CN111367350A - Photovoltaic maximum power tracking control method based on rolling small window - Google Patents

Photovoltaic maximum power tracking control method based on rolling small window Download PDF

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CN111367350A
CN111367350A CN202010138705.5A CN202010138705A CN111367350A CN 111367350 A CN111367350 A CN 111367350A CN 202010138705 A CN202010138705 A CN 202010138705A CN 111367350 A CN111367350 A CN 111367350A
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small window
change
maximum power
duty ratio
photovoltaic
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李星硕
徐峥嵘
丁树业
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Nanjing University
Nanjing Normal University
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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
    • 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

Abstract

The invention discloses a photovoltaic maximum power tracking control method based on a rolling small window, which comprises the steps of sampling voltage and current output by a photovoltaic module to obtain a sampling voltage value V and a current value I, and then calculating the change delta P of photovoltaic output power and the change delta V of output voltage; determining the change direction of the duty ratio D according to the changes of the delta P and the delta V; storing data of four continuous duty ratios into a rolling small window, wherein if the duty ratios change once, the small window rolls once to detect whether the maximum power point is tracked or not, and gradually stabilizing fluctuation after the maximum power point is tracked; and setting a threshold value of delta V in a stable fluctuation state, emptying a small window once the external environment changes, initializing the step length, and tracking the maximum power point again. The invention can quickly track the maximum power point, reduce unnecessary disturbance under stable external conditions and improve the tracking precision.

Description

Photovoltaic maximum power tracking control method based on rolling small window
Technical Field
The invention relates to the technical field of photovoltaic power generation engineering, in particular to a photovoltaic maximum power tracking control method based on a rolling small window.
Background
Solar energy is one of the most important renewable energy sources in the current energy structure reform of the world. However, the photovoltaic array is affected by external environmental factors such as illumination or temperature, and the output voltage and current of the photovoltaic array exhibit obvious nonlinear characteristics. Therefore, how to adjust the output power of the photovoltaic module in real time and achieve Maximum Power Point Tracking (MPPT) in any external environment is very important.
The existing MPPT technology mainly comprises a fixed step size and a variable step size. The traditional fixed-step MPPT algorithm mainly comprises a disturbance observation method (P & O), a conductance increment method (INC) and a Hill Climbing method (Hill clinmbig). The fixed-step algorithm has the advantages of simplicity, low cost, easiness in implementation and better effect under the condition of stable weather conditions. But the response speed is slow when the external environment is suddenly changed. Although the variable-step MPPT algorithm can solve the problem of response speed, the method for determining the step size is too complex, the step size is too small when the variable-step MPPT algorithm is close to the MPP, so that the tracking speed is reduced, and the system complexity is high. And whether it is a fixed step or variable step algorithm, it still has disturbance after tracking to the Maximum Power Point (MPP).
Disclosure of Invention
The technical problem to be solved by the invention is to provide a photovoltaic maximum power point tracking control method based on a rolling small window, which can quickly track a maximum power point, reduce unnecessary disturbance under a stable external condition and improve tracking precision.
In order to solve the technical problem, the invention provides a photovoltaic maximum power tracking control method based on a rolling small window, which comprises the following steps:
(1) initializing a step length step of duty ratio change, a small window sampling frequency f and a flat suppression fluctuation identifier steady;
(2) sampling the voltage value V and the current value I, calculating the change delta P of the photovoltaic output power and the change delta V of the output voltage, determining the change direction of the duty ratio according to a P & O method, and storing the changed duty ratio data into a rolling small window, wherein the duty ratio is changed once, and the small window is sampled once;
(3) when the sampling frequency reaches four times, the small window starts to roll and is cross-compared with the previous small window, when the small windows are not cross-equal, the step length of the duty ratio is unchanged, when the small windows are cross-equal, the maximum power point is considered to be tracked, and the step length of the duty ratio is halved, namely
Figure BDA0002398252920000021
(4) When the step length of the duty ratio is less than 0.25%, the system is judged to enter a zero oscillation state, and the step length of the duty ratio is equal to 0 at the moment, namely the duty ratio is not changed;
(5) when the small window intersections are detected to be equal for the first time, the system is judged to enter a fluctuation stabilizing state, and the threshold value | delta V & lt & gtof the change of the output voltage is setmaxIf the output voltage change does not exceed the threshold value, the external environment is judged not to be changed, the system continues to stabilize fluctuation, if the output voltage change exceeds the threshold value, the external environment is judged to be changed, the system is initialized, the step (1) is returned, and the maximum power point is tracked again.
Preferably, in the step (2), the determining the change direction of the duty ratio according to the P & O method specifically includes:
four consecutive duty cycle values will be stored for analysis by the bin, with a change in duty cycle, the bin rolling once, the real-time duty cycle being stored as the first data of the bin, and the remaining three data being conjugated to the last bin, with the specific data for each bin being as follows:
Figure BDA0002398252920000022
the change of the duty ratio is mainly based on the change Δ P of the photovoltaic output power and the change Δ V of the photovoltaic output voltage, and the specific calculation formula is as follows:
Figure BDA0002398252920000023
the values of Δ P and Δ V determine the direction the algorithm tracks, as follows:
Figure BDA0002398252920000024
where step is the step size of each change in duty cycle, the size of which is determined by whether the data stored in the rolling small window cross equally.
Preferably, in step (3), the specific criterion for equality of small window crossing is as follows:
Figure BDA0002398252920000025
preferably, in step (5), the threshold | Δ V of the change in output voltage ismaxThe concrete formula of (1) is as follows:
Figure BDA0002398252920000026
wherein stepmaxIs the maximum value of the duty cycle step length after the system enters a steady fluctuation state, D (t)maxIs the maximum value of the duty ratio, V, after the system enters a steady fluctuation stateo4Refers to the maximum open circuit voltage of the system.
The invention has the beneficial effects that: the maximum power point can be quickly tracked, unnecessary disturbance is reduced under a stable external condition, and the tracking precision is improved.
Drawings
Fig. 1 is a schematic diagram of a photovoltaic maximum power tracking control system based on a rolling small window according to the present invention.
FIG. 2 is a diagram illustrating information stored in the rolling widget according to the present invention.
FIG. 3 is a schematic diagram of a criterion for determining the intersection equality of rolling windows according to the present invention.
FIG. 4 is a schematic diagram of the duty cycle variation of the environmental transition after entering the smooth fluctuation state.
Fig. 5 is a schematic flow chart of the photovoltaic maximum power tracking control method based on the rolling small window.
Fig. 6 is a schematic diagram showing a comparison of simulation results of the rolling small window-based photovoltaic maximum power tracking control method and the conventional P & O method under a stable environment condition.
Fig. 7 is a schematic diagram showing a comparison of simulation results of the rolling small window-based photovoltaic maximum power tracking control method and the conventional P & O method under the condition of environmental change.
Detailed Description
A photovoltaic maximum power tracking control method based on a rolling small window comprises the following steps:
(1) initializing a step length step of duty ratio change, a small window sampling frequency f and a flat suppression fluctuation identifier steady;
(2) sampling the voltage value V and the current value I, calculating the change delta P of the photovoltaic output power and the change delta V of the output voltage, determining the change direction of the duty ratio according to a P & O method, and storing the changed duty ratio data into a rolling small window, wherein the duty ratio is changed once, and the small window is sampled once;
(3) when the sampling frequency reaches four times, the small window starts to roll and is cross-compared with the previous small window, when the small windows are not cross-equal, the step length of the duty ratio is unchanged, when the small windows are cross-equal, the maximum power point is considered to be tracked, and the step length of the duty ratio is halved, namely
Figure BDA0002398252920000031
(4) When the step length of the duty ratio is less than 0.25%, the system is judged to enter a zero oscillation state, and the step length of the duty ratio is equal to 0 at the moment, namely the duty ratio is not changed;
(5) when the small window intersections are detected to be equal for the first time, the system is judged to enter a fluctuation stabilizing state, and the threshold value | delta V & lt & gtof the change of the output voltage is setmaxIf the output voltage change does not exceed the threshold value, the external environment is judged not to be changed, the system continues to stabilize fluctuation, if the output voltage change exceeds the threshold value, the external environment is judged to be changed, the system is initialized, the step (1) is returned, and the maximum power point is tracked again.
Fig. 1 is a block diagram of the system of the present invention, which includes a photovoltaic model, a DC-DC converter and an MPPT control module thereof. The photovoltaic module mainly provides output power, and the output characteristics of the photovoltaic module are closely related to the ambient temperature, illumination and the like; the DC-DC converter is used as a power interface between the photovoltaic module and a load and provides voltage or current conversion; the MPPT control module performs a specific maximum power point tracking control method and then adjusts a duty ratio of the DC-DC converter so that the photovoltaic module always outputs maximum power in any operating condition.
As shown in fig. 2, in this algorithm, four consecutive duty cycle values will be stored for analysis by the bin, with one change in duty cycle, the bin rolling once, the real-time duty cycle being stored as the first data of the bin, and the remaining three data being conjugated to the last bin. The specific data of each small window is as follows:
Figure BDA0002398252920000041
in the algorithm, the change of the duty ratio is mainly based on the change Δ P of the photovoltaic output power and the change Δ V of the photovoltaic output voltage, and the specific calculation formula is as follows:
Figure BDA0002398252920000042
the values of Δ P and Δ V determine the direction the algorithm tracks, as follows:
Figure BDA0002398252920000043
where step is the step size of each change in duty cycle, the size of which is determined by whether the data stored in the rolling small window cross equally. As shown in fig. 3, it is determined that the rolling windows are detected to be equal, that is, the Maximum Power Point (MPP) is detected, and unnecessary disturbances under stable conditions begin to be reduced, where the specific criteria are as follows:
Figure BDA0002398252920000044
as shown in fig. 3, when no data cross equality is detected in the small window (W1 ≠ W2), it indicates that the maximum power point has not been tracked yet or that the disturbance in the periphery of the tracked maximum power point has not started; when the data stored in the small window are detected to be equal in cross (W2 ═ W3), it is said that the maximum power point has been tracked and the disturbance around the maximum power point has started, and the disturbance starts to be stabilized, and the specific formula is as follows:
Figure BDA0002398252920000051
in the above situations, when the external environment changes, if the external environment changes, the maximum power point cannot be tracked due to continuous flat fluctuation. At this time, a voltage fluctuation threshold needs to be set, if the voltage fluctuation threshold is exceeded during fluctuation stabilization, it indicates that external conditions change, the step length needs to be adjusted to an initial step length, and the maximum power point needs to be tracked again. The specific derivation process of the voltage fluctuation threshold is as follows:
Figure BDA0002398252920000052
then the specific formula for Δ V is:
Figure BDA0002398252920000053
the maximum open-circuit voltage of the photovoltaic system adopted by the invention is 17.3V, the duty ratio of the photovoltaic system generally fluctuates between 0.3 and 0.8, and the maximum step length when the photovoltaic system enters a fluctuation stabilizing state is 0.5 percent
Figure BDA0002398252920000054
However, when the external environment changes, | Δ V | is much larger than this, so in the present algorithm, when entering the steady fluctuation state, the following is set:
if | Δ V | is more than or equal to 0.5; initializing step length and emptying the small window.
As shown in fig. 4, after the surge state is stabilized, when the voltage surge exceeding the threshold is detected, the initial step size is reduced, the small window is cleared, and the maximum power point is tracked again.
Fig. 5 shows a complete flow chart of the whole algorithm. Wherein "steady" is used to identify whether the system enters a steady fluctuation state, and if the system enters the steady fluctuation state, it is necessary to determine whether the external condition changes by comparing | Δ V | with its threshold; and f is used for judging whether the sampling of the data in the small window is finished or not and whether the rolling comparison can be carried out or not.
Fig. 6 is a graph comparing simulation results of the rolling small window-based photovoltaic maximum power tracking control method and the conventional P & O method under the condition of stable environment. As can be seen from fig. 6, the method of the present invention can track the maximum power point more quickly, and can quickly and unnecessarily disturb the maximum power point after tracking the maximum power point, thereby improving the tracking accuracy.
Fig. 7 is a graph comparing simulation results of the rolling small window-based photovoltaic maximum power tracking control method and the conventional P & O method under the condition of environmental change. As can be seen from fig. 7, the method of the present invention can quickly identify the environmental change and track to the maximum power point more quickly under different conditions.

Claims (4)

1. A photovoltaic maximum power tracking control method based on a rolling small window is characterized by comprising the following steps:
(1) initializing a step length step of duty ratio change, a small window sampling frequency f and a flat suppression fluctuation identifier steady;
(2) sampling the voltage value V and the current value I, calculating the change delta P of the photovoltaic output power and the change delta V of the output voltage, determining the change direction of the duty ratio according to a P & O method, and storing the changed duty ratio data into a rolling small window, wherein the duty ratio changes once and the small window samples once;
(3) when the sampling frequency reaches four times, the small window starts to roll and is cross-compared with the previous small window, when the small window is not cross-equal, the step length of the duty ratio is unchanged, when the small window is cross-equal, the maximum power point is considered to be tracked, and the step length of the duty ratio is halved, namely
Figure FDA0002398252910000011
(4) When the step length of the duty ratio is less than 0.25%, the system is judged to enter a zero oscillation state, and the step length of the duty ratio is equal to 0 at the moment, namely the duty ratio is not changed;
(5) when the small window intersections are detected to be equal for the first time, the system is judged to enter a fluctuation stabilizing state, and the threshold value | delta V & lt & gtof the change of the output voltage is setmaxIf the output voltage change does not exceed the threshold value, the external environment is judged not to be changed, the system continues to stabilize fluctuation, if the output voltage change exceeds the threshold value, the external environment is judged to be changed, the system is initialized, the step (1) is carried out, and the maximum power point is tracked again.
2. The photovoltaic maximum power tracking control method based on the rolling small window as claimed in claim 1, wherein in the step (2), the determining the change direction of the duty ratio according to the P & O method specifically comprises:
four consecutive duty cycle values will be stored for analysis by the bin, with a change in duty cycle, the bin rolling once, the real-time duty cycle being stored as the first data of the bin, and the remaining three data being conjugated to the last bin, with the specific data for each bin being as follows:
Figure FDA0002398252910000012
the change of the duty ratio is mainly based on the change Δ P of the photovoltaic output power and the change Δ V of the photovoltaic output voltage, and the specific calculation formula is as follows:
Figure FDA0002398252910000013
the values of Δ P and Δ V determine the direction the algorithm tracks, as follows:
Figure FDA0002398252910000014
where step is the step size of each change in duty cycle, the size of which is determined by whether the data stored in the rolling small window cross equally.
3. The rolling small window-based photovoltaic maximum power tracking control method according to claim 1, wherein in the step (3), the specific criterion that the small window crossings are equal is as follows:
Figure FDA0002398252910000021
4. the rolling small window-based photovoltaic maximum power tracking control method according to claim 1, wherein in the step (5), the threshold | Δ V of the output voltage change ismaxThe concrete formula of (1) is as follows:
Figure FDA0002398252910000022
wherein stepmaxIs the maximum value of the duty cycle step length after the system enters a steady fluctuation state, D (t)maxIs the maximum value of the duty ratio, V, after the system enters a steady fluctuation stateocRefers to the maximum open circuit voltage of the system.
CN202010138705.5A 2020-03-03 2020-03-03 Photovoltaic maximum power tracking control method based on rolling small window Pending CN111367350A (en)

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CN114035644A (en) * 2021-10-21 2022-02-11 西安理工大学 Control method for eliminating steady-state oscillation of photovoltaic power generation system by improving P & O method

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CN111969945A (en) * 2020-08-17 2020-11-20 博阳能源科技有限公司 quasi-MPPT novel photovoltaic panel tracking method, equipment and storage medium
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CN114035644A (en) * 2021-10-21 2022-02-11 西安理工大学 Control method for eliminating steady-state oscillation of photovoltaic power generation system by improving P & O method

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