Method and device for controlling a plurality of cells of an electrical energy storage device

Abstract

Method for controlling a plurality of cells of an electrical energy storage device, in particular a battery of a motor vehicle, said method comprising a step (20) of selectively charging and / or discharging said cells using an electrical charging and / or discharging circuit and a step (22) of evaluating a voltage at the terminals of at least one of said cells, said step (22) of evaluating the voltage at the terminals being carried out simultaneously with said step (20) of charging and / or discharging and comprising a step of measuring a voltage at points, called measurement points, of said circuit and a step of determining said voltage at the terminals taking into account said voltage recorded at the measurement points and a voltage disturbance induced by said step (20) of charging and / or discharging. Figure for abstract: Figure 4

Description

Title of the invention: Method and device for controlling a plurality of cells of an electrical energy storage device

[0001] The invention relates to a method and a device for controlling a plurality of cells of an electrical energy storage device. It will find its applications, in particular, in the control of the battery cells of a motor vehicle.

[0002] In this field, electrical energy storage devices are known which are formed from a set of cells, each containing a portion of the electrical charge of the storage device. The cells are electrically connected in series to achieve the power levels required for the storage device.

[0003] In motor vehicles, a control system selectively allows a current supply to an electrical machine used for moving the vehicle, this from said storage device whose cells are then discharged, or a current supply to said storage device, for example from a terminal and / or, through said electrical machine, by regenerative braking, the cells of said storage device then being recharged.

[0004] Such a storage device is considered unbalanced when the cells do not have the same electrical charge. These differences may occur due to manufacturing processes, variations in the materials used, dimensional variations, or environmental conditions. However, keeping all cells in the electrical energy storage device with the same electrical charge level is preferred to utilize the full capacity of the battery.

[0005] [Fig.l] illustrates this in the form of a histogram in the case of a storage device comprising two cells C1, C2 connected in series and presenting, at a given moment, an imbalance, here a difference in electrical charge of 15% as represented according to the first two bars 1a, 1b of the histogram.

[0006] In the case where the battery is charged, without having compensated for this imbalance in the meantime, the charging process must stop as soon as the first of the cells reaches its maximum electrical charge. Indeed, since the cells are in series, continuing the charging process would present numerous disadvantages. The other cell of the battery will then have reached only 85% of its full electrical charge storage capacity, as represented by the following two bars 2a, 2b of the histogram.

[0007] In the case of the discharge phase, the situation is identical. The electric vehicle will be able to use the energy from the storage device until a first of the cells reaches its lowest electrical charge, as shown in last bar 3a of the rhistogram. Therefore, only 85% of the battery capacity is usable due to the cell imbalance. In addition, we have unused charge stored in the other cell Cl of the storage device.

[0008] In the end, we understand that, between charge and discharge, we will only be able to use a part of the total charge range as long as the cells present such an imbalance.

[0009] To overcome this drawback, it is known to balance the charge of the electric cells with each other, using a circuit for selectively charging and / or discharging the cells integrated into a storage device control system. Such a balancing process is triggered periodically, for example when the vehicle is stationary.

[0010] In [Fig. 2], an electrical energy storage device 4 has been illustrated comprising cells 6. To simplify the representation, the electrical energy storage device 4 here comprises three cells 6 respectively delivering a voltage V1, V2, V3. Said cells 6 have an internal resistance Ril, Ri2 and Ri3. These cells 6 are respectively connected by resistance wires Rwl, Rw2, Rw3 and Rw4 to a device 10 for controlling the cells 6.

[0011] Said control device 10 is formed, in particular, of a dedicated integrated circuit or ASIC (according to the English acronym application-specific integrated circuit). It comprises switches CB1, CB2, CB3 associated respectively with each of the cells 6. These are, for example, field effect transistors. They selectively trigger the charging and / or discharging of the cells 6. The control device 10 comprises a balancing circuit having an impedance Rb, Cb, this for each of the cells 6. In the figure, the switches CB1 and CB3 associated with the cells 6 delivering the voltage V1 and V3 are open and the switch CB2 associated with the cell 6 delivering the voltage V2 is closed which makes it possible to discharge said cell 6 delivering the voltage V2.

[0012] The control device 10 further comprises a voltage measurement circuit, shown in dotted lines [in green in the provisional drawings], configured to deliver voltages VcO, Vcl, Vc2, Vc3 at ports 12, in order to know the voltage between terminals of each of the cells 6. Said measurement circuit comprises measurement wires having a specific impedance denoted Rm, Cv. Said measurement circuit is configured so that the impedance Rm, Cv of the balancing circuit filters the noise before measuring the voltage at ports 12.

[0013] A disadvantage of such a configuration is that the discharge of the cells 6 produces a disturbance in the voltage measurement. More precisely, if all the switches CB1, CB2, CB3 are open, no current flows in the circuit and the voltage of each of the cells is equal to the difference between the voltages measured by the control device 10 at the ports 12.

[0014] On the other hand, when the discharge process is active, as in [Fig.2] where the switch CB2 linked to cell 2 is closed, the current i2 flowing in the corresponding wire and resistance Rb is no longer zero. The voltage difference measured at the ports Vcl, Vc2 is then no longer equal to the voltage across cell 6 delivering voltage V2 and its value decreases because it is affected by the interaction of the current i2 with the wire and resistance Rb in question. In addition, the measurement for the other two cells increases when they share a connection wire with their neighbor.

[0015] This is illustrated in [Fig. 3] where the abscissa axis represents time and the ordinate axis represents the electrical voltage. As long as the discharge process is not active, as is the case over the time periods tl and tl', the voltage measurement is not disturbed. On the other hand, when the discharge process is active, as is the case over the time period t2, the measurement is disturbed. Here, we see that the voltage v2 relative to the cell 6 delivering the voltage V2 decreases and the voltages vl, v3 relative to the cells 6 delivering the voltages VI, V3 increase.

[0016] Today, to overcome this drawback, when the control device 10 has to measure the voltages at the terminals of the cells, the charging and / or discharging process is momentarily interrupted to avoid the disturbance of the measurements mentioned above. The time required to carry out a measurement depends on the RC filter used in the ASIC and the technology of this ASIC. In a typical case, there is a loss of up to 7.5% of the effective discharge time (75 ms per second). In eight hours, which is a typical balancing time, this means more than thirty minutes lost, which is particularly penalizing.

[0017] The invention aims to at least partially overcome the above drawbacks and to this end proposes a method for controlling a plurality of cells of an electrical energy storage device, in particular a battery of a motor vehicle, said method comprising a step of selectively charging and / or discharging said cells using an electrical charging and / or discharging circuit and a step of evaluating a voltage at the terminals of at least one of said cells, said step of evaluating the voltage at the terminals being carried out simultaneously with said charging and / or discharging step and comprising a step of measuring a voltage at points, called measurement points, of said circuit and a step of determining said voltage at the terminals taking into account said voltage recorded at the measurement points and a voltage disturbance induced by said charging and / or discharging step.

[0018] The invention takes advantage of the observation made by the applicant that the disturbance induced in the circuit by the charging and / or discharging of the cells between the value of the voltage at their terminals and the value of the voltage at the measurement points of the circuit is a deterministic phenomenon. It is thus possible to know or at least to approach this disturbance and to evaluate the voltage at the terminals of the cells by taking into account account of this. In this way, the balancing of the cells can be continued without interrupting it to check their state of charge, while avoiding the use of a specific circuit for measuring the voltage at the terminals of said cells.

[0019] According to various additional characteristics of the invention, which may be taken together or separately and which form as many embodiments of the invention: - said method comprises a step of estimating said disturbance by voltage measurement, - said estimation step comprises a first step of measuring the voltage at said measurement points, called the first reference voltage, while said cell charging and / or discharging step is inactive, and a second step of measuring the voltage at said measurement points, called the second reference voltage, while said charging and / or discharging step is active, - said step of estimating the disturbance comprises a calculation of a voltage offset between said second reference voltage and said first reference voltage, - said step of determining the voltage at the terminals exploits said voltage offset, - said step of evaluating the voltage at the terminals is carried out repeatedly, - said step of estimating the disturbance is carried out according to a frequency much lower than the said terminal voltage evaluation step, - said step of estimating the disturbance is carried out each time the voltage at the terminals has changed by at least 5%, in particular by 10%, - said step of charging and / or discharging the cells is carried out in order to tend towards balancing the cells.

[0020] The invention also relates to a control device on board a motor vehicle comprising hardware and / or software elements implementing the control method as described above.

[0021] According to various additional characteristics of the invention, which may be taken together or separately and which form as many embodiments of the invention: - said device comprises a battery control system, - said device comprises a microcontroller and integrated circuits with ap specific application.

[0022] The invention also relates to a motor vehicle comprising said control device.

[0023] The invention also relates to a computer program product comprising ins program code instructions recorded on a computer-readable medium for implementing the steps of the control method described above, when said program is running on a computer.

[0024] The invention further relates to a computer-readable data recording medium on which is recorded a computer program comprising program code instructions for implementing the control method as described above.

[0025] The invention will be better understood, and other aims, details, characteristics and advantages thereof will appear more clearly during the detailed explanatory description which follows, of at least one embodiment of the invention given by way of purely illustrative and non-limiting example, with reference to the appended schematic drawings among which:

[0026] [Fig-1] schematically illustrates, as already mentioned, a charging process and / or discharging cells of an electrical energy storage device in the event of cell imbalance;

[0027] [Fig.2] illustrates schematically, as already commented, an example of electrical energy storage device to which the control method according to the invention is likely to be applied;

[0028] [Fig.3] illustrates schematically, as already commented, the disturbances observed in the voltage measurement in the case of cell discharge with the storage device of [Fig.2];

[0029] [Fig.4] schematically illustrates in the form of a timing diagram an example implementation of the control method in accordance with the invention.

[0030] It should first be noted that the terms “first”, “second”, “third”, etc. are only used to distinguish the components concerned from each other and do not indicate an order or a possible importance of said components.

[0031] As illustrated, the invention relates to a method of controlling a plurality of cells of an electrical energy storage device.

[0032] Said method applies, for example, to an electrical energy storage device comprising, as explained above in relation to [Fig. 2], a set of cells 6, each containing a part of an electrical charge of the storage device, illustrated 4. The cells 6 are electrically connected in series to achieve the power levels required for the storage device 4. The electrical energy storage device 4 here comprises three cells 6 respectively delivering a voltage V1, V2, V3 but it could comprise a higher number of cells while remaining in accordance with the invention. Said storage device 4 forms, in particular, a battery of a motor vehicle, in particular a battery used for the motorization of the vehicle.

[0033] In such an application, a circuit, not shown, selectively allows a current supply to an electrical machine used for moving the vehicle, this from said storage device 4 whose cells 6 are then discharged, or a current supply to said storage device, for example from a fixed terminal and / or, through said electrical machine, by regenerative braking, the cells 6 of said storage device then being recharged.

[0034] In order to optimize the operation of said storage device 4, as has been explained in relation to [Fig.l] in the case of discharge, the control method according to the invention allows selective charging and / or discharging of each of the cells 6, in particular with a view to balancing their electrical charge. Such a balancing process is triggered periodically, for example when the vehicle is stationary.

[0035] Said method uses for this a control device 10 for the cells 6. Said control device 10 is integrated, in particular, in a control system for the storage device 4. Here, the cells 6 are connected by resistance wires Rwl, Rw2, Rw3 and Rw4 to the control device 10 for the cells 6.

[0036] As already indicated, said control device 10 is formed, in particular, of a dedicated integrated circuit or ASIC (according to the English acronym application-specific integrated circuit). It comprises switches CB1, CB2, CB3 associated respectively with each of the cells 6. These are, for example, field effect transistors. Here, they selectively trigger the discharge of the cells 6, depending on their open or closed state. The control device 10 further comprises a first circuit connecting the resistance wires Rwl, Rw2, Rw3 and Rw4 to the switches CB1, CB2, CB3. Said first circuit has an impedance Rb, Cb opposite each of the switches CB1, CB2, CB3, this for each of the cells 6. In the figure, the switches CB1 and CB3 associated with the cells 6 delivering the voltage V1 and V3 are open and the switch CB2 associated with the cell 6 delivering the voltage V2 is closed which allows said cell 6 delivering the voltage V2 to be discharged.

[0037] The control device 10 further comprises a voltage measurement circuit, shown in dotted lines [in green in the provisional drawings]. Said measurement circuit is configured, for example, to deliver voltages VcO, Vcl, Vc2, Vc3 at ports 12, in order to know the voltage between terminals of each of the cells 6. Said measurement circuit comprises measurement wires having a specific impedance denoted Rm, Cv. Said measurement circuit is configured so that the impedance Rm, Cv of the first circuit filters the noise before measuring the voltages VcO, Vcl, Vc2, Vc3 at ports 12.

[0038] As illustrated in [Fig.4], said method comprising a step 20 of selective charging and / or discharging of said cells 6, preferably in order to tend towards the balancing of said cells 6, and a step 22 of evaluating a voltage at the terminals of at least one of said cells 6. According to the illustration mode used for this figure, said steps 20, 22 are active when the corresponding signal is equal to 1 and inactive when the signal is equal to 0. Said step 20 of selective charging and / or discharging of said cells 6 is carried out using an electrical charging and / or discharging circuit comprising here said first circuit and said voltage measuring circuit.

[0039] According to the invention, as can be seen in the figure, said step 22 of evaluating the voltage across the terminals of the cells 6 is carried out simultaneously with said step 20 of selective charging and / or discharging. Furthermore, said step 22 of evaluating the voltage across the terminals of the cells 6 comprises a step of measuring a voltage at points, called measurement points, of said circuit, corresponding here to the ports 12, and a step of determining said voltage across the terminals of the cells 6 taking into account said voltage recorded at the measurement points 12 and a voltage disturbance induced by said charging and / or discharging step 20.

[0040] According to the analysis carried out by the applicant, the disturbance induced in the circuit by the charging and / or discharging of the cells 6 between the value of the voltage at their terminals and the value of the voltage at the measurement points 12 of the circuit is a deterministic phenomenon. It is thus possible to know or at least to determine an approximate value of this disturbance and to evaluate the voltage at the terminals of the cells 6 from the measurement made at the measurement points by taking into account said disturbance. In this way, it is possible to continue the process of charging and / or discharging the cells without interrupting it to check their state of charge and this while avoiding the use of a specific circuit for measuring the voltage at the terminals of the cells.

[0041] In the configuration of [Fig.2], by way of example, the voltage V3 relating to the corresponding cell 6, is determined from the difference in the voltages Vc3 and Vc2, as measured, and from the corresponding voltage disturbance, induced by said charging and / or discharging step 20, as it will have been determined.

[0042] Preferably, said step 22 of evaluating the voltage at the terminals is carried out repeatedly, periodically or not. In the figure, it is represented in the form of spikes 220 because the time necessary to evaluate the voltage at the terminals of the cells 6 is very short compared to the duration of the step(s) 20 of charging and / or discharging the cells 6.

[0043] Still preferably, said method comprises a step 24 of estimating said disturbance by voltage measurement. As previously, in [Fig.4], said step 24 occurs when the corresponding signal is equal to 1.

[0044] According to the illustrated embodiment, said estimation step 24 comprises a first step 240 of measuring the voltage at said measurement points 12, called the first reference voltage, while said step 20 of charging and / or discharging the cells 6 is inactive, and a second step 242 of measuring the voltage at said measurement points, called second reference voltage, while said step 20 of charging the cells 6 and / or discharging is active.

[0045] Said step 24 of estimating the disturbance further comprises a calculation of a voltage offset between said second reference voltage and said first reference voltage. Said step 22 of determining the voltage at the terminals of the cells exploits said voltage offset.

[0046] By way of example, the voltages VcO, Vcl, Vc2, Vc3 are measured when the step 20 of charging and / or discharging the cells 6 is inactive and the corresponding values ​​are stored in a memory of said control device in the form of voltage VciRi. Said voltages VcO, Vcl, Vc2, Vc3 are then measured when the step 20 of charging and / or discharging the cells 6 is active, this by scanning the different charging and / or discharging configurations, such as the configuration of [Fig.2], and the corresponding values ​​are stored in said memory in the form of voltage VciR2. The disturbance associated with each cell 6 is then calculated.

[0047] For this, according to the same example as above, to determine the disturbance associated with the cell 6 delivering the voltage V3, we calculate, on the one hand, a first voltage difference Vc3 / 2Ri between Vc3Ri and Vc2Rb then a second voltage difference Vc3 / 2R2 between Vc3R2 and Vc2R2. The corresponding disturbance is then estimated as being the difference between Vc3 / 2R2 and Vc3 / 2R[ and this disturbance value will be used in the following during several successive evaluations of the voltage V3 from the measurement of the voltages Vc3 and Vc2.

[0048] As a variant, said step of estimating the disturbance is carried out by calculation, in particular from knowledge and / or an evaluation of the electrical characteristics of the charging and / or discharging circuit.

[0049] Said step 24 of estimating the disturbance is carried out, for example, according to a frequency much lower than said step 22 of evaluating the voltage at the terminals of the cells 6. In this sense, the time scale of [Fig. 4] is not continuous. It has been dilated to better represent the periods T1, T1' where said step of estimating the disturbance is active compared to the time period T2 during which said steps of evaluating the voltage at the terminals of the cells 6 occur. Furthermore, the number of occurrences of step 22 of evaluating the voltage between two periods T1, T1' of estimating the voltage is not necessarily illustrative.

[0050] In this regard, advantageously, said step 24 of estimating the disturbance is carried out each time that the voltage at the terminals of one and / or more of the cells 6 has changed by at least 5%, in particular by 10%.

[0051] The invention also relates to the cell control device 6. One embodiment has already been mentioned above in relation to [Fig.2]. Preferably, said device is configured to be embedded in a motor vehicle. Said device comprises hardware and / or software elements implementing the control method described above. The invention also relates to such a motor vehicle.

[0052] The invention further relates to a computer program product comprising program code instructions recorded on a computer-readable medium for implementing the steps of the control method described above, when said program operates on a computer.

[0053] The invention also relates to a data recording medium, readable by a computer, on which is recorded a computer program comprising program code instructions for implementing the control method described above.

Claims

Claims

1. Method for controlling a plurality of cells (6) of an electrical energy storage device (4), in particular a battery of a motor vehicle, said method comprising a step (20) of selectively charging and / or discharging said cells (6) using an electrical charging and / or discharging circuit and a step (22) of evaluating a voltage at the terminals of at least one of said cells (6), said step (22) of evaluating the voltage at the terminals being carried out simultaneously with said step (20) of charging and / or discharging and comprising a step of measuring a voltage at points (12), called measurement points, of said circuit and a step of determining said voltage at the terminals taking into account said voltage recorded at the measurement points (12) and a voltage disturbance induced by said step (20) of charging and / or discharging.

2. Method according to the preceding claim in which said method comprises a step (24) of estimating said disturbance by voltage measurement.

3. Method according to the preceding claim in which said estimation step (24) comprises a first step (240) of measuring the voltage at said measurement points, called the first reference voltage, while said step (20) of charging and / or discharging the cells (6) is inactive, and a second step (242) of measuring the voltage at said measurement points (12), called the second reference voltage, while said step (20) of charging and / or discharging is active.

4. Method according to the preceding claim in which said step (24) of estimating the disturbance comprises a calculation of a voltage offset between said second reference voltage and said first reference voltage.

5. Method according to any one of claims 3 or 4 in which said step (22) of evaluating the terminal voltage is carried out repeatedly and said step (24) of estimating the disturbance is carried out at a frequency much lower than said step (22) of evaluating the terminal voltage.

6. Method according to the preceding claim in which said step (24) of estimating the disturbance is carried out each time the voltage at the terminals has changed by at least 5%, in particular by 10%.

7. On-board control device in a motor vehicle comprising hardware and / or software elements implementing the control method according to any one of the preceding claims.

8. Motor vehicle comprising said control device according to the preceding claim.

9. A computer program product comprising program code instructions recorded on a computer-readable medium for implementing the steps of the control method according to any one of claims 1 to 6, when said program is running on a computer.

10. A computer-readable data storage medium on which is recorded a computer program comprising program code instructions for implementing the control method according to any one of claims 1 to 6.

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