JP2012150902A - Protection circuit of secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a protection circuit of a secondary battery which can prevent damage from spreading by disconnecting only a short-circuited unit cell from the circuit system in safety when internal short circuit occurs in any one unit cell in a battery pack.SOLUTION: A battery pack is configured by connecting a plurality of unit cells E1, E2, ...En, and fuses F1, F2, ...Fn are connected in series with the unit cells, respectively. Diodes D1, D2, ...Dn are connected in parallel with the fuses, an anode is connected to the anode side of the unit cell and a cathode is connected to the opposite side. A secondary battery U is configured by connecting a plurality of battery packs in series.

Description

  In the present invention, a plurality of unit batteries (unit cells) are connected in parallel to form an assembled battery, and the assembled batteries are connected in a plurality of stages in series to generate a high voltage and a high current. The present invention relates to a secondary battery (battery), and particularly to a protection circuit when a short circuit occurs in the unit battery.

  Lithium ion batteries, nickel metal hydride batteries, and the like are used as power drive energy sources for hybrid vehicles (HEV) and electric vehicles (EV). Since these unit batteries have a low output voltage and a small current capacity, a plurality of unit batteries are connected in parallel to form an assembled battery, and this assembled battery is connected in a plurality of stages in series, or a plurality of unit batteries. Are connected in series to form an assembled battery, and a secondary battery having a circuit configuration in which the assembled batteries are connected in parallel in a plurality of rows is used.

  In such secondary batteries, measures against overcharge / overdischarge, load short circuit, battery internal short circuit, and the like are necessary. For this reason, the voltage monitoring as the whole circuit of a secondary battery is performed, and the adjustment circuit which adjusts charging / discharging, and the protection circuit with respect to the time of abnormality are added. Further, for example, a technique for detecting a reverse charge state or an overcharge state of unit batteries connected in series and avoiding them has been proposed (see Patent Document 1).

JP 2001-6751 A

  However, although the above technique protects the entire circuit of the secondary battery including the load, when the unit battery is connected in parallel and an internal short circuit occurs in one of the assembled batteries, a short circuit occurs. Only the unit battery cannot be safely separated from the circuit system.

  The present invention has been made based on the above-described circumstances. A secondary battery in which a plurality of unit batteries are connected in parallel to form an assembled battery, and the assembled battery is connected in a plurality of stages in series. It is an object of the present invention to provide a secondary battery protection circuit capable of safely separating only a unit battery in which a short circuit has occurred from a circuit system and preventing an increase in damage when an internal short circuit occurs in the unit battery. To do.

  The secondary battery protection circuit of the present invention comprises a plurality of unit cells connected in parallel to form an assembled battery, each unit battery connected in series with a fuse, a diode connected in parallel to the fuse, and the unit battery An anode is connected to the anode side, and a cathode is connected to the opposite side. A plurality of the assembled batteries are connected in series to form a secondary battery.

  Thereby, with respect to the internal short circuit of the unit battery, the fuse connected in series with the unit battery is blown, and the unit battery is separated from the circuit system, thereby preventing the damage from being expanded. And by providing a diode in series with each unit battery constituting the assembled battery, the voltage across the diode can be clamped to the forward voltage, and the high voltage of the secondary battery is applied to the fuse at the time of fusing The defective unit battery can be safely separated without any trouble. Therefore, it is possible to use a low-voltage type fuse, and a safe and inexpensive protection circuit can be formed.

It is a circuit diagram which shows the secondary battery of one Example of this invention. It is a circuit diagram which shows one set assembled battery part of the said secondary battery. It is a circuit diagram which shows operation | movement of the assembled battery part when one fuse blows. It is a circuit diagram which shows operation | movement of the assembled battery part when all the fuses blow out. It is a circuit diagram which shows the electric current path | route when the internal short circuit arises in the unit battery of the said 1 set assembled battery part. It is a graph which shows the relationship between the short circuit current Is and the current IFn which flows into each fuse in the unit battery in which the internal short circuit has occurred.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 6. In addition, in each figure, the same code | symbol is attached | subjected and demonstrated to the same or equivalent member or element.

  FIG. 1 shows a secondary battery according to an embodiment of the present invention, and FIG. 2 shows a set of the assembled batteries. A set of assembled batteries constituting the secondary battery U of the present invention has unit batteries E1, E2,... En connected in parallel, and fuses F1, F2,. The diodes D1, D2,... Dn are connected in parallel to the fuses. Each diode has an anode connected to the anode side of the unit cell and a cathode connected to the opposite side.

  The secondary battery U is configured by connecting a plurality of the above assembled batteries in series. The output of each assembled battery is about 3.7 V in the case of a Li-ion battery, but by connecting several tens of stages to hundreds of tens of stages in series, a high voltage of several hundred V required for driving an automobile can be obtained. Can supply. A load R is connected to the secondary battery U, and a main fuse F0 is connected to the load R in series.

  Lithium ion secondary batteries have a problem that an internal short circuit occurs due to a conductive foreign matter mixed in the battery during manufacture of the battery or a deformation of the battery. In addition, the anode-cathode separator is thermally deformed due to heat generation during an internal short circuit, and the hole through which ions pass is blocked, which may increase the resistance value and suppress the short-circuit current, but may subsequently short-circuit again. For this reason, it is effective to arrange a fuse so that the short-circuit current does not spread to other unit batteries.

  When each unit battery is operating normally, a load current flows evenly through each unit battery, assuming that the electromotive force of each unit battery is the same within the assembled battery. However, when an internal short circuit occurs in a certain unit battery E1 constituting the assembled battery, current flows into the unit battery E1 from the other unit batteries E2,... En, and if the allowable capacity of the fuse F1 is exceeded, the fuse F1. Blows out.

  FIG. 3 shows the operation of the assembled battery in this case. That is, when the unit battery E1 causes an internal short circuit and the fuse F1 is melted and opened, the electromotive force of the unit battery E1 does not become higher than the electromotive forces of the unit batteries E2 to En. Since the fuses F2 to Fn are not blown, the potential on the diode cathode side of the fuse F1 becomes higher than the potential on the anode side, and the reverse bias is applied, so that the diode D1 does not conduct.

  Accordingly, the unit battery E1 that has caused the internal short circuit is connected to the assembled battery via the diode D1, but the diode D1 is reverse-biased and is substantially disconnected from the assembled battery. In the other unit cells E2 to En, the supply of the short-circuit current is stopped, so that the spread of damage due to overcurrent can be prevented. At this time, the load current Io is substantially shared by the unit batteries E2 to En operating normally.

  FIG. 4 shows the operation when the fuses F1 to Fn are all blown simultaneously or finally. When the diodes D1 to Dn are not present, that is, when only the fuse is simply connected in series to the unit battery, the high voltage of the entire secondary battery is applied to both ends of the fuse that is blown last. For this reason, there is a possibility that the fuse may burst or follow, and a large fuse that is not a surface mount type with a high voltage rating must be used, and the secondary battery module becomes large and difficult to be surface mounted. Existed.

  However, by connecting the diodes D1 to Dn in parallel to the fuses F1 to Fn, even when all of the fuses F1 to Fn are blown simultaneously or finally, the voltage between the fuse terminals is the forward direction of the diodes D1 to Dn. Clamped to voltage Vf. Therefore, even when all of the fuses F1 to Fn are melted simultaneously or finally, the above-described damage state is not caused, and a small surface mount fuse having a low voltage rating can be used. In addition, even after all the fuses are blown out, the unit battery E2 to En is connected to the secondary battery circuit via the diodes D2 to Dn in the assembled battery part, so the overall energy supply capacity does not stop completely, It is possible to operate the load temporarily. The unit battery E1 is separated from the energy supply path to the load because the electromotive force is reduced due to an internal short circuit and the diode D1 is reverse biased and becomes non-conductive.

  Here, the diodes D1 to Dn are used for prevention of inflow of a short-circuit current after the fuse is blown and clamping to the forward voltage Vf when the last fuse is blown. In addition, it is preferable to use a voltage having a forward voltage Vf as small as possible.

  As shown in FIG. 1, the secondary battery U includes a main fuse F0, and when the load R is short-circuited, the main fuse F0 is blown first. This can be realized by making the combined fusing characteristics of the fuses F1 to Fn slower than the fusing characteristics of the main fuse F0. As a result, the entire voltage of the secondary battery U after the fuse is blown is applied to the main fuse F0, and the fuses F1 to Fn have a low voltage rating regardless of the presence or absence of the diodes D1. A fuse can be used.

  In general, power fuses have a fuse element with a thickness, length, and material that determines the amount of current that the fuse element blows, and adjust the heat dissipation by using a core material or a quenching agent that contacts the fuse element. Thus, the time until fusing can be adjusted. From the fusing characteristics defined by these, a fuse having fusing characteristics suitable as F1, F2,... Fn and F0 can be selected.

  In addition, when any unit battery fails due to an internal short circuit when the load current Io exists, the balance of the current flowing through each unit battery is lost. In this case, the fuse connected in series to the unit battery in which the failure has occurred does not necessarily blow out first.

  In the assembled battery shown in FIG. 5, it is assumed that an internal short circuit occurs in the unit battery E1, and a short circuit current Is flows. Then, it is assumed that the rated current Io flows through the assembled battery as a whole. Accordingly, the short-circuit current Is and the rated current Io flow in opposite directions, and both currents cancel each other in the fuse F1 entering the unit battery E1 in which the internal short circuit occurs, and both currents overlap in fuses entering the other unit batteries. Flowing.

  FIG. 6 shows the current flowing through each unit battery corresponding to the short-circuit current Is when the assembled battery is a 2-parallel, 3-parallel, 4-parallel, 5-parallel, or 10-parallel circuit. The current flowing through the fuse F1 entering the unit battery E1 is shown, and the positive slope straight line shows the current flowing through the fuses F1 through Fn entering the other unit cells E2 through En. Therefore, in the case of two parallel circuits, the short-circuit current increases. When Is = Io, IF1 is 0, whereas IF2 is Io, and the fuse fusing point is twice the rated current (in this case, sharing). When the rated current is set to Io / 2, the fuse F2 is blown.

  On the other hand, when the number of parallel circuits is large, for example, 10 parallel circuits, IF1 becomes −0.2Io when the short-circuit current Is = 0.3Io (in this case, the shared rated current becomes Io / 10). The fuse F1 is blown. As described above, when the number of parallel circuits is large, the fuse of the unit battery in which the internal short circuit occurs is blown.

  Although one embodiment of the present invention has been described so far, it is needless to say that the present invention is not limited to the above-described embodiment, and may be implemented in various forms within the scope of the technical idea.

  INDUSTRIAL APPLICABILITY The present invention can be used for a secondary battery that generates a high voltage and a high current by connecting a large number of unit batteries such as lithium ion secondary batteries in series and parallel.

Claims (3)

A plurality of unit batteries are connected in parallel to form an assembled battery,
Each unit battery is connected in series with a fuse,
A protection circuit for a secondary battery, wherein a diode is connected in parallel with the fuse, an anode is connected to the unit battery anode side, and a cathode is connected to the opposite side.   The secondary battery protection circuit according to claim 1, wherein a secondary battery is configured by connecting a plurality of the assembled batteries in series.   The main fuse is connected in series between the secondary battery and a load, and the fusing characteristic of the fuse connected in series to the unit battery is made slower than the fusing characteristic of the main fuse. Secondary battery protection circuit.

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