Classifications

• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
  • G05F1/00—Automatic systems in which deviations of an electric quantity from one or more predetermined values are detected at the output of the system and fed back to a device within the system to restore the detected quantity to its predetermined value or values, i.e. retroactive systems
  • G05F1/66—Regulating electric power
  • G05F1/67—Regulating electric power to the maximum power available from a generator, e.g. from solar cell
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/02—Details
  • H01L31/02016—Circuit arrangements of general character for the devices
  • H01L31/02019—Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier
  • H01L31/02021—Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier for solar cells
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • 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

Definitions

• the present invention relates to the field of photovoltaic generators and more specifically photovoltaic modules integrating electronics; such a model includes a photovoltaic generator and an electronic management system for photovoltaic cells.
• a photovoltaic generator comprises one or more photovoltaic cells (PV) connected in series and / or in parallel.
• a photovoltaic cell essentially consists of a diode (pn junction or pin) made from a semiconductor material. This material has the property of absorbing light energy, a significant part of which can be transferred to charge carriers (electrons and holes).
• the maximum potential difference (open circuit voltage, V oc ) and the maximum current (short circuit current, l cc ) that the photovoltaic cell can supply are a function of both the materials constituting the entire cell and conditions surrounding this cell (including illumination through the spectral intensity, temperature, ).
• the models are significantly different - referring more to the concept of donor and acceptor materials in which electron-hole pairs called excitons are created. The purpose remains the same: to separate charge carriers to collect and generate a current.
• FIG. 1 schematically illustrates an example of a photovoltaic generator (according to the state of the art).
• Most photovoltaic generators consist of at least one panel itself consisting of photovoltaic cells connected in series and / or in parallel. Several groups of cells can be connected in series to increase the total voltage of the panel; one can also connect several groups of cells in parallel to increase the intensity delivered by the system. In the same way, several panels can be connected in series and / or in parallel to increase the voltage and / or the amperage of the generator according to the application.
• FIG. 1 illustrates a photovoltaic generator comprising two parallel branches each comprising three groups of cells 2.
• non-return diodes 3 and bypass diodes 4 can be provided.
• the anti-return diodes 3 are connected in series to each parallel branch of the generator in order to avoid the circulation in the cells of a negative current coming from the load or from other branches of the generator.
• the bypass diodes 4 are connected in anti-parallel to groups 2 of cells. The bypass diodes 4 make it possible to isolate a group 2 of cells presenting a fault or a shading problem and solve the problem of hot spots (or "hot spots" in English terminology).
• the maximum voltage of the generator corresponds to the sum of the maximum voltages of the cells which constitute it and the maximum current that can deliver the generator corresponds to the sum of the maximum currents of the cells.
• the maximum voltage V oc of a cell is reached for a cell taken off-load, that is for a zero-rated current (open circuit), and the maximum current l cc of a cell is reached when its terminals are short-circuited, that is to say for a zero voltage across the cell.
• the maximum values V oc and l cc depend on the technology and the material used to make the photovoltaic cell.
• the maximum value of the current l cc also depends strongly on the level of sunshine of the cell.
• a photovoltaic cell thus has a non-linear current / voltage characteristic ( PV , V PV ) and a power characteristic with a maximum power point (PPM or MPP) which corresponds to optimal values of voltage V op t and current op t.
• Figure 2 shows the current-voltage (IPV, V pv ) and power-voltage ( PV PV , PV PV ) characteristics of a photovoltaic cell with its maximum power point (identified by PPM in the figure).
• a photovoltaic generator will have a non-linear current / voltage characteristic and a power characteristic with a maximum power point. If some of the cells are omitted, or if more than one of the cells are defective, the MPP maximum power point of that group will be moved.
• Such an MPPT command may be associated with one or more static converter (s) (CS) which, depending on the application, may be a DC-AC converter (DC / AC according to the acronym used in English) or a DC-DC converter (DC / DC according to the acronym used in English).
• CS static converter
• Figure 1 shows a static converter 8 DC / AC connected to the output of the generator and collecting the electrical energy produced by all the cells of the generator to deliver it to a load. Depending on the needs of the load, the converter may be required to increase or decrease the output voltage and / or to ripple the output voltage.
• FIG. 1 also shows a command MPPT 6 associated with the converter 8.
• the MPPT command 6 is designed to control the converter (s) 8 in order to obtain an input voltage which corresponds to the optimum voltage value V op t of the photovoltaic generator (GPV) corresponding to the maximum point of the characteristic power.
• the point of maximum power depends on several variable parameters over time, including the amount of sunshine, the temperature or the aging of the cells or the number of cells in working condition.
• the efficiency of the photovoltaic generator is not too much affected by the dysfunction or shading of certain cells.
• the electrical efficiency of the generator depends directly on the state of each photovoltaic cell.
• the power delivered by the photovoltaic generator will vary. In particular, it will be possible to use, depending on the power, not one but two or three or more converters.
• the method consists of adapting the number of converters (cells or phases) as a function of the evolution of the power produced by the GPV. Indeed, the use of a single converter is not necessarily advantageous to handle large power variations, the conversion efficiency is affected.
• a power converter formed from a single phase (or a single converter) has its efficiency which decreases when the PV power supplied is maximum, while the structure comprising three converters tends to maintain a quasi-constant efficiency whatever the PV power delivered. This will translate into more energy transfer to the battery.
• FIG. 3 represents such an arrangement, comprising, at the output of the PV cells, three CSs (which in this case are variable converters or BOOSTs). These converters are actuated according to the power generated, compared to the peak power of the device (Ppeak).
• CSs variable converters or BOOSTs
• Ppeak peak power of the device
• the invention provides an electronic management system of a photovoltaic generator, the system comprising:
• each converter (1 1, 12, 13) being electrically connected to at least one photovoltaic cell (10) of said generator,
• the variation of the number of connected converters is done by varying the photovoltaic power, by comparing the power generated at thresholds P1, P2, ... Pn-1, after a delay time t.
• the delay time t is between 3 and 20 minutes, preferably between 5 and 15 minutes.
• the value of the time t depends on the state of the components of the converters.
• the value of the time t depends on the meteorological conditions, chosen in particular from the location of the generator and the season.
• the converters are connected in turn.
• the rotation of the converters is done during the variation of the number of converters engaged.
• the rotation of the converters depends on the state of the components of the converters.
• the subject of the invention is also a photovoltaic generator comprising:
• At least one photovoltaic cell At least one photovoltaic cell
• the subject of the invention is also a method for controlling a photovoltaic generator comprising:
• At least one photovoltaic cell At least one photovoltaic cell
• each converter (1 1, 12, 13) being electrically connected to at least one photovoltaic cell (10);
• said method comprising the steps of:
• connection being made after a delay time t if the connection conditions are still fulfilled.
• said method comprises the following steps, implemented according to periods:
• step (b1 1) then compare to the first threshold P1, and if the power value is greater than this threshold the routine returns to step (b) and if the value is lower than this threshold P1, there is triggering a timer t;
• step (b12) if the timer has been triggered, then again compares to the first threshold P1, and if the power value is greater than this threshold the routine returns to step (b) after having reset the timer and if the value is below this threshold P1, there is determination of the flow or not of the delay time and if not resumed comparison to the value P1;
• step (b13) when the delay time has elapsed, then return to step (a)
• step (b21) then compare to the second threshold P2, and if the power value is greater than this threshold the routine returns to step (b2) and if the value is lower than this threshold P 1, there is triggering a timer t;
• step (b22) if the timer has been triggered, then the second threshold P2 is compared, and if the power value is greater than this threshold, the routine returns to step (b2) after resetting the timer and if value is below this threshold P2, there is determination of the flow or not of the delay time and if not resumed comparison to the value P2; (b13) when the delay time has elapsed, then there is return to step (a) or step (b);
• the ith converter is no longer connected when the other converters are connected when all the converters are not connected.
• the method comprises the steps of:
• the converter rotation stage is performed when the measured power value changes between the thresholds Pi-1 and Pi.
• the method comprises the steps of:
• the methods of the invention are particularly suitable for the generators according to the invention.
• FIG. 2 already described, the current-voltage and theoretical power characteristics of a photovoltaic cell
• FIG. 3 shows a diagram of a GPV comprising several converters (here 3 BOOST type static converters);
• FIG. 5 shows the algorithm according to one embodiment of the invention
• FIGS. 6a and 6b show an enlargement of two zones of the faux curve as a function of the time of the day with application of the invention and indication of the number of CSs engaged;
• FIG. 7 shows an example of photovoltaic production profile, PV power (PV PV ) as a function of time.
• FIGS. 9a and 9b represent the values of P, n and P or t in the cases without and with the algorithm of the invention.
• the thresholds P1 and P2 are conventionally 1/3 and 2/3 of the P peak power, here 28 and 56W, respectively.
• the invention proposes an electronic management system of a photovoltaic generator comprising a plurality of converters (of cells or phases) which can be DC / AC or DC / DC, typically three converters, connected to photovoltaic cells.
• the converters are electrically connected to at least one photovoltaic cell in order to harvest the energy produced by this cell and transfer it to a load.
• load is the electrical application for which the energy produced by the photovoltaic generator is intended.
• CS will be the acronym used in the following to designate a converter (here static).
• this MPPT maximum power point search command may implement an algorithm that identifies the influence of a voltage change on the power delivered by the generator and causes an offset of the voltage in the direction identified as increasing the power.
• an algorithm consists in measuring the power delivered by the generator for a first voltage and, after a certain time, in imposing a second voltage higher than the first and then measuring or estimating the corresponding power.
• the next step of the algorithm is to impose a third voltage even greater.
• the third applied voltage is lower than the first voltage.
• the system can permanently adapt the voltage at the terminals of the photovoltaic generator in order to get as close as possible to the point of maximum power. It is understood that other algorithms can be implemented for the MPPT command.
• FIG. 3 represents such a diagram, and the GPV comprises a photovoltaic unit 10, connected to CSs 1 1, 12 and 13 (BOOST 1, 2 and 3) and to an MPPT control 14, the output of the CS being connected to a battery 15.
• CSs 1 1, 12 and 13 BOOST 1, 2 and 3
• MPPT control 14 the output of the CS being connected to a battery 15.
• the number of CSs engaged is a function of the power that is sent to the CSs. In known manner, the number varies according to the detection of a threshold. In the case of 3 CSs, the application of the state of the art corresponds to two predetermined thresholds for changing the number of the converter. Depending on the power measured by the MPPT management system, namely less than 1/3 P peak, between 1/3 and 2/3 P peak and more than 2/3 P peak, then the management system engages one, two or three converters . Other threshold values may be used where appropriate.
• FIG. 4 shows the power generated and the number of CSs engaged as a function of the time of day.
• the invention is based on the use of a time t of power stabilization (or delay).
• the change in the number of CSs will only be allowed after the expiry of this time t or lag time. Thus, a fast variation will not be taken into account and the number of CS will remain identical during the phase including oscillations.
• This stabilization time t varies according to the system. It can be typically of the order of 3 minutes to 20 minutes, for example between 5 minutes and 15 minutes.
• a possible algorithm for implementing the stabilization time t is given in FIG. We start from a state with a given power. In a first step, the power PV, P PV (which corresponds to PIN for the CSs) is determined.
• this PPV power is lower than the first threshold P1 (taken for example equal to 1/3), then the answer to the logical question is "no" and only one CS is engaged; the routine goes back to the beginning. If this PPV power is greater than the first threshold, then the answer to the logical question is "yes"; then we go to the second stage of the routine.
• the next logical question is again a comparison with the first threshold P1. If the PPV power is greater than the first threshold P1, then the answer to the logical question is "no" and the routine returns to the beginning of the second step. If the answer is or i, then the timer is triggered. According to the state of the art, the answer necessarily led to the transition to 1 CS. In the invention, this passage is not made and instead triggers a delay. From time to time, according to a defined period, the value of the PPV power is measured and compared with the first threshold P1. If the value is higher, then the answer to the logical question is "no" and the routine returns to the beginning of the second step: we are still in the conditions in which we need 2 CSs.
• the timer is reset in this case. So we see that the fact of having waited allowed not to make a round-trip between 2 states and thus to gain in term of fatigue of the components of the system. If during the comparison the value is lower than the threshold P1, then we proceed to the next logical question. The next logical question is the question of timing out.
• the next logical question is again a comparison to the second threshold P2. If the PPV power is greater than the second threshold P2, then the answer to the logical question is "no" and the routine returns to the beginning of the second branch. If the answer is yes, then the timer is triggered. According to the state of the art, the answer necessarily led to the transition to 2 (or 1) CS. In the invention, this passage is not made and instead triggers a delay. From time to time, according to a defined period, the value of the PPV power is measured and compared with the second threshold P2. If the value is higher, then the answer to the logical question is "no" and the routine returns to the beginning of the second branch: we are still in the conditions in which we need 3 CSs.
• the timer is reset in this case. So we see that the fact of having waited allowed not to make a round-trip between 2 states and thus to gain in term of fatigue of the components of the system. If during the comparison the value is lower than the threshold P2, then we proceed to the next logical question.
• the next logical question is the question of timing out.
• the defined period referred to above is fixed or may vary according to certain conditions, especially meteorological: it is not necessary to implement the routine with a sunshine that is known constant.
• the duration of this period is very variable, and can be of the order of the second, the ten seconds, the minute or more if necessary.
• the period will however remain advantageously less than the stabilization time t.
• Figures 6a and 6b show, in an enlarged manner, the number of CS engaged with the implementation of the algorithm according to the invention, for two parts taken in the curve of Figure 4.
• This stabilization time has the effect of reducing the thermal and electrical stresses experienced by the active components during these untimely variations in power.
• the thermal variations induce mechanical stresses at the semiconductor level, due in large part to the difference in the coefficients of expansion of the materials used during manufacture, for example 4ppm / ° C for silicon against 16ppm / ° C for copper and 24ppm / ° C for aluminum.
• FIG. 7 is an example of a photovoltaic production profile, PV power (PV PV ) as a function of time.
• PV PV photovoltaic production profile
• the system In normal operation, the system will move from point 1 (high power - 3 inverters enabled) to point 2 (low power - only 1 converter enabled). Two converters will therefore stop abruptly creating a thermal cycle of strong ⁇ °.
• the three converters will continue to operate in point 2.
• the temperature of the three converters will therefore gradually decrease because the power is distributed in the three cells. If the power has not increased between points 2 and 3, two of the converters will be disconnected and therefore only one converter will work in point 3. Thanks to this principle, it is possible to limit the importance of variations ⁇ ° and therefore limit the importance of thermal cycles.
• Stabilization time is the time during which the 3 CSs will be active between points 2 and 3 (or another combination of CS). This stabilization or delay time t can be fixed in the system algorithm or it can be modified according to several criteria.
• a first criterion is meteorology itself.
• the climatic conditions vary from one zone to another and therefore the time delay can be optimized according to the zone in which the GPV is implanted. Indeed, in some climates, there is little alternating clouds (for example a Mediterranean climate) or on the contrary there can be many (for example an oceanic climate).
• the weather conditions also vary according to the seasons, and the time delay can be adapted according to the month of use.
• a second criterion is the behavior of the components themselves, and in particular their behavior as a function of the power, of the temperature (in particular of the transistors or of the whole system).
• the stabilization or delay time t may especially be modulated according to the temperature of the components.
• the system integrates a CS rotation routine to avoid the continuous solicitation of a single CS.
• the converter CS 1 1 is permanently connected, and therefore receives the current to be converted permanently.
• the other CSs are used depending on changes in the generation of PV power.
• CS 1 1 is therefore permanently solicited, and is further subjected to power changes to be processed during PV power variations.
• the reliability of the system is reduced because one of the components is solicited permanently.
• the rotation can be controlled during PV power changes generated by the panels or can be controlled depending on the state of the converters, or both.
• a random assignment command can also be used.
• the CH ent ng ent of CS a lieu when the number of committed CSs increases. For example, if the CS 1 1 is connected, and the command determines that it is necessary to use 2 CS, then the CS 12 and 13 will be engaged, while the CS 1 1 will no longer be connected. If the number of CSs returns to one unit, then the CS 12 (or CS 13) will be connected, rather than the CS 1 1 which will still be idle. In case the 3 CSs have to be connected, the rotation takes place when returning to 1 or 2 CSs.
• the change of CS takes place due to a calculation of use of the CSs.
• This calculation can be based on the duration of use, the rotation is done so as to ensure a substantially equal duration of use for all the CS, over a given period.
• This period can be a day, several days or a fraction of a day, for example one or several hours, this duration can also be a function of the time of the day and / or the season.
• the CS that must be engaged is the one that has been the least used, namely the one having had the lowest time of use.
• the calculation can also be done by counting not the duration but the number of uses or solicitations of the CS, regardless of the duration of use.
• the CS to be engaged is the one that has been requested the least number of times. It is also possible to envisage an embodiment in which the two variants are associated.
• the rotation is done randomly, a random generator then being provided in the management system.
• the choice is made randomly, possibly in "shuffle” mode if necessary (this mode corresponds to a mode in which the CS which has been used is excluded from the random selection).
• the rotation of the CSs occurs when the number of CSs engaged is changed. It is of course possible to provide for this rotation to occur when the number of CSs engaged is constant (as long as it is different from the maximum number).
• a routine can be provided which exchanges this CS with a CS initially at rest, so that a CS is not used continuously for more than a given duration.
• the rotation of the engaged converters has the effect of further reducing the thermal and electrical stresses experienced by the active components during power variations.
• the thermal variations induce mechanical stresses at the level of the semiconductors, the result of which is the appearance of microcracks on the contacts, even going as far as breaking it.
• the embodiment of rotation of the CS aims to distribute on all converters thermal and electrical stress.
• the electronic management system according to the invention may also include security functions, controlling the stopping of the converters, following a message for example of overheating of the GPV components.
• the electronic management system according to the invention may also include an anti-theft function.
• the management system according to the invention can furthermore transmit information relating to the operating status of the groups of cells and / or the converters to a central office of an electrical network. This makes it easier to maintain GPVs. In particular, the operator responsible for maintenance is thus notified faster of a malfunction of certain groups of photovoltaic cells or certain converters and can take action accordingly.
• the management system according to the invention may be wholly or partly integrated into a photovoltaic generator.
• multi-junction photovoltaic devices can be used. It then becomes necessary to manage the problem of the electrical coupling of the different junctions.
• a multi-junction photovoltaic device designates a photovoltaic device consisting of several simple junctions stacked so as to increase the solar spectrum absorption zone by the device. Photovoltaic devices with tandem junctions make it possible to obtain a better electrical conversion efficiency.
• the main disadvantage of the electrical coupling in a photovoltaic device with tandem junction is the need for an agreement of the performance of the photovoltaic cells constituting the tandem, whatever the conditions of sunshine.
• the system makes it possible to obtain a multi-junction photovoltaic device operating with photovoltaic cells decoupled electrically and each optimally managed via the management system according to the invention.
• the test protocol used to evaluate the energy gain provided by the method according to the invention consisted in using the same input source (solar simulator) and the same multi-phase power card (behavior of the identical electrical components).
• the simulator allowed to apply in both cases the same power profile (for example the production of a module with a peak power of 85 W on a relatively sunny day), while obtaining the MPP was carried out by the same MPPT command, During this test, a 24 V battery was used, to which was associated an electronic charge to guarantee permanently the nominal voltage of the latter (24 V).
• Figure 10 shows the measurement scheme used.
• the thresholds used are the classic 1/3 and 2/3 thresholds.
• FIGS. 9a and 9b represent the values of P, n and P or t in the cases without and with the algorithm of the invention. Note in the case according to the invention that when the number of CS goes from 3 to 1, there is a slight drop in the output power, reflecting a gain in terms of efficiency (for low power, the performance is better with only one CS).

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