JP2005086878A - Charging control system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging control system which can stop safely and surely charging at overcharging time by taking a cell balance, without using a high accuracy voltage-measuring circuit. <P>SOLUTION: The charging control system includes each single cell 1, which has shunt regulators 7 set to 4.2V of the charging voltage of the single cell 1 at the operating voltage, and an overcharge voltage detector 8 for detecting the overcharging voltage 4.25V of the single cell 1 connected in parallel. A charger 11 starts constant-current charging into a battery 2 at a charging current of 1A for the maximum energizing current value or more of the shunt regulators 7, continues the constant-current charging at the current value of the charging current as one half, when the energizing current value of any of the shunt regulators 7 becomes 0.1A or larger, and finishes charging, by cutting off the charging current when any overcharging voltage detector 8 detects overcharged voltage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charging control system for a secondary battery, and more particularly to a charging control system for charging an assembled battery in which a plurality of secondary batteries are connected in series with a charging power source.

  Conventionally, in order to charge an assembled battery in which a plurality of secondary batteries (single cells) are connected in series, a charging power source is connected to the + terminal and the − terminal of the assembled battery, and a predetermined charging voltage and charging current are used. A charge control system that charges each unit cell simultaneously has been used. In addition, a charge control system that measures the voltage of each unit cell and charges the battery in an assembled battery using a lithium ion battery that has been put into practical use recently is used. The reason why the cell balance function is necessary is that, if the state of charge between the individual cells is different, the capacity that can be charged and discharged as an assembled battery is reduced and the life is also shortened. If it is a nickel metal hydride battery, it is possible to achieve cell balance by overcharging, but a lithium ion battery using a non-aqueous organic solvent as an electrolyte cannot be overcharged. A cell balance function that aligns the state of charge is essential.

  For this reason, in the charging of a lithium ion battery, a technique is known in which a bypass resistor is connected in parallel with each unit cell to perform a bypass discharge to align the state of charge, that is, a cell balance operation is performed (for example, Patent Document 1). reference). In this technique, for example, as shown in FIG. 4, a bypass resistor 2 and a switching element 3 are connected to the unit cell 1, and charging is performed by performing bypass discharge for each unit cell 1 in series. Yes. The voltage of the unit cell 1 is converted into a voltage having the negative terminal of the assembled battery as the ground using the differential amplifier 4, and the converted output is connected to the A / D converter input of the microcomputer 6 through the multiplexer 5. The port output of the microcomputer 6 selects an input channel of the multiplexer, that is, a single cell, and also serves as a control output of the switching element 3. The microcomputer 6 switches the open voltage of the single cell 1 while controlling the multiplexer at the time of system start-up, measures it with an A / D converter, calculates the remaining capacity calculated from the open voltage of the single cell 1, and calculates four single cells. The switching element 3 is controlled only for the capacity that is the difference from the minimum remaining capacity, and the bypass discharge operation is performed.

  As described above, the voltage of a single cell is measured using an A / D converter. However, it is difficult in terms of cost to provide an A / D converter for each single cell. The battery voltage will be measured. In addition, since the cells are connected in series in the assembled battery, the voltage of the cell can be directly measured with high accuracy by the A / D converter unless the power supply of the A / D converter is isolated and the measurement input is switched. Therefore, a voltage detection circuit that connects the ground terminal of the A / D converter to the negative terminal of the lowest unit cell of the assembled battery and converts the voltage of the unit cell to the ground terminal level has been used (for example, Patent Documents). 2). Such a voltage detection circuit is composed of a combination of a voltage dividing circuit and a differential amplifier circuit. In order to achieve cell balance, it is necessary to accurately measure the voltage of a single cell as a digital value. For example, in the case of a lithium ion battery module for automobiles that has been put into practical use, the voltage is measured with an accuracy of about ± 50 mV. ing.

JP 2000-92732 A JP 2001-231177 A

  However, in the above prior art, in order to ensure a voltage detection accuracy of about ± 50 mV, a high-precision resistor and a low-offset voltage operational amplifier are required, resulting in a complicated circuit configuration and high cost. . In addition, for example, in order to perform charging control of an assembled battery for automobiles or the like using a lithium ion battery having a high energy density and attention should be paid to overcharging, it is necessary to reliably prevent overcharging from the viewpoint of safety.

  An object of the present invention is to provide a charge control system that can balance a cell without using a high-accuracy voltage measurement circuit and can safely stop charging when overcharged.

  In order to solve the above-mentioned problem, a first aspect of the present invention is that a shunt regulator whose operating voltage is set to a charging voltage of a unit cell and an overcharge detection circuit for detecting the overcharging voltage of the unit cell are all unit cells. The battery packs connected in parallel are charged with a constant current with a charging current equal to or less than the maximum energization current value of the shunt regulator, and the charge current is cut off when any of the overcharge detection circuits detects an overcharge voltage. It is characterized by that.

  In the first aspect, the shunt regulator whose operating voltage is set to the charging voltage of the unit cell is connected in parallel to the unit cell, and the constant current charging is performed with the charging current equal to or less than the maximum energization current value of the shunt regulator. When the battery voltage reaches the charging voltage of the single cell, current flows through the shunt regulator, and all the single cells are aligned with the operating voltage of the shunt regulator, so that the cell balance of all the single cells can be achieved and overcharge voltage is detected. Since the overcharge detection circuit is connected in parallel to the cells and any of the overcharge detection circuits detects the overcharge voltage, the charging current is cut off, so the shunt regulator breaks down and the cell voltage rises. Even so, the charging can be stopped by cutting off the charging current to prevent the unit cell from being overcharged, so that safety can be ensured.

  In order to solve the above problems, the second aspect of the present invention includes a shunt regulator whose operating voltage is set to the charging voltage of the unit cell and an overcharge detection circuit for detecting the overcharging voltage of the unit cell. When a battery pack connected in parallel to a single battery starts constant-current charging with a charging current equal to or greater than the maximum energization current value of the shunt regulator, and when the energization current value of any of the shunt regulators exceeds a set value The constant current charging is continued by lowering the current value of the charging current, and the charging current is cut off when any of the overcharge detection circuits detects an overcharge voltage.

  In the second aspect, constant current charging is started with a charging current equal to or greater than the maximum energization current value of the shunt regulator, and when the energization current value of any of the shunt regulators exceeds the set value, the current value of the charging current is decreased. Therefore, even if the maximum current value of the shunt regulator is small, the charging current can be increased until it reaches the operating voltage of the shunt regulator. In addition, since all the cells are aligned with the operating voltage of the shunt regulator, it is possible to balance the cells of all the cells, and connect an overcharge detection circuit that detects the overcharge voltage to the cell and either overcharge. Since the detection circuit detects the overcharge voltage, the charging current is cut off, so even if the shunt regulator breaks down and the cell voltage rises, It is possible to prevent overcharging of the cell to terminate charging by blocking the flow, it is possible to ensure safety.

  According to the first aspect of the present invention, the shunt regulator whose operating voltage is set to the charging voltage of the unit cell is connected in parallel to the unit cell, and constant current charging is performed with a charging current equal to or less than the maximum energization current value of the shunt regulator. Therefore, when charging progresses and reaches the charging voltage of the single cell, current flows to the shunt regulator, and all the single cells are aligned with the operating voltage of the shunt regulator. Since an overcharge detection circuit that detects the charging voltage is connected in parallel to the single battery and any of the overcharge detection circuits detects the overcharge voltage, the charging current is cut off. Even if the voltage of the battery rises, it is possible to stop charging by cutting off the charging current and prevent overcharging of the unit cell, so safety can be ensured. It is possible to obtain the effect say.

  Further, according to the second aspect of the present invention, when constant current charging is started with a charging current equal to or greater than the maximum energization current value of the shunt regulator, and when the energization current value of any of the shunt regulators exceeds the set value, Since the constant current charging is continued by reducing the current value of the charging current, the charging current can be increased until the shunt regulator operating voltage is reached even if the maximum energization current value of the shunt regulator is small. A single cell can be charged and all the single cells are aligned with the operating voltage of the shunt regulator, so that the cell balance of all single cells can be achieved, and an overcharge detection circuit that detects overcharge voltage is connected to the single cell. However, when any overcharge detection circuit detects an overcharge voltage, the charge current is cut off. Be increased, it is possible to prevent overcharging of the cell to terminate charging the interruption of the charging current, it is possible to ensure safety, it is possible to obtain an effect that.

  Hereinafter, an embodiment of a charge control system according to the present invention will be described with reference to the drawings.

  As shown in FIG. 1, the charge control system 20 of the present embodiment includes an assembled battery 2 in which four unit cells 1-1 to 1-4 (hereinafter collectively referred to as a unit cell 1) are connected in series. A shunt regulator 7 having a built-in bandgap reference power source and set to the charging voltage of the cell 1, an overcharge voltage detection circuit 8 for detecting the overcharge voltage of the cell 1, and OR The charging state detection part which has the circuits 9 and 10 and the charger 11 for charging the assembled battery 2 are comprised.

  Each cell 1 is connected in parallel with a shunt regulator 7 and an overcharge voltage detection circuit 8. The shunt regulator 7 has a terminal for outputting a high level signal when the energization current during operation becomes equal to or higher than a set value, and this terminal is connected to the input side of the OR circuit 9. The overcharge voltage detection circuit 8 has a terminal for outputting a high level signal when an overcharge voltage larger than the charge voltage of the unit cell 1 is detected, and this terminal is connected to the input side of the OR circuit 10. Has been.

  As shown in FIG. 2, the charger 11 includes a charging power source 12, a constant voltage circuit 13 such as a D / D converter that converts the power supplied from the charging power source 12 into a constant voltage and a constant current, and a backflow prevention diode 14. And a switch 15 such as an FET and a microcomputer (hereinafter referred to as a microcomputer) 16. The microcomputer 16 includes a CPU that performs arithmetic processing, a ROM that stores a control program, a RAM that serves as a work area for the CPU, two input ports (an overcharge detection input port and a shunt regulator operation detection input port described later, see FIG. 1), A switch control port for turning off the switch 15 by being connected to the switch 15 via the signal line and outputting a high level signal, and a high level signal being connected to the constant voltage circuit 13 via the signal line The constant voltage circuit control port for reducing the charging current of the constant voltage circuit 15 is provided.

  As shown in FIG. 1, during charging, the + terminal and the − terminal of the assembled battery 2 are connected to the + charging terminal and the − charging terminal of the charger 11, respectively. The output sides of the OR circuits 9 and 10 are connected to the overcharge detection input port and the shunt regulator operation detection input port of the charger 11 (microcomputer 16).

  In this example, a lithium ion battery having a battery capacity of 1 Ah is used for the unit cell 1, and a shunt regulator 7 having a set voltage of 4.2 V that is the charge voltage of the unit cell 1 and a set current of 0.1 A is used. It was. In addition, the setting voltage of the overcharge voltage detection circuit 8 is 4.25 V, the charger 11 has a maximum charging current of 1 A, and every time a high level signal is received from the microcomputer 16, the charging current is reduced by half. .

  Next, the operation of the charging control system 20 of the present embodiment will be described with the CPU of the microcomputer 16 as a main component. When the microcomputer 16 is turned on, the CPU sets the output to the signal line to a low level so that the switch 15 is turned on in the initial setting process, and turns on when the charge state detection unit is connected. A charging routine is executed by a signal from a switch (not shown).

  When the charger 11 is connected to the charging state detection unit, the battery pack 2 starts constant current charging with a charging current (1A) larger than the maximum energization current of the shunt regulator 7. When the charging of each unit cell 1 proceeds and the voltage of any unit cell 1 reaches 4.2 V, an energization current starts to flow through the shunt regulator 7 connected in parallel to the unit cell 1, and the energization current of the shunt regulator 7 Becomes 0.1 A of the set current, the shunt regulator 7 outputs a high level signal to the input side of the OR circuit 9. Accordingly, the output of the OR circuit 9 becomes a high level when the energization current of any shunt regulator 7 becomes equal to or higher than the set current (0.1 A). The CPU receives this signal via the shunt regulator operation detection input port, and lowers the charging current of the constant voltage circuit 13 by half (0.5 A).

  As a result, the energization current of the shunt regulator connected in parallel to the unit cell 1 that has reached 4.2 V is less than 0.1 A. The assembled battery 2 is continuously charged with a half charge current, and each unit cell 1 is further charged. When the energizing current of any shunt regulator 7 becomes 0.1 A, the shunt regulator 7 outputs a high level signal to the input side of the OR circuit 9. The CPU further reduces the charging current of the constant voltage circuit 13 by half (0.25 A) and continues constant current charging. Hereinafter, this operation is repeatedly executed. When the charging current becomes almost zero, an LED (not shown) is turned on to notify the end of charging and the charging routine is ended. The determination of whether the charging current has become almost zero can be made by, for example, counting the number of high level signals output to the constant voltage circuit 13.

  On the other hand, the input side of the OR circuit 10 is connected to the output of the overcharge voltage detection circuit 8. For this reason, when any of the overcharge voltage detection circuits 8 detects 4.25 V set as the overcharge voltage, the overcharge voltage detection circuit 8 outputs a high level signal to the input side of the OR circuit 10. The CPU receives this signal via the shunt regulator operation detection input port, outputs a high level signal to the signal line connected to the switch 15, and ends the charging routine. As a result, the switch 15 is turned off, and the charging current supplied from the charger 11 to the assembled battery 2 is interrupted. In this case, an LED having a different color from the LED described above may be lit to notify the forced stop of charging.

  In FIG. 3, the transition of the charging voltage characteristic of the cell 1 and the electric current of the charger 11 when the assembled battery 2 is charged by the charge control system 20 of the present embodiment is shown. As shown in FIG. 3, after detecting that the voltage of the unit cell 1 has reached 4.2 V and the energizing current starts to flow through the shunt regulator 7 and the energizing current of the shunt regulator 7 becomes 0.1 A, the charging current The operation in which the constant current charging is continued is reduced by half. Eventually, the charging current value of the charger 11 is less than 0.1 A, and the voltages of all the unit cells 1 are almost equal to 4.2V.

  In the charging control system 20 of the present embodiment, constant current charging is started with a charging current (1A) that is equal to or greater than the maximum energizing current value of the shunt regulator 7, and the energizing current value of any shunt regulator 7 is set to a set value (0.1A). ) Since the current value of the charging current of the charger 11 is lowered and constant current charging is continued when the above is reached, charging is continued until the operating voltage of the shunt regulator 7 is reached even if the maximum energization current value of the shunt regulator 7 is small. Since the current can be increased, all the cells 1 can be charged in a short time, and all the cells 1 are equal to the operating voltage (4.2 V) of the shunt regulator 7, so that the cell balance of all the cells 1 is maintained. Can do.

  Further, in the charge control system 20 of the present embodiment, the shunt regulator 7 including the band gap type reference voltage source is exemplified, but this type of shunt regulator has a precision of ± 1% at a relatively low cost. The charging voltage of the lithium ion battery is about 4.1 to 4.2 V, and the accuracy of ± 40 mV is obtained with the accuracy of ± 1%, and the accuracy of ± 50 mV of the conventional technology that has been secured by investing high cost. It will not fade.

  Furthermore, in the charge control system 20 of the present embodiment, an overcharge voltage detection circuit 8 that detects an overcharge voltage (4.25 V) is connected to the single cell 1 in parallel, and any one of the overcharge voltage detection circuits 8 is connected. Since the charging current is cut off when the overcharge voltage (4.25 V) is detected, even if the shunt regulator 7 breaks down and the voltage of the cell 1 rises, the charging is terminated by cutting off the charging current, and the cell 1 Can be prevented from overcharging. Therefore, safety can be ensured even when the charge control system 20 is used in an assembled battery for automobiles using a lithium ion battery that should be noted for overcharging.

  In the present embodiment, an example is shown in which constant current charging is started with a charging current greater than or equal to the maximum energization current value of the shunt regulator 7. However, constant current charging is performed with a charging current that is less than or equal to the maximum current value of the shunt regulator 7. May be. In this configuration, when charging progresses and reaches the set voltage of the shunt regulator 7, a current flows through the shunt regulator 7, and the voltage of the single cell 1 is suppressed to a predetermined charging voltage (4.2V). Therefore, the unit cell 1 is not overcharged, and the charging voltage becomes the operating voltage of the shunt regulator 7, and therefore, when a sufficient charging time has elapsed, the charging current almost flows into the shunt regulator 7 and the unit cell 1. Thus, the voltage of the single cell 1 is all equal to the operating voltage of the shunt regulator 7. Therefore, the unit cell 1 is charged with a voltage having the accuracy of the operating voltage of the shunt regulator 7. In this way, compared with the present embodiment, the output terminal from the shunt regulator 7 and the OR circuit 9 are not necessary, and the configuration of the microcomputer 16 and the constant voltage circuit 13 can be simplified. And miniaturization can be achieved.

  Further, since the maximum energization current of the shunt regulator 7 can be increased only by externally attaching a transistor, a transistor may be added as necessary.

  The charge control system of the present invention can balance the cell without using a high-accuracy voltage measurement circuit, and can safely and reliably stop charging in the event of overcharging. is there.

It is a block circuit diagram of the charge control system of an embodiment to which the present invention is applicable. It is a schematic block circuit diagram of the charger of the charge control system of the embodiment. It is a characteristic diagram which shows transition of the charging voltage characteristic of the cell of the charge control system of embodiment, and the electric current of a charger. It is a block circuit diagram of the charge control system of a prior art.

Explanation of symbols

1 cell 2 assembled battery 7 shunt regulator 8 overcharge voltage detection circuit (overcharge detection circuit)
20 Charge control system

Claims (2)

  A shunt regulator whose operating voltage is set to the charging voltage of the unit cell and an overcharge detection circuit that detects the overcharging voltage of the unit cell are connected to all the unit cells in parallel. A charging control system for a secondary battery, wherein charging is performed at a constant current with the following charging current, and the charging current is cut off when any of the overcharge detection circuits detects an overcharge voltage.   A shunt regulator whose operating voltage is set to the charging voltage of the unit cell and an overcharge detection circuit that detects the overcharging voltage of the unit cell are connected to all the unit cells in parallel. The constant current charging is started with the above charging current, and when the energization current value of any of the shunt regulators is equal to or higher than a set value, the current value of the charging current is decreased and the constant current charging is continued. A charge control system for a secondary battery, wherein the charge current is cut off when an overcharge detection circuit detects an overcharge voltage.