CN104237711A - Fast and reliable low voltage through determination method - Google Patents
Fast and reliable low voltage through determination method Download PDFInfo
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- CN104237711A CN104237711A CN201410542146.9A CN201410542146A CN104237711A CN 104237711 A CN104237711 A CN 104237711A CN 201410542146 A CN201410542146 A CN 201410542146A CN 104237711 A CN104237711 A CN 104237711A
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Abstract
The invention discloses a fast and reliable low voltage through determination method, and the method adopts the positive-sequence voltage d axle component combination corresponding to the three-phase voltage instantaneous value for judging, the d axle positive-sequence component of the power grid voltage instantaneous value is expressed in the formula, the d axle negative-sequence component of the power grid voltage instantaneous value is also expressed in the formula, both components are the constant; when the value expressed in the formula is less than the value expressed in the formula, the power grid voltage is reduced, for the low voltage through, the time for executing the method is short, so that the inverter can work quickly, and the speedability of the photovoltaic power generation system is raised.
Description
Technical field
The invention belongs to field of new energy generation, particularly relate to the decision method of the low voltage crossing of a kind of photovoltaic DC-to-AC converter and fan converter.
Background technology
Require as follows to the low voltage crossing of photo-voltaic power generation station and wind energy turbine set in " State Grid Corporation of China's photovoltaic plant access electric power network technique specifies " and " State Grid Corporation of China's wind energy turbine set access electric power network technique specifies ": large-scale and medium-sized photovoltaic plant or wind energy turbine set should possess the ability of certain withstand voltage exception, avoid the off-grid when electrical network is abnormal, cause the loss of electric network source.
When and site in FIG below voltage profile line time, allow photovoltaic plant or wind energy turbine set to stop to power network line power transmission.With reference to figure 1, U
l0for the minimum voltage restriction run, get 0.9 times of rated voltage, U
l1for needing the lower voltage limit of tolerance, T
1for Voltage Drop is to U
l1in time, needs to keep the grid-connected time, T
2for Voltage Drop is to U
l0in time, needs to keep the grid-connected time.In photovoltaic plant access standard, U
l0get 0.9 times of rated voltage, U
l1get 0.2 times of rated voltage, T
1get 1s, T
2get 3s; In wind energy turbine set access standard, U
l0get 0.9 times of rated voltage, U
l1get 0.2 times of rated voltage, T
1get 0.625s, T
2get 3s.
Existing low voltage crossing decision method is judge that whether the amplitude of three-phase voltage is lower than 0.9 times of rated voltage, but this kind of method needs the information of voltage at least needing a power frequency period, just can calculate the ratings of three-phase voltage, therefore at least delayed 0.02s on the time, makes the rapidity of system when electric voltage exception be restricted.During traditional mode of falling judges, when judging according to instantaneous value, rapidity requirement can reach requirement, but (90% imbalance falls and 80% imbalance is fallen) is owing to the probability of erroneous judgement occurring comparatively greatly when either shallow is fallen, thus affects the operation of low voltage crossing algorithm and the quality of electrical network.
Chinese patent publication No. is separately had to be: CN102854421A, date of publication is the method for rapidly judging that 2013.1.2 discloses a kind of low voltage ride through of photovoltaic inverter, described method adopts formula U=Ua*Ua+Ub*Ub+Uc*Uc to calculate, in formula, Ua, Ub, Uc are respectively A, B, C three-phase power grid voltage instantaneous value, the U value according to calculating judges: when calculating U value and being less than threshold value U1, judges that line voltage there occurs and falls; When calculating U value and being less than threshold value U2, then judge that line voltage is lower than the lower voltage limit needing tolerance, inverter disconnects electrical network, out of service.This kind of determination methods is owing to being adopt instantaneous value to judge, the promptness judged meets the demands substantially, but easily there is erroneous judgement, when such as electrical network occurs that harmonic content is larger, or when flickering and saltus step appear in line voltage, all there will be the phenomenon of erroneous judgement, when either shallow is fallen, easily occur erroneous judgement simultaneously, judge that precision is not high, patent described herein can overcome this type of misjudgment phenomenon completely.
Summary of the invention
The present invention is in order to overcome the restriction of system in the process rapidity and accuracy of line voltage abnormal conditions, shorten the time judged and the accuracy improving criterion, propose a kind of low voltage crossing decision method of fast and reliable, the system of decreasing is in when either shallow is fallen and judges by accident.
In order to solve the problems of the technologies described above, the technical solution used in the present invention is:
A low voltage crossing decision method for fast and reliable, is characterized in that: described method adopts the positive sequence voltage d axle component that three-phase voltage instantaneous value is corresponding
in conjunction with
judge, in formula
for the d axle positive-sequence component of line voltage instantaneous value,
for the d axle negative sequence component of electric three-phase power grid voltage instantaneous value,
for constant; When calculating
be less than
or
value is less than
time, judge that line voltage there occurs and fall, photovoltaic inverter system can make action accurately and quickly.
Further,
with
during for dropping to the normal minimum restriction run, according to above-mentioned formulae discovery threshold value out.
Further,
with
the threshold value calculated when dropping to 0.9 times of rated voltage for line voltage is single-phase.
Further, fall criterion to adopt
with
the mode combined, two criterions adopt or mode, can avoid judging by accident when unbalanced either shallow is fallen.
Further, exist
value is less than
or
be less than
time, photovoltaic DC-to-AC converter enters low voltage crossing control algolithm, carries out low voltage crossing control, continues to generate electricity by way of merging two or more grid systems.
Further, grid voltage sags be divided into single-phasely asymmetricly to fall, two-phase is asymmetricly fallen, three-phase symmetrical falls.
Further, control cycle detection time of grid voltage sags is 200us.
The present invention has the following advantages: when low voltage crossing occurs, and the method for the present invention time used is shorter, thus makes the rapid action of inverter, improves the rapidity of photovoltaic generating system; And publication No. is: the patent of CN102854421A, flickering or saltus step appear in, voltage comparatively large at mains by harmonics, easily there is erroneous judgement, simultaneously when either shallow is fallen, the precision judged is inadequate, instant invention overcomes problems, improves the stability that system judges.
Accompanying drawing explanation
Fig. 1 is the requirement regulation schematic diagram that CHEAA.COM company of the present invention accesses big-and-middle-sized photovoltaic plant and wind farm grid-connected point.
Fig. 2 is the sampling and processing flow process of line voltage in the present invention.
It is asymmetric when dropping to 0.9 times of rated voltage that to be A phase line voltage of the present invention at 1 second place occur Fig. 3
value,
value and
the schematic diagram of value, black fine line represents
the representative of value, black thick dashed line
the representative of value, black heavy line
value, C value is 5.
Fig. 4 is that A, B, C three-phase power grid voltage of the present invention symmetry is when dropping to 0.9 times of rated voltage
value,
value,
the schematic diagram of value, black fine line represents
the representative of value, black thick dashed line
the representative of value, black heavy line
value, C value is 5.
Embodiment
Embodiment 1
A low voltage crossing decision method for fast and reliable, with reference to figure 2, by line voltage Acquisition Circuit and voltage processing circuitry, sends into the AD conversion unit of digital processing unit, collects the instantaneous value of three-phase power grid voltage by voltage signal.Principle is as follows: line voltage Acquisition Circuit converts line voltage (large voltage) to small voltage signal, and small voltage signal transacting by operational amplifier, follower, resistance, electric capacity, to improve sampling impedance, is improved load-carrying ability by voltage processing circuitry; Adopt low-pass first order filter and the fertile low-pass filter of second order Bart Si of resistance capacitance composition, comparatively level and smooth line voltage sampled signal (small voltage of 0V-3V) can be obtained; Sampled output signal is sent into the AD conversion pin of digital processing unit, carry out the calculating of instantaneous value.
After three-phase voltage being collected digital processing unit by external circuit, obtain three-phase instantaneous value
,
,
, voltage can be analyzed to positive sequence
, negative phase-sequence
and zero sequence
, in the system not having neutral point, system can be analyzed to positive sequence and negative phase-sequence two symmetrical components, namely
=0, patent of the present invention is based on the system without neutral point.
With reference to formula (1), in formula, three-phase power grid voltage instantaneous value is decomposed into the form of positive sequence voltage and negative sequence voltage sum,
,
,
represent three-phase power grid voltage instantaneous value respectively,
,
be respectively electrical network phase voltage positive sequence, negative phase-sequence first-harmonic peak value.
With reference to formula (2),
,
be respectively the dq axle component of line voltage,
,
,
,
represent the dq component of line voltage positive-negative sequence respectively.Formula 2 shows, line voltage d axle component is made up of two parts, first step part
for DC quantity, Part II
for 100HZ of ac.
Grid voltage sags is divided into three-phase symmetrical to fall falling with asymmetrical three-phase, and asymmetrical three-phase falls to be divided into and single-phasely asymmetricly falls fall asymmetric with two-phase.When three-phase symmetrical falls generation, positive sequence d axle component
reduce, therefore
in
a DC quantity can be decreased to rapidly, as shown in Figure 3; When asymmetrical three-phase falls, there is negative sequence component in line voltage d axle
, positive sequence d axle component
reduce, therefore
in
a DC quantity can be decreased to rapidly.In fact, due to the impact by mode of the falling difference of electrical network and sampling error etc., electrical network is falling moment, and this DC quantity there will be minor fluctuations, when judging that either shallow is fallen, occurs erroneous judgement probability comparatively greatly, in conjunction with
judge, can address this problem.
When electrical network three-phase symmetrical falls,
,
remain unchanged,
be decreased to certain value rapidly, then
be decreased to certain value rapidly; When electrical network three-phase imbalance falls,
,
increase to certain value rapidly,
be decreased to certain value rapidly, then
be decreased to rapidly a definite value.
See Fig. 4, for value A, B, C three phase network (balance is fallen) to drop to 0.9 times of rated voltage during at 0.1 second, with reference to figure 3, be value A phase electrical network (balance is fallen) to drop to 0.9 times of rated voltage during at 0.1 second place, now digital processing unit can detect in another control cycle 200us
with
be worth change, low voltage crossing logic control algorithm will be performed, and make inverter make corresponding actions.When falling the degree of depth and being darker, now corresponding value and the difference of threshold value are larger, are more prone to judge.
The present invention adopts line voltage positive sequence d axle component
with
the method combined carries out criterion, between two criterions be or relation, this criterion calculates simple, and easy to implement in engineering.
Circular:
By line voltage Acquisition Circuit, A/D converting unit, the instantaneous value of three-phase power grid voltage is collected in digital processing unit, under three-phase voltage instantaneous value is transformed into d-q coordinate system by coordinate transform mode, according to formula 2 principle voltage vector resolved into the d-q axle component under positive-negative sequence component, obtain positive sequence d axle component, and calculate U value by formula 3.
Calculate balance to fall and uneven when dropping to normal minimum voltage restriction (getting 0.9 times of rated voltage) run
with
value, fall in single-phase imbalance, two-phase imbalance fall to fall with three-phase equilibrium several fall mode under, single-phase when falling
maximum, to fall in single-phase imbalance, under two-phase imbalance falls operating mode, single-phase when falling
maximum, this value is set as threshold value
with
.
By what calculate
value and
value compares with threshold value, when
be less than threshold value
or
be less than threshold value
time, think that line voltage there occurs and fall, be judged to be low voltage crossing operating mode, system performs low voltage crossing flow process, continues to generate electricity by way of merging two or more grid systems, in conjunction with
value judges, is intended to solve the misjudgment phenomenon when either shallow imbalance is fallen.
The criterion method taked by this invention, can obtain good effect.For 500KW photovoltaic DC-to-AC converter, when adopting the method for the amplitude of traditional three phase network, when low voltage crossing occurs, detect that this situation required time is at least a power frequency period (0.02s), when adopting instantaneous value to judge, due to the impact of Voltage Drop mode difference and sampling error etc., can judge by accident, when adopting method of the present invention, experience a control cycle (200 μ s), just can carry out criterion fast, and there will not be erroneous judgement situation when either shallow is fallen, the rapidity and the stability that are conducive to raising photovoltaic generating system control.
Claims (7)
1. a low voltage crossing decision method for fast and reliable, is characterized in that: described method adopts the positive sequence voltage d axle component that three-phase voltage instantaneous value is corresponding
in conjunction with
judge, in formula
for the d axle positive-sequence component of line voltage instantaneous value,
for the d axle negative sequence component of electric three-phase power grid voltage instantaneous value,
for constant; When calculating
be less than
or
value is less than
time, judge that line voltage there occurs and fall.
2. the low voltage crossing decision method of fast and reliable according to claim 1, is characterized in that:
with
during for dropping to the normal minimum restriction run, according to above-mentioned formulae discovery threshold value out.
3. the low voltage crossing decision method of fast and reliable according to claim 2, is characterized in that:
with
the threshold value calculated when dropping to 0.9 times of rated voltage for line voltage is single-phase.
4. the low voltage crossing decision method of fast and reliable according to claim 1, is characterized in that: fall criterion and adopt
with
the mode combined, two criterions adopt or mode.
5. the low voltage crossing decision method of fast and reliable according to claim 1, is characterized in that:
value is less than
or
be less than
time, photovoltaic DC-to-AC converter enters low voltage crossing control algolithm, carries out low voltage crossing control, continues to generate electricity by way of merging two or more grid systems.
6. the low voltage crossing decision method of fast and reliable according to claim 1, is characterized in that: grid voltage sags be divided into single-phasely asymmetricly to fall, two-phase is asymmetricly fallen, three-phase symmetrical falls.
7. the low voltage crossing decision method of fast and reliable according to claim 1, is characterized in that: control cycle detection time of grid voltage sags is 200 μ s.
Priority Applications (1)
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|---|---|---|---|
| CN201410542146.9A CN104237711B (en) | 2014-10-15 | 2014-10-15 | A kind of fast and reliable low voltage crossing decision method |
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|---|---|---|---|
| CN201410542146.9A CN104237711B (en) | 2014-10-15 | 2014-10-15 | A kind of fast and reliable low voltage crossing decision method |
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| CN104237711A true CN104237711A (en) | 2014-12-24 |
| CN104237711B CN104237711B (en) | 2017-07-14 |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105116195A (en) * | 2015-07-13 | 2015-12-02 | 中国人民解放军海军工程大学 | Voltage drop detection method suitable for power grid voltage large harmonic content |
| CN108123486A (en) * | 2016-11-30 | 2018-06-05 | 北京金风科创风电设备有限公司 | The control method and device of wind electric converter low voltage crossing |
| CN108123485A (en) * | 2016-11-30 | 2018-06-05 | 北京金风科创风电设备有限公司 | The control method and device of wind electric converter high voltage crossing |
| CN112448412A (en) * | 2020-10-28 | 2021-03-05 | 爱士惟新能源技术(扬中)有限公司 | Control method for low voltage ride through of photovoltaic inverter |
| CN113985114A (en) * | 2021-11-25 | 2022-01-28 | 福州大学 | Power grid voltage drop detection method in low voltage ride through |
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Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN105116195A (en) * | 2015-07-13 | 2015-12-02 | 中国人民解放军海军工程大学 | Voltage drop detection method suitable for power grid voltage large harmonic content |
| CN105116195B (en) * | 2015-07-13 | 2018-07-06 | 中国人民解放军海军工程大学 | Suitable for the big method for detecting voltage drop of Voltage Harmonic content |
| CN108123486A (en) * | 2016-11-30 | 2018-06-05 | 北京金风科创风电设备有限公司 | The control method and device of wind electric converter low voltage crossing |
| CN108123485A (en) * | 2016-11-30 | 2018-06-05 | 北京金风科创风电设备有限公司 | The control method and device of wind electric converter high voltage crossing |
| CN108123486B (en) * | 2016-11-30 | 2020-03-24 | 北京金风科创风电设备有限公司 | Control method and device for low voltage ride through of wind power converter |
| CN112448412A (en) * | 2020-10-28 | 2021-03-05 | 爱士惟新能源技术(扬中)有限公司 | Control method for low voltage ride through of photovoltaic inverter |
| CN113985114A (en) * | 2021-11-25 | 2022-01-28 | 福州大学 | Power grid voltage drop detection method in low voltage ride through |
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| Publication number | Publication date |
|---|---|
| CN104237711B (en) | 2017-07-14 |
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Address after: 618000 No. 18, Third Section of Lushan South Road, Deyang City, Sichuan Province Patentee after: Dongfang Electric Automatic Control Engineering Co., Ltd. Address before: 618099 No. 18, Section 3, Lushan South Road, Deyang City, Sichuan Province Patentee before: Sichuan Orient Electric Automatic Control Engineering Co., Ltd. |