CN112817365B - MPPT method and system for improving control precision - Google Patents

MPPT method and system for improving control precision Download PDF

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CN112817365B
CN112817365B CN202110015795.3A CN202110015795A CN112817365B CN 112817365 B CN112817365 B CN 112817365B CN 202110015795 A CN202110015795 A CN 202110015795A CN 112817365 B CN112817365 B CN 112817365B
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sampling
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CN112817365A (en
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颜云岭
王鹏程
王成瑞
吴国栋
李作才
裴杰
曹传钊
曹曦
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Huaneng Taishan New Energy Co ltd
Huaneng Clean Energy Research Institute
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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
    • G05F1/66—Regulating electric power
    • G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/30—Electrical components
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The invention discloses an MPPT method and an MPPT system for improving control precision, and belongs to the field of new energy control. The MPPT method for improving the control precision selects the proper number of n samples according to the sampling precision of the system; selecting a proper disturbance threshold value delta P according to the power grade of the control system; according to the change speed of the output power of the photovoltaic array, different disturbance step sizes delta U and disturbance periods T are selected to realize the rapid tracking of the maximum power point under different working conditions, and further the MPPT efficiency is improved.

Description

MPPT method and system for improving control precision
Technical Field
The invention belongs to the technical field of new energy control, and particularly relates to an MPPT method and an MPPT system for improving control precision.
Background
The rapid development of the new energy industry puts higher requirements on various performance indexes of a control system. Among them, how to improve the Maximum Power Point Tracking (MPPT) efficiency of control is always a research focus.
At present, various MPPT control methods are mature and applied, such as a common constant voltage method, a disturbance observation method, an admittance increment method, a dP-P & O method and the like [1 ].
The commonly used disturbance observation method achieves the purpose of adjusting the output power P (k) of the photovoltaic array by periodically changing the output voltage U (k) of the photovoltaic array. The specific scheme is as follows: sampling the output current I (k) and the output voltage U (k) of the photovoltaic array in the current period, calculating the output power P (k) of the current period, and comparing the output power P (k-1) with the output power P (k-1) of the previous period. When P (k) is more than or equal to P (k-1), the output voltage U (k) of the photovoltaic array is changed along the original direction; when P (k) < P (k-1), the photovoltaic array output voltage U (k) is varied in the opposite direction.
The photovoltaic power generation system is a nonlinear and interference-prone complex system [2], in the prior art, MPPT control is mostly carried out after voltage and current sampling and filtering, and the accuracy of control is influenced. On the other hand, the step size of the disturbance is fixed, so that there is a back-and-forth oscillation of power at the maximum power point, and there is a power loss.
Disclosure of Invention
The invention aims to provide an MPPT method and an MPPT system for improving control precision, and aims to solve the problem that the MPPT method in the prior art is not accurate enough.
In order to realize the purpose, the following technical scheme is adopted:
an MPPT method for improving control accuracy comprises the following steps:
sampling n sampling periods of the photovoltaic array in the kth disturbance period, and recording the output current of the xth sampling period as Ik(x) The output voltage is recorded as Uk(x)；
Sampling n sampling periods of the photovoltaic array in the k-1 th disturbance period, and recording the output current of the x sampling period as Ik-1(x) The output voltage is recorded as Uk-1(x)；
Calculating the total output power P (k) of n sampling periods in the k perturbation period;
calculating the total output power P (k-1) of n sampling periods in the k-1 th disturbance period;
calculating the difference value between P (k) and P (k-1) to obtain delta P (k);
and adjusting the disturbance direction A according to the magnitude relation between the power disturbance threshold value delta P (k) and the power disturbance threshold value delta P.
Preferably, the method further comprises the following steps:
calculating the command voltage U of the kth disturbance periodref(k) Will command the voltage Uref(k) As the voltage input to the photovoltaic inverter.
Preferably, the command voltage Uref(k) The calculation method of (c) is as follows:
Uref(k)＝Uref(k-1)+A*ΔU
in the formula: a is the disturbance direction; delta U is a disturbance step length; u shaperefAnd (k-1) is the command voltage of the k-1 th disturbance period.
Preferably, p (k) is calculated as follows:
Figure BDA0002885895560000021
preferably, P (k-1) is calculated as follows:
Figure BDA0002885895560000022
preferably, the disturbance direction a is adjusted according to a magnitude relation between Δ P (k) and the power disturbance threshold Δ P, specifically:
when Δ P (k) > Δ P, keeping the original perturbation direction a ═ 1 × a;
when Δ P (k) < - Δ P, then change the perturbation direction a (-1) × a;
when | Δ P (k) | ≦ Δ P, a ═ 0.
Preferably, the value range of n is 1 to [ T/T ], T is the disturbance period duration, and T is the sampling period duration.
Preferably, a is initially 1.
The invention provides another technical scheme that:
a system for the MPPT method for improving control accuracy, comprising:
the sampling module is used for sampling n sampling periods of the photovoltaic array in the kth disturbance period and marking the output current of the xth sampling period as Ik(x) The output voltage is recorded as Uk(x) (ii) a Sampling n sampling periods of the photovoltaic array in the k-1 th disturbance period, and recording the output current of the x sampling period as Ik-1(x) The output voltage is recorded as Uk-1(x)；
The total power calculating module is used for calculating the output total power P (k) of n sampling periods in the k perturbation period; calculating the total output power P (k-1) of n sampling periods in the k-1 th disturbance period;
the difference value calculating module is used for calculating the difference value between P (k) and P (k-1) to obtain delta P (k);
and the disturbance direction adjusting module is used for adjusting the disturbance direction A according to the magnitude relation between the power disturbance threshold value delta P (k) and the delta P.
Preferably, the method further comprises the following steps: a voltage input instruction module for calculating the instruction voltage U of the kth disturbance periodref(k) Will command the voltage Uref(k) And inputting the voltage into the photovoltaic inverter.
The beneficial effects of the invention are as follows:
1. according to the MPPT method for improving the control precision, provided by the embodiment of the invention, the proper number n of sampling cycles is selected according to the sampling precision of a system; selecting a proper disturbance threshold value delta P according to the power grade of the inverter; according to the change speed of the output power of the photovoltaic array, different disturbance step sizes delta U and disturbance periods T are selected to realize the rapid tracking of the maximum power point under different working conditions, and further the MPPT efficiency is improved.
2. According to the MPPT method for improving the control precision, provided by the embodiment of the invention, the total power difference of two continuous MPPT is calculated by integrating the sampling data in the disturbance period, the disturbance direction is adjusted by comparing the difference value with the preset threshold value, so that the precision of the MPPT control algorithm is improved, the number n of the sampling periods can be selected according to the actual operation condition of the photovoltaic inverter, and the MPPT efficiency is improved.
3. The MPPT method for improving the control precision provided by the embodiment of the invention adds the disturbance power threshold value delta P (k), which is equivalent to forming a hysteresis control and avoiding oscillation near the maximum power point.
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The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a control flowchart of an MPPT method for improving control accuracy according to an embodiment of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The following detailed description is exemplary in nature and is intended to provide further details of the invention. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention.
As shown in fig. 1, an MPPT method for improving control accuracy provided in an embodiment of the present invention includes the following steps:
1) sampling n sampling periods of the photovoltaic array in the kth disturbance period, and recording the output current of the xth sampling period as Ik(x) The output voltage is recorded as Uk(x) Calculating the total output power from the 1 st to the nth sampling period
Figure BDA0002885895560000041
Figure BDA0002885895560000042
The number n of sampling periods is selected according to the sampling precision of the system.
2) Similarly, in the k-1 th disturbance period, n sampling periods of the photovoltaic array are sampled, and the output current of the x sampling period is marked as Ik-1(x) The output voltage is recorded as Uk-1(x) Calculating the total output power from the 1 st to the nth sampling period
Figure BDA0002885895560000043
3) And calculating the total power difference DeltaP (k) of two continuous MPPT times, and the total power difference DeltaP (k) is P (k) to P (k-1).
4) Selecting a proper disturbance threshold value delta P according to the power grade of the inverter; adjusting the disturbance direction A according to the magnitude relation between the power disturbance threshold value delta P (k) and the Δ P, which is as follows:
when Δ P (k) > Δ P, keeping the original perturbation direction a ═ 1 × a;
when Δ P (k) < - Δ P, then change the perturbation direction a (-1) × a;
when | Δ P (k) | ≦ Δ P, a ═ 0.
5) Finally, according to the command voltage Uref(k) Will command the voltage Uref(k) As a voltage input to the photovoltaic inverter; command voltage Uref(k) The calculation formula of (2) is as follows:
Uref(k)＝Uref(k-1)+A*ΔU
delta U is a disturbance step length and is determined according to the speed of the output power change of the photovoltaic array; u shaperefAnd (k-1) is the command voltage of the k-1 th disturbance period.
On the basis of the scheme, n in the step 1) can be 1 to [ T/T ]. T is sampling period duration, T is disturbance period duration, and the T is determined according to the speed of the output power change of the photovoltaic array; in this embodiment, for the photovoltaic inverter, the sampling period duration T is much smaller than the disturbance period duration T.
Based on the above scheme, the initial value of a in step 4) is 1, and Δ P is an acceptable power disturbance threshold.
On the basis of the above scheme, in step 5), the perturbation step size Δ U refers to a change value of the voltage command at each MPPT.
The steps are improved on the basis of the perturbation method, and the idea of improving the control precision of the invention can be implanted into various MPPT methods, so that the method has good popularization. The value of n can be adjusted according to the performance parameters of the actual system.
Those not described in detail in this specification are within the skill of the art.
The present invention relates to the following technical terms:
1. MPPT Maximum Power Point Tracking (Maximum Power Point Tracking): the variation of output voltage and current generated by the variation of the surface temperature and solar irradiance of the solar array is tracked and controlled, so that the array is always kept in the working state of maximum output, and the adjustment action for obtaining the maximum power output is called maximum power point tracking.
2. Disturbance step size Δ U: the change value of the voltage command at each time of MPPT control.
3. Sampling period t: and the sampling plate samples the output voltage and current of the solar photovoltaic array.
4. Disturbance period T: time intervals of two consecutive MPPT controls.
Accessories:
references (e.g. patents/papers/standards)
Document 1: chinese patent G05F1/67.20171003
Document 2: sun Deda photovoltaic power generation system maximum power point tracking research [ D ]. Jinan: Shandong university, 2014.
It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.

Claims (6)

1. An MPPT method for improving control precision is characterized by comprising the following steps:
sampling n sampling periods of the photovoltaic array in the kth disturbance period, and recording the output current of the xth sampling period as Ik(x) The output voltage is recorded as Uk(x)；
Sampling n sampling periods of the photovoltaic array in the k-1 th disturbance period, and recording the output current of the x sampling period as Ik-1(x) The output voltage is recorded as Uk-1(x)；
Calculating the total output power P (k) of n sampling periods in the k perturbation period;
calculating the total output power P (k-1) of n sampling periods in the k-1 th disturbance period;
calculating the difference value between P (k) and P (k-1) to obtain delta P (k);
adjusting the disturbance direction A according to the magnitude relation between the power disturbance threshold value delta P (k) and the power disturbance threshold value delta P;
further comprising the steps of:
calculating the command voltage U of the kth disturbance periodref(k) Will command the voltage Uref(k) As a voltage input to the photovoltaic inverter;
adjusting the disturbance direction A according to the magnitude relation between the power disturbance threshold value delta P (k) and the power disturbance threshold value delta P, specifically:
when Δ P (k) > Δ P, keeping the original perturbation direction a ═ 1 × a;
when Δ P (k) < - Δ P, then change the perturbation direction a (-1) × a;
when | Δ P (k) | ≦ Δ P, a ═ 0; the initial value of A is 1;
command voltage Uref(k) The calculation method of (c) is as follows:
Uref(k)＝Uref(k-1)+A*ΔU
in the formula: a is the disturbance direction; delta U is a disturbance step length; u shaperefAnd (k-1) is the command voltage of the k-1 th disturbance period.
2. The MPPT method for improving control accuracy according to claim 1, wherein p (k) is calculated as follows:
Figure FDA0003535196720000011
3. the MPPT method for improving control accuracy according to claim 1, wherein P (k-1) is calculated as follows:
Figure FDA0003535196720000012
4. the MPPT method for improving control accuracy according to claim 1, wherein a value range of n is 1 to [ T/T ], T is a disturbance period duration, and T is a sampling period duration.
5. A system for the MPPT method of increasing control accuracy of claim 1, comprising:
the sampling module is used for sampling n sampling periods of the photovoltaic array in the kth disturbance period and marking the output current of the xth sampling period as Ik(x) The output voltage is recorded as Uk(x) (ii) a Sampling n sampling periods of the photovoltaic array in the k-1 th disturbance period, and recording the output current of the x sampling period as Ik-1(x) The output voltage is recorded as Uk-1(x)；
The total power calculating module is used for calculating the output total power P (k) of n sampling periods in the k perturbation period; calculating the total output power P (k-1) of n sampling periods in the k-1 th disturbance period;
the difference value calculating module is used for calculating the difference value between P (k) and P (k-1) to obtain delta P (k);
and the disturbance direction adjusting module is used for adjusting the disturbance direction A according to the magnitude relation between the power disturbance threshold value delta P (k) and the delta P.
6. The system for improving MPPT method of control accuracy as set forth in claim 5, further comprising: a voltage input instruction module for calculating the instruction voltage U of the kth disturbance periodref(k) Will command the voltage Uref(k) And inputting the voltage into the photovoltaic inverter.
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