CN103019293A - Maximum power point tracking method for rapidly self-adapting step length of photovoltaic array - Google Patents

Abstract

The invention provides a maximum power point tracking method for rapidly self-adapting step length of a photovoltaic array to solve a technical problem. The method is simple in design thinking and easy to realize; and the step length can be also automatically adjusted to track a maximum power point of the photovoltaic array. According to the invention, the self-adaptive step length v (v=/dP/dV/) is beyond a neighborhood U (Pmax, epsilon) of the maximum power point by using a logarithm operation form, so that larger stable step length is kept; and within the neighborhood U (Pmax, epsilon) of the maximum power point, the self-adaptive step length v is further rapidly reduced and the step length v of 0 at the maximum power point is guaranteed, so that the self-adaptive step length v is more sensitive and the tracking speed of the system is increased and tracking accuracy of a system is improved.

Description

A kind of for the quick self-adapted maximum power point tracing method of photovoltaic array step-length

Technical field

The present invention relates to the photovoltaic array maximum power point tracing method, especially relate to a kind of for the quick self-adapted maximum power point tracing method of photovoltaic array step-length.

Background technology

MPPT maximum power point tracking (MPPT) technology almost is a most important part in the photovoltaic system.(Perturb and Observe is called for short P﹠amp in constant voltage process, disturbance observation; O), on the classical way basis such as incremental conductance method (IncrementalConductance, be called for short IncCond), proposed a large amount of improved MPPT methods and be applied.

The constant voltage ratio juris is to ignore environment temperature to the impact of system, will export corresponding voltage data as the output voltage of photovoltaic array from the maximum power point that the manufacturer obtains.Its is simple to operate to be easy to realize, and because control voltage is certain, concuss can not occur, has preferably stability.But take the monocrystalline silicon photovoltaic array as example, when 1 ℃ of environment temperature rising, open-circuit voltage decline 0.4%-0.5% like this, has affected the tracking accuracy of constant voltage process greatly, is difficult to carry out accurately MPPT maximum power point tracking, causes energy loss.

The disturbance observation is by comparing the output power P of this photovoltaic array _I+1With output power P last time _iDetermining increases or reduces the tracking that the photovoltaic array operating voltage realizes maximum power point, such as Fig. 1; If P _I+1-P _i0, illustrate that the duty of photovoltaic array is positioned at the section of going up a slope, namely the left end of maximum power point needs to continue to increase operating voltage, and is close to maximum power point from the left side; If P _I+1-P _i＜0, reduce operating voltage, close to maximum power point from the right; Final photovoltaic array works near the maximum power point.Incremental conductance method is the tracking of finishing maximum power point by the method for the instantaneous admittance of comparing photovoltaic array and admittance change amount; The condition that reaches maximum power point is: the output admittance variable quantity equals to export the negative value of instantaneous admittance, i.e. dI/dU=-I/U.It is simple that the advantage of disturbance observation and incremental conductance method is to control thinking, and it is comparatively convenient to realize, can realize maximum power point is followed the tracks of comparatively accurately.But, when the suitable step-length v of setting follows the tracks of maximum power point, although larger step-length v can improve system to the intensity of illumination response speed, also can strengthen near the oscillation amplitude maximum power point simultaneously, thereby affect tracking accuracy.For tracking velocity and the tracking accuracy of taking into account the MPPT method, A.al-amoudi in 1998 etc. are at " Optimal control of agrid-connected PV system for maximum power point tracking and unity power factor " (Seventh International Conference on Power Electronics and Variable Speed Drives, when No.456) having proposed in the literary composition near arriving maximum power point, the thought that tracing step reduces by half.Namely when not arriving maximum power point, P _i＜P _I+1, whenever P _iP _I+1, so, P _iBe maximum power point, then step-length reduces by half, and continues to judge P under new step-length _iWith P _I+1Relation.Aircraft pursuit course shows as the indentation rising in the method, reduces gradually oscillation amplitude near the maximum power point.The variable step thought that proposes adopts constant large step-length can arrive fast near the maximum power point deficiency that perturbation amplitude is excessive though remedied traditional MPPT method.But the method still exists initial step length large, near the long shortcoming of the duration of oscillation maximum power point, and this section vibration is inevitably, and it still can not solve near the contradiction of the MPPT maximum power point tracking accuracy and runtime maximum power point fully.

For overcoming the problems referred to above, the adaptive step method is arisen at the historic moment.Incremental conductance method is based on more less near the maximum power point admittance, the maximum power point place | and dP/dV|=0 judges whether to trace into maximum power point.Therefore, the people such as Fang Luo are at document " A Variable Step Maximum Power Point Tracking MethodUsing Differential Equation Solution " (2nd IEEE Conference on IndustrialElectronics andApplications, 2007) establish adaptive step V=M*|dP/dV| in, wherein M represents adaptive step correction constant.Choose suitable M value, can guarantee that adaptive step v is larger when distance maximum power point position far away; And near maximum power point the time, automatically reduce step-length v, to eliminate near the maximum power point vibration that causes because of large step-length, improved tracking accuracy.But this adaptive step v is affected greatly by photovoltaic property curve P-V rate of curve, and when the P-V rate of curve was larger, adaptive step v was larger; When the P-V rate of curve hour, adaptive step v is less, this has just limited its tracking velocity.Qiang Mei in 2011 etc. are at " A Novel Improved Variable Step-Size Incremental-Resistance MPPT Methodfor PV Systems " (IEEE Transactions on Industrial Electronics, 58 (6), 2011) having proposed adaptive step in the literary composition presses $v=V_{\max }*\sin \mathrm{\θ}=V_{\max }*\left|\mathrm{dP}\right|\mathrm{dV}|/\sqrt{1+{|\mathrm{dP}/\mathrm{dV}|}^2}$ Carry out adaptive method, wherein V _MaxBe maximum step-length, θ is the angle of slope and V axle in the photovoltaic property curve P-V curve.The v=M*|dP/dV| that compares, the method can be in the P-V rate of curve hour, and adaptive step v also still keeps larger step-length, and arrives peak power neighborhood of a point U (P _Max, ε) in, just begin to reduce step-length, thereby when guaranteeing tracking accuracy, improved tracking velocity.

So, at peak power neighborhood of a point U (P _Max, ε) in the time, how further to reduce rapidly adaptive step v, be the key that further improves tracking velocity.When guaranteeing tracking accuracy, further improving tracking velocity is exactly emphasis of the present invention.

Summary of the invention

To be solved by this invention is quick tracking and the high precision tracking problem of maximum power point in the photovoltaic array, and provide a kind of for the quick self-adapted maximum power point tracing method of photovoltaic array step-length, this method not only mentality of designing simply is easy to realize, can also automatically adjust the maximum power point that step-length is come tracking photovoltaic array.This method proposes adaptive step v and adopts the logarithm operation form, makes v=|dP/dV| at peak power neighborhood of a point U (P _Max, ε) outside, keep larger, stable step-length; At peak power neighborhood of a point U (P _Max, ε) in, further reduce rapidly adaptive step v, and guarantee the maximum power point step-length v=0 of place, make adaptive step v sensitiveer, improve tracking velocity and the tracking accuracy of system.

The present invention solves the problems of the technologies described above the technical scheme of taking: a kind of for the quick self-adapted maximum power point tracing method of photovoltaic array step-length, comprise following steps:

1. take constant voltage process system the unloading phase, make initial voltage V that (0) reduces to rapidly 80% of open-circuit voltage Vr, namely V (0)=Vr*80% simultaneously according to initial voltage V (0)=Vr*80%, samples to initial current I (0);

2. after the unloading phase of system, finishing, photovoltaic array output voltage and output current are sampled V (k) expression k (k=1,2, ..., the K) output voltage of inferior sampling, I (k) expression k (k=1,2 ..., the K) output current of inferior sampling;

Output voltage variable quantity dV=V (k) when 3. calculating respectively the k time sampling-V (k-1); Output current variable quantity dI=I (k)-I (k-1); Power variation dP=I (k) * V (k)-I (k-1) * V (k-1);

4. dV is carried out condition judgment:

If a) satisfy dV ≠ 0, then calculate N=dP/dV, wherein N represents photovoltaic array P-V rate of curve.

I. N is carried out condition judgment:

If satisfy N 〉=0, then calculate adaptive step

v=M*Vr*log ₂(|N|+1)/(log ₂(|N|+1)+1)；

If satisfy N＜0, then calculate adaptive step

v=-M*Vr*log ₂(|N|+1)/(log ₂(|N|+1)+1)；

Wherein M represents adaptive step correction constant, and M*Vr represents maximum step value.|| absolute value operation is asked in expression;

Ii revise and substitute output voltage values V ' (k)=V (k)+v;

Iii. according to revised output voltage V ' (k), output current is carried out resampling (k) substitute I (k) by I ';

Iv. when adaptive step v ≠ 0, return step 2.;

When adaptive step v=0, can obtain output voltage V ' (k) and output current I ' (k) so that output power P ' (k)=I ' (k) * V ' be maximum power point (k), the tracking of realization maximum power point;

B) if satisfy dV=0, then dI is carried out condition judgment:

If satisfy dI=0, then step-length v=0 can obtain output voltage V (k) and output current I (k), so that output power P (k)=I (k) * V (k) is maximum power point, realizes the tracking of maximum power point;

If satisfy dI ≠ 0, then return step 1.; Until satisfy dI=0, then step-length v=0 can obtain output voltage V (k) and output current I (k), so that output power P (k)=I (k) * V (k) is maximum power point, realizes the tracking of maximum power point.

Compared with prior art, the invention has the advantages that not only mentality of designing simply is easy to realize, can also automatically adjust the maximum power point that step-length is come tracking photovoltaic array, this method proposes adaptive step v and adopts the logarithm operation form, makes v=|dP/dV| at peak power neighborhood of a point U (P _Max, ε) outside, keep larger, stable step-length; At peak power neighborhood of a point U (P _Max, ε) in, further reduce rapidly adaptive step v, and guarantee the maximum power point step-length v=0 of place, make adaptive step v sensitiveer, improve tracking velocity and the tracking accuracy of system.

Description of drawings

Fig. 1 is photovoltaic property curve P-V curve;

Fig. 2 is FB(flow block) of the present invention;

Fig. 3 be matlab emulation adaptive step v=|dP/dV|,

$v=V_{\max }*\sin \mathrm{\θ}=V_{\max }*|\mathrm{dp}/\mathrm{dV}|/\sqrt{1+{|\mathrm{dP}/\mathrm{dV}|}^2},$

V=M*Vr*log ₂(| dP/dV|+1)/(log ₂Curve when (| dP/dV|+1)+1);

Fig. 4 be matlab emulation adaptive step v=|dP/dV|,

$v=V_{\max }*\sin \mathrm{\θ}=V_{\max }*|\mathrm{dp}/\mathrm{dV}|/\sqrt{1+{|\mathrm{dP}/\mathrm{dV}|}^2},$

V=M*Vr*log ₂(| dP/dV|+1)/(log ₂MPPT maximum power point tracking curve when (| dP/dV|+1)+1).

Embodiment

Below in conjunction with the accompanying drawing example the present invention is described in further detail.

As shown in Figure 2, a kind of for the quick self-adapted maximum power point tracing method of photovoltaic array step-length, may further comprise the steps:

1. take constant voltage process system the unloading phase, make initial voltage V that (0) reduces to rapidly 80% of open-circuit voltage Vr, namely V (0)=Vr*80% simultaneously according to initial voltage V (0)=Vr*80%, samples to initial current I (0).For example, adopt typical solar panel Solarex MSX60, open-circuit voltage Vr=21.000V; So, initial voltage V (0)=Vr*80%=16.800V, initial current I (0)=3.5952A.

2. after the unloading phase of system, finishing, photovoltaic array output voltage and output current are sampled V (k) expression k (k=1,2 ..., the K) output voltage of inferior sampling, I (k) expression k (k=1,2 ..., the K) output current of inferior sampling.According to above step, sample for the first time, i.e. k=1; V (1)=16.633V, I (1)=3.6226A.

Output voltage variable quantity dV=V (k) when 3. calculating respectively the k time sampling-V (k-1), output current variable quantity dI=I (k)-I (k-1), power variation dP=I (k) * V (k)-I (k-1) * V (k-1).According to above step, when sampling for the first time, i.e. k=1; Output voltage variable quantity dV=V (1)-V (0)=-0.167V, output current variable quantity dI=I (1)-I (0)=0.0274A, power variation dP=I (1) * V (1)-I (0) * V (0)=-0.145W.

4. dV is carried out condition judgment:

If a) satisfy dV ≠ 0, then calculate N=dP/dV, wherein N represents photovoltaic array P-V rate of curve.

I. N is carried out condition judgment:

If satisfy N 〉=0, then calculate adaptive step

v=M*Vr*log ₂(|N|+1)/(log ₂(|N|+1)+1)；

If satisfy N＜0, then calculate adaptive step

v=-M*Vr*log ₂(|N|+1)/(log ₂(|N|+1)+1)；

Wherein M represents adaptive step correction constant, and M*Vr represents maximum step value.|| absolute value operation is asked in expression;

Ii revise and substitute output voltage values V ' (k)=V (k)+v;

Iii. according to revised output voltage V ' (k), output current is carried out resampling (k) substitute I (k) by I ';

Iv. when adaptive step v ≠ 0, return step 2.;

When adaptive step v=0, can obtain output voltage V ' (k) and output current I ' (k) so that output power P ' (k)=I ' (k) * V ' be maximum power point (k), the tracking of realization maximum power point;

B) if satisfy dV=0, then dI is carried out condition judgment:

If satisfy dI=0, then step-length v=0 can obtain output voltage V (k) and output current I (k), so that output power P (k)=I (k) * V (k) is maximum power point, realizes the tracking of maximum power point;

If satisfy dI ≠ 0, then return step 1.; Until satisfy dI=0, then step-length v=0 can obtain output voltage V (k) and output current I (k), so that output power P (k)=I (k) * V (k) is maximum power point, realizes the tracking of maximum power point.

According to above step, obviously N=dP/dV=0.871 〉=0 is then calculated in dV ≠ 0, so, and adaptive step v=M*Vr*log ₂(| N|+1)/(log ₂(| N|+1)+1)=0.100.Revise and alternative output voltage values V ' (1)=V (1)+0.100=16.733V, to output current carry out resampling by I ' (k)=3.6067A substitutes I (k).Obviously, adaptive step v ≠ 0 o'clock, then return step 2., until when adaptive step v=0, can obtain output voltage V ' (k) and output current I ' (k), so that output power P ' (k)=I ' (k) * V ' be maximum power point (k), realize the tracking of maximum power point.

Feasibility and the validity of MPPT maximum power point tracking of the present invention (MPPT) method can further specify by following simulation result.

Table 1

Table 1 is under same test platform (the theoretical maximum power point power of test platform 60.472W, maximum power point voltage 17.000V), the emulated data of different MPPT methods.Table 1 shows under identical test platform, and the present invention is being better than some other method aspect tracking velocity and the tracking accuracy.Adopt the adaptive step simulation curve of the inventive method and Fang Luo method, Qiang Mei method more as shown in Figure 3, and the MPPT maximum power point tracking simulation curve more as shown in Figure 4.Among Fig. 3 the peak power vertex neighborhood is expressed as U (17.000,0.25000).Only analyze photovoltaic array P-V family curve ascent stage, compare three curves, adaptive step v=|dP/dV| is (υ=14.000V) just begin to subtract in distance maximum power point position far away

Little, compare v=log ₂(| dP/dV|+1)/(log ₂(| dP/dV|+1)+1) and

Need the time more of a specified duration to reach maximum power point.Outside peak power vertex neighborhood U (17.000,0.25000), adaptive step v=log ₂(| dP/dV|+1)/(log ₂(| dP/dV|+1)+1) with

The same, larger, stable step-length is arranged; And in peak power vertex neighborhood U (17.000,0.25000), adaptive step log ₂(| dP/dV|+1)/(log ₂(| dP/dV|+1)+1) with $v=|\mathrm{dP}/\mathrm{dV}|/\sqrt{1+{|\mathrm{dP}/\mathrm{dV}|}^2}$ Compare, can reduce more rapidly adaptive step v, and the step-length v=0 of maximum power point place, higher tracking velocity and tracking accuracy obtained.Fig. 4 shows under identical test platform, and the tracking velocity of the inventive method is better than other two kinds of methods.Table 2 is the tracking data of three kinds of MPPT methods when following the tracks of maximum power point among Fig. 4.As seen from Table 2, Fang Luo method needed for 7 steps finished the 60.471W tracking, Qiang Mei method needs 6 to go on foot the tracking of finishing 60.472W, and this method only needed for 5 steps finished the tracking of 60.472W, showed that the tracking velocity of this method and tracking accuracy are better than other two kinds of methods.

Table 2

Claims (1)

1. one kind is used for the quick self-adapted maximum power point tracing method of photovoltaic array step-length, it is characterized in that comprising following steps:

1. take constant voltage process system the unloading phase, make initial voltage V that (0) reduces to rapidly 80% of open-circuit voltage Vr, namely V (0)=Vr*80% simultaneously according to initial voltage V (0)=Vr*80%, samples to initial current I (0);

2. after the unloading phase of system, finishing, photovoltaic array output voltage and output current are sampled V (k) expression k (k=1,2, ..., the K) output voltage of inferior sampling, I (k) expression k (k=1,2 ..., the K) output current of inferior sampling;

Output voltage variable quantity dV=V (k) when 3. calculating respectively the k time sampling-V (k-1); Output current variable quantity dI=I (k)-I (k-1); Power variation dP=I (k) * V (k)-I (k-1) * V (k-1);

4. dV is carried out condition judgment:

If a) satisfy dV ≠ 0, then calculate N=dP/dV, wherein N represents photovoltaic array P-V rate of curve;

I. N is carried out condition judgment:

If satisfy N 〉=0, then calculate adaptive step

v=M*Vr*log ₂(|N|+1)/(log ₂(|N|+1)+1)；

If satisfy N＜0, then calculate adaptive step

v=-M*Vr*log ₂(|N|+1)/(log ₂(|N|+1)+1)；

Wherein M represents adaptive step correction constant, and M*Vr represents maximum step value; || absolute value operation is asked in expression;

Ii revise and substitute output voltage values V ' (k)=V (k)+v;

Iii. according to revised output voltage V ' (k), output current is carried out resampling (k) substitute I (k) by I ';

Iv. when adaptive step v ≠ 0, return step 2.;

When adaptive step v=0, can obtain output voltage V ' (k) and output current I ' (k) so that output power P ' (k)=I ' (k) * V ' be maximum power point (k), the tracking of realization maximum power point;

B) if satisfy dV=0, then dI is carried out condition judgment:

If satisfy dI=0, then step-length v=0 can obtain output voltage V (k) and output current I (k), so that output power P (k)=I (k) * V (k) is maximum power point, realizes the tracking of maximum power point;

If satisfy dI ≠ 0, then return step 1.; Until satisfy dI=0, then step-length v=0 can obtain output voltage V (k) and output current I (k), so that output power P (k)=I (k) * V (k) is maximum power point, realizes the tracking of maximum power point.

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