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CN116991195B - Photovoltaic MPPT control system based on sliding mode variable structure-global comparison composite algorithm - Google Patents

Photovoltaic MPPT control system based on sliding mode variable structure-global comparison composite algorithm

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Publication number
CN116991195B
CN116991195B CN202310887304.3A CN202310887304A CN116991195B CN 116991195 B CN116991195 B CN 116991195B CN 202310887304 A CN202310887304 A CN 202310887304A CN 116991195 B CN116991195 B CN 116991195B
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algorithm
photovoltaic
sliding mode
power
variable structure
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CN116991195A (en
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葛强
孙涛
王明礼
汤新宇
龙恒
张益铭
王璐
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Yangzhou University
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Yangzhou 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
    • 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
    • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of DC power input into DC power output
    • H02M3/02—Conversion of DC power input into DC power output without intermediate conversion into AC
    • H02M3/04—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters
    • H02M3/10—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155—Conversion of DC power input into DC power output without intermediate conversion into AC by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02J2101/24—
    • 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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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

本发明公开了光伏MPPT控制领域内的一种基于滑模变结构‑全局比较复合算法的光伏MPPT控制系统，包括温度光照变量模块，光伏阵列，DC‑DC变换器，电压电流传感器，温度光照传感器，MPPT算法模块，PWM模块，DSP数字信号处理器，电源电路，驱动电路和计算机显示器；所述温度光照变量模块用于模拟光伏阵列因树枝、电杆而产生的阴影遮挡；所述MPPT算法模块采用主算法——滑模变结构控制算法并辅以全局比较算法，周期性搜索阴影遮挡下光伏阵列的最大功率点；本发明能够避免传统算法追踪到局部极值问题，防止光伏阵列因遮阴而出现高热烧毁，提高跟踪速度，精度和安全性，并且削弱全局最大功率点附近的振荡。

The present invention discloses a photovoltaic MPPT control system based on a sliding mode variable structure-global comparison composite algorithm in the field of photovoltaic MPPT control. The control system comprises a temperature and light variable module, a photovoltaic array, a DC-DC converter, a voltage and current sensor, a temperature and light sensor, an MPPT algorithm module, a PWM module, a DSP digital signal processor, a power supply circuit, a drive circuit, and a computer display. The temperature and light variable module is used to simulate shadows caused by tree branches and poles on the photovoltaic array. The MPPT algorithm module uses a main algorithm, a sliding mode variable structure control algorithm, supplemented by a global comparison algorithm, to periodically search for the maximum power point of the photovoltaic array under shadows. The present invention can avoid the problem of traditional algorithms tracking local extreme values, prevent the photovoltaic array from being burned out due to high heat caused by shading, improve tracking speed, accuracy, and safety, and weaken oscillations near the global maximum power point.

Description

Photovoltaic MPPT control system based on sliding mode variable structure-global comparison compound algorithm
Technical Field
The invention relates to the technical field of photovoltaic MPPT control, in particular to a photovoltaic MPPT control system based on a sliding mode variable structure-global comparison compound algorithm.
Background
In recent years, the consumption speed of traditional fossil fuels is faster and faster, the energy problem is more and more prominent, and solar energy is taken as a representative of clean energy and is gradually paid attention to. The progress of the photovoltaic industry is continuously accelerated, the number of photovoltaic power stations is increased, and the photovoltaic power stations can convert light energy into electric energy through a series of photovoltaic cell panels, so that the energy problem and the environmental pollution are effectively relieved.
Solar photovoltaic technology is widely applied, however, the conversion efficiency is not high, which is a main problem restricting the development and application of the technology, so that the research of the maximum power point tracking algorithm is one of hot spot problems in the research of a photovoltaic power generation system. On the basis of an MPPT algorithm, the photovoltaic power generation system is shielded and cannot uniformly receive illumination, so that the efficiency of the photovoltaic power generation system is greatly reduced, even a local heating phenomenon (hot spot phenomenon) is generated, and irreversible damage such as aging acceleration of a power generation module is caused.
The traditional MPPT algorithm has the advantages of simple structure, lower manufacturing cost and more convenient realization, but inevitably has problems such as low control precision, slower tracking speed, oscillation after stable power, and the like. In particular, when the photovoltaic cell is in an open air environment, the change of temperature and illumination has a greater influence on the power generation efficiency of the system, and the control effect of the MPPT algorithm is more compromised under shadow shielding. Once the battery is locally shaded, multiple power peaks appear in the P-U curve, and the MPPT algorithm may track the wrong maximum power point due to erroneous judgment. Furthermore, the blocked areas may also generate thermal power that damages the photovoltaic cells.
In the prior art, a photovoltaic MPPT control method under a partial shadow is provided, the patent application number is CN201510228788.6, the application date is 2015-05-06, the authorization number is CN106200752B, the authorization date is 2017-11-03, the photovoltaic MPPT control method under the partial shadow adopts a power scanning method and a maximum power tracking method based on sliding mode control, a method of limiting power by a voltage threshold and a current threshold is utilized to scan global maximum power, theoretical analysis is feasible, the voltage current threshold can change along with the change of the environment in engineering application, the effect of taking a fixed value as the threshold is not necessarily ideal, even if the effect of being adjustable, the testing process is complex, the design control rate of a supercoiled algorithm is adopted, the engineering calculation amount is large, the complexity is high, the stability of the sliding mode control algorithm is not proved in the technical scheme, and the system is possibly unstable and cannot be used if the system is actually caused.
Disclosure of Invention
Aiming at the defects of the MPPT algorithm in actual photovoltaic power generation, the invention provides a photovoltaic MPPT control system based on a sliding mode variable structure-global comparison compound algorithm, which effectively solves the problems of error tracking, poor rapidness, poor stability, low efficiency, low precision and the like when tracking the maximum power point, can find out the correct maximum power point under the shadow shielding condition, improves the output efficiency of the system, and prevents the system from being damaged due to local hot spots.
The technical scheme is that the photovoltaic MPPT control system based on the sliding mode variable structure-global comparison compound algorithm comprises a temperature illumination variable module, a photovoltaic array, a DC-DC converter, a voltage current sensor, a temperature illumination sensor, an MPPT algorithm module, a PWM module, a DSP digital signal processor, a power supply circuit, a driving circuit and a computer display, wherein the temperature illumination variable module is used for simulating shadow shielding of the photovoltaic array due to branches and electric poles, and the MPPT algorithm module adopts a main algorithm, namely the sliding mode variable structure control algorithm, and is assisted with the global comparison algorithm to periodically search the maximum power point of the photovoltaic array under the shadow shielding.
As a further improvement of the invention, the photovoltaic array comprises a photovoltaic cell unit I, a photovoltaic cell unit II and a photovoltaic cell unit III which are connected in series, and a bypass diode is respectively connected in parallel outside the photovoltaic cell unit I, the photovoltaic cell unit II and the photovoltaic cell unit III.
As a further improvement of the invention, the DC-DC converter adopts a Boost circuit, the Boost circuit comprises a capacitor C1 and an inductor L, one ends of the capacitor C1 and the inductor L are connected with a forward port of the photovoltaic array, the other ends of the inductor L are connected with a drain electrode of the switching tube MOS and a diode anode, a diode cathode is connected with one end of the capacitor C2 and the load resistor R, and the capacitor C1, the capacitor C2, the switching tube source electrode and the load resistor R are connected into a cathode of the photovoltaic array.
As a further improvement of the invention, the design method of the sliding mode variable structure control algorithm comprises the following steps:
S01, establishing a photovoltaic cell mathematical model and solving partial derivatives thereof according to a photovoltaic cell equivalent circuit and a system main circuit-Boost circuit;
mathematical model of photovoltaic cell:
And (3) calculating deviation guide:
Wherein I pv represents a photovoltaic cell output current, V pv represents a photovoltaic cell output voltage, I ph represents a photovoltaic cell photo-generated current, I D0 represents a reverse saturation current, q represents an electron charge, a represents a diode factor, K represents boltzmann constant, T represents absolute temperature, I L represents an inductance current, V O represents a load side output voltage, and I O represents a load side output current;
s02, building a Boost circuit equivalent mathematical model according to two states of the MOS tube when the MOS tube is turned on and turned off;
(MOS transistor is conducted), (MOS tube off) (5)
Defining u=1, and 0 to represent on and off of the MOS transistor, the following equation can be obtained:
It is rewritten as a general state space equation:
Wherein the method comprises the steps of
S03, constructing a sliding mode surface (a sliding mode switching function) S and a control rate u;
because at the point of maximum power of the photovoltaic, there is
Can obtain the slip form surface
The setting control rate u consists of two parts, namely an equivalent control u eq and a variable structure control u sw, namely:
u=ueq+usw (11)
in order to ensure that the system can reach the sliding mode surface quickly while resisting interference, u sw adopts an index approach rate, namely:
usw=-ε*sign(s)-ks(ε>0,k>0) (12)
in the present invention, ε=0.03 and k=0.005 are obtained, and u eq is derived as follows:
As a result of being on the face of the slide, The method can obtain:
To sum up
S04, judging the stability of the sliding mode controller by utilizing a Liapunov function, and according to the following conditionTo stabilize the system, i.e. proveThe stability judging process is as follows:
i PV≈IL is due to the presence of the capacitor C1 in the system, and the following equation is obtained:
from the above (3) and (4)
When S >0, since ε >0, k >0, so
ThenAt this time
When S <0, since ε >0, k >0, so
ThenAt this time
The stability of the main controller, i.e. the sliding mode variable structure controller, can be judged.
As a further improvement of the invention, the design method of the global comparison algorithm comprises the following steps:
the method comprises the steps of 1, setting a global comparison time threshold value to be 0.5s at the same time when the sliding mode variable structure control algorithm starts to operate, namely, starting the global comparison algorithm every 0.5s by taking the global comparison time threshold value as a period, setting a power difference threshold value to be 15W in the period searching process, and setting the power difference threshold value as a basis for emergency starting of the global comparison algorithm due to instantaneous power change under the condition of suddenly changing shadow shielding at a certain moment;
Step 2, discretizing voltage and current data, setting the position of power preservation to be acquired at each moment as a real-time output power array Ps= [ ], and setting the position of system duty cycle preservation to be acquired at each moment as a real-time duty cycle array Ds= [ ];
Step 3, taking an I-V characteristic curve from an open circuit state to a short circuit state as a control process to acquire data, arranging real-time power and corresponding real-time duty ratio in an array in the form of data points, setting 5 data points as one cycle to be sampled once so as to ensure the searching efficiency of an algorithm, setting the duty ratio step length to be 0.005, continuously superposing the duty ratio in the step length of +0.005 in the process of sampling the power if the initial duty ratio is 0.1, simultaneously sampling the duty ratio, and continuously reducing the duty ratio in the step length of-0.005 in the process of sampling the power if the initial duty ratio is 0.9, and simultaneously sampling the duty ratio;
Step 4, outputting the maximum power of the photovoltaic array I-V characteristic obtained by the algorithm in the global process from open circuit to short circuit in a code instruction form for solving the maximum value, and finding out the corresponding duty ratio;
And 5, comparing the maximum power obtained by the global comparison algorithm with the maximum power obtained by the sliding mode variable structure algorithm, if the maximum power is equal, maintaining, if the maximum power is unequal, replacing the current power with a larger value, tracking the global maximum power according to the sliding mode surface and the control rate, and if the period of 0.5s arrives, re-entering the step1, and circularly searching.
As a further improvement of the invention, the voltage and current sensor samples voltage and current signals output by the photovoltaic array under shadow shielding and then sends the voltage and current signals to the MPPT algorithm module, the MPPT algorithm module is connected with the PWM module, and the PWM module outputs PWM waves to the MOSFET in the Boost circuit.
As a further improvement of the invention, the power supply circuit and the driving circuit are both connected with a DSP digital signal processor, and the DSP digital signal processor is internally provided with an A/D, D/A converter and a plurality of chips for executing read-write operation and is connected with a computer display.
Compared with the prior art, the invention has the beneficial effects that:
1. The system can quickly respond to the change of the external environment under the condition of simulating shadows, and can accurately find out the real maximum power point even if a plurality of power peaks occur due to uneven illumination distribution of the photovoltaic component.
2. Compared with the traditional MPPT control algorithm which can not track the global power peak under the shading condition and can only track the global power peak under the partial shading condition by using the single sliding mode control algorithm, the composite algorithm can automatically search the global power peak every 0.5s, if the shading area is suddenly changed within 0.5s, the global comparison process can be added, so that the composite algorithm can always stabilize at the global power peak under any condition, and the problem that the index approach rate parameter can not be adaptively adjusted by using the single sliding mode control is effectively solved by utilizing the mode of comparing the power and the duty ratio at each moment, so that the composite algorithm has higher efficiency in practical use.
3. The system can effectively solve the problem of hot spots possibly occurring in a shading environment, and improves the working safety of the photovoltaic array.
Drawings
Fig. 1 is a schematic structural view of a preferred embodiment of the present invention.
Fig. 2 is a simulation model diagram of a preferred embodiment of the present invention.
Fig. 3 is a schematic diagram of the Boost circuit operation of the MOS transistor in the present invention when turned on and off.
Fig. 4 is a graph showing the comparison of the global power peak effect of the P-U curve tracked by the sliding-mode-global comparison compound algorithm and the single sliding-mode control algorithm of the photovoltaic array according to the present invention under standard illumination (shading condition a).
FIG. 5 is a graph showing the comparison of the global power peak effect of the tracking P-U curve of the sliding mode-global comparison compound algorithm and the single sliding mode control algorithm of the photovoltaic array under the shading condition B.
FIG. 6 is a graph showing the comparison of the global power peak effect of the tracking P-U curve of the composite sliding mode-global comparison algorithm and the single sliding mode control algorithm of the photovoltaic array under the shading condition C.
FIG. 7 is a graph showing the comparison of the global power peak effect of the tracking P-U curve of the sliding mode-global comparison compound algorithm and the single sliding mode control algorithm of the photovoltaic array under the shading condition D.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the invention. The drawings are schematic representations, not physical drawings, and are not to be construed as limiting the present patent, and some parts of the drawings may be omitted, enlarged or reduced in order to better explain the embodiments of the present invention, and it is understood that some well-known structures in the drawings and descriptions thereof may be omitted to those skilled in the art.
The photovoltaic MPPT control system based on the sliding mode variable structure-global comparison compound algorithm comprises a temperature illumination variable module, a photovoltaic array, a DC-DC converter, a voltage current sensor, a temperature illumination sensor, an MPPT algorithm module, a PWM module, a DSP digital signal processor, a power supply circuit, a driving circuit and a computer display, wherein the photovoltaic array comprises a photovoltaic cell unit I, a photovoltaic cell unit II and a photovoltaic cell unit III which are connected in series.
In an embodiment, since the P-U characteristic curve of the photovoltaic cell can generate a plurality of power peaks due to shielding when the photovoltaic cell is actually used, the accuracy of tracking the maximum power point by the algorithm should be paid attention to when testing the algorithm. The temperature illumination variable module is used for simulating local shielding of the photovoltaic array caused by branches and electric poles in actual use. Here, 4 simulated lighting conditions were employed, respectively:
Shading condition A (cell 1:1000W/m 2, cell 2:1000W/m 2, cell 3:1000W/m 2).
Shading condition B (cell 1:1000W/m 2, cell 2:1000W/m 2, cell 3:400W/m 2).
Shading condition C (cell 1:1000W/m 2, cell 2:200W/m 2, cell 3:200W/m 2).
Shading condition D (cell 1:1000W/m 2, cell 2:500W/m 2, cell 3:100W/m 2).
Under different degrees of illumination, each photovoltaic cell unit outputs different voltages. The 4 shade conditions A, B, C, D include single power peak, double power peak, and triple power peak conditions that may occur in an actual photovoltaic power generation system.
The bypass diode is respectively connected in parallel outside the three photovoltaic battery units connected in series in the embodiment, a part of diodes are conducted under shadow shielding, and because currents in the series loop are consistent, different short-circuit current ranges can be divided according to different illumination intensities, and the photo-generated currents of the three photovoltaic battery units are correspondingly different, the output power can be three conditions, namely, 3 photovoltaic battery units are output simultaneously, 2 photovoltaic battery units are output simultaneously, and 1 photovoltaic battery unit is output singly, so that a multi-power peak P-U curve under shadow shielding is obtained.
The DC-DC converter adopts a Boost circuit, the Boost circuit comprises a capacitor C1 and an inductor L, one ends of the capacitor C1 and the inductor L are connected with a forward port of a photovoltaic array, the other ends of the inductor L are connected with a drain electrode of a switching tube MOS and a diode anode, a diode cathode is connected with one end of a capacitor C2 and a load resistor R, the capacitor C1, the capacitor C2, a source electrode of the switching tube and the load resistor R are connected with a cathode of the photovoltaic array, a voltage current signal output by the photovoltaic array is shielded by a sampling shadow and is input into a voltage current sensor together with a temperature illumination variable and is input into a data acquisition module, an MPPT algorithm module is designed by adopting a sliding mode-global comparison compound algorithm in a code form and is connected with a PWM module, the MPPT module is used for processing an electric signal, a control signal is converted into adjustment of a duty ratio, and the PWM module outputs PWM waves to a grid electrode of the switching tube, so that stable power tracking can be realized while an accurate maximum power point is found.
In the embodiment, the hardware circuit comprises a power supply circuit, a driving circuit and a DSP digital signal processor besides a voltage and current sensor and a DC-DC converter, wherein the power supply circuit supplies power to the DSP, the driving circuit is connected with the DSP to convert the acquired electric signals into a proper interval, an A/D, D/A converter and a plurality of chips for executing read-write operation are arranged in the DSP and are connected with a computer display, and the output waveform processed by the sliding mode-global comparison compound algorithm is displayed on the computer display.
As shown in fig. 2 and 3, in order to build a simulation model diagram of a photovoltaic MPPT control system based on a sliding mode variable structure-global comparison composite algorithm under shadow shielding, the main algorithm of the invention, namely the sliding mode variable structure control algorithm, can be designed according to a mathematical expression of a photovoltaic cell and a Boost circuit working process when a MOS tube is on-off, and comprises the following steps:
And S01, setting the following parameters according to a photovoltaic cell equivalent circuit and a system main circuit, namely a Boost circuit, and establishing a photovoltaic cell mathematical model and obtaining partial derivatives of the photovoltaic cell mathematical model.
Wherein, the ratio of the photovoltaic array to the photovoltaic cell output voltage is 3:1, and the ratio of the output current is 1:1.
Mathematical model of photovoltaic cell:
And (3) calculating deviation guide:
S02, building a Boost circuit equivalent mathematical model according to two states of the MOS tube when the MOS tube is turned on and turned off.
(MOS transistor is conducted),(MOS tube off) (5)
Defining u=1, 0 to represent on and off of the MOS transistor, respectively, the following formula can be obtained:
It is rewritten as a general state space equation:
Wherein the method comprises the steps of
S03, constructing a sliding mode surface (sliding mode switching function) S and a control rate u.
Because at the point of maximum power of the photovoltaic, there is
Can obtain the slip form surface
The setting control rate u consists of two parts, namely an equivalent control u eq and a variable structure control u sw, namely:
u=ueq+usw (11)
in order to ensure that the system can reach the sliding mode surface quickly while resisting interference, u sw adopts an index approach rate, namely:
usw=-ε*sign(s)-ks(ε>0,k>0) (12)
In the present invention, epsilon=0.03 and k=0.005 are taken. The procedure for deriving u eq is as follows:
As a result of being on the face of the slide, The method can obtain:
To sum up
S04, judging the stability of the sliding mode controller by utilizing a Liapunov function. According toTo stabilize the system, i.e. proveThe stability judging process is as follows:
I PV≈IL is due to the presence of capacitor C1 in the system. And then the following formula is obtained:
from the above (3) and (4)
When S >0, since ε >0, k >0, so
ThenAt this time
When S <0, since ε >0, k >0, so
ThenAt this time
The stability of the main controller-sliding mode variable structure controller can be judged.
In the embodiment, the power tracking effect of the single sliding mode controller on the photovoltaic power generation system under 4 shading conditions is tested first, and the tracking effect is found to be capable of tracking a global power peak value only under partial shading conditions, and the tracked power fluctuation is huge or local power peak value is tracked under certain shading conditions, so that the single sliding mode controller cannot ensure the maximum stability and the maximum power generation efficiency of the power generation system. The system can be enabled to re-track the global maximum power under a certain shading condition by continuously changing the index approach rate parameter values in the sliding mode controller, namely, certain parameter values in the system need to be manually changed in real time for realizing global tracking by a single sliding mode controller, which is obviously not preferable in practical application.
Therefore, in order to enable parameters of the index approach rate in the sliding mode control algorithm to be suitable for all shadow shielding environments and enable the parameters to realize the global self-optimizing function, a global comparison algorithm is added in the operation of the sliding mode control algorithm, and actual power peaks under shadow shielding are periodically searched, and the specific design steps are as follows:
And 1, when the sliding mode variable structure control algorithm starts to operate, setting the time threshold of global comparison to be 0.5s, namely starting the global comparison algorithm every 0.5s by taking the time threshold as a period. Setting the power difference threshold to be 15W in the period searching process, and taking the power difference threshold as the basis for emergency starting of the global comparison algorithm due to instantaneous power change under the condition of suddenly changing shadow shielding at a certain moment. An initial duty cycle of 0.1 or 0.9 is defined.
And 2, discretizing voltage and current data, setting the position of power preservation to be acquired at each moment as a real-time output power array Ps= [ ], and setting the position of system duty cycle preservation to be acquired at each moment as a real-time duty cycle array Ds= [ ].
And 3, carrying out data acquisition by taking an I-V characteristic curve from an open circuit state to a short circuit state as a control process, arranging real-time power and corresponding real-time duty ratio in an array in the form of data points, and setting 5 data points as one cycle of sampling to ensure the searching efficiency of an algorithm. Setting the duty cycle step length to be 0.005, wherein if the initial duty cycle is 0.1, the duty cycle is continuously overlapped with the step length of +0.005 in the process of sampling power and the duty cycle is sampled at the same time, and if the initial duty cycle is 0.9, the duty cycle is continuously reduced with the step length of-0.005 in the process of sampling power and the duty cycle is sampled at the same time.
And 4, outputting the maximum power of the photovoltaic array I-V characteristic obtained by the algorithm in the global process from open circuit to short circuit in a code instruction form for solving the maximum value, and finding out the corresponding duty ratio.
And 5, comparing the maximum power obtained by the global comparison algorithm with the maximum power obtained by the sliding mode variable structure algorithm, if the maximum power is equal to the maximum power obtained by the sliding mode variable structure algorithm, maintaining the maximum power, if the maximum power is unequal, replacing the current power with a larger value, and then tracking the global maximum power according to the sliding mode surface and the control rate. And (5) if the period of 0.5s is up, re-entering the step (1), and circularly searching.
The above-designed composite algorithm is applied to the embodiment of the system, and the obtained results are shown in fig. 4-7.
As shown in fig. 4, the photovoltaic cell P-U curve for shading condition a has only one maximum power point, with a value of about 120W. At the moment, the global power peak can be tracked by using a sliding mode-global comparison compound algorithm and a single sliding mode control algorithm, and the tracking speed of the single sliding mode control algorithm is extremely high and is superior to that of the compound algorithm. The composite algorithm takes 0.08s because of the periodic comparison.
As shown in fig. 5, the photovoltaic cell P-U curve for shading condition B has two maximum power points, while the global power peak is about 76W. At the moment, the global power peak can be tracked by the sliding mode-global comparison compound algorithm as the single sliding mode control algorithm, the tracking speed of the single sliding mode control algorithm is still better than that of the compound algorithm, and the time of the compound algorithm is 0.07s.
As shown in fig. 6, the photovoltaic cell P-U curve for shading condition C has two maximum power points, while the global power peak is about 32W. At this time, the single sliding mode control algorithm generates severe power fluctuation during tracking, the upper and lower power limits differ by about 15W, and the stability of the output power of the power generation system cannot be maintained at all. The sliding mode-global comparison compound algorithm tracks the global power peak and stably maintains the peak, and the time is 0.06s.
As shown in fig. 7, the photovoltaic cell P-U curve for the shading condition D has three maximum power points, while the global power peak is about 44W. At this time, the single sliding mode control algorithm can only track local power peaks, and the electric energy loss is large. The sliding mode-global comparison compound algorithm basically tracks a global power peak value of about 42W, 2W of power is lost in the tracking process due to heavy shielding, but the tracking effect of a global maximum power point is still achieved and kept stable, the electric energy utilization rate is high, and the time is 0.09s.
Therefore, the sliding mode-global comparison compound algorithm has the advantages of extremely high response speed, extremely small overshoot, high output precision and efficiency, good stability, system safety and good market application space.
The invention is not limited to the above embodiments, and based on the technical solution disclosed in the invention, a person skilled in the art may make some substitutions and modifications to some technical features thereof without creative effort according to the technical content disclosed, and all the substitutions and modifications are within the protection scope of the invention.

Claims (6)

1.基于滑模变结构-全局比较复合算法的光伏MPPT控制系统，其特征在于，包括温度光照变量模块，光伏阵列，DC-DC变换器，电压电流传感器，温度光照传感器，MPPT算法模块，PWM模块，DSP数字信号处理器，电源电路，驱动电路和计算机显示器；1. A photovoltaic MPPT control system based on a sliding mode variable structure-global comparison composite algorithm, characterized by including a temperature and light variable module, a photovoltaic array, a DC-DC converter, a voltage and current sensor, a temperature and light sensor, an MPPT algorithm module, a PWM module, a DSP digital signal processor, a power supply circuit, a drive circuit, and a computer display; 所述温度光照变量模块用于模拟光伏阵列因树枝、电杆而产生的阴影遮挡；所述MPPT算法模块采用主算法——滑模变结构控制算法并辅以全局比较算法，周期性搜索阴影遮挡下光伏阵列的最大功率点；The temperature and light variable module is used to simulate the shadowing of the photovoltaic array caused by tree branches and poles; the MPPT algorithm module uses the main algorithm - sliding mode variable structure control algorithm and supplemented by a global comparison algorithm to periodically search for the maximum power point of the photovoltaic array under shadowing; 所述滑模变结构控制算法的设计方法包括以下步骤：The design method of the sliding mode variable structure control algorithm comprises the following steps: S01：根据光伏电池等效电路及系统主回路——Boost电路，建立光伏电池数学模型并求其偏导数；S01: Based on the photovoltaic cell equivalent circuit and the system main circuit - Boost circuit, establish the photovoltaic cell mathematical model and calculate its partial derivatives; 光伏电池数学模型：Mathematical model of photovoltaic cells: 求其偏导： Find its partial derivative: 式中，Ipv表示光伏电池输出电流，Vpv表示光伏电池输出电压，Iph表示光伏电池光生电流，ID0表示反向饱和电流，q表示电子电荷，A表示二极管因子，K表示玻尔兹曼常数，T表示绝对温度，IL表示电感电流，VO表示负载端输出电压，IO表示负载端输出电流；Where, Ipv represents the output current of the photovoltaic cell, Vpv represents the output voltage of the photovoltaic cell, Iph represents the photocurrent of the photovoltaic cell, Id0 represents the reverse saturation current, q represents the electron charge, A represents the diode factor, K represents the Boltzmann constant, T represents the absolute temperature, Il represents the inductor current, Vo represents the output voltage at the load end, and Io represents the output current at the load end; S02：根据MOS管导通和关断时的两种状态可建立Boost电路等效数学模型；S02: Based on the two states of the MOS tube when it is turned on and off, an equivalent mathematical model of the Boost circuit can be established; 定义u＝1,0分别表示MOS管的通、断，可以得到下式：Define u＝1, 0 to represent the on and off of the MOS tube respectively, and we can get the following formula: 将其改写为一般状态空间方程式形式：Rewriting this into the general state-space equation form: 其中 in S03：构造滑模面(滑模切换函数)S和控制率u；S03: Construct sliding surface (sliding mode switching function) S and control rate u; 因为在光伏最大功率点处时，有Because at the maximum power point of photovoltaic, there is 可得滑模面 The sliding surface can be obtained 设定控制率u由等效控制ueq和变结构控制usw两部分组成，即：The set control rate u consists of two parts: equivalent control u eq and variable structure control u sw , namely: u＝ueq+usw (11)u＝u eq +u sw (11) 为保证系统在抗干扰的同时能够快速到达滑模面，usw采用指数趋近率，即：In order to ensure that the system can quickly reach the sliding surface while resisting interference, u sw adopts an exponential approach rate, that is: usw＝-ε*sign(s)-ks(ε＞0,k＞0) (12)u sw =-ε*sign(s)-ks(ε＞0,k＞0) (12) 取ε＝0.03,k＝0.005；推导ueq的过程如下：Take ε = 0.03, k = 0.005; the process of deriving u eq is as follows: 由于在滑模面上时，可得：Since on the sliding surface, We can get: 综上 In summary S04：利用李亚普诺夫函数判定滑模控制器稳定性；根据要使系统稳定，即证明判稳过程如下：S04: Using Lyapunov function to determine the stability of sliding mode controller; To make the system stable, we need to prove The stability judgment process is as follows: 由于系统中电容C1的存在，所以IPV≈IL；进而得下式：Due to the presence of capacitor C1 in the system, I PV ≈ I L ; thus, the following equation is obtained: 由前述(3)、(4)式可得 From the above formulas (3) and (4), we can get 当S＞0时，由于ε＞0，k＞0，所以 When S＞0, since ε＞0, k＞0, so 则此时 but at this time 当S＜0时，由于ε＞0，k＞0，所以 When S＜0, since ε＞0, k＞0, so 则此时 but at this time 可判定主控制器——滑模变结构控制器稳定。It can be determined that the main controller - sliding mode variable structure controller is stable. 2.根据权利要求1所述的基于滑模变结构-全局比较复合算法的光伏MPPT控制系统，其特征在于，所述光伏阵列包括串联的光伏电池单元一、光伏电池单元二和光伏电池单元三，所述光伏电池单元一、光伏电池单元二和光伏电池单元三外分别并联一个旁路二极管。2. The photovoltaic MPPT control system based on the sliding mode variable structure-global comparison composite algorithm according to claim 1 is characterized in that the photovoltaic array includes a photovoltaic cell unit 1, a photovoltaic cell unit 2 and a photovoltaic cell unit 3 connected in series, and a bypass diode is connected in parallel to each of the photovoltaic cell unit 1, the photovoltaic cell unit 2 and the photovoltaic cell unit 3. 3.根据权利要求2所述的基于滑模变结构-全局比较复合算法的光伏MPPT控制系统，其特征在于，所述DC-DC变换器采用Boost电路，所述Boost电路包括电容C1和电感L，所述电容C1和电感L的一端连接光伏阵列的正向端口，所述电感L的另一端连接开关管MOS的漏极和二极管阳极，所述二极管阴极连接电容C2的一端和负载电阻R，所述电容C1、电容C2、开关管源极和负载电阻R接进光伏阵列负极。3. The photovoltaic MPPT control system based on the sliding mode variable structure-global comparison composite algorithm according to claim 2 is characterized in that the DC-DC converter adopts a Boost circuit, the Boost circuit includes a capacitor C1 and an inductor L, one end of the capacitor C1 and the inductor L is connected to the forward port of the photovoltaic array, the other end of the inductor L is connected to the drain of the switching tube MOS and the anode of the diode, the cathode of the diode is connected to one end of the capacitor C2 and the load resistor R, and the capacitor C1, capacitor C2, the source of the switching tube and the load resistor R are connected to the negative pole of the photovoltaic array. 4.根据权利要求1所述的基于滑模变结构-全局比较复合算法的光伏MPPT控制系统，其特征在于，所述全局比较算法的设计方法步骤如下：4. The photovoltaic MPPT control system based on the sliding mode variable structure-global comparison composite algorithm according to claim 1 is characterized in that the design method steps of the global comparison algorithm are as follows: 步骤1：在所述滑模变结构控制算法运行开始时，同时设定全局比较的时间阈值为0.5s，即以此时间阈值为一个周期，每隔0.5s启动一次全局比较算法；周期搜索过程中设定功率差阈值为15W，作为某时刻突然改变阴影遮挡情况下功率瞬时变化而紧急启动全局比较算法的依据；定义初始占空比为0.1或0.9；Step 1: When the sliding mode variable structure control algorithm starts running, the global comparison time threshold is set to 0.5s. That is, the global comparison algorithm is started every 0.5s with this time threshold as a cycle; during the cycle search process, the power difference threshold is set to 15W, as a basis for urgently starting the global comparison algorithm when the power suddenly changes due to shadow occlusion; the initial duty cycle is defined as 0.1 or 0.9; 步骤2：离散化电压电流数据，设定每一时刻要采集的功率保存的位置为实时输出功率数组Ps＝[]，设定每一时刻要采集的系统占空比保存的位置为实时占空比数组Ds＝[]；Step 2: Discretize the voltage and current data, set the location where the power to be collected at each moment is stored as the real-time output power array Ps = [], and set the location where the system duty cycle to be collected at each moment is stored as the real-time duty cycle array Ds = []; 步骤3：以I-V特性曲线从开路状态到短路状态为一个控制过程进行数据采集，并将实时功率与对应的实时占空比以数据点的形式在数组中罗列，设定以5个数据点为一个循环采样一次，以保证算法搜索的效率；设定占空比步长为0.005，此时若初始占空比为0.1，则在采样功率的过程中，占空比以+0.005的步长持续叠加，同时采样占空比；若初始占空比为0.9，则在采样功率的过程中，占空比以-0.005的步长持续削减，同时采样占空比；Step 3: Data is collected using the I-V characteristic curve from the open-circuit state to the short-circuit state as a control process, and the real-time power and the corresponding real-time duty cycle are listed in an array in the form of data points. The sampling cycle is set to 5 data points as a cycle to ensure the efficiency of the algorithm search; the duty cycle step is set to 0.005. At this time, if the initial duty cycle is 0.1, the duty cycle is continuously added in steps of +0.005 during the power sampling process, and the duty cycle is sampled at the same time; if the initial duty cycle is 0.9, the duty cycle is continuously reduced in steps of -0.005 during the power sampling process, and the duty cycle is sampled at the same time; 步骤4：以求最大值的代码指令形式输出该算法得到的光伏阵列I-V特性从开路到短路这一全局过程中的最大功率，并找到对应的占空比；Step 4: Output the maximum power of the PV array I-V characteristic from open circuit to short circuit obtained by the algorithm in the form of a maximum value code instruction, and find the corresponding duty cycle; 步骤5：将全局比较算法得到的最大功率与滑模变结构算法得到的最大功率进行比较，若相等则维持，若不等则将其中较大值取代当前功率，再依据滑模面和控制率进行全局最大功率跟踪；0.5s周期到，则重新进入步骤1，循环搜索。Step 5: Compare the maximum power obtained by the global comparison algorithm with the maximum power obtained by the sliding mode variable structure algorithm. If they are equal, maintain them. If they are not equal, replace the current power with the larger value. Then, perform global maximum power tracking based on the sliding mode surface and control rate. When the 0.5s period expires, re-enter step 1 and cyclically search. 5.根据权利要求3或4所述的基于滑模变结构-全局比较复合算法的光伏MPPT控制系统，其特征在于，所述电压电流传感器采样阴影遮挡下光伏阵列输出的电压电流信号后送至MPPT算法模块，所述MPPT算法模块与PWM模块连接，PWM模块输出PWM波至Boost电路中的MOSFET。5. The photovoltaic MPPT control system based on the sliding mode variable structure-global comparison composite algorithm according to claim 3 or 4 is characterized in that the voltage and current sensors sample the voltage and current signals output by the photovoltaic array under shadow and send them to the MPPT algorithm module, the MPPT algorithm module is connected to the PWM module, and the PWM module outputs PWM waves to the MOSFET in the Boost circuit. 6.根据权利要求1-4任一项所述的基于滑模变结构-全局比较复合算法的光伏MPPT控制系统，其特征在于，所述电源电路和驱动电路均与DSP数字信号处理器相连，所述DSP数字信号处理器内置A/D、D/A转换器和若干执行读写操作的芯片并与计算机显示器连接。6. The photovoltaic MPPT control system based on the sliding mode variable structure-global comparison composite algorithm according to any one of claims 1 to 4, characterized in that the power supply circuit and the drive circuit are both connected to a DSP digital signal processor, and the DSP digital signal processor has built-in A/D, D/A converters and several chips that perform read and write operations and is connected to a computer display.
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