DE102012214878A1 - Method for charge equalization with manufacture and repair of lithium ion battery system for e.g. wind-power plant, involves limiting and aborting balancing current on given amount larger than zero when current falls below given amount - Google Patents

Abstract

The method involves registering electrical parallel connections to connect battery cells. The open circuit voltage is registered to associate battery cell according to magnitude and direction. The registered data is evaluated to identify battery cells having wrong polarity or amount concerning open circuit voltage. The balancing current in Kirchhoff's stitch is measured during electrical parallel connection of battery cells and ruled. The balancing current is limited on given amount larger than zero of charge equalization and aborted when balancing current falls below given amount.

Description

The present invention relates to a method for charge compensation in the manufacture and / or repair of a battery system with several steps, such as registering all to be connected in electrical parallel battery cells, measuring the open circuit voltage of each battery cell or register the open circuit voltage such that each battery cell exactly their open circuit voltage after Amount and direction is assigned.

State of the art

It is becoming apparent that in the future both in stationary applications (for example in wind turbines) and in vehicles (for example in hybrid and electric vehicles), more and more new battery systems will be used. Battery systems are constructed of battery cells or battery modules, which are electrically connected in the battery system. The cells are connected in series and optionally in parallel. In a parallel circuit, a distinction is made between a parallel connection of cell strings, which consist of several series-connected individual cells (parallel connection then takes place, for example, at the module level or at the level of the entire battery) and a direct parallel connection of individual cells.

In lithium-ion batteries for electric and hybrid vehicles currently state of the art that either pure series circuits of battery cells or - if the capacity of the cells for the required energy content at a maximum maximum voltage of the battery is not sufficient - additionally used a parallel circuit at the cell level becomes. The parallel connection is "hard", that is, the cells are connected as low as possible with each other. The electrical connection of the cells is, after the cells have been mechanically fixed, for example, in a battery module, made by placing a metallic cell connector and then screwing or welding. In 1 By way of example, the serial interconnection of 3 times a parallel configuration of 2 cells each to a so-called 3s2p (3 in series, 2 in parallel) configuration according to the prior art is shown.

The following problem arises during the manufacture and repair of arrangements which comprise a parallel connection of cells: If the cells have different states of charge, very high compensation currents flow when the cell connectors are put on (this also applies to screwed and welded connections). The reason for this is that different initial voltages of the battery cells discharge via their very low internal resistance. For clarification, an example of lithium-ion battery cells is listed, as they are currently being developed by SB LiMotive to the series: A 60 ampere-hour cell has in the range of medium states of charge at room temperature for short-term pulse loads internal resistance in the range of 300 micro-ohms. If the cells have a difference in charge state of 20% when repairing the battery, this leads to differences in the voltage in the range of up to 400 milli-volts. If the cell connectors are set up to produce the parallel connection, equalizing currents in the range of 670 amps result. Among other things, this can lead to sparking at the terminals, which is undesirable in the production process or in the repair of a battery system and is often not permitted for safety reasons.

State of the art in the manufacture of battery modules is that in the cells prior to introduction into the manufacturing process with a separate device, a charge compensation is made. This is done by contacting ohmic resistors in exactly the pairing in which the cells are later installed in parallel. The resistors are chosen so large that no sparks occur during the contacting. As a result, the resistance level is so high that the compensation process takes a long time. This is not effective for mass production with high volumes. In addition, after the charge equalization, the cells must be paired into the production process of the battery modules or battery systems. This is associated with the risk of mismatching and extra effort. When repairing a battery system, the situation is often even more complicated.

Disclosure of the invention

According to the invention, a method for charge equalization in the production and / or repair of a battery system is provided, comprising the steps of: registering all the battery cells to be connected in electrical parallel connection; Measuring the open circuit voltage of each battery cell; Registering the no-load voltage such that each battery cell is assigned exactly its no-load voltage in terms of magnitude and direction; Evaluating the registered data so as to identify those battery cells having an incorrect polarity or an incorrect amount with respect to the open circuit voltage; electrical parallel connection of a pair of battery cells in a Kirchoffoff mesh; Measuring the equalizing current in the mesh; and regulating the equalizing current in the mesh, the equalizing current being limited to a predetermined first amount greater than zero and undershooting a predetermined second amount greater than zero is turned off.

A battery system in the sense of this disclosure is, for example, an electrical interconnection of individual battery cells, preferably lithium-ion batteries, and their compact arrangement (mechanical fixation) by means of mechanical connection and subsequent electrical contact (for example by screw or welded connection) for measurements, charge compensation and electrical parallel. Battery cells are in particular repeatedly rechargeable batteries, which are also known under the name secondary batteries.

In the context of, for example, a module manufacturing process, the term "registering all battery cells to be connected in electrical parallel connection" means that each battery cell provided for an electrical parallel connection is uniquely assigned a symbol, for example a number or an address. So that on the one hand can be closed by a symbol on exactly one battery cell and on the other hand can be closed by each provided for a parallel connection battery cell to exactly one symbol. The symbol may, for example, be noted in an electronic (or in paper form) batch list, where preferably the order of the stacked battery cells is identical to the order of entry in the list. But also the preferably releasable attachment of the symbol to the respective battery cell itself is conceivable, as for example, two- or three-dimensional code or as an electromagnetic resonance element, such as an RFID chip.

The measurement of the open circuit voltage of each battery cell in terms of magnitude and direction should on the one hand exclude an incorrect polarity and on the other hand batteries with excessive voltage loss, and thus suspected faulty identify and also be used to determine the duration of the application of a compensation current. The open circuit voltage according to preferably also amount and direction is stored so that it can be associated with the symbol. As a result, for example, at a later time, when the batteries have been contacted for imminent charge equalization, the result of the measurement can be retrieved and used for the regulation of the compensation current.

The parallel connection of two battery cells, positive pole to positive pole and negative pole to negative pole, creates a Kirchhoff mesh, in which at each point the amount of the equalizing current is the same.

The compensation current is measured either in the mesh by detecting the voltage drop across an electrical resistance in the mesh or by means of an external sensor which is indirectly connected to the mesh via suitable physical parameters, for example a Hall element for detecting the magnetic field.

The advantage gained by measuring and registering extends, for example, to an increased audit security in the sense of documented production quality which can be traced at any time, which also allows a systematic recognition and evaluation of errors. A further advantage is that larger deviations in the charge states of the cells to be switched in parallel can be controlled by the method according to the invention.

In a preferred embodiment, in the event that the open circuit voltage has an incorrect polarity or an incorrect amount, an audible or visual warning signal is output. This can for example be done directly after measurement and evaluation of the open circuit voltage or at a later date or at another location, for example, to tap and sort out the corresponding cell of a treadmill. The advantage of this is the improvement of the quality, because a signal that can be easily detected by humans can be perceived with greater certainty and therefore the possibly intended intervention of the human being in the process is more likely to take place. Thus, the reverse polarity of a cell to be switched in parallel, which may occur, for example, if a repair is carried out improperly, can be better controlled.

It is also preferable to use manufacturing data of the battery cell and to carry out an adjustment of the then open circuit voltage at the time of the last charging (in the production) with the recently measured open circuit voltage (in the course of preparing the compensation current), thus identifying those battery cells in which the Self-discharge exceeds a predetermined amount.

Particularly in the field of automated and multi-stage production steps at possibly also different locations, this is advantageous in order to sort out defective cells in good time and to be able to systematically improve the production process. It is also advantageous as a result of the storage of the data according to the invention to preclude any confusion of the cells after the charge equalization until the completion of the parallel connection.

It is also conceivable that the self-discharge is determined from a quotient of the difference of the open-circuit voltages of the battery cell from two times, and a time range, which is formed by both times. The self-discharge of a battery cell can be understood as an electrical potential difference, the amount of which falls over a time range. The quotient is formed such that in the numerator of a break there is an electrical voltage, and in the denominator of the break, there is a time, the voltage expressing the potential difference and the time corresponding to a time range between two times. In this case, a time is, for example, the time at which the battery cell was charged in the course of production and their open-circuit voltage was detected in a timely manner, and the other time, for example, that time at which the open circuit voltage of the battery cell is measured within the compensation current method.

Also preferred is a variant in which the compensating current is detected by means of a current sensor, in particular by picking up a drop voltage across an ohmic resistance in the mesh. Advantage is the simple and inexpensive way of immediate detection of the compensation current.

In a likewise preferred variant, the regulation of the compensation current contains an electronically controlled resistor. The advantage here is a contact free of sparks or arcs, as well as an arbitrarily customizable course of the compensation current.

A further preferred variant results from the fact that the termination of the charge compensation is effected by high-impedance switching of the electronically controlled resistor.

Again, there is the advantage of a freed from sparks or arcs current separation.

It is also conceivable that the electronically controlled resistor is formed by an anti-series circuit with two MOSFETs.

The control of each metal oxide semiconductor field effect transistor via a control voltage (gate-source voltage) or a control potential (gate potential), whereby the current flow is controlled from drain to source. The advantage here is the inexpensive production and high power / performance. By anti-series circuit this disclosure means the electrical series connection of two, for example similar p- and n-layered transistors such that they are connected in series with respect to the main current path and are also connected by that contact which characterizes a similar terminal pole for both transistors, for example either drain or source.

drawings

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

1 a battery of parallel and serially connected battery cells according to the prior art,

2 a battery of parallel and serially connected battery cells with inventive compensation current control and compensation current measurement,

3 two battery cells connected in parallel in a compensating current leading loop with regulation and measurement of the compensation current,

4 two in a time axis superimposed diagrams, time course of the voltage of the battery cells and time course of the compensation current, and

5 an anti-series circuit with two MOSFETs.

Embodiments of the invention

In the 1 is a schematic representation of the view from above of a standing battery module according to the prior art, wherein the 6 battery cells already mechanically fixed and in production in the pattern 3s2p (3 in series, 2 in parallel) are electrically connected. The electrical and mechanical connection 100 connects either only two negative poles or only two plus poles of two battery cells and therefore serves only the electrical parallel connection of the corresponding pole. The electrical and mechanical connection 110 connects both two minus poles and two plus poles of two battery cells, so a total of 4 poles, because the connection 110 operated both a parallel connection and a series connection.

The 2 also shows a schematic representation of a view from above of a stationary battery module with inventive circuit. Here is a positive pole of a first battery cell 240 connected to a positive pole of a second battery cell 250 , The connection leads via a compensation current control 200 , Also connected are the negative poles of the battery cells 240 and 250 , so that the two battery cells are electrically connected in parallel. The connection of the negative poles leads via a current sensor 210 , which in this embodiment is a connecting element to which a magnetically sensitive Hall element has been releasably attached. The parallel connection of a third battery cell 260 with a fourth is with another current sensor 220 and provided a further compensation current control. The parallel connection of a fifth and a sixth battery cell is in turn connected to a current sensor 230 and also equipped with a further compensation flow control.

3 represents a Kirchoffoff mesh, which is a first battery cell 310 with a second battery cell 320 connected in parallel and by means of a current sensor 340 one by means of regulation 300 regulated equalizing current 330 detected with appropriate current direction.

4 shows two diagrams arranged one above the other within a time axis: The upper diagram shows a voltage-time curve of a first compensation voltage 410 a first battery cell and a second compensation voltage 420 a second, parallel to the first, according to 3 switched, battery cell. The lower diagram shows the corresponding compensation current i, which at the beginning of the compensation process 450 (t = 0 s) the limited value 440 occupies and from a time t1 in a falling course 430 goes over, wherein from t1 the range of the current limit is left to a predetermined value, while time t2 arises because the compensating current falls below a predetermined amount and thus the balancing process is terminated and therefore the compensating current i falls to zero. Between the beginning and t1, the voltage curves are shown in the upper diagram 410 . 420 linear, because during this period of time the current is limited.

5 represents a first MOSFET 500 and a second MOSFET 530 which are connected in push-pull circuit, also called anti-series circuit, and for protection against incorrect currents a first diode 510 for the first MOSFET 500 and a second diode 520 for the second MOSFET.

Claims (8)

Method for charge equalization in the manufacture and / or repair of a battery system, comprising the following steps: (i) registering all battery cells to be connected in electrical parallel connection ( 310 . 320 ); (ii) measuring the open circuit voltage of each battery cell; (iii) registering the no-load voltage such that each battery cell is assigned exactly its no-load voltage in magnitude and direction; (iv) evaluating the registered data so as to identify those battery cells having an incorrect polarity or magnitude with respect to the open circuit voltage; (v) electrical parallel connection of a pair of battery cells in a Kirchoffoff mesh; (vi) measuring ( 340 ) of the equalizing current ( 330 ) in the mesh; and (vii) rules ( 300 ) of the equalizing current ( 330 ) in the mesh, the equalizing current ( 330 ) is limited to a predetermined first amount greater than zero and aborted when falling below a predetermined second amount greater than zero, the charge equalization. Method according to claim 1 with a step additionally following step (iv): (viii) outputting an audible or visual warning signal in the event that the open circuit voltage has an incorrect polarity or an incorrect amount. Method according to one of the preceding claims with further steps: (ix) Evaluation of manufacturing data of the battery cell ( 310 . 320 ) and adjusting an open circuit voltage at the time of the last charging with the open circuit voltage measured in step (ii); (x) identifying battery cells ( 310 . 320 ), which have a self-discharge as a result of the adjustment, and the self-discharge exceeds a predetermined amount. The method of claim 3, wherein the self-discharge is determined from a quotient of the difference of the open-circuit voltages of the battery cell from two times (t1, t2), and a time range formed by both times (t1, t2). Method according to one of the preceding claims, wherein the compensating current ( 330 ) is detected by means of a current sensor. Method according to one of the preceding claims, wherein the control ( 300 ) of the equalizing current ( 330 ) contains an electronically controlled resistor. The method of claim 6, wherein the cancellation of the charge compensation by high impedance switching of the electronically controlled resistor takes place. Method according to claim 6 or 7, wherein the electronically controlled resistor is provided by an anti-series circuit comprising two MOSFETs ( 500 . 530 ) is formed.

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