CHARGING DEVICE AND METHOD FOR CHARGING AN ELECTRICAL ENERGY STORE

Abstract

A charging device (1) and a method for charging an electrical energy store (2), wherein the charging device (1) has an open-loop control unit (12) and a controller (9), and the charging device (1) is configured to charge the electrical energy store (2) to a defined state of charge within a predefined charging period and, in addition, to control a charging current and a secondary-reaction current of the electrical energy store (2).

Claims

1. A charger (1) for an electrical energy store (2), wherein the charger (1) has an open-loop control unit (12) and a closed-loop control unit (9), wherein the charger (1) is configured to charge the electrical energy store (2) to a defined state of charge within a preset charging time and, to set a charging current and a side reaction current of the electrical energy store (2).

2. The charger (1) as claimed in claim 1, wherein the charger (1) has an evaluation unit (5), which has at least one terminal for a sensor of the electrical energy store (2), wherein the evaluation unit (5) is configured to determine at least aging of the electrical energy store (2) by means of a simplified linear electrothermal aging model of the electrical energy store (2).

3. The charger (1) as claimed in claim 2, wherein the evaluation unit (5) is connected in signal-conducting fashion to the open-loop control unit (12) and/or to the closed-loop control unit.

4. The charger (1) as claimed in claim 1, wherein the open-loop control unit (12) is configured to subject a first charging current (I1) and a first side reaction current (J1) to open-loop control in such a way that the electrical energy store (2) is charged to the defined state of charge within the preset charging time.

5. The charger (1) as claimed in claim 1, wherein the open-loop control unit (12) has an optimization means (3) configured to optimize a charging profile by numerically determining a minimum of a loss function of a parameter (d) of the charging profile.

6. The charger (1) as claimed in claim 1, wherein the open-loop control unit (12) has a charge open-loop control means (11) configured to subject the first charging current (I1) to open-loop control according to an optimized charging profile.

7. The charger (1) as claimed in claim 1, wherein the closed-loop control unit (9) is configured to subject a third charging current (I3) to closed-loop control in such a way that a second side reaction current (J2) of the electrical energy store (2) is minimized.

8. The charger (1) as claimed in claim 1, wherein the charger (1) has a summation means (8), which is arranged between the open-loop control unit (12) and the closed-loop control unit (9), on one side, and an output terminal (13) of the charger (1), on the other side, in particular wherein the summation means (8) is configured to add the first charging current (I1) or a second charging current (12) from the open-loop control unit (12) and the third charging current (13) from the closed-loop control unit (9) and to generate a fourth charging current (14).

9. The charger (1) as claimed in claim 8, wherein the charger (1) has a low-pass filter (4), which is arranged between the open-loop control unit (12) and the summation means (8).

10. The charger (1) as claimed in claim 8, wherein the charger (1) has a comparison means (10), which is arranged between the open-loop control unit (12) and the ageing evaluation means (7), on one side, and the summation means (8), on the other side, wherein the comparison means (10) is configured to compare the first side reaction current (J1) and the second side reaction current (J2).

11. A method for charging an electrical energy store (2) by means of a charger (1) having an open-loop control unit (12) and a closed-loop control unit (9), wherein the charger (1) is configured to charge the electrical energy store (2) to a defined state of charge within a preset charging time and to set a charging current and a side reaction current of the electrical energy store (2), wherein the method comprises an open-loop control steps and a closed-loop control steps, which run simultaneously, wherein the electrical energy store (2) is charged to a defined state of charge within a preset charging time and a charging current and a side reaction current of the electrical energy store (2) are set.

12. The method (100) as claimed in claim 11, wherein a present state of charge and/or a present state of health and/or a second side reaction current (J2) are determined from sensor data of the electrical energy store (2) means of a simplified linear electrothermal aging model of the electrical energy store (2).

13. The method (100) as claimed in claim 11, wherein a charging profile, in particular an affine or polynomial charging profile, is optimized, in particular by numerically determining a minimum of a loss function of a parameter (d) of the charging profile, in particular by means of a gradient method, wherein a first charging current (I1) and a first side reaction current (J1) are subjected to open-loop control according to an optimized charging profile.

14. The method (100) as claimed in claim 13, wherein the first side reaction current (J1) is compared with the second side reaction current (J2), and a third charging current (I3) is generated, wherein the third charging current (I3) is equal to zero when the first side reaction current (J1) has the same value as the second side reaction current (J2) and/or wherein, when the first side reaction current (J1) and the second side reaction current (J2) have different values, the third charging current (I3) is determined in such a way that the ageing of the electrical energy store (2) is minimized, wherein the third charging current (I3) and the second charging current (I2) are added, and a fourth charging current (I4) is generated, wherein the electrical energy store (2) is charged with the fourth charging current (I4).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In the following section, the invention will be explained on the basis of exemplary embodiments from which further inventive features can result to which the invention is not restricted in terms of its scope, however. The exemplary embodiments are illustrated in the drawings, in which:

[0029] FIG. 1 shows a schematic illustration of a method according to the invention for charging an electrical energy store 2 by means of the charger 1 according to the invention,

[0030] FIG. 2 shows an affine charging profile for a current Ia as a function of the time t with a total charge Qc, a charging time tch and an initial current Iao,

[0031] FIG. 3 shows a polynomial charging profile for a current Ip as a function of the time t with a total charge Qc, a charging time tch and an initial current Ipo, and

[0032] FIG. 4 shows a global loss function f of a polynomial charging profile as a function of an optimization parameter d.

DETAILED DESCRIPTION

[0033] FIG. 1 illustrates the charger 1 according to the invention and the electrical energy store 2 schematically.

[0034] The charger 1 has: [0035] an open-loop control unit 12, having an optimization means 3 and a charge open-loop control means 11, [0036] a low-pass filter 4, [0037] an evaluation unit 5, which has a state-of-charge evaluation means 6 and an ageing evaluation means 7, [0038] a summation means 8, [0039] a closed-loop control means 9, and [0040] a comparison means 10.

[0041] The evaluation unit 5 is connected in signal-conducting fashion to the electrical energy store 2 and is designed to receive sensor signals from sensors, in particular from a temperature sensor and at least one cell voltage sensor, of the electrical energy store 2. The evaluation unit 5 is designed to evaluate the sensor signals, in particular a temperature T and at least one cell voltage Uc of the electrical energy store 2 and, from this, to determine state parameters of the electrical energy store 2 by means of a fourth charging current I4. For this purpose, the evaluation unit 5 has at least one state-of-charge evaluation means 6 and an ageing evaluation means 7.

[0042] The evaluation unit 7 is designed to determine state parameters of the electrical energy store 2 by means of the sensor signals. In this case, the evaluation unit 7 uses a simplified linear electrothermal aging model of the electrical energy store 2 which has been approximated by means of a Volterra series.

[0043] The state-of-charge evaluation means 6 is designed to determine a present state of charge of the electrical energy store 2. The state-of-charge evaluation means 6 is connected in signal-conducting fashion to the open-loop control unit 12. The state-of-charge evaluation means 6 is designed to send the present state of charge to the open-loop control unit 12.

[0044] The ageing evaluation means 7 is designed to determine a state of health of the electrical energy store 2 and a resultant second side reaction current J2. The ageing evaluation means 7 is connected in signal-conducting fashion to the comparison means 10. The ageing evaluation means 7 is designed to send the second side reaction current J2 to the comparison means 10.

[0045] A side reaction current is in this case a current which occurs owing to side reactions in a cell of the electrical energy store 2, such as, for example, dendrite growth or separation of the electrolyte on the anode, owing to the ageing of the cell during charging.

[0046] The open-loop control unit 12 is designed to subject a first charging current I1 for charging the electrical energy store 2 and a resultant first side reaction current J1 to open-loop control by means of the state of charge of the electrical energy store 2.

[0047] For this purpose, the open-loop control unit 12 has an optimization means 3 and a charge open-loop control means 11.

[0048] The optimization means 3 is designed to determine charging parameters of a charging profile starting from the present state of charge of the electrical energy store 2, an available charging time tch and a defined state of charge, which can be reached within the charging time tch, by means of a total charge Qc.

[0049] In a first exemplary embodiment, the charging profile is in the form of an affine charging profile Ia(t), as illustrated in FIG. 2. The affine charging profile is linear and has, as a single parameter, a gradient a which is calculated as follows:

[00001]$\begin{array}{cc}a=\frac{2\left(I_{a0}{t}_{ch}-Qc\right)}{t_{ch}^2}& \left(1\right)\end{array}$

[0050] In a second exemplary embodiment, the charging profile is in the form of a polynomial charging profile Ip(t), as illustrated in FIG. 3. By means of the boundary conditions, whereby the current is constant at the time t=0 and at the time t=tch, that is to say the time derivative of the current is equal to zero at these times, the total charge Qc is predefined and the initial current Ipo is positive and is limited by the cell capacity of the electrical energy store 2, the polynomial charging profile Ip(t) can be represented as follows:

[00002]$\begin{array}{cc}\mathrm{Ip}\left(t\right)=\frac{Qc+0.25d{t}_{ch}^4}{t_{ch}}-1.5d{t}_{ch}{t}^2+d{t}^3& \left(2\right)\end{array}$

[0051] The parameter d of the polynomial charging profile Ip(t) has a loss function f(d) which has a parabolic shape that is still open at the top, as illustrated in FIG. 4. The minimum of the loss function f(d) corresponds to a value for the parameter d which produces a polynomial charging profile Ip(t) that causes minimum aging of the electrical energy store 2.

[0052] The optimization means 3 is designed to numerically determine the minimum of the loss function f(d). A gradient method is used for this purpose: the gradient of the loss function f(d) at the outer limit values dmin and dmax of the loss function f(d) and at a mean value dm of the loss function f(d) halfway between the outer limit values dmin and dmax is first of all determined. That range of the parameter d in which the sign of the gradient is reversed and the approximation method is continued with the limit values of this range is then selected. In FIG. 4, this is the range between the mean value dm and the upper limit value dmax, since the gradient is negative for the values dmin and dm and the gradient is positive for the value dmax. As the result, an optimized parameter dopt, for which the loss function f(d) has a minimum, is determined.

[0053] The optimization means 3 is designed to output the optimized parameter dopt to the charge open-loop control means 11.

[0054] The charge open-loop control means 11 is designed to determine an optimized charging profile Ip(t) for the first current I1 and the resultant first side reaction current J1 by using the optimized parameter dopt and inserting it into formula (2).

[0055] The open-loop control unit 12 is electrically conductively connected to the low-pass filter 4. The open-loop control unit is designed to conduct the first charging current I1 to the low-pass filter 4.

[0056] The low-pass filter 4 electrically conductively connects the open-loop control unit 12 to the summation means 8. The low-pass filter 4 is designed to smooth the first charging current I1 and to convert it into a second charging current I2 and to conduct the second charging current I2 to the summation means 8.

[0057] The open-loop control unit 12 is connected in signal-conducting fashion to the comparison means 10. The open-loop control unit 12 is designed to send the first side reaction current J1 to the comparison means 10.

[0058] The comparison means 10 is arranged between the second open-loop control means 11 and the closed-loop control unit 9. The comparison means 10 is arranged between the ageing evaluation means 7 and the closed-loop control unit 9. The comparison means 10 is designed to receive and compare the first side reaction current J1 and the second side reaction current, in particular to form a differential side reaction current, which is the difference between the first side reaction current J1 and the second side reaction current J2. The result of the comparison between the first side reaction current J1 and the second side reaction current J2 is sent to the closed-loop control unit 9.

[0059] The closed-loop control unit 9 is arranged between the summation means 8 and the comparison means 10. The closed-loop control unit 9 is designed, on the basis of the present second side reaction current J2 of the electrical energy store, to generate a third charging current I3 for charging the electrical energy store 2, which third charging current effects a side reaction current in the electrical energy store 2 which corresponds to a minimum ageing of the electrical energy store 2. The closed-loop control unit 9 is electrically conductively connected to the summation means 8 and is designed to conduct the third charging current I3 to the summation means 8.

[0060] The closed-loop control unit 9 uses a closed-loop control method which is frequency-based and uses fractional differentiation orders as parameters, in particular a CRONE method. In this case, numerical linear models of a nonlinear energy store model are used.

[0061] The summation means 8 acts as a node between the low-pass filter 4 and the closed-loop control unit 9, on one side, and the electrical energy store 2 and the evaluation unit 5, on the other side. The summation means 8 is designed to add the second charging current I2 and the third charging current I3 and, from this, to generate a fourth charging current as the sum, which is used for charging the electrical energy store 2. For this purpose, the summation means 8 is electrically conductively connected to the electrical energy store 2. Furthermore, the summation means 8 is connected in signal-conducting fashion to the evaluation unit 5 in order to send the fourth charging current I4 to the evaluation unit 5.

[0062] The method according to the invention for charging an electrical energy store 2 has open-loop control method steps and closed-loop control method steps, which run simultaneously or parallel in time.

[0063] In a first method step, a present state of charge and a present state of health of the electrical energy store 2, which effects a present second side reaction current J2 in the electrical energy store 2, are determined. In this case, use is made of a simplified linear electrothermal aging model of the electrical energy store 2 which has been approximated by means of a Volterra series.

[0064] In open-loop control method steps, a first charging current I1 and a first side reaction current J1 of the electrical energy store 2 are generated using the present state of charge, a defined state of charge to be achieved by means of charging and the available charging time tch.

[0065] In a first open-loop control method step, a minimum of a loss function f(d) of a parameter d of a polynomial charging profile Ip(t) is numerically determined. A gradient method is used for this purpose: the gradient of the loss function f(d) at the outer limit values dmin and dmax of the loss function f(d) and at a mean value dm of the loss function f(d) halfway between the outer limit values dmin and dmax is first of all determined. That range of the parameter d in which the sign of the gradient is reversed and the approximation method is continued with the limit values of this range is then selected.

[0066] In a second open-loop control method step, an optimized polynomial charging profile Ip(t) is determined for the first current I1 and the resultant first side reaction current J1 by using the optimized parameter dopt and inserting it into formula (2).

[0067] In a third open-loop control method step, the first charging current I1 is smoothed to give a second charging current I2 .

[0068] In a first closed-loop control method step, the first side reaction current J1 is compared with the second side reaction current J2, and a third charging current I3 is generated. In this case, the third charging current I3 is equal to zero when the first side reaction current J1 has the same value as the second side reaction current J2. When the first side reaction current J1 and the second side reaction current J2 have different values, the third charging current is determined in such a way that the ageing of the electrical energy store 2 is minimized.

[0069] In a second closed-loop control method step, the third charging current I3 and the second charging current I2 are added, and a fourth charging current I4 is generated as the sum. In this case, the fourth charging current I4 has the same value as the second charging current I2 when the third charging current I3 is equal to zero.

[0070] In a second method step, the electrical energy store 2 is charged with the second charging current I2 or the fourth charging current I4, wherein the second charging current is used when a fourth charging current I4 is not available, and the fourth charging current is used when a fourth charging current I4 is available.

[0071] Thereafter, the method is continued with the first method step.

[0072] An electrical energy store is in this case understood to mean a rechargeable energy store, in particular having an electrochemical energy store cell and/or an energy store module having at least one electrochemical energy store cell and/or an energy store pack having at least one energy store module. The energy store cell can be in the form of a lithium-based battery cell, in particular lithium-ion battery cell. Alternatively, the energy store cell is in the form of a lithium-polymer battery cell or a nickel-metal hydride battery cell or a lead-acid battery cell or a lithium-air battery cell or a lithium-sulfur battery cell.