Fuel cell system switch detection method and fuel cell system

Abstract

The switch detection method for the fuel cell system comprises the following detection steps executed in the power-on or power-off process of a direct-current voltage converter of the fuel cell system: switching on a switch in a power supply line between the direct-current voltage converter and a power cell; recording a switch upstream side voltage and a switch downstream side voltage in the power supply line; integrating the absolute value of the difference value between the switch upstream side voltage and the switch downstream side voltage over time in a set time period to obtain an integrated value; judging whether the integral value is greater than a preset threshold value or not; if the integral value is greater than or equal to the threshold value, determining that the switch has no adhesion fault; and if the integral value is smaller than the threshold value, determining that the switch has an adhesion fault.

Description

Technical Field

[0001] The present application relates to a switch detection method for a fuel cell system and a fuel cell system using the method. Background Art

[0002] In a fuel cell system, the fuel cell stack and the power battery (high-voltage battery) are connected via a DC / DC converter, enabling the fuel cell stack to charge the power battery. The output of the DC / DC converter is connected to the power battery via a power supply circuit. A switch is provided in the power supply circuit to control the power supply circuit by opening and closing the switch.

[0003] In some cases, especially when a fault occurs, it is necessary to open the switch to disconnect the electrical connection between the DC / DC converter and the power battery. However, if the switch is stuck, it may not be possible to open the switch in time. For this reason, it is usually necessary to perform a sticking test on the switch when the DC / DC converter is powered on or off, that is, during the power-on or power-off process of the DC / DC converter, the switch is turned on, and then after a preset time (for example, 2 seconds), the difference between the voltage upstream of the switch and the voltage downstream of the switch in the power supply line is measured. If the absolute value of the difference is greater than or equal to a preset threshold value, for example, 15V, within the anti-shake time window (for example, 50 milliseconds), it is judged that the switch can be opened normally; if the absolute value of the difference is less than the preset threshold value within the anti-shake time window, it is judged that the switch is stuck and cannot be opened normally.

[0004] In this existing switch sticking detection method, whether the switch can be opened normally is judged only by the difference between the upstream and downstream voltages of the switch within the anti-shake time window. However, in the event of switch sticking, the voltage downstream of the switch (i.e., the voltage on the power battery side) may change in different forms, causing the difference between the upstream and downstream voltages of the switch within the anti-shake time window to be greater than the preset threshold, thereby mistakenly judging that the switch can be opened normally. Therefore, the reliability of this existing switch sticking detection method needs to be improved. Summary of the Invention

[0005] The present application aims to provide a solution that can more reliably detect switch sticking failures in a fuel cell system.

[0006] According to one aspect of the present application, a switch detection method for a fuel cell system is provided. The fuel cell system includes a fuel cell stack, a DC voltage converter, and a power battery. The DC voltage converter is connected to the power battery via a power supply line. The power supply line is provided with a switch for controlling the connection and disconnection between the DC voltage converter and the power battery. The switch detection method includes the following detection steps performed during powering on or off of the DC voltage converter:

[0007] turning on the switch;

[0008] Recording a voltage on an upstream side of a switch and a voltage on a downstream side of a switch in the power supply line;

[0009] Integrating the absolute value of the difference between the voltage on the upstream side of the switch and the voltage on the downstream side of the switch with respect to time within a set period of time to obtain an integral value;

[0010] Determine whether the integral value is greater than a preset threshold; if the integral value is greater than or equal to the threshold, determine that the switch does not have a sticking fault; if the integral value is less than the threshold, determine that the switch has a sticking fault.

[0011] In another aspect, the present application provides a fuel cell system comprising:

[0012] A fuel cell stack, a DC voltage converter, and a power battery, wherein the DC voltage converter is connected to the power battery via a power supply line, and a switch is provided in the power supply line for controlling the connection and disconnection between the DC voltage converter and the power battery; and

[0013] A control unit is configured to at least control the operation of the fuel cell stack, the DC voltage converter, the power battery, and the opening and closing of the switch, and is configured to be able to execute the switch detection method of the present application to detect the switch.

[0014] According to the fuel cell system switch detection method of the present application, by integrating the difference between the upstream and downstream voltages of the switch within a period of time, it is determined whether the switch has a adhesion fault based on the integrated value. This method is suitable for scenarios where the voltage downstream of the switch changes in different forms when a adhesion fault occurs, and the detection reliability is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The foregoing and other aspects of the present application will be more fully understood through the following detailed description made with reference to the accompanying drawings, in which:

[0016] Figure 1 is a schematic diagram of a fuel cell system according to one embodiment of the present application;

[0017] Figure 2 is a graph showing the voltage changes upstream and downstream of the switch when the fuel cell system is in the DC / DC converter power-off state;

[0018] Figure 3 is a graph showing the voltage changes upstream and downstream of the switch when the fuel cell system is in the DC / DC converter power-on state;

[0019] Figure 4 is an exemplary flow chart of the switch detection method of the fuel cell system. DETAILED DESCRIPTION

[0020] The present application relates generally to fuel cell systems. Figure 1 An exemplary embodiment of the fuel cell system is shown in FIG. The fuel cell system includes a fuel cell stack 1, a direct current voltage converter (DC / DC converter) 2, a power battery 3, and a control unit 4. Among them, the DC / DC converter 2 is arranged between the fuel cell stack 1 and the power battery 3, and is used to adjust the electric energy from the fuel cell stack 1 to be compatible with the input power supply (charging power supply) of the power battery 3 so as to charge the power battery 3. The power battery 3 and the fuel cell stack 1 can be used alone or in combination as a driving source for equipment (such as a vehicle) that adopts the fuel cell system. For example, when used in a vehicle, the power battery 3 and the fuel cell stack 1 can be used alone or in combination to supply power to the drive motor of the vehicle according to the driving strategy of the vehicle. The power battery 3 can also be called a high-voltage battery to distinguish it from the auxiliary battery (low-voltage battery) in the equipment used to supply power to the control system.

[0021] The input of the DC / DC converter 2 is connected to the output of the fuel cell stack 1. The output of the DC / DC converter 2 is connected to the input of the power battery 3 via a power supply circuit. The power supply circuit includes a positive power supply circuit L1 connected between the positive output of the DC / DC converter 2 and the positive input of the power battery 3, and a negative power supply circuit L2 connected between the negative output of the DC / DC converter 2 and the negative input of the power battery 3.

[0022] Switches are provided in the power supply circuits to control the on / off connection between the DC / DC converter 2 and the power battery 3. In the illustrated example, a switch Cp is provided in the positive power supply circuit L1, and a switch Cn is provided in the negative power supply circuit L2. The switches may be contactors or other forms.

[0023] The control unit 4 is configured to control at least the operation of the fuel cell stack 1, the DC / DC converter 2, the power battery 3 and the switch, including adjusting the steady-state output voltage and power of the DC / DC converter 2, controlling the opening and closing of the switch, etc.

[0024] In addition, the control unit 4 also obtains the switch upstream voltage Vin and the switch downstream voltage Vout between the positive power supply line L1 and the negative power supply line L2. The upstream side of the switch refers to the side of the switch connected to the DC / DC converter 2, and the downstream side of the switch refers to the side of the switch connected to the power battery 3. Specifically, the switch upstream voltage Vin is measured between the positive power supply line L1 upstream of the switch Cp and the negative power supply line L2 upstream of the switch Cn, while the switch downstream voltage Vout is measured between the positive power supply line L1 downstream of the switch Cp and the negative power supply line L2 downstream of the switch Cn.

[0025] In addition, a resistor / capacitor (not shown) may be connected between the positive power supply line L1 and the negative power supply line L2 near the output end of the DC / DC converter 2; in this case, the measurement point of the voltage Vin on the upstream side of the switch should be taken from a position in the power supply line downstream of the resistor / capacitor, that is, a position between the resistor / capacitor and the switch.

[0026] exist Figure 1 During operation of the fuel cell system shown, if the fuel cell system itself or a device employing the fuel cell system experiences a fault, the control unit 4 must promptly shut down the DC / DC converter 2 and open switches Cp and Cn to disconnect the power supply line, thereby stopping the supply of electrical energy from the fuel cell stack 1 to the power battery 3 via the DC / DC converter 2. However, if switches Cp and Cn become stuck, they may not be opened promptly and correctly.

[0027] To this end, in accordance with safety standards, this application proposes a switch detection method applicable to this fuel cell system. During power-up or power-down of the DC / DC converter, one of the switches (i.e., the switch under test) is opened while the other remains closed to perform sticking detection. This diagnostic method can be executed in the control unit 4.

[0028] The switch detection method of the present application is based on the following understanding: when a DC / DC converter is powered on or off, the voltage Vout on the downstream side of the switch may change in different forms after a switch is turned on, as described below.

[0029] First refer to Figure 2 Describes the various changes that may occur in the downstream voltage Vout after the switch under test is turned on during the power-off operation of the DC / DC converter. Figure 2In the figure, the horizontal axis represents time t, where t1 represents the time when the switch under test is opened. The vertical axis represents voltage V, where V0 represents the steady-state output voltage of the DC / DC converter 2 (adjustable by the control unit 4). The curves in the figure represent the upstream voltage Vin and various possible downstream voltages Vout. At time t1, the control unit 4 shuts down the DC / DC converter 2 and simultaneously (or nearly simultaneously, for example, slightly before or after time t1) opens the switch under test, while the other switch remains closed. The control unit 4 monitors the changes in the upstream voltage Vin and the downstream voltage Vout over time. Starting from time t1, the upstream voltage Vin decreases in a roughly linear manner from the steady-state output voltage V0 of the DC / DC converter 2 to zero. On the other hand, under normal circumstances, the downstream voltage (represented by the curve Vout1) remains approximately constant at V0 (possibly with a slight decay), indicating that the switch under test is opening normally. However, in some cases, the downstream voltage (represented by the curve Vout2) fluctuates downward starting from time t1. In other cases, the downstream voltage (represented by curve Vout3) decreases from time t1 at a slope similar to that of the upstream voltage Vin. The situations represented by curves Vout2 and Vout3 are usually related to switch sticking.

[0030] Next, refer to Figure 3 This section describes various possible changes in the downstream voltage Vout after the switch under test is opened during DC / DC converter power-up. At time t1, control unit 4 turns on DC / DC converter 2 and simultaneously (or nearly simultaneously, for example, slightly before or after time t1) opens the switch under test, while the other switch remains closed. Control unit 4 monitors the changes in upstream voltage Vin and downstream voltage Vout over time. Starting at time t1, upstream voltage Vin increases approximately linearly from 0 until reaching the steady-state output voltage V0 of DC / DC converter 2. On the other hand, under normal circumstances, the downstream voltage (represented by curve Vout1) remains approximately constant at 0, indicating that the switch under test is opening normally. However, in some cases, the downstream voltage (represented by curve Vout2) fluctuates and rises starting at time t1. In other cases, the downstream voltage (represented by curve Vout3) rises starting at time t1 at a similar slope to the upstream voltage Vin. The situations represented by curves Vout2 and Vout3 are generally associated with switch sticking.

[0031] In the switch sticking detection performed during the power-on or power-off process of a DC / DC converter, if the difference between the upstream and downstream voltages of the switch at a certain time is greater than or equal to a certain threshold value to determine whether the switch can be opened normally and there is no sticking fault, then switch sticking will often be missed in the case represented by curve Vout3 (the downstream voltage rises or falls in a fluctuating manner). There is also a certain possibility of missing the switch sticking in the case represented by curve Vout2 (the downstream voltage rises or falls with a slope similar to that of the upstream voltage).

[0032] To ensure that sticking of the switch under test can be correctly detected in all variations of the downstream voltage Vout during switch sticking detection performed during the power-up or power-down process of a DC / DC converter, the switch detection method of the present application determines whether the switch under test can be normally opened by determining whether the integral of the absolute value of the voltage difference between the upstream and downstream sides of the switch under test over time within a set period Δt after the switch under test is turned on is greater than a preset threshold value Vth, that is:

[0033] If the integral value of |Vin-Vout| in the period Δt is ≥ Vth, it is determined that the switch under test can be opened normally; if the integral value of |Vin-Vout| in the period Δt is <Vth,则判断受测开关存在粘连,不能正常打开。

[0034] The starting point and length of the time period Δt, and the size of the threshold value Vth are all calibrable and / or adjustable. The starting point of the time period Δt is usually set to time t1 when the tested switch is opened in the switch adhesion detection, or slightly later than time t1 (for example, about 0.5 seconds later than time t1). The time period Δt can be specifically set based on different switch (contactor) models, for example, it can usually be set to 3 seconds to 8 seconds, preferably about 5 seconds. The threshold value Vth can also be specifically set based on different switch (contactor) models, for example, it can usually be set to 50 volts·seconds to 120 volts·seconds, preferably about 85 volts·seconds. In addition, the setting value of the threshold value Vth is also positively correlated with the value of the time period Δt, that is, the longer the time period Δt, the larger the threshold value Vth.

[0035] An exemplary process of the switch detection method applicable to the fuel cell system of the present application is as follows: Figure 4 The method can be executed by the aforementioned control unit 4.

[0036] In this process, in step S1 , the DC / DC converter is started (ie, powered on) or shut down (ie, powered off), and the tested switch of the fuel cell system is opened (the other switch remains closed).

[0037] Next, in step S2 , the voltage on the upstream side of the switch under test and the voltage on the downstream side of the switch under test in the power supply line of the fuel cell system are recorded.

[0038] Next, in step S3 , the absolute value of the difference between the voltage on the upstream side of the switch under test and the voltage on the downstream side of the switch under test is integrated with respect to time within a set period Δt.

[0039] Next, in step S4, it is determined whether the absolute value of the difference between the upstream and downstream voltages of the tested switch is greater than the preset threshold value Vth over the time period Δt; if the judgment result is yes, go to step S5; if the judgment result is no, go to step S6.

[0040] In step S5 , it is determined that the switch under test can be opened normally and does not have a sticking fault, and the switch under test passes the switch sticking test.

[0041] In step S6 , it is determined that the switch under test cannot be opened normally and may be stuck. The switch under test fails the switch sticking test and a fault is reported, for example, by the control unit 4 via CAN.

[0042] For the two switches (e.g., contactors) Cp and Cn in the fuel cell system, they can be alternately tested for adhesion when the DC / DC converter is powered on and off. For example, the switch Cp is tested for adhesion when the DC / DC converter is powered on (the switch Cn remains closed), and the switch Cn is tested for adhesion when the DC / DC converter is powered off (the switch Cp remains closed). Alternatively, the two switches can be alternately tested for adhesion only when the system is powered on (or only when the system is powered off). Considering that performing adhesion detection when the DC / DC converter is powered off has little effect on the operation of the system and the equipment, the two switches can be alternately tested for adhesion only when the DC / DC converter is powered off.

[0043] The switch detection method of the present application is also applicable to the case where the power supply circuit of the fuel cell system is only equipped with one switch (contactor). For example, the system is only equipped with a switch Cp in the positive power supply circuit L1, and no switch is provided in the negative power supply circuit L2; in this case, the switch upstream side voltage Vin is measured between the positive power supply circuit L1 and the negative power supply circuit L2 upstream of the switch Cp, and the switch downstream side voltage Vout is measured between the positive power supply circuit L1 and the negative power supply circuit L2 downstream of the switch Cp. Alternatively, the system is only equipped with a switch Cn in the negative power supply circuit L2, and no switch is provided in the positive power supply circuit L1; in this case, the switch upstream side voltage Vin is measured between the positive power supply circuit L1 and the negative power supply circuit L2 upstream of the switch Cn, and the switch downstream side voltage Vout is measured between the positive power supply circuit L1 and the negative power supply circuit L2 downstream of the switch Cn.

[0044] In the case where only one switch is provided on the power supply circuit, the aforementioned detection method can also be used to perform a sticking detection on the DC / DC converter when it is powered on or off. The switch can be detected for sticking only when the DC / DC converter is powered off.

[0045] The present application also relates to a computer program product, which includes executable instructions, which can implement the above-mentioned detection method when executed by a processor (such as the processor in the control unit 4).

[0046] Those skilled in the art may make adaptive modifications to various details of the switch detection method of the present application according to the specific configuration of the fuel cell system.

[0047] According to the fuel cell system of the present application and the switch detection method applicable therein, by integrating the difference between the upstream and downstream voltages of the switch within a preset period of time after the tested switch is turned on, it is judged whether the switch has a adhesion fault based on the integrated value. When various adhesion faults exist in the tested switch, it is possible to accurately detect the presence of adhesion faults, thereby improving the detection reliability and accuracy and reducing the chances of missed diagnosis and misdiagnosis.

[0048] Although the present application is described herein with reference to specific embodiments, the scope of the present application is not limited to the details shown. Various modifications may be made to these details without departing from the basic principles of the present application.

Claims

1. A switch detection method for a fuel cell system, the fuel cell system comprising a fuel cell stack (1), a DC voltage converter (2), and a power battery (3), the DC voltage converter (2) being connected to the power battery (3) via a power supply line, the power supply line (L1, L2) being provided with switches (Cp, Cn) for controlling the connection and disconnection between the DC voltage converter (2) and the power battery (3), the switch detection method comprising the following detection steps performed during the power-on or power-off process of the DC voltage converter: turning on the switch; Recording a voltage on an upstream side of a switch and a voltage on a downstream side of a switch in the power supply line (L1, L2); Integrating the absolute value of the difference between the voltage on the upstream side of the switch and the voltage on the downstream side of the switch over time within a set period (Δt) to obtain an integral value; Determine whether the integral value is greater than a preset threshold (Vth); if the integral value is greater than or equal to the threshold, determine that the switch does not have a sticking fault; if the integral value is less than the threshold, determine that the switch has a sticking fault.

2. The switch detection method according to claim 1, wherein: The time period (Δt) starts at a time point when the switch is turned on; or, the starting point of the time period (Δt) is later than a time point when the switch is turned on.

3. The switch detection method according to claim 1 or 2, wherein: The time period (Δt) is 3 seconds to 8 seconds, preferably about 5 seconds, and the threshold value (Vth) is 50 volt·second to 120 volt·second, preferably about 85 volt·second.

4. The switch detection method according to any one of claims 1 to 3, wherein: The time period (Δt) and the threshold value (Vth) are calibratable and / or adjustable.

5. The switch detection method according to any one of claims 1 to 4, wherein: The threshold value (Vth) is set in positive correlation with the period (Δt).

6. The switch detection method according to any one of claims 1 to 5, wherein: The switch is opened while the DC voltage converter (2) is turned on or off.

7. The switch detection method according to any one of claims 1 to 6, wherein: The power supply circuit (L1, L2) comprises a positive power supply circuit (L1) and a negative power supply circuit (L2), switches are respectively provided in the positive power supply circuit (L1) and the negative power supply circuit (L2), wherein the detection step is performed on one of the switches during the power-on or power-off process of the DC voltage converter.

8. The switch detection method according to claim 7, wherein: The detection step is performed on one of the switches during a power-on operation of the DC voltage converter, and the detection step is performed on the other switch during a power-off operation of the DC voltage converter.

9. The switch detection method according to any one of claims 1 to 6, wherein: The detection step is performed on the switch only during power-down operation of the DC voltage converter.

10. A fuel cell system comprising: A fuel cell stack (1), a DC voltage converter (2), and a power battery (3), wherein the DC voltage converter (2) is connected to the power battery (3) via a power supply line, and switches (Cp, Cn) are provided in the power supply lines (L1, L2) for controlling connection and disconnection between the DC voltage converter (2) and the power battery (3); as well as A control unit (4) configured to at least control the operation of the fuel cell stack (1), the DC voltage converter (2), the power battery (3), and the opening and closing of the switch, and configured to be able to execute the switch detection method described in any one of claims 1 to 9 to detect the switch.

11. A computer program product, comprising executable instructions, which, when executed by a processor, can implement the switch detection method according to any one of claims 1 to 9.

Images