CN102608496A - Improved type positive feedback active frequency deviation island detection method - Google Patents
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- CN102608496A CN102608496A CN2012100694225A CN201210069422A CN102608496A CN 102608496 A CN102608496 A CN 102608496A CN 2012100694225 A CN2012100694225 A CN 2012100694225A CN 201210069422 A CN201210069422 A CN 201210069422A CN 102608496 A CN102608496 A CN 102608496A
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Abstract
The invention discloses an improved type positive feedback active frequency deviation island detection method, comprising the following steps of: detecting a current frequency of a power grid public point; comparing the current frequency with a last-time frequency to obtain frequency change delta f of the power grid public point; calculating frequency disturbance quantity cf according to a formula: cf=cf'0+k delta f, wherein the cf'0=sign(delta f)*cf0; when the delta f is more than or equal to 0, sign(delta f)=1; when the delta f is less than 0, sign(delta f)=-1; the cf0 is an initial disturbance quantity and the k is feedback gain; and judging whether the frequency disturbance quantity exceeds a frequency threshold value range or not, if so, generating an island on a power grid.
Description
Technical field
The present invention relates to the photovoltaic new energy field, in particular to a kind of modified positive feedback intentional frequency offset island detection method.
Background technology
When public electric wire net broke down, distributed power source and electrical network broke away from, and independent of local electric, this running status is called isolated island.The generation of isolated island generally is unpredictable, need in time to detect and start protection, otherwise consequence is very serious.Therefore, stipulate in the IEEE Std.929-2000 standard: combining inverter must have island detection and isolated island defencive function.In case electrical network is stopped power supply, combining inverter must detect island state and stop electric towards periphery in 2s.
The anti-isolated island method great majority of present photovoltaic DC-to-AC converter employing intentional frequency offset method (Active Frequency Drift, AFD).The intentional frequency offset method adopts and applies the generation that the power frequency disturbance detects isolated island.And the size of frequency disturbance amount is directly proportional with the detection speed of intentional frequency offset method; But the grid-connected current total harmonic distortion with grid-connected photovoltaic system is inversely proportional to; Be that the frequency disturbance value of measuring is big more; Then detection time short more, but bigger frequency disturbance amount can increase the harmonic content of grid-connected current.Therefore the detection time of isolated island and grid-connected current total harmonic distortion are the good and bad important indicators of evaluating testing method.
The intentional frequency offset method exposes its shortcoming gradually.Then proposed the band positive feedback the intentional frequency offset method (Active Frequency Drift with Positive Feedback, AFDPF).
For better describing AFDPF, introduce AFD earlier.AFD carries out island detection through the frequency at skew common point place as the reference frequency of inverter output current, and this side-play amount is a fixed value.Its synoptic diagram is as shown in Figure 1.
The frequency of adjustment output current makes it slightly higher than electric voltage frequency, the voltage zero passage not if the electric current half-wave has been accomplished, and then impressed current is given as zero, arrives up to voltage over zero, and electric current just begins next half-wave.Behind grid cut-off, the frequency of common point receives the influence of power frequency and departs from initial value, and overrun can detect isolated island.Fig. 1 is an intentional frequency offset island detection method synoptic diagram in the prior art; Among Fig. 1, V
PccBe point of common coupling voltage, be line voltage when being incorporated into the power networks; T
VIt is the corresponding cycle; I is the inverter output current; t
ZBe the current chopping time.
The active shift frequency island detection method (AFDPF) of band positive feedback is introduced positive feedback on the basis of the frequency shift (FS) of AFD, quicken common point electric voltage frequency skew normal value, makes that detecting the blind area further reduces.Frequency disturbance amount cf expression formula is following:
cf＝cf
0+k(f-f
g)
Cf wherein
0Be the initial disturbance amount, k is a feedback gain, f and f
gBe respectively common point electric voltage frequency and electrical network rated frequency.
The shortcoming of AFDPF method is: a, initial offset direction are single.Load characteristic is different, and when electrical network broke down, the change direction of frequency maybe be in the opposite direction with disturbing signal, and this can cause the error accumulation of frequency slower, thereby prolongs the island detection time.In particular cases, load causes failing to judge of island effect to the effect of the equilibrium activity meeting counteracting frequency disturbance of frequency.B, under the electrical network normal condition, mains frequency fluctuation when overfrequency protection domain (but not), f-f
gBe not equal to 0, can cause the frequency disturbance amount to increase, influence the waveform quality of grid-connected current.
Summary of the invention
The present invention provides a kind of modified positive feedback intentional frequency offset island detection method, in order to improve speed and the precision that electrical network detects the isolated island ability.。
For achieving the above object, the invention provides a kind of modified positive feedback intentional frequency offset island detection method, it may further comprise the steps:
The current frequency of detection of grid common point compares current frequency and last secondary frequencies, obtains electrical network common point change of frequency Δ f;
According to following formula calculated rate disturbance quantity cf:
cf＝cf′
0+kΔf，
Wherein, cf '
0=sign (Δ f) * cf
0, when Δ f>=0, sign (Δ f)=1, when Δ f＜0, sign (Δ f)=-1, cf
0Be the initial disturbance amount, k is a feedback gain;
Whether determination frequency disturbance quantity cf exceeds the frequency threshold scope, if judged result is for being that then isolated island appears in electrical network.
Further, confirm sign function sign (Δ f) according to following method:
With a plurality of cycles be one group, the direction that record electrical network common point electric voltage frequency changes, the i.e. sign of Δ f; If Δ f＞0, electrical network common point change of frequency then is recorded as ascendant trend one time, if Δ f＜0; Then be recorded as a downtrending, the number of times of ascendant trend and downtrending in these a plurality of cycles relatively then is as if the number of times of the ascendant trend number of times greater than downtrending; Then these a plurality of cycle common point electric voltage frequencies are judged to ascendant trend, sign (Δ f)=1, otherwise sign (Δ f)=-1 then.
Further, confirm sign function sign (Δ f) according to following method:
If Δ f＞cf
0, sign (Δ f)=1 then, if Δ f＜-cf
0, if sign (Δ f)=-1 then is Δ f ∈ [cf
0, cf
0], then sign (Δ f) is consistent with the last computation value.
The detection method of the foregoing description has been considered different load characteristics, can locate perturbation direction rapidly according to load characteristic, has accelerated detection speed; And the common point electric voltage frequency deviation that adopts twice measurement has been eliminated because the problem that the disturbance quantity that electrical network self fluctuation causes increases can not impact the electric network performance index as positive feedback.
Description of drawings
In order to be illustrated more clearly in the embodiment of the invention or technical scheme of the prior art; To do to introduce simply to the accompanying drawing of required use in embodiment or the description of the Prior Art below; Obviously, the accompanying drawing in describing below only is some embodiments of the present invention, for those of ordinary skills; Under the prerequisite of not paying creative work, can also obtain other accompanying drawing according to these accompanying drawings.
Fig. 1 is an intentional frequency offset island detection method synoptic diagram in the prior art;
Fig. 2 is the modified positive feedback intentional frequency offset island detection method process flow diagram of one embodiment of the invention.
Embodiment
To combine the accompanying drawing in the embodiment of the invention below, the technical scheme in the embodiment of the invention is carried out clear, intactly description, obviously, described embodiment only is the present invention's part embodiment, rather than whole embodiment.Based on the embodiment among the present invention, those of ordinary skills are not paying the every other embodiment that is obtained under the creative work prerequisite, all belong to the scope of the present invention's protection.
Fig. 2 is the modified positive feedback intentional frequency offset island detection method process flow diagram of one embodiment of the invention.As shown in Figure 2, present embodiment provides a kind of modified AFDPF method, and this method may further comprise the steps:
The current frequency of detection of grid common point compares current frequency and last secondary frequencies, obtains electrical network common point change of frequency Δ f;
According to following formula calculated rate disturbance quantity cf:
cf＝cf′
0+kΔf，
Wherein, cf '
0=sign (Δ f) * cf
0, when Δ f>=0, sign (Δ f)=1, when Δ f＜0, sign (Δ f)=-1, cf
0Be the initial disturbance amount, k is a feedback gain;
Whether determination frequency disturbance quantity cf exceeds the frequency threshold scope, if judged result is for being that then isolated island appears in electrical network.
In the present embodiment, control loop is introduced positive feedback with the difference DELTA f of current frequency and last secondary frequencies, and Δ f gets signed number, symbology the direction of frequency shift (FS).If local load is perception, then its resonance frequency is greater than mains frequency, so grid cut-off moment, and system frequency generally can change to the direction that frequency increases, this moment Δ f＞0, cf '
0＞0, frequency disturbance amount cf quickens system frequency is pulled out upper frequency limit for just; If local load is capacitive, then its resonance frequency is less than mains frequency, so grid cut-off moment, and system frequency generally can change to the direction that frequency reduces, this moment Δ f＜0, cf '
0＜0, disturbance quantity cf quickens system frequency is pulled out lower-frequency limit for negative frequently.
When electrical network just often, Δ f is similar to zero, frequency disturbance amount cf equals initial disturbance amount cf
0, owing to introduced positive feedback, cf
0Value can be very little, and influence can be ignored to power network current.
It is thus clear that the detection method of the foregoing description has been considered different load characteristics, can locate perturbation direction rapidly according to load characteristic, accelerated detection speed; And the common point electric voltage frequency deviation that adopts twice measurement has been eliminated because the problem that the disturbance quantity that electrical network self fluctuation causes increases can not impact the electric network performance index as positive feedback.
But because circuit noise and the existence that detects error, each common point electric voltage frequency that detects can strict conformance, for avoiding the perturbation direction frequent variations, can adopt following two kinds of methods:
(1) be one group with 10 cycles, the direction that record common point electric voltage frequency changes, the i.e. sign of Δ f; If Δ f＞0, then be recorded as ascendant trend one time, if Δ f＜0 item is recorded as a downtrending; The number of times of ascendant trend and downtrending in 10 cycles relatively then, as if the number of times of the ascendant trend number of times greater than downtrending, then being judged to these 10 cycle common point electric voltage frequencies is ascendant trend; Sign (Δ f)=1, otherwise sign (Δ f)=-1 then.This method is through interior variation tendency of more a plurality of cycles, can not judge by accident owing to electrical network saltus step and interference.
(2) if Δ f＞cf
0, sign (Δ f)=1 then; If Δ f＜-cf
0, sign (Δ f)=-1 then; If Δ f ∈ [cf
0, cf
0], then sign (Δ f) and last computation value are consistent, and are-1 like the last computation value of sign (Δ f), and then the current calculated value of sign (Δ f) also is-1.This method has been avoided the frequent variations of perturbation direction through the mode that threshold value is set.
As shown in Figure 2, after the frequency error Δ f process P link, with initial disturbance amount cf '
0Addition obtains the total disturbance quantity of this secondary frequencies, then through amplitude limit output.When electrical network just often, common point electric voltage frequency fluctuation is very little, Δ f is similar to zero, amount of positive feedback is zero, to the not influence of grid-connected current quality.When isolated island took place, frequency squinted, if the frequency forward migration, and Δ f＞0 then, cf '
0＞0, again Δ f is introduced positive feedback, this moment, disturbance quantity was cf
0+ k Δ f is equivalent to and strengthens the forward disturbance, and disturbance quantity is increasing, and the skew of common point electric voltage frequency is also increasing, forms the forward migration positive feedback system, exceeds standard until frequency, reaches the purpose of isolated island protection.In like manner if the frequency negative offset, Δ f＜0 then, cf '
0＜0, again Δ f is introduced positive feedback, this moment, disturbance quantity was-cf
0-k| Δ f| is equivalent to and strengthens the negative sense disturbance, and disturbance quantity is increasing, and the skew of common point electric voltage frequency is also increasing, forms the negative offset positive feedback system, exceeds standard until frequency, reaches the purpose of isolated island protection.Simultaneously frequency disturbance amount cf is carried out amplitude limit, prevent the misoperation that electrical network saltus step and interference cause.
In sum, the above embodiment of the present invention has realized following beneficial effect:
Adopt said method of the present invention, when electrical network just often, grid-connected current and common point voltage keep homophase, power factor is greater than 0.99, the frequency disturbance amount is to the not influence of grid-connected current waveform quality.Adopt the local load of parallelly connected RLC load simulation, the value of the RLC through adjustment changes load characteristic.The test proof, under various different loads characteristics, when isolated island took place, system all can protect in 2s.Considered the influence factor in the practical application simultaneously, had the advantages that exploitativeness is strong, reliability is high, detection speed is fast.
One of ordinary skill in the art will appreciate that: accompanying drawing is the synoptic diagram of an embodiment, and module in the accompanying drawing or flow process might not be that embodiment of the present invention is necessary.
One of ordinary skill in the art will appreciate that: the module in the device among the embodiment can be described according to embodiment and be distributed in the device of embodiment, also can carry out respective change and be arranged in the one or more devices that are different from present embodiment.The module of the foregoing description can be merged into a module, also can further split into a plurality of submodules.
What should explain at last is: above embodiment is only in order to explaining technical scheme of the present invention, but not to its restriction; Although with reference to previous embodiment the present invention has been carried out detailed explanation, those of ordinary skill in the art is to be understood that: it still can be made amendment to the technical scheme that previous embodiment is put down in writing, and perhaps part technical characterictic wherein is equal to replacement; And these are revised or replacement, do not make the spirit and the scope of the essence disengaging embodiment of the invention technical scheme of relevant art scheme.
Claims (3)
1. a modified positive feedback intentional frequency offset island detection method is characterized in that, may further comprise the steps:
The current frequency of detection of grid common point compares said current frequency and last secondary frequencies, obtains electrical network common point change of frequency Δ f;
According to following formula calculated rate disturbance quantity cf:
cf＝cf′
0+kΔf，
Wherein, cf '
0=sign (Δ f) * cf
0, when Δ f>=0, sign (Δ f)=1, when Δ f＜0, sign (Δ f)=-1, cf
0Be the initial disturbance amount, k is a feedback gain;
Judge whether said frequency disturbance amount cf exceeds the frequency threshold scope, if judged result is for being that then isolated island appears in electrical network.
2. positive feedback according to claim 1 is frequency displacement skew island detection method initiatively, it is characterized in that, confirms sign function sign (Δ f) according to following method:
With a plurality of cycles be one group, the direction that record electrical network common point electric voltage frequency changes, the i.e. sign of Δ f; If Δ f＞0, electrical network common point change of frequency then is recorded as ascendant trend one time, if Δ f＜0; Then be recorded as a downtrending, the number of times of ascendant trend and downtrending in these a plurality of cycles relatively then is as if the number of times of the ascendant trend number of times greater than downtrending; Then these a plurality of cycle common point electric voltage frequencies are judged to ascendant trend, sign (Δ f)=1, otherwise sign (Δ f)=-1 then.
3. positive feedback according to claim 1 is frequency displacement skew island detection method initiatively, it is characterized in that, confirms sign function sign (Δ f) according to following method:
If Δ f＞cf
0, sign (Δ f)=1 then, if Δ f＜-cf
0, if sign (Δ f)=-1 then is Δ f ∈ [cf
0, cf
0], then sign (Δ f) is consistent with the last computation value.
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| CN103760434A (en) * | 2013-12-27 | 2014-04-30 | 浙江工业大学 | Self-adaption phase deviation island detection method based on fuzzy control |
| CN104198841A (en) * | 2014-08-08 | 2014-12-10 | 武汉理工大学 | Method for detecting island in photovoltaic grid-connected inverter |
| CN104267315A (en) * | 2014-10-16 | 2015-01-07 | 山东大学 | Combined type island detection method based on initiative frequency shift and voltage amplitude change |
| WO2016054842A1 (en) * | 2014-10-09 | 2016-04-14 | 湖南大学 | Combined islanding detection method |
| CN106841926A (en) * | 2017-03-14 | 2017-06-13 | 哈尔滨理工大学 | Photovoltaic parallel in system island detection method based on non-blind area self adaptation AFDPF algorithms |
| CN107979091A (en) * | 2017-12-19 | 2018-05-01 | 宁夏大学 | A kind of quick positive feedback Active Frequency Drift Islanding Detection Method |
| CN108333478A (en) * | 2018-02-12 | 2018-07-27 | 哈尔滨理工大学 | A kind of island detection method that FIR bandpass filterings are combined with parameter adaptive AFDPF |
| CN110729762A (en) * | 2019-11-22 | 2020-01-24 | 科华恒盛股份有限公司 | Island disturbance method, system and terminal equipment |
| CN111257670A (en) * | 2020-01-16 | 2020-06-09 | 中南大学 | Method for determining island detection positive feedback gain range |
| CN111856172A (en) * | 2019-04-24 | 2020-10-30 | 上海电机学院 | Island detection method based on active frequency deviation method |
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| CN103091604A (en) * | 2013-01-29 | 2013-05-08 | 深圳市京泉华科技股份有限公司 | Island detection method and detection device for grid-connected photovoltaic power generation system |
| CN103091604B (en) * | 2013-01-29 | 2015-10-28 | 深圳市京泉华科技股份有限公司 | A kind of island detection method of grid-connected photovoltaic system and pick-up unit |
| CN103760434A (en) * | 2013-12-27 | 2014-04-30 | 浙江工业大学 | Self-adaption phase deviation island detection method based on fuzzy control |
| CN104198841A (en) * | 2014-08-08 | 2014-12-10 | 武汉理工大学 | Method for detecting island in photovoltaic grid-connected inverter |
| CN104198841B (en) * | 2014-08-08 | 2017-03-29 | 武汉理工大学 | A kind of island detection method in photovoltaic combining inverter |
| WO2016054842A1 (en) * | 2014-10-09 | 2016-04-14 | 湖南大学 | Combined islanding detection method |
| CN104267315A (en) * | 2014-10-16 | 2015-01-07 | 山东大学 | Combined type island detection method based on initiative frequency shift and voltage amplitude change |
| CN104267315B (en) * | 2014-10-16 | 2015-11-25 | 山东大学 | Based on the composite type island detection method that intentional frequency offset and voltage magnitude change |
| CN106841926A (en) * | 2017-03-14 | 2017-06-13 | 哈尔滨理工大学 | Photovoltaic parallel in system island detection method based on non-blind area self adaptation AFDPF algorithms |
| CN107979091A (en) * | 2017-12-19 | 2018-05-01 | 宁夏大学 | A kind of quick positive feedback Active Frequency Drift Islanding Detection Method |
| CN107979091B (en) * | 2017-12-19 | 2021-05-07 | 宁夏大学 | Rapid positive feedback active frequency shift type island detection method |
| CN108333478A (en) * | 2018-02-12 | 2018-07-27 | 哈尔滨理工大学 | A kind of island detection method that FIR bandpass filterings are combined with parameter adaptive AFDPF |
| CN111856172A (en) * | 2019-04-24 | 2020-10-30 | 上海电机学院 | Island detection method based on active frequency deviation method |
| CN110729762A (en) * | 2019-11-22 | 2020-01-24 | 科华恒盛股份有限公司 | Island disturbance method, system and terminal equipment |
| WO2021098595A1 (en) * | 2019-11-22 | 2021-05-27 | 科华恒盛股份有限公司 | Islanding disturbance method and system, and terminal device |
| CN110729762B (en) * | 2019-11-22 | 2021-09-21 | 科华数据股份有限公司 | Island disturbance method, system and terminal equipment |
| CN111257670A (en) * | 2020-01-16 | 2020-06-09 | 中南大学 | Method for determining island detection positive feedback gain range |
| CN111257670B (en) * | 2020-01-16 | 2021-04-23 | 中南大学 | Method for determining island detection positive feedback gain range |
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Application publication date: 20120725 |