JP2000078756A - Rechargeable battery charge status management device - Google Patents

Abstract

(57) [Problem] To provide a secondary battery charge state management device capable of accurately detecting a charge state of a secondary battery that is repeatedly charged and discharged at random from its terminal voltage. SOLUTION: A detecting means for detecting an open-circuit voltage of a secondary battery, a table storing a relation between an open-circuit voltage of the secondary battery and a state of charge thereof, and a storage means for storing a maximum state of charge of the secondary battery are provided. The charge state detecting means detects an open circuit voltage after the discharge is stopped (step S8), and refers to a table based on the open circuit voltage to determine its charge state SOCx (step S9). When the state of charge SOCx is lower than the minimum state of charge SOCmin stored in the storage means (step S10), the state of charge SOCx is output as the current state of charge SOC (step S12). SOCmin is updated (step S11).

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. It is noted that the device has a predetermined hysteresis characteristic as shown in FIG. 1 and that the open-circuit voltage after the discharge is stopped is stable without depending on the discharge current as shown in FIG.

That is, according to the present invention, the secondary battery is charged from the initial state of charge SOC3 which is a predetermined discharge start condition to the state of charge SOC0.
Characteristics of discharge voltage (discharge curve)
A from the initial state of charge SOC3 to the state of charge SO
After discharging to the state of charge SOC1 before reaching C0, once
The secondary battery was charged to the state of charge SOC2, and then changed again (discharge curve) B when discharged to the state of charge SOC1, but was discharged further beyond the state of charge SOC1. Attention is paid to the fact that the change characteristic of the discharge voltage at the time coincides with the change characteristic A described above.

In particular, as shown in FIG. 2, the open-circuit voltage of the secondary battery after the discharge is stopped slightly decreases from the terminal voltage at the time when the discharge is stopped due to its impedance and the discharge current. However, as shown by a broken line in the figure, the voltage rises with different characteristics, but after a lapse of a certain time t, the voltage rises by a certain voltage from the terminal voltage at the time of stopping charging and settles down. Therefore, paying attention to this open-circuit voltage, as shown by the broken line in FIG. 1, attention is focused on that the charge state at that time is accurately indicated without the charge / discharge characteristic C depending on the discharge current.

Therefore, a charge management device for a secondary battery according to the present invention includes a detecting means for detecting the open voltage Vb of the secondary battery, particularly after the discharge is stopped, and a charge control device for the secondary battery. Between the open-circuit voltage Vb and its state of charge SOC
For example, based on a table storing a relationship consisting of characteristics as shown in FIG. 1, storage means for storing a minimum state of charge SOCmin of the secondary battery, and further based on an open-circuit voltage Vb after the discharge is stopped detected by the detection means. The state of charge SOCx of the secondary battery is determined by referring to the table, and when the state of charge SOCx determined from the table falls below the minimum state of charge SOCmin stored in the storage means, the state of charge SOCx is charged to the current state of charge. It is characterized in that a charge state detecting means for outputting as the state SOC and for updating the minimum charge state SOCmin stored in the storage means in the charge state SOC is provided.

That is, by referring to the table, the state of charge SOCx of the secondary battery is temporarily determined from the open-circuit voltage Vb after the discharge of the secondary battery is stopped, and this state of charge SOCx is stored in the storage means. Is determined to be below the minimum state of charge SOCmin. When the state of charge SOCx is lower than the minimum state of charge SOCmin, it is determined that the open circuit voltage Vb at the time of stopping the discharge has changed according to the characteristic C stored in the table, and the state of charge SOCx obtained from the table is changed to the current state of charge. State SO
C is output. At the same time, the storage means is updated by setting the state of charge SOC at this time as a new minimum state of charge SOCmin.

The open-circuit voltage Vb is detected as a battery voltage after a lapse of a predetermined time after the discharge of the secondary battery is stopped. Further, according to a preferred aspect of the present invention, as set forth in claim 3, an initial state detecting means for detecting that the secondary battery has reached an initial state SOC0 of discharge start and prohibiting charging of the secondary battery is provided. It is further characterized by being provided. Claim 4
And a discharge control unit for prohibiting discharge to the secondary battery in accordance with the minimum state of charge SOCmin stored in the storage unit.

That is, by prohibiting excessive charging and excessive discharging of the secondary battery, the discharge characteristics themselves are prevented from changing, and the accuracy of detecting the state of charge SOC by the terminal voltage Vb is guaranteed. ing.

[0012]

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. 3 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 has a voltage detector 1 for detecting its terminal voltage, in particular, an open-circuit voltage Vb after the discharge is stopped, and a current detector 2 for detecting its charge / discharge current Ib.
A temperature detector 3 for detecting the battery temperature Tb is provided. The charge state detection unit 4 basically detects the stop of the discharge to the secondary battery BAT from the charge / discharge current detected by the current detection unit 2, and sends the voltage detection unit 1 a predetermined time after the discharge stop. Based on the open-circuit voltage Vb of the secondary battery BAT detected in the above, the table 5 incorporated in the state-of-charge detecting section is referred to, and the minimum value storing section 6 is stored.
Has the role of detecting the state of charge SOC of the secondary battery BAT in accordance with the minimum state of charge SOCmin stored in the storage device.

By the way, the above-mentioned table 5 contains the secondary battery BA.
The relationship (change characteristic C) between the open circuit 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 characteristics unique to the secondary battery BAT. The terminal voltage Vb and the state of charge SOC when the secondary battery BAT is continuously discharged from the predetermined initial state of discharge SOC3 to the state of charge SOC0 at the lower limit thereof according to the characteristics stored in the table 5.
Is shown. Table 5 shows the terminal voltage Vb and the state of charge SOC when the battery is continuously charged from the lower limit state of charge SOC0 to the fully charged state (initial discharge state) SOC3.
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 first initializes a counter for measuring a predetermined time after the discharge is stopped to zero (0) [Step S3]. In this state, the charge / discharge current Ib obtained by the current detection unit 2 is input [Step S4], and it is determined whether the charge / discharge current Ib has become zero (0), that is, whether the discharge has stopped [ Step S
5]. When the charge / discharge current Ib is not zero (0), it is determined that the discharge to the secondary battery BAT is continued, and the process returns to the step S3 described above. Therefore, in this case, the counter is initialized to zero (0) again, and the detection of the charging / discharging current Ib is performed.

If it is detected that the charge / discharge current Ib has become zero (0), it is determined that the discharge has stopped [Step S5], and the counter is counted to measure the time after the discharge has stopped. Increment [Step S
6]. Then, it is determined whether or not the elapsed time after the discharge stop indicated by the value measured by the counter has reached a predetermined opening time [Step S7]. The increment of the counter and the determination thereof are repeatedly performed until the elapsed time after the stop of the discharge reaches the opening time. However, if the charging / discharging current Ib is detected again in step S4 when the elapsed time is measured by the counter, it is determined that the discharge has been restarted before a predetermined time has elapsed after the discharge is stopped.
The process is interrupted, and the process returns to the process from step S3 described above.

If a certain time has elapsed after the discharge of the secondary battery BAT is stopped (step S7),
Next, the open-circuit voltage Vb of the secondary battery BAT detected by the voltage detector 1 is input [Step S8]. Then, according to the input open-circuit voltage Vb, the state of charge SOC corresponding to the open-circuit voltage Vb is determined as a temporary state of charge SOCx by referring to the table 5 [Step S9].

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 S10). When it is determined by this determination that the state of charge SOCx has not reached the minimum state of charge SOCmin, the open voltage Vb at that time belongs to the change characteristic C shown in FIG. It is not clear whether the minimum value belongs or not.
Since the discharge voltage after charging from the minimum state of charge SOCmin stored in is not known, this is ignored.
Then, the process returns to the step S4, and a series of processes from the input process of the charging / discharging current Ib is repeatedly executed again.

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 open circuit voltage Vb is stored in the table 5 irrespective of the current state of discharge. It is determined that it has changed according to the charge / discharge characteristics C. That is, it is determined that the state of charge is lower than 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 SOCmin, and the minimum value storage unit 6 is stored in the state of charge SOCx.
To update. That is, the charge state SOCx is stored in the minimum value storage unit 6 as a new minimum charge state SOCmin [Step S11]. At the same time, the state of charge SOCx is output as the current state of charge SOC [Step S1]
2]. Thereafter, the process returns to the step 4, and a series of processes from the input process of the charging / discharging current Ib is repeatedly executed.

Thus, the charging state is determined from the open-circuit voltage Vb of the secondary battery BAT in accordance with the charging / discharging characteristics stored in the table 5 while referring to the minimum charging state SOCmin stored in the minimum value storage unit 6 as described above. According to this apparatus for calculating the SOC, even if the charging and discharging of the secondary battery BAT are repeated randomly, the state of charge SO of the secondary battery BAT is determined from the open voltage Vb at the time of discharging.
C can be accurately detected. Moreover, the charge / discharge current I
The state of charge SOC can be accurately grasped from the open-circuit voltage Vb after the discharge is stopped, without depending on b and regardless of the change in the charge / discharge characteristics due to the temporary discharge. In particular, since the state of charge SOC is obtained from the terminal voltage Vb after a lapse of a predetermined time after the discharge is stopped, the state of charge SOC can be easily and accurately obtained without being affected by the charging / discharging current Ib. Can have a great effect in practice.

By the way, the apparatus for managing the state of charge of a secondary battery according to the present invention can be configured to further include an initial state detector 7 as shown in FIG. 5, for example, in addition to the above-described configuration 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. The above-described initial discharge state SOC3 of the secondary battery BAT is detected based on each detection value. When the initial state SOC3 is detected, the minimum value storage unit 6 is reset, and the switch SW1 is opened to open the secondary battery BAT. It plays a role in prohibiting charging of the next battery BAT. Incidentally, the detection of the initial state SOC3 is based on the detection of the secondary battery BA.
In accordance with the terminal voltage Vb at the time of charging of T, the operation is performed by referring to Table 5 described above.

The provision of the initial state detector 7 functioning in this way prevents the rechargeable battery BAT from being overcharged and keeps the initial state of charge SOC3 at the initial state of the charge / discharge characteristics stored in the table 5 described above. 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 above-described open voltage Vb at the time of discharging.

Further, as shown in FIG. 6, the minimum state of charge SOCmin stored in the minimum value storage unit 6 is further compared with a predetermined judgment threshold value, and the minimum state of charge SOCmin reaches the lower limit state of charge SOC0. When the secondary battery BAT
It is also effective to provide a discharge control unit 8 that prohibits any further discharge from. In this case, the discharge control unit 8 may forcibly turn off the switch SW2.

The provision of such a discharge control section 8 prevents the secondary battery BAT from being over-discharged, so that the battery characteristics of the secondary battery BAT do not deteriorate. 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 and the discharge is prohibited, 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 open 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 charging of T, the initial state of charge may be detected, for example, from the integrated value of the charge / discharge current. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0027]

As described above, according to the present invention, according to the relationship between the open circuit voltage stored in the table and the state of charge (charge / discharge characteristics), the state of charge of the secondary battery is determined from the open circuit voltage after the discharge is stopped. When the state of charge is lower than the stored minimum state of charge, it is output as the current state of charge, and at the same time, the minimum state of charge is updated. Can be easily and accurately detected. In particular, the state of charge can be determined with high accuracy without depending on the charge / discharge current. 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, so that the battery is always stable. This has a great effect in practical use, such as being able to determine the state of charge of the secondary battery from the open voltage when the discharge is stopped.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship (change characteristic) between an open-circuit voltage and a charged state of a secondary battery as a basis of the present invention.

FIG. 2 is a diagram showing changes in terminal voltage during charging of a secondary battery and changes in open-circuit voltage after charging is stopped.

FIG. 3 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. 4 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. 5 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. 6 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 CB21 CB22 CB23 CB31 CB32 CB33 CC01 CC02 CC03 CC04 CC14 CC27 CC28 2G035 AA01 AB03 AC01 AC02 AC19 AD23 AD26 AD27 AD28 AD45 5G003 AA01 BA01 CA01 CA11 DA04 DA13 EA05 EA07 5H030 AA03 AA04 AA08 AS08 AS18 BB01 BB21 FF44 FF52

Claims (4)

[Claims] 1. A detecting means for detecting an open-circuit voltage after discharging of a secondary battery, a table storing a relationship between an open-circuit voltage of the secondary battery and its charge state, and a minimum charge state of the secondary battery. A storage unit for storing, and a charge state of the secondary battery is obtained by referring to the table based on the open-circuit voltage detected by the detection unit, and the charge state is a minimum charge state stored in the storage unit. A charging state detection unit that outputs the state of charge as a current state of charge when the state of charge falls below the current state of charge and updates a minimum state of charge stored in the storage unit in the state of charge. State management device. 2. The charging of the secondary battery according to claim 1, wherein the open-circuit voltage is obtained as a battery voltage of the secondary battery after a lapse of a predetermined time from when the discharge of the secondary battery is stopped. State management device. 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.