Patent Publication Number: US-2021194255-A1

Title: Energy hub apparatus and energy management method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority benefit of Korean Patent Application No. 10-2019-0095016, filed on Aug. 5, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present invention relates to an energy hub apparatus and an energy management method for relaying and storing energy in charging and discharging power in an ESS rack. 
     BACKGROUND ART 
     Recently, research and development on secondary batteries have been actively conducted. Here, the secondary batteries, as batteries that can be charged and discharged, mean that they include conventional Ni/Cd batteries and Ni/MH batteries, and recent lithium ion batteries. Among the secondary batteries, the lithium ion battery has an advantage that the energy density is much higher than that of the conventional Ni/Cd battery and Ni/MH battery, and further, the lithium ion battery can be manufactured with a tendency of a small size so that it is used as a power source for a mobile apparatus. The usage range of such a lithium ion battery extends as a power source for electric vehicles, so that the lithium ion battery attracts attention as a next generation energy storage medium. 
     In addition, a secondary battery is generally used as a battery pack including a battery module in which a plurality of battery cells is connected in series and/or in parallel. And, a state and an operation of a battery pack are managed and controlled by a battery management system (BMS). 
     In particular, an Energy Storage System (ESS) is used to devise a mobile ESS in that existing gasoline vehicles, liquefied natural gas (LNG) vessels/carriers/tank ships, and oil tankers transport energy materials. At this time, it is necessary to maintain the ESS in a high charging state for a long period of time. 
     DISCLOSURE 
     Technical Problem 
     In the present invention, since a mobile ESS needs to maintain a high charging state for a long period of time during long-term movement, an energy hub apparatus can be used to solve this. 
     Technical Solution 
     According to an embodiment of the present invention, an energy hub apparatus includes: a first communicator configured to receive respective state of charge (SOC) information and state of health (SOH) information from a plurality of battery management systems (BMS), each BMS being configured to monitor and control an ESS rack; a controller configured to determine at least one ESS rack to perform discharging or charging using at least one of load output information, SOC information, and SOH information received from an external device; and an energy storage configured to receive power from the at least one ESS rack among the plurality of ESS racks and transmit the power to an external load. 
     According to an embodiment of the present invention, the energy hub apparatus further includes a second communicator configured to receive the load output information from the external device and to transmit the load output information to the controller, wherein when the controller controls discharge of the at least one ESS rack, the controller sets a number of ESS racks among the plurality of ESS racks to perform discharging using the received load output information and selects the at least one ESS rack among the number of ESS racks to perform discharging using the SOC information and the SOH information, and when the load output information is not satisfied by considering an SOC value of each of the discharging ESS racks for the set number of ESS racks, the controller resets the number of ESS racks to perform discharging. 
     In the energy hub apparatus according to an embodiment of the present invention, the controller further uses a number of discharges of the plurality of ESS racks when selecting the discharging ESS rack. 
     The energy hub apparatus according to an embodiment of the present invention further includes a power receiver configured to receive power from the at least one ESS rack, the energy storage stores power received from the power receiver and outputs power to the external load according to the load output information, the load output information includes output voltage and output current. 
     The energy hub apparatus according to an embodiment of the present invention further includes a switch configured to switch from an off state to an on state to receive power from the at least one ESS rack; and a voltage converter configured to convert power received from the at least one ESS rack into a chargeable voltage for the enemy storage. 
     In the energy hub apparatus according to an embodiment of the present invention, when the controller controls charging of the at least one ESS rack, the energy storage is charged by receiving power from a power supply, and the controller determines, as an at least one charging ESS rack, the at least one ESS rack in which the SOC is smaller than a preset first value and the SOH is larger than a second preset value among the plurality of ESS racks. 
     The energy hub apparatus according to an embodiment of the present invention further includes a switch configured to switch from an off state to an on state in order to charge the at least one ESS rack selected as the charging ESS rack, and when the switch is switched to the on state, the charging ESS rack is charged by the power stored in the energy storage. 
     The energy hub apparatus according to an embodiment of the present invention, the controller is further configured to diagnose whether an abnormality occurs in the at least one ESS rack performing discharging or charging while the at least one ESS rack is performing discharging or charging, and when at least one of an abnormal current, an abnormal voltage, or an abnormal output path occurs in the at least one ESS rack performing discharging or charging, the switch switches from the on state to the off state to stop discharging or charging of the at least one ESS rack in which an abnormality occurs. 
     An energy management method according to an embodiment of the present invention includes: receiving, by an energy hub apparatus, SOC information and SOH information from a plurality of BMSs, each BMS monitors and controls an ESS; determining, by the energy hub apparatus, at least one ESS rack to perform discharging or charging among the plurality of ESS racks using at least one of load output information received from an external device, the SOC information, and SOH information, storing energy, by the energy hub apparatus, by receiving power from the at least one ESS rack among the plurality of ESS racks; and transmitting, by the energy hub apparatus, the stored energy to an external load. 
     In the energy management method according to an embodiment of the present invention, the determining of the at least one ESS rack includes: setting a number of discharging ESS racks to perform discharging using the load output information; and determining at least one discharging ESS rack to perform discharge using the SOC information and the SOH information of each ESS rack, and the energy management method further includes re-performing setting the number of discharging ESS racks to perform discharging if the load output information is not satisfied even when considering a SOC value of each of the discharging ESS racks for the set number of ESS racks. 
     In the energy management method according to an embodiment of the present invention, in the determining of the at least one discharging ESS rack, the number of discharges of each ESS rack is further used. 
     In the energy management method according to an embodiment of the present invention, in the storing of the energy, the power received from the at least one discharging ESS rack is converted to a preset voltage to store the power, and in the transmitting of the stored energy to the external load, the stored energy is transmitted according to the load output information. 
     The energy management method according to an embodiment of the present invention further includes: applying power to the energy hub apparatus from an external power source; and performing charging by determining the at least one ESS rack to perform charging using the charged energy based on the SOC information and the SOH information, when the at least one ESS rack determined to perform charging has a SOC smaller than a first preset value, and an SOH is greater than a second preset value. 
     Advantageous Effects 
     Through the energy hub apparatus and the energy management method according to an embodiment of the present invention, there is an effect that the ESS in a high state of charge can be preserved for a long time. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a simplified configuration diagram of an energy hub apparatus according to an embodiment of the present invention. 
         FIG. 2  is a simplified configuration diagram of an energy hub apparatus according to an embodiment of the present invention. 
         FIG. 3  is a flowchart of an energy output method according to an embodiment of the present invention. 
         FIG. 4  is a flowchart of a method of charging an ESS rack according to an embodiment of the present invention. 
         FIG. 5  is a flowchart of a method for diagnosing an ESS rack according to an embodiment of the present invention. 
     
    
    
     BEST MODE 
     Hereinafter, various embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this document, the same reference numerals are used for the same components in the drawings, and duplicate descriptions for the same components are omitted. 
     For various embodiments of the present invention disclosed in this document, specific structural or functional descriptions are exemplified only for the purpose of explaining an embodiment of the present invention, and various embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in this document. 
     The terms such as “1st”, “2nd”, “first”, “second”, and the like used herein may refer to modifying various different elements of various embodiments of the present disclosure, but do not limit the elements. For example, a first component may be referred to as a second component and vice versa without departing from the technical scope of the present invention. 
     Terms used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the scope of other embodiments. The terms of a singular form may include plural forms unless they have a clearly different meaning in the context. 
     Otherwise indicated herein, all the terms used herein, which include technical or scientific terms, may have the same meaning that is generally understood by a person skilled in the art. In general, the terms defined in the dictionary should be considered to have the same meaning as the contextual meaning of the related art, and, unless clearly defined herein, should not be understood as having an ideal or excessively formal meaning. In any cases, even the terms defined in this specification cannot be interpreted as excluding embodiments of the present invention. 
       FIG. 1  is a simplified configuration diagram of an energy hub apparatus according to an embodiment of the present invention. 
     An energy hub apparatus  100  includes an energy hub controller  102 , an ESS dam  104 , and a DC/DC converter  106 . Accordingly, there are DC/DC converters whose number corresponds to the number of corresponding ESS racks. The DC/DC converter  106  is connected to each ESS rack  110  through a switch element  108 . 
     The operation of the energy hub apparatus will be schematically described through the configuration of the enemy hub apparatus  100  of  FIG. 1 . 
     Load output information is received from an external device. The received load output information may include voltage, current, or power quality of output power. Based on the received load output information, the energy hub controller  102  sets the number of ESS racks to perform discharging. After setting the number of ESS racks, the energy hub controller  102  determines an ESS rack to perform discharging by using SOC information, SOH information, and the number of discharges of each ESS rack. 
     Specifically, among the plurality of ESS racks related to the energy hub apparatus  100 , the ESS rack in which the SOC value is greater than the preset first value, the SOH value is compared between the ESS racks, and there is a relatively small number of discharges is determined as the final discharging ESS rack. 
     SOH information between each ESS rack selects excellent SOH through relative comparison. In addition, it is also possible to preset a condition in which only the ESS rack is used for discharging when the SOH is greater than the second preset value. 
     In addition, among a plurality of ESS racks, an ESS rack with a small (e.g., lowest) number of discharges may be selected as a discharging ESS rack with priority. Alternatively, an ESS rack discharged less than a preset number of times can be selected. 
     That is, based on the received load output information, the energy hub controller may select an optimal ESS rack to perform discharging using SOC information, SOH information, and discharge number of each of the plurality of ESS racks. 
     However, if it is determined that the SOC information of each ESS rack does not satisfy the load output information according to the number of determined ESS racks, the energy hub controller  102  resets the number of discharging ESS racks, and again determines an optimal ESS rack to perform discharging by using SOC information, SOH information, and the number of discharges of each of the plurality of ESS racks. 
     When the optimum ESS rack to perform discharging is determined, the switch  108  connected to the corresponding ESS rack is turned on. When the switch  108  is turned on, the energy hub apparatus  100  receives power from the ESS rack and the ESS dam  104  stores the energy. 
     However, the DC/DC conversion unit  106  is located between each of the plurality of ESS racks and the ESS dam  104 , respectively, so that before energy is stored in the ESS dam  104 , the DC/DC conversion unit  106  converts the voltage of power received from the ESS rack into a voltage that can be charged to the ESS darn  104 . 
     The ESS dam  104 , which is charged with energy by receiving power from the ESS rack, outputs power to an external load according to the received load output information. 
     Meanwhile, the ESS dam  104  may be charged by applying power from an external power source. At least one ESS rack among a plurality of ESS racks connected to the energy hub apparatus  100  may be charged by using the energy charged in the ESS dam  104 . 
     At this time, the energy hub controller  102  selects an ESS rack to perform charging among a plurality of connected ESS racks. The energy hub controller  102  determines, as a charging ESS rack, an ESS rack having an SOC smaller than a first preset value and a SOH greater than a second preset value among the plurality of ESS racks. 
     When determining the charging ESS rack to perform charging, if the SOH is smaller than the second preset value, it is determined as a defective ESS rack. Because the defective ESS rack needs maintenance later, it does not require charging, so that it is not to perform charging. In addition, such a defective ESS can be a subject of diagnosis. 
     The energy stored in the ESS dam  104  is transmitted to the charging ESS rack determined as a charging target. At this time, charging proceeds according to the state of the ESS rack. For example, an ESS rack capable of fast charging is performed with specialized charging with good SOH, and an ESS rack with a large number of uses or an ESS rack with a relatively low SOH is a rack requiring slow charging management. 
     In addition, the energy huh apparatus  100  may detect whether an unintended abnormal value is derived when charging or discharging a related ESS rack. 
     The energy hub apparatus  100  diagnoses at least one ESS rack performing charging or discharging in order to determine the ESS rack in which an abnormality occurs. 
     When a situation in which an abnormal value rather than an intended value is derived from a charging or discharging situation is detected, the energy hub apparatus  100  diagnoses an ESS rack in which an abnormal situation occurs. First, the energy hub apparatus  100  diagnoses whether an unintended current occurs in a specific ESS rack. For example, a situation in which an unintended current occurs may be a case where a charging current flows in reverse from an ESS rack being discharged or a discharging current flows from an ESS rack being charged. In addition, the energy hub apparatus  100  checks whether the ESS rack voltage is an intended value. The case where the ESS rack applies an unintended voltage may include overvoltage, undervoltage, short circuit, or open circuit. In addition, the energy hub apparatus  100  diagnoses whether the ESS rack forms a normal output path. For example, abnormal circuits include short circuits and open circuits. 
     When it is determined that a specific ESS rack among at least one ESS rack in which the energy hub apparatus  100  is charging or discharging is not normal, the switch element of the corresponding ESS rack is switched from the on state to the off state. 
       FIG. 2 . is a block diagram of another energy hub apparatus according to an embodiment of the present invention. 
     The energy hub apparatus  100  includes a power reception unit/power receiver  200 , a switch unit/switch  202 , a first communication unit/communicator  204 , a voltage conversion unit/voltage converter  206 , an energy storage unit/energy storage  208 , a second communication unit/communicator  210 , a control unit (e.g., controller/processor)  212 , and a diagnosis unit  214 . Here, the control unit  212  corresponds to the energy hub controller  102  in  FIG. 1 , the energy storage unit  208  corresponds to the ESS dam  104 , and the voltage conversion unit  206  corresponds to the DC/DC conversion unit  106 . 
     The energy hub apparatus  100  is connected to a plurality of ESS racks, as shown in  FIG. 1 . The energy hub apparatus  100  receives or transmits power from or to at least one ESS rack among ESS racks connected to perform charging or discharging. 
     When the ESS rack to perform charging or discharging is determined, the power reception unit  200  receives power or transmits power from or to the corresponding ESS rack. 
     When determining at least one ESS rack to perform discharging in order to transmit power to the load among a plurality of ESS racks connected to the control unit  212 , the switch unit  202  switches the switch element connected to the corresponding ESS rack from an off state to an on state. At this time, the switch element may be connected between the ESS rack and the power reception unit  200 . 
     Or, when determining at least one ESS rack to perform charging among a plurality of ESS racks connected to the control unit  212 , the switch unit  202  switches the switch element connected to the corresponding ESS rack from an off state to an on state. 
     Or, when the control unit  212  detects an abnormality in a specific ESS rack performing discharging or charging, the switch unit  202  switches the switch element connected to the corresponding ESS rack from an on state to an oft state. 
     The first communication unit  204  receives SOC information and SOH information of each ESS rack from a plurality of ESS racks. In addition, the first communication unit  204  may receive voltage or current information of each ESS rack from a plurality of ESS racks. 
     The SOC information and SOH information of the plurality of ESS racks received by the first communication unit  204  are transmitted to the control unit  212  to determine the ESS rack to perform discharging or charging. 
     The voltage conversion unit  206  converts the voltage of the power received from the power reception unit  200  into a voltage that can be charged to the energy storage unit  208 . The power reception unit  200  may be a plurality of configurations corresponding to each of a plurality of ESS racks, and the voltage conversion unit  206  may also be a plurality of configurations corresponding to each of a plurality of ESS racks. 
     The energy storage unit  208  may store power received from at least one ESS rack performing discharge. Power received from the at least one ESS rack is converted into a voltage that can be stored in the energy storage unit  208  in the voltage conversion unit  206  and transmitted to the energy storage unit  208 . The power stored in the energy storage unit  208  is transmitted to the load according to the load output information previously received by the external load. 
     In addition, the energy storage unit  208  may charge the ESS rack by transmitting power to at least one ESS rack that performs charging. When an ESS rack to perform charging is determined based on SOC information and SOH information received from a plurality of ESS racks, power can be transmitted to the corresponding ESS rack. The power can perform charging according to the characteristics of the ESS rack. In case of fast charging, frequent use, or relatively poor SOP ESS rack, an ESS rack with good SOH can be charged by a slow charging management method. 
     The second communication unit  210  receives load output information from an external device. The load output information may be voltage, current, or power quality of output power. Based on the load output information received from the second communication unit  210 , the ESS rack to perform discharging is determined, and the energy stored in the energy storage unit  208  transmits power to the external load. 
     When receiving the load output information from the second communication unit, the control unit  212  determines an ESS rack to perform discharging among a plurality of connected ESS racks. The control unit  212  determines an ESS rack to perform discharging based on the load output information. Then, the control unit  212  determines a discharging ESS rack to perform discharging using the SOC information, SOH information, and the number of discharges of each of the received plurality of ESS racks. The control unit  212  uses SOH information of a plurality of ESS racks to first discharge an ESS rack having a relatively excellent SOH value. In this case, by setting the SOH value in advance, it is possible to set to discharge only ESS racks having an SOH value equal to or greater than the preset value. In addition, the control unit  212  may determine the discharging ESS rack in consideration of the number of times of use among the plurality of ESS racks. Through the relative comparison between ESS racks, the discharging ESS rack can be determined in the order of the ESS rack with the lowest number of uses (the number of discharges). At this time, instead of a relative comparison, ESS racks used less than a preset number of times can be set as priority. In addition, the control unit  212  may determine the discharging ESS rack in consideration of SOC among a plurality of ESS racks. However, even if a plurality of ESS racks are combined with the determined number of discharging ESS racks, when it is determined that the power to be outputted to the load is not satisfied even when the SOCs of each ESS rack are combined, the control unit  212  adjusts the number of discharging ESS racks to perform discharging again. Subsequently, the control unit  212  determines the ESS rack to perform discharging again with the adjusted number based on SOC information, the number of discharges, and SOH information. 
     When the control unit  212  determines the discharging ESS rack, the switch unit  202  causes the switch element connected to the corresponding ESS rack to be switched from an off state to an on state. 
     The control unit  212  may perform charging of the ESS rack. Specifically, when power is applied to the energy storage unit  208  from an external power source and the energy storage unit  208  is charged, the ESS rack to perform charging may be determined using the charged power. 
     The control unit  212  may determine using SOC information and SOH information of a plurality of connected ESS racks in order to determine an ESS rack to perform charging. Specifically, if the SOC value of the plurality of ESS racks is smaller than a preset value, the charging ESS rack to perform charging may be a target. In addition, when the SOH value of the plurality of ESS racks is greater than a preset value, the charging ESS rack to perform charging can be targeted. That is, if the SOC value among the plurality of ESS racks is smaller than the first preset value and the SOH value is greater than the second preset value, the charging ESS rack is determined. At this time, the SOC value of the ESS rack may not be considered, and only the SOH value may be considered to determine the charging ESS rack. 
     Among the plurality of ESS racks, an ESS rack whose SOH value is lower than the preset second value is a defective rack and may be taken care of at a later stage of diagnosis. When determining the charging ESS rack, the control unit  212  causes the switch unit  202  to switch the switch element connected to the corresponding ESS rack from an off state to an on state. 
     In addition, the control unit  212  controls to perform charging according to the state of the charging ESS rack. For example, an ESS rack with good SOH can be controlled to perform fast charging, and an ESS rack with a large number of uses or relatively poor SOH can be controlled to be charged slowly. 
     The diagnosis unit  214  diagnoses an ESS rack performing charging or discharging when an abnormal current value or voltage value is detected during charging or discharging. 
     Specifically, the diagnosis unit  214  detects an unintended current in the ESS rack performing charging or discharging. For example, it detects the case where the charging current flows reversely from the ESS rack performing discharging or the discharging current flows reversely from the ESS rack performing charging. 
     In addition, the diagnosis unit  214  detects an unintended voltage in the ESS rack performing charging or discharging. For example, when an overvoltage, undervoltage, short circuit, or open circuit occurs in the corresponding ESS rack, an unintended voltage may be detected. Alternatively, an abnormality may be detected even in the case of a short or open circuit other than a normal output path. 
     When the diagnosis unit  214  detects an unintended current or voltage in an ESS rack performing charging or discharging, the diagnosis unit  214  transmits an abnormal signal of the corresponding ESS rack to the control unit  212 . 
     The control unit  212  receiving an abnormal signal of a specific ESS rack from the diagnosis unit  214  causes the switch unit  202  to switch the switch element of the corresponding ESS rack from an ON state to an OFF state. 
       FIG. 3  is a flowchart of an energy output method according to an embodiment of the present invention. 
     The second communication unit  210  receives load output information from an external device (S 300 ). The load output information may be voltage, current, or power quality of output power. Based on the load output information received from the second communication unit, the ESS rack to perform discharging is determined, and the energy stored in the energy storage unit  208  transmits power to the external load. 
     When receiving the load output information from the second communication unit, the control unit  212  selects/determines the number of ESS racks to perform discharging among a plurality of connected ESS racks (S 302 ). 
     Subsequently, based on the load output information, the control unit  212  selects/determines an (optimal) ESS rack to perform discharging using SOH, SOC, and the number of discharges of each ESS rack (S 304 ). 
     The control unit  212  uses SOH information of a plurality of ESS racks to first discharge an ESS rack having a relatively excellent SOH value. In this case, by setting the SOH value in advance, it is possible to set to discharge only ESS racks having an SOH value equal to or greater than the preset value. In addition, the control unit  212  may determine the discharging ESS rack in consideration of the number of times of use among the plurality of ESS racks. Through the relative comparison between ESS racks, the discharging ESS rack can be determined in the order of the ESS rack with the lowest number of uses (e.g., the number of discharges). At this time, instead of a relative comparison, ESS racks used less than a preset number of times can be set as priority. In addition, the control unit  212  may determine the discharging ESS rack in consideration of SOC among a plurality of ESS racks. 
     The control unit  212  determines whether the SOC of the ESS rack is sufficient based on the proper load output (S 306 ). 
     Even if multiple ESS racks are combined with the determined number of discharging ESS racks, when the control unit  212  determines that the power to be outputted to the load is not satisfied even when the SOCs of each ESS rack are combined, the control unit  212  adjusts the number of discharging ESS racks to perform discharging again. Therefore, the control unit  212  determines the number of ESS racks to perform discharging from among the plurality of ESS racks connected again (S 302 ). 
     If the control unit  212  determines that the SOC of the ESS rack is sufficient due to the proper load output, the control unit  212  switches the switch of the ESS rack whose discharge is determined from the off state to the on state (S 308 ). 
     When the control unit  212  determines the discharging ESS rack, the switch unit  202  causes the switch element connected to the corresponding ESS rack to be switched from an off state to an on state. Accordingly, when determining at least one ESS rack to perform discharging in order to deliver power to the load among a plurality of ESS racks connected to the control unit  212 , the switch unit  202  switches the switch element connected to the corresponding ESS rack from an off state to an on state. 
     When the switch element connected to the discharging ESS rack is turned on, power is transmitted from each discharging ESS rack to each power reception unit  200 . Accordingly, the voltage conversion unit  206  converts the voltage of the power received from the power reception unit  200  into a voltage that can be charged to the energy storage unit  208 . The power reception unit  200  may be a plurality of configurations corresponding to each of a plurality of ESS racks, and the voltage conversion unit  206  may also be a plurality of configurations corresponding to each of a plurality of ESS racks. 
     The switch element connected to the discharging ESS rack is turned on, and after receiving power from the discharging ESS rack and converting it to a voltage that can be stored in the energy storage unit  208 , the voltage is stored in the energy storage unit  208  (S 310 ). 
     Then, the power stored in the energy storage unit  208  is transmitted to the load according to the load output information previously received by the external load (S 312 ). 
       FIG. 4  is a flowchart of a method of charging an ESS rack according to an embodiment of the present invention. 
     The control unit  212  controls power to be transmitted from an external power source to the energy storage unit  208  when charging the connected ESS rack. Accordingly, the energy storage unit  208  is charged by receiving power from an external power source (S 400 ). 
     Subsequently, the control unit  212  determines an ESS rack to perform charging using the power stored in the energy storage unit  208  based on each of SOC information and SOH information (S 402 ). 
     The control unit may determine using SOC information and SOH information of a plurality of connected ESS racks in order to determine an ESS rack to perform charging. Specifically, if the SOC value of the plurality of ESS racks is smaller than a preset value, the charging ESS rack to perform charging may be a target. In addition, when the SOH value of the plurality of ESS racks is greater than a preset value, the charging ESS rack to perform charging can be targeted. That is, if the SOC value among the plurality of ESS racks is smaller than the first preset value and the SOH value is greater than the second preset value, the charging ESS rack is determined. At this time, the SOC value of the ESS rack may not be considered, and only the SOH value may be considered to determine the charging ESS rack. 
     Here, the control unit  212  compares the SOH of the ESS rack with a preset second value (S 404 ). If the SOH of a specific ESS rack is less than a preset value, the corresponding ESS rack is determined as a defective ESS rack and does not proceed with charging (S 406 ). 
     When determining the charging ESS rack, the control unit  212  causes the switch unit  202  to switch the switch element connected to the corresponding ESS rack from an off state to an on state. Accordingly, the ESS rack is charged (S 408 ). 
     In addition, the control unit  212  controls to perform charging according to the state of the charging ESS rack. For example, an ESS rack with good SOH can be controlled to perform fast charging, and an ESS rack with a large number of uses or relatively poor SOP can be controlled to he charged slowly. 
       FIG. 5  is a flowchart of a method for diagnosing an ESS rack according to an embodiment of the present invention. 
     The diagnosis unit  214  diagnoses an ESS rack performing charging or discharging when an abnormal current value or voltage value is detected during charging or discharging (S 500 ). 
     Subsequently, the diagnosis unit  214  diagnoses/checks whether an abnormal current is generated in any of the ESS racks performing charging or discharging (S 502 ). 
     Specifically, when the diagnosis unit  214  detects an unintended current in the ESS rack performing charging or discharging, it may determine that an abnormality occurs in the corresponding rack. For example, it detects the case where the charging current flows reversely from the ESS rack performing discharging or the discharging current flows reversely from the ESS rack performing charging. 
     Further, when the diagnosis unit  214  detects/checks for an unintended voltage in the ESS rack performing charging or discharging, it may determine that an abnormality occurs in the corresponding rack (S 504 ). For example, when an overvoltage, undervoltage, short circuit, or open circuit occurs in the corresponding ESS rack, an unintended voltage may be detected. 
     In addition, the diagnosis unit  214  diagnoses/checks whether there is an output path abnormality of the ESS rack performing charging or discharging (S 506 ). 
     When at least one of a current error, a voltage error, or an output path error is diagnosed in the ESS rack performing charging or discharging, the switch connected to the corresponding ESS rack is turned off (e.g., the abnormal ESS rack is switched off) (S 508 ). 
     In the above, even though all the components constituting the embodiments of the present invention are described as being combined into one or operating in combination, the present invention is not necessarily limited to these embodiments. That is, within the scope of the object of the present invention, all of the constituent elements may be selectively combined and operated in one or more. 
     In addition, the terms “include”, “compose”, or “have” as described above means that the corresponding component can be intrinsic, unless otherwise stated, so that it should be interpreted that other components may be further included, not excluded. All terms, including technical or scientific terms, can be interpreted as having the same meaning as generally understood by a person skilled in the art to which the present invention belongs, unless otherwise defined. Generally used terms, such as predefined terms, should be interpreted as being consistent with the contextual meaning of the related art, and are not to be interpreted in an ideal or excessively formal sense, unless explicitly defined in the present invention. 
     The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical spirit of the present invention, but to explain, and the scope of the technical spirit of the present invention is not limited by these embodiments. The scope of protection of the present invention should be construed according to the following claims, and all technical ideas falling within the scope of the same shall be construed as falling within the scope of the present invention.