JP2007024475A - Storage type air conditioning system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a storage type air conditioning system capable of efficiently equalizing electric power demand. <P>SOLUTION: The storage type air conditioning system has air conditioners 2A, 2B and a storage battery 33 for storing commercial electric power of a commercial power source 10, and supplies stored electric power and the commercial electric power, stored in the storage battery 33, to operate the air conditioners 2A, 2B. The storage type air conditioning system comprises a storage air-conditioning controller 33 carrying out charge to the storage battery 33 at night when electric power demand is less, and discharging stored electric power charged in the storage battery 33, in a discharge period T2 including at least a peak period T3 of electric power demand. The storage air-conditioning controller 33 is constituted to control the discharge of the stored electric power so that the residual electric power amount Wz of the stored electric power is almost zero at the end of the discharge period T2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power storage type air conditioning system.

  In recent years, in summer and winter, the difference in power consumption between day and night has tended to become very large, which has been an adverse effect on the efficient supply of power. In particular, in order to cope with environmental problems and energy problems such as global warming, it is important to improve the efficiency of power supply by leveling power demand. It is said that one of the main causes of the difference in daily power demand is air conditioning power demand, and the simultaneous operation of air conditioners during hot summers or cold winters has boosted the peak value of power demand. It is believed that. Conventionally, a heat storage type air conditioner has been proposed as an air conditioner for solving such problems (see, for example, Patent Document 1).

A heat storage type air conditioner operates an air conditioner at night when electric power demand is low, stores heat or stores heat in a heat storage material, and performs air conditioning using the heat in the daytime. By doing so, the peak of power demand generated during the daytime can be shifted to nighttime, which can contribute to the leveling of power demand as a whole. As a typical heat storage type air conditioner, there is an ice heat storage type air conditioner using ice as a heat storage material.
JP 2004-301400 A

  However, in the ice heat storage type air conditioner, since ice is produced by the heat pump action, since the evaporation temperature of the refrigerant is low, the efficiency becomes lower and the energy saving effect is lower than in the normal cooling operation. In addition, there is a problem that the cooling and heating capacities are unbalanced due to the difference between the latent heat in ice storage and the sensible heat of hot water during heating.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a power storage type air conditioning system capable of efficiently leveling power demand.

  In order to achieve the above object, the present invention includes one or a plurality of air conditioners and a storage battery that stores commercial power of a commercial power source, and supplies the stored power and the commercial power stored in the storage battery. A power storage air conditioning system for operating the air conditioner, wherein the storage battery is charged at night when power demand is low, and the storage battery is charged at least during a discharge period including a peak period of the power demand Power storage control means for discharging power is provided, wherein the power storage control means controls the discharge of the stored power so that the remaining power amount of the stored power becomes substantially zero at the end of the discharge period.

  Further, the present invention, in the above invention, further comprises storage means for storing a power demand fluctuation prediction pattern that is a predicted value of a fluctuation pattern of a daily power demand, wherein the power storage control means includes the power demand fluctuation prediction pattern, A discharge pattern of the stored electric power in the discharge period is determined based on an upper limit value of the power consumption of the commercial power source at a power demand peak.

  In the above invention, the present invention further comprises a remaining amount detecting means for detecting a remaining power amount of the stored power of the storage battery, wherein the storage control means is configured such that when the power demand fluctuation prediction pattern on the next day is the same as this time, The discharge pattern of the next day is corrected based on the remaining power amount at the end of the discharge period.

  In the above invention, the present invention further comprises a remaining amount detecting means for detecting a remaining power amount of the stored power of the storage battery, wherein the storage control means is based on the remaining power amount detected within the discharge period. The discharge pattern in the remaining time of the discharge period is corrected.

  In the above invention, the present invention further includes a temperature sensor that detects an air temperature, and the power storage control unit corrects the power demand fluctuation prediction pattern based on the air temperature, and the corrected power demand fluctuation prediction pattern. The discharge pattern is determined based on the above.

  Moreover, the present invention is characterized in that, in the above-mentioned invention, the power storage control means increases the discharge power amount in the peak period of the discharge period.

  According to the present invention, the storage battery is charged with commercial power, and the storage battery is charged at night when power demand is low, and the storage battery is charged at least during a discharge period including a peak period of the power demand. Since the stored power is discharged, the power demand can be leveled efficiently.

Embodiments of the present invention will be described below with reference to the drawings.
<First embodiment>
FIG. 1 is a block diagram showing a schematic configuration of a power storage type air conditioning system 1 according to the present embodiment. The power storage type air conditioning system 1 includes an air conditioner group 2, a power storage unit 3, and a PCS controller 4. The air conditioner group 2 includes an outdoor unit and a plurality of air conditioners 2A and 2B (two in the illustrated example) each including one or a plurality of indoor units connected to the outdoor unit by a refrigerant circuit. The air conditioners 2A and 2B are connected in parallel to an AC load line 11 to which, for example, AC 200V is supplied.

  The power storage unit 3 is connected to a power storage power supply line 13 branched from the power supply line 12 of the commercial power supply 10 that supplies AC power of, for example, AC 200 V, and stores the commercial power. It has an air conditioning controller 31, a battery charger 32, and a storage battery 33. The stored power supply line 13 is branched into two systems. A DC power source 30 is connected to one stored power supply line system 13A, and a battery charger 32 is connected to the other stored power supply line system 13B.

  The DC power supply 30 generates operating voltages for various circuits, converts AC power from the commercial power supply 10 into DC power of a predetermined voltage (for example, 5 V), and supplies the DC power to the power storage air conditioning controller 31. The power storage air-conditioning controller 31 controls the power storage / discharge of the power storage unit 3. The power storage air-conditioning controller 31 incorporates a memory 31 </ b> A such as an EEPROM and operates according to a control program stored in the memory 31 </ b> A. The battery charger 32 incorporates a converter circuit 32A that converts AC power from the commercial power supply 10 into DC power and outputs the DC power. Under the instruction of the power storage air conditioning controller 31, the DC power is supplied via the battery charging line 14. Supplied to the storage battery 33. In the present embodiment, the power storage air-conditioning controller 31A outputs a charge start signal to the storage battery 33 to the battery charger 32 during the night time when the power demand is relatively small during the day, Charging to the storage battery 33 is started. The storage battery 33 is a lead storage battery or a battery such as nickel cadmium, nickel-hydrogen, nickel-zinc, sodium-sulfur, zebra battery, lithium, and the like, and is charged via a battery discharge line 15 drawn from the storage battery 33. The generated power is output to the PCS controller 4.

  The PCS controller 4 is interposed between the power supply line 12 from the commercial power supply 10 and the AC load line 11 and links the stored power to the commercial power at a predetermined ratio under the instruction of the power storage air conditioning controller 31. This is output to the AC load line 11. That is, the PCS controller 4 includes an inverter circuit 4A that is connected to the battery discharge line 15 and converts the DC power supplied from the storage battery 33 into AC power and outputs the AC power to the AC load line 11. 31A outputs a control signal to the PCS controller 4 so that the stored power of the storage battery 33 is supplied to the AC load line 11 at a predetermined rate during the daytime when the power demand is relatively large during the day. Control is performed so that commercial power is supplied during other time periods.

  According to the power storage air conditioning system 1 having such a configuration, the power storage air conditioning controller 31 controls the PCS controller 4 so that the stored power and commercial power of the storage battery 33 are supplied to the AC load line 11 during the peak time of power demand. Since only commercial power is supplied to the AC load line 11 during other time periods, stored power and commercial power are supplied from the storage battery 33 during daytime periods when the power demand peaks. Since the air conditioners 2A and 2B are operated and the storage battery 33 is charged at night when the power demand is small, the consumption amount of the commercial power supply 10 at the time of power peak is suppressed.

  Here, in the electricity storage type air conditioning system 1, as described above, when operating the air conditioners 2 </ b> A and 2 </ b> B during the daytime when the power demand is relatively large during the day, not only the stored power but also the commercial power is used. In addition, the air conditioners 2A and 2B are supplied. That is, as long as the storage battery 33 has a capacity that can sufficiently store the power used by the air conditioners 2A and 2B during the daytime, the storage battery can be used without using commercial power during the daytime. Although it is possible to operate each of the air conditioners 2A and 2B with only the electric power stored in 33, the cost of the storage battery 33 becomes very high, which is not realistic.

  Therefore, in the power storage type air conditioning system 1, the cost of the storage battery 33 is reduced by supplying stored power and commercial power to the air conditioners 2A and 2B during the daytime. At this time, in the present embodiment, the storage battery 33 is always discharged during the daytime period to continue supplying the stored power, thereby reducing the power consumption of the commercial power in the daytime period as a whole. (So-called peak shift).

  Specifically, in the present embodiment, the power demand, that is, the daily fluctuation prediction pattern P of the cooling / heating load ratio of the air conditioner group 2 (hereinafter referred to as “heating / heating load prediction pattern P”) Only a plurality of patterns are stored in advance in the memory 31A in association with each season. The heating / cooling load ratio indicates the ratio of the required load to the maximum value of the heating / cooling load, and can be regarded as substantially equivalent to the fluctuation pattern of the daily power demand. In general, since most of the air conditioner group 2 is operated for air conditioning operation in the daytime, as shown in FIG. 2, the heating / cooling load ratio tends to be higher in the daytime period than in the nighttime. When the air conditioner group 2 is operated only with commercial power, the fluctuation pattern of the commercial power consumption (hereinafter referred to as “commercial power prediction pattern” C) is approximated to the cooling / heating load prediction pattern P. Become. Therefore, as shown in FIG. 3, by discharging the storage battery 33 with the discharge pattern H that always bears a certain ratio of the heating / cooling load ratio with the stored power during the time period between Chiru-to, the commercial power The fluctuation pattern Ca can be a pattern in which the commercial power prediction pattern C is shifted downward as a whole, and the daily power demand is leveled.

  Describing in detail the discharge control of the stored power at this time, as shown in FIG. 4, the power storage air-conditioning controller 31 determines a cooling / heating load prediction pattern P suitable for the current season based on the current date and reads it from the memory 31A ( Step Sa1). Next, the power storage air conditioning controller 31 determines the discharge pattern H in the daytime period based on the peak value Pmax of the air conditioning load prediction pattern P (step Sa2). Specifically, as shown in FIG. 3 above, an upper limit value G (hereinafter referred to as “commercial power burden upper limit value G”) of the ratio of sharing the power consumed by the heating and cooling load with commercial power is set in advance. The power storage air-conditioning controller 31 assigns a ratio A (hereinafter referred to as “discharge power share ratio A”) corresponding to (Pmax−G) to the discharge power so that the ratio of the commercial power to the power consumption of the heating / cooling load can be increased. The commercial power burden upper limit G is not exceeded. Then, the power storage air-conditioning controller 31 determines, as the discharge pattern H, a pattern that is always discharged at the discharge power share ratio A during the daytime period. The discharge power Wh in the case of the discharge power share ratio A is discharge power Wh = Wd × A, where Wd is the power consumption when the heating / cooling load ratio is 100%.

  Here, the time when the air conditioning operation of the room by each of the air conditioners 2A and 2B can be started is set in advance as the discharge start time t0 (for example, 8:00), and the processing of the above steps Sa1 and Sa2 is the discharge start time. It is performed before t0. When the discharge start time t0 is reached, as shown in FIG. 4, the power storage air-conditioning controller 31 controls the PCS controller 4 to discharge the storage battery 33 in accordance with the discharge pattern H (step Sa3). As a result, in the daytime hours, a certain percentage of the power consumption due to the heating and cooling load is compensated by the discharge power of the storage battery 33, so that the power consumption pattern of the commercial power shifts downward by ΔP (= A) as a whole. In the daytime, power demand and its peak are pushed down. In addition, at night when the power demand is relatively small, as described above, charging of the storage battery 33 is executed and the commercial power is consumed to increase the power demand. Therefore, the power demand throughout the day and night is leveled. .

  By the way, depending on the discharge power share ratio A, the actual operating state of the air conditioners 2A and 2B, the deterioration of the storage battery 33, the storage power of the storage battery 33 is insufficient in the discharge period T2, or at the start of the night charge period T1. There is a risk that the stored power remains. Therefore, in the present embodiment, when the next day's heating / cooling load prediction pattern P is the same as that of today, the discharge pattern H of the next day is corrected according to the excess or deficiency of the stored power of the storage battery 33.

That is, when the one-day discharge period T2 ends and the night charge period T1 starts (for example, 22:00), the power storage air-conditioning controller 31 has the next day as the turn of the season as shown in FIG. (Step Sa4), and if the next day is a change of season (step Sa4: Yes), the next day's heating / cooling load prediction pattern P is different from this time, so the discharge pattern H is not corrected.
On the other hand, when the next day is not the turn of the season (step Sa4: No), the power storage air-conditioning controller 31 corrects the discharge pattern H of the next day according to the excess or deficiency of the stored battery 33 (step Sa6). Specifically, the power storage air-conditioning controller 31 detects the remaining power amount of the storage battery 33 based on the detection result of the remaining amount detector 34 (see FIG. 1), and at the start of the charging period T0 as shown in FIG. When the stored power remains, the discharge power burden ratio A of the discharge pattern H is increased according to the remaining power amount, and when the stored power is insufficient, the discharge power burden ratio A of the discharge pattern H is decreased. .

  For example, when the remaining power amount Wz of the storage battery 33 is greater than zero, the discharge pattern H is corrected so as to increase the discharge power burden ratio A according to the value of (remaining power amount Wz / time length of the discharge period T2). For example, when the remaining power amount Wz of the storage battery 33 is zero, the full charge capacity of the storage battery 33 is Wj, and the discharge power share ratio A is a value corresponding to (Wj / time length of the discharge period T2) ( That is, the discharge power share ratio A is reduced to the maximum value). As a result, the stored power is discharged without excess or deficiency during the discharge period T2.

  As described above, according to the present embodiment, the storage battery 33 for storing the commercial power of the commercial power supply 10 is provided during the night, and the stored power of the storage battery 33 is supplied together with the commercial power during the daytime when the power demand increases. Since it is configured to supply and operate each air conditioner 2A, 2B and store the nighttime power not in the heat storage material but in the storage battery 33 that is more efficient than the heat storage material, the power stored at night can be efficiently used in the daytime. It can be used, and thereby, the daily power demand can be leveled efficiently.

  In addition, according to the present embodiment, since the discharge of the storage battery 33 is controlled so that the remaining power amount of the stored power becomes substantially zero at the end of the discharge period T2, the power stored in the night time Can be used up efficiently. In general, since the nighttime power rate is set lower than the daytime power rate, the power rate can be reduced by storing the nighttime power in the storage battery 33 and using it during the daytime.

  In addition, according to the present embodiment, the heating / cooling load ratio prediction pattern P that is regarded as substantially the same pattern as the power demand fluctuation prediction pattern, and the use of commercial power at the peak of the heating / cooling load ratio (that is, at the peak of power demand). Since the discharge pattern H of the stored power in the discharge period T2 is determined based on the load upper limit value G of the electric energy, the storage battery 33 can be discharged efficiently according to the power demand situation of the day.

  Further, according to the present embodiment, when the heating / cooling load ratio prediction pattern P of the next day is the same as this time, the discharge pattern H of the next day is corrected based on the remaining power amount at the end of the discharge period T2, Even when there is a deviation between the actual fluctuation pattern of the cooling / heating load ratio and the prediction pattern P of the heating / cooling load ratio, the storage battery 33 can be discharged according to the power demand situation, and more The stored power can be used up reliably.

<Second Embodiment>
In 1st Embodiment mentioned above, in order to discharge the electrical storage electric power of the storage battery 33 without excess and deficiency within the discharge period T2, when the discharge period T2 is complete | finished, the discharge pattern H of the next day is based on the remaining electric energy of the storage battery 33. I corrected it. On the other hand, in the present embodiment, the discharge pattern H is corrected in the middle of the discharge period T2.

  That is, as shown in FIG. 6, in the present embodiment, during the discharge period T2, the power storage air conditioning controller at time t1 (for example, 16:00) after the time zone in which the heating / cooling load ratio reaches its peak has elapsed. 31 detects the remaining power amount of the storage battery 33 based on the detection result of the remaining amount detector 34, and based on the remaining power amount, sets the discharge pattern H to use up the stored power within the remaining time of the discharge period T2. to correct.

FIG. 7 is a flowchart of the discharge control process according to the present embodiment. In this figure, the same processes as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.
As shown in the figure, when the current time is time t1 in the discharge period T2 (step Sb1: YES), the power storage air-conditioning controller 31 receives the remaining power amount of the storage battery 33 from the remaining amount detector 34 (see FIG. 1). Wz is detected (step Sb2), and the discharge pattern H in the remaining time of the discharge period T2 is corrected based on the remaining power amount Wz and the remaining time of the discharge period T2 (step Sb4). Specifically, for this correction, in order to use up the remaining power amount Wz in the remaining time, the power storage air-conditioning controller 31 calculates the discharge power burden ratio A after this time t1 as (remaining power amount Wz / remaining time of discharge period T2). ) Is corrected to the discharge pattern H having a burden ratio corresponding to the value of. The power storage air-conditioning controller 31 then discharges the storage battery 33 based on the corrected discharge pattern H for the remaining time of the discharge period T2 (step Sb4).

  With the above processing, as shown in FIG. 6, when the remaining power amount Wz can be insufficient in the remaining period of the discharging period T2, the discharge power burden ratio A of the discharge pattern H is reduced, and the remaining power is reduced. When the amount Wz remains, the discharge power share ratio A of the discharge pattern H is increased, and the stored power of the storage battery 33 can be used up at the end of the discharge period T2.

  Thus, according to the present embodiment, in addition to the effects of the first embodiment described above, the following effects are further achieved. That is, since the discharge pattern H in the remaining time of the discharge period T2 is corrected based on the remaining power amount of the storage battery 33 detected during the discharge period T2, the actual fluctuation pattern of the cooling / heating load ratio and the cooling / heating load ratio Even when there is a deviation from the predicted pattern P, the stored power can be used up reliably and efficiently every day.

<Third Embodiment>
In the first and second embodiments described above, the commercial power fluctuation pattern Ca obtained by shifting the commercial power prediction pattern C as a whole downward is obtained by always discharging the stored power of a certain amount of power during the daytime. I tried to get it. In contrast, in the present embodiment, as shown in FIG. 8, in addition to always discharging a constant amount of stored power during the daytime period, a peak period T3 (time t2 including a peak of the heating / cooling load ratio) is included. In time t3), the power storage air-conditioning controller 31 increases the discharge amount of the stored power to lower the peak of the commercial power fluctuation pattern Ca (so-called peak cut).

  That is, in the present embodiment, when the power storage air-conditioning controller 31 determines the discharge pattern H in the daytime period based on the peak value Pmax of the cooling / heating load prediction pattern P (step Sa1), as shown in FIG. In the peak period T3, the discharge power burden ratio A is increased by the peak cut rate B (%). Thus, in the peak period T3, the commercial power fluctuation pattern Ca is shifted downward from the commercial power prediction pattern C by the cut rate B in addition to the peak shift ΔP, and the peak of the commercial power consumption is cut. The Thereby, in addition to leveling of power demand, it is also possible to suppress the peak of power demand. For example, it is possible to control so that demand power does not exceed contract power of commercial power.

  As described above, when the discharge power share A is increased by the peak cut rate B (%) only during the peak period T3, the discharge amount of the stored power increases by the increase, so the end of the discharge period T2 There is a risk that the stored power will run out before. Therefore, the discharge power burden ratio A in the discharge period T2 before the peak period T3 or after the peak period T3 may be reduced in advance. For example, in the summer, the power demand is higher in the afternoon than in the morning, so the discharge power burden ratio A in the period before the peak period T3 is reduced in advance, and in winter, Since the power demand is higher in the morning than in the afternoon, the discharge power burden ratio A in the period after the peak period T3 is set to a discharge pattern H that has been reduced in advance.

  At this time, in order to use up the stored power during the discharge period T2, the discharge pattern H of the next day is changed according to the remaining power amount Wz of the storage battery 33 at the end of the discharge period T2, as in the first embodiment. On the other hand, the peak cut rate B or the discharge power share ratio A may be corrected, and, similarly to the second embodiment, the discharge period according to the remaining power amount Wz of the storage battery 33 when the peak period T3 has elapsed. You may correct | amend the discharge electric power burden ratio A in the remaining time of T2.

  Thus, according to the present embodiment, in addition to the effects of the first and second embodiments described above, the discharge power share ratio A is increased by the peak cut rate B only during the peak period T3. Since the discharge pattern H is used, in addition to leveling of power demand, it is possible to suppress the peak of power demand. For example, it is possible to control so that demand power does not exceed contract power of commercial power.

The first to third embodiments described above merely show one aspect of the present invention, and can be arbitrarily modified and applied within the scope of the present invention.
For example, as shown by the phantom line in FIG. 1, the temperature sensor 50 is provided in the electric storage air conditioning system 1 to detect the outside air temperature before the start of the discharge period T2, and for each season and outside air temperature. The cooling / heating load prediction pattern P may be stored in the memory 31A in advance, and the power storage air conditioning controller 31 may select the cooling / heating load prediction pattern P based on the season and the outside air temperature.
Thereby, it is possible to select a cooling / heating load prediction pattern P that is more suitable for the fluctuation pattern of the heating / cooling load ratio of the day that is greatly affected by the daily temperature difference, and the discharge pattern H can be selected according to the cooling / heating load prediction pattern P. By determining, a more efficient discharge pattern H can be obtained.
In addition, the cooling / heating load prediction pattern P is previously stored in the memory 31A for each season, and the storage / air conditioning controller 31 selects the cooling / heating load prediction pattern P selected based on the season based on the outside air temperature. And the discharge pattern H may be determined based on the corrected heating / cooling load prediction pattern P.

1 is a circuit diagram showing a schematic configuration of a power storage air conditioning system according to a first embodiment of the present invention. It is a figure which shows an example of the air-conditioning negative prediction pattern. It is a figure for demonstrating a peak shift operation | movement. It is a flowchart of the discharge control which concerns on 1st Embodiment. It is a figure for demonstrating correction | amendment of the discharge pattern based on the remaining electric energy which concerns on 1st Embodiment. It is a figure for demonstrating correction | amendment of the discharge pattern based on the remaining electric energy which concerns on 2nd Embodiment. It is a flowchart of the discharge control which concerns on 2nd Embodiment. It is a figure for demonstrating peak shift and peak cut operation | movement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Power storage type air conditioning system 2A, 2B Air conditioner 3 Power storage unit 4 PCS controller 31 Power storage air conditioning controller 31A Memory 33 Storage battery P Heating / cooling load prediction pattern T0 Night charge period T2 Discharge period T3 Peak period Wz Remaining electric energy

Claims (6)

An energy storage air conditioning system that includes one or a plurality of air conditioners and a storage battery that stores commercial power of a commercial power supply, and operates the air conditioner by supplying the stored power stored in the storage battery and the commercial power. There,
The power storage control means for performing charging to the storage battery at night when power demand is low, and discharging stored power charged in the storage battery in a discharge period including at least a peak period of the power demand,
The storage type air conditioning system, wherein the storage control means controls the discharge of the stored power so that a remaining power amount of the stored power becomes substantially zero at the end of the discharge period. Comprising storage means for storing a power demand fluctuation prediction pattern, which is a predicted value of a fluctuation pattern of a daily power demand,
The power storage control means includes
2. The discharge pattern of the stored power during the discharge period is determined based on the power demand fluctuation prediction pattern and an upper limit value of the amount of power used by the commercial power source at the time of the power demand peak. The electricity storage type air conditioning system described in 1. Further comprising a remaining amount detecting means for detecting a remaining power amount of the stored power of the storage battery,
The power storage control means includes
The storage-type air conditioning according to claim 2, wherein when the power demand fluctuation prediction pattern of the next day is the same as this time, the discharge pattern of the next day is corrected based on the remaining power amount at the end of the discharge period. system. Further comprising a remaining amount detecting means for detecting a remaining power amount of the stored power of the storage battery,
The power storage control means includes
The electricity storage type air conditioning system according to claim 2, wherein the discharge pattern in the remaining time of the discharge period is corrected based on the remaining power amount detected within the discharge period. A temperature sensor for detecting the temperature;
The power storage control means includes
The power demand fluctuation prediction pattern is corrected based on the temperature, and the discharge pattern is determined based on the corrected power demand fluctuation prediction pattern. Power storage air conditioning system. The power storage control means includes
The electric storage air conditioning system according to any one of claims 1 to 5, wherein the discharge electric energy is increased in the peak period of the discharge period.

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