Energy Storage System

Abstract

To simultaneously realizes the long life of a power storage battery and the stabilization of the DC system to which the power storage battery is connected.SOLUTION: A power storage system (30) includes a power storage battery (34), and a charge / discharge request unit (27) that requests a charge / discharge current for the power storage battery, and charges the power storage battery with a current that is suppressed with respect to a requested current when the battery voltage of the storage battery exceeds a charge suppression start voltage in a case in which a charge request is received, and discharge the power storage battery with a curtailed current relative to the requested current when the battery voltage of the storage battery is less than a discharge suppression start voltage in a case in which a discharge request is received.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an energy storage system. [Background technology]

[0002] An electric power system is constructed by connecting power generation facilities and load facilities via power transmission and distribution facilities. In the electric power system, the supply of electricity from the power generation facilities and the demand for electricity from the load facilities are balanced.

[0003] An energy storage system is connected to the above-mentioned power grid and used as a means for balancing the supply and demand of electricity. By connecting an energy storage system equipped with a storage battery to the power grid, when the supply of electricity exceeds the demand, the excess electricity can be charged into the storage battery, and when the supply of electricity is insufficient compared to the demand, the shortage can be compensated for by discharging electricity from the storage battery.

[0004] Such a power storage system for stabilizing an AC system is disclosed in Patent Document 1. In the power storage system of Patent Document 1, consideration is given to the charge limit and discharge limit of the storage battery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-27874 Summary of the Invention [Problem to be solved by the invention]

[0006] The above-mentioned prior art discloses the operation of a power storage system for stabilizing an AC system, but does not disclose the operation of a power storage system for a DC system.

[0007] One aspect of the present invention aims to realize an energy storage system connected to a DC system that extends the life of the storage battery while minimizing the hindrance to efficient operation for maintaining the supply-demand balance of the DC system. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, a power storage system according to one aspect of the present invention is a power storage system that supplies and receives power to a DC system, the DC system being a DC system including a DC bus and a charge / discharge request unit that issues a required charge or discharge request to the power storage system, the power storage system also including a storage battery that stores power, a conversion device that charges and discharges the storage battery and supplies power to the DC bus, and a control unit that controls the conversion device, and when the control unit receives the charge request from the charge / discharge request unit, The conversion device charges the storage battery with a current corresponding to the charge request when the terminal-to-terminal voltage is equal to or lower than a charge suppression start voltage, and with a current that is more suppressed than the charge request when the terminal-to-terminal voltage exceeds the charge suppression start voltage. Furthermore, upon receiving the discharge request from the charge / discharge request unit, the conversion device discharges the storage battery with a current corresponding to the discharge request when the terminal-to-terminal voltage of the storage battery is equal to or higher than a discharge suppression start voltage that is set to a value smaller than the charge suppression start voltage, and with a current that is more suppressed than the discharge request when the terminal-to-terminal voltage is lower than the discharge suppression start voltage. [Effects of the Invention]

[0009] According to one aspect of the present invention, it is possible to simultaneously achieve a longer life of a storage battery and stabilization of a DC system to which the storage battery is connected. [Brief explanation of the drawings]

[0010] [Figure 1] 1 shows a configuration diagram of a power system according to a first embodiment of the present invention. [Figure 2] 1 shows a block diagram of a power storage system and a DC system according to a first embodiment of the present invention. [Figure 3]2 shows a flowchart relating to charging and discharging of the power storage system according to the first embodiment of the present invention. [Figure 4] 3 shows the relationship between the battery voltage of the storage battery and the suppression gain when the power storage system according to the first embodiment of the present invention is charging. [Figure 5] 3 shows the relationship between the battery voltage of the storage battery and the suppression gain during discharging in the power storage system according to the first embodiment of the present invention. [Figure 6] 4 shows changes in voltage, current, and SOC in an example of operation during charging of the power storage system according to the first embodiment of the present invention. [Figure 7] 10 shows the relationship between the battery voltage of the storage battery and the suppression gain when the power storage system according to the second embodiment of the present invention is charging. [Figure 8] 10 shows changes in the battery voltage and current of the storage battery in an example of operation during charging of the power storage system according to the second embodiment of the present invention. [Figure 9] 10 shows the relationship between the SOC and the open-circuit voltage of the storage battery of the power storage system according to the third embodiment of the present invention. [Figure 10] 10 shows the relationship between the battery voltage of the storage battery and the suppression gain when the power storage system according to the third embodiment of the present invention is charging. [Figure 11] 10 shows changes in the battery voltage and current of the storage battery in an example of operation during charging of the power storage system according to the third embodiment of the present invention when the internal impedance of the storage battery is large. [Figure 12] 10 shows changes in the battery voltage and current of the storage battery in an example of operation during charging of the power storage system according to the third embodiment of the present invention when the internal impedance of the storage battery is small. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Embodiment 1] Hereinafter, one embodiment of the present invention will be described in detail with reference to FIGS.

[0012] (Configuration of power system 1) Fig. 1 shows a configuration diagram of a power system 1 according to a first embodiment of the present invention. Fig. 2 shows a block diagram of a power storage system 30 and a DC system 20 according to the first embodiment of the present invention.

[0013] The power system 1 includes an AC system 10, a DC system 20, and a power storage system 30. The AC system 10 includes a commercial power source 11, a transformer 12, and an AC-DC converter 13. The DC system 20 includes a first DC circuit breaker 21, a bus (DC bus) 22, a first DC-DC converter 23, a power generation device 24, a DC load 25, an EV (Electric Vehicle) charging station 26, and a charge / discharge request unit 27. The power storage system 30 includes a control unit 31, a second DC-DC converter (conversion device) 32, a second DC circuit breaker 33, and a storage battery 34.

[0014] Commercial power supply 11 is an AC power supply. Transformer 12 is connected to commercial power supply 11 and is a transformer that transforms the voltage of AC power. AC-DC converter 13 is connected to transformer 12 and converts AC power into DC power. The AC-DC converter may be a rectifier circuit such as a diode bridge. DC system 20 may be able to sell power to commercial power supply 11 in addition to purchasing power from it.

[0015] The first DC circuit breaker 21 is connected to the AC-DC converter 13 and is a protective device that opens when the current flowing through the first DC circuit breaker 21 is equal to or greater than the rated current. One of the connection terminals between the AC-DC converter 13 and the first DC circuit breaker 21 may be grounded.

[0016] A bus 22 is connected to the secondary side of the first DC circuit breaker 21, and a plurality of DC circuits are connected via the bus 22.

[0017] The first DC-DC converter 23 is connected to the bus 22 and inputs and outputs current to and from the bus 22. The power generation device 24 is connected to the first DC-DC converter 23 and is a device that generates DC power. For example, the power generation device 24 may be a power generation device that uses natural energy, such as a solar power generation device, a wind power generation device, or a geothermal power generation device.

[0018] The DC load 25 is a DC load connected to the bus bar 22. The EV charging station 26 is a charging station for EVs connected to the bus bar 22.

[0019] In the power system 1, the power generation device 24, DC load 25, and EV charging station 26 connected to the bus bar 22 are examples, and other consumption equipment, power generation equipment, and power storage equipment may also be connected.

[0020] The charge / discharge request unit 27 issues a required charge request or discharge request to the power storage system 30. The required charge request or discharge request may be calculated in advance based on predicted power usage or power generation in the DC grid 20. The charge / discharge request unit 27 may also receive and relay a charge request or discharge request from a higher-level control device that controls multiple power storage systems 30. The charge request and discharge request may include information regarding the current to be charged or discharged.

[0021] The second DC-DC converter 32 is connected to the bus 22 and inputs and outputs current to and from the bus 22. The second DC circuit breaker 33 is connected to the second DC-DC converter 32 and is a protective device that opens when the current flowing through the second DC circuit breaker 33 is equal to or greater than the rated current. The storage battery 34 is a secondary battery connected to the second DC circuit breaker 33 and is capable of storing, charging, and discharging DC power. Therefore, the second DC-DC converter 32 charges and discharges the storage battery 34, supplying and receiving power to and from the bus 22.

[0022] The control unit 31 controls the second DC-DC converter 32 to pass a required current in a required direction (charging or discharging) based on a command from the charge / discharge request unit 27. At this time, the control unit 31 acquires the battery voltage (terminal voltage of the storage battery 34) Vbat, current Ibat, and SOC (State Of Charge) of the storage battery 34.

[0023] (Charging and discharging operation of power storage system 30) FIG. 3 shows a flowchart relating to charging and discharging of the power storage system according to the first embodiment of the present invention.

[0024] First, the control unit 31 measures the voltage (battery voltage Vbat) of the storage battery 34 (S11). The control unit 31 determines whether the battery voltage Vbat is greater than a predetermined upper limit voltage Vhigh (S12). If Vbat is greater than Vhigh, the process proceeds to S13. If Vbat is equal to or less than Vhigh, the process proceeds to S16.

[0025] In S13, the control unit 31 determines whether the storage battery 34 is being charged. If the storage battery 34 is being charged, the control unit 31 reduces the charging current Ibat to prevent overcharging (S14). If the storage battery 34 is being discharged, there is a power margin, so the discharging continues (S15).

[0026] In S16, the control unit 31 determines whether the battery voltage Vbat is greater than a predetermined lower limit voltage Vlow (S12). If Vbat is less than Vlow, the process proceeds to S17, and if Vbat is equal to or greater than Vlow, the process proceeds to S20.

[0027] In S17, the control unit 31 determines whether the storage battery 34 is discharging. If the storage battery 34 is discharging, the discharge current Ibat is reduced to prevent over-discharge (S18). If the storage battery 34 is charging, there is still room for charging, so charging continues (S19).

[0028] Therefore, while the battery voltage Vbat is within the range between the upper limit voltage Vhigh and the lower limit voltage Vlow, the storage battery 34 is charged and discharged without suppressing the charge / discharge current Ibat. On the other hand, when the battery voltage Vbat is outside the range between the upper limit voltage Vhigh and the lower limit voltage Vlow, the charge / discharge current Ibat is suppressed to prevent overcharging and overdischarging of the storage battery 34. The upper limit voltage Vhigh and the lower limit voltage Vlow will be described in detail below.

[0029] (Charging operation of storage battery 34) Fig. 4 shows the relationship between the battery voltage Vbat of the storage battery 34 and the suppression gain when the power storage system according to the first embodiment of the present invention is charging. A charge suppression start voltage (= Vhigh) and a charge stop voltage (= OV (OverVolt): rated upper limit voltage) are defined with a predetermined battery voltage fluctuation taken into account relative to the rated voltage of the storage battery 34. The charge stop voltage is set to a value greater than the charge suppression start voltage. The charge suppression start voltage is the voltage at which the suppression gain starts to be lowered during charging, and the charge stop voltage is the voltage at which charging is stopped.

[0030] If charging is continued even when the battery voltage Vbat is equal to or higher than the charge stop voltage, the battery voltage Vbat will rise further, causing deterioration of the battery. To prevent deterioration of the storage battery 34, charging is stopped at the charge stop voltage.

[0031] For example, the charge suppression start voltage is +5% of the rated voltage, and the charge stop voltage is +10% of the rated voltage. The values ​​of the charge suppression start voltage and charge stop voltage relative to the rated voltage are not limited to these values ​​and may be any values. Furthermore, they are not limited to being multiplied by a coefficient, and may be values ​​that take an offset into account.

[0032] The charging current Ibat at which the storage battery 34 is charged is the current corresponding to the charge request multiplied by a suppression gain that takes a value between 0 and 1. The suppression gain during charging is 1 until the battery voltage Vbat reaches the charge suppression start voltage, and the storage battery 34 can be charged with a current corresponding to the charge request. In contrast, when the battery voltage Vbat exceeds the charge suppression start voltage and is below the charge stop voltage, the suppression gain takes a value between 0 and 1, changing so that the suppression gain is 1 at the charge suppression start voltage and 0 at the charge stop voltage.

[0033] That is, when the control unit 31 receives a charge request from the charge / discharge request unit 27, the processing differs depending on the battery voltage Vbat. If the battery voltage Vbat is equal to or lower than the charge suppression start voltage, charging is performed with a current according to the charge request. On the other hand, if the battery voltage Vbat is higher than the charge suppression start voltage but lower than the charge stop voltage, charging is performed with a current that is more suppressed than the current in the charge request. Furthermore, if the battery voltage Vbat is equal to or higher than the charge stop voltage, charging to the storage battery 34 is not performed.

[0034] The suppression gain may be changed, for example, linearly, but is not limited to this, and may be controlled so that the suppression of current is strengthened (the current Ibat is reduced) as the battery voltage Vbat increases. In particular, it is preferable that the suppression gain be changed in a continuous manner.

[0035] Without this suppression gain operation (current suppression), even if charging is stopped at the charge stop voltage, the rise in battery voltage does not stop immediately, resulting in deterioration of the storage battery 34. For this reason, by gradually weakening the charging from a charge suppression start voltage that is set before the charge stop voltage, charging can be stopped when the battery voltage is below the charge stop voltage.

[0036] (Discharge operation of storage battery 34) FIG. 5 shows the relationship between the voltage of the storage battery 34 and the suppression gain during discharging in the power storage system according to the first embodiment of the present invention. With respect to the rated voltage of the storage battery 34, a discharge suppression start voltage (=Vlow) and a discharge stop voltage (=UV (UnderVolt): rated lower limit voltage) are defined taking into account predetermined battery voltage fluctuations. The discharge suppression start voltage is set to a value smaller than the charge suppression start voltage. The discharge stop voltage is set to a value smaller than the discharge suppression start voltage. The discharge suppression start voltage is the voltage at which the suppression gain during discharging starts to be lowered, and the discharge stop voltage is the voltage at which discharging is stopped.

[0037] If discharging is performed even when the battery voltage Vbat is below the discharge stop voltage, the battery voltage Vbat will drop further, causing battery deterioration. In order to prevent deterioration of the storage battery 34, discharging is stopped at the discharge stop voltage.

[0038] For example, the discharge suppression start voltage is -5% of the rated voltage, and the discharge stop voltage is -10% of the rated voltage. The values ​​of the discharge suppression start voltage and discharge stop voltage relative to the rated voltage are not limited to these values ​​and may be any values. Furthermore, they are not limited to being multiplied by a coefficient and may be values ​​that take an offset into account.

[0039] The discharge current Ibat discharged by the storage battery 34 is the current corresponding to the discharge request multiplied by a suppression gain that takes a value between 0 and 1. The suppression gain during discharge is 1 until the battery voltage Vbat reaches the discharge suppression start voltage, and the storage battery 34 can discharge with a current corresponding to the discharge request. On the other hand, when the battery voltage Vbat falls below the discharge suppression start voltage and is equal to or higher than the discharge stop voltage, the suppression gain takes a value between 0 and 1, changing so that the suppression gain is 1 at the discharge suppression start voltage and 0 at the discharge stop voltage. The discharge current Ibat changes as the suppression gain changes according to the battery voltage Vbat. The discharge current Ibat is the rated current of the storage battery 34 multiplied by the suppression gain.

[0040] That is, when the control unit 31 receives a discharge request from the charge / discharge request unit 27, the processing differs depending on the battery voltage Vbat. If the battery voltage Vbat is equal to or higher than the discharge suppression start voltage, discharge is performed at a current according to the discharge request. On the other hand, if the battery voltage Vbat is lower than the discharge suppression start voltage but higher than the discharge stop voltage, discharge is performed at a current that is more suppressed than the discharge request. Furthermore, if the battery voltage Vbat is lower than the discharge stop voltage, discharge from the storage battery 34 is not performed.

[0041] The suppression gain may be changed, for example, linearly, but is not limited to this, and may be controlled so that the suppression of current is strengthened (the current Ibat is reduced) as the battery voltage Vbat decreases. In particular, it is preferable that the suppression gain be changed in a continuous manner.

[0042] Without this suppression gain operation (current suppression), even if discharge is stopped at the discharge stop voltage, the drop in battery voltage does not stop immediately, resulting in deterioration of the storage battery 34. For this reason, by gradually weakening the discharge from a discharge suppression start voltage that is set in advance of the discharge stop voltage, discharge can be stopped when the battery voltage reaches or exceeds the discharge stop voltage.

[0043] (Changes over time during charging and discharging of the storage battery 34) Therefore, when the storage battery 34 is charging, the battery voltage Vbat exceeds the charge suppression start voltage, causing the suppression gain to gradually decrease, preventing overcharging of the storage battery 34. On the other hand, when the storage battery 34 is discharging, the battery voltage Vbat falls below the discharge suppression start voltage, causing the suppression gain to gradually decrease, preventing overdischarging of the storage battery 34.

[0044] Fig. 6 shows changes in voltage, current, and SOC during an example of charging operation of the power storage system according to the first embodiment of the present invention. Regarding the current Ibat in Fig. 6, discharging is shown as positive. In the simulation of this application, the charging stop voltage is 635V, and the discharging stop voltage is 475V.

[0045] As shown in Figure 6, before charging starts, the battery voltage Vbat becomes higher than the bus voltage. As time passes, the battery voltage Vbat exceeds the charge suppression start voltage (625 V in this application) and gradually approaches the charge stop voltage (635 V in this application).

[0046] Regarding the current Ibat to the storage battery 34, when the battery voltage Vbat is less than the charge suppression start voltage, the charging current Ibat continues to charge at a nearly constant value. In contrast, when the battery voltage Vbat exceeds the charge stop voltage, the suppression gain decreases, causing the absolute value of the charging current Ibat to decrease, and when the battery voltage Vbat is close to the charge stop voltage, the charging current Ibat gradually approaches 0.

[0047] Regarding the SOC of the storage battery 34, when the battery voltage Vbat is less than the charge suppression start voltage, the SOC increases almost linearly, but once the battery voltage Vbat exceeds the charge suppression start voltage, the rate at which the SOC increases decreases, and eventually the rate becomes zero, and charging stops.

[0048] If charging and discharging are stopped in a stepwise manner (if the suppression gain is suddenly changed from 1 to 0), the battery voltage, storage battery current, and bus voltage will fluctuate suddenly, which may cause equipment on the DC system to suddenly stop. Also, when the battery voltage Vbat is close to the charging stop voltage and discharging stop voltage, the charging and discharging states will switch frequently, which may cause hunting.

[0049] In the first embodiment, the suppression gain is gradually reduced according to the battery voltage Vbat, so that the DC system voltage (bus voltage) does not change suddenly, and the DC system devices do not stop operating, and the DC system can be stabilized. Furthermore, by adjusting the suppression gain, sudden fluctuations in the battery voltage Vbat can be suppressed, and overshooting to the charge stop voltage and discharge stop voltage can be prevented, making it easier to stabilize the battery voltage Vbat.

[0050] Therefore, by performing the control according to the first embodiment during charging, it is possible to prevent overcharging of the storage battery 34, as well as to prevent a sudden rise in the bus voltage, and to prevent the bus voltage from exceeding the rated voltage of the equipment connected to the DC system. Although the operation during charging has been described, this is not limited to charging, and the same applies to discharging. That is, it is possible to prevent overdischarging of the storage battery 34, as well as to prevent a sudden drop in the bus voltage, and to prevent the DC equipment from falling outside the rated voltage range. This allows the storage battery 34 to have a longer life.

[0051] [Embodiment 2] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0052] In the first embodiment, the charge / discharge current Ibat is suppressed when the charge suppression start voltage or the discharge suppression start voltage is set as a threshold. Therefore, the storage battery 34 cannot be utilized with a sufficient current Ibat over the entire range from the discharge stop voltage to the charge stop voltage of the storage battery 34. In addition, the suppression of charge / discharge starts when the voltage is below the discharge suppression start voltage or above the charge suppression start voltage, which may result in excessive suppression.

[0053] (Adjustment of suppression gain by charge / discharge current Ibat) Therefore, in the second embodiment, in contrast to the first embodiment, a power storage system 30 is shown that utilizes a sufficient current Ibat over the entire voltage range from the discharge stop voltage to the charge stop voltage of the storage battery 34.

[0054] Fig. 7 shows the relationship between the battery voltage Vbat of the storage battery and the suppression gain during charging in the power storage system 30 according to the second embodiment of the present invention. As shown in Fig. 7, in the second embodiment, the charge suppression start voltage (or the discharge suppression start voltage) is changed without changing the charge stop voltage (or the discharge stop voltage) for each current corresponding to the charge request or the discharge request. In other words, the slope of the suppression gain is changed.

[0055] The larger the current corresponding to the charge or discharge request, the larger the voltage change due to the internal impedance Z of the storage battery 34, and therefore the larger the change in the battery voltage Vbat of the storage battery 34. Therefore, the larger the charge / discharge current Ibat, the more likely the battery voltage Vbat is to overshoot the charge stop voltage. To prevent overshoot, when the charge / discharge current Ibat is large, the suppression gain begins to be adjusted earlier.

[0056] On the other hand, the smaller the current corresponding to the charge or discharge request, the more gradual the change in the battery voltage of the storage battery 34, making it less likely that the battery voltage Vbat will overshoot the charge stop voltage. Therefore, when the charge or discharge current Ibat is small, the suppression gain can be adjusted more slowly.

[0057] That is, the smaller the current corresponding to the charge request, the greater the charge suppression start voltage, even if the charge suppression start voltage is set to a larger value, and the smaller the current corresponding to the discharge request, the less the battery voltage will fall below the discharge stop voltage, even if the discharge suppression start voltage is set to a smaller value. Therefore, since the battery voltage does not fall outside the voltage range from the discharge stop voltage to the charge stop voltage, deterioration of the storage battery 34 can be prevented, and a longer lifespan can be achieved. Furthermore, the wider voltage range in which sufficient current can be charged and discharged promotes the utilization of the storage battery 34.

[0058] Furthermore, when the current corresponding to the charge request or discharge request is small, even if the battery voltage becomes less than the charge suppression start voltage or becomes equal to or greater than the discharge suppression start voltage, the small current reduces fluctuations in the battery voltage and reduces the possibility of degrading the storage battery 34. Therefore, it is possible to prevent excessive suppression of the current in the voltage range from the discharge stop voltage to the charge stop voltage of the storage battery 34.

[0059] 8 shows changes in the battery voltage Vbat and current Ibat of the storage battery in an example of charging operation of the power storage system according to embodiment 2 of the present invention. The gray line, white line, and black line are graphs of the battery voltage and charging current Ibat over time when there is no control based on battery voltage fluctuations and charging continues even after the charging stop voltage is exceeded, when control according to embodiment 1 is performed, and when control according to embodiment 2 is performed, respectively.

[0060] The gray line in Figure 8 shows that, unlike the other two cases, the battery voltage Vbat is high and exceeds the battery's charging stop voltage. In contrast, the white and black lines in Figure 8 show that the battery voltage Vbat does not rise too much and is controlled to be below the battery's charging stop voltage.

[0061] Furthermore, the black line shows a higher battery voltage Vbat than the white line within the voltage range from the discharge stop voltage to the charge stop voltage, and it can be seen that the storage battery 34 can be utilized over a wider voltage range. Furthermore, in Figure 8, there is a portion where the white line and the black line diverge (approximately 0.25 to 0.27 in Figure 8), and by considering the current Ibat in addition to the battery voltage Vbat, it can be seen that the black line can utilize the storage battery 34 over a wider range than the white line. While the explanation has been given for the case of charging, similar control is possible for the case of discharging as well, and similar effects can be obtained.

[0062] Therefore, by taking into account the charge / discharge current Ibat in addition to the battery voltage Vbat, it is possible to prevent overcharging and overdischarging, while making use of sufficient current Ibat to the very limits of the voltage range from the discharge stop voltage to the charge stop voltage of the storage battery 34.

[0063] [Embodiment 3] Other embodiments of the present invention will be described below. For ease of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0064] (Suppression gain adjustment by internal impedance) In the third embodiment, similar to the second embodiment, a different power storage system is shown that utilizes the storage battery 34 with a sufficient current Ibat over the entire range from the discharge stop voltage to the charge stop voltage of the storage battery 34, as compared to the first embodiment.

[0065] 9 shows the relationship between the SOC and the open-circuit voltage Vsoc of the storage battery 34 in the power storage system according to the third embodiment of the present invention. The open-circuit voltage Vsoc of the storage battery 34 is calculated from the SOC based on a characteristic table specific to each storage battery 34.

[0066] Here, by using the open circuit voltage Vsoc, the internal impedance of the storage battery 34 can be calculated using the following equation.

[0067] Z=|(Vbat-Vsoc) / Ibat| It is generally known that the accuracy of calculating the internal impedance of a storage battery is poor. Therefore, it is not preferable to perform control using the internal impedance. However, in the third embodiment, the internal impedance is only used to adjust the suppression gain as described below, and it can be said that even if the accuracy is poor, it is necessary and sufficient.

[0068] Fig. 10 shows the relationship between the battery voltage of the storage battery and the suppression gain during charging of the power storage system according to the third embodiment of the present invention. As shown in Fig. 10, in the third embodiment, the slope of the suppression gain is changed according to the internal impedance Z of the storage battery 34 without changing the charge stop voltage (or discharge stop voltage). In other words, this is equivalent to changing the charge suppression start voltage (or discharge suppression start voltage).

[0069] Even with the same current Ibat, the greater the internal impedance Z of the storage battery 34, the greater the likelihood that the battery voltage Vbat will increase. Therefore, the greater the internal impedance Z, the more likely the battery voltage Vbat will overshoot the charging stop voltage. To prevent overshoot, when the internal impedance Z is large, the suppression gain begins to be adjusted earlier.

[0070] On the other hand, the smaller the internal impedance Z of the storage battery 34, the less likely the battery voltage Vbat is to increase, and therefore the less likely the battery voltage Vbat is to overshoot the charging stop voltage. Therefore, when the internal impedance Z is small, the suppression gain can be adjusted more slowly.

[0071] That is, the smaller the internal impedance of the storage battery, the less likely the battery voltage will exceed the charge stop voltage, even if the charge suppression start voltage is set to a larger value. Also, the smaller the internal impedance of the storage battery, the less likely the battery voltage will fall below the discharge stop voltage, even if the discharge suppression start voltage is set to a smaller value. Therefore, since the battery voltage does not fall outside the voltage range from the discharge stop voltage to the charge stop voltage, deterioration of the storage battery 34 can be prevented, and a longer lifespan can be achieved. Furthermore, the wider voltage range in which sufficient current can be charged and discharged promotes the utilization of the storage battery 34.

[0072] Furthermore, when the internal impedance is small, even if the battery voltage becomes less than the charge suppression start voltage or becomes equal to or greater than the discharge suppression start voltage, the small internal impedance reduces fluctuations in the battery voltage, reducing the possibility of deteriorating the storage battery 34. Therefore, it is possible to prevent excessive suppression of current in the voltage range from the discharge stop voltage to the charge stop voltage of the storage battery 34.

[0073] Fig. 11 shows changes in the battery voltage and current of the storage battery in an example of operation during charging of the power storage system according to embodiment 3 of the present invention when the internal impedance of the storage battery is large. Fig. 12 shows changes in the battery voltage and current of the storage battery in an example of operation during charging of the power storage system according to embodiment 3 of the present invention when the internal impedance of the storage battery is small. The gray line, white line, and black line are graphs of the battery voltage and charging current Ibat versus time when there is no control due to battery voltage fluctuation and charging continues even after the charging stop voltage is exceeded, when control according to embodiment 1 is performed, and when control according to embodiment 3 is performed, respectively.

[0074] The gray lines in Figures 11 and 12 show that, unlike the other two cases, the battery voltage Vbat is high and exceeds the battery's charging stop voltage. In contrast, the white and black lines in Figures 11 and 12 show that the battery voltage Vbat does not rise too much and is controlled to be below the battery's charging stop voltage.

[0075] Furthermore, the black line has a higher battery voltage Vbat than the white line within the voltage range from the discharge stop voltage to the charge stop voltage, and it can be seen that the storage battery 34 can be utilized over a wider voltage range. Furthermore, in Figures 11 and 12, there is a portion where the white line and the black line diverge (approximately 0.25 to 0.27 in Figures 11 and 12), and by considering the internal impedance Z in addition to the battery voltage Vbat, it can be seen that the black line can utilize the storage battery 34 over a wider range than the white line. Although the explanation was given for the case of charging, similar control is possible for the case of discharging as well, and similar effects can be obtained.

[0076] Therefore, by taking into account the internal impedance Z in addition to the battery voltage Vbat, it is possible to prevent overcharging and over-discharging, while making use of sufficient current Ibat to the very limits of the voltage range from the discharge stop voltage to the charge stop voltage of the storage battery 34.

[0077] 〔summary〕 In order to solve the above-mentioned problems, a power storage system according to one aspect of the present invention is a power storage system that supplies and receives power to a DC system, the DC system being a DC system including a DC bus and a charge / discharge request unit that issues a required charge or discharge request to the power storage system, the power storage system also including a storage battery that stores power, a conversion device that charges and discharges the storage battery and supplies power to the DC bus, and a control unit that controls the conversion device, and when the control unit receives the charge request from the charge / discharge request unit, The conversion device charges the storage battery with a current corresponding to the charge request when the terminal-to-terminal voltage is equal to or lower than a charge suppression start voltage, and with a current that is more suppressed than the charge request when the terminal-to-terminal voltage exceeds the charge suppression start voltage. Furthermore, upon receiving the discharge request from the charge / discharge request unit, the conversion device discharges the storage battery with a current corresponding to the discharge request when the terminal-to-terminal voltage of the storage battery is equal to or higher than a discharge suppression start voltage that is set to a value smaller than the charge suppression start voltage, and with a current that is more suppressed than the discharge request when the terminal-to-terminal voltage is lower than the discharge suppression start voltage.

[0078] According to the above configuration, the control unit receives a charge request or a discharge request from the charge / discharge request unit, thereby performing charging or discharging, and can suppress the current according to the terminal voltage of the storage battery, thereby preventing overcharging and overdischarging of the storage battery.

[0079] When the control unit receives the charging request from the charge / discharge request unit, it may stop charging of the storage battery using the conversion device if the terminal voltage of the storage battery is equal to or greater than a charging stop voltage set to a value greater than the charging suppression start voltage, and when it receives the discharging request from the charge / discharge request unit, it may stop discharging of the storage battery using the conversion device if the terminal voltage of the storage battery is equal to or less than a discharging stop voltage set to a value smaller than the discharging suppression start voltage.

[0080] According to the above configuration, charging and discharging can be stopped according to the terminal voltage of the storage battery, and therefore, current does not flow outside the voltage range from the discharge stop voltage to the charge stop voltage of the storage battery, thereby preventing overcharging and overdischarging of the storage battery.

[0081] The control unit may be configured to increase the current suppression as the terminal voltage of the storage battery increases from the charge suppression start voltage to the charge stop voltage, and to increase the current suppression as the terminal voltage decreases from the discharge suppression start voltage to the discharge stop voltage.

[0082] According to the above configuration, the degree of current suppression can be adjusted according to the terminal voltage of the storage battery, making it easier to prevent the battery voltage of the storage battery from falling outside the voltage range from the discharge stop voltage to the charge stop voltage.

[0083] The current that causes the converter to charge and discharge the storage battery may be a continuous value relative to the terminal voltage of the storage battery.

[0084] According to the above configuration, it is possible to prevent the voltage of the bus from changing suddenly, and it becomes easier to prevent the voltage of the device connected to the bus from falling outside the voltage range from the discharge stop voltage to the charge stop voltage.

[0085] The charge suppression start voltage may be set to a larger value as the current corresponding to the charge request decreases, and the discharge suppression start voltage may be set to a smaller value as the current corresponding to the discharge request decreases.

[0086] According to the above configuration, by changing the charge suppression start voltage and discharge suppression start voltage depending on the current corresponding to the charge request and discharge request, the storage battery can be used without suppressing the current over a wide range of voltages from the discharge stop voltage to the charge stop voltage of the storage battery, thereby improving the utilization of the storage battery.

[0087] The charge suppression start voltage may be set to a larger value as the internal impedance of the storage battery decreases, and the discharge suppression start voltage may be set to a smaller value as the internal impedance of the storage battery decreases.

[0088] According to the above configuration, by changing the charge suppression start voltage and discharge suppression start voltage according to the internal impedance of the storage battery, the storage battery can be used without suppressing the current over a wide voltage range from the discharge stop voltage to the charge stop voltage of the storage battery, thereby improving the utilization of the storage battery.

[0089] A power generating device and / or a DC load may be connected to the bus bar.

[0090] According to the above configuration, the storage battery can be charged by the power generation device.

[0091] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0092] 1 Power system 10 AC system 11 Commercial power supply 12 Transformer 13 AC-DC converter 20 DC system 21 First DC circuit breaker 22 bus (DC bus) 23 First DC-DC converter 24 Power generating equipment 25 DC load 26 EV charging stations 27 Charging and discharging request section 30 Energy Storage System 31 Control Unit 32 Second DC-DC converter (conversion device) 33 Second DC circuit breaker 34 Storage battery

Claims

1. An energy storage system that supplies and receives power to a DC system, the DC system is a DC system including a DC bus and a charge / discharge request unit that issues a required charge request or discharge request to the power storage system, a storage battery for storing electricity; a conversion device that charges and discharges the storage battery and supplies power to the DC bus; a control unit that controls the conversion device, The control unit When the charging request is received from the charging / discharging request unit, causing the conversion device to charge the storage battery with a current according to the charge request when the terminal voltage of the storage battery is equal to or lower than a charge suppression start voltage, and with a current obtained by multiplying the current according to the charge request by a first suppression gain when the terminal voltage of the storage battery exceeds the charge suppression start voltage; When the discharge request is received from the charge / discharge request unit, The power storage system causes the conversion device to discharge the storage battery with a current corresponding to the discharge request when the terminal voltage of the storage battery is equal to or greater than a discharge suppression start voltage that is set to a value smaller than the charge suppression start voltage, and with a current obtained by multiplying the current corresponding to the discharge request by a second suppression gain when the terminal voltage of the storage battery is less than the discharge suppression start voltage.

2. The control unit When the terminal voltage of the storage battery is equal to or higher than a charge stop voltage that is set to a value greater than the charge suppression start voltage, the conversion device is not allowed to charge the storage battery; 2. The power storage system according to claim 1, wherein the conversion device is not caused to discharge the storage battery when the terminal voltage of the storage battery is equal to or lower than a discharge stop voltage that is set to a value smaller than the discharge suppression start voltage.

3. The control unit Regarding charging the storage battery with a current that is suppressed more than the charging request, Control is performed so that current suppression is strengthened as the inter-terminal voltage of the storage battery increases from the charge suppression start voltage to the charge stop voltage, and Regarding discharging from the storage battery at a current that is suppressed more than the discharge request, 3. The power storage system according to claim 2, wherein control is performed such that current suppression is strengthened as the inter-terminal voltage of the storage battery decreases from the discharge suppression start voltage to the discharge stop voltage.

4. The control unit Regarding charging the storage battery with a current that is suppressed more than the charging request, Control is performed so that current suppression is gradually strengthened as the terminal voltage of the storage battery increases from the charge suppression start voltage to the charge stop voltage, and Regarding discharging from the storage battery at a current that is suppressed more than the discharge request, 4. The power storage system according to claim 2, wherein current suppression is controlled to be gradually strengthened as the inter-terminal voltage of the storage battery decreases from the discharge suppression start voltage to the discharge stop voltage.

5. The charge suppression start voltage is set to a larger value as the current corresponding to the charge request decreases, and The power storage system according to claim 1 , wherein the discharge suppression start voltage is set to a smaller value as the current corresponding to the discharge request is smaller.

6. The charge suppression start voltage is set to a larger value as the internal impedance of the storage battery decreases, and The power storage system according to claim 1 , wherein the discharge suppression start voltage is set to a smaller value as the internal impedance of the storage battery decreases.

7. The power storage system according to claim 1 , wherein the DC system is a DC system in which a power generation device is connected to the DC bus.

Images