Discharge current control device and discharge current control method

Abstract

To provide a discharge current control device capable of maximally utilizing a battery capacity for power supply.SOLUTION: A discharge current control device stores an overdischarge determination threshold V_od used for overdischarge determination, a voltage threshold V_ctr set to a value larger than the overdischarge determination threshold, and a dischargeable current lower limit set to a value smaller than a dischargeable current normal value and larger than 0. The discharge current control device is configured to perform control for switching a dischargeable current value Iout of a storage battery 4 from the dischargeable current normal value to the dischargeable current lower limit value when a voltage of the storage battery 4 becomes smaller than the voltage threshold during discharge of the storage battery 4.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] 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 a power storage system. [Background technology]

[0002] The power storage system described in Patent Document 1 has a function of monitoring the voltage of the storage battery during discharge, and when the voltage becomes smaller than an over-discharge determination threshold, stops discharging from the storage battery, thereby protecting the storage battery from over-discharge (i.e., an over-discharge protection function). Note that in Patent Document 1, the "over-discharge determination threshold" is called a "second voltage value Vu," and is set to a value several percent before the remaining capacity at which the storage battery reaches an over-discharge state. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-175864 Summary of the Invention [Problem to be solved by the invention]

[0004] Generally, a storage battery has a characteristic that the larger the discharge current, the larger the voltage drop. Therefore, in the technology described in Patent Document 1, when the discharge current of a storage battery is large, if the battery voltage drops suddenly and falls below the over-discharge determination threshold, discharge is stopped from the viewpoint of 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 is an abbreviation for state of charge.

[0005] For example, if the battery discharge current is large when the remaining battery capacity is 10%, 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 about 10% smaller. In particular, in low-temperature environments, the voltage drop of a storage battery increases when the discharge current is large, so the actual usable battery capacity may be reduced by 10% or more of the rated capacity.

[0006] In view of the above, an object of the present invention is to provide a discharge current control device and a discharge current control method that can make maximum use of battery capacity for power supply. [Means for solving the problem]

[0007] In order to achieve the above object, claim 1 -5 The invention relates to: A discharge current control device for controlling a discharge current of a storage battery (4), an overdischarge determination threshold (V_od) used for determining overdischarge, a voltage threshold (V_ctr) set to a value greater than the overdischarge determination threshold, and a dischargeable current lower limit set to a value smaller than a dischargeable current value in normal times and greater than 0 are stored; 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 when 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 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 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 5, a throttle release voltage threshold (V_rel) for releasing the control that switches the current value that can be discharged from the storage battery 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 current value that can be discharged from the storage battery from the dischargeable current lower limit to the dischargeable current value under normal conditions.

[0008] According to this, even if the discharge current of the storage battery 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 storage battery switches from the normal discharge current value to the discharge current lower limit. This limits the current value discharged from the storage battery, thereby suppressing a sudden drop in battery voltage. Specifically, when the current value that can be discharged from the storage battery switches to the discharge current lower limit, the battery voltage rises once and then gradually drops. Therefore, even when the discharge current of the storage battery is large, a sudden drop in battery voltage is suppressed 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 original battery capacity to be used to its full potential for power supply.

[0011] Also, claims 7-12 The present invention provides 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 overdischarge determination threshold value (V_od) used for overdischarge determination, and a voltage threshold value (V_ctr) that is larger than the overdischarge determination threshold value are set; 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 (Iout) that can be discharged from the storage battery from the normal dischargeable current value to the dischargeable current lower limit value. Furthermore, in the invention according to claim 7, 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 8, 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 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 is switched to the dischargeable current lower limit value, When the voltage of the storage battery becomes higher than the throttle release voltage threshold, the current value that can be discharged from the storage battery is controlled to be switched 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.

[0015] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram showing 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. [Figure 2] 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. FIG. [Figure 3] 4 is a graph showing an example of discharge current control according to the first embodiment. [Figure 4] 3 is a flowchart showing a control process executed by the discharge current control device according to the first embodiment. [Figure 5] 1 is a graph showing an example of conventional discharge current control. [Figure 6] 10 is a graph showing an example of discharge current control according to the second embodiment. [Figure 7A] 10 is a flowchart showing a control process executed by a discharge current control device according to a second embodiment. [Figure 7B] 10 is a flowchart showing a control process executed by a discharge current control device according to a second embodiment. [Figure 8A] 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. [Figure 8B] 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. [Figure 9] 10 is a graph showing an example of discharge current control according to a second modified example of the second embodiment. [Figure 10] 10 is a graph showing an example of discharge current control according to the third embodiment. [Figure 11]10 is a graph showing an example of discharge current control according to the fourth embodiment. [Figure 12] 10 is a flowchart showing a control process executed by a discharge current control device according to a fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following embodiments, identical or equivalent parts are designated by the same reference numerals, and description thereof will be omitted.

[0018] (First embodiment) A first embodiment will be described with reference to the drawings. In the first embodiment, a power storage system in which a discharge current control device and a discharge current control method are used will be described.

[0019] Fig. 1 shows one example of the configuration of a power storage system (hereinafter referred to as "first example configuration"). As shown in Fig. 1, the power storage system has a storage battery 4, a power generation device 5, a power storage device 6, etc. electrically connected 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.

[0020] 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 configured to include 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.

[0021] The memory of the control unit 7 of the storage battery 4 stores an over-discharge determination threshold V_od, a voltage threshold V_ctr, a dischargeable current lower limit, a throttle release voltage threshold V_rel, and the like, in order to control charging and discharging of the battery module.

[0022] 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 several percent before the remaining capacity at which the storage battery 4 reaches an over-discharge state.

[0023] The voltage threshold V_ctr is a threshold set to a value greater than the overdischarge determination threshold V_od, and is a threshold 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.

[0024] 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 fixed value that is set in advance, or may be determined by mapping an optimal value using parameters such as the remaining capacity (hereinafter referred to as the "SOC") of the storage battery 4 to be displayed to the user and the battery temperature.

[0025] The throttling 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 dischargeable current lower limit value and returning it to the normal dischargeable current value. The throttling release voltage threshold V_rel is set to a value greater than the voltage threshold V_ctr. The throttling release voltage threshold V_rel may be a value determined according to the battery temperature, or may be a unique value for simplification.

[0026] The power generation device 5 is configured, for example, from a photovoltaic power generation device (PV) and a fuel cell device. PV stands for photovoltaics. The power storage device 6 is configured, for example, from an in-vehicle storage battery (V2X). V2X stands for Vehicle to X. The power generation device 5 and the power storage device 6 each have control units 8 and 9 that control their own charging and discharging.

[0027] The storage battery 4, the power generation device 5, and the power storage device 6 are controlled by a system controller 10. The system controller 10 is configured, for example, by an energy management system (EMS) terminal. EMS includes HEMS, BEMS, FEMS, CEMS, etc. HEMS is an abbreviation for Home Energy Management Service. BEMS is an abbreviation for Building and Energy Management System. FEMS is an abbreviation for Factory Energy Management System. CEMS is an abbreviation for Community Energy Management System. Note that, for example, a HEMS is used as the system controller 10 for a system that manages energy in a home. The system controller 10 monitors and optimizes the performance of the storage battery 4, the power generation device 5, and the power storage device 6. Note that in FIG. 1, communication lines between the system controller 10 and control units 7 to 9 of the storage battery 4, the power generation device 5, and the power storage device 6, respectively, are indicated by dashed lines.

[0028] FIG. 2 shows another example configuration of the power storage system (hereinafter referred to as "second example configuration"). As shown in FIG. 2, in the power storage system, a storage battery 4, a power generation device 5, a power storage device 6, and the like are electrically connected to a power line 3 that supplies power from a grid 1 to a load 2 via a power conditioner 11. In this specification, power conditioners that can be connected to multiple devices, such as a hybrid power conditioner that can be connected to two devices and a tri-brid power conditioner that can be connected to three devices, are collectively referred to as "power conditioners." The power conditioner 11 has 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, and 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 a program 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 module of the storage battery 4.

[0029] 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 be continuously 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 stopping operation. This control is particularly effective during stand-alone operation when the grid 1 experiences a power outage, when it is not possible to rely on the power supply from the grid 1.

[0030] 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 "discharge current control device."

[0031] Next, the discharge current control of the storage battery 4 by the discharge current control device according to the first embodiment will be described.

[0032] FIG. 3 shows an example of discharge current control executed by the discharge current control device when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

[0033] The vertical axis of Fig. 3(A) 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. 3(A) represents time [ms]. The solid line A in Fig. 3(A) shows the transition of the battery voltage when the discharge current of the storage battery 4 is large. The solid line B in Fig. 3(A) shows the SOC.

[0034] On the other hand, the vertical axis of Fig. 3(B) represents current [A]. The horizontal axis of Fig. 3(B) represents time [ms]. The solid line C in Fig. 3(B) represents the dischargeable current value Iout. Note that these are the same as in Figs. 5, 6, 9 to 11, which will be referred to in the following explanation, except for the symbols attached to the solid lines.

[0035] As shown by solid line A in Fig. 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 Fig. 3(B), the dischargeable current value Iout is set to the normal dischargeable current value before time t1 and before time t2. Therefore, the storage battery 4 can discharge within a range equal to or less than the normal dischargeable current value before time t1 and before time t2.

[0036] As shown by solid line A in FIG. 3A, 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 dischargeable current lower limit value. Therefore, as shown by solid line C in FIG. 3B, at time t2, the dischargeable current value Iout is switched from the normal dischargeable current value to the dischargeable current lower limit value. Therefore, from time t2 to time t4, the storage battery 4 can discharge within the range of the dischargeable current lower limit value. In other words, the discharge current of the storage battery 4, which was in a range equal to or less than the normal dischargeable current value from before time t1 to time t2, is narrowed to a range equal to or less than the dischargeable current lower limit value after time t2.

[0037] 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. Therefore, a sudden drop in battery voltage is suppressed, and the time it takes for the battery voltage to drop to the overdischarge determination threshold V_od is lengthened. 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.

[0038] As shown by the solid line B in Fig. 3(A), the SOC shows a substantially constant rate of decrease after time t2, and reaches 0% at time t4. Therefore, even when the discharge current of the storage battery 4 is large, the discharge current control device according to 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.

[0039] Next, the discharge current control executed by the discharge current control device of the first embodiment will be described with reference to the flowchart of Fig. 4. This control process is repeatedly executed at predetermined control time intervals.

[0040] First, in step S10, the dischargeable power value Wout(t) and the 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 the 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 a dischargeable current base value Iout_b(t), which serves as a 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, and therefore the symbols are suffixed with (t).

[0041] Next, in step S20, it is determined whether the SOC is 0%. Whether the SOC is 0% or not is determined by whether the battery voltage is lower than the overdischarge determination threshold V_od. Specifically, if the battery voltage is lower than the overdischarge determination threshold V_od, it is determined that the SOC is 0%. On the other hand, if the battery voltage is equal to or higher than the overdischarge determination threshold V_od, it is determined that the SOC is not 0%.

[0042] If the SOC is 0%, the process proceeds to step S30. In step S30, the dischargeable current limit value Iout_c(t) is set to zero.

[0043] 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, so the symbol ends with (T). In step S40, if the battery voltage V(t) is greater than the throttle release voltage threshold V_rel(T), the process proceeds to step S50. In step S50, state=0 (i.e., the state flag is set to "0"). This cancels the control in step S70, described below, in which state=1 (i.e., the state flag is set to "1"). After step S50, the process proceeds to step S60.

[0044] On the other hand, if the battery voltage V(t) is equal to or lower than the throttling release voltage threshold V_rel(T) in step S40, the process 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, the process proceeds to step S70. In step S70, state=1 (i.e., the state flag is "1") is set, and then the process proceeds to step S80. In step S80, the dischargeable current throttling value Iout_c(t) is set to the dischargeable current lower limit value.

[0045] On the other hand, if the battery voltage V(t) is equal to or greater than the voltage threshold V_ctr in step S60, the process proceeds to step S90. In step S90, it is determined whether the state is "1." If the state is not "1" (i.e., if state=0), the process proceeds to step S100. In step S100, the dischargeable current limit value Iout_c(t) is set to the dischargeable current base value Iout_b(t).

[0046] On the other hand, if the state is "1" in step S70, the process proceeds to step S110. In step S110, the dischargeable current throttle value Iout_c(t) is set as the dischargeable current lower limit value.

[0047] 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) and the dischargeable current throttle value Iout_c(t).

[0048] After step S120, the above-described control process is repeated from S10.

[0049] Here, for comparison with the discharge current control performed by the discharge current control device of the first embodiment described above, the discharge current control performed by a discharge current control device of a comparative example will be described. The discharge current control device of the comparative example stores an over-discharge determination threshold V_od, a throttling 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 lower limit dischargeable current value.

[0050] FIG. 5 shows the discharge current control executed 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.

[0051] As shown by the solid line D in Fig. 5(A), after time t11, the battery voltage drops sharply due to the large discharge current of the storage battery 4. As shown by the solid line F in Fig. 5(B), the dischargeable current value Iout is set to the normal dischargeable current value before time t11 and before time t12. Therefore, the storage battery 4 can discharge within a range equal to or less than the normal dischargeable current value before time t11 and before time t12.

[0052] As shown by solid line D in Figure 5(A), at time t12, the battery voltage becomes smaller than the overdischarge 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 capacity in the battery.

[0053] The dashed line G in Figure 5(A) shows the case where the original remaining battery capacity is discharged to the lower limit of the rated capacity. As shown by this dashed line G, if the SOC continues to decrease at a constant rate after time t12, the SOC will 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 of the hatched area H in Figure 5(B).

[0054] In contrast to such a 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 provide the resulting effects.

[0055] (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.

[0056] (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 if there is a shortage of discharge power supplied from the storage battery 4 to the load 2, 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, as it is not possible to rely on the power supply from the grid 1.

[0057] (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 throttling 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.

[0058] (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.

[0059] (Second embodiment) The second embodiment will be described. In the second embodiment, the discharge current control executed by the discharge current control device of the first embodiment is partially changed, and the rest of the second embodiment is the same as the first embodiment, so only the parts that are different from the first embodiment will be described.

[0060] 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.

[0061] 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 the SOC and battery temperature.

[0062] The discharge current control of the storage battery 4 by the discharge current control device according to the second embodiment will be described.

[0063] FIG. 6 shows an example of discharge current control executed by the discharge current control device when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

[0064] As shown by the solid line I in Fig. 6(A), the battery voltage drops sharply after time t21 due to the large discharge current of the storage battery 4. As shown by the solid line J in Fig. 6(B), the dischargeable current value Iout is set to the normal dischargeable current value before time t21 and before time t22. Therefore, the storage battery 4 can discharge within a range equal to or less than the normal dischargeable current value before time t21 and before time t22.

[0065] As shown by the solid line I in FIG. 6A, at time t22, 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 first dischargeable current lower limit. Therefore, as shown by the solid line J in FIG. 6B, 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 range of the dischargeable current lower limit. In other words, the discharge current of the storage battery 4, which was in a range equal to or less than the normal dischargeable current value from before time t21 to time t22, is narrowed to a range equal to or less than the first dischargeable current lower limit after time t22.

[0066] After time t22, the discharge current is reduced, thereby preventing a sudden drop in battery voltage. Specifically, as shown by the solid line I in FIG. 6A, the battery voltage rises once after time t22, and then gradually drops after time t23. Then, as shown by the solid line J in FIG. 6B, 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. That is, 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 the range of the second dischargeable current lower limit after time t24.

[0067] As shown by the solid line I in FIG. 6A, after time t24, the battery voltage rises once and then gradually drops. 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 performing the discharge current control described above to gradually lower the dischargeable current value.

[0068] Next, the discharge current control executed by the discharge current control device of the second embodiment will be described with reference to the flowcharts of Figures 7A and 7B. This control process is repeatedly executed at predetermined control time intervals.

[0069] First, in step S210, the dischargeable power value Wout(t) and the battery voltage V(t) of the storage battery 4 are acquired. 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 of the discharge current of the storage battery 4.

[0070] Next, in step S220, it is determined whether the SOC is 0%. Whether the SOC is 0% or not is determined by whether the battery voltage is lower than the overdischarge determination threshold V_od. Specifically, if the battery voltage is lower than the overdischarge determination threshold V_od, it is determined that the SOC is 0%. On the other hand, if the battery voltage is equal to or higher than the overdischarge determination threshold V_od, it is determined that the SOC is not 0%.

[0071] If the SOC is 0%, the process proceeds to step S230. In step S230, the dischargeable current limit value Iout_c(t) is set to zero.

[0072] 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), the process proceeds to step S250. In step S250, state=0 (i.e., state flag "0"). This cancels the control in step S280 (described later) where state=1 (i.e., state flag "1") or the control in step S310 where state=2 (i.e., state flag "2"). After step S250, the process proceeds to step S260.

[0073] On the other hand, if the battery voltage V(t) is equal to or less than the throttle release voltage threshold V_rel(T) in step S240, the process skips step S250 and proceeds to step S260. 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, the process proceeds to step S270.

[0074] 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, the process proceeds to step S280. Then, in step S280, state is switched to 1 (i.e., the state flag is set to "1"), and then the process 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.

[0075] On the other hand, if state=0 (i.e., the current state flag is not "0") in step S270, the process 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 after the state flag transitions from "0" to "1" that takes into account the response speed of the control circuit and the sensor reading speed. 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, which occurs when 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.

[0076] If the predetermined time T [ms] has not elapsed since state=1 (i.e., the state flag is set to "1") in step S300, the process 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.

[0077] On the other hand, if the predetermined time T [ms] or more has elapsed since state=1 (i.e., the state flag is "1") in step S300, the process proceeds to step S310. After state=2 (i.e., the state flag is "2") in step S310, the process proceeds to step S320. In step S320, the dischargeable current throttle value Iout_c(t) is set to the second dischargeable current lower limit value.

[0078] On the other hand, if the battery voltage V(t) is equal to or greater than the voltage threshold V_ctr in step S260, the process proceeds to step S330. In step S330, it is determined whether state is greater than "0". If state is equal to or less than "0" (i.e., if state=0), the process 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).

[0079] On the other hand, if state is greater than "0" in step S330 (i.e., if state = 1 or 2), the process 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).

[0080] 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) and the dischargeable current throttle value Iout_c(t).

[0081] After step S360, the above-described control process is repeated again from S210.

[0082] 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.

[0083] 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 drop 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 for power supply.

[0084] (First modified example of the 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.

[0085] In the above description of the second embodiment, step S300 determines whether or not 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 or not the change in battery voltage is greater than 0 (i.e., increasing). Specifically, if the change in battery voltage per unit time is greater than 0 (i.e., increasing), the process 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., constant or decreasing), the process proceeds to step S310 (i.e., state=2 is switched to).

[0086] The discharge current control device and the discharge current control method according to the first modified example of the second embodiment described above have the following configuration and provide the following effects.

[0087] In the first modification of 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, when 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. This allows the first modification of the second embodiment to achieve the same effects as the second embodiment.

[0088] (Second Modification of the Second Embodiment) A second modified example 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 modified example of the second embodiment when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

[0089] In the first embodiment, the control for reducing the dischargeable current value Iout in two stages has been described, and in the second embodiment and its first modified example, the control for reducing the dischargeable current value Iout in three stages has been described. In contrast, in the second modified example of the second embodiment, the control for reducing the dischargeable current value Iout in multiple stages is performed.

[0090] FIG. 9 shows an example of discharge current control executed by the discharge current control device when the discharge current of the storage battery 4 is large and the battery voltage drops suddenly.

[0091] As shown by the solid line K in Fig. 9(A), after time t31, the battery voltage drops sharply due to the large discharge current of the storage battery 4. As shown by the solid line L in Fig. 9(B), between time t31 and time t32, the dischargeable current value Iout is set to the normal dischargeable current value.

[0092] As shown by the solid line K in FIG. 9A, 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 modification 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 FIG. 9B, after time t32, the dischargeable current value Iout continuously decreases over time.

[0093] 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.

[0094] (Third embodiment) A third embodiment will be described. The third embodiment is also different from the first embodiment in that the discharge current control executed by the discharge current control device is partially changed, and the rest is the same as the first embodiment, so only the parts that are different from the first embodiment will be described.

[0095] The discharge current control device of the third embodiment is also 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 third 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.

[0096] 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 Fig. 10. Fig. 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.

[0097] As shown by the solid line M in Fig. 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 Fig. 10(B), the dischargeable current value Iout is set to the normal dischargeable current value before time t41 and before time t42. Therefore, the storage battery 4 can discharge within a range equal to or less than the normal dischargeable current value before time t41 and before time t42.

[0098] As shown by the solid line M in FIG. 10(A), at time t42, the battery voltage becomes smaller than 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 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 equal to or less than the normal dischargeable current value from before time t41 to time t42, is narrowed to a range equal to or less than the first dischargeable current lower limit after time t42.

[0099] After time t42, the discharge current is reduced, suppressing a sudden drop in battery voltage. Specifically, as shown by the solid line M in FIG. 10A, the battery voltage rises once after time t42, and then begins to gradually decrease after time t43. Then, at time t44, the battery voltage falls below the voltage threshold V_ctr again. As a result, as shown by the solid line O in FIG. 10B, 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. That is, the discharge current of the storage battery 4, which was within the range of the first dischargeable current normal value between time t42 and time t44, is reduced to the range of the second dischargeable current lower limit after time t44.

[0100] As shown by the solid line M in Figure 10(A), the battery voltage rises after time t44, and then begins to gradually decrease after time t45. Then, at time t46, the battery voltage falls below the overdischarge determination threshold V_od. Therefore, the discharge current control device sets the dischargeable current value Iout to 0 and stops discharging.

[0101] 10(A), the SOC shows a nearly constant rate of decrease and reaches 0% at time t46. Therefore, even when the discharge current of the storage battery 4 is large, the discharge current control device according to 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.

[0102] (Fourth embodiment) The fourth embodiment will be described. The fourth embodiment is similar to the first embodiment in that the discharge current control performed 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.

[0103] The discharge current control device of the fourth embodiment is also configured to switch the dischargeable current lower limit in multiple stages. At least a first voltage threshold V_ctr1 and a second voltage threshold V_ctr2 are stored in the memory of the discharge current control device of the fourth embodiment 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. Note that, in addition to the first and second voltage thresholds, three or more voltage thresholds may be stored as the voltage threshold V_ctr.

[0104] 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 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.

[0105] 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 Fig. 11. Fig. 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.

[0106] As shown by the solid line P in Fig. 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 Fig. 11(B), the dischargeable current value Iout is set to the normal dischargeable current value before time t51 and before time t52. Therefore, the storage battery 4 can discharge within a range equal to or less than the normal dischargeable current value before time t51 and before time t52.

[0107] As shown by the solid line P in FIG. 11(A), the battery voltage becomes smaller than the first voltage threshold V_ctr1 at time t52. As a result, as shown by the solid line R in FIG. 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 equal to or less than the normal dischargeable current value from before time t51 to time t52, is narrowed to a range equal to or less than the first dischargeable current lower limit after time t52.

[0108] After time t52, the discharge current is reduced, suppressing 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, and then begins to gradually decrease after time t53. Then, at time t54, the battery voltage becomes smaller than 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. That is, the discharge current of the storage battery 4, which was in a range equal to or less than the first normal dischargeable current value between time t52 and time t54, is reduced to a range equal to or less than the second dischargeable current lower limit after time t54.

[0109] As shown by the solid line P in Figure 11(A), the battery voltage rises after time t54, and then begins to gradually decrease after time t55. Then, at time t56, the battery voltage falls below the overdischarge determination threshold V_od. Therefore, the discharge current control device sets the dischargeable current value Iout to 0 and stops discharging.

[0110] 11(A), the SOC shows a nearly constant rate of decrease and reaches 0% at time t56. Therefore, even when the discharge current of the storage battery 4 is large, the discharge current control device according to 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.

[0111] In the control of the fourth embodiment, when the discharge current of the storage battery 4 is large, if the battery voltage decreases faster than the response speed of the control circuit and the sensor reading speed, the battery voltage may become lower than 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 switching it from the normal dischargeable current value to the second dischargeable current lower limit value. Then, when the voltage of the storage battery 4 becomes lower than 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.

[0112] (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.

[0113] The discharge current control device of the fifth embodiment stores a map of optimal values ​​for the dischargeable current throttle value Iout_c(t) using the SOC and battery temperature as parameters.The discharge current control device then references the 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 has a map table for SOCs from 0 to 100%.

[0114] The discharge current control executed by the discharge current control device of the fifth embodiment will be described with reference to the flowchart of Fig. 12. This control process is repeatedly executed at predetermined control time intervals.

[0115] First, in step S410, the dischargeable power value Wout(t) and the battery voltage V(t) of the storage battery 4 are acquired. 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 of the discharge current of the storage battery 4.

[0116] Next, in step S420, it is determined whether the SOC is 0%. Whether the SOC is 0% or not is determined by whether the battery voltage is lower than the overdischarge determination threshold V_od. Specifically, if the battery voltage is lower than the overdischarge determination threshold V_od, it is determined that the SOC is 0%. On the other hand, if the battery voltage is equal to or higher than the overdischarge determination threshold V_od, it is determined that the SOC is not 0%.

[0117] If the SOC is 0%, the process proceeds to step S430. In step S430, the dischargeable current limit value Iout_c(t) is set to zero.

[0118] 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.

[0119] 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) and the dischargeable current throttle value Iout_c(t).

[0120] After step S450, the above-described control process is repeated again from S410.

[0121] 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.

[0122] (Other embodiments) (1) In each of the above embodiments, as the power storage system in which the discharge current control device and the discharge current control method are used, a system for managing the energy of a house that supplies power to a load 2 such as a household electrical appliance has been described as an example. However, the present invention is not limited thereto. For example, it may be a system for managing the energy of a building, a factory, or the entire region.

[0123] (2) In each of the above embodiments, each voltage used for comparing the measured voltage with the voltage threshold value has been unified as the battery voltage. However, the present invention is not limited thereto. Each voltage used for comparing the measured voltage with the voltage threshold value may be regarded as the battery cell voltage. 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) < V_cell_ctr(t). At this time, step S10 of the flowchart is Iout(t) = Wout(t) / Vtotal(t), where Vtotal(t) is the total voltage value obtained by connecting cells in series.

[0124] The present invention is not limited to the above-described embodiments, and can be appropriately modified within the scope described in the claims. Also, each of the above embodiments and a part thereof are not unrelated to each other, and can be appropriately combined except in cases where the combination is clearly impossible. Further, in each of the above embodiments, the elements constituting the embodiment are not necessarily essential except in cases where it is clearly specified as essential and cases where it is considered clearly essential in principle. Also, in each of the above embodiments, when numerical values such as the number, numerical value, quantity, range, etc. of the components of the embodiment are mentioned, they are not limited to the specific number except in cases where it is clearly specified as essential and cases where it is clearly limited to a specific number in principle. Also, in each of the above embodiments, when referring to the shape, positional relationship, etc. of the components, etc., they are not limited to the specific shape, positional relationship, etc. except in cases where it is clearly specified and cases where it is clearly limited to a specific shape, positional relationship, etc. in principle.

Explanation of Reference Numerals

[0125] 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

1. 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.

2. A discharge current control device for controlling the 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.

3. A discharge current control device for controlling the 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.

4. A discharge current control device for controlling the 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.

5. A discharge current control device for controlling the 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.

6. The storage battery 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.

7. 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.

8. 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, 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.

9. 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.

10. 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 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, 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.

11. 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 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; setting a throttle release voltage threshold (V_rel) for releasing the control that has switched the value of the current 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.

12. 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.

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