阅读说明：本技术 一种模块化多电平换流器损耗评估方法及系统 (Loss assessment method and system for modular multilevel converter ) 是由 甘德树 陈建福 曹安瑛 丘冠新 刘尧 林桂辉 杜成涛 王超 刘行健 裴星宇 廖石 于 2021-10-14 设计创作，主要内容包括：本申请公开了一种模块化多电平换流器损耗评估方法及系统,其中方法包括：获取换流器在不同时刻的n组历史运行数据,历史运行数据包括：换流器的交流侧有功功率、交流侧无功功率、同一时刻的直流侧有功功率、同一时刻开关器件的开关频率,n为正整数；根据历史运行数据计算换流器损耗并进行归一化处理后,通过奈尔检测法进行数据清洗,得到清洗后的第一运行数据；将电流变量替换为功率变量,并加入功率频率拟合项构建损耗特性描述方程；通过第一运行数据对损耗特性描述方程进行拟合,并对拟合后的函数进行求解,得到换流器的损耗。从而解决了现有技术对换流器损耗评估的准确性较差且难以确定损耗因子的技术问题。(The application discloses a loss assessment method and system for a modular multilevel converter, wherein the method comprises the following steps: obtaining n groups of historical operation data of the converter at different moments, wherein the historical operation data comprises: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter are respectively controlled by the controller, and n is a positive integer; calculating the loss of the current converter according to historical operating data, carrying out normalization processing, and then carrying out data cleaning through a Nall detection method to obtain cleaned first operating data; replacing the current variable with a power variable, and adding a power frequency fitting term to construct a loss characteristic description equation; and fitting the loss characteristic description equation through the first operation data, and solving the fitted function to obtain the loss of the converter. Therefore, the technical problems that the accuracy of the loss evaluation of the converter is poor and the loss factor is difficult to determine in the prior art are solved.)

1. A loss assessment method for a modular multilevel converter is characterized by comprising the following steps:

obtaining n groups of historical operation data of the converter at different time, wherein the historical operation data comprises: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter are respectively controlled by the controller, and n is a positive integer;

calculating the loss of the current converter according to the historical operating data, carrying out normalization processing, and then carrying out data cleaning through a Nall detection method to obtain cleaned first operating data;

replacing the current variable with a power variable, and adding a power frequency fitting term to construct a loss characteristic description equation;

and fitting the loss characteristic description equation through the first operation data, and solving the fitted function to obtain the loss of the converter.

2. The method according to claim 1, wherein after calculating the converter loss according to the historical operating data and performing normalization processing, performing data cleaning by using a neel detection method to obtain cleaned first operating data specifically comprises:

respectively substituting the active power at the alternating current side and the active power at the direct current side in each group of historical operating data into a converter loss calculation formula for calculation to obtain n groups of converter losses at different moments;

on the basis of a normalization formula, after normalization processing is carried out on the losses of the n groups of converters respectively, the standard deviation of the losses of the n groups of converters is calculated;

and calculating to obtain statistic according to the standard deviation, and performing Neel detection based on the statistic to obtain the first operation data.

3. The modular multilevel converter loss evaluation method according to claim 1, wherein the loss characterization equation is:

；

in the formula (I), the compound is shown in the specification,in order to reduce the losses of the inverter,in order to fix the loss of the inverter,in order to be a factor of loss of the switching frequency,in order to obtain the power primary loss factor,in order to obtain the power secondary loss coefficient,for the purpose of said switching frequency, the switching frequency,for the active power on the ac side,and the reactive power is the reactive power of the alternating current side.

4. The method according to claim 1, wherein the fitting the loss characterization equation according to the first operation data and solving the fitted function to obtain the loss of the converter specifically comprises:

fitting parameters in the loss characteristic description equation through the first operation data, determining parameters of the loss characteristic by using a least square method, and constructing to obtain a fitting function;

and respectively solving the partial derivatives of the variables in the fitting function by a method for solving the extreme value of the multivariate function, making the fitting function equal to zero to obtain a partial derivative function, and calculating the partial derivative function to obtain the loss of the converter.

5. The modular multilevel converter loss assessment method according to claim 4, wherein the fitting function is:

；

in the formula (I), the compound is shown in the specification,in order to fix the loss of the inverter,in order to be a factor of loss of the switching frequency,in order to obtain the power primary loss factor,in order to obtain the power secondary loss coefficient,、a primary power variable and a secondary power variable of the equation are described for the loss characteristic,is the switching frequency of the i-th group,to the switching frequencyIs fed byAnd (4) calculating the converter loss by using the group operation data.

6. The method of claim 2, wherein the converter loss calculation formula is:

；

in the formula (I), the compound is shown in the specification,to the switching frequencyIs fed byThe converter losses calculated from the group historical operating data,、are respectively the firstAnd active power effective values of an AC side and a DC side of the converter in the group operation data.

7. The modular multilevel converter loss assessment method according to claim 2, wherein the normalization formula is:

；

in the formula (I), the compound is shown in the specification,is as followsA converter loss normalization represented by the group historical operating data,to the switching frequencyIs fed byThe converter losses calculated from the group historical operating data,is as followsAnd the active power effective value of the AC side of the converter in the group operation data.

8. A modular multilevel converter loss assessment system, comprising:

the obtaining unit is used for obtaining n groups of historical operation data of the converter at different moments, and the historical operation data comprises: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter are respectively controlled by the controller, and n is a positive integer;

the cleaning unit is used for calculating the loss of the converter according to the historical operating data, carrying out normalization processing, and then cleaning data through a Neel detection method to obtain cleaned first operating data;

the building unit is used for replacing the current variable with a power variable and adding a power frequency fitting term to build a loss characteristic description equation;

and the fitting unit is used for fitting the loss characteristic description equation through the first operation data and solving the fitted function to obtain the loss of the converter.

9. The modular multilevel converter loss evaluation system of claim 8, wherein the wash unit is specifically configured to:

respectively substituting the active power at the alternating current side and the active power at the direct current side in each group of historical operating data into a converter loss calculation formula for calculation to obtain n groups of converter losses at different moments;

on the basis of a normalization formula, after normalization processing is carried out on the losses of the n groups of converters respectively, the standard deviation of the losses of the n groups of converters is calculated;

and calculating to obtain statistic according to the standard deviation, and performing Neel detection based on the statistic to obtain the first operation data.

10. The modular multilevel converter loss evaluation system of claim 8, wherein the fitting unit is specifically configured to:

fitting parameters in the loss characteristic description equation through the first operation data, determining parameters of the loss characteristic by using a least square method, and constructing to obtain a fitting function;

and respectively solving the partial derivatives of the variables in the fitting function by a method for solving the extreme value of the multivariate function, making the fitting function equal to zero to obtain a partial derivative function, and calculating the partial derivative function to obtain the loss of the converter.

Technical Field

The application relates to the technical field of flexible direct current transmission, in particular to a loss evaluation method and system for a modular multilevel converter.

Background

At present, a Modular Multilevel Converter (MMC) has been widely applied to the fields of flexible direct current transmission, flexible direct current distribution, flexible interconnection of an alternating current power grid, low-voltage direct current remote supply and the like, and is a core electric energy conversion device for constructing a novel power system network frame. As the MMC sub-modules are numerous, the operation working conditions are complex, the circuit topology types are various, and the selectable types of the power switch devices are rich, the accurate loss evaluation of the MMC sub-modules is difficult. The lack of an effective quantitative evaluation method for the loss characteristics of the converter results in that the loss of the converter is difficult to reduce by a method for reasonably distributing the power flow in direct current power transmission and distribution occasions where the converter is widely applied, and the economical efficiency of system operation is influenced.

At present, the loss of the existing converter is composed of nonlinear loss, linear loss and necessary loss as in the technical scheme with the patent number of CN 109193667A. The technical scheme has the following main problems; the influence of different switching frequencies of a switching device on the loss characteristic of the converter is not considered, the loss characteristic of the power switching device under different switching frequencies cannot be reflected by representing the fixed loss of the converter by a constant, and the accuracy of loss evaluation is reduced; secondly, the loss factors are difficult to determine, various loss components need to be considered comprehensively from the aspects of topology and working principle, and the loss factors are difficult to determine accurately.

Disclosure of Invention

The application provides a loss evaluation method and system for a modular multilevel converter, which are used for solving the technical problems that the accuracy of loss evaluation of the converter in the prior art is poor and loss factors are difficult to determine.

In view of the above, a first aspect of the present application provides a modular multilevel converter loss assessment method, including:

obtaining n groups of historical operation data of the converter at different time, wherein the historical operation data comprises: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter are respectively controlled by the controller, and n is a positive integer;

calculating the loss of the current converter according to the historical operating data, carrying out normalization processing, and then carrying out data cleaning through a Nall detection method to obtain cleaned first operating data;

replacing the current variable with a power variable, and adding a power frequency fitting term to construct a loss characteristic description equation;

and fitting the loss characteristic description equation through the first operation data, and solving the fitted function to obtain the loss of the converter.

Optionally, after calculating the converter loss according to the historical operating data and performing normalization processing, performing data cleaning by using a neel detection method to obtain cleaned first operating data, and specifically including:

respectively substituting the active power at the alternating current side and the active power at the direct current side in each group of historical operating data into a converter loss calculation formula for calculation to obtain n groups of converter losses at different moments;

on the basis of a normalization formula, after normalization processing is carried out on the losses of the n groups of converters respectively, the standard deviation of the losses of the n groups of converters is calculated;

and calculating to obtain statistic according to the standard deviation, and performing Neel detection based on the statistic to obtain the first operation data.

Optionally, the loss characteristic description equation is:

；

in the formula (I), the compound is shown in the specification,in order to reduce the losses of the inverter,in order to fix the loss of the inverter,in order to be a factor of loss of the switching frequency,in order to obtain the power primary loss factor,in order to obtain the power secondary loss coefficient,for the purpose of said switching frequency, the switching frequency,for the active power on the ac side,and the reactive power is the reactive power of the alternating current side.

Optionally, the fitting the loss characteristic description equation through the first operation data, and solving a fitted function to obtain the loss of the converter specifically include:

fitting parameters in the loss characteristic description equation through the first operation data, determining parameters of the loss characteristic by using a least square method, and constructing to obtain a fitting function;

and respectively solving the partial derivatives of the variables in the fitting function by a method for solving the extreme value of the multivariate function, making the fitting function equal to zero to obtain a partial derivative function, and calculating the partial derivative function to obtain the loss of the converter.

Optionally, the fitting function is:

；

in the formula (I), the compound is shown in the specification,in order to fix the loss of the inverter,in order to be a factor of loss of the switching frequency,in order to obtain the power primary loss factor,in order to obtain the power secondary loss coefficient,、a primary power variable and a secondary power variable of the equation are described for the loss characteristic,is the switching frequency of the i-th group,to the switching frequencyIs fed byAnd (4) calculating the converter loss by using the group operation data.

Optionally, the converter loss calculation formula is:

；

in the formula (I), the compound is shown in the specification,to the switching frequencyIs fed byThe converter losses calculated from the group historical operating data,、are respectively the firstAnd active power effective values of an AC side and a DC side of the converter in the group operation data.

Optionally, the normalization formula is:

；

in the formula (I), the compound is shown in the specification,is as followsA converter loss normalization represented by the group historical operating data,to the switching frequencyIs fed byThe converter losses calculated from the group historical operating data,is as followsAnd the active power effective value of the AC side of the converter in the group operation data.

A second aspect of the present application provides a modular multilevel converter loss assessment system, the system comprising:

the obtaining unit is used for obtaining n groups of historical operation data of the converter at different moments, and the historical operation data comprises: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter are respectively controlled by the controller, and n is a positive integer;

the cleaning unit is used for calculating the loss of the converter according to the historical operating data, carrying out normalization processing, and then cleaning data through a Neel detection method to obtain cleaned first operating data;

the building unit is used for replacing the current variable with a power variable and adding a power frequency fitting term to build a loss characteristic description equation;

and the fitting unit is used for fitting the loss characteristic description equation through the first operation data and solving the fitted function to obtain the loss of the converter.

Optionally, the cleaning unit is specifically configured to:

respectively substituting the active power at the alternating current side and the active power at the direct current side in each group of historical operating data into a converter loss calculation formula for calculation to obtain n groups of converter losses at different moments;

on the basis of a normalization formula, after normalization processing is carried out on the losses of the n groups of converters respectively, the standard deviation of the losses of the n groups of converters is calculated;

and calculating to obtain statistic according to the standard deviation, and performing Neel detection based on the statistic to obtain the first operation data.

Optionally, the fitting unit is specifically configured to:

fitting parameters in the loss characteristic description equation through the first operation data, determining parameters of the loss characteristic by using a least square method, and constructing to obtain a fitting function;

and respectively solving the partial derivatives of the variables in the fitting function by a method for solving the extreme value of the multivariate function, making the fitting function equal to zero to obtain a partial derivative function, and calculating the partial derivative function to obtain the loss of the converter.

According to the technical scheme, the method has the following advantages:

the application provides a loss evaluation method of a modular multilevel converter, which solves the problem that the influence of the switching frequency of a power device on the loss characteristic of the converter is not considered in the existing loss evaluation method of the converter by adding a fitting item related to the switching frequency into a loss characteristic equation. Meanwhile, the historical operation data of the converter is used for fitting the parameters of the loss characteristic equation, a method for calculating the loss characteristic equation parameters according to topology and working principle or measuring the loss characteristic parameters through field test in the prior art is replaced, the difficulty of determining the loss factor is greatly reduced, and the method can be still used for dynamically evaluating the loss characteristic of the converter after the body parameters are changed due to long-term operation of equipment. Furthermore, after the loss characteristic fitting equation provided by the application is subjected to linearization processing, the nonlinear complexity of a fitting curve is reduced, the overall loss characteristic of the converter can be fitted by using less operation data, a new measuring device is not needed, delivery tests of various electrical quantities and non-electrical quantities are not needed, the loss evaluation process is simplified, and the method is suitable for the overall loss evaluation of converters with different sub-modules and different topological structures. Therefore, the technical problems that the accuracy of the loss evaluation of the converter is poor and the loss factor is difficult to determine in the prior art are solved.

Drawings

Fig. 1 is a schematic flowchart of a first embodiment of a loss evaluation method for a modular multilevel converter provided in an embodiment of the present application;

fig. 2 is a schematic flowchart of a second embodiment of a loss evaluation method for a modular multilevel converter provided in the embodiment of the present application;

fig. 3 is a schematic structural diagram of an embodiment of a modular multilevel converter loss evaluation system provided in an embodiment of the present application.

Detailed Description

In order to make the technical solutions of the present application better understood, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Referring to fig. 1, a loss evaluation method for a modular multilevel converter according to an embodiment of the present application includes:

step 101, obtaining n groups of historical operating data of the current converter at different moments, wherein the historical operating data comprises: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter, wherein n is a positive integer.

It should be noted that, in this embodiment, historical operating data of a plurality of sets of ac ports and dc ports of a converter on a cross section at different times are acquired by a scheduling automation system, and it can be understood that the historical operating data of the same set are acquired at the same time. Specifically, the historical operating data of the present embodiment includes: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of the switching device at the same moment of the converter. According to the method and the device, the historical operation data of the current converter on different switch working frequencies and different discontinuities are collected, so that the obtained data have universal representativeness under different load rates, and the accuracy of loss assessment is improved.

102, calculating the loss of the converter according to historical operating data, carrying out normalization processing, and then cleaning data through a Neel detection method to obtain cleaned first operating data.

It should be noted that, in this embodiment, the converter loss is calculated according to the historical operating data, specifically:

for a given switching frequencyObtained underCalculating the converter loss represented by each group of operation data according to the operation data of the converter on the section of the group at different time：

；

In the formula (I), the compound is shown in the specification,indicating switching frequencyIs fed byThe converter losses calculated from the group historical operating data,、respectively representAnd active power effective values of an alternating current side and a direct current side of the converter in the group historical operation data.

The normalization process in this embodiment specifically includes:

carrying out normalization processing on the converter loss of each group of historical operating data to obtain。

；

In the formula (I), the compound is shown in the specification,is as followsA converter loss normalization represented by the group historical operating data,to the switching frequencyIs fed byThe converter losses calculated from the group historical operating data,is as followsAnd the active power effective value of the AC side of the converter in the group operation data.

In this embodiment, data cleaning is performed by a neel detection method to obtain first operation data after cleaning, which specifically includes:

(1) computingStandard deviation of group loss data；

；

；

Wherein the content of the first and second substances,is the average of the loss sample data.

(2) Specifying maximum values in loss samplesTo assume outliersAnd calculating statistics；

；

According to the detected levelAnd sample volumeCritical value table of the Charnell testIf, ifJudging the data to be an abnormal value, and removing the abnormal value and then continuing the neel detection on the residual data; otherwise, no outliers are found.

And 103, replacing the current variable with a power variable, and adding a power frequency fitting term to construct a loss characteristic description equation.

It should be noted that, in order to fully consider various factors affecting the loss of the converter and improve the accuracy of the loss evaluation, a power device switching frequency fitting term is added on the basis of the existing loss evaluation method in the embodiment. In addition, in order to directly employ the historical operation data, the present embodiment replaces the current variable with the power variable. Thus, the loss characteristic description equation is constructed as follows:

；

in the formula (I), the compound is shown in the specification,in order to reduce the losses of the inverter,in order to fix the loss of the inverter,in order to be a factor of loss of the switching frequency,in order to obtain the power primary loss factor,in order to obtain the power secondary loss coefficient,for the purpose of said switching frequency, the switching frequency,for the active power on the ac side,and the reactive power is the reactive power of the alternating current side.

Furthermore, in order to reduce the nonlinearity of the loss characteristic equation and facilitate the subsequent determination of parameters by using a linear fitting method、Respectively represent the primary power variable and the secondary power variable in the above formula, and the above formula is rewritten as:

；

and step 104, fitting the loss characteristic description equation through the first operation data, and solving the fitted function to obtain the loss of the converter.

It should be noted that, in this embodiment, the parameters in the loss characteristic equation are fitted by using the cleaned first operation data, and the parameters of the loss characteristic are determined by using the least square method, so that the fitted function is obtained as:

；

in the formula (I), the compound is shown in the specification,in order to fix the loss of the inverter,in order to be a factor of loss of the switching frequency,in order to obtain the power primary loss factor,in order to obtain the power secondary loss coefficient,、a primary power variable and a secondary power variable of the equation are described for the loss characteristic,the switching frequency of the ith group,to the switching frequencyIs fed byAnd (4) calculating the converter loss by using the group operation data.

Further, by using a method for solving an extreme value of a multivariate function, respectively solving partial derivatives of variables in the above formula, and making the partial derivatives equal to zero, obtaining:

；

and solving the equation to obtain the value of each parameter in the loss characteristic equation, thereby obtaining the loss of the converter.

The first embodiment of the loss evaluation method for the modular multilevel converter provided in the embodiment of the present application is described above, and the second embodiment of the loss evaluation method for the modular multilevel converter provided in the embodiment of the present application is described below.

Referring to fig. 2, a second embodiment of the present invention provides a method for evaluating loss of a blocking multilevel converter, including:

step 201, obtaining n groups of historical operating data of the current converter at different time, wherein the historical operating data comprises: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter, wherein n is a positive integer.

And step 202, substituting the active power of the alternating current side and the active power of the direct current side in each group of historical operating data into a converter loss calculation formula for calculation to obtain n groups of converter losses at different moments.

And 203, respectively carrying out normalization processing on the n groups of converter losses based on a normalization formula, and then calculating the standard deviation of the n groups of converter losses.

And 204, calculating to obtain statistic according to the standard deviation, and performing Neel detection based on the statistic to obtain first operation data.

And step 205, replacing the current variable with a power variable, and adding a power frequency fitting term to construct a loss characteristic description equation.

And step 206, fitting parameters in the loss characteristic description equation through the first operation data, determining the parameters of the loss characteristic by using a least square method, and constructing to obtain a fitting function.

And step 207, respectively solving the partial derivatives of the variables in the fitting function by a method for solving the extreme value of the multivariate function, making the fitting function equal to zero to obtain a partial derivative function, and calculating the partial derivative function to obtain the loss of the converter.

The steps 201-207 of the present embodiment are similar to the description of the steps 101-104 of the embodiment, please refer to the description of the steps 101-104 of the embodiment, which will not be described herein again.

The embodiment provides a loss evaluation method for a modular multilevel converter, which solves the problem that the influence of the switching frequency of a power device on the loss characteristic of the converter is not considered in the existing loss evaluation method for the converter by adding a fitting term related to the switching frequency into a loss characteristic equation. Meanwhile, the historical operation data of the converter is used for fitting the parameters of the loss characteristic equation, a method for calculating the loss characteristic equation parameters according to topology and working principle or measuring the loss characteristic parameters through field test in the prior art is replaced, the difficulty of determining the loss factor is greatly reduced, and the method can be still used for dynamically evaluating the loss characteristic of the converter after the body parameters are changed due to long-term operation of equipment. Furthermore, after the loss characteristic fitting equation provided by the application is subjected to linearization processing, the nonlinear complexity of a fitting curve is reduced, the overall loss characteristic of the converter can be fitted by using less operation data, a new measuring device is not needed, delivery tests of various electrical quantities and non-electrical quantities are not needed, the loss evaluation process is simplified, and the method is suitable for the overall loss evaluation of converters with different sub-modules and different topological structures. Therefore, the technical problems that the accuracy of the loss evaluation of the converter is poor and the loss factor is difficult to determine in the prior art are solved.

In the above, a second embodiment of the method for evaluating loss of a modular multilevel converter provided in the embodiment of the present application is described below as an embodiment of a system for evaluating loss of a modular multilevel converter provided in the embodiment of the present application.

Referring to fig. 3, an exemplary embodiment of a system for evaluating loss of a block multilevel converter includes:

an obtaining unit 301, configured to obtain n sets of historical operation data of the converter at different time instants, where the historical operation data includes: the active power at the alternating current side, the reactive power at the alternating current side, the active power at the direct current side at the same moment and the switching frequency of a switching device at the same moment of the converter, wherein n is a positive integer.

And the cleaning unit 302 is configured to calculate converter loss according to the historical operating data, perform normalization processing, and perform data cleaning by using a neel detection method to obtain cleaned first operating data.

And the constructing unit 303 is configured to replace the current variable with a power variable, and add a power frequency fitting term to construct a loss characteristic description equation.

And the fitting unit 304 is configured to fit the loss characteristic description equation through the first operation data, and solve the fitted function to obtain the loss of the converter.

It is clear to those skilled in the art that, for convenience and brevity of description, the specific working processes of the above-described systems, apparatuses and units may refer to the corresponding processes in the foregoing method embodiments, and are not described herein again.

The terms "first," "second," "third," "fourth," and the like in the description of the application and the above-described figures, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

It should be understood that in the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" for describing an association relationship of associated objects, indicating that there may be three relationships, e.g., "a and/or B" may indicate: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b, c may be single or plural.

In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus and method may be implemented in other manners. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present application may be substantially implemented or contributed to by the prior art, or all or part of the technical solution may be embodied in a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present application. And the aforementioned storage medium includes: a U disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.

The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions in the embodiments of the present application.