Frequency protection method and device, equipment, storage medium and product

Abstract

The invention discloses a frequency protection method, device and equipment, a storage medium and a product, and relates to the technical field of power system protection and control. The method comprises the following steps: converting a three-phase measured voltage signal into a square wave signal of a three-phase line voltage through a frequency measurement circuit, and calculating a first measurement frequency according to the square wave width of the square wave signal; performing analog-to-digital conversion on the three-phase measured voltage signal to obtain a three-phase digital voltage signal, and calculating a second measurement frequency according to a three-phase line voltage corresponding to the three-phase digital voltage signal by adopting a zero crossing point frequency algorithm; calculating a third measurement frequency according to the three-phase digital voltage signal by adopting a positive sequence component frequency algorithm; the frequency protection action is executed when the duration of any measurement frequency meeting the frequency protection starting condition exceeds the time threshold value and at least one of the other two measurement frequencies meets the frequency protection starting condition, interference in the frequency measurement process is effectively reduced, and the frequency measurement accuracy and the frequency protection reliability are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power system protection and control, and in particular to a frequency protection method, device, relay, storage medium and product. Background Art

[0002] Frequency protection is an important technology in the power system. Its core function is to protect the frequency of the power grid to operate stably within a reasonable range and to avoid irreversible damage to the power system caused by excessive frequency deviation.

[0003] In the renewable energy power system, since the renewable energy power supply mode itself is unstable, the frequency protection function will have various interference problems. For example, during wind power generation or photovoltaic power generation, the fluctuation of wind speed will cause voltage fluctuation, flicker and harmonics. The existence of these problems may affect the accuracy of the frequency protection function of the device and even make its operation unreliable.

[0004] Therefore, in order to ensure the safe and stable operation of the power system, more effective and reliable frequency protection methods are needed to deal with these interference problems. Summary of the invention

[0005] The present invention provides a frequency protection method, device, equipment, storage medium and product to solve the problem of low accuracy and reliability of existing frequency protection functions due to interference in new energy power systems.

[0006] In a first aspect, an embodiment of the present invention provides a frequency protection method, including:

[0007] Obtain the three-phase measured voltage signal of the grid connection point of the power system;

[0008] The three-phase measured voltage signal is converted into a square wave signal of a three-phase line voltage by a frequency measuring circuit, and a first measurement frequency is calculated according to a square wave width of the square wave signal;

[0009] Performing analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and using a zero-crossing frequency algorithm to calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal;

[0010] Using a positive sequence component frequency algorithm, a third measurement frequency is calculated according to the three-phase digital voltage signal;

[0011] When the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition, a frequency protection action is performed.

[0012] In a second aspect, an embodiment of the present invention provides a frequency protection device, including:

[0013] A measured signal acquisition module, used to acquire a three-phase measured voltage signal of a grid connection point of the power system;

[0014] A first frequency measurement module, used for converting the three-phase measured voltage signal into a square wave signal of the three-phase line voltage through a frequency measurement circuit, and calculating a first measurement frequency according to the square wave width of the square wave signal;

[0015] A second frequency measurement module, used for performing analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and calculating a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal using a zero-crossing frequency algorithm;

[0016] A third frequency measurement module, configured to calculate a third measurement frequency according to the three-phase digital voltage signal by using a positive sequence component frequency algorithm;

[0017] A frequency protection execution module is used to execute a frequency protection action when the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection startup condition exceeds a time threshold and at least one of the other two measurement frequencies meets the frequency protection startup condition.

[0018] In a third aspect, an embodiment of the present invention provides a frequency protection device, the frequency protection device comprising:

[0019] at least one processor; and

[0020] a memory communicatively connected to the at least one processor; wherein,

[0021] The memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can execute the frequency protection method described in any embodiment of the present invention.

[0022] In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, wherein the computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to implement the frequency protection method described in any embodiment of the present invention when executed.

[0023] In a fifth aspect, an embodiment of the present invention provides a computer program product including a computer program, and when the computer program is executed by a processor, the frequency protection method described in any embodiment of the present invention is implemented.

[0024] The technical solution of the embodiment of the present invention is to obtain a three-phase measured voltage signal of a grid-connected point of an electric power system; convert the three-phase measured voltage signal into a square wave signal of a three-phase line voltage through a frequency measuring circuit, and calculate a first measurement frequency according to the square wave width of the square wave signal; perform analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and use a zero-crossing frequency algorithm to calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal; use a positive-sequence component frequency algorithm to calculate a third measurement frequency according to the three-phase digital voltage signal; and execute a frequency protection action when the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition. This embodiment measures three measurement frequencies of the three-phase measured voltage signal through three different frequency measurement methods, and performs frequency protection based on whether the three measurement frequencies meet the frequency protection start-up conditions and the duration of meeting the frequency protection start-up conditions. This can, to a certain extent, improve the problem of inaccurate frequency protection judgment caused by instantaneous changes in the frequency measured by a single frequency measurement method under interference, effectively reduce interference in the frequency measurement process, improve the accuracy of frequency measurement, and improve the reliability of frequency protection.

[0025] It should be understood that the contents described in this section are not intended to identify the key or important features of the embodiments of the present invention, nor are they intended to limit the scope of the present invention. Other features of the present invention will become easily understood through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 A flowchart of a frequency protection method provided in Embodiment 1 of the present invention;

[0028] Figure 2 A flowchart of another frequency protection method provided in Embodiment 1 of the present invention;

[0029] Figure 3 A schematic diagram of the structure of a frequency protection device provided in Embodiment 2 of the present invention;

[0030] Figure 4 It is a structural schematic diagram of a frequency protection device for implementing the frequency protection method of an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0032] It should be noted that the terms "first", "second" and "third" etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0033] Embodiment 1

[0034] Figure 1 This is a flow chart of a frequency protection method provided in the first embodiment of the present invention. This embodiment is applicable to the case where a frequency protection action is performed when the frequency of the power grid of the power system is not within a reasonable range. The method can be performed by a frequency protection device, which can be implemented in the form of hardware and / or software, and the frequency protection device can be configured in a relay. Figure 1 As shown, the method includes:

[0035] S110, obtaining three-phase measured voltage signals of the grid connection point of the power system.

[0036] The grid connection point of the power system can be considered as the point where the power source is connected to the grid. The primary high voltage connected to the grid connection point is converted into a standard low voltage on the secondary side through the primary voltage transformer. The three-phase measured voltage signal can be understood as a three-phase voltage signal for measuring frequency, and the three-phase measured voltage signal can be a standard low voltage signal collected from the secondary side of the grid connection point.

[0037] Specifically, a sampling point is set on the three-phase busbar on the secondary side of the grid connection point of the power system, and the voltage signal of the sampling point is sampled as the three-phase measured voltage signal.

[0038] S120. Convert the three-phase measured voltage signal into a square wave signal corresponding to the three-phase line voltage through a frequency measuring circuit, and calculate a first measurement frequency according to the square wave width of the square wave signal.

[0039] The three-phase line voltage can be understood as the voltage difference between any two phases of the three-phase measured voltage signal. The frequency measurement circuit outputs the three-phase line voltage in the form of a square wave.

[0040] The first measurement frequency can be understood as a frequency measured by a frequency measuring circuit and is used for making a frequency protection decision.

[0041] Specifically, by connecting the frequency measuring circuits at the sampling points on the three-phase bus, the measured voltage signal sampled from each phase is converted into a square wave signal of the three-line voltage through the frequency measuring circuit, and the square wave width of the square wave signal of each line voltage is obtained by capturing the level change of the back end of the voltage comparator through the interrupt signal, and the first frequency of the line voltage is determined according to the square wave width, and the first measurement frequency can be determined according to the first frequency of the three-phase line voltage. In the case of limited interference, the frequency difference of the three-phase line voltage should be very small, so the first frequency of the three-phase line voltage can be averaged to obtain the first measurement frequency. When averaging the first frequency to obtain the first measurement frequency, the influence of the power grid interference on the first frequency can also be further considered.

[0042] In an optional embodiment, the frequency measuring circuit includes: a low-pass filter, a voltage transformer, an integration circuit and a comparison circuit, the low-pass filter is used to filter the sampled measured voltage signal to eliminate certain interference. The three-phase measured voltage signal is converted into a micro-voltage three-phase measured voltage signal through the voltage transformer, and the micro-voltage measured voltage signal is converted into a square wave signal of the three-phase line voltage through the integration circuit and the comparison circuit.

[0043] S130, performing analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and using a zero-crossing frequency algorithm to calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal.

[0044] Among them, the three-phase digital voltage signal can be understood as a digital voltage signal obtained by sampling. The second measurement frequency can be understood as a frequency measured based on the zero-crossing frequency algorithm, which is used to make frequency protection decisions. The main idea of ​​the zero-crossing frequency algorithm is to detect the moment when the voltage passes through the zero point when the AC signal switches from the positive half cycle to the negative half cycle or from the negative half cycle to the positive half cycle during its cycle, and generate a corresponding signal output at this moment.

[0045] Specifically, the three-phase measured voltage signal is converted into a digital form according to a preset sampling frequency to obtain a three-phase digital voltage signal, and the three-phase line voltage is calculated based on the three-phase digital voltage signal. The frequency of each line voltage is calculated using a zero-crossing frequency algorithm to obtain a second frequency of the three-phase line voltage; in the case of limited interference, the frequency of the three-phase line voltage should be very small, so the second frequency of the three-phase line voltage can be averaged to obtain a second measurement frequency. When averaging the second frequency to obtain the second measurement frequency, the influence of the grid interference on the second frequency can also be further considered.

[0046] Exemplarily, the method of calculating the three-phase line voltage according to the three-phase digital voltage signal may be: defining the three-phase voltage of the three-phase digital voltage signal at the i-th sampling point as V A [i],V B [i],V C [i], the corresponding three-phase line voltages are U AB [i],U BC [i],U CA [i]So,

[0047] U AB [i] = V A [i]-V B [i];

[0048] U BC [i] = V B [i]-V C [i];

[0049] U CA [i] = V C [i]-V A [i].

[0050] S140. Calculate a third measurement frequency according to the three-phase digital voltage signal using a positive sequence component frequency algorithm.

[0051] The third measured frequency can be understood as a frequency measured based on a positive sequence component frequency algorithm, which is used for frequency protection decision. The main idea of ​​the positive sequence component frequency algorithm is to decompose the voltage in a three-phase power system into positive sequence components to calculate the frequency.

[0052] Specifically, the three-phase digital voltage signal is processed and the positive sequence component is extracted to obtain a positive sequence voltage signal. The fundamental frequency is extracted according to the positive sequence voltage signal, and the third measurement frequency is determined according to the fundamental frequency. When determining the third measurement frequency, the influence of the grid interference on the fundamental frequency can be further considered, and the fundamental frequency can be corrected to obtain the third measurement frequency.

[0053] The frequency measurement circuit used in this embodiment has the characteristics of fast speed and high precision in steady state; the zero-crossing frequency algorithm used to measure the frequency has the characteristics of strong resistance to common-mode interference; the positive-sequence software frequency measurement has the characteristics of strong resistance to differential-mode interference.

[0054] S150: When the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition, execute a frequency protection action.

[0055] Among them, the frequency protection start-up condition can be understood as the condition that requires the start-up of frequency protection. Frequency protection may include: low frequency protection and / or over frequency protection. The frequency protection start-up condition corresponding to the low frequency protection may be that the frequency is less than the frequency threshold, and the frequency protection start-up condition corresponding to the over frequency protection may be that the frequency is greater than the frequency threshold. The frequency threshold and the time threshold may be determined according to the application scenario of the frequency protection and the frequency protection requirements. The frequency protection action may include cutting off the fault area, triggering the start-up of the backup power supply, issuing an alarm signal or tripping, etc.

[0056] Specifically, it is determined whether the first measured frequency, the second measured frequency, and the third measured frequency meet the frequency protection start-up condition. If the frequency protection start-up condition is met, the duration of meeting the frequency protection start-up condition is recorded. Since each frequency calculation method is applicable to different scenarios, and the frequency measurement may be inaccurate due to interference, if the duration of any measured frequency meeting the frequency protection start-up condition exceeds the time threshold, it cannot be said that the frequency is beyond the normal range. It is necessary to determine whether at least one of the other two measured frequencies meets the frequency protection start-up condition. If at least one of the other two measured frequencies meets the frequency protection start-up condition, it is considered that the frequency is beyond the normal range and frequency protection is required, and the frequency protection action is executed.

[0057] The technical solution of the embodiment of the present invention is to obtain a three-phase measured voltage signal of a grid-connected point of an electric power system; convert the three-phase measured voltage signal into a square wave signal of a three-phase line voltage through a frequency measuring circuit, and calculate a first measurement frequency according to the square wave width of the square wave signal; perform analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and use a zero-crossing frequency algorithm to calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal; use a positive-sequence component frequency algorithm to calculate a third measurement frequency according to the three-phase digital voltage signal; and execute a frequency protection action when the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition. This embodiment measures three measurement frequencies of the three-phase measured voltage signal through three different frequency measurement methods, and performs frequency protection based on whether the three measurement frequencies meet the frequency protection start-up conditions and the duration of meeting the frequency protection start-up conditions. This can, to a certain extent, improve the problem of inaccurate frequency protection judgment caused by instantaneous changes in the frequency measured by a single frequency measurement method under interference, effectively reduce interference in the frequency measurement process, improve the accuracy of frequency measurement, and improve the reliability of frequency protection.

[0058] As an optional embodiment of the embodiment of the present application, 150, when the duration for which any one of the first measurement frequency, the second measurement frequency, and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition, the step of performing a frequency protection action includes:

[0059] 151. When any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets a frequency protection start condition, start a frequency protection control device.

[0060] The frequency protection control device may be understood as a device for executing frequency protection actions, such as a relay.

[0061] Specifically, when any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition, the frequency protection control device is used to execute the frequency protection action.

[0062] 152. Determine a measurement frequency that satisfies the frequency protection startup condition as a target measurement frequency, and obtain a duration for which the target measurement frequency satisfies the frequency protection startup condition.

[0063] The target measurement frequency may be understood as a measurement frequency among the first measurement frequency, the second measurement frequency and the third measurement frequency that meets the frequency protection start condition.

[0064] Specifically, the measurement frequency that meets the frequency protection start condition is determined as the target measurement frequency, and timing is started from the moment when the target measurement frequency meets the frequency protection start condition to obtain the duration for which the target measurement frequency meets the frequency protection start condition.

[0065] 153. When the duration exceeds the time threshold, if at least one of the other two measurement frequencies meets the frequency protection start condition, control the frequency protection control device to perform a frequency protection action.

[0066] Specifically, when the duration that a target measurement frequency meets the frequency protection start condition exceeds a time threshold, if at least one of the other two measurement frequencies meets the frequency protection condition, the frequency protection control device is controlled to perform a frequency protection action.

[0067] This embodiment adopts a frequency protection strategy of hierarchical response. When any measured frequency meets the frequency protection condition, the frequency protection control device is started. Before executing any frequency protection action, there is enough time to confirm whether it is necessary to affect and wait for the power system to automatically restore to normal frequency, avoiding unnecessary intervention, and being able to perform frequency protection in time when the frequency is abnormal. When the duration of one of the measured frequencies meeting the frequency protection condition exceeds the time threshold, and at least another measured frequency also meets the frequency protection condition, the frequency protection control device is controlled to perform the frequency protection action, which ensures the sensitivity, reliability and effectiveness of the frequency protection and reduces the risk of false operation.

[0068] In an optional embodiment, 152, the step of obtaining the duration for which the target measurement frequency meets the frequency protection start condition includes:

[0069] 1521. When the target measurement frequency meets a frequency protection start condition, accumulate the duration according to a measurement duration corresponding to the target measurement frequency.

[0070] The measurement duration corresponding to the target measurement frequency can be understood as the time interval for updating the target measurement frequency. The duration can be understood as the time during which each updated target measurement frequency continuously meets the frequency protection start condition.

[0071] Specifically, the initial value of the duration is set to zero. When the target measurement frequency meets the frequency protection start condition, the measurement duration of the target measurement frequency is obtained, and the measurement duration is accumulated on the duration. For example, the duration is defined as T sum , the measurement time is Δt,T sum =T sum+Δt means that the measurement duration is accumulated on the duration to update the duration. It is understandable that due to the fluctuation of the frequency of the measured voltage signal, the measurement durations of different frequency measurement methods and the same frequency measurement method in different frequency measurement cycles may be different.

[0072] 1522. If the target measurement frequency does not meet the frequency protection start condition, clear the duration.

[0073] Specifically, once the target measurement frequency does not meet the frequency protection start condition, the duration corresponding to the target measurement frequency is reset to zero, that is, T is set. sum =0, when the target measurement frequency meets the frequency protection start condition again, it needs to be re-timed.

[0074] This embodiment uses the duration that the target measurement frequency meets the frequency protection start condition as one of the conditions for executing the frequency protection action, thereby reducing the impact of frequency mutation caused by interference on frequency protection.

[0075] As another optional embodiment of the embodiment of the present application, S120, the step of calculating the first measurement frequency according to the square wave width of the square wave signal includes:

[0076] S121. For each line voltage in the three-phase line voltages, calculate two consecutive half-wave widths of a square wave signal corresponding to the line voltage; the half-wave width is a time difference between a rising edge and a falling edge of the square wave signal.

[0077] The half-wave width may be understood as the high-level time difference between the rising edge and the falling edge, and may include the time difference between the rising edge and the falling edge, and the low-level time difference between the falling edge and the rising edge.

[0078] Specifically, the time difference between the rising edge and the falling edge of the square wave signal corresponding to the line voltage is obtained as a half-wave width, and two consecutive half-wave widths are obtained continuously. Ignoring interference, the two consecutive half-wave widths should satisfy symmetry, but in the actual power system, the half-wave widths may be different or even very different due to various interferences.

[0079] S122. If the difference between the two consecutive half-wave widths is less than the difference threshold, the sum of the two consecutive half-wave widths is determined as the full-wave width, and the first frequency of the line voltage is updated according to the full-wave width; the first frequency is the frequency of the square wave signal corresponding to the line voltage.

[0080] The full wave width can be understood as the time difference between a rising edge and the next rising edge. The first frequency can be understood as the frequency of the square wave signal of each line voltage output by the frequency measuring circuit. The difference threshold can be understood as the maximum difference that satisfies the square wave symmetry.

[0081] Specifically, if the difference between two consecutive half-wave widths is less than the difference threshold, indicating that the square wave signal of the line voltage satisfies the square wave symmetry, the two consecutive half-wave widths are summed to obtain the full-wave width. The first frequency of the line voltage is updated according to the full-wave width.

[0082] S123: If the difference between the two consecutive half-wave widths is not less than the difference threshold, maintaining the first frequency of the line voltage unchanged.

[0083] Specifically, if the difference between two consecutive half-wave widths is not less than the difference threshold, it means that the single-phase square wave signal does not satisfy the square wave symmetry. At this time, the measured frequency is inaccurate, so the first frequency of the line voltage is not updated, and the first frequency of the line voltage measured in the previous measurement cycle remains unchanged.

[0084] S124. Calculate the first measurement frequency according to the first frequency of the three-phase line voltage.

[0085] Specifically, the first measurement frequency is obtained by synthesizing the first frequency of the three-phase line voltage measured by the frequency measurement circuit. For example, the average value of the first frequency of the three-phase line voltage is determined as the first measurement frequency of the three-phase measured voltage signal.

[0086] In a specific example, the rising edge and falling edge times t1, t2, t3, ... t i ; Get two consecutive half-wave widths, t i -t i-1 and t i+1 -t i ; Define the difference threshold as T th , if (t i+1 -t i )-(t i -t i-1 ) <T t h, then the full-wave width of the three-phase square wave signal is calculated as mn=AB,BC,CA,U mn represents the line voltage between phase m and phase n; thus determining the full wave width of the three-phase line voltage is The first frequencies of the three-phase line voltages are

[0087] This embodiment captures the half-wave width of the square wave signal of the line voltage to determine the first frequency, thereby improving the frequency measurement speed, and fully considers the influence of interference on the square wave signal when determining the first frequency, thereby improving the accuracy of the first frequency.

[0088] In an optional embodiment, S124, the step of calculating the first measurement frequency according to the first frequency of the three-phase line voltage includes:

[0089] S1241. For each line voltage in the three-phase line voltage, if a first frequency of the line voltage exceeds a preset frequency fluctuation range or the line voltage is less than a voltage threshold, the first frequency is set to a rated frequency.

[0090] The preset frequency fluctuation range can be understood as the range of frequency fluctuation allowed by the frequency protection, for example, the rated frequency f e ±5Hz; voltage threshold U th It can be understood as the minimum frequency measurement voltage allowed by frequency protection.

[0091] Specifically, if the first frequency of the line voltage exceeds the preset frequency fluctuation range or the fundamental amplitude of the line voltage is less than the voltage threshold, the first frequency of the line voltage is set to the rated frequency. or Or U mn th but Otherwise, the first measurement frequency is calculated using the first frequency of the line voltage measured by the frequency measuring circuit.

[0092] S1242: If the difference between the first frequencies of any two line voltages in the three-phase line voltages does not exceed a frequency difference threshold, determining an average value of the first frequencies of the three-phase line voltages as the first measurement frequency.

[0093] Specifically, if the difference between the first frequencies of any two line voltages in the three-phase line voltages does not exceed the frequency difference threshold, that is, and and Then calculate the average value of the first frequency of the three-phase line voltage The average value of the first frequency f ave1 Determined as the first measurement frequency f1, that is, f1 = f ave1 .

[0094] S1243. If the difference between the first frequencies of two line voltages in the three-phase line voltages exceeds a frequency difference threshold, remove the line voltage with the largest absolute deviation of the first frequency, and determine the average of the first frequencies of the other two line voltages as the first measurement frequency.

[0095] ​For example, if the difference between the first frequencies of two line voltages in the three-phase line voltage exceeds the frequency difference threshold f th ,For example and and Then the absolute deviations of the first frequency and the average value of the three-phase line voltage are calculated as follows: Remove the line voltage with the largest absolute deviation, such as The average value of the first frequencies of the other two line voltages is determined as the first measurement frequency, that is,

[0096] In this embodiment, when the first frequencies of the line voltages differ greatly, after removing the line voltage with the largest absolute deviation of the first frequency, the average value of the first frequencies of the other two line voltages is determined as the first measurement frequency, thereby reducing the influence of interference on the first measurement frequency and improving the accuracy of the first measurement frequency.

[0097] As another optional embodiment of the embodiment of the present application, S130, the step of using a zero-crossing frequency algorithm to calculate the second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal includes:

[0098] S131, calculating the second frequency of the three-phase line voltage using a zero-crossing frequency algorithm;

[0099] For example, for the line voltage U corresponding to the three-phase digital voltage signal AB , if U AB [i]×U AB [i-1]<0, the i-th point is the first zero-crossing point. If U AB [i+N-1]×U AB [i+N]<0, then the i+N-1th point is recorded as the second zero-crossing point, and N is the number of sampling points contained in the measurement period T.

[0100] in, Indicates the second measurement duration for calculating the line voltage between phases AB using the zero-crossing frequency algorithm; The second measurement frequency of the line voltage between the AB phases is calculated by using the zero-crossing frequency algorithm. (N-3)×t represents the time of the N-2 sampling points between the first zero-crossing point and the second zero-crossing point among the N sampling points; Indicates the time of the first zero crossing; Indicates the time of the second zero crossing.

[0101] Understandably, and The calculation method of is similar, and will not be described in detail in this embodiment.

[0102] S132. Calculate the second measurement frequency according to the second frequency of the three-phase line voltage.

[0103] Specifically, the second measurement frequency is obtained by synthesizing the second frequency of the three-phase line voltage measured based on the zero-crossing frequency algorithm. For example, the average value of the second frequency of the three-phase line voltage is determined as the second measurement frequency of the three-phase measured voltage signal.

[0104] In an optional embodiment, S132, the step of calculating the second measurement frequency according to the second frequency of the three-phase line voltage includes:

[0105] S1321. For any line voltage, if the second frequency of the line voltage exceeds a preset frequency fluctuation range or the fundamental amplitude of the line voltage is less than a voltage threshold, the second frequency is set to a rated frequency.

[0106] Specifically, if the second frequency of the line voltage exceeds the preset frequency fluctuation range, the second frequency of the line voltage is set to the rated frequency. or Or U mn th ,but Otherwise, the second measurement frequency is calculated using the second frequency of the line voltage measured using the zero-crossing frequency algorithm.

[0107] Exemplarily, the fundamental amplitude of the line voltage may be calculated by calculating the real part and the imaginary part of the fundamental amplitude of the line voltage based on Fourier transform, such as:

[0108]

[0109] S1322: If the difference between the second frequencies of any two line voltages in the three-phase line voltages does not exceed a frequency difference threshold, then an average value of the second frequencies of the three-phase digital voltage signal is determined as the second measurement frequency.

[0110] Specifically, if the difference between the second frequencies of any two line voltages in the three-phase line voltages does not exceed the frequency difference threshold, that is, and and Then calculate the average value of the second frequency of the three-phase line voltage The average value of the second frequency f ave2 Determined as the second measurement frequency f2, that is, f2 = f ave2 .

[0111] S1333: If the difference between the second frequencies of two line voltages in the three-phase line voltages exceeds a frequency difference threshold, remove the line voltage with the largest absolute deviation of the second frequency, and determine the average value of the second frequencies of the other two line voltages as the second measurement frequency.​

[0112] For example, if the difference between the second frequencies of two line voltages in the three-phase line voltage exceeds the frequency difference threshold f th ,For example and and Then the absolute deviations of the second frequency and the average value of the three-phase line voltage are calculated as follows: Remove the line voltage with the largest absolute deviation, such as The average value of the first frequencies of the other two line voltages is determined as the second measurement frequency, that is,

[0113] In this embodiment, when the second frequencies of the line voltages differ greatly, after removing the line voltage with the largest absolute deviation of the second frequency, the average value of the second frequencies of the other two line voltages is determined as the second measurement frequency. This can reduce the impact of interference on the second measurement frequency and improve the accuracy of the second measurement frequency.

[0114] As an optional embodiment of the embodiment of the present application, S140, the step of using a positive sequence component frequency algorithm to calculate a third measurement frequency according to the three-phase digital voltage signal includes:

[0115] S141. Calculate the phase difference of the fundamental positive sequence voltage in two consecutive measurement cycles according to the three-phase line voltage of the three-phase digital voltage signal, and calculate the fundamental frequency deviation according to the phase difference and the fundamental rated frequency.

[0116] The fundamental frequency deviation can be understood as the deviation between the frequency of the fundamental voltage and the fundamental rated frequency.

[0117] Specifically, the fundamental rated frequency is defined as The initial phase angle is The fundamental frequency deviation is Δf ′ , the phase difference of the fundamental positive sequence voltage in two consecutive measurement cycles for:

[0118]

[0119] Real part of fundamental positive sequence voltage:

[0120] Imaginary part of fundamental positive sequence voltage:

[0121] Among them, U Ar ,U Br ,u Cr The real part of the three-phase digital voltage signal of A, B, and C respectively; U Ai ,U Bi ,UCi It is the imaginary part of the three-phase digital voltage signal of A, B, and C. U′ i and U′ r The calculation is similar to that of , and the real part and the imaginary part of the three-phase digital voltage signal can be calculated according to the Fourier formula, which will not be described in detail in the embodiment of the present invention.

[0122] As long as Δf ′ The trend is getting smaller and smaller, then Thus we get

[0123] S142: Determine the sum of the fundamental wave frequency deviation and the fundamental wave rated frequency as the fundamental wave correction frequency, and determine the ratio of the fundamental wave rated frequency to the fundamental wave correction frequency as the correction coefficient.

[0124] Specifically, the correction coefficient is expressed as the fundamental wave rated frequency f0 and the fundamental wave correction frequency f0+Δf ′ The ratio R is:

[0125]

[0126] S143, correcting the phase difference according to the fundamental wave positive sequence voltage and the correction coefficient to obtain a corrected phase difference, and calculating a fundamental wave corrected frequency deviation according to the corrected phase difference and the fundamental wave rated frequency.

[0127] Specifically, according to the phase difference The formula and correction coefficient R are used to calculate the corrected phase difference. for:

[0128]

[0129] According to the corrected phase difference The fundamental wave corrected frequency deviation Δf is calculated by using the fundamental wave rated frequency f0 as follows:

[0130]

[0131] S144: Determine the sum of the fundamental wave corrected frequency deviation and the fundamental wave rated frequency as a third frequency.

[0132] Specifically, the third frequency f3 ′ It can be expressed as:

[0133]

[0134] S145. If the third frequency exceeds a preset frequency fluctuation range or the fundamental positive sequence voltage is less than a voltage threshold, the rated frequency is determined as the third measurement frequency; otherwise, the third frequency is determined as the third measurement frequency.

[0135] Specifically, if the third frequency exceeds the preset frequency fluctuation range or the fundamental positive sequence voltage is less than the voltage threshold, the third frequency of the line voltage is set to the rated frequency. For example, if f′3>f e +5Hz or f′3 <f e +5Hz, or U th Then f3=f e Otherwise, the third frequency f′3 is determined as the third measurement frequency f3.

[0136] This embodiment adopts a positive-sequence component frequency algorithm to calculate the phase difference of the fundamental positive-sequence voltage, and corrects the phase difference according to a correction coefficient determined by the phase difference and the fundamental rated frequency to obtain a corrected phase difference, and determines the third measurement frequency according to the corrected phase difference and the fundamental rated frequency, thereby reducing the influence of interference on the third measurement frequency and improving the accuracy of the third measurement frequency.

[0137] In a specific example, Figure 2 This is a flow chart of another frequency protection method provided in Embodiment 1 of the present invention. Figure 2 As shown, the first measurement frequency is obtained by the frequency measuring circuit, the second measurement frequency is calculated by the zero-crossing frequency algorithm, and the third measurement frequency is calculated by the positive-sequence component frequency algorithm; when any measurement frequency meets the frequency protection start-up condition, the frequency protection control device is started; when the duration of the measurement frequency that meets the frequency protection start-up condition exceeds the time threshold, if at least one of the other two measurement frequencies meets the frequency protection start-up condition, the frequency protection control device is controlled to perform the frequency protection action. The frequency protection strategy using hierarchical response can perform frequency protection in a timely manner when the frequency is abnormal. When the duration of one of the measurement frequencies meeting the frequency protection condition exceeds the time threshold, and at least another measurement frequency also meets the frequency protection condition, the frequency protection control device is controlled to perform the frequency protection action, which ensures the sensitivity, reliability and effectiveness of the frequency protection and reduces the risk of false operation.

[0138] Embodiment 2

[0139] Figure 3 This is a schematic diagram of the structure of a frequency protection device provided in Embodiment 2 of the present invention. Figure 3 As shown, the device includes: a measured signal acquisition module 210, a first frequency measurement module 220, a second frequency measurement module 230, a third frequency measurement module 240 and a frequency protection execution module 250; wherein,

[0140] A measured signal acquisition module 210 is used to acquire a three-phase measured voltage signal of a grid connection point of the power system;

[0141] ​A first frequency measurement module 220, configured to convert the three-phase measured voltage signal into a square wave signal of a three-phase line voltage through a frequency measurement circuit, and calculate a first measurement frequency according to a square wave width of the square wave signal;

[0142] A second frequency measurement module 230, configured to perform analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal using a zero-crossing frequency algorithm;

[0143] A third frequency measurement module 240, configured to calculate a third measurement frequency according to the three-phase digital voltage signal by using a positive sequence component frequency algorithm;

[0144] The frequency protection execution module 250 is used to execute a frequency protection action when the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start-up condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start-up condition.

[0145] The technical solution of the embodiment of the present invention is to obtain a three-phase measured voltage signal of a grid-connected point of an electric power system; convert the three-phase measured voltage signal into a square wave signal of a three-phase line voltage through a frequency measuring circuit, and calculate a first measurement frequency according to the square wave width of the square wave signal; perform analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and use a zero-crossing frequency algorithm to calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal; use a positive-sequence component frequency algorithm to calculate a third measurement frequency according to the three-phase digital voltage signal; and execute a frequency protection action when the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition. This embodiment measures three measurement frequencies of the three-phase measured voltage signal through three different frequency measurement methods, and performs frequency protection based on whether the three measurement frequencies meet the frequency protection start-up conditions and the duration of meeting the frequency protection start-up conditions. This can, to a certain extent, improve the problem of inaccurate frequency protection judgment caused by instantaneous changes in the frequency measured by a single frequency measurement method under interference, effectively reduce interference in the frequency measurement process, improve the accuracy of frequency measurement, and improve the reliability of frequency protection.

[0146] Optionally, the frequency protection execution module includes:

[0147] A frequency protection starting unit, configured to start the frequency protection control device when any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection starting condition;

[0148] a duration determination unit, configured to determine the measurement frequency that satisfies the frequency protection startup condition as the target measurement frequency, and obtain the duration that the target measurement frequency satisfies the frequency protection startup condition;

[0149] The frequency protection execution unit is used to control the frequency protection control device to execute the frequency protection action when the duration exceeds the time threshold and if at least one of the other two measured frequencies meets the frequency protection start condition.

[0150] Optionally, the duration determination unit is specifically configured to:

[0151] When the target measurement frequency meets the frequency protection start condition, the duration is accumulated according to the measurement duration corresponding to the target measurement frequency;

[0152] If the target measurement frequency does not meet the frequency protection start condition, the duration is cleared.

[0153] Optionally, the first frequency measurement module includes:

[0154] A half-wave width determination unit, configured to calculate, for each line voltage in the three-phase line voltages, two consecutive half-wave widths of a square wave signal corresponding to the line voltage; the half-wave width being a time difference between a rising edge and a falling edge of the square wave signal;

[0155] A first frequency updating unit, configured to determine the sum of the two consecutive half-wave widths as the full-wave width if the difference between the two consecutive half-wave widths is less than a difference threshold, and update the first frequency of the line voltage according to the full-wave width; the first frequency is the frequency of the square wave signal corresponding to the line voltage; a first frequency maintaining unit, configured to maintain the first frequency of the line voltage unchanged if the difference between the two consecutive half-wave widths is not less than a difference threshold;

[0156] The first measurement frequency determination unit is configured to calculate the first measurement frequency according to the first frequency of the three-phase line voltage.

[0157] Optionally, the first measurement frequency determining unit is specifically configured to:

[0158] For each line voltage in the three-phase line voltage, if the first frequency of the line voltage exceeds a preset frequency fluctuation range or the line voltage is less than a voltage threshold, setting the first frequency to a rated frequency;

[0159] If the difference between the first frequencies of any two line voltages in the three-phase line voltages does not exceed the frequency difference threshold, determining the average value of the first frequencies of the three-phase line voltages as the first measurement frequency;

[0160] If the difference between the first frequencies of two line voltages in the three-phase line voltages exceeds the frequency difference threshold, the line voltage with the largest absolute deviation of the first frequency is removed, and the average of the first frequencies of the other two line voltages is determined as the first measurement frequency.

[0161] Optionally, the second frequency measurement module includes:

[0162] A second frequency calculation unit, used for calculating the second frequency of the three-phase line voltage by adopting a zero-crossing frequency algorithm;

[0163] The second measurement frequency determination unit is configured to calculate the second measurement frequency according to the second frequency of the three-phase line voltage.

[0164] Optionally, the second measurement frequency determining unit is specifically configured to:

[0165] For any line voltage, if the second frequency of the line voltage exceeds a preset frequency fluctuation range or the fundamental amplitude of the line voltage is less than a voltage threshold, the second frequency is set to a rated frequency;

[0166] If the difference between the second frequencies of any two line voltages in the three-phase line voltages does not exceed the frequency difference threshold, then determining the average value of the second frequencies of the three-phase digital voltage signal as the second measurement frequency;

[0167] If the difference between the second frequencies of two line voltages in the three-phase line voltages exceeds the frequency difference threshold, the line voltage with the largest absolute deviation of the second frequency is removed, and the average value of the second frequencies of the other two line voltages is determined as the second measurement frequency.

[0168] Optionally, the third frequency measurement module is specifically used to:

[0169] Calculating the phase difference of the fundamental positive sequence voltage in two consecutive measurement cycles according to the three-phase line voltage of the three-phase digital voltage signal, and calculating the fundamental frequency deviation according to the phase difference and the fundamental rated frequency;

[0170] The sum of the fundamental wave frequency deviation and the fundamental wave rated frequency is determined as the fundamental wave correction frequency, and the ratio of the fundamental wave rated frequency to the fundamental wave correction frequency is determined as the correction coefficient;

[0171] Correcting the phase difference according to the fundamental wave positive sequence voltage and the correction coefficient to obtain a corrected phase difference, and calculating a fundamental wave corrected frequency deviation according to the corrected phase difference and the fundamental wave rated frequency;

[0172] Determine the sum of the fundamental wave corrected frequency deviation and the fundamental wave rated frequency as a third frequency;

[0173] If the third frequency exceeds a preset frequency fluctuation range or the fundamental positive sequence voltage is less than a voltage threshold, the rated frequency is determined as the third measurement frequency; otherwise, the third frequency is determined as the third measurement frequency.

[0174] The frequency protection device provided in the embodiment of the present invention can execute the frequency protection method provided in any embodiment of the present invention, and has the corresponding functional modules and beneficial effects of the execution method.

[0175] Embodiment 3

[0176] Figure 4 A schematic diagram of a frequency protection device 10 that can be used to implement an embodiment of the present invention is shown. The frequency protection device is intended to represent various forms of devices for protecting frequency, such as relays. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the present invention described and / or claimed herein.

[0177] like Figure 4 As shown, the frequency protection device 10 includes at least one processor 11, and a memory connected to the at least one processor 11, such as a read-only memory (ROM) 12, a random access memory (RAM) 13, etc., wherein the memory stores a computer program that can be executed by at least one processor, and the processor 11 can perform various appropriate actions and processes according to the computer program stored in the read-only memory (ROM) 12 or the computer program loaded from the storage unit 18 to the random access memory (RAM) 13. In the RAM 13, various programs and data required for the operation of the frequency protection device 10 can also be stored. The processor 11, the ROM 12, and the RAM 13 are connected to each other through a bus 14. An input / output (I / O) interface 15 is also connected to the bus 14.

[0178] A number of components in the frequency protection device 10 are connected to the I / O interface 15, including: an input unit 16, such as a keyboard, a mouse, etc.; an output unit 17, such as various types of displays, speakers, etc.; a storage unit 18, such as a disk, an optical disk, etc.; and a communication unit 19, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 19 allows the frequency protection device 10 to exchange information / data with other devices through a computer network such as the Internet and / or various telecommunication networks.

[0179] The processor 11 may be a variety of general and / or special processing components with processing and computing capabilities. Some examples of the processor 11 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various special artificial intelligence (AI) computing chips, various processors running machine learning model algorithms, a digital signal processor (DSP), and any appropriate processor, controller, microcontroller, etc. The processor 11 performs the various methods and processes described above, such as a frequency protection method.

[0180] In some embodiments, the frequency protection method may be implemented as a computer program, which is tangibly contained in a computer-readable storage medium, such as a storage unit 18. In some embodiments, part or all of the computer program may be loaded and / or installed on the frequency protection device 10 via the ROM 12 and / or the communication unit 19. When the computer program is loaded into the RAM 13 and executed by the processor 11, one or more steps of the frequency protection method described above may be performed. Alternatively, in other embodiments, the processor 11 may be configured to perform the frequency protection method in any other suitable manner (e.g., by means of firmware).

[0181] Various implementations of the systems and techniques described above herein can be implemented in digital electronic circuit systems, integrated circuit systems, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), load programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include: being implemented in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which can be a special purpose or general purpose programmable processor that can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit data and instructions to the storage system, the at least one input device, and the at least one output device.

[0182] In some embodiments, the frequency protection method may be implemented as a computer program, which is invisibly included in a computer program product. The computer program implements the frequency protection method of the present invention when executed by a processor. The computer program product can be understood as a software product that implements its solution mainly through a computer program. The computer program for implementing the method of the present invention can be written in any combination of one or more programming languages. These computer programs can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that when the computer program is executed by the processor, the functions / operations specified in the flow chart and / or block diagram are implemented. The computer program can be executed entirely on the machine, partially on the machine, partially on the machine as an independent software package and partially on a remote machine, or entirely on a remote machine or server.

[0183] In the context of the present invention, a computer-readable storage medium may be a tangible medium that may contain or store a computer program for use by or in combination with an instruction execution system, device or equipment. A computer-readable storage medium may include, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, devices or equipment, or any suitable combination of the foregoing. Alternatively, a computer-readable storage medium may be a machine-readable signal medium. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0184] The systems and techniques described herein may be implemented in a computing system that includes backend components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes frontend components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such backend components, middleware components, or frontend components. The components of the system may be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: a local area network (LAN), a wide area network (WAN), a blockchain network, and the Internet.

[0185] A computing system may include a client and a server. The client and the server are generally remote from each other and usually interact through a communication network. The client and server relationship is generated by computer programs running on the corresponding computers and having a client-server relationship with each other. The server may be a cloud server, also known as a cloud computing server or cloud host, which is a host product in the cloud computing service system to solve the defects of difficult management and weak business scalability in traditional physical hosts and VPS services.

[0186] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the present invention can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solution of the present invention can be achieved, and this document does not limit this.

[0187] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A frequency protection method, characterized in that: include: Obtain the three-phase measured voltage signal of the grid connection point of the power system; The three-phase measured voltage signal is converted into a square wave signal of a three-phase line voltage by a frequency measuring circuit, and a first measurement frequency is calculated according to a square wave width of the square wave signal; Performing analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and using a zero-crossing frequency algorithm to calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal; Using a positive sequence component frequency algorithm, a third measurement frequency is calculated according to the three-phase digital voltage signal; When the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition, a frequency protection action is performed.

2. The method according to claim 1, characterized in that The step of executing a frequency protection action when the duration for which any one of the first measurement frequency, the second measurement frequency, and the third measurement frequency meets the frequency protection start condition exceeds a time threshold, and at least one of the other two measurement frequencies meets the frequency protection start condition, includes: When any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection start condition, starting the frequency protection control device; Determining a measurement frequency that satisfies the frequency protection startup condition as a target measurement frequency, and obtaining a duration for which the target measurement frequency satisfies the frequency protection startup condition; When the duration exceeds the time threshold, if at least one of the other two measurement frequencies meets the frequency protection start condition, the frequency protection control device is controlled to perform a frequency protection action.

3. The method according to claim 2, characterized in that The step of obtaining the duration during which the target measurement frequency meets the frequency protection start condition comprises: When the target measurement frequency meets the frequency protection start condition, the duration is accumulated according to the measurement duration corresponding to the target measurement frequency; If the target measurement frequency does not meet the frequency protection start condition, the duration is cleared.

4. The method according to claim 1, characterized in that: The step of calculating the first measurement frequency according to the square wave width of the square wave signal comprises: For each of the three-phase line voltages, two consecutive half-wave widths of a square wave signal corresponding to the line voltage are calculated; the half-wave width is the time difference between a rising edge and a falling edge of the square wave signal; If the difference between the two consecutive half-wave widths is less than the difference threshold, the sum of the two consecutive half-wave widths is determined as the full-wave width, and the first frequency of the line voltage is updated according to the full-wave width; the first frequency is the frequency of the square wave signal corresponding to the line voltage; If the difference between the two consecutive half-wave widths is not less than the difference threshold, maintaining the first frequency of the line voltage unchanged; The first measurement frequency is calculated according to the first frequency of the three-phase line voltage.

5. The method according to claim 4, characterized in that The step of calculating the first measurement frequency according to the first frequency of the three-phase line voltage comprises: For each line voltage in the three-phase line voltage, if the first frequency of the line voltage exceeds a preset frequency fluctuation range or the line voltage is less than a voltage threshold, setting the first frequency to a rated frequency; If the difference between the first frequencies of any two line voltages in the three-phase line voltages does not exceed the frequency difference threshold, determining the average value of the first frequencies of the three-phase line voltages as the first measurement frequency; If the difference between the first frequencies of two line voltages in the three-phase line voltages exceeds the frequency difference threshold, the line voltage with the largest absolute deviation of the first frequency is removed, and the average of the first frequencies of the other two line voltages is determined as the first measurement frequency.

6. The method according to claim 1, characterized in that The step of using a zero-crossing frequency algorithm to calculate a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal comprises: Calculating the second frequency of the three-phase line voltage using a zero-crossing frequency algorithm; The second measurement frequency is calculated according to the second frequency of the three-phase line voltage.

7. The method according to claim 6, characterized in that The step of calculating the second measurement frequency according to the second frequency of the three-phase line voltage comprises: For any line voltage, if the second frequency of the line voltage exceeds a preset frequency fluctuation range or the fundamental amplitude of the line voltage is less than a voltage threshold, the second frequency is set to a rated frequency; If the difference between the second frequencies of any two line voltages in the three-phase line voltages does not exceed the frequency difference threshold, then determining the average value of the second frequencies of the three-phase digital voltage signal as the second measurement frequency; If the difference between the second frequencies of two line voltages in the three-phase line voltages exceeds the frequency difference threshold, the line voltage with the largest absolute deviation of the second frequency is removed, and the average value of the second frequencies of the other two line voltages is determined as the second measurement frequency.

8. The method according to claim 1, characterized in that The step of using a positive sequence component frequency algorithm to calculate a third measurement frequency according to the three-phase digital voltage signal comprises: Calculating the phase difference of the fundamental positive sequence voltage in two consecutive measurement cycles according to the three-phase line voltage of the three-phase digital voltage signal, and calculating the fundamental frequency deviation according to the phase difference and the fundamental rated frequency; The sum of the fundamental wave frequency deviation and the fundamental wave rated frequency is determined as the fundamental wave correction frequency, and the ratio of the fundamental wave rated frequency to the fundamental wave correction frequency is determined as the correction coefficient; Correcting the phase difference according to the fundamental wave positive sequence voltage and the correction coefficient to obtain a corrected phase difference; and calculating a fundamental wave corrected frequency deviation according to the corrected phase difference and the fundamental wave rated frequency; Determine the sum of the fundamental wave corrected frequency deviation and the fundamental wave rated frequency as a third frequency; If the third frequency exceeds a preset frequency fluctuation range or the fundamental positive sequence voltage is less than a voltage threshold, the rated frequency is determined as the third measurement frequency; otherwise, the third frequency is determined as the third measurement frequency.

9. A frequency protection device, characterized in that: include: A measured signal acquisition module, used to acquire a three-phase measured voltage signal of a grid connection point of the power system; A first frequency measurement module, used for converting the three-phase measured voltage signal into a square wave signal of the three-phase line voltage through a frequency measurement circuit, and calculating a first measurement frequency according to the square wave width of the square wave signal; A second frequency measurement module, used for performing analog-to-digital conversion on the three-phase measured voltage signal into a three-phase digital voltage signal, and calculating a second measurement frequency according to the three-phase line voltage corresponding to the three-phase digital voltage signal using a zero-crossing frequency algorithm; A third frequency measurement module, configured to calculate a third measurement frequency according to the three-phase digital voltage signal by using a positive sequence component frequency algorithm; A frequency protection execution module is used to execute a frequency protection action when the duration for which any one of the first measurement frequency, the second measurement frequency and the third measurement frequency meets the frequency protection startup condition exceeds a time threshold and at least one of the other two measurement frequencies meets the frequency protection startup condition.

10. A frequency protection device, characterized in that: The frequency protection device comprises: at least one processor; and a memory communicatively connected to the at least one processor; wherein, The memory stores a computer program executable by the at least one processor, and the computer program is executed by the at least one processor so that the at least one processor can perform the frequency protection method according to any one of claims 1 to 8.

11. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to implement the frequency protection method according to any one of claims 1 to 8 when executed.

12. A computer program product, characterized in that The computer program product comprises a computer program, which, when executed by a processor, implements the frequency protection method according to any one of claims 1 to 8.

Images