JP7437605B2 - Charging control device, power storage device, charging control method - Google Patents

Description

The present invention relates to a method of charging a power storage element.

CCCV charging is a method of charging a power storage element. CCCV charging is a method of charging with a constant current until the voltage of the electricity storage element reaches the CV voltage, and then charging the secondary battery with a constant voltage. Patent Document 1 below discloses that when switching from CC charging to CV charging, the charging current is reduced between CC charging and CV charging for the purpose of accurately matching the voltage of the storage element with the CV voltage. It is described that an area is provided in which charging is performed while the battery is being charged.

Patent No. 5525862

Electrode deposition may occur during charging of power storage elements such as lithium ion secondary batteries. Electrodeposition is a phenomenon in which metal ions such as lithium are deposited on a negative electrode, and is known to occur due to a decrease in negative electrode potential.

The present invention was completed based on the above circumstances, and an object of the present invention is to suppress the occurrence of electrodeposition.

The charge control device for a power storage element includes a calculation unit that calculates a current command value of a charging current of the power storage element so as not to exceed a current limit value defined by a current limit characteristic, and the current limit characteristic In a first region where the voltage of the element is equal to or lower than the first voltage, which is lower than the CV voltage during CV charging, the current limit value is constant, and the voltage of the storage element is in the first region from the first voltage to the CV voltage. In the second region, the higher the voltage, the lower the current limit value is, and when the temperature of the power storage element is a first temperature, the CV voltage is the first CV voltage, and the temperature of the power storage element is lower than the first temperature. At a second temperature, the CV voltage is a second CV voltage that is lower than the first CV voltage.

With the above configuration, it is possible to suppress the occurrence of electrodeposition.

A block diagram showing the electrical configuration of a battery and a charging device for Embodiment 1. Exploded perspective view of battery Top view of secondary battery Cross-sectional view taken along line AA in Figure 3A Current profile and voltage profile during CCCV charging Diagram showing current limit characteristics Diagram showing SOC-OCV correlation Diagram showing the first current limit characteristic Flowchart of current command value calculation process Diagram showing battery charging characteristics Diagram showing the second current limit characteristic Diagram showing the change pattern of CV voltage Flowchart of current command value calculation process Diagram showing the change pattern of CV voltage Diagram showing the change pattern of CV voltage Diagram showing the change pattern of CV voltage Top view of assembled battery Diagram showing the third current limiting characteristic L3

The charge control device for a power storage element includes a calculation unit that calculates a current command value of a charging current of the power storage element so as not to exceed a current limit value defined by a current limit characteristic, and the current limit characteristic In a first region where the voltage of the element is equal to or lower than the first voltage, which is lower than the CV voltage during CV charging, the current limit value is constant, and the voltage of the storage element is in the first region from the first voltage to the CV voltage. In the second region, the higher the voltage, the lower the current limit value is, and when the temperature of the power storage element is a first temperature, the CV voltage is the first CV voltage, and the temperature of the power storage element is lower than the first temperature. At a second temperature, the CV voltage is a second CV voltage that is lower than the first CV voltage.

In this configuration, since the current limit value decreases in the second region, the charging current decreases while the power storage element increases from the first voltage to the CV voltage during charging. Therefore, electrodeposition of the electricity storage element can be suppressed. In this configuration, since the CV voltage of the current limiting characteristic varies depending on the temperature, by using the current limiting characteristic according to the temperature of the storage element, electrodeposition can be suppressed even when the ease of occurrence of electrodeposition depends on temperature. You can. Since the CV voltage is suppressed to a lower voltage during charging at the second temperature compared to charging at the first temperature, it is possible to suppress the occurrence of electrodeposition during charging at the second temperature.

When the temperature of the electricity storage element is a third temperature higher than the first temperature, the CV voltage may be a third CV voltage higher than the first CV voltage. With this configuration, the CV voltage can be set to a higher value during charging at the third temperature than during charging at the first temperature. Therefore, at the third temperature, the chargeable range (current-carrying range) can be expanded and the capacity of the power storage device can be increased.

In the first region, the current limit value may be constant regardless of the temperature of the power storage element. With this configuration, the chargeable range (energized range) of the first region can be kept constant regardless of the temperature.

The calculation unit calculates the current command value in the second region to a value that lags behind the current limit value based on a current limit value defined by the current limit characteristic and a past current command value. You may. In this configuration, since the current command value in the second region is set to a value that lags behind the current limit value, changes in the current command value can be alleviated. Therefore, in the second region, vibrations in the current command value can be suppressed.

<Embodiment 1>
1. Description of Battery 50 and Charging Device 10 FIG. 1 is a block diagram showing the electrical configuration of battery 50 and charging device 10. As shown in FIG. The battery 50 includes a current interrupting device 53, a battery pack 60 including a plurality of battery cells 62, a current measuring resistor 54, a management device 100, and a temperature sensor 115. Battery cell 62 is an example of a power storage element. The battery cell 62 is, for example, a lithium ion secondary battery.

The current interrupting device 53, the current measuring resistor 54, and the assembled battery 60 are connected in series via power lines 55P and 55N. The power line 55P is a power line that connects the positive external terminal 51 and the positive electrode of the assembled battery 60. The power line 55N is a power line that connects the negative external terminal 52 and the negative electrode of the assembled battery 60. The current interrupting device 53 and the current measuring resistor 54 are located on the positive electrode side of the assembled battery 60, and are provided in the power line 55P on the positive electrode side.

The current interrupting device 53 can be configured by a contact switch (mechanical type) such as a relay, or a semiconductor switch such as an FET or a transistor. By opening the current interrupting device 53, the current of the battery 50 can be interrupted.

The current measuring resistor 54 generates a voltage according to the current I [A] of the assembled battery 60 . Discharging and charging can be determined from the polarity (positive or negative) of the voltage across the current measuring resistor 54. The temperature sensor 115 measures the temperature T [° C.] of the assembled battery 60 using a contact type or a non-contact type.

The management device 100 is provided in the circuit board unit 65. The management device 100 includes a voltage detection circuit 110, a processing section 120, and a power supply circuit 130. The voltage detection circuit 110 is connected to both ends of each battery cell 62 by a signal line, and measures the cell voltage V of each battery cell 62 and the total voltage of the assembled battery 60. The total voltage of the assembled battery 60 is the total voltage of the plurality of battery cells 62 connected in series.

The processing unit 120 includes a CPU 121 having an arithmetic function and a memory 123 that is a storage unit. The processing unit 120 monitors the current I of the assembled battery 60, the voltage V of each battery cell 62, the total voltage of the assembled battery 60, and the temperature T from the outputs of the current measuring resistor 54, the voltage detection circuit 110, and the temperature sensor 115. The processing unit 120 has a charging control function for the battery 50, and performs calculation processing to calculate a current command value Io of the charging current in a current reduction region H2, which will be described later. The processing unit 120 is an example of the "calculation unit" of the present invention, and the management device is an example of the "charging control device" of the present invention.

The memory 123 is a nonvolatile storage medium such as flash memory or EEPROM. The memory 123 stores a monitoring program for monitoring the state of the assembled battery 60 and data necessary for executing the monitoring program.

The memory 123 stores a calculation program for calculating the current command value Io of the charging current and data necessary for executing the calculation program (current limiting characteristics shown in FIG. 5, past current command values, etc.). The calculation program can be written on a recording medium such as a CD-ROM.

The charging device 10 includes a current detection resistor 11, a charging circuit 13, and a CPU 15, and is connected to external terminals 51 and 52 of the battery 50. The CPU 15 controls the magnitude of the charging current via the charging circuit 13. Current detection resistor 11 is provided to detect charging current.

The battery 50 includes a container 71, as shown in FIG. The container 71 includes a main body 73 and a lid 74 made of a synthetic resin material. The main body 73 has a cylindrical shape with a bottom. The main body 73 includes a bottom part 75 and four side parts 76. An upper opening 77 is formed at the upper end portion by the four side portions 76 .

The housing body 71 houses the assembled battery 60 and the circuit board unit 65. The assembled battery 60 has a plurality of battery cells 62. The battery cell 62 may be a lithium ion secondary battery cell. The circuit board unit 65 is arranged above the assembled battery 60.

The lid 74 closes the upper opening 77 of the main body 73. An outer peripheral wall 78 is provided around the lid body 74. The lid body 74 has a protrusion 79 that is approximately T-shaped in plan view. A positive external terminal 51 is fixed to one corner of the front portion of the lid 74, and a negative external terminal 52 is fixed to the other corner.

As shown in FIGS. 3A and 3B, the battery cell 62 has an electrode body 83 housed in a rectangular parallelepiped-shaped case 82 together with a non-aqueous electrolyte. The case 82 includes a case body 84 and a lid 85 that closes an upper opening of the case body 84.

Although not shown in detail, the electrode body 83 has a porous structure between a negative electrode element made of a base material made of copper foil coated with an active material and a positive electrode element made of a base material made of aluminum foil coated with an active material. A separator made of resin film is arranged. All of these are band-shaped, and are wound in a flat shape so that they can be accommodated in the case body 84, with the negative electrode element and the positive electrode element shifted to opposite sides in the width direction with respect to the separator. .

A positive electrode terminal 87 is connected to the positive electrode element via a positive electrode current collector 86, and a negative electrode terminal 89 is connected to the negative electrode element via a negative electrode current collector 88. The positive electrode current collector 86 and the negative electrode current collector 88 include a flat pedestal portion 90 and leg portions 91 extending from the pedestal portion 90. A through hole is formed in the pedestal portion 90. The leg portion 91 is connected to the positive electrode element or the negative electrode element. The positive electrode terminal 87 and the negative electrode terminal 89 consist of a terminal main body portion 92 and a shaft portion 93 that projects downward from the center portion of the lower surface thereof. Among them, the terminal main body portion 92 and the shaft portion 93 of the positive electrode terminal 87 are integrally molded from aluminum (a single material). In the negative electrode terminal 89, the terminal main body part 92 is made of aluminum, and the shaft part 93 is made of copper, and these are assembled together. The terminal main bodies 92 of the positive terminal 87 and the negative terminal 89 are arranged at both ends of the lid 85 with a gasket 94 made of an insulating material interposed therebetween, and are exposed to the outside from the gasket 94.

Lid 85 has a pressure release valve 95. The pressure release valve 95 is located between the positive terminal 87 and the negative terminal 89, as shown in FIG. 3A. The pressure release valve 95 opens to lower the internal pressure of the case 82 when the internal pressure of the case 82 exceeds a limit value.

2. Battery Charging Control (A) Current Limiting Characteristics and Suppression of Electrodeposition FIG. 4 shows the current profile I and voltage profile V of the battery cell 62 during CCCV charging. CCCV charging is a method in which the battery cell 62 is charged with a constant current until it reaches the CV voltage (CC charging), and then the battery cell 62 is charged with a constant voltage (CV charging) with the CV voltage.

In the final stage of the CC region (region immediately before transition to the CV region) F, the voltage is high and the charging current is large, so electrodeposition easily occurs in the battery cell 62. Electrodeposition is a phenomenon in which lithium metal is deposited on the negative electrode during charging, and is known to occur due to a decrease in negative electrode potential.

FIG. 5 shows a first current limit characteristic L1 showing the relationship between the maximum cell voltage and the current limit value. The first current limit characteristic L1 has three regions: a CC region H1, a current reduction region H2, and a CV region H3, and a current limit value is determined for each region H1 to H3. The maximum cell voltage is the maximum voltage of the plurality of battery cells 62 connected in series. The data of the first current limiting characteristic L1 shown in FIG. 5 is stored in the memory 123.

The CC region H1 is a region where the maximum cell voltage of the battery cell 62 is Vo to Vs. The CC area H1 is an area where the battery 50 is charged with constant current (CC charging). The current reduction region H2 is a region where the maximum cell voltage of the battery cell 62 is between Vs and Vc. The current reduction region H2 is a region in which the battery 50 is charged while reducing the charging current as the cell voltage increases. The CV region H3 is a region where the maximum cell voltage is equal to or higher than Vc. The CV region H3 is a region where charging is temporarily stopped when the maximum cell voltage becomes equal to or higher than the CV voltage.

Vo is the lowest voltage of the battery cell 62. Vs is a first voltage larger than Vo and smaller than Vc. Vc is a control target voltage (CV voltage) of the maximum cell voltage of the battery cell 62 during constant voltage charging (CV charging) by repeating the current limit region H2 and the CV region H3. The processing unit 120 determines where the battery 50 is located in the three regions H1 to H3 during charging by comparing the measured value (highest cell voltage) of the voltage detection circuit 110 with Vs and Vc. I can do it.

In the CC region H1, the current limit value is defined by a horizontal straight line M1. The current limit value is constant regardless of the maximum cell voltage, and its value is the maximum allowable current (rated current) Imax of the battery cell 62. The CC area H1 corresponds to the "first area" of the present invention.

When starting charging the battery 50, the processing unit 120 reads data on the current limit value Imax defined by the first current limit characteristic L1 of FIG. 5 from the memory 123 and sends it to the charging device 10. The charging device 10 determines a current command value Io of the charging current based on constraints on the output power of the charging device 10, etc. within a range that does not exceed the current limit value Imax transmitted from the processing unit 120, and controls the battery 50 on the CC. Charge.

In this example, the current command value Io in the CC region H1 is determined by the charging device 10, but it may be determined by the management device 100 and notified to the charging device 10.

When the maximum cell voltage of the battery cell 62 rises to the first voltage Vs due to charging in the CC region H1, the current reduction region H2 is entered.

In the current reduction region H2, the current limit value is defined by a downward-sloping straight line M2 connecting points A and B in FIG. The current limit value decreases linearly from the maximum allowable current Imax to 0 while the maximum cell voltage of the battery cell 62 changes from Vs to Vc. The current reduction region H2 corresponds to the "second region" of the present invention.

In the current reduction region H2, the processing unit 120 calculates the current command value Io of the charging current at the control cycle tn, with the current limit value determined by the straight line M2 as the upper limit. Then, the processing unit 120 transmits the calculated current command value Io to the charging device 10. Charging device 10 outputs a charging current based on current command value Io transmitted from processing unit 120, and charges battery 50.

By reducing the current limit value as the maximum cell voltage increases within the current reduction region H2, it is possible to prevent electrodeposition from occurring when the cell voltage of the battery cell 62 rises to around the CV voltage Vc due to charging. It can be suppressed.

When the maximum cell voltage of the battery cell 62 rises to the CV voltage Vc due to charging in the current reduction region H2, the state shifts to the CV region H3. The CV region H3 corresponds to the "third region" of the present invention.

As shown in FIG. 5, the current limit value in the CV region H3 is 0 [A]. Therefore, after the transition to the CV region H3, the processing unit 120 notifies the charging device 10 that the current command value is 0 [A]. The charging device 10 temporarily stops charging the battery 50 after shifting to the CV region H3. When charging stops, the voltage increase due to the internal resistance disappears, so the maximum cell voltage of the battery cell 62 decreases from the CV voltage Vc and returns to the current reduction region H2.

Returning to the current reduction region H2, as described above, the processing unit 120 calculates the current command value Io at the control period tn, with the current limit value determined by the straight line M2 as the upper limit. Then, the charging device 10 outputs a charging current to the battery 50 based on the current command value Io transmitted from the processing unit 120, and charges the battery 50. When the maximum cell voltage of the battery cell 62 reaches the CV voltage Vc, the current reduction region H2 shifts to the CV region H3.

In this way, by repeating charging in the current reduction region H2 and stopping charging in the CV region H3, the battery 50 can be charged at a constant voltage (CV charging) while maintaining the maximum cell voltage at the CV voltage Vc. . The higher the maximum cell voltage (the closer it is to the CV voltage Vc), the lower the current is used for charging, so it is possible to suppress the occurrence of electrodeposition during CV charging.

As the battery 50 approaches full charge, the charging current for the battery 50 gradually decreases. In this example, the charging termination determination condition is set to 0.2A, and when the charging current becomes 0.2A or less, charging is terminated. When the battery 50 approaches full charge, even if charging is stopped, the maximum cell voltage will hardly drop from the CV voltage Vc, and the charging stopped state will continue, so it is possible to ensure that the charging stopped state continues for a predetermined period of time. , may also be used as a charging termination condition.

(B) Suppression of vibration of current command value FIG. 6 is an OCV curve of the battery cell 62. The SOC (state of charge) is the ratio of the remaining capacity Cr to the actual capacity (available capacity) Ca of the battery cell 62, as shown in (1) below. OCV (open circuit voltage) is the open circuit voltage of the battery cell 62.

SOC=(Cr/Ca)×100 (1)

The OCV curve X1 has a plateau region where the amount of change in OCV with respect to the amount of change in SOC is almost flat. The plateau region is a region where the amount of change in OCV with respect to the amount of change in SOC is 2 [mV/%] or less. The plateau region is generally located in a range of SOC from 31% to 97%. A region where the SOC is 31% or less and a region where the SOC is 97% or more are high change regions where the amount of change in OCV relative to the amount of change in SOC is larger than the plateau region.

A broken line X2 in FIG. 6 is a charging curve showing the voltage change of the battery cell 62 when charging at a predetermined rate. The charging curve X2 is shifted upward from the OCV curve X1, and even though the SOC value is the same, the voltage value is higher. This voltage difference ΔV is a voltage increase due to the internal resistance of the battery cell 62, and depends on the magnitude of the charging current.

The voltage increase due to the internal resistance of the battery cell 62 becomes smaller as the charging current decreases. As shown in FIG. 7, in the current reduction region H2, when the maximum cell voltage of the battery cell 62 increases from V1 to V2, when the current command value Io of the charging current is lowered from I1 to I2, the voltage due to the internal resistance The rise becomes smaller. Therefore, the maximum cell voltage of the battery cell 62 decreases from V2 to V3. When the maximum cell voltage drops to V3, the current command value Io of the charging current is raised from I2 to I3.

In this way, when the current command value Io of the charging current I is lowered as the maximum cell voltage increases, the current command value Io may oscillate because the maximum cell voltage is repeatedly raised and lowered.

The processing unit 120 calculates the current command value Io_n within the current reduction region H2 at a predetermined control period n according to the following equation (2).

Io_n＝(1－m)×Io_n _-1 + m×I_limit・・・・・・(2)
Io_n _-1 is the previous value of the current command value. I_limit is a current limit value corresponding to the maximum cell voltage defined by the first current limit characteristic L1. m is a ratio that determines the magnitude of the delay of Io_n with respect to I_limit (m<1).

An example of calculating the current command value Io_n is shown. It is assumed that the previous value of the current command value is I1, the current value of the maximum cell voltage is V2, and the current limit value corresponding to the maximum cell voltage V2 defined by the first current limit characteristic L1 is I2. When the ratio m is 0.5, the current command value Io_n is (I1+I2)/0.5, which is an intermediate value between the previous value I1 of the current command value and the current limit value I2.

The calculation formula (2) calculates the current command value Io_n by weighting the previous value Io_n _-1 of the current command value and the current limit value I_limit according to the ratio m, and adding both values. ing. The obtained current command value Io_n has a delay with respect to the current limit value defined by the first current limit characteristic L1 in FIG. The delay is that the current command value does not change to the current limit value defined by the first current limit characteristic L1, and the current command value has a difference Δ with respect to the current limit value. The smaller the ratio m is, the larger the delay is, and the closer the ratio m is to 1, the smaller the delay is.

By providing such a delay, it is possible to alleviate a sudden change in the current command value Io_n, and it is possible to suppress vibrations in the current command value Io.

The oscillation of the current command value Io becomes more pronounced as the OCV curve becomes steeper. Therefore, it is preferable to vary the ratio m depending on the curve (inclination size) of the OCV curve. That is, when charging a secondary battery whose OCV curve is steep and has a large slope in the voltage band (Vs to Vc) of the current reduction region H2, it is preferable to reduce the ratio m. In the voltage band (Vs to Vc) of the current reduction region H2, when charging a secondary battery whose OCV curve is gentle and has a small slope, it is preferable to increase the ratio m (make it close to 1).

FIG. 8 is a flowchart of the current command value calculation process. The calculation process of the current command value Io is composed of seven steps S10 to S70, and is repeatedly executed at a predetermined control period tn in the current reduction region H2. The control period tn is, for example, 1 [sec].

In S10, the processing unit 120 calculates the cell voltage V of each battery cell 62, the total voltage of the battery pack 60, the charging current I, and the battery pack 60 from the outputs of the voltage detection circuit 110, current measuring resistor 54, and temperature sensor 115. Obtain measurement data of temperature T.

In S20, the processing unit 120 determines whether there is an abnormality in the measurement data. If there is an abnormality in the measurement data (S20: YES), error processing is performed. The error process is, for example, a process of notifying the charging device 10 of an abnormality and requesting the charging device 10 to stop charging.

If the measurement data is normal (S20: NO), the process moves to S40, and the processing unit 120 determines whether the control period tn has elapsed since the previous process.

If the control period tn has elapsed since the previous process (S40: YES), the process moves to S50, and the processing unit 120 performs a process of reading data of the first current limiting characteristic L1 shown in FIG. 5 from the memory 123.

After reading the first current limiting characteristic L1, the process moves to S60, and the processing unit 120 controls the current limit corresponding to the maximum cell voltage defined by the previous value Io_n _-1 of the current command value and the first current limiting characteristic L1. Based on the value I_limit, the current command value Io_n is calculated from the above equation (2).

Thereafter, the process moves to S70, and the processing unit 120 transmits the calculated current command value Io_n to the charging device 10.

The processes of S10 to S70 are repeated at each control period tn, and the current command value Io_n is transmitted from the management device 100 to the charging device 10 at each control period tn. Then, the charging device 10 controls the charging current in the current reduction region H2 based on the transmitted current command value Io_n.

FIG. 9 is a graph showing the charging characteristics of the battery 50, with the left vertical axis representing cell voltage, the right vertical axis representing current, and the horizontal axis representing time. Y1 represents the profile of the current command value after the delay according to equation (2), Y2 represents the profile of the charging current output by the charging device 10, and Y3 represents the profile of the maximum cell voltage.

3. Battery temperature and current limiting characteristics Electrode deposition may depend on battery temperature. For example, a lithium ion secondary battery has a characteristic that its internal resistance is higher at low temperatures than at high temperatures. Therefore, the deposition voltage and current are lower at low temperatures than at high temperatures. The electrodeposition voltage is the voltage at which electrodeposition occurs, and the electrodeposition current is the current at which electrodeposition occurs.

FIG. 10 shows the second current limit characteristic L2 showing the relationship between the maximum cell voltage and the current limit value. The second current limiting characteristic L2 is different from the first current limiting characteristic L1 shown in FIG. It has current limiting characteristics.

As shown in FIGS. 10 and 11, the CV voltage Vc is set in three patterns, and changes in three stages from Vc1 to Vc3 according to the three temperature zones T1 to T3. Vc1 is a CV voltage in the first temperature zone T1. Vc2 is the CV voltage in the second temperature zone T2. Vc3 is the CV voltage in the third temperature zone T3.

The two threshold temperatures Ta and Tb that divide the temperature zones T1 to T3 are, for example, Ta=0°C and Tb=10°C.

The magnitude relationship between the temperature and CV voltage in each temperature zone is T2<T1<T3, Vc2<Vc1<Vc3, and the CV voltage Vc1 in the middle temperature zone T1 is the reference voltage, and the CV voltage Vc2 in the low temperature zone T2 is the reference voltage. The CV voltage Vc3 in the high temperature zone T3 is lower than the voltage Vc1 and higher than the reference voltage Vc1. Vc1 corresponds to the "first CV voltage" of the present invention. Vc2 corresponds to the "second CV voltage" of the present invention, and Vc3 corresponds to the "third CV voltage".

Similar to the CV voltage Vc, the first voltage Vs is also set in three patterns, Vs1, Vs2, and Vs3, depending on the three temperature zones T1 to T3. Vs1 is the first voltage in the first temperature zone T1. Vs2 is the first voltage in the second temperature zone. Vs3 is the first voltage in the third temperature zone T3.

The magnitude relationship between the temperature and the first voltage in each temperature zone is T2<T1<T3, Vs2<Vs1<Vs3, and with the first voltage Vs1 in the middle temperature zone T1 as the reference voltage, the first voltage in the low temperature zone T2 Vs2 is lower than the reference voltage Vs1, and the first voltage Vs3 in the high temperature zone T3 is higher than the reference voltage Vs1.

Straight lines M21 to M23 indicate current limit values in the current reduction region H2. The straight line M21 is a right-sloping straight line connecting the points A1 and B1 in FIG. 10, and is the current limit value in the first temperature zone T1. Straight line M22 is a right-sloping straight line connecting point A2 and point B2 in FIG. 10, and is the current limit value in the second temperature zone T2. The straight line M23 is a right-sloping straight line connecting the points A3 and B3 in FIG. 10, and is the current limit value in the third temperature zone T3. Points A1 to A3 are points where the current limit value is Imax and voltages are Vs1 to Vs3, and points B1 to B3 are points where the current limit value is zero and voltages are Vc1 to Vc3.

In this way, in the second current limiting characteristic L2, the straight lines that determine the current limiting value of the current reduction region H2 are set in three patterns M21 to M23, depending on the three temperature zones T1 to T3.

The three straight lines M21 to M23 have the same slope and are moved in parallel in the horizontal axis direction, and the straight line M22 in the low temperature zone T2 is in the low voltage direction (left side in FIG. 10) with respect to the straight line M21 in the medium temperature zone T1. It is located in In other words, in the low temperature zone T2, compared to the medium temperature zone T1, the current reduction region H2 itself has moved toward a lower voltage, and the maximum cell voltage is limited to a lower voltage during charging in the current reduction region H2. You can. Therefore, the occurrence of electrodeposition can be suppressed in the low temperature zone T2.

The straight line M23 of the high temperature zone T3 is located in the high voltage direction (on the right side of FIG. 10) with respect to the straight line M21 of the medium temperature zone T1. In other words, in the high temperature zone T3, compared to the medium temperature zone T1, the current reduction region H2 itself moves in the high voltage direction, and the maximum cell voltage is maintained at a high voltage during charging in the current reduction region H2. You can. Therefore, in the high temperature zone T3, the chargeable range (current-carrying range) can be expanded.

In the second current limiting characteristic L2, the current limiting value of the CC region H1 is constant regardless of the temperature of the assembled battery 60, and is the maximum allowable current Imax. By doing so, the chargeable range (current-carrying range) of the CC region H1 can be kept constant regardless of the temperature. The data of the current limit characteristic shown in FIG. 10 is stored in the memory 123.

FIG. 12 is a flowchart of the current command value calculation process. The current command value calculation process in FIG. 12 differs from the calculation process in FIG. 8 in the process of S55.

In S10, the processing unit 120 calculates the cell voltage V of each battery cell 62, the total voltage of the battery pack 60, the charging current I, and the battery pack 60 from the outputs of the voltage detection circuit 110, current measuring resistor 54, and temperature sensor 115. Obtain measurement data of temperature T.

In S20, the processing unit 120 determines whether there is an abnormality in the measurement data. If the measurement data is normal (S20: NO), the process moves to S40, and the processing unit 120 determines whether the control period tn has elapsed since the previous process.

If the control period tn has elapsed since the previous process (S40: YES), the process moves to S55, and the processing unit 120 stores the data of the current limiting characteristic corresponding to the temperature T of the assembled battery 60 acquired in S10 in the memory 123. Performs the process of reading from. For example, when the temperature T is included in the first temperature zone T1, the data of the horizontal straight line M1 is read as the current limit value of the CC region H1, and the data of the horizontal straight line M1 is read as the current limit value of the current reduction region H2. Data on straight line M21 is read.

After reading the current limiting characteristics, the process moves to S60, and the processing unit 120 calculates the above equation (2) based on the previous current command value Io_n _-1 and the current limiting value I_limit defined by the current limiting characteristics. From this, the current command value Io_n is calculated.

Thereafter, the process moves to S70, and the processing unit 120 transmits the calculated current command value Io_n to the charging device 10.

Since the processes of S10 to S70 are repeated at the control period tn, when the temperature T of the assembled battery 60 changes, the current limiting characteristic L of the temperature range corresponding to the temperature T after the change is read out. Then, a current command value Io_n is calculated based on the read current limiting characteristic L.

In the second current limit characteristic L2, the straight line that determines the current limit value of the current reduction region H2 is set in three patterns M21 to M23 according to the three temperature zones T1 to T3. Compared to the temperature zone T1, the straight line M2 that defines the current limit value is set in the lower voltage direction.

Therefore, since the maximum cell voltage can be limited to a low voltage during charging in the current reduction region H2, it is possible to suppress the occurrence of electrodeposition during charging in the low temperature zone T2.

In the high temperature zone T3, since the straight line M2 that defines the current limit value is set in the high voltage direction compared to the medium temperature zone T1, the chargeable range (current-carrying region) of the battery 50 is expanded at high temperatures. , it is possible to increase the capacity of the battery 50.

4. Effects In this method, a current reduction region H2 is provided between the CC region H1 and the CV region H3, and as the battery cell 62 increases to the CV voltage Vc during charging, the charging current decreases. Therefore, electrodeposition in the battery cells 62 can be suppressed.

<Other embodiments>
The present invention is not limited to the embodiments described above and illustrated in the drawings; for example, the following embodiments are also included within the technical scope of the present invention.

(1) The battery 50 of Embodiments 1 and 2 can be widely applied regardless of the application, such as industrial use such as a power storage device of a solar power generation system, UPS (uninterruptible power supply), or vehicle use.

(2) In the first embodiment, the battery cell 62 is illustrated as an example of the power storage element. The storage element may be a capacitor. The battery cell is not limited to a lithium ion secondary battery cell, but may be other secondary battery cells such as a lead acid battery cell, a nickel metal hydride battery cell, or a lithium air battery cell. The power storage element is not limited to the case where a plurality of power storage elements are connected in series or in series and parallel, and may be configured as a single cell.

(3) In the first embodiment, an example was shown in which charging is controlled by the maximum cell voltage of the battery cells 62, but charging may be controlled by the total voltage of the assembled battery 60.

(4) Since lithium ion secondary battery cells are prone to electrodeposition at low temperatures, in Embodiment 1, the CV voltage Vc2 in temperature zone T2 (low temperature) is set to be lower than the CV voltage Vc1 in temperature zone T1 (medium temperature). was also lowered. In the case of a battery cell in which electrodeposition is likely to occur not only at low temperatures but also in some temperature ranges, the CV voltage may be lowered only in those temperature ranges.

(5) In the first embodiment, the CV voltage Vc3 in the temperature zone T3 (high temperature) is set higher than the CV voltage Vc1 in the temperature zone T1 (medium temperature). The CV voltage Vc3 in the temperature zone T3 (high temperature) may be the same as the CV voltage Vc1 in the temperature zone T1 (medium temperature).

(6) In the first embodiment, in the second current limiting characteristic L2, the CV voltage Vc is changed in three stages of Vc1 to Vc3 according to the temperature ranges T1 to T3. As shown in FIG. 13, hysteresis may be added to the voltage change by changing the threshold temperature T depending on whether the voltage changes in a higher direction or lower. By providing hysteresis, it is possible to suppress chattering (repetitive rise and fall) of the CV voltage Vc near the threshold temperature. Ta1 is the threshold temperature when changing from Vc1 to Vc2, and Ta2 is the threshold temperature when changing from Vc2 to Vc1. Tb1 is the threshold temperature when changing from Vc3 to Vc1, and Tb2 is the threshold temperature when changing from Vc1 to Vc3.

The CV voltage Vc is not limited to a stepwise change as shown in FIG. 11, but may be changed in an inclined manner as shown in FIG. The CV voltage Vc may be continuously changed in proportion to the temperature of the assembled battery 60, as shown in FIG.

(7) In the first embodiment, the current limit value in the current reduction region H2 is defined by one straight line M2 in the first current limit characteristic L1, but if the current limit value decreases as the voltage increases, It may be defined by a curve or multiple straight lines. The same applies to the second current limiting characteristic L2 and the third current limiting characteristic L3.

(8) In the first embodiment, the temperature of the assembled battery 60 was measured by the temperature sensor 115. The temperature at multiple locations on the assembled battery 60 may be measured. As shown in FIG. 16, even if the first temperature sensor 115A measures the temperature T of the battery cell 62A located at the end, and the second temperature sensor 115B measures the temperature T of the battery cell 62B located at the center. good. The battery cell 62A is easily affected by environmental temperature, and the battery cell 62B is easily affected by heat trapping. It may be determined whether the temperature of the assembled battery 60 is higher or lower than the threshold temperature Ta on the low temperature side based on the temperature of the battery cell 62A, which is easily influenced by the environmental temperature. It may be determined whether the temperature of the assembled battery 60 is higher or lower than the high-temperature side threshold temperature Tb based on the temperature of the battery cell 62B, which is susceptible to heat trapping.

(9) In the first embodiment, in the second current limiting characteristic L2, the first voltage Vs is set to different values depending on the three temperature zones T1 to T3. The number of temperature zones T may be other than three.

(10) In the first current limit characteristic L1, the current limit value in the current reduction region H2 is defined by a straight line M2 connecting point A corresponding to the maximum allowable current Imax and point B corresponding to 0 [A]. . The current limit value of the current reduction region H2 corresponds to a point A corresponding to the maximum allowable current Imax and a predetermined current value Ia larger than 0 [A], as shown in the third current limit characteristic L3 shown in FIG. It may be defined by a straight line M3 connecting point C and. In this case, during CV charging by repeating the current reduction region H2 and the CV region H3, the battery 50 is charged with a charging current equal to or higher than the predetermined current value Ia. The predetermined current value Ia is preferably a current value smaller than the current value (0.2 A in the first embodiment) applied to the charging end determination condition. If the predetermined current value Ia is made larger than the current value applied to the charging end determination condition, the charging current will be controlled to be higher than the current value applied to the determining condition, making it impossible to detect the charging end determining condition. By setting the predetermined current value Ia to be less than or equal to the current value applied to the charge end determination condition, the charge end determination condition can be detected.

(11) In the first embodiment, current limit values are set for three regions: the CC region H1, the current reduction region H2, and the CV region H3. When charging is stopped in the CV region H3, if the current command value Io is controlled to 0 [A] in the processing unit 120 in the CV region H3, there is no need to set it as the current limit value. As the current limiting characteristic, at least only the CC region H1 and the current reduction region H2 may be set.

(12) In the first embodiment, the battery 50 was CV-charged at the CV voltage Vc by repeating charging in the current reduction region H2 and stopping charging in the CV region H3. In addition to this, the battery 50 may be CV-charged while controlling the charging current to maintain the CV voltage Vc in the CV region H3. In this case, it is preferable to set the current limit value in the CV region H3 so that electrodeposition does not occur during CV charging in the CV region.

(13) In the first embodiment, the processing unit 120 of the battery 50 calculates the current command value Io. In addition to this, the charging device 10 may calculate the current command value Io. That is, the CPU 15 of the charging device 10 may be used as the charging control device. In this case, data on the current limiting characteristics is held in the internal memory of the charging device 10, and the processing unit 120 sends the charging device 10 a current command value Io such as data on the cell voltage of each battery cell 62 and the temperature T of the assembled battery. It is a good idea to send the data necessary for the calculation.

(14) In the first embodiment, the current command value is a value that lags behind the current limit value. A delay is not necessarily required and may be absent. In the first embodiment described above, when calculating (2), the previous value of the current command value is used as an example of the past current command value, but it is also possible to use a value other than the previous value, such as the value two days before good. As the past current command value, both the previous value and the value before the previous time may be used.

(15) The present technology can be applied to a charging control program for a power storage device. The charging control program for the power storage device is a program that causes a computer to execute calculation processing for calculating a current command value of the charging current of the power storage element so as not to exceed a current limit value defined by the current limit characteristic. The current limiting characteristic is such that the current limit value is constant in a first region below a first voltage, where the voltage of the electricity storage element is lower than the CV voltage during CV charging, and the voltage of the electricity storage element is lower than the first voltage. In the second region from the voltage to the CV voltage, the higher the voltage, the lower the current limit value. When the temperature of the electricity storage element is a first temperature, the CV voltage is a first CV voltage, and when the temperature of the electricity storage element is a second temperature lower than the first temperature, the CV voltage is lower than the first CV voltage. The second CV voltage is also lower. The present technology can be applied to a recording medium that records a charging control program for a power storage device. The computer is the processing unit 120, for example.

10 Charging device 50 Battery (power storage device)
60 Assembled battery 62 Lithium ion secondary battery (power storage element)
100 Management device (charging control device)
120 Processing unit (calculation unit)
H1 CC area (first area)
H2 Current reduction region (second region)
H3 CV area (third area)
L1 First current limiting characteristic L2 Second current limiting characteristic L3 Third current limiting characteristic

Claims (7)

A charging control device for a power storage element,
comprising a calculation unit that calculates a current command value of the charging current of the electricity storage element so as not to exceed a current limit value defined by the current limit characteristic;
The current limiting characteristic is
In a first region where the voltage of the electricity storage element is lower than the first voltage, which is lower than the CV voltage during CV charging, the current limit value is constant;
In a second region where the voltage of the electricity storage element is from the first voltage to the CV voltage, the higher the voltage, the lower the current limit value,
When the temperature of the electricity storage element is a first temperature, the CV voltage is a first CV voltage,
When the temperature of the electricity storage element is a second temperature lower than the first temperature, the CV voltage is a second CV voltage lower than the first CV voltage,
The first voltage when the CV voltage is the second CV voltage is lower than the first voltage when the CV voltage is the first CV voltage . The charging control device according to claim 1,
When the temperature of the electricity storage element is a third temperature higher than the first temperature,
The CV voltage is a third CV voltage higher than the first CV voltage ,
The first voltage when the CV voltage is the third CV voltage is higher than the first voltage when the CV voltage is the first CV voltage . The charging control device according to claim 1 or 2,
In the first region, the current limit value is constant regardless of the temperature of the power storage element. The charging control device according to any one of claims 1 to 3,
The calculation unit calculates the current command value in the second region to a value that lags behind the current limit value based on a current limit value defined by the current limit characteristic and a past current command value. charging control device. A power storage element,
A power storage device comprising the charging control device according to any one of claims 1 to 4. A charging control method for a power storage element, the method comprising:
a calculation step of calculating a current command value of a charging current of the electricity storage element so as not to exceed a current limit value defined by a current limit characteristic;
The current limiting characteristic is
In a first region where the voltage of the electricity storage element is lower than the first voltage, which is lower than the CV voltage during CV charging, the current limit value is constant;
In a second region where the voltage of the electricity storage element is from the first voltage to the CV voltage, the higher the voltage, the lower the current limit value,
When the temperature of the electricity storage element is a first temperature, the CV voltage is the first CV voltage, and when the temperature of the electricity storage element is a second temperature lower than the first temperature, the CV voltage is the first CV voltage. a second CV voltage lower than
The first voltage when the CV voltage is the second CV voltage is lower than the first voltage when the CV voltage is the first CV voltage . The charging control method according to claim 6,
When the temperature of the electricity storage element is a third temperature higher than the first temperature,
The CV voltage is a third CV voltage higher than the first CV voltage,
The first voltage when the CV voltage is the third CV voltage is higher than the first voltage when the CV voltage is the first CV voltage .

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