Method for impedance-controlled fast charging, control unit for a charging system, stored energy source, and working device

Abstract

A method is provided for impedance-controlled fast charging of a stored electrical energy source of a working device, in particular of a stored energy source in a vehicle. In the method: a variable characteristic of an impedance of the stored energy source is detected; a present charging current for charging the stored electrical energy source is set as a function of the variable characteristic of the impedance; the present charging current is temporarily reduced with a steep edge by temporarily connecting a resistive load to the stored energy source and feeding the load using the stored energy source; and a voltage response of the stored energy source to the steep edge is detected as the variable characteristic of the impedance of the stored energy source and is used as the basis for setting the present charging current.

Claims

1. A method for impedance-controlled fast charging of a stored electrical energy source, the method comprising: detecting a variable characteristic of an impedance of the stored electrical energy source; setting a present charging current for charging the stored electrical energy source as a function of the variable characteristic of the impedance; temporarily reducing the present charging current with a steep edge by temporarily connecting a resistive load to the stored electrical energy source and feeding said resistive load using said stored electrical energy source; and detecting a voltage response of the stored electrical energy source to the steep edge as the variable characteristic of the impedance of the stored electrical energy source and using the voltage response as a basis for setting the present charging current.

2. The method according to claim 1, wherein the stored electrical energy source is a vehicle energy store and the working device is a vehicle.

3. The method according to claim 1, wherein a heater is employed as the resistive load and, for the reduction of the present charging current, is connected to the stored electrical energy source for operation of the heater.

4. The method according to claim 3, wherein the heater is a dedicated heater for the stored electrical energy source.

5. The method according to claim 4, wherein the heater is a battery-specific or cell-specific heater employed on or in the stored electrical energy source.

6. The method according to claim 5, wherein the heater is configured as a sheet heating element.

7. The method according to claim 1, wherein by way of the resistive load, a generator or electrical machine of the working device is employed in an active short-circuit state.

8. The method according to claim 1, wherein by way of the resistive load, a further energy store to be charged is employed in a DC/DC coupling arrangement with the stored electrical energy source.

9. The method according to claim 1, wherein charging of the stored electrical energy source is controlled or regulated: locally and/or decentrally for the stored electrical energy source, or centrally and in combination with the stored electrical energy source for a plurality of energy stores.

10. The method according to claim 1, wherein the charging of a plurality of energy stores is controlled or regulated, wherein: detection of a voltage response of a fundamental or respective energy store is executed locally and/or decentrally, an evaluation and/or appraisal of the voltage responses of a plurality of energy stores is executed centrally, and/or a common charging strategy is selected for a plurality of energy stores on the basis of an energy store having a lowest impedance of all the energy stores.

11. The method according to claim 1, wherein the temporary reduction of the present charging current is executed: for diagnostic purposes, at a frequency within a range of approximately 0.1 Hz to approximately 10 Hz, in the manner of a discharge pulse, having a pulse duration in a low-frequency component with a length of approximately 1 second, having a discharge time of 5 ms, having a control response to a decaying charging current of 995 ms, and/or having a pulse duration in the high-frequency component within the range of approximately 5 ms to approximately 10 ms; and/or for standardized intercalation, at a frequency within a range of approximately 50 Hz to approximately 200 Hz and/or at a scanning rate of 10%.

12. A control unit for a charging system, comprising: a control chip and/or an ASIC arranged on or in a stored electrical energy source centrally or decentrally for one or more stored electrical energy sources, wherein the control unit is operatively configured to carry out the acts of: detecting a variable characteristic of an impedance of the stored electrical energy source; setting a present charging current for charging the stored electrical energy source as a function of the variable characteristic of the impedance; temporarily reducing the present charging current with a steep edge by temporarily connecting a resistive load to the stored electrical energy source and feeding said resistive load using said stored electrical energy source; and detecting a voltage response of the stored electrical energy source to the steep edge as the variable characteristic of the impedance of the stored electrical energy source and using the voltage response as a basis for setting the present charging current.

13. A charging system for impedance-controlled fast charging, the system comprising: a stored electrical energy source of a working device; and a control unit according to claim 12.

14. The charging system according to claim 13, wherein the stored electrical energy source is a vehicle energy store and the working device is a vehicle.

15. A working device, comprising: a stored electrical energy source; and a control unit according to claim 12, wherein the control unit is separate from or incorporated in the stored electrical energy source.

16. The working device according to claim 15, wherein the working device is a vehicle and the stored electrical energy source is a vehicle energy store.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 represents, in the form of a schematic block diagram, the structure of one form of embodiment of a charging system according to the invention, with a working device which is configured according to the invention.

(2) FIG. 2 represents, in the form of an exploded perspective diagram, one form of embodiment of an energy store which is configured according to the invention, particularly in the form of a cell.

(3) FIG. 3 illustrates, by reference to a graph incorporating a charging curve, a charging strategy which can be generated by means of one form of embodiment of the method according to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(4) Exemplary embodiments and the technical background to the invention are described in detail hereinafter, with reference to FIGS. 1 to 3. Identical and equivalent, together with identically and equivalently acting elements and components are identified by the same reference symbols. The detailed description of the elements and components identified is not repeated in every instance of their occurrence.

(5) The features represented, and further properties, can be isolated from one another in an arbitrary manner, and can be mutually combined in an arbitrary manner, without departing from the core of the invention.

(6) FIG. 1 represents, in the form of a schematic block diagram, the structure of one form of embodiment of a charging system 100, with a working device 1 which is configured accordingly.

(7) The charging system 100 according to FIG. 1 comprises a working device 1, for example in the form of a vehicle 1′, in which an electrical energy store 20 is configured, in this case in the form of a vehicle energy store 20′, in order to supply in-service units of the working device 1 with energy. Moreover, for the charging of the energy store 20, a charging unit 80 is configured, which is controllably connectable to the terminals 23 and 24 of the energy store.

(8) For the control of the charging process, particularly in the manner according to the invention, a control unit 10 is provided. This can be configured in the form of components on or in the energy store 20 wherein, however, in the case represented in FIG. 1, the control unit is arranged separately from the energy store 20.

(9) The control unit 10 is designed to initiate, execute and/or control a method for the impedance-controlled fast charging of the energy store 20.

(10) To this end, the control unit 10 is capable, during a charging process, of the temporary connection of a specified ohmic load 30, or a general load, to the energy store 20 such that, during the connection of the load 30 to the energy store 20, the charging current in the energy store 20 reduces, wherein the reduction occurs with a comparatively steep ramp in excess of 20 A/s, such that this abrupt drop can be employed for an impedance analysis or similar, namely, by the detection of a corresponding voltage response of the energy store 20, optionally with evaluation.

(11) In the form of embodiment represented in FIG. 1, various loads 30 are indicated, namely, a heating device 40 which is arranged in the immediate spatial vicinity of the energy store 20, for example in the form of a sheet heating element, a further energy store 60, which is electrically connectable to the fundamental energy store 20 by means of a DC/DC coupling, and a generator 50 which, in active short-circuit operation, can also function as a load 30.

(12) FIG. 2 represents, in the form of an exploded perspective diagram, one form of embodiment of an energy store 20 which is configured according to the invention, in the form of a vehicle energy store 20′, particularly in the form of a cell.

(13) In this form of embodiment of the energy store 20 as a vehicle energy store 20′, the heating device 40 is configured in the form of a sheet heating element in the housing 21, and is arranged between the electrode stacks 22. In the region of the terminals 23 and 24 of the energy store 20, the control unit 10, with corresponding switching units, is configured. However, this arrangement is not mandatory, but is indicated for exemplary purposes only.

(14) By reference to a graph 90 having a charging curve 93, FIG. 3 illustrates a charging strategy which can be generated by means of one form of embodiment of the method according to the invention.

(15) Time is plotted on the x-axis 91 of the graph 90, and the present charging current I(t) is plotted on the y-axis 92.

(16) It can be seen that the charging curve 93 comprises a high charging phase 91-1, having corresponding charging segments or charging pulses 93-1 with comparatively high and constant values for the charging current I(t). This is followed by an intermediate charging phase 91-2 or transitional charging phase, in which the value of the charging current I(t)—particularly, but not necessarily, in a linear manner—reduces over time, terminating in a low charging phase 91-3, with comparatively low and constant values for the charging current I(t).

(17) Between the individual charging segments 93-1 or charging pulses, temporary and, in comparison with the charging segments 93-1, short-term discharge pulses or discharge segments 93-2 occur, which assume a steeply falling ramp for the characteristic of the value of the charging current I(t). These discharge pulses 93-2, having a steeply falling ramp, can be employed, for example, for the detection and evaluation of a resulting voltage response of the energy store 20, namely, for the deduction of a characteristic variable for the impedance of the energy store 20. In the simplest case, this can be a variable which directly describes the corresponding voltage drop across the energy store.

(18) The respective ramp characteristic can extend from the charging regime 92-1 on the y-axis 92 via the value zero into the discharging regime 92-2; however, this is not mandatory—a drop which proceeds within the charging regime 92-1 is sufficient for the execution of the concept according to the invention.

(19) This feature, and further features and properties of the present invention, are described in greater detail with reference to the following considerations:

(20) Fast charging of an energy store by means of a CCCV method (CCCV: constant current, constant voltage) or by means of a multi-step method (MSCC: multi-step, constant current) in an impedance-controlled manner is possible in mobile terminal devices having only a lithium-ion cell. In order to determine variations in impedance, current variations—for example within the range of a few Hz or a few 100 Hz up to the kHz range—for example having pulse widths in the range of a few milliseconds, for example 1 ms to 10 ms—and/or with a switchover from charging to discharging, are imposed, and the voltage response is measured.

(21) In an electric vehicle 1′ or a hybrid vehicle—described in summary as a working device 1—by means of the charging column—described in summary as a charging unit 80—no such current variations are generated, as a charging column of this type can only charge, but cannot discharge the energy store of a corresponding vehicle.

(22) Moreover, a current ramp or edge which can be generated by means of charging columns 80 is limited to a value of 20 A/s. This is not sufficient for the deduction of a characteristic variable for the impedance of an energy store 20.

(23) By means of the application according to the invention, and particularly by the integration of one or more sheet heating elements 40 or general ohmic loads 30 in a cell of an energy store of a working device 1, particularly of a vehicle 1′, during an ongoing fast charging process, discharging can also be executed by means of the cell by the load 30 being connected. By the connection of the ohmic load 30, discharge currents are generated and/or current is reduced to the requisite degree.

(24) Any switching elements employed must be capable of switching in a sufficiently rapid manner, for example within the range of a few Hz or a few 100 Hz up to the kHz range, for example having pulse widths in the range of a few milliseconds, for example 1 ms to 10 ms. Insofar as possible, switching must also be executed in a cell-specific manner, or must be feasible per module or per high-voltage battery. The switching elements must also be rated with a corresponding current-carrying capacity.

(25) However, by the measures according to the invention, a measurement of impedance, for example by means of a chip or an ASIC—described in summary as a control unit 10 according to the invention—can be executed in proximity to the cell or, in general, on the energy store 20.

(26) The chip or ASIC, by way of a control unit 10, can also control the necessary switches and/or can incorporate or constitute the latter.

(27) As the “discharge pulses” are only of a short duration, the input of heat to the ohmic loads 30, and particularly to the sheet heating element 40, is comparatively low.

(28) The rating of the value of the ohmic resistance of the ohmic load 30 vis-à-vis the cell resistance can be dimensioned such that, in the event of simultaneous charging and the activation of the ohmic load 30, particularly the sheet heating element 40, the energy store 20 in the form of the cell is also discharged.

(29) Impedance-based control, in the event of fast charging, is superimposed by a thermal downrating of current, in order to ensure that a given temperature limit in the cells is not exceeded. Moreover, as a function of the cell voltage, the value of a maximum or peak current is defined.

(30) As a load, alternatively to an exclusively ohmic load, a second energy store 60 can be provided in the working device 1 or in the vehicle 1′, in order to generate discharge pulses. In this case, the energy stores 20, 20′ and 60 are connected to one another by means of a DC/DC coupling 70.

(31) On the grounds that, for example, an ohmic load 30 in the form of a sheet heating element 40 internally or externally to a cell to be charged is employed as a load for the generation of high-frequency discharge pulses during charging, impedance-controlled fast charging is also possible on a charging column and on all charging units 80 which do not have a facility for the delivery of appropriate discharge pulses.

(32) Discharge pulses moreover provide the following advantages: The charging of a double layer of electrodes can be avoided. There is no resulting region which is limited by diffusion. A lower effective resistance results in reduced waste heat. The anode potential can remain at a higher level. According to the invention, there is a reduced risk of plating with respect to metallic lithium. In consequence, the service life of the energy store is extended. Additionally, shorter charging times can be achieved. Higher charging capacities are also possible.

(33) By means of the current flux via the sheet heating element 40 or, in general, by means of the ohmic resistance of the ohmic load 30, the cell—described in summary as the energy store 20—additionally undergoes heat-up. This is conducive to fast charging, and additionally improves service life, restricts the limited risk of plating with respect to metallic lithium, and reduces resistance, particularly in conjunction with an increase in the anode potential.

(34) Impedance-controlled fast charging according to the invention can be effectively regulated and operated such that, in the event of high cell voltages, the current is reduced or the anode potential never falls to an excessively low level such that, additionally, plating is prevented.

LIST OF REFERENCE SYMBOLS

(35) 1 Working device

(36) 1′ Vehicle

(37) 10 Control unit

(38) 20 Energy store, store for electrical energy

(39) 20′ Vehicle energy store

(40) 21 Housing

(41) 22 Electrode arrangement/stack

(42) 23 Terminal

(43) 24 Terminal

(44) 30 Ohmic load

(45) 40 Heating device

(46) 50 Generator

(47) 60 (Further) energy store

(48) 70 DC/DC coupling

(49) 80 Charging unit

(50) 90 Graph

(51) 91 x-axis

(52) 91-1 High charging phase

(53) 91-2 Transitional charging phase

(54) 91-3 Low charging phase

(55) 92 y-axis

(56) 92-1 Charging regime

(57) 92-2 Discharging regime

(58) 93 Trace

(59) 93-1 Charging segment, charging pulse

(60) 93-1 Discharge segment, discharge pulse

(61) 100 Charging system