An "electricity-hydrogen-electricity" coupled energy conversion system and its application method

Abstract

The present invention belongs to the technical field of power system dispatching automation, and provides an "electricity-hydrogen-electricity" coupled energy conversion system and its application method. The "electricity-hydrogen-electricity" coupled energy conversion system of the present invention utilizes the pressure of oxygen as the cathode intake pressure of the fuel cell stack, so that there is no need for an air compressor to provide the cathode intake pressure of the fuel cell stack through compressed air; and then the air intake can be replaced by an ordinary blower, thereby greatly reducing the energy consumption of the auxiliary system. In this way, the mixing of air and oxygen is achieved to obtain oxygen-enriched air, which improves the electrical efficiency of the hydrogen fuel cell stack. More importantly, the use of an air compressor is abandoned, the energy consumption of the auxiliary system is reduced, and the overall efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system is ultimately improved. The "electricity-hydrogen-electricity" coupled energy conversion system of the present invention has an overall efficiency improvement of 11.36% compared to the traditional "electricity-hydrogen-electricity" coupled energy conversion system.

Description

Technical Field

[0001] The present invention relates to the technical field of power system dispatching automation, and in particular to an "electricity-hydrogen-electricity" coupled energy conversion system and an application method thereof. Background Art

[0002] Renewable energy sources such as wind power and photovoltaics are highly volatile and intermittent, making it difficult to match their power generation with electricity demand in real time. Power generation often exceeds or exceeds power consumption. Hydrogen energy storage technology, on the other hand, can produce hydrogen through water electrolysis when renewable energy power generation exceeds electricity demand, converting excess electricity into hydrogen for storage. When renewable energy power generation is insufficient to meet electricity demand, fuel cell power generation technology can convert stored hydrogen into electricity, supplying it to the grid and filling the energy gap. However, the overall efficiency of the current "electricity-hydrogen-electricity" coupled energy conversion system is relatively low. Summary of the Invention

[0003] In light of this, the present invention aims to provide an "electricity-hydrogen-electricity" coupled energy conversion system and its application method. The "electricity-hydrogen-electricity" coupled energy conversion system provided by the present invention has low energy consumption, improves the "hydrogen-electricity" energy conversion efficiency of the hydrogen fuel cell stack, and ultimately improves the overall efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] The present invention provides an "electricity-hydrogen-electricity" coupled energy conversion system, comprising an electrolyzer and a fuel cell stack;

[0006] The direct current outputted by renewable energy is connected to the electrolyzer; the electrolyzer is a high-pressure electrolyzer that uses electrolysis technology to generate high-pressure hydrogen and high-pressure oxygen;

[0007] The oxygen generated by the electrolyzer is transported to the cathode of the fuel cell stack through the oxygen gas path; the pressure of the oxygen generated by the electrolyzer is used to provide the intake pressure for the cathode of the fuel cell stack;

[0008] The hydrogen generated by the electrolyzer is transported to the anode of the fuel cell stack through the hydrogen gas path;

[0009] Along the oxygen delivery direction, the oxygen gas path is sequentially provided with an oxygen constant pressure buffer tank, a pressure control component and a gas mixing device;

[0010] The oxygen constant pressure buffer tank includes an intelligent pressure relief valve, which receives feedback from the anode outlet pressure signal of the electrolyzer. When the pressure of the oxygen constant pressure buffer tank is higher than the anode outlet pressure of the electrolyzer, the pressure is relieved, and when it is lower than the anode outlet pressure of the electrolyzer, the pressure is closed.

[0011] The gas mixing device includes two gas inlets and one gas outlet, one gas inlet of the gas mixing device is communicated with the gas outlet of the pressure control component, and the other gas inlet of the gas mixing device is communicated with the blowing device.

[0012] Preferably, the oxygen constant pressure buffer cell includes a gas inlet and a gas outlet; the gas inlet of the oxygen constant pressure buffer cell is connected to the anode outlet of the electrolyzer, and the gas outlet of the oxygen constant pressure buffer cell is connected to the gas inlet of the pressure control assembly.

[0013] Preferably, the intelligent pressure relief valve is used to maintain the pressure of the oxygen constant pressure buffer tank consistent with the anode outlet pressure of the electrolyzer.

[0014] Preferably, the pressure control component receives the inlet pressure signal feedback of the fuel cell stack, reduces the outlet pressure of the oxygen constant pressure buffer tank, and controls the inlet pressure of the fuel cell stack to a set value.

[0015] Preferably, the blowing device is an air blower.

[0016] Preferably, a first humidifier is provided between the gas mixing device and the fuel cell stack.

[0017] Preferably, a hydrogen storage tank is provided on the hydrogen gas path.

[0018] Preferably, a second humidifier is provided between the hydrogen storage tank and the fuel cell stack.

[0019] Preferably, the fuel cell stack is also connected to a power consumption terminal.

[0020] The present invention also provides an application method of the "electricity-hydrogen-electricity" coupled energy conversion system described in the above technical solution, comprising the following steps:

[0021] The electrolyzer is started, and when the oxygen generated by the electrolyzer makes the pressure of the oxygen constant pressure buffer tank consistent with the pressure of the anode outlet of the electrolyzer and remains stable, the pressure control component, the gas mixing device, the air blowing device and the fuel cell stack are turned on.

[0022] The present invention provides an "electricity-hydrogen-electricity" coupled energy conversion system.

[0023] The inventors discovered that in traditional "electricity-hydrogen-electricity" coupled energy conversion systems, the "electricity-to-hydrogen" energy conversion efficiency of water electrolysis is 60%-80%, while the "hydrogen-to-electricity" energy conversion efficiency of hydrogen fuel cell stacks is only 30%-45%. The hydrogen fuel cell stack is the primary factor limiting the overall efficiency of this coupled "electricity-hydrogen-electricity" energy conversion system. Furthermore, the inventors discovered that the hydrogen fuel cell stack's auxiliary system requires an air compressor, which compresses air and then passes it through the fuel cell stack's cathode to maintain the fuel cell stack's reaction and generate electricity. However, air compressors consume significant energy (accounting for a significant portion of the auxiliary system's total energy consumption), resulting in low energy conversion efficiency for the hydrogen fuel cell stack. Therefore, to improve the overall efficiency of the coupled "electricity-hydrogen-electricity" energy conversion system, it is necessary to not only increase the stack's electrical efficiency but also reduce the energy consumption of the auxiliary system. Reducing the energy consumption of the auxiliary system, and thus the air compressor, is crucial. The "electricity-hydrogen-electricity" coupled energy conversion system provided by the present invention utilizes the pressure of the oxygen generated by the electrolyzer as the intake pressure of the cathode of the fuel cell stack, so that there is no need for an air compressor to provide the intake pressure of the cathode of the fuel cell stack through compressed air; and then the air intake can be replaced by an ordinary blower, and the blower only needs to provide the air flow, thereby greatly reducing the energy consumption of the auxiliary system. The design of the oxygen constant pressure buffer tank ensures the constant oxygen flow while ensuring that no external energy consumption is introduced. In this way, sufficient oxygen and air are mixed to obtain oxygen-enriched air, thereby improving the electrical efficiency of the hydrogen fuel cell stack. More importantly, the present invention abandons the use of an air compressor, reduces the energy consumption of the auxiliary system, and ultimately improves the overall efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system. The data of the embodiment show that the "electricity-hydrogen-electricity" coupled energy conversion system provided by the present invention has an overall efficiency improvement of up to 11.36% compared with the traditional "electricity-hydrogen-electricity" coupled energy conversion system.

[0024] The present invention also provides an application method for the "electricity-hydrogen-electricity" coupled energy conversion system described in the above technical solution. In principle, the anode outlet pressure of the electrolyzer and the gas pressure of the oxygen constant-pressure buffer tank are higher than the inlet pressure of the fuel cell stack. Therefore, when starting the system described in the above technical solution, the electrolyzer should be started first, and after the pressure in the oxygen constant-pressure buffer tank stabilizes, the subsequent accessories should be started. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of an “electricity-hydrogen-electricity” coupled energy conversion system in one embodiment of the present invention;

[0026] Figure 2 This is the performance curve of a single fuel cell under different oxygen concentrations;

[0027] Figure 3Schematic diagram of the traditional "electricity-hydrogen-electricity" coupled energy conversion system. DETAILED DESCRIPTION

[0028] The present invention provides an "electricity-hydrogen-electricity" coupled energy conversion system, comprising an electrolyzer and a fuel cell stack;

[0029] The direct current outputted by renewable energy is connected to the electrolyzer; the electrolyzer is a high-pressure electrolyzer that uses electrolysis technology to generate high-pressure hydrogen and high-pressure oxygen;

[0030] The oxygen generated by the electrolyzer is transported to the cathode of the fuel cell stack through the oxygen gas path; the pressure of the oxygen generated by the electrolyzer is used to provide the intake pressure for the cathode of the fuel cell stack;

[0031] The hydrogen generated by the electrolyzer is transported to the anode of the fuel cell stack through the hydrogen gas path;

[0032] Along the oxygen delivery direction, the oxygen gas path is sequentially provided with an oxygen constant pressure buffer tank, a pressure control component and a gas mixing device;

[0033] The oxygen constant pressure buffer tank includes an intelligent pressure relief valve, which receives feedback from the anode outlet pressure signal of the electrolyzer. When the pressure of the oxygen constant pressure buffer tank is higher than the anode outlet pressure of the electrolyzer, the pressure is relieved, and when it is lower than the anode outlet pressure of the electrolyzer, the pressure is closed.

[0034] The gas mixing device includes two gas inlets and one gas outlet, one gas inlet of the gas mixing device is communicated with the gas outlet of the pressure control component, and the other gas inlet of the gas mixing device is communicated with the blowing device.

[0035] The "electricity-hydrogen-electricity" coupled energy conversion system provided by the present invention includes an electrolyzer, to which direct current output from renewable energy is connected; the electrolyzer is a high-pressure electrolyzer that uses electrolysis technology to produce high-pressure hydrogen and high-pressure oxygen. In the present invention, the anode of the electrolyzer preferably produces high-pressure oxygen, and the oxygen produced by the electrolyzer is self-pressurized; the cathode of the electrolyzer preferably produces high-pressure hydrogen, and the hydrogen produced by the electrolyzer is self-pressurized.

[0036] In the present invention, the oxygen generated by the electrolyzer is transported to the cathode of the fuel cell stack via an oxygen gas path. In the present invention, an oxygen constant pressure buffer tank, a pressure control component and a gas mixing device are sequentially arranged on the oxygen gas path along the oxygen transport direction.

[0037] In the present invention, the oxygen constant-pressure buffer cell includes an intelligent pressure relief valve, which receives the pressure signal feedback from the anode outlet of the electrolyzer. When the pressure of the oxygen constant-pressure buffer cell is higher than the anode outlet pressure of the electrolyzer, the pressure is relieved, and when it is lower, the pressure is closed. In the present invention, the intelligent pressure relief valve is used to maintain the pressure of the oxygen constant-pressure buffer cell consistent with the anode outlet pressure of the electrolyzer. In the present invention, the oxygen constant-pressure buffer cell preferably includes a gas inlet and a gas outlet; the gas inlet of the oxygen constant-pressure buffer cell is connected to the anode outlet of the electrolyzer, and the gas outlet of the oxygen constant-pressure buffer cell is connected to the gas inlet of the pressure control component. In the present invention, the oxygen constant-pressure buffer cell can form an oxygen buffer zone on the oxygen pipeline, play a role in stabilizing pressure and flow, and avoid the gas pressure at the front end of the pressure control component suddenly dropping below the pressure required by the fuel cell inlet when the oxygen flow demand at the rear end increases.

[0038] In the present invention, the oxygen constant pressure buffer tank is used to collect oxygen to ensure a constant oxygen flow rate at the rear end.

[0039] In the present invention, the pressure control assembly receives feedback from the fuel cell stack's inlet pressure signal, reduces the outlet pressure of the oxygen constant-pressure buffer tank, and controls the fuel cell stack's inlet pressure to a set value. In the present invention, the pressure control assembly is capable of controlling the oxygen delivery pressure to stabilize the fuel cell stack's inlet pressure. In the present invention, the pressure control assembly is capable of achieving pressure-controlled oxygen delivery.

[0040] In the present invention, the gas mixing device includes two gas inlets and one gas outlet. One gas inlet of the gas mixing device is connected to the gas outlet of the pressure control assembly, and the other gas inlet of the gas mixing device is connected to a blower, preferably an air blower. In the present invention, the gas mixing device is capable of mixing oxygen and air entering from the two gas inlets to form oxygen-enriched air; the resulting oxygen-enriched air is delivered to the cathode of the fuel reactor through the gas outlet of the gas mixing device.

[0041] The present invention utilizes the pressure of the oxygen generated by the electrolyzer to supply the required pressure to the cathode inlet of the fuel cell stack, thus abandoning the design of using an air compressor to provide pressure by compressed air in the traditional system; and then the air intake can be replaced by an ordinary blower, and the blower only provides the flow of air, thereby greatly reducing the energy consumption of the auxiliary system. In this way, the mixing of air and oxygen is achieved to obtain oxygen-enriched air. More importantly, the use of an air compressor is abandoned, the energy consumption of the auxiliary system is reduced, the energy conversion efficiency of the hydrogen fuel cell stack is improved, and ultimately the overall efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system is improved. In the present invention, a first humidifier is preferably provided between the mixing device and the fuel reactor, and the first humidifier is used to increase the temperature and humidity of the oxygen-enriched air in the oxygen gas path.

[0042] In the present invention, the hydrogen generated by the electrolyzer is transported to the anode of the fuel cell stack via a hydrogen gas circuit. A hydrogen storage tank is preferably provided on the hydrogen gas circuit, capable of storing the hydrogen generated by the electrolyzer for use in the system or other applications. A second humidifier is preferably provided between the hydrogen storage tank and the fuel cell stack, configured to increase the temperature and humidity of the hydrogen in the hydrogen gas circuit.

[0043] The "electricity-hydrogen-electricity" coupled energy conversion system provided by the present invention includes a fuel cell stack, which generates electricity by using transported oxygen, air (oxygen and air form oxygen-enriched air) and hydrogen.

[0044] In the present invention, the fuel cell stack is preferably further connected to a power-consuming end, which is preferably a power grid or an electrical appliance.

[0045] Figure 1 Schematic diagram of an "electricity-hydrogen-electricity" coupled energy conversion system in a specific embodiment of the present invention. Figure 1 In the embodiment, the "electricity-hydrogen-electricity" coupled energy conversion system includes an electrolyzer and a fuel cell stack, and the direct current outputted by renewable energy is connected to the electrolyzer; the electrolyzer is a high-pressure electrolyzer, and the high-pressure electrolyzer uses electrolysis technology to generate high-pressure hydrogen and high-pressure oxygen; the oxygen generated by the electrolyzer is transported to the cathode of the fuel cell stack through the oxygen gas path; along the oxygen transport direction, an oxygen constant pressure buffer tank, a pressure control component, a mixing device and a first humidifier are sequentially arranged on the oxygen gas path, and the mixing device includes two gas inlets and one gas outlet, one gas inlet of the mixing device is connected to the gas outlet of the pressure control component, and the other gas inlet of the mixing device is connected to the blowing device, and the gas outlet of the mixing device is connected to the first humidifier; the hydrogen generated by the electrolyzer is transported to the anode of the fuel cell stack through the hydrogen gas path; a hydrogen storage tank and a second humidifier are sequentially arranged on the hydrogen gas path. The following is combined with Figure 1The schematic diagram of the "electricity-hydrogen-electricity" coupled energy conversion system shown briefly describes its working principle: the direct current output by renewable energy provides electricity to the high-voltage electrolyzer, which electrolyzes water in the high-voltage electrolyzer into high-pressure oxygen and high-pressure hydrogen. The high-pressure oxygen generated at the anode of the electrolyzer is buffered by an oxygen constant-pressure buffer tank. The oxygen in the oxygen constant-pressure buffer tank is pressure-controlled and transported through a pressure control component. It is mixed with air introduced by the blower in a mixing device to form oxygen-enriched air. The oxygen-enriched air is output through the gas outlet of the mixing device, heated and humidified by a first humidifier, and then transported to the cathode of the fuel cell stack; the high-pressure hydrogen generated at the cathode of the high-pressure electrolyzer enters the hydrogen storage tank, which is heated and humidified by a second humidifier and then transported to the anode of the fuel cell stack; the fuel cell stack uses the hydrogen at the anode and the oxygen-enriched air at the cathode to generate electricity. The resulting direct current can be directly connected to electrical appliances or connected to the grid through a DC / AC system for power generation.

[0046] The present invention also provides an application method of the "electricity-hydrogen-electricity" coupled energy conversion system described in the above technical solution, comprising the following steps:

[0047] The electrolyzer is started, and when the oxygen generated by the electrolyzer makes the pressure of the oxygen constant pressure buffer tank consistent with the pressure of the anode outlet of the electrolyzer and remains stable, the pressure control component, the gas mixing device, the air blowing device and the fuel cell stack are turned on.

[0048] Figure 2 The performance curve of a single fuel cell under different oxygen concentrations is shown in Figure 2. Figure 2 It can be seen that the voltage and power density change with the current density at different oxygen concentrations. The higher the oxygen concentration, the greater the voltage and power density at the same current density, which means that the battery has higher output performance under this condition.

[0049] Based on experimental results at different oxygen concentrations, we determined the performance of the same membrane electrode under different oxygen concentrations. The voltage corresponding to a current density of 1A / cm² was used to characterize the performance of the membrane electrode. The results showed that higher oxygen concentrations resulted in better performance.

[0050] In addition, according to the fuel cell stack efficiency calculation formula provided in the national standard GB / T 24554-2022 "Fuel Cell Engine Performance Test Method", the fuel cell stack efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system provided by the present invention was calculated at different oxygen enrichment concentrations. The results are shown in Table 1. The fuel cell stack efficiency calculation formula is as follows:

[0051]

[0052] Traditional "electricity-hydrogen-electricity" coupled energy conversion system ( Figure 3The overall efficiency difference between the energy conversion system of the "electricity-hydrogen-electricity" coupling provided by the present invention is calculated as follows:

[0053] According to the calculation formula of the air compressor provided in the article (https: / / doi.org / 10.1016 / j.fuel.2024.133495), it is as follows:

[0054]

[0055] in, P CP is the power consumption of the air compressor, W; τ cp is the compressor load torque; ω cp is the compressor rotation angular frequency, rad / s; V cp is the rotation speed, rpm; C p is the specific heat capacity of air (J / (kg·K)); γ is the specific heat ratio of air, unitless; p sm and p atm are the supply manifold and atmospheric pressure (Pa), respectively; T atm is the atmospheric temperature (K); W cp is the mass flow rate, kg / s.

[0056] Under oxygen-rich conditions, when the cathode flow rate is fixed at 3SLPM, if an air compressor is used, while maintaining a constant pressure ratio between the compressor outlet and inlet, as the oxygen concentration in the oxygen-enriched air increases, the flow rate of air output by the air compressor will continue to decrease. According to the above air compressor calculation formula, the air compressor loss is proportional to the air flow rate, and the overall efficiency of the air compressor at this time can be calculated. When pure oxygen is input to the cathode, the air compressor non-operating loss is 0.

[0057] Furthermore, if the pressure at the air compressor outlet is nearly equal to the atmospheric pressure at the inlet, meaning it is not compressing gas and is simply providing air flow, the power loss of the air compressor is negligible. Therefore, a conventional blower can be used in place of the air compressor, solely providing air flow. This frees up the energy consumed by the air compressor, significantly reducing losses in the auxiliary system and thereby improving the overall efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system.

[0058] According to the literature (Wang Feijie. Research on Efficiency Matching Design of Fuel Cell Power Stations [J]. Electrical Applications, 2024, 43(05): 65-73), the auxiliary system loss is assumed to be 10%. The air compressor is considered to account for the majority of the auxiliary system loss, assuming it accounts for 8%. The efficiency calculation formula for the system in the national standard GB / T 24554-2022 "Fuel Cell Engine Performance Test Method" is used to calculate the efficiency of the conventional and present systems. The efficiency calculation formula for the system is as follows:

[0059]

[0060] Among them, P F is the fuel cell engine power, kW; P S is the fuel cell stack power, kW; P A is the auxiliary system power, kW; η F is the fuel cell engine efficiency; m H2 is the hydrogen flow rate, in grams per second, g / s; LHV H2 , low calorific value of hydrogen, 1.2×10 5 kJ / kg.

[0061] Will be at 1A / cm 2 The system efficiencies of the conventional and present invention-provided "electricity-hydrogen-electricity" coupled energy conversion systems during operation are summarized in Table 1.

[0062] Table 1 System efficiency at different oxygen enrichment concentrations

[0063]

[0064] As can be seen from Table 1: Based on the data in the literature (Wang Feijie. Research on Efficiency Matching Design of Fuel Cell Power Station [J]. Electrical Application, 2024, 43(05): 65-73.), assuming that the hydrogen utilization rate is 98%, it can be concluded that when the oxygen concentration increases from 21% to 100%, the efficiency of the fuel cell stack is increased by 3.36% at most. Compared with the "electricity-hydrogen-electricity" coupled energy conversion system with an air compressor, the efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system without an air compressor of the present invention is higher at different oxygen concentrations (the efficiency is consistent at 100% oxygen concentration because the air compressor is not working at this time). In addition, compared with the traditional "electricity-hydrogen-electricity" coupled energy conversion system (with an air compressor and air is input to the cathode), the overall efficiency of the "electricity-hydrogen-electricity" coupled energy conversion system without an air compressor of the present invention is increased by up to 11.36%.

[0065] Comparative Example 1

[0066] The difference from Example 1 is that the air blower is replaced by an air compressor, and the pressure control component and the oxygen constant pressure buffer tank are removed.

[0067] Compared to Comparative Example 1, the present invention primarily utilizes the inherent pressure of the oxygen generated in the electrolyzer to meet the required pressure at the cathode inlet of the fuel cell stack. A conventional blower replaces the air compressor, serving solely as a flow-generating unit. This eliminates the need for a compressor to meet the required pressure at the cathode inlet of the fuel cell stack, significantly reducing back-of-house (BOP) losses and improving overall efficiency. Furthermore, to ensure the proper operation of this design, an oxygen constant-pressure buffer tank is added to ensure an adequate oxygen flow rate. High-pressure oxygen generated at the anode of the high-pressure electrolyzer flows naturally into the oxygen constant-pressure buffer tank without being compressed by a compressor, thus introducing no additional energy consumption. The pressure in the oxygen constant-pressure buffer tank is equal to the anode outlet pressure of the high-pressure electrolyzer. Oxygen overflows through a pressure relief valve to maintain a constant pressure in the oxygen constant-pressure buffer tank, preventing the operation of the high-pressure electrolyzer from being affected by excessive pressure. In principle, the gas pressure at the electrolyzer anode and the oxygen constant-pressure buffer tank should be higher than the fuel cell stack inlet pressure. During system startup, the electrolyzer should be started first, and subsequent accessories should be started only after the pressure in the oxygen constant-pressure buffer tank stabilizes.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. An "electricity-hydrogen-electricity" coupled energy conversion system, characterized in that: including electrolyzers and fuel cell stacks; The direct current outputted by renewable energy is connected to the electrolyzer; the electrolyzer is a high-pressure electrolyzer that uses electrolysis technology to generate high-pressure hydrogen and high-pressure oxygen; The oxygen generated by the electrolyzer is transported to the cathode of the fuel cell stack through the oxygen gas path; the pressure of the oxygen generated by the electrolyzer is used to provide the intake pressure for the cathode of the fuel cell stack; The hydrogen generated by the electrolyzer is transported to the anode of the fuel cell stack through the hydrogen gas path; Along the oxygen delivery direction, the oxygen gas path is sequentially provided with an oxygen constant pressure buffer tank, a pressure control component and a gas mixing device; The oxygen constant pressure buffer tank includes an intelligent pressure relief valve, which receives feedback from the anode outlet pressure signal of the electrolyzer. When the pressure of the oxygen constant pressure buffer tank is higher than the anode outlet pressure of the electrolyzer, the pressure is relieved, and when it is lower than the anode outlet pressure of the electrolyzer, the pressure is closed. The gas mixing device includes two gas inlets and one gas outlet, one gas inlet of the gas mixing device is connected to the gas outlet of the pressure control component, and the other gas inlet of the gas mixing device is connected to the blowing device; The fuel cell stack generates electrical energy using the supplied oxygen, air and hydrogen; The blowing device is an air blower.

2. The "electricity-hydrogen-electricity" coupled energy conversion system according to claim 1 is characterized in that: The oxygen constant pressure buffer cell includes a gas inlet and a gas outlet; the gas inlet of the oxygen constant pressure buffer cell is connected to the anode outlet of the electrolyzer, and the gas outlet of the oxygen constant pressure buffer cell is connected to the gas inlet of the pressure control component.

3. The "electricity-hydrogen-electricity" coupled energy conversion system according to claim 1, characterized in that: The intelligent pressure relief valve is used to maintain the pressure of the oxygen constant pressure buffer tank consistent with the anode outlet pressure of the electrolyzer.

4. The "electricity-hydrogen-electricity" coupled energy conversion system according to claim 1, characterized in that: The pressure control component receives the inlet pressure signal feedback of the fuel cell stack, reduces the outlet pressure of the oxygen constant pressure buffer tank, and controls the inlet pressure of the fuel cell stack to a set value.

5. The "electricity-hydrogen-electricity" coupled energy conversion system according to claim 1, characterized in that: A first humidifier is provided between the gas mixing device and the fuel cell stack.

6. The "electricity-hydrogen-electricity" coupled energy conversion system according to claim 1, characterized in that: A hydrogen storage tank is provided on the hydrogen gas path.

7. The "electricity-hydrogen-electricity" coupled energy conversion system according to claim 6, characterized in that: A second humidifier is provided between the hydrogen storage tank and the fuel cell stack.

8. The "electricity-hydrogen-electricity" coupled energy conversion system according to claim 1, characterized in that: The fuel cell stack is also connected to a power consumption terminal.

9. The application method of the "electricity-hydrogen-electricity" coupled energy conversion system according to any one of claims 1 to 8, characterized in that: The following steps are involved: The electrolyzer is started, and when the oxygen generated by the electrolyzer makes the pressure of the oxygen constant pressure buffer tank consistent with the pressure of the anode outlet of the electrolyzer and remains stable, the pressure control component, the gas mixing device, the air blowing device and the fuel cell stack are turned on.

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