Method and device for controlling an electrochemical accumulator battery

Abstract

Title: Method and Device for Controlling an Electrochemical Storage Battery. A device and method for controlling an electrochemical storage battery, said battery being connected upstream to a suitable power source for charging it and downstream to a device that it powers, comprising the steps of: disconnecting the battery from the power source; measuring the open-circuit voltage of the battery; comparing said open-circuit voltage with a predetermined upper voltage threshold; if the open-circuit voltage is above this threshold, disconnecting the battery from the downstream device; otherwise, connecting the battery to the downstream device; and connecting the battery to the power source. Figure for abstract: [Fig. 3]

Description

Title of the invention: Method and device for controlling a battery of electrochemical accumulators

[0001] The invention relates generally to the field of the use of electrochemical accumulator batteries, particularly lithium batteries, and more specifically to the testing of such batteries to verify their compatibility and suitability for the proper functioning of an installation. The outcome of the testing is to prevent any possibility of operation if the test proves negative. In other words, the objective of the invention is to ensure the safe replacement of a battery or battery pack in a self-contained device by preventing operation if the inserted battery model is not technically compatible with the device's control circuit.With this in mind, taking the example of battery powering a roller shutter motor, including powering its control unit, it is planned to prohibit the motor from being controlled if the replacement battery is not of an authorized type, that is to say, validated as being technically compatible with the intended control method.

[0002] The type of battery initially supplied—for example, by the manufacturer—with a self-contained device is suited to its intended use and, in particular, has specific charging characteristics for normal operation within a given temperature range. However, with the same external shape and very similar, or even identical, dimensions, several types of batteries with unsuitable properties can be found on the market. The risk of error for an inexperienced user is therefore significant, given that the consequences of an incorrect choice can range from a simple malfunction to a fire or explosion. It should also be noted that the most readily available battery cells or accumulators on the market, and often the least expensive, are also those that present the greatest risks in the event of misuse.

[0003] The most common solution to this problem has been to package the accumulators / cells inside a sealed pack in a plastic casing or heat-shrink tubing, also incorporating control electronics (known as a BMS). The electronic control unit, for example in the form of a circuit board, is designed, among other things, to ensure that the battery cells are not subjected to damaging overcharges. Access to the accumulators, i.e., the individual battery cells, is then impossible without cutting open the casing or tubing enclosing the pack. To further limit any risk of using a non-compliant battery, a label is This warning, usually affixed to the battery pack, informs the user that the battery must be replaced with an identical model. An additional safeguard may be provided by a specific connector, which effectively dictates the replacement battery model.

[0004] This approach, however, has some drawbacks: - adding an electronic control module included in the battery pack increases the cost of the solution, firstly because of the cost of mounting and assembling the module itself, and secondly also because it may contain some redundant electronic components that can be used both in the module and for controlling the final device it powers (current or voltage measurement components, microcontroller-type calculation unit, etc.), and which must then be doubled; - Replacing worn batteries inevitably involves replacing the control electronics, even if the latter is generally still functional; - the volume occupied by the battery is then significantly greater than the sum total of the accumulators that make up the pack.

[0005] To avoid these drawbacks, primarily to reduce costs but also to facilitate the recycling of used batteries, the functions related to the electronic control of the battery have been relocated to the main electronic control board of the final device. This leads to a reduction in the number of electronic components required and a simplification of the battery pack design, which is effectively reduced to a group of cells equipped with a connection device. In this case, however, the battery cells are once again accessible, and this no longer prevents the user from attempting to replace them themselves when they are worn out. However, as we have seen, if the user uses components different from those supplied or recommended by the manufacturer, the consequences can be disastrous.

[0006] More specifically, for example, if the nature and chemical structure of the replacement battery differ from those of the original battery, the maximum permissible charging voltage is often no longer compatible with the resulting control mode of the existing electronics, hence a risk of overcharging. Conversely, a battery recharged to too low a level will not allow the device to function normally. Worse still, recharging a battery, for example a lithium battery, whose open-circuit voltage is very low, can lead to a polarity reversal. Finally, if the operating temperature exceeds the recommendations of the replacement battery, thermal runaway can occur and generate a fire.

[0007] The objective of the present invention is to overcome these multiple problems by proposing a simple and reliable solution to inhibit the operation of the battery-powered device (for example, a roller shutter motor) if the chosen replacement battery is not of a type compatible with the intended application.

[0008] To this end, the invention relates first to a method for controlling a battery of electrochemical accumulators, said battery being connected upstream to an energy source suitable for charging it and downstream to a device that it powers, a method which, according to the invention, comprises the following steps: - disconnecting the battery from the power source; - measurement of the battery's open-circuit voltage; - comparison of said open-circuit voltage with a higher voltage threshold predetermined; - if the open-circuit voltage is above this threshold, disconnect the battery from the downstream device; - otherwise, connect the battery to the downstream device; and - connect the battery to the power source.

[0009] When the open-circuit voltage is measured above the predetermined upper voltage threshold stored in battery voltage control means that may be included in an electronic control unit, for example, of a roller shutter motor (an example that will be used continuously hereafter), the result is considered inconclusive within the meaning of the objectives of the invention, and the software or electronic logic of said control unit prevents the motor from operating and / or the battery from charging. The motor malfunction is considered to be information, for the user, indicating the non-compliance of the battery they are attempting to install.

[0010] According to an additional possibility, two distinct thresholds can be used in the control process. In addition to the upper threshold mentioned above, a lower threshold can be implemented. In this case, the process comprises the following additional steps: - if the open-circuit voltage is lower than the predetermined upper voltage threshold, comparison of said open-circuit voltage with a predetermined lower voltage threshold; - if the open-circuit voltage is below this threshold, disconnect the battery from the downstream device; - otherwise, connect the battery to the downstream device; and - connect the battery to the power source.

[0011] Correct operation is then considered not in relation to a single threshold, but in reality in relation to an operating range, which is more restrictive: as soon as the replacement battery is not in the interval defined by the respective upper and lower thresholds, the system - in fact the means of controlling the voltage of the system - deduces the non-conformity of the battery whose implantation is attempted, and prevents normal operation.

[0012] Preferably, according to the method of the invention, after disconnecting the battery from the power source, a timer is activated to stabilize the battery's open-circuit voltage. Given the importance of measuring the open-circuit voltage in the process, it is indeed desirable to allow any transient phenomena that may result from the initial disconnection to pass.

[0013] The present invention also covers a control device for a battery of electrochemical accumulators for implementing the process described above, as it comprises: - a source of energy; - means of controlling the battery voltage; - means of connecting the battery to the control means of the battery voltage; - a first switching stage between the upstream energy source and the battery; and - a second switching stage between the battery and the downstream device, - the means for controlling the battery voltage, including: • means of measuring the voltage across the terminals of the accumulator battery; • means of comparing said voltage with at least a predetermined voltage threshold; • means of storing the voltage threshold(s); and • two outputs connected respectively to the first switching stage and the second switching stage.

[0014] According to a first embodiment, the means for measuring the open-circuit voltage may consist of at least one analog-to-digital converter. The voltage applied to the analog input of the converter is therefore transformed into a digital value. In this case, preferably, each analog-to-digital converter can be connected to a microcontroller performing the comparison, the outputs of which are connected respectively to the first and second switching stages. In the method specific to the invention, depending on the results of the comparison, the battery charging can be prevented, as well as the operation of the downstream device, for example a roller shutter drive motor.

[0015] In a second embodiment, the comparison means may consist of at least one analog comparator. Their number depends on the nature of the processing performed, namely with respect to a single upper threshold or to an interval bounded by two thresholds. Since the signals from the comparator(s) are analog, analog processing is naturally applied to them. According to a preferred option, the output of each comparator may be connected, via a combinational logic stage combining the outputs of the comparators, to a logic flip-flop whose outputs are connected respectively to the first switching stage and the second switching stage. The signals at the output of the logic flip-flop, depending on their binary level, enable or prevent the charging of the battery and the powering of the device respectively by closing or opening the switching mechanisms.

[0016] According to yet another variant, which combines certain aspects of the two solutions above, the output of each comparator can be connected to a microcontroller performing the comparison(s) and whose outputs are connected respectively to the first switching stage and the second switching stage.

[0017] In the invention, moreover, the switching stage is preferably made up of a relay or at least one transistor, which receives the signal from one of the outputs of the control means, and opens or closes the main functional path of the circuit of the invention, namely the power connection by the battery of the device downstream and the battery charging connection by the energy source upstream of the latter.

[0018] It should be noted that the battery voltage control means may also include a visual and / or audible warning system activated in the event of battery non-compliance. The user is thus clearly and immediately informed of the problem, which reinforces the system's information.

[0019] Furthermore, according to a preferred configuration, the reasons for which have been discussed previously, the battery voltage control means can be placed on an electronic control board for the downstream device powered by the battery. This board is then separate from the battery pack and includes—in addition to components specific to controlling the device in the intended application—components for managing and controlling the battery's charging capability. These components, as mentioned, can sometimes also be used to control the downstream device, for example, an electric roller shutter motor, thus avoiding functional redundancies.

[0020] The invention will be better understood with the aid of the following detailed description of the method and control devices of an electrochemical accumulator battery according to the invention, with reference to the accompanying drawings, for which:

[0021] [Fig-1] illustrates the problem solved by the invention by presenting an open-circuit voltage curve of an LFP (LiFePO4) lithium battery as a function of its charge level;

[0022] [Fig.2] completes the understanding of the problem by presenting an open-circuit voltage curve of an NMC technology lithium battery (LiNiMnC02) as a function of its charge rate;

[0023] [Fig.3] represents a flowchart detailing the steps of the process according to the present invention;

[0024] [Fig.4] shows a synoptic diagram of a first variant of the implementation device of the process of the previous figure;

[0025] [Fig. 5] represents a block diagram of a second variant of said device; and

[0026] [Fig.6] illustrates, according to the same synoptic diagram, a variant of said device combining the variants of figures 2 and 3.

[0027] With reference to Figures 1 and 2, which help to formalize the technical problem underlying the present invention, examples of open-circuit voltage (OCV) curves as a function of state of charge (SOC) for two different lithium cell technologies are shown in said figures. The curve in [Fig. 1] concerns LFP (LiFePO4) technology batteries, while the curve in [Fig. 2] concerns NMC (LiNiMnCoO2) technology batteries. These are two distinct technologies for which the charging responses are quite different. A new lithium cell is generally charged to at least 30% of its total capacity, and the open-circuit voltage (VOC) is therefore found on the rising plateau of the curve. At 30% charge, the VOC is around 3.25 V for LFP versus more than 3.5 V for NMC. An intermediate threshold of 3.4 V thus allows the battery type to be distinguished at the time of connection.In this case, to prevent an NMC technology battery from being mistakenly connected to a device normally powered by an LFP technology battery, we would take, for example, minimum and maximum voltage thresholds of Umin = 2 V and Umax = 3.4 V respectively. In the opposite case, we would take, for example, minimum and maximum thresholds of Umin = 3.4 V and Umax = 4.2 V respectively.

[0028] With reference to [Fig. 3], the method of the invention carries out all the different possible steps aimed at checking the "conformity" of a battery of accumulators for its intended use, starting with a disconnection of the battery from the power source followed by a time delay aimed at stabilizing the The battery voltage is measured when disconnected. Once the time delay has elapsed, its open-circuit voltage is measured, which serves as the essential benchmark from which the rest of the process unfolds. The first step involves comparing this open-circuit voltage with a predetermined upper voltage threshold. If the open-circuit voltage exceeds this threshold, the battery is disconnected from the downstream device, such as the drive motor of a roller shutter, because the control system then considers the battery in use unsuitable. It does not meet the technical standards set by the designers. In the extended version of the process, shown in [Fig. 3], a second comparison is performed.

[0029] This time, the battery's open-circuit voltage is compared to a predetermined lower voltage threshold. If the open-circuit voltage is below this threshold, the system disconnects the battery from the downstream device. If the outcome of these two tests leads to the conclusion that the open-circuit voltage is between the upper and lower thresholds, a dual connection is made, to the downstream device and to the upstream power source. In other words, the installed battery is validated as conforming to the expected technical specifications.

[0030] With reference to [Fig. 4], according to a more structural approach and in a first possible embodiment, previously referred to as the first variant, two switching devices, C1 and C2, are respectively placed downstream of a power source and upstream of the application device, an electric motor driving a roller shutter in the example already mentioned. The open-circuit voltage of the battery is measured at the time of its insertion or connection to an electronic board comprising a battery charge management (BMS) circuit or system, and a microcontroller that performs at least one comparison with a stored threshold value to verify that the measured value is within a predefined range, or simply below a maximum threshold. The voltage measurement is performed by an analog-to-digital converter.If the result is inconclusive, the microcontroller software will prevent both the battery from charging and the device from operating. In the structure of [Fig. 4], this translates into signals emitted from the microcontroller's output to the switching devices or stages (relay or transistor(s)...) C1 and C2. Two separate microcontroller outputs are connected to the two switches C1 and C2, with at least C2 open if the test result is negative. In this case, the application does not function, and the user is thus informed of the problem. As mentioned previously, an additional warning device such as an indicator light or an audible signal can be added to reinforce the information.

[0031] Figures 5 and 6 show variants in which the basic structure of the battery control device of the invention remains the same; only the means for measuring the battery's open-circuit voltage and the processing means (comparison, etc.) change. The basic structure is that which appears in the succession of blocks arranged in a line on the left of Figures 4 to 6, the modifications taking place in the branches located on the right of said figures. Thus, in [Fig. 5], the open-circuit voltage value, an analog parameter, is processed by an analog comparator whose binary output is sent to a logic flip-flop controlling the opening or closing of the switching devices C1 and C2, via separate connections. If there is a double comparison, therefore with two thresholds, a combinational logic stage (see in [Fig. 6]) is used.5]) is necessary to combine the signals from the two comparators and correctly reflect the combined state of the outputs of the two analog comparators at the input of the logic flip-flop. Figure 6 proposes a structure that combines those of Figures 4 and 5: the comparator is analog, but the processing stage, which performs the comparison, is a microcontroller.

[0032] In the preceding description, according to one possible, but not exhaustive, application of the invention, the battery may be used to power the drive motor of a moving element for closing, blocking, sun protection, or screening, for example, a motorized shutter. The method and devices of the invention generally relate to electrochemical accumulator batteries, particularly lithium batteries, specific examples of which have been mentioned, which are intended to be charged by connection to an external power source and, for example, to supply electrical power to the electric drive motor of such a moving element. Furthermore, the present invention is not limited to the type of battery explicitly mentioned earlier in the description or shown in Figures 1 and 2, but can be applied to any type of electrochemical accumulator battery.

Claims

Demands

1. A method for controlling an electrochemical accumulator battery, said battery being connected upstream to a suitable energy source for charging it and downstream to a device that it powers, comprising the following steps: - disconnecting the battery from the energy source; - measuring the open-circuit voltage of the battery; - comparing said open-circuit voltage with a predetermined upper voltage threshold; - if the open-circuit voltage is higher than this threshold, disconnecting the battery from the downstream device; - otherwise, connecting the battery to the downstream device; and - connecting the battery to the energy source.

2. A method for controlling an electrochemical accumulator battery according to the preceding claim, characterized in that: - if the open-circuit voltage is less than the predetermined upper voltage threshold, comparison of said open-circuit voltage with a predetermined lower voltage threshold; - if the open-circuit voltage is less than this threshold, disconnection of the battery from the downstream device; - otherwise, connection of the battery to the downstream device; and - connection of the battery to the power source.

3. A method for controlling an electrochemical accumulator battery according to any one of the preceding claims, characterized in that, after disconnecting the battery from the energy source, the activation of a timer for stabilizing the open-circuit voltage of the battery is triggered.

4. A control device for an electrochemical accumulator battery for implementing the method according to the preceding claims, characterized in that it comprises: - an energy source; - means for controlling the battery voltage; - means for connecting the battery to the battery control means; - a first switching stage (Cl) between the upstream energy source and the accumulator battery; and - a second switching stage (C2) between the storage battery and the downstream device, - battery voltage control means comprising: • means for measuring the voltage across the storage battery terminals; • means for comparing said voltage with at least one predetermined voltage threshold; • means for storing the voltage threshold(s); and • two outputs connected respectively to the first switching stage (Cl) and the second switching stage (C2).

5. Control device for an electrochemical accumulator battery according to the preceding claim, characterized in that the means for measuring the open-circuit voltage consist of at least one analog-to-digital converter.

6. Control device for an electrochemical accumulator battery according to the preceding claim, characterized in that the analog-to-digital converter is connected to a microcontroller performing the comparison and whose outputs are connected respectively to the first switching stage (Cl) and the second switching stage (C2).

7. Control device for an electrochemical accumulator battery according to claim 4, characterized in that the comparison means consist of at least one analog comparator.

8. Control device for an electrochemical accumulator battery according to the preceding claim, characterized in that the output of each comparator is connected, via a combinational logic stage combining the output of the comparators, to a logic flip-flop whose outputs are connected respectively to the first switching stage (Cl) and the second switching stage (C2).

9. Control device for an electrochemical accumulator battery according to claim 7, characterized in that the output of each comparator is connected to a microcontroller performing the comparison(s) and whose outputs are connected respectively to the first switching stage (Cl) and the second switching stage (C2).

10. Control device for an electrochemical accumulator battery according to any one of claims 4 to 9, characterized in that the switching stage (Cl, C2) consists of a relay or at least one transistor.

11. Control device for an electrochemical accumulator battery according to any one of claims 4 to 10, characterized in that the battery voltage control means comprise a visual and / or audible warning system activated in the event of battery non-compliance.

12. Control device for an electrochemical accumulator battery according to any one of claims 4 to 11, characterized in that the means for controlling the battery voltage are placed on an electronic control board for the downstream device powered by the battery.

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