Method for operating an electrical energy storage device

Abstract

The invention relates to a method for operating an electrical energy store, wherein a discharge process (L1, L2, L3, L4) is carried out, in which the electrical energy store is discharged with a determined discharge current; energy (E1, E2, E3, E4) extracted from the electrical energy store during the discharge process (L1, L2, L3, L4) is acquired; the acquired, extracted energy (E1, E2, E3, E4) is compared with a limit value (G1, G2, G3, G4); and a message is generated if the acquired, extracted energy (E1, E2, E3, E4) is less than the limit value (G1, G2, G3, G4).

Description

Technical Field

[0001] The invention relates to a method for operating an electrical energy store. The method according to the invention is used in particular for diagnosing an electrical energy store which in particular comprises a hybrid supercapacitor and which is used in a motor vehicle. Prior art

[0002] Motor vehicles have electrical energy storage devices. In motor vehicles with internal combustion engines, the electrical energy storage devices are used in particular as starter batteries and for operating electromechanical brake systems. Conventional lead-acid batteries or lead-acid batteries and also lithium-ion batteries are used as electrical energy storage devices, for example. The battery system in a motor vehicle is designed in such a way that it meets the requirements of the vehicle manufacturers regarding the usable energy and the power that can be drawn.

[0003] In addition to the generally known lithium-ion batteries (LIBs), electrochemical capacitors, also called supercapacitors (SCs), play an increasingly important role. Supercapacitors that are already available on the market are used not only for mobile applications, but also for stationary systems. Electrochemical energy storage devices are characterized by their energy and power density. In general, supercapacitors have a higher power density and a lower energy density than lithium-ion batteries. Therefore, lithium-ion batteries are preferred for energy-intensive applications, and supercapacitors are preferred for power-intensive applications.

[0004] Supercapacitors are generally divided into "electric double layer capacitors" (EDLC), "pseudocapacitors" and hybrid supercapacitors (HSC). "Electric double layer capacitors" and "pseudocapacitors" have a relatively high power density, but a relatively low energy density. Hybrid supercapacitors, on the other hand, have a relatively high power density and a relatively high energy density. Hybrid supercapacitors therefore have the properties of lithium-ion batteries and supercapacitors.

[0005] In particular, when operating an electromechanical brake system, hybrid supercapacitors can be used advantageously as additional electrical energy storage. When the onboard electrical system of the motor vehicle stops functioning, sufficient energy is still stored in the hybrid supercapacitor to perform at least one braking process of the motor vehicle. Hybrid supercapacitors have a limited service life, which depends on various parameters. An exact prediction of the service life is difficult. However, for safety-related applications, it is necessary to predict the stoppage of the energy storage and to replace it in good time.

[0006] A method for diagnosing a battery is known from US 2014 / 0129163 A1, whereby the state of the battery can be determined. In this case, information about environmental conditions during battery operation and information about operating parameters during battery operation are detected. The state of the battery is determined from the detected information and a state model.

[0007] US 2013 / 310565 A1 discloses a device and a method for determining the state of a battery cell, wherein in particular the power available in the battery cell and the energy of the battery cell are recorded and shown in a diagram. Summary of the invention

[0008] A method is proposed for operating an electrical energy store which is used, for example, for operating an electromechanical brake system in a motor vehicle, in particular after the rest of the onboard electrical system of the motor vehicle has been shut down.

[0009] According to the invention, a discharging process is carried out in which the electrical energy storage device is discharged with a defined discharge current. Such a controlled discharging process can be carried out, for example, after each motor vehicle stop or after each motor vehicle engine shutdown.

[0010] During the discharge process, energy is drawn from the electrical energy store, which corresponds to energy that is available for operating an electromechanical brake system of the motor vehicle after the rest of the onboard electrical system of the motor vehicle has come to a standstill.

[0011] The energy thus obtained and drawn from the electrical energy store is then compared with a limit value which corresponds, for example, to the energy required to operate an electromechanical brake system of the motor vehicle after the rest of the onboard electrical system of the motor vehicle has come to a standstill.

[0012] If the energy obtained and drawn from the energy storage device is less than a limit value, a corresponding notification is generated, for example, an optical and / or acoustic indication via the infotainment system of the motor vehicle, via a warning light and / or via an external third unit (e.g., a smartphone), and is used to inform the driver.

[0013] If the energy drawn from the energy storage device is less than the limit value, the energy storage device no longer has sufficient energy to operate the electromechanical brake system after the rest of the onboard electrical system of the motor vehicle has stopped functioning. In this case, it can be assumed that the energy storage device has stopped functioning soon and that a replacement should be carried out promptly in order to ensure continued safe operation of the motor vehicle.

[0014] The service life of an electrical energy store depends, for example, on the operating temperature, the state of charge during regular use, and the voltage level. However, the regular charging and discharging rate and the number of charge-discharge cycles also have an influence on the service life.

[0015] According to an advantageous embodiment of the invention, the discharge current is kept constant during the discharge process. It has been shown that the operation of an electromechanical brake system of a motor vehicle can be simulated relatively well with a constant discharge current. Furthermore, the computational effort for determining the energy drawn from the electrical energy storage device is simplified if the discharge current is kept constant during the discharge process.

[0016] According to an advantageous development of the invention, for example, after the engine of the motor vehicle has been switched off and before the engine of the motor vehicle has been restarted, a plurality of discharging processes of the electrical energy storage device are carried out in close temporal succession. In this case, after the previously carried out discharging process, the electrical energy storage device is charged again, and a further discharging process is carried out in which the electrical energy storage device is again discharged with a certain discharging current.

[0017] In this case, the energy drawn from the electrical energy store during the further discharging process is detected and compared with a limit value. If the energy drawn from the electrical energy store is less than the limit value, a corresponding message is also generated. The discharge current during the further discharging process is different from the discharge current during the previously performed discharging process.

[0018] Advantageously, during the discharge process a time period is measured, during which the electrical energy store is discharged. The energy drawn from the electrical energy store during the discharge process is then derived from the determined discharge current and the measured time period. For the energy drawn from the electrical energy store:

[0019] ΔE=UxIxΔt [Wh]

[0020] According to a preferred embodiment of the invention, the power generated by the electrical energy store during the discharge process is also detected. The energy drawn from the electrical energy store during the discharge process and the power generated by the electrical energy store during the discharge process can advantageously be represented in a Ragone diagram. From the Ragone diagram, the remaining service life of the electrical energy store can be read and, if necessary, a near-future shutdown of the electrical energy store can therefore be predicted.

[0021] For this purpose, the voltage present at the electrical energy store is preferably measured during the discharge process, and the power generated by the electrical energy store during the discharge process is determined from the determined discharge current and the measured voltage. For the power generated by the electrical energy store, the following applies:

[0022] P=U×I [W]

[0023] In addition, the power density of the electrical energy store can be determined from the power generated by the electrical energy store during the discharge process and the weight of the electrical energy store. For the power density of the electrical energy store, the following applies:

[0024] Power density = P[W] / m[kg]

[0025] The energy density of the electrical energy store can also be determined from the energy extracted from the electrical energy store during the discharge process and the weight of the electrical energy store. For the energy density of the electrical energy store:

[0026] Energy density = E[Wh] / m[kg]

[0027] The energy density of the energy storage device and the power density of the energy storage device can also be advantageously shown in a Lagung diagram. From this Lagung diagram, the remaining service life of the energy storage device can also be read and, if necessary, the near future shutdown of the energy storage device can therefore be predicted.

[0028] The method according to the invention can be used particularly advantageously if the electrical energy store comprises at least one hybrid supercapacitor.

[0029] The method according to the invention is advantageously used in a motor vehicle, in particular a motor vehicle having an internal combustion engine.

[0030] Advantages of the present invention:

[0031] The method according to the invention enables a relatively accurate prediction of the remaining service life of the electric energy storage device and of its immediate deactivation. Thus, the electric energy storage device can be replaced in good time when it no longer has enough energy to operate the electromechanical brake system after the rest of the onboard power supply of the motor vehicle has stopped operating. The discharge process can advantageously be carried out when the motor vehicle is stationary or when the engine of the motor vehicle is switched off. The discharge process can therefore be carried out at the following time: when the electromechanical brake system is no longer required. The method according to the invention can also be carried out relatively simply here. No high computing power is required to carry out the method according to the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Embodiments of the present invention are explained in more detail with reference to the drawings and the following description.

[0033] The accompanying drawings show:

[0034] Figure 1 A schematic representation of an onboard electrical system of a motor vehicle and

[0035] Figure 2 Exemplary Ragon diagram for a number of discharge processes of an electrical energy store. DETAILED DESCRIPTION

[0036] In the following description of embodiments of the invention, identical or similar elements are identified with the same reference numerals, wherein a repeated description of these elements in each case is omitted. The figures merely schematically illustrate the subject matter of the invention.

[0037] Figure 1 A schematic illustration of an onboard electrical system 20 of a motor vehicle is shown. Onboard electrical system 20 comprises a starter battery 12 for supplying a plurality of loads 18 (not shown in detail here) in the motor vehicle. Loads 18 include, for example, a starter and a lighting device.

[0038] The onboard power supply 20 comprises in particular an electromechanical brake system 14, which is fed by the starter battery 12 during normal driving operation of the motor vehicle. In addition, a main switch 16 is provided, by means of which the starter battery 12 can be disconnected from the load 18 and in particular from the electromechanical brake system 14. The starter battery 12 is disconnected from the load 18 and from the electromechanical brake system 14, for example, when the motor vehicle is stationary. In the event of a fault in the onboard power supply 20, the main switch 16 acts as a fuse and disconnects the load 18 and the electromechanical brake system 14 from the onboard power supply 20. The load 18 and the electromechanical brake system 14 each also have their own switch, not shown here, for switching on and off.

[0039] Onboard electrical system 20 further comprises electrical energy storage device 10 , which in the present case comprises one or more hybrid supercapacitors. Electrical energy storage device 10 is used in particular for operating electromechanical brake system 14 after the rest of onboard electrical system 20 has been shut down, that is to say when starter battery 12 is disconnected from electromechanical brake system 14 by main switch 16 .

[0040] The hybrid supercapacitor of the electrical energy store 10 has two electrodes, each of which comprises a current discharger and is separated from one another by a separator. The transport of charge between the electrodes is ensured by the electrolyte or components of the electrolyte. The electrodes comprise conventional superconcentrators as active materials, and materials which are capable of redox reactions with charge carriers of the electrolyte and thereby form insertion compounds, which are also referred to as electrostatically active materials. The energy storage principle of the hybrid supercapacitor is based on the formation of an electrochemical double layer combined with the formation of a faradaic lithium insertion compound.

[0041] The hybrid supercapacitor includes, for example, a viscous electrolyte. The viscous electrolyte is, for example, a carbonate, an ionic fluid (Ionische Flüssigkeit) or a gel-electrolyte. The hybrid supercapacitor may also include a solid electrolyte. The solid electrolyte is, for example, a polymer-electrolyte. The separator of the hybrid supercapacitor is formed by an insulating material having a porous structure. Suitable materials are in particular polymers, such as cellulose, polyolefins, polyesters and fluorinated polymers. Particularly preferred polymers are cellulose, polyethylene, polypropylene, polyethylene terephthalate, polytetrafluoroethylene and polyvinylidene fluoride. In addition, the separator may include a ceramic material.

[0042] The onboard electrical system 20 additionally comprises a discharge unit 30. By means of the discharge unit 30, the electrical energy store 10 can be discharged with a defined discharge current I. In particular, the electrical energy store 10 can be discharged with the defined discharge current I by means of the discharge unit 30. The discharge unit 30 also comprises devices (not shown) for measuring the discharge current I and for measuring the voltage U present at the electrical energy store 10.

[0043] For the diagnosis of the electric energy storage device 10, for example, after the motor vehicle has stopped or after the engine of the motor vehicle has been switched off, a plurality of controlled discharge processes L1, L2, L3, L4 of the electric energy storage device 10 are successively carried out. In this case, during each discharge process L1, L2, L3, L4, the energy E1, E2, E3, E4 drawn from the electric energy storage device 10 and the power P1, P2, P3, P4 generated by the electric energy storage device 10 during the discharge process L1, L2, L3, L4 are acquired.

[0044] The energy E1, E2, E3, E4 respectively extracted from the electrical energy storage device 10 during such discharge processes L1, L2, L3, L4 and the power P1, P2, P3, P4 respectively generated by the electrical energy storage device 10 during the discharge processes L1, L2, L3, L4 are shown in the Lagone diagram. Figure 2 An exemplary Lagung diagram is shown for a plurality of, in the present case four, discharging processes L1 , L2 , L3 , L4 of electrical energy storage device 10 .

[0045] First, a first discharging process L1 is carried out by means of the discharging unit 30 , during which the electrical energy store 10 is discharged with a certain discharging current I. The discharging current I is constant during the first discharging process L1 . The voltage U present at the electrical energy store 10 is also measured during the first discharging process L1 .

[0046] During the first discharge process L1 a time period is measured during which the electrical energy store 10 is discharged. From the determined discharge current I and the measured time period a first energy E1 is derived which is withdrawn from the electrical energy store 10 during the first discharge process L1.

[0047] Furthermore, a first power P1 generated by the electrical energy store 10 during the first discharge process L1 is determined from the determined discharge current I and the measured voltage U. The first energy E1 and the first power P1 form a data pair which is associated with the first discharge process L1 and which is shown in a Lagone diagram.

[0048] Then, the electrical energy storage device 10 is charged again and a second discharge process L2 is carried out. In this process, a second energy E2 and a second power P2 generated during the second discharge process L2 are obtained, which is extracted from the electrical energy storage device 10 during the second discharge process L2. The second energy E2 and the second power P2 form a data pair, which is assigned to the second discharge process L2 and is shown in the Lagone diagram.

[0049] The electrical energy storage device 10 is then charged again and a third discharge process L3 is carried out. In this case, a third energy E3 and a third power P3 generated during the third discharge process L3 are obtained, which is extracted from the electrical energy storage device 10 during the third discharge process L3. The third energy E3 and the third power P3 form a data pair, which is assigned to the third discharge process L3 and is shown in the Lagone diagram.

[0050] Likewise, the electrical energy storage device 10 is charged again and a fourth discharge process L4 is carried out. In this case, a fourth energy E4 and a fourth power P4 generated during the fourth discharge process L4 are obtained, which is extracted from the electrical energy storage device 10 during the fourth discharge process L4. The fourth energy E4 and the fourth power P4 form a data pair, which is assigned to the fourth discharge process L4 and is shown in the Lagone diagram.

[0051] The discharge current I is different in the discharge processes L1, L2, L3, and L4. The discharge current I in the first discharge process L1 is smaller than that in the second discharge process L2. The discharge current I in the second discharge process L2 is smaller than that in the third discharge process L3. The discharge current I in the third discharge process L3 is smaller than that in the fourth discharge process L4.

[0052] The Ragon diagram also shows the following data pairs, which are associated with a first reference discharge process Lx1, a second reference discharge process Lx2, a third reference discharge process Lx3 and a fourth reference discharge process Lx4. The reference discharge processes Lx1, Lx2, Lx3, Lx4 start with a reference energy store 10 which is aged and still has just enough energy to operate the electromechanical brake system 14 after the rest of the onboard electrical system 20 of the motor vehicle has stopped operating.

[0053] The discharge current I during the first reference-discharge process Lx1 is equal to the discharge current I during the first discharge process L1. The discharge current I during the second reference-discharge process Lx2 is equal to the discharge current I during the second discharge process L2. The discharge current I during the third reference-discharge process Lx3 is equal to the discharge current I during the third discharge process L3. The discharge current I during the fourth reference-discharge process Lx4 is equal to the discharge current I during the fourth discharge process L4.

[0054] The energy extracted from the reference energy storage 10 during the first reference discharge process Lx1 corresponds to the first limit value G1. The energy extracted from the reference energy storage 10 during the second reference discharge process Lx2 corresponds to the second limit value G2. The energy extracted from the reference energy storage 10 during the third reference discharge process Lx3 corresponds to the third limit value G3. The energy extracted from the reference energy storage 10 during the fourth reference discharge process Lx4 corresponds to the fourth limit value G4.

[0055] The energy E1, E2, E3, E4 extracted from the energy storage device 10 during the discharge process L1, L2, L3, L4 is then compared with the limit values ​​G1, G2, G3, G4. If the first energy E1 is less than the first limit value G1, a corresponding message is generated. If the second energy E2 is less than the second limit value G2, a corresponding message is generated. If the third energy E3 is less than the third limit value G3, a corresponding message is generated. If the fourth energy E4 is less than the fourth limit value G4, a corresponding message is generated.

[0056] The Lagone diagram also shows data pairs which are associated with a first new discharge process Ln1, a second new discharge process Ln2, a third new discharge process Ln3 and a fourth new discharge process Ln4. The new discharge processes Ln1, Ln2, Ln3, Ln4 are started here with a new electrical energy store 10 which has not aged.

[0057] The discharge current I at the time of the first new-discharge process Ln1 is equal to the discharge current I at the first discharge process L1. The discharge current I at the time of the second new-discharge process Ln2 is equal to the discharge current I at the second discharge process L2. The discharge current I at the time of the third new-discharge process Ln3 is equal to the discharge current I at the third discharge process L3. The discharge current I at the time of the fourth new-discharge process Ln4 is equal to the discharge current I at the fourth discharge process L4.

[0058] The invention is not limited to the embodiments described here and the aspects emphasized therein. On the contrary, within the scope of the preferred embodiments, a large number of variants are possible, which are within the technical means of a person skilled in the art.

Claims

1. A method for operating an electrical energy store (10), wherein a discharging process (L1, L2, L3, L4) is carried out, in which the electrical energy store (10) is discharged with a certain discharge current (I); Receiving energy (E1, E2, E3, E4) extracted from an electrical energy storage device (10) during a discharge process (L1, L2, L3, L4); comparing the acquired, extracted energy (E1, E2, E3, E4) with limit values ​​(G1, G2, G3, G4); and generating a notification when the acquired, extracted energy (E1, E2, E3, E4) is less than said limit value (G1, G2, G3, G4), wherein the electrical energy store (10) is charged again after a previously performed discharging process (L1, L2, L3, L4) and a further discharging process (L1, L2, L3, L4) is performed, in which the electrical energy store (10) is discharged with a determined discharging current (I); Receiving energy (E1, E2, E3, E4) extracted from the electrical energy storage device (10) during a further discharge process (L1, L2, L3, L4); And the acquired, extracted energy (E1, E2, E3, E4) is compared with a limit value (G1, G2, G3, G4); and if the acquired, extracted energy (E1, E2, E3, E4) is less than the limit value (G1, G2, G3, G4), a notification is generated; wherein the discharge current (I) during the further discharge process (L1, L2, L3, L4) is different from the discharge current (I) during the previously performed discharge process (L1, L2, L3, L4).

2. The method according to claim 1, wherein during the discharging process (L1, L2, L3, L4), the discharge current (I) is kept constant.

3. The method according to claim 1 or 2, wherein during the discharge process (L1, L2, L3, L4) a time period is measured, during which the electrical energy storage device (10) is discharged; and The energy (E1, E2, E3, E4) extracted from the electrical energy storage device (10) during a discharging process (L1, L2, L3, L4) is determined from a determined discharging current (I) and a measured time period.

4. The method according to claim 1 or 2, wherein the power (P1, P2, P3, P4) generated by the electrical energy storage device (10) during the discharge process (L1, L2, L3, L4) is detected.

5. A method according to claim 4, wherein the voltage (U) applied to the energy storage device (10) is measured during the discharge process (L1, L2, L3, L4); and the power (P1, P2, P3, P4) generated by the energy storage device (10) during the discharge process (L1, L2, L3, L4) is obtained from the determined discharge current (I) and the measured voltage (U).

6. A method according to claim 4, wherein the power density of the electric energy storage device (10) is obtained from the power (P1, P2, P3, P4) generated by the electric energy storage device (10) during the discharge process (L1, L2, L3, L4) and the weight of the electric energy storage device (10).

7. A method according to claim 1 or 2, wherein the energy density of the electric energy storage device (10) is obtained from the energy (E1, E2, E3, E4) extracted from the electric energy storage device (10) during the discharge process (L1, L2, L3, L4) and the weight of the electric energy storage device (10).

8. The method according to claim 1 or 2, wherein the electrical energy storage (10) comprises at least one hybrid supercapacitor.

9. Use of the method according to any of the preceding claims in a motor vehicle.

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