Micro-grid and grid-connected operation method containing solid oxide fuel cell

Abstract

The application discloses a micro-grid containing a solid oxide fuel cell and a grid-connected operation method. The micro-grid comprises a solid oxide fuel cell power generation system, an energy storage system, a controller, an AC grid-connected switch, a DC bus, a power converter, the solid oxide fuel cell power generation system comprises a methanol aqueous solution storage tank, a reforming chamber, a solid oxide fuel cell, heating and power auxiliary devices, a first DC / DC converter, a second DC / DC converter and a first DC grid-connected switch; the controller is used for acquiring data of the solid oxide fuel cell power generation system, the energy storage system, the DC bus and a power grid, and is used for controlling the solid oxide fuel cell power generation system, the energy storage system, the AC grid-connected switch and the power converter to work. When the system starts, the self-heating start and the grid-connected operation of the micro-grid are realized through a reasonable energy scheduling method, and after the grid connection, the internal electric energy flow of the micro-grid is automatically managed and automatically protected in an island mode according to the state of the power grid.

Description

Technical Field

[0001] This invention relates to the field of fuel cell technology, and in particular to a microgrid containing a solid oxide fuel cell and a method for grid-connected operation. Background Technology

[0002] A microgrid is a small-scale power generation and distribution system that organically integrates distributed power sources, loads, and energy storage devices. It can operate connected to the main power grid or disconnect from the grid to operate independently when the grid fails or is needed. It is an important means of adjusting the energy structure and achieving sustainable energy development. As a more flexible and user-friendly new power system structure, microgrids urgently need to find power sources with environmentally friendly and efficient characteristics.

[0003] Fuel cells, as clean and efficient energy conversion devices, have great application prospects in the field of microgrids. Based on the different electrolytes, fuel cells can be classified into alkaline fuel cells (AFC), phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), proton exchange membrane fuel cells (PEMFC), and solid oxide fuel cells (SOFC). Among them, solid oxide fuel cells are currently the most efficient fuel cell technology, featuring wide fuel applicability, high waste heat quality, low maintenance costs, and modular assembly, making them a key power source choice for microgrids.

[0004] Current research on the control of fuel cell microgrids mainly focuses on proton exchange membrane fuel cells, and the content is mostly concentrated on the scheduling, management, optimization, and configuration of electrical energy. However, solid oxide fuel cells require the construction of a gas supply and high-temperature environment to achieve external power supply, possessing dual characteristics of load and power source. At the same time, the operation involves the coupling effects of multiple variables such as electricity, current, and heat, making traditional microgrid grid-connected operation control methods difficult to apply to this field. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a microgrid containing a solid oxide fuel cell and a grid-connected operation method. During system startup, the load characteristics of the solid oxide fuel cell are comprehensively considered. Through a reasonable energy dispatching method, the self-heating startup and grid-connected operation of the solid oxide fuel cell are satisfied. Furthermore, after grid connection is completed, intelligent management of the internal power flow of the microgrid and automatic islanding protection can be implemented according to the status of the main grid, which is more conducive to ensuring the safety of the microgrid and the stability of the distribution network.

[0006] To solve the above problems, the present invention adopts the following technical solution:

[0007] This invention discloses a microgrid containing a solid oxide fuel cell, comprising a solid oxide fuel cell power generation system, an energy storage system, a controller, an AC grid-connected switch, a DC bus, and a power converter. The solid oxide fuel cell power generation system includes a methanol-water solution storage tank, a reforming chamber, a solid oxide fuel cell, heating and power auxiliary devices, a first DC / DC converter, a second DC / DC converter, and a first DC grid-connected switch. The outlet of the methanol-water solution storage tank is connected to the inlet of the reforming chamber via a connecting pipe, and the outlet of the reforming chamber is connected to the inlet of the solid oxide fuel cell via a connecting pipe. The solid oxide fuel cell is electrically connected to the DC bus sequentially via the first DC / DC converter and the first DC grid-connected switch. The heating and power auxiliary devices are electrically connected to the DC bus via the second DC / DC converter. The energy storage system is electrically connected to the DC bus. The DC side of the power converter is electrically connected to the DC bus via the AC grid-connected switch, and the AC side of the power converter is electrically connected to the mains power grid. The heating and power auxiliary devices are used to provide heat to the solid oxide fuel cell, heat to the reforming chamber, and pumping power to the reforming chamber.

[0008] The controller is used to acquire data from the solid oxide fuel cell power generation system, energy storage system, DC bus, and mains power grid, and to control the operation of the solid oxide fuel cell power generation system, energy storage system, AC grid-connected switch, and power converter.

[0009] In this scheme, the controller acquires real-time electrical, thermal, and current data from the main grid, DC bus, solid oxide fuel cell power generation system, and energy storage system. Based on the acquired data, it adjusts the operating modes of the solid oxide fuel cell power generation system, energy storage system, AC grid connection switch, and power converter to complete the grid connection / off-grid operation of the microgrid and the main grid.

[0010] Preferably, the heating and power auxiliary device includes a pump for drawing methanol aqueous solution from the methanol aqueous solution storage tank into the reforming chamber, a gas pump for outputting reforming gas from the reforming chamber to the solid oxide fuel cell, a first heating module for heating the reforming chamber, and a second heating module for heating the solid oxide fuel cell.

[0011] Preferably, the energy storage system includes an energy storage battery, a battery management system, a third DC / DC converter, and a second DC grid-connected switch. The energy storage battery is electrically connected to the DC bus in sequence through the battery management system, the third DC / DC converter, and the second DC grid-connected switch.

[0012] The present invention provides a grid-connected operation method for a microgrid containing a solid oxide fuel cell, used in the aforementioned microgrid containing a solid oxide fuel cell, comprising the following steps:

[0013] S1: The controller monitors the state of charge of the energy storage battery in real time. When the SOC value of the energy storage battery is less than the set value A, the external charger is turned on to charge the energy storage battery until the SOC value of the energy storage battery reaches the set value A and then charging stops. When the SOC value of the energy storage battery is greater than or equal to the set value A, the second DC grid-connected switch is closed and the third DC / DC converter is adjusted to constant voltage working mode to build DC bus voltage.

[0014] S2: Start the solid oxide fuel cell power generation system to enable it to supply power to external systems;

[0015] S3: Adjust the first DC / DC converter to constant current operating mode. When the high voltage side voltage of the first DC / DC converter reaches the set value B, close the first DC grid-connected switch.

[0016] S4: Adjust the power converter to DC-side voltage regulation mode, monitor whether the microgrid and the main grid meet the synchronization conditions, and if they do, close the AC grid connection switch to complete the grid connection operation between the microgrid and the main grid.

[0017] S5: When the SOC value of the energy storage battery is less than the set value A, adjust the third DC / DC converter to the low-voltage side constant current working mode to charge the energy storage battery. When the SOC value of the energy storage battery is greater than or equal to the set value A, adjust the third DC / DC converter to the idle mode.

[0018] Preferably, step S2 includes the following steps: controlling the operation of heating and power auxiliary devices to make the reforming chamber temperature reach a set value C1, the solid oxide fuel cell temperature reach a set value C2, the methanol solution inlet flow rate in the reforming chamber reach a set value C3, and the reforming gas outlet flow rate in the reforming chamber reach a set value C4, so that the solid oxide fuel cell power generation system has the ability to supply power to the outside.

[0019] During startup, the controller first determines the SOC value of the energy storage battery. If the SOC value is less than the set value A, the energy storage battery is charged through an external charger until the SOC value reaches the set value A before the energy storage battery is connected to the DC bus to supply power to the solid oxide fuel cell power generation system.

[0020] After the solid oxide fuel cell power generation system is powered, the heating and power auxiliary devices operate. The liquid pump draws the methanol-water solution from the methanol-water solution storage tank into the reforming chamber, and the gas pump outputs the reformed gas from the reforming chamber to the solid oxide fuel cell. The first heating module heats the reforming chamber, and the second heating module heats the solid oxide fuel cell. When the reforming chamber temperature reaches the set value C, the solid oxide fuel cell temperature reaches the set value C2, the methanol-water solution flow rate reaches the set value C3, and the reformed gas output flow rate reaches the set value C4, the solid oxide fuel cell power generation system has the ability to supply power to the outside. At this time, the first DC / DC converter is adjusted to constant current operating mode. When the high voltage side voltage of the first DC / DC converter reaches the set value B, the first DC grid connection switch is closed to connect the solid oxide fuel cell power generation system to the DC bus.

[0021] After the solid oxide fuel cell power generation system and energy storage system are connected to the DC bus, the power converter is adjusted to DC-side voltage regulation mode. When the microgrid and the main grid meet the synchronization conditions, the AC grid connection switch is closed to connect the microgrid to the main grid, completing the grid connection operation. After grid connection, if the SOC value of the energy storage battery is less than the set value A, the energy storage battery is charged until the SOC value reaches the set value A before charging stops. A is 0.2-0.5V, B is 300-500V, C1 is 200-250 kWh, C2 is 600-650 kWh, C3 is 3-5 ml / min, and C4 is 1-2 L / min.

[0022] Preferably, the grid-connected operation method of the microgrid containing a solid oxide fuel cell further includes the following steps:

[0023] The controller monitors the voltage on the main grid side in real time and compares the microgrid side voltage U with the rated voltage Un on the main grid side.

[0024] When 0.9Un≤U≤1.1Un, maintain normal grid-connected operation;

[0025] When 1.1Un<U≤1.2Un, the power converter is adjusted to PQ working mode, the third DC / DC converter is adjusted to constant voltage working mode, the first DC grid-connected switch is opened, and the microgrid absorbs electrical energy from the main grid at the rated power of the energy storage system.

[0026] When 0.5Un≤U<0.9Un, the power converter is adjusted to PQ working mode, the third DC / DC converter is adjusted to constant voltage working mode, the first DC grid-connected switch is closed, and the microgrid outputs electrical energy to the main grid with the sum of the rated power of the energy storage system and the solid oxide fuel cell power generation system.

[0027] When U < 0.5Un or U > 1.2Un, the AC grid-connected switch is opened, disconnecting the microgrid from the main grid, and the third DC / DC converter is adjusted to constant voltage operating mode to maintain the voltage balance inside the microgrid.

[0028] After grid connection is completed, intelligent management of the power flow within the microgrid and automatic islanding protection are implemented based on the status of the main grid to ensure the safety of the microgrid and the stability of the distribution network.

[0029] The beneficial effects of the present invention are: (1) During the system startup process, the load characteristics of the solid oxide fuel cell are comprehensively considered, and the self-heating startup and grid connection operation of the solid oxide fuel cell are met through a reasonable energy dispatching method. (2) After grid connection is completed, the power flow inside the microgrid can be intelligently managed and automatically islanded according to the status of the main grid, which is more conducive to ensuring the safety of the microgrid and the stability of the distribution network. Attached Figure Description

[0030] Figure 1 This is a structural schematic diagram of an embodiment.

[0031] In the diagram: 1. Solid oxide fuel cell power generation system; 2. Energy storage system; 3. Controller; 4. AC grid-connected switch; 5. DC bus; 6. Power converter; 7. Methanol-water solution storage tank; 8. Reforming chamber; 9. Solid oxide fuel cell; 10. Heating and power auxiliary devices; 11. First DC / DC converter; 12. Second DC / DC converter; 13. First DC grid-connected switch; 14. Energy storage battery; 15. Battery management system; 16. Third DC / DC converter; 17. Second DC grid-connected switch. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below through embodiments and in conjunction with the accompanying drawings.

[0033] Example: This example describes a microgrid containing a solid oxide fuel cell, such as... Figure 1As shown, the system includes a solid oxide fuel cell power generation system 1, an energy storage system 2, a controller 3, an AC grid-connected switch 4, a DC bus 5, and a power converter 6. The solid oxide fuel cell power generation system 1 includes a methanol-water solution storage tank 7, a reforming chamber 8, a solid oxide fuel cell 9, heating and power auxiliary devices 10, a first DC / DC converter 11, a second DC / DC converter 12, and a first DC grid-connected switch 13. The outlet of the methanol-water solution storage tank 7 is connected to the inlet of the reforming chamber 8 via a connecting pipe, and the outlet of the reforming chamber 8 is connected to the inlet of the solid oxide fuel cell 9 via a connecting pipe. The gas inlet is connected to the solid oxide fuel cell 9, which is electrically connected to the DC bus 5 via the first DC / DC converter 11 and the first DC grid-connected switch 13. The heating and power auxiliary device 10 is electrically connected to the DC bus 5 via the second DC / DC converter 12. The energy storage system 2 is electrically connected to the DC bus 5. The DC side of the power converter 6 is electrically connected to the DC bus 5 via the AC grid-connected switch 4. The AC side of the power converter 6 is electrically connected to the main power grid. The heating and power auxiliary device 10 is used to provide heat to the solid oxide fuel cell, heat to the reforming chamber, and pumping power to the reforming chamber.

[0034] The energy storage system 2 includes an energy storage battery 14, a battery management system 15, a third DC / DC converter 16, and a second DC grid-connected switch 17. The energy storage battery 14 is electrically connected to the DC bus 5 in sequence through the battery management system 15, the third DC / DC converter 16, and the second DC grid-connected switch 17.

[0035] Controller 3 is used to acquire data from the solid oxide fuel cell power generation system, energy storage system, DC bus, and mains grid, and to control the operation of the solid oxide fuel cell power generation system, energy storage system, AC grid-connected switch, and power converter.

[0036] The heating and power auxiliary device 10 includes a pump for drawing methanol aqueous solution from a methanol aqueous solution storage tank into a reforming chamber, a gas pump for outputting reforming gas from the reforming chamber to a solid oxide fuel cell, a first heating module for heating the reforming chamber, and a second heating module for heating the solid oxide fuel cell.

[0037] In this scheme, the controller acquires real-time electrical, thermal, and current data from the main grid, DC bus, solid oxide fuel cell power generation system, and energy storage system. Based on the acquired data, it adjusts the operating modes of the solid oxide fuel cell power generation system, energy storage system, AC grid connection switch, and power converter to complete the grid connection / off-grid operation of the microgrid and the main grid. The controller includes a data acquisition unit, a communication unit, and a control unit.

[0038] This embodiment provides a grid-connected operation method for a microgrid containing a solid oxide fuel cell, used in the aforementioned microgrid containing a solid oxide fuel cell, comprising the following steps:

[0039] S1: The controller monitors the state of charge (SOC) of the energy storage battery in real time. When the SOC value of the energy storage battery is <0.4, the external charger is connected to charge the energy storage battery until the SOC value of the energy storage battery reaches the set value A and then charging stops. When the SOC value of the energy storage battery is ≥0.4, the second DC grid-connected switch is closed and the third DC / DC converter is adjusted to constant voltage working mode to build DC bus voltage.

[0040] S2: Controls the operation of heating and power auxiliary devices to achieve a reforming chamber temperature of 230 degrees Celsius, a solid oxide fuel cell temperature of 630 degrees Celsius, a methanol solution inlet flow rate of 4 ml / min in the reforming chamber, and a reformed gas outlet flow rate of 1.76 L / min in the reforming chamber, enabling the solid oxide fuel cell power generation system to provide external power supply.

[0041] S3: Adjust the first DC / DC converter to constant current operating mode. When the high voltage side voltage of the first DC / DC converter reaches 400V, close the first DC grid-connected switch.

[0042] S4: Adjust the power converter to DC-side voltage regulation mode, monitor whether the microgrid and the main grid meet the synchronization conditions, and if they do, close the AC grid connection switch to complete the grid connection operation between the microgrid and the main grid.

[0043] S5: When the SOC value of the energy storage battery is <0.4, adjust the third DC / DC converter to the low-voltage side constant current working mode to charge the energy storage battery. When the SOC value of the energy storage battery is ≥0.4, adjust the third DC / DC converter to the idle mode.

[0044] After the microgrid is connected to the main grid, the controller monitors the voltage on the main grid side in real time and compares the microgrid side voltage U with the main grid side rated voltage Un.

[0045] When 0.9Un≤U≤1.1Un, maintain normal grid-connected operation;

[0046] When 1.1Un<U≤1.2Un, the power converter is adjusted to PQ working mode, the third DC / DC converter is adjusted to constant voltage working mode, the first DC grid-connected switch is opened, and the microgrid absorbs electrical energy from the main grid at the rated power of the energy storage system.

[0047] When 0.5Un≤U<0.9Un, the power converter is adjusted to PQ working mode, the third DC / DC converter is adjusted to constant voltage working mode, the first DC grid-connected switch is closed, and the microgrid outputs electrical energy to the main grid with the sum of the rated power of the energy storage system and the solid oxide fuel cell power generation system.

[0048] When U < 0.5Un or U > 1.2Un, the AC grid-connected switch is opened, disconnecting the microgrid from the main grid, and the third DC / DC converter is adjusted to constant voltage operating mode to maintain the voltage balance inside the microgrid.

[0049] In this scheme, at startup, the controller first determines the SOC value of the energy storage battery. If the SOC value is less than 0.4, it first controls the external charger to charge the energy storage battery until the SOC value reaches 0.4 before connecting the energy storage battery to the DC bus to supply power to the solid oxide fuel cell power generation system. The energy storage battery is electrically connected to the external charger, which is controlled by the controller.

[0050] After the solid oxide fuel cell power generation system receives power, the heating and power auxiliary devices operate. The liquid pump draws the methanol-water solution from the methanol-water solution storage tank into the reforming chamber, and the gas pump outputs the reformed gas from the reforming chamber to the solid oxide fuel cell. The first heating module heats the reforming chamber, and the second heating module heats the solid oxide fuel cell. When the reforming chamber temperature reaches 230 degrees Celsius, the solid oxide fuel cell temperature reaches 630 degrees Celsius, the methanol-water solution inflow rate reaches 4 ml / min, and the reformed gas outflow rate reaches 1.76 L / min, the solid oxide fuel cell power generation system has the ability to supply power externally. At this time, the first DC / DC converter is adjusted to constant current operating mode. When the high-voltage side voltage of the first DC / DC converter reaches 400V, the first DC grid connection switch is closed to connect the solid oxide fuel cell power generation system to the DC bus.

[0051] After the solid oxide fuel cell power generation system and energy storage system are connected to the DC bus, the power converter is adjusted to DC side voltage regulation mode. When the microgrid and the main grid meet the synchronization conditions, the AC grid connection switch is closed to connect the microgrid to the main grid and complete the grid connection operation. After grid connection, if the SOC value of the energy storage battery is less than 0.4, the energy storage battery is charged until the SOC value reaches 0.4 before charging stops.

[0052] During system startup, the load characteristics of the solid oxide fuel cell were comprehensively considered, and a reasonable energy dispatch method was used to meet the self-heating startup and grid connection requirements of the solid oxide fuel cell. After grid connection was completed, intelligent management of the power flow within the microgrid and automatic islanding protection were implemented based on the status of the main grid to ensure the safety of the microgrid and the stability of the distribution network.

Claims

1. A method for grid-connected operation of a microgrid containing a solid oxide fuel cell, used in a microgrid containing a solid oxide fuel cell, characterized in that, The microgrid includes a solid oxide fuel cell power generation system (1), an energy storage system (2), a controller (3), an AC grid-connected switch (4), a DC bus (5), and a power converter (6). The solid oxide fuel cell power generation system (1) includes a methanol-water solution storage tank (7), a reforming chamber (8), a solid oxide fuel cell (9), heating and power auxiliary devices (10), a first DC / DC converter (11), a second DC / DC converter (12), and a first DC grid-connected switch (13). The outlet of the methanol-water solution storage tank (7) is connected to the inlet of the reforming chamber (8) via a connecting pipe, and the outlet of the reforming chamber (8) is connected to the solid oxide fuel cell (9) via a connecting pipe. The solid oxide fuel cell (9) is connected to the air inlet of the solid oxide fuel cell (9) in sequence through the first DC / DC converter (11) and the first DC grid-connected switch (13) and the DC bus (5). The heating and power auxiliary device (10) is connected to the DC bus (5) through the second DC / DC converter (12). The energy storage system (2) is connected to the DC bus (5). The DC side of the power converter (6) is connected to the DC bus (5) through the AC grid-connected switch (4). The AC side of the power converter (6) is connected to the main grid. The heating and power auxiliary device (10) is used to provide heat to the solid oxide fuel cell, provide heat to the reforming chamber, and provide pumping and gas delivery power to the reforming chamber. The controller (3) is used to acquire data from the solid oxide fuel cell power generation system, energy storage system, DC bus, and power grid, and to control the operation of the solid oxide fuel cell power generation system, energy storage system, AC grid-connected switch, and power converter. The energy storage system (2) includes an energy storage battery (14), a battery management system (15), a third DC / DC converter (16), and a second DC grid-connected switch (17). The energy storage battery (14) is electrically connected to the DC bus (5) in sequence through the battery management system (15), the third DC / DC converter (16), and the second DC grid-connected switch (17). The heating and power auxiliary device (10) includes a pump for pumping methanol aqueous solution from the methanol aqueous solution storage tank into the reforming chamber, a gas pump for outputting reforming gas from the reforming chamber to the solid oxide fuel cell, a first heating module for heating the reforming chamber, and a second heating module for heating the solid oxide fuel cell. The grid-connected operation method includes the following steps: S1: The controller monitors the state of charge (SOC) of the energy storage battery in real time. When the SOC value of the energy storage battery is <0.4, the external charger is connected to charge the energy storage battery until the SOC value of the energy storage battery reaches 0.4 and then charging stops. When the SOC value of the energy storage battery is ≥0.4, the second DC grid-connected switch is closed and the third DC / DC converter is adjusted to constant voltage working mode to build DC bus voltage. S2: Controls the operation of heating and power auxiliary devices to achieve a reforming chamber temperature of 230 degrees Celsius, a solid oxide fuel cell temperature of 630 degrees Celsius, a methanol solution inlet flow rate of 4 ml / min in the reforming chamber, and a reformed gas outlet flow rate of 1.76 L / min in the reforming chamber, enabling the solid oxide fuel cell power generation system to provide external power supply. S3: Adjust the first DC / DC converter to constant current operating mode. When the high voltage side voltage of the first DC / DC converter reaches 400V, close the first DC grid-connected switch. S4: Adjust the power converter to DC-side voltage regulation mode, monitor whether the microgrid and the main grid meet the synchronization conditions, and if they do, close the AC grid connection switch to complete the grid connection operation between the microgrid and the main grid. S5: When the SOC value of the energy storage battery is <0.4, adjust the third DC / DC converter to the low-voltage side constant current working mode to charge the energy storage battery. When the SOC value of the energy storage battery is ≥0.4, adjust the third DC / DC converter to the idle mode. After the microgrid is connected to the main grid, the controller monitors the voltage on the main grid side in real time and compares the microgrid side voltage U with the main grid side rated voltage Un. When 0.9Un≤U≤1.1Un, maintain normal grid-connected operation; When 1.1Un<U≤1.2Un, the power converter is adjusted to PQ working mode, the third DC / DC converter is adjusted to constant voltage working mode, the first DC grid-connected switch is opened, and the microgrid absorbs electrical energy from the main grid at the rated power of the energy storage system. When 0.5Un≤U<0.9Un, the power converter is adjusted to PQ working mode, the third DC / DC converter is adjusted to constant voltage working mode, the first DC grid-connected switch is closed, and the microgrid outputs electrical energy to the main grid with the sum of the rated power of the energy storage system and the solid oxide fuel cell power generation system. When U < 0.5Un or U > 1.2Un, the AC grid-connected switch is opened, disconnecting the microgrid from the main grid, and the third DC / DC converter is adjusted to constant voltage operating mode to maintain the voltage balance inside the microgrid.

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