Diagnostic method and diagnostic system for an electrochemical energy storage cell

Abstract

A diagnostic method and a diagnostic system for an electrochemical energy storage cell, and a vehicle including the diagnostic system. An electrical current due to an electrical connection between the energy storage cell and a central load is modulated at a first excitation frequency and is measured centrally. An electrical voltage at the energy storage cell is measured and a first impedance value is determined based on the electrical current and the electrical voltage. Also, a previously-known electrical current due to an electrical connection between the energy storage cell and a predefined cell-individual load is modulated at a second excitation frequency. The electrical voltage occurring at the energy storage cell is measured and a second impedance value is determined based on the previously-known electrical current and the electrical voltage. Diagnostic information is determined and output based on a comparison of the first impedance value with the second impedance value.

Claims

1. A diagnostic method for an electrochemical energy storage cell, the method comprising: modulating, at a first excitation frequency, a first electric current occurring due to an electrical connection between the energy storage cell and a central load; measuring a modulated electric current resulting from the modulating of the first electric current; measuring a first electric voltage present on the energy storage cell; determining a first impedance value based on the modulated electric current and the first electric voltage; modulating, at a second excitation frequency, a previously known second electric current occurring due to an electrical connection between the energy storage cell and a predefined cell-specific load; measuring a second electric voltage present on the energy storage cell; determining a second impedance value based on the previously known second electric current and the second electric voltage; determining diagnostic information based on a comparison of the first impedance value with the second impedance value; and outputting the diagnostic information; wherein the second excitation frequency is selected to differ from the first excitation frequency, and the previously known second electric current occurring due to the electrical connection of the energy storage cell with the predefined cell-specific load is modulated simultaneously with the modulation of the first electric current occurring due to the electrical connection of the energy storage cell with the central load.

2. The diagnostic method according to claim 1, wherein the diagnostic information is taken into account in the context of at least one future measurement of an electric voltage occurring on the energy storage cell due to the electrical connection of the energy storage cell with the predefined cell-specific load.

3. The diagnostic method according to claim 1, wherein at least one of the first electric current and the first electric voltage is filtered with respect to the first or second excitation frequency.

4. A diagnostic system for an electrochemical energy storage cell which is designed to execute a diagnostic method, the diagnostic system comprising: a controller configured to control a cell-specific evaluation device to modulate, at a first excitation frequency, a first electric current occurring due to an electrical connection between the energy storage cell and a central load; measure a modulated electric current resulting from the modulating of the first electric current; measure a first electric voltage present on the energy storage cell; determine a first impedance value based on the modulated electric current and the first electric voltage; modulate, at a second excitation frequency, a previously known second electric current occurring due to an electrical connection between the energy storage cell and a predefined cell-specific load; measure a second electric voltage present on the energy storage cell; determine a second impedance value based on the previously known second electric current and the second electric voltage; determine diagnostic information based on a comparison of the first impedance value with the second impedance value; and output the diagnostic information; wherein the second excitation frequency is selected to differ from the first excitation frequency, and the previously known second electric current occurring due to the electrical connection of the energy storage cell with the predefined cell-specific load is modulated simultaneously with the modulation of the first electric current occurring due to the electrical connection of the energy storage cell with the central load.

5. The diagnostic system according to claim 4, comprising: a central current measuring assembly configured to measure the first electrical current occurring due to the electrical connection of the energy storage cell with the central load; and the cell-specific evaluation device configured to determine the second impedance value based on the previously known second electric current and the second electric voltage; wherein the central current measuring assembly is designed to output an amplitude of the first electric current occurring due to the electrical connection of the energy storage cell with the central load to the cell-specific evaluation device, and the cell-specific evaluation device is designed, additionally to the second impedance value, to further determine the first impedance value based on the amplitude of the first electric current output by the central current measuring assembly and an amplitude of the first electric voltage.

6. A motor vehicle having an electrical energy storage cell and a diagnostic system according to claim 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagnostic system according to the invention for an electrochemical energy storage cell;

(2) FIG. 2 shows an electrochemical energy storage cell having a cell-specific evaluation device;

(3) FIG. 3 shows a diagnostic method according to the invention for an electrochemical energy storage cell, in a first embodiment; and

(4) FIG. 4 shows a diagnostic method according to the invention for an electrochemical energy storage cell, in a second embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1 shows a diagnostic system 100 according to the invention for electrochemical energy storage cells 10, each having a cell-specific evaluation device 11 (single cell chip, or SCC; also known as a single cell monitor, or SCM) and a central control apparatus 20. The energy storage cells 10 are series-connected and, in combination, constitute an electrochemical energy store which, for example, supplies a vehicle with electrical energy. To this end, the electrochemical energy store, as represented in an exemplary manner, can be integrated in a high-voltage region of a vehicle network of the vehicle. In particular, the energy store is electrically connected to a motor control device 30 or to an inverter, in order to deliver DC supplied by the energy storage cells 10 in the form of AC to an electrical machine 40, for example to an electric motor for driving the vehicle. The energy store is also electrically connected to a DC voltage converter 50, which delivers the DC supplied at a lower voltage in an on-board network 60 of the vehicle.

(6) The motor control device 30 or the electrical machine 40, or the DC voltage converter 50 or the on-board network 60 which, in the routine operation of the vehicle, draw electrical energy from the energy store, in a preferred manner, constitute a central load 80. The central load 80 is thus variable, particularly according to the operating state of the vehicle. According to the invention, the flow of electric current associated with this loading of the energy storage cells 10 is modulated by the central load 80.

(7) The preferably high-frequency modulation is executed at a first excitation frequency. Accordingly, the central load 80, i.e. the motor controller 30 or the DC voltage converter 50 can be prompted to modulate the current at the first excitation frequency by a central energy store control device 21 (battery monitoring unit or BMU) of the control apparatus 20. The central loading of the energy storage cells 10 generated in this manner corresponds to an excitation, on the basis of which an impedance of the energy storage cells 10 can be centrally determined.

(8) For the determination of the impedance, the control apparatus 20 comprises a current measuring assembly 23, which is designed to measure the electric current I occurring due to the electrical connection of the energy storage cells 10 with the central load 80. In the example represented, the current measuring assembly 23 is integrated in a central power contactor 22 of the control apparatus 20, for example on a circuit board.

(9) The electric voltage, which is also necessary for the determination of the impedance, which is present on the energy storage cells 10 in the event of the electrical connection with the central load 80, is measured in each case on or in each of the energy storage cells 10 by the corresponding evaluation device 11. An evaluation device 11 of this type can be configured, for example, as a chip, which is designed to measure the electric voltage occurring on the respective energy storage cell 10. The impedance determined on the basis of the measured electric current and the measured electric voltage is also described as the first impedance.

(10) The voltage value determined can be transmitted, for example via a data link 70, to the central energy store control device 21 of the control apparatus 20. In this case, the first impedance can be determined by the control apparatus.

(11) Alternatively, the first impedance for each of the energy storage cells 10 can also be determined, in each case, by the cell-specific evaluation device 11. To this end, the electric current measured by the current measuring assembly 23 is transmitted via the data link 70 to the evaluation devices 11.

(12) In order to improve the accuracy of this first impedance measurement, which is executed by means of central excitation, the measured electric current and the measured electric voltage can be filtered with respect to the first excitation frequency, for example by means of a Fourier decomposition. This filtering, at least in part, can be executed by the control apparatus 20. Alternatively, however, the filtering can also be executed, at least in part, by the evaluation device 11.

(13) Preferably, the evaluation devices 11 are not only designed to determine electric voltages occurring in the event of the electrical connection of the energy storage cells 10 with the central load 80, but also to directly determine a second, cell-specific impedance of the respective energy storage cell 10. To this end, the evaluation devices 11 can modulate a previously known electric current, occurring due to an electrical connection of the respective energy storage cell 10 with a respectively predefined cell-specific load, for example a shunt of the evaluation device 11, and measure the electric voltage occurring on the respective energy storage cell 10.

(14) The preferably high-frequency cell-specific modulation is executed at a second excitation frequency. The loading of the energy storage cell 10 generated in this manner corresponds to an excitation, on the basis of which the impedance of the energy storage cells 10 can be determined in a cell-specific manner.

(15) In evaluation devices 11 of this design, in order to output a pure voltage value on the control apparatus 20 for the central determination of impedance, the evaluation devices 11 can be configured such that, in the context of the cell-specific determination of impedance, not only the predefined electric current corresponding to the predefined cell-specific load is considered, but also an electric current of 1 A is assumed. The impedance Z=U/1 A thus determined by the evaluation device 11 will then correspond directly to the electric voltage occurring on the respective energy storage cell 10.

(16) The control apparatus 20, particularly the central energy store control device 21, is preferably designed to compare the first impedance, which is centrally determined by the control apparatus 20, with each second impedance which is respectively determined by each of the evaluation devices in a cell-specific manner and, on the basis of the comparison, to constitute and output diagnostic information with respect to the impedance measurements. Given that, for the first impedance measurement, the electric current occurring due to central loading is accurately measured by means of the current measuring assembly 23 whereas, for each of the second impedance measurements, the predetermined electric current occurring due to cell-specific loading is only assumed, the first impedance measurement can be considered to be more reliable, and the second impedances determined can therefore be validated by reference to the first impedance determined. Optionally, the evaluation devices 11 can also be calibrated by means of the diagnostic information, in order to improve the reliability of future cell-specific impedance measurements by the evaluation devices 11, for example during the operation of the vehicle.

(17) FIG. 2 shows an electrochemical energy storage cell 10 having a cell-specific evaluation device 11, which incorporates a voltage measuring assembly 12 for measuring an electric voltage U occurring due to an electrical connection of the energy storage cell 10, particularly of an electrode assembly 13, with a predefined cell-specific load 14. The evaluation device 11 further comprises a cell-specific switching assembly 15 for the modulation of the previously known electric current occurring during the electrical connection. Both the current measuring assembly 12 and the cell-specific load 14 and/or the cell-specific switching assembly 15 can be constituents of the evaluation device 11, particularly of an integrated circuit or chip.

(18) The evaluation device 11, as described in detail with reference to FIG. 1, is designed to execute a cell-specific impedance measurement. Alternatively or additionally, the evaluation device 11 can be designed, as also described with reference to FIG. 1, to measure an electric voltage occurring due to the electrical connection of the energy storage cell 10 with a central load, thereby also permitting a determination of the impedance by reference to an external and centrally-injected current.

(19) FIG. 3 shows a diagnostic method 1 according to the invention for an electrochemical energy storage cell, in a first form of embodiment. By means of the diagnostic method 1, for example, a cell-specific impedance measurement can be validated and/or a corresponding measuring assembly can be calibrated.

(20) In a process step S1, a central energy store control device (battery monitoring unit or BMU) of a control apparatus of an electrochemical energy store, which incorporates the energy storage cell, initiates the method 1, particularly a calibration sequence, for example by the output of a starting signal to a central switching assembly of the control apparatus. This calibration sequence is preferably executed prior to the start of operation of the energy storage cell.

(21) In a process step S2, this switching assembly modulates an electric current occurring due to an electrical connection of a central, particularly a variable, load with the energy storage cell at a first excitation frequency f.sub.1 which is dictated by the energy store control device. The modulation imposes a central excitation upon the energy storage cell, on the basis of which a first impedance Z.sub.ext can be determined in a subsequent process step S7.

(22) In a further process step S3, by means of a current measuring assembly of the control apparatus, an electric current I occurring due to the connection is measured. At least essentially simultaneously, in a process step S5, by means of a cell-specific evaluation device (single cell monitor, or SCM; also known as a single cell chip, or SCC), which is designed for the cell-specific determination of a second impedance Z.sub.SCM in a subsequent process step S10, initiates an impedance measurement under the assumption of an electric current flow of 1 A, associated with central excitation which is external to the store.

(23) In subsequent process steps S4, S6, firstly, the measured electric current I can be filtered by the central energy store control device, for example wherein a Fourier coefficient F of the electric current I is determined at the first excitation frequency f.sub.1 and, secondly, the electric voltage measured in the form of the impedance Z=U/1 can be filtered by the evaluation device, for example wherein a Fourier coefficient F of the electric voltage U is determined at the first excitation frequency f.sub.1.

(24) The first impedance Z.sub.ext can be determined by the central control apparatus, where the voltage measured by the evaluation device is delivered to the central control apparatus. However, it is also possible for the injected current, particularly the current measured by means of the current measuring assembly, to be delivered to the cell-specific evaluation device, such that the first impedance Z.sub.ext can be determined directly by the evaluation device.

(25) After the calculation of the first impedance Z.sub.ext on the basis of the Fourier coefficients F for the electric current I and the electric voltage U determined in process step S7, the central excitation is interrupted in the further process step S8, and a cell-specific impedance measurement for determining the second impedance Z.sub.SCM is initiated. By modulation of a previously known current I.sub.SCM occurring due to the electrical connection of the energy storage cell with a predefined, i.e. constant, cell-specific load, a cell-specific excitation is imposed upon the energy storage cell at a second excitation frequency which, in this form of embodiment, corresponds to the first excitation frequency f.sub.1. The resulting electric voltage U is measured in process step S10, and is correlated with the previously known electric current I.sub.SCM to give the cell-specific second impedance Z.sub.SCM.

(26) The second impedance Z.sub.SCM thus determined is preferably transmitted to the central energy store control device where, in process step S11, it is compared with the previously determined first impedance Z.sub.ext. In the context of the comparison, diagnostic information, for example a corrective factor, is determined and output, for example saved in the central energy store control device or transmitted to the evaluation apparatus, in order to permit the correction of future cell-specific impedance measurements.

(27) FIG. 4 shows a diagnostic method 1 according to the invention for an energy storage cell, in a second form of embodiment. In an analogous manner to the form of embodiment described in conjunction with FIG. 3, an impedance measurement is initiated by a central energy store control device of a control apparatus for an energy store, which incorporates the energy storage cell, in a process step S1a, for example during the operation of a vehicle, during which electrical energy is drawn from the energy store or the energy storage cell.

(28) In a further process step S2a, a switching assembly of the control apparatus modulates the electric current I occurring due to an electrical connection of the energy storage cell with a central load, which is external to the store, at a first excitation frequency f.sub.1. In a subsequent process step S3a, the electric current I occurring is measured by a current measuring assembly of the control apparatus, and is filtered, for example a Fourier coefficient F is calculated at the first excitation frequency f.sub.1.

(29) At least essentially simultaneously, in a further process step S4a, a cell-specific impedance measurement is initiated by an evaluation device of the energy storage cell, wherein a previously known current flowing as a result of the electrical connection of the energy storage cell with a predefined cell-specific load is modulated at a second excitation frequency f.sub.2, which differs from the first excitation frequency f.sub.1. A measurement of the likewise occurring electric voltage U therefore permits the evaluation device to determine a second impedance Z.sub.SCM on the basis of the previously known electric current I.sub.SCM and the measured electric voltage U.

(30) In this form of embodiment, process step S4a also includes the determination of an electric voltage U occurring due to the electrical connection of the energy storage cell with the central load. To this end, as described in detail in conjunction with FIG. 3, an electric current flow of 1 A is assumed, such that the impedance Z.sub.ext,SCM determined by the evaluation device corresponds directly to the electric voltage U occurring.

(31) In order to permit the mutual distinction or separation of the contributions to the measured electric voltage U, firstly due to the electrical connection of the energy storage cell to the central load, and secondly due to the electrical connection of the energy storage cell with the cell-specific load, the measured electric voltage U is filtered, particularly by the decomposition of Fourier coefficients F at the first excitation frequency f.sub.1 and the second excitation frequency f.sub.2. On the basis of the Fourier coefficient F of the voltage U at the second excitation frequency f.sub.2 and the previously known electric current I.sub.SCM, the second impedance Z.sub.SCM can be determined by the evaluation device. On the basis of the Fourier coefficient F of the voltage U at the first excitation frequency f.sub.1, the impedance Z.sub.ext,SCM corresponding to the electric voltage U associated with excitation at the first excitation frequency f.sub.1 can be determined by the evaluation device, on the basis of which, in a further process step S5a, in consideration of the electric current I determined or the Fourier coefficient F thereof, at the first excitation frequency f.sub.1, the first impedance Z.sub.ext can be determined by the central energy store control device. The first impedance Z.sub.ext and the second impedance Z.sub.SCM are compared with one another, for example in order to validate the measured cell-specific impedance Z.sub.SCM.

(32) Whilst at least one exemplary form of embodiment has been described heretofore, it should be observed that a large number of variations thereof exist. It should also be observed that the exemplary forms of embodiment described only represent non-limiting examples, and are not intended to restrict the scope, the applicability or the configuration of the devices and methods described herein. Instead, the preceding description is intended to provide a person skilled in the art with instruction in the implementation of at least one exemplary form of embodiment, wherein it is understood that different variations in the mode of operation and the arrangement of elements described in an exemplary form of embodiment can be undertaken, without departing from the subject matter which is respectively established in the attached claims, or from any legal equivalents thereof.

LIST OF REFERENCE SYMBOLS

(33) 1 Diagnostic method

(34) S1-S12 Process steps

(35) S1a-S5a Process steps

(36) 10 Energy storage cell

(37) 11 Evaluation device

(38) 12 Voltage measuring assembly

(39) 13 Electrode assembly

(40) 14 Cell-specific load

(41) 15 Cell-specific switching assembly

(42) 20 Control apparatus

(43) 21 Central energy store control device

(44) 22 Central power contactor

(45) 23 Current measuring assembly

(46) 30 Motor control device/inverter

(47) 40 Electrical machine

(48) 50 DC voltage converter

(49) 60 On-board network

(50) 70 Data link

(51) 80 Central load

(52) 100 Diagnostic system

(53) U Electric voltage

(54) I Electric current

(55) I.sub.SCM Previously known electric current

(56) F Fourier coefficient

(57) Z.sub.ext,SCM Impedance corresponding to the measured voltage

(58) Z.sub.ext First impedance

(59) Z.sub.SCM Second impedance

(60) f.sub.1 First excitation frequency

(61) f.sub.2 Second excitation frequency