Method and Device for Estimating the Usable Charge Capacity of an Electrical Energy Store

Abstract

A method for estimating the usable charge capacity of an electrical energy store includes determining a nominal initial charge capacity and a maximum initial estimation error of a new or slightly degraded energy store; determining one or more nominal charge capacities and one or more maximum estimation errors for the degraded energy store; interpolating a graph for the nominal charge capacity and for the maximum lower and upper estimation errors between the interpolation points of the nominal charge capacity and the interpolation points of the maximum estimation errors; and estimating a nominal charge state, a current usable charge capacity with a lower estimation reserve, and a current usable charge capacity with an upper estimation reserve for a current degradation state of the electrical energy store.

Claims

1.-8. (canceled)

9. A method for estimating a usable charge capacity of an electrical energy store, the method comprising: determining a nominal initial charge capacity and a maximum initial estimation error of a new or degraded energy store; determining one or more nominal charge capacities and one or more maximum estimation errors for the degraded energy store; interpolating a characteristic of a nominal charge capacity and of maximum lower and upper estimation errors between interpolation points of the nominal initial charge capacity and the one or more nominal charge capacities, and interpolation points of the maximum initial estimation error and the one or more maximum estimation errors; and estimating a nominal state-of-charge, a current usable charge capacity with a lower estimation reserve, and a current usable charge capacity with an upper estimation reserve for a current degradation state of the electrical energy store.

10. The method according to claim 9, wherein interpolation for two of the interpolation points is executed in a linear manner and, for more than two of the interpolation points, in a sectionally linear manner.

11. The method according to claim 9, wherein interpolation for two of the interpolation points is executed in a linear manner and, for more than two of the interpolation points, by way of a regression curve defined by a least squares method.

12. The method according to claim 9, wherein interpolation for two of the interpolation points is executed by way of a typical model curve for the electrical energy store and, for more than two of the interpolation points, by way of a connecting curve or a regression curve, which connects the interpolation points or which minimizes a sum of deviation squares of the interpolation points.

13. The method according to claim 9, wherein interpolation of the usable charge capacity and the maximum estimation error is executed by way of a knowledge-based system or a neural network, which is trainable by way of known degradation states, known charge capacities and thus associated estimation errors of the electrical energy store.

14. The method according to claim 9, wherein individual interpolation points or an overall characteristic of the nominal charge capacity and the maximum lower and upper estimation errors for the electrical energy store are plotted and/or preset, and/or are adjusted and/or expanded in a course of degradation.

15. A device comprising: a processer for executing the method according to claim 9; circuits for monitoring of energy storage cells; a battery management system; and an indicator system for indicating the current usable charge capacity, the current degradation state, and/or a residual service life of the electrical energy store.

16. A vehicle comprising the device according to claim 15.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows an exemplary embodiment of the method, with reference to a diagram SOC(t).

[0026] FIG. 2 shows an exemplary embodiment of the method, with reference to a flow diagram.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 shows a diagram 100 for the illustration of an exemplary embodiment of the method according to the invention for estimating the usable charge capacity of an electrical energy store. During the service life of an electrical energy store, the nominal initial charge capacity 300, represented by the nominal maximum achievable state-of-charge SOC(t) of a new or slightly degraded energy store plotted against the operating time t, declines and, further to a degree of degradation, achieves an impaired and degraded nominal charge capacity 350. In the exemplary embodiment represented here, the characteristic of the nominal maximum achievable state-of-charge SOC(t) 150 is linear. In other exemplary embodiments, a different characteristic may be present. In particular, exemplary embodiments having a piecewise linear or non-linear characteristic are known. Additionally, it is also possible for only individual interpolation points to be known, for example by way of measurements, which are interpolated by way of linear, piecewise linear or non-linear characteristic curves.

[0028] However, the aging and degradation of an electrical energy store may not only result in a decline in the nominal maximum achievable state-of-charge SOC(t) 150, but also in an impaired estimability of the nominal charge capacity and the nominal maximum achievable state-of-charge. The actual decline in the nominal maximum achievable state-of-charge SOC(t) 150 in the course of the service life of the energy store is thus compounded by an increase in the inaccuracy of estimation which, in the case of a new or slightly degraded energy store, by way of approximation, commences with a relatively low maximum initial estimation error 200, 400 but which, due to aging and degradation, increases with the operating time t and, in the case of an older and more severely degraded energy store, by way of approximation, is expressed by a greater maximum estimation error 250, 450. With a specific probability, the estimation error lies between a maximum lower estimation error 130 and a maximum upper estimation error 230, in the shaded region of FIG. 1.

[0029] In consequence, the actual maximum achievable state-of- charge SOC(t) can lie between a lower estimation limit 130 and an upper estimation limit 230. In the present exemplary embodiment, the estimation limits 130, 230 are also linear but, in the same way as the nominal maximum achievable state of charge SOC(t) 150, can be represented by piecewise linear or non-linear characteristics, or by individual interpolation points, between which interpolation is required.

[0030] Inaccuracy of estimation requires a dynamic estimation reserve 130, 230, which increases in relation to the nominal maximum achievable state-of-charge SOC(t) 150 over the operating time t, and the consideration of which is essential to the energy management of the vehicle, if the actual maximum achievable state-of-charge SOC(t) of the electrical energy store is not to be over-estimated and the vehicle thus rendered unroadworthy, while the energy management system continues to indicate a residual range. Accordingly, in each degradation state of the energy store, the current usable charge capacity must be supplemented by a lower estimation reserve 130 and an upper estimation reserve 230.

[0031] The lower estimation reserve 110 for a new or slightly degraded energy store would not be sufficient for an energy store which is further degraded, whereas the lower estimation reserve 120 for a more degraded energy store would be too great for a new or slightly degraded energy store. In consequence, a constant estimation reserve over the duration of service life should consistently be tailored to the maximum state-of-charge SOC.sub.old 450 of the older and correspondingly more degraded energy store which is still achievable. Correspondingly, an excessively low range estimation for a vehicle having a new or slightly degraded energy store should be accepted, and an excessively low maximum achievable state-of-charge SOC.sub.new,1 410 applied. However, an accurate range estimation is of considerable significance for a battery-powered vehicle, both with respect to roadworthiness and with respect to the exploitation of available range such that, in the case of a new or slightly degraded energy store, the estimation of the actual maximum achievable state-of-charge SOC.sub.new,2 420 should also be executed.

[0032] By way of a dynamic estimation reserve 130, 230, the range associated with a new or slightly degraded energy store increases from SOC.sub.new,1 410 to SOC.sub.new,2 420. Accordingly, in the course of driving operation and on the basis of experience, depending upon the technology of the energy store employed, improvements in range of between 2 and 10% can be achieved.

[0033] The estimation method 100 can be implemented in a control device, particularly in a battery control device, and executed in the vehicle. The additional complexity of computing required for this purpose, in the case of linear interpolation, is limited, although somewhat greater in the case of non-linear regression. The employment of a neural network for the execution of the estimation method is advantageous, by way of which slow variations in the estimation curves can be learned in the course of driving operation. As a result, subsequent adjustments can be incorporated in the estimation method by a self-learning process.

[0034] FIG. 2 shows a flow diagram for an exemplary embodiment of the method 500, having the process steps 501, 502, 503, 504.

LIST OF REFERENCE SYMBOLS

[0035] 100 Estimation method [0036] 110 Lower estimation reserve, maximum lower estimation error for a new energy store [0037] 120 Lower estimation reserve, maximum lower estimation error for a degraded energy store [0038] 130 Dynamic lower estimation reserve, dynamic lower estimation error [0039] 150 Nominal charge capacity SOC(t) [0040] 200 Maximum upper estimation error for a new energy store [0041] 210 Upper estimation reserve, maximum upper estimation error for a new energy store [0042] 220 Upper estimation reserve, maximum upper estimation error for a degraded energy store [0043] 230 Dynamic upper estimation reserve or dynamic upper estimation error [0044] 250 Maximum upper estimation error of a degraded energy store [0045] 300 Nominal charge capacity SOC(t) of a new energy store [0046] 350 Nominal charge capacity SOC(t) of a degraded energy store [0047] 400 Maximum lower estimation error of a new energy store [0048] 410 Estimation SOC.sub.new,1 for a new energy store, with an excessively large estimation reserve [0049] 420 Estimation SOC.sub.new,2 for a new energy store, with an appropriate estimation reserve [0050] 450 Maximum lower estimation error of a degraded energy store