FR3098456A1 - Method of acquiring a pilot charge signal by an electric vehicle - Google Patents

Abstract

Method for acquiring a charging pilot signal by a rechargeable electric vehicle, this signal being emitted by an electric charging station, this signal being a pulse-width modulated signal. The method comprises the following steps, for each pulse (9) of the charge pilot signal:- at the end of a calibrated delay (16) whose starting point is the rising edge (10), carrying out an acquisition sequence comprising at least two measurements (17,18,19,20) of the voltage of the charge pilot signal, the time interval between two of these measurements (17,18,19,20) being equal to a predetermined interval duration (21); - select a reference voltage for the pulse (9), among the voltage measurements (17,18,19,20) of the acquisition sequence. Figure for abstract: Fig. 4

Description

Method for acquiring a charging pilot signal by an electric vehicle

The invention relates to the field of rechargeable electric vehicles and relates more particularly to the charging of electric vehicles on electric charging terminals specifically provided for this use.

The term “electric vehicle” here refers to both exclusively electric-powered vehicles and hybrid vehicles. These vehicles include an electric accumulator, usually a battery pack, which can be recharged when connecting the electric vehicle to an electric power source. The vehicles concerned here are all vehicles whose propulsion is done at least partially by an electric motor powered by an electric energy accumulator which is rechargeable.

The development of electric vehicles, and of the infrastructure allowing their recharging, has led to the development of recharging stations according to technical norms and standards allowing the generalization of these recharging stations on the territory and the possibility of recharging different types of vehicles on these charging stations.

Known charging stations include at least one electric charging terminal. These electric charging stations are commonly referred to as EVSE (“Electric Vehicle Supply Equipment”). These charging stations generally provide direct current and high power, allowing rapid charging of an electric vehicle.

These charging stations are connected to electric vehicles by a standardized connector which includes a power connection for the actual charging of the electric accumulators, as well as a data connection allowing communication between the charging station and the vehicle. This communication is necessary for example to check that the charging station is available for charging as well as other information such as the power that can be supplied, etc.

Known charging terminals may for example comply with the IEC standard (“International Electrotechnical Commission”) IEC61851-1. This standard notably defines the communication protocols used between an electric vehicle and the charging station to which the vehicle is connected.

The charging station emits, via its data connection, a control signal comprising the information intended for the electric vehicle. This signal is referred to as the “load pilot signal”. This load pilot signal is a Pulse Width Modulation (PWM) signal providing information in two forms:
- the duty cycle of each pulse;
- the voltage level of each pulse.

When an electric vehicle is connected to such a charging station, this vehicle must acquire these two types of information. In other words, the electric vehicle must determine, for each pulse of the signal, what is the voltage level as well as the duty cycle of the pulse, in order to acquire the information coming from the charging station and coded in the form of voltage and duty cycle.

To ensure this acquisition, current electric vehicles are generally designed to acquire the charging pilot signal by sampling it at high frequency. For a signal frequency of 1 kHz, this sampling is for example carried out at values which can reach 1 MHz. The charge pilot signal is sampled using an analog/digital converter and then is reconstructed digitally so that it can be analyzed by removing any irregularities. The duty cycle and voltage level of each pulse are then determined. The charge pilot signal is thus digitized in order to identify the profile of each signal pulse, freeing itself from edge effects and other disturbances.

High-frequency sampling mobilizes significant hardware and software resources. Most electric vehicles thus have a dedicated computer for communication with the charging station. This dedicated computer has its own means of calculation such as a microcontroller, as well as an analog/digital converter for sampling.

The aim of the invention is to improve the methods for acquiring a charging pilot signal so as to reduce the resources necessary for communication between a vehicle and a charging station.

To this end, the invention relates to a method for acquiring a charging pilot signal by a rechargeable electric vehicle, this signal being emitted by an electric charging station, this signal being a pulse-width modulated signal having a variable duty cycle between a minimum value and a maximum value constituting first information, and having a variable voltage level constituting second information. This method comprises the following steps, for each pulse of the charge pilot signal:
- detecting a rising edge of the charge pilot signal corresponding to the start of the pulse;
- at the end of a calibrated delay whose starting point is the rising edge, carry out an acquisition sequence comprising at least two measurements of the voltage of the charge pilot signal, the time interval between two of these measurements being equal at a predetermined interval duration;
- detecting a falling edge of the charge pilot signal corresponding to the end of the pulse;
- determine the duty cycle of the pulse;
- select a reference voltage for the pulse, among the voltage measurements of the acquisition sequence.

In a method according to the invention, the need for hardware and software resources is very significantly reduced compared to high-frequency sampling. The load pilot signal is no longer sampled. The information needed to determine the voltage level of each pulse is taken directly from a small number of measurements.

According to one embodiment, the acquisition sequence comprises between three and ten voltage measurements, which is sufficient for example for a pulse-width modulated signal whose frequency is 1 kHz. If we compare with a high frequency sampling (for example a sampling at 1 MHz), the latter leads to perform about 1000 voltage measurements for each pulse. The number of voltage measurements according to the invention, for example from 3 to 10 voltage measurements per pulse, is in this example divided by 100 or more.

The implementation of the method according to the invention requires very low hardware and software resources, which lowers the cost of the hardware necessary within the electric vehicle.

The reduction in the necessary hardware and software resources is such that the implementation of the method no longer requires a computer dedicated to this function. Consequently, the charge pilot signal acquisition function can be assigned to another computer already present in the vehicle, for example the supervision unit of the electric vehicle, which manages the charge and the batteries, or even the unit engine control unit for a hybrid vehicle, or any other electronic control unit. These other electronic control units of the vehicle generally already have an analog/digital converter used for other functions and which can be used in addition for the implementation of the method. The low resources necessary for the implementation of the method make it possible to share the resources of an analog/digital converter already provided for other functions.

Thus, in a particularly advantageous embodiment, the implementation of the method for acquiring the charge pilot signal does not require any specific hardware resource and simply requires reprogramming of another electronic control unit of the vehicle which can implement the process without requiring scaling up.

This significant reduction in the resources necessary for the acquisition of the charge pilot signal is achieved thanks to the acquisition sequence whose calibrated delay positions the start of the acquisition sequence and whose predetermined interval durations guarantee that at least one voltage measurement is freed from most of the signal disturbances that occur just after the rising edge of each pulse.

According to a preferred characteristic, the first voltage measurement of the acquisition sequence is carried out during a pulse, before the falling edge of this pulse, and this for any pulse, even those corresponding to the minimum duty cycle.

The method according to the invention may comprise the following additional characteristics, alone or in combination:
- the calibrated delay is less than the pulse duration which corresponds to said minimum value of the duty cycle, the pulse duration being defined as the duration passing between the rising edge and the falling edge of the pulse;
- the calibrated delay is less than the pulse duration which corresponds to said minimum value of the duty cycle, reduced by the time required to perform a voltage measurement;
- the calibrated delay is equal to the duration of the pulse of the charge pilot signal which corresponds to said minimum value of the duty cycle, reduced by 5 to 10 μs;
the method comprises a step of initializing a hardware trigger at the time of the rising edge, this hardware trigger triggering the acquisition sequence once the calibrated delay has elapsed;
- the voltage of the charge pilot signal is variable among a plurality of predefined voltage levels, and the step of selecting a reference voltage for the pulse is carried out by comparison between the values of the voltage measurements of the acquisition sequence and said predefined voltage levels, the chosen reference voltage being the voltage value which is equal to a predefined voltage level;
- if two voltage values are equal to a predefined voltage level, the chosen reference voltage is the voltage value closest to the falling edge of the pulse;
- the step of selecting a reference voltage for the pulse is carried out from an index table indicating, according to the duty cycle of the pulse, the voltage measurement to be chosen in the acquisition sequence;
- the index table indicates, for each duty cycle, the voltage measurement which, within an acquisition sequence, is located the latest before the falling edge;
the acquisition sequence comprises three to ten measurements of the voltage of the charge pilot signal, and preferably four measurements of the voltage of the charge pilot signal.

The invention also relates to an electronic control unit which is characterized in that it comprises means for implementing all the steps of a method according to the invention.

Other characteristics and advantages of the invention will emerge from the description given of it below, by way of indication and in no way limiting, with reference to the appended drawings, in which:

Figure 1 schematically illustrates an electric vehicle connected to a charging station;

FIG. 2 represents an example of a charge pilot signal;

Figure 3 illustrates an example of the actual shape of a charge pilot signal pulse;

FIG. 4 schematically illustrates an acquisition sequence of the method according to the invention;

Figure 5 is similar to Figure 4 in a situation where the duty cycle is minimal;

Figure 6 is similar to Figure 4 in a situation where the duty cycle is maximum;

FIG. 7 schematically represents an electric vehicle electronic control unit, suitable for implementing the method according to the invention.

Figure 1 is a schematic representation illustrating an electric vehicle 1 connected to a charging station 2 via a connector 3.

The connector 3 comprises a power connection (not shown) which allows the effective charging of the batteries of the electric vehicle, as well as a data connection 4 by which a charging pilot signal is transmitted from the charging station 2 to the electric vehicle.

The charging pilot signal emitted by the charging station 2 informs the electric vehicle of the charging conditions, gives instructions to the vehicle to start charging, or any other information useful or necessary for the charging operation of the vehicle batteries.

The charging station 2 emits the charging pilot signal thanks to a circuit 5 producing a pulse-width modulated signal, each pulse of which is characterized by its width and also by its height. The information contained in the charge pilot signal is therefore encoded in two ways:
- by the duty cycle of each pulse, ie by the width of the pulse;
- by the voltage of each pulse, ie by the height of the pulse.

A large amount of information can thus be coded, in parallel or in combination, by the voltage and the duty cycle of each pulse, the pulses succeeding each other at the frequency of the signal. For example, the duty cycle can inform the electric vehicle of the charging power available, while the voltage level can determine whether the conditions are favorable for charging to take place.

For the acquisition of the charge pilot signal, the electric vehicle 1 has a voltage measurement circuit 6 and a frequency measurement circuit 7. The voltage measurement circuit 6 allows the electric vehicle to perform voltage measurements to determine the voltage level of each signal pulse. The frequency measurement circuit 7 makes it possible to determine the frequency of the signal and the duty cycle of each pulse.

The electric vehicle 1 also comprises a charge controller 8 adapted to control the charge of the vehicle and to receive for this the information coming from the circuits 6, 7, that is to say the information transmitted by the charging terminal 2 via the load pilot signal.

FIG. 2 illustrates a charging pilot signal emitted by the charging station 2 and acquired by the electric vehicle 1 thanks to its voltage measurement 6 and frequency measurement 7 circuits.

In this schematic illustrative example, nine pulses 9 of the charge pilot signal are shown. In this example, all pulses have the same 50% duty cycle. Each pulse 9 starts with a rising edge 10, settles at a constant voltage value over a width determined by the duty cycle, and ends with a falling edge 11. In the example illustrated in FIG. 2, for a load pilot signal frequency of 1 kHz, and a duty cycle of 50%, the width of a pulse 9 is 500 μs.

Although in the example illustrated in FIG. 2 all the pulses 9 have the same duty cycle, this duty cycle may in reality vary from one pulse to another depending on the information to be transmitted by the charging terminal 2 The duty cycle can take any value between a minimum value and a maximum value predefined for the charging station. In this example, the range of possible duty cycles is: 3% - 98%.

The charge pilot signal of FIG. 2 also presents for each pulse 9 a voltage level which also carries information. In the example of figure 2, two voltage levels are represented: 9 V and 6 V.

The coding of the information thanks to the variation of the duty cycle and the voltage level of the pulses 9 is not the subject of the present description and will not be described in more detail here. The IEC61851-1 standard provides examples of encoding information using these two parameters. Similarly, any other protocol can be considered to implement these two parameters and encode the information. The object of the present description is the acquisition by the electric vehicle of the duty cycle and voltage level values, with a view to obtaining the information thus coded.

Figure 3 gives an example of the real shape of a pulse 9 of the charge pilot signal, measured with an oscilloscope. The pulses 9 are of course not rectangular as in the theoretical example of FIG. 2, but indeed present anomalies and other oscillation phenomena.

In this example of FIG. 3, the duty cycle of pulse 9 is 16% and the voltage level of this pulse 9 is 8 V. The duty cycle of 16% corresponds in this example to a width 12 of l pulse 9 of 160 µs. The pulse width is defined as the time between the rising edge 10 and the falling edge 11.

Among the anomalies and oscillation phenomena observed for pulse 9, the most important is a voltage peak 13 appearing just after the rising edge 10. The width 14 of this voltage peak 13 is here 45 μs (for this report 16% duty cycle). The voltage spike 13 occurs for each of the 9 pulses. The width 14 of the voltage spike 13 increases with the duty cycle of the 9 pulse.

Pulse 9 also has a substantially constant range 15 which extends according to the voltage level specific to the pulse considered, here 8 V.

The acquisition of the value of the duty cycle of a pulse 9 consists for the frequency measurement circuit 7 in determining the width of the pulse 9, that is to say in measuring the duration 12 between the rising edge 10 and the falling edge 11. The measurement of the period of the signal is made possible by measuring the time between two rising edges 10 of two successive pulses 9. Circuit 7 determines the duty cycle of a pulse by establishing the ratio of the duration of the pulse with the period of the signal.

With regard to the voltage level of the pulse 9, this is measured by the voltage measuring circuit 6 which must necessarily measure the voltage at the level of the constant range 15. A measurement outside the constant range 15 , and in particular at the voltage peak 13, would distort the measurement. In the example of figure 3, the voltage peak 13 peaks at a voltage of 11.2 V while the voltage level of the considered pulse 9 is 8 V at the constant range 15.

Note that neither the duty cycle nor the voltage level of a pulse 9 is known in advance by the electric vehicle. The difficulty in determining the voltage level of a pulse 9 lies in the need to make at least one voltage measurement in the constant range 9, and to select this measurement as the reference voltage for the pulse. This reference voltage is the voltage that was actually emitted by the charging station for this pulse.

Figure 4 illustrates the method of measuring the voltage level of a pulse 9. The electric vehicle is first connected to the charging station and the latter emits a charging pilot signal. FIG. 4 schematically illustrates the first pulse 9, the voltage level of which is 6 V, of this charge pilot signal.

In a first step, the rising edge 10 is detected. In this example, the rising edge 10 is detected when a voltage above a certain threshold is measured.

From the rising edge 10, a trigger is initialized. This trigger is provided to trigger an acquisition sequence at the end of a delay 16 (hereinafter referred to as the "calibrated delay"), the starting point of which is the detection of the rising edge 10. This trigger is preferably a hardware trigger ( “hardware trigger”, in English), that is to say a routine in low-level programming language which is directly connected to an input/output line of the microcontroller. Such a hardware trigger is independent of the programs executed by the microcontroller and guarantees the correct measurement of the calibrated delay 16. The hardware trigger counts the time elapsed from the rising edge 10 and, at the end of the calibrated delay 16, the sequence acquisition starts with a first measurement of the voltage 17 of the signal.

After this first voltage measurement 17, at least one other measurement of the signal voltage is carried out to constitute the acquisition sequence. In the present example, three other voltage measurements 18, 19, 20 are carried out and the acquisition sequence thus comprises four voltage measurements. The voltage measurements are carried out at regular intervals, once a predetermined interval duration 21 has elapsed since the previous voltage measurement.

Each of the voltage measurements 17, 18, 19, 20 is here schematized by a square wave. Each voltage measurement requiring a certain time to be carried out (materially dependent on the voltage measurement circuit used), these pulses have a duration represented by a width 22. In the present example, the duration 22 is 3.4 μs.

In this example relating to a load pilot signal with a frequency of 1 kHz, the calibrated delay 16 is 22.5 μs and the predetermined interval duration 21 is 30 μs. The choice of the calibrated delay 16, the number of voltage measurements of the acquisition sequence, and the predetermined interval duration 21, is made so that the following criteria are met:
- the first voltage measurement 17 of the acquisition sequence must be carried out during the pulse, that is to say between the rising edge 10 and the falling edge 11 of the pulse, and this whatever the cyclical report ;
- at least one voltage measurement must be located outside the voltage peak 13.

In the example illustrated in FIG. 13, relating to a median duty cycle, the first voltage measurement 17 fulfills these two criteria on its own.

Figures 5 and 6 are similar to Figure 4 but illustrate the situation, respectively, for the minimum duty cycle and for the maximum duty cycle. Regardless of the duty cycle of the load pilot signal, illustrated by the three examples in Figures 4 to 6, the configuration of the acquisition sequence does not change. The calibrated delay 16 and the interval durations 21 are constants.

In Figure 5, the minimum duty cycle is, according to the example, 3%. In this situation, only the first voltage measurement 17 is carried out at the moment of the pulse 9, that is to say before the falling edge 11. The other three voltage measurements 18, 19, 20 return a zero value. The reference voltage for pulse 9, chosen for this case, will therefore be the result of the first measurement 17, i.e. 6 V.

Figure 5 also illustrates the situation in which the calibration of the calibrated delay is carried out. In this situation of minimum size of the constant range 15, the calibrated delay is adjusted so that the first voltage measurement 17 of the acquisition sequence is located just before the falling edge, taking into account the time 22 necessary for the realization of this measurement 17. In the present example, for a minimum duty cycle of 3%, the falling edge 11 occurs 30 μs after the rising edge 10. A calibrated delay 16 set at 22.5 μs makes it possible to perform the measurement of voltage lasting 3.4 µs (with a margin) before the arrival of the falling edge 11. Preferably, the calibrated delay 16 is equal to the duration of the duration of the pulse which corresponds to said minimum value of the duty cycle (here , 30 µs), decreased from 5 to 10 µs.

This calibration of the calibrated delay 16 is carried out during the programming of the electronic module in charge of acquiring the charge pilot signal, within the electric vehicle, knowing the minimum and maximum values defining the range of possible duty cycles (in view of example of a charging station standard or specification). Once the calibration of the calibrated delay 16 has been carried out, the value of the delay obtained (in our example: 22.5 μs) is then stored in the electronic module. The first voltage measurement 17 will thus be with certainty on the constant range 15 even for a pulse 9 corresponding to the minimum duty cycle, which offers the smallest constant range 15.

FIG. 6 illustrates the case of the maximum duty cycle of the charge pilot signal, which in this example is 98%. In this situation, the pulse width is 980 µs. As shown schematically in Figure 6, the voltage peak 13 has increased in duration, following the increase in the duty cycle.

The first voltage measurement 17 is always located before the falling edge 11 but is now performed during the voltage peak 13 and its value is therefore distorted. In this case, the last two voltage measurements 19, 20 are located outside the voltage peak and before the falling edge 11. These voltage measurements 19, 20 are therefore carried out in the constant range 15 and their value can be chosen as reference voltage for pulse 9. Preferably, the latest voltage measurement 20, that is to say the closest to the falling edge 11, will be taken into account, because the further the voltage measurement is from the rising edge 10, and therefore of the voltage peak 13, the less this measurement will undergo disturbances linked to the voltage peak 13.

Figure 6 also illustrates the situation in which the calibration of the predetermined interval duration 21 is carried out, as well as the choice of the number of voltage measurements of the acquisition sequence. In this situation of maximum size of the voltage peak 13, the number of voltage measurements 18, 19, 20 in addition to the first voltage measurement, and the interval duration 21 are adjusted so that the last voltage measurement 20 of the acquisition sequence is located just before the falling edge, taking into account the time 22 necessary for carrying out this measurement 20. In the present example, for a maximum duty cycle of 98%, the falling edge 11 occurs 980 μs after the rising edge 10. A calibrated delay 16 fixed at 22.5 μs and an interval duration 21 fixed at 30 μs make it possible to carry out the last voltage measurement at 112.5 μs, which makes it possible to carry out this measurement largely before the arrival of the falling edge 11. In this example, it is in fact considered that a voltage peak 13 will never last more than 100 μs.

This calibration guarantees that at least one of the other voltage measurements 18, 19, 20 is located on the constant range 15, outside the voltage peak 13 or any other pulse onset disturbance.

As for the calibrated delay 16, the number of voltage measurements 17, 18, 19, 20 of the acquisition sequence, and the value of the interval duration 21 is stored in the relevant electronic module of the electric vehicle, during its programming. At least the last voltage measurement is thus guaranteed to be on the constant range 15 and outside the voltage peak 13, even for a pulse 9 corresponding to the maximum duty cycle, which offers the most extended voltage peak 13 in duration .

FIG. 7 schematically represents an electric vehicle control/command unit 23 suitable for implementing the method. This is, for example, an electric or hybrid vehicle supervisor HEVC (“Hybrid Electric Vehicle Controller”).

This unit 23 is intended to supervise various functions of the electric vehicle, in a conventional manner, and is here moreover employed to implement the charging pilot signal acquisition method. No dedicated hardware is therefore necessary to carry out the acquisition of the charge pilot signal.

The module 23 comprises a hardware filter 24 ("hardware filter") connected to the signal connector 4 (shown in Figure 1) and therefore receiving on its input 25 the load pilot signal.

Module 23 also includes a microcontroller 23 to which filter 24 is connected. Within the microcontroller 23, the filter 24 is connected to a chronograph module 26 (“timer module”, in English) as well as to an analog/digital converter 27. The chronograph module 26 receives from the filter 24 a threshold detection signal and thus makes it possible to detect the rising 10 and falling 11 edges of the signal. The analog/digital converter 27 receives from the filter 24 the voltage of the signal and therefore allows the realization of the voltage measurements of the acquisition sequence.

The chronograph module 26 also implements the hardware trigger 28 making it possible to determine the flow of the calibrated delay 16 from the rising edge of each pulse.

FIG. 5 schematizes by a rectangle 30 the operation of determining the duty cycle of the charge pilot signal, and by a rectangle 31 the voltage measurements carried out in the acquisition sequence for each pulse of the signal.

The two elements 30, 31 come together for an operation 32 of selecting the voltage measurement 17, 18, 19, 20 which is chosen as the reference voltage for a pulse. The selection operation 32 is linked to the general strategy of the supervisor module (schematized by the rectangle 33) which will take into account the information communicated by the charging station 2, via the charging pilot signal.

The selection step 32 can be carried out in various ways.

For example, the selection step 32 can be performed by analyzing and comparing the voltage measurements 17, 18, 19, 20. If the possible voltage level for a pulse corresponds to a value which is chosen from among a plurality of predefined values , all voltage measurements that are zero or do not correspond to these predefined values can be discarded. Only the voltage measurements giving a voltage corresponding to a possible voltage level, among the choices available to the charging station, are taken into account. Among these voltage measurements taken into account, the latest is chosen as the reference voltage for the considered pulse.

According to another embodiment, the choice of the voltage measurement 17, 18, 19, 20 to be taken into account is made according to the duty cycle of the pulse considered. At this step of the method, this duty cycle is known to the microcontroller thanks to step 30. The choice of the voltage measurement is made from an index table listing which voltage measurement to take into account in function of the duty cycle, the voltage measurement being identified by its position within the acquisition sequence (first measurement 17, second measurement 18, third measurement 19, fourth measurement 20, in the present example).

The behavior of a 9 pulse is similar for the same duty cycle, with respect to the establishment of the constant range 15. In other words, two pulses with the same duty cycle will both present a constant value after the same duration which depends of this duty cycle. The index table therefore indicates, for each duty cycle, or for each range of duty cycle, the voltage measurement which will notably have the characteristic of being on the constant range 15 of the pulse. The index table can be elaborated during the programming of the microcontroller and stored in memory.

In the present example, the first voltage measurement is performed after a delay (which is the calibrated delay 16) of 22.5 µs after the rising edge 10, the second voltage measurement 18 occurs at a delay of 52.5 µs after the rising edge 10, the third voltage measurement 19 occurs after a delay of 82.5 µs after the rising edge 10, and the fourth voltage measurement 20 occurs after a delay of 112.5 µs after the rising edge 10. The table index can be, in this example:
- duty cycle less than 6%: the first voltage measurement 17 is chosen as the reference voltage for the pulse;
- duty cycle between 6% and 9%: the second voltage measurement 18 is chosen as reference voltage for the pulse;
- duty cycle is between 9% and 12%: the third voltage measurement 19 is chosen as reference voltage for the pulse;
- duty cycle is greater than 12%, the fourth voltage measurement 20 is chosen as the reference voltage for the pulse.

Alternative embodiments of the method for acquiring the charge pilot signal can be implemented without departing from the scope of the invention. In particular, the number of acquisition sequence voltage measurements, the calibrated delay, and the interval duration can be modified to adapt to any other load pilot signal, with its frequency and its duty cycle range, as well as the behavior of its voltage spike, or any other pulse onset disturbance.

Claims (11)

Method for acquiring a charging pilot signal by a rechargeable electric vehicle, this signal being emitted by an electric charging station, this signal being a pulse-width modulated signal having a variable duty cycle between a minimum value and a maximum value constituting first information, and having a variable voltage level constituting second information, this method being characterized in that it comprises the following steps, for each pulse (9) of the charge pilot signal:
- detecting a rising edge (10) of the charge pilot signal corresponding to the start of the pulse (9);
- at the end of a calibrated delay (16) whose starting point is the rising edge (10), carry out an acquisition sequence comprising at least two measurements (17,18,19,20) of the voltage of the pilot signal load, the time interval between two of these measurements (17,18,19,20) being equal to a predetermined interval duration (21);
- detecting a falling edge (11) of the charge pilot signal corresponding to the end of the pulse (9);
- determining the duty cycle of the pulse (9);
- select a reference voltage for the pulse (9), among the voltage measurements (17,18,19,20) of the acquisition sequence. Method according to Claim 1, characterized in that the calibrated delay (16) is less than the duration of the pulse which corresponds to the said minimum value of the duty cycle, the duration of the pulse being defined as the duration passing between the edge rising (10) and the falling edge (11) of the pulse (9). Method according to any one of the preceding claims, characterized in that the calibrated delay (16) is less than the duration of the pulse which corresponds to the said minimum value of the duty cycle, reduced by the time (22) necessary for carrying out a voltage measurement. Method according to any one of the preceding claims, characterized in that the calibrated delay (16) is equal to the duration of the pulse of the charge pilot signal which corresponds to the said minimum value of the duty cycle, reduced by 5 to 10 µs . Method according to any one of the preceding claims, characterized in that it includes a step of initializing a hardware trigger (28) at the time of the rising edge (10), this hardware trigger (28) triggering the acquisition sequence once once the calibrated delay (16) has elapsed. Method according to any one of the preceding claims, characterized in that the voltage of the charge pilot signal is variable among a plurality of predefined voltage levels, and in that the step of selecting a reference voltage for the pulse is carried out by comparison between the values of the voltage measurements (17,18,19,20) of the acquisition sequence and said predefined voltage levels, the chosen reference voltage being the voltage value which is equal to a voltage level preset. Method according to Claim 6, characterized in that, if two voltage values are equal to a predefined voltage level, the reference voltage chosen is the voltage value closest to the falling edge (11) of the pulse (9 ). Method according to any one of Claims 1 to 5, characterized in that the step of selecting a reference voltage for the pulse is carried out from an index table indicating, as a function of the duty cycle of the pulse, the voltage measurement to be chosen in the acquisition sequence. Method according to Claim 8, characterized in that the index table indicates, for each duty cycle, the voltage measurement which, within an acquisition sequence, is located the latest before the falling edge. Method according to any one of the preceding claims, characterized in that the acquisition sequence comprises three to ten measurements of the voltage of the charge pilot signal, and preferably four measurements of the voltage of the charge pilot signal. Electronic control unit, characterized in that it comprises means for implementing all the steps of a method according to any one of Claims 1 to 10.