CN103713687B - Photovoltaic MPPT control method based on fuzzy PI two-way linear prediction - Google Patents

Photovoltaic MPPT control method based on fuzzy PI two-way linear prediction Download PDF

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CN103713687B
CN103713687B CN201310698337.XA CN201310698337A CN103713687B CN 103713687 B CN103713687 B CN 103713687B CN 201310698337 A CN201310698337 A CN 201310698337A CN 103713687 B CN103713687 B CN 103713687B
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maximum power
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power point
point
error
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CN103713687A (en
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徐伟
唐磊
曲荣海
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Huazhong University of Science and Technology
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The invention discloses a photovoltaic MPPT control method based on fuzzy PI two-way linear prediction. The method includes the following steps, (1), 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; (2), 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)=dP/du=(P(k)-P(k-1))/(u(k)-u(k-1)), delta e(k)=e(k)- e(k-1), k represents the period, P represents the power, and u represents the voltage; (3), 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

Based on the photovoltaic MPPT control method of fuzzy PI two-way linear prediction
Technical field
The invention belongs to technical field of photovoltaic power generation, more specifically, relate to a kind of photovoltaic MPPT control method based on fuzzy PI two-way linear prediction.
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, and more and more receive publicity, 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 limit the large-scale promotion application of sun power.Therefore, how effectively increasing the output power of solar cell, thus 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 change 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 just reaches 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 the working point adjusting photovoltaic cell in real time, 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 opened loop control method based on output characteristics.Wherein, closed-loop control method mainly contains disturbance observation (P & O) and conductance tiny increment method (INC).Disturbance observation is widely used because of its simple and practical feature, but search speed is slow and there is the problems such as vibration and erroneous judgement.Although conductance tiny increment method precision is higher, search speed is still slower.The common opened loop control method based on output characteristics has determines voltage-tracing method, and it has simple feature fast, but tracking accuracy is poor.
Summary of the invention
For above defect or the Improvement requirement of prior art, the invention provides a kind of photovoltaic MPPT control method based on fuzzy PI two-way linear prediction, efficiently solve the problem that traditional MPPT control method cannot take into account tracking velocity and computational accuracy, can follow the tracks of maximum power point rapidly and accurately, simple and practical.
For achieving the above object, according to one aspect of the present invention, provide a kind of photovoltaic MPPT control method, it is characterized in that, comprise the steps: that (1) obtains the power-voltage characteristic curve of photovoltaic cell, utilization level curve near tangent carries out bidirectional linear prediction, approaches maximum power point, calculates approximate maximum power point; (2) on the basis of approximate maximum power point, disturbance observation is utilized 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 are the cycle, and P is power, and u is voltage; (3) using error e (k) and the input of error transform Δ e (k) as fuzzy controller, fuzzy controller adopts Mamdani fuzzy reasoning method, set-point can be arrived fast for target with output power, set up fuzzy control rule, realize MPPT maximum power point tracking.
Preferably, described step (1) comprises the steps: that (1-1) takes up an official post at power-voltage characteristic curve further and gets 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 the voltage that maximum power point is corresponding, U oCfor open-circuit voltage; (1-2) cross the tangent line of A and the B rate of doing work-voltage response respectively, intersection point is O; (1-3) using point identical with O point horizontal ordinate on power-voltage characteristic curve as approximate maximum power point; (1-4) when larger change occurs light intensity, when causing power variation Δ P to be greater than threshold value T, return step (1-1), otherwise order performs step (2).
Preferably, in described step (3), determine PI parameter K according to error e (k) and error transform Δ e (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 conceived 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, photovoltaic PV curve is substituted with two single-point Hermite Interpolations, higher to the precision of prediction of PV curve.
2, predicted by bidirectional linear, drastically increase the speed of maximal power tracing.Be applicable to the photovoltaic cell of different fill factor, curve factor.
Accompanying drawing explanation
Fig. 1 is the photovoltaic MPPT control method process flow diagram based on fuzzy PI two-way linear prediction 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 clearly understand, 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, be not intended to limit the present invention.In addition, if below in described each embodiment of the present invention involved technical characteristic do not form conflict each other and just can mutually combine.
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 characteristic curve of photovoltaic cell, utilization level curve near tangent carries out bidirectional linear prediction, approaches maximum power point, calculates approximate maximum power point.Comprise the steps: further
(1-1) as shown in Figure 2, take up an official post at power-voltage characteristic curve P (u) of photovoltaic cell 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 the voltage that maximum power point is corresponding, U oCfor open-circuit voltage.
(1-2) cross tangent line OA and OB of A and the B rate of doing work-voltage response respectively, 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 following the Representation Equation respectively:
H OA ( u ) = P &prime; ( U L ) &times; ( u - U L ) + P ( U L ) H OB ( u ) = P &prime; ( U R ) &times; ( u - U R ) + P ( U R ) - - - ( 1 )
(1-3) by the power-voltage characteristic curve 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| be the absolute value of the horizontal ordinate difference of approximate maximum power point C and actual maximum power point D.
Structure auxiliary function or particularly, for tangent line OA, 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 ( u ) = P &prime; &prime; ( &xi; ) 2 &times; [ P ( U R ) - P ( U L ) + P &prime; ( U L ) &times; ( U L - U R ) P &prime; ( U L ) - P &prime; ( U R ) ] 2
(1-4) when larger change occurs light intensity, when causing power variation Δ P to be greater than threshold value T, step (1-1) is returned, to reduce search time; If change is less than this threshold value, then order performs 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 ( k ) = dP du = P ( k ) - P ( k - 1 ) u ( k ) - u ( k - 1 ) , Δe(k)=e(k)-e(k-1)。
(3) using error e (k) and the input of error transform Δ e (k) as fuzzy controller, fuzzy controller adopts Mamdani fuzzy reasoning method, set-point can be arrived fast for target with output power, set up fuzzy control rule, realize MPPT maximum power point tracking.
Particularly, PI parameter K is determined according to error e (k) and error transform Δ e (k) pand K i, fuzzy set is that { 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 amendments done within the spirit and principles in the present invention, equivalent replacement and improvement etc., all should be included within protection scope of the present invention.

Claims (3)

1. a photovoltaic MPPT control method, is characterized in that, comprises the steps:
(1) obtain the power-voltage characteristic curve of photovoltaic cell, utilization level curve near tangent carries out bidirectional linear prediction, approaches maximum power point, calculates approximate maximum power point;
Comprise the steps: further
(1-1) take up an official post at power-voltage characteristic curve 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 the voltage that maximum power point is corresponding, U oCfor open-circuit voltage;
(1-2) cross the tangent line of A and the B rate of doing work-voltage response respectively, intersection point is O;
(1-3) using point identical with O point horizontal ordinate on power-voltage characteristic curve as approximate maximum power point;
(1-4) when larger change occurs light intensity, when causing power variation Δ P to be greater than threshold value T, return step (1-1), otherwise order performs step (2);
(2) on the basis of approximate maximum power point, disturbance observation is utilized 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 are the cycle, and P is power, and u is voltage;
(3) using error e (k) and the input of error transform Δ e (k) as fuzzy controller, fuzzy controller adopts Mamdani fuzzy reasoning method, set-point can be arrived fast for target with output power, set up fuzzy control rule, realize MPPT maximum power point tracking.
2. photovoltaic MPPT control method as claimed in claim 1, is characterized in that, in described step (3), determines PI parameter K according to error e (k) and error transform Δ e (k) pand K i.
3. photovoltaic MPPT control method as claimed in claim 1 or 2, is characterized in that, fuzzy set be PB, PS, ZE, NS, NB}, fuzzy control rule is as follows:
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