CN103713687A - Photovoltaic MPPT control method based on fuzzy PI two-way linear prediction - Google Patents

Abstract

The invention discloses a photovoltaic MPPT control method based on fuzzy PI two-way linear prediction. The method includes the following steps that first, a power-voltage characteristic curve of a photovoltaic cell is obtained, two-way linear prediction is performed through the tangent line of the characteristic curve to approach the maximum power point, and the approximate maximum power point is obtained through calculation; second, on the basis of the approximate maximum power point, the actual maximum power point is tracked with a perturbation and observation method, and the error e(k) and the error conversion delta e(k) are calculated, wherein delta e(k)= e(k)- e(k-1), the k represents the period, P represents the power, and u represents the voltage; third, the error e(k) and the error conversion delta e(k) serve as input of a fuzzy controller, the Mamdani fuzzy reasoning method is adopted for the fuzzy controller, a fuzzy control rule is established with the target that the output power can fast reach a given value, and maximum power point tracking is achieved. The method effectively solves the problem that the tracking speed and the calculating precision can not be taken into consideration at the same time with a traditional MPPT control method, the maximum power point can be tracked fast and accurately, and the method is simple and practical.

Description

Photovoltaic MPPT control method based on the prediction of PI type Fuzzy bidirectional linear

Technical field

The invention belongs to photovoltaic power generation technology field, more specifically, relate to a kind of photovoltaic MPPT control method based on the prediction of PI type Fuzzy bidirectional linear.

Background technology

Due to the shortage day by day of the conventional energy resourcess such as oil, sun power is as a kind of regenerative resource, and reserves are sufficient, more and more receive publicity, and photovoltaic generation is one of major way utilizing sun power.But at present photovoltaic cell exist conversion efficiency on the low side, be subject to the defects such as weather effect, seriously limited the large-scale promotion application of sun power.Therefore, how effectively increasing the output power of solar cell, thereby make full use of sun power, is an important directions of photovoltaic research.

The output voltage of photovoltaic cell and output current have strong non-linear with the variation of intensity of sunshine and battery junction temperature.Under certain Intensity of the sunlight and environment temperature, photovoltaic cell can be operated in different output voltages, but only when a certain output voltage, the output power of photovoltaic cell just can reach maximal value, at this moment the working point of photovoltaic cell has just reached the peak of output power-voltage curve, be referred to as maximum power point (Maximum Power Point, MPP).Therefore, in photovoltaic generating system, improve the whole efficiency of system, an important approach is exactly to adjust in real time the working point of photovoltaic cell, make it to always work near maximum power point, this process is just referred to as MPPT maximum power point tracking (Maximum Power Point Tracking, MPPT).

At present, MPPT control method mainly comprises closed-loop control method and the control of the open loop based on output characteristics method.Wherein, closed-loop control method mainly contains disturbance observation (P & O) and electricity is led micro-gaining rate method (INC).Disturbance observation is widely used because of its simple and practical feature, but search speed is slow and have problems such as vibration and erroneous judgement.Although it is higher that electricity is led micro-gaining rate method precision, search speed is still slower.The common open loop control method based on output characteristics has the voltage-tracing of determining method, and it has fast simple feature, but tracking accuracy is poor.

Summary of the invention

Above defect or Improvement requirement for prior art, the invention provides a kind of photovoltaic MPPT control method based on the prediction of PI type Fuzzy bidirectional linear, efficiently solve traditional MPPT control method and cannot take into account the problem of tracking velocity and computational accuracy, can to maximum power point, follow the tracks of rapidly and accurately, simple and practical.

For achieving the above object, according to one aspect of the present invention, a kind of photovoltaic MPPT control method is provided, it is characterized in that, comprise the steps: that (1) obtains the power-voltage response of photovoltaic cell, utilize characteristic tangent line to carry out bidirectional linear prediction, approach maximum power point, calculate approximate maximum power point; (2) on the basis of approximate maximum power point, utilize disturbance observation to follow the tracks of actual maximum power point, error of calculation e (k) and error transform Δ e (k), wherein,

Δ e (k)=e (k)-e (k-1), k is the cycle, and P is power, and u is voltage; (3) input using error e (k) and error transform Δ e (k) as fuzzy controller, fuzzy controller adopts Mamdani fuzzy reasoning method, the output power of take can arrive set-point fast as target, sets up fuzzy control rule, realizes MPPT maximum power point tracking.

Preferably, described step (1) further comprises the steps: that (1-1) takes up an official post and get 2 A (U at power-voltage response _l, P (U _l)) and B (U _r, P (U _r)), make U _l∈ [0, U _m], U _r∈ [U _m, U _oC], wherein, U _mfor voltage corresponding to maximum power point, U _oCfor open-circuit voltage; (1-2) cross respectively the tangent line of A and the B rate of doing work-voltage response, intersection point is O; (1-3) using point identical with O point horizontal ordinate on power-voltage response as approximate maximum power point; (1-4) when larger variation occurs light intensity, while causing power variation Δ P to be greater than threshold value T, return to step (1-1), otherwise, order execution step (2).

Preferably, in described step (3), according to error e (k) and error transform Δ e (k), determine PI parameter K _pand K _i.

Preferably, fuzzy set be PB, PS, ZE, NS, NB}, fuzzy control rule is as follows:

In general, the above technical scheme of conceiving by the present invention compared with prior art, has following beneficial effect:

1, according to the constant pressure and flow zone properties of photovoltaic PV curve, with two single-point Hermite Interpolations, substitute photovoltaic PV curve, higher to the precision of prediction of PV curve.

2, by bidirectional linear, predict, greatly improved the speed of maximal power tracing.Be applicable to the photovoltaic cell of different fill factor, curve factors.

Accompanying drawing explanation

Fig. 1 is the photovoltaic MPPT control method process flow diagram based on the prediction of PI type Fuzzy bidirectional linear of the embodiment of the present invention;

Fig. 2 is bidirectional linear prediction schematic diagram.

Embodiment

In order to make object of the present invention, technical scheme and advantage clearer, below in conjunction with drawings and Examples, the present invention is further elaborated.Should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.In addition,, in each embodiment of described the present invention, involved technical characterictic just can not combine mutually as long as do not form each other conflict.

As shown in Figure 1, the photovoltaic MPPT control method based on the prediction of fuzzy proportional integral (PI) bidirectional linear of the embodiment of the present invention comprises the steps:

(1) obtain the power-voltage response of photovoltaic cell, utilize characteristic tangent line to carry out bidirectional linear prediction, approach maximum power point, calculate approximate maximum power point.Further comprise the steps:

(1-1) as shown in Figure 2, at power-voltage response P (u) of photovoltaic cell, take up an official post and get 2 A (U _l, P (U _l)) and B (U _r, P (U _r)), make U _l∈ [0, U _m], U _r∈ [U _m, U _oC], wherein, U _mfor voltage corresponding to maximum power point, U _oCfor open-circuit voltage.

(1-2) cross respectively tangent line OA and the OB of A and the B rate of doing work-voltage response, O is the intersection point of OA and OB.The slope of OA and OB is respectively P ' (U _l) and P ' (U _r), wherein, P ' (U _l) >0, P ' (U _r) <0.The angle of OA and OB and transverse axis is respectively θ _land θ _r, wherein, 0 ° of < θ _l<90 °, 0 ° of < θ _r<90 °.

Particularly, OA and OB can use respectively following the Representation Equation:

$\left\{\begin{array}{c}{H}_{\mathrm{OA}}\left(u\right)=P^{\&prime;}\left(U_L\right)\&times;(u-U_L)+P\left(U_L\right)\\ H_{\mathrm{OB}}\left(u\right)=P^{\&prime;}\left(U_R\right)\&times;(u-U_R)+P\left(U_R\right)\end{array}\right.---\left(1\right)$

(1-3) by the power-voltage response of photovoltaic cell with O point horizontal ordinate U _oidentical some C is as approximate maximum power point.

Wherein, the absolute error E of linear prediction _abs=| H _oA(U _o)-P (U _o) | be the length of OC, residue hunting zone E _rest=| U _o-U _m| for being similar to the absolute value of the horizontal ordinate difference of maximum power point C and actual maximum power point D.

Structure auxiliary function

or

particularly, take tangent line OA as example, E (U _l)=P (U _l)-H _oA(U _l)=0 and E ' (U _l)=P ' (U _l)-H ' _oA(U _l)=0, linear prediction error E (u)=λ (u) (u-U _l) ², wherein, λ (u) is undetermined coefficient.Structure auxiliary function

According to Rolle theorem, there is u=ξ, make

the error that convolution (1) obtains bidirectional linear prediction is:

$E\left(u\right)=\frac{P^{\&prime;\&prime;}\left(\mathrm{\&xi;}\right)}{2}\&times;{\left[\frac{P\left(U_R\right)-P\left(U_L\right)+P^{\&prime;}\left(U_L\right)\&times;(U_L-U_R)}{P^{\&prime;}\left(U_L\right)-P^{\&prime;}\left(U_R\right)}\right]}^2$

(1-4) when larger variation occurs light intensity, while causing power variation Δ P to be greater than threshold value T, return to step (1-1), to reduce search time; If change, be less than this threshold value, order execution step (2).

(2) on the basis of approximate maximum power point C, utilize disturbance observation to follow the tracks of actual maximum power point, error of calculation e (k) and error transform Δ e (k), wherein, k is the cycle, $e\left(k\right)=\frac{\mathrm{dP}}{\mathrm{du}}=\frac{P\left(k\right)-P(k-1)}{u\left(k\right)-u(k-1)},$ Δe(k)=e(k)-e(k-1)。

(3) input using error e (k) and error transform Δ e (k) as fuzzy controller, fuzzy controller adopts Mamdani fuzzy reasoning method, the output power of take can arrive set-point fast as target, sets up fuzzy control rule, realizes MPPT maximum power point tracking.

Particularly, according to error e (k) and error transform Δ e (k), determine PI parameter K _pand K _i, fuzzy set be PB, PS, ZE, NS, NB}, fuzzy control rule is as shown in table 1.

Table 1 fuzzy control rule

Those skilled in the art will readily understand; the foregoing is only preferred embodiment of the present invention; not in order to limit the present invention, all any modifications of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.

Claims (4)

1. a photovoltaic MPPT control method, is characterized in that, comprises the steps:

(1) obtain the power-voltage response of photovoltaic cell, utilize characteristic tangent line to carry out bidirectional linear prediction, approach maximum power point, calculate approximate maximum power point;

(2) on the basis of approximate maximum power point, utilize disturbance observation to follow the tracks of actual maximum power point, error of calculation e (k) and error transform Δ e (k), wherein,

Δ e (k)=e (k)-e (k-1), k is the cycle, and P is power, and u is voltage;

(3) input using error e (k) and error transform Δ e (k) as fuzzy controller, fuzzy controller adopts Mamdani fuzzy reasoning method, the output power of take can arrive set-point fast as target, sets up fuzzy control rule, realizes MPPT maximum power point tracking.

2. photovoltaic MPPT control method as claimed in claim 1, is characterized in that, described step (1) further comprises the steps:

(1-1) at power-voltage response, take up an official post and get 2 A (U _l, P (U _l)) and B (U _r, P (U _r)), make U _l∈ [0, U _m], U _r∈ [U _m, U _oC], wherein, U _mfor voltage corresponding to maximum power point, U _oCfor open-circuit voltage;

(1-2) cross respectively the tangent line of A and the B rate of doing work-voltage response, intersection point is O;

(1-3) using point identical with O point horizontal ordinate on power-voltage response as approximate maximum power point;

(1-4) when larger variation occurs light intensity, while causing power variation Δ P to be greater than threshold value T, return to step (1-1), otherwise, order execution step (2).

3. photovoltaic MPPT control method as claimed in claim 1 or 2, is characterized in that, in described step (3), according to error e (k) and error transform Δ e (k), determines PI parameter K _pand K _i.

4. photovoltaic MPPT control method as claimed any one in claims 1 to 3, is characterized in that, fuzzy set be PB, PS, ZE, NS, NB}, fuzzy control rule is as follows:

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