JP7753982B2 - Discharge current control device and discharge current control method - Google Patents

Description

The present invention relates to a discharge current control device and a discharge current control method for controlling the discharge current of a storage battery in an energy storage system.

The energy storage system described in Patent Document 1 has a function to monitor the voltage of the storage battery during discharge, and if the voltage falls below the over-discharge determination threshold, stop discharging from the storage battery, thereby protecting the storage battery from over-discharge (i.e., an over-discharge protection function). In Patent Document 1, the "over-discharge determination threshold" is called the "second voltage value Vu," and is set a few percent before the remaining capacity at which the storage battery enters an over-discharge state.

JP 2012-175864 A

Generally, a storage battery has the characteristic that the larger the discharge current, the greater the voltage drop. Therefore, with the technology described in Patent Document 1, when the discharge current of a storage battery is large and the battery voltage drops suddenly below the over-discharge determination threshold, discharge is stopped as a protection function, even if there is still some remaining battery capacity, and the remaining capacity (hereinafter referred to as "SOC") displayed to the user at that time is set to 0%. SOC stands for state of charge.

For example, if the battery has a remaining capacity of 10% and the discharge current of the storage battery is large, and the battery voltage drops suddenly below the over-discharge threshold, the over-discharge protection function will prevent further discharge even though there is still capacity to discharge the remaining 10%, and the SOC will be displayed as 0%, causing the apparent battery capacity to appear approximately 10% smaller.
In particular, in a low-temperature environment, the voltage drop of a storage battery increases when the discharge current is large, and the actual usable battery capacity may be reduced by 10% or more of the rated capacity.

In view of the above, the present invention aims to provide a discharge current control device and a discharge current control method that can maximize the use of battery capacity for power supply.

In order to achieve the above object, the inventions according to claims 1 to 5 are as follows:
A discharge current control device for controlling a discharge current of a storage battery (4),
an over-discharge determination threshold (V_od) used for determining over-discharge, a voltage threshold (V_ctr) set to a value greater than the over-discharge determination threshold, and a dischargeable current lower limit value set to a value smaller than a dischargeable current value in normal times and greater than 0,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, the current value (Iout) that can be discharged from the storage battery is controlled to be switched from the normal dischargeable current value to the lower limit of the dischargeable current value.
Furthermore, in the invention according to claim 1, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and after a predetermined time has elapsed since the execution of this control, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In the invention according to claim 2, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
When the voltage of the storage battery becomes smaller than the voltage threshold during discharging of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and if the amount of change in battery voltage per hour remains constant or decreases after a predetermined time has elapsed since the control was executed, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In the invention according to claim 3, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
When the voltage of the storage battery becomes smaller than the voltage threshold during discharging of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and when the voltage of the storage battery becomes smaller than the voltage threshold again after a predetermined time has elapsed since the execution of this control, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In the invention according to claim 4, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
the voltage thresholds include a first voltage threshold (V_ctr1) for switching from the normal dischargeable current value to the first dischargeable current lower limit value, and a second voltage threshold (V_ctr2) for switching from the first dischargeable current lower limit value to the second dischargeable current lower limit value,
When the voltage of the storage battery becomes smaller than the first voltage threshold or the second voltage threshold during discharging of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and when the voltage of the storage battery becomes smaller than the second voltage threshold after a predetermined time has elapsed since the control was executed, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In the invention according to claim 5, a throttle release voltage threshold (V_rel) for releasing the control in which the current value that can be discharged from the storage battery has been switched to the dischargeable current lower limit value is stored,
When the voltage of the storage battery becomes higher than the throttle release voltage threshold, control is performed to switch the value of the current that can be discharged from the storage battery from the dischargeable current lower limit value to the dischargeable current value under normal conditions.

According to this, even if the battery discharge current is large and the battery voltage drops suddenly, when the battery voltage falls below the voltage threshold, the current value that can be discharged from the battery switches from the normal discharge current value to the discharge current lower limit. This limits the current value discharged from the battery, thereby preventing a sudden drop in battery voltage. Specifically, when the current value that can be discharged from the battery switches to the discharge current lower limit, the battery voltage rises once and then gradually drops. Therefore, even when the battery discharge current is large, a sudden drop in battery voltage is prevented midway, preventing the battery voltage from dropping below the over-discharge determination threshold even when there is still some remaining battery capacity, and allowing the actual battery capacity to be used to its full potential for power supply.

The inventions according to claims 7 to 12 provide a discharge current control method for controlling the discharge current of a storage battery (4), comprising:
a dischargeable current value during normal operation, a dischargeable current lower limit value that is smaller than the dischargeable current value during normal operation and larger than 0, an over-discharge determination threshold value (V_od) used for determining over-discharge, and a voltage threshold value (V_ctr) that is larger than the over-discharge determination threshold value are set;
When the voltage of the storage battery becomes lower than the voltage threshold during discharge of the storage battery, control is performed to switch the current value (Iout) that can be discharged from the storage battery from the normal dischargeable current value to the lower limit of the dischargeable current value.
In a seventh aspect of the present invention, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and after a predetermined time has elapsed since the control was executed, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In an eighth aspect of the present invention, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
When the voltage of the storage battery becomes smaller than the voltage threshold during discharge of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and if the amount of change per unit time in the battery voltage remains constant or decreases after a predetermined time has elapsed since the control was executed, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In the invention according to claim 9, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
When the voltage of the storage battery becomes smaller than the voltage threshold during discharging of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and when the voltage of the storage battery becomes smaller than the voltage threshold again after a predetermined time has elapsed since the control was executed, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In the invention according to claim 10, the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
the voltage thresholds include a first voltage threshold (V_ctr1) for switching from the normal dischargeable current value to the first dischargeable current lower limit value, and a second voltage threshold (V_ctr2) for switching from the first dischargeable current lower limit value to the second dischargeable current lower limit value,
When the voltage of the storage battery becomes lower than the first voltage threshold or the second voltage threshold during discharging of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and when the voltage of the storage battery becomes lower than the second voltage threshold after a predetermined time has elapsed since the control was executed, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
In the invention according to claim 11, a throttle release voltage threshold (V_rel) is set to release the control in which the current value that can be discharged from the storage battery has been switched to the dischargeable current lower limit value,
When the voltage of the storage battery becomes higher than the throttle release voltage threshold, control is performed to switch the current value that can be discharged from the storage battery from the dischargeable current lower limit to the dischargeable current value in normal operation.
In the invention according to claim 12, a power storage system in which the storage battery is used is connected to a power generation device (4) capable of supplying power to a load (2) together with the storage battery, a power storage device (5), and a commercial power system (1),
When the discharge power supplied from the storage battery to the load is insufficient, control is performed to supply power to the load from at least one of the power generation device, the power storage device, and the commercial power system.

Note that the reference symbols in parentheses attached to each component indicate an example of the correspondence between that component and the specific components described in the embodiments described below.

1 is a schematic diagram illustrating an example of the configuration of a power storage system in which a discharge current control device and a discharge current control method according to a first embodiment are used; FIG. 4 is a schematic diagram showing another example of the configuration of a power storage system in which the discharge current control device and the discharge current control method according to the first embodiment are used. 4 is a graph showing an example of discharge current control according to the first embodiment. 3 is a flowchart showing a control process executed by the discharge current control device according to the first embodiment. 1 is a graph showing an example of conventional discharge current control. 10 is a graph showing an example of discharge current control according to the second embodiment. 10 is a flowchart showing a control process executed by a discharge current control device according to a second embodiment. 10 is a flowchart showing a control process executed by a discharge current control device according to a second embodiment. 10 is a flowchart showing a control process executed by a discharge current control device according to a first modified example of the second embodiment. 10 is a flowchart showing a control process executed by a discharge current control device according to a first modified example of the second embodiment. 10 is a graph showing an example of discharge current control according to a second modified example of the second embodiment. 10 is a graph showing an example of discharge current control according to the third embodiment. 10 is a graph showing an example of discharge current control according to the fourth embodiment. 10 is a flowchart showing a control process executed by a discharge current control device according to a fifth embodiment.

Embodiments of the present invention will be described below with reference to the drawings. Note that, in the following embodiments, identical or equivalent parts will be designated by the same reference numerals, and their description will be omitted.

(First embodiment)
A first embodiment will be described with reference to the drawings. In the first embodiment, a power storage system using a discharge current control device and a discharge current control method will be described.

Figure 1 shows one example configuration of a power storage system (hereinafter referred to as "first example configuration"). As shown in Figure 1, the power storage system electrically connects a storage battery 4, a power generation device 5, a power storage device 6, etc. to a power line 3 that supplies power from a commercial power system 1 (hereinafter simply referred to as "system 1") to a load 2 such as a home appliance.

The storage battery 4 has a battery module (not shown) in which multiple battery cells are connected in series or series-parallel, and a control unit 7 that controls the battery module. The control unit 7 is composed of a microcomputer including a processor and memories such as ROM and RAM, and its peripheral circuits. The control unit 7 controls the charging and discharging of the battery module by the processor executing a program stored in the memory. Therefore, in the first configuration example of the power storage system, the control unit 7 of the storage battery 4 corresponds to an example of a discharge current control device that controls the discharge current of the storage battery 4.

The memory of the control unit 7 of the storage battery 4 stores the over-discharge determination threshold V_od, voltage threshold V_ctr, dischargeable current lower limit, throttle release voltage threshold V_rel, and other data to control the charging and discharging of the battery module.

The over-discharge determination threshold V_od is a threshold used to determine whether the storage battery 4 is over-discharged. The over-discharge determination threshold V_od is set to a value a few percent before the remaining capacity at which the storage battery 4 reaches an over-discharge state.

The voltage threshold V_ctr is a threshold set to a value greater than the overdischarge determination threshold V_od, and is used to switch the current value that can be discharged from the storage battery 4 (hereinafter referred to as the "dischargeable current value Iout"). The voltage threshold V_ctr can be a fixed value.

The dischargeable current lower limit is a current value that is set to a value that is smaller than the dischargeable current value under normal conditions (hereinafter referred to as the "normal dischargeable current value") and greater than 0. The dischargeable current lower limit may be a preset fixed value, or may be determined by mapping the optimal value using parameters such as the remaining capacity of the storage battery 4 (hereinafter referred to as the "SOC") and battery temperature to be displayed to the user.

The throttle release voltage threshold V_rel is a threshold used when canceling the control that switched the dischargeable current value Iout from the normal dischargeable current value to the lower limit dischargeable current value and returning it to the normal dischargeable current value. The throttle release voltage threshold V_rel is set to a value greater than the voltage threshold V_ctr. The throttle release voltage threshold V_rel may also be a value determined according to the battery temperature, or may be a unique value for simplicity.

The power generation device 5 is composed of, for example, a solar power generation device (PV) and a fuel cell device. PV stands for photovoltaics. The power storage device 6 is composed of, for example, an on-board storage battery (V2X). V2X stands for Vehicle to X. The power generation device 5 and power storage device 6 each have control units 8 and 9 that control their own charging and discharging.

The storage battery 4, power generation device 5, and power storage device 6 are controlled by a system controller 10. The system controller 10 is, for example, configured as an energy management system (EMS) terminal. EMS includes HEMS, BEMS, FEMS, CEMS, etc. HEMS stands for Home Energy Management Service. BEMS stands for Building and Energy Management System. FEMS stands for Factory Energy Management System. CEMS stands for Community Energy Management System. Note that a HEMS is used as the system controller 10 for a system that manages residential energy. The system controller 10 monitors and optimizes the performance of the storage battery 4, power generation device 5, and power storage device 6. Note that in Figure 1, dashed lines indicate communication lines between the system controller 10 and the control units 7-9 of the storage battery 4, power generation device 5, and power storage device 6, respectively.

Figure 2 also shows another example configuration of a power storage system (hereinafter referred to as the "second example configuration"). As shown in Figure 2, the power storage system electrically connects a storage battery 4, a power generation device 5, a power storage device 6, and the like to a power line 3 that supplies power from a grid 1 to a load 2 via a power conditioner 11. Note that, in this specification, power conditioners that can connect to multiple devices, such as hybrid power conditioners that can connect to two devices and tri-brid power conditioners that can connect to three devices, are collectively referred to as "power conditioners." The power conditioner 11 includes a power converter (not shown) and a control unit 12. The power converter includes an inverter, a converter, and the like. The control unit 12 includes a microcomputer including a processor and memories such as ROM and RAM, as well as its peripheral circuits. The control unit 12 controls the charging and discharging of the storage battery 4, the power generation device 5, and the power storage device 6 by the processor executing programs stored in the memory. Therefore, in the second configuration example of the power storage system, the control unit 12 of the power conditioner 11 corresponds to an example of a discharge current control device that controls the discharge current of the storage battery 4. The memory of the control unit 12 of the power conditioner 11 also stores an overdischarge determination threshold V_od, a voltage threshold V_ctr, a dischargeable current lower limit, a throttle release voltage threshold V_rel, and the like, for controlling the charging and discharging of the battery modules of the storage battery 4.

As described above, the power conditioner 11 controls the charging and discharging of the storage battery 4, the power generation device 5, and the power storage device 6. Therefore, when there is a shortage of discharged power supplied from the storage battery 4 to the load 2, the power conditioner 11 can execute control to supply power to the load 2 from at least one of the power generation device 5 other than the storage battery 4, the power storage device 6, and the grid 1. This allows power to continue to be supplied to the load 2 from other power sources even when there is a shortage of discharged power supplied from the storage battery 4 to the load 2, thereby preventing the load 2 from shutting down. This control is particularly effective during stand-alone operation when the grid 1 experiences a power outage, when power supply from the grid 1 cannot be relied upon.

In the following description, the control unit 7 of the storage battery 4 in the first configuration example and the control unit 12 of the power conditioner 11 in the second configuration example that controls the discharge current of the storage battery 4 are referred to as the "discharge current control device."

Next, we will explain how the discharge current control of the storage battery 4 is performed by the discharge current control device according to the first embodiment.

Figure 3 shows an example of discharge current control performed by the discharge current control device when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

The vertical axis of Fig. 3A represents the voltage (i.e., battery voltage) [V] of the storage battery 4 and the percentage [%] of the SOC, and the horizontal axis of Fig. 3A represents time [ms].
A solid line A in Fig. 3A indicates the transition of the battery voltage when the discharge current of the storage battery 4 is large. A solid line B in Fig. 3A indicates the SOC.

On the other hand, the vertical axis of Figure 3(B) represents current [A]. The horizontal axis of Figure 3(B) represents time [ms]. Solid line C in Figure 3(B) represents the dischargeable current value Iout. Note that these are the same as in Figures 5, 6, and 9 to 11, which will be referenced in the following explanation, except for the symbols attached to the solid lines.

As shown by solid line A in Figure 3(A), after time t1, the battery voltage drops sharply due to the large discharge current of the storage battery 4. As shown by solid line C in Figure 3(B), from before time t1 to time t2, the dischargeable current value Iout is set to the normal dischargeable current value. Therefore, from before time t1 to time t2, the storage battery 4 can discharge within a range below the normal dischargeable current value.

As shown by solid line A in Figure 3(A), at time t2, the battery voltage becomes smaller than the voltage threshold V_ctr. As a result, the discharge current control device executes control to switch the dischargeable current value Iout from the normal dischargeable current value to the lower limit dischargeable current value. Therefore, as shown by solid line C in Figure 3(B), at time t2, the dischargeable current value Iout is switched from the normal dischargeable current value to the lower limit dischargeable current value. Therefore, between time t2 and time t4, the storage battery 4 can discharge within the range of the lower limit dischargeable current value. In other words, the discharge current of the storage battery 4, which was in a range below the normal dischargeable current value from before time t1 to time t2, is narrowed to a range below the lower limit dischargeable current value from time t2 onwards.

After time t2, when the discharge current is reduced, a sudden drop in battery voltage is suppressed. Specifically, as shown by solid line A in Figure 3(A), the battery voltage rises once after time t2, and then begins to drop gradually after time t3. This suppresses a sudden drop in battery voltage, lengthening the time it takes for the battery voltage to drop to the overdischarge determination threshold V_od. Then, at time t4, the battery voltage becomes smaller than the overdischarge determination threshold V_od. Therefore, the discharge current control device sets the dischargeable current value Iout to 0 at time t4, and stops discharging.

As shown by solid line B in Figure 3(A), the SOC shows a nearly constant rate of decline after time t2, reaching 0% at time t4. Therefore, even when the discharge current of storage battery 4 is large, the discharge current control device of the first embodiment can use the battery capacity up to the lower limit of the rated capacity by performing the discharge current control described above.

Next, the discharge current control performed by the discharge current control device of the first embodiment will be explained with reference to the flowchart in Figure 4. This control process is repeatedly performed at predetermined control time intervals.

First, in step S10, the dischargeable power value Wout(t) and battery voltage V(t) of the storage battery 4 are acquired. The discharge current control device may acquire information about the dischargeable power value Wout(t) and battery voltage V(t) from a battery control ECU (not shown), or may acquire this information itself. ECU stands for Electronic Control Unit. The discharge current control device then calculates the dischargeable current base value Iout_b(t), which serves as the base value for the discharge current of the storage battery 4, by dividing the dischargeable power value Wout(t) by the battery voltage V(t). Note that all of these values are values at the control time when the control process is executed, so the symbols are suffixed with (t).

Next, in step S20, it is determined whether the SOC is 0%. Whether the SOC is 0% is determined by whether the battery voltage is lower than the over-discharge determination threshold V_od. Specifically, if the battery voltage is lower than the over-discharge determination threshold V_od, the SOC is determined to be 0%. On the other hand, if the battery voltage is equal to or higher than the over-discharge determination threshold V_od, the SOC is determined to be not 0%.

If the SOC is 0%, processing proceeds to step S30. In step S30, the dischargeable current limit value Iout_c(t) is set to 0.

On the other hand, if the SOC is not 0% in step S20, the process proceeds to step S40.
In step S40, it is determined whether the battery voltage V(t) is greater than the throttle release voltage threshold V_rel(T). In this embodiment, the throttle release voltage threshold V_rel(T) is a value determined according to the battery temperature, and therefore the symbol ends with (T).
If the battery voltage V(t) is greater than the throttle release voltage threshold V_rel(T) in step S40, the process proceeds to step S50. In step S50, state is set to 0 (i.e., the state flag is set to "0"). This cancels the control in step S70, described below, in which state was set to 1 (i.e., the state flag was set to "1"). After step S50, the process proceeds to step S60.

On the other hand, if in step S40 the battery voltage V(t) is equal to or lower than the throttle release voltage threshold V_rel(T), processing proceeds to step S60 without going through step S50. In step S60, it is determined whether the battery voltage V(t) is lower than the voltage threshold V_ctr. If the battery voltage V(t) is lower than the voltage threshold V_ctr, processing proceeds to step S70. In step S70, state = 1 (i.e., the state flag is "1") is set, and then processing proceeds to step S80. In step S80, the dischargeable current throttle value Iout_c(t) is set to the dischargeable current lower limit value.

On the other hand, if the battery voltage V(t) is equal to or greater than the voltage threshold V_ctr in step S60, processing proceeds to step S90. In step S90, it is determined whether state is "1". If state is not "1" (i.e., if state = 0), processing proceeds to step S100. In step S100, the dischargeable current throttle value Iout_c(t) is set to the dischargeable current base value Iout_b(t).

On the other hand, if state is "1" in step S70, processing proceeds to step S110. In step S110, the dischargeable current limit value Iout_c(t) is set as the dischargeable current lower limit value.

After steps S30, S80, S100, and S110, the process proceeds to step S120. In step S120, the dischargeable current value Iout(t) is set to the smaller of the dischargeable current base value Iout_b(t) or the dischargeable current throttle value Iout_c(t).

After step S120, the above-described control process is repeated again from S10.

Here, we will explain the discharge current control performed by a discharge current control device of a comparative example, for comparison with the discharge current control performed by the discharge current control device of the first embodiment described above. The discharge current control device of the comparative example stores an overdischarge determination threshold V_od, a throttle release voltage threshold V_rel, and a normal dischargeable current value in its memory, but does not store a voltage threshold V_ctr or a dischargeable current lower limit value.

Figure 5 shows the discharge current control performed by the discharge current control device of the comparative example when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

As shown by solid line D in Figure 5(A), after time t11, the battery voltage drops sharply due to the large discharge current of storage battery 4. As shown by solid line F in Figure 5(B), from before time t11 to time t12, the dischargeable current value Iout is set to the normal dischargeable current value. Therefore, from before time t11 to time t12, storage battery 4 can discharge within a range below the normal dischargeable current value.

As shown by solid line D in Figure 5(A), at time t12, the battery voltage becomes smaller than the over-discharge determination threshold V_od. As a result, the discharge current control device sets the dischargeable current value Iout to 0 and stops discharging. At this time, as shown by solid line E, the SOC drops sharply to 0% at time t12, even though there is still some remaining battery capacity.

Dotted line G in Figure 5(A) shows what would happen if the original remaining battery capacity were discharged to the lower limit of the rated capacity. As shown by this dashed line G, if the SOC continued to decrease at a constant rate after time t12, the SOC would reach 0% at time t13. Therefore, in the comparative example, it can be seen that the original battery capacity cannot be discharged by the amount indicated by the hatched area H in Figure 5(B).

In contrast to the discharge current control device of the comparative example, the discharge current control device and discharge current control method of the first embodiment have the following configuration and the resulting effects:

(1) The discharge current control device of this embodiment is configured to control the dischargeable current value Iout of the storage battery 4 to be switched from the normal dischargeable current value to the lower limit dischargeable current value when the voltage of the storage battery 4 becomes lower than the voltage threshold V_ctr during discharging of the storage battery 4.
According to this, even when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly, if the battery voltage falls below the voltage threshold V_ctr before reaching the overdischarge determination threshold V_od, the dischargeable current value Iout of the storage battery 4 is switched from the normal dischargeable current value to the dischargeable current lower limit value. This reduces the dischargeable current value Iout of the storage battery 4, thereby suppressing a sudden drop in the battery voltage. Specifically, when the dischargeable current value Iout of the storage battery 4 switches to the dischargeable current lower limit value, the battery voltage rises once and then gradually drops, as shown by the solid line A in FIG. 3 . Therefore, by suppressing a sudden drop in the battery voltage, it is possible to prevent the battery voltage from falling below the overdischarge determination threshold V_od and stopping discharge even when there is still some remaining battery capacity, thereby making it possible to maximize the use of the original battery capacity for power supply.

(2) In this embodiment, when there is a shortage of discharge power supplied from the storage battery 4 to the load 2, the discharge current control device is configured to supply power to the load 2 from at least one of the power generation device 5 other than the storage battery 4, the power storage device 6, and the system 1.
According to this, even when the discharge power supplied from the storage battery 4 to the load 2 is insufficient, the discharge current control device can continue to supply power to the load 2 by supplying power to the load 2 from another power source, thereby preventing the load 2 from stopping operation. This control is particularly effective during stand-alone operation when the grid 1 experiences a power outage, since the power supply from the grid 1 cannot be relied upon.

(3) In this embodiment, the discharge current control device is configured to control the dischargeable current value Iout of the storage battery 4 to be switched from the dischargeable current lower limit value to the dischargeable current normal value when the voltage of the storage battery 4 becomes greater than the throttling release voltage threshold V_rel.
According to this, when the storage battery 4 is charged and the battery voltage becomes higher than the throttle release voltage threshold V_rel, the dischargeable current value Iout of the storage battery 4 switches from the dischargeable current lower limit value back to the dischargeable current normal value.

(4) The discharge current control method of this embodiment controls the dischargeable current value Iout of the storage battery 4 to be switched from the normal dischargeable current value to the lower limit dischargeable current value when the voltage of the storage battery 4 becomes lower than the voltage threshold V_ctr during discharging of the storage battery 4.
According to this control method, even if the discharge current of the storage battery 4 is large and the battery voltage drops suddenly, control is executed to suppress the sudden drop in battery voltage during the voltage drop, so that the original battery capacity can be used to the maximum for power supply.

Second Embodiment
The second embodiment is different from the first embodiment in that the discharge current control executed by the discharge current control device is partially changed, and the other parts are the same as those of the first embodiment, so only the parts that are different from the first embodiment will be described.

The discharge current control device of the second embodiment is configured to switch the dischargeable current lower limit value in multiple stages. At least a first dischargeable current lower limit value and a second dischargeable current lower limit value are stored in the memory of the discharge current control device of the second embodiment as the dischargeable current lower limit values. The second dischargeable current lower limit value is a value smaller than the first dischargeable current lower limit value. Note that, in addition to the first and second dischargeable current lower limit values, three or more dischargeable current lower limit values may be stored as the dischargeable current lower limit values.

The first and second dischargeable current lower limit values may be preset fixed values, as in the first embodiment, or may be determined by mapping optimal values using parameters such as SOC and battery temperature.

This section describes how the discharge current control of the storage battery 4 is performed using the discharge current control device according to the second embodiment.

Figure 6 shows an example of discharge current control performed by the discharge current control device when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

As shown by solid line I in Figure 6(A), after time t21, the battery voltage drops sharply due to the large discharge current of storage battery 4. As shown by solid line J in Figure 6(B), from before time t21 to time t22, the dischargeable current value Iout is set to the normal dischargeable current value. Therefore, from before time t21 to time t22, storage battery 4 can discharge within a range below the normal dischargeable current value.

As shown by solid line I in Figure 6(A), at time t22, the battery voltage becomes lower than the voltage threshold V_ctr. As a result, the discharge current control device executes control to switch the dischargeable current value Iout from the normal dischargeable current value to the first dischargeable current lower limit. Therefore, as shown by solid line J in Figure 6(B), at time t22, the dischargeable current value Iout is switched from the normal dischargeable current value to the first dischargeable current lower limit. Therefore, between time t22 and time t24, the storage battery 4 can discharge within the dischargeable current lower limit. In other words, the discharge current of the storage battery 4, which was in a range below the normal dischargeable current value from before time t21 to time t22, is narrowed to a range below the first dischargeable current lower limit from time t22 onwards.

After time t22, the discharge current is reduced, preventing a sudden drop in battery voltage. Specifically, as shown by solid line I in Figure 6(A), the battery voltage rises once after time t22, and then begins to gradually decrease after time t23. Then, as shown by solid line J in Figure 6(B), at time t24, a predetermined time T [ms] after time t22, the discharge current control device switches the dischargeable current value Iout from the first dischargeable current lower limit to the second dischargeable current lower limit. Therefore, between time t24 and time t26, the storage battery 4 can discharge within the range of the second dischargeable current lower limit. In other words, the discharge current of the storage battery 4, which was within the range of the first dischargeable current normal value between time t22 and time t24, is reduced to within the range of the second dischargeable current lower limit after time t24.

As shown by the solid line I in Figure 6 (A), after time t24, the battery voltage rises once and then gradually decreases. Then, at time t25, the battery voltage becomes smaller than the overdischarge determination threshold V_od. Therefore, the discharge current control device sets the dischargeable current value Iout to 0 and stops discharging. Therefore, even when the discharge current of the storage battery 4 is large, the discharge current control device of the second embodiment can use the battery capacity up to the lower limit of the rated capacity by gradually lowering the dischargeable current value using the discharge current control described above.

Next, the discharge current control performed by the discharge current control device of the second embodiment will be described with reference to the flowcharts in Figures 7A and 7B. This control process is repeatedly performed at predetermined control time intervals.

First, in step S210, the dischargeable power value Wout(t) and battery voltage V(t) of the storage battery 4 are obtained. Then, the dischargeable power value Wout(t) is divided by the battery voltage V(t) to calculate the dischargeable current base value Iout_b(t), which is the base value for the discharge current of the storage battery 4.

Next, in step S220, it is determined whether the SOC is 0%. Whether the SOC is 0% is determined by whether the battery voltage is lower than the over-discharge determination threshold V_od. Specifically, if the battery voltage is lower than the over-discharge determination threshold V_od, the SOC is determined to be 0%. On the other hand, if the battery voltage is equal to or higher than the over-discharge determination threshold V_od, the SOC is determined to be not 0%.

If the SOC is 0%, processing proceeds to step S230. In step S230, the dischargeable current limit value Iout_c(t) is set to 0.

On the other hand, if the SOC is not 0% in step S220, the process proceeds to step S240.
In step S240, it is determined whether the battery voltage V(t) is greater than the throttle release voltage threshold V_rel(T). If the battery voltage V(t) is greater than the throttle release voltage threshold V_rel(T), processing proceeds to step S250. In step S250, state is set to 0 (i.e., state flag is "0"). This cancels the control in step S280 (described later) in which state was set to 1 (i.e., state flag was "1"), or the control in step S310 in which state was set to 2 (i.e., state flag was "2"). After step S250, processing proceeds to step S260.

On the other hand, if in step S240 the battery voltage V(t) is equal to or less than the throttle release voltage threshold V_rel(T), processing proceeds to step S260 without going through step S250. In step S260, it is determined whether the battery voltage V(t) is less than the voltage threshold V_ctr. If the battery voltage V(t) is less than the voltage threshold V_ctr, processing proceeds to step S270.

In step S270, it is determined whether the current state flag is state = 0. If state = 0 (i.e., the current state flag is "0") in step S270, processing proceeds to step S280. Then, in step S280, state is switched to 1 (i.e., the state flag is set to "1"), and processing proceeds to step S290. In step S290, the dischargeable current limit value Iout_c(t) is set to the first dischargeable current lower limit value.

On the other hand, if state = 0 (i.e., the current state flag is not "0") in step S270, processing proceeds to step S300. Then, it is determined whether a predetermined time T [ms] or more has elapsed since state = 1 (i.e., the state flag is "1") in step S300. This determination process makes it possible to set a voltage reading wait time that takes into account the response speed of the control circuit and the sensor reading speed after the state flag transitions from "0" to "1." The voltage reading wait time is set for the following reason: After the discharge current is reduced, the battery voltage temporarily increases. If the battery voltage were to be monitored during this time, this control would be affected by chattering, in which the battery voltage repeatedly increases and decreases in a short period of time. Therefore, by temporarily not monitoring the battery voltage, the effects of chattering can be prevented.

If the predetermined time T [ms] has not elapsed since state = 1 (i.e., the state flag is set to "1") in step S300, processing proceeds to step S290. In step S290, the dischargeable current throttle value Iout_c(t) is set to the first dischargeable current lower limit value.

On the other hand, if a predetermined time T [ms] or more has elapsed since state = 1 (i.e., the state flag is "1") in step S300, processing proceeds to step S310. In step S310, state = 2 (i.e., the state flag is "2") is set, and processing proceeds to step S320. In step S320, the dischargeable current limit value Iout_c(t) is set to the second dischargeable current lower limit value.

On the other hand, if the battery voltage V(t) is greater than or equal to the voltage threshold V_ctr in step S260, processing proceeds to step S330. In step S330, it is determined whether state is greater than "0". If state is less than or equal to "0" (i.e., state = 0), processing proceeds to step S340. In step S340, the dischargeable current throttle value Iout_c(t) is set to the dischargeable current base value Iout_b(t).

On the other hand, if state is greater than "0" in step S330 (i.e., if state = 1 or 2), processing proceeds to step S350. In step S350, the dischargeable current limit value Iout_c(t) is set to the previous dischargeable current lower limit value (i.e., the first dischargeable current lower limit value or the second dischargeable current lower limit value).

After steps S230, S290, S320, S340, and S350, the process proceeds to step S360. In step S360, the dischargeable current value Iout(t) is set to the smaller of the dischargeable current base value Iout_b(t) or the dischargeable current throttle value Iout_c(t).

After step S360, the above-described control process is repeated again from S210.

The discharge current control device and discharge current control method of the second embodiment described above have the following configuration and provide the following effects.

In the second embodiment, when the voltage of the storage battery 4 becomes lower than the voltage threshold V_ctr during discharging of the storage battery 4, control is performed to switch the dischargeable current value Iout of the storage battery 4 from the normal dischargeable current value to the first dischargeable current lower limit value. Furthermore, after a predetermined time T [ms] has elapsed since the execution of this control, control is performed to switch the dischargeable current value Iout from the first dischargeable current lower limit value to the second dischargeable current lower limit value.
According to this, by reducing the dischargeable current value Iout of the storage battery 4 in multiple stages, a sudden decrease in the discharge current can be suppressed, the battery voltage can be gradually reduced, and the original battery capacity can be used to the maximum extent for power supply.

(First Modification of Second Embodiment)
A first modified example of the second embodiment will be described with reference to the flowcharts of Figures 8A and 8B. As shown in Figure 8B, in the first modified example of the second embodiment, the process described in step S300 in the description of the second embodiment above is changed to step S301.

In the above description of the second embodiment, step S300 determines whether a predetermined time T [ms] or more has elapsed since state = 1 (i.e., the state flag is "1"). In contrast, in the first modified example of the second embodiment, step S301 determines whether a change in battery voltage has occurred. Specifically, if the change in battery voltage per unit time is greater than 0 (i.e., if it is increasing), processing proceeds to step S290 (i.e., state = 1 is maintained). On the other hand, if the change in battery voltage per unit time is equal to or less than 0 (i.e., if it is constant or decreasing), processing proceeds to step S310 (i.e., state = 2 is switched).

The discharge current control device and discharge current control method of the first variant of the second embodiment described above have the following configuration and provide the following effects.

In the first modified example of the second embodiment, if the voltage of the storage battery 4 becomes lower than the voltage threshold V_ctr during discharge of the storage battery 4, control is performed to switch the dischargeable current value Iout of the storage battery 4 from the normal dischargeable current value to the first dischargeable current lower limit value. Furthermore, if the battery voltage remains constant or decreases after a predetermined time has elapsed since the execution of this control, control is performed to switch the dischargeable current value Iout from the first dischargeable current lower limit value to the second dischargeable current lower limit value. As a result, the first modified example of the second embodiment can achieve the same effects as the second embodiment.

(Second Modification of Second Embodiment)
A second modification of the second embodiment will be described with reference to the graph of Fig. 9. Fig. 9 shows an example of discharge current control performed by the discharge current control device of the second modification of the second embodiment when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

In the first embodiment described above, control is described in which the dischargeable current value Iout is reduced in two stages, while in the second embodiment and its first variant described above, control is described in which the dischargeable current value Iout is reduced in three stages. In contrast, the second variant of the second embodiment controls the dischargeable current value Iout to be reduced in multiple stages.

Figure 9 shows an example of discharge current control performed by the discharge current control device when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

As shown by the solid line K in Figure 9(A), from time t31 onwards, the battery voltage drops sharply due to the large discharge current of the storage battery 4. As shown by the solid line L in Figure 9(B), between time t31 and time t32, the dischargeable current value Iout is set to the normal dischargeable current value.

As shown by the solid line K in Figure 9 (A), at time t32, the battery voltage becomes smaller than the voltage threshold V_ctr. As a result, the discharge current control device executes control to switch the dischargeable current value Iout from the normal dischargeable current value to the dischargeable current lower limit value. Here, in the second variant of the second embodiment, control is executed to lower the dischargeable current lower limit value in multiple stages over time. Therefore, as shown by the solid line L in Figure 9 (B), from time t32 onwards, the dischargeable current value Iout continuously decreases over time.

Then, at time t33, the discharge current control device sets the dischargeable current value Iout to 0 and stops discharging. Therefore, even when the discharge current of the storage battery 4 is large, the discharge current control device of the second modified example of the second embodiment can use the battery capacity up to the lower limit of the rated capacity by performing control to continuously lower the dischargeable current value over time through discharge current control.

(Third embodiment)
A third embodiment will be described. The third embodiment is similar to the first embodiment in that the discharge current control executed by the discharge current control device is partially changed, but the remaining parts are the same as the first embodiment. Therefore, only the parts that are different from the first embodiment will be described.

The discharge current control device of the third embodiment is also configured to switch the dischargeable current lower limit in multiple stages. At least a first dischargeable current lower limit and a second dischargeable current lower limit are stored in the memory of the discharge current control device of the third embodiment as the dischargeable current lower limit. The second dischargeable current lower limit is a value smaller than the first dischargeable current lower limit. Note that, in addition to the first and second dischargeable current lower limit, three or more dischargeable current lower limit values may be stored as the dischargeable current lower limit.

The discharge current control of the storage battery 4 by the discharge current control device of the third embodiment will be described with reference to Figure 10. Figure 10 shows an example of the discharge current control performed by the discharge current control device of the third embodiment when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

As shown by the solid line M in Figure 10(A), after time t41, the battery voltage drops sharply due to the large discharge current of the storage battery 4. As shown by the solid line O in Figure 10(B), from before time t41 to time t42, the dischargeable current value Iout is set to the normal dischargeable current value. Therefore, from before time t41 to time t42, the storage battery 4 can discharge within a range below the normal dischargeable current value.

As shown by the solid line M in Figure 10(A), at time t42 the battery voltage becomes lower than the voltage threshold V_ctr. As a result, as shown by the solid line O in Figure 10(B), the discharge current control device switches the dischargeable current value Iout from the normal dischargeable current value to the first dischargeable current lower limit. Therefore, between time t42 and time t44, the storage battery 4 can discharge within the range of the first dischargeable current lower limit. In other words, the discharge current of the storage battery 4, which was in a range below the normal dischargeable current value from before time t41 to time t42, is narrowed to a range below the first dischargeable current lower limit from time t42 onwards.

After time t42, the discharge current is reduced, preventing a sudden drop in battery voltage. Specifically, as shown by the solid line M in FIG. 10(A), the battery voltage rises once after time t42, then begins to gradually decrease after time t43. Then, at time t44, the battery voltage again falls below the voltage threshold V_ctr. As a result, as shown by the solid line O in FIG. 10(B), the discharge current control device switches the dischargeable current value Iout from the first dischargeable current lower limit to the second dischargeable current lower limit. Therefore, between time t44 and time t46, the storage battery 4 can discharge within the range of the second dischargeable current lower limit. In other words, the discharge current of the storage battery 4, which was below the first normal dischargeable current value between time t42 and time t44, is reduced to below the second dischargeable current lower limit after time t44.

As shown by the solid line M in Figure 10(A), the battery voltage rises once after time t44, and then begins to gradually decrease after time t45. Then, at time t46, the battery voltage becomes smaller than the overdischarge determination threshold V_od. Therefore, the discharge current control device sets the dischargeable current value Iout to 0 and stops discharging.

As shown by the solid line N in Figure 10(A), the SOC shows a nearly constant rate of decline, reaching 0% at time t46. Therefore, the discharge current control device of the third embodiment can use the battery capacity up to the lower limit of the rated capacity by performing the discharge current control described above, even when the discharge current of the storage battery 4 is large.

(Fourth embodiment)
A fourth embodiment will be described. The fourth embodiment is similar to the first embodiment in that the discharge current control executed by the discharge current control device is partially changed, but the remaining parts are the same as the first embodiment, and therefore only the parts that are different from the first embodiment will be described.

The discharge current control device of the fourth embodiment is also configured to switch the dischargeable current lower limit in multiple stages. The memory of the discharge current control device of the fourth embodiment stores at least a first voltage threshold V_ctr1 and a second voltage threshold V_ctr2 as the voltage threshold V_ctr. The first voltage threshold V_ctr1 is a voltage threshold for switching from the normal dischargeable current value to the first dischargeable current lower limit. The second voltage threshold V_ctr2 is a voltage threshold for switching from the first dischargeable current lower limit to the second dischargeable current lower limit. In addition to the first and second voltage thresholds, three or more voltage thresholds may be stored as the voltage threshold V_ctr.

Furthermore, as in the second and third embodiments, the memory of the discharge current control device of the fourth embodiment stores at least a first dischargeable current lower limit and a second dischargeable current lower limit as the dischargeable current lower limit. The second dischargeable current lower limit is a value smaller than the first dischargeable current lower limit. Note that, in addition to the first and second dischargeable current lower limit, three or more dischargeable current lower limit values may be stored as the dischargeable current lower limit.

The discharge current control of the storage battery 4 by the discharge current control device of the fourth embodiment will be described with reference to Figure 11. Figure 11 shows an example of the discharge current control performed by the discharge current control device of the fourth embodiment when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

As shown by the solid line P in Figure 11(A), after time t51, the battery voltage drops sharply due to the large discharge current of the storage battery 4. As shown by the solid line R in Figure 11(B), from before time t51 to time t52, the dischargeable current value Iout is set to the normal dischargeable current value. Therefore, from before time t51 to time t52, the storage battery 4 can discharge within a range below the normal dischargeable current value.

As shown by solid line P in Figure 11(A), at time t52, the battery voltage becomes smaller than the first voltage threshold V_ctr1. As a result, as shown by solid line R in Figure 11(B), the discharge current control device switches the dischargeable current value Iout from the normal dischargeable current value to the first dischargeable current lower limit at time t52. Therefore, between time t52 and time t54, the storage battery 4 can discharge within the range of the first dischargeable current lower limit. In other words, the discharge current of the storage battery 4, which was in a range below the normal dischargeable current value from before time t51 to time t52, is narrowed to a range below the first dischargeable current lower limit from time t52 onwards.

After time t52, the discharge current is reduced, preventing a sudden drop in battery voltage. Specifically, as shown by the solid line P in FIG. 11A, the battery voltage rises once after time t52, then begins to gradually decrease after time t53. Then, at time t54, the battery voltage falls below the second voltage threshold V_ctr2. As a result, as shown by the solid line R in FIG. 11B, the discharge current control device switches the dischargeable current value Iout from the first dischargeable current lower limit to the second dischargeable current lower limit at time t54. Therefore, between time t54 and time t56, the storage battery 4 can discharge within the range of the second dischargeable current lower limit. In other words, the discharge current of the storage battery 4, which was below the first normal dischargeable current value between time t52 and time t54, is reduced to below the second dischargeable current lower limit after time t54.

As shown by the solid line P in Figure 11 (A), the battery voltage rises once after time t54, and then begins to gradually decrease after time t55. Then, at time t56, the battery voltage becomes smaller than the overdischarge determination threshold V_od. Therefore, the discharge current control device sets the dischargeable current value Iout to 0 and stops discharging.

As shown by the solid line Q in Figure 11 (A), the SOC shows a nearly constant rate of decline, reaching 0% at time t56. Therefore, even when the discharge current of the storage battery 4 is large, the discharge current control device of the fourth embodiment can use the battery capacity up to the lower limit of the rated capacity by performing the discharge current control described above.

Note that in the control of the fourth embodiment, when the discharge current of the storage battery 4 is large, if the battery voltage drops faster than the control circuit's response speed and sensor reading speed, the battery voltage may fall below the second voltage threshold V_ctr2 without passing through the first voltage threshold V_ctr1. Even in this case, the discharge current control device controls the dischargeable current value Iout to be switched to the first dischargeable current lower limit value, rather than directly from the normal dischargeable current value to the second dischargeable current lower limit value. Then, when the voltage of the storage battery 4 falls below the second voltage threshold V_ctr2 after a predetermined time has elapsed since the execution of this control, the dischargeable current value Iout is controlled to be switched from the first dischargeable current lower limit value to the second dischargeable current lower limit value. This prevents a sudden drop in the dischargeable current value Iout.

Fifth Embodiment
A fifth embodiment will be described below. In the fifth embodiment, the discharge current control executed by the discharge current control device is changed from the first embodiment and the like.

The discharge current control device of the fifth embodiment stores a map of optimal values for the dischargeable current limit value Iout_c(t) using SOC and battery temperature as parameters. The discharge current control device then references this map and executes control to determine the optimal discharge current value based on the SOC and battery temperature at the control time. It is preferable that the discharge current control device have a map table for SOCs from 0 to 100%.

The discharge current control performed by the discharge current control device of the fifth embodiment will be described with reference to the flowchart in Figure 12. This control process is repeatedly performed at predetermined control time intervals.

First, in step S410, the dischargeable power value Wout(t) and battery voltage V(t) of the storage battery 4 are obtained. Then, the dischargeable power value Wout(t) is divided by the battery voltage V(t) to calculate the dischargeable current base value Iout_b(t), which is the base value for the discharge current of the storage battery 4.

Next, in step S420, it is determined whether the SOC is 0%. Whether the SOC is 0% is determined by whether the battery voltage is lower than the over-discharge determination threshold V_od. Specifically, if the battery voltage is lower than the over-discharge determination threshold V_od, the SOC is determined to be 0%. On the other hand, if the battery voltage is equal to or higher than the over-discharge determination threshold V_od, the SOC is determined to be not 0%.

If the SOC is 0%, processing proceeds to step S430. In step S430, the dischargeable current limit value Iout_c(t) is set to 0.

On the other hand, if the SOC is not 0% in step S420, the process proceeds to step S440.
In step S440, the discharge current control device refers to the map described above and determines the dischargeable current throttle value Iout_c(t) as an optimum discharge current value according to the SOC and battery temperature at the control time.

After steps S430 and S440, the process proceeds to step S450. In step S450, the dischargeable current value Iout(t) is set to the smaller of the dischargeable current base value Iout_b(t) or the dischargeable current throttle value Iout_c(t).

After step S450, the above-described control process is repeated again from S410.

In the discharge current control device and discharge current control method of the fifth embodiment described above, the dischargeable current value Iout is reduced in multiple stages to gradually reduce the battery voltage, thereby making maximum use of the original battery capacity for power supply.

(Other embodiments)
(1) In each of the above embodiments, a system for managing the energy of a home that supplies power to a load 2 such as a home appliance has been described as an example of a power storage system in which a discharge current control device and a discharge current control method are used. However, the present invention is not limited to this, and the system may also be, for example, a system for managing the energy of a building, a factory, or an entire region.

(2) In each of the above embodiments, the voltages used to compare the measured voltage with the voltage threshold are unified as battery voltages. However, this is not limiting, and the voltages used to compare the measured voltage with the voltage threshold may be considered as battery cell voltages.
For example, in step S40 of the flowchart of Fig. 4 described in the first embodiment, it is determined that cell voltage_rel(T)<battery cell voltage V(t). Also, in step S60, it is determined that battery cell voltage V(t)<Vcell_ctr(t).
At this time, in step S10 of the flowchart, Iout(t)=Wout(t)/Vtotal(t), where Vtotal(t) is the total voltage value of the cells connected in series.

The present invention is not limited to the above-described embodiments and can be modified as appropriate within the scope of the claims. Furthermore, the above-described embodiments and portions thereof are not unrelated to each other and can be combined as appropriate, except where such combinations are clearly impossible. It goes without saying that, in the above-described embodiments, the elements constituting the embodiments are not necessarily essential, except where expressly stated as essential or where they are clearly considered essential in principle. Furthermore, in the above-described embodiments, when numerical values such as the number, value, amount, or range of components of the embodiments are mentioned, they are not limited to that specific number, except where expressly stated as essential or where they are clearly limited to a specific number in principle. Furthermore, in the above-described embodiments, when the shape, positional relationship, etc. of components, etc. are mentioned, they are not limited to that shape, positional relationship, etc., except where expressly stated as essential or where they are clearly limited to a specific shape, positional relationship, etc. in principle.

4: storage battery,
7: control unit (discharge current control device),
12: control unit (discharge current control device),
V_od: over-discharge determination threshold,
V_ctr: voltage threshold,
Iout: Dischargeable current value

Claims (12)

A discharge current control device for controlling a discharge current of a storage battery (4),
an over-discharge determination threshold (V_od) used for determining over-discharge, a voltage threshold (V_ctr) set to a value greater than the over-discharge determination threshold, and a dischargeable current lower limit value set to a value smaller than a dischargeable current value in normal times and greater than 0,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value ,
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
A discharge current control device configured to, when the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, perform control to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and after a predetermined time has elapsed since the execution of this control, perform control to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control device for controlling a discharge current of a storage battery (4),
an over-discharge determination threshold (V_od) used for determining over-discharge, a voltage threshold (V_ctr) set to a value greater than the over-discharge determination threshold, and a dischargeable current lower limit value set to a value smaller than a dischargeable current value in normal times and greater than 0,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value,
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
a discharge current control device configured to, when the voltage of the storage battery becomes lower than the voltage threshold during discharge of the storage battery, perform control to switch the value of the current that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and, when a predetermined time has elapsed since the execution of this control, the amount of change in battery voltage per hour remains constant or decreases, perform control to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control device for controlling a discharge current of a storage battery (4),
an over-discharge determination threshold (V_od) used for determining over-discharge, a voltage threshold (V_ctr) set to a value greater than the over-discharge determination threshold, and a dischargeable current lower limit value set to a value smaller than a dischargeable current value in normal times and greater than 0,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value,
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
a discharge current control device configured to, when the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, perform control to switch the value of the current that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and, when the voltage of the storage battery becomes lower than the voltage threshold again after a predetermined time has elapsed since the execution of this control, perform control to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control device for controlling a discharge current of a storage battery (4),
an over-discharge determination threshold (V_od) used for determining over-discharge, a voltage threshold (V_ctr) set to a value greater than the over-discharge determination threshold, and a dischargeable current lower limit value set to a value smaller than a dischargeable current value in normal times and greater than 0,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value,
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
the voltage thresholds include a first voltage threshold (V_ctr1) for switching from the normal dischargeable current value to the first dischargeable current lower limit value, and a second voltage threshold (V_ctr2) for switching from the first dischargeable current lower limit value to the second dischargeable current lower limit value,
a discharge current control device configured to, when the voltage of the storage battery becomes lower than the first voltage threshold or the second voltage threshold during discharging of the storage battery, perform control to switch the value of the current that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and, when the voltage of the storage battery becomes lower than the second voltage threshold after a predetermined time has elapsed since the execution of this control, perform control to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control device for controlling a discharge current of a storage battery (4),
an over-discharge determination threshold (V_od) used for determining over-discharge, a voltage threshold (V_ctr) set to a value greater than the over-discharge determination threshold, and a dischargeable current lower limit value set to a value smaller than a dischargeable current value in normal times and greater than 0,
When the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value,
a throttling release voltage threshold (V_rel) for releasing the control that has switched the current value that can be discharged from the storage battery to the dischargeable current lower limit value is stored;
A discharge current control device configured to control switching of the current value that can be discharged from the storage battery from the dischargeable current lower limit value to the normal dischargeable current value when the voltage of the storage battery becomes greater than the throttling release voltage threshold. The power storage system in which the storage battery is used is connected to a power generation device (4) capable of supplying power to a load (2) together with the storage battery, a power storage device (5), and a commercial power system (1),
6. The discharge current control device according to claim 1, wherein when the discharge power supplied from the storage battery to the load is insufficient, control is performed to supply power to the load from at least one of the power generation device, the power storage device, and the commercial power system. A discharge current control method for controlling a discharge current of a storage battery (4), comprising:
a dischargeable current value during normal operation, a dischargeable current lower limit value that is smaller than the dischargeable current value during normal operation and larger than 0, an over-discharge determination threshold value (V_od) used for determining over-discharge, and a voltage threshold value (V_ctr) that is larger than the over-discharge determination threshold value are set;
When the voltage of the storage battery becomes lower than the voltage threshold value during discharging of the storage battery, a control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value;
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
A discharge current control method, comprising: when the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, performing control to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value; and after a predetermined time has elapsed since the execution of this control, performing control to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control method for controlling a discharge current of a storage battery (4), comprising:
a dischargeable current value during normal operation, a dischargeable current lower limit value that is smaller than the dischargeable current value during normal operation and larger than 0, an over-discharge determination threshold value (V_od) used for determining over-discharge, and a voltage threshold value (V_ctr) that is larger than the over-discharge determination threshold value are set;
When the voltage of the storage battery becomes lower than the voltage threshold value during discharging of the storage battery, control is performed to switch the current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value;
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
A discharge current control method, in which, when the voltage of the storage battery becomes lower than the voltage threshold during discharge of the storage battery, control is performed to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value, and if the amount of change per hour in the battery voltage remains constant or decreases after a predetermined time has elapsed since the control was executed, control is performed to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control method for controlling a discharge current of a storage battery (4), comprising:
a dischargeable current value during normal operation, a dischargeable current lower limit value that is smaller than the dischargeable current value during normal operation and larger than 0, an over-discharge determination threshold value (V_od) used for determining over-discharge, and a voltage threshold value (V_ctr) that is larger than the over-discharge determination threshold value are set;
When the voltage of the storage battery becomes lower than the voltage threshold value during discharging of the storage battery, a control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value;
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
A discharge current control method, comprising: when the voltage of the storage battery becomes lower than the voltage threshold during discharging of the storage battery, performing control to switch the current value that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value; and when the voltage of the storage battery becomes lower than the voltage threshold again after a predetermined time has elapsed since the execution of this control, performing control to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control method for controlling a discharge current of a storage battery (4), comprising:
a dischargeable current value during normal operation, a dischargeable current lower limit value that is smaller than the dischargeable current value during normal operation and larger than 0, an over-discharge determination threshold value (V_od) used for determining over-discharge, and a voltage threshold value (V_ctr) that is larger than the over-discharge determination threshold value are set;
When the voltage of the storage battery becomes lower than the voltage threshold value during discharging of the storage battery, control is performed to switch the current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value;
the dischargeable current lower limit value includes a first dischargeable current lower limit value and a second dischargeable current lower limit value that is smaller than the first dischargeable current lower limit value,
the voltage thresholds include a first voltage threshold (V_ctr1) for switching from the normal dischargeable current value to the first dischargeable current lower limit value, and a second voltage threshold (V_ctr2) for switching from the first dischargeable current lower limit value to the second dischargeable current lower limit value,
A discharge current control method, comprising: when the voltage of the storage battery becomes lower than the first voltage threshold or the second voltage threshold during discharging of the storage battery, performing control to switch the value of the current that can be discharged from the storage battery from the normal dischargeable current value to the first dischargeable current lower limit value; and when the voltage of the storage battery becomes lower than the second voltage threshold after a predetermined time has elapsed since the execution of this control, performing control to switch from the first dischargeable current lower limit value to the second dischargeable current lower limit value. A discharge current control method for controlling a discharge current of a storage battery (4), comprising:
a dischargeable current value during normal operation, a dischargeable current lower limit value that is smaller than the dischargeable current value during normal operation and larger than 0, an over-discharge determination threshold value (V_od) used for determining over-discharge, and a voltage threshold value (V_ctr) that is larger than the over-discharge determination threshold value are set;
When the voltage of the storage battery becomes lower than the voltage threshold value during discharging of the storage battery, control is performed to switch the current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value;
setting a throttle release voltage threshold (V_rel) for releasing the control that has switched the current value that can be discharged from the storage battery to the dischargeable current lower limit value;
A discharge current control method for controlling switching of a current value that can be discharged from the storage battery from the dischargeable current lower limit value to the normal dischargeable current value when the voltage of the storage battery becomes greater than the throttling release voltage threshold value. A discharge current control method for controlling a discharge current of a storage battery (4), comprising:
a dischargeable current value during normal operation, a dischargeable current lower limit value that is smaller than the dischargeable current value during normal operation and larger than 0, an over-discharge determination threshold value (V_od) used for determining over-discharge, and a voltage threshold value (V_ctr) that is larger than the over-discharge determination threshold value are set;
When the voltage of the storage battery becomes lower than the voltage threshold value during discharging of the storage battery, a control is performed to switch a current value (Iout) that can be discharged from the storage battery from the dischargeable current value in normal times to the dischargeable current lower limit value;
The power storage system in which the storage battery is used is connected to a power generation device (4) capable of supplying power to a load (2) together with the storage battery, a power storage device (5), and a commercial power system (1),
A discharge current control method for controlling power supply to the load from at least one of the power generation device, the power storage device, and the commercial power system when the discharge power supplied from the storage battery to the load is insufficient.