Microgrid system and control method thereof

Abstract

The invention provides a micro-grid system and a control method thereof. The micro-grid system comprises new energy power generation equipment, an energy storage battery, an energy storage converter, an alternating current bus, a controller and a load. The output end of the new energy power generation equipment is connected with the AC bus which is also connected with the load. The input end of the energy storage converter is connected with the energy storage battery, and the output end is connected with the AC bus. And in the black start process of the micro-grid system, if the residual electric quantity of the energy storage battery is smaller than the residual electric quantity threshold value and the input power of the new energy power generation equipment is larger than or equal to the total rated power of the load, the controller controls the new energy power generation equipment to be in a grid construction type control mode. Wherein the new energy power generation equipment comprises at least one of a photovoltaic inverter, a wind driven generator and a hydroelectric generating set. By adopting the application, the micro-grid system can realize deoiling networking operation under the condition that the energy storage converter does not have an independent networking operation condition.

Description

Technical Field

[0001] The present application relates to the field of power supply technology, and in particular to a microgrid system and a control method thereof. Background Art

[0002] At present, microgrid systems mainly adopt Figure 1 The system architecture shown includes a PV inverter, energy storage converter, load, and diesel generator. Both the energy storage converter and diesel generator utilize grid-building technology, establishing microgrid system voltage, frequency, and other grid indicators for grid startup. The PV inverter utilizes grid-following technology, operating on the grid created by the energy storage converter or diesel generator.

[0003] When a microgrid system is in an isolated state (i.e., the microgrid system is operating independently of the main grid) and requires a black start, the system controller in the microgrid system controls the energy storage converter or diesel generator to operate in a grid-forming control mode, so that the energy storage converter or diesel generator establishes the voltage and frequency of the microgrid system. After the energy storage converter or diesel generator establishes the voltage and frequency of the microgrid system, the system controller controls the photovoltaic inverter to operate in a grid-following control mode, so that the photovoltaic inverter operates in dependence on the voltage and frequency of the microgrid system. Simply put, in an isolated state, an existing microgrid system requires an energy storage converter or diesel generator as a starting power source to operate in a network, that is, to establish the voltage and frequency of the microgrid system.

[0004] However, the energy storage inverter's networking capability, or its ability to perform a black start, is strongly correlated with the remaining state of charge (SOC) of the energy storage battery connected to the energy storage inverter. When the SOC of the energy storage battery falls below the black start threshold, the energy storage inverter will be unable to perform a black start to establish the voltage and frequency of the microgrid system. In this case, the microgrid system can only rely on diesel generators for networking and operation, which use non-clean renewable energy. Therefore, when the SOC of the energy storage unit falls below the black start threshold, it is particularly important for the microgrid system to achieve oil-free networking and operation. Summary of the Invention

[0005] The present application provides a microgrid system and a control method thereof, which can enable the microgrid system to achieve oil-free networking operation when the energy storage converter does not have the conditions for independent networking operation.

[0006] In a first aspect, the present application provides a microgrid system comprising a new energy power generation device, an energy storage battery, an energy storage converter, an AC bus, a controller, and a load. The output of the new energy power generation device is connected to the AC bus, which is also connected to the load. The input of the energy storage converter is connected to the energy storage battery, and the output of the energy storage converter is connected to the AC bus. When the remaining charge of the energy storage battery is less than a remaining charge threshold and the input power of the new energy power generation device is greater than or equal to the total rated power of the load, the remaining charge of the energy storage battery is insufficient to support the independent grid-forming operation of the energy storage converter, and the input power of the new energy power generation device is sufficient to support the independent grid-forming operation of the new energy power generation device. In this case, the controller is configured to control the new energy power generation device to be in a grid-forming control mode during a black start of the microgrid system, so that the new energy power generation device establishes the voltage and frequency required by the microgrid system to power the load. The new energy power generation device comprises at least one of a photovoltaic inverter, a wind turbine, and a hydroelectric generator set.

[0007] It is understandable that when the energy storage converter does not meet the conditions for independent grid operation and the new energy power generation equipment does, the microgrid system can complete a black start by controlling the voltage and frequency required by the new energy power generation equipment to build the microgrid system. In other words, controlling the new energy power generation equipment as the starting power source for network operation. Simply put, the microgrid system adds a black start network operation mode for new energy power generation equipment. Since the energy used by the new energy power generation equipment is solar, wind, or hydropower, all of which are clean and renewable energy sources, the microgrid system can achieve oil-free network operation even when the energy storage converter does not meet the conditions for independent grid operation.

[0008] In one possible implementation, the controller is also used to control the energy storage converter to be in a grid-following control mode when the new energy power generation equipment is in a grid-forming control mode, so that the energy storage converter follows the new energy power generation equipment to provide the voltage and frequency required by the microgrid system to jointly power the load.

[0009] In one possible implementation, when the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load, the remaining power of the energy storage battery is sufficient to support the independent networking and operation of the energy storage converter, and the input power of the new energy power generation equipment is insufficient to support the independent networking and operation of the new energy power generation equipment. At this time, the controller is also used to control the energy storage converter to be in a networking control mode during the black start of the microgrid system.

[0010] In this embodiment, when the energy storage converter is capable of independent network operation and the new energy generation equipment is not, the microgrid system can complete a black start by controlling the energy storage converter as the starting power source for network operation. Furthermore, this energy storage converter black start network operation mode also enables the microgrid system to achieve oil-free network operation when the new energy generation equipment is not capable of independent network operation.

[0011] In a possible implementation, the controller is further configured to control the new energy power generation equipment to be in a grid-following control mode when the energy storage converter is in a grid-forming control mode.

[0012] In one possible embodiment, the controller is also used to control at least one power generation device among the new energy power generation device and the energy storage converter to be in a grid-type control mode if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation device is greater than or equal to the total rated power of the load during the black start of the microgrid system.

[0013] In this embodiment, when both the renewable energy generation equipment and the energy storage converter are capable of independent network operation, the microgrid system can be networked and operated by controlling the renewable energy generation equipment and / or the energy storage converter as the starting power source, thereby completing a black start of the microgrid system. Furthermore, this black start networking mode of renewable energy generation equipment and / or the energy storage converter enables the microgrid system to operate without oil.

[0014] In one possible embodiment, the microgrid system further includes a diesel generator, the output end of which is connected to the AC bus. The controller is further configured to control the diesel generator to enter a grid-forming control mode during a black start of the microgrid system if the remaining charge of the energy storage battery is greater than or equal to a remaining charge threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load.

[0015] In this embodiment, when both the new energy power generation equipment and the energy storage converter have the conditions for independent network operation, the microgrid system can also be networked and operated by controlling the diesel generator as the starting power supply to complete the black start of the microgrid system, making the networking operation mode of the microgrid system diverse.

[0016] In one possible embodiment, the microgrid system further includes a diesel generator, the output end of which is connected to the AC bus. The controller is further configured to control the diesel generator to operate in a grid-forming control mode, or to control both the diesel generator and the new energy power generation equipment to operate in the grid-forming control mode, if the remaining charge of the energy storage battery is less than a remaining charge threshold and the input power of the new energy power generation equipment is less than the total rated power of the loads during a black start of the microgrid system.

[0017] In this embodiment, when the new energy power generation equipment and the energy storage converter do not have the conditions for independent network operation, the microgrid system can also control the diesel generator, or the diesel generator and the new energy power generation equipment, as the starting power supply to carry out network operation, so that the microgrid system can successfully complete the black start.

[0018] In the second aspect, the present application provides a photovoltaic inverter for use in a microgrid system. The microgrid system also includes an energy storage battery, an energy storage converter, an AC bus, and a load. The input end of the photovoltaic inverter is used to connect to the photovoltaic module, and the output end of the photovoltaic inverter is connected to the AC bus. The input end of the energy storage converter is connected to the energy storage battery, the output end of the energy storage converter is connected to the AC bus, and the AC bus is also connected to the load. When the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the photovoltaic inverter is greater than or equal to the total rated power of the load, the remaining power of the energy storage battery is insufficient to support the energy storage converter to operate independently in a network, and the input power of the photovoltaic inverter is sufficient to support the photovoltaic inverter to operate independently in a network. At this time, the photovoltaic inverter is used in a network-type control mode during the black start process of the microgrid system.

[0019] It's understandable that the PV inverter can serve as a startup power source for networking and operation, completing a black start of the microgrid system, even when the energy storage converter doesn't have the conditions for standalone grid operation, but the PV inverter does. Simply put, the microgrid system adds the PV inverter's black start networking mode. Furthermore, because the PV inverter uses solar energy, a clean and renewable energy source, it enables oil-free networking and operation even when the energy storage converter doesn't have the conditions for standalone grid operation.

[0020] In one possible implementation, the photovoltaic inverter is further configured to operate in a grid-following control mode when the energy storage converter is in a grid-forming control mode. During a black start of the microgrid system, if the remaining charge of the energy storage battery is greater than or equal to a remaining charge threshold and the input power of the photovoltaic inverter is less than the total rated power of the loads, the energy storage converter operates in the grid-forming control mode.

[0021] In one possible implementation, the photovoltaic inverter is also used to be in a grid-forming control mode during a black start of the microgrid system if the remaining power of the energy storage battery is greater than or equal to a remaining power threshold and the input power of the photovoltaic inverter is greater than or equal to the total rated power of the load.

[0022] In one possible embodiment, the microgrid system further includes a diesel generator, the output end of which is connected to the AC bus. The photovoltaic inverter is also configured to operate in a grid-forming control mode during a black start of the microgrid system if the remaining charge of the energy storage battery is less than a remaining charge threshold and the input power of the new energy power generation equipment is less than the total rated power of the load. Furthermore, the diesel generator also operates in a grid-forming control mode when the remaining charge of the energy storage battery is less than a remaining charge threshold and the input power of the new energy power generation equipment is less than the total rated power of the load.

[0023] In a third aspect, the present application provides a control method for a microgrid system, which is applied to a microgrid system. The microgrid system includes a new energy power generation device, an energy storage battery, an energy storage converter, an AC bus, a controller, and a load. The output end of the new energy power generation device is connected to the AC bus, and the AC bus is also connected to the load. The input end of the energy storage converter is connected to the energy storage battery, and the output end of the energy storage converter is connected to the AC bus. The method includes: during the black start process of the microgrid system, if the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the new energy power generation device is greater than or equal to the total rated power of the load, controlling the new energy power generation device to be in a grid-type control mode. The new energy power generation device includes at least one of a photovoltaic inverter, a wind turbine, and a hydropower generator set.

[0024] In a possible implementation, the microgrid system controls the energy storage converter to be in a grid-following control mode when the new energy power generation equipment is in a grid-building control mode.

[0025] In one possible implementation, during the black start of the microgrid system, if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load, the microgrid system also controls the energy storage converter to be in a grid-forming control mode.

[0026] In a possible implementation, the microgrid system controls the new energy power generation equipment to be in a grid-following control mode when the energy storage converter is in a grid-building control mode.

[0027] In one possible implementation, during the black start of the microgrid system, if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load, the microgrid system also controls at least one of the new energy power generation equipment and the energy storage converter to be in a grid-type control mode.

[0028] In one possible implementation, the microgrid system further includes a diesel generator, the output end of which is connected to the AC bus. During a black start of the microgrid system, if the remaining charge of the energy storage battery is greater than or equal to a remaining charge threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load, the microgrid system further controls the diesel generator to operate in a grid-forming control mode.

[0029] In one possible embodiment, the microgrid system further includes a diesel generator, the output end of which is connected to the AC bus. During a black start of the microgrid system, if the remaining charge of the energy storage battery is less than a remaining charge threshold and the input power of the new energy power generation equipment is less than the total rated power of the load, the microgrid system further controls the diesel generator to operate in a grid-forming control mode, or controls both the diesel generator and the new energy power generation equipment to operate in a grid-forming control mode.

[0030] It should be understood that the implementation and beneficial effects of the above-mentioned aspects of the present application can be referenced to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a structural diagram of a microgrid system provided by the prior art;

[0032] Figure 2 This is a schematic diagram of an application scenario of the microgrid system provided by this application;

[0033] Figure 3 This is a structural diagram of the microgrid system provided by this application;

[0034] Figure 4 is another structural schematic diagram of the microgrid system provided by this application;

[0035] Figure 5 This is a flow chart of a control method for a microgrid system provided by the present application;

[0036] Figure 6 This is another flowchart of the control method of the microgrid system provided by this application. DETAILED DESCRIPTION

[0037] The microgrid system provided in this application is applicable to a variety of application areas, including hybrid photovoltaic and energy storage power generation, new energy smart microgrids, and power transmission and distribution. The microgrid system provided in this application is suitable for different application scenarios, such as hybrid photovoltaic and energy storage power supply scenarios and new energy isolated grid operation scenarios. The following uses the new energy isolated grid operation scenario as an example for illustration.

[0038] See also Figure 2 , Figure 2 This is a schematic diagram of the application scenario of the microgrid system provided by this application. In the scenario of isolated new energy grid operation, the new energy power generation equipment provided by this application is Figure 2 The photovoltaic inverter shown in the figure, the microgrid system provided by this application is Figure 2 The microgrid system shown. The microgrid system includes a photovoltaic inverter, a photovoltaic module, a plurality of energy storage converters, a plurality of energy storage batteries, a plurality of transformers, an AC bus, a controller and loads (i.e., loads a1, ..., and load an). The input end of the photovoltaic inverter is connected to the photovoltaic module, and the output end of the photovoltaic inverter is connected to the AC bus through one of the multiple transformers; the input end of each of the multiple energy storage converters is connected to one of the multiple energy storage batteries, and the output end of each energy storage converter is connected to the AC bus through one of the multiple transformers; each of the multiple loads is connected to the AC bus through one of the multiple transformers. Optionally, the microgrid system also includes a diesel generator, which is connected to the AC bus through a transformer.

[0039] When the remaining charge of each energy storage battery is less than the remaining charge threshold and the input power of the photovoltaic inverter is greater than or equal to the total rated power of the loads (i.e., the sum of the rated powers of loads a1 to an), the remaining charge of each energy storage battery is insufficient to support the independent grid operation of the energy storage converter connected to each energy storage battery, that is, each energy storage converter does not have the conditions for independent grid operation. In addition, the output power of the photovoltaic module is sufficient to support the independent grid operation of the photovoltaic inverter, that is, the photovoltaic inverter has the conditions for independent grid operation. At this time, during the black start process of the microgrid system, the controller controls the photovoltaic inverter to be in a grid-type control mode. Here, the power generation equipment (such as a photovoltaic inverter) is in a grid-type control mode, which can be understood as the power generation equipment externally appearing as a voltage source. Specifically, the power generation equipment constructs the voltage and frequency of the microgrid system to power the load. That is, the output voltage value of the power generation equipment is positively correlated with the operating voltage value of the load, and the output voltage frequency of the power generation equipment is the same as the operating voltage frequency of the load. The positive correlation between the output voltage value of the power generation equipment and the operating voltage value of the load is caused by the transformer connected between the output end of the power generation equipment and the load. Taking a photovoltaic inverter as an example, the positive correlation between the inverter's output voltage and the load's operating voltage means that the ratio of the inverter's output voltage to the load's operating voltage is equal to the product of the turns ratios of the two transformers connected between the inverter and the load. The transformer's turns ratio is the ratio of the number of turns in the primary winding to the number of turns in the secondary winding. Furthermore, the grid-based control mode offers strong support for the power grid and can effectively address issues such as reduced short-circuit capacity and missing moment of inertia in new power systems.

[0040] It is understandable that the microgrid system provided by this application not only uses the energy storage converter as the system's starting power supply, but also adds a photovoltaic inverter as the system's starting power supply. Therefore, during the black start process of the microgrid system, when the energy storage converter does not have the conditions for independent network operation, the microgrid system controls the photovoltaic inverter to construct the voltage and frequency of the microgrid system to achieve the network operation of the microgrid system. In short, the microgrid system provided by this application adds a photovoltaic inverter black start network operation mode. Since the energy used by the photovoltaic inverter is solar energy, which is a clean and renewable energy source, the microgrid system can achieve oil-free network operation when the energy storage converter does not have the conditions for independent network operation.

[0041] The above is only an example of the application scenarios of the microgrid system provided by this application, and is not an exhaustive list. This application does not limit the application scenarios.

[0042] The following combination Figure 3 and Figure 4 The working principle of the microgrid system provided in this application is illustrated by way of example.

[0043] See also Figure 3 , Figure 3 This is a schematic diagram of the structure of the microgrid system provided by this application. Figure 3 As shown, microgrid system 1 includes a new energy generation device 11, an energy storage battery 12, an energy storage converter 13, an AC bus, a controller 14, and a load 15. The output of the new energy generation device 11 is connected to the AC bus, which is also connected to the load 15. The input of the energy storage converter 13 is connected to the energy storage battery 12, and the output of the energy storage converter 13 is connected to the AC bus. Figure 3 The black solid lines in the figure represent electrical connection lines, and the black dashed lines represent communication transmission lines.

[0044] When the remaining power of the energy storage battery 12 is less than the remaining power threshold and the input power of the new energy power generation equipment 11 is greater than or equal to the total rated power of the load 15, the remaining power of the energy storage battery 12 is insufficient to support the independent grid operation of the energy storage converter 13, and the input power of the new energy power generation equipment 11 is sufficient to support the independent grid operation of the new energy power generation equipment 11. At this time, the controller 14 controls the new energy power generation equipment 11 to be in the grid-type control mode during the black start of the microgrid system 1.

[0045] The remaining power threshold is the minimum value of the remaining power of the energy storage battery 12 when the energy storage converter 13 can be in a grid-type control mode. The new energy power generation equipment 11 includes at least one of a photovoltaic inverter, a wind turbine, and a hydroelectric generator set. It should be noted that when the number of new energy power generation equipment 11 is multiple, that is, when the new energy power generation equipment 11 includes at least two of the photovoltaic inverter, the wind turbine, and the hydroelectric generator set, the input power of the new energy power generation equipment 11 in this application is the sum of the input powers of at least two of the photovoltaic inverter, the wind turbine, and the hydroelectric generator set. Furthermore, when the number of new energy power generation equipment 11 is one or more, the control method for the output voltage of the new energy power generation equipment 11 when it is in a grid-type control mode is the same, that is, the output voltage value of each new energy power generation equipment in the at least one new energy power generation equipment is positively correlated with the operating voltage value of the load 15 and the output voltage frequency of each new energy power generation equipment is the same as the operating voltage frequency of the load 15. The only difference is the control of the output power. Specifically, when the number of new energy power generation equipment 11 is one, the output power of one new energy power generation equipment is the total rated power of the load 15; when the number of new energy power generation equipment 11 is multiple, the sum of the output powers of multiple new energy power generation equipment is the total rated power of the load 15.

[0046] It is understandable that when the energy storage converter 13 does not meet the conditions for independent network operation and the new energy power generation equipment 11 meets the conditions for independent network operation, the microgrid system 1 can complete a black start by controlling the new energy power generation equipment 11 to establish the voltage and frequency required for the microgrid system 1. In other words, the microgrid system 1 is controlled to use the new energy power generation equipment 11 as a starting power source for network operation. In short, the microgrid system 1 adds a black start network operation mode for the new energy power generation equipment 11. Since the energy used by the new energy power generation equipment 11 is solar energy, wind energy, or hydropower, all of which are clean and renewable energy sources, the microgrid system 1 can achieve oil-free network operation even when the energy storage converter 13 does not meet the conditions for independent network operation.

[0047] Since the working principle of the microgrid system provided by the present application is similar regardless of whether the new energy power generation equipment 11 is any one, any two or all of the photovoltaic inverter, wind turbine and hydroelectric generator set, the following takes the new energy power generation equipment 11 as an example of a photovoltaic inverter, combined with Figure 4 The microgrid system shown in the figure is introduced.

[0048] See also Figure 4 , Figure 4 This is another structural diagram of the microgrid system provided by this application. Figure 4 As shown, the new energy power generation equipment is a photovoltaic inverter 111, and the microgrid system 1 also includes a photovoltaic module 16, a transformer 171, a transformer 172, and a transformer 173. The input of the photovoltaic inverter 111 is connected to the photovoltaic module 16, and the output of the photovoltaic inverter 111 is connected to the AC bus through the transformer 171. The output of the energy storage converter 13 is connected to the AC bus through the transformer 172, and the load 15 is connected to the AC bus through the transformer 173. Optionally, the microgrid system 1 also includes a transformer 174 and a diesel generator 18, and the output of the diesel generator 18 is connected to the AC bus through the transformer 174.

[0049] In one embodiment, the photovoltaic inverter 111 has the conditions for independent grid operation and the energy storage converter 13 does not have the conditions for independent grid operation. The microgrid system 1 realizes a black start by controlling the photovoltaic inverter 111 to operate in a grid and the energy storage converter 13 to operate in a grid-following manner, as follows:

[0050] When the remaining charge of the energy storage battery 12 is less than the remaining charge threshold and the input power of the photovoltaic inverter 111 (i.e., the output power of the photovoltaic assembly 16) is greater than or equal to the total rated power of the load 15, the remaining charge of the energy storage battery 12 is insufficient to support independent grid-forming operation of the energy storage converter 13, and the output power of the photovoltaic assembly 16 is sufficient to support independent grid-forming operation of the photovoltaic inverter 111. In this case, during the black start of the microgrid system 1, the controller 14 controls the photovoltaic inverter 111 to be in a grid-forming control mode, so that the photovoltaic inverter 111 establishes the voltage and frequency required by the microgrid system 1 to supply power to the load 15. Furthermore, when the photovoltaic inverter 111 is in the grid-forming control mode, the controller 14 controls the energy storage converter 13 to be in a grid-following control mode, so that the energy storage converter 13 follows the photovoltaic inverter 111 in providing the voltage and frequency required by the microgrid system 1, thereby jointly supplying power to the load 15.

[0051] Among them, the input power of the photovoltaic inverter 111 can be the meteorological data (such as light, temperature) obtained by the controller 14 based on the preset frequency (such as the local climate change frequency where the photovoltaic component 16 is located), and the mapping relationship between the meteorological data and the output power of the photovoltaic component, and the output power of the photovoltaic component corresponding to the current meteorological data, that is, the predicted output power of the photovoltaic component 16; the input power of the photovoltaic inverter 111 can also be the actual output power of the photovoltaic component 16, or the smaller value between the predicted output power and the actual output power of the photovoltaic component 16. In addition, the output voltage value of the photovoltaic inverter 111 is positively correlated with the operating voltage value of the load 15, specifically referring to. Here, the power generation equipment (such as the energy storage converter) is in the grid-following control mode, which can be understood as the power generation equipment acting as a current source to the outside. The power generation equipment cannot provide voltage and frequency support for the microgrid system and relies on the voltage and frequency of the microgrid system to operate. For this embodiment, the photovoltaic inverter 111 constructs the voltage and frequency of the microgrid system 1. Therefore, the energy storage converter 13 is in the grid-following control mode, which can be understood as the energy storage converter 13 follows the photovoltaic inverter 111 to provide the voltage and frequency required by the microgrid system 1 to jointly power the load 15. That is, the output voltage value of the energy storage converter 13 follows the output voltage value of the photovoltaic inverter 111, and the output voltage frequency of the energy storage converter 13 follows the output voltage frequency of the photovoltaic inverter 111.

[0052] It is understood that when the energy storage converter 13 does not meet the conditions for independent grid operation, but the photovoltaic inverter 111 does, microgrid system 1 can complete a black start of microgrid system 1 by controlling the photovoltaic inverter 111 as the starting power source for grid operation and controlling the energy storage converter 13 to follow the grid. Simply put, microgrid system 1 adds a black start grid operation mode for photovoltaic inverter 111. Furthermore, because photovoltaic inverter 111 uses solar energy, a clean and renewable energy source, microgrid system 1 can achieve oil-free grid operation even when the energy storage converter 13 does not meet the conditions for independent grid operation.

[0053] In another embodiment, the photovoltaic inverter 111 does not have the conditions for independent grid operation and the energy storage converter 13 has the conditions for independent grid operation. The microgrid system 1 realizes a black start by controlling the energy storage converter 13 to operate in a grid and the photovoltaic inverter 111 to operate in a grid-following manner, as follows:

[0054] When the remaining charge of energy storage battery 12 is greater than or equal to the remaining charge threshold and the input power of photovoltaic inverter 111 is less than the total rated power of load 15, the remaining charge of energy storage battery 12 is sufficient to support independent grid-connected operation of energy storage inverter 13, and the output power of photovoltaic assembly 16 is insufficient to support independent grid-connected operation of photovoltaic inverter 111. In this case, during the black start process of microgrid system 1, controller 14 controls energy storage inverter 13 to be in a grid-connected control mode, so that energy storage inverter 13 establishes the voltage and frequency required by microgrid system 1 to supply power to load 15. Controller 14 also controls photovoltaic inverter 111 to be in a grid-following control mode when energy storage inverter 13 is in the grid-connected control mode, so that photovoltaic inverter 111 follows energy storage inverter 13 in providing the voltage and frequency required by microgrid system 1, thereby jointly supplying power to load 15.

[0055] It is understood that when the energy storage converter 13 meets the conditions for independent grid operation and the photovoltaic inverter 111 does not, the microgrid system 1 can complete a black start of the microgrid system 1 by controlling the energy storage converter 13 as the starting power source to perform grid operation and controlling the photovoltaic inverter 111 to operate in conjunction with the grid. Simply put, before performing a black start, in this embodiment, the microgrid system 1 first determines whether the photovoltaic inverter 111 and the energy storage converter 13 meet the conditions for independent grid operation. Then, during the black start process, the microgrid system 1 ensures that the microgrid system 1 successfully completes the black start, i.e., restores power smoothly, by controlling the energy storage converter 13 to operate in conjunction with the grid. Furthermore, the black start operation mode of the energy storage converter 13 enables the microgrid system 1 to achieve oil-free grid operation even when the photovoltaic inverter 111 does not meet the conditions for independent grid operation.

[0056] In another embodiment, the photovoltaic inverter 111 and the energy storage converter 13 are both capable of independent network operation conditions. The microgrid system 1 can achieve a black start by controlling the photovoltaic inverter 111 and / or the energy storage converter 13 to operate in a networked manner, as follows:

[0057] When the remaining charge of energy storage battery 12 is greater than or equal to the remaining charge threshold and the input power of photovoltaic inverter 111 is greater than or equal to the total rated power of load 15, the remaining charge of energy storage battery 12 is sufficient to support independent grid-connected operation of energy storage converter 13, and the output power of photovoltaic assembly 16 is sufficient to support independent grid-connected operation of photovoltaic inverter 111. In this case, during the black start process of microgrid system 1, controller 14 controls at least one power generation device among photovoltaic inverter 111 and energy storage converter 13 to enter grid-connected control mode, so that photovoltaic inverter 111 and / or energy storage converter 13 establish the voltage and frequency required by microgrid system 1 to supply power to load 15. Optionally, when the number of the at least one power generation device is one, controller 14 may further control the other power generation device among photovoltaic inverter 111 and energy storage converter 13 to enter grid-following control mode after one power generation device among photovoltaic inverter 111 and energy storage converter 13 enters grid-connected control mode.

[0058] It is understood that, when both the photovoltaic inverter 111 and the energy storage converter 13 are capable of independent network operation, the microgrid system 1 can be networked and operated by controlling the photovoltaic inverter 111 and / or the energy storage converter 13 as the starting power source, thereby completing a black start of the microgrid system 1. Furthermore, the black start network operation mode of the photovoltaic inverter 111 and / or the energy storage converter 13 enables the microgrid system 1 to achieve oil-free network operation.

[0059] In another embodiment, the photovoltaic inverter 111 and the energy storage converter 13 are both capable of independent network operation. The microgrid system 1 can also achieve black start by controlling the diesel generator 18 to operate in a network, as follows:

[0060] When the remaining power of the energy storage battery 12 is greater than or equal to the remaining power threshold and the input power of the photovoltaic inverter 111 is greater than or equal to the total rated power of the load 15, the remaining power of the energy storage battery 12 is sufficient to support the independent grid-forming operation of the energy storage converter 13, and the output power of the photovoltaic assembly 16 is sufficient to support the independent grid-forming operation of the photovoltaic inverter 111. At this time, during the black start process of the microgrid system 1, the controller 14 controls the diesel generator 18 to be in the grid-forming control mode, so that the diesel generator 18 establishes the voltage and frequency required by the microgrid system 1 to power the load 15. Optionally, the controller 14 may also control the photovoltaic inverter 111 and / or the energy storage converter 13 to be in the grid-following control mode after the diesel generator 18 is in the grid-forming control mode.

[0061] It is understandable that when the photovoltaic inverter 111 and the energy storage converter 13 of the microgrid system 1 both have the conditions for independent network operation, the microgrid system 1 can also be networked and operated by controlling the diesel generator 18 as a starting power supply to complete the black start of the microgrid system 1, making the network operation mode of the microgrid system 1 diverse.

[0062] In another embodiment, the photovoltaic inverter 111 and the energy storage converter 13 do not have the conditions for independent network operation. The microgrid system 1 can also achieve black start by controlling the diesel generator 18 to operate in a network, as follows:

[0063] When the remaining power of the energy storage battery 12 is less than the remaining power threshold and the input power of the photovoltaic inverter 111 is less than the total rated power of the load 15, the remaining power of the energy storage battery 12 is insufficient to support the independent grid-forming operation of the energy storage converter 13, and the output power of the photovoltaic assembly 16 is insufficient to support the independent grid-forming operation of the photovoltaic inverter 111. In this case, during the black start of the microgrid system 1, the controller 14 controls the diesel generator 18 to be in a grid-forming control mode, so that the diesel generator 18 establishes the voltage and frequency required by the microgrid system 1 to supply power to the load 15. Optionally, the controller 14 may also control the photovoltaic inverter 111 and / or the energy storage converter 13 to be in a grid-following control mode after the diesel generator 18 is in the grid-forming control mode.

[0064] It is understandable that when the photovoltaic inverter 111 and the energy storage converter 13 do not have the conditions for independent network operation, the microgrid system 1 can also be networked and operated by controlling the diesel generator 18 as the starting power supply, so that the microgrid system 1 can successfully complete the black start.

[0065] In another embodiment, the photovoltaic inverter 111 and the energy storage converter 13 do not have the conditions for independent network operation. The microgrid system 1 can also realize black start by controlling the diesel generator 18 and the photovoltaic inverter 111 to operate in a network together, as follows:

[0066] When the remaining power of the energy storage battery 12 is less than the remaining power threshold and the input power of the photovoltaic inverter 111 is less than the total rated power of the load 15, the remaining power of the energy storage battery 12 is insufficient to support the independent grid-forming operation of the energy storage converter 13, and the output power of the photovoltaic assembly 16 is insufficient to support the independent grid-forming operation of the photovoltaic inverter 111. At this time, during the black start process of the microgrid system 1, the controller 14 controls the diesel generator 18 and the photovoltaic inverter 111 to be in a grid-forming control mode, so that the diesel generator 18 and the photovoltaic inverter 111 jointly construct the voltage and frequency required by the microgrid system 1 to power the load 15. Optionally, the controller 14 may also control the energy storage converter 13 to be in a grid-following control mode after the diesel generator 18 and the photovoltaic inverter 111 are in the grid-forming control mode.

[0067] In addition, in actual control, when the controller 14 controls the diesel generator 18 and the photovoltaic inverter 111 to be in the grid-type control mode, in addition to controlling their respective output voltages to meet the operating voltage of the load 15, it also controls the output power of the diesel generator 18 to be the absolute value of the difference between the output power of the photovoltaic component 16 and the total rated power of the load 15. In other words, the diesel generator 18 only needs to make up for the power lacking in the photovoltaic inverter 111 for independent grid operation, thereby minimizing the output power proportion of the diesel generator 18 when the photovoltaic inverter 111 and the diesel generator 18 are networked together, and thereby minimizing the oil content of the microgrid system 1 when the photovoltaic inverter 111 and the energy storage converter 13 do not have the conditions for independent grid operation.

[0068] It can be understood that when the photovoltaic inverter 111 and the energy storage converter 13 do not have the conditions for independent network operation, the microgrid system 1 can also be networked and operated by controlling the diesel generator 18 and the photovoltaic inverter 111 as starting power supplies. This not only enables the microgrid system 1 to successfully complete the black start, but also increases the diversity of the network operation mode of the microgrid system 1.

[0069] In the present application, the microgrid system 1 will first determine whether the new energy power generation equipment 11 and the energy storage converter 13 have the conditions for independent network operation before performing a black start. Afterwards, during the black start process, the microgrid system 1 controls the network operation of the power generation equipment that has the conditions for independent network operation among the new energy power generation equipment 11 and the energy storage converter 13 to ensure that the microgrid system 1 can successfully achieve a black start, thereby enabling the microgrid system 1 to achieve oil-free network operation when the new energy power generation equipment 11 or the energy storage converter 13 do not have the conditions for independent network operation. In addition, the microgrid system 1 also controls the network operation of the diesel generator 18 when both the new energy power generation equipment 11 and the energy storage converter 13 do not have the conditions for independent network operation to ensure that the microgrid system 1 can still achieve a black start smoothly.

[0070] See also Figure 5 , Figure 5 This is a flow chart of the control method of the microgrid system provided by the present application. The control method of the microgrid system provided by the embodiment of the present application is applicable to Figure 3 and Figure 4 The microgrid system 1 shown. The control method of the microgrid system may include the following steps:

[0071] S101, obtaining the remaining power of the energy storage battery and the input power of the new energy power generation equipment.

[0072] The controller in the microgrid system can obtain the remaining power of the energy storage battery and the input power of the renewable energy power generation equipment by communicating with the energy storage converter and the renewable energy power generation equipment.

[0073] S102, during the black start of the microgrid system, if the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load, the new energy power generation equipment is controlled to be in a grid-forming control mode.

[0074] The renewable energy power generation equipment includes at least one of a photovoltaic inverter, a wind turbine, and a hydroelectric generator set. The renewable energy power generation equipment is in a grid-forming control mode, which can be understood as the voltage and frequency of the microgrid system constructed by the renewable energy power generation equipment to power the load. Specifically, the output voltage of the renewable energy power generation equipment is positively correlated with the operating voltage of the load, and the output voltage frequency of the renewable energy power generation equipment is the same as the operating voltage frequency of the load.

[0075] Optionally, the controller in the microgrid system also controls the energy storage inverter to be in a grid-following control mode when the new energy power generation equipment is in a grid-forming control mode, so that the energy storage inverter follows the photovoltaic inverter to provide the voltage and frequency required by the microgrid system to jointly power the load, that is, the output voltage value of the energy storage inverter follows the output voltage value of the photovoltaic inverter, and the output voltage frequency of the energy storage inverter follows the output voltage frequency of the photovoltaic inverter.

[0076] In this application, when the energy storage converter does not have the conditions for independent network operation and the new energy power generation equipment has the conditions for independent network operation, the microgrid system can complete the black start of the microgrid system by controlling the new energy power generation equipment as the starting power source to perform network operation. Simply put, the microgrid system has added a network operation mode of black start for the new energy power generation equipment. Since the energy used by the new energy power generation equipment is solar energy, wind energy or hydropower, which are all clean and renewable energy sources, the microgrid system can achieve oil-free network operation when the energy storage converter does not have the conditions for independent network operation.

[0077] See also Figure 6 , Figure 6 This is another flow chart of the control method of the microgrid system provided by the present application. The control method of the microgrid system provided by the embodiment of the present application is applicable to Figure 3 and Figure 4 The microgrid system 1 shown. The control method of the microgrid system may include the following steps:

[0078] S201, obtaining the remaining power of the energy storage battery and the input power of the new energy power generation equipment.

[0079] S202: Determine whether the remaining power of the energy storage battery is less than a remaining power threshold.

[0080] S203 , determining whether the input power of the new energy power generation equipment is less than the total rated power of the load.

[0081] The controller in the microgrid system executes step S204 when the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load; executes step S205 when the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load; executes step S206 when the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load; executes step S207 when the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load.

[0082] S204, during the black start process of the microgrid system, the diesel generator is controlled, or the diesel generator and the new energy power generation equipment are in a grid-forming control mode.

[0083] During the black start of the microgrid system, the controller controls the diesel generator to be in a grid-forming control mode so that the diesel generator builds the voltage and frequency of the microgrid system to power the load; or controls both the diesel generator and the new energy power generation equipment to be in a grid-forming control mode so that the diesel generator and the new energy power generation equipment jointly build the voltage and frequency of the microgrid system to power the load.

[0084] S205 , during the black start process of the microgrid system, the new energy power generation equipment is controlled to be in a grid-forming control mode, and the energy storage converter is controlled to be in a grid-following control mode.

[0085] During a black start of the microgrid system, the controller places the renewable energy generation equipment in grid-forming control mode, enabling it to establish the voltage and frequency of the microgrid system to power the load. Furthermore, while the renewable energy generation equipment is in grid-forming control mode, the controller places the energy storage converter in grid-following control mode, enabling it to follow the renewable energy generation equipment in providing the voltage and frequency required by the microgrid system to power the load.

[0086] S206 , during the black start process of the microgrid system, the energy storage converter is controlled to be in a grid-forming control mode, and the new energy power generation equipment is controlled to be in a grid-following control mode.

[0087] During a black start of the microgrid system, the controller places the energy storage converter in grid-forming control mode, enabling it to establish the voltage and frequency of the microgrid system to power the load. Furthermore, while the energy storage converter is in grid-forming control mode, the controller places the renewable energy generation equipment in grid-following control mode, enabling it to follow the energy storage converter in providing the voltage and frequency required by the microgrid system and, together, power the load.

[0088] S207 , during the black start process of the microgrid system, controlling the new energy power generation equipment, energy storage converter or diesel generator to be in a grid-forming control mode.

[0089] During the black start process of the microgrid system, the controller controls at least one of the new energy power generation equipment and the energy storage converter to be in a grid-forming control mode, so that the at least one power generation equipment builds the voltage and frequency of the microgrid system to supply power to the load; or controls the diesel generator to be in a grid-forming control mode, so that the diesel generator builds the voltage and frequency of the microgrid system to supply power to the load.

[0090] In a specific implementation, more operations performed by the controller in the control method of the microgrid system provided in this application can be found in Figure 3 and Figure 4 The implementation method executed by the controller 14 in the microgrid system 1 shown is not repeated here.

[0091] In this application, before performing a black start, the microgrid system will first determine whether the new energy power generation equipment and the energy storage converter have the conditions for independent network operation. Afterwards, during the black start process, the microgrid system ensures that the microgrid system can successfully achieve a black start by controlling the network operation of the power generation equipment among the new energy power generation equipment and the energy storage converter that have the conditions for independent network operation. This allows the microgrid system to achieve oil-free network operation when the new energy power generation equipment or the energy storage converter does not have the conditions for independent network operation. In addition, when neither the new energy power generation equipment nor the energy storage converter has the conditions for independent network operation, the microgrid system ensures that the microgrid system can still achieve a black start by controlling the network operation of the diesel generator.

[0092] The above are only specific embodiments of the present application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A microgrid system, characterized in that: The microgrid system includes new energy power generation equipment, energy storage batteries, energy storage converters, AC busbars, controllers, and loads, wherein: The output end of the new energy power generation equipment is connected to the AC bus, and the AC bus is also connected to the load; The input end of the energy storage converter is connected to the energy storage battery, and the output end of the energy storage converter is connected to the AC bus; The controller is configured to control the new energy power generation device to be in a grid-forming control mode if, during a black start of the microgrid system, the remaining power of the energy storage battery is less than a remaining power threshold and the input power of the new energy power generation device is greater than or equal to the total rated power of the load; The new energy power generation equipment includes at least one of a photovoltaic inverter, a wind turbine and a hydroelectric generator.

2. The microgrid system according to claim 1, characterized in that: The controller is further configured to control the energy storage converter to be in a grid-following control mode when the new energy power generation equipment is in the grid-forming control mode.

3. The microgrid system according to claim 1 or 2, characterized in that: The controller is also used to control the energy storage converter to be in a grid-type control mode if, during the black start of the microgrid system, the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load.

4. The microgrid system according to claim 3, characterized in that: The controller is further configured to control the new energy power generation equipment to be in a grid-following control mode when the energy storage converter is in a grid-forming control mode.

5. The microgrid system according to any one of claims 1 to 4, characterized in that: The controller is also used to control at least one of the new energy power generation equipment and the energy storage converter to be in a grid-type control mode during a black start of the microgrid system if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load.

6. The microgrid system according to any one of claims 1 to 4, characterized in that: The microgrid system further includes a diesel generator, the output end of which is connected to the AC bus; The controller is also used to control the diesel generator to be in a grid-type control mode during the black start of the microgrid system if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load.

7. The microgrid system according to any one of claims 1 to 6, characterized in that: The microgrid system further includes a diesel generator, the output end of which is connected to the AC bus; The controller is also used to control the diesel generator to be in a grid-forming control mode, or to control both the diesel generator and the new energy power generation equipment to be in a grid-forming control mode, if the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load during the black start of the microgrid system.

8. A control method for a microgrid system, characterized in that: Applied to the microgrid system, the microgrid system includes a new energy power generation device, an energy storage battery, an energy storage converter, an AC bus and a load, wherein the output end of the new energy power generation device is connected to the AC bus, and the AC bus is also connected to the load; the input end of the energy storage converter is connected to the energy storage battery, and the output end of the energy storage converter is connected to the AC bus; The method comprises: During the black start of the microgrid system, if the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load, controlling the new energy power generation equipment to be in a grid-forming control mode; The new energy power generation equipment includes at least one of a photovoltaic inverter, a wind turbine and a hydroelectric generator.

9. The method according to claim 8, characterized in that The method further comprises: When the new energy power generation equipment is in the grid-forming control mode, the energy storage converter is controlled to be in the grid-following control mode.

10. The method according to claim 8 or 9, characterized in that The method further comprises: During the black start of the microgrid system, if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load, the energy storage converter is controlled to be in a grid-type control mode.

11. The method according to claim 10, characterized in that The method further comprises: When the energy storage converter is in a grid-forming control mode, the new energy power generation equipment is controlled to be in a grid-following control mode.

12. The method according to any one of claims 8 to 11, characterized in that The method further comprises: During the black start of the microgrid system, if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load, at least one power generation equipment among the new energy power generation equipment and the energy storage converter is controlled to be in a grid-type control mode.

13. The method according to any one of claims 8 to 11, characterized in that: The microgrid system further includes a diesel generator, the output end of which is connected to the AC bus; The method further comprises: During the black start of the microgrid system, if the remaining power of the energy storage battery is greater than or equal to the remaining power threshold and the input power of the new energy power generation equipment is greater than or equal to the total rated power of the load, the diesel generator is controlled to be in a grid-type control mode.

14. The method according to any one of claims 8 to 13, characterized in that: The microgrid system further includes a diesel generator, the output end of which is connected to the AC bus; The method further comprises: During the black start of the microgrid system, if the remaining power of the energy storage battery is less than the remaining power threshold and the input power of the new energy power generation equipment is less than the total rated power of the load, the diesel generator is controlled to be in a grid-forming control mode, or both the diesel generator and the new energy power generation equipment are controlled to be in a grid-forming control mode.

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