DE102018201032A1 - Method for operating an electrical energy store - Google Patents

Abstract

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

Description

The invention relates to a method for operating an electrical energy store. The method according to the invention is used inter alia for the diagnosis of the electrical energy store, which in particular comprises a hybrid supercapacitor, and which is used in a motor vehicle.

State of the art

A motor vehicle has an electrical energy store. In a motor vehicle with an internal combustion engine, the electrical energy store is used inter alia as a starter battery and for operating an electromechanical brake system. As electrical energy storage, for example, conventional lead-acid batteries, or lead-acid batteries, but also lithium-ion batteries are used. Battery systems in motor vehicles are to be designed in such a way that they meet the requirements of automobile manufacturers with regard to available energy and retrievable power.

In addition to the well-known lithium-ion batteries (LIB) play electrochemical capacitors, also called supercapacitors (SC), an increasingly important role. Supercapacitors already available on the market are used both for automotive applications and for stationary systems. Electrochemical energy stores can be characterized by their energy and power density. In general, supercapacitors have a higher power density and a lower energy density than lithium-ion batteries. Thus, lithium ion batteries are preferred for energy intensive applications and supercapacitors for high power applications.

In general, supercapacitors are 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. By contrast, hybrid supercapacitors have a relatively high power density and a relatively high energy density. Hybrid supercapacitors thus have properties of lithium-ion batteries and supercapacitors.

Among other things, in the operation of electromechanical brake systems in particular hybrid supercapacitors are advantageously used as additional electrical energy storage. In case of failure of the vehicle electrical system of the motor vehicle enough energy is stored in the hybrid supercapacitor to perform at least one braking operation of the motor vehicle. Hybrid supercapacitors have a limited lifetime, depending on various parameters. Accurate life prediction is difficult. In a safety-relevant application, however, it is necessary to predict a failure of the energy storage and to carry out an exchange in good time.

From the US 2014/0129163 A1 a method for diagnosing a battery is known, whereby a state of the battery can be determined. This information about environmental conditions during operation of the battery and information about operating parameters during operation of the battery is detected. From the acquired information and a state model, the state of the battery is determined.

From the US 2012/310565 A1 For example, an apparatus and a method for determining a state of battery cells are known. At the same time, a power available in the battery cells and an energy of the battery cells are recorded below and displayed in a diagram.

Disclosure of the invention

A method for operating an electrical energy store is proposed. The electrical energy store is used for example for operating an electromechanical brake system in a motor vehicle, in particular after a failure of the rest of the electrical system of the motor vehicle.

According to the invention, a discharging process is carried out in which the electrical energy store is discharged with a defined discharge current. Such a controlled discharge process can be performed, for example, after each shutdown of the motor vehicle, or after each shutdown of the engine of the motor vehicle.

During the discharging process, an energy taken from the electrical energy store is determined. The energy taken from the electrical energy storage corresponds to an energy that after a failure of the rest of the electrical system of the motor vehicle would be available to operate the electromechanical braking system of the motor vehicle.

The thus determined, the electrical energy storage removed energy is then compared with a limit. The limit value corresponds for example to energy that would be required to operate the electromechanical brake system after a failure of the rest of the electrical system of the motor vehicle.

If the determined energy taken from the electrical energy store is smaller than the limit value, a corresponding message is generated. Said message is for example an optical and / or acoustic display by an infotainment system of the motor vehicle, by a warning lamp and / or by an external third unit such as a smartphone and is used to inform the driver.

If the energy taken from the electrical energy store is less than the said limit value, then the electrical energy store no longer has sufficient energy to operate the electromechanical brake system after a failure of the rest of the electrical system of the motor vehicle. In this case, it is to be assumed that the electrical energy store will soon fail, and replacement should be carried out in good time in order to ensure further safe operation of the motor vehicle.

The life of the electrical energy storage device depends, for example, on an operating temperature, a regularly used state of charge and a voltage level. But even a regular charging speed and discharge speed and a number of charge-discharge cycles has an impact on the life.

According to an advantageous embodiment of the invention, the discharge current remains constant during the discharge process. It has been found that with a constant discharge current, an actuation of the electromechanical brake system of the motor vehicle can be simulated relatively well. Furthermore, the calculation effort for determining the energy taken from the electrical energy store is simplified if the discharge current remains constant during the discharge process.

According to an advantageous development of the invention, a plurality of discharging operations of the electrical energy store are carried out chronologically immediately after each other, for example after switching off the engine of the motor vehicle and before restarting the engine of the motor vehicle. In this case, the electrical energy storage is recharged after a previously carried out discharge, and a further discharge is performed, in which the electrical energy storage is discharged again with a defined discharge current.

In this case, an energy taken from the electrical energy store during the further discharge process is determined, and the determined energy removed from the electrical energy store is compared with a limit value. A corresponding message is also generated if the determined energy removed from the electrical energy store is smaller than this limit value. The discharge current during the further discharge process is different from the discharge current during the previously performed discharge process.

Advantageously, during the discharge process, a period of time is measured up to which the electrical energy store is discharged. The energy taken from the electrical energy store during the discharge process is then determined from the defined discharge current and the measured time span. For the energy taken from the electrical energy storage, the following applies: $$\Delta \text{e}=\text{U}\times \text{I}\times \Delta \text{t}$$

According to a preferred embodiment of the invention, a power provided by the electrical energy store during the discharging process is also determined. The energy taken from the electrical energy store during the discharging process and the power delivered by the electrical energy store during the discharging process can advantageously be represented in a ragone diagram. From the ragone diagram can be read a remaining life of the electrical energy storage and thus possibly a rapid failure of the electrical energy storage can be predicted.

For this purpose, a voltage applied to the electrical energy store is preferably measured during the discharging process, and the power supplied by the electrical energy store during the discharging process is determined from the defined discharge current and the measured voltage. For the power provided by the electrical energy storage: $$\text{P}=\text{U}\times \text{I}$$

In addition, a power density of the electrical energy store can be determined from the power provided by the electrical energy store during the discharge process and a weight of the electrical energy store. For the power density of the electrical energy storage applies: $$\text{power density}=\text{P}\left[\text{W}\right]/\text{m}\left[\text{kg}\right]$$

Likewise, in addition to the energy removed from the electrical energy storage device during the discharge process and a weight of the electrical energy storage, an energy density of the electrical energy storage can be determined. For the energy density of the electrical energy storage applies: $$\text{energy density}=\text{e}\left[\text{Wh}\right]/\text{m}\left[\text{kg}\right]$$

Also, the determined energy density of the electrical energy storage and the determined power density of the electrical energy storage can be advantageously represented in a ragone diagram. Also from this Ragone diagram can read a remaining life of the electrical energy storage and thus possibly a speedy failure of the electrical energy storage can be predicted.

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

The inventive method is advantageously used in a motor vehicle, in particular in a motor vehicle with an internal combustion engine.

Advantages of the invention

The inventive method allows a relatively accurate prediction of the remaining life and a rapid failure of the electrical energy storage. Thus, the electrical energy storage can be replaced in time if the electrical energy storage no longer has sufficient energy to operate after a failure of the rest of the electrical system of the motor vehicle, the electromechanical braking system. The discharging process can advantageously be carried out when the motor vehicle is switched off, or when the motor of the motor vehicle is switched off. The discharge process can therefore be carried out in a time when the electromechanical brake system is not needed. The inventive method is also relatively easy to carry out. For performing the method according to the invention no high computing power is required.

list of figures

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below.

• 1 eine schematische Darstellung eines Bordnetzes eines Kraftfahrzeugs und
• 2 ein beispielhaftes Ragone-Diagramm über mehrere Entladevorgänge eines elektrischen Energiespeichers.

Show it:

• 1 a schematic representation of a vehicle electrical system of a motor vehicle and
• 2 an exemplary Ragone diagram over several discharges of an electrical energy storage.

Embodiments of the invention

In the following description of the embodiments of the invention, the same or similar elements are denoted by the same reference numerals, wherein a repeated description of these elements is dispensed with in individual cases. The figures illustrate the subject matter of the invention only schematically.

1 shows a schematic representation of a vehicle electrical system 20 of a motor vehicle. The electrical system 20 includes a starter battery 12 for the supply of several, not shown in detail consumers 18 in the motor vehicle. To the consumers 18 include, for example, a starter and a lighting system.

The electrical system 20 includes in particular an electromechanical brake system 14 , which in normal driving operation of the motor vehicle from the starter battery 12 is supplied. There is also a main switch 16 provided by means of which the starter battery 12 from the consumers 18 and in particular of the electromechanical brake system 14 can be separated. The starter battery 12 For example, when parking the motor vehicle by the consumers 18 and the electromechanical braking system 14 separated. In case of a fault in the electrical system 20 the main switch works 16 as a backup and disconnects consumers 18 as well as the electromechanical brake system 14 also from the electrical system 20 , The consumers 18 and the electromechanical brake system 14 each still own, not shown switch for connecting and disconnecting.

The electrical system 20 further includes an electrical energy storage 10 , which in this case comprises one or more hybrid supercapacitors. The electrical energy storage 10 is used in particular for operating the electromechanical brake system 14 after a failure of the rest of the electrical system 20 So if the starter battery 12 through the main switch 16 from the electromechanical brake system 14 is disconnected.

A hybrid supercapacitor of the electrical energy storage 10 has two electrodes, each comprising a current collector and separated by a separator. The transport of electrical charges between the electrodes is ensured by electrolytes or compositions of electrolytes. The Electrodes include as active material a conventional supercapacitor material, also referred to as static capacitive active material, as well as a material capable of undergoing a redox reaction with the charge carriers of the electrolyte and forming an intercalation compound thereof. The energy storage principle of the hybrid supercapacitor is based on the formation of an electrochemical double layer in combination with the formation of a faradischen lithium-Interkallationsverbindung.

The hybrid supercapacitor includes, for example, a viscous electrolyte. The viscous electrolyte is, for example, a carbonate, an ionic liquid or a gel electrolyte. A hybrid supercapacitor may also comprise a solid electrolyte. The solid electrolyte is, for example, a polymer electrolyte. The separator of the hybrid supercapacitor is formed of 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, polytetrafluoroethene and polyvinylidene fluoride. Furthermore, the separator may comprise ceramic materials.

The electrical system 20 additionally includes a discharge unit 30 , By means of the unloading unit 30 can the electrical energy storage 10 be discharged with a defined discharge current I. In particular, the electrical energy storage 10 by means of the unloading unit 30 be discharged with a defined discharge current I. The unloading unit 30 also includes means, not shown here, for measuring the discharge current I and for measuring a voltage at the electrical energy store 10 applied voltage U.

For diagnosis of the electrical energy storage 10 For example, after switching off the motor vehicle, or after switching off the engine of the motor vehicle, several controlled discharging successively L1 . L2 . L3 . L4 of the electrical energy storage 10 carried out. It will be at every unloading process L1 . L2 . L3 . L4 a the electrical energy storage 10 extracted energy E1 . E2 . E3 . E4 and one of the electrical energy storage 10 during the unloading process L1 . L2 . L3 . L4 rendered service P1 . P2 . P3 . P4 determined.

The the electrical energy storage 10 during such unloading L1 . L2 . L3 . L4 each extracted energy E1 . E2 . E3 . E4 and the of the electrical energy storage 10 during the unloading process L1 . L2 . L3 . L4 each performed service P1 . P2 . P3 . P4 are displayed in a ragone diagram. 2 shows an exemplary Ragone diagram over several, in this case four, unloading operations L1 . L2 . L3 . L4 of the electrical energy storage 10 ,

First, by means of the discharge unit 30 a first unloading process L1 performed in which the electrical energy storage 10 with a defined discharge current I unloaded. The discharge current I is during the first discharge L1 constant. During the first unloading process L1 also becomes one on the electrical energy storage 10 voltage applied U measured.

During the first unloading process L1 a period of time is measured, up to which the electrical energy store 10 is discharged. From the defined discharge current I and the measured time becomes the first energy E1 determines that the electrical energy storage 10 during the first unloading process L1 is removed.

Furthermore, from the defined discharge current I and the measured voltage U from the electrical energy storage 10 during the first unloading process L1 performed first performance P1 determined. The first energy E1 and the first performance P1 form a data pair, which is the first unloading L1 is assigned, and which is shown in the Ragone diagram.

Subsequently, the electrical energy storage 10 recharged and it will be a second unloading L2 carried out. This will be the second energy E2 that the electric energy storage 10 during the second unloading L2 is removed, and during the second unloading L2 performed second performance P2 determined. The second energy E2 and the second performance P2 form a data pair, which is the second unloading process L2 is assigned, and which is shown in the Ragone diagram.

Then the electrical energy storage 10 recharged and it becomes a third unloading L3 carried out. This will be the third energy E3 that the electric energy storage 10 during the third unloading L3 is removed, and during the third unloading L3 performed third performance P3 determined. The third energy E3 and the third achievement P3 form a data pair which is the third unloading process L3 is assigned, and which is shown in the Ragone diagram.

Also, the electrical energy storage 10 recharged and it will be a fourth unloading L4 carried out. This will be the fourth energy E4 that the electric energy storage 10 during the fourth unloading process L4 taken during the fourth unloading L4 performed fourth performance P4 determined. The fourth energy E4 and the fourth achievement P4 form a data pair which is the fourth unloading process L4 is assigned, and which is shown in the Ragone diagram.

The discharge currents I are in the process of unloading L1 . L2 . L3 . L4 different. The present is the discharge current I at the first unloading L1 smaller than in the second unloading process L2 , The discharge current I in the second unloading process L2 is smaller than the third unloading L3 , The discharge current I at the third unloading L3 is smaller than in the fourth unloading process L4 ,

The ragone diagram further shows data pairs which are a first reference discharge process lx1 , a second reference unloading process L x2 , a third reference unloading process Lx3 and a fourth reference unloading operation LX4 assigned. The reference unloading operations lx1 . L x2 . Lx3 . LX4 were doing it with a reference energy storage 10 recorded, which is aged and just has enough energy to after a failure of the rest of the electrical system 20 of the motor vehicle, the electromechanical brake system 14 to operate.

The discharge current I at the first reference unloading lx1 is equal to the discharge current I at the first unloading L1 , The discharge current I in the second reference unloading process L x2 is equal to the discharge current I in the second unloading process L2 , The discharge current I at the third reference unloading process Lx3 is equal to the discharge current I at the third unloading L3 , The discharge current I at the fourth reference unloading process LX4 is equal to the discharge current I in the fourth unloading process L4 ,

The the reference energy storage 10 at the first reference unloading process lx1 taken energy corresponds to a first limit G1 , The the reference energy storage 10 at the second reference unloading process L x2 taken energy corresponds to a second limit G2 , The the reference energy storage 10 at the third reference unloading process Lx3 taken energy corresponds to a third limit G3 , The the reference energy storage 10 at the fourth reference unloading process LX4 taken energy corresponds to a fourth limit G4 ,

The the electrical energy storage 10 during unloading L1 . L2 . L3 . L4 extracted energy E1 . E2 . E3 . E4 then comes with the limits G1 . G2 . G3 . G4 compared. When the first energy E1 is less than the first limit G1 a corresponding message is generated. If the second energy E2 less than the second limit G2 a corresponding message is generated. If the third energy E3 is less than the third limit G3 a corresponding message is generated. When the fourth energy E4 is less than the fourth limit G4 a corresponding message is generated.

The ragone diagram also shows data pairs which are a first reload n1 , a second reload ln2 , a third re-unloading process ln3 and a fourth reload Ln4 assigned. The new unloading operations n1 . ln2 . ln3 . Ln4 were doing it with a new electrical energy storage 10 taken, which has not aged.

The discharge current I at the first re-unloading n1 is equal to the discharge current I at the first unloading L1 , The discharge current I at the second re-unloading ln2 is equal to the discharge current I in the second unloading process L2 , The discharge current I at the third re-unloading ln3 is equal to the discharge current I at the third unloading L3 , The discharge current I at the fourth re-unloading Ln4 is equal to the discharge current I in the fourth unloading process L4 ,

The invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, within the scope given by the claims a variety of modifications are possible, which are within the scope of expert action.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The 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

• US 2014/0129163 A1 [0006]
• US 2012310565 A1 [0007]

Claims (10)

Method for operating an electrical energy store (10), wherein a discharge process (L1, L2, L3, L4) is carried out, in which the electrical energy store (10) is discharged with a defined discharge current (I); an energy (E1, E2, E3, E4) taken from the electrical energy store (10) during the discharging process (L1, L2, L3, L4) is determined; the determined extracted energy (E1, E2, E3, E4) is compared with a limit value (G1, G2, G3, G4); and a message is generated if the determined extracted energy (E1, E2, E3, E4) is smaller than the limit value (G1, G2, G3, G4). Method according to Claim 1 , wherein during the discharging process (L1, L2, L3, L4) the discharge current (I) remains constant. Method according to one of the preceding claims, wherein is recharged after a previously carried out discharging process (L1, L2, L3, L4) of the electrical energy storage device (10); and a further discharge process (L1, L2, L3, L4) is carried out, in which the electrical energy store (10) is discharged with a defined discharge current (I); an energy (E1, E2, E3, E4) removed from the electrical energy store (10) during the further discharge process (L1, L2, L3, L4) is determined; the determined extracted energy (E1, E2, E3, E4) is compared with a limit value (G1, G2, G3, G4); and a message is generated if the determined extracted energy (E1, E2, E3, E4) is less than the limit value (G1, G2, G3, G4); wherein the discharge current (I) in the further discharging process (L1, L2, L3, L4) is different from the discharge current (I) in the previously performed discharging process (L1, L2, L3, L4). Method according to one of the preceding claims, wherein during the discharge process (L1, L2, L3, L4) a period of time is measured up to which the electrical energy store (10) is discharged; and the energy (E1, E2, E3, E4) removed from the electrical energy store (10) during the discharging process (L1, L2, L3, L4) is determined from the defined discharge current (I) and the measured time span. Method according to one of the preceding claims, wherein a power (P1, P2, P3, P4) provided by the electrical energy store (10) during the discharging process (L1, L2, L3, L4) is determined. Method according to Claim 5 wherein during the discharging process (L1, L2, L3, L4) a voltage (U) applied to the electrical energy store (10) is measured; and the power (P1, P2, P3, P4) provided by the electrical energy store (10) during the discharging process (L1, L2, L3, L4) is determined from the defined discharge current (I) and the measured voltage (U). Method according to one of Claims 5 to 6 , wherein from the of the electrical energy store (10) during the discharging process (L1, L2, L3, L4) provided power (P1, P2, P3, P4) and a weight of the electrical energy store (10) has a power density of the electrical energy store (10 ) is determined. Method according to one of the preceding claims, wherein from the electrical energy storage (10) during the discharge process (L1, L2, L3, L4) extracted energy (E1, E2, E3, E4) and a weight of the electrical energy storage (10) has an energy density of the electrical energy store (10) is determined. Method according to one of the preceding claims, wherein the electrical energy store (10) comprises at least one hybrid supercapacitor. Use of the method according to one of the preceding claims in a motor vehicle.

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