CN107741544A - A kind of isolated island detection decision method of distributed photovoltaic power generation system - Google Patents
A kind of isolated island detection decision method of distributed photovoltaic power generation system Download PDFInfo
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Abstract
A kind of isolated island detection decision method of distributed photovoltaic power generation system, belong to the isolated island detection technique field of photovoltaic generating system, by the component coefficient for separating the fundamental wave in mains voltage signal, triple-frequency harmonics, quintuple harmonics, and carry out time domain, frequency-domain analysis calculating, the setting of judgement threshold is tracked in conjunction with dynamic, decision threshold, amplitude threshold are such as mutated, avoids the presence of isolated island check frequency to the full extent, improves detection, judgement precision.
Description
Technical field
The invention belongs to the isolated island detection technique field of photovoltaic generating system, and in particular to a kind of distributed photovoltaic system
Isolated island detects decision method.
Background technology
Because it is close to load centre, have reduces the transmission power loss of power distribution network, improves electric energy distributed photovoltaic system
Service efficiency the advantages of, obtained country widely popularize, more and more installed extensively simultaneously in enterprise, resident
Use.Island phenomenon often occurs in distributed photovoltaic system in the application, this phenomenon refer to when power network because failure cause tripping operation or
During interruption maintenance, the electricity generation system of each user terminal fails to detect the state in time and continue to generate electricity, and is formed certainly with own load
By independent islanded system；The generation of island phenomenon can greatly jeopardize the personal safety of maintenance personal on power network line, also may be used
The quality of power supply is influenceed to cause certain impact to the protection switch equipment in distribution system, and when power system restoration is normal
It is asynchronous and cause the loss phase of distributed photovoltaic system to power that phase in short-term can be produced.Therefore must be to distributed photovoltaic power generation
The island phenomenon of system detect and handle in time, to avoid unnecessary harm.
Harmonic detection is most commonly used that in existing passive island detection method, is realized based on Fast Fourier Transform (FFT)
's；And traditional fast fourier transform algorithm can accurately not judge harmonic wave occur at the time of, the duration, this is due to
Harmonic content very little in power network, traditional algorithm is used alone and is possible to meeting because calculating mutation time inaccuracy, harmonic content meter
It is dumb integral error, judgement threshold setting to be present in calculation, and then causes the check frequency into isolated island.
The content of the invention
The technical problem to be solved in the present invention is to provide a kind of isolated island of distributed photovoltaic system to detect decision method, passes through
Fundamental wave, triple-frequency harmonics, the component coefficient of quintuple harmonics in mains voltage signal are separated, and carries out time domain, frequency-domain analysis calculating,
The setting of judgement threshold is tracked in conjunction with dynamic, avoids the presence of isolated island check frequency to the full extent, detection is improved, judges
Precision.
The technological means that the present invention uses is：A kind of isolated island detection decision method of distributed photovoltaic power generation system, including
Following steps：
Step A. samples to the output voltage waveforms of distributed photovoltaic power generation system, sample frequency 6.4kHz；
Step B. carries out wavelet transformation to sampled signal, obtains including at least fundamental wave, triple-frequency harmonics, the component system of quintuple harmonics
Number；
Step C. obtains the average value D of each component coefficient absolute value obtained in step B in a data windowmeanAnd absolutely
To the maximum D of valuemax, calculate (Dmax-Dmean)/ Dmean:
If result of calculation is not more than the mutation decision threshold pre-set, N is set to 0；
Otherwise, N=N+1, wherein N represent the continuous occurrence number that result of calculation is more than the mutation decision threshold pre-set；
The component coefficient of the fundamental wave obtained in step B, triple-frequency harmonics, quintuple harmonics is filtered and inverse wavelet transform by step D.
And then time domain waveform is obtained, then Fast Fourier Transform (FFT) is carried out, fundamental wave, triple-frequency harmonics, the virtual value of quintuple harmonics are extracted afterwards
E1、E2、E3, E is calculated respectively2/ E1*100%、E3/ E1*100%：
If the amplitude threshold that two result of calculations are not pre-set both greater than, M are set to 0；
Otherwise, M=M+1, wherein M represent the continuous occurrence number that two result of calculations are both greater than the amplitude threshold pre-set,；
Step E. calculates mutation duration t1 and amplitude mutation duration t2 according to current N, M respectively, if t1 is more than in advance
The mutation duration threshold and t2 first set is more than the amplitude duration threshold pre-set, then it is assumed that there is isolated island,
Send trip command；
Step F. to the cycle of pusher 1/4, repeats the above steps data window.
Further, in the step C, a data window is 20ms.
Further, the computational methods of mutation duration t1：It is each to judge timing node, according to formula（N-1）
T/4 is calculated, and result of calculation is designated as to be mutated duration t1, T represents the data window cycle；The amplitude is mutated duration t2
Computational methods：It is each to judge timing node, according to formula（M-1）T/4 is calculated, when result of calculation is designated as into amplitude mutation persistently
Between t2；In above formula, T represents the data window cycle.
Further, in step C, mutation decision threshold is dynamic setting, and its method to set up comprises the following steps：
Step 1）Mutation decision threshold is arranged to 0 during function input initialization；
Step 2）Judge to be mutated whether decision threshold is 0, if 0, then the component coefficient of fundamental wave is arranged to mutation and judges valve
Value；
Step 3）Obtain the average value D of each component coefficient absolute value obtained in a data window in step BmeanAnd definitely
The maximum D of valuemax, calculate (Dmax-Dmean)/ Dmean, and result of calculation is stored；
Step 4）2 seconds are often spent, if T1 is equal to 0, the data when premutation decision threshold will be not more than in the result of calculation of storage
Arithmetic mean calculating is carried out, then mutation decision threshold is arranged to by 2 times of arithmetic average result；
If T1 is not equal to 0, mutation duration t1 is calculated according to current time and T1, if t1 is more than mutation duration door
2-5 times of sill, the data in the result of calculation of storage are subjected to arithmetic mean calculating, then 1.2 times of arithmetic average result are set
Mutation decision threshold is set to, T1 is set to 0.
Further, in step D, the amplitude threshold is Ref1 and Ref2 respectively, and to be set dynamically, its method to set up
Comprise the following steps：
Step 1）Amplitude threshold Ref1 and Ref2 are arranged to 1 during function input initialization；
Step 2）Calculate fundamental wave, triple-frequency harmonics, the virtual value E of quintuple harmonics1、E2、E3, E is calculated respectively2/ E1*100%、E3/
E1* 100%, and two result of calculations are each stored by group；
Step 3）1.6 s are often crossed, if T2 is equal to 0, each self-corresponding current width will be not more than in the result of calculation of two groups of storages
The data of value threshold carry out arithmetic mean calculating respectively, then are arranged to each self-corresponding by 2 times of two arithmetic average results
Amplitude threshold；
If T2 is not equal to 0, amplitude mutation duration t2 is calculated according to current time and T2, mutation is held if t2 is more than amplitude
Data in the result of calculation of two groups of storages are carried out arithmetic mean calculating, then two are counted by continuous 2-5 times of time period threshold respectively
1.2 times of average results are arranged to each self-corresponding amplitude threshold, and T2 is set to 0.
Further, the mutation duration threshold is 1s, and the amplitude duration threshold is 800ms.
Further, the sample frequency in the step A is controlled by high-speed dsp processor.
Further, sampled signal is carried out in the step B wavelet transformation using Daubechies4 wave filters and
Mallat fast algorithms.
Further, the component coefficient in the step B is wavelet coefficient di (n), i=1,2,3,4,5,6,
In above formula, n represents discrete sampling time straw line, di(n) fundamental wave wavelet coefficient, corresponding sub-band are represented as [0, fs/
64], remaining wavelet coefficient di(n), i=2, sub-band is [f corresponding to 3,4,5,6s/28-i, fs/27-i], fsRepresent sampling
Frequency.
Further, the means being filtered in the step D to the component coefficient of fundamental wave, triple-frequency harmonics, quintuple harmonics
Using passband comb filter.
Distributed photovoltaic power generation system is to export power frequency 50Hz cycle Sine wave by DC inversion by photovoltaic DC-to-AC converter,
Itself output waveform in proportion contained by odd harmonic it is higher, such as in low-frequency range third and fifth harmonic change table
Existing is more obvious；Therefore the present invention mainly passes through high-speed dsp processor, Daubechies4 wave filters, passband comb filtering
The hardware such as device and Mallat fast algorithms, inverse wavelet transform algorithm, fast fourier transform algorithm, are realized to line voltage ripple
Fundamental wave in shape, three times, quintuple harmonics characteristic quantity extracted, judge threshold further according to dynamic, and then judge distributed photovoltaic
Electricity generation system whether there is island phenomenon.
Beneficial effect caused by the present invention：1）The present invention by being filtered to the voltage signal of power network and wavelet transformation,
Can accurately analyze, differentiate the mutation time of origin of harmonic wave such as third and fifth harmonic, and according to after wavelet reconstruction when
It is amplitude that domain waveform, which calculates higher harmonic content, is combining dynamic tracking judgement threshold as being mutated decision threshold, amplitude threshold
Setting so that the differentiation of island phenomenon more accurately without blindly, reducing the presence of check frequency, ensureing distribution to greatest extent
The reliance security that formula photovoltaic generating system is incorporated into the power networks；2）Dynamic tracking judgement threshold is such as mutated decision threshold, amplitude door
The setting of sill, can solve the blindness of judgement threshold setting in the past, and big degree reduces check frequency and increases decision method
Adaptivity and accuracy, so that this method is more accurate, reaction is rapider.
Brief description of the drawings
Fig. 1 is the FB(flow block) of the present invention.
Embodiment
Referring to accompanying drawing 1, the isolated island detection decision method of distributed photovoltaic power generation system provided by the invention, is based at a high speed
The hardware such as DSP Processor, Daubechies4 wave filters, passband comb filter and Mallat fast algorithms, inverse wavelet transform
Algorithm, fast fourier transform algorithm comprise the following steps come what is realized：
Step A. samples to the output voltage waveforms of distributed photovoltaic power generation system, sample frequency 6.4kHz；It is above-mentioned to adopt
Sample frequency is controlled by high-speed dsp processor；As shown in figure 1, the sample of sampling is sampling queue f (n)；
Step B. carries out wavelet transformation to sampled signal, obtains including at least fundamental wave, triple-frequency harmonics, the component system of quintuple harmonics
Number；The component coefficient carried out to sampled signal after wavelet transformation is wavelet coefficient di(n), i=1,2,3,4,5,6,
Wherein, the wavelet transform filter group employed in wavelet transformation is Daubechies4 wave filters, and wavelet coefficient uses
Mallat fast algorithms calculate；
In above formula, n represents discrete sampling time straw line, di(n) fundamental wave wavelet coefficient, corresponding sub-band are represented as [0, fs/
64], remaining wavelet coefficient di(n), i=2, sub-band is [f corresponding to 3,4,5,6s/28-i, fs/27-i], fsRepresent sampling
Frequency；
The scope of above-mentioned sub-band be followed successively by [0,100], [100,200], [200,400], [400,800], [800,
1600]、 [1600,3200]HZ。
Using the division of the harmonic band of above-mentioned sampled signal, it can make each sub-band as far as possible containing single harmonic wave point
Desired harmonic signal, can effectively be distributed in each sub-band by amount, make the wavelet coefficient that calculates more representative, especially
It can be such that third and fifth harmonic respectively falls near second sub-band center and the 3rd sub-band center.
Step C. obtains the average value D of each component coefficient absolute value obtained in step B in a data windowmeanWith
And the maximum D of absolute valuemax, calculate (Dmax-Dmean)/ Dmean：
If result of calculation is not more than the mutation decision threshold pre-set, N is set to 0；
Otherwise, N=N+1, wherein N represent the continuous occurrence number that result of calculation is more than the mutation decision threshold pre-set；It is above-mentioned
When result of calculation is more than the mutation decision threshold pre-set, represents current data window and harmonic wave catastrophe point occur.
Step D. by the fundamental wave obtained in step B, triple-frequency harmonics, quintuple harmonics component coefficient be filtered it is anti-with small echo
Convert and then obtain time domain waveform, then carry out Fast Fourier Transform (FFT), extract fundamental wave afterwards, triple-frequency harmonics, quintuple harmonics have
Valid value E1、E2、E3, E is calculated respectively2/ E1*100%、E3/ E1*100%：
If the amplitude threshold that two result of calculations are not pre-set both greater than, M are set to 0；
Otherwise, M=M+1, wherein M represent the continuous occurrence number that two result of calculations are both greater than the amplitude threshold pre-set；On
When stating the amplitude threshold that two result of calculations appearance are both greater than pre-set, the harmonic content i.e. amplitude of current data window is represented
The change of matter occurs.
In step D, the means being filtered for the component coefficient of fundamental wave, triple-frequency harmonics, quintuple harmonics are passband combs
Shape wave filter, passband comb filter are realized based on Fast Fourier Transform (FFT), can make the width of fundamental frequency harmonic secondary frequencies
Value response is 1, i.e., by fundamental frequency and the harmonic frequency of fundamental frequency integral multiple, carries out denoising Processing.
Step E. is according to Na、MaMutation duration t1 and amplitude mutation duration t2 are calculated respectively, if t1 is more than in advance
The mutation duration threshold and t2 first set is more than the amplitude duration threshold pre-set, then it is assumed that there is isolated island,
Send trip command；If mutation duration t1 and amplitude mutation duration t2 both greater than do not pre-set, each corresponded to
Mutation duration threshold and amplitude duration threshold, then it is assumed that system is stable, island phenomenon does not occur.Because small echo becomes
Change is swift in response, and Fourier transformation assignment calculates accurately, but has integration to be delayed, thus two judge setting for duration threshold
Put difference：Burst duration threshold is set as 1s, and amplitude duration threshold is set as 800ms.
Step F. to the cycle of pusher 1/4, repeats the above steps data window.One data window is 20ms, between calculating
1/4 cycle is divided into, the data window calculated every time circulates this process to 1/4 cycle of pusher.
The computational methods of above-mentioned middle mutation duration t1：It is each to judge timing node, according to formula（N-1）T/4 is calculated,
Result of calculation is designated as to be mutated duration t1, T represents the data window cycle；The calculating of above-mentioned middle amplitude mutation duration t2
Method：It is each to judge timing node, according to formula（M-1）T/4 is calculated, and result of calculation is designated as into amplitude mutation duration t2；
In above formula, T represents the data window cycle.It is also understood that mutation duration t1 and amplitude are mutated duration t2
Meter sensitivity is 5ms, if result of calculation has mutation situation twice in succession, mutation or amplitude mutation duration are exactly
5ms, if continuously having calculated mutation three times, the duration is exactly 10ms, if continuous four calculating has mutation, when continuing
Between be exactly 15ms, by that analogy.
By the mutation decision threshold in step C and D, amplitude threshold be set to dynamic tracking judgement threshold, can solve with
Toward the blindness of judgement threshold setting, check frequency is reduced to the full extent, increases the adaptivity and accuracy of decision method,
So that the method for the present invention judges that more accurate, reaction is more rapid；And conventional static judgement threshold, can only be according to warp
Test value and one very big judgement threshold value is set, so directly result in the blind area increase of judgement, and empirical value is not yet
Together, it is difficult to suit measures to local conditions.Therefore, the dynamic setting of mutation decision threshold, amplitude threshold of the invention is equivalent to Adaptable System
Real-time condition, the mutation situation of higher hamonic wave can be distinguished from matter, makes judgement more accurate.
Therefore, the method to set up of the mutation decision threshold of dynamic setting comprises the following steps：
Step 1）Mutation decision threshold is arranged to 0 during function input initialization；
Step 2）Judge to be mutated whether decision threshold is 0, if 0, then the component coefficient of fundamental wave is arranged to mutation and judges valve
Value；
Step 3）Obtain the average value D of each component coefficient absolute value obtained in a data window in step BmeanAnd definitely
The maximum D of valuemax, calculate (Dmax-Dmean)/ Dmean, and result of calculation is stored；
Step 4）2 seconds are often spent, if T1 is equal to 0, the data when premutation decision threshold will be not more than in the result of calculation of storage
Arithmetic mean calculating is carried out, then mutation decision threshold is arranged to by 2 times of arithmetic average result；
If T1 is not equal to 0, mutation duration t1 is calculated according to current time and T1, if t1 is more than mutation duration door
2-5 times of sill, the data in the result of calculation of storage are subjected to arithmetic mean calculating, then 1.2 times of arithmetic average result are set
Mutation decision threshold is set to, T1 is set to 0.
Amplitude threshold is Ref1 and Ref2 respectively, and is dynamic setting, and its method to set up comprises the following steps：
Step 1）Amplitude threshold Ref1 and Ref2 are arranged to 1 during function input initialization；
Step 2）Calculate fundamental wave, triple-frequency harmonics, the virtual value E of quintuple harmonics1、E2、E3, E is calculated respectively2/ E1*100%、E3/
E1* 100%, and two result of calculations are each stored by group；
Step 3）1.6 s are often crossed, if T2 is equal to 0, each self-corresponding current width will be not more than in the result of calculation of two groups of storages
The data of value threshold carry out arithmetic mean calculating respectively, then are arranged to each self-corresponding by 2 times of two arithmetic average results
Amplitude threshold；
If T2 is not equal to 0, amplitude mutation duration t2 is calculated according to current time and T2, mutation is held if t2 is more than amplitude
Data in the result of calculation of two groups of storages are carried out arithmetic mean calculating, then two are counted by continuous 2-5 times of time period threshold respectively
1.2 times of average results are arranged to each self-corresponding amplitude threshold, and T2 is set to 0.
Above-mentioned mutation decision threshold, amplitude threshold are when function puts into and initialized, in order to avoid malfunction, now to judging
Threshold carries out specially treated, is judged according to the threshold of specially treated, is not regarded as that " island phenomenon " occurs in system, but initially
Mutation decision threshold, amplitude threshold renewal can be adjusted in real time according to the higher hamonic wave situation of current system quickly, therefore will not
Substantial influence is caused on distributed photovoltaic power generation system.
Claims (10)
1. the isolated island detection decision method of a kind of distributed photovoltaic power generation system, it is characterised in that comprise the following steps：
Step A. samples to the output voltage waveforms of distributed photovoltaic power generation system, sample frequency 6.4kHz；
Step B. carries out wavelet transformation to sampled signal, obtains including at least fundamental wave, triple-frequency harmonics, the component system of quintuple harmonics
Number；
Step C. obtains the average value D of each component coefficient absolute value obtained in step B in a data windowmeanAnd absolutely
To the maximum D of valuemax, calculate (Dmax-Dmean)/ Dmean：
If result of calculation is not more than the mutation decision threshold pre-set, N is set to 0；
Otherwise, N=N+1, wherein N represent the continuous occurrence number that result of calculation is more than the mutation decision threshold pre-set；
The component coefficient of the fundamental wave obtained in step B, triple-frequency harmonics, quintuple harmonics is filtered and inverse wavelet transform by step D.
And then time domain waveform is obtained, then Fast Fourier Transform (FFT) is carried out, fundamental wave, triple-frequency harmonics, the virtual value of quintuple harmonics are extracted afterwards
E1、E2、E3, E is calculated respectively2/ E1*100%、E3/ E1*100%：
If the amplitude threshold that two result of calculations are not pre-set both greater than, M are set to 0；
Otherwise, M=M+1, wherein M represent the continuous occurrence number that two result of calculations are both greater than the amplitude threshold pre-set；
Step E. calculates mutation duration t1 and amplitude mutation duration t2 according to current N, M respectively, if t1 is more than in advance
The mutation duration threshold and t2 first set is more than the amplitude duration threshold pre-set, then it is assumed that there is isolated island,
Send trip command；
Step F. to the cycle of pusher 1/4, repeats the above steps data window.
2. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 1, it is characterised in that：
In the step C, a data window is 20ms.
3. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 1, it is characterised in that：It is described
It is mutated the computational methods of duration t1：It is each to judge timing node, according to formula（N-1）T/4 is calculated, and result of calculation is designated as
Duration t1 is mutated, T represents the data window cycle；
The computational methods of amplitude mutation duration t2：It is each to judge timing node, according to formula（M-1）T/4 is calculated, will
Result of calculation is designated as amplitude mutation duration t2；
In above formula, T represents the data window cycle.
4. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 3, it is characterised in that：Step
In C, mutation decision threshold is dynamic setting, and its method to set up comprises the following steps：
Step 1）Mutation decision threshold is arranged to 0 during function input initialization；
Step 2）Judge to be mutated whether decision threshold is 0, if 0, then the component coefficient of fundamental wave is arranged to mutation and judges valve
Value；
Step 3）Obtain the average value D of each component coefficient absolute value obtained in a data window in step BmeanAnd definitely
The maximum D of valuemax, calculate (Dmax-Dmean)/ Dmean, and result of calculation is stored；
Step 4）2 seconds are often spent, if T1 is equal to 0, the data when premutation decision threshold will be not more than in the result of calculation of storage
Arithmetic mean calculating is carried out, then mutation decision threshold is arranged to by 2 times of arithmetic average result；
If T1 is not equal to 0, mutation duration t1 is calculated according to current time and T1, if t1 is more than mutation duration door
2-5 times of sill, the data in the result of calculation of storage are subjected to arithmetic mean calculating, then 1.2 times of arithmetic average result are set
Mutation decision threshold is set to, T1 is set to 0.
5. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 3, it is characterised in that：Step
In D, the amplitude threshold is Ref1 and Ref2 respectively, and is dynamic setting, and its method to set up comprises the following steps：
Step 1）Amplitude threshold Ref1 and Ref2 are arranged to 1 during function input initialization；
Step 2）Calculate fundamental wave, triple-frequency harmonics, the virtual value E of quintuple harmonics1、E2、E3, E is calculated respectively2/ E1*100%、E3/ E1*
100%, and two result of calculations are each stored by group；
Step 3）1.6 s are often crossed, if T2 is equal to 0, each self-corresponding current width will be not more than in the result of calculation of two groups of storages
The data of value threshold carry out arithmetic mean calculating respectively, then are arranged to each self-corresponding by 2 times of two arithmetic average results
Amplitude threshold；
If T2 is not equal to 0, amplitude mutation duration t2 is calculated according to current time and T2, mutation is held if t2 is more than amplitude
Data in the result of calculation of two groups of storages are carried out arithmetic mean calculating, then two are counted by continuous 2-5 times of time period threshold respectively
1.2 times of average results are arranged to each self-corresponding amplitude threshold, and T2 is set to 0.
6. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 1, it is characterised in that：It is described
It is 1s to be mutated duration threshold, and the amplitude duration threshold is 800ms.
7. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 1, it is characterised in that：It is described
Sample frequency in step A is controlled by high-speed dsp processor.
8. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 1, it is characterised in that：It is described
Wavelet transformation is carried out using Daubechies4 wave filters and Mallat fast algorithms to sampled signal in step B.
9. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 1, it is characterised in that：It is described
Component coefficient in step B is wavelet coefficient di(n), i=1,2,3,4,5,6,
In above formula, n represents discrete sampling time straw line, di(n) fundamental wave wavelet coefficient, corresponding sub-band are represented as [0, fs/
64], remaining wavelet coefficient di(n), i=2, sub-band is [f corresponding to 3,4,5,6s/28-i, fs/27-i], fsRepresent sampling frequency
Rate.
10. the isolated island detection decision method of distributed photovoltaic power generation system according to claim 1, it is characterised in that：Institute
State in step D to the means that the component coefficient of fundamental wave, triple-frequency harmonics, quintuple harmonics is filtered using passband comb filtering
Device.
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| CN109387713A (en) * | 2018-10-17 | 2019-02-26 | 东北大学 | A kind of mixed method of distributed grid-connected isolated island detection |
| CN109387713B (en) * | 2018-10-17 | 2020-09-15 | 东北大学 | Hybrid method for distributed grid-connected island detection |
| CN110286283A (en) * | 2019-06-25 | 2019-09-27 | 国网河北省电力有限公司石家庄供电分公司 | Micro-grid island detection method and system |
| CN110286283B (en) * | 2019-06-25 | 2022-04-22 | 国网河北省电力有限公司石家庄供电分公司 | Microgrid island detection method and system |
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