JP2011101517A - Battery pack - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery pack that facilitates reliable charging of a secondary battery where a plurality of battery cells are connected in series without being affected by variations of characteristics of the battery cells. <P>SOLUTION: The battery pack includes a current limiting resistor which is selectively inserted into a charging path of the secondary battery and limits charging current to the secondary battery and a bypass switch element bypassing the current limiting resistor. When the secondary battery is charged, the bypass switch element is conducted. When terminal voltage in one of a plurality of battery cells reaches overcharge protection voltage which is previously set during charging, the bypass switch element is interrupted and charging of the secondary battery is continued. When the terminal voltage of one of the plurality of battery cells reaches the overcharge protection voltage which is previously set while the bypass switch element is interrupted, a charging inhibition switch element is interrupted and charging of the secondary battery is inhibited. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a battery pack including a secondary battery in which a plurality of battery cells are connected in series and a charge control unit thereof.

  When a battery pack including a secondary battery is connected to a charger for charging, it is important to charge the secondary battery safely, as well as to efficiently charge the secondary battery to a fully charged state. In particular, when a lithium ion battery is used as a secondary battery, it is required to sufficiently ensure the safety of charging. Therefore, the secondary battery is charged exclusively by limiting the maximum charging voltage and limiting the maximum charging current (see, for example, Patent Document 1).

  Incidentally, the battery pack generally has a secondary battery in which a plurality of battery cells are connected in series and parallel, and is inserted in series in the charging path of the secondary battery to block the charging path and A charge prohibiting switch element for prohibiting charging; voltage detecting means for detecting a terminal voltage (cell voltage) of the secondary battery; and a terminal voltage (cell voltage) of the secondary battery detected by the voltage detecting means. When the battery reaches the overcharge protection voltage (maximum charging voltage), the charging control unit is configured to block the charging prohibiting switch element and prohibit (stop) charging the secondary battery.

  Specifically, for example, as shown in FIG. 4, the charge control unit determines whether or not the cell voltage in the secondary battery exceeds the overcharge protection voltage <Step S1> until a predetermined charge stop condition is reached. The secondary battery is charged <Step S2>. When the cell voltage exceeds the overcharge protection voltage <Step S1>, the charging prohibition switch element is cut off to prohibit (stop) charging the secondary battery <Step S3>. Thereafter, by determining the open terminal voltage of the secondary battery <Step S4>, it is determined whether the secondary battery has been normally charged until full charge, or whether charging has ended abnormally before reaching full charge. It has become.

JP 2009-44946 A

  By the way, about the several battery cell which comprises a secondary battery, even if what has the uniform characteristic is used exclusively, it cannot be denied that there exists variation in the battery characteristic for every battery cell strictly. For this reason, when the secondary battery is charged, the terminal voltage (cell voltage) of each battery cell also varies somewhat. Then, when charging a secondary battery in which two battery cells are connected in series, for example, as shown in FIG. 5, the terminal voltage (cell voltage) V1 of one battery cell at the time of charging reaches the maximum charging voltage described above. At that time, the charge control unit described above shuts off the charge prohibition switch element and prohibits (stops) charging the secondary battery, so that the other battery cell remains in an insufficiently charged state, that is, Charging is stopped before the cell voltage V2 becomes sufficiently high. As a result, the terminal voltage of the secondary battery obtained by adding the charging voltages V1 and V2 of the two battery cells, the open circuit voltage OCV after completion of charging does not satisfy the preset voltage threshold for error identification, This will be determined as charging abnormality.

  The present invention has been made in view of such circumstances, and the object thereof is to easily and recharge a secondary battery in which a plurality of battery cells are connected in series without being influenced by the characteristic variation of each battery cell. An object of the present invention is to provide a battery pack configured so that it can be reliably charged.

In order to achieve the above-described object, the battery pack according to the present invention includes a secondary battery in which a plurality of battery cells (for example, lithium ion batteries) are connected in series, and a charging path of the secondary battery. A charge prohibiting switch element that inhibits charging of the secondary battery by cutting off the current, and a current limiting resistor that is selectively inserted in the charging path of the secondary battery to limit the charging current to the secondary battery, A bypass switch element connected in parallel to the current limiting resistor and bypassing the current limiting resistor, a voltage detecting means for detecting a terminal voltage of each battery cell, and a terminal voltage detected by the voltage detecting means A charge control unit for driving the charge prohibition switch element and the bypass switch element,
In particular, the charge control unit causes the charge prohibition switch element and the bypass switch element to be electrically connected to each other when the secondary battery is charged, and any of the battery cells in the state where the bypass switch element is electrically connected. When the terminal voltage of the battery reaches a preset overcharge protection voltage, the bypass switch element is shut off to continue charging the secondary battery. When any one of the terminal voltages reaches a preset overcharge protection voltage, the charging prohibition switch element is cut off to prohibit charging of the secondary battery.

  The charging control unit is configured to inhibit the charging when the terminal voltage of any of the plurality of battery cells exceeds the overcharge protection voltage regardless of whether the bypass switch element is on or off. It is desirable that the switch element be forcibly cut off to prohibit charging of the secondary battery.

  In addition, the above-described battery pack preferably further includes a current detection unit that detects a charging current of the secondary battery. In the charging control unit, the charging current detected by the current detection unit is a preset current value. It is desirable to provide a full charge detection means for outputting a charge completion signal to the effect that the secondary battery has reached a full charge state to the charger.

  According to the battery pack having the configuration described above, the secondary battery is charged in a state where the current limiting resistor is bypassed at the time of charging, and one of the battery cells constituting the secondary battery is included in the charging process. When the terminal voltage (cell voltage) reaches a preset overcharge protection voltage, the bypass switch element is cut off, and a current limiting resistor is inserted in series in the charging path of the secondary battery. As a result, since the charging current for the secondary battery is reduced, the terminal voltage (cell voltage) of each battery cell is lowered, and charging for the secondary battery is continued in this state. And only when the terminal voltage (cell voltage) in the plurality of battery cells reaches a preset overcharge protection voltage in the charging process under the charging current limit accompanying the interruption of the bypass switch element, Since the switch element for prohibiting charging is cut off, the secondary battery can be reliably charged to a fully charged state.

1 is a schematic configuration diagram of a battery pack according to an embodiment of the present invention. The figure which shows the example of the procedure of the charge control in the battery pack shown in FIG. The figure which shows the mode of charge with respect to the secondary battery and battery cell in the pack battery shown in FIG. The figure which shows the example of the procedure of the charge control in the conventional battery pack. The figure which shows the mode of charge with respect to the secondary battery and battery cell in the conventional pack battery.

Hereinafter, a battery pack according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a main part of a battery pack according to the present invention, wherein 1 is a secondary battery configured by connecting a plurality of battery cells 2 in series. The battery cell 2 consists of a lithium ion battery, for example. 1 shows a secondary battery 1 in which two battery cells 2 are connected in series. Generally, depending on battery specifications (output voltage and current capacity) required for a battery pack, A secondary battery 1 is configured by connecting battery cells 2 in series and parallel. Specifically, since the cell voltage of the lithium ion battery is nominally 3.7 V, in the so-called 12 V specification secondary battery 1, the secondary battery 1 is configured by connecting lithium ion batteries in three or four stages in series. Composed.

  The battery pack basically includes a switch element (for example, FET) 3 for preventing overcharge (for prohibiting charging) and a switch for preventing overdischarge (for preventing discharge) in the charge / discharge path of the secondary battery 1 described above. An element (for example, FET) 4 is interposed in series, and the terminal voltage (cell voltage) of each battery cell 2 in the secondary battery 1 is detected to drive the switch elements 3 and 4 in a cut-off manner. Control means 5 is provided for protecting the secondary battery 1 from overcharge and overdischarge. The control means 5 is composed of, for example, a microcomputer provided with voltage detection means 5a for detecting the cell voltage, a dedicated protection IC, or the like.

  Although not particularly shown in FIG. 1, the battery pack incorporates current detection means for detecting the charge / discharge current of the secondary battery 1, and the control means 5 has a charging current for the secondary battery 1. To a full charge detecting means for detecting the full charge of the secondary battery 1. Further, the control means 5 is provided with a communication means, a control signal output means and the like for notifying the charger side (not shown) when the full charge of the secondary battery 1 is detected.

  In addition to such basic functions, the battery pack according to the present invention is further inserted in series in the charging / discharging path (charging path) of the secondary battery 1 to limit the charging current to the secondary battery 1. A current limiting resistor 6 is provided, and a bypass switch element (for example, FET) 7 is connected in parallel to the current limiting resistor 6 and bypasses the current limiting resistor 6 from the charge / discharge path. This bypass switch element (eg, FET) 7 is normally turned on to bypass the current limiting resistor 6, and as described later, one terminal voltage (cell voltage) in the plurality of battery cells 2 is described above. When the overcharge protection voltage is reached, it is shut off under the control of the control means 5.

  That is, in the battery pack according to the present invention, the control means 5 individually detects each cell voltage (terminal voltage) of the plurality of battery cells 2 constituting the secondary battery 1 by the voltage detection means 5a. Yes. Then, charging of the secondary battery 1 is started in a state in which the bypass switch element 7 is turned on, thereby bypassing the current limiting resistor 6. In addition, when the secondary battery 1 is a lithium ion battery, a constant current (maximum of about 0.5 to 1.0 C) and a constant voltage (maximum of about 4.2 V / cell) charging are used. To do. When the terminal voltage of the secondary battery 1 (battery cell 2) is equal to or higher than a predetermined set value or the charge current is equal to or lower than the predetermined set value, this is determined as full charge.

  When charging is started in this manner, the control means 5 first reaches the overcharge protection voltage set in advance, for example, as shown in FIG. In the case of a lithium ion battery, it is determined whether it has reached 4.25 V or not (step S11). If the terminal voltage of each battery cell 2 has not reached the overcharge protection voltage (4.25 V), it is determined whether or not a preset charge stop condition is satisfied <step S12>, and the charge stop condition The charging of the secondary battery 1 is continued while determining the cell voltage of the battery cell 2 until is satisfied.

  Note that the charging stop condition is, for example, when the secondary battery 1 is fully charged and the charging current of the secondary battery is reduced, and the charging current is reduced to a preset current value. Set as Such a function of detecting a decrease in charging current and stopping the charging can be provided in a charger that charges the battery pack.

  When one cell voltage among the plurality of battery cells 2 exceeds the overcharge protection voltage in the charging process <step S11>, the control means 5 determines whether the bypass switch element 7 is in the cut-off state. It is determined whether or not <Step S13>. That is, it is determined whether or not the current limiting resistor 6 is inserted in the charging path of the secondary battery 1 to limit the charging current. When the bypass switch element 7 is in a conductive state and the charging current is not limited by the current limiting resistor 6, for example, as shown in FIG. On the other hand, the bypass switch element 7 is cut off <step S14>, assuming that the battery voltage has risen faster than the other battery cells due to variations in characteristics between the battery cells, and the cell voltage has increased. The charging current for the secondary battery 1 is limited.

  By limiting the charging current for the secondary battery 1 in this way, the terminal voltage (cell voltage) of each battery cell 2 decreases due to its internal resistance, and falls below the overcharge protection voltage described above. . As a result, each battery cell 2 of the secondary battery 1 is slowly charged under a limited current. Then, it is determined whether or not the charging current has decreased to the above-described charging stop condition <step S12>.

  When the cell voltage of one of the plurality of battery cells 2 exceeds the overcharge protection voltage and the bypass switch element 7 is in the cut-off state <Step S13>, the control means 5 Even though the charging current for the secondary battery 1 is limited, it is determined that the terminal voltage of the battery cell 2 exceeds the overcharge protection voltage and the safe charging condition is not satisfied. In this case, the control means 5 shuts off the charging prohibition (overcharge prevention) switch element 3 and forcibly stops the charging of the secondary battery 1 (step S15).

  The control means 5 controls the charging of the secondary battery 1 as described above, and when the charging stop condition for the secondary battery 1 is satisfied, the open terminal of the secondary battery 1 after the charging is stopped next. The voltage is detected, and it is determined whether or not the open terminal voltage OCV exceeds a preset error identification voltage threshold value, that is, whether or not the secondary battery 1 is sufficiently charged <step S16>. When the open terminal voltage OCV of the secondary battery 1 is sufficiently high, it is determined that the charging has been normally completed. When the open terminal voltage OCV is lower than the error identification voltage threshold, It is determined that the secondary battery 1 is not sufficiently charged due to the abnormality of the secondary battery 1. That is, it is determined that the charging of the secondary battery 1 has ended abnormally.

  Thus, according to the battery pack configured as described above, even if one terminal voltage (cell voltage) among the plurality of battery cells 1 constituting the secondary battery 1 is reached, the secondary battery 1 is immediately subjected to this state. Since charging is continued by stopping the charging without stopping the charging, even if the characteristics of the plurality of battery cells 2 vary, the battery cells 2 can be sufficiently charged. In particular, each battery cell 2 can be slowly charged with a current-limited charging current until the charging stop condition for the secondary battery 1 is satisfied. Therefore, even if there is some variation in the characteristics between the plurality of battery cells 2 constituting the secondary battery 1, the secondary battery 1 can be surely charged to the charge capacity that fully utilizes the characteristics of these battery cells 2. Moreover, it can be charged easily. In addition, the charging safety can be sufficiently ensured.

  The present invention is not limited to the embodiment described above. For example, the number of battery cells 2 constituting the secondary battery 1 and the number of series connection stages thereof may be determined according to the specifications required for the battery pack as described above. In the embodiment shown in FIG. 1, the switch elements 3, 4, and 7 are inserted in the positive line of the secondary battery 1, but may be inserted in the negative line of the secondary battery 1. Needless to say. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

1 Secondary battery 2 Battery cell 3 Overcharge prevention switch element (FET)
4 Overdischarge prevention switch element (FET)
5 Control means (microcomputer or protection IC)
5a Voltage detection means 7 Bypass switch element (FET)

Claims (4)

A secondary battery in which a plurality of battery cells are connected in series;
A charging prohibition switch element that is inserted into the charging path of the secondary battery to block the charging path and prohibit charging of the secondary battery;
A current limiting resistor that is selectively inserted in a charging path of the secondary battery to limit a charging current for the secondary battery;
A bypass switch element connected in parallel to the current limiting resistor and bypassing the current limiting resistor;
Voltage detecting means for detecting the terminal voltage of each battery cell, and
A charge control unit for driving the charge prohibition switch element and the bypass switch element according to the terminal voltage detected by the voltage detection means,
The charging control unit causes the charging prohibition switch element and the bypass switch element to conduct at the time of charging the secondary battery, and in any state of the battery cell in a state where the bypass switch element is conducted. When the terminal voltage reaches a preset overcharge protection voltage, the bypass switch element is shut off to continue charging the secondary battery, and the bypass switch element is shut off in the battery cell. A battery pack characterized in that when any one of the terminal voltages reaches a preset overcharge protection voltage, the charge prohibition switch element is cut off to prohibit charging of the secondary battery.   The battery pack according to claim 1, wherein the plurality of battery cells constituting the secondary battery are lithium ion batteries.   The charge control unit, when any terminal voltage in the plurality of battery cells exceeds the overcharge protection voltage, the charge inhibition switch element regardless of the conduction / cutoff state of the bypass switch element. The battery pack according to claim 1, wherein the battery is forcibly blocked to prohibit charging of the secondary battery. The battery pack according to any one of claims 1 to 3,
Furthermore, it has a current detection means for detecting the charging current of the secondary battery,
When the charging control unit detects that the charging current detected by the current detecting unit is lower than a preset current value, a charging completion signal indicating that the secondary battery has reached a fully charged state with respect to a charger. A battery pack comprising: a full charge detection means for outputting

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