WO2014097190A2 - Procédé de commande d'une installation photovoltaïque et appareil de commande correspondant - Google Patents

Procédé de commande d'une installation photovoltaïque et appareil de commande correspondant Download PDF

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Publication number
WO2014097190A2
WO2014097190A2 PCT/IB2013/061108 IB2013061108W WO2014097190A2 WO 2014097190 A2 WO2014097190 A2 WO 2014097190A2 IB 2013061108 W IB2013061108 W IB 2013061108W WO 2014097190 A2 WO2014097190 A2 WO 2014097190A2
Authority
WO
WIPO (PCT)
Prior art keywords
electric energy
string
photovoltaic
energy converter
switch
Prior art date
Application number
PCT/IB2013/061108
Other languages
English (en)
Other versions
WO2014097190A3 (fr
Inventor
Alberto TESSAROLO
Martino BAILONI
Lorenzo BRANZ
Original Assignee
Universita' Degli Studi Di Trieste
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Universita' Degli Studi Di Trieste filed Critical Universita' Degli Studi Di Trieste
Publication of WO2014097190A2 publication Critical patent/WO2014097190A2/fr
Publication of WO2014097190A3 publication Critical patent/WO2014097190A3/fr

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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
    • 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 concerns a method and an apparatus to control a photovoltaic plant, suitable to determine the optimum functioning thereof at least in the start-up or restart step of the plant.
  • the present apparatus can be applied for example in multi-string photovoltaic plants, where string means an array of photovoltaic modules or panels, connected in series to each other and in turn at entrance to an electric converter, such as an inverter.
  • Photovoltaic plants comprising a plurality of photovoltaic panels connected to an energy converter or inverter, which is in turn associated with the electric mains.
  • photovoltaic plants most common today comprise a plurality of photovoltaic modules connected to each other in series to form said strings, each of which is in turn connected at entrance to the inverter.
  • the inverter is normally controlled by a control apparatus which implements algorithms suitable to determine optimum functioning conditions of the plant.
  • MPPT Maximum Power Point Tracker
  • Apparatuses are also known, from documents WO-A-2012/014182, EP-A- 0.206.253 and DE-A-37.27.026, which maximize the electric energy produced by a photovoltaic power generator.
  • document WO-A-2012/014182 describes an apparatus interposed between a photovoltaic generator and an inverter and configured to make level the electric energy generated by the photovoltaic generator and to limit overloads on the inverter.
  • the leveling of the electric energy is obtained by suitably commanding an electronic switch of the apparatus for the whole period of time in which the plant is functioning.
  • Documents EP-A-0.206.253 and DE-A-37.27.026 instead describe an apparatus connected between a photovoltaic plant and an electric energy accumulator, for example a battery.
  • the apparatus comprises an electronic switch connected in parallel to the photovoltaic plant and to the energy accumulator and able to be selectively activated with a high frequency of activation/de-activation to limit overloads of electric energy on the accumulator.
  • the delivery of electric current of the whole string is limited by the module that generates least current, and the electric power delivered by the plant is less than what would theoretically be possible based on the irradiation conditions.
  • One purpose of the present invention is to obtain a control apparatus for a photovoltaic plant able to improve its functioning efficiency in the start-up condition with one or more panels shadowed.
  • Another purpose is to perfect a method to control the functioning of a photovoltaic plant that allows to improve the overall functioning efficiency in the start-up condition of the whole plant with one or more panels shadowed.
  • the Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.
  • an apparatus is used to control the start-up step of a photovoltaic plant that comprises at least a string of photovoltaic modules reciprocally connected in series and each provided with at least a bypass diode provided to short circuit or bypass the respective photovoltaic module in the event of shadowing or malfunctioning thereof.
  • the photovoltaic plant is in turn connected with an electric energy converter, such as an inverter.
  • the diodes bypass the respective photovoltaic module or part of it if at its heads a negative difference in potential is created, corresponding to the condition in which the corresponding photovoltaic module is subject to even partial shadowing or malfunctioning.
  • control apparatus comprises a switch and a low-impedance load connected to each other in series and in turn connected in parallel to the string and to the electric energy converter.
  • switch shall include a switch of the electromechanical type, an electronic switch or any other equivalent electronic, electromechanical or capacitive component.
  • the switch is able to be selectively activated temporarily during the start-up step in order to make an electric current circulate in the string, generated by the non-shadowed photovoltaic modules.
  • the electric current generated is sufficient to put under conduction the bypass diodes of the shadowed or malfunctioning photovoltaic modules, short-circuiting them.
  • the switch is selectively openable and closable to determine respectively a first condition in which the string of photovoltaic modules is put in a condition such as to generate a current sufficient to activate the bypass diodes relating to the shadowed or non-functioning photovoltaic modules, and a second condition in which the string is directly connected to the electric energy converter for the normal supply of electric energy to the mains.
  • the electric current in the string can even reach a current value corresponding to the short circuit current.
  • the string When the switch is opened or de-activated, the string is returned to connect with the electric energy converter, removing the low-impedance load, to determine the transfer of the energy produced by the photovoltaic plant to the mains.
  • this condition is characterized by the fact that the bypass diodes associated with the shadowed photovoltaic modules are momentarily under conduction, and they remain in this state for as long as the shadowed and/or non-functioning condition remains.
  • the current absorbed by the electric energy converter is sufficient to keep under conduction the bypass diodes relating to the shadowed photovoltaic modules.
  • the condition necessary so that the bypass diodes of the photovoltaic modules can enter into conduction is that the electric current circulating in the string must be sufficient to directly polarize the bypass diodes relating to the shadowed or non-functioning photovoltaic modules.
  • bypass diodes are inversely polarized by the positive voltage created at the heads of the photovoltaic module, also due to conditions of partial shadowing.
  • the converter tends to pursue a considerably low value of power, corresponding to a reduced electric current circulating in the string and which depends on the type of photovoltaic plant.
  • the MPPT algorithm of the electric energy converter or inverter can make the converter absorb an electric current equal to the maximum power deliverable by the shadowed panels and not those correctly exposed.
  • the electric current circulating may not be sufficient to put under conduction the bypass diodes of possible shadowed or non- functioning photovoltaic modules in order to exclude them.
  • the photovoltaic plant may remain for a long time in these conditions, typically for as long as the shadow remains on one or more modules, and may deliver a much lower energy compared with that which is actually available.
  • the purpose of the apparatus is therefore to contrast a malfunctioning that can occur when the photovoltaic plant is started up, that is, when the electric energy converter is connected to the plant and if one or more photovoltaic modules of the string are in shadow.
  • the apparatus comprises a controller configured to command at least the closing and opening of the switch. In this way it is possible to determine automatically the moments of opening and closing of the switch so that the processes described above can take place.
  • a timer device is associated with the controller, suitable to determine at least the temporal moments of opening and closing of the switch.
  • the apparatus comprises a measuring device chosen from a group comprising at least one of either a voltmeter, an ammeter, a wattmeter suitable to detect respective electric quantities of the photovoltaic plant so as to determine, for example, the start-up moment.
  • the present invention also concerns a method to control the start-up step of a photovoltaic plant associated with an electric energy converter.
  • the start-up step comprises at least the activation of an electric energy converter connected to the photovoltaic plant in order to supply electric energy to the mains.
  • the method comprises at least a first step in which a switch is temporarily activated to connect a low-impedance load in parallel to the string and to the electric energy converter and to make an electric current circulate in the string, generated by the non-shadowed photovoltaic modules, sufficient to put under conduction the bypass diodes of the shadowed or malfunctioning photovoltaic modules, short-circuiting the shadowed or malfunctioning photovoltaic modules.
  • the method comprises a subsequent second step in which the switch is de-activated and the string is connected in series to the electric energy converter.
  • the present invention also concerns the photovoltaic plant that comprises a control apparatus as described above.
  • - fig. 1 is a schematic representation of the application of a control apparatus on a photovoltaic plant
  • a control apparatus is indicated in its entirety by the reference number 10 and is connected in parallel between a photovoltaic plant 1 1 and an electric energy converter 14, or inverter, suitable to convert the electric energy produced by the photovoltaic plant 1 1 from direct to alternate.
  • the photovoltaic plant 1 1 is electrically connected with the inverter 14 by electric connections.
  • the photovoltaic plant 1 1 comprises a plurality of photovoltaic modules 12, in this case photovoltaic panels, hereafter indicated simply by the word panels 12.
  • the photovoltaic plant 11 comprises for example three strings 13 of four panels 12 connected in series, although configurations are possible in which each string 13 comprises two, three, five or more panels 12, and also in which one, two, four or more strings 13 can be present.
  • the inverter 14 may comprise a controller 14a configured to implement an MPPT algorithm in order to optimize the delivery of electric energy during the normal functioning of the photovoltaic plant 11.
  • Fig. 2 concerns another form of embodiment of the present invention, in which to simplify comprehension the photovoltaic plant 11 comprises a single string 13, associated as indicated above to the inverter 14. At least one semiconductor diode 15, or other equivalent electric bypass device, is connected in a known manner and in parallel with each panel 12, and is suitable to short circuit the respective panel 12 when a voltage is applied upon it in the opposite sense to that normally produced by the panel 12.
  • the string 13 is provided with terminals 16 which are connected both to the control apparatus 10 according to the present invention and also to the inverter 14.
  • control apparatus 10 comprises a switch 18 connected in parallel between the string 13 and the inverter 14.
  • the switch 18 is the electromechanical or electronic type, for example a semiconductor electronic device.
  • the inverter 14 When the switch 18 is in the open condition, the inverter 14 is directly connected in series with the string 13 and the photovoltaic plant 11 begins to function in the known manner.
  • low-impedance we mean a connection in which the impedance has a reduced value, for example variable from zero to some tens of Ohms, irrespective of whether it is resistive, inductive or capacitive, or values that in any case are sufficient to set a string current able to put the bypass diodes under conduction.
  • a connection is provided of a low-impedance load 20, in the case shown here a resistance, although it is not excluded that in other forms of embodiment it can be a capacitor, an inductance or a combination of the above.
  • the low-impedance load 20 allows to prevent damage to the panels 12 or to possible other electric/electronic devices provided in the string 13, due to the creation of high electric current.
  • the low-impedance load 20 is the variable type, such as for example a rheostat, the value of which can be set by the user, for example using a cursor, depending on the characteristics of the photovoltaic plant 1 1.
  • variable-type low-impedance load 20 can also be obtained with electronic power devices, for example MOSFET.
  • the controller 19 can also be configured to regulate the value of the low- impedance load 20 if it is the variable type.
  • controller 19 is connected with the controller 14a of the inverter 14. In still other forms of embodiment, the controller 19 is the same controller 14a provided for the inverter 14.
  • a timer device 21 is also associated with the controller 19, which cooperates with the controller 19 to determine the moments of opening and/or closing of the switch 18.
  • the functions obtained by the controller 19 and/or the timer 21 can be implemented by digital electronic devices, or again by a suitable electric or electromechanical circuitry.
  • control apparatus 10 comprises a measuring device 17 to measure an electric quantity of the string 13.
  • the measuring device 17 in this case for example a wattmeter, is suitable to detect the power delivered by the string 13 of panels 12 and can be of any known type.
  • the measuring device 17 is a voltmeter connected in parallel to the terminals 16 and suitable to detect the electric voltage.
  • the measuring device 17 is an ampmeter connected in series with the string 13 and suitable to measure the electric current.
  • the measuring device 17 can be associated with the controller 19 to control and process the data acquired by the measuring device 17.
  • the controller 19 detects the electric quantities relating to the string 13 and, if unacceptable values of said quantities are reached, commands the switch 18 to open to prevent damage to the panels 12 or possible electric or electronic components associated with them.
  • the inverter 14 can in turn be connected to an electric mains 22 to supply to one or more user devices the electric energy produced by the photovoltaic plant 11.
  • a method to control the photovoltaic plant 1 1 provides a start-up step of the photovoltaic plant 1 1 which determines the start of generation of electric energy.
  • start-up step it is provided to activate the inverter 14 to start the generation of electric energy for the electric mains 22.
  • Some forms of embodiment provide that the inverter 14 is activated in manual mode and at the user's discretion.
  • a step is provided to insert the low- impedance load by closing the switch 18. During the period of time when the switch 18 is closed, a current circulates in the string 13 of panels 12, generated by the non-shadowed panels 12 and which can also assume a short-circuit value.
  • the first time interval Tl is counted by the timer 21 and is settable by the user so as to guarantee that the inverter 14 has completed its start-up procedure, and that it is possible to subsequently proceed, short-circuiting the string 13.
  • each diode 15 activated determines a bypass condition of the respective panel 12 in the string 13 to which it is associated.
  • the second time interval T2 is counted by the timer 21 and is settable by the user.
  • the second time interval T2 is a value that can vary between 1 and 20 seconds, preferably between 1 and 10 seconds, even more preferably between 1 and 5 seconds.
  • the second time interval T2 must in any case be sufficient to guarantee that an electric current is created in the string such as to polarize the diodes 15.
  • the individual string 13 no longer goes into a functioning condition adequate for that of the panel 12 that produces least electric energy, as in the state of the art, but into the most advantageous functioning condition, that is, that of the non-shadowed panels 12, and able to deliver maximum electric power.
  • the MPPT algorithm considers the string 13 as formed only by the non-shadowed panels 12 and therefore reaches the actual work point with most efficiency for that number of non-shadowed panels 12.
  • the short-circuit condition by the diodes 15 can remain active for as long as the panel 12 is able to supply a current comparable with that of the other panels 12 belonging to the string 13. Beyond this condition, at the heads of the panel 12 that was shadowed a positive difference in potential is re-established, which deactivates the short-circuit action of the respective diode 15.
  • the MPPT algorithms usually implemented by the inverter 14 are able to recognize the actual power deliverable by the photovoltaic plant 1 1 and hence make it function, right from its start-up step and even when there are shadowed panels 12, in an optimum condition, that is, with maximum deliverable power, in relation to the number of panels 12 actually not shadowed.
  • Fig. 3 compares the development of energy produced in the course of one day by a plant using the method according to the present invention (line of dashes) and a traditional plant (continuous line).
  • line of dashes a traditional plant
  • MPPT optimization algorithm
  • control apparatus 10 instead of being an external or separate component with respect to the inverter 14, is an integral part of it.
  • control apparatus 10 may be provided that said functions performed by the control apparatus 10 are implemented directly by the inverter 14 itself, using its electronic switches and suitably modifying the management and control software of the inverter 14, to comprise inside it the functions performed by the controller 19 and timer 21.
  • Some forms of embodiment can also provide to drive the switch 18 in manual mode.
  • the user can decide to activate the control apparatus 10 according to the present invention even after the plant has started, for example to verify its functioning.
  • control method can be included in a computer program that can be memorized in a mean readable by a computer that contains the instructions which, when executed by the controller 19, determine the execution of the control method using the control apparatus 10 according to the present invention.

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  • Engineering & Computer Science (AREA)
  • Electromagnetism (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Automation & Control Theory (AREA)
  • Photovoltaic Devices (AREA)
  • Charge And Discharge Circuits For Batteries Or The Like (AREA)
  • Supply And Distribution Of Alternating Current (AREA)
  • Control Of Electrical Variables (AREA)

Abstract

Cette invention concerne un appareil de commande d'une installation photovoltaïque (11) comprenant au moins un chapelet (13) de modules photovoltaïques (12) reliés à un convertisseur de courant (14). Et un commutateur (18) connecté en dérivation audit chapelet (13) et audit convertisseur de courant (14).
PCT/IB2013/061108 2012-12-18 2013-12-18 Procédé de commande d'une installation photovoltaïque et appareil de commande correspondant WO2014097190A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
IT000218A ITUD20120218A1 (it) 2012-12-18 2012-12-18 Apparato di controllo di un impianto fotovoltaico e relativo metodo di controllo
ITUD2012A000218 2012-12-18

Publications (2)

Publication Number Publication Date
WO2014097190A2 true WO2014097190A2 (fr) 2014-06-26
WO2014097190A3 WO2014097190A3 (fr) 2014-11-06

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IT (1) ITUD20120218A1 (fr)
WO (1) WO2014097190A2 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115293370A (zh) * 2022-05-16 2022-11-04 华能南京金陵发电有限公司 一种分布式光伏电站的数字一体化运维管理系统

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0206253A1 (fr) 1985-06-20 1986-12-30 Siemens Aktiengesellschaft Circuit d'alimentation d'une charge électrique à partir d'un générateur solaire
DE3727026A1 (de) 1987-08-13 1989-02-23 Siemens Ag Schaltungsanordnung zur speisung einer elektrischen last aus einem solargenerator
WO2012014182A1 (fr) 2010-07-30 2012-02-02 Bitron S.P.A. Procédé et dispositif destinés à rendre maximale la puissance électrique produite par un générateur, en particulier un générateur fondé sur une source d'énergie renouvelable

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2012026593A1 (fr) * 2010-08-27 2012-03-01 学校法人 幾徳学園 Système de production d'électricité solaire, dispositif de commande utilisé pour un système de production d'électricité solaire, ainsi que procédé de commande et programme pour celui-ci
US9018800B2 (en) * 2010-11-19 2015-04-28 Texas Instruments Incorporated High efficiency wide load range buck/boost/bridge photovoltaic micro-converter
US8664931B2 (en) * 2011-06-13 2014-03-04 Perpetua Power Source Technologies, Inc. Self-optimizing energy harvester using generator having a variable source voltage

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0206253A1 (fr) 1985-06-20 1986-12-30 Siemens Aktiengesellschaft Circuit d'alimentation d'une charge électrique à partir d'un générateur solaire
DE3727026A1 (de) 1987-08-13 1989-02-23 Siemens Ag Schaltungsanordnung zur speisung einer elektrischen last aus einem solargenerator
WO2012014182A1 (fr) 2010-07-30 2012-02-02 Bitron S.P.A. Procédé et dispositif destinés à rendre maximale la puissance électrique produite par un générateur, en particulier un générateur fondé sur une source d'énergie renouvelable

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN115293370A (zh) * 2022-05-16 2022-11-04 华能南京金陵发电有限公司 一种分布式光伏电站的数字一体化运维管理系统

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Publication number Publication date
ITUD20120218A1 (it) 2014-06-19
WO2014097190A3 (fr) 2014-11-06

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