CN103955253B - Based on the photovoltaic array multimodal value maximum power point tracing method of power closed loop scanning - Google Patents
Based on the photovoltaic array multimodal value maximum power point tracing method of power closed loop scanning Download PDFInfo
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Abstract
The invention discloses a kind of photovoltaic array multimodal value MPPT maximum power point tracking (MPPT-Maximum Power Point Tracking) method based on the scanning of power closed loop.It is made up of three phases, and the first stage is the whole scan realizing multi-peak curve based on power closed-loop control, completes the location of maximum power point; Subordinate phase is 3 the collaborative variable step disturbance observation processes realized based on particle swarm optimization algorithm, realizes the Local Search near maximum power point; Phase III determines voltage steady track process, and simultaneously the judgement of environmentally change information, activates the process of first or subordinate phase.The present invention can both realize the MPPT maximum power point tracking of photovoltaic array under unimodal or multimodal situation, there is not disturbance observation method, the erroneous judgement of conductance increment method and oscillation problem; What can overcome the existence of existing method loses the problem more, dynamic process is slower by dynamic following function simultaneously.The present invention can find global maximum power point effectively, realizes quick, stable, the accurate tracking of maximum power point.
Description
Technical Field
The invention belongs to the photovoltaic power generation technology in the field of electrical engineering, and particularly relates to a Maximum power point Tracking (MPPT-Maximum Power Point Tracking) method of a photovoltaic array in a photovoltaic power generation system under the condition of uneven illumination.
Background
Solar energy is a renewable energy source, and has the advantages of wide distribution, sustainability and no pollution. Photovoltaic power generation technology is one of the basic approaches to effectively utilize solar energy resources. At present, various photovoltaic power generation technologies including photovoltaic grid connection are greatly supported by governments of various countries.
Although the photovoltaic power generation technology has a good application prospect, as a newer technology, the photovoltaic power generation technology still faces a plurality of problems to be solved, wherein one of the problems is the problem of shadow shielding of a photovoltaic array. The shadow shielding problem is caused by inconsistent output characteristics of the photovoltaic cell or the photovoltaic module, different orientation and inclination angle of the photovoltaic cell during engineering installation, local shielding of buildings, dust accumulation and coverage and the like. When the photovoltaic array is shaded by shadows, the output characteristic curve of the photovoltaic array shows the characteristic of multiple peaks, so that the photovoltaic array is difficult to work at the global maximum power point, and the operation efficiency of a photovoltaic power generation system is remarkably reduced; statistically, the efficiency of the photovoltaic array is reduced by more than 15% due to shadow masking. The maximum power point tracking control of the photovoltaic array is a basic way for improving the generating efficiency of the photovoltaic array, and under the normal condition of no shadow shielding, the output characteristic curve of the photovoltaic array is a single-peak value curve, so that the maximum power point of a system is easy to find.
Recently, common single-peak maximum power point tracking methods mainly include a disturbance observation method, a conductance increment method, a constant voltage method, a hysteresis comparison method and the like. The methods are mainly suitable for maximum power point tracking of a photovoltaic system under a single-peak condition, and the existing single-peak maximum power point tracking method is difficult to adapt to a multi-peak situation caused by shadow masking. Therefore, the design of the maximum power point tracking method which can be simultaneously suitable for single-peak and multi-peak situations has outstanding engineering significance.
At present, a tracking control method of a maximum power point under a multi-peak condition becomes a research hotspot problem of a photovoltaic power generation technology, which has both deep theoretical analysis made by academic papers and practical engineering methods, such as the invention patent application of 'a photovoltaic array multi-peak maximum power point tracking method' (CN103123514A) and 'a photovoltaic array global maximum power point fast optimization method under local shadow' (CN 103324239A). Wherein,
the invention discloses a photovoltaic array multi-peak maximum power point tracking method disclosed in 2013, 5 and 29, CN103123514A, which is characterized in that a peak where a global Maximum Power Point (MPP) is located is preliminarily selected according to the open-circuit voltage and the short-circuit current of a photovoltaic array when no shadow exists; then taking the ratio of the voltage of the maximum power point of the photovoltaic array to the number of the photovoltaic modules connected in series when no shadow exists as a reference, selecting a maximum power tracking (MPPT) search step length, and searching MPPs on the left side and the right side respectively until a certain MPP is searched, wherein the corresponding output power value is greater than the MPP output power values on the left side and the right side, and the MPP is considered as the global MPP; and finally, maintaining the photovoltaic array to operate in the global MPP, monitoring the change of the operation condition in real time, and restarting the multimodal MPPT strategy if the operation condition changes. However, this tracking method has the following disadvantages:
1) the implementation requires much information depending on the photovoltaic array: the open-circuit voltage, the short-circuit current, the component type and the component serial number of the photovoltaic array and the like of the photovoltaic array in the absence of shadows are described in step 1, and the defect determines that the method is not strong in environmental adaptability;
2) the scanning of the output power curve of the photovoltaic array is realized by adopting voltage closed-loop control, and the position of the maximum power point can be determined only by point-by-point scanning, so that the dynamic scanning process is too slow;
3) the local search in the method adopts a 'disturbance observation method' and a 'conductance incremental method', and the two methods have the problems of misjudgment in a dynamic process and small-range oscillation in a steady-state tracking process, so that the dynamic stability and the steady-state accuracy are not high;
4) the basic idea of the method is as described in an IEEE document A Study on Two stagemaximam Power Point Tracking Control of a Photovoltaic System undersupportiallyshaped analysis Condition in 2003, wherein the Two-stage maximum Power Tracking method of the Photovoltaic System under a local shielding condition is researched, namely, a whole conference statement of the IEEE energy society in 2003, the method can make misjudgment under partial Conditions, namely, the basis of selecting the existence range of the global MPP is not universally adaptive, and the judgment result is sometimes wrong;
5) and no judgment conditions for detecting the dynamic change of the environment and restarting the MPPT method are given, namely the algorithm is incomplete.
The invention discloses a rapid optimization method for a global maximum power point of a photovoltaic array under a local shadow, which is disclosed in the patent application publication specification CN103324239A of China invention in 25.9.2013.A 'fruit fly correction algorithm' is adopted to realize global search and an 'improved golden separation method' is adopted to finish local search. The main disadvantages of the existing method include:
1) the adopted global search strategy, namely the 'modified fruit fly algorithm' is similar to the 'PSO algorithm', and is an evolutionary algorithm, although the evolutionary algorithm has the advantage of high convergence speed when optimizing in a multidimensional space, the evolutionary algorithm is not obvious in rapidity in the face of the extreme value search problem of a photovoltaic array P-V curve, and meanwhile, the search performance of the 'modified fruit fly algorithm' depends on the selection of an initial working point, so that the situation that the maximum power point of the whole world cannot be converged exists;
2) the method adopts voltage closed-loop search, the implementation process of the method also needs to adopt a point-by-point scanning process, and the power values of a plurality of working points in the search process are far smaller than the power of the maximum power working point, so that the dynamic power loss is large, and the problem of multiple large fluctuation of the voltage of the working points exists;
3) and no judgment conditions for detecting the dynamic change of the environment and restarting the MPPT method are given, and the algorithm is incomplete.
Disclosure of Invention
The invention aims to solve the technical problems of poor environmental adaptability, more power loss in the global search process, failure in global maximum power point tracking and power oscillation in the prior art, and provides a photovoltaic array multi-peak maximum power point tracking method based on power closed-loop scanning, which can quickly and stably track the global maximum power point under the condition of multiple peaks so as to improve the power generation efficiency of a photovoltaic array.
In order to solve the technical problem of the invention, the adopted technical scheme is as follows: the photovoltaic array multi-peak maximum power point tracking method based on power closed-loop scanning comprises the steps of detecting the output voltage and the output current of a photovoltaic array on line, particularly,
step 1, power closed-loop control scanning: firstly, the output voltage and the output current of the photovoltaic array are detected on line to obtain the real-time output power output by the photovoltaic array, and then the real-time output power tracks the reference power by using power closed-loop control, so that a control signal of a maximum power point tracking circuit is obtained;
step 2, determine whether the output voltage of the photovoltaic array is less than the lowest operating voltage of the photovoltaic inverter? If the value is less than the preset value, switching to the step 3, otherwise, repeating the step 1 and the step 2;
step 3, three-point cooperative variable step length local search: setting three initial working points based on the maximum output power of the photovoltaic array and the corresponding output voltage value thereof obtained in the step 1 and the step 2, sequentially working the photovoltaic array to the three working points by using voltage closed-loop control, simultaneously obtaining the output power of each working point by using the output voltage and the output current of the photovoltaic array detected on line, updating the global maximum power point information and the maximum power point information experienced by each working point when the maximum power point tracking period is finished, and jointly determining the working voltage of the next round of the three working points by using the obtained information of the three working points after the three working points work in turn once;
step 4, determine whether the three operating points are close enough according to the voltage values of the three operating points? If the following conditions are met: pm≠0、Um-Um1＜Ustep/10、Um-Um2＜Ustep/10、Um-Um3＜Ustep[ 10 ] simultaneously, wherein PmFor a known maximum power pointPower, UmVoltage, U, of known maximum power pointm1、Um2、Um3Respectively, the voltage value, U, at the maximum power point experienced by each of the three operating pointsstepIf the initial disturbance step length is enough, the step 5 is switched to, and if not, the steps 3 and 4 are repeated;
step 5, constant voltage steady state tracking: firstly, stabilizing the output voltage of the photovoltaic array on the maximum power point determined in the step 3 and the step 4 by using voltage closed-loop control, calculating real-time output power by using the output voltage and the output current of the photovoltaic array detected in real time, and then calculating the relative power variation and accumulating the relative power variation by comparing the real-time output power with the maximum output power obtained in the step 3 and the step 4;
step 6, based on the relative power variation, determine whether the environment has changed drastically? If yes, restarting the step 1;
step 7, based on the accumulated relative power variation, determine whether the environment has changed slowly? If yes, restarting the step 3, otherwise, turning to the step 5.
The photovoltaic array multi-peak maximum power point tracking method based on power closed-loop scanning is further improved as follows:
the power closed-loop control in step 1 is performed by updating the global maximum power point information by comparing the real-time output power with the known global maximum power after each time the real-time output power is obtained, that is, if P ═ Upv*Ipv＞PmThen U ism＝Upv,PmP is real-time output power, UpvPhotovoltaic array output voltage, I, for real-time detectionpvPhotovoltaic array output current, U, for real-time detectionmVoltage, P, of known maximum power pointmIs the power at which the maximum power point is known.
The reference power in step 1 is represented by formula Pr(k)＝Pr(k-1)+PstepDeterminingP in the formular(k) For the current reference power, P, to be trackedr(k-1) reference power, P, for last trackingstepIs a step size of the reference power change.
The three initial working points in the step 3 are according to U1(k)＝Um，U2(k)＝Um-Ustep，U3(k)＝Um+UstepDetermine U therein1(k) Voltage, U, at a first operating point2(k) Voltage, U, of the second operating point3(k) Voltage, U, at a third operating pointmVoltage, U, of known maximum power pointstepIs the initial perturbation step size.
The working voltages of the next three working points in the step 3 are determined according to the following formula:
in the formula1(k)、ΔU2(k)、ΔU3(k) Voltage disturbance quantity, delta U, of tracking period of current maximum power point of three working points1(k-1)、ΔU2(k-1)、ΔU3(k-1) is the voltage disturbance quantity of the maximum power point tracking period before the three working points, Um1、Um2、Um3For maximum power point voltage values, U, experienced by each of the three operating points1(k-1)、U2(k-1)、U3(k-1) is the voltage of the maximum power point tracking period before three working points, and omega belongs to (0,1) and c1∈(0,1)、c2Belongs to (0,1) as working point voltage step lengthAnd adjusting the parameters.
The relative power variation and the accumulated relative power variation in the step 5 are calculated according to the following formulas: ep＝1-Upv*Ipv/Pm，E＝ΣEpIn the formula EpThe relative power variation of the current maximum power point tracking period is E, and the accumulated relative power variation of a plurality of tracking periods is E.
When the step 1 is restarted in the step 6, the power reference value is according to Pr(k)＝(Upv*Ipv) Setting/2 while resetting maximum power point power Pm0, U in the formulapvPhotovoltaic array output voltage, I, for real-time detectionpvAnd outputting current for the photovoltaic array detected in real time.
The step of determining that the environment has changed slowly in step 7 is,
(1) judging whether the steady-state tracking period time recorded by the timer exceeds a specified time, if so, resetting the timer and accumulating the relative power variation, otherwise, continuing to time;
(2) if the accumulated power relative change E is larger than 0.05 in a specified time, which indicates that the environment slightly changes, namely a slight deviation occurs between the actual maximum power point and the memorized maximum power point, the step 3 is restarted to perform local search.
The invention discloses a photovoltaic array multi-peak maximum power point tracking method based on power closed-loop scanning, which quickly realizes the positioning of a global maximum power point under the condition of multi-peak values and realizes the accurate tracking of the global maximum power point, and has the advantages that:
1. the photovoltaic array detection system does not depend on any known information of the photovoltaic array, and operates completely according to online detection information.
2. The instability of a valley point region on the output power curve of the photovoltaic array is controlled by utilizing the power closed loop, the region without the maximum power point is automatically skipped, the position of the maximum power point can be determined without point-by-point scanning, the dynamic process is fast, and the power loss is small.
3. The global MPP searching range is not selected in advance, the searching process does not depend on a starting point, and therefore the phenomenon that the global MPP searching range cannot be converged to the global maximum power point does not exist.
4. A three-point cooperative variable step size searching method based on a PSO algorithm is adopted near the global maximum power point, the problem of misjudgment in the dynamic process of the existing method is solved by using the convergence characteristic of the method, steady-state power oscillation is avoided, and the steady-state tracking precision is improved. The actual test result is that the tracking precision based on the PSO algorithm is as high as 99.9%, and the steady-state precision of the traditional 'disturbance observation method' and the traditional 'conductance incremental method' is less than 98%.
5. Under the dynamic condition, the search process can be restarted according to the degree of environmental change, and the quick response of the environmental change is realized.
6. Particularly, the power closed-loop control in step 1 of the method is locally stable on the output curve of the photovoltaic array, and when the reference power is greater than the maximum power point existing in the output curve of the photovoltaic array, the output voltage of the photovoltaic array slides to the lowest working voltage of the photovoltaic inverter, so that the output curve of the photovoltaic array is scanned. Unlike the prior art, in the other existing methods, the maximum power point information is updated once every maximum power point tracking period, and the power closed-loop control of the method is updated once every sampling period. Even though other methods also update the maximum power point information with every sampling period, there is no practical significance, and the fundamental reason is that the above-mentioned "power closed-loop control is locally stable on the photovoltaic array output curve".
Drawings
FIG. 1 is a general flow diagram of the present invention.
Fig. 2 is a schematic diagram of a circuit implementing the present invention.
Fig. 3 is a schematic diagram of a static multi-peak tracking process.
Fig. 4 is a schematic diagram of a restart process in case of an environmental mutation.
FIG. 5 is a flow chart of an embodiment of the present invention.
Fig. 6 is a flowchart of a sampling control routine.
Fig. 7 is a flowchart of a restart three-point collaborative search process-initialization procedure.
Detailed Description
The technical scheme of the invention is clearly and completely described below with reference to the accompanying drawings. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and other embodiments obtained by those skilled in the art without inventive labor based on the embodiments of the present invention belong to the protection scope of the patent.
The embodiment of the invention provides a photovoltaic array multi-peak maximum power point tracking method based on power closed-loop scanning, and aims to solve the problems of slow tracking process, more energy loss and failure in tracking a maximum power point in the prior art.
The hardware circuit of the invention comprises a detection circuit of photovoltaic array output voltage, output current and direct current bus voltage. The photovoltaic grid-connected inverter adopts a two-stage structure, and the front stage is a DC-DC conversion circuit and is used for completing maximum power point tracking; the rear stage is a DC-AC inverter circuit, and the balance of the photovoltaic array injection energy and the inversion output energy is realized through the stable control of the bus voltage. When the system is electrified, the initialization of the maximum power point tracking circuit and the program is completed, and the initialization of the maximum power point tracking program variable is completed.
Fig. 2 is a circuit scheme for implementing the present invention. The circuit scheme comprises a photovoltaic array and a photovoltaic array output voltage UpvDetection circuit and photovoltaic array output current IpvAnd a detection circuit composed of an inductor L, a switching tube T, a diode D and a DC bus capacitor CDCThe BOOST circuit, the grid-connected inverter circuit and the maximum power point tracking control circuit are formed. The maximum power point tracking method disclosed by the invention is based on the U detected on linepv，IpvInformation, obtaining duty ratio signal of control BOOST circuit through maximum power point tracking operation, if the duty ratio signal of control BOOST circuit is increased, IpvIncrease, UpvDecrease; otherwise if the duty cycle is reduced, IpvDecrease of UpvAnd is increased.
For the static multi-peak condition shown in fig. 3, when the hardware system supported by the present invention is powered on, the BOOST circuit and the grid-connected inverter circuit do not work, and the operating point of the photovoltaic array is located at point a in fig. 3, i.e., the open-circuit voltage. At this time, the sampling control period T of the system is setS50uS, maximum power point tracking period Tmppt1 second. Executing a sampling control program once in each sampling control period, and collecting the output voltage and the output current of the photovoltaic array once; and executing a maximum power point tracking program once every maximum power point tracking period, and changing reference power or reference voltage once. When programming, define SmpptAs an indication of the stage at which the maximum power point tracking is located.
For the multi-peak P-V curve shown in fig. 3, the basic steps of the multi-peak maximum power point tracking method disclosed by the present invention are as follows:
referring to figures 1, 2, 3, 4, 5, 6 and 7,
step 1, power closed-loop control scanning:
in each maximum power point tracking period, the maximum power point tracking method gives a reference power value in a mode of 'current reference power value being the last reference power value + power step length'. The sampling control procedure is called once in each control period before the next maximum power point tracking period comes.
In the sampling process, the output voltage and the output current of the photovoltaic array are detected on line to obtain the real-time output power output by the photovoltaic array. And then, the power closed-loop control is utilized to enable the real-time output power to track the reference power, so that a control signal of the maximum power point tracking circuit is obtained.
The process of power closed-loop control is that after each time of obtaining real-time output power, the real-time output power is compared with the known global maximum power to update the global maximum power point information, namely if P is Upv*Ipv＞PmThen U ism＝Upv,PmP is real-time output power, UpvPhotovoltaic array output voltage, I, for real-time detectionpvPhotovoltaic array output current, U, for real-time detectionmVoltage, P, of known maximum power pointmIs the power at which the maximum power point is known. The reference power of the power closed-loop control is represented by the formula Pr(k)＝Pr(k-1)+PstepDetermining P in the formular(k) For the current reference power, P, to be trackedr(k-1) reference power, P, for last trackingstepIs a step size of the reference power change. Because the power closed-loop control is locally stable on the output curve of the photovoltaic array, when the reference power is greater than the maximum power point existing in the output curve of the photovoltaic array, the output voltage of the photovoltaic array slides to the lowest working voltage of the photovoltaic inverter, and the scanning of the output curve of the photovoltaic array is realized.
Step 2, determine whether the output voltage of the photovoltaic array is less than the lowest operating voltage of the photovoltaic inverter? And (3) if the value is less than the preset value, switching to the step (3), otherwise, repeating the step (1) and the step (2).
By repeating steps 1 and 2, the system operating point passes through a → b → c → d → e → f → g → h (U) in the order of fig. 3min) The scanning of the output voltage range of the photovoltaic array is realized, and the positioning of the global maximum power point M is realized. For point e → f, g → h (U) in FIG. 3min) In the region between points, the power closed-loop control completes e → f point in one maximum power point tracking periodAnd (6) scanning. Maximum power point information (U) after the scanning process is finishedm，Pm) Information of "1" points near the global maximum power point M point.
Step 3, three-point cooperative variable step length local search:
firstly, based on the maximum output power point information (U) of the photovoltaic array obtained in the step 1 and the step 2m，Pm) Setting three initial working points; the three initial operating points are according to U1(k)＝Um，U2(k)＝Um-Ustep，U3(k)＝Um+UstepDetermine U therein1(k) Voltage, U, at a first operating point2(k) Voltage, U, of the second operating point3(k) Voltage, U, at a third operating pointmVoltage, U, of known maximum power pointstepIs the initial perturbation step size. In the next three maximum power point periods, the photovoltaic array sequentially works to three working points through voltage closed-loop control (variable C)WMarking the current working point), and obtaining the output power of each working point by using the output voltage and the output current of the photovoltaic array detected on line. And when the maximum power point tracking period is finished, updating the global maximum power point information and the maximum power point information experienced by each working point. After the three working points work in turn once, the obtained information of the three working points is utilized to jointly determine the working voltages of the three working points in the next round; the working voltages of the three working points of the next round are determined according to the following formula:
in the formula1(k)、ΔU2(k)、ΔU3(k) Voltage disturbance quantity, delta U, of tracking period of current maximum power point of three working points1(k-1)、ΔU2(k-1)、ΔU3(k-1) is the voltage disturbance quantity of the maximum power point tracking period before the three working points, Um1、Um2、Um3For maximum power point voltage values, U, experienced by each of the three operating points1(k-1)、U2(k-1)、U3(k-1) is the voltage of the maximum power point tracking period before three working points, and omega belongs to (0,1) and c1∈(0,1)、c2And epsilon (0,1) is a working point voltage step length adjusting parameter.
Step 4, determine whether the three operating points are close enough according to the voltage values of the three operating points? If the following conditions are met: pm≠0、Um-Um1＜Ustep/10、Um-Um2＜Ustep/10、Um-Um3＜Ustep[ 10 ] simultaneously, wherein PmPower, U, of known maximum power pointmVoltage, U, of known maximum power pointm1、Um2、Um3Respectively, the voltage value, U, at the maximum power point experienced by each of the three operating pointsstepFor the initial perturbation step size, step 5 is performed for close enough, otherwise, the above steps 3 and 4 are repeated. By repeating steps 3 and 4, the operating point of the system will converge to the global maximum power point M, i.e. Um＝UM,Pm＝PMWherein U isM,PMRespectively, voltage and power at point M.
Step 5, constant voltage steady state tracking:
firstly, voltage closed-loop control is utilized to stabilize the output voltage of the photovoltaic array on the maximum power point determined in the step 3 and the step 4, namely Upv＝Um＝UM. And calculating the real-time output power by using the photovoltaic array output voltage and the output current detected in real time. Then, the real-time output is performed by comparisonCalculating the relative power variation and the accumulated relative power variation according to the following formulas based on the power and the maximum output power obtained in the steps 3 and 4: ep＝1-Upv*Ipv/Pm，E＝ΣEpIn the formula EpThe relative power variation of the current maximum power point tracking period is E, and the accumulated relative power variation of a plurality of tracking periods is E. And when the fixed voltage is stably tracked, the maximum power point information is not updated any more.
Step 6, based on the relative power variation, determine whether the environment has changed drastically? If yes, the power reference value P is set firstr(k)＝(Upv*Ipv) /2, resetting the maximum power point power P simultaneouslym0, U in the formulapvPhotovoltaic array output voltage, I, for real-time detectionpvAnd outputting current for the photovoltaic array detected in real time. Step 1 is restarted to perform rescan, and step 1 is restarted in both cases as shown in fig. 4.
Step 7, based on the accumulated relative power variation, determine whether the environment has changed slowly? If yes, restarting the step 3, otherwise, turning to the step 5. When judging whether the environment slowly changes, firstly judging whether the steady-state tracking period time recorded by the timer exceeds the specified time, if so, resetting the timer and accumulating the relative power variation, otherwise, continuing to time; if the accumulated power relative variation E is larger than 0.05 in a specified time, which indicates that the environment slightly changes, namely a slight deviation occurs between the actual maximum power point and the memorized maximum power point, the step 3 is restarted to perform three-point cooperative variable step size local search.
The above search process is a specific implementation process of the present invention, and the relevant flow charts of the maximum power point tracking process are shown in fig. 5, fig. 6 and fig. 7.
Claims (8)
1. A photovoltaic array multi-peak maximum power point tracking method based on power closed-loop scanning comprises the steps of detecting the output voltage and the output current of a photovoltaic array on line, and is characterized by comprising the following steps:
step 1, firstly, detecting output voltage and output current of a photovoltaic array on line to obtain real-time output power output by the photovoltaic array, and then utilizing power closed-loop control to enable the real-time output power to track reference power so as to obtain a control signal of a maximum power point tracking circuit;
step 2, judging whether the output voltage of the photovoltaic array is smaller than the lowest working voltage of the photovoltaic inverter, if so, turning to step 3, otherwise, repeating the step 1 and the step 2;
step 3, setting three initial working points based on the maximum output power of the photovoltaic array and the corresponding output voltage value thereof obtained in the step 1 and the step 2, sequentially working the photovoltaic array to the three working points by using voltage closed-loop control, simultaneously obtaining the output power of each working point by using the output voltage and the output current of the online detected photovoltaic array, updating the global maximum power point information and the maximum power point information experienced by each working point when the maximum power point tracking period is finished, and jointly determining the working voltage of the next round of three working points by using the obtained information of the three working points after the three working points work in turn;
step 4, judging whether the three working points simultaneously meet the following conditions according to the voltage values of the three working points: pm≠0、Um-Um1＜Ustep/10、Um-Um2＜Ustep/10、Um-Um3＜Ustep/10, wherein PmPower, U, of known maximum power pointmVoltage, U, of known maximum power pointm1、Um2、Um3Respectively, the voltage value, U, at the maximum power point experienced by each of the three operating pointsstepIf the disturbance step length is the initial disturbance step length, the step 5 is carried out, and if the disturbance step length is not the initial disturbance step length, the step 3 and the step 4 are repeated;
step 5, firstly, stabilizing the output voltage of the photovoltaic array on the maximum power point determined in the step 3 and the step 4 by using voltage closed-loop control, then calculating real-time output power by using the output voltage and the output current of the photovoltaic array detected in real time, and then calculating the relative power variation and accumulating the relative power variation by comparing the real-time output power with the maximum output power obtained in the step 3 and the step 4;
step 6, judging whether the environment is changed violently or not based on the relative power variation, and if so, restarting the step 1;
and 7, judging whether the environment slowly changes or not based on the accumulated relative power variation, if so, restarting the step 3, and otherwise, turning to the step 5.
2. The method as claimed in claim 1, wherein the power closed-loop control in step 1 is performed by comparing the real-time output power with the known global maximum power to update the global maximum power point information after each time the real-time output power is obtained, i.e. if P ═ U-pv*Ipv＞PmThen U ism＝Upv,PmP in the formula is real-time output power, UpvPhotovoltaic array output voltage, I, for real-time detectionpvPhotovoltaic array output current, U, for real-time detectionmVoltage, P, of known maximum power pointmIs the power at which the maximum power point is known.
3. The method of claim 1, wherein the reference power in step 1 is represented by formula Pr(k)＝Pr(k-1)+PstepDetermining P in the formular(k) For the current reference power, P, to be trackedr(k-1) reference power, P, for last trackingstepIs a step size of the reference power change.
4. The method as claimed in claim 1, wherein the three initial operating points in step 3 are according to U1(k)＝Um，U2(k)＝Um-Ustep，U3(k)＝Um+UstepDetermine U therein1(k) Voltage, U, at a first operating point2(k) Voltage, U, of the second operating point3(k) Voltage, U, at a third operating pointmVoltage, U, of known maximum power pointstepIs the initial perturbation step size.
5. The method for tracking the maximum power point of the photovoltaic array with multiple peaks based on the power closed-loop scanning as claimed in claim 1, wherein the operating voltages of the next three operating points in the step 3 are determined according to the following formula:
in the formula1(k)、ΔU2(k)、ΔU3(k) Voltage disturbance quantity, delta U, of tracking period of current maximum power point of three working points1(k-1)、ΔU2(k-1)、ΔU3(k-1) is the voltage disturbance quantity of the maximum power point tracking period before the three working points, Um1、Um2、Um3For maximum power point voltage values, U, experienced by each of the three operating points1(k-1)、U2(k-1)、U3(k-1) is the voltage of the maximum power point tracking period before three working points, and omega belongs to (0,1) and c1∈(0,1)、c2And epsilon (0,1) is a working point voltage step length adjusting parameter.
6. The method of claim 2, wherein the relative power variation and the accumulated relative power variation in step 5 are calculated according to the following equations: ep＝1-Upv*Ipv/Pm，E＝ΣEpIn the formula EpThe relative power variation of the current maximum power point tracking period is E, and the accumulated relative power variation of a plurality of tracking periods is E.
7. The method of claim 1, wherein the power reference value is P when restarting step 1 in step 6r(k)＝(Upv*Ipv) Setting/2 while resetting maximum power point power Pm0, U in the formulapvPhotovoltaic array output voltage, I, for real-time detectionpvAnd outputting current for the photovoltaic array detected in real time.
8. The method for tracking the maximum power point of the photovoltaic array with multiple peaks based on the power closed-loop scanning as claimed in claim 1, wherein the step of determining that the environment in step 7 has changed slowly comprises,
(1) judging whether the steady-state tracking period time recorded by the timer exceeds a specified time, if so, resetting the timer and accumulating the relative power variation, otherwise, continuing to time;
(2) if the accumulated power relative change E is larger than 0.05 in a specified time, which indicates that the environment slightly changes, namely a slight deviation occurs between the actual maximum power point and the memorized maximum power point, the step 3 is restarted to perform local search.
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| CN106527570B (en) * | 2016-12-20 | 2018-06-15 | 湘潭大学 | A kind of photovoltaic array multimodal maximum power group hunting optimizes tracking |
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