A low temperature start-up method and control system for a fuel cell

Abstract

The application discloses a low-temperature starting method and a control system of a fuel cell. The fuel cell comprises a stack. The low-temperature starting method of the fuel cell comprises the following steps: injecting an alternating disturbance signal into the stack when the fuel cell is in a low-temperature state; obtaining impedance information of the stack at multiple characteristic frequencies during the process of injecting the alternating disturbance signal into the stack; obtaining pulse parameters according to the impedance information of the stack at the characteristic frequencies; injecting a heating pulse into the stack according to the pulse parameters; obtaining a current temperature of the fuel cell after injecting the heating pulse into the stack; returning to the step of injecting the alternating disturbance signal into the stack when the fuel cell is in the low-temperature state when the temperature is lower than a preset temperature; and starting the fuel cell when the temperature is greater than or equal to the preset temperature. The method can overcome the inherent defects of local measurement and hysteresis of a temperature sensor, reduce the risks of membrane perforation and catalyst dissolution caused by local overheating, and significantly improve the energy efficiency and safety of low-temperature starting.

Description

Technical Field

[0001] This invention relates to the field of fuel cells, and more particularly to a method and control system for low-temperature start-up of a fuel cell. Background Technology

[0002] When a fuel cell starts up in a low-temperature environment (below 0°C), the water remaining inside and generated during the reaction will rapidly freeze. Ice crystals not only block the gas transport channels of the porous electrodes, preventing reactant gases from reaching the catalyst layer and causing a sudden voltage drop leading to startup failure, but also cause irreversible mechanical damage to the membrane electrode assembly due to volume expansion. Repeated freeze-thaw cycles accelerate the degradation of the fuel cell stack performance. Furthermore, the low temperature itself reduces catalyst activity and increases internal resistance, further deteriorating startup performance.

[0003] Currently, pulsed current heating is a common method for heating fuel cells. In existing technologies, the parameters of the pulsed current are fixed, and the heating time is adjusted based on feedback from a temperature sensor. Applying a fixed high-current pulse to a melted ice-covered area for an extended period can lead to excessive localized heat generation, accelerating catalyst dissolution and proton exchange membrane perforation in that area. Temperature sensors can only measure localized temperatures and suffer from temperature hysteresis; they also cannot differentiate between the effects of ice thickness and membrane dehydration based on temperature data, resulting in misjudgments of the overall stack condition and a mismatch between heating parameters and actual requirements. Furthermore, current heating methods require continuous heating until the overall temperature reaches the target level, failing to optimize for localized ice conditions, resulting in low energy efficiency and energy waste. Summary of the Invention

[0004] This invention provides a method and control system for low-temperature start-up of fuel cells to improve energy efficiency, response speed and safety during low-temperature start-up.

[0005] According to one aspect of the present invention, a method for cryogenic start-up of a fuel cell is provided, the fuel cell comprising a stack, including:

[0006] When the fuel cell stack is in a low-temperature state, an AC disturbance signal is injected into the fuel cell stack;

[0007] During the process of injecting the AC disturbance signal into the fuel cell stack, the impedance information of the fuel cell stack at multiple characteristic frequencies is obtained;

[0008] The pulse parameters are obtained based on the impedance information of the fuel cell stack at each of the characteristic frequencies.

[0009] A heating pulse is injected into the fuel cell stack according to the pulse parameters;

[0010] After injecting a heating pulse into the fuel cell stack, the current temperature of the fuel cell stack is obtained;

[0011] When the current temperature is lower than the preset temperature, return to the step of injecting an AC disturbance signal into the fuel cell when the fuel cell is in a low temperature state;

[0012] The fuel cell is started when the current temperature is greater than or equal to the preset temperature.

[0013] Optionally, during the process of injecting AC disturbance signals into the fuel cell stack, impedance information of the fuel cell stack at multiple characteristic frequencies is obtained, including:

[0014] During the process of injecting an AC disturbance signal into the fuel cell stack, the Nyquist plot is obtained;

[0015] Based on the Nyquist plot, the impedance information of the fuel cell stack at multiple characteristic frequencies is obtained.

[0016] Optionally, pulse parameters are obtained based on the impedance information of the fuel cell stack at each of the characteristic frequencies, including:

[0017] Based on the impedance information of the fuel cell stack at each of the characteristic frequencies, the low-temperature fault type of the fuel cell stack is obtained; the low-temperature fault type includes gas channel blockage, impaired catalytic activity, and excessively low membrane hydration.

[0018] The pulse parameters are obtained based on the low-temperature fault type.

[0019] Optionally, the plurality of characteristic frequencies include a first characteristic frequency, a second characteristic frequency, and a third characteristic frequency; the first characteristic frequency is less than the second characteristic frequency, and the second characteristic frequency is less than the third characteristic frequency; the impedance information includes the real part of the impedance, the imaginary part of the impedance, and the phase angle;

[0020] Based on the impedance information of the fuel cell stack at each of the characteristic frequencies, the cryogenic fault type of the fuel cell stack is obtained, including:

[0021] When the real part of the impedance of the fuel cell stack at the first characteristic frequency is greater than the real part of the first preset impedance, and the imaginary part of the impedance of the fuel cell stack at the first characteristic frequency is greater than the imaginary part of the first preset impedance, the cryogenic fault type is determined to be the gas channel blockage.

[0022] When the phase angle of the fuel cell stack at the second characteristic frequency is greater than a preset phase angle, the low-temperature fault type is determined to be impaired catalytic activity;

[0023] When the real part of the impedance of the fuel cell stack at the third characteristic frequency is greater than the real part of the second preset impedance, the low temperature fault type is determined to be the membrane hydration being too low.

[0024] Optionally, the first characteristic frequency is FC1, the second characteristic frequency is FC2, and the third characteristic frequency is FC3;

[0025] 1Hz≤FC1<20Hz, 20Hz≤FC2<100Hz, 1kHz≤FC3<10kHz.

[0026] Optionally, the pulse parameters include: pulse frequency, pulse current, and pulse duty cycle;

[0027] The pulse parameters are obtained according to the low-temperature fault type, including:

[0028] When the low-temperature fault type is gas channel blockage, the pulse frequency is determined to be a first pulse frequency F1, the pulse current is determined to be a first pulse current J1, and the pulse duty cycle is determined to be a first pulse duty cycle D1.

[0029] Where 0.1Hz≤F1<1Hz, 1A / cm 2 ≤J1≤2A / cm 2 50% <D1≤80%。

[0030] Optionally, the pulse parameters include: pulse frequency, pulse current, and pulse duty cycle;

[0031] The pulse parameters are obtained according to the low-temperature fault type, including:

[0032] When the low-temperature fault type is impaired catalytic activity, the pulse frequency is determined to be the second pulse frequency F2, the pulse current is determined to be the second pulse current J2, and the pulse duty cycle is determined to be the second pulse duty cycle D2.

[0033] Where 1Hz≤F2<10Hz, 0.5A / cm 2 ≤J2<1A / cm 2 , 30% < D2 ≤ 50%.

[0034] Optionally, the pulse parameters include: pulse frequency, pulse current, and pulse duty cycle;

[0035] The pulse parameters are obtained according to the low-temperature fault type, including:

[0036] When the low-temperature fault type is that the membrane hydration is too low, the pulse frequency is determined to be the third pulse frequency F3, the pulse current is determined to be the third pulse current J3, and the pulse duty cycle is determined to be the third pulse duty cycle D3.

[0037] Where 10kHz≤F3≤10kHz, 0.1A / cm 2 ≤J3<0.5A / cm 2, 10%≤D3≤30%.

[0038] According to another aspect of the present invention, a control system for a fuel cell is provided, comprising: a controller, a pulse generator, and a lock-in amplifier; the fuel cell includes a stack.

[0039] The pulse generator is used to generate heating pulses and provide the heating pulses to the fuel cell stack;

[0040] The lock-in amplifier is used to generate an AC disturbance signal and provide the AC disturbance signal to the fuel cell stack;

[0041] The controller is electrically connected to the pulse generator and the lock-in amplifier, respectively, and is used to execute the above-described low-temperature start-up method for the fuel cell.

[0042] Optionally, the control system of the fuel cell further includes: a temperature sensor and an impedance information acquisition module;

[0043] Both the temperature sensor and the impedance information acquisition module are electrically and / or communicatively connected to the controller.

[0044] The temperature sensor is used to acquire the temperature of the fuel cell stack and send the temperature to the controller. The impedance information acquisition module is used to acquire the impedance information of the fuel cell stack and send the impedance information to the controller.

[0045] The low-temperature start-up method for fuel cells provided in this invention first injects an AC disturbance signal into the fuel cell stack when it is in a low-temperature state. During the injection process, the impedance information of the fuel cell stack at multiple characteristic frequencies is acquired. This allows for the differentiation of ice thickness and membrane dehydration status without relying on temperature sensors, enabling accurate judgment of the overall state of the fuel cell stack. It also avoids the feedback delay and state misjudgment problems caused by temperature sensors, which can only measure local temperatures and have temperature hysteresis. Then, based on the impedance information of the fuel cell stack at each characteristic frequency, pulse parameters matching the current actual needs are adaptively acquired, and heating pulses are injected into the fuel cell stack accordingly. This avoids the problem of local overheating caused by a fixed high-current pulse acting on the melted area for a long time. After the heating pulse is injected, the current temperature of the fuel cell is acquired. If the current temperature is lower than the preset temperature, the process returns to re-execute the injection of the AC disturbance signal and subsequent steps. The pulse parameters for the next round are adjusted through a closed loop using impedance information to achieve differentiated and optimized heating of the local ice layer state. If the current temperature is greater than or equal to the preset temperature, the fuel cell is started. It not only overcomes the inherent defects of local measurement and hysteresis of temperature sensors, but also reduces the risk of membrane perforation and catalyst dissolution caused by local overheating, avoids the energy waste caused by continuous overall heating to reach the target temperature, and significantly improves the energy efficiency, response speed and safety of low temperature start-up.

[0046] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a flowchart of a low-temperature start-up method for a fuel cell provided in an embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram of a Nyquist curve provided in an embodiment of the present invention;

[0050] Figure 3 This is a schematic diagram of another Nyquist curve provided in an embodiment of the present invention;

[0051] Figure 4 This is a flowchart of another low-temperature start-up method for a fuel cell provided in an embodiment of the present invention;

[0052] Figure 5 This is a schematic diagram of the structure of a fuel cell control system provided in an embodiment of the present invention. Detailed Implementation

[0053] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0054] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0055] This invention provides a method for low-temperature start-up of a fuel cell, which can safely and effectively heat the fuel cell at low temperatures and reduce heating energy consumption. This method can be executed by a controller in the fuel cell control system.

[0056] Figure 1 This is a flowchart of a low-temperature start-up method for a fuel cell provided in an embodiment of the present invention, as shown below. Figure 1 As shown, the low-temperature start-up method for this fuel cell includes:

[0057] S110. When the fuel cell stack is in a low-temperature state, inject an AC disturbance signal into the fuel cell stack.

[0058] Specifically, the fuel cell stack is the main structure of a fuel cell. The temperature of the fuel cell reflects the temperature of the stack. To detect whether the stack is in a low-temperature state, the ambient temperature of the fuel cell can be used to determine whether the fuel cell is in a low-temperature state, and thus the temperature of the stack can be determined. Alternatively, for more precise temperature acquisition, temperature sensors (such as thermocouples or thermistors) installed inside the fuel cell, on its surface, or in the coolant circulation pipeline can be used to collect the stack temperature in real time. The low-temperature state can be detected based on the collected temperature; for example, if the collected temperature is below 0°C, the stack is considered to be in a low-temperature state. When the stack is in a low-temperature state, it can be heated by intermittently injecting heating pulses. During the intervals between heating pulse injections, an AC disturbance signal can be injected into the stack to detect its current frozen state. This can also be understood as follows: before each heating pulse is injected into the stack, an AC disturbance signal is injected first. The pulse parameters of the heating pulse are determined based on the impedance information generated by the stack based on the AC disturbance signal. Then, the heating pulse is injected into the fuel cell based on the determined pulse parameters. Specifically, a small-amplitude AC disturbance signal, such as a small-amplitude sinusoidal AC current disturbance signal or sinusoidal AC voltage disturbance signal, can be output to the fuel cell via a frequency response analyzer or electrochemical workstation. Simultaneously, the voltage and current response signals at the positive and negative terminals of the fuel cell stack can be acquired. In particular, the AC disturbance signal can have a small current, for example, 5% of the heating pulse current; furthermore, the AC disturbance signal can be a signal that continuously varies from high frequency to low frequency (e.g., 1Hz to 10kHz).

[0059] S120. During the process of injecting AC disturbance signals into the fuel cell stack, the impedance information of the fuel cell stack at multiple characteristic frequencies is obtained.

[0060] Specifically, during the injection of AC disturbance signals into the fuel cell stack, the voltage and current response signals at both ends of the stack are simultaneously acquired. The multi-channel data acquisition and analysis modules in the controller can be used to extract impedance information at various characteristic frequencies based on the acquired voltage and current response signals, thereby obtaining the impedance information of the fuel cell under low-temperature conditions. This impedance information is used to determine the icing state inside the stack, the degree of membrane dryness, and the state of the reaction interface (i.e., the catalyst layer), and thus determine the pulse parameters such as the current amplitude, pulse frequency, and duty cycle of the subsequent injected heating pulse current, avoiding localized overheating or membrane damage caused by blindly applying heating pulses.

[0061] For example, when obtaining impedance information of the fuel cell at multiple characteristic frequencies during the process of injecting AC disturbance signals into the fuel cell, the Nyquist spectrum can be obtained during the process of injecting AC disturbance signals into the fuel cell; based on the Nyquist spectrum, the impedance information of the fuel cell at multiple characteristic frequencies can be obtained.

[0062] Specifically, based on the acquired voltage and current response signals at various characteristic frequencies, the impedance magnitude and phase angle at each frequency can be extracted, and then the corresponding real and imaginary impedances can be calculated. Specifically, with the real impedance as the abscissa and the negative value of the imaginary impedance as the ordinate, the impedance information at each characteristic frequency point is plotted sequentially on the same complex plane coordinate system, thus obtaining the Nyquist plot of the fuel cell stack. Based on the obtained Nyquist plot, impedance information at multiple characteristic frequencies can be directly read or calculated through fitting. Figure 2 This is a schematic diagram of a Nyquist curve provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of another Nyquist curve provided in an embodiment of the present invention. Figure 2 and Figure 3 In the graph, the horizontal axis represents the real part of the impedance Z′ (Ω), and the vertical axis represents the imaginary part of the impedance -Z′′ (Ω). (Reference) Figure 2 or Figure 3 In the high-frequency region, the real part of the impedance corresponding to the intersection point 'a' of the F1 Nyquist curve and the horizontal axis is the ohmic impedance of the fuel cell; in the mid-frequency region, the diameter of the semicircular arc characterizes the charge transfer impedance of the fuel cell; in the low-frequency region, the characteristic of the approximately 45° oblique line (such as...) Figure 2 As shown, the projection length of the oblique line on the real axis) or the semicircular arc appearing in the low-frequency region (such as... Figure 3 The diameter (as shown) is used to determine the diffusion impedance of the fuel cell. Therefore, based on the same Nyquist plot, the real impedance, imaginary impedance, and phase angle of the fuel cell at multiple characteristic frequencies can be obtained, leading to comprehensive impedance information such as the ohmic impedance, charge transfer impedance, and diffusion impedance of the fuel cell.

[0063] S130. Obtain pulse parameters based on the impedance information of the fuel cell stack at each characteristic frequency.

[0064] Specifically, after obtaining the impedance information of the fuel cell stack at various characteristic frequencies, the pulse parameters of the heating pulse used for cryogenic heating can be determined based on a preset impedance-pulse parameter mapping relationship or an empirical model. The pulse parameters include at least one or more combinations of pulse current amplitude, pulse frequency, pulse duty cycle, and pulse period.

[0065] Alternatively, in another feasible embodiment of the present invention, when obtaining pulse parameters based on the impedance information of the fuel cell stack at each characteristic frequency, the low-temperature fault type of the fuel cell stack can be obtained first based on the impedance information of the fuel cell stack at each characteristic frequency; the low-temperature fault type includes gas channel blockage, impaired catalytic activity, and excessively low membrane hydration; and then the pulse parameters can be obtained based on the low-temperature fault type.

[0066] Specifically, cryogenic fault types (such as gas channel blockage, impaired catalytic activity, or excessively low membrane hydration) are often difficult to distinguish. Using a fixed pulse parameter for heating indiscriminately can easily lead to a mismatch between the heating strategy and the actual fault, resulting in either low heating efficiency or, in severe cases, exacerbated membrane dehydration or localized overheating. To address this issue, the specific cryogenic fault type can first be identified based on the impedance information of the fuel cell stack at various characteristic frequencies (e.g., by observing the changes in ohmic impedance in the high-frequency region, charge transfer impedance in the mid-frequency region, and diffusion impedance in the low-frequency region of the Nyquist plot). Then, based on a pre-established mapping relationship between cryogenic fault types and pulse parameters, corresponding pulse parameters can be adaptively obtained for different cryogenic fault types.

[0067] S140. Inject heating pulses into the fuel cell according to the pulse parameters.

[0068] Specifically, after determining the pulse parameters, a heating pulse can be injected into the fuel cell stack or its dedicated heating circuit according to the determined pulse parameters through a pulse current generating circuit or a programmable DC power supply, and the generated ohmic heat can be used to raise the temperature of the fuel cell.

[0069] S150: After injecting a heating pulse into the fuel cell stack, obtain the current temperature of the fuel cell stack.

[0070] S160. Determine whether the current temperature is lower than the preset temperature; if yes, return to step S110; if no, proceed to step S170.

[0071] S170, Start the fuel cell.

[0072] Specifically, after injecting a heating pulse into the fuel cell stack, the current temperature of the stack can be obtained again using any of the methods mentioned above, and then compared with a preset temperature. The preset temperature can be the critical minimum temperature at which the fuel cell can generate electricity normally. If the current temperature of the stack is lower than the preset temperature, it indicates that the fuel cell has not yet reached the temperature conditions required for normal startup. At this time, an AC disturbance signal is injected into the stack again, and the cycle of measuring impedance information and injecting heating pulses begins again, until the temperature of the stack meets the startup requirements. If the current temperature of the stack reaches or exceeds the preset temperature, the process of measuring impedance information and injecting heating pulses is stopped, and reactant gases (hydrogen and air) are introduced into the stack and a load is connected, allowing the fuel cell to enter normal power generation mode.

[0073] The low-temperature start-up method for fuel cells provided in this invention first injects an AC disturbance signal into the fuel cell stack when the stack is in a low-temperature state. During the injection process, the impedance information of the stack at multiple characteristic frequencies is acquired. This allows for the differentiation of the icing state, membrane dryness, and catalyst layer state within the stack without relying on temperature sensors, enabling accurate judgment of the overall stack state. This avoids the feedback delay and state misjudgment caused by temperature sensors that can only measure local temperatures and suffer from temperature hysteresis. Then, based on the impedance information of the stack at each characteristic frequency, pulse parameters matching the current actual needs are adaptively acquired, and heating pulses are injected into the stack accordingly. This avoids the problem of local overheating caused by a fixed high-current pulse acting on the melted area for a long time. After injecting the heating pulse, the current temperature of the stack is acquired. If the current temperature is lower than the preset temperature, the process returns to re-injecting the AC disturbance signal and subsequent steps. The pulse parameters for the next round are adjusted through a closed loop using impedance information to achieve differentiated and optimized heating of the local ice layer state. If the current temperature is greater than or equal to the preset temperature, the fuel cell is started. It not only overcomes the inherent defects of local measurement and hysteresis of temperature sensors, but also reduces the risk of membrane perforation and catalyst dissolution caused by local overheating, avoids the energy waste caused by continuous overall heating to reach the target temperature, and significantly improves the energy efficiency, response speed and safety of low temperature start-up.

[0074] In one embodiment, the plurality of characteristic frequencies include a first characteristic frequency, a second characteristic frequency, and a third characteristic frequency; the first characteristic frequency is less than the second characteristic frequency, and the second characteristic frequency is less than the third characteristic frequency; the impedance information includes the real part of the impedance, the imaginary part of the impedance, and the phase angle.

[0075] Specifically, multiple characteristic frequencies are distinguished into a first characteristic frequency, a second characteristic frequency, and a third characteristic frequency, satisfying that the first characteristic frequency is less than the second characteristic frequency, and the second characteristic frequency is less than the third characteristic frequency. For example, the first characteristic frequency is FC1, the second characteristic frequency is FC2, and the third characteristic frequency is FC3; 1Hz ≤ FC1 < 20Hz, 20Hz ≤ FC2 < 100Hz, 1kHz ≤ FC3 < 10kHz. That is, the first characteristic frequency is a low-frequency characteristic frequency, the second characteristic frequency is a mid-frequency characteristic frequency, and the third characteristic frequency is a high-frequency characteristic frequency. During the injection of AC disturbance signals into the fuel cell stack, impedance information at these three characteristic frequencies is obtained respectively. This impedance information includes the real part of the impedance, the imaginary part of the impedance, and the phase angle. By comparing the changes in the real part of impedance, the sign of the imaginary part of impedance, and the magnitude of the phase angle at different frequency bands, the contributions of the diffusion process (characterized by impedance information in the low-frequency band), the charge transfer process (characterized by impedance information in the mid-frequency band), and the ohmic conduction process (characterized by impedance information in the high-frequency band) can be decoupled and analyzed. This allows for a more accurate differentiation of different low-temperature fault types, such as gas channel blockage, impaired catalytic activity, and excessively low membrane hydration. Therefore, by setting three characteristic frequencies (low-frequency, mid-frequency, and high-frequency) and acquiring multi-dimensional impedance information, a comprehensive characterization of multiple physical processes in a fuel cell can be achieved with fewer frequency points, improving fault identification accuracy while ensuring diagnostic efficiency.

[0076] Optional, Figure 4 This is a flowchart of another low-temperature start-up method for a fuel cell provided in an embodiment of the present invention, as shown below. Figure 4 As shown, the low-temperature start-up method for this fuel cell includes:

[0077] S211. When the fuel cell stack is in a low-temperature state, inject an AC disturbance signal into the fuel cell stack.

[0078] S212. During the process of injecting AC disturbance signals into the fuel cell stack, obtain the impedance information of the fuel cell stack at multiple characteristic frequencies; execute steps S213, S215, and S217.

[0079] S213. When the real part of the impedance of the fuel cell stack at the first characteristic frequency is greater than the real part of the first preset impedance, and the imaginary part of the impedance of the fuel cell stack at the first characteristic frequency is greater than the imaginary part of the first preset impedance, the low-temperature fault type is determined to be gas channel blockage.

[0080] Specifically, gas channel blockage (such as ice accumulation or freezing of generated water within the flow channels) and other cryogenic fault types such as membrane dehydration are easily confused in terms of low-frequency impedance characteristics, making it difficult to distinguish them based on changes in a single impedance information (e.g., changes in only the real part of the impedance or only the imaginary part). Therefore, the sensitivity of at least two impedance information types in the low-frequency band (i.e., impedance information at the first characteristic frequency) to the diffusion process can be utilized. For example, a dual judgment method combining the real and imaginary parts of the impedance can be used to distinguish between gas channel blockage and other cryogenic fault types such as membrane dehydration. Specifically, a real impedance greater than a first preset real impedance indicates that the gas diffusion channel is blocked, leading to increased mass transfer resistance. Conversely, an imaginary impedance (typically negative in the low-frequency band, i.e., capacitive reactance) greater than the first preset imaginary impedance (i.e., less negative, or closer to zero) indicates that ice blockage weakens the double-layer capacitance effect. Therefore, when both the real and imaginary impedances of the fuel cell stack at the first characteristic frequency are greater than the first preset real impedance and the first preset imaginary impedance, the cryogenic fault type can be determined to be gas channel blockage. By combining the real and imaginary parts of the impedance, gas channel blockage can be accurately distinguished from other cryogenic fault types. This provides a reliable basis for selecting high-amplitude, low-frequency heating pulses for blockage faults, avoiding misjudgment that could lead to incorrect pulse parameter matching and ultimately membrane damage during heating.

[0081] S214. When the low-temperature fault type is gas channel blockage, determine the pulse frequency as the first pulse frequency, the pulse current as the first pulse current, and the pulse duty cycle as the first pulse duty cycle; execute step S219.

[0082] The first pulse frequency F1, the first pulse current J1, and the first pulse duty cycle D1 satisfy the following conditions: 0.1Hz ≤ F1 < 1Hz, 1A / cm². 2 ≤J1≤2A / cm 2 50% <D1≤80%。

[0083] Specifically, gas channel blockage is mainly caused by ice buildup in the flow channel or gas diffusion layer, requiring high-energy-density heating pulses to quickly melt the ice. However, improper pulse parameters, such as excessively high frequency causing heat to concentrate on the surface and hindering conduction to deeper ice layers, insufficient current to generate enough ohmic heat, or excessively low duty cycle leading to rapid heat loss, will all affect the de-icing effect and energy efficiency. To address this issue, after determining that the low-temperature fault type is gas channel blockage, the pulse frequency is determined to be the first pulse frequency F1, the pulse current to be the first pulse current J1, and the pulse duty cycle to be the first pulse duty cycle D1. Furthermore, the optimal parameter range is defined as follows: the first pulse frequency F1 satisfies 0.1Hz ≤ F1 < 1Hz, and the first pulse current J1 satisfies 1A / cm². 2 ≤J1≤2A / cm2 , the first pulse duty cycle D1 satisfies 50% < D1 ≤ 80%. Wherein, a lower pulse frequency (0.1 Hz to 1 Hz) helps prolong the action time of each pulse, so that Joule heat can be sufficiently conducted to the ice layer interface; a higher pulse current density (1 A / cm² to 2 A / cm²) can generate sufficient heat to rapidly melt accumulated ice; a higher duty cycle (50% to 80%) ensures that heat does not dissipate too quickly during the pulse interval and maintains an effective heating temperature. Through the comprehensive limitation of the above parameter ranges, efficient and rapid deicing heating for gas channel blockage faults is realized, and the risks of local overheating and membrane damage caused by excessively high current or excessively large duty cycle are avoided at the same time.

[0084] S215, when the phase angle of the electric stack at the second characteristic frequency is greater than the preset phase angle, determining that the low-temperature fault type is impaired catalytic activity.

[0085] Specifically, the decrease of catalytic activity is related to the increase of charge transfer resistance, but charge transfer resistance is simultaneously affected by temperature and membrane water content, so it is difficult to identify it alone. Accordingly, the characteristic that the impedance information of the intermediate frequency band (the impedance information at the second characteristic frequency) is sensitive to the charge transfer process can be utilized, and a phase angle threshold (i.e., the preset phase angle) is set as the judgment basis. In the intermediate frequency band, a healthy catalytic layer presents a characteristic phase angle peak. When the catalyst activity decreases, the charge transfer resistance increases, leading to an increase in the phase angle peak. Therefore, when the phase angle of the electric stack at the second characteristic frequency is greater than the preset phase angle, it can be determined that the low-temperature fault type is impaired catalytic activity. Through the judgment with a single threshold of phase angle, whether the catalytic activity is impaired can be quickly identified, which provides a basis for subsequent selection of protective pulse parameters.

[0086] S216, when the low-temperature fault type is impaired catalytic activity, determining the pulse frequency as a second pulse frequency, the pulse current as a second pulse current, and the pulse duty cycle as a second pulse duty cycle; executing step S219.

[0087] wherein, the second pulse frequency F2, the second pulse current J2 and the second pulse duty cycle D2 respectively satisfy: 1 Hz ≤ F2 < 10 Hz, 0.5 A / cm 2 ≤ J2 < 1 A / cm 2 , 30% < D2 ≤ 50%.

[0088] Specifically, impaired catalytic activity is usually caused by a decrease in reaction rate due to low temperature or partial coverage of the catalyst surface. In such cases, using a high-current-density heating pulse, similar to that used when gas channels are blocked, can rapidly raise the temperature, but the localized high temperature will accelerate further dissolution and aggregation of the catalyst, leading to irreversible activity loss. To address this issue, after determining that the low-temperature fault type is impaired catalytic activity, the pulse frequency can be set to a second pulse frequency F2, the pulse current to a second pulse current J2, and the pulse duty cycle to a second pulse duty cycle D2, with further limitations on the optimal parameter range. The second pulse frequency F2 is set to a medium frequency, i.e., 1Hz ≤ F2 < 10Hz. Compared to the low-frequency pulses below 1Hz used when gas channels are blocked, this allows for a more uniform distribution of heat within the microstructure of the catalyst layer, preventing excessive heat concentration in a localized area. The second pulse current J2 is set to a moderately low current density, i.e., 0.5A / cm². 2 ≤J2<1A / cm 2 Compared to the high current density of 1A / cm² to 2A / cm² when the gas channel is blocked, this method generates relatively mild ohmic heat, avoiding secondary thermal shock or electrochemical corrosion to the damaged catalyst layer, while still providing sufficient heating power to effectively raise the catalyst layer temperature. The second pulse duty cycle D2 is set to a medium duty cycle, i.e., 30% < D2 ≤ 50%, which achieves a reasonable balance between heating and heat dissipation. This ensures sufficient heating time to restore catalytic activity while preventing heat accumulation and localized overheating through appropriate intervals. By comprehensively limiting the above parameter ranges, a mild, uniform, and controllable protective heating effect can be achieved for catalytically damaged faults. While raising the fuel cell temperature to restore catalytic activity, it minimizes further dissolution, agglomeration, and degradation of the catalyst, thereby extending the stack's lifespan.

[0089] S217. When the real part of the impedance of the fuel cell stack at the third characteristic frequency is greater than the real part of the second preset impedance, the low temperature fault type is determined to be low membrane hydration.

[0090] Specifically, the membrane hydration state directly affects the ohmic internal resistance (i.e., the real part of the impedance) of the fuel cell, and the ohmic internal resistance is negatively correlated with the degree of membrane hydration. Under high-frequency conditions, the real part of the impedance mainly represents the ohmic resistance of the proton exchange membrane. Therefore, the impedance information in the high-frequency band (i.e., the impedance information at the third characteristic frequency) can be used to mainly reflect the characteristics of the ohmic resistance, and a second preset real part of the impedance can be set as the judgment criterion. Therefore, when the real part of the impedance of the fuel cell at the third characteristic frequency is greater than the second preset real part of the impedance, the low-temperature fault type can be determined as low membrane hydration. By comparing the real part of the high-frequency band impedance with the second preset real part of the impedance, the dryness or wetness state of the membrane can be effectively determined, thus providing a basis for subsequent humidification or heating strategies.

[0091] S218. When the low temperature fault type is low membrane hydration, determine that the pulse frequency is the third pulse frequency, the pulse current is the third pulse current, and the pulse duty cycle is the third pulse duty cycle; execute step S219.

[0092] Among them, the third pulse frequency F3, the third pulse current J3, and the third pulse duty cycle D3 respectively satisfy: 10Hz≤F3≤100Hz, 0.1A / cm 2 ≤J3<0.5A / cm 2 , 10%≤D3≤30%.

[0093] Specifically, when the membrane hydration is too low (i.e., the membrane is dry), the ohmic resistance of the proton exchange membrane increases significantly. If high current or low-frequency pulse heating is used, excessive ohmic heat can easily be generated locally on the membrane, leading to membrane cracking or perforation. Simultaneously, the dry membrane is extremely sensitive to water loss, and the heating process should avoid further exacerbating dehydration. To address this issue, after determining that the low-temperature fault type is due to excessive membrane hydration, regarding the pulse frequency, a third pulse frequency F3 in the mid-to-high frequency range can be used, i.e., the third pulse frequency F3 satisfies 10Hz≤F3≤100Hz. This can generate ohmic heat while avoiding excessive heat concentration in a localized area, achieving a more uniform heating effect. Regarding the pulse current, a lower third current density J3 can be used, i.e., the third current density J3 satisfies 0.1A / cm². 2 ≤J3<0.5A / cm 2 This approach generates gentler ohmic heat, effectively preventing localized overheating and thus avoiding membrane cracking or perforation while raising the membrane temperature. Regarding the pulse duty cycle, a lower third duty cycle D3 can be used (10% ≤ D3 ≤ 30%), providing a longer pulse interval. This facilitates the proton exchange membrane's reabsorption of moisture from the environment or adjacent components, preventing further cracking due to continuous moisture loss during heating. By comprehensively limiting these parameter ranges, a gentle and safe protective heating method can be achieved to address low membrane hydration, effectively protecting the membrane's moisture state while raising the temperature. This prevents membrane perforation or irreversible damage caused by overheating, thereby extending the stack's lifespan.

[0094] S219. Inject heating pulses into the fuel cell stack according to the pulse parameters.

[0095] S220. After injecting a heating pulse into the fuel cell stack, obtain the current temperature of the fuel cell stack.

[0096] S221. Determine whether the current temperature is lower than the preset temperature; if yes, return to step S211; if no, proceed to step S222.

[0097] S222, Start the fuel cell.

[0098] Based on the same inventive concept, embodiments of the present invention also provide a heating system for a fuel cell. Figure 5 This is a schematic diagram of the structure of a fuel cell control system provided in an embodiment of the present invention, as shown below. Figure 5 As shown, the control system of the fuel cell includes a controller 11, a pulse generator 12, and a lock-in amplifier 13. The controller 11 is used to execute the low-temperature start-up method of the fuel cell provided in any embodiment of the present invention. Therefore, the control system of the fuel cell provided in the embodiments of the present invention includes the technical features of the low-temperature start-up method of the fuel cell provided in any embodiment of the present invention, and can achieve the beneficial effects of the low-temperature start-up method of the fuel cell provided in any embodiment of the present invention. The similarities can be referred to the above description of the low-temperature start-up method of the fuel cell provided in the embodiments of the present invention, and will not be repeated here.

[0099] The fuel cell 20 includes a stack 21; the controller 11 is electrically connected to a pulse generator 12 and a lock-in amplifier 13; the pulse generator 12 generates heating pulses and provides them to the stack 21; the lock-in amplifier 13 generates AC disturbance signals and provides them to the stack 21. For example, the pulse generator 12 can be electrically connected to an external DC power supply 14 to receive DC power signals. The pulse generator 12 can be an H-bridge pulse generator, capable of generating corresponding heating pulses based on the DC power signals under the control of the controller 11. Before each generation of heating pulses by the pulse generator 12, the controller 11 first controls the lock-in amplifier 13 to generate AC disturbance signals.

[0100] For example, the controller 11 includes a multi-channel data acquisition module 111 and a data analysis module 112. The multi-channel data acquisition module 111 can acquire impedance information and temperature information of the fuel cell stack 21, and output the acquired impedance information and temperature information to the data analysis module 112. The data analysis module 112 can process the impedance information and temperature information based on the method provided in any embodiment of the present invention, thereby outputting corresponding control signals to the pulse generator 12 and the lock-in amplifier 13.

[0101] Optional, continue to refer to Figure 5The fuel cell control system also includes a temperature sensor 15 and an impedance information acquisition module 16. Both the temperature sensor 15 and the impedance information acquisition module 16 are electrically and / or communicatively connected to the controller 11. The temperature sensor 15 is used to acquire the temperature of the fuel cell stack 21 and send the temperature to the controller 11. The impedance information acquisition module 16 is used to acquire the impedance information of the fuel cell stack and send the impedance information to the controller 11. The temperature sensor 15 can be installed in the coolant circulation pipe 22 of the fuel cell 20, and the impedance information acquisition module 16 can be installed at the total positive and total negative terminals of the fuel cell stack 21 (not shown in the figure) to acquire the response voltage and response current of the fuel cell stack 21.

[0102] For example, the fuel cell 20 also includes a reactant gas supply module 23 and a gas exhaust module 24; both the reactant gas supply module 23 and the gas exhaust module 24 can be equipped with gas pipelines and valves, and the valves in the reactant gas supply module 23 and the gas exhaust module 24 can be electrically connected and / or communicatively connected to the controller 11 (not shown in the figure), so that when pulse heating is performed and when the stack reaches the start-up temperature, the controller 11 can timely control the valves in the reactant gas supply module 23 and the gas exhaust module 24 to supply reactant gas to the stack 21, and to timely discharge the reacted gas and the gas that did not participate in the reaction.

[0103] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for low-temperature start-up of a fuel cell, the fuel cell comprising a stack, characterized in that, include: When the fuel cell stack is in a low-temperature state, an AC disturbance signal is injected into the fuel cell stack; During the process of injecting the AC disturbance signal into the fuel cell stack, the impedance information of the fuel cell stack at multiple characteristic frequencies is obtained; The pulse parameters are obtained based on the impedance information of the fuel cell stack at each of the characteristic frequencies. A heating pulse is injected into the fuel cell stack according to the pulse parameters; After injecting a heating pulse into the fuel cell stack, the current temperature of the fuel cell stack is obtained; When the current temperature is lower than the preset temperature, return to the step of injecting an AC disturbance signal into the fuel cell when the fuel cell is in a low temperature state; The fuel cell is started when the current temperature is greater than or equal to the preset temperature.

2. The low-temperature start-up method for a fuel cell according to claim 1, characterized in that, During the process of injecting AC disturbance signals into the fuel cell stack, impedance information of the fuel cell stack at multiple characteristic frequencies is obtained, including: During the process of injecting an AC disturbance signal into the fuel cell stack, the Nyquist plot is obtained; Based on the Nyquist plot, the impedance information of the fuel cell stack at multiple characteristic frequencies is obtained.

3. The low-temperature start-up method for a fuel cell according to claim 1, characterized in that, The pulse parameters are obtained based on the impedance information of the fuel cell stack at each of the characteristic frequencies, including: Based on the impedance information of the fuel cell stack at each of the characteristic frequencies, the low-temperature fault type of the fuel cell stack is obtained; the low-temperature fault type includes gas channel blockage, impaired catalytic activity, and excessively low membrane hydration. The pulse parameters are obtained based on the low-temperature fault type.

4. The low-temperature start-up method for a fuel cell according to claim 3, characterized in that, The plurality of characteristic frequencies include a first characteristic frequency, a second characteristic frequency, and a third characteristic frequency; the first characteristic frequency is less than the second characteristic frequency, and the second characteristic frequency is less than the third characteristic frequency; the impedance information includes the real part of the impedance, the imaginary part of the impedance, and the phase angle; Based on the impedance information of the fuel cell stack at each of the characteristic frequencies, the cryogenic fault type of the fuel cell stack is obtained, including: When the real part of the impedance of the fuel cell stack at the first characteristic frequency is greater than the real part of the first preset impedance, and the imaginary part of the impedance of the fuel cell stack at the first characteristic frequency is greater than the imaginary part of the first preset impedance, the cryogenic fault type is determined to be the gas channel blockage. When the phase angle of the fuel cell stack at the second characteristic frequency is greater than a preset phase angle, the low-temperature fault type is determined to be impaired catalytic activity; When the real part of the impedance of the fuel cell stack at the third characteristic frequency is greater than the real part of the second preset impedance, the low temperature fault type is determined to be the membrane hydration being too low.

5. The low-temperature start-up method for a fuel cell according to claim 4, characterized in that, The first characteristic frequency is FC1, the second characteristic frequency is FC2, and the third characteristic frequency is FC3; 1Hz≤FC1<20Hz, 20Hz≤FC2<100Hz, 1kHz≤FC3<10kHz.

6. The low-temperature start-up method for a fuel cell according to claim 3, characterized in that, The pulse parameters include: pulse frequency, pulse current, and pulse duty cycle; The pulse parameters are obtained according to the low-temperature fault type, including: When the low-temperature fault type is gas channel blockage, the pulse frequency is determined to be a first pulse frequency F1, the pulse current is determined to be a first pulse current J1, and the pulse duty cycle is determined to be a first pulse duty cycle D1. Where 0.1Hz≤F1<1Hz, 1A / cm 2 ≤J1≤2A / cm 2 50% <D1≤80%。 7. The low-temperature start-up method for a fuel cell according to claim 3, characterized in that, The pulse parameters include: pulse frequency, pulse current, and pulse duty cycle; The pulse parameters are obtained according to the low-temperature fault type, including: When the low-temperature fault type is impaired catalytic activity, the pulse frequency is determined to be the second pulse frequency F2, the pulse current is determined to be the second pulse current J2, and the pulse duty cycle is determined to be the second pulse duty cycle D2. Where 1Hz≤F2<10Hz, 0.5A / cm 2 ≤J2<1A / cm 2 , 30% < D2 ≤ 50%.

8. The low-temperature start-up method for a fuel cell according to claim 3, characterized in that, The pulse parameters include: pulse frequency, pulse current, and pulse duty cycle; The pulse parameters are obtained according to the low-temperature fault type, including: When the low-temperature fault type is that the membrane hydration is too low, the pulse frequency is determined to be the third pulse frequency F3, the pulse current is determined to be the third pulse current J3, and the pulse duty cycle is determined to be the third pulse duty cycle D3. Where 10Hz≤F3≤100Hz, 0.1A / cm 2 ≤J3<0.5A / cm 2 , 10%≤D3≤30%.

9. A control system for a fuel cell, characterized in that, include: The controller, pulse generator, and lock-in amplifier; the fuel cell includes a stack; The pulse generator is used to generate heating pulses and provide the heating pulses to the fuel cell stack; The lock-in amplifier is used to generate an AC disturbance signal and provide the AC disturbance signal to the fuel cell stack; The controller is electrically connected to the pulse generator and the lock-in amplifier respectively, and the controller is used to execute the low-temperature start-up method of the fuel cell according to any one of claims 1 to 8.

10. The control system for a fuel cell according to claim 9, characterized in that, Also includes: Temperature sensor and impedance information acquisition module; Both the temperature sensor and the impedance information acquisition module are electrically and / or communicatively connected to the controller. The temperature sensor is used to acquire the temperature of the fuel cell stack and send the temperature to the controller. The impedance information acquisition module is used to acquire the impedance information of the fuel cell stack and send the impedance information to the controller.

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