METHOD FOR CONTROLLING A CHARGING CURRENT LIMITING VALUE FOR A BATTERY MANAGEMENT SYSTEM, BATTERY MANAGEMENT SYSTEM

Abstract

A method for controlling a charging current limiting value for a battery management system. In one example, the method includes determining, for a measured temperature and a prescribed state of charge, reference currents for various time intervals; calculating a corresponding reference time constant for each reference current by using a model for the calculation of a mean value of a charging current based on a continuous current; constituting a diagram for the relationship between the reference time constant and the reference current; determining a predictive time constant by the comparison of a measured value of a charging current with the reference currents; calculating a predictive limiting mean value of the charging current; and calculating a first predictive limiting value i.sub.predS for a short predictive time t.sub.predS, a second predictive limiting value i.sub.predL for a long predictive time t.sub.predL, and a third predictive limiting value i.sub.predP for a continuous predictive time.

Claims

1. A method for controlling a charging current limiting value for a battery management system, comprising the following steps: Determination, for a measured temperature T.sub.sens and a prescribed state of charge SOC, of reference currents i.sub.ref for various time intervals t.sub.ref; Calculation of a corresponding reference time constant τ.sub.ref for each reference current i.sub.ref by the application of a model for the calculation of a mean value i.sub.avrg of a charging current i.sub.req with reference to a continuous current i.sub.cont, which corresponds to the minimum current permissible without lithium plating; Constitution of a diagram for the relationship between the reference time constant τ.sub.ref and the reference current i.sub.ref, with reference to the calculated reference time constants τ.sub.ref and the reference currents i.sub.ref determined for each specific temperature T and each specific state of charge SOC; Determination of a predictive time constant τ.sub.pred by the comparison of a measured value i.sub.sens of a charging current i.sub.req with the reference currents i.sub.ref; and Calculation of a predictive limiting mean value i.sub.pred of the charging current i.sub.req, on the basis of the continuous current i.sub.cont, a predictive time t.sub.pred and the predictive time constant τ.sub.pred.

2. The method according to claim 1, wherein the model for the calculation of a mean value i.sub.avrg of the charging current i.sub.req is configured in the form of a PT1-element.

3. The method according to claim 2, wherein an additional point [i.sub.min; τ.sub.relax] is inserted in the diagram for the relationship between the reference time constant τ.sub.ref and the reference current i.sub.ref.

4. The method according to claim 1, wherein the calculation of the predictive time constant τ.sub.pred corresponding to the measured value i.sub.sens of the charging current i.sub.req is executed by linear interpolation.

5. The method according to claim 1, wherein, a first predictive limiting value i.sub.predS for a short predictive time t.sub.predS, a second predictive limiting value i.sub.predL for a long predictive time t.sub.predL, and a third predictive limiting value i.sub.preP for a continuous predictive time t.sub.predP are calculated.

6. The method according to claim 5, wherein a constant k=et.sub.pred/τ is defined in the calculation of the first predictive limiting value i.sub.predS.

7. A battery management system configured to control a charging current limiting value for a battery management system, by: determining, for a measured temperature T.sub.sens and a prescribed state of charge SOC, reference currents i.sub.ref for various time intervals t.sub.ref; calculating a corresponding reference time constant τ.sub.ref for each reference current i.sub.ref by the application of a model for the calculation of a mean value i.sub.avrg of a charging current i.sub.req with reference to a continuous current i.sub.cont, which corresponds to the minimum current permissible without lithium plating; constituting a diagram for the relationship between the reference time constant τ.sub.ref and the reference current i.sub.ref, with reference to the calculated reference time constants τ.sub.ref and the reference currents i.sub.ref determined for each specific temperature T and each specific state of charge SOC; determining a predictive time constant τ.sub.pred by the comparison of a measured value i.sub.sens of a charging current i.sub.req with the reference currents i.sub.ref; and calculating a predictive limiting mean value i.sub.pred of the charging current i.sub.req, on the basis of the continuous current i.sub.cont, a predictive time t.sub.pred and the predictive time constant τ.sub.pred.

8. A battery having one or more battery cells, which is configured to control a charging current limiting value for a battery management system, by: determining, for a measured temperature T.sub.sens and a prescribed state of charge SOC, reference currents i.sub.ref for various time intervals t.sub.ref; calculating a corresponding reference time constant τ.sub.ref for each reference current i.sub.ref by the application of a model for the calculation of a mean value i.sub.avrg of a charging current i.sub.req with reference to a continuous current i.sub.cont, which corresponds to the minimum current permissible without lithium plating; constituting a diagram for the relationship between the reference time constant τ.sub.ref and the reference current i.sub.ref, with reference to the calculated reference time constants τ.sub.ref and the reference currents i.sub.ref determined for each specific temperature T and each specific state of charge SOC; determining a predictive time constant T.sub.pred by the comparison of a measured value i.sub.sens of a charging current i.sub.req with the reference currents i.sub.ref; and calculating a predictive limiting mean value i.sub.pred of the charging current i.sub.req, on the basis of the continuous current i.sub.cont, a predictive time t.sub.pred and the predictive time constant τ.sub.pred.

9. A vehicle, which comprises a battery management system configured to control a charging current limiting value for a battery management system, by: determining, for a measured temperature T.sub.sens and a prescribed state of charge SOC, reference currents i.sub.ref for various time intervals t.sub.ref; calculating a corresponding reference time constant τ.sub.ref for each reference current i.sub.ref by the application of a model for the calculation of a mean value i.sub.avrg of a charging current i.sub.req with reference to a continuous current i.sub.cont, which corresponds to the minimum current permissible without lithium plating; constituting a diagram for the relationship between the reference time constant τ.sub.ref and the reference current i.sub.ref, with reference to the calculated reference time constants τ.sub.ref and the reference currents i.sub.ref determined for each specific temperature T and each specific state of charge SOC; determining a predictive time constant T.sub.pred by the comparison of a measured value i.sub.sens of a charging current i.sub.req with the reference currents i.sub.ref; and calculating a predictive limiting mean value i.sub.pred of the charging current i.sub.req, on the basis of the continuous current i.sub.cont, a predictive time t.sub.pred and the predictive time constant τ.sub.pred.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Embodiments of the invention are described in greater detail with reference to the drawings and the following description.

[0056] In the drawings:

[0057] FIG. 1 shows a schematic representation of the anticipated behavior of a charging current limiting value,

[0058] FIG. 2 shows a schematic representation of a diagram for determining a predictive time constant τ.sub.pred,

[0059] FIG. 3.1 shows a schematic representation of a temporal characteristic of a limiting mean value i.sub.pred,

[0060] FIG. 3.2 shows a schematic representation of a temporal characteristic of a mean value i.sub.avrg of the charging current i.sub.req according to FIG. 3.1,

[0061] FIG. 3.3 shows a schematic representation of a temporal characteristic of the predictive time constant τ.sub.pred according to FIG. 3.1,

[0062] FIG. 4.1 shows a schematic representation of a temporal characteristic of a charging current i.sub.req,

[0063] FIG. 4.2 shows a schematic representation of a temporal characteristic of a measured voltage u.sub.sens of the battery cell according to FIG. 4.1,

[0064] FIG. 4.3 shows a schematic representation of a temperature characteristic of a charging current i.sub.req with limitation of the mean value i.sub.avrg thereof according to FIG. 4.1,

[0065] FIG. 5.1 shows a schematic representation of a temporal characteristic of a charging current i.sub.req, with limitation of the mean value i.sub.avrg thereof according to a first example,

[0066] FIG. 5.2 shows a schematic representation of a temporal characteristic of a predictive time constant i.sub.pred according to FIG. 5.1,

[0067] FIG. 5.3 shows a schematic representation of a temporal characteristic of a state of charge SOC and a temporal characteristic of a measured temperature T.sub.sens according to FIG. 5.1,

[0068] FIG. 6.1 shows a schematic representation of a temporal characteristic of a charging current i.sub.req, with limitation of the mean value i.sub.avrg thereof, according to a second example,

[0069] FIG. 6.2 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 6.1,

[0070] FIG. 6.3 shows a schematic representation of a temporal characteristic of a state of charge SOC and a temporal characteristic of a measured temperature T.sub.sens according to FIG. 6.1, and

[0071] FIG. 7 shows a sequence for the method according to the invention.

[0072] In the following description of embodiments of the invention, identical or similar elements are identified by the same reference symbols, wherein any repeated description of these elements in individual cases is omitted. The figures represent the subject matter of the invention in a schematic manner only.

DETAILED DESCRIPTION

[0073] FIG. 1 shows a schematic representation of the anticipated behavior of a charging current limiting value of a battery cell. It is anticipated that, by the employment of dynamic limiting values i.sub.D in a battery management system for the monitoring and control of the battery cell, the initial value of a charging current i.sub.req, in a first phase 12 of duration, for example, 30 s, is not reduced, and these dynamic limiting values i.sub.D are converged in a second phase 14 thereafter to constitute continuous limiting values i.sub.C. In a third phase 16, the cell current i.sub.req is then limited by the continuous limiting values i.sub.C.

[0074] FIG. 2 shows a schematic representation of a diagram for determining a predictive time constant τ.sub.pred. This diagram is clarified hereinafter with reference to a model for the calculation of a mean value i.sub.avrg of a charging current i.sub.req using a PT1-element.

[0075] As described above, a time constant τ is calculated for each specific reference current i.sub.ref, a specific time interval t.sub.ref and a specific temperature T and a specific state of charge SOC. In the present case, in FIG. 2, for a specific temperature T, a reference time constant τ.sub.ref30s for a reference current i.sub.ref30s of duration 30 s, a reference time constant τ.sub.ref10s for a reference current i.sub.ref10s of duration 10 s and a reference time constant τ.sub.ref2s for a reference current i.sub.ref2s of duration 2 s are calculated.

[0076] By means of these data, a diagram is plotted for the relationship between the time constant τ and the reference current i.sub.ref in FIG. 2.

[0077] The measured value i.sub.sens of the charging current i.sub.req is compared with the reference current i.sub.ref for a specific time interval t.sub.ref, in order to derive an appropriate predictive time constant τ.sub.pred.

[0078] If, for example, the measured value i.sub.sens of the charging current i.sub.req is equal to the reference current i.sub.ref2s, a predictive time constant i.sub.pred is calculated which is equal to the reference time constant τ.sub.ref2s which has been calculated for the reference current i.sub.ref2s. The reduction of the charging current i.sub.req then commences after 2 s.

[0079] If, for example, the measured value i.sub.sens of the charging current i.sub.req is greater than the reference current i.sub.ref10s, but is smaller than the reference current i.sub.ref2s, a predictive time constant τ.sub.pred is determined by linear interpolation between the reference time constant τ.sub.ref10s and the reference time constant τ.sub.ref2s.

[0080] Moreover, in the diagram according to FIG. 2, an additional point [i.sub.min; T.sub.relax] is inserted. This point is inserted, in order to define a relaxation time constant τ.sub.relax for the battery cell in a relaxed or quasi-relaxed state. Thus, i.sub.min represents a small current. By means of this definition, a small relaxation time constant τ.sub.relax can be selected in order to permit, for example, a high recuperation current. This new point can thus be dependent upon the temperature T and the state of charge SOC.

[0081] FIG. 3.1 shows a schematic representation of a temporal characteristic of a limiting mean value i.sub.pred. A measured value i.sub.sens of the charging current i.sub.req of 60 A is detected. A charging current i.sub.req of 60 A is only permissible for a time of 2 s, without causing lithium plating. A limiting mean value i.sub.pred is thus calculated by the method proposed according to the invention. Reduction of the charging current i.sub.req then commences after 2 s. The limiting mean value i.sub.pred ultimately converges to a continuous current i.sub.cont, which corresponds to the maximum permissible continuous charging current i.sub.req.

[0082] FIG. 3.2 shows a schematic representation of a temporal characteristic of a mean value i.sub.avrg of the charging current i.sub.req according to FIG. 3.1, whereas FIG. 3.3 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 3.1. From FIG. 3.3, it can be seen that the predictive time constant τ.sub.pred is adjusted according to the measured value i.sub.sens of the charging current i.sub.req.

[0083] FIG. 4.1 shows a schematic representation of a temporal characteristic of a charging current i.sub.req. The charging current i.sub.req is pulse-shaped, and comprises two current pulses with equal measured values i.sub.sens of 60 A. The duration of the respective current pulses is 2 s. At time t.sub.1, a first current pulse is transmitted, and the first current pulse ends at time t.sub.2. At time t.sub.3, a second current pulse is transmitted, and the second current pulse ends at time t.sub.4.

[0084] FIG. 4.2 shows a schematic representation of a temporal characteristic of a measured voltage u.sub.sens of the battery cell according to FIG. 4.1. The measured voltage u.sub.sens of the battery cell has a no-load voltage u.sub.OCV at first. Charging with the charging current i.sub.req increases the measured voltage u.sub.sens of the battery cell. The measured voltage u.sub.sens of the battery cell decreases only from the time t.sub.2. In an intermediate time period t.sub.relax between the first and the second current pulse, specifically between the time t.sub.2 and the time t.sub.3, the measured voltage u.sub.sens decreases at a rate of, for example, 1 mV/min to the no-load voltage u.sub.OCV. This intermediate time period t.sub.relax is also described as the relaxation time.

[0085] FIG. 4.3 shows a schematic representation of a temporal characteristic of a charging current i.sub.req, with the limitation of the mean value i.sub.avrg thereof. The calculated limiting mean value i.sub.pred also rises during the intermediate time period t.sub.relax or the relaxation time, in order to allow the second current pulse. A cell must be stress-relieved or relaxed, before a further current pulse can be delivered at the maximum permissible capacity. In a resting cell, the measured voltage corresponds to the no-load voltage u.sub.OCV. For this reason, it is important that a sufficiently long relaxation time should be incorporated, in order to permit the second current pulse. This relaxation time corresponds to the time required for the measured voltage to achieve the no-load voltage of the cell. It will then be possible to set the maximum power, with no risk of lithium plating. This parameter can vary, according to the temperature T, the state of charge SOC and the current strength of the previously employed pulse.

[0086] FIG. 5.1 shows a schematic representation of a temporal characteristic of a charging current i.sub.req, with limitation of the mean value i.sub.avrg thereof, according to a first example, whereas FIG. 5.2 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 5.1, and FIG. 5.3 shows a schematic representation of a temporal characteristic of a state of charge SOC and a temporal characteristic of a measured temperature T.sub.sens according to FIG. 5.1.

[0087] Temporal characteristics of a relaxed battery cell are represented having an initial state of charge SOC of 85%. An initial temperature T of the battery cell is −10° C. The battery cell is thus charged with a charging current i.sub.req of 175 A for a time of 30 s. The state of charge SOC and the measured temperature T.sub.sens remain unchanged.

[0088] From FIG. 5.1, it can be seen that, at time point t=10 s, a first current pulse, which represents the charging current i.sub.req, having a measured value i.sub.sens of 175 A, is transmitted to the battery cell. The duration of the first current pulse is 30 s. From the data sheet for the battery cell 34, it can be determined that a current pulse of 175 A at a temperature T of −10° C. and a state of charge SOC of 85% is only permissible for 10 s. A predictive time constant T.sub.pred and a limiting mean value i.sub.pred, which converge to a continuous current i.sub.cont, are calculated. From FIG. 5.1, it can further be seen that, at time point t=20 s, i.e. after 10 s following the transmission of the first current pulse, the reduction of the first current pulse commences. The first current pulse is reduced to the continuous current i.sub.cont. Only at the end of the first current pulse does the limiting mean value i.sub.pred begin to rise again, in order to permit a further current pulse. At time point t=100 s, a second current pulse, which is equal to the first current pulse, is transmitted to the battery cell. Given the loaded state of the battery cell, reduction of the second current pulse commences earlier.

[0089] FIG. 6.1 shows a schematic representation of a temporal characteristic of a charging current i.sub.req, with limitation of the mean value i.sub.avrg thereof, according to a second example, whereas FIG. 6.2 shows a schematic representation of a temporal characteristic of a predictive time constant i.sub.pred according to FIG. 6.1, and FIG. 6.3 shows a schematic representation of a temporal characteristic of a state of charge SOC and a temporal characteristic of a measured temperature T.sub.sens according to FIG. 6.1.

[0090] The temporal characteristics are represented for a relaxed battery cell having an initial state of charge SOC of 85%. An initial temperature T of the battery cell is −10° C. The battery cell is charged with a charging current i.sub.req of 175 A for a time of 30 s. The state of charge SOC remains unchanged, whereas the measured temperature T.sub.sens rises during the duration of the current pulse.

[0091] From FIG. 6.1, it can be seen that, at time point t=10 s, a current pulse, which represents the charging current i.sub.req, having a measured value i.sub.sens of 175 A, is transmitted to the battery cell. The duration of the current pulse is 30 s. From the data sheet for the battery cell, it can be determined that a current pulse of 175 A at a temperature T of −10° C. and a state of charge SOC of 85% is only permissible for 10 s. A predictive time constant T.sub.pred and a limiting mean value i.sub.pred, which converges to a continuous current i.sub.cont, are calculated. As the measured temperature T.sub.sens of the battery cell varies over the duration of the current pulse, the predictive time constant i.sub.pred is calculated dynamically. From FIG. 6.1, it can further be seen that the reduction of the current pulse commences somewhat later. The current pulse reduces to the continuous current i.sub.cont. The continuous current i.sub.cont also adjusts to the temperature T.

[0092] FIG. 7 shows a sequence for the method according to the invention. In a step S1, for a measured temperature T.sub.sens and a prescribed state of charge SOC, reference currents i.sub.ref are determined for various time intervals t.sub.ref. For example, for a measured temperature T.sub.sens of 25° C. and a prescribed state of charge SOC, reference currents i.sub.ref2s, i.sub.ref10s, i.sub.ref30s are determined for the corresponding time intervals t.sub.ref of 2 s, 10 s and 30 s. If, for example, the temperatures T defined in the cell data sheet are from 20° C. and 30° C., these reference currents i.sub.ref can be interpolated, if this is permitted by the cell data sheet.

[0093] In a step S2, for each reference current i.sub.ref, a corresponding reference time constant τ.sub.ref is calculated by the application of a model for the calculation of a mean value i.sub.avrg of a charging current i.sub.req with reference to a continuous current i.sub.cont, which corresponds to the minimum current permissible without lithium plating. For example, if it proceeds from the cell data sheet that a current of 150 A is only permitted to last for 2 s, this current must then be permitted for 2 s or less. To this end, the reference time constant τ.sub.ref is adjusted such that the limiting value for current occurs at 2 s or earlier. For example, for the respective reference currents i.sub.ref2s, i.sub.ref10s and i.sub.ref30s, a corresponding reference time constant τ.sub.ref2s, τ.sub.ref10s and τ.sub.ref30s is calculated. The model is preferably configured in the form of a PT1-element.

[0094] In a step S3, with reference to the calculated reference time constants τ.sub.ref and the reference currents i.sub.ref determined, a diagram is constituted for the relationship between the reference time constant τ.sub.ref and the reference current i.sub.ref for each specified temperature T and each specified state of charge SOC.

[0095] In a step S4, a predictive time constant T.sub.pred is determined by the comparison of a measured value i.sub.sens of a charging current i.sub.req with the reference currents i.sub.ref. If the measured value i.sub.sens of the charging current i.sub.req is equal to a reference current i.sub.ref, the predictive time constant T.sub.pred is equal to the reference time constant τ.sub.ref which corresponds to this reference current i.sub.ref. Otherwise, the predictive time constant T.sub.pred is determined by interpolation.

[0096] In a step S5, a predictive limiting mean value i.sub.pred of the charging current i.sub.req is calculated on the basis of the continuous current i.sub.cont, a predictive time t.sub.pred and the predictive time constant τ.sub.pred. The predictive time can be customer-specific.

[0097] In a step S6, on the basis of the limiting mean value i.sub.pred, a first predictive limiting value i.sub.predS for a short predictive time t.sub.predS, a second predictive limiting value i.sub.predL for a long predictive time t.sub.predL and a third predictive limiting value i.sub.predP for a continuous predictive time t.sub.predp are calculated. For example, a time of less than 2 s can be defined as a short predictive time t.sub.predS. For example, a long predictive time t.sub.predL can be equal to 2 s, whereas a continuous predictive time t.sub.predP can be equal to 10 s.

[0098] The invention is not limited to the exemplary embodiments described herein and the aspects thereof indicated. Instead, within the field indicated by the claims, a plurality of variations are possible, which lie within the practice of a person skilled in the art.