METHOD AND ARRANGEMENT FOR DETERMINING A VALUE OF THE STATE OF ENERGY OF A BATTERY IN A VEHICLE

Abstract

Disclosed is a method for determining a value of the state of energy of a rechargeable battery in a vehicle, the battery being connected to an electric consumer; the method including: determining the state of charge as a measure of the present capacity of the battery; and determining the state of energy as an indication of at least the remaining charge and discharge energy of the battery. The disclosed method further includes: calculating and determining the value of the state of energy based on at least one parameter which is related to the operation of the electric consumer and where the at least one parameter varies depending on a mode for operating the vehicle or electric consumer during charging or discharging of the battery. Also disclosed is an arrangement for determining a value of the state of energy of a rechargeable battery in a vehicle.

Claims

1. Method for determining a value of the state of energy (SOE) of a rechargeable battery (5) in a vehicle (1; 1), said battery (5) being connected to an electric consumer (4); said method comprising: determining the state of charge (SOC) as a measure of the present capacity of said battery (5); and determining said state of energy (SOE) as an indication of at least the remaining charge and discharge energy of said battery (5); wherein said method comprises: calculating and determining said value of the state of energy (SOE) based on at least one parameter (I, R, SOCmax, SOCmin) which is related to the operation of said electric consumer (4) and where said at least one parameter (I, R, SOCmax, SOCmin) varies depending on a mode for operating said vehicle (1; 1) or electric consumer (4) during charging or discharging of said battery (5).

2. Method according to claim 1, further comprising: determining the state of energy (SOE) based on said state of charge (SOC) of said battery (5) as calculated between a lowest allowed state of charge (SOCmin) and a highest allowed state of charge (SOCmax) for a given battery current (I).

3. Method according to claim 2, further comprising: determining a state of energy (SOE) for charging said battery (5), based on said state of charge (SOC) of said battery (5), as calculated between the present state of charge (SOC*) and a highest allowed state of charge (SOCmax) for a given battery current (I), said highest allowed state of charge (SOCmax) being dependent on said mode.

4. Method according to claim 2, further comprising: determining a state of energy (SOE) for discharging said battery (5), based on said state of charge (SOC) of said battery (5), as calculated between a lowest allowed state of charge (SOCmin) and the present state of charge (SOC*) for a given battery current (I), said lowest allowed state of charge (SOCmin) being dependent on said mode.

5. Method according to claim 1, further comprising: determining said state of energy (SOE) depending on at least one of the following battery parameters: the cell capacity; the present state of charge (SOC); the open circuit voltage (OCV); resistive and non-resistive losses; the voltage drop (RI); and the temperature (T); wherein at least one of said battery parameters are dependent on said mode.

6. Method according to claim 1, further comprising: determining a maximum remaining distance for the vehicle (1; 1) to travel without charging said battery (5) based on said state of energy (SOE).

7. Method according to claim 1, further comprising: determining a time period for fully charging said battery (5) based on said state of energy (SOE).

8. Method according to claim 1, further comprising: determining a measure of the capacity of said battery (5) of supplying electric power to auxiliary equipment (11) based on said state of energy (SOE).

9. An arrangement in a vehicle (1; 1) for determining a value of the state of energy (SOE) of a rechargeable battery (5) connected to an electric consumer (4) in said vehicle (1; 1′); said arrangement comprising a control unit (6) being connected to said battery (5) and configured for determining the state of charge (SOC) as a measure of the present capacity of said battery (5) and for determining said state of energy (SOE) as an indication of at least the remaining charge and discharge energy of said battery (5); wherein said control unit (3) is further configured for calculating and determining said value of the state of energy (SOE) based on at least one parameter (I, R, SOCmax, SOCmin) which is related to the operation of said electric consumer (4) and where said at least one parameter (I, R, SOCmax, SOCmin) varies depending on a mode for operating said vehicle (1; 1) or electric consumer (4) during charging or discharging of said battery (5).

10. Arrangement according to claim 9, wherein said battery (5) is constituted by a traction battery.

11. Arrangement according to claim 9, wherein the electric consumer (4) is an electric machine (3) for propulsion of said vehicle (1).

12. Vehicle (1) of the electric vehicle type or hybrid electric vehicle type, comprising an electric machine (4) and further comprising an arrangement according to claim 9.

13. (canceled)

14. A non-transitory computer readable medium on which is stored a computer program comprising program code which, when executed by a computer, performs the steps of claim 1.

15. Method according to claim 3, further comprising: determining a state of energy (SOE) for discharging said battery (5), based on said state of charge (SOC) of said battery (5), as calculated between a lowest allowed state of charge (SOCmin) and the present state of charge (SOC*) for a given battery current (I), said lowest allowed state of charge (SOCmin) being dependent on said mode.

16. Method according to claim 2, further comprising: determining said state of energy (SOE) depending on at least one of the following battery parameters: the cell capacity; the present state of charge (SOC); the open circuit voltage (OCV); resistive and non-resistive losses; the voltage drop (RI); and the temperature (T); wherein at least one of said battery parameters are dependent on said mode.

17. Method according to claim 3, further comprising: determining said state of energy (SOE) depending on at least one of the following battery parameters: the cell capacity; the present state of charge (SOC); the open circuit voltage (OCV); resistive and non-resistive losses; the voltage drop (RI); and the temperature (T); wherein at least one of said battery parameters are dependent on said mode.

18. Method according to claim 4, further comprising: determining said state of energy (SOE) depending on at least one of the following battery parameters: the cell capacity; the present state of charge (SOC); the open circuit voltage (OCV); resistive and non-resistive losses; the voltage drop (RI); and the temperature (T); wherein at least one of said battery parameters are dependent on said mode.

19. Method according to claim 2, further comprising: determining a maximum remaining distance for the vehicle (1; 1) to travel without charging said battery (5) based on said state of energy (SOE).

20. Method according to claim 3, further comprising: determining a maximum remaining distance for the vehicle (1; 1) to travel without charging said battery (5) based on said state of energy (SOE).

21. Method according to claim 4, further comprising: determining a maximum remaining distance for the vehicle (1; 1) to travel without charging said battery (5) based on said state of energy (SOE).

Description

BRIEF DESCRIPTION OF DRAWINGS

[0023] The invention will now be described with reference to an embodiment and with reference to the appended drawings, wherein:

[0024] FIG. 1 shows a schematic view of an arrangement for charging an electric consumer in its most basic form;

[0025] FIGS. 2a, 2b and 2c are diagrams showing the principles of determining the state of energy (SOE) according to the invention; and

[0026] FIG. 3 is a schematic view of a further embodiment of the invention; and

[0027] FIG. 4 is a schematic flow chart describing the principles of the invention.

PREFERRED EMBODIMENT

[0028] Different aspects of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings. The method and apparatus disclosed herein can, however, be realized in many different forms and should not be construed as being limited to the aspects set forth herein.

[0029] With reference initially to FIG. 1, there is shown a simplified diagram of a vehicle 1 having a front axle 2 and a rear axle 3. The vehicle 1 is of the type which is operated by means of an electric consumer in the form of an electric machine 4. According to the embodiment, the electric machine 4 is configured so as to drive the rear axle 3. However, the invention is not limited to this embodiment only but can be applied to other types of configurations wherein an electric machine can be arranged to drive at least one vehicle axle or where one or more electric machines can be arranged to drive one or more individual wheels.

[0030] As will be discussed below, the electric machine 4 can be combined with an internal combustion engine so as to operate the vehicle 1 with either electric drive or with the combustion engine, or a combination of both.

[0031] Furthermore, the electric machine 4 is supplied with electric energy from an energy storage system in the form of a battery unit 5, which consequently is a traction battery for the electric machine 4 and which comprises a plurality of battery cells (not shown in detail in FIG. 1). According to known technology, the battery cells are connected in series in order to provide an output DC voltage with a desired voltage level suitable for driving the electric machine 4. Suitably, the battery cells are of lithium-ion type, but other types may also be used.

[0032] As shown in FIG. 1, the battery 5 and the electric machine 4 are connected to each other via a power control unit 6. Also, the battery 5 can be charged via an external charger unit 7 which is an external electric power supply to which the battery 5 can be connected when it is suitable to charge the battery 5. It can be noted that according to an aspect, the vehicle 1 is configured for regenerative braking, allowing charging of the battery 5 during braking of the vehicle 1. The principles of regenerative braking are previously known as such, and for this reason they are not described here.

[0033] As mentioned above, the state of energy (SOE) of the battery 5 provides information about the remaining charge energy and discharge energy at the present state of charge (SOC) of the battery, as well as the total energy of the battery. This principle is described in FIG. 2a, which is a diagram showing how the SOC varies with the voltage U of the battery 5. It should be noted that the SOC generally corresponds to the level of charge Q of the battery 5 and constitutes a measure of the present capacity of the battery 5 in relation to a nominal capacity of the battery 5.

[0034] With reference to FIG. 2a, the state of energy (SOE) of the battery 5 can be determined as a measure of the remaining charge and discharge energy of the battery 5, i.e. the area under the curve representing the relationship between the battery voltage U and the SOC. The value of the SOE—as determined when the battery 5 has a certain SOC—varies depending on certain parameters, such as for example the resistance R of the battery 5 and also the current I which is applied to the battery 5 (during charging) or, alternatively, which is drawn from the battery 5 (during discharging). The SOE also varies depending on the highest allowed state of charge (SOCmax) and the lowest allowed state of charge (SOCmin) of the battery 5.

[0035] In this regard, SOCmax corresponds to the highest allowed state of charge of the battery 5 wherein no further charging of the battery 5 is allowed, whereas SOCmin corresponds to the lowest allowed state of charge of the battery 5 wherein the battery 5 must be charged in order to allow operation of the electric machine 4. According to the embodiment, the state of energy (SOE) of the battery 5 is determined by means of the power control unit 6 (see FIG. 1).

[0036] With reference to FIG. 2a, it should be noted that the remaining charge energy (i.e. until the battery 5 is fully charged) can be determined from the area under the SOC-curve as determined from the current SOC value (indicated as “SOC*” in FIG. 2a) and to the SOCmax value. This area is indicated by a pattern of broken lines in FIG. 2a. In a corresponding manner, the remaining discharge energy (i.e. remaining until a battery is discharged so much that it reaches the SOCmin value) can be determined as the area under the SOC-curve as regarded from the SOC* value and to the SOCmin value. This area is indicated by a pattern of small triangles in FIG. 2a.

[0037] An important principle of this disclosure is that one or more parameters which can be used to determine the SOE, such as the battery resistance R and current I, and the SOCmin and SOCmax values, will vary depending on a mode of the vehicle 1, i.e. depending on the present operating conditions of the vehicle 1 and the battery 5.

[0038] The SOE determines how much energy there is left to a fully charged battery and to a completely discharged battery, i.e. how much energy there is left to the SOCmax and to the SOCmin for a certain charge current. This energy is found by calculating the area under the SOC curve. Also, the SOCmax and SOCmin values can be dependent on the vehicle mode. This means that the SOCmax and SOCmin values, as well as the charge/discharge current, are input parameters to the SOE calculation. As a result, the present vehicle mode is an input parameter to the SOE calculation.

[0039] The term “vehicle mode” is used to indicate a mode for operating the vehicle 1 or battery 5 during charging or discharging of the battery 5. According to a first example, a first vehicle mode can be a situation in which the battery 5 is charged with an external charger unit 7 supplying a very high power during a short time, which means that the SOCmax will be lower than in a second vehicle mode in which the battery 5 is charged with a relatively low power during a longer time. In the second mode, the SOCmax will be higher than in the first mode.

[0040] According to further example, a vehicle mode can be a situation in which the battery 5 is used for supplying power to the electric machine 4 (while discharging the battery 5), wherein the discharge current is relatively high for a vehicle driving at a relatively high speed, and relatively low for a vehicle driving at a relatively low speed. Furthermore, the discharge current can be expected to be higher for a vehicle having a relatively high weight as compared with a corresponding discharge current for a vehicle having a relatively low weight.

[0041] Generally, a specific vehicle mode can be a condition involving a relatively high battery current, whereas a further vehicle mode can be a condition involving a relatively low battery current.

[0042] As further examples, the term “vehicle mode” can also be used to describe situations in which external information such as weather information or navigational information (suitably according to the GPS standard) is used to influence the magnitude of the current, resistance or SOCmin and SOCmax values.

[0043] Furthermore, the “vehicle mode” can also be used in order to calculate the nominal energy of the battery. This is obtained by setting the current to 0 A, setting the SOCmax parameter to 100% and setting the SOCmin parameter to 0%. It is also possible to calculate the nominal energy corresponding to another SOC window than 0%-100%.

[0044] Furthermore, certain other parameters also affect the calculation of the SOE parameter, such as the following parameters of the battery 5: [0045] the cell capacity (Q(Ah)); [0046] the present state of charge (SOC); [0047] the open circuit voltage (OCV); [0048] the resistive and non-resistive losses; [0049] the voltage drop (RI); and [0050] the present temperature (T).

[0051] The term “present temperature” as mentioned above may refer not only to the present temperature but also to an expected temperature during an upcoming cycle. As a further alternative, the algorithm may use a nominal temperature, i.e. disregarding the specific present temperature, for example during calculation of the nominal energy of the battery 5.

[0052] At least the resistance and the voltage drop of the battery 5 are dependent on the vehicle mode. For this reason too, the calculation of the state of energy is dependent on the present vehicle mode.

[0053] In summary, the state of energy (SOE) can be calculated and determined based on at least one parameter which relates to the operation of the vehicle 1 or the battery 5 and where said parameter varies depending on present vehicle mode during charging or discharging of said battery 5. Different modes can consequently be used to predict parameters such as the applied or withdrawn battery current and the SOCmax and SOCmin in order to optimize the calculation of the SOE.

[0054] In this manner, it can be determined how much energy there is needed (during charging) to a fully charged battery and how much energy there is available (during discharging) to a completely discharged battery. This makes it possible to calculate a remaining travelling distance and also makes it possible to calculate the time it will take to completely recharge the battery 5. It will be also be possible to determine the total amount of energy between SOCmin and SOCmax.

[0055] With reference to FIG. 2b, there is shown a situation which corresponds to charging of the battery 5. The energy which is required in order to charge the battery to a capacity corresponding to SOCmax is indicated by means of a number of broken lines. This particular situation takes into account a particular voltage drop (i.e. R*I, where R is the resistance over the battery 5 and I is the battery current). This means that the voltage over the battery 5 corresponds to the sum of the open circuit voltage and the voltage drop, i.e.

U=OCV+R*I

[0056] The magnitude of this voltage drop can be expected to depend on the vehicle mode, i.e. the present operation conditions of the vehicle 1 and the battery 5. Consequently, by adapting the calculation of the SOE parameter to the current vehicle mode, a more accurate estimation of the SOE can be obtained as compared with the case in which only the relationship between the battery voltage and the SOC parameter is used to determine the SOE.

[0057] In a corresponding manner, FIG. 2c shows a situation corresponding to discharging of the battery 5, which can occur for example while the battery 5 is used to operate the electric machine 4. The energy which is used during this discharging of the battery 5 to a capacity corresponding to SOCmin is indicated as an area filled with a pattern of small triangles. This particular situation too takes into account a particular voltage drop (i.e. R*I, where R is the resistance over the battery 5 and I is the battery current) which depends on the vehicle mode, i.e. the current operation conditions of the vehicle 1 and the battery 5. Consequently, in this situation too, the SOE parameter can be determined in a very accurate manner.

[0058] FIG. 3 shows a schematic drawing of a further embodiment which is an alternative to the embodiment shown in FIG. 1. The features in FIG. 1 which correspond to similar components in the embodiment in FIG. 3 are indicated with the same reference numerals. Accordingly, a vehicle 1′ comprises a front axle 2 and a rear axle 3, wherein an electric machine 4 is configured for driving the rear axle 3. A battery unit 5 is connected to the electric machine 4 via a power control unit 6. Furthermore, an external charger unit 7 can be connected to the battery 5 for charging thereof.

[0059] Furthermore, the vehicle 1′ shown in FIG. 3 comprises an internal combustion engine 8 which is arranged for driving the front axle 2 via a transmission 9. The internal combustion engine 8 is also associated with a generator 10. The vehicle 1′ is of the plug-in hybrid type in which the combustion engine 8 can be used during certain operating conditions and the electric machine 4 can be used during certain other operating conditions. During operation of the combustion engine 8, the battery 5 is charged via the generator 10. The principles for combined operation of a combustion engine and an electric machine in a hybrid vehicle are generally known, and for this reason not described in greater detail here.

[0060] Also, further electric consumers may be used in the vehicle 1′, for example in the form of auxiliary electric consumers 11 such as pumps, actuators and other electric devices. Such auxiliary electric consumers 11 are also supplied with electric power from the battery 5. According to the embodiment of FIG. 3, the electric machine 4 drives the rear axle 3 and the internal combustion engine 2 drives the front axle 2, but other alternatives for driving the axles 2, 3 are possible within the scope of the invention, for example that both the combustion engine and electric motor drive the rear axle.

[0061] During certain modes of operation of the vehicle 1′, it may be suitable to use only the electric machine 3 for propulsion of the vehicle 1′. This means that the battery 5 will deliver the required power to the electric machine 4, which in turn drives the rear axle 3. During other modes of operation of the vehicle 1′, for example when the state of charge of the battery 5 is determined as not being sufficient for operating the vehicle 1′ by means of the electric machine 4, the internal combustion engine 8 is connected, via the transmission 9, to the front axle 2. The manner in which an electric machine and an internal combustion engine can be used for operating a vehicle is generally previously known and for this reason, it is not described in any greater detail here.

[0062] FIG. 4 is a flow chart showing the principles of the invention, which shows one example of a vehicle mode, more precisely a situation involving normal operation of the electric machine 4 by means of the battery 5. This means that the battery 5 is discharged during such a phase (see step 12 in FIG. 4). During this phase, the battery current I and the resistance R are continuously measured (step 13). Also, during this phase, the SOCmax and SOCmin values are determined. These values depend on the present vehicle mode, as explained above.

[0063] Furthermore, the available energy in the battery 5 is determined based on at least the current I, the resistance R and the SOCmax and SOCmin (step 14). Finally, a measure of the state of energy, for example in the form of the available energy until the battery 5 reaches the SOCmin value, can be displayed to the driver of the vehicle (not shown) in the form of available power expressed in kW, or can be displayed to the driver as a remaining distance which can be travelled until the battery 5 needs recharging (step 15). As a further alternative, a measure of the time period which is required in order to fully charge the battery 5 could be displayed.

[0064] The invention is not limited to the embodiments described above, but can be varied within the scope of the subsequent claims. For example, the invention can be used for any type of vehicle having a chargeable energy storage system which is configured for operating an electric consumer such as an electric machine and in which there is a desire to monitor the available energy of the energy storage system.

[0065] Also, the invention can be used for virtually any type of vehicle which is operated by means of at least an electric machine. For example, the invention can be used for a hybrid vehicle, such as a plug-in hybrid vehicle, or a full electric vehicle which is operated by means of an electric machine only. Information related to the SOE can be displayed to a driver of a vehicle, in order to present information as to the range, i.e. the highest allowed distance which can be travelled with the vehicle, or other relevant information regarding the status of the battery.