CN102255329B - Island detection method of photovoltaic grid connected system - Google Patents
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Abstract
The invention discloses an island detection method of a photovoltaic grid connected system in the field of application of a photovoltaic grid connected system control technology. The island detection method is characterized in that a frequency deviation positive feedback coefficient k is self-adaptively regulated by sections through detecting a change time n of a voltage frequency fu at a point of common coupling (PCC) towards a certain direction, thus frequency deviation is accelerated; and if the absolute value of the change time n exceeds 12, the voltage frequency fu at the PCC does not exceed the limit, two continuous working frequency periods of negative pulse current amplitude interference are applied and low-voltage protection is triggered, thus an island is detected. The method has the advantages of little influence on power grid harmonic waves and active output of the photovoltaic grid connected system and high detection speed.
Description
Technical field
The present invention relates to a kind of island detection method of photovoltaic parallel in system, belong to photovoltaic parallel in system control technology application.
Background technology
When the isolated island phenomenon of photovoltaic combining inverter refers to electrical network due to reason interruption of power supply such as electric fault or natural causes, inverter is still to the electrical network transmission of electric energy, with a uncontrollable self-energizing isolated island of public electric wire net system of the common formation of local load.The island detection method of inverter side is by whether the people can be divided into passive type (passive) and active (active) 2 kinds for applying disturbance, passive type detects the voltage referred to by detecting the common point place and overvoltage/under voltage, overfrequency/under-frequency isolated island detection method, Phase jump detection method, voltage harmonic detection method etc. whether occur extremely can being divided into, there is simple, the easy realization of principle, on the quality of power supply without advantages such as impacts, but, while adopting separately wherein any island detection method, there will be larger detection blind area; And the active detecting method has been broken the balance between system and load under the islet operation by adding to disturb, make common-node voltage exceed threshold range, thereby detect isolated island.Common active detecting method has active frequency drift method, automatic phase deflection method and current amplitude interference method etc.
The principle of active frequency drift method is: the frequency of controlling grid-connected current perturbation; make the frequency slightly high (or lower slightly) of photovoltaic grid connection inverter output current frequency ratio point of common coupling voltage; when mains supply is normal; the point of common coupling frequency is not changed by clamping down on of mains frequency; once electrical network decompression; the point of common coupling frequency will be offset by the impact of given current perturbation frequency, finally exceed the frequency protection set point and block inverter, realize island protect.The method is a kind of method of active detection preferably, without adding any hardware, as long as the frequency interferences coefficient applied is enough large, just can guarantee very high isolated island recall rate, but the current distortion that its given value of current non-sine is introduced, can produce harmful effect to the quality of power supply is to hinder the key factor that the active alone island detection method is widely used; Current amplitude disturbs ratio juris to be: by periodically given current amplitude being applied to interference, by judging that whether grid-connected Coupling point voltage is out-of-limit, determine whether having occurred isolated island.The method does not exist and detects blind area, but has reduced the meritorious output of photovoltaic grid-connected inversion, take and reduces generating efficiency as cost.
Therefore, how to guarantee that both fast detecting went out isolated island, that again the quality of power supply of parallel network power generation and efficiency are caused affects minimum, is the key of isolated island detection technique.
Summary of the invention
The object of the invention is to for above-mentioned deficiency of the prior art, propose a kind of littlely on mains by harmonics impact, detection speed is fast, and the meritorious output of photovoltaic parallel in system is affected to the island detection method of little photovoltaic parallel in system.
This inventive method is characterised in that: by detecting the electric voltage frequency f of point of common coupling PCC place
utowards the change frequency n of certain direction, thereby adaptive segmentation regulating frequency offset positive feedback coefficient k is accelerated frequency shift (FS), and if the absolute value of this change frequency n surpass 12 times, the electric voltage frequency f of point of common coupling PCC place
unot out-of-limit yet, apply the negative pulse current amplitude that continues 2 power frequency periods and disturb, trigger under-voltage protection, thereby detect isolated island.
The present invention is achieved through the following technical solutions:
Step 1 set the n initial value be 0 and n be integer;
Step 2 by zero cross detection circuit by the voltage u of point of common coupling PCC place
pccduring zero passage, rising edge or trailing edge signal are sent into digital processing unit, and calculate in real time the voltage cycle T of point of common coupling PCC place
u, and then obtain the electric voltage frequency f of point of common coupling PCC place
u;
If the electric voltage frequency f of step 3 point of common coupling PCC place
uincrease, n is from increasing 1; If the electric voltage frequency f of point of common coupling PCC place
ureduce, n is from subtracting 1; If the electric voltage frequency f of point of common coupling PCC place
uconstant, n remains unchanged;
The step 4 judgement electric voltage frequency f of point of common coupling PCC place
uscope and the voltage u of point of common coupling PCC place that frequency threshold is set have whether been exceeded
pccwhether exceeded the scope that voltage threshold is set, if the electric voltage frequency f of point of common coupling PCC place
uthe scope and the voltage u of point of common coupling PCC place that at frequency threshold, set
pccin the scope of also setting at voltage threshold, enter step 5; Otherwise, judge that isolated island occurs; Described frequency threshold comprises upper frequency limit threshold value and lower-frequency limit threshold value, and the upper frequency limit threshold value is 50.5Hz, and the lower-frequency limit threshold value is 49.5Hz; Described voltage threshold comprises upper voltage limit threshold value and lower voltage limit threshold value, and the upper voltage limit threshold value is (220 * 1.1) V, and the lower voltage limit threshold value is (220 * 0.88) V;
Step 5 calculates truncation function cf by formula (1) and (2), and wherein k is frequency shift (FS) positive feedback coefficient;
cf＝k(f
u-50) (2)
Step 6 calculates grid-connected current perturbation amplitude I by formula (3)
0;
In formula (3): I
mfor specified grid-connected current amplitude, the A of unit;
Δ t is the negative pulse duration, the s of unit;
Step 7 calculates grid-connected current perturbation i by formula (4)
give, adopt this grid-connected current perturbation i
givephotovoltaic parallel in system is applied to disturbance, proceeds to step 2,
The present invention compared with prior art, has following beneficial effect:
(1) little on the mains by harmonics impact.When the mains frequency normal fluctuation, consider the maximum situation that reaches 0.2Hz of fluctuation, as long as | n| is no more than 3 times, by formula (1) and (2), knows truncation function cf=0.001, apply the frequency interferences of low aberration rate, guarantee that isolated island detects the mains by harmonics that electrical network is caused and approaches 0; Only when | n| surpasses 3 times, just increase gradually frequency shift (FS) positive feedback coefficient k, truncation function cf is along with the increase of k just starts to increase by 0.001 gradually, and when | during n|=12, truncation function cf gets maximum, be only also 0.027, guarantee that isolated island detects the harmonic content that electrical network is caused and remains at low levels always;
(2) detection speed is fast.Shown in (1), the present invention proposes the thinking of self adaptation selecting frequency skew positive feedback coefficient k value, when | the n| value is larger, and the electric voltage frequency f of point of common coupling PCC place is described
ulasting change frequency towards certain direction is more, the possibility that the isolated island phenomenon occurs is larger, by formula (1) regulating frequency offset positive feedback coefficient k, increased gradually, strengthening gradually frequency shift (FS) disturbs, progressively dwindle the blind area that isolated island detects, accelerate frequency out-of-limit, thereby judge fast the generation of isolated island phenomenon;
(3) little on the meritorious output impact of photovoltaic parallel in system.Shown in (3), only working as | n| surpasses 12 times, i.e. the electric voltage frequency f of point of common coupling PCC place
utowards certain direction, continue to have changed at least 12 times, fault can absolutely prove when electrical network may occur, just apply the negative pulse current amplitude and disturb, and the negative pulse current amplitude applied disturbs only lasting 2 power frequency periods, the impact of minimizing on the meritorious output of photovoltaic parallel in system as far as possible.
The accompanying drawing explanation
The flow chart that Fig. 1 is island detection method of the present invention.
Fig. 2 is for adopting the simulated effect figure of the inventive method.
Embodiment
The present invention specifically is achieved through the following technical solutions:
Step 1 set the n initial value be 0 and n be integer;
Step 2 by zero cross detection circuit by the voltage u of point of common coupling PCC place
pccduring zero passage, rising edge or trailing edge signal are sent into digital processing unit, and calculate in real time the voltage cycle T of point of common coupling PCC place
u, and then obtain the electric voltage frequency f of point of common coupling PCC place
u; Described zero cross detection circuit is current known technology, for example can adopt document (Zheng Fei, take tree Min, Zhou Xingpeng, Wang Xin. the grid-connected control [J] based on the FPGA digital phase-locked loop. power electronic technology, 2010,44 (6): the zero cross detection circuit block diagram shown in Fig. 2 of the 54th page 53-54);
If the electric voltage frequency f of step 3 point of common coupling PCC place
uincrease, n is from increasing 1; If the electric voltage frequency f of point of common coupling PCC place
ureduce, n is from subtracting 1; If the electric voltage frequency f of point of common coupling PCC place
uconstant, n remains unchanged;
The step 4 judgement electric voltage frequency f of point of common coupling PCC place
uscope and the voltage u of point of common coupling PCC place that frequency threshold is set have whether been exceeded
pccwhether exceeded the scope that voltage threshold is set, if the electric voltage frequency f of point of common coupling PCC place
uthe scope and the voltage u of point of common coupling PCC place that at frequency threshold, set
pccin the scope of also setting at voltage threshold, enter step 5; Otherwise, judge that isolated island occurs;
Step 5 calculates truncation function cf by formula (1) and (2), and wherein k is frequency shift (FS) positive feedback coefficient.On the one hand, little on the mains by harmonics impact, because when the mains frequency normal fluctuation, consider the maximum situation that reaches 0.2Hz of fluctuation, as long as | n| is no more than 3 times, by formula (1) and (2), know truncation function cf=0.001, apply the frequency interferences of low aberration rate, guarantee that isolated island detects the mains by harmonics that electrical network is caused and approaches 0, only when | n| surpasses 3 times, just increase gradually frequency shift (FS) positive feedback coefficient k, truncation function cf is along with the increase of k just starts to increase by 0.001 gradually, and when | during n|=12, truncation function cf gets maximum, be only also 0.027, guarantee that isolated island detects the harmonic content that electrical network is caused and remains at low levels always, on the other hand, detection speed is fast, and shown in (1), the present invention proposes the thinking of self adaptation selecting frequency skew positive feedback coefficient k value, when | the n| value is larger, and the electric voltage frequency f of point of common coupling PCC place is described
ulasting change frequency towards certain direction is more, the possibility that the isolated island phenomenon occurs is larger, by formula (1) regulating frequency offset positive feedback coefficient k, increased gradually, strengthening gradually frequency shift (FS) disturbs, progressively dwindle the blind area that isolated island detects, accelerate frequency out-of-limit, thereby judge fast the generation of isolated island phenomenon,
cf＝k(f
u-50) (2)
Step 6 calculates grid-connected current perturbation amplitude I by formula (3)
0.From formula (3), only working as | n| surpasses 12 times, i.e. the electric voltage frequency f of point of common coupling PCC place
utowards certain direction, continue to have changed at least 12 times, fault can absolutely prove when electrical network may occur, just apply the negative pulse current amplitude and disturb, and the negative pulse current amplitude applied disturbs only lasting 2 power frequency periods, the impact of minimizing on the meritorious output of photovoltaic parallel in system as far as possible;
In formula (3): I
mfor specified grid-connected current amplitude, the A of unit;
Δ t is the negative pulse duration, the s of unit;
Step 7 calculates grid-connected current perturbation i by formula (4)
give, adopt this grid-connected current perturbation i
givephotovoltaic parallel in system is applied to disturbance, proceeds to step 2,
With reference to the accompanying drawings and in conjunction with Matlab/Simulink & The present invention is described in further detail to the simulation example of single-phase photovoltaic grid-connected system for Simpowersystems.But the invention is not restricted to given example.
Concrete simulation parameter is as follows: the single-phase photovoltaic grid-connected system rated output power is 5kW, load employing and the RLC shunt load that the single-phase photovoltaic grid-connected system power output balances each other and quality factor are 2.5, the line voltage effective value is 220V, the upper voltage limit threshold value of the voltage threshold of voltage protection is (220 * 1.1) V, and the lower voltage limit threshold value is (220 * 0.88) V; The electrical network rated frequency is 50Hz, and the upper frequency limit threshold value of the frequency domain threshold value of frequency protection is 50.5Hz, and the lower-frequency limit threshold value is 49.5Hz.The failure condition of emulation is: at 0.3s constantly; grid cut-off, single-phase photovoltaic grid-connected system and load form a self-centered isolated island, require the island detection method must be at 0.3s thereafter; be to detect isolated island in High-Speed Automatic reclosure time, thereby realize effective island protect.
Adopt the simulated effect figure of the inventive method as shown in Figure 2, as seen from Figure 2:
(1), when electrical network does not cut off the power supply between 0～0.3s, the electric voltage frequency f of point of common coupling PCC place detected
ufluctuation in 50 ± 0.1Hz scope, due to | n| does not surpass 3 times, thinks and does not have the isolated island phenomenon to occur, and frequency shift (FS) positive feedback coefficient k is taken as 0.01, and truncation function cf is no more than 0.001, only applies the frequency interferences of low aberration rate;
(2) when after 0.3s moment grid cut-off, | n| surpasses 3 times very soon, and frequency shift (FS) positive feedback coefficient k take 0.015 as slope, proportional increase with | the increase of n|, correspondingly truncation function cf also increases towards negative direction gradually, accelerates the electric voltage frequency f of point of common coupling PCC place
uto the underfrequency protection value, 49.5Hz approaches;
(3) due to when | when n| equals 12 times, the electric voltage frequency f of point of common coupling PCC place
ufor 49.64Hz, do not reach the lower-frequency limit threshold value 49.5Hz of the frequency domain threshold value of frequency protection, therefore, apply current perturbation amplitude I
0negative pulse disturb, and continue two power frequency periods, thereby trigger under-voltage protection; success realizes at 0.6s; be that High-Speed Automatic reclosing action stops being incorporated into the power networks of single-phase photovoltaic grid-connected system before, the whole time that detects isolated island is only 0.272s, at 0.572s, constantly detects isolated island.
Claims (2)
1. the island detection method of a photovoltaic parallel in system is characterized in that according to the following steps photovoltaic parallel in system being carried out to the isolated island detection:
Step 1 set the n initial value be 0 and n be integer;
Step 2 by zero cross detection circuit by the voltage u of point of common coupling PCC place
pccduring zero passage, rising edge or trailing edge signal are sent into digital processing unit, and calculate in real time the voltage cycle T of point of common coupling PCC place
u, and then obtain the electric voltage frequency f of point of common coupling PCC place
u;
If the electric voltage frequency f of step 3 point of common coupling PCC place
uincrease, n is from increasing 1; If the electric voltage frequency f of point of common coupling PCC place
ureduce, n is from subtracting 1; If the electric voltage frequency f of point of common coupling PCC place
uconstant, n remains unchanged;
The step 4 judgement electric voltage frequency f of point of common coupling PCC place
uscope and the voltage u of point of common coupling PCC place that frequency threshold is set have whether been exceeded
pccwhether exceeded the scope that voltage threshold is set, if the electric voltage frequency f of point of common coupling PCC place
uthe scope and the voltage u of point of common coupling PCC place that at frequency threshold, set
pccin the scope of also setting at voltage threshold, enter step 5; Otherwise, judge that isolated island occurs;
Step 5 calculates truncation function cf by formula (1) and (2), and wherein k is frequency shift (FS) positive feedback coefficient;
cf＝k(f
u-50) (2)
Step 6 calculates grid-connected current perturbation amplitude I by formula (3)
0;
In formula (3): I
mfor specified grid-connected current amplitude, the A of unit;
Δ t is the negative pulse duration, the s of unit;
Step 7 calculates grid-connected current perturbation i by formula (4)
give, adopt this grid-connected current perturbation i
givephotovoltaic parallel in system is applied to disturbance, proceeds to step 2,
2. the island detection method of photovoltaic parallel in system as claimed in claim 1, is characterized in that, described frequency threshold comprises upper frequency limit threshold value and lower-frequency limit threshold value, and the upper frequency limit threshold value is 50.5Hz, and the lower-frequency limit threshold value is 49.5Hz; Described voltage threshold comprises upper voltage limit threshold value and lower voltage limit threshold value, and the upper voltage limit threshold value is 220 * 1.1V, and the lower voltage limit threshold value is 220 * 0.88V.
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| CN102624027B (en) * | 2012-03-26 | 2014-03-05 | 东北大学 | Multiprocess island effect detection device and method |
| CN102723735B (en) * | 2012-06-29 | 2015-06-17 | 京东方科技集团股份有限公司 | Island detection method and system |
| US9520819B2 (en) | 2014-02-28 | 2016-12-13 | General Electric Company | System and method for controlling a power generation system based on a detected islanding event |
| CN103941118B (en) * | 2014-03-26 | 2017-01-04 | 中国科学院电工研究所 | Island detection method for photovoltaic power generation grid-connected inverter group system |
| CN103969549B (en) * | 2014-04-18 | 2016-08-17 | 珠海许继电气有限公司 | The island detection method of power-supply device and isolated island detecting device |
| CN104062529B (en) * | 2014-07-09 | 2017-06-13 | 华北电力大学 | A kind of island detection method |
| CN104237712B (en) * | 2014-10-16 | 2017-06-13 | 华北电力大学 | Island detection method and device and island disposal system |
| CN104267317B (en) * | 2014-10-21 | 2017-02-22 | 华北电力大学 | Islanding detection method based on reactance layered switching |
| CN104485683B (en) * | 2014-12-23 | 2018-07-06 | 南京南瑞继保电气有限公司 | A kind of isolated island turns networking method |
| CN104882904B (en) * | 2015-02-16 | 2017-06-16 | 国网宁夏电力公司 | A kind of anti-isolated island guard method of new photovoltaic plant passive type |
| CN106383297A (en) * | 2016-11-07 | 2017-02-08 | 燕山大学 | Frequency acceleration positive feedback island detection method with hysteresis |
| CN108110785B (en) | 2016-11-24 | 2021-04-20 | 华为技术有限公司 | Inverter anti-islanding control system |
| CN107526009B (en) * | 2017-09-13 | 2019-04-05 | 国电南瑞科技股份有限公司 | It is a kind of that Interlocking Methods are detected according to the isolated island of frequency and curent change timing |
| CN107612026B (en) * | 2017-09-13 | 2020-11-03 | 国电南瑞科技股份有限公司 | Island detection method based on multi-band harmonic voltage and frequency |
| CN107979091B (en) * | 2017-12-19 | 2021-05-07 | 宁夏大学 | Rapid positive feedback active frequency shift type island detection method |
| CN108445424B (en) * | 2018-02-13 | 2020-05-08 | 天津大学 | Hybrid inverter type distributed power supply island detection method |
| CN108680822B (en) * | 2018-08-20 | 2021-01-26 | 金陵科技学院 | Self-adaptive island detection method and capacitive load judgment method thereof |
| CN109031045B (en) * | 2018-08-21 | 2020-09-29 | 东北大学 | Active power-voltage cross correlation degree island detection method based on self-adaptive threshold selection |
| CN111856172A (en) * | 2019-04-24 | 2020-10-30 | 上海电机学院 | Island detection method based on active frequency deviation method |
| CN110632413B (en) * | 2019-09-02 | 2022-02-11 | 国网吉林省电力有限公司 | Reactive power disturbance island detection method triggered in delayed mode |
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| EP1764894A1 (en) * | 2005-09-19 | 2007-03-21 | ABB Schweiz AG | Method for detecting islanding operation of a distributed generator |
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