JP7502007B2 - Charge control device and charge control method - Google Patents

Description

The present invention relates to a method for charging a storage element.

CCCV charging is a method for charging a storage element. CCCV charging is a method in which the storage element is charged with a constant current until its voltage reaches the CV voltage, and then the secondary battery is charged with a constant voltage. The following Patent Document 1 describes the provision of a region between CC charging and CV charging in which charging is performed while the charging current is reduced, in order to accurately match the voltage of the storage element to the CV voltage when switching from CC charging to CV charging.

Patent No. 5525862

In energy storage devices such as lithium-ion secondary batteries, electrodeposition may occur during charging. Electrodeposition is a phenomenon in which metal ions such as lithium are deposited on the negative electrode, and is known to occur due to a decrease in the negative electrode potential.

The present invention was developed based on the above circumstances, and aims to suppress the occurrence of electrolytic deposition while suppressing the vibration of the current command value.

The charging control device for the storage element includes a calculation unit that calculates a current command value for the charging current of the storage element so as not to exceed a current limit value defined by a current limit characteristic. The current limit characteristic is such that in a first region where the voltage of the storage element is equal to or lower than a first voltage, which is lower than the CV voltage during CV charging, the current limit value is constant, and in a second region where the voltage of the storage element is from the first voltage to the CV voltage, the current limit value decreases as the voltage increases. The current limit characteristic is such that a plurality of current limit values in the first region and a plurality of current limit values in the second region are set according to the temperature of the storage element, and the slope at which the current limit value decreases in response to an increase in voltage in the second region differs for the plurality of current limit characteristics. The calculation unit calculates the current command value for the second region to a value that has a delay with respect to the current limit value based on the current limit value defined by the current limit characteristic and past current command values.

It is possible to suppress the occurrence of electrolytic deposition while suppressing the vibration of the current command value.

FIG. 1 is a block diagram showing the electrical configuration of a battery and a charging device according to a first embodiment. Plan view of secondary battery 2A is a cross-sectional view taken along line AA of FIG. Current and voltage waveforms during CCCV charging Current limiting characteristics A diagram showing the correlation between SOC and OCV Current limiting characteristics Flowchart of current command value calculation process Battery charging characteristics FIG. 11 is a diagram showing current limiting characteristics for the second embodiment. Flowchart of current command value calculation process FIG. 13 is a diagram showing current limiting characteristics of another embodiment. Block diagram of a solar power generation system Current limit values for other charging modes Current limit values for other charging modes Current limit values for other charging modes Current limit values for other charging modes Flowchart of charging control process

The charging control device for the storage element includes a calculation unit that calculates a current command value for the charging current of the storage element so as not to exceed a current limit value defined by a current limit characteristic. The current limit characteristic is such that in a first region where the voltage of the storage element is equal to or lower than a first voltage, which is lower than the CV voltage during CV charging, the current limit value is constant, and in a second region where the voltage of the storage element is from the first voltage to the CV voltage, the current limit value decreases as the voltage increases. The current limit characteristic is such that a plurality of current limit values in the first region and a plurality of current limit values in the second region are set according to the temperature of the storage element, and the slope at which the current limit value decreases in response to an increase in voltage in the second region differs for the plurality of current limit characteristics. The calculation unit calculates the current command value for the second region to a value that has a delay with respect to the current limit value based on the current limit value defined by the current limit characteristic and past current command values.

In this method, since the current limit value is decreased in the second region, the charging current is decreased while the storage element rises from the first voltage to the CV voltage during charging. Therefore, it is possible to suppress electrodeposition of the storage element. In this method, since the current command value in the second region is a value that is delayed with respect to the current limit value, it is possible to mitigate the change in the current command value. Therefore, it is possible to suppress the vibration of the current command value in the second region. In addition, by suppressing the vibration of the current command value, it is possible to suppress the occurrence of current noise during charging. By suppressing the current noise, it is possible to suppress the occurrence of electrodeposition. Furthermore, since the peak of the charging current can be suppressed, it is possible to suppress the load on the charging device. When the charging device displays information such as the current value and the power value, it is possible to suppress the vibration of the displayed value, making it easier for the end user to check the displayed value. By using the current limit characteristic according to the temperature of the storage element, it is possible to suppress electrodeposition regardless of the temperature of the storage element.

In the second region, the current limit value may change linearly. This method makes it easier to calculate the current command value compared to when the current limit value changes curvedly. Also, compared to when the current limit value changes curvedly, the change in the current command value calculated to be a delayed value relative to the current limit value can be made closer to a constant, thereby suppressing vibrations in the current command value.

The calculation unit may determine a current command value for the charging current for the storage element by adding the current limit value and the past current command value, weighted using a ratio. With this method, the current command value can be made to gradually follow the current limit value between the first voltage and the CV voltage.

The ratio may vary depending on the magnitude of the curve of the voltage band corresponding to the second region in the OCV curve that indicates the OCV-SOC correlation of the storage element. Vibrations in the current command value are correlated with the magnitude of the curve of the OCV curve. With this method, the ratio varies depending on the magnitude of the curve of the OCV curve, so that vibrations in the current command value can be further suppressed.

<Embodiment 1>
1. Description of the battery 50 and the charging device 10 Fig. 1 is a block diagram showing the electrical configuration of the battery 50 and the charging device 10. The battery 50 may be a power storage device of a solar power generation system. The battery 50 includes a current interruption device 53, a battery pack 60 consisting of a plurality of secondary batteries 62, a current measurement resistor 54, a management device 100, and a temperature sensor 115. The secondary batteries 62 are an example of a power storage element. As an example, the secondary batteries 62 are lithium ion secondary batteries.

The current interruption device 53, the current measurement resistor 54, and the battery pack 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 battery pack 60. The power line 55N is a power line that connects the negative external terminal 52 and the negative electrode of the battery pack 60. The current interruption device 53 and the current measurement resistor 54 are located on the positive electrode side of the battery pack 60 and are provided on the positive electrode side power line 55P.

The current interruption device 53 can be configured with a contact switch (mechanical) such as a relay, or a semiconductor switch such as an FET or transistor. By opening the current interruption 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 battery pack 60. Discharging and charging can be determined from the polarity (positive/negative) of the voltage across the current measuring resistor 54. The temperature sensor 115 is of the contact or non-contact type and measures the temperature T [°C] of the battery pack 60.

The management device 100 is provided on the circuit board unit 65. The management device 100 includes a voltage detection circuit 110, a processing unit 120, and a power supply circuit 130. The voltage detection circuit 110 is connected to both ends of each lithium ion secondary battery 62 by a signal line, and measures the cell voltage V of each lithium ion secondary battery 62 and the total voltage of the assembled battery 60. The total voltage of the assembled battery 60 is the sum of the voltages of the multiple lithium ion secondary batteries 62 connected in series.

The processing unit 120 includes a CPU 121 having a calculation function, and a memory 123 which is a storage unit. The processing unit 120 monitors the current I of the battery pack 60, the voltage V of each lithium ion secondary battery 62, and the total voltage and temperature T of the battery pack 60 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 a calculation process to calculate a current command value Io for the charging current in a current reduction region H2 described below. 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 non-volatile storage medium such as a flash memory or an EEPROM. The memory 123 stores a monitoring program for monitoring the state of the battery pack 60 and data required to execute the monitoring program.

Memory 123 stores a calculation program for calculating the current command value Io of the charging current and data required for executing the calculation program (such as the current limiting characteristics shown in FIG. 4 and past current command values). The calculation program can be written to a recording medium such as a CD-ROM.

The charging device 10 may be a power conditioner. 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 a battery 50. The CPU 15 controls the magnitude of the charging current via the charging circuit 13. The current detection resistor 11 is provided to detect the charging current.

As shown in Figures 2A and 2B, the lithium ion secondary battery 62 contains an electrode body 83 together with a non-aqueous electrolyte in a rectangular parallelepiped case 82. The case 82 has a case body 84 and a lid 85 that closes the upper opening.

The electrode body 83, although not shown in detail, is composed of a negative electrode element in which an active material is applied to a substrate made of copper foil, and a positive electrode element in which an active material is applied to a substrate made of aluminum foil, with a separator made of a porous resin film disposed between them. Both of these are strip-shaped, and the negative electrode element and the positive electrode element are shifted to opposite sides in the width direction relative to the separator, and are wound in a flat shape so that they can be housed in the case body 84.

A positive terminal 87 is connected to the positive element via a positive collector 86, and a negative terminal 89 is connected to the negative element via a negative collector 88. The positive collector 86 and the negative collector 88 each consist of a flat base 90 and a leg 91 extending from the base 90. A through hole is formed in the base 90. The leg 91 is connected to the positive element or the negative element. The positive terminal 87 and the negative terminal 89 each consist of a terminal body 92 and a shaft 93 protruding downward from the center of the lower surface. Of these, the terminal body 92 and the shaft 93 of the positive terminal 87 are integrally formed from aluminum (a single material). In the negative terminal 89, the terminal body 92 is made of aluminum, and the shaft 93 is made of copper, and these are assembled together. The terminal body parts 92 of the positive terminal 87 and the negative terminal 89 are arranged on both ends of the lid 85 via gaskets 94 made of an insulating material and are exposed to the outside from the gaskets 94.

The lid 85 has a pressure relief valve 95. The pressure relief valve 95 is located between the positive terminal 87 and the negative terminal 89 as shown in FIG. 2A. The pressure relief valve 95 opens to reduce 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. 3 shows the current waveforms I and V of a lithium-ion secondary battery 62 during CCCV charging. CCCV charging is a method in which the lithium-ion secondary battery 62 is charged at a constant current (CC charging) until it reaches the CV voltage, and then the secondary battery 62 is constant-voltage charged (CV charging) at the CV voltage.

At the end of the CC region (the region immediately before the transition to the CV region) F, the voltage is high and the charging current is large, so that electrodeposition is likely to occur in the lithium-ion secondary battery 62. Electrodeposition is a phenomenon in which lithium metal deposits on the negative electrode during charging, and is known to occur due to a decrease in the negative electrode potential.

Figure 4 shows the current limiting characteristic that indicates the relationship between the maximum cell voltage and the current limiting value. The current limiting characteristic has three regions: CC region H1, current reduction region H2, and CV region H3, and a current limiting value is defined for each of the regions H1 to H3. The maximum cell voltage is the maximum voltage of the multiple lithium ion secondary batteries 62 connected in series. The data of the current limiting characteristic shown in Figure 4 is stored in memory 123.

The CC region H1 is a region where the maximum cell voltage of the lithium ion secondary battery 62 is between Vo and Vs. The CC region H1 is a region where the battery 50 is charged with a constant current (CC charging). The current reduction region H2 is a region where the maximum cell voltage of the lithium ion secondary battery 62 is between Vs and Vc. The current reduction region H2 is a region where the battery 50 is charged while the charging current is reduced as the cell voltage increases. The CV region H3 is a region where the maximum cell voltage is equal to or greater than Vc. The CV region H3 is a region where charging is temporarily halted when the maximum cell voltage is equal to or greater than the CV voltage.

Vo is the minimum voltage of the lithium ion secondary battery 62. Vs is a first voltage that is greater than Vo and less than Vc. Vc is the control target voltage (CV voltage) of the maximum cell voltage of the lithium ion secondary battery 62 during constant voltage charging (CV charging) by repeating the current limiting region H2 and the CV region H3. By comparing the measurement value (maximum cell voltage) of the voltage detection circuit 110 with Vs and Vc, the processing unit 120 can determine where the battery 50 is located among the three regions H1 to H3 during charging.

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 lithium ion secondary battery 62. The CC region H1 corresponds to the "first region" of the present invention.

When charging of the battery 50 starts, the processing unit 120 reads data on the current limit value Imax defined by the current limit characteristic of FIG. 4 from the memory 123 and sends it to the charging device 10. The charging device 10 determines the current command value Io of the charging current based on the output power constraints of the charging device 10 and other factors within a range that does not exceed the current limit value Imax sent from the processing unit 120, and CC-charges the battery 50.

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

When the maximum cell voltage of the lithium ion secondary battery 62 rises to the first voltage Vs due to charging in the CC region H1, it transitions to the current reduction region H2.

In the current reduction region H2, the current limit value is defined by a straight line M2 sloping downward to the right that connects points A and B in FIG. 4. The current limit value decreases linearly from the maximum allowable current Imax to 0 while the maximum cell voltage of the lithium ion secondary battery 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 period tn, with the current limit value determined by the straight line M2 as the upper limit. The processing unit 120 then transmits the calculated current command value Io to the charging device 10. The charging device 10 outputs a charging current based on the current command value Io transmitted from the processing unit 120, and charges the 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 electrolytic deposition from occurring when the cell voltage of the lithium ion secondary battery 62 rises to near the CV voltage Vc due to charging.

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

As shown in FIG. 4, 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]. After the transition to the CV region H3, the charging device 10 temporarily suspends charging of the battery 50. When charging stops, the voltage increase due to internal resistance disappears, and the maximum cell voltage of the lithium ion secondary battery 62 drops 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. The charging device 10 then 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 lithium ion secondary battery 62 reaches the CV voltage Vc, the current reduction region H2 transitions to the CV region H3.

In this way, by repeatedly charging in the current reduction region H2 and stopping charging in the CV region H3, the battery 50 can be constant-voltage charged (CV charged) while maintaining the maximum cell voltage at the CV voltage Vc. In addition, the higher the maximum cell voltage is (the closer it is to the CV voltage Vc), the lower the current used for charging, which can prevent electrodeposition from occurring during CV charging.

When the battery 50 is close to being fully charged, the charging current of the battery 50 gradually decreases. In this example, the charging end determination condition is set to 0.2 A as an example, and charging ends when the charging current falls to 0.2 A or less. Also, when the battery 50 is close to being fully charged, 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 the charging end condition may be that the charging stopped state continues for a predetermined period of time.

(B) Suppression of Vibration of Current Command Value Fig. 5 is an OCV curve of the lithium ion secondary battery 62. As shown in the following (1), SOC (state of charge) is the ratio of remaining capacity Cr to actual capacity (available capacity) Ca of the secondary battery 62. OCV (open circuit voltage) is the open circuit voltage of the secondary battery 62.

SOC = (Cr/Ca) x 100 (1)

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

The dashed line X2 in Figure 5 is a charging curve that shows the voltage change of the lithium-ion secondary battery 62 when it is charged at a specified rate. The charging curve X2 is shifted upward from the OCV curve X1, and has a higher voltage value even if the SOC value is the same. This voltage difference ΔV is the voltage increase due to the internal resistance of the lithium-ion secondary battery 62, and depends on the magnitude of the charging current.

The voltage rise due to the internal resistance of the lithium-ion secondary battery 62 decreases as the charging current decreases. As shown in FIG. 6, in the current reduction region H2, when the maximum cell voltage of the lithium-ion secondary battery 62 increases from V1 to V2, lowering the current command value Io of the charging current from I1 to I2 reduces the voltage rise due to the internal resistance. Therefore, the maximum cell voltage of the secondary battery 62 decreases from V2 to V3. When the maximum cell voltage decreases to V3, the current command value Io of the charging current is raised from I2 to I3.

In this way, if the current command value Io of the charging current I is lowered as the maximum cell voltage increases, the maximum cell voltage will repeatedly increase and decrease, which may cause the current command value Io to oscillate.

The processing unit 120 calculates the current command value Io_n in the current reduction region H2 at a given control period n according to the following formula (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 the current limit value corresponding to the maximum cell voltage defined by the current limit characteristic. m is the ratio that determines the amount of delay of Io_n relative to I_limit (m<1).

An example of calculating the current command value Io_n is shown below. 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 current limit characteristic is I2. When the ratio m is 0.5, the current command value Io_n is (I1 + I2) / 0.5, which is the intermediate value between the previous current command value I1 and the current limit value I2.

The calculation formula (2) obtains the current command value Io_n by adding the previous value Io_n _-1 of the current command value and the current limit value I_limit while weighting them according to the ratio m. The obtained current command value Io_n has a delay with respect to the current limit value defined by the current limit characteristic in Fig. 4. The delay means that the current command value does not change to the current limit value defined by the current limit characteristic, and the current command value has a difference Δ with respect to the current limit value. The smaller the ratio m, the larger the delay, and the closer the ratio m is to 1, the smaller the delay.

By having such a delay, it is possible to mitigate sudden changes in the current command value Io_n and suppress vibrations in the current command value Io.

The oscillation of the current command value Io becomes more pronounced as the curve of the OCV curve becomes steeper. Therefore, it is advisable to vary the ratio m according to the curve (slope) of the OCV curve. In other words, when charging a secondary battery with a steep OCV curve with a large slope in the voltage range (Vs to Vc) of the current reduction region H2, it is advisable to set the ratio m small. When charging a secondary battery with a gentle OCV curve with a small slope in the voltage range (Vs to Vc) of the current reduction region H2, it is advisable to set the ratio m large (closer to 1).

Figure 7 is a flowchart of the calculation process of the current command value. The calculation process of the current command value Io consists of seven steps, S10 to S70, and is executed repeatedly at a predetermined control period tn in the current reduction region H2. As an example, the control period tn is 1 sec.

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

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 processing is, for example, a process of notifying the charging device 10 of the abnormality and requesting that charging be stopped.

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

If the control period tn has elapsed since the previous processing (S40: YES), the process proceeds to S50, and the processing unit 120 performs processing to read the data of the current limiting characteristics shown in FIG. 4 from the memory 123.

After reading out the current limiting characteristic, the process proceeds to S60, where the processing unit 120 calculates a current command value Io_n using the above equation (2) based on the previous value Io_n _-1 of the current command value and the current limiting value I_limit corresponding to the maximum cell voltage defined by the current limiting characteristic.

Then, the process proceeds to S70, where the processing unit 120 transmits the calculated current command value Io_n to the charging device 10.

The processing of S10 to S70 is repeated at a control period tn, and a 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.

Figure 8 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 waveform of the current command value after the delay according to equation (2), Y2 represents the waveform of the charging current output by the charging device 10, and Y3 represents the waveform of the maximum cell voltage.

3. Effects In this method, a current reduction region H2 is provided between the CC region H1 and the CV region H3, and during charging, as the secondary battery 62 rises to the CV voltage Vc, the charging current decreases. Therefore, it is possible to suppress electrodeposition in the lithium ion secondary battery 62. In this method, the current command value Io is set to a value that is delayed with respect to the current limit value defined by the current limit characteristic, so that the change in the current command value Io can be mitigated. Therefore, in the current reduction region H2, it is possible to suppress the vibration of the current command value Io. In addition, by suppressing the vibration of the current command value, it is possible to suppress the occurrence of current noise during charging. By suppressing the current noise, it is possible to suppress the occurrence of electrodeposition. Furthermore, since the peak of the charging current can be suppressed, it is possible to suppress the load on the charging device 10. When the charging device 10 displays information such as a current value or a power value, it is possible to suppress the vibration of the displayed value, making it easier for the end user to check the displayed value.

In the current reduction region H2, the current limit value is defined by a straight line M2. By defining the current limit value by a straight line M2, the calculation of the current command value Io is easier and the charging speed is faster than when the current limit value is defined by a curve such as a quadratic curve. In addition, compared to when the current limit value is defined by a curve such as a quadratic curve, the following effects are achieved. The current command value Io is calculated to a value that lags behind the current limit value according to the control characteristics such as the curve of the OCV curve. By defining the current limit value by a straight line M2, the change in the current command value Io can be made closer to a constant, thereby suppressing the vibration of the current command value Io.

<Embodiment 2>
In the second embodiment, a current limiting characteristic is provided according to the temperature T of the battery pack 60. As shown in FIG. 9, three current limiting characteristics La to Lc are provided according to temperatures Ta to Tc. The current limiting characteristics La to Lc are stored in the memory 123. The current limiting characteristics La to Lc have different maximum allowable current Imax values, and the lower the temperature T, the smaller the maximum allowable current Imax. The current limiting value in the current reduction region H2 has different slopes according to temperatures Ta to Tc, and the higher the temperature, the larger the slope (absolute value). The magnitude relationship of the temperatures T is Ta>Tb>Tc.

Figure 10 is a flowchart of the calculation process of the current command value. The calculation process of the current command value in Figure 10 differs from the calculation process in Figure 7 in the process of S55.

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

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 proceeds to S40, where the processing unit 120 determines whether a control period tn has elapsed since the previous process.

If the control period tn has elapsed since the previous process (S40: YES), the process proceeds to S55, and the processing unit 120 performs a process of reading from the memory 123 the data on the current limiting characteristics corresponding to the temperature T of the battery pack 60 obtained in S10.

After reading out the current limiting characteristic, the process proceeds to S60, where the processing unit 120 calculates the current command value Io_n according to the above formula (2) based on the previous current command value Io_n _-1 and the current limit value I_limit defined by the current limiting characteristic.

Then, the process proceeds to S70, where 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 a control period tn, so that when there is a temperature change in the battery pack 60, the current limiting characteristics corresponding to the changed temperature are read out. Then, the current command value Io_n is calculated based on the read current limiting characteristics.

Lithium ion secondary batteries 62 are known to have a large internal resistance at low temperatures, and when charging at low temperatures, the potential of the negative electrode drops, making it easy for electrodeposition to occur. In the second embodiment, a current limiting characteristic is set for each temperature of the battery pack 60, and the lower the temperature, the smaller the maximum allowable current Imax. Therefore, it is possible to suppress the occurrence of electrodeposition when charging at low temperatures.

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

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

(2) In the first embodiment, an example was shown in which charging was controlled by the maximum cell voltage of the secondary battery 62, but charging may also be controlled by the total voltage of the battery pack 60.

(3) In the first embodiment, the current limit value of the current reduction region H2 is defined by a single straight line M2, but it may be defined by a curve or multiple straight lines as long as the current limit value decreases with increasing voltage.

(4) In the first embodiment, the current command value Io is calculated by the processing unit 120 of the battery 50. Alternatively, the current command value Io may be calculated by the charging device 10. In other words, the CPU 15 of the charging device 10 may serve as a charging control device. In this case, data on the current limiting characteristics may be stored in the internal memory of the charging device 10, and data required for calculating the current command value Io, such as data on the cell voltage of each secondary battery 62 and the temperature T of the battery pack, may be transmitted from the processing unit 120 to the charging device 10.

(5) In the first embodiment, the current command value Io is calculated based on the formula (2). The current command value Io may be calculated using a formula other than the formula (2) as long as it is based on the current limit value defined by the current limit characteristic and the previous value of the current command value and obtains a value with a delay relative to the current limit value. In the first embodiment, the previous value of the current command value is used as an example of the past current command value, but a value other than the previous value, such as the value before last, may be used. In addition, both the previous value and the value before last may be used as the past current command value.

(6) In the first embodiment, the current limit value of the current reduction region H2 is defined by a straight line M2 that connects point A corresponding to the maximum allowable current Imax and point B corresponding to 0 [A]. As shown in FIG. 11, the straight line M2 that defines the current limit value of the current reduction region H2 may be defined by a straight line M3 that connects point A corresponding to the maximum allowable current Imax and point C corresponding to a predetermined current value Ia greater than 0 [A]. 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 greater than the predetermined current value Ia. In addition, the predetermined current value Ia may be set to a current value smaller than the current value (0.2 A in the first embodiment) that is applied to the charging end determination condition. If the predetermined current value Ia is set to a value larger than the current value that is applied to the charging end determination condition, the charging current is controlled to a value greater than the current value that is applied to the determination condition, and the charging end determination condition cannot be detected. By setting the predetermined current value Ia to a current value that is equal to or less than the current value that is applied to the charging end determination condition, the charging end determination condition can be detected.

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

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

(9) The present technology can be applied to a charging control program for a power storage device. The charging control program for a power storage device is a program that causes a computer to execute a calculation process for calculating a current command value for the charging current of the power storage element so as not to exceed a current limit value defined by a current limit characteristic. The current limit characteristic has a constant current limit value in a first region where the voltage of the power storage element is equal to or lower than a first voltage, which is lower than the CV voltage during CV charging, and the current limit value decreases as the voltage of the power storage element increases in a second region where the voltage of the power storage element is between the first voltage and the CV voltage. The current limit characteristic has a plurality of current limit values in the first region and a plurality of current limit values in the second region, which are set according to the temperature of the power storage element, and the slope at which the current limit value decreases in response to an increase in voltage in the second region differs among the plurality of current limit characteristics. In the calculation process, the current command value of the charging current for the power storage element is calculated to a value having a delay with respect to the current limit value in the second region, based on the current limit value defined by the current limit characteristic and a past current command value. This technology can be applied to a recording medium that records a charging control program for a power storage device. One example of the computer is the processing unit 120.

(10) The above-mentioned embodiment relates to a charge control method in CCCV charging. FIG. 12 is a block diagram of a solar power generation system 200. The solar power generation system 200 has a solar power generation panel 210, a power conditioner 230, and a power storage device 250. Y indicates the boundary with the power grid 300. The power conditioner 230 is a power control device and has a control unit 235 that performs power control and charge control. The solar power generation system 200 can charge the power storage device 250 with the surplus power generated by the solar power generation panel 210 in order to effectively use the power generated by the solar power generation panel 210. In addition, when the load R is smaller than the power received from the power grid 300, the power storage device 250 can also be charged by the power from the power grid 300. In this way, the solar power generation system 200 is charged from the solar power generation panel 210 and from the power grid 300, and there are various charge and discharge modes other than CCCV charging. In the solar power generation system 200, the charging current from the power conditioner 230 to the power storage device 250 may suddenly change due to fluctuations in sunlight (fluctuations in illuminance) or fluctuations in the load R connected to the solar power generation system 200.

For example, when charging with power generated by the photovoltaic power generation panel 210, as shown in FIG. 13, the charging current PCS from the power conditioner 230 may temporarily (e.g., stepwise) decrease at time T1 due to the blocking of sunlight by clouds, and then recover. In such a charging mode, as shown in FIG. 14, it is preferable to set the current limit value L to a transition with smaller fluctuations than the fluctuations of the charging current PCS. The "current limit value L" here may be a value determined instead of the current limit value determined from the current limit characteristic stored in advance in the memory 123 for CCCV charging as in the above-mentioned embodiment. The lower value of the current limit value determined from the current limit characteristic of the first and second embodiments and the current limit value L shown in FIG. 14 may be used as the current command value.

As shown in FIG. 13, if the current limit value L remains constant at the value at time T1 (the value obtained by adding a predetermined value α to the charging current PCS immediately before time T1), the charging current PCS will increase sharply (part A in FIG. 13) at time T2 when solar power generation is restored, and depending on the SOC of the storage element, electrodeposition may occur. In order to avoid electrodeposition, it is possible to set the current limit value L so that the charging current PCS does not increase excessively at time T2.

On the other hand, the power conditioner 230 is required to return to the original output state before the instantaneous power outage within 1 second in the event of an instantaneous power outage (instantaneous power outage). For example, consider the case where the time between time T1 and time T2 in FIG. 13 is within 1 second (the charging current PCS suddenly decreases and then increases within 1 second). If the current limit value L is set so that the charging current PCS does not increase excessively at time T2, there is a possibility that the requirements for the power conditioner 230 cannot be satisfied. For example, assume that the power system 300 experiences an instantaneous power outage during the period in which the storage device 250 is being charged with power from the power system 300. As shown in FIG. 13, the current limit value L from time T1 to time T2 is set to a value Lc obtained by adding a predetermined value α to the charging current PCS during the instantaneous power outage. In this case, when the power supply recovers from the momentary power outage, the charging current PCS immediately after the power supply recovers is limited to the current limit value Lc, and it takes time for the power conditioner 230 to return to the state in which it outputs the charging current PCS before the momentary power outage to the power storage device 250.

From the above, not only when the charging current PCS increases suddenly (time T2), but also when the charging current PCS decreases suddenly (time T1), the fluctuation of the current limit value L may be made smaller than the fluctuation of the charging current PCS. That is, in the example of FIG. 14, the current limit value L is set to Lo until time T1 when the charging current PCS decreases suddenly. Lo is a value obtained by adding a predetermined value α to the charging current PCS just before time T1. Then, after time T1, the current limit value L is changed according to a straight line La whose change per unit time is smaller than the change in PCS at time T1, so that the fluctuation of the current limit value L at each point after time T1 is smaller than the fluctuation of the charging current PCS at time T1. In this example, the current limit value L is decreased according to the straight line La until time T2 when the charging current PCS increases. In addition, after time T2 when the charging current PCS increases rapidly, the current limit value L is changed according to a straight line Lb, which has a smaller change per unit time than the change in the charging current PCS at time T2, so that the fluctuations in the current limit value L at each point in time after time T2 are smaller than the fluctuations in the charging current PCS at time T2. In this example, the current limit value is changed according to the straight line Lb until time T4 when the current limit value L reaches the current limit value Lo immediately before time T1.

For comparison, FIG. 15 shows the current limit value L1 (an example of equal fluctuation) when the value is changed by the same amount in accordance with the fluctuation of the charging current PCS. When the current limit value is changed by the same amount in accordance with the fluctuation of the charging current PCS, when the charging current PCS changes, the current limit value also changes accordingly, and as shown in FIG. 15, the difference between the current limit value and the charging current PCS is maintained at a predetermined value α. Therefore, the amount by which the charging current PCS can be increased at one time is limited to the predetermined value α, so the time (T2 to T3) from when the charging current PCS starts to increase until it returns to its original value becomes longer than in FIG. 14, and it can be understood that it is difficult to satisfy the requirements for the power conditioner 230. The predetermined value α may be determined based on the temperature of the storage element to avoid electrolytic deposition.

By making the fluctuation of the current limit value L smaller than the fluctuation of the charging current PCS, it is possible to mitigate a sudden increase in the charging current PCS at time T2 while satisfying the above-mentioned requirements for the power conditioner 230. In addition, it is possible to mitigate a sudden change in the displayed value for the end user. The current limit value L may be a discrete value instead of the continuous value shown in Fig. 14, or may be a value that is calculated at every predetermined time (e.g., at a control period) and decreases or increases stepwise over time.
It is preferable that the absolute value of the slope (absolute value of the slope of Lb) of the current limit value L when it increases over time following the charging current PCS is greater than the absolute value of the slope (absolute value of the slope of La) when it decreases over time following the charging current PCS. This makes it easier to satisfy the above-mentioned requirements for the power conditioner 230. Even in an operation mode of the power conditioner 230 other than during an instantaneous power outage, the charging current PCS can be restored at an early timing (at time T3) when sunlight is restored, for example, and the storage element can be charged efficiently.

In the example of FIG. 14, the charging current PCS changed in a step-like manner. As shown in FIG. 16, the charging current PCS may change in a trapezoidal shape. When the charging current PCS changes in a trapezoidal shape, it is preferable to make the absolute value of the slope of the straight line La when the current limit value L decreases smaller than the absolute value of the slope of the straight line PCSa when the charging current PCS decreases. Also, it is preferable to make the absolute value of the slope of the straight line Lb when the current limit value L decreases smaller than the absolute value of the slope of the straight line PCSb when the charging current PCS increases. Also, in order to suppress electrodeposition, it is preferable to make the fluctuation of the current limit value L at time T2 when the charging current PCS increases suddenly smaller than the fluctuation of the charging current PCS.

Figure 17 is a flow chart of the charging control process executed by the power conditioner 230. The charging control process is composed of four steps, S100 to S130. Here, charging from the solar power generation panel 210 is considered. When charging of the power storage device 250 starts, the control unit 235 of the power conditioner 230 detects the charging current PCS (S100) and calculates the current limit value L based on the detected charging current PCS (S110). Then, the control unit 235 charges the power storage device 250 using the current limit value L as a current command value (S120). In parallel with charging, the control unit 235 detects the SOC (state of charge) from the voltage of the power storage device 250 and determines whether to continue charging (S130). While charging continues, the processes of S100 to S130 are repeatedly executed at a control cycle.

If there is no change in the power generation state of the solar power generation panel 210, the charging current PCS is constant and does not fluctuate. In this case, in S110, the current limit value L is calculated to be a value that is a predetermined value α greater than the charging current PCS, and the storage device 250 is charged with a constant charging current PCS.

On the other hand, if there is a fluctuation in the charging current PCS due to weather conditions or the like, in S110 the control unit 235 calculates the current limit value L so that the fluctuation is smaller than that of the charging current PCS. For example, if a sudden decrease in the charging current PCS is detected at time T1 shown in FIG. 14, the current limit value L is changed according to line La during the period from time T1 to time T2. Also, if a sudden increase in the charging current PCS is detected at time T2, the current limit value L is changed according to line Lb during the period from time T2 to time T4.

In this way, even if the sunlight blocked at time T1 recovers at time T2, the charging current PCS is limited by the current limit value L, so that it does not immediately return to the state before the sunlight was blocked, but returns stepwise within a range that does not exceed the current limit value L, thereby preventing a sudden increase in the charging current PCS. This charging control process can dynamically vary the charging power to the power storage device 250 when the power generation state of the solar power generation panel 210 changes or when the power system 300 experiences an instantaneous interruption. This charging control process may be applied to a charging mode other than CCCV charging, or may be applied to charging in the CC region in CCCV charging.
14, the timing of the charge current PCS is set to coincide with the timing of the current limit value L. The timing of the current limit value L is not necessarily required to coincide as long as it is near the time when PCS is decreasing (near time T1). The same applies to the case where the current limit value L is increasing.

In summary, the charging control method may have the following configuration.
(Configuration 1)
A charging control method for a storage element that dynamically varies a charging power, the charging control method including a calculation step of calculating a current limit value of the charging current based on a charging current from a charging device, wherein in the calculation step, the fluctuation of the current limit value is calculated to be a value smaller than the fluctuation of the charging current.
(Configuration 2)
A charging control method, in which, when a charging current from the charging device decreases at a first time point and recovers at a second time point, the current limit value is decreased after the first time point and increased from around the second time point.
(Configuration 3)
A charging control method, wherein a slope of the current limit value increasing over time from near the second time point is greater than a slope of the current limit value decreasing over time from the first time point.

10... Charging device 50... Battery (electricity storage device)
60... Battery pack 62... Lithium ion secondary battery (storage element)
100...Management device (charging control device)
120... Processing unit (calculation unit)
H1...CC region (first region)
H2...Current reduction region (second region)
H3...CV region (third region)

Claims (7)

A charging control device for a storage element,
A calculation unit calculates a current command value of the charging current of the 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 storage element is equal to or lower than a first voltage that is lower than a CV voltage during CV charging, a current limit value is constant;
In a second region in which the voltage of the storage element is from the first voltage to the CV voltage, the higher the voltage, the smaller the current limit value,
The current limiting characteristic is
a current limiting value in the first region and a current limiting value in the second region are provided in a plurality of values according to a temperature of the energy storage element, and a slope at which the current limiting value in the second region decreases in response to an increase in voltage differs among the plurality of current limiting characteristics;
The calculation unit calculates the current command value in the second region to a value having a delay with respect to the current limit value based on a current limit value defined by the current limit characteristic and a past current command value. The charge control device according to claim 1,
A charging control device, wherein in the second region, the current limit value changes linearly. The charge control device according to claim 1 or 2,
The calculation unit determines a current command value of a charging current for the storage element by weighting and adding the current limit value and a past current command value using a ratio. The charge control device according to claim 3,
The ratio differs depending on the magnitude of a curve of a voltage zone corresponding to the second region in an OCV curve indicating an OCV-SOC correlation of the power storage element. A method for controlling charging of a storage element, comprising:
A calculation step of calculating a current command value of the charging current of the 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 storage element is equal to or lower than a first voltage that is lower than a CV voltage during CV charging, a current limit value is constant;
In a second region in which the voltage of the storage element is from the first voltage to the CV voltage, the higher the voltage, the smaller the current limit value,
The current limiting characteristic is
a current limiting value in the first region and a current limiting value in the second region are provided in a plurality of values according to a temperature of the energy storage element, and a slope at which the current limiting value in the second region decreases in response to an increase in voltage differs among the plurality of current limiting characteristics;
A charging control method, in which in the calculation step, a current command value in the second region is calculated to be a value having a delay with respect to the current limit value based on a current limit value defined by the current limit characteristic and past current command values. A charging control method for a storage element, which dynamically varies charging power, comprising:
A calculation step of calculating a current limit value of the charging current based on a charging current from a charging device,
In the calculation step, the fluctuation of the current limit value is calculated to be smaller than the fluctuation of the charging current;
A charging control method, in which, when the charging current from the charging device decreases at a first time point and recovers at a second time point, the current limit value is linearly decreased from the first time point to the second time point, starting from the current limit value immediately before the first time point, and linearly increased from the second time point. The charging control method for a storage element according to claim 6 ,
A charging control method, wherein a slope of the current limit value increasing over time from near the second time point is greater than a slope of the current limit value decreasing over time from the first time point.

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