WO2015128190A1

WO2015128190A1 - Method for monitoring the thermal stress of balancing resistors

Info

Publication number: WO2015128190A1
Application number: PCT/EP2015/052859
Authority: WO
Inventors: Ulrich Zimmermann
Original assignee: Robert Bosch Gmbh
Priority date: 2014-02-27
Filing date: 2015-02-11
Publication date: 2015-09-03
Also published as: DE102014203606A1

Abstract

The invention relates to a method for monitoring the thermal stress of balancing resistors in a battery apparatus having a plurality of battery cells. In this case, the invention provides – for a thermal stress TBV on balancing resistors to be ascertained, caused by a multiplicity of varying temperature swings (5) on account of use of the balancing resistors for balancing processes in a manner that varies in terms of frequency (6', 6'', 6''') and intensity, – for an equivalent number of temperature swings (5) of a particular prescribed or prescribable level to be determined that exert on the balancing resistors a thermal stress TBA that corresponds to the previously ascertained thermal stress TBV, and – for the equivalent number to be compared with a prescribed or prescribable threshold value and for a signal to be output when the threshold value is reached or exceeded. The invention additionally relates to a battery apparatus having a plurality of battery cells and a balancing device that has a control device that is set up to monitor the thermal stress of balancing resistors, and to a battery-operated vehicle having such a battery apparatus.

Description

description

title

Method for monitoring the thermal load of balancing resistors

The invention relates to a method for monitoring the thermal load of balancing resistors in a battery device having a plurality of battery cells.

State of the art

There is a growing demand for electrical energy storage systems that find many uses in both stationary and mobile applications. As such examples, u.a. Emergency power systems or electric / hybrid vehicles are listed.

The electrical energy storage device is designed for such applications mostly as a battery with a plurality of battery cells, which are connected in series and or also in parallel with each other electrically to the battery. In this way, batteries can be provided with power and / or energy data adapted to the respective application.

Among other things, due to production fluctuations in the individual battery cells in terms of electrical properties (eg voltage, capacitance, internal impedance) differences are observed. In a battery, the individual battery cells are therefore never identical in terms of their aging state and their electrical power. Usually, in battery cells, which are connected in a row in the battery, ie in series, the discharging process is stopped as soon as one of

Battery cell has reached its discharge voltage limit. The same applies to the charging of the battery. The charging stops as soon as the

Charge voltage limit of one of the battery cells is reached. The weakest cell is therefore the first to be fully charged or discharged. Thus, the battery or the battery module is always only as good as its / its weakest cell. In order to be able to provide a battery with similarly loadable cells and, moreover, to prevent the individual battery cells from aging differently due to different voltage states, methods for so-called cell balancing are known, which aim to balance the voltages of the individual battery cells to have.

Without such a voltage and charge compensation drifts the

State of charge of the different cells in operation due to slightly different capacities and slightly different

Self-discharges of the cells or modules apart.

With regard to the methods for cell balancing, a distinction is made between active and passive cell balancing, with an active cell balancing by means of a battery management system, a charge equalization taking place under the memory modules in such a way that the energy of the cells that are too highly charged, which is the highest cell voltage, is distributed to low-charged cells with low cell voltage. With passive cell balancing, those cells with the highest battery voltage are deliberately discharged, for example at fixed predetermined intervals, until all cells have the same voltage. The discharge usually takes place via balancing resistors, so that this method is also called "resistive balancing".

The electrical energy to be discharged is converted into heat via balancing resistors.

Here are the caused due to the heat generated

Temperature fluctuations a thermal load on the entire battery, "

but especially for the balancing resistors themselves. These are exposed to a variety of temperature changes over the life of the battery. The temperature changes vary with the height of the Temperarturhübe, which depends on whether one or more balancing resistors are used simultaneously.

The multiplicity and the magnitude of the temperature changes represent a not inconsiderable thermal load for the solder joints of the balancing resistors, so that they are subject to the risk of tearing or breakage due to material fatigue. Not only is this risk associated with the risk of a failure of a balancing resistor, but in particular in moving batteries, for example in vehicle batteries, a falling balancing resistance can lead to considerable consequential damage such as short-circuits and fires. It is therefore necessary to recognize such a risk in good time before the occurrence of a corresponding damage.

Documents US 2012/0094151 A1 and JP 201 1 -155752 A show

different measures for monitoring the thermal load of balancing resistors in a battery device.

Disclosure of the invention

The invention relates to a method for monitoring the thermal load of balancing resistors in a battery device having a plurality of battery cells. The invention further relates to a

Battery device with a plurality of battery cells and a balancing device, which has a control device which is set up for monitoring the thermal load of balancing resistors and a

battery-powered vehicle with such a battery device.

Advantageous embodiments of the invention are specified in the subclaims.

According to the invention, a method for monitoring the thermal load of balancing resistors in a battery device having a plurality of battery cells is provided, which is characterized by the steps of Determining a thermal load TBV of balancing resistors, caused by a plurality of varying Tertels due to a varying in frequency and intensity of the use of balancing resistors for balancing operations, a determination of an equivalent number of temperature strokes of a certain predetermined or predetermined height, the on the balancing resistors exercise a thermal load TBA, which corresponds to the previously determined thermal load TBV and a comparison of the equivalent number with a predetermined or predeterminable threshold and output a signal when reaching or exceeding the threshold. In other words, the thermal load TBV caused by a plurality of varying temperature strokes is represented by the number of temperature strokes of a given height and the thermal load caused by the single temperature stroke of this predetermined height.

The advantage of this method is that it is a method for the

Measurement of a successful or already performed thermal load provides, so that the determined measured value comparable to a permissible limit or threshold value and the occurrence of a caused by thermal load loss case is averted. That's the procedure

For example, when monitoring a vehicle battery suitable to notify a driver that, for example, a permissible maintenance interval or an acceptable aging limit of the balancing resistors

containing control unit has been reached and this has to be maintained or replaced.

It is an advantageous feature of this method that such signaling is not only due to, for example, the expiration of a fixed time interval or a fixed number of charging cycles, but in dependence on the actual thermal load.

The thermal load is caused by a variety in their height varying temperature changes. Much of this is due to temperature swings that arise due to the use of balancing resistors for balancing operations. It is the height of the Temperarturhube caused by the balancing, depending on the number of balancing resistors, the balancing is performed simultaneously.

This number in turn can scatter significantly depending on the battery or battery module and depends strongly on an equal distribution of battery cell characteristics of the operated within a string battery cells.

If, for example, a single battery cell has a high self-discharge rate in a battery module having six battery cells, the remaining five battery cells must be discharged relatively frequently via balancing to the same discharge state. Thus, it is relatively common to expect the use of five balancing resistors, combined with a relatively high temperature swing.

On the other hand, if the voltage, capacity and self-discharge values are almost identical in all battery cells, then balancing is comparatively rare and probably only required for isolated battery cells. The resulting temperature strokes are therefore comparatively small and comparatively rare.

Since the battery characteristics vary due to aging processes, it is difficult to predict an expected, balancing-related thermal load. Accordingly, the indication of the

A method according to the invention, which specifies a method for monitoring the thermal load of the balancing resistors, which takes into account the actual thermal load due to the use of the balancing resistances for balancing operations.

In this case, the thermal load TBV determined in a first step, which results on the basis of a multiplicity of varying temperature strokes, is converted in a second step into an equivalent number of temperature strokes of a specific predetermined or predefinable, thus non-varying, but fixed height. In other words, a number of temperature strokes of a fixed height is determined, which results in a thermal Load TBA of the balancing resistors leads, which corresponds to the caused by the plurality of varying temperature strokes thermal load TBV.

The advantage of this second step is that a wide variety of histories can be represented in terms of thermal loading by a single value, the equivalent number.

This value is compared in a third step with a predetermined or predeterminable threshold value at the time of reaching or exceeding which a signal is emitted. In this case, the threshold value can be selected, for example, such that the signal is emitted at a thermal load TBA of 90% of a thermal load TBmax, at which cracking or breaking of the solder joint is to be expected. In the example of using the method for monitoring a vehicle battery, this may mean that the driver is informed, for example via an indicator in the dashboard, that a permitted balance load of the control unit is 90% consumed and that it must be replaced.

Advantageously, the determination of the thermal load TBV of the balancing resistors is carried out in such a way that a determination of a distribution function takes place on the height of the temperature strokes, which occur on the basis of a use of the balancing resistors, so that the thermal load TBV through the

Distribution function is writable.

By means of such a distribution function, the frequency of temperature strokes of a respective height can be described; cumulatively, it describes the thermal load TBV which has arisen due to the balancing.

Advantageously, the determination of the distribution function on the height of the temperature strokes takes place in such a way that a determination of the number and frequency of use of the balancing resistors takes place and from this a calculation of a distribution function over the height of the temperature strokes on the basis of a

given heating function, which determines the dependence of _

Temperature strokes of the number of simultaneously used balancing resistors describes.

Such an approach has the advantage that no temperature data must be collected for the determination of the distribution function over the temperature strokes. Rather, the temperature swings are calculated on the basis of mostly available data on the successful balancing processes, including the number of balancing transactions and the number of involved

Battery cells respectively the associated balancing resistors is required. This data may be available, for example, from a memory of the control device, also called field data acquisition device.

Via a heating function, an assignment of temperature strokes to a predetermined number of balancing resistances involved in the balancing can be specified, so that on the basis of the data of the control device

Distribution function can be formed over the temperature strokes.

Advantageously, as an intermediate step during or after the determination of the number and frequency of use of the balancing resistors, a classification of the number of simultaneously used balancing resistors takes place. Such class division advantageously takes place in such a way that classes are formed for the simultaneous use of up to 5, from 6 to 10, from 1 to 20 and from over 20 balancing resistors. Such a classification helps to reduce the complexity of the process.

Advantageously, the heating function is performed by the control device, usually in two parts as Cell Supervision Circuit CSC and Battery Control Unit BCU, measured and / or stored in the battery device during use of the balancing resistors. In this case, a measurement of the heating function can be done once during a first commissioning. Alternatively, the heating function can also be preprogrammed or fed via interfaces usually present in the control device.

Further advantageously, the method is designed such that before the

Determination of an equivalent number of predefined or predefinable Temperature strokes to the thermal load TBV, caused by the use of balancing resistors, a base load is added. This is advantageously done by adding a distribution function representing the base load before the conversion of the aforementioned distribution function to an equivalent number of predetermined or predefinable temperature strokes to the distribution function. Advantageously, this base load corresponds to the number of temperature strokes due to the change of the ambient temperature and / or of the control device switch-on periods. This way, at the

Determination of the thermal load TBV considers the entire load spectrum of temperature changes.

In an advantageous embodiment of the method this is characterized

characterized in that the determination of an equivalent number of

Temperaturhüben a certain predetermined or predetermined height, which exert on the balancing resistors a thermal load TBA, which corresponds to the previously determined thermal load TBV, via suitable

Aging and / or acceleration laws, in particular Coffin-Manson, takes place.

Such an embodiment of the method enables a good description and conversion of the due to the temperature changes

Material fatigue in the solder joints, which is subject to no linear, but exponential dependence.

The invention furthermore relates to a battery device having a plurality of battery cells and a balancing device, which has a control device and balancing resistors for balancing the battery cells, and wherein monitoring by the control device of the thermal load of the balancing resistors according to a method of the preceding claims , As well as a battery-powered vehicle with such a battery device.

Due to the monitoring, such a battery device offers a high level of operational safety, as required, in particular, in the automotive industry. The invention will be explained in more detail below with reference to the figures of exemplary embodiments. Show it:

1 shows examples of distribution functions of the balancing number n over the number N of balancing resistors

2 shows an example of a heating function

3 shows examples of distribution functions of the number n 'of

Temperature strokes above their height AT

4 shows examples of an equivalent number A determined by transformation of the distribution function TBV

Fig. 1 shows three examples of distribution functions 1 1, 21, 31 of the balancing number n over the number N of balancing resistors. In other words, the three distribution functions 1 1, 21, 31 describe for three

Battery devices (battery device 1, battery device 2,

Battery device 3), how often balancing with a number of N

Balancing resistors was performed. In this case, the three distribution functions 1 1, 21, 31 designate three identical battery devices, hereinafter also referred to as batteries, but the battery cell characteristics of the battery cells connected in series within the batteries differ from one another due to production and / or aging. This manifests itself in

different charging / discharging efficiencies of the battery cells, which require a more or less frequent balancing with more or less involved battery cells. Decisive for the frequency of balancing with many

Battery cells is the maximum self-discharge difference between the

Battery cells of a battery.

Thus, the distribution function 1 1 belongs to a battery whose battery cells have low Selbstentladedifferenzen of 0.15 mV / day. The low Selbstentladedifferenz requires only minor corrections to the state of charge individual battery cells, the most common therefore only a single battery cell is involved. Balancing with many battery cells is rare or never necessary.

The distribution function 21 belongs to a battery whose battery cells have average self-discharge differences of 0.3 mV / day. Because of the bigger ones

Deviations of the charging states among each other are most often involved in the balancing of two battery cells with their respective balancing resistors. The distribution function 31 belongs to a battery whose battery cells are high

Have self-discharge differences of 0.5 mV / day. This means that due to, for example, a single very bad battery cell all the others have to be discharged relatively frequently via their balancing resistors. The most common value 6 ^"' results in the distribution function 31 for the simultaneous use of a high number 4 of participating balancing

Resistors.

The use of a high number 4 of balancing resistors takes place correspondingly less frequently with the associated frequency values 6 ^' and 6 ^" for the distribution functions 11 and 21. The data for generating the distribution functions can be taken from a field data acquisition device of a control device which comprises a BCU and a CSC consists.

Fig. 2 shows an example of a heating function in a graph in which the number N of balancing resistors is plotted versus a temperature rise. This heating function is for a number of 4 participating balancing resistors to see a corresponding increase in temperature 5. The characteristic is not linear, the temperature increase increases disproportionately with increasing number of simultaneously used balancing resistors.

FIG. 3 shows three examples of a distribution function 12, 22, 32, which describe the frequency 6 ^' , 6 ^" , 6 ^{"' of} a temperature lift 5. With increasing

Self-discharge difference 7 increases the frequency (or number n ') of higher

Temperature lifts. The distribution functions 12, 22, 32 for describing the frequencies of temperature strokes are via the heating function in FIG. 2 from the distribution functions 1 1, 21, 31 in Fig. 1 can be determined. They indicate which thermal load TBV the balancing resistors are subject to due to their use. Fig. 4 shows three examples of an equivalent number A 13, 23, 33 which over

Coffin-Manson are derived from the three distribution functions 12, 22, 32 shown in FIG. To do this, the thermal loads become everyone

Temperature according to the equations of Coffin-Manson transformed into a corresponding load at a predetermined temperature and summed. A division into temperature classes or a classification of the number of resistors involved in the balancing reduces the associated costs

Calculation. The equivalent number A 13, 23, 33, which represents the thermal load of the balancing resistors TBV, is comparable to a threshold value 8 for monitoring them.

Claims

claims

1 . A method for monitoring the thermal load of balancing resistors in a battery device having a plurality of

Battery cells, characterized by the steps

Determination of a thermal load TBV of balancing resistors, caused by a multiplicity of varying temperature ranges (5) due to a use of the balancing resistances for balancing processes varying in frequency (6 ^' , 6 ^" , 6 ^"' ) and intensity.

Determining an equivalent number (13, 23, 33) of temperature strokes (5) of a specific predetermined or predetermined height, which exert on the balancing resistors a thermal load TBA which corresponds to the previously determined thermal load TBV,

Comparison of the equivalent number (13, 23, 33) with a predetermined or predefinable threshold value (8) and delivery of a signal upon reaching or exceeding the threshold value (8).

2. The method according to claim 1, characterized in that for determining the thermal load TBV of the balancing resistors

Determination of a distribution function (12, 22, 32) over the height of the

Temperature strokes (5) takes place, which take place on the basis of a use of balancing resistors, wherein the thermal load TBV by the distribution function (12, 22, 32) is writable.

3. The method according to claim 2, characterized in that for determining the distribution function (12, 22, 32) over the height of the temperature strokes (5), first a Determination of number and frequency (1 1, 21, 31) of the use of balancing resistors and one

Calculation of a distribution function (12, 22, 32) over the height of the temperature strokes (5) by means of a predetermined heating function, which describes the dependence of the temperature strokes (5) on the number (4) of the simultaneously used balancing resistors.

A method according to claim 3, characterized in that as an intermediate step during or after the determination of the number and frequency (1 1, 21, 31) of the use of the balancing resistors initially a classification with respect to the number (4) simultaneously used balancing resistors.

Method according to one of claims 3 or 4, characterized in that the heating function is measured and / or stored by a control device in the battery device during use of the balancing resistors.

Method according to one of the preceding claims, characterized in that prior to the determination of an equivalent number (13, 23, 33) of predetermined or predeterminable temperature strokes (5) to the thermal load TBV, caused by the use of the balancing resistors, a base load is added ,

A method according to claim 6, characterized in that the base load the number of temperature strokes (5) due to the change of

Ambient temperature and / or corresponds to controller Einschaltperioden.

Method according to one of the preceding claims, characterized in that the determination of an equivalent number (13, 23, 33) of

Temperature strokes (5) of a certain predetermined or predeterminable height, which exert on the balancing resistors a thermal load TBA, which corresponds to the previously determined thermal load TBV, via suitable aging and / or acceleration laws, in particular Coffin-Manson.

9. Battery device with a plurality of battery cells and a balancing device having a control device and balancing resistors for balancing the battery cells, characterized in that the control device is configured to perform a monitoring of the thermal load of the balancing resistors according to a method of the preceding claims.

10. Battery-powered vehicle with a battery device according to claim 9.