Patent Publication Number: US-2023134388-A1

Title: Energy storage system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Pursuant to 35 U.S.C. § 119(a), this application claims the benefit of earlier filing date and right of priority to Korean Patent Application No. 10-2021-0149666, filed on Nov. 3, 2021, the contents of which are incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to an energy storage system, and more particularly, to a battery-based energy storage system and an operating method thereof. 
     2. Description of the Related Art 
     An energy storage system is a system that stores or charges external power, and outputs or discharges stored power to the outside (e.g., an external entity). To this end, the energy storage system includes a battery, and a power conditioning system that is used for supplying power to the battery or outputting power from the battery. 
     In order to increase the total battery capacity, battery cells may be connected and used. Battery cells may be chemically and physically different (e.g., from each other), and thus there may be a difference in capacity. 
     The total capacity of battery is determined according to a series/parallel connection structure (or configuration) of the battery cells. In a high-voltage series configuration, as a difference in capacity between battery cells or sets of battery cells increases while charging/discharging is repeated (or maintained), there is a problem in that the battery capacity that can be used by consumers compared to the total capacity of the battery is reduced. In addition, some batteries may be overcharged due to battery imbalance. 
     Since the energy storage system has the possibility of accidents such as explosion, ignition, and gas emission, various technologies have been proposed to improve safety. For example, Korean Patent Publication No. 2006-0059680 discloses a circuit for protecting circuits and battery cells from short circuit and overvoltage, and Korean Patent Publication No. 2018-0103212 discloses a battery and battery protection circuit. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention have been made in view of the above problems, and an object of an embodiment of the present disclosure is to provide an energy storage system capable of improving the lifespan, stability, and efficiency of a battery by reducing a voltage difference between batteries. 
     Another object of an embodiment of the present disclosure is to provide an energy storage system capable of reducing the possibility of ignition by preventing overcharging due to battery imbalance. 
     Another object of an embodiment of the present disclosure is to provide an energy storage system capable of preventing (e.g., at an earlier time) complete discharge of a battery and improving battery lifespan. 
     Another object of an embodiment of the present disclosure is to provide an energy storage system capable of balancing battery imbalance with a small number of switches. 
     Another object of an embodiment of the present disclosure is to easily (or readily) implement a series/parallel configuration of a desired capacity, and provide an energy storage system with a high degree of freedom in designing a battery cell module. 
     In order to achieve the above object, the energy storage system according to embodiments of the present disclosure may improve the lifespan, stability, and efficiency of a battery by changing a battery connection structure (or configuration). 
     In order to achieve the above object, the energy storage system according to embodiments of the present disclosure uses cell arrays, each including battery cells connected in parallel, the cell arrays connected in a series structure (or configuration), and then converts the cell arrays into a parallel configuration, thereby preventing battery imbalance. 
     In order to achieve the above object, in the energy storage system according to embodiments of the present disclosure, a main circuit configuration may be separated to protect a control circuit from a problem inside the battery pack. 
     The energy storage system according to an embodiment of the present disclosure includes: a plurality of cell arrays, each including a respective plurality of battery cells connected in parallel; and a plurality of switches coupled to the plurality of cell arrays, and configured to connect the plurality of cell arrays in series, wherein the plurality of switches are operable to connect the plurality of cell arrays in parallel. 
     The plurality of switches may include a single pole double throw (SPDT) switch. 
     One switch may be coupled to a positive terminal of the plurality of cell arrays, and one switch may be coupled to a negative terminal of the plurality of cell arrays. 
     The plurality of switches may be configured to be operated such that a positive terminal of one of the plurality of cell arrays is connected to a negative terminal of another one of the plurality of cell arrays, and then, positive terminals of the plurality of cell arrays are connected to each other and negative terminals of the plurality of cell arrays are connected to each other. 
     A number of the plurality of switches may be equal to two times a number of the plurality of cell arrays connected in series. 
     The energy storage system according to an embodiment of the present disclosure may further include: a battery management system configured to control the plurality of switches based on a voltage difference of the plurality of cell arrays. 
     During charging, in a state in which a full charge condition is satisfied, the battery management system may be further configured to change a connection state of the plurality of cell arrays from a series configuration to a parallel configuration based on the voltage difference of the plurality of cell arrays being equal to or greater than a first reference value. 
     In a parallel configuration state, the battery management system may be further configured to change a connection state of the plurality of cell arrays from a parallel configuration to a series configuration based on the voltage difference of the plurality of cell arrays being less than a second reference value. 
     The battery management system may be further configured to change a connection state of the plurality of cell arrays from a series configuration to a parallel configuration based on the voltage difference of the plurality of cell arrays being equal to or greater than a certain reference value, and change the connection state of the plurality of cell arrays from the parallel configuration to the series configuration based on a preset time elapsing. 
     The battery management system may be further configured to turn off some internal power sources of the energy storage system and operate the plurality of switches. 
     The energy storage system according to an embodiment of the present disclosure may further include: a plurality of battery packs, each including a respective plurality of cell arrays. 
     The battery management system may further include: battery pack circuit boards disposed in each of the plurality of battery packs, and configured to obtain state information of the plurality of battery cells of each battery pack; and a main circuit board coupled to the battery pack circuit boards by a communication line, and configured to receive state information obtained from each battery pack by the battery pack circuit boards. 
     The plurality of battery packs may be connected in series by a power line, and the power line may be connected to the main circuit board. 
     The energy storage system according to an embodiment of the present disclosure may further include: a plurality of bus bars to which the plurality of battery cells connected in parallel are connected. 
     One input terminal of the plurality of switches may be coupled to a positive terminal or a negative terminal of the plurality of cell arrays, and two output terminals of the plurality of switches may be coupled to different bus bars. 
     The energy storage system according to another embodiment of the present disclosure includes a plurality of battery packs including a first battery module, a second battery module disposed to face the first battery module, and a high current bus bar connecting the first battery module and the second battery module, wherein each of the first battery module and the second battery module includes: a plurality of cell arrays, each including a respective plurality of battery cells connected in parallel; and a plurality of switches coupled to the plurality of cell arrays and configured to connect the plurality of cell arrays in series, wherein the plurality of switches are operable to connect the plurality of cell arrays in parallel. 
     The plurality of switches may include a single pole double throw (SPDT) switch. 
     The energy storage system according to another embodiment of the present disclosure may further include a battery management system configured to control the plurality of switches based on a voltage difference of the plurality of cell arrays. 
     During charging, in a state in which a full charge condition is satisfied, the battery management system is further configured to change a connection state of the plurality of cell arrays from a series configuration to a parallel configuration based on the voltage difference of the plurality of cell arrays being equal to or greater than a first reference value. 
     In a parallel configuration state, the battery management system may be further configured to change a connection state of the plurality of cell arrays from a parallel configuration to a series configuration based on the voltage difference of the plurality of cell arrays being less than a second reference value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will be more apparent from the following detailed description in conjunction with the accompanying drawings, in which: 
         FIGS.  1 A and  1 B  are conceptual diagrams of an energy supply system including an energy storage system according to an embodiment of the present disclosure; 
         FIG.  2    is a conceptual diagram of a home energy service system including an energy storage system according to an embodiment of the present disclosure; 
         FIGS.  3 A and  3 B  are diagrams illustrating an energy storage system installation type according to an embodiment of the present disclosure; 
         FIG.  4    is a conceptual diagram of a home energy service system including an energy storage system according to an embodiment of the present disclosure; 
         FIG.  5    is an exploded perspective view of an energy storage system including a plurality of battery packs according to an embodiment of the present disclosure; 
         FIG.  6    is a front view of an energy storage system in a state in which a door is removed; 
         FIG.  7    is a cross-sectional view of one side of the energy storage system of  FIG.  6   ; 
         FIG.  8    is a perspective view of a battery pack according to an embodiment of the present disclosure; 
         FIG.  9    is an exploded view of a battery pack according to an embodiment of the present disclosure; 
         FIG.  10    is a perspective view of a battery module according to an embodiment of the present disclosure; 
         FIG.  11    is an exploded view of a battery module according to an embodiment of the present disclosure; 
         FIG.  12    is a front view of a battery module according to an embodiment of the present disclosure; 
         FIG.  13    is an exploded perspective view of a battery module and a sensing substrate according to an embodiment of the present disclosure; 
         FIG.  14    is a perspective view of a battery module and a battery pack circuit substrate according to an embodiment of the present disclosure; 
         FIG.  15 A  is a side view of the battery module and the battery pack circuit substrate of  FIG.  14    in a coupled state; 
         FIG.  15 B  is another side view of the battery module and the battery pack circuit substrate of  FIG.  14    in a coupled state; 
         FIG.  16    is a diagram illustrating a connection between the battery pack and a battery management system according to an embodiment of the present disclosure; 
         FIGS.  17 A to  17 C  are diagrams illustrating a battery imbalance; 
         FIGS.  18  to  20    are diagrams illustrating a battery connection structure (or configuration) according to an embodiment of the present disclosure; and 
         FIG.  21    is a flowchart illustrating a method of operating an energy storage system according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. However, it is understood that the present disclosure is not limited to these embodiments and may be modified in various forms. 
     In the drawings, in order to clearly and briefly describe embodiments of the present disclosure, the illustration of parts irrelevant to the description is omitted, and the same reference numerals are used for the same or extremely similar parts throughout the specification. 
     Hereinafter, the suffixes “module” and “unit” of elements herein are used for convenience of description and thus may be used interchangeably and do not have any distinguishable meanings or functions. Thus, the terms “module” and “unit” may be interchangeably used. 
     It will be understood that, although the terms “first”, “second”, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. 
     The labels top U, bottom D, left Le, right Ri, front F, and rear R used in the drawings are used to describe a battery pack and an energy storage system including the battery pack, and may be set differently according to standard. 
     The labels indicating height direction (h+, h-), length direction (1+, 1-), and width direction (w+, w-) of the battery module used in  FIGS.  10  to  13    are used to describe the battery module, and may be set differently according to standard. 
       FIGS.  1 A and  1 B  are conceptual diagrams of an energy supply system including an energy storage system according to an embodiment of the present disclosure. 
     Referring to  FIGS.  1 A and  1 B , the energy supply system includes a battery-based (see, e.g., battery  35 ) energy storage system  1  in which electrical energy is stored, a load  7  that is a power demander (or consumer), and a grid  9  provided as an external power supply source. 
     The energy storage system  1  includes a battery  35  that stores (charges) the electric energy received from the grid  9 , or the like in the form of direct current (DC) and/or outputs (discharges) the stored electric energy to the grid  9 , or the like, a power conditioning system (PCS)  32  for converting electrical characteristics (e.g. AC/DC interconversion, frequency, voltage) for charging or discharging the battery  35 , and a battery management system  34  (BMS) that monitors and manages information (or parameters) such as current, voltage, and temperature of the battery  35 . 
     The grid  9  may include a power generation facility for generating electric power, a transmission line, and the like. The load  7  may include a home appliance such as a refrigerator, a washing machine, an air conditioner, a TV, a robot cleaner, and a robot, a mobile electronic device such as a vehicle and a drone, and the like, as a consumer that consumes power. 
     The energy storage system  1  may store power from outside the system  1  in the battery  35  and then output power to outside the system  1 . For example, the energy storage system  1  may receive DC power or AC power from outside the system  1 , store it in the battery  35 , and then output the DC power or AC power to outside the system  1 . 
     Since the battery  35  mainly stores DC power, the energy storage system  1  may receive DC power or convert the received AC power to DC power and store it in the battery  35 , and may convert the DC power stored in the battery  35 , and may supply the converted power to the grid  9  or the load  7 . 
     The power conditioning system  32  in the energy storage system  1  may perform power conversion and voltage-charge the battery  35 , or may supply the DC power stored in the battery  35  to the grid  9  or the load  7 . 
     The energy storage system  1  may charge the battery  35  based on power supplied from the system and discharge the battery  35  when necessary. For example, the electric energy stored in the battery  35  may be supplied to the load  7  in an emergency such as a power outage, or at a time, date, or season when the electric energy supplied from the grid  9  is expensive. 
     The energy storage system  1  has the advantage of being able to improve the safety and convenience of new renewable energy generation by storing electric energy generated from a new renewable energy source such as sunlight, and to be used as an emergency power source. In addition, when the energy storage system  1  is used, it is possible to perform load leveling for a load having large fluctuations in (or over) time and season, and to save energy consumption and cost. 
     The battery management system  34  may measure the temperature, current, voltage, state of charge, and the like of the battery  35 , and monitor the state of the battery  35 . In addition, the battery management system  34  may control and manage the operating environment of the battery  35  to be optimized based on the state information of the battery  35 . 
     The energy storage system  1  may include a power management system  31   a  (PMS) that controls the power conditioning system  32 . 
     The power management system  31   a  may perform a function of monitoring and controlling the states of the battery  35  and the power conditioning system  32 . The power management system  31   a  may be a controller that controls the overall operation of the energy storage system  1 . 
     The power conditioning system  32  may control power distribution of the battery  35  according to a control command of the power management system  31   a . The power conditioning system  32  may convert power according to the grid  9 , a power generation means such as photovoltaic light, and the connection state of the battery  35  and the load  7 . 
     The power management system  31   a  may receive state information of the battery  35  from the battery management system  34 . A control command may be transmitted to the power conditioning system  32  and the battery management system  34 . 
     The power management system  31   a  may include a communication means such as a Wi-Fi communication module, and a memory. Various information necessary for the operation of the energy storage system  1  may be stored in the memory. In some embodiments, the power management system  31   a  may include a plurality of switches and control a power supply path. 
     The power management system  31   a  and/or the battery management system  34  may calculate a state of charge (SOC) of the battery  35  using various well-known SOC calculation methods such as a coulomb counting method and a method of calculating a SOC based on an open circuit voltage (OCV). The battery  35  may overheat and irreversibly operate when the state of charge exceeds a maximum state of charge. Similarly, when the state of charge is less than or equal to the minimum state of charge, the battery may deteriorate and become unrecoverable. The power management system  31   a  and/or the battery management system  34  may monitor the internal temperature, the state of charge of the battery  35 , and the like in real-time to control an optimal usage area and maximum input/output power. 
     The power management system  31   a  may operate under the control of an energy management system (EMS)  31   b , which is an upper controller. The power management system  31   a  may control the energy storage system  1  by receiving a command from the energy management system  31   b , and may transmit the state of the energy storage system  1  to the energy management system  31   b . The energy management system  31   b  may be provided in the energy storage system  1  or may be provided in (or at) an upper system of the energy storage system  1 . 
     The energy management system  31   b  may receive information such as charge information, power usage, and environmental information, and may control the energy storage system  1  according to the energy production, storage, and consumption patterns of user. The energy management system  31   b  may be provided as an operating system for monitoring and controlling the power management system  31   a . 
     The controller for controlling the overall operation of the energy storage system  1  may include the power management system  31   a  and/or the energy management system  31   b . In some embodiments, one of the power management system  31   a  or the energy management system  31   b  may also perform another function(s). In addition, the power management system  31   a  and the energy management system  31   b  may be integrated into one controller to be integrally provided. 
     The installation capacity of the energy storage system  1  varies according to the customer’s installation condition, and a plurality of power conditioning systems  32  and batteries  35  may be connected (or coupled) to expand according to a required capacity. 
     The energy storage system  1  may be connected to at least one generating plant (see generating plant  3  of  FIG.  2   ) separately from the grid  9 . A generating plant  3  may include a wind generating plant that outputs DC power, a hydroelectric generating plant that outputs DC power using hydroelectric power, a tidal generating plant that outputs DC power using tidal power, thermal generating plant that outputs DC power using heat such as geothermal heat, or the like. Hereinafter, for convenience of description, the generating plant  3  will be primarily described with reference to a photovoltaic plant (or generator). 
       FIG.  2    is a conceptual diagram of a home energy service system including an energy storage system according to an embodiment of the present disclosure. 
     The home energy service system according to an embodiment of the present disclosure may include the energy storage system  1 , and may be configured as a cloud-based (see, e.g., cloud  5 ) intelligent energy service platform for integrated energy service management. 
     Referring to  FIG.  2   , the home energy service system is mainly implemented in a home, and may manage the supply, consumption, and storage of energy (power) in the home. 
     The energy storage system  1  may be connected to a grid  9  such as a power plant  8 , a generating plant such as a photovoltaic generator  3 , a plurality of loads  7   a  to  7   g , and sensors (not shown) to configure a home energy service system. 
     The loads  7   a  to  7   g  may be a heat pump  7   a , a dishwasher  7   b , a washing machine  7   c , a boiler  7   d , an air conditioner  7   e , a thermostat  7   f , an electric vehicle (EV) charger  7   g , a smart lighting  7   h , or the like. 
     The home energy service system may include other loads in addition to the loads (e.g., smart devices) illustrated in  FIG.  2   . For example, the home energy service system may include several lights in addition to the smart lighting  7   h  having one or more communication modules. In addition, the home energy service system may include a home appliance that does not include a communication module. 
     Some of the loads  7   a  to  7   g  are set as essential loads, so that power may be supplied from the energy storage system  1  when a power outage occurs. For example, a refrigerator and at least some lighting devices may be set as essential loads that require backup in case of power failure. 
     The energy storage system  1  can communicate with the devices  7   a  to  7   g , and the sensors through a short-range wireless communication module. For example, the short-range wireless communication module may be at least one of Bluetooth, Wi-Fi, or Zigbee. In addition, the energy storage system  1 , the devices  7   a  to  7   g , and the sensors may be connected to an Internet network. 
     The energy management system  31   b  may communicate with the energy storage system  1 , the devices  7   a  to  7   g , the sensors, and the cloud  5  through an Internet network, and short-range wireless communication. 
     The energy management system  31   b  and/or the cloud  5  may transmit information received from the energy storage device  1 , the devices  7   a  to  7   g , and sensors and information determined using the received information to a terminal  6 . The terminal  6  may be implemented as a smart phone, a PC, a notebook computer, a tablet PC, or the like. In some embodiments, an application for controlling the operation of the home energy service system may be installed and executed in (or at) the terminal  6 . 
     The home energy service system may include a meter  2 . The meter  2  may be provided between the power grid  9  such as the power plant  8  and the energy storage system  1 . The meter  2  may measure the amount of power supplied to the home from the power plant  8  and consumed. In addition, the meter  2  may be provided inside the energy storage system  1 . The meter  2  may measure the amount of power discharged from the energy storage system  1 . The amount of power discharged from the energy storage system  1  may include the amount of power supplied (sold) from the energy storage system  1  to the power grid  9 , and the amount of power supplied from the energy storage system  1  to the devices  7   a  to  7   g . 
     The energy storage system  1  may store the power supplied from the photovoltaic generator  2  and/or the power plant  8 , or the residual power remaining after the supplied power is consumed. 
     The meter  2  may be implemented using a smart meter. The smart meter may include a communication module for transmitting information related to power usage to the cloud  5  and/or the energy management system  31   b . 
       FIGS.  3 A and  3 B  are diagrams illustrating an energy storage system installation type according to an embodiment of the present disclosure. 
     The home energy storage system  1  may be divided into (or categorized as) an AC-coupled energy storage system (ESS) (see  FIG.  3 A ) and a DC-coupled ESS (see  FIG.  3 B ) according to an installation type. 
     The photovoltaic plant includes a photovoltaic panel  3 . Depending on the type of photovoltaic installation, the photovoltaic plant may include a photovoltaic panel  3  and a photovoltaic (PV) inverter  4  that converts DC power supplied from the photovoltaic panel  3  into AC power (see  FIG.  3 A ). Thus, it is possible to implement the system more economically, as the energy storage system  1  independent of the existing grid  9  can be used. 
     In addition, according to an embodiment, the power conditioning system  32  of the energy storage system  1  and the PV inverter  4  may be implemented as an integrated power conversion device (see  FIG.  3 B ). In this case, the DC power output from the photovoltaic panel  3  is input to the power conditioning system  32 . The DC power may be transmitted to and stored in the battery  35 . In addition, the power conditioning system  32  may convert DC power into AC power and supply the converted power to the grid  9 . Accordingly, a more efficient system implementation can be achieved. 
       FIG.  4    is a conceptual diagram of a home energy service system including an energy storage system according to an embodiment of the present disclosure. 
     Referring to  FIG.  4   , the energy storage system  1  may be connected to the grid  9  such as the power plant  8 , the power plant such as the photovoltaic generator  3 , and a plurality of loads  7   x   1  and  7   y   1 . 
     Electrical energy generated by the photovoltaic generator  3  may be converted in the PV inverter  4  and supplied to the grid  9 , the energy storage system  1 , and the loads  7   x   1  and  7   y   1 . As described with reference to  FIGS.  3 A and  3 B , according to the type of installation, the electrical energy generated by the photovoltaic generator  3  may be converted in the energy storage system  1 , and supplied to the grid  9 , the energy storage system  1 , and the loads  7   x   1 ,  7   y   1 . 
     The energy storage system  1  is provided with one or more wireless communication modules, and may communicate with the terminal  6 . The user may monitor and control the state of the energy storage system  1  and the home energy service system through the terminal  6 . In addition, the home energy service system may provide a cloud-based (see, e.g., cloud  5 ) service. The user may communicate with the cloud  5  through the terminal  6  regardless of location (e.g., of the user) and monitor and control the state of the home energy service system. 
     According to an embodiment of the present disclosure, the above-described battery  35 , the battery management system  34 , and the power conditioning system  32  may be disposed inside a casing  12  (see, e.g.,  FIG.  5   ). Since the battery  35 , the battery management system  34 , and the power conditioning system  32  integrated in the casing  12  can store and convert power, they may be referred to as an all-in-one energy storage system  1   a . 
     In addition, in separate enclosures  1   b  outside the casing  12 , a configuration for power distribution such as a power management system  31   a , an auto transfer switch (ATS), a smart meter, and a switch, and a communication module for communication with the terminal  6 , the cloud  5 , and the like may be disposed. A configuration in which configurations related to power distribution and management are integrated in one enclosure may be referred to as a smart energy box  1   b . 
     The above-described power management system  31   a  may be received (or disposed) in the smart energy box  1   b . A controller for controlling the overall power supply connection of the energy storage system  1  may be disposed in the smart energy box  1   b . The controller may be the above mentioned power management system  31   a . 
     In addition, switches are received (or disposed) in the smart energy box  1   b  to control the connection state of the connected grid power source  8 ,  9 , the photovoltaic generator  3 , the battery  35  of all-in-one energy storage system  1   a , and loads  7   x   1 ,  7   y   1 . The loads  7   x   1 ,  7   y   1  may be connected to the smart energy box  1   b  through the load panel  7   x   2 ,  7   y   2 . 
     The smart energy box  1   b  is connected to the grid power source  8 ,  9  and the photovoltaic generator  3 . In addition, when a power failure occurs in the system  8 ,  9 , the auto transfer switch (ATS), which may be disposed in the smart energy box  1   b , is switched so that the electric energy which is produced by the photovoltaic generator  3  or stored in the battery  35  is supplied to a certain load  7   y   1 . 
     Alternatively, the power management system  31   a  may perform an auto transfer switch ATS function. For example, when a power failure occurs in the system  8 ,  9 , the power management system  31   a  may control a switch such as a relay so that the electrical energy that is produced by the photovoltaic generator  3  or stored in the battery  35  is transmitted to a certain load  7   y   1 . 
     A current sensor, a smart meter, or the like may be disposed in each current supply path. Electric energy of the electricity produced through the energy storage system  1  and the photovoltaic generator  3  may be measured and managed by a smart meter (or at least a current sensor). 
     The energy storage system  1  according to an embodiment of the present disclosure includes at least an all-in-one energy storage system  1   a . In addition, the energy storage system  1  according to an embodiment of the present disclosure includes the all-in-one energy storage system  1   a  and the smart energy box  1   b , thereby providing an integrated service that can simply and efficiently perform storage, supply, distribution, communication, and control of power. 
     The energy storage system  1  according to an embodiment of the present disclosure may operate in a plurality of operation modes. In a PV self consumption mode, photovoltaic generation power is first used in the load, and the remaining power is stored in the energy storage system  1 . For example, when more power is generated in the photovoltaic generator  3  than the amount of power used by the loads  7   x   1  and  7   y   1  during the day, the battery  35  is charged. 
     In a charge/discharge mode based on a rate system, four time zones may be set and input, the battery  35  may be discharged during a time period when the electric rate is expensive, and the battery  35  may be charged during a time period when the electric rate is cheap. The energy storage system  1  may help a user to save electric rate (or electricity costs) in the charge/discharge mode based on a rate system. 
     A backup-only mode is a mode for emergency situations such as power outages, and can operate, with the highest priority, such that when a typhoon is expected (or predicted) by a weather forecast or there is a possibility of other power outages, the battery  35  may be charged up to a maximum and supplied to an essential load  7   y   1  in an emergency. 
     The energy storage system  1  of the present disclosure will be described with reference to  FIGS.  5  to  7   . More particularly, detailed structures of the all-in-one energy storage system  1   a  are disclosed. 
       FIG.  5    is an exploded perspective view of an energy storage system including a plurality of battery packs according to an embodiment of the present disclosure,  FIG.  6    is a front view of an energy storage system in a state in which a door is removed, and  FIG.  7    is a cross-sectional view of one side of the energy storage system of  FIG.  6   . 
     Referring to  FIG.  5   , the energy storage system  1  includes at least one battery pack  10 , a casing  12  forming a space in which at least one battery pack  10  is disposed, a door  28  for opening and closing the front surface (or a front) of the casing  12 , a power conditioning system  32  (PCS) which is disposed inside the casing  12  and converts the characteristics of electricity so as to charge or discharge a battery, and a battery management system (BMS) that monitors information (or parameters) such as current, voltage, and temperature of the battery cell  101  (see, e.g.,  FIG.  10   ). 
     The casing  12  may have an open front shape. The casing  12  may include a casing rear wall  14  covering the rear, a pair of casing side walls  20  extending to the front from both side ends of the casing rear wall  14 , a casing top wall  24  extending to the front from the upper end of the casing rear wall  14 , and a casing base  26  extending to the front from the lower end of the casing rear wall  14 . The casing rear wall  14  includes a pack fastening portion  16  formed to be fastened with the battery pack  10  and a contact plate  18  protruding to (or toward) the front to contact a heat dissipation plate  124  (see, e.g.,  FIG.  7   ) of the battery pack  10 . 
     Referring to  FIG.  5   , the contact plate  18  may be disposed to protrude to the front from the casing rear wall  14 . The contact plate  18  may be disposed to contact one side of the heat dissipation plate  124 . Accordingly, heat emitted from the plurality of battery cells  101  disposed inside the battery pack  10  may be radiated outside through the heat dissipation plate  124  and the contact plate  18 . 
     A switch  22   a ,  22   b  for turning on/off the power of the energy storage system  1  may be disposed in (or at) one of the pair of casing sidewalls  20 . In the present disclosure, a first switch  22   a  and a second switch  22   b  are disposed to enhance the safety of the power supply or the safety of the operation of the energy storage system  1 . 
     The power conditioning system  32  may include a circuit substrate  33  and an insulated gate bipolar transistor (IGBT) that is disposed in (or at) one side of the circuit substrate  33  and performs power conversion. 
     The battery monitoring system may include a battery pack circuit substrate  220  (see, e.g.,  FIG.  9   ) disposed in each of the plurality of battery packs  10   a ,  10   b ,  10   c ,  10   d , and a main circuit substrate  34   a  which is disposed inside the casing  12  and connected to a plurality of battery pack circuit substrates  220  through a communication line  36 . 
     The main circuit substrate  34   a  may be connected (or coupled) to the battery pack circuit substrate  220  disposed in each of the plurality of battery packs  10   a ,  10   b ,  10   c , and  10   d  by (or via) the communication line  36 . The main circuit substrate  34   a  may be connected to a power line  198  extending from the battery pack  10 . 
     At least one battery pack  10   a ,  10   b ,  10   c , and  10   d  may be disposed inside the casing  12 . For example, a plurality of battery packs  10   a ,  10   b ,  10   c , and  10   d  are disposed inside the casing  12 . The plurality of battery packs  10   a ,  10   b ,  10   c , and  10   d  may be disposed in (or along) the vertical direction. 
     The plurality of battery packs  10   a ,  10   b ,  10   c , and  10   d  may be disposed such that the upper end and lower end of each side bracket  250   a ,  250   b  (see, e.g.,  FIG.  8   ) contact each other. Each of the battery packs  10   a ,  10   b ,  10   c , and  10   d  disposed vertically is disposed such that the battery module  100   a ,  100   b  and the top cover  230  do not contact each other (see, e.g.,  FIG.  9   ). 
     Each of the plurality of battery packs  10  is fixedly disposed in the casing  12 . Each of the plurality of battery packs  10   a ,  10   b ,  10   c , and  10   d  is fastened to the pack fastening portion  16  disposed in the casing rear wall  14 . That is, the fixing bracket  270  (see, e.g.,  FIG.  6   ) of each of the plurality of battery packs  10   a ,  10   b ,  10   c , and  10   d  is fastened to the pack fastening portion  16 . The pack fastening portion  16  may be disposed to protrude to (or toward) the front from the casing rear wall  14  like (or similar to) the contact plate  18 . 
     The contact plate  18  may be disposed to protrude to the front from the casing rear wall  14 . Accordingly, the contact plate  18  may be disposed to be in contact with a heat dissipation plate  124  included in the battery pack  10 . 
     One battery pack  10  includes two battery modules  100   a  and  100   b . Accordingly, two heat dissipation plates  124  are disposed in one battery pack  10 . One heat dissipation plate  124  included in the battery pack  10  is disposed to face the casing rear wall  14 , and the other heat dissipation plate  124  is disposed to face the door  28 . 
     One heat dissipation plate  124  is disposed to contact the contact plate  18  disposed in the casing rear wall  14 , and the other heat dissipation plate  124  is disposed to be spaced apart from the door  28 . The other heat dissipation plate  124  may be cooled by air flowing inside the casing  12 . 
       FIG.  8    is a perspective view of a battery pack according to an embodiment of the present disclosure, and  FIG.  9    is an exploded view of a battery pack according to an embodiment of the present disclosure. 
     The energy storage system of the present disclosure may include a battery pack  10  in which a plurality of battery cells  101  are connected in series and in parallel. The energy storage system may include a plurality of battery packs  10   a ,  10   b ,  10   c , and  10   d  (refer to  FIG.  5   ). 
     First, a configuration of one battery pack  10  will be described with reference to  FIGS.  8  to  9   . The battery pack  10  includes at least one battery module  100   a ,  100   b  at which a plurality of battery cells  101  are connected in series and parallel, an upper fixing bracket  200  which is disposed in (or at) an upper portion of the battery module  100   a ,  100   b  and fixes the disposition (or positioning) of the battery module  100   a ,  100   b , a lower fixing bracket  210  which is disposed in (or at) a lower portion of the battery module  100   a ,  100   b  and fixes the disposition of the battery modules  100   a  and  100   b , a pair of side brackets  250   a ,  250   b  which are disposed in (or at) side surfaces of the battery module  100   a ,  100   b  and fixes the disposition of the battery module  100   a ,  100   b , a pair of side covers  240   a ,  240   b  which are disposed in (or at) side surfaces of the battery module  100   a ,  100   b , and in which a cooling hole  242   a  is formed, a cooling fan  280  which is disposed in one side surface of the battery module  100   a ,  100   b  and forms an air flow inside the battery module  100   a ,  100   b , a battery pack circuit substrate  220  which is disposed in (or at) the upper side of the upper fixing bracket  200  and collects sensing information of the battery module  100   a ,  100   b , and a top cover  230  which is disposed in (or at) the upper side of the upper fixing bracket  200  and covers the upper side of the battery pack circuit substrate  220 . 
     The battery pack  10  includes at least one battery module  100   a ,  100   b . Referring to  FIG.  9   , the battery pack  10  of the present disclosure includes a battery module assembly  100  configured of two battery modules  100   a ,  100   b  which are electrically connected (or coupled) to each other and physically fixed. The battery module assembly  100  includes a first battery module  100   a  and a second battery module  100   b  disposed to face each other. 
       FIG.  10    is a perspective view of a battery module according to an embodiment of the present disclosure and  FIG.  11    is an exploded view of a battery module according to an embodiment of the present disclosure. 
       FIG.  12    is a front view of a battery module according to an embodiment of the present disclosure and  FIG.  13    is an exploded perspective view of a battery module and a sensing substrate according to an embodiment of the present disclosure. 
     Hereinafter, the first battery module  100   a  of the present disclosure will be described with reference to  FIGS.  10  to  13   . The configuration and shape of the first battery module  100   a  described below may also be applied (or applicable) to the second battery module  100   b . 
     The battery module described in  FIGS.  10  to  13    may be described with reference to a vertical direction based on the height direction (h+, h-) of the battery module. The battery module described in  FIGS.  10  to  13    may be described with reference to the left-right direction based on the length direction (1+, 1-) of the battery module. The battery module described in  FIGS.  10  to  13    may be described with reference to the front-rear direction based on the width direction (w+, w-) of the battery module. The direction setting of the battery module used in  FIGS.  10  to  13    may be different from the direction setting in a structure of the battery pack  10  described with reference to other drawings. In the battery module described in  FIGS.  10  to  13   , the width direction (w+, w-) of the battery module may be described as a first direction, and the length direction (1+, 1-) of the battery module may be described as a second direction. 
     The first battery module  100   a  includes a plurality of battery cells  101 , a first frame  110  for fixing the lower portion of the plurality of battery cells  101 , a second frame  130  for fixing the upper portion of the plurality of battery cells  101 , a heat dissipation plate  124  which is disposed in (or at) the lower side of the first frame  110  and dissipates heat generated from the battery cell  101 , a plurality of bus bars which are disposed in (or at) the upper side of the second frame  130  and electrically connect the plurality of battery cells  101 , and a sensing substrate  190  which is disposed in (or at) the upper side of the second frame  130  and detects information of the plurality of battery cells  101 . 
     The first frame  110  and the second frame  130  may fix the disposition (or positioning) of the plurality of battery cells  101 . In the first frame  110  and the second frame  130 , the plurality of battery cells  101  are disposed to be spaced apart from each other. Since the plurality of battery cells  101  are spaced apart from each other, air may flow into a space between the plurality of battery cells  101  by the operation of the cooling fan  280  described below. 
     The first frame  110  fixes the lower end of the battery cell  101 . The first frame  110  includes a lower plate  112  having a plurality of battery cell holes  112   a  formed therein, a first fixing protrusion  114  which protrudes upward from the upper surface of the lower plate  112  and fixes the disposition of the battery cell  101 , a pair of first sidewalls  116  which protrudes upward from both ends of the lower plate  112 , and a pair of first end walls  118  which protrudes upward from both ends of the lower plate  112  and connects both ends of the pair of first side walls  116 . 
     The pair of first sidewalls  116  may be disposed parallel to a first cell array  102  described below. The pair of first end walls  118  may be disposed perpendicular to the pair of first side walls  116 . 
     Referring to  FIG.  13   , the first frame  110  includes a first fastening protrusion  120  protruding to be fastened to the second frame  130 , and a module fastening protrusion  122  protruding to be fastened with the first frame  110  included in the second battery module  100   b  disposed adjacently. A frame screw  125  for fastening the second frame  130  and the first frame  110  is disposed in the first fastening protrusion  120 . A module screw  194  (see, e.g.,  FIG.  15 A ) for fastening the first battery module  100   a  and the second battery module  100   b  is disposed in the module fastening protrusion  122 . The frame screw  125  fastens the second frame  130  and the first frame  110 . The frame screw  125  may fix the disposition of the plurality of battery cells  101  by fastening the second frame  130  and the first frame  110 . 
     The plurality of battery cells  101  are fixedly disposed in the second frame  130  and the first frame  110 . A plurality of battery cells  101  are disposed in series and in parallel. The plurality of battery cells  101  are fixedly disposed by a first fixing protrusion  114  of the first frame  110  and a second fixing protrusion  134  of the second frame  130 . 
     Referring to  FIG.  12   , the plurality of battery cells  101  are spaced apart from each other in (or along) the length direction (1+, 1-) and the width direction (w+, w-) of the battery module. 
     The plurality of battery cells  101  includes a cell array connected in parallel to one bus bar. The cell array may refer to a set electrically connected in parallel to one bus bar. 
     The first battery module  100   a  may include a plurality of cell arrays  102  and  103  electrically connected in series. The plurality of cell arrays  102  and  103  are electrically connected to each other in series. The first battery module  100   a  has a plurality of cell arrays  102  and  103  connected in series. 
     The plurality of cell arrays  102  and  103  may include a first cell array  102  in which a plurality of battery cells  101  are disposed in (or along) a straight line, and a second cell array  103  in which a plurality of cell array rows and columns are disposed. 
     The first battery module  100   a  may include a first cell array  102  in which a plurality of battery cells  101  are disposed in (or along) a straight line, and a second cell array  103  in which a plurality of rows and columns are disposed. 
     Referring to  FIG.  12   , in the first cell array  102 , a plurality of battery cells  101  are disposed in (or at) the left and right side in (or along) the length direction (1+, 1-) of the first battery module  100   a . The plurality of first cell arrays  102  are disposed in (or at) the front and rear side in (or along) the width direction (w+, w-) of the first battery module  100   a . 
     Referring to  FIG.  12   , the second cell array  103  includes a plurality of battery cells  101  spaced apart from each other in the width direction (w+, w-) and the length direction (1+, 1-) of the first battery module  100   a . 
     The first battery module  100   a  includes a first cell group  105  in which a plurality of first cell arrays  102  are disposed in parallel, and a second cell group  106  that includes at least one second cell array  103  and is disposed in (or at) one side of the first cell group  105 . 
     The first battery module  100   a  includes a first cell group  105  in which a plurality of first cell arrays  102  are connected in series, and a third cell group  107  in which a plurality of first cell arrays  102  are connected in series, and which are spaced apart from the first cell group  105 . The second cell group is disposed between the first cell group  105  and the third cell group  107 . 
     In the first cell group  105 , a plurality of first cell arrays  102  are connected in series. In the first cell group  105 , a plurality of first cell arrays  102  are spaced apart from each other in (or along) the width direction of the battery module. The plurality of first cell arrays  102  included in the first cell group  105  are spaced apart in (or along) a direction perpendicular to the direction in which the plurality of battery cells  101  included in each of the first cell arrays  102  are disposed. 
     Referring to  FIG.  12   , nine battery cells  101  connected in parallel are disposed in each of the first cell array  102  and the second cell array  103 . Referring to  FIG.  12   , in the first cell array  102 , nine battery cells  101  are spaced apart from each other in (or along) the length direction of the battery module. In the second cell array  103 , nine battery cells are spaced apart from each other in a plurality of rows and a plurality of columns. Referring to  FIG.  12   , in the second cell array  103 , three battery cells  101  that are spaced apart from each other in (or along) the width direction of the battery module are spaced apart from each other in the length direction of the battery module. Here, the length direction (1+, 1-) of the battery module may be set as (or may refer to) a column direction, and the width direction (w+, w-) of the battery module may be set as (or may refer to) a row direction. 
     Referring to  FIG.  12   , each of the first cell group  105  and the third cell group  107  is disposed such that six first cell arrays  102  are connected in series. In each of the first cell group  105  and the third cell group  107 , six first cell arrays  102  are spaced apart from each other in (or along) the width direction of the battery module. 
     Referring to  FIG.  12   , the second cell group  106  includes two second cell arrays  103 . The two second cell arrays  103  are spaced apart from each other in (or along) the width direction of the battery module. The two second cell arrays  103   are connected in parallel to each other. Each of the two second cell arrays  103  is disposed symmetrically with respect to the horizontal bar  166  of a third bus bar  160  described below. 
     The first battery module  100   a  includes a plurality of bus bars which are disposed between the plurality of battery cells  101 , and electrically connect the plurality of battery cells  101 . Each of the plurality of bus bars connects in parallel the plurality of battery cells included in a cell array disposed adjacent to each other. Each of the plurality of bus bars may connect in series two cell arrays disposed adjacent to each other. 
     The plurality of bus bars includes a first bus bar  150  connecting the two first cell arrays  102  in series, a second bus bar  152  connecting the first cell array  102  and the second cell array  103  in series, and a third bus bar  160  connecting the two second cell arrays  103  in series. 
     The plurality of bus bars include a fourth bus bar  170  connected to one first cell array  102  in series. The plurality of bus bars include a fourth bus bar  170  which is connected to one first cell array  102  in series and connected to the other battery module  100   b  included in the same battery pack  10 , and a fifth bus bar  180  which is connected to one first cell array  102  in series and connected to one battery module included in the other battery pack  10 . The fourth bus bar  170  and the fifth bus bar  180  may have the same shape. 
     The first bus bar  150  is disposed between two first cell arrays  102  spaced apart from each other in (or along) the length direction of the battery module. The first bus bar  150  connects in parallel a plurality of battery cells  101  included in one first cell array  102 . The first bus bar  150  connects in series the two first cell arrays  102  disposed in (or along) the length direction (1+, 1-) of the battery module. 
     Referring to  FIG.  12   , the first bus bar  150  is electrically connected to a positive terminal  101   a  of each of the battery cells  101  of the first cell array  102  which is disposed in (or at) the front in (or along) the width direction (w+, w-) of the battery module, and the first bus bar  150  is electrically connected to a negative terminal  101   b  of each of the battery cells  101  of the first cell array  102  which is disposed in (or at) the rear in (or along) the width direction (w+, w-) of the battery module. 
     Referring to  FIG.  12   , in the battery cell  101 , the positive terminal  101   a  and the negative terminal  101   b  are partitioned in (or at) the upper end thereof. In the battery cell  101 , the positive terminal  101   a  is disposed in (or at) the center of a top surface formed in a circle, and the negative terminal  101   b  is disposed in (or at) the circumference portion of the positive terminal  101   a . Each of the plurality of battery cells  101  may be connected to each of the plurality of bus bars through a cell connector  101   c ,  101   d . 
     The first bus bar  150  has a straight bar shape. The first bus bar  150  is disposed between the two first cell arrays  102 . The first bus bar  150  is connected to the positive terminal of the plurality of battery cells  101  included in the first cell array  102  disposed in one side, and is connected to the negative terminal of the plurality of battery cells  101  included in the first cell array  102  disposed in the other side. 
     The first bus bar  150  is disposed between the plurality of first cell arrays  102  disposed in the first cell group  105  and the third cell group  107 . 
     The second bus bar  152  connects the first cell array  102  and the second cell array  103  in series. The second bus bar  152  includes a first connecting bar  154  connected to the first cell array  102  and a second connecting bar  156  connected to the second cell array  103 . The second bus bar  152  is disposed perpendicular to the first connecting bar  154 . The second bus bar  152  includes an extension portion  158  that extends from the first connecting bar  154  and is connected to the second connecting bar  156 . 
     The first connecting bar  154  may be connected to different electrode terminals of the second connecting bar  156  and the battery cell. Referring to  FIG.  12   , the first connecting bar  154  is connected to the positive terminal  101   a  of the battery cell  101  included in the first cell array  102 , and the second connecting bar  156  is connected to the negative terminal  101   b  of the battery cell  101  included in the second cell array  103 . However, this is in reference to one embodiment, and it is possible for the connecting bars  154 ,  156  to be connected to an opposite electrode terminal. 
     The first connecting bar  154  is disposed in (or at) one side of the first cell array  102 . The first connecting bar  154  has a straight bar shape extending in (or along) the length direction of the battery module. The extension portion  158  has a straight bar shape extending in (or along) the direction in which the first connecting bar  154  extends. 
     The second connecting bar  156  is disposed perpendicular to the first connecting bar  154 . The second connecting bar  156  has a straight bar shape extending in (or along) the width direction (w+, w-) of the battery module. The second connecting bar  156  may be disposed in (or at) one side of the plurality of battery cells  101  included in the second cell array  103 . The second connecting bar  156  may be disposed between the plurality of battery cells  101  included in the second cell array  103 . The second connecting bar  156  extends in (or along) the width direction (w+, w-) of the battery module, and is connected to the battery cell  101  disposed in (or at) one side or both sides. 
     The second connecting bar  156  includes a connecting bar  156   a  and a connecting bar  156   b  spaced apart from the connecting bar  156   a . The connecting bar  156   a  is disposed between the plurality of battery cells  101 , and the connecting bar  156   b  is disposed in (or at) one side of the plurality of battery cells  101 . 
     The third bus bar  160  connects in series the two second cell arrays  103  spaced apart from each other. The third bus bar  160  includes a first vertical bar  162  connected to one cell array among the plurality of second cell arrays  103 , a second vertical bar  164  connected to the other cell array among the plurality of second cell arrays  103 , and a horizontal bar  166  which is disposed between the plurality of second cell arrays  103  and connected to the first vertical bar  162  and the second vertical bar  164 . The first vertical bar  162  and the second vertical bar  164  may be symmetrically disposed with respect to the horizontal bar  166 . 
     A plurality of second vertical bars  164  may be disposed to be spaced apart from each other in (or along) the length direction (1+, 1-) of the battery module. Referring to  FIG.  12   , a vertical bar  164   a , and a vertical bar  164   b  which is spaced apart from the vertical bar  164   a  in (or along) the length direction of the battery module may be included. 
     The first vertical bar  162  or the second vertical bar  164  may be disposed parallel to the second connecting bar  156  of the second bus bar  152 . The battery cell  101  included in the second cell array  103  may be disposed between the first vertical bar  162  and the second connecting bar  156 . Similarly, the battery cell  101  included in the second cell array  103  may be disposed between the second vertical bar  164  and the second connecting bar  156 . 
     The first battery module  100   a  includes a fourth bus bar  170  connected to the second battery module  100   b  included in the same battery pack  10 , and a fifth bus bar  180  connected to a battery module included in another battery pack  10 . 
     The fourth bus bar  170  is connected to the second battery module  100   b  which is another battery module included in the same battery pack  10 . That is, the fourth bus bar  170  is connected to the second battery module  100   b  included in the same battery pack  10  through a high current bus bar  196  (see, e.g.,  FIG.  15 A ) described below. 
     The fifth bus bar  180  is connected to another battery pack  10 . That is, the fifth bus bar  180  may be connected to a battery module included in another battery pack  10  through a power line  198  described below. 
     The fourth bus bar  170  includes a cell connecting bar  172  which is disposed in one side of the first cell array  102 , and connects in parallel the plurality of battery cells  101  included in the first cell array  102 , and an additional connecting bar  174  which is vertically bent from the cell connecting bar  172  and extends along the end wall of the second frame  130 . 
     The cell connecting bar  172  is disposed in (or at) the second sidewall  136  of the second frame  130 . The cell connecting bar  172  may be disposed to surround a portion of the outer circumference of the second sidewall  136 . The additional connecting bar  174  is disposed outside the second end wall  138  of the second frame  130 . 
     The additional connecting bar  174  includes a connecting hanger  176  to which the high current bus bar  196  is connected. The connecting hanger  176  is provided with a groove  178  opened upward. The high current bus bar  196  may be seated on the connecting hanger  176  through the groove  178 . The high current bus bar  196  may be fixedly disposed in the connecting hanger  176  through a separate fastening screw while seated on the connecting hanger  176 . 
     The fifth bus bar  180  may have the same configuration and shape as the fourth bus bar. That is, the fifth bus bar  180  includes a cell connecting bar  182  and an additional connecting bar  184 . The additional connecting bar  184  of the fifth bus bar  180  includes a connecting hanger  186  to which a terminal  198   a  of the power line  198  is connected. The connecting hanger  186  is provided with a groove  188  into which the terminal  198   a  of the power line  198  is inserted. 
     The sensing substrate  190  is electrically connected to a plurality of bus bars disposed inside the first battery module  100   a . The sensing substrate  190  may be electrically connected to each of the plurality of first bus bars  150 , the plurality of second bus bars  152 , the third bus bar  160 , and the plurality of fourth bus bars  170 . The sensing substrate  190  is connected to each of the plurality of bus bars, so that information such as voltage and current values of the plurality of battery cells  101  included in the plurality of cell arrays can be obtained. 
     The sensing substrate  190  may have a rectangular ring shape. The sensing substrate  190  may be disposed between the first cell group  105  and the third cell group  107 . The sensing substrate  190  may be disposed to surround the second cell group  106 . The sensing substrate  190  may be disposed to partially overlap the second bus bar  152 . 
       FIG.  14    is a perspective view of a battery module and a battery pack circuit substrate according to an embodiment of the present disclosure,  FIG.  15 A  is a side view of the battery module and the battery pack circuit substrate of  FIG.  14    in a coupled state, and  FIG.  15 B  is another side view of the battery module and the battery pack circuit substrate of  FIG.  14    in a coupled state. 
     Referring to  FIG.  14    to 15B, the battery pack  10  includes an upper fixing bracket  200  which is disposed in (or at) an upper portion of the battery module  100   a ,  100   b  and fixes the battery module  100   a ,  100   b , a lower fixing bracket  210  which is disposed in (or at) a lower portion of the battery module  100   a ,  100   b  and fixes the battery modules  100   a  and  100   b , a battery pack circuit substrate  220  which is disposed in (or at) an upper side of the upper fixing bracket  200  and collects sensing information of the battery module  100   a ,  100   b , and a spacer  222  which separates the battery pack circuit substrate  220  from the upper fixing bracket  200 . 
     The upper fixing bracket  200  is disposed in (or at) an upper side of the battery module  100   a ,  100   b . The upper fixing bracket  200  includes an upper board  202  that covers at least a portion of the upper side of the battery module  100   a ,  100   b , a first upper holder  204   a  which is bent downward from the front end of the upper board  202  and disposed to be in contact with the front portion of the battery module  100   a ,  100   b , a second upper holder  204   b  which is bent downward from the rear end of the upper board  202  and disposed to be in contact with the rear portion of the battery module  100   a ,  100   b , a first upper mounter  206   a  which is bent downward from a side end of the upper board  202  and coupled to a side of the battery module  100   a ,  100   b , a second upper mounter  206   b  which is bent downward from the other side end of the upper board  202  and coupled to the other side of the battery module  100   a ,  100   b , and a rear bender  208  which is bent upward from the rear end of the upper board  202 . 
     The upper board  202  is disposed in (or at) the upper side of the battery module  100   a ,  100   b . Each of the first upper mounter  206   a  and the second upper mounter  206   b  is disposed to surround the front and rear of the battery module  100   a ,  100   b . Accordingly, the first upper mounter  206   a  and the second upper mounter  206   b  may maintain a state in which the first battery module  100   a  and the second battery module  100   b  are coupled. 
     A pair of first upper mounters  206   a  spaced apart in the front-rear direction are disposed in (or at) one side end of the upper board  202 . A pair of second upper mounters  206   b  spaced apart in the front-rear direction are disposed in (or at) the other side end of the upper board  202 . 
     The pair of first upper mounters  206   a  are coupled to the first fastening hole  123  (see, e.g.,  FIG.  15 A ) formed in the first battery module  100   a  and the second battery module  100   b . In each of the pair of first upper mounters  206   a , a first upper mounter hole  206   ah  is formed in a position corresponding to the first fastening hole  123 . Similarly, the pair of second upper mounters  206   b  are coupled to the first fastening hole  123  formed in the first battery module  100   a  and the second battery module  100   b , and a second upper mounter hole  206   bh  is formed in a position corresponding to the first fastening hole  123 . 
     The position of the upper fixing bracket  200  can be fixed in (or at) the upper side of the battery module  100   a ,  100   b  by the first upper holder  204   a , the second upper holder  204   b , the first upper mounter  206   a , and the second upper mounter  206   b . That is, due to the above structure, the upper fixing bracket  200  can maintain the structure of the battery module  100   a ,  100   b . 
     The upper fixing bracket  200  is fixed to the first frame  110  of each of the first battery module  100   a  and the second battery module  100   b . Each of the first upper mounter  206   a  and the second upper mounter  206   b  of the upper fixing bracket  200  is fixed to the first fastening hole  123  formed in the first frame  110  of each of the first battery module  100   a  and the second battery module  100   b . 
     The rear bender  208  may fix a top cover  230  described below. The rear bender  208  may be fixed to a rear wall  234  of the top cover  230 . The rear bender  208  may limit the rear movement of the top cover  230 . Accordingly, it is possible to facilitate fastening of the top cover  230  and the upper fixing bracket  200 . 
     The lower fixing bracket  210  is disposed in (or at) the lower side of the battery module  100   a ,  100   b . The lower fixing bracket  210  includes a lower board  212  that covers at least a portion of the lower portion of the battery module  100   a ,  100   b , a first lower holder  214   a  which is bent upward from the front end of the lower board  212  and disposed to be in contact with the front portion of the battery module  100   a ,  100   b , a second lower holder  214   b  which is bent upward from the rear end of the lower board  212  and disposed to be in contact with the rear portion of the battery module  100   a ,  100   b , a first lower mounter  216   a  which is bent upward from a side end of the lower board  212  and coupled to a side of the battery module  100   a ,  100   b , and a second lower mounter  216   b  which is bent upward from the other side end of the lower board  212  and coupled to the other side of the battery module  100 . 
     Each of the first lower mounter  216   a  and the second lower mounter  216   b  is disposed to surround the front and rear of the battery module  100   a ,  100   b . Accordingly, the first lower mounter  216   a  and the second lower mounter  216   b  may maintain a state in which the first battery module  100   a  and the second battery module  100   b  are coupled. 
     A pair of first lower mounters  216   a  spaced apart in the front-rear direction are disposed in (or at) one side end of the lower board  212 . A pair of second lower mounters  216   b  spaced apart in the front-rear direction are disposed in (or at) the other side end of the lower board  212 . 
     The pair of first lower mounters  216   a  are coupled to the first fastening hole  123  formed in the first battery module  100   a  and the second battery module  100   b . In each of the pair of first lower mounters  216   a , a first lower mounter hole  216   ah  is formed in a position corresponding to the first fastening hole  123 . Similarly, the pair of second lower mounters  216   b  are coupled to the first fastening hole  123  formed in the first battery module  100   a  and the second battery module  100   b , and a second lower mounter hole  216   bh  is formed in a position corresponding to the first fastening hole  123 . 
     The lower fixing bracket  210  is fixed to the first frame  110  of each of the first battery module  100   a  and the second battery module  100   b . Each of the first lower mounter  216   a  and the second lower mounter  216   b  of the lower fixing bracket  210  is fixed to the first fastening hole  123  formed in the first frame  110  of each of the first battery module  100   a  and the second battery module  100   b . 
     The battery pack circuit substrate  220  may be fixedly disposed in (or at) the upper side of the upper fixing bracket  200 . The battery pack circuit substrate  220  is connected to the sensing substrate  190 , the bus bar, or a thermistor  224  described below to receive information of a plurality of battery cells  101  disposed inside the battery pack  10 . The battery pack circuit substrate  220  may transmit information of the plurality of battery cells  101  to the main circuit substrate  34   a  described below. 
     The battery pack circuit substrate  220  may be spaced apart from the upper fixing bracket  200  to be above the upper fixing bracket  200 . A plurality of spacers  222  are disposed, between the battery pack circuit substrate  220  and the upper fixing bracket  200 , to space the battery pack circuit substrate  220  upward from (e.g., to be above) the upper fixing bracket  200 . The plurality of spacers  222  may be disposed in (or at) an edge portion of the battery pack circuit substrate  220 . 
       FIG.  16    is a diagram illustrating a connection between the battery pack and the battery management system according to an embodiment of the present disclosure. 
     Referring to  FIG.  16   , the battery  35  that stores received electrical energy in DC form or outputs the stored electrical energy may include a plurality of battery packs  10 . Each battery pack  10  includes a plurality of battery cells  101  connected in series and in parallel. 
     The battery pack  10  may include battery modules  100   a  and  100   b  in which the plurality of battery cells  101  are connected in series and in parallel, and the battery modules  100   a  and  100   b  may be electrically connected to each other. 
     The battery cells  101  may be connected in series to increase voltage, and may be connected in parallel to increase capacity. In order to increase both the voltage and the capacity, the battery cells  101  may be connected in series and parallel. 
     The battery management system  34  for monitoring the state information of the battery  35  includes battery pack circuit boards  220  which are disposed in each of the plurality of battery packs  10 , and obtain state information of the plurality of battery cells  101  included in each battery pack  10 , and a main circuit board  34   a  which is connected (or coupled) to the battery pack circuit boards  220  by (or via) a communication line  36 , and receives the state information obtained from each battery pack  10  from the battery pack circuit boards  220 . 
     The energy storage system  1  according to an embodiment of the present disclosure includes the battery  35  that stores the received electrical energy in the form of direct current, or outputs the stored electrical energy, the power conditioning system  32  for converting an electrical characteristic so as to charge or discharge the battery  35 , and the battery management system  34  for monitoring the state information of the battery  35 . The battery  35  includes a plurality of battery packs  10  respectively including a plurality of battery cells  101 , and the battery management system  34  includes battery pack circuit boards  220  which are disposed in each of the plurality of battery packs  10  and obtain state information of a plurality of battery cells  101  included in each battery pack  10 , and a main circuit board  34   a  which is connected to the battery pack circuit boards  220  by (or via) a communication line  36  and receives state information obtained from each battery pack  10  from the battery pack circuit boards  220 . 
     According to an embodiment of the present disclosure, by separately designing the control circuit  34   a  including a configuration for managing the battery  35  (particularly a configuration for safety control) from (or relative to) the battery cell sensing circuit (of the battery pack circuit boards  220 ), it is possible to perform the main function of the battery management system  34  and protect the control circuit  34   a  that manages the plurality of battery packs  10 . 
     In the battery management system  34 , a circuit composed of main components including a microcomputer unit (or microcomputer)  1780  among circuits for safety control may be separately configured. For example, when four battery packs  10  are configured to be connected, the battery management system  34  may be designed with one control circuit unit block  34   a  including the microcomputer unit  1780 , and four battery unit blocks  220 . 
     When the battery pack  10  is short-circuited due to an internal problem, the battery unit block  220  directly connected to the battery cell  101  may be damaged. However, the safety control circuit  34   a  is designed independently and can be protected without damage. 
     In addition, since the control circuit  34   a  and the battery cell sensing circuit (of the battery pack circuit boards  220 ) are separately configured, each circuit board  34   a ,  220  can be made to be smaller in size. 
     The state information transmitted from the battery pack circuit boards  220  to the main circuit board  34   a  may include at least one of current data, voltage data, or temperature data. In addition, some of the state information may be measured by a sensor mounted in the main circuit board  34   a . 
     The battery pack circuit boards  220  are sensing and interface boards for sensing voltage, current, and temperature of the battery cells  101 . In the battery pack circuit boards  220 , a component for obtaining voltage, current, and temperature data of a plurality of battery cells  101  and an interface component for transmitting the obtained data to the main circuit board  34   a  may be mounted. The voltage, current, and temperature data of the plurality of battery cells  101  may be directly obtained from a sensor mounted in the battery pack circuit boards  220 , or may be transmitted to the battery pack circuit substrates (or boards)  220  from a sensor disposed in (or at) the battery cell  101 . 
     The plurality of battery packs  10  are connected in series by the power line  198 . The power line  198  is connected to the main circuit board  34   a . That is, the plurality of battery packs  10  and the main circuit board  34   a  are connected by the power line  198 , and the voltages of the plurality of battery packs  10  are combined and applied to the main circuit board  34   a . For example, a plurality of 4 kWh battery packs may be connected in series and disposed inside the casing  12 . Two 4 kWh battery packs  10  may be connected to implement a total of 8 kWh combined, three 4 kWh battery packs  10  may be connected to implement a total of 12 kWh combined, and four 4 kWh battery packs  10  may be connected to implement a total of 16 kWh combined. 
     Two battery modules  100   a  and  100   b  may be combined to form a battery module assembly  100 , and the battery pack circuit board  220  may be disposed in (or at) an upper portion of the battery module assembly  100 . 
     The power conditioning system  32  for converting electrical characteristics for charging or discharging the battery  35  may be disposed in (or at) the upper side of the main circuit board  34   a . 
       FIGS.  17 A to  17 C  are diagrams illustrating a battery imbalance. 
       FIG.  17 A  illustrates an initial state of a battery. 
     The capacity of the battery is naturally decreased as time is elapsed. Therefore, the minimum capacity is guaranteed within a certain period based on the natural decrease rate. When a fresh-cell and a three-month/six-month/nine-month old or a one-year old cell are mixed and used, an imbalance state may be created as shown in  FIG.  17 A . Referring to  FIG.  17 A , the capacities of a second battery cell  1720  and a fourth battery cell  1740  are lower than the capacities of a first battery cell  1710  and a fifth battery cell  1750 , and higher than the capacity of the third battery cell  1730 . 
     When a plurality of battery cells  1710 ,  1720 ,  1730 ,  1740 , and  1750  are connected in series, an imbalance phenomenon becomes more prominent, and thus, to address this phenomenon, they can be connected in parallel. 
     More preferably, at least five or more battery cells  1710 ,  1720 ,  1730 ,  1740 ,  1750  may be connected in parallel. The total battery voltage may be increased by connecting parallel-connected battery cells in series. 
       FIG.  17 B  illustrates charging a battery to a full charge state. 
     Referring to  FIG.  17 B , a plurality of battery cells  1710 ,  1720 ,  1730 ,  1740 , and  1750  are charged together. When the second battery cell  1720  and the fourth battery cell  1740  become fully charged, the third battery Cell  1730  may not yet reach a full state of charge. 
     At this time, when (or if) the over voltage protection setting is set too high compared to a full charge voltage, the first battery cell  1710  and the fifth battery cell  1750  may be overcharged (indicated by a box), and cause a fire. 
       FIG.  17 C  illustrates a full discharge state of battery. 
     Referring to  FIG.  17 C , when a plurality of battery cells  1710 ,  1720 ,  1730 ,  1740 , and  1750  are discharged together, a cell  1730  may fall below a level capable of recharging and may decrease to a level requiring after-service (AS). 
     Complete discharge may mean (or refer to) a state in which 50% of Li+ of cathode active material has moved toward a negative electrode. In contrast, over-discharging is determined as (or may refer to) a situation in which the stable state of the cathode active material is collapsed or shall be collapsed (e.g., approaching collapse), and if the voltage is lower than a protection reference value, a permanent failure may be determined. Here, it may be preferable to replace the corresponding product with a new product. 
     Even if the product is managed at the level of (or with respect to) the protection reference value, AS may be possibly necessary due to low-current charging after problems occur, and/or long-term storage. 
     The capacity of the battery naturally decreases as time elapses. In a situation where cells having different production times are used in combination, when cells having a large difference in physical properties are mixed, the battery state may become imbalanced, and the efficiency and lifespan of the energy storage system may decrease. There is a possibility of a safety accident due to over-charging, and/or over-discharging. 
     According to an embodiment of the present disclosure, the batteries having a series structure (or configuration) are converted into a parallel (or configuration) by switching the series/parallel nature of the battery cell connection structure (or configuration), and the energy storage system  1  itself can correct the imbalance between the batteries. 
       FIGS.  18  to  20    are diagrams for explaining a battery connection structure (or configuration) according to an embodiment of the present disclosure. 
     The energy storage system  1  according to an embodiment of the present disclosure includes a plurality of cell arrays  102 , each including a respective plurality of battery cells  101  connected in parallel. The cell array  102  in which the plurality of battery cells  101  are connected in parallel may be the above-described first cell array  102 . 
     A set of a plurality of cell arrays  102  connected in series may be the first and third cell groups  105  and  107  described above (e.g., with reference to  FIG.  12   ). 
     In addition, the set of a plurality of cell arrays  102  connected in series may be a second cell array  103  including a plurality of battery cells  101  connected in series and in parallel and/or a second cell group  106  including the same. 
     The energy storage system  1  according to an embodiment of the present disclosure includes a plurality of switches  1931 ,  1932 ,  1933 ,  1934 ,  1935 ,  1936  which are connected (or coupled) to the plurality of cell arrays  102 , and connect the plurality of cell arrays  102  in series. In addition, the plurality of switches  1931 ,  1932 ,  1933 ,  1934 ,  1935 ,  1936  may be switched (or operated) such that the plurality of cell arrays  102  are connected in parallel. 
     That is, the plurality of cell arrays  102  may be connected in series in a default state, and when the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932  are switched, the connection state of the plurality of cell arrays  102  may be converted into a parallel structure (or configuration), in which the plurality of cell arrays  102  are connected in parallel. The plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be switched (or operated) to convert from a configuration where the switches connect a positive terminal of a cell array of the plurality of cell arrays  101  to the negative terminal of another cell array, to a configuration where the switches connect the positive terminals of the plurality of cell arrays  101  to each other and connect the negative terminals of the plurality of cell arrays  101  to each other. 
       FIGS.  18  to  20    illustrate three cell arrays  102  in which four battery cells  101  are connected in parallel, in order to intuitively display the connection configuration. In addition, three cell arrays  102  may be connected in series. In this case, a configuration in which four battery cells are connected in parallel and three cell arrays  102  are connected in series may be a default state (structure of 3S4P). 
     One of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be connected to a positive terminal of the plurality of cell arrays  102 , and another one of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be connected to a negative terminal of the plurality of cell arrays  102  . 
     Referring to  FIGS.  18  to  20   , a cell array A  1810  includes four battery cells  1811 ,  1812 ,  1813 , and  1814  connected in parallel. A first switch  1911  may be connected (or coupled) to a positive terminal A+ of the cell array A  1810 , and a second switch  1912  may be connected (or coupled) to a negative terminal A- of the cell array A  1810 . Since the four battery cells  1811 ,  1812 ,  1813 , and  1814  connected in parallel have the same voltage, the voltage of the cell array A  1810 , i.e., the voltage between the positive terminal A+ and the negative terminal A-, is the same as (or equal to) the respective voltages of the battery cells  1811 ,  1812 ,  1813 ,  1814 . 
     A cell array B  1820  includes four battery cells  1821 ,  1822 ,  1823 ,  1824  connected in parallel. A third switch  1921  may be connected to the positive terminal B+ of the cell array B  1820 , and a fourth switch  1922  may be connected to the negative terminal B- of the cell array B  1820 . The voltage of the cell array B  1820 , i.e., the voltage between the positive terminal B+ and the negative terminal B-, is the same as (or equal to) the respective voltages of the battery cells  1821 ,  1822 ,  1823 , and  1824 . 
     A cell array C  1830  includes four battery cells  1831 ,  1832 ,  1833 , and  1834  connected in parallel. A fifth switch  1931  may be connected to the positive terminal C+ of the cell array C  1830 , and a sixth switch  1932  may be connected to the negative terminal C- of the cell array C  1830 . The voltage of the cell array C  1830 , i.e., the voltage between the positive terminal C+ and the negative terminal C-, is the same as (or equal to) the respective voltages of the battery cells  1831 ,  1832 ,  1833 , and  1834 . 
     The four battery cells  101  connected in parallel in one cell array  102  have the same potential difference, but when the other cell arrays  102  continuously charge/discharge, a voltage difference may occur. For example, the battery cells of the cell array A  1810  have the same potential difference. However, the potential difference may not be equal to the potential difference of the battery cells of the cell array B  1820 . 
     The energy storage system  1  according to an embodiment of the present disclosure may operate a plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932  to match the voltage balance of the cell arrays  1810 ,  1820 ,  1830 , when a voltage difference of a switching reference value (e.g., 0.5 V) or higher set based on a natural capacity decrease rate and yield occurs (or appears) between the cell arrays  1810 ,  1820 ,  1830 . 
     The voltage of the cell array  1810  is the same as the voltages of the battery cells included therein (battery cells  1811 ,  1812 ,  1813 ,  1814 ). Similarly, the voltage of the cell array  1820  is the same as the voltages of the battery cells included therein (battery cells  1821 ,  1822 ,  1823 ,  1824 ). Similarly, the voltage of the cell array  1830  is the same as the voltages of the battery cells included therein (battery cells  1831 ,  1832 ,  1833 ,  1834 ). Therefore, when the voltages of the cell arrays ( 1810 ,  1820 ,  1830 ) are matched, the voltages of the battery cells {( 1811 ,  1812 ,  1813 ,  1814 ), ( 1821 ,  1822 ,  1823 ,  1824 ), ( 1831 ,  1832 ,  1833 ,  1834 )} are also matched. 
     According to an embodiment of the present disclosure, the connection structure (or configuration) of the battery cells having a series/parallel structure (or configuration) is converted by switching in terms of a circuit. In addition, a cell balancing circuit may be configured using a number of switches (e.g., six switches in the examples of  FIGS.  18  to  20   ) smaller than the number of cells (e.g., twelve cells in the examples of  FIGS.  18  to  20   ), by connecting the switches ( 1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932 ) to the cell arrays ( 1810 ,  1820 ,  1830 ) containing the battery cells {( 1811 ,  1812 ,  1813 ,  1814 ), ( 1821 ,  1822 ,  1823 ,  1824 ), ( 1831 ,  1832 ,  1833 ,  1834 )} connected in parallel. As the number of cells increases, the effect of reducing the number of switches may be greater. 
     The plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be (or include) a single pole double throw (SPDT) switch. For example, each of the switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be an SPDT switch. As a device that can be used for SPDT, a switch circuit using transistor (TR)/FET low power consumption is available. 
       FIGS.  19  and  20    are diagrams illustrating a switching of connection structure (or configuration) using an SPDT switch.  FIG.  19    illustrates a series structure (or configuration), and  FIG.  20    illustrates a parallel structure (or configuration). 
     Referring to  FIG.  19    (see, e.g., solid-line connections), the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  form a path connected to a first output terminal T1 (e.g., the positive terminal A+ of the cell array A  1810 ). Accordingly, the negative terminal A- of the cell array A  1810  may be connected to the positive terminal B+ of the cell array B  1820 , and the negative terminal B- of the cell array B  1820  may be connected to the positive terminal C+ of the cell array C  1830 . In this way, the cell arrays  1810 ,  1820 , and  1830  may be connected in series. 
     Referring to  FIG.  20    (see, e.g., solid-line connections), the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  form a path connected to a second output terminal T2, respectively. Accordingly, the negative terminal A- of the cell array A  1810 , the negative terminal B- of the cell array B  1820 , and the negative terminal C- of the cell array C  1830  are connected, and the positive terminal A+ of the cell array A  1810 , the positive terminal B+ of the cell array B  1820 , and the positive terminal C+ of the cell array C  1830  are connected. In this way, the cell arrays  1810 ,  1820 , and  1830  may be connected in parallel. When the cell arrays  1810 ,  1820 , and  1830  are connected in a parallel structure (or configuration), twelve battery cells [( 1811 ,  1812 ,  1813 ,  1814 ), ( 1821 ,  1822 ,  1823 ,  1824 ), ( 1831 ,  1832 ,  1833 ,  1834 )] may be connected in a single parallel structure (or configuration), and be balanced with the same voltage. 
     The number of the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be twice the number of the plurality of cell arrays  101  connected in series. Referring to  FIGS.  18  to  20   , in a 3S4P structure (a cell structure in which three cell arrays may be connected in series and four cells are connected in parallel in each cell array), a structure where all of twelve battery cells ( 1811 ,  1812 ,  1813 ,  1814 ) ( 1821 ,  1822 ,  1823 ,  1824 ) ( 1831 ,  1832 ,  1833 ,  1834 ) are in parallel can be made by using six SPDTs ( 1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932 ). In the case of 28S9P, if 56 SPDTs are used, all of 252 batteries can be made to be a parallel structure so as to be balanced. 
     According to an embodiment of the present disclosure, an imbalance between the battery packs  10  containing a plurality of battery cells  101  connected in series and parallel can also be adjusted. When switches are disposed in (or at) the terminals of the battery pack  10 , and a voltage imbalance occurs between the battery packs  10 , it is converted to a parallel structure (or configuration) in which (+) terminal is connected to (+) terminal and in which (-) terminal is connected to (-) terminal, so that the balance can be achieved by itself. 
     If each battery pack  10  is a 7S14P structure having a default state in which 14 battery cells  101  are connected in parallel (in each cell array  102 ) and  7  cell arrays  102  are connected in series, all of 98 battery cells  101  may be connected in parallel by using  14  SPDT switches. 
     If the energy storage system  1  includes four 7S14P battery packs  10 , the energy storage system  1  may balance  392  battery cells  101  by using  56  SPDT switches. 
     According to an embodiment of the present disclosure, a balancing circuit capable of converting a series/parallel structure (or configuration) with a simple structure may be configured. 
     The battery management system  34  may monitor state information of the battery  35  and control a connection structure of the battery  35 . The battery management system  34  may control the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  based on voltage difference(s) between the plurality of cell arrays  102 . 
     When it is determined that an imbalance state has occurred while monitoring the current battery voltage state and current state, the battery management system  34  operates the switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932  such that the connection structure (or configuration) of the plurality of cell arrays  101  or the plurality of battery packs  10  is converted into a parallel structure (or configuration). 
     When a voltage difference of (or between) the plurality of cell arrays  102  is greater than or equal to a first reference value, in a state where the full charge condition is satisfied, during charging, the battery management system  34  may change the connection state of the plurality of cell arrays  102  from a series structure (or configuration) to a parallel structure (or configuration). 
     Then, in the parallel structure (or configuration) state, when the voltage difference of the plurality of cell arrays  101  is less than a second reference value, the battery management system  34  may change the connection state of the plurality of cell arrays  101  from a parallel structure (or configuration) to a series structure (or configuration). Here, the second reference value may be set lower than the first reference value. 
     Alternatively, when the voltage difference between the plurality of cell arrays  101  is greater than or equal to a certain reference value, the battery management system  34  may change the connection state of the plurality of cell arrays from a series structure (or configuration) to a parallel structure (or configuration), and when a preset time elapses, may change the connection state of the plurality of cell arrays  101  from a parallel structure (or configuration) to a series structure (or configuration). 
     According to an embodiment of the present disclosure, the battery imbalance can be adjusted, thereby increasing the degree of freedom in designing a series/parallel structure (or configuration) of a desired capacity. 
     When the serial-to-parallel conversion structure (or configuration) according to the embodiment of the present disclosure is reflected in the production process of the energy storage system  1 , it is easy to assemble with the same capacity even with the battery cells  101  having different production times, and the voltage difference between the batteries  35  can be reduced. Accordingly, first-in-first-out and inventory expansion are possible, productivity can be improved, and manufacturing cost can be reduced. 
     According to an embodiment of the present disclosure, for safety, the battery management system  34  may turn off some internal power sources of the energy storage system  1 , and may switch the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932 . The battery management system  34  may operate the switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932 , after turning off the internal power of the battery. 
     The battery management system  34  includes battery pack circuit boards  220  which are disposed in each of the plurality of battery packs  10 , and obtain state information of a plurality of battery cells  101  contained in each battery pack  10 , and a main circuit board  34   a  which is connected to the battery pack circuit boards  220  by a communication line, and receives state information obtained from each battery pack  10  by the battery pack circuit boards  220 . 
     According to an embodiment of the present disclosure, it is possible to protect a control circuit  34   a  that performs the main function of the battery management system  34  and manages the plurality of battery packs  10 , by designing the control circuit  34   a  including a configuration (particularly, a configuration for safety control) for managing the battery  35  separately from a battery cell sensing circuit  220 . 
     According to an embodiment of the present disclosure, it is possible to prevent overcharging due to voltage imbalance, thereby eliminating the possibility of ignition. In addition, according to an embodiment of the present disclosure, it is possible to prevent (e.g., at an earlier time) the complete discharging of the battery. 
     According to an embodiment of the present disclosure, the plurality of battery cells  101  connected in parallel may be respectively connected to the above-described bus bar  150 . 
     In addition, one input terminal (of each) of the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932  is connected to the positive terminal of the plurality of cell arrays  102 . Another input terminal of (each of) the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932  may be connected to the negative terminal of the plurality of cell arrays  102 . In addition, two output terminals of the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be connected to different bus bars  150 . Accordingly, the connection structure (or configuration) of the plurality of cell arrays  101  can be converted by changing the bus bar  150  connected by the switching operation of the switch  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932 . 
     When the connection structure (or configuration) of the plurality of cell arrays  102  is a series structure in the default state, the negative terminal of any one cell array  102  may be connected to, and the positive terminal of another cell array  102  may be connected to any one bus bar  150 . In this way, a plurality of cell arrays  102  may be connected in series. When the switch  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932  operates, the output of the cell arrays  102  may be connected to another bus bar  150  to form a parallel structure (or configuration). 
     As described with reference to  FIGS.  1  to  20   , the energy storage system  1  according to an embodiment of the present disclosure may include a plurality of battery packs  10  including a first battery module  100   a , a second battery module  100   b  disposed to face the first battery module  100   a , and a high current bus bar  196  connecting the first battery module  100   a  and the second battery module  100   b . 
     Each of the first battery module  100   a  and the second battery module  100   b  includes a plurality of cell arrays  102 , each including a respective plurality of battery cells  101  connected in parallel, and a plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 ,  1932  which are connected (or coupled) to the plurality of cell arrays  102 , and connect the plurality of cell arrays  102  in series. The plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be switched (or operated) to perform a balancing operation so that the plurality of cell arrays  102  may be connected in parallel. 
     The plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  may be (or include) a single pole double throw (SPDT) switch. 
     The battery management system  34  may control the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  based on the voltage difference(s) between the plurality of cell arrays  102 . 
     For example, when the voltage difference of the plurality of cell arrays  102  is equal to or greater than a first reference value in a state during charging where the full charge condition is satisfied, the battery management system  34  may change the connection state of the plurality of cell arrays from a series structure (or configuration) to a parallel structure (or configuration). 
     When the voltage difference of the plurality of cell arrays  102  is less than a second reference value in the parallel structure (or configuration) state, the battery management system  34  may change the connection state of the plurality of cell arrays  102  from a parallel structure (or configuration) to a series structure (or configuration). 
       FIG.  21    is a flowchart illustrating a method of operating an energy storage system according to an embodiment of the present disclosure. 
     Referring to  FIG.  21   , the battery  35  may be charged (S 2110 ), until the battery  35  satisfies a full charge condition (e.g., 4.1 V, 50 mA) (S 2115 ). 
     When the battery is charged, if the battery cell  101  having the highest voltage in battery  35  reaches the full charge condition, the remaining battery cells  101  cannot be charged even though they need to be charged (e.g., even though they are capable of being charged further). In addition, when the battery is discharged, if the battery cell  101  having the lowest voltage reaches a full discharge condition, even a more usable battery cannot be discharged further. Therefore, there is a need for a method to solve the voltage imbalance of the battery cell  101  during battery charging/discharging. 
     The battery management system  34  may monitor the voltage and current of the battery  35  (S 2120 ). In the state where the full charge condition is satisfied (S 2115 ), if the voltage difference of the plurality of cell arrays  102  is greater than or equal to the first reference value (e.g., 50mV) (S 2125 ), the battery management system  34  may perform the balancing operation (see, e.g., S 2130 ). 
     For example, as described with reference to  FIGS.  18  to  20   , the battery management system  34  may operate the plurality of switches  1911 ,  1912 ,  1921 ,  1922 ,  1931 , and  1932  to change the connection state of the plurality of cell arrays from a series structure (or configuration) to a parallel structure (or configuration) (S 2135 ). 
     In the parallel structure state (S 2140 ), if the voltage difference of the plurality of cell arrays  102  is less than a second reference value (e.g., 20 mV) lower than the first reference value of S 2125  (S 2145 ), the battery management system  34  may determine that the imbalance state has been resolved. Therefore, in the parallel structure state (S 2140 ), if the voltage difference of the plurality of cell arrays  102  is less than the second reference value (S 2145 ), the battery management system  34  may prepare for discharging by changing the connection state of the plurality of cell arrays  102  from a parallel structure (or configuration) to a series structure (or configuration) (S 2135 ). 
     The parallel structure change parameter (the first reference value (see S 2125 )) may arbitrarily set the battery lifespan and voltage difference, and the conditions for releasing to the series structure again (see S 2145 ) can also be changed according to the temperature and the battery charging SOC. 
     According to an embodiment, the battery management system  34  maintains the parallel structure state for a certain time (S 2140 ), and discharge can be prepared by automatically changing the connection state of the plurality of cell arrays  102  from a parallel structure (or configuration) to a series structure (or configuration) after the certain time has elapsed. 
     If there is an imbalance between the batteries, the usable capacity that can be used by consumers becomes smaller. Accordingly, when a set voltage difference occurs (S 2125 ), the battery management system  34  may turn off the external power of the battery system, and facilitate a balance between the batteries in a parallel structure (or configuration) for a certain period of time. By applying a software (SW) timer, it operates normally after a certain period of time. The certain period of time of the timer is a parameter that can be applied differently depending on the temperature and the charge state of the SOC. 
     If the voltage difference of the plurality of cell arrays  102  is less than the first reference value (S 2125 ), the battery management system  34  may control the battery  35  in a discharge standby state (S 2135 ). In this case, since the plurality of cell arrays  102  are not changed from the serial structure (or configuration) that is a default state, it is not necessary to change the battery connection structure (or configuration). 
     According to at least one embodiment of the present disclosure, the lifespan, stability, and efficiency of the battery may be improved by reducing the voltage difference between the batteries. 
     In addition, according to at least one embodiment of the present disclosure, it is possible to prevent (e.g., at an earlier time) the complete discharge of the battery and improve the battery lifespan. 
     In addition, according to at least one embodiment of the present disclosure, it is possible to prevent overcharging due to battery imbalance, thereby reducing the possibility of ignition. 
     In addition, according to at least one embodiment of the present disclosure, battery imbalance may be adjusted with a small number of switches. 
     In addition, according to an embodiment of the present disclosure, a series/parallel structure (or configuration) of a desired capacity can be easily implemented, thereby increasing the design freedom of the battery cell module. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and detail may be made herein without departing from the spirit and scope of the present invention as defined by the following claims and such modifications and variations should not be understood as being outside the scope of the technical idea or aspect of the present invention.