Single-low fault elimination method and device for fuel cell system

Abstract

The invention relates to the technical field of fuel cells, and discloses a single low fault elimination method and device for a fuel cell system, and the method comprises the steps: controlling a fuel cell stack to be in a no-load state when it is determined that the fuel cell stack has a single low fault, and controlling the fuel cell system where the fuel cell stack is located to enter an open-circuit purging state; when the duration of the open-circuit purging state of the fuel cell system reaches a preset first time, gradually increasing the load pulling current magnitude of the fuel cell stack, and controlling the fuel cell system to enter a gradual load pulling purging state; and when the fuel cell system is in a step-by-step load pulling and purging state, detecting the current density of the fuel cell and whether the fuel cell stack has a single-low fault in real time, and adjusting the load pulling current magnitude of the fuel cell stack or controlling the fuel cell system to enter an open-circuit purging state according to a detection result until the single-low fault of the fuel cell stack is eliminated. According to the invention, the purging efficiency and the purging effect can be effectively improved, so that the elimination efficiency of a single-low fault is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fuel cells, and in particular to a method and device for eliminating single low faults of a fuel cell system. Background Art

[0002] As the number of fuel cell vehicles gradually increases, more and more fuel cell system failures have begun to attract attention, among which "single low" (single-chip voltage low) failures are particularly serious. When a fuel cell has a single low failure, if it is not handled in time, it may cause the single low situation to deteriorate further, or even produce reverse polarity, which will have a destructive effect on the fuel cell stack membrane electrode, and then cause problems such as stack performance degradation and poor air tightness. There are generally two reasons for single low. One is component reasons, such as excessive humidity in the hydrogen source causing excessive humidity in the stack anode, or insufficient air tightness of components causing gas leakage; the other is stack reasons, such as the stack leaking coolant, causing blockage of the plate flow channel, causing the fuel cell to pull a small power, which will also cause a single low problem.

[0003] Most of the existing fuel cell coolant temperature control is to troubleshoot the single low due to component reasons. For example, troubleshooting is carried out by reducing the ejector inlet pressure and opening the anode drain valve. However, it takes a certain amount of time for the measures adopted by this method to take effect, and during this period of time, the single low fault may be further aggravated. For another example, the control strategy of the fuel cell is changed to a certain extent to eliminate the single low fault. However, this method cannot solve the single low problem caused by flow channel blockage caused by internal leakage of the stack coolant. Therefore, the current single low troubleshooting method is not timely enough, the troubleshooting effect is not good, and it has limitations, and can only eliminate the single low fault caused by component reasons. Summary of the invention

[0004] The present invention provides a method and device for troubleshooting a single low fault of a fuel cell system, which can effectively improve the purge efficiency and purge effect, thereby improving the efficiency of troubleshooting a single low fault.

[0005] In order to solve the above technical problems, the present invention provides a single low fault troubleshooting method for a fuel cell system, comprising:

[0006] When it is determined that a single low fault exists in the fuel cell stack, the fuel cell stack is controlled to be in a no-load state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open circuit purge state;

[0007] When the duration of the open circuit purge state of the fuel cell system reaches a preset first time, gradually increasing the load current of the fuel cell stack, and controlling the fuel cell system to enter a gradual load purge state;

[0008] When the fuel cell system is in a step-by-step load-purge state, the fuel cell electrical density and whether the fuel cell stack has a single-low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted or the fuel cell system is controlled to enter an open-circuit purge state according to the detection result until the single-low fault of the fuel cell stack is eliminated.

[0009] When determining that a single low fault exists in a fuel cell stack, the present invention stops the current loading behavior of the fuel cell stack, controls the fuel cell stack to be in an unloaded state, prevents the occurrence of a single low fault again, and controls the fuel cell system in which the fuel cell stack is located to enter an open circuit purge state to purge out the impurities blocked in the stack. When the fuel cell system continues to be in an open circuit purge state for a preset first time, the loading current of the fuel cell stack is gradually increased to increase the stack temperature of the fuel cell stack, and the fuel cell system is controlled to enter a step-by-step loading and purge state to further eliminate impurities in the stack and improve the purge efficiency. In the step-by-step loading and purge state, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, and the purge state of the fuel cell system is adjusted accordingly according to the detection results to eliminate the single low fault. By reasonably controlling the purge state of the fuel cell system, a better purge effect can be achieved, thereby improving the efficiency of eliminating single low faults.

[0010] Furthermore, the determination that the fuel cell stack has a single low fault is specifically as follows:

[0011] Obtain the minimum single-chip voltage and average single-chip voltage of the fuel cell stack;

[0012] Calculating a voltage difference according to the minimum single-chip voltage and the average single-chip voltage;

[0013] comparing the voltage difference with a preset voltage threshold;

[0014] When the voltage difference is greater than the preset voltage threshold, it is determined that a single low fault exists in the fuel cell stack.

[0015] Furthermore, the controlling the fuel cell system in which the fuel cell stack is located to enter an open circuit purge state is specifically as follows:

[0016] Obtain basic data of fuel cell stack;

[0017] Calculating air flow rate according to basic data of the fuel cell stack;

[0018] Determine the no-load hydrogen inlet pressure according to the air flow rate and the preset first pressure increment;

[0019] Hydrogen is introduced into the fuel cell system where the fuel cell stack is located according to the no-load hydrogen inlet pressure, so that the fuel cell system enters an open-circuit purge state.

[0020] Furthermore, the air flow rate is calculated according to the basic data of the fuel cell stack, specifically:

[0021] Obtain the active area of ​​a single cell of the fuel cell stack, the number of fuel cell stack sheets, the preset current density and the excess coefficient of the fuel cell stack from the basic data of the fuel cell stack;

[0022] The air flow rate is calculated according to the active area of ​​the fuel cell stack, the number of fuel cell stacks, the preset current density and the stack excess coefficient. The specific formula is:

[0023] Flow air =0.0166*S bat *I*N cell *Stoic

[0024] Where, Flow air is the air flow rate; S bat is the active area of ​​a single cell in the fuel cell stack; I is the preset current density; N cell is the number of fuel cell stacks; Stoic is the excess coefficient of the stack.

[0025] Furthermore, the no-load hydrogen inlet pressure is determined according to the air flow rate and the preset first pressure increment, specifically:

[0026] Calculating the air pressure according to the flow-pressure conversion relationship and the air flow;

[0027] The no-load hydrogen gas inlet pressure is determined according to the air pressure and the preset first pressure increment; the no-load hydrogen gas inlet pressure is greater than the sum of the air pressure and the preset first pressure increment.

[0028] Further, the stepwise increase of the load current of the fuel cell stack and the control of the fuel cell system to enter a stepwise load purge state are specifically as follows:

[0029] gradually increasing the load current of the fuel cell stack according to a preset current increment;

[0030] Whenever the load current of the fuel cell stack increases by a preset current increment, the load hydrogen inlet pressure is determined according to the air flow and the preset second pressure increment;

[0031] Hydrogen is introduced into the fuel cell system according to the hydrogen loading stack pressure, so that the fuel cell system enters a step-by-step loading and purging state.

[0032] Furthermore, when the fuel cell system is in a stepwise load-purge state, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted or the fuel cell system is controlled to enter an open circuit purge state according to the detection result, specifically:

[0033] Real-time detection of the duration of the step-by-step load purge state of the fuel cell system;

[0034] When the duration of the step-by-step loading and purging state does not reach the preset second time, real-time detection of the fuel cell electrical tightness and whether the fuel cell stack has a single low fault is generated, and the loading current of the fuel cell stack is adjusted according to the detection result;

[0035] When the duration of the step-by-step load purge state reaches a preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and it is determined whether the fuel cell system enters an open circuit purge state based on the detection result.

[0036] Furthermore, when the duration of the step-by-step loading and purging state does not reach the preset second time, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the loading current of the fuel cell stack is adjusted according to the detection result, specifically:

[0037] When the duration of the step-by-step loading and purging state does not reach the preset second time, determining whether the electric density of the fuel cell reaches the preset current density;

[0038] If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated;

[0039] If the fuel cell electric density does not reach the preset current density and the fuel cell stack does not have a single low fault, increasing the load current of the fuel cell stack according to the preset current increment;

[0040] If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the current step-by-step load purge state of the fuel cell system is maintained.

[0041] Furthermore, when the duration of the step-by-step loading and purging state reaches a preset second time, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and according to the detection result, it is determined whether the fuel cell system enters an open circuit purging state, specifically:

[0042] When the duration of the step-by-step loading and purging state reaches a preset second time, determining whether the electric density of the fuel cell reaches a preset current density;

[0043] If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated;

[0044] If the fuel cell electrical density does not reach the preset current density and the fuel cell stack does not have a single low fault, the fuel cell system is controlled to enter a step-by-step load purge state again;

[0045] If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the fuel cell system is controlled to enter an open circuit purge state.

[0046] Accordingly, the present invention provides a single low fault troubleshooting device for a fuel cell system, comprising: a first purge control module, a second purge control module and a third purge control module;

[0047] The first purge control module is used to control the fuel cell stack to be in a no-load state and control the fuel cell system in which the fuel cell stack is located to enter an open-circuit purge state when it is determined that the fuel cell stack has a single low fault;

[0048] The second purge control module is used to gradually increase the load current of the fuel cell stack and control the fuel cell system to enter a step-by-step load purge state when the duration of the open circuit purge state of the fuel cell system reaches a preset first time;

[0049] The third purge control module is used to detect the fuel cell electrical density and whether there is a single low fault in the fuel cell stack in real time when the fuel cell system is in a step-by-step load purge state, generate a detection result, and adjust the load current of the fuel cell stack or control the fuel cell system to enter an open circuit purge state according to the detection result until the single low fault of the fuel cell stack is eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A schematic flow chart of an embodiment of a method for troubleshooting a single low fault of a fuel cell system provided by the present invention;

[0051] Figure 2 A schematic flow chart of another embodiment of a single low fault troubleshooting method for a fuel cell system provided by the present invention;

[0052] Figure 3 A schematic structural diagram of an embodiment of a single low fault troubleshooting device for a fuel cell system provided by the present invention. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] The flowcharts shown in the accompanying drawings are only examples and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may also be decomposed, combined or partially merged, so the actual execution order may change according to actual conditions.

[0055] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0056] Example 1

[0057] like Figure 1 FIG. 1 is a flow chart of an embodiment of a method for troubleshooting a single low fault of a fuel cell system provided by the present invention. The method includes steps 101 to 103, and each step is specifically as follows:

[0058] Step 101: When it is determined that a single low fault exists in a fuel cell stack, the fuel cell stack is controlled to be in a no-load state, and a fuel cell system in which the fuel cell stack is located is controlled to enter an open-circuit purge state.

[0059] Step 102: When the duration of the open-circuit purge state of the fuel cell system reaches a preset first time, gradually increase the load current of the fuel cell stack, and control the fuel cell system to enter a gradual load purge state.

[0060] Step 103: When the fuel cell system is in a stepwise load-purge state, the fuel cell electrical density and whether the fuel cell stack has a single-low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted according to the detection result or the fuel cell system is controlled to enter an open-circuit purge state until the single-low fault of the fuel cell stack is eliminated.

[0061] In an embodiment of the present invention, when it is determined that a single low fault exists in a fuel cell stack, the current loading behavior of the fuel cell stack is stopped, the fuel cell stack is controlled to be in a no-load state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open circuit purge state to purge out impurities blocked in the stack. Open circuit purge means purge without load, that is, under the condition that the fuel cell stack does not load current, hydrogen and air are respectively introduced into the anode and cathode of the fuel cell for purge. When performing open circuit purge, the fuel cell stack is not loaded, so a single low fault will not occur again. At this time, gas is introduced for purge to purge out impurities blocked in the stack.

[0062] In an embodiment of the present invention, a duration is preset for the open-circuit purge state of the fuel cell system. When the fuel cell system continues in the open-circuit purge state for a preset first time, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a step-by-step load purge state to further remove impurities in the stack. By increasing the load current of the fuel cell stack, the stack temperature of the fuel cell stack can be increased, thereby speeding up the purge work efficiency. Controlling the fuel cell system to enter a step-by-step load purge state, gradually increasing the load current of the fuel cell stack, and realizing a step-by-step load purge can perform a more comprehensive purge, further remove impurities in the stack, and thereby improve the efficiency of eliminating single low faults.

[0063] In the embodiment of the present invention, in the step-by-step loading and purging state, the fuel cell electrical density and the fuel cell stack are detected in real time to see if there is a single low fault, and the purging state of the fuel cell system is adjusted accordingly according to the detection result to eliminate the single low fault. By detecting the purging condition of the fuel cell system in real time and then reasonably adjusting the purging state of the fuel cell system, the purging efficiency can be effectively improved, thereby achieving a better purging effect.

[0064] In summary, the embodiment of the present invention provides a method for troubleshooting a single-low fault in a fuel cell system. When it is determined that a single-low fault exists in a fuel cell stack, the fuel cell stack is controlled to be in an unloaded state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open-circuit purge state; when the duration of the open-circuit purge state of the fuel cell system reaches a preset first time, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a step-by-step load purge state; when the fuel cell system is in a step-by-step load purge state, the fuel cell electrical density and whether the fuel cell stack has a single-low fault are detected in real time, and the load current of the fuel cell stack is adjusted according to the detection result or the fuel cell system is controlled to enter an open-circuit purge state until the single-low fault of the fuel cell stack is eliminated. The present invention can effectively improve the purge efficiency and the purge effect, thereby improving the efficiency of eliminating single-low faults.

[0065] Example 2

[0066] like Figure 1 FIG. 1 is a flow chart of an embodiment of a method for troubleshooting a single low fault of a fuel cell system provided by the present invention. The method includes steps 101 to 103, and each step is specifically as follows:

[0067] Step 101: When it is determined that a fuel cell stack has a single low fault, the fuel cell stack is controlled to be in a no-load state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open-circuit purge state.

[0068] Further, in the embodiment of the present invention, it is determined that the fuel cell stack has a single low fault, specifically:

[0069] Obtain the minimum single-chip voltage and average single-chip voltage of the fuel cell stack;

[0070] Calculating a voltage difference according to the minimum single-chip voltage and the average single-chip voltage;

[0071] comparing the voltage difference with a preset voltage threshold;

[0072] When the voltage difference is greater than the preset voltage threshold, it is determined that a single low fault exists in the fuel cell stack.

[0073] In an embodiment of the present invention, the cell voltage monitor (Cell Voltage Monitor, CVM) is used to detect the single-chip voltage of the fuel cell stack, and the real-time single-chip voltage minimum value and average value can be obtained to form the minimum single-chip voltage and average single-chip voltage of the fuel cell stack. According to the obtained minimum single-chip voltage and average single-chip voltage, the voltage difference between the two is calculated. The preset voltage threshold is obtained, and the calculated voltage difference is compared with the preset voltage threshold. If the voltage difference is greater than the preset voltage threshold, it is determined that the fuel cell stack has a single low fault. Among them, the preset voltage threshold can be provided by the stack supplier. Usually, when the voltage difference is greater than 200mV, the single-chip voltage is in a low state. Therefore, the preset voltage threshold can be set to be greater than 200mV.

[0074] In the embodiment of the present invention, when it is determined that a single low fault exists in the fuel cell stack, the fuel cell system is deloaded, the boost DC converter (DC Converter for Fuel Cell EV, DCF) in the fuel cell system is controlled to shut down, so that the fuel cell stack is in a no-load state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open circuit purge state. In the open circuit purge state, the fuel cell system is not loaded, and only a large flow rate purge is performed to ensure that the coolant or impurities blocked at the fuel cell stack plate can be blown out or effectively reduced.

[0075] Furthermore, in an embodiment of the present invention, the fuel cell system in which the fuel cell stack is located is controlled to enter an open circuit purge state, specifically:

[0076] Obtain basic data of fuel cell stack;

[0077] Calculating air flow rate according to basic data of the fuel cell stack;

[0078] Determine the no-load hydrogen inlet pressure according to the air flow rate and the preset first pressure increment;

[0079] Hydrogen is introduced into the fuel cell system where the fuel cell stack is located according to the no-load hydrogen inlet pressure, so that the fuel cell system enters an open-circuit purge state.

[0080] Furthermore, in an embodiment of the present invention, the air flow rate is calculated according to the basic data of the fuel cell stack, specifically:

[0081] Obtain the active area of ​​a single cell of the fuel cell stack, the number of fuel cell stack sheets, the preset current density and the excess coefficient of the fuel cell stack from the basic data of the fuel cell stack;

[0082] The air flow rate is calculated according to the active area of ​​the fuel cell stack, the number of fuel cell stacks, the preset current density and the stack excess coefficient. The specific formula is:

[0083] Flow air =0.0166*S bat *I*N cell *Stoic

[0084] Where, Flow air is the air flow rate; S bat is the active area of ​​a single cell in the fuel cell stack; I is the preset current density; N cell is the number of fuel cell stacks; Stoic is the excess coefficient of the stack.

[0085] In an embodiment of the present invention, the air flow rate can be calculated based on the active area of ​​a fuel cell stack, the number of fuel cell stacks, the preset current density and the stack excess coefficient data of the fuel cell stack. As an example, the preset current density I can be set to 1.0 and the stack excess coefficient can be set to 2.0 to ensure that there is enough flow to purge the stack plate flow channel.

[0086] Further, in an embodiment of the present invention, the no-load hydrogen inlet pressure is determined according to the air flow rate and the preset first pressure increment, specifically:

[0087] Calculating the air pressure according to the flow-pressure conversion relationship and the air flow;

[0088] The no-load hydrogen gas inlet pressure is determined according to the air pressure and the preset first pressure increment; the no-load hydrogen gas inlet pressure is greater than the sum of the air pressure and the preset first pressure increment.

[0089] In an embodiment of the present invention, the air pressure can be determined according to the flow-pressure conversion relationship and the calculated air flow. For example, the air pressure can be calculated using the formula (flow = pressure / resistance). Since the pressure difference between hydrogen and air needs to be limited to a certain range during the operation of the fuel cell stack, and the hydrogen pressure generally changes with the air pressure, and in order to ensure the gas concentration, the hydrogen pressure is generally greater than a certain value of the air pressure, so a preset first pressure increment can be set in advance, and the no-load hydrogen inlet pressure is set to be greater than the sum of the air pressure and the preset first pressure increment. Among them, for different fuel cell stacks, the preset first pressure increment is also different, and the preset first pressure increment can be set to 10kPa.

[0090] In an embodiment of the present invention, the fuel cell system is controlled to enter an open circuit purge state, and the anode drain valve can also be controlled to enter a fast-open state, that is, the opening time / closing time of the drain valve is greater than 1. For example, the drain valve is controlled to cycle from closed for 1 second to open for 2 seconds. In the fast-open state of the anode drain valve, the anode gas flow rate change can be effectively increased to improve the purge effect.

[0091] When the present invention determines that a single low fault exists in a fuel cell stack, the current loading behavior of the fuel cell stack is stopped, the fuel cell stack is controlled to be in a no-load state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open circuit purge state to purge out the impurities blocked in the stack. Open circuit purge means purge without load, that is, under the condition that the fuel cell stack does not pull current, hydrogen and air are respectively introduced into the anode and cathode of the fuel cell for purge. When performing open circuit purge, the fuel cell stack is not loaded, so a single low fault will not occur again. At this time, gas is introduced for purge to purge out the impurities blocked in the stack.

[0092] Step 102: When the duration of the open-circuit purge state of the fuel cell system reaches a preset first time, gradually increase the load current of the fuel cell stack, and control the fuel cell system to enter a gradual load purge state.

[0093] In the embodiment of the present invention, in order to prevent the possible damage to the fuel cell stack caused by the long-term open circuit voltage, a preset first time is set for the total duration of the open circuit purge state of the fuel cell system. The preset first time can be provided by the fuel cell stack supplier and is generally not more than 30 seconds.

[0094] In an embodiment of the present invention, when the duration of the open circuit purge state of the fuel cell system reaches a preset first time, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a gradual load purge state. In the gradual load purge state, the fuel cell system has a higher operating condition and is loaded slowly from a low load. After a certain period of operation, impurities in the flow channel of the fuel cell stack can be completely removed.

[0095] Furthermore, in an embodiment of the present invention, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a step-by-step load purge state, specifically:

[0096] gradually increasing the load current of the fuel cell stack according to a preset current increment;

[0097] Whenever the load current of the fuel cell stack increases by a preset current increment, the load hydrogen inlet pressure is determined according to the air flow and the preset second pressure increment;

[0098] Hydrogen is introduced into the fuel cell system according to the hydrogen loading stack pressure, so that the fuel cell system enters a step-by-step loading and purging state.

[0099] In the embodiment of the present invention, the operating conditions of the fuel cell system are preset, including the preset current increment, the preset current density and the stack excess coefficient for calculating the air flow, and the second pressure increment required for determining the pressure of the hydrogen gas entering the stack. In the step-by-step loading and purging state, the loading current of the fuel cell stack is gradually increased according to the preset current increment, and the hydrogen gas entering the stack pressure is recalculated whenever the loading current of the fuel cell stack changes.

[0100] In the embodiment of the present invention, compared with the no-load state, when the fuel cell stack is in a loaded state, the hydrogen pressure should be increased to ensure a better reflux flow, so the second pressure increment is set to be greater than the first pressure increment.

[0101] As an example of an embodiment of the present invention, the preset current density can be set to 1.0, and the stack excess coefficient can be set to 2.1, so as to calculate the air flow rate; based on the flow-pressure conversion relationship, the air pressure can be calculated according to the air flow rate; the second pressure increment can be set to 20kPa, so as to determine that the pressure of the hydrogen gas entering the stack is greater than the sum of the air pressure and the preset second pressure increment. The electric density of the preset current increment is set to 0.1, and the load current of the fuel cell stack is controlled to start from 0, and the preset current increment with an electric density of 0.1 is increased each time.

[0102] In an embodiment of the present invention, the fuel cell system is controlled to enter a step-by-step load purge state, and the fuel cell coolant temperature can be controlled to maintain in a range close to the upper temperature limit, thereby improving the purge efficiency by increasing the temperature. The anode drain valve is also controlled to enter a fast-open state, that is, the opening time / closing time of the drain valve is greater than 1. For example, the drain valve is controlled to cycle between closing for 1s and opening for 2s. In the fast-open state of the anode drain valve, the anode gas flow rate change can be effectively increased, thereby improving the purge effect.

[0103] The present invention pre-sets a duration for the open-circuit purge state of the fuel cell system. When the fuel cell system continues to be in the open-circuit purge state for a preset first time, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a step-by-step load purge state to further remove impurities in the stack. By increasing the load current of the fuel cell stack, the stack temperature of the fuel cell stack can be increased, thereby speeding up the purge work efficiency. Controlling the fuel cell system to enter a step-by-step load purge state, gradually increasing the load current of the fuel cell stack, and realizing a step-by-step load purge can perform a more comprehensive purge, further remove impurities in the stack, thereby improving the efficiency of eliminating single low faults.

[0104] Step 103: When the fuel cell system is in a stepwise load-purge state, the fuel cell electrical density and whether the fuel cell stack has a single-low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted according to the detection result or the fuel cell system is controlled to enter an open-circuit purge state until the single-low fault of the fuel cell stack is eliminated.

[0105] Further, in an embodiment of the present invention, when the fuel cell system is in a stepwise load-purge state, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted or the fuel cell system is controlled to enter an open circuit purge state according to the detection result, specifically:

[0106] Real-time detection of the duration of the step-by-step load purge state of the fuel cell system;

[0107] When the duration of the step-by-step loading and purging state does not reach the preset second time, real-time detection of the fuel cell electrical tightness and whether the fuel cell stack has a single low fault is generated, and the loading current of the fuel cell stack is adjusted according to the detection result;

[0108] When the duration of the step-by-step load purge state reaches a preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and it is determined whether the fuel cell system enters an open circuit purge state based on the detection result.

[0109] In an embodiment of the present invention, a preset second time is set for the total duration of the step-by-step load purge state of the fuel cell system. During the preset second time, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted according to the detection result, so that the fuel cell system is still in the step-by-step load purge state. When the duration of the step-by-step load purge state reaches the preset second time, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and according to the detection result, it is determined whether the fuel cell system will enter the open circuit purge state or the step-by-step load purge state next, or exit the purge state and enter the normal operation state.

[0110] Further, in an embodiment of the present invention, when the duration of the step-by-step loading and purging state does not reach the preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the loading current of the fuel cell stack is adjusted according to the detection result, specifically:

[0111] When the duration of the step-by-step loading and purging state does not reach the preset second time, determining whether the electric density of the fuel cell reaches the preset current density;

[0112] If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated;

[0113] If the fuel cell electric density does not reach the preset current density and the fuel cell stack does not have a single low fault, increasing the load current of the fuel cell stack according to the preset current increment;

[0114] If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the current step-by-step load purge state of the fuel cell system is maintained.

[0115] In the embodiment of the present invention, the fuel cell electrical density is detected in real time within the preset second time, and the fuel cell electrical density is used to determine whether the fuel cell system has completed the single low fault elimination and whether it can exit the gradual load purge state. When the detected fuel cell electrical density reaches the preset current density, it can be determined that the single low fault of the fuel cell stack has been eliminated, and at this time, the fuel cell system is controlled to exit the gradual load purge state and enter the normal operation state.

[0116] In an embodiment of the present invention, if the detected fuel cell electrical density does not reach the preset current density, it is determined whether the fuel cell stack has a single low fault at this time. If there is no single low fault, the load current of the fuel cell stack is increased according to the preset current increment, and the fuel cell system is controlled to continue to perform load purge. If there is a single low fault, the current load current of the fuel cell stack is maintained, and the fuel cell system is controlled to continue to perform load purge.

[0117] In an embodiment of the present invention, a method for determining whether a fuel cell stack has a single low fault is to obtain the lowest single-chip voltage and the average single-chip voltage of the fuel cell stack in real time, calculate the voltage difference between the lowest single-chip voltage and the average single-chip voltage, and determine that the fuel cell stack has a single low fault when the voltage difference is greater than a preset voltage threshold. The preset voltage threshold can be set to different levels according to the load current of the fuel cell stack, such as 600mV, 400mV, and 200mV.

[0118] Further, in an embodiment of the present invention, when the duration of the step-by-step loading and purging state reaches a preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and it is determined whether the fuel cell system enters an open circuit purging state based on the detection result, specifically:

[0119] When the duration of the step-by-step loading and purging state reaches a preset second time, determining whether the electric density of the fuel cell reaches a preset current density;

[0120] If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated;

[0121] If the fuel cell electrical density does not reach the preset current density and the fuel cell stack does not have a single low fault, the fuel cell system is controlled to enter a step-by-step load purge state again;

[0122] If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the fuel cell system is controlled to enter an open circuit purge state.

[0123] In an embodiment of the present invention, when the duration of the step-by-step load purge state reaches a preset second time, the fuel cell electrical density is detected in real time, and the fuel cell electrical density is used to determine whether the fuel cell system has completed the single low fault elimination and whether it can exit the step-by-step load purge state. When the detected fuel cell electrical density reaches a preset current density, it can be determined that the single low fault of the fuel cell stack has been eliminated, and at this time, the fuel cell system is controlled to exit the step-by-step load purge state and enter the normal operation state.

[0124] In an embodiment of the present invention, if the detected fuel cell electric density does not reach the preset current density, it is determined whether the fuel cell stack has a single low fault at this time. If there is no single low fault, the fuel cell system is controlled to continue to load purge, and the duration of the gradual load purge state is recalculated. If there is a single low fault, the fuel cell stack is controlled to be in an unloaded state, and the fuel cell system is controlled to enter an open circuit purge state.

[0125] In an embodiment of the present invention, a method for determining whether a fuel cell stack has a single low fault is to obtain the lowest single-chip voltage and the average single-chip voltage of the fuel cell stack in real time, calculate the voltage difference between the lowest single-chip voltage and the average single-chip voltage, and determine that the fuel cell stack has a single low fault when the voltage difference is greater than a preset voltage threshold. The preset voltage threshold can be set to different levels according to the load current of the fuel cell stack, such as 600mV, 400mV, and 200mV.

[0126] The present invention detects the fuel cell electrical density and whether the fuel cell stack has a single low fault in real time during the step-by-step loading and purging state, and adjusts the purging state of the fuel cell system accordingly according to the detection result to eliminate the single low fault. By detecting the purging condition of the fuel cell system in real time and then reasonably adjusting the purging state of the fuel cell system, the purging efficiency can be effectively improved, thereby achieving a better purging effect.

[0127] As an example of an embodiment of the present invention, see Figure 2 , is a flow chart of another embodiment of the single-low fault troubleshooting method for the fuel cell system provided by the present invention. In the fuel cell system, the CVM is used to obtain the average single-chip voltage and the lowest single-chip voltage of the fuel cell stack, and the voltage difference between the average single-chip voltage and the lowest single-chip voltage is calculated. If the voltage difference is greater than the preset voltage threshold, it is determined that a single-low fault has occurred, and the DCF is controlled to gradually reduce the load and shut down, and the load current of the fuel cell stack is reduced to 0, and an open circuit purge is performed. When the duration of the open circuit purge state meets the preset first time, the gradual load purge state is entered, and the operating conditions of the fuel cell system are set to the operating conditions under high electrical density, and 0.1A / cm is added to the fuel cell stack each time. 2 The current corresponding to the electric density is 40A. When the duration of the step-by-step loading and purge state meets the preset second time, it is determined whether a single low fault occurs at this time. If so, purge at the current current point of the fuel cell stack; if not, continue to increase the fuel cell stack by 0.1A / cm 2 Repeat this step until the fuel cell stack reaches 1.0A / cm 2 The current corresponding to the electrical density.

[0128] In summary, the embodiment of the present invention provides a method for troubleshooting a single-low fault in a fuel cell system. When it is determined that a single-low fault exists in a fuel cell stack, the fuel cell stack is controlled to be in an unloaded state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open-circuit purge state; when the duration of the open-circuit purge state of the fuel cell system reaches a preset first time, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a step-by-step load purge state; when the fuel cell system is in a step-by-step load purge state, the fuel cell electrical density and whether the fuel cell stack has a single-low fault are detected in real time, and the load current of the fuel cell stack is adjusted according to the detection result or the fuel cell system is controlled to enter an open-circuit purge state until the single-low fault of the fuel cell stack is eliminated. The present invention can effectively improve the purge efficiency and the purge effect, thereby improving the efficiency of eliminating single-low faults.

[0129] Example 3

[0130] See also Figure 3 , is a structural schematic diagram of an embodiment of a single low fault troubleshooting device for a fuel cell system provided by the present invention, the device includes a first purge control module, a second purge control module and a third purge control module;

[0131] The first purge control module 201 is used to control the fuel cell stack to be in a no-load state and control the fuel cell system in which the fuel cell stack is located to enter an open-circuit purge state when it is determined that the fuel cell stack has a single low fault;

[0132] The second purge control module 202 is used to gradually increase the load current of the fuel cell stack and control the fuel cell system to enter a step-by-step load purge state when the duration of the open circuit purge state of the fuel cell system reaches a preset first time;

[0133] The third purge control module 203 is used to detect the fuel cell electrical density and whether there is a single low fault in the fuel cell stack in real time when the fuel cell system is in a step-by-step load purge state, generate a detection result, and adjust the load current of the fuel cell stack or control the fuel cell system to enter an open circuit purge state according to the detection result until the single low fault of the fuel cell stack is eliminated.

[0134] Further, in the embodiment of the present invention, it is determined that the fuel cell stack has a single low fault, specifically:

[0135] Obtain the minimum single-chip voltage and average single-chip voltage of the fuel cell stack;

[0136] Calculating a voltage difference according to the minimum single-chip voltage and the average single-chip voltage;

[0137] comparing the voltage difference with a preset voltage threshold;

[0138] When the voltage difference is greater than the preset voltage threshold, it is determined that a single low fault exists in the fuel cell stack.

[0139] Furthermore, in an embodiment of the present invention, the fuel cell system in which the fuel cell stack is located is controlled to enter an open circuit purge state, specifically:

[0140] Obtain basic data of fuel cell stack;

[0141] Calculating air flow rate according to basic data of the fuel cell stack;

[0142] Determine the no-load hydrogen inlet pressure according to the air flow rate and the preset first pressure increment;

[0143] Hydrogen is introduced into the fuel cell system where the fuel cell stack is located according to the no-load hydrogen inlet pressure, so that the fuel cell system enters an open-circuit purge state.

[0144] Furthermore, in an embodiment of the present invention, the air flow rate is calculated according to the basic data of the fuel cell stack, specifically:

[0145] Obtain the active area of ​​a single cell of the fuel cell stack, the number of fuel cell stack sheets, the preset current density and the excess coefficient of the fuel cell stack from the basic data of the fuel cell stack;

[0146] The air flow rate is calculated according to the active area of ​​the fuel cell stack, the number of fuel cell stacks, the preset current density and the stack excess coefficient. The specific formula is:

[0147] Flow air =0.0166*S bat *I*N cell *Stoic

[0148] In the formula, Flow air is the air flow rate; S bat is the active area of ​​a single cell in the fuel cell stack; I is the preset current density; N cell is the number of fuel cell stacks; Stoic is the excess coefficient of the stack.

[0149] Further, in an embodiment of the present invention, the no-load hydrogen inlet pressure is determined according to the air flow rate and the preset first pressure increment, specifically:

[0150] Calculating the air pressure according to the flow-pressure conversion relationship and the air flow;

[0151] The no-load hydrogen gas inlet pressure is determined according to the air pressure and the preset first pressure increment; the no-load hydrogen gas inlet pressure is greater than the sum of the air pressure and the preset first pressure increment.

[0152] Furthermore, in an embodiment of the present invention, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a step-by-step load purge state, specifically:

[0153] gradually increasing the load current of the fuel cell stack according to a preset current increment;

[0154] Whenever the load current of the fuel cell stack increases by a preset current increment, the load hydrogen gas inlet pressure is determined according to the air flow and the preset second pressure increment;

[0155] Hydrogen is introduced into the fuel cell system according to the hydrogen loading stack pressure, so that the fuel cell system enters a step-by-step loading and purging state.

[0156] Further, in an embodiment of the present invention, when the fuel cell system is in a stepwise load-purge state, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted or the fuel cell system is controlled to enter an open circuit purge state according to the detection result, specifically:

[0157] Real-time detection of the duration of the step-by-step load purge state of the fuel cell system;

[0158] When the duration of the step-by-step loading and purging state does not reach the preset second time, real-time detection of the fuel cell electrical tightness and whether the fuel cell stack has a single low fault is generated, and the loading current of the fuel cell stack is adjusted according to the detection result;

[0159] When the duration of the step-by-step load purge state reaches a preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and it is determined whether the fuel cell system enters an open circuit purge state based on the detection result.

[0160] Further, in an embodiment of the present invention, when the duration of the step-by-step loading and purging state does not reach the preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the loading current of the fuel cell stack is adjusted according to the detection result, specifically:

[0161] When the duration of the step-by-step loading and purging state does not reach the preset second time, determining whether the electric density of the fuel cell reaches the preset current density;

[0162] If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated;

[0163] If the fuel cell electric density does not reach the preset current density and the fuel cell stack does not have a single low fault, increasing the load current of the fuel cell stack according to the preset current increment;

[0164] If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the current step-by-step load purge state of the fuel cell system is maintained.

[0165] Further, in an embodiment of the present invention, when the duration of the step-by-step loading and purging state reaches a preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and it is determined whether the fuel cell system enters an open circuit purging state based on the detection result, specifically:

[0166] When the duration of the step-by-step loading and purging state reaches a preset second time, determining whether the electric density of the fuel cell reaches a preset current density;

[0167] If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated;

[0168] If the fuel cell electrical density does not reach the preset current density and the fuel cell stack does not have a single low fault, the fuel cell system is controlled to enter a step-by-step load purge state again;

[0169] If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the fuel cell system is controlled to enter an open circuit purge state.

[0170] In summary, the embodiment of the present invention provides a single-low fault troubleshooting device for a fuel cell system, which is based on the organic combination of modules. When it is determined that a single-low fault exists in a fuel cell stack, the fuel cell stack is controlled to be in an unloaded state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open-circuit purge state; when the duration of the open-circuit purge state of the fuel cell system reaches a preset first time, the load current of the fuel cell stack is gradually increased, and the fuel cell system is controlled to enter a step-by-step load purge state; when the fuel cell system is in a step-by-step load purge state, the fuel cell electrical density and whether the fuel cell stack has a single-low fault are detected in real time, and the load current of the fuel cell stack is adjusted according to the detection result or the fuel cell system is controlled to enter an open-circuit purge state until the single-low fault of the fuel cell stack is eliminated. The present invention can effectively improve the purge efficiency and the purge effect, thereby improving the efficiency of eliminating single-low faults.

[0171] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. It is particularly pointed out that for those skilled in the art, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for troubleshooting a single low fault of a fuel cell system, characterized in that: include: When it is determined that a single low fault exists in the fuel cell stack, the fuel cell stack is controlled to be in a no-load state, and the fuel cell system in which the fuel cell stack is located is controlled to enter an open circuit purge state; When the duration of the open circuit purge state of the fuel cell system reaches a preset first time, gradually increasing the load current of the fuel cell stack, and controlling the fuel cell system to enter a gradual load purge state; When the fuel cell system is in a step-by-step load-purge state, the fuel cell electrical density and whether the fuel cell stack has a single-low fault are detected in real time, a detection result is generated, and the load current of the fuel cell stack is adjusted or the fuel cell system is controlled to enter an open-circuit purge state according to the detection result until the single-low fault of the fuel cell stack is eliminated.

2. The single low fault troubleshooting method of the fuel cell system according to claim 1, characterized in that: The determination that a single low fault exists in the fuel cell stack is specifically as follows: Obtain the minimum single-chip voltage and average single-chip voltage of the fuel cell stack; Calculating a voltage difference according to the minimum single-chip voltage and the average single-chip voltage; comparing the voltage difference with a preset voltage threshold; When the voltage difference is greater than the preset voltage threshold, it is determined that a single low fault exists in the fuel cell stack.

3. The single low fault troubleshooting method of the fuel cell system according to claim 2, characterized in that: The controlling the fuel cell system in which the fuel cell stack is located to enter an open circuit purge state is specifically: Obtain basic data of fuel cell stack; Calculating air flow rate according to basic data of the fuel cell stack; Determine the no-load hydrogen inlet pressure according to the air flow rate and the preset first pressure increment; Hydrogen is introduced into the fuel cell system where the fuel cell stack is located according to the no-load hydrogen inlet pressure, so that the fuel cell system enters an open-circuit purge state.

4. The single low fault troubleshooting method of the fuel cell system according to claim 3, characterized in that: The air flow rate is calculated according to the basic data of the fuel cell stack, specifically: Obtain the active area of ​​a single cell of the fuel cell stack, the number of fuel cell stack sheets, the preset current density and the excess coefficient of the fuel cell stack from the basic data of the fuel cell stack; The air flow rate is calculated according to the active area of ​​the fuel cell stack, the number of fuel cell stacks, the preset current density and the stack excess coefficient. The specific formula is: Flow air =0.0166*S bat *I*N cell *Stoic Where, Flow air is the air flow rate; S bat is the active area of ​​a single cell in the fuel cell stack; I is the preset current density; N cell is the number of fuel cell stacks; Stoic is the excess coefficient of the stack.

5. The single low fault troubleshooting method of the fuel cell system according to claim 4, characterized in that: The step of determining the no-load hydrogen inlet pressure according to the air flow rate and the preset first pressure increment is specifically: Calculating the air pressure according to the flow-pressure conversion relationship and the air flow; The no-load hydrogen gas inlet pressure is determined according to the air pressure and the preset first pressure increment; the no-load hydrogen gas inlet pressure is greater than the sum of the air pressure and the preset first pressure increment.

6. The single low fault troubleshooting method of the fuel cell system according to claim 5, characterized in that: The stepwise increasing of the load current of the fuel cell stack and controlling the fuel cell system to enter a stepwise load purge state is specifically as follows: gradually increasing the load current of the fuel cell stack according to a preset current increment; Whenever the load current of the fuel cell stack increases by a preset current increment, the load hydrogen gas inlet pressure is determined according to the air flow and the preset second pressure increment; Hydrogen is introduced into the fuel cell system according to the hydrogen loading stack pressure, so that the fuel cell system enters a step-by-step loading and purging state.

7. The single low fault troubleshooting method of the fuel cell system according to claim 6, characterized in that: When the fuel cell system is in a step-by-step loading and purging state, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the loading current of the fuel cell stack is adjusted or the fuel cell system is controlled to enter an open circuit purging state according to the detection result, specifically: Real-time detection of the duration of the step-by-step load purge state of the fuel cell system; When the duration of the step-by-step loading and purging state does not reach the preset second time, real-time detection of the fuel cell electrical tightness and whether the fuel cell stack has a single low fault is generated, and the loading current of the fuel cell stack is adjusted according to the detection result; When the duration of the step-by-step load purge state reaches a preset second time, the fuel cell electrical tightness and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and it is determined whether the fuel cell system enters an open circuit purge state based on the detection result.

8. The single low fault troubleshooting method of the fuel cell system according to claim 7, characterized in that: When the duration of the step-by-step loading and purging state does not reach the preset second time, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and the loading current of the fuel cell stack is adjusted according to the detection result, specifically: When the duration of the step-by-step loading and purging state does not reach the preset second time, determining whether the electric density of the fuel cell reaches the preset current density; If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated; If the fuel cell electric density does not reach the preset current density and the fuel cell stack does not have a single low fault, increasing the load current of the fuel cell stack according to the preset current increment; If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the current step-by-step load purge state of the fuel cell system is maintained.

9. The single low fault troubleshooting method of the fuel cell system according to claim 7, characterized in that: When the duration of the step-by-step loading and purging state reaches a preset second time, the fuel cell electrical density and whether the fuel cell stack has a single low fault are detected in real time, a detection result is generated, and whether the fuel cell system enters an open circuit purging state is determined according to the detection result, specifically: When the duration of the step-by-step loading and purging state reaches a preset second time, determining whether the electric density of the fuel cell reaches a preset current density; If the fuel cell electric density reaches a preset current density, the fuel cell system is controlled to exit the step-by-step load purge state, and it is determined that the single low fault of the fuel cell stack has been eliminated; If the fuel cell electrical density does not reach the preset current density and the fuel cell stack does not have a single low fault, the fuel cell system is controlled to enter a step-by-step load purge state again; If the fuel cell electrical density does not reach the preset current density and a single low fault exists in the fuel cell stack, the fuel cell system is controlled to enter an open circuit purge state.

10. A single low fault troubleshooting device for a fuel cell system, characterized in that: include: a first purge control module, a second purge control module, and a third purge control module; The first purge control module is used to control the fuel cell stack to be in a no-load state and control the fuel cell system in which the fuel cell stack is located to enter an open-circuit purge state when it is determined that the fuel cell stack has a single low fault; The second purge control module is used to gradually increase the load current of the fuel cell stack and control the fuel cell system to enter a step-by-step load purge state when the duration of the open circuit purge state of the fuel cell system reaches a preset first time; The third purge control module is used to detect the fuel cell electrical density and whether there is a single low fault in the fuel cell stack in real time when the fuel cell system is in a step-by-step load purge state, generate a detection result, and adjust the load current of the fuel cell stack or control the fuel cell system to enter an open circuit purge state according to the detection result until the single low fault of the fuel cell stack is eliminated.

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