SYSTEMS

Technical field of the Invention

The present invention relates to the management of batteries (module, or single battery, or a battery pack), for electric or partially electric propulsion systems, for example, electric traction vehicles. In the course of the description, reference will be made to electric vehicles for the sake of convenience, but it is understood that the invention is applicable to any system that uses electric propulsion even in partial mode: for example, land, marine, aircraft, industrial vehicles, hybrid vehicles, human-driven or self-driving vehicles.

Background Art

According to known technique and with reference to Figure 1, electric propulsion systems, for example electric motor vehicles, generally use a lithium-ion battery pack which is first formed by assembling a single module 20 consisting of elementary cells 10, with electrical interconnection in series and / or in parallel; then, one or more modules are installed in a framed structure of the battery 30, whose shape and internal layout are adapted to the vehicle body. This assembly constitutes a single battery; finally, a plurality of batteries are installed on board the vehicle, such batteries forming the battery pack 40. The latter will also be equipped with an adequate thermal management system (TMS) and battery management system (BMS) from an electrical I electronic point of view. The Battery Management System (BMS) is a part of the energy management system, fast acting, much more complex and must interface with other on-board systems such as engine management, climate control, communications and systems safety.

One of the main tasks of the battery management system is to ensure that the cells are properly balanced. If the cells are unbalanced at the beginning or end of a charge / discharge cycle, the cells themselves will position themselves in ranges outside their operating voltage window, which will rapidly degrade the cell and reduce the functionality and performance of the module as a whole. This can also increase the chances of the battery failing. For this reason, it is necessary that individual cell voltage monitoring be performed and that the appropriate circuitry and logic exist at the module level to keep the cells within their voltage window while they are charged and discharged.

It is also known that lithium-ion batteries use a lithium compound on the cathode and graphite or lithium titanate on the anode. These batteries have a high energy density, poor memory effect and low selfdischarge. At the same time, however, they can pose a safety hazard as they contain a flammable electrolyte and can cause explosions and fires if damaged or incorrectly charged.

The reason is that the various chemicals in lithium batteries are susceptible to chemical damage (for example, cathode fouling, molecular breakage, etc.) due to even very slight overvoltage (for example, of the order of millivolts) during charging or at charge current levels greater than internal chemistry can tolerate in the different charge / discharge cycles. In addition, lithium-ion cells also have specified temperature windows and maximum charge and discharge current limits.

Therefore, the battery management system calculates the maximum charge and discharge current that a module can withstand and has adequate circuits to protect against currents above these limits. The battery management system also monitors module temperature, while more advanced battery management systems measure the temperature of individual cells.

Due to the variations in the physic-chemical characteristics between cell and cell, there is, at an industrial level, a significant production variability of the individual cells; to limit the consequent risk of a high nonhomogeneity of the modules of a battery and therefore in the batches of commercial battery packs with lithium-ion cells, it is consolidated practice to proceed with a very strict selection of lithium-ion cells (with consequent production waste and negative impacts on costs) and their classification at the end of the production line in very narrow ranges of characteristics (with consequent assembly of modules, or batteries, or battery packs with significantly different performances, depending on the choice made by the battery manufacturers or OEMs).

The modules, batteries and battery packs also present a further problem of performance loss (with the same nominal characteristics) due to the design of the module connectors and the thermal management of the system.

This inhomogeneity affects the impedance and capacity, the charge I discharge behavior and the degradation rate of the single cell, and therefore the performance, reliability and duration of the battery pack, with negative impacts on operation, maintenance and costs of the electric vehicles.

As the purpose of a Battery Management System (BMS) is to optimize the performance of the battery pack, maximizing the utilization of the energy storage capacity, minimizing the charging process and extending the operating life, with today's technology a correct functioning of the BMS can only occur (as mentioned above) in case of a very narrow range of inhomogeneities between the lithium-ion cells and a very limited deviation of the products from the nominal specifications of the battery pack: very narrow tolerances of materials and sophisticated manufacturing processes or selection of cells with similar characteristics are the key industrial approaches today, with a significant impact on the final cost of the product.

It is therefore necessary to define a method of managing a battery of electric or partially electric propulsion systems, for example electric traction vehicles, which does not require the strict control of sophisticated cell tolerances or the selection of cells of the battery pack and I or the individual modules, such cells having similar characteristics.

Summary of the Invention

In order to substantially solve the technical problems highlighted above, the present invention defines a method of managing a battery or a battery pack of electric or partially electric propulsion systems, for example electric traction vehicles, which makes use of: - a "smart" battery management system equipped with a physical model of the battery pack and appropriate control strategies,

- one or more "technical data sets", corresponding to the specific sample of the battery pack installed on the vehicle which, in particular, report the deviations from cell to cell with respect to nominal values.

The at least one "technical data set" includes an alphanumeric code readable by the BMS when any vehicle is turned on, which summarizes the peculiar characteristics of each cell, (in other words, its "identity card") and also its sensitivity to temperature variations, which will affect its performance in the module and / or in the battery and / or in the battery pack due to the cell-cell thermal non-uniformity as well as that due to the type and layout of the thermal management system found at the battery pack and, moreover, the electrical deviation of the connectors between the different modules from the nominal reference value.

The method according to the present invention will comprise the steps of measuring the deviations of the characteristics from the nominal value of the individual lithium-ion cells, the modules and the entire battery pack; transferring the technical data set obtained from the battery (or from the battery pack); decoding the technical data set; and supplying the same to the battery management system. Finally, the method includes the phase of using, by the battery management system, this technical data set to compensate for the variations between the different cells and / or between the different battery modules, in order to better manage, in terms of charge I discharge and duration, the individual cells, overcoming the criticalities of the module and / or the battery and / or the battery pack as a whole. Therefore, according to the present invention, a method is provided for the management of batteries that supply electric or partially electric propulsion systems, for example electric traction vehicles, having the characteristics set out in the independent claim, attached to the present description.

Further preferred and I or particularly advantageous embodiments of the invention are described according to the characteristics set out in the attached dependent claims.

Brief Description of the Drawings

The invention will now be described with reference to the attached drawings, which illustrate a non-limiting example of implementation, in which:

- Figure 1 is a schematic representation of the assembly of a battery pack used to power electric traction vehicles,

- Figure 2 is the same Figure 1 highlighting the macro-phases of the method of managing a battery or a battery pack, according to the present invention, and

- Figure 3 is a more detailed block diagram of the method of managing a battery or a battery pack.

Detailed Description

Just by way of non-limiting example, the present invention will now be described according to a preferred embodiment. In order to better describe the proposed method, it is appropriate to recall some important parameters of a battery and in particular of a battery with lithium-ion cells.

Battery state of charge (SOC) means its current capacity, related to the last charge-discharge cycle.

Battery state of health (SOH) is a "measure" that reflects the general condition of a battery and its ability to deliver specified performance compared to a new battery; in fact, during the life of a battery, its performance tends to gradually deteriorate due to irreversible physical and chemical changes that occur with use and with age until the battery is no longer usable.

State of charge and state of health of Li-ion batteries are affected by several factors, such as cell materials, module and battery pack design, usable capacity, charge-discharge rate, hysteresis, temperature and rate of discharge, self-discharge, aging.

Each single cell contributes to the determination of these parameters and, therefore, the "deep" knowledge of the single cell of a module and / or of a battery and / or of a battery pack becomes strategic for the optimal functioning of the entire battery pack.

According to an aspect of the present invention, the management method of batteries that power electric or partially electric propulsion systems, for example electric traction vehicles, comprises the following macro-phases (see Figure 2):

- S100 characterizing the cells 10 at the end of the production line and coding the cells according to the performed characterization,

- S200 managing, by means of the battery management system (BMS) and the battery thermal management system (BTM), the hardware and software relating to the modules 20 and / or the batteries 30 and / or the battery pack 40. With reference to Figure 2, the characterization at the end of the line (EoL) of the lithium-ion cells allows a more refined and motivated selection by production classes; in this way the percentage of waste and I or initial use of the cells in "minor" applications is reduced and, above all and consequently, the cost of batteries for automotive use is significantly reduced.

The adoption of an appropriate code also allows the optimal use of lithium-ion cells of "lower" classes, by transmitting the unique characteristics of the individual cells of modules and / or batteries and / or battery packs to the BMS. In fact, according to the present invention, it will be possible to manage in an optimal way also cells of different classes in the same module; therefore, it will no longer be necessary to make a strict classification of the cells at the end of the production line.

Finally, thanks to the ability of the battery management system (BMS) to manage a wider range of cells in an optimized way, it will be possible to reduce the current production quota of cells that are immediately destined for non-automotive applications (and therefore less profitable for the cell manufacturer, at the same cost of production); these other applications can instead conveniently take advantage of the re-use of batteries, at the end of their life in the automotive field; this will have a significant and effective positive impact on waste management and the consequent impact on the production of CO2, intrinsic in the recycling of lithium ion cells.

In particular, the method makes use of:

- a "smart" battery management system (BMS), equipped with a physical model of the battery pack 40 and appropriate control strategies,

- one or more "technical data sets", corresponding to the specific sample of the battery pack installed on the vehicle which, in particular, report the deviations from cell to cell with respect to the nominal values.

The at least one "technical data set" includes an alphanumeric code readable by the battery pack control system (BMS) when the vehicle is switched on, which summarizes the electrochemical non-uniformity between the cells 10, as well as that due to the type and layout of the thermal management system found at the level of the battery pack 40 and, moreover, the electrical deviation of the connectors between the different modules from the nominal reference value.

The macro-steps of the method according to the present invention can be further specified as follows (see Figure 3).

In particular, the macro-phase S100 ("characterizing the cells at the end of the production line and coding the cells according to the performed characterization") can be divided into the following phases:

- SI 10 measuring the deviations of the characteristics from the nominal value of the individual lithium-ion cells 10, thus generating a "technical data set",

- S120 coding and applying the technical data set to the individual cells 10.

The macro-phase S200 ("managing, by means of the battery management system (BMS) and the battery thermal management system (BTM), the hardware and software relating to modules 20 and/or batteries 30 and/or to the battery pack 40") can be declined in the following phases: - S210 decoding the technical data set by the battery management system (BMS),

- S220 using, by means of the battery management system, this technical data set to compensate for the variations between the different cells 10 and/or between the different modules 20 of the battery 30 and/or of the battery pack 40, in order to compensate for the deviation of the characteristics from the nominal value of the different cells, the deviation from the nominal value of electrical connections inside the modules (in particular, the fluctuation of the resistance value of the electrical connections) and the thermal inhomogeneity of cells and battery pack.

This last concept represents the essence of the present invention. In fact, the known methodologies, based on the equivalent circuit model (ECM) approach, aim to support:

- the design of a battery pack to estimate the impact of degradation and thermal imbalance in the pack itself; in this case, the ECM can be used as a CAE tool to perform a parametric analysis of the battery robustness project, in the event of the presence of a few unhealthy cells;

- the on-line estimate of the load status (SoC) and health status (SoH) of a battery module (or battery, or battery pack), due to cell-cell degradation in operating conditions; in this case the ECM can be used as a control strategy, to be implemented in the BMS for a better prediction of the battery health status (the relevant parameters of each single cell are the current and voltage ratios between all cells).

In other words, these methodologies are based on battery modules assembled with cells having small dispersion of performance (i.e. selected in very narrow degrees) and such methodologies detect a limited number of parameters (i.e. only current and voltage, roughly related to the real performance of the cells).

On the contrary, the present invention, as explained above, is characterized by:

- the use of a wider dispersion band of the cell performances for the assembly of the modules, thanks to a more accurate information of the performances of the single cells, based on more suitable and fine parameters (for example, parameters related to phenomena electrochemicals on surfaces of the crystalline microstructure of the anode), measured at the end of the cell production process and stored in a digital code marked on each cell and readable by the battery management system (BMS) in the assembled battery pack;

- the adoption of a suitable and specially developed control strategy, to be implemented in the BMS, to optimize the individual charge / discharge phases in operation, overcoming the cell-cell performance differential, and therefore improving the battery capacity, increasing the battery life and the elimination of the usual energy losses due to the traditional cell balancing process "a posteriori".

The advantages mentioned above are achievable because the BMS collect, from the beginning, the individual performances of each cell, and also their thermal non-uniformity in operation inside the battery pack, and therefore can manage, with the appropriate strategy indicated above, the charge phase and the discharge phase of the individual cells with an "a priori" cell balancing approach. Advantageously, the technical data set is presented in the form of an alphanumeric data set which can be condensed into a linearly developed barcode or a two-dimensional symbology code or other appropriate coding, for example the "Radio Frequency Identification (RFID).

The alphanumeric data set can be applied to the single cell at the end of the production line; moreover, to take into account the nonuniformity of the connectors and the thermal state of the individual cells, due to the layout of the battery 30, the same will be equipped with a further alphanumeric code. These alphanumeric codes will be created using any methodology, for example by imprinting the code on a special plate for laser marking. Alternatively, or in a complementary way, the alphanumeric data set could also be stored in the electronics of the battery pack 40. Furthermore, the alphanumeric data set could also be stored in the identification and diagnosis control unit, already existing on the battery pack, and automatically read by the Battery Management System (BMS) upon connection.

The decoding phase can also be carried out using known methods. Preferably, a scanner or an RFID tag reader can be used to read the technical data set. Alternatively, as already stated, if the alphanumeric data set were stored in the battery pack identification and diagnosis control unit, it would be automatically read by the battery management system (BMS) at the instant of connection.

More specifically, the algorithm implemented in the battery management system (BMS) is able to estimate the "initial" factory value (end-of-line test), the values of which will then be modified during operation, based on the SOH, through the adaptive self-learning algorithm. The results processed by the method can also be sent to the vehicle displays using the "CAN-bus", or the "Controller Area Network", a serial standard for buses, used to connect various electronic control units.

The algorithm is used to record past history for maintenance purposes or to predict vehicle mileage: the remaining range, based on recent driving or usage patterns, is calculated based on the current state of charge, corrected by the current health status and consumed energy.

As already mentioned, the input data for the BMS algorithm comprise an alphanumeric data set, for example an alphanumeric string, which characterize each sample of the complete battery pack 40 (or of the single battery 30, if applicable) and its individual modules 20.

The alphanumeric string contains at least the following parameters:

- deviation of the characteristics of the individual cells 10 from the nominal value. For example, the standard AC impedance response, which may be available from the conventional screening test performed by the cell manufacturer to ascertain the quality requirements for various components;

- internal electrical connections to the modules 20 and to the battery pack 40, characterizing the deviation from the nominal value. For example, the ohmic resistance that might be available from a conventional end-of- line test performed by the battery pack manufacturer to ascertain the quality requirements of the battery pack;

- parameters related to electrochemical phenomena on the surfaces of the crystalline microstructure of the anode; - thermal inhomogeneity of the cells inside the battery pack 40. For example, the temperature of the single cell 10 under specified conditions, which could be available from a further end-of-line test and is correlated to the thermal management circuits and the position of the individual 10 cells within the layout of the battery pack 40.

Finally, it is sufficient that the control algorithm of the battery management system (BMS) is able to read the technical data set of the battery 30 or the battery pack 40.

The advantages that the proposed methodology presents are various and all contribute to improving the management of electric-powered vehicles. In fact, a more reliable estimate of the vehicle autonomy will be possible, thanks to a better determination of the configurational and structural characteristics of the individual cells, as well as their deviation (when "new") from the nominal reference values, for which the management system battery (BMS) can proceed in a faster, more effective and more efficient way, in defining state of charge, state of health, etc., in operation during the life of the battery pack; a longer duration of the battery 30 or the battery pack 40, thanks to the targeted control of the charge/discharge of the individual cells 10; lower energy consumption due to the elimination of cell leveling; a more robust limp-home guarantee due to the ability to detect and bypass weaker cells, but not a complete module.

Finally, thanks to the present methodology, it will be possible to assemble modules 20 provided with cells 10 having much wider ranges of deviation from nominal values than is currently done and/or the selection of cells in classes. The proposed invention should definitively reduce the production cost of the lithium-ion battery pack for motor vehicles and also allow an improvement in the optimization of the use of the battery.

In addition to the embodiment of the invention, as described above, it is to be understood that numerous other variants exist. It is also to be understood that such embodiments are exemplary only and limit neither the scope of the invention, nor its applications, nor its possible configurations. On the contrary, although the above description allows the skilled person to carry out the present invention at least according to an exemplary embodiment thereof, it must be understood that many variants of the components described are possible, without thereby departing from the scope of the invention, as defined in the attached claims, which are interpreted literally and/or according to their legal equivalents.