DE102013214817A1 - Method for diagnosing a condition of a battery - Google Patents

Abstract

The invention relates to a method for diagnosing a condition of a battery having a plurality of battery units. It is provided that a charge state compensation requirement value is determined, possible diagnosis options are determined, the determined state of charge compensation value is compared with a demand threshold for a determined possible diagnostic option and from this the state of the battery units is diagnosed. A computer program and a battery management system, which are set up to carry out the method, as well as a battery and a motor vehicle, whose drive system is connected to such a battery, are also specified.

Description

State of the art

The invention relates to a method for diagnosing a condition of a battery having a plurality of battery units.

The invention also relates to a computer program and a battery management system, which are set up to carry out the method. Furthermore, a battery and a motor vehicle are specified with such a battery.

Hybrid and electric vehicles use battery packs in nickel-metal hydride technology or lithium-ion technology, which consist of a large number of series-connected electrochemical cells. A battery management system is used to monitor the battery and, in addition to the safety monitoring, should ensure the longest possible battery life.

One task of the battery management system is to match the state of charge (SOC) of the individual battery units despite different self-discharges and different charging efficiencies. This is done for example by a suitable symmetrization of the battery units (balancing), which is usually made resistive. For this purpose, a resistor and a switching element is provided for each battery unit in order to discharge individual battery units specifically via this so-called balancing resistor. Such a method for charge state compensation of battery units is for example in the DE 10 2009 002 466 A1 described. In this document, a so-called inductive cell balancing is also described, wherein the circuit concept for the approximation of the cell voltages based on an inductive intermediate storage of the transported electrical energy. The document also discloses a battery diagnosis which is started only when an operating state of a consumer supplied by the battery indicates that it is not operating in a main mode.

Disclosure of the invention

Advantages of the invention

• a) Ermitteln eines Ladezustandsausgleichsbedarfswertes;
• b) Ermitteln von möglichen Diagnoseoptionen;
• c) Vergleichen des ermittelten Ladezustandsausgleichsbedarfswertes mit einem Bedarfsschwellwert für eine ermittelte mögliche Diagnoseoption und
• d) Diagnostizieren des Zustands der Batterieeinheiten.

In a method according to the invention for diagnosing a condition of a battery which has a plurality of battery units, the following steps are provided:

• a) determining a state of charge balance demand value;
• b) determining possible diagnostic options;
• c) comparing the determined state of charge compensation demand value with a demand threshold value for a determined possible diagnostic option and
• d) diagnosing the condition of the battery units.

In step a), a state of charge compensation value is determined for each battery unit. Thus, it can be determined which battery unit is defective or inferior.

The diagnosis of the state of the battery is made in the form of the diagnosis of the state of the battery units in step d) based on the result of the comparison in step c).

Advantageously, upon detection of a significant deviation of the determined state of charge compensation requirement value with the demand threshold value for the determined possible diagnostic option, it can be concluded that defective or inferior battery units are involved. In step d), an identification of the defective or inferior battery units, z. Example, by storing an entry in a fault memory, by issuing a warning signal or, for example, by transferring the vehicle into a so-called limp home state, for example, if a plurality of battery units have been identified as defective or inferior. The driver can then arrange for the replacement of the affected battery units.

Advantageous developments and improvements of the method specified in the independent claim are possible by the measures listed in the dependent claims.

According to one embodiment, the possible diagnostic options in step b) include a first diagnostic option, which relates to an increased self-discharge rate of at least one battery unit, preferably increased self-discharge rates of all battery units. The self-discharge rate may be considered as a measure of the state of health (SOH) of the battery pack. Advantageously, the increased self-discharge rate of the affected battery units is therefore concluded on the basis of the charge state compensation requirement value.

It is preferably provided that the possibility of the first diagnostic option is determined on the basis of the presence of a limited SOC window (SOC, state of charge). This is possible for example by discharging and then charging the battery unit to the original state of charge or by charging and then Discharged. Particularly advantageous is an SOC window that is within a range achieved for a particular type of vehicle, such as an electric vehicle (EV) or hybrid vehicle (HEV), typically on each day of travel. In a hybrid vehicle, it is advantageous if the limited SOC window is defined by SOC values of 40% and 50%. In an electric vehicle, it is advantageous if the limited SOC window is defined by SOC values above 80% or above 90%.

According to a preferred embodiment, the possible diagnostic options include a second diagnostic option, which relates to a capacity loss of at least one battery unit, preferably capacity losses of all battery units. The capacity loss is caused by the aging of the battery unit and provides in the context of the invention provides a further measure of the health of the battery unit. It is therefore particularly advantageous to infer a possible loss of capacity of the affected battery units on the basis of the charge state compensation requirement value.

Preferably, the second diagnostic option is determined based on the presence of a period of time shorter than a reference period, for example, shorter than one hour or less than two hours. In particular, the second diagnostic option may be determined based on the presence of a SOC stroke of at least 20% within a maximum of 1 to 2 hours.

According to the invention, a computer program is also proposed according to which one of the methods described herein is performed when the computer program is executed on a programmable computer device. The computer program is preferably executed on a battery control device accompanying normal operation. In particular, the computer program may be a module for implementing a battery diagnostic system or a module for implementing a battery management system of a vehicle. The computer program can be stored on a machine-readable storage medium, for example on a permanent or rewritable storage medium or in association with a computer device, for example on a portable storage, such as a CD-ROM, a DVD, a USB stick or a memory card. Additionally or alternatively, the computer program may be provided on a computing device, such as on a server or a cloud server, for downloading, for example via a data network such as the Internet, or a communication connection such as a telephone line or wireless connection.

According to the invention, a battery management system (BMS) is also provided with a unit for determining a state of charge compensation demand value, a unit for determining possible diagnostic options, a unit for comparing the determined demand value with a demand threshold for a determined diagnostic option and a unit for diagnosing the state of the battery units.

The invention also provides a battery, in particular a lithium-ion battery or a nickel-metal hydride battery, which comprises a battery management system and can be connected to a drive system of a motor vehicle, wherein the battery management system is designed and / or set up as described above to carry out the method according to the invention.

The terms "battery" and "battery unit" are used in the present description, the usual parlance used for accumulator or Akkumulatoreinheit. The battery preferably comprises one or more battery units, which may designate a battery cell, a battery module, a module string or a battery pack. As a battery pack while several cells are referred to, which are spatially combined and often provided with a housing or with a sheath. The battery cells are preferably firmly connected to each other and interconnected circuitry, for example, connected in series or parallel to modules. Several modules can be connected to so-called battery direct converters (BDCs) and several battery direct converters to a so-called battery direct inverter (BDI).

According to the invention, a motor vehicle is also provided with such a battery, wherein the battery is connected to a drive system of the motor vehicle. Preferably, the method is used in electrically powered vehicles, in which an interconnection of multiple battery cells to provide the necessary drive voltage of the vehicle takes place.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description. Show it:

1 a schematic representation of a battery management system in communication with multiple battery units,

2 a method according to the invention according to a first embodiment,

3 a method according to the invention according to a second embodiment and

4 a diagram with normalized charge state compensation values.

Embodiments of the invention

1 shows a battery management system 2 which is set up, several battery units 4 to monitor and / or control. The battery management system 2 is set up to carry out the method according to the invention. The communication between the battery management system 2 and the battery units 4 takes place via suitable communication units 14 . 16 as interfaces to a communication channel 18 , for example to a CAN bus.

The battery management system 2 has a unit 6 for determining a state of charge compensation demand value. The unit 6 to determine the demand value is set up by the battery units 4 To obtain measured values and / or measured data, from this, the state of charge compensation value individually for each battery unit 4 to investigate. The determination of the state of charge compensation required value can for example take place regularly or be coupled to specific events or operating states of the vehicle. In order to conclude the state of health of the battery unit by evaluating the charge state equalization requirement value, the framework conditions in the demand determination are decisive.

This is shown by the example with 2 battery units:
A first battery unit is denoted Tiefindex L and a second with Tiefindex S. The battery units have different self-discharges,
Self-discharge: σ _L , σ _S,
as well as different capacities,
Capacity: C _L > C _p.

It results at the time t in the battery units, the charge Q _L (t) = Q _L (0) + ΔQ _L (t) - σ _L (t), Q _S (t) = Q _S (0) + ΔQ _S (t) - σ _S (t), where ΔQ (t) means a charge / discharge stroke.

The charge state compensation requirement results from the following equation: Q _L (t) / C _L - Q _S (t) / C _S = (Q _L (0) C _S - Q _S (0) C _L ) / (C _L C _S ) + {(C _L - C _S ) / (C _L C _S )} · ΔQ (t) - {(C _S σ _L - C _L σ _S ) / (C _L C _S )} · t = C * + ΔC · ΔQ (t) - σ * · t, the charge state equalization requirement ΔSOC (Δt) = Q _L (t) / C _L - Q _S (t) / C _S, an initial debalancing C * = (Q _L (0) C _S -Q _S (0) C _L ) / (C _L C _S ), a maze delta .DELTA.C · .DELTA.Q (t) = {(C _L - C _S) / (C _L C _S)} (t) · .DELTA.Q and a self-discharge delta σ * · t = {(C _S σ _L - C _L σ _S ) / (C _L C _S )} · t be distinguished, so ΔSOC (Δt) = C * + ΔC · ΔQ - σ * · Δt.

For the initial debalancing, C * = 0 can be set when the charge states are compensated. The parameters time t, and the charge flow rate Q are variable. As a result, two cases can be distinguished:
Case 1: Fixed SOC window, ie ΔQ = 0, achievable by discharging and recharging to the original state of charge. In this case will ΔSOC (Δt) = -σ * · Δt.

In case 1, large self-discharge differences can be determined based on the charge state equalization requirement.

Case 2: A SOC stroke in a short time, ie σ * · Δt ≈ 0. In this case ΔSOC (Δt ≈ 0) = ΔC · ΔQ.

In case 2, large capacity differences can be determined based on the charge state equalization requirement.

In order to obtain a diagnosis for all battery units of a battery pack having more than two battery units, the above-described method is performed with each battery unit as compared with any reference battery unit. A suitable reference battery unit is, for example, the one with the lowest SOC in the battery pack. In this way, the diagnosis for all battery units is feasible. The increased self-discharge rate is measured relative to other cells. If all cells discharge evenly fast, then the diagnosis can not detect this. This Case is very unlikely even at about 100 cells.

The battery management system has one unit 8th for determining diagnostic options that checks the framework for charge state equalization requirements determination for the presence of possible diagnostic options. The unit 8th to obtain diagnostic options receives measured values and / or measured data from the battery units 4 , in particular information about the state of charge of the battery units (SOC) to determine the presence of a limited SOC window. In particular, the device 8th to determine diagnostic options, also configured to determine if two detected charge state balance demand values were determined in a limited SOC window, for example, in a SOC window with SOC values of 40% and 50%.

The device 8th for determining the diagnostic options also includes a time measuring unit, which can determine if two determined demand values for the battery balancing, whether they were determined within a period of time that is shorter than a reference period.

The battery management system 2 also has a unit 10 for comparing the determined charge state compensation demand value with a demand threshold for a determined diagnostic option. If the unit 8th For example, in order to determine diagnostic options, a charge state equalization requirement determination has been determined in the limited SOC window, it can be concluded from the charge state equalization requirement to an increased self-discharge rate of the battery unit. Whether such an increased self-discharge rate of the battery unit is present determines the unit 10 by comparing the determined charge state equalization requirement value with the corresponding increased self-discharge rate demand threshold. If the unit 8th Alternatively, or in addition to determining a sufficient SOC stroke to determine diagnostic options, the unit compares 10 for comparing the determined demand value with the demand threshold, the capacity loss of the cell with a critical capacity loss.

The battery management system 2 also has a unit 12 for diagnosing the state of the battery units, which data from the unit 10 to compare the determined demand value with a demand threshold. The device 12 diagnosing the condition of the batteries identifies defective or inferior battery units by storing entries in the fault memory associated with the battery units or by issuing a warning signal to the driver of the vehicle.

2 shows an exemplary embodiment of the method according to the invention. In a step S0, the method is initiated, for example by detection of a specific operating state of the vehicle or by expiry of a defined time. In a step S1, a charge state compensation requirement value is determined for a battery unit. In a step S2, a further charge state compensation requirement value is determined. In a step S3, it is determined whether the state-of-charge compensation demand values determined in steps S1 and S2 have been determined in a limited SOC window. If so, a diagnosis is made in step S4 regarding the self-discharge rate of the battery pack. If not, it is determined in a step S5 whether the charge state compensation requirement values determined in steps S1 and S2 have been determined within a time period which is shorter than a reference period. If so, a capacity diagnosis is performed in a step S6. If not, the process is restarted, whereby the last detected state of charge compensation demand value can be used again, so that in the following step S1 can be omitted.

3 shows an alternative embodiment of the method according to the invention. Steps S0, S1 and S2 become the same as with reference to 2 described executed. This in 3 The method illustrated differs from that of 2 just in the order of checking the possible diagnostic options. Accordingly, in a step S7, it is first checked whether the ascertained state of charge compensation requirement values were determined within a period of time which is shorter than a reference period. If so, the capacity diagnosis is performed in a step S8. If not, it is checked in a step S9 whether the ascertained state of charge compensation requirement values were determined within a limited SOC window. If so, the self-discharge diagnosis is performed in a step S10. If not, the procedure is as described with reference to 2 described restarted.

Of course, further embodiments of the method are possible in which the determination of the individual diagnostic options are checked independently.

4 shows a diagram in which a standardized charge state compensation requirement ΔSOC / ΔC is plotted over the time t. In a first area 20 ΔSOC / ΔC> 0 such that ΔQ> 0. In a second area 22 ΔSOC / ΔC <0, so that ΔQ <0. Recognizable occurs a reversal in the charge state balance requirement of the batteries. Out 4 It can be seen that at the upper SOC limit, a higher capacity battery pack would discharge while at the lower SOC limit, the lower capacity battery pack would be discharged. The capacity-related demand is therefore reversed, while the demand based on self-discharge is not reversed.

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

• DE 102009002466 A1 [0004]

Claims (9)

Method for diagnosing a condition of a battery comprising a plurality of battery units ( 4 ), comprising the steps of: a) determining (S1, S2) a state of charge compensation demand value; b) determining (S3, S5, S7, S9) possible diagnostic options; c) comparing the determined state of charge balance demand value with a demand threshold for a determined possible diagnostic option; d) diagnosing (S4, S6, S8, S10) the state of the battery units ( 4 ). A method according to claim 1, characterized in that the diagnostic options comprise a first diagnostic option which increases the self-discharge rates of the battery units ( 4 ). A method according to claim 2, characterized in that the possibility of the first diagnostic option is determined on the basis of the presence of a limited SOC window. Method according to one of the preceding claims, characterized in that the diagnostic options include a second diagnostic option, which capacity losses of the battery units ( 4 ). A method according to claim 4, characterized in that the possibility of the second diagnostic option is determined based on the presence of a period of time which is shorter than a reference period. A computer program for performing any of the methods of any one of claims 1 to 5 when the computer program is executed on a programmable computing device. Battery management system ( 2 ) of a battery containing several battery units ( 4 ), with a unit ( 6 ) for determining a state of charge compensation demand value, a unit ( 8th ) for determining possible diagnostic options, a unit ( 10 ) for comparing the determined state of charge compensation demand value with a demand threshold for a determined possible diagnostic option and a unit ( 12 ) for diagnosing the state of the battery units ( 4 ). Battery containing multiple battery units ( 4 ) and a battery management system ( 2 ) according to claim 7. Motor vehicle with a battery according to claim 8, wherein the battery is connected to a drive system of the motor vehicle.

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