JP2000078757A - Charged state managing apparatus for secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a charged state managing apparatus for second battery in which the charged state of a second battery being charged/discharged repeatedly at ransom can be detected accurately from the terminal voltage thereof. SOLUTION: The charged state managing apparatus for second battery comprises means for detecting the terminal voltage of a second battery, a table storing relationship between the terminal voltage of the second battery and the charged state thereof, and means for storing the maximum charged state of the second battery. A charged state detecting means determines the charged state SOCx based on the terminal voltage at the time of discharge with reference to the table (steps S3, 4). If the charged state SOCx is lower than a minimum charged state SOCmin stored in the memory means (step S5), the charged state SOCx is outputted as a current charged state SOC (step S7) and the minimum charged state SOCmin is updated by the charged state SOC (step S6).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery charge state management device capable of accurately detecting the charge state of a secondary battery such as a nickel metal hydride battery and managing the charge state.

[0002]

2. Description of the Related Art Battery voltage of a secondary battery such as a nickel-metal hydride battery exhibits different characteristics between charging and discharging, and generally has a hysteresis characteristic. In particular, changes in the charge voltage and the discharge voltage change depending on the state of charge at the start of charging and at the start of discharging. Therefore, when charging and discharging of the secondary battery are repeated at random, it is difficult to grasp the state of charge using the battery voltage.

[0003]

Therefore, in the prior art, for example, the charge / discharge current of the secondary battery is always detected, and the detected current amount is successively integrated with the initial value of the charge amount in the secondary battery. The state of charge is grasped. However, when the charge amount of the secondary battery is obtained by current integration, there is a problem in that the integration error is accumulated, so that the state of charge cannot be accurately grasped. For this reason, it has also been difficult to perform management such as preventing overcharge of the secondary battery or preventing deep discharge.

The present invention has been made in view of such circumstances, and has as its object to reduce the state of charge of a secondary battery even when charging and discharging of the secondary battery are repeated at random. An object of the present invention is to provide a secondary battery charge state management device that can accurately detect the charge state and effectively manage the charge state.

[0005]

In order to achieve the above-mentioned object, a secondary battery charge state management apparatus according to the present invention uses a diagram to show the relationship between the battery voltage and the state of charge during charge / discharge of the secondary battery. Note that it has a predetermined hysteresis characteristic as shown in FIG. That is, according to the present invention, the change characteristic (discharge curve) A of the discharge voltage when the secondary battery is discharged from the predetermined initial state of charge SOC3 to the state of charge SOC0 and the state before the secondary state changes from the initial state of charge SOC3 to the state of charge SOC0 After the secondary battery is discharged to the charged state SOC1, the secondary battery is once charged to the charged state SOC2, and thereafter, the discharge voltage change characteristic (discharge curve) B when the secondary battery is discharged again to the charged state SOC1 is different. , The state of charge SOC1
It is noted that the change characteristic of the discharge voltage when the discharge is further exceeded exceeds the change characteristic A described above.

[0006] Therefore, the secondary battery charge management device according to the present invention is characterized in that the terminal voltage V
b, a table storing a relation between the terminal voltage Vb of the secondary battery and its state of charge SOC, for example, as shown in FIG. 1, and a minimum state of charge of the secondary battery SOCmin And a charge state S of the secondary battery with reference to the table based on the terminal voltage Vb at the time of discharge detected by the detection means.
OCx is obtained, and the state of charge SOCx obtained from the table is stored in the minimum state of charge SO stored in the storage means.
When the charge state is lower than Cmin, the charge state SOCx is output as the current charge state SOC, and the charge state detection means is configured to update the minimum charge state SOCmin stored in the storage means with the charge state SOC. .

That is, by referring to the table, the state of charge SOCx of the secondary battery is temporarily determined from the terminal voltage Vb at the time of discharge of the secondary battery.
It is determined whether or not Cx falls below the minimum state of charge SOCmin stored in the storage means. When the state of charge SOCx falls below the minimum state of charge SOCmin, it is determined that the terminal voltage Vb at the time of discharging has changed according to the characteristic A stored in the table, and the state of charge SOCx obtained from the table is changed to the current state of charge. It is characterized in that it is output as the state of charge SOC. At the same time, the storage means is updated by setting this state of charge SOC as a new minimum state of charge SOCmin.

Incidentally, the terminal voltage Vb is detected as a battery voltage when the secondary battery is discharged, as described in claim 2. Further, according to a preferred aspect of the present invention, as described in claim 3, an initial state detecting means for detecting that the secondary battery has reached an initial state of discharge start SOC3 and prohibiting charging of the secondary battery is provided. It is further characterized by being provided. According to a fourth aspect of the present invention, the apparatus further comprises discharge control means for inhibiting discharge to the secondary battery in accordance with the minimum state of charge SOCmin stored in the storage means.

That is, by prohibiting excessive charging and discharging of the secondary battery, the discharge characteristic itself is prevented from changing,
This guarantees the detection accuracy of the state of charge SOC based on the terminal voltage Vb at the time of discharging.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of an apparatus for managing the state of charge of a secondary battery according to an embodiment of the present invention. FIG. 2 is a diagram showing a schematic configuration of the charging state management device according to the first embodiment, in which BAT is a secondary battery such as a nickel-metal hydride battery, PS is a charging power source for the secondary battery BAT,
RL is the load of the secondary battery BAT. Secondary battery B
When the AT is used as a drive source of a hybrid car using both an internal combustion engine and an electric motor, the charging power source PS is driven by a generator driven by an internal combustion engine or the like, and the load RL is driven by a secondary battery. Electric motor
It is realized as. It is needless to say that the electric motor can be used as a generator by being driven by an internal combustion engine. Thus, the secondary battery BAT is selectively connected to the charging power source PS or the load RL via the switches SW1 and SW2, and its charging and discharging are respectively controlled.

The secondary battery BAT includes a voltage detector 1 for detecting its terminal voltage Vb, a current detector 2 for detecting its charging / discharging current Ib, and a temperature detector 3 for detecting a battery temperature Tb. Each is provided. The charge state detector 4 basically refers to the table 5 built in the charge state detector based on the terminal voltage Vb at the time of discharging the secondary battery BAT detected by the voltage detector 1. And the minimum state of charge S stored in the minimum value storage unit 6.
The state of charge SOC of the secondary battery BAT according to OCmin
Is responsible for detecting

By the way, the above-mentioned table 5 stores the secondary battery BA.
The relationship (change characteristic) between the terminal voltage Vb of T and the state of charge SOC thereof as shown in FIG. 1 is stored in advance in accordance with the battery characteristic unique to the secondary battery BAT. Based on the characteristics stored in Table 5, the terminal voltage Vb when the secondary battery BAT is discharged from the discharge initial state SOC3, which is a predetermined state of charge, to the lower limit, the state of charge SOC0.
And the state of charge SOC. Table 5
The terminal voltage Vb when the battery is continuously charged from the lower limit state of charge SOC0 to the full state of charge (discharge initial state) SOC3.
The relationship between and the state of charge SOC may be stored together. That is, the charge / discharge characteristics of the secondary battery BAT within the allowable maximum operation guarantee range may be stored in the table 5.

The charge state detector 4 is, for example, shown in FIG.
, The state of charge SOC of the secondary battery BAT is detected. That is, the charging state detecting unit 4 first sets the secondary battery BAT in a predetermined initial state,
Is initially set to the state of charge SOC3 at the beginning of the discharge indicated by the charge / discharge characteristics stored in [1] (step S1). Thereafter, in this initial state, the state of charge SOC3 at the beginning of the discharge start is initially set as the minimum state of charge SOCmin in the minimum value storage unit 6 [Step S].
2]. These processes are executed, for example, as pre-processes prior to the start of operation of the device.

Thereafter, the state-of-charge detecting section 4 inputs the terminal voltage Vb of the secondary battery BAT at the time of discharging detected by the voltage detecting section 1, for example, at a predetermined cycle [Step S3]. Then, according to the input terminal voltage Vb, the state of charge SOC corresponding to the terminal voltage Vb is determined as a temporary state of charge SOCx with reference to the table 5 [Step S4]. Next, referring to the minimum state of charge SOCmin stored in the minimum value storage unit 6, it is determined whether or not the state of charge SOCx is lower than the minimum state of charge SOCmin (step S5). When it is determined by this determination that the state of charge SOCx has not reached the minimum state of charge SOCmin, the terminal voltage Vb at that time belongs to the change characteristic A shown in FIG. Since it is unknown, it is rather unknown how much the discharge voltage after recharging from the minimum state-of-charge SOCmin stored in the minimum value storage unit 6 is ignored. Then, the process returns to step S3, and the terminal voltage Vb at the next detection timing is input.

On the other hand, if it is detected in step S5 that the state of charge SOCx falls below the minimum state of charge SOCmin, the discharge terminal voltage Vb is stored in the table 5 regardless of the state of charge up to that time. It is determined that it has changed according to the stored charge / discharge characteristics A. That is, it is determined that the discharge is proceeding below the minimum state of charge SOCmin. Therefore, in this case, it is assumed that the state of charge SOCx is the latest minimum state of charge, and the minimum value storage unit 6 is stored in the state of charge SOCx.
To update. That is, the state of charge SOCx is stored in the minimum value storage unit 6 as a new minimum state of charge SOCmin [Step S6]. At the same time, the state of charge SOCx is output as the current state of charge SOC [step S7]. Thereafter, the process returns to the step 3, and the same process is repeatedly executed for the discharge terminal voltage Vb input at the next timing.

Thus, according to the charging / discharging characteristic stored in the table 5, the discharge terminal voltage Vb of the rechargeable battery BAT is referred to by referring to the minimum state of charge SOCmin stored in the minimum value storage unit 6. State SOC
According to the present apparatus, the charging state SOC of the secondary battery BAT can be accurately detected from the terminal voltage Vb at the time of discharging even if the charging and discharging of the secondary battery BAT are repeated at random. Can be. In addition, regardless of the change in the charging / discharging characteristics due to the temporary discharge, a large practical effect can be achieved such that the state of charge SOC can be accurately grasped from the terminal voltage Vb at the time of discharging.

The device for managing the state of charge of a secondary battery according to the present invention may further comprise, for example, an initial state detector 7 as shown in FIG. 4 in addition to the structure shown in FIG. . That is, the initial state detection unit 7 inputs the terminal voltage Vb, the charge / discharge current Ib, and the battery temperature Tb detected by the voltage detection unit 1, the current detection unit 2, and the temperature detection unit 3, respectively. Based on each detected value, the above-described initial state SOC3 of the discharge start of the secondary battery BAT is described.
When the initial state SOC3 is detected, the minimum value storage unit 6 is reset, and the switch SW
1 and plays a role of prohibiting charging of the secondary battery BAT. Incidentally, the detection of the initial state SOC0 is performed by referring to the above-described Table 5 according to the terminal voltage Vb at the time of charging the secondary battery BAT.

The provision of the initial state detector 7 which functions as described above prevents overcharge of the secondary battery BAT and keeps the initial discharge state SOC3 in the initial state of the charge / discharge characteristics stored in the above-mentioned table 5. Therefore, the actual charge / discharge characteristics of the secondary battery BAT do not change from the charge / discharge characteristics stored in the table 5. Therefore, it is possible to always stably guarantee the detection accuracy of the state of charge SOC based on the terminal voltage Vb at the time of discharging described above.

Further, as shown in FIG. 5, the minimum state of charge SOCmin stored in the minimum value storage unit 6 is further compared with a predetermined judgment threshold value, and when the minimum state of charge SOCmin reaches its lower limit value, It is also effective to provide a discharge control unit 8 for prohibiting further discharge of the secondary battery BAT. In this case, the discharge control unit 8 may forcibly turn off the switch SW2.

If such a discharge control unit 8 is provided, the secondary battery BAT will not be over-discharged, and the battery characteristics of the secondary battery BAT will not be degraded. In particular, the minimum state of charge SOC0 of the charge / discharge characteristics stored in Table 5
Is set as the discharge prohibition determination threshold value, it is possible to prevent the actual charge / discharge characteristics of the secondary battery BAT from being changed from the charge / discharge characteristics stored in the table 5 due to further discharge. .

When the switch SW2 is turned off to set the discharge prohibition state, only the charging of the secondary battery BAT is permitted, for example. At the time of detection, the above-described discharge prohibition may be reset. Note that the present invention is not limited to the above embodiments.
For example, the state of charge SOC may be similarly obtained from the terminal voltage Vb during charging. However, in this case, for example, the charge is managed with the minimum charge state of the charge / discharge characteristics stored in Table 5 as an initial state.
The state of charge at that time may be obtained from the charge / discharge characteristics stored in the table 5 while storing the maximum state of charge SOCmax associated with charging. Also, the above-mentioned secondary battery BA
In controlling the T charge, the initial charge state may be detected from the integrated value of the charge / discharge current, for example. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0022]

As described above, according to the present invention, the state of charge is determined from the discharge terminal voltage of the secondary battery in accordance with the relationship between the terminal voltage stored in the table and its state of charge (charge / discharge characteristics). When the state of charge falls below the stored minimum state of charge, this is output as the current state of charge, and at the same time the minimum state of charge is updated. And it can detect correctly. In addition, since charging and discharging of the secondary battery are controlled in accordance with the detected state of charge, the charging and discharging characteristics of the secondary battery can be matched with the charging and discharging characteristics stored in the table, and therefore, are always stable. In addition, the present invention has a great effect in practical use, such as being able to determine the state of charge of the secondary battery from the terminal voltage at the time of discharging.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship (change characteristic) between a terminal voltage and a state of charge of a secondary battery as a basis of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a secondary battery charge state management device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a procedure of a processing operation in a charge state detection unit in the charge state management device according to the present invention.

FIG. 4 is a block diagram showing a schematic configuration of a secondary battery charge state management device according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a schematic configuration of a secondary battery charge state management device according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Voltage detection part 2 Current detection part 3 Temperature detection part 4 Charge state detection part 5 Table 6 Minimum value storage part 7 Initial state detection part 8 Discharge control part BAT Secondary battery PS Charging power supply RL load DRL dummy load

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Norihito Kurisu 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (72) Inventor Hirotaka Hayashida 72 Horikawa-cho, Sai-ku, Kawasaki-shi, Kanagawa Pref. (72) Inventor Yoshio Tobita 1-1-1 Shibaura, Minato-ku, Tokyo F-term (reference) 2G016 CA00 CA03 CB11 CB12 CB13 CB23 CB31 CB33 CC03 CC04 CC12 CC14 CC27 CC28 5G003 AA01 BA01 CA11 DA04 DA13 EA05 EA07 5H030 AA03 AA04 AS08 AS18 BB01 BB21 FF43 FF44

Claims (4)

[Claims] 1. A detecting means for detecting a terminal voltage of a secondary battery, a table storing a relation between a terminal voltage of the secondary battery and a state of charge thereof, and a storage storing a minimum state of charge of the secondary battery. Means, and obtains the state of charge of the secondary battery by referring to the table based on the terminal voltage detected by the detecting means, and when the state of charge is lower than the minimum state of charge stored in the storage means, And a charge state detecting means for outputting the charge state as a current charge state and updating a minimum charge state stored in the storage means in the charge state. . 2. The charge state management device for a secondary battery according to claim 1, wherein the terminal voltage is detected as a battery voltage when the secondary battery is discharged. 3. The charge state management device for a secondary battery according to claim 1, further comprising: detecting that the secondary battery has reached an initial state of discharge start, and prohibiting charging of the secondary battery. An apparatus for managing a state of charge of a secondary battery, comprising a state detecting means. 4. The apparatus for managing a state of charge of a secondary battery according to claim 1, further comprising discharge control means for inhibiting discharge to said secondary battery according to a minimum charge state stored in said storage means. A charge state management device for a secondary battery.