CN116455249A - Method for judging current direction of bridge arm of modularized multi-level converter and control system - Google Patents

Method for judging current direction of bridge arm of modularized multi-level converter and control system Download PDF

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Publication number
CN116455249A
CN116455249A CN202210015604.8A CN202210015604A CN116455249A CN 116455249 A CN116455249 A CN 116455249A CN 202210015604 A CN202210015604 A CN 202210015604A CN 116455249 A CN116455249 A CN 116455249A
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China
Prior art keywords
current
bridge arm
value
threshold value
voltage
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CN202210015604.8A
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Chinese (zh)
Inventor
卢宇
董云龙
张君君
邵震霞
周谷庆
胡兆庆
任铁强
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NR Electric Co Ltd
NR Engineering Co Ltd
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NR Electric Co Ltd
NR Engineering Co Ltd
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Priority to CN202210015604.8A priority Critical patent/CN116455249A/en
Priority to PCT/CN2023/071017 priority patent/WO2023131300A1/en
Publication of CN116455249A publication Critical patent/CN116455249A/en
Pending legal-status Critical Current

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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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • 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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The application provides a judgment method, a control system, electronic equipment and a computer storage medium for a bridge arm current direction of a modularized multi-level converter. The judging method comprises the following steps: comparing the acquired current value of the bridge arm with a set first positive threshold value and a set second negative threshold value; when the current value is smaller than the first positive threshold value and larger than the second negative threshold value, determining the direction of the current by adopting a first judging mode; the first judging mode comprises the step of taking the positive and negative of the periodic variation of the voltage of the capacitor in the bridge arm as the direction of the current; or, reversing the direction of the current according to a fixed period, and taking the reversing result as the direction of the current. When the bridge arm current is smaller, the bridge arm current direction is judged by adopting fixed period overturning or according to the change of the capacitance voltage of the submodule in the bridge arm, so that the problem of bridge arm current sampling distortion caused by factors such as current sampling zero drift and the like under the condition of small current can be avoided.

Description

Method for judging current direction of bridge arm of modularized multi-level converter and control system
Technical Field
The application relates to the technical field of power electronics, in particular to a method for judging the current direction of a bridge arm of a modular multilevel converter, a control system, electronic equipment and a computer readable medium.
Background
The modularized multi-level converter (modular multilevel converter, MMC) is widely applied to the fields of power electronic systems such as flexible direct current transmission engineering, static synchronous compensators, low-frequency transmission and the like. Each bridge arm of the modularized multi-level converter is formed by connecting N sub-modules in series. The number of converter submodules invested is generally controlled by a valve control system. The valve control system is an intermediate bridge between the converter control protection system and the converter submodule. The valve control system receives and modulates the control instruction of the converter control protection system to obtain the number of submodules required to be input by each converter bridge arm, and finally selects a proper submodule to be input.
When selecting the submodules to be input, the general principle is to select the submodule input with smaller voltage when the bridge arm is charged (i.e. the current direction of the bridge arm is positive), and select the submodule input with larger voltage when the bridge arm is discharged (i.e. the current direction of the bridge arm is negative), so that the balance of the voltage of the submodule in the whole bridge arm is realized. Therefore, the judgment of the current direction of the bridge arm is one of key functions of the valve control system. The accurate and effective bridge arm current direction judging strategy plays an important role in voltage control of the converter submodule and in switching frequency inhibition of the submodule.
Currently, the current direction of a bridge arm is generally judged by the positive and negative of a bridge arm current sampling value. When the bridge arm current sampling value is smaller, due to factors such as sampling zero drift and noise, the judgment method has error in direction judgment when the bridge arm current is smaller, so that the input of the submodule is disordered, the problems of overvoltage, high-frequency input and the like of the submodule are caused, and the operation safety of the system is endangered. In addition, in the method for judging the bridge arm current direction by setting the anti-shake time under the low current working condition, the bridge arm current is distorted near zero due to factors such as sampling errors and the like. Therefore, the true current direction cannot be accurately determined only by the anti-shake time.
Disclosure of Invention
Based on this, in order to solve the problem that the traditional current direction judging method has current direction judging errors when the current sampling value is smaller, the application provides a judging method for the current direction of a bridge arm of a modularized multi-level converter, which comprises the following steps:
comparing the acquired current value of the bridge arm with a set first positive threshold value and a set second negative threshold value;
when the current value is smaller than the first positive threshold value and larger than the second negative threshold value, determining the direction of the current by adopting a first judging mode; wherein the first judging mode comprises the following steps of,
taking the positive and negative of the periodic variation of the voltage of the capacitor in the bridge arm as the direction of the current; or (b)
And turning over the direction of the current according to a fixed period, and taking the turning over result as the direction of the current.
According to some embodiments of the present application, when the duration of the periodic variation of the voltage of the capacitor in the bridge arm is not less than the first anti-shake time or the duration of the periodic variation is not less than the second anti-shake time, the positive and negative of the periodic variation are taken as the direction of the current.
According to some embodiments of the application, the periodic variation includes:
and the difference value between the voltage of the capacitor in the bridge arm in the current period and the voltage of the capacitor in the bridge arm in the previous period.
According to some embodiments of the application, the voltage of the capacitor comprises:
the sum of the voltages of the capacitors of all the sub-modules in the bridge arm; or (b)
And the average voltage of the capacitance of all the sub-modules in the bridge arm.
According to some embodiments of the present application, the inverting the current according to a fixed period includes:
and changing the current direction of the bridge arm once every first period.
According to some embodiments of the present application, the first period comprises: n times or one of N times of the current period of the bridge arm, wherein N is a natural number greater than or equal to 1.
According to some embodiments of the present application, the first determination mode is used to determine the direction of the current when the current value is less than the first positive threshold and the duration of time that is greater than the second negative threshold is not less than a third anti-shake time.
According to some embodiments of the present application, the determining method further includes:
when the current value is larger than or equal to the first positive threshold value or smaller than or equal to the second negative threshold value, determining the direction of the current by adopting a second judging mode; wherein the second judging mode comprises,
and taking the positive and negative of the current value as the direction of the current.
According to some embodiments of the present application, the second judgment mode is used to determine the direction of the current when the duration of the current value being greater than or equal to the first positive threshold or less than or equal to the second negative threshold is not less than a fourth anti-shake time.
According to a first aspect of the present application, there is provided a control system for a modular multilevel converter, comprising,
an inverter;
the measuring unit is used for measuring the current value of each bridge arm or the voltage value of the capacitor of each submodule in the converter;
the valve control system is used for receiving the current value of the bridge arm or the voltage value of the capacitor measured by the measuring unit;
the converter control protection system is used for sending voltage reference waves of bridge arms of the converter to the valve control system;
the valve control system is also used for controlling the input quantity of the bridge arms of the current converter according to the voltage reference wave, judging the current direction of the bridge arms of the current converter according to the current value or the voltage value by adopting the judging method, and further sending a trigger command to the current converter according to the current direction.
According to another aspect of the present application, there is provided a method comprising:
one or more processors;
a storage means for storing one or more programs;
when the one or more programs are executed by the one or more processors, the one or more processors are caused to implement the above-described determination method.
According to another aspect of the present application, there is also provided a computer readable medium having stored thereon a computer program which, when executed by a processor, implements the above-mentioned determination method.
According to the bridge arm current direction judging method of the modularized multi-level converter, when the bridge arm current is large, the bridge arm current direction is judged according to the magnitude relation between the bridge arm current sampling value and the threshold value; when the bridge arm current is smaller, the bridge arm current direction is judged by adopting fixed period overturning or according to the change of the capacitance voltage of the submodule in the bridge arm, so that the problem of bridge arm current sampling distortion caused by factors such as current sampling zero drift and the like under the condition of small current can be avoided. The judging method can accurately judge the bridge arm current direction under any working condition, particularly under the low-running working condition of small bridge arm current, provides accurate instructions for the input control strategy of the submodule of the valve control system, and ensures the safe and reliable running of the system to the maximum extent under the full working condition.
Additional aspects and advantages of the application 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 application.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly described below, and it is apparent that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained by those skilled in the art from these drawings without departing from the scope of protection of the present application.
Fig. 1 shows a schematic diagram of one leg of a modular multilevel converter according to an exemplary embodiment of the application;
fig. 2 shows a flowchart of a method for determining a bridge arm current direction according to a first exemplary embodiment of the present application;
fig. 3 shows a flowchart of a method for determining a bridge arm current direction according to a second exemplary embodiment of the present application;
fig. 4 shows a schematic diagram of a decision logic of a bridge arm current direction according to a second exemplary embodiment of the present application;
fig. 5 shows a schematic diagram of a bridge arm current direction according to a second exemplary embodiment of the present application;
fig. 6 is a flowchart illustrating a method for determining a bridge arm current direction according to a third exemplary embodiment of the present application;
FIG. 7 shows a logic diagram of a first determination mode according to a third example embodiment of the present application;
fig. 8 shows a schematic diagram of a bridge arm current direction in a first determination mode according to a third exemplary embodiment of the present application;
fig. 9 is a flowchart showing a method for determining a bridge arm current direction according to a fourth exemplary embodiment of the present application;
fig. 10 shows a schematic diagram of a decision logic of a bridge arm current direction according to a fourth exemplary embodiment of the present application;
fig. 11 shows a schematic diagram of a bridge arm current direction according to a fourth example embodiment of the present application;
fig. 12 shows a schematic diagram of a modular multilevel converter control system according to an example embodiment of the application;
fig. 13 shows a block diagram of an electronic device for modular multilevel converter leg current direction determination according to an example embodiment of the present application.
Detailed Description
Example embodiments are described more fully below with reference to the accompanying drawings. However, the exemplary embodiments may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. These embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and thus a repetitive description thereof will be omitted.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the present application. One skilled in the relevant art will recognize, however, that the aspects of the application can be practiced without one or more of the specific details, or with other methods, components, devices, steps, etc. In other instances, well-known methods, devices, implementations, or operations are not shown or described in detail to avoid obscuring aspects of the application.
It will be understood that, although the terms first, second, etc. may be used herein to describe various components, these components should not be limited by these terms. These terms are used to distinguish one element from another element. Thus, a first component discussed below could be termed a second component without departing from the teachings of the present application concept. As used herein, the term "and/or" includes any one of the associated listed items and all combinations of one or more.
Those skilled in the art will appreciate that the drawings are schematic representations of example embodiments and may not be to scale. The modules or flows in the figures are not necessarily required to practice the present application and therefore should not be taken to limit the scope of the present application.
Fig. 1 shows a schematic diagram of one leg of a modular multilevel converter according to an exemplary embodiment of the application.
According to an exemplary embodiment of the present application, as shown in fig. 1, one leg 100 of the modular multilevel converter 1000 is composed of N sub-modules 110 connected in series, for example, a 1-sub-module, a 2-sub-module, a 3-sub-module, a … …, an N-sub-module connected in series with each other. The topology of each sub-module 110 may take a variety of forms, such as half-bridge, full-bridge-like, etc. The half-bridge submodule 110 includes a dc capacitor 111 and a parallel circuit formed by connecting the IGBT1 and the IGBT2 in series. Each IGBT is connected in parallel with one reverse diode 112.
For the bridge arm of the converter shown in fig. 1, in order to solve the problem that the traditional current direction judging method has a current direction judging error when the current sampling value is smaller, the application provides a current direction judging method, according to the bridge arm current sampling value, the working condition of the bridge arm is determined, and then different judging modes are selected for judging, so that the problem of the current direction judging error when the current sampling value is smaller is avoided, namely, when the current value of the bridge arm is larger (the absolute value of the current is greater than 0.00001-1 times of the current peak value, for example, five thousandths of a time, the adjustment can be specifically performed according to actual conditions), the current direction of the bridge arm is judged to be in a normal working condition, and the current direction of the bridge arm is obtained according to the comparison between the bridge arm current sampling value and the threshold value; when the bridge arm current value is smaller (the absolute value of the current is smaller than 0.00001-1 times of the current peak value, for example, five thousandths of a meter, the adjustment can be specifically performed according to the actual situation), after the low-load working condition is judged, the bridge arm current direction is obtained by adopting the judging methods of fixed period overturning, submodule capacitor voltage criterion and the like.
Fig. 2 shows a flowchart of a method for determining a bridge arm current direction according to a first exemplary embodiment of the present application.
As shown in fig. 2, according to a first exemplary embodiment of the present application, a method for determining a bridge arm current direction of a modular multilevel converter provided in the present application includes the following steps.
In step S210, the collected current value of the bridge arm is compared with a set first positive threshold value and a second negative threshold value. Normally, when the bridge arm current value Ib of the converter Is greater than or equal to the set first positive threshold value Is1 or less than or equal to the set second negative threshold value Is2, the converter Is in a normal working condition (i.e., ib > Is1 or Ib < Is 2); when the bridge arm current value Ib of the converter Is smaller than the set first threshold value Is1 and larger than the set second negative threshold value Is2 (i.e. Is2< Ib < Is 1), the converter Is in a low-load working condition. According to some embodiments of the present application, the first positive threshold value for judging the working condition of the inverter may be set to 0.00001-1 times (e.g. five thousandths) of the positive peak value of the bridge arm current, and the second negative threshold value may also be set to 0.00001-1 times (e.g. five thousandths) of the negative peak value of the bridge arm current.
In step S220, when the current value is smaller than the first positive threshold and larger than the second negative threshold, determining the direction of the current by using a first judgment mode; the first judging mode comprises the steps of controlling the direction of the current to be overturned according to a fixed period, and taking the overturned result as the direction of the current.
When the collected current value of the bridge arm is smaller than the first positive threshold value and larger than the second negative threshold value, the converter can be judged to be in a low-load working condition. At this time, the bridge arm current may be controlled to be inverted according to a fixed period, for example, the current direction of the bridge arm is changed once every first period. And after the period overturn, taking the generated bridge arm current direction as a judgment result.
According to some embodiments of the present application, the first period may be N times or one-N times the current period of the bridge arm, where N is a natural number greater than or equal to 1. For example, the first period may be 0.5Ts, where Ts is the theoretical period of the bridge arm current. For the traditional modularized multi-level converter with flexible direct current transmission, the period of the bridge arm current is 20ms, and the direction of the bridge arm current can be changed every 10 ms.
According to some embodiments of the present application, anti-shake time may also be set for the determination of low load conditions. For example, when the current value of the bridge arm is smaller than the first positive threshold value and the duration time of the current value larger than the second negative threshold value is not smaller than the set third anti-shake time, the direction of the current is determined by adopting the first judging mode. By setting the anti-shake time, frequent switching of the working condition judgment result can be avoided. According to an embodiment of the present application, the third anti-shake time may be set to a plurality of task cycle times.
Fig. 3 shows a flowchart of a method for determining a bridge arm current direction according to a second exemplary embodiment of the present application.
According to another embodiment of the present application, the judging method shown in fig. 2 may further include the following steps.
In step S230, when the current value is greater than or equal to the first positive threshold or less than or equal to the second negative threshold, determining the direction of the current by using a second determination mode; wherein the second judgment mode includes taking the positive and negative of the current value as the direction of the current.
When the current value of the bridge arm is larger than or equal to a first set positive threshold value or smaller than or equal to a second set negative threshold value, the bridge arm is in a normal working condition, and the current direction can be judged through the positive and negative of the collected current value.
According to some embodiments of the present application, anti-shake time may also be set for the determination of normal operating conditions. For example, when the duration of the current value of the bridge arm is not less than the fourth anti-shake time and is greater than or equal to the first positive threshold or less than or equal to the second negative threshold, the direction of the current is determined by adopting the second judgment mode. By setting the anti-shake time, frequent switching of the working condition judgment result can be avoided. According to the embodiment of the present application, the fourth anti-shake time may also be set to a plurality of task cycle times.
Fig. 4 shows a schematic diagram of a decision logic of a bridge arm current direction according to a second exemplary embodiment of the present application. Fig. 5 shows a schematic diagram of a bridge arm current direction according to a second exemplary embodiment of the present application.
When the current direction of the bridge arm is judged by adopting the current direction judging method shown in fig. 3, the logic of the judging process is shown in fig. 4.
In S410, the arm current direction determination for each task cycle is started.
In S420, the sampled value of the bridge arm current is compared with a set threshold value, so as to determine the working condition of the bridge arm current and the corresponding judgment mode of the current direction. That is, when the bridge arm current is in the low-load condition, a low-load judgment mode (first judgment mode) is adopted; when the bridge arm current is in the normal working condition, a normal judgment mode (a second judgment mode) is adopted. In the judging process of the normal working condition and the low-load working condition, the anti-shake time T (see fig. 5) can be set, so that frequent switching of judging modes is avoided. The anti-shake time may be set to a plurality of task cycle times.
In S430, it is determined whether to adopt the normal judgment mode according to the judgment result of the current sampling value. Referring to FIG. 5, when the bridge arm current Is greater than or equal to a positive threshold value Is1 (Ib. Gtoreq.Is1) or the bridge arm current Is less than or equal to a negative threshold value Is2 (Ib. Gtoreq.Is2), a normal judgment mode Is adopted; when the bridge arm current sampling value Is larger than the negative threshold value Is2 and smaller than the positive threshold value Is1 (Is 2< Ib < Is 1), a low-load judgment mode Is adopted.
In S440, the direction of the bridge arm current is determined by the normal determination method. Judging the current direction of the bridge arm according to the magnitude relation between the bridge arm current sampling value and the threshold value, and when the bridge arm current sampling value Is greater than or equal to a positive threshold value Is1 (Ib Is 1), the current direction of the bridge arm Is a positive direction, and Is a charging direction (see figure 5); when the bridge arm current Is equal to or less than the negative threshold Is2 (Ib. Ltoreq.is2), the bridge arm current direction Is the negative direction, and Is the discharge direction at this time (see fig. 5).
In S450, the current direction of the bridge arm is determined by a low-load determination method. And under the low-load working condition, periodically turning over the current direction, and taking the turning over result as the judged current direction. For example, the bridge arm current direction is changed every 0.5Ts, where Ts is the theoretical period of the bridge arm current. For the traditional modularized multi-level converter for flexible direct current transmission, the period of the bridge arm current is 20ms, and the direction of the bridge arm current is converted every 10 ms.
In S460, a bridge arm current direction determination result is generated.
In S470, the current-operation bridge arm current direction determination method is ended.
Fig. 6 shows a flowchart of a method for determining a bridge arm current direction according to a third exemplary embodiment of the present application.
As shown in fig. 6, according to a third exemplary embodiment of the present application, a method for determining a bridge arm current direction of a modular multilevel converter provided in the present application includes the following steps.
In step S610, the collected current value of the bridge arm is compared with a set first positive threshold value and a second negative threshold value. Normally, when the bridge arm current value Ib of the converter Is greater than or equal to the set first positive threshold value Is1 or less than or equal to the set second negative threshold value Is2, the converter Is in a normal working condition (i.e., ib > Is1 or Ib < Is 2); when the bridge arm current value Ib of the converter Is smaller than the set first threshold value Is1 and larger than the set second negative threshold value Is2 (i.e. Is2< Ib < Is 1), the converter Is in a low-load working condition.
In step S620, when the current value is smaller than the first positive threshold and larger than the second negative threshold, determining a direction of the current using a first determination mode; the first judging mode includes taking the positive and negative of the periodic variation of the voltage of the capacitor in the bridge arm as the direction of the current. That is, when the periodic variation is greater than zero, the bridge arm current is in the positive direction and in the charging state; when the periodic variation is less than zero, the bridge arm current is in a negative direction and is in a discharge state. When the period change amount is zero, the last judgment result is maintained.
According to some embodiments of the present application, the period change amount is a difference Δuc (n) between the voltage Uc (n) of the capacitor in the bridge arm in the current period and the voltage Uc (n-1) of the capacitor in the bridge arm in the previous period: Δuc (n) =uc (n) -Uc (n-1). The voltage Uc (n) of the capacitor may be the sum of the voltages of the capacitors of all the sub-modules in the bridge arm, or may be the average voltage of the capacitors of all the sub-modules in the bridge arm.
According to some embodiments of the present application, the anti-shake time may also be set for the periodic variation of the voltage of the capacitor in the bridge arm. For example, when the duration of the period change amount of the voltage of the capacitor in the bridge arm is not less than the first anti-shake time or the duration of the period change amount is negative is not less than the second anti-shake time, the positive and negative of the period change amount is taken as the direction of the current. The first anti-shake time and the second anti-shake time may be equal or unequal, and specific setting may be performed according to actual requirements.
FIG. 7 shows a logic diagram of a first determination mode according to a third example embodiment of the present application; fig. 8 shows a schematic diagram of a bridge arm current direction in a first determination mode according to a third exemplary embodiment of the present application.
The judgment logic of the first judgment mode shown in fig. 6 is as follows:
in S710, the bridge arm current direction determination for each duty cycle under the low-load condition is started.
In S720, the capacitor voltages of the sub-modules in the bridge arm are summed, and the sub-module capacitor voltage and Uc (n) of the current period are calculated and recorded.
In S730, the submodule capacitor voltage sum Uc (n) in the current period is differenced from the submodule capacitor voltage sum Uc (n-1) in the previous period to obtain a period change Δuc (n) of the submodule capacitor voltage sum in the current period:
ΔUc(n)＝Uc(n)-Uc(n-1)
in S740, a determination is made as to a trend of the sum of the sub-module capacitance voltages. Specifically, the period variation Δuc (n) of the sum of the sub-module capacitance voltages of the current period is compared with zero.
In S750, it is determined whether the variation of the sub-module capacitance voltage sum is greater than zero. Specifically, as shown in fig. 8, when the duration of the period variation of the sum of the capacitance voltages of the sub-modules is greater than zero and is greater than the first anti-shake time T1, the bridge arm current is determined to be in the positive direction and is in the charging state.
In S760, it is determined whether the sub-module capacitance voltage and the variation amount are smaller than zero. Specifically, when the duration of the period variation of the sum of the capacitance voltages of the sub-modules is smaller than zero and is longer than the second anti-shake time T2, the bridge arm current is judged to be in a negative direction and is in a discharge state.
In S770, the arm current direction determination result is generated.
In S780, the current-operation bridge arm current direction determination method is ended.
Fig. 9 shows a flowchart of a method for determining a bridge arm current direction according to a fourth exemplary embodiment of the present application.
According to another embodiment of the present application, the judging method shown in fig. 6 may further include the following steps.
As shown in fig. 8, in step S630, when the current value is greater than or equal to the first positive threshold value or less than or equal to the second negative threshold value, determining the direction of the current using a second determination mode; wherein the second judgment mode includes taking the positive and negative of the current value as the direction of the current.
When the current value of the bridge arm is larger than or equal to a first set positive threshold value or smaller than or equal to a second set negative threshold value, the bridge arm is in a normal working condition, and the current direction can be judged through the positive and negative of the collected current value.
According to some embodiments of the present application, anti-shake time may also be set for the determination of normal operating conditions. For example, when the duration of the current value of the bridge arm is not less than the fourth anti-shake time and is greater than or equal to the first positive threshold or less than or equal to the second negative threshold, the direction of the current is determined by adopting the second judgment mode. By setting the anti-shake time, frequent switching of the working condition judgment result can be avoided. According to the embodiment of the present application, the fourth anti-shake time may also be set to a plurality of task cycle times.
Fig. 10 shows a schematic diagram of a decision logic of a bridge arm current direction according to a fourth exemplary embodiment of the present application; fig. 11 shows a schematic diagram of a bridge arm current direction according to a fourth exemplary embodiment of the present application.
When the current direction determination method shown in fig. 9 is used to determine the current direction of the bridge arm, the logic of the determination process is shown in fig. 10.
In S910, the arm current direction determination for each task cycle is started.
In S920, the sampled value of the bridge arm current is compared with a set threshold value, so as to determine the working condition of the bridge arm current and the corresponding judgment mode of the current direction. That is, when the bridge arm current is in the low-load condition, a low-load judgment mode (first judgment mode) is adopted; when the bridge arm current is in the normal working condition, a normal judgment mode (a second judgment mode) is adopted. In the judging process of the normal working condition and the low-load working condition, the anti-shake time T (see fig. 11) can be set, so that frequent switching of the judging modes is avoided. The anti-shake time may be set to a plurality of task cycle times.
In S930, it is determined whether to adopt a normal determination mode according to the determination result of the current sampling value. Referring to FIG. 10, when the bridge arm current Is equal to or greater than a positive threshold Is1 (Ib. Gtoreq.Is1) or equal to or less than a negative threshold Is2 (Ib. Gtoreq.Is2), a normal judgment mode Is adopted; when the bridge arm current sampling value Is larger than the negative threshold value Is2 and smaller than the positive threshold value Is1 (Is 2< Ib < Is 1), a low-load judgment mode Is adopted.
In S940, the direction of the bridge arm current is determined by a normal determination method. Judging the current direction of the bridge arm according to the magnitude relation between the bridge arm current sampling value and the threshold value, and when the bridge arm current sampling value Is greater than or equal to a positive threshold value Is1 (Ib Is 1), the current direction of the bridge arm Is a positive direction (see FIG. 11); when the arm current Is equal to or less than the negative threshold Is2 (Ib. Ltoreq.is2), the arm current direction Is a negative direction (see fig. 11).
In S950, the current direction of the bridge arm is determined by a low-load determination method. And under the low-load working condition, judging the current direction of the bridge arm according to the periodic variation of the capacitor voltage of the sub-module in the bridge arm. When the periodic variation of the capacitor voltage is greater than zero, the current direction of the bridge arm is the positive direction; when the periodic variation of the capacitor voltage is smaller than zero, the bridge arm current direction is a negative direction. In order to avoid frequent changes in the bridge arm current direction, a certain anti-shake time may be set in the above comparison.
In S960, a bridge arm current direction determination result is generated.
In S970, the current-operation bridge arm current direction determination method is ended.
Fig. 12 shows a schematic diagram of a modular multilevel converter control system according to an example embodiment of the application.
According to another aspect of the present application, a control system 2000 of a modular multilevel converter is also provided. Referring to fig. 12, the control system 2000 includes an inverter 1000, a measurement unit 1100, a valve control system 1200, and a protection system 1300. Wherein each leg of the converter 1000 comprises a plurality of sub-modules. The measurement unit 1200 is used for measuring current values of respective bridge arms or voltage values of capacitances of respective sub-modules in the inverter 1000. The valve control system 1300 is configured to receive a current value of a bridge arm or a voltage value of a capacitor measured by the measurement unit 1200. The inverter control protection system 1300 is configured to send a voltage reference wave of a bridge arm of the inverter to the valve control system. The valve control system 1200 is an intermediate bridge between the converter control protection system 1300 and the converter 1000, and is further configured to generate the number of input submodules of each bridge arm according to the voltage reference wave modulation, control the input number of the bridge arms of the converter, determine the current direction of the bridge arms of the converter according to the current value or the voltage value by using the determination method, and send a trigger command to the converter according to the current direction.
Fig. 13 shows a block diagram of an electronic device for modular multilevel converter leg current direction determination according to an example embodiment of the present application.
According to another aspect of the application, an electronic device for judging the bridge arm current direction of the modular multilevel converter is also provided. The control apparatus 500 shown in fig. 13 is only one example, and should not impose any limitation on the functions and the scope of use of the embodiments of the present application.
As shown in fig. 13, the control device 500 is in the form of a general purpose computing device. The components of the control device 500 may include, but are not limited to: at least one processing unit 510, at least one memory unit 520, a bus 530 connecting the different system components (including the memory unit 520 and the processing unit 510), and the like.
The storage unit 520 stores program codes that can be executed by the processing unit 510, so that the processing unit 510 performs the bridge arm current direction determination method according to the above embodiments of the present application described in the present specification.
The storage unit 520 may include readable media in the form of volatile storage units, such as Random Access Memory (RAM) 5201 and/or cache memory unit 5202, and may further include Read Only Memory (ROM) 5203.
The storage unit 520 may also include a program/utility 5204 having a set (at least one) of program modules 5205, such program modules 5205 including, but not limited to: an operating system, one or more application programs, other program modules, and program data, each or some combination of which may include an implementation of a network environment.
Bus 530 may be one or more of several types of bus structures including a memory unit bus or memory unit controller, a peripheral bus, an accelerated graphics port, a processing unit, or a local bus using any of a variety of bus architectures.
The electronic device 500 may also communicate with one or more external devices 5001 (e.g., touch screen, keyboard, pointing device, bluetooth device, etc.), one or more devices that enable a user to interact with the electronic device 500, and/or any device (e.g., router, modem, etc.) that enables the electronic device 500 to communicate with one or more other computing devices. Such communication may occur through an input/output (I/O) interface 550. Also, electronic device 500 may communicate with one or more networks such as a Local Area Network (LAN), a Wide Area Network (WAN), and/or a public network, such as the Internet, through network adapter 560. The network adapter 560 may communicate with other modules of the electronic device 500 via the bus 530. It should be appreciated that although not shown, other hardware and/or software modules may be used in connection with electronic device 500, including, but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, data backup storage systems, and the like.
According to another aspect of the present application, there is also provided a computer readable medium having stored thereon a computer program which, when executed by a processor, implements the above-mentioned determination method.
According to the bridge arm current direction judging method of the modularized multi-level converter, when the bridge arm current is small, the bridge arm current direction is judged by adopting fixed period overturning or according to the change of the capacitance voltage of the inner submodule of the bridge arm, so that the problem of bridge arm current sampling distortion caused by factors such as current sampling zero drift and the like under the condition of small current can be avoided. The judging method can accurately judge the bridge arm current direction under any working condition, particularly under the low-running working condition of small bridge arm current, provides accurate instructions for the input control strategy of the submodule of the valve control system, and ensures the safe and reliable running of the system to the maximum extent under the full working condition.
The foregoing has outlined rather broadly the more detailed description of embodiments of the present application, wherein specific examples have been provided herein to illustrate the principles and embodiments of the present application, and wherein the above examples are provided to assist in the understanding of the methods and concepts of the present application. Meanwhile, based on the ideas of the present application, those skilled in the art can make changes or modifications on the specific embodiments and application scope of the present application, which belong to the scope of the protection of the present application. In view of the foregoing, this description should not be construed as limiting the application.

Claims (12)

1. A judgment method for the current direction of a bridge arm of a modularized multi-level converter is characterized by comprising the following steps:
comparing the acquired current value of the bridge arm with a set first positive threshold value and a set second negative threshold value;
when the current value is smaller than the first positive threshold value and larger than the second negative threshold value, determining the direction of the current by adopting a first judging mode; wherein the first judging mode comprises the following steps of,
taking the positive and negative of the periodic variation of the voltage of the capacitor in the bridge arm as the direction of the current; or (b)
And turning over the direction of the current according to a fixed period, and taking the turning over result as the direction of the current.
2. The judgment method according to claim 1, wherein when a duration of a positive value of a periodic variation of a voltage of a capacitor in the arm is not less than a first anti-shake time or a duration of a negative value of the periodic variation is not less than a second anti-shake time, positive and negative values of the periodic variation are taken as directions of the currents.
3. The judgment method according to claim 1, wherein the period change amount includes:
and the difference value between the voltage of the capacitor in the bridge arm in the current period and the voltage of the capacitor in the bridge arm in the previous period.
4. A method of determining as claimed in claim 3 wherein the voltage of the capacitor comprises:
the sum of the voltages of the capacitors of all the sub-modules in the bridge arm; or (b)
And the average voltage of the capacitance of all the sub-modules in the bridge arm.
5. The method according to claim 1, wherein the inverting the current according to a fixed period includes:
and changing the current direction of the bridge arm once every first period.
6. The method of determining according to claim 5, wherein the first period comprises:
n times or one of N times of the current period of the bridge arm, wherein N is a natural number greater than or equal to 1.
7. The judgment method according to claim 1, wherein the direction of the current is determined using the first judgment mode when the current value is smaller than the first positive threshold value and the duration of time that is larger than the second negative threshold value is not smaller than a third anti-shake time.
8. The judgment method according to claim 1, further comprising:
when the current value is larger than or equal to the first positive threshold value or smaller than or equal to the second negative threshold value, determining the direction of the current by adopting a second judging mode;
wherein the second judgment mode includes taking the positive and negative of the current value as the direction of the current.
9. The judgment method according to claim 8, wherein the direction of the current is determined using the second judgment mode when the duration of the current value being equal to or greater than the first positive threshold value or equal to or less than the second negative threshold value is not less than a fourth anti-shake time.
10. A control system of a modularized multi-level converter comprises,
an inverter;
the measuring unit is used for measuring the current value of each bridge arm or the voltage value of the capacitor of each submodule in the converter;
the valve control system is used for receiving the current value of the bridge arm or the voltage value of the capacitor measured by the measuring unit;
the converter control protection system is used for sending voltage reference waves of bridge arms of the converter to the valve control system;
it is characterized in that the method comprises the steps of,
the valve control system is further configured to control the input number of the bridge arms of the converter according to the voltage reference wave, determine the current direction of the bridge arms of the converter according to the current value or the voltage value by adopting the determination method according to any one of claims 1 to 9, and send a trigger command to the converter according to the current direction.
11. An electronic device, comprising:
one or more processors;
a storage means for storing one or more programs;
when executed by the one or more processors, causes the one or more processors to implement the method of determining of any of claims 1-9.
12. A computer readable medium having stored thereon a computer program, characterized in that the program, when executed by a processor, implements the judgment method of any one of claims 1-9.
CN202210015604.8A 2022-01-07 2022-01-07 Method for judging current direction of bridge arm of modularized multi-level converter and control system Pending CN116455249A (en)

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