Method and apparatus for determining the frequency of a power system

Abstract

The application provides a method and device for determining the frequency of a power system. The method comprises: obtaining a first fundamental signal and a first frequency according to the first fundamental signal, the first fundamental signal being generated by a power signal passing through a first band-pass filter, the amplitude-frequency characteristic of the passband of the first band-pass filter being able to change with the sampling frequency; obtaining a second fundamental signal and a second frequency according to the second fundamental signal, the second fundamental signal being generated by the power signal passing through a second band-pass filter, the amplitude-frequency characteristic of the passband of the second band-pass filter being fixed, the power signal reaching the first band-pass filter and the second band-pass filter at the same time; and determining the real-time frequency of the power system according to the sampling frequency, the first frequency and the second frequency. Thus, the real-time frequency of the power system can be quickly obtained when the frequency of the power system changes.

Description

Technical Field

[0001] The present invention relates to the field of power systems, and in particular to a method and device for determining the frequency of a power system. Background Art

[0002] The frequency of the power system is an important parameter for the safe and stable operation of the power system. It can reflect the power quality of the entire power system. That is, the frequency measurement of the power system is the basis of the power quality monitoring device. The stability and reliability of frequency measurement determines the reliability of other measured quantities.

[0003] The frequency of power systems changes dynamically. For example, when there is an imbalance or unstable power output in the power system, its frequency will change. Accurately and timely obtaining the real-time frequency of the power system has become an urgent problem that needs to be solved. Summary of the Invention

[0004] In view of this, the present invention proposes a method for determining the frequency of a power system, comprising: sampling a power signal of the power system according to a sampling frequency, and further comprising:

[0005] Acquire a first fundamental wave signal, and acquire a first frequency based on the first fundamental wave signal, wherein the first fundamental wave signal is generated by passing a power signal through a first bandpass filter, and the amplitude-frequency characteristic of the passband of the first bandpass filter can change with the change of the sampling frequency;

[0006] Obtaining a second fundamental wave signal and obtaining a second frequency based on the second fundamental wave signal, wherein the second fundamental wave signal is generated by passing the power signal through a second bandpass filter, the amplitude-frequency characteristic of the passband of the second bandpass filter is fixed, and the power signal reaches the first bandpass filter and the second bandpass filter at the same time;

[0007] The real-time frequency of the power system is determined according to the sampling frequency, the first frequency, and the second frequency.

[0008] In this way, the frequency of the same power signal is adjusted through two channels. The filtering characteristics of one channel change with the sampling frequency, and the cleanest fundamental signal can be obtained to determine the real-time frequency of the power system, which is equivalent to fine-tuning. The filtering characteristics of the other channel have little to do with the sampling frequency, and a fundamental signal with a fixed bandwidth can be obtained to determine the real-time frequency of the power system. The combination of these two bandpass filters can not only extract the largest fundamental component under the condition of stable power system, but also quickly obtain its real-time frequency when the frequency of the power system changes.

[0009] According to the method described above, optionally, determining the real-time frequency of the power system according to the sampling frequency, the first frequency, and the second frequency includes:

[0010] If the absolute value of the difference between the sampling frequency and the second frequency is less than or equal to a first threshold, and the difference between the first frequency and the second frequency is less than or equal to a second threshold, the first frequency is used as the real-time frequency of the power system; otherwise, the second frequency is used as the real-time frequency of the power system. This determination method can make the result more accurate.

[0011] According to the above method, optionally, after determining the real-time frequency of the power system based on the frequency of the signal, the first frequency, and the second frequency, the method further includes: updating the value of the sampling frequency to the real-time frequency, and returning to perform the operation of sampling the power signal of the power system at a sampling frequency. In this way, the sampling frequency is continuously updated so that the sampling frequency continuously approaches the real-time frequency of the power system, thereby enabling the real-time frequency of the power system to be accurately and timely obtained.

[0012] According to the method described above, optionally, obtaining a first frequency according to the first fundamental wave signal includes:

[0013] determining an attenuation degree of the first fundamental wave signal;

[0014] Determine whether the attenuation degree is greater than or equal to a third threshold value. If the judgment result is yes, use the first frequency determined last time as the final first frequency. If the judgment result is no, use the first fundamental wave signal as the target signal, process the target signal according to the zero-crossing method, and use the frequency obtained after processing as the first frequency.

[0015] According to the method described above, optionally, obtaining a second frequency according to the second fundamental wave signal includes: using the second fundamental wave signal as a target signal, processing the target signal according to a zero-crossing method, and using the frequency obtained after processing as the second frequency.

[0016] According to the method described above, optionally, processing the target signal according to the zero-crossing method includes:

[0017] Dividing the waveform of the target signal into a plurality of continuous first waveforms, where the starting point and the ending point of each first waveform are two adjacent zero points; determining first number groups, where each first number group includes at least one first waveform, and the absolute value of the difference in time length between the first waveforms in the same first number group is less than a fourth threshold;

[0018] Determining target number groups from the first number groups, wherein the number of first waveforms included in the target waveform is greater than or equal to a first preset threshold, and the first number groups other than the target number groups are used as reference number groups;

[0019] If the total number of first waveforms included in each target number group is greater than or equal to a second preset threshold value of the total number of all first waveforms, or if the number of reference number groups between any two target number groups is less than or equal to a third preset threshold value, the final frequency is determined according to the target number group as the frequency after processing the target signal.

[0020] In this way, the clustering principle is used to select useful half-cycles to calculate the frequency. It has a strong ability to suppress amplitude and phase changes, and can more effectively suppress overshoot or undershoot in the dynamic process, thereby more accurately determining the real-time frequency of the power system.

[0021] According to the method described above, optionally, determining a final frequency as the frequency after processing the target signal according to the target number group includes:

[0022] The final frequency=P / (2×the sum of the time lengths of the first waveforms in each target number group), where P is the number of all first waveforms in each target number group.

[0023] According to the method described above, optionally, processing the target signal according to the zero-crossing method includes:

[0024] Dividing the waveform of the target signal into a plurality of continuous second waveforms, wherein the starting point and the end point of each second waveform are two adjacent zero points;

[0025] Determine each second number group according to the time length corresponding to each second waveform, wherein the difference between the time lengths corresponding to the second waveforms included in each second number group is less than a fifth threshold;

[0026] After removing the M second number groups with the largest average values ​​of the corresponding time lengths and the N second number groups with the smallest average values ​​of the corresponding time lengths, a final frequency is determined based on the remaining second number groups as the frequency after processing the target signal, where M and N are positive integers.

[0027] In this way, the clustering principle is used to select useful half-cycles to calculate the frequency. It has a strong ability to suppress amplitude and phase changes, with less calculation, and most random interference can be well suppressed, thus being able to more accurately determine the real-time frequency of the power system.

[0028] According to the method described above, optionally, determining a final frequency as the frequency after processing the target signal based on the remaining second number group includes:

[0029] The final frequency=Q / (2×the sum of the time lengths of the second waveforms in each remaining target number group), where P.

[0030] According to the method described above, optionally, the first band-pass filter is a digital filter; the second band-pass filter includes multiple digital filters with the same amplitude-frequency characteristics, each digital filter corresponds to a band-pass, and before obtaining a second fundamental wave signal, it also includes: selecting a digital filter from the digital filters according to the sampling frequency, so that the second fundamental wave signal passes through the selected digital filter.

[0031] According to the method described above, optionally, the time length of the power signal is greater than or equal to 5 signal cycles, which can provide sufficient sampling points to calculate the real-time frequency of the power system.

[0032] A device for determining the frequency of a power system, comprising: a sampling unit for sampling a power signal of the power system according to a sampling frequency, characterized in that the device further comprises:

[0033] a first acquisition unit, configured to acquire a first fundamental wave signal and obtain a first frequency based on the first fundamental wave signal, wherein the first fundamental wave signal is generated by passing a power signal through a first bandpass filter, and the amplitude-frequency characteristic of the passband of the first bandpass filter can change with the change of the sampling frequency;

[0034] a second acquisition unit, configured to acquire a second fundamental wave signal and obtain a second frequency based on the second fundamental wave signal, wherein the second fundamental wave signal is generated after the power signal passes through a second band-pass filter, the amplitude-frequency characteristic of the passband of the second band-pass filter is fixed, and the power signal reaches the first band-pass filter and the second band-pass filter at the same time;

[0035] A determining unit is configured to determine a real-time frequency of the power system according to the sampling frequency, the first frequency, and the second frequency.

[0036] According to the above device, optionally, the determining unit is specifically configured to:

[0037] If the absolute value of the difference between the sampling frequency and the second frequency is less than or equal to a first threshold, and the difference between the first frequency and the second frequency is less than or equal to a second threshold, the first frequency is used as the real-time frequency of the power system; otherwise, the second frequency is used as the real-time frequency of the power system.

[0038] According to the apparatus as described above, optionally, an updating unit is further included, wherein the updating unit is configured to update the value of the sampling frequency to the real-time frequency and trigger the sampling unit.

[0039] According to the above device, optionally, the first acquiring unit includes:

[0040] a first determining subunit, configured to determine an attenuation degree of the first fundamental wave signal;

[0041] a first determining subunit, configured to determine whether the attenuation degree is greater than or equal to a third threshold, and if so, use the last determined first frequency as the final first frequency; and if not, trigger a first processing subunit;

[0042] The first processing subunit is configured to use the first fundamental wave signal as a target signal, process the target signal according to a zero-crossing method, and use a frequency obtained after the processing as the first frequency.

[0043] According to the apparatus as described above, optionally, the second acquiring unit is specifically configured to: use the second fundamental wave signal as a target signal, process the target signal according to a zero-crossing method, and use a frequency obtained after the processing as the second frequency.

[0044] According to the above device, optionally, when the target signal is processed using a zero-crossing method, the first processing subunit and the second acquiring unit are specifically configured to:

[0045] Dividing the waveform of the target signal into a plurality of continuous first waveforms, where the starting point and the ending point of each first waveform are two adjacent zero points; determining first number groups, where each first number group includes at least one first waveform, and the absolute value of the difference in time length between the first waveforms in the same first number group is less than a fourth threshold;

[0046] Determining target number groups from the first number groups, wherein the number of first waveforms included in the target waveform is greater than or equal to a first preset threshold, and the first number groups other than the target number groups are used as reference number groups;

[0047] If the total number of first waveforms included in each target number group is greater than or equal to a second preset threshold value of the total number of all first waveforms, or if the number of reference number groups between any two target number groups is less than or equal to a third preset threshold value, the final frequency is determined according to the target number group as the frequency after processing the target signal.

[0048] According to the above device, optionally, when the target signal is processed using a zero-crossing method, the first processing subunit and the second acquiring unit are specifically configured to:

[0049] Dividing the waveform of the target signal into a plurality of continuous second waveforms, wherein the starting point and the end point of each second waveform are two adjacent zero points;

[0050] Determine each second number group according to the time length corresponding to each second waveform, wherein the difference between the time lengths corresponding to the second waveforms included in each second number group is less than a fifth threshold;

[0051] After removing the M second number groups with the largest average values ​​of the corresponding time lengths and the N second number groups with the smallest average values ​​of the corresponding time lengths, a final frequency is determined based on the remaining second number groups as the frequency after processing the target signal, where M and N are positive integers.

[0052] According to the device as described above, optionally, the first bandpass filter is a digital filter;

[0053] The second bandpass filter includes a plurality of digital filters with the same amplitude-frequency characteristics, and each digital filter corresponds to a bandpass.

[0054] The present invention also provides a device for determining the frequency of a power system, comprising:

[0055] at least one memory for storing instructions;

[0056] At least one processor is configured to execute the method for determining the frequency of a power system according to any one of the above items according to instructions stored in the memory.

[0057] The present invention also provides a readable storage medium, wherein the readable storage medium stores machine-readable instructions. When the machine-readable instructions are executed by a machine, the machine executes the method for determining the frequency of the power system according to any one of the above items. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, so that those skilled in the art will understand the above and other features and advantages of the present invention more clearly. In the accompanying drawings:

[0059] Figure 1 FIG. 4 is a flow chart of a method for determining the frequency of a power system according to an embodiment of the present invention.

[0060] Figure 2A FIG. 4 is a flow chart of processing a target signal using a zero-crossing method according to another embodiment of the present invention.

[0061] Figure 2B Schematic diagram for classifying the first cycle of the target signal

[0062] Figure 3FIG. 4 is a flow chart of processing a target signal using a zero-crossing method according to another embodiment of the present invention.

[0063] Figures 4A to 4C FIG. 1 is a schematic diagram of errors in the method for determining the frequency of a power system according to the present invention.

[0064] Figure 5A FIG. 1 is a schematic structural diagram of an apparatus for determining the frequency of a power system according to an embodiment of the present invention.

[0065] Figure 5B FIG. 4 is a schematic structural diagram of an apparatus for determining the frequency of a power system according to another embodiment of the present invention.

[0066] Figure 6 FIG. 1 is a schematic structural diagram of an apparatus for determining the frequency of a power system according to another embodiment of the present invention. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail with reference to the following examples.

[0068] Example 1

[0069] This embodiment provides a method for determining the frequency of a power system. The method is performed by a device for determining the frequency of a power system, which can be integrated into a power quality monitoring device.

[0070] like Figure 1 FIG. 1 is a flow chart of a method for determining the frequency of a power system according to this embodiment. The method includes:

[0071] Step 100: Sampling the power signal of the power system according to a sampling frequency.

[0072] For example, the initial sampling frequency can be set according to the initial frequency of the power system, for example, set to be consistent with the initial frequency. If the rated frequency of the power system is 50 Hz, the sampling frequency of this step can be set to 50 Hz. Frequency is used to represent the sampling speed or sampling rate, that is, the number of samples extracted from the power signal per second and composed of discrete signals. Optionally, the power signal is a signal stream. The time window corresponding to the method for determining the frequency of the power system in this embodiment is greater than or equal to 5 signal periods of the power signal, that is, at least the sampling process includes at least 5 cycles.

[0073] After step 100 and before step 101, operations such as decimation and anti-aliasing filtering may be performed to perform preliminary filtering. Specific operations such as decimation and anti-aliasing filtering on the power signal belong to the prior art and will not be described in detail here.

[0074] Step 101: obtain a first fundamental wave signal and obtain a first frequency based on the first fundamental wave signal. The first fundamental wave signal is generated by a power signal passing through a first bandpass filter. The passband of the first bandpass filter can change with the change of the sampling frequency.

[0075] The power signal, for example, originates from a power system busbar and can be obtained directly or through secondary-side equipment, without limitation. The power signal, after passing through the first bandpass filter, is called the first fundamental wave signal. The fundamental wave is the sinusoidal component of a periodic oscillation that has the same longest period as the oscillation.

[0076] The first bandpass filter here can be hardware or software that can realize the bandpass filtering function, specifically a digital filter. The amplitude-frequency characteristics of the passband of the first bandpass filter can change with the change of the sampling frequency. How to realize the first bandpass filter belongs to the existing technology and will not be repeated here. For example, if the sampling frequency is 47Hz, then the passband of the first bandpass filter may be 45-50Hz. The passband of the filter here refers to the frequency range of the signal allowed to pass through the filter, that is, the frequency band that the signal can pass through. The function of the first bandpass filter is to obtain the fundamental signal of the power signal in the largest amount. Among them, the amplitude-frequency characteristic is the relationship between the amplitude ratio and the frequency.

[0077] The first frequency obtained from the first fundamental wave signal can be selected based on actual needs. For example, the frequency of the first fundamental wave signal can be directly used as the first frequency, or the frequency of the first fundamental wave signal can be processed accordingly to use it as the first frequency, or the first frequency can be determined based on the attenuation degree of the first fundamental wave signal. For example, if the attenuation degree is greater than or equal to a third threshold, the first frequency determined previously is used as the first frequency in step 101. If the attenuation degree is less than the third threshold, the first fundamental wave signal can be processed using a zero-crossing method to obtain the first frequency. The third threshold here can be determined based on actual needs, for example, 15-25 dB.

[0078] Step 102: Obtain a second fundamental wave signal and obtain a second frequency based on the second fundamental wave signal. The second fundamental wave signal is generated after the power signal passes through a second band-pass filter. The passband of the second band-pass filter is fixed, and the power signal reaches the first band-pass filter and the second band-pass filter at the same time.

[0079] After passing through the second bandpass filter, the power signal is called the second fundamental wave signal. That is, for the same power signal, it reaches the first and second bandpass filters simultaneously through two paths. After passing through the first bandpass filter, the power signal is called the first fundamental wave signal, and after passing through the second bandpass filter, the power signal is called the second fundamental wave signal.

[0080] The second bandpass filter here can be software capable of implementing bandpass filtering functions, specifically through a combination of multiple digital filters. The difference between the second bandpass filter and the first bandpass filter is that its passband is fixed, meaning that regardless of the frequency of the signal passing through, its passband remains fixed. The specific implementation of this second bandpass filter is as follows: the second bandpass filter includes multiple digital filters, each corresponding to a bandpass. Once the sampling frequency is determined, the corresponding digital filter is determined based on the sampling frequency. The characteristics of each digital filter remain essentially consistent, ensuring that the amplitude-frequency characteristics of the filter remain approximately consistent across the entire measurement range. For power systems, although their frequency changes in real time, the difference is minimal, meaning that it varies within a range near the initial frequency of the power system, with a maximum frequency change rate of no more than 5 Hz / s. Typically, frequency changes are very slow. Therefore, an appropriate digital filter can be selected for the second bandpass filter based on the power system sampling.

[0081] Specifically, for example, if the sampling frequency is 47 Hz, the second bandpass filter includes three digital filters with passbands of 30 Hz-35 Hz, 35 Hz-40 Hz, and 40 Hz-50 Hz, then when the sampling frequency is identified as 47 Hz, the digital filter with a passband of 40 Hz-50 Hz is selected.

[0082] The first frequency can be obtained according to the second fundamental wave signal according to actual needs. For example, the frequency of the second fundamental wave signal is directly used as the second frequency, or the frequency of the second fundamental wave signal is processed accordingly and used as the second frequency, for example, the second frequency is obtained by processing the second fundamental wave signal through the zero-crossing method.

[0083] Step 103: Determine the real-time frequency of the power system according to the sampling frequency, the first frequency, and the second frequency.

[0084] For example, if the absolute value of the difference between the sampling frequency and the second frequency is less than or equal to a first threshold, and the difference between the first and second frequencies is less than or equal to a second threshold, the first frequency is used as the real-time frequency of the power system; otherwise, the second frequency is used as the real-time frequency of the power system. Because the second frequency is generated based on the power signal after passing through the second bandpass filter, the amplitude-frequency characteristics of the second bandpass filter's passband are minimally affected by the sampling frequency. Therefore, the second frequency is close to the real-time frequency of the power signal. If the difference between the sampling frequency and the second frequency is large, it indicates that the sampling frequency differs significantly from the real-time frequency of the power system, and the second frequency should be used. If the difference between the sampling frequency and the second frequency is small, it indicates that the sampling frequency and the second frequency are close, and the first frequency can be used as the real-time frequency. Furthermore, the difference between the second and first frequencies is used to determine whether to ultimately use the first frequency. This is because if the difference between the second and first frequencies is large, it indicates that the real-time frequency of the power system is fluctuating, and the second frequency should be used. If the difference between the second and first frequencies is small, it indicates that the real-time frequency of the power system is relatively stable, and the first frequency can be further determined as the real-time frequency of the power system. The first threshold and the second threshold here can be set according to actual needs. For example, the first threshold is 0.01 Hz-0.5 Hz, and the second threshold is 2 Hz-5 Hz.

[0085] Optionally, after step 103, the method further includes: updating the sampling frequency to the real-time frequency, and returning to step 100. In this way, the sampling frequency is continuously updated so that the sampling frequency continuously approaches the real-time frequency of the power system, thereby accurately and timely acquiring the real-time frequency of the power system.

[0086] In this embodiment, the frequency of the same power signal is adjusted through two channels, wherein the filtering characteristics of one channel change with the sampling frequency, and the cleanest fundamental signal can be obtained to determine the real-time frequency of the power system, which is equivalent to fine-tuning; the filtering characteristics of the other channel have little to do with the sampling frequency, and a fundamental signal with a fixed bandwidth can be obtained to determine the real-time frequency of the power system. The combination of these two band-pass filters can not only extract the largest fundamental component under the condition of stable power system, but also quickly obtain its real-time frequency when the frequency of the power system changes.

[0087] Example 2

[0088] This embodiment further supplements the method for determining the frequency of the power system in Example 1. This embodiment primarily supplements the zero-crossing method mentioned in Example 1. When calculating the corresponding frequency from the fundamental wave signal using the zero-crossing method, the specific method is the same, differing only in the objects processed. Therefore, in this embodiment, the first fundamental wave signal and the second fundamental wave signal are collectively referred to as target signals.

[0089] like Figure 2A FIG. 1 is a flow chart showing a process of processing a target signal using a zero-crossing method according to this embodiment. The method includes:

[0090] Step 201 : dividing the waveform of the target signal into a plurality of continuous first waveforms, wherein the starting point and the ending point of each first waveform are two adjacent zero points.

[0091] For example, if the waveform of the target signal is a sine wave, the waveform between two adjacent zero points is taken as the first waveform. It can be regarded as half a cycle of the target signal as a first waveform. Figure 2B The A1 row shown shows n first waveforms, where T(i) represents the i-th first waveform.

[0092] Step 202 : determining first number groups, each of which includes at least one first waveform, and wherein the absolute value of the time length difference between the first waveforms in the same first number group is smaller than a fourth threshold.

[0093] For example, the first waveforms can be arranged sequentially according to their time lengths. The time length of each first waveform is the difference between the time corresponding to its end position and the time corresponding to its start position. First waveforms with similar time lengths are then grouped together. The fourth threshold here can be set according to actual needs, for example, between 0.001 Hz and 0.1 Hz.

[0094] like Figure 2B As shown, the first waveforms are sorted in order according to their time lengths, see row B1, starting from ST(1) to ST(n). For first waveforms with smaller time length differences, they are divided into a first number group. Among them, ST(j) represents the jth first waveform. Figure 2B It can be seen from FIG that m first number groups are formed, and the first waveforms in the same first number group are adjacent to each other in sequence, and Gm represents the mth first number group.

[0095] Step 203: determining target number groups from the first number groups, wherein the number of first waveforms included in the target waveform is greater than or equal to a first preset threshold, and the first number groups other than the target number groups are used as reference number groups.

[0096] The number of first waveforms in each target waveform that is greater than or equal to a first preset threshold value will be regarded as a target number group. The first preset threshold value can be 3-5, for example Figure 2B As shown, the third first number group will be regarded as the target number group.

[0097] In step 204, if the total number of first waveforms included in each target number group is greater than or equal to a second preset threshold value of the total number of all first waveforms, or if the number of reference number groups between any two target number groups is less than or equal to a third preset threshold value, a final frequency is determined based on the target number group as the frequency after processing the target signal. The second and third preset threshold values ​​can be set as needed, for example, 60% to 80%, and the third preset threshold value can be set, for example, 2 to 4.

[0098] The final frequency = P / (2×the sum of the time lengths of the first waveforms in each target number group), where P is the number of all first waveforms in each target number group.

[0099] The zero-crossing method of this embodiment utilizes the clustering principle to select useful half-cycles for frequency calculation. This method strongly suppresses amplitude and phase variations, effectively suppressing overshoot and undershoot during dynamic processes, and thus more accurately determines the real-time frequency of the power system. Signals acquired at mixed sampling frequencies can also be processed (e.g., discarded) in this method, eliminating distorted waveforms.

[0100] Example 3

[0101] This embodiment further supplements the method for determining the frequency of the power system in Example 1. This embodiment primarily supplements the zero-crossing method mentioned in Example 1. When calculating the corresponding frequency from the fundamental wave signal using the zero-crossing method, the specific method is the same, differing only in the objects processed. Therefore, in this embodiment, the first fundamental wave signal and the second fundamental wave signal are collectively referred to as target signals.

[0102] like Figure 3 FIG. 1 is a flow chart showing a process of processing a target signal using a zero-crossing method according to this embodiment. The method includes:

[0103] Step 301 : dividing the waveform of the target signal into a plurality of continuous second waveforms, wherein the starting point and the ending point of each second waveform are two adjacent zero points.

[0104] For example, if the waveform of the target signal is a sine wave, the waveform between two adjacent zero points is used as the second waveform.

[0105] Step 302 : determining each second number group according to the time length corresponding to each second waveform, wherein the difference between the time lengths corresponding to the second waveforms included in each second number group is less than a fifth threshold.

[0106] For example, the second waveforms can be sorted in order according to their time length. The time length of each second waveform is the difference between the time corresponding to its end position and the time corresponding to its start position. The fifth threshold can be set according to actual needs, for example, 0.1 Hz.

[0107] In step 303, after removing the M second number groups with the largest average values ​​of the corresponding time lengths and the N second number groups with the smallest average values ​​of the corresponding time lengths, a final frequency is determined based on the remaining second number groups as the frequency after processing the target signal, where M and N are positive integers.

[0108] In this embodiment, the average value of the time lengths corresponding to the second number groups can be calculated first, and then sorted from largest to smallest based on the average value. The first M second number groups and the last N second number groups are removed, and the second frequency is determined based on the remaining second number groups. Of course, a traversal method can also be used to find the M second number groups with the largest average values ​​and the N second number groups with the smallest average values, which is not limited here.

[0109] Optionally, the second frequency here=Q / (2×the sum of the time lengths of the second waveforms in the remaining second number groups), where Q is the number of all second waveforms in the remaining second number groups.

[0110] The zero-crossing method in this embodiment utilizes the clustering principle to select useful half-cycles for frequency calculation. This method strongly suppresses amplitude and phase variations, requires minimal computation, and effectively suppresses most random interference, enabling more accurate determination of the power system's real-time frequency. Furthermore, signals acquired at mixed sampling frequencies can be processed (e.g., discarded) in this optimized zero-crossing method, eliminating distorted waveforms.

[0111] Example 4

[0112] This embodiment provides some experiments to illustrate the method for determining the frequency of a power system according to the above embodiment. In this embodiment, 10% subharmonics and 10% interharmonics are injected into the power signal. The subharmonic frequency is 0.5 times the real-time frequency of the power signal, and the interharmonic frequency is 1.5 times the real-time frequency of the power signal.

[0113] Experiment 1: Frequency Jump Down

[0114] In this experiment, a simulation signal is used to simulate the power signal of the power system. The initial frequency of the power signal is 50Hz, and then the frequency of the power signal is linearly reduced from 50Hz to 42.5Hz with a step size of 0.01Hz. The initial phase changes from -π to π with a step size of π / 200, and the duration of each frequency jump is 0.8s. Figure 4AAs shown, it shows the results of Experiment 1, where the horizontal axis is the real-time frequency of the simulation signal, and the vertical axis is the absolute value of the error between the frequency obtained by the method for determining the frequency of the power system according to the aforementioned embodiment and the real-time frequency of the simulation signal. It can be seen that the error is very small, not exceeding 0.0168Hz.

[0115] Experiment 2: Frequency Jump Up

[0116] In this experiment, a simulation signal is used to simulate the power signal of the power system. The initial frequency of the power signal is 50Hz, and then the frequency of the power signal is linearly increased from 50Hz to 57.5Hz with a step size of 0.01Hz. The initial phase changes from -π to π with a step size of π / 200, and the duration of each frequency jump is 0.8s. Figure 4B As shown, it shows the results of Experiment 2, where the horizontal axis is the real-time frequency of the simulation signal, and the vertical axis is the absolute value of the error between the frequency obtained by the method for determining the frequency of the power system according to the aforementioned embodiment and the real-time frequency of the simulation signal. It can be seen that the error is very small, not exceeding 0.0168Hz.

[0117] Experiment 3: Voltage dip or voltage swell

[0118] In this experiment, a simulation signal is used to simulate the power signal of the power system. The initial frequency of the power signal is 50Hz, the stable amplitude is always 1, and the voltage of the power signal changes linearly from 10% to 90% of the stable amplitude with a step size of 1%. For each change in voltage, the phase jump changes from -π to π with a step size of π / 100. Figure 4C As shown, the horizontal axis corresponds to the change in the voltage value of the simulation signal, and the vertical axis is the absolute value of the error between the frequency obtained by the method for determining the frequency of the power system according to the aforementioned embodiment and the real-time frequency of the simulation signal. It can be seen that the error is very small and does not exceed 0.012Hz.

[0119] It can be seen that the real-time frequency of the power system determined by the method of the above embodiment is highly accurate.

[0120] Example 5

[0121] This embodiment provides a device for determining the frequency of a power system, which is used to perform the method for determining the frequency of a power system in Embodiment 1. The device can be integrated into a power quality monitoring device or provided separately, without limitation.

[0122] like Figure 5A FIG2 is a schematic diagram of the structure of the apparatus for determining the frequency of a power system according to this embodiment. The apparatus for determining the frequency of a power system includes a sampling unit 501 , a first obtaining unit 502 , a second obtaining unit 503 and a determining unit 504 .

[0123] Among them, the sampling unit 501 is used to sample the power signal of the power system according to a sampling frequency; the first acquisition unit 502 is used to obtain a first fundamental wave signal and obtain a first frequency based on the first fundamental wave signal. The first fundamental wave signal is generated after an power signal passes through a first band-pass filter, and the amplitude-frequency characteristics of the passband of the first band-pass filter can change with the change of the sampling frequency; the second acquisition unit 503 is used to obtain a second fundamental wave signal and obtain a second frequency based on the second fundamental wave signal. The second fundamental wave signal is generated after the power signal passes through a second band-pass filter. The amplitude-frequency characteristics of the passband of the second band-pass filter are fixed, and the time when the power signal reaches the first band-pass filter and the second band-pass filter is the same; the determination unit 504 is used to determine the real-time frequency of the power system based on the sampling frequency, the first frequency and the second frequency.

[0124] Optionally, the determination unit 504 is specifically used to: if the absolute value of the difference between the sampling frequency and the second frequency is less than or equal to a first threshold, and the difference between the first frequency and the second frequency is less than or equal to a second threshold, then use the first frequency as the real-time frequency of the power system; otherwise, use the second frequency as the real-time frequency of the power system.

[0125] Alternatively, as Figure 5B As shown, the apparatus for determining the frequency of a power system in this embodiment further includes an updating unit. The updating unit 505 is configured to update the value of the sampling frequency to a real-time frequency and trigger the sampling unit 501 .

[0126] Optionally, the first bandpass filter is a digital filter; the second bandpass filter includes multiple digital filters with identical amplitude-frequency characteristics, each corresponding to a bandpass. The specific method for selecting the digital filters in the second bandpass filter to provide a fixed bandpass is consistent with that described in the previous embodiment and will not be further elaborated here.

[0127] The working methods of the various units in this embodiment are the same as those in the previous embodiment and will not be described again here.

[0128] In this embodiment, the frequency of the same power signal is adjusted through two channels, wherein the filtering characteristics of one channel change with the sampling frequency, and the cleanest fundamental signal can be obtained to determine the real-time frequency of the power system, which is equivalent to fine-tuning; the filtering characteristics of the other channel have little to do with the sampling frequency, and a fundamental signal with a fixed bandwidth can be obtained to determine the real-time frequency of the power system. The combination of these two band-pass filters can not only extract the largest fundamental component under the condition of stable power system, but also quickly obtain its real-time frequency when the frequency of the power system changes.

[0129] Example 6

[0130] This embodiment further supplements the device for determining the frequency of the power system in the previous embodiment.

[0131] like Figure 6 As shown, the first acquisition unit 502 of this embodiment includes a first determination subunit 5021, a first judgment subunit 5022, and a first processing subunit 5023. The first determination subunit 5021 is configured to determine the attenuation degree of the first fundamental wave signal; the first judgment subunit 5022 is configured to determine whether the attenuation degree is greater than or equal to a third threshold; if the judgment result is yes, the previously determined first frequency is used as the final first frequency; if the judgment result is no, a first processing subunit 5023 is triggered; the first processing subunit 5023 is configured to use the first fundamental wave signal as the target signal, process the target signal according to the zero-crossing method, and use the frequency obtained after processing as the first frequency.

[0132] The second acquiring unit 503 is specifically configured to: use the second fundamental wave signal as the target signal, process the target signal according to the zero-crossing method, and use the frequency obtained after the processing as the second frequency.

[0133] Optionally, when the zero-crossing method is used to process the target signal, the first processing sub-unit 5023 and the second acquisition unit 503 are specifically used to: divide the waveform of the target signal into multiple continuous first waveforms, the starting point and end point of each first waveform being two adjacent zero points; determine each first number group, each first number group including at least one first waveform, and the absolute value of the difference in time length between each first waveform in the same first number group is less than a fourth threshold; determine each target number group from each first number group, the number of first waveforms included in the target waveform is greater than or equal to a first preset threshold value, and the first number group other than the target number group is used as a reference number group; if the total number of first waveforms included in each target number group is greater than or equal to the second preset threshold value of the total number of all first waveforms, or if the number of reference number groups between any two target number groups is less than or equal to the third preset threshold value, then determine the final frequency according to the target number group as the frequency after processing the target signal.

[0134] Alternatively, when the target signal is processed using the zero-crossing method, the first processing sub-unit 5023 and the second acquisition unit 503 are specifically used to: divide the waveform of the target signal into multiple continuous second waveforms, the starting point and end point of each second waveform being two adjacent zero points; determine each second number group according to the time length corresponding to each second waveform, and the difference between the time lengths corresponding to the second waveforms included in each second number group is less than a fifth threshold; after removing the M second number groups with the largest average value of the corresponding time lengths and the N second number groups with the smallest average value of the corresponding time lengths, determine the final frequency according to the remaining second number groups as the frequency after processing the target signal, where M and N are positive integers.

[0135] When the zero-crossing method is used to process the signal, the time length of the signal is greater than or equal to 5 signal periods, that is, it includes at least 5 cycles.

[0136] The working methods of the various units in this embodiment are the same as those in the previous embodiment and will not be described again here.

[0137] According to the zero-crossing method of this embodiment, the clustering principle is used to select useful half cycles to calculate the frequency, which can more accurately determine the real-time frequency of the power system.

[0138] The present invention also provides an apparatus for determining the frequency of a power system, comprising at least one memory and at least one processor. The memory is configured to store instructions, and the processor is configured to execute the method for determining the frequency of a power system described in any of the aforementioned embodiments according to the instructions stored in the memory.

[0139] An embodiment of the present invention further provides a readable storage medium having machine-readable instructions stored therein, wherein when the machine-readable instructions are executed by a machine, the machine executes the method for determining the frequency of a power system described in any of the aforementioned embodiments.

[0140] The readable medium stores machine-readable instructions that, when executed by a processor, cause the processor to perform any of the aforementioned methods. Specifically, a system or device equipped with a readable storage medium may be provided, wherein the readable storage medium stores software program code that implements the functions of any of the aforementioned embodiments, and causes a computer or processor of the system or device to read and execute the machine-readable instructions stored in the readable storage medium.

[0141] In this case, the program code itself read from the machine-readable medium can realize the function of any one of the above embodiments, and thus the machine-readable code and the machine-readable storage medium storing the machine-readable code constitute part of the present invention.

[0142] Examples of readable storage media include floppy disks, hard disks, magneto-optical disks, optical disks (e.g., CD-ROMs, CD-Rs, CD-RWs, DVD-ROMs, DVD-RAMs, DVD-RWs, DVD+RWs), magnetic tapes, non-volatile memory cards, and ROMs. Alternatively, the program code may be downloaded from a server computer or a cloud via a communication network.

[0143] Those skilled in the art will appreciate that the various embodiments disclosed above may be modified and altered in various ways without departing from the essence of the invention. Therefore, the scope of protection of the present invention shall be defined by the appended claims.

[0144] It should be noted that not all steps and units in the above processes and system structure diagrams are required, and certain steps or units can be omitted according to actual needs. The execution order of each step is not fixed and can be adjusted as needed. The device structure described in the above embodiments can be a physical structure or a logical structure, that is, some units may be implemented by the same physical entity, or some units may be implemented by multiple physical entities, or may be implemented by certain components in multiple independent devices.

[0145] In the above embodiments, the hardware unit can be realized by mechanical means or electrical means. For example, a hardware unit or a processor can include a permanent dedicated circuit or logic (such as a special processor, FPGA or ASIC) to complete the corresponding operation. The hardware unit or the processor can also include programmable logic or circuit (such as a general-purpose processor or other programmable processors), which can be temporarily set up by software to complete the corresponding operation. Concrete implementation (mechanical means or dedicated permanent circuit or temporarily set circuit) can be determined based on the consideration in cost and time.

[0146] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Methods for determining the frequency of the power system, including: The power signal of the power system is sampled according to a sampling frequency, wherein the method further comprises: Acquire a first fundamental wave signal, and acquire a first frequency based on the first fundamental wave signal, wherein the first fundamental wave signal is generated by passing a power signal through a first bandpass filter, and the amplitude-frequency characteristic of the passband of the first bandpass filter can change with the change of the sampling frequency; Obtaining a second fundamental wave signal and obtaining a second frequency based on the second fundamental wave signal, wherein the second fundamental wave signal is generated by passing the power signal through a second bandpass filter, the amplitude-frequency characteristic of the passband of the second bandpass filter is fixed, and the power signal reaches the first bandpass filter and the second bandpass filter at the same time; Determining the real-time frequency of the power system according to the sampling frequency, the first frequency, and the second frequency; Acquiring a first frequency according to the first fundamental wave signal includes: determining an attenuation degree of the first fundamental wave signal; determining whether the attenuation degree is greater than or equal to a third threshold; if so, using the previously determined first frequency as the final first frequency; and if not, using the first fundamental wave signal as the target signal, processing the target signal according to a zero-crossing method, and using the frequency obtained after the processing as the first frequency; Processing the target signal according to the zero-crossing method includes: Dividing the waveform of the target signal into a plurality of continuous first waveforms, where the starting point and the ending point of each first waveform are two adjacent zero points; determining first number groups, where each first number group includes at least one first waveform, and the absolute value of the difference in time length between the first waveforms in the same first number group is less than a fourth threshold; Determining target number groups from the first number groups, wherein the number of first waveforms included in the target signal is greater than or equal to a first preset threshold, and the first number groups other than the target number groups are used as reference number groups; If the total number of first waveforms included in each target number group is greater than or equal to a second preset threshold value of the total number of all first waveforms, or if the number of reference number groups between any two target number groups is less than or equal to a third preset threshold value, determining a final frequency based on the target number group as the frequency after processing the target signal; or Processing the target signal according to the zero-crossing method includes: Dividing the waveform of the target signal into a plurality of continuous second waveforms, wherein the starting point and the end point of each second waveform are two adjacent zero points; Determine each second number group according to the time length corresponding to each second waveform, wherein the difference between the time lengths corresponding to the second waveforms included in each second number group is less than a fifth threshold; After removing the M second number groups with the largest average values ​​of the corresponding time lengths and the N second number groups with the smallest average values ​​of the corresponding time lengths, a final frequency is determined based on the remaining second number groups as the frequency after processing the target signal, where M and N are positive integers.

2. The method according to claim 1, characterized in that Determining the real-time frequency of the power system according to the sampling frequency, the first frequency, and the second frequency includes: If the absolute value of the difference between the sampling frequency and the second frequency is less than or equal to a first threshold, and the difference between the first frequency and the second frequency is less than or equal to a second threshold, the first frequency is used as the real-time frequency of the power system; otherwise, the second frequency is used as the real-time frequency of the power system.

3. The method according to claim 2, characterized in that After determining the real-time frequency of the power system according to the frequency of the signal, the first frequency, and the second frequency, the method further includes: The value of the sampling frequency is updated to the real-time frequency, and the operation of sampling the power signal of the power system according to a sampling frequency is returned to be executed.

4. The method according to claim 1, characterized in that Acquiring a second frequency according to the second fundamental wave signal includes: using the second fundamental wave signal as a target signal, processing the target signal according to a zero-crossing method, and using a frequency obtained after the processing as the second frequency.

5. The method according to claim 1, wherein Determining a final frequency as the frequency after processing the target signal according to the target number group includes: The final frequency=P / (2×the sum of the time lengths of the first waveforms in each target number group), where P is the number of all first waveforms in each target number group.

6. The method according to claim 1, characterized in that Determining a final frequency as the frequency after processing the target signal according to the remaining second number group includes: The final frequency=Q / (2×the sum of the time lengths of the second waveforms in the remaining target number groups), where Q is the number of all second waveforms in the remaining second number groups.

7. The method according to claim 1, characterized in that The first bandpass filter is a digital filter; The second bandpass filter includes multiple digital filters with the same amplitude-frequency characteristics, each digital filter corresponds to a bandpass, and before obtaining a second fundamental wave signal, it also includes: selecting a digital filter from the digital filters according to the sampling frequency, so that the second fundamental wave signal passes through the selected digital filter.

8. The method according to claim 1, characterized in that The time length of the power signal is greater than or equal to 5 signal cycles.

9. Devices for determining the frequency of an electric power system, including: A sampling unit, configured to sample the power signal of the power system at a sampling frequency, wherein the device further comprises: a first acquisition unit, configured to acquire a first fundamental wave signal and obtain a first frequency based on the first fundamental wave signal, wherein the first fundamental wave signal is generated by passing a power signal through a first bandpass filter, and the amplitude-frequency characteristic of the passband of the first bandpass filter can change with the change of the sampling frequency; a second acquisition unit, configured to acquire a second fundamental wave signal and obtain a second frequency based on the second fundamental wave signal, wherein the second fundamental wave signal is generated after the power signal passes through a second band-pass filter, the amplitude-frequency characteristic of the passband of the second band-pass filter is fixed, and the power signal reaches the first band-pass filter and the second band-pass filter at the same time; a determining unit, configured to determine a real-time frequency of the power system according to the sampling frequency, the first frequency, and the second frequency; The first acquiring unit includes: a first determining subunit, configured to determine an attenuation degree of the first fundamental wave signal; a first determining subunit, configured to determine whether the attenuation degree is greater than or equal to a third threshold, and if so, use the last determined first frequency as the final first frequency; and if not, trigger a first processing subunit; The first processing subunit is configured to use the first fundamental wave signal as a target signal, process the target signal according to a zero-crossing method, and use a frequency obtained after the processing as the first frequency; When the zero-crossing method is used to process the target signal, the first processing subunit and the second acquiring unit are specifically configured to: Dividing the waveform of the target signal into a plurality of continuous first waveforms, where the starting point and the ending point of each first waveform are two adjacent zero points; determining first number groups, where each first number group includes at least one first waveform, and the absolute value of the difference in time length between the first waveforms in the same first number group is less than a fourth threshold; Determining target number groups from the first number groups, wherein the number of first waveforms included in the target signal is greater than or equal to a first preset threshold, and the first number groups other than the target number groups are used as reference number groups; If the total number of first waveforms included in each target number group is greater than or equal to a second preset threshold value of the total number of all first waveforms, or if the number of reference number groups between any two target number groups is less than or equal to a third preset threshold value, determining a final frequency based on the target number group as the frequency after processing the target signal; or When the zero-crossing method is used to process the target signal, the first processing subunit and the second acquiring unit are specifically configured to: Dividing the waveform of the target signal into a plurality of continuous second waveforms, wherein the starting point and the end point of each second waveform are two adjacent zero points; Determine each second number group according to the time length corresponding to each second waveform, wherein the difference between the time lengths corresponding to the second waveforms included in each second number group is less than a fifth threshold; After removing the M second number groups with the largest average values ​​of the corresponding time lengths and the N second number groups with the smallest average values ​​of the corresponding time lengths, a final frequency is determined based on the remaining second number groups as the frequency after processing the target signal, where M and N are positive integers.

10. The device according to claim 9, characterized in that The determining unit is specifically configured to: If the absolute value of the difference between the sampling frequency and the second frequency is less than or equal to a first threshold, and the difference between the first frequency and the second frequency is less than or equal to a second threshold, the first frequency is used as the real-time frequency of the power system; otherwise, the second frequency is used as the real-time frequency of the power system.

11. The device according to claim 10, characterized in that The system further comprises an updating unit, which is used to update the value of the sampling frequency to the real-time frequency and trigger the sampling unit.

12. The device according to claim 9, characterized in that The second acquisition unit is specifically configured to: use the second fundamental wave signal as a target signal, process the target signal according to a zero-crossing method, and use a frequency obtained after the processing as the second frequency.

13. The device according to claim 9, characterized in that When the first processing subunit and the second acquiring unit determine a final frequency as the frequency after processing the target signal based on the target number group, the first processing subunit and the second acquiring unit are specifically configured to: the final frequency = P / (2×the sum of the time lengths of the first waveforms in each of the target number groups), where P is the number of all first waveforms in each of the target number groups; or When the first processing subunit and the second acquisition unit determine the final frequency as the frequency after processing the target signal based on the remaining second number groups, they are specifically configured to: the final frequency = Q / (2×the sum of the time lengths of the second waveforms in each remaining target number group), where Q is the number of all second waveforms in the remaining second number groups.

14. The device according to claim 9, characterized in that The first bandpass filter is a digital filter; The second bandpass filter includes a plurality of digital filters with the same amplitude-frequency characteristics, and each digital filter corresponds to a bandpass.

15. Device for determining the frequency of an electric power system, characterized in that include: at least one memory for storing instructions; At least one processor is configured to execute the method for determining the frequency of a power system according to any one of claims 1 to 8 according to instructions stored in the memory.

16. A readable storage medium, characterized in that The readable storage medium stores machine-readable instructions. When the machine-readable instructions are executed by a machine, the machine performs the method for determining the frequency of a power system according to any one of claims 1 to 8.

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