WO2020019103A1 - Photovoltaic power system - Google Patents

Photovoltaic power system Download PDF

Info

Publication number
WO2020019103A1
WO2020019103A1 PCT/CN2018/096605 CN2018096605W WO2020019103A1 WO 2020019103 A1 WO2020019103 A1 WO 2020019103A1 CN 2018096605 W CN2018096605 W CN 2018096605W WO 2020019103 A1 WO2020019103 A1 WO 2020019103A1
Authority
WO
WIPO (PCT)
Prior art keywords
power converter
panel
converter
photovoltaic
current
Prior art date
Application number
PCT/CN2018/096605
Other languages
French (fr)
Inventor
Xiaobo Yang
Wenliang Zhang
Sheng ZONG
Chunming YUAN
Guoxing FAN
Original Assignee
Abb Schweiz Ag
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 Abb Schweiz Ag filed Critical Abb Schweiz Ag
Priority to PCT/CN2018/096605 priority Critical patent/WO2020019103A1/en
Publication of WO2020019103A1 publication Critical patent/WO2020019103A1/en

Links

Images

Classifications

    • 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
    • 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
    • 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
    • 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 invention relates to photovoltaic power system, and more particularly to a photovoltaic power system having means for removing snow.
  • PV panel photovoltaic panel
  • Patent JP 2000 156 940 A discloses a method for controlling a converter in which an inverter is constructed by a bidirectional converter.
  • the technical solution as disclosed by the Patent JP 2000 156 940 A has a diode connected with the string of photovoltaic panels in anti-series to block current flow from the converter to the photovoltaic panel, and a controllable bypass device connected with the diode in parallel for conducting snow-melting current from the converter to the photovoltaic panel.
  • a controllable bypass device connected with the diode in parallel for conducting snow-melting current from the converter to the photovoltaic panel.
  • a photovoltaic power system including: at least one PV panel assembly having at least one PV panel, a central power converter having a DC side and an AC side to be electrically coupled to an AC grid, at least one distributed power converter each having a first DC side electrically coupled to a corresponding one of the at least one PV panel assembly and a second DC side electrically coupled with the DC side of the central power converter, and a control system, for controlling operation of the central power converter and the at least one distributed power converter so that electric power flows in a forward direction or a backward direction; wherein: in the forward direction, the electric power generated by the at least one photovoltaic panel of the at least one PV panel assembly from electromagnetic radiation is supplied to the AC grid; and in the backward direction, the electric power from the AC grid is supplied to the at least one photovoltaic panel of the at least one PV panel assembly.
  • the photovoltaic power system further includes a voltage sensor for measuring voltage at the DC side of the central power converter and at least one current sensor each for measuring current of a corresponding one of the at least one PV panel assembly; wherein: the control system controls the operation of the central power converter so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor, and the control system controls the operation of the distributed power converter so as to regulate its current based on the current measurement by the current sensor.
  • the control system controls the operation of the central power converter so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor
  • the control system controls the operation of the distributed power converter so as to regulate its current based on the current measurement by the current sensor.
  • the distributed power converter is a bi-directional DC-DC converter
  • the central power converter is a bi-directional DC-AC converter.
  • the at least one photovoltaic panel of the PV panel assembly are connected in series.
  • control system controls the operation of the distributed power converter based on the current measurement and the voltage measurement so that it operates in MPPT when the electric power flows in the forward direction.
  • the value of the output current of the distributed power converter in the backward direction is a function of ambient temperature of the photovoltaic power system.
  • FIG. 1 is a configuration view of a photovoltaic power system according to an embodiment of present invention
  • FIG. 2 shows a typical voltage-current characteristics of PV panel according to an embodiment of present invention
  • FIG. 3 shows converter topology the distributed power converter uses according to an embodiment of present invention
  • FIG. 4 shows bidirectional converter according to an embodiment of present invention.
  • FIG. 5 depicts a non-isolated topology in the form of a three phase 2-level inverter according to an embodiment of present invention.
  • FIG. 1 is a configuration view of a photovoltaic power system according to an embodiment of present invention.
  • a photovoltaic power system 1 includes at least one PV panel assembly 100, 101, a central power converter 11, at least one distributed power converter 120, 121, and a control system 13.
  • the skilled person should understand that they can choose any number of the PV panel assemblies and any number of distributed power converters upon the requirement of the photovoltaic power system.
  • two PV panel assemblies 100, 101 and two distributed power converters 120, 121 are exemplified for description of present invention.
  • the PV panel assembly 100, 101 includes at least one PV panel 140, 141.
  • the central power converter 11 has a DC side and an AC side to be electrically coupled to an AC grid.
  • the distributed power converter 120, 121 has a first DC side electrically coupled to a corresponding one of the at least one PV panel assembly 100, 101 and a second DC side electrically coupled with the DC side of the central power converter 11.
  • the skilled person should understand that they can choose any number of the PV panels consisting of one of the PV panel assemblies upon the requirement of the photovoltaic power system.
  • the photovoltaic panels of the same PV panel assembly are connected in series to form a string.
  • the PV panel 140, 141 can be an array of PV cells wherein the individual cells can take on any variety of constructions such as but not limited to monocrystalline, polycrystalline, and thin film.
  • the array of PV cells are typically (but not necessarily always) assembled in close proximity to one another and in some forms can be coupled with a common carrier/substrate to form a unitary PV cell construction.
  • Such a unitary construction can allow for ease of transportation, installation, and maintenance.
  • the unitary construction can be mechanically and/or electrically connected with other unitary constructions to form the array of PV cells that provide power.
  • the PV panel can include an arrangement of sufficient numbers of individual PV cells to provide any range of power, such as power above 100 W to set forth just one non-limiting example.
  • FIG. 2 shows a typical voltage-current characteristics of PV panel.
  • a horizontal axis illustrates a terminal voltage of the PV panel, and a vertical axis illustrates a total value of the current which is output from the PV panel.
  • the PV cell is able to operate in either of the 1 st quadrant and the 4 th quadrant of the V-I characteristics. Where the PV panel operates in the 1 st quadrant, it is capable of producing and/or contributing useful electric power to the grid. While in the 4 th quadrant, each of the PV cells of the PV panel operates as a diode under forward conduction mode conducting a current injected into it; under this operation condition, the PV panels become passive load and dissipate heat.
  • PV panel will be melt when a water membrane formed between PV panel surface and the snow coating, which helps the whole snow pack drifts from the PV panel.
  • PV panel may operate in either of two modes, producing electric power to the grid or behaving as passive load and dissipating heat.
  • the PV system 1 of the first embodiment has two operation modes. One is a power generating mode that in the forward direction Df, the electric power generated by the photovoltaic panel 140, 141of the PV panel assembly 100, 101 from electromagnetic radiation is supplied to the AC grid; the other is a snow melting mode that in the backward direction Db, the electric power from the AC grid is supplied to the photovoltaic panel 140, 141 of the PV panel assembly 100, 101.
  • the control system 13 controls operation of the central power converter 11 and the distributed power converter 120, 121 so that electric power flows in the forward direction Df, where the PV power system 1 operates in the power generating mode. And, at the time of snow, the control system 13 controls operation of the central power converter 11 and the distributed power converter 120, 121 so that the electric power flows in the backward direction Db, where the PV power system 1 operates in the snow melting mode.
  • the DC electric power obtained from the PV panel assembly 100, 101 is converted by the distributed power converter 120, 121 and output at its second DC side, which, in turn, is converted by the central power converter 11 outputting and supplying an AC electric power at its AC side to the grid.
  • the AC electric power obtained from the grid is converted by the central power converter 11 outputting and supplying DC electric power at its DC side, which, in turn, is converted by the distributed power converter 120, 121 outputting and supplying DC electric power at its first DC side to the PV panel assembly 100, 101 to increase a temperature of the PV panel.
  • the distributed power converter 120, 121 can take on a number of forms and in general is structured to bi-directional DC-DC converter. As will be described in more detail below, the distributed power converter 120, 121 can include/be integrated or coupled with other functioning components such as a Maximum Power Point Tracker (MPPT) . The additional functioning components can either be included with the distributed power converter 120, 121 or implemented by the control system 13.
  • MPPT Maximum Power Point Tracker
  • an MPPT module can be used to seek out the maximum power point of the PV panel assembly 100, 101.
  • the MPPT and distributed power converter 120, 121 can be structured such that the input voltage to the distributed power converter 120, 121 is regulated by the MPPT module to “float” to whatever voltage yields maximum power from the PV panel assembly 100, 101 (in turn the distributed power converter 120, 121 can be structured such that its output is at a fixed voltage but the current allowed to “float” ) .
  • the MPPT can be located within the physical confines of a housing of the distributed power converter 120, 121 and/or integrated or coupled to it, but the MPPT can alternatively be located elsewhere in the PV panel assembly 100, 101. It will be appreciated that the MPPT can be implemented via digital and/or analog techniques, and can take on a variety of forms including perturb and observe, incremental conductance, current sweep, and constant voltage, to set forth just a few nonlimiting examples.
  • the central power converter 11 to which one or more distributed power converter 120, 121 are connected can take on a variety of forms.
  • the central power converter 11 can be a bidirectional DC-AC converter, non-limiting embodiments of which are shown and discussed further below.
  • the central power converter 11 can include a transformer. While the distributed power converters 120, 121 are shown as standing off from the PV panel assemblies 100, 101, in some embodiments the distributed power converters 120, 121 can be integrated with or in closer proximity to the PV panel assemblies 100, 101, no matter what the form of the central power converter 11.
  • the central power converter 11 can provide active and reactive power, AC voltage control, low voltage ride through, and randomization of timing for trip and reconnection.
  • the central power converter 11 can be connected to distributed power converters 120, 121 through plug and play devices.
  • a DC bus 15 routed between the central power converter 11 and distributed power converter 120, 121 can include on at least one end a connector (male or female) that incorporates plug and play features.
  • plug and play connectors permit are unlike hardwired connections in that they permit rapid connection and disconnection, and may also provide some degree of environmental protection.
  • the plug and play connectors can furthermore have features that permit the connector to be secured in place, such as through a clip, etc.
  • a power outlet of the distributed power converter 120, 121 can be a fixed base terminal (male or female) structured to receive a cable having a complementary shaped connection device.
  • the distributed power converter 120, 121 can include a cable, for example a hardwired cable, that has a cable ending with a plug and play device (male or female) useful for connection with a complementary plug and play device associated with the central power converter 11.
  • the plug and play connection devices can thus be considered to encompass terminal side and cable ended side connections, whether those connections are male or female.
  • the plug and play connection devices can be installed in a separate cabinet, or together with the central inverter in the same cabinet.
  • the plug and play devices can also be used in other components such as: between the PV panel assembly 100, 101 and the distributed power converter 120, 121; in the mechanical connection between the distributed power converter 120, 121 and the DC bus 15 (which in one form is an LVDC bus) ; and in the mechanical connection between the DC bus 15 and the central power converter 11.
  • a voltage sensor 16 and a current sensor 17 can be incorporated into one or more components of the PV power system 1, such as but not limited to the distributed power converter 120, 121 and/or the central power converter 11.
  • the sensors can include one or more communications devices (transmitter, receiver, transceiver, for example) can transmit to and receive data from the control system 13, and can do so using any variety of techniques.
  • the sensors can use industrial bus, cell and/or pager networks, satellite, licensed and/or unlicensed radio, and power line communication.
  • the sensors can be used in a network environment such as fixed wireless, mesh network, etc.
  • the smart meter can be structured to communicate status information such as but not limited to power, voltage, and current. In some forms the status information can be real-time while in others can additionally and/or alternatively include historic information. The status information can be compiled through measurement and/or be calculated.
  • the voltage sensor 16 can be a voltage transformer arranged at the DC side of the central power converter 11, for measuring voltage at the DC side of the central power converter 11.
  • the current sensor 17 can be a current transformer arranged at the PV panel assembly 100, 101, for measuring current of a corresponding one of the PV panel assembly 100, 101.
  • control system 13 may control the operation of the distributed power converter 120, 121 based on the current measurement and the voltage measurement so that it operates in maximum power point tracker (MPPT) when the electric power flows in the forward direction.
  • MPPT maximum power point tracker
  • the value of the output current of the distributed power converter 120, 121 in the backward direction is a function of ambient temperature of the photovoltaic power system.
  • the control system 13 may control the operation of the central power converter 11 so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor 16; further, the control system 13 may control the operation of the distributed power converter 120, 121 so as to regulate its current based on the current measurement by the current sensor 17.
  • the control system 13 takes the voltage and current count at point B as reference and controls the operation of the central power converter 11 so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor 16, and further controls the operation of the distributed power converter 120, 121 so as to regulate its current based on the current measurement by the current sensor 17.
  • distributed power converter 120, 121 can also regulate its current based on the current measurement by the current sensor 17.
  • the dependence between voltage and current of the DC bus 15 can be de-coupled by separately control of them by separate devices, the central power converter and the distributed power converter. This makes it possible for flexibly supplying snow-melting current under different ambient temperature conditions.
  • Still another feature of the present application provides wherein the distributed power converter is used for conversion electric power for melting the snow in the backward direction, and wherein the distributed power converter also provides function of MPPT in the forward direction.
  • the distributed power converter 120, 121 can take on a variety of isolated or non-isolated forms in any of the various embodiments herein, such as buck-boost converter, as shown in FIG. 3.
  • the distributed power converter includes two DC sides UDC1, UDC2, two capacitors C1, C2, and four controllable semiconductors each with anti-paralleled diode Q1, Q2, Q3, Q4.
  • Some DC-DC converters are designed to move power in only one direction, from dedicated input to output, for example full-bridge converter which can be made bidirectional and able to move power in either direction by paralleling some of their diodes D5, D6, D7, D8 with controllable power semiconductors Q5, Q6, Q7, Q8 as shown in FIG. 4, while keeping the rest of elements unchanged, including four controllable semiconductors each with anti-paralleled diode Q1, Q2, Q3, Q4 and two capacitors C1, C2 and the two DC sides UDC1, UDC2.
  • the central power converter 11 can also take on a variety of forms.
  • a DC-AC converter with bidirectional power flow can be realized by coupling a PWM inverter to the DC-link.
  • the DC-link quantity is then impressed by an energy storage element that is common to both stages, which is a capacitor C for the voltage DC-link or an inductor L for the current DC-link.
  • FIG. 5 depicts a non-isolated topology in the form of a three phase 2-level inverter, including six controllable semiconductors each with anti-paralleled diode Q1 to Q6 linked in full bridge and a capacitor.
  • Other topologies included three level converter, modular multilevel converter, Z-source inverter and so forth.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

It provides a photovoltaic power system (1), including: at least one PV panel assembly (100, 101), having at least one PV panel (140, 141), a central power converter (11) having a DC side and an AC side to be electrically coupled to an AC grid, at least one distributed power converter (120, 121) each having a first DC side electrically coupled to a corresponding one of the at least one PV panel assembly (100, 101) and a second DC side electrically coupled with the DC side of the central power converter (11), and a control system (13), for controlling operation of the central power converter (11) and the at least one distributed power converter (120, 121) so that electric power flows in a forward direction or a backward direction; wherein: in the forward direction, the electric power generated by the at least one PV panel (140, 141) of the at least one PV panel assembly (100, 101) from electromagnetic radiation is supplied to the AC grid; and in the backward direction, the electric power from the AC grid is supplied to the at least one PV panel (140, 141) of the at least one PV panel assembly (100, 101). It provides an alternative solution capable of controlling bidirectional power flow, in which either supplying snow-melting current to the PV panel (140, 141) or converting and transmitting electric power generated by the PV panel (140, 141) to the AC grid.

Description

PHOTOVOLTAIC POWER SYSTEM Technical Field
The invention relates to photovoltaic power system, and more particularly to a photovoltaic power system having means for removing snow.
Background Art
Recently, a photovoltaic power system where photovoltaic panels and a power system are interconnected through a converter, has been widely used. Since the photovoltaic panel (PV panel) obtains the generated power by electromagnetic radiation, a quantity of the generated power is reduced or the power generation is not possible when the electromagnetic radiation is partially or completely blocked. As one of causes which block the electromagnetic radiation, there is snow that is accumulated on the photovoltaic panel.
In order to remove the snow covering the photovoltaic panels, Patent JP 2000 156 940 A discloses a method for controlling a converter in which an inverter is constructed by a bidirectional converter.
The technical solution as disclosed by the Patent JP 2000 156 940 A has a diode connected with the string of photovoltaic panels in anti-series to block current flow from the converter to the photovoltaic panel, and a controllable bypass device connected with the diode in parallel for conducting snow-melting current from the converter to the photovoltaic panel. When the snow melting current is supplied by supplying the fixed voltage to the PV panel with the bidirectional converter, a fixed voltage is applied to a string of photovoltaic panels by the converter, and the photovoltaic panels are heated and the snow melting is achieved by making a snow melting current flow from the converter to the photovoltaic panels.
Brief Summary of the Invention
It is therefore an objective of the invention to provide a photovoltaic power system, including: at least one PV panel assembly having at least one PV panel, a central power converter having a DC side and an AC side to be electrically coupled to an AC grid, at least one distributed power converter each having a first DC side electrically coupled to a corresponding one of the at least one PV panel assembly and a second DC side electrically coupled with the DC side of the central power converter, and a control system, for controlling operation of the central power converter and the at least one distributed power converter so that electric power flows in a forward direction or a backward direction; wherein: in the forward direction, the electric power generated by the at least one photovoltaic panel of the at least one PV panel assembly from electromagnetic radiation is supplied to the AC grid; and in the backward direction, the electric power from the AC grid is supplied to the at least one photovoltaic panel of the at least one PV panel assembly.
By having the photovoltaic power system according to present invention, in light of the absence of the bypass device connected with the diode in parallel for conducting snow-melting current from the converter to the photovoltaic panel, it provides an alternative solution capable of controlling bidirectional power flow, in which either supplying snow-melting current to the PV panel or converting and transmitting electric power generated by the PV panel to grid.
Preferably, the photovoltaic power system further includes a voltage sensor for measuring voltage at the DC side of the central power converter and at least one current sensor each for measuring current of a corresponding one of the at least one PV panel assembly; wherein: the control system controls the operation of the central power converter so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor, and the control system controls the operation of the distributed power converter so as to regulate its current based on the current measurement by the current sensor. This allows the dependence between voltage and current of the DC bus to be de-coupled by separately control of them by separate devices, the central power converter and the distributed power converter. This makes it possible for flexibly supplying snow-melting current under different ambient temperature conditions.
Preferably, the distributed power converter is a bi-directional DC-DC converter, and the central power converter is a bi-directional DC-AC converter.
Preferably, the at least one photovoltaic panel of the PV panel assembly are connected in series.
Preferably, the control system controls the operation of the distributed power converter based on the current measurement and the voltage measurement so that it operates in MPPT when the electric power flows in the forward direction.
Preferably, the value of the output current of the distributed power converter in the backward direction is a function of ambient temperature of the photovoltaic power system.
Brief Description of the Drawings
The subject matter of the invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the drawings, in which:
FIG. 1 is a configuration view of a photovoltaic power system according to an embodiment of present invention;
FIG. 2 shows a typical voltage-current characteristics of PV panel according to an embodiment of present invention;
FIG. 3 shows converter topology the distributed power converter uses according to an embodiment of present invention;
FIG. 4 shows bidirectional converter according to an embodiment of present invention; and
FIG. 5 depicts a non-isolated topology in the form of a three phase 2-level inverter according to an embodiment of present invention.
The reference symbols used in the drawings, and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures.
Preferred Embodiments of the Invention
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed,  but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. Note, the headings are for organizational purposes only and are not meant to be used to limit or interpret the description or claims. Furthermore, note that the word "may" is used throughout this application in a permissive sense (i.e., having the potential to, being able to) , not a mandatory sense (i.e., must) . "The term "include" , and derivations thereof, mean "including, but not limited to" . The term "connected" means "directly or indirectly connected" , and the term "coupled" means "directly or indirectly connected" .
FIG. 1 is a configuration view of a photovoltaic power system according to an embodiment of present invention. As shown in FIG. 1, a photovoltaic power system 1 includes at least one  PV panel assembly  100, 101, a central power converter 11, at least one  distributed power converter  120, 121, and a control system 13. The skilled person should understand that they can choose any number of the PV panel assemblies and any number of distributed power converters upon the requirement of the photovoltaic power system. In this embodiment, two  PV panel assemblies  100, 101 and two  distributed power converters  120, 121 are exemplified for description of present invention. The  PV panel assembly  100, 101 includes at least one PV panel 140, 141. The central power converter 11 has a DC side and an AC side to be electrically coupled to an AC grid. The  distributed power converter  120, 121 has a first DC side electrically coupled to a corresponding one of the at least one  PV panel assembly  100, 101 and a second DC side electrically coupled with the DC side of the central power converter 11. The skilled person should understand that they can choose any number of the PV panels consisting of one of the PV panel assemblies upon the requirement of the photovoltaic power system. The photovoltaic panels of the same PV panel assembly are connected in series to form a string.
The PV panel 140, 141 can be an array of PV cells wherein the individual cells can take on any variety of constructions such as but not limited to monocrystalline, polycrystalline, and thin film. The array of PV cells are typically (but not necessarily always) assembled in close proximity to one another and in some forms can be coupled with a common carrier/substrate to form a unitary PV cell construction. Such a unitary construction can allow for ease of transportation, installation, and maintenance. The unitary construction can be mechanically and/or electrically connected with other unitary constructions to form the array of PV cells that provide power. The PV panel can include an arrangement of sufficient numbers of individual PV cells to provide any range of power, such as power above 100 W to set forth just one non-limiting example.
FIG. 2 shows a typical voltage-current characteristics of PV panel. A horizontal axis illustrates a terminal voltage of the PV panel, and a vertical axis illustrates a total value of the current which is output from the PV panel. As shown in FIG 2, the PV cell is able to operate in either of the 1 st quadrant and the 4 th quadrant of the V-I characteristics. Where the PV panel operates in the 1 st quadrant, it is capable of producing and/or contributing useful electric power to the grid. While in the 4 th quadrant, each of the PV cells of the PV panel operates as a diode under forward conduction mode conducting a current injected into it; under this operation condition, the PV panels become passive load and dissipate heat. The snow covering the PV panel will be melt when a water membrane formed between PV panel surface and the snow coating, which helps the whole snow pack drifts from the PV panel. PV panel may operate in either of two modes, producing electric power to the grid or behaving as passive load and dissipating heat.
The PV system 1 of the first embodiment, has two operation modes. One is a power generating mode that in the forward direction Df, the electric power generated by the photovoltaic panel 140, 141of the  PV panel assembly  100, 101 from electromagnetic  radiation is supplied to the AC grid; the other is a snow melting mode that in the backward direction Db, the electric power from the AC grid is supplied to the photovoltaic panel 140, 141 of the  PV panel assembly  100, 101.
By the two modes, in a state of being with solar radiation, the control system 13 controls operation of the central power converter 11 and the  distributed power converter  120, 121 so that electric power flows in the forward direction Df, where the PV power system 1 operates in the power generating mode. And, at the time of snow, the control system 13 controls operation of the central power converter 11 and the  distributed power converter  120, 121 so that the electric power flows in the backward direction Db, where the PV power system 1 operates in the snow melting mode.
In this embodiment for example, in the state of being with solar radiation, the DC electric power obtained from the  PV panel assembly  100, 101 is converted by the  distributed power converter  120, 121 and output at its second DC side, which, in turn, is converted by the central power converter 11 outputting and supplying an AC electric power at its AC side to the grid. In the state of snow melting, the AC electric power obtained from the grid is converted by the central power converter 11 outputting and supplying DC electric power at its DC side, which, in turn, is converted by the  distributed power converter  120, 121 outputting and supplying DC electric power at its first DC side to the  PV panel assembly  100, 101 to increase a temperature of the PV panel.
The  distributed power converter  120, 121 can take on a number of forms and in general is structured to bi-directional DC-DC converter. As will be described in more detail below, the  distributed power converter  120, 121 can include/be integrated or coupled with other functioning components such as a Maximum Power Point Tracker (MPPT) . The additional functioning components can either be included with the  distributed power converter  120, 121 or implemented by the control system 13.
As will be appreciated, in the state of being with solar radiation, an MPPT module can be used to seek out the maximum power point of the  PV panel assembly  100, 101. In some embodiments the MPPT and distributed  power converter  120, 121 can be structured such that the input voltage to the distributed  power converter  120, 121 is regulated by the MPPT module to “float” to whatever voltage yields maximum power from the PV panel assembly 100, 101 (in turn the distributed  power converter  120, 121 can be structured such that its output is at a fixed voltage but the current allowed to “float” ) . The MPPT can be located within the physical confines of a housing of the distributed  power converter  120, 121 and/or integrated or coupled to it, but the MPPT can alternatively be located elsewhere in the  PV panel assembly  100, 101. It will be appreciated that the MPPT can be implemented via digital and/or analog techniques, and can take on a variety of forms including perturb and observe, incremental conductance, current sweep, and constant voltage, to set forth just a few nonlimiting examples.
The central power converter 11 to which one or more distributed  power converter  120, 121 are connected can take on a variety of forms. For example, the central power converter 11 can be a bidirectional DC-AC converter, non-limiting embodiments of which are shown and discussed further below. In some embodiments the central power converter 11 can include a transformer. While the distributed  power converters  120, 121 are shown as standing off from the  PV panel assemblies  100, 101, in some embodiments the distributed  power converters  120, 121 can be integrated with or in closer proximity to the  PV panel assemblies  100, 101, no matter what the form of the central power converter 11. The central power converter 11 can provide active and reactive power, AC voltage control, low voltage ride through, and randomization of timing for trip and reconnection.
The central power converter 11 can be connected to distributed  power converters  120, 121  through plug and play devices. For example, a DC bus 15 routed between the central power converter 11 and distributed  power converter  120, 121 can include on at least one end a connector (male or female) that incorporates plug and play features. As will be appreciated, plug and play connectors permit are unlike hardwired connections in that they permit rapid connection and disconnection, and may also provide some degree of environmental protection. The plug and play connectors can furthermore have features that permit the connector to be secured in place, such as through a clip, etc. In one embodiment a power outlet of the distributed  power converter  120, 121 can be a fixed base terminal (male or female) structured to receive a cable having a complementary shaped connection device. In another form the distributed  power converter  120, 121 can include a cable, for example a hardwired cable, that has a cable ending with a plug and play device (male or female) useful for connection with a complementary plug and play device associated with the central power converter 11. The plug and play connection devices can thus be considered to encompass terminal side and cable ended side connections, whether those connections are male or female. The plug and play connection devices can be installed in a separate cabinet, or together with the central inverter in the same cabinet.
The plug and play devices can also be used in other components such as: between the  PV panel assembly  100, 101 and the distributed  power converter  120, 121; in the mechanical connection between the distributed  power converter  120, 121 and the DC bus 15 (which in one form is an LVDC bus) ; and in the mechanical connection between the DC bus 15 and the central power converter 11.
Furthermore, it will be appreciated that a voltage sensor 16 and a current sensor 17 can be incorporated into one or more components of the PV power system 1, such as but not limited to the distributed  power converter  120, 121 and/or the central power converter 11. The sensors can include one or more communications devices (transmitter, receiver, transceiver, for example) can transmit to and receive data from the control system 13, and can do so using any variety of techniques. For example, the sensors can use industrial bus, cell and/or pager networks, satellite, licensed and/or unlicensed radio, and power line communication. Furthermore, the sensors can be used in a network environment such as fixed wireless, mesh network, etc. The smart meter can be structured to communicate status information such as but not limited to power, voltage, and current. In some forms the status information can be real-time while in others can additionally and/or alternatively include historic information. The status information can be compiled through measurement and/or be calculated.
In some embodiment, the voltage sensor 16 can be a voltage transformer arranged at the DC side of the central power converter 11, for measuring voltage at the DC side of the central power converter 11. Besides, the current sensor 17 can be a current transformer arranged at the  PV panel assembly  100, 101, for measuring current of a corresponding one of the  PV panel assembly  100, 101.
In some embodiment, the control system 13 may control the operation of the distributed  power converter  120, 121 based on the current measurement and the voltage measurement so that it operates in maximum power point tracker (MPPT) when the electric power flows in the forward direction.
An operation point of the PV panel 140, 141 at the time of the snow melting run will be descried by using FIG. 2.
The value of the output current of the distributed  power converter  120, 121 in the backward direction is a function of ambient temperature of the photovoltaic power system. When a heavy snow is on the panel, since the temperature of the panel is low, it is desirable to run the snow-melting following the characteristic of the string becomes V-I characteristic which is illustrated as “Heavy snow coating” . To keep the operation point on the desired curve, for  example at operation point A, by taking the voltage and current count at point A as reference, the control system 13 may control the operation of the central power converter 11 so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor 16; further, the control system 13 may control the operation of the distributed  power converter  120, 121 so as to regulate its current based on the current measurement by the current sensor 17. If the time elapses, the temperature of the  PV panel  100, 101 is further increased, and V-I characteristic is to be changed to point B on the curve indicated by “Moderate snow coating” . To keep the operation point at point B on the new curve, similarly, the control system 13 takes the voltage and current count at point B as reference and controls the operation of the central power converter 11 so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor 16, and further controls the operation of the distributed  power converter  120, 121 so as to regulate its current based on the current measurement by the current sensor 17. In some cases, distributed  power converter  120, 121 can also regulate its current based on the current measurement by the current sensor 17.
In the embodiment of the instant application, the dependence between voltage and current of the DC bus 15 can be de-coupled by separately control of them by separate devices, the central power converter and the distributed power converter. This makes it possible for flexibly supplying snow-melting current under different ambient temperature conditions.
Still another feature of the present application provides wherein the distributed power converter is used for conversion electric power for melting the snow in the backward direction, and wherein the distributed power converter also provides function of MPPT in the forward direction.
The distributed  power converter  120, 121 can take on a variety of isolated or non-isolated forms in any of the various embodiments herein, such as buck-boost converter, as shown in FIG. 3. The distributed power converter includes two DC sides UDC1, UDC2, two capacitors C1, C2, and four controllable semiconductors each with anti-paralleled diode Q1, Q2, Q3, Q4. Some DC-DC converters are designed to move power in only one direction, from dedicated input to output, for example full-bridge converter which can be made bidirectional and able to move power in either direction by paralleling some of their diodes D5, D6, D7, D8 with controllable power semiconductors Q5, Q6, Q7, Q8 as shown in FIG. 4, while keeping the rest of elements unchanged, including four controllable semiconductors each with anti-paralleled diode Q1, Q2, Q3, Q4 and two capacitors C1, C2 and the two DC sides UDC1, UDC2.
In similar fashion, the central power converter 11 can also take on a variety of forms.
A DC-AC converter with bidirectional power flow can be realized by coupling a PWM inverter to the DC-link. The DC-link quantity is then impressed by an energy storage element that is common to both stages, which is a capacitor C for the voltage DC-link or an inductor L for the current DC-link. For example, FIG. 5 depicts a non-isolated topology in the form of a three phase 2-level inverter, including six controllable semiconductors each with anti-paralleled diode Q1 to Q6 linked in full bridge and a capacitor. Other topologies included three level converter, modular multilevel converter, Z-source inverter and so forth.
Though the present invention has been described on the basis of some preferred embodiments, those skilled in the art should appreciate that those embodiments should by no way limit the scope of the present invention. Without departing from the spirit and concept of the present invention, any variations and modifications to the embodiments should be within the apprehension of those with ordinary knowledge and skills in the art, and therefore fall in the scope of the present invention which is defined by the accompanied claims.

Claims (8)

  1. A photovoltaic power system, including:
    at least one PV panel assembly having at least one PV panel;
    a central power converter having a DC side and an AC side to be electrically coupled to an AC grid;
    at least one distributed power converter each having a first DC side electrically coupled to a corresponding one of the at least one PV panel assembly and a second DC side electrically coupled with the DC side of the central power converter; and
    a control system, for controlling operation of the central power converter and the at least one distributed power converter so that electric power flows in a forward direction or a backward direction;
    wherein:
    in the forward direction, the electric power generated by the at least one photovoltaic panel of the at least one PV panel assembly from electromagnetic radiation is supplied to the AC grid; and
    in the backward direction, the electric power from the AC grid is supplied to the at least one photovoltaic panel of the at least one PV panel assembly.
  2. The photovoltaic power system according to claim 1, further including:
    a voltage sensor, for measuring voltage at the DC side of the central power converter;
    wherein:
    the control system controls the operation of the central power converter so as to regulate the voltage at its DC side based on the voltage measurement by the voltage sensor.
  3. The photovoltaic power system according to claim 2, further including:
    at least one current sensor each for measuring current of a corresponding one of the at least one PV panel assembly;
    wherein:
    the control system controls the operation of the distributed power converter so as to regulate its current based on the current measurement by the current sensor.
  4. The photovoltaic power system according to claim 1 or 2 or 3, further including:
    a DC bus, electrically coupling the second DC side of the distributed power converter and the DC side of the central power converter.
  5. The photovoltaic power system according to claim 1 or 2 or 3, wherein:
    the distributed power converter is a bi-directional DC-DC converter; and
    the central power converter is a bi-directional DC-AC converter.
  6. The photovoltaic power system according to claim 1 or 2 or 3, wherein:
    the at least one photovoltaic panel of the PV panel assembly are connected in series.
  7. The photovoltaic power system according to claim 3, wherein:
    the control system controls the operation of the distributed power converter based on the current measurement and the voltage measurement so that it operates in MPPT when the electric power flows in the forward direction.
  8. The photovoltaic power system according to claim 3, wherein:
    the value of the output current of the distributed power converter in the backward direction is a function of ambient temperature of the photovoltaic power system.
PCT/CN2018/096605 2018-07-23 2018-07-23 Photovoltaic power system WO2020019103A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/CN2018/096605 WO2020019103A1 (en) 2018-07-23 2018-07-23 Photovoltaic power system

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/CN2018/096605 WO2020019103A1 (en) 2018-07-23 2018-07-23 Photovoltaic power system

Publications (1)

Publication Number Publication Date
WO2020019103A1 true WO2020019103A1 (en) 2020-01-30

Family

ID=69180770

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/CN2018/096605 WO2020019103A1 (en) 2018-07-23 2018-07-23 Photovoltaic power system

Country Status (1)

Country Link
WO (1) WO2020019103A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111969704A (en) * 2020-08-10 2020-11-20 中山大学 Photovoltaic cell control circuit and control method
WO2022082769A1 (en) * 2020-10-23 2022-04-28 华为数字能源技术有限公司 Backward flowing slow-start circuit of string photovoltaic inverter

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140062209A1 (en) * 2012-09-06 2014-03-06 Eaton Corporation Photovoltaic system and method employing a number of maximum power point tracking mechanisms
CN204156540U (en) * 2014-11-13 2015-02-11 株洲变流技术国家工程研究中心有限公司 A kind of solar module ice melting system
US20150160676A1 (en) * 2013-12-06 2015-06-11 Shangzhi Pan Multi-input pv inverter with independent mppt and minimum energy storage
US20160254780A1 (en) * 2015-02-27 2016-09-01 Hitachi, Ltd. Power Conversion Apparatus and Photovoltaic System

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20140062209A1 (en) * 2012-09-06 2014-03-06 Eaton Corporation Photovoltaic system and method employing a number of maximum power point tracking mechanisms
US20150160676A1 (en) * 2013-12-06 2015-06-11 Shangzhi Pan Multi-input pv inverter with independent mppt and minimum energy storage
CN204156540U (en) * 2014-11-13 2015-02-11 株洲变流技术国家工程研究中心有限公司 A kind of solar module ice melting system
US20160254780A1 (en) * 2015-02-27 2016-09-01 Hitachi, Ltd. Power Conversion Apparatus and Photovoltaic System

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN111969704A (en) * 2020-08-10 2020-11-20 中山大学 Photovoltaic cell control circuit and control method
CN111969704B (en) * 2020-08-10 2021-07-20 中山大学 Photovoltaic cell control circuit and control method
WO2022082769A1 (en) * 2020-10-23 2022-04-28 华为数字能源技术有限公司 Backward flowing slow-start circuit of string photovoltaic inverter
CN114667678A (en) * 2020-10-23 2022-06-24 华为数字能源技术有限公司 Reverse-filling slow-start circuit of string type photovoltaic inverter
EP4220941A4 (en) * 2020-10-23 2023-09-20 Huawei Digital Power Technologies Co., Ltd. Backward flowing slow-start circuit of string photovoltaic inverter
CN114667678B (en) * 2020-10-23 2024-05-03 华为数字能源技术有限公司 Reverse-filling slow-starting circuit of string-type photovoltaic inverter

Similar Documents

Publication Publication Date Title
US11275398B2 (en) DC microgrid for interconnecting distributed electricity generation, loads, and storage
EP2807737B1 (en) Stacked voltage source inverter with separate dc sources
US20200036191A1 (en) Distributed substring architecture for maximum power point tracking of energy sources
US12032080B2 (en) Safety mechanisms, wake up and shutdown methods in distributed power installations
EP3742572B1 (en) Photovoltaic power generation system and photovoltaic power transmission method
US20090189574A1 (en) Simplified maximum power point control utilizing the pv array voltage at the maximum power point
EP2043160A2 (en) Universal interface for a photovoltaic module
CN102447384A (en) Converters and inverters for photovoltaic power systems
CN102447427A (en) Photovoltaic power systems
WO2017048821A1 (en) Pv system having distributed dc-dc-converters
KR20170011614A (en) Photovoltaic module, and photovoltaic system including the same
AU2016401814A1 (en) Installation for powering auxiliary equipment in electrical energy generation plants
WO2020019103A1 (en) Photovoltaic power system
EP3809470A1 (en) Method and apparatus for melting snow
KR20190061937A (en) Photovoltaic module and photovoltaic including the same
KR20180023389A (en) Photovoltaic module and photovoltaic system including the same
US10205420B2 (en) Photovoltaic module and photovoltaic system comprising the same
EP3723281B1 (en) Power wiring device
CN111466077A (en) Power wiring device
KR20240088483A (en) PV(photovoltaic) module
KR20230072637A (en) power converting apparatus
KR20240117943A (en) PV(photovoltaic) module
KR20240088484A (en) PV(photovoltaic) module
JP2014112318A (en) Control unit, power generation control unit, photovoltaic power generation system, control method and power generation control method

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 18927485

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 18927485

Country of ref document: EP

Kind code of ref document: A1