CN103677066B - Photovoltaic array maximum power point tracing method of quick self-adapting step length - Google Patents

Abstract

The invention discloses a photovoltaic array maximum power point tracing method of a quick self-adapting step length. The method comprises the steps that a small maximum power point neighbourhood U (Pmax, epsilon) is determined, the step length of the provided self-adapting step length v step is automatically adjusted, and the maximum step length delta v max is kept to be tracked outside the maximum power point neighbourhood U (Pmax, epsilon); in the maximum power point neighbourhood U (Pmax, epsilon), the self-adapting step length v step is further reduced fast, the step length v step at the maximum power point is kept to be zero, tracking precision is guaranteed, and meanwhile the tracking speed of a system is improved.

Description

A kind of maximum power point of photovoltaic array tracking of quick self-adapted step-length

Technical field

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

Background technology

MPPT maximum power point tracking (MPPT) technology is almost a most important part in photovoltaic system.At constant voltage process, disturbance observation (Perturb and Observe, be called for short P & O), incremental conductance method (Incremental Conductance, be called for short IncCond) etc. on classical way basis, proposed a large amount of MPPT method of improving and be applied.Wherein, for overcoming the contradiction of MPPT maximum power point tracking accuracy and runtime, adaptive step method is arisen at the historic moment.

Recently, A.K.Abdelsalam is at document " High-performance adaptive perturb and observe MPPT technique for photovoltaic-based microgrids " (IEEE Transactions on Power Electronics, 26 (4), 2011) propose to produce self-adaptation disturbance by the difference DELTA P of photovoltaic array two continuous power signals, he defines adaptive step v _{step_1}=M × | Δ P|.Wherein, M value is test the constant determined, | Δ P| represents the difference of power signal | P _i-P _i-1|.K. ?J.Lee at document " An adaptive maximum power point tracking scheme based on a variable scaling factor for photovoltaic systems " (IEEE transactions on Energy conversion, 27 (4), 2012) then by formula distortion, obtains dP _max=I × dU+U × dI, definition adaptive step v _{step_2}=M × | I × dU+U × dI|.Choosing of these two kinds of adaptive steps is in fact v _step=M × | the distortion of dP/dU|, can ensure when the position that distance maximum power point is far away, adaptive step v _steplarger; And time near maximum power point, automatically reduce step-length v _step, to eliminate near maximum power point because of the vibration that large step-length causes, improve tracking accuracy.But this adaptive step v _stepthe impact of light volt linearity curve P-V rate of curve is large, when P-V rate of curve is larger, and adaptive step v _steplarger; When P-V rate of curve is less, adaptive step v _stepless, which limits its tracking velocity.

A.Ahmed in document " A Fast PV Power Tracking Control Algorithm With Reduced Power Mode " (IEEE transactions on Energy conversion, 28 (3), 2013) by formula distortion, definition wherein max (| dU/dI|) represents one group that produces experiment | dU/dI| data get maximal value.In the process of maximum power point (dP/dU>0), when U increases, | dU/dI| reduces, and | U/I| increases, and causes adaptive step v _stepreducing, until at maximum power point place | dU/dI|=|U/I|, ensures adaptive step v _step=0.But the method, when solving tracking velocity and this conflict of tracking accuracy, still fails to propose effective strategy.

Patent disclosed in March, 2013 " a kind of maximum power point tracing method quick self-adapted for photovoltaic array step-length ", for the problems referred to above, proposes following strategy: definition adaptive step

V _{step_4}=Δ v _max× ln (| dP/dV|+1)/ln (| dP/dV|+1)+1, meet when P-V rate of curve is larger, adaptive step v _steplarger; When P-V rate of curve is less, relatively large adaptive step v still can be kept _step, until arrive peak power vertex neighborhood U (P _max, ε) in, just start to reduce step-length rapidly, thus while guarantee tracking accuracy, improve tracking velocity.

So, how to be converted into quantitative test by qualitative analysis, to determine a less peak power vertex neighborhood U (P _max, ε), become while guarantee tracking accuracy, improve the key of tracking velocity further, also become emphasis of the present invention simultaneously.

Summary of the invention

To be solved by this inventionly be to provide a kind of while guarantee tracking accuracy, improve further the maximum power point of photovoltaic array tracking of the quick self-adapted step-length of tracking velocity.

The present invention solves the problems of the technologies described above taked technical scheme: a kind of maximum power point of photovoltaic array tracking of quick self-adapted step-length, comprises following steps:

1., after system starts, sample to photovoltaic array output voltage and output current, V (k) represents kth (k=0,1,2 ..., the k) output voltage of secondary sampling, I (k) represents kth (k=0,1,2 ..., the k) output current of secondary sampling; Wherein, initial voltage V (0) is 80% of open-circuit voltage Vr, i.e. V (0)=Vr × 80%;

2. calculate power variation dP=I (k) × V (k)-I (the k-1) × V (k-1) when kth time is sampled, and dP carries out condition judgment:

A) if meet dP=0, then adaptive step v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

B) if meet dP ≠ 0, then calculate output voltage variable quantity dV=V (the k)-V (k-1) when kth time is sampled, and condition judgment carried out to dV:

If a) meet dV=0, then calculate output current variable quantity dI=I (the k)-I (k-1) when kth time is sampled, and condition judgment carried out to dI:

If i. meet dI=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

If ii. meet dI ≠ 0, then return step 1.; Until meet dI=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

If b) meet dV ≠ 0, then calculate x=dP/dV, wherein x represents photovoltaic array P-V rate of curve;

I. condition judgment is carried out to x:

If meet 0≤x<1, then calculate adaptive step v _step=Δ v _max× | x-xlnx|;

If meet-1<x<0, then calculate adaptive step v _step=Δ v _max× || x|-|x|ln|x||;

If meet x>=1 or x≤-1, then calculate adaptive step v _step=Δ v _max;

Wherein Δ v _max=M × Vr represents maximum step value; M represents adaptive step correction constant; ||

Represent and ask absolute value operation;

Ii. revise and substitute output voltage values V'(k)=V (k)+v _step, resampling is carried out by I'(k to output current) and substitute I (k);

Iii. as adaptive step v _stepwhen ≠ 0, return step 1.;

As adaptive step v _stepone group of output voltage V'(k can be obtained when=0), output current I'(k), make output power P'(k)=V'(k) × I'(k) be maximum power point, realize the tracking of maximum power point.

Compared with prior art, the present invention first calculates dP, avoids arriving maximum power point, but still blindly calculates adaptive step v _stepspecial circumstances occur; DV, dI are calculated, tackles because illuminance abrupt variation causes output current to change dI ≠ 0, and adaptive step v _stepthe special circumstances of=0, system restart, finds new maximum power point.Main advantage of the present invention is to determine a less peak power vertex neighborhood U (P _max, ε), make at peak power neighborhood of a point U (P _max, ε) outward, namely when dP/dV>=1 or dP/dV≤-1, the adaptive step v of proposition _step=Δ v _max, keep maximum step delta v _maxmaximum power point is followed the tracks of; At peak power neighborhood of a point U (P _max, ε) in, namely during-1<dP/dV<1, the adaptive step v of proposition _step=Δ v _max× || dP/dV|-|dP/dV|ln|dP/dV||, reaches and reduces adaptive step rapidly, and ensures maximum power point place step-length v _stepthe requirement of=0, makes, while guarantee tracking accuracy, to improve the tracking velocity of system.

Accompanying drawing explanation

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

Fig. 2 is flowage structure block diagram of the present invention;

Fig. 3 A is that matlab emulates adaptive step v _{step_1}=M × | Δ P|,

v _{step_2}=M×|I×dU+U×dI|、

$v_{\mathrm{step}\_3}=M\&times;\left|\frac{|\mathrm{dU}/\mathrm{dI}|-|U/I|}{\max \left(\right|\mathrm{dU}/\mathrm{dI}\left|\right)}\right|,$

v _{step_4}=Δv _max×ln(|dP/dV|+1)/ln(|dP/dV|+1)+1、

$v_{\mathrm{step}\_5}=\left\{\begin{array}{cc}\mathrm{\&Delta;}{v}_{\max }\&times;\left|\right|\mathrm{dP}/\mathrm{dU}|-|\mathrm{dP}/\mathrm{dU}\left|\ln \right|\mathrm{dP}/\mathrm{dU}\left|\right|& ,|\mathrm{dP}/\mathrm{dU}|<1\\ \mathrm{\&Delta;}{v}_{\max }& ,|\mathrm{dP}/\mathrm{dU}|\&GreaterEqual;1\end{array}\right.$

Time curve;

Fig. 3 B is the partial enlarged drawing of Fig. 3 A;

Fig. 4 A is that matlab emulates adaptive step v _{step_1}=M × | Δ P|,

v _{step_2}=M×|I×dU+U×dI|、

$v_{\mathrm{step}\_3}=M\&times;\left|\frac{|\mathrm{dU}/\mathrm{dI}|-|U/I|}{\max \left(\right|\mathrm{dU}/\mathrm{dI}\left|\right)}\right|,$

v _{step_4}=Δv _max×ln(|dP/dV|+1)/ln(|dP/dV|+1)+1、

$v_{\mathrm{step}\_5}=\left\{\begin{array}{cc}\mathrm{\&Delta;}{v}_{\max }\&times;\left|\right|\mathrm{dP}/\mathrm{dU}|-|\mathrm{dP}/\mathrm{dU}\left|\ln \right|\mathrm{dP}/\mathrm{dU}\left|\right|& ,|\mathrm{dP}/\mathrm{dU}|<1\\ \mathrm{\&Delta;}{v}_{\max }& ,|\mathrm{dP}/\mathrm{dU}|\&GreaterEqual;1\end{array}\right.$

Time MPPT maximum power point tracking curve;

Fig. 4 B is the partial enlarged drawing of Fig. 4 A.

Embodiment

Below in conjunction with attached Example, the present invention is described in further detail.

As shown in Figure 2, a kind of maximum power point of photovoltaic array tracking of quick self-adapted step-length, comprises the following steps:

1., after system starts, sample to photovoltaic array output voltage and output current, V (k) represents kth (k=0,1,2 ..., K) output voltage of secondary sampling, I (k) represents kth (k=0,1,2 ..., K) output current of secondary sampling; Wherein, initial voltage V (0) is 80% of open-circuit voltage Vr, i.e. V (0)=Vr × 80%; Such as, typical solar panel Solarex MSX60, open-circuit voltage Vr=21.000V is adopted; So, initial voltage V (0)=Vr × 80%=16.800V, initial current I (0)=3.5952A; First time sampling, i.e. k=1; V (1)=16.905V, I (1)=3.5760A.

2. calculate power variation dP=I (k) × V (k)-I (the k-1) × V (k-1) when kth time is sampled, and dP carries out condition judgment:

A) if meet dP=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

B) if meet dP ≠ 0, then calculate output voltage variable quantity dV=V (the k)-V (k-1) when kth time is sampled, and condition judgment carried out to dV:

If a) meet dV=0, then calculate output current variable quantity dI=I (the k)-I (k-1) when kth time is sampled, and condition judgment carried out to dI:

If i. meet dI=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

If ii. meet dI ≠ 0, then return step 1.; Until meet dI=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

If b) meet dV ≠ 0, then calculate x=dP/dV, wherein x represents photovoltaic array P-V rate of curve;

I. condition judgment is carried out to x:

If meet 0≤x<1, then calculate adaptive step v _step=Δ v _max× | x-xlnx|;

If meet-1<x<0, then calculate adaptive step v _step=Δ v _max× || x|-|x|ln|x||;

If meet x>=1 or x≤-1, then calculate adaptive step v _step=Δ v _max;

Wherein Δ v _max=M × Vr represents maximum step value; M represents adaptive step correction constant; || represent and ask absolute value operation;

Ii. revise and substitute output voltage values V'(k)=V (k)+v _step, resampling is carried out by I'(k to output current) and substitute I (k);

Iii. as adaptive step v _stepwhen ≠ 0, return step 1.;

As adaptive step v _stepone group of output voltage V'(k can be obtained when=0), output current I'(k), make output power P'(k)=V'(k) × I'(k) be maximum power point, realize the tracking of maximum power point.

According to above step, when first time samples, i.e. k=1; Power variation dP=I (1) × V (1)-I (0) × V (0)=0.053W, output voltage variable quantity dV=V (1)-V (0)=0.105V.Obvious dP ≠ 0, dV ≠ 0, then calculate x=dP/dV=0.505>=0 and x<1, so, adaptive step v _step=Δ v _max× | x-xlnx|=0.089.Revise and substitute output voltage values V'(1)=V (1)+0.100=16.994V, resampling is carried out by I'(k to output current)=3.5584A substitutes I (k).Obviously, adaptive step v _stepwhen ≠ 0, then return step 1., until as adaptive step v _stepone group of output voltage V'(k can be obtained when=0), output current I'(k), make output power P'(k)=V'(k) × I'(k) be maximum power point, realize the tracking of maximum power point.

The feasibility of MPPT maximum power point tracking of the present invention (MPPT) method and validity can be further illustrated by following simulation result.

Table 1

Table 1 is under same test platform (test platform theoretical maximum power point power 60.4727W, maximum power point voltage 17.02V), the emulated data of different MPPT method.Table 1 shows that, under identical test platform, the inventive method is with adaptive step v _{step_1}and v _{step_2}compare, tracking accuracy is improved, close to theoretical maximum power point; Increase in tracking velocity, wherein comparatively adaptive step v _{step_4}improve 34.8%.Adopt the adaptive step simulation curve of the inventive method and other four kinds of methods more as shown in Figure 3, and MPPT maximum power point tracking simulation curve more as shown in Figure 4.Peak power vertex neighborhood is expressed as U (17.02,0.27) in Fig. 3.Only analyze photovoltaic array P-V family curve ascent stage, adaptive step v _{step_3}meet the position v that distance maximum power point is far away _{step_3}larger; And the nearer position of distance maximum power point and even to maximum power point place, adaptive step v _{step_3}monotone decreasing is the condition of zero, but v _{step_3}there is not the maximum step delta v determined _max, the selection of constant M exists the contradiction between tracking velocity and tracking accuracy.V _{step_2}, and v _{step_1}similar, just start to reduce at the position V=14.00V that distance maximum power point is far away, compare v _{step_4}and v _{step_5}, need the time more of a specified duration to reach maximum power point.In position V ∈ (14.00V, 17.29V) that maximum power point is nearer, v _{step_4}start progressively to reduce, and v _{step_5}still remain larger, stable step-length, until in peak power vertex neighborhood U (17.02,0.27), v _{step_5}just start rapid reduction, and at maximum power point place step-length v _{step_5}=0, obtain higher tracking velocity and tracking accuracy.Fig. 4 shows under identical test platform, and the tracking velocity of the inventive method is better than other four kinds of methods.Table 2 is the tracking data of five kinds of MPPT methods when following the tracks of maximum power point in Fig. 4.Associative list 2 and Fig. 4 known, v _{step_4}5 steps are needed to complete the tracking of 60.4727W; v _{step_2}complete the tracking of 60.4679W in the 9th step, tracking accuracy is higher, there is the error of 0.008% with theoretical maximum power point; v _{step_3}complete the tracking of 60.4234W in the 9th step, tracking accuracy is not high, there is the error of 0.082% with theoretical maximum power point; And step function v in this paper _{step_5}only need 3 steps to complete the tracking of 60.4727W, show that the inventive method is while guarantee tracking accuracy, improves the tracking velocity of system.

Table 2

Power points	v step_1	v step_2	v step_3	v step_4	v step_5
						1	26.5763	32.4762	60.1774	60.2008	60.4529
2	48.1562	53.5172	60.3041	60.3235	60.4719
						3	59.8171	57.8430	60.4092	60.4155	60.4727
4	56.8518	55.2887	60.4511	60.4608
						5	59.2934	58.4491	60.4653	60.4727
6	60.2408	60.1690	60.4701
						7	60.4035	60.4538	60.4718
8	60.4214	60.4674	60.4727
						9	60.4234	60.4679

Claims (1)

1. a maximum power point of photovoltaic array tracking for quick self-adapted step-length, is characterized in that comprising following steps:

1., after system starts, sample to photovoltaic array output voltage and output current, V (k) represents kth (k=0,1,2 ..., the k) output voltage of secondary sampling, I (k) represents kth (k=0,1,2 ..., the k) output current of secondary sampling; Wherein, initial voltage V (0) is 80% of open-circuit voltage Vr, i.e. V (0)=Vr × 80%;

2. calculate power variation dP=I (k) × V (k)-I (the k-1) × V (k-1) when kth time is sampled, and dP carries out condition judgment:

A) if meet dP=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

B) if meet dP ≠ 0, then calculate output voltage variable quantity dV=V (the k)-V (k-1) when kth time is sampled, and condition judgment carried out to dV:

If a) meet dV=0, then calculate output current variable quantity dI=I (the k)-I (k-1) when kth time is sampled, and condition judgment carried out to dI:

If i. meet dI=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

If ii. meet dI ≠ 0, then return step 1.; Until meet dI=0, then step-length v _step=0, one group of output voltage V (k), output current I (k) can be obtained, make output power P (k)=V (k) × I (k) for maximum power point, realize the tracking of maximum power point;

If b) meet dV ≠ 0, then calculate x=dP/dV, wherein x represents photovoltaic array P-V rate of curve;

I. condition judgment is carried out to x:

If meet 0≤x<1, then calculate adaptive step v _step=Δ v _max× | x-xlnx|;

If meet-1<x<0, then calculate adaptive step v _step=Δ v _max× || x|-|x|ln|x||;

If meet x>=1 or x≤-1, then calculate adaptive step v _step=Δ v _max;

Wherein Δ v _max=M × Vr represents maximum step value; M represents adaptive step correction constant; || represent and ask absolute value operation;

Ii. revise and substitute output voltage values V'(k)=V (k)+v _step, resampling is carried out by I'(k to output current) and substitute I (k);

Iii. as adaptive step v _stepwhen ≠ 0, return step 1.;

As adaptive step v _stepone group of output voltage V'(k can be obtained when=0), output current I'(k), make output power P'(k)=V'(k) × I'(k) be maximum power point, realize the tracking of maximum power point.