Analyzing and controlling performance in a composite battery module

Abstract

A method for performance analysis and use management of a battery module is disclosed, wherein the battery module includes a multitude of interconnected battery cells and a battery management system with a plurality of dedicated analysis/control units (ACUs) that analyze performance of the battery module, the ACUs being assigned to individual battery cells and/or battery blocks of battery module. The method includes measuring current and voltage of one or more of an individual battery cell and a battery block; calculating a charge removal from the one or more of the individual battery cell and the battery block; calculating a loading charge of the one or more of the individual battery cell and the battery block; determining the remaining charge of the one or more of the individual battery cell and the battery block; and failure monitoring of the one or more of the individual battery cell and the battery block.

Claims

1. A method for performance analysis and use management of a battery module in an electric vehicle, wherein the battery module comprises a multitude of interconnected battery cells and a battery management system with a plurality of dedicated analysis/control units (ACUs) that analyze performance of the battery module, the ACUs being assigned to individual battery cells and the ACUs being assigned to battery blocks of the battery module, the method comprising: measuring current and voltage of one or more of an individual battery cell and one or more of the battery blocks; calculating a charge removal from the one or more of the individual battery cells and one or more of the battery blocks; calculating a charge increase of the one or more of the individual battery cells and one or more of the battery blocks; determining a remaining charge of the one or more of the individual battery cells and one or more of the battery blocks based on the charge removal and the charge increase; performing failure monitoring of the one or more of the individual battery cells and one or more of the battery blocks by comparing the remaining charge and the charge removal with references levels to determine if the one or more of the individual battery cells and one or more of the battery blocks has reached a predefined level of degradation; based on a determination that the remaining charge of the one or more of the individual battery cells and one or more of the battery blocks is below a threshold value, activating one or more of a spare battery cell and a spare battery block of the battery module to extend the range of the electric vehicle; and transmitting a signal identifying the ACU of the battery block and the battery cell, wherein the signal is transmitted wirelessly, wherein the plurality of dedicated ACUs communicate over a same RF channel using a time domain multiple access scheme.

2. The method according to claim 1, wherein the failure monitoring of the one or more of the individual battery cells comprises issuing a warning if the one or more of the individual battery cells is found to have reached a predefined level of degradation.

3. The method according to claim 2, wherein the warning is issued to one of a vehicle control unit and a charger control unit.

4. The method according to claim 1, wherein the failure monitoring of the one or more of the individual battery cells comprises active switching of the one or more of the individual battery cells if the one or more of the individual battery cells is found to have reached the predefined level of degradation.

5. The method of claim 4, wherein the failure monitoring of the one or more of the individual battery cells comprises adding one or more of the spare battery cell and the spare battery block as a replacement for the degraded one or more of the individual battery cells.

6. The method according to claim 1, wherein the voltage measurement is performed through power contacts of the one or more of the individual battery cells.

7. The method according to claim 1, wherein the current measurement is performed using a Hall effect probe located in proximity of one of the power contacts of the one or more of the individual battery cells.

8. A non-transitory, computer readable medium having computer readable instructions stored thereon that, when executed by a computer, implement a method for performance analysis and use management of a battery module in an electric vehicle, wherein the battery module comprises a multitude of interconnected battery cells and a battery management system with a plurality of dedicated analysis/control units (ACUs) that analyze performance of the battery module, the ACUs being assigned to individual battery cells and the ACUs being assigned to battery blocks of the battery module, wherein the method comprises: measuring current and voltage of one or more of an individual battery cells and one or more battery blocks; calculating a charge removal from the one or more of the individual battery cells and one or more of the battery blocks; calculating a charge increase of the one or more of the individual battery cells and one or more of the battery blocks; determining the remaining charge of the one or more of the individual battery cells and one or more of the battery blocks based on the charge removal and the charge increase; performing failure monitoring of the one or more of the individual battery cells and one or more of the battery blocks by comparing the remaining charge and the charge removal with references levels to determine if the one or more of the individual battery cells and one or more of the battery blocks has reached a predefined level of degradation; based on a determination that the remaining charge of the one or more of the individual battery cells and one or more of the battery blocks is below a threshold value, activating one or more of a spare battery cell and a spare battery block of the battery module to extend the range of the electric vehicle; and transmitting a signal identifying the ACU of the battery block and the battery cell, wherein the signal is transmitted wirelessly, wherein the plurality of dedicated ACUs communicate over a same RF channel using a time domain multiple access scheme.

9. The computer readable medium according to claim 8, wherein the failure monitoring of the one or more of the individual battery cells comprises issuing a warning if the one or more of the individual battery cells is found to have reached a predefined level of degradation.

10. The computer readable medium according to claim 9, wherein the warning is issued to one of a vehicle control unit and a charger control unit.

11. The computer readable medium according to claim 8, wherein the failure monitoring of the one or more of the individual battery cells comprises active switching of the one or more of the individual battery cells if the one or more of the individual battery cells is found to have reached the predefined level of degradation.

12. The computer readable medium according to claim 11, wherein the failure monitoring of the one or more of the individual battery cells comprises adding one or more of the spare battery cell and the spare battery block as a replacement for the degraded one or more of the individual battery cells.

13. The computer readable medium according to claim 8, wherein the voltage measurement is performed through power contacts of the one or more of the individual battery cells.

14. The computer readable medium according to claim 8, wherein the current measurement is performed using a Hall effect probe located in proximity of one of the power contacts of the one or more of the individual battery cells.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) The present invention embodiments may best be understood from the following detailed description, but not restricted to the embodiments, in which:

(2) FIG. 1 is a schematic circuit diagram of a battery module with a multitude of electrically interconnected battery cells;

(3) FIG. 2a is a schematic circuit diagram of a plurality of battery cells arranged in a serial array, each battery cell being equipped with an analysis/control unit (ACU);

(4) FIG. 2b is a schematic circuit diagram of a plurality of battery cells arranged in a serial array, the serial array being equipped with a shared ACU;

(5) FIG. 3a is a schematic circuit diagram of ACU chip of FIG. 2a;

(6) FIG. 3b is a schematic sectional view of a battery cell with the associated ACU chip;

(7) FIG. 4a is a diagram of cell voltage as a function of time for two selected battery cells;

(8) FIG. 4b is a diagram of cell energy as a function of time for two selected battery cells; and

(9) FIG. 5 is a schematic flow diagram of an exemplary embodiment of a method for analyzing and controlling the performance of a battery module.

(10) In the drawings, like elements are referred to with equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention. Moreover, the drawings are intended to depict only typical embodiments of the invention and therefore should not be considered as limiting the scope of the invention.

DETAILED DESCRIPTION

(11) While the above described patents disclose various methods for battery analysis and monitoring based on a variety of parameters of the battery, they do not provide a detailed analysis of the actual state of individual battery cells within a battery module. In order to obtain a detailed picture of the actual battery state, however, it is desirable to be able to test and evaluate battery module capability with a high granularity, i.e., down to cell level.

(12) There is also a need for a battery management system with real time and online feedback capability for reporting the actual state of individual battery cells as well as of the battery module as a whole. Moreover, it is desirable to integrate additional features such as an ability to quickly react in case of the failure or malfunction of individual battery cells within the battery module by automatically initiating maintenance actions if a given cell has reached a predefined level of degradation. This is of especially high importance if the battery module is to be used in a vehicle drive system.

(13) FIG. 1 shows a schematic view of a battery module 10 to be used in a drive system of an electric vehicle. The battery module 10 comprises a multitude of electrically interconnected electrochemical battery cells 20, for example, Li-ion cells. Each of the battery cells 20 is capable of storing chemical energy and converting it into electrical energy. The cells 20 are rechargeable in the sense that they may be charged/discharged multiple times. The cells 20 may be connected in series to achieve a desired output voltage and/or in parallel to provide a desired amount of current source capability. Battery cells 20 within module 10 may be grouped into blocks 15. In the embodiment of FIG. 1, cells 20 are connected in serial arrays to form blocks (strings) 15 which are in turn connected in parallel to form battery module 10.

(14) Battery module 10 comprises a battery management system 100 with a multitude of analysis and control units (ACUs) 30 which are placed in various locations within battery module 10 and are integrated into the electrical network of battery module 10. As an example, FIG. 2a shows a detailed circuit diagram of a part of battery module 10 comprising a string 15 of battery cells 20 which are connected in serial array. Each battery cell 20 is provided with a dedicated analysis/control unit (ACU) 30 which is connected in parallel with this particular battery cell 20. Using ACU 30, selected operating parameters of associated battery cell 20 may be monitored during operational mode as well as in charge mode. Moreover, ACU 30 comprises capabilities enabling it to execute control functions on associated battery cell 20.

(15) FIG. 3a depicts a schematic layout of an ASIC embodiment 40 of ACU 30 with sub-circuits (function blocks) for identification, measurement and transmission. ACU chip 40 is connected to ground pin 21 and to positive terminal pin 22 of battery cell 20. ACU chip 40 contains a variety of sensors such as a thermal sensor 42, a voltage sensor 43 and a magnetic field sensor 44 the data of which may be used for inferring cell current.

(16) Magnetic field sensor 44 may be a GMR (giant magnetic resonance) sensor and is used for carrying out current measurements via a magnetic field (Hall effect) measurement on the respective battery cell 20: According to Ampere's law, an electric current I flowing through a wire (such as electrical contact pins 21, 22 of battery cell 20) produces a magnetic field B. The path integral of the magnetic field B along a closed curve C surrounding this wire is proportional to the current I.sub.enc flowing through the wire:
{right arrow over (B)}d{right arrow over (l)}=μ.sub.0I.sub.enc,
where μ.sub.0 is the magnetic constant. Thus, by placing ACU chip 40 in close vicinity of power pins 21 or 22 of battery cell 20, current through this cell may be measured. Measurement accuracy may be enhanced by dimensioning ACU chip 40 in such a way that magnetic field sensor 44 may be positioned immediately adjacent to one of the contact pins 21 and encircles this power pin 21 (at least partly). This is depicted schematically in FIG. 3b which shows a schematic sectional view of battery cell 20 with the associated ACU chip 40 partly enclosing power pin 21.

(17) Besides sensors 42, 43, 44, ACU chip 40 comprises a transmission circuit 46 for transmitting data acquired by the sensors 42, 43, 44 to a collector unit 50 of battery module 10 (see FIG. 1). Transmission circuit 45 comprises a modulator 46 which transforms output signals issued by the sensors 42, 43, 44 into an appropriate format for physical transmission to a demodulator 52 located in collector unit 50 which collects signals issued from various battery cells 20 contained in battery module 10. An identification circuit 47 attaches a unique digital identification number which allows signals sent to collector unit 50 to be tracked back to the specific battery cell 20 they originate from. Transmission circuit 45 may comprise an RF (radio frequency) unit 48 for enabling wireless communication between ACU chip 40 of battery cell 20 and collector unit 50 of battery module 10.

(18) A data management unit (DMU) 49 comprises means for controlling data transfer from sensors 42, 43, 44 to transmission circuit 45. Data management unit 49 may also comprise additional features such as a logical unit to be used for diagnostics and (pre-) evaluation of the sensor signals and/or memory for storing measured data, historical data, threshold/reference data and/or software for performing diagnostics. In order to allow signals from multiple sensors 42, 43, 44 to be transmitted to collector unit 50 in an orderly fashion, data management unit 49 contains a multiplexer which is used to switch between the signals issued by the various sensors 42, 43, 44 of ACU chip 40.

(19) ACU chip 40 may also include hardware features such as bypass diodes and/or switches 35, which may, for example, be used to short-circuit battery cell 20 in the case that measured power and/or temperature data acquired by sensors 42, 43, 44 attached to battery cell 20 exceed or fall below a pre-determined threshold value, indicating that battery cell 20 may be degraded or defective. If any battery cell 20 within battery module 10 fails, this has an impact on the module's performance. If, for example, a battery cell 20′ in a serial array with other battery cells 20 (such as the one depicted in FIG. 2a) fails, this defective cell 20′ acts as a current trap and causes the current through string 15 to sag. If this occurs, it is desirable to short-circuit defective battery cell 20′ so that while the total voltage of the overall string 15 will be reduced by the voltage of the defective cell 20′, the overall current will not diminish. As described above, ACU chip 40 may comprise means (e.g., diodes and/or switches 35) to short-circuit its respective battery cell 20 temporarily or permanently. Switch 35 may, for example, be embodied as a power MOSFET.

(20) Note that in the embodiment of FIG. 3a, no additional wiring (besides wires connecting ACU chip 40 to battery cell 20) is required for communicating measurement data collected by sensors 42, 43, 44 to collector unit 50, since ACU chip 40 uses an RF unit 48 for wireless transmission of cell performance information to the collector unit 50 on module level. Power line communication is possible as well, using the DC lines with encoded signals dedicated to the unique cell. In order to allow ACUs 30 belonging to different battery cells 20, 20′ within battery module 10 to use the same RF channel, a time domain multiple access (TDMA) scheme may be used for data transmission. All output signals originating from any specific battery cell 20′ are coded using identification circuit 47 so as to individually identify the ACU 30′ (and the battery cell 20′) from which they were issued. Thus, all transmitted measured data and information about cell performance can be tracked back to a specific ACU chip 40′ and to the specific battery cell 20′ it is attached to.

(21) Collector unit 50 of battery module 10 comprises a data acquisition and RF (de)modulating device 52 connected to a demodulation and data acquisition interface (DDI) 54. Besides data acquisition and demodulation, collector unit 50 may contain a multitude of additional functions such as temperature and voltage sensors, a multiplexer for switching between inputs from the various battery cells 20, 20′, storage for storing historical data furnished by the various ACUs 30, a CPU for data (pre-)evaluation etc. In particular, collector unit 50 may comprise a control system 60 for triggering measurements and/or activating switches in selected ACU chips. For example, collector unit 50 is embodied as an ASIC chip which is physically identical to ACU units 40 of the individual battery cells 20, so that only one single type of ASIC is required.

(22) Battery management system 100 as shown in FIGS. 2a and 3a allows real time battery performance analysis and control with a very high granularity, i.e., down to cell level. ACUs 30 of battery cells 20 furnish online data on the actual state of relevant operational parameters within the respective cell 20. By collecting and evaluating measurements of these parameters over a period of time, historical data of these parameters may be acquired which enable predictions of future performance of this specific battery cell 20. Moreover, individual battery cells 20 can be controlled independently (by activating switch 35). Performance prediction as well as the ability to eliminate failing individual cells 20 from the battery network enables a highly efficient management and optimized performance of battery module 10. In addition, it is possible to add spare individual cells to the battery network, thus enabling a high efficiency and high power availability.

(23) FIG. 5 shows a schematic flow diagram of an analysis/control method 300 which may be implemented using ACU chips 40 dedicated to battery cells 20. Due to sensors 43, 44, each ACU chip 40 is capable of measuring a current I.sub.enc flowing through power pin 21 of the respective battery cell 20 and of measuring the voltage U of this cell 20 (block 310), and thus computing the power P=U*I of this cell. In particular, power changes during battery charge and discharge can be monitored (blocks 320 and 330). From this, the actual charge status of each battery cell 20 may be inferred (block 340). The time dependence of the cell power, as well as the battery charge, are indicators of the actual performance and degradation of battery cell 20 and may be used to predict the long-term performance of this cell 20. In particular, history data on the discharge behavior and the changes of remnant charge over time are important indicators for degradation prediction.

(24) This is illustrated in FIG. 4a which shows a diagram of cell voltage as a function of time as measured for two battery cells 20 inside a 30 Ampere-hour battery module being discharged with a constant current of 3 Amperes. Curve 120a of cell voltage of a first battery cell 20 is seen to remain on a higher level for a longer time than curve 120b of a second battery cell 20. FIG. 4b shows a diagram of cell energy as a function of time of the two battery cells 20 inside the 30 Ampere-hour battery module being discharged with a constant current of 3 Amperes. In this diagram, measured power U*I was integrated over time in intervals of 15 min, so that each data point corresponds to the energy delivered in a 15 minute time interval. As is seen from FIG. 4b, curve 220a of cell energy of a first battery cell 20 is seen to remain on a higher level for a longer time than curve 220b of a second battery cell 20. Next to curves 120a/b, 220a/b corresponding to the measured data (solid lines), FIGS. 4a and 4b show curves (dotted lines) corresponding to polynomial fits of these data; these fits are seen to accurately reproduce the measured curves. Polynomial fits thus yield good estimates of the time behavior of both the remaining charge and the predicted life time of battery cells 20. In particular, the slopes of the discharge curves (FIG. 4a) are a good indicator of battery lifetime, performance and cell degradation.

(25) ACU 30 thus furnishes a variety of information which can be used for a battery availability test in order to monitor the actual status of the battery, performance history and prediction, detection of weak performers, lifetime forecast, etc., down to cell level. In particular, cell history may be monitored by taking advantage of ACU 30 data on voltage/current and cell temperature as a function of time. From these data, energy (integrated over time), discharge curves in operation and actual battery capacity may be inferred. By defining references/thresholds for the battery discharge and the energy content of battery cells 20 and by comparing these with the data furnished by ACU 30, actual performance status of any given battery cell may be assessed. In particular, degraded and underperforming battery cells may be identified (block 360 in method 300). Once a given cell has been identified as defective, it may be removed from the battery module 10 using switch 35 (block 370). In addition (or instead), a warning may be issued (block 380) to the vehicle operating system and or to a battery charger system (block 370). Also, removed (defective) cells may be replaced by spare cells if these are available in the battery network.

(26) While in the embodiment of FIG. 2a each battery cell 20 is assigned its own dedicated ACU 30, a second embodiment of the invention, shown in FIG. 2b, has a dedicated analysis/control units (ACU) 30′ is assigned to each string 15′ of several battery cells 20′. In this embodiment, the respective ACU chip 40′ manages analysis, control and monitoring of the entire string 15′ of battery cells 20. ACU chip 40′ furnishes data on the relevant parameters of the whole string 15′ and comprises a switch 35′ for electrically disconnecting the whole string 15′ from the remaining battery cells of battery module 10. While FIG. 2b shows an embodiment of an ACU chip 40′ managing a string 15′ of battery cells, the underlying principle of managing multiple electrically connected cells 20′ with a single ACU chip 40′ may be generally applied to a set of serialized and/or parallel cells 20′ forming cell blocks 15, 15′. A cell block monitoring arrangement of the type of FIG. 2b (in contrast to the single cell monitoring arrangement of FIG. 2a) does not permit analysis and control down to individual cell level, but it is more cost effective since it requires less ACUs 30′ for analyzing/controlling a given battery module 10.

(27) Note that various combinations of single cell management of FIG. 2a and the cell block management of FIG. 2b are possible. For example, block management of FIG. 2b can be enhanced by attaching an ACU chip 40″ to each individual battery cell 20′ (illustrated by dotted lines in FIG. 2b), where ACU chips 40″ have only monitoring capability whereas ACU chip 40′ has both monitoring and control capability. ACU chips 40″ enable analysis and monitoring capability on single cell level (i.e., with a very high granularity), whereas ACU chip 40′ executes control on string level (via switch 35′) and enables additional data transparency and availability, for example, when analyzing history data taken in operational mode as well as in charge mode of battery module 10.

(28) Battery module 10 may contain spare blocks 15″ (see FIG. 1) which are switched off during proper operation of the battery 10. This is especially useful if battery 10 is to be used in an electric drive system. If control system 60 detects failing battery cells 20, the corresponding block 15 can be switched off and a spare block can be added in order to maintain adequate performance level of battery module 10. This increases reliability and comfort. Moreover, spare blocks may be used for range extension in case of urgent need. Note that in the embodiment of FIG. 2a, this capability can be applied down to cell level.

(29) Using battery management system 100, cell 20 and/or block 15 performance may be monitored during operation. Based on these data, the cells/blocks best suited for a given operational state may be determined and linked to the battery module 10 for optimized performance. This decision may be taken in a precautionary way, for example, in view of aging characteristics of individual cells/blocks. More generally, management system 100 may be used for managing and improving maintenance cycles down to cell/block level, since ACUs 30 yield information for real time notification and service guidance.

(30) If the battery module 10 is used as part of an electrical drive system of a vehicle, the discharge curves in operation (voltage and current) may be correlated to driven distance and speed. The actual battery capacity (i.e. the remaining charge) may be evaluated in order to give the driver an estimate of the cruising range and to provide the driver with feedback on how to optimize driving performance for achieving maximum battery network availability. Moreover, the data collected by battery management system 100 may be loaded into the vehicle CPU 70 for further evaluation and/or may be transferred to a charge station CPU 70 during battery charging and/or via the WEB (see FIG. 1). In the charge station, the charge curve of individual cells/blocks may be monitored as a function of time. A count of the number and frequency of charge cycles yields information on the usage of this individual cell 20. Communication of battery controller 60 to vehicle and/or charge station CPU 70 may furthermore implement deep discharge protection and overcharge protection as well as emergency reporting and life time reporting.

(31) While the invention has been described with reference to a preferred embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.