CN103645767A - Maximum power point tracking method based on power stepping disturbance - Google Patents

Abstract

The invention discloses a maximum power point tracking method based on power stepping disturbance. In a single-stage photovoltaic connected grid power generation system, stable work points of a photovoltaic array are all in a right area including the maximum power point, and the left side of the maximum power point is an unstable work area. The operation track of photovoltaic array output voltage can be changed by controlling the magnitude of connected grid power in the unstable work area, and accordingly the operation track enters a stable work area. According to the method, an array output voltage value does not need to be collected for power judgment, a maximum power point tracking algorithm can be achieved if the photovoltaic array output voltage is observed, and accordingly the algorithm cannot be influenced by sampling quantization errors.

Description

A kind of maximum power point tracing method based on power stepping disturbance

Technical field

The invention belongs to the renewable generation of electricity by new energy technical field of distributed solar, be specifically related to a kind of maximum power point tracing method based on power stepping disturbance.

Background technology

The characteristics of output power of photovoltaic cell has very strong non-linear, and its peak power output and peak power output point voltage and electric current are along with the factors vary such as unbalanced degree of temperature, intensity of illumination, illumination.Only have the effective MPPT maximum power point tracking algorithm of employing, could improve the utilization factor of photovoltaic generating system to photovoltaic cell component electric energy.

At present, the method that photovoltaic generating system is realized MPPT maximum power point tracking has a lot: determine voltage method, disturbance observation, increment conductance method, short-circuit current method etc., but these methods respectively have its relative merits and the scope of application.Determining voltage method, to utilize the maximum power point voltage of photovoltaic cell and the ratio of its open-circuit voltage be this characteristic of a constant (being approximately 0.78), and the output voltage of controlling photovoltaic array meets the open-circuit voltage of 0.78 times.The method is controlled simple, is easy to realize, and tracking velocity is fast, but when extraneous environmental change causes open-circuit voltage to change, the output power of photovoltaic cell can depart from maximum power point.Disturbance observation is to utilize the characteristic single peak feature of photovoltaic array P-V, the output voltage of disturbance light photovoltaic array or electric current, observe the variation of photovoltaic array output power, the trend changing according to power continuously changes disturbance voltage or direction of current, makes it be operated in maximum power point place.The method is controlled simple, less demanding to detecting element, but can cause concussion and erroneous judgement.Increment conductance method is also to utilize single peak feature of its P-V curve, makes dP/dV=0, and

therefore will

condition as judgement maximum power point.The method is controlled accurately, fast response time, but algorithm is complicated, and detecting element is had relatively high expectations, and also there will be concussion and misjudgment phenomenon.

When MPPT maximum power point tracking algorithm adopts digitized form to realize, the digitizing meeting of some algorithm causes some impacts to MPPT maximum power point tracking performance, even can make in some cases MPPT maximum power point tracking lose efficacy, in the situation that not considering noise, quantization error is one of reason causing the inefficacy of digitizing MPPT maximum power point tracking algorithm.So need to find a kind of maximum power point tracing method to solve the impact of sample quantization error on MPPT maximum power point tracking.

Summary of the invention

The object of this invention is to provide a kind of maximum power point tracing method based on power stepping disturbance, under the stable prerequisite of array voltage, inverter output power is carried out to stepping increase, whether observe array voltage in steady operation region, solved the problem that existing maximum power point tracing method quantization error causes algorithm to lose efficacy.

The technical solution adopted in the present invention is, the maximum power point tracing method based on power stepping disturbance is specifically implemented according to following steps:

Step 1: the stable state impedance model of setting up Single-Stage Grid Connected Solar Inverter System;

Step 2: the dynamic mathematical models of setting up Single-Stage Grid Connected Solar Inverter System;

Step 3: the stability of analyzing Single-Stage Grid Connected Solar Inverter System;

Step 4: realize MPPT maximum power point tracking on stability analysis basis.

Feature of the present invention is also,

The stable state impedance model of setting up Single-Stage Grid Connected Solar Inverter System wherein, specifically according to following steps, implement:

Monophase system is stable state active power of output P ideally _1Pbe expressed as:

P _1p=λI _iV _g，

Wherein, I _iwith V _gbe respectively the effective value of grid-connected current and line voltage, λ is power factor; The work efficiency that represents combining inverter with η, the circuit equivalent impedance R of system DC filter capacitor C aft section _1Pbe expressed as:

$R_{1p}=\frac{{V_{\mathrm{pv}}}^2}{P_{1p}/\mathrm{\&eta;}}=\mathrm{\&eta;}\frac{{{\mathrm{<figure-callout\; id="2"\; label="V\; pv"\; filenames="HDA0000365408700000021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{pv}}}^2}{{\mathrm{\&lambda;I}}_i{V}_g},$

In formula, V _pVequal DC bus-bar voltage;

Three-phase system is its active power of output P ideally _3Pbe expressed as:

$P_{3p}=\frac{3}{2}{V}_q{I}_q,$

Wherein, I _qwith V _qbe respectively grid-connected current and the line voltage q axle real component under two-phase rotating coordinate system; Three-phase system DC filter capacitor aft section equiva lent impedance R _3Pbe expressed as:

$R_{3p}=\frac{{V_{\mathrm{pv}}}^2}{P_{3p}/\mathrm{\&eta;}}=\mathrm{\&eta;}\frac{{{2\mathrm{<figure-callout\; id="2"\; label="V\; pv"\; filenames="HDA0000365408700000021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{pv}}}^2}{{3V}_q{I}_q},$

From above formula:

$R_{1p}\&Proportional;\frac{1}{I_i},R_{3p}\&Proportional;\frac{1}{I_q},$

The amplitude size of grid-connected current is directly proportional to the output power of combining inverter, that is:

I _i∝P _1p，I _q∝P _3p，

There is proportionate relationship in grid-connected output power and photovoltaic array output power:

P _1p=ηP _pv，P _3p=ηP _pv。

The dynamic mathematical models of setting up Single-Stage Grid Connected Solar Inverter System wherein, specifically according to following steps, implement:

The voltage at capacitor C two ends equates with photovoltaic array voltage, with i _pV, i _c, i _outthe momentary current that represents respectively photovoltaic array output momentary current, the instantaneous charging current of DC filter capacitor and filter capacitor aft section circuit, v _pVrepresent photovoltaic array output instantaneous voltage, p _outfor photovoltaic array instantaneous output:

$i_{\mathrm{pv}}=i_c+i_{\mathrm{out}}=C\frac{{\mathrm{dv}}_{\mathrm{pv}}}{\mathrm{dt}}+\frac{p_{\mathrm{out}}}{v_{\mathrm{pv}}},$

In conjunction with photovoltaic cell component mathematical model (I _z=f (I _ph, V)=Iph-ε [exp (ξ V _z)-1]) can obtain as shown in the formula the photovoltaic generating system dynamic model representing with above formula, in formula,

$\left\{\begin{array}{c}{\stackrel{\&CenterDot;}{v}}_{\mathrm{pv}}=\frac{I_{\mathrm{ph}}}{C}-\frac{\mathrm{\&epsiv;}}{C}[\exp \left(\mathrm{\&xi;}{v}_{\mathrm{pv}}\right)-1]-\frac{p_{\mathrm{out}}}{{\mathrm{Cv}}_{\mathrm{pv}}}\\ v_{\mathrm{pv}}=v_{\mathrm{pv}}\left(0\right)+{\stackrel{\&CenterDot;}{v}}_{\mathrm{pv}}\end{array}\right.,$

Wherein, I _zfor photovoltaic module output current, I _phfor the equivalent photogenerated current of battery component, V _zfor photovoltaic module output voltage, ε=n _pi ₀, n _pfor batteries in parallel connection number of unit, I ₀for the P-N knot reverse saturation current of photovoltaic cell inside equivalent diode, ξ=q/n _ck _ctn _sq is electronic charge, n _cfor the diode characteristic factor, k _cfor Boltzmann constant, T is photovoltaic cell absolute temperature, n _sfor series-connected cell number of unit;

For monophase system, in output power, contain alternating component, be ideally described as:

$p_{\mathrm{out}}=\stackrel{\&OverBar;}{p}+\stackrel{\&OverBar;}{p}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000365408700000021.png"\; state="\{\{state\}\}">cos</figure-callout>}2{\mathrm{\&omega;}}_{g}t,$

Wherein,

for average output power, ω _gfor mains frequency;

For three-phase system, ideally in its output power, only contain flip-flop, with following formula, represent:

$p_{\mathrm{out}}=\stackrel{\&OverBar;}{p},$

In DC filter capacitor, store certain energy, and exist:

p _pv=p _out+i _cv _pv。

The stability of analysis Single-Stage Grid Connected Solar Inverter System wherein, specifically implements according to following steps: the stable operating point of photovoltaic array is all comprising the right side area of maximum power point, and maximum power point left field is astable workspace; When unstable region, by controlling grid-connected watt level, change the movement locus of photovoltaic array output voltage, thereby make it enter stable work area.

Wherein realize MPPT maximum power point tracking, adopt power step-by-step method, specifically according to following steps, implement: with grid-connected reference current amplitude signal I _refreplace photovoltaic array output power, first photovoltaic array voltage is sampled, sampled result leaves variable V in _pVin, and then calculate current to determining voltage signal V _refwith V _pVdifference e _v;

If e _va value continuous several times calculated value e front with it _{v_1}equate, think photovoltaic array output voltage stabilization, now by V _pVvalue be given to determining voltage signal V _ref, then according to the disturbance increment dI of front once given output current _refwith e _vratio size determine new given grid-connected current amplitude increment dI _refsize, and recalculate the given I of grid-connected current amplitude _ref;

Work as e _vvalue is greater than e _{v_1}during value, illustrate that line voltage declines, when if the continuous decline of line voltage cannot be stablized, now adoption rate controller reduces grid-connected current amplitude containment photovoltaic array voltage drop trend, and make photovoltaic array voltage move to stable point by stable trajectory, after photovoltaic array output voltage stabilization, again increase combining inverter output power value, repeat observation and the processing of array voltage;

Work as e _vvalue is less than e _{v_1}during value, explanation is in the situation that combining inverter output power is certain, in the process that array output voltage is rising, now array voltage moves with stable trajectory, it finally can converge on stable point, thus at array output voltage ascent stage, do not change grid-connected output power, after its steady operation, increase gradually again combining inverter output power, finally realize MPPT maximum power point tracking function.

The invention has the beneficial effects as follows, need not gather array output power value and carry out power judgement, only need just observe and can realize MPPT maximum power point tracking algorithm photovoltaic array output voltage, so this algorithm can not be subject to the impact of sample quantization error, and controlled quentity controlled variable precision is higher, given stepping power increment is less, gets over the accurately peak power output point of tracking photovoltaic array, and the method can adopt step length changing method realize the quick tracking under steady state conditions according to system output power value in addition.

Accompanying drawing explanation

Fig. 1 is two class Single-Stage Grid Connected Solar Inverter Systems, and wherein (a) is single-phase single-grade formula grid-connected photovoltaic system, is (b) three-phase single-level formula grid-connected photovoltaic system;

Fig. 2 is single stage type grid-connected system equivalent electrical circuit;

Fig. 3 is P-V characteristic and the R-V family curve of photovoltaic array;

Fig. 4 be photovoltaic array I-V characteristic from different equipower lines between relation;

Fig. 5 is photovoltaic array band power source load module;

Fig. 6 is P-V family curve under realistic model Plays condition;

Fig. 7 is the array voltage motion analysis of desirable three-phase single-level formula grid-connected system initialization when maximum power point right side, wherein (a) is that given output power is less than maximum power point power situation, is (b) power situation that given output power is greater than maximum power point;

Fig. 8 is the array voltage motion analysis of desirable three-phase single-level formula grid-connected system initialization when maximum power point left side;

Array voltage stability analysis when Fig. 9 is desirable single-phase single-grade formula grid-connected system output power point variation, (a) is V _pv(0) <V _mand (0) array voltage movement locus time, (b) is V _pv(0) <V _mand

(0) array voltage movement locus time, (c) is V _pv(0) >V _mand

(0) array voltage movement locus time, (d) is V _pv(0) >V _mand

(0) array voltage movement locus time, (e) is V _pv(0) >V _mand

time array voltage movement locus, (f) be V _pv(0) >V _mand

time array voltage movement locus;

Figure 10 is power stepping MPPT maximum power point tracking algorithm flow chart.

Embodiment

Below in conjunction with the drawings and specific embodiments, the present invention is described in detail.

The present invention proposes power step-by-step method and realizes MPPT maximum power point tracking, and Fig. 1 the present invention is based on hardware circuit basis, and wherein C is DC side filter capacitor, and L is AC filter inductance, and MPPT maximum power point tracking adopts power step-by-step method.The specific algorithm of power step-by-step method can be realized like this: with grid-connected reference current amplitude signal I _refreplace photovoltaic array output power.Figure 10 is the software flow pattern that power step-by-step method realizes MPPT maximum power point tracking, specifically according to following steps, implements:

Step 1: the stable state impedance model of setting up Single-Stage Grid Connected Solar Inverter System.Concrete steps are:

Monophase system shown in Fig. 1 (a), ideally its stable state active power of output P _1Pcan be expressed as:

P _1p=λI _iV _g （1）

Wherein, I _iwith V _gbe respectively the effective value of grid-connected current and line voltage, λ is power factor.If represent the work efficiency of combining inverter with η, the circuit equivalent impedance R of system DC filter capacitor C aft section _1Pcan be expressed as:

$R_{1p}=\frac{{V_{\mathrm{pv}}}^2}{P_{1p}/\mathrm{\&eta;}}=\mathrm{\&eta;}\frac{{{\mathrm{<figure-callout\; id="2"\; label="V\; pv"\; filenames="HDA0000365408700000021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{pv}}}^2}{{\mathrm{\&lambda;I}}_i{V}_g}---\left(2\right)$

In formula, V _pVequal DC bus-bar voltage.

To the three-phase system shown in Fig. 1 (b), ideally its active power of output P _3Pcan be expressed as:

$P_{3p}=\frac{3}{2}{V}_q{I}_q---\left(3\right)$

Wherein, I _qwith V _qbe respectively grid-connected current and the line voltage q axle real component under two-phase rotating coordinate system.In like manner, three-phase system DC filter capacitor aft section equiva lent impedance R _3Pcan be expressed as:

$R_{3p}=\frac{{V_{\mathrm{pv}}}^2}{P_{3p}/\mathrm{\&eta;}}=\mathrm{\&eta;}\frac{{{2\mathrm{<figure-callout\; id="2"\; label="V\; pv"\; filenames="HDA0000365408700000021.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{pv}}}^2}{{3V}_q{I}_q}---\left(4\right)$

So the photovoltaic generating system main circuit shown in Fig. 1 can be reduced to Fig. 2 equivalent electrical circuit, R=R in single-phase situation _1P, R=R in three-phase situation _3P.Fig. 3 is the R-V family curve of photovoltaic array.Contrast P-V family curve is known, R in photovoltaic array operating voltage range along with the rising of array output voltage monotone increasing, so by regulating R value can change photovoltaic array working point.

From formula (1)～(4):

$R_{1p}\&Proportional;\frac{1}{I_i},R_{3p}\&Proportional;\frac{1}{I_q}---\left(5\right)$

Due to I _ior I _qthe controlled volume of combining inverter, so can be by controlling I _ior I _qvalue regulates equivalent resistance R value, thereby regulates the operating voltage point of photovoltaic array.But because line voltage is normally stable, and with the variation of grid-connected current, do not change, thus the amplitude of grid-connected current size be directly proportional to the output power of combining inverter, i.e. existence:

I _i∝P _1p，I _q∝P _3p （6）

There is proportionate relationship in grid-connected output power and photovoltaic array output power:

P _1p=ηP _pv，P _3p=ηP _pv （7）

As shown in Figure 4, three constant power curve P1, P2 and P3 exist: P1>P2>P3.The I-V family curve of photovoltaic array intersects from different equipower lines, wherein only has an equipower line and I-V family curve to have an intersection point, and this equipower line is corresponding photovoltaic array peak power output.So how to control grid-connected current, realize the control to photovoltaic array working point, and then realize MPPT maximum power point tracking, also need the dynamic mathematical models of setting up photovoltaic array to analyze.

Step 2: set up the dynamic mathematical models of Single-Stage Grid Connected Solar Inverter System, concrete steps are:

The grid-connected current of take be take output power as controlled quentity controlled variable as controlled quentity controlled variable can be equivalent to, so can set up the model of photovoltaic array band power source load as shown in Figure 5, ignores the pressure drop of anti-reverse charging diode, and the voltage at capacitor C two ends equates with photovoltaic array voltage, with i _pV, i _c, i _outthe momentary current that represents respectively photovoltaic array output momentary current, the instantaneous charging current of DC filter capacitor and filter capacitor aft section circuit, v _pVrepresent photovoltaic array output instantaneous voltage, p _outfor photovoltaic array instantaneous output, exist:

$i_{\mathrm{pv}}=i_c+i_{\mathrm{out}}=C\frac{{\mathrm{dv}}_{\mathrm{pv}}}{\mathrm{dt}}+\frac{p_{\mathrm{out}}}{v_{\mathrm{pv}}}---\left(8\right)$

In conjunction with photovoltaic cell component mathematical model (I _z=f (I _ph, V)=I _ph-ε [exp (ξ V _z)-1]) can obtain with formula (8) the photovoltaic generating system dynamic model representing suc as formula (9).In formula,

$\left\{\begin{array}{c}{\stackrel{\&CenterDot;}{v}}_{\mathrm{pv}}=\frac{I_{\mathrm{ph}}}{C}-\frac{\mathrm{\&epsiv;}}{C}[\exp \left(\mathrm{\&xi;}{v}_{\mathrm{pv}}\right)-1]-\frac{p_{\mathrm{out}}}{{\mathrm{Cv}}_{\mathrm{pv}}}\\ v_{\mathrm{pv}}=v_{\mathrm{pv}}\left(0\right)+{\stackrel{\&CenterDot;}{v}}_{\mathrm{pv}}\end{array}\right.---\left(9\right)$

Wherein, I _zfor photovoltaic module output current, I _phfor the equivalent photogenerated current of battery component, V _zfor photovoltaic module output voltage, ε=n _pi ₀(n _pfor batteries in parallel connection number of unit, I ₀p-N knot reverse saturation current for photovoltaic cell inside equivalent diode), ξ=q/n _ck _ctn _s(q is electronic charge, n _cfor the diode characteristic factor, k _cfor Boltzmann constant, T is photovoltaic cell absolute temperature, n _sfor series-connected cell number of unit).

For monophase system, in its output power, contain alternating component, ideally can be described as:

$p_{\mathrm{out}}=\stackrel{\&OverBar;}{p}+\stackrel{\&OverBar;}{p}\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="HDA0000365408700000021.png"\; state="\{\{state\}\}">cos</figure-callout>}2{\mathrm{\&omega;}}_{g}t---\left(10\right)$

Wherein,

for average output power, ω _gfor mains frequency.

For three-phase system, ideally in its output power, only contain flip-flop, by formula (11), represent.

$p_{\mathrm{out}}=\stackrel{\&OverBar;}{p}---\left(11\right)$

In DC filter capacitor, store certain energy, and exist:

p _pv=p _out+i _cv _pv （12）

Step 3: for the stability of the model analysis system of above foundation;

For the model shown in Fig. 5 in the given output power situation of difference

with V _pVrelation is carried out emulation, and analytic system is when output power changes

movement locus also draws system stability rule.Fig. 6 is photovoltaic array P-V family curve and the parameter thereof that emulation adopts, wherein P _mppfor the peak power output of photovoltaic array under standard conditions (referring to intensity of illumination S=1000w/m2, temperature T=300K, air quality AM=1.5), be about 964W, V _mppfor photovoltaic array peak power voltage, be about 215V.DC filter capacitor value is 1000 μ F.

Fig. 7, Fig. 8 have represented the movement locus of desirable three-phase single-level formula photovoltaic generating system working point in the given output power situation of difference.

Fig. 7 is the voltage Phase Diagram Analysis of photovoltaic array initialization point when maximum power point voltage right side.Work as p _out<p _mpptime, the voltage movement locus of photovoltaic array is as shown in Figure 7 (a).Initialization point is located at a point, and output power is about 958W.If given power P _out=700W<958W, V _pvalong Line1, move and stablize gradually the point to b, b point photovoltaic array output power is 700W; If given power p now _out=500W<700W, V _pvalong Line2, move and stablize gradually the point to c, c point photovoltaic array output power is 500W; Continue given output power p _out=300W<500W, light V _pvalong Line3, move and stablize gradually the point to d, d point photovoltaic array output power is 300W; Continue to change given output power and make p _out=500W, V _pvalong Line4, return and stablize the point to c; Further change given output power and make p _out=700W, V _pvalong Line5, return and stablize the point to b; Again change given output power and make p _out=958W, V _pvalong Line6, return and stablize the point to a.Visible Line1, Line2, Line3, Line4, Line5, Line6 are stable motion track.If given output power p _out=1000W>P _mpp, V _pvmovement locus as Fig. 7 (b), visible, when initialization point is respectively a, b, c, d, photovoltaic array voltage moves along track Line1 to Line4, array voltage all constantly declines, and after moving to maximum power point voltage left side, decline rate is accelerated gradually, so these movement locus are unsteady motion track.

Fig. 8 is the voltage Phase Diagram Analysis of photovoltaic array initialization point when maximum power point voltage left side.Three different initialization point a, b, c, its corresponding photovoltaic array output power is about respectively 480W, 698W, 900W.For three different initialization point a, b, c, given output power is 300W, 500W, 700W respectively, V _pvalong Line1, Line3, Line7, move and be stabilized in respectively f, e, d respectively, these three is stable trajectory; To three different initialization point a, b, c, given output power is 500W, 700W, 958W respectively, V _pvalong Line2, Line4, Line6, move respectively, decline rate constantly increases, and these three is astable track.Draw thus, photovoltaic array initialization point is in the situation of maximum power point voltage left side, if given output power is less than initialization point power, array voltage will converge to maximum power point voltage right side along stable trajectory; If given output power is greater than initialization point power, array voltage is with astable track descending motion, and decline rate constantly increases.

As the above analysis, for three-phase photovoltaic generating system, photovoltaic array maximum power point right side area is stable work area, and its left field is non-stable work area.

Fig. 9 has represented the movement locus of desirable single-phase single-grade formula grid-connected system working point in the given output power situation of difference.From formula (10), the output power p of single-phase photovoltaic generating system _outthere is the of ac of 2 times of mains frequencies, because given output power signal has periodically feature, so voltage movement locus is oscillating curve in Fig. 9.

Initialization point (the operating voltage V of Fig. 9 (a) and (b) _pv(0)=140V, output power P(0)=698W) be positioned at maximum power point (V _mpp=215V, P _mpp=964W) left side, given respectively

for 700W, 500W, (a) movement locus is progressively dispersed, and is (b) stable limit cycle.Fig. 9 (c) initialization point (operating voltage V (d) _pv(0)=250V, output power P(0)=702W) on maximum power point right side, given respectively

for 500W, 900W, (c) (d) is all stable limit cycle.Fig. 9 (e) initialization point (operating voltage V (f) _pv(0)=140V, output power P(0)=698W) on maximum power point right side, given respectively

for 964W, 1000W, be (e) stable limit cycle, (f) movement locus is progressively dispersed.

From above-mentioned analysis equally, for single-phase photovoltaic generating system, photovoltaic array maximum power point right side area is stable work area, and its left field is non-stable work area.

In a word, Single-Stage Grid Connected Solar Inverter System (three-phase or single-phase), the stable operating point of photovoltaic array is all comprising the right side area of maximum power point, maximum power point left field is astable workspace.When unstable region, can change by controlling grid-connected watt level the movement locus of photovoltaic array output voltage, thereby make it enter stable work area.

Step 4: propose on stability analysis basis, propose power step-by-step method:

The present invention proposes power step-by-step method and realizes MPPT maximum power point tracking, specifically describe as follows: during the work of stage photovoltaic single electricity generation system, can when working, photovoltaic array voltage stabilization increase combining inverter output power with a fixed step size, if photovoltaic array voltage drop speed reduces gradually and again tends towards stability, prove that photovoltaic array output voltage is positioned at peak power output point voltage right side, now can continue to increase grid-connected inverters output power; If array voltage fall off rate increases gradually, magnitude of voltage cannot be stablized, now prove that photovoltaic array is operated in maximum power point left side, now should reduce grid-connected performance number and make photovoltaic array operating voltage return to maximum power point voltage right side, stable rear continuation increases grid-connected output power with a fixed step size makes photovoltaic array operating voltage point be tending towards maximum power point voltage.In photovoltaic array output voltage change procedure, can grid-connected output power value not changed.

First photovoltaic array voltage is sampled, sampled result leaves variable V in _pVin, and then calculate current to determining voltage signal V _refwith V _pVdifference e _v.

According to e _vvalue to grid-connected current amplitude signal I _refcontrol, and then realize the tracking of maximum power point, specifically describe as follows:

If e _va value continuous several times calculated value e front with it _{v_1}equate (for example counter j1>=5), think photovoltaic array output voltage stabilization, now by V _pVvalue be given to determining voltage signal V _ref, then according to the disturbance increment dI of front once given output current _refwith e _vratio size determine new given grid-connected current amplitude increment dI _refsize, and recalculate the given I of grid-connected current amplitude _ref.

Work as e _vvalue is greater than e _{v_1}during value, illustrate that line voltage declines, for example, when if the continuous decline of line voltage cannot be stablized (counter j2>=10), known according to the kinetic characteristic of photovoltaic array output voltage, now adoption rate controller reduces grid-connected current amplitude and can contain photovoltaic array voltage drop trend, and can make photovoltaic array voltage move to stable point by stable trajectory, the scale-up factor that in figure, kp is proportional controller, after photovoltaic array output voltage stabilization, combining inverter output power value be can again increase, observation and the processing of array voltage repeated.

Work as e _vvalue is less than e _{v_1}during value, explanation is in the situation that combining inverter output power is certain, in the process that array output voltage is rising, now array voltage moves with stable trajectory, it finally can converge on stable point, thus at array output voltage ascent stage, do not change grid-connected output power, after its steady operation, increase gradually again combining inverter output power, finally realize MPPT maximum power point tracking function.

Although the present invention does not have performance of dynamic tracking, but can realize rapidly and accurately MPPT maximum power point tracking under its steady state conditions, only need pair array output voltage to sample and observation, it is embodied as low, algorithm is simple and reliable, and can effectively avoid busbar voltage collapse phenomenon, and this algorithm is not subject to the impact of illumination power in addition, can realize effective steady track of total power section, so the method is applicable to the weak and relatively stable occasion of illumination of illumination.

Claims (5)

1. the maximum power point tracing method based on power stepping disturbance, is characterized in that, specifically according to following steps, implements:

Step 1: the stable state impedance model of setting up Single-Stage Grid Connected Solar Inverter System;

Step 2: the dynamic mathematical models of setting up Single-Stage Grid Connected Solar Inverter System;

Step 3: the stability of analyzing Single-Stage Grid Connected Solar Inverter System;

Step 4: realize MPPT maximum power point tracking on stability analysis basis.

2. the maximum power point tracing method based on power stepping disturbance according to claim 1, is characterized in that, described step 1 is set up the stable state impedance model of Single-Stage Grid Connected Solar Inverter System, specifically according to following steps, implements:

Monophase system is stable state active power of output P ideally _1Pbe expressed as:

P _1p＝λI _iV _g，

Wherein, I _iwith V _gbe respectively the effective value of grid-connected current and line voltage, λ is power factor; The work efficiency that represents combining inverter with η, the circuit equivalent impedance R of system DC filter capacitor C aft section _1Pbe expressed as:

In formula, V _pVequal DC bus-bar voltage;

Three-phase system is its active power of output P ideally _3Pbe expressed as:

Wherein, I _qwith V _qbe respectively grid-connected current and the line voltage q axle real component under two-phase rotating coordinate system; Three-phase system DC filter capacitor aft section equiva lent impedance R _3Pbe expressed as:

From above formula:

The amplitude size of grid-connected current is directly proportional to the output power of combining inverter, that is:

I _i∝P _1p，I _q∝P _3p，

There is proportionate relationship in grid-connected output power and photovoltaic array output power:

P _1p＝ηP _pv，P _3p＝ηP _pv。

3. the maximum power point tracing method based on power stepping disturbance according to claim 1, is characterized in that, described step 2 is set up the dynamic mathematical models of Single-Stage Grid Connected Solar Inverter System, specifically according to following steps, implements:

The voltage at capacitor C two ends equates with photovoltaic array voltage, with i _pV, i _c, i _outthe momentary current that represents respectively photovoltaic array output momentary current, the instantaneous charging current of DC filter capacitor and filter capacitor aft section circuit, v _pVrepresent photovoltaic array output instantaneous voltage, p _outfor photovoltaic array instantaneous output:

In conjunction with photovoltaic cell component mathematical model (I _z=f (I _ph, V)=I _ph-ε [exp (ξ V _z)-1]) can obtain as shown in the formula the photovoltaic generating system dynamic model representing with above formula, in formula,

Wherein, I _zfor photovoltaic module output current, I _phfor the equivalent photogenerated current of battery component, V _zfor photovoltaic module output voltage, ε=n _pi ₀, n _pfor batteries in parallel connection number of unit, I ₀for the P-N knot reverse saturation current of photovoltaic cell inside equivalent diode, ξ=q/n _ck _ctn _sq is electronic charge, n _cfor the diode characteristic factor, k _cfor Boltzmann constant, T is photovoltaic cell absolute temperature, n _sfor series-connected cell number of unit;

For monophase system, in output power, contain alternating component, be ideally described as:

Wherein,

for average output power, ω _gfor mains frequency;

For three-phase system, ideally in its output power, only contain flip-flop, with following formula, represent:

In DC filter capacitor, store certain energy, and exist:

p _pv＝p _out+i _cv _pv。

4. the maximum power point tracing method based on power stepping disturbance according to claim 1, it is characterized in that, described step 3 is analyzed the stability of Single-Stage Grid Connected Solar Inverter System, specifically according to following steps, implement: the stable operating point of photovoltaic array is all comprising the right side area of maximum power point, and maximum power point left field is astable workspace; When unstable region, by controlling grid-connected watt level, change the movement locus of photovoltaic array output voltage, thereby make it enter stable work area.

5. the maximum power point tracing method based on power stepping disturbance according to claim 1, is characterized in that, described step 4 realizes MPPT maximum power point tracking, adopts power step-by-step method, specifically according to following steps, implements: with grid-connected reference current amplitude signal I _refreplace photovoltaic array output power, first photovoltaic array voltage is sampled, sampled result leaves variable V in _pVin, and then calculate current to determining voltage signal V _refwith V _pVdifference e _v;

If e _va value continuous several times calculated value e front with it _{v_1}equate, think photovoltaic array output voltage stabilization, now by V _pVvalue be given to determining voltage signal V _ref, then according to the disturbance increment dI of front once given output current _refwith e _vratio size determine new given grid-connected current amplitude increment dI _refsize, and recalculate the given I of grid-connected current amplitude _ref;

Work as e _vvalue is greater than e _{v_1}during value, illustrate that line voltage declines, when if the continuous decline of line voltage cannot be stablized, now adoption rate controller reduces grid-connected current amplitude containment photovoltaic array voltage drop trend, and make photovoltaic array voltage move to stable point by stable trajectory, after photovoltaic array output voltage stabilization, again increase combining inverter output power value, repeat observation and the processing of array voltage;

Work as e _vvalue is less than e _{v_1}during value, explanation is in the situation that combining inverter output power is certain, in the process that array output voltage is rising, now array voltage moves with stable trajectory, it finally can converge on stable point, thus at array output voltage ascent stage, do not change grid-connected output power, after its steady operation, increase gradually again combining inverter output power, finally realize MPPT maximum power point tracking function.

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