JP7762029B2 - Battery control method - Google Patents

Description

The present invention relates to a storage battery control method.

Power supply systems in which solar panels are installed on the roofs of homes and the electricity generated by the solar panels is used for household power are becoming common. A battery storage unit for use in such power supply systems has been proposed, in which multiple battery cells are connected in series to form a battery stack, enabling the desired voltage to be obtained (see, for example, Patent Document 1). For example, the voltage of a lithium-ion battery cell is approximately 2V to 4V. In contrast, the voltage of a household power supply is several hundred volts. In this case, by connecting several dozen battery cells in series, a voltage of several hundred volts for household use can be secured.

Balancing is essential for the battery cells that make up a battery stack. Therefore, such storage battery units are equipped with an AFE (Analog Front End) that detects the voltage of each battery cell, and a balance adjustment circuit. This allows the AFE to detect the voltage of each battery cell and controls the charge level of each battery cell so that it is uniform.

Balancing typically involves detecting the voltage of each battery cell, determining the cell capacity of each battery cell from the detected voltage, and controlling the charge amount of each battery to equalize the cell capacity of the battery cells depending on the usage environment, connected circuit components, and the passage of time. Charge amount control is performed using an AFE or balancing circuit to equalize the voltage of each battery cell. The cell voltage of a battery cell can be detected, for example, from the voltage when no current is flowing (OCV (Open Circuit Voltage)), the charge curve, or the discharge curve.

However, depending on the type of battery cell, the OCV curve, charge curve, or discharge curve may be nearly flat, making it difficult to detect the relationship between the cell voltage and the cell capacity of the battery cell. For example, in the OCV curve of a lithium iron phosphate battery (LFP), the region where the state of charge (SOC) is between 20% and 95% is a flat region where the OCV voltage changes very little with changes in the cell capacity of the battery cell. The region where the SOC is 95% or higher is a variable region where the OCV voltage changes in response to changes in the cell capacity of the battery cell. In the flat region, the OCV voltage remains constant at approximately 3.2V to 3.4V. The flat region is reached when the OCV voltage drops below 3.45V, for example.

In the variable region, the OCV voltage changes in response to changes in the cell capacity of the battery cell. Therefore, by detecting the OCV voltage of each battery cell and determining the cell capacity of each battery cell from the detected OCV voltage, it is possible to perform balance adjustments according to the determined cell capacity. However, in the flat region, the OCV voltage barely changes in response to changes in the cell capacity of the battery cell, making it difficult to detect the OCV voltage of each battery cell and determine the cell capacity of each battery cell from the detected OCV voltage.

Therefore, in general, when using a battery such as a lithium iron phosphate battery, the balance circuit operates by reducing the current value when fully charging and charging over a long period of time, so that the OCV voltage after full charging does not become a voltage lower than the change region.
Furthermore, to confirm a stable OCV voltage, the OCV voltage is detected after a long period of time. The cell capacity of each battery cell is determined from the detected OCV voltage, and balancing is performed according to the determined cell capacity.

Japanese Patent Application Laid-Open No. 2020-156200

As described above, when using battery cells such as lithium iron phosphate batteries, the current value is reduced and the charging time is long when the storage battery is fully charged. Furthermore, the battery is left for a long time after full charge to confirm a stable OCV voltage. This allows the OCV voltage of each battery cell to be detected in a range where the OCV voltage changes in response to changes in the cell capacity of the battery cell, making it possible to perform balance adjustment.
However, this method requires a long time to fully charge the battery, and it is necessary to ensure that a sufficient time has elapsed since the battery was fully charged in order to detect the OCV voltage. Furthermore, since a sufficient time is required after full charging, there is a problem in that if the battery is immediately discharged, it is not possible to perform balance adjustment.

To address this issue, it is possible to increase the charging current value to shorten the charging time until full charge, or to shorten the time elapsed after full charge for detecting the OCV voltage.
However, the relationship between the OCV voltage and the cell capacity of a battery cell after a predetermined time has elapsed since the battery was fully charged fluctuates depending on the current of the battery cell at the end of charging. Therefore, if the charging current value is increased and the elapsed time for stabilizing the OCV voltage is extended, the OCV voltage will drop to the flat region. This makes it difficult to detect the OCV voltage of each battery cell and determine the cell capacity of each battery cell from the detected OCV voltage. In particular, if the battery cell is degraded, the OCV voltage is more likely to drop to the flat region after the predetermined time has elapsed.
Therefore, when balancing a storage battery after fully charging it, it is necessary to take into consideration the time elapsed since it was fully charged, the current value at the end of charging, the degree of deterioration of the battery cells, etc.

As mentioned above, the relationship between the OCV voltage and the cell capacity of a battery cell a predetermined time after the battery is fully charged varies depending on the current of the battery cell at the end of charging. When charging a home battery system from a commercial power grid, the charging current is a constant current value. However, with solar power generation, for example, the current of the battery cell at the end of charging can vary greatly depending on the weather. Therefore, when balancing a battery a predetermined time after the battery is fully charged, it is necessary to determine the cell capacity of each battery cell taking into account the current value at the end of charging.

In view of the above-mentioned problems, an object of the present invention is to provide a storage battery control method that can obtain the cell capacity of each battery more accurately in a shorter time when balancing a storage battery in which multiple battery cells are connected in series.

A storage battery control method according to one aspect of the present invention includes a current detection step for detecting the current value at the end of charging when a storage battery having multiple battery cells connected in series is fully charged; a cell voltage detection step for detecting the cell voltage of each battery cell a predetermined time after full charge; and a calculation step for calculating the cell capacity of each battery cell from the detected current value and cell voltage.

According to the present invention, when balancing a storage battery in which multiple battery cells are connected in series after it is fully charged, the current value at the end of charging is detected, the cell voltage is detected after a predetermined time has elapsed, and the cell capacity is calculated from the detected current value and cell voltage. This allows the cell capacity of the battery cells to be obtained accurately and stably even when the battery cells are deteriorated or the charging current is unstable, such as in solar power generation. Therefore, when balancing a storage battery in which multiple battery cells are connected in series, the cell capacity of each battery can be obtained more accurately in a shorter time.

1 is a block diagram showing an overview of a power supply system according to the present invention; 1 is an explanatory diagram illustrating an overview of a storage battery unit used in a power supply system according to the present invention. 10 is an explanatory diagram illustrating an outline of a relay cable connecting a connector of a battery module and a connector of a control management module. FIG. 10 is an explanatory diagram illustrating an outline of a relay cable connecting a connector of a battery module and a connector of a control management module. FIG. FIG. 2 is an explanatory diagram of an example of a battery module. FIG. 2 is a block diagram showing the configuration of a control management module. FIG. 2 is a block diagram showing an overview of an AFE circuit element disposed on a BMS substrate. FIG. 10 is an explanatory diagram illustrating an arrangement of AFE circuit elements corresponding to a battery module. 1 is a graph showing the relationship between voltage and SOC of a lithium iron phosphate battery. 10 is a graph comparing the change characteristics of the OCV voltage with respect to the elapsed time after full charge, based on the magnitude of the current value at the end of charging. 10 is a graph showing the relationship between the OCV voltage 10 minutes after full charge and the capacity difference from full charge of the battery cell for each degree of cell deterioration. 10 is a graph showing the relationship between the OCV voltage one minute after full charge and the capacity difference from full charge of the battery cell for each degree of cell deterioration. 10 is a graph showing the relationship between the difference in capacity from full charge of a battery cell one minute after full charge and the OCV voltage, depending on the magnitude of the current value at the end of charging. 10 is an example of a table showing the relationship between the OCV voltage and the cell capacity for each current at the end of charging. 4 is a flowchart showing an example of operation processing of a balancing circuit in the storage battery control method according to the first embodiment of the present invention. 10 is a flowchart showing an operation process of a balancing circuit in a storage battery control method according to a second embodiment of the present invention. FIG. 10 is a block diagram showing an outline of another example of the configuration of the power supply system according to the present invention. FIG. 10 is a block diagram showing an outline of another configuration example of a power supply system according to the present invention.

The present invention relates to a storage battery control method that can acquire the cell capacity of each battery in a shorter time and with higher accuracy when controlling the state of charge of each battery cell of a storage battery in which multiple battery cells are connected in series.
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

<1. The entire system>
The overall system of the present invention will be described with reference to FIGS.

(Outline of the power supply system)
First, an outline of a power supply system according to the present invention will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an outline of a power supply system 10 according to the present invention.
As shown in FIG. 1 , a power supply system 10 according to an embodiment of the present invention includes a power conditioner 1 , a solar panel 2 , and a storage battery unit 3 .

Power conditioner 1 converts between DC and AC power, controls power supply voltage, and purchases and sells electricity. Specifically, commercial power supply 5 uses AC power, while solar power generation and storage use DC power. Furthermore, the voltage of commercial power supply 5 differs from the voltage of the batteries used in solar panels 2 and storage battery unit 3. Power conditioner 1 converts between DC and AC power and controls power supply voltage between commercial power supply 5, solar panels 2, and storage battery unit 3. Power conditioner 1 then supplies power to distribution board 6, which distributes the power to the outlets in each room.

The solar panel 2 can generate electricity during the daytime when the sun is out, but cannot generate electricity at night when the sun sets, resulting in an unstable amount of power generated. The storage battery unit 3 can be charged from the power grid via the commercial power source 5 and power conditioner 1 during the day, and can also be charged via the solar panel 2 and power conditioner 1, and can supplement the power supply via the power conditioner 1. The storage battery unit 3 can be charged from the grid via the commercial power source 5 and power conditioner 1 at night, and can also supplement the power supply via the power conditioner 1.

In addition, the power conditioner 1 performs processes such as purchasing and selling electricity, such as purchasing power from the commercial power source 5 when there is a power shortage, and selling power to the commercial power source 5 when there is surplus electricity generated by the solar panel 2.

The power supply system 10 can also incorporate an EV (Electric Vehicle) stand 4. The EV stand 4 can be used to charge electric vehicles and also to store power using the batteries installed in the electric vehicles. The EV stand 4 can also supplement the power supply via the power conditioner 1.

(storage battery unit)
Here, an overview of the storage battery unit 3 used in the power supply system 10 according to the present invention will be described with reference to Fig. 2. Fig. 2 is an explanatory diagram illustrating the overview of the storage battery unit 3 used in the power supply system 10 according to the present invention.
2, the storage battery unit 3 is composed of, for example, seven battery modules 11-1 to 11-7 and a control management module 12. The battery modules 11-1 to 11-7 are provided with battery stacks each consisting of a plurality of battery cells. The battery modules 11-1 to 11-7 are also provided with connectors 13-1 to 13-7 and connectors 14-1 to 14-7, respectively.

The control management module 12 manages the charge/discharge status of the battery modules 11-1 to 11-7. The control management module 12 is equipped with connectors 45-1 to 45-7 and connectors 56-1 to 56-7.

Connectors 13-1 to 13-7 of battery modules 11-1 to 11-7 and connectors 45-1 to 45-7 of the control management module 12 are connected by relay cables 60-1 to 60-7 as shown in FIG. 3. Connectors 14-1 to 14-7 of battery modules 11-1 to 11-7 and connectors 56-1 to 56-7 of the control management module 12 are connected by relay cables 70-1 to 70-7 as shown in FIG. 4.

(Relay cable)
Here, an overview of the relay cable that connects the connector of the battery module and the connector of the control management module will be described with reference to FIGS.

Figure 3 is an explanatory diagram showing the outline of the relay cables 60 (60-1 to 60-7) that connect the connectors 13-1 to 13-7 of the battery modules 11-1 to 11-7 to the connectors 45-1 to 45-7 of the control management module 12.

As shown in Figure 3, the relay cable 60 consists of connectors 61 (61-1 to 61-n) on the battery modules 11-1 to 11-7 side, connectors 62 (62-1 to 62-7) on the control management module 12 side, and cables 63 (63-1 to 63-7) between them. Cables 63 (63-1 to 63-7) are two wires, one for the positive electrode and one for the negative electrode.

Figure 4 is an explanatory diagram showing the outline of the relay cables 70 (70-1 to 70-7) that connect the connectors 14-1 to 14-7 of the battery modules 11-1 to 11-7 to the connectors 56-1 to 56-7 of the control management module 12.

As shown in Figure 4, relay cables 70 (70-1 to 70-7) consist of connectors 71 (71-1 to 71-7) on the battery module 11-1 to 11-7 side, connectors 72 (72-1 to 72-7) on the control management module 12 side, and cables 73 (73-1 to 73-7) between them. Cables 73 (73-1 to 73-7) consist of wiring in a number corresponding to the number of battery cells that make up the battery stack.

(battery module)
An example of a battery module will now be described with reference to Fig. 5. Fig. 5 is an explanatory diagram of an example of a battery module 11 (11-1 to 11-7). Note that the battery modules 11-1 to 11-7 are all configured in the same manner.

As shown in FIG. 5, the battery module 11 (11-1 to 11-7) has a battery stack consisting of battery cells 20-1, 20-2, ..., 20-n connected in series. The battery cells 20-1, 20-2, ..., 20-n are, for example, lithium iron phosphate ion batteries. Lithium iron phosphate ion batteries use lithium iron phosphate as the positive electrode, and are characterized by their high safety as their crystalline structure is resistant to breakdown even when heat is generated inside the battery. The cell voltage of each battery cell 20-1, 20-2, ..., 20-n varies depending on the cell structure. For lithium ion batteries, the cell voltage is, for example, 2V to 4V. For lithium iron phosphate ion batteries, the cell voltage is, for example, approximately 2.5V to 3.6V.

Battery modules 11 (11-1 to 11-7) are provided with connectors 13 (13-1 to 13-7) and connectors 14 (14-1 to 14-7). Connectors 13 (13-1 to 13-7) are connectors for charging and discharging battery modules 11. Connectors 14 (14-1 to 14-7) are connectors for monitoring the cell voltages of battery cells 20-1, 20-2, ..., 20-n.

(Control Management Module)
The configuration of the control management module will now be described with reference to Fig. 6. Fig. 6 is a block diagram showing the configuration of the control management module 12.
As shown in FIG. 6, the control management module 12 is equipped with a terminal block 31, a breaker 33, a high-voltage (HV) board 40, and a battery management system (BMS) board 50.

The terminal block 31 is a connector that connects wiring from the power conditioner 1 (PCS: Power Conditioning System). The terminal block 31 is provided with a positive terminal 31a, a negative terminal 31b, and a ground terminal 31c. In this example, the ground terminal 31c is connected to the housing as a zero potential. The wiring extending from the positive terminal 31a and negative terminal 31b of the terminal block 31 forms the charge/discharge lines 35a and 35b. The breaker 33 is used for protection when a large current flows.

The communication connector 32 is a connector that connects a shielded wire for communication from the power conditioner 1. The communication connector 32 is connected to the communication connector 51 on the BMS board 50. Data from the power conditioner 1 is received via the communication connector 32 and sent to the microprocessor 54. Data from the microprocessor 54 is also sent to the power conditioner 1 via the communication connector 32.

The HV board 40 is a board used to charge and discharge the battery modules 11-1 to 11-7. The HV board 40 is equipped with a relay 41, a current sensor 42, a communication connector 43, and connectors 45-1 to 45-7.

The relay 41 is a switch that starts and stops the operation of the storage battery unit 3. The current sensor 42 detects the charging and discharging current to and from the battery modules 11-1 to 11-7. The communication connector 43 is connected to the communication connector 52 on the BMS board 50. The communication connector 43 transmits the detected current of the current sensor 42 to the microprocessor 54, for example.

Connectors 45-1 to 45-7 are terminals that connect to connectors 13-1 to 13-7 on the battery modules 11-1 to 11-7 side, respectively. Connectors 13-1 to 13-7 on the battery modules 11-1 to 11-7 side are connectors for charging and discharging, and wiring from both ends of battery cells 20-1, 20-2, ..., 20-n that make up the battery stack is led out from connectors 13-1 to 13-7. Connectors 45-1 to 45-7 are connected in series to obtain the desired charging and discharging voltages. The positive electrode of connector 45-1, which has the highest potential, is connected to charge and discharge line 35a, and the negative electrode of connector 45-7, which has the lowest potential, is connected to charge and discharge line 35b.

The BMS board 50 is a board used to monitor and control the status of battery modules 11-1 to 11-7. The BMS board 50 is equipped with communication connectors 51 and 52, an AFE (Analog Front End) 53, a microprocessor 54, an optical isolation element 55, and connectors 56-1 to 56-7.

The communication connector 51 is connected to the communication connector 32 and transmits and receives data to and from the power conditioner 1. The communication connector 52 is connected to the communication connector 43 and transmits and receives data to and from the HV board 40.

AFE 53 detects the cell voltage of each battery module 11-1 to 11-7 and converts it into digital data.

The microprocessor 54 performs various controls based on data from the power conditioner 1, data from the HV board 40, data from the AFE 53, etc.

The optical isolation element 55 is an element such as a photocoupler or digital isolator, and connects the AFE 53 and the microprocessor 54. Because a high voltage is applied to the AFE 53, the optical isolation element 55 provides isolation between the AFE 53 and the microprocessor 54.

Connectors 56-1 to 56-7 are terminals that connect to connectors 14-1 to 14-7 on the battery modules 11-1 to 11-7 side, respectively. Connectors 14 (14-1 to 14-7) are connectors for monitoring the cell voltages of battery cells 20-1, 20-2, ..., 20-n. Connectors 56-1 to 56-7 transmit the cell voltages of battery modules 11-1 to 11-7, respectively, to the BMS board 50 side.

(AFE circuit element)
An overview of the AFE circuit element disposed on the BMS board will now be described with reference to Fig. 7. Fig. 7 is a block diagram showing an overview of the AFE circuit element 530 disposed on the BMS board 50.
In the present invention, the function of the AFE 53 is realized by arranging AFE circuit elements 530 as shown in Fig. 7 in the number corresponding to the battery modules 11-1 to 11-7. Note that the following description will be limited to the portion of the function of the AFE circuit element 530 that is necessary for explaining the present invention. Note that the number of AFE circuit elements 530 is not limited to the number corresponding to the battery modules 11-1 to 11-7. For example, one AFE circuit element 530 may be connected to two battery modules.

In Figure 7, terminals A1, A2, ..., Am (m is an arbitrary integer) are measurement terminals for detecting the cell voltage of the battery stack. When detecting the cell voltage of the battery stack, the battery cells are connected in the order from terminal A1 to terminal Am, from the electrode with the highest potential to the electrode with the lowest potential.

The resistor Ra and switch circuit Sa between the terminals A1, A2, ..., Am are used to balance the battery cells. That is, when the switch circuit Sa is turned on, both poles of the battery cells are connected via the resistor Ra, and the energy in the battery cells is consumed by Joule heat. This causes the energy of the battery cells with the most charge to be consumed, and the charge levels of each battery cell can be equalized.
In the example shown in FIG. 7, a passive balancing circuit is used, but the present invention can be applied to an active balancing circuit as well. Furthermore, the balancing of the charge amounts of the battery cells is not necessarily limited to the above-described configuration. A configuration in which each battery module is equipped with a microprocessor and an AFE may also be used. Furthermore, the balancing circuit may be realized by a balance adjustment circuit configuration other than the AFE.

Terminals D1 and D2 are terminals for inputting and outputting data. Data is input and output between the AFE 53 and the microprocessor 54 via terminals D1 and D2.

Now, referring to Figure 8, we will explain the arrangement of AFE circuit elements corresponding to battery modules. Figure 8 is an explanatory diagram showing the arrangement of AFE circuit elements 530-1 to 530-7 corresponding to battery modules 11-1 to 11-7.

As shown in FIG. 5, battery modules 11-1 to 11-7 are provided with a battery stack consisting of battery cells 20-1, 20-2, ..., 20-n. Both ends and the inter-stage of each battery cell 20-1, 20-2, ..., 20-n are connected to terminals A1, A2, ..., Am of AFE circuit elements 530-1 to 530-7, respectively. Furthermore, each AFE circuit element 530-1 to 530-7 is connected in series.

With the configuration shown in FIG. 8, the cell voltages of the battery cells that make up the battery stacks of each battery module 11-1 to 11-7 are detected by AFE circuit elements 530-1 to 530-7. The cell voltages of the battery cells that make up the battery stacks of each battery module 11-1 to 11-7 are then converted to digital values by AFE circuit elements 530-1 to 530-7 and sent to microprocessor 54 via optical isolation element 55.

2. First Embodiment
The entire system of the present invention has been described above. Next, a first embodiment of the present invention will be described with reference to FIGS.
The storage battery control method according to the present invention is applied to charge control of the battery modules 11-1 to 11-7 in the storage battery unit 3 configured as described above.

As mentioned above, battery modules 11-1 to 11-7 are equipped with a battery stack in which multiple battery cells 20-1 to 20-n are connected in series. In a configuration in which battery cells 20-1 to 20-n are connected in series, balance adjustment is required to ensure that the cell capacity of the battery cells remains constant. Balance adjustment is performed by the AFE circuit element 530 shown in Figure 7.

The AFE circuit element 530 shown in Figure 7 is a passive system that discharges the stored energy in the battery cells to equalize the cell capacities. In this case, the cell capacity of each battery cell 20-1 to 20-n is discharged to match the cell with the lowest capacity. The discharge amount is determined by the discharge current from the battery cells 20-1 to 20-n and the discharge time. When using the AFE circuit element 530 shown in Figure 7, the discharge current is determined by the resistor Ra and the on-resistance value of the MOS transistor that forms the switch circuit Sa, and the discharge time is determined by the on-time of the switch circuit Sa. Therefore, the discharge amount can be managed by the resistance value of the resistor Ra and the on-time of the switch circuit Sa.

The cell capacity of a battery cell can usually be detected by the OCV voltage (cell voltage), which is the open circuit voltage of the battery cell. However, depending on the type of battery cell, the OCV curve, charge curve, or discharge curve may be almost flat, making it difficult to detect the relationship between the cell voltage and SOC (State of Charge).

(Relationship between OCV voltage and SOC)
Here, the relationship between the OCV voltage and SOC of a lithium iron phosphate battery will be described with reference to Fig. 9. Fig. 9 is a graph showing the relationship between the OCV voltage and SOC of a lithium iron phosphate battery. In Fig. 9, the horizontal axis represents the SOC, and the vertical axis represents the OCV voltage. The OCV voltage is the cell voltage of a battery cell in an open circuit. The SOC is the ratio of the remaining capacity to the maximum capacity of the battery cell (i.e., the charging rate), and is an index of the cell capacity.

As shown in Figure 9, in the OCV curve of a lithium iron phosphate battery, the region between 20% and 95% SOC is a flat region where the OCV voltage changes very little with changes in the cell capacity of the battery cell. The region above 95% SOC is a variable region where the OCV voltage changes in response to changes in the cell capacity of the battery cell. In the variable region, the OCV voltage changes in response to changes in the cell capacity of the battery cell. Therefore, by detecting the OCV voltage of each battery cell and determining the cell capacity of each battery cell from this OCV voltage, it is possible to perform balance adjustments according to the cell capacity. However, in the flat region, the OCV voltage changes very little with changes in the cell capacity of the battery cell, making it difficult to detect the OCV voltage of each battery cell and determine the cell capacity of each battery cell from the OCV voltage.

Therefore, in the first embodiment, balancing is performed after the storage battery is fully charged. In other words, when the storage battery is fully charged, the SOC of the battery cell enters a change region where the SOC is 95% or higher. In this change region, the OCV voltage changes in accordance with changes in the cell capacity of the battery cell. Therefore, by detecting the OCV voltage of each battery cell and determining the cell capacity of each battery cell from this OCV voltage, balancing can be performed according to the cell capacity.

When balancing a battery after it has been fully charged, the process must take into full consideration factors such as the time elapsed since full charge, the current value at the end of charging (e.g., just before full charge), and the degree of deterioration of the battery cells.

(Influence of time elapsed since full charge)
Here, the influence of the time elapsed since full charge will be described with reference to Fig. 10. Fig. 10 is a graph comparing the change characteristics of the OCV voltage with the time elapsed since full charge, based on the magnitude of the current value at the end of charging. In Fig. 10, the horizontal axis represents the time elapsed since full charge, and the vertical axis represents the OCV voltage. Furthermore, characteristic A11 is the characteristic when the current value at the end of charging is small, and characteristic A12 is the characteristic when the current value at the end of charging is large.

As shown in Figure 10, the OCV voltage of a battery cell after full charge decreases over time after full charge and then stabilizes. This basic characteristic is the same whether the current is small or large. However, the degree of OCV voltage decrease varies depending on the current value at the end of charging. As shown by characteristic A11, the degree of OCV voltage decrease is small when the current is small, and as shown by characteristic A12, the degree of OCV voltage decrease is large when the current is large. When the current is large, the OCV voltage drops below 3.45 V 500 seconds after full charge, and the SOC enters a flat region between 20% and 95%. This makes it difficult to detect the OCV voltage and determine the cell capacity of each battery cell.

(Influence of the degree of deterioration of the battery cells)
Here, the influence of the degree of deterioration of the battery cells will be described with reference to FIGS. 11 and 12. FIG.
11 is a graph showing the relationship between the OCV voltage 10 minutes after full charge and the difference in capacity from full charge of the battery cell for each degree of cell degradation. In FIG. 11, the horizontal axis represents the difference in capacity from full charge of the battery cell, and the vertical axis represents the OCV voltage. Furthermore, characteristic B11 represents the characteristic when there is almost no battery degradation, characteristic B12 represents the characteristic when there is moderate battery degradation, and characteristic B13 represents the characteristic when there is significant battery degradation.

As shown in Figure 11, 10 minutes after full charge, the OCV voltage decreases as the difference in capacity from full charge of the battery cell increases. This basic characteristic remains the same regardless of the degree of battery degradation. When there is no battery degradation, as shown by characteristic B11, even if the OCV voltage decreases, it can remain above 3.45 V. However, when the battery is severely deteriorated, as shown by characteristic B13, the OCV voltage drops to 3.45 V or below 10 minutes after full charge, and the slope of the curve becomes smaller. Even when the battery is moderately deteriorated, as shown by characteristic B12, the OCV voltage drops to 3.45 V or below as the difference in capacity from full charge increases. When the OCV voltage drops to 3.45 V or below, the SOC enters a flat region between 20% and 95%. This makes it difficult to detect the OCV voltage and determine the cell capacity of each battery cell.

In contrast, Figure 12 is a graph showing the relationship between the OCV voltage one minute after full charge and the difference in capacity from full charge of the battery cell, for each degree of cell degradation. In Figure 12, the horizontal axis represents the difference in capacity from full charge of the battery cell, and the vertical axis represents the OCV voltage. Furthermore, characteristic B21 represents the characteristic when there is almost no battery degradation, characteristic B22 represents the characteristic when there is moderate battery degradation, and characteristic B23 represents the characteristic when there is significant battery degradation.

As shown in Figure 12, one minute after full charge, as shown by characteristics B21 to B23, even if the OCV voltage drops, it can be maintained at 3.45V or higher, regardless of the degree of battery deterioration. If the OCV voltage is 3.45V or higher, a change range where the SOC is 95% or higher can be ensured. Therefore, the cell capacity of each battery cell can be determined by detecting the OCV voltage.

Based on the above considerations, if balancing is performed after a storage battery is fully charged, it is necessary to wait an appropriate amount of time after full charging before performing the process. The appropriate amount of time is a time that allows the OCV voltage after the elapsed time to be maintained at a voltage higher than the flat region (e.g., 3.45 V) where the OCV voltage hardly changes in response to changes in the cell capacity of the battery cells. Specifically, it is considered desirable to set the amount of time that has elapsed since full charging to, for example, one minute (an example of a predetermined amount of time).

In other words, if the time elapsed since full charge is set long, for example to 10 minutes, the OCV voltage can be stabilized. However, as shown in Figure 11, depending on the degree of battery cell deterioration, the OCV voltage may fall below 3.45V, causing the SOC to enter a flat region between 20% and 95%, making it difficult to detect the OCV voltage and determine the cell capacity of each battery cell. In contrast, if the time elapsed since full charge is set to, for example, 1 minute, as shown in Figure 12, the OCV voltage will rise to 3.45V or higher, and the OCV voltage can be maintained in the variable region.

(Influence of current value at the end of charging)
Next, we consider the variation in the capacity difference between battery cells due to the current value at the end of charging. As shown in Figure 10, the OCV voltage of a battery cell after full charge decreases over time. The degree of decrease in OCV voltage at this time varies depending on the current value at the end of charging. In particular, with solar power generation, the current value at the end of charging varies greatly depending on the weather. Therefore, in order to accurately calculate the cell capacity of a battery cell from the OCV voltage one minute after full charge, it is necessary to detect the current value at the end of charging.

Now, with reference to Figure 13, we will explain the effect of the current value at the end of charging. Figure 13 is a graph showing the relationship between the difference in capacity from full charge of a battery cell one minute after full charge and the OCV voltage of the battery cell, depending on the magnitude of the current value at the end of charging. In Figure 13, the horizontal axis represents the difference in capacity from full charge, and the vertical axis represents the OCV voltage one minute after charging is stopped. Furthermore, characteristic C11 represents the characteristic when the current value at the end of charging is small, and characteristic C12 represents the characteristic when the current value at the end of charging is large.

As can be seen by comparing characteristics C11 and C12 in Figure 13, when the current value at the end of charging is small, the OCV voltage tends to be higher than when the current value is large. Therefore, when detecting the OCV voltage and determining the cell capacity of a battery cell during balance adjustment, it is necessary to calculate the cell capacity taking into account the current value at the end of charging. In particular, when the current value is unstable, such as when charging using sunlight, it is necessary to take into account the current value at the end of charging.

In this invention, therefore, a pre-prepared table showing the relationship between cell voltage and cell capacity is used to calculate the cell capacity of each battery cell from the detected current value and OCV voltage. In the first embodiment, multiple tables are prepared in advance according to the current value at the end of charging. When performing balance adjustment, a table corresponding to the detected current value at the end of charging is selected from the multiple pre-prepared tables, and the selected table is used to calculate the cell capacity of each battery cell from the detected OCV voltage of each battery cell.

Here, a table showing the relationship between the OCV voltage and the cell capacity will be described with reference to Fig. 14. Fig. 14 is an example of a table showing the relationship between the OCV voltage and the cell capacity for each current at the end of charging.
14, this table describes the OCV voltage and cell capacity of the battery cell in association with each other. Therefore, if the OCV voltage of the battery cell is known, the cell capacity of the battery cell can be calculated using this table. For example, if the OCV voltage of a battery cell detected during balance adjustment is 3.58 V, the cell capacity of the battery cell is 650 mAh.
This table is stored in a memory element within the microprocessor 54 or in an external memory element.

(operation)
The operation processing of the balancing circuit in the storage battery control method will be described with reference to Fig. 15. Fig. 15 is a flowchart showing the operation processing of the balancing circuit in the storage battery control method according to the first embodiment of the present invention. In the first embodiment, a memory element in the microprocessor 54 is provided with a plurality of tables, each for a different current value, in which the correspondence relationship between the OCV voltage and the cell capacity of the battery cell as shown in Fig. 14 is described.

The microprocessor 54 detects the current at the end of charging (step S101). Specifically, the microprocessor 54 detects the current immediately before full charge.
The microprocessor 54 detects whether the storage battery is fully charged based on whether the cell voltage of each battery cell detected during charging of the storage battery and the charging current of the storage battery unit 3 satisfy predetermined conditions. For example, the microprocessor 54 detects that the storage battery is fully charged when the cell voltage of each battery cell and the charging current of the storage battery unit 3 satisfy the following three conditions (conditions I to III):
The first condition (Condition I) is that the cell voltage of each battery cell is a charging voltage at which the storage battery can be determined to be fully charged. The voltage at which the storage battery can be determined to be fully charged is a voltage that is greater than 65% of the capacity ratio from the change region to the full charge voltage.
The second condition (condition II) is that the charging current charged to the storage battery unit 3 is a charging current that allows the storage battery to be determined as fully charged. The charging current that allows the storage battery to be determined as fully charged is the minimum charging current generated by solar power generation within the maximum charging current from the commercial grid.
The third condition (condition III) is that the conditions I and II remain in effect for the final charging time during which the battery can be determined to be fully charged. The final charging time during which the battery can be determined to be fully charged is the time during which the voltage at the charging current does not stably fall below the level at which the battery can be determined to be fully charged.
As described above, the microprocessor 54 detects that the storage battery is fully charged when the state in which both Condition I and Condition II are satisfied has elapsed for the predetermined time period specified by Condition III.
The state immediately before full charge refers to the state immediately before the predetermined time period of condition III elapses while both conditions I and II are satisfied. That is, in step S101, the microprocessor 54 detects the current immediately before the predetermined time period of condition III elapses while both conditions I and II are satisfied.

Next, the microprocessor 54 detects full charge when the above conditions I to III are met (step S102).
After detecting full charge, the microprocessor 54 determines whether or not to operate the balancing circuit (step S103). If it is determined that operation of the balancing circuit is necessary (step S103/YES), the microprocessor 54 proceeds to step S104. On the other hand, if it is determined that operation of the balancing circuit is not necessary (step S103/NO), the microprocessor 54 ends the process.

When the process proceeds to step S104, the microprocessor 54 waits until one minute has elapsed since the full charge was detected (step S104).
One minute after detecting the full charge, the microprocessor 54 detects the OCV voltage of each of the battery cells 20-1 to 20-n (step S105). Specifically, the microprocessor 54 acquires from the AFE 53 the measured value of the OCV voltage of each of the battery cells 20-1 to 20-n detected by the AFE 53.

The microprocessor 54 selects a table according to the current value at the end of charging (step S106). Specifically, the microprocessor 54 selects a table of current values corresponding to the current value detected in step S101 immediately before full charge.
Next, the microprocessor 54 calculates the cell capacity of each of the battery cells 20-1 to 20-n from the OCV voltage of each of the battery cells 20-1 to 20-n using a table (step S107). Specifically, the microprocessor 54 calculates the cell capacity of each of the battery cells 20-1 to 20-n corresponding to the OCV voltage of each of the battery cells 20-1 to 20-n detected in step S105 using the table selected in step S106.

The microprocessor 54 then operates the balancing circuit of the AFE circuit element 530 in accordance with the capacity difference between each of the battery cells 20-1 to 20-n (step S108). Specifically, the microprocessor 54 controls the balancing circuit based on the capacity difference calculated from the calculated cell capacity of each of the battery cells 20-1 to 20-n, thereby equalizing the cell voltages of each of the battery cells 20-1 to 20-n. The microprocessor 54 then terminates the process.

3. Second embodiment
Having described the first embodiment of the present invention, a second embodiment of the present invention will now be described with reference to FIG.
In the first embodiment described above, an example was described in which the storage element in the microprocessor 54 stores a plurality of tables in which the correspondence relationship between the OCV voltage and the cell capacity of the battery cell is described, the tables being prepared according to the current value at the end of charging. In contrast, in the second embodiment, it is sufficient to prepare one table in which the correspondence relationship between the OCV voltage and the cell capacity of the battery cell is described. Specifically, in the second embodiment, an example will be described in which it is sufficient to prepare one table corresponding to one predetermined current value.

(operation)
The operation process of the balancing circuit in the storage battery control method will be described with reference to Fig. 16. Fig. 16 is a flowchart showing the operation process of the balancing circuit in the storage battery control method according to the second embodiment of the present invention.

The microprocessor 54 detects the current at the end of charging and adjusts it so that the current value at the end of charging converges to a constant value (step S201). Specifically, the microprocessor 54 detects the current just before full charge and adjusts it so that the detected current value corresponds to a current value stored in a prepared table. In other words, the microprocessor 54 causes the current value at the end of charging to converge to a predetermined current value.

Next, the microprocessor 54 detects full charge (step S202).
After detecting full charge, the microprocessor 54 determines whether or not to operate the balancing circuit (step S203). If it is determined that operation of the balancing circuit is necessary (step S203/YES), the microprocessor 54 proceeds to step S204. On the other hand, if it is determined that operation of the balancing circuit is not necessary (step S203/NO), the microprocessor 54 ends the process.

When the process proceeds to step S204, the microprocessor 54 waits until one minute has elapsed since the full charge was detected (step S204).
One minute after detecting the full charge, the microprocessor 54 detects the OCV voltage of each of the battery cells 20-1 to 20-n (step S205). Specifically, the microprocessor 54 acquires from the AFE 53 the measured values of the OCV voltage of each of the battery cells 20-1 to 20-n detected by the AFE 53.

Next, the microprocessor 54 uses a previously prepared table to calculate the cell capacity of each battery cell 20-1 to 20-n from the OCV voltage of each battery cell 20-1 to 20-n (step S206). Specifically, the microprocessor 54 uses the table to calculate the cell capacity of each battery cell 20-1 to 20-n corresponding to the OCV voltage of each battery cell 20-1 to 20-n detected in step S205.

The microprocessor 54 then operates the balancing circuit of the AFE circuit element 530 in accordance with the capacity difference between each of the battery cells 20-1 to 20-n (step S207). Specifically, the microprocessor 54 controls the balancing circuit based on the capacity difference calculated from the calculated cell capacity of each of the battery cells 20-1 to 20-n, thereby equalizing the cell voltages of each of the battery cells 20-1 to 20-n. The microprocessor 54 then terminates the process.

In the second embodiment, since the relationship between the OCV voltage and the battery cell capacity changes depending on the current value at the end of charging, the current value at the end of charging is set to converge to a constant value. This makes it possible to operate with a single table.

In the first embodiment described above, multiple tables describing the correspondence between the OCV voltage and cell capacity of the battery cell are prepared for each current value, allowing for responses to fluctuating current values. In the second embodiment, the current value at the end of charging is adjusted to be constant, allowing for responses with a single table. Furthermore, instead of a table, a formula may be prepared that can calculate cell capacity from the current value and OCV voltage at the end of charging, and this formula may be used to calculate cell capacity from the detected current value and OCV voltage at the end of charging.

As described above, the storage battery control method according to an embodiment of the present invention is a method for controlling the state of charge of each battery cell in a storage battery in which multiple battery cells are connected in series. This storage battery control method includes a current detection process, a cell voltage detection process, and a calculation process.

In the current detection process, when a storage battery consisting of multiple battery cells connected in series is fully charged, the current value at the end of charging is detected. In the cell voltage detection process, the cell voltage of each battery cell is detected a predetermined time after full charging. In the calculation process, the cell capacity of each battery cell is calculated from the detected current value and cell voltage.

With this configuration, the battery control method according to an embodiment of the present invention, when balancing a battery after fully charging it, can detect the OCV voltage in a range where the OCV voltage changes in accordance with changes in the cell capacity of the battery cells after full charging. Therefore, the battery control method according to an embodiment of the present invention can determine the cell capacity of each battery cell from the OCV voltage in a range where the OCV voltage changes after the battery is fully charged.

Therefore, the battery control method according to an embodiment of the present invention makes it possible to obtain the cell capacity of each battery more accurately and in a shorter time when balancing a battery in which multiple battery cells are connected in series.

The embodiments of the present invention have been described above.
In the above-described embodiment, the power supply system may have the configuration shown in Fig. 17. Fig. 17 is a block diagram showing an outline of another configuration example of the power supply system according to the present invention. In a power supply system 10A in Fig. 17, the solar panel 2, the storage battery unit 3, and the EV stand 4 are each independently connected to power conditioners 1A, 1B, and 1C, respectively.
In FIG. 17 , each of power conditioners 1A, 1B, and 1C supplies or demands power (electrical energy) between a solar panel 2, a storage battery unit 3, and an EV stand 4, respectively, via a distribution board 6.
The configuration and operation of the storage battery unit 3 in FIG. 17 are similar to those of the storage battery unit 3 in each of the embodiments already described.

Furthermore, in the above-described embodiment, the power supply system may have the configuration shown in Fig. 18. Fig. 18 is a block diagram showing an outline of another configuration example of a power supply system according to the present invention. In a power supply system 10B in Fig. 18, the solar panel 2 and the storage battery unit 3 are each connected to a power conditioner 1D, and the EV stand 4 is connected to a power conditioner 1C.
In FIG. 18 , each of power conditioners 1</b>C and 1</b>D supplies or demands power (electrical energy) between a solar panel 2 , a storage battery unit 3 , and an EV stand 4 via a distribution board 6 .
The configuration and operation of the storage battery unit 3 in FIG. 15 are similar to those of the storage battery unit 3 in each of the embodiments already described.

Also, all or part of the power supply system 10 in the above-described embodiment may be implemented by a computer. In this case, a program for implementing this function may be recorded on a computer-readable recording medium, and the program may be loaded into a computer system and executed. Note that the term "computer system" as used herein includes hardware such as an OS and peripheral devices. Furthermore, "computer-readable recording medium" refers to portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, as well as storage devices such as hard disks built into a computer system. Furthermore, "computer-readable recording medium" may also include media that dynamically store programs for a short period of time, such as communication lines used when transmitting programs over networks such as the Internet or telephone lines, or media that store programs for a fixed period of time, such as volatile memory within a computer system that serves as a server or client. The program may be designed to implement some of the above-described functions, or may be capable of implementing the above-described functions in combination with programs already stored in the computer system, or may be implemented using a programmable logic device such as an FPGA.

The above describes in detail an embodiment of the present invention with reference to the drawings, but the specific configuration is not limited to this embodiment and includes designs that do not deviate from the gist of the present invention.

3... Battery unit, 11 (11-1 to 11-7)... Battery module, 12... Control management module, 13 (13-1 to 13-7)... Connector, 14 (14-1 to 14-7)... Connector, 53... AFE, 54... Microprocessor, 530-1 to 530-7... AFE circuit elements

Claims (7)

a current detection step of detecting a current value at the end of charging when a storage battery having a plurality of battery cells connected in series is fully charged;
a cell voltage detection step of detecting the cell voltage of each battery cell after a predetermined time has elapsed since full charge;
a calculation step of calculating a cell capacity of each battery cell from the detected current value and cell voltage;
Including,
In the calculation step, a cell capacity of each battery cell is calculated from the detected current value and cell voltage using a table indicating a relationship between cell voltage and cell capacity that is prepared in advance.
Battery control method. a current detection step of detecting a current value at the end of charging when a storage battery having a plurality of battery cells connected in series is fully charged;
a cell voltage detection step of detecting the cell voltage of each battery cell after a predetermined time has elapsed since full charge;
a calculation step of calculating a cell capacity of each battery cell from the detected current value and cell voltage;
Including,
The predetermined elapsed time is a time that allows the cell voltage to be maintained at a voltage higher than a voltage in a flat region where the cell voltage hardly changes with changes in the cell capacity of the battery cell.
Battery control method. the table is a plurality of tables prepared according to current values at the end of charging,
In the calculation step, a table corresponding to the detected current value is selected from the plurality of prepared tables, and the selected table is used to calculate the cell capacity of each battery cell from the detected cell voltage of each battery cell.
The battery control method according to claim 1 . the table is a single table prepared as a table corresponding to a single predetermined current value,
In the current detection step, the current value at the end of charging is converged to the predetermined current value;
In the calculation step, the cell capacity of each battery cell is calculated from the detected cell voltage of each battery cell using the one prepared table.
The battery control method according to claim 1 . In the calculation step, a cell capacity of each battery cell is calculated from the detected current value and cell voltage using a calculation formula for calculating a cell capacity from a current value and a cell voltage at the end of charging.
The battery control method according to claim 2 . The predetermined elapsed time is one minute.
The battery control method according to claim 2 . a control step of controlling a balancing circuit based on the capacity difference calculated from the calculated capacities of each battery cell to equalize the cell voltages of each battery cell;
The battery control method according to any one of claims 1 to 6 , further comprising: