CN111245023B - Microgrid parallel-parallel operation switching system and switching method - Google Patents
Microgrid parallel-parallel operation switching system and switching method Download PDFInfo
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- CN111245023B CN111245023B CN202010213821.9A CN202010213821A CN111245023B CN 111245023 B CN111245023 B CN 111245023B CN 202010213821 A CN202010213821 A CN 202010213821A CN 111245023 B CN111245023 B CN 111245023B
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- 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
- H02J3/28—Arrangements for balancing of the load in a network by storage of energy
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- 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
Abstract
The invention discloses a micro-grid parallel-parallel operation switching system, which comprises: the system comprises a medium-voltage direct-current power distribution network, a direct-current transformer, a low-voltage direct-current micro-grid, a switch module and a first circuit breaker; the low-voltage direct-current micro-grid comprises an energy storage system, a photovoltaic system and a direct-current load system; the medium-voltage direct-current power distribution network is connected with the direct-current transformer through the switch module, and the direct-current transformer is respectively connected with the energy storage system, the photovoltaic system and the direct-current load system through the first circuit breaker; the invention also discloses a micro-grid parallel-parallel operation switching method; according to the technical scheme, the grid-connected and off-grid switching between the medium-voltage direct-current power distribution network and the low-voltage direct-current micro-grid can be realized, and the stability and the reliability of grid-connected and off-grid switching operation are improved.
Description
Technical Field
The invention relates to the technical field of power grid control, in particular to a switching system and a switching method for parallel operation and separate operation of a micro-grid.
Background
The direct-current micro-grid serving as a novel power distribution network has incomparable advantages of an alternating-current micro-grid in the aspects of operation reliability, energy utilization efficiency and operation flexibility. With the technology of the medium-voltage direct-current power distribution network becoming mature day by day, the voltage reduction from the medium-voltage direct-current power distribution network to the low-voltage direct-current power distribution network becomes possible, the direct-current power distribution network directly reduces the voltage through the power electronic transformer, the energy transmission efficiency can be improved, the direct-current micro-grid is matched, and meanwhile, the reliability of power supply can also be improved. In order to realize voltage reduction from a medium-voltage direct-current distribution network to a low-voltage direct-current distribution network, two common schemes exist in the prior art:
the self-adaptive technology-based intelligent microgrid grid-connected and off-grid switching system comprises a grid-connected bus, an off-grid bus, a double-switch, a distributed power supply, an energy storage device and a load; a first contact of the double-cut switch is connected with a grid-connected bus, a second contact of the double-cut switch is connected with an off-grid bus, and a connector of the double-cut switch is connected with a distributed power supply, an energy storage device or a load; and the grid-connected bus is connected with a large power grid. The grid-connected and off-grid switching system realizes the function of independently switching the grid-connected and off-grid states of the distributed power supply, the energy storage device and the load by utilizing the grid-connected bus, the off-grid bus and the plurality of double-cut switches. Although the device of the first scheme can realize switching between the grid-connected bus and the off-grid bus of the microgrid, the device is only suitable for the low-voltage alternating-current microgrid which adopts a technical scheme-switching scheme and cannot realize seamless switching in the switching process due to the fact that the response speed of a double-switching device is low, and safe and reliable operation of equipment is affected, and the device is only suitable for the low-voltage alternating-current microgrid.
Scheme two adopts and sets up direct current circuit breaker in the middling pressure side, and the circuit breaker accepts and leaves the net controller and carries out and leave the net operation. However, the strategy of the second scheme can cause the investment of the breaker equipment to be increased, and due to the fact that the opening and closing time of the breaker has discreteness, the breaker has large overvoltage or overcurrent impact on the equipment, and meanwhile, the microgrid system can have large disturbance.
Therefore, a grid-connected and off-grid switching strategy capable of improving the operation stability and reliability of the medium-voltage direct-current power distribution network and the low-voltage direct-current micro-grid is urgently needed in the market.
Disclosure of Invention
The invention provides a switching system and a switching method for parallel operation and offline operation of a microgrid, which can realize parallel and offline switching between a medium-voltage direct-current power distribution network and a low-voltage direct-current microgrid and improve stability and reliability of parallel and offline switching operation.
In order to solve the above technical problem, an embodiment of the present invention provides a microgrid parallel-to-parallel operation switching system, including: the system comprises a medium-voltage direct-current power distribution network, a direct-current transformer, a low-voltage direct-current micro-grid, a switch module and a first circuit breaker; the low-voltage direct-current micro-grid comprises an energy storage system, a photovoltaic system and a direct-current load system;
the medium-voltage direct-current power distribution network is connected with the direct-current transformer through the switch module, and the direct-current transformer is respectively connected with the energy storage system, the photovoltaic system and the direct-current load system through the first circuit breaker.
Preferably, the dc load system includes a charging pile system and other load systems such as an air conditioner and an illumination system, and the dc transformer is connected to the charging pile system and the dc load system through the first circuit breaker.
Preferably, the microgrid parallel-to-parallel operation switching system further comprises: a second circuit breaker, a third circuit breaker, a fourth circuit breaker and a fifth circuit breaker;
one end of the second circuit breaker is connected with the first circuit breaker, and the other end of the second circuit breaker is connected with the energy storage system; one end of the third circuit breaker is connected with the first circuit breaker, and the other end of the third circuit breaker is connected with the photovoltaic system; one end of the fourth circuit breaker is connected with the first circuit breaker, and the other end of the fourth circuit breaker is connected with the charging pile system; and one end of the fifth circuit breaker is connected with the first circuit breaker, and the other end of the fifth circuit breaker is connected with the direct-current load system.
Preferably, the switch module includes an isolation switch, and the medium-voltage dc distribution network is connected to the dc transformer through the isolation switch.
The embodiment of the invention also provides a microgrid grid-connected and off-grid switching method, which is used for controlling the microgrid grid-connected and off-grid switching system to carry out grid-connected and off-grid switching, and comprises the following steps:
according to the received planned grid-connected to grid-disconnected switching instruction, controlling a load grading management mode and a photovoltaic power control mode of the low-voltage direct-current micro-grid so as to realize the non-power-outage switching of the grid-connected to grid-disconnected low-voltage direct-current micro-grid;
when the conditions such as upper-level power grid faults or external disturbance occur, starting an unplanned grid-connected to off-grid switching control strategy, judging the load power of the low-voltage direct-current micro-grid and the output power of the energy storage system, and controlling the operation mode of the low-voltage direct-current micro-grid according to the load power and the output power;
under the condition of switching from grid-connected to grid-connected in a planned mode, according to a received switching instruction from grid-connected to grid-connected, the droop curve of the energy storage system and the closing state of the first breaker are controlled, and therefore uninterrupted switching from grid-connected to grid-connected of the low-voltage direct-current micro-grid is achieved.
Under the condition of switching from a planned grid connection to a grid disconnection, as an optimal scheme, according to a received planned grid connection to grid disconnection switching instruction, controlling a load hierarchical management and photovoltaic power control mode of the low-voltage direct-current micro-grid to realize the uninterrupted switching from the grid connection to the grid disconnection of the low-voltage direct-current micro-grid, specifically comprising the following steps of:
the method comprises the steps that a power control mode of an energy storage system is controlled to be converted into a voltage droop control mode, so that the energy storage system and a direct current transformer maintain the direct current bus voltage of a low-voltage direct current micro-grid together;
converting a voltage control mode of the direct-current transformer into a power control mode, and adjusting the switching power of the first circuit breaker to be within a preset switching power numerical range;
and when the total voltage value of the low-voltage direct-current micro-grid is within a preset voltage value range, controlling the direct-current transformer to quit running, locking the direct-current transformer in order and controlling the first breaker to be disconnected, and completing grid-connected to off-grid switching.
As a preferred scheme, when a superior grid fault or external disturbance occurs, an unplanned grid-connected to grid-disconnected switching control strategy is started, the load power of the low-voltage dc microgrid and the output power of the energy storage system are automatically judged, and the operation mode of the low-voltage dc microgrid is controlled according to the numerical values of the load power and the output power, specifically:
controlling the direct current transformer to be locked in advance and allowing the photovoltaic system to quit operation;
judging a power supply and power, and when the load power of the low-voltage direct-current micro-grid is not greater than the output power of the energy storage system, controlling the power control mode of the energy storage system to be converted into a voltage droop control mode so that the energy storage system independently maintains the voltage of a low-voltage direct-current bus and simultaneously controls a first breaker to be switched off;
and judging the power supply and the power, and controlling the low-voltage direct-current micro-grid to stop running when the load power of the low-voltage direct-current micro-grid is greater than the output power of the energy storage system until the load of the low-voltage direct-current micro-grid is put into stage after the low-voltage direct-current micro-grid is manually restarted to execute restarting.
As a preferred scheme, the step of controlling the droop curve adjustment of the energy storage system and the closing state of the first breaker according to the received switching instruction from the off-grid to the on-grid to realize the switching of the low-voltage direct-current microgrid from the off-grid to the on-grid without power outage specifically comprises the following steps:
the method comprises the following steps that the difference between the voltage value of a low-voltage direct-current bus of a low-voltage direct-current micro-grid and the voltage value of a low-voltage direct-current bus at the low-voltage side of a direct-current transformer is within a preset voltage value difference value range by adjusting a droop curve of an energy storage system;
when the difference value between the voltages at the two sides of the first circuit breaker reaches a preset allowable switching range, controlling the first circuit breaker to be closed so as to complete switching from an off-grid mode to a grid-connected mode; and after the switching of the off-grid to on-grid mode is completed, controlling the droop control mode of the energy storage system to be converted into a power switching mode.
An embodiment of the present invention further provides a computer-readable storage medium, where the computer-readable storage medium includes a stored computer program; wherein the computer program, when running, controls a device in which the computer-readable storage medium is located to execute the microgrid on-line and off-line operation switching method according to any one of the above.
The embodiment of the present invention further provides a terminal device, which includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, where the processor, when executing the computer program, implements the microgrid on-off operation switching method according to any one of the above.
Compared with the prior art, the embodiment of the invention has the following beneficial effects:
1. by combining and applying the switching system and the switching method for the parallel-connection and separate-operation of the microgrid, the parallel-connection and separate-operation switching between the medium-voltage direct-current power distribution network and the low-voltage direct-current microgrid can be realized, and the stability and the reliability of the parallel-connection and separate-operation switching operation are improved.
2. Set up isolator between medium voltage direct current distribution network and direct current transformer, compare with the scheme that uses the circuit breaker among the prior art, can save the cost more.
3. Through the control cooperation of the low-voltage side direct-current first circuit breaker, the energy storage system and the direct-current transformer, seamless switching between a low-voltage direct-current micro-grid and a medium-voltage direct-current power distribution network can be realized.
Drawings
FIG. 1: the invention discloses a structural schematic diagram of a microgrid parallel-parallel operation switching system in an embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, a preferred embodiment of the present invention provides a microgrid parallel-to-grid/offline switching system, including: the system comprises a medium-voltage direct-current power distribution network, a direct-current transformer, a low-voltage direct-current micro-grid, a switch module and a first circuit breaker; the low-voltage direct-current micro-grid comprises an energy storage system, a photovoltaic system and a direct-current load system; the medium-voltage direct-current power distribution network is connected with the direct-current transformer through the switch module, and the direct-current transformer is respectively connected with the energy storage system, the photovoltaic system and the direct-current load system through the first circuit breaker.
By combining and applying the switching system and the switching method for the parallel-connection and separate-operation of the microgrid, the parallel-connection and separate-operation switching between the medium-voltage direct-current power distribution network and the low-voltage direct-current microgrid can be realized, and the stability and the reliability of the parallel-connection and separate-operation switching operation are improved.
In a preferred embodiment, the dc load system includes a charging pile system and a dc load system, and the dc transformer is connected to the charging pile system and the dc load system through the first circuit breaker.
In any of the above embodiments, the microgrid on-board and off-board operation switching system further comprises: a second circuit breaker, a third circuit breaker, a fourth circuit breaker and a fifth circuit breaker; one end of the second circuit breaker is connected with the first circuit breaker, and the other end of the second circuit breaker is connected with the energy storage system; one end of the third circuit breaker is connected with the first circuit breaker, and the other end of the third circuit breaker is connected with the photovoltaic system; one end of the fourth circuit breaker is connected with the first circuit breaker, and the other end of the fourth circuit breaker is connected with the charging pile system; and one end of the fifth circuit breaker is connected with the first circuit breaker, and the other end of the fifth circuit breaker is connected with the direct-current load system.
In any of the above embodiments, the switch module includes an isolation switch, and the medium-voltage dc distribution network is connected to the dc transformer through the isolation switch. According to the technical scheme, the isolating switch is arranged between the medium-voltage direct-current power distribution network and the direct-current transformer, and compared with the scheme of using the circuit breaker in the prior art, the cost can be saved.
The direct-current micro-grid operating in the grid-connected mode needs to disconnect the first circuit breaker CB1 due to equipment maintenance or fault isolation, and is switched from the grid-connected operation mode to the off-grid operation mode; when the overhaul is finished or the fault is recovered, the first circuit breaker CB1 needs to be closed again, and the off-grid operation mode is switched to the grid-connected operation mode. The switching from the grid-connected operation to the off-grid operation of the direct-current microgrid comprises planned switching and unplanned switching.
The embodiment of the invention also provides a microgrid grid-connected and off-grid switching method, which is used for controlling the microgrid grid-connected and off-grid switching system to carry out grid-connected and off-grid switching, and comprises the following steps:
switching one: and controlling a load grading management mode and a photovoltaic power control mode of the low-voltage direct-current micro-grid according to the received planned grid-connected to grid-disconnected switching instruction so as to realize the non-power-outage switching of the low-voltage direct-current micro-grid from grid-connected to grid-disconnected. The method comprises the following steps: s1, controlling the power control mode of the energy storage system to be converted into a voltage droop control mode, so that the energy storage system and the direct current transformer jointly maintain the direct current bus voltage of the low-voltage direct current microgrid; s2, converting the voltage control mode of the direct current transformer into a power control mode, and adjusting the exchange power of the first circuit breaker to a preset switching power value range; and S3, when the total voltage value of the low-voltage direct-current micro-grid is within the preset voltage value range, controlling the direct-current transformer to quit running, locking the direct-current transformer in order and controlling the first breaker to be disconnected, and completing grid-connected to off-grid switching.
Specifically, the planned switching control instruction may be issued by a power grid dispatching mechanism or by a direct current microgrid operation control system. When the conditions such as upper-level power grid faults or external disturbance occur and the voltage of the grid-connected point of the micro-grid exceeds a set range, the direct-current micro-grid can be switched to an off-grid operation mode. The planned grid-connected to off-grid switching can be matched with load grading management and photovoltaic power control, and the system is switched without power failure. The concrete measures are as follows:
a. after the direct current micro-grid control system receives a conversion instruction from grid connection to off-grid connection, the control energy storage system is converted into voltage droop control through power control, and the voltage droop control and the direct current transformer jointly maintain the direct current bus voltage of the low-voltage direct current micro-grid (at the moment, the low-voltage side of the direct current transformer is also used for voltage droop control);
b. converting a voltage control mode of a direct current transformer into a power control mode, adjusting switching power of a grid-connected point to be within an allowable switching range, and if necessary, synchronously cutting off load (when a micro grid absorbs power of a higher-level power grid) or limiting photovoltaic output (when the micro grid outputs power to the higher-level power grid) in a grading mode, so that on one hand, the load of a system is ensured not to exceed the current power supply capacity of an energy storage system, and on the other hand, the current or the switching power of the grid-connected point is reduced to be in an allowable;
c. and after the energy storage system successfully supports the direct-current microgrid, the direct-current transformer quits running, the direct-current transformer is locked in order, and a low-voltage side switch of the direct-current transformer is disconnected, so that grid connection to off-grid switching is completed.
When load grading removal and photovoltaic power control are carried out, smooth switching control is adopted, and current impact is too large, voltage transient change is too large, and misoperation of a protection system is prevented in the switching process.
Switching to a second mode: when the conditions such as upper-level power grid faults or external disturbance occur, an unplanned grid-connected to grid-disconnected switching control strategy is started, the controller automatically judges the load power of the low-voltage direct-current micro-grid and the output power of the energy storage system, and the operation mode of the low-voltage direct-current micro-grid is controlled according to the load power and the output power. The method comprises the following steps: s1, controlling the direct current transformer to be locked and allowing the photovoltaic system to quit operation; s2, when the load power of the low-voltage direct-current micro-grid is not larger than the output power of the energy storage system, controlling the power control mode of the energy storage system to be converted into a voltage droop control mode, so that the energy storage system independently maintains the voltage of a low-voltage direct-current bus and controls the first breaker to be disconnected; and S3, when the load power of the low-voltage direct-current microgrid is greater than the output power of the energy storage system, controlling the low-voltage direct-current microgrid to stop running until the load of the low-voltage direct-current microgrid is put into graded investment after the low-voltage direct-current microgrid is manually and is started black to restart.
Specifically, an unscheduled grid-connected to off-grid switching may be caused by a fault or a large disturbance of the upper-level grid, and the specific steps are as follows:
a. the direct-current transformer is firstly locked to isolate a superior power grid;
b. the photovoltaic system is used as an unstable power supply to be locked and escaped, and the system is put into the system after being successfully converted into off-grid operation;
c. and according to whether the load exceeds the power supply capacity of the energy storage system, different switching coping strategies are provided in a classified manner. When the load power is not greater than the energy storage system power, the energy storage system detects that the voltage of the direct current bus falls to a trigger limit value, the direct current bus is automatically converted into voltage droop control, the voltage of the low-voltage direct current bus is independently maintained, and meanwhile, the low-side switch of the direct current transformer is controlled to be switched off;
d. and after the system is successfully switched to off-network operation, the system is operated according to an off-network operation control strategy. When the load power is larger than the energy storage system power, the energy storage system cannot support the system to operate, the direct-current micro-grid operation stopping strategy is adopted to deal with the problem, the follow-up system is restarted by manual black start, and the load is put into use in a grading mode.
And (3) switching: and controlling the droop curve adjustment of the energy storage system and the closing state of the first breaker according to the received switching instruction from the off-grid to the on-grid so as to realize the switching of the low-voltage direct-current micro-grid from the off-grid to the on-grid without power failure. The method comprises the following steps: s1, adjusting a droop curve of the energy storage system to enable the difference between the voltage value of the low-voltage direct-current bus of the low-voltage direct-current microgrid and the voltage value of the low-voltage direct-current bus on the low-voltage side of the direct-current transformer to be within a preset voltage value difference range; s2, when the difference value between the voltages at the two sides of the first breaker reaches the preset allowable switching range, controlling the first breaker to close so as to complete the switching from the off-grid mode to the on-grid mode; and after the switching of the off-grid to on-grid mode is completed, controlling the droop control mode of the energy storage system to be converted into a power switching mode.
Specifically, the direct-current microgrid operating in an off-grid operation mode is subjected to grid connection instruction issuing by a direct-current microgrid operation control system due to the fact that +/-10 kV distribution network side faults are eliminated or planned grid connection is achieved, and a non-power-outage switching mode is achieved. The specific implementation mode is as follows:
1) after the direct current micro-grid operation control system receives an off-grid to on-grid switching instruction, the droop curve of the energy storage system is adjusted to enable the voltage of the low-voltage direct current bus of the direct current micro-grid to be continuously close to the voltage of the low-voltage direct current bus on the low-voltage side of the direct current transformer
2) When the voltage difference value of the two sides of the grid-connected switch reaches the allowable switching range, the direct-current grid-connected device controls the direct-current circuit breaker CB1 on the low-voltage side of the direct-current transformer to be closed, and switching of the off-grid to grid-connected mode is completed.
At the moment, the direct-current microgrid system operates in a grid-connected mode, and in order to enable the energy storage system not to be used as a main power source of the system, the direct-current microgrid operation control system issues an instruction to enable the energy storage system to be switched from a droop control mode to a power control mode. Because medium voltage distribution network side fault is eliminated or grid connection is planned, the direct current microgrid is switched to a grid connection operation mode from an off-grid operation mode, and switching without power outage can be realized.
The technical scheme of the invention has the advantages that:
1) through the control cooperation of the low-voltage side direct current CB1, the energy storage system and the direct current transformer, the seamless switching between the low-voltage direct current micro-grid and the medium-voltage direct current distribution network can be realized.
2) The medium-voltage side of the topological structure only needs to be provided with the direct-current isolating switch, and does not need to be provided with the direct-current breaker, so that the equipment investment can be saved.
3) The direct current transformer and the energy storage system are both provided with a droop control function, and the system can stably run in the grid-connected and off-grid switching process through a reasonable grid-connected and off-grid switching sequence and a droop control algorithm, so that external faults are effectively isolated.
4) Compared with the prior art, the technical scheme has the advantages that the seamless switching between the medium-voltage direct-current power distribution network and the low-voltage direct-current micro-grid is realized under the most economic condition through reasonable grid-connection and grid-disconnection switching steps and the droop control algorithm program of the direct-current transformer and the energy storage system, so that the technical scheme is simple and economical to realize, the power supply reliability of the direct-current micro-grid can be improved, and the micro-grid can be ensured to run without power failure.
An embodiment of the present invention further provides a computer-readable storage medium, where the computer-readable storage medium includes a stored computer program; when the computer program runs, the device where the computer readable storage medium is located is controlled to execute the microgrid grid-on-grid/off-grid switching method according to any one of the above embodiments.
The embodiment of the present invention further provides a terminal device, where the terminal device includes a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, and the processor, when executing the computer program, implements the microgrid parallel-to-grid and offline switching method according to any of the above embodiments.
Preferably, the computer program may be divided into one or more modules/units (e.g., computer program) that are stored in the memory and executed by the processor to implement the invention. The one or more modules/units may be a series of computer program instruction segments capable of performing specific functions, which are used for describing the execution process of the computer program in the terminal device.
The Processor may be a Central Processing Unit (CPU), other general purpose Processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), an off-the-shelf Programmable Gate Array (FPGA) or other Programmable logic device, a discrete Gate or transistor logic device, a discrete hardware component, etc., the general purpose Processor may be a microprocessor, or the Processor may be any conventional Processor, the Processor is a control center of the terminal device, and various interfaces and lines are used to connect various parts of the terminal device.
The memory mainly includes a program storage area and a data storage area, wherein the program storage area may store an operating system, an application program required for at least one function, and the like, and the data storage area may store related data and the like. In addition, the memory may be a high speed random access memory, may also be a non-volatile memory, such as a plug-in hard disk, a Smart Media Card (SMC), a Secure Digital (SD) Card, a Flash Card (Flash Card), and the like, or may also be other volatile solid state memory devices.
It should be noted that the terminal device may include, but is not limited to, a processor and a memory, and those skilled in the art will understand that the terminal device is only an example and does not constitute a limitation of the terminal device, and may include more or less components, or combine some components, or different components.
The above-mentioned embodiments are provided to further explain the objects, technical solutions and advantages of the present invention in detail, and it should be understood that the above-mentioned embodiments are only examples of the present invention and are not intended to limit the scope of the present invention. It should be understood that any modifications, equivalents, improvements and the like, which come within the spirit and principle of the invention, may occur to those skilled in the art and are intended to be included within the scope of the invention.
Claims (10)
1. A microgrid on-grid and off-grid operation switching system, comprising: the system comprises a medium-voltage direct-current power distribution network, a direct-current transformer, a low-voltage direct-current micro-grid, a switch module and a first circuit breaker; the low-voltage direct-current micro-grid comprises an energy storage system, a photovoltaic system and a direct-current load system;
the medium-voltage direct-current power distribution network is connected with the direct-current transformer through the switch module, and the direct-current transformer is respectively connected with the energy storage system, the photovoltaic system and the direct-current load system through the first circuit breaker;
the low-voltage direct-current micro-grid is used for switching to a load grading management and photovoltaic power control mode according to a received planned grid-connected to grid-disconnected switching instruction, and switching the grid-connected to the grid-disconnected without power failure through the energy storage system and a control strategy of the direct-current transformer;
the system is also used for starting an unplanned grid-connected to off-grid switching control strategy when a superior grid fault or external disturbance occurs, judging the load power and the output power of the energy storage system, and switching the operation mode according to the load power and the output power;
and the energy storage system is also used for controlling the adjustment of the droop curve of the energy storage system and the closing state of the first breaker according to the received switching instruction from the off-grid to the on-grid so as to realize the uninterrupted switching from the off-grid to the on-grid.
2. The microgrid on-off operation switching system of claim 1, wherein the direct current load system comprises a charging pile system and a direct current load system, and the direct current transformer is connected with the charging pile system and the direct current load system through the first circuit breaker respectively.
3. The microgrid on-board and off-board operation switching system of claim 2, further comprising: a second circuit breaker, a third circuit breaker, a fourth circuit breaker and a fifth circuit breaker;
one end of the second circuit breaker is connected with the first circuit breaker, and the other end of the second circuit breaker is connected with the energy storage system; one end of the third circuit breaker is connected with the first circuit breaker, and the other end of the third circuit breaker is connected with the photovoltaic system; one end of the fourth circuit breaker is connected with the first circuit breaker, and the other end of the fourth circuit breaker is connected with the charging pile system; and one end of the fifth circuit breaker is connected with the first circuit breaker, and the other end of the fifth circuit breaker is connected with the direct-current load system.
4. The microgrid on-board and off-board operation switching system of claim 3, wherein the switch module comprises a disconnector through which the medium voltage direct current distribution grid is connected with the direct current transformer.
5. A microgrid grid-on and grid-off operation switching method for controlling the microgrid grid-on and grid-off operation switching system according to any one of claims 1 to 4, comprising the steps of:
according to a received planned grid-connected to grid-disconnected switching instruction, controlling a load grading management mode and a photovoltaic power control mode of the low-voltage direct-current micro-grid, and realizing the grid-connected to grid-disconnected switching of the low-voltage direct-current micro-grid through a control strategy of an energy storage and direct-current transformer;
when a superior power grid fault or external disturbance condition occurs, starting an unplanned grid-connected to off-grid switching control strategy, judging the load power of the low-voltage direct-current micro-power grid and the output power of the energy storage system, and controlling the operation mode of the low-voltage direct-current micro-power grid according to the load power and the output power;
and controlling the droop curve adjustment of the energy storage system and the closing state of the first breaker according to the received switching instruction from the off-grid to the on-grid so as to realize the switching of the low-voltage direct-current micro-grid from the off-grid to the on-grid without power failure.
6. The microgrid grid-connected and off-grid operation switching method according to claim 5, wherein the step of controlling a load grading management and photovoltaic power control mode of the low-voltage direct-current microgrid according to the received planned grid-connected to off-grid switching instruction so as to realize the non-power-outage switching of the grid-connected to off-grid of the low-voltage direct-current microgrid is specifically as follows:
the method comprises the steps that a power control mode of an energy storage system is controlled to be converted into a voltage droop control mode, so that the energy storage system and a direct current transformer maintain the direct current bus voltage of a low-voltage direct current micro-grid together;
converting a voltage control mode of the direct-current transformer into a power control mode, and adjusting the switching power of the first circuit breaker to be within a preset switching power numerical range;
and when the total voltage value of the low-voltage direct-current micro-grid is within a preset voltage value range, controlling the direct-current transformer to quit running, locking the direct-current transformer in order and controlling the first breaker to be disconnected, and completing grid-connected to off-grid switching.
7. The microgrid on-off operation switching method according to claim 5, wherein the step of starting an unplanned grid-connected to off-grid control strategy when a superior grid fault or external disturbance condition occurs, judging the load power of the low-voltage direct-current microgrid and the output power of the energy storage system, and controlling the operation mode of the low-voltage direct-current microgrid according to the values of the load power and the output power specifically comprises the following steps:
controlling the direct current transformer to be locked in advance and allowing the photovoltaic system to quit operation;
judging a power supply and power, and when the load power of the low-voltage direct-current micro-grid is not greater than the output power of the energy storage system, controlling the power control mode of the energy storage system to be converted into a voltage droop control mode so that the energy storage system independently maintains the voltage of a low-voltage direct-current bus and simultaneously controls a first breaker to be switched off;
and judging the power supply and the power, and controlling the low-voltage direct-current micro-grid to stop running when the load power of the low-voltage direct-current micro-grid is greater than the output power of the energy storage system until the load of the low-voltage direct-current micro-grid is put into stage after the low-voltage direct-current micro-grid is manually restarted to execute restarting.
8. The microgrid on-grid and off-grid operation switching method according to claim 5, wherein the step of controlling the droop curve adjustment of the energy storage system and the closing state of the first circuit breaker according to the received off-grid to on-grid switching instruction so as to realize off-grid to on-grid uninterrupted switching of the low-voltage direct-current microgrid specifically comprises the following steps:
the method comprises the following steps that the difference between the voltage value of a low-voltage direct-current bus of a low-voltage direct-current micro-grid and the voltage value of a low-voltage direct-current bus at the low-voltage side of a direct-current transformer is within a preset voltage value difference value range by adjusting a droop curve of an energy storage system;
when the difference value between the voltages at the two sides of the first circuit breaker reaches a preset allowable switching range, controlling the first circuit breaker to be closed so as to complete switching from an off-grid mode to a grid-connected mode; and after the switching of the off-grid to on-grid mode is completed, controlling the droop control mode of the energy storage system to be converted into a power switching mode.
9. A computer-readable storage medium, characterized in that the computer-readable storage medium comprises a stored computer program; wherein the computer program controls the device in which the computer readable storage medium is located to execute the microgrid on-line and off-line operation switching method according to any one of claims 5 to 8 when executed.
10. A terminal device comprising a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, the processor implementing the microgrid run-on and run-off switching method according to any one of claims 5 to 8 when executing the computer program.
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