JP3132798B2 - Storage battery charge control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage battery for a mobile body mounted on a mobile body such as an electric vehicle, particularly in the form of an assembled battery composed of an assembly of sealed nickel-metal hydride storage batteries. It relates to a device to be controlled.

[0002]

2. Description of the Related Art A storage battery used for an electric vehicle or the like is an assembled battery formed by connecting a number of storage cells of a sealed nickel-metal hydride storage battery. This assembled battery is, for example, 240
The nickel-metal hydride storage cells are all connected in series to obtain a nominal output voltage of about 288V. When charging such an assembled battery, it is important to accurately detect that the assembled battery has reached a fully charged state (hereinafter referred to as fully charged) and stop the charging. If you continue charging after full charge, it will be overcharged,
Oxygen or hydrogen gas is generated in the nickel-hydrogen storage battery cell, and the internal pressure (hereinafter referred to as internal pressure) increases. As a result, gas may be released from a safety valve normally provided in a sealed nickel-metal hydride storage battery. If the released gas is ignited by any ignition source, there is a risk of an accident such as an explosion.

[0003] Conventional methods for detecting that the battery has reached a full charge include, for example, a method in which a terminal voltage (hereinafter, simply referred to as a voltage) at the time of charging the battery pack rises at the end of the charging process. There are those that detect based on a temperature change in the nickel-metal hydride storage battery cells, those that detect based on a temperature change rate that is a temporal change in the temperature in the nickel-metal hydride storage battery cells, and the like.

[0004] When the battery pack is mounted on an automobile, for example, the blast cooling is usually performed during charging or discharging of the mounted battery. Therefore, the temperature of the battery pack varies greatly depending on the environment in which the automobile is used. The temperature range is, for example, -20 ° C.
To + 70 ° C. The temperature of the nickel-metal hydride storage battery cell (hereinafter simply referred to as “temperature”) is −20 ° C. or higher + 4
In a range of 0 ° C. or lower (hereinafter referred to as a low temperature range), a state of charge of 90% to 95% before reaching full charge (“state of charge” is a ratio indicating how much of the nominal capacity of the storage battery has been charged). In the above case, it indicates that the electric energy of 90% to 95% of the nominal capacity of the nickel-metal hydride storage battery has been stored. When the battery is fully charged, the state of charge is 100%. The rate of change of temperature increases rapidly. Therefore, by detecting the rate of change of the voltage or the temperature and comparing it with a predetermined set value, it is possible to accurately detect that the battery is fully charged.

[0005]

Generally, the chargeable electric energy of a nickel-metal hydride storage battery decreases as the temperature increases. In particular, when the temperature exceeds 40 ° C. (hereinafter, referred to as a high temperature range), the temperature significantly decreases as the temperature increases.
For example, when the temperature is 45 ° C., the amount of power that can be charged is about 85% of that at normal temperature. The reason will be described below.

The maximum internal pressure of a standard nickel-metal hydride storage battery cell for an electric vehicle is 3 to 5 kgf / cm ² when a resin container such as a polypropylene resin is used. For example, in a battery cell having a maximum internal pressure of 3 kgf / cm ² , if the internal pressure exceeds 3 kgf / cm ² , a safety valve operates and gas inside leaks to the outside. Therefore, during normal charging, control is performed so that the internal pressure does not exceed ² kgf / cm ² for safety. When the nickel-hydrogen storage battery cell is charged at a high temperature, the equilibrium pressure of the hydrogen storage alloy, which is the active material of the negative electrode, increases, and the amount of hydrogen that can be stored decreases. Increase. As a result, the internal pressure of the nickel-metal hydride storage battery cell increases. Therefore, if the battery is charged to the state of charge of 100%, the internal pressure may exceed the above maximum internal pressure of 3 kgf / cm ² . Therefore, it is necessary to stop charging when the state of charge reaches 85 to 90% so that the internal pressure is maintained in a safe range of ² kgf / cm ² or less sufficiently lower than the maximum internal pressure.
That is, it is necessary to terminate charging before reaching full charging. In this case, it is impossible to use a conventional detection method that utilizes a temperature change rate that rapidly increases just before reaching full charge. Therefore, it has not been possible to accurately determine the timing at which charging should be stopped in a high temperature range, and to solve this problem.

[0007]

According to a first aspect of the present invention, there is provided a voltage detecting means for detecting a voltage between both terminals during charging of an assembled battery constituted by connecting a plurality of nickel-metal hydride storage battery cells. A temperature sensor provided in at least one of the nickel-metal hydride storage battery cells, for detecting the temperature thereof, current detecting means for detecting a charging current of the battery pack, based on detection outputs of the voltage detecting means and the current detecting means, A charging power supply control circuit for controlling charging power supplied to the assembled battery, the temperature of the nickel-metal hydride storage battery provided with the temperature sensor,
A temperature change rate calculating means for calculating a temperature change rate representing a temporal change in temperature based on a detection output of the temperature sensor during charging when the temperature is in a low temperature range equal to or lower than a preset temperature, and a predetermined temperature change rate; Comparing means for comparing a temperature change rate measured during charging obtained by the means for setting in advance and the temperature change rate calculating means with a temperature change rate according to the set setting; and A signal for controlling the charging power to the charging power supply control circuit when the temperature change rate by the temperature sensor is exceeded, and the temperature of the nickel-metal hydride storage battery provided with the temperature sensor is in a high temperature range exceeding a preset temperature. At one time, based on detection outputs of the current detection means and the temperature sensor during charging, a voltage set in advance for temperature and current is set. Set the limit value, and the voltage detected by said voltage detecting means and a control means for providing a control signal for controlling the charging power to the charging power supply control circuit when exceeding the set voltage limit.

According to the second aspect of the present invention, the charging power supply control circuit is configured to be capable of switching between constant power charging and constant current charging. When the charging voltage is equal to or lower than the voltage upper limit in the high temperature range, the power is set to constant power charging.In the low temperature range, the temperature change rate measured during the charging exceeds the temperature change rate according to the setting. It is characterized in that constant current charging is performed when the value exceeds the upper limit. The invention according to claim 3 is characterized in that the low temperature range is + 40 ° C. or lower and −20 ° C.
° C or higher, and the high temperature range is a temperature range from a temperature exceeding + 40 ° C to a temperature ranging from + 70 ° C or lower. The invention according to claim 4, wherein the upper voltage limit set for the temperature and the current is determined for a plurality of upper and lower limits of temperature and current, and when there is a battery temperature between the adjacent temperatures, The upper limit of the voltage is determined by linear interpolation based on the upper and lower temperatures and the upper and lower limits of the current.

[0009]

According to the first aspect of the present invention, in a low temperature range where the temperature is equal to or lower than a predetermined value, the charge switching point is detected by a rapid increase in the temperature change rate at the end of the charging process. In a high temperature range where the temperature exceeds the predetermined value, the charging voltage exceeds a predetermined voltage upper limit value with respect to the temperature and the current, so that the charging switching point is detected, and the next charging process, for example, the supplementation by the constant current is performed. Transition to charging. According to the invention of claim 2, by switching between constant power charging and constant current charging by the charging power supply control circuit, charging is efficiently performed with constant power in most of the charging process, and overcharging does not occur at the end of the charging process. As described above, charging is performed for a predetermined time with a constant current selected in advance to a value smaller than the charging current at the time of constant power charging. According to the third aspect of the present invention, the low temperature range is + 40 ° C.
Hereinafter, the temperature range is -20 ° C or higher, and the high temperature range is + 40 ° C.
By setting the temperature range higher than + 70 ° C., a charge control suitable for the temperature characteristics of the nickel-metal hydride storage battery is selected. According to the fourth aspect of the present invention, the upper limit value of the voltage corresponding to each of the upper limit value and the lower limit value of the plurality of temperatures and currents is used,
The voltage upper limit for an arbitrary temperature and current is determined by a linear interpolation method.

[0010]

FIG. 1 is a block circuit diagram of a charge control device for a nickel-metal hydride storage battery according to an embodiment of the present invention. In FIG. 1, a battery pack 1 is a storage battery mounted on a moving body such as an automobile, and is configured by connecting 240 nickel-metal hydride storage battery cells (hereinafter simply referred to as “battery storage cells”) in series. I have. The method of connecting a large number of battery cells in the assembled battery 1 is not limited to the above-described series connection, but may be a combination of parallel connection and series connection. Since the nominal voltage of one battery cell is about 1.2 volts, the nominal terminal voltage of the battery pack 1 is about 288 volts. The voltage between the terminals at both ends of the battery pack 1 is detected by a voltage sensor 2 which is a means for detecting a voltage of a voltage measuring device or the like.

The battery pack 1 is provided with a temperature sensor 3 for detecting a temperature T in the storage battery cell. It is desirable that the temperature sensor 3 is attached to, for example, a storage battery cell that emits the least heat among the battery packs 1 and thus has a high temperature. The detection output of the voltage sensor 2 is input to a charge control circuit 5 and is converted into a digital signal by an analog / digital converter (hereinafter abbreviated as ADC) 6. The digital signal of the ADC 6 is input to the CPU 11 and the processing described later is performed. The detection output of the temperature sensor 3 is ADC7.
Is input to The output of the ADC 7 is input to the CPU 11 via the measurement control circuit 10 and the temperature change rate calculation circuit 12. The charging power supply 20 is a DC power supply having a certain capacity, and its DC output is applied to the battery pack 1 via the charging power supply control circuit 14 of the charging control circuit 5. The output current of the DC power supply 20 (charging current, hereinafter simply referred to as “current”) is detected by the current sensor 4. The current value detected by the current sensor 4 is converted into a digital signal by
It is input to PU11.

Next, the operation of the charging control device according to the present embodiment will be described. Assuming that the temperature of the storage battery cell detected by the temperature sensor 3 (hereinafter simply referred to as “temperature”) is T, the temperature T is measured by the measurement control circuit 10 for six times, for example, every 10 seconds for one minute. Take a measurement, part 6
The average value of the measurement results of the batches is the average temperature T1, T for one minute.
2, T3... Are obtained every minute. The predetermined time for obtaining the average temperature can be set to an appropriate value between 30 seconds and about 10 minutes. The average temperatures T1, T2, T3,... Thus obtained are input to the temperature change rate calculation circuit 12. In the temperature change rate calculation circuit 12, a certain 1
The difference dT between the average temperature T1 for one minute and the average temperature T2 for the next one minute (T2-T1 = dT) is obtained, and the unit time d of the difference dT is obtained.
temperature change rate TV (TV = dT / d
t) is calculated and output to its output terminal. The temperature change rate TV data thus output is input to the CPU 11.

In the charging control device of the present invention, charging is controlled based on the detection values of the voltage sensor 2 and the temperature sensor 3, and one of two control modes is selected according to the detected temperature T. (Steps 101 and 102 in the flowchart of FIG. 3). The first control mode is selected when the temperature T is equal to or lower than 40 ° C. (hereinafter, referred to as a “low temperature range”). In this case, based on the temperature change rate TV,
Control charging. If the temperature T exceeds 40 ° C. (hereinafter, referred to as “high temperature range”), the second control mode is selected, and the charging voltage (the terminal voltage of the battery pack being charged; V ").

[First Control Mode] Charging control in a low-temperature region where the temperature T is 40 ° C. or lower. The operation of the first control mode represents the temporal change of the voltage V during charging and the temperature change rate TV shown in FIG. This will be described with reference to a graph and the flowchart of FIG. In FIG. 2, the horizontal axis represents time t, and the vertical axis represents voltage V and temperature change rate TV. At time t1 on the horizontal axis, the battery pack 1 has about 90% of its capacity.
%, And the voltage is V1 at this time. The temperature change rate is TV1. After time t1,
The voltage V and the temperature change rate TV rise rapidly, and the slopes of both curves become steep. The CPU 11 is configured to determine that the constant power charging has been completed when the temperature change rate TV exceeds the set value TV1, and then performs the constant current charging until time t2. When the current value becomes equal to or greater than the set value TV2 at time t2, the charging switch 14 is opened to stop charging, and the current is interrupted.
The voltage at this time is V2. When the charging switch 14 is opened, the terminal voltage drops to a value slightly lower than V1 in a short time. In the flowchart of FIG.
If it is determined that the temperature is in the low temperature range, constant power charging is performed in step 103. The temperature change rate TV obtained in step 104 is compared with a set value TV1 set in advance in step 105, and if it is equal to or larger than the set value, switching to constant current charging is performed in step 106. This constant current charging is stopped when the set time is reached (steps 107 and 108).

[Second Control Mode] Charge control in a high temperature range where the temperature T exceeds 40 ° C. Next, charge control in a high temperature range will be described. In a high temperature region where the temperature T of the storage battery cell exceeds 40 ° C., the charge control is performed based on the value of the voltage V. In the second control mode, until the charging voltage reaches the upper voltage limit, constant power charging is performed while controlling the current by the charging switch 14 so that the power (the product of the voltage and the current) supplied to the storage battery is constant. (Step 109 in FIG. 4). The voltage V rises due to the charging, but when the voltage V exceeds a voltage upper limit value E (hereinafter, simply referred to as a “voltage upper limit value”) of the charging voltage described in detail later, the current is kept constant from the constant power charging. Switching to constant current charging for charging (steps 113 and 11 in FIG. 4)
4). Normally, the current value at the time of constant-current charging is set to be a fraction to one-tenth of that at the time of constant-power charging. Constant current charging is CP
The charging is performed for a set time set in advance by U11. When the set time is exceeded, the constant current charging is stopped, and the charging is completed (steps 115, 116, and 117 in FIG. 4).

The constant power charging has an advantage that the charging time can be shortened since the current value at the initial stage of charging is larger than that of the constant power charging.

Next, the voltage upper limit value E will be described. While charging the storage battery, its internal pressure is always 2 kgf / cm ²
Control not to exceed. For this purpose, an experiment is performed in advance in a high-temperature region, and a voltage V when the internal pressure reaches 1 kgf / cm ² by constant current charging at the upper limit current value and the lower limit value, respectively, is obtained in advance. The voltage obtained by such an experiment is the voltage upper limit E shown in Table 1.

[0018]

[Table 1]

The test storage batteries used in the experiments shown in Table 1 were 24
The assembled battery was a series connection of zero nickel-hydrogen storage battery cells, and had an electric capacity of 100 Ah. In the constant power charging, charging is performed with, for example, 4.7 KW of power. The temperature T is a temperature detected by the temperature sensor 3 provided in a predetermined storage battery cell in the battery pack, and is + 40 ° C.
To + 70 ° C. The voltage upper limit value E indicates the upper limit of the voltage V for each of the above-mentioned temperatures T for each of the upper limit 15A of the charging current and the lower limit 10A. The numerical value of the voltage upper limit value E ranges from + 40 ° C. to +7 for the temperature T.
It is determined every 10 ° C. in the range up to 0 ° C., and is defined only for two current values, that is, when the current I is 10 A and 15 A. Therefore, the detected temperature and current are shown in Table 1.
In the case of an intermediate value other than the values described in (1), linear interpolation is performed to obtain the voltage upper limit value E corresponding to the intermediate value. Next, an example of the linear interpolation calculation will be described.

[Example of linear interpolation calculation] Temperature T is 40 ° C. and 50 ° C.
(40 + ΔT) ° C. between 0 ° C. (where 0 <ΔT <1
0), when the charging current I is between 10 A and 15 A (10 + Δ
I) In the case of A (where 0 <ΔI <5), first, the temperature (40+
ΔT) The voltage upper limit value at ° C is calculated by the following formulas (1) and (2).
Is calculated by the following calculation.

[0021]

(Equation 1)

[0022]

(Equation 2)

Next, with respect to the calculation results of the equations (1) and (2), the interpolation calculation of the equation (3) for the current (10 + ΔI) A is performed.

[0024]

(Equation 3) The calculation result of Expression (3) is a voltage upper limit value E obtained by interpolating an arbitrary temperature and current value between 40 ° C. and 50 ° C. The voltage upper limit value E at a temperature between 50 ° C. and 60 ° C. and between 60 ° C. and 70 ° C. can be obtained in the same manner. The above-described interpolation calculation of the voltage upper limit value E and the control operation based thereon are performed by the CPU 11 in steps 110 and 1 in FIG.
This is performed as shown at 11, 112 and 113.

[0025]

According to the first aspect of the present invention, the temperature is 40 ° C.
In the following low-temperature range, the temperature change rate rapidly increases at the end of the charging process, so that the switching point from constant power charging to constant current charging is determined from the temperature change rate. And the temperature is 4
In a high temperature range exceeding 0 ° C., the charging completion point is determined based on a predetermined voltage upper limit value for the temperature and the charging current. Therefore, it is possible to accurately determine the charging completion time point in all the temperature ranges in which the nickel-metal hydride battery is used. According to the second aspect of the present invention, since most of the charging process is performed with constant power, the charging time is shorter than in the case where only constant current charging is performed.

According to the third aspect of the present invention, the low temperature range is increased by +40.
By setting the high temperature range below + 40 ° C. and below + 40 ° C., charge control suitable for the temperature characteristics of the nickel-metal hydride storage battery can be performed. According to the invention of claim 4, by linearly interpolating between the discrete values of the current and the temperature, an accurate voltage upper limit value can be obtained even at an arbitrary current and temperature between the discrete values.

[Brief description of the drawings]

FIG. 1 is a block diagram of a nickel-hydrogen storage battery charge control device according to an embodiment of the present invention;

FIG. 2 is a graph showing temporal changes in voltage and temperature change rate during charging of a large nickel-metal hydride storage battery;

FIG. 3 is a flowchart showing the operation of charge control in a low-temperature region according to the embodiment;

FIG. 4 is a flowchart showing the operation of charge control in a high-temperature region according to the embodiment;

[Explanation of symbols]

 2 Voltage sensor 3 Temperature sensor

──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Noboru Ito 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (58) Surveyed fields (Int.Cl. ⁷ , DB name) H02J ^7/ 00-7/12 H02J ⁷ /34-7/36

Claims (4)

(57) [Claims] 1. A voltage detecting means for detecting a voltage between both terminals of a battery pack formed by connecting a plurality of nickel-metal hydride storage cells during charging, provided in at least one of the plurality of nickel-metal hydride storage cells. A temperature sensor for detecting the temperature of the battery; a current detecting means for detecting a charging current of the battery pack; and a charge for controlling charging power supplied to the battery pack based on detection outputs of the voltage detecting means and the current detecting means. A power supply control circuit, when the temperature of the nickel-metal hydride storage battery provided with the temperature sensor is in a low temperature range equal to or lower than a preset temperature, a temporal change in temperature based on a detection output of the temperature sensor during charging; Temperature change rate calculating means for obtaining a temperature change rate representing the following, means for presetting a predetermined temperature change rate, and charging obtained by the temperature change rate calculating means. Comparing means for comparing the temperature change rate by the measurement with the temperature change rate by the set setting, and charging power to the charging power supply control circuit when the temperature change rate during charging exceeds the temperature change rate by the setting. When the temperature of the nickel-metal hydride storage battery provided with the temperature sensor is in a high temperature range exceeding a preset temperature, the current detection unit and the temperature sensor detect during charging. Based on the output, with respect to temperature and current,
A control means for setting a preset voltage upper limit value and providing a control signal for controlling charging power to a charging power control circuit when the voltage detected by the voltage detecting means exceeds the set voltage upper limit value. Control device for a nickel-metal hydride storage battery. 2. The charging power supply control circuit is configured to be able to switch between constant power charging and constant current charging in accordance with a control signal of the control means. Constant rate charging when the charging voltage is equal to or less than the voltage upper limit in the high temperature range, the temperature change rate measured during the charging exceeds the temperature change rate set by the measurement in the low temperature range, and the charging voltage in the high temperature range. 2. The charge control device for a nickel-metal hydride storage battery according to claim 1, wherein constant current charging is performed when the voltage exceeds a voltage upper limit value. 3. The low temperature range is + 40 ° C. or lower and −20 ° C.
2. The charge control device for a nickel-metal hydride storage battery according to claim 1, wherein the temperature range is as described above, and the high temperature range is a temperature range from a temperature exceeding + 40 ° C. to a temperature not exceeding + 70 ° C. 3. 4. A voltage upper limit set for the temperature and current is defined for a plurality of upper and lower limits of temperature and current, and when the temperature of the storage battery is between the adjacent temperatures, the voltage 2. The charge control device for a nickel-metal hydride storage battery according to claim 1, wherein an upper limit value is determined by linear interpolation based on upper and lower temperatures and upper and lower limits of the current.