METHOD FOR CHARGING AND/OR DISCHARGING A RECHARGEABLE ENERGY STORE

Abstract

A method for charging and/or discharging an energy store with a current I.sub.0, wherein the energy store has at least one cell block having a number J of series-connected battery cells, at least some of the battery cells of which may have different efficiencies η.sub.N, where 1≤N≤J, has the following method steps: determining the battery cell having the lowest efficiency η.sub.min, and adjusting the efficiency η.sub.N of all the other battery cells to this lowest efficiency η.sub.min such that the adjusted efficiency η.sub.N′ of the battery cells is n.sub.N′=η.sub.min.

Claims

1: A method for charging and/or discharging an energy store (1) with a current I.sub.0, wherein the energy store (1) has at least one cell block (2) having a number J of series-connected battery cells (3, 4, 5, 6, 7), at least some of the battery cells (3, 4, 5, 6, 7) of which may have different efficiencies η.sub.N, where 1≤N≤J, having the following method steps: determining the battery cell (3, 4, 5, 6, 7) having the lowest efficiency η.sub.min, adjusting the efficiency η.sub.N of all the other battery cells (3, 4, 5, 6, 7) to this lowest efficiency η.sub.min such that for the adjusted efficiency η.sub.N′ of the battery cells applies: η.sub.N′=η.sub.min.

2: The method according to claim 1, wherein prior to the adjustment of the efficiencies η.sub.N to η.sub.min the battery cell (3, 4, 5, 6, 7) with the lowest efficiency η.sub.min is determined wherein all battery cells (3, 4, 5, 6, 7) in the cell block (2) are first charged to their end-of-charge voltage, the cell block (2) is then discharged to a specific proportion of its nominal capacitance, the cell block (2) is subsequently charged until at least one battery cell (3, 4, 5, 6, 7) has reached its end-of-charge voltage and the battery cell (3, 4, 5, 6, 7) with the lowest efficiency η.sub.min is then defined as the battery cell which has the smallest cell voltage U.sub.Zmin of all battery cells (3, 4, 5, 6, 7).

3: The method according to claim 2, wherein after the cell block has finished being charged the cell voltage U.sub.Z0,N for all battery cells (3, 4, 5, 6, 7) is determined and wherein for each of the battery cells (3, 4, 5, 6, 7) the energy or the power E.sub.taken,N that is taken from the respective battery cell (3, 4, 5, 6, 7) during charging or discharging is determined from the difference U.sub.Z0,N−U.sub.Zmin, so that its thus adjusted efficiency η.sub.N′ corresponds to the efficiency η.sub.min.

4: The method according to claim 3, wherein the cell voltages U.sub.Z0,N or the efficiencies η.sub.N derived from the cell voltages are stored.

5: The method according to claim 1, wherein prior to the adjustment of the efficiencies η.sub.N to η.sub.min the battery cell with the lowest efficiency η.sub.min is determined wherein the cell block (2) is charged and while the cell block (2) is being charged a charging current I.sub.0 is stepped at least once, wherein the cell voltage of all battery cells (3, 4, 5, 6, 7) is recorded over a period of time before, during and after the step change in the charging current I.sub.0, wherein for every battery cell (3, 4, 5, 6, 7) the difference U.sub.N,current step between the highest cell voltage U.sub.N,max and the lowest cell voltage U.sub.N,min over this period of time is formed at U.sub.N,current step=U.sub.N,max−U.sub.N,min, and wherein the battery cell (3, 4, 5, 6, 7) with the lowest efficiency η.sub.min is defined as the battery cell (3, 4, 5, 6, 7) for which the difference U.sub.N,current step is greatest with U.sub.current step,max.

6: The method according to claim 1, wherein prior to the adjustment of the efficiencies η.sub.N to η.sub.min the battery cell with the lowest efficiency η.sub.min is determined wherein the cell block (2) is discharged and while the cell block is being discharged a discharging current I.sub.0 is stepped at least once, wherein the cell voltage of all battery cells (3, 4, 5, 6, 7) is recorded over a period of time before, during and after the step change in the discharging current I.sub.0, wherein for every battery cell (3, 4, 5, 6, 7) the difference U.sub.N,current step between the highest cell voltage U.sub.N,max and the lowest cell voltage U.sub.N,min over this period of time is formed at U.sub.N,current step=U.sub.N,max−U.sub.N,min, and wherein the battery cell (3, 4, 5, 6, 7) with the lowest efficiency η.sub.min is defined as the battery cell (3, 4, 5, 6, 7) for which the difference U.sub.N,current step is greatest with U.sub.current step,max.

7: The method according to claim 5, wherein for each of the battery cells (3, 4, 5, 6, 7) the energy or power E.sub.taken,N that is taken from the respective battery cell during charging or discharging is determined from the difference U.sub.current step,max and U.sub.N,current step, so that its thus adjusted efficiency η.sub.N′ corresponds to the efficiency η.sub.min.

8: The method according to claim 3, wherein for each battery cell (3, 4, 5, 6, 7) the energy or the power E.sub.taken,N, that is taken from the respective battery cell (3, 4, 5, 6, 7) during charging or discharging, so that its adjusted efficiency η.sub.N′ corresponds to the efficiency η.sub.min, is stored.

9: The method according to claim 1, wherein the capacitance of the battery cell (3, 4, 5, 6, 7) with the lowest efficiency η.sub.min is determined.

10: The method according to claim 1, wherein the cell voltages of the battery cells (3, 4, 5, 6, 7) are measured regularly after the cell block has been charged.

11: The method according to claim 1, wherein at certain intervals immediately after charging the cell block the cell voltage U.sub.Z,N of all battery cells (3, 4, 5, 6, 7) is determined and compared with the end-of-charge voltage U.sub.L,N, and wherein in the event of a deviation of the cell voltage U.sub.Z,N of a battery cell (3, 4, 5, 6, 7) from its end-of-charge voltage U.sub.L,N by more than a specified limit value the energy or the power E.sub.taken,N, that is taken from the relevant battery cell (3, 4, 5, 6, 7) or all other battery cells for the adjustment of its efficiency to the efficiency η.sub.min, is adjusted.

12: The method according to claim 11, wherein in the event of a deviation of the cell voltage U.sub.Z,N of the battery cell (3, 4, 5, 6, 7) with the lowest efficiency η.sub.N=η.sub.min from the end-of-charge voltage U.sub.L,N by more than a specified limit value, the energy or the power E.sub.taken,N, that is taken from all other battery cells (3, 4, 5, 6, 7) for the adjustment of its efficiency to the efficiency η.sub.min, is adjusted.

13: The method according to claim 11, wherein in the event of a deviation of the cell voltage U.sub.Z,N of a battery cell (3, 4, 5, 6, 7), for which η.sub.N>η.sub.min previously applied, from the end-of-charge voltage U.sub.L,N by more than a specified limit value, the energy or power E.sub.taken,N taken from this battery cell (3, 4, 5, 6, 7) for the adjustment of the efficiency is reduced to E.sub.taken,N′, such that in future ΔU.sub.N=0 applies for the voltage difference ΔU.sub.N=U.sub.L,N−U.sub.Z,N.

14: The method according to claim 13, wherein in the case of a battery cell (3, 4, 5, 6, 7), for which η.sub.N>η.sub.min previously applied and for which it is found that the voltage difference is ΔU.sub.N=U.sub.L,N−U.sub.Z,N>0 despite a reduction to E.sub.taken,N′=0, this battery cell (3, 4, 5, 6, 7) is henceforth defined as the battery cell with the lowest efficiency η.sub.min′, and wherein the efficiencies of all other battery cells (3, 4, 5, 6, 7) are adjusted to this new lowest efficiency η.sub.min′.

15: The method according to claim 1, wherein the charging current or the discharging current is stepped at least once while the cell block (2) is being charged or discharged, wherein a resulting step change in the cell voltage is recorded as a voltage response for all battery cells (3, 4, 5, 6, 7) and compared with one another for the battery cells (3, 4, 5, 6, 7), and wherein the energy or the power E.sub.taken,N, that is taken from a battery cell (3, 4, 5, 6, 7) or multiple battery cells (3, 4, 5, 6, 7) for the adjustment of its efficiency to the efficiency η.sub.min, is adjusted if, for at least one battery cell (3, 4, 5, 6, 7), the step change in the cell voltage deviates quantitatively from the changes in the cell voltages of the other battery cells (3, 4, 5, 6, 7) by more than a specified limit value.

16: The method according to claim 15, wherein in the event of a deviation of the step change in the cell voltage of the battery cell (3, 4, 5, 6, 7) with the lowest efficiency η.sub.N=η.sub.min from the changes in the cell voltages of the other battery cells by more than a specified limit value, the energy or the power E.sub.taken,N, that is taken from all other battery cells (3, 4, 5, 6, 7) for the adjustment of its efficiency to the efficiency η.sub.min, is adjusted.

17: The method according to claim 15, wherein in the event of a deviation of the step change in the cell voltage of a battery cell (3, 4, 5, 6, 7), for which η.sub.N>η.sub.min previously applied, from the step change of the other battery cells (3, 4, 5, 6, 7) by more than a specified limit value, the energy or the power E.sub.taken,N, that is taken from this battery cell (3, 4, 5, 6, 7) for the adjustment of its efficiency, is reduced to E.sub.taken,N′ such that in the event of a step change in the charging or discharging current in the future the step change in the cell voltage of this battery cell (3, 4, 5, 6, 7) essentially corresponds to the step changes in the cell voltages of the other battery cells (3, 4, 5, 6, 7).

18: The method according to claim 17, wherein in the case of a battery cell for which η.sub.N>η.sub.min previously applied and for which it is found that the step change in the cell voltage of this battery cell (3, 4, 5, 6, 7) as a response to a step change in the charging current or discharging current is greater than the step changes in the cell voltages of the other battery cells (3, 4, 5, 6, 7) by more than a specified limit value despite a reduction to E.sub.taken,N′=0, this battery cell (3, 4, 5, 6, 7) is henceforth defined as the battery cell with the lowest efficiency η.sub.min′, and wherein the efficiencies of all other battery cells (3, 4, 5, 6, 7) are adjusted to this new lowest efficiency η.sub.min′.

19: The method according to claim 1, wherein the efficiency is adjusted using switchable resistors R.sub.N, whereby each battery cell is equipped with a switchable resistor.

20: The method according to claim 19, wherein the resistor R.sub.N (8, 9, 10, 11, 12) of the battery cells (3, 4, 5, 6, 7) is set such that for each combination of battery cell (3, 4, 5, 6, 7) and associated switchable resistor (8, 9, 10, 11, 12) the efficiency is η.sub.N′ =η.sub.min.

21: The method according to claim 19, wherein the switchable resistors (8, 9, 10, 11, 12) are only connected in parallel over a period of time of the charging process or discharging process of the battery cells (3, 4, 5, 6, 7).

22: The method according to claim 21, wherein the duration of the period of time for each battery cell. (3, 4, 5, 6, 7) is set such that for each combination of battery cell (3, 4, 5, 6, 7) and associated switchable resistor (8, 9, 10, 11, 12) the efficiency is η.sub.N′=η.sub.min.

23: The method according to claim 1, wherein the efficiency is adjusted using DC-DC converters, wherein each battery cell (3, 4, 5, 6, 7) is equipped with one DC-DC converter and the DC-DC converter is set such that for each combination of battery cell (3, 4, 5, 6, 7) and DC-DC converter the efficiency is η.sub.N′=η.sub.min.

Description

DRAWING

[0049] The drawing shows a model embodiment of the subject matter of the invention. Illustration:

[0050] FIG. 1 Wiring diagram of an energy store.

DESCRIPTION OF THE MODEL EMBODIMENT

[0051] FIG. 1 represents a wiring diagram of an energy store 1 that is used, for example, to supply energy to a supply network of a building and can be charged and discharged by a system for generating renewable energy (photovoltaic installation, wind turbine, biogas plant, etc.), for example via a bidirectional AC/DC converter 100. In the model embodiment represented the energy store 1 comprises a cell block 2 having multiple rechargeable battery cells 3, 4, 5, 6, 7 connected to one another in series. Each of the battery cells 3 to 7 is equipped with a switchable resistor 8, 9, 10, 11, 12, whereby the switchable resistor 8 of the battery cell 3 is connected in parallel. The same applies analogously for the resistors 9, 10, 11, 12 and the battery cells 4, 5, 6, 7. Switchable means that the resistors are connected in parallel to the battery cells for a limited period of time while the cell block is being charged or discharged.

[0052] A monitoring and storage device 13 which is connected via corresponding data lines 14 both to the switchable resistors 8 to 12 and to the bidirectional AC/DC converter 100 is provided to check the state of charge or discharge of the individual battery cells 3 to 7.

[0053] The determination of the battery cell with the lowest efficiency and the adjustment of the efficiencies of the other battery cells to this lowest efficiency are described below:

[0054] All battery cells 3 to 7 in the cell block 2 are first charged until they reach their end-of-charge voltage. The cell block 2 is then discharged until it reaches 50% of its nominal capacitance. The cell block is subsequently charged again until one of the battery cells is the first to reach its end-of-charge voltage. In this model embodiment let it be the battery cell 5. At the moment the battery cell 5 reaches its end-of-charge voltage, the voltage differences between the cell voltage of the battery cell 5 and the cell voltages of the other battery cells 3, 4, 6, 7 are determined. The voltage differences allow conclusions to be drawn about the differences in efficiency. The battery cell 3, 4, 6, 7 which has the greatest voltage difference to the battery cell 5 is defined as the battery cell with the lowest efficiency η.sub.min. In this model embodiment let it be the battery cell 6.

[0055] The efficiencies η.sub.N at N ϵ{3, 4, 5, 7} of the battery cells 3, 4, 5, 7 are subsequently adjusted to the efficiency η.sub.min in that the switching times of the switchable resistors 8 to 12 for the charging process and discharging process are determined. In the case of the battery cell 6, the associated resistor 11 is not connected in parallel during the charging process or the discharging process since the efficiency of this battery cell is already the lowest efficiency: η.sub.6=η.sub.min. In the case of the battery cell with the best efficiency, in this model embodiment the battery cell 5, the associated switchable resistor 10 is switched on for the longest time.

[0056] Switching the switchable resistors 8, 9, 10 and 12 ensures that the losses during the charging and discharging of all battery cells 3 to 7 are the same and therefore the efficiency of all battery cells 3 to 7 corresponds to the efficiency η.sub.min: η.sub.3=η.sub.4=η.sub.5=η.sub.6=η.sub.7=η.sub.min

[0057] All battery cells 3 to 7 thereby reach their end-of-charge voltage simultaneously when the cell block 2 is being charged.

[0058] All features of the invention can be material to the invention both individually and in any combination.

REFERENCE NUMBERS

[0059] 1 Energy store [0060] 2 Cell block [0061] 3 Battery cell [0062] 4 Battery cell [0063] 5 Battery cell [0064] 6 Battery cell [0065] 7 Battery cell [0066] 8 Switchable resistor [0067] 9 Switchable resistor [0068] 10 Switchable resistor [0069] 11 Switchable resistor [0070] 12 Switchable resistor [0071] 13 Monitoring and storage device [0072] 14 Data line [0073] 100 Bidirectional AC/DC converter