阅读说明：本技术 一种用于不同频率下对电气量测量的方法及装置 (Method and device for measuring electric quantity under different frequencies ) 是由 肖遥 刘家严 夏国庆 于 2021-06-25 设计创作，主要内容包括：本发明公开了一种用于不同频率下对电气量测量的方法及装置,所述方法包括：确定软硬件的采样频率f-s；获取预设采样频率范围下所需要采样数量的范围；获取所有的采样数量对应的傅里叶系数并存储备用；根据软硬件的采样频率,获取每个采样数量对应的频率边界；根据输入频率选择所需要的采样数量；实时存储当前时刻前推2*N-(max)个采样点的数据,N-(max)表示最大采样数量；根据当前输入频率所选择的采样数量,调用其对应的傅里叶系数,同时取出当前输入频率所选择的采样数量对应的采样点数据进行电气量计算；本发明的优点在于：电气量测量的计算误差小,软硬件要求低以及准确度高。(The invention discloses a method and a device for measuring electric quantity under different frequencies, wherein the method comprises the following steps: determining the sampling frequency f of software and hardware s (ii) a Acquiring the range of the required sampling quantity under the preset sampling frequency range; acquiring Fourier coefficients corresponding to all the sampling quantities and storing the Fourier coefficients for later use; acquiring a frequency boundary corresponding to each sampling quantity according to the sampling frequency of the software and the hardware; selecting the required sampling number according to the input frequency; real-time storage of current time advance 2 x N max Data of a sampling point, N max Represents the maximum number of samples; according to the sampling quantity selected by the current input frequency, calling the corresponding Fourier coefficient, and simultaneously taking out sampling point data corresponding to the sampling quantity selected by the current input frequency to calculate the electrical quantity; the invention has the advantages that: the calculation error of the electrical quantity measurement is small, the requirements of software and hardware are low, and the accuracy is high.)

1. A method for measuring electrical quantities at different frequencies, the method comprising:

the method comprises the following steps: determining the sampling frequency f of software and hardware_s；

Step two: acquiring the range of the required sampling quantity under the preset sampling frequency range;

step three: acquiring Fourier coefficients corresponding to all the sampling quantities and storing the Fourier coefficients for later use;

step four: acquiring a frequency boundary corresponding to each sampling quantity according to the sampling frequency of the software and the hardware;

step five: selecting the required sampling number according to the input frequency;

step six: real-time storage of current time advance 2 x N_maxData of a sampling point, N_maxRepresents the maximum number of samples;

step seven: and calling the corresponding Fourier coefficient according to the sampling number selected by the current input frequency, and simultaneously taking out sampling point data corresponding to the sampling number selected by the current input frequency to calculate the electrical quantity.

2. A method for measuring electrical quantities at different frequencies according to claim 1, wherein the second step comprises: the preset sampling frequency range is 45Hz to 55Hz, and the range of the required sampling number N between 45Hz and 55Hz is as follows:

minimum number N_min＝(f_s/55) rounding down;

maximum number N_max＝(f_sAnd/45) rounding up.

3. A method for measuring electrical quantities at different frequencies according to claim 1, wherein the third step comprises:

by the formulaObtainingThe kth real part Fourier coefficients corresponding to all the sampling numbers;

by the formulaAcquiring the kth imaginary Fourier coefficient corresponding to all the sampling numbers;

k is the number of the Fourier coefficient, the value range is from 1 to N, and N is the number of samples required in the preset sampling frequency range; when n is 2 or more, the number of harmonics is represented, and n is 1 or more, the fundamental wave is represented.

4. A method for measuring electrical quantities at different frequencies according to claim 2, characterised in that said fourth step comprises: the preset sampling frequency range from 45Hz to 55Hz is divided into 45Hz and f from small to large₁、f₂、f₃、、、、、、f_max-1、f_max55Hz, wherein, f₁、f₂、f₃、、、、、、f_max-1、f_maxDividing the frequency boundary from left to right by f₁As the initial value, the numerator is not changed, the denominators are reduced by one, and when dividing the frequency boundary from right to left, f is used_maxAnd adding the denominators one by one to the initial value, keeping the numerators unchanged, and stopping dividing when an equal frequency boundary appears in the process of dividing the frequency boundary from left to right and dividing the frequency boundary from right to left.

5. A method for measuring electrical quantities at different frequencies according to claim 4, characterised in that in step four

6. A method for measuring electrical quantities at different frequencies according to claim 5, wherein the step five comprises:

when f is more than or equal to 45<f₁The method comprises the following steps: N-N_max；

When f is₁≤f<f₂The method comprises the following steps: N-N_max-1；

When f is₂≤f<f₃The method comprises the following steps: N-N_max-2；

When f is_max-1≤f<f_maxThe method comprises the following steps: N-N_min+1；

When f is_maxWhen f is not less than 55: N-N_min；

f is the current input frequency.

7. A method for measuring electrical quantities at different frequencies according to claim 6, wherein the seventh step comprises:

the electrical quantities are voltage and phase, and are calculated by formulaAnd acquiring an effective value of the voltage, wherein,i_kdata representing a kth sample point within a cycle;

by the formulaThe phase is acquired.

8. An apparatus for measuring electrical quantities at different frequencies, the apparatus comprising:

a hardware sampling frequency acquisition module for determining the sampling frequency f of the hardware and the software_s；

The sampling number range acquisition module is used for acquiring the range of the required sampling number in a preset sampling frequency range;

the Fourier coefficient acquisition module is used for acquiring Fourier coefficients corresponding to all the sampling numbers and storing the Fourier coefficients for later use;

the frequency boundary acquisition module is used for acquiring a frequency boundary corresponding to each sampling quantity according to the sampling frequency of software and hardware;

the sampling quantity selection module is used for selecting the required sampling quantity according to the input frequency;

a storage module for storing the current forward push 2 × N in real time_maxData of a sampling point, N_maxRepresents the maximum number of samples;

and the electrical quantity calculation module is used for calling the corresponding Fourier coefficient according to the sampling quantity selected by the current input frequency and simultaneously taking out the sampling point data corresponding to the sampling quantity selected by the current input frequency to calculate the electrical quantity.

9. The apparatus of claim 8, wherein the sampling number range acquisition module is further configured to: the preset sampling frequency range is 45Hz to 55Hz, and the range of the required sampling number N between 45Hz and 55Hz is as follows:

minimum number N_min＝(f_s/55) rounding down;

maximum number N_max＝(f_sAnd/45) rounding up.

10. The apparatus of claim 8, wherein the fourier coefficient obtaining module is further configured to:

by the formulaAcquiring the kth real part Fourier coefficient corresponding to all the sampling numbers;

by the formulaAcquiring the kth imaginary Fourier coefficient corresponding to all the sampling numbers;

k is the number of the Fourier coefficient, the value range is from 1 to N, and N is the number of samples required in the preset sampling frequency range; when n is 2 or more, the number of harmonics is represented, and n is 1 or more, the fundamental wave is represented.

Technical Field

The invention relates to the field of electrical quantity measurement, in particular to a method and a device for measuring electrical quantity under different frequencies.

Background

When electric energy is used as clean energy to be applied to daily life more and more widely, the quality of the electric energy is more and more emphasized, and the performance of a measurement and control device for monitoring electric quantity in a transformer substation and a power plant is required to be improved gradually. At present, many devices for collecting electrical quantity are converted into digital quantity by using a Fourier algorithm, for full-wave Fourier, the number of sampling points in one cycle is the same as the number of Fourier coefficients, data can be accurate, but the sampling frequency is fixed, when the frequency is different, the number of sampling points of each cycle is different, so that a larger error occurs in calculation, the sampling precision can be improved by reducing the error, but the requirement on hardware is improved; or frequency conversion sampling is used, but the accuracy of wave recording when a fault occurs cannot be guaranteed, so that the electric quantity measuring method in the prior art has larger calculation error, high hardware requirement and lower accuracy when the sampling frequency is different.

Chinese patent application No. 201310229000.4 discloses a method and system for measuring electrical parameters with wide variation, which is suitable for a microgrid connected to a medium-and small-capacity wind generating set, the method includes: performing discrete sampling on the instantaneous voltage signal to obtain a discrete voltage signal, and performing sliding window iterative discrete Fourier transform on the discrete voltage signal by combining a phase-locked negative feedback phase angle signal to obtain a phase difference signal; carrying out proportional integral adjustment on the phase difference signal to obtain the fundamental wave angular frequency of the zero phase difference signal; obtaining output frequency from the fundamental wave angular frequency, performing discrete integration on the output frequency, adding the discrete integration and the fundamental wave angular frequency to obtain a phase angle, and performing phase-locking negative feedback on the phase angle; and calculating effective values of voltage and current according to the output frequency. The method solves the problem of digital phase locking of the voltage with wide frequency variation range, and provides an input parameter measuring method for the rapid power control of medium and small-capacity wind turbines. But the patent application is only applicable to the case where the output frequency is fixed.

Disclosure of Invention

The invention aims to solve the technical problems that in the prior art, when the sampling frequency is different, the electric quantity measuring method has larger calculation error, high hardware requirement and lower accuracy.

The invention solves the technical problems through the following technical means: a method for measuring electrical quantities at different frequencies, the method comprising:

the method comprises the following steps: determining the sampling frequency f of software and hardware_s；

Step two: acquiring the range of the required sampling quantity under the preset sampling frequency range;

step three: acquiring Fourier coefficients corresponding to all the sampling quantities and storing the Fourier coefficients for later use;

step four: acquiring a frequency boundary corresponding to each sampling quantity according to the sampling frequency of the software and the hardware;

step five: selecting the required sampling number according to the input frequency;

step six: real-time storage of current time advance 2 x N_maxData of a sampling point, N_maxRepresents the maximum number of samples;

step seven: and calling the corresponding Fourier coefficient according to the sampling number selected by the current input frequency, and simultaneously taking out sampling point data corresponding to the sampling number selected by the current input frequency to calculate the electrical quantity.

According to the invention, when the sampling frequencies are different, the sampling frequencies of software and hardware do not need to be changed, the requirements on the software and hardware are reduced, the sampling number required by each cycle under different frequencies is calculated according to the preset sampling frequency range, the Fourier coefficients corresponding to each sampling number are respectively prepared, when the frequencies are changed, the Fourier coefficients under the corresponding frequencies are respectively called for calculation, the calculation result is accurate, the calculation error is small, the algorithm is easy to realize, the reliability is high, and the accuracy of electric quantity collection can be improved.

Further, the second step comprises: the preset sampling frequency range is 45Hz to 55Hz, and the range of the required sampling number N between 45Hz and 55Hz is as follows:

minimum number N_min＝(f_s/55) rounding down;

maximum number N_max＝(f_sAnd/45) rounding up.

Further, the third step includes:

by the formulaAcquiring the kth real part Fourier coefficient corresponding to all the sampling numbers;

by the formulaAcquiring the kth imaginary Fourier coefficient corresponding to all the sampling numbers;

k is the number of the Fourier coefficient, the value range is from 1 to N, and N is the number of samples required in the preset sampling frequency range; when n is 2 or more, the number of harmonics is represented, and n is 1 or more, the fundamental wave is represented.

Further, the fourth step includes: the preset sampling frequency range from 45Hz to 55Hz is divided into 45Hz and f from small to large₁、f₂、f₃、、、、、、f_max-1、f_max55Hz, wherein, f₁、f₂、f₃、、、、、、f_max-1、f_maxDividing the frequency boundary from left to right by f₁As the initial value, the numerator is not changed, the denominators are reduced by one, and when dividing the frequency boundary from right to left, f is used_maxAnd adding the denominators one by one to the initial value, keeping the numerators unchanged, and stopping dividing when an equal frequency boundary appears in the process of dividing the frequency boundary from left to right and dividing the frequency boundary from right to left.

Further, in the fourth step

Further, the fifth step includes:

when f is more than or equal to 45<f₁The method comprises the following steps: N-N_max；

When f is₁≤f<f₂The method comprises the following steps: N-N_max-1；

When f is₂≤f<f₃The method comprises the following steps: N-N_max-2；

When f is_max-1≤f<f_maxThe method comprises the following steps: N-N_min+1；

When f is_maxWhen f is not less than 55: N-N_min；

f is the current input frequency.

Still further, the seventh step includes:

the electrical quantities are voltage and phase, and are calculated by formulaAnd acquiring an effective value of the voltage, wherein,i_kdata representing a kth sample point within a cycle;

by the formulaThe phase is acquired.

The present invention also provides a device for measuring electrical quantities at different frequencies, the device comprising:

a hardware sampling frequency acquisition module for determining the sampling frequency f of the hardware and the software_s；

The sampling number range acquisition module is used for acquiring the range of the required sampling number in a preset sampling frequency range;

the Fourier coefficient acquisition module is used for acquiring Fourier coefficients corresponding to all the sampling numbers and storing the Fourier coefficients for later use;

the frequency boundary acquisition module is used for acquiring a frequency boundary corresponding to each sampling quantity according to the sampling frequency of software and hardware;

the sampling quantity selection module is used for selecting the required sampling quantity according to the input frequency;

a storage module for storing the current forward push 2 × N in real time_maxData of a sampling point, N_maxRepresents the maximum number of samples;

and the electrical quantity calculation module is used for calling the corresponding Fourier coefficient according to the sampling quantity selected by the current input frequency and simultaneously taking out the sampling point data corresponding to the sampling quantity selected by the current input frequency to calculate the electrical quantity.

Further, the sampling number range obtaining module is further configured to: the preset sampling frequency range is 45Hz to 55Hz, and the range of the required sampling number N between 45Hz and 55Hz is as follows:

minimum number N_min＝(f_s/55) rounding down;

maximum number N_max＝(f_sAnd/45) rounding up.

Further, the fourier coefficient obtaining module is further configured to:

by the formulaAcquiring the kth real part Fourier coefficient corresponding to all the sampling numbers;

by the formulaAcquiring the kth imaginary Fourier coefficient corresponding to all the sampling numbers;

k is the number of the Fourier coefficient, the value range is from 1 to N, and N is the number of samples required in the preset sampling frequency range; when n is 2 or more, the number of harmonics is represented, and n is 1 or more, the fundamental wave is represented.

Still further, the frequency boundary acquisition module is further configured to: the preset sampling frequency range from 45Hz to 55Hz is divided into 45Hz and f from small to large₁、f₂、f₃、、、、、、f_max-1、f_max55Hz, wherein, f₁、f₂、f₃、、、、、、f_max-1、f_maxDividing the frequency boundary from left to right by f₁As the initial value, the numerator is not changed, the denominators are reduced by one, and when dividing the frequency boundary from right to left, f is used_maxAs an initial value, the numerator is unchanged, the denominators are added one by one, and the frequency boundary division is performed from left to rightThe division is stopped when an equal frequency boundary occurs during the division of the frequency boundary from right to left.

Further, in the frequency boundary acquisition module

Still further, the sample number selection module is further configured to:

when f is more than or equal to 45<f₁The method comprises the following steps: N-N_max；

When f is₁≤f<f₂The method comprises the following steps: N-N_max-1；

When f is₂≤f<f₃The method comprises the following steps: N-N_max-2；

When f is_max-1≤f<f_maxThe method comprises the following steps: N-N_min+1；

When f is_maxWhen f is not less than 55: N-N_min；

f is the current input frequency.

Still further, the electrical quantity calculation module is further configured to:

the electrical quantities are voltage and phase, and are calculated by formulaAnd acquiring an effective value of the voltage, wherein,i_kdata representing a kth sample point within a cycle;

by the formulaThe phase is acquired.

The invention has the advantages that: according to the invention, when the sampling frequencies are different, the sampling frequencies of software and hardware do not need to be changed, the requirements on the software and hardware are reduced, the sampling number required by each cycle under different frequencies is calculated according to the preset sampling frequency range, the Fourier coefficients corresponding to each sampling number are respectively prepared, when the frequencies are changed, the Fourier coefficients under the corresponding frequencies are respectively called for calculation, the calculation result is accurate, the calculation error is small, the algorithm is easy to realize, the reliability is high, and the accuracy of electric quantity collection can be improved.

Drawings

Fig. 1 is a flowchart of an algorithm for measuring electrical quantities at different frequencies according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all 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 invention.

Example 1

As shown in fig. 1, a method for measuring electrical quantities at different frequencies, the method comprising:

the method comprises the following steps: determining the sampling frequency f of software and hardware_s；

Step two: acquiring the range of the required sampling quantity under the preset sampling frequency range; the specific process is as follows: the preset sampling frequency range is 45Hz to 55Hz, and the range of the required sampling number N between 45Hz and 55Hz is as follows:

minimum number N_min＝(f_s/55) rounding down;

maximum number N_max＝(f_sAnd/45) rounding up.

Step three: acquiring Fourier coefficients corresponding to all the sampling quantities and storing the Fourier coefficients for later use; the specific process is as follows: by the formulaObtain the second corresponding to all the sampling numbersk real Fourier coefficients;

by the formulaAcquiring the kth imaginary Fourier coefficient corresponding to all the sampling numbers;

k is the number of the Fourier coefficient, the value range is from 1 to N, and N is the number of samples required in the preset sampling frequency range; when n is 2 or more, the number of harmonics is represented, and n is 1 or more, the fundamental wave is represented.

Step four: acquiring a frequency boundary corresponding to each sampling quantity according to the sampling frequency of the software and the hardware; the specific process is as follows: the preset sampling frequency range from 45Hz to 55Hz is divided into 45Hz and f from small to large₁、f₂、f₃、、、、、、f_max-1、f_max55Hz, wherein, f₁、f₂、f₃、、、、、、f_max-1、f_maxDividing the frequency boundary from left to right by f₁As the initial value, the numerator is not changed, the denominators are reduced by one, and when dividing the frequency boundary from right to left, f is used_maxAnd adding the denominators one by one to the initial value, keeping the numerators unchanged, and stopping dividing when an equal frequency boundary appears in the process of dividing the frequency boundary from left to right and dividing the frequency boundary from right to left. See table 1 for various frequency boundaries in this example.

TABLE 1 frequency boundary partitioning

E.g. N_min＝9，N_maxWhen the number is equal to 11,f₁、f₂、f₃、、、、、、f_max-1、f_maxdividing the frequency boundary from left to right to obtainAs an initial value, the numerator is unchanged and the denominators are reduced by one, i.e.Dividing the frequency boundary from right to left to obtainAs an initial value, the numerator is unchanged and the denominators are added one by one, i.e. The division is stopped when an equal frequency boundary occurs during the frequency boundary division from left to right and from right to left, from which it can be seen that,andthe phase of the two phases is equal to each other,andequal, so divide from left to right into f₂From right to left to f_maxThe division is stopped at that time, or divided from left to right to f₁From right to left to f_max-1The division is stopped at that time.

Also for example, N_min＝37，N_maxWhen equal to 44 (N)_minAnd N_maxFor random value example, in practical application, the value is according to N_minAnd N_maxThe calculation formula (c) performs the calculation value),f₁、f₂、f₃、、、、、、f_max-1、f_maxdividing the frequency boundary from left to right to obtainAs an initial value, the numerator is unchanged and the denominators are reduced by one, i.e. Dividing the frequency boundary from right to left to obtainAs an initial value, the numerator is unchanged and the denominators are added one by one, i.e. The division is stopped when an equal frequency boundary occurs during the frequency boundary division from left to right and from right to left, from which it can be seen that,andthe phase of the two phases is equal to each other,andequal, so divide from left to right into f₃From right to left to f_max-4The division is stopped at that time, or divided from left to right to f₄From right to left to f_max-3The partitioning is stopped at that time, and other data is equal, for example,andand in the same way, the description is omitted, and only one equal frequency division point needs to be found for division, and one of the division modes is adopted when a plurality of frequency division points exist.

Step five: selecting the required sampling number according to the input frequency; the specific process is as follows:

when f is more than or equal to 45<f₁The method comprises the following steps: N-N_max；

When f is₁≤f<f₂The method comprises the following steps: N-N_max-1；

When f is₂≤f<f₃The method comprises the following steps: N-N_max-2；

、、、、、、、

When f is_max-1≤f<f_maxThe method comprises the following steps: N-N_min+1；

When f is_maxWhen f is not less than 55: N-N_min；

f is the current input frequency.

Step six: real-time storage of current time advance 2 x N_maxData of a sampling point, N_maxRepresents the maximum number of samples;

step seven: and calling the corresponding Fourier coefficient according to the sampling number selected by the current input frequency, and simultaneously taking out sampling point data corresponding to the sampling number selected by the current input frequency to calculate the electrical quantity. The specific process is as follows:

the electrical quantities are voltage and phase, and are calculated by formulaAnd acquiring an effective value of the voltage, wherein,i_kdata representing a kth sample point within a cycle;

by the formulaThe phase is acquired.

Through the technical scheme, when the sampling frequencies are different, the sampling frequencies of software and hardware do not need to be changed, the requirements on the software and hardware are reduced, the sampling number required by each cycle under different frequencies is calculated according to the preset sampling frequency range, the Fourier coefficients corresponding to the sampling numbers are respectively prepared, when the frequencies are changed, the Fourier coefficients under the corresponding frequencies are respectively called for calculation, the calculation result is accurate, the calculation error is small, the algorithm is easy to realize, the reliability is high, and the accuracy of electric quantity collection can be improved.

Example 2

Based on embodiment 1 of the present invention, embodiment 2 of the present invention further provides a device for measuring electrical quantity at different frequencies, where the device includes:

a hardware sampling frequency acquisition module for determining the sampling frequency f of the hardware and the software_s；

The sampling number range acquisition module is used for acquiring the range of the required sampling number in a preset sampling frequency range;

the Fourier coefficient acquisition module is used for acquiring Fourier coefficients corresponding to all the sampling numbers and storing the Fourier coefficients for later use;

the frequency boundary acquisition module is used for acquiring a frequency boundary corresponding to each sampling quantity according to the sampling frequency of software and hardware;

the sampling quantity selection module is used for selecting the required sampling quantity according to the input frequency;

a storage module for storing the current forward push 2 × N in real time_maxData of a sampling point, N_maxRepresents the maximum number of samples;

and the electrical quantity calculation module is used for calling the corresponding Fourier coefficient according to the sampling quantity selected by the current input frequency and simultaneously taking out the sampling point data corresponding to the sampling quantity selected by the current input frequency to calculate the electrical quantity.

Specifically, the sampling number range obtaining module is further configured to: the preset sampling frequency range is 45Hz to 55Hz, and the range of the required sampling number N between 45Hz and 55Hz is as follows:

minimum number N_min＝(f_s/55) rounding down;

maximum number N_max＝(f_sAnd/45) rounding up.

Specifically, the fourier coefficient obtaining module is further configured to:

by the formulaAcquiring the kth real part Fourier coefficient corresponding to all the sampling numbers;

by the formulaAcquiring the kth imaginary Fourier coefficient corresponding to all the sampling numbers;

k is the number of the Fourier coefficient, the value range is from 1 to N, and N is the number of samples required in the preset sampling frequency range; when n is 2 or more, the number of harmonics is represented, and n is 1 or more, the fundamental wave is represented.

More specifically, the frequency boundary acquisition module is further configured to: the preset sampling frequency range from 45Hz to 55Hz is divided into 45Hz and f from small to large₁、f₂、f₃、、、、、、f_max-1、f_max55Hz, wherein, f₁、f₂、f₃、、、、、、f_max-1、f_maxDividing the frequency boundary from left to right by f₁As the initial value, the numerator is not changed, the denominators are reduced by one, and when dividing the frequency boundary from right to left, f is used_maxAnd adding the denominators one by one to the initial value, keeping the numerators unchanged, and stopping dividing when an equal frequency boundary appears in the process of dividing the frequency boundary from left to right and dividing the frequency boundary from right to left.

More specifically, the frequency boundary acquisition module

More specifically, the sample number selection module is further configured to:

when f is more than or equal to 45<f₁The method comprises the following steps: N-N_max；

When f is₁≤f<f₂The method comprises the following steps: N-N_max-1；

When f is₂≤f<f₃The method comprises the following steps: N-N_max-2；

When f is_max-1≤f<f_maxThe method comprises the following steps: N-N_min+1；

When f is_maxWhen f is not less than 55: N-N_min；

f is the current input frequency.

More specifically, the electrical quantity calculation module is further configured to:

the electrical quantities are voltage and phase, and are calculated by formulaAnd acquiring an effective value of the voltage, wherein,i_kdata representing a kth sample point within a cycle;

by the formulaThe phase is acquired.

The above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will 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 of the embodiments of the present invention.