JP3279071B2 - Battery pack charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charger for a battery pack using a plurality of secondary batteries connected in series, and more particularly to a battery pack for a non-aqueous secondary battery such as a lithium secondary battery having no sealing reaction. The present invention relates to a charging device suitable for a battery.

[0002]

2. Description of the Related Art In an electric vehicle or the like, an assembled battery in which a plurality of secondary batteries are connected in series is used. In the case of such an assembled battery, the degree of reduction in the discharge capacity (the amount of electricity that can be discharged) differs for each battery. For example, there is a difference in the self-discharge amount and the charge acceptance rate (charge / discharge efficiency) due to manufacturing variations among the batteries and the temperature distribution is not uniform when used in an assembled battery. The degree of reduction differs for each battery. Therefore DOD
(Depth of discharge: 100% for full discharge, 0% for full charge) The discharge capacity from 0% varies among the batteries, thereby reducing the discharge capacity of the assembled battery. That is, at the time of discharging, a battery having a reduced discharge capacity is quickly discharged and over-discharged, and the over-discharged battery becomes a load of another battery, and all batteries do not reach a DOD of 100%. Then, the voltage drops, and the battery pack ends discharging. On the other hand, when charging, DOD1
The battery that did not reach 00% first reaches DOD 0% and the voltage rises, and charging ends. However, the battery that has been overdischarged during discharging ends charging without reaching DOD 0%. And the difference in the discharge capacity of each battery also widens. Therefore, when charging and discharging are repeated, the battery having a small discharge capacity is always insufficiently charged, so that the variation becomes large and the discharge capacity of the whole assembled battery decreases. In general, in the case of a secondary battery, if the battery is overcharged beyond the end-of-charge voltage or overdischarged after the end-of-discharge voltage, its life is shortened. In particular, a non-aqueous secondary battery such as a lithium battery is used. In such a case, the tendency is strong. Therefore, when even one of the assembled batteries reaches the end-of-charge voltage or end-of-discharge voltage, it is necessary to end the charging and discharging of the assembled battery.
As described above, in a battery pack in which a plurality of secondary batteries are connected in series, there is a problem that the discharge capacity and DOD vary, and the discharge capacity of the whole battery pack decreases.

As a first conventional example for addressing the above problem, there is one disclosed in, for example, Japanese Patent Application Laid-Open No. 51-85437. This device performs a uniform charging by increasing the charging voltage or the charging current when the variation in the voltage of each battery constituting the assembled battery increases. A second conventional example is disclosed in JP-A-61-206179.
Is described in Japanese Unexamined Patent Application Publication No. 2000-205,878. In this device, a bypass circuit is connected in parallel to each of the batteries constituting the assembled battery, a fully charged battery conducts the bypass circuit to reduce the charging current, and a battery that has not been charged continues charging. This reduces the variation. Also, the third
An example of the prior art is disclosed in Japanese Patent Application Laid-Open No. 5-64377. This conventional example describes a battery that stops charging when at least one battery has reached a full charge, and a battery that has a circuit that bypasses a charging current for a battery that has reached a full charge. ing. FIG.
Is the battery voltage V when activating the bypass circuit of the battery that has reached full charge (end-of-charge voltage) as described above.
b, current Ib flowing through the battery, current I flowing through the bypass circuit
FIG. 4 is a characteristic diagram showing a change in bp. As shown in FIG. 6, the start of charging to the time t _1, the bypass circuit is turned off, it is referred to as battery current Ib the current of the charging circuit. Then gradually increases the battery voltage Vb by the charging, activating the bypass circuit at the time t ₁ has reached the charge voltage. Thereafter, the current Ibp flowing through the bypass circuit is gradually increased so that the battery voltage Vb does not exceed the charge termination voltage, and the battery current Ib is gradually decreased. At time t ₂ is the charging current is 0. As described above, by operating the bypass circuit to reduce the charging current for a battery that has reached a full charge (end-of-charge voltage), and continuing normal charging for other batteries that have not reached a full charge. Variations can be eliminated.

[0004]

However, the method described in the first conventional example is effective in the case of a lead-acid secondary battery, but is effective in the case of a non-aqueous secondary battery such as a lithium battery. Is
When an overvoltage is applied as in the first conventional example, there is a problem that the life of the battery is seriously adversely affected as described above. In the second conventional example and the third conventional example, since the charging current of the fully charged battery is bypassed, there is a problem as follows. That is, when charging, the battery is not always charged until the battery is fully charged, and the charging is often terminated halfway. However, in the above-described conventional example, the variation eliminating function does not work unless the battery is fully charged. Is always difficult to eliminate. Further, when handling large power such as an electric vehicle, since a simple constant voltage diode is difficult to use in terms of power, a series circuit of a resistor and a switching element (FET, etc.) is used as the bypass circuit. Is connected to each battery in parallel. However, as shown in the characteristics of FIG.
In the case of controlling the current flowing through the bypass circuit, the method of controlling the switching element in an analog manner to vary the bypass current causes a problem that the power loss of the FET increases and a large-capacity FET and a heat sink are required. Therefore, the duty cycle of the on-off time of the FET is controlled by P
It is desirable to adopt the WM control method. However, in the case of a battery, the battery voltage when the bypass circuit is turned off and the battery voltage when the battery is turned on are different due to the internal resistance. When the bypass circuit is operated for a battery that is fully charged, when the FET is turned on and off, the applied voltage becomes higher than a specified voltage when the FET is turned off, which adversely affects the life of the battery.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and a first object of the present invention is to effectively reduce variations among batteries even when full charge is not performed. A second object of the present invention is to provide a charging device for an assembled battery capable of effectively reducing the variation of each battery constituting the assembled battery without using a large-capacity FET or a heat sink. It is to provide a charging device.

[0006]

Means for Solving the Problems In order to achieve the above object, the present invention is configured as described in the claims. That is, according to the first aspect of the present invention, in a device for charging an assembled battery in which a plurality of secondary batteries are connected in series, the device comprises a series circuit of a resistor and a switching element, and is connected in parallel to each battery of the assembled battery. A bypass circuit connected to the battery pack, voltage detecting means for detecting the voltage of each battery in the battery pack, and the lowest voltage and the other battery voltages among the battery voltages at the time of charging detected by the voltage detecting means. The battery is compared with a voltage, and for a battery whose voltage difference exceeds a first predetermined value, the bypass circuit is turned on,
And a control device that controls to shut off the bypass circuit when the voltage difference becomes equal to or less than a second predetermined value that is lower than the first predetermined value. The configuration of claim 1 corresponds to, for example, the configuration of FIG. 1 described later and the control described in the flowchart of FIG.

Further, the first predetermined value and the second predetermined value are, for example, as set forth in claim 2, wherein the first predetermined value is a fluctuation range of the battery voltage, that is, a charge end voltage and a discharge end. The difference between the voltage and the desired variation ratio is set to the same value as the desired variation voltage obtained by multiplying the difference by a desired variation ratio. When the battery bypass circuit is turned on,
The difference between the terminal voltages Vt of the two batteries when the voltage difference between the two batteries is set to 0 for the net battery voltage Vc excluding the voltage drop due to the internal resistance of the batteries is set as a second predetermined value.

[0008] The control device may be, for example,
As described in above, according to the voltage difference between the lowest voltage and the voltage of each of the other batteries, the above bypass circuits are controlled such that the larger the voltage difference, the larger the bypass current value. Further, the control device changes the bypass current value by performing PWM control on the switching element, for example, as described in claim 4. Further, for example, as described in claim 5, the control device, for a battery bypass circuit in which the terminal voltage of the battery when the switching element is off exceeds the charge end voltage,
The switching element is controlled to be always on. The configurations of claims 3 to 5 correspond to, for example, the control of the flowchart of FIG. 3 described later. Also,
The secondary battery is, for example, a non-aqueous secondary battery as described in claim 6, and the non-aqueous secondary battery is a lithium secondary battery as described in claim 7. However,
The present invention can be applied to an assembled battery of another secondary battery such as a lead-acid secondary battery.

[0009]

According to the present invention, the lowest voltage among the voltages of the batteries at the time of charging is compared with the voltages of the other batteries, and the batteries whose voltage difference exceeds a first predetermined value are bypassed. The circuit is made conductive to reduce the charging current, and when the voltage difference becomes equal to or less than a second predetermined value lower than the first predetermined value, the bypass circuit is controlled to be cut off. With the above control, the charging current of the battery having the difference between the lowest voltage and the first predetermined value or more is significantly reduced because the bypass circuit connected in parallel is turned on. Therefore, charging of the battery with a high voltage is suppressed,
Since the battery with a low voltage is mainly charged, the variation as a whole is reduced. In addition, when the battery having a low voltage is charged and the voltage increases, as a result, when the difference between the voltage of the battery and the battery whose bypass circuit is on becomes small, the bypass circuit is turned off and the battery is also charged. And evenly charge the entire battery. In particular, in the present invention, since the bypass circuit is controlled from the time of charging based on the lowest voltage as described above, it functions to always reduce variations regardless of whether or not the battery is fully charged.

Further, the first predetermined value and the second predetermined value are set as described in claim 2. That is, the first
Is determined by multiplying the variation width by a desired variation ratio (a ratio of the allowable variation to the variation range). For example, in the case of a lithium battery, the charge end voltage is 4.2 V
Since the discharge end voltage is 2.5 V, the fluctuation width is 1.7 V
Assuming that the allowable variation ratio is 3%,
The desired variation voltage is 1.7 × 0.03 = 0.051 V, and this value is the first predetermined value. In addition, the second predetermined value is a value when the voltage difference between the two batteries at the net battery voltage excluding the voltage drop due to the internal resistance is 0 when the bypass circuit of the battery with the higher voltage is turned on. Terminal voltage of both batteries in (value including voltage drop due to internal resistance)
May be set to a second predetermined value.

According to a third aspect of the present invention, according to a voltage difference between the lowest voltage and the voltage of each of the other batteries, the bypass current value is controlled to increase as the voltage difference increases. DOD values can be more accurately aligned. Also, as described in claim 4 and claim 5,
The current value is changed by performing PWM control on the switching element, and in a bypass circuit of a battery in which the terminal voltage of the battery exceeds the charge termination voltage when the switching element is off, the switching element is always on. Thus, even if the transistors are turned on and off by PWM control, the battery voltage does not exceed the charge end voltage, and there is no possibility that the battery life will be adversely affected. Therefore, large capacity F
No ET or heat sink is required.

Further, in the conventional apparatus, since the voltage of each battery constituting the assembled battery varies, it is necessary to detect the voltage of each battery in order to detect the discharge capacity of the entire assembled battery. Although it was necessary to provide a voltage sensor for each battery, in the present invention, even when the battery is not fully charged, the variation of each battery is eliminated, and the voltage of each battery becomes substantially equal for each charge. When detecting the discharge capacity, only the voltage of the assembled battery needs to be detected.
Therefore, for example, when the assembled battery is used as a driving battery for an electric vehicle, the discharge capacity can be easily detected only by providing the vehicle with one voltage sensor that detects the voltage of the entire assembled battery. There is also an advantage.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments. FIG. 1 is a block diagram of one embodiment of the present invention. In FIG. 1, reference numeral 1 denotes an assembled battery, in which secondary batteries 1a to 1n (hereinafter simply referred to as batteries) are connected in series. Further, 2a to 2n are resistors, 3a to 3n are transistors such as FETs, for example, and a circuit in which 2 and 3 are connected in series is connected in parallel to each of the batteries 1a to 1n as a bypass circuit. 4a to 4n are voltage sensors for detecting the terminal voltage of each battery, 5 is a control device (to be described in detail later), 6 is a contactor for opening and closing a charging current, 7 is a charging circuit, 8 is start / stop of charging. Is a charge signal switch for instructing a charge signal. The control device 5 is configured by, for example, an analog circuit or a microcomputer. The charging circuit 7 is a circuit that converts, for example, an AC commercial power supply to a desired charging voltage, converts the AC power into DC, and outputs the DC. In the apparatus shown in FIG. 1, when the charging signal switch 8 is turned on, the charging circuit 7 is operated, and the contactor 6 is turned on by the control device 5, and current flows from the charging circuit 7 to the battery pack 1 to perform charging. It is.

FIG. 2 is a flowchart showing a first embodiment of the charging control in the control device 5 of FIG. Less than,
The operation of the device of FIG. 1 will be described based on FIG. In FIG. 2, in step S1, the charging signal switch 8 is turned on.
The control device 5 determines whether or not to start charging in response to the OFF,
If "YES", in step S2, the contactor 6 is turned on to start charging. In this case, all the bypass circuits are off, that is, all the transistors 3a to 3n are off. Next, in step S3, each battery 1a constituting the battery pack 1 is used by using each of the voltage sensors 4a to 4n.
１1n are detected. Next, in step S4, the lowest voltage Vmin among these voltages is detected. In step S5, a voltage difference Dd between Vmin and the voltage of each of the other batteries is detected. Next, step S
In step 6, the voltage difference Dd is compared with a _first predetermined value ΔV ₁ (to be described in detail later). For a battery in which Dd ≧ ΔV ₁ and the bypass circuit is off, the bypass circuit is turned off. Turn on. Specifically, a signal is sent from the control device 5 to turn on the transistor of the bypass circuit. By the above control, the lowest voltage and the first predetermined value Δ
Battery is V ₁ or more differences, a bypass circuit connected in parallel because it is turned on, the charging current is significantly reduced. Therefore, the charging of the battery with a high voltage is suppressed, and the battery with a low voltage is mainly charged, so that the variation as a whole is reduced. Next, in step S7, each of the above voltage differences Dd is compared with a _second predetermined value ΔV ₂ (ΔV ₁ > ΔV ₂ , which will be described in detail later), ΔV ₂ ≧ Dd, and the bypass circuit is turned on. For a dead battery, its bypass circuit is turned off. Specifically, a signal is sent from the control device 5 to turn off the transistor of the bypass circuit. According to the above control, the battery having the low voltage is charged, and as a result of the voltage increase, when the difference between the voltage of the battery while the bypass circuit is on is reduced, the bypass circuit is turned off and the battery is charged. Can be charged, and the entire battery can be charged evenly.

Next, in step S8, the voltage of the battery whose bypass circuit is off, that is, the battery being charged, is the charge end voltage (for example, 4.2 in the case of a lithium battery).
For those that have reached V), the bypass circuit is turned on to suppress charging. With the above control, overcharging is not performed for a battery that has reached full charge early, and charging can be continued for a battery that has not yet reached full charge. Next, in step S9, it is determined whether or not there is a battery whose charging circuit has reached the charge cut-off voltage in the battery in which the bypass circuit is turned on, that is, the charging current is suppressed. Is repeated, and if there is, charging is ended in step S10. In particular,
A signal is sent from the control device 5 to turn off the contactor 6. As described above, in the present embodiment, since the bypass circuit is controlled from the time of charging based on the lowest voltage, it functions to always reduce the variation regardless of whether or not the battery is fully charged. If the voltage and current of the charging circuit 7 can be adjusted, if "YES" in step S9, the charging is not terminated, the charging current from the charging circuit 7 is reduced, and the voltage of the battery is reduced. Charging can be continued without reaching the end voltage. This can further reduce the variation among the batteries.

Next, the first predetermined value ΔV ₁ and the second predetermined value ΔV ₁
Will be described predetermined value [Delta] V _2. FIG. 4 is an equivalent circuit diagram of the secondary battery, and the battery as shown in FIG. 4A is represented as a series circuit of an internal resistance r and a capacitance C as shown in FIG. The terminal voltage Vt of the battery is expressed as the sum of the voltage Vc of the capacitor C and the voltage difference Vr across the internal resistance r. In the case of a lithium secondary battery, the charge end voltage (D
OD0%) is 4.2V, discharge end voltage (DOD100
%) Is 2.5 V, which is a value at the voltage Vc in the equivalent circuit of FIG. However, since the voltage that can be detected is the terminal voltage Vt, it is necessary to set the first predetermined value ΔV ₁ and the second predetermined value ΔV ₂ in consideration of the voltage drop Vr due to the internal resistance r. Vc, Vr, and Vt of the battery with the lowest voltage are represented by Vcmin and Vr, respectively.
min, Vtmin, the charging current flowing is Ibatmin, and Vc, Vr, Vt of another certain battery are Vcn, Vrn,
Vtn, the charging current flowing is Ibatn, and the current flowing through the bypass circuit is Ibpn. In this case, the following equations (1) and (2) hold.

Vtn = Vcn + Vrn (Equation 1) Vtmin = Vcmin + Vrmin (Equation 2) First, the first predetermined value ΔV ₁ will be described. Assuming that the variation among the batteries is suppressed to 3% or less, the fluctuation range of the battery voltage is 4.2-2.5 = 1.7.
The voltage difference of Vc is 1.7 × 0.03 = 0.051V. In this case, since the bypass circuit is off, the current flowing through each battery is the same, and therefore Vrmin = Vrn
Therefore, the following expression (3) is established from the above expression (1) and expression (2). Vcn−Vcmin = Vtn−Vtmin (Equation 3) As can be seen from Equation (3), when the bypass circuit is off, the voltage difference at the battery voltage Vc excluding the voltage drop due to the internal resistance is the terminal It is equal to the voltage difference at the voltage Vt. Therefore, the first predetermined value ΔV ₁ may be set to 0.051V. That is, the first predetermined value ΔV ₁ may be set to the same value as the desired variation voltage obtained by multiplying the variation range of the battery voltage by the desired variation ratio (%).

Next, the second predetermined value ΔV ₂ will be described. In this case, the bypass circuit of the battery with the lowest voltage is turned off, the bypass circuit of another certain battery is turned on, and V
The Vtn-Vtmin which definitive when cn = Vcmin may be set to [Delta] V _2. That is, when the bypass circuit of the battery with the higher voltage is turned on, the terminal voltage Vt of both batteries in the case where the voltage difference between both batteries at the net battery voltage Vc excluding the voltage drop due to the internal resistance is 0 May be set to ΔV ₂ . Hereinafter, an actual example will be described. For example, 80A
h, and the charging current Ichg from the charging circuit is 4
0A and the bypass current of the bypass circuit is 10A. In this case, the internal resistance r of the battery is about 0.16 Ω · Ah in the case of a lithium secondary battery, and thus is 0.1 at 80 Ah.
002Ω. Therefore, Vtn = Vcn + 0.002 (Ichg-Ibpn) = Vcn + 0.0
6 Vtmin = Vcmin + 0.002 × Ichg = Vcmin + 0.08 Therefore, the following equation (4) holds. Vtn-Vtmin = (Vcn + 0.06 ) - (Vcmin + 0.08) ... ( Equation 4) as the, [Delta] V _2, since values of Vtn-Vtmin which definitive when Vcn = Vcmin, from equation (4), [Delta] V ₂ = Vtn-Vtmin = 0.06-0.08 = -0.02 That is, in the case of this example, ΔV ₂ = −0.02
V may be set. That is, when the terminal voltage of the battery whose bypass circuit is on is lower by 0.02 V than the terminal voltage of the battery with the lowest voltage, the control is performed so that the bypass circuit is turned off. In this case, the net battery voltage Vc excluding the voltage drop due to the internal resistance is
Both batteries are equal at Vcn = Vcmin.

Next, FIG. 3 is a flow chart showing the arithmetic processing in the second embodiment of the present invention. The circuit of the device is the same as that of FIG. In FIG. 3, steps S1 to S5 are the same as those in FIG. Next, in step S11, a duty ratio for controlling a bypass current flowing through each bypass circuit is calculated. This bypass current is, for example, a value proportional to each voltage difference Dd obtained in step S5. Therefore, the duty ratio is obtained by multiplying each voltage difference Dd by a predetermined coefficient K. Then, in step S12, the transistors of each bypass circuit are turned on / off according to the respective duty ratios obtained above, and PWM control is performed. next,
In step S13, when the bypass circuit is off, the battery that has reached the charging end voltage always turns on the transistor of the bypass circuit (duty ratio = 100%).
Next, in step S14, it is determined whether or not any of the batteries whose transistors have been constantly turned on has reached the charging end voltage. If "YES", the charging is terminated in step S15, and "NO""", The process returns to step S4 to repeat the above control. As described above, by making the value of the current flowing through the bypass circuit (accordingly, the charging current) variable according to the voltage difference from the battery having the lowest voltage, the value of DOD can be more accurately obtained than the control of FIG. Can be aligned.

In the above control, step S
In 13, when the bypass circuit is off, the battery that has reached the charging end voltage is controlled so that the transistor of the bypass circuit is always on. Therefore, even if the transistor is turned on and off by the duty control, the voltage of the battery does not exceed the charge end voltage, and there is no possibility that the life of the battery is adversely affected. FIG. 5 is a characteristic diagram showing the above relationship. In FIG. 5, the horizontal axis represents DOD (depth of discharge), and the vertical axis represents the voltage of the battery during charging. The solid line indicates the voltage characteristic when the bypass circuit is on, and the dashed line indicates the voltage characteristic when the bypass circuit is off. In addition, 4.2V is the charge end voltage of the lithium battery and 2.5V is the discharge end voltage as well. As shown in FIG. 5, when the bypass circuit is off (the charging current is large), the battery voltage reaches the charge end voltage 4.2V at the point of DOD = x%. At this time, if the bypass circuit is on (the charging current is small), the battery voltage has not yet reached the charging end voltage. However, when the PWM control is performed, the bypass circuit alternately turns on and off, so that when the DOD is closer to 0% than x%, the battery voltage exceeds the charge end voltage at the time of off, and Has a negative effect on life. Therefore, in this embodiment,
When the bypass circuit is off, the battery that has reached the charging end voltage is controlled so that the transistor of the bypass circuit is always on. That is, on the right side of x% in FIG. 5, the transistor is always turned on, and rises according to the characteristics of the solid line.

If there is no problem with the power capacity of the transistor in the bypass circuit and the heat capacity of the heat sink, the transistor may be controlled in an analog manner to change the bypass current. Further, in the conventional device, since the voltage of each battery constituting the assembled battery varies, it is necessary to detect the voltage of each battery in order to detect the discharge capacity of the entire assembled battery. Needs to be provided with a voltage sensor. In this regard, in the present invention, even when the battery is not fully charged, the variation of each battery is eliminated, and the voltage of each battery is substantially equal for each charge. It is sufficient to detect only the voltage as Therefore, for example, when the assembled battery is used as a driving battery for an electric vehicle, a voltage sensor for detecting the voltage of each battery is required for a charging device (the configuration shown in FIG. 1) provided in a home or a charging station. Has the advantage that the discharge capacity can be easily detected only by providing one voltage sensor for detecting the voltage of the whole assembled battery. In addition, the present invention is suitable as a charging device for a non-aqueous secondary battery such as a lithium secondary battery, but can be applied to other secondary batteries such as a lead-acid secondary battery, of course. Variations between the batteries can be effectively reduced.

[0022]

As described above, according to the present invention, by operating the bypass circuit from the beginning of charging in accordance with the voltage difference from the battery with the lowest voltage, each battery can be charged even when full charging is not performed. And the variation of the discharge capacity and the voltage of the semiconductor device can be effectively reduced. Also, by switching the control in accordance with the battery voltage when the bypass circuit is off, the variation in each battery constituting the assembled battery can be achieved without using a large capacity FET or heat sink without adversely affecting the battery life. Can be effectively reduced.
Even when the battery is not fully charged, the variation of each battery is eliminated, and the voltage of each battery is substantially equal for each charge, so when detecting the discharge capacity of the assembled battery, only the voltage of the assembled battery is detected. do it. Therefore, only by providing one voltage sensor for detecting the voltage of the entire battery pack,
There is also an advantage that the discharge capacity can be easily detected.

[Brief description of the drawings]

FIG. 1 is a block diagram of one embodiment of the present invention.

FIG. 2 is a flowchart showing a calculation process according to the first embodiment of the present invention.

FIG. 3 is a flowchart illustrating a calculation process according to a second embodiment of the present invention.

FIG. 4 is an equivalent circuit diagram of a secondary battery.

FIG. 5 is a characteristic diagram showing charging characteristics in the present invention.

FIG. 6 is a characteristic diagram showing voltage-current characteristics in a conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Battery pack 5 ... Control device 1a-1n ... Battery 6 ... Contact 2a-2n ... Resistance 7 ... Charging circuit 3a-3n ... Transistor 8 ... Charge signal switch 4a-4n ... Voltage sensor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02J ⁷ /02-7/12 H02J 7/34-7/36 H01M 10/44

Claims (7)

(57) [Claims] An apparatus for charging an assembled battery in which a plurality of secondary batteries are connected in series, comprising a series circuit of a resistor and a switching element, wherein a bypass circuit is connected in parallel to each battery of the assembled battery. A voltage detecting means for detecting the voltage of each battery of the battery pack, and comparing the lowest voltage and the voltage of each of the other batteries among the voltages of the batteries at the time of charging detected by the voltage detecting means, When the voltage difference exceeds a first predetermined value, the bypass circuit is turned on. When the voltage difference becomes equal to or less than a second predetermined value lower than the first predetermined value, the bypass circuit is turned off. And a control device for controlling so as to shut off the charging device. 2. The method according to claim 1, wherein the first predetermined value is a fluctuation range of the battery voltage,
That is, the difference between the end-of-charge voltage and the end-of-discharge voltage is set to the same value as the desired variation voltage obtained by multiplying the difference by the desired variation ratio, and the second predetermined value is a bypass circuit of the battery with the lowest voltage. Is off and the bypass circuit of the battery with the higher voltage is turned on, and when the voltage difference between the two batteries is 0 with respect to the net battery voltage Vc excluding the voltage drop due to the internal resistance of the battery. 2. The battery charger according to claim 1, wherein a difference between the terminal voltages Vt of the two batteries is set as a second predetermined value. 3. The control device controls each of the bypass circuits according to a voltage difference between the lowest voltage and the voltage of each of the other batteries such that the larger the voltage difference, the larger the bypass current value. The charging device for an assembled battery according to claim 1 or 2, wherein 4. The battery charger according to claim 3, wherein the controller changes the bypass current value by performing PWM control on the switching element of the bypass circuit. 5. The control device according to claim 1, wherein the control circuit controls the switching element so that the switching element is always on in a battery bypass circuit in which the terminal voltage of the battery when the switching element is off exceeds the charge cutoff voltage. The charging device for a battery pack according to claim 4, wherein 6. The battery pack charging device according to claim 1, wherein the secondary battery is a non-aqueous secondary battery. 7. The battery charger according to claim 6, wherein the non-aqueous secondary battery is a lithium secondary battery.