CN108181966B - Photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning - Google Patents

Photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning Download PDF

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CN108181966B
CN108181966B CN201711473669.2A CN201711473669A CN108181966B CN 108181966 B CN108181966 B CN 108181966B CN 201711473669 A CN201711473669 A CN 201711473669A CN 108181966 B CN108181966 B CN 108181966B
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photovoltaic
scanning
power
phase
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CN108181966A (en
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宁平华
张庆丰
王珍
缸明义
童鑫
张奇
夏兴国
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MA'ANSHAN TECHNICAL COLLEGE
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    • 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
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

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Abstract

The invention discloses a photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning, and belongs to the technical field of photovoltaic MPPT rapid tracking. The invention comprises four control stages, specifically: scan preparation phase, voltage scan phase, PWM preparation phase and PWM control phaseSegment according to uC1If it is 0, u is selectedC1if not, executing a scanning preparation stage to quickly discharge C1; u. ofC1And if the value is 0, the scanning preparation phase is skipped and the voltage scanning phase is directly entered. And after the voltage scanning stage is finished, sequentially entering a PWM preparation stage and a PWM stage. When the environment changes, the environment is detectedLess than 0.9PmaxOr greater than 1.1PmaxThe restart algorithm searches for a new global maximum power point. The method can effectively eliminate the interference of the local power peak value, and realize effective identification and tracking locking of the global maximum power point under the complex environment of local shadow.

Description

Photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning
Technical Field
the invention relates to the technical field of photovoltaic MPPT fast tracking, in particular to a photovoltaic MPPT control circuit and a photovoltaic multimodal MPP fast tracking method based on voltage-power scanning.
background
The output voltage of a single photovoltaic battery unit is very low, and in practical application, a plurality of battery units are required to be connected in series and in parallel, and then the final output voltage and power are improved to meet the input requirements of field electrical appliances or inverters. After a plurality of same photovoltaic battery units are connected in series, when the illumination and the temperature are the same, the output power of the series battery pack only has one peak point, and the MPPT can be well realized by a conventional hill climbing method, a disturbance observation method and an admittance incremental method, so that the power generation efficiency is improved. However, if the output characteristics of each photovoltaic cell unit are not consistent when the shadow of clouds, trees, equipment or other structures or the local shadow caused by dust, leaves or impurities accumulated on the surface of the module is encountered, the output of the series circuit usually has a plurality of peak points, but only one peak point is the global maximum power point. The overall output power capability of the centralized system in partial shadow is severely degraded, sometimes resulting in failure of the entire battery pack if a certain cell in the series fails. At this time, if the conventional MPPT method is adopted, it is easy to fall into a certain local power extreme point, and the global maximum power point cannot be tracked in time.
the existing maximum power tracking method which presents a multi-peak characteristic to photovoltaic power output adopts the following schemes. One is to change the property of P-V multi-peak by adding a hardware compensation circuit, so that the output of the multi-peak photovoltaic system presents a single-peak characteristic, and then tracking is carried out by using a conventional MPPT method. And the second method is to adopt intelligent control methods based on a fuzzy algorithm, a particle swarm algorithm, a neural network and the like, and has higher rapidity and accuracy than a conventional algorithm under the condition of multi-peak output of a photovoltaic system. In the first method, the addition of the compensation circuit makes the system structure more complicated, resulting in a significant increase in cost. The second method has the defects of complicated parameter setting, generally relying on experience only, poor portability, difficult realization of engineering and the like.
Through retrieval, in the prior art, there are many schemes for realizing maximum power tracking, such as chinese patent application No. 201710106511.5, whose application date is 2017, 2 month and 27 day, the name of the invention creation is: a photovoltaic inverter multi-peak MPPT method based on an improved conductance incremental method; according to the application, real-time shadow monitoring is realized by taking photovoltaic array information as inverter control parameters, shadow change is accurately and effectively judged, the maximum power preliminary scanning is carried out by taking a sectional fixed step length point-to-incremental method as a global maximum power point scanning algorithm, and the global maximum power is accurately tracked by adopting a sectional variable step length conductance incremental method after the preliminary scanning is finished. The application can avoid the triggering of the power fluctuation to the global maximum power point scanning algorithm when no shadow exists, and can improve the scanning efficiency. However, the application has the defects that the parameter setting is complicated and generally only depends on experience, and further improvement is still needed in application.
Disclosure of Invention
1. Technical problem to be solved by the invention
The invention aims to overcome the defects in the prior art and provides a photovoltaic MPPT control circuit and a photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning.
2. Technical scheme
In order to achieve the purpose, the technical scheme provided by the invention is as follows:
The photovoltaic MPPT control circuit comprises a photovoltaic power supply and voltage scanning circuit, a switch conversion circuit and a load, wherein the photovoltaic power supply and voltage scanning circuit comprises a plurality of series-parallel photovoltaic panels, the output ends of the photovoltaic panels are connected with capacitors C1 in parallel, an ammeter IS and a switch K1 are connected between the output ends of the photovoltaic panels and the capacitors C1 in series, and a voltmeter VS1 IS connected to the capacitors C1 in parallel; a switch K2 is arranged between the capacitor C1 and the input end of the switch conversion circuit, the output end of the switch conversion circuit is connected with a load, and a voltmeter VS2 is connected in parallel on the load.
Furthermore, the switch conversion circuit is a BUCK, BOOST, BUCK-BOOST or CUK switch conversion circuit.
furthermore, the switching conversion circuit adopts a CUK circuit, the CUK circuit comprises a switching tube Q, an input end inductor L1, an output end inductor L2, an input-output coupling capacitor C2, freewheeling diodes D5, D6 and a diode D7, the anode of the freewheeling diode D5 is grounded, and the cathode of the freewheeling diode D5 is connected with the input end inductor L1; the anode of the diode D7 is connected with the cathode of the freewheeling diode D6, and the cathode of the diode D7 is connected with the load input terminal.
The invention relates to a photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning, which comprises four control stages, specifically: a scan preparation phase, a voltage scan phase, a PWM preparation phase and a PWM control phase, wherein:
1) Step1 scanning preparation phase: at the stage, the K1 is controlled to be disconnected, and the C1 is disconnected from the photovoltaic power supply; k2 is closed, the switch tube Q is conducted, C1 discharges to 0V through L1 and Q, and the stage is finished; if C1 is not charged, then this phase is skipped directly;
2) Step2 voltage scan phase: the stage controls K1 to close, K2 to open, the photovoltaic power supply is connected with C1 only, the CUK conversion circuit is isolated, and the C1 voltage is charged by the photovoltaic power supply from 0V to the open-circuit voltage U close to the photovoltaic power supplyOCAcquiring voltage and current of the output end of the photovoltaic power supply, and calculating instantaneous power through voltage and current signals;
3) Step3PWM preparation phase: at the stage, K1 and K2 are controlled to be closed all the time, Q is switched on and off alternately, and the Q is switched on and off through uC1And comprises ubesta window voltage (u) ofbest-A,ubest+ B) is compared to determine that Q is conducted when the window voltage is higher than the upper limit of the window voltage, and u is conducted after Q is conductedC1lowering the voltage to lower limit of window voltage, turning off Q, and turning off uC1The energy storage of C2, L1 and L2 is continuously increased by repeating the steps for a plurality of times until the average power of the photovoltaic is close to PmaxWhen so, the stage is ended;
4) Step4PWM stage: at the stage, the K1 and the K2 are controlled to be in a closed state all the time, and the voltage at the two ends of the C1 is always kept at u by controlling the on-off of QbestNearby, the photovoltaic power supply works at the maximum power point; when a deviation P of the average power of a certain period of time is detectedmaxAnd when a certain amount of time is needed, searching the maximum power point again, and repeating the process from Step1 to Step 4.
Furthermore, in the control process, the instantaneous power calculated by integrating the sampled voltage and current is filtered and compared with the average power in the previous unit timeComparing, and if not out of tolerance, participating the value in the pairOperation generates newOtherwise the value is discarded.
Furthermore, the Step2 voltage scanning phase generates new signals continuously by filtering in the scanning processUsing them in combination with PmaxCompare if, ifGreater than PmaxThen useUpdating Pmaxand will uC1Value update ubest(ii) a The starting voltage of the scanning process is 0V, and the end value of the scanning voltage is 0.95UOCThe global maximum power P is obtained at the end of the processmaxAnd its corresponding voltage ubest。
Further, Q is switched on and off via uC1And window voltage (0.95 u)best,1.05ubest) And carrying out comparison and determination.
further, when detectingor greater than 0.9PmaxThe restart algorithm searches for a new global maximum power point.
3. Advantageous effects
Compared with the prior art, the technical scheme provided by the invention has the following remarkable effects:
(1) According to the photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning, the voltage-power characteristic curve of photovoltaic output is known globally, the maximum power point of photovoltaic under the current environment is locked, the power curve of power relative to voltage change under the current environment is collected before control, interference of local power peak values can be eliminated in a limited way, and effective identification and tracking locking of the global maximum power point under the complex environment of local shadow are realized;
(2) The invention relates to a photovoltaic multimodal MPP (maximum power point tracking) quick tracking method based on voltage-power scanning, which is characterized in that instantaneous power calculated by multiplying sampled voltage and current in a control flow is filtered and then is compared with the average power in the previous unit timeperforming comparison to update average powerThe influence of external interference and internal noise on the correct operation of the control flow can be prevented;
(3) The invention relates to a photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning, which is characterized in that the end value of scanning voltage is set to be 0.95U in the voltage scanning stageOCThe distribution range of the global maximum power point can be ensured, and the time consumption of the scanning process is greatly reduced;
(4) The invention relates to a photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning, wherein a voltage window (0.95 u) is set in a PWM stagebest,1.05ubest)，uC1the Q is controlled to be turned on when the upper limit voltage of the window is higher than the lower limit voltage of the window, and the Q is controlled to be turned off when the lower limit voltage of the window is lower than the lower limit voltage of the window, so that the lower switching loss is kept, and the photovoltaic working point is stabilized at ubestNearby, the locking of the global maximum power point is realized;
(5) The photovoltaic MPPT control circuit is simple in structural design and convenient to realize, and has strong practicability by being combined with a photovoltaic multi-peak MPP fast tracking method based on voltage-power scanning.
drawings
Fig. 1 is a topological schematic diagram of a photovoltaic MPPT port voltage scanning main circuit according to the present invention;
FIGS. 2-5 are schematic diagrams of the working components of the port voltage scanning main circuit in different periods of time according to the present invention;
FIG. 6 is a waveform diagram of key signals in various working states of the present invention;
FIG. 7 is a main control flow chart of the present invention;
FIG. 8 is a control flow diagram of the voltage sweep stage of the present invention;
FIG. 9 is a control flow diagram of the PWM phase of the present invention;
FIG. 10 is a schematic diagram of a simulation model established by the present invention;
FIG. 11 is a waveform diagram of a simulation of the present invention;
Fig. 12 (a) and (b) show waveforms of voltage, power and current when the illumination intensity of the present invention is varied.
Detailed Description
for a further understanding of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings and examples.
The photovoltaic MPPT technology in a single-peak state or a multi-peak state at present considers a photovoltaic power supply as a black box, the voltage of a photovoltaic output end is disturbed by methods such as changing the duty ratio of a switching converter in a load state so as to change the output power of a photovoltaic panel, and whether and how to adjust the duty ratio in the next step are determined according to the change situation of the power. The method is characterized in that the disturbance is carried out under load, a large number of capacitive and inductive energy storage elements exist in a load circuit, the disturbance action is delayed under the action of the energy storage elements, and if the delay is improperly set, a correct signal cannot be obtained, and the system cannot obtain the maximum power point. Meanwhile, the energy utilization rate of the photovoltaic power supply is reduced due to the fact that multiple times of disturbance are needed and the adjustment time is long after each disturbance. The methods can meet the requirements for MPPT in a single-peak state with simpler control requirements, and the effect like 'blind feeling' is difficult to satisfy in a multi-peak state. The root cause of the above problem is that the controller has no global knowledge about the voltage-power characteristic curve of the photovoltaic output, and cannot lock the maximum power point of the photovoltaic under the current environment. Based on the above analysis, a power curve of power versus voltage change in the current environment must be collected before control to solve the above problem. The process is called photovoltaic output port voltage power scanning, and is called port voltage scanning for short. In order to reduce the power loss in the port scanning process, the time of the scanning process is required to be as short as possible and to reduce the signal distortion as much as possible on the premise of satisfying the sampling theorem.
Example 1
As shown in fig. 1, a photovoltaic MPPT control circuit of this embodiment IS a photovoltaic power supply and voltage scanning circuit, and includes a plurality of series-parallel photovoltaic panels, a capacitor C1 connected in parallel to a photovoltaic output terminal, switches K1 and K2 for switching a circuit connection relationship, and meters VS1 and IS for measuring an output terminal voltage and a current. And II is a switch conversion circuit which can be a BUCK, a BOOST or a BUCK-BOOST or a CUK switch conversion circuit, and the CUK circuit is selected in the embodiment. III is a load, and the load can be one or a combination of a storage battery, a direct current appliance or an inverter. The buck-boost circuit CUK is selected in the embodiment because the circuit is directed to an independent photovoltaic system, and the direct loads of the circuit are large-capacity lead-acid storage batteries B1 and B2. Because the voltage corresponding to the maximum power point is higher when the illumination is strong, the voltage needs to be reduced to charge the storage battery at the moment; and when the illumination is weak, the voltage corresponding to the maximum power point is low and may be lower than the charging voltage of the livestock battery, and at the moment, boosting charging is needed. The CUK circuit comprises a switching tube Q, an input end inductor L1, an output end inductor L2, an input and output coupling capacitor C2 and a freewheeling diode D6. In addition, in order to prevent the current mutation of the L1 from causing overvoltage to cause damage to the circuit when the K2 is switched off, a freewheeling diode D5 is arranged; a diode D7 is added on the basis of a CUK circuit for preventing the reverse discharge of the storage battery, and a voltmeter VS2 is used for measuring the terminal voltage of the storage battery.
The working process of the circuit for realizing the rapid MPPT of the embodiment is four in total: the method comprises a scanning preparation phase, a voltage scanning phase, a PWM preparation phase and a PWM control phase. With reference to fig. 2 to 6, the four working processes are specifically described as follows:
1) Step1 Scan preparation phase (time period t0-t1 in FIG. 6): the period is active as shown in fig. 2, and the inactive elements and lines are shown in dotted lines (the same applies below). At the moment, the K1 is controlled to be disconnected, and the C1 is disconnected from the photovoltaic power supply; k2 is closed, Q is on, C1 discharges to 0V through L1 and Q, and this phase ends. If C1 is not charged, the process is directly skipped.
at this stage, the photovoltaic array is in an open circuit state, and energy cannot be transmitted to the load end, sothis process should be as short as possible in order to improve the overall energy conversion efficiency. The stage is prepared for the next step of scanning a voltage power curve, so that the main aim of discharging the C1 is to discharge the C1, and a loop1 is used for realizing the aim, and in an ideal state, the equivalent series resistance of the C1 and the L1 and the on-state resistance of the Q in the loop1 loop are small and can be ignored. Therefore, the loop is a series second-order zero-input response circuit consisting of C1 and L1, and the discharge time is C1 capacitance C1Inductance L11And the initial voltage u of the C1 at t0c1(t0), initial current i of L1L1(t0) four main factors are determined and should satisfy the following relationships (in the following equations, only the reference direction of the voltage or current is labeled on the same element in fig. 1, and the reference direction of the voltage or current for the non-labeled reference direction is determined in the associated reference relationship with the scalar quantity, the same applies below):
KVL：-uc1+uL1＝0
KCL：i(t)＝-ic1(t)＝iL1(t)
The comprehensive formula can be obtained:
The characteristic equation of the second-order circuit is as follows:
L1C1S2+1＝0
The characteristic root is a pair of conjugate pure virtual roots:
The initial voltage of C1 is u according to t0c1(t0), the initial current of L1 is iL1(t0), it is found that:
the time required for the voltage at C1 to drop from its initial value to zero would be:
2) Step2 voltage scan phase (time period t1-t2 in fig. 6): in the activated state in the period, as shown in fig. 3, the control K1 is closed, the control K2 is opened, the photovoltaic power supply is connected with C1 only, and the CUK conversion circuit is isolated. The voltage of C1 is charged by the photovoltaic power supply from 0V to near the open-circuit voltage U of the photovoltaic power supplyOC. The process must accurately collect the voltage and current at the output end of the photovoltaic power supply through a sensor or a meter, and calculate the instantaneous power through hardware or software according to the voltage and current signals. The voltage power curve of the photovoltaic power supply is scanned through the process, and the theoretical maximum power point PmaxAnd its corresponding voltage ubestWill also be calculated. Therefore, accurate measurement and recording of data in this process is critical to achieving fast MPPT.
However, since the photovoltaic array does not operate at the maximum power point for most of the time in this process, the duration of the photovoltaic array should be as short as possible based on satisfying the AD sampling time, and the value is determined by the loop3, which has the following relationship:
KVL：uPV-uC1＝0
KCL：i(t)＝iPV＝iC1
Can be combined to obtain
The length of time consumed and iPVAnd C1 capacitance, and iPVAnd depends on factors such as the light, temperature, etc. of the environment in which it is located. In order to qualitatively analyze the relationship between them, the analysis calculation was performed by taking the illumination distribution S2 as an example under the standard temperature condition. From table 1, it can be known that the photovoltaic output current under the condition is divided into four regions, each region has an inflection point, the current before the inflection point is close to a constant, and the current after the inflection point is suddenly reduced to the stable current of the next region. For simplifying the analysis calculation, the current before the inflection point is regarded as a constant, and the curve after the inflection point is regarded as a straight line, so eight different intervals are obtained, and the current of each interval is shown in table 2.
TABLE 1 characteristics of each operating region with illumination intensity distribution S2
TABLE 2 approximate and average currents for each operating window with illumination intensity distribution S2
The eight intervals in table 2 are integrated to obtain:
3) Step3PWM preparation phase (period t2-t5 in fig. 6): after the last stage, only C1 is in a fully charged state, the energy storage elements such as C2, L1 and L2 are in a state of no energy storage or a small amount of energy storage, and a transient process is needed before the CUK enters a steady state. In the process, K1 and K2 are controlled to be closed all the time, Q is controlled to be switched on and off alternately, and the ideal target for controlling the on and off of Q is to enable u to be switched on and offC1Is always equal to ubest. However, the C1 continuously exchanges energy u with the outsideC1Also dynamically changing, so the ideal state is difficult to achieve, we can only go back to the next order uC1At ubestThe vicinity fluctuates. Q can thus be switched on and off by uC1And comprises ubestA window voltage (u) ofbest-A,ubest+ B) is compared to determine that Q is conducted when the window voltage is higher than the upper limit of the window voltage, and u is conducted after Q is conductedC1Lowering the voltage to lower limit of window voltage, turning off Q, and turning off uC1The energy storage of C2, L1 and L2 is continuously increased by repeating the steps for a plurality of times until the average power of the photovoltaic is close to PmaxWhen this is the case, this phase ends.
4) Step4PWM phase (period t5-t7 in FIG. 6): the CUK circuit enters a steady-state working state, the control K1 and the control K2 are still in a closed state all the time, and the voltage at two ends of the C1 is always kept at u through the on-off control of Qbestnear, photovoltaic power supplies operate at maximum power points. When a deviation P of the average power of a certain period of time is detectedmaxIf the amount is a certain amount, the process from Step1 to Step4 is retried because the external environment changes and the maximum power point needs to be searched again.
The on-state process and the off-state process of the two PWM preparation and PWM periods are active components as shown in fig. 4 and 5, respectively. The transformation ratio formula of the output voltage and the input voltage of the CUK circuit is as follows, wherein D is the control pulse duty ratio of the switching tube Q:
referring to fig. 7, the main control flow of the present embodiment mainly selects the four subroutines Step1-Step4 by different condition determinations to accomplish the control objectives of the different stages. First, system initialization is performed, and then according to uC1If it is 0, branch selection is made. u. ofC1If not, executing step1 subroutine to quickly discharge C1; u. ofC1if 0, Step1 is skipped and the routine goes directly to Step 2. After Step2 is finished, the PWM preparation phase subroutine Step3 and the PWM phase subroutine Step4 are sequentially performed. When the environment changes, the environment is detectedLess than 0.9Pmaxor greater than 1.1PmaxThe restart algorithm searches for a new global maximum power point.
To prevent fromthe influence of external interference and internal noise on the correct operation of the control flow is avoided, the photovoltaic output power is also unlikely to change suddenly in consideration of the continuity of the change of the real environment, the instantaneous power calculated by the product of the sampled voltage and current in the control flow is filtered, and the instantaneous power and the average power in the previous unit time (the time is determined by specific circuit parameters and sampling time) are combinedMaking a comparison if the absolute value of the difference does not exceedthe value is added and then averaged to generate a new valueOtherwise the value is discarded.
The flow of Step2 subroutine is shown in fig. 8, and from the foregoing analysis, the objective at this stage is to scan the photovoltaic power curve and select the global maximum power point PmaxAnd the corresponding voltage ubest. New ones are generated by filtering continuously during scanningUsing them in combination with Pmaxcompare if, ifGreater than PmaxThen useUpdating PmaxAnd will uC1Value update ubest. The starting voltage of the scanning process is 0V, and it can be seen from Table 2 that u is small due to the small currentC1The rise time in the last interval accounts for approximately 40% of the total elapsed time, but the probability of the global maximum power occurring in the second half of the region is close to 0. Thus, the algorithm sets the end of scan voltage value to 0.95UOCNot only can ensure the distribution range of the global maximum power point, but also can greatly reducethe scanning process is time consuming.
The control flow in the PWM phase is shown in FIG. 9, where the goal is to apply the photovoltaic output voltage, i.e., uC1Is locked at ubestSame as the PWM preparation phase, also face the first uC1Is dynamically adjusted, e.g. directly with uC1and ubestthe comparison result is used as a signal for controlling the switching tube Q, which causes the switching frequency to be too high and the switching loss to rise. Therefore, the present embodiment sets a voltage window (0.95 u)best,1.05ubest)，uC1and controlling Q to be opened when the voltage is higher than the upper limit voltage of the window, and controlling Q to be closed when the voltage is lower than the lower limit voltage of the window. Therefore, the switching loss can be kept low, and the photovoltaic working point can be stabilized at ubestAnd nearby, locking the global maximum power point.
To verify the feasibility of the present embodiment, a simulation model was created in Matlab software as shown in fig. 10, in which the illumination intensity value of PV1 was set to be 1000, the illumination intensities of PV2 and PV3 were the same and adjustable, and were set to be variable Ir2, and the illumination intensity of PV4 was also adjustable, and were set to be variable Ir 3. The values of Ir2 and Ir3 in time domains (0-1 ms), (1-2 ms) and (2-3 ms) after the start of the simulation are (1000,500), (500,250) and (750,500), respectively. As can be seen from the waveform diagram 11 of the photovoltaic output power, the embodiment can find and rapidly perform global scanning to find the maximum power point within 0.5ms after the illumination intensity changes, and can stably lock the system operating point near the global maximum power point.
In order to verify the working performance of a designed circuit and an algorithm, a photovoltaic maximum power point tracking test device is manufactured, and the main parameters are as follows:
TABLE 3 Main parameters of the test apparatus
The photovoltaic panel is irradiated by four independent adjustable light sources, the change of illumination intensity under the natural condition is simulated, local shadows are generated to check the working performance of the system, and (a) in fig. 12 is the voltage, power and electricity of the photovoltaic output end when the illumination intensity is weakened from strongThe flow waveform (b) in fig. 12 corresponds to a case where the illumination intensity changes from weak to strong. Δ t1The delay time from the illumination change to the starting algorithm; Δ t2The algorithm is validated to the time to track and lock to the global maximum power point and reach steady state. It can be seen from the figure that the total adjustment time Δ t of the algorithm is no matter whether the illumination is changed from strong to weak or from weak to strong1+Δt1All are less than 1ms, and the reaction is quick. The tracked power point is closer to the maximum power point obtained by simulation from the power waveform, which shows that the embodiment can limitedly eliminate the interference of the local power peak value, and realize effective identification and tracking locking of the global maximum power point in the complex environment of local shadow.
The present invention and its embodiments have been described above schematically, without limitation, and what is shown in the drawings is only one of the embodiments of the present invention, and the actual structure is not limited thereto. Therefore, if the person skilled in the art receives the teaching, without departing from the spirit of the invention, the person skilled in the art shall not inventively design the similar structural modes and embodiments to the technical solution, but shall fall within the scope of the invention.

Claims (4)

1. a photovoltaic multimodal MPP rapid tracking method based on voltage-power scanning is characterized in that: the photovoltaic MPPT control circuit used by the method comprises a photovoltaic power supply and voltage scanning circuit, a switch conversion circuit and a load, wherein the photovoltaic power supply and voltage scanning circuit comprises a plurality of series-parallel photovoltaic panels, the output ends of the photovoltaic panels are connected with capacitors C1 in parallel, an ammeter IS and a switch K1 are connected between the output ends of the photovoltaic panels and the capacitors C1 in series, and a voltmeter VS1 IS connected on the capacitor C1 in parallel; a switch K2 is arranged between the capacitor C1 and the input end of the switch conversion circuit, the output end of the switch conversion circuit is connected with a load, and a voltmeter VS2 is connected in parallel on the load;
The switch conversion circuit adopts a CUK circuit, the CUK circuit comprises a switching tube Q, an input end inductor L1, an output end inductor L2, an input and output coupling capacitor C2, freewheeling diodes D5, D6 and a diode D7, the anode of the freewheeling diode D5 is grounded, and the cathode of the freewheeling diode D5 is connected with the input end inductor L1; the anode of the diode D7 is connected with the cathode of the freewheeling diode D6, and the cathode of the diode D7 is connected with the load input end;
The method comprises four control stages, specifically: a scan preparation phase, a voltage scan phase, a PWM preparation phase and a PWM control phase, wherein:
1) Step1 scanning preparation phase: at the stage, the K1 is controlled to be disconnected, and the C1 is disconnected from the photovoltaic power supply; k2 is closed, the switch tube Q is conducted, C1 discharges to 0V through L1 and Q, and the stage is finished; if C1 is not charged, then this phase is skipped directly;
2) Step2 voltage scan phase: the stage controls K1 to close, K2 to open, the photovoltaic power supply is connected with C1 only, the CUK conversion circuit is isolated, and the C1 voltage is charged by the photovoltaic power supply from 0V to the open-circuit voltage U close to the photovoltaic power supplyOCAcquiring voltage and current of the output end of the photovoltaic power supply, and calculating instantaneous power through voltage and current signals;
3) Step3PWM preparation phase: at the stage, K1 and K2 are controlled to be closed all the time, Q is switched on and off alternately, and the Q is switched on and off through uC1And window voltage (0.95 u)best,1.05ubest) Comparing and determining, and turning on Q when the window voltage is higher than the upper limit of the window voltage, and after Q is turned on, u is turned onC1lowering the voltage to lower limit of window voltage, turning off Q, and turning off uC1The energy storage of C2, L1 and L2 is continuously increased by repeating the steps for a plurality of times until the average power of the photovoltaic is close to PmaxWhen so, the stage is ended;
4) Step4PWM phase: at the stage, the K1 and the K2 are controlled to be in a closed state all the time, and the voltage at the two ends of the C1 is always kept at u by controlling the on-off of QbestNearby, the photovoltaic power supply works at the maximum power point; when a deviation P of the average power of a certain period of time is detectedmaxAnd when a certain amount of time is needed, searching the maximum power point again, and repeating the process from Step1 to Step 4.
2. The photovoltaic multimodal MPP fast tracking method based on voltage-power scanning as claimed in claim 1, wherein: in the control process, the instantaneous power calculated by integrating the sampled voltage and current is filtered and averaged with the average power in the previous unit timePower ofmaking a comparison if the absolute value of the difference does not exceedparticipating the instantaneous power value in the pairOperation generates newotherwise the instantaneous power value is discarded.
3. The photovoltaic multimodal MPP fast tracking method based on voltage-power scanning as claimed in claim 2, wherein: step2 voltage scanning stage, generating new voltage continuously by filtering in the scanning processUsing them in combination with PmaxCompare if, ifGreater than PmaxThen useUpdating PmaxAnd will uC1value update ubest(ii) a The starting voltage of the scanning process is 0V, and the end value of the scanning voltage is 0.95UOCThe global maximum power P is obtained at the end of the processmaxAnd its corresponding voltage ubest。
4. the photovoltaic multimodal MPP fast tracking method based on voltage-power scanning as claimed in claim 3, characterized in that: when detecting thatLess than 0.9PmaxOr greater than 1.1PmaxThe restart algorithm searches for a new global maximum power point.
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