Method for controlling electrical insulation performance

Abstract

The invention relates to a method for checking the electrical insulation performance of a motor vehicle comprising an electrical circuit and a traction battery supplying the electrical circuit and including relays for switching the electrical circuit and a battery management system, wherein the method comprises the steps of: Measuring (100) a first impedance value of a leakage current through a first predetermined electrical resistance; If (200) the first impedance value is less than a first predetermined threshold value, then: measuring (220) a second impedance value of a leakage current through a second predetermined electrical resistance with a value lower than the first electrical resistance; if (230) the second impedance value is less than a second predetermined threshold value, then opening (300) the switching relays to disable the motor vehicle. Figure 1

Description

Title of the invention: Method for controlling electrical insulation performance. Technical field of the invention

[0001] The invention relates, in general, to the technical field of electrical circuits for electric or hybrid motor vehicles. In particular, the invention relates to a method for monitoring the electrical insulation performance of the electrical circuit of a motor vehicle. Prior art

[0002] Electric or hybrid motor vehicles are equipped with a traction battery that includes a device for monitoring the electrical insulation performance (insulation resistance) of an electrical circuit of the motor vehicle powered by the traction battery. To this end, the traction battery includes a battery management system (also called a BMS) which comprises a dedicated electronic circuit that switches electrical resistances of a predetermined value through switching transistors. By measuring the effect of these switching operations on the voltage across the traction battery terminals, the battery management system determines an insulation resistance and triggers a protection mode if necessary.

[0003] Currently, the protection method consists of the battery management system permanently opening relays when it determines an insulation resistance below a regulatory threshold of 500 Ohm / V.

[0004] However, insulation losses are common in electric or hybrid vehicles. The electrical circuit design of these vehicles is, of course, intended to prevent them, but they do occur, particularly following component wear and high humidity levels due to exceptional conditions (river crossing, heavy monsoon, etc.). These insulation losses can be transient and never reappear. One way to limit the impact on a vehicle user is to wait until the vehicle has stopped before disconnecting it, considering that an insulation fault is not dangerous while the user is driving, but it can become dangerous if they attempt to open the vehicle's hood, for example.

[0005] Furthermore, these insulation faults may not be dangerous, depending on their impedance level, but as there is currently no way to determine this with existing means. Ultimately, the motor vehicle breaks down often unnecessarily, causing inconvenience to the user of the motor vehicle. Description of the invention

[0006] The invention aims to remedy all or part of the drawbacks of the prior art by proposing in particular a solution to reduce unnecessary breakdowns of the motor vehicle in the event of insulation faults while ensuring the safety of the user to the extent necessary.

[0007] To this end, according to a first aspect of the invention, a method for controlling the electrical insulation performance of a motor vehicle is proposed, comprising an electrical circuit and a traction battery supplying the electrical circuit and including relays for switching the electrical circuit and a battery management system, wherein the method comprises the steps of: a. Measurement of a first impedance value of a leakage current through a first predetermined electrical resistance; and, b. If the first impedance value is less than a predetermined threshold value, then: i. measurement of a second impedance value of a leakage current through a second predetermined electrical resistance with a value lower than the first electrical resistance; and, ii. if the second impedance value is less than a second predetermined threshold value, then the switching relays will open to disable the motor vehicle during the next motor vehicle shutdown.

[0008] According to one embodiment, step b) includes a substep of lighting up a warning light for repair.

[0009] According to one embodiment, steps i. and ii. are triggered if the motor vehicle is moving.

[0010] According to one embodiment, steps i. and ii. are triggered if no switching relay is detected stuck.

[0011] According to one embodiment, steps i. and ii. are triggered if no disconnection is detected in the electrical circuit.

[0012] According to one embodiment, during step a), a first impedance value measurement is carried out on a positive branch of the electrical circuit and a second impedance value measurement is carried out on a negative branch of the electrical circuit.

[0013] According to one embodiment, steps i. and ii. are triggered if either of the first and second impedance value measurements is less than the first predetermined threshold value.

[0014] According to another aspect of the invention, a battery management system is provided comprising a first stage for measuring a leakage current including a first predetermined electrical resistance, in which the battery management system further comprises a second stage for detecting a leakage current including a second electrical resistance of lower value than the first electrical resistance, the battery management system being arranged so as to implement a method for controlling the electrical insulation performance of a motor vehicle having at least one of the preceding technical characteristics.

[0015] According to yet another aspect of the invention, a traction battery is provided for an electric or hybrid motor vehicle, in which the traction battery includes a battery management system having one of the preceding technical characteristics.

[0016] According to yet another aspect of the invention, a motor vehicle is provided comprising a traction battery having one of the preceding technical characteristics. brief description of the figures

[0017] Other features and advantages of the invention will become apparent from the following description, with reference to the accompanying figures, which illustrate: • [Fig-1]: a flowchart illustrating a method for controlling electrical insulation performance according to the invention; • [Fig. 2]: a schematic view of a motor vehicle in which the electrical insulation performance control method according to the invention of [Fig. 1] is implemented; and, • [Fig.3]: a schematic view detailing part of the battery management system of the motor vehicle in [Fig.2].

[0018] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. DETAILED description of a method of implementation

[0019] Figure 2 schematically illustrates an electric or hybrid motor vehicle 1. The motor vehicle 1 comprises a traction battery 2, a battery management system 3 for managing the traction battery 2 and generally integrated within said traction battery 2. In addition, the motor vehicle 1 includes an electrical circuit 4 electrically connected to the traction battery 2 via a positive line and a negative line, through switching relays. 51, 52. The switching relays 51, 52 are generally controlled to open or close by the battery management system 3. In addition, the battery management system 3 is electrically connected to the positive and negative lines linking the traction battery 2 to the electrical circuit 4.

[0020] In a manner known per se, the battery management system 3 has a dedicated electronic stage that switches electrical resistors RO of predetermined and precise values ​​through controlled switches 31, 32 (see [Fig. 3]), which are, for example, switching transistors. Each electrical resistor RO is connected at one terminal to one of the positive and negative lines via an associated controlled switch 31, 32 and at another terminal to the ground of the motor vehicle 1. By observing the effect of these switching operations on the voltage across the traction battery 2, the battery management system 3 is configured to deduce an insulation resistance. Numerous embodiments exist, depending on the battery management system supplier, with various improvements.The general principle is to switch electrical resistances R0 above a regulatory threshold of 250 kΩ (nominal voltage of the traction battery x 5000 mAh / V), for example, 500 kΩ, for a nominal voltage of traction battery 2 of 500 V. This allows for measurement accuracy in an area where detection is required. This requires switching electrical resistances R0 of the same order of magnitude as the value to be measured. In our example, an electrical resistance R0 of 5 MΩ would also work but would degrade the measurement accuracy. When the battery management system performs the measurement, it switches electrical resistances R0 that alternately connect the positive and negative lines to the ground of vehicle 1. This is equivalent to intentionally inducing (known) insulation losses; the ground of vehicle 1 is thus brought to the voltage of traction battery 2.It's important to understand that this process is continuous. Therefore, the resulting insulation loss must remain within regulatory limits, meaning it must exceed 250 kOhms in this case. This is indeed the case if 500 kOhm electrical resistances (R0) are switched. It would not be the case if, for example, 50 kOhm electrical resistances were switched.

[0021] It should be noted that the regulatory threshold of 500 Ohm / V is actually very conservative. For a battery voltage of 500V, the value of 250 kOhm ensures a leakage current of only 1 mA through the electrical resistances R0. This value of 1 mA is in fact roughly equal to the threshold of human perception and is far below a truly safe value of around 150 mA. The value of 150 mA corresponds to an insulation resistance of only 2.8 kOhm, therefore well below 250 kOhm, for a voltage of 500V. Thus, currently, the motor vehicle 1 is disabled by a leakage current of 1 mA (250 kOhm). While the leakage current is actually dangerous at 150 mA (R2.8 kOhm), when the battery management system detects a fault, it only means that the insulation resistance is less than 250 kOhm.

[0022] It follows from the above that ideally the following should be done: the motor vehicle should be disabled by opening the switching relays 51, 52 when the ignition is switched off if the measured electrical insulation resistance is less than 2.8 kOhms, and only a warning light should illuminate, prompting the user to have the motor vehicle repaired 1, if the measured electrical insulation resistance is between 2.8 kOhms and 250 kOhms. In order to have a safety margin, the leakage current should not exceed 20 mA, which corresponds to an electrical insulation resistance of 25 kOhms for a voltage of 500V.Thus, the vehicle would be disabled by opening the switching relays 51, 52 when the ignition is switched off if the measured electrical insulation resistance is less than 25 kOhms, and only a warning light would illuminate, prompting the user to have the vehicle repaired 1, if the measured electrical insulation resistance is between 25 kOhms and 250 kOhms. This would prevent the vehicle from being disabled for unsafe faults between 25 kOhms and 250 kOhms, as is currently the case.

[0023] With reference to [Fig.3], we will further describe a battery management system 3 according to the invention.

[0024] The battery management system 3 includes a first detection stage as previously described. The first detection stage includes electrical resistors R0 of a predetermined value, here two in number. Each of the electrical resistors R0 is connected at one of its terminals to one of the positive and negative lines via an associated controlled switch 31, 32 and at another of its terminals to the ground of the motor vehicle 1. A value of the electrical resistors R0 is chosen so as to be greater than or equal to the regulatory threshold of 5000 hm / V, for example for a nominal voltage of the traction battery 2 of 500V, a value greater than or equal to 250 kOhm, such as a value of 500 kOhm.

[0025] Furthermore, the battery management system includes a second detection stage similar to the first detection stage. The second detection stage comprises electrical resistors RI, here two in number, with a determined value lower than the value of the electrical resistors R0 of the first detection stage. Each of the electrical resistors RI is connected at one of its terminals to one of the positive and negative lines via an associated controlled switch 33, 34 and at another of its terminals to the ground of the motor vehicle 1. A value of the electrical resistors RI is, for example, for a nominal voltage of the traction battery 2 of 500V, 25kΩ.

[0026] The first detection stage is implemented, and then the second detection stage is implemented. The two detection stages are not implemented simultaneously.

[0027] In practice, an insulation measurement takes approximately thirty seconds when the electrical resistance is around 250 kOhms. This is because the measurement is performed by observing the voltages across the traction battery 2 on the positive and negative lines, but these voltages fluctuate transiently before stabilizing at a value that allows for measurement. However, an insulation measurement with an electrical resistance of 25 kOhms is faster; in our example, it is approximately twenty times (500 kOhms / 25 kOhms) faster than the activation of the first detection stage.

[0028] Since activation of the second detection stage generates an insulation fault below the regulatory threshold, it is necessary to activate it only briefly once, if the first detection stage has detected an insulation fault. Furthermore, activation of the second detection stage is only carried out under conditions guaranteeing the absence of risk to the customer, namely: the motor vehicle 1 is in motion, no connector disconnection is detected on the motor vehicle 1, the insulation fault detected by the first detection stage is on only one of the positive and negative lines (asymmetrical), and no switching relay 51, 52 is detected as stuck (opening the switching relay is possible if necessary).

[0029] The principle is thus to explore the severity of the insulation fault by activating the second detection stage, only once.

[0030] With regard to [Fig. 1], we will describe a method for controlling electrical insulation performance according to the invention which can be implemented in the battery management system 3 previously described.

[0031] In a first step 100, the electrical insulation performance control method according to the invention performs a first impedance measurement of a leakage current through a first predetermined electrical resistance R0. To do this, the electrical insulation performance control method according to the invention controls the pilot-operated switch 31, 32 to close so as to connect the first electrical resistance R0 to one of the positive and negative lines. Two impedance measurements are thus performed: an impedance measurement related to the positive line and an impedance measurement related to the negative line.

[0032] In a second step 200, the electrical insulation performance control method according to the invention compares the first impedance value thus measured with a first predetermined threshold value. If the first impedance value is greater than the first predetermined threshold value, then the electrical insulation performance control method according to the invention returns to the first step 100.

[0033] If the first impedance value is less than the first predetermined threshold value, the electrical insulation performance control method according to the invention proceeds to a substep 210 of illuminating a warning light for repair. Generally, the warning light is located on the dashboard of the motor vehicle 1.

[0034] Next, the electrical insulation performance testing method according to the invention proceeds to a substep 220 of measuring a second impedance value of a leakage current through a second predetermined electrical resistance RI with a value lower than that of the first electrical resistance R0. To this end, the electrical insulation performance testing method according to the invention controls the pilot-operated switch 33, 34 to close so as to connect the second electrical resistance RI to one of the positive and negative lines. As in the first step, two impedance measurements are thus performed: one impedance measurement related to the positive line and one impedance measurement related to the negative line. Alternatively, if, following the first step 100, the insulation fault was detected on only one of the positive and negative lines, then the measurement in substep 220 is performed only on the same positive or negative line.

[0035] In a substep 230, the electrical insulation performance control method according to the invention compares the second impedance value thus measured with a second predetermined threshold value. If the second impedance value is greater than the second predetermined threshold value, then the electrical insulation performance control method according to the invention returns to the first step 100.

[0036] If the second impedance value is less than the second predetermined threshold value, then the electrical insulation performance control method according to the invention proceeds, in a step 300, to open the switching relays 51, 52 to disable the motor vehicle 1 at the next stop of the motor vehicle 1.

[0037] The electrical insulation performance control method according to the invention only triggers substeps 220 and 230 if the motor vehicle 1 is moving, no connector disconnection is detected on the motor vehicle 1, the insulation fault detected by the first detection stage is on only one of the positive and negative lines, there is no switching relay 51,52 detected stuck.

[0038] It should be noted that when the electrical insulation performance control method according to the invention detects an insulation fault during the second stage 200, it is quite possible that the actual insulation fault is of very low impedance, even below the second threshold value. Since the second detection stage is only activated if the first detection stage has detected a fault, An implementation of the electrical insulation performance control method according to the invention does not introduce any additional risk compared to the prior art situation. However, it allows for a reconfiguration adapted to the actual hazard level of the observed situation.

[0039] Naturally, the invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different embodiments of the invention without departing from the scope of the invention.

[0040] It is emphasized that all features, as they are apparent to a person skilled in the art from the present description, drawings and attached claims, even if in practice they have only been described in relation to other specific features, both individually and in any combinations, may be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances render such combinations impossible or meaningless.

Claims

Demands

1. A method for checking the electrical insulation performance of a motor vehicle comprising an electrical circuit (4) and a traction battery (2) supplying the electrical circuit and comprising switching relays (51, 52) to the electrical circuit and a battery management system (3), the battery management system comprising a first predetermined electrical resistance (RO), wherein, the battery management system comprising a second predetermined electrical resistance (RI), the method comprises steps of: a. Measuring (100) a first impedance value of a leakage current through the first predetermined electrical resistance; and, b. If (200) the first impedance value is less than a first predetermined threshold value, then: i.measurement (220) of a second impedance value of a leakage current through the second predetermined electrical resistance of a value less than the first electrical resistance; and, ii. if (230) the second impedance value is less than a second predetermined threshold value, then opening of the switching relays to disable the motor vehicle at the next motor vehicle stop.

2. Method according to claim 1, characterized in that step b) comprises a substep of lighting up a warning light for repair.

3. A method according to any one of claims 1 to 2, characterized in that steps i. and ii. are triggered if the motor vehicle is moving.

4. A method according to any one of claims 1 to 3, characterized in that steps i. and ii. are triggered if no switching relay is detected stuck.

5. A method according to any one of claims 1 to 3, characterized in that steps i. and ii. are triggered if no disconnection is detected in the electrical circuit.

6. A method according to any one of claims 1 to 5, characterized in that, during step a), a first impedance value measurement is carried out on a positive branch of the electrical circuit and a second impedance value measurement is carried out on a negative branch of the electrical circuit.

7. Method according to claim 6, characterized in that steps i. and ii. are triggered if one of the first and second impedance value measurements is less than the first predetermined threshold value.

8. Battery management system (3) comprising a first leakage current measurement stage including a first predetermined electrical resistance (RO), wherein the battery management system further comprises a second leakage current detection stage including a second electrical resistance (RI) of lower value than the first electrical resistance, the battery management system being arranged to implement a method for checking the electrical insulation performance of a motor vehicle according to any one of claims 1 to 7.

9. Traction battery (2) for an electric or hybrid motor vehicle, wherein the traction battery comprises a battery management system according to claim 8.

10. Motor vehicle, characterized in that it comprises a traction battery according to claim 9.

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