Fuel cell thermal management system and cold start control method thereof

Abstract

The application discloses a fuel cell thermal management system and a cold start control method thereof, and belongs to the technical field of fuel cells. The system comprises a fuel cell stack, a driving pump, a thermostat, a radiator, a first electrically-controlled three-way valve, a heater and a second electrically-controlled three-way valve. The thermostat has a first outlet connected with the radiator and a second outlet bypassing the radiator; the first electrically-controlled three-way valve has an inlet connected with the second outlet of the thermostat, a first outlet connected with an inlet of the heater, and an outlet of the heater and an outlet of the radiator are merged to form a merged flow path; the second electrically-controlled three-way valve has an inlet connected with the merged flow path, a first outlet connected with an inlet of the stack, and a second outlet connected with an inlet of the driving pump. The application can reduce the flow of the cooling liquid into the fuel cell stack during the cold start, avoid the self-produced heat of the fuel cell stack from being taken away, and simultaneously make the cooling liquid outside the fuel cell stack circulate and be heated by the heater, so that the rapid heating is realized, and the low-temperature cold start time of the fuel cell is effectively shortened.

Description

Technical Field

[0001] This invention belongs to the field of fuel cell engine technology, specifically relating to a fuel cell thermal management system and its cold start control method. Background Technology

[0002] A fuel cell engine is a power generation device that directly converts the chemical energy of hydrogen and oxygen into electrical energy. During its operation, the accompanying electrochemical reactions not only generate electricity but also release a large amount of heat. To ensure the efficient and stable operation of the fuel cell stack within a suitable temperature range, a thermal management system is essential. The core functions of the thermal management system include system cooling and system heating: system cooling removes excess heat generated by the fuel cell stack, preventing damage to the proton exchange membrane due to overheating; system heating, in low-temperature environments (e.g., below 0°C), uses an external heating device to raise the temperature of the coolant, enabling the fuel cell stack to quickly reach its normal operating temperature and achieve cold start.

[0003] Currently, fuel cell thermal management systems typically consist of two loops: a large loop and a small loop, switched by a thermostat. When heat dissipation demand is high, the coolant flows through an external radiator to form a large loop; when heat dissipation demand is low or insulation is required, the coolant bypasses the radiator to form a small loop. This architecture can effectively balance heat dissipation and insulation requirements under normal operating conditions; however, it still struggles to cope well with low-temperature cold start conditions.

[0004] Therefore, there is also a solution that integrates a PTC (Positive Temperature Coefficient) heater in the small circulation loop. During cold start, the system switches to the small circulation loop and activates the heater to heat the coolant, hoping to transfer the heat to the fuel cell stack through the heated coolant. However, this solution has the following inherent drawbacks: First, due to the limitations of the vehicle's electrical load, the PTC heater has limited power, while the cooling loop has a large volume and high heat capacity, requiring a large amount of heat and taking a long time to heat the entire system. Second, the continuous operation of the drive pump causes all the coolant in the small circulation loop to circulate continuously, and the heat generated by the PTC heater is dispersed throughout the loop, making it difficult to target and quickly heat the coolant entering the fuel cell stack. Third, in the early stages of cold start, the fuel cell stack has limited self-generated heat due to the low temperature, but the coolant continuously flowing through the fuel cell stack will quickly carry away this self-generated heat and diffuse it throughout the loop, resulting in heat not being effectively accumulated in the fuel cell stack itself, which severely restricts the heating rate of the fuel cell stack. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a fuel cell thermal management system and its cold start control method, the purpose of which is to effectively shorten the low-temperature cold start time of fuel cells, avoid the ineffective removal of heat generated by the fuel cell stack by the circulating coolant, and improve the heating efficiency of the heater on the coolant.

[0006] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution: According to a first aspect of the present invention, a fuel cell thermal management system is provided, comprising: The first circulation loop includes a fuel cell stack, a drive pump, a thermostat, and a radiator connected in a closed loop via pipelines; the thermostat has a first outlet connected to the radiator and a second outlet bypassing the radiator. The second circulation loop includes the fuel cell stack, the drive pump, the thermostat, the first electrically controlled three-way valve, and the heater, which are connected in a closed loop via pipelines. The inlet of the first electrically controlled three-way valve is connected to the second outlet of the thermostat, the first outlet of the first electrically controlled three-way valve is connected to the inlet of the heater, and the outlet of the heater merges with the outlet of the radiator to form a converging flow path. The second electrically controlled three-way valve has its inlet connected to the confluence flow path, its first outlet connected to the coolant inlet of the fuel cell stack, and its second outlet connected to the inlet of the drive pump.

[0007] In one possible implementation of the first aspect, a first temperature sensor and a first flow meter are provided on the pipeline between the first outlet of the second electrically controlled three-way valve and the coolant inlet of the fuel cell stack; a second temperature sensor and a second flow meter are provided on the pipeline between the drive pump and the coolant outlet of the fuel cell stack.

[0008] In one possible implementation of the first aspect, the second outlet of the first electrically controlled three-way valve merges with the outlet of the radiator to form the merging flow path, and a fourth flow meter is provided on the pipeline where the second outlet of the first electrically controlled three-way valve is located, a fifth flow meter is provided on the pipeline between the first outlet of the first electrically controlled three-way valve and the heater, and a third flow meter is provided on the pipeline between the thermostat and the first electrically controlled three-way valve.

[0009] In one possible implementation of the first aspect, the heater is a PTC heater.

[0010] According to a second aspect of the present invention, a cold start control method for the aforementioned fuel cell thermal management system is provided, comprising: S1, In cold start mode, all coolant flows into the second circulation loop through the second outlet of the thermostat to bypass the radiator, and the first electronically controlled three-way valve is controlled to make all coolant flow through the heater. S2, control the second electronically controlled three-way valve to open intermittently, so that part of the coolant enters the fuel cell stack and the other part of the coolant returns to the drive pump, while the fuel cell stack operates in a low-efficiency heat generation mode; S3, when the outlet temperature of the fuel cell stack rises to the first preset temperature threshold, the second electrically controlled three-way valve is switched from intermittent opening to continuous opening, and the opening degree of the second electrically controlled three-way valve is adjusted so that the flow rate of the coolant entering the fuel cell stack is the first preset flow rate value, while maintaining the inefficient heat generation mode. S4, when the outlet temperature rises to the second preset temperature threshold, the fuel cell stack is switched from low-efficiency heat generation mode to medium-efficiency heat generation mode, and the second electronically controlled three-way valve is adjusted so that the flow rate of coolant entering the fuel cell stack is the second preset flow rate value. S5, when the outlet temperature rises to the third preset temperature threshold, the fuel cell stack is switched to normal power generation mode, and the second electronically controlled three-way valve is controlled to fully open the first outlet and close the second outlet, so that all the coolant enters the fuel cell stack. S6, when the outlet temperature rises to the fourth preset temperature threshold, the flow path of the coolant to the heater is cut off, and the cold start process ends.

[0011] In one possible implementation of the second aspect, step S2, controlling the second electrically controlled three-way valve to open intermittently, specifically involves: The second electrically controlled three-way valve is made to operate periodically with preset opening and closing intervals.

[0012] In one possible implementation of the second aspect, in step S3, the operation of the fuel cell stack in an inefficient heat generation mode is achieved by reducing the average single-cell voltage of the fuel cell stack. In step S4, switching the fuel cell stack from low-efficiency heat generation mode to medium-efficiency heat generation mode is achieved by increasing the average single-cell voltage of the fuel cell stack and restoring some of the power generation efficiency. In step S5, switching the fuel cell stack to normal power generation mode is achieved by restoring the normal power generation efficiency of the fuel cell stack.

[0013] In one possible implementation of the second aspect, both the first preset flow rate value and the second preset flow rate value are less than the flow rate of coolant entering the fuel cell stack during normal operation, and the first preset flow rate value and the second preset flow rate value are obtained through calibration tests.

[0014] In one possible implementation of the second aspect, prior to step S1, the following is also included: Determine whether the temperature of the fuel cell stack is not greater than the preset cold start temperature threshold. If so, enter the cold start mode.

[0015] In one possible implementation of the second aspect, the preset cold start temperature threshold is 0°C, and the first preset temperature threshold, the second preset temperature threshold, the third preset temperature threshold and the fourth preset temperature threshold increase sequentially.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: The fuel cell thermal management system of this invention includes a second electrically controlled three-way valve at the inlet of the coolant into the fuel cell stack. This second valve, in conjunction with the thermostat, the first electrically controlled three-way valve, and the heater, enables precise control of the coolant flow path during cold start-up. Specifically, the system can either guide the coolant into the fuel cell stack or allow it to bypass the stack and return directly to the drive pump, forming an independent circulating heating loop outside the fuel cell stack. During the initial cold start phase, the flow of coolant into the fuel cell stack can be significantly reduced or even temporarily cut off. Because the amount of coolant entering the stack is drastically reduced, more of the heat generated by the fuel cell stack through inefficient power generation is retained within the stack itself, rather than being rapidly carried away and diffused throughout the system by the large volume of flowing coolant, allowing the stack temperature to rise more quickly. Simultaneously, the coolant diverted outside the stack is not stagnant but continuously flows through the heater under the drive pump, undergoing repeated heating. Thus, when coolant is needed to enter the stack, it is preheated, preventing a drastic cooling shock to the fuel cell stack. Therefore, this invention constructs a cold start mode with separate internal and external heating: the internal fuel cell stack rapidly heats up by generating its own heat, while the coolant outside the fuel cell stack is continuously heated by a heater in an independent loop. The two operate independently yet in synergy, fundamentally solving the problem of heat dispersion and slow heating of the fuel cell stack caused by the overall circulation heating of the coolant in traditional solutions, effectively shortening the cold start time of the fuel cell in low-temperature environments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of a fuel cell thermal management system according to an embodiment of the present invention.

[0019] In the diagram: 1. Fuel cell stack; 2. Drive pump; 3. Thermostat; 4. Radiator; 5. First electrically controlled three-way valve; 6. Heater; 7. Second electrically controlled three-way valve; 8. First temperature sensor; 9. Second temperature sensor; 10. First flow meter; 11. Second flow meter; 12. Third flow meter; 13. Fourth flow meter; 14. Fifth flow meter. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, an embodiment of the present invention provides a fuel cell thermal management system, comprising the following: The first circulation loop includes a fuel cell stack 1, a drive pump 2, a thermostat 3, and a radiator 4 connected in a closed loop via pipelines. The thermostat 3 has a first outlet connected to the radiator 4 and a second outlet bypassing the radiator 4. In other words, the first circulation loop connects the fuel cell stack 1, drive pump 2, thermostat 3, and radiator 4 in a closed loop via pipelines. The thermostat 3 has two outlets: the first outlet is connected to the radiator 4, and the second outlet bypasses the radiator 4. Coolant flows out from the coolant outlet of the fuel cell stack 1 and is pumped into the inlet of the thermostat 3 via the drive pump 2. When the coolant temperature is high and requires cooling, the thermostat 3 opens the first outlet, and the coolant flows out after being cooled by the radiator 4, participating in subsequent circulation.

[0022] The second circulation loop includes a fuel cell stack 1, a drive pump 2, a thermostat 3, a first electrically controlled three-way valve 5, and a heater 6, which are connected in a closed loop via pipelines. The inlet of the first electrically controlled three-way valve 5 is connected to the second outlet of the thermostat 3, and the first outlet of the first electrically controlled three-way valve 5 is connected to the inlet of the heater 6. The outlet of the heater 6 merges with the outlet of the radiator 4 to form a converging flow path. In other words, the second circulation loop connects the fuel cell stack 1, the drive pump 2, the thermostat 3, the first electrically controlled three-way valve 5, and the heater 6 in a closed loop via pipelines. The inlet of the first electrically controlled three-way valve 5 is connected to the second outlet of the thermostat 3, the first outlet of the first electrically controlled three-way valve 5 is connected to the inlet of the heater 6, and the outlet of the heater 6 merges with the outlet of the radiator 4 to form a converging flow path.

[0023] The second electrically controlled three-way valve 7 has its inlet connected to the merging flow path, its first outlet connected to the coolant inlet of the fuel cell stack 1, and its second outlet connected to the inlet of the drive pump 2. In other words, the second electrically controlled three-way valve 7 is located after the aforementioned merging flow path. Its inlet is connected to this merging flow path, its first outlet is connected to the coolant inlet of the fuel cell stack 1, and its second outlet is connected to the inlet of the drive pump 2. By adjusting the second electrically controlled three-way valve 7, the flow rate of coolant entering the fuel cell stack 1 and the flow rate of coolant directly returning to the drive pump 2 can be controlled.

[0024] It should be noted that the fuel cell stack 1 is the component where hydrogen and oxygen undergo an electrochemical reaction to generate electrical and thermal energy; the drive pump 2 provides power for the circulation of coolant in the system; the thermostat 3 is used to automatically switch or allocate the flow path to the radiator 4 according to the coolant temperature; the radiator 4 is used to dissipate the heat in the coolant to the environment; the first electrically controlled three-way valve 5 and the second electrically controlled three-way valve 7 are both controllable electric three-way valves, which can adjust the opening degree or on / off state of each outlet according to control commands; the heater 6 is used to heat the coolant when needed.

[0025] In one possible implementation, such as Figure 1 As shown, a first temperature sensor 8 and a first flow meter 10 are installed on the pipeline between the first outlet of the second electronically controlled three-way valve 7 and the coolant inlet of the fuel cell stack 1; a second temperature sensor 9 and a second flow meter 11 are installed on the pipeline between the drive pump 2 and the coolant outlet of the fuel cell stack 1.

[0026] In other words, the first temperature sensor 8 and the first flow meter 10 are located before the inlet of the fuel cell stack 1, and can monitor the state of the coolant about to enter the fuel cell stack 1 in real time; the second temperature sensor 9 and the second flow meter 11 are located after the outlet of the fuel cell stack 1, and can accurately reflect the temperature change inside the fuel cell stack 1 and the flow rate of the coolant flowing out of the fuel cell stack 1.

[0027] In one possible implementation, such as Figure 1 As shown, the second outlet of the first electrically controlled three-way valve 5 merges with the outlet of the radiator 4 to form a confluence flow path, and a fourth flow meter 13 is installed on the pipeline where the second outlet of the first electrically controlled three-way valve 5 is located. A fifth flow meter 14 is installed on the pipeline between the first outlet of the first electrically controlled three-way valve 5 and the heater 6, and a third flow meter 12 is installed on the pipeline between the thermostat 3 and the first electrically controlled three-way valve 5.

[0028] In other words, the third flow meter 12 is installed between the thermostat 3 and the first electrically controlled three-way valve 5 to monitor the total flow rate flowing out of the second outlet of the thermostat 3; the fourth flow meter 13 is installed in the pipeline where the second outlet of the first electrically controlled three-way valve 5 is located to monitor the flow rate flowing directly from the bypass heater 6 to the confluence point; and the fifth flow meter 14 is installed between the first outlet of the first electrically controlled three-way valve 5 and the heater 6 to monitor the flow rate entering the heater 6 and being heated. The installation of these flow meters enables the system to accurately grasp the flow distribution of each branch.

[0029] In one possible implementation, heater 6 is a PTC heater. PTC heaters have a positive temperature coefficient, which enables them to provide greater heating power at low temperatures and have a self-limiting temperature function, making them suitable for cold start scenarios of fuel cells.

[0030] In one embodiment, the fuel cell thermal management system is explained in more detail below: The fuel cell stack 1 has a channel for coolant to flow through. The coolant flows in from the coolant inlet of the fuel cell stack 1, absorbs the heat generated by the fuel cell stack 1, and flows out from the coolant outlet.

[0031] Drive pump 2 is installed downstream of the coolant outlet of fuel cell stack 1, providing power for the coolant circulation of the entire system. Coolant flowing from drive pump 2 enters thermostat 3. Thermostat 3 is a valve component that automatically adjusts according to coolant temperature or receives external control commands, having one inlet and two outlets. The first outlet connects to the inlet of radiator 4, guiding coolant to radiator 4 when cooling is required; the second outlet bypasses radiator 4, allowing coolant to be directly introduced into subsequent pipelines when cooling is not required.

[0032] Radiator 4 dissipates heat from the coolant into the environment, and its outlet pipe merges with other branches in the system. Between the second outlet of thermostat 3 and the outlet of radiator 4, a first electrically controlled three-way valve 5 and a heater 6 are also installed. The inlet of the first electrically controlled three-way valve 5 is connected to the second outlet of thermostat 3, its first outlet is connected to the inlet of heater 6, and its second outlet is directly connected to the outlet of radiator 4. The outlet of heater 6 and the outlet of radiator 4 merge through a pipe, forming a confluence flow path. This arrangement allows the coolant flowing from the second outlet of thermostat 3 to be adjusted according to the opening degree of the first electrically controlled three-way valve 5, selectively allowing it to flow entirely through heater 6 for heating, bypass heater 6 and flow directly to the confluence point, or having its flow distributed proportionally.

[0033] Following the aforementioned confluence flow path, a second electrically controlled three-way valve 7 is installed. The inlet of the second electrically controlled three-way valve 7 is connected to the aforementioned confluence flow path, that is, to the common pipeline connecting the outlets of the heater 6 and the radiator 4. The second electrically controlled three-way valve 7 has two outlets: the first outlet is connected to the coolant inlet of the fuel cell stack 1, and the second outlet is connected to the inlet of the drive pump 2. By adjusting the opening of the second electrically controlled three-way valve 7, the flow rate of coolant entering the fuel cell stack 1 and the flow rate of coolant returning directly to the drive pump 2 can be precisely controlled.

[0034] At this point, two main circulation loops are formed in the system. The first circulation loop, also known as the large circulation loop, has the following path in sequence: fuel cell stack 1, drive pump 2, thermostat 3 first outlet, radiator 4, confluence flow path, second electronically controlled three-way valve 7, and fuel cell stack 1. When thermostat 3 opens its first outlet and the second electronically controlled three-way valve 7 opens its first outlet, the coolant flows back to fuel cell stack 1 after being cooled by radiator 4, thus achieving system heat dissipation.

[0035] The second circulation loop, also known as the small circulation loop, has the following path: fuel cell stack 1, drive pump 2, thermostat 3 second outlet, first electronically controlled three-way valve 5 first outlet, heater 6, confluence flow path, second electronically controlled three-way valve 7, fuel cell stack 1. When thermostat 3 opens its second outlet and first electronically controlled three-way valve 5 opens its first outlet, the coolant, heated by heater 6, flows back to fuel cell stack 1 for system heating. Crucially, through the second outlet of second electronically controlled three-way valve 7, the system can also establish an external circulation path for fuel cell stack 1: the coolant flowing from drive pump 2, after passing through thermostat 3, first electronically controlled three-way valve 5, and heater 6, reaches the confluence flow path but does not enter fuel cell stack 1. Instead, it returns directly to drive pump 2 inlet through the second outlet of second electronically controlled three-way valve 7, forming a closed loop sequentially to drive pump 2, thermostat 3, first electronically controlled three-way valve 5, heater 6, second electronically controlled three-way valve 7, and drive pump 2. This external circulation path allows the coolant to be continuously heated without entering the fuel cell stack 1, achieving separate heating inside and outside during cold start.

[0036] To achieve precise monitoring and control of the system status, multiple sensors and flow meters are also installed in the system. A first temperature sensor 8 and a first flow meter 10 are installed on the pipeline between the first outlet of the second electrically controlled three-way valve 7 and the coolant inlet of the fuel cell stack 1, respectively, to measure the temperature and flow rate of the coolant entering the fuel cell stack 1. A second temperature sensor 9 and a second flow meter 11 are installed on the pipeline between the drive pump 2 and the coolant outlet of the fuel cell stack 1, respectively, to measure the temperature and flow rate of the coolant leaving the fuel cell stack 1. The coolant temperature after leaving the fuel cell stack 1 is a core parameter for determining the temperature status of the fuel cell stack 1 and the cold start process. Furthermore, a third flow meter 12 is installed on the pipeline between the thermostat 3 and the first electrically controlled three-way valve 5, to measure the total flow rate flowing out from the second outlet of the thermostat 3. A fourth flow meter 13 is installed on the pipeline where the second outlet of the first electrically controlled three-way valve 5 is located, to measure the flow rate of the bypass heater 6 flowing directly to the confluence point. A fifth flow meter 14 is installed on the pipeline between the first outlet of the first electrically controlled three-way valve 5 and the heater 6 to measure the flow rate entering the heater 6 for heating. It should be understood that the signal provided by the above-mentioned monitoring element is sent to the controller, and the controller performs closed-loop control on the speed of the drive pump 2, the opening degree of the first electrically controlled three-way valve 5, the opening degree of the second electrically controlled three-way valve 7, and the start and stop of the heater 6 according to the preset control logic.

[0037] The present invention also provides a cold start control method for the above-mentioned fuel cell thermal management system, specifically including the following steps: S1, in cold start mode, all coolant flows into the second circulation loop through the second outlet of thermostat 3 to bypass radiator 4, and controls the first electronically controlled three-way valve 5 to make all coolant flow through heater 6. S2 controls the second electronically controlled three-way valve 7 to open intermittently, allowing a portion of the coolant to enter the fuel cell stack 1 and another portion of the coolant to return to the drive pump 2, while simultaneously enabling the fuel cell stack 1 to operate in a low-efficiency heat generation mode.

[0038] S3, when the outlet temperature of the fuel cell stack 1 rises to the first preset temperature threshold, the second electronically controlled three-way valve 7 is switched from intermittent opening to continuous opening, and the opening degree of the second electronically controlled three-way valve 7 is adjusted so that the flow rate of the coolant entering the fuel cell stack 1 is the first preset flow rate value, while maintaining the low-efficiency heat generation mode.

[0039] S4, when the outlet temperature rises to the second preset temperature threshold, the fuel cell stack 1 is switched from low-efficiency heat generation mode to medium-efficiency heat generation mode, and the second electronically controlled three-way valve 7 is adjusted so that the flow rate of coolant entering the fuel cell stack 1 is the second preset flow rate value.

[0040] S5, when the outlet temperature rises to the third preset temperature threshold, switch the fuel cell stack 1 to normal power generation mode and control the second electronically controlled three-way valve 7 to fully open its first outlet and close its second outlet so that all the coolant enters the fuel cell stack 1.

[0041] S6, when the outlet temperature rises to the fourth preset temperature threshold, the flow path of coolant to heater 6 is cut off, and the cold start process ends.

[0042] In detail, in cold start mode, preheating mode one is executed first. At this time, thermostat 3 is controlled to open its second outlet and close its first outlet, allowing all coolant to flow into the second circulation loop via the second outlet, thus bypassing radiator 4 and preventing heat loss. Simultaneously, the first electrically controlled three-way valve 5 is controlled to fully open its first outlet and close its second outlet, allowing all coolant to flow through heater 6 for heating. Drive pump 2 operates at a preset first speed r1, lower than its rated speed, to reduce the coolant circulation flow rate. For example, the rated speed of drive pump 2 is 3000 rpm, and r1 is 800 rpm. The second electrically controlled three-way valve 7 opens intermittently. During opening, a portion of the coolant enters fuel cell stack 1, while the other portion returns directly to drive pump 2 through the second outlet of the second electrically controlled three-way valve 7. During closing, all coolant returns to drive pump 2 through the second outlet of the second electrically controlled three-way valve 7 and does not enter fuel cell stack 1. At the same time, the fuel cell stack 1 operates in an inefficient heat generation mode. This inefficient heat generation mode is achieved by reducing the average single-cell voltage of the fuel cell stack 1, so that the fuel cell stack 1 operates at a lower voltage, reducing power generation efficiency while increasing the heat generation ratio, thus enabling the fuel cell stack 1 to generate more heat while generating electricity.

[0043] When the temperature detected by the second temperature sensor 9 rises to the first preset temperature threshold T1, the cold start enters preheating mode two. At this time, the second electrically controlled three-way valve 7 switches from intermittent opening to continuous opening, and its opening degree is adjusted to stabilize the flow rate of coolant entering the fuel cell stack 1 at a preset first preset flow rate value a. The first preset flow rate value a is less than the flow rate of coolant entering the fuel cell stack 1 during normal operation. The first preset flow rate value a is obtained through calibration tests and is relatively low. For example, a can be 5 L / min, the purpose of which is to reduce the flow rate of coolant entering the fuel cell stack 1 and avoid excessive heat generated by the fuel cell stack 1 being carried away. At the same time, the coolant returning from the second outlet of the second electrically controlled three-way valve 7 to the drive pump 2 continues to flow through the heater 6 in the second circulation loop and is repeatedly heated. In this stage, the fuel cell stack 1 still operates in an inefficient heat generation mode, and the temperature inside the fuel cell stack 1 continues to rise rapidly.

[0044] When the temperature detected by the second temperature sensor 9 rises to the second preset temperature threshold T2, the cold start enters preheating mode three. At this time, the fuel cell stack 1 switches to medium-efficiency heat generation mode. The medium-efficiency heat generation mode is achieved by increasing the average single-cell voltage of the fuel cell stack 1, but compared with preheating mode one, it restores some power generation efficiency and reduces some heat generation. The drive pump 2 still operates at a preset second speed r2, which is lower than the calibrated speed. For example, r2 is 1000 rpm. The first electronically controlled three-way valve 5 controls the proportion of coolant flowing through the heater 6, and the second electronically controlled three-way valve 7 adjusts the coolant flow rate entering the fuel cell stack 1 to a second preset flow rate value b. The second preset flow rate value b is also obtained through calibration tests and is less than the coolant flow rate entering the fuel cell stack 1 during normal operation. For example, b is 10 L / min, while the coolant flow rate entering the fuel cell stack 1 during normal operation is 30 L / min.

[0045] When the temperature detected by the second temperature sensor 9 rises to the third preset temperature threshold T3, the cold start enters recovery mode. At this time, the fuel cell stack 1 switches to normal power generation mode, that is, it restores the normal power generation efficiency of the fuel cell stack 1 and no longer deliberately reduces the average single-cell voltage of the fuel cell stack 1, that is, it no longer deliberately increases heat generation. The second electrically controlled three-way valve 7 is controlled to fully open its first outlet and close its second outlet, allowing all coolant to enter the fuel cell stack 1 and restore normal circulation. The drive pump 2 resumes operation at its calibrated speed, the coolant still follows a small circulation, and the first electrically controlled three-way valve 5 continues to control the flow rate through the heater 6.

[0046] When the temperature detected by the second temperature sensor 9 rises to the fourth preset temperature threshold T4, the cold start process ends. At this time, the first electrically controlled three-way valve 5 is controlled to cut off the flow of coolant to the heater 6, the heater 6 stops working, and the system enters normal operation mode.

[0047] In one possible implementation, step S2, controlling the second electrically controlled three-way valve 7 to open intermittently, specifically involves causing the second electrically controlled three-way valve 7 to perform periodic operations with preset opening intervals Δt1 and closing intervals Δt2. The specific values ​​of the opening interval Δt1 and closing interval Δt2 can be determined based on the system calibration results; for example, Δt1 is 2 seconds and Δt2 is 5 seconds.

[0048] Furthermore, during the execution of the intermittent actions described above, dynamic closed-loop regulation of the flow rate is also performed based on temperature difference feedback: the controller acquires the temperature of the fuel cell inlet coolant collected by the first temperature sensor 8 and the temperature collected by the second temperature sensor 9 in real time, and calculates the temperature difference between the two; if the temperature difference is greater than the preset temperature difference threshold, it indicates that the internal temperature of the fuel cell is much higher than the inlet coolant temperature. At this time, in order to prevent the external low-temperature coolant from entering the fuel cell at a large flow rate and causing thermal shock to the core components of the fuel cell, the system controls the second electrically controlled three-way valve 7 to adopt a first opening degree within the opening interval. This first opening degree is less than the standard opening degree calculated based on the current water pump speed and the first preset flow rate value, so as to further reduce the coolant flow rate entering the fuel cell; if the temperature difference is less than or equal to the temperature difference threshold, it indicates that the temperature difference between the inside and outside of the fuel cell is within an acceptable stable range. Then, the second electrically controlled three-way valve 7 is controlled to adopt a second opening degree within the opening interval. This second opening degree is greater than or equal to the standard opening degree, so as to appropriately increase the inlet flow rate and accelerate the rapid exchange of heat and temperature balance between the inside and outside of the fuel cell. By introducing this closed-loop regulation mechanism based on temperature difference feedback, the risk of thermal shock under large temperature difference conditions during the initial cold start can be effectively prevented, protecting the safety of core components such as the proton exchange membrane inside the fuel cell stack.

[0049] In one possible implementation, before step S1, the method further includes: determining whether the temperature of the fuel cell stack 1 is not greater than a preset cold start temperature threshold; if so, entering the cold start mode; in other words, detecting the outlet temperature of the fuel cell stack 1 through the second temperature sensor 9, and when the temperature is not greater than the preset cold start temperature threshold, the system determines to enter the cold start mode.

[0050] Furthermore, before determining the temperature of fuel cell stack 1 against the preset cold start temperature threshold, an adaptive correction step based on the stack aging state is executed: First, the cumulative operating time or cumulative start-stop count of fuel cell stack 1 is obtained as a quantitative indicator characterizing the degree of stack aging; then, based on the cumulative operating time or cumulative start-stop count, a preset stack aging compensation mapping table is consulted to obtain the aging compensation coefficient corresponding to the current aging degree; then, the preset cold start temperature threshold and the first, second, third, and fourth preset temperature thresholds in subsequent steps are corrected using this aging compensation coefficient, wherein the correction rule is: the deeper the stack aging degree, the lower the corresponding threshold is corrected, to adapt to the actual operating conditions of increased internal resistance and changed heat generation characteristics of the aged stack; finally, the system uses the corrected threshold chain to execute the cold start comparison and control steps. Through the above adaptive threshold adjustment based on aging state, the optimal cold start control effect can be ensured throughout the entire life cycle of the fuel cell stack.

[0051] Preferably, the preset cold start temperature threshold is 0°C, and the first preset temperature threshold T1, the second preset temperature threshold T2, the third preset temperature threshold T3, and the fourth preset temperature threshold T4 increase sequentially. In a specific embodiment, T1 is 5°C, T2 is 15°C, T3 is 30°C, and T4 is 50°C. Of course, the specific values ​​of the above temperature thresholds are only examples. In practical applications, these thresholds can be adaptively adjusted according to the aforementioned aging compensation coefficient to meet the cold start control requirements of different usage stages.

[0052] Through the aforementioned system structure and method, this invention achieves rapid cold start of the fuel cell. In the initial stage of cold start, the flow rate of coolant entering the fuel cell stack 1 is minimized by the second electrically controlled three-way valve 7, allowing the self-generated heat of the fuel cell stack 1 to effectively accumulate inside, achieving rapid heating of the fuel cell stack 1. Simultaneously, the coolant outside the fuel cell stack 1 is continuously heated by the heater 6 in a small circulation loop, forming a separate heating pattern inside and outside, preventing temperature fluctuations caused by coolant entering the fuel cell stack 1. As the temperature of the fuel cell stack 1 gradually increases, the system adjusts the flow rate of coolant entering the fuel cell stack 1 and the heat generation mode of the fuel cell stack 1 in stages, ultimately smoothly transitioning to normal operating conditions. The entire process significantly shortens the cold start time in low-temperature environments.

[0053] In the description of this invention, it should be understood that the terms "upper", "lower", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0054] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0055] In this invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0056] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that they are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0057] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0058] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the scope of the technology disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention.

Claims

1. A fuel cell thermal management system, characterized in that, include: The first circulation loop includes a fuel cell stack (1), a drive pump (2), a thermostat (3), and a radiator (4) connected in a closed loop via pipelines; the thermostat (3) has a first outlet connected to the radiator (4) and a second outlet bypassing the radiator (4); The second circulation loop includes the fuel cell stack (1), the drive pump (2), the thermostat (3), the first electrically controlled three-way valve (5), and the heater (6) connected in a closed loop via pipelines; the inlet of the first electrically controlled three-way valve (5) is connected to the second outlet of the thermostat (3), the first outlet of the first electrically controlled three-way valve (5) is connected to the inlet of the heater (6), and the outlet of the heater (6) merges with the outlet of the radiator (4) to form a merging flow path; The inlet of the second electrically controlled three-way valve (7) is connected to the confluence flow path, the first outlet of the second electrically controlled three-way valve (7) is connected to the coolant inlet of the fuel cell stack (1), and the second outlet of the second electrically controlled three-way valve (7) is connected to the inlet of the drive pump (2).

2. The fuel cell thermal management system according to claim 1, characterized in that, A first temperature sensor (8) and a first flow meter (10) are installed on the pipeline between the first outlet of the second electronically controlled three-way valve (7) and the coolant inlet of the fuel cell stack (1); a second temperature sensor (9) and a second flow meter (11) are installed on the pipeline between the drive pump (2) and the coolant outlet of the fuel cell stack (1).

3. The fuel cell thermal management system according to claim 1, characterized in that, The second outlet of the first electrically controlled three-way valve (5) merges with the outlet of the radiator (4) to form the merging flow path, and a fourth flow meter (13) is installed on the pipeline where the second outlet of the first electrically controlled three-way valve (5) is located. A fifth flow meter (14) is installed on the pipeline between the first outlet of the first electrically controlled three-way valve (5) and the heater (6). A third flow meter (12) is installed on the pipeline between the thermostat (3) and the first electrically controlled three-way valve (5).

4. A fuel cell thermal management system according to claim 1, characterized in that, The heater (6) is a PTC heater.

5. A cold start control method for a fuel cell thermal management system as described in any one of claims 1 to 4, characterized in that, include: In cold start mode, all the coolant flows into the second circulation loop through the second outlet of the thermostat (3) to bypass the radiator (4), and the first electronically controlled three-way valve (5) is controlled to make all the coolant flow through the heater (6). The second electronically controlled three-way valve (7) is opened intermittently, so that a portion of the coolant enters the fuel cell stack (1) and another portion of the coolant returns to the drive pump (2), while the fuel cell stack (1) is operated in an inefficient heat generation mode. When the outlet temperature of the fuel cell stack (1) rises to the first preset temperature threshold, the second electronically controlled three-way valve (7) is switched from intermittent opening to continuous opening, and the opening degree of the second electronically controlled three-way valve (7) is adjusted so that the flow rate of the coolant entering the fuel cell stack (1) is the first preset flow rate value, while maintaining the inefficient heat generation mode. When the outlet temperature rises to the second preset temperature threshold, the fuel cell stack (1) is switched from low-efficiency heat generation mode to medium-efficiency heat generation mode, and the second electronically controlled three-way valve (7) is adjusted so that the flow rate of the coolant entering the fuel cell stack (1) is the second preset flow rate value. When the outlet temperature rises to the third preset temperature threshold, the fuel cell stack (1) is switched to normal power generation mode and the second electronically controlled three-way valve (7) is controlled to fully open its first outlet and close its second outlet so that all the coolant enters the fuel cell stack (1). When the outlet temperature rises to the fourth preset temperature threshold, the flow path of the coolant to the heater (6) is cut off, and the cold start process ends.

6. The cold start control method according to claim 5, characterized in that, The control of the second electrically controlled three-way valve (7) to open intermittently is specifically as follows: The second electrically controlled three-way valve (7) is made to operate periodically with preset opening and closing intervals.

7. The cold start control method according to claim 5, characterized in that, The operation of the fuel cell stack (1) in an inefficient heat generation mode is achieved by reducing the average single-cell voltage of the fuel cell stack (1); The switching of the fuel cell stack (1) from low-efficiency heat generation mode to medium-efficiency heat generation mode is achieved by increasing the average single-cell voltage of the fuel cell stack (1) and restoring part of the power generation efficiency. Switching the fuel cell stack (1) to normal power generation mode is achieved by restoring the normal power generation efficiency of the fuel cell stack (1).

8. The cold start control method according to claim 5, characterized in that, Both the first preset flow rate value and the second preset flow rate value are less than the flow rate of coolant entering the fuel cell stack (1) during normal operation, and the first preset flow rate value and the second preset flow rate value are obtained through calibration tests.

9. The cold start control method according to claim 5, characterized in that, Prior to the cold start mode, the following is also included: Determine whether the temperature of the fuel cell stack (1) is not greater than the preset cold start temperature threshold. If so, enter the cold start mode.

10. The cold start control method according to claim 9, characterized in that, The preset cold start temperature threshold is 0°C, and the first preset temperature threshold, the second preset temperature threshold, the third preset temperature threshold and the fourth preset temperature threshold increase sequentially.

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