Patent Publication Number: US-2020303929-A1

Title: Power supply system, control system and power control method for power supply system

Description:
TECHNICAL FIELD 
     The present invention relates to a power supply system and a power conditioner. 
     BACKGROUND ART 
     A power supply device including a number of serial and parallel connected secondary batteries is used as a power storage for peak cutting in home use, business facility use, factory use, and the like. Alternatively, the power supply device is used also in a power plant and the like. The peak cutting is performed to supply electric power in a time slot in which electric power consumption is at its peak (for example, around 1 pm to 4 pm) such that electric power is charged in the power supply device in the other time slots (for example, in the middle of the night) and the charged electric power is discharged at a peak time slot to supplement electric power at a peak time. In particular, in recent years, use of the natural energy represented by solar power generation and wind-power generation has been gathering attention; however, an electric source of these natural energies is not stable, and the power supply device is therefore used also in order to realize stable supply of electric power in a power system network by storing electric power temporarily in the power supply device in a power plant or a substation and by discharging the stored electric power. 
     In such a power supply device, in order to store a large amount of electric power, a number of secondary batteries are connected to configure a modularized power supply device, and a plurality of power supply units are combined to structure a power supply system, so that increased electric power can be supplied (for example, see PTL 1). The power supply units in such a power supply system is managed by a high-order controller that totally manages the power supply units, and the overall power control is performed by a power conditioner. The power conditioner performs power control of each power supply unit such that the each power supply unit is charged and discharged. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Unexamined Japanese Patent Publication No. 2010-092841 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     However, the power supply system according to the background art has a problem that when there occurs a power deviation among the power supply units, the power control cannot be performed appropriately. For example, if only one power supply unit is used, the power conditioner communicates with the power supply unit on a one-on-one basis, and the power control of charging and discharging can be performed relatively easily.  
       FIG. 2  shows a power supply system in which power conditioner  240  controls charging and discharging power of one power supply unit  210 . Power supply unit  210  shown in this drawing includes switch  214 , unit controller (a battery management unit: hereinafter, referred to as a “BMU”)  212  and battery aggregation  211 . Switch  214  is a component for switching between a connected state in which power supply unit  210  is connected to power conditioner  240  and a shut-off state in which power supply unit  210  is shut off at the time of abnormality or the like. BMU  212  is a component for monitoring a condition of battery aggregation  211 . Further, BMU  212  communicates the condition of the battery aggregation to power conditioner  240 . On the basis of the condition of the battery aggregation, power conditioner  240  determines the electric power of charging and discharging and communicates the electric power to BMU  212  of power supply unit  210  to perform charging and discharging. Here, the information communicated from power supply unit  210  to power conditioner  240  includes possible charging and discharging power (a state of power: hereinafter, referred to as a “SOP”), which is maximum power at the time of communicating the information, and power supply unit  210  can be charged and discharged at the maximum power. Regarding an example of the SOP communicated from power supply unit  210  to power conditioner  240 , the charging SOP is maximized when power supply unit  210  is constant-current charged, and the charging SOP is gradually decreased when power supply unit  210  is constant-voltage charged. Further, when power supply unit  210  becomes fully charged, the charging SOP is set to 0, and at the same time, the discharging SOP is maximized. In addition, when power supply unit  210  is completely discharged, the discharging SOP is set to 0, and the charging SOP is maximized. Further, if power supply unit  210  operates abnormally or is broken, the discharging SOP and the charging SOP are both set to 0. Further, when battery aggregation  211  is in a constant current (CC) charging and discharging region, the charging SOP and the discharging SOP are normally at their maximum. 
     On the other hand, power conditioner  240  communicates a charging and discharging power command value (a power of battery: hereinafter, referred to as a “POB”) to power supply unit  210  on the basis of a power command value from a high-order system or from outside, and the SOP. Thus, POB SOP is constantly satisfied. 
     As described above, if a number of power supply units  210  connected to power conditioner  240  is one, power conditioner  240  communicates with the power supply unit on a one-on-one basis; therefore, the control of charging and discharging power can be relatively easily performed. In contrast, if a plurality of power supply units are connected to a single power conditioner, the configuration is as shown in  FIG. 3 . In this example, four power supply units  310  are connected to single power conditioner  340 . Each power supply unit  310  includes unit controller (BMU)  312 , switch  314 , and battery aggregation  311 . 
     Power conditioner  340  receives SOP1 to SOP4 from power supply units  310 # 1  to  310 # 4 , respectively, and calculates the possible charging and discharging power (herein after, referred to as a “total SOP”) of all power supply units  310 . Here, the total SOP is calculated by the following equation, supposing that power supply unit  310  satisfying SOP=0 is to be separated from power conditioner  340 .  
       Total SOP=(minimum SOP of SOPn)×(total number of power supply unit not satisfying SOP=0)
 
     where n=1 to N, and N is a total number of the power supply units. 
     With this total SOP used as an upper limit, power conditioner  340  determines the total charging and discharging power (total POB) from the power command value and performs the charging and discharging on power supply units  310  at electric power of the total POB. In this way, power conditioner  340  suppresses the electric power such that the electric power is kept equal to or smaller than the total SOP. With this arrangement, the electric power can be appropriately suppressed even in a case in which the SOP has become 0 for some reason, for example, in a case in which a certain power supply unit stops. Further, even if the SOP of a certain power supply unit becomes low, the electric power can be suppressed equal to or smaller than the minimum SOP. In other words, POBn≤SOPn holds. Note that power supply unit  301  satisfying SOP=0 is supposed to be separated; however, in the case in which power supply unit  301  is not separated, POBn≤SOPn can be satisfied by setting the total SOP to 0. 
     However, battery conditions of the power supply units are not necessarily constant, and the degree of deterioration and the like of the power supply units have variations, which differences tend to become larger with the duration of use. Here, the conditions of the secondary battery cells included in each of the power supply units have variations of characteristics among the power supply units, for example, an internal resistance, a voltage, an SOC (state of charge), a degree of degradation, a temperature, and the like, in addition, the variations of wiring resistances and the like, and current ratios among the power supply units are thus not equal. Therefore, there are current deviations occurring among the power supply units, which state is referred to as a power deviation. 
     The charging and discharging control, of above power conditioner  340  in the configuration of  FIG. 3 , based on the total SOP is based on the assumption that there is no power deviation occurring among power supply units  310 . In other words, if a power deviation occurs among power supply units  310 , the rating or the SOP can be exceeded in some power supply unit  310  if electric power suppression is based on the total SOP. In other words, if a power deviation occurs, POBn≤SOPn may not hold in some cases. As a result, the power supply system can abnormally stop for a reason such as an abnormal current. 
     The present invention has been made in view of the above background. One of objects of the present invention is to provide a power supply system and a power conditioner in which it is possible to appropriately control charging and discharging even if a power deviation occurs between power supply units in a power supply system using a plurality of power supply units. 
     Solution to Problem 
     A power supply system according to a first aspect of the present invention can be configured to include: a plurality of power supply units; and a control system to which the power supply units are parallel connected. Each of the power supply units includes: a battery aggregation including a plurality of secondary battery cells serial and parallel connected, a unit controller that acquires battery information about electric power at which the battery aggregation is chargeable and dischargeable and that outputs the battery information to the control system; and a switch that switches connection and disconnection between the power supply unit and the control system. The control system includes: a power conditioner that is parallel connected to the plurality of power supply units and is connected to an external power system, and receives electric power from the power system and charges the power supply units with the received electric power, and receives electric power from the power supply units and discharges the received electric power to the power system; a master controller that collects the battery information output from the unit controller of each of the power supply units; and a system controller that communicates to the power conditioner electric power required to the power supply system as a power command. In a case where the power conditioner determines, according to the power command from the system controller, a working total power POBall, which is a summation of electric power at which each of the power supply units is charged and discharged, the power conditioner determines possible total power to be in a range that possible individual power of each of the power supply units is not exceeded. The possible total power is determined from the possible individual power, of each of the power supply units, determined based on the battery information detected by each of the unit controllers, collected by the master controller from each of the unit controllers. The power conditioner causes charging and discharging of each of the power supply units within the calculated working individual power 
     With the above configuration, even in a situation in which there is a power deviation, POBn≤SOPn holds, the system does not stop, and an operation of charging and discharging can therefore be continued. This makes it possible to perform charging and discharging control depending on the power deviation, and an unintended system failure can thus be avoided. 
     Further, in a power supply system according to a second aspect of the present invention, the master controller can be configured to detect a power deviation between the power supply units and to send out the power deviation to the power conditioner. The above configuration enables appropriate adjustment of charging and discharging power. 
     Further, in a power supply system according to a third aspect of the present invention, the master controller can be configured to detect the power deviation between the power supply units at a predetermined cycle or at a time when a change in electric power is detected, and to constantly suppress the working individual power equal to or smaller than individual maximum charging and discharging power (SOP), based on the detected power deviation. The above configuration enables appropriate adjustment of the charging and discharging power, coping with the battery condition temporally varying from hour to hour. When it is measured by the above configuration at an appropriate time whether there is a power deviation occurring, it is possible to perform the charging and discharging control depending on the power deviation, and an unintended system failure can thus be avoided. 
     Still further, in a power supply system according to a fourth aspect of the present invention, each of the unit controllers can be configured to determine the possible individual power, based on the battery information of the battery aggregation connected to each of the unit controllers.  
     Still further, in a power supply system according to a fifth aspect of the present invention, the master controller can be configured to determine the working individual power, based on the possible individual power sent out from each of the unit controllers connected to the master controller. 
     Still further, in a power supply system according to a sixth aspect of the present invention, the master controller can be configured to calculate power deviation ratio DOBn of each of the power supply units, assuming that a ratio for power supply unit #m, which is one of power supply units # 1  to #n and with which (n-th working individual power POBn)/(n-th possible individual power SOPn) is largest, is 1, where 1≤m≤n. 
     Still further, in a power supply system according to a seventh aspect of the present invention, the master controller can be configured to determine the possible total power by the following equation. 
       Possible total power=SOPm×(working total power)/(m-th working individual power POBm)
 
     Still further, in a power supply system according to an eighth aspect of the present invention, the power conditioner can be configured to turn off the switch of the power supply unit that is one of the power supply units and whose possible individual power has become 0. By separating a power supply unit whose SOP has become 0 from the power conditioner with the above configuration, the power supply unit can be protected from being overcharged or over-discharged.  
     Still further, a control system according to a ninth aspect of the present invention can be configured such that each of the switches includes a charge switch and a discharge switch. The power conditioner turns off the charge switch of the power supply unit that is one of the power supply units and whose chargeable individual power has become 0, and the power conditioner turns off the discharge switch of the power supply unit that is one of the power supply units and whose dischargeable individual power has become 0. 
     Still further, a control system according to a tenth aspect of the present invention is a control system for a power supply system in which a plurality of power supply units are parallel connected and in which charging and discharging of each of the power supply units is controlled, and the control system can be configured to include: a power conditioner that is parallel connected to a plurality of power supply units and is connected to an external power system, and receives electric power from the power system and charges the power supply units with the received electric power, and receives electric power from the power supply units and discharges the received electric power to the power system; a master controller that collects battery information having been output from each of the power supply units; and a system controller that communicates to the power conditioner electric power required to the power supply system as a power command. The power conditioner causes charging and discharging of each of the power supply units within working individual power, based on possible total power at which all the power supply units are chargeable and dischargeable. The possible total power is determined from possible individual power, of each of the power supply units, determined based on the battery information detected on each of the power supply units. The working individual power is determined based on a power deviation indicating a difference of a charging and discharging power between the power supply units. 
     The above configuration makes it possible to perform charging and discharging control depending on the power deviation, and an unintended system failure can thus be avoided. 
     Still further, a power control method of a power supply system according to an eleventh aspect of the present invention is a power control method in a power supply system including a plurality of power supply units and a control system to which the plurality of power supply units are parallel connected, and the power control method can include the steps of: receiving, by the control system, electric power required to the power supply system as a power command; acquiring battery information about electric power at which a battery aggregation included in each of the power supply units is chargeable and dischargeable, and outputting the acquired battery information to the control system, wherein the battery aggregation includes a plurality of secondary battery cells serial or parallel connected; determining, based on the battery information of the power supply units: possible individual power indicating electric power at which each of the power supply units is chargeable and dischargeable; possible total power indicating electric power at which all the power supply units are chargeable and dischargeable; and a power deviation indicating a difference of charging and discharging power between the power supply units, determining, based on the determined possible individual power, the determined possible total power, the determined power deviation, and the power command, working individual power in a range that the working individual power does not exceed the possible individual power of each of the power supply units, wherein the working individual power is electric power at which each power supply unit is charged and discharged. 
     This makes it possible to perform charging and discharging control depending on the power deviation, and an unintended system failure can thus be avoided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram showing a power supply system according to an exemplary embodiment of the present invention. 
         FIG. 2  is a block diagram showing a power supply system in which a single power supply unit is connected to a single power conditioner. 
         FIG. 3  is a block diagram showing a power supply system in which a plurality of power supply units are connected to a single power conditioner. 
         FIG. 4  is a table showing conditions of each battery module of  FIG. 3  at a time of power control of each power supply unit. 
         FIG. 5  is a table showing conditions of each battery module of  FIG. 1  at a time of power control of each power supply unit. 
         FIG. 6  is a block diagram showing a power supply system according to a modified example. 
     
    
    
     DESCRIPTION OF EMBODIMENT 
     An exemplary embodiment of the present invention is described below with reference to the drawings. However, the exemplary embodiment described below shows an example of the present invention, and the present invention is not limited to the following example. Further, in the present specification, components shown in the claims are not limited to the components of the exemplary embodiment. In particular, it is not intended to limit the sizes, materials, and shapes of components and relative arrangement between the components, which are described in the exemplary embodiment, to the scope of the present invention unless otherwise specified. The sizes and the like are mere explanation examples. However, the sizes and the positional relation of the components in each drawing are exaggerated for clearing the explanation in some cases. Furthermore, in the following description, the same names or the same reference marks denote the same components or the same types of components, and detailed description is therefore appropriately omitted. Further, regarding the elements constituting the present invention, a plurality of elements may be formed of the same component, and a single component may serve as a plurality of elements. To the contrary, the function of a single component may be realized by a plurality of components in cooperation. 
     Hereinafter, as an example of a power supply system according to an exemplary embodiment of the present invention, an example is described in which the present invention is applied to a large-scale power storage device to be used for a natural energy power plant and the like such as solar power generation and wind-power generation. This power storage device once stores electric power generated by solar power generation or wind-power generation and then supplies the electric power to power system ES. 
       FIG. 1  is a block diagram showing power supply system  1000  according to an exemplary embodiment of the present invention. Power supply system  1000  shown in this drawing includes a plurality of power supply units  10  and control system  100  to which these power supply units  10  are parallel connected. Control system  100  includes power conditioner  140 , system controller  160 , and master controller (M-BMU)  120 . 
     (Power Supply Unit  10 ) 
     Each power supply unit  10  includes battery aggregation  11 , unit controller (BMU)  12 , and switch  14 . In each battery aggregation  11 , a plurality of battery modules  1  are series and parallel connected. Further, each battery module  1  is configured with a plurality of series and parallel connected secondary battery cells. 
     (Unit Controller  12 ) 
     Unit controller  12  is connected to battery aggregation  11  and acquires battery information relating to electric power at which battery aggregation  11  can be charged and discharged. Unit controller  12  is connected to master controller  120  and outputs the battery information. 
     Here, the battery information represents conditions of battery aggregations  11  (or battery modules or secondary battery cells constituting battery aggregations  11 ) included in power supply units  10 , for example, internal resistances, voltages, currents, SOCs, degrees of degradation, temperatures, and the like. 
     (Switch  14 ) 
     Switch  14  is a component for switching connection and disconnection between each power supply unit  10  and power conditioner  140 . In the example of  FIG. 1 , switch  14  is disposed between battery aggregation  11  and power conditioner  140  and is switched on and off by unit controller  12 . Switch  14  may be separately disposed in a charging direction and in a discharging direction. In this case, the switch includes a charge switch and a discharge switch. Then, the power conditioner turns off the charge switch of a power supply unit whose chargeable individual power has become 0, and turns off the discharge switch of a power supply unit whose dischargeable individual power has become 0, among the power supply units. 
     (Control System  100 ) 
     On the other hand, control system  100  includes power conditioner  140 , system controller  160 , and master controller  120 . Regarding these components, instead of preparing individual components as shown  FIG. 1 , arbitrary components can be integrated into one body. 
     (Power Conditioner  140 ) 
     Power conditioner  140  is parallel connected to switches  14  of power supply units  10 . Further, power conditioner  140  is connected to a power system. Power conditioner  140  receives electric power from the power system to charge power supply units  10 , and conversely receives electric power from power supply units  10  to discharge the electric power to the power system. 
     (System Controller  160 ) 
     System controller  160  is a component to communicate to power conditioner  140  electric power of charging and discharging required to power supply system  1000  as a power command. System controller  160  receives a power command value, for example, through communication with a high-order system or an external device. Alternatively, system controller  160  may be configured to autonomously generate a power command value. 
     (Master Controller  120 ) 
     Master controller  120  is connected to unit controller  12  of each power supply unit  10  to collect information (battery information) about a battery condition of each power supply unit  10 . Further, master controller  120  determines a possible total power SOPall at which all power supply units  10  can be charged and discharged on the basis of the collected battery information. On the basis of the possible total power determined by master controller  120 , power conditioner  140  inputs and outputs electric power for charging and discharging, from and to power supply unit  10 . 
     In this control system  100 , system controller  160  communicates a power command to power conditioner  140 . On the other hand, master controller  120  sends out the battery information from each of unit controllers  12  to power conditioner  140 . Power conditioner  140  receives this information and determines a possible total power SOPall (hereinafter, also referred to as a “total SOP”) at which all power supply units  10  can be charged and discharged on the basis of the battery information sent out from master controller  120 . On the other hand, the power deviation among power supply units  10  is detected, and a working total power POBall (hereinafter, also referred to as a “total POB”) is determined on the basis of the power deviation, where the working total power POBall is a summation of electric power at which each power supply unit  10  is charged and discharged, and charging and discharging are then performed on power supply units  10  at the total POB. Since the charging and discharging are performed at the total POB, a working individual power POBn, which is an individual charging and discharging power for each power supply unit  10 , is determined (the power deviation will be described later in detail). 
     Note that the possible total power and the possible individual power may be determined by the master controller or the unit controller other than by power conditioner  140 . For example, the unit controller determines the possible individual power of the power supply unit on the basis of the battery information of the battery aggregation connected to the unit controller. In the example of  FIG. 1 , unit controllers  12  of respective power supply units  10  calculate a possible individual power SOP1 of power supply unit  10 # 1 , a possible individual power SOP2 of power supply unit  10 # 2 , a possible individual power SOP3 of power supply unit  10 # 3 , and a possible individual power SOP4 of power supply unit  10 # 4 . On the basis of the thus calculated possible individual power of power supply units  10 , the possible total power SOP is calculated by master controller  120 . Further, master controller  120  and unit controllers  12  control turning on and off of switches  14  such that, if the SOP is 0 or abnormality has occurred in one of power supply units  10 , the one of power supply units  10  is separated from power conditioner  140 . By this operation, even if certain power supply unit  10  stops or the SOPn has become 0, an appropriated power control operation is ensured. 
     (Power Control Method By Power Supply System Relating to Comparative Example) 
     Here, a description is given to electric current control on the power supply unit in a power supply system according to the comparative example. In the power supply system relating to the comparative example, a chargeable and dischargeable maximum power is calculated for each power supply unit. Then, from the SOPn of each power supply unit, the total SOP is calculated and is communicated to the power conditioner. For example, the possible total power SOP can be expressed by the following equation, where a number of the connected power supply units is n. 
       Possible total power SOP=(minimum SOP of SOPn)×(connection number of power supply units being connected to the power conditioner)  Equation 1
 
     With this arrangement, even when the possible individual power SOP of a certain power supply unit becomes low, the electric power can be kept to the minimum SOP or smaller. In other words, with respect to each power supply unit, POBn≤SOPn holds. 
     (Power Deviation) 
     Equation 1 holds appropriately when there is no power deviation occurring among the power supply units. However, in practice, the possible individual power of each power supply unit depends on a battery condition and is not necessarily constant. Therefore, among the power supply units, there occurs a variation in a possible individual power, in other words, a power deviation. As a result, in the power control based on the above-described total SOP, POBn≤SOPn may not hold for a certain power supply unit, and a rating or an individual SOP may be exceeded. In this case, there is a concern that the power supply system may stop due to an abnormal current or other causes. To address this issue, in the present exemplary embodiment, charging and discharging control is performed in view of such a power deviation. 
     Here, in order to describe a problem caused by a power deviation, a discussion is made on a power supply system as the power supply system relating to the comparative example, in which four power supply units  310 # 1  to  310 # 4  are connected to common power conditioner  340  as shown in  FIG. 3 .  FIG. 4  shows conditions of the battery modules at the time of the power control by which power supply units  310  are charged and discharged. In this table, among condition numbers 1 to 8, there are differences in the power commands sent from system controller  160 , and the battery conditions, possible individual power, and the like of the battery modules. In the upper columns of  FIG. 4  (condition numbers 1 to 4), there is no power deviation occurring among power supply units  310 # 1  to  310 # 4 , in other words, the columns show the conditions of the battery modules in which a ratio of the possible individual power of power supply units  310  is 1:1:1:1. On the other hand, in the lower columns of  FIG. 4  (condition numbers 5 to 8), there are power deviations occurring among power supply units  310 # 1  to  310 # 4 , and the columns show the conditions of the battery modules in which the current ratio of power supply units  310  is 5:4:4:3. Note that the power command and the total SOP are made to correspond to one another between condition numbers 1 to 4 and condition number 5 to 8. 
     (Comparative Example: When There is no Power Deviation) 
     In  FIG. 4 , for example, in the case of condition number 1, with respect to the possible individual power SOP1 to SOP4 of power supply units  310 # 1  to  310 # 4 , a dischargeable individual power SOP representing a dischargeable electric power (hereinafter, also referred to as a“discharging SOP”) and a chargeable individual power SOP (hereinafter, also referred to as a“charging SOP”) representing chargeable electric power are both 60 kW. Therefore, the minimum SOP of SOPn is calculated to be 60 kW according to Equation 1, and a possible total power SOPall for all power supply units  310 # 1  to  310 # 4  is 60 kW×4=240 kW for both of discharging and charging. In addition, the power command sent from system controller  160  is 160 kW and is within the possible total power SOPall, and the working total power POBall can be 160 kW, which is the same as the power command. Therefore, this power command can be executed. Further, the working individual power of each power supply unit  310  is 160 kW×1/4=40 kW. Here, since the possible individual power SOP1 to SOP4 of power supply units  310  are each 60 kW for both of the discharging SOP and the charging SOP as described above, the working individual power of 40 kW can be dealt with, and POBn≤SOPn thus holds. 
     Similarly, in the case of condition number 2, as is the case with condition number 1, the possible total power SOPall is 60 kW×4=240 kW for both of discharging and charging. In addition, since the power command is 240 kW, the workable electric power POBall is similarly 240 kW, and each working individual power is 60 kW. Here, since the possible individual power of each power supply unit  310  is 60 kW for both of the discharging SOP and the charging SOP, the working individual power of 60 kW can be dealt with, and POBn≤SOPn thus holds. 
     On the other hand, in the case of condition number 3, the possible individual power SOP of each of power supply units  310 # 2  to  310 # 4  is 60 kW for both of the charging SOP and the discharging SOP as is the case with condition numbers 1 and 2. In addition, power supply unit  310 # 1  is in a fully-charged condition or in a condition in which charging is prohibited for some reason, and the discharging SOP and the charging SOP are respectively 60 kW and 0. Therefore, discharging is possible; however, at the time of charging, switch  14  is turned off to be separated from power conditioner  140 , and power supply unit  310 # 1  is not charged. In this condition, the possible total power SOPall at the time of charging is 60 kW×3=180 kW. Here, if the power command for charging is 240 kW, the power command is greater than the possible total power SOPall; therefore, the working total power POBall is limited to 180 kW. Further, regarding the working individual power of each power supply unit  310 , power supply unit  310 # 1  is separated from power conditioner  140  and is thus not an object of charging; the working individual power POB2 to POB4 of power supply units  310 # 2  to  310 # 4  each are 180 kW×(1/3)=60 kW. 
     Moreover, in the case of condition number 4, regarding possible individual power SOP for each of power supply units  310 # 2  to  310 # 4 , the charging SOP and the discharging SOP are both 60 kW as is the case with condition numbers 1 to 3, but power supply unit  310 # 1  is being charged with a constant current or is in a condition in which the charging power is set lower than other power supply units  310 # 2  to  310 # 4  because of some reason. Thus, the discharging SOP is 60 kW, but the charging SOP is 20 kW. In this condition, since the minimum SOP at the time of charging is 20 kW, the possible total power SOPall is 20 kW×4=80 kW according to Equation 1. Here, if the power command is 240 kW, the power command is greater than the possible total power SOPall, and the working total power POBall is therefore limited to 80 kW. In addition, the working individual power for charging each of power supply units  310 # 1  to  310 # 4  is 80 kW×1/4=20 kW. On the other hand, regarding the possible individual power of each power supply unit  310 , the discharging SOP of each power supply unit  310  is 60 kW, the charging SOP of power supply unit  310 # 1  is 20 kW, and the charging SOP of each of power supply units  310 # 2  to  310 # 4  is 60 kW. Therefore, every power supply unit can deal with working individual power of 20 kW, and POBn SOPn thus holds. Note that when battery aggregation  11  is in a constant current (CC) charging and discharging region, the charging SOP and the discharging SOP are normally both at their maximums. 
     (Comparative Example: When There is Power Deviation) 
     As described above, in the condition in which there is no power deviation among power supply units  310 , charging and discharging power control can be appropriately performed in any of the cases of condition numbers 1 to 4. Next, a discussion is made on condition numbers 5 to 8, in which the power deviations among power supply units  310 # 1  to  310 # 4  are represented by a current ratio of 5:4:4:3. Note that the power command, the total POB, the discharging SOP, and the charging SOP are made to correspond to one another between condition numbers 5 to 8 and condition numbers 1 to 4. 
     First, in the case of condition number 5, regarding the possible individual power SOP of power supply units  310 # 1  to  310 # 4 , the charging SOP and the discharging SOP are both 60 kW as is the case with condition number 1; therefore, the possible total power SOPall, which is a summation of the possible individual power SOP of power supply units  310 # 1  to  310 # 4 , is calculated to be 60 kW×4=240 kW according to Equation 1. In addition, since the power command is 160 kW and is within the possible total power SOPall, the working total power POBall can be 160 kW, which is the same as the power command. Therefore, this power command can be executed. Further, regarding the working individual power of each of power supply units  310 , the working total power POBall is distributed based on the power deviation. Here, since the power deviation is 5:4:4:3, when 160 kW is distributed according to this ratio, the working individual power POB1 of power supply unit  310 # 1  is 160 kW×(5/16)=50 kW, the working individual power POB2 of power supply unit  310 # 2  is 160 kW×(4/16)=40 kW, the working individual power POB3 of power supply unit  310 # 3  is 160 kW×(4/16)=40 kW, and the working individual power POB4 of power supply unit  310 # 4  is 160 kW×(3/16)=30 kW. Since any working individual power POBn is within the charging SOP and the discharging SOP, POBn≤SOPn holds, and charging and discharging can thus be appropriately performed. 
     Next, in the case of condition number 6, regarding the possible individual power SOP of power supply units  310 # 1  to  310 # 4 , the charging SOP and the discharging SOP are both 60 kW as is the case with condition number 2 and condition number 5; therefore, the possible total power SOPall is 60 kW×4=240 kW. In addition, since the power command is 240 kW and is within the possible total power SOPall, the working total power POBall can be 240 kW, which is the same as the power command. However, when the working individual power of each of power supply units  310  is distributed according to the power deviation, the working individual power POB1 of power supply unit  310 # 1  is 240 kW×(5/16)=75 kW, the working individual power POB2 of power supply unit  310 # 2  is 240 kW×(4/16)=60 kW, the working individual power POB3 of power supply unit  310 # 3  is 240 kW×(4/16)=60 kW, and the working individual power POB4 of power supply unit  310 # 4  is 240 kW×(3/16)=45 kW. In this case, POBn≤SOPn holds for power supply units  310 # 2  to  310 # 4 , but for power supply unit  310 # 1 , the working individual power POB1 is 75 kW and exceeds 60 kW of the possible individual power SOP1; therefore, POBn≤SOPn does not hold, and the rating is exceeded. 
     Further, in the case of condition number 7, regarding the possible individual power SOP of each of power supply units  310 # 2  to  310 # 4 , the charging SOP and the discharging SOP are both 60 kW as is the case with condition number 3. However, power supply unit  310 # 1  is in a fully-charged condition or a condition in which charging is prohibited because of some reason; therefore, the discharging SOP is 60 kW, but the charging SOP is 0. Therefore, charging is possible, but power supply unit  310 # 1  is separated from the power supply system at the time of charging. Therefore, power supply unit  310 # 1  is not charged. In this condition, the possible total power SOPall at the time of charging is 60 kW× 3 = 180  kW. Here, if the power command for charging is 240 kW, the power command exceeds the possible total power SOPall; therefore, the working total power POBall is limited to 180 kW. Further, regarding the working individual power of charging each power supply unit  310 , since power supply unit  310 # 1  does not function because of being separated, the working individual power POB2 of power supply unit  310 # 2  is 180 kW×(4/16)=65 kW, the working individual power POB3 of power supply unit  310 # 3  is 180 kW×(4/16)=65 kW, and the working individual power POB4 of power supply unit  310 # 4  is 180 kW×(3/16)=49 kW. In this case, POBn≤SOPn holds for power supply unit  310 # 4 ; however, for power supply units  310 # 2  and  310 # 3 , although each of the possible individual power SOP2 and SOP3 is 60 kW, each of the working individual power POB2 and POB3 is 65 kW. As a result, POBn≤SOPn does not hold at the time of charging, and the rating is exceeded. 
     Further, in the case of condition number 8, regarding possible individual power SOP for each of power supply units  310 # 2  to  310 # 4 , the charging SOP and the discharging SOP are both 60 kW, but power supply unit  310 # 1  is being charged with a constant voltage or is in a condition in which the charging power is set lower than other power supply units  310 # 2  to  310 # 4  because of some reason. Therefore, the discharging SOP is 60 kW, but the charging SOP is 20 kW. In this condition, the possible total power SOPall at the time of charging is calculated to be 20 kW×4=80 kW according to Equation 1. Here, if the power command is 240 kW, the power command is greater than the possible total power SOPall, and the working total power POBall is therefore limited to 80 kW. Further, regarding the working individual power of charging each power supply unit  310 , the working individual power POB1 of power supply unit  310 # 1  is 80 kW×(5/16)=25 kW, the working individual power POB2 of power supply unit  310 # 2  is 80 kW×(4/16)=20 kW, the working individual power POB3 of power supply unit  310 # 3  is 80 kW×(4/16)=20 kW, and the working individual power POB4 of power supply unit  310 # 4  is 80 kW×(3/16)=15 kW. In this case, POBn≤SOPn holds for power supply units  310 # 2  to  310 # 4 ; however, for power supply units  310 # 1 , although the possible individual power SOP1 is 20 kW, the working individual power POB1 is 25 kW. As a result, POBn≤SOPn does not hold at the time of charging, and the rating is exceeded. 
     (Power Control Method According to Exemplary Embodiment) 
     As described above, if there is a power deviation, a problem can occur, for example, the power supply system abnormality stops due to an incident in which the rating is exceeded in a part of power supply units even under the same condition. To address this issue, in the present exemplary embodiment, the working total power POBall is determined on the basis of the power deviation, and then on the basis of the working individual power POBall, charging and discharging of each power supply unit is controlled. Specifically, a chargeable and dischargeable maximum power is calculated for each power supply unit. With this arrangement, the charging SOPn and the discharging SOPn of each power supply unit are calculated. In addition, a measurement is performed at an appropriate time to detect whether there is a power deviation occurring. Specifically, a voltage and a current are continuously measured at an appropriate time to measure POBn/SOPn. Here, as described above, the SOPn is a possible individual power of power supply unit n, and the POBn is a working individual power of power supply unit n. 
     In the above-described manner, the power supply system calculates the total SOP (possible total power SOPall) from the SOPn, the POBn, and the power deviation information measured at an appropriate time, and the power supply system communicates the calculated total SOP to power conditioner  140 . In the present exemplary embodiment, following Equation 2 is calculated to obtain the total SOP. 
     
       
         
           
             
               
                 
                   
                     Total 
                      
                     
                         
                     
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                     SOP 
                   
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                         Σ 
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                             all 
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                             power 
                              
                             
                                 
                             
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                             supply 
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                             power 
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                             supply 
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                             unit 
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                             with 
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                              
                             SOP 
                           
                           = 
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                         ( 
                         
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                         SOPm 
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                          
                         DOBn 
                       
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                           SOPm 
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                             Σ 
                             ( 
                             
                               POBn 
                               / 
                               POBm 
                             
                             ) 
                           
                         
                         = 
                         
                           
                             SOPm 
                             × 
                             
                               
                                 Σ 
                                 ( 
                                 POBn 
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                               POBm 
                             
                           
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                                 ( 
                                 
                                   total 
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                   Equation 
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                   2 
                 
               
             
           
         
       
     
     In above Equation 2, DOBn represents a normalized power deviation ratio. DOBn represents the ratio of the electric power of each of the power supply units and is normalized such that the ratio of power supply unit #m with which the above POBn/SOPn is largest is 1. The numeral n for the power supply unit with which the POBn/SOPn is largest is substituted by m. 
     Note that, as described above, power supply unit #n is supposed to be separated from power conditioner  140  at the time when the SOPn becomes 0. If power supply unit #n is not separated, the total SOP needs to be set to 0. 
     Power conditioner  140  follows the power command and suppresses electric power such that the charging and discharging power is kept not greater than the total SOP. With this configuration, in a situation in which there is a power deviation occurring, even when a certain power supply unit stops or the SOPn becomes 0, an appropriate electric power suppression can be performed. Further, even when the SOPn of a certain power supply unit decreases, it is possible to keep the electric power of the certain power supply unit not greater than the SOPn. In other words, it is possible to maintain the condition of POBn≤SOPn. As a result, even in a situation in which there is a power deviation occurring, the system does not stop, and an operation of charging and discharging can be continued. Here, a description is given, with reference to  FIG. 5 , on an example in which charging and discharging control is performed, in the conditions corresponding to  FIG. 4 , by a power control method according to the present exemplary embodiment. With reference to  FIG. 5 , the power command, the discharging SOP, and the charging SOP of condition numbers 1 to 8 are made to be identical to the examples represented by condition numbers 1 to 8 of  FIG. 4 . 
     (Exemplary Embodiment When There is no Power Deviation) 
     Also in  FIG. 5 , the examples represented by condition numbers 1 to 4 show the case in which there is no power deviation occurring among power supply units  10 # 1  to  10 # 4  as is the case with condition numbers 1 to 4 of  FIG. 4  and in which the discharging SOP and the charging SOP of power supply units  10  are each 1:1:1:1. 
     First, in the case of condition number 1, regarding the possible individual power SOP of each of power supply units  10 # 1  to  10 # 4 , the charging SOP and the discharging SOP are both 60 kW as is the case with condition number 1 of  FIG. 4 , and the total POB (working total power POBall) is 160 kW. Here, with respect to each of power supply units  10 # 1  to  10 # 4 , power deviation ratio dob_n is calculated. Note that power deviation ratio dob_n is not normalized as the DOBn, and satisfies Σdob_n=1. Regarding power supply unit  10 # 1 , dob_1=POB1/SOP1=40 kW/(40+40+40+40) kW=0.25, regarding power supply unit  10 # 2 , dob_2=POB2/SOP2=40 kW/(40+40+40+40) kW=0.25, regarding power supply unit  10 # 3 , dob_3=POB3/SOP3=40 kW/(40+40+40+40) kW=0.25, and regarding power supply unit  10 # 4 , dob_4 32  POB4/SOP4=40 kW/(40+40+40+40) kW=0.25. 
     Therefore, power deviation ratios dob_n for power supply units  10 # 1  to  10 # 4  are the same, and power supply unit  10  having maximum power deviation ratio dob_n is supposed here to be power supply unit  10 # 1  (m=1). Thus, when the total SOP (possible total power SOPall) is calculated according to Equation 2, total SOP=SOPm×(total POB)/POBm=SOP1×(total POB)/POB1=60 kW×160 kW/40 kW=240 kW. Further, regarding the working individual power of each power supply unit  10 , the working individual power POB1 of power supply unit  10 # 1  is 160 kW×dob_1=40 kW, the working individual power POB2 of power supply unit  10 # 2  is 160 kW×dob_2=40 kW, the working individual power POB3 of power supply unit  10 # 3  is  160  kW×dob_3=40 kW, and the working individual power POB4 of power supply unit  10 # 4  is 160 kW×dob_4=40 kW. Here, since the possible individual power SOP1 to SOP4 of power supply units  10  are each 60 kW for both of the discharging SOP and the charging SOP as described above, the working individual power of 40 kW can be dealt with, and POBn≤SOPn thus holds. As a result, the result is the same as in the case of condition number 1 of  FIG. 4 . 
     Similarly, in the case of condition number 2, the possible total power SOPall is 60 kW×4=240 kW for both of discharging and charging, and the total POB is 240 kW as is the case with condition number 1. Further, power deviation ratios dob_n for power supply units  10 # 1  to  10 # 4  are the same, and power supply unit  10  having maximum power deviation ratio dob_n is also supposed here to be power supply unit  10 # 1  (m=1). Thus, the total SOP (possible total power SOPall) is calculated according to Equation 2, as total SOP=SOPm×(total POB)/POBm=SOP1×(total POB)/POB1=60 kW×240 kW/60 kW=240 kW. Further, regarding the working individual power of each power supply unit  10 , the working individual power POB1 of power supply unit  10 # 1  is  240  kW×dob_1=60 kW, the working individual power POB2 of power supply unit  10 # 2  is 240 kW×dob_2=60 kW, the working individual power POB3 of power supply unit  10 # 3  is 240 kW×dob_3=60 kW, and the working individual power POB4 of power supply unit  10 # 4  is 240 kW×dob_4=60 kW. Here, since the possible individual power SOP1 to SOP4 of power supply units  10  are each 60 kW for both of the discharging SOP and the charging SOP as described above, the working individual power of 60 kW can be dealt with, and POBn≤SOPn thus holds, resulting in the same situation as in the case of condition number 2 of  FIG. 4  as a result. 
     On the other hand, in the case of condition number 3, the total POB is 180 kW, and the possible individual power SOP of power supply units  10 # 2  to  10 # 4  are each 60 kW for both of the charging SOP and the discharging SOP as is the case with condition numbers 1 and 2. Further, since power supply unit  10 # 1  is fully charged, the discharging SOP is 60 kW, and the charging SOP is 0. Therefore, power supply unit  10 # 1  can be discharged but is separated from power conditioner  140  at the time of charging. Note that power deviation ratios dob_n for power supply units  10 # 2  to  10 # 4  are the same, and power supply unit  10  having maximum power deviation ratio dob_n is supposed here to be power supply unit  10 # 2  (m=2). In this condition, the possible total power SOPall at the time of charging is calculated according to Equation 2, as total SOP=SOPm×(total POB)/POBm=SOP2×(total POB)/POB2=60 kW×180 kW/60 kW=180 kW. Further, regarding the working individual power of each power supply unit  10 , power supply unit  10 # 1  is separated from power conditioner  140  and is thus not taken into account, the working individual power POB2 of power supply unit  10 # 2  is 180 kW×dob_2=60 kW, the working individual power POB3 of power supply unit  10 # 3  is 180 kW×dob_3=60 kW, and the working individual power POB4 of power supply unit  10 # 4  is 180 kW×dob_4=60 kW. Any of the working individual power POB2 to POB  4  can be dealt with by 60 kW of the charging SOP, and POBn≤SOPn thus holds, resulting in the same situation as in the case of condition number 3 of  FIG. 4  as a result. 
     Further, in the case of condition number  4 , the total POB is 80 kW, and the possible individual power SOP of each of power supply units  10 # 2  to  10 # 4  is 60 kW for both of the charging SOP and the discharging SOP as is the case with condition numbers 1 to 3; however, since power supply unit  10 # 1  is being charged by constant voltage charging, the discharging SOP is 60 kW, and the charging SOP is 20 kW. Note that, regarding power supply units  10 # 1  to  10 # 4 , since power deviation ratios dob_n at the time of charging are the same, and power supply unit  10  having maximum power deviation ratio dob_n is also supposed here to be power supply unit  10 # 1  (m=1). In this condition, the possible total power SOPall is calculated according to Equation 2, as total SOP=SOPm×(total POB)/POBm=SOP1×(total POB)/POB1=20 kW×80 kW/20 kW=80 kW. Further, regarding the working individual power of each power supply unit  10 , the working individual power POB1 of power supply unit  10 # 1  is 80 kW×dob_1=20 kW, the working individual power POB2 of power supply unit  10 # 2  is 80 kW×dob_2=20 kW, the working individual power POB3 of power supply unit  10 # 3  is 80 kW×dob_3=20 kW, and the working individual power POB4 of power supply unit  10 # 4  is 80 kW×dob_4=20 kW. Any of the working individual power can be dealt with by 20 kW and 60 kW of the charging SOP1 to SOP4, and POBn≤SOPn thus holds, resulting in the same situation as in the case of condition number  4  of  FIG. 4  as a result. 
     (Exemplary Embodiment: When There is Power Deviation) 
     As described above, by the power control method according to the exemplary embodiment, also in the condition in which there is no power deviation among power supply units  10 , charging and discharging power control can be appropriately performed in any of the cases of condition numbers 1 to 4. Next, a discussion is made on condition numbers 5 to 8 in the case in which the power deviation of power supply units  10 # 1  to  10 # 4  is a current ratio of 5:4:4:3 as is the case with  FIG. 5 . Note that the power command, the total POB, the discharging SOP, and the charging SOP are made to correspond to one another between condition numbers 5 to 8 and condition numbers 1 to 4.  
     First, in the case of condition number  5 , regarding the possible individual power SOP of each of power supply units  10 # 1  to  10 # 4 , the charging SOP and the discharging SOP are both 60 kW as is the case with condition number 1, and the total POB is 160 kW. Further, power deviation ratio dob_n calculated with respect to each of power supply units  10 # 1  to  10 # 4  is as follows: regarding power supply unit  10 # 1 , dob_1=POB1/(total POB)=50 kW/160 kW=0.3125; regarding power supply unit  10 # 2 , dob_22=POB2/(total POB)=40 kW/160 kW=0.25; regarding power supply unit  10 # 3 , dob_3 32  POB3/(total POB)=40 kW/160 kW=0.25; and regarding power supply unit  10 # 4 , dob_4=POB4/(total POB)=30 kW/160 kW=0.1875. Therefore, power supply unit  10  having maximum power deviation ratio dob_n is power supply unit  10 # 1  (m=1). Thus, when the total SOP (possible total power SOPall) is calculated according to Equation 2, total SOP=SOPm×(total POB)/POBm=SOP1×(total POB)/POB1=60 kW×160 kW/50 kW=192 kW. Further, regarding the working individual power of each power supply unit  10 , the working individual power POB1 of power supply unit  10 # 1  is 160 kW×dob_1=50 kW, the working individual power POB2 of power supply unit  10 # 2  is  160  kW×dob_2=40 kW, the working individual power POB3 of power supply unit  10 # 3  is 160 kW×dob_3=40 kW, and the working individual power POB4 of power supply unit  10 # 4  is 160 kW×dob_4=40 kW. Here, since the possible individual power SOP1 to SOP4 of power supply units  10  are each 60 kW for both of the discharging SOP and the charging SOP as described above, each working individual power POBn can be dealt with, and POBn≤SOPn thus holds. 
     Next, in the case of condition number 6, regarding the possible individual power SOP of each of power supply units  10 # 1  to  10 # 4 , the charging and the discharging SOP are both 60 kW as is the case with condition number 2, and the total POB is 192 kW. Further, power deviation ratio dob_n calculated with respect to each of power supply units  10 # 1  to  10 # 4  is as follows: regarding power supply unit  10 # 1 , dob_1=POB1/(total POB)=60 kW/192 kW=0.3125; regarding power supply unit  10 # 2 , dob_2=POB2/(total POB)=48 kW/192 kW=0.25; regarding power supply unit  10 # 3 , dob_3=POB3/(total POB)=48 kW/192 kW=0.25; and regarding power supply unit  10 # 4 , dob_4=POB4/(total POB)=36 kW/192 kW=0.1875. Therefore, power supply unit  10  having maximum power deviation ratio dob_n is power supply unit  10 # 1  (m=1). Thus, when the total SOP is calculated according to Equation 2, total SOP=SOPm×(total POB)/POBm=SOP1×(total POB)/POB1=60 kW×192 kW/60 kW=192 kW. Further, regarding the working individual power of each power supply unit  10 , the working individual power POB1 of power supply unit  10 # 1  is 192 kW×dob_1=60 kW, the working individual power POB2 of power supply unit  10 # 2  is 192 kW×dob_2=48 kW, the working individual power POB3 of power supply unit  10 # 3  is  192  kW×dob_3=48 kW, and the working individual power POB4 of power supply unit  10 # 4  is 192 kW×dob_4=36 kW. Here, since the possible individual power SOP1 to SOP4 of power supply units  10  are each 60 kW for both of the discharging SOP and the charging SOP as described above, each working individual power POBn can be dealt with, and POBn≤SOPn thus holds. Compared with the same condition in  FIG. 4 , the working individual power of power supply unit  10 # 1  is lowered from 75 kW to 60 kW, and it is thus possible to prevent the possible individual power, that is, a maximum rated power from being exceeded, whereby the power supply system can stably operate. 
     Further, in the case of condition number 7, regarding the possible individual power SOP of each of power supply units  10 # 2  to  10 # 4 , the charging SOP and the discharging SOP are both 60 kW as is the case with condition number 3; however, power supply unit  10 # 1  is fully charged, whereby the discharging SOP is 60 kW, and the charging SOP is 0. Therefore, charging is possible, but power supply unit  10 # 1  is separated from the power supply system at the time of charging. In addition, the total POB is 165 kW. Here, power deviation ratio dob_n, at the time of charging, calculated with respect to each of power supply units  10 # 2  to  10 # 4  is as follows: regarding power supply unit  10 # 2 , dob_2=POB2/(total POB)=60 kW/165 kW=0.3637; regarding power supply unit  10 # 3 , dob_3=POB3/(total POB)=60 kW/165 kW=0.3637; and regarding power supply unit  10 # 4 , dob_4=POB4/(total POB)=45 kW/165 kW=0.2728. Therefore, power supply unit  10  having maximum power deviation ratio dob_n is power supply units  10 # 2  and  10 # 3 . Here, when the total SOP at the time of charging is calculated according to Equation 2 assuming that power supply unit  10  having the maximum power deviation is power supply unit  10 # 2  (m=2), total SOP=SOPm×(total POB)/POBm=SOP2×(total POB)/POB2=60 kW×165 kW/60 kW=165 kW. Further, regarding the working individual power, at the time of charging, of each power supply unit  10 , the working individual power POB2 of power supply unit  10 # 2  is 165 kW×dob_2=60 kW, the working individual power POB3 of power supply unit  10 # 3  is 165 kW×dob_3=60 kW, and the working individual power POB4 of power supply unit  10 # 4  is 165 kW×dob_4=45 kW. Here, since the possible individual power SOP2 to SOP4 of each of power supply units  10  is 60 kW for both of the discharging SOP and the charging SOP as described above, each working individual power POBn can be dealt with, and POBn≤SOPn thus holds. Compared with the same condition in  FIG. 4 , the working individual power of each of power supply units  10 # 2  and  10 # 3  is lowered from 65 kW to 60 kW, and it is thus possible to prevent the maximum rated power from being exceeded, whereby the power supply system can stably operate. 
     Further, in the case of condition number 8, as is the case with condition number 4, the possible individual power SOP of each of power supply units  10 # 2  to  10 # 4  is 60 kW for both of the charging SOP and the discharging SOP, power supply unit  10 # 1  is being charged by constant voltage charging, the discharging SOP is 60 kW, and the charging SOP is 20 kW. In addition, the total POB is 64 kW. Here, power deviation ratio dob_n, at the time of charging, calculated with respect to each of power supply units  10 # 1  to  10 # 4  is as follows: regarding power supply unit  10 # 1 , dob_1=POB1/(total POB)= 2 0 kW/64 kW=0.3125; regarding power supply unit  10 # 2 , dob_2=POB2/(total POB)=16 kW/64 kW=0.25; regarding power supply unit  10 # 3 , dob_3=POB3/(total POB)=16 kW/64 kW=0.25; and regarding power supply unit  10 # 4 , dob_4=POB4/(total POB)=12 kW/64 kW=0.1875. Therefore, power supply unit  10  having maximum power deviation ratio dob_n is power supply unit  10 # 1 . Thus, when the total SOP at the time of charging is calculated by Equation 2 where m=1, the calculation result is total SOP=SOPm×(total POB)/POBm=SOP1×(total POB)/POB1=20 kW×64 kW/20 kW=64 kW. Further, regarding the working individual power, at the time of charging, of each power supply unit  10 , the working individual power POB1 of power supply unit  10 # 1  is 64 kW×dob_1=20 kW, the working individual power POB2 of power supply unit  10 # 2  is 64 kW×dob_2=16 kW, the working individual power POB3 of power supply unit  10 # 3  is 64 kW×dob_3=16 kW, and the working individual power POB4 of power supply unit  10 # 4  is 64 kW×dob_4=12 kW. Thus, the possible individual power SOP1 to SOP4 of power supply units  10  can respectively deal with working individual power POB1 to POB4, and POBn≤SOPn thus holds. Compared with the same condition in  FIG. 4 , the working individual power of power supply unit  10 # 1  is lowered from 25 kW to 20 kW, and it is thus possible to prevent the maximum rated power from being exceeded, whereby the power supply system can stably operate. 
     By using the above method, it is possible to perform charging and discharging control depending on the power deviation, and an unintended system failure can thus be avoided. 
     Note that the power deviation can be detected at a constant cycle, and the working individual power can be updated on the basis of the detected power deviation. This arrangement enables appropriate adjustment of the charging and discharging power, coping with the battery condition temporally varying from hour to hour. The power deviation is preferably detected on the controller on the unit side and sent out to master controller  120 . However, the present invention does not limit the timing of detection of the power deviation to a cyclic detection, and the detection can be performed at an arbitrary timing. For example, the detection timing may be varied, for example, the detection may be performed at the time when an issue implying change in the power deviation occurs, or the detection may be performed at long intervals when the power deviation does not often change or at short intervals when the power deviation often changes. Further, the method for measuring the power deviation and the like is not limited to the measurement of a voltage or a current, and other methods can be used appropriately.  
     Further, in the example of  FIG. 1 , master controller  120  calculates the power deviation and communicates the power deviation to power conditioner  140 ; however, other than this configuration, the power deviation may be calculated by the system controller or the power conditioner. Alternatively, the function of calculating the power deviation may be provided on the unit controller side. For example, in a power supply system according to a modified example shown  FIG. 6 , unit controller  12 ′ of power supply unit  10 # 1  includes the function of calculating the power deviation and plays a role of the master controller. In this case, the master controller does not need to be provided. 
     INDUSTRIAL APPLICABILITY 
     A power supply system and a power conditioner according to the present invention can be suitably used as a large-scale power storage device used in a power plant or the like and as a controller of the power storage device. 
     REFERENCE MARKS IN THE DRAWINGS 
       1000  power supply system 
       1  battery module 
       10 ,  10 # 1  to  10 # 4 ,  210 ,  310 ,  310 # 1  to  310 # 4  power supply unit 
       11 ,  211 ,  311  battery aggregation 
       12 ,  12 ′,  212 ,  312  unit controller (BMU) 
       14 ,  214 ,  314  switch 
       100  control system 
       120  master controller (M-BMU) 
       140 ,  240 ,  340  power conditioner 
       160  system controller 
     ES power system