CN112986744A - Frequency fault tolerance detection method and system under transient fault condition of power system - Google Patents
Frequency fault tolerance detection method and system under transient fault condition of power system Download PDFInfo
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Abstract
The invention discloses a frequency fault tolerance detection method and a system under the condition of transient fault of a power systemx a (t) At a fixed sampling frequencyf s Sampling to obtain discrete power grid signal sampling sequencex(n) (ii) a Detecting whether the power system has transient fault, and if the power system has transient fault, sampling the power grid signalx(n) Reacquiring after transient fault, otherwise, aiming at discrete sequencex(n) Frequency shift filtering and frequency measurement are carried out to obtain estimated fundamental frequencyf est. The invention can reduce the frequency measurement error caused by the transient fault of the power system and can ensure that the frequency measurement still has enough precision under the condition that the power system has the transient fault.
Description
Technical Field
The invention relates to a frequency detection technology of a power system, in particular to a frequency fault-tolerant detection method and system under the condition of transient fault of the power system.
Background
Frequency is a key parameter of an electric power system, and the safe and stable operation of the whole power grid is often dependent on accurate measurement of the frequency. Therefore, frequency measurement is widely applied to the fields of power quality monitoring, synchronous phasor measurement, power system protection, state evaluation and the like. However, when a transient fault occurs in an actual power system, the accuracy of the grid frequency measurement is susceptible to the system transient fault due to distortion of the waveform of the grid signal. Particularly, when transient faults such as amplitude jump and phase jump occur in the system, the power grid signal has a discontinuity point, so that a large error is brought to a traditional power grid frequency measurement algorithm.
The frequency detection method of the existing power system mainly comprises the following steps: (1) discrete Fourier Transform algorithm (DFT): the method has the characteristics of simplicity, small calculated amount, easiness in system embedding realization and the like, and is widely applied to Phase Measurement Units (PMUs). However, under the asynchronous sampling condition, the DFT algorithm has inherent defects of spectrum leakage and barrier effect, so that the measurement result is not accurate. (2) The phasor measurement algorithm of the improved discrete Fourier transform: on the basis of a discrete Fourier transform algorithm, a frequency measurement method based on quasi-positive sequence DFT, a frequency measurement method based on adaptive filter coefficients, a phasor measurement algorithm based on Clarke transform and a frequency measurement method based on a filter bank are proposed to improve the precision of frequency measurement. However, the above algorithms all have an important drawback that when a transient fault occurs in the power system, the measurement result has a large error, thereby causing a malfunction of the relay protection device. This is because the transient fault of the power system may cause a discontinuous point in the waveform of the grid signal, and the conventional frequency measurement algorithm usually assumes that the waveform of the grid signal is continuous, and if the frequency detection is performed by using these algorithms including these discontinuous points, a large deviation may occur in the frequency detection result. (3) Phasor measurement algorithm for frequency protection action delay: in order to prevent the relay protection device from misoperation caused by frequency measurement errors in the transient fault of the power system, relevant inverter manufacturers provide a correction strategy, namely, after the frequency fluctuation is detected, the protection action delay operation of 2-5 seconds is adopted, so that the self-protection tripping misoperation caused by the frequency error measurement is avoided. However, when the system frequency is actually deviated, the delay operation added by the method can delay the solar inverter to take protective measures with serious consequences.
Disclosure of Invention
The technical problems to be solved by the invention are as follows: the invention can reduce frequency measurement errors caused by the transient fault of the power system and can ensure that the frequency measurement still has enough precision under the condition of the transient fault of the power system.
In order to solve the technical problems, the invention adopts the technical scheme that:
a frequency fault-tolerant detection method under the condition of transient fault of a power system comprises the following steps:
1) will simulate the grid signalx a (t) According to the sampling frequencyf s Sampling to obtain discrete power grid signal sampling sequencex(n)；
2) Detecting whether the power system has transient fault, and if the power system has transient fault, sampling the power grid signalx(n) Re-acquiring after the transient fault, and skipping to execute the step 1); otherwise, skipping to execute the next step;
3) for dispersionSequence ofx(n) Frequency shift filtering and frequency measurement are carried out to obtain estimated fundamental frequencyf est。
Optionally, the step 2) of detecting whether the power system has a transient fault includes: calculating a transient fault detection value by adopting a transient fault detection operator shown in the following formula;
ψ(ζ(n))=|ζ(n)-ζ(n+1)|
in the above formula, the first and second carbon atoms are,ψ(ζ(n) Is a transient fault detection value is detected,ζ(n) Andζ(n+1) respectively representnTime of day andna sampled voltage signal value at +1 time; and judging whether the transient fault detection value exceeds a preset transient fault judgment threshold value, if so, judging that the power system has a transient fault, otherwise, judging that the power system has no transient fault.
Optionally, anThe functional expression of the sampled voltage signal value at a time is as follows:
in the above formula, the first and second carbon atoms are,ζ(n) Means an arbitrarynThe value of the sampled voltage signal at a time,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,f r for the actual fundamental frequency of the power grid,
is composed ofhThe initial phase of the sub-harmonic is,tis time.
Optionally, step 2) is preceded by a step of determining a preset transient fault determination threshold, and a calculation function expression of the preset transient fault determination threshold is as follows:
in the above formula, the first and second carbon atoms are,A thr represents a preset transient fault determination threshold value,Ain order to simulate the amplitude of the grid signal,f r for the actual fundamental frequency of the power grid,f s is the sampling frequency.
Optionally, the power grid signal sampling sequence of step 2) is lastx(n) Retrieving after a transient fault means that a grid signal is sampled by a grid signal sampling sequencex(n) Sampling time of slavet start Is arranged ast start =t jump +T s Whereint jump In order to be the moment of occurrence of a transient fault,T s and the transient fault duration of the power grid signal.
Optionally, step 3) comprises:
3.1) sampling sequence of the obtained power grid signalx(n) Sampling sequence for obtaining frequency-shift power grid signal sampling power grid signal by carrying out signal frequency spectrum shiftingx s (n)；
3.2) sampling sequence of frequency-shift power grid signalx s (n) Filtering by a sliding mean convolution filter;
3.3) sampling sequence from filtered frequency-shifted network signalsx f (n) Selecting middle two data points to calculate frequency deviation deltaf；
3.4) normalizing the nominal frequency of the power systemf nom Plus frequency offset deltafObtaining an estimated fundamental frequencyf est。
Optionally, the power grid signal sampling sequence obtained in step 3.1) isx(n) The signal frequency spectrum shifting refers to the sampling sequence of the obtained power grid signalx(n) Multiplied by a frequency shift factor
WhereinjIs the unit of an imaginary number,ω nom represents a nominal normalized digital angular frequency,nis the sample sequence number.
Optionally, sliding in step 3.2)The mean convolution filter ispThe order sliding mean convolution filter has a calculation function expressed as follows:
in the above formula, the first and second carbon atoms are,h p (n) To representpAn order sliding mean convolution filter is used to filter,h av (m) Is a sub-moving average filter, and is,mis the serial number of the sliding average filter,Mis the length of the sub-sliding mean filter, and the length of the sub-sliding mean filterMTaking the value as the sampling frequencyf s And nominal frequency of power systemf nom The ratio of (a) to (b).
Optionally, calculating the frequency offset Δ in step 3.3)fThe function of (a) is expressed as follows:
in the above formula, the first and second carbon atoms are,n 1,n 2respectively filtered frequency shift power grid signal sampling sequencesx f (n) The serial numbers of the middle two data points selected in (1),u f (n 1) Is the sequence of values for the first data point,u f (n 2) Is the sequence of values for the second data point,Mis the length of the sub-sliding mean filter, and the length of the sub-sliding mean filterMTaking the value as the sampling frequencyf s And nominal frequency of power systemf nom The ratio of (a) to (b),f nom is the nominal frequency of the power system.
In addition, the invention also provides a frequency fault-tolerant detection system in case of a transient fault of a power system, which comprises a microprocessor and a memory which are connected with each other, wherein the microprocessor is programmed or configured to execute the steps of the frequency fault-tolerant detection method in case of the transient fault of the power system.
Furthermore, the present invention also provides a computer-readable storage medium having stored therein a computer program programmed or configured to execute the method of frequency fault-tolerant detection in case of a transient fault of the power system.
Compared with the prior art, the invention has the following advantages:
1. aiming at the problem that the error is increased due to the transient fault in the traditional frequency shift filtering method, the invention combines the transient fault detection on the basis of the frequency shift filtering, can reduce the influence of the transient fault on the measurement, can reduce the frequency measurement error caused by the transient fault of the power system, and can ensure that the frequency measurement still has enough precision under the condition that the transient fault occurs in the power system.
2. The invention can be used for a three-phase system and a single-phase system, and has the advantage of good universality.
Drawings
FIG. 1 is a schematic diagram of a basic flow of a method according to an embodiment of the present invention.
Fig. 2 is an example of a detection result of a grid signal when a transient fault exists in the embodiment of the present invention.
FIG. 3 is a graph showing the magnitude-frequency response of different order sliding mean convolution filters according to an embodiment of the present invention.
Detailed Description
As shown in fig. 1, the frequency fault-tolerant detection method in the case of the transient fault of the power system in the embodiment includes:
1) will simulate the grid signalx a (t) According to the sampling frequencyf s Sampling to obtain discrete power grid signal sampling sequencex(n)；
2) Detecting whether the power system has transient fault, and if the power system has transient fault, sampling the power grid signalx(n) Re-acquiring after the transient fault, and skipping to execute the step 1); otherwise, skipping to execute the next step;
3) for discrete sequencesx(n) Frequency shift filtering and frequency measurement are carried out to obtain estimated fundamental frequencyf est。
Transient faults (transient faults) are system short-circuit faults which are usually caused by lightning or by the fact that a trunk, livestock and the like contact a power transmission line and can be recovered by cutting off current for a short time; more than 90% of faults in the power system are transient faults or augmented by transient faults. Under transient faults, the frequency, amplitude and waveform of the voltage are changed violently, and how to deal with the operation of the relay protection device, namely whether a relay protection switch is started or not to cut off a line, is achieved. At this time, the monitored frequency value has a large error, so the frequency needs to be measured after the action of the protection device is finished and the transient fault is finished. In order to achieve accurate detection of the transient fault, as an optional implementation manner, the detecting whether the transient fault occurs in the power system in step 2) of this embodiment includes: calculating a transient fault detection value by adopting a transient fault detection operator shown in the following formula;
ψ(ζ(n))=|ζ(n)-ζ(n+1)| （1）
in the above formula, the first and second carbon atoms are,ψ(ζ(n) Is a transient fault detection value is detected,ζ(n) Andζ(n+1) respectively representnTime of day andna sampled voltage signal value at +1 time; and judging whether the transient fault detection value exceeds a preset transient fault judgment threshold value, if so, judging that the power system has a transient fault, otherwise, judging that the power system has no transient fault.
In this embodiment, the firstnThe functional expression of the sampled voltage signal value at a time is as follows:
in the above formula, the first and second carbon atoms are,ζ(n) Means an arbitrarynThe value of the sampled voltage signal at a time,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,f r for the actual fundamental frequency of the power grid,
is composed ofhThe initial phase of the sub-harmonic is,tis time.
In this embodiment, step 2) further includes, before determining the preset transient fault determination threshold, where a calculation function expression of the preset transient fault determination threshold is as follows:
in the above formula, the first and second carbon atoms are,A thr represents a preset transient fault determination threshold value,Ain order to simulate the amplitude of the grid signal,f r for the actual fundamental frequency of the power grid,f s is the sampling frequency.
In this embodiment, step 2) further includes the following step of deriving and determining a transient fault detection operator:
s1) determining a simulated grid signal considering that the actual grid is usually polluted by a harmonic sourcex a (t) At a certain momenttThe model of (a) is:
in the above formula, the first and second carbon atoms are,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,f r for the actual fundamental frequency of the power grid,
is composed ofhThe initial phase of the sub-harmonic is,tis time.
S2) to analog grid signalsx a (t) At a certain momenttObtaining the simulated power grid signal by model derivationx a (t) Derivative of (2)
：
In the above formula, the first and second carbon atoms are,
for simulating grid signalsx a (t) The derivative of (c).
S3) to analog grid signalsx a (t) Derivative of (2)
Both sides are divided by 2πf r And is defined as the value of the sampled voltage signalζ(t)：
S4) setting the sampling frequency asf s And sampling the voltage signal valueζ(t) Respectively at adjacent timet 1Andt 2sampling at a moment, then having-t 1-t 2|=T s =1/f s WhereinT s For the duration of the transient fault of the power grid signal, a transient fault detection operator may be defined as:
in the above formula, the first and second carbon atoms are,ψ(ζ(t) In order to be a transient fault detection operator,ζ(t 1) Andζ(t 2) Are respectively ast 1Andt 2the value of the sampled voltage signal at a time,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,f r for the actual fundamental frequency of the power grid,
is composed ofhThe initial phase of the sub-harmonic is,tis time. According to the relevant national standard, the voltage total harmonic distortion rate can not exceed a preset threshold (for example, GB/T14549-93 specifies that the voltage total harmonic distortion rate can not exceed 5%), so that the transient fault detection operator can detect the transient fault when the actual voltage signal has no transient faultψ(ζ(t) The preset transient fault judgment threshold value obtained by the calculation of the formula (3) is not exceeded normallyA thr 。
S5) to the sampled voltage signal valueζ(t) Discretization processing is carried out, and the following results can be obtained:
in the above formula, the first and second carbon atoms are,
sampling sequences for grid signalsx(n) Derivative, grid signal sampling sequencex(n-1) For the last sequence of samples of the grid signal,f r for the actual fundamental frequency of the power grid,f s is the sampling frequency, where n =2,3, …,N，Nand (4) sampling the total number of the sequences for the power grid signal. If the transient fault of phase jump exists in the voltage signal of the power grid, the voltage signal is not conductive at the jump position, namely, a first-class discontinuity point exists, so that the numerical value calculated by the formula (7) is far larger than the preset transient fault judgment threshold valueA thr 。
For example, a certain grid signal with a phase jumps 1(t) The expression is as follows:
in the above formula, the first and second carbon atoms are,A 1is the signal amplitude value of =1 p.u.,f 1=50Hz is the fundamental frequency,t 1=0.04s is the phase jump occurrence time,
and the phase jump quantity is =30 DEG, and the sampling frequency of the signal is 6.4 kHz. The actual voltage signal, the resulting amplitude of the transient fault detection operator and the threshold value are shown in fig. 2, respectively. As can be seen from fig. 2, the amplitude calculated by the formula (7) has a sudden change during the phase jump, and the detected amplitude is much larger than the predetermined transient fault judgment thresholdA thr . Therefore, the specific moment when the transient fault occurs can be accurately positioned by the transient fault detection operator and the threshold detection.
In this embodiment, the power grid signal sampling sequence for sampling the power grid signal in step 2-x(n) Retrieving after a transient fault means that a grid signal is sampled by a grid signal sampling sequencex(n) Sampling time of slavet start Is arranged ast start =t jump +T s Whereint jump In order to be the moment of occurrence of a transient fault,T s and the transient fault duration of the power grid signal.
In this embodiment, step 3) is configured to accurately estimate the frequency of the voltage signal by using a frequency shift filtering method after obtaining the occurrence time of the transient fault, where step 3) includes:
3.1) sampling sequence of the obtained power grid signalx(n) Carrying out signal frequency spectrum shifting to obtain a frequency-shifting power grid signal sampling sequencex s (n)；
3.2) sampling sequence of frequency-shift power grid signalx s (n) Filtering by a sliding mean convolution filter;
3.3) sampling the grid signal sampling sequence from the filtered frequency-shifted grid signalx f (n) Selecting middle two data points to calculate frequency deviation deltaf；
3.4) normalizing the nominal frequency of the power systemf nom Plus frequency offset deltafObtaining an estimated fundamental frequencyf est。
In this embodiment, the power grid signal sampling sequence obtained in step 3.1) is obtainedx(n) Performing signal spectrum shiftingShifting refers to the sampling sequence of the obtained electric network signalx(n) Multiplied by a frequency shift factor
WhereinjIs the unit of an imaginary number,ω nom represents a nominal normalized digital angular frequency,nis the sample sequence number.
Step 1) simulating a power grid signalx a (t) According to the sampling frequencyf s =1/T s Carrying out uniform sampling to obtain a discrete power grid signal sampling sequencex(n) The following can be obtained:
in the above formula, the first and second carbon atoms are,x(n) In order to sample the sequence of the grid signal,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,ω r in order to actually normalize the angular frequency of the signal,
is composed ofhThe initial phase of the subharmonic. Wherein the sampling numbernSatisfy- ∞<n<Infinity, actual normalized angular frequencyω r Is calculated in a manner thatω r =2πf r /f s . In this embodiment, the sampling frequency is selectedf s For nominal frequency of power systemf nom Integer multiples of (d), i.e.:f s =Mf nom then there isω r =2πf r /( Mf nom ). Discrete power grid signal sampling sequence according to Euler formulax(n) The rewrite is:
in the above formula, the first and second carbon atoms are,x(n) In order to sample the sequence of the grid signal,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,ω r in order to actually normalize the angular frequency of the signal,
is composed ofhThe initial phase of the subharmonic. Multiplying both sides of equation (11) by a frequency shift factor
Then, there are:
in the above formula, the first and second carbon atoms are,x s (n) Is a power grid signal sampling sequence after frequency shift,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,ω r in order to actually normalize the angular frequency of the signal,
is composed ofhThe initial phase of the sub-harmonic is,ω nom for a nominal normalized angular frequency, the formula of the calculation function is:ω nom =2πf nom /f s =2π/M. As shown in the formula (12), the grid signal sampling sequence after frequency shiftx s (n) Respectively with frequency components ofhω r And- hω r Is moved to hω r +ω nom And- hω r +ω nom 。
Step 3.2) for sampling the frequency-shifted grid signal into a grid signal sampling sequencex s (n) Filtering with a moving average convolution filter, also called a moving average filter, whose time domain expression is：
In the above formula, the first and second carbon atoms are,h av (n) Which is representative of a moving average filter,Mis the length of the sub-sliding mean filter, and the length of the sub-sliding mean filterMTaking the value as the sampling frequencyf s And nominal frequency of power systemf nom The ratio of (a) to (b). By performing a Discrete Time Fourier Transform (DTFT) on equation (13), the frequency spectrum of the sliding average filter can be obtained as follows:
in the above formula, the first and second carbon atoms are,h av (e jω ) Which represents the frequency spectrum of the moving average filter,ωis a digital angular frequency.
Further, the amplitude-frequency response can be obtained as follows:
in the above formula, [ mu ] fh av (e jω ) I denotes the frequency spectrum of the sliding mean filter whenω=2πk/M，k=0,1,…,M-1 hour, spectrum of sliding mean filterh av (e jω ) L =0. Sampling sequence of power grid signal after frequency shiftx s (n) The digital angular frequency of (a) is divided into a negative frequency partω n (h)=(-hω r +ω nom ) And a positive frequency part of (ω p (h)=(hω r +ω nom ) Two portions). Due to the fact thathWhen the ratio is not less than 1,ω n (1)=ω nom – ω r 0, substitute it into formula (15)Can obtainh(e jωn(1)) 1, whereinh(e jωn(1)) And | represents the fundamental amplitude. In the same way, whenhNot equal to 1, ah(e jωn(h)) | ≈ 0 and ≈h(e jωp(h)) | ≈ 0 where | ≈h(e jωn(h)) | represents the amplitude of the positive frequency, |h(e jωp(h)) And | represents a negative frequency amplitude. I.e. only the frequency component after filtering by the mean filterω nom –ω r Is well preserved and other frequency components are effectively filtered.
For better suppression, the sliding mean convolution filter in step 3.2) of this embodiment ispThe order sliding mean convolution filter has a calculation function expressed as follows:
in the above formula, the first and second carbon atoms are,h p (n) To representpAn order sliding mean convolution filter is used to filter,h av (m) Is a sub-moving average filter, and is,mis the serial number of the sliding average filter,Mis the length of the sub-sliding mean filter, and the length of the sub-sliding mean filterMTaking the value as the sampling frequencyf s And nominal frequency of power systemf nom The ratio of (a) to (b).pOrder sliding mean convolution filter length ofp(M-1)+1. Fig. 3 shows the amplitude-frequency characteristic of the 1 st to 4 th order sliding mean convolution filter. From FIG. 3 and the convolution theorem, it can be seen that the rejection capability of the sliding mean convolution filter depends on the filter orderpThe increase and the strength.
In this embodiment, the frequency offset Δ is calculated in step 3.3)fThe function of (a) is expressed as follows:
in the above formula, the first and second carbon atoms are,n 1,n 2respectively filtered frequency shift power grid signal sampling sequencesx f (n) The serial numbers of the middle two data points selected in (1),u f (n 1) Is the sequence of values for the first data point,u f (n 2) Is the sequence of values for the second data point,Mis the length of the sub-sliding mean filter, and the length of the sub-sliding mean filterMTaking the value as the sampling frequencyf s And nominal frequency of power systemf nom The ratio of (a) to (b),f nom is the nominal frequency of the power system.
Power grid signal sampling sequence after frequency shiftx s (n) After filtering by the sliding mean convolution filter, it can be expressed as:
in the above formula, the first and second carbon atoms are,x f (n) Is a power grid signal sampling sequence filtered by a sliding mean convolution filter,x s (n) Representing the frequency shifted grid signal sample sequence,h p (n) To representpAn order sliding mean convolution filter is used to filter,A h is composed ofhThe magnitude of the sub-harmonics,ω nom in order to be a nominal normalized angular frequency,ω r in order to actually normalize the angular frequency of the signal,nis a sequence number, and is a serial number,
is the fundamental initial phase. From a sequence of samples of a grid signal filtered by a sliding mean convolution filterx f (n) Two points in the middlex f (n 1) Andx f (n 2) Then there are:
in the above formula, the first and second carbon atoms are,n 1,n 2respectively filtered frequency shift power grid signal sampling sequencesx s (n) The serial numbers of the middle two data points selected in (1),u f (n 1) Is the sequence of values for the first data point,u f (n 2) Is the sequence of values for the second data point,ω nom in order to be a nominal normalized angular frequency,ω r the angular frequency is actually normalized. Combined vertical type (19) andf nom =f r+Δfthen there are:
thus, the calculated frequency offset Δ of equation (17) can be obtainedfIs used for the functional expression of (1).
In summary, in order to reduce the frequency measurement error caused by the transient fault of the power system, the method of the present embodiment first constructs a fault detection operator to detect the occurrence of the transient fault in real time. And if the transient fault is detected, marking the sampling time interval of the transient fault and acquiring the signal sampling sequence again after the transient fault interval. And if the transient fault is not detected, adopting frequency shift filtering to measure the frequency of the power grid in real time. The transient fault detection operator in the algorithm can accurately and effectively track transient fault data in the power grid signal in real time. In order to verify and calculate the effectiveness and feasibility of the algorithm, a large number of simulation experiments are performed in the context of the existence of different phase angle jump values, different sag occurrence moments, different grid signal models, a PSCAD simulation model based on an IEEE 118 bus and the like in a power system. Simulation experiment results show that the method can effectively identify and mark the error frequency when the power system has transient faults and accurately measure the power system frequency when the power system has no faults. In addition, the method of the embodiment can also be used for phasor measurement of single-phase and three-phase systems.
In addition, the present embodiment also provides a frequency fault-tolerant detection system in case of a transient fault of a power system, which includes a microprocessor and a memory connected to each other, wherein the microprocessor is programmed or configured to execute the steps of the aforementioned frequency fault-tolerant detection method in case of a transient fault of a power system.
Furthermore, the present embodiment also provides a computer-readable storage medium having stored therein a computer program programmed or configured to execute the aforementioned frequency fault-tolerant detection method in the event of a transient fault of a power system.
As will be appreciated by one skilled in the art, embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-readable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein. The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the application. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks. These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks. These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may occur to those skilled in the art without departing from the principle of the invention, and are considered to be within the scope of the invention.
Claims (10)
1. A frequency fault-tolerant detection method under the condition of transient fault of a power system is characterized by comprising the following steps:
1) will simulate the grid signalx a (t) According to the sampling frequencyf s Sampling to obtain discrete power grid signal sampling sequencex(n)；
2) Detecting whether the power system has transient fault, and if the power system has transient fault, sampling the power grid signalx(n) Re-acquiring after the transient fault, and skipping to execute the step 1); otherwise, skipping to execute the next step;
3) for discrete sequencesx(n) Frequency shift filtering and frequency measurement are carried out to obtain estimated fundamental frequencyf est；
Step 2) detecting whether the power system has a transient fault comprises the following steps: calculating a transient fault detection value by adopting a transient fault detection operator shown in the following formula;
ψ(ζ(n))=|ζ(n)-ζ(n+1)|
in the above formula, the first and second carbon atoms are,ψ(ζ(n) Is temporarily madeThe value of the state fault detection is,ζ(n) Andζ(n+1) respectively representnTime of day andna sampled voltage signal value at +1 time; and judging whether the transient fault detection value exceeds a preset transient fault judgment threshold value, if so, judging that the power system has a transient fault, otherwise, judging that the power system has no transient fault.
2. The method of claim 1, wherein the first step is a frequency fault tolerant detection method in case of a transient fault in the power systemnThe functional expression of the sampled voltage signal value at a time is as follows:
in the above formula, the first and second carbon atoms are,ζ(n) Means an arbitrarynThe value of the sampled voltage signal at a time,His the highest order of the harmonic wave,hin the order of the harmonics,A h is composed ofhThe magnitude of the sub-harmonics,f r for the actual fundamental frequency of the power grid,
is composed ofhThe initial phase of the sub-harmonic is,tis time.
3. The method according to claim 1, wherein step 2) is preceded by a step of determining a preset transient fault determination threshold, and the calculation function expression of the preset transient fault determination threshold is as follows:
in the above formula, the first and second carbon atoms are,A thr represents a preset transient fault determination threshold value,Ain order to simulate the amplitude of the grid signal,f r for the actual fundamental frequency of the grid，f s Is the sampling frequency.
4. The method according to claim 1, wherein the grid signal sampling sequence is mapped in step 2) to a frequency fault-tolerant detection method in case of a transient fault in the power systemx(n) Retrieving after a transient fault means that a power grid signal sampling sequence is mapped to a mapping tablex(n) Sampling time of slavet start Is arranged ast start =t jump +T s Whereint jump In order to be the moment of occurrence of a transient fault,T s and the transient fault duration of the power grid signal.
5. The method for detecting frequency fault tolerance in the case of a transient fault in a power system according to claim 1, wherein step 3) comprises:
3.1) sampling sequence of the obtained power grid signalx(n) Carrying out signal frequency spectrum shifting to obtain a frequency-shifting power grid signal sampling sequencex s (n)；
3.2) sampling sequence of frequency-shift power grid signalx s (n) Filtering by a sliding mean convolution filter;
3.3) sampling sequence from filtered frequency-shifted network signalsx f (n) Selecting middle two data points to calculate frequency deviation deltaf；
3.4) normalizing the nominal frequency of the power systemf nom Plus frequency offset deltafObtaining an estimated fundamental frequencyf est。
6. The method for detecting frequency fault tolerance in case of transient fault of power system according to claim 5, wherein the sampling sequence of grid signal obtained in step 3.1) isx(n) The signal frequency spectrum shifting refers to the sampling sequence of the obtained power grid signalx(n) Multiplied by a frequency shift factor
WhereinjIs the unit of an imaginary number,ω nom represents a nominal normalized digital angular frequency,nis the sample sequence number.
7. The method for detecting frequency fault tolerance in case of transient fault in power system according to claim 5, wherein the step 3.2) is performed by using a sliding mean convolution filterpThe order sliding mean convolution filter has a calculation function expressed as follows:
in the above formula, the first and second carbon atoms are,h p (n) To representpAn order sliding mean convolution filter is used to filter,h av (m) Is a sub-moving average filter, and is,mis the serial number of the sliding average filter,Mis the length of the sub-sliding mean filter, and the length of the sub-sliding mean filterMTaking the value as the sampling frequencyf s And nominal frequency of power systemf nom The ratio of (a) to (b).
8. The method for detecting frequency fault tolerance under transient fault condition of power system as claimed in claim 5, wherein in step 3.3), the frequency deviation Δ is calculatedfThe function of (a) is expressed as follows:
in the above formula, the first and second carbon atoms are,n 1,n 2respectively filtered frequency shift power grid signal sampling sequencesx f (n) The serial numbers of the middle two data points selected in (1),u f (n 1) Is the sequence of values for the first data point,u f (n 2) Is the sequence of values for the second data point,Mfiltering for sub-sliding meansLength of the filter, and length of the sub-sliding mean filterMTaking the value as the sampling frequencyf s And nominal frequency of power systemf nom The ratio of (a) to (b),f nom is the nominal frequency of the power system.
9. A frequency fault-tolerant detection system in case of a transient fault in an electric power system, comprising a microprocessor and a memory connected to each other, characterized in that the microprocessor is programmed or configured to perform the steps of the method for frequency fault-tolerant detection in case of a transient fault in an electric power system according to any one of claims 1 to 8.
10. A computer-readable storage medium having stored thereon a computer program programmed or configured to perform a method for frequency fault-tolerant detection in case of a transient fault in a power system according to any one of claims 1 to 8.
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