Patent Application
20190023145
The present disclosure is related to a control device for controlling charging of a rechargeable battery and also to a method of charging of a rechargeable battery.
Rechargeable batteries, also called secondary cells, have become increasingly important as energy storages, in particular for vehicles. Such vehicles may be hybrid vehicles comprising an internal combustion engine and one or more electric motors or purely electrically driven vehicles.
A suitable rechargeable battery for such a vehicle may be a solid-state bipolar battery or other, e.g. liquid type batteries, in particular a laminated Li-ion battery. The rechargeable battery may be realized by a single cell or it may include a set of preferably identical cells. In the latter case the battery is also called a battery pack.
The battery or the battery pack may further include a control device for controlling charging and/or discharging. The control device monitors state of charge (SOC) of the battery and it shall avoid the battery from operating outside its safe operating area. Such a battery or battery pack is also called smart battery/smart battery pack. It is also possible that the control device is provided by the vehicle.
One important aspect of charge control is to assure that any overcharging and/or over-discharging of the battery is avoided. For this purpose the battery voltage may be monitored, which is increasing during charging. In case the determined battery voltage exceeds a predetermined upper voltage limit, it is recognized by the control device that the battery is fully charged and charging is stopped.
However, during the lifetime of a battery the charging and discharging procedures may lead to a degradation of the laminated layers of the battery. In particular the laminated electrodes may be affected by the degradation. The degradation leads to increased resistance which in turn increases the measured voltage of the battery during charging.
As a result, when charging a battery with lamination degradation, the measured voltage reaches the predetermined upper voltage limit sooner, and the control device erroneously recognizes that the battery is fully charged. Although the battery is actually not yet fully charged (not SOC100%), charging is finished. This means that the available amount of energy decreases due to the degradation dispersion.
EP 1 458 047 A2 discloses a charge control system for preventing overcharge of single cell layers. For this purpose one of the positive and the negative electrode active material layer of the battery is made of a changeable electrode active material, and the other is made of an unchangeable electrode active material. The changeable electrode active material is an active material having a specific characteristic based on which the charging is controlled.
However, in the above technology only limited materials can be applied to the electrode layers of the battery. Moreover, the system may not be able to compensate a large degradation.
Currently, it remains desirable to provide a control device which provides a reliable charging control function and which is suitable for different battery types.
Therefore, according to embodiments of the present disclosure, a control device is provided for controlling charging of a rechargeable battery. The control device is configured to:
By providing such a configuration it is possible to control charging based on the determined voltage decrement or drop of the battery when the charging is stopped. Such a voltage drop is relatively high, in case the battery has already suffered from lamination degradation, as the degradation leads to a higher resistance and thus to a higher voltage of the battery during charging. In other words, if the voltage drop is higher than the predetermined threshold, it can be determined that the relatively high voltage of the battery during charging is due to lamination degradation and not due to an actually fully charged state of the battery. In this case the charging is continued.
The control device and the procedure performed by the control device are suitable for all types of solid-state bipolar batteries. However, the control device may also be applied to other battery types, like liquid type batteries, as e.g. Li-ion batteries.
The control device may further be configured to, when the determined voltage difference exceeds the predetermined threshold, increase the predetermined upper voltage limit by a predetermined voltage increment and restart charging of the battery, or restart charging of the battery for a limited time interval and re-determine the voltage difference after stopping charging.
In this way charging can be continued in a suitable extent by continually increasing the predetermined upper voltage limit or by continuing charging for one or more limited time periods. In case the predetermined upper voltage limit is increased by a predetermined voltage increment, a further charging cycle can be performed by restarting charging and stopping charging, when the determined voltage exceeds the incremented predetermined upper voltage limit. In case charging is continued for a limited time period, charging is stopped after that time period automatically and the voltage difference is again compared with the predetermined threshold. Accordingly, said charging for a limited time period also defines a charging cycle. In other words the procedure of the invention can be performed repeatedly in several cycles, until the battery is actually fully charged.
Preferably, the control device may be configured to set the upper voltage limit such that an overvoltage of the battery is avoided. In this regard it is noted that the predetermined upper voltage limit does normally not constitute the actually critical upper limit but is rather chosen such that a new battery without degradation is charged until the desired full charge state is reached. Therefore this predetermined upper voltage limit may be increased, e.g. by 10%, 30%, 50% or 100%, without causing any actually dangerous overvoltage.
The control device may further be configured to, when the determined voltage difference does not exceed the predetermined threshold, determine that the battery is fully charged and reset the predetermined threshold.
In other words, the control device may recognize based on the determined voltage difference, whether the battery is fully charged or charging has to be continued. As it will be described in more detail below, the predetermined threshold may be determined each time the battery is charged. Therefore the predetermined threshold may also be reset, when charging has been completed.
In particular, the control device may be configured to determine the threshold based on the state of charge of the battery before starting charging.
In other words the threshold may be determined before starting charging or when charging is started. The state of charge of the battery before charging is started may be more the lower limit of a predetermined allowed SOC range, e.g. 60%. The determined state of the charge (SOC) before starting charging may be considered when determining the threshold, as the SOC may have an influence on the determined voltage difference. The threshold namely depends on internal resistance of the battery. Also internal resistance depends on SOC of the battery. Therefore, when the SOC is low, it is preferable to increase the threshold. In other words, the lower the SOC is before starting charging, the more the threshold may be increased.
Furthermore the threshold may be determined additionally or alternatively based on a determined degradation of the battery.
The degradation of the battery may be determined based on a temperature/frequency distribution of the battery and a predetermined degradation rate of the battery.
The determination of the degradation of the battery may be based on the Arrhenius equation.
The temperature/frequency distribution of the battery may be determined by recording for each temperature of the battery how much time the battery had this temperature during its lifetime.
In other words, the temperature data of the battery may be collected during the life time of the battery, i.e. during its usage and the rests between usages. The temperature/frequency distribution may be established by accumulating for each temperature the battery had during its past life time, how long the battery had this temperature.
Preferably, the control device may comprise a voltage sensor for determining the voltage of the battery. This voltage sensor may also be used for determining the state of charge of the battery. Alternatively the control device may comprise a further voltage sensor for determining the state of charge of the battery.
The control device may comprise a temperature sensor for determining the temperature of the battery.
The disclosure further relates to a battery pack. The battery pack may comprise at least one battery, in particular a solid state bipolar battery, and a control device as described above.
The disclosure further relates to a battery charging system. Said battery charging system may comprise at least one battery, in particular a solid state bipolar battery, a charging device for the battery, and a control device as described above.
According to a further aspect the disclosure relates to a vehicle comprising an electric motor and a battery pack, as described above.
Alternatively the vehicle may comprise an electric motor, at least one battery, in particular a solid state bipolar battery, and in addition a control device, as described above.
Moreover the disclosure relates to a method of controlling charging of a rechargeable battery. The method comprises the steps of:
Preferably, when the determined voltage difference exceeds the predetermined threshold, the predetermined upper voltage limit is increased by a predetermined voltage increment and charging of the battery restarted, or charging of the battery is restarted for a limited time interval and after stopping charging the voltage difference is re-determined.
The upper voltage limit may be set such that an overvoltage of the battery is avoided.
When the determined voltage difference does not exceed the predetermined threshold, it is preferably determined that the battery is fully charged and the predetermined threshold may be reset.
The threshold may be determined based on the state of charge of the battery before starting charging.
The threshold may be determined based on a determined degradation of the battery.
The degradation of the battery may be determined based on a temperature/frequency distribution of the battery and a predetermined degradation rate of the battery.
The degradation of the battery may be determined based on the determined voltage difference.
The determination of the degradation of the battery may be based on the Arrhenius equation.
The temperature/frequency distribution of the battery may be determined by recording for each temperature of the battery how much time the battery had this temperature during its lifetime.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description, serve to explain the principles thereof.
Reference will now be made in detail to exemplary embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
The battery 2 is connected to a charging device 5 which is configured to charge the battery 2. For this purpose the charging device 5 may comprise an electric control circuit, as e.g. a power electronics circuit. The charging device may further comprise or be connected to a connector for external charging by an external power source. The connector may be e.g. a plug or a wireless connector system. In case the vehicle is a hybrid vehicle, the charging device may further be connected to the electrical generator of the internal combustion engine of the vehicle. Consequently, the battery 2 may be charged, when the internal combustion engine is operating and/or when the vehicle is connected to an external power source. Furthermore the battery 2 may be discharged, in order to operate the vehicle 1, in particular the electric motor 4. The battery 2 may further be discharged in a battery treatment and/or recovery procedure.
In order to control charging and discharging the vehicle 2 is provided with the control device 6 and sensors 7. For this purpose the control device 6 monitors the battery 2 via the sensors 7 and controls the charging device 5. The control device 6 and/or the sensors 7 may also be comprised by the battery 2. The control device may be an electronic control circuit (ECU). It may also comprise a data storage. It is also possible that the vehicle comprises a smart battery charging system with a smart battery and a smart charging device. In other words, both the battery and the vehicle may comprise each an ECU which operate together and form together the control device according to the invention. Furthermore the control device 6 may comprise or may be part of a battery management system.
The control device 6 may comprise an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), a combinational logic circuit, a memory that executes one or more software programs, and/or other suitable components that provide the described functionality of the control device 6.
The sensors 7 may comprise one or more temperature sensors 8 for measuring the temperature of the battery 2, an SOC (state of charge) sensor 9 for measuring the state of charge of the battery 2 and a voltage sensor 10 for measuring the voltage of the battery. The SOC sensor 9 may also be a voltage sensor, wherein the measured voltage is used to determine the SOC of the battery. In this case the SOC sensor may be the same sensor as the voltage sensor 10 or it may be an additional sensor. Of course, the SOC sensor 9 may also comprise other sensor types to determine the SOC of the battery, as it is well known in the art.
In step S11 the procedure is started. The start may be triggered by a determination of the control device that charging of the battery is necessary (e.g. due to a low SOC) and/or by the fact that charging becomes possible (e.g. due to operation of the internal combustion engine or due to a connection to an external electrical power source). Moreover in step S11 the threshold ΔVT may be determined. This determination procedure is described in detail in the following, in particular in context of
In step S12 charging of the battery is started.
In step S13 the voltage Vx of the battery is measured, preferably during charging. Hence, the voltage Vx is monitored, preferably continuously. It is then determined, whether the measured voltage Vx of the battery exceeds a predetermined upper voltage limit Vmax. If it does not, charging is continued. However, if the measured voltage Vx of the battery exceeds the predetermined upper voltage limit Vmax, the method continues with step S14. Accordingly, the voltage Vx of the battery continuously increases during charging and charging is stopped, when Vx exceeds Vmax.
Said upper voltage limit Vmax is preferably dependant on the battery type and is determined by pre-experiment. The control device may receive respective information from the battery, e.g. directly the value of Vmax of the battery or any ID of the battery. In the latter case the control device may look up in a data storage the battery specific value of Vmax based on the received ID. It is noted that Vmax and Vx are preferably absolute (i.e. positive) values.
In step S14 charging is stopped at least for a limited time, as e.g. maximally 0.02 s, 0.05 s, 0.1 s or 0.2 s. Preferably also discharging may be stopped for this time. In a conventional charging control procedure charging would be finally stopped in step S14, even if the battery was actually not fully charged.
In step S15 the voltage Vx of the battery is measured again, however now in the state that charging (and eventually even discharging) is stopped due to the charging interruption started in S14. Then the voltage difference ΔVx between the predetermined upper voltage limit and the voltage Vx measured in step S15 after stopping charging is determined. Since the voltage Vx measured in step S15 is regularly lower than that one measured during charging in step S13, ΔVx is a voltage decrement.
Alternatively the voltage difference ΔVx may also be the difference between the voltage Vx measured in step S13 directly before stopping charging and the voltage Vx measured in step S15 after stopping charging.
This voltage decrement is at least partially due to a lamination degradation of the battery, as the degradation leads to a higher resistance and thus to a higher voltage of the battery during charging. It can be consequently determined that, if the voltage decrement is relatively high, there is lamination degradation which has caused the measured voltage during charging in step S13 to exceed the upper voltage limit Vmax.
In step S16 it is determined, whether the determined voltage difference ΔVx exceeds the predetermined threshold ΔVT. In case it does not, it is determined that charging is completed and hence charging is stopped finally in step S18 However, in case ΔVx exceeds ΔVT, The procedure continues with step S17. It is noted that ΔVx and ΔVT are preferably absolute (i.e. positive) values.
In step S17 a new value is set as upper voltage limit Vmax. In particular, the upper voltage limit Vmax may be increased by a predetermined increment, e.g. by 0.1V, 0.2V, 0.5V, 1V or 2V. Then the procedure returns to step S12 and charging is restarted. Preferably, the upper voltage limit Vmax is reset to its initial value, when charging is stopped finally in step S18.
In this way the cycle of the control procedure from step S12 to S17 can be repeated several times, in particular as long as ΔVx exceeds ΔVT. In other words, the charging procedure is controlled primarily based on the comparison of ΔVx with ΔVT. The comparison of Vx with Vmax is merely used to trigger the comparison of ΔVx with ΔVT. With each cycle Vmax may be increased, in order to allow a higher voltage Vx during charging. In this way the SOC of the battery will be increased and ΔVx regularly becomes smaller. When the battery just starts charging in step S11, ΔVx is usually higher than ΔVT if the battery has already suffered from lamination degradation. But in case that the voltage Vx is increased (and therefore SOC is increased), Vx becomes a smaller value because ΔVx depends on the internal resistance of the battery. Also internal resistance depends on SOC, i.e. when SOC is increasing, the internal resistance is decreasing. Accordingly, with increasing SOC, ΔVx regularly decreases until it does not exceed ΔVT any more. Then charging is stopped finally in step S18.
Alternatively to a new setting of Vmax in step S17 the procedure may also directly restart charging for a predetermined time interval, and subsequently move to step S14. In other words, if ΔVx exceeds ΔVT in step S16, the battery may be charged for a limited predetermined time interval, as e.g. 5 s, 10 s or 30 s, and charging may then be stopped after this time interval in step S14, where the procedure continues with steps S15 and S16.
The procedure of
In step S22 SOC (state of charge) data of the battery are determined. For this purpose the SOC sensor 9 may be used, as described above.
In step S23 the threshold ΔVT is determined based on the determined SOC and the currently determined degradation αx of the battery. The determination of αx is described in detail below in context of
In step S25 it is monitored whether charging has been stopped finally, what corresponds to step S18 in
In step S32 temperature data of battery are obtained. For this purpose the temperature sensor 8 may be used. However, these data may include not only the current temperature of the battery, but also historic temperature data since the last time the procedure of
In step S33 the temperature frequency distribution Tx is established or, in case a temperature frequency distribution Tx already exists, it is updated. For this purpose the collected temperature data obtained in step S32 are accumulated, wherein the accumulated time for each measured temperature is expressed as its inverse, i.e. as frequency. The temperature frequency distribution Tx is described in more detail below in context of
In step S34 the degradation αx of the battery is determined based on the temperature frequency distribution Tx and the predetermined battery-type specific degradation rate β. This determination, i.e. calculation, is described in the following with reference to
Basically the calculation of the degradation αx is based on the Arrhenius equation, as generally known in the art. The degradation αx is calculated by
wherein:
t=time
c=ln(A)
b=−(E/R)
The current degradation αx is thereby an accumulated value, i.e. the currently calculated degradation and the sum of all formerly calculated degradations, as e.g.:
αx1=α1+α2+α3
with:
The values for the temperature T and for the time t can thereby be derived from the temperature frequency distribution Tx as shown in
The degradation rate β is calculated based on the equation:
wherein:
k=predetermined reaction rate constant (or rate constant)
A=constant
Ea=activation energy
R=gas constant
The parameters k, A, Ea and R are known by pre-experiment of the specific battery type of the used battery or are generally known parameters.
When k⇒β:
Accordingly, the parameters b and c for the calculation of degradation αx can be determined by:
b=−(E/R)
c=ln(A)
The resulting diagram of the degradation rate β is shown in
The threshold ΔVT is preferably mapped to the determined degradation αx in a look-up map, i.e.:
αx1⇒ΔVT1
αx2⇒ΔVT2
αx3⇒ΔVT3
etc.
This relation between ΔVT and ax is preferably determined in a pre-experiment and is specific for the battery-type of the used battery. The look-up map may be stored in a data storage of the control-device or of the battery (in case of a smart battery).
Preferably also the determined SOC of the battery is considered when determining ΔVT. The control device may also have information regarding the relationship between SOC and ΔVT such as in the above-mentioned look-up map of ax. For example in said look-up map an additional column for SOC values may be added.
The continuous line thereby represents a battery without any degradation, e.g. a new battery. The measured voltage Vx of such a battery reaches during charging the upper voltage limit Vmax, when the SOC reaches 100%. As an effect, it is correctly determined that charging is completed and charging is stopped.
The dashed line represents a battery with lamination degradation, e.g. a used battery. The measured voltage Vx of such a battery increases more strongly during charging due to the higher resistance caused by the lamination degradation. The voltage Vx therefore reaches already the upper voltage limit Vmax, when the SOC is about 80%. As an effect, it is erroneously determined that charging is completed and charging is stopped. This can be avoided by the invention as described in context of
However, before stopping charging completely, it is determined whether the voltage difference ΔVx exceeds a predetermined threshold ΔVT, as described above in context of step S16 of
Throughout the disclosure, including the claims, the term “comprising a” should be understood as being synonymous with “comprising at least one” unless otherwise stated. In addition, any range set forth in the description, including the claims should be understood as including its end value(s) unless otherwise stated. Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms “substantially” and/or “approximately” and/or “generally” should be understood to mean falling within such accepted tolerances.
Where any standards of national, international, or other standards body are referenced (e.g., ISO, etc.), such references are intended to refer to the standard as defined by the national or international standards body as of the priority date of the present specification. Any subsequent substantive changes to such standards are not intended to modify the scope and/or definitions of the present disclosure and/or claims.
Although the present disclosure herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure.
It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2016/051987 | 1/29/2016 | WO | 00 |
