DE102011005603A1 - Electric battery and method for measuring cell voltages in an electric battery - Google Patents

Abstract

The invention relates to an electric battery with a plurality of series-connected cells (12) and a voltage measuring device (20) for measuring the cell voltages (Vc), wherein for each cell (12) a first conduction path between a first cell terminal (c1) and a first measuring terminal (m1) of the voltage measuring device (20) and a second conduction path between a second cell terminal (c2) and a second measuring terminal (m2) of the voltage measuring device (20) runs in order to measure the relevant cell voltage (Vc) can. In order to increase the reliability and validity of the results of the cell voltage measurements, it is provided according to the invention that between a first circuit node (K) of the first line path and a second circuit node (L) of the second line path, a series connection of a connection resistor (Rb) and a controllable switching element ( T), and that in the second conduction path between the second cell terminal (c2) and the second circuit node (L), an auxiliary resistor (Rh) is arranged to perform a redundant measurement of the same cell voltage (Vc) when the switching element (T) is closed.

Description

The present invention generally relates to the monitoring of operating parameters of an electric battery composed of a plurality of battery cells, such as a traction battery of an electric or hybrid vehicle.

More particularly, the invention relates to an electric battery having a plurality of series-connected cells and a voltage measuring device for measuring the cell voltages, wherein for each cell a first conduction path between a first cell terminal of this cell and a first measuring terminal of the voltage measuring device, and wherein and a second conduction path between a second cell connection of this cell and a second measuring terminal of the voltage measuring device runs (About these line paths, the cell voltage in question can be measured). Furthermore, the invention relates to a method for measuring the cell voltages in such an electric battery using said voltage measuring device.

Electric batteries and method of cell voltage measurement of the aforementioned type are known from the prior art. By means of the two line paths provided for each cell, all cell voltages can advantageously be measured "directly" in a simple manner by transmitting a first cell potential (eg positive cell potential) via the first conduction path and a second cell potential (eg negative cell potential) the second conduction path to the associated measuring terminals of the voltage measuring device are performed. Under the condition of a virtually negligible measuring current, which can often be met without further ado, this direct voltage measurement does not preclude the conduction paths being resistive or intentionally provided with corresponding line resistances (in order to protect the relevant cell in the event of an input-side short circuit of the relevant voltage measurement channel). Incidentally, the values of such line resistances can also be taken into account in this measurement (together with the values of the "internal resistances" of the cells).

It is also known from the prior art to perform a "cell balancing" in an electric battery of the above type in order to eliminate any irregularities in the charge states of the individual cells from time to time. According to the concept of so-called "passive balancing", one or more of the cells (with a relatively high state of charge) are selected for this purpose on the basis of a cell voltage monitoring and individually discharged somewhat. The unloading passage used for this purpose can, for. B. as a resistive and activated switchable connection passage (discharge passage) between the first conduction path and the second conduction path can be provided.

In the case of batteries and measuring methods of the type of interest here, a fundamental problem is that due to a failure of individual electrical components which can never be completely excluded, incorrect results can be obtained in the measurement of cell voltages. Apart from ensuring a proper measurement operation, it would therefore be desirable to at least detect possible error cases or the underlying (component) errors in as many conceivable error cases in practice.

It is therefore an object of the present invention, in an electric battery or in a measuring method of the type described above, to increase the reliability and validity of the results of cell voltage measurements, and in particular to be able to better recognize any errors, for example, due to component failure.

In the case of the electric battery according to the invention, this object is achieved in that a series connection of a connection resistor and a controllable switching element runs between a first circuit node of the first line path and a second circuit node of the second line path, and that in the second line path between the second cell connection and the second circuit node an auxiliary resistor is arranged in order to be able to perform a redundant measurement of the same cell voltage when the switching element is closed. When the switching element is closed, the two circuit nodes or the two conduction paths form a "tap on a voltage divider which contains the connection resistance and the auxiliary resistance or is formed from these two resistors, so that the (redundant)" second partial measurement "carried out in this state Result results in a voltage corresponding to a fraction of the cell voltage in question, this fraction is given by the electrical properties of the components involved and thus known.

Here is a simple example: If the mentioned voltage divider is formed only of connection resistance, auxiliary resistance and the intermediate switching element (with, for example, negligible volume resistance in the closed state), and connection resistance and auxiliary resistance z. B. have the same value, so when the switching element is closed redundant measurement provides a voltage that is half as large as that when the switching element is open measured voltage (cell voltage) is. If an evaluation of the results of these two redundant partial measurements shows that the two measured voltages are not in the expected relationship to each other, there is an error case that may even be narrowed down even more favorably by a more accurate evaluation. In particular, results of optionally performed further partial measurements can also be used for this purpose (as described further below).

The invention is particularly suitable for cell voltage measurement on an electric battery with integrated battery monitoring. In this case, the voltage measuring device provided according to the invention forms part or functional part of the battery monitoring. In addition, such a battery monitoring, z. B. may be integrated in the form of an electronic monitoring circuit together with a cell stack in a battery case, also fulfill other monitoring tasks. Such a monitoring task may consist, for example, in the measurement of one or more cell temperatures. The battery monitoring can also fulfill control tasks, such as the control of a cooling or temperature control of the battery or of individual battery cells (based on a previous cell temperature measurement) or the control of a cell voltage equalization (eg based on a preceding cell voltage measurement).

In one embodiment of the invention, the electric battery is the traction battery of an electric or hybrid vehicle, for example comprising at least one "cell block" comprising at least 10, in particular at least 20 battery cells.

The invention is not limited to any particular type of battery cells. In one embodiment, z. For example, lithium-based cells (eg, lithium-ion cells).

The voltage measuring device may advantageously comprise one or more AD (analog / digital) converters, by means of which the voltage prevailing between the first measuring connection and the second measuring connection is converted into a digital representation, so that advantageously a digital further processing, in particular for the purpose of a more accurate evaluation the results of cell voltage measurement is possible.

In one embodiment, a first line resistance is arranged in the first line path between the first circuit node and the first measuring terminal, and / or a second line resistance is arranged in the second line path between the second circuit node and the second measuring terminal. Thus, a short circuit protection is advantageously realized, in the event that the voltage measuring device (eg AD converter device) causes a short circuit.

Preferably, at least the passages of the first conduction path and the second conduction path extending between the first circuit node and the first measurement connection or between the second circuit node and the second measurement connection are each provided with a line resistance. These resistors can z. B. be sized with identical resistance.

In one embodiment, the first measurement port and the second measurement port are interconnected via a buffer capacitor.

In one embodiment it is provided that the value of the auxiliary resistance is greater than 0.1 times the value of the connection resistance and / or the value of the auxiliary resistance is less than 10 times the value of the connection resistance. It can thus advantageously be achieved that the voltages which result during the first partial measurement and the second partial measurement do not deviate too much from one another, and thus in particular no "measuring range changeover" is required at the voltage measuring device.

In the method according to the invention for measuring the cell voltages in an electric battery of the type described above, it is provided that a measurement of at least one of the cell voltages is carried out both when the switching element is open and when the switching element of the relevant series connection is closed. These two measurements have already been referred to above as "first partial measurement" and "second partial measurement".

In this measuring method, a diagnosis of the cell voltage measurement is preferably also carried out on the basis of a comparison of the results of the two partial measurements.

An error case detectable by the diagnosis is present in particular if the results of the two partial measurements do not "match one another".

In the diagnosis, in addition to the result of the first partial measurement and / or the result of the second partial measurement, the result of at least one further partial measurement can also be used. In this regard, the following is of particular importance:
The battery according to the invention contains a series connection of several (eg 10 or more) electrical cell, wherein for each cell, a "first conduction path" and a "second conduction path" (and the other circuit components described above) are provided, and in the case of immediately adjacent cells in the cell series circuit is also clear that the "second conduction path" of a Cell simultaneously represents the "first conduction path" of an adjacent cell (or vice versa).

In the previous description of the measurement of a specific cell voltage, it has always been assumed that the voltage measured in this case is the voltage which results between the first measuring terminal and the second measuring terminal of the "associated" two conducting paths, the "first partial measuring" and the " second part measurement "are to be distinguished according to whether the" associated "switching element is open or closed.

As will be explained in more detail below in the description of an embodiment, however, other "partial measurements" are possible in which there is no such 1: 1 assignment between the measured cell voltage and the pair of conduction paths used for this purpose, ie z. B. for measuring the cell voltage of a particular cell not (only) a measurement on the "associated" line path pair but (additionally) via the "adjacent" line path pair.

Expressed in another way, the inventive design of the electric battery advantageously allows the implementation of even more "partial measurements" (in addition to the first and second partial measurements mentioned) in the context of an extended cell voltage measurement strategy, which advantageously the redundancy and error detection options are further increased.

The enlargement of the redundancy with a cell voltage measurement or cell voltage monitoring with the help of the execution of the mentioned partial measurements made possible by the invention by no means excludes that further measures to increase the redundancy are taken. This includes z. B. the repeated execution of a partial measurement, or z. Example, the multiple implementation of a partial measurement by means of different inputs (eg., Different AD converter (inputs) of a "multi-channel ADC") of the voltage measuring device (eg, after appropriate switching from one measurement input to another measurement input).

An advantageous method for operating an electric battery within the scope of the invention provides that besides a measurement of the cell voltages by means of a method of the type described above, an equalization ("balancing") of the cell charging states (eg cell voltages) by targeted temporary closing the switching elements is performed on those cells which have a relatively high state of charge or a relatively high cell voltage.

Such a so-called "passive balancing" can very advantageously already be carried out with those components which are present anyway in the case of the electric battery according to the invention (when the switching element is closed, a suitable discharge current flows via the associated connection resistor and the associated auxiliary resistor).

The invention will be further described by means of an embodiment with reference to the accompanying drawings. They show:

1 a block diagram of an electric battery with an integrated monitoring electronics, and

2 a block diagram of a detail from 1 ,

1 shows an electric battery 10 , z. As a traction battery of an electric or hybrid vehicle, with several series-connected electrochemical battery cells 12 (here: lithium-ion cells) and a monitoring electronics 14 ,

With the cells 12 For example, they may be so-called flat cells that stack one or more cell stacks or cell blocks within a battery case 16 form, with the monitoring electronics 14 structurally combined with the cell stack (s) likewise in this housing 16 is housed.

The monitoring electronics 14 includes in the example shown a central monitoring unit 18 as if by double arrows in 1 symbolized in communication with other devices of the monitoring electronics 14 as well as with an external control and / or monitoring device. In the present application example, the external device may be, for example, a central control component of an electric drive system of the relevant vehicle. In particular, the communication of the monitoring electronics 14 with such external units can, for. B. via a standardized bus system (eg., CAN bus).

Within the monitoring electronics 14 communicates the central monitoring unit 18 in particular with a series of 12-channel ADC ("analog-digital-converter") - units, hereinafter also referred to as "converter". In 1 is one of these converters 20 designated and acts as a voltage measuring device for direct measurement of the cell voltages of twelve cells 12 in the series connection of the cells 12 are arranged adjacent to each other. The twelve cells 12 that of the with 20 designated transducers are monitored for their cell voltages are in 1 outlined by a dashed line. In the 1 between these twelve cells 12 and the converter 20 indicated electrical connection arrangement serves the technical implementation of the cell voltage measurement and a so-called cell equalization ("balancing"). Both will be described below with reference to the 2 described in more detail.

2 illustrates the attachment of said twelve cells 12 to those cells 12 monitoring converter 20 , From these cells 12 are in 2 only the last six shown. Their cell voltages are designated Vc7 to Vc12.

How out 2 is evident for each cell 12 a cell 12 with connections of the converter 20 connecting circuitry is provided which repeats from cell to cell as shown. In the following, therefore, only such a circuit arrangement will be described in more detail by way of example, that is to say to the cell 12 associated with the cell voltage Vc12 wiring.

For this cell 12 A "first conduction path" runs between a first (positive) cell connection c1 and a first measurement connection m1 of the converter 20 and a "second conduction path" between a second (negative) cell terminal c2 and a second sense terminal m2 of the transducer 20 ,

The first conduction path extends from c1 via a first circuit node K and a line resistance Rf1 to the terminal m1. The second conduction path extends from c2 via an auxiliary resistor Rh, a second circuit node L and a second line resistance Rf2 to the connection m2.

The measuring connections m1 and m2 form the input of one of the twelve measuring channels of the (12-channel) converter 20 , A voltage VIN12 prevailing between the measuring terminals m1, m2 is supplied by the converter 20 converted into a digital signal (and as a measurement result in digital form to the central monitoring unit 18 the monitoring electronics communicates).

It is clear that the respective cell voltage Vc12 can be measured in a simple manner via the two conduction paths, since the cell voltage Vc12 can be conducted via these conduction paths directly to the relevant transducer input m1, m2, so that the voltage VIN12 measured there corresponds to the cell voltage Vc12. This type of measurement of the voltage VIN12 is also referred to below as "direct measurement" or "first partial measurement".

At this point it should be noted that in the illustrated embodiment, as in 2 easily comprehensible, single of the "conductive paths", "circuit nodes", "measuring terminals" common to each other adjacent to the cells 12 or cell voltages Vc are formed and used. So z. For example, the "second conduction path" for the cell with the cell voltage Vc12 is at the same time the "first conduction path" for the cell with the cell voltage Vc11. The "second circuit node" for the cell voltage cell Vc12 is at the same time the "first circuit node" for the cell with cell voltage Vc11, etc.

From the circuit node K of the first line path, a connection passage consisting of a connection resistor Rb and a transistor T goes to the circuit node L of the second line path. The "first partial measurement" is carried out in a high-resistance state of the connection passage, i. H. with transistor T. open

For switching the transistor T whose control terminal is connected to a corresponding output terminal of the converter 20 connected.

By the transistor T is brought into the conductive state by a corresponding drive signal, the associated cell 12 be discharged via the connection passage Rb, T between the nodes K and L.

Such a discharge of individual cells 12 is performed in the illustrated example in the context of a so-called cell equalization ("balancing"), based on a previous cell voltage measurement, the charge states of the individual cells 12 to match each other from time to time.

The method used here, relatively heavily charged cells 12 Unloading via a (resistive) discharge passage is commonly referred to as "passive balancing". This does not exclude that in the electric battery described here, alternatively or additionally, a so-called "active balancing" is performed in which individual cells are identified with relatively low charge and then actively charged to a more or less equal state of charge for all cells to effect.

In the illustrated example, the production of an electrical line connection between the nodes K and L, via the connection resistor Rb and the transistor T, but in addition to performing a further measurement operation for the cell voltage Vc12 by means of the associated measuring channel or input m1, m2 is used. When the transistor T is closed, the voltage VIN12 measurable between the measuring terminals m1, m2 results as a voltage drop at the series connection of the resistor Rb and the transistor T, wherein the voltage drop component at the transistor T is in practice mostly negligible (or taken into account in the measurement evaluation) ). This voltage drop is a certain fraction of the cell voltage Vc12, so that the measurement of VIN12 at conducting transistor T is also a measurement of Vc12. This redundant measurement of a cell voltage Vc by measuring the voltage VIN prevailing at the associated converter input m1, m2 is also referred to below as "indirect measurement" or "second partial measurement".

When carrying out both the first and the second partial measurement (eg, immediately following one another), it is advantageous not only to increase the redundancy and thus the reliability or informative value of the cell voltage measurement, but also to detect any errors, for example. B. those components possible or simplified, which have a significant influence on the value of the measured voltage (eg., VIN12).

In the illustrated embodiment, the two line resistances Rf1 and Rf2 have identical resistance values. The resistance values of the resistors Rb and Rh are preferably of the same order of magnitude and may be e.g. B. also be provided with mutually identical resistance value. In addition, in the example shown, a buffer capacitor Cf is provided, which connects the measuring terminals m1 and m2 with each other.

At the electric battery 10 is in the context of cell voltage monitoring for each of the cells 12 in each case a measurement of the relevant cell voltage is carried out in the manner described above, ie both with the associated transistor T open as well as with the associated transistor T closed. A comparison of the two partial measurements is made by the monitoring electronics 14 Furthermore, a diagnosis of the cell voltage measurement is performed, so that advantageously identified cases of errors and, if necessary, certain types of errors can be identified or localized.

Interestingly, the in 2 shown wiring between the cells 12 and the illustrated converter 20 (and the other converters 20 ) to carry out even more individual measuring operations or partial measurements in order to further increase the redundancy and the error diagnosis possibilities.

In the following, by way of example, such a measuring procedure for determining the cell voltage Vc12, Vc11, Vc10,... Is explained, which uses additional measuring processes in addition to the first and second partial measurements of these cell voltages Vc12, Vc11, Vc10,.

In the procedure z. B. first, the cell voltage Vc12 by means of a "first partial measurement" and a "second partial measurement" are determined. Where: VIN12 = Vc12 (first partial measurement) VIN12 = Vc12 - Vc12 × Rh / Rb (second partial measurement)

From each of these partial measurements, Vc12 can be determined.

Then (or simultaneously with the second partial measurement of Vc12), a measurement is made with the "adjacent channel" leading to the cell 12 belongs to the cell voltage Vc11, in which case the transistor T of this adjacent channel is also closed. It then applies: VIN11 = Vc11 + Vc12 × Rh / Rb (further individual measurements)

The voltage VIN11 applied to the measuring terminals of the adjacent channel and thus measured is thus a linear combination of the cell voltages Vc11 and Vc12. From the voltage VIN11 measured in this way, the cell voltage Vc11 can thus be determined by inserting the cell voltage Vc12 known from the first and second partial measurements into the above relationship.

This determination of Vc11 advantageously represents a third redundant measurement of the cell voltage Vc11 (in addition to the first and second partial measurements of the cell voltage Vc11 by means of the measuring channel associated with Vc11).

The above-described measuring procedure can be continued in a corresponding manner for multiply redundant determination of further cell voltages (eg Vc10, Vc9,...), And is preferably carried out by means of a software algorithm, which can also include the calculation steps required for the result evaluation.

Claims (7)

Electric battery with several cells connected in series ( 12 ) and one Voltage measuring device ( 20 ) for measuring the cell voltages (Vc), wherein for each cell ( 12 ) a first conduction path between a first cell terminal (c1) of this cell ( 12 ) and a first measuring terminal (m1) of the voltage measuring device ( 20 ) and a second conduction path between a second cell terminal (c2) of this cell ( 12 ) and a second measuring connection (m2) of the voltage measuring device ( 20 ) runs in order to be able to measure the relevant cell voltage (Vc), characterized in that between a first circuit node (K) of the first line path and a second circuit node (L) of the second line path , a series connection of a connection resistor (Rb) and a controllable switching element (T) runs, and that in the second conduction path between the second cell terminal (c2) and the second circuit node (L), an auxiliary resistor (Rh) is arranged to perform a redundant measurement of the same cell voltage (Vc) when the switching element (T) is closed , Electric battery according to claim 1, wherein in the first conduction path between the first circuit node (K) and the first measuring terminal (m1), a first line resistance (Rf1) is arranged and / or wherein in the second conduction path between the second circuit node (L) and the second measuring terminal (m2) a second line resistance (Rf2) is arranged. Electric battery according to one of the preceding claims, wherein the first measuring terminal (m1) and the second measuring terminal (m2) via a buffer capacitor (Cf) are interconnected. An electric battery according to any one of the preceding claims, wherein the value of the auxiliary resistance (Rh) is greater than 0.1 times the value of the connection resistance (Rb) and / or the value of the auxiliary resistance (Rh) is less than 10 times the value of the connection resistance (Rb). Method for measuring the cell voltages in an electric battery ( 10 ) according to one of the preceding claims, using the tension measuring device ( 20 ), wherein a measurement of at least one of the cell voltages (Vc) is carried out both when the switching element (T) is open and when the switching element (T) of the relevant series connection is closed. Method according to claim 5, wherein a diagnosis of the cell voltage measurement is also carried out on the basis of a comparison of the results of the two partial measurements. Method for operating an electric battery ( 10 ) according to one of claims 1 to 4, comprising a measurement of the cell voltages (Vc) by means of a method according to claim 5 or 6, further comprising a homogenization of the cell charge states by targeted temporary closing of the switching elements on those cells ( 12 ), which have a relatively high cell charging state.

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