CN113422531B

CN113422531B - MMC neutron module capacitor voltage-sharing method and device

Info

Publication number: CN113422531B
Application number: CN202110973408.7A
Authority: CN
Inventors: 周登波; 宋述波; 周勇; 焦华; 郭云汉; 邓健俊; 叶鑫; 郑锐举; 顾硕铭; 徐攀腾; 朱博; 廖晨江; 严海健; 焦石; 杨学广; 李倩; 陈海永
Original assignee: Guangzhou Bureau of Extra High Voltage Power Transmission Co
Current assignee: Guangzhou Bureau of Extra High Voltage Power Transmission Co
Priority date: 2021-08-24
Filing date: 2021-08-24
Publication date: 2021-12-03
Anticipated expiration: 2041-08-24
Also published as: CN113422531A

Abstract

The application relates to a capacitance voltage-sharing method and device for a MMC (Modular multilevel converter) sub-module, which are used for obtaining an initial switching state vector of a bridge arm sub-module, reading a capacitance voltage initial value vector of the bridge arm sub-module in a control period, dividing a sub-module capacitance voltage sequence into a plurality of large groups according to the capacitance voltage initial value vector of the bridge arm sub-module based on a control method of a voltage dispersion threshold, and respectively classifying capacitance voltage initial value vector elements of the bridge arm sub-module in the large groups into affiliated sub-intervals to form a plurality of buckets; according to the initial switching state vector, applying a bucket sorting algorithm to carry out capacitance voltage sharing on the bridge arm sub-modules to obtain the switching state vector of the bridge arm sub-modules in the control period; and controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period. In the whole process, the algorithm time complexity and the submodule switching frequency can be effectively reduced, and efficient and accurate MMC neutron module capacitor voltage sharing is realized.

Description

MMC neutron module capacitor voltage-sharing method and device

Technical Field

The application relates to the technical field of smart power grids, in particular to a method and a device for equalizing voltage of a neutron module capacitor of an MMC (Modular Multilevel Converter), computer equipment and a storage medium.

Background

In the field of long-distance large-capacity power transmission, direct-current power transmission has better economy than alternating-current power transmission, so that a plurality of high-voltage direct-current power transmission projects which are put into operation or under construction exist in China. In addition, the development of the power electronic technology promotes the application of a flexible direct current based on voltage source converter (VSC-HVDC), the technology overcomes the problems of commutation failure and the like in the conventional direct current transmission, and the VSC-HVDC also has the advantages of flexible control mode and capability of independently controlling active power and reactive power. At present, scholars propose a topological structure of a modular multilevel converter, the problems that the traditional two-level value VSC-HVDC switching frequency is too high, output harmonic is large, a passive filter is needed and the like are solved well, and the topological structure gradually becomes a preferred topological structure of a flexible direct current transmission project.

When MMC-HVDC normally works, the converter valve control system receives the voltage reference wave U of the valve group control system_refThe output level value of each submodule is changed in real time, the number of submodules put into a bridge arm is controlled to change the voltage of the bridge arm, and therefore the current conversion function is achieved. The implementation scheme of the converter valve control system algorithm comprises two major categories of a carrier phase shift modulation technology and a step wave modulation technology, wherein the step wave modulation technology is suitable for a long-distance large-capacity MMC-HVDC with a high level value number, and the algorithm comprises two steps of a nearest level value approximation method and a bubble sorting method.

The traditional voltage-sharing algorithm is based on a bubble sorting method, however, the bubble sorting method is a sorting algorithm with higher time complexity, and for MMC-HVDC with n +1 level value, the time complexity is up to o (n). For MMC-HVDC with long distance and large capacity, the number of sub-modules is often as high as hundreds to thousands, so that along with the increase of the number of the sub-modules, the bubble sorting algorithm can greatly increase the operation amount, thereby providing harsh requirements for controlling host hardware. In addition, an IGBT (Insulated Gate Bipolar Transistor) element has a certain switching loss in both the on and off processes. In MMC-HVDC engineering application, frequent switching of a large number of sub-modules enables switching loss to be ignored or even greater than on-state loss, and meanwhile, too high switching frequency can obviously reduce the service life of a power semiconductor element, so that the traditional voltage-sharing algorithm needs to be improved to reduce the switching frequency of the sub-modules, and more efficient and accurate voltage sharing is realized.

Disclosure of Invention

In view of the foregoing, there is a need to provide an efficient and accurate MMC submodule capacitor voltage equalizing method, apparatus, computer device and storage medium.

A MMC neutron module capacitor voltage-sharing method comprises the following steps:

obtaining an initial switching state vector of the bridge arm submodule, and reading an initial value vector of the capacitor voltage of the bridge arm submodule in the control period;

according to a control method based on a voltage dispersion threshold value, a submodule capacitor voltage sequence is divided into a plurality of large groups according to an initial value vector of capacitor voltage of a bridge arm submodule;

aiming at the divided large groups, respectively classifying the capacitance voltage initial value vector elements of the bridge arm sub-modules in the large groups into the sub-intervals to which the bridge arm sub-modules belong to form a plurality of buckets;

according to the initial switching state vector, applying a bucket sorting algorithm to carry out capacitance voltage sharing on the bridge arm sub-modules to obtain the switching state vector of the bridge arm sub-modules in the control period;

and controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period.

In one embodiment, the method for controlling based on the voltage dispersion threshold value, wherein the step of dividing the sub-module capacitor voltage sequence into a plurality of large groups according to the initial value vector of the capacitor voltage of the sub-module of the bridge arm comprises the following steps:

acquiring a given bucket interval length per unit value and a voltage threshold coefficient which are sent by the control period modulation link;

according to the initial value vector of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient, dividing the submodule capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group based on a control method of a voltage dispersion threshold;

within each large group, the partitioning is done according to a per unit value of the given bucket interval length.

In one embodiment, according to the initial value vector of the capacitor voltage of the sub-modules of the bridge arm and the voltage threshold coefficient, the method for controlling the voltage dispersion threshold value divides the sub-module capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group, and comprises the following steps:

according to the initial value vector of the capacitor voltage of the bridge arm submodule,

calculating the average value of the capacitor voltage of the bridge arm submodule;

determining critical values of upper and lower limits of an allowable range of the capacitor voltage of the bridge arm submodule according to the average value of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient;

and dividing the sub-module capacitor voltage sequence into a large group of a high-voltage group, a normal group and a low-voltage group according to the critical values of the upper limit and the lower limit of the allowable range of the bridge arm sub-module capacitor voltage.

In one embodiment, the step of performing capacitance voltage equalization on the bridge arm sub-modules by applying a bucket sorting algorithm according to the initial switching state vector to obtain the switching state vector of the bridge arm sub-modules in the control period includes:

acquiring an input submodule number instruction sent by the control period modulation link;

if the bridge arm sub-modules are in a discharging state, setting the switching state corresponding values of all the sub-modules of the high-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the low-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment;

if the bridge arm sub-modules are in a charging state, setting the switching state corresponding values of all the sub-modules of the low-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the high-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment;

adjusting the level values of elements in the switching state vector until the counted number is equal to the number corresponding to the number of the input sub-module commands, and forming the switching state vector of the bridge arm sub-module in the control period;

wherein the first level value is 1 and the second level value is 0.

In one embodiment, adjusting the level values of the elements in the switching state vector until the counted number is equal to the number corresponding to the number of the input sub-module instructions includes:

if the bridge arm sub-modules are in a discharging state, comparing the counted number with the number corresponding to the number command of the input sub-modules; if the number of the elements is larger than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the number command of the input sub-modules; if the number of the elements is smaller than the preset value, sequentially resetting the elements of the first level value to be second level values according to the sequence of the voltage interval from high to low until the counted number is equal to the number corresponding to the input sub-module number instruction;

if the bridge arm sub-modules are in a charging state, comparing the counted number with the number corresponding to the number command of the input sub-modules; if the number of the elements is larger than the preset value, sequentially resetting the elements of the first level value to be second level values according to the sequence of the voltage intervals from high to low until the counted number is equal to the number corresponding to the input sub-module number instruction; and if the number of the elements is smaller than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the input sub-module number instruction.

In one embodiment, obtaining the initial switching state vector of the bridge arm submodule includes:

and obtaining the switching state vector of the bridge arm submodule in the previous control period.

In one embodiment, after controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period, the method further includes:

and taking the switching state vector of the bridge arm sub-module in the control period as the switching state vector of the bridge arm sub-module in the next control period.

The utility model provides a MMC neutron module electric capacity voltage-sharing device, the device includes:

the initial quantity acquisition module is used for acquiring initial switching state vectors of the bridge arm sub-modules and reading initial value vectors of capacitance and voltage of the bridge arm sub-modules in the control period;

the dividing module is used for dividing the sub-module capacitor voltage sequence into a plurality of large groups according to the initial value vector of the capacitor voltage of the sub-module of the bridge arm based on the control method of the voltage dispersion threshold;

the bucket entering module is used for respectively entering the capacitance voltage initial value vector elements of the bridge arm sub-modules in the large group into the sub-intervals to which the bridge arm sub-modules belong to the large group to form a plurality of buckets;

the voltage equalizing module is used for carrying out capacitance voltage equalizing on the bridge arm sub-modules by applying a bucket sorting algorithm according to the initial switching state vector to obtain the switching state vector of the bridge arm sub-modules in the control period;

and the control module is used for controlling the switching of the bridge arm sub-modules according to the switching state vectors of the bridge arm sub-modules in the control period.

A computer device comprising a memory and a processor, the memory storing a computer program, the processor implementing the following steps when executing the computer program:

A computer-readable storage medium, on which a computer program is stored which, when executed by a processor, carries out the steps of:

According to the MMC sub-module capacitor voltage-sharing method, the MMC sub-module capacitor voltage-sharing device, the computer equipment and the storage medium, the initial switching state vector of the bridge arm sub-module is obtained, the initial value vector of the capacitor voltage of the bridge arm sub-module in the control period is read, the sub-module capacitor voltage sequence is divided into a plurality of large groups according to the initial value vector of the capacitor voltage of the bridge arm sub-module based on the control method of the voltage dispersion threshold, and the elements of the initial value vector of the capacitor voltage of the bridge arm sub-module in the large groups are respectively classified into the sub-sections to which the elements belong to the large groups to form a plurality of buckets; according to the initial switching state vector, applying a bucket sorting algorithm to carry out capacitance voltage sharing on the bridge arm sub-modules to obtain the switching state vector of the bridge arm sub-modules in the control period; and controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period. In the whole process, a control method based on a voltage dispersion threshold value and a bucket sorting algorithm are adopted to subdivide the sub-module capacitor voltage, the algorithm time complexity and the sub-module switching frequency can be effectively reduced, and efficient and accurate MMC sub-module capacitor voltage sharing is achieved.

Drawings

FIG. 1 is a schematic flow chart of a method for equalizing voltage of a capacitor of a submodule in an MMC according to an embodiment;

FIG. 2 is a schematic diagram illustrating a sub-flow of S200 according to an embodiment;

FIG. 3 is a schematic sub-flow chart of S400 in one embodiment;

FIG. 4 is a schematic flow chart of a method for equalizing voltage of a sub-module capacitor in an MMC in an application example;

FIG. 5 is a block diagram of a capacitive voltage-sharing device of a submodule in an embodiment of the MMC;

FIG. 6 is a diagram illustrating an internal structure of a computer device according to an embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In order to explain in detail the technical principle of the MMC neutron module capacitor voltage-sharing method of the present application, and the substantial difference and the significant technical progress between the MMC neutron module capacitor voltage-sharing method and the conventional technology, an algorithm adopted by the conventional MMC neutron module capacitor voltage-sharing method will be introduced first, the conventional algorithm mainly includes two steps of a nearest level approximation method and a bubble sorting method, and the specific flow is as follows:

the Nearest Level Modulation (NLM) method is a Modulation strategy suitable for multi-Level current converter, and its basic principle is to use the Nearest of bridge armLevel approximation to three-phase sine modulation wave (i.e. voltage reference value U)_ref）

The number of submodules put into the bridge arm at any moment is as follows:

(1)

in the formula n_up、n_downRespectively the number of the upper bridge arm investment sub-modules and the lower bridge arm investment sub-modules, N is the total number of the upper bridge arm sub-modules and the lower bridge arm sub-modules, u is the total number of the upper bridge arm sub-modules and the lower bridge arm sub-modules_refIs a reference voltage instantaneous value u_{c_avg}Round (·) is a rounding function for the submodule capacitor voltage average. The multi-level design enables the NLM algorithm to track the reference voltage at a lower switching frequency.

And after the number of the added submodules is determined by adopting an NLM method, a submodule capacitor voltage equalizing algorithm of the valve control layer is used for determining the specifically added submodules. The voltage-sharing algorithm based on the bubbling sorting method has the following specific flow:

1. receiving a bridge arm input submodule number instruction n obtained in a modulation process_on；

2. Judging the charge-discharge state of the submodule according to the current direction of the bridge arm: if bridge arm current i_arm>0, the sub-module capacitor is in a charging state at the moment, and the bridge arm current i_arm<0 is in a discharge state;

3. sequencing the capacitor voltages of the sub-modules by using a bubble sequencing method: performing multi-round traversal on the submodule voltage arrays, comparing adjacent elements pairwise, and exchanging positions if a reverse order exists;

if the sub-module capacitor is in a charging state at the moment, putting n with the lowest capacitor voltage_onA sub-module; if the sub-module capacitor is discharged, the highest n of the capacitor voltage is put into_onAnd the sub-modules are used for ensuring that the capacitor voltage of each sub-module keeps relatively uniform voltage.

In-depth research finds that the conventional voltage-sharing algorithm is based on a bubble sorting method, however, the bubble sorting method is a sorting algorithm with higher time complexity, and for the MMC-HVDC with n +1 level, the time complexity is as high as o (n). For MMC-HVDC with long distance and large capacity, the number of sub-modules is often as high as hundreds to thousands, so that along with the increase of the number of the sub-modules, the bubble sorting algorithm can greatly increase the operation amount, thereby providing harsh requirements for controlling host hardware. In addition, the IGBT element has a certain switching loss in both the on and off processes. In MMC-HVDC engineering application, frequent switching of a large number of sub-modules enables switching loss to be not ignored or even to be larger than on-state loss, and meanwhile, too high switching frequency can obviously reduce the service life of a power semiconductor element, so that the conventional voltage-sharing algorithm needs to be improved to reduce the switching frequency of the sub-modules.

In one embodiment, as shown in fig. 1, there is provided an MMC sub-module capacitor voltage equalizing method, including the following steps:

s100: and acquiring initial switching state vectors of the bridge arm sub-modules, and reading initial value vectors of capacitance and voltage of the bridge arm sub-modules in the control period.

The initial switching state vector of the bridge arm submodule refers to an initial switching state vector of the bridge arm submodule prepared in an initial stage of the control period, and when the initial switching state vector is a first control period (t = 0), the initial switching state vector can be an initial value preset in the control period, and when the initial switching state vector is not the first control period, the initial switching state vector can be a switching state vector of the bridge arm submodule in the previous control period. Reading initial value vector U of capacitor voltage of submodule on bridge arm in MMC (modular multilevel converter)_C。

S200: according to the control method based on the voltage dispersion threshold, the sub-module capacitor voltage sequence is divided into a plurality of large groups according to the initial value vector of the capacitor voltage of the sub-module of the bridge arm.

The bridge arm comprises a plurality of sub-modules, each sub-module has a corresponding capacitance voltage initial value, the capacitance voltages of the sub-modules are counted to form a sub-module capacitance voltage sequence, and the sub-module capacitance voltage sequence is divided into a plurality of large groups based on a control method of a voltage dispersion threshold value. Specifically, the average value of capacitance and voltage of bridge arm sub-modules is calculated, critical values of upper and lower limits of an allowable range of the capacitance and voltage of the sub-modules are determined on the basis of the average value, the capacitance and voltage sequence of the sub-modules is divided into 3 large groups according to the critical values of the upper and lower limits of the allowable range of the capacitance and voltage of the sub-modules, the large groups can be divided into a plurality of sections, and each section can comprise two small groups which are respectively used for storing numbers of the sub-modules which are input and not input in the control period.

S300: and aiming at the divided large groups, respectively classifying the capacitance voltage initial value vector elements of the bridge arm sub-modules in the large groups into the sub-intervals to which the bridge arm sub-modules belong to form a plurality of buckets.

Traversing the initial submodule switching state vector and the bridge arm submodule capacitor voltage initial value vector, and dividing the bridge arm submodule capacitor voltage initial value vector U according to the divided intervals_cRespectively classifying the obtained data into the belonged buckets, and creating a switching state vector S with the length of n_on. Furthermore, the switching state vector S can be used_onIs initialized to S_oldThe equal vectors can not change the original switching state as much as possible, and the switching frequency is reduced.

S400: and according to the initial switching state vector, applying a bucket sorting algorithm to carry out capacitance voltage sharing on the bridge arm sub-modules to obtain the switching state vector of the bridge arm sub-modules in the control period.

And according to the created switching state vector, performing capacitance voltage equalization on the bridge arm sub-modules by using a bucket sorting algorithm to obtain the switching state vector of the bridge arm sub-modules in the control period. Specifically, based on the element bucket entering condition obtained after the processing of S300, the switching states of the submodules are orderly adjusted by applying a bucket sorting algorithm until the capacitors of the bridge arm submodules are equalized, so that the requirement of the control period is met.

S500: and controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period.

And controlling the switching of the bridge arm sub-modules according to the determined switching state vector of the bridge arm sub-modules in the control period, so as to realize the capacitance voltage sharing of the MMC sub-modules. Specifically, after the switching of the bridge arm sub-modules is controlled according to the switching state vector of the bridge arm sub-modules in the control cycle, the switching state vector of the bridge arm sub-modules in the control cycle can be used as the switching state vector of the bridge arm sub-modules in the next control cycle, so as to provide an initial data source for the next control cycle.

According to the MMC sub-module capacitor voltage-sharing method, an initial switching state vector of a bridge arm sub-module is obtained, a capacitor voltage initial value vector of the bridge arm sub-module in the control period is read, a sub-module capacitor voltage sequence is divided into a plurality of large groups according to the capacitor voltage initial value vector of the bridge arm sub-module based on a voltage dispersion threshold control method, and capacitor voltage initial value vector elements of the bridge arm sub-module in the large groups are respectively classified into sub-sections to which the large groups belong to form a plurality of buckets; according to the initial switching state vector, applying a bucket sorting algorithm to carry out capacitance voltage sharing on the bridge arm sub-modules to obtain the switching state vector of the bridge arm sub-modules in the control period; and controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period. In the whole process, a control method based on a voltage dispersion threshold value and a bucket sorting algorithm are adopted to subdivide the sub-module capacitor voltage, the algorithm time complexity and the sub-module switching frequency can be effectively reduced, and efficient and accurate MMC sub-module capacitor voltage sharing is achieved.

As shown in fig. 2, in one embodiment, S200 includes:

s220: acquiring a given bucket interval length per unit value and a voltage threshold coefficient which are sent by the control period modulation link;

s240: according to the initial value vector of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient, dividing the submodule capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group based on a control method of a voltage dispersion threshold;

s260: within each large group, the partitioning is done according to a per unit value of the given bucket interval length.

Before the interval division is carried out, the per-unit value of the length of the given bucket interval sent out by the control period in the regulation environment needs to be read

And a voltage threshold coefficient α; counting a submodule capacitor voltage sequence according to an initial value vector of capacitor voltage of a submodule of a bridge arm, and controlling the submodule by adopting a voltage dispersion threshold value control methodThe module capacitor voltage sequence is divided into a high-voltage group, a normal group and a low-voltage group from high to low. Specifically, the average value of the capacitance and voltage of the bridge arm submodule can be calculated; determining critical values of upper and lower limits of an allowable range of the capacitor voltage of the bridge arm submodule according to the average value of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient; according to the critical values of the upper limit and the lower limit of the allowable range of the capacitor voltage of the sub-modules of the bridge arm, the capacitor voltage sequences of the sub-modules are divided into large groups of a high-voltage group, a normal group and a low-voltage group, and then each large group is divided according to the per unit value of the interval length of a given barrel.

To elaborate on the contents of the above embodiments, the contents will be described in detail below using rigorous mathematical formulas. The whole dividing process comprises the following steps:

the method comprises the following steps: reading the initial value direction U of the capacitor voltage of all sub-modules of the same bridge arm in the current control period_cCounting the maximum and minimum values of the sub-module capacitor voltage sequence

、

And calculating the average value of the capacitor voltage of the bridge arm submodule:

(2)

on the basis of the average value of the capacitor voltage, determining the critical value of the upper limit and the lower limit of the allowable range of the capacitor voltage of the submodule according to a voltage threshold coefficient alpha:

(3)

step two: to be provided with

Dividing the sub-modules into high-voltage groups and positive groups according to the capacitor voltage from high to low as boundaryNormal group and low voltage group, and the per unit value is determined according to the given voltage interval length in each group

The number of the intervals contained in each large group is as follows:

(4)

in which ceil is an upward rounding function, n_bucket-high、n_{bucket-medium}、n_bucket-lowThe number of the intervals formed by dividing the high-voltage group, the normal group and the low-voltage group is respectively, the capacitance voltage sequence is divided into a plurality of small intervals, and each interval comprises two groups which are respectively used for storing the numbers of sub-modules which are already put into and are not put into the current control period. Traversing the capacitor voltage vector U of the sub-module in the previous control period_cAnd put them into the belonging barrels respectively. Creating a switching state vector S with length n_onInitialized to and S_oldEqual vectors.

As shown in fig. 3, in one embodiment, S400:

s420: acquiring an input submodule number instruction sent by the control period modulation link;

s442: if the bridge arm sub-modules are in a discharging state, setting the switching state corresponding values of all the sub-modules of the high-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the low-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment;

s444: if the bridge arm sub-modules are in a charging state, setting the switching state corresponding values of all the sub-modules of the low-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the high-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment;

s460: adjusting the level values of elements in the switching state vector until the counted number is equal to the number corresponding to the number of the input sub-module commands, and forming the switching state vector of the bridge arm sub-module in the control period; wherein the first level value is 1 and the second level value is 0.

The input sub-module number instruction sent by the control period modulation link may be data directly read when the control period is started, and the input sub-module number instruction is used for determining the number of sub-modules required to be input in the control period. Aiming at the condition that the bridge arm sub-modules are in a discharging state or a charging state, different sub-module switching adjustment strategies need to be adopted. Similarly, the charge-discharge state of the submodule can be judged according to the current direction of the bridge arm: if bridge arm current i_arm>0, the sub-module capacitor is in a charging state at the moment, and the bridge arm current i_arm<0 is in the discharge state.

Specifically, if the bridge arm sub-modules are in a discharging state, setting the switching state corresponding values of all sub-modules of the high-voltage group in the switching state vector as first level values, setting the switching state of all sub-modules of the low-voltage group in the switching state vector as second level values, and if the bridge arm sub-modules are in a charging state, setting the switching state corresponding values of all sub-modules of the low-voltage group in the switching state vector as first level values, and setting the switching state of all sub-modules of the high-voltage group in the switching state vector as second level values, wherein generally speaking, the first level is a high level, that is, the first level value is 1; the second level is low, i.e. the second level value is 0. And comparing the number of the elements in the switching state vector obtained by statistics, which is the first level value, with the number corresponding to the number of the input sub-module instructions, and adjusting the level values of the elements in the switching state vector in a targeted manner, namely adjusting the switching state of the sub-modules until the counted number is equal to the number corresponding to the number of the input sub-module instructions, so as to form the switching state vector of the bridge arm sub-module in the control period.

For the purpose of detailed description, the switching state vector S of the control period is adjusted and formed in the above embodiment_onThe specific procedure of (1) will be referred to below as a first level value; an example in which the second level value is 0 is explained in detail.

When the sub-module is in the discharging state, S is added_onThe corresponding values of all the sub-modules of the medium-high voltage set are set to be 1, and the switching states of all the sub-modules of the low-voltage set are set to be 0. Count S at this time_onThe number n of medium elements 1, according to the specific input number instruction n_onPerforming individual adjustment: if n is<n_onSetting the element with the value of 0 as 1 until n = n in sequence from high to low in the voltage interval_on(ii) a If n is>n_onSequentially setting the elements with the value 1 to zero until n = n according to the sequence of the voltage interval from low to high_onForming the switching state vector S of the control period_on；

When the sub-module is in the charging state, S_onThe corresponding values of all the sub-modules of the medium and low voltage set are set to be 1, and the switching states of all the sub-modules of the high voltage set are set to be 0. Count S at this time_onThe number n of medium elements 1, according to the specific input number instruction n_onPerforming individual treatmentAdjusting: if n is>n_onSetting the element with the value 1 as 0 until n = n in sequence from high to low in the voltage interval_on(ii) a If n is<n_onSequentially setting the elements with the value of 0 to 1 until n = n according to the sequence of the voltage interval from low to high_onForming the switching state vector S of the control period_on。

In order to describe the technical scheme and effect of the method for equalizing voltage of a capacitor of a sub-module of an MMC in detail, a specific example is adopted, and detailed description is given below with reference to a specific flowchart of fig. 4. The whole MMC neutron module capacitor voltage-sharing scheme comprises the following steps:

1. after receiving a trigger pulse signal started in the control period, numbering the serial sub-modules of each bridge arm, and reading a switching state vector S of the sub-module in the previous control period_oldAnd an input subblock number instruction n sent by the control period modulation link_onPer unit value of given barrel interval length

And a voltage threshold coefficient α;

2. reading initial value vectors U of capacitor voltages of all sub-modules of the same bridge arm in the current control period_cCounting the maximum and minimum values of the sub-module capacitor voltage sequence

、

(2)

(3)

3. to be provided with

、

Dividing the sub-modules into three groups of high-voltage group, normal group and low-voltage group from high to low according to the capacitor voltage as a boundary, and determining per unit value inside each group according to the given voltage interval length

The number of the intervals contained in each large group is as follows:

(4)

in which ceil is an upward rounding function, n_bucket-high、n_{bucket-medium}、n_bucket-lowThe number of the intervals formed by dividing the high-voltage group, the normal group and the low-voltage group is respectively, the capacitance voltage sequence is divided into a plurality of small intervals, and each interval comprises two groups which are respectively used for storing the numbers of sub-modules which are already put into and are not put into the current control period. Traversing previous control period submodule switching state vector S_oldAnd submodule capacitor voltage vector U_cAnd put them into the belonging barrels respectively. Creating a switching state vector S with length n_onInitialized to and S_oldAn equal vector;

4. when the sub-module is in the discharging state, S is added_onThe corresponding values of all the sub-modules of the medium-high voltage set are set to be 1, and the switching states of all the sub-modules of the low-voltage set are set to be 0. Count S at this time_onThe number n of medium elements 1, according to the specific input number instruction n_onPerforming individual adjustment: if n is<n_onSetting the element with the value of 0 as 1 until n = n in sequence from high to low in the voltage interval_on(ii) a If n is>n_onSequentially setting the elements with the value 1 to zero until n = n according to the sequence of the voltage interval from low to high_onForming the switching state vector S of the control period_on；

5. When the sub-module is in the charging state, S_onThe corresponding values of all the sub-modules of the medium and low voltage set are set to be 1, and the switching states of all the sub-modules of the high voltage set are set to be 0. Count S at this time_onThe number n of medium elements 1, according to the specific input number instruction n_onPerforming individual adjustment: if n is>n_onSetting the element with the value 1 as 0 until n = n in sequence from high to low in the voltage interval_on(ii) a If n is<n_onSequentially setting the elements with the value of 0 to 1 until n = n according to the sequence of the voltage interval from low to high_onForming the switching state vector S of the control period_on；

6. Output switching state vector S_onTo control the switching of the bridge arm submodule and to control S_oldAnd updating for the next control period.

It should be understood that, although the steps in the flowcharts are shown in sequence as indicated by the arrows, the steps are not necessarily performed in sequence as indicated by the arrows. The steps are not performed in the exact order shown and described, and may be performed in other orders, unless explicitly stated otherwise. Moreover, at least a part of the steps in each of the flowcharts described above may include multiple steps or multiple stages, which are not necessarily performed at the same time, but may be performed at different times, and the order of performing the steps or stages is not necessarily sequential, but may be performed alternately or alternately with other steps or at least a part of the steps or stages in other steps.

In one embodiment, as shown in fig. 5, the present application further provides an MMC neutron module capacitor voltage-sharing device, which includes:

the initial quantity obtaining module 100 is configured to obtain an initial switching state vector of the bridge arm submodule, and read an initial value vector of a capacitor voltage of the bridge arm submodule in the control period;

the dividing module 200 is used for dividing the sub-module capacitor voltage sequence into a plurality of large groups according to the initial value vector of the capacitor voltage of the sub-module of the bridge arm based on the control method of the voltage dispersion threshold;

a bucket entering module 300, configured to, for the divided large groups, respectively enter the initial value vector elements of the capacitance and voltage of the sub-modules of the bridge arm in the large groups into the sub-intervals to which the large groups belong, so as to form a plurality of buckets;

the voltage equalizing module 400 is used for performing capacitance voltage equalizing on the bridge arm sub-modules by applying a bucket sorting algorithm according to the initial switching state vector to obtain the switching state vector of the bridge arm sub-modules in the control period;

and the control module 500 is used for controlling the switching of the bridge arm sub-modules according to the switching state vectors of the bridge arm sub-modules in the control period.

The MMC sub-module capacitor voltage-sharing device obtains an initial switching state vector of a bridge arm sub-module, reads a capacitor voltage initial value vector of the bridge arm sub-module in the control period, divides a sub-module capacitor voltage sequence into a plurality of large groups according to the capacitor voltage initial value vector of the bridge arm sub-module based on a control method of a voltage dispersion threshold value, and for the divided large groups, puts capacitor voltage initial value vector elements of the bridge arm sub-module in the large groups into sub-sections to which the large groups belong respectively to form a plurality of buckets; according to the initial switching state vector, applying a bucket sorting algorithm to carry out capacitance voltage sharing on the bridge arm sub-modules to obtain the switching state vector of the bridge arm sub-modules in the control period; and controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period. In the whole process, a control method based on a voltage dispersion threshold value and a bucket sorting algorithm are adopted to subdivide the sub-module capacitor voltage, the algorithm time complexity and the sub-module switching frequency can be effectively reduced, and efficient and accurate MMC sub-module capacitor voltage sharing is achieved.

In one embodiment, the dividing module 200 is further configured to obtain a per unit value of the length of a given bucket interval and a voltage threshold coefficient, which are sent by the control period modulation link; according to the initial value vector of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient, dividing the submodule capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group based on a control method of a voltage dispersion threshold; within each large group, the partitioning is done according to a per unit value of the given bucket interval length.

In one embodiment, the dividing module 200 is further configured to calculate an average value of the capacitor voltages of the bridge arm sub-modules according to the initial value vector of the capacitor voltages of the bridge arm sub-modules; determining critical values of upper and lower limits of an allowable range of the capacitor voltage of the bridge arm submodule according to the average value of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient; and dividing the sub-module capacitor voltage sequence into a large group of a high-voltage group, a normal group and a low-voltage group according to the critical values of the upper limit and the lower limit of the allowable range of the bridge arm sub-module capacitor voltage.

In one embodiment, the voltage equalizing module 400 is further configured to obtain an input sub-module number instruction sent by the control period modulating link; if the bridge arm sub-modules are in a discharging state, setting the switching state corresponding values of all the sub-modules of the high-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the low-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; if the bridge arm sub-modules are in a charging state, setting the switching state corresponding values of all the sub-modules of the low-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the high-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; adjusting the level values of elements in the switching state vector until the counted number is equal to the number corresponding to the number of the input sub-module commands, and forming the switching state vector of the bridge arm sub-module in the control period; wherein the first level value is 1 and the second level value is 0.

In one embodiment, the voltage equalizing module 400 is further configured to compare the counted number with the number corresponding to the number of input sub-modules if the bridge arm sub-modules are in a discharging state; if the number of the elements is larger than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the number command of the input sub-modules; if the number of the elements is smaller than the preset value, sequentially resetting the elements of the first level value to be second level values according to the sequence of the voltage interval from high to low until the counted number is equal to the number corresponding to the input sub-module number instruction; if the bridge arm sub-modules are in a charging state, comparing the counted number with the number corresponding to the number command of the input sub-modules; if the number of the elements is larger than the preset value, sequentially resetting the elements of the first level value to be second level values according to the sequence of the voltage intervals from high to low until the counted number is equal to the number corresponding to the input sub-module number instruction; and if the number of the elements is smaller than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the input sub-module number instruction.

In one embodiment, the initial quantity obtaining module 100 is further configured to obtain a switching state vector of the bridge arm sub-module in the previous control period.

In one embodiment, the control module 500 is further configured to use the switching state vector of the bridge arm sub-module in the control cycle as the switching state vector of the bridge arm sub-module in the next control cycle.

For a specific embodiment of the MMC neutron module capacitor voltage-sharing device, reference may be made to the above embodiment of the MMC neutron module capacitor voltage-sharing method, which is not described herein again. All modules in the MMC sub-module capacitor voltage equalizing device can be completely or partially realized through software, hardware and a combination of the software and the hardware. The modules can be embedded in a hardware form or independent from a processor in the computer device, and can also be stored in a memory in the computer device in a software form, so that the processor can call and execute operations corresponding to the modules.

Practical popularization and application and experimental simulation verification show that the MMC neutron module capacitor voltage-sharing method and device can control the maximum dispersion of the capacitance voltage of the submodule within a set dispersion threshold, meanwhile, the average switching frequency of a submodule power device is obviously reduced, and for high-level MMC-HVDC, the comparison operation times are obviously lower than that of a traditional sequencing voltage-sharing strategy. The scheme of the application has the advantages that the bucket sorting algorithm is combined with the control method based on the voltage dispersion threshold, compared with a capacitance voltage balance control strategy based on the submodule input priority, the submodule capacitance voltage is subdivided by utilizing the bucket sorting idea, the input priority of the submodule is further refined under the condition that the time complexity of the algorithm is not remarkably increased, and the algorithm has more obvious advantages in the aspect of voltage-sharing effect when the control frequency is low or the number of input submodules in adjacent control periods is greatly changed. Compared with the traditional voltage-sharing algorithm, the time complexity of the algorithm and the switching frequency of the sub-modules can be reduced simultaneously, and the switching frequency, the time complexity and the voltage-sharing effect can be flexibly selected or rejected by adjusting two parameters of the capacitance voltage dispersion threshold and the voltage interval length.

In one embodiment, a computer device is provided, which may be a server, and its internal structure diagram may be as shown in fig. 6. The computer device includes a processor, a memory, and a network interface connected by a system bus. Wherein the processor of the computer device is configured to provide computing and control capabilities. The memory of the computer device comprises a nonvolatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of an operating system and computer programs in the non-volatile storage medium. The database of the computer equipment is used for storing preset initial data or historical data cached in the last control period. The network interface of the computer device is used for communicating with an external terminal through a network connection. The computer program is executed by a processor to implement a method for equalizing capacitance of sub-modules in an MMC.

Those skilled in the art will appreciate that the architecture shown in fig. 6 is merely a block diagram of some of the structures associated with the disclosed aspects and is not intended to limit the computing devices to which the disclosed aspects apply, as particular computing devices may include more or less components than those shown, or may combine certain components, or have a different arrangement of components.

In one embodiment, a computer device is provided, comprising a memory and a processor, the memory having a computer program stored therein, the processor implementing the following steps when executing the computer program:

In one embodiment, the processor, when executing the computer program, further performs the steps of:

acquiring a given bucket interval length per unit value and a voltage threshold coefficient which are sent by the control period modulation link; according to the initial value vector of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient, dividing the submodule capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group based on a control method of a voltage dispersion threshold; within each large group, the partitioning is done according to a per unit value of the given bucket interval length.

calculating the average value of the capacitor voltage of the bridge arm submodule according to the initial value vector of the capacitor voltage of the bridge arm submodule; determining critical values of upper and lower limits of an allowable range of the capacitor voltage of the bridge arm submodule according to the average value of the capacitor voltage of the bridge arm submodule and a voltage threshold coefficient; and dividing the sub-module capacitor voltage sequence into a large group of a high-voltage group, a normal group and a low-voltage group according to the critical values of the upper limit and the lower limit of the allowable range of the bridge arm sub-module capacitor voltage.

acquiring an input submodule number instruction sent by the control period modulation link; if the bridge arm sub-modules are in a discharging state, setting the switching state corresponding values of all the sub-modules of the high-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the low-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; if the bridge arm sub-modules are in a charging state, setting the switching state corresponding values of all the sub-modules of the low-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the high-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; adjusting the level values of elements in the switching state vector until the counted number is equal to the number corresponding to the number of the input sub-module commands, and forming the switching state vector of the bridge arm sub-module in the control period; wherein the first level value is 1 and the second level value is 0.

if the bridge arm sub-modules are in a discharging state, comparing the counted number with the number corresponding to the number command of the input sub-modules; if the number of the elements is larger than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the number command of the input sub-modules; if the number of the elements is smaller than the preset value, sequentially resetting the elements of the first level value to be second level values according to the sequence of the voltage interval from high to low until the counted number is equal to the number corresponding to the input sub-module number instruction; if the bridge arm sub-modules are in a charging state, comparing the counted number with the number corresponding to the number command of the input sub-modules; if the number of the elements is larger than the preset value, sequentially resetting the elements of the first level value to be second level values according to the sequence of the voltage intervals from high to low until the counted number is equal to the number corresponding to the input sub-module number instruction; and if the number of the elements is smaller than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the input sub-module number instruction.

In one embodiment, a computer-readable storage medium is provided, having a computer program stored thereon, which when executed by a processor, performs the steps of:

In one embodiment, the computer program when executed by the processor further performs the steps of:

It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by hardware instructions of a computer program, which can be stored in a non-volatile computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. Any reference to memory, storage, database or other medium used in the embodiments provided herein can include at least one of non-volatile and volatile memory. Non-volatile Memory may include Read-Only Memory (ROM), magnetic tape, floppy disk, flash Memory, optical storage, or the like. Volatile Memory can include Random Access Memory (RAM) or external cache Memory. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM), among others.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A MMC neutron module capacitor voltage-sharing method is characterized by comprising the following steps:

according to the control method based on the voltage dispersion threshold, dividing the sub-module capacitor voltage sequence into a plurality of large groups according to the initial value vector of the capacitor voltage of the sub-module of the bridge arm;

controlling the switching of the bridge arm sub-modules according to the switching state vectors of the bridge arm sub-modules in the control period;

the control method based on the voltage dispersion threshold divides the sub-module capacitor voltage sequence into a plurality of large groups according to the initial value vector of the capacitor voltage of the sub-module of the bridge arm, and comprises the following steps: acquiring a given bucket interval length per unit value and a voltage threshold coefficient which are sent by the control period modulation link; according to the initial value vector of the capacitor voltage of the bridge arm submodule and the voltage threshold coefficient, dividing the submodule capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group based on a control method of a voltage dispersion threshold; dividing each large group according to the per unit value of the given bucket interval length;

the step of applying a bucket sorting algorithm to carry out capacitance voltage sharing on the bridge arm sub-modules according to the initial switching state vector to obtain the switching state vector of the bridge arm sub-modules in the control period comprises the following steps: acquiring an input submodule number instruction sent by the control period modulation link; if the bridge arm sub-modules are in a discharging state, setting the switching state corresponding values of all sub-modules of the high-voltage group in the switching state vector as first level values, setting the switching states of all sub-modules of the low-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; if the bridge arm sub-modules are in a charging state, setting the switching state corresponding values of all the sub-modules of the low-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the high-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; and adjusting the level values of elements in the switching state vector until the counted number is equal to the number corresponding to the number command of the switching sub-modules, so as to form the switching state vector of the bridge arm sub-modules in the control period.

2. The method of claim 1, wherein the dividing the sub-module capacitor voltage sequence into a large group of a high-voltage group, a normal group and a low-voltage group according to the initial value vector of the bridge arm sub-module capacitor voltage and the voltage threshold coefficient based on a control method of a voltage dispersion threshold comprises:

determining critical values of upper and lower limits of an allowable range of the capacitor voltage of the bridge arm submodule according to the average value of the capacitor voltage of the bridge arm submodule and the voltage threshold coefficient;

and dividing the sub-module capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group according to the critical values of the upper limit and the lower limit of the allowable range of the bridge arm sub-module capacitor voltage.

3. The method of claim 1, wherein the first level value is 1 and the second level value is 0.

4. The method of claim 1, wherein the adjusting level values of elements in the switching state vector until the counted number is equal to the corresponding number of the invested submodule number instructions comprises:

if the bridge arm sub-modules are in a discharging state, comparing the counted number with the number corresponding to the number command of the input sub-modules; if the number of the elements is larger than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the input submodule number instruction; if the number of the elements is smaller than the preset value, sequentially resetting the elements of the first level value to second level values according to the sequence of the voltage interval from high to low until the counted number is equal to the number corresponding to the input submodule number instruction;

if the bridge arm sub-modules are in a charging state, comparing the counted number with the number corresponding to the number command of the input sub-modules; if the number of the elements is larger than the preset value, sequentially resetting the elements of the first level value to second level values according to the sequence of the voltage intervals from high to low until the counted number is equal to the number corresponding to the input submodule number instruction; and if the number of the elements is smaller than the preset value, sequentially resetting the elements of the second level value to the first level value according to the sequence of the voltage interval from low to high until the counted number is equal to the number corresponding to the input submodule number instruction.

5. The method of claim 1, wherein the obtaining of the initial switching state vector of the bridge arm sub-module comprises:

6. The method according to claim 1, wherein after controlling the switching of the bridge arm sub-modules according to the switching state vector of the bridge arm sub-modules in the control period, the method further comprises:

7. The utility model provides a MMC neutron module electric capacity voltage-sharing device which characterized in that, the device includes:

the dividing module is used for acquiring a per unit value of the length of a given bucket interval and a voltage threshold coefficient which are sent by the control period modulation link; according to the initial value vector of the capacitor voltage of the bridge arm submodule and the voltage threshold coefficient, dividing the submodule capacitor voltage sequence into a high-voltage group, a normal group and a low-voltage group based on a control method of a voltage dispersion threshold; dividing each large group according to the per unit value of the given bucket interval length;

the voltage equalizing module is used for acquiring an input submodule number instruction sent by the control period modulating link; if the bridge arm sub-modules are in a discharging state, setting the switching state corresponding values of all sub-modules of the high-voltage group in the switching state vector as first level values, setting the switching states of all sub-modules of the low-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; if the bridge arm sub-modules are in a charging state, setting the switching state corresponding values of all the sub-modules of the low-voltage group in the switching state vector as first level values, setting the switching states of all the sub-modules of the high-voltage group in the switching state vector as second level values, and counting the number of elements in the switching state vector which are the first level values at the moment; adjusting the level values of elements in the switching state vector until the counted number is equal to the number corresponding to the number of the input sub-module number instructions, and forming the switching state vector of the bridge arm sub-module in the control period;

8. A computer device comprising a memory and a processor, the memory storing a computer program, characterized in that the processor, when executing the computer program, implements the steps of the method of any of claims 1 to 6.

9. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 6.