Photovoltaic array multi-peak maximum power point tracing method based on the scanning of power closed loop
Technical field
The invention belongs to the photovoltaic power generation technology in electrical engineering field, be specifically related to the MPPT maximum power point tracking of photovoltaic array under uneven illumination condition in a kind of photovoltaic generating system and control (MPPT-Maximum Power Point Tracking) method.
Background technology
Sun power, as a kind of regenerative resource, has widely distributed, sustainable, free of contamination advantage.Photovoltaic power generation technology is one of Basic Ways of effectively utilizing solar energy resources.At present, comprise that grid-connected various photovoltaic power generation technologies have been subjected to the support energetically of national governments.
Although photovoltaic power generation technology has a good application prospect, it is also faced with many problems to be solved that has as a kind of newer technology, and one of them is that photovoltaic array shade covers problem.Cause that the reason that shade covers problem has, photovoltaic cell towards, buildings partial occlusion different from inclination angle and laying dust covering etc. during inconsistent, the project installation of photovoltaic cell or the output characteristics of photovoltaic module own.When photovoltaic array is covered by shade, the output characteristic curve of photovoltaic array will show multi-peak feature, now be difficult to make photovoltaic array to be operated in global maximum power point, and the operational efficiency of photovoltaic generating system significantly declines; According to statistics, by shade, covering the photovoltaic array decrease in efficiency causing can be up to more than 15%.It is the Basic Ways that improves photovoltaic array generating efficiency that photovoltaic array MPPT maximum power point tracking is controlled, and at shadow-free, covers under normal circumstances, and the output characteristic curve of photovoltaic array is single peak curve, now than the maximum power point that is easier to find system.
In the recent period, conventional unimodal value maximum power point tracing method mainly comprises disturbance observation method, conductance increment method, constant voltage process and stagnant ring relative method etc.These methods are mainly applicable to the MPPT maximum power point tracking of photovoltaic system under single peak value condition, and for covered the multi-peak situation causing by shade, existing unimodal value maximum power point tracing method is difficult to adapt to.Therefore the maximum power point tracing method that, design can be applicable to unimodal value and multi-peak situation simultaneously has outstanding engineering significance.
At present, under multi-peak condition, the tracking and controlling method of maximum power point has become the study hotspot problem of photovoltaic power generation technology, this existing scientific paper has been done deep theoretical analysis to this, also the engineering method that has practical application, as the quick optimization method > of photovoltaic array global maximum power point > (CN103324239A) under application for a patent for invention < < photovoltaic array multimodal maximum power point tracing method > > (CN103123514A) and the local shade of < <.Wherein,
Chinese invention patent application prospectus CN103123514A is in disclosed < < photovoltaic array multimodal maximum power point tracing method > > on May 29th, 2013, is that open-circuit voltage and the short-circuit current of photovoltaic array tentatively chosen global maximum power point (MPP) mountain peak, place during first according to shadow-free; While take shadow-free, the voltage of photovoltaic array maximum power point is benchmark with the ratio of the photovoltaic module quantity of connecting again, choose maximal power tracing (MPPT) step-size in search, search for respectively the MPP of the left and right sides, until search certain MPP, its corresponding output power value is greater than the MPP output power value of its left and right sides, thinks that this MPP is overall MPP; Finally maintain photovoltaic array and run on overall MPP, and the variation of Real-Time Monitoring service condition, if service condition changes, restart multimodal MPPT strategy.But this tracking exists following deficiency:
1) implementation procedure need to depend on numerous information of photovoltaic array: the component type in photovoltaic array open-circuit voltage during shadow-free, short-circuit current, photovoltaic array, assembly series connection number etc., specifically refer to described in its step 1, this defect has determined that the environmental suitability of the method is not strong;
2) adopt voltage close loop to control the scanning that realizes photovoltaic array output power curve, must could determine the position of maximum power point by point by point scanning, caused the process of dynamic scan too slow;
3) what the Local Search in the method adopted is " disturbance observation method " and " conductance increment method ", and these two kinds of methods exist dynamic process erroneous judgement, steady track process oscillation problem among a small circle, cause the accuracy of its dynamic stability and stable state not high;
4) basic ideas of the method are as described in IEEE document " A Study on a Two Stage Maximum Power Point Tracking Control of a Photovoltaic System under Partially Shaded Insolation Conditions " in 2003 (" a kind of two stages maximum power tracking methods research of photovoltaic system in partial occlusion situation "---IEEE energy science in 2003 can plenary session collection of thesis), it can make erroneous judgement under part situation, " select the scope of the existence of overall MPP " according to generally not adapting to, the result of judgement is wrong sometimes,
5) do not provide the detection of environment dynamic change, the Rule of judgment that MPPT method is restarted, algorithm is incomplete.
Under the local shade of disclosed < < on September 25th, 2013, the quick optimization method > of photovoltaic array global maximum power point > adopts Chinese invention patent application prospectus CN103324239A is that " revising fruit bat algorithm " realizes global search, " improving gold separation method " completes Local Search.Its existence mainly not foot point comprise:
1) the global search strategy adopting---" revising fruit bat algorithm " is similar to " PSO algorithm ", it is all a kind of evolution algorithm, though it has when hyperspace optimizing, there is fast convergence rate, but the extremum search problem in the face of photovoltaic array P-V curve, its rapidity performance is not obvious, and the search performance of simultaneously " revising fruit bat algorithm " depends on the selection of initialization point, exists the situation that can not converge to global maximum power point;
2) what adopt is voltage close loop search, its implementation procedure also must adopt point by point scanning process, in search procedure, the performance number of a lot of working points, much smaller than peak power power of operating point, so loss of active power is larger, also exists the repeatedly fluctuation problem of quiescent potential simultaneously;
3) do not provide the detection of environment dynamic change, the Rule of judgment that MPPT method is restarted, algorithm is incomplete.
Summary of the invention
The technical problem to be solved in the present invention is for the environmental suitability existing in prior art is strong, global search process power loss is more, global maximum power point is followed the tracks of unsuccessfully and oscillation of power problem, provide a kind of can fast and stable trace into the global maximum power point under multi-peak situation, to improve the photovoltaic array multi-peak maximum power point tracing method based on the scanning of power closed loop of the generating efficiency of photovoltaic array.
For solving technical matters of the present invention, the technical scheme adopting is: the photovoltaic array multi-peak maximum power point tracing method based on the scanning of power closed loop comprises output voltage, the output current of online detection photovoltaic array, particularly,
Step 1, power closed-loop control scanning: first by online output voltage, the output current that detects photovoltaic array, to obtain the real-time output power of photovoltaic array output, the closed-loop control of recycling power makes real-time output power track reference power, thereby obtains the control signal of MPPT maximum power point tracking circuit;
Does step 2, judge that photovoltaic array output voltage is less than the minimum operating voltage of photovoltaic DC-to-AC converter? while being less than, proceed to step 3, otherwise repeating step 1 and step 2;
Step 3, 3 collaborative variable step Local Searches: first photovoltaic array peak power output and corresponding output voltage values thereof based on obtaining in step 1 and step 2, set three initialization points, recycling voltage close loop is controlled, photovoltaic array is worked on three working points successively, utilize the online photovoltaic array output voltage detecting simultaneously, output current, obtain the output power of each working point, when MPPT maximum power point tracking end cycle, upgrade the peak power dot information of global maximum power point information and each working point experience, when three working points take turns to operate after one time, utilize the information of three working points that obtain jointly to determine the operating voltage of three working points of next round,
Does step 4, judge according to the magnitude of voltage of three working points whether three working points enough approach? if following condition: P
m≠ 0, U
m-U
m1< U
step/ 10, U
m-U
m2< U
step/ 10, U
m-U
m3< U
step/ 10 meet simultaneously, P wherein
mpower, U for known maximum power point
mvoltage, U for known maximum power point
m1, U
m2, U
m3be respectively magnitude of voltage, the U at the maximum power point place that three working points experience separately
stepfor initial disturbance step-length, for enough approaching and proceed to step 5, otherwise repeat above-mentioned steps 3 and step 4;
Step 5, determine voltage steady track: first utilize voltage close loop to control, the output voltage stabilization that makes photovoltaic array is on the definite maximum power point of step 3, step 4, photovoltaic array output voltage and output current that recycling detects in real time, calculate real-time output power, afterwards, the peak power output obtaining by more real-time output power and step 3, step 4, calculates relative power variable quantity and accumulative total relative power variable quantity;
Does step 6, based on relative power variable quantity, judge that acute variation has occurred environment? if so, reboot step 1;
Does step 7, based on accumulative total relative power variable quantity, judge that slow variation has occurred environment? if so, reboot step 3, otherwise proceed to step 5.
Further improvement as the photovoltaic array multi-peak maximum power point tracing method based on the scanning of power closed loop:
The process of the power closed-loop control in described step 1 is, after obtaining each time real-time output power, by the comparison of real-time output power and known global maximum power, to upgrade global maximum power point information, even P=U
pv* I
pv> P
m, U
m=U
pv, P
m=P,, the P in formula is real-time output power, U
pvfor photovoltaic array output voltage, the I detecting in real time
pvfor photovoltaic array output current, the U detecting in real time
mvoltage, P for known maximum power point
mpower for known maximum power point.
Reference power in described step 1 is by formula P
r(k)=P
r(k-1)+P
stepdetermine the P in formula
r(k) current reference power, the P for following the tracks of
r(k-1) be last reference power, the P following the tracks of
stepstep-length for reference power variation.
Three initialization points in described step 3 are according to U
1(k)=U
m, U
2(k)=U
m-U
step, U
3(k)=U
m+ U
stepdetermine U wherein
1(k) be voltage, the U of first job point
2(k) be voltage, the U of second working point
3(k) be voltage, the U of the 3rd working point
mvoltage, U for known maximum power point
stepfor initial disturbance step-length.
The operating voltage of three working points of next round in described step 3 is determined according to following formula:
Δ U in formula
1(k), Δ U
2(k), Δ U
3(k) be the voltage disturbance amount in three current MPPT maximum power point tracking cycles of working point, Δ U
1(k-1), Δ U
2(k-1), Δ U
3(k-1) be the voltage disturbance amount in three previous MPPT maximum power point tracking cycles of working point, U
m1, U
m2, U
m3be the maximum power point voltage value that three working points experience separately, U
1(k-1), U
2(k-1), U
3(k-1) be the voltage in three previous MPPT maximum power point tracking cycles of working point, ω ∈ (0,1), c
1∈ (0,1), c
2∈ (0,1) is quiescent potential step-length adjusting parameter.
Relative power variable quantity in described step 5 and accumulative total relative power variable quantity calculate according to following formula: E
p=1-U
pv* I
pv/ P
m, E=Σ E
p, the E in formula
pfor the relative power variable quantity in current MPPT maximum power point tracking cycle, the accumulative total relative power variable quantity that E is a plurality of tracking cycles.
During reboot step 1 in described step 6, value and power reference is according to P
r(k)=(U
pv* I
pv)/2 are set, and maximum power point power P resets simultaneously
m=0, the U in formula
pvfor photovoltaic array output voltage, the I detecting in real time
pvfor the photovoltaic array output current detecting in real time.
The determining step that slow variation has occurred environment in described step 7 is,
(1) whether the steady track that judges timer record exceeds schedule time cycle length, if overtime, reset timer and accumulative total relative power variable quantity, otherwise continue timing;
(2) if at the appointed time, integral power relative variation E > 0.05, represent that slight variation has occurred environment, between actual maximum power point and the maximum power point of memory, slight skew has occurred, reboot step 3 is carried out Local Search.
Photovoltaic array multi-peak maximum power point tracing method based on the scanning of power closed loop disclosed by the invention, under multi-peak situation, realized rapidly the location of global maximum power point, and realized the accurate tracking of global maximum power point, its beneficial effect is embodied in:
1. not relying on the information of any known photovoltaic array, is according to online detection information operation completely.
2. utilize the instability in power closed-loop control " valley point " region on photovoltaic array output power curve, automatically skip the region that does not have maximum power point, without point by point scanning, just can determine the position of maximum power point, dynamic process is fast, and power loss is little.
3. the scope of not selecting in advance overall MPP search, search procedure does not rely on starting point yet, so there is not the phenomenon that can not converge to global maximum power point.
4. near global maximum power point, adopted " 3 collaborative variable step-size search methods " based on PSO algorithm, utilize the convergence property of the method, overcome the erroneous judgement problem that existing method dynamic process exists, avoided steady state power vibration, improved steady-state tracking precision.The result of actual test is, adopt tracking accuracy based on PSO algorithm up to 99.9%, and traditional " disturbance observation method " and the stable state accuracy of " conductance increment method " is all less than 98%.
5. under current intelligence, can restart search procedure according to the degree of environmental change, realize the quick response of environmental change.
6. especially it should be noted that, power closed-loop control in this method step 1 is local stability on photovoltaic array curve of output, when reference power is greater than the maximum power point of photovoltaic array curve of output existence, the output voltage of photovoltaic array will slide to the minimum operating voltage of photovoltaic DC-to-AC converter, thereby realize the scanning of photovoltaic array curve of output.Be different from prior art, existing other method is all each MPPT maximum power point tracking cycle just to upgrade peak power dot information one time, and the power closed-loop control of this method is to upgrade once in each sampling period.Even if other method also adopts each sampling period to upgrade peak power dot information, there is no practical significance yet, its basic reason is just above-mentioned " power closed-loop control is local stability on photovoltaic array curve of output ".
Accompanying drawing explanation
Fig. 1 is overview flow chart of the present invention.
Fig. 2 realizes circuit theory diagrams of the present invention.
Fig. 3 is static multi-peak tracing process schematic diagram.
Restarting process schematic diagram when Fig. 4 is environmental catastrophe.
Fig. 5 is specific embodiment of the invention process flow diagram.
Fig. 6 is controlling of sampling program flow diagram.
Fig. 7 is restarted 3 collaboratively searching process-initialize routine process flow diagrams.
Embodiment
Below in conjunction with accompanying drawing, technical scheme of the present invention is carried out to clear, complete description.Obvious described embodiment is only a part for the embodiment of the present invention, and based on embodiments of the invention, other embodiment that those skilled in the art obtains under the prerequisite of not making creative work, belongs to the protection domain of this patent.
Embodiments of the invention provide a kind of photovoltaic array multi-peak maximum power point tracing method based on power closed loop scanning, and to solve, the tracing process that prior art exists is slow, energy loss is more, and the problem of following the tracks of maximum power point failure.
Hardware circuit of the present invention should comprise the testing circuit of photovoltaic array output voltage, output current, DC bus-bar voltage.Photovoltaic combining inverter adopts two-stage type structure, and prime is DC-DC translation circuit, for completing MPPT maximum power point tracking; Rear class is DC-AC inverter circuit, realizes the balance of photovoltaic array Implantation Energy and inversion output energy by the stable control of busbar voltage.System completes the initialization of MPPT maximum power point tracking circuit and program when powering on, and completes the initialization of MPPT maximum power point tracking program variable.
Fig. 2 is for implementing a kind of circuit arrangement of the present invention.This circuit arrangement comprises photovoltaic array, photovoltaic array output voltage U
pvtesting circuit, photovoltaic array output current I
pvtesting circuit, and by inductance L, switch transistor T, diode D and dc-link capacitance C
dCthe BOOST circuit forming, grid-connected inverter circuit, MPPT maximum power point tracking control circuit.Maximum power point tracing method disclosed by the invention is according to the online U detecting
pv, I
pvinformation, obtains the duty cycle signals of controlling BOOST circuit through MPPT maximum power point tracking computing, increase, I if control the duty cycle signals of BOOST circuit
pvincrease U
pvreduce; If otherwise dutycycle reduce, I
pvreduce U
pvincrease.
For the static multi-peak situation shown in Fig. 3, when the hardware system that the present invention relies on powers on, BOOST circuit and grid-connected inverter circuit are not yet worked, and the working point of photovoltaic array is arranged in a point of Fig. 3, i.e. open-circuit voltage place.The controlling of sampling cycle T of initialization system now
s=50uS, MPPT maximum power point tracking cycle T
mppt=1 second.Each controlling of sampling cycle is carried out a controlling of sampling program, gathers output voltage and the output current of a photovoltaic array; Each is carried out a MPPT maximum power point tracking program in MPPT maximum power point tracking cycle, changes reference power or reference voltage.During programming, definition S
mpptsign as the MPPT maximum power point tracking stage of living in.
For multi-peak P-V curve as shown in Figure 3, the basic step of multi-peak maximum power point tracing method disclosed by the invention is as follows:
Referring to Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6 and Fig. 7,
Step 1, power closed-loop control scanning:
In each MPPT maximum power point tracking, in the cycle, maximum power point tracing method is according to the given reference power value of mode of " current reference power value=last reference power value+power step size ".Before the next MPPT maximum power point tracking cycle arrives, in each control cycle, can call controlling of sampling program one time.
In sampling process, first by online output voltage, the output current that detects photovoltaic array, to obtain the real-time output power of photovoltaic array output.The closed-loop control of recycling power makes real-time output power track reference power, thereby obtains the control signal of MPPT maximum power point tracking circuit.
The process of power closed-loop control is, after obtaining each time real-time output power, by the comparison of real-time output power and known global maximum power, to upgrade global maximum power point information, even P=U
pv* I
pv> P
m, U
m=U
pv, P
m=P,, the P in formula is real-time output power, U
pvfor photovoltaic array output voltage, the I detecting in real time
pvfor photovoltaic array output current, the U detecting in real time
mvoltage, P for known maximum power point
mpower for known maximum power point.The reference power of power closed-loop control is by formula P
r(k)=P
r(k-1)+P
stepdetermine the P in formula
r(k) current reference power, the P for following the tracks of
r(k-1) be last reference power, the P following the tracks of
stepstep-length for reference power variation.Due on photovoltaic array curve of output, power closed-loop control is local stability, when reference power is greater than the maximum power point of photovoltaic array curve of output existence, the output voltage of photovoltaic array will slide to the minimum operating voltage of photovoltaic DC-to-AC converter, realize the scanning of photovoltaic array curve of output.
Does step 2, judge that photovoltaic array output voltage is less than the minimum operating voltage of photovoltaic DC-to-AC converter? while being less than, proceed to step 3, otherwise repeating step 1 and step 2.
By repeating step 1 and step 2, system works point passes through successively a → b → c → d → e → f → g → h (U on Fig. 3
min), realize the scanning of photovoltaic array output voltage range, and realized the location of global maximum power point M.For e in Fig. 3 → f point, g → h (U
min) region between point, power closed-loop control completes a MPPT maximum power point tracking scanning that e → f is ordered in the cycle.After scanning process finishes, peak power dot information (U
m, P
m) be near the information of " 1 " point global maximum power point M point.
Step 3,3 collaborative variable step Local Searches:
The first photovoltaic array peak power output dot information (U based on obtaining in step 1, step 2
m, P
m), set three initialization points; Three initialization points are according to U
1(k)=U
m, U
2(k)=U
m-U
step, U
3(k)=U
m+ U
stepdetermine U wherein
1(k) be voltage, the U of first job point
2(k) be voltage, the U of second working point
3(k) be voltage, the U of the 3rd working point
mvoltage, U for known maximum power point
stepfor initial disturbance step-length.In ensuing three peak powers, in dot cycle, by voltage close loop, control, make photovoltaic array (the variable C on three working points that works successively
wfor present operating point mark), utilize online photovoltaic array output voltage, the output current detecting simultaneously, obtain the output power of each working point.When MPPT maximum power point tracking end cycle, upgrade the peak power dot information of global maximum power point information and each working point experience.When three working points take turns to operate after one time, utilize the information of three working points that obtain jointly to determine the operating voltage of three working points of next round; Wherein, the operating voltage of three working points of next round is determined according to following formula:
Δ U in formula
1(k), Δ U
2(k), Δ U
3(k) be the voltage disturbance amount in three current MPPT maximum power point tracking cycles of working point, Δ U
1(k-1), Δ U
2(k-1), Δ U
3(k-1) be the voltage disturbance amount in three previous MPPT maximum power point tracking cycles of working point, U
m1, U
m2, U
m3be the maximum power point voltage value that three working points experience separately, U
1(k-1), U
2(k-1), U
3(k-1) be the voltage in three previous MPPT maximum power point tracking cycles of working point, ω ∈ (0,1), c
1∈ (0,1), c
2∈ (0,1) is quiescent potential step-length adjusting parameter.
Does step 4, judge according to the magnitude of voltage of three working points whether three working points enough approach? if following condition: P
m≠ 0, U
m-U
m1< U
step/ 10, U
m-U
m2< U
step/ 10, U
m-U
m3< U
step/ 10 meet simultaneously, P wherein
mpower, U for known maximum power point
mvoltage, U for known maximum power point
m1, U
m2, U
m3be respectively magnitude of voltage, the U at the maximum power point place that three working points experience separately
stepfor initial disturbance step-length, for enough approaching and proceed to step 5, otherwise repeat above-mentioned steps 3 and step 4.By repeating step 3 and step 4, the working point of system will converge to global maximum power point M, i.e. U
m=U
m, P
m=P
m, U wherein
m, P
mbe respectively voltage and power that M is ordered.
Step 5, determine voltage steady track:
First utilize voltage close loop to control, the output voltage stabilization that makes photovoltaic array on the definite maximum power point of step 3, step 4, i.e. U
pv=U
m=U
m.Photovoltaic array output voltage and output current that recycling detects in real time, calculate real-time output power.Afterwards, the peak power output obtaining by more real-time output power and step 3, step 4, calculates relative power variable quantity and accumulative total relative power variable quantity: E according to following formula
p=1-U
pv* I
pv/ P
m, E=Σ E
p, the E in formula
pfor the relative power variable quantity in current MPPT maximum power point tracking cycle, the accumulative total relative power variable quantity that E is a plurality of tracking cycles.While determining voltage steady track, peak power dot information no longer upgrades.
Does step 6, based on relative power variable quantity, judge that acute variation has occurred environment? if first setting power reference value P
r(k)=(U
pv* I
pv)/2, maximum power point power P resets simultaneously
m=0, the U in formula
pvfor photovoltaic array output voltage, the I detecting in real time
pvfor the photovoltaic array output current detecting in real time.Reboot step 1 rescans again, under two kinds of situations as shown in Figure 4, and all can reboot step 1.
Does step 7, based on accumulative total relative power variable quantity, judge that slow variation has occurred environment? if so, reboot step 3, otherwise proceed to step 5.When judging whether environment occurs slowly to change, first judge whether the steady track of timer record exceeds schedule time cycle length, if overtime, reset timer and accumulative total relative power variable quantity, otherwise continue timing; If at the appointed time, integral power relative variation E > 0.05, represent that slight variation has occurred environment, between actual maximum power point and the maximum power point of memory, slight skew has occurred, reboot step 3 is carried out 3 collaborative variable step Local Searches.
Above-mentioned search procedure is a specific implementation process of the present invention, and the dependence diagram of MPPT maximum power point tracking process is as shown in Fig. 5, Fig. 6 and Fig. 7.