JP3991620B2 - Control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control circuit, and more particularly to a battery pack control circuit in which a plurality of lithium secondary batteries are connected in series, and a resistor and a switch connected in parallel to each lithium secondary battery constituting the battery pack. Related control circuit.
[0002]
[Prior art]
Conventionally, in an assembled battery in which a plurality of single cells such as lithium secondary batteries are connected in series, for example, as disclosed in Japanese Patent Application Laid-Open No. 2000-92732, a voltage measurement circuit, a switch, Capacitance that reduces the voltage difference between the cells by connecting the capacitance adjustment circuit consisting of bypass resistors for capacity adjustment in parallel and turning on the cells of the cells with high open circuit voltage to discharge the cells. Adjustment control has been performed. In particular, in a lithium ion battery using amorphous carbon, which has a high correlation between open circuit voltage and remaining capacity, as a negative electrode active material, control is performed to reduce the variation in unit cell voltage and align the remaining capacity.
[0003]
Specifically, the open circuit voltage (open voltage) of all the cells is measured in a state where the charging / discharging current does not flow in the assembled battery at the time of starting the system, and the remaining capacity of each cell is calculated from the value. Discharge the unit cell to the bypass resistor during the calculated discharge time corresponding to the bypass discharge amount (hereinafter referred to as bypass discharge time), with the amount of electricity that is the difference from the unit cell with the least remaining capacity as the bypass discharge amount. The method to make is taken. The bypass resistor is connected during charging / discharging of the assembled battery in which the control circuit operates. When a bypass resistor is connected during charging, the charging current flowing through the battery is reduced compared to when the bypass resistor is not connected. When a bypass resistor is connected during discharging, the bypass resistor is reduced compared to when the bypass resistor is not connected. Only the discharge current flowing through the battery for the flowing current increases, and the capacity can be adjusted to make the difference in the remaining capacity of the single cells.
[0004]
FIG. 6 shows a configuration example of a conventional control circuit that performs such capacity adjustment control. As shown in FIG. 6, a series circuit of a bypass resistor 2 and a switch 3 is connected in parallel to each single battery constituting the 4-series assembled battery group 1. Further, both ends of each unit cell are connected to the input side of the differential amplifier 4 for voltage detection, the output side of the differential amplifier 4 is connected to the input side of the multiplexer 5, and the output side of the multiplexer 5 is It is connected to the A / D conversion input of the microcomputer 6. The microcomputer 6 performs the input designation of the multiplexer 5 from the output port and performs A / D conversion to measure the open circuit voltage of the designated single cell as a digital value. The microcomputer 6 communicates with the host system that performs charge / discharge control via the communication interface 9 for the measured voltage data and the like. The output port of the microcomputer 6 is also connected to the switch 3, and the switch 3 is turned on during the bypass discharge time as described above.
[0005]
The entire control circuit including the microcomputer 6 operates upon receiving power supply from the power supply unit 7. Power supply from the power supply unit 7 is performed by operation control from the host system. A high level signal is input to the photocoupler 8 to set the power supply unit 7 in a power supply state, and a low level signal is input to the photocoupler 8 to supply power. The unit 7 is brought into a power supply non-supply state. For this reason, when charging and discharging the assembled battery group 1, the host system sends a high level signal to the photocoupler 8 to operate the entire control circuit including the microcomputer 6, and outputs a low level signal after the end of charging and discharging. Shut-down control is performed so that the current consumption of the control circuit is zero when sent to the photocoupler 8. This shutdown control is necessary for preventing each cell from being discharged when the assembled battery group 1 is left for a long period of time. The host system receives open circuit voltage data of all the single cells of the assembled battery group 1 from the microcomputer 6 via the communication interface 9 by communication, calculates the above-described remaining capacity and bypass discharge amount, and calculates the bypass discharge amount as data. To the microcomputer 6. The microcomputer 6 calculates the bypass discharge time from the bypass discharge amount, and during the bypass discharge time, the signal of the output port connected to the switch 3 is set to the high level to turn on the switch 3 and perform the bypass discharge to the bypass resistor 2. Let it be done. 6 shows the circuit configuration of a 4-series assembled battery. In an actual assembled battery, four or more cells are connected in series, and there are a plurality of control circuits. 6 transmits and receives data by communication with the host system. Further, it is known that each switch 3 shown in FIG. 6 can generally be composed of two FETs (or transistors) and a plurality of resistors.
[0006]
The reason for adjusting the capacity of each unit cell in this way is that when the remaining capacity of a specific unit cell deviates from the average value for some reason, the average voltage value of the entire assembled battery is in a normal charge / discharge state. This is because overcharge or overdischarge occurs. When the battery is overcharged or overdischarged, the discharge characteristics of the assembled battery are deteriorated, the safety is reduced by overcharging, the life is shortened by overdischarge, and the like. Causes of the remaining capacity shift include variations in self-discharge of individual cells constituting the assembled battery, temperature variations during charging / discharging, variations in charging efficiency, and the like. In particular, with lithium secondary batteries, it is difficult to completely charge the battery until the end of its life. Unlike lead batteries and nickel metal hydride batteries, which can be recharged periodically to make the remaining capacity uniform. The capacity adjustment function is indispensable. In addition, since the lithium secondary battery has a high energy density and the internal pressure of the battery rises drastically when it falls into an overcharged state, the control circuit must perform high-accuracy detection of the overcharge voltage. When the charge level deviates from the average value, the overcharge detection function operates early, and charging is stopped due to an erroneous determination of an abnormal state. Research and development has been done.
[0007]
[Problems to be solved by the invention]
However, when a conventional control circuit is used, the capacity adjustment period is limited to the period during which the control circuit is operating, that is, when the assembled battery is being charged / discharged. When discharging and leaving for a long period of time are repeated, there is a problem that the capacity adjustment effect is not sufficient. In particular, a large capacity lithium secondary battery of 100 Ah class is used as a unit cell constituting an assembled battery for electric vehicles and the like, and it is repeatedly used for a short time and left for a relatively short time by using a small capacity bypass resistor. Even under these conditions, capacity adjustment will not work effectively unless a large-capacity bypass resistor is used, resulting in large variations in cell-to-cell voltage, that is, variations in remaining capacity, leading to degradation of battery characteristics and life characteristics. There was a high possibility that it would be.
[0008]
This example will be specifically described with reference to the drawings. FIG. 7 shows the transition of the voltage of a single cell (hereinafter also referred to as a cell) when charging / discharging while performing capacity adjustment for 10 hours every week by conventional capacity adjustment control. The unit cell used is a lithium ion battery with a rated capacity of 90 Ah, and the bypass resistance is 39Ω. The number of series as a battery pack is 96 cells, and the control circuit shown in FIG. 6 is used. In this control circuit, during charging / discharging, the charge / discharge amount is controlled so that the charging rate (SOC = residual capacity / full charge capacity) of the assembled battery after completion of charging / discharging is 50%. In addition, as described above, the capacity adjustment control is performed such that the open circuit voltage before the charging / discharging current flows at the time of starting the system is measured, and the remaining capacity is calculated and discharged by the capacity differential bypass resistance with the cell having the smallest remaining capacity. It has been. As shown in FIG. 7, the variation in the cell voltage increases with the number of days elapsed, but since the capacity is periodically adjusted, the variation in the cell voltage is suppressed, and the maximum deviation which is the maximum value of the difference from the average voltage is also 20 mV. Less than.
[0009]
FIG. 8 shows the transition of the cell voltage when charging and discharging are performed while adjusting the capacity for 2 hours every week under the same conditions. As shown in FIG. 8, when the capacity adjustment time is as short as 2h, the variation in the cell voltage increases as the number of days elapses, and the maximum deviation after 90 days is as large as 60 mV and is still increasing. It is in.
[0010]
As described above, in the capacity adjustment control using the conventional control circuit, when the charging / discharging time of the assembled battery is short and the leaving period is long, the variation of the cell voltage becomes large, and the battery characteristics and the life characteristics deteriorate. The potential is great. This is because the amount of bypass discharge that can be controlled by the capacity adjustment time cannot correct the variation in the remaining capacity drop caused by self-discharge or the like while it is left.
[0011]
In order to solve this problem, it is conceivable to increase the amount of bypass discharge by setting the bypass resistor to a large capacity, but there are limitations in terms of heat generation, volume, and cost of the bypass resistor and the switch. Although it is conceivable to always operate the control circuit, the current consumption of the control circuit becomes a value that cannot be ignored, so that there is a problem that the lithium secondary battery is discharged and energy loss occurs while it is left unattended. .
[0012]
In view of the above-mentioned case, the present invention is capable of aligning the remaining capacity of the lithium secondary battery even when the charging / discharging time of the assembled battery is short and the leaving period is long without using a large-capacity resistor. It is an object of the present invention to provide a control circuit for an assembled battery that can minimize the above.
[0013]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention provides a control circuit for an assembled battery in which a plurality of lithium secondary batteries are connected in series, and a resistor and a switch are provided in each lithium secondary battery constituting the assembled battery. In a control circuit connected in parallel, a measurement means for measuring an open circuit voltage of each lithium secondary battery, a power supply means for supplying power to the measurement means, and the measurement before the start of charging / discharging of the assembled battery Calculated from the open circuit voltage measured by the means and the charging time of the assembled battery during the discharge time corresponding to the difference between the remaining capacity value of each lithium secondary battery and the minimum remaining capacity value of the remaining capacity values. the completion of discharge be continued by receiving the supply of the operating power from the power supply means bypassing the discharge control of the oN state of the switch is performed after the calculation of the discharge time, after the end of the bypass discharge control, the overall control circuit And a control means for controlling said power supply means so that the low power consumption state.
[0014]
In the present invention, the control means receives the supply of the operating power from the power supply means even after the charging / discharging of the assembled battery, and continues the bypass discharge for the calculated discharge time with the switch turned on. The remaining capacity of each lithium secondary battery can be set to the same value without using the power supply, and the power supply means is controlled so that the entire control circuit is in a low power consumption state after the end of the bypass discharge control. The discharge from the lithium secondary battery at the time can be suppressed. Here, the low power consumption state refers to a state where the supply of power from the power supply means to the measurement means and / or the control means is stopped.
[0015]
In this case, if the control means controls the power supply from the power supply means so that only the circuit portion that performs the bypass discharge control is activated after the charging / discharging of the assembled battery, the other operation of the control circuit For example, since it is possible to stop the power supply to the circuit part that performs the overcharge / overdischarge detection function, the communication function with the host system, etc., from the lithium secondary battery due to the consumption current of the control circuit after the completion of charge / discharge Can be reduced. At this time, if all or part of the elements of the circuit portion for performing the bypass discharge control is configured by a CMOS IC, the low power consumption characteristics of the CMOS IC depend on the current consumption of the control circuit after the end of charge / discharge. The discharge from the lithium secondary battery can be further reduced. In addition, since the CMOS type IC has a wide operating voltage range and can be operated by the voltage across the lithium secondary battery, the operating power supply of the circuit portion that performs the bypass discharge control is supplied from the lithium secondary battery that is the target of the bypass discharge control. In this way, the circuit portion that performs bypass discharge control can be simplified.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
Next, a first embodiment of a control circuit according to the present invention will be described with reference to the drawings. In the following embodiments, the same reference numerals are given to the same circuit components as those of the conventional control circuit shown in FIG. 6, and the description thereof is omitted, and only different portions will be described.
[0017]
As shown in FIG. 1, the control circuit of the present embodiment is different from that of the conventional control circuit only in that the output port of the microcomputer 6 is connected to the power supply unit 7, as is apparent from comparison with FIG. Is different. In this control circuit, in addition to being able to control the power supply unit 7 from an external host system to a power supply state / power supply non-supply state via a photocoupler 8, a high level signal from an output port of the microcomputer 6 or The circuit configuration can be controlled to a power supply state or a power supply non-supply state by outputting a low level signal.
[0018]
In the control circuit of the present embodiment, in addition to the operation of the conventional control circuit, capacity adjustment is performed by the bypass resistor 2 connected in parallel to each lithium ion battery (lithium secondary battery) constituting the assembled battery group 1. If the power supply unit 7 is controlled to be in a power supply state by the output of the high level signal from the output port of the microcomputer 6, the power supply even after the charging / discharging of the assembled battery group 1 is completed and the photocoupler 8 is turned off. The power supply from the unit 7 to the entire control circuit is continued. For this reason, the high level signal is continuously sent to the switch 3, and the bypass discharge of the lithium ion battery by the bypass resistor 2 is continued, so that the capacity adjustment is performed to the end without being stopped. The power supply from the power supply unit 7 is stopped after the bypass discharge of all the lithium ion batteries constituting the assembled battery group 1 is completed. The output of the low level signal to the switch 3 is performed individually for each switch 3 connected to the lithium ion battery after the bypass discharge time has elapsed. When the capacity adjustment of all the lithium ion batteries is completed, the micro level signal is output. A low level signal is output from the output port of the computer 6 to the power supply unit 7. As a result, the control circuit of the present embodiment enters a shutdown state in which current consumption is substantially zero.
[0019]
In the control circuit of this embodiment, even after the charging / discharging of the assembled battery group 1 is completed, bypass discharge of the lithium ion battery can be continued and capacity adjustment can be performed to the end, so that the charging / discharging time is short and the leaving period is long. Even when the operation is repeated, the variation in the battery voltage of each lithium ion battery constituting the assembled battery group 1 can be kept small.
[0020]
Further, in the control circuit of this embodiment, after the capacity adjustment, the control circuit is shut down and the current consumption is almost zero, so that the current consumption of the lithium ion battery that is left unattended can be minimized.
[0021]
Furthermore, in the control circuit of the present embodiment, the same bypass resistor and switch as in the conventional control circuit can be used without using a large-capacity bypass resistor, so that the heat generation, capacity, and cost of the resistor and switch element can be reduced. Can be suppressed.
[0022]
FIG. 2 shows the transition of the cell voltage and the maximum deviation when the assembled battery group 1 is actually left for 1 week and repeatedly charged and discharged for 2 hours. The measurement conditions are the same as those in the conventional control circuit described above. As is clear from FIG. 2, the battery voltage of each lithium ion battery constituting the assembled battery group 1 is small, and the maximum deviation is less than 20 mV even after 90 days. The same characteristics as in the case of 10 hours were obtained (see FIG. 7), and the increase in average deviation and the subsequent increase tendency as the number of days left as shown in FIG. 8 did not appear.
[0023]
(Second Embodiment)
Next, a second embodiment of the control circuit according to the present invention will be described.
[0024]
As shown in FIG. 3, the control circuit of the present embodiment is different from the control circuit of the first embodiment in that the power supply unit 7 has two power supply systems. That is, one power supply system of the power supply unit 7 is connected to a bypass discharge control unit (a circuit part that performs bypass discharge control) including the microcomputer 6 and the switch 3, and the other power supply system of the power supply unit 7 is The non-bypass discharge controller including the differential amplifier circuit 4, the multiplexer circuit 5, and the communication interface circuit 9 is connected.
[0025]
For this reason, in the control circuit of this embodiment, power is supplied to the bypass discharge control unit at the time of capacity adjustment after the end of charge / discharge, and power supply to the non-bypass discharge control unit other than the bypass discharge control unit is stopped to Current consumption from the lithium ion battery during adjustment can be reduced. Since the input voltage of the power supply unit 7 is the total voltage of the assembled battery group 1, the input current to the power supply unit 7 is discharged from all the lithium ion batteries in the assembled battery group 1. The actual consumption current of the control circuit of this embodiment can be reduced to 30 mA with a consumption current value that does not include the bypass current at the time of capacity adjustment, whereas the consumption current value at the time of charge / discharge is 55 mA. there were.
[0026]
(Third embodiment)
Next, a third embodiment of the control circuit according to the present invention will be described.
[0027]
As shown in FIG. 4, the control circuit according to the present embodiment includes a microcomputer 11 having a low power consumption constituted by a CMOS IC for bypass discharge control in addition to the main microcomputer 6, and a power supply unit 7. The control circuit is different from the control circuit of the first embodiment in that the power supply unit 10 supplies power to a bypass discharge control unit including the microcomputer 11 and the switch 3. The microcomputer 6 has two communication serial ports, one of which is used for communication with the microcomputer 11 (serial port 2). Further, the output port of the microcomputer 11 is connected to the switch 3 and the power supply unit 10, and the microcomputer 11 controls the on / off of these. The power supply unit 10 is also connected to the output port of the microcomputer 6 and is controlled to be turned on by the microcomputer 6. The control circuit of the present embodiment is different from the control circuit of the first embodiment in that the output port of the microcomputer 6 is not connected to the power supply unit 7 or the switch 3.
[0028]
The control circuit of this embodiment performs the following operation when adjusting the capacitance. The microcomputer 6 calculates the bypass discharge time from the bypass discharge amount of each lithium ion battery obtained by communication from the host system, sets the signal of the output port connected to the power supply unit 10 to the high level, the microcomputer 11 and the switch 3 To supply power. When power is supplied and the microcomputer 11 is activated, data on the bypass discharge time is transmitted from the serial port 2 of the microcomputer 6 to the serial port of the microcomputer 11 by communication. The microcomputer 11 performs a bypass discharge control operation in which the switch 3 is turned on only during the bypass discharge time according to the received bypass discharge time data.
[0029]
Further, after charging / discharging of the assembled battery group 1 is completed, power supply from the power supply unit 7 to the non-bypass discharge control circuit including the microcomputer 6, the differential amplifier 4, the multiplexer 5 and the communication interface 9 is stopped, and non-bypass discharge control is performed. Even if the operation of the circuit stops, the microcomputer 11 controls the power supply unit 10 to be in an ON state, and the bypass discharge control circuit including the microcomputer 11 and the switch 3 operates by receiving power supply from the power supply unit 10 and bypasses. Continue discharging. When the bypass discharge of all the lithium ion batteries constituting the assembled battery group 1 is completed, the microcomputer 11 controls the power supply unit 10 from the output port to stop the power supply, whereby the control circuit of this embodiment has low power consumption. It becomes the shutdown state.
[0030]
The microcomputer 11 of the present embodiment uses a CMOS type and low power consumption IC, and has a function of simply turning off the output port after a set time has elapsed except during communication operation with the microcomputer 6. Therefore, it is possible to further reduce power consumption by using an operation clock that can be switched to a low frequency and driving at a low frequency during the capacity adjustment operation. By actually using a 4-bit microcomputer capable of operating with a CMOS type 32.768 kHz clock, the current consumption not including the bypass current during capacity adjustment could be less than 5 mA.
[0031]
(Fourth embodiment)
Next, a fourth embodiment of the control circuit according to the present invention will be described.
[0032]
As shown in FIG. 5, in the control circuit of this embodiment, the on / off control of the switch 3 is performed by a high level or low level output signal from the CMOS type timer IC 12, and the output port of the microcomputer 6 is the timer IC 12 This is different from the first embodiment in that it is connected to. The timer IC 12 is directly supplied with power from the lithium ion battery and is not supplied with power from the power supply unit 7. The timer IC 12 is set with a timer operation time by serial communication with the microcomputer 6. When the timer IC 12 receives the bypass discharge time from the microcomputer 6 by communication, a high level signal is sent to the switch 3 during the set operation time. The output is made to turn on the switch 3. In the operation of this control circuit, the timer IC 12 receives the bypass discharge time by communication from the microcomputer 6 at the start of capacity adjustment, the bypass discharge is performed during the set operation time, and the bypass discharge is terminated. It becomes a low power consumption state. In the control circuit of the present embodiment, the power supply unit 10 for the bypass control circuit, which is necessary in the third embodiment, is unnecessary, and thus the control circuit can be simplified.
[0033]
The timer IC 12 of the present embodiment is a CMOS IC, and has a wide operating power supply voltage range in addition to low power consumption. In particular, the timer IC 12 can sufficiently operate at about 2.5 to 4.2 V, which is a charge / discharge voltage of a lithium ion battery. Therefore, stable operation can be performed even when operating power for performing bypass discharge control is supplied from both ends of the lithium ion battery. Further, in the present embodiment, after the timer IC 12 receives the bypass discharge time from the microcomputer 6 by communication, the operation of the microcomputer 6 is unnecessary, so that the power supply from the power supply unit 7 may be stopped. .
[0034]
In the above embodiment, an example is shown in which the multiplexer 5 is used to measure the open circuit voltage of each lithium ion battery. However, the present invention is based on the technique disclosed in Japanese Patent Application No. 11-79205. By using it, the control circuit can be configured without using an expensive multiplexer. In the above embodiment, the microcomputer 6 calculates the bypass discharge time. However, the bypass discharge time may be calculated on the host system side.
[0035]
【The invention's effect】
As described above, according to the present invention, after the charging and discharging of the assembled battery, the control means receives the operation power from the power supply means and performs the bypass discharge for the discharge time calculated with the switch turned on. Since the remaining capacity of each lithium ion battery can be made to be the same value, the power supply means is controlled so that the entire control circuit is in a low power consumption state after the end of the bypass discharge control. The effect that the discharge from the lithium ion battery can be suppressed can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a control circuit according to a first embodiment to which the present invention is applicable.
FIG. 2 is a characteristic diagram showing the transition of the cell voltage and maximum deviation of each lithium ion battery when the control circuit of the first embodiment is used and repeated for 1 week and charged and discharged for 2 hours.
FIG. 3 is a block diagram showing a schematic configuration of a control circuit according to a second embodiment to which the present invention is applicable.
FIG. 4 is a block diagram showing a schematic configuration of a control circuit according to a third embodiment to which the present invention is applicable.
FIG. 5 is a block diagram showing a schematic configuration of a control circuit according to a fourth embodiment to which the present invention is applicable.
FIG. 6 is a block diagram showing a schematic configuration of a conventional control circuit.
FIG. 7 is a characteristic diagram showing the transition of the cell voltage and maximum deviation of each lithium ion battery when a conventional control circuit is used and the charging and discharging for 10 hours are repeated.
FIG. 8 is a characteristic diagram showing the transition of the cell voltage and maximum deviation of each lithium ion battery when a conventional control circuit is used and the charging and discharging for 2 hours are repeated.
[Explanation of symbols]
1 assembled battery group (assembled battery)
2 Resistor 3 Switch (Part of the circuit that performs bypass discharge control)
4 Differential amplifier (part of measuring means)
5 Multiplexer (part of measuring means)
6, 11 Microcomputer (part of measurement means, control means, part of circuit part performing bypass discharge control)
7, 10 Power supply (Power supply means)
8 Photocoupler 9 Communication interface 12 CMOS timer IC (part of control means, part of circuit part performing bypass discharge control)

Claims (4)

A control circuit for an assembled battery in which a plurality of lithium secondary batteries are connected in series, wherein a resistance and a switch are connected in parallel to each lithium secondary battery constituting the assembled battery,
Measuring means for measuring the open circuit voltage of each lithium secondary battery;
Power supply means for supplying power to the measurement means;
Calculated from the open circuit voltage measured by the measuring means before the start of charging / discharging of the assembled battery, and corresponds to the difference between the remaining capacity value of each lithium secondary battery and the minimum remaining capacity value of the remaining capacity values During the discharge time, after the calculation of the discharge time, the bypass discharge control that continuously receives the operation power supply from the power supply means and turns on the switch after the charging / discharging of the assembled battery is performed, Control means for controlling the power supply means so that the entire control circuit is in a low power consumption state after the end of the bypass discharge control;
A control circuit comprising:   2. The control circuit according to claim 1, wherein the control unit controls the power supply unit so that only a circuit portion that performs the bypass discharge control is activated after charging and discharging of the assembled battery.   3. The control circuit according to claim 2, wherein all or a part of the elements of the circuit portion that performs the bypass discharge control is configured by a CMOS IC.   4. The control circuit according to claim 3, wherein operating power of a circuit portion that performs the bypass discharge control is supplied from a lithium secondary battery that is a target of the bypass discharge control. 5.

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