Equilibrium method

Abstract

A method is disclosed for controlling cell balancing (20-35) of a battery (2) of an electrical accumulator of an electrical system (1), the method including balancing selected cells for each subgroup with the cells having the greatest amount of charge to be balanced.

Description

Technical Field

[0001] The present invention relates to a method for equalizing cells of a battery of an electric accumulator.

[0002] In particular, the present invention relates to the management of batteries of electric or hybrid vehicles.

[0003] An electric vehicle, a hybrid vehicle or even a rechargeable hybrid vehicle comprises a battery of an electric accumulator formed from a number of cells in series and / or in parallel.

[0004] In the battery of the accumulator, all the cells have similar characteristics to other cells, however, physical variations or differences remain, such as variations in capacity in ampere-hours (Ah) and resistance in ohms (Ω). In general, temporary variations in the state of these cells also occur, such as differences in the state of charge (SOC) and / or temperature.

[0005] Over time and during the use of the battery, all these physical variations and differences in state cause the cells to age differently. This difference in the rate of aging of the cells causes the state of health (SOH) to be different for each cell.

[0006] However, the difference in the state of charge between cells connected in series is a limiting parameter since the total usable capacity of the battery is directly affected. Specifically, the greater the difference in charge between cells, the more the total usable capacity of the battery decreases. This therefore has an adverse effect on the range of an electric vehicle.

[0007] This is the reason why it is necessary to equalize the cells regularly. Equalization is carried out directly and independently by a battery management system (BMS).

[0008] In most cases, it is a problem of so-called "dissipative" equilibration (also called "passive" equilibration), which involves equipping the charge state of a cell by discharging the cell into a resistor to a target charge state, generally the state of charge of the cell with the lowest charge state.

[0009] When the balancing circuit is properly sized, in other words, when the balancing current is sufficient and the balancing measure is used regularly, the variation in charge state between cells will be kept below a given threshold. This threshold depends particularly on the accuracy of the cell voltage measurement.

[0010] However, this balancing measure can only be activated while the vehicle is in operation.

[0011] These measures, therefore, do not allow for the avoidance of cell imbalance during long parking phases.

[0012] Additionally, it is known that conventional cell balancing is not sized to balance a sufficient number of ampere-hours for an electric vehicle during the operating phase.

[0013] Therefore, for example, in the context of conventional balancing and using a 130-ohm balancing resistor, if we consider an automated vehicle user profile with a nominal cell voltage of 2.5V, 25 days of use per month, a worst-case scenario of a 20-minute daily commute, and 1 hour and 20 minutes of charging per month, in this exact case, active balancing, considering a 140Ah cell, would only be able to rebalance 0.064423077Ah for a need of 0.7Ah.

[0014] Therefore, in order to ensure that the cell is balanced under any profile of automated vehicle use, it is necessary to deploy a standalone balancing strategy that is performed when the automated vehicle is stationary. Stationary means that the automated vehicle is shut down and its computer is shut down.

[0015] The objective is to avoid drawing power from the vehicle's onboard power grid, as this operation requires the use of a stationary, fully automated computer, including the BMS.

[0016] This creates a need for a method to equilibrate a standalone cell that operates when the automated vehicle is stationary and does not cause the cell to overheat or over-discharge.

[0017] The document US 2018 / 0354387 A1, which describes a method for balancing battery cells when an autonomous vehicle is stationary, is particularly well known in the prior art, and this method implements standalone integrated circuits such as application-specific integrated circuits (ASICs). However, the method described is relatively inefficient and does not allow for the optimization of the autonomous vehicle's range.

[0018] Thus, the present invention aims to provide a standalone, optimized cell balancing solution that operates when the automatic vehicle is stationary and does not cause battery overheating or overheating of the battery management unit, nor does it cause cell over-discharge.

[0019] For this purpose, a method for controlling the balancing of battery cells in an electrical accumulator of an electrical system comprising a main control unit and a plurality of standalone slave devices, The cells of the battery are divided into a plurality of subgroups, each associated with a standalone slave device, and the cells of each subgroup are arranged adjacent to one another. Each cell in each subgroup is connected to a circuit in a standalone slave device, which includes an associated controlled switch and an associated resistor. The resistors of each standalone slave device are connected in a row. For each subgroup, each standalone slave device is configured to receive control commands from the main management unit and to control the controlled switch in response to the received control commands in order to balance the charge of the cells in the subgroup. A method is provided.

[0020] The method described above applies to each standalone slave device in each subgroup of a cell, - For each cell associated with the standalone slave device, receive the amount of charge to be balanced, - Determining the cell having the maximum amount of charge to be balanced among the set of cells associated with the standalone slave device, - Selecting other cells in the subgroup associated with a resistor that is not adjacent to the resistor associated with the cell having the maximum amount of charge to be balanced, as candidate cells for equilibrium. - From the selection of candidate cells, exclude cells whose charge to be equilibrated is below a predetermined threshold, - Commanding the standalone slave device to control the connected switch to equilibrate the selected candidate cell with the cell having the maximum amount of charge to be equilibrated, - Shut down the main control unit during the balancing process. It includes a step to perform the following:

[0021] The method thereby allows for the balancing of battery cells when the main control unit is off by discharging the cells to be balanced into their associated resistors, which enables optimal balancing to be achieved while ensuring that the balancing does not cause overheating of the slave device, particularly the balancing resistors, through the selection of non-adjacent resistors, and while avoiding over-discharge, particularly through the definition of a predetermined threshold that defines whether a cell is eligible for balancing.

[0022] Advantageously and non - limitingly, for each subgroup, the resistor associated with the cell is identified by a numerical identifier by a stand - alone slave device, and the resistors are arranged within each subgroup such that two adjacent resistors have numerical identifiers of different parities. The selection step is preceded by an identification step in which the parity value of the resistor associated with the cell having the maximum amount of charge to be balanced is identified. The selection step comprises selecting a cell associated with a resistor having the same parity as the parity determined for the resistor of the cell having the maximum amount of charge to be balanced as a candidate cell for balancing.

[0023] Thereby, the candidate cells are selected for balancing by selecting the cells associated with resistors of the same parity as the resistor of the cell to be balanced. Thus, resistors not adjacent to the resistor of the cell to be balanced are detected in a relatively simple manner. This enables a selection method that is fast and relatively simple from the perspective of the algorithm to be obtained.

[0024] Advantageously and non - limitingly, the predetermined threshold is determined according to the maximum duration of the stand - alone operation of the stand - alone slave device multiplied by the maximum balancing current between two cells. This makes it possible to obtain relevant and relatively optimal thresholds.

[0025] However, the present invention is not limited to such calculations. According to one alternative form, the predetermined threshold can be set in a step prior to the execution of the method.

[0026] The present invention is also a main management unit of an electrical system comprising a battery of an electric accumulator and a plurality of stand - alone slave devices, wherein the cells of the battery are divided into a plurality of subgroups, each associated with one stand - alone slave device, and the cells of each subgroup are arranged adjacent to each other. Each cell of each subgroup is respectively connected to a circuit in a stand-alone slave device comprising an associated controlled switch and an associated resistor, the resistors of each stand-alone slave device being connected in a row, for each subgroup, each stand-alone slave device being configured to receive a control command from the main management unit and to control the controlled switch in response to the received control command so as to equalize the charge of the cells of the subgroup, the main management unit being - means for receiving, for each cell associated with a stand-alone slave device, the amount of charge to be equalized; - means for determining, for each stand-alone slave device, the cell having the maximum amount of charge to be equalized among the set of cells associated with the stand-alone slave device; - means for selecting, as candidate cells for equalization, the other cells of the subgroup associated with resistors not adjacent to the resistor associated with the cell having the maximum amount of charge to be equalized; - means for excluding, for each stand-alone slave device, cells for which the charge to be equalized is less than a predetermined threshold from the selection of candidate cells; - means for commanding each stand-alone slave device to control the connected switches so as to equalize the selected candidate cells and the cell having the maximum amount of charge to be equalized; - means for achieving an automatic shutdown during equalization characterized in that it comprises. Relates to a main management unit.

[0027] The present invention also relates to an electrical system comprising a battery of an electric accumulator, a plurality of stand-alone slave devices and a main management unit as described above, the unit being configured to execute the method as described above.

[0028] The present invention also relates to an automatic vehicle equipped with an electrical system as described above.

[0029] Further details and advantages of the present invention will become apparent from reading the description of one particular embodiment of the present invention given below with reference to the accompanying drawings, which is given as a non-limiting instruction. [Brief explanation of the drawing]

[0030] [Figure 1] This is a schematic diagram of an electrical system according to the present invention. [Figure 2] This is a flowchart of one implementation form of the method according to the present invention. [Modes for carrying out the invention]

[0031] Since Figures 1 and 2 relate to the same first embodiment of the present invention, Figures 1 and 2 are discussed together.

[0032] The electrical system 1 of an electric vehicle, hybrid vehicle, or rechargeable hybrid vehicle comprises an electric accumulator battery 2.

[0033] This battery 2 of the electric accumulator consists of multiple separate cells 20 to 35 arranged in close proximity to one another.

[0034] In this example, the cells are numbered so that they can also be identified by their parity value, with even-numbered cells associated with even numbers and odd-numbered cells associated with odd numbers, and the cells are thus aligned so that even-numbered cells alternate with odd-numbered cells.

[0035] The cell is divided into two subgroups 201 and 202, with the first subgroup 201 comprising cells 20 to 27, and the second subgroup comprising cells 28 to 35.

[0036] In this example, each subgroup 201, 202 comprises eight cells, but the present invention is not limited to this single example. Specifically, it is known that a subgroup may comprise between six and twelve batteries, and those skilled in the art can similarly construct smaller or larger subgroups, although the effectiveness of the present invention may be consequently diminished.

[0037] Each subgroup of the cell 201, 202 is associated with a single standalone slave device 4, 4', which in this embodiment is an application-specific integrated circuit (ASIC). However, the standalone slave device 4, 4' is not limited to this single type of component. In non-limiting examples, the standalone slave device 4, 4' may be a field-programmable gate array (FPGA), a microcontroller, or a microprocessor.

[0038] The standalone slave devices 4, 4' further comprise, for each cell, a controlled switch 60-75 and a resistor 80-95, for example, a resistor between 50 ohms and 150 ohms, in this embodiment a resistor of 100 ohms.

[0039] For each cell 20-35, the circuit is located within the associated slave devices 4, 4', thereby enabling the cells 20-35 to be balanced. This circuit comprises resistors 80-95 and controlled switches 60-75 in series.

[0040] When cells 20-35 are balanced, they discharge into their associated resistors 80-95, and this discharge brings about balance. In other words, the charge in cells 20-35 is reduced by discharging into their associated resistors 80-95 to bring their charge to a balanced level. However, this situation leads to significant heating of the associated resistors 80-95.

[0041] The conventional arrangement of resistors 80-95 in standalone slave devices 4, 4' is a single-row arrangement, that is, resistors 80-95 are spatially aligned adjacent to each other in each of the standalone slave devices, as shown in Figure 1.

[0042] Each standalone slave device 4, 4' is configured to control switches 60-67 and 68-75, respectively, associated with cells 20-27 and 28-35 of the standalone slave device 4, 4'.

[0043] By controlling switches 60-75 to close, the standalone slave devices 4, 4' thereby allow the associated cells 20-35 to be balanced with respect to other cells 20-35 of the same subgroup 201, 202.

[0044] However, when cells 20-35 are balanced, the associated resistors 80-95 become hot. Therefore, it is desirable to avoid discharging two adjacent cells 20-35 simultaneously, as this can cause the adjacent resistors 80-95 to overheat and malfunction.

[0045] The electrical system 1 includes a main control unit 5 that controls the operation of standalone slave devices 4, 4'. In other words, the main control unit 5 is the master unit of the standalone slave devices 4, 4'.

[0046] The main management unit 5 may be, for example, an onboard computer or any other computing device capable of communicating and receiving measurement information from the battery cells and controlling commands given to standalone slave devices 4, 4'.

[0047] This main control unit 5 and standalone slave devices 4, 4' form an assembly commonly known as a battery management system (BMS).

[0048] The main control unit 5 executes a method 30 to control standalone slave devices 4, 4' to balance cells 20-35 so that when this balancing is actually performed, cells 20-35 of battery 2 may be shut down.

[0049] In this embodiment, this method 30 is triggered when the main control unit 5 receives a shutdown or standby command. Thus, when a command to shut down or put the automated vehicle into sleep mode is sent to the main control unit 5, the main control unit 5 performs the following method 30 to organize battery balancing during the shutdown or sleep period of the automated vehicle.

[0050] This method 30 comprises steps that are implemented in parallel or in series for each subgroup 201, 202.

[0051] As a result, for each subgroup 201, 202, step 301 is first performed to receive the amount of charge to be balanced for each cell 20-35 associated with the standalone slave devices 4, 4'.

[0052] In this embodiment, what is meant by charge is a charge value in units of ampere-hours, generally written as Ah, or in units of coulombs C.

[0053] Next, among the set of cells 20-35 of this standalone slave device 4,4', the cell having the maximum amount of charge to be balanced is determined 302.

[0054] Next, a cell from the same subgroup that allows the voltage to be balanced with the cell 302 determined above is selected, namely cell 304.

[0055] For this purpose, in this embodiment, a step is performed in which cells are selected based on the parity values ​​of the resistors 80-95 associated with the cells. In detail, this solution allows for a relatively rapid implementation in terms of the algorithm to be implemented.

[0056] In this example, cells 20 through 35 are each associated with one resistor 80 through 85, which has the same reference number unit. This means, for example, that cell 21 is associated with resistor 81, both of which have odd values.

[0057] As explained previously, heating of adjacent resistors 80-95 must be avoided.

[0058] This allows the first step to identify the parity values ​​of the cell resistors 80-95 determined in the preceding step 302.

[0059] For this purpose, each cell 20-35 and each associated resistor 80-95 in subgroups 201 and 202 are associated with a numerical value, for example, the reference number of each cell 20-35 and each resistor 80-95 in this example, and the remainder when this value is divided by 2 by Euclidean is checked to determine whether the number is even if it is zero, or odd if it is not zero.

[0060] However, the present invention is not limited to this single method of determining cell parity, and it is within the capabilities of those skilled in the art to implement any method deemed preferable. Specifically, a parity indicator, for example, a binary value, may be associated with each cell, in some cases so that the cell parity does not have to be recalculated multiple times.

[0061] Furthermore, although this first example of the embodiment is based on parity selection, provisioning may be carried out to select non-adjacent cell resistors through the selection of resistors whose values ​​congruent modulo N > 2 with respect to the cell resistors determined in step 302. For example, it is possible to select a resistor separated by two other resistors, or in other words, one of three resistors, and therefore a resistor whose values ​​congruent modulo 3 with respect to the resistors determined in step 302.

[0062] Next, a set of candidate cells for balancing is selected, which comprises all cells of a subgroup, wherein the associated resistors 80-95 have the same parity as determined for the resistors of the cells to be balanced.

[0063] Next, cells whose charge to be equilibrated is below a predetermined threshold are excluded from this set of candidate cells.305

[0064] The predetermined threshold is calculated by multiplying the maximum balanced current by the product of the maximum operating times of the standalone slave devices 4 and 4'.

[0065] In the case of an ASIC, the maximum time is defined to be, for example, in the range of 1 to 2 hours, the maximum duration is, for example, 3640 seconds, and the maximum balancing current is, for example, in the range of values ​​of 20 mA to 100 mA.

[0066] However, the present invention is not limited to this strict order in which the selection step 304 and exclusion step 305 are performed. For example, provisioning may first be performed on all cells to be excluded 305, all cells having a charge below a predetermined threshold that should be equilibrated, and then provisioning may be performed on cells to be selected from all the remaining cells that have the same parity as determined for the cells to be equilibrated. The selection result is still the same.

[0067] Next, a step is performed in which the standalone slave devices associated with these subgroups 201 and 202 are instructed to equilibrate the selected candidate cells with the cell having the maximum amount of charge to be equilibrated by controlling the associated controlled switches.

[0068] Next, when all standalone slave devices 4, 4' receive a balancing command, the main management unit 5 is shut down or put into sleep mode.

[0069] The method 30 described above advantageously allows each of the standalone slave devices 4, 4', which is, for example, an ASIC, to be individually controlled to drive configured controlled balancing switches 60-75 for a predetermined time, which is either predetermined or configurable as needed, when the main management unit 5, for example, a BMS, is put into sleep mode.

[0070] The method is, - Through the selection of non-adjacent cells 20-35 to be balanced, to avoid causing abnormal heating of resistors 80-95, - Through the definition of a minimum threshold, to prevent over-discharge of cells, Without degrading the performance of the autonomous vehicle in any way, the method operates in a completely standalone manner. It is further composed.

[0071] According to the second embodiment, cells of the same subgroups 201, 202 are selected to balance the voltage with the determined cell 302 using a technique other than parity selection of the first embodiment. In this second embodiment, all cells that are not adjacent to the cell to be balanced are selected. For this purpose, the associated standalone slave device may have any type of data organization that enables such a decision, for example, a map of the arrangement of cells in subgroups 201, 202 may be stored in memory.

[0072] Such a method for controlling the equilibrium of battery cells in "sleep" mode can be applied to any other system for monitoring multi-cell batteries to limit imbalances between cells, thereby enabling autonomy not only in the automotive sector but also in any other field where implementation involves electronics.

[0073] Such methods may be employed, for example, to limit imbalances between cells in a laptop computer battery.

[0074] The method can also be implemented in a stationary system when the power supply of the system's battery management unit is subject to consumption constraints.

Claims

1. A method (30) for controlling the balancing of cells (20-35) of an electric accumulator battery (2) of an electric system (1) comprising a main control unit (5), a plurality of standalone slave devices (4, 4') connected to the main control unit (5), and an electric accumulator battery (2) connected to the plurality of standalone slave devices (4, 4'), The cells (20-35) of the battery (2) are divided into a plurality of subgroups (201, 202), each of which is associated with a single standalone slave device (4, 4'), and the cells (20-35) of each subgroup (201, 202) are arranged adjacent to each other. Each cell (20-35) of each subgroup (201, 202) is connected to a circuit in the standalone slave device (4, 4') which includes an associated controlled switch (60-75) and an associated resistor (80-95). The resistors (80-95) of each standalone slave device (4, 4') are arranged in a line so that they are adjacent to each other with space between them. For each subgroup (201, 202), each standalone slave device (4, 4') is configured to receive a control command from the main management unit (5) and to control the controlled switches (60-75) in accordance with the received control command to balance the charge of the cells in the subgroup (201, 202). The above method involves the main management unit (5) performing the following actions for each standalone slave device (4, 4') of each subgroup (201, 202) of the cell: For each cell (20-35) associated with the standalone slave device (4, 4'), the amount of charge to be balanced is received (301), (302) Determining which of the set of cells (20-35) associated with the standalone slave device (4, 4') has the maximum amount of charge to be balanced among the set of cells (20-35), As candidate cells for equilibration, select other cells (20-35) of the subgroup (201, 202) associated with resistors (80-95) that are not adjacent to the resistor associated with the cell having the maximum amount of charge to be equilibrated (304), From the selection of candidate cells, cells whose charge to be equilibrated is less than a predetermined threshold are excluded (305), Controlling the connected switches (60-75) to balance the cell having the maximum amount of charge to be balanced with the cell of the selection of candidate cells by the control command (306), Shutting down the main control unit (5) during the balancing process A feature that includes the step of performing Method (30).

2. For each subgroup (201, 202), the resistors (80-95) associated with the cells (20-35) are identified by the standalone slave device (4, 4') by numerical identifiers, the resistors (80-95) are arranged in each subgroup (201, 202) such that two adjacent resistors (80-95) have different parity numerical identifiers, and the selecting step (304) is preceded by an identifying step (303) in which the parity values ​​of the resistors associated with the cell having the maximum amount of charge to be balanced are identified. The method according to claim 1 (30), characterized in that the selection step (304) includes selecting cells (20-35) associated with resistors (80-95) having other numerical identifiers of parity identical to the parity determined for the resistor of the cell having the maximum amount of charge to be balanced, as candidate cells for equilibration.

3. The method according to claim 1 or 2 (30), characterized in that the predetermined threshold is determined according to the maximum duration of standalone operation of the standalone slave device (4, 4') multiplied by the maximum balancing current between the two cells.

4. The method (30) according to claim 1 or 2, characterized in that the predetermined threshold is set in a step prior to the execution of the method (30).

5. A main control unit (5) of an electrical system (1) comprising an electric accumulator battery (2) and a plurality of standalone slave devices (4, 4'), wherein the plurality of standalone slave devices (4, 4') are connected to the main control unit (5), and the electric accumulator battery (2) is connected to the plurality of standalone slave devices (4, 4'), The cells (20-35) of the battery (2) are divided into a plurality of subgroups (201, 202), each of which is associated with one standalone slave device (4, 4'), and the cells (20-35) of each subgroup (201, 202) are arranged adjacent to each other. Each cell (20-35) of each subgroup (201, 202) is connected to a circuit in the standalone slave device (4, 4') which includes an associated controlled switch (60-75) and an associated resistor (80-95). The resistors (80-95) of each standalone slave device (4, 4') are arranged in a line so that they are adjacent to each other with space between them. For each subgroup (201, 202), each standalone slave device (4, 4') is configured to receive a control command from the main management unit (5) and to control the controlled switches (60-75) in accordance with the received control command to balance the charge of the cells in the subgroup (201, 202). The aforementioned main control unit (5) is For each cell (20-35) associated with the standalone slave device (4, 4'), means for receiving the amount of charge to be balanced, For each standalone slave device (4, 4'), means for determining the cell having the maximum amount of charge to be balanced among the set of cells (20-35) associated with each standalone slave device (4, 4'), Means for selecting, as candidate cells for equilibration, other cells (20-35) of the subgroup associated with resistors (80-95) that are not adjacent to the resistor associated with the cell having the maximum amount of charge to be equilibrated, For each standalone slave device (4, 4'), means for excluding cells from the selection of candidate cells whose charge to be balanced is less than a predetermined threshold, Means for instructing each standalone slave device (4, 4') by control command to control the connected switches (60-75) to balance the cell having the maximum amount of charge to be balanced with the cell of the selection of candidate cells, Means for achieving automatic shutdown during balancing and A feature comprising: Main control unit (5).

6. An electrical system (1) comprising an electric accumulator battery (2), a plurality of standalone slave devices (4, 4'), and a main control unit (5) according to claim 5, wherein the main control unit (5) is configured to perform the method according to any one of claims 1 to 4.

7. An automatic vehicle comprising the electrical system (1) according to claim 6.

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