DE102021005087A1 - Method for monitoring a traction battery - Google Patents

Abstract

The invention relates to a method for monitoring a traction battery for an electrically powered vehicle, a plurality of slave controllers (3) each measuring cell voltages of a number (N) of battery cells (4) of the traction battery, the slave controllers (3) each measuring wireless data, comprising the cell voltages, a maximum cell voltage (U _max), a minimum cell voltage (U _min) and a fault status (FS) determined and transmitted to a master controller (2), wherein each of the slave controller (3) each a mean value ( U ) of the cell voltages is determined and transmitted with a first bit width to the master controller (2), and that from each of the slave controllers (3) differences (Δ) in the number (N) of cell voltages to the mean value ( U ) are determined and transmitted to the master controller (2) with a second bit width, the first bit width being greater than the second bit width.

Description

The invention relates to a method for monitoring a traction battery for an electrically driven vehicle according to the preamble of claim 1.

In the case of high-voltage traction batteries for electrically powered vehicles, between 100 and 200 cells are often connected in series, depending on whether it is a system with an operating voltage of 400 V or 800 V. Each individual cell voltage should be monitored in order to enable optimal operation and protection against overcharging. In order to enable the most dynamic operational management possible and thus maximum exhaustion of the cell voltage limits, the cell voltages should be present at a battery control device with high frequency and low latency. This is mostly implemented through the transmission on a dedicated daisy chain communication from cell monitoring ASICs to the battery control unit with a bandwidth of up to 2 Mbit / s. Since the cabling of these cell monitoring ASICs is both costly and a possible source of error due to interruptions in the line, newer cell monitoring devices provide for radio transmission (often in the frequency range of 2.4 GHz). This is accompanied by a bandwidth limitation.

The LTC6813 multi-cell battery monitor from Analog Devices enables the cell voltage to be measured and transmitted at intervals of approximately 1 ms. In practice, however, the sample rate is reduced because, in addition to the cell voltage measurement, diagnoses also have to be carried out, so that typically 10 ms are achieved.

1. a) das Referenzmodulsteuergerät versendet einen Referenzmesswert auf dem Kommunikationskanal,
2. b) die Modulsteuergeräte bestimmen Differenzwerte eigener Messwerte zum Referenzmesswert,
3. c) die Modulsteuergeräte versenden die Differenzwerte der eigenen Messwerte zum Referenzmesswert auf dem Kommunikationskanal und
4. d) das Hauptsteuergerät rekonstruiert die Messwerte der Modulsteuergeräte anhand der Differenzwerte und des Referenzmesswerts.

the DE 10 2013 217 451 A1 describes a method for data transmission in a battery management system with at least one main control device and a number of module control devices that send measured values to the main control device via a communication channel. It is provided that one of the module control devices is a reference module control device. The procedure comprises the following steps:

1. a) the reference module control device sends a reference measured value on the communication channel,
2. b) the module control devices determine differential values of their own measured values to the reference measured value,
3. c) the module control devices send the differential values of their own measured values to the reference measured value on the communication channel and
4. d) the main control device reconstructs the measured values of the module control devices based on the difference values and the reference measured value.

The invention is based on the object of specifying a novel method for monitoring a traction battery for an electrically driven vehicle.

The object is achieved according to the invention by a method for monitoring a traction battery for an electrically driven vehicle with the features of claim 1 or 2.

Advantageous refinements of the invention are the subject matter of the subclaims.

In a method according to the invention for monitoring a traction battery for an electrically driven vehicle, a plurality of slave controllers each measure cell voltages of a number of battery cells of the traction battery, the slave controllers each wirelessly providing data including the cell voltages, a maximum cell voltage, a minimum cell voltage and an error status bit, and transmit it to a master controller. According to the invention, a mean value of the cell voltages is determined by each of the slave controllers and transmitted to the master controller with a first bit width, with each of the slave controllers determining differences between the number of cell voltages and the mean value and sending them to the master with a second bit width. Controller are transmitted, the first bit width is greater than the second bit width.

1. 1. Minimal- und Maximalspannungen mit hoher Frequenz mit möglichst kleiner Abweichung zu übertragen,
2. 2. die einzelnen Zellspannungen mit geringerer Frequenz und zusätzlich reduzierter Bandbreite zu übertragen, ohne die Auflösung zu beeinträchtigen,
3. 3. die unter 2. aufgestellte Forderung vom Betriebszustand skalieren zu können, wobei während dynamischer Phasen die Zellspannung nicht mit voller Auflösung von jeder Zelle vorliegen muss.

The method according to the invention meets the high demands of drive train control in the vehicle with regard to data rate and latency and allows:

1. 1. to transmit minimum and maximum voltages at high frequency with the smallest possible deviation,
2. 2. to transmit the individual cell voltages with a lower frequency and additionally reduced bandwidth without impairing the resolution,
3. 3. To be able to scale the requirement of the operating state set out under 2., whereby the cell voltage does not have to be present with full resolution of each cell during dynamic phases.

Another advantage is the faster provision of maximum and minimum values for control algorithms. These can be as smaller Data packets are packaged and can be transmitted independently of other, in particular non-time-critical, measured variables.

Embodiments of the invention are explained in more detail below with reference to drawings.

• 1 eine schematische Ansicht eines Batterieüberwachungssystems,
• 2 eine schematische Ansicht eines Verfahrens zur Batterieüberwachung, und
• 3 eine schematische Ansicht eines Verfahrens zur Informationsverarbeitung im Batterieüberwachungssystem.

Show:

• 1 a schematic view of a battery monitoring system,
• 2 a schematic view of a method for battery monitoring, and
• 3 a schematic view of a method for information processing in the battery monitoring system.

Corresponding parts are provided with the same reference symbols in all figures.

1 Figure 3 is a schematic view of a battery monitoring system 1 , especially for a traction battery of an electrically powered vehicle. The battery monitoring system 1 includes a master controller 2 and a plurality of slave controllers 3 (also called nodes), which can be designed as ASICs and each for monitoring a number N of battery cells 4th configured. The slave controller 3 communicate with the master controller via radio, for example in the frequency range of 2.4 GHz 2 .

The data necessary for regulating a drive train of the vehicle and for safety, in particular a maximum cell voltage U _max , a minimum cell voltage U _min and an error status bit are always transmitted with a sampling rate of 10 ms or less. Depending on the number N of the battery cells 4th , the channel quality or bandwidth and the operating status of the battery cells 4th can transmit the cell voltages of the battery cells 4th be scaled. Every cell voltage is no longer transmitted with full resolution, for example 16 bits, but only the mean value U the cell voltages of a slave controller 3 monitored battery cells 4th with a first, in particular higher, bit width, for example 10 bits, and the difference Δ the cell voltage of each individual from the slave controller 3 monitored battery cell 4th to this mean U with a second, in particular lower, bit width, for example 6 bits. Here one makes use of the fact that the battery cells 4th are connected in series, so the voltage changes in the same way depending on the current and for the correct functioning of a battery anyway by the battery monitoring system 1 Care must be taken that the cell voltages are within a narrow range.

The constant transmission of the maximum and minimum cell voltage Umax, Umin ensures that this value is also achieved in the event of a faulty battery cell 4th is transmitted extremely precisely and the battery monitoring system 1 can react correctly. In particular, it can be clearly established whether at least one of the cell voltages is outside a normal operating window and is therefore relevant to safety. If the spread of the cell voltages is generally higher, then either the data rate can be reduced and the bit width for the difference Δ (also referred to as delta bit) can be increased or resolution can be waived. In a further approach, it could simply be one strongly from the mean U different cell voltage of a battery cell 4th marked as being outside the range of the differential voltage range.

A distinction can also be made between two forms: In a first embodiment, the mean values are U the cell voltages from the respective slave controller 3 calculated (so several mean values are calculated U transfer). In a second embodiment, the mean value U the cell voltages from the master controller 2 calculated and the slave controllers 3 made available.

2 Figure 3 is a schematic view of a method for battery monitoring. The slave controller 3 monitors the number N of battery cells 4th and measures their cell voltages, for example with a sampling rate of 10 ms. The slave controller 3 has an analog front end 5 in which an analog-digital conversion of the measured cell voltages is carried out. The slave controller 3 also has a minimum value determiner 6th to determine a minimum value U _min the cell voltages, a maximum value calculator 7th to determine a maximum value U _max the cell voltages and a low-pass filter 8th for each of the cell voltages. Next, the slave controller instructs 3 an averager 9 to form an average U all through the low pass filter 8th filtered cell voltages, for example with a bit width of 16 bits. Next, the slave controller instructs 3 a subtracter 10 for the formation of N Differences Δ from the respective through the low-pass filter 8th filtered cell voltages with the mean value U on, for example with a bandwidth of 8 bits. Next, the slave controller instructs 3 a scheduling module 11 (Scheduler), which has the minimum value with a sampling rate of 10 ms, for example U _min , the maximum value U _max , an error status bit FS , the mean U and the N Differences Δ receives as input values and according to a schedule via a wireless transmitter unit 12th to the master controller 2 transmits. The cell monitoring electronics, ie the slave controllers 3 , perform diagnostics to identify faulty conditions, such as an open test lead to a battery cell 4th to be able to detect. If such If the diagnosis is successful, the measured voltages are to be regarded as invalid. Since this, as well as exceeding a maximum or minimum voltage, can represent a safety-critical state, it must also be transmitted, in particular in a 10 ms grid.

In a further embodiment it can be provided that the mean value U not in the slave controller 3 , but in the master controller 2 for all battery cells 4th the battery, not just the one on one of the slave controllers 3 connected battery cells 4th , is determined. 3 is a schematic view of a method for information processing in the battery monitoring system 1 according to this further embodiment.

Do this in one step S1 initially all cell voltages from the slave controllers 3 determined and sent to the master controller 2 transmitted in full length. The master controller 2 calculates the mean value from this U for all battery cells 4th . For example, it can be provided that the difference is expected with the following resolution: Umean = 3.70 and 4mV / bit with 8-bit resolution and 500mV full deflection (signed, therefore half) or Umean = 3.77 and 0.4mV / bit with 8 bit resolution and 50mV full deflection. It can also be provided that the master controller 2 the individual cell voltage values are reconstructed.

• In einem Schritt S2 sendet der Master-Controller 2 den Mittelwert U an die Slave-Controller 3. Diese berechnen in einem Schritt S3 unter Nutzung dieses Mittelwerts U die N Differenzen Δ aus den jeweiligen durch den Tiefpassfilter 8 gefilterten Zellspannungen zum Mittelwert U und senden die Differenzen Δ an den Master-Controller 2 zurück. Der Master-Controller 2 berechnet in einem Schritt S4 aus den empfangenen Differenzen Δ einen Mittelwert Δ der Differenzen Δ und daraus einen neuen Mittelwert U für alle Batteriezellen 4 und beginnt die Schleife von vorn bei Schritt S2.

Then the following process is repeated in a loop:

• In one step S2 sends the master controller 2 the mean U to the slave controller 3 . Calculate these in one step S3 using this mean U the N Differences Δ from the respective through the low-pass filter 8th filtered cell voltages to the mean U and send the differences Δ to the master controller 2 return. The master controller 2 calculated in one step S4 from the differences received Δ an average Δ of the differences Δ and from this a new mean value U for all battery cells 4th and start the loop over at step S2 .

A plausibility check can be provided in which it is determined whether the mean value U between the minimum value U _min and the maximum value U _max lies. If it doesn't, then an error has occurred and step S1 must be run again.

In addition to the mean value U the cell voltages also a cell current from the master controller 2 via broadcast to the slave controller 3 be transmitted. As a result, cell resistances (impedances) can appear on the slave controllers 3 can be calculated directly.

• Liegt die maximale Differenz Δ außerhalb des Wertebereichs des Signals für die zu sendende Differenz Δ entsprechend dessen Bitbreite, dann wird diese abgeschnitten. Entsprechend müssen für einen Überlauf in negativer oder positiver Richtung Werte reserviert werden, um dies zu erkennen. Beispielsweise könnte bei 8-Bit, einer maximalen Zellspreizung von 200mV und einer Auflösung von 1mV der Wert 0xFF für einen positiven Überlauf und der Wert 0x00 für einen negativen Überlauf reserviert sein.

The following boundary conditions can be relevant for the procedure:

• Is the maximum difference Δ outside the range of values of the signal for the difference to be sent Δ according to its bit width, then this is cut off. Correspondingly, values must be reserved for an overflow in negative or positive direction in order to recognize this. For example, with 8-bit, a maximum cell spread of 200mV and a resolution of 1mV, the value 0xFF could be reserved for a positive overflow and the value 0x00 for a negative overflow.

List of reference symbols

1

Battery monitoring system

2

Master controller

3

Slave controller

4th

Battery cell

5

analog frontend

6th

Minimum appraiser

7th

Maximum value calculator

8th

Low pass filter

9

Averaging

10

Subtraction term

11

Scheduling module

12th

Sending unit

FS

Error status bit

N

number

S1 to S4

step

Umin

Minimum value, minimum cell voltage

Umax

Maximum value, maximum cell voltage

U

Average

Δ

difference

Δ

Mean of the differences

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102013217451 A1 [0004]

Claims (8)

A method for monitoring a traction battery for an electrically powered vehicle, wherein a plurality of slave controllers (3) each measure cell voltages of a number (N) of battery cells (4) of the traction battery, the slave controller (3) each comprising wireless data determine the cell voltages, a maximum cell voltage (U _max ), a minimum cell voltage (U _min ) and an error status bit (FS) and transmit them to a master controller (2), characterized in that each of the slave controllers ( 3) a mean value each ( U ) of the cell voltages is determined and transmitted with a first bit width to the master controller (2), and that from each of the slave controllers (3) differences (Δ) in the number (N) of cell voltages to the mean value ( U ) are determined and transmitted to the master controller (2) with a second bit width, the first bit width being greater than the second bit width. A method for monitoring a traction battery for an electrically powered vehicle, wherein a plurality of slave controllers (3) each measure cell voltages of a number (N) of battery cells (4) of the traction battery, the slave controller (3) each comprising wireless data determine the cell voltages, a maximum cell voltage (U _max ), a minimum cell voltage (U _min ) and an error status bit (FS) and transmit them to a master controller (2), characterized in that each of the slave controllers ( 3) all cell voltages are determined and transmitted to the master controller (2), with the master controller (2) calculating an average value from the cell voltages ( U ) is calculated for all battery cells (4), with the following steps being carried out in a loop: - The master controller (2) sends the mean value ( U ) to the slave controller (3), - the slave controller (3) calculate differences (Δ) between the number (N) of cell voltages and the mean value ( U ) and send the differences (Δ) to the master controller (2), and - the master controller (2) calculates an average ( Δ ) of the differences (Δ) and from this a new mean value ( U ) the cell voltages for all battery cells (4). Procedure according to Claim 1 or 2 , characterized in that the data is transmitted with a sampling rate of 10 ms or less. Method according to one of the Claims 1 or 3 , characterized in that the first bit width is 10 bits or 16 bits. Method according to one of the Claims 1 , 3 or 4th , characterized in that the second bit width is 6 bits or 8 bits. Method according to one of the Claims 1 or 3 until 5 , characterized in that with a higher spread of the cell voltages either the sampling rate is reduced and the bit width for the difference (Δ) is increased or the resolution for the difference (Δ) is reduced Method according to one of the preceding claims, characterized in that a strongly different from the mean value ( U ) Different cell voltage of a battery cell (4) is identified as being outside of a differential voltage range. Procedure according to Claim 2 , characterized in that it is determined whether the mean value ( U ) lies between the minimum value (U _min ) and the maximum value (U _max ) and that otherwise all cell voltages are determined by each of the slave controllers (3) and transmitted to the master controller (2) with the full bit width, whereby the master Controller (2) calculates the mean value from the cell voltages ( U ) is calculated for all battery cells (4) and executes the loop again.

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