Measuring battery leakage current

Abstract

Method for measuring a leakage current of a battery (BAT), said method comprising the successive steps of: performing a first plurality of measurements (Vmid1) of a difference between the intermediate potential (Vmid) and the high voltage ground (GND) of the vehicle; using the switching means so that the third resistor (R3) is electrically connected between the intermediate potential (Vmid) and the high potential (BAT+) of the battery (BAT); performing a second plurality of measurements (Vmid2) of the intermediate voltage; deducing from the second plurality of measurements (Vmid2) a second stabilized value of the intermediate voltage (Vstab2); deducing the values ​​of the first parasitic resistance (RIP) and the second parasitic resistance (RIM); and deducing the leakage current across the terminals of the first parasitic resistance (RIP) and the second parasitic resistance (RIM). Abstract figure: Figure 2.

Description

Title of the invention: Measurement of the leakage current of a battery Technical field

[0001] The invention relates to a current sensor intended to measure a high intensity electric current, in particular an electric current with an intensity greater than or equal to 200 A continuously.

[0002] A particularly advantageous application of such a current sensor concerns the field of electric or hybrid motor vehicles, and in particular the measurements of current at the input and / or output of a battery in such a vehicle. Prior art

[0003] Current sensors are known in the prior art for measuring an electric current at the input and / or output of an electric battery, where said battery is intended to power an electric motor in an electric or hybrid motor vehicle. Such current sensors may be based on a sensitive component of the resistor bar type, or more commonly a "busbar shunt". Such a sensitive component is constituted by a resistive bar (or "shunt", in English), framed by two interconnection plates (or "busbar", in English).

[0004] The resistive bar is formed of an electrically resistive material, and thus forms a measuring resistor. It is soldered on each side to a respective interconnection plate, simply ensuring the passage of current. In use, each respective of the interconnection plates is connected to an electrical circuit incorporating the battery.

[0005] The sensitive component is connected to a printed circuit board, which receives current measuring electronics. The current measuring electronics is configured to carry out an electrical voltage measurement, and to deduce a current value therefrom taking into account the known electrical resistance of the resistive bar. The printed circuit board is advantageously superimposed on the sensitive component, and connected to the latter at the level of solder points between the sensitive component and the printed circuit board.

[0006] It is known from the prior art to use an electrical circuit such as that of [Fig.l] in order to measure a leakage current of a traction battery of a motor vehicle. In particular, this measurement of the leakage current signals whether there is a risk for a user in contact with the electrical circuit.

[0007] The architecture of the electrical circuit 2 comprises:

[0008] - a battery BAT comprising a high potential BAT+ and a low potential BAT-, the difference between the high potential BAT+ and the low potential BAT- defining a VBAT voltage,

[0009] - a voltage divider bridge PI comprising a first resistor RI and a second resistor R2 electrically connected to each other at a midpoint defining an intermediate potential Vmid, the first resistor RI being electrically connected between the intermediate potential Vmid and the high potential of the battery BAT+, the second resistor R2 being electrically connected between the intermediate potential Vmid and the low potential BAT- of the battery BAT,

[0010] - a third resistor R3 capable of being electrically connected or not between the intermediate potential Vmid and the high potential BAT+ of the battery BAT by a switch SW 1 of switching means, and

[0011] - a fourth resistor R4 capable of being electrically connected or not between the intermediate potential Vmid and the low potential BAT- of the battery BAT by a switch SW2 of said switching means, the intermediate potential Vmid being intended to be electrically connected to a high voltage ground GND of a vehicle.

[0012] In addition, the vehicle defines: - between the intermediate potential Vmid and the high potential BAT+, a first construction capacity CyP, a first parasitic resistance RIP connected in parallel to each other, and - between the intermediate potential Vmid and the low potential BAT-, a second construction capacity CyM and a second parasitic resistance RIM connected in parallel to each other.

[0013] The first and second CyP, CyM construction capacitors have capacitances typically equal to 1 pP.

[0014] The first and second parasitic resistors are crossed by a potential with which the user can be in contact.

[0015] The battery leakage current is translated by the values ​​of the first and second parasitic resistances RIP and RIM, which are linked to the value of the intermediate voltage Vmid.

[0016] However, the charging time of the first and second construction capacities CyP, CyM requires waiting before being able to measure a value of the intermediate voltage in stabilized mode.

[0017] Typically, the potential difference between the intermediate potential Vmid and the high voltage ground GND stabilizes from about five times the time of the charging time constant of the first and second construction capacitors CyP, CyM. This difference is called the intermediate voltage.

[0018] Before reaching the stabilized regime, the intermediate voltage is in a so-called transient regime during which it is not possible to measure a stabilized value of the intermediate voltage.

[0019] Since the duration of this measurement is limited in time, there is a risk that it will be carried out during this transient regime. The measured value being false, it is possible that the leakage current is too high for a user in contact with the electrical circuit without the electrical circuit being able to signal such a danger. Summary

[0020] For this purpose, the present document relates to a method for measuring a leakage current of a battery of an electrical circuit, said circuit comprising:

[0021] - the battery, said battery being a traction battery of a motor vehicle and comprising a high potential and a low potential,

[0022] - a voltage divider bridge comprising a first resistor and a second resistor resistors electrically connected to each other at a midpoint defining an intermediate potential, the first resistor being electrically connected between the intermediate potential and the high potential of the battery, the second resistor being electrically connected between the intermediate potential and the low potential of the battery,

[0023] - a third resistor capable of being electrically connected or not between the intermediate potential and the high potential of the battery by switching means,

[0024] - a fourth resistor capable of being electrically connected or not between the intermediate potential and the low potential of the battery by said switching means, the intermediate potential being intended to be electrically connected to a high voltage ground of a vehicle,

[0025] said vehicle defining a first construction capacitance and a first parasitic resistance connected in parallel to each other between the intermediate potential and the high potential,

[0026] said vehicle defining a second construction capacitance and a second parasitic resistance connected in parallel with each other between the intermediate potential and the low potential,

[0027] said method comprising the successive steps consisting of:

[0028] a) using the switching means so that the third resistor is not electrically connected between the intermediate potential and the high potential of the battery and so that the fourth resistor is not electrically connected between the intermediate potential and the low potential of the battery,

[0029] b) measuring an initial value of the intermediate voltage, if the initial value of the intermediate voltage is less than or equal to half of a difference between the high potential and the low potential of the battery, the following steps of the method are carried out according to a first case, otherwise the following steps of the method are carried out according to a second case,

[0030] c) in the first case, using the switching means so that the third resistor is electrically connected between the intermediate potential and the high potential of the battery and so that the fourth resistor is not electrically connected between the intermediate potential and the low potential of the battery; in the second case, using the switching means so that the third resistor is not electrically connected between the intermediate potential and the high potential of the battery and so that the fourth resistor is electrically connected between the intermediate potential and the low potential of the battery;

[0031] d) performing a first plurality of measurements of a difference between the intermediate potential and the high voltage ground of the vehicle, said difference corresponding to an intermediate voltage, said first plurality of measurements being spaced in time over a first time interval and comprising a measurement of the intermediate voltage at the upper terminal of the first time interval;

[0032] e) deducing from the first plurality of measurements a first stabilized value of the intermediate voltage;

[0033] f) using the switching means so that the third resistor is not electrically connected between the intermediate potential and the high potential of the battery and so that the fourth resistor is not electrically connected between the intermediate potential and the low potential of the battery;

[0034] g) performing a second plurality of measurements of the intermediate voltage, said second plurality of measurements being spaced in time over a second time interval and comprising a measurement of the intermediate voltage at the upper terminal of the second time interval;

[0035] h) deducing from the second plurality of measurements a second stabilized value of the intermediate voltage;

[0036] i) deducing, by calculation, and using said first and second stabilized values ​​of the intermediate voltage, the values ​​of the first parasitic resistance and of the second parasitic resistance; and

[0037] j) deducing, by calculation, the leakage current at the terminals of the first parasitic resistance and the second parasitic resistance.

[0038] In the remainder of the document, intermediate voltage means the potential difference between the midpoint and the high voltage ground of the vehicle.

[0039] In this way, even if the first or second plurality of measurements does not include the first or second stabilized value of the intermediate voltage respectively, an approximate value of the first or second stabilized value of the intermediate voltage can be deduced therefrom.

[0040] In other words, the method makes it possible to overcome the limit imposed by the charging time of the first and second construction capacities.

[0041] Even if the first and second plurality of measurements are carried out in the transient regime, the method makes it possible to deduce therefrom the values ​​of the first and second stabilized values ​​of the intermediate voltage, and therefore the leakage current at the terminals of the first parasitic resistance and the second parasitic resistance.

[0042] Therefore, the faster calculation (in a shorter time) of the leakage current limits the risk that the leakage current is too high for a user in contact with the electrical circuit without the electrical circuit being able to signal such a danger.

[0043] The circuit may further comprise a first additional voltage divider bridge comprising the second resistor and a measuring resistor electrically connected to each other at a first additional midpoint defining a measuring potential. The difference between the measuring potential and the vehicle ground is a measuring voltage which is a fraction of the intermediate voltage.

[0044] Since the intermediate voltage may be of an order of magnitude too large for a voltage measuring instrument, measuring this measuring voltage makes it possible to overcome this limitation and to measure the evolution of the intermediate voltage through the measuring voltage. Typically the intermediate voltage is between 400 and 800 V.

[0045] The circuit may further comprise a second additional voltage divider bridge comprising the fourth resistor and a diagnostic resistor electrically connected to each other at a second additional midpoint defining a diagnostic potential. The difference between the diagnostic potential and the vehicle ground is a diagnostic voltage which makes it possible to check the operating state of the switching means.

[0046] The switching means may comprise a first switch arranged between the midpoint and the third resistor and / or a second switch arranged between the midpoint and the fourth resistor.

[0047] The choice of the first or second case makes it possible to measure more significant variations in the intermediate voltage.

[0048] This is why it is desired to increase the intermediate voltage in the first case, by electrically connecting the third resistor between the intermediate potential and the high potential of the battery and by not electrically connecting the fourth resistor between the intermediate potential and the low potential of the battery, by the switching means.

[0049] And conversely, it is desired to reduce the intermediate voltage in the second case, by not electrically connecting the third resistor between the intermediate potential and the high potential of the battery and by electrically connecting the fourth resistor between the intermediate potential and the low potential of the battery, by the switching means.

[0050] If the difference between the measurement of the intermediate voltage at the upper terminal of the first time interval and a measurement which precedes it among the first plurality of measurements of the intermediate voltage is greater than a first threshold voltage, step (e) comprises the sub-steps consisting of:

[0051] (el) performing a first extrapolation of the first plurality of measurements of the intermediate voltage, using a first extrapolation function, the first extrapolation function being, in the second case, a decreasing exponential function representing a discharge of the first and second construction capacitors of the vehicle, and in the first case, an increasing exponential function representing a charge of the first and second construction capacitors of the vehicle;

[0052] (e2) deduce, by calculation, the first stabilized value of the intermediate voltage,

[0053] otherwise the first stabilized value of the intermediate voltage is equal to the measurement of the intermediate voltage at the upper terminal of the first time interval.

[0054] During the transient regime of the charging or discharging of the first and second construction capacitors of the vehicle, the value of the intermediate voltage increases or decreases respectively over time. The difference between the measurement of the intermediate voltage at the upper terminal of the first time interval and a measurement which precedes it among the first plurality of measurements of the intermediate voltage is therefore large during this transient regime (i.e. larger than the first threshold voltage).

[0055] Also, steps (e1) and (e2) are carried out to determine the first stabilized value of the intermediate voltage.

[0056] On the contrary, during the stabilized regime of the charge of the first and second construction capacitors of the vehicle, the value of the intermediate voltage remains more or less constant and equal to the first stabilized value of the intermediate voltage.

[0057] The difference between the measurement of the intermediate voltage at the upper terminal of the first time interval and a measurement which precedes it among the first plurality of measurements of the intermediate voltage is therefore small during this stabilized regime (i.e. smaller than the first threshold voltage).

[0058] Also, it can be concluded in this case that the first stabilized value of the intermediate voltage is equal to the measurement of the intermediate voltage at the upper limit of the first time interval.

[0059] The first extrapolation function can be defined by the following formula: E * (1 - + F0, with E a voltage constant, r is a time constant, and VO the value of the intermediate voltage at the start of step (d).

[0060] At t = 0 s, the value of the intermediate voltage is equal to VO.

[0061] As t increases, the term . t tends towards 1 and the value of (1 - the intermediate voltage then tends towards a first stabilized value, here: E + V0.

[0062] We can consider that for t large enough (i.e. for , t close enough to 1), 1 1 — 6 f I the intermediate voltage switches from transient to steady state. The value of t for which this switch is made is defined by the first threshold voltage.

[0063] The extrapolation of step (el) may comprise the sub-steps consisting of:

[0064] (el-a) determining the time constant r by a convergence loop; and

[0065] (el-b) deducing the voltage constant E.

[0066] The first plurality of measurements can make it possible to obtain a two-equation system of the intermediate voltage at two instants.

[0067] By coupling the two equations, we obtain a single equation with the time constant r as the unknown.

[0068] Step (el-a) can be performed by a solver of this equation.

[0069] The solver can be a convergence loop that will test values ​​of the time constant r in the equation until converging to the exact value.

[0070] The solver may be a convergence loop that will test values ​​of the time constant r in the equation until converging to a value with an error less than 0.01.

[0071] For example, the convergence loop may be an alternation of positive and negative increments at the time constant r with adjustment of the increments at each iteration.

[0072] The increments can be between 0.01 s and 1 s.

[0073] If the difference between the measurement of the intermediate voltage at the upper terminal of the second time interval and a measurement preceding it among the second plurality of measurements of the intermediate voltage is greater than a second threshold voltage, step (h) comprises the sub-steps consisting of:

[0074] (hl) performing a second extrapolation of the second plurality of measurements of the intermediate voltage, using a second extrapolation function, the second extrapolation function being, in the second case, an increasing exponential function representing a charge of the first and second construction capacitors of the vehicle, and in the first case, a decreasing exponential function representing a discharge of the first and second construction capacitors of the vehicle;

[0075] (h2) deduce, by calculation, the second stabilized value of the intermediate voltage;

[0076] otherwise the second stabilized value of the intermediate voltage is equal to the measurement of the intermediate voltage at the upper terminal of the second time interval.

[0077] The variants presented for step (e) and the first plurality of measurements of the intermediate voltage can be transposed to step (h) and the second plurality of measurements of the intermediate voltage.

[0078] The second extrapolation function can be defined by the following formula: | jj + X /

[0079] with E' a voltage constant, r' is a time constant, and V0' the value of the intermediate voltage at the start of step (g).

[0080] At t = 0 s, the value of the intermediate voltage is equal to V0'.

[0081] As t increases, the term t tends towards 1 and the value of ¢1 - the intermediate voltage then tends towards a second stabilized value, here: E' + V0'.

[0082] We can consider that for t large enough (i.e. for t close enough to 1), ¢1 — the intermediate voltage switches from transient to steady state. The value of t for which this switch is made is defined by the first threshold voltage.

[0083] The extrapolation of step (hl) may comprise the sub-steps consisting of:

[0084] (hl-a) determining the time constant r' by a convergence loop; and

[0085] (hl-b) deduce the voltage constant E'.

[0086] The second plurality of measurements can make it possible to obtain a two-equation system of the intermediate voltage at two instants.

[0087] By coupling the two equations, we obtain a single equation with the time constant r as the unknown.

[0088] Step (hl-a) can be performed by a solver of this equation.

[0089] The solver can be a convergence loop that will test values ​​of the time constant r in the equation until converging to the exact value.

[0090] The solver may be a convergence loop that will test values ​​of the time constant r in the equation until converging to a value with an error less than 0.01.

[0091] For example, the convergence loop may be an alternation of positive and negative increments at the time constant r with adjustment of the increments at each iteration.

[0092] The increments can be between 0.01 s and 1 s.

[0093] The first threshold voltage and / or the second threshold voltage may be between 1 mV and 20 mV.

[0094] The present document also relates to a computer comprising a processor and a memory, said processor having access to the memory to read the steps stored in the memory, said computer being characterized in that it is configured for the implementation of each of the steps of a method according to the aforementioned type.

[0095] This document also relates to a motor vehicle equipped with the battery and a computer according to the aforementioned type. Brief description of the drawings

[0096] Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

[0097] [Fig-1] is a schematic view of an electrical circuit for measuring a current of leakage of a battery according to the prior art,

[0098] [Fig.2] illustrates the different stages of a leakage current measurement process of a battery according to an embodiment of this document,

[0099] [Fig.3] is a schematic view of an electrical circuit for measuring a current of leakage of a battery according to step (a) of the method of [Fig.2],

[0100] [Fig.4] is a schematic view of an electrical circuit for measuring a current of leakage of a battery according to step (c) of the method of [Fig.2], according to the second case,

[0101] [Fig.5] is a graph of the evolution of the intermediate voltage according to step (d) from the process of [Fig.2] to the closing of SW2, according to the second case,

[0102] [Fig.6] is a schematic view of an electrical circuit for measuring a current of leakage of a battery according to step (f) of the method of [Fig.2], according to the second case, and

[0103] [Fig.7] is a graph of the evolution of the intermediate voltage according to step (g) from the process of [Fig.2] to the opening of SW2, according to the second case. Description of the embodiments

[0104] [Fig.2] illustrates the different steps of the method for measuring a leakage current of a battery according to an embodiment of the present document.

[0105] The electrical circuit for measuring the leakage current is that of [Fig.3], which comprises:

[0106] - the traction battery BAT of a motor vehicle, the latter comprising a high potential BAT+ and low potential BAT-,

[0107] - a voltage divider bridge PI comprising a first resistor RI and a second resistor R2 electrically connected to each other at a midpoint defining an intermediate potential Vmid, the first resistor RI being electrically connected between the intermediate potential Vmid and the high potential of the battery BAT+, the second resistor R2 being electrically connected between the intermediate potential Vmid and the low potential of the battery BAT-,

[0108] - a third resistor R3 capable of being electrically connected or not between the intermediate potential Vmid and the high potential of the battery BAT+ by a switch SW 1 of switching means, and

[0109] - a fourth resistor R4 capable of being electrically connected or not between the intermediate potential Vmid and the low potential of the battery BAT- by a switch SW2 of said switching means, the intermediate potential Vmid being intended to be electrically connected to a ground GND of a vehicle.

[0110] The vehicle defines: - on the one hand, a first construction capacity CyP and a first parasitic resistance RIP connected in parallel to each other between the intermediate potential Vmid and the high potential BAT+, and - on the other hand, a second construction capacity CyM and a second parasitic resistance RIM connected in parallel to each other between the intermediate potential Vmid and the low potential BAT-,

[0111] The circuit further comprises:

[0112] - a first additional voltage divider bridge comprising the second re resistance R2 and a measuring resistor RMEAS electrically connected to each other at a first additional midpoint defining a measuring potential VISO_MEAS. The difference between the measuring potential VISO_MEAS and the low potential of the battery BAT- is a measuring voltage VISO_MEAS which is a fraction of the intermediate voltage Vmid, and

[0113] - a second additional voltage divider bridge comprising the fourth re resistor R4 and a diagnostic resistor RDIAG electrically connected to each other at a first additional midpoint defining a diagnostic potential VISO_DIAG. The difference between the measuring potential VISO_DIAG and the low potential of the battery BAT- is a diagnostic voltage VISO_DIAG which allows the correct operation of switches SW1, SW2 to be checked.

[0114] In the following, by measurement of the intermediate voltage Vinit, Vmidl and Vmid2 is meant the deduction of the measurement of the intermediate voltage through the measurement voltage VISO_MEAS.

[0115] During a step (a) of the method, the switching means are used so that the third resistor R3 is not electrically connected between the intermediate potential Vmid and the high potential BAT+ of the battery BAT and so that the fourth resistor R4 is not electrically connected between the intermediate potential Vmid and the low potential BAT- of the battery BAT. In other words, the switches SW 1 and SW2 are opened.

[0116] During a step (b) of the method, an initial value of the intermediate voltage Vinit is measured, if the initial value of the intermediate voltage Vinit is less than or equal to half of a difference between the high potential BAT+ and the low potential BAT- of the battery BAT, the following steps of the process are carried out according to the first case, otherwise the following steps of the process are carried out according to the second case.

[0117] The initial value of the intermediate voltage measured here is Vinit = 350 V.

[0118] With VBAT = 600 V, Vinit > VBAT / 2, we continue the process according to the second case.

[0119] In the first case, the switching means are used so that the third resistor R3 is electrically connected between the intermediate potential Vmid and the high potential BAT+ of the battery BAT and so that the fourth resistor R4 is not electrically connected between the intermediate potential Vmid and the low potential BAT- of the battery BAT. In other words, SW 1 is closed in the first case.

[0120] In the second case, the switching means are used so that the third resistor R3 is not electrically connected between the intermediate potential Vmid and the high potential BAT+ of the battery BAT and so that the fourth resistor R4 is electrically connected between the intermediate potential Vmid and the low potential BAT- of the battery BAT. In other words, SW2 is closed in the second case, and the electrical circuit is in the configuration illustrated in [Fig.4].

[0121] During a step (d) of the method, a first plurality of measurements Vmidl of a difference between the intermediate potential Vmid and the high voltage ground GND of the vehicle are carried out.

[0122] This difference corresponds to an intermediate voltage Vmidl in this configuration.

[0123] Reference is now made to [Fig.5] which is a graph of the intermediate voltage Vmidl over time. The first plurality of measurements of the intermediate voltage Vmidl comprises measurements V0 at t0 = 0 s, V2.5 at t2.5 = 2.5 s, V4.3 at t4.3 = 4.3 and V5 at t5 = 5 s over a first time interval with a lower bound t0 and an upper bound t5.

[0124] During a step (e) of the method, a first stabilized value Vstabl of the intermediate voltage Vmidl is deduced from the first plurality of measurements.

[0125] It is observed that the measured values ​​are in the transient regime of Vmidl, in particular, it is observed that V5 - V4.3 > Vseuill with Vseuill = 0.01 V.

[0126] In this case, step (e) comprises sub-steps (e1) and (e2).

[0127] During sub-step (el), a first extrapolation of the second plurality of measurements of the intermediate voltage Vmidl is carried out, using an increasing exponential function representing a discharge of the first and second capacitors CyP, CyM of the vehicle construction. The intermediate voltage Vmidl is defined by the following charge function:

[0128] [Math.l] FmFH(t) = E * 4- FO with E a voltage constant, r is a time constant.

[0129] Sub-step (el) itself comprises several sub-steps (el-a) and (el-b).

[0130] During sub-step (el-a), the time constant r is determined by a convergence loop.

[0131] Let us take for example a first system with two equations comprising the equations of V5 and V2.5.

[0132] We then have the equations:

[0133] [Math.2] = tj + FO

[0134] [Math.3] / î5X F5 = E * (1 - + F0

[0135] By coupling the two equations, we obtain:

[0136] [Math.4] / t2.5\ / r5\ (F5 - F0) * (^1 - er ) = (F2.5 - FO) « (1 - and )

[0137] Subsequently, a solver is used to solve this equation. This solver will first test a first value of the time constant r and then will carry out positive and / or negative increments of r to converge towards an approximate value of r.

[0138] Here we measure V5 = 0.577V, V2.5 = 0.754V and V0 = 1.483V.

[0139] It is possible to define a precision of the approximate value of r, by imposing that the terms on both sides of the equality must be equal to plus or minus a voltage uncertainty, or by imposing minimum values ​​of increments.

[0140] With minimal increments of 0.01 s, we find r = 5.03 s.

[0141] During a sub-step (el-b) of the method, the voltage constant E is then deduced using the following formula:

[0142] [Math.5] / ts \ E = (F5 - F0) / (1 - er )

[0143] We then find E = - 0.9641 V.

[0144] We then deduce during a step (e2) the first stabilized value Vstabl of the intermediate voltage with Vstabl = E + VO = 0.518 V.

[0145] Then, during a step (f) of the method, the switch that was closed in step (c) is opened, either in the first case SW1, or in the second case SW2. Thus the third resistor R3 is not electrically connected between the intermediate potential Vmid and the high potential BAT+ of the battery BAT and the fourth resistor R4 is not electrically connected between the intermediate potential Vmid and the low potential BAT- of the battery BAT.

[0146] We are in a second electrical configuration illustrated in [Fig.6].

[0147] Similar to step (d), during a step (g) of the method, a second plurality of measurements of the intermediate voltage Vmid2 are carried out in this second configuration.

[0148] Reference is now made to [Fig.7] which is a graph of the inter intermediate voltage Vmid2 over time. The second plurality of measurements of the intermediate voltage Vmid2 comprises measurements V0' at t0' = 0s, V2' at t2' = 2s, V5' at t5' = 5s and V7' at t7' = 7s over a second time interval with a lower bound t0 and an upper bound t7.

[0149] It is observed that the measured values ​​are in the transient regime of Vmid2, in particular, it is observed that V7' - V5' > Vseuil2 with Vseuil2 = 0.01 V.

[0150] In this case, step (h) comprises sub-steps (hl) and (h2).

[0151] During sub-step (hl), a second extrapolation of the second is carried out plurality of measurements of the intermediate voltage Vmid2, using an increasing exponential function representing a charge of the first and second capacitors CyP, CyM of vehicle construction. The intermediate voltage Vmid2 is defined by the following charge function:

[0152] [Math.6] Vmïd2(t) = Ef * (1 - q- Ï7Q' with E' a voltage constant, r' is a time constant.

[0153] Sub-step (hl) itself comprises several sub-steps (hl-a) and (hl-b).

[0154] During sub-step (hl-a), the time constant r' is determined by a convergence loop.

[0155] Let us take for example a second two-equation system comprising the equations of V5' and V7'.

[0156] We then have the following equations:

[0157] [Math.7] - F' > ( i - eVTT j -f- 70'

[0158] [Math. 8] y7' = Ef * fl - e““P j + WX

[0159]

[0160] By coupling the two equations, we obtain:

[0161] [Math.9] (F7' * I 1 - e PI = (V5' - 70') 41- I

[0162] Similarly, the solver used in step (el-a) is used to solve the equation.

[0163] Here we measure V7' = 1.245 V, V5' = 1.129 V and V0' = 0.521 V.

[0164] Of course, it is also possible to use in the first and second systems of equations other measures than those chosen from the first and second pluralities of measures respectively.

[0165] In our case, with minimal increments of 0.01 s, we find r' = 5.03 s.

[0166] During a sub-step (hl-b) of the method, the voltage constant E' is then deduced from using the following formula:

[0167] [Math. 10] E! = (V7f - RO') / (1 - e ' )

[0168] We then find E' = 0.9641 V.

[0169] We then deduce during a step (h2) the second stabilized value Vstab2 from the intermediate voltage with Vstab2 = E' + V0' = 1.485 V.

[0170] During a step (i) of the method, the values ​​of the first parasitic resistance RIP and of the second parasitic resistance RIM are deduced by calculation, and using said first and second stabilized values ​​of the intermediate voltage Vstabl, Vstab2.

[0171] During a step (j) of the method, the leakage current at the terminals of the first parasitic resistance RIP and the second parasitic resistance RIM is deduced by calculation.

Claims

Claims

1. Method for measuring a leakage current of a battery (BAT) of an electrical circuit, said circuit comprising: - the battery (BAT), said battery (BAT) being a traction battery (BAT) of a motor vehicle and comprising a high potential (BAT+) and a low potential (BAT-), - a voltage divider bridge comprising a first resistor (RI) and a second resistor electrically connected to each other at a midpoint defining an intermediate potential (Vmid), the first resistor (RI) being electrically connected between the intermediate potential (Vmid) and the high potential (BAT+) of the battery (BAT), the second resistor (R2) being electrically connected between the intermediate potential (Vmid) and the low potential (BAT-) of the battery (BAT),- a third resistor (R3) capable of being electrically connected or not between the intermediate potential (Vmid) and the high potential (BAT+) of the battery (BAT) by switching means (SW1, SW2), - a fourth resistor (R4) capable of being electrically connected or not between the intermediate potential (Vmid) and the low potential (BAT-) of the battery (BAT) by said switching means (SW1, SW2), the intermediate potential (Vmid) being intended to be electrically connected to a high voltage ground (GND) of a vehicle, said vehicle defining a first construction capacitance (CyP) and a first parasitic resistance (RIP) connected in parallel with each other between the intermediate potential (Vmid) and the high potential (BAT+), said vehicle defining a second construction capacitance (CyM) and a second parasitic resistance (RIM) connected in parallel with each other between the intermediate potential (Vmid) and the low potential (BAT-),said method comprising the successive steps consisting of:, a. using the switching means (SW1, SW2) so that the third resistor (R3) is not electrically connected between the intermediate potential (Vmid) and the high potential (BAT+) of the battery (BAT) and so that the fourth resistor (R4) is not electrically connected between the intermediate potential (Vmid) and the low potential (BAT-) of the battery (BAT), b. measure an initial value of an intermediate voltage (Vinit) corresponding to the potential difference between the intermediate potential (Vmid) and said high voltage ground (GND) of the vehicle, if the initial value of the intermediate voltage (Vinit) is less than or equal to half of a difference between the high potential (BAT+) and the low potential (BAT-) of the battery (BAT), the following steps of the method are carried out according to a first case, otherwise the following steps of the method are carried out according to a second case, c. in the first case, use the switching means (SW1, SW2) so that the third resistor (R3) is electrically connected between the intermediate potential (Vmid) and the high potential (BAT+) of the battery (BAT) and so that the fourth resistor (R4) is not electrically connected between the intermediate potential (Vmid) and the low potential (BAT-) of the battery (BAT); in the second case, use the switching means (SW1, SW2) so that the third resistor (R3) is not electrically connected between the intermediate potential (Vmid) and the high potential (BAT+) of the battery (BAT) and so that the fourth resistor (R4) is electrically connected between the intermediate potential (Vmid) and the low potential (BAT-) of the battery (BAT); d. performing a first plurality of measurements (Vmidl) of a difference between the intermediate potential (Vmid) and the high voltage ground (GND) of the vehicle, said difference corresponding to an intermediate voltage, said first plurality of measurements (Vmidl) being spaced in time over a first time interval and comprising a measurement of the intermediate voltage at the upper terminal of the first time interval; e. deducing from the first plurality of measurements (Vmidl) a first stabilized value of the intermediate voltage (Vstabl); f. use the switching means (SW1, SW2) so that the third resistor (R3) is not electrically connected between the intermediate potential (Vmid) and the high potential (BAT+) of the battery (BAT) and so that the fourth resistor (R4) is not electrically connected between the intermediate potential (Vmid) and the low potential (BAT-) of the battery (BAT) switching means (SW1, SW2), g. performing a second plurality of measurements (Vmid2) of the intermediate voltage, said second plurality of measurements (Vmid2) being spaced in time over a second time interval and comprising a measurement of the intermediate voltage at the upper terminal of the second time interval; h. deducing from the second plurality of measurements (Vmid2) a second stabilized value of the intermediate voltage (Vstab2); i. deducing, by calculation, and using said first and second stabilized values ​​of the intermediate voltage, the values ​​of the first parasitic resistance (RIP) and of the second parasitic resistance (RIM); and j. deduce, by calculation, the leakage current across the terminals of the first parasitic resistance (RIP) and the second parasitic resistance (RIM).

2. Method according to the preceding claim, in which, if the difference between the measurement of the intermediate voltage at the upper terminal of the first time interval and a measurement which precedes it among the first plurality of measurements (Vmidl) of the intermediate voltage is greater than a first threshold voltage, step (e) comprises the sub-steps consisting of: (el) performing a first extrapolation of the first plurality of measurements (Vmidl) of the intermediate voltage, using a first extrapolation function, the first extrapolation function being, in the second case, a decreasing exponential function representing a discharge of the first and second construction capacitors (CyP, CyM) of the vehicle, and in the first case, an increasing exponential function representing a charge of the first and second construction capacitors (CyP, CyM) of the vehicle; (e2) deduce, by calculation, the first stabilized value of the intermediate voltage (Vstabl), otherwise the first stabilized value of the intermediate voltage (Vstabl) is equal to the measurement of the intermediate voltage at the upper terminal of the first time interval.

3. Method according to the preceding claim, in which the first extrapolation function is defined by the following formula: E * ( 1 — e T ) + ^0« with E a voltage constant, r is a time constant, and V0 the value of the intermediate voltage at the start of step (d).

4. Method according to the preceding claim, in which the extrapolation of step (el) comprises the sub-steps consisting of: (el-a) determining the time constant r by a convergence loop; and (el-b) deducing the voltage constant E.

5. Method according to one of the preceding claims, in which, if the difference between the measurement of the intermediate voltage at the upper terminal of the second time interval and a measurement which precedes it among the second plurality of measurements (Vmid2) of the intermediate voltage is greater than a second threshold voltage, step (h) comprises the substeps consisting of: (hl) carrying out a second extrapolation of the second plurality of measurements (Vmid2) of the intermediate voltage, using a second extrapolation function, the second extrapolation function being, in the second case, an increasing exponential function representing a charge of the first and second construction capacitors (CyP, CyM) of the vehicle, and in the first case, a decreasing exponential function representing a discharge of the first and second construction capacitors (CyP, CyM) of the vehicle;(h2) deduce, by calculation, the second stabilized value of the intermediate voltage (Vstab2); otherwise the second stabilized value of the intermediate voltage (Vstab2) is equal to the measurement of the intermediate voltage at the upper limit of the second time interval.;

6. Method according to the preceding claim, in which the second extrapolation function is defined by the following formula: E1 * (1 - with E' a voltage constant, r' is a time constant, and V0' the value of the intermediate voltage at the start of step (g).

7. Method according to the preceding claim, in which the extrapolation of step (hl) comprises the sub-steps consisting of: (hl-a) determining the time constant r' by a convergence loop; and (hl-b) deducing the voltage constant E'.

8. Method according to one of claims 2 to 7, in which the first threshold voltage and / or the second threshold voltage (Vseuill, Vseuil2) is between 1 mV and 20 mV.

9. A computer comprising a processor and a memory, said processor having access to the memory to read the steps stored in the memory, said computer being characterized in that it is configured to implement each of the steps of a method according to one of the preceding claims.

10. Motor vehicle equipped with a battery (BAT) and a computer according to the preceding claim.

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