CN110311542B - Control method and control device for virtual reactance of modular multilevel converter - Google Patents

Control method and control device for virtual reactance of modular multilevel converter Download PDF

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CN110311542B
CN110311542B CN201910615337.6A CN201910615337A CN110311542B CN 110311542 B CN110311542 B CN 110311542B CN 201910615337 A CN201910615337 A CN 201910615337A CN 110311542 B CN110311542 B CN 110311542B
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CN110311542A (en
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周月宾
饶宏
许树楷
朱喆
李笑倩
宋强
赵彪
魏应冬
袁志昌
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Tsinghua University
Research Institute of Southern Power Grid Co Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • H02M1/325—Means for protecting converters other than automatic disconnection with means for allowing continuous operation despite a fault, i.e. fault tolerant converters

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Abstract

The invention discloses a control method and a control device for virtual reactance of a modular multilevel converter, wherein the method comprises the following steps: receiving a control instruction sent by a superior controller of the modular multilevel converter, and dynamically calculating the alternating current reference voltage of the modular multilevel converter according to the control instruction; determining a target direct-current short-circuit current rise rate according to the initial value controlled by the latched virtual reactance to obtain a sub-module capacitor discharge index, and superposing the sub-module capacitor discharge index on an alternating-current reference voltage to carry out amplitude limiting to obtain a bridge arm reference voltage; and performing pulse modulation and direct-current capacitor voltage balance control according to the reference voltage of the bridge arm to generate a pulse signal for switching control. According to the control method provided by the embodiment of the invention, the uninterrupted operation capability of the direct current fault of the whole system can be improved, the extra cost caused by the direct current limiting reactance is reduced, and the problems of system transient performance reduction and low direct current protection sensitivity caused by overlarge direct current limiting reactance are avoided.

Description

Control method and control device for virtual reactance of modular multilevel converter
Technical Field
The invention relates to the technical field of power electronic converters, in particular to a control method and a control device for virtual reactance of a modular multilevel converter.
Background
MMC (Modular Multilevel Converter) belongs to a voltage source type power electronic Converter and is based on an insulated gate bipolar transistorThe full-control power electronic device and the pulse width modulation technology can stably control the transmission of active power and reactive power between the alternating current and direct current systems. The circuit principle of the MMC is shown in fig. 1. The MMC comprises three phase units of a, b and c, and each phase unit comprises two bridge arms, namely an upper bridge arm and a lower bridge arm, and the total number of the bridge arms is six. The three phase units are connected in parallel between a direct current positive pole and a direct current negative pole, and the middle points of the upper bridge arm and the lower bridge arm of the three phase units are connected with a three-phase alternating current system. Each bridge arm is formed by connecting N sub-modules in series. Each submodule is composed of two insulated gate bipolar transistors S1、S2Two freewheeling diodes D1、D2And a DC capacitor CdAnd (4) forming. The MMC has many technical advantages, such as a modular structure, and is easy to reach a high voltage level; the multi-level working mode is beneficial to improving the transmission efficiency; the high-quality output voltage waveform does not need to be provided with an alternating current filter and the like, so that the high-quality output voltage waveform plays an important role in a direct current power grid and is widely paid attention under the scenes of regional power grid interconnection, renewable energy access and the like.
The direct current short circuit fault is a key problem to be solved when the MMC operates safely and reliably. The uninterrupted operation capability of the direct current fault is a new requirement of direct current protection on the MMC. Since the development speed of the direct-current short-circuit current is fast, in order to limit the short-circuit current to a safe level immediately after a fault occurs, a direct-current-limiting reactance with a large resistance value needs to be added on a line, and adverse effects are brought to the dynamic performance and stability of a system. In the related art, the dc current-limiting reactance optimization scheme mainly adds a current-limiting device, such as a superconducting current limiter, a dc circuit breaker with a current-limiting function, an MMC topology with a current-limiting module, and the like, and increases the impedance of a fault loop by adding an additional element, although the current-limiting reactance optimization scheme has a certain current-limiting effect, the additional cost is high.
Disclosure of Invention
The present invention is directed to solving, at least to some extent, one of the technical problems in the related art.
Therefore, an object of the present invention is to provide a method for controlling a virtual reactance of a modular multilevel converter, which can improve the uninterrupted operation capability of a dc fault of the whole system and reduce the additional cost caused by a dc current-limiting reactance.
Another object of the present invention is to provide a virtual reactance control apparatus for a modular multilevel converter.
In order to achieve the above object, an embodiment of the invention provides a virtual reactance control method for a modular multilevel converter, which includes the following steps: receiving a control instruction sent by a superior controller of the modular multilevel converter, and dynamically calculating the alternating current reference voltage of the modular multilevel converter according to the control instruction; determining a target direct-current short-circuit current rise rate according to an initial value controlled by the latched virtual reactance to obtain a sub-module capacitor discharge index, and superposing the sub-module capacitor discharge index on the alternating-current reference voltage to carry out amplitude limiting to obtain a bridge arm reference voltage; and performing pulse modulation and direct-current capacitor voltage balance control according to the bridge arm reference voltage to generate a pulse signal for switching control.
The method for controlling the virtual reactance of the modular multilevel converter can enable the MMC to present the virtual reactance characteristic during the uninterrupted operation, directly control the rising speed of the short-circuit current, realize the limitation of the short-circuit current and the optimization of the direct current limiting reactance parameter, improve the uninterrupted operation capability of the direct current fault of the whole system, reduce the extra cost brought by the direct current limiting reactance, and avoid the problems of the transient performance reduction of the system and the low direct current protection sensitivity caused by the overlarge direct current limiting reactance.
In addition, the virtual reactance control method of the modular multilevel converter according to the above embodiment of the present invention may further have the following additional technical features:
optionally, in an embodiment of the present invention, the control command includes one or more of an active power command, a reactive power command, a direct current voltage command, and an alternating current voltage command.
Further, in an embodiment of the present invention, the determining a target dc short-circuit current rise rate according to the initial value of the latched virtual reactance control includes: after the fault judgment is delayed, starting virtual reactance control, latching the direct current measured in real time at the current moment and the mean value of the sub-module capacitor voltage, and generating the initial value; and obtaining the target direct current short circuit current increase rate according to the on-off time, the on-off current and the fault judgment delay of the direct current circuit breaker.
In an embodiment of the present invention, a calculation formula of the target dc short-circuit current rise rate is:
Figure BDA0002123746300000021
wherein, tBIs the cut-off time of the DC circuit breaker, IBFor said switching current, tDDetermining a delay for the fault;
and the calculation formula of the sub-module capacitance discharge index is as follows:
Figure BDA0002123746300000022
wherein N represents the number of bridge arm submodules, LsRepresenting bridge arm inductance, LdcRepresenting the dc line inductance.
Further, in an embodiment of the present invention, the generating the pulse signal for switching control includes: and carrying out switching control on the sub-module insulated gate bipolar transistor according to the pulse signal.
In order to achieve the above object, according to another embodiment of the present invention, a virtual reactance control apparatus for a modular multilevel converter is provided, including: the receiving module is used for receiving a control instruction sent by a superior controller of the modular multilevel converter and dynamically calculating the alternating current reference voltage of the modular multilevel converter according to the control instruction; the acquisition module is used for determining the target direct-current short-circuit current rise rate according to the initial value of latching virtual reactance control to obtain a sub-module capacitor discharge index, and the sub-module capacitor discharge index is superposed on the alternating-current reference voltage to carry out amplitude limiting to obtain bridge arm reference voltage; and the control module is used for performing pulse modulation and direct-current capacitor voltage balance control according to the bridge arm reference voltage, and generating a pulse signal for switching control.
The virtual reactance control device of the modular multilevel converter in the embodiment of the invention enables the MMC to present the virtual reactance characteristic during the uninterrupted operation, directly controls the rising speed of the short-circuit current, realizes the limitation of the short-circuit current and the optimization of the parameters of the direct current limiting reactance, improves the uninterrupted operation capability of the direct current fault of the whole system, reduces the extra cost brought by the direct current limiting reactance, and avoids the problems of the transient performance reduction of the system and the low sensitivity of the direct current protection caused by the overlarge direct current limiting reactance.
In addition, the virtual reactance control device of the modular multilevel converter according to the above embodiment of the present invention may further have the following additional technical features:
optionally, in an embodiment of the present invention, the control command includes one or more of an active power command, a reactive power command, a direct current voltage command, and an alternating current voltage command.
Further, in an embodiment of the present invention, the obtaining module includes: the generating unit is used for starting virtual reactance control after the fault judgment delay, latching the direct current measured in real time at the current moment and the mean value of the sub-module capacitor voltage, and generating the initial value; and the acquisition unit is used for acquiring the target direct-current short-circuit current increase rate according to the on-off time, the on-off current and the fault judgment delay of the direct-current circuit breaker.
In an embodiment of the present invention, a calculation formula of the target dc short-circuit current rise rate is:
Figure BDA0002123746300000031
wherein, tBIs the cut-off time of the DC circuit breaker, IBFor said switching current, tDDetermining a delay for the fault;
and the calculation formula of the sub-module capacitance discharge index is as follows:
Figure BDA0002123746300000032
wherein N represents the number of bridge arm submodules, LsRepresenting bridge arm inductance, LdcRepresenting the dc line inductance.
Further, in an embodiment of the present invention, the control module is further configured to perform switching control on the sub-module insulated gate bipolar transistor according to the pulse signal.
Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Drawings
The foregoing and/or additional aspects and advantages of the present invention will become apparent and readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
FIG. 1 is a schematic diagram of a DC short circuit of a MMC and a typical submodule in the related art;
fig. 2 is a flowchart of a virtual reactance control method of a modular multilevel converter according to an embodiment of the present invention;
fig. 3 is a flowchart of a virtual reactance control method of a modular multilevel converter according to an embodiment of the present invention;
fig. 4 is a block schematic diagram of a virtual reactance control device of a modular multilevel converter according to an embodiment of the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative and intended to be illustrative of the invention and are not to be construed as limiting the invention.
The virtual reactance control method and the control device for the modular multilevel converter according to the embodiment of the invention are described below with reference to the accompanying drawings, and first, the virtual reactance control method for the modular multilevel converter according to the embodiment of the invention will be described with reference to the accompanying drawings.
Fig. 2 is a flowchart of a virtual reactance control method for a modular multilevel converter according to an embodiment of the present invention.
As shown in fig. 2, the virtual reactance control method of the modular multilevel converter includes the following steps:
in step S1, a control command sent by the upper controller of the modular multilevel converter is received, and the ac reference voltage of the modular multilevel converter is dynamically calculated according to the control command.
It is understood that in the embodiment of the present invention, the ac reference voltage of the modular multilevel converter is first dynamically calculated according to the instruction sent by the superior controller.
Optionally, in an embodiment of the invention, the control command comprises one or more of an active power command, a reactive power command, a direct voltage command and an alternating voltage command.
For example, as shown in fig. 3, the system consists of a converter-level control, a virtual reactance control and a bottom-level control, and step S1 is the converter-level control, specifically, the three-phase ac reference voltage of the modular multilevel converter is dynamically calculated according to an active power command, a reactive power command, a dc voltage command and an ac voltage command sent by the upper-level controller of the modular multilevel converter
Figure BDA0002123746300000041
In step S2, a target dc short-circuit current increase rate is determined according to the initial value of the latched virtual reactance control, and a sub-module capacitance discharge index is obtained and superimposed on the ac reference voltage to perform amplitude limiting to obtain a bridge arm reference voltage.
That is, then, according to the initial value of the latched virtual reactance control, a control target of the direct current short-circuit current rise rate is set, the capacitance discharge index of the sub-module is calculated, and the sub-module is superposed on the obtained alternating current reference voltage and subjected to amplitude limiting to obtain the bridge arm reference voltage.
Further, in one embodiment of the present invention, determining a target dc short-circuit current rise rate from an initial value of the latched virtual reactance control includes: after the fault judgment is delayed, starting virtual reactance control, latching the direct current measured in real time at the current moment and the mean value of the sub-module capacitor voltage, and generating an initial value; and obtaining the target direct-current short-circuit current increase rate according to the on-off time, the on-off current and the fault judgment delay of the direct-current circuit breaker.
In one embodiment of the present invention, the calculation formula of the target dc short-circuit current rise rate is:
Figure BDA0002123746300000051
wherein, tBFor the breaking time of DC circuit breakers, IBTo cut off the current, tDDetermining a delay for the fault;
and the calculation formula of the sub-module capacitance discharge index is as follows:
Figure BDA0002123746300000052
wherein N represents the number of bridge arm submodules, LsRepresenting bridge arm inductance, LdcRepresenting the dc line inductance.
Specifically, as shown in fig. 3, step S102 is a virtual reactance control, specifically including:
step S21: latching initial values of the virtual reactance control: after a fault occurs and after certain fault judgment delay, the virtual reactance control is started, and the direct current I measured at the moment in real time is latcheddc0Sum sub-module capacitor voltage average value Uc0As an initial value.
Step S22: setting a target value of the virtual reactance control: selecting the DC short-circuit current rise rate as a control target of virtual reactance control according to the on-off time t of the DC breakerBAnd a switching current IBFault judgment delay tDThe calculation formula is shown as formula (1):
Figure BDA0002123746300000053
step S23: calculating the capacitance discharge index D of the submodule*: calculating a sub-module capacitance discharge index D according to the virtual reactance characteristic of the modular multilevel converter and the target value of virtual reactance control*The calculation formula is shown in formula (2):
Figure BDA0002123746300000054
wherein N represents the number of bridge arm submodules, LsRepresenting bridge arm inductance, LdcRepresenting the dc line inductance.
Step S24: calculating the reference voltage of a bridge arm: superimposing the sub-module capacitance discharge index D to the AC reference voltage
Figure BDA0002123746300000055
Figure BDA0002123746300000056
Respectively generating six bridge arm reference voltages
Figure BDA0002123746300000057
And the obtained bridge arm reference voltage is compared
Figure BDA0002123746300000058
In [0, 2D ]]Limiting the amplitude within the range to obtain the final bridge arm reference voltage
Figure BDA0002123746300000059
The calculation formula is shown in formula (3):
Figure BDA0002123746300000061
in step S3, pulse modulation and dc capacitor voltage balance control are performed based on the bridge arm reference voltage, and a pulse signal is generated and switching control is performed.
In conclusion, according to the obtained bridge arm reference voltage, pulse modulation and direct current capacitor voltage balance control are carried out, a pulse signal is generated for carrying out switch control, the MMC can be enabled to present a virtual reactance characteristic in the uninterrupted operation period, the rising speed of the short-circuit current is directly controlled, the limitation of the short-circuit current and the optimization of direct current limiting reactance parameters are realized, the uninterrupted operation capability of the direct current fault of the whole system is improved, the extra cost brought by the direct current limiting reactance is reduced, and the problems of system transient performance reduction and low direct current protection sensitivity caused by the overlarge direct current limiting reactance are avoided.
Further, in an embodiment of the present invention, generating a pulse signal for switching control includes: and performing switching control on the sub-module insulated gate bipolar transistor according to the pulse signal.
That is, as shown in fig. 3, step S3 is a floor control based on the obtained bridge arm reference voltage
Figure BDA0002123746300000062
Figure BDA0002123746300000063
Performing pulse modulation and direct-current capacitor voltage balance control to generate a pulse signal; and then, the submodule insulated gate bipolar transistor is subjected to switching control according to the obtained pulse signal, so that the MMC presents a virtual reactance characteristic during the uninterrupted operation period through intervening capacitor discharge, the rising speed of short-circuit current can be directly controlled, the limitation of the short-circuit current and the optimization of direct current limiting reactance parameters are realized, the uninterrupted operation capacity of direct current faults of the whole system is improved, the extra cost brought by the direct current limiting reactance is reduced, and the problems of system transient performance reduction and low direct current protection sensitivity caused by the overlarge direct current limiting reactance are solved.
In summary, the virtual reactance control method of the modular multilevel converter according to the embodiment of the present invention, the MMC can present virtual reactance characteristic during the uninterrupted operation, directly control the rising speed of short-circuit current, realize the limitation of short-circuit current and the optimization of direct current limiting reactance parameters, improve the uninterrupted operation capability of direct current fault of the whole system, reduce the extra cost brought by the direct current limiting reactance, avoid the problems of system transient performance reduction and low direct current protection sensitivity caused by overlarge direct current limiting reactance, namely, the control capability of the MMC can be utilized to realize virtual reactance control, and the direct current limiting reactance is replaced to carry out active flexible current limiting, so that the direct current limiting reactance parameter can be further optimized, the method has important significance for enhancing the uninterrupted operation capability of the system during the direct current fault and improving the stability, dynamic performance and economic benefit of the system.
Next, a virtual reactance control apparatus of a modular multilevel converter according to an embodiment of the present invention will be described with reference to the accompanying drawings.
Fig. 4 is a block schematic diagram of a virtual reactance control device of a modular multilevel converter according to an embodiment of the present invention.
As shown in fig. 4, the virtual reactance control device 10 of the modular multilevel converter includes: a receiving module 100, an obtaining module 200 and a control module 300.
The receiving module 100 is configured to receive a control instruction sent by a superior controller of the modular multilevel converter, and dynamically calculate an ac reference voltage of the modular multilevel converter according to the control instruction.
The obtaining module 200 is configured to determine a target dc short-circuit current increase rate according to an initial value of the latched virtual reactance control, obtain a sub-module capacitance discharge index, and superimpose the sub-module capacitance discharge index on the ac reference voltage to perform amplitude limiting to obtain a bridge arm reference voltage.
The control module 300 is configured to perform pulse modulation and dc capacitor voltage balance control according to the bridge arm reference voltage, and generate a pulse signal for on-off control.
Optionally, in an embodiment of the invention, the control command comprises one or more of an active power command, a reactive power command, a direct voltage command and an alternating voltage command.
Further, in an embodiment of the present invention, the obtaining module 200 includes: the device comprises a generating unit and an acquiring unit.
The generating unit is used for starting virtual reactance control after fault judgment delay, latching the direct current measured in real time at the current moment and the mean value of the sub-module capacitor voltage, and generating an initial value.
The acquisition unit is used for acquiring the target direct-current short-circuit current increase rate according to the on-off time, the on-off current and the fault judgment delay of the direct-current circuit breaker.
In one embodiment of the present invention, the calculation formula of the target dc short-circuit current rise rate is:
Figure BDA0002123746300000071
wherein, tBFor the breaking time of DC circuit breakers, IBTo cut off the current, tDDetermining a delay for the fault;
and the calculation formula of the sub-module capacitance discharge index is as follows:
Figure BDA0002123746300000072
wherein N represents the number of bridge arm submodules, LsRepresenting bridge arm inductance, LdcRepresenting the dc line inductance.
Further, in an embodiment of the present invention, as shown in fig. 4, the control module 300 is further configured to perform switching control on the sub-module insulated gate bipolar transistor according to the pulse signal.
It should be noted that the foregoing explanation on the embodiment of the virtual reactance control method of the modular multilevel converter is also applicable to the virtual reactance control apparatus of the modular multilevel converter of the embodiment, and details are not repeated herein.
According to the virtual reactance control device of the modular multilevel converter, the MMC is enabled to present the virtual reactance characteristic during the uninterrupted operation period, the rising speed of the short-circuit current is directly controlled, the limitation of the short-circuit current and the optimization of the direct current limiting reactance parameter are realized, the uninterrupted operation capability of the direct current fault of the whole system is improved, the extra cost brought by the direct current limiting reactance is reduced, and the problems of the transient performance reduction of the system and the low direct current protection sensitivity caused by the overlarge direct current limiting reactance are avoided.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or N embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "N" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more N executable instructions for implementing steps of a custom logic function or process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of implementing the embodiments of the present invention.
The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or N wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the N steps or methods may be implemented in software or firmware stored in a memory and executed by a suitable instruction execution system. If implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.
In addition, functional units in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.
The storage medium mentioned above may be a read-only memory, a magnetic or optical disk, etc. Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims (6)

1. A virtual reactance control method of a modular multilevel converter is characterized by comprising the following steps:
receiving a control instruction sent by a superior controller of the modular multilevel converter, and dynamically calculating the alternating current reference voltage of the modular multilevel converter according to the control instruction;
determining a target direct-current short-circuit current rise rate according to the initial value controlled by the latching virtual reactance to obtain a sub-module capacitance discharge index, and superposing the sub-module capacitance discharge index on the alternating-current reference voltage to perform amplitude limiting to obtain a bridge arm reference voltage, wherein the determining of the target direct-current short-circuit current rise rate according to the initial value controlled by the latching virtual reactance comprises the following steps: after the fault judgment is delayed, starting virtual reactance control, latching the direct current measured in real time at the current moment and the mean value of the sub-module capacitor voltage, and generating the initial value; obtaining the target direct-current short-circuit current rise rate according to the on-off time, the on-off current and the fault judgment delay of the direct-current circuit breaker; the calculation formula of the target direct current short-circuit current rise rate is as follows:
Figure FDA0002531677730000011
wherein, tBIs the cut-off time of the DC circuit breaker, IBFor said switching current, tDDetermining a delay for the fault; and the calculation formula of the sub-module capacitance discharge index is as follows:
Figure FDA0002531677730000012
wherein N represents the number of bridge arm submodules, LsRepresenting bridge arm inductance, LdcRepresents the dc line inductance; and
and performing pulse modulation and direct-current capacitor voltage balance control according to the bridge arm reference voltage to generate a pulse signal for switching control.
2. The method of claim 1, wherein the control commands comprise one or more of an active power command, a reactive power command, a direct current voltage command, and an alternating current voltage command.
3. The method of claim 1, wherein the generating a pulse signal for switching control comprises:
and carrying out switching control on the sub-module insulated gate bipolar transistor according to the pulse signal.
4. A virtual reactance control device of a modular multilevel converter is characterized by comprising:
the receiving module is used for receiving a control instruction sent by a superior controller of the modular multilevel converter and dynamically calculating the alternating current reference voltage of the modular multilevel converter according to the control instruction;
the acquisition module is used for determining the target direct-current short-circuit current rise rate according to the initial value of latching virtual reactance control to obtain a sub-module capacitor discharge index, and the sub-module capacitor discharge index is superposed on the alternating-current reference voltage to carry out amplitude limiting to obtain bridge arm reference voltage; wherein the acquisition module comprises: a generating unit for starting the virtual reactance control and latching the current time after the fault judgment delayThe initial value is generated by the direct current measured in real time and the mean value of the sub-module capacitor voltage; the acquisition unit is used for acquiring the target direct-current short-circuit current rise rate according to the on-off time, the on-off current and the fault judgment delay of the direct-current circuit breaker; the calculation formula of the target direct current short-circuit current rise rate is as follows:
Figure FDA0002531677730000021
wherein, tBIs the cut-off time of the DC circuit breaker, IBFor said switching current, tDDetermining a delay for the fault; and the calculation formula of the sub-module capacitance discharge index is as follows:
Figure FDA0002531677730000022
wherein N represents the number of bridge arm submodules, LsRepresenting bridge arm inductance, LdcRepresents the dc line inductance; and
and the control module is used for performing pulse modulation and direct-current capacitor voltage balance control according to the bridge arm reference voltage, and generating a pulse signal for switching control.
5. The apparatus of claim 4, wherein the control commands comprise one or more of an active power command, a reactive power command, a direct current voltage command, and an alternating current voltage command.
6. The apparatus of claim 4, wherein the control module is further configured to switch control a sub-module IGBT according to the pulse signal.
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