WO2012014182A1 - Method and device for maximizing the electrical power produced by a generator, particularly a generator based on a renewable power source - Google Patents

Method and device for maximizing the electrical power produced by a generator, particularly a generator based on a renewable power source Download PDF

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Publication number
WO2012014182A1
WO2012014182A1 PCT/IB2011/053389 IB2011053389W WO2012014182A1 WO 2012014182 A1 WO2012014182 A1 WO 2012014182A1 IB 2011053389 W IB2011053389 W IB 2011053389W WO 2012014182 A1 WO2012014182 A1 WO 2012014182A1
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WO
WIPO (PCT)
Prior art keywords
converter
signal
generator
input
current
Prior art date
Application number
PCT/IB2011/053389
Other languages
French (fr)
Inventor
Giovanni Petrone
Enrico Bianconi
Giovanni Spagnuolo
Nicola Femia
Massimo Vitelli
Francisco Javier Calvente Calvo
Roberto Giral Castillon
Carlos Andres Ramos Paja
Original Assignee
Bitron S.P.A.
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.)
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Publication date
Application filed by Bitron S.P.A. filed Critical Bitron S.P.A.
Publication of WO2012014182A1 publication Critical patent/WO2012014182A1/en

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Classifications

    • GPHYSICS
    • G05CONTROLLING; REGULATING
    • G05FSYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
    • G05F1/00Automatic 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
    • G05F1/66Regulating electric power
    • G05F1/67Regulating electric power to the maximum power available from a generator, e.g. from solar cell
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381Dispersed generators
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02JCIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2300/00Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20The dispersed energy generation being of renewable origin
    • H02J2300/22The renewable source being solar energy
    • H02J2300/24The renewable source being solar energy of photovoltaic origin
    • H02J2300/26The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • YGENERAL 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
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00Energy generation through renewable energy sources
    • Y02E10/50Photovoltaic [PV] energy
    • Y02E10/56Power conversion systems, e.g. maximum power point trackers

Definitions

  • the present invention relates to a method and a device for controlling an electrical generator whose power varies in time, in particular a generator based on a renewable power source, such as a photovoltaic or wind-powered generator, or a power carrier for which the time profile of the generated power is not known in advance, connected to an AC or DC load, or connected to the electrical mains.
  • a renewable power source such as a photovoltaic or wind-powered generator, or a power carrier for which the time profile of the generated power is not known in advance, connected to an AC or DC load, or connected to the electrical mains.
  • the invention relates to a control method acting on a power conversion system, comprising the steps of
  • Figure 1 of the attached drawings shows, in the form of a diagram which is partially a block diagram, a possible configuration of the system to which the method according to the invention can be applied.
  • the diagram relates to a photovoltaic application connected to the single-phase electrical mains, and is provided purely by way of example and solely for the purpose of describing the method proposed by the invention, being non-limiting in respect of the type of generator used and the conversion circuit used, in terms of its type and its connection to the single-phase or three-phase AC electrical mains or to an isolated load of the AC or DC type.
  • the letters PV indicate a photovoltaic generator, formed by an array of panels, and the number 1 indicates the associated conversion system.
  • This conversion system 1 comprises a DC-DC converter 2 and a DC-AC converter 3.
  • a parallel-connected capacitor Cj n is interposed between the input of the DC-DC converter 2 and the photovoltaic generator PV.
  • a bulk capacitor C b is connected in parallel on the DC link 4 which interconnects the converters 2 and 3. .
  • the DC-DC converter 2 is associated with a transferred power control module, indicated as a whole by 5.
  • This module 5 receives at its input, in a known way, a signal indicating the voltage at the input of the converter 2, and a signal indicating the current flowing from or returning towards the photovoltaic generator PV.
  • the module 5 supplies a control signal to the converter 2, the characteristics of this signal modifying the driving of one or more electronic switches included in the converter 2.
  • a corresponding control module 6 is associated with the converter or inverter 3. This module drives the inverter 3 as a function of the voltage V b detected across the capacitor Cb, and of the voltage V g and the current I g at the output of the converter 3.
  • the inverter 3 causes an oscillation of the voltage V b across the capacitor C b at a frequency (of 100 Hz for example) which is equal to twice the frequency (50 Hz for example) of the network ACN.
  • This oscillation is propagated through the converter 2 and the control module 5, and disturbs the voltage Vpv of the generator PV. This causes a decrease in the power produced by the photovoltaic generator and can lead to a malfunction of the MPPT control module 5.
  • One object of the present invention is to overcome the aforementioned disadvantages of prior art conversion systems.
  • a second object is to extend the possibilities of "immunizing” the generator from all disturbances originating from the output of the DC-DC converter (2), either in applications connected to the mains or in applications operating in “island” mode (in DC or in AC).
  • a third object is to increase the efficiency of the maximum power point tracking of the generator provided by the controller (5).
  • the first loop is dedicated to tracking the current variations caused by "exogenous" variables (such as the incident solar radiation in the case of a photovoltaic generator), while the second loop is dedicated to maximizing the power produced by the system.
  • a conversion method of the type described initially is implemented according to the invention, and is characterized in that it detects the magnitude of the current flowing in the first capacitor and determines the duty cycle of the aforesaid driving signal in predetermined ways as a function of the detected magnitude of the current.
  • the input receives, in a known way, a signal indicating the voltage at the input of the converter 2, and a signal indicating the current flowing from or returning towards the photovoltaic generator PV.
  • the second control loop provides the first control loop with a reference signal whose characteristics modify the driving of one or more electronic switches included in the converter 2.
  • the current flowing during operation in the parallel-connected input capacitor "reflects" very rapidly the variations in current and voltage of the photovoltaic generator due to the variations of the solar radiation conditions. This enables a fast response time to be achieved.
  • the conversion system according to the invention can provide good rejection not only of the oscillations at the frequency which is double the mains frequency, but also of all other disturbances, owing to the fact that, in the configuration of the system proposed as an example of application to photovoltaic systems, all the disturbances originating either from the output of the converter 2 or from the generator are reflected in the current flowing in the parallel-connected input capacitor.
  • the application of the present invention requires the identification of any electrical variable which is instantaneously modified by the variations of the disturbances originating from the generator or from the converter 2, and which can be used in place of the input capacitor current.
  • Figure 1 shows the architecture of a prior art conversion system
  • Figure 2 is a diagram showing an embodiment of a conversion system according to the present invention.
  • a DC-DC converter is coupled, through a parallel-connected capacitor, to a direct current electrical generator whose power is variable in time, particularly a generator based on a renewable power source.
  • the DC-DC converter is, for example, a boost converter or a buck converter, and comprises at least one controlled electronic switch, driven by a signal having a variable duty cycle.
  • the conversion method according to the invention is primarily characterized by the fact that a double loop control system is implemented in the MPPT control unit 5: the first loop (or inner loop) is dedicated to tracking the current variations caused by "exogenous" variables (such as the incident solar radiation in the case of a photovoltaic generator), while the second loop is dedicated to maximizing the power produced by the system.
  • the first loop or inner loop
  • the second loop is dedicated to maximizing the power produced by the system.
  • the method according to the invention requires the identification of an electrical variable which is modified virtually instantaneously by the variations or disturbances originating from the generator or from the input converter.
  • the magnitude of the current flowing in the capacitor is detected during operation, and the duty cycle of the driving signal applied to the electronic switch of the DC-DC converter is determined as a function of the detected magnitude of this current.
  • the DC-DC converter 2 is of the boost type, and comprises a series inductor L, a controlled electronic switch M such as a MOSFET, and a diode D.
  • the invention can also be applied equally well when using DC- DC converters of other types, such as buck converters.
  • the inductor L is connected between the photovoltaic generator PV and the anode of a diode D, the cathode of which is connected to the DC-AC converter or inverter 3 through one of the two conductors of the DC link 4.
  • the drain of the transistor M is connected to the anode of the diode D, while its source is connected to the earth GND (to which the other conductor of the DC link 4 is connected), and its gate is connected to the output of a control circuit CC.
  • control circuit CC drives the transistor M with a square wave signal whose duty cycle is variable in predetermined ways as a function of two control signals applied to its two inputs.
  • a first input signal of the control circuit CC is a signal supplied by a first current detector 7 associated with the parallel-connected input capacitor Cj n .
  • a second input signal is supplied to the control circuit CC by the control module 5.
  • the control module 5 receives at its input a signal Ipv from a current detector 8 associated with a conductor which couples the photovoltaic generator PV to the DC-DC converter 2, particularly the conductor connected to the inductor L of the converter.
  • Another signal V PV is sent to the control module 5 through a connection 9 to the conductor with which the current detector 8 is associated.
  • the signals V PV and Ipv delivered to the control module 5 represent the voltage and current at the output of the photovoltaic generator PV.
  • control module 5 comprises a multiplier 10 which receives the voltage signal Vpv and the current signal Ipv- This multiplier supplies at its output a signal Ppv representing the power at the output of the photovoltaic generator PV, in other words at the input of the DC-DC converter 2.
  • the signals Ipv and Vpv which are delivered to the multiplier 10 could be branched from the upper conductor of the DC link 4, in such a way that the multiplier 10 would supply the power at the output of the converter 2.
  • the output of the multiplier 10 is coupled to the input of an MPPT device 1 1 , of a known type, which supplies at its output a reference voltage VREF sent to an input of a subtraction device 12.
  • the signal Vpy is applied to a further input of the subtraction device 12.
  • This subtraction device 12 supplies at its output an error signal V e proportional to the difference between the voltage Vp V and the reference voltage VREF-
  • the error signal V e is delivered to the input of a correction network 13, which supplies from its output the signal I V R to the control circuit CC of the DC-DC converter 2.
  • control module 5 The architecture of the control module 5 described above is substantially conventional.
  • a distinctive feature of the conversion system 1 according to the present invention is the fact that the operation of the DC-DC converter 2 is driven as a function of the detected magnitude Ici n of the current flowing in the parallel-connected input capacitor Cj n .
  • this current in the photovoltaic application, can "reflect" the variations of solar radiation in a very rapid way, unlike the current in the inductor L.
  • the photovoltaic generator PV is immediately modified by the variations in solar radiation, but the known methods of implementing the MPPT function in the unit 5 cannot react instantaneously to these variations. It is the object of the invention to overcome this limitation.
  • the conversion system 1 of Figure 2 provides efficient rejection of disturbances at the frequency which is twice that of the network ACN, and of any other disturbances, because these have an immediate effect on the current in the parallel -connected input capacitor.
  • the disturbance rejection band depends on the design characteristics of the control circuit CC associated with the DC-DC converter 2, which must have a large bandwidth and can be based, for example, on non-linear control methods such as "sliding mode" or "one cycle” control.
  • the principle of the invention remaining the same, the forms of embodiment and the details of construction may be varied widely with respect to those described and illustrated, which have been given purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the attached claims.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Electromagnetism (AREA)
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  • Life Sciences & Earth Sciences (AREA)
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Abstract

The method comprises the operations of: coupling a DC-DC converter (2) to the generator (PV) through a first, parallel- connected capacitor (Cin), the converter (2) comprising at least one electronic switch (M), driving the switch (M) by means of a driving signal having a variable duty cycle in predetermined ways as a function of a control signal generated on the basis of a predetermined MPPT algorithm; identifying an electrical quantity (ICin) capable of reflecting, in a substantially instantaneous manner, the effects of disturbances originating from the generator (PV) and/or the DC-DC converter (2), detecting the magnitude of the electrical quantity (ICin), and determining the duty cycle of the driving signal in a predetermined way as a function of the detected magnitude of this quantity (ICin).

Description

Method and device for maximizing the electrical power produced by a generator, particularly a generator based on a renewable power source
The present invention relates to a method and a device for controlling an electrical generator whose power varies in time, in particular a generator based on a renewable power source, such as a photovoltaic or wind-powered generator, or a power carrier for which the time profile of the generated power is not known in advance, connected to an AC or DC load, or connected to the electrical mains.
More specifically, the invention relates to a control method acting on a power conversion system, comprising the steps of
coupling a DC-DC converter to the generator through a first, parallel-connected capacitor, the converter comprising at least one electronic switch;
driving the switch by means of a driving signal having a duty cycle which is variable in predetermined ways, using a reference signal generated on the basis of a predetermined MPPT algorithm.
Prior art
Figure 1 of the attached drawings shows, in the form of a diagram which is partially a block diagram, a possible configuration of the system to which the method according to the invention can be applied. The diagram relates to a photovoltaic application connected to the single-phase electrical mains, and is provided purely by way of example and solely for the purpose of describing the method proposed by the invention, being non-limiting in respect of the type of generator used and the conversion circuit used, in terms of its type and its connection to the single-phase or three-phase AC electrical mains or to an isolated load of the AC or DC type.
In Figure 1 of the attached drawings, the letters PV indicate a photovoltaic generator, formed by an array of panels, and the number 1 indicates the associated conversion system. This conversion system 1 comprises a DC-DC converter 2 and a DC-AC converter 3. A parallel-connected capacitor Cjn is interposed between the input of the DC-DC converter 2 and the photovoltaic generator PV. A bulk capacitor Cb is connected in parallel on the DC link 4 which interconnects the converters 2 and 3. .The DC-DC converter 2 is associated with a transferred power control module, indicated as a whole by 5. This module 5 receives at its input, in a known way, a signal indicating the voltage at the input of the converter 2, and a signal indicating the current flowing from or returning towards the photovoltaic generator PV. The module 5 supplies a control signal to the converter 2, the characteristics of this signal modifying the driving of one or more electronic switches included in the converter 2.
A corresponding control module 6 is associated with the converter or inverter 3. This module drives the inverter 3 as a function of the voltage Vb detected across the capacitor Cb, and of the voltage Vg and the current Ig at the output of the converter 3.
Problems of the prior art
In the operation of a conventional converter of the type shown in Figure 1 , the inverter 3 causes an oscillation of the voltage Vb across the capacitor Cb at a frequency (of 100 Hz for example) which is equal to twice the frequency (50 Hz for example) of the network ACN. This oscillation is propagated through the converter 2 and the control module 5, and disturbs the voltage Vpv of the generator PV. This causes a decrease in the power produced by the photovoltaic generator and can lead to a malfunction of the MPPT control module 5.
In order to overcome this problem in the prior art, a capacitor Cb having a rather high capacitance is chosen. However, this makes it necessary to use electrolytic capacitors.
Objects of the invention
One object of the present invention is to overcome the aforementioned disadvantages of prior art conversion systems.
*
A second object is to extend the possibilities of "immunizing" the generator from all disturbances originating from the output of the DC-DC converter (2), either in applications connected to the mains or in applications operating in "island" mode (in DC or in AC).
A third object is to increase the efficiency of the maximum power point tracking of the generator provided by the controller (5).
These and other objects are achieved according to the invention with a method whose principal characteristics are defined in the attached Claim 1.
As described below with reference to Figure 2, the aforesaid objects are achieved in practice by the provision of a double control loop in the MPPT unit 5: the first loop is dedicated to tracking the current variations caused by "exogenous" variables (such as the incident solar radiation in the case of a photovoltaic generator), while the second loop is dedicated to maximizing the power produced by the system.
In the first loop, a conversion method of the type described initially is implemented according to the invention, and is characterized in that it detects the magnitude of the current flowing in the first capacitor and determines the duty cycle of the aforesaid driving signal in predetermined ways as a function of the detected magnitude of the current.
In the second loop, the input receives, in a known way, a signal indicating the voltage at the input of the converter 2, and a signal indicating the current flowing from or returning towards the photovoltaic generator PV. The second control loop provides the first control loop with a reference signal whose characteristics modify the driving of one or more electronic switches included in the converter 2.
The aforesaid objects are also achieved according to the invention with a conversion system whose principal characteristics are defined in Claim 4.
In a conversion system of this type, for a photovoltaic generator (for example), the current flowing during operation in the parallel-connected input capacitor "reflects" very rapidly the variations in current and voltage of the photovoltaic generator due to the variations of the solar radiation conditions. This enables a fast response time to be achieved.
The conversion system according to the invention can provide good rejection not only of the oscillations at the frequency which is double the mains frequency, but also of all other disturbances, owing to the fact that, in the configuration of the system proposed as an example of application to photovoltaic systems, all the disturbances originating either from the output of the converter 2 or from the generator are reflected in the current flowing in the parallel-connected input capacitor.
The application of the present invention requires the identification of any electrical variable which is instantaneously modified by the variations of the disturbances originating from the generator or from the converter 2, and which can be used in place of the input capacitor current.
Description of the drawings
Other characteristics and advantages of the invention will become clear from the following detailed description which is given purely by way of non-limiting example with reference to the attached drawings, in which:
Figure 1, described above, shows the architecture of a prior art conversion system, and
Figure 2 is a diagram showing an embodiment of a conversion system according to the present invention.
Detailed description of embodiments
Before a detailed description of a non-limiting example of a conversion system according to the invention is given, the principal features of the conversion method according to the invention will be indicated.
In this method, a DC-DC converter is coupled, through a parallel-connected capacitor, to a direct current electrical generator whose power is variable in time, particularly a generator based on a renewable power source. The DC-DC converter is, for example, a boost converter or a buck converter, and comprises at least one controlled electronic switch, driven by a signal having a variable duty cycle.
The conversion method according to the invention is primarily characterized by the fact that a double loop control system is implemented in the MPPT control unit 5: the first loop (or inner loop) is dedicated to tracking the current variations caused by "exogenous" variables (such as the incident solar radiation in the case of a photovoltaic generator), while the second loop is dedicated to maximizing the power produced by the system.
The method according to the invention requires the identification of an electrical variable which is modified virtually instantaneously by the variations or disturbances originating from the generator or from the input converter.
In the exemplary case, relating to a photovoltaic application, the magnitude of the current flowing in the capacitor is detected during operation, and the duty cycle of the driving signal applied to the electronic switch of the DC-DC converter is determined as a function of the detected magnitude of this current.
A specific example of embodiment will now be given with reference to the diagram in Figure 2.
In Figure 2, components described previously have been given the same alphanumerical references as those used before in relation to Figure 1.
In the embodiment shown by way of example in Figure 2, the DC-DC converter 2 is of the boost type, and comprises a series inductor L, a controlled electronic switch M such as a MOSFET, and a diode D. The invention can also be applied equally well when using DC- DC converters of other types, such as buck converters.
With reference to Figure 2, the inductor L is connected between the photovoltaic generator PV and the anode of a diode D, the cathode of which is connected to the DC-AC converter or inverter 3 through one of the two conductors of the DC link 4. The drain of the transistor M is connected to the anode of the diode D, while its source is connected to the earth GND (to which the other conductor of the DC link 4 is connected), and its gate is connected to the output of a control circuit CC.
In operation, the control circuit CC drives the transistor M with a square wave signal whose duty cycle is variable in predetermined ways as a function of two control signals applied to its two inputs.
A first input signal of the control circuit CC, indicated by Ιαη, is a signal supplied by a first current detector 7 associated with the parallel-connected input capacitor Cjn. A second input signal, indicated by IVR, is supplied to the control circuit CC by the control module 5.
The control module 5 receives at its input a signal Ipv from a current detector 8 associated with a conductor which couples the photovoltaic generator PV to the DC-DC converter 2, particularly the conductor connected to the inductor L of the converter.
Another signal VPV is sent to the control module 5 through a connection 9 to the conductor with which the current detector 8 is associated.
In operation, the signals VPV and Ipv delivered to the control module 5 represent the voltage and current at the output of the photovoltaic generator PV.
In the embodiment shown schematically in Figure 2, the control module 5 comprises a multiplier 10 which receives the voltage signal Vpv and the current signal Ipv- This multiplier supplies at its output a signal Ppv representing the power at the output of the photovoltaic generator PV, in other words at the input of the DC-DC converter 2.
In an alternative embodiment (not shown), the signals Ipv and Vpv which are delivered to the multiplier 10 could be branched from the upper conductor of the DC link 4, in such a way that the multiplier 10 would supply the power at the output of the converter 2. The output of the multiplier 10 is coupled to the input of an MPPT device 1 1 , of a known type, which supplies at its output a reference voltage VREF sent to an input of a subtraction device 12.
The signal Vpy is applied to a further input of the subtraction device 12. This subtraction device 12 supplies at its output an error signal Ve proportional to the difference between the voltage VpV and the reference voltage VREF-
The error signal Ve is delivered to the input of a correction network 13, which supplies from its output the signal IVR to the control circuit CC of the DC-DC converter 2.
The architecture of the control module 5 described above is substantially conventional.
A distinctive feature of the conversion system 1 according to the present invention is the fact that the operation of the DC-DC converter 2 is driven as a function of the detected magnitude Icin of the current flowing in the parallel-connected input capacitor Cjn.
As mentioned above, this current, in the photovoltaic application, can "reflect" the variations of solar radiation in a very rapid way, unlike the current in the inductor L. In the conventional system of Figure 1 , the photovoltaic generator PV is immediately modified by the variations in solar radiation, but the known methods of implementing the MPPT function in the unit 5 cannot react instantaneously to these variations. It is the object of the invention to overcome this limitation.
The conversion system 1 of Figure 2 provides efficient rejection of disturbances at the frequency which is twice that of the network ACN, and of any other disturbances, because these have an immediate effect on the current in the parallel -connected input capacitor.
The disturbance rejection band depends on the design characteristics of the control circuit CC associated with the DC-DC converter 2, which must have a large bandwidth and can be based, for example, on non-linear control methods such as "sliding mode" or "one cycle" control. Naturally, the principle of the invention remaining the same, the forms of embodiment and the details of construction may be varied widely with respect to those described and illustrated, which have been given purely by way of non-limiting example, without thereby departing from the scope of the invention as defined in the attached claims.

Claims

1. Method for maximizing the power produced by a direct current electrical generator (PV) whose power is variable in time, in particular a generator based on a power source of a renewable type, and a load (3) or an electrical network (ACN), comprising the steps of coupling a DC-DC converter (2) to the generator (PV) through a first, parallel- connected capacitor (Cjn), the converter (2) comprising at least one electronic switch (M), driving the switch (M) by means of a driving signal having a variable duty cycle, in predetermined ways as a function of a control signal generated on the basis of a predetermined MPPT algorithm;
the method being characterized by the steps of
identifying an electrical quantity (Ιαη) capable of reflecting, in a substantially instantaneous manner, the effects of disturbances originating from the generator (PV) and/or the DC-DC converter (2),
detecting the magnitude of the electrical quantity (Icin), and
determining the duty cycle of the driving signal in a predetermined way as a function of the detected magnitude of the quantity (Ιαη
2. Method according to Claim 1 , in which the electrical quantity is the current (Icin) flowing through the first capacitor (Cjn).
3. Method according to Claim 2, in which use is made of double-loop control for determining the driving signal, including
a first control loop adapted to provide a first signal (Icin) indicating the current flowing through the first capacitor (Cjn) and capable of modifying the duty cycle of the driving signal as a function of the detected magnitude of the current, and
a second control loop, using the detected values of the voltage (Vpv) at the input of the converter (2) and the current (Ipv) flowing from or returning to the generator (PV) for generating a reference signal (VREF) utilized to modify the duty cycle of the driving signal.
4. Conversion method according to Claim 3, comprising the operations of:
detecting the magnitude of the current flowing from the generator (PV) towards the DC-DC converter (2) and the voltage at the input of the DC-DC converter (2) to generate a signal representing the power (PPV) at the input of the DC-DC converter (2),
generating, by means of an MPPT algorithm, a reference voltage (VREF) as a function of the power (PPV) at the input of the DC-DC converter (2),
providing an error signal (Ve) indicating the difference between the voltage at the input of the DC-DC converter (2) and the reference voltage (VREF), and
driving the at least one electronic switch (M) of the DC-DC converter (2) by means of a signal whose duty cycle varies additionally as a function of the error signal (Ve).
5. System for maximizing the electrical power produced by an electrical generator (PV) whose power varies in time, in particular a generator based on a power source of a renewable type, and a load (3) or an electrical network (ACN), comprising
a DC-DC converter (2) having an input intended to be coupled to the generator (PV) through a first, parallel-connected capacitor (Cjn), and an output intended to be coupled to the load (3) or the network (ACN) through a second, parallel-connected capacitor (Cb); the converter (2) comprising at least one electronic switch (M) and an associated control circuit (CC) adapted to drive the switch (M) by means of a signal having a duty cycle which is variable in a predetermined manner as a function of an input signal; and wherein the DC-DC converter (2) is associated with a control module (5) adapted to implement an MPPT function and designed to apply to the control circuit (CC) a second control signal (IVR) having predetermined characteristics;
the conversion system (1) being characterized in that it also comprises a first detector (7) associated with the first capacitor (Cjn) and adapted to provide the control circuit (CC) of the DC-DC converter (2) with a first input signal (Icin) indicating the detected magnitude of a predetermined electrical quantity capable of reflecting in a substantially instantaneous manner the effect of variations or disturbances originating from the generator (PV) and/or from the DC-DC converter (2), the control circuit (CC) being designed to drive the at least one electronic switch (M) of the DC-DC converter (2) in a predetermined way as a function of the detected magnitude of the electrical quantity (Icin) and of the signal (IVR) provided by the control module (5).
6. System according to Claim 5, in which the electrical quantity is the magnitude of the current (Ιαη) flowing in the first capacitor (Cjn).
7. System according to Claim 6, comprising
a first control loop adapted to provide a first signal (Icm) indicating the current flowing in the first capacitor (Cjn) and capable of modifying the duty cycle of the driving signal as a function of the detected magnitude of the current, and
a second control loop, utilizing the detected values of the voltage (Vpv) at the input of the converter (2) and of the current (Ipv) flowing from or returning towards the generator (PV) for generating a reference signal (VREF) utilized for modifying the duty cycle of the driving signal.
8. System according to Claim 7, comprising further second and third detectors (8, 9) adapted to provide signals indicating the magnitude of the current (Ipv) flowing from the generator (PV) to the DC-DC converter (2) and the voltage (VPV) at the input of the DC- DC converter (2), respectively, and in which the module (5) for controlling the power transferred by the DC-DC converter (2) comprises
a multiplier (10) coupled to the second and third detectors (8, 9) and adapted to provide a signal (Ppv) representing the power at the input of the DC-DC converter (2), an MPPT device (11) connected to the output of the multiplier (10) and designed to provide at its output a reference voltage (VREF), and
a subtracting device (12) coupled to the third detector (9) and the output of the MPPT device (1 1) for providing an error signal (Ve) indicating the difference between the voltage (Vpv) at the input of the DC-DC converter (2) and the reference voltage (VREF), the error signal being usable for driving the control circuit (CC) of the DC-DC converter (2).
9. System according to one of Claims 5 to 8, in which the control circuit (CC) of the DC-DC converter (2) is of a type adapted to implement a non-linear control method, such as the "sliding mode" or "one cycle" method.
PCT/IB2011/053389 2010-07-30 2011-07-29 Method and device for maximizing the electrical power produced by a generator, particularly a generator based on a renewable power source WO2012014182A1 (en)

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