CN103744469A - Multi-peak maximum power point tracking method of photovoltaic inverter - Google Patents
Multi-peak maximum power point tracking method of photovoltaic inverter Download PDFInfo
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Abstract
The invention discloses a multi-peak maximum power point tracking method of a photovoltaic inverter. Coarse scanning and fine scanning are performed alternately during a scanning step, the coarse scanning determines the local areas of crests, the fine scanning determines the local maximum power points in the local areas of the crests, the maximum power points of the whole P-V curve are found from the local maximum power points, and maximum power points tracking is achieved. The scanning step further comprises a scanning initializing step which determines the scanning range, the known areas, the minimum power judging points and the scanning directions. The method has the advantages that scanning time is reduced greatly by setting the scanning range, the known areas and the minimum power judging points, and excessive large voltage fluctuation caused by scanning is reduced by setting the scanning directions; maximum power point tracking is achieved accurately through the coarse scanning and the fine scanning, and voltage fluctuation is reduced by the coarse scanning and the fine scanning which are performed alternately.
Description
technical field
The present invention relates to photovoltaic DC-to-AC converter technical field, particularly a kind of multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter.
Background technology
Because solar panel in photovoltaic DC-to-AC converter exists the I-V(current-voltage as shown in Fig. 1 (a)) curve characteristic, cause its P-V(power-voltage) output characteristic curve is epirelief parabolic shape, as shown in Fig. 1 (b).According to the characteristic of P-V curve, photovoltaic DC-to-AC converter needs constantly to regulate the DC reference voltage of self, makes stable output power on the top of P-V curve, and maximum power point (MPP) is located, and it has higher inversion efficiency guarantee.By regulating DC reference voltage to obtain the more method of multi output power, be called maximum power point tracking (MPPT).
Because the power of the solar panel of monolithic is too small and output voltage only has tens volts, and photovoltaic DC-to-AC converter is all often to take kilowatt output power as unit, grid-connected voltage is also far above the output voltage of monoblock battery plate, therefore, in actual applications, cell panel all provides direct current in the mode of group string.Under the pattern of cell panel formation group string array, if during normal power generation, panel array exists that local shade blocks that (as cloud, dust), cell panel parameter are inconsistent, cell panel temperature rise square one not each other, can cause the P-V curve of cell panel not overlap, thereby the whole P-V curve that causes cell plate group string presents the form of multi-peak, as shown in Figure 2.
Traditional MPPT, be by continuous relatively before and after voltage and the power of point, come gradually close to optimum direction, until be stabilized in a peak point place.But, occurring under the P-V curve condition of multi-peak, traditional MPPT only can start to find from open-circuit voltage (being the low order end of P-V curve), after finding first peak point (the D point in Fig. 2), just no longer continue to find, but be stabilized in D point, thus fail to find real peak power point (real peak power point is at C point), cause certain power generation loss.
In order to solve the problem that can not accurately find peak power point when traditional MPPT faces multi-peak situation, someone has proposed first to carry out P-V curve and has scanned comprehensively, analyzes each peak point position, then carries out conventional maximum power point tracking.Although the method can be found out peak power point accurately, but still there are three defects: 1) P-V curve is scanned comprehensively, will inevitably make DC reference voltage be reduced to minimum point from the peak of MPPT voltage range, cause output power to present larger fluctuation; 2) in order to guarantee the accuracy of scanning, scanning step need arrange littlely, can cause sweep time longer, if increase scanning step, the phenomenon that easily occurs crossing over again crest, causes scanning inaccurate; 3) scanning triggers the timing scan that adopt more, and it is larger that sweep frequency arranges difficulty, if scanning too frequently can cause power dissipation, the number of times of scanning may cause again accurately tracking maximum power point very little.
Summary of the invention
The object of the invention is to overcome the deficiency that in prior art, the existing maximum power point tracking of scanning is inaccurate comprehensively, sweep time is long, a kind of multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter is provided, in the situation that ensureing accurate tracking maximum power point, avoid voltage fluctuation large, reduce sweep time.A further object of the present invention is reasonably under scanning triggering mode, to scan, accurately following the trail of maximum power point.
In order to realize foregoing invention object, the invention provides following technical scheme:
A multi-peak maximum power point tracking method for photovoltaic DC-to-AC converter, comprises scanning step, and described scanning step is:
According to coarse scanning step-length, carry out coarse scanning, determine between adjacent two constant power points and whether have crest, if existed, in the regional area between these adjacent two constant power points, according to close scanning step-length, carry out close scanning, mark the local maximum power point in this regional area, then continue to carry out coarse scanning according to aforesaid coarse scanning step-length and determine next local maximum power point; Process coarse scanning and close scanning intert to be carried out, and marks the local maximum power point in crest place regional areas all in sweep limit; Finally according to the local maximum power point in each regional area, find out the maximum power point in whole sweep limit; Described constant power point is the intersection point of constant power straight line in sweep limit and P-V curve, and described constant power straight line is less than the power of current MPPT by performance number and power points that both differ setting value forms.
Preferably, in said method, before scanning step, also comprise scanning initialization step: ceiling voltage and the minimum voltage of according to the open-circuit voltage of inverter, determining sweep limit, and the voltage that judges current MPPT respectively with the difference of ceiling voltage and minimum voltage, if the difference of the voltage of current MPPT and ceiling voltage is greater than the difference of voltage and the minimum voltage of current MPPT, in scanning step from low-voltage to high voltage scanning direction, otherwise from high voltage to low-voltage scanning direction.The object of setting direction of scanning is in order to start scanning from the lower one end of voltage difference, the voltage fluctuation while scanning to reduce.
Preferably, in said method, 60%～90% of the open-circuit voltage that described sweep limit is photovoltaic DC-to-AC converter, 60% of open-circuit voltage is the minimum voltage of sweep limit, 90% of open-circuit voltage is the ceiling voltage of sweep limit.60%～90% of the open-circuit voltage of take is sweep limit, has avoided whole voltage range to scan, and has reduced sweep time greatly.
Preferably, in said method, in scanning initialization step, also comprise step: according to the voltage of current MPPT, the voltage regime of the voltage phase difference setting voltage value of mark and current MPPT is local non-scanning area.Because the crest in the non-scanning area in part is known, do not there is scanning meaning, while therefore scanning in sweep limit, for the non-scanning area in part, do not scan, further to reduce sweep time.
Further, in said method, in scanning step, when carrying out coarse scanning, according to coarse scanning step-length, often move and move a step, record voltage and the power of respective point in a P-V curve, and the intersection point of mark P-V curve and constant power straight line is constant power point, often mark a constant power point, according to the derivative of constant power point and direction of scanning, judge between current constant power point and previous constant power point whether have crest, if exist, carry out close scanning in the regional area between these two constant power points, otherwise proceed coarse scanning.
Further, in said method, describedly according to the derivative of constant power point and direction of scanning, judge between current constant power point and previous constant power point whether exist the method for crest to be: from low-voltage to high voltage scanning direction, if the derivative of previous constant power point is for just, for negative, between these adjacent two constant power points, there is crest in the derivative of current constant power point; From high voltage to low-voltage scanning direction, if the derivative of previous constant power point is negative, for just, there is crest between these adjacent two constant power points in the derivative of current constant power point.
Preferably, in above-mentioned steps, before scanning initialization step, also comprise that scanning triggers determining step, described scanning triggers determination methods: every an environment temperature judgement cycle, carry out an environmental temperature fluctuation and detect, within an environment temperature judgement cycle, if environment temperature rises or declines, surpass design temperature undulating quantity, trigger a multimodal scanning, otherwise not trigger sweep.
As another kind of embodiment, described scanning triggers determination methods: every a power electric current judgement cycle, carry out output power and output current fluctuation detects, at a power electric current in the judgement cycle, if the output power of inverter rises or declines over the power swing value of setting, and output current also rises or declines over the current fluctuation value of setting, trigger a multimodal scanning, otherwise not trigger sweep.
As another kind of embodiment, described scanning triggers determination methods: the temperature difference in judgement inverter between panel array, if the temperature difference between adjacent two panel arrays surpasses the temperature value of setting, and it is different that adjacent twice sweep triggers Rule of judgment, trigger a multimodal scanning, otherwise not trigger sweep.
compared with prior art, beneficial effect of the present invention:
The multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter of the present invention comprises scanning initialization step and scanning step, in scanning initialization step, by the setting of sweep limit, known region, lowest power judging point and direction of scanning, reduce sweep time greatly, improved scan efficiency.In scanning step, comprise coarse scanning stage and close scanning stage, the coarse scanning stage determines whether regional area exists crest, the close scanning stage is determined the local maximum power point in the regional area that has crest, last local maximum power point in each regional area, find out the maximum power point of whole P-V curve, realize peak power point tracking, effectively solve traditional MPPT and may find the shortcoming less than GMPP in multimodal situation; And coarse scanning and close scanning intert to be carried out, and after regional area close scanning finishes, returns and proceeds coarse scanning, avoids voltage fluctuation excessive.
In addition, the inventive method adopts three kinds of scannings to trigger judgment mode and scans triggering judgement, just trigger sweep when meeting trigger condition, the drawback of having avoided traditional timing scan to bring, reduced the disturbance that scanning itself brings, shorten sweep time, promoted the efficiency of scanning, indirectly promoted the work efficiency of photovoltaic DC-to-AC converter.
Accompanying drawing explanation:
Fig. 1 (a) is the current-voltage curve figure of monoblock battery plate in photovoltaic DC-to-AC converter; Fig. 1 (b) is the power-voltage curve of monoblock battery plate in photovoltaic DC-to-AC converter.
Fig. 2 is the power-voltage curve of cell plate group string in photovoltaic DC-to-AC converter.
Fig. 3 is the process flow diagram of maximum power point tracking method of the present invention.
Fig. 4 carries out multimodal in maximum power point tracking process for application the inventive method and scans schematic diagram.
Embodiment
Below in conjunction with test example and embodiment, the present invention is described in further detail.But this should be interpreted as to the scope of the above-mentioned theme of the present invention only limits to following embodiment, all technology realizing based on content of the present invention all belong to scope of the present invention.
With reference to figure 3, Fig. 4, the LMPP in Fig. 4 (Local Maximum Power Point) is local maximum power point, represents regional area maximum value position point in powertrace, and regional area maximum value refer to the power maximal value in this regional area; GMPP(Global Maximum Power Point) be global maximum power point, represent in whole powertrace, the location point at maximum maximum value place.
The multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter of the present invention, comprises scanning initialization step and scanning step, and wherein scanning step comprises again coarse scanning step and close scanning step.With reference to figure 3, concrete, the inventive method comprises the following steps:
S1: in the situation that multimodal scanning is triggered, judge whether to scan initialization, if not, enter S2, scan initialization procedure; If yes then enter S3, enter sweep phase.
S2: scan initialization, initialization procedure comprises the following steps:
S21: record voltage U and the power of current MPPT, and determine lowest power judging point according to the performance number of current MPPT, at sweep phase, power does not carry out close scanning lower than the region of lowest power judging point.Simultaneously, the voltage regime of the voltage phase difference voltage U 0 of mark and current MPPT is known region, be region [U-U0, U+U0] be labeled as known region, so-called known region refers to the crest known (inverter operates in this place originally) in this region, therefore do not need this region to scan, therefore can be described as again local non-scanning area.
With reference to there being a minimum voltage distance (depending on cell panel quantity and physical characteristics factor) between 4, two crests of figure, in this voltage distances length, can not there are two crests.Therefore mark known region, can skip known region scanning (known region not being scanned), to reduce sweep time during scanning.For example, suppose that in Fig. 4, B point position is 540V, C point position is 650V, and current MPPT is in C point crest location, and voltage U 0 value is 20V, and known region is 630V～670V so, does not need scanning in 630V～670V region during scanning.
S22: ceiling voltage and the minimum voltage of determining sweep limit according to open-circuit voltage, and the voltage that judges current MPPT respectively with the difference of ceiling voltage and the difference of minimum voltage, the difference of the voltage of definition ceiling voltage and current MPPT is U1, defining the voltage of current MPPT and the difference of minimum voltage is U2, if U1≤U2, enters S23; Otherwise enter S24.
P-V curve presents multi-peak state and generally comes across the time period that sunlight is more sufficient (got rid of early morning and other evening), and at sunlight in more sufficient time period, the open-circuit voltage of cell panel is that relatively determine, stable numerical value.According to the characteristic of multimodal P-V curve, GMPP be usually located at open-circuit voltage 60% ~ 90% between position, therefore, 60% ~ 90% the scope interscan at open-circuit voltage can reduce a large amount of sweep times, therefore 60% ~ 90% scope of open-circuit voltage is defined as to sweep limit, 60% of open-circuit voltage is the minimum voltage of sweep limit, and 90% of open-circuit voltage is the ceiling voltage of sweep limit.For example, cell panel open-circuit voltage is 800V, sweep limit is 480V ~ 720V so, that is to say in this voltage range, can carry out primary voltage scanning from low to high or from high to low, if (be voltage from low to high) scanning from left to right, 720V is exactly end position, if turn left from the right side (be voltage from high to low), 480V is exactly end position.The voltage of supposing current MPPT is 650V, and due to 650V-480V>720V-650V, multimodal scanning is from turning left in the right side, and 480V is exactly scan end position.The voltage span that moves to 720V from 650V only has 70V, and has 170V from the voltage span that 650V moves to 480V, in order to reduce as much as possible the fluctuation of voltage, therefore chooses the scanning of turning left from the right side.
S23: the scanning (from high voltage to low-voltage scanning direction) of turning left from the right side at sweep phase, before scanning, first judge whether ceiling voltage position belongs to known region, if belonged to, scan start point is current MPPT voltage location point of living in, that is to say from current MPPT voltage location of living in and starts scanning; If do not belonged to, scan start point is ceiling voltage position.Then enter sweep phase.
S24: scan from left to right (from low-voltage to high voltage scanning direction) at sweep phase, before scanning, first judge whether minimum voltage position belongs to known region, if belonged to, scan start point is current MPPT voltage location point of living in, if do not belonged to, starts scanning from minimum voltage position.Then enter sweep phase.
In step S23 and S24, after having determined direction of scanning, further determine scan start point, as previously mentioned, in the known region of current MPPT voltage location of living in, do not need to scan, therefore judge that whether ceiling voltage and minimum voltage are at known region, if just do not start scanning from ceiling voltage/minimum voltage at known region, further reduce sweep time.
S3: before carrying out multimodal scanning, first judge current whether been scanned, if been scanned enters S4, enter the Information Statistics stage; If there is no been scanned, proceed scanning.Scanning process comprises coarse scanning and close scanning, concrete:
Under the coarse scanning stage, for example, according to coarse scanning step-length (coarse scanning step-length refers to larger step-length, 20V mono-step), scan and move, and record voltage and the power information of each step scanning.In coarse scanning process, once, first the end position that whether can surpass sweep limit is moved in judgement next time, if can surpass end position, stops scanning next time, enters the Information Statistics stage in every movement; If can not surpass end position, continue mobile.Judge that the mobile method that whether can surpass the end position of sweep limit is next time, judge whether the distance of end position and current location is less than coarse scanning step-length, if distance is less than coarse scanning step-length, mobile meeting next time surpasses end position.Simultaneously in scanning moving process, judge between the power whether lowest power judging point move for twice in front and back, if between the power that lowest power judging point moves for twice in front and back, constant power point of mark, the voltage that the front and back two step average voltages of take are constant power point.According to the derivative of constant power point and direction of scanning, determine that between every two constant power points be crest or trough.Take direction of scanning for scanning be from left to right example, the derivative of previous constant power point is for just, the derivative of a rear constant power point is to bear, and is crest so between these adjacent two constant power points; Otherwise the derivative of previous constant power point is for negative, the derivative of a rear constant power point, for just, is trough between these adjacent two constant power points so.If be crest between current constant power point and previous constant power point, take the ending point that this constant power point is close scanning region, the starting point that previous constant power point is close scanning region, enters the close scanning stage.If be trough between current constant power point and previous constant power point, do not carry out close scanning, with this, further reduce sweep time.
It should be noted that, the setting of coarse scanning step-length is quite important, if arrange to such an extent that too little meeting causes sweep time long, if arrange too greatly, can cause having a plurality of crests and trough between two constant power points, and then cause MPPT trace location inaccurate.The setting of coarse scanning step-length is relevant with the physical parameter of cell panel, by emulation, obtains P-V curve, to obtain suitable coarse scanning step-length, is unlikely to sweep time to ensure in long and between two constant power points, only has a crest or trough ensureing.
With reference to figure 4, suppose that in current P-V curve, A point power is 60W, B point is 140W, C point is 100W, and photovoltaic DC-to-AC converter is just running on C point place at present.If now multimodal triggers judgement and sends scanning application, require inverter to carry out multimodal scanning, for fear of unnecessary judgement, improve scan efficiency, inverter is according to current power (100W), down mark a constant power straight line (for example getting 80W), the power of this constant power straight line is lowest power judging point (80W is lowest power judging point), constant power straight line does not carry out close scanning with lower area (being that power is lower than the region of lowest power judging point), because constant power straight line is necessarily very low with the power of lower area, even if there is crest to exist also not in all senses, as A point, the meaning that there is no close scanning.Therefore lowest power judging point is set, avoids too much sweep time.
With reference to figure 4, in the process of coarse scanning, must have the both sides up and down that two scanning sample points lay respectively at constant power straight line, between these two scanning sample points, (comprise this two scanning sample points) and certainly exist a point, its power equals the power of constant power straight line, this point is defined as constant power point, that is to say that the intersection point of constant power straight line and P-V curve is defined as constant power point, and the voltage of getting constant power point is the mean value of two scanning sample point voltages of the upper and lower both sides of constant power straight line.As shown in Figure 4, the voltage of two scanning sample points is respectively 480V and 500V(coarse scanning step-length is 20V), between these two scanning sample points, there is a constant power point (No. 1 constant power point shown in figure).Owing to there not being straight-line segment in P-V curve, therefore between any two constant power points, must there is a crest or trough, according to the derivative at constant power point place and direction of scanning, can judge between two constant power points it is crest or trough.
Under the close scanning stage, according to close scanning step-length (less step-length, as 10V mono-step), scan and move, and record voltage and the power information of each step.In a close scanning region, when scanning power peak, carry out LMPP mark one time, then exit close scanning, get back to the position of coarse scanning stage final step, proceed coarse scanning.Coarse scanning is to find out crest place regional area, and close scanning is in this regional area, to find out the power points at crest place.As shown in Figure 4, for example, carry out from right to left coarse scanning, when scanning No. 3 power points, found out No. 3 and No. 4 two constant power points, judge so between these two constant power points and have crest or trough; Through judging between these two constant power points, there is crest, now from current location (No. 3 constant power points), be retracted into constant power point No. 4 at once, carry out close scanning left; After verifying crest C, get back at once again current location, continue to carry out coarse scanning left.If first carry out coarse scanning, after finishing, coarse scanning carries out again close scanning, and can cause so voltage fluctuation excessive.In the inventive method, coarse scanning and close scanning intert to be carried out, if scan certain regional area in coarse scanning process, there is crest, enter the close scanning stage, find out the peak power point in this region, after this regional area close scanning finishes, return again and proceed coarse scanning, with this, avoid voltage fluctuation excessive.
S4: under the Information Statistics stage, relatively all LMPP points of mark, draw prominent GMPP position in all LMPP points, completes to obtain the maximum power point tracking of multi-peak.
Adopt timing scan triggering mode, find suitable trigger rate, through the maximum power point tracking method of above-mentioned multi-peak, also can find out comparatively accurately, faster maximum power point.But it is larger that sweep frequency arranges difficulty, if scanning too frequently can cause power dissipation, the number of times of scanning may cause again accurately tracking maximum power point very little.In addition, cause the basic reason of the appearance of multimodal P-V curve to have three kinds: the intensity of illumination inconsistent (shade, dirt problems) that cell panel receives each other; Between cell plate group string, there is certain temperature difference (caused by many factors, intensity of illumination is inconsistent also can cause temperature difference); Cell panel physical parameter each other inconsistent (cell panel type difference causes).Because the inconsistent reason of the light intensity that causes receiving between cell panel is complicated and changeable), and also approximate random (hot spot effect etc.) of some reason of occurring of temperature difference, therefore, with timing scan triggering mode, solve a random case a bit unreasonable.
Therefore, in the present embodiment, provide a kind of scanning of more science to trigger judgment mode, concrete, comprise step:
(1) judge that whether current time is in allowing to carry out the time period of multimodal scanning, if allowed, enter step (2), if do not allowed, refuse multimodal scanning and trigger.That is to say, judge that inverter is current whether in multimodal scan period, if inverter is current, in multimodal scan period, stops scanning and trigger judgement, only at inverter, during stable operation, just carry out trigger sweep judgement.
(2) every an environment temperature judgement cycle, carry out an environmental temperature fluctuation and detect, within an environment temperature judgement cycle, if environment temperature rises or declines, surpass design temperature undulating quantity, trigger a multimodal scanning, otherwise not trigger sweep.After application multimodal been scanned, take this time constantly as initial time, take this environment temperature is constantly initial temperature, enters the next environment temperature judgement cycle.For example the set environment temperature judgement cycle is 30 minutes, and the undulating quantity of environment temperature is set as 3 ℃.The time when inverter of take brings into operation is initial time (the 0th minute), and the initial time of take environment temperature constantly, as initial temperature T0, is supposed T0=25 ℃.Between the 0th minute to the 29th minute and 59 seconds, if environment temperature surpasses 28 ℃ (T0+ undulating quantity) or lower than 22 ℃ (T0-undulating quantitys), apply for that a multimodal scanning triggers.If between the 0th minute to the 29th minute and 59 seconds, environment temperature does not surpass 28 ℃ and lower than 22 ℃, and, when timing is in the time of full 30 minutes, the time of take is now new initial time, and take this environment temperature is constantly initial temperature, enters new one and takes turns the cycle.
Every a power electric current judgement cycle, carry out output power and output current fluctuation detects, at a power electric current in the judgement cycle, if output power rises or declines over the power swing value of setting, and output current also rises or declines over the current fluctuation value of setting, trigger a multimodal scanning, otherwise not trigger sweep.After application multimodal been scanned, take this time constantly as initial time, take this output current is constantly initial current, this output power is constantly initial power, enters the next power electric current judgement cycle.
Temperature difference between judgement panel array, if exist temperature difference and temperature difference to surpass the temperature value of setting between adjacent two panel arrays, and adjacent twice triggering Rule of judgment is identical, be that adjacent twice trigger condition is that temperature difference between same Battery pack plate array surpasses the temperature value of setting, do not trigger multimodal scanning; If adjacent, trigger Rule of judgment twice different, trigger a multimodal scanning.For example cell plate group string has 4 panel arrays in parallel, the temperature of each panel array one of them cell panel of stochastic sampling, and there is four temperature information T1, T2, T3, T4 in 4 panel arrays in parallel.The temperature difference of getting trigger sweep is 10 ℃ (panel array situation is depended in the setting of this value).If there is temperature difference between adjacent two panel arrays, and temperature difference surpasses the temperature gap of setting, if T2 is 60 ℃, T3 is 75 degrees Celsius, and last triggering is because differ more than 10 ℃ between T2 and T3, the temperature difference between this multimodal scanning triggering invalid (because it is identical to trigger reason twice, being all because T2 and the same Battery pack plate array of T3() is over 10 ℃).If last triggering is because all differ more than 10 ℃ between T1 and T2, T2 and T3, this is that this triggers effectively because T2 and T3 differ 15 ℃.
It should be noted that, it is the relation of "or" that three kinds of scannings that provide in above-mentioned steps (2) trigger between judgement, meets wherein any trigger condition and triggers multimodal scanning.
As previously mentioned, cause main cause that the whole P-V curve of cell plate group string presents the form of multi-peak to be that intensity of illumination between cell panel is inconsistent, to have temperature difference, and cause intensity of illumination factor inconsistent, that have temperature difference, be all random, so P-V curve present multi-peak phenomenon and must not occur.If there is not multi-peak phenomenon the same day or only occurred on a small quantity peak phenomenon often, if employing timing scan, within one day, at least there is multimodal scanning for several times, expend sweep time, cause the inverter can not output energy as much as possible, and timing scan also may occur scanning and the situation of scanning not, lose the meaning of scanning.And adopt trigger sweep mode, and when meeting scanning trigger condition, just carry out multimodal scanning, avoided expend unnecessary sweep time, reduced sweep time.Meanwhile, trigger sweep has also been avoided scanning and the not situation of scanning generation.
Disclosed all features in this instructions, or the step in disclosed all methods or process, except mutually exclusive feature and/or step, all can combine by any way.Disclosed arbitrary feature in this instructions (comprising any accessory claim, summary and accompanying drawing), unless narration especially all can be replaced by other equivalences or the alternative features with similar object.That is,, unless narration especially, each feature is an example in a series of equivalences or similar characteristics.
Claims (9)
1. a multi-peak maximum power point tracking method for photovoltaic DC-to-AC converter, comprises scanning step, it is characterized in that, described scanning step is:
According to coarse scanning step-length, carry out coarse scanning, determine between adjacent two constant power points and whether have crest, if existed, in the regional area between these adjacent two constant power points, according to close scanning step-length, carry out close scanning, mark the local maximum power point in this regional area, then continue to carry out coarse scanning according to aforesaid coarse scanning step-length and determine next local maximum power point; Process coarse scanning and close scanning intert to be carried out, and marks the local maximum power point in crest place regional areas all in sweep limit; Finally according to the local maximum power point in each regional area, find out the maximum power point in whole sweep limit; Described constant power point is the intersection point of constant power straight line in sweep limit and P-V curve, and described constant power straight line is less than the power of current MPPT by performance number and power points that both differ setting value forms.
2. the multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter according to claim 1, it is characterized in that, before scanning step, also comprise scanning initialization step: ceiling voltage and the minimum voltage of according to the open-circuit voltage of inverter, determining sweep limit, and the voltage that judges current MPPT respectively with the difference of ceiling voltage and the difference of minimum voltage, if the difference of the voltage of current MPPT and ceiling voltage is greater than the difference of voltage and the minimum voltage of current MPPT, in scanning step from low-voltage to high voltage scanning direction, otherwise from high voltage to low-voltage scanning direction.
3. the multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter according to claim 2, it is characterized in that, described sweep limit be photovoltaic DC-to-AC converter open-circuit voltage 60%～90%, 60% of open-circuit voltage is the minimum voltage of sweep limit, and 90% of open-circuit voltage is the ceiling voltage of sweep limit.
4. the multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter according to claim 2, it is characterized in that, in described scanning initialization step, also comprise step: according to the voltage of current MPPT, the voltage regime of the voltage phase difference setting voltage value of mark and current MPPT is local non-scanning area.
5. the multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter according to claim 1, it is characterized in that, in described scanning step, when carrying out coarse scanning, according to coarse scanning step-length, often move and move a step, record voltage and the power of respective point in a P-V curve, and the intersection point of mark P-V curve and constant power straight line is constant power point, often mark a constant power point, according to the derivative of constant power point and direction of scanning, judge between current constant power point and previous constant power point whether have crest, if exist, carry out close scanning in the regional area between these two constant power points, otherwise proceed coarse scanning.
6. the multi-peak maximum power point tracking method of photovoltaic DC-to-AC converter according to claim 5, it is characterized in that, describedly according to the derivative of constant power point and direction of scanning, judge between current constant power point and previous constant power point whether exist the method for crest to be: from low-voltage to high voltage scanning direction, if the derivative of previous constant power point is for just, for negative, between these adjacent two constant power points, there is crest in the derivative of current constant power point; From high voltage to low-voltage scanning direction, if the derivative of previous constant power point is negative, for just, there is crest between these adjacent two constant power points in the derivative of current constant power point.
7. according to the multi-peak maximum power point tracking method of the photovoltaic DC-to-AC converter one of claim 2 to 6 Suo Shu, it is characterized in that, before scanning initialization step, also comprise that scanning triggers determining step, described scanning triggers determination methods: every an environment temperature judgement cycle, carry out an environmental temperature fluctuation and detect, within an environment temperature judgement cycle, if environment temperature rises or declines, surpass design temperature undulating quantity, trigger a multimodal scanning, otherwise not trigger sweep.
8. according to the multi-peak maximum power point tracking method of the photovoltaic DC-to-AC converter one of claim 2 to 6 Suo Shu, it is characterized in that, before scanning initialization step, also comprise that scanning triggers determining step, described scanning triggers determination methods: every a power electric current judgement cycle, carry out output power and output current fluctuation detects, at a power electric current in the judgement cycle, if the output power of inverter rises or declines over the power swing value of setting, and output current also rises or declines over the current fluctuation value of setting, trigger a multimodal scanning, otherwise not trigger sweep.
9. according to the multi-peak maximum power point tracking method of the photovoltaic DC-to-AC converter one of claim 2 to 6 Suo Shu, it is characterized in that, before scanning initialization step, also comprise that scanning triggers determining step, described scanning triggers determination methods: the temperature difference in judgement inverter between panel array, if the temperature difference between adjacent two panel arrays surpasses the temperature value of setting, and adjacent twice sweep trigger condition is different, trigger a multimodal scanning, otherwise not trigger sweep.
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