Device for charging and / or discharging an energy storage device and method for determining a correction factor and / or predetermined energy storage information

Abstract

Device (1) for charging or discharging an energy storage device (3) with a determination device (4) for determining a state of charge of the energy storage device (3), which is designed to determine a first actual value (7) of an impedance variable (8) and to determine the state of charge (10) on the basis of the first actual value (7) and a predetermined energy storage information item (9), wherein the or a further determination device (4) of the device is designed to - repeatedly detecting a first voltage change (11) of a charging voltage (12), - upon fulfillment of a triggering condition (14), the fulfillment of which depends on the last detected first voltage change (11), to change the charging current (13) and to detect a second voltage change (15-18) resulting from the change in the charging current (13), - to determine a second actual value (19) of the impedance quantity (8) as a function of the second voltage change (15-18), and - on the one hand, to determine a correction factor (20) on the basis of the second actual value (19), wherein the determination device (4) is in this case set up to additionally take the correction factor (20) into account when determining the state of charge (10), and / or on the other hand, to specify the predetermined energy storage information (9) as a function of the second actual value (19).

Description

[0001] The invention relates to a device for charging and / or discharging an energy storage device, comprising a determination device for determining a state of charge of the energy storage device, wherein the determination device is configured to determine a first actual value of an impedance variable that describes a resistance and / or an impedance of the energy storage device, and to determine the state of charge based on the first actual value and a predetermined piece of energy storage information. In addition, the invention relates to a method for determining a correction factor and / or a predetermined piece of energy storage information, which serves to determine a state of charge of the energy storage device based on a first actual value of an impedance variable that describes a resistance and / or an impedance of the energy storage device.

[0002] When using rechargeable batteries or accumulators, it is often highly important to be able to determine the current state of charge with good accuracy, for example, to estimate the remaining range of an electrically powered vehicle and / or to optimally utilize a stationary buffer storage device. In the simplest case, one can attempt to determine the state of charge based on the battery's open-circuit voltage.

[0003] However, for many battery types, such as lithium iron phosphate batteries or sodium-ion batteries, the voltage characteristics are very flat over wide ranges of the state of charge, so that only a very rough estimate of the state of charge is possible based on the open-circuit voltage. For other battery types, such as lead-acid batteries, hysteresis effects of the open-circuit voltage occur, which can lead to significant errors when estimating the state of charge based on the open-circuit voltage.

[0004] The aforementioned errors and inaccuracies can be avoided or at least reduced if the internal resistance or impedance of the battery is measured and evaluated instead of the open-circuit voltage to determine the state of charge. Determining the state of charge based on impedance measurements is known, for example, from document DE 10 2014 014 031 A1.

[0005] However, this poses the problem that the internal resistance and impedance of a battery also depend on the battery's aging state. Therefore, determining the state of charge becomes less accurate with increasing battery usage time.

[0006] In principle, an attempt can be made to take battery aging into account by starting from a fully charged battery where the state of charge is known, determining the actual current state of charge by integrating currents flowing into and out of the battery and using this to iteratively adapt a characteristic curve that indicates the relationship between the state of charge and the impedance or internal resistance.

[0007] However, due to the current integration used, such a determination of the current state of charge can result in quite large errors, especially if the battery is rarely fully charged. Therefore, even when using such a correction, relatively large errors can still occur in the determination of the state of charge.

[0008] To avoid excessive distortion of the characteristic curve due to an error in the determined current state of charge, the characteristic curve should also be adjusted iteratively only in small steps, so that learning the aging state or an updated characteristic curve of the battery requires a large number of charging and discharging cycles. As long as such a learning interval is not completed, for example, after a battery with an unknown aging state has been installed and / or a control unit that monitors the battery has been replaced, large errors in determining the state of charge and thus, for example, in estimating the remaining range can result over a relatively long operating period.

[0009] The invention is therefore based on the object of further improving the estimation of a state of charge of an energy storage device, in particular in a motor vehicle or in a stationary buffer storage device.

[0010] The object is achieved by a device of the type mentioned above, wherein the or a further detection device of the device is designed to - repeatedly detecting a first voltage change of a charging voltage that drops across the energy storage device while the energy storage device is being charged or discharged by a charging current, - when a trigger condition is met, the fulfilment of which depends on the last detected first voltage change, to change the charging current and to detect a second voltage change resulting from the change in the charging current, - to determine a second actual value of the impedance quantity as a function of the second voltage change, and - on the one hand, to determine a correction factor on the basis of the second actual value, wherein the determination device is in this case set up to additionally take the correction factor into account when determining the state of charge, and / or on the other hand, to specify the predetermined energy storage information as a function of the second actual value.

[0011] The invention exploits the fact that a charging characteristic curve of an energy storage device, which describes the relationship between the state of charge and the charging voltage drop across the energy storage device for a given charging current, exhibits a sudden increase in at least one defined state of charge for many energy storage devices, particularly chemical energy storage devices, the position of which is essentially independent of the aging state of the energy storage device. Such a defined state of charge can be precisely determined, for example, during conditioning of the energy storage device or during measurement of the energy storage device as part of cell qualification or similar.

[0012] Thus, at certain charge levels, the derivative of the voltage drop across the energy storage device suddenly changes when the defined charge level is reached, or it has a value that is above or below a defined limit once the defined charge level is reached. The first voltage change can therefore be considered, in particular, the derivative of the charging voltage with respect to the charge level.

[0013] If the charging current is known over time, this derivative can be determined from the charging voltage's time profile or time derivative. If an at least approximately constant charging current is used for charging or discharging at the time the trigger condition is evaluated, the time derivative of the charging voltage can also be evaluated directly as the first voltage change, since this is proportional to the charging voltage's derivative with respect to the state of charge, using a charging current-dependent scaling factor.

[0014] If the trigger condition evaluates, for example, an exceedance or undershoot of a specified limit due to the change in charging voltage, or the presence of a sufficiently significant change in the change in charging voltage between two detections, the achievement of the defined state of charge can be detected with good accuracy. The change in the charging current when the trigger condition is met and thus when a defined state of charge is reached can be used to determine the actual impedance value for this defined state of charge as the second actual value.

[0015] Fulfillment of the triggering condition may indicate the presence of a defined state of charge, wherein the predetermined energy storage information or preliminary energy storage information, on the basis of which the predetermined energy storage information is to be specified as a function of the second actual value, assigns a reference value of the impedance variable to the defined state of charge, wherein the further determination device or devices is configured to additionally take the reference value into account when determining the correction factor or when specifying the predetermined energy storage information.

[0016] The specified energy storage information, or previous energy storage information, on the basis of which the specified energy storage information is specified based on the second actual value, can describe a relationship between values of the impedance variable and the state of charge. It can define the relationship between these variables, for example, as a functional relationship or as a look-up table.

[0017] The specified or previous energy storage information can thus specify the reference value of the impedance quantity for the defined state of charge. The deviation of the second actual value from the reference value is thus a measure of how much the actual behavior of the energy storage device deviates from the behavior defined by the specified or previous energy storage information, for example, due to aging.

[0018] A correction factor can thus be determined by comparing the reference value with the second actual value for the impedance variable. In particular, the correction factor can be calculated as the quotient of the reference value and the second actual value. This allows a correction factor to be obtained, which can be multiplied by the first actual value when determining the state of charge to obtain an intermediate result that can be translated into the state of charge using the specified energy storage information.

[0019] Conversely, it is alternatively possible to scale a previous piece of energy storage information, for example, one that was originally predefined or previously determined, in particular such that the value of the impedance variable specified for the defined state of charge by the resulting predefined energy storage information coincides with the second actual value. In this case, scaling preferably occurs exclusively with respect to the impedance variable axis, since, as explained above, the position of the defined state of charge generally does not change, or changes only very slightly and thus negligibly, as the energy storage device ages.

[0020] In the simplest case, the trigger condition can only be used to check whether exactly one defined state of charge has been reached. However, it is also possible for the trigger condition to be met whenever any of several different defined states of charge is present. For example, the inventive approach was used in its development for energy storage devices whose charging curve is considerably steeper in the range of approximately 30% charge and above approximately 97% charge than in neighboring sections, so that these states of charge can be considered as defined states of charge for which the trigger condition can be met.In this case, the exact degree of charge at which the respective defined state of charge occurs can vary considerably due to production tolerances, for example by several percent or even by 10% or more, so that it can be expedient to identify the respective defined state of charge during the manufacture or testing of the respective energy storage device and to store it, for example, in the further detection device or an internal data storage device of the energy storage device.

[0021] Determining which of several defined charge states for which the trigger condition can be met can be achieved by considering preceding events. For example, it is obvious that during a discharge starting from an essentially fully charged energy storage device, the higher of the defined charge states is reached first before the lower of the defined charge states.

[0022] However, particularly robust validation or detection of the correctly defined state of charge can be achieved if, based on a respective detected defined state of charge or based on at least one reference state of charge, for example, based on a nearly complete charge or a nearly complete discharge, a current integration is additionally performed to estimate the current state of charge. As already explained above, determining the state of charge by current integration is potentially highly error-prone. However, at least sufficient accuracy can typically be achieved to validate the detection of a defined state of charge and / or to enable differentiation between several defined states of charge for which the trigger condition can be met.

[0023] In particular, the further determination device or devices can be configured to detect the presence of a reference state of charge and / or the defined state of charge and / or a respective one of the defined states of charge and, based on the reference state of charge and / or the respective defined state of charge, to determine a change in charge by integrating the charging current, wherein the fulfillment of the triggering condition and / or the selection of a defined state of charge from a plurality of defined states of charge for which the triggering condition can be fulfilled additionally depends on the change in charge.

[0024] As already explained above, the reference state of charge can be identified as, in particular, an at least nearly complete charge or an at least nearly complete discharge. In at least one of these charge ranges, the characteristic curve describing the relationship between the voltage drop across the energy storage device and the state of charge is typically steep, so that the state of charge can be determined with good accuracy directly from the voltage drop across the energy storage device, and the presence of the reference state of charge can thus be robustly detected, essentially independent of the aging of the energy storage device.

[0025] The or further determination device can be configured to change the charging current when the triggering condition is met in such a way that it is increased or decreased by a predetermined amount of change, and to determine the second actual value as a function, on the one hand, of the difference between the charging voltage before the change in the charging current and the charging voltage after the change in the charging current and, on the other hand, of the predetermined amount of change.

[0026] In the simplest case, the second actual value can be determined by dividing the difference in the charging voltages by the amount of change in the charging current in order to determine an at least approximately ohmic resistance of the energy storage device as an impedance variable.

[0027] The charging voltage is preferably detected only after a certain rest period of, for example, at least 0.5 seconds, or at least 1 second, or at least 2 seconds, or at least 5 seconds after the change in the charging current, so that the voltage is detected particularly in the equilibrium state after voltage oscillations or similar effects that can occur with a sudden current change have subsided. This is particularly useful if the change in the charging current occurs through a switching operation and is therefore step-like. Alternatively or additionally, it may be useful to increase or decrease the charging current in a ramp-like manner to avoid switching transients in the charging voltage.

[0028] To increase measurement accuracy, the charging current can be increased or decreased in several stages. In this case, a preliminary impedance value can be determined for each stage, and the second actual value can be calculated, for example, by averaging the preliminary impedance values.

[0029] In particular, the amount of change can be specified in such a way that the amount of the charging current is reduced when the triggering condition is met and, particularly preferably, is reduced to zero.

[0030] The or further determining device(s) can be configured to change the charging current upon fulfillment of the triggering condition such that its magnitude is reduced in a first change step and increased in a second change step, or vice versa. The or further determining device(s) can then determine both the first change in the charging voltage resulting from the first change step and the second change in the charging voltage resulting from the second change step as the second voltage change, and the second actual value can be determined as a function of both the first and the second change in the charging voltage.

[0031] In particular, the second change step allows the charging current to be reset to its original value, which existed before the first change step. This allows, for example, an ongoing charging or discharging process of the energy storage device to be continued after a brief interruption.

[0032] Between the change steps, the charging current can be kept at a constant value for a waiting interval. The voltage measurement for the charging current present between the change steps can only be performed during this waiting interval after a certain waiting time for voltage stabilization, for example, only at the end of the waiting interval.

[0033] In particular, it is possible that a respective provisional impedance value is determined on the basis of the change in the charging current amount in the respective change step and the respective change in the charging voltage, wherein the second actual value can be calculated, for example, as an average value of the provisional impedance values.

[0034] The or further determination device can be configured to detect a temporal profile of the charging voltage resulting from the change in the charging current and, by evaluating this temporal profile, to determine the second actual value in such a way that it describes the imaginary part of a complex impedance and / or a capacitance and / or an inductance of the energy storage device.

[0035] The temporal progression can be recorded, in particular, by recording several measured values for the charging voltage at, in particular, constant, intervals. In the simplest case, the charging current can be varied at least approximately in a step-like or ramp-like manner, for example, to determine a real component of the impedance or ohmic resistance, as explained above.

[0036] Depending on the capacitance or inductance of the energy storage device, or generally on the complex impedance, overvoltages and / or oscillations can occur and / or, depending on the imaginary part of the impedance, different time constants for the change in the charging voltage can result. Based on the magnitude of the overvoltage, the amplitude and / or frequency of oscillations, and / or the determined time constant for a rise or fall in the charging voltage, the imaginary impedance, capacitance, or inductance can be determined using known models or equivalent circuits for the energy storage device.

[0037] The or further detection device can be configured to alternately increase and decrease the charging current several times when the triggering condition is met. In particular, the charging current can be modulated with one or, in particular sequentially, with several different frequencies and / or with a waveform resulting from the superposition of several oscillation frequencies.

[0038] Since different imaginary parts of the impedance or different capacitances or inductances of the energy storage device result in different frequency components of the recorded voltage curve of the charging voltage having different amplitudes or phase positions with respect to the change in the charging current, these quantities can be determined particularly accurately and with low susceptibility to interference.

[0039] The energy storage device can be a lithium iron phosphate-based or sodium ion-based energy storage device. Tests conducted during the development of the invention have shown that, although these energy storage types exhibit a substantially flat charging characteristic over a wide range of charge states, within this range they typically exhibit a significantly different gradient of the characteristic curve in at least one very narrow charge state range, making the inventive approach particularly suitable for these energy storage types.

[0040] The device can in particular be or comprise a motor vehicle or a stationary charging device for charging an energy storage device of a motor vehicle, wherein the motor vehicle or the charging device comprises the and / or the further detection device.

[0041] As already explained at the beginning, determining the state of charge in a motor vehicle is particularly relevant when the energy storage system feeds a drive motor and thus determines or at least influences the remaining range of the vehicle. Estimating such a remaining range is particularly relevant for purely electrically powered vehicles. However, estimating the state of charge is also highly relevant in hybrid vehicles, for example, to select an optimal operating strategy regarding the use of the combustion engine and the electric motor.

[0042] However, the device can also be or comprise a stationary buffer storage device. In particular, the energy storage device can be a buffer storage device of a stationary charging device for motor vehicles. Such buffer storage devices can, for example, make it possible to temporarily provide high charging power for the rapid charging of motor vehicles or their energy storage devices, even if the stationary charging device itself is only supplied with relatively low power, for example via a normal power grid and / or via local renewable energy sources, such as solar cells. Such a concept is implemented, for example, in the Audi® charging hub. In order to achieve long service lives for such buffer storage devices, and since some of the batteries installed in such buffer storage devices are already used and aging effects can therefore be particularly relevant, the method according to the invention is particularly relevant in this case.

[0043] Alternatively, the device could be a home storage system, i.e., a buffer storage unit for a building. Such buffer storage units are often used in conjunction with a solar energy system, for example.

[0044] In a preferred embodiment of the device according to the invention, the and the further determination device are provided in the motor vehicle or the stationary charging device, or the determination device provided in the motor vehicle or the stationary charging device is used both to determine the state of charge and to determine the correction factor or to specify the predefined energy storage information. In this case, the correction factor or the predefined energy storage information can be updated upon fulfillment of the respective triggering condition in a variety of operating situations.

[0045] In particular, such an update can be performed, regardless of the type of charging station used, whenever the motor vehicle is charged from an external energy source, where the charging exceeds the defined state of charge or at least one of the defined states of charge. In principle, corresponding updates or determinations are also possible, for example, during recuperation of the motor vehicle or even during discharging of the energy storage device during normal driving. In the latter case, additional conditions should preferably be considered within the trigger condition to avoid unexpected or otherwise detrimental reductions in driving performance due to the reduction in charging current.

[0046] Alternatively, it would also be possible for the detection device implemented in the motor vehicle to exclusively determine the state of charge and, in contrast to the known state of the art, additionally utilize the correction factor or the predefined energy storage information adjusted based on experience. In this case, the determination of the correction factor or the predefined energy storage information can be performed, for example, by a charging device used to charge the energy storage device, which, together with the motor vehicle, forms the device.

[0047] In addition to the device according to the invention, the invention relates to a method for determining a correction factor and / or a predetermined energy storage information, which serves to determine a state of charge of an energy storage device on the basis of a first actual value of an impedance variable that describes a resistance and / or an impedance of the energy storage device, wherein the method comprises the following steps: - repeatedly detecting a first voltage change of a charging voltage that drops across the energy storage device while the energy storage device is being charged or discharged by a charging current, - Changing the charging current and detecting a second voltage change resulting from the change in the charging current when a trigger condition is met, the fulfilment of which depends on the last detected first voltage change, - Determining a second actual value of the impedance quantity as a function of the second voltage change, and - Determining the correction factor based on the second actual value and / or specifying the specified energy storage information depending on the second actual value.

[0048] Details on determining the correction factor and specifying the energy storage information have already been explained above with reference to the device according to the invention. The use of the correction factor and the specified energy storage information to determine the state of charge has also been explained in detail there. Therefore, repetition of this information will be omitted.

[0049] The method according to the invention can be further developed with the features explained above with regard to the device, with the advantages mentioned therein, and vice versa. The method can include additional steps for determining the state of charge, as already explained above.

[0050] In particular, a processing device is also disclosed which is designed to carry out the method according to the invention on its own or when connected to an energy storage device.

[0051] Further advantages and details of the invention will become apparent from the following exemplary embodiments and the accompanying drawings. These schematically show: Fig. 1 an embodiment of the device according to the invention, Fig. 2 is a flowchart of an embodiment of the method according to the invention, which is carried out by the Fig. 1 shown device is implemented, and Fig. 3 & 4 exemplary charging voltage curves, which are shown in Fig. 1 and Fig. 2 shown embodiments.

[0052] Fig. 1 shows a device 1 for charging and discharging an energy storage device 3. In the example shown, the device 1 is implemented by a motor vehicle 2. In the usage situation shown, the motor vehicle 2 is connected to a stationary charging device 5, which in the example is a charging station, in order to charge the energy storage device 3 via a power conditioning device 6, for example, a power converter of the motor vehicle 2.

[0053] The motor vehicle 2 comprises a determination device 4 for determining a state of charge 10 of the energy storage device 3. In principle, an attempt could be made to infer the state of charge 10 from the charging voltage 12 or, after reducing the charging current 13 to zero, the open circuit voltage of the energy storage device 3. However, if, for example, an energy storage device 3 based on lithium iron phosphate or sodium ions is used, the charging voltage 12 and also the open circuit voltage can have almost constant values over a wide range of states of charge 10, as in the exemplary characteristic curve in Fig. 3 is recognizable.

[0054] Therefore, the state of charge 10 in the example is instead calculated according to the Fig. 2 to the right of the dashed line 28, which comprises steps S9 to S11.

[0055] In step S9, a first actual value 7 of an impedance variable 8, which in the example describes an ohmic resistance, is determined. It is known that the ohmic resistance of an energy storage device 3 or other impedance variables 8 for a variety of energy storage devices, in particular for chemical accumulators, provide a good measure of the state of charge, since they vary monotonically with a sufficient gradient over at least some of the possible states of charge. Thus, a predetermined piece of energy storage information 9, which describes the relationship between the impedance variable 8 and the state of charge 10, could in principle be used directly to determine the state of charge 10 based on the actual value 7.

[0056] As already explained in the general part of the description, the relationship between an impedance value 8 and the state of charge 10 changes with increasing age or with increasing number of charging and discharging cycles of the energy storage device 3. In order to take this into account, in the device 1 or in the Fig. 2, a correction factor 20 is additionally used, the determination of which will be explained in more detail later in steps S1 to S8.

[0057] In step S10, the first actual value 7 determined in step S9 is multiplied by the correction factor 20 to determine the scaled actual value 27. This is then used to determine the state of charge 10 based on the relationship between the impedance variable 8 and the state of charge 10 specified by the energy storage information 9, which can be in the form of a look-up table, for example. Aging of the energy storage device 3 can thus be taken into account by appropriately adjusting the correction factor 20. This can significantly improve the accuracy of determining the state of charge, which can also improve estimates of the ranges of the motor vehicle 2, for example if the vehicle is to be powered purely electrically using energy from the energy storage device 3.

[0058] As in Fig. 2 is schematically represented by the line 28, the determination of the correction factor 20 in steps S1 to S8 forms a separate sub-process from the determination of the state of charge 10 in steps S9 to S11, which, for example, only takes place in certain suitable operating situations, for example exclusively when charging the energy storage device from an external energy source, as in Fig. 1, or whose steps could even be carried out by a separate determination device, which could, for example, be part of the charging device 5. However, as already explained in the general section, if the determination of the correction factor 20 is implemented within the motor vehicle, the determination or adjustment of the correction factor can also be carried out in other operating situations, for example during recuperation or when discharging the energy storage device 3 during driving.

[0059] In a suitable operating situation, for example when Fig. During the charging of the energy storage device 3 shown in Figure 1, a first voltage change 11 of a charging voltage 12 that drops across the energy storage device 3 is detected in step S1. If an at least approximately constant charging current 13 is used, the voltage change 11 can be determined directly as a time derivative of the charging voltage.

[0060] As shown in the example characteristic curve in Fig. As can be seen in Figure 3, the gradient of the characteristic curve changes significantly at two defined charge states 21, 22. Reaching these defined charge states 21, 22 can thus be detected, for example, within the scope of the trigger condition 14 checked in step S2 by comparing the last detected voltage change 11 with a limit value. If the trigger condition 14 is not met, the process is repeated from step S1.

[0061] If the triggering condition 14 is met, the determination device 4 in the example first reduces the amount of the charging current 3 by a predetermined change amount 26, for example, by appropriately controlling the current conditioning device. The charging current 13 could in particular be reduced to zero. However, in the example, it is assumed that after the reduction of the charging current amount in step S3, charging continues with a low charging current. Thus, the charging voltage 12 can continue to be plotted against the state of charge 10 even when using such a temporary reduction in the charging current, without leading to ambiguities. Such a charging voltage curve is shown by way of example in Fig. 4 is shown for the case that, within the scope of the same charging process, a temporary reduction in the charging current 13 occurs for both defined charging states 21, 22.

[0062] As in Fig. 4, the reduction of the charging current 13 also leads to a reduction of the charging voltage 12 due to the ohmic resistance of the energy storage device 3. The reduced charging voltage 12 is detected in step S4 after a short waiting interval after the reduction of the charging current 13 in order to determine the second voltage change 15 or 17 by forming the difference between the charging voltage 12 detected before and after the charging current reduction.

[0063] By dividing the second voltage change 15, 17 by the change in the charging current 26, a second actual value 19 for the impedance variable 8 could, in principle, be determined directly. This second actual value 19 describes the current ohmic resistance of the energy storage device. However, for a more precise determination of the second actual value 19, the quotient determined in step S4 is first temporarily stored as an intermediate result 29.

[0064] In step S5, the charging current 13 is then increased by the change amount 26 and thus back to its original value. As shown in Fig. 4, this also results in an increase in the charging voltage, whereby, after a short waiting time for voltage stabilization, the second voltage change 16 or 18 is again determined in step S6. The detected voltage change 16, 18 is again divided by the change amount 26 to determine another preliminary impedance value as the intermediate result 30.

[0065] The second actual value 19 of the impedance quantity 8, which in the example describes the ohmic resistance actually present at the respective defined charge state 21, 22 due to aging processes and similar effects, can then be determined by averaging between the intermediate results 29, 30 for the respective charge state 21, 22.

[0066] In step S7, the relationship between impedance variable 8 and state of charge 10 specified by energy storage information 9 is used to specify the respectively assigned impedance variable 8 as a reference value 23 of impedance variable 8 for the respective defined state of charge 21, 22. Reference value 23 may, in particular, correspond to a previous actual value of impedance variable 8, which was available, for example, immediately after the manufacture of energy storage device 3 or during a previous determination or adaptation of energy storage information 9.

[0067] In the example shown, it is now assumed that the ohmic resistance used in the example as impedance variable 8 changes at least approximately uniformly or by the same factor for different charge states 10 as the energy storage device 3 ages. Therefore, the correction factor 20 is determined in step S8 by dividing the reference value 23 by the second actual value 19. If, as already explained above, the scaled actual value 27 is then determined in step S10 by multiplying the first actual value 7 by the correction factor 20, for example, an increase in the ohmic resistance of the energy storage device 3 resulting from ageing of the energy storage device 3, which increases the first actual value 7, is essentially compensated for by the correction factor 20, as long as this was determined not too long ago or not too many charging cycles ago.

[0068] Since different reference values 23 result for the various defined states of charge 21, 22 in step S7, it is necessary to consider which of the defined states of charge 21, 22 actually exists when the change condition 14 is met. For this purpose, the preceding operation or the previously existing operating states of the energy storage device 3 are expediently taken into account.

[0069] Since charging characteristics of energy storage devices typically have steep charging voltage curves at very low and very high charge states 10, as is exemplified in Fig.3, the reference charge states 24, 25 there can be detected with good accuracy based on the charging voltage itself or its change over time, with aging of the energy storage device 3 typically leading to only minor deviations. If the presence of a respective one of the defined charge states 21, 22 is robustly detected by the trigger condition 14, then, for example, when charging starting from the reference charge state 24, it is clear that a first fulfillment of the trigger condition 14 corresponds to the achievement of the defined charge state 21 and the charge state 22 can only be achieved after further charging after the defined charge state 21 has been achieved. Since it is known whether charging or discharging is currently taking place, it can always be detected which of the defined charge states 21, 22 actually exists when the change condition 14 is fulfilled.

[0070] As already explained in detail in the general part, the robustness of the detection of the presence of one of the defined charge states 21, 22 or of the differentiation between the presence of different defined charge states can be further improved if, starting from the last detected reference charge state 24, 25 or defined charge state 21, 22, a change in the charging state of the energy storage device 3 is determined by integrating the charging current 13 in a manner known per se.

[0071] The example explained above assumes that the ohmic resistance is evaluated as an impedance variable 8 to determine the state of charge 10. Additionally or alternatively, imaginary parts of a complex impedance or an inductance and / or a capacitance of the energy storage device 3 can also be used to determine the state of charge 10. In this case, the energy storage information 9 can describe the relationship between the state of charge 10 and the respective impedance variable 8 used.

[0072] If the method explained above is to be used in this case to determine a suitable correction factor 20, a corresponding value, for example a capacitance, an inductance or the imaginary part of the impedance of the energy storage device 3, should also be determined as the second actual value 19 for the impedance value 8.

[0073] This can be achieved, for example, by superimposing an oscillating additional current with one or more frequency components on the charging current when the trigger condition 14 is met. By evaluating the phase position and / or amplitude of various frequency components of the resulting charging voltage 12, the aforementioned variables can be determined in a conventional manner. Further approaches and details for determining actual values of such impedance variables 8 have already been explained in the general section.

[0074] Instead of the scaling of the first actual value 7 of the impedance variable 8 used in the example, it would also be possible to leave this actual value 7 unchanged and instead scale the energy storage information 9 or the impedance variables 8 described by this and assigned to the individual charge states 10. For this purpose, in step S7, provisional energy storage information can initially be used instead of the specified energy storage information 9 in order to determine the respective reference value 23 for the impedance variable 8. In step S8, instead of determining the correction factor, the specified energy storage information 9 can then be specified. For this purpose, the impedance variable 8 specified by the provisional energy storage information for the respective charge state 10 can be multiplied by a scaling factor, which can be determined by dividing the second actual value 19 by the reference value 23.When using such a predetermined energy storage information 9, the scaling in step S10 can then be omitted.

[0075] As already explained in the general part of the description, the explained method can additionally or alternatively also be used to control the charging and / or discharging of an energy storage device (not shown) of the charging device 5, wherein for this purpose a determination device (not shown) can be integrated into the charging device 5, which implements the method. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2014 014 031 A1

[0004]

Claims

[1] Device (1) for charging and / or discharging an energy storage device (3) with a determination device (4) for determining a state of charge of the energy storage device (3), wherein the determination device (4) is designed to determine a first actual value (7) of an impedance variable (8) which describes a resistance and / or an impedance of the energy storage device (3) and to determine the state of charge (10) on the basis of the first actual value (7) and a predetermined energy storage information item (9), characterized by that the or a further detection device (4) of the device is designed to - repeatedly detecting a first voltage change (11) of a charging voltage (12) which drops across the energy storage device (3) while the energy storage device (3) is being charged or discharged by a charging current (13), - upon fulfillment of a triggering condition (14), the fulfillment of which depends on the last detected first voltage change (11), to change the charging current (13) and to detect a second voltage change (15-18) resulting from the change in the charging current (13), - to determine a second actual value (19) of the impedance quantity (8) as a function of the second voltage change (15-18), and - on the one hand, to determine a correction factor (20) on the basis of the second actual value (19), wherein the determination device (4) is in this case set up to additionally take the correction factor (20) into account when determining the state of charge (10), and / or on the other hand, to specify the predetermined energy storage information (9) as a function of the second actual value (19). [2] Device according to claim 1, characterized byin that the fulfillment of the triggering condition (14) indicates the presence of a defined state of charge (21, 22), wherein the predetermined energy storage information (9) or a preliminary energy storage information, on the basis of which the predetermined energy storage information (9) is to be predetermined as a function of the second actual value (19), assigns a reference value (23) of the impedance variable (8) to the defined state of charge (21, 22), wherein the or the further determination device (4) is set up to additionally take the reference value (23) into account when determining the correction factor (20) or when specifying the predetermined energy storage information (9). [3] Device according to claim 1 or 2, characterized byin that the or the further determination device (4) is configured to detect the presence of a reference charge state (24, 25) and / or the defined charge state (21, 22) and / or a respective one of the defined charge states (21, 22) and, starting from the reference charge state (24, 25) and / or the respective defined charge state (21, 22), to determine a change in charge by integrating the charging current (13), wherein the fulfillment of the triggering condition (14) and / or the selection of a defined charge state (21, 22) from a plurality of defined charge states (21, 22) for which the triggering condition (14) can be fulfilled additionally depends on the change in charge. [4] Device according to one of the preceding claims, characterized bythat the or the further determination device (4) is set up to change the charging current (13) when the triggering condition (14) is met in such a way that it is increased or decreased by a predetermined amount of change (26), and to determine the second actual value (23) as a function, on the one hand, of the difference between the charging voltage (12) before the change in the charging current (13) and the charging voltage (12) after the change in the charging current (13) and, on the other hand, of the predetermined amount of change (26). [5] Device according to one of the preceding claims, characterized by that the further investigative body (4) is set up to - to change the charging current (13) when the triggering condition (14) is fulfilled in such a way that its amount is reduced in a first change step (S3) and increased in a second change step (S5) or vice versa, - to determine as the second voltage change (15-18) both the first change in the charging voltage (13) by the first change step (S3) and the second change in the charging voltage (13) by the second change step (S5), and - to determine the second actual value (19) as a function of both the first and the second change in the charging voltage (13). [6] Device according to one of the preceding claims, characterized by in that the or the further determination device (4) is designed to detect a temporal profile of the charging voltage (12) resulting from the change in the charging current (13) and to determine the second actual value (19) by evaluating this temporal profile in such a way that it describes the imaginary part of a complex impedance and / or a capacitance and / or an inductance of the energy store (4). [7] Device according to claim 6, characterized bythat the or the further detection device (4) is designed to increase and decrease the charging current (13) several times alternately when the triggering condition (13) is fulfilled. [8] Device according to one of the preceding claims, characterized by that the energy storage device (3) is an energy storage device based on lithium iron phosphate or on sodium ions. [9] Device according to one of the preceding claims, characterized by that the device (1) is or comprises a motor vehicle (2) or a stationary charging device (5) for charging an energy storage device of a motor vehicle (2), wherein the motor vehicle (2) or the charging device (5) comprises the and / or the further detection device (4). [10] Method for determining a correction factor (20) and / or a predetermined energy storage information (9), which serves to determine a state of charge (10) of an energy storage device (3) on the basis of a first actual value (7) of an impedance variable (8) which describes a resistance and / or an impedance of the energy storage device (3), comprising the steps: - repeatedly detecting a first voltage change (11) of a charging voltage (12) which drops across the energy storage device (3) while the energy storage device (3) is being charged or discharged by a charging current (13), - changing the charging current (13) and detecting a second voltage change (15-18) resulting from the change in the charging current (13) when a triggering condition (14) is met, the fulfilment of which depends on the last detected first voltage change (11), - determining a second actual value (19) of the impedance quantity (8) as a function of the second voltage change (15-18), and - Determining the correction factor (20) on the basis of the second actual value (19) and / or specifying the predetermined energy storage information (9) as a function of the second actual value (20).

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