JP2002101565A - Voltage regulation device for battery pack and method of voltage regulation for battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form and implement with lower cost a device or a method for controlling dispersion of the terminal voltage of a battery pack. SOLUTION: A battery pack 22 in which a plurality of unit cells 23 made up of lithium secondary battery is applied to battery for driving a traction motor of HEV, and a CPU 38 of a battery pack supervisory circuit part 26 controls the drive of the traction motor through a vehicle control circuit part 29 as such that the discharge from or charge to the battery pack 22 is preferentially performed when comparators 31U, 31L of a cell status monitor circuit part 25 exceeds the upper limit voltage Vu or is below the lower limit voltage Vl. Then, when the dispersion of the terminal voltage of each unit cell 23 which composes a sell group 24 is determined to be extended beyond the predetermined level, a mean unit cell voltage VCM charges the upper limit voltage Vu to exceed by the predetermined voltage Δ and the dispersion of the terminal voltage is adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an assembled battery voltage adjusting device for adjusting the variation in terminal voltage of each unit cell in an assembled battery constituted by connecting a plurality of unit cells each composed of a secondary battery in series. And a voltage adjustment method for the battery pack.

[0002]

2. Description of the Related Art In recent years, a hybrid electric vehicle (hereinafter, referred to as a hybrid vehicle) combining a mechanism of an electric vehicle and a gasoline engine has been developed for the purpose of achieving both low pollution and high running performance.
HEV) has been developed. Although a high-voltage secondary battery is required as a battery for driving the HEV motor, a lithium battery is attracting attention as a substitute for a lead, nickel cadmium, nickel-metal hydride battery, or the like because of the need for small size and light weight. Lithium batteries have a weight energy density that is about three to four times higher than lead or nickel cadmium batteries of the same capacity, and are expected to be applied as suitable for HEVs that require small size and light weight. I have.

[0003] However, lithium batteries are susceptible to overcharge and overdischarge, and if not used within a specified voltage range, the material may decompose and the capacity may be significantly reduced, or the battery may become unusable due to abnormal heat generation. There is. Therefore, when using a lithium battery, the upper limit voltage and the lower limit voltage are clearly specified, and charge / discharge control is performed so that the terminal voltage is within the range, or a protection circuit that limits the voltage range is used as a set. It is common to use.

[0004] A battery used in an electric vehicle or an HEV requires a high voltage to drive a motor. Therefore, a battery is usually configured by connecting a plurality of unit cells in series. For example, in order to obtain a battery voltage of 300 V, about 150 batteries are used for a 2 V lead battery per unit cell, and 2 batteries are used for a 1.2 V nickel hydrogen battery per unit cell.
For a lithium battery of about 50 cells and 3.6 V per unit cell, it is necessary to connect about 80 cells in series.

In this case, a problem is a variation in terminal voltage between the unit cells based on a state of charge (hereinafter, referred to as SOC) of each unit cell. In the state of being connected in series, the current flowing through each unit cell is equal, but the remaining capacity of each unit cell always varies, so that the terminal voltage of each unit cell also differs. In such a state, even if the charge control is performed by monitoring the voltage between the terminals of the battery pack, it is merely controlling the average voltage of the unit cells constituting the battery pack, and the terminal voltage is higher than the average voltage. The cell becomes overcharged,
A unit cell having a terminal voltage lower than the average voltage tends to be over-discharged.

In a battery using a water-soluble electrolyte such as a lead battery, a nickel cadmium battery, or a nickel hydride battery, even if overdischarge or overcharge occurs, the performance of the battery is slightly deteriorated and the battery cannot be used. In addition, the use of electrolysis of water and substitution reaction (sealing reaction) in overcharging can eliminate voltage fluctuations per unit cell to some extent (equal charging), and voltage control per unit cell is costly. In general, control is performed with reference to only the voltage between both ends of the battery pack, since this leads to an increase in the battery voltage.

However, when a lithium battery is used as a multi-series battery pack, the unit cells may be overcharged or overdischarged because overcharging or overdischarging may render the battery unusable as described above. It is necessary to take countermeasures to prevent the state. Further, in the lithium battery, since the electrolyte is organic and not water-soluble, a sealing reaction does not occur, and the function of promoting uniform charging does not work. Therefore, the voltage variation among the unit cells gradually increases without being eliminated, and eventually becomes completely unusable.

[0008]

As a technique for solving the above-mentioned problem, for example, Japanese Unexamined Patent Publication No. 7-336905 discloses a technique in which a discharge circuit comprising a resistor and a switch is connected in parallel to each unit cell. When the terminal voltage of the battery pack varies, the charging current is divided during charging of the battery pack to adjust the voltage dispersion.

FIG. 7 shows a specific configuration example of this prior art. The assembled battery 1 includes a plurality (n) of unit cells 2
(1),..., 2 (n) are connected in series,
At both ends of each unit cell 2, a discharge circuit 3 and a voltage detector 4 are configured by connecting a discharge resistor 3a and a switch 3b composed of a transistor or an FET in series.
Are connected respectively. The output signal of the voltage detector 4 is supplied to the CPU 5 via the multiplexer 5 and the A / D converter 6.
7 given.

The CPU 7 refers to the terminal voltage of each unit cell 2 at regular time intervals and stores the same in the memory 8.
Among them, a control signal is output to the decoder 9 in order to discharge the one having a higher terminal voltage or to bypass the charging current. The control signal is decoded by the decoder 9 and output to the switch 3b of the discharge circuit 3 of the corresponding unit cell 2 via a photocoupler (not shown) or the like. Then, the switch 3b is closed and the resistor 3a
, The discharge of the unit cell 2 or the bypass of the charging current is performed.

In such a configuration, the discharge circuit 3, the voltage detector 4, the photocoupler, and the like are required for the number of the unit cells 2, and there is a problem that the total number of parts is increased. In addition, the number of unit cells 2 that can be controlled by one CPU 7 is limited to about 10 to 20 due to limitations on insulation (breakdown voltage) and controllability. Therefore, in order to apply to HEV, etc.,
The configuration is such that the control of each group is shared by the corresponding CPUs 7 by dividing them into groups of about 20 unit cells 2, and a higher-level CPU 7H for controlling the plurality of CPUs 7 is arranged. There is a need.

For example, when 80 lithium batteries are used as the battery pack 1, the configuration is 10 × 8 groups or 20 × 4 groups. As a result, five or nine CPUs 7, which are expensive parts, are required.
In order to perform communication between the PU 7 and the host CPU 7H, the communication interfaces 10 and 10H are also required, so that an increase in cost cannot be avoided.

The present invention has been made in view of the above circumstances, and an object of the present invention is to configure or implement an apparatus or a method for controlling variations in terminal voltages constituting an assembled battery at lower cost.

[0014]

According to the voltage adjusting device for an assembled battery according to the present invention, the charging / discharging control means is configured such that, when the upper limit voltage detecting means detects a unit cell exceeding the upper limit voltage, the assembled battery is controlled. The drive of the load is controlled so that the discharge from the battery is preferentially performed. When the charge / discharge control means determines that the variation in the terminal voltage of each unit cell constituting the cell group has expanded to a predetermined level or more, the charging / discharging control means charges the unit cell until the average unit cell voltage of the cell group exceeds the upper limit voltage by a predetermined voltage. By doing so, the variation of the terminal voltage is adjusted.

That is, when charging is performed until the average unit cell voltage exceeds the upper limit voltage for the cell group in which the variation in the terminal voltage is increased, the unit cell in which the terminal voltage exceeds the upper limit voltage in that state, By the operation of the discharging means, the battery is discharged until the voltage falls below the upper limit voltage. As a result, the terminal voltages of the unit cells constituting the cell group are all set near the upper limit voltage, and the variation in the terminal voltages is surely eliminated.

The voltage detecting means performs the voltage detection for each cell group including some of the unit cells, and the charging / discharging controlling means determines that the voltage variation has increased by the detection result by the upper limit voltage detecting means and the voltage. Since the determination is made based on the average unit cell voltage of the cell group obtained from the voltage detected by the detecting means, it is not necessary to detect the voltage for each unit cell, unlike the related art. Further, since the upper limit voltage detecting means can be configured using, for example, an inexpensive comparator or the like, it is possible to configure the entire apparatus on a small scale and at low cost.

According to the second aspect of the present invention, the detection signal of the upper limit voltage detection means is output to the charge / discharge control means as a logical sum signal for each unit cell for each cell group. The number of output signals to the discharge control means becomes one for one cell group, and the number of signal lines can be reduced.

According to the third aspect of the present invention, the upper limit voltage detecting means and the discharging means are always connected to each unit cell, and the upper limit voltage detecting means supplies the unit cell or the cell group whose voltage is to be detected. Alternatively, since the operation power is supplied from any of the assembled batteries, the power supply wiring can be shortened as much as possible. Further, since power supply from the outside is unnecessary, power supply wiring and power supply components for the power supply are unnecessary, so that the configuration can be simplified and the cost can be reduced.

According to the present invention, the charge / discharge control means gives priority to the discharge from the assembled battery when the lower limit voltage detecting means detects a unit cell lower than the lower limit voltage. And control the driving of the load to be performed. Then, even when the charge / discharge control means determines that the variation in the terminal voltage of each unit cell constituting the cell group has expanded to a predetermined level or more, the average unit cell voltage of the cell group increases the upper limit voltage by the predetermined voltage. By charging until the voltage exceeds the threshold, the variation in terminal voltage is adjusted.

That is, even if the state where the variation of the terminal voltage is increased is detected on the lower limit voltage side, charging is performed until the average unit cell voltage of the cell group exceeds the upper limit voltage as in the first embodiment. For example, the terminal voltage of each unit cell constituting the cell group is adjusted to be near the upper limit voltage by the same operation. Therefore, also in this case, variations in terminal voltage can be reliably eliminated.

According to the fifth aspect of the present invention, the detection signal of the lower limit voltage detector is output to the charge / discharge controller as a logical sum signal for each unit cell for each cell group. The output number of the detection signal on the voltage side is also 1
One cell group is provided, and the number of signal lines can be reduced.

According to the voltage adjusting device for a battery pack of the present invention, the lower limit voltage detecting means is always connected to each unit cell, and supplies power for operation from any of the unit cell, the cell group or the battery pack. Therefore, the power supply wiring can be shortened as much as possible.

According to the battery voltage adjusting device of the present invention, the charging / discharging control means adjusts the predetermined voltage when adjusting the variation of the terminal voltage, and the upper limit voltage detecting means adjusts the upper limit voltage during the charging process. The setting is made based on the voltage variation obtained from the average unit cell voltage at the time when the unit cell exceeding the unit cell is detected.

That is, after charging until the average unit cell voltage exceeds the upper limit voltage in the dispersion adjustment operation, the unit cells whose terminal voltages are higher than the upper limit voltage are discharged to eliminate the dispersion of the terminal voltages. . Therefore, the average unit cell voltage is set to exceed the upper limit voltage by a predetermined voltage in the first charge in consideration of a margin for discharging later.

If any of the unit cells reaches the upper limit voltage during the charging process in the adjustment operation, the degree of voltage variation can be accurately grasped from the difference between the upper limit voltage and the average unit cell voltage at that time. It is. Therefore, if the predetermined voltage is set based on the voltage variation obtained at the above time, charging can be performed so as to equalize the terminal voltage variation of each unit cell as much as possible. It is possible to do.

According to the voltage adjusting device for a battery pack, the charge / discharge control means performs the terminal voltage variation adjustment control when the driving of the load is stopped. That is, when the load is driven, charging and discharging with a large current is performed between the assembled battery and the load, and the voltage fluctuation of the unit cell is large. Therefore, if the charge / discharge control means performs the adjustment control of the variation when the driving of the load is stopped, the voltage variation does not occur, and the variation can be accurately adjusted. In addition, since the adjustment time can be extended, the current capacity of the discharging means can be set small, and the cost can be further reduced.

[0027] According to the voltage control apparatus for a battery pack according to the ninth aspect, the charge / discharge control means is configured such that when the driving of the load is started, the average unit cell voltage of the cell group falls between the upper limit voltage and the lower limit voltage. The adjustment control is performed so as to be in the vicinity of the control center voltage. In other words, as an initial state when the driving of the load is started, the average unit cell voltage of the cell group is at a level that is somewhat distant from the upper limit voltage and the lower limit voltage (for example, a level approximately intermediate between the two). This is advantageous because charge / discharge control can be easily performed. Therefore, by performing such control,
Charge / discharge control of the assembled battery can be more easily performed.

According to the voltage adjusting device for an assembled battery according to the present invention, the present invention is applied to an assembled battery having a high energy density but requiring a stricter countermeasure for overcharge and overdischarge as a unit cell. By doing so, the voltage variation of the lithium battery can be adjusted and safely controlled, and then the performance of the battery can be fully utilized and utilized.

According to the battery pack voltage adjusting device of the present invention, since the battery pack is used as a driving battery for an electric vehicle or a hybrid electric vehicle, many unit cells are connected in series to obtain a high voltage output. The use efficiency of the driving battery configured as described above can be sufficiently improved.

According to the battery pack voltage adjusting device of the twelfth aspect, the charge / discharge control means performs the terminal voltage variation adjustment control when the ignition switch of the vehicle is turned off. In addition, the driving of the driving motor of the automobile as a load is stopped, and it is possible to perform the adjustment with high accuracy by performing the adjustment control of the variation during a period in which charging and discharging with a large current is not performed with the assembled battery. ,
The current capacity of the discharging means can be set small.

In addition, since most vehicles have a longer stopped period than a running period, it is possible to sufficiently perform variation adjustment during the stopped period. Can be prevented.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an assembled battery used for a HEV drive battery will be described below with reference to FIGS. FIG. 2 shows the HEV
FIG. 2 is a functional block diagram schematically showing an electrical configuration for driving the traveling motor 21 of FIG. In this case, the battery pack 22
Of the plurality of unit cells 23 forming the unit cell 2
3 is one cell group 24, and a cell state monitoring circuit unit 25 is connected in parallel for each cell group 24. Note that the unit cell 23 is formed of a lithium secondary battery.

The cell state monitoring circuit unit 25 detects only that any one of the unit cells 23 in the corresponding cell group 24 has been overcharged or overdischarged, and outputs the detection signal to the battery pack control circuit unit. 26.
That is, the overcharge detection signal is output to the battery pack control circuit unit 26 via the signal line 27U, and the overdischarge detection signal is output to the battery pack control circuit unit 26 via the signal line 27L. A current sensor 28 is inserted in the negative side main power supply line L (−) of the battery pack 22, and the current detection signal is given to a battery pack control circuit unit (charge / discharge control unit) 26.

The assembled battery control circuit section 26 grasps the state of the assembled battery 22 from these detection signals, and controls the vehicle control circuit section 2.
9, a charge / discharge control command is output. Vehicle control circuit 29
Drives the traveling motor 21 using the battery pack 22 as a driving power source based on the charge / discharge control command and vehicle traveling information (vehicle speed, engine torque, accelerator opening, etc.) given by various sensors and the like. Inverter 30 for
The driving signal is output to the CPU. Battery pack 22
And the inverter 30 are connected to the positive and negative power lines L
(+) And L (-).

FIG. 1 shows a detailed electrical configuration centered on the cell state monitoring circuit section 25, which is a portion of the assembled battery 22 corresponding to the i-th cell group 24 (i). . Two sets of comparators 31 for each unit cell 23
U and 31L are arranged. The comparator 31U (upper limit voltage detecting means) compares the terminal voltage of the unit cell 23 divided by the resistors 32a and 32b with the reference voltage Vu (upper limit voltage,
For example, the terminal voltage is equivalent to 3.9 V). Since the unit cell 23 may be charged to exceed the upper limit voltage as described later, the upper limit voltage is set to the full charge voltage (SOC 100%) of the lithium secondary battery.
(For example, a voltage corresponding to 80% SOC).

The comparator 31L (lower limit voltage detecting means) compares the terminal voltage of the unit cell 23 divided by the resistors 33a and 33b with a reference voltage Vl (lower limit voltage, for example, 3.5V). Has become. In this case, the lower limit voltage is SOC 0% to 2 of the lithium secondary battery.
The voltage may be set to an appropriate voltage of about 0%. The comparators 31U and 31L are connected to the corresponding unit cells 23, respectively.
More power for operation is obtained.

The output signals of the comparators 31U and 31L are supplied to an OR gate 34 and a NAND gate (Negative logic input O).
R) 35, and the output signals of the OR gate 34 and the NAND gate 35
The upper limit voltage detection signal and the lower limit voltage detection signal are given to the battery pack control circuit section 26 via U and 27L. Inside the battery pack control circuit section 26, the signal lines 27U, 27
L is connected to the input side of the photocouplers 36U and 36L, and the output side of the photocouplers 36U and 36L is connected to the input port of the CPU 38 via the multiplexer 37.

That is, when the terminal voltage of any one or more unit cells 23 exceeds the upper limit voltage Vu and the corresponding comparator 31U goes high, the OR gate 34 turns the output terminal high and turns the photocoupler 36U on. An upper limit voltage detection signal is output via the switch. Also, N
The AND gate 35 is connected to any one or more of the unit cells 23.
When the terminal voltage falls below the lower limit voltage Vl and the corresponding comparator 31L goes low, the output terminal goes high, and a lower limit voltage detection signal is output via the photocoupler 36L.

Each unit cell 23 of the cell group 24
Are connected in parallel to a resistor 39 and an NPN transistor 40 having a collector connected to the resistor 39. The output signal of each comparator 31U is provided to the base of each transistor 40. A series circuit of the resistor 39 and the transistor 40 forms a bypass circuit (discharge means) 41,
When the output signal of the comparator 31U goes high, the transistor 40 is turned on, and the corresponding unit cell 23
Are discharged through the resistor 39.

In the battery pack control circuit 26, a voltage detector (voltage detecting means) 42 is provided at both terminals of the cell group 24.
The output signal of the voltage detector 42 is connected to the input port of the CPU 38 via the multiplexer 43.

The CPU 38 of the battery pack control circuit 26 uses the upper limit voltage detection signal and the lower limit voltage detection signal output from the cell state monitoring circuit 25 to determine the state of the unit cells 23 that make up each cell group 24 (all are normal. It is possible to recognize whether the terminal voltage is within the terminal voltage range, and whether any of the terminals has exceeded the upper limit voltage or has fallen below the lower limit voltage. The CPU 38 uses the RAM 44 as a work area, and stores data and the like necessary for processing.

Next, the operation of the present embodiment will be described with reference to FIGS. FIG. 5 is an example of a state in which the voltage of the unit cell 23 of one cell group 24 changes when the HEV runs, and shows changes in the highest cell voltage VCH, the lowest cell voltage VCL, and the average cell voltage VCM. HEV
When the vehicle travels, the battery pack 22 is discharged when the traveling motor 21 is driven to assist the driving force of the gasoline engine (not shown), and the voltage decreases. When the vehicle is traveling, the vehicle is charged when the regenerative power generated by the traveling motor 21 is received, and the voltage rises. Therefore, the average cell voltage VCM becomes
Charge / discharge is controlled so as to converge on the control center voltage Vm between the upper limit voltage Vu and the lower limit voltage Vl.

However, since each unit cell 23 has a variation in terminal voltage, the maximum cell voltage VCH and the minimum cell voltage VCL generally change in a state where the variation is offset from the average cell voltage VCM. In the present embodiment, the battery pack control circuit unit 26 can calculate the average cell voltage VCM from the terminal voltages of the cell group 24 detected by the voltage detector 42, but the highest cell voltage VCH and the lowest cell voltage VCL
Cannot be measured directly.

Therefore, the CPU 3 of the battery pack control circuit 26
8 controls charging and discharging so that the average cell voltage VCM falls within the following range, assuming that a predetermined voltage variation Vd has occurred in advance. Vl + Vd ≦ VCM ≦ Vu−Vd (1)

FIGS. 3 and 4 are flowcharts showing the contents of control by the CPU 38 of the battery pack control circuit 26. The CPU 38 actually performs the processing described below via the multiplexers 43 and 37 in each cell group 24.
This is performed for each cell group 24, but only one cell group 24 will be described below.

First, the CPU 38 reads the terminal voltage of the cell group 24 detected by the voltage detector 42 and detects the average cell voltage VCM by dividing the terminal voltage by the number of serially connected unit cells 23 "6". (Step S1). And
In subsequent steps S2 and S3, it is determined whether or not the average cell voltage VCM is within the range of the equation (1).

If the average cell voltage VCM falls below the level obtained by adding the voltage variation Vd to the lower limit voltage Vl, and the determination in step S2 is "NO" (see FIG. 5), the CPU 38
Outputs an output restriction command to the vehicle control circuit unit 29 (step S20). Then, since the vehicle control circuit unit 29 controls the driving of the traveling motor 21 so as to suppress the driving, the discharge of the assembled battery 22 is suppressed, the charging becomes dominant, and the average cell voltage VCM of the cell group 24 increases.

On the other hand, when the average cell voltage VCM exceeds the level obtained by subtracting the voltage variation Vd from the upper limit voltage Vu, the step S
If the determination is “NO” in 3 (see FIG. 5), C
PU 38 outputs a regeneration restriction command to vehicle control circuit unit 29 (step S21). Then, the vehicle control circuit unit 29
Means that the electric power generated by the traveling motor 21 is the battery pack 2
Since control is performed so as not to regenerate to the second side (for example, a short-circuit loop of regenerative power is formed in the inverter 30), charging of the assembled battery 22 is suppressed, and discharge becomes dominant, and the average cell voltage VCM of the cell group 24 decreases. I do.

If the average cell voltage VCM is within the range of the equation (1) (both "YES" in steps S2 and S3), C
The PU 38 determines whether a lower limit voltage detection signal or an upper limit voltage detection signal has been output from the cell state monitoring circuit unit 25 (Steps S4 and S5).

As described above, when a lithium secondary battery is used for the unit cell 23, when a voltage variation occurs, it tends to gradually expand without naturally canceling, and the maximum cell voltage VC
H, the difference between the minimum cell voltage VCL and the average cell voltage VCM gradually increases. Then, even if the average cell voltage VCM is within the range of the equation (1), as shown in FIG.
CL may be lower than the lower limit voltage Vl, or the highest cell voltage VCH may be higher than the upper limit voltage Vu as shown in FIG.

In the case shown in FIG. 5, since the cell state monitoring circuit section 25 outputs a lower limit voltage detection signal, the CPU 38
Determines "YES" in the step S4, shifts to the step S20, outputs an output restriction command to the vehicle control circuit unit 29, and performs the same adjustment as that shown in FIG. Also,
In the case shown in FIG. 5, since the cell state monitoring circuit unit 25 outputs an upper limit voltage detection signal, the CPU 38
5, “YES” is determined, the process proceeds to step S21, and a regeneration restriction command is output to the vehicle control circuit unit 29, and FIG.
The same adjustment is made as in the case shown in FIG.

When the HEV is operating, the charge / discharge current for the battery pack 22 fluctuates greatly. And
Since the unit cell 23 has an internal resistance, a voltage rise due to the internal resistance appears in a magnitude that cannot be ignored, and the terminal voltage may fluctuate greatly. Therefore, for example, the detection signal output is sampled a plurality of times so that the output determination of the lower limit and upper limit voltage detection signals is not immediately determined only by the temporary voltage change of the unit cell 23.
If the output of the detection signal is obtained with a predetermined probability, it is determined to be significant.

By adjusting as described above, the terminal voltage of each unit cell 23 is maintained between the lower limit voltage Vl and the upper limit voltage Vu, but as the voltage variation increases, the chargeable / dischargeable range becomes larger. It gradually narrows.

Then, the CPU 38 determines in step S20,
After the execution of S21, the average cell voltage VCM is detected again (Step S22), and it is determined whether or not the variation of the terminal voltage between the unit cells 23 has expanded to a predetermined level or more (Step S23). The determination here is made by the cell state monitoring circuit unit 2
5 is based on the output probability (output frequency within a certain observation time) when the lower limit or upper limit voltage detection signal is output and the average cell voltage VCM at that time.

That is, when the output probability of the lower limit or upper limit voltage detection signal exceeds a predetermined ratio, the minimum cell voltage becomes Vl
Or the highest cell voltage can be regarded as having reached Vu, so that the voltage variation can be grasped from the difference between the average cell voltage VCM and Vl or Vu at that time. Further, even though the average cell voltage VCM is within the range of Vl + Vd and Vu-Vd, the variation can be considered to have exceeded Vd since the output probability of the upper limit or lower limit voltage detection has exceeded a predetermined ratio. Therefore, in such a case, it is determined that the variation is enlarged.

In this case, it is preferable that the influence of the voltage fluctuation due to the internal resistance of the unit cell 23 is also eliminated as much as possible. Therefore, CPU3
8 monitors the charge / discharge current flowing through the battery pack 22 by the current sensor 28 and holds the internal resistance value that can be grasped in advance as data, thereby calculating and subtracting the voltage rise due to the internal resistance. Variation expansion is accurately determined only by pure electromotive force.

In step S23, the CPU 38
If it is determined that the voltage variation has increased to a predetermined level or more ("YES"), an adjustment flag is set in the flag storage area of the RAM 44 (step S24), and the process proceeds to step S7. In step S7, it is determined whether or not the ignition switch of the HEV is OFF. If it is determined that the HEV is not driving but driving ("NO"), the process returns to step S1.

In steps S4 and S5, the lower limit,
If none of the upper limit detection signals is output (both are “NO”), the CPU 38 outputs an output limit command,
If the regenerative control command has been output to the vehicle control circuit unit 29, the command is released (step S6), and then step S6
Move to 7.

That is, even if the CPU 38 determines in step S23 that the voltage variation has increased, if the HEV is in operation, the CPU 38 only sets the flag and does not immediately perform the adjustment operation. Then, the ignition switch of the HEV is turned off (step S7, "YES").
When the operation of the EV is stopped, the CPU 38
It is determined whether or not the adjustment flag is set by referring to the flag storage area (step S8). If the adjustment flag is not set ("NO"), the control waits until the ignition switch is turned on again (step S9,
"YES"), and returns to step S1.

Next, the control for adjusting the voltage variation will be described with reference to FIG. In FIG. 6A, at time t01
The minimum cell voltage VCL (unit cell 23 (C
If 4)) falls below the lower limit voltage Vl, it is assumed that the determination of the voltage variation expansion is made and the adjustment flag is set in step S8 ("YES"). Then, CPU3
8 shifts to step S10 to perform the voltage variation adjustment control. Note that, even when the ignition switch is turned off, in order to allow the battery pack monitoring circuit unit 26 to perform subsequent adjustment control, power is supplied to each unit for a certain period even when the ignition switch is turned off. The HEV is configured so that a timer or the like operates.

First, the CPU 38 controls the vehicle control circuit 29
, A regenerative electric power is generated by the traveling motor 21 to charge the battery pack 22 (step S1).
0). Here, reference is made to FIG. As shown in FIG. 6A, the highest cell voltage VCH is the unit cell 23 (C1),
The terminal voltage decreases in the order of 23 (C2), 23 (C3), and 23 (C4).

At time t1, when the charging in step S10 is started, the average cell voltage VCM of the cell group 24 increases. Then, when detecting the average cell voltage VCM (step S11), the CPU 38 proceeds to step S11.
a, and if the predetermined voltage Δ is determined (“YE
S)) The process proceeds to step S12, and if the predetermined voltage Δ is not determined (“NO”), the process proceeds to step S11b.

In steps S11b and S11c, a predetermined voltage Δ is set from the average cell voltage VCM at the time when the highest cell voltage VCH reaches the upper limit voltage Vu in the charging process. That is, at time t11 shown in FIG. 6, when the maximum cell voltage VCH reaches the upper limit voltage Vu, the voltage variation Vx at that time can be obtained from the difference between the upper limit voltage Vu and the average cell voltage VCM. Vx = Vu−VCM (2) Then, the predetermined voltage Δ is, for example, 1 / (1) of the voltage variation Vx.
Set to 2. Δ = Vx / 2 = (Vu−VCM) / 2 (3)

When the predetermined voltage Δ is set in step S11c as described above, the CPU 38 thereafter determines “YES” in step S11a, and proceeds to step S12, in which the average cell voltage VCM is set to the upper limit voltage Vl by a predetermined voltage. Until the voltage becomes equal to or higher than the voltage obtained by adding Δ (“YES”), step S10
Return to and continue charging.

At time t2 shown in FIG. 6, if "YES" is determined in the step S12, the CPU 38
Outputs a charge stop command to the vehicle control circuit unit 29 to stop charging the battery pack 22 (step S13).
Then, as in step S9, the process waits until the ignition switch of the HEV is turned on (step S1).
4).

As a result of the charging as described above, the inner terminal voltage of the unit cell 23 of the cell group 24 becomes higher than the upper limit voltage Vu.
23 (C1) to 23 (C3) are discharged by the corresponding bypass circuit 41 acting (FIG. 6 (c), time t11 to t23), the variation of the terminal voltage gradually converges. Accordingly, the average cell voltage VCM also decreases. Then, at time t23, all the unit cells 2
When the terminal voltage of the terminal No. 3 falls below the upper limit voltage Vu, the adjustment operation of the voltage variation ends.

After the variation adjustment operation is completed, at a time t3 shown in FIG. 6, the ignition switch is turned on and the operation of the HEV is started again (step S1).
4, "YES"), and the CPU 38 again detects the average cell voltage VCM at that time (step S15). And
It is determined whether or not the average cell voltage VCM is substantially equal to the control center voltage Vm (Step S16). That is, when the operation of the HEV is started, it is desirable that the average cell voltage VCM be close to the control center voltage Vm because the subsequent charge / discharge control becomes easier.

In step S16, the average cell voltage V
When the difference between CM and the control center voltage Vm is large (VCM >> V
m, “NO”), the CPU 38 outputs a discharge command to the vehicle control circuit unit 29 to drive the traveling motor 21 to drive the battery pack 2
2 is discharged (step S17), the process proceeds to step S15, and when the two are almost equal (step S1).
6, "YES") A discharge stop command is output to the vehicle control circuit 29 (step S18). When the adjustment flag is reset (step S19), the process returns to step S1.

In this embodiment, the determination of the variation in the terminal voltage is performed on the lower limit voltage side. However, when the determination of the variation on the upper limit voltage is performed, the adjustment control of the voltage variation is performed in exactly the same manner.

As described above, according to the present embodiment, the assembled battery 22 in which a plurality of unit cells 23 each composed of a lithium secondary battery are connected in series is used as a driving battery for driving the traveling motor 21 of the HEV. The CPU 38 of the battery pack monitoring circuit unit 26 applies the unit cell 2 whose comparators 31U and 31L of the cell state monitoring circuit unit 25 have exceeded the upper limit voltage Vu.
3 or drive of the traveling motor 21 via the vehicle control circuit 29 so that when the unit cell 23 which is lower than the lower limit voltage Vl is detected, the discharging or charging from the battery pack 22 is performed with priority. Is determined, and it is determined that the terminal voltage variation of each unit cell 23 constituting the cell group 24 has expanded to a predetermined level or more, the average unit cell voltage VCM
Is adjusted to exceed the upper limit voltage Vu by a predetermined voltage Δ to adjust the variation in terminal voltage.

Then, the unit cell 23 whose terminal voltage is higher than the upper limit voltage Vu is discharged by the bypass circuit 41 until the terminal voltage becomes lower than the upper limit voltage Vu.
The terminal voltages of the unit cells 23 constituting the cell group 24 are all adjusted so as to be near the upper limit voltage Vu. Therefore, it is possible to surely eliminate the variations in the terminal voltages.

Further, the voltage detector 42 performs voltage detection for each cell group 24, and the CPU 38 determines that the voltage variation has increased based on the detection results by the comparators 31U and 31L and the average unit cell voltage VCM of the cell group 24. Therefore, unlike the related art, each unit cell 23
It is not necessary to detect the voltage every time, and it is possible to prevent an increase in the size of the device.

Further, according to the present embodiment, the battery pack 22 is
Since the drive battery is used as an EV drive battery, the efficiency of use of the drive battery formed by connecting many unit cells 23 in series to obtain a high voltage output can be sufficiently improved. Further, since the present invention is applied to the battery pack 22 having a lithium cell having a high energy density but requiring more strict measures for overcharge and overdischarge as the unit cell 23, the voltage variation of the lithium battery can be adjusted to safely. Under control,
The performance of the battery can be fully utilized and utilized.

In addition, according to the present embodiment, the detection signals of the comparators 31U and 31L are output to the CPU 38 as a logical sum signal for each unit cell 23 for each cell group 24, so that the number of output signals to the CPU 38 is one. The number is two per cell group 24, and the number of signal lines can be reduced. Then, the comparators 31U and 31L and the bypass circuit 41 are always connected to each unit cell 23, and the comparator 31U and 31L are supplied with operating power from the unit cell 23. Further, since the cell state monitoring circuit unit 25 is composed of a comparator, a reference voltage source, a logic circuit element, a transistor, and the like, current consumption during operation is small, and sufficient operation power can be obtained from the cell group 24. is there. Therefore, the power supply line does not need to be extended from the outside for a long time, and the wiring can be simplified. In addition, except for the bypass circuit 41 having a relatively large current carrying capacity, I
Since the components are configured by components that can be converted to C, the configuration of the entire device can be reduced and the cost can be reduced by using an IC.

The CPU 38 sets the predetermined voltage Δ based on the voltage variation Vx obtained from the average unit cell voltage VCM at the time when the comparator 31U detects the unit cell 23 exceeding the upper limit voltage Vu in the charging process. Therefore, it is possible to accurately grasp the degree of voltage variation and perform charging so as to equalize the terminal voltage variation of the unit cell 23 as much as possible, and it is possible to more reliably adjust the voltage variation.

According to the present embodiment, the CPU 38
In Japanese Patent Application Laid-Open No. H11-207, the terminal voltage variation adjustment control is performed when the ignition switch of the HEV is turned off and the driving of the traveling motor 21 is stopped. That is, since most vehicles have a longer period of stoppage than a period of travel, variation adjustment can be sufficiently performed during the stop period, and the current capacity of the bypass circuit 41 can be set smaller. Cost can be further reduced. In addition, by performing the variation adjustment control during a period in which charging and discharging with a large current is not performed between the assembled battery 22 and the traveling motor 21, accurate adjustment can be performed without voltage fluctuation of the assembled battery 22. it can. Further, it is possible to prevent the variation adjustment control from affecting the traveling of the HEV.

Further, the CPU 38 controls the driving motor 2
When the driving of No. 1 is started, the adjustment control is performed so that the average unit cell voltage VCM of the cell group 24 becomes close to the control center voltage Vm between the upper limit voltage Vu and the lower limit voltage Vl. That is, the average cell voltage V of the cell group 24 is set as an initial state when the driving of the traveling motor 21 is started.
It is advantageous that the CM is at a level that is somewhat distant from the upper limit voltage Vu and the lower limit voltage Vl (for example, a level approximately intermediate between the two), since subsequent charge / discharge control is easier to perform. Therefore, by performing such control, the charge / discharge control of the battery pack 22 can be more easily performed.

The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications or extensions are possible. The number of unit cells connected in series per cell group is not limited to “6”, and may include all unit cells constituting the battery pack. However, when the unit cell 23 is a lithium battery having an average voltage of 3.6 V, it is considered that 4 to 6 series are appropriate in view of the problem of the withstand voltage of the element used in the cell state monitoring circuit unit 25 and the like. In the case where the cell information monitoring circuit unit 25 or the like is formed into an IC for the purpose of cost reduction or miniaturization, it is considered that the limit of six series is from the viewpoint of withstand voltage. In general, overdischarge is not a big problem compared to overcharge, so the configuration of the comparator 31L for overdischarge may be omitted by trade-off with cost. Even in this case, the variation adjustment control can be similarly performed, and overdischarge can be controlled to some extent only by the cell group voltage.

The logic levels of the upper limit detection signal and the lower limit detection signal may be, for example, a high level in a normal state and a low level at the time of detection. However, in the case of the high level, the operating current flows to slightly discharge the unit cell.
In the case of the lower limit detection in which the remaining capacity is small, it is preferable to set the logic level to low. The setting of the predetermined voltage Δ is not limited to the expression (3), and may be appropriately set within the range of the voltage variation Vx, or may be set to a voltage exceeding the voltage variation Vx. If it is determined “YES” in step S9, the process may proceed to step S15. At this time, if it is assumed that the average cell voltage VCM may be lower than the control center voltage Vm, step S1
It is sufficient to add a process of outputting a charge command after step 6.

The unit cell is not limited to a lithium battery, but may be a lead battery or a nickel battery as well. As described above, these secondary batteries are more resistant to overcharging and overdischarging, and thus require less strict voltage control than lithium batteries.However, by applying the present invention, the performance and life as an assembled battery are improved. We can expect to do. Further, the present invention may be applied to a cell module in which a plurality of unit cells connected in series are connected in parallel. It is not limited to electric vehicles and HEVs, but is also constructed by connecting a plurality of unit cells in series, such as small consumer devices such as notebook personal computers and portable VTRs, and secondary battery facilities for power storage. Any battery that uses a battery can be applied.

[Brief description of the drawings]

FIG. 1 shows an embodiment in which the present invention is applied to an assembled battery used as a driving battery of an HEV, and is a diagram showing a detailed electric configuration centering on a cell state monitoring circuit unit.

FIG. 2 is a functional block diagram schematically showing an electric configuration for driving a traveling motor of the HEV.

FIG. 3 is a flowchart showing control contents of a CPU of a battery pack control circuit unit (part 1).

FIG. 4 is a flowchart illustrating control performed by a CPU of a battery pack control circuit (part 2);

FIG. 5 is a diagram showing an example of a state in which a voltage of a unit cell in one cell group changes during traveling of an HEV.

FIG. 6 is a diagram showing a terminal voltage change of each unit cell in a case where terminal voltage variation adjustment control is performed on a cell group.

FIG. 7 is a diagram corresponding to FIG. 2 showing a conventional technique.

[Explanation of symbols]

21 is a traveling motor (load), 22 is an assembled battery, 23 is a unit cell, 24 is a cell group, 26 is an assembled battery control circuit (charge / discharge control means), 27U and 27L are signal lines, and 31U.
Denotes a comparator (upper limit voltage detecting means), 31L denotes a comparator (lower limit voltage detecting means), 38 denotes a CPU, 41 denotes a bypass circuit (discharging means), and 42 denotes a voltage detector (voltage detecting means).

Claims (17)

[Claims] 1. An upper limit voltage detecting means for detecting that a terminal voltage of each unit cell exceeds an upper limit voltage for an assembled battery formed by connecting a plurality of unit cells each formed of a secondary battery in series. A discharge unit configured to discharge the unit cell that has detected that the upper limit voltage has exceeded the upper limit voltage; and a voltage of a cell group including some of the unit cells constituting the battery pack is detected. Voltage detection means, comprising: a charge / discharge control means for controlling charge / discharge performed between the battery pack and the load, wherein the charge / discharge control means includes a unit cell in which the upper limit voltage detection means exceeds an upper limit voltage. If it is detected, the driving of the load is controlled so that the discharging from the battery pack is performed with priority, and the detection result of the upper limit voltage detecting means and the voltage detected by the voltage detecting means are controlled. Based on the average unit cell voltage of more the cell group obtained,
When it is determined that the variation in the terminal voltage of each unit cell constituting the cell group has expanded to a predetermined level or more, the charging is performed until the average unit cell voltage of the cell group exceeds the upper limit voltage by a predetermined voltage. A voltage adjustment device for a battery pack, wherein the voltage adjustment device performs control so as to adjust variation in terminal voltage. 2. The set according to claim 1, wherein the detection signal of said upper limit voltage detection means is output to said charge / discharge control means as a logical sum signal for each unit cell for each of said cell groups. Battery voltage regulator. 3. The upper limit voltage detecting means and the discharging means are always connected to each unit cell, and the upper limit voltage detecting means is supplied with operating power from any of the unit cells, the cell group or the assembled battery. 3. The voltage regulator for a battery pack according to claim 1, wherein the voltage is adjusted. 4. A charge / discharge control means for detecting that a terminal voltage of each unit cell has fallen below a lower limit voltage, wherein the charge / discharge control means comprises a unit cell having a lower limit voltage fall below the lower limit voltage. Is detected, the drive of the load is controlled so that the charging of the battery pack is performed with priority, and the voltage obtained by the detection result by the lower limit voltage detection means and the voltage detected by the voltage detection means is obtained. Based on the average unit cell voltage of the cell group, even when it is determined that the variation of the terminal voltage of each unit cell constituting the cell group has expanded to a predetermined level or more, the variation of the terminal voltage is adjusted. The voltage controller for a battery pack according to any one of claims 1 to 3, wherein the voltage controller controls the voltage. 5. The set according to claim 4, wherein the detection signal of said lower limit voltage detection means is output to said charge / discharge control means as a logical sum signal for each unit cell for each of said cell groups. Battery voltage regulator. 6. The apparatus according to claim 5, wherein said lower limit voltage detecting means is always connected to each unit cell, and is supplied with operating power from any one of the unit cell, the cell group and the battery pack. 7. The voltage adjusting device for an assembled battery according to 6. 7. The charge / discharge control means, when adjusting the variation of the terminal voltage, adjusts the predetermined voltage at the time when the upper limit voltage detecting means detects a unit cell exceeding the upper limit voltage in a charging process. 7. The voltage adjusting device for an assembled battery according to claim 1, wherein the voltage is set based on a voltage variation obtained from an average unit cell voltage. 8. The battery pack according to claim 1, wherein the charge / discharge control means performs the terminal voltage variation adjustment control when the driving of the load is stopped. Voltage regulator. 9. The charge / discharge control means, wherein when the driving of the load is started, an average unit cell voltage of the cell group is set close to a control center voltage between the upper limit voltage and the lower limit voltage. The voltage adjustment device for a battery pack according to claim 8, wherein the adjustment control is performed so as to be as follows. 10. The voltage adjusting device for an assembled battery according to claim 1, wherein the unit cell is a lithium battery. 11. The voltage adjusting device for an assembled battery according to claim 1, wherein the assembled battery is used as a driving battery of an electric vehicle or a hybrid electric vehicle. 12. The voltage adjustment device according to claim 11, wherein the charge / discharge control means performs the terminal voltage variation adjustment control when an ignition switch of the vehicle is turned off. 13. A battery pack comprising a plurality of unit cells each comprising a secondary battery connected in series, wherein the unit cell whose upper limit voltage detecting means detects that the terminal voltage has exceeded the upper limit voltage is discharged by the discharging means. Discharging, detecting the voltage of a cell group consisting of some of the unit cells constituting the assembled battery by voltage detecting means, and controlling the charge and discharge when the upper limit voltage detecting means detects the unit cell exceeding the upper limit voltage. The means controls the driving of the load connected to the battery pack so that the discharge from the battery pack is performed preferentially. Based on the calculated average unit cell voltage of the cell group, the variation of the terminal voltage of each unit cell constituting the cell group has expanded to a predetermined level or more. A voltage adjustment method for a battery pack, comprising: adjusting the variation of the terminal voltage by charging until the average unit cell voltage of the cell group exceeds the upper limit voltage by a predetermined voltage when the discharge control unit determines. . 14. The charge / discharge control, wherein the lower-limit voltage detector detects that the terminal voltage of each unit cell has fallen below the lower-limit voltage, and when the lower-limit voltage detector detects a unit cell having fallen below the lower-limit voltage, Means for controlling the driving of the load so that charging of the battery pack is performed with priority, and an average unit of the cell group obtained from a detection result by the lower limit voltage detection means and a voltage detected by the voltage detection means. Adjusting the variation of the terminal voltage even when the charging / discharging control means determines that the variation of the terminal voltage of each unit cell constituting the cell group has expanded to a predetermined level or more based on the cell voltage. 14. The method for adjusting the voltage of a battery pack according to claim 13, wherein: 15. The charge / discharge control unit, when adjusting the variation of the terminal voltage, adjusts the predetermined voltage at the time when the upper limit voltage detecting unit detects a unit cell exceeding the upper limit voltage in a charging process. The voltage adjustment method for a battery pack according to claim 13 or 14, wherein the setting is performed based on a voltage variation obtained from the average unit cell voltage. 16. The assembled battery according to claim 13, wherein said charge / discharge control means performs said terminal voltage variation adjustment control when said driving of said load is stopped. Voltage adjustment method. 17. The charge / discharge control means adjusts an average unit cell voltage to be near a control center voltage between the upper limit voltage and the lower limit voltage when driving of the load is started. The method according to claim 16, wherein the control is performed.