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

Abstract

A method for controlling a cell current limiting value for a battery management system. In some examples, the method includes determining quadratic reference currents of a battery cell; calculating a corresponding reference time constant for each reference current using a model for the calculation of a RMS value of a cell current by reference to a continuous current; constituting a diagram for the relationship between the reference time constant and the quadratic reference current; determining a predictive time constant by the comparison of a quadratic measured value of a cell current with the quadratic reference currents; calculating a predictive RMS limiting value of the cell current; calculating a first predictive limiting value for a short predictive time, a second predictive limiting value for a long predictive time, and a third predictive limiting value for a continuous predictive time; and calculating additional RMS limiting value for the cell current.

Claims

1. A method for controlling a cell current limiting value for a battery management system, comprising the following steps: Determination of quadratic reference currents i.sub.ref.sup.2 of a battery cell (34), at a measured temperature T.sub.sens, for different 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 RMS value i.sub.RMS of a cell current i.sub.req by reference to a continuous current i.sub.cont, which corresponds to the minimum current in the charging or discharging device which causes no thermal damage; Constitution of a diagram for the relationship between the reference time constant τ.sub.ref and the quadratic reference current i.sub.ref.sup.2, by reference to the calculated reference time constants τ.sub.ref and the quadratic reference currents i.sub.ref.sup.2 determined for each specific temperature T; Determination of a predictive time constant τ.sub.pred by the comparison of a quadratic measured value i.sub.sens.sup.2 of a cell current i.sub.req with the quadratic reference currents i.sub.ref.sup.2; and Calculation of a predictive RMS limiting value i.sub.pred of the cell 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 RMS value i.sub.RMS of a cell current i.sub.req is configured in the form of a PT1-element.

3. 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 he cell current i.sub.req is executed by linear interpolation.

4. The method according to claim 1, wherein, on the basis of the predictive RMS limiting 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.

5. The method according to claim 1, wherein an additional RMS limiting value i.sub.limT for the cell current i.sub.req is calculated by reference to a maximum permissible temperature T.sub.max of the battery cell (34) and the measured temperature T.sub.sens of the battery cell (34).

6. The method according to claim 1, wherein a proportional-integral controller (32) is employed, having a proportionally-acting component and an integrally-acting component.

7. The method according to claim 6, wherein the proportional-integral controller (32) comprises an anti-windup structure and/or the integrally-acting component of the proportional-integral controller (32) is only activated in the event that the measured temperature T.sub.sens exceeds the maximum permissible temperature T.sub.max and/or if the measured temperature T.sub.sens exceeds a predefined temperature threshold value, and the RMS value i.sub.RMS of the cell current i.sub.req exceeds a predefined current threshold value.

8. A battery management system configured to control a cell current limiting value for a battery management system, by: determining quadratic reference currents i.sub.ref.sup.2 of a battery cell (34), at a measured temperature T.sub.sens, for different 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 RMS value i.sub.RMS of a cell current i.sub.req by reference to a continuous current i.sub.cont, which corresponds to the minimum current in the charging or discharging device which causes no thermal damage; constituting a diagram for the relationship between the reference time constant τ.sub.ref and the quadratic reference current i.sub.ref.sup.2, by reference to the calculated reference time constants τ.sub.ref and the quadratic reference currents i.sub.ref.sup.2 determined for each specific temperature T; determining a predictive time constant τ.sub.pred by the comparison of a quadratic measured value i.sub.sens.sup.2, of a cell current i.sub.req with the quadratic reference currents i.sub.ref.sup.2; and calculating a predictive RMS limiting value i.sub.pred of the cell 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 battery having one or more battery cells (34), where in the battery is configured to control a cell current limiting value for a battery management system, by: determining quadratic reference currents i.sub.ref.sup.2 of a battery cell (34), at a measured temperature T.sub.sens, for different 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 RMS value i.sub.RMS of a cell current i.sub.req by reference to a continuous current i.sub.cont, which corresponds to the minimum current in the charging or discharging device which causes no thermal damage; constituting a diagram for the relationship between the reference time constant τ.sub.ref and the quadratic reference current i.sub.ref.sup.2, by reference to the calculated reference time constants τ.sub.ref and the quadratic reference currents i.sub.ref.sup.2 determined for each specific temperature T; determining a predictive time constant τ.sub.pred by the comparison of a quadratic measured value i.sub.sens.sup.2, of a cell current i.sub.req with the quadratic reference currents i.sub.ref.sup.2; and calculating a predictive RMS limiting value i.sub.pred of the cell 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.

10. A vehicle comprising a battery management system configured to determine quadratic reference currents i.sub.ref.sup.2 of a battery cell (34), at a measured temperature T.sub.sens, for different time intervals t.sub.ref; calculate 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 RMS value i.sub.RMS of a cell current i.sub.req by reference to a continuous current i.sub.cont, which corresponds to the minimum current in the charging or discharging device which causes no thermal damage; constitute a diagram for the relationship between the reference time constant τ.sub.ref and the quadratic reference current i.sub.ref.sup.2, by reference to the calculated reference time constants τ.sub.ref and the quadratic reference currents i.sub.ref.sup.2 determined for each specific temperature T; determine a predictive time constant τ.sub.pred by the comparison of a quadratic measured value i.sub.sens.sup.2, of a cell current i.sub.req with the quadratic reference currents i.sub.ref.sup.2; and calculate a predictive RMS limiting value i.sub.pred of the cell 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

[0071] Embodiments of the invention are described in greater detail with reference to the drawings and the following description.

[0072] In the drawings:

[0073] FIG. 1 shows a schematic representation of the anticipated behavior of a cell current limiting value,

[0074] FIG. 2 shows a schematic representation of a diagram for determining a predictive time constant τ.sub.pred,

[0075] FIG. 3 shows a block circuit diagram of a control loop,

[0076] FIG. 4.1 shows a schematic representation of a temporal characteristic of a predictive RMS limiting value i.sub.pred,

[0077] FIG. 4.2 shows a schematic representation of a temporal characteristic of a RMS value i.sub.RMS of the cell current i.sub.req according to FIG. 4.1,

[0078] FIG. 4.3 shows a schematic representation of a temperature characteristic of a measured temperature T.sub.sens of the battery cell according to FIG. 4.1,

[0079] FIG. 4.4 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 4.1,

[0080] FIG. 5.1 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with no limitation of the RMS value i.sub.RMS thereof,

[0081] FIG. 5.2 shows a schematic representation of a temporal characteristic of a measured temperature T.sub.sens of the battery cell according to FIG. 5.1,

[0082] FIG. 5.3 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with limitation of the RMS value i.sub.RMS thereof,

[0083] FIG. 5.4 shows a schematic representation of a temporal characteristic of a measured temperature T.sub.sens of the battery cell according to FIG. 5.3,

[0084] FIG. 6.1 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with limitation of the RMS value i.sub.RMS thereof, according to a first example,

[0085] FIG. 6.2 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 6.1,

[0086] 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,

[0087] FIG. 7.1 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with limitation of the RMS value i.sub.RMS thereof, according to a second example,

[0088] FIG. 7.2 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 7.1,

[0089] FIG. 7.3 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. 7.1, and

[0090] FIG. 8 shows a sequence for the method according to the invention.

[0091] 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

[0092] FIG. 1 shows a schematic representation of the anticipated behavior of a cell current limiting value of a battery cell 34 (see FIG. 3). 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 34, the initial value of a cell current i.sub.req, in a first phase 12 of duration, for example, 30s, is not reduced, and these limiting values 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.

[0093] FIG. 2 shows a schematic representation of a diagram for the calculation of a predictive time constant τ.sub.pred. This diagram is clarified hereinafter with reference to a model for the calculation of a RMS value i.sub.RMS of a cell current i.sub.req using a PT1-element.

[0094] 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. 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 30s, a reference time constant τ.sub.ref10s for a reference current i.sub.ref10s of duration 10s and a reference time constant τ.sub.ref2s for a reference current i.sub.ref2s of duration 2s are calculated.

[0095] By means of these data, a diagram is plotted for the relationship between the time constant τ and the quadratic reference current i.sub.ref.sup.2 in FIG. 2.

[0096] The quadratic measured value i.sub.sens the cell current i.sub.req is compared with the quadratic reference current i.sub.ref.sup.2 for a specific time interval t.sub.ref, in order to derive an appropriate predictive time constant τ.sub.pred.

[0097] If, for example, the quadratic measured value i.sub.sens of the cell current i.sub.req is equal to the quadratic reference current i.sub.ref2s.sup.2, a predictive time constant τ.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 cell current i.sub.req then commences after 2s.

[0098] If, for example, the quadratic measured value i.sub.sens of the cell current i.sub.req is greater than the quadratic reference current i.sub.ref10s.sup.2, but is smaller than the quadratic reference current i.sub.ref2s.sup.2, 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.

[0099] Moreover, in the diagram according to FIG. 2, an additional point [i.sub.min.sup.2; τ.sub.relax] is inserted. This point is inserted, in order to define a relaxation time constant τ.sub.relax for the battery cell 34 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.

[0100] FIG. 3 shows a block circuit diagram of a control loop 30 for the control of the battery cell 34. The control loop 30 comprises a proportional-integral controller 32 for controlling the battery cell 34. The temperature T of the battery cell 34, designated as the measured temperature T.sub.sens is measured, and is compared with a maximum permissible temperature T.sub.max of the battery cell 34. The difference ε between the measured temperature T.sub.sens and the maximum permissible temperature T.sub.max is transmitted to the proportional-integral controller 32 as an input value. The proportional-integral controller 32, by reference to the difference ε, calculates an additional RMS limiting value i.sub.limT of the cell current i.sub.req as an output value.

[0101] For the purposes of control, the present temperature T is firstly measured. Thereafter, the additional RMS limiting value i.sub.limT is calculated by the proportional-integral controller 32. The continuous current i.sub.cont is then reduced, if the additional RMS limiting value i.sub.limT is smaller than the continuous current i.sub.cont. The predictive RMS limiting value i.sub.pred adjusted thereafter. These is control steps are repeated, such that the predictive RMS limiting value i.sub.pred adjusted dynamically.

[0102] FIG. 4.1 shows a schematic representation of a temporal characteristic of a predictive RMS limiting value i.sub.pred. A measured values i.sub.sens of a cell current i.sub.req of 400A is detected. A cell current i.sub.req of 400A is only permissible for a time of 10s, without causing thermal damage. A is predictive RMS limiting value i.sub.pred thus calculated by the method proposed according to the invention. Reduction of the cell current i.sub.req then commences after 10s. The predictive RMS limiting value i.sub.pred ultimately converges to a continuous current i.sub.cont, which corresponds to the maximum permissible continuous cell current i.sub.req.

[0103] FIG. 4.2 shows a schematic representation of a temporal characteristic of a RMS value i.sub.RMS of the cell current i.sub.req according to FIG. 4.1, whereas FIG. 4.3 shows a schematic representation of a temporal characteristic of a measured temperature T.sub.sens of the battery cell 34 according to FIG. 4.1, and FIG. 4.4 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 4.1. From FIG. 4.4, it can be seen that the predictive time constant τ.sub.pred is adjusted according to the measured value i.sub.sens of the cell current i.sub.req and the measured temperature T.sub.sens.

[0104] FIG. 5.1 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with no limitation of the RMS value i.sub.RMS thereof. The cell current i.sub.req is pulse-shaped, and comprises two current pulses with equal measured values i.sub.sens of 400A. The duration of the respective current pulses is 10s. 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. FIG. 5.2 shows a schematic representation of a temporal characteristic of a measured temperature T.sub.sens of the battery cell 34 according to FIG. 5.1. The measured temperature T.sub.sens rises during the duration of the first current pulse, and falls during an intermediate time period, which is also described as the relaxation time t.sub.relax, between the two current pulses, i.e. between the time points t.sub.2 and t.sub.3. The measured temperature T.sub.sens rises again during the duration of the second current pulse and, at a time point t.sub.5, exceeds the maximum permissible temperature T.sub.max.

[0105] FIG. 5.3 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with the limitation of the RMS value i.sub.RMS thereof, whereas FIG. 5.4 shows a schematic representation of a temporal characteristic of a measured temperature T.sub.sens of the battery cell 34 according to FIG. 5.3. The predictive RMS limiting value i.sub.pred is calculated. The two current pulses represented in FIG. 5.3 are equal to the current pulses in FIG. 5.1. From FIG. 5.3, it can be seen that the cell current i.sub.req, with effect from time point t.sub.5, is limited by the first predictive RMS limiting value i.sub.pred. Accordingly, the measured temperature T.sub.sens does not exceed the maximum permissible temperature T.sub.max. The relaxation effect of the battery cell 34 is also exploited. From FIG. 5.3 it can further be seen that, in the relaxation time t.sub.relax, the predictive RMS limiting value i.sub.pred rises again, thus permitting a larger 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 uocv of the cell. For this reason, it is important that a sufficiently long relaxation time t.sub.relax should be incorporated, in order to permit the second current pulse. This relaxation time t.sub.relax 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 thermal damage. This parameter can vary, according to the temperature T and the current strength of the previously employed pulse.

[0106] FIG. 6.1 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with limitation of the RMS value i.sub.RMS thereof, according to a first example, whereas FIG. 6.2 shows a schematic representation of a temporal characteristic of a predictive time constant τ.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.

[0107] Temporal characteristics of a relaxed battery cell 34 are represented having an initial state of charge SOC of 85%. An initial temperature T of the battery cell 34 is −10° C. The battery cell 34 is thus charged with a cell current i.sub.req of 175A for a time of 30s. The state of charge SOC and the measured temperature T.sub.sens remain unchanged.

[0108] From FIG. 6.1, it can be seen that, at time point t=10 s, a first current pulse, which represents the cell current i.sub.req, having a measured value i.sub.sens of 175A, is transmitted to the battery cell 34. The duration of the first current pulse is 30s. From the data sheet for the battery cell 34, it can be determined that a current pulse of 175A at a temperature T of −10° C. and a state of charge SOC of 85% is only permissible for 10s. A predictive time constant τ.sub.pred and a predictive RMS limiting value i.sub.pred, which converge to a continuous current i.sub.cont, are calculated. From FIG. 6.1, it can further be seen that, at time point t=20 s, i.e. after 10s 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 predictive RMS limiting value i.sub.pred begin to rise again, in order to permit a further current pulse. At time point t=100s, a second current pulse, which is equal to the first current pulse, is transmitted to the battery cell 34. Given the loaded state of the battery cell 34, reduction of the second current pulse commences earlier.

[0109] FIG. 7.1 shows a schematic representation of a temporal characteristic of a cell current i.sub.req, with limitation of the RMS value i.sub.RMS thereof, according to a second example, whereas FIG. 7.2 shows a schematic representation of a temporal characteristic of a predictive time constant τ.sub.pred according to FIG. 7.1, and FIG. 7.3 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. 7.1.

[0110] Temporal characteristics are represented for a relaxed battery cell 34 having an initial state of charge SOC of 85%. An initial temperature T of the battery cell 34 is −10° C. The battery cell 34 is charged with a cell current i.sub.req of 175A for a time of 30s. The state of charge SOC remains unchanged, whereas the measured temperature T.sub.sens rises during the duration of the current pulse.

[0111] From FIG. 7.1, it can be seen that, at time point t=10s, a current pulse, which represents the cell current i.sub.req, having a measured value i.sub.sens of 175A, is transmitted to the battery cell 34. The duration of the current pulse is 30s. From the data sheet for the battery cell 34, it can be determined that a current pulse of 175A at a temperature T of −10° C. and a state of charge of 85% is only permissible for 10s. A predictive time constant τ.sub.pred and a predictive RMS limiting 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 34 varies over the duration of the current pulse, the predictive time constant τ.sub.pred is calculated dynamically. From FIG. 7.1, 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.

[0112] FIG. 8 shows a sequence for the method according to the invention. In a step S1, for a measured temperature T.sub.sens, quadratic reference currents i.sub.ref.sup.2 of a battery cell 34 are determined for different time intervals t.sub.ref. For example, for a measured temperature T.sub.sens of 25° C., quadratic reference currents i.sub.ref2s.sup.2, i.sub.ref10s.sup.2, i.sub.ref30s.sup.2 are determined for the corresponding time intervals t.sub.ref of 2s, 10s and 30s. If, for example, the temperatures T defined in the cell data sheet are 20° C. and 30° C., these quadratic reference currents i.sub.ref2s.sup.2, i.sub.ref10s.sup.2, i.sub.ref30s.sup.2 can be interpolated, if this is permitted by the cell data sheet.

[0113] 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 RMS value i.sub.RMS of a cell current i.sub.req by reference to a continuous current i.sub.cont, which corresponds to the minimum current in the charging or discharging device which causes no thermal damage. For example, if it proceeds from the cell data sheet that a current of 150 A is only permitted to last for 2s, this current must then be permitted for 2s or less. To this end, the reference time constant τ.sub.ref is adjusted such that the limiting value for current is achieved at 2s 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.

[0114] In a step S3, by reference to the calculated reference time constants τ.sub.ref and the quadratic reference currents i.sub.ref.sup.2 thus determined, a diagram is then constituted for the relationship between the reference time constant τ.sub.ref and the quadratic reference current i.sub.ref.sup.2, for each specified temperature T.

[0115] In a step S4, a predictive time constant τ.sub.pred is determined by the comparison of a quadratic measured value i.sub.sens.sup.2 of a cell current i.sub.req with the quadratic reference currents i.sub.ref.sup.2. If the quadratic measured value i.sub.sens.sup.2 of the cell current i.sub.req is equal to a quadratic reference current i.sub.ref.sup.2, the predictive time constant τ.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 τ.sub.pred is determined by interpolation.

[0116] In a step S5, a predictive RMS limiting value i.sub.pred of the cell 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 t.sub.pred can be customer-specific.

[0117] In a step S6, on the basis of the predictive RMS limiting 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 2s can be defined as a short predictive time t.sub.predS. For example, a long predictive time t.sub.predL can be equal to 2s, whereas a continuous predictive time t.sub.predP can be equal to 10s.

[0118] In a step S7, an additional RMS limiting value i.sub.limT for the cell current i.sub.req is calculated by reference to a maximum permissible temperature T.sub.max of the battery cell 34 and the measured temperature T.sub.sens of the battery cell 34. This additional RMS limiting value i.sub.limT is employed for thermal derating. The continuous current i.sub.cont is limited by the additional RMS limiting value i.sub.limT, and is reduced in the event of thermal derating.

[0119] 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.