WO2015014761A1 - Method for diagnosing a state of a battery - Google Patents

Abstract

The invention relates to a method for diagnosing a state of a battery which has a plurality of battery units. Provision is made here for a state-of-charge balancing demand value to be determined, for possible diagnosis options to be determined, for the determined state-of-charge balancing demand value to be compared with a demand threshold value for a determined possible diagnosis option and for the state of the battery units to be diagnosed from this. In addition, a computer program and a battery management system are specified which are designed for implementing the method, as well as a battery and a motor vehicle having a drive system which is connected to such a battery.

Description

 Description Method for diagnosing a condition of a battery Prior 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.

A task of the battery management system is, state of charge (SOC) of the individual battery units despite different self discharges and

different charging efficiencies to one another. 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 described for example in DE 10 2009 002 466 A1. In this document, a so-called inductive cell balancing is also described, wherein the circuit concept for aligning the cell voltages based on an inductive intermediate storage of the transported electrical energy. The document also discloses a battery diagnosis that only then is started 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

In a method according to the invention for diagnosing a condition of a battery comprising a plurality of battery units, the following steps are provided: a) determining a state of charge compensation required value; b) determining possible diagnostic options; c) comparing the determined state of charge compensation requirement value with a

 Demand Threshold for a Determined Possible Diagnostic Option; and d) Diagnose 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 takes place in the form of the diagnosis of the state of the battery units in step d) on the basis of the result of the comparison in step c).

When determining a significant deviation of the determined

State of charge equalization value to the demand threshold for the identified potential diagnostic option for defective or inferior battery units. 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 in a so-called limp frome 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 includes an increased self-discharge rate of at least one

Battery unit, preferably increased self-discharge rates of all battery units concerns. The self-discharge rate may be considered as a measure of the state of health (SOH) of the battery pack. Advantageously, therefore, is based on the

State of charge compensation value is closed to the increased self-discharge rate of the affected battery units.

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 subsequent discharge.

Particularly advantageous is an SOC window that is within a range that is typically achieved on each day of travel for a particular type of vehicle, such as an electric vehicle (EV) or a hybrid vehicle (HEV, hybrid electrical vehicle). 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 that is shorter than a reference period, for example, shorter than one hour or less than two Hours. In particular, the second diagnostic option can be determined based on the presence of an 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. The computer program can in particular be a module for implementing a battery diagnostic system or a module for implementing a

Battery management system of a vehicle act. The computer program can be stored on a machine-readable storage medium, such as 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 requirement value with a demand threshold for a diagnosed diagnostic option and a unit for diagnosing the state of the battery units.

According to the invention, a battery, in particular a lithium-ion battery or a nickel-metal hydride battery is also provided, the

Battery management system comprises and is connectable to a drive system of a motor vehicle, wherein the battery management system is formed as described above and / or is arranged to carry out the inventive method.

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 designate a battery cell, a battery module, a module string or a battery pack can. 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 for

Provision of 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:

Figure 1 is a schematic representation of a battery management system in

 Communication with several battery units,

FIG. 2 shows a method according to the invention according to a first embodiment,

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

FIG. 4 shows a diagram with standardized charge state compensation values.

Embodiments of the invention

1 shows a battery management system 2, which is set up, several

Monitor and / or control battery units 4. 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 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

Charge state equalization demand value. The demand value determination unit 6 is set up to receive measured values and / or measured data from the battery units 4 in order to determine the charge state compensation requirement value individually for each battery unit 4. 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: a _L , σ _δ, as well as different capacities, capacity: C _L > C _s. It results at the time t in the battery units, the charge

Qi_ (t) = Qi_ (0) + AQ _L (t) - a _L (t)

Qs (t) = Q _s (0) + AQ _s (t) - as (t), where AQ (t) means a charge / discharge stroke.

The charge state compensation requirement results from the following equation:

Q _L (t) / C _L - Qs (t) / C _s = (QL (O) CS - Qs (0) C _L ) / (C _L Cs) + {(C _L - C _s ) / (C _L C _S )} - AQ (t)

- {(C _s a _L - C _L a _s ) / (C _L Cs)} - t = C ^* + AC- AQ (t) - a ^* -t,

wherein the charge state compensation requirement ASOC (At) = Q _L (t) / C _L - Qs (t) / C _s , an initial debalancing C ^* = (Q _L (0) Cs - Qs (0) C _L ) / (C _L Cs) _! a maze delta

AC-AQ (t) = {(C _L -Cs) / (C _L C _S )} -AQ (t) and a self-discharge delta σ = {(C _s a _L - C _L a _s ) / (C _L Cs) } -t, so

ASOC (At) = C ^* + ΔΟ-ΔΟ - σ ^* -Δί.

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 ΔΟ = 0, achievable by discharging and recharging to the original state of charge. In this case, ASOC (At) = -σ ^* -Δί.

In case 1, the charge state equalization requirement can be large

Detecting self-discharge differences. Case 2: A SOC stroke in a short time, ie σ ^* -Δί ^« 0. In this case ASOC (At ^« 0) = AC-AQ.

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 method described above is repeated with each

Battery unit performed in comparison to 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. However, this case is very unlikely even at about 100 cells.

The battery management system has a unit 8 for determining diagnostic options, which checks the conditions during the charge state equalization requirement determination for the presence of possible diagnostic options. The unit 8 for determining 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 diagnostic option determination means 8 is also arranged to determine whether two detected charge state equalization demand values have been determined in a limited SOC window, for example, in a SOC window with SOC values of 40% and 50%.

The means 8 for determining the diagnostic options also includes a

Timing unit, which can determine if two determined demand values for the battery balancing, if 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 requirement value with a demand threshold for a determined diagnostic option. For example, if the diagnostic option determination unit 8 has determined a charge state balance demand value determination in the limited SOC window, the charge state balance requirement may change to one increased self-discharge rate of the battery unit are closed. Whether such an increased self-discharge rate of the battery unit is present, the unit 10 determines by comparing the determined charge state compensation requirement value with the

corresponding demand threshold for the increased self-discharge rate. If the diagnostic option determination unit 8 alternatively or in addition thereto

has determined sufficient SOC stroke in a short time, the unit compares 10 to

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 receives data from the unit 10 for comparing the determined demand value with a demand threshold. The means 12 for diagnosing the condition of the batteries identifies defective or inferior ones

Battery units by storing entries in the battery units associated with fault memories or outputs a warning signal to the driver of the vehicle.

Fig. 2 shows an exemplary embodiment of the method according to the invention. In a step S0, the method is initiated, for example by detecting a specific operating state of the vehicle or by lapse 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 determined in steps S1 and S2

 Sufficiency level demand values 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.

Fig. 3 shows an alternative embodiment of the method according to the invention. The steps SO, S1 and S2 are executed as described with reference to FIG. The method shown in Fig. 3 differs from that of Fig. 2 only in the

Order of verification of possible diagnostic options. Accordingly, in one Step S7 first checks whether the determined state of charge compensation demand values were determined within a period that 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, in step S10, the

 Self-discharge diagnosis performed. If not, the process is restarted as described with reference to FIG. 2.

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 ASOC / AC is plotted over the time t. In a first area 20, ASOC / AC> 0, so AQ> 0. In a second area 22, ASOC / AC <0, so that AQ <0. Recognizable occurs a reversal in the charge state balance requirement of the batteries. It can be seen from Fig. 4 that at the upper SOC limit, a higher capacity battery pack would be discharged, while at the lower SOC limit, the smaller 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 range specified by the claims, a variety of modifications are possible in the context

professional action.

Claims

claims 1 . A method of 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 compensation 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). 2. The method according to claim 1, characterized in that the diagnostic options include a first diagnostic option, which relates to increased self-discharge rates of the battery units (4). 3. The method according to claim 2, characterized in that the possibility of the first diagnostic option based on the presence of a limited SOC window is determined. 4. The method according to any one of the preceding claims, characterized in that the diagnostic options include a second diagnostic option, which relates to capacity losses of the battery units (4). 5. The method according to claim 4, characterized in that the possibility of the second diagnostic option is determined on the basis of the presence of a period of time which is shorter than a reference period. A computer program for performing one of the methods of any of claims 1 to 5 when the computer program is executed on a programmable computer device. 7. A battery management system (2) of a battery, which has a plurality of battery units (4), with a unit (6) for determining a state of charge compensation need value, a unit (8) for determining possible diagnostic options, a unit (10) for comparing the determined  A state of charge equalization demand value having a demand threshold for a determined possible diagnostic option and a unit (12) for diagnosing the state of the battery units (4). A battery comprising a plurality of battery units (4) and a battery management system (2) according to claim 7. 9. Motor vehicle with a battery according to claim 8, wherein the battery with a Drive system of the motor vehicle is connected.