Abstract:
An energy management system includes: a first interface configured to receive a first power from a power generation system; a second interface configured to couple to the power generation system, a power grid, and a storage device, and to receive at least one of the first power from the power generation system, a second power from the power grid, or a third power from the storage device, and to supply a fourth power to at least one of the power grid or a load; and a third interface configured to receive the third power from the storage device, and to supply a fifth power to the storage device for storage.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of U.S. Provisional Application No. 61/262,883, filed on Nov. 19, 2009, in the United States Patent and Trademark Office, the entire content of which is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field 
         [0003]    One or more embodiments of the present invention relate to an energy management system, and more particularly, to a grid-connected energy storage system including an energy management system. 
         [0004]    2. Description of the Related Art 
         [0005]    Interest in harnessing renewable or green energy resources has been increasing recently. Various forms of renewable energy resources (e.g., solar, wind or geothermal power) are harnessed to generate electricity. The generated electricity is supplied to the power grid to reach homes and businesses. Prior to being supplied to the power grid, the generated electricity may be stored in a storage device. Further, systems need to be put into place to accommodate interruptions in the supply of power from the renewable energy resource. Also, it is necessary to convert the power into a form that may be appropriately stored or utilized. 
       SUMMARY OF THE INVENTION 
       [0006]    An aspect of an embodiment of the present invention is directed toward a grid-connected energy storage system including an energy management system. 
         [0007]    An embodiment of the present invention provides an energy management system including: a first interface configured to receive a first power from a power generation system; a second interface configured to couple to the power generation system, a power grid, and a storage device, and to receive at least one of the first power from the power generation system, a second power from the power grid, or a third power from the storage device, and to supply a fourth power to at least one of the power grid or a load; and a third interface configured to receive the third power from the storage device, and to supply a fifth power to the storage device for storage. 
         [0008]    The second interface may be configured to receive the second power and the first power converted by the first interface concurrently or at different times. 
         [0009]    The third interface may be further configured to receive at least one of the first power converted by the first interface or the second power converted by the second interface. 
         [0010]    The third interface may be configured to receive the third power, the first power converted by the first interface, and the second power converted by the second interface, concurrently or at different times. 
         [0011]    The system may be configured to store the first power in the storage device via the third interface as the fifth power, or to transfer the first power via the second interface to at least one of the power grid or the load as the fourth power. 
         [0012]    The system may be further configured to supply the first power or the third power to the load as the fourth power even if the power grid is in a normal operating state. 
         [0013]    The system may be configured to store the second power from the power grid in the storage device via the second and third interfaces as the fifth power, or to supply the second power to the load. 
         [0014]    The system may be configured to supply the third power from the storage device via the second interface to the power grid or the load as the fourth power. 
         [0015]    The first interface may include a first power converter configured to convert the first power from DC or AC power to a DC sixth power. 
         [0016]    The first power converter may be further configured to perform maximum power point tracking control to obtain a maximum power generated by the power generation system. 
         [0017]    The second interface may include a second power converter and the third interface may include a third power converter, wherein the second power converter is configured to: convert the DC sixth power to the fourth power, which is an AC power; convert a seventh power from the third power converter from DC power to the fourth power; and convert the second power from AC power to an eighth power, which is a DC power, and wherein the third power converter is configured to: convert the sixth power or the eighth power to the fifth power; and convert the third power to the seventh power. 
         [0018]    The second power converter may be further configured to control a power conversion efficiency. 
         [0019]    The third power converter may be further configured to control a power conversion efficiency. 
         [0020]    The energy management system may further include: a first switch between the second power converter, and the power grid and the load; and a second switch between the first switch and the power grid wherein the first and second switches are configured to be controlled in accordance with a control signal from a controller. 
         [0021]    The controller may be configured to turn the first switch on and the second switch off to supply the fourth power to the load. 
         [0022]    The energy management system may further include a controller configured to: receive at least one of a voltage sensing signal, a current sensing signal or a temperature sensing signal from at least one of the first, second and third power converters; output a pulse width modulation control signal to at least one of the first, second or third power converters; monitor a status of at least one of the storage device, the power grid, or the load; determine a driving mode; and control conversion operations and/or efficiencies of at least one of the first, second, and third converters or the first and second switches. 
         [0023]    The energy management system may further include a DC stabilizer between the first and third power converters and the second power converter, and configured to maintain a constant DC voltage level at an input of the second power converter and at an input of the third power converter. 
         [0024]    The DC stabilizer may include a capacitor. 
         [0025]    The first interface may include a maximum power point tracking converter configured to: convert the AC or DC first power to a sixth power, which is a DC power; and perform a maximum power point tracking control for tracking the maximum output voltage from the power generation system. 
         [0026]    The second interface may include a bi-directional inverter and the third interface may include a bi-directional converter, wherein the bi-directional inverter is configured to: convert the DC sixth power to the fourth power, which is an AC power; convert a seventh power from the bi-directional converter from DC power to the fourth power; and convert the second power from AC power to an eighth power, which is a DC power, and wherein the bi-directional converter is configured to: convert the sixth power or the eighth power to the fifth power; and convert the third power to the seventh power. 
         [0027]    The energy management system may further include a DC link capacitor between the bi-directional inverter, and the MPPT converter and the bi-directional converter, and configured to: supply the sixth power to the bi-directional inverter or the bi-directional converter; and stabilize the DC voltage level at an input of the bi-directional converter and at an input of the bi-directional inverter. 
         [0028]    The energy management system may further include a battery management system between the third interface and the storage device, and configured to control charging and discharging operations of the storage device. 
         [0029]    The battery management system may further be configured to perform at least one of an over-charge protection function, an over-discharging protection function, an over-current protection function, an overheat protection function, or a cell balancing operation, by determining voltage, current, and temperature of the storage device. 
         [0030]    The storage device may include a battery. 
         [0031]    Another embodiment of the present invention provides an energy storage system including the energy management system and the storage device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]    The accompanying drawings, together with the specification, illustrate exemplary embodiments of the present invention, and, together with the description, serve to explain the principles of the present invention. 
           [0033]      FIG. 1  is a block diagram of a grid-connected energy storage system according to an embodiment of the present invention; 
           [0034]      FIG. 2  is a detailed block diagram of the grid-connected energy storage system of  FIG. 1 ; 
           [0035]      FIG. 3  is a block diagram of a grid-connected energy storage system according to another embodiment of the present invention; 
           [0036]      FIG. 4  is a diagram illustrating flows of a power signal and a control signal in the grid-connected energy storage system of  FIG. 3 ; 
           [0037]      FIG. 5  is a flowchart illustrating operations of a grid-connected energy storage system according to an embodiment of the present invention; and 
           [0038]      FIG. 6  is a flowchart illustrating operations of a grid-connected energy storage system according to an embodiment of the present invention. 
       
    
    
     EXPLANATIONS OF CERTAIN REFERENCE NUMERALS 
       [0039]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 100, 200: grid-connected energy 
                   
               
               
                 storage system 
               
               
                 110, 210: energy management system 
               
               
                 120: storage device 
                 130, 230: power generation system 
               
               
                 140, 240: grid 
                 150, 250: load 
               
               
                 111: first power converter 
                 112: second power converter 
               
               
                 113: third power converter 
                 114: controller 
               
               
                 116, 216: first switch 
                 117, 217: second switch 
               
               
                 118: DC link portion 
                 211: MPPT converter 
               
               
                 212: bi-directional inverter 
                 213: bi-directional converter 
               
               
                 214: integrated controller 
                 215: BMS 
               
               
                 220: battery 
               
               
                   
               
             
          
         
       
     
       DETAILED DESCRIPTION 
       [0040]    In the following detailed description, only certain exemplary embodiments of the present invention have been shown and described, simply by way of illustration. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. 
         [0041]    Embodiments of the present invention will be described in more detail with reference to accompanying drawings. Certain parts for comprehension of operations according to the embodiments of the present invention are described below, and certain other parts may be omitted in order not to complicate understanding of the present invention. 
         [0042]      FIG. 1  is a block diagram of a grid-connected energy storage system  100  according to an embodiment of the present invention. 
         [0043]    Referring to  FIG. 1 , the grid-connected energy storage system  100  of the present embodiment includes an energy management system  110  and a storage device  120 , and the grid-connected energy storage system  100  is connected to a power generation system  130 , a grid  140 , and a load  150 . 
         [0044]    The energy management system  110  receives power from the power generation system  130 ; and transfers the power to the grid  140  or stores the power in the storage device  120  or supplies the power to the load  150 . The generated power may be direct current (DC) power or alternating current (AC) power. 
         [0045]    The energy management system  110  stores the power generated in the power generation system  130  in the storage device  120  or transfers the generated power to the grid  140  or supplies the generated power to the load  150 . In addition, the energy management system  110  may transfer the power stored in the storage device  120  to the grid  140 , may supply the stored power to the load  150 , or may store the power supplied from the grid  140  in the storage device  120 . Also, the energy management system  110  performs an uninterruptible power supply (UPS) operation in an abnormal state, for example, during a power failure of the grid  140 , the energy management system  110  may be configured to supply the power to the load  150 . Otherwise, the energy management system  110  may supply the power generated by the power generation system  130  and the power stored in the storage system  120  to the load  150  even when the grid  140  is in a normal state. 
         [0046]    The energy management system  110  performs a power conversion operation for storing the generated power in the storage device  120 , a power conversion operation for storing the generated power to the grid  140  or the load  150 , a power conversion operation for storing the power of the grid  140  in the storage device  120 , and a power conversion operation for supplying the power stored in the storage device  120  to the grid  140  or the load  150 . In addition, the energy management system  110  monitors states of the storage device  120 , the grid  140 , and the load  150  in order to distribute the power generated by the power generation system  130 , the power supplied from the grid  140 , or the power stored in the storage device  120  to the storage device  120 , the grid  140 , and/or the load  150 . 
         [0047]    The storage device  120  is a large capacity storage device for storing the power supplied from the energy management system  110 . The supplied power is converted from the power generated by the power generation system  130 , or is converted from the utility power supplied from the grid  140 . The power stored in the storage device  120  may be supplied to the grid  140  or to the load  150  according to control of the energy management system  110 . The storage device  120  includes a secondary rechargeable battery, for example, a nickel-cadmium battery, a lead acid battery, a nickel metal hydride (NiMH) battery, a lithium ion battery, and/or a lithium polymer battery. 
         [0048]    In the present embodiment, the grid-connected energy storage system  100  is configured to include the energy management system  110  and the storage system  120 . However, the present invention is not limited thereto, and the grid-connected energy storage system may include the energy management system formed integrally with the storage device. 
         [0049]    The power generation system  130  includes a system for generating electrical energy by using renewable energy, for example, an energy source such as solar energy, wind power, or tidal power. For example, when the power generation system  130  is a photovoltaic power generation system, a solar array converts solar light into electrical energy. In addition, the photovoltaic power generation system includes a plurality of modules which are connected in series and/or in parallel to each other and a supporter. However, the power generation system  130  may alternatively include a system for generating electrical energy by using some other suitable type of energy and/or power source. 
         [0050]    Structures of the energy management system  110  and the grid-connected energy storage system  100  including the energy management system  110  will be described in more detail with reference to  FIG. 2 . 
         [0051]      FIG. 2  is a detailed block diagram of the grid-connected energy storage system  100  of  FIG. 1 . 
         [0052]    Referring to  FIG. 2 , the energy management system  110  includes a first power converter  111 , a second power converter  112 , a third power converter  113 , a controller  114 , a first switch  116 , a second switch  117 , and a DC link portion  118 . The energy management system  110  is connected (or coupled) to the power generation system  130 , the storage device  120 , the grid  140 , and the load  150 . Flows of the power between the components of  FIG. 2  are denoted by solid lines, and flows of control signals are denoted by dotted lines. 
         [0053]    The first power converter  111  is connected (or coupled) between the power generation system  130  and a first node N 1 , and converts the power (or first power) generated by the power generation system  130  to transfer the power to the first node N 1 . The power generated by the power generation system  130  may be DC power or AC power, and accordingly, the first power converter  111  converts the AC power or the DC power respectively to DC power of different voltages. The first power converter  111  may perform a rectification operation to convert the AC power to DC power (or sixth power), or may operate as a converter to convert the DC power to DC power (or sixth power) of different voltages. In addition, the first power converter  111  performs maximum power point tracking (MPPT) control in order to obtain the maximum power generated by a photovoltaic power generation system  131 , a wind power generation system  132 , or a tidal power generation system  133 , according to a control (or control signal) of the controller  114 . 
         [0054]    The second power converter  112  is connected (or coupled) between the first node N 1  and the grid  140 , and operates as an inverter to convert the DC power converted by the first power converter  111  to AC power (or fourth power) for the grid  140  or converts the DC power converted by the third power converter  113  to AC power (or fourth power) for the grid  140 . In addition, the second power converter  112  performs a rectification operation, that is, converts the utility AC power (or second power) supplied from the grid  140  to DC power (or eighth power) to transfer the DC power to the first node N 1 . Also, the second power converter  112  controls a conversion efficiency of power according to control of the controller  114 . 
         [0055]    The third power converter  113  is connected (or coupled) between the first node N 1  and the storage device  120 , and converts the DC power supplied via the first node N 1  to DC power (or fifth power) of different voltages to transfer the converted DC power to the storage device  120 . In addition, the third power converter  113  converts the DC power (or third power) stored in the storage device  120  to DC power (or seventh power) of different voltages to transfer the converted DC power to the first node N 1 . That is, the third power converter  113  operates as a converter which converts the DC power to DC power of different voltages. Also, the third power converter  113  controls a conversion efficiency according to the control of the controller  114 . 
         [0056]    The first switch  116  is connected (or coupled) between the second power converter  112  and a second node N 2 . The second switch  117  is connected between the second node N 2  and the grid  140 . The first switch  116  and the second switch  117  are configured to block the power(s) flowing between the second power converter  112 , the grid  140 , and the load  150  (e.g., the second power and/or fourth power), according to the control of the controller  114 . The first switch  116  and the second switch  117  may be circuit breakers. Switching operations of the first and second switches  116  and  117  are controlled by the controller  114 . 
         [0057]    The DC link portion  118  maintains a DC voltage level at the first node N 1  to be at a DC link level. The voltage level at the first node N 1  may be unstable due to an instantaneous voltage sag of the power generation system  130  or the grid  140 , or a peak load of the load  150 . However, the voltage at the first node N 1  should be stabilized in order for the second power converter  112  and the third power converter  113  to operate normally. Therefore, the DC link portion  118  maintains the DC voltage level at the first node N 1  at a constant DC link voltage level. 
         [0058]    The controller  114  controls overall operation of the grid-connected energy storage system  110 . The controller  114  receives voltage sensing signals, current sensing signals, and temperature sensing signals sensed by the first, second, and third power converters  111 ,  112 , and  113 , and then outputs pulse width modulation (PWM) control signals to switching devices of the first through third power converters  111 ,  112 , and  113  to control the conversion efficiencies. In addition, the controller  114  monitors states of the storage device  120 , the grid  140 , and the load  150 , and determines a driving mode, for example, a power supply mode for supplying the power generated by the power generation system  130  to the grid  140 , a power storage mode for storing the power in the storage device  120 , and a power supply mode for supplying the power to the load  150 , according to the monitored states of the storage device  120 , the grid  140 , and the load  150 . The controller  114  controls the conversion operations and efficiencies of the first to third converters  111 ,  112 ,  113  and turning on/off operations of the first and second switches  116  and  117 , according to the determined driving mode. 
         [0059]    The power generation system  130  generates power (or first power) and outputs the generated power to the energy management system  110 . The power generation system  130  may be the photovoltaic system  131 , the wind power generation system  132 , or the tidal power generation system  133 . Otherwise, the power generation system  130  may be a power generation system generating power from renewable energy, such as geothermal energy. In particular, a solar battery generating power by using the photovoltaic energy may be easily installed in a house or a plant, and thus, may be suitable for the grid-connected energy storage system  100  which is distributed in each house. 
         [0060]    The grid  140  may include a power plant, a substation, and power transmission cables. When the grid  140  is in a normal state, the grid  140  supplies the power to the storage device  120  or to the load  150  according to the turning on/off of the first and second switches  116  and  117 , and receives the power supplied from the storage device  120  or the power generated from the power generation system  130 . When the grid  140  is in an abnormal state caused by, for example, electric failure or electric repair work, the power supply from the grid  140  to the storage device  120  or to the load  150  is stopped, and the power supply from the storage device  120  to the grid  140  is also stopped. 
         [0061]    The load  150  consumes the power generated by the power generation system  130 , the power stored in the storage device  120 , and/or the power supplied from the grid  140 . The load  150  may be, for example, a house or a plant. 
         [0062]      FIG. 3  is a block diagram of a grid-connected energy storage system  200  according to another embodiment of the present invention. 
         [0063]    Referring to  FIG. 3 , an energy management system  210  includes an MPPT converter  211 , a bi-directional inverter  212 , a bi-directional converter  213 , an integrated controller  214 , a battery management system (BMS)  215 , the first switch  216 , the second switch  217 , and a DC link capacitor  218 . The energy management system  210  is connected to a battery  220 , a photovoltaic (PV) system  230  including a solar panel  231 , the grid  240 , and the load  250 . 
         [0064]    The MPPT converter  211  converts a DC voltage (or first power) output from the solar battery  231  to a DC voltage of the first node N 1 . Since an output of the solar panel  231  varies depending on weather conditions, such as solar radiation and temperature, and a load condition, the MPPT converter  211  controls the solar panel  231  to generate the maximum amount of power. That is, the MPPT converter  211  operates as a boost DC-DC converter, which boosts the DC voltage output from the solar battery  231  and outputs the boosted DC voltage, and as an MPPT controller. For example, the MPPT converter  211  may output a DC voltage in the range of about 300 V to about 600 V. In addition, the MPPT converter  211  performs the MPPT control for tracking the maximum output voltage from the solar battery  231 . The MPPT control may be executed by a perturbation and observation (P&amp;O) control method, an incremental conductance (IncCond) control method, or a power versus voltage control method. The P&amp;O control method increases or reduces a reference voltage by measuring a current and a voltage of the solar panel  231 . The IncCond control method is to control the output DC voltage by comparing an output conductance with an incremental conductance of the solar panel  231 , and the power versus voltage control method is to control the output DC voltage by using a slope of a power versus voltage characteristic. Other MPPT control methods may also be used. 
         [0065]    The DC link capacitor  218  is connected (or coupled) between the first node N 1  and the bi-directional inverter  212  in parallel. The DC link capacitor  218  supplies the DC voltage (or sixth power) output from the MPPT converter  211  to the bi-directional inverter  212  or the bi-directional converter  213  while maintaining the DC voltage level at the DC link level, for example, DC 380 V. The DC link capacitor  218  may be an aluminum electrolytic capacitor, a polymer capacitor, or a multi layer ceramic capacitor (MLC). The voltage level at the first node N 1  may be unstable due to variation in the DC voltage output from the solar battery  231 , the instantaneous voltage sag of the grid  240 , or the peak load occurring at the load  250 . Therefore, the DC link capacitor  218  provides the bi-directional converter  213  and the bi-directional inverter  212  with the stabilized DC link voltage for normally operating the bi-directional converter  213  and the bi-directional inverter  212 . In the present embodiment illustrated in  FIG. 3 , the DC link capacitor  218  is separately formed, however, the DC link capacitor  218  may be included in the bi-directional converter  213 , the bi-directional inverter  212 , or the MPPT converter  211 . 
         [0066]    The bi-directional inverter  212  is connected (or coupled) between the first node N 1  and the grid  240 . The bi-directional inverter  212  converts the DC voltage (or sixth power) output from the MPPT converter  211  and the DC voltage (or seventh power) output from the bi-directional converter  213  to an AC voltage (or fourth power) of the grid  240  or the load  250 , and converts the AC voltage (or second power) supplied from the grid  240  to the DC voltage (or eighth power) to transfer the DC voltage to the first node N 1 . That is, the bi-directional inverter  212  operates both as an inverter for converting the DC voltage to the AC voltage and as a rectifier for converting the AC voltage to DC voltage. 
         [0067]    The bi-directional inverter  212  rectifies the AC voltage (or second power) input from the grid  240  via the first and second switches  216  and  217  to the DC voltage (or eighth power) which is to be stored in the battery  220 , and converts the DC voltage output from the battery  220  to AC voltage (or fourth power) for the grid  240 . The AC voltage output to the grid  240  should match a power quality standard of the grid  240 , for example, a power factor of 0.9 or greater and a total harmonic distortion (THD) of 5% or less. To this end, the bi-directional inverter  212  synchronizes a phase of the AC voltage with a phase of the grid  240  to prevent reactive power from being generated (or reduce the likelihood of reactive power being generated), and adjusts the AC voltage level. In addition, the bi-directional inverter  212  may include a filter for removing a harmonic from the AC voltage output to the grid  240 , and the filter may have functions such as restriction of a voltage changing range, power factor improvement, removal (or reduction) of DC component, and protection of transient phenomena. The bi-directional inverter  212  of the present embodiment performs both as an inverter which converts the DC power of the power generation system  230  or the battery  220  to AC power to be supplied to the grid  240  or the load  250 , and a rectifier which converts the AC power supplied from the grid  240  to DC power to be supplied to the battery  220 . 
         [0068]    The bi-directional converter  213  is connected between the first node N 1  and the battery  220 , and converts the DC voltage (or sixth power or the eighth power) at the first node N 1  to the DC voltage (or fifth power) to be stored in the battery  220 . In addition, the bi-directional converter  213  converts the DC voltage (or third power) stored in the battery  220  to a suitable DC voltage (or seventh power) level to be transferred to the first node N 1 . For example, when the DC power (or first power) generated by the photovoltaic power generation system  230  is charged in the battery  220  or the AC power (or second power) supplied from the grid  240  is charged in the battery  220 , that is, in a battery charging mode, the bi-directional converter  213  functions as a converter which decompresses (or reduces) the DC voltage level at the first node N 1  or the DC link voltage level maintained by the DC link capacitor  218 , for example, a DC voltage of 380 V, down to a battery storing voltage, for example, a DC voltage of 100V. In addition, when the power (or third power) charged in the battery  220  is supplied to the grid  240  or to the load  250 , that is, in a battery discharging mode, the bi-directional converter  213  functions as a converter which boosts the battery storing voltage, for example, a DC voltage of 100 V, to the DC voltage level at the first node N 1  or the DC link voltage level, for example, a DC voltage of 380 V. The bi-directional converter  213  of the present embodiment converts the DC power generated by the photovoltaic power generation system  230  or the DC power converted from the AC power supplied from the grid  240  to DC power to be stored in the battery  220 , and converts the DC power stored in the battery  220  to DC power to be input into the bi-directional inverter  212  for supplying the DC power to the grid  240  or to the load  250 . 
         [0069]    The battery  220  stores the power supplied from the photovoltaic power generation system  230  or the grid  240 . The battery  220  may include a plurality of battery cells which are connected in series or in parallel with each other to increase a capacity and an output thereof, and charging and discharging operations of the battery  220  are controlled by the BMS  215  or the integrated controller  214 . The battery  220  may include various suitable kinds of battery cells, for example, a nickel-cadmium battery, a lead-acid battery, an NiMH battery, a lithium ion battery, and/or a lithium polymer battery. The number of battery cells configuring the battery  220  may be determined according to a power capacity required by the grid-connected energy storage system  200  and/or conditions of designing the battery  220 . 
         [0070]    The BMS  215  is connected to the battery  220 , and controls the charging/discharging operations of the battery  220 , according to the control of the integrated controller  214 . The power discharged from the battery  220  to the bi-directional converter  213  and the power charged in the battery  220  from the bi-directional converter  213  are transferred via the BMS  215 . In addition, the BMS  215  may have functions such as an over-charging protection, an over-discharging protection, an over-current protection, an overheat protection, and a cell balancing operation. To this end, the BMS  215  detects the voltage, current, and temperature of the battery  220  to determine a state of charge (SOC) and a state of health (SOH) of the battery  220 , thereby monitoring remaining power and lifespan of the battery  220 . 
         [0071]    The BMS  215  may include a micro-computer which performs a sensing function for detecting the voltage, current, and temperature of the battery  220  and determines the over-charging, the over-discharging, the over-current, the cell balancing, the SOC, and the SOH, and a protection circuit, which protects the charging/discharging, fusing, and cooling of the battery  220  according to a control signal of the micro-computer. In  FIG. 3 , the BMS  215  is included in the energy management system  210  and is separated from the battery  220 , however, a battery pack including the BMS  215  and the battery  220  as an integrated body may be formed. In addition, the BMS  215  controls the charging and discharging operations of the battery  220 , and transfers status information of the battery  220 , for example, information about charged power amount obtained from the determined SOC, to the integrated controller  214 . 
         [0072]    The first switch  216  is connected between the bi-directional inverter  212  and the second node N 2 . The second switch  217  is connected between the second node N 2  and the grid  240 . The first and second switches  216  and  217  are turned on or turned off by the control of the integrated controller  214 , and supply or block the power of the photovoltaic power generation system  230  or the battery to the grid  240  or to the load  250 , and supply or block the power from the grid  240  to the load  250  or the battery  220 . For example, when the power generated by the photovoltaic power generation system  230  or the power stored in the battery  220  is supplied to the grid  240 , the integrated controller  214  turns the first and second switches  216  and  217  on. In addition, when only the power from the grid  240  is supplied to the load  250 , the integrated controller  214  turns the first switch  216  off and turns the second switch  217  on. 
         [0073]    The second switch  217  blocks the power supply to the grid  240  and makes the grid-connected energy storage system  200  solely operate according to the control of the integrated controller  214 , when an abnormal situation occurs in the grid  240 , for example, an electric failure occurs or distribution lines need to be repaired. At this time, the integrated controller  214  separates the energy management system  210  from the grid  240  to prevent (or reduce the likelihood of) an accident, such as an electric shock applied to a worker working on the line management or repair from occurring, and to prevent the grid  240  from (or reduce the likelihood of the grid  240 ) negatively affecting electrical equipment due to the operation in the abnormal state. In addition, when the grid  240  recovers to the normal state from the operation in the abnormal state, that is, the power generated by the photovoltaic power generation system  230  or the power stored in the battery  220  is supplied to the load  250 , a phase difference is generated between the voltage of the grid  240  and the output voltage of the battery  220  which is in the sole operating state, and thus, the energy management system  210  may be damaged. The integrated controller  214  performs a sole operation preventing control in order to address the above problem. 
         [0074]    The integrated controller  214  controls overall operations of the energy management system  210 . The control operations of the integrated controller  214  will be described with reference to  FIG. 4  in more detail. 
         [0075]      FIG. 4  is a diagram illustrating flows of the power and control signals in the grid-connected energy storage system  200  of  FIG. 3 . 
         [0076]    Referring to  FIG. 4 , the flow of power between the internal components in the grid-connected energy storage system  200  of  FIG. 3  and the control flow of the integrated controller  214  are illustrated. As shown in  FIG. 4 , the DC level voltage converted by the MPPT converter  211  is supplied to the bi-directional inverter  212  and the bi-directional converter  213 . In addition, the DC level voltage supplied to the bi-directional inverter  212  is converted to the AC voltage by the bi-directional inverter  212  to be supplied to the grid  240 , or the DC level voltage supplied to the bi-directional converter  213  is converted to the DC voltage by the bi-directional converter  213  to be charged in the battery  220  and is charged in the battery  220  via the BMS  215 . The DC voltage charged in the battery  220  is converted to an input DC voltage level of the bi-directional inverter  212  by the bi-directional converter  213 , and then, is converted to the AC voltage suitable for the standard of the grid by the bi-directional inverter  212  to be supplied to the grid  240 . 
         [0077]    The integrated controller  214  controls overall operations of the grid-connected energy storage system  200 , and determines an operating mode of the system  200 , for example, determines whether the generated power will be supplied to the grid, to the load, or stored in the battery, and whether the power supplied from the grid will be stored in the battery. 
         [0078]    The integrated controller  214  transmits control signals for controlling switching operations of the MPPT converter  211 , the bi-directional inverter  212 , and the bi-directional converter  213 . The control signals may reduce a loss of power caused by the power conversion executed by the converter  211  or  213 , or the inverter  212  by controlling a duty ratio with respect to the input voltage of the each converter or the inverter. To this end, the integrated controller  214  receives signals for sensing the voltage, the current, and the temperature at an input terminal of each of the MPPT converter  211 , the bi-directional inverter  212 , and the bi-directional converter  213 , and transmits the converter control signal and the inverter control signal based on the received sensing signals. 
         [0079]    The integrated controller  214  receives grid information including information about the grid status and information about the voltage, the current, and the temperature of the grid from the grid  240 . The integrated controller  214  determines whether or not the abnormal situation occurs in the grid  240  and whether or not the power of the grid is returned, and performs a sole operation prevention control through a controlling operation for blocking the power supply to the grid  240  and a controlling operation of matching the output of the bi-directional inverter  212  and the supplied power of the grid  240  after returning the power of the grid  240 . 
         [0080]    The integrated controller  214  receives a battery status signal, that is, a signal indicating the charging/discharging states of the battery, through communication with the BMS  215 , and determines the operating mode of the system  200  based on the received signal. In addition, the integrated controller  214  transmits a signal for controlling charging/discharging of the battery to the BMS  215  according to the operating mode, and the BMS  215  controls the charging and discharging operations of the battery  220  according to the transmitted signal. 
         [0081]      FIG. 5  is a flowchart illustrating a method of operating a grid-connected energy storage system according to an embodiment of the present invention. 
         [0082]    Referring to  FIG. 5 , a renewable energy generation system generates power in operation  500 . The renewable energy generation system may be, but is not limited to, a photovoltaic energy generation system, a wind power generation system, and/or a tidal power generation system, and the generated power may be DC power or AC power. In operation  502 , a voltage of the generated power is converted to a DC link voltage. The DC link voltage is a DC voltage having a constant DC voltage level to be input to an inverter or a converter from the power having an unstable voltage level generated in operation  500 . 
         [0083]    In operation  504 , it is determined whether the power generated in operation  500  will be supplied to a grid or to a load, or will be stored in a battery. The above determination of operation  504  is based on a current power selling price to the system, the generated power amount, required load&#39;s power consumption amount, and/or the power charged in the battery. As a result of the determination of operation  504 , if it is determined that the generated power is to be stored in the battery, the DC link voltage converted in operation  502  is converted to the battery charging voltage and charged in the battery in operations  506  and  508 . 
         [0084]    As a result of the determination of operation  504 , if the generated power is to be supplied to the grid or to the load, the DC link voltage converted in operation  502  is converted to an AC voltage which corresponds to AC voltage standard of the grid or the load in operation  510 . In operation  512 , it is determined whether the AC voltage will be supplied to the grid or to the load. In operation  514 , the AC voltage is supplied to the grid, and in operation  516 , the AC voltage is supplied to the load. 
         [0085]      FIG. 6  is a flowchart illustrating a method of operating a grid-connected energy storage system according to another embodiment of the present invention. 
         [0086]    Referring to  FIG. 6 , a grid condition is monitored in operation  600 . The grid condition may include information about whether an electric failure occurs or not in the grid, whether the power is returned in the grid, whether distribution lines are repaired, and information about voltage, current, and temperature of the grid. In operation  602 , it is sensed whether an abnormal state occurs in the grid. In operation  604 , the power supply to the grid is blocked. When the power supply to the grid is blocked, the grid-connected energy storage system may solely operate in a stabilized state. In operation  606 , a battery discharging mode is selected. At this time, if the power is sufficiently generated by the renewable energy generation system, the power generated by the renewable energy generation system may be supplied to the load. In operation  608 , the power stored in the battery is supplied to the load. In operation  610 , it is determined whether the abnormal situation of the grid is finished. If it is determined that the abnormal situation of the grid is finished, the blockage of the grid is released in operation  612 . Before releasing the blockage of the grid, a current status of the power in the grid may be checked, and then, it may be tested whether the voltage of the grid and a grid connected voltage of the energy storage system, that is, the power supplied to the grid, match each other. In operation  614 , a battery charging mode is selected, and in operation  616 , the power generated by the renewable energy generation system or the power of the grid is stored in the battery. The charging is executed to a level at which the battery may supply the power sufficiently in the above abnormal situation, and after that, the power generated by the renewable energy generation system is supplied to the battery, the load, or the grid if necessary. 
         [0087]    While the present invention has been described in connection with certain exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, and equivalents thereof.