Patent Publication Number: US-2023138447-A1

Title: Energy storage system and method for operating the same

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. 10-2021-0149667, filed on Nov. 3, 2021, the contents of which are hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to an energy storage system and an operating method thereof, 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. To this end, the energy storage system includes a battery, and a power conditioning system is used for supplying power to the battery or outputting power from the battery. 
     The battery state of charge (SOC) is called as a charge amount, a remaining capacity, or a charging state, and represents a capacity currently stored in a battery compared to a usable capacity in the battery. SOC is usually expressed as a percentage, and is estimated by various methods such as a voltage measurement method and a coulomb counting method. 
     The coulomb counting method calculates the SOC by measuring and integrating the output current over the entire operating time. That is, the SOC is estimated by integrating the charge/discharge current measured through a current sensor. The current measurement value output from the current sensor is different from the actual current flowing through the battery. Such a difference may be accumulated as time elapses. The accuracy of the coulomb counting method may gradually decrease as time elapses due to a measurement error of the current sensor. 
     The voltage measurement method measures an open circuit voltage (OCV) of the battery, and estimates the SOC of the battery using an OCV table of the battery. Since the voltage measurement method estimates the SOC by using an open circuit voltage in a non-charge/discharge state, it is difficult to use in a charge/discharge state and is greatly affected by external factor such as temperature. In addition, during battery charging/discharging, a voltage fluctuation range may occur due to an internal resistance (IR) of the battery, and may be affected by the internal resistance. 
     Conventional coulomb counting method and voltage measurement method has a problem in that an error occurs in SOC estimation due to an error of current and voltage sensors, an effect of micro-current, an error in sensing hardware, and the like, and the errors are accumulated as the measurement is prolonged. In addition, there is a problem in that the SOC estimated by the coulomb counting method and the voltage measurement method varies greatly due to various error factors. 
     The accuracy of SOC estimation is an important factor in battery safety and system reliability, such as prevention of over-charging and over-discharging. Accordingly, various methods for more accurately calculating the SOC have been proposed. For example, Korean Patent Publication No. 10-2006-0129962 discloses an apparatus and method for estimating a remaining battery capacity having an improved accuracy using a neural network algorithm. Korean Patent Publication No. 10-201900106126 discloses a method and apparatus for estimating a SOC-OCV profile reflecting the degradation rate of a secondary battery. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problems, and an object of the present disclosure is to provide an energy storage system capable of accurately calculating a battery state of charge (SOC), and an operating method thereof. 
     Another object of the present disclosure is to provide an energy storage system capable of preventing over-charging and over-discharging of a battery due to an SOC error, and an operating method thereof. 
     Another object of the present disclosure is to provide a storage system capable of reducing the frequency of fault occurrence due to erroneous detection by improving the accuracy of SOC calculation, and an operating method thereof. 
     Another object of the present disclosure is to provide an energy storage system capable of improving battery safety and system reliability by accurately calculating SOC, and an operating method thereof. 
     In order to achieve the above object, an energy storage system and an operating method thereof according to embodiments of the present disclosure may accurately calculate a state of charge (SOC) by reflecting the influence of internal resistance. 
     In order to achieve the above object, an energy storage system and an operating method thereof according to embodiments of the present disclosure may accurately calculate SOC to improve battery safety and system reliability. 
     In order to achieve the above object, an energy storage system according to an embodiment of the present disclosure includes a battery configured to store a received electrical energy in a form of direct current, or to output the stored electrical energy; and a battery management system configured to control the battery, wherein the battery management system includes: a sensing unit comprising a plurality of sensors for measuring voltage, current, and temperature of the battery; a memory configured to store an open circuit voltage table and an internal resistance table; and a microcomputer unit configured to determine an internal resistance of the battery from the internal resistance table by using data detected by the sensing unit, to calculate a battery real voltage reflecting a voltage drop due to the internal resistance of the battery, and to determine a state of charge (SOC) by using the battery real voltage. 
     The microcomputer unit determines an initial SOC from the open circuit voltage table by using a battery voltage detected by the sensing unit, determines C-rate by using a battery current detected by the sensing unit, and determines the internal resistance of the battery from the internal resistance table, by using a battery temperature detected by the sensing unit, the initial SOC, and the C-rate. 
     As noted below, C-rate is called a charge rate, a discharge rate, a charge/discharge rate, or the like, is a unit for setting a current value during charging/discharging, and may be calculated according to the equation of C-rate(A) = charge/discharge current (A)/rated capacity of battery. 
     The microcomputer unit determines C-rate by using a battery current detected by the sensing unit, and determines the internal resistance of the battery from the internal resistance table, by using a battery temperature detected by the sensing unit, the SOC, and the C-rate. 
     The battery includes a plurality of battery cells, wherein the sensor for measuring the temperature of the battery is a thermistor disposed in an outer periphery of at least one of the plurality of battery cells, and wherein the temperature of the battery is based on at least one of temperature data sensed by the thermistor. 
     The battery includes a plurality of battery packs respectively including a plurality of battery cells, wherein the battery management system includes: a battery pack circuit boards disposed in each of the plurality of battery packs, and to obtain state information of the plurality of battery cells comprised in each of the battery packs; and a main circuit board connected to the battery pack circuit boards by a communication line, and to receive state information obtained by each battery pack from the battery pack circuit boards. 
     The microcomputer unit and the memory are mounted in the main circuit board. 
     The microcomputer unit calculates the battery real voltage by a different equation according to a charging/discharging state. 
     The battery is charging, the microcomputer unit calculates a voltage drop value by multiplying a charging current measured by the sensing unit and the internal resistance, and calculates the battery real voltage by subtracting the voltage drop value from a battery voltage measured by the sensing unit. 
     When the battery is discharging, the microcomputer unit calculates a voltage drop value by multiplying a discharge current measured by the sensing unit and the internal resistance, and calculates the battery real voltage by adding the voltage drop value to a battery voltage measured by the sensing unit. 
     The microcomputer unit calculates the internal resistance when the battery is being charged or discharged. 
     When a no-load state continues for a certain period of time, the microcomputer unit determines an SOC from the open circuit voltage table by using a battery voltage detected by the sensing unit, and updates the SOC. 
     When the battery starts charging or discharging, the microcomputer unit resets a counting of the no-load state. 
     In order to achieve the above object, a method of operating an energy storage system according to embodiments of the present disclosure includes measuring a battery current; determining a C-rate using the measured battery current; measuring a battery temperature; determining an internal resistance of a battery from a stored internal resistance table, by using the C-rate, the battery temperature, and a stored SOC; calculating a battery real voltage reflecting a voltage drop caused by the internal resistance of the battery; and updating a state of charge (SOC) using the battery real voltage. 
     A method of operating an energy storage system according to embodiments of the present disclosure further includes measuring a voltage of the battery; and determining an initial state of charge (SOC) from a stored open circuit voltage table using the measured voltage of the battery, wherein determining an internal resistance of a battery includes determining the internal resistance of the battery from the stored internal resistance table by using the C-rate, the battery temperature, and the initial SOC. 
     A method of operating an energy storage system according to embodiments of the present disclosure further includes checking a charging/discharging state of the battery, wherein when the battery is being charged or discharged, the battery current is measured. 
     Calculating a battery real voltage includes calculating the battery real voltage by using a different equation according to a charging/discharging state of the battery. 
     When the battery is charging, a voltage drop value is calculated by multiplying a charging current measured by a sensing unit and the internal resistance, and the battery real voltage is calculated by subtracting the voltage drop value from a battery voltage measured by the sensing unit. 
     When the battery is discharging, a voltage drop value is calculated by multiplying a discharge current measured by a sensing unit and the internal resistance, and the battery real voltage is calculated by adding the voltage drop value to a battery voltage measured by the sensing unit. 
     A method of operating an energy storage system according to embodiments of the present disclosure further includes determining an SOC from an open circuit voltage table by using a battery voltage detected by a sensing unit, and updating the SOC, when a no-load state continues for a certain period of time. 
     A method of operating an energy storage system according to embodiments of the present disclosure further includes resetting a counting of the no-load state, when the battery starts charging or discharging. 
    
    
     
       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  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 of a battery module and a battery pack circuit substrate according to an embodiment of the present disclosure; 
         FIG.  15 A  is one side view in a coupled state of  FIG.  14   ; 
         FIG.  15 B  is the other side view in a coupled state of  FIG.  14   ; 
         FIG.  16    is a diagram for explaining a connection between the battery pack and a battery management system according to an embodiment of the present disclosure; 
         FIG.  17    is a cross-sectional view of a battery pack according to an embodiment of the present disclosure; 
         FIG.  18    is a cross-sectional view for explaining a disposition of battery cells inside a battery pack; 
         FIG.  19    is a perspective view of a thermistor according to an embodiment of the present disclosure; 
         FIG.  20    is a block diagram of an energy storage system according to an embodiment of the present disclosure; 
         FIGS.  21  and  22    are diagrams for explaining an internal resistance of a battery; 
         FIG.  23    is a diagram for explaining a SOC and an open circuit voltage; 
         FIG.  24    is a diagram illustrating a change in internal resistance according to a battery temperature; 
         FIG.  25    is a graph illustrating battery internal resistance according to battery temperature, SOC, and C-rate; 
         FIGS.  26 A and  26 B  are tables illustrating battery internal resistance according to battery temperature, SOC, and C-rate; 
         FIG.  27    is a flowchart illustrating a method of operating an energy storage system according to an embodiment of the present disclosure; and 
         FIG.  28    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 obvious 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 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 “module” and the “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 top U, bottom D, left Le, right Ri, front F, and rear R used in 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 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 energy storage system  1  in which electrical energy is stored in a battery  35 , a load  7  that is a power demander, 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) or outputs (discharges) the stored electric energy to the grid  9 , or the like, a power conditioning system  32  (PCS) 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 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 an external in the battery  35  and then output power to the external. For example, the energy storage system  1  may receive DC power or AC power from the external, store it in the battery  35 , and then output the DC power or AC power to the external. 
     Meanwhile, 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 to the grid  9  or the load  7 . 
     At this time, 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 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 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  optimized based on the state information of the battery  35 . 
     Meanwhile, 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 . 
     Meanwhile, 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 the SOC of the battery  35  using various well-known SOC calculation methods such as a coulomb counting method and a method of calculating a state of charge (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 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  and the energy management system  31   b  may also perform the other function. In addition, the power management system  31   a  and the energy management system  31   b  may be integrated into one controller so as to be integrally provided. 
     Meanwhile, the installation capacity of the energy storage system  1  varies according to the customer’s installation condition, and a plurality of the power conditioning systems  32  with a corresponding plurality of batteries  35  may be connected to expand to a required capacity. 
     The energy storage system  1  may be connected to at least one generating plant (refer to  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 photovoltaic plant will be mainly described as the generating plant  3 . 
       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 5-based 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 , and the like. 
     The home energy service system may include other loads in addition to the 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. 
     Meanwhile, 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, and 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 a 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 the 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 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. 
     Meanwhile, the meter  2  may be implemented of 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 an AC-coupled 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 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  FIG.  3   , 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 . 
     Meanwhile, 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  5  based service. The user may communicate with the cloud  5  through the terminal  6  regardless of location 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 one casing  12 . Since the battery  35 , the battery management system  34 , and the power conditioning system  32  integrated in one 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  1  may be referred to as a smart energy box  1   b . 
     The above-described power management system  31   a  may be received 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 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 . 
     Meanwhile, 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 that 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  may be disposed in the smart energy box  1   b . 
     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 . 
     Meanwhile, 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 (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. 
     Meanwhile, 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 than the amount of power used by the loads  7   x   1  and  7   y   1  in the photovoltaic generator  3  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 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 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,  FIG.  7    is a cross-sectional view of one side 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 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 such as current, voltage, and temperature of the battery cell  101 . 
     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  fastened with the battery pack  10  and a contact plate  18  protruding to the front to contact the heat dissipation plate  124  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 to the 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 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 one side of the circuit substrate  33  and performs power conversion. 
     The battery monitoring system may include a battery pack circuit substrate  220  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 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 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 . 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 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  contact each other. At this time, 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. 
     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  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 the front from the casing rear wall  14  like 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 in contact with one 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 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  to which a plurality of battery cells  101  are connected in series and parallel, an upper fixing bracket  200  which is disposed in an upper portion of the battery module  100   a ,  100   b  and fixes the disposition of the battery module  100   a ,  100   b , a lower fixing bracket  210  which is disposed in a lower portion of the battery module  100  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 both 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 both 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 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 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.  2   , 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 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 to the second battery module  100   b . 
     The battery module described in  FIGS.  10  to  13    may be described in 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 in 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 in 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 in 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 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 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 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 of the plurality of battery cells  101 . In the first frame  110  and the second frame  130 , the plurality of battery cells  101  are 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  fastened to the second frame  130 , and a module fastening protrusion  122  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  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 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 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 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 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 the left and right side in the length direction (1+, 1-) of the first battery module  100   a . The plurality of first cell arrays  102  are disposed in the front and rear side in 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 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 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 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 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 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 a column direction, and the width direction (w+, w-) of the battery module may be set as 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 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 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 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 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 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 the length direction (1+, 1-) of the battery module. 
     Referring to  FIG.  12   , it 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 the front in the width direction (w+, w-) of the battery module with respect to the first bus bar  150 , and 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 the rear in the width direction (w+, w-) of the battery module with respect to the first bus bar  150 . 
     Referring to  FIG.  12   , in the battery cell  101 , the positive terminal  101   a  and the negative terminal  101   b  are partitioned in the upper end thereof. In the battery cell  101 , the positive terminal  101   a  is disposed in the center of a top surface formed in a circle, and the negative terminal  101   b  is disposed in 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 just an embodiment and it is possible to be connected to opposite electrode terminal. 
     The first connecting bar  154  is disposed in one side of the first cell array  102 . The first connecting bar  154  has a straight bar shape extending in the length direction of the battery module. The extension portion  158  has a straight bar shape extending in 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 the width direction (w+, w-) of the battery module. The second connecting bar  156  may be disposed in 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 the width direction (w+, w-) of the battery module, and is connected to the battery cell  101  disposed in one side or both sides. 
     The second connecting bar  156  includes a second-first connecting bar  156   a  and a second-second connecting bar  156   b  spaced apart from the second-first connecting bar  156   a . The second-first connecting bar  156   a  is disposed between the plurality of battery cells  101 , and the second-second connecting bar  156   b  is disposed in 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 spaced apart from each other in the length direction (1+, 1-) of the battery module. Referring to  FIG.  12   , a second-first vertical bar  164   a , and a second-second vertical bar  164   b  which is spaced apart from the second-first vertical bar  164   a  in 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 one battery module included in other 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  described below. 
     The fifth bus bar  180  is connected to other battery pack  10 . That is, the fifth bus bar  180  may be connected to a battery module included in other 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 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 , respectively. 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 of a battery module and a battery pack circuit substrate according to an embodiment of the present disclosure,  FIG.  15 A  is one side view in a coupled state of  FIG.  14   , and  FIG.  15 B  is the other side view in a coupled state of  FIG.  14   . 
     Referring to  FIGS.  14  to  15 B  , the battery pack  10  includes an upper fixing bracket  200  which is disposed in 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 a lower portion of the battery module  100  and fixes the battery modules  100   a  and  100   b , a battery pack circuit substrate  220  which is disposed in 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 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 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 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 one side end of the upper board  202  and coupled to one 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 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 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 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  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 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 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 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 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 one side end of the lower board  212  and coupled to one 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 the 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 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 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 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  upward. 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 the upper fixing bracket  200 . The plurality of spacers  222  may be disposed in an edge portion of the battery pack circuit substrate  220 . 
       FIG.  16    is a diagram for explaining 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 a 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 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. 
     Meanwhile, the battery management system  34  for monitoring the state information of the battery  35  includes a 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 to the battery pack circuit boards  220  by 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 is disposed in each of the plurality of battery packs  10  and obtains 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 a communication line 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 the battery cell sensing circuit  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 the microcomputer unit  1780  among circuits for safety control may be separately configured. For example, when four battery packs  10  are 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  220  are separately configured, each circuit board  34   a ,  220  can be made smaller. 
     Meanwhile, 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, voltage, and 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 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  220  from a sensor disposed in the battery cell  101  side. 
     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 combination 8 kWh, three 4 kWh battery packs  10  may be connected to implement a combination 12 kWh, and four 4 kWh battery packs  10  may be connected to implement a combination 16 kWh. 
     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 an upper portion of the battery module assembly  100 . 
     Meanwhile, the power conditioning system  32  for converting electrical characteristics for charging or discharging the battery  35  may be disposed in the upper side of the main circuit board  34   a . 
       FIG.  17    is a cross-sectional view of a battery pack according to an embodiment of the present disclosure,  FIG.  18    is a cross-sectional view for explaining a disposition of battery cells inside a battery pack,  FIG.  19    is a perspective view of a thermistor according to an embodiment of the present disclosure. 
     Hereinafter, a structure for heat dissipation of the battery pack will be described with reference to  FIGS.  17  to  19   . 
     Referring to  FIG.  17   , a plurality of battery cells  101  are spaced apart from each other in four directions which are perpendicular to each other. Referring to  FIG.  17   , a plurality of battery cells  101  are spaced apart from each other in up, down, left, and right directions. 
     The disposition of the plurality of battery cells  101  is fixed by the second fixing protrusion  134  of the second frame  130  and the first fixing protrusion  114  of the first frame  110 . 
     Referring to  FIG.  17   , a distance D1 between the battery cell  101  and other adjacently disposed battery cell  101  may be 0.1 to 0.2 times a diameter  101 D of the battery cell  101 . An air flow may be formed between the spacing of the plurality of battery cells  101  by the operation of the cooling fan  280 . 
     Referring to  FIG.  18   , a distance D2 between the second fixing protrusion  134  of the second frame  130  and the first fixing protrusion  114  of the first frame  110  may be 0.5 to 0.9 times the height  101 H of the battery cell  101 . Accordingly, the area in which the outer circumference of the battery cell  101  is in contact with the flowing air can be maximized. 
     The cooling fan  280  operates to discharge the air inside the battery module  100   a ,  100   b  to the outside. Accordingly, when the cooling fan  280  operates, external air is supplied to the battery module  100   a ,  100   b  through the cooling hole  242   a  of the side cover  240  where the cooling fan  280  is not disposed. In addition, when the cooling fan  280  operates, the air inside the battery module  100   a ,  100   b  may be discharged to the outside through the cooling hole  242   a  of the side cover  240  in which the cooling fan  280  is disposed. 
     Referring to  FIG.  17   , the cover plate  242  of each of the pair of side covers  240   a  and  240   b  is spaced apart from one side end of the battery module  100   a ,  100   b . The size of the cooling hole  242   a  is formed smaller than the size of one side surface of the battery module  100   a ,  100   b . Accordingly, the cover plate  242  having the cooling hole  242   a  formed therein is spaced apart from one side end of the battery module  100   a ,  100   b  so that the air introduced through the cooling hole  242   a  flows to each of the plurality of battery cells  101 . 
     The heat dissipation plate  124  is disposed in a lower portion of each of the plurality of battery cells  101 . The heat dissipation plate  124  may be formed of an aluminum material to dissipate heat generated in the battery cell  101  to the outside. Each of the plurality of battery cells  101  may be adhered to the heat dissipation plate  124  through a conductive adhesive solution. 
     The conductive adhesive solution, which is a bonding solution containing alumina, fixes the heat dissipation plate  124  disposed in a lower portion of the battery cell  101  and transfers heat generated from the battery cell  101  to the heat dissipation plate  124 . 
     In some of the plurality of battery cells  101 , a thermistor  224  for measuring the temperature of the battery cell  101 , and a mounting ring  226  for fixing the disposition of the thermistor  224  to the outer circumference of the battery cell  101  are disposed. The thermistor  224  may be disposed in the battery cell  101  disposed in a portion where mainly temperature is increased among the plurality of battery cells  101 . 
     The mounting ring  226  has an open ring shape at one side, and forms a mounting groove  226   a  in which the thermistor  224  is mounted at one side that is not opened. The mounting ring  226  is mounted in the outer circumference of the battery cell  101  to bring the thermistor  224  into contact with the outer circumferential surface of the battery cell  101 . 
     The thermistor  224  is connected to the battery pack circuit substrate  220  through the signal line  199 . The thermistor  224  may transmit temperature information detected by the battery cell  101  to the battery pack circuit substrate  220 . The battery pack  10  may adjust the rotation speed of the cooling fan  280  based on the temperature information detected from the thermistor  224 . 
     The heat dissipation plate  124  may be disposed to contact one side of the casing  12  described below. The casing  12  is configured to accommodate at least one battery pack  10 . Accordingly, the heat dissipation plate  124  may transfer the heat received from the battery cell  101  to the casing  12 . 
     When the temperature of the battery  35  rises to a high temperature and is continuously used, the battery life is reduced. In addition, when the temperature of the battery  35  is used at a low temperature, internal resistance is increased, so that efficiency is lowered and high output is difficult. 
     Accordingly, according to an embodiment of the present disclosure, charging/discharging of the battery may be controlled based on the temperature of the battery cell  101  sensed by the thermistor  224 . 
       FIG.  20    is a block diagram of an energy storage system according to an embodiment of the present disclosure, and illustrates an internal block of the battery management system  34 . 
     As described above, the energy storage system  1  according to an embodiment of the present disclosure includes a battery  35  and a battery management system  34  for controlling the battery  35 . 
     Referring to  FIG.  20   , the battery management system  34  according to an embodiment of the present disclosure includes a sensing unit  2040  including a sensor for measuring voltage, current, and temperature of the battery  35 , a memory  2030  that stores data necessary for the operation of the battery management system  34 , and a microcomputer unit  2020  that controls the overall operation of the battery management system  34 . 
     In addition, the battery management system  34  may further include an interface  2010  and communicate with the power conditioning system  32  through the interface  2010 . For example, the interface  2010  may communicate with the power conditioning system  32  in a CAN communication method. 
     The sensor for measuring the temperature of the battery  35  may be a thermistor  224  disposed in the outer periphery of at least one of the plurality of battery cells  101 . In addition, the temperature of the battery  35  may be based on at least one of temperature data sensed by the thermistor  224 . For example, the temperature of the battery  35  may be an average value or a maximum value of temperature data sensed by the thermistor  224 . 
     Meanwhile, as described with reference to  FIG.  16   , the battery management system  34  may include 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 by each battery pack  10  from the battery pack circuit boards  220 . Here, the microcomputer unit  2020  and the memory  2130  may be mounted in the main circuit board  34   a . The plurality of battery packs  10  may be connected in series by a power line  198 , and the power line  198  may be connected to the main circuit board  34   a . Accordingly, when a short-circuit occurs due to an internal problem of the battery pack  10 , even if the battery pack circuit boards  220  directly connected to the battery cell  101  are damaged, the microcomputer unit  2020  and the memory  2130  of the independently designed main circuit board  34   a  may be protected without damage. 
     Meanwhile, the thermistor  224  and the battery pack circuit board  220  included in each of the plurality of battery packs  10  may be connected by wire. 
     The memory  2030  may store an open circuit voltage (OCV) table and an internal resistance (IR) table. 
       FIGS.  21  and  22    are diagrams for explaining an internal resistance of a battery.  FIG.  21    is a diagram illustrating a voltage drop due to an internal resistance during battery discharging, and illustrates a current direction during discharging and a corresponding polarity of the internal resistance R 0 .  FIG.  22    is a diagram illustrating a change in open circuit voltage according to battery discharge. 
     Referring to  FIGS.  21  and  22   , a voltage drop occurs due to the internal resistance R 0 while the current flows during discharging, and accordingly, a difference by the voltage drop due to the internal resistance R 0 occurs between the open circuit voltage OCV and the battery voltage Vb. Although there is a difference in the direction and polarity of current when charging the battery, a voltage drop due to the internal resistance R 0 shall occur. Therefore, an error occurs in estimating the SOC using only the open circuit voltage OCV. 
     According to an embodiment of the present disclosure, battery internal resistance is determined and used for SOC estimation, in addition to using OCV. 
     The open circuit voltage table may include corresponding battery SOC and open circuit voltage data. That is, the open circuit voltage table may include open circuit voltage data for each battery SOC or battery SOC for each open circuit voltage. Accordingly, the battery SOC or open circuit voltage data may be mapped to other remaining data. In some cases, the open circuit voltage table may include data in the form of a table or a graph. 
       FIG.  23    is a diagram for explaining the SOC and the open circuit voltage, and shows an example of the open circuit voltage (OCV) for each battery SOC measured experimentally. Referring to  FIG.  23   , when the battery SOC is known, a corresponding open circuit voltage may be mapped, and when the open circuit voltage is known, a corresponding battery SOC may be mapped. The microcomputer unit  2020  may estimate the SOC corresponding to the battery voltage (open circuit voltage or battery real voltage) measured using the open circuit voltage table. 
     The internal resistance table includes an internal resistance value corresponding to battery temperature, battery SOC, and C-rate value. That is, the internal resistance table includes internal resistance data corresponding to battery temperature, battery SOC, and C-rate condition. Accordingly, the internal resistance table may include a data structure capable of mapping a corresponding internal resistance value by using battery temperature, battery SOC, and C-rate value. In some cases, the internal resistance table may include data in the form of a table or a graph. 
     In the present disclosure, it is important to accurately calculate the battery internal resistance as a key factor in estimating the battery state of charge (SOC). 
       FIG.  24    is a diagram illustrating a change in internal resistance according to battery temerature, and shows a change in internal resistance according to battery voltage under different temperature condition. Referring to  FIG.  24   , the internal resistance at the same battery voltage is different according to the battery temperature condition. Therefore, it can be checked that the battery temperature influences the internal resistance. However, other data are needed for accurate internal resistance. 
       FIG.  25    is a graph illustrating battery internal resistance according to battery temperature, SOC, and C-rate, and  FIGS.  26 A and  26 B  are tables illustrating battery internal resistance according to battery temperature, SOC, and C-rate. 
     Referring to  FIGS.  25 ,  26 A and  26 B , it is shown as a function of cell temperature, SOC, and C-Rate. Therefore, it is possible to form a table by measuring the internal resistance of battery for each battery temperature, for each SOC, and for each C-Rate. The internal resistance table may be stored in the memory  2030 . Thereafter, during actual battery charging/discharging, a current internal resistance of the battery is determined by using the internal resistance table, and an accurate SOC is estimated by compensating the voltage drop due to the internal resistance of the battery according to the charging/discharging current. 
     According to an embodiment of the present disclosure, the power management system  31   a  and/or the battery management system  34  calculates the internal resistance of the battery, by utilizing the battery temperature, the current battery SOC value, and the battery C-Rate to improve the estimation accuracy of the battery state of charge (SOC). 
     The power management system  31   a  and/or the battery management system  34  calculates the battery SOC by using a result (battery real voltage) of calculating the battery voltage by compensating a voltage drop caused by the internal resistance IR of the battery during charging/discharging of the battery and the OCV table. Hereinafter, the case in which the battery management system  34 , particularly, the microcomputer unit  2020  calculates the SOC is exemplified. 
     When charging/discharging the battery  35 , the microcomputer unit  2020  may control the C-rate based on the temperature of the battery, SOC, and the like. 
     C-rate is called a charge rate, a discharge rate, a charge/discharge rate, or the like, is a unit for setting a current value during charging/discharging, and may be calculated according to the equation of C-rate(A) = charge/discharge current (A)/rated capacity of battery. 
     The microcomputer unit  2020  may calculate a state of charge (SOC) of the battery  35 , and control charging and discharging of the battery based on the calculated state of charge and the temperature of the battery  35 . 
     The microcomputer unit  2020  determines the internal resistance of the battery from the internal resistance table by using the data detected by the sensing unit  2040 . 
     The microcomputer unit  2020  uses the data detected by the sensing unit  2040  to determine the current (the latest data) battery temperature, the battery SOC, and the C-rate, and determine the internal resistance of the battery corresponding to the current battery temperature, the battery SOC, and the C-rate from the internal resistance table. 
     In addition, the microcomputer unit  2020  calculates a battery real voltage reflecting a voltage drop due to the battery internal resistance, and determines a state of charge (SOC) by using the battery real voltage. 
     The battery real voltage is a result of calculating the voltage of the battery by compensating a voltage drop due to the internal resistance IR of the battery, and the voltage drop is the product of the internal resistance of the battery and the charging/discharging current. The microcomputer unit  2020  calculates a battery real voltage by reflecting the voltage drop to the battery measurement voltage sensed by the sensing unit  2030 . 
     The microcomputer unit  2020  controls the sensing unit  2040  to measure the open circuit voltage of the battery  35 , and may decide an initial SOC corresponding to the open circuit voltage measured by using the open circuit voltage table stored in the memory  2030 . 
     The microcomputer unit  2020  may determine the initial SOC from the open circuit voltage table by using the battery voltage detected by the sensing unit  2040 . 
     In addition, the microcomputer unit  2020  may determine the C-rate by using the battery current detected by the sensing unit  2040 , and may determine the internal resistance of the battery from the internal resistance table by using the battery temperature detected by the sensing unit  2040 , the initial SOC, and the C-rate. 
     The microcomputer unit  2020  calculates a battery real voltage reflecting the voltage drop due to the battery internal resistance, and determines the SOC by using the battery real voltage. That is, the microcomputer unit  2020  determines the internal resistance by using the initial SOC, and calculates the SOC again by using the determined internal resistance, thereby improving the accuracy while correcting the SOC by reflecting the voltage drop due to the internal resistance. 
     In addition, thereafter, the accuracy can be further improved by determining the internal resistance by using the corrected SOC and then calculating the SOC again by using the determined internal resistance. 
     The microcomputer unit  2020  may determine the C-rate by using the battery current detected by the sensing unit  2040 , and may determine the internal resistance of the battery from the internal resistance table by using the battery temperature detected by the sensing unit  2040 , the SOC, and the C-rate. That is, the microcomputer unit  2020  may determine the most accurate internal resistance by using the current (the latest data) battery temperature, the SOC, and the C-rate, and use it to correct the SOC. Accordingly, it is possible to continuously increase the accuracy of the SOC estimation. 
     Meanwhile, the microcomputer unit  2020  may calculate the battery real voltage by using a different equation according to a charging/discharging state. 
     For example, when the battery is being charged, the microcomputer unit  2020  may calculate a voltage drop value by multiplying the charging current measured by the sensing unit  2040  and the internal resistance, and may calculate the battery real voltage by subtracting the voltage drop value from the battery voltage measured by the sensing unit  2040 . 
     When the battery is being discharged, the microcomputer unit  2020  may calculate a voltage drop value by multiplying the discharge current measured by the sensing unit  2040  and the internal resistance, and may calculate the battery real voltage by adding the voltage drop value to the battery voltage measured by the sensing unit  2040 . 
     According to an embodiment of the present disclosure, it is possible to optimize the battery charge/discharge power amount by accurately calculating the SOC, and to improve the battery over-charging and over-discharging problems caused by the SOC error. 
     The fault criterion is satisfied by the SOC calculation error, and the operation may be stopped by an occurrence of fault and a measure corresponding to the fault. For example, an over-voltage fault and an under-voltage fault may be generated, and operation may be stopped or a certain measure may be required. However, according to at least one of the embodiments of the present disclosure, it is possible to reduce the frequency of occurrence of faults due to false detection by improving the accuracy of SOC calculation, thereby achieving an efficient operation. 
     Meanwhile, the microcomputer unit  2020  may calculate the internal resistance when the battery  35  is being charged or discharged. When the battery  35  is being charged or discharged as current flows through the battery  35 , a voltage drop due to the internal resistance occurs. 
     Accordingly, the microcomputer unit  2020  may calculate the internal resistance when the battery  35  is charging or discharging, and accurately calculate a final SOC by using the battery voltage reflecting the voltage drop due to the internal resistance. 
     In addition, the microcomputer unit  2020  may determine the SOC from the open circuit voltage table by using the battery voltage detected by the sensing unit  2040  when a no-load state continues for a certain period of time or more, and update the SOC. 
     If the battery starts charging or discharging, the microcomputer unit  2020  may reset counting of the no-load state. 
       FIG.  27    is a flowchart illustrating a method of operating an energy storage system according to an embodiment of the present disclosure. 
     Referring to  FIG.  27   , the microcomputer unit  2020  may determine the C-rate by using the battery current measured by the sensing unit  2040  (S 2725 ). 
     The microcomputer unit  2020  may determine a battery temperature used for a control, based on at least one of the battery temperature measured by the sensing unit  2040  (S 2730 ). 
     The microcomputer unit  2020  may determine the internal resistance of the battery from the internal resistance table stored in the memory  2030 , by using the determined C-rate, the decided battery temperature, and the stored SOC (S 2735 ). 
     Thereafter, the microcomputer unit  2020  calculates a battery real voltage reflecting the voltage drop due to the battery internal resistance (S 2745 , S 2750 ), and may update the state of charge (SOC) by using the battery real voltage (S 2760 ). The final SOC may be accurately calculated by updating the SOC using the internal resistance. 
     According to an embodiment of the present disclosure, when initial power is applied, the microcomputer unit  2020  may estimate the current battery SOC, by using the battery open circuit voltage (OCV) table (S 2710 ). 
     In an initial time when there is no stored SOC value, the sensing unit  2040  measures the voltage of the battery  35  (S 2705 ), and the microcomputer unit  2020  may determine an initial state of charge (SOC) from the stored open circuit voltage table by using the measured battery voltage (S 2710 ). 
     In this case, the microcomputer unit  2020  may determine the internal resistance of the battery from the internal resistance table stored in the memory  2030 , by using the determined C-rate, the determined battery temperature, and the initial SOC (S 2735 ). 
     According to an embodiment of the present disclosure, since a voltage drop due to the internal resistance occurs during charging or discharging, the microcomputer unit  2020  checks the charging/discharging state of the battery  35  (S 2715 ), and may measure the battery current (S 2725 ), when the battery  35  is being charged or discharged (S 2720 ). 
     Meanwhile, according to the charging/discharging state of the battery  35  (S 2740 ), the microcomputer unit  2020  may calculate the battery real voltage by using a different equation (S 2745 , S 2750 ). 
     When the battery is being charged (S 2740 ), the microcomputer unit  2020  may calculate a voltage drop value by multiplying the charging current measured by the sensing unit  2040  and the internal resistance, and may calculate the battery real voltage by subtracting the voltage drop value from the battery voltage measured by the sensing unit  2040  (S 2745 ). 
     When the battery is being discharged (S 2740 ), the microcomputer unit  2020  may calculate a voltage drop value by multiplying the discharging current measured by the sensing unit  2040  and the internal resistance, and may calculate the battery real voltage by adding the voltage drop value to the battery voltage measured by the sensing unit  2040  (S 2750 ). 
     According to an embodiment of the present disclosure, the microcomputer unit  2020  may check whether the battery state is charging or discharging (S 2740 ), compensate the voltage drop due to the internal resistance of the battery, calculate the battery real voltage (S 2745 , S 2750 ), and then update a final SOC by using the OCV Table (S 2760 ). The final SOC is used in subsequent checks of whether the battery is charging/discharging (S 2720 ). 
       FIG.  28    is a flowchart illustrating a method of operating an energy storage system according to an embodiment of the present disclosure. 
     Referring to  FIG.  28   , the microcomputer unit  2020  may monitor a duration time of no-load state (S 2810 ). The no-load state is a state in which charging/discharging of the battery is stopped (STOP), and when the battery starts charging or discharging, the duration time of no-load state may be reset. 
     If the no-load state continues for a certain period of time or more (S 2820 ), the microcomputer  2020  determines the SOC from the open circuit voltage table by using the battery voltage detected by the sensing unit S 2820 , and may update the SOC (S 2830 ). 
     According to at least one of the embodiments of the present disclosure, it is possible to accurately calculate a battery state of charge (SOC) and improve battery safety and system reliability. 
     According to at least one of the embodiments of the present disclosure, it is possible to prevent over-charging and over-discharging of a battery due to an SOC error and reduce the frequency of occurrence of a fault due to erroneous detection. 
     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 individually from the technical idea or aspect of the present invention.