Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
  • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
  • H02J3/381—Dispersed generators
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for AC mains or AC distribution networks
  • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
  • H02J3/388—Islanding, i.e. disconnection of local power supply from the network
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
  • H02J2300/20—The dispersed energy generation being of renewable origin
  • H02J2300/22—The renewable source being solar energy
  • H02J2300/24—The renewable source being solar energy of photovoltaic origin
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/56—Power conversion systems, e.g. maximum power point trackers

Definitions

• the present invention pertains to power systems wherein power is converted from one form to another, and, in particular, to a system and method for providing periodic electrical isolation in a power system, such as a solar power generation system, in a scheduled manner.
• PV photovoltaic
• DC direct current
• the DC output of the PV array is provided to a solar inverter, which is an electrical power conversion device that converts the variable DC output of the PV array into an AC current that can be provided to the commercial electrical grid.
• Solar inverters are well known and are manufactured and sold by a number of companies, such as, without limitation, the assignee of the present invention.
• PV array is typically electrically isolated from the electrical grid when not generating power (usually overnight).
• an isolating device e.g., a DC or AC breaker, contactor or switch
• Most PV arrays and solar inverters have a life of about 25 years or so.
• a power conversion apparatus for use with a source of current of a first type (e.g., DC, wherein the source is a PV cell array) is provided, wherein the power conversion system is structured to automatically electrically isolate the source of current from a load (e.g., an electrical grid) on a periodic basis including a plurality of intervals.
• a load e.g., an electrical grid
• the apparatus includes a power converter portion (e.g., a solar inverter) structured to convert current of the first type to current of a second type (e.g., AC), a first selectively operable electrical isolation device structured to be provided between the source and an input of the power converter portion to provide selective electrical isolation between the source and the power converter portion, a second selectively operable electrical isolation device structured to be provided between an output of the power converter portion and the load to provide selective electrical isolation between the power converter portion and the load, and a control unit operatively coupled to the first selectively operable electrical isolation device and the second selectively operable electrical isolation device.
• a power converter portion e.g., a solar inverter
• a first selectively operable electrical isolation device structured to be provided between the source and an input of the power converter portion to provide selective electrical isolation between the source and the power converter portion
• a second selectively operable electrical isolation device structured to be provided between an output of the power converter portion and the load to provide selective electrical isolation between the power converter portion and the load
• the control unit is structured to, for each of the intervals, determine, based on certain control logic, which one of the first selectively operable electrical isolation device and the second selectively operable electrical isolation is to be a scheduled isolation device for the interval and cause the determined scheduled isolation device to move to an electrically isolating condition during the interval.
• a method of automatically electrically isolating a source of current of a first type (e.g., DC, wherein the source is a PV cell array) from a load (e.g., an electrical grid) on a periodic basis comprising a plurality of intervals employs a power converter portion (e.g., a solar inverter) structured to convert current of the first type to current of a second type (e.g., AC), a first selectively operable electrical isolation device structured to provide selective electrical isolation between the source and the power converter portion, and a second selectively operable electrical isolation device structured to provide selective electrical isolation between the power converter portion and the load.
• a power converter portion e.g., a solar inverter
• a first selectively operable electrical isolation device structured to provide selective electrical isolation between the source and the power converter portion
• a second selectively operable electrical isolation device structured to provide selective electrical isolation between the power converter portion and the load.
• the method includes, for each of the intervals: (i) determining, based on certain control logic, which one of the first selectively operable electrical isolation device and the second selectively operable electrical isolation is to be a scheduled isolation device for the interval, and (ii) causing the determined scheduled isolation device to move to an electrically isolating condition during the interval.
• FIG. 1 is a block diagram of a solar power generation system according to an exemplary embodiment of the present invention
• FIG. 2 is a flowchart illustrating a method of providing electrical isolation for the solar power generation system of FIG. 1 according to one particular, non-limiting exemplary embodiment.
• the statement that two or more parts or components "engage” one another shall mean that the parts exert a force against one another either directly or through one or more intermediate parts or components.
• the term “number” shall mean one or an integer greater than one (i.e., a plurality).
• top, bottom, left, right, upper, lower, front, back, and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.
• FIG. 1 is a block diagram of a solar power generation system 2 according to an exemplary embodiment of the present invention.
• Solar power generation system 2 includes a PV cell array 4 comprising a number of PV modules, wherein each PV module includes a number of interconnected PV cells.
• PV cell array 4 is structured to generate DC power by converting sunlight into DC electrical current using the photovoltaic effect.
• Solar power generation system 2 also includes a solar inverter 6.
• Solar inverter 6 is structured to convert the DC electrical current generated by PV cell array 4 into AC power that is suitable for provision to a commercial electrical grid 8.
• Solar inverters are well known in the art, and thus will not be described in detail herein.
• One suitable example solar inverter is described in United States Patent No. 8,184,460. It should be noted, however, that solar inverter 6 may includes multiple conversion stages or bridges in series or parallel, or multiple conversion modules in serial or parallel.
• solar power generation system 2 also includes a selectively operable DC isolation device 10 that is positioned in between PV cell array 4 and solar inverter 6.
• a selectively operable DC isolation device shall mean an electrical apparatus that is structured to provide selective DC electrical isolation between two electrical components by isolating single or multiple conductors, and shall include, without limitation, a DC circuit breaker, a DC contactor or a DC switch.
• Selectively operable DC isolation device 10 is able to provide electrical isolation between PV cell array 4 and solar inverter 6 as needed.
• selectively operable DC isolation device 10 includes internal logic for automatically providing isolation when certain fault conditions are detected, and a manual actuator mechanism for providing isolation upon manual actuation, such as when maintenance needs to be performed on solar power generation system 2.
• Solar power generation system 2 further includes a selectively operable AC isolation device 12 that is positioned in between solar inverter 6 and electrical grid 8.
• a selectively operable AC isolation device shall mean an electrical apparatus that is structured to provide selective AC electrical isolation between two electrical components by isolating single or multiple conductors, and shall include, without limitation, an AC circuit breaker, an AC contactor or an AC switch.
• Selectively operable AC isolation device 12 is able to provide electrical isolation between solar inverter 6 and electrical grid 8 as needed.
• selectively operable AC isolation device 12 includes internal logic for automatically providing isolation when certain fault conditions are detected, and a manual actuator mechanism for providing isolation upon manual actuation, such as when maintenance needs to be performed on solar power generation system 2.
• solar power generation system 2 includes a control unit 14, which comprises a controller, such as, without limitation, a
• Control unit 14 is operatively coupled to both selectively operable DC isolation device 10 and selectively operable AC isolation device 12, and includes routines for causing selectively operable DC isolation device 10 and selectively operable AC isolation device 12 to be opened on a regular, periodic basis according to a predetermined schedule.
• PV cell array 4 the DC source
• PV cell array 4 must be electrically isolated from electrical grid 8 according to a regular schedule, typically overnight when PV cell array 4 is not generating power.
• selectively operable DC isolation device 10 and selectively operable AC isolation device 12 share the responsibility for this isolation function, wherein only one of those two devices is used to provide the regular, periodic electrical isolation (i.e.., not for fault detection or maintenance) at any one time, and wherein the particular one of those two devices that is for that purpose is determined in a
• FIG. 2 is a flowchart illustrating a method of employing
• selectively operable DC isolation device 10 and selectively operable AC isolation device 12 to share the responsibility for providing electrical isolation for solar power generation system 2 according to one particular, non-limiting exemplary embodiment wherein isolation is provided once a day, overnight, when PV cell array 4 is not generating power.
• the method illustrated in FIG. 2 is, in the exemplary embodiment, implemented in one or more routines stored in control unit 14 such that control unit 14 is able to control (i.e., open and close) selectively operable DC isolation device 10 and selectively operable AC isolation device 12 using certain control logic as dictated by the method.
• step 20 begins at step 20, wherein
• control unit 14 determines whether the current time is equal to a predefined "isolation commencement time", which is the time at which the isolation of PV cell array is to begin.
• the "isolation commencement time” can be a non-changing value, such as 9:00 PM, or may be configured to change periodically as lighting conditions change (e.g., as the time of the year (season) changes). If the answer at step 20 is no, then the method returns to step 20 and in effect waits for the current time to equal the predefined
• step 22 control unit 14 determines which one of selectively operable DC isolation device 10 and selectively operable AC isolation device 12 is the current "scheduled isolation device.” As noted elsewhere herein, this will be determined based on a particular, predefined schedule wherein the two devices are used in some alternating fashion. Any of a number of different parameters/criteria may be used to establish the particular schedule, and a number of particular example embodiments are described elsewhere herein. Regardless of which manner is chosen to establish the schedule, the schedule will result in one of selectively operable DC isolation device 10 and selectively operable AC isolation device 12 being established as the current "scheduled isolation device" in step 22.
• control unit 14 automatically actuates the
• control unit 14 determines whether the current time is equal to a predefined "isolation termination time", which is the time at which the isolation of PV cell array is to end.
• the "isolation termination time” can be a non-changing value, such as 6:00 AM, or may be configured to change periodically as lighting conditions change (e.g., as the time of the year (season) changes).
• step 26 If the answer at step 26 is no, then the method returns to step 26 and in effect waits for the current time to equal the predefined "isolation termination time.” If, however, the answer at step 26 is yes, then the method proceeds to step 28, wherein control unit 14 automatically actuates the current "scheduled isolation device” to cause it to be in a non-electrically isolating condition. The method then returns to step 20, to wait for the next "isolation commencement time" to occur.
• isolation device selectively operable DC isolation device 10 or selectively operable AC isolation device 12
• isolation device selectively operable DC isolation device 10
• some isolation events are accomplished with selectively operable DC isolation device 10, with the specific intent to keep the AC side connected (e.g., some overnights may require keeping the AC connected but isolating DC).
• the schedule that is employed in step 22 is based on the expected cycle lifetime of each of selectively operable DC isolation device 10 and selectively operable AC isolation device 12.
• the use of one isolation device relative to the other may be based on the ratio of the cycle lifetime of one to the other. For example, if selectively operable DC isolation device 10 has 10K cycle lifetime and selectively operable AC isolation device 12 has 5K cycle lifetime, a ratio of 2:1 may be used such that selectively operable AC isolation device 12 will only be used every third day (with selectively operable DC isolation device 10 being used the other days).
• the schedule that is employed in step 22 is based on the past use history of each of selectively operable DC isolation device 10 and selectively operable AC isolation device 12 and the ratio of their expected cycle lifetimes. For example, if selectively operable DC isolation device 10 has a 10K cycle lifetime and selectively operable AC isolation device 12 has a 5K cycle lifetime, and selectively operable DC isolation device 10 has been used 4000 times while selectively operable AC isolation device 12 has been used 1800 times, selectively operable AC isolation device 12 will be used to bring the usage ratio closer to the desired 2:1 based on the ratio of their expected cycle lifetimes.
• This technique/control logic also allows for optimal device scheduling even if outside factors affect the number of cycles on each device. In contrast to a simple "every third day" isolation scheme or similar, if other device operations cause the cycle count to deviate from desired, this method will correct them.
• the schedule that is employed in step 22 is based on the past use history of each of selectively operable DC isolation device 10 and selectively operable AC isolation device 12, their expected cycle lifetimes, and their expected future use patterns. Other system operations may require isolation device
• the schedule would heavily bias usage of selectively operable AC isolation device 12 initially to ensure sufficient cycle life is available on selectively operable DC isolation device 10. This may be as extreme as only using selectively operable AC isolation device 12 until it comes close to its maximum cycle limit, and selectively operable DC isolation device 10 from then onward.
• the present invention may be applied to other type of power systems wherein power is converted from one form to another and two electrical isolation devices may be employed.
• the present invention may also be employed in connection with wind turbines, motor drives, DC-DC converters, DC-AC converters, AC-AC conversion, variable frequency drives, etc.

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

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• 2013
  • 2013-09-16 CA CA2883843A patent/CA2883843A1/fr not_active Abandoned
  • 2013-09-16 BR BR112015005896A patent/BR112015005896A2/pt not_active IP Right Cessation
  • 2013-09-16 WO PCT/IB2013/002778 patent/WO2014045125A2/fr not_active Ceased

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