JP2012147600A - Discharging method of storage battery provided in power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a discharging method capable of maximally obtaining a merit from the difference between a daytime power rate and nighttime power rate, and capable of operating a power storage device and correcting variations of cell output voltage at the same time, and furthermore capable of maintaining the operation of the power storage device in a state of an excellent SOC accuracy.SOLUTION: A discharging method comprises: a ratio reduction process for reducing a ratio of present charging amount to a charging capacity of a storage battery by discharging the storage battery and supplying power to a load; and a charging process for charging the storage battery, after the ratio reduction process, by the power supplied from a power system. At the ratio reduction process, the ratio is made to become closer to a lower limit ratio provided as the lower limit of the ratio for the discharging before the charging process is started. The ratio of the storage battery can be reduced by making the output voltage of the storage battery closer to a usage lower limit voltage VL of the storage battery.

Description

  The present invention relates to a method for discharging a storage battery provided in an electric power storage device that is connected to an electric power system and stores electric power.

[Power supply method for excess of contract power when contract power is exceeded]
When power is supplied from a power system of a power company to a load such as a home or a factory, contract power is determined in advance in a contract between the power company and the load side. The contract power Po is the maximum power that can be used by the load side in the contract between the power company and the load. When power exceeding the contracted power is used in the load, it is necessary to pay the contract surplus from the load side to the power company, or the fee paid from the load side to the power company in the contract becomes high.

  Here, even if a consumer such as a home or a factory consumes power exceeding the contract power at the load, the power between the power system and the load can be supplied so that the power exceeding the contract power can be supplied. A storage device is provided. The power storage device includes a storage battery (battery), and can charge the storage battery (store charge in the storage battery) by supplying power from the power system to the storage battery. And a storage battery discharges the electric charge stored by charge, for example, when electric power exceeding contract electric power is consumed in load. Accordingly, power is supplied to the load. In this way, consumers such as households and factories respond to the situation where power is consumed beyond contracted power.

  When the power consumption of the load exceeds the contract power, there are several methods for supplying the excess power to the contract power. Here, as an example, a method using a peak cut operation and a peak shift operation are used. A method of using will be described.

  In the peak cut operation, an upper limit of power supplied from the power system is determined. The upper limit is, for example, contract power.

  When the power is consumed in the load exceeding the upper limit, the power system supplies the contract power to the load. At the same time, as the storage battery of the power storage device discharges the electric charge stored by charging, the excess of contract power in the power consumption of the load is supplied to the load. Thereby, it is possible to cope with a situation where power is consumed exceeding the contract power, and it is possible to prevent the power supplied from the power system from exceeding the contract power.

  On the other hand, in the peak shift operation, the power charged (charged) in the storage battery at night is discharged in the daytime with a predetermined constant power. The constant power described here is independent of the contract power.

  First, consider the first time zone in which the power consumption of the load does not exceed the contract power. In such a first time zone, normal power supply is performed from the power system to the load.

  Next, consider the second time zone in which the power consumption of the load is expected to exceed the contract power. In such a second time zone, consumers such as homes and factories use storage batteries together with the power system. Thereby, electric power is supplied to the load. In the second time zone, the constant power is discharged from the storage battery regardless of the value of power supplied from the power system to the load.

  However, if the power supplied to the load exceeds the power consumption of the load due to the discharge of the storage battery, a reverse power flow from the storage battery to the power system occurs. Therefore, in practice, the constant power may be limited so that a reverse power flow does not occur.

  The important point in the peak shift operation described above is that the power supplied from the storage battery to the load is constant even when there is a time period during which the power consumption of the load does not exceed the contract power in the second time period. The point is that the power remains unchanged.

  As for performing the peak cut operation as described above, Patent Document 1 discloses a power storage device that performs a peak cut operation and a load leveling operation. The load leveling operation is an operation in which the storage battery is charged at night when the power rate is lower than the daytime, and the charged storage battery is discharged to the load during the daytime when the power consumption is large.

[Correction of variation in cell output voltage]
The storage battery mentioned above is comprised from the some cell, and the electric power supply from the storage battery is performed by supplying electric power from each cell.

  At this time, while charging and discharging are individually repeated in each cell, the output voltage of the cell may be different in each cell. That is, the cell output voltage may vary.

  If the output voltage of the cell varies, the life of each cell may vary, or the storage battery circuit may be burdened. In addition, since the voltage of all the cells is supplied when supplying power to the load, even if the output voltage of the cell varies, the accuracy of power supply to the load is not affected.

  Therefore, Patent Document 2 discloses that all cells constituting a storage battery are charged for a predetermined time with a smaller current after being overcharged, as a method for correcting variations in the output voltage of the cells. Yes. By performing such charging, all cells are uniformly overcharged (that is, evenly charged), and variations in the output voltage of the cells are corrected.

  In addition, the overcharge mentioned above is going to store an electric charge exceeding the full charge which is the state in which the electric charge was fully accumulate | stored.

[SOC correction]
Generally, the relative charge level called SOC (state of charge) is defined as the ratio of the remaining charge to the charge capacity of the storage battery.

  The SOC can be measured by, for example, a coulomb counter. In the coulomb counter, a coulomb counting process is performed to integrate the current flowing into the storage battery (current input to the storage battery) and the current flowing out of the storage battery (current output from the storage battery).

  However, due to the measurement error or calculation error in the current input to the storage battery and the current output from the storage battery, between the charge state measured with a coulomb counter or the like and the actual charge state in the storage battery, An error may occur.

  Therefore, in the conventional power storage device, the storage battery is completely discharged periodically or when there is a request from a control system that controls the charging and discharging of the storage battery (the remaining charge of the storage battery is made zero). . The SOC can be corrected based on the charge amount in this complete discharge.

JP 2002-271994 A (published on September 20, 2002) JP 2004-273295 A (published September 30, 2004)

  First, in the above [Power supply method for excess when contract power is exceeded], the power storage device of Patent Document 1 discloses that peak cut operation and load leveling operation are performed. Stated. However, the power storage device of Patent Document 1 has the following problems.

  The amount of power consumed by the load changes every day. In the power storage device of Patent Document 1, when the amount of power consumed by the load is small, the problem is that the storage battery cannot be discharged so that the output voltage of the storage battery reaches the use lower limit voltage by the time when charging at night starts. Has a point.

  Here, the use lower limit voltage is a lower limit of a voltage at which the storage battery can be safely discharged.

  By having the above-mentioned problems, the power storage device of Patent Document 1 has a reduced amount of charge at night compared to the case where the storage battery is discharged so that the output voltage of the storage battery reaches the lower limit voltage. Therefore, it is not possible to sufficiently obtain a merit due to the difference between the electricity bill for the daytime and the electricity bill for the night (the merit that the electricity bill is reduced by charging at night when the electricity bill is cheaper than the daytime).

  Secondly, in the above [Correction of cell voltage variation], the invention according to Patent Document 2 described overcharging the storage battery in order to correct the variation in the output voltage of the cell. However, the overcharge is to further accumulate charges from the full charge as described above, so that there is a possibility that the storage battery is damaged, which is problematic in terms of safety.

  In addition, in the invention according to Patent Document 2, the time for correcting the variation in the output voltage of the cell depends on the capacity of the storage battery, but usually requires about one day. For this reason, the power storage device cannot be operated on the day when the variation is corrected (power cannot be supplied to the load based on the discharge of the storage battery).

  Furthermore, in the invention according to Patent Document 2, it is conceivable to provide a circuit for performing correction for each cell in correcting the variation in the output voltage of the cell. However, the number of circuits for correction increases as the number of cells increases. This increases the manufacturing cost and operational cost.

  Thirdly, in the conventional power storage device described in [SOC correction], the SOC due to complete discharge of the storage battery is periodically or only when there is a request from the control system that controls the charge and discharge of the storage battery. Perform the correction. For this reason, when the frequency of SOC correction is lower than the required frequency, the power storage device is operated in a state where the accuracy of the SOC is poor (in a state where an error occurs in the measured SOC). There is a problem in terms of. Further, in the conventional power storage device described in [SOC correction], it is necessary to provide a special day for correcting the SOC, and there is a problem that the power storage device cannot be operated on this day. .

  The present invention has been made in view of the above-described conventional problems, and an object thereof is to provide a power storage device that can obtain the maximum benefit from the difference between a daytime electricity charge and a nighttime electricity charge. It is providing the discharge method of a storage battery.

  In order to solve the above-described problem, the discharge method of the present invention is a storage battery discharge method provided in a power storage device that is connected to a power system that supplies power to a load and stores the power supplied to the load. By discharging the storage battery and supplying power to the load, a ratio reduction step of reducing the ratio of the current charge amount to the charge capacity of the storage battery, and after the ratio reduction step, by the power supplied from the power system A charging step of charging the storage battery, and in the ratio reduction step, the ratio is brought close to a lower limit ratio that is the lower limit ratio set for discharging before the charging step is started. And

  The discharge method includes a ratio reduction step of discharging the storage battery and supplying power to the load to bring the ratio closer to the lower limit ratio before the charging step is started.

  Thereby, the ratio of the storage battery is closer to the lower limit ratio, which is the ratio of the lower limit set for discharging, than the ratio of the conventional storage battery, and no charge remains in the storage battery.

  Therefore, since the amount of charge in the above storage battery is larger than that in the conventional power storage device, the battery can be charged at the night when the electricity charge is lower than that in the daytime. This will maximize the benefits of lower power bills. Moreover, the use efficiency of the storage battery is improved as compared with a storage battery of a conventional power storage device. Furthermore, the effect of the load leveling operation, which is the operation of charging the storage battery at night when the power rate is lower than the daytime, and discharging the charged battery to the load during the daytime when the power consumption is higher than the nighttime, is the conventional power storage device. Get higher.

  In the discharging method, in the ratio reduction step, when the power exceeding the upper limit power that is the upper limit power supplied from the power system to the load is required, the excess power from the upper limit power is transferred from the storage battery. Charging of the storage battery is started in the charging step from the last time of the time zone in which the operation to supply the load is performed or the last time of the time zone in which the power consumption of the load is expected to exceed the upper limit power Until that time, the ratio may be lowered by discharging the storage battery and supplying power to the load.

  Thereby, the said ratio can be approximated to the said lower limit ratio.

  In the discharging method, when the storage battery is discharged in the ratio reduction step, the storage battery may be discharged at a low current that is a constant current that does not affect the life of the storage battery.

  In the discharge method, discharge is performed at the low current from the beginning to the end. Considering the characteristic that the life of the storage battery is shortened when the current during discharge is further increased, the ratio reduction step has the advantage that the influence on the life of the storage battery is the smallest.

  In the discharge method, in the ratio reduction step, when the output voltage of the storage battery is larger than a predetermined threshold voltage, the current does not affect the life of the storage battery, and the constant current is higher than the low current that is a constant current, While discharging the said storage battery, when the output voltage of the said storage battery is below the said threshold voltage, you may discharge the said storage battery with the said low current.

  In the discharge method, the current in the discharge is higher than the low current until the output voltage of the storage battery becomes equal to or lower than the threshold voltage. Therefore, it has the merit that the time until the ratio reduction step is completed can be further shortened.

  In the discharging method, in the ratio reduction step, when the output voltage of the storage battery is larger than a predetermined threshold voltage, the storage battery is discharged with a power that does not flow back from the storage battery to the power system. When the output voltage of the storage battery is equal to or lower than the threshold voltage, the storage battery may be discharged with a low current that is a constant current that does not affect the life of the storage battery.

  In the discharge method, the electric power is discharged with electric power that does not flow back to the electric power system. Therefore, there is an advantage that the time until the ratio reduction process is completed can be shortened.

  In the discharging method, the low current may be a constant current capable of discharging a storage battery having a nominal capacity value for at least 5 hours continuously. Thereby, in the said ratio reduction process, the said storage battery can be discharged at least 5 hours continuously by the said low electric current.

  In any one of the above discharge methods, the storage battery is charged at night when the power rate is lower than the daytime by discharging the charged storage battery before the ratio reduction step, and charging is performed during the daytime when the power consumption is large. A load leveling step for leveling the load by discharging the stored battery to the load may be further included.

  In any of the above discharge methods, when the load leveling step requires power exceeding an upper limit power that is an upper limit power supplied from the power system to the load, the upper limit power is calculated from the power system. While supplying to the load, a peak cut step of supplying excess power from the upper limit power to the load from the storage battery, and a time zone in which the power consumption of the load is expected to exceed the upper limit power, While supplying the said electric power from the said electric power grid | system to the said load, at least any one of the peak shift process of supplying the predetermined fixed electric power to the said load from the said storage battery may be included.

  Thereby, the load leveling effect higher than the case where the conventional power storage device is used can be obtained.

  In any one of the above discharge methods, the load is the most important load that needs to be supplied with power when a power outage or sag occurs in the power system, and the power when the power outage occurs in the power system. It includes an important load that does not require supply, and the output of the electric power system is connected to the most important load, and when there is no power outage or instantaneous drop in the electric power system, the output of the electric power system is In addition to connecting to the important load, when a power failure occurs in the power system, the power system may further include a switching step of performing control so that the output of the power system is not connected to the important load.

  As a result, in the power system, when the power failure or the instantaneous voltage drop occurs, the power is continuously supplied to the most important load, and when the power failure occurs, the power is not supplied to the important load. Can be made.

  In any one of the above discharge methods, the storage battery is composed of a plurality of cells, and the difference in output voltage between the cells can be reduced in the ratio reduction step. Therefore, the plurality of cells constituting the storage battery Variation in output voltage can be corrected.

  In the correction of the variation in the output voltage of the cell according to the present invention, it is not necessary to perform overcharge to store the charge beyond the full charge which is a state in which the charge is sufficiently stored as in the conventional method. . For this reason, the storage battery is not damaged by overcharge, which is advantageous from the conventional method in terms of safety.

  In the present invention, the variation in the output voltage of the cell can be corrected by the ratio reduction discharge performed every day. Therefore, unlike the conventional method, it is not necessary to provide a day for correcting the variation in the output voltage of the cell, and it is possible to achieve both the operation of the power storage device and the correction of the variation in the output voltage of the cell. .

  Furthermore, in the power storage device, variations in the output voltage of the cell can be corrected with a minimum configuration for charging and discharging. For this reason, unlike the conventional method, it is not necessary to provide a circuit for correcting variation in the output voltage of the cell for each cell. Therefore, manufacturing cost and operation cost can be reduced as compared with the conventional method.

  Any of the above discharge methods may further include a ratio correction step of correcting the ratio measured by the measuring device that measures the ratio according to the amount of charge discharged in the ratio reduction step.

  The ratio can be corrected by the ratio correction step. Then, by performing the ratio correction step every day, the ratio can be corrected every day.

  Therefore, unlike the conventional power storage device, it is not necessary to provide a special day for correcting the ratio, and the power storage device is operated with a high accuracy of the ratio (maintaining a high level ratio). Can continue to do. That is, in the power storage device, the ratio correction (maintenance) can be performed every day and without stopping the operation of the power storage device. For this reason, the power storage device has advantages over conventional power storage devices in terms of reliability and facility maintenance.

  Further, since the ratio can be displayed (or grasped) with high accuracy every day, the load leveling operation described above can be performed reliably. At the same time, the load leveling operation and the ratio correction can be performed as a series of operations.

  As described above, according to the discharging method of the present invention, it is possible to obtain the maximum benefit from the difference between the daytime electricity rate and the nighttime electricity rate, and also to vary the operation of the power storage device and the output voltage of the cell. Correction can be made compatible, and the power storage device can be continuously operated with a high accuracy of the ratio.

  As described above, the discharge method of the present invention discharges the storage battery and supplies power to the load, thereby reducing the ratio of the current charge amount to the charge capacity of the storage battery, and the ratio reduction process. A charging step of charging the storage battery with electric power supplied from the power system, and in the ratio reduction step, the ratio is set to a lower limit set for discharging until the charging step is started. This is a method of approaching the lower limit ratio which is the above ratio.

  Therefore, there is an effect of providing a method for discharging a storage battery included in the power storage device, which can obtain the maximum benefit of the difference between the electricity bill for the day and the electricity bill for the night.

It is a graph which shows three SOC reduction | decrease discharge proposed in embodiment of this invention, (a) is a graph which shows 1st SOC reduction | restoration discharge, (b) shows 2nd SOC reduction | restoration discharge. It is a graph and (c) is a graph which shows 3rd SOC reduction | restoration discharge. It is a block diagram which shows the electric power storage apparatus which concerns on embodiment of this invention. It is a graph which shows the time of using a peak cut operation | movement in the driving | operation of the electric power storage apparatus which concerns on embodiment of this invention. 5 is a graph when a peak shift operation is used in the operation of the power storage device according to the embodiment of the present invention. It is a graph which shows the relationship between the electric current and the output voltage of a cell at the time of the correction | amendment in the output voltage of a cell.

  One embodiment of the present invention will be described below with reference to FIGS. First, the power storage device 1 according to the present embodiment will be described with reference to FIG. In addition, the discharge method of the storage battery 6 concerning this embodiment is a discharge method of the storage battery 6 with which the electric power storage apparatus 1 which is connected to the electric power grid | system 2 which supplies electric power to the load mentioned later, and stores the electric power supplied to the said load is provided. is there.

[Power storage device 1]
FIG. 2 is a block diagram showing the power storage device 1 according to this embodiment. The power storage device 1 is a power storage device that is connected to a three-phase power system 2 and stores power. The power storage device 1 is a high-speed SW (switching) circuit 3, a two-winding transformer 4, a power converter 5, a storage battery (battery). ) 6, a switch 9 and a switch control circuit 10. In addition to the power storage device 1, FIG. 2 shows a commercial power system 2, the most important load 7, and the important load 8. The definition of the most important load 7 and the important load 8 will be described later.

  In FIG. 2, the output of the power system 2 is connected to one end of the high-speed SW circuit 3. The other end of the high-speed SW circuit 3 is connected to one end of the two-winding transformer 4, the input end of the most important load 7, and one end of the switch 9. The other end of the switch 9 is connected to the input end of the important load 8. The other end of the two-winding transformer 4 is connected to one end of the power converter 5. The other end of the power converter 5 is connected to the storage battery 6. The switch control signal Sc output from the switch control circuit 10 is input to the control input terminal of the switch 9.

  The power system 2 can supply the AC power P to the most important load 7 and the important load 8 via the high-speed SW circuit 3. The AC power P supplied to the most important load 7 and the important load 8 can be arbitrarily adjusted within the range of the contract power Po (upper limit power) described later.

  The high-speed SW circuit 3 opens between the power system 2 and the most important load 7 and the important load 8 when an accident occurs on the power system 2 side of the power company.

  The storage battery 6 can store the DC power P2 by charging shown below (charging process). In charging, first, AC power P output from the power system 2 is input to the two-winding transformer 4 via the high-speed SW circuit 3. In the two-winding transformer 4, the voltage of the AC power P is converted, and the AC power P <b> 1 whose voltage is converted is input from the two-winding transformer 4 to the power converter 5. In the power converter 5, the AC power P1 whose voltage has been converted is converted into DC power P2. The storage battery 6 is charged by supplying the direct-current power P <b> 2 from the power converter 5 to the storage battery 6.

  Further, the two-winding transformer 4, the power converter 5, and the storage battery 6 discharge based on the DC power P2 ′ stored in the storage battery 6 by the above charging, that is, the most important load 7 and the important load. AC power P ′ is supplied to 8. The discharge is performed as necessary, but when it is performed will be described later.

  Discharging is performed by the following process. First, the switch 9 whose opening / closing is controlled by the switch control signal Sc output from the switch control circuit 10 is normally closed. The normal time is when there is no power failure or voltage drop. At the same time, DC power P <b> 2 ′ stored in the storage battery 6 is output to the power converter 5. In the power converter 5, the input DC power P <b> 2 ′ is converted into AC power P <b> 1 ′, and the AC power P <b> 1 ′ is output to the two-winding transformer 4. In the two-winding transformer 4, voltage conversion of the AC power P <b> 1 ′ is performed, and the AC power P ′ whose voltage is converted is supplied to the most important load 7 and the important load 8. In this way, the storage battery 6 is discharged.

[Most important load 7 and important load 8]
Here, the most important load 7 and the important load 8 in FIG. 2 will be described below. In the electric power system 2 of FIG. 2, a power failure or instantaneous voltage drop (instantaneous voltage drop) may occur. In this case, the AC power P is not normally supplied to the most important load 7 and the important load 8.

  The most important load 7 is a load that needs to be supplied with electric power even if a power failure or instantaneous drop occurs. For this reason, when a power failure or instantaneous drop occurs in the power system 2, the storage battery 6 is discharged to the most important load 7. Thereby, the most important load 7 continues to be supplied with power.

  On the other hand, the important load 8 is a load that does not need to be supplied with power when a power failure occurs (the important load 8 needs to continue to be supplied with power when an instantaneous drop occurs). . For this reason, the switch control circuit 10 opens the switch 9 by sending a switch control signal Sc to the switch 9 when a power failure or instantaneous drop occurs in the power system 2. Thereby, in the power system 2, when a power failure or a momentary drop occurs, the power is continuously supplied to the most important load 7, and when the power failure occurs, the power is not supplied to the important load 8. (Switching process).

  As described above, in the power storage device 1, discharging is performed. Here, as an example of discharge, a method using a peak cut operation and a method using a peak shift operation will be described.

[Peak cut operation]
FIG. 3 is a graph showing when the peak cut operation is used in the operation (operation) of the power storage device 1. The horizontal axis of FIG. 3 and FIGS. 1 and 4 described later is time t. The peak cut operation will be described below.

  In the following description, when “load” is simply described, the load 20 including the most important load 7 and the important load 8 is indicated unless otherwise specified.

  In the peak cut operation, an upper limit of the AC power P supplied from the power system 2 is determined. This upper limit is, for example, contract power Po.

  The contract power Po is the maximum power that can be used by the load side in the contract between the power company and the load. When the power is used exceeding the contract power Po in the load, it becomes necessary to pay the contract surplus to the power company from the load side, or the fee paid to the power company in the contract becomes high.

  In FIG. 3, a case is considered in which the most important load 7 and the important load 8 consume power exceeding the contract power Po from time t1 to time t2 (final time). In this case, the power system 2 supplies the contract power Po to the most important load 7 and the important load 8. At the same time, when the storage battery 6 of the power storage device 1 is discharged, AC power P ′ as an excess from the contract power Po in the power consumption PL of the load is supplied to the load (peak cut process). As a result, it is possible to cope with a situation where power is consumed in the load exceeding the contract power Po, and the AC battery P supplied from the power system 2 contracts when the storage battery 6 of the power storage device 1 is discharged. It is possible to prevent the electric power Po from being exceeded.

  In the graph of FIG. 3, the peak cut operation is performed between time t6 and time t7 and between time t8 and time t2.

[Peak shift operation]
FIG. 4 is a graph when the peak shift operation is used in the operation of the power storage device 1. The peak shift operation will be described below.

  In the peak shift operation, the power charged (charged) in the storage battery 6 at night is discharged in the daytime with a predetermined constant power. The constant power described here is irrelevant to the contract power Po.

  First, consider the first time zone in which the power consumption of the load does not exceed the contract power Po. In FIG. 4, the first time zone is the time from time t0 to time t3 and the time after time t4 (final time). In such a first time zone, AC power P is supplied from the power system 2 to the load.

  Next, consider the second time zone in which the power consumption of the load is expected to exceed the contract power Po. In FIG. 4, the second time zone in which the peak shift operation is performed is from time t3 to time t4.

  In such a second time zone, consumers such as homes and factories use the storage battery 6 together with the power system 2. Thereby, electric power is supplied to the load. Specifically, the DC power P2 'is supplied from the storage battery 6 to the power converter 5, and the constant power is supplied to the load (peak shift process). In the second time zone, the constant power is discharged from the storage battery 6 regardless of the value of power supplied from the power system 2 to the load.

  However, if the power supplied to the load exceeds the power consumption of the load due to the discharge of the storage battery 6, a reverse flow from the storage battery 6 to the power system 2 occurs (the power flows back from the storage battery 6 to the power system 2). ). Therefore, in practice, the constant power may be limited so that a reverse power flow does not occur.

  The important point in the above-described peak shift operation is that the power supplied from the storage battery 6 to the load is the above even if there is a time zone in which the power consumption of the load does not exceed the contract power Po in the second time zone. The point is that the power remains constant.

  As described above, in the configuration using the power storage device 1 according to the present embodiment (configuration in FIG. 2), the peak cut operation is performed from the time t1 to the time t2, or between the time t3 and the time t4. By performing the peak shift operation, it is possible to cope with a situation where the power consumption of the load exceeds the contract power Po.

  In the second time zone, it is also assumed that the power consumption of the load exceeds the power due to the peak shift operation (the sum of the power supplied to the power system 2 and the constant power). Such a case is dealt with by performing a peak shift operation and a peak cut operation.

  In the configuration of FIG. 2, the storage battery 6 is charged, but charging is performed during a night charging time zone, which is a night time zone where the power rate is lower than during the daytime. In FIG. 3, the night charging time zone is from time t0 to time t1 and after the night charging start time t5, which is the night time when charging of the storage battery 6 is started. In FIG. 4, the first time zone is the night charge time zone (the time from time t0 to time t3 and the time after time t4 is the night charge time zone).

[SOC reduction discharge]
FIG. 1 is a graph showing three SOC reduction discharges proposed in this embodiment. 1A is a graph showing a first SOC reduction discharge, FIG. 1B is a graph showing a second SOC reduction discharge, and FIG. 1C is a third SOC reduction discharge. It is a graph which shows discharge.

  In FIG. 1, I6 indicates the output current of the storage battery 6, and V6 indicates the output voltage of the storage battery 6. The use lower limit voltage VL (lower limit voltage) and the threshold voltage Vth will be described later.

  First, SOC reduction discharge will be described. The SOC reduction discharge is a discharge that lowers the SOC (ratio) of the storage battery 6 (ratio reduction process). When the output voltage of the storage battery 6 is brought close to the use lower limit voltage VL of the storage battery 6 by the SOC reduction discharge, the SOC of the storage battery 6 is lowered (the lower limit SOC (lower limit ratio) which is the lower limit SOC set for discharge). Can be approached). The use lower limit voltage VL is the lower limit of the voltage at which the storage battery 6 can be discharged safely.

  As described in the section “Problems to be Solved by the Invention”, the amount of power consumed by the load changes every day. And, in the case of a day when the amount of power consumed by the load is small, the conventional power storage device cannot discharge the storage battery so that the output voltage of the storage battery reaches the use lower limit voltage by the time when the night charge starts. Had a point.

  Therefore, in the power storage device 1 according to the present embodiment, from the time t2 when the peak cut time period ends (or the time t4 when the second time period for performing the peak shift operation ends) to the night charge start time t5. The SOC reduction discharge is performed in the discharge time zone. As a result, the output voltage of the storage battery 6 becomes closer to the use lower limit voltage VL than the output voltage of the conventional storage battery, and no charge remains in the storage battery 6.

  Therefore, since the storage battery 6 of the power storage device 1 has a larger amount of charge at night than the storage battery of the conventional power storage device, the merit due to the difference between the daytime electricity charge and the nighttime electricity charge (the electricity charge is higher than the daytime). It is possible to obtain the maximum benefit) by charging at a cheap night. Moreover, the use efficiency of the storage battery 6 of the power storage device 1 is improved as compared with the storage battery of the conventional power storage device. In addition, the effect of the load leveling operation (load leveling process), which is the operation of charging the storage battery at night when the power rate is lower than the daytime, and discharging the charged battery to the load during the daytime when the power consumption is higher than at night ( The load leveling effect) is also higher than that of the conventional power storage device.

  Even when the peak cut operation is not performed once in one day (when the load power consumption PL does not exceed the contract power Po once), the time for performing the SOC reduction discharge does not change (described above). Thus, it is from the time t2 when the peak cut time period ends to the night charging start time t5).

  Moreover, even if the power consumption PL of the load exceeds the contract power Po by the start of the SOC reduction discharge until the night charge start time t5, the SOC reduction discharge is continued. In this case, the end time of the SOC reduction discharge is earlier than when the power consumption PL of the load does not exceed the contract power Po. And since the time slot | zone which performs SOC reduction | restoration discharge is not a peak cut time slot | zone, even if the power consumption PL of load exceeds contract electric power Po at the time of SOC reduction | restoration discharge, peak cut operation | movement is not performed.

  Further, FIGS. 1A to 1C all show the SOC reduction discharge when the peak cut operation is performed, but the same applies to the peak shift operation. That is, in the power storage device 1 according to the present embodiment, the SOC reduction discharge is performed from the time t4 when the peak shift operation time period ends to the night charge start time t5. Then, even if the power consumption PL of the load exceeds the contract power Po during the SOC reduction discharge, the SOC reduction discharge is continued without performing the peak shift operation.

  Here, the maximum advantage is obtained when the output voltage of the storage battery 6 reaches the use lower limit voltage VL by the night charging start time t5, but the start time of “SOC reduction discharge” (in FIG. 1). If the time t2) is late, the use lower limit voltage VL may not be reached at the start of charging at night. The start time of “SOC reduction discharge” is determined in advance in a time table or the like, but the start time may be changed in consideration of the power consumption tendency of the previous day. By doing so, the start time of “SOC reduction discharge” is advanced, and the output voltage of the storage battery 6 can reach the use lower limit voltage VL by the night charge start time t5. Therefore, the above merits can be obtained to the maximum. In this case, “SOC reduction discharge” is referred to as “SOC lower limit reaching discharge”.

  Here, each of the three SOC reduction discharges shown in FIGS. 1A to 1C, that is, the first SOC reduction discharge to the third SOC reduction discharge will be described.

[First SOC reduction discharge]
The first SOC reduction discharge in FIG. 1A will be described below. In the first SOC reduction discharge, discharge is performed at a constant low current from the time t2 when the peak cut time period ends to the night charge start time t5 (that is, low power corresponding to the low current is discharged). To do). Thereby, the output voltage of the storage battery 6 can be brought close to the use lower limit voltage VL by the night charge start time t5 (when possible, the use voltage reaches the use lower limit voltage VL).

  The low current in the above description is a current in a range where the influence on the life of the storage battery 6 is extremely small (a level that does not affect the life of the storage battery and a constant current), and varies depending on the performance of the storage battery 6. When the low current is expressed using “C” in the technical field of the battery, for example, the current is 0 to 0.2 C. However, the low current varies depending on the performance of the storage battery 6, so the low current is 0 to 0.2 C. It is clear that the range is not limited to 0.2C.

  The above-mentioned “C” will be described. A current of 1 C is a constant current that discharges a cell having a capacity of a nominal capacity value and completes the discharge in just one hour. When illustrated using numerical values, in the storage battery 6 having a nominal capacity value of 2.2 Ah (ampere hour), 1C = 2.2 A (ampere).

  Moreover, the current of 0.2 C is a current that does not substantially affect the characteristics of the storage battery 6 and the performance of the storage battery 6, and is a constant current that causes the storage battery 6 having a nominal capacity value to finish discharging in 5 hours. (A constant low current capable of discharging a storage battery having a nominal capacity value for at least 5 hours continuously). When using numerical values as in the case of the current of 1 C, for example, in the storage battery 6 having a nominal capacity value of 2.2 Ah (ampere hour), 0.2C = 0.44 A (ampere).

  The first SOC reduction discharge is discharged at a low current from the beginning to the end. For this reason, time until SOC reduction discharge is completed becomes longer than the 2nd and 3rd SOC reduction discharge mentioned later. However, in consideration of the characteristic that the life of the storage battery 6 is shortened when the current during discharge is further increased, the first SOC reduction discharge has an advantage that the influence on the life of the storage battery 6 is the smallest.

[Second SOC reduction discharge]
The second SOC reduction discharge in FIG. 1B will be described below. In the second SOC reduction discharge, discharge is performed at a constant current higher than the low current until the output voltage V6 of the storage battery 6 becomes equal to or lower than a predetermined threshold voltage Vth. And when the output voltage V6 of the storage battery 6 becomes below the threshold voltage Vth, it discharges with the said low current.

  In the second SOC reduction discharge, the current in the discharge is higher than the low current until the output voltage V6 of the storage battery 6 becomes equal to or lower than the predetermined threshold voltage Vth. Therefore, there is an advantage that the time until the output voltage reduction is completed can be made shorter than that of the first SOC reduction discharge.

[Third SOC reduction discharge]
The third SOC reduction discharge in FIG. 1C will be described below. In the 3rd SOC reduction discharge, it discharges with the maximum electric power which can be discharged until the output voltage V6 of the storage battery 6 becomes below the predetermined threshold voltage Vth. The maximum dischargeable power described here is power in a range where reverse power flow does not occur, and is equal to or lower than power consumption of the load. Further, the reverse power flow means that power is returned from the storage battery 6 to the power system 2 in reverse when the power supplied to the load exceeds the power consumption of the load. And when the output voltage V6 of the storage battery 6 becomes below the threshold voltage Vth, it discharges with the said low current.

  In the third SOC reduction discharge, the discharge is performed with the maximum dischargeable power. Therefore, there is a merit that the time until the SOC reduction discharge is completed can be made the shortest among the three SOC reduction discharges (the first SOC reduction discharge to the third SOC reduction discharge).

  In the power storage device 1 of FIG. 2, any one of the first to third SOC reduction discharges is performed. For example, if the storage battery 6 has a large charge when starting the SOC reduction discharge, It is more preferable to perform 2 SOC reduction discharge or 3rd SOC reduction discharge. Further, if the influence on the life of the storage battery 6 is to be made as small as possible, the first SOC reduction discharge may be performed.

[Correction of variation in cell output voltage]
The storage battery 6 shown in FIG. 2 is comprised from the some cell, and the electric power supply (discharge) from the storage battery 6 is performed by supplying electric power from each cell.

  At this time, while charging and discharging are individually repeated in each cell, the cell output voltage may be different in each cell (that is, the cell output voltage may vary).

  If the output voltage of the cell varies, the life of each cell may vary, or the circuit of the storage battery 6 may be burdened. In addition, since the voltage of all the cells is supplied when supplying power to the load, even if the output voltage of the cell varies, the accuracy of power supply to the load is not affected.

  However, in the power storage device 1 according to the present embodiment, any one of the first to third SOC reduction discharges is performed. Thus, since the output voltage of the storage battery 6 approaches the lower limit voltage VL of use than the output voltage of the conventional storage battery until the night charging start time t5, the output between the cells is performed by performing the SOC reduction discharge. The voltage difference can be reduced, that is, variations in output voltages of a plurality of cells constituting the storage battery 6 can be corrected.

  The current when correcting the variation in the output voltage of the cell does not need to be lower than the low current, and may be equal to the low current, for example. Thereby, since the output voltage of the storage battery 6 reliably reaches the use lower limit voltage VL, the output voltage of the cell is also reliably corrected.

  In the correction of the variation in the output voltage of the cell proposed in the present embodiment, as in the conventional method, the overcharge that tries to store the charge is performed beyond the full charge that is a state in which the charge is sufficiently stored. There is no need. For this reason, since the storage battery 6 is not damaged by overcharge, it is more advantageous than the conventional method in terms of safety.

  Further, the variation in the output voltage of the cell can be performed after the end of the SOC reduction discharge performed every day. For this reason, it is not necessary to provide a day for correcting the variation in the output voltage of the cell as in the conventional method, and both the operation of the power storage device 1 and the correction of the variation in the output voltage of the cell can be achieved. .

  Furthermore, the power storage device 1 can correct variations in the cell output voltage with a minimum configuration for charging and discharging. For this reason, unlike the conventional method, it is not necessary to provide a circuit for correcting variation in the output voltage of the cell for each cell. Therefore, manufacturing cost and operation cost can be reduced as compared with the conventional method.

  FIG. 5 is a graph showing the relationship between the current and the cell output voltage when correcting variations in the cell output voltage. The current is a current I6 output from the storage battery 6 when discharging.

  The graph of FIG. 5 is a graph in the case where the storage battery 6 is composed of four cells. At time t9 when the current I6 is larger, the output voltages of the four cells (four cell voltages V1 to V4) are in the range of 2.90V to 2.97V. On the other hand, at the time t10 when the current I6 is smaller, the four cell voltages V1 to V4 are in the range of 2.90V to 2.92V.

  As described above, by reducing the current I6 output from the storage battery 6 when discharging, the discharge amount can be reduced and fine adjustment of the discharge can be performed, so that the variation in the cell voltage can be further reduced.

[SOC correction]
Generally, the relative charge level called SOC is defined as the ratio of the remaining charge (current charge) to the charge capacity of the storage battery.

  The SOC can be measured by a measuring device 21 (for example, a coulomb counter) connected to the storage battery 6. In the coulomb counter, a coulomb counting process is performed to integrate the current flowing into the storage battery (current input to the storage battery) and the current flowing out of the storage battery (current output from the storage battery).

  Here, due to a measurement error or a calculation error in the current input to the storage battery 6 and the current output from the storage battery 6, the charge state measured by a coulomb counter or the like and the actual charge state in the storage battery In some cases, an error occurs (the accuracy of the SOC deteriorates). When the accuracy of the SOC is deteriorated, the accuracy of charge / discharge control of the storage battery is deteriorated.

  For this reason, in the conventional power storage device, the storage battery is completely discharged periodically or when there is a request from a control system that controls the charging and discharging of the storage battery (the remaining charge of the storage battery is reduced to zero). ). Then, the SOC is corrected based on the charge amount in this complete discharge.

  In addition, in the conventional electric power storage apparatus which correct | amends SOC as mentioned above, it cannot grasp | ascertain when a use lower limit voltage is reached at the time of normal operation.

  On the other hand, in the power storage device 1 according to the present embodiment, any one of the first to third SOC reduction discharges can be performed every day. Based on the discharge amount in the SOC reduction discharge, the SOC can be corrected every day (ratio correction step).

  Therefore, unlike the conventional power storage device, it is not necessary to provide a special day for correcting the SOC, and the power storage device 1 is operated with a high SOC accuracy (maintaining a high level of SOC). Can continue to do. That is, in the power storage device 1 according to the present embodiment, the SOC correction (maintenance) can be performed every day without stopping the operation of the power storage device 1. For this reason, the power storage device 1 has advantages over the conventional power storage device in terms of reliability and facility maintenance.

  In addition, since the SOC can be displayed (or grasped) with high accuracy every day, the load leveling operation described above can be performed with peace of mind. At the same time, the load leveling operation and the SOC correction can be performed as a series of operations.

  The current for correcting the SOC does not need to be lower than the low current, and may be equal to the low current, for example. Thereby, since the output voltage of the storage battery 6 reliably reaches the use lower limit voltage VL, the amount of discharge until it reaches the use lower limit voltage VL can be accurately grasped, and the SOC is also reliably corrected.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  The discharge method of the present invention can obtain the maximum merit by the difference between the electricity bill for daytime and the electricity bill for night, and can achieve both the operation of the power storage device and the variation correction of the output voltage of the cell. In addition, since the power storage device can be continuously operated with a high SOC accuracy, it can be suitably used for a load whose power consumption exceeds contract power.

DESCRIPTION OF SYMBOLS 1 Power storage device 2 Power system 3 High-speed SW circuit 4 Two-winding transformer 5 Power converter 6 Storage battery 7 Most important load 8 Important load 9 Switch 20 Load 21 Measuring device 10 Switch control circuit I6 Current P AC power P 'AC power P1 AC power P1 'AC power P2 DC power PL Power consumption Po Contract power (upper limit power)
Sc switch control signal V1 to V4 Cell voltage V6 Output voltage VL Lower limit voltage (lower limit voltage)
Vth threshold voltage t time t0, t1, t3, t6 to t10 time t2 time t4 time t5 night charge start time

Claims (11)

A method for discharging a storage battery, which is connected to an electric power system that supplies electric power to a load and includes an electric power storage device that stores electric power supplied to the load,
A ratio reduction step of reducing the ratio of the current charge amount to the charge capacity of the storage battery by discharging the storage battery and supplying power to the load;
A charging step of charging the storage battery with electric power supplied from the power system after the ratio reduction step;
In the ratio reducing step, the ratio is brought close to a lower limit ratio that is the lower limit ratio set for discharging before the charging step is started. In the above ratio reduction process,
When power exceeding the upper limit power, which is the upper limit power supplied from the power system to the load, is required, the end of the time period for performing the operation of supplying the excess power from the upper limit power to the load from the storage battery The storage battery is discharged from the time or the last time in the time zone in which the power consumption of the load is expected to exceed the upper limit power to the time when charging of the storage battery is started in the charging step. The discharge method according to claim 1, wherein the ratio is lowered by supplying electric power to the load.   3. The discharging method according to claim 2, wherein when the storage battery is discharged in the ratio reduction step, the storage battery is discharged at a low current that is a constant current that does not affect the life of the storage battery. . In the above ratio reduction process,
When the output voltage of the storage battery is greater than a predetermined threshold voltage, the storage battery is discharged with a constant current higher than a low current that is a constant current to a degree that does not affect the life of the storage battery,
The discharging method according to claim 2, wherein when the output voltage of the storage battery is equal to or lower than the threshold voltage, the storage battery is discharged with the low current. In the above ratio reduction process,
When the output voltage of the storage battery is greater than a predetermined threshold voltage, the storage battery is discharged with power that does not flow back from the storage battery to the power system, and
3. The discharging method according to claim 2, wherein when the output voltage of the storage battery is equal to or lower than the threshold voltage, the storage battery is discharged at a low current that is a constant current that does not affect the life of the storage battery. .   6. The discharging method according to claim 3, wherein the low current is a constant current capable of discharging a storage battery having a capacity of a nominal capacity value for at least 5 hours continuously.   Before the ratio reduction step, the charged storage battery is discharged to charge the storage battery at night when the power rate is lower than the daytime, and from the charged storage battery to the load during the daytime when the power consumption is large. The discharge method according to claim 1, further comprising a load leveling step of leveling the load by discharging. The load leveling process is
When power exceeding the upper limit power, which is the upper limit power supplied from the power system to the load, is required, the upper limit power is supplied from the power system to the load, and the excess power from the upper limit power is In the peak cut step of supplying the load from the storage battery to the load, and in a time zone where the power consumption of the load is expected to exceed the upper limit power, the power is supplied from the power system to the load and is set in advance. The discharge method according to claim 7, further comprising at least one of a peak shift step of supplying a certain amount of electric power from the storage battery to the load. The load is a most important load that requires power supply when a power failure or instantaneous drop occurs in the power system, and an important load that does not require power supply when a power failure occurs in the power system. Including
The output of the power system is connected to the most important load,
Control that does not connect the output of the power system to the important load when a power failure occurs in the power system, and connects the output of the power system to the important load when the power system does not cause a power failure or instantaneous drop The discharge method according to claim 2, further comprising a switching step of performing the operation. The storage battery is composed of a plurality of cells,
The discharge method according to any one of claims 1 to 9, wherein in the ratio reduction step, a difference in output voltage between the cells can be reduced.   The ratio correction step of correcting the ratio measured by the measuring device for measuring the ratio according to the amount of charge discharged in the ratio reduction step is further included. 2. The discharge method according to item 1.

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