performs a delayed input processing on the sub-module that is switched from cut-off to input, and when the bridge arm current is in the discharging direction, the present invention performs a delayed removal processing on the sub-module that is switched from input to cut-off, thereby compensating for the lack or excess of the bridge arm voltage caused by the dead time, reducing the AC and DC harmonics in the operation process of the modular multilevel converter, reducing the internal circulating current of the converter, and improving the operation characteristics of the flexible DC transmission system.

[0005] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0006] In a first aspect, the present invention provides a module dead zone compensation control method for a modular multilevel converter, comprising:

[0007] In each valve control cycle, the switching control instruction of each submodule is obtained according to the bridge arm modulation voltage instruction, the result of the submodule voltage sorting and the direction of the bridge arm current;

[0008] According to the switching control instruction, the charging and discharging status of the bridge arm current is determined; if the bridge arm current is in the charging direction, the submodule that is switched from cut-off to switched-on is controlled with a delay; if the bridge arm current is in the discharging direction, the submodule that is switched from switched-on to cut-off is controlled with a delay.

[0009] Furthermore, the number of bridge arm submodules put into operation is obtained according to the ratio of the bridge arm modulation voltage instruction and the rated working voltage of the submodule; if the current of the bridge arm is in the charging direction, the input instructions are issued in sequence according to the number of submodules put into operation in the order of the voltage values ​​of the submodules in the bridge arm from small to large, and the removal instructions are issued to the remaining submodules in the bridge arm; when the bridge arm modulation voltage instruction corresponds to the current of the bridge arm in the discharging direction, the input instructions are issued in sequence according to the number of submodules put into operation in the order of the voltage values ​​of the submodules from large to small, and the removal instructions are issued to the remaining submodules in the bridge arm.

[0010] Furthermore, when the bridge arm current is in the charging direction, the number of submodules in the previous control cycle that are in the on state and the number of submodules that receive the removal instruction in the current control cycle are counted;

[0011] Count the submodules that were in the cut-off state in the previous control cycle and the submodules that received the input command in the current control cycle, and send delay commands to the submodule controllers in turn; until the number of submodules that send delays reaches the number of submodules that received the cut-off command in the current control cycle, or all submodules that have been switched from cut-off to input have received delay commands.

[0012] Furthermore, when the bridge arm current is in the discharge direction, the number of submodules in the cut-off state in the previous control cycle and the number of submodules that receive the input instruction in the current control cycle are counted;

[0013] Count the submodules that were in the on state in the previous control cycle and the submodules that received the removal instruction in the current control cycle, and send delay instructions to the submodule controllers in turn; until the number of submodules with delays reaches the number of submodules that received the on-state instruction in the current control cycle, or all submodules that have been switched from on to off have received delay instructions.

[0014] Furthermore, the dead zone compensation time is preset according to the switching characteristics of a specific power device.

[0015] Further, the dead zone compensation time set for the integrated gate-commutated thyristor power device is greater than the dead zone compensation time set for the insulated gate bipolar transistor power device.

[0016] In a second aspect, the present invention further provides a module dead zone compensation control system for a modular multilevel converter, comprising:

[0017] The switching control instruction acquisition module is configured to: in each valve control cycle, obtain the switching control instruction of each submodule according to the bridge arm modulation voltage instruction, the result of the submodule voltage sorting and the direction of the bridge arm current;

[0018] The dead zone compensation control module is configured to: determine the charging and discharging conditions of the bridge arm current according to the switching control instruction; if the bridge arm current is in the charging direction, delay the switching-in control of the submodule that is switched from being switched-in to being switched-in; if the bridge arm current is in the discharging direction, delay the switching-in control of the submodule that is switched from being switched-in to being switched-in to being switched-in

[0019] In a third aspect, the present invention further provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the module dead zone compensation control method of the modular multilevel converter described in the first aspect.

[0020] In a fourth aspect, the present invention further provides an electronic device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, wherein when the processor executes the program, the steps of the module dead zone compensation control method of the modular multilevel converter described in the first aspect are implemented.

[0021] In a fifth aspect, the present invention further provides a computer program product, comprising a computer program, and when the computer program is executed by a processor, the steps of the module dead zone compensation control method of the modular multilevel converter described in the first aspect are implemented.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention first obtains the switching control instruction of each submodule according to the bridge arm modulation voltage instruction, the result of the submodule voltage sorting and the direction of the bridge arm current in each valve control cycle; then, the charging and discharging status of the bridge arm current is determined according to the switching control instruction; if the bridge arm current is in the charging direction, the submodule that is switched from cut-off to switched-on is controlled to be switched-on with delay; if the bridge arm current is in the discharging direction, the submodule that is switched from switched-on to cut-off is controlled to be switched-on with delay; by counting the instruction change submodules under different current directions, and then delaying the instructions of the submodules with opposite state changes, the missing or redundant bridge arm voltage caused by the dead time is compensated, the AC and DC harmonics in the MMC operation process can be reduced, the internal circulating current of the converter is reduced, the operation characteristics of the flexible DC power transmission system are improved, and the lightweight purpose of the flexible DC power transmission system is achieved on the basis of ensuring the operation characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The drawings in the specification that constitute a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments of this embodiment and their descriptions are used to explain this embodiment and do not constitute improper limitations on this embodiment.

[0025] Figure 1 This is a schematic diagram of the structure of a modular multilevel converter according to Embodiment 1 of the present invention;

[0026] Figure 2 Schematic diagram of the external characteristic influence of the dead zone on the submodule instruction change in the charge and discharge direction of Example 1 of the present invention;

[0027] Figure 3 This is a flow chart of the control method of Example 1 of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0029] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0030] Modular multilevel converter (MMC), MMC generally has 3 phase units, each phase unit consists of an upper bridge arm and a lower bridge arm, each bridge arm consists of several sub-modules and a bridge arm reactor in series to meet the application requirements of high voltage and large capacity. MMC has the ability to independently control active power and reactive power, can provide AC voltage control for island networks, and is suitable for offshore wind power DC transmission systems.

[0031] Embodiment 1:

[0032] With the vigorous development of green energy, potential energy bases in the future are mostly in desert areas and deep sea areas, which are far away from the load center. It is difficult to consume large-scale renewable energy bases on site, and large-scale long-distance transmission is required. In recent years, with the rapid development of high-power power electronics technology, flexible direct current transmission based on modular multi-level converters has been rapidly developed and applied. Flexible direct current transmission technology has the advantages of being able to supply power to isolated island networks, no commutation failure, low voltage harmonic content and high waveform quality, and the ability to flexibly and quickly adjust active power and reactive power. This has led to a wide range of application needs for flexible transmission technology in the power system, of which the most typical application scenario is large-scale clean energy transmission such as offshore wind power.

[0033] With the exhaustion of offshore resources, offshore wind power will further develop in the deep and offshore areas in the future. The flexible DC transmission system with black start capability and independent AC voltage control capability is the main system solution for deep and offshore wind power transmission. However, the expensive offshore flexible DC converter station has restricted the development of offshore wind power to a certain extent. It is of great significance to the development of wind power to study and break through the technical problems of offshore wind power transmission, reduce the cost of offshore wind power transmission system, improve the economic efficiency of offshore wind power generation, and realize the parity of offshore wind power access to the grid.

[0034] In order to achieve lightweight flexible DC transmission system, the use of higher voltage submodules and thus reduce the number of submodules is the most effective technical means to reduce the volume and weight of the converter valve. Power semiconductors with higher voltage specifications are gradually meeting the conditions for engineering applications, such as 6.5kV IGCT. The use of higher specification power semiconductors can increase the operating voltage of the submodules and reduce the number of submodules, thereby achieving compactness and lightness of the entire converter. However, the IGCT device requires a certain amount of time to reach a stable state during the switching process. The switching characteristics of the device itself determine that the submodule needs to be set with a longer dead time, even up to 40us to 50us. During the operation of the converter, the long dead time of the submodule affects the accuracy of the output voltage of the bridge arm, further leading to problems such as increased AC and DC harmonics and increased internal circulating current of the converter.

[0035] In order to solve the above problem, this embodiment provides a module dead zone compensation control method for a modular multilevel converter, which counts the command change sub-modules under different current directions, and then delays the sub-module commands with opposite state changes, thereby compensating for the lack or excess of bridge arm voltage caused by the dead time. It can reduce the AC and DC harmonics in the MMC operation process, reduce the internal circulating current of the converter, and improve the operating characteristics of the flexible DC transmission system. On the basis of ensuring the operating characteristics, the purpose of lightweighting the flexible DC transmission system is achieved.

[0036] As shown in the figure, it is the topological structure of the modular multilevel converter. The modular multilevel converter includes three phase units, each phase unit includes an upper bridge arm and a lower bridge arm, each bridge arm includes several submodules and a bridge arm reactor, and several submodules and one bridge arm reactor are connected in series.

[0037] like Figure 2 As shown in the figure, when the dead time of the submodule is large, when the bridge arm current is in the charging direction, the output voltage of the submodule that changes from input to removal does not change in time, and when the bridge arm current is in the discharging direction, the output voltage of the submodule that changes from removal to input does not change in time. For submodules with long dead time, such as submodules based on IGCT power devices, during the operation of the converter, the long dead time of the submodule affects the accuracy of the bridge arm output voltage, further leading to problems such as increased AC and DC harmonics and increased internal circulating current of the converter.

[0038] like Figure 3 As shown, the compensation control strategy can be used to improve the influence of the dead zone on the submodule and the bridge arm output voltage. When the bridge arm current is in the charging direction, the submodule that is switched from cut-off to switched-on is delayed to be switched-on. When the bridge arm current is in the discharging direction, the submodule that is switched from switched-on to cut-off is delayed to be switched-off. This can compensate for the lack or excess of the bridge arm voltage caused by the dead zone time, reduce the AC and DC harmonics in the MMC operation process, reduce the internal circulating current of the converter, and improve the operation characteristics of the flexible DC transmission system. Specifically:

[0039] S1, in each valve control cycle, according to the bridge arm modulation voltage instruction U arm , the result of submodule voltage sorting, bridge arm current I arm direction, and calculate the switching control instructions for each submodule.

[0040] Specifically, firstly, the number of submodules in the bridge arm N is calculated by dividing the bridge arm modulation voltage instruction by the rated working voltage of the submodule. in =U arm / U sm Then, if the current of the bridge arm is in the charging direction, N in When the bridge arm modulation voltage instruction corresponds to the current of the bridge arm in the discharge direction, N submodules are issued in the order of the voltage value from large to small. in An input instruction is issued to the remaining sub-modules in the bridge arm, and a removal instruction is issued to the remaining sub-modules in the bridge arm.

[0041] According to the charging and discharging conditions of the bridge arm current, the dead zone voltage of the submodule is compensated respectively, and step S2 and / or step S3 are executed:

[0042] S2. When the bridge arm current is in the charging direction, count the number of submodules that were in the on state in the previous control cycle and the number of submodules that received the removal command in this control cycle. in_to_cut Then, count the submodules that were in the cut-off state in the previous control cycle and the submodules that received the input command in this control cycle, and send delay commands to the submodule controllers in turn until one of the following two conditions is met, then stop sending: the number of submodules that send delays reaches N in_to_cut The sub-modules that have been cut off or switched on have all received the delay instruction.

[0043] The submodule controller that receives the delay instruction performs a delay operation on the new instruction: maintains the original instruction for a dead time, and then updates it to a new switching instruction.

[0044] S3, when the bridge arm current is in the discharge direction, count the number of submodules in the cut-off state in the previous control cycle and the number of submodules that receive the input command in this control cycle N cut_to_in .

[0045] Then, count the submodules that were in the on-state in the previous control cycle and the submodules that received the removal command in this control cycle, and send delay commands to the submodule controllers in turn until one of the following two conditions is met, then stop sending: the number of submodules that send delays reaches N cut_to_in All sub-modules that have been put into operation or removed from operation have received delay instructions.

[0046] The submodule controller that receives the delay instruction performs a delay operation on the new instruction: maintains the original instruction for a dead time, and then updates it to a new switching instruction.

[0047] Optionally, the dead zone compensation time may be pre-set according to the switching characteristics of the specific power device, thereby improving the control flexibility. For example, a longer dead zone compensation time (e.g., 40us) may be set for the IGCT power device, and a shorter dead zone compensation time (10us to 20us) may be set for the IGBT power device; the dead zone compensation time set for the IGCT power device is greater than the dead zone compensation time set for the IGBT power device.

[0048] After receiving the delay instruction sent by the upper controller, the submodule controller will continue to maintain the original switching instruction for a dead zone compensation time, and then update it to the newly received switching instruction.

[0049] Embodiment 2:

[0050] This embodiment provides a module dead zone compensation control system for a modular multilevel converter, including:

[0051] The switching control instruction acquisition module is configured to: in each valve control cycle, obtain the switching control instruction of each submodule according to the bridge arm modulation voltage instruction, the result of the submodule voltage sorting and the direction of the bridge arm current;

[0052] The dead zone compensation control module is configured to: determine the charging and discharging conditions of the bridge arm current according to the switching control instruction; if the bridge arm current is in the charging direction, delay the switching-in control of the submodule that is switched from being switched-in to being switched-in; if the bridge arm current is in the discharging direction, delay the switching-in control of the submodule that is switched from being switched-in to being switched-in to being switched-in

[0053] The working method of the system is the same as the module dead zone compensation control method of the modular multi-level converter in Example 1, and will not be described in detail here.

[0054] Embodiment 3:

[0055] This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the program is executed by a processor, the steps of the module dead zone compensation control method of the modular multilevel converter described in Embodiment 1 are implemented.

[0056] Embodiment 4:

[0057] This embodiment provides an electronic device, including a memory, a processor, and a computer program stored in the memory and capable of running on the processor. When the processor executes the program, the steps of the module dead zone compensation control method of the modular multilevel converter described in Example 1 are implemented.

[0058] Embodiment 5:

[0059] This embodiment provides a computer program product, which includes a computer program. When the computer program is executed by a processor, the steps of the module dead zone compensation control method of the modular multilevel converter described in Embodiment 1 are implemented.

[0060] The above description is only a preferred embodiment of the present embodiment and is not intended to limit the present embodiment. For those skilled in the art, the present embodiment may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. A module dead zone compensation control method for a modular multilevel converter, characterized in that: include: In each valve control cycle, the switching control instruction of each submodule is obtained according to the bridge arm modulation voltage instruction, the result of the submodule voltage sorting and the direction of the bridge arm current; According to the switching control instruction, the charging and discharging status of the bridge arm current is determined; if the bridge arm current is in the charging direction, the submodule that is switched from cut-off to switched-on is controlled with a delay; if the bridge arm current is in the discharging direction, the submodule that is switched from switched-on to cut-off is controlled with a delay.

2. A module dead zone compensation control method for a modular multilevel converter according to claim 1, characterized in that: According to the ratio of the bridge arm modulation voltage instruction and the rated working voltage of the submodule, the number of bridge arm submodules put into operation is obtained; if the current of the bridge arm is in the charging direction, the input instructions are issued in sequence according to the number of submodules put into operation in the order of the voltage values ​​of the submodules in the bridge arm from small to large, and the removal instructions are issued to the remaining submodules in the bridge arm; when the bridge arm modulation voltage instruction corresponds to the current of the bridge arm in the discharging direction, the input instructions are issued in sequence according to the number of submodules put into operation in the order of the voltage values ​​of the submodules from large to small, and the removal instructions are issued to the remaining submodules in the bridge arm.

3. The module dead zone compensation control method of a modular multilevel converter according to claim 1, characterized in that: When the bridge arm current is in the charging direction, count the number of submodules that were in the on state in the previous control cycle and the number of submodules that received the removal instruction in the current control cycle; Count the submodules that were in the cut-off state in the previous control cycle and the submodules that received the input command in the current control cycle, and send delay commands to the submodule controllers in turn; until the number of submodules that send delays reaches the number of submodules that received the cut-off command in the current control cycle, or all submodules that have been switched from cut-off to input have received delay commands.

4. The module dead zone compensation control method of a modular multilevel converter according to claim 1, characterized in that: When the bridge arm current is in the discharge direction, the number of submodules in the cut-off state in the previous control cycle and the number of submodules that have received the input instruction in the current control cycle are counted; Count the submodules that were in the on state in the previous control cycle and the submodules that received the removal instruction in the current control cycle, and send delay instructions to the submodule controllers in turn; until the number of submodules with delays reaches the number of submodules that received the on-state instruction in the current control cycle, or all submodules that have been switched from on to off have received delay instructions.

5. The module dead zone compensation control method of a modular multilevel converter according to claim 1, characterized in that: The dead zone compensation time is preset according to the switching characteristics of the specific power device.

6. A module dead zone compensation control method for a modular multilevel converter according to claim 5, characterized in that: The dead time compensation time set for the integrated gate commutated thyristor power device is greater than the dead time compensation time set for the insulated gate bipolar transistor power device.

7. A module dead zone compensation control system for a modular multilevel converter, characterized in that: include: The switching control instruction acquisition module is configured to: in each valve control cycle, obtain the switching control instruction of each submodule according to the bridge arm modulation voltage instruction, the result of the submodule voltage sorting and the direction of the bridge arm current; The dead zone compensation control module is configured to: determine the charging and discharging conditions of the bridge arm current according to the switching control instruction; if the bridge arm current is in the charging direction, delay the switching-in control of the submodule that is switched from being switched-in to being switched-in; if the bridge arm current is in the discharging direction, delay the switching-in control of the submodule that is switched from being switched-in to being switched-in to being switched-in 8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the program is executed by a processor, the steps of the module dead zone compensation control method of a modular multilevel converter are implemented.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the program, the steps of the module dead zone compensation control method of the modular multilevel converter are implemented as described in any one of claims 1 to 6.

10. A computer program product, characterized in that The computer program product comprises a computer program, and when the computer program is executed by a processor, the steps of the module dead zone compensation control method of a modular multilevel converter are implemented.

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