Control method and device for fuel cell system and machine readable storage medium

Abstract

The invention relates to a control method and device for a fuel cell system and a machine readable storage medium. The method comprises the following steps: detecting that the voltage of at least one battery unit in a plurality of battery units is equal to or lower than a first voltage threshold value or a DCDC converter has a fault; turning off the at least one first switch; the anode circulating unit is kept running; during the first time period, the cathode gas supply pipeline and the cathode gas exhaust pipeline are kept communicated, the bypass pipeline is kept disconnected, the first purification pipeline is communicated with each unit time according to a first time proportion, and the second purification pipeline is communicated with each unit time according to a second time proportion; and during a second time period, the cathode gas supply pipeline and the cathode exhaust pipeline are kept disconnected, the bypass pipeline is kept communicated, the first purification pipeline is communicated in a third time proportion smaller than the first time proportion in unit time, and the second purification pipeline is communicated in a fourth time proportion smaller than the second time proportion in unit time.

Description

Technical Field

[0001] The present application generally relates to fuel cell technology, and more specifically, to control methods, devices, and machine-readable storage media for fuel cell systems. Background Art

[0002] Fuel cell systems that generate electricity by electrochemical reactions between fuel and oxidant are increasingly widely used to provide electricity, especially in the field of electric vehicles. For example, proton exchange membrane fuel cells (PEMFCs) are used in fuel cell systems, which use hydrogen as fuel and oxygen as oxidant. During the operation of PEMFC, hydrogen and oxygen in the air undergo electrochemical reactions inside the stack to produce a large amount of water. In addition, the stack includes a plurality of battery cells connected in series, and the voltage consistency between each battery cell directly affects the power generation efficiency of the fuel cell system. However, the difference in conditions for electrochemical reactions inside the stack may cause the voltage of a certain battery cell to be significantly lower than that of other battery cells, which is also called the single low phenomenon. Under the single low phenomenon, the control device for the fuel cell system can control the stack to actively discharge so that the fuel cell system is shut down urgently. At present, the active discharge of the stack is completed by means of a DCDC converter, or by means of a discharge resistor when the DCDC converter is damaged, but the active discharge will further aggravate the single low phenomenon, and even cause the voltage reverse polarity phenomenon, which is very unfavorable to the life of the stack. Moreover, during the emergency shutdown process, the drainage of water inside the fuel cell stack is often neglected, which is not conducive to restarting the fuel cell system, especially in a low-temperature environment. Summary of the invention

[0003] The present application aims to provide an improved control method, device and machine-readable storage medium for a fuel cell system to overcome the above defects.

[0004] According to one aspect of the present application, a control method for a fuel cell system is provided, the fuel cell system comprising: at least one stack, comprising a plurality of battery cells having an anode flow channel and a cathode flow channel in common and electrically connected to a DCDC converter via at least one first switch; an anode circulation unit, which can be operated to allow hydrogen to flow to the anode flow channel and to cyclically supply a fluid from the anode flow channel to the anode flow channel; a cathode gas supply line and a cathode exhaust line, both of which can be connected to allow air to flow to the cathode flow channel via the cathode gas supply line and the fluid from the cathode flow channel to be discharged from the cathode exhaust line; a bypass line, which can be connected to allow the air to flow from the cathode gas supply line to the cathode exhaust line via the bypass line; a first purge line, which can be connected to allow liquid in the fluid from the anode flow channel to flow to the cathode exhaust line via the first purge line, and a second purge line, which can be connected to allow a portion of the gas in the fluid from the anode flow channel to flow to the cathode exhaust line via the second purge line. The method comprises: detecting that the voltage of at least one battery cell among the plurality of battery cells is equal to or lower than a first voltage threshold or that a DCDC converter fails; disconnecting the at least one first switch so that the at least one battery stack has an open circuit voltage; keeping the anode circulation unit running; and during a first time period after disconnecting the at least one first switch, keeping the cathode gas supply line and the cathode exhaust line connected, keeping the bypass line cut off, keeping the first purification line connected at a first time ratio per unit time, and keeping the second purification line connected at a second time ratio per unit time; and during a second time period after the first time period, keeping the cathode gas supply line and the cathode exhaust line cut off, keeping the bypass line connected, keeping the first purification line connected at a third time ratio per unit time that is smaller than the first time ratio, and keeping the second purification line connected at a fourth time ratio per unit time that is smaller than the second time ratio.

[0005] Optionally, the method further comprises: after the second period, detecting that the open circuit voltage is equal to or lower than a second voltage threshold; and keeping the bypass line, the first purge line and the second purge line cut off, and then stopping the operation of the anode circulation unit.

[0006] Optionally, the at least one fuel cell stack is electrically connected to at least one discharge resistor via at least one second switch, and the method further includes: after the second time period, detecting that the open circuit voltage is higher than a second voltage threshold; turning on the at least one second switch until the open circuit voltage is equal to or lower than the second voltage threshold; and turning off the at least one second switch, and keeping the bypass line, the first purge line and the second purge line cut off, and then stopping the anode circulation unit.

[0007] Optionally, the first time ratio is separated from the second time ratio on the time axis, and the third time ratio is separated from the fourth time ratio on the time axis.

[0008] Optionally, the fuel cell system further includes an air compressor that delivers the air to the cathode gas supply line, and the method further includes: during the first time period, increasing the speed of the air compressor to a first speed threshold; and / or during the second time period, reducing the speed of the air compressor to a second speed threshold that is lower than the first speed threshold.

[0009] Optionally, the fuel cell system further comprises a throttle valve disposed on the cathode exhaust pipeline, and the method further comprises: after disconnecting the at least one first switch, fully opening the throttle valve.

[0010] Optionally, the method further includes: during a first sub-period starting from the first time period, causing the temperature of the air to be higher than a first temperature threshold, and during a second sub-period of the first time period after the first sub-period, causing the temperature of the air to be equal to or lower than a second temperature threshold lower than the first temperature threshold.

[0011] Optionally, the method further includes at least one of the following: the length of the first sub-period is 2 to 5 times the length of the second sub-period; the first temperature threshold is in the range of 50°C to 80°C; and the second temperature threshold and / or the duration of the second sub-period is determined based on the external ambient temperature.

[0012] According to another aspect of the present application, a control device for a fuel cell system is provided, which includes: a processor; and a memory having executable instructions stored thereon, wherein the executable instructions, when executed, enable the processor to execute the above-mentioned control method for the fuel cell system.

[0013] According to yet another aspect of the present application, a machine-readable storage medium is provided, which stores executable instructions, and when the executable instructions are executed by a processor, the above-mentioned control method for a fuel cell system is implemented.

[0014] The control method, device and machine-readable storage medium for a fuel cell system provided in the present application provide a flexible solution for shutting down the fuel cell system to prevent active discharge of the stack from adversely affecting the life of the stack when the voltage of a certain battery cell is significantly lower than the voltage of other battery cells, while helping to maintain the water inside the stack at an appropriate level during shutdown.

[0015] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings, which constitute a part of the specification, illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0017] Figure 1 is a schematic block diagram of a fuel cell system and an external circuit electrically connected to the fuel cell system according to one embodiment of the present application.

[0018] Figure 2 is a schematic diagram of a fuel cell unit of a fuel cell system according to one embodiment of the present application.

[0019] Figure 3 is a flow chart of a control method for a fuel cell system according to one embodiment of the present application. DETAILED DESCRIPTION

[0020] Some preferred embodiments of the present application are described in detail below with reference to examples. It should be understood by those skilled in the art that these embodiments are merely exemplary and are not intended to limit the present application in any way. In addition, the features in the embodiments of the present application may be combined with each other unless they conflict. In the accompanying drawings, other components are omitted for the sake of brevity, but this does not mean that the fuel cell system of the present application may not include other components. It should be understood that the size, proportional relationship and number of components of the components in the accompanying drawings are not intended to limit the present application.

[0021] Figure 1 A fuel cell system (hereinafter referred to as a battery system) 10 according to an embodiment of the present application and an external circuit 14 electrically connected to the battery system 10 are schematically shown, which can be arranged in an electric vehicle as an electrical system to provide power to various electrical devices in the electric vehicle (for example, an electric motor, a power battery, etc.).

[0022] First, the battery system 10 itself includes at least one fuel cell stack (hereinafter referred to as the stack), the stack 12 has a positive electrode and a negative electrode, and a DCDC converter 16 is provided on the external circuit 14 for converting the high voltage from the stack 12 into a desired low voltage, and the DCDC converter 16 is then electrically connected to, for example, the on-board power grid 17, so as to provide power to various electrical devices in the electric vehicle. In addition, at least one first switch is further provided on the external circuit 14, for example, the at least one first switch includes a positive relay 18 provided between the positive electrode of the stack 12 and the positive electrode of the input end of the DCDC converter 16 and a negative relay 20 provided between the negative electrode of the stack 12 and the negative electrode of the input end of the DCDC converter 16, when the at least one first switch is turned on, the stack 12 is electrically connected to the DCDC converter 16, and when the at least one first switch is turned off, the stack 12 is disconnected from the DCDC converter 16, so that the stack 12 has an open circuit voltage. In addition, at least one discharge resistor 22 and at least one second switch 24 (for example, a normally open switch) connected in series with the at least one discharge resistor 22 are further provided on the external circuit 14, and the at least one discharge resistor 22 is connected in parallel to the DCDC converter 16. When the at least one second switch 24 is turned on, the battery stack 12 is electrically connected to the at least one discharge resistor 22, so that the at least one discharge resistor 22 can help quickly discharge the current or voltage of the discharge stack 12. When the at least one second switch 24 is turned off, the battery stack 12 is disconnected from the at least one discharge resistor 22.

[0023] Secondly, the battery stack 12 includes a plurality of fuel cell units (hereinafter referred to as battery units, such as Figure 2 As shown) 200, and the multiple battery cells 200 are connected in series in sequence. Figure 2 A battery cell 200 of the battery stack 12 is schematically shown. Figure 2As shown, the battery unit 200 generally includes a cathode plate 201, an anode plate 203, a proton exchange membrane 205, a cathode gas diffusion layer / microporous layer 207 and a cathode catalyst layer 209 between the cathode plate 201 and the proton exchange membrane 205, and an anode gas diffusion layer / microporous layer 211 and an anode catalyst layer 213 between the anode plate 203 and the proton exchange membrane 205. The cathode gas diffusion layer / microporous layer 207, the cathode catalyst layer 209, the anode gas diffusion layer / microporous layer 211, the anode catalyst layer 213 and the proton exchange membrane 205 are generally made into one piece and are referred to as a membrane electrode (MEA). A cathode flow field (not shown) and an anode flow field (also not shown) are formed on the cathode plate 201 and the anode plate 203, respectively. The cathode flow fields of the cathode plates 201 of the plurality of battery cells 200 constitute cathode flow channels (not shown) of the battery stack 12 , and the anode flow fields of the anode plates 203 of the plurality of battery cells 200 constitute anode flow channels (also not shown) of the battery stack 12 .

[0024] Back again Figure 1The battery system 10 further includes an anode circulation unit, which includes: a fuel gas source, for example, a hydrogen source 26 such as a hydrogen tank; an anode supply pipeline 27, which is configured to be fluidly connected between the hydrogen source 26 and the anode inlet 103 of the anode flow channel of the stack 12; a fuel gas supply device provided on the anode supply pipeline 27, for example, a hydrogen supply device 28, for example, the hydrogen supply device 28 includes an ejector and a hydrogen injector separated from each other or integrated into one; and a recirculation pipeline 30, which is configured to be fluidly connected between the anode outlet 107 of the anode flow channel of the stack 12 and the hydrogen supply device 28, and recirculates the fluid flowing out of the anode outlet 107 to the hydrogen supply device 28. A circulation pump 32 is provided on the recirculation pipeline 30 to help recirculate the fluid flowing out of the anode outlet 107 to the hydrogen supply device 28. The circulation pump 32 can be controlled to switch between an operating state and an inactive state. The circulation pump 32 pumps the fluid flowing out of the anode outlet 107 toward the hydrogen supply device 28 when it is in operation. In this case, this fluid can be referred to as a "recirculation flow", which refers to a fluid mixture including product water, unconsumed hydrogen and invalid gas (e.g., nitrogen). The circulation pump 32 blocks the flow of the fluid flowing out of the anode outlet 107 toward the hydrogen supply device 28 when it is in a deactivated state. The hydrogen supply device 28 can also be controlled to switch between an operating state and a deactivated state. The hydrogen supply device 28 supplies hydrogen from the hydrogen source 26 and the recirculation flow (if any) from the recirculation pipeline 30 to the anode inlet 103 when it is in an operating state, and ensures that the common gas pressure of the hydrogen and the recirculation flow flowing to the anode inlet 103 at least reaches the minimum gas pressure threshold, and blocks the flow from the hydrogen source 26 and the recirculation pipeline 30 to the anode inlet 103 when it is in a deactivated state. Therefore, during the operation of the anode circulation unit, at least one of the circulation pump 32 and the hydrogen supply device 28 is in an operating state.

[0025] In addition, a first valve 34 (e.g., a solenoid valve) may be provided on the anode gas supply pipeline 27. The first valve 34 is located between the hydrogen source 26 and the hydrogen supply device 28 and may be controlled to switch between an open state and a closed state. When the first valve 34 is in an open state, the anode gas supply pipeline 27 is connected, and when the first valve 34 is in a closed state, the anode gas supply pipeline 27 is cut off.

[0026] It is understandable that various components such as filters, heat exchangers, temperature sensors, pressure sensors and / or valves may be provided on the anode gas supply line 27 and the recirculation line 30 as required.

[0027] The battery system 10 further includes: an air compressor 36; a cathode gas supply line 38, which is configured to be fluidically connected between the cathode inlet 117 of the cathode flow channel of the fuel cell stack 12 and the air compressor 36; and a second valve 40 (e.g., a solenoid valve) disposed on the cathode gas supply line 38, for example, the second valve 40 is adjacent to the cathode inlet 117. The air compressor 36 can be controlled to switch between an operating state and an inactive state, and the air compressor 36 can have different rotation speeds when in the operating state to pressurize the oxidizing gas (e.g., air) from the oxidizing gas source 42 (e.g., the atmospheric environment surrounding the fuel cell system 10) to different degrees, and the rotation speed of the air compressor 36 is zero when in the inactive state. The second valve 40 can be controlled to switch between an open state and a closed state. When the second valve 40 is in a punched state, the cathode gas supply line 38 can be connected to deliver pressurized air to the cathode inlet 117, and when the second valve 40 is in a closed state, the cathode gas supply line 38 can be cut off to stop supplying air to the cathode inlet 117.

[0028] Optionally, a humidifier 44 and / or a heat exchanger (not shown) may be further provided on the cathode gas supply line 38. The humidifier 44 is located between the second valve 40 and the air compressor 36 and may be controlled to switch between an operating state and an inactive state. When the humidifier 44 is in the operating state, it may humidify the air flowing through the humidifier 44, and when the humidifier 44 is in the inactive state, it may not humidify the air flowing through the humidifier 44. The heat exchanger is also located between the second valve 40 and the air compressor 36 and may be controlled to switch between an operating state and an inactive state. When the heat exchanger is in the operating state, it may heat / cool the air flowing through the heat exchanger to a desired temperature, and when the heat exchanger is in the inactive state, it may not heat / cool the air flowing through the heat exchanger.

[0029] The battery system 10 further includes: a cathode exhaust line 45 configured to be fluidically connected to a cathode outlet 121 of a cathode flow channel of the battery stack 12; a throttle valve 46 disposed on the cathode exhaust line 45, the opening of which is adjustable to adjust the gas pressure in a portion of the cathode exhaust line 45 upstream of the throttle valve 46, the cathode flow channel of the battery stack 12, and the cathode gas supply line 38; and a third valve 48 (e.g., a solenoid valve) disposed on the cathode exhaust line 45, the third valve 48 being located between the cathode outlet 121 and the throttle valve 46 and, for example, adjacent to the cathode outlet 121, and being controllable to switch between an open state and a closed state, the third valve 48 being able to connect the cathode exhaust line 45 when in an open state to discharge the fluid from the cathode flow channel from the cathode exhaust line 45, and the third valve 48 being able to cut off the cathode exhaust line 45 when in a closed state to block the fluid from the cathode flow channel from being discharged from the cathode exhaust line 45. With the aid of Figure 2It is understood that the hydrogen entering the anode flow field reacts electrochemically with the oxygen in the air entering the cathode flow field. Specifically, the hydrogen is adsorbed by the anode catalyst layer 213 via the anode gas diffusion layer / microporous layer 211 and ionized into hydrogen ions and electrons. The proton exchange membrane 205 conducts hydrogen ions and blocks other substances (e.g., hydrogen and air) different from hydrogen ions to a certain extent, so that the hydrogen ions are transferred to the cathode catalyst layer 209 via the proton exchange membrane 205, and the electrons flow to the cathode catalyst layer 209 through the external circuit 14 to form an electric current, and the oxygen is then combined with the hydrogen ions and electrons in the cathode catalyst layer 209 to form product water. Therefore, the fluid from the cathode flow channel includes the air and product water remaining after the electrochemical reaction.

[0030] It is understandable that various components such as filters, temperature sensors, pressure sensors and / or valves may be provided on the cathode gas supply line 38 and the cathode exhaust line 45 as required.

[0031] The battery system 10 further includes: a bypass line 50, which is configured to fluidically connect the cathode gas supply line 38 and the cathode exhaust line 45, one end of the bypass line 50 connected to the cathode gas supply line 38 is located upstream of the second valve 40, and the other end of the bypass line 50 connected to the cathode exhaust line 45 is located between the third valve 48 and the throttle valve 46; and a fourth valve 52 (for example, a solenoid valve) arranged on the bypass line 50, the fourth valve 52 can be controlled to switch between an open state and a closed state, and the fourth valve 52 can connect the bypass line 50 when it is in the open state so that air flows from the cathode gas supply line 38 to the cathode exhaust line 45 via the bypass line 50 instead of via the cathode flow channel, and the fourth valve 52 can cut off the bypass line 50 when it is in the closed state.

[0032] In order to make the power generation efficiency of the stack 12 meet the requirements, more hydrogen is usually supplied to the anode flow channel than the amount calculated based on stoichiometry, so the fluid from the anode flow channel contains unconsumed hydrogen, and a certain amount of product water and ineffective gases such as nitrogen will diffuse into the anode flow channel through the proton exchange membrane 205. Therefore, the amount of product water and nitrogen in the recirculation line 30 increases over time. The recirculation line 30 must be intermittently purified to ensure that the power generation efficiency of the stack 12 does not decrease due to excessive product water content and nitrogen concentration in the recirculation line 30.

[0033] Therefore, the anode circulation unit includes a liquid separation device 54 and a gas separation device 56 disposed on the recirculation pipeline 30, and the liquid separation device 54 and the gas separation device 56 are located in parallel between the anode outlet 107 and the circulation pump 32, so as to filter out the product water and nitrogen in the fluid flowing out of the anode outlet 107, respectively. For example, the liquid separation device 54 includes a collection container for accommodating the filtered product water. For example, the liquid separation device 54 includes an upper compartment and a lower compartment, and the nitrogen with a heavier relative molecular mass is more likely to fill the lower compartment.

[0034] Accordingly, the battery system 10 further includes: a first purification line 58, which is configured to fluidically connect the liquid separation device 54, especially the collecting container and the cathode exhaust line 45, and one end of the first purification line 58 connected to the cathode exhaust line 45 is located downstream of the throttle valve 46; and a fifth valve 60 (for example, a solenoid valve) arranged on the first purification line 58, the fifth valve 60 can be controlled to switch between an open state and a closed state, and the fifth valve 60 can connect the first purification line 58 when it is in the open state to discharge the fluid containing the product water from the collecting container and possibly containing some hydrogen, etc. from the cathode exhaust line 45 via the first purification line 58, and the fifth valve 60 can cut off the first purification line 58 when it is in the closed state to block the discharge of the product water from the collecting container.

[0035] Accordingly, the battery system 10 further includes: a second purification line 62, which is configured to fluidically connect the gas separation device 56, especially the lower compartment and the cathode exhaust line 45, and one end of the second purification line 62 connected to the cathode exhaust line 45 is located downstream of the throttle valve 46; and a sixth valve 64 (for example, a solenoid valve) arranged on the second purification line 62, the sixth valve 64 can be controlled to switch between an open state and a closed state, and the sixth valve 64 can connect the second purification line 62 when it is in the open state to discharge the fluid containing nitrogen from the lower compartment and possibly containing some hydrogen, etc. from the cathode exhaust line 45 via the second purification line 62, and the sixth valve 64 can cut off the second purification line 62 when it is in the closed state to block the discharge of nitrogen from the lower compartment.

[0036] Figure 3 A flow chart of a control method for a battery system according to one embodiment of the present application is shown. Such a control method is particularly suitable for shutting down the battery system 10 and includes the steps described in detail below.

[0037] Step S101. Detecting / receiving the first information or the second information, the first information indicates that the voltage of at least one of the plurality of battery cells is equal to or lower than the first voltage threshold, that is, indicating a single low phenomenon, and the second information indicates that the DCDC converter 16 is faulty. Based on the first information, it is not recommended to actively discharge the battery stack 12 with the aid of the DCDC converter 16, which is likely to further aggravate the single low phenomenon and even cause a voltage reverse polarity phenomenon. Based on the second information, the DCDC converter 16 will no longer be suitable for actively discharging the battery stack 12.

[0038] Step S102 . Based on the detection / reception of the first information or the second information, the at least one first switch is turned off so that the at least one battery stack has an open circuit voltage. Excessive open circuit voltage needs to be consumed to ensure the safety of the battery stack 12 .

[0039] Step S103. After disconnecting the at least one first switch, the anode circulation unit is still kept running. The way in which the anode circulation unit keeps running after disconnecting the at least one first switch can be the same as or different from that before disconnecting the at least one first switch, that is, the running mode of at least one of the circulation pump 32 and the hydrogen supply device 28 after disconnecting the at least one first switch can be the same as or different from that before disconnecting the at least one first switch. One purpose of step S103 is to keep the gas pressure in the anode side of the stack 12 composed of the anode plate 203, the cathode gas diffusion layer / microporous layer 211 and the anode catalyst layer 213 slightly higher than the gas pressure in the cathode side of the stack 12 composed of the cathode plate 201, the cathode gas diffusion layer / microporous layer 207 and the cathode catalyst layer 209, so as to facilitate the chemical reaction between hydrogen and oxygen. It should be noted that although at least one of the first switches is disconnected, the electrons generated by the ionization of hydrogen cannot flow to the cathode catalyst layer 209 through the external circuit 14, but hydrogen and oxygen will still react chemically inside each battery cell 200 or inside the battery stack 12 to consume the hydrogen and oxygen.

[0040] Step S104. During the first period after the at least one first switch is turned off, the cathode gas supply line 38 and the cathode exhaust line 45 are kept connected, the bypass line 50 is kept cut off, the first purge line 58 is connected at a first time ratio per unit time, and the second purge line 62 is connected at a second time ratio per unit time. One purpose of step S104 is to allow the cathode side of the stack 12 to be purged to a certain extent so that the water on the cathode side of the stack 12 is maintained at a suitable level when shutting down.

[0041] Optionally, during the first period, the speed of the air compressor 36 is increased to a first speed threshold. For example, the first speed threshold may improve the efficiency of the purging.

[0042] Step S105. During a second period after the first period, the cathode gas supply line 38 and the cathode exhaust line 45 remain cut off, the bypass line 50 remains connected, the first purge line 58 is connected at a third time ratio per unit time, and the second purge line 62 is connected at a fourth time ratio per unit time.

[0043] During the second period, the cathode gas supply line 38 and the cathode exhaust line 45 are cut off at the same time, and a relatively isolated space area can be formed in the cathode flow channel, a part of the cathode gas supply line 38 downstream of the second valve 40, and a part of the cathode exhaust line 45 upstream of the third valve 48. The oxygen in this relatively isolated space is consumed due to the chemical reaction with the hydrogen, so that the open circuit voltage continues to decrease, and a part of the hydrogen will continue to pass through the proton exchange membrane 205 to enter the cathode side of the stack 12. Therefore, during the second period, the anode circulation unit is kept running to maintain the gas pressure on the anode side of the stack 12, which can be set based on the gas pressure of the external environment instead of referring to the gas pressure on the cathode side of the stack 12.

[0044] Since there is less and less oxygen in this relatively isolated space, the intensity of the chemical reaction between oxygen and hydrogen is also getting lower and lower. Therefore, the frequency required for the recirculation line 30 to be intermittently purified is also reduced, the third time ratio will be smaller than the first time ratio, and the fourth time ratio will be smaller than the second time ratio.

[0045] In addition, since the cathode gas supply line 38 and the cathode exhaust line 45 are cut off at the same time, the bypass line 50 will remain connected to help the air from the gas compressor 36 to be discharged. The discharged air can be used to dilute the hydrogen that may be contained in the fluid discharged through the first purification line 58 and the second purification line 62.

[0046] Optionally, during the second period, the rotation speed of the air compressor 36 is reduced to a second rotation speed threshold, which is lower than the first rotation speed threshold and may be a minimum rotation speed of the air compressor 36 .

[0047] Optionally, after the at least one first switch is opened, the throttle valve 46 is fully opened to no longer control the gas pressure on the cathode side of the fuel cell stack 12 .

[0048] Step S106 . After the second period, the open circuit voltage is detected / received and it is determined whether the open circuit voltage has dropped to be equal to or lower than a second voltage threshold.

[0049] Step S107 . If it is determined that the open circuit voltage is equal to or lower than the second voltage threshold, the bypass line 50 , the first purge line 58 and the second purge line 62 are kept cut off, and then the anode circulation unit is stopped to complete the shutdown of the battery system 10 .

[0050] Step S108. If it is determined that the open circuit voltage is higher than the second voltage threshold, the at least one second switch 24 is turned on for a period of time to help discharge the voltage of the discharge stack 12 with the help of the at least one discharge resistor 22 until the open circuit voltage is equal to or lower than the second voltage threshold, and then the at least one second switch 24 is turned off. While the at least one second switch 24 is turned off, the bypass line 50, the first purge line 58, and the second purge line 62 are kept cut off, and then the anode circulation unit is stopped to complete the shutdown of the battery system.

[0051] Optionally, the first time ratio and the second time ratio are separated, staggered or non-overlapping on the time axis to ensure that hydrogen that may be contained in the fluid discharged through the first purification line 58 and the second purification line 62 is not discharged into the cathode exhaust line 45 at the same time to cause excessive hydrogen.

[0052] Optionally, during the first sub-period at the beginning of the first period, the temperature of the air is made higher than the first temperature threshold, for example, by heating with the aid of a heat exchanger, so as to perform a high-temperature purge on the cathode side of the stack 12. For example, the first temperature threshold is in the range of 50°C to 80°C, preferably in the range of 60°C to 70°C.

[0053] Then, during a second sub-period after the first sub-period of the first time period, the temperature of the air is equal to or lower than the second temperature threshold, for example, by cooling with the aid of a heat exchanger, so as to perform a low-temperature purge on the cathode side of the stack 12. The second temperature threshold is lower than the first temperature threshold. For example, the second temperature threshold and / or the duration of the second sub-period are determined based on the ambient temperature, i.e., the ambient temperature outside the battery system 10. Generally speaking, the second temperature threshold is close to the ambient temperature, and if the ambient temperature is higher, the duration of the second sub-period is shorter.

[0054] Optionally, the length of the first sub-period is 2 to 5 times the length of the second sub-period;

[0055] Optionally, the total duration of the first time period is fixed to provide a second time period that is long enough for the open circuit voltage to drop.

[0056] It should be understood that various components controlled herein (such as various valves, hydrogen supply devices, circulation pumps, and air compressors, etc.) can be powered by power batteries.

[0057] The present application also provides a control device for the battery system 10, which may be, for example, a fuel cell control unit (FCCU) of the battery system 10 or any other type of control device. The control device includes a processor and a memory, on which executable instructions are stored, and when the executable instructions are executed, the processor executes a control method for the battery system 10. The processor may be implemented using electronic hardware, computer software, or any combination thereof. Whether these processors are implemented as hardware or software will depend on the specific application and the overall design constraints imposed on the control device. As an example, the processor, any part of the processor, or any combination of processors given in the present application may be implemented as a microprocessor, a microcontroller, a digital signal processor (DSP), a field programmable gate array (FPGA), a programmable logic device (PLD), a state machine, a gate logic, a discrete hardware circuit, and other suitable processing components configured to perform the various functions described in the present application. The functions of the processor, any part of the processor, or any combination of processors given in the present application may be implemented as software executed by a microprocessor, a microcontroller, a DSP, or other suitable platforms.

[0058] The present application also provides a machine-readable storage medium storing executable instructions, which, when executed by a processor, implement a control method for a fuel cell system.

[0059] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration and not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A control method for a fuel cell system (10), the fuel cell system (10) comprising: At least one battery stack (12) comprising a plurality of battery cells having an anode flow channel and a cathode flow channel in common and electrically connected to a DCDC converter (16) via at least one first switch; an anode circulation unit operable to allow hydrogen to flow to the anode flow channel and cyclically supply a fluid from the anode flow channel to the anode flow channel; a cathode gas supply line (38) and a cathode exhaust line (45) which are communicable to allow air to flow to the cathode flow channel through the cathode gas supply line (38) and fluid from the cathode flow channel to be exhausted from the cathode exhaust line (45); a bypass line (50) communicable to allow the air to flow from the cathode air supply line (38) to the cathode exhaust line (45) via the bypass line (50); a first purge line (58) communicable to allow liquid in the fluid from the anode flow channel to flow to the cathode exhaust line (45) via the first purge line (58), and a second purge line (62) which is connectable to allow a portion of the gas in the fluid from the anode flow channel to flow to the cathode exhaust line (45) via the second purge line, The method comprises: - detecting that the voltage of at least one of the plurality of battery cells is equal to or lower than a first voltage threshold or that a DCDC converter (16) fails; - opening the at least one first switch so that the at least one battery stack (12) has an open circuit voltage; - keeping the anode circulation unit running; and - during a first period after the at least one first switch is turned off, the cathode gas supply line (38) and the cathode exhaust line (45) remain connected, the bypass line (50) remains blocked, the first purge line (58) is connected at a first time ratio per unit time, and the second purge line (62) is connected at a second time ratio per unit time; and - During a second time period after the first time period, the cathode gas supply line (38) and the cathode exhaust line (45) remain cut off, the bypass line (50) remains connected, the first purge line (58) is connected at a third time ratio per unit time that is smaller than the first time ratio, and the second purge line (62) is connected at a fourth time ratio per unit time that is smaller than the second time ratio.

2. The control method for a fuel cell system (10) according to claim 1, characterized in that: The method further comprises: - after the second period, detecting that the open circuit voltage is equal to or lower than a second voltage threshold; and - The bypass line (50), the first purge line (58) and the second purge line (62) are kept cut off, and then the anode circulation unit is stopped.

3. The control method for a fuel cell system (10) according to claim 1, characterized in that: The at least one battery stack (12) is electrically connected to at least one discharge resistor (22) via at least one second switch (24), and the method further comprises: - after the second period, detecting that the open circuit voltage is higher than a second voltage threshold; - turning on the at least one second switch (24) until the open circuit voltage is equal to or lower than a second voltage threshold; and - opening the at least one second switch (24), and keeping the bypass line (50), the first purge line (58) and the second purge line (62) cut off, and then stopping the operation of the anode circulation unit.

4. The control method for a fuel cell system (10) according to any one of claims 1 to 3, characterized in that: The first time ratio is spaced apart from the second time ratio on a time axis, and the third time ratio is spaced apart from the fourth time ratio on a time axis.

5. The control method for a fuel cell system (10) according to any one of claims 1 to 3, characterized in that: The fuel cell system (10) further comprises an air compressor (36) for delivering the air to the cathode air supply pipeline (38), and the method further comprises: - during the first period, increasing the speed of the air compressor (36) to a first speed threshold; and / or - during the second period, reducing the rotational speed of the air compressor (36) to a second rotational speed threshold value which is lower than the first rotational speed threshold value.

6. The control method for a fuel cell system (10) according to any one of claims 1 to 3, characterized in that: The fuel cell system (10) further comprises a throttle valve (46) disposed on the cathode exhaust pipeline (45), and the method further comprises: After the at least one first switch is opened, the throttle valve (46) is fully opened.

7. The control method for a fuel cell system (10) according to any one of claims 1 to 3, characterized in that: The method further comprises: - during a first sub-period at the beginning of the first period, causing the temperature of the air to be above a first temperature threshold, and - during a second sub-period of the first period following the first sub-period, causing the temperature of the air to be equal to or lower than a second temperature threshold value lower than the first temperature threshold value.

8. The control method for a fuel cell system (10) according to claim 7, characterized in that: Further including at least one of the following: - the length of the first sub-period is 2 to 5 times the length of the second sub-period; - the first temperature threshold is in the range of 50°C to 80°C; and - Determine the second temperature threshold and / or the duration of the second sub-period based on the ambient temperature.

9. A control device for a fuel cell system (10), comprising: processor; and A memory having executable instructions stored thereon, wherein when the executable instructions are executed, the processor executes the control method for the fuel cell system (10) according to any one of claims 1 to 8.

10. A machine-readable storage medium storing executable instructions, wherein the executable instructions, when executed by a processor, implement the control method for a fuel cell system (10) according to any one of claims 1 to 8.

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