CN101741101B - Method for realizing network access current of unity power factor of grid-connected inverter and internal anti-islanding - Google Patents
Method for realizing network access current of unity power factor of grid-connected inverter and internal anti-islanding Download PDFInfo
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- CN101741101B CN101741101B CN2010101009039A CN201010100903A CN101741101B CN 101741101 B CN101741101 B CN 101741101B CN 2010101009039 A CN2010101009039 A CN 2010101009039A CN 201010100903 A CN201010100903 A CN 201010100903A CN 101741101 B CN101741101 B CN 101741101B
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Abstract
The invention discloses a method for realizing a network access current of a unity power factor of a grid-connected inverter and internal anti-islanding, which belongs to control technology of inverters. The method comprises the following steps: phase difference detection, frequency droop calculation, reference current generation, grid voltage feed-forward and a proportional integral controller. A frequency droop algorithm comprises the following steps: performing real-time calculation on a phase difference between the network access current and a grid voltage; multiplying the phase difference by a droop coefficient to obtain a frequency variable quantity; and subtracting the frequency variable quantity from a previous frequency output quantity of the last frequency droop algorithm so as to obtain an output quantity of a new frequency droop algorithm. The method realizes phase control of the network access current of the grid-connected inverter, realizes the network access current of the unity power factor, and internally realizes an anti-islanding measure of frequency drift positive feedback of the grid-connected inverter at the same time. Therefore, the method is of a simple and effective realizing mode.
Description
Technical field
A kind of combining inverter network access current unit power factor that the present invention relates to in the control method of anti-isolated island, belong to the control technology field of converter.
Background technology
Energy crisis and ecological deterioration make the countries in the world active development comprise regenerative resources such as photovoltaic, wind energy.Utilize the distributed power generation technology of these energy to become the important component part of the global energy strategy of sustainable development.One of new forms of energy distributed power generation research focus is the inverter control technology that is incorporated into the power networks.The control method of combining inverter can be divided into current-mode control and voltage-type control, and the middle low power single-phase grid-connected inverter generally adopts current-mode control at present.The proportional integral control of the common method of Current Control, stagnate ring control, dead beat control and the control of ratio resonance etc., all these control methods all need adopt Phase Lock Technique that the reference current phase place of following the tracks of line voltage is provided for the inverter current control ring.Because there is the influence of phase lag and the decay of network access filter phases and signal sampling and calculating time-delay etc. in parameter be provided with of inverter current ring controller under consideration stability, exists certain fundamental phase poor between actual network access electric current and the current reference.Relevant international standard; Like IEEE15471 etc.; All requiring the network access power factor greater than 0.999 (being that phase difference is less than 2.6 degree), mainly be the phase place of in digit chip, regulating the accurate electric current of inverter current cyclic group to this way to solve the problem at present, and this control method belongs to adjusted open loop; Its precision is not high, and receives the influence of network access size of current obvious.Therefore need find a kind of method that can effectively address this problem.
In addition; The requisite measure that the anti-isolated island measure of combining inverter is assurance equipment and network operation personal security; Majority is to be the perturbation motion method of cost to sacrifice network access electric current quality or loss network access power etc. in existing island detection technology, and it is bigger to detect the blind area.
Sagging control method comes from synchronous generator in the electric power system theory that is incorporated into the power networks, and can realize Control Parameter, like voltage or frequency, real-time regulated.But this method is by more being applied in DC converter parallel connection and the inverter parallel control technology at present, and its application in the current-mode control combining inverter does not also appear in the newspapers.
Summary of the invention
The objective of the invention is to overcome above-mentioned defective, provide a kind of novel inverter that PHASE-LOCKED LOOP PLL TECHNIQUE and sagging control method are combined to be incorporated into the power networks and lock control strategy mutually.Thereby the phase difference through real-time detection network access electric current and line voltage carries out the frequency of sagging calculating adjustment network access current reference comes the floating voltage phase place, realizes the unity power factor of network access electric current.
The present invention adopts following technical scheme for realizing above-mentioned purpose:
The present invention realizes the method for network access current of unity power factor of grid-connected inverter; Said method is following: network access electric current and line voltage are obtained phase difference through phase difference detection; Said phase difference is obtained the reference current frequency after the sagging calculating of overfrequency; With said reference current frequency and the synthetic network access reference current of reference current amplitude; Said network access reference current and network access current feedback subtracted each other produce difference between current and export regulation voltage, said regulation voltage and the addition of voltage feed-forward control amount are obtained modulating wave through pi controller, with modulating wave through acting on generation network access electric current on the network access filter with the difference of line voltage behind the amplifying circuit.
Realize the inherent anti-isolated island method of combining inverter unity power factor; The frequency output variable of the sagging calculating of said frequency is for calculating in real time the phase difference of network access electric current and line voltage and obtain frequency variation with sagging multiplication, thereby deducts the output variable that this frequency variation obtains the new sagging algorithm of frequency with the preceding secondary frequencies output variable of the sagging algorithm of frequency again; After combining inverter got into island state, the sagging calculating of frequency made the positive feedback of network access reference current frequency quicken continuous decrease or the increase of reference frequency and makes inverter generation under-frequency or overfrequency, thereby realizes the isolated island protection.
The phase difference that the invention enables network access electric current and line voltage is zero, and can realize the anti-isolated island measure of the frequency drift positive feedback of combining inverter.
Description of drawings
Fig. 1 is the control block diagram and the power circuit of control method of the present invention, (a) based on the sagging network access current phase control block diagram of frequency; (b) single-phase full bridge synchronization inverter main circuit;
Fig. 2 is the relation curve of network access electric current and electric network voltage phase difference and circuit parameter and controller parameter under traditional network access current phase control mode, and (a) phase difference is with the inductance change curve; (b) phase difference is with the proportionality coefficient change curve; (c) phase difference is with electric current loop integral coefficient change curve;
Fig. 3 is the contrast of network access current phase control strategy of the present invention and conventional phase control strategy, networking electric current and grid voltage waveform when (a) adopting the traditional locks phase method; (b) line voltage and network access current waveform under the present invention;
Fig. 4 is the operation oscillogram of the sagging control method of frequency of the present invention at island state, t
1Moment electric network power-fail, combining inverter gets into islet operation state, t
2Constantly detect under-frequency, accomplish the island detection protection.
The main symbol of above-mentioned accompanying drawing and label title: U
D---the inverter input voltage; S
1～S
4---power switch pipe; u
g---line voltage; L
1, L
2---the network access filter inductance; i
o---the network access electric current; u
o---inverter output voltage (filter inductance outside electrical network end); θ---the phase difference of network access electric current and line voltage; ω---network access current reference angular frequency; I
o *---network access reference current amplitude; i
o *---the network access reference current; K
p---the ratio amplification coefficient; K
i---integral coefficient; K
PWM---the inverter bridge multiplication factor; K
N---the voltage feed-forward control amplification coefficient; u
Inv---inverter bridge mid point output voltage; u
L---filter inductance voltage.
Embodiment
Be elaborated below in conjunction with the technical scheme of accompanying drawing to invention:
Accompanying drawing 1 has been described the main circuit of phase control block diagram of the present invention and enforcement, is made up of phase difference detection, the sagging calculating of frequency, reference current generation, voltage feed-forward control and pi controller.
Network access reference current i
o *Obtain phase reference from phase-locked loop pll.At K
N=1/K
PWMThe time, its closed loop transfer function, is suc as formula shown in (1).
The phase difference of network access electric current and line voltage is:
Can find out that from (2) formula the parameter that influences phase difference has 3: L, k
pAnd k
i, accompanying drawing 2 is the relation curves for network access electric current and electric network voltage phase difference and circuit parameter and controller parameter.Accompanying drawing 2 (a) has provided the change curve of phase difference with the filter inductance value, can find out, along with the increase of filter inductance sense value, phase difference increases gradually; Accompanying drawing 2 (b) has provided the curve when phase difference changes with the electric current loop proportionality coefficient, can find out, with the increase of proportionality coefficient, phase difference increases afterwards earlier and reduces; In the accompanying drawing 2 (c), phase difference reduces with the increase of integral coefficient.In order to guarantee comparatively pure network access electric current, filter inductance sense value can not be too little; Under the prerequisite of certain current tracking precision, need guarantee system stability again, the proportionality coefficient of electric current loop and integral coefficient should not be got too big.Therefore, theoretically, the outer phase compensation device of plus not, the phase difference of network access electric current and line voltage is inevitable, if consider the time-delay of electric network voltage phase detection link again, phase difference is just considerable.
The phase-locked loop that the present invention is based in the combining inverter control strategy of droop characteristic software phase-lock loop is the phase-locked loop with sagging characteristic, and its output frequency is controlled by the phase difference of combining inverter network access electric current and line voltage.Each power frequency period obtains the difference θ of the phase place of network access electric current and line voltage, detects the electrical network angular frequency simultaneously
o, the frequency of next periodic basis electric current of inverter is confirmed by formula (3).
ω(k)＝ω(k-1)-k
ω·θ (3)
If it is leading to detect electric network voltage phase; Be that θ is a negative value, through sagging computing formula, the frequency of reference current that obtains following one-period is greater than the frequency of line voltage; So in the time of next cycle; Phase difference between them will dwindle, and through several power frequency periods, finally the phase difference between them equals 0; In like manner can explain θ be on the occasion of the time situation.
An instantiation of the present invention is following: input voltage U
D=400V, line voltage U
Grid=240VRMS, mains frequency f
Grid=50Hz, rated power P
N=1kW; Filter inductance L
1=L
2=5mH; Switching frequency f=10kHz; K
p=1; K
i=1000; K
ω=50.Accompanying drawing 3～4 is the concrete oscillogram of this instance, and wherein, accompanying drawing 3 is contrasts of network access electric current and electric network voltage phase difference under network access electric current of the present invention and electric network voltage phase difference and the traditional control method; Accompanying drawing 4 is the present invention's operation oscillograms at island state.
Claims (1)
1. method that realizes network access current of unity power factor of grid-connected inverter; It is characterized in that said method is following: network access electric current and line voltage are obtained phase difference through phase difference detection; Said phase difference is obtained the reference current frequency after the sagging calculating of overfrequency; With said reference current frequency and the synthetic network access reference current of reference current amplitude; Said network access reference current and network access current feedback subtracted each other produce difference between current and export regulation voltage, said regulation voltage and the addition of voltage feed-forward control amount are obtained modulating wave through pi controller, with modulating wave through acting on generation network access electric current on the network access filter with the difference of line voltage behind the amplifying circuit; Wherein, The frequency output variable of the sagging calculating of said frequency is for calculating in real time the phase difference of network access electric current and line voltage and obtain frequency variation with sagging multiplication, thereby deducts the output variable that this frequency variation obtains the new sagging algorithm of frequency with the preceding secondary frequencies output variable of the sagging algorithm of frequency again; After combining inverter got into island state, the sagging calculating of frequency made the positive feedback of network access reference current frequency quicken continuous decrease or the increase of reference current frequency and makes inverter generation under-frequency or overfrequency, thereby realizes the isolated island protection.
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| CN2010101009039A CN101741101B (en) | 2010-01-22 | 2010-01-22 | Method for realizing network access current of unity power factor of grid-connected inverter and internal anti-islanding |
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| Application Number | Priority Date | Filing Date | Title |
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| CN2010101009039A CN101741101B (en) | 2010-01-22 | 2010-01-22 | Method for realizing network access current of unity power factor of grid-connected inverter and internal anti-islanding |
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| CN101741101A CN101741101A (en) | 2010-06-16 |
| CN101741101B true CN101741101B (en) | 2012-11-21 |
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|---|---|---|---|---|
| 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 |
| US11777322B2 (en) | 2020-06-03 | 2023-10-03 | Delta Electronics (Shanghai) Co., Ltd | Islanding detection mothod for inverter and apparatus |
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| CN101969272B (en) * | 2010-09-21 | 2013-04-17 | 电子科技大学 | Grid-connected current control device of photovoltaic inverter |
| CN102510064B (en) * | 2011-11-08 | 2015-02-18 | 山东大学 | Improved droop control method in micro electric network detached island operation control system |
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Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN1972061B (en) * | 2005-11-21 | 2010-11-17 | 中国科学院电工研究所 | Apparatus and method of recovering voltage amplitude and phase in drooping method of outer characteristic |
| CN100539381C (en) * | 2005-12-30 | 2009-09-09 | 中国科学院电工研究所 | A kind of control method of network-connecting generation inverter output current |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| 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 |
| US11777322B2 (en) | 2020-06-03 | 2023-10-03 | Delta Electronics (Shanghai) Co., Ltd | Islanding detection mothod for inverter and apparatus |
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| CN101741101A (en) | 2010-06-16 |
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