Circuit and method for monitoring insulation performance of fuel cell stack

Abstract

There is provided a circuit for monitoring an insulating property of a fuel cell stack, comprising: a low-frequency voltage source for negatively injecting a low-frequency signal only to a high-voltage bus of the fuel cell stack; a first resistor; and a second resistor; wherein the low-frequency voltage source, the first resistor and the second resistor are connected in series, and the low-frequency voltage source, the first resistor and the second resistor which are connected in series are connected with a high-voltage bus negative ground insulation resistor of the fuel cell stack in parallel; and the voltage on the first resistor can be measured so as to be used for determining the insulating property of the fuel cell stack. Therefore, the low-frequency voltage source only injects the low-frequency signal at the negative single side of the high-voltage bus, so that only the insulating property of the negative single side of the high-voltage bus is reduced, and the insulating property of the positive side of the high-voltage bus is not influenced.

Description

Technical Field

[0001] This invention relates to the field of electric vehicles, and more particularly to the monitoring of the insulation performance of fuel cell stacks in electric vehicles. Background Technology

[0002] In recent years, fuel cell stacks have been widely used in electric vehicles. The insulation performance between the fuel cell stack and the vehicle body has become a key concern. Currently, various methods exist for monitoring the insulation performance of fuel cell stacks, such as the balanced bridge method, the unbalanced bridge method, and the low-frequency signal injection method. However, there is still room for improvement in current methods. Summary of the Invention

[0003] It is desirable to provide a circuit and method for monitoring the insulation performance of a fuel cell stack that reduces the insulation performance of only the negative side (high voltage bus negative) of the fuel cell stack without affecting the insulation performance of the positive side (high voltage bus positive) of the fuel cell stack.

[0004] According to one aspect, a circuit for monitoring the insulation performance of a fuel cell stack is provided, comprising: a low-frequency voltage source for injecting a low-frequency signal into the negative high-voltage bus of the fuel cell stack; and a first resistor and a second resistor; wherein the low-frequency voltage source, the first resistor, and the second resistor are connected in series, and the low-frequency voltage source, the first resistor, and the second resistor, connected in series with each other, are connected in parallel with the negative insulation resistance to ground of the high-voltage bus of the fuel cell stack; and wherein the voltage across the first resistor is measured to determine the insulation performance of the fuel cell stack.

[0005] According to another aspect, an apparatus for monitoring the insulation performance of a fuel cell stack is provided, comprising: an acquisition unit that acquires a voltage on a first resistor in a circuit for monitoring the insulation performance of a fuel cell stack according to various embodiments of the present invention; and a processing unit that determines the insulation performance of the fuel cell stack based on the voltage on the first resistor.

[0006] According to another aspect, a method for monitoring the insulation performance of a fuel cell stack is provided, comprising: acquiring a voltage across a first resistor in a circuit for monitoring the insulation performance of a fuel cell stack according to various embodiments of the present invention; and determining the insulation performance of the fuel cell stack based on the voltage across the first resistor.

[0007] According to another aspect, a computer-readable medium is provided that stores computer program code, which, when executed, causes a controller to perform a method for monitoring the insulation performance of a fuel cell stack according to various embodiments of the invention.

[0008] According to another aspect, a computer program product is provided, comprising computer program code that, when executed, causes a controller to perform a method for monitoring the insulation performance of a fuel cell stack according to various embodiments of the invention.

[0009] According to various embodiments of the present invention, the low-frequency voltage source injects a low-frequency signal only on the negative side of the high-voltage bus. Therefore, a resistor is connected in parallel only across the insulation resistance Rn of the negative side of the high-voltage bus, thereby reducing the insulation performance only on the negative side of the high-voltage bus without affecting the insulation performance on the positive side. Attached Figure Description

[0010] In the accompanying drawings, embodiments are illustrated by way of example only and not by way of limitation, and similar reference numerals in the drawings refer to similar elements.

[0011] Figure 1 The circuit diagram for a typical low-frequency signal injection method is shown;

[0012] Figure 2 A circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to an embodiment of the present invention is shown;

[0013] Figure 3 It shows according to Figure 2 The diagram shown is a simplified circuit diagram of a circuit used to monitor the insulation performance of a fuel cell stack.

[0014] Figure 4 A circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to another embodiment of the present invention is shown;

[0015] Figure 5 A circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to another embodiment of the present invention is shown;

[0016] Figure 6 A circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to another embodiment of the present invention is shown;

[0017] Figure 7 A block diagram of an apparatus for monitoring the insulation performance of a fuel cell stack according to an embodiment of the present invention is shown.

[0018] Figure 8 A flowchart of a method for monitoring the insulation performance of a fuel cell stack according to an embodiment of the present invention is shown.

[0019] Various aspects and features of the embodiments of the present invention have been described with reference to the accompanying drawings. The drawings are merely illustrative and not restrictive. Furthermore, not all parts of the device in the embodiments of the present invention are indicated by reference numerals in the drawings; some drawings only indicate relevant components, which does not limit the various parts to what is shown in the drawings. Detailed Implementation

[0020] Figure 1 The circuit diagram for a typical low-frequency signal injection method is shown. (For example...) Figure 1 As shown, Rp is the equivalent insulation resistance of the high-voltage busbar to ground, hereinafter referred to as the high-voltage busbar to ground insulation resistance; Rn is the equivalent insulation resistance of the high-voltage busbar to ground, hereinafter referred to as the high-voltage busbar to ground insulation resistance. Insulation resistances Rp and Rn can represent the insulation performance between the fuel cell stack and the vehicle.

[0021] like Figure 1 As shown, according to the common low-frequency signal injection method, a low-frequency AC signal is injected from a low-frequency voltage source Vin into both the positive and negative sides of the high-voltage busbar; this is called double-sided injection. Based on this double-sided injection, resistors need to be connected in parallel on both the positive and negative sides of the high-voltage busbar, such as resistor R1 connected in parallel with the insulation resistance Rp of the positive side of the high-voltage busbar to ground and resistor R2 connected in parallel with the insulation resistance Rn of the negative side of the high-voltage busbar to ground. This will adversely reduce the insulation performance of both the positive and negative sides of the high-voltage busbar.

[0022] Figure 2 A circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to an embodiment of the present invention is shown. (The last sentence appears to be incomplete and possibly refers to a different circuit.) Figure 1 The circuit diagrams shown are different. The low-frequency voltage source Vin injects a low-frequency signal only on the negative side of the high-voltage bus. Therefore, a resistor is connected in parallel only with the insulation resistance Rn of the negative side of the high-voltage bus, thus reducing the insulation performance only on the negative side of the high-voltage bus without affecting the insulation performance on the positive side.

[0023] Specifically, the circuit used to monitor the insulation performance of the fuel cell stack (as shown in the dashed box) includes a low-frequency voltage source Vin, a first resistor RL1, and a second resistor RL2. The low-frequency voltage source Vin, the first resistor RL1, and the second resistor RL2 are connected in series with each other and are connected in parallel as a whole with the negative-to-ground insulation resistance Rn of the high-voltage bus.

[0024] In such Figure 2In the illustrated embodiment, the low-frequency voltage source Vin includes a first terminal and a second terminal. The first terminal is connected to the vehicle body, specifically the connection point of the high-voltage bus positive-to-ground insulation resistance Rp and the high-voltage bus negative-to-ground insulation resistance Rn. The second terminal is connected to a second resistor RL2. The second resistor RL2 is connected in series with the first resistor RL1, and the other end of the first resistor RL1 is connected to the high-voltage bus negative. In short, the low-frequency voltage source Vin, the first resistor RL1, and the second resistor RL2 are connected in parallel to the insulation resistance Rn, thereby injecting a low-frequency signal only into the high-voltage bus negative through the low-frequency voltage source Vin. The voltage across the first resistor RL1 is measured as an output to determine the insulation performance of the fuel cell stack; that is, the first resistor RL1 acts as a sampling resistor, while the second resistor RL2 acts as a voltage divider resistor. However, it is also conceivable that the second resistor RL2 can be used as a sampling resistor to measure the voltage across it as an output to determine the insulation performance of the fuel cell stack, without departing from the scope of this invention. Furthermore, the series connection order of the first resistor RL1 and the second resistor RL2 can be arbitrarily interchanged.

[0025] Figure 3 It shows according to Figure 2 The diagram shown is a simplified circuit diagram for monitoring the insulation performance of a fuel cell stack.

[0026] When the low-frequency voltage source Vin acts alone, such as Figure 2 The circuit shown can be equivalent to Figure 3 The circuit diagram shown in (I) is as follows. And when the fuel cell stack V... 堆 When used alone, such as Figure 2 The circuit shown can be equivalent to Figure 3 The circuit diagram shown in (II) is shown in the diagram.

[0027] When the low-frequency voltage source acts alone, according to Figure 3 As shown in (I),

[0028]

[0029] Wherein, Ri is the resistance value obtained by connecting the positive-to-ground insulation resistance Rp of the high-voltage busbar and the negative-to-ground insulation resistance Rn of the high-voltage busbar in parallel, that is, Ri=Rp∥Rn.

[0030] When the fuel cell stack operates independently, according to Figure 3 As shown in (II) in the middle,

[0031]

[0032] According to the superposition theorem:

[0033]

[0034] In the above formula, there are only three unknowns: Rp, Rn, and Ri. Since Vin is a controllable injected square wave signal with two states, Vin and 0, the voltage VL across the first resistor also has two states, named VL_H and VL_L respectively. Therefore, we have:

[0035]

[0036] Subtracting the two equations, we get:

[0037]

[0038] RL1 and RL2 are the resistance values ​​of the first resistor and the second resistor, respectively. Vin is the voltage value injected by the low-frequency voltage source. VL_H and VL_L are the signals detected on the first resistor when the voltage value injected by the low-frequency voltage source is high and the signals detected on the first resistor when the voltage value injected by the low-frequency voltage source is low, respectively. The above formula contains only one unknown variable Ri, so the insulation resistance value Ri can be calculated according to the above formula.

[0039] As can be seen from the above derivation process, the parallel value Ri of the high-voltage busbar positive-to-ground insulation resistance Rp and the high-voltage busbar negative-to-ground insulation resistance Rn can be calculated. In insulation performance monitoring, for safety reasons, it is generally desirable that the resistance value obtained through insulation performance monitoring is less than the actual insulation resistance value. The parallel value Ri of the high-voltage busbar positive-to-ground insulation resistance Rp and the high-voltage busbar negative-to-ground insulation resistance Rn calculated above is obviously less than the actual values ​​of Rp and Rn, which precisely meets the requirements of safety considerations. At the same time, this simplifies the calculation steps in the software.

[0040] Figure 4 A circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to another embodiment of the present invention is shown. (Compared to...) Figure 2 The difference in the circuit diagram shown is that, Figure 4 In the circuit diagram shown, two other resistors, RL3 and RL4, are connected in parallel with the first resistor RL1.

[0041] Specifically, such as Figure 4 As shown, in addition to Figure 2In addition to the low-frequency voltage source Vin, the first resistor RL1, and the second resistor RL2 shown, the circuit for monitoring the insulation performance of the fuel cell stack also includes a third resistor RL3, a fourth resistor RL4, a first switch K1, and a second switch K2. The first switch K1 and the third resistor RL3 are connected in series to form a first branch, and the second switch K2 and the fourth resistor RL4 are connected in series to form a second branch. The first switch K1 and the third resistor RL3, connected in series together (the first branch), are connected in parallel to the first resistor RL1. Simultaneously, the second switch K2 and the fourth resistor RL4, connected in series together (the second branch), are connected in parallel to the first resistor RL1.

[0042] Although Figure 4 The diagram illustrates the case where two resistors and their corresponding switches are connected in parallel with the first resistor RL1. This is not a limitation; any number of resistors can be connected in parallel with the first resistor RL1, which can be set as needed.

[0043] In other words, in addition to the first resistor RL1 and the second resistor RL2, the circuit for monitoring the insulation performance of the fuel cell stack may also include one or more resistors (such as a third resistor and a fourth resistor) and one or more switches (such as a first switch and a second switch). Each of these one or more resistors is connected in series with a corresponding switch to form one or more branches, and each branch formed by connecting each resistor in series with its corresponding switch is connected in parallel with the first resistor RL1. By opening or closing the switches in each branch, the corresponding resistors of these one or more resistors can be connected in parallel to the first resistor RL1, thereby reducing the voltage drop across the first resistor RL1.

[0044] Since the voltage sampling of VL is acquired by the central control unit (MCU), and the detection range of the MCU itself is limited, in order to accommodate different combinations of insulation resistance Rp and Rn, and in order to measure a wider range of insulation resistance as much as possible, multiple resistors and corresponding switches are connected in parallel with the first resistor RL1. By controlling these switches to connect different resistors in parallel with the first resistor RL1, the voltage division on the first resistor RL1, which serves as the sampling resistor, can be changed, thereby providing different detection ranges.

[0045] by Figure 4 Taking the situation shown as an example, when the voltage detected on the first resistor RL1 exceeds the detection range of the MCU, the first switch K1 can be controlled to change from the open state to the closed state, thereby connecting the third resistor RL3 in parallel with the first resistor RL1. The total resistance value obtained after the first resistor RL1 and the third resistor RL3 are connected in parallel becomes smaller, and the output voltage VL detected on the first resistor RL1 becomes smaller, so the output voltage VL may be within the detection range of the MCU.

[0046] Similarly, when the voltage detected on the first resistor RL1 after the third resistor RL3 is connected in parallel still exceeds the detection range of the MCU, the second switch K2 can be further controlled to change from the open state to the closed state, thereby connecting the fourth resistor RL4 in parallel with the first resistor RL1. The total resistance value obtained after the first resistor RL1, the third resistor RL3 and the fourth resistor RL4 are connected in parallel is further reduced, and the output voltage VL detected on the first resistor RL1 is further reduced, so the output voltage VL may be within the detection range of the MCU.

[0047] By connecting the first resistor RL1 in parallel with multiple resistors and corresponding switches, the detection range of the output voltage VL can be increased, which in turn increases the detection range of the insulation resistance, thus increasing the monitoring range of the insulation performance of the battery stack.

[0048] Figure 5 A circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to another embodiment of the present invention is shown. Figure 5 The circuit shown is Figure 4 The difference in the circuit diagram shown is that an additional switch KL is added to connect in series with the low-frequency voltage source Vin, the first resistor RL1, and the second resistor RL2.

[0049] According to various embodiments of the present invention, low-frequency voltage is injected only into the negative side of the high-voltage bus, and an additional resistor is connected in parallel only to the negative side of the high-voltage bus. Monitoring the insulation performance with such a resistor in parallel would reduce the insulation performance on the negative side of the high-voltage bus. Therefore, it is desirable to disconnect the resistor connected in parallel to the negative side of the high-voltage bus when insulation performance monitoring is not required.

[0050] Therefore, as Figure 5 The illustrated embodiment introduces an additional switch KL, which is connected in series with a first resistor RL1, a second resistor RL2, and a low-frequency voltage source Vin. When the additional switch KL is closed, the low-frequency voltage source can be used to inject a low-frequency signal into the negative high-voltage bus of the fuel cell stack. When the additional switch KL is open, the low-frequency voltage source is disconnected from the negative high-voltage bus, thus preventing insulation performance monitoring. When insulation performance monitoring is not required, the additional switch KL can be controlled to change from a closed state to an open state, thereby disconnecting the resistor connected in parallel between the negative high-voltage bus and ground.

[0051] For example, before stacking a fuel cell stack, the insulation resistance of the stack system needs to be checked. Stacking is only permitted when the insulation resistance is within a safe range. This means that an insulation resistance check must be performed before each fuel cell stack stack is stacked. In this case, an additional switch KL can be closed. After the stack is stacked, a corresponding instruction will be received to disable the insulation resistance check function. In this scenario, an instruction can be given to open the additional switch KL after stacking.

[0052] Figure 6 A more detailed circuit diagram of a circuit for monitoring the insulation performance of a fuel cell stack according to another embodiment of the present invention is shown.

[0053] like Figure 6 As shown, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) is used as the switch. Specifically, the low-frequency voltage source Vin, the second resistor RL2, the first resistor RL1, the third resistor RL3, and the fourth resistor RL4 connected in parallel, and the MOSFETs Q1 and Q2 are connected in series. The MOSFETs Q1 and Q2 are controlled by receiving the IMD_EN_IV control signal to open or close the switch, thus enabling or disabling the insulation performance monitoring function. MOSFETs Q1 and Q2 are back-to-back MOSFETs, meaning they are connected in a back-to-back configuration to prevent backflow between the battery stack and the low-frequency signal source. The body diode is shown only for ease of understanding and to illustrate its backflow prevention function.

[0054] In addition, MOSFETs Q3 and Q4 are controlled by the IMD_SW_M_DO and IMD_SW_L_DO control signals to determine whether to connect the corresponding third resistor RL3 and fourth resistor RL4 in parallel with the first resistor RL1, thereby increasing the monitoring range of insulation performance as needed.

[0055] Although the body diodes are shown only in MOSFETs Q1 and Q2, it can be understood that MOSFETs Q3 and Q4 also include body diodes.

[0056] The above is for reference only. Figure 2-6 The structure of a circuit for monitoring the insulation performance of a fuel cell stack according to various embodiments of the present invention is described. It is evident that these embodiments can be combined with each other, or some components can be modified to achieve corresponding technical effects.

[0057] The following is for reference. Figure 7 and Figure 8 This invention describes an apparatus and method for monitoring the insulation performance of a fuel cell stack according to an embodiment of the present invention.

[0058] like Figure 7 As shown, the device 10 for monitoring the insulation performance of a fuel cell stack includes an acquisition unit 11, a processing unit 12, and a control unit 13. Optionally, the device 10 may further include reference to the above... Figure 2-6 The circuit described.

[0059] The acquisition unit 11 acquires circuits (e.g., circuits for monitoring the insulation performance of fuel cell stacks according to various embodiments of the present invention) Figure 2-6The voltage VL on the first resistor RL1 (shown) is used to determine the insulation performance of the fuel cell stack. In particular, the processing unit 12 determines the parallel resistance value Ri between the high-voltage bus positive-to-ground insulation resistance Rp and the high-voltage bus negative-to-ground insulation resistance Rn based on the voltage VL on the first resistor RL1.

[0060] Specifically, as described above, the parallel resistance value Ri can be determined using the following formula:

[0061]

[0062] Wherein, RL1 and RL2 are the resistance values ​​of the first resistor and the second resistor, respectively; Vin is the voltage value injected by the low-frequency voltage source; VL_H and VL_L are the signals detected on the first resistor when the voltage value injected by the low-frequency voltage source is high and the signals detected on the first resistor when the voltage value injected by the low-frequency voltage source is low, respectively; and Ri is the parallel resistance value.

[0063] Control unit 13 can generate control signals to provide various control signals for the operation of the circuit, such as controlling... Figure 2-6 The switches shown are shown.

[0064] In one embodiment, the control unit 13 generates a control signal to control one or more switches in a circuit according to various embodiments of the present invention, including first switches K1 and Q3 and second switches K2 and Q4, such that any one of the switches is opened or closed. When the arbitrary switch is opened, the connection between the corresponding resistor connected in series with the arbitrary switch and the first resistor RL1 is broken; when the arbitrary switch is closed, the corresponding resistor connected in series with the arbitrary switch is connected in parallel with the first resistor RL1.

[0065] In another embodiment, control unit 13 generates a control signal to control an additional switch KL in the circuit according to various embodiments of the invention, thereby causing it to be opened or closed. When the additional switch KL is opened, the low-frequency voltage source is disconnected from the negative high-voltage bus, and when the additional switch KL is closed, the low-frequency voltage source can be used to inject a low-frequency signal into the negative high-voltage bus of the fuel cell stack.

[0066] like Figure 8 As shown, according to one embodiment of a method 100 for monitoring the insulation performance of a fuel cell stack, in step 110, the voltage across a first resistor RL1 in a circuit for monitoring the insulation performance of a fuel cell stack according to various embodiments of the present invention is obtained; this voltage can be detected by means of... Figure 2-6 The voltage across the first resistor RL1 in the circuit shown can be obtained directly, or it can be received from an external source.

[0067] Then, at step 120, the insulation performance of the fuel cell stack is determined based on the voltage across the first resistor. Specifically, the parallel resistance value between the high-voltage bus positive-to-ground insulation resistance and the high-voltage bus negative-to-ground insulation resistance can be determined based on the voltage across the first resistor, and the calculation method has been described above.

[0068] Furthermore, the method 100 may also include control steps, particularly for, such as Figure 2-6 The circuit diagram shown illustrates the control of each switch.

[0069] In one embodiment, the method further includes: controlling any one of one or more switches (including a first switch and a second switch) in the circuit to be opened or closed in response to a control signal; when the arbitrary switch is opened, the connection between the corresponding resistor connected in series with the arbitrary switch and the first resistor RL1 is disconnected; when the arbitrary switch is closed, the corresponding resistor connected in series with the arbitrary switch is connected in parallel with the first resistor RL1.

[0070] In another embodiment, the method further includes: controlling another switch KL in the circuit to be opened or closed in response to a control signal; when the other switch is opened, the low-frequency voltage source is disconnected from the negative high-voltage bus; and when the other switch is closed, the low-frequency voltage source can be used to inject the low-frequency signal into the negative high-voltage bus of the fuel cell stack.

[0071] The various steps of the method and apparatus of the present invention can be implemented by software or corresponding hardware, or by means of a processing unit / control unit to achieve the functions of the above-described steps. Specifically, the apparatus according to various embodiments of the present invention can be incorporated into the power transmission unit (PTU) of an electric vehicle, or can be implemented by a microcontroller unit (MCU).

[0072] It is understood that the methods of the various embodiments of this disclosure can be implemented under the control of a computer program / software. This software can be loaded into the working memory of a controller and, when run, is used to execute the methods according to the various embodiments of this disclosure.

[0073] It is understood that the exemplary embodiments of this disclosure cover both: creating / using computer programs / software of this disclosure from the outset, and converting existing programs / software to use computer programs / software of this disclosure by means of updates.

[0074] According to another embodiment of this disclosure, a computer program product, or a machine-readable medium (such as a computer), such as a CD-ROM, is provided, including computer program code that, when executed, causes a computer or processor to perform methods according to various embodiments of this disclosure. The machine-readable medium is, for example, an optical storage medium or a solid-state medium supplied together with or as part of other hardware.

[0075] The foregoing has described specific embodiments of this disclosure. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims may be performed in a different order than that shown in the embodiments and may still achieve the desired result. Furthermore, the processes depicted in the drawings do not necessarily require the specific or sequential order shown to achieve the desired result. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0076] The present disclosure has been described above with reference to specific embodiments. Those skilled in the art should understand that the technical solutions of the present disclosure can be implemented in various ways without departing from the spirit and essential characteristics of the present disclosure. The specific embodiments are merely illustrative and not restrictive. Furthermore, these embodiments can be arbitrarily combined to achieve the purposes of the present disclosure. The scope of protection of the present disclosure is defined by the appended claims.

[0077] The word "comprising" in the specification and claims does not exclude the presence of other elements or steps. The terms "first," "second," and the order of the various "steps" and the steps shown in the figures do not limit their sequence or quantity. The functions of the various elements described in the specification or recited in the claims can also be separated or combined, and implemented by multiple corresponding elements or a single element.

Claims

1. A circuit for monitoring the insulation performance of a fuel cell stack, comprising: A low-frequency voltage source is used to negatively inject low-frequency signals only into the high-voltage bus of the fuel cell stack; First resistor; Second resistor; The low-frequency voltage source, the first resistor, and the second resistor are connected in series, and the low-frequency voltage source, the first resistor, and the second resistor connected in series are connected in parallel with the negative ground insulation resistance of the high-voltage bus of the fuel cell stack. Furthermore, the voltage across the first resistor can be measured to determine the insulation performance of the fuel cell stack.

2. The circuit according to claim 1 further includes: One or more resistors; and One or more switches, each of which is connected in series with a corresponding resistor in one or more resistors to form one or more branches, each of which is connected in parallel with the first resistor. When any of the one or more switches is turned on, the connection between the corresponding resistor connected in series with the switch and the first resistor is broken. When any of the switches is turned off, the corresponding resistor connected in series with the switch is connected in parallel with the first resistor.

3. The circuit according to claim 2, wherein, The one or more resistors include a third resistor and a fourth resistor, and the one or more switches include a first switch and a second switch, wherein the first switch is connected in series with the third resistor to form a first branch, and the second switch is connected in series with the fourth resistor to form a second branch; Furthermore, the first branch and the second branch are respectively connected in parallel with the first resistor.

4. The circuit according to any one of claims 1-3, further comprising: The other switch is connected in series with the low-frequency voltage source, the first resistor, and the second resistor. When the other switch is opened, the low-frequency voltage source is disconnected from the negative high-voltage bus. When the other switch is closed, the low-frequency voltage source can be used to inject the low-frequency signal into the negative high-voltage bus of the fuel cell stack.

5. The circuit according to claim 2, wherein, The one or more switches are MOSFETs.

6. The circuit according to claim 4, wherein, The other switch is a back-to-back MOSFET.

7. A device for monitoring the insulation performance of a fuel cell stack, comprising: The acquisition unit acquires the voltage on the first resistor in the circuit for monitoring the insulation performance of a fuel cell stack according to any one of claims 1-6; and The processing unit determines the insulation performance of the fuel cell stack based on the voltage across the first resistor.

8. The device according to claim 7, in, The processing unit determines the parallel resistance value between the positive-to-ground insulation resistance of the high-voltage busbar and the negative-to-ground insulation resistance of the high-voltage busbar based on the voltage on the first resistor.

9. The device according to claim 8, wherein, The value of the parallel resistance is determined by the following formula: Wherein, RL1 and RL2 are the resistance values ​​of the first resistor and the second resistor, respectively; Vin is the voltage value injected by the low-frequency voltage source; VL_H and VL_L are the signals detected on the first resistor when the voltage value injected by the low-frequency voltage source is high and the signals detected on the first resistor when the voltage value injected by the low-frequency voltage source is low, respectively; and Ri is the parallel resistance value.

10. The device according to claim 7, wherein, The circuit includes one or more switches according to claim 2, and the device further includes: A control unit, which responds to a control signal to control any one of the one or more switches in the circuit to be opened or closed, wherein when any one switch is opened, the connection between the corresponding resistor connected in series with the arbitrary switch and the first resistor is broken, and when any one switch is closed, the corresponding resistor connected in series with the arbitrary switch is connected in parallel with the first resistor.

11. The device according to any one of claims 7-10, wherein, The circuit includes an additional switch as claimed in claim 4, and the device further includes: A control unit, which responds to a control signal to control the opening or closing of the additional switch in the circuit, wherein when the additional switch is opened, the low-frequency voltage source is disconnected from the negative high-voltage bus, and when the additional switch is closed, the low-frequency voltage source is capable of injecting the low-frequency signal into the negative high-voltage bus of the fuel cell stack.

12. A method for monitoring the insulation performance of a fuel cell stack, comprising: Obtain the voltage across the first resistor in the circuit for monitoring the insulation performance of a fuel cell stack according to any one of claims 1-6; and The insulation performance of the fuel cell stack is determined based on the voltage across the first resistor.

13. The method of claim 12, further comprising: The parallel resistance value between the positive-to-ground insulation resistance of the high-voltage busbar and the negative-to-ground insulation resistance of the high-voltage busbar is determined based on the voltage on the first resistor.

14. The method according to claim 12, in, The circuit includes one or more switches according to claim 2, and the method further includes: controlling any one of the one or more switches to be opened or closed in response to a control signal; when any switch is opened, the connection between the corresponding resistor connected in series with the arbitrary switch and the first resistor is broken; when any switch is closed, the corresponding resistor connected in series with the arbitrary switch is connected in parallel with the first resistor; or The circuit includes an additional switch according to claim 4, and the method further includes: controlling the additional switch to be opened or closed in response to a control signal; when the additional switch is opened, the low-frequency voltage source is disconnected from the negative high-voltage bus; and when the additional switch is closed, the low-frequency voltage source can be used to inject the low-frequency signal into the negative high-voltage bus of the fuel cell stack.

15. A computer program product comprising computer program code, which, when executed, causes a processing unit and / or a control unit to perform the method for monitoring the insulation performance of a fuel cell stack according to any one of claims 12-14.

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