Patent Description:
Improving safety and comfort is always a concern in the automotive industry. For electrically powered vehicles, such as electric or hybrid powered vehicles, insulation of the high voltage battery is of significant importance to guarantee safety of the entire vehicle and its occupants. A high voltage battery in the present disclosure may be regarded as a battery with a nominal voltage of 50V or more, and specifically 100V or more.

The battery of a vehicle functions as an energy storage element for powering an electrical motor and thus enabling the vehicle to move. The battery may be part of the floor structure of the vehicle. A battery may include several cells, e. g lithium-ion cells grouped into modules.

The chassis of a vehicle such as a car may generally be considered a vehicle frame providing structural support of the vehicle. The chassis may be mainly made of steel. Specific insulation cabling, materials and coatings may be used to insulate the chassis from the battery. However, battery cable insulation and materials may deteriorate gradually or suddenly. Environmental factors such as humidity influence the insulation resistance as well.

Accordingly, electrically powered vehicles may require systems that check whether the insulation level of the battery is adequate or not before performing specific tasks. Such a task is for instance the start of the electrically powered vehicle, which may be dangerous for the occupants or even the vehicle itself if the battery is poorly insulated.

Therefore, before enabling the start of the vehicle, an electrical resistance between the battery and the chassis may need to be determined. This resistance will be referred to in the present disclosure as insulation resistance.

Depending on the value of the insulation resistance, e.g. if it is higher or lower than a predetermined threshold value, the start of the vehicle may be enabled or disabled.

<CIT> discloses an insulation resistance measuring device and method for calculating insulation resistance.

Currently, commercial sensors facilitating the determination of the insulation resistance exist. However, on average, sensors of this kind usually require about <NUM> seconds to obtain a rough measurement and about <NUM> seconds to obtain a definite value. The <NUM>-second time measurement just provides an indication in the event of very serious isolation fault.

Thus, in order to implement such a system safely, a driver may have to wait a considerable time (a few seconds or more) before a check has been performed on whether the insulation between the battery and the chassis is sufficient for a safe start of the vehicle. This time corresponds with the time needed to obtain the definite insulation resistance value.

The present disclosure provides, methods and systems that aim to avoid or reduce at least some of the aforementioned advantages.

In an aspect of the present disclosure, a system for measuring an insulation resistance between a battery and a chassis of an electrically powered vehicle is provided in accordance with claim <NUM>. The system comprises a voltage divider being configured to be connected in parallel with the battery and the chassis. The voltage divider comprises a first portion including a switch and a second portion including a first resistor. The first resistor and the switch are connected in series. The system further comprises a switch control unit configured to change a state of the switch; a voltage measurement unit configured to measure the voltage across the first resistor; and a voltage extrapolation unit configured to obtain a stationary value of the voltage at the first resistor by extrapolating two or more voltage values measured by the voltage measurement unit.

According to this aspect, an insulation resistance value may be determined more quickly, particularly because of the use of the voltage extrapolation unit. The voltage extrapolation unit avoids having to wait for a voltage over the resistor to stabilize, thus saving time in determining this voltage.

Therefore, an insulation resistance value may be quickly obtained by the use of a voltage divider comprising a single switch.

In examples of this aspect, the determination of two stationary voltage values across the resistor of measurement in a voltage divider may be used to determine an insulation resistance value.

The stationary voltages are determined by extrapolation.

Herein, an insulation resistance may be understood as an indicator of the electrical resistance between the battery and the chassis. The insulation resistance may include two values, one with respect to the positive terminal of the battery (RISO,P) and another one with respect to the negative terminal of the battery (RISO,N).

Herein, a voltage divider may be understood as an electrical circuit able to turn a large voltage into a smaller one. A voltage divider may for instance include two resistors.

Herein, extrapolating may be understood as predicting a value based on extending a known ensemble of values beyond the range covered by the known values.

Herein, a stationary voltage may refer to a voltage that no longer evolves with time due to the fact that the cause previously making it vary has stopped. For example, if a capacitor is being charged and this is making a voltage to vary, the voltage may become stationary when the capacitor is fully charge and thus no longer causes the voltage to vary. When the voltage is stationary it may be said that the voltage is in a stationary state.

In a further aspect of the present disclosure, a method according to claim <NUM> for measuring an insulation resistance between a battery and a chassis of an electrically powered vehicle by the system described throughout this disclosure is provided. The method comprises starting the battery; measuring a first plurality of voltages across the first resistor by the voltage measurement unit; determining a first stationary voltage across the first resistor based on an extrapolation of the first plurality of voltages by the voltage extrapolation unit, and interrupting the extrapolation; changing a state of the switch by the switch control unit; measuring a second plurality of voltages across the first resistor by the voltage measurement unit; determining a second stationary voltage across the first resistor based on an extrapolation of the second plurality of voltages by the voltage extrapolation unit and interrupting the extrapolation; and calculating the insulation resistance using the determined first and second stationary voltages across the first resistor.

The following figures are provided for enabling a good understand of various aspects of the present disclosure, but should not be considered as limiting in any way.

Even though examples are particularly shown for a system and a method for determining an insulation resistance in electrically powered vehicles throughout this disclosure, the same system and method may be used in hybrid vehicles and other electrical machines and/or in other applications as well.

In ideal conditions, an electrical circuit between the chassis , represented by a ground <NUM>, and the battery <NUM> would be fully resistive. Thus, an insulation resistance <NUM> may be provided between the terminals of the battery <NUM> and the chassis <NUM>. In particular, an insulation resistance RISO,P may be provided between the positive (+) terminal of the battery <NUM> and the chassis <NUM>, and an insulation resistance RISO,N may be provided between the negative (-) terminal of the battery <NUM> and the chassis <NUM>. In this situation, a voltage measured between the battery and the chassis would be substantially constant.

However, in real conditions and as schematically illustrated in <FIG>, an electrical separation between the battery <NUM> and the chassis <NUM> is also capacitive. Therefore, an electrical connection between the battery <NUM> and the chassis <NUM> may also be represented by two capacitors <NUM>, one CISO,P between the positive terminal (+) of the battery <NUM> and the chassis <NUM>, and another one CISO,N between the negative terminal (-) of the battery <NUM> and the chassis <NUM>. The resistances <NUM> (RISO,P and RISO,N) and the capacitors <NUM> (CISO,P and CISO,N) are connected in parallel.

In an aspect of the present disclosure, a system <NUM> for measuring an insulation resistance <NUM> (RISO,P, RISO,N) between a battery <NUM> and a chassis <NUM> of an electrically powered vehicle may be provided. An example of this system is schematically illustrated in <FIG>.

The system <NUM> comprises a voltage divider <NUM>, a switch control unit <NUM> (SWCU), a voltage measurement unit <NUM> (VMU) and a voltage extrapolation unit <NUM> (VEU). The voltage divider <NUM> includes a first resistor <NUM> connected in series with a switch <NUM>. The voltage divider <NUM> is configured to be connected in parallel with the battery <NUM> and the chassis <NUM> as e.g. shown in <FIG>.

In particular, the voltage divider <NUM> comprises a first portion <NUM> and a second portion <NUM>. The first portion <NUM> is electrically connected to a terminal of the battery <NUM> and the second portion <NUM> is electrically connected to the other terminal of the battery <NUM>. In this example, the first portion <NUM> is connected to the positive (+) terminal of the battery <NUM> and the second portion <NUM> is connected to the negative (-) terminal of the battery <NUM> in <FIG>. Independently to which terminal of the battery <NUM> may be connected to, the first portion <NUM> includes a switch <NUM> and the second portion <NUM> includes a first resistor <NUM>. The second portion is electrically connected <NUM> to the chassis <NUM>.

Besides electrically connecting the second portion <NUM> of the voltage divider <NUM> to the chassis <NUM>, connection <NUM> electrically also connects the voltage divider <NUM> and the chassis <NUM> to the insulation resistance RISO,P and RISO,N as well as the capacitors CISO,P and CISO,N. In addition, when the switch <NUM> is closed, current may flow between the first <NUM> and second <NUM> portions of the voltage divider <NUM>.

Although not illustrated in <FIG>, the SWCU <NUM>, VMU <NUM> and VEU <NUM> may be connected as shown in the example of <FIG>.

The switch control unit <NUM> is configured to change a state of the switch <NUM>. The voltage measurement unit <NUM> is configured to measure the voltage across the first resistor <NUM>. The voltage extrapolation unit <NUM> is configured to obtain a stationary value <NUM> (see <FIG>) of the voltage at the first resistor <NUM> by extrapolating two or more voltage values measured by the voltage measurement unit <NUM>. Obtaining may herein be regarded as calculating or estimating or a combination of both.

The voltage measurement unit <NUM> may measure a plurality of voltages across the first resistor <NUM> when the switch <NUM> is in a certain state. A switch may have two states: ON and OFF (or "CLOSED" and "OPEN"). When a switch is in the ON state, the switch is closed and allows current to pass, and when a switch is in the OFF state, the switch is open and does not allow current to pass.

The voltage across the first resistor <NUM> is not necessarily constant over time, but rather follows an exponential curve, as schematically represented in <FIG>. In particular, when the capacitors <NUM> are storing energy, i.e. they are charging, the voltage across the first resistor <NUM> may be low. On the contrary, when the capacitors <NUM> are discharging, the voltage across the first resistor <NUM> may increase. Changing the state of the switch <NUM> (from ON to OFF or from OFF to ON), which has been indicated in <FIG> with dashed vertical lines labeled as "SW", may thus enable to change from a charge to a discharge process or from a discharge to a charge process of the capacitors <NUM>, and thus change the voltage across the first resistor <NUM>.

Therefore, a plurality of voltage values across the first resistor <NUM> may be obtained when the switch is in a certain state and another plurality of voltage values across the first resistor <NUM> may be obtained when the switch is in the other state. These two voltage values may be used to determine the values of the insulation resistance RISO,P and RISO,N. These voltage values should be stationary values <NUM> in order to obtain accurate values of RISO,P and RISO,N. Stationary or "stable" values may be understood as values that no longer evolve over time, but rather that they are stable, as illustrated by horizontal lines in <FIG>. These voltage values may be obtained when a charging or discharging process has finished. , such a discharge or charge process no longer causes variation of the voltage across the first resistor <NUM> with time.

According to the present disclosure, a plurality of voltage values across the first resistor <NUM> may be measured by the voltage measurement unit <NUM> when the switch <NUM> is in a certain state, i.e. ON or OFF. In some examples, each time the VMU <NUM> measures a voltage value, it may be transmitted to the voltage extrapolation unit <NUM>. In some other examples, the VMU <NUM> may also store a set of values before sending them to the VEU <NUM>. In some of these examples, the VMU <NUM> may measure and store ten voltage values across the first resistor <NUM> before sending the ten voltage values to the VEU <NUM>. The number of voltage values included in a set of voltage values that the VMU <NUM> may send to the VEU <NUM> may be likewise be less or more than ten in other examples.

In case the VMU <NUM> measures one voltage value and transmits it to the VEU <NUM> (i.e. no grouping of values is made), the VMU <NUM> may or may not store such value. If each voltage value is transmitted after a measurement, the transmission may be performed immediately after the measurement. , in this case the VMU <NUM> does not wait to send the voltage value.

The voltage extrapolation unit <NUM> may receive the voltage values measured and sent by the voltage measurement unit <NUM>. The solid line in <FIG> represents a plurality of values measured by the VMU <NUM> and received by the VEU <NUM> according to an example.

The VEU <NUM> may use an extrapolation algorithm to determine a first stationary voltage <NUM> at the first resistor <NUM>. The dashed curve corresponds to an extrapolation curve determined by the VEU <NUM> based on the measured voltages across the first resistor <NUM> according to an example. The star <NUM> illustrates the determined first stationary voltage <NUM> in this example.

In some examples, the algorithm may use an asymptotic function.

In some examples, the algorithm may use the following equation and work as explained below: <MAT> V(t) represents a voltage across the first resistor <NUM> at instant t, VS is the stationary voltage across the first resistor <NUM> and b is a parameter (constant) related to the resistive and capacitive nature of the circuit.

In some examples, during extrapolation, the parameter b may be varied so as to fit measurements. Extrapolation may be stopped when the parameter b is found which fits sufficiently well with the measurements. The stationary voltage may then be calculated.

A first guess of the parameter b may be provided. Such a first guess might be based e.g. on values determined in previous occasions. This value and a plurality of voltage measurements (solid curve in <FIG>) across the first resistor <NUM> may be introduced in the above equation (written in vector form) in order to get a first estimation of VS. If in a subsequent iteration, the same VS value is found, it may be concluded that the parameter b was determined correctly. If however, subsequent determinations of Vs differ more than a threshold value from each other, then the parameter b may be adapted.

In other words, the VS value is used to calculate the function V(t) according to the above equation (dashed curve in <FIG>) and compared to the measured V(t) values, to see if the assumed value for "b" is correct.

If the difference between these curves is less than a predetermined threshold, the calculated voltage curve (solid line in <FIG>) and the measured data (dashed line in <FIG>) are deemed to be close enough and the value VS <NUM> is deemed to have been found.

If the difference is more than the predetermined threshold, another approximation of the parameter b may be calculated. This new value of b may be then used to calculate or estimate VS in a subsequent iteration. This process may be repeated until the calculated curve of the voltages across the first resistor <NUM> is deemed to be close enough to the measured voltages. When this happens, a stationary value VS <NUM> is deemed to have been found.

In some of these examples, a Newton-Raphson method may be used during the extrapolation. In particular, this method may be used to find a better approximation of the parameter b mentioned above.

This extrapolated voltage value <NUM> may correspond to a voltage that the VMU <NUM> may measure later in the stationary state (i.e. when stationary voltage may be measured) if the measurement process was not interrupted, i.e. once a charging or discharging process has ended and the voltage across the first resistor <NUM> no longer varies due to such a process.

However, due to the extrapolation process, it is not necessary to wait until the voltage value stabilizes to know what the stationary value <NUM> may be, but a first stationary voltage <NUM> may be determined in advance by the VEU <NUM> from the values it received from the VMU <NUM> (black curve in <FIG>).

The voltage extrapolation unit <NUM> may interrupt, i.e. end, the extrapolation process and send a signal to the switch control unit <NUM> indicating the SWCU <NUM> to change the state of the switch <NUM>.

In some examples, the VEU <NUM> may interrupt the extrapolation process after a certain period of time has elapsed. In some other examples, the VEU <NUM> may interrupt the extrapolation after having determined a stationary voltage value <NUM> across the first resistor <NUM> which is deemed sufficiently precise. For example, if a difference between a stationary voltage determined in a current step and in the previous step is less than a predetermined threshold, the extrapolated stationary voltage value in the current step may be deemed precise enough and the extrapolation process may be stopped.

As illustrated by a dashed vertical line in <FIG>, once the switch control unit <NUM> has received the indication from the voltage extrapolation unit <NUM>, the SWCU <NUM> may change the state of the switch <NUM>.

As the state of the switch <NUM> may have changed well before the arrival to the stationary state due to the use of an extrapolation process to anticipate a stationary voltage <NUM> across the first resistor <NUM>, time may have been saved in the subsequent calculation of the insulation resistance <NUM>.

Due to the change of the state of the switch <NUM>, the voltage across the first resistor <NUM> has also changed and a second plurality of voltage values across the first resistor <NUM> may be measured by the voltage measurement unit <NUM> and a second stationary voltage at the first resistor <NUM> may be extrapolated by the VEU <NUM>. Again, the extrapolation process may enable the reduction of the time necessary to arrive to a stationary value <NUM> of the voltage across the first resistor <NUM>.

Two values of the stationary voltage across may be sufficient to calculate the insulation resistance RISO,P and RISO,N. This may be explained further below.

The voltage measurement unit <NUM>, the voltage extrapolation unit <NUM> and the switch control unit <NUM> may each comprise a memory including instructions and a processor configured to execute the instructions stored in the memory. For example, the VMU <NUM> may include instructions for measuring the voltage across the first resistor <NUM> at a certain frequency, the VEU <NUM> may include instructions for performing an extrapolation method and interrupting it when a condition is met, and the SWCU <NUM> may include instructions for changing the state of the switch <NUM> upon receiving signaling from the VEU <NUM>.

The VMU <NUM> may comprise measurement elements configured to measure a voltage across the first resistor <NUM>. In an example, the VMU <NUM> may include a voltmeter to this end.

In some examples, as illustrated in <FIG>, the VMU <NUM> and the VEU <NUM> may be part of an estimation unit <NUM>. The VMU <NUM> and the VEU <NUM> may communicate through wires or wirelessly. Likewise, the VEU <NUM> and the SWCU <NUM> may communicate through wires or wirelessly. In some of these examples, the estimation unit <NUM> may be a single unit, i.e. the estimation unit (including VMU and VEU) may be integrated in a single chip or may be included in a chip.

In some examples, the voltage divider <NUM> may further comprise a second <NUM> and third <NUM> resistors connected in series with the first resistor <NUM> and the switch <NUM>, the third resistor <NUM> being placed between the first <NUM> and second <NUM> resistors.

In particular, the first portion <NUM> of the voltage divider <NUM> may further comprise a second resistor <NUM> and the second portion <NUM> of the voltage divider may further comprise a third resistor <NUM>. The electrical connection <NUM> between the voltage divider <NUM> and the chassis <NUM> may be provided between the switch <NUM> and the third resistor <NUM>.

In some examples, the resistance of the second <NUM> and third <NUM> resistors may be higher than the resistance of the first resistor <NUM>. In some examples, the resistance of the second <NUM> and third <NUM> resistors may be similar or substantially equal.

Having the second <NUM> and third <NUM> resistors may enable a decrease in the current circulating in the voltage divider <NUM>, in particular when the resistance of the second <NUM> and third <NUM> resistors have values of resistance larger than the first <NUM> resistor. Safety may be increased by the presence of the second <NUM> and third <NUM> resistors.

In some examples, the resistance of the second <NUM> and third <NUM> resistors may be between <NUM> and <NUM> times larger than the resistance of the first resistor <NUM>. In an example, the first resistor <NUM> may have a resistance of <NUM> ohms and the second <NUM> and third <NUM> resistors may have a resistance of <NUM> ohms.

In some examples, the resistance values of the first <NUM> resistor may be adjusted, e.g. optimized, such that voltages between <NUM> and <NUM> volts, and more in particular between <NUM> and <NUM> volts, may be measured by the voltage measurement unit <NUM>.

In some examples, the switch <NUM> may be connected between the second <NUM> and third <NUM> resistors, as shown in <FIG>. An electrical connection <NUM> between the switch <NUM> and the third resistor <NUM> and the chassis <NUM> may be provided as illustrated in <FIG>. For example, a wire connecting the switch <NUM> and the third resistor <NUM> may be put in electrical connection <NUM> with the chassis <NUM>.

As schematically illustrated in <FIG>, the chassis <NUM> may be regarded as including a connection to the ground. a connection to the ground may be provided between the switch <NUM> and the third resistor <NUM>. Accordingly, when the voltage divider <NUM> is connected in parallel with the battery <NUM> and the chassis <NUM>, current may always flow through the first resistor <NUM> no matter the state of the switch <NUM> (ON or OFF).

In some examples, the voltage divider <NUM> may further comprise an additional switch <NUM> between the first <NUM> and the third <NUM> resistors. The additional switch <NUM> is not configured to be used with relation to the extrapolation procedure and the insulation resistance <NUM> determination. The additional switch <NUM> may be used merely to ensure that an insulation exists between each terminal of the battery <NUM> and the chassis <NUM> once the voltage divider <NUM> is connected to it.

In another aspect of the invention, a method <NUM> for measuring an insulation resistance <NUM> RISO,P, RISO,N between a battery <NUM> and a chassis <NUM> of an electrically powered vehicle is provided. The method <NUM> is performed by the system for measuring an insulation resistance <NUM> referred to with respect to <FIG>. Thus, the system <NUM>, in particular the voltage divider <NUM>, is connected in parallel with the battery <NUM> and the chassis <NUM>. In some examples, the first portion <NUM> of the voltage divider <NUM> may be connected to the positive terminal (+) of the battery <NUM> and the second portion <NUM> of the voltage divider <NUM> may be connected to the negative (-) terminal of the battery <NUM>, as illustrated in <FIG>. The extrapolation concepts described with regard to <FIG> also apply to this method.

The method comprises, at block <NUM>, starting the battery <NUM>. Therefore, the vehicle may be powered and current may flow through the electrical circuit formed by the battery <NUM>, the chassis <NUM> and the voltage divider <NUM>.

The switch <NUM> is either open (OFF) or closed (ON). In some examples the switch <NUM> may be open, and in some other examples the switch <NUM> may be closed.

The method further comprises, at block <NUM>, measuring a first plurality of voltages across the first resistor <NUM> by the voltage measurement unit <NUM>.

The voltage values may be measured at a certain frequency. In some examples, the first plurality of voltages across the first resistor <NUM> may be measured at a frequency between <NUM> and <NUM>, for instance at about <NUM>.

In other words, in some examples, a time between two consecutive measurements of a voltage value across the first resistor <NUM> may be between <NUM> and <NUM> milliseconds. In an example, a voltage value across the first resistor <NUM> may be measured each <NUM> milliseconds.

In some examples, the frequency of measurements or time between consecutive measurements of a voltage value across the first resistor <NUM> may vary. For example, the frequency of measurement (and possibly the corresponding calculation) may be higher when the extrapolation is closer to being stopped, than the frequency of the "first" measurements, at the beginning of extrapolation.

In some examples, the voltage measurement unit <NUM> may send each measured voltage value to the voltage extrapolation unit <NUM> immediately after the measurement. In some other examples, the VMU <NUM> may store a set of voltage measurements before sending them to the VEU <NUM>. In an example, the VMU <NUM> may send sets of ten voltage values measured across the first resistor <NUM> after the tenth voltage value has been acquired.

In some examples the first plurality of voltages across the first resistor <NUM> measured by the VMU <NUM> may include between <NUM> and <NUM> measurements, more in particular between <NUM> and <NUM> measurements, and even more in particular between <NUM> and <NUM> measurements.

The method further comprises, at block <NUM>, by the voltage extrapolation unit <NUM>, determining a first stationary voltage <NUM> across the first resistor <NUM> based on an extrapolation of the first plurality of voltages and interrupting the extrapolation.

The VEU <NUM> may use any suitable extrapolation method. In some examples, a Newton-Raphson method may be used during the extrapolation.

In some examples, the determination may be performed before the interruption of the extrapolation. That is to say, the VEU <NUM> may determine a stationary voltage, and since a stationary voltage has been determined, the extrapolation is stopped.

In some of these examples, a stationary voltage <NUM> may be deemed found after a condition is met. In an example, a stationary voltage may be deemed found by the VEU <NUM> when a difference between an extrapolated voltage value in a current iteration of the extrapolation and an extrapolated voltage value in the previous iteration of the extrapolation is below a predetermined threshold.

In some examples, the determination may be performed after the interruption of the extrapolation. In some of these examples, the VEU <NUM> may interrupt the extrapolation after a certain period of time, e.g. a predetermined period of time, has elapsed. The VEU <NUM> may select the latest estimated stationary voltage value as the first stationary voltage in some examples.

Determining first and interrupting after the determination may enhance the flexibility of the method, as the time and voltage measurements required for determining a first stationary voltage may vary depending e.g. on which electrical vehicle the system <NUM> may be mounted to.

In some examples, measuring the first plurality of voltage values (block <NUM>) and determining a first stationary voltage and interrupting the extrapolation (block <NUM>) may be performed in less than <NUM> second, optionally between <NUM> and <NUM> seconds.

The method further comprises, at block <NUM>, changing a state of the switch <NUM> by the switch control unit <NUM>.

Once the VEU <NUM> has determined a first stationary voltage <NUM> across the first resistor <NUM>, the VEU <NUM> may send to the SWCU <NUM> an instruction to change the state of the switch <NUM> after the determination of a first stationary voltage at the first resistor <NUM> and interruption of the extrapolation.

The SWCU <NUM> may receive the instruction of the VEU <NUM> and thus change the state of the switch <NUM>. In some examples the switch may be closed if it was open during steps <NUM> and <NUM>, and vice versa in some other examples.

In accordance herewith, once the extrapolation is stopped, e.g. after a stationary voltage value has been determined, the state of the switch <NUM> will change. If the state of the switch <NUM> changes from OFF to ON, current may flow between the first <NUM> and second <NUM> portions of the voltage divider <NUM>.

The method further comprises, at block <NUM>, measuring a second plurality of voltages across the first resistor <NUM> by the voltage measurement unit <NUM>.

The particularities commented above with respect to the measurement of the first plurality of voltages across the first resistor <NUM> may apply to the measurement of the second plurality of voltages.

In some examples, a frequency of measurements (and possibly corresponding calculations) may vary during the first plurality of measurements (at block <NUM>). For example, the frequency of measurement (and possibly the corresponding calculation) may be higher when the extrapolation is closer to being stopped, than the frequency of the "first" measurements, at the beginning of extrapolation.

In some examples, the voltage measurement unit <NUM> may send each measured voltage value to the voltage extrapolation unit <NUM> immediately after the measurement.

The method may further comprise, at block <NUM>, determining a second stationary voltage across the first resistor <NUM> based on an extrapolation by the voltage extrapolation unit <NUM>, of the second plurality of voltages and interrupting the extrapolation.

The particularities commented above with respect to the steps <NUM> may apply to the step <NUM> as well. The VEU <NUM> may use any suitable extrapolation method. In some examples, a Newton-Raphson method may be used during the extrapolation. In some examples, the determination of the second stationary voltage may be performed before the interruption of the extrapolation. In some examples, measuring the second plurality of voltage values (block <NUM>) and determining a second stationary voltage and interrupting the extrapolation (block <NUM>) may be performed in less than <NUM> second, optionally between <NUM> and <NUM> seconds.

The method may further comprise, at block <NUM>, calculating the insulation resistance <NUM> RISO,P and RISO,N using the determined first and second stationary voltages across the first resistor.

In some examples, the voltage extrapolation unit <NUM> may perform this calculation. In some other examples, the estimation unit <NUM> may perform this calculation. For example, the estimation unit <NUM> may include a memory with instructions for calculating the insulation resistance <NUM> and a processor able to perform the calculation according to the stored instructions. Still in some other examples, another unit included in the system <NUM> may perform this task.

In some examples, calculating the insulation resistance <NUM> may comprise solving an equation system based on Kirchhoff's laws. Kirchhoff's laws are well known to the skilled person. The equations may be formulated according the electrical circuits that may be formed when the switch is in one state and when the switch is in the other state. As the first and second determined voltages across the first resistor <NUM> are values relating to the stationary state, the electrical circuit illustrated in <FIG> may be represented without capacitors <NUM>, e.g. as represented in <FIG>.

In some of these examples, mesh analysis, also known as mesh current method, may be used to write a system of five equations. <FIG> illustrate an application of mesh analysis according to an example.

In <FIG> the switch <NUM> is open, e.g. during the determination of the first stationary voltage across the first resistor <NUM>, and according to the mesh current method, currents I<NUM> <NUM> and I<NUM> <NUM> may be represented as shown in this figure.

In view of <FIG>, two equations with four unknowns, namely currents I<NUM> <NUM> and I<NUM> <NUM> as well as the insulation resistance RISO,P and RISO,N, may be determined for the situation in which the switch is open. These two equations may look as follows: <MAT> <MAT>.

Similarly, in <FIG> the switch <NUM> is closed, e.g. during the determination of the second stationary voltage across the first resistor <NUM>, and according to the mesh current method, currents I<NUM> <NUM>, I<NUM> <NUM> and I<NUM> <NUM> may be represented as shown in this figure.

In view of <FIG>, three equations with four unknowns (currents I<NUM> <NUM>, I<NUM> <NUM> and I<NUM> <NUM>, as well as the insulation resistance RISO,P and RISO,N), may be written. These three equations may look as follows: <MAT> <MAT> <MAT>.

By knowing the determined first and second stationary voltages across the first resistor <NUM>, these values may be introduced in the abovementioned equations, thereby obtaining a system of five equations with <NUM> unknowns (currents I<NUM> <NUM>, I<NUM> <NUM> and I<NUM> <NUM> and the insulation resistance RISO,P and RISO,N).

Accordingly, by solving such equation system, the insulation resistance <NUM> RISO,P and RISO,N may be calculated at block <NUM> according to an example.

In some examples a value for the insulation resistance RISO,P and RISO,N may be calculated in less than <NUM> seconds, optionally in less than <NUM> seconds, after the start of the method.

In some examples, the method further comprises starting the vehicle if the calculated insulation resistance is above a predetermined threshold.

In some examples, if a calculated insulation resistance value is below a predetermined threshold, the vehicle may not be started. In some of these examples, a signal indicating such an event may be emitted. For instance, an acoustic signal may be emitted, or an alarm may appear on a vehicle display. In some examples, the system or device for measuring an insulation resistance may be configured to intervene directly on the battery system.

In some examples, more than two pluralities of voltage across the first resistor <NUM> may be measured by the voltage measurement unit <NUM>. Thus, in some examples, the voltage extrapolation unit <NUM> may determine more than two stationary voltage values across the first resistor <NUM>, i.e. it may perform more than two extrapolations. In some of these examples, the stationary voltages for each state of the switch <NUM> may be selected among the available values for the calculation of the insulation resistance <NUM>. In some other examples, the stationary voltages for each state of the switch <NUM> may be averaged (one averaging operation per switch state) for the calculation of the insulation resistance <NUM>.

Claim 1:
A method (<NUM>) for measuring an insulation resistance (<NUM>) between a battery (<NUM>) and a chassis (<NUM>) of an electrically powered vehicle, wherein
one terminal of the battery (<NUM>) is electrically connected to a first portion (<NUM>) of a voltage divider (<NUM>) comprising a switch (<NUM>), and wherein
another terminal of the battery (<NUM>) is electrically connected to a second portion (<NUM>) of the voltage divider (<NUM>) comprising a first resistor (<NUM>), wherein
when the switch (<NUM>) is in a closed state a flow of current is allowed between the first portion (<NUM>) and the second portion (<NUM>) of the voltage divider (<NUM>), the method (<NUM>) comprising:
starting the battery;
measuring (<NUM>) by a voltage measurement unit (<NUM>) a first plurality of voltages across the first resistor (<NUM>) of the voltage divider (<NUM>);
determining (<NUM>) a first stationary voltage across the first resistor (<NUM>) based on an extrapolation of the first plurality of voltages by a voltage extrapolation unit (<NUM>), and interrupting the extrapolation;
changing (<NUM>) a state of the switch (<NUM>) by a switch control unit (<NUM>);
after changing (<NUM>) the state of the switch (<NUM>), measuring (<NUM>) a second plurality of voltages across the first resistor (<NUM>) by the voltage measurement unit (<NUM>);
determining (<NUM>) a second stationary voltage across the first resistor (<NUM>) based on an extrapolation of the second plurality of voltages by the voltage extrapolation unit (<NUM>), and interrupting the extrapolation; and
calculating (<NUM>) the insulation resistance (<NUM>) using the determined first and second stationary voltages across the first resistor (<NUM>).