JPH10257683A - Charging-discharging circuit for combined batteries - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable effective use of electric energy for unit secondary batteries connected in series. SOLUTION: One end side of a choke coil 16 is connected to an intermediate node 15 which connect cells 10A and 10B of a unit secondary battery in series, and the other end side of the choke coil 16 is connected to both positive and negative output terminals 13 and 14 of the series circuit, through the intermediary of switching circuits 19 and 22. When a terminal voltage of the cell 10A rises, for instance, this is detected by a voltage control circuit 23, a transistor 17 conducts a switching operation at a prescribed period, and a diode 18 also conducts a switching operation later than the transistor. According to this constitution, a current made to flow through the choke coil 16 at the on time of the transistor 17 flows as a charging current of the cell 10B, and a voltage between the two cells 10A and 10B can be standardized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging / discharging circuit for a battery pack comprising a pair of unit secondary batteries connected in series.

[0002]

2. Description of the Related Art For example, a power battery incorporated in an electric vehicle is configured to secure a high voltage by connecting a plurality of unit secondary batteries in series. When charging such an assembled battery, it is unavoidable that the charged state of each battery varies due to variations in the capacity and internal impedance of each unit secondary battery. However, since each unit secondary battery is connected in series, a charging current of the same magnitude flows in each battery, and a variation in a charging state appears as a variation in a terminal voltage. I will invite you.

As an example for preventing such overcharge of some secondary batteries, a shunt regulator system as shown in FIG. 3 has been conventionally employed. This is because the transistor 2 is connected in parallel with each unit secondary battery 1 and the current i
Can be bypassed to the transistor 2 and the battery 1
When the charging of the battery 1 progresses and the terminal voltage rises, this is detected and the bypass current ib is increased to narrow the charging current ic to the battery 1 to prevent overcharging.

[0004]

However, the above configuration has a drawback that the product of the bypass current ib flowing into the transistor 2 and the terminal voltage vc in each unit secondary battery 1 results in a loss, resulting in poor charging efficiency. . In addition to the poor charging efficiency, even if the unit secondary battery 1 is fully charged and the bypass current ib flows through the transistor 2, the charging current ic of the other uncharged unit secondary battery 1 is equal to the current Since it cannot be increased beyond i (ic ≦
i) In order to complete the entire charging, one has to wait for the completion of the charging of the unit secondary battery 1 that is undercharged, and the charging time cannot be reduced.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to level the terminal voltage of each unit secondary battery connected in series.
An object of the present invention is to provide a charge / discharge circuit for an assembled battery that can reduce the charging time.

[0006]

According to the present invention, there is provided a charge / discharge circuit for a battery pack for charging and discharging by connecting a pair of unit secondary batteries in series between positive and negative output terminals. One end of the choke coil is connected to the intermediate connection point of the battery, and the other end of the choke coil is connected to each of the positive and negative output terminals via a switching circuit, and one of the unit secondary battery pairs is connected. When the voltage becomes higher than that of the other, the switching circuit connected to the unit secondary battery is turned on and then opened to turn on the other switching circuit, thereby storing the voltage in the choke coil. It is characterized in that a current is caused to flow in the charging direction to the other unit secondary battery on the low voltage side by the electromagnetic energy.

[0007]

According to the first aspect of the present invention, when one of the unit secondary batteries has a higher voltage than the other,
The switching circuit connected to the unit secondary battery is turned on. As a result, current flows from the unit secondary battery to the choke coil. Thereafter, the switching circuit is turned off, and the switching circuit of the other unit secondary battery on the low voltage side is turned on instead. Then, an electromotive force that causes current to flow in the same direction is induced by the electromagnetic energy stored in the choke coil, and, based on the electromotive force, the unit secondary battery on the low voltage side is charged in the charging direction. Electric current flows.

Accordingly, when the voltage of one unit secondary battery rises, energy is transferred to the unit secondary battery having a lower voltage via the choke coil, and the voltage of the unit secondary battery on the higher voltage side is increased. And the voltage of the unit secondary battery on the low voltage side can be increased, so that both unit secondary batteries can be balanced.

As described above, the balance between the two unit secondary batteries can be balanced by the transfer of energy. This is because overcharging and overdischarging of some unit secondary batteries are prevented and the electric energy of each unit secondary battery is reduced. Means that can be used effectively. In particular, the loss can be greatly reduced compared to the conventional shunt regulator method in which the unit secondary battery whose terminal voltage has risen during charging simply bypasses the current and causes a loss. Faster charging is possible for a short time.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment> A first embodiment of the present invention will be described below with reference to FIG. In this embodiment, two cells 10A, 10A of a lithium ion battery are used as unit secondary batteries.
B illustrates an assembled battery in which B is connected in series between both output terminals 13 and 14. The cells 10A and 10B have the same specifications. One end of a choke coil 16 is connected to an intermediate connection point 15 between both cells 10A and 10B, and the other end is connected to a positive output terminal 13 via a switching circuit 19 in which a transistor 17 and a diode 18 are connected in parallel. The other end of the choke coil 16 is connected to the negative output terminal 14 via a switching circuit 22 in which a transistor 20 and a diode 21 are connected in parallel.

Each of the transistors 17 and 20 of the switching circuits 19 and 22 is, for example, a PNP type. When the transistor 17 is turned on, a current flows from the cell 10A to the choke coil 16 to the left in the figure, and the transistor 20 is turned on. Then, a current flows from the cell 10B to the choke coil 16 to the right. Since the diodes 18 and 21 are turned on when the potential on the anode side exceeds the potential on the cathode side, both switching circuits 19 and 2 are turned on.
Reference numeral 2 indicates that current flows freely upward in the figure, and current flows only downward when the transistor 17 is turned on.

The transistors 17 and 20 are connected to the voltage control circuit 2
3 controls the base potential. The voltage control circuit 23 detects the terminal voltages of the cells 10A and 10B. When the voltage of the cell 10A is higher than that of the cell 10B, the voltage control circuit 23 turns on the transistor 17 intermittently at a predetermined cycle, And the voltage of the cell 10B is
If it is higher, the transistor 20 is turned on intermittently at a predetermined cycle.

The operation of the above configuration is as follows. At the time of charging the assembled battery, a charging power supply is connected between the output terminals 13 and 14 to flow a charging current. The charging current is 10A for each cell,
10B flows in series, and the charging of each cell 10A, 10B gradually progresses. However, the state of charge of each cell varies due to variations in the remaining capacity, internal impedance, and the like of each cell 10A, 10B, and the terminal voltage may not increase similarly. Here, for example, it is assumed that the terminal voltage of the upper cell 10A becomes higher than the lower cell 10B by a predetermined value or more. Then, the deviation of the terminal voltage is corrected by the voltage control circuit 23.
Is detected by the switching circuit 19 of the cell 10A.
Transistor 17 is turned on intermittently at a predetermined cycle. At the moment when the transistor 17 is turned on, a current flows in the choke coil 16 in the direction of arrow A from the cell 10A side as shown in FIG. Then, when the transistor 17 turns from on to off, an electromotive force that causes a current to flow in the same arrow A direction is induced by the electromagnetic energy stored in the choke coil 16. Then, the diode 21 of the switching circuit 22 turns on naturally, so that a charging current flows through the cell 10B on the low voltage side based on the electromotive force. Then, since the switching operation of turning on the transistor 17 and the diode 21 as described above is repeated, the electromagnetic energy stored in the choke coil 16 when the transistor 17 is turned on moves to the cell 10B side by turning on the diode 21. It is used for charging. Such a state continues until the cell 10B reaches the terminal voltage of the cell 10A and becomes balanced.

As described above, the fact that the terminal voltage of the cell 10A rises first and the transistor 17 performs the switching operation originally means that a part of the current flowing through the cell 10A is transferred to the cell 10B via the choke coil 16. , Flows as the charging current of the cell 10B. Here, cell 1
Since the charging current supplied from the original terminal 13 flows through OB, an extra charging current flows superimposed on the current, which promotes the charging of the cell 10B.

As described above, in this embodiment, the electric energy on the side of the cell 10A having the higher terminal voltage can be transferred to the cell 10B having the lower voltage via the choke coil 16 to contribute to the charging thereof. In addition, the loss can be greatly reduced as compared with the conventional shunt regulator system in which the current is simply bypassed to cause a loss in a fully charged cell. In addition, when the terminal voltage of one cell 10A rises, the electric energy applied thereto is transferred to the other uncharged cell 10B, so that the charging of the uncharged cell 10B is promoted, and the entire battery pack is charged. Completion is accelerated, and short-time charging becomes possible.

When the battery pack is discharged, each cell 10A
Although the degree of decrease in the terminal voltage is not always equal due to the variation in the internal impedance of the device, when the deviation of the terminal voltage reaches a predetermined value, the terminal operates in the same manner as described above. For example, if the voltage of the cell 10A decreases early, the transistor 20 of the cell 10B performs a switching operation at a predetermined cycle, and the diode 1 of the cell 10A.
8 performs a switching operation with a delay. As a result, a current flows through the choke coil 16 in the direction of arrow B when the transistor 20 is turned on, and a current flows in the same direction when the transistor 20 is turned off and the diode 18 is turned on.
A flows as a charging current or a load current of A. As a result, it is possible to suppress a decrease in the terminal voltage of the cell 10A and prevent overdischarge.

<Second Embodiment> FIG. 2 shows a second embodiment of the present invention. The difference from the first embodiment is that the number of cells in series is 4, and two adjacent cells are provided with the same charge / discharge circuit as in the first embodiment. Each cell is denoted by reference numerals 10A to 10D. However, since each switching circuit has the same configuration as that of the first embodiment, the same portions are denoted by the same reference numerals and redundant description is omitted. Further, in the same figure, the voltage control circuit 23 has the same configuration as that of the first embodiment, and the transistors 17, 2
Although ON / OFF of 0 is controlled, it is omitted for simplification of the drawing.

In this embodiment, for example, when the uppermost cell 10A in the figure approaches full charge during charging and the terminal voltage becomes higher than that of the second cell, the transistor 17 corresponding to the cell 10A is turned on at a predetermined cycle. A switching operation is performed, and the diode 18 performs a switching operation deviating therefrom. As a result, the cell 1 is connected via the choke coil 16.
The current on the 0A side moves to the cell 10B side to promote charging of the cell 10B. As a result, the second-stage cell 10B
Is higher than that of the third-stage cell 10C, the second-stage left-side transistor 17 performs a switching operation at a predetermined cycle, and the third-stage left-side diode 21 switches later than this. Since the operation is performed, the charging of the third-stage cell 10C is eventually promoted.

As described above, according to the present embodiment, electric energy can be transferred between adjacent cells 10A via the choke coil 16, and energy can be transferred to the uncharged cell 10A at any position. Since the battery can be moved, the loss at the time of charging can be greatly reduced as in the first embodiment, and the effect that the entire assembled battery can be charged in a short time can be obtained.

<Other Embodiments>

The present invention is not limited to the embodiments described with reference to the above description and the drawings. For example, the following embodiments are also included in the technical scope of the present invention. Various changes can be made without departing from the scope of the present invention.

(1) In each of the above embodiments, the transistors 17, 20 and the diode 18,
Although the 21 parallel circuits have been illustrated, the invention is not limited to this, and other switching elements such as FETs can be used.

(2) The charging time may be limited by a timer to prevent overcharging, or charging may be stopped when the terminal voltage of each cell reaches a limit value.

(3) In each of the above embodiments, the case where the unit secondary battery is a lithium ion battery cell has been described. However, the present invention is not limited to this, and various secondary batteries such as a lead storage battery and a nickel cadmium secondary battery may be used. Alternatively, each unit secondary battery may be a battery module formed by combining a plurality of cells.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment.

FIG. 3 is a circuit diagram showing a conventional secondary battery charging circuit.

[Explanation of symbols]

 10A to 10D cells (unit secondary batteries) 13 positive electrode output terminals 14 negative electrode output terminals 15 intermediate connection points 16 choke coils 19 and 22 switching circuits 23 voltage control circuits

Claims (1)

[Claims] 1. A charging / discharging circuit for a battery pack for connecting and discharging a pair of unit secondary batteries in series between positive and negative output terminals, wherein one end of a choke coil is connected to an intermediate connection point between the two unit secondary batteries. And the other end of the choke coil is connected to each of the positive and negative terminals via a switching circuit, and when one of the unit secondary battery pairs has a higher voltage than the other, the After the switching circuit connected to the unit secondary battery is turned on, it is opened and the other switching circuit is turned on, whereby the other unit on the low voltage side is turned on by the electromagnetic energy stored in the choke coil. A charge / discharge circuit for an assembled battery, wherein a current flows in a charging direction to a secondary battery.