Multi-energy microgrid power supply system based on hydrogen fuel cell and control method

Abstract

The invention discloses a multi-energy micro-grid power supply system based on a hydrogen fuel cell and a control method. The micro-grid power supply system comprises an intelligent grid-connected switch, an electrical load, an isolation transformer, an energy storage converter, a hydrogen fuel cell system, an energy storage lithium battery system and a local energy management system. The control method comprises the steps that when a power grid loses power or a PCC switch is switched off, an energy storage converter PCS is automatically switched to an off-grid operation mode or is switched to an off-grid operation mode according to an off-grid command, and stored electric energy is continuously used for on-load operation; when the power grid recovers or is converted into grid connection in a planned manner, the PCS is automatically synchronized to a state which is synchronous with the power grid or according to a grid connection command, and the intelligent static switch is closed to be converted into grid connection operation. According to a coordination control strategy among the PCS converter, the intelligent grid-connected switch and the energy storage battery and an SOC grading strategy between the fuel battery and the energy storage battery, functions of millisecond-level fast switching of grid-connected and off-grid operation, variable load fast energy scheduling control of a load and the like are realized.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy microgrids, and in particular to a multi-energy microgrid power supply system and a control method based on a hydrogen fuel cell. Background Art

[0002] Hydrogen energy can be widely used in traditional energy sources, new hydrogen-powered compounds, and hydrogen-powered power generation, such as distributed thermal energy and secondary sources. Hydrogen fuel cells significantly reduce pollution, aligning with national promotion policies. However, as humanity continues to consume non-renewable energy sources like oil and coal, their reserves are gradually decreasing, leading to energy shortages. Hydrogen energy and hydrogen-oxygen fuel cells offer high energy conversion efficiency, low noise levels, and environmental friendliness, making them suitable for widespread use as alternatives. However, the following challenges remain: First, insufficient dynamic response: hydrogen fuel cells have a slow power response rate, making it difficult to match sudden load demands; second, low energy coordination efficiency: the lack of a dynamic optimization strategy for the coordinated control of utility power, fuel cells, and lithium batteries results in low energy utilization; third, delays in on-grid and off-grid switching: millisecond-level switching times are difficult to achieve, impacting the continuous power supply of critical loads. Therefore, a multi-energy coordinated control method based on the power generation characteristics of hydrogen fuel cells, dynamic SOC control of energy storage batteries, and multi-energy coordinated control is needed to achieve seamless on-grid and off-grid switching and rapid load response. Summary of the Invention

[0003] Purpose of the invention: The purpose of the present invention is to provide a multi-energy microgrid power supply system and control method based on hydrogen fuel cells.

[0004] Technical solution: The multi-energy microgrid power supply system based on hydrogen fuel cells described in the present invention includes an intelligent grid-connected switch, power loads, an isolation transformer, an energy storage inverter, a hydrogen fuel cell subsystem, an energy storage lithium battery subsystem and a local energy management system; the mains power is connected to a 400V AC bus via an intelligent grid-connected switch, and the 400V AC bus outputs multiple power loads, is equipped with an AC frame circuit breaker, is equipped with a lithium iron phosphate battery, the battery stack power is not less than 200kWh, and is equipped with a hydrogen fuel cell. The hydrogen fuel cells are respectively connected in parallel to form one DC output after DC / DC conversion, and the DC output of the hydrogen fuel cell and the DC side of the energy storage lithium battery system are respectively connected to the DC side of the energy storage inverter via DC cables, and then connected to the 400V AC bus through the DC / AC inverter inside the energy storage inverter via an isolation transformer.

[0005] Furthermore, the energy storage lithium battery system uses lithium iron phosphate batteries with a rated voltage of 660V-665.5V and a battery stack capacity of not less than 200kWh to meet the backup power supply requirements.

[0006] Furthermore, the main circuit of the intelligent grid-connected switch adopts a bidirectional thyristor semiconductor switch device and has a built-in fast grid fault detection algorithm.

[0007] Furthermore, the local device manager continuously collects hardware device data and completes real-time monitoring, battery evaluation, operation and maintenance management, and system management functional modules for a series of model management, data management, interface management, access management, etc.; it adopts a layered distributed design and is divided into an optimization control layer, a coordination control layer, and a local control layer.

[0008] The control method of the multi-energy microgrid power supply system based on hydrogen fuel cells described in the present invention is that when the grid loses power or the PCC switch is disconnected, the energy storage converter PCS will automatically or according to the off-grid command switch to the off-grid operation mode, and continue to use the stored electric energy to operate with load; when the grid is restored or planned to be connected to the grid, the PCS will automatically or according to the grid-connected command automatically synchronize to the state of the same period as the grid, close the intelligent static switch and switch to grid-connected operation; the operation modes are divided into grid-connected operation, off-grid operation, grid-connected to off-grid operation and off-grid to grid-connected operation.

[0009] Furthermore, during the grid-connected operation, the mains power is the main power source, the microgrid power supply system is the backup power source, the mains power is used to power the load and to power important auxiliary power sources, and at the same time, the energy management system monitors the SOC capacity of the energy storage battery online. When the capacity of the energy storage battery is low, the energy storage battery is charged by the mains power to keep the SOC of the energy storage battery greater than a high value.

[0010] Furthermore, when the grid-connected to off-grid operation is switched, the energy storage battery serves as a voltage source and the fuel cell serves as a power source to jointly supply power to the load; the PCS operates in VSG mode off-grid to quickly stabilize the AC side bus voltage and frequency; the fuel cell DC / DC operates in PQ power source mode; if a fault occurs in the external power grid, the intelligent grid-connected switch has a built-in fast grid fault detection algorithm for positive sequence components, frequency, and voltage amplitude change rate, which separates the microgrid system from the faulty power grid within a set time, and at the same time switches the PCS operation mode to VSG mode, and cooperates with the PCS DC / AC to enable the microgrid system to operate off-grid and switch to off-grid control.

[0011] Furthermore, during off-grid operation, the energy storage battery acts as a voltage source and the fuel cell acts as a power source to jointly power the load; the PCS operates in VSG mode to quickly stabilize the AC side bus voltage and frequency; the fuel cell DC / DC operates in PQ power source mode; the generated power is calculated by the master control PLC to determine the hydrogen production amount;

[0012] Before the fuel cell is started, the energy storage battery is converted from DC / AC into AC power through the energy storage converter to provide AC power for the external load;

[0013] During the fuel cell startup process, the fuel cell DC / DC operates in the PQ power source mode, and the microgrid coordination controller determines the fuel cell power according to the energy storage SOC value; the fuel cell power generation starts from 0 and increases the power;

[0014] After the fuel cell is running stably, the fuel cell and the energy storage battery jointly bear all AC and DC loads; the microgrid coordination controller determines the fuel cell's power generation power and the energy storage battery's charging and discharging strategy based on load changes and energy storage SOC values.

[0015] Furthermore, during off-grid operation, the fuel cell and energy storage battery system jointly provide power to the load, with the energy storage battery serving as a DC voltage source and the fuel cell serving as a power source. The system comprises three parts:

[0016] (1) Rapid coordinated control of fuel cell and energy storage battery power: The microgrid coordination controller controls the fuel cell power generation and the charge and discharge state and charge and discharge power of the energy storage battery according to the actual load changes and the SOC value of the energy storage battery; SOC hierarchical control strategy:

[0017] When SOC>80%, the lithium battery is used for power supply first and the fuel cell is shut down;

[0018] When 50%≤SOC≤80%, the power of fuel cell and lithium battery is allocated according to the load demand ratio;

[0019] When SOC < 50%, the mains supply is started and the fuel cell is triggered to output the maximum power;

[0020] (2) Secondary frequency and voltage regulation control on the AC side: When the system load increases or decreases, the microgrid coordination controller sends adjustment instructions to the energy storage converter to stabilize the frequency and voltage of the microgrid within the rated range; when the system load increases, the microgrid coordination controller sends adjustment instructions to the DC / AC according to the droop curve to complete secondary frequency regulation;

[0021] (3) DC side voltage control: The DC side energy storage lithium battery and fuel cell are connected in parallel and connected to the DC side busbar of the energy storage converter PCS. They are then connected to 400V AC through the DC / AC inverter and isolation transformer inside the PCS.

[0022] Furthermore, during the off-grid to grid-connected operation, the remote control point and off-grid control of the background remote control microgrid coordination control system screen are monitored, the static switch is controlled to close, and the mains power is controlled to be connected. The automatic control logic is as follows:

[0023] The microgrid coordination controller adjusts the voltage and frequency on the microgrid side according to the voltage and frequency on the system side until the synchronous closing conditions are met and then closes the static switch. At the same time, the DC / AC of the PCS is switched to the grid-connected power source mode, and the system enters the grid-connected operation mode.

[0024] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the present invention adopts a common DC bus mode of hydrogen fuel cells and energy storage lithium batteries, and configures key equipment such as power supply-supported energy storage inverters, intelligent grid-connected switches, and isolation transformers to realize hybrid microgrid power supply of three electric energy sources: mains electricity, hydrogen fuel cells, and energy storage lithium batteries; according to the coordinated control strategy between PCS inverters, intelligent grid-connected switches, and energy storage batteries, and the SOC grading strategy between fuel cells and energy storage batteries, millisecond-level fast switching of on-grid and off-grid operation, as well as load-changing fast energy scheduling control and other functions are realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a wiring diagram of the microgrid power supply system of the present invention;

[0026] Figure 2 Monitor system diagram for local energy management system;

[0027] Figure 3 This is a diagram of the grid-connected to off-grid control method of the present invention. DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0029] like Figure 1 As shown, the multi-energy microgrid power supply system based on hydrogen fuel cells of the present invention includes an intelligent grid-connected switch, a power load, an isolation transformer, an energy storage inverter, a hydrogen fuel cell system, an energy storage lithium battery system and a local energy management system; different electrical energies are smoothly converted into the same AC or DC electrical energy through power electronic equipment such as energy storage inverters, and the output of the power supply is controlled through the energy management system, so that the power supply and energy storage are output at a specified voltage and frequency or active and reactive power.

[0030] The microgrid power supply system leverages the reliability, continuity, and flexibility of the energy storage system, coupled with an intelligent grid-connected switch, to provide uninterrupted power supply in the event of external grid failures or planned outages, ensuring stable operation of critical and sensitive loads. The intelligent grid-connected switch utilizes bidirectional thyristor semiconductor switching devices in its main circuit and features a built-in fast grid fault detection algorithm, rapidly isolating the microgrid system from the faulty grid in less than 10ms. This enables automatic on / off-grid switching. In the event of a grid fault, it works with the energy storage converter to switch the system to off-grid operation. Once the grid recovers, it automatically assists the energy storage converter in synchronous grid-connected operation, improving power supply reliability.

[0031] The local energy management system centrally collects and manages real-time data from subsystems such as lithium-ion batteries and fuel cells, providing a suitable human-machine interface. This enables coordinated control of these subsystems and the mains, enabling hybrid microgrid power supply from the mains, hydrogen fuel cells, and lithium iron phosphate storage, and enabling rapid energy dispatch control for variable loads.

[0032] The system can charge and discharge the energy storage battery modules for self-maintenance by connecting to the mains or in the power station's self-maintenance mode, ensuring the system is in good backup condition. It supports both online and offline backup modes. When a mains power outage is detected, the system automatically starts up and controls the output of the energy storage lithium battery, achieving seamless power transfer. In offline backup mode, if a mains power outage is detected, the operator can manually start the system and output power to the power user as needed.

[0033] The microgrid power supply system is equipped with a voltage-supported storage converter (PCS), an intelligent static switch, and other equipment. Its operating modes include grid-connected mode, off-grid mode, grid-connected-to-off-grid mode, and off-grid-to-grid mode. In the event of a grid power outage or disconnection of the PCC switch, the PCS automatically switches to off-grid mode or responds to an off-grid command, continuing to operate with stored energy. Upon grid recovery or a planned grid connection, the PCS automatically synchronizes to the grid or responds to a grid connection command, closing the intelligent static switch and transitioning to grid-connected operation.

[0034] Main connection of the microgrid power supply system: The mains power is connected to the 400V AC busbar via an intelligent grid-connected switch. The 400V AC busbar outputs multiple AC loads and is equipped with an AC frame circuit breaker to supply power to the station and user loads.

[0035] It is equipped with one set of 3.2V / 280Ah lithium iron phosphate batteries with a battery stack capacity of 200kWh; it is equipped with two hydrogen fuel cells; the two fuel cells are converted in parallel by two DC / DC converters to form one DC output, and the DC output of the hydrogen fuel cell and the DC side of the energy storage lithium battery are connected to the DC side of the energy storage converter (PCS) via DC cables, and then connected to the 400V AC bus through the DC / AC inverter inside the energy storage converter (PCS) via an isolation transformer.

[0036] 1. Energy storage lithium battery system

[0037] A 3.2V / 280Ah lithium iron phosphate battery is selected with a rated voltage of 665.5V and a battery stack capacity of 200kWh, which can meet the backup power demand for 1 hour.

[0038] 2. Power Storage Converter (PCS)

[0039] The PCS parameters are matched with those of the fuel cell system and the energy storage lithium battery system, taking into account the peak current and peak load generated during the startup of some impact loads, partial system redundancy, and the optimal operating efficiency of the transformer. The energy storage converter (PCS) has a rated power of 500kW.

[0040] 3. Intelligent grid-connected switch

[0041] The intelligent grid-connected switch serves as a connecting switch between the energy storage / load bus and the power grid. It is installed at the common connection point. The main circuit uses a bidirectional thyristor semiconductor switch device and has a built-in fast grid fault detection algorithm. It can quickly separate the energy storage or microgrid system from the faulty grid with a switching time of less than 10ms.

[0042] The rated power of the intelligent grid-connected switchgear is designed to be 500kW.

[0043] 4. Isolation transformer

[0044] The isolation transformer effectively isolates electrical interference between the input and output terminals, ensuring output voltage and current stability. Based on external load requirements and auxiliary power, the isolation transformer has a rated capacity of 500kVA. It utilizes a dry-type, epoxy-resin, vacuum-cast design (the foil-wound coil is encapsulated with epoxy resin).

[0045] 5. Local Energy Management System (EMS)

[0046] like Figure 2 As shown, the local device manager continuously collects hardware device data and completes real-time monitoring, battery evaluation, operation and maintenance management, system management and other functional modules through a series of model management, data management, interface management, access management, etc.

[0047] The system adopts a hierarchical distributed design, divided into an optimization control layer, a coordination control layer, and a local control layer. This hierarchical distributed control system combines the high reliability of a distributed control system with the ease of expansion of a centralized control system. By effectively leveraging the coordination and cooperation between different levels of control and protection, it achieves stable and economical operation of the microgrid system. The control layer network features redundant design, making it independent, safe, and reliable. The high-performance microgrid coordination control device, with millisecond-level response speeds, enables seamless switching between different microgrid operating modes.

[0048] Optimize control layer configuration

[0049] The operator station and engineer station are configured to display the system primary wiring diagram and system parameter information, allowing users to view the operating status of the monitoring system in real time. The station control layer is equipped with a network switch for access to the station control layer and coordination control layer equipment.

[0050] Coordinated control layer configuration

[0051] A microgrid coordination control device is configured for coordinated control and protection of the microgrid. By switching the energy storage device control mode and effectively controlling the fuel cell load in both on-grid and off-grid operation modes, it ensures uninterrupted power supply to the load and maintains power and frequency stability during microgrid operation. A protocol conversion device is also configured with built-in embedded configuration software to collect data from the BMS, fans, and other equipment, providing time synchronization, telecontrol, and protocol conversion capabilities.

[0052] Local control layer configuration

[0053] Equipped with energy storage converter controller, grid-connected switch controller, protection and measurement and control devices, etc. When the grid is disconnected unplanned or planned, the intelligent static switch cooperates with the energy storage converter to quickly disconnect from the faulty grid, maintaining stable voltage and frequency operation of the microgrid.

[0054] 6. Microgrid power supply system control method

[0055] The microgrid power supply system operates in four modes: grid-connected, off-grid, grid-connected-to-off-grid, and off-grid-to-grid. If the grid loses power or the PCC switch is disconnected, the PCS will automatically or in response to an off-grid command switch to off-grid operation mode, continuing to operate with stored energy. If the grid recovers or a planned grid connection is established, the PCS will automatically or in response to a grid connection command synchronize to the grid, closing the intelligent static switch and transitioning to grid-connected operation.

[0056] 6.1 Grid-connected operation mode control method

[0057] During grid-connected operation, mains power is the main power source, and the microgrid power supply system is the backup power source. Mains power is used to power the load and important auxiliary power sources. At the same time, the energy management system monitors the SOC capacity of the energy storage battery online. When the energy storage battery capacity is low, the energy storage battery is charged through mains power to keep the SOC of the energy storage battery greater than the high value.

[0058] 6.2 Control Method for Grid-Connected to Off-Grid Operation Mode

[0059] When the external grid fails, the mains power is switched to the microgrid system, switching from grid-connected to off-grid operation. During off-grid operation, the energy storage battery acts as a voltage source and the fuel cell acts as a power source, jointly supplying power to the load. The PCS operates in VSG mode, rapidly stabilizing the AC bus voltage and frequency. The fuel cell DC / DC system operates in PQ power source mode.

[0060] When the external power grid fails, the intelligent grid-connected switch has a built-in fast grid fault detection algorithm based on positive sequence component, frequency, and voltage amplitude change rate. It can separate the microgrid system from the faulty grid within 10ms, and switch the PCS operation mode to VSG mode. It can also work with the DC / AC of the PCS to enable the microgrid system to smoothly switch to off-grid operation. Figure 3 shown.

[0061] Automatically execute the off-grid operation strategy, and the system enters the off-grid operation mode; the PCS energy storage converter switches to the VSG voltage source mode, and the fuel cell DC / DC operates in the PQ power source mode;

[0062] 6.3 Off-grid operation mode control strategy

[0063] During off-grid operation, the energy storage battery acts as a voltage source and the fuel cell acts as a power source to jointly power the load; the PCS operates in VSG mode to quickly stabilize the AC bus voltage and frequency; the fuel cell DC / DC operates in PQ power source mode;

[0064] Before the fuel cell is started, the energy storage battery is converted from DC / AC into AC power through the energy storage converter to provide AC power for the external load;

[0065] During the fuel cell startup process, the fuel cell DC / DC operates in the PQ power source mode. The microgrid coordination controller determines the fuel cell power according to the energy storage SOC value (the hydrogen production amount is calculated by the master control PLC); the fuel cell power generation starts from 0 and increases in power;

[0066] After the fuel cell is running stably, the fuel cell and the energy storage battery jointly bear all AC and DC loads; the microgrid coordination controller determines the fuel cell's power generation power (the hydrogen production amount is determined by the master control PLC) and the energy storage battery's charging and discharging strategy based on load changes and the energy storage SOC value.

[0067] During off-grid operation, the fuel cell and energy storage battery system jointly provide power to the load; the energy storage battery acts as a DC voltage source, and the fuel cell acts as a power source. The control strategy is divided into three parts:

[0068] (1) Rapid coordinated control of fuel cell and energy storage battery power: Based on the power balance principle, the microgrid coordination controller controls the fuel cell power generation and the charge and discharge state and charge and discharge power of the energy storage battery according to the actual load changes and the SOC value of the energy storage battery; SOC hierarchical control strategy:

[0069] When SOC>80%, the lithium battery is used for power supply first and the fuel cell is shut down;

[0070] When 50%≤SOC≤80%, the power of fuel cell and lithium battery is allocated according to the load demand ratio;

[0071] When SOC is less than 50%, the mains supply is started and the fuel cell is triggered to output the maximum power.

[0072] (2) Secondary frequency and voltage regulation on the AC side: When the system load increases or decreases, the microgrid coordination controller sends regulation instructions to the energy storage converter to stabilize the frequency and voltage of the microgrid within the rated range. When the system load increases, the microgrid coordination controller sends regulation instructions to the DC / AC according to the droop curve to complete secondary frequency regulation and stabilize the frequency at fn (50Hz). The voltage regulation method is the same as the frequency regulation method.

[0073] (3) DC side voltage control:

[0074] The DC side consists of energy storage lithium batteries and fuel cells connected in parallel, connected to the DC side busbar of the PCS energy storage converter, and then connected to 400V AC through the DC / AC inverter inside the energy storage converter (PCS) and the isolation transformer.

[0075] The lithium-ion battery, acting as the DC voltage source, ensures the DC voltage is within the appropriate voltage range of the energy storage converter. The battery voltage and the SOC value are closely related. The microgrid coordination controller monitors and controls the battery SOC to ensure it remains above the low alarm threshold (20%) and above the high alarm threshold (90%), thus maintaining the DC bus voltage within an appropriate range.

[0076] According to the power balance principle, the microgrid coordination controller controls the fuel cell power generation and the charging and discharging of the energy storage battery according to the actual changes in the load and the SOC value of the energy storage battery, which can ensure that the SOC of the energy storage lithium battery operates within a reasonable constant value range, thereby ensuring the stability of the DC side bus voltage.

[0077] 6.4 Control Strategy for Off-Grid to Grid-Connected Operation Mode

[0078] During off-grid operation, when the external power grid resumes power supply, the main power supply is switched from the methanol power plant to the mains power supply, that is, off-grid to grid-connected operation.

[0079] Switch from off-grid to grid-connected. By monitoring the background remote control "Microgrid Coordination Control System" screen, click the remote control point "On-grid and Off-grid Control" to control the static switch to close and control the mains power access. This process is automatically completed by the controller. The automatic control logic is as follows:

[0080] The microgrid coordination controller adjusts the voltage and frequency on the microgrid side according to the voltage and frequency on the system side until the synchronous closing conditions are met and the static switch is closed. At the same time, the DC / AC of the PCS is switched to the PQ (grid-connected power source) mode. The system enters the grid-connected operation mode and executes the grid-connected operation strategy.

Claims

1. A multi-energy microgrid power supply system based on hydrogen fuel cells, characterized in that: It includes an intelligent grid-connected switch, power loads, an isolation transformer, an energy storage converter, a hydrogen fuel cell system, an energy storage lithium battery system and a local energy management system; the mains power is connected to the 400V AC bus through the intelligent grid-connected switch, the 400V AC bus outputs multiple power loads, is equipped with an AC frame circuit breaker, is equipped with lithium iron phosphate batteries, the battery stack capacity is not less than 200kWh, and is equipped with a hydrogen fuel cell. The hydrogen fuel cells are respectively connected in parallel to form one DC output after DC / DC conversion. The DC output of the hydrogen fuel cell and the DC side of the energy storage lithium battery system are respectively connected to the DC side of the energy storage converter via DC cables, and then connected to the 400V AC bus through the DC / AC inverter inside the energy storage converter via an isolation transformer.

2. The multi-energy microgrid power supply system based on hydrogen fuel cells according to claim 1 is characterized in that: The energy storage lithium battery system uses lithium iron phosphate batteries with a rated voltage of 660V-665.5V and a battery stack capacity of not less than 200kWh to meet backup power requirements.

3. The multi-energy microgrid power supply system based on hydrogen fuel cells according to claim 1 is characterized in that: The main circuit of the intelligent grid-connected switch adopts a bidirectional thyristor semiconductor switch device and has a built-in fast grid fault detection algorithm.

4. The multi-energy microgrid power supply system based on hydrogen fuel cells according to claim 1 is characterized in that: The local device manager continuously collects hardware device data and completes real-time monitoring, battery evaluation, operation and maintenance management, and system management functional modules through a series of model management, data management, interface management, access management, etc.; it adopts a layered distributed design and is divided into an optimization control layer, a coordination control layer, and a local control layer.

5. A method for controlling a multi-energy microgrid power supply system based on a hydrogen fuel cell, characterized in that: When the grid loses power or the PCC switch is disconnected, the energy storage converter PCS will automatically switch to off-grid operation mode or according to an off-grid command, and continue to operate with load using the stored electricity; when the grid recovers or is planned to be connected to the grid, the PCS will automatically synchronize to the same state as the grid or according to a grid connection command, close the intelligent static switch and switch to grid-connected operation; the operation modes are divided into grid-connected operation, off-grid operation, grid-connected to off-grid operation, and off-grid to grid-connected operation.

6. The method for controlling a multi-energy microgrid power supply system based on a hydrogen fuel cell according to claim 5, characterized in that: During the grid-connected operation, the mains power is the main power source, the microgrid power supply system is the backup power source, the mains power is used to power the load and to power important auxiliary power sources, and at the same time, the energy management system monitors the SOC capacity of the energy storage battery online. When the energy storage battery capacity is low, the energy storage battery is charged by the mains power to keep the SOC of the energy storage battery greater than a high value.

7. The method for controlling a multi-energy microgrid power supply system based on a hydrogen fuel cell according to claim 5, characterized in that: During the on-grid to off-grid operation, the energy storage battery serves as a voltage source and the fuel cell serves as a power source to jointly supply power to the load; the PCS operates in VSG mode off-grid to quickly stabilize the AC side bus voltage and frequency; the fuel cell DC / DC operates in PQ power source mode; if a fault occurs in the external power grid, the intelligent grid-connected switch has a built-in fast power grid fault detection algorithm for positive sequence components, frequency, and voltage amplitude change rate, which separates the microgrid system from the faulty power grid within a set time, and at the same time switches the PCS operation mode to VSG mode, and cooperates with the PCS DC / AC to enable the microgrid system to operate off-grid and switch to off-grid control.

8. The method for controlling a multi-energy microgrid power supply system based on a hydrogen fuel cell according to claim 5, characterized in that: During off-grid operation, the energy storage battery acts as a voltage source and the fuel cell acts as a power source to jointly power the load; the PCS operates in VSG mode to quickly stabilize the AC side bus voltage and frequency; the fuel cell DC / DC operates in PQ power source mode; the generated power is calculated by the master control PLC to determine the hydrogen production amount; Before the fuel cell is started, the energy storage battery is converted from DC / AC into AC power through the energy storage converter to provide AC power for the external load. During the fuel cell startup process, the fuel cell DC / DC operates in the PQ power source mode, and the microgrid coordination controller determines the fuel cell power according to the energy storage SOC value; the fuel cell power generation starts from 0 and increases the power; After the fuel cell is running stably, the fuel cell and the energy storage battery jointly bear all AC and DC loads; the microgrid coordination controller determines the fuel cell's power generation power and the energy storage battery's charging and discharging strategy based on load changes and energy storage SOC values.

9. The method for controlling a multi-energy microgrid power supply system based on a hydrogen fuel cell according to claim 5, characterized in that: During off-grid operation, the fuel cell and energy storage battery system jointly provide power for the load, with the energy storage battery serving as a DC voltage source and the fuel cell serving as a power source. The system includes three parts: (1) Rapid coordinated control of fuel cell and energy storage battery power: The microgrid coordination controller controls the fuel cell power generation and the charge and discharge state and charge and discharge power of the energy storage battery according to the actual load changes and the SOC value of the energy storage battery; SOC hierarchical control strategy: When SOC>80%, the lithium battery is used for power supply first and the fuel cell is shut down; When 50%≤SOC≤80%, the power of fuel cell and lithium battery is allocated according to the load demand ratio; When SOC < 50%, the mains supply is started and the fuel cell is triggered to output the maximum power; (2) Secondary frequency and voltage regulation control on the AC side: When the system load increases or decreases, the microgrid coordination controller sends adjustment instructions to the energy storage converter to stabilize the frequency and voltage of the microgrid within the rated range; when the system load increases, the microgrid coordination controller sends adjustment instructions to the DC / AC according to the droop curve to complete secondary frequency regulation; (3) DC side voltage control: The DC side energy storage lithium battery and fuel cell are connected in parallel and connected to the DC side busbar of the energy storage converter PCS. They are then connected to 400V AC through the DC / AC inverter and isolation transformer inside the PCS.

10. The method for controlling a multi-energy microgrid power supply system based on a hydrogen fuel cell according to claim 5, characterized in that: During off-grid to grid-connected operation, the remote control point and off-grid control are controlled by monitoring the background remote control microgrid coordination control system screen, controlling the static switch to close, and controlling the mains power access. The automatic control logic is as follows: The microgrid coordination controller adjusts the voltage and frequency on the microgrid side according to the voltage and frequency on the system side until the synchronous closing conditions are met and then closes the static switch. At the same time, the DC / AC of the PCS is switched to the grid-connected power source mode, and the system enters the grid-connected operation mode.

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