DE102006033629B4 - Method and device for determining the state of a battery - Google Patents

Abstract

Method for determining the state (Ri, SOC, SOH) of a battery (1) having a plurality of cells (1a-1n) or groups of cells (2a, 2b) in which the battery (1) briefly loads and the voltage response (U (t) ) of individual cells (1a-1n) or cell groups (2a, 2b) is evaluated so as to determine the state (Ri, SOC, SOH) of the cells (1a-1n) or cell groups (2a, 2b), wherein - a classification procedure (Steps 10-12), in which the cells (1a-1n) or groups are classified according to their state (Ri, SOC, SOH), and thereafter a sequential diagnostic procedure (steps 13-16 ), in which the order of evaluation of the cells (1a-1n) or groups (2a, 2b) depends on their classification.

Description

State of the art

The invention relates to a method for determining the state of a battery according to claim 1 and to a corresponding device according to patent claim 7.

Known vehicle batteries such. B. NiMH batteries, Li-ion batteries or DLC batteries (DLC: double-layer capacitor), consist of several series-connected single cells, each having a partial voltage of a few volts, z. B. 2 V generate. The number of cells determines the rated voltage of the battery, the z. B. 12 V or 42 V, in hybrid vehicles can also be 500V.

Due to manufacturing tolerances or thermal influences, the state of charge SOC (state of charge) or the SOH (state of health) or the internal resistance Ri of the individual cells is usually different. This significantly affects the performance of the battery, since the cell with the lowest state of charge and the cell with the highest state of charge for the charging and discharging of the battery have a limiting effect. That is, the battery can not be recharged until the fullest cell is fully charged and will not be discharged until the charge of the void cell is exhausted. The deviation of the individual cells from each other usually increases with increasing life or load of the battery. In order to ensure a reliable power supply of an electrical network, it is necessary to monitor the individual cells or cell groups of the battery.

This is z. B. known to charge the battery with a short current pulse (in loading or unloading) and to evaluate the voltage response of the individual cells or individual cell groups. For this purpose, so-called battery state detection devices (BZE) are used, which basically comprise a control device with an algorithm (mathematical model) stored therein, which consists of measured battery operating variables, such. For example, the battery current, the battery voltage, and the battery temperature calculate the current battery condition (Ri, SOC, or SOH).

The evaluation of the voltage responses of the individual cells can be done either in parallel or sequentially. The parallel evaluation is relatively complicated and compute-intensive, since, in particular in the case of hybrid batteries, which may comprise 100 or more cells, correspondingly many measured values must be processed simultaneously. On the other hand, the sequential evaluation has the disadvantage that, although the diagnosis of the cells evaluated first (after the current pulse) is still relatively accurate, the diagnosis of the cells evaluated last corresponds only insufficiently with the actual state of the cells, since the cell voltage in the time period between load and voltage measurement is already changed by other influences. The condition of the battery can thus be determined only relatively inaccurate. In the publication GB 2 328 288 A For example, a battery condition determination and classification method and apparatus are described wherein a profile of a battery response signal is analyzed for a test signal and used for classification.

In the publication US 2004/0 155 626 A1 a device and a method for determining the state and mechanical sorting of a battery are described, wherein the mechanical sorting is based on the result of the state determination. In this case, the device has a conveyor belt which supplies the battery to a battery test device, where the determination of the electrical condition of the battery takes place.

The publication GB 1 454 358 A describes a method for determining the state of a lead-acid battery, wherein the lead-acid battery is classified in a discharging process as in good condition, when a voltage difference between the start and battery voltage after a predefined period of time falls below a voltage difference reference value. Otherwise, a charging process is carried out and a charging current in the battery is compared with a current reference value, wherein when the current reference value is undershot, the battery is classified as being in a defective state.

Disclosure of the invention

It is therefore the object of the present invention to provide a method for the diagnosis of batteries, which is particularly accurate and can be carried out with little processing effort.

This object is achieved according to the invention by the features specified in claim 1 and in claim 7. Further embodiments of the invention are the subject of dependent claims.

An essential aspect of the invention is first to perform a classification of the cells, in which the cells or groups are classified according to their state of charge or their performance, and then to perform a sequential diagnosis, in which the order of evaluation is determined by the classification , The state of charge or the performance thus determines the order of evaluation and not the physical arrangement of the cells or Groups. Cells or groups of cells whose condition is poor or even "critical" are preferably evaluated immediately after the current load, and those whose condition is safe, at a later date. The accuracy of the evaluation of even weaker cells or groups of cells can thus be significantly improved and thereby the reliability of the power supply can be increased.

In the classification procedure, the battery is preferably loaded with a current pulse and the individual cells or cell groups (hereinafter referred to as "cells") then dependent on their voltage response in different classes, eg. B. A, B and C divided. The classification can be performed sequentially or in parallel.

In the later diagnostic procedure, depending on your classification, the individual cells may also be evaluated more frequently or less frequently. That is, after a current load, it is not absolutely necessary to evaluate all the cells. Rather, it is sufficient, stronger cells z. For example, evaluate only every nth time. Weaker cells or cell groups are preferably evaluated more frequently. As a result, the computational effort can be further reduced.

According to a preferred embodiment of the invention, the cells are evaluated sequentially in the diagnostic procedure. However, a (partially) parallel evaluation is also conceivable.

The classification of the cells is preferably carried out at certain time intervals. As a result, it is possible to respond to changes in individual cells during the operating life of the battery.

The number of classes can be 3, for example, such. "Strong cells", "medium cells" and "weak cells" or cell groups. Alternatively, of course, more or less classes can be introduced. In extreme cases, the cells or groups could also be sorted in the order of their current state. For each cell or group, a quasi-own "class" forms with only one element.

Brief description of the drawings

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

1 a schematic representation of an arrangement for checking a battery; and

2 the essential procedural steps of a method for monitoring a vehicle battery.

Embodiments of the invention

1 shows an arrangement for monitoring a vehicle battery 1 in terms of state of charge (SOC), power (SOH) or internal resistance (R _i ). The vehicle battery 1 includes a plurality of rows connected in series 1a - 1n , each having a partial voltage of a few volts, z. B. 2 V deliver. At the battery 1 In the present example, this is a Li-ion battery of a hybrid vehicle containing more than 100 cells 1a - 1n and provides a voltage in the range of several 100V.

The single cells 1a - 1n are via associated connections 6a - 6o each separately addressable. Multiple cells 1a - 1n can also be in groups 2a . 2 B be summarized. An electronics 4 , each with the individual cells 1a - 1n or groups 2a , b is used to evaluate the cells or groups. The Electronic 4 , z. As a controller includes for this purpose an evaluation algorithm 5 consisting of different battery state variables, in particular the battery current I, the cell voltage and the temperature, the internal resistance Ri; the state of charge (SOC) and / or the capacity (SOH) of the cells 1a - 1n or groups 2a , b calculated. The battery current I is detected by means of a current sensor 3 measured and via a corresponding input I the controller 4 fed.

In order to determine the condition of the battery, a two-stage procedure is carried out in which the cells 1a - 1n or groups 2a . 2 B first classified according to their performance, and then a sequential diagnosis is performed in which the cells 1a - 1n or groups 2a . 2 B be evaluated sooner or later after the load depending on their classification. The exact procedure is described below with reference to 2 explained in more detail.

2 shows the essential steps of a method for monitoring a battery 1 with several cells 1a - 1n which are separately addressable.

In the classification procedure (steps 10 - 12 ) is the battery 1 initially loaded with a current pulse (in the discharge or charging direction) and the voltage response of the cells 1a - 1n or groups 2a , b evaluated to determine the internal resistance Ri, state of charge (SOC) or power (SOH). The classification can be sequential or (partly) parallel (step 12 ).

Depending on the reaction of the cells 1a - 1n or cell groups 2a . 2 B become the cells 1a - 1n or groups 2a . 2 B then in step 12 into different classes, eg B. A, B and C classified. Alternatively, of course, more or less classes could be set up. For example, class A includes cells 1a - 1n with high state of charge, class B, cells with a medium state of charge and the class C cells with a low state of charge. The latter are for the performance of the battery 1 crucial and therefore need to be monitored very closely.

In the following diagnostic procedure (steps 13 - 16 ), the cells become 1a - 1n or groups 2a . 2 B then evaluated sequentially, depending on their classification. This is done by the battery in step 13 initially charged again with a current pulse .DELTA.I and then in step 14 first the weaker cells 1a - 1n or cell groups 2a . 2 B from class C, then the cells or groups of cells contained in class B and then in class A. 2a . 2 B evaluated.

Not all cells need to be in a diagnostic cycle 1a - 1n or cell groups 2a . 2 B be checked. Optionally z. For example, such cells 1a - 1n or cell groups 2a . 2 B , which are relatively strong and thus rather uncritical, can only be checked in every nth cycle. As a result, further computing power can be saved.

The classification of cells 1a - 1n can be repeated at certain intervals. This allows the classification to be adapted to a possibly changed state.

Claims (7)

Method for determining the state (Ri, SOC, SOH) of a battery ( 1 ) with several cells ( 1a - 1n ) or cell groups ( 2a . 2 B ), where the battery ( 1 ) and the voltage response (U (t)) of individual cells ( 1a - 1n ) or cell groups ( 2a . 2 B ) is evaluated so as to determine the state (Ri, SOC, SOH) of the cells ( 1a - 1n ) or cell groups ( 2a . 2 B ), wherein - a classification procedure (steps 10 - 12 ), in which the cells ( 1a - 1n ) or groups or groups, depending on their condition (Ri, SOC, SOH), and then a sequential diagnostic procedure (steps 13 - 16 ), in which the order of evaluation of the cells ( 1a - 1n ) or groups ( 2a . 2 B ) according to their classification. A method according to claim 1, characterized in that in the diagnostic procedure (steps 13 - 16 ) the cells ( 1a - 1n ) or groups ( 2a . 2 B ) with a worse condition (Ri, SOC, SOH) are evaluated earlier than those with a better condition (Ri, SOC, SOH). Method according to claim 1 or 2, characterized in that the cells ( 1a - 1n ) or groups ( 2a . 2 B ) are evaluated more frequently or less frequently depending on their classification. Method according to one of the preceding claims, characterized in that the cells ( 1a - 1n ) or groups ( 2a . 2 B ) in the diagnostic procedure (steps 13 - 16 ) are evaluated sequentially. Method according to one of the preceding claims, characterized in that the cells ( 1a - 1n ) or groups ( 2a . 2 B ) are reclassified at certain intervals. Method according to one of the preceding claims, characterized in that the cells ( 1a - 1n ) or groups ( 2a . 2 B ) are classified into at least three different classes (A, B, C). Contraption ( 4 ) for determining the state (Ri, SOC, SOH) of a battery ( 1 ) with several cells ( 1a - 1n ) or cell groups ( 2a . 2 B ), where means ( 5 ) are provided for carrying out one of the methods described above.

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