CN106647921A - Improved MPPT algorithm with reduced influence of partial shading on photovoltaic system - Google Patents
Improved MPPT algorithm with reduced influence of partial shading on photovoltaic system Download PDFInfo
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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
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- 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 present invention discloses an improved MPPT algorithm with reduced influence of partial shading on a photovoltaic system. First step: a true maximum power point domain is determined, and the operating voltage of the system is shifted thereto with guaranteed celerity of tracking; given that the intersection point of the equivalent resistance line Rpm = Vpm/Ipm and the V-I characteristic curve for photovoltaic arrays under uniform light is the maximum power point, and the operating voltage at the end of the first step is determined by using the intersection point of this line and the V-I characteristic curve for photovoltaic arrays under partial shading; to prevent false tracking caused by the local minimum point and the pseudo maximum power point to the algorithm, the extreme points tracked during scanning are required to be recorded in the first step; and second step: maximum power point tracking is carried out from the operating voltage determined in the first step by using the incremental conductance algorithm. The improved MPPT algorithm with reduced influence of partial shading on a photovoltaic system may be less affected by the environment with high accuracy, less false tracking and good operating effect.
Description
Technical field
The present invention relates to a kind of mitigate the improvement MPPT algorithm that local shades affect on photovoltaic system.
Background technology
As energy crisis and environmental pollution increase increasingly, photovoltaic generation is used as the important way using emerging green energy resource
Footpath, is just increasingly subject to people's attention.However, photovoltaic cell is affected by the external environment larger and photoelectric transformation efficiency is relatively low,
In modern photovoltaic generating system, the power output for usually requiring that photovoltaic array keeps maximum.Therefore, the maximum work of photovoltaic system
Rate point tracking (MPPT) becomes requisite important step during photovoltaic generation.
At present conventional MPPT algorithm mainly has：Constant voltage process, perturbation observation method, conductance increment method, open circuit voltage method,
Short circuit current method and their innovatory algorithm etc., these algorithms respectively have advantage under uniform illumination, are applied to different occasions.So
And when photovoltaic array is subject to partial occlusion and receives uneven illumination, P-U characteristic curves can change, and produce multiple peaks
It is worth, now conventional MPPT algorithm may be absorbed in local peaking and fail, and make photovoltaic system to be operated in real maximum
On power points.Chinese scholars propose photovoltaic system multi-peak MPPT algorithm under various local shades for this problem, than
Such as：Current scanning method, short current pulses method, particle swarm optimization algorithm, Fibonacci search methods, compound MPPT algorithm etc..This
A little algorithms all have global peak decision-making function in principle, but certain defect is there is also in practical application, such as：Current scanning
The scanning step of method is difficult to control to, and easily by itself electric parameter change affected, algorithm is excessively depended on, so as to reduce
The versatility and transplantability of algorithm；Short current pulses method needs to be periodically introducing current impulse, can be to rear class current transformer
Control produce disturbance；Particle swarm optimization algorithm needs the state variable for introducing more, control method complexity；Fibonacci is searched
Rope method is seldom applied because algorithm is complicated with high costs.Although compound MPPT algorithm also compares dependence array parameter, its
With tracking thinking is simple, algorithm is write and easily, to environmental catastrophe respond very fast, less to rear class control disturbance etc. many excellent
Point, therefore application is wider.
The content of the invention
It is an object of the invention to provide the improvement MPPT that a kind of good mitigation local shades of effect affect on photovoltaic system
Algorithm.
The present invention technical solution be：
It is a kind of to mitigate the improvement MPPT algorithm that local shades affect on photovoltaic system, it is characterized in that：
The first step：Determine the field of a real maximum power point, system operating voltage is moved on to herein, it is ensured that tracking
Rapidity；Equivalent resistive conductor R under known uniform illuminationpm=Vpm/IpmMaximum is with the intersection point of photovoltaic array VA characteristic curve
Power points, using the intersection point of this line and photovoltaic array under local shadow VA characteristic curve to determine the first step at the end of work
Voltage；In order to prevent local minimum point and pseudo- maximum power point from causing tracking error to algorithm, in the first step writing scan is needed
During the extreme point that traces into and be compared；
Second step is to proceed by MPPT maximum power point tracking from the operating voltage that the first step determines using conductance increment method.
Described mitigates the improvement MPPT algorithm that local shades affect on photovoltaic system, concrete steps：
The first step：Initialize the electric parameter of photovoltaic array cell panel and block pattern；
Second step：Calculate photovoltaic array resistance：Rpv=V/I；Wherein V is photovoltaic array voltage, and I is photovoltaic array electric current；
3rd step：Calculate the equivalent resistance of photovoltaic cell under uniform illumination：Rpm=Vpm/Ipm；VpmFor equivalent voltage；IpmFor
Equivalent current；
4th step：Relatively equivalent resistance RpmWith photovoltaic array resistance RpvSize, if Rpm<Rpv, then local is preserved maximum
Value, and second step is returned, otherwise, perform the 5th step；
5th step：MPPT maximum power point tracking is carried out using conductance increment method；
6th step：Judge whether photovoltaic array power output changes, if changing, obtain opening for photovoltaic array
Road voltage VocWith short circuit current Isc, and the 7th step is performed, otherwise, perform the 8th step；
7th step：Judge photovoltaic array short circuit current IscWhether change, if changing, return the 5th step, it is no
Then, second step is returned；
8th step：Judge whether tracked power points is maximum power point, if so, then perform the 9th step, otherwise, return
Maximum power point, and return the 5th step；
9th step：Locking maximum power point.
The present invention is affected by environment little, and high precision, tracking error is little, good working effect.
Description of the drawings
With reference to the accompanying drawings and examples the invention will be further described.
Fig. 1, Fig. 2, Fig. 3, Fig. 4 are singly to go here and there the output characteristics schematic diagram of array shown in table 1.
Fig. 5 is that the present invention improves compound MPPT algorithm flow chart.
Fig. 6 is artificial circuit master-plan block diagram.
Fig. 7 is the Simulink emulation module schematic diagrames of single string array.
Fig. 8 is the Simulink emulation module schematic diagrames of MPPT.
Fig. 9 is the Simulink emulation module schematic diagrames of Boost circuit.
Figure 10 is that maximum power point tends to oscillograph aircraft pursuit course (power output) schematic diagram during voltage source region.
Figure 11 is that maximum power point tends to oscillograph aircraft pursuit course (operating voltage) schematic diagram during voltage source region.
Figure 12 is that maximum power point tends to oscillograph aircraft pursuit course (operating current) schematic diagram during voltage source region.
Figure 13 is that maximum power point tends to output-power fluctuation schematic diagram when voltage source district system is stablized.
Figure 14 is that maximum power point tends to voltage pulsation schematic diagram when voltage source district system is stablized.
Figure 15 is that maximum power point tends to current fluctuation schematic diagram when voltage source district system is stablized.
Figure 16 is that maximum power point tends to oscillograph power output aircraft pursuit course schematic diagram during current source region.
Figure 17 is that maximum power point tends to oscillograph operating voltage aircraft pursuit course schematic diagram during current source region.
Figure 18 is that maximum power point tends to oscillograph operating current aircraft pursuit course schematic diagram during current source region.
Figure 19 is that maximum power point tends to output-power fluctuation schematic diagram during current source region system stability.
Figure 20 is that maximum power point tends to voltage pulsation schematic diagram during current source region system stability.
Figure 21 is that maximum power point tends to current fluctuation schematic diagram during current source region system stability.
Specific embodiment
1 local shades place an order string array output characteristics
1.1 local shades place an order string array Mathematical Modeling
In order to analyze the output characteristics of single string array, it is necessary first to set up the Mathematical Modeling of single string array exactly.In reality
In the application of border, photovoltaic cell manufacturer can provide the user open-circuit voltage V of the product under standard test conditionoc, short circuit electricity
Stream Isc, maximum power point voltage VmWith maximum power point electric current Im.In view of analysis and the convenience for calculating, standard ginseng can be set up
Contacting between number and output characteristics, so selecting solar cell engineering Mathematical Modeling herein：
I=Isc-C1Isc[exp(V/C2Voc)-1] (1)
I：Photovoltaic cell output current；
Isc：Photovoltaic cell short circuit current；
C1：Parametric equation, is shown in formula (2)；
V：Photovoltaic cell output voltage；
C2：Parametric equation, is shown in formula (3)；
Voc：Photovoltaic cell open-circuit voltage.
Wherein,
C1=(1-Im/Isc)exp(-Vm/C2Voc) (2)
C1：In parametric equation, generation, returns formula (1)；
Im：Maximum power of photovoltaic cell point electric current；
Isc：Photovoltaic cell short circuit current；
Vm：Maximum power of photovoltaic cell point voltage；
C2：Parametric equation, is shown in formula (3)；
Voc：Photovoltaic cell open-circuit voltage.
C2=(Vm/Voc-1)[ln(1-Im/Isc)]-1 (3)
C2：In parametric equation, generation, returns formula (1)；
Vm：Maximum power of photovoltaic cell point voltage；
Voc：Photovoltaic cell open-circuit voltage；
Im：Maximum power of photovoltaic cell point electric current；
Isc：Photovoltaic cell short circuit current.
When battery temperature and intensity of illumination change, the formula that may be referred to document offer recalculates Isc、Voc、
Im、VmEtc. parameter, it is possible to obtain the output characteristics under New Terms.
In order to obtain sufficiently large output voltage, generally by monomer photovoltaic cell by series-parallel mode in practical application
It is combined into large-sized photovoltaic array.Assume that photovoltaic array battery strings quantity in parallel is Np, the electricity connected in each battery strings
Pond plate quantity is Ns, then according to formula (1), the Mathematical Modeling of the photovoltaic array can be described with equation below under uniform illumination：
Ia=IscNp{1-C1[exp(Va/C2NsVoc)-1]} (4)
Ia：Photovoltaic array output current；
Isc：Photovoltaic cell short circuit current；
Np：Photovoltaic array battery strings quantity in parallel；
C1：Parametric equation, is shown in formula (2)；
Va：Photovoltaic array output voltage；
C2：Parametric equation, is shown in formula (3)；
Ns：The photovoltaic cell quantity connected in battery strings；
Voc：Photovoltaic cell open-circuit voltage.
By the N in equation (4)pTake 1, that is, obtain uniform illumination place an order string array Mathematical Modeling.But when array because
Blocking for a variety of causes and when forming local shades, the illumination of array received is no longer uniform, and now the Mathematical Modeling of equation (4) is just
It is no longer applicable.
From simplest circumstance of occlusion analysis set up local shades place an order string array Mathematical Modeling.Assume a single string battle array
Row are by Ns1Individual unblanketed photovoltaic cell and Ns2Individual hypographous photovoltaic cell two parts are composed in series, Isc1And Isc2It is right respectively
Answer the short circuit current of two parts battery strings.In order to prevent hot spot effect, each photovoltaic cell will bypass diode in parallel.When
Array output current I>Isc2When, more than Isc2Electric current flow through from hypographous photovoltaic cell bypass diode in parallel, now
The external power output of only unblanketed photovoltaic cell, hypographous photovoltaic cell and its bypass diode all become power consumption
Load, now C-V characteristic for shadow-free battery C-V characteristic；As array output current I≤Isc2When, corresponding bypass two
Pole pipe forms reverse biased, and now C-V characteristic is the C-V characteristic for having shade battery.Analyze based on more than, the list string array
Mathematical Modeling can be represented [12] by following piecewise function：
I：Single string array output current；
Isc1：Shadow-free blocks the short circuit current of substring in single string array；
C1：Parametric equation, is shown in formula (2)；
V：Single string array output voltage；
C2：Parametric equation, is shown in formula (3)；
Ns1The photovoltaic cell quantity that shadow-free is blocked in individual single string array；
Voc1：Shadow-free blocks the open-circuit voltage of substring in single string array；
Isc2：There is the short circuit current of shadow occlusion substring in single string array；
Ns2There is the photovoltaic cell quantity of shadow occlusion in individual single string array；
Voc2：There is the open-circuit voltage of shadow occlusion substring in single string array.
When there are various different local shades on singly string array and blocking, the short circuit of the battery strings under different illumination intensity
Electric current is also differed.Now the Mathematical Modeling of single string array is similar to the piecewise function of formula (5), and segmentation limit still depends on battle array
Row output current I and each short circuit current IscnThe magnitude relationship of (n is the quantity of the different illumination intensity received on single string array).
So, formula (5) is local shades and places an order the string most basic Mathematical Modeling of array.For the accuracy of formula (5) model, there is document
Prove that the model can accurately emulate local shades and place an order the output characteristics of string array by measured data of experiment, this section point
Analysis local shades place an order the output characteristics of string array, mainly improve compound MPPT algorithm and provide theoretical foundation to draw, therefore
The experimental verification process to the model is not discussed herein.
Impact of 1.2 local shades to single string array output characteristics
According to the segmentation thought of formula (5) model, simulated program is write using MATLAB language, arbitrarily local can be emulated cloudy
Shadow blocks the output characteristics of the string array that places an order.For the ease of analysis, the concept of the shading factor is firstly introduced into[12-13]：
E：The shading factor；
Esh：Intensity of illumination under shadowed condition；
Eref：With reference to intensity of illumination (1000W/m2)。
In formula, EshFor the intensity of illumination under shadowed condition, ErefIt is to refer to intensity of illumination, generally takes 1000W/m2.Therefore,
The span of the shading factor is between 0～1.
Choose a series of different single string arrays of pattern that block to be emulated, per strip array series-connected cell plate number Ns=10,
Batteries in parallel connection string number Np=1, Ns1～Ns3Partial intensity of illumination is respectively 1000W/m2、500W/m2、200W/m2, specifically block
Pattern is as shown in table 1：
Singly string array blocks pattern to the emulation of table 1
P1～P5：The label of the single string array of 5 of emulation；
Ns1～Ns3：The photovoltaic cell quantity that single string array is connected respectively under 3 kinds of intensities of illumination；
E：The shading factor.
From the canonical parameter of the STP150S-24/Ac type solar panels of STP company：Voc=43.3V, Isc
=4.72A, Vm=34.5V, Im=4.35A, temperature is set to 25 DEG C.
The I-U characteristics of P1 under uniform illumination are can be seen that in single knee shape, P-U characteristics exist single with reference to table 1 and Fig. 1, Fig. 2
Peak value；
There are 2 kinds of different intensities of illumination in P2, its I-U characteristic is in 2 stairsteppings, and P-U characteristics have 2 peak values；P3
Similarly meet such rule.When single string array or wherein one section have more a kind of intensity of illumination because of shadow occlusion, the moon
The output characteristics of shadow part has the process of one section of decline, i.e. power output and reduces, so as to cause I-U characteristics to have more a ladder
Shape, P-U characteristics have more a local peaking.Therefore, several intensities of illumination are received on single string array, its I-U characteristic is just in several
Individual stairstepping, P-U characteristics there is several peak values.
Fig. 3, P2, P4, P5 in 4 are irradiated by two kinds of intensities of illumination, shading factor E=0.5, carefully contrast P2,
Two peak values of P4, P5, position and size are affected by the cell panel quantity that is blocked.When blocking cell panel number Ns2>E×NsWhen,
Maximum power point is located at right side, that is, tend to voltage source region, now has the cell panel of shield portions in maximum power point, such as schemes
Shown in P4 in 4；When blocking cell panel number Ns2<E×NsWhen, maximum power point is located at left side, that is, tend to current source region, now
The cell panel of unobstructed part is in maximum power point, as shown in the P5 in Fig. 4；If Ns2=E × Ns, then two-part maximum work
Rate is almost equal, and as shown in P2 in Fig. 4, the now selection of maximum power point depends on external loading size.
Emulate by more than and analyze, the presence of local shades can produce very big shadow to the output characteristics of single string array really
Ring, more complicated especially as shadow condition, the local peaking of generation is also more, and this easily causes conventional MPPT algorithm to photovoltaic
The tracking error of system maximum power point, affects the delivery efficiency of photovoltaic generating system, it is therefore desirable to adopt for local shades problem
Appropriate solution is taken, to mitigate impact of the local shades to photovoltaic system.
The improvement of 2 compound MPPT algorithms
Mitigate local shades mainly has two kinds to the method that photovoltaic system affects：The first is the structure of change system, will
Centralized structure is changed to the structure of string data or many string datas, or even directly adopts DC Module structure, so can be simultaneously
Solve the problems, such as that global peak declines and local peak interference.But, transform controller in system can be caused using such method
Quantity rolls up, and increases system complexity, system Construction cost is improved, so should not adopt, the light of current practice
Volt system is still substantially using the structure of photovoltaic cell connection in series-parallel；Second is reservation system centralized configuration, and research possesses the overall situation
The MPPT algorithm of peak value decision-making function, Research Challenges essentially consist in the interference problem for overcoming local peaking, rapidly and accurately track
To real maximum power point.Photovoltaic system multi-peak MPPT algorithm common at present is slightly introduced in preface part, according to it
Pluses and minuses, select compound MPPT algorithm to do photovoltaic system multi-peak MPPT maximum power point tracking research herein, and for wherein
Some problems are slightly improved.
The principle of conventional composite MPPT algorithm is divided into two steps：The first step is it needs to be determined that the neck of a real maximum power point
Domain, system operating voltage is moved on to herein, it is ensured that the rapidity of tracking.Equivalent resistive conductor R under known uniform illuminationpm=Vpm/Ipm
Maximum power point is with the intersection point of photovoltaic array VA characteristic curve, it is possible to using photovoltaic battle array under this line and local shades
The intersection point of row VA characteristic curve to determine the first step at the end of operating voltage；Second step is using traditional perturbation observation method
The operating voltage determined from the first step proceeds by MPPT maximum power point tracking.Conventional composite MPPT algorithm is designed and program in algorithm
In compiling procedure, easily there is following Railway Project：
1) when the operating voltage that the first step determines falls local minimum point, now dP/dI=0 also sets up, algorithm meeting
Therefore it is real maximum power point to be mistakenly considered current local minimum point, causes tracking error；
2) when the operating voltage that the first step determines falls pseudo- maximum power point, may be by pseudo- maximum power point as true
Positive maximum power point, causes tracking error；
Although 3) second step adopts perturbation observation method tracking efficiency higher and easy realization, near maximum power point
Fluctuation it is larger, it is impossible to meet certain required precision, and be mutated because of external environment and cause algorithm to fail.
For problem above, need slightly modified to conventional composite MPPT algorithm：
1) in order to prevent local minimum point and pseudo- maximum power point from causing tracking error to algorithm, in the first step record is needed
The extreme point that traces in scanning process is simultaneously compared；
2) second step avoids using perturbation observation method, selects tracking accuracy of a relatively high and less conductance affected by environment
Method of addition.
Thought is improved based on more than, the compound MPPT algorithm flow chart after improvement is as shown in figure 8, concrete steps：
The first step：Initialize the electric parameter of photovoltaic array cell panel and block pattern；
Second step：Calculate photovoltaic array resistance：Rpv=V/I；Wherein V is photovoltaic array voltage, and I is photovoltaic array electric current；
3rd step：Calculate the equivalent resistance of photovoltaic cell under uniform illumination：Rpm=Vpm/Ipm；VpmFor equivalent voltage；IpmFor
Equivalent current；
4th step：Relatively equivalent resistance RpmWith photovoltaic array resistance RpvSize, if Rpm<Rpv, then local is preserved maximum
Value, and second step is returned, otherwise, perform the 5th step；
5th step：MPPT maximum power point tracking is carried out using conductance increment method；
6th step：Judge whether photovoltaic array power output changes, if changing, obtain opening for photovoltaic array
Road voltage VocWith short circuit current Isc, and the 7th step is performed, otherwise, perform the 8th step；
7th step：Judge photovoltaic array short circuit current IscWhether change, if changing, return the 5th step, it is no
Then, second step is returned；
8th step：Judge whether tracked power points is maximum power point, if so, then perform the 9th step, otherwise, return
Maximum power point, and return the 5th step；
9th step：Locking maximum power point.
3 artificial circuits are designed and calculated with component parameters
Fig. 9 is artificial circuit master-plan block diagram, mainly includes PV modules, DC-DC conversion circuit and pwm control circuit three
It is most of.The effect of DC-DC conversion circuit is the output voltage for adjusting photovoltaic system to be preferably tracked.Herein with PV
Used as the input voltage of DC-DC conversion circuit, because the output voltage of PV modules is less than normal, needs are risen the output voltage of module
Pressure, so the DC-DC conversion circuit of this paper selects Boost circuit；The effect of pwm control circuit is then to produce to have different duties
The square wave of ratio, controls the break-make of FET in translation circuit, makes output voltage values size adjustable.
The Simulink emulation modules of 3.1 single string arrays
The Simulink emulation modules of single string array are as shown in Figure 7.Wherein, V is an externally input voltage, it is possible thereby to calculate
Go out the output current of single string array, then foreign current is converted into by controllable current source, be output to from output interface 2
External circuit.S-Function in figure is the S function write using MATLAB language, be local shades place an order string array mathematics
The Simulink package module that the m file non-patterned modes of model are represented.Because photovoltaic cell is typical non-thread
Property element, its output characteristic curve be nonlinear curve, so in artificial circuit, using S function m files and Simulink are made
Module relation gets up.4 output valves Isc_new、Voc_new、Im_newIt is the new ginseng that obtains with external environment change calculations with Vm_new
Number, the tracking for participating in MPPT modules is calculated.
The Simulink emulation modules of 3.2MPPT
The Simulink emulation modules of MPPT are as shown in Figure 8.Here according to the compound MPPT algorithm stream of improvement shown in Fig. 5
Journey, the S function equally write using MATLAB language will improve the m Document encapsulations of compound MPPT algorithm into Simulink modules,
M files are made to be associated with Simulink.Because the carrier of this paper algorithms is generally PC or single-chip microcomputer, if using sinusoidal pulsewidth
Modulation system then also needs to build sine-wave generator in addition controlling inverter, makes algorithm become complicated.Therefore directly make herein
The control signal exported with MPPT modules is compared with the triangular wave of certain frequency, so as to construct the side of suitable duty ratio
Ripple.
The Simulink emulation modules of 3.3 Boost circuits are calculated with parameter
The Simulink emulation modules of Boost circuit are as shown in figure 9, for adjusting the output voltage of single string array to meet
The demand of MPPT maximum power point tracking, wherein there is three main component parameters to need calculating, i.e. switching tube frequency f, energy storage inductor
Value L and filtering capacitance C.
3.3.1 the calculating of switching tube frequency f
Switching tube frequency is less, and the time that system reaches stable state is longer, needs the inductance chosen also bigger, big inductance increasing
The volume and weight of system is added, has made system become heavy, but at the same time had the advantage that the loss of switching tube diminishes, made
Increased with the life-span；Switching tube frequency is bigger, and the operating efficiency of system can be obviously improved, and the inductance value of selection is also less, and system is little
Skilful light and flexible, but the at the same time loss of switching tube is also clearly, caloric value aggravation.So, consider system effectiveness,
The factor of each side such as volume, weight, cost, loss, switching tube frequency f of this paper selects 50kHZ.
3.3.2 the selection of energy storage inductor L
When gate-controlled switch is in on-state, energy storage inductor obtains energy and puts aside from power end；At gate-controlled switch
When off-state, energy storage inductor charges to electric capacity and provides energy to load simultaneously with power supply.By theory analysis, Boost
The step-up formula of circuit is：
Wherein UoAnd UiRespectively output voltage and input voltage, D is dutycycle.Ignore the loss of circuit, input power with
Power output is equal, i.e. Pi=Po, UiIi=UoIo, so having
Wherein IiAnd IoRespectively input current and output current.The standard that energy storage inductor is chosen is to ensure that circuit work
Make electric current continuous, now the ripple component of inductive current should meet relational expression：
ΔiL：Inductive current ripple component；
ton：Switching tube service time；
Ui：Input voltage；
L：Energy storage inductor value；
D：Dutycycle；
T：Work period；
Ii：Input current.
Wherein tonIt is switching tube service time, T is the work period, so, inductance value should meet：
L：Energy storage inductor value；
Ui：Input voltage；
Ii：Input current；
D：Dutycycle；
T：Work period；
Uo：Output voltage；
f：Switching tube frequency；
Io：Output current.
Herein select 10 pieces of characteristic Simulations when STP company STP150S-24/Ac type solar panel strings
Into single string array as research object, maximum open circuit voltage is 433V to joint group, and output voltage is 500V, and generally array reaches most
Voltage when high-power is about the 78% of open-circuit voltage, so can calculate dutycycle D by formula (7) is about 30%, switch
Pipe frequency selects 50kHZ, brings in formula (10) and consider above numerical value into certain allowance, and the selection of this paper energy storage inductors value is
800μH。
3.3.3 the selection of filter capacitor C
When gate-controlled switch is in on-state, the voltage on electric capacity powers to the load；When gate-controlled switch is in off-state, energy storage
Inductance charges to electric capacity simultaneously with power supply[20].The quantity of electric charge for assuming electric capacity is Q, then only when switching tube is turned off in a cycle
(toff) when just have Q>0, the output ripple voltage formed by Q is：
ΔUo：The output ripple voltage formed by the quantity of electric charge；
Q：The quantity of electric charge；
C：Filtering capacitance；
Io：Output current；
toff：The switching tube turn-off time；
D：Dutycycle；
T：Work period.
C：Filtering capacitance；
Io：Output current；
D：Dutycycle；
T：Work period；
ΔUo：The output ripple voltage formed by the quantity of electric charge.
Each variable value is all constant, and output ripple voltage takes the 0.2% of output voltage, brings in formula (12) and considers and be certain
Allowance, this paper filtering capacitances select be 10 μ F.
4 simulation results
With reference to Section 1 local shades place an order the string analysis of array output characteristics, the improved compound MPPT algorithm of Section 2 and
The photovoltaic system multi-peak MPPT artificial circuits of Section 3 design, to two kinds of different offices of single string array P-U characteristic curves bimodal
Portion's shadow occlusion situation carries out MPPT emulation, the compound MPPT algorithm after checking improvement.
4.1 maximum power points tend to voltage source region
The STP150S-24/Ac type solar panels of 10 pieces of STP companies of selection are together in series and constitute single string battle array
Row, the canonical parameter of cell panel is Voc=43.3V, Isc=4.72A, Vm=34.5V, Im=4.35A, temperature is set to 25 DEG C, its
In 2 pieces of cell panels be in 1000W/m2Uniform illumination under, 8 pieces of cell panels are affected by shadow occlusion, and intensity of illumination is 500W/m2,
Draw its theoretical output characteristic curve as shown in the P4 in Fig. 3,4 by model emulation.Using the photovoltaic system designed in Section 3
Multi-peak MPPT artificial circuits are improved the maximal power tracing emulation of compound MPPT algorithm, and the tracking obtained from oscillograph is bent
Line is as shown in figs. 10-12：
When system working stability, the fluctuation of power output, operating voltage and operating current is as illustrated in figs. 13-15：
Knowable to Fig. 3,4 simulation curve P4, the pattern of blocking place an order string array theoretical power output be about
720.68W, quiescent potential is 328V, and operating point electric current is 2.197A.Improvement is can be seen that from the aircraft pursuit course of Figure 10-15
Compound MPPT algorithm analogue system can lock maximum power point in 0.52s or so, and the maximum power point for tracing into is about 719.9W,
Power swing amplitude is about 1.9W, and quiescent potential is stable in 328V or so, and voltage pulsation amplitude is about 12V, operating point electric current
Stablize in 2.195A or so, current fluctuation amplitude is about 0.080A.
4.2 maximum power points tend to current source region
Single string array of selection is identical with 4.1 sections, and cell panel canonical parameter is constant, temperature-resistant, and the pattern of blocking is changed to it
In 8 pieces of cell panels be in 1000W/m2Uniform illumination under, 2 pieces of cell panels are affected by shadow occlusion, and intensity of illumination is 500W/m2,
Draw its theoretical output characteristic curve as shown in the P5 in Fig. 3,4 by model emulation.Obtain from the oscillograph of MPPT analogue systems
The aircraft pursuit course for arriving is as shown in figs. 16-18；
When system working stability, the fluctuation of power output, operating voltage and operating current is as shown in figs. 19-21；
Knowable to Fig. 3,4 simulation curve P5, the pattern of blocking place an order string array theoretical power output be about
1201.88W, quiescent potential is 279V, and operating point electric current is 4.295A.From aircraft pursuit course as can be seen that improving compound MPPT
Algorithm simulating system can lock maximum power point in 0.5s or so, and the maximum power point for tracing into is about 1197W, power swing width
Degree is about 13W, and quiescent potential is stable in 280V or so, and voltage pulsation amplitude is about 22V, and operating point current stabilization is in 4.275A
Left and right, current fluctuation amplitude is about 0.350A.
Contrast improves peak power of the compound MPPT algorithm to single string array under two kinds of different local shades circumstance of occlusion
Point tracking emulation, no matter maximum power point tends to voltage source region or tends to current source region, the algorithm have it is good with
Track performance, can rapidly and accurately trace into actual maximum power point and lock maximum power point, not by local minimum
The interference of point and pseudo- maximum power point, tracking error is in the range of 6% that engineering is allowed.
MPPT：MPPT maximum power point tracking (Maximum Power Point Tracking)；
Voc：Photovoltaic cell open-circuit voltage；
Isc：Photovoltaic cell short circuit current；
Vm：Maximum power of photovoltaic cell point voltage；
Im：Maximum power of photovoltaic cell point electric current；
I-U characteristics：I-E characteristic (C-V characteristic)；
P-U characteristics：Power-voltage characteristic；
Rpv：Photovoltaic cell resistance；
Rpm：Equivalent resistance.
Vpm：Equivalent voltage；
Ipm：Equivalent current；
PV：Photovoltaic (battery)；
DC-DC：DC-to-dc；
PWM：Pulse width modulation ((Pulse Width Modulation)；
Boost circuit：Booster circuit.
5 summarize
Herein for asking that conventional composite MPPT algorithm is likely to occur in tracking photovoltaic system multi-peak maximum power point
Topic, it is proposed that follow-on compound MPPT algorithm, i.e., increased preservation local most during scanning maximum power point field
The link for being worth greatly and comparing, it is of a relatively high using precision and affected less by environmental change during locking maximum power point
Conductance increment method substituting traditional perturbation observation method.By building artificial circuit in MATLAB/Simulink, using changing
Compound MPPT algorithm after entering, the string maximum power point of photovoltaic array that places an order to local shades respectively tends to voltage source region and electric current
Two kinds of different situations of source region are tracked emulation.Simulation results show, no matter actual maximum power point falls within where, changes
Compound MPPT algorithm after entering can rapidly and accurately be tracked and locked, and local minimum point and puppet will not be subject to maximum
The interference of power points.
Claims (2)
1. it is a kind of to mitigate the improvement MPPT algorithm that local shades affect on photovoltaic system, it is characterized in that：
The first step：Determine the field of a real maximum power point, system operating voltage moved on to herein, it is ensured that tracking it is quick
Property；Equivalent resistive conductor under known uniform illuminationR pm =V pm /I pm Peak power is with the intersection point of photovoltaic array VA characteristic curve
Point, using the intersection point of this line and photovoltaic array under local shadow VA characteristic curve to determine the first step at the end of work electricity
Pressure；In order to prevent local minimum point and pseudo- maximum power point from causing tracking error to algorithm, in the first step writing scan is needed
The extreme point that traces in journey is simultaneously compared；
Second step is to proceed by MPPT maximum power point tracking from the operating voltage that the first step determines using conductance increment method.
2. it is according to claim 1 to mitigate the improvement MPPT algorithm that local shades affect on photovoltaic system, it is characterized in that：Tool
Body step：
The first step：Initialize the electric parameter of photovoltaic array cell panel and block pattern；
Second step：Calculate photovoltaic array resistance：R pv =V/I；Wherein V is photovoltaic array voltage, and I is photovoltaic array electric current；
3rd step：Calculate the equivalent resistance of photovoltaic cell under uniform illumination：R pm =V pm /I pm ；V pm For equivalent voltage；I pm For equivalent electric
Stream；
4th step：Compare equivalent resistanceR pm With photovoltaic array resistanceR pv Size, ifR pm <R pv , then local maximum is preserved, and
Second step is returned, otherwise, the 5th step is performed；
5th step：MPPT maximum power point tracking is carried out using conductance increment method；
6th step：Judge whether photovoltaic array power output changes, if changing, obtain the open circuit electricity of photovoltaic array
PressureV oc And short circuit currentI sc , and the 7th step is performed, otherwise, perform the 8th step；
7th step：Judge photovoltaic array short circuit currentI sc Whether change, if changing, return the 5th step, otherwise, return
Return second step；
8th step：Judge whether tracked power points is maximum power point, if so, then perform the 9th step, otherwise, return maximum
Power points, and return the 5th step；
9th step：Locking maximum power point.
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